Citation
Purification and functional characterization of human polymorphonuclear leukocyte actin polymerization inhibitor

Material Information

Title:
Purification and functional characterization of human polymorphonuclear leukocyte actin polymerization inhibitor
Creator:
Maun, Noel Anthony, 1968-
Publication Date:
Language:
English
Physical Description:
ix, 160 leaves : ill. ; 29 cm.

Subjects

Subjects / Keywords:
Actins ( jstor )
Annexins ( jstor )
Calcium ( jstor )
Chromatography ( jstor )
Microfilaments ( jstor )
Monomers ( jstor )
Neutrophils ( jstor )
Polymerization ( jstor )
Profilins ( jstor )
Purification ( jstor )
Actins -- biosynthesis ( mesh )
Actins -- isolation & purification ( mesh )
Cytoskeleton -- metabolism ( mesh )
Cytoskeleton -- physiology ( mesh )
Cytoskeleton -- ultrastructure ( mesh )
Microfilaments -- metabolism ( mesh )
Microfilaments -- physiology ( mesh )
Microfilaments -- ultrastructure ( mesh )
Neutrophils ( mesh )
Genre:
bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

Notes

Thesis:
Thesis (Ph. D.)--University of Florida, 1995.
Bibliography:
Includes bibliographical references (leaves 144-159).
General Note:
Typescript.
General Note:
Vita.
Statement of Responsibility:
by Noel Anthony Maun.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
50281502 ( OCLC )
ocm50281502
0028310379 ( ALEPH )

Downloads

This item has the following downloads:

EL7XQ7RKC_D4W9PY.xml

AA00012900_00001.pdf

purificationfunc00maun_0162.txt

AA00012900_00001_0035.txt

purificationfunc00maun_0103.txt

AA00012900_00001_0139.txt

AA00012900_00001_0040.txt

AA00012900_00001_0052.txt

AA00012900_00001_0088.txt

AA00012900_00001_0070.txt

AA00012900_00001_0053.txt

AA00012900_00001_0072.txt

AA00012900_00001_0055.txt

AA00012900_00001_0026.txt

AA00012900_00001_0061.txt

AA00012900_00001_0151.txt

purificationfunc00maun_0137.txt

AA00012900_00001_0081.txt

purificationfunc00maun_0041.txt

purificationfunc00maun_0024.txt

AA00012900_00001_0134.txt

AA00012900_00001_0086.txt

AA00012900_00001_0092.txt

AA00012900_00001_0101.txt

AA00012900_00001_0143.txt

purificationfunc00maun_0150.txt

AA00012900_00001_0152.txt

purificationfunc00maun_0126.txt

AA00012900_00001_0093.txt

AA00012900_00001_0159.txt

purificationfunc00maun_0097.txt

AA00012900_00001_0173.txt

AA00012900_00001_0138.txt

AA00012900_00001_0109.txt

AA00012900_00001_0017.txt

AA00012900_00001_0147.txt

AA00012900_00001_0027.txt

purificationfunc00maun_0088.txt

purificationfunc00maun_0058.txt

purificationfunc00maun_0123.txt

purificationfunc00maun_0100.txt

purificationfunc00maun_0086.txt

AA00012900_00001_0171.txt

AA00012900_00001_pdf.txt

purificationfunc00maun_0119.txt

purificationfunc00maun_0071.txt

purificationfunc00maun_0168.txt

purificationfunc00maun_0127.txt

AA00012900_00001_0011.txt

purificationfunc00maun_0003.txt

purificationfunc00maun_0128.txt

AA00012900_00001_0170.txt

AA00012900_00001_0023.txt

AA00012900_00001_0111.txt

purificationfunc00maun_0110.txt

AA00012900_00001_0167.txt

AA00012900_00001_0018.txt

purificationfunc00maun_0032.txt

AA00012900_00001_0020.txt

AA00012900_00001_0008.txt

purificationfunc00maun_0164.txt

purificationfunc00maun_0001.txt

purificationfunc00maun_0171.txt

AA00012900_00001_0128.txt

purificationfunc00maun_0019.txt

purificationfunc00maun_0045.txt

AA00012900_00001_0014.txt

purificationfunc00maun_0053.txt

AA00012900_00001_0041.txt

purificationfunc00maun_0064.txt

purificationfunc00maun_0015.txt

AA00012900_00001_0029.txt

purificationfunc00maun_0006.txt

purificationfunc00maun_0147.txt

purificationfunc00maun_0158.txt

purificationfunc00maun_0040.txt

purificationfunc00maun_0065.txt

AA00012900_00001_0096.txt

purificationfunc00maun_0122.txt

purificationfunc00maun_0061.txt

purificationfunc00maun_0151.txt

purificationfunc00maun_0118.txt

AA00012900_00001_0136.txt

AA00012900_00001_0012.txt

purificationfunc00maun_0025.txt

purificationfunc00maun_0034.txt

AA00012900_00001_0069.txt

AA00012900_00001_0100.txt

AA00012900_00001_0074.txt

purificationfunc00maun_0099.txt

AA00012900_00001_0038.txt

AA00012900_00001_0137.txt

AA00012900_00001_0058.txt

purificationfunc00maun_0023.txt

purificationfunc00maun_0029.txt

AA00012900_00001_0108.txt

AA00012900_00001_0080.txt

purificationfunc00maun_0002.txt

AA00012900_00001_0068.txt

purificationfunc00maun_0114.txt

purificationfunc00maun_0095.txt

AA00012900_00001_0051.txt

AA00012900_00001_0063.txt

AA00012900_00001_0007.txt

AA00012900_00001_0153.txt

AA00012900_00001_0165.txt

purificationfunc00maun_0016.txt

purificationfunc00maun_0170.txt

purificationfunc00maun_0084.txt

AA00012900_00001_0114.txt

purificationfunc00maun_0105.txt

purificationfunc00maun_0067.txt

AA00012900_00001_0036.txt

purificationfunc00maun_0138.txt

purificationfunc00maun_0108.txt

AA00012900_00001_0126.txt

purificationfunc00maun_0018.txt

AA00012900_00001_0085.txt

AA00012900_00001_0098.txt

purificationfunc00maun_0169.txt

AA00012900_00001_0002.txt

AA00012900_00001_0130.txt

purificationfunc00maun_0132.txt

purificationfunc00maun_0113.txt

AA00012900_00001_0168.txt

AA00012900_00001_0084.txt

purificationfunc00maun_0130.txt

purificationfunc00maun_0044.txt

purificationfunc00maun_0131.txt

AA00012900_00001_0022.txt

AA00012900_00001_0142.txt

purificationfunc00maun_0038.txt

AA00012900_00001_0157.txt

purificationfunc00maun_0083.txt

purificationfunc00maun_0145.txt

purificationfunc00maun_0111.txt

purificationfunc00maun_0121.txt

purificationfunc00maun_0060.txt

AA00012900_00001_0166.txt

AA00012900_00001_0030.txt

purificationfunc00maun_0055.txt

purificationfunc00maun_0090.txt

purificationfunc00maun_0056.txt

purificationfunc00maun_0157.txt

purificationfunc00maun_0011.txt

purificationfunc00maun_0068.txt

purificationfunc00maun_0148.txt

purificationfunc00maun_0079.txt

AA00012900_00001_0094.txt

AA00012900_00001_0037.txt

purificationfunc00maun_0010.txt

purificationfunc00maun_0074.txt

AA00012900_00001_0054.txt

AA00012900_00001_0116.txt

AA00012900_00001_0003.txt

purificationfunc00maun_0046.txt

AA00012900_00001_0091.txt

purificationfunc00maun_0004.txt

purificationfunc00maun_0160.txt

AA00012900_00001_0132.txt

purificationfunc00maun_0026.txt

purificationfunc00maun_0076.txt

AA00012900_00001_0005.txt

AA00012900_00001_0028.txt

purificationfunc00maun_0153.txt

AA00012900_00001_0042.txt

AA00012900_00001_0024.txt

AA00012900_00001_0048.txt

AA00012900_00001_0039.txt

purificationfunc00maun_0057.txt

AA00012900_00001_0129.txt

purificationfunc00maun_0030.txt

AA00012900_00001_0119.txt

purificationfunc00maun_0091.txt

AA00012900_00001_0135.txt

AA00012900_00001_0140.txt

purificationfunc00maun_0139.txt

purificationfunc00maun_0009.txt

purificationfunc00maun_0035.txt

purificationfunc00maun_0098.txt

AA00012900_00001_0160.txt

AA00012900_00001_0016.txt

AA00012900_00001_0103.txt

AA00012900_00001_0044.txt

AA00012900_00001_0047.txt

purificationfunc00maun_0112.txt

purificationfunc00maun_0163.txt

purificationfunc00maun_0093.txt

AA00012900_00001_0106.txt

AA00012900_00001_0154.txt

AA00012900_00001_0079.txt

EL7XQ7RKC_D4W9PY_xml.txt

AA00012900_00001_0124.txt

purificationfunc00maun_0096.txt

purificationfunc00maun_0089.txt

AA00012900_00001_0078.txt

purificationfunc00maun_0049.txt

purificationfunc00maun_0048.txt

AA00012900_00001_0133.txt

purificationfunc00maun_0154.txt

purificationfunc00maun_0134.txt

purificationfunc00maun_0051.txt

AA00012900_00001_0120.txt

purificationfunc00maun_0081.txt

purificationfunc00maun_0167.txt

AA00012900_00001_0025.txt

purificationfunc00maun_0106.txt

purificationfunc00maun_0000.txt

AA00012900_00001_0075.txt

purificationfunc00maun_0146.txt

AA00012900_00001_0117.txt

AA00012900_00001_0095.txt

AA00012900_00001_0155.txt

purificationfunc00maun_0012.txt

purificationfunc00maun_0143.txt

AA00012900_00001_0110.txt

purificationfunc00maun_0027.txt

AA00012900_00001_0049.txt

purificationfunc00maun_0052.txt

AA00012900_00001_0013.txt

purificationfunc00maun_0063.txt

AA00012900_00001_0087.txt

purificationfunc00maun_0149.txt

AA00012900_00001_0073.txt

purificationfunc00maun_0043.txt

purificationfunc00maun_0050.txt

purificationfunc00maun_0092.txt

AA00012900_00001_0083.txt

AA00012900_00001_0046.txt

AA00012900_00001_0163.txt

AA00012900_00001_0112.txt

AA00012900_00001_0077.txt

purificationfunc00maun_0066.txt

purificationfunc00maun_0159.txt

purificationfunc00maun_0073.txt

purificationfunc00maun_0135.txt

AA00012900_00001_0050.txt

AA00012900_00001_0118.txt

AA00012900_00001_0009.txt

purificationfunc00maun_0136.txt

purificationfunc00maun_0077.txt

purificationfunc00maun_0152.txt

purificationfunc00maun_0072.txt

AA00012900_00001_0019.txt

purificationfunc00maun_0047.txt

AA00012900_00001_0064.txt

purificationfunc00maun_0172.txt

AA00012900_00001_0032.txt

AA00012900_00001_0158.txt

purificationfunc00maun_0039.txt

purificationfunc00maun_0166.txt

purificationfunc00maun_0021.txt

AA00012900_00001_0010.txt

purificationfunc00maun_0069.txt

purificationfunc00maun_0133.txt

AA00012900_00001_0065.txt

AA00012900_00001_0144.txt

purificationfunc00maun_0042.txt

AA00012900_00001_0161.txt

AA00012900_00001_0001.txt

purificationfunc00maun_0014.txt

AA00012900_00001_0090.txt

AA00012900_00001_0146.txt

AA00012900_00001_0057.txt

AA00012900_00001_0113.txt

AA00012900_00001_0104.txt

AA00012900_00001_0125.txt

AA00012900_00001_0062.txt

AA00012900_00001_0021.txt

purificationfunc00maun_0013.txt

purificationfunc00maun_0124.txt

purificationfunc00maun_0085.txt

purificationfunc00maun_0107.txt

AA00012900_00001_0121.txt

AA00012900_00001_0071.txt

AA00012900_00001_0122.txt

purificationfunc00maun_0144.txt

purificationfunc00maun_0078.txt

AA00012900_00001_0145.txt

AA00012900_00001_0076.txt

AA00012900_00001_0066.txt

AA00012900_00001_0164.txt

purificationfunc00maun_0120.txt

purificationfunc00maun_0161.txt

purificationfunc00maun_0033.txt

AA00012900_00001_0148.txt

purificationfunc00maun_0155.txt

purificationfunc00maun_0031.txt

purificationfunc00maun_0117.txt

AA00012900_00001_0123.txt

purificationfunc00maun_0165.txt

purificationfunc00maun_0022.txt

AA00012900_00001_0169.txt

AA00012900_00001_0006.txt

purificationfunc00maun_0070.txt

AA00012900_00001_0045.txt

AA00012900_00001_0067.txt

AA00012900_00001_0156.txt

AA00012900_00001_0015.txt

purificationfunc00maun_0007.txt

purificationfunc00maun_0129.txt

AA00012900_00001_0107.txt

AA00012900_00001_0043.txt

purificationfunc00maun_0116.txt

AA00012900_00001_0115.txt

purificationfunc00maun_0094.txt

purificationfunc00maun_0005.txt

AA00012900_00001_0099.txt

purificationfunc00maun_0109.txt

purificationfunc00maun_0125.txt

AA00012900_00001_0097.txt

purificationfunc00maun_0087.txt

purificationfunc00maun_0036.txt

AA00012900_00001_0127.txt

AA00012900_00001_0031.txt

AA00012900_00001_0172.txt

purificationfunc00maun_0140.txt

AA00012900_00001_0059.txt

purificationfunc00maun_0141.txt

AA00012900_00001_0105.txt

AA00012900_00001_0034.txt

AA00012900_00001_0131.txt

AA00012900_00001_0089.txt

AA00012900_00001_0102.txt

purificationfunc00maun_0115.txt

purificationfunc00maun_0017.txt

purificationfunc00maun_0020.txt

AA00012900_00001_0082.txt

purificationfunc00maun_0028.txt

purificationfunc00maun_0054.txt

purificationfunc00maun_0101.txt

AA00012900_00001_0060.txt

purificationfunc00maun_0075.txt

purificationfunc00maun_0008.txt

purificationfunc00maun_0102.txt

purificationfunc00maun_0037.txt

AA00012900_00001_0056.txt

AA00012900_00001_0150.txt

purificationfunc00maun_0082.txt

AA00012900_00001_0033.txt

purificationfunc00maun_0104.txt

purificationfunc00maun_0062.txt

AA00012900_00001_0004.txt

purificationfunc00maun_0080.txt

AA00012900_00001_0162.txt

purificationfunc00maun_0059.txt

AA00012900_00001_0149.txt

AA00012900_00001_0141.txt

purificationfunc00maun_0142.txt

purificationfunc00maun_0156.txt


Full Text










PURIFICATION AND FUNCTIONAL CHARACTERIZATION OF HUMAN
POLYMORPHONUCLEAR LEUKOCYTE ACTIN POLYMERIZATION INHIBITOR











By

NOEL ANTHONY MAUN


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE
UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY


UNIVERSITY OF FLORIDA


1995






























This dissertation is dedicated to all the teachers who have guided
my education at the University of Florida.













ACKNOWLEDGMENTS


I would like to thank the members of my graduate committee for
their assistance and willingness to be a part of my education. Drs. Purich,

Baker, Driscoll, and Nick's constant support throughout my graduate work
enabled me to carry the project forward. I am especially indebted to my
mentor, Dr. Frederick Southwick, for his continued encouragement and
constant scientific guidance. His traits of perpetual enthusiasm, sincerity,

willingness to learn and dedication to basic science and clinical medicine
have provided a model I hope to equal someday. I would also like to

thank Dr. Purich for always being available when advice was needed. Our
discussions were always enjoyable, and I hope someday to be able to
explain complicated topics as simply and elegantly as he always does.

Special thanks also goes out to Dr. Mary Jo Koroly for a wonderful

introduction to the basic sciences. My tenure in the lab would not have

been as enjoyable if it were not for the many friends that I have made
during graduate school.

Finally, I would like to thank my family for their love, patience, and

support throughout my education.















TABLE OF CONTENTS



ACKNOWLEDGMENTS ........................................... iii

LIST OF FIGURES ............................................... vi

ABSTRACT.................................................. viii

CHAPTERS

1 INTRODUCTION ...................................... 1

Overview ............................................. 1
The Human Neutrophil ................................. 2
Actin ................................................ 4
Actin Binding Proteins ................... ..............14
Actin Dynamics in PMN ................................ 21
Calcium Independent Model For Polymerization ........... 31
PMN Actin Polymerization Inhibitor ...................... 35

2 MATERIALS AND METHODS ............................. 37

Isolation Of Human Polymorphonuclear Leukocytes
(PM N ).................... ... .................... 37
Purification Of CapZ From Human PMN ................... 37
Purification of Muscle Actin ............................ 40
Amino Acid Sequence Analysis .......................... 40
Polyacrylamide Gel Electrophoresis And Western Blot
Analysis .......................................... 41
Actin Binding Studies ................................. 43
Lipid-Binding And Capping-Inhibition Studies ............. 45
Promyelocyte Differentiation Studies ..................... 47
Fluorescence Microscopy .............................. 50








3 PURIFICATION AND IDENTIFICATION OF CAPZ AS THE PMN
ACTIN POLYMERIZATION INHIBITOR ..................... 52

Introduction ......................................... 52
R results ................... ........................... 52
D discussion ........................................... 75

4 FUNCTIONAL CHARACTERIZATION OF PMN CAPZ ............ 88

Introduction............... ... ....... ................ 88
Results .............................................. 89
Discussion..................... ..................... 103

5 DEVELOPMENTAL EXPRESSION AND INTRACELLULAR
LOCALIZATION OF ANNEXIN VI IN PMN .................. 113

Introduction ........................................ 113
Results ................... ... ....................... 115
Discussion.......................................... 131

6 CONCLUSIONS AND FUTURE DIRECTIONS ................. 136

Conclusions ......................................... 136
Future Directions .................................... 139


REFERENCES ................................................. 144

BIOGRAPHICAL SKETCH ....................................... 160















LIST OF FIGURES


Figure page

1-1 Actin and its spontaneous polymerization in salt ............ 8


1-2 Rate constants for the association and dissociation
of ATP-actin and ADP-actin at filament ends .............. 11

1-3 fMet-Leu-Phe induced phospholipase C signaling
pathway ........................................... 26

1-4 Regulation of actin assembly in PMN ...................... 34

3-1 PMN actin polymerization inhibitor ....................... 54

3-2 Amino-terminal sequence analysis of PMN actin
polymerization inhibitor ...............................57

3-3 Nondenaturing polyacrylamide gel electrophoresis .......... 61

3-4 SDS-PAGE of phospholipid affinity chromatography,
and anti-annexin VI western analysis ................... .64

3-5 Western blot analysis of PMN inhibitory fractions
probed with capZ antisera ............................. 67

3-6 DEAE-anion exchange chromatography of PMN extract ........ 70

3-7 High S-cation exchange chromatography of PMN
actin polymerization inhibitor ......................... 72

3-8 Mono Q-anion exchange chromatography of PMN
actin polymerization inhibitor ......................... 74

3-9 Western blot analysis of PMN actin polymerization
inhibitor purified to Mono Q chromatography ............ 77

3-10 Hydroxylapatite column chromatography ................. 79








3-11 Silver stained peak fractions from Mono Q
and HA chromatography .............................. 81

4-1 Effects of purified capZ on actin filament
depolymerization ......................................91

4-2 Effects of purified capZ on actin filament polymerization
from spectrin/band 4.1/actin nuclei ..................... 94

4-3 Effects of neutrophil capZ on the extent of
actin polymerization .................................. 97

4-4 Effects of neutrophil capZ on G-actin nucleation ...........100

4-5 Actin filament severing assay ........................... 102

4-6 Effects of capZ on polymerization from
gelsolin:actin nuclei ................................ 105

4-7 Effects of PIP2 on capZ barbed-end
capping activity ............... .................. .. 107

5-1 Northern analysis of PMN and U937 ...................... 117

5-2 Northern analysis of HL-60 differentiated to
neutrophil-like or macrophage-like cells ................. 120

5-3 Western analysis of HL-60 differentiated to
neutrophil-like or macrophage-like cells ................. 123

5-4 Indirect immunofluorescence microscopy of PMN. 126

5-5 Confocal microscopy of PMN stained with
anti-annexin VI antibodies ............................ 128

5-6 Confocal microscopy of peripheral blood
monocytes stained with anti-annexin VI
antibodies ......................................... 130

5-7 Quantitation of annexin VI in human
neutrophil cytoplasmic extracts ....................... 133














Abstract of Dissertation Presented to the Graduate School of the University
of Florida in Partial Fulfillment of the Requirements for the Degree of
Doctor of Philosophy

PURIFICATION AND FUNCTIONAL CHARACTERIZATION OF HUMAN
POLYMORPHONUCLEAR LEUKOCYTE ACTIN POLYMERIZATION INHIBITOR

By

NOEL ANTHONY MAUN

May, 1995

Chairperson: Daniel L Purich, Ph.D.
Cochairperson: Frederick S. Southwick, M.D.
Major Department: Biochemistry and Molecular Biology
Actin polymerization inhibitor, an activity from human
polymorphonuclear leukocytes (PMN) which lowers the viscosity of actin
filament solutions, was previously purified by our laboratory. The calcium

independent nature of the activity suggests it may be involved in the
motile behavior of PMN based on the current theories regarding the

regulation of actin filament assembly. This activity has been found by
additional column chromatography steps and Western blot analysis to be

the heterodimeric capping protein capZ. The actin regulatory activity of
this non-muscle capZ was assessed utilizing pyrenylactin. Similar to
skeletal muscle capZ and other members of the capping protein family, I
report that non-muscle capZ purified from PMN blocks monomer exchange
at the barbed ends of actin filaments under both polymerizing and
depolymerizing conditions with an apparent disassociation constant for

capping of 3 nM. Similar to the activity reported for actin polymerization







inhibitor, PMN capZ's capping activity is independent of Ca2+ and is
inhibited by increasing the KCI concentration from 0.1 M to 0.6 M. As
observed in all previously studied barbed-end capping proteins, PMN
capZ's capping function is inhibited by phosphatidylinositol 4,5-
bisphosphate (PIP2) micelles, 1/2 maximal inhibition being observed at

5.5 pg ml-1. Phosphatidylcholine, phosphatidylserine, or
phosphatidylinositol (11 pg ml-1) fail to inhibit capping function. The
PMN capZ's effects on actin assembly are confined to an interaction with
the barbed ends of actin filaments. This protein does not cap actin
filament pointed ends, does not sever preformed filaments, and fails to
interact significantly with actin monomers. Kinetic studies reveal no
enhancement of the nucleation step in actin assembly. This first report of
a capZ-related protein isolated from mammalian phagocytes suggests that
capZ is likely to play an important role in the regulation of actin filament
assembly in phagocytic cells.













CHAPTER 1
INTRODUCTION


Overview


Cellular motility is a complex process which mandates the ability of
a cell to change its shape. In response to an external stimulus, outer
membrane receptors receive motivational signals and transmit this
information intracellularly. Subsequently, a cascade of events is initiated
which allow the cell to change its morphology and generate force for
motion towards the extracellular signal. A likely candidate which appears

central to this behavior is the self-assembling protein actin. Actin is the

most highly conserved and abundant protein in eukaryotic cells; and, in
addition, is the predominant filament of the cytoskeletal network. Unlike
in the sarcomere of muscle cells, non-muscle actin filaments are randomly
arranged in a fashion which enables the generation of force in three

dimensions rather than two dimensions. It is becoming increasingly

apparent that actin filament assembly/disassembly is vital to the process

of cell motility and shape change, and that the randomness of this
assembly is prevented by a group of regulatory proteins known
collectively as actinn binding proteins." This is a very exciting time for the
field of cellular motility and cell shape change. Amoebae, tumor cells,
leukocytes, fibroblasts, epithelial cells, and many other different cell types

share the ability to move by crawling across solid substrates utilizing a







similar process (Stossel, 1993). Our deeper understanding of the
molecular events involved may lead to a better understanding of the
biological processes which rely on cellular motility such as embryonic
development, inflammation, wound healing, tumor invasion, and host
defense. The work entailed in this dissertation centers around an actin
binding activity purified from human polymorphonuclear leukocytes

(PMN), one of the most highly motile animal cell types (10 20 pm/min)
(Howard & Meyer, 1984).


The Human Neutrophil


The neutrophil is one of the most motile cell types in the human
body; its primary purpose is to engulf and kill invading pathogens.
Histologically, polymorphonuclear granulocytes can be subdivided into
three distinct cell types named according to their staining characteristics;
the neutrophil (> 90 %), basophil, and eosinophil. Despite originating
from the same progenitor stem cell, each has a functionally distinct
immunological role (Williams et al., 1990). For the purposes of this
dissertation, the terms neutrophil, polymorphonuclear leukocyte (PMN),
and granulocyte will be used synonymously to denote neutrophil
leukocytes. In the normal human adult, the life span of the PMN is spent
in three environments: marrow, blood, and tissues (Bainton, 1992).
Proliferation and terminal differentiation occur primarily in the marrow
compartment over a period of approximately 10 days (Gallin, 1988). They
are subsequently released into the blood. This intravascular pool of
granulocytes representing only 5 % of the total number in the body is
equally divided between a freely circulating pool and a marginated pool







that is adherent to, or closely associated with, the lining of the blood
vessels (Golde, 1990). Individual cells move back and forth behaving
kinetically as a single pool. The neutrophils' stay in the blood is short,
with an approximate half-life of 6 7 hours, from where they subsequently
enter the extravascular space (Dancey et al., 1976). It is estimated that
approximately 100 billion PMN enter and leave the circulation daily
(Walker & Willemze, 1980). Despite this number, their fate after
migrating to tissues is unknown. Based on in vitro survivability of
peripheral PMN, it is thought that they probably remain functional for 1-2
days, and are then cleared (Golde, 1990).
Neutrophils are first-line defenders against invading
microorganisms. The frequent and severe infections that occur in persons
whose neutrophils are deficient quantitatively (neutropenia) or
qualitatively (e.g. chronic granulomatous disease or neutrophil actin
dysfunction) attest to the central role of this cell in host defense
mechanisms. They are the predominant leukocyte in peripheral blood
comprising two-thirds to three-fourths (4,000 8,000/mm3) of the
peripheral white blood cell count.

It is estimated that the bone marrow compartment houses PMN
reserves in excess of 100-fold the quantity found in peripheral blood.
These stores are readily discharged in response to bodily invasion.
Neutrophils are commissioned to seek, attack, and destroy pathogens and
so are endowed with the facility to rapidly advance and engage the enemy.
The major functions through which neutrophils carry out this mission
include chemotaxis, adherence, aggregation, phagocytosis, degranulation,
and generation of toxic metabolites. In part, these properties are
dependent upon an extensive rearrangement of the actin filament system







in certain parts of or throughout the cell (Stossel, 1992). The properties
of PMN chemotaxis, phagocytosis, adherence, and degranulation (the
principle movements) have gained the most attention in regards to the
relationship to cytoplasmic actin assembly.
In attempts to familiarize itself to the environment, the neutrophil
(and all animal cells to a certain extent) constantly forms and dissolves
diverse protrusions from its surface. Dependent upon external signals,
these protrusions take on particular shapes known as veils, ruffles, pleats,
filopodia, microvilli, and pseudopodia. Evidence suggests actin is
responsible for the elasticity of this organelle-deplete, actin-enriched
cortical region (Bretscher, 1991). The predominance of an agonistic signal
in certain regions allows for the formation of peripheral protrusions which
eventually lead to the motile properties of the neutrophil.


Actin


Actin Isoforms
In 1942 Bruno Straub discovered and isolated actin from rabbit
skeletal muscle (Straub, 1942). Nonmuscle cell actin was first purified
from Physarium by Hatano and Oosawa (1966). It has since been realized
that actin is ubiquitous prokaryoticc, plant, and animal cells), and often
the most abundant protein component in cells. Initially, it was thought
there were three major isoforms of actin in mammalian cells (Garrels &
Gibson, 1976). One muscle (a) and two non-muscle isoforms (3,
predominant non-muscle form, and y, second non-muscle form) could be
distinguished by isoelectric focusing; each with apparently distinct pIs
between 5.40 and 5.44. It has since been demonstrated in mammals and







birds that at least six actin isoforms exist (three a, one 3, and two y) and
are expressed in a tissue specific manner (Vandekerckhove & Weber, 1978;
Vandekerckhove & Weber, 1984). They differ from one another by only a
few amino acid residues, mainly in the first 20 N-terminal amino acids.
Utilizing near physiologic conditions, no major differences in the
polymerization characteristics of muscle vs. non-muscle isoforms of actin
are noted (Korn, 1982). As reviewed by Herman (1993), recent
compelling evidence suggests there are functional differences amongst the
muscle and non-muscle isoforms. Based on this evidence which includes
isoform-specific antibody localization and gene replacement studies, he
proposes a model cell wherein the nonmuscle isoforms are found in
regions of moving cytoplasm/cell cortex, and the muscle isoforms compose
the static microfilament bundles (stress fibers or myofibrils). Curiously, it
was recently noted that the cytoplasmic mRNAs for the p and y actin
isoforms are differentially segregated in myoblasts (Hill & Gunning, 1993),
and overexpression of either differentially impacts the cytoarchitecture of
these cells (Schevzov et al., 1992). This suggests subtle functional
differences exist even amongst the nonmuscle isoforms.


Actin Structure
Actin consists of a single polypeptide chain of 375 amino acid
residues, with a molecular weight of about 42 kDa (G-actin). It has long
been known that G-actin contains a divalent cation and an adenine
nucleotide binding site. Both sites are occupied in all forms of purified
actin. Due to its tendency to polymerize, the formation of actin crystals
and thus its atomic structure had eluded researchers for many years.
Utilizing the ability of deoxyribonuclease I (DNase I) to inhibit







polymerization, Kabash et al. (1990) were finally able to solve the
structure of the actin (muscle isoform) molecule to atomic (2.8 and 3.0 A)
resolution. Using this atomic structure along with lower resolution
analyses, the G-actin molecule can be described as an oblate sphere
(overall dimensions of 5.5 X 5.5 X 3.5 nm) composed of two major
domains (small and large) which are separated by a pronounced cleft. The
small and large domains are further divided into subdomains 1 & 2, and
subdomains 3 & 4 respectively. The four subdomains are stabilized
mainly by interactions with the nucleotide and divalent cation bound
within the cleft formed between the major domains. The crystalline
structure of beta-actin (non-muscle isoform) completed with profilin was
recently solved to 2.55 A. When compared to the c-actin structure of
Kabash et al., they appeared structurally similar with a notable 5' rotation
between the major domains.
The polar actin monomers can polymerize to form a polar actin
filament (F-actin). Geometrically, the filament can be described as a two-
start, double-stranded, right-handed helix with approximately 13 subunits
per turn. The precise orientation of the actin subunits is uncertain, but it

is thought that subdomain 2 of the monomer represents the "-" end (see
"Polymerization" below), and "+" end (see below) is within subdomain 3.

Multiple inter- and intrastrand contacts between the subunits exist. The
structure of the filament is very complicated and has yet to be directly
characterized at the atomic level. Holmes et al. (1990) have proposed an
atomic model of the actin filament which they derived from the atomic
model of the G-actin molecule and low resolution (8 A) F-actin structural
data. The intermolecular contact points in this model were recently
reviewed by Mannherz (1992).

























Figure 1-1. Actin and its spontaneous polymerization in salt. The filament
shown here is decorated with heavy meromyosin which binds at a 45"
angle distinguishing the 2 ends of the filament. The barbed-end (+) is the
fast-growing end, and the pointed end (-) is the slow-growing end of the
filament.








+


SSalt ./
0)







Polymerization

The 42,000 dalton actin monomer (G-actin) can non-covalently self-
associate and polymerize to form filaments (F-actin) in the presence of
monovalent (KC1) or divalent (MgCl2, CaC12) salts, and hence increase the

solution viscosity. The theory of actin polymerization has been reviewed
extensively by several authors (Korn, 1982; Stossel et al., 1985; Pollard &
Cooper 1986; Pollard, 1990), and will be briefly discussed. Actin
polymerization is at least a two-step process: nucleation followed by
elongation. Nucleation, the rate-limiting, thermodynamically-unfavorable
step, occurs when 3 molecules of actin associate to form the nucleus for
further assembly. Polymerization/elongation cannot proceed unless the G-
actin concentration is above a critical concentration (Cc), which is defined
as the minimum concentration of G-actin required to form a polymer
(Pollard & Cooper, 1986). The Cc value is sensitive to the ionic conditions,
pH, temperature, and nucleotide content of the reaction solution
(Zimmerle & Frieden, 1986; Zimmerle & Frieden, 1988). Despite the
minimal requirements, many groups have simulated physiologic
conditions (0.1 M KCI, 1mM MgCl2, EGTA-to chelate Ca2+, 1mM ATP, and

pH 7.4) during their analysis of polymerization kinetics. As alluded to
earlier, at near physiologic conditions the critical concentrations for
assembly of muscle and non-muscle actin isoforms are virtually
indistinguishable. Under defined conditions, actin filament assembly
reaches a steady-state as a result of actin molecules continually being
exchanged between actin filaments and the critical concentration of
monomers without affecting the overall F-actin content.
The actin filament has two kinetically different ends (barbed "+"
and pointed "-") defined by the arrowhead pattern produced when an


























Figure 1-2. Rate constants for the association and dissociation of ATP-
actin and ADP-actin at filament ends. Adapted from Pollard (Curr. Opin.
Cell Biol. 1990. 2: 33-40)







ATP


1 0.7
1.2 \











12,


0.13 .3
S 0.3


\ \8
4


SATP
Unit K+ = pmol-l s-1
K. = s-1







actin filament is labeled with heavy meromyosin ("rigor" conformation)
and visualized by electron microscopy (Huxley, 1963). The barbed (+)
ends have a greater exchange rate and a lower critical concentration (Cc+
= 0.1 pM) for monomer binding than the pointed (-) ends (Cc- = 0.6 pM)

(Bonder et al., 1983). Thus, the barbed ends are the more kinetically
active and preferred ends for filament growth. At steady-state, i. e. when
the association rate equals the dissociation rate, the apparent critical
concentration for the entire filament (Cc = 0.15 pM) is closer to that of the
barbed end (Korn, 1982). As a result, a steady-state condition termed
"treadmilling" occurs in which monomers slowly dissociate from the
pointed ends allowing new monomers to rapidly add on to the barbed
ends (Neuhaus et al., 1983; Wanger et al., 1985).
Actin polymerization is more rapid in the presence of ATP than in
the presence of ADP (Carlier et al., 1984; Pollard, 1984). This is not due to
energy made available through ATP-hydrolysis since polymerization can
occur faster than ATP-hydrolysis (Carlier et al., 1984). The differential
polymerization rates could be explained by the fact that ATP-G-actin has a
higher affinity and a lower dissociation rate than ADP-G-actin (Pollard &
Cooper, 1986). The hydrolysis of the ATP within the actin molecule
consists of two temporally distinct steps: the chemical cleavage of ATP
resulting in an ADP-Pi-actin followed by the slower release of Pi into the

medium (Korn et al., 1987). Additionally, it has been shown that the
cleavage of ATP occurs vectorally (Carlier et al., 1987). This suggests that
if one examines a filament during the polymerization of ATP-actin, the
newly added actin molecules are ATP-actin followed by ADP-Pi-actin, and
most internally, ADP-actin (Carlier, 1991). Since the dissociation rate of
ATP-actin is slower than ADP-actin, the delayed ATP hydrolysis promotes







actin filament assembly. Under these conditions, the extent of this "ATP-
cap" is dependent upon the polymerization rate. In contrast,
depolymerization is facilitated by the exposure of these internal ADP-actin
molecules. In this model, the presence of ATP and its hydrolysis may
partially regulate the rapid reorganization of actin structures.

Using electron microscopy to monitor the elongation rates of
preformed filaments as a function of added G-actin has enabled the
determination of the rate constants for the "elongation" reactions (Bonder
et al., 1983; Pollard, 1986). The differences between ATP-actin and ADP-
actin result in eight main reactions (Figure 1-2). Several labs have
determined various rate constants, and at least two labs have generated all
eight (Pollard, 1986; Korn et al., 1987). There is general agreement (at
least within an order of magnitude) regarding the values of these rate
constants.

The different affinities of the various forms of nucleotide-bound
actin monomers for filaments may be due to conformational changes. In
Kabsch's atomic models comparing ATP- and ADP-actin, there are direct

interactions between the calcium ion and the p- and y- phosphates of ATP
(3 alone with ADP) within the cleft, and subtle differences in the hydrogen
bonds formed between the phosphate groups with neighboring amino
acids (Kabsch et al., 1990). The atomic structure of Mg2+-ATP-actin,
although, may be quite different, as suggested by the fluorescence
difference seen when AEDANS (N-acetyl-Nl-[sulfo-1-
napthyl]ethylenediamine) labeled actin is in a Mg2+ verses a Ca2+
environment (Selden et al., 1986). Despite the literature available on the
effects of calcium or magnesium binding to actin (Estes, 1992), this







complicated topic will not be covered. Additionally, it is generally
accepted that Mg2+ is the divalent cation bound to actin in the cell.


Actin Binding Proteins


Background
It was recognized early on that at least 50 % of the actin in extracts
from various non-muscle cells is nonpolymerized, in stark contrast to
muscle cells in which nearly 100 % of the actin is polymerized (Korn,
1982). Based on the earlier findings that nonmuscle isoforms of actin
share the same polymerization kinetics and critical concentrations as
muscle isoforms, it was hypothesized that the polymerization of actin in
nonmuscle cells was regulated through the interaction of actin with other
cellular components. This hypothesis was amply supported by the
identification of nonmuscle cell proteins that have specific interactions
with G-actin and/or F-actin.
On the basis of their ability to interact with actin in vitro, these
proteins were collectively termed "actin-binding proteins" (Stossel et al.,
1985; Pollard & Cooper, 1986; Hartwig & Kwiatkowski, 1991). Today, over
100 such nonmuscle proteins have been described. They are felt to be
responsible for the coordinated regulation of nonmuscle cell actin

polymerization considered necessary for motile activities as well as the
maintenance of structural integrity. Actin-binding proteins can be
subdivided into groups that either control the three-dimensional
arrangement of actin filaments (cross-linking and bundling proteins),

apply force to the actin-filament network (myosins), or regulate actin-
filament number and length (capping, severing, nucleating, and monomer-







binding proteins). Although the groups that control the three-dimensional
arrangement of actin filaments (gelation to solution or gel-sol reaction)
and those that apply force (contraction of actin gels) to the network are
almost certainly involved with the motile behavior of PMN (Condeelis,
1993), this discussion on actin-binding proteins will be limited to the
subset controlling actin-filament number and length.
The regulation of actin filament number and length is achieved by
four principle mechanisms. First, capping describes the ability of a
regulatory protein to bind to either the barbed ("+") or pointed ("-") end
of an actin filament preventing further addition or loss of monomers at
the particular end "capped." Severing is the mechanism whereby an actin-
binding protein is able to interact with the side of a filament and disrupt
the intermolecular interactions at that site, thus breaking the filament in
two. This is usually achieved by binding a "barbed" region within the
filament, and thus one of the newly severed fragments is capped at their
barbed end (Weeds & Maciver, 1993). The third mechanism, nucleation,
describes the ability of a protein to initiate elongation of actin filaments
without a lag phase. This may be achieved by either the rapid induction
of a polymerization-favorable conformation or stabilization of
intermediates in the formation of the trimeric nucleus. The forth
mechanism describes the ability of an actin binding protein to sequester
monomers in a 1:1 complex and inhibit their incorporation into filaments.
Therefore, if monomer-binding proteins are added to a solution of actin
monomers in stoichiometric amounts, the final extent of polymerization
upon the addition of salts will be decreased. The decrease will be
dependent upon the critical concentration of actin and the dissociation
constant of the interaction with actin monomers. It must be noted that the







in vitro analysis and in vivo interpretation of function of actin binding
proteins is often complicated by their ability to utilize more than one
mechanism to regulate actin filaments.


Monomer Sequestering Proteins

A high concentration of actin, well above the Cc necessary for
assembly at both ends of the filament, is stored in an unpolymerized form
in nonmuscle cells (100 200 UM or greater in PMN, assuming a uniform
distribution) and becomes available for assembly into filaments upon cell
activation. Monomer sequestering proteins are felt to account for a
majority of the unpolymerized actin found in these cells. The two major
families of proteins in this class are the profilins and the thymosins.
Mammalian profilins are low-molecular-weight proteins with Mr

around 15,000. Initially purified from spleen (Carlsson et al., 1977), it
has since been found in almost all mammalian cell types including PMN,
macrophages, and platelets (Southwick & Young, 1990; DiNubile &
Southwick, 1985; Markey et al., 1978). Purified profilin is able to
reversibly bind actin monomers with an apparent dissociation constant
(Kd) in the range of 1 to 10 pM (Larsson & Lindberg, 1988; Goldschmidt-
Clermont et al., 1991). For many years, profilin was thought to be the
major sequestering protein in nonmuscle cells, and simple sequestration
was its primary function. Estimations of profilin concentrations made
initially in platelets and subsequently in PMN suggested the concentration
of profilin (~40 pM) present within these cells is insufficient, when using
the simple model of sequestration, to account for the amount of
nonpolymerized actin (-100 200 pM) in resting states (Lind et al., 1987;
Southwick & Young, 1990).







In search for additional monomer sequestering proteins, a 5 kD
peptide was discovered in high concentrations in human platelets (Safer et
al., 1990). Sequence analysis revealed identity to a peptide believed to be
a thymic hormone, thymosin f4 (T94) (Safer et al., 1991). Based on its

wide distribution pattern and lack of secretary activity, this protein is no
longer believed to be a hormone. The dissociation constant (Kd) for the
TI4-actin complex has been reported to be in the 0.4 2.0 pM range

(Nachmias, 1993). It is calculated that in human PMN the cytoplasmic
concentration of Tf4 is ~150 pM, and together with profilin can account

for the sequestration of a majority of the G-actin in resting PMN
(Cassimeris et al., 1992). The amount of actin sequestered can be
estimated using the following equation for the dissociation constant (Kd)

of the sequestered monomer (Stossel et al., 1985):
Kd = [sequestering protein]free [Cc actin]/[sequestered G-actin]

Note that the concentration of sequestered actin is quite sensitive to the
critical concentration of actin.

With the recent suggestions that thymosin R4 alone is capable of
sequestering a majority of the G-actin in resting cells (platelets ~560 pM;
Weber et al., 1992), the question arose as to the role of the ubiquitous
protein profilin. Still controversial, several different actin regulatory
functions for profilin besides its ability to sequester monomers have been
proposed (Theriot & Mitchison, 1993). In the writer's opinion, the most
fascinating proposed mechanism is this protein's ability to interact
catalytically with actin in a fashion promoting exchange of the bound
nucleotide and divalent cation. It was noted early on that Acanthamoeba
profilin interacts with G-actin to increase the rate of exchange of the
bound nucleotide (Mockrin & Korn, 1980). This is consistent with







structural data obtained by chemical cross-linking and X-ray
crystallography which suggests profilin binds to actin in subdomain 3, a
region opposite the cleft wherein the adenosine nucleotide and divalent
cation bind (Vandekerckhove et al., 1989). The binding of DNase I to
subdomain 1 inhibits the nucleotide exchange rate, most likely by blocking
its exit from the cleft (Hitchcock, 1980; Mannherz et al., 1980). It is
foreseeable that conformational changes induced upon the binding of
profilin may alter the nucleotide and divalent cation binding sites within
the cleft. It was recently demonstrated that profilin, when bound to actin,
increases the off rate constant (k-) of the bound nucleotide by 1,000-fold

(Goldschmidt-Clermont et al., 1991). More importantly, kinetic modeling
of the nucleotide exchange rates revealed that at substoichiometric
amounts profilin is still able to accelerate the nucleotide exchange of the
whole actin population. In this model, the catalytic mechanism is possible
because the rate of profilin's exchange between actin monomers is
relatively rapid (sub-second), but slower than the rapid dissociation of
actin ligands (nucleotide, divalent cation) which occurs during the
transient binding of profilin to each actin molecule (Goldschmidt-
Clermont et al., 1991). As discussed earlier, the kinetics of actin
polymerization are highly dependent upon the type of nucleotide bound.
Therefore, this mechanism may be central to the cell's ability to rapidly
"recharge" actin molecules which are continuously being cycled through

polymerization in highly motile regions of the cell.


Capping Proteins

Experimental evidence suggests the assembly of actin in nonmuscle
cells occurs by addition of monomers to the barbed ends of actin filaments







(Wallace et al., 1984; Carson et al., 1986). All capping proteins purified
from non-muscle cells thus far cap (in vitro) the barbed ends of F-actin
filaments. Inhibiting exchange at the high affinity, barbed end effectively
raises the Cc to that of the pointed end. The steady-state result of the
interaction of these capping proteins with actin is increasing the
concentration of the G-actin pool and creating a large number of relatively
short filaments. Two proteins, accumentin and l-actinin, were originally
reported to cap the pointed end of F-actin filaments, but their activities
have since been shown to actually be barbed end capping of filaments
(acumentin) (Young, Maun, and Southwick unpublished data; Maruyama
et al., 1990). Barbed-end capping proteins are grouped based on their
functional and structural characteristics (Hartwig & Kwiatkowski, 1991;
Weeds & Maciver, 1993). The two major families of capping proteins are
the gelsolin family and the capZ family. The major functional difference
between these families is that proteins in the gelsolin family require
calcium to initiate the interaction with actin whereas the capping activity
of the capZ family occurs independently of calcium.
The gelsolin family of capping proteins is composed of the
structurally related mammalian (gelsolin, villin, capG, and scinderin) and
invertebrate proteins (fragmin and severin) (Mishra et al., 1994). Each
member is able to nucleate filament assembly and sever preformed
filaments (except capG; Southwick & DiNubile, 1986) in addition to their
collective ability to cap the barbed end. The founding and best
characterized member is gelsolin. Originally purified from rabbit alveolar
macrophages as a 91 kDa protein, gelsolin is now known to be widely
distributed (including muscle cells) (Yin & Stossel, 1979; Yin et al., 1981).







As reviewed by Stossel et al., (1985), the three in vitro effects of
gelsolin on actin are differentially dependent upon the Ca2+
concentration. Severing has the most stringent calcium requirement, and
does not occur in the presence of submicromolar Ca2+. Barbed-end
capping occurs to a small extent in the presence of submicromolar Ca2+,
but this activity is markedly enhanced at higher calcium concentrations.
Gelsolin is able to nucleate filament assembly in the presence of calcium

by forming a complex (1 gelsolin: 2 actin) with two molecules of actin
(Janmey et al., 1985). Removal of calcium by EGTA dissociates one of the
actin monomers leaving behind a stable 1:1 gelsolin-actin complex. This
EGTA-resistant complex is unable to sever filaments, but can now bind the
barbed ends of filaments with high affinity even at submicromolar calcium
concentrations. Gelsolin has also been isolated as an alternatively spliced,
93 kDa, plasma form differing from the cytoplasmic form by the presence
of an additional 25 N-terminal amino acids (Kwiatkowski et al., 1986).
The secreted gelsolin is hypothesized to maintain and buffer a low plasma
actin filament content even when the cytoplasmic components of cells are
spilled into the vasculature during processes such as injury.

The capZ family includes heterodimeric proteins with subunits of
30-35 kDa which are able to bind the barbed end of actin filaments
independently of calcium. Most members described can nucleate filament
assembly, but all lack the ability to sever filaments. CapZ, a heterodimeric
protein with subunits of Mr = 36,000 (a-subunit) and 32,000 (P-subunit)
daltons, is the best characterized member of this family (Casella et al.,
1986). Purified skeletal-muscle capZ caps the barbed end of filaments
with an apparent dissociation constant of approximately 0.5 1 nM
(Caldwell et al., 1989a). It was originally purified from skeletal muscle







and localized to the sarcomeric Z-line (Casella et al., 1987). CapZ has
subsequently been recognized in nonmuscle cells as well (Caldwell et al.,
1989b; Schafer et al., 1992). It has recently been recognized that barbed-
end capping proteins purified from Acanthamoeba (Isenberg et al., 1980),
Dictyostelium (Schleicher et al., 1984), Xenopus (Ankenbauer et al., 1989),
Saccharomyces (Amatruda & Cooper, 1992) and bovine brain (Kilimann &
Isenberg, 1982) are indeed analogues of capZ. The presence of
mammalian capZ in highly motile cell types such as PMN and macrophages
has yet to be noted. It was recently reported to be present in human
platelets (Barkalow & Hartwig, 1994; Nachmias et al., 1994).


Actin Dynamics In PMN


PMN Chemoattractants

Chemoattractants are substances which have the ability to induce
directed migration. The three major groups of neutrophil
chemoattractants are described as complement-derived (C5a), leukocyte-
derived (LTB4, PAF, 11-8), and bacterial-derived (formylated peptides, e.g.
fMet-Leu-Phe). Neutrophils can sense a chemotactic concentration
gradient as small as 1 % across their dimension (Zigmond, 1977). As
discussed below, the rapid, chemoattractant-induced polymerization of
actin is probably the best understood transduction mechanism involved in
regulating the actin microfilament network. Overall, the transduction
mechanisms which regulate cellular actin assembly, although, remain
poorly understood.
Curiously, nanomolar concentrations of chemoattractants are
enough to induce shape change and locomotion in neutrophils, whereas it







takes much higher (micromolar) concentrations to induce the microbicidal
mechanisms of PMN (Gallin, 1988). Chemoattractants transmit their signal
through specific surface receptors, and many appear to utilize a common
signal transduction pathway. The bimodall" response of PMN to
chemoattractants (differential triggering of motile verses microbicidal
functions) is currently thought to result from the activation of additional
transduction pathways dependent upon the extent of the chemotactic
stimulus (Snyderman & Uhing, 1992). The remaining discussion in this
chapter will focus on the rapid actin assembly occurring during the initial
phase as the transductional events of the second phase are poorly
understood. The fMet-Leu-Phe peptide has been termed the neutrophil
"pan-activator" for its ability to induce almost all major PMN functions in

addition to chemotaxis (Becker, 1987), and consequently its signal
transduction mechanisms have been extensively studied (for review see
Snyderman & Uhing, 1992).


Rapid Polymerization In Response To fMet-Leu-Phe

The overall morphology of PMN dramatically changes in response to
chemotactic stimulation (Fechheimer & Zigmond, 1983; Howard & Oresajo,
1985). At rest the cells are spherical, and upon stimulation form
peripheral ruffles or lamellipodia at their surface which have been shown
microscopically to be highly concentrated in F-actin (Fechheimer &
Zigmond, 1983; Sheterline, et al., 1984a). Neutrophils contain
approximately 5 pg actin/cell, which correlates to roughly 10 % of the
total cellular protein in these cells (Sheterline et al., 1984b). Others have
calculated that actin represents as high as 20 % of PMN extracts
(Southwick & Young, 1990). Probably the best evidence suggesting actin







dynamics is important in PMN cell motility are the changes in the ratios of
monomeric to filamentous actin seen when cells are stimulated to undergo
motility. The rapid, chemoattractant-induced actin polymerization
response occurs in many eukaryotic cells, in addition to PMN, which are
able to undergo "amoeboid-like" motility (Stossel, 1992; Caterina &
Devreotes, 1991).

In resting PMN approximately 30 40 % of the total actin
concentration is F-actin (Feichheimer & Zigmond, 1983; Sheterline et al.,
1984b; Bengtsson et al., 1986). Assuming a uniform distribution, this
corresponds to roughly 100 pM F-actin and 200 pM G-actin (Southwick &
Young, 1990). Remarkably, several laboratories have demonstrated that
within 30 seconds or less of fMet-Leu-Phe stimulation, the actin filament
content doubles (F-actin: -100 -> 200 pM) (Shalit et al., 1987; Howard &
Meyer, 1984; Fechheimer & Zigmond, 1983; Omann et al., 1987; Lofgren et
al., 1993). Cytochalasins, in vitro inhibitors of actin polymerization,
inhibit the morphological changes associated with neutrophil motility
(Zigmond & Hirsch, 1972) as well as the induced rise in polymerized actin
(Southwick et al., 1989; Cassimeris et al., 1990; White et al., 1983).
Furthermore, the dose dependency of the fMet-Leu-Phe-induced
chemotaxis and the rapid, actin-polymerization response are similar
(Howard & Meyer, 1984).

Dynamic changes in actin filament content occur during other PMN
motile events such as phagocytosis, degranulation, and adherence. A
nearly twofold rise in actin filament content is also observed during these
neutrophil functions (Boyles & Bainton, 1981; Fechheimer & Zigmond,
1983; Southwick et al., 1989), but the dissection of the transduction
cascade is complicated by the activation of multiple pathways. Although







these functions can be initiated by fMLP stimulation, their predominant
signal transduction pathways appear to be different (Southwick et al.,
1989; Rosales et al., 1994).


fMet-Leu-Phe Signal Transduction Pathway
The N-formylated methionyl peptides such as fMet-Leu-Phe activate
neutrophils by binding to a specific cell surface receptor. The primary
structure of the fMet-Leu-Phe receptor has been deduced from its cDNA
sequence, revealing it belongs to the G-protein-coupled receptor family
(Boulay et al., 1990). Nearly all G-protein-coupled receptors share a
similar sequence motif which allows for seven-transmembrane-segments
(7-TMS motif) that span the lipid bilayer (Dohlman et al., 1991). The
recent sequence data only confirmed what had been suspected about the
fMet-Leu-Phe signal transduction cascade based on biochemical studies.
Pertussis toxin, a well known inhibitor of some G-proteins, inhibits
many chemotactic responses in a concentration dependent fashion (Brandt
et al., 1985; Becker et al., 1985; Bengtsson et al., 1986). Guanine
nucleotides, and not adenine compounds, regulate the affinity state of the

plasma purified f-Met-Leu-Phe receptors (Sklar et al., 1987). Chemotactic
factors stimulate membrane associated GTPase-activity and guanine
nucleotides can potentiate fMet-Leu-Phe induced activation (Feltner et al.,
1986; Verghese et al., 1986). Additionally, a GTP-binding, 40 kDa
pertussis-toxin-substrate complex copurifies with the fMet-Leu-Phe
receptor after several chromatographic steps. Immunochemical
identification and cDNA sequence analysis reveal the PMN G-protein
coupled to the fMet-Leu-Phe receptor is of the Gi2 (pertussis toxin


















Figure 1-3. fMet-Leu-Phe induced phospholipase C signaling pathway. Stimulation of PMN results in the
doubling of intracellular F-actin in < 30 sec.

















PIP2


PKC


GIP GDP


Calciosome > TCa2+







sensitive, phospholipase C activator) subtype (Snyderman & Uhing, 1992;
Kaziro et al., 1991).
The kinetics and dose-dependency of the fMet-Leu-Phe-induced
actin polymerization burst coincides with the rapid, initial phase of the
fMet-Leu-Phe response (discussed under "PMN chemoattractants"). The
following sequence of major intracellular events comprise this initial
phase. In short, binding of fMet-Leu-Phe to its receptor results in the
dissociation of a membrane-bound, heterotrimeric, GTP-binding protein
(G-protein). This activated G-protein (Gi2-alpha subunit) transiently

activates phospholipase C to produce two second messengers, 1,2-
diacylglycerol (DAG) and inositol (1,4,5) triphosphate (IP3) from
phosphatidylinositol(4,5) bisphosphate (PIP2) hydrolysis. Inositol

triphosphate releases intracellular stores of calcium, while DAG activates
protein kinase C. The rapid cleavage of PIP2 by PKC results in the
conversion of other phosphoinositides such as PIP and PIP3 to PIP2. The
conversion of phosphoinositides is regulated by a large number of kinases
and phosphatases that add or remove phosphates on the inositol ring
(Janmey, 1994). Temporal studies show rapid (< 5 sec) elevations in
phosphoinositide metabolism and cytosolic calcium levels following fMet-
Leu-Phe stimulation. The molecular mechanisms responsible for the
cytochalasin-sensitive, rapid (< 15-30 sec) and dramatic increase in actin
polymerization in response to fMet-Leu-Phe remain unknown, but are
thought to involve these molecules.

Calcium And Protein Kinase C-Indeoendent. Phosohoinositide-Dependent
fMLP-Induced Actin Polymerization Response
Modulation of the transductional cascade using traditional
pharmacological agents demonstrates that neither calcium or protein







kinase C (PKC) are primarily associated with the rapid polymerization of
actin in PMN stimulated with fMet-Leu-Phe. Since this fMet-Leu-Phe-
induced increase in F-actin content in PMN is totally abolished if cells are
pretreated with pertussis toxin (Bengtsson et al., 1986; Omann et al.,
1991), investigators have actively pursued potential signals distal to the G-
protein, but proximal to calcium release and protein kinase C activation.
In addition to calcium, the in vitro actin regulatory activities of various
actin binding proteins are modulated by phosphoinositides. These in vitro
findings in combination with the observation that phosphoinositides are
rapidly turned over in PMN stimulated with fMet-Leu-Phe has led to the
hypothesis that phosphoinositides are primarily involved in the regulation
of the rapid, actin-polymerization response (Stossel, 1989; Janmey, 1994).
Phorbol esters, exemplified by phorbol myristate acetate (PMA),
have been shown to bind, translocate, and activate PKC in human
neutrophils (Castagna et al., 1982; Nishihira et al., 1986), and are
consequently utilized as specific PKC activators. Only minor increases in
F-actin content are noted when resting human neutrophils are stimulated
with levels of PMA that phosphorylate much more effectively than fMLP

(Bengtsson et al., 1986; Howard & Wang, 1987). Conversely, several
protein kinase inhibitors with relative specificity for PKC (i.e.,
staurosporine, CGP 41251, and H7), when used at functional
concentrations, do not significantly alter the rapid, 2-fold increase in F-
actin seen within 30 seconds of fMet-Leu-Phe stimulation of neutrophils
(Niggli & Keller, 1991; Keller & Niggli, 1993; Sham et al., 1993).
Additionally, neutrophil chemotaxis induced by fMet-Leu-Phe is only
slightly inhibited by staurosporine (Boonen et al., 1993).







Chemotactic stimulation increases the intracellular free calcium
concentration, [Ca2+], from the 100 nM level at rest to micromolar levels
(Janmey, 1994). Despite buffering resting neutrophil [Ca2+]i with calcium

chelators (e.g., EGTA, quin-2, BAPTA), the cells are still capable of
migrating at normal rates (Elferink & Deierkauf, 1985; Meshulam et al.,
1986; Zigmond et al., 1988). The fMLP-induced rise in [Ca2+] involves
both the release of calcium from intracellular stores (via IP3) and influx

across the membrane. The use of fluorescent calcium indicators (quin2 or
fura2) reveals the "biphasic" nature of this fMLP-induced increase (Lew et
al., 1984; Lew et al., 1986; Anderson et al., 1986). The prolonged second
phase is eliminated by removal of extracellular calcium, while the rapid
first phase remains unaffected. The rapid doubling of F-actin in response
to fMet-Leu-Phe stimulation is temporally associated with the initial rise in
[Ca2+]i caused by IP3 (Snyderman & Uhing, 1992). Preventing the fMet-
Leu-Phe-induced rise in calcium with calcium chelators has no effect on
the neutrophil's ability to double its F-actin content within 15 30 seconds
(Sha'afi et al., 1986; Downey et al., 1990; Sham et al., 1993). Neutrophil
migration is a complex process that involves the continuous cycling of
polymerization and depolymerization. It is possible that the repetitive
increases in intracellular calcium in migrating PMN (Marks & Maxfield,
1990; Jaconi et al., 1990) may actually enhance depolymerization of actin
filaments by activating the severing activity of proteins like gelsolin
(Downey et al., 1990).
With increasing evidence suggesting neither calcium nor protein
kinase C activation were necessary for the chemoattractant-induced actin
polymerization seen in PMN, the signaling role of phosphoinositides was
actively investigated. It has been known for over 30 years that







phosphoinositide phospholipids such as PIP2 can form complexes with

certain proteins (Janmey, 1994). Since phosphoinositide turnover via
phospholipase C hydrolysis of PIP2 is one of the major intracellular events

occurring proximal to either the increase in calcium or activation of
protein kinase C in activated PMN, the proposal that phosphoinositides
might regulate actin assembly seems plausible (Lassing & Lindberg, 1985;
Stossel, 1993). With the finding that phosphoinositides modulate the in
vitro interaction of profilin with actin, Lassing and Lindberg proposed
phosphoinositides may regulate actin assembly in cells. They were able to
demonstrate that actin sequestered by profilin can be dissociated by PIP2,

thus leading to actin polymerization (Lassing & Lindberg, 1985). Since
that time, numerous other actin-binding proteins have been shown to
interact with phosphoinositides (Isenberg, 1991; Janmey, 1994).
Interestingly, the interaction of barbed-end capping proteins with actin is
also specifically inhibited in the presence of polyphosphoinositide
phospholipids (Janmey, 1994).

Stossel has recently proposed a model that integrates motile signal
transduction events with the modulation of actin binding proteins in
attempts to explain how animal cells are able to crawl in response to a
stimulus (Stossel, 1993). The motile behavior of certain animal cells is
partly explained by the rapid polymerization of actin. In this model, a
motile stimulus results in the rapid turnover of intracellular
phosphoinositides. This in turn causes release of sequestered monomers
of actin, and prevention of barbed-end cap formation. The net result
would be a rapid polymerization of monomeric actin onto the barbed-ends
of actin filaments.







Utilizing fluorescent actin probes, it can be demonstrated that
fibroblasts undergo actin filament assembly and disassembly. The
lamellipodium of a cultured fibroblasts includes a dense network of actin
filaments (Wang, 1985). Fluorescence photobleaching of a discrete region
within the lamellipodium demonstrates centripetal movement and
eventual disappearance at the proximal edge of the actin band, a process
not unlike treadmilling. Their finding suggests actin filaments within the
lamellipodium are undergoing net assembly at their distal, membrane-
directed barbed ends and net disassembly at their proximal pointed ends
(Wang, 1985). Electron micrographs of neutrophils whose actin filaments
are decorated with heavy meromyosin reveal the barbed ends of actin
filaments are directed peripherally towards the membrane (Pryzwansky et
al., 1983). In addition, when PMN are stimulated with fMet-Leu-Phe, the
number of nucleation sites for actin polymerization is increased
transiently (Carson et al., 1986). These nucleation sites are sensitive to
cytochalasin, a drug whose actin inhibitory activity is partly explained by
its ability to cap the barbed-end of filaments, and they sediment with the
detergent insoluble actin cytoskeleton (Carson et al., 1986). These
findings suggests that neutrophils rapidly increase their F-actin content by
increasing the number of free barbed-ends upon chemotactic stimulation.


Calcium Independent Model For Polymerization


The two mammalian cell types which undergo a rapid (5 30 sec.)
doubling of actin in response to stimulation are phagocytes neutrophilss
and macrophages) and platelets. Profilin and thymosin 94 have both been

purified in these cell types. The only capping proteins that have been







purified from phagocytes are members of the calcium-dependent/gelsolin
capping-protein family. CapZ was recently noted in platelets (see
"Capping Proteins")
A simple model integrating what is currently known about
neutrophils and other motile cells is suggested by Stossel (1993). At rest,
a majority of the actin filaments are capped at their membrane-proximal
barbed-ends. This leads to a critical concentration of free actin monomers
close to the dissociation constant of the freely-exchanging minus-end (~1.0
pM). As discussed earlier, the concentrations of monomer sequestering
proteins (profilin and thymosin R4) and their affinities for actin
monomers (Kd ~0.5 5 pM) can explain the high amounts of

unpolymerized actin in resting neutrophils (> 60 %). Stimulation of
neutrophils with chemotactic peptide causes an increased
phosphoinositide turnover (Snyderman & Uhing, 1992; Janmey, 1994).
Based on the findings that profilin and the barbed-end capping proteins
bind the phosphoinositides PIP and PIP2 thereby inhibiting their ability to

bind to actin, it is thought that phosphoinositides mediate the signal
transduction between the surface receptors and actin assembly (Stossel,
1993). In this model it is explained that phosphoinositides cause the
uncapping of membrane-proximal barbed-ends, thus lowering the critical
concentration of actin monomers in that region closer to that of the
barbed-end (0.1 0.3 pM). Since the critical concentration of free actin
monomers is lowered, a majority of the sequestered actin can be released
into the polymerizable pool (see "Monomer Sequestering Proteins").
Stimulation of neutrophils may activate profilin's ability to increase the
nucleotide exchange rate of actin molecules, thus ensuring a continuous

supply of ATP-actin available for rapid polymerization (Goldschmidt-


















Figure 1-4. Regulation of actin assembly in PMN. This simple model attempts to explain the rapid
assembly of actin in fMet-Leu-Phe stimulated PMN.






Rest


+-C XDOCOOO


ID


[IK


fMLP < 30 sec
(tPhosphoinositide Turnover)

Gelsolin/Ca2+
+ CC _

[] OOO 0 ADP


ATP

r n ATP







Clermont et al., 1991). The role of profilin in activated PMN remains
controversial since the PIP2 effect would theoretically prevent ATP/ADP

exchange.
There have been no reports of calcium-independent capping
proteins in neutrophils or macrophages. Two abstracts were recently
presented at the ASCB (American Society for Cell Biology) meeting
December, 1994 noting the presence of capZ in platelets (Barkalow &
Hartwig, 1994; Nachmias et al., 1994). These three cells are the
mammalian model cells for understanding the signal transduction
mechanisms leading to rapid actin assembly. As discussed above, the
rapid polymerization response in neutrophils can occur independently of
calcium. It is upon these premises that we have further investigated the
calcium insensitive activity of PMN Actin Polymerization Inhibitor, an
activity originally purified by my mentor Dr. Southwick.


PMN Actin Polymerization Inhibitor


A Maior Calcium-Independent Activity In PMN Extracts

Approximately 15 years ago, Southwick and Stossel isolated an actin
binding activity from human neutrophils thought to account for much of
the unpolymerized actin in granulocyte extracts (Southwick & Stossel,
1981). This activity, PMN actin polymerization inhibitor, was shown to
decrease the viscosity of purified skeletal-muscle actin under polymerizing
conditions in the presence of 1 mM EGTA and absence of added calcium.
Substoichiometric concentrations of the inhibitor were still able to
decrease the viscosity of purified actin allowed to polymerize in the
presence of 0.1 M KC1. PMN Actin Polymerization Inhibitor was purified







from granulocyte extracts by DEAE-ion exchange chromatography and gel-
filtration chromatography. The viscosity lowering activity of the column
fractions was monitored using a Cannon-Manning semi-microviscometer.
The purified inhibitor was noted to contain polypeptides of 65,000 and
62,000 daltons by SDS-PAGE. The Stokes radius of the inhibitor was
reportedly 32 A and the s20,w was 4.8. These data were felt to be

compatible with the inhibitor being a globular monomer with a native
molecular weight similar to that of the 65,000 and 62,000-dalton peptides
resolved by SDS-Page. Increasing KCI concentrations from 0.1 0.6 M KCI
reversed the inhibition.

All activity studies were done in the absence of added calcium and
presence of 1 mM EGTA to avoid the potential contaminating activity of
the calcium dependent protein gelsolin. The PMN actin polymerization
inhibitor is hence a major calcium-independent actin filament regulatory
protein. The recent findings that the PMN actin polymerization-burst in
response to fMet-Leu-Phe occurs independently of calcium has prompted
my further examination of this inhibitor's actin regulatory role.













CHAPTER 2
MATERIALS AND METHODS


Isolation Of Human Polvmorphonuclear Leukocvtes (PMN)


Fresh leukocyte enriched fractions from the whole blood of healthy
donors were obtained from the community blood bank. For each
preparation, 15 45 buffy coat units were used. Further isolation of
leukocytes was accomplished using a variation of the technique described
by Southwick and Stossel (1981). Briefly, leukocyte enriched fractions
were pooled and sedimented through Dextran T-500 (Pharmacia Biotech
Inc., Piscataway, NJ). This procedure yielded on average 85 % PMN the
remainder of the cells representing lymphocytes (12 %) and monocytes (3
%). In some cases this procedure was followed by Ficoll-sodium diatrizoate
sedimentation. This procedure increased the purity of PMN to 95 %. CapZ
obtained from granulocytes isolated with or without a Ficoll-sodium
diatrizoate sedimentation resulted in purified protein with identical actin
binding activity. Higher yields of PMN capZ were achieved using dextran
alone.


Purification Of CapZ From Human PMN


All steps were done at 4 'C whenever feasible. The initial
procedures used were nearly identical to those described previously







(Southwick & Stossel, 1981). Briefly, cells were cooled to 4 "C and washed
twice in normal saline, treated with 5 mM diisopropylfluorophosphate
(DFP) for 15 min and then resuspended in 3 volumes of a solution
containing 5 mM dithiothreitol (DTT), 2 mM ATP, 20 mM EGTA, 20 mM
imidazole-HCL, pH 7.5, 1 mM phenylmethylsulfonyl fluoride (PMSF), 1
g/100 ml leupeptin, 4 g/100 ml aprotonin, and 7.8 g/100 ml benzamidine
(homogenization solution). Cells were broken by nitrogen cavitation at
900 psi. This procedure ruptured greater than 95 % of all cells, as
monitored by phase microscopy. The homogenates were centrifuged at
12,100 X g for 60 min. The supernatant was dialyzed against 500
volumes of S2 buffer (10 mM Imidazole pH 7.8, 5 mM DTT, 1 mM MgCl2,

1 mM ATP, 1 mM EGTA) for 3 hrs, then diluted 1:1 with S2 buffer and
applied to a 1.5 cm X 16.5 cm DEAE-Sepharose CL-6B anion exchange
column (Pharmacia Biotech Inc. Piscataway, NJ) equilibrated with 120-200
ml of S2 buffer. After application of the supernatant, the column was
washed with 60 ml of 0.08 M KCI in S2 buffer, followed by 250 ml linear,
0.08-0.4 M KCI, gradient in S2 buffer. Eluted fractions were analyzed by
coomassie blue stained SDS-PAGE and by falling ball microviscometry
(MacLean-Fletcher & Pollard, 1980). Fractions that lowered the viscosity
of F-actin under low Ca2+ conditions were pooled and concentrated to a
volume of 0.5-3.0 ml (< 10 mg/ml) in a nitrogen pressure concentrator
using an Amicon PM-30 ultrafiltration membrane (Amicon Corp.,
Lexington, Mass.). The concentrated sample was then subjected to gel
filtration using a protein-pak 125 (Waters Associates, Milford, MA) column
equilibrated, and eluted with 0.1 M KCI in S2 buffer. Several precautions
were taken to limit activation of the abundant proteases present in PMN.
Isolation of PMN was performed using plastic to avoid generalized







activation by adherence to glass, Purified PMN were treated with the
potent neutral serine protease inhibitor DFP, cells were homogenized in
the presence of EGTA and a protease inhibitor cocktail, and efforts were
made to maintain the purification at 4 *C. As originally reported
(Southwick & Stossel, 1981), the PMN viscosity lowering activity at this
stage copurified with two polypeptides in the 60 68 kDa range.
In efforts to further purify this activity, three additional columns
were utilized in the following order; High S (Bio-Rad Laboratories, Inc.,
Hercules, CA), Mono Q(Pharmacia Biotech Inc., Piscataway, NJ), and
HTP/hydroxylapatite (Bio-Rad Laboratories, Inc., Hercules, CA). To
minimize protein loss during screening activity of these additional
columns, the Band 4.1 capping assay was substituted for the falling-ball
microviscometry assay (see "Actin Binding Studies" below). For the High
S cation exchange chromatography, active fractions were pooled and
dialyzed against a buffer containing 8 mM MES pH 6.0, 1mM sodium azide,
and 0.1 mM PMSF (buffer S). The dialyzed fractions were then applied to
a 5 ml Econo-Pac High S cation exchange column which had been
equilibrated with buffer S. The column was washed with 5 ml of buffer S,
followed by a 30 ml (1 ml/min) linear salt gradient to 0.150 M KCI in
buffer S. Active fractions from the High S column were pooled then
dialyzed against S2 buffer. After preclearing the fractions by
centrifugation at 10,000 X g for 5 minutes, they were applied to a Mono Q
HR 5/5 anion exchange column equilibrated with S2 buffer. The column
was then washed with 5 ml (1 ml/min) of 0.1 M KCI in S2 buffer, and
followed by a 12 ml linear gradient, 0.1 0.3 M KC1, gradient in S2 buffer.
Similar to the purification step described by Casella et al. (1986), our final
step entailed pooling and dialyzing Mono Qactive fractions against a 10







mM potassium phosphate buffer pH 7.0 containing 0.1 mM DTT. This
sample was then applied to a 1 ml hydroxylapatite (Econo-Pac HTP)
column equilibrated with the same buffer, and eluted with a linear
gradient to 75 mM potassium phosphate pH 7.0, and 0.1 mM DTT. Active
fractions were quantified using the Quantigold assay (Diversified Biotech)
and then stored at -20 *C in 30 % ethylene glycol (under these storage
conditions the specific activity of the protein remained stable for >3
months).


Purification Of Muscle Actin


Actin was purified from rabbit skeletal-muscle by the method of
Spudich and Watt (1971). Monomeric actin was gel filtered through a
Superdex 200 16/60 (Pharmacia Biotech Inc., Piscataway, NJ) column for
polymerization kinetic studies. Pyrenylactin was prepared according to
Kouyama and Mihashi (1981) with the modifications described previously
(Young et al., 1990). Actin concentrations were calculated using the
extinction coefficient of 24.9 mM-1 cm-1 at 290 nm with the correction for

pyrenyl absorption according to Selden and colleagues (1983).


Amino Acid Sequence Analysis


Peptides were electroblotted from SDS-polyacrylamide gels onto
polyvinylidene difluoride (PVDF) membranes using a transfer buffer
containing 12.5 mM Tris, 96 mM glycine, 10 % ethanol, pH 8.3 as
previously described (Mozdzanowski et al., 1992). The samples were
blotted, stained, and sent to our collaborator Dr. David W. Speicher at The







Wistar Institute Philadelphila, PA for amino acid sequence analysis.
Coomassie blue stained bands were excised and sequenced on an Applied
Biosystems model 475A sequencer using gas phase TFA delivery and an
on-line model 120A PTH analyzer with modifications as previously
described (Reim et al., 1992). Acetonitrile and tetrahydrofuran were from
J. T. Baker. All other sequencer solvents and reagents were from Applied
Biosystems.


Polvacrvlamide Gel Electrophoresis And Western Blot Analysis


SDS-PAGE

Protein samples were subjected to electrophoresis on 10 %
discontinuous pH mini (Bio-Rad Laboratories, Inc., Hercules,
CA) or mid-sized (Hoefer Scientific Instruments, San Francisco, CA) SDS-
PAGE. Molecular weights (Mr) of proteins of interest were determined by

simultaneous electrophoresis of other polypeptides of known molecular
weights, and plotting their relative mobility verses log Mr. Proteins were

visualized by staining the gels with Coomassie brilliant blue R-250 or
Silver (Silver stain plus kit, Bio-Rad Laboratories, Inc., Hercules, CA).


Immunoblotting

The electrophoresed proteins were then transferred to nitrocellulose
paper (graphite electroblotter, Millipore) using standard protocols
(Towbin et al., 1979). The transferred blots were subjected to a blocking
step in 3 5 % non-fat dry milk in phosphate-buffered saline (PBS) and 0.3
% tween-20 for at least three hours. The primary antibodies were diluted
appropriately in the blocking solution (anti human annexin VI at 1:4000







(monoclonal) & 1:7500 polyclonall), anti human L-plastin at 1:500, anti
chicken capZ alpha and beta 1:300) and incubated with the blot for 1 hour
at room temperature. After subsequent washes with PBS-tween, the blots
were incubated with the appropriate alkaline phosphatase-conjugated
secondary antibody for 40 60 minutes. The detection was in an alkaline
phosphatase buffer (0.1 M Tris, 5 mM MgCI2, 0.1 M NaCI) containing 30

pg/ml nitro blue tetrazolium (Sigma Chemical Company, Saint Louis, MO)
and 20 pg/ml BCIP (5-bromo-4-chloro-3-indolyl phosphate, Sigma).
The annexin VI concentration in neutrophil extracts was determined
using a method similar to that described by Dabiri et al. (1992). The
immuno-reactivities of the polypeptides in neutrophil extracts were
compared to known concentrations of purified annexin VI using a
scanning laser densitometer (Zeineh Model SLR-2D/1D, Biomed
Instruments, Inc.). A linear standard curve could be generated relating
densitometry integration units to protein concentration.


Nondenaturing Polvacrvlamide Gel Electrophoresis
Neutrophil actin polymerization inhibitor containing predominantly
annexin VI and L-plastin were subjected to 7.5 % nondenaturing
polyacrylamide gel electrophoresis (mid-sized gel, Hoefer Scientific
Instruments, San Francisco, CA) according to the method of Safer (1989).
Samples were added 1:1 (volume:volume) with 10 % glycerol in the
running buffer with <1 mg of bromophenol blue (tracking dye). A
heterogeneous population of monomers, dimers, and trimers of bovine
serum albumin (BSA) are formed when placed in solution, and therefore
15 pg of BSA (fraction V, Sigma Chemical Company, Saint Louis, MO; 1







mg/ml in water) was run simultaneously to the proteins of interest as
evidence of nondenaturing resolution of proteins.


Actin Binding Studies


Pyrene actin was used for all kinetic studies. Fluorescence intensity
was monitored using a Perkin-Elmer LS-5 fluorescence spectrophotometer
with excitation and emission wavelengths of 364 nm and 407 nm
respectively.


Depolymerization Assay

Pyrene labeled actin (2 pM) was allowed to polymerize to steady
state in the presence of 1 mM EGTA or 1 mM calcium. The F-actin was
then diluted to 50 nM into a buffer containing 10 mM Imidazole pH 7.5,
0.5 mM ATP, 0.1 M KC1, 1 mM MgCl2, 1 mM DTT (Buffer P) in the presence

of varying concentrations of capZ (Southwick & DiNubile, 1986). The
reaction was observed for 30 min at 25 'C.


Actin-Spectrin Nuclei Elongation Assay

Red blood cell derived spectrin/band 4.1/actin nuclei (rbc nuclei)
were isolated according to the methods of Casella et al. (1986). Pyrene-

labeled G-actin (0.55 pM) was added to a mixture of 1.25 pg/ml of rbc
nuclei, varying concentrations of capZ and buffer P containing 1 mM
EGTA. In the absence of rbc nuclei, this concentration of pyrene actin
(0.55 pM) failed to spontaneously polymerize during the time course of
our experiments (15 min). The capZ and rbc nuclei were allowed to
incubate for 2 min prior to the addition of the pyrene actin.







Steady-State Assay

Pyrene-labeled actin in buffer P with 1 mM EGTA was allowed to
polymerize at room temperature for 18 hours (steady-state), and the
critical concentration was determined by plotting the total actin
concentration verses the steady-state fluorescence (correcting for
fluorescence values at t = 0). The effects of various concentrations
(substoichiometric relative to actin) of capZ on the steady-state
fluorescence of pyrene actin (0.9 pM or 3 pM) was measured. The steady-
state G-actin concentration (apparent critical concentration) of the
solutions was calculated from the decrease in steady-state fluorescence
relative to pyrene actin controls. The fluorescent signal of pyrene actin is
proportional to polymer weight concentration (Cooper et al., 1983).


Nucleation Assay

For this assay, 1.5 pM pyrene labeled G-actin was allowed to
polymerize in buffer P in the presence of varying concentrations of capZ.
The effects of capZ on this polymerization rate were assessed by
fluorimetry (Southwick & DiNubile, 1986).


Severing Assay

Gelsolin (0.01 pM) and pyrene actin (2 pM) were copolymerized
(molar ratio 1:200) to steady-state, forming barbed-end capped filaments
(Casella et al., 1986). These filaments were then diluted to 100 nM in
buffer P containing 1 mM calcium and varying concentrations of capZ.







Monomer Sequestration Assay

Gelsolin and non-pyrene labeled actin were copolymerized at high
molar ratios (1:16) in buffer P forming nuclei for pointed end
polymerization. Pyrene labeled G-actin (final of 0.8 pM) was added to
buffer P containing gelsolin/actin nuclei (15 nM/0.24 pM) and varying
concentrations of capZ (Young et al., 1990). This assay was repeated in
the presence of G-actin that was 50 % labeled to examine the possibility
that capZ binds pyrenylactin with lower affinity. These reactions were
performed in the presence of either 1 mM EGTA or 0.5 mM calcium.


Falling Ball Microviscometry

The falling ball assay of MacLean-Fletcher and Pollard (1980) was
used to follow the relative activities of individual elution fractions at
various stages during the purification of neutrophil capZ. Rabbit skeletal
muscle actin (final concentration of 10 pM) was polymerized in the
presence of sample. After 2 hours at room temperature, the solutions
were drawn into glass capillary tubes. Relative viscosities are reflected by

the speed of steel balls traversing the tube (angled at 15).


Lipid-Binding And Capping-Inhibition Studies


Phosphatidylcholine (PC), phosphatidylinositol (PI),
Phosphatidylserine (PS) were purchased from Sigma (St. Louis, MO) and
used without further purification. Phosphatidylinositol 4,5-bisphosphate
(PIP2) was obtained from Calbiochem.







Annexin VI Binding To Multilamellar Vesicles

For the annexin VI lipid binding studies PC and PS were treated as
previously described by Blackwood, et al. (1990). Partially purified
neutrophil annexin VI was incubated at 25 "C for 15 minutes with either PS
or PC in buffer P containing 0.2 mM EGTA and varying concentrations of
calcium. Each mixture was then centrifuged at 12,000 X g in a table top
microfuge for 15 min at 25 C. Supernatants and pellets were subjected to
SDS-PAGE and stained with Coomassie brilliant blue. The relative amounts
of annexin VI in the pellets and supernatants were determined by laser
densitometry.


Phospholipid Column
A 3.5 ml sepharose-4B phospholipid column composed of PS/PC/PE
(2:2:1) was built in attempts to separate annexin VI and L-plastin, the two
predominant proteins copurified with the PMN actin polymerization
inhibitor after gel-filtration chromatography. The phospholipid column,
which exploits the ability of annexin proteins to bind acidic phospholipids,
was constructed according to the methods of Meers and colleagues (1987).


Modulation Of Capping Activity By Phosphoinositides
The ability of various lipids to block capZ filament end capping was
also examined. The phospholipids PIP2, PI, PC and PS were treated as

previously described (Janmey & Stossel, 1989). The modulation of capZ
actin binding function was assessed using the depolymerization assay (see
above). CapZ (36 nM final concentration) was first added to
polymerization buffer, followed by the addition of phospholipids from
previously sonicated stock solutions and resonicated in a water bath







sonicator at room temperature for 15 sec. After 1 min to allow the lipid-

capZ mixture to equilibrate, pyrene labeled F-actin was added (25 pl of 2
pM F-actin to a final volume of 1 ml). The inhibition of capZ capping was
assessed by measuring the initial slopes of depolymerization in the
presence of varying amounts of PIP2.


Promyelocyte Differentiation Studies


RNA Isolation And Northern Blots

Total RNA was extracted by a guanidinium thiocyanate (GITC)
method (Chomczynski & Sacchi, 1987). The cells of interest were lysed in
a GITC buffer (4 M guanidinium isothiocyanate, 25 mM sodium acetate, pH
7.0, 0.5 % sarcosyl, and 0.1 M R-mercaptoethanol) with vigorous pipetting
and vortexing. Two milliliters (2 ml) of GITC buffer was added to 0.5- 1.0
X 107 cells. The following was sequentially added to the extract with

thorough mixing by inversion in between: 0.07 volume 3 M sodium
acetate pH 5.2, 1 volume cold water-saturated phenol, and 0.2 volume of
chloroform/ alcohol (49:1). The mixture was shaken vigorously for 10 sec
and kept on ice for 15 in and centrifuged in a Beckman JA-20 rotor at
10,000 X g for 20 min. The aqueous phase was carefully removed and
precipitated with 1:1 volume of cold for 1 hour to overnight at -20 C.
After another 10,000 X g spin, the RNA pellet was resuspended in 300 pI of
GITC buffer and precipitated another time with 2.5 volumes of cold 95 %
ethanol at -20 C. The final pellet was washed with 70 % ethanol, dried
and resuspended in 0.5 % SDS in diethylpyrocarbonate (DEPC) treated
water. To eliminate any contaminating proteins and to remove the SDS,
the samples were heated at 65 C for 15 min, kept on ice for 15 min (to







precipitate the SDS), and microfuged for 5 min. The clear supernatant was
transferred into a clean tube and the concentration and purity of the
sample was analyzed by a spectrophotometer.
The RNA samples were prepared for electrophoresis as follows. The
RNA (10 pg/sample) was completely lyophilized and resuspended in 10 pl
of a sample mix containing 250 pl deionized formamide, 90 p1 37 9
formaldehyde, 26 pl 10 X MOPS (3-[N-morpholino]propanesulfonic acid)
buffer (1 X MOPS buffer = 0.2 M MOPS, 0.05 M sodium acetate, 0.01 M
Na2EDTA, pH 7.0), 10 p1 of ethidium bromide (10 mg/ml stock solution)
and 30 p1 of loading dye. The samples were heated at 67 'C for 15 min,
cooled on ice and were electrophoresed in 1.2 % agarose gels with 2.2 M
formaldehyde in 1 X MOPS buffer. The gel was transferred to
nitrocellulose membrane in 20 X SSC (IX SSC = 0.15 M NaCI and 0.015 M
sodium citrate) by standard capillary blotting. The blots were hybridized
with random-primed probes (1 X 106 cpm/ml) at 42 C in 5 X Denhardt's
solution, 5 X SSPE (IX SSPE = 0.15 M NaCI, 0.01 M NaH2PO4-H20, and

0.001 M EDTA), 50 % formamide (Fluka), 0.1 % SDS, and 150 pg/ml
salmon sperm DNA. After a room temperature rinse in 2 X SSC, 0.1 % SDS,
the filter was washed at 65 'C in 2 X SSC, 0.1 % SDS for 30 min followed by
a brief wash in 0.2 X SSC, 0.1 % SDS until the background was low by a
Geiger counter survey.


Generation Of Annexin VI cDNA Probe
Total RNA was isolated from human neutrophils as described above.
Using the published cDNA sequence for human annexin VI, upstream and
downstream oligonucleotide (25 base-pairs each) primers were
synthesized (I.C.B.R. DNA synthesis laboratory, University of Florida). The







Perkin-Elmer Cetus R.T.-P.C.R. kit was utilized to generate a 1057 base-pair

(bp) annexin VI DNA fragment from neutrophil total RNA via a reverse
transcription reaction immediately followed by initiation of the
polymerase chain reaction (Perkin-Elmer Cetus DNA Thermal Cycler model
480). The ends of the 1057 bp DNA fragment were blunt-ended with the
Klenow fragment of DNA polymerase, and ligated into the E. coli vector
pBluescript II SK + (Stratagene Cloning Systems, Lajolla, CA) at the Sma I
polylinker site. The 1057 bp, subcloned, annexin VI-cDNA-fragment (bp #
32 1088) was verified by sequencing (I.C.B.R. DNA sequencing facility,
University of Florida).


Cell Culture And Induction Of Differentiation

The human promyeloblast leukemic cell line HL-60 (Gallagher et al.,
1979) was obtained from ATCC (American Type Culture Collection,
Rockville, MD) and maintained in RPMI 1640 medium supplemented with
10% iron-supplemented calf serum (Gibco BRL, Gaithersburg, MD) and 2
mM glutamine. This cell line can be induced to differentiate towards the
neutrophil lineage or macrophage lineage depending upon the
pharmacologic exposure (Collins, 1987). Differentiation of HL-60 cells was
induced according to the methods previously described by Dabiri et al.
(1992) Briefly, exponentially growing HL-60 cells (> 1 X 106 cells/ml)
were plated at 0.5 X 106 cells/ml and treated at time zero with the

appropriate pharmacologic agents. For macrophage differentiation, HL-60
cells were treated with phorbal 12-myristate-13 acetate (PMA, Sigma) at 10
nM (6.2 ng/ml), and for granulocyte differentiation the HL-60 cells were
treated with 1.5 % dimethyl sulfoxide (DMSO, Sigma Chemical Company,
Saint Louis, MO). At appropriate time points after differentiation, RNA or







cellular protein was isolated and analyzed by Northern or Western blots as

described earlier. For Western studies, the total protein concentrations
were calculated on the last day of the experiment using the same standard
curve. Samples from earlier time points were rapidly collected (saving an
aliquot for determination of protein concentration), placed in gel sample
buffer, and stored at -70' C until the final sample was processed.


Fluorescence Microscopy


Human neutrophils and monocytes were isolated from peripheral
blood by sedimentation through PolymorphprepTM, a sodium-metrizoate,
dextran 500 solution (Nycomed Pharma As, distributed by Gibco BRL,
Gaithersburg, MD). The cells were resuspended in Hank's balanced salt
solution (Gibco BRL, Gaithersburg, MD), and allowed to adhere to glass
coverslips for 15 20 min in a 37 "C C02 incubator. The adherent cells

were treated for immunofluorescence by fixation for 20 min at room
temperature in 3 % formaldehyde (prepared from paraformaldehyde)
made in standard salt (0.1 M KC1, 0.01 M KPO4 buffer, 0.001 M MgCl2, pH

7.0), permeabilization in 0.1 % Triton-X 100 in standard salt, 5 min
overlay with 50 mM ammonium chloride in standard salt, and rinses with
standard salt between steps (Sanger et al., 1980). The following reactions
were carried out in a moist chamber in a 37 "C C02 incubator, the cells

were then blocked with 10 % goat serum in standard salt for 30 min,
followed by 45 min incubation with monoclonal antibodies (0.01 Jg/pl
anti-human annexin VI, control antibodies were a kind gift from Maurice
Swanson, Univ. of Fla., College of Medicine: anti-human hnRNP-M protein
& anti-yeast polyadenylated RNA-binding protein, Nab-1) (Datar et al.,







1993; Wilson et al., 1994) and used at concentrations greater than the

anti-annexin VI as determined by immunoblots of the antibodies run on
SDS-PAGE, rinses in standard salt, incubation with fluorescein
isothiocyanate (FITC)-conjugated goat anti-mouse IgG1 (heavy chain
specific; Fisher Scientific, Pittsburgh, PA) for 30 min, followed with rinses
in standard salt. The coverslips were mounted in glycerol containing an
antioxidant to prevent fluorescence quenching (90 % glycerol, 10 % 0.25
M Tris pH 8.0, 2.3 % 1,4 1,4-diazabicyclo-[22.2.2] octane obtained from
Sigma). The cells were observed and photographed using a Nikon Diaphot
inverted microscope (Nikon, Tokyo, Japan) set up for epifluorescence.
Photographs were taken through the camera port using Tri-X Pan film
(Kodak). The film exposure lengths and print development times were
kept identical to photographs of PMN stained with anti-annexin VI.
Confocal microscopy was conducted with the assistance of Michael Paddy
(1.C.B.R. Confocal microscopy facility, University of Florida).
Approximately 30 images 1 pm thick were taken with a z-increment of 0.3
pm. Digitized images were obtained using Dr. Paddy's microscope and
processed with an Image-1 video image analyzer (Universal Imaging Corp.,
West Chester, PA), and finally stored on a Panasonic laser disk recorder.














CHAPTER 3
PURIFICATION AND IDENTIFICATION OF CAPZ AS THE PMN ACTIN
POLYMERIZATION INHIBITOR


Introduction


The viscosity lowering activity of PMN actin polymerization

inhibitor, as originally published, was thought to be composed of two
related polypeptides of 62,000 and 65,000 daltons (Southwick & Stossel,

1981). The polypeptides purified with this activity, although, were not
identified. This chapter outlines the efforts to identify the PMN inhibitor,
and my eventual discovery that the ~65 kDa, heterodimeric-protein capZ

is solely responsible for the actin viscosity-lowering activity.


Results


Identification Of The Two Maior Polypeptides (~ 66 And 68 kDa)
Copurified With The Neutrophil Actin Polymerization Inhibitor

The calcium independent activity called human neutrophil actin
polymerization inhibitor was purified using ion exchange chromatography
and gel filtration (see methods) (Figure 3-1, lane 2). Yields and purity
were identical to the previously reported purifications (Southwick &
Stossel, 1981). The two polypeptides copurified with the inhibitor were
noted to have Mr of 66,000 and 68,000 when fractionated through a

discontinuous pH, 10 % SDS-PAGE. Similar to previous reports, highly

























Figure 3-1. PMN actin polymerization inhibitor. The PMN inhibitor
purified by DEAE-anion exchange and gel-filtration chromatography. Lane
2 represents the PMN inhibitor subjected to 10 % SDS-PAGE with standards
(lane 1; Mr = X 103) and stained with Coomassie blue. Fractions were
subjected to Western analysis and probed with antibodies to annexin VI
(lane 3) or L-plastin (lane 4).
















205


116
97.4


66




45






29


3 4


1 2







purified fractions (> 90 % composed of the 66 and 68 kDa polypeptides as
assessed by densitometry scanning of Coomassie blue stained SDS-PAGE)

lowered the viscosity of actin filament solutions as measured by falling-
ball microviscometry. The minor proteins, if present, (usually < 10 %)
were composed of a 42 kDa polypeptide believed to be actin (rabbit
skeletal muscle actin comigrates with this band) and a 55 kDa polypeptide
later found to be an L-plastin degradation product (see below). Active
fractions, composed predominantly of the 66 and 68 kDa polypeptides,
were separated on SDS-PAGE, transferred onto polyvinylidene difluoride
(PVDF), stained and sent to our collaborator Dr. David W. Speicher (The
Wistar Institute, Philadelphia, PA) for amino-acid sequence analysis. The
original analysis performed after BNPS-Skatole digestion (the amino-
termini of the polypeptides were blocked) resulted in sequence
information solely from the 68 kDa polypeptide. As shown in Figure 3-2A,
two fragments from the 68 kDa polypeptide yielded sequences of 18 and
23 amino acids which were identical to amino acids 193 210 and 344 -
366 respectively of human annexin VI (Crompton et al., 1988; Sudhof et
al., 1988). Immunoblots probed with a monoclonal antibody to human
placental annexin VI (Zymed Laboratories, Inc., South San Francisco, CA)
only revealed the 68 kDa polypeptide (Figure 3-1, lane 3). Polyclonal
antibodies to human annexin VI (rabbit antisera was a kind gift from Dr.
Joel D. Ernst, University of California, San Francisco) detected the 68 kDa
annexin VI, but also failed to recognize the 66 kDa polypeptide (data not
shown).

Amino acid sequence analysis of the 66 and 68 kDa polypeptides
containing neutrophil activity was repeated. Samples were prepared as
described above, and sent to The Wistar Institute (Protein


















Figure 3-2. Amino-terminal sequence analysis of PMN actin
polymerization inhibitor. Since the amino termini were blocked,
microsequence analysis was performed on the predominant cleavage
products of the upper peptide (Skatole) or lower peptide (Trypsin)
component. The 68 kDa upper band is identical to annexin VI and the 66
kDa peptide is identical to L-plastin.






















A. UPPER BAND (SKATOLE cleavage)

188 213
human Anx VI GELKWGTDEAQFIYILGNRSKQHLRL

pep 1 GTDEAQFIYILGNRSKQI

339 369
human Anx VI AYQMWELSAVARVELKGTVRPANDFNPDADA

pep 2 ELSAVARVELKGTVRPANDFNP





B. LOWER BAND (TRYPSIN cleavage)
62 = 79
human L-Plastin SEEE YAFVNWINK LEN

pep 1 AFVNWINK

512 534
human L-Plastin GGQ VNDDIIVNWVNETLREAEK

pep 2 fNDDIIVNWVNETLR







Microsequencing Facility). For this analysis, the two polypeptide bands
were digested with trypsin. Comparative HPLC peptide maps (post-trypsin
digestion) with a trypsin control demonstrated that almost all major peaks
in the 68 kDa sample were different from those generated from the 66 kDa
sample. The masses of the major trypsin cleavage peptides were
determined by MALDI mass spectrometry. Most major peak masses from
the 68 kDa sample agreed with expected masses of limit tryptic peptides of
annexin VI. In contrast, only a few major peaks in the 66 kDa sample
could possibly fit with annexin peptides. Two of the major peptides
generated by trypsin digestion of the 66 kDa band were sequenced, and
revealed a perfect match with the protein L-plastin. As shown in Figure 3-
2B, N-terminal sequence analysis of these two major peptides yielded
sequences of 9 and 15 amino acids which were identical to amino acids 67
- 75 and 516 530 respectively of human L-plastin (Lin et al., 1988). To
further confirm the identity of the 66 kDa polypeptide western blot
analysis was performed using a mouse monoclonal anti-human L-plastin (a
kind gift from Dr. Yuziro Namba, Kyoto University, Japan). As shown in
Figure 3-1 (lane 4), the antibody specifically cross-reacts with the lower,
66 kDa polypeptide. The antibody also cross-reacts with a polypeptide
with approximate Mr of 55,000. This band is felt to be a degradation

product of the neutrophil L-plastin, as it is absent in fresh PMN extract and

increases with storage of the PMN inhibitor fractions (data not shown). A
similar molecular weight L-plastin degradation product has been
previously reported (Pacaud & Derancourt, 1993).







Separation Of Annexin VI From L-Plastin

The following experiments were conducted in attempts to correlate
the neutrophil actin polymerization inhibitory activity with one of the two
proteins or a complex formed between them. Additional chromatography
steps were added in attempts to separate annexin VI from L-plastin.
Neither phenylsepharose (Pharmacia Biotech, Inc., Piscataway, NJ) or Affi-
Gel blue (Bio-Rad Laboratories, Inc., Hercules, CA) chromatography
separated the two proteins. The viscosity lowering activity was noted to
coelute with the annexin VI and L-plastin proteins during Affi-Gel blue
chromatography (the viscosity lowering activity was not monitored in the
fractions obtained from phenylsepharose chromatography).
The difficulty in separating these two proteins raised the possibility
that annexin VI and L-plastin were forming a complex. Nondenaturing
polyacrylamide gel electrophoresis was used to test this possibility (Figure
3-3). Active fractions containing both annexin VI and L-plastin (Figure 3-
3, lane 2), purified annexin VI (lane 1) (via liposome purification, see
below), recombinant human L-plastin (lane 3) (purified from E. coll by Dr.
Clarence Young for unrelated studies in our laboratory), and bovine
albumin (lane *) (indicator of the nondenaturing conditions of the assay)
were each subjected to nondenaturing electrophoresis. If a complex was
formed by annexin VI and L-plastin in active fractions, one might expect a
migration pattern different from lanes containing the purified annexin VI
(Figure 3-3, lane 1) or purified L-plastin (Figure 3-3, lane 3). This
difference would most likely appear as a slower migrating band in
fractions where a complex is formed (analogous to the decreasing
mobilities of monomer, dimer, and trimer species of native bovine
albumin seen in Figure 3-3A lane *). The samples were run in triplicate

















Figure 3-3. Nondenaturing polyacrylamide gel electrophoresis. PMN inhibitor (lane 2; 12pg) was
subjected to native gel electrophoresis in search of evidence suggesting complex formation between L-
plastin & annexin VI. Purified annexin VI (lane 1; 6 pg) and purified L-plastin (lane 2; 6 pg) were run to
enable the determination of a mobility shift when the two proteins are present. Panel A is a Coomassie
stained gel of the various fractions (starred lane contains 15 pg of albumin/BSA). Gels were run in
triplicate for western analysis with antibodies to annexin VI (Panel B) or L-plastin (Panel C).












A B C












* 1 2 3 1 2 3 1 2 3







for Coomassie blue staining and immunoblot analysis. As shown in Figure

3-3B, antibodies to annexin VI (Zymed Laboratories, Inc., South San
Francisco, CA) reveal one band in the active fraction. The similar
migration pattern shared by annexin VI in purified and active fractions

(Figure 3-3B, lane 1 and lane 2), suggests annexin VI does not take part in
complex formation. Although the L-plastin antibody reveals two closely
spaced reactive bands in the active fraction (Figure 3-3C, lane 2), they
both migrate separately from annexin VI. The detection of two L-plastin
bands in active fractions (Figure 3-3C, lane 2) and only one in the purified
(recombinant L-plastin) fractions (lane 3) most likely results from post-
translational modification of the PMN isolated L-plastin. Furthermore, L-
plastin is a known phosphoprotein (Zu et al., 1990). It is well established
that bacteria are incapable of many of the post-translational modifications
seen in eukaryotes, and thus could explain the appearance of one band
with L-plastin recombinantly expressed and purified from E. coli. It is
notable that recombinant L-plastin does not decrease the viscosity of actin
solutions (Dr. C. Young, unpublished data). These data derived from
nondenaturing polyacrylamide gel-electrophoresis suggest no complex is
formed between the annexin VI and L-plastin present in the neutrophil
actin polymerization inhibitory activity.

To further clarify which protein was responsible for the actin
viscosity lowering activity, attempts were made to separate annexin VI by
methods previously developed for studying the membrane binding
properties of annexins (Blackwood & Ernst, 1990). In this assay,
phosphatidylserine liposomes were prepared as described, and added to
active fractions. After incubation in the presence of calcium, the
liposomes were separated from the fractions by centrifugation. This


























Figure 3-4. SDS-PAGE of phospholipid affinity chromatography, and anti-
annexin VI western analysis. PMN inhibitor was exposed to a mixed-lipid-
vesicle column in the presence of calcium. The activity remained in the
fall through (lane 2). Annexin VI (> 95 % pure) was eluted with 1mM
excess EGTA. Fractions were transferred to nitrocellulose and probed with
antibodies to annexin VI. The same molecular weight standards in Figure
3-1 were used (HMW Std).















- OWi


* 1 2


1 2


w -







method was able to remove > 60 % of annexin VI from those fractions

purified by DEAE-ion exchange and gel-filtration chromatography.
Phospholipid affinity chromatography (Chapter 2), as well, incompletely
separated annexin VI from the neutrophil activity (Figure 3-4, lane 2).
The neutrophil actin polymerization inhibitory activity remained in
fractions partially depleted of annexin VI and predominantly composed of
L-plastin, and was not associated with the highly purified annexin VI (> 90
%) (Figure 3-4, lane 1).

Purification And Identification Of PMN Actin Polymerization Inhibitor As
C=Z
In efforts to avoid phospholipid contamination and the addition of
calcium, other chromatographic methods were tested. After DEAE-anion
exchange chromatography and gel-filtration, the neutrophil inhibitory
activity was applied to a Mono Qanion exchange column and eluted with a
KC1 gradient (Chapter 2). Surprisingly, the activity coeluted with annexin
VI and not L-plastin (data not shown). The peak activity, although,
correlated with a fraction in which no protein was seen by Coomassie
staining of the fractions run on SDS-PAGE (no predominant band was seen
by silver staining as well). However, Western blots of this and three other
active fractions from previous purifications probed with antisera from a
goat immunized with chicken, skeletal-muscle capZ (kindly provided by
Dr. J. Cooper, Washington University, St. Louis, MO) revealed two
immunoreactive bands (Figure 3-5) in the appropriate molecular weight
range of the heterodimeric, skeletal-muscle protein capZ (Mr between

30,000 40,000). The DEAE-anion exchange fractions from the
subsequent purification were subjected to immunoblot analysis and
probed with the capZ antisera as well (Figure 3-6). Peak capZ



























Figure 3-5. Western blot analysis of PMN inhibitory fractions probed with
capZ antisera. Fractions from the four most recently purified PMN actin
polymerization inhibitor purified by DEAE-ion exchange and gel-filtration
chromatography each had detectable levels of both subunits (a and p) of
capZ.


















2;


1 2 34







immunoreactive peptides (Figure 3-6C fraction # 36 42) were found to
correlate with the neutrophil actin polymerization inhibitory activity. As
seen in Figure 3-6, the viscosity lowering activity was maximal in fractions
36 42 (panel C). These fractions also represented the peak capZ, annexin
VI (68 kDa), and L-plastin (66 kDa) fractions.
A scheme utilizing three additional columns was empirically devised
to separate annexin VI and L-plastin and further purify the neutrophil
actin polymerization inhibitor (High S, Mono Q, and hydroxylapatite).
Active fractions composed predominantly of annexin VI and L-plastin were
further separated by High S-cation exchange chromatography (Figure 3-7)
under similar conditions utilized during the purification of skeletal muscle
capZ. Figure 3-7A represents the typical separation achieved by this
method. The polymerization inhibitory activity correlates with L-plastin
(fraction # 28 42). Fractions # 62 86 are composed of annexin VI
(Figure 3-7B) as detected by Western analysis. Similar to the
phospholipid-purified annexin VI, no activity was detected for fractions of
annexin VI separated by High S-ion exchange chromatography (Figure 3-
7C, fraction # 62 70).
Active fractions after High S chromatography were applied to a
Mono Qanion exchange column and eluted with KC1 (Figure 3-8A) as
described earlier (Chapter 2). Despite the presence of PMSF in dialysis
solutions and maintenance of all procedures at 4 C, the 55 kDa L-plastin
degradation product was formed in significant amounts by this stage of
the purification (Figure 3-8C, fraction # 28 34: lower band). Mono Q
chromatography separated the peak L-plastin fractions (Figure 3-8C
fraction # 29 32), but not its degradation product (see fraction # 26 28)
from the neutrophil actin polymerization inhibitor. The purification was


















Figure 3-6. DEAE-anion exchange chromatography of PMN extract.
Extracts were eluted with a linear KCI gradient as described (Chapter 2).
Eluted proteins were subjected to 10 % SDS-PAGE (with HMW stds) and
stained with Coomassie (Panel A) or transferred to nitrocellulose and
probed with antisera to chicken skeletal-muscle capZ (Panel B). Relative
activities (Panel C) were reported as the ability of fractions to decrease the
viscosity of actin solutions (10 pM) as measured by falling ball
microviscometry.

















Ui!



S


24 32 36 40
n 30 34 38 42


-. :4'


Fraction #


4-


I I
44 52


-.
-n ,3 3i
11 i::;


















Figure 3-7. High S-cation exchange chromatography of PMN actin polymerization inhibitor. PMN
inhibitor consisting predominantly of annexin VI and L-plastin was bound to a High S column (Chapter 2)
and eluted with a 0 0.15 M linear KC1 gradient. Fractions were subjected to 10 % SDS-PAGE (with HMW
stds) and stained with Coomassie (Panel A). Fractions were transferred to nitrocellulose and probed with
antibodies to annexin VI (Panel B). Relative activities are reported as the ability to prevent actin
polymerization from actin filament nuclei isolated from red blood cells (Panel C).










A B


Anti-Annexin VI






62 66 70




Std 16 24 30 34 38 42 50 58 66 74 86
12 20 28 32 37 40 46 54 62 70 78 82 I




C









Fraction i#
























Figure 3-8. Mono Q-anion exchange chromatography of PMN actin
polymerization inhibitor. Peak activities from High S chromatography
were pooled and allowed to adhere to a Mono Q column. The proteins
were eluted with a 0.1 0.3 M linear KC1 gradient, and subjected to 10 %
SDS-PAGE (with HMW stds). The 10 % SDS-PAGE gel shown was first
stained with Coomassie blue (Panel A), and then silver stained (Panel A').
The relative activities (Panel B) were measured as in Figure 3-7. Fractions
were also transferred to nitrocellulose and probed with antibodies to L-
plastin (Panel C).








































14 18 22 24 26 28 30 34 38 Std 14 18 22 24 26 28 30 34 38 Std
12 16 20 23 25 27 29 32 36 40 12 16 20 23 25 27 29 32 36 40


C: 16 1 8 20 22 23 24 25 26 27 28 29 30 32 34 36 8
Fmrauon


Anti-L-plastin





26 27 28 29 30 31 32







carried out to this extent on three separate occasions, each resulting in the
isolation of polypeptides with approximate Mr of 55,000 (L-plastin

degradation product), 36,000, and 32,000 seen upon silver staining (for
examples see Figure 3-8A' lanes 26 and 27 or Figure 3-11, lane 3).
Western analysis identified the 36 and 32 kDa bands as capZ (Figure
3-9A & B, lane 2). As shown in Figure 3-8 (panel A verses panel A', lanes
26 & 27), the presence of these peptides after Mono Qchromatography is
revealed by silver staining. Hydroxylapatite chromatography of these
fractions successfully separated the L-plastin degradation product from
the actin-filament-shortening activity (Figure 3-10, fraction 21 verses
fraction 22). The activity was strictly associated with capZ (Figure 3-10).
Although several minor bands were seen below the 36 and 32 kDa
polypeptides in Figure 3-10, they were not seen when fraction 21 was
separated on other occasions (Figure 3-11, lane 4). Several possibilities
including degradation, resolution of isomers or an artifact of the
procedure can explain this finding.


Discussion


Proteins that bind to actin and modulate actin filament assembly are
also hypothesized to regulate the finely coordinated assembly and
disassembly of the microfilament network in motile cells. Based on
viscometric studies, actin polymerization inhibitor is thought to play an
important role in the regulation of actin filament length in PMN.
Originally, my purifications focused on the 62 and 65 kDa proteins, and so
the identity of these polypeptides was pursued.
























Figure 3-9. Western blot analysis of PMN actin polymerization inhibitor
purified to Mono Q chromatography. Peak fractions from Mono Q
chromatography (lane 2) (see Figure 3-8) were separated by 10 % SDS-
PAGE (with HMW stds), and either stained (Panel A) with Coomassie or
subjected to Western analysis (Panel B) probing with antisera to chicken
skeletal-muscle capZ. Lane 1 is 30 pg PMN extract, while a total of 3 pg of
protein was loaded in lane 2.














1 2


1 2


I


p.
a11

























Figure 3-10. Hydroxylapatite column chromatography. As a final
purification step, peak active fractions from Mono Qchromatography were
subjected to hydroxylapatite (HA) column chromatography as described
(Chapter 2). Fractions were subjected to 10 % SDS-PAGE and silver stained
(Panel A). Relative activities were measured as in Figure 3-7.




























17 18 19 20 21 22 23 24 25






B

1.0





0.5





0.0


Fraction #


.r", ..; ..p .























Figure 3-11. Silver stained peak fractions from Mono Q and HA
chromatography. PMN extract (14 pg; lane 2), Mono Qpeak activity (2pg;
lane 3), HA peak activity (0.25 pg; lane 4), and HMW std (lane 1) were
subjected to 10 % SDS-PAGE and silver stained. Arrowheads point to the
36 kDa and 32 kDa subunits of capZ.























1 2 3







The molecular weights of the polypeptides copurified with the
viscosity lowering activity were currently found to be 66,000 and 68,000
when separated by 10 % SDS-PAGE (originally determined with 5 15 %
SDS-PAGE). Initial sequence analysis of the polypeptides resulted solely in
the identification of the 68 kDa upper band as annexin VI. Their shared
physical properties (Mr and pl) suggested the 66 kDa polypeptide was

related. It was speculated that the 68 kDa protein was susceptible to
known neutral proteolytic activity in human granulocytes (Southwick &
Stossel, 1981).
Despite the recognition of only the upper band by anti-annexin VI
immunoblot analysis, it was thought that the epitope recognized by this
monoclonal antibody (Zymed Laboratories, Inc., South San Francisco, CA)
was not present in the 66 kDa polypeptide. The annexins are a large
family of related proteins (Chapter 5). The structural similarity amongst
the annexin proteins limits the number of epitopes specific to each
member. The annexins have divergent sequences at their amino termini
(Creutz, 1992), and therefore it is likely that the monoclonal anti-annexin
VI-specific antibody recognizes an epitope in this region. It seemed
plausible that the 66 kDa polypeptide was a partially degraded form of
annexin VI that had lost the epitope recognized by the monoclonal
antibody. Alternative explanations included the possibility the 66 kDa
peptide was an alternatively spliced annexin VI lacking the epitope
(Crompton et al., 1988), the 66 kDa peptide was annexin VI post-
translationally modified in a manner preventing recognition of the
epitope, or the 66 kDa peptide was an unrelated peptide. To test these
possible explanations, the peptides were probed with a polyclonal antisera
specific to human annexin VI (Dr. Joel Ernst). Similar to the monoclonal







antibody to annexin VI, the polyclonal antisera only recognized the 68 kDa

polypeptide. These findings suggested that the 66 kDa protein was not a
degradation product of annexin VI.
To determine the identity of this protein, active fractions were again
prepared for amino acid sequence determination as described earlier (see
Results), and sent to our collaborator D. W. Speicher at The Wistar
Institute. Utilizing improved techniques, the 68 kDa band was once more
identified as annexin VI while the 66 kDa band was identified as L-plastin.
Based on previously published cDNA sequences, the predicted molecular
weights of annexin VI and L-plastin are 75,901 and 70,306 respectively
(Sudhof et al., 1988; Lin et al., 1988).
There have been no prior reports of annexin VI and L-plastin
copurified, probably a reflection of the abundance of both proteins in
neutrophils and the tissue specific expression of L-plastin (limited to
transformed and hematopoetic cells) (Lin et al. 1988). I was unable to
detect a complex formation between these proteins as evidenced by the
inability of annexin VI and L-plastin antibodies to recognize a common
band in active fractions resolved by native acrylamide gel electrophoresis.
Biochemical analysis reported by several laboratories repeatedly
demonstrates Mr between 64,000 70,000 and pi between 5.3 and 5.6 for

both proteins. The shared physical properties explains why we
consistently copurified these two proteins.

Earlier reports have implicated both annexin VI and L-plastin as
cytoskeletal regulatory proteins. They therefore remained likely
candidates responsible for the activity of neutrophil actin polymerization
inhibitor. Annexin VI isolated from bovine hepatic tissue was recently
observed to cosediment with actin filaments in a calcium dependent (>







100 pM) fashion (Hosoya et al., 1992). L-plastin has been shown to bundle
actin filaments in a calcium dependent manner (Namba et al., 1992). This

group was able to demonstrate by electron microscopy that L-plastin
induces actin bundle formation in vitro in the presence of low free calcium
concentrations (10 100 nM), and this property is lost as the calcium
concentration is elevated (1 10 pM). A separate group (Pacaud et al.,
1993) was able to demonstrate that L-plastin increases the viscosity of
actin solutions at low free calcium concentrations (< 0.1 pM), but the
viscosity of L-plastin/actin solutions was progressively lowered to control
levels actinn polymerized alone) as the free calcium concentration was
elevated (> 10 pM). The reported interactions of annexin VI or L-plastin
with actin, although, could not readily explain the calcium-independent
viscosity-lowering effect of the neutrophil actin polymerization inhibitor.
Annexin VI purified by either the phospholipid affinity column or
the High S cation exchange chromatography did not possess the
neutrophil inhibitory activity. Additionally, L-plastin could also be
separated from the neutrophil actin polymerization inhibitor (see Results)

by Mono Q-anion exchange chromatography. The ability to separate both
proteins from the activity proves the activity of PMN actin polymerization
inhibitor is not due to annexin VI or L-plastin.
It was subsequently discovered that capZ was responsible for the
inhibitory activity. Utilizing three additional chromatography columns,
the neutrophil actin polymerization inhibitor was successfully separated
from annexin VI and L-plastin (Figures 3-7, 3-8, and 3-9). Silver stained
polyacrylamide gels of the various purification steps reveal that active
fractions consistently correlate with the presence of the 36 and 32 kDa
capZ bands. My purification of the activity to these bands, and their







recognition by antibodies to capZ proves this protein is responsible for the
PMN actin polymerization inhibitor.
CapZ is a heterodimeric protein with subunits of Mr 36,000 (a-

subunit) and 32,000 (P-subunit) (Casella et al., 1986). Members of this
family are capable of binding the barbed end of actin filaments with high
affinity (~ 0.5 10 nM) independently of calcium. Binding to the barbed
end of actin filaments effectively decreases the apparent viscosity of actin
solutions by two mechanisms. First, this interaction results in the
shortening of the average filament length, and secondly it raises the
critical concentration to that of the pointed end. The elucidation that
PMN actin polymerization inhibitor is identical to capZ was complicated by
several factors. The limited number of human PMN available for
purification, capZ's high affinity interaction with actin, its decreased
sensitivity to Coomassie staining, the predominance of annexin VI and L-
plastin in active fractions, and most notably the physical properties shared
by these three proteins each added to my difficulties in identifying capZ as
the PMN inhibitor.

The use of the human neutrophil system greatly limits the starting
material. These immune cells have developed an effective antimicrobial
repertoire which includes a diverse collection of proteolytic molecules. A
packed cell volume of ~ 20 25 ml (derived from > 20 liters of peripheral
blood) was isolated during the largest preparations. With this amount of
cells, less than 1 gram of protein remains after clarification of the
homogenized cells. This is in stark contrast to the two previous published
purifications of capZ from animal cells (chicken skeletal muscle and
bovine brain). With the purification from chicken skeletal muscle, 1000 g
of chicken breast muscle are typically utilized to purify ~1 mg capZ







(Casella et al., 1986, Caldwell et al., 1989). Purification of capZ from
bovine brain similarly requires ~ 1000 g starting material (4 brains)
(Kilimann and Isenberg, 1982). Our final yield of PMN capZ after
hydroxylapatite chromatography (-10 pg) was about one-tenth of those in
chicken muscle capZ preparations. This finding is not surprising
considering the abundant proteolytic activity commonly seen in extracts
made from these phagocytes. Secondly, the ability of capZ to interact with
actin with such high affinity (> 250 ng/ml, based on Kd ~3 nM) (see

Chapter 4) allowed for detection of activity with minimal protein as seen
by stained polyacrylamide gels. The problem was further complicated by
the identification of the two major polypeptides copurified with the
activity as previously studied actin binding proteins.
Lastly, the elusiveness of capZ resulted primarily from its physical
properties and staining characteristics. The consistent purification of
annexin VI and L-plastin with capZ is currently explained by the similar
native molecular weights and isoelectric points shared by these three
proteins (annexin VI/L-plastin: Mr 64,000 70,000 and pi 5.3 5.6 for

both proteins). The molecular weights of bovine brain and chicken
skeletal muscle capZ were reported as 63,000 (pl 5.75) and 61,000
respectively (Kilimann and Isenberg, 1982; Casella et al., 1986). A Stokes
radius of 32 A was determined for the PMN actin polymerization inhibitor
by analytical gel filtration following the viscosity lowering activity
(Southwick & Stossel, 1981). This closely resembles the Stokes radii
determined for bovine brain (35.5 A) and chicken skeletal muscle (37 A)
(Kilimann and Isenberg, 1982; Casella et al., 1986). Many
chromatographic techniques rely on variations of MW or pi to separate
proteins. The physical properties shared by these three proteins







necessitates the use of several columns to purify the neutrophil inhibitory
activity.

In summary, the exhaustive purification protocols have
demonstrated human neutrophil actin polymerization inhibitor is capZ, a
heterodimeric protein consisting of two subunits with Mr of 36,000 and

32,000 as detected by silver staining active fractions separated by SDS-

PAGE. Western blot analysis of peak inhibitory activity from Mono Q
chromatography fractions reveals immunoreactivity of the 36 and 32 kDa

polypeptides with antisera made to chicken skeletal-muscle capZ,
supporting my conclusion that the 36 and 32 kDa polypeptides further
purified by hydroxylapatite were identical to the capZ immunoreactive

peptides. Together these findings presented in Chapter 3 indicate that the

previously published neutrophil actin polymerization inhibitor is indeed
related, if not identical, to the skeletal muscle form of capZ. In addition,

neither of the polypeptides originally identified as the neutrophil inhibitor
(currently identified in this work as annexin VI and L-plastin) contributes

to the activity of PMN actin polymerization inhibitor.














CHAPTER 4
FUNCTIONAL CHARACTERIZATION OF PMN CAPZ


Introduction


The PMN actin polymerization inhibitor was originally isolated in
the presence of EGTA primarily to distinguish it from the calcium-
dependent viscosity-lowering activity of gelsolin (Yin & Stossel, 1979).
The importance of this characteristic is suggested by the recent findings of

calcium-independent actin assembly in PMN (reviewed in Chapter 1).
Based on the current theories of actin regulatory proteins (Pollard &
Cooper, 1986), several interactions with actin could explain the actin
viscosity lowering effect originally reported for PMN actin polymerization

inhibitor (Southwick & Stossel, 1981). Proteins that sequester actin
molecules away from the polymerizable pool would lower the viscosity of

actin solutions. Additionally, interactions which shorten the average

length of actin filaments such as severing or capping (barbed or pointed
end) would also lead to a relative decrease in the final viscosity.

Conversely, actin binding proteins that cross-link or bundle actin

filaments would be expected to raise the viscosity of actin solutions. The
identification of the neutrophil activity as capZ suggests the viscosity

lowering effect results from the ability of this protein to cap the barbed-
end of actin filaments.







The characterization of the specific interactions of proteins with
actin was at first limited to those expert in the techniques of electron
microscopy. By this method the lengths of filaments can be directly
visualized, the kinetics of assembly at each end of the actin filament can

be simultaneously analyzed (using morphologically identifiable nuclei
such as heavy-meromyosin-labeled actin oligomers or Limulus sperm
acrosomal actin bundles), and the three-dimensional configuration of
actin solutions can be monitored. With the development of fluorescent
labels covalently attached to actin, most notably pyrene-labeled actin,
spectrophometric analysis of actin polymerization has become an
alternative, more accessible technique to study specific interactions and
kinetics of actin filament assembly (Kouyama & Mihashi, 1981; Cooper et
al., 1983). In efforts to further characterize the viscosity lowering activity
of PMN capZ, its effects on actin polymerization were studied utilizing
pyrene actin.


Results


Barbed-End Capping Activity

As shown in Figure 4-1A, capZ slowed the rate of actin filament
disassembly in a concentration dependent fashion. The marked slowing in
the depolymerization rate was most consistent with blocking of monomer
release from the barbed end of actin filaments. The apparent dissociation
constant for the interaction of capZ with the barbed end (Kd app) was

approximately 3 nM. CapZ inhibited actin depolymerization to a similar
extent in the presence as well as in the absence of Ca2+ (Figure 4-1B).
When filaments are diluted, they rapidly depolymerize from their ends in

















Figure 4-1. Effects of purified capZ on actin filament depolymerization. Pyrene actin (2pM) was allowed
to polymerize to steady state in the presence of 1 mM EGTA (Panel A) or 1 mM CaC12 (Panel B). At time
zero, aliquots of the F-actin were diluted 1/40 (final concentration 50 nM) into varying concentrations of
purified neutrophil capZ in buffer P containing EGTA (Panel A) or 1 mM CaC12 (Panel B). Fluorescence
intensity was monitored over time. Numbers next to symbols represent the final concentrations of capZ.














EGTA


22
A A

M M


M M M M M
Krn..


215aM
A 27nM
A 13.lnM
3.4M
* 0Control


0 E


U"
0 10 20 30

Time (min)


Calcium


O aM
A 18iM
0 9UMn
S* 3.6nM
D Control


o
[]


0 10 20 30


Time (min)




Full Text
Calciosome


Figure 5-6. Confocal microscopy of peripheral blood monocytes stained
with anti-annexin VI antibodies. These experiments were done in tandem
to Figure 5-5. Panel A is stained with anti-annexin VI antibodies, and
Panel B is stained with anti-nab-1 antibodies.


31
Utilizing fluorescent actin probes, it can be demonstrated that
fibroblasts undergo actin filament assembly and disassembly. The
lamellipodium of a cultured fibroblasts includes a dense network of actin
filaments (Wang, 1985). Fluorescence photobleaching of a discrete region
within the lamellipodium demonstrates centripetal movement and
eventual disappearance at the proximal edge of the actin band, a process
not unlike treadmilling. Their finding suggests actin filaments within the
lamellipodium are undergoing net assembly at their distal, membrane-
directed barbed ends and net disassembly at their proximal pointed ends
(Wang, 1985). Electron micrographs of neutrophils whose actin filaments
are decorated with heavy meromyosin reveal the barbed ends of actin
filaments are directed peripherally towards the membrane (Pryzwansky et
al., 1983). In addition, when PMN are stimulated with fMet-Leu-Phe, the
number of nucleation sites for actin polymerization is increased
transiently (Carson et al., 1986). These nucleation sites are sensitive to
cytochalasin, a drug whose actin inhibitory activity is partly explained by
its ability to cap the barbed-end of filaments, and they sediment with the
detergent insoluble actin cytoskeleton (Carson et al., 1986). These
findings suggests that neutrophils rapidly increase their F-actin content by
increasing the number of free barbed-ends upon chemotactic stimulation.
Calcium Independent Model For Polymerization
The two mammalian cell types which undergo a rapid (< 30 sec.)
doubling of actin in response to stimulation are phagocytes (neutrophils
and macrophages) and platelets. Profilin and thymosin 134 have both been
purified in these cell types. The only capping proteins that have been


43
mg/ml in water) was run simultaneously to the proteins of interest as
evidence of nondenaturing resolution of proteins.
Actin Binding Studies
Pyrene actin was used for all kinetic studies. Fluorescence intensity
was monitored using a Perkin-Elmer LS-5 fluorescence spectrophotometer
with excitation and emission wavelengths of 364 nm and 407 nm
respectively.
Denolvmerization Assay
Pyrene labeled actin (2 pM) was allowed to polymerize to steady
state in the presence of 1 mM EGTA or 1 mM calcium. The F-actin was
then diluted to 50 nM into a buffer containing 10 mM Imidazole pH 7.5,
0.5 mM ATP, 0.1 M KC1, 1 mM MgCl2, 1 mM DTT (Buffer P) in the presence
of varying concentrations of capZ (Southwick & DiNubile, 1986). The
reaction was observed for 30 min at 25 C.
Actin-Spectrin Nuclei Elongation Assay
Red blood cell derived spectrin/band 4.1/actin nuclei (rbc nuclei)
were isolated according to the methods of Casella et al. (1986). Pyrene-
labeled G-actin (0.55 pM) was added to a mixture of 1.25 pg/ml of rbc
nuclei, varying concentrations of capZ and buffer P containing 1 mM
EGTA. In the absence of rbc nuclei, this concentration of pyrene actin
(0.55 pM) failed to spontaneously polymerize during the time course of
our experiments (15 min). The capZ and rbc nuclei were allowed to
incubate for 2 min prior to the addition of the pyrene actin.


Fraction
Relative Activity
CO
o o
O Ln o


1
O'
1
2
3
1


44
Steady-Stals-Assay
Pyrene-labeled actin in buffer P with 1 mM EGTA was allowed to
polymerize at room temperature for 18 hours (steady-state), and the
critical concentration was determined by plotting the total actin
concentration verses the steady-state fluorescence (correcting for
fluorescence values at t = 0). The effects of various concentrations
(substoichiometric relative to actin) of capZ on the steady-state
fluorescence of pyrene actin (0.9 pM or 3 pM) was measured. The steady-
state G-actin concentration (apparent critical concentration) of the
solutions was calculated from the decrease in steady-state fluorescence
relative to pyrene actin controls. The fluorescent signal of pyrene actin is
proportional to polymer weight concentration (Cooper et al., 1983).
Nucleation Assay
For this assay, 1.5 pM pyrene labeled G-actin was allowed to
polymerize in buffer P in the presence of varying concentrations of capZ.
The effects of capZ on this polymerization rate were assessed by
fluorimetry (Southwick & DiNubile, 1986).
Severing Assay
Gelsolin (0.01 pM) and pyrene actin (2 pM) were copolymerized
(molar ratio 1:200) to steady-state, forming barbed-end capped filaments
(Casella et al., 1986). These filaments were then diluted to 100 nM in
buffer P containing 1 mM calcium and varying concentrations of capZ.


Figure 3-4. SDS-PAGE of phospholipid affinity chromatography, and anti-
annexin VI western analysis. PMN inhibitor was exposed to a mixed-lipid-
vesicle column in the presence of calcium. The activity remained in the
fall through (lane 2). Annexin VI (> 95 % pure) was eluted with ImM
excess EGTA. Fractions were transferred to nitrocellulose and probed with
antibodies to annexin VI. The same molecular weight standards in Figure
3-1 were used (HMW Std).


46
Annexin VI Binding To Multilamellar Vesicles
For the annexin VI lipid binding studies PC and PS were treated as
previously described by Blackwood, et al. (1990). Partially purified
neutrophil annexin VI was incubated at 25 C for 15 minutes with either PS
or PC in buffer P containing 0.2 mM EGTA and varying concentrations of
calcium. Each mixture was then centrifuged at 12,000 X g in a table top
microfuge for 15 min at 25 C. Supernatants and pellets were subjected to
SDS-PAGE and stained with Coomassie brilliant blue. The relative amounts
of annexin VI in the pellets and supernatants were determined by laser
densitometry.
Phospholipid Column
A 3.5 ml sepharose-4B phospholipid column composed of PS/PC/PE
(2:2:1) was built in attempts to separate annexin VI and L-plastin, the two
predominant proteins copurified with the PMN actin polymerization
inhibitor after gel-filtration chromatography. The phospholipid column,
which exploits the ability of annexin proteins to bind acidic phospholipids,
was constructed according to the methods of Meers and colleagues (1987).
Modulation Of Capping Activity Bv Phosphoinositides
The ability of various lipids to block capZ filament end capping was
also examined. The phospholipids PIP2, PI, PC and PS were treated as
previously described (Janmey & Stossel, 1989). The modulation of capZ
actin binding function was assessed using the depolymerization assay (see
above). CapZ (36 nM final concentration) was first added to
polymerization buffer, followed by the addition of phospholipids from
previously sonicated stock solutions and resonicated in a water bath


17
In search for additional monomer sequestering proteins, a 5 kD
peptide was discovered in high concentrations in human platelets (Safer et
al., 1990). Sequence analysis revealed identity to a peptide believed to be
a thymic hormone, thymosin B4 (T&4) (Safer et al., 1991). Based on its
wide distribution pattern and lack of secretory activity, this protein is no
longer believed to be a hormone. The dissociation constant (Kd) for the
T&4-actin complex has been reported to be in the 0.4 2.0 pM range
(Nachmias, 1993). It is calculated that in human PMN the cytoplasmic
concentration of TK4 is -150 pM, and together with profilin can account
for the sequestration of a majority of the G-actin in resting PMN
(Cassimeris et al., 1992). The amount of actin sequestered can be
estimated using the following equation for the dissociation constant (Kd)
of the sequestered monomer (Stossel et al., 1985):
Kd = [sequestering proteinjfree [Cc actin]/[sequestered G-actin]
Note that the concentration of sequestered actin is quite sensitive to the
critical concentration of actin.
With the recent suggestions that thymosin 15,4 alone is capable of
sequestering a majority of the G-actin in resting cells (platelets -560 pM;
Weber et al., 1992), the question arose as to the role of the ubiquitous
protein profilin. Still controversial, several different actin regulatory
functions for profilin besides its ability to sequester monomers have been
proposed (Theriot & Mitchison, 1993). In the writer's opinion, the most
fascinating proposed mechanism is this protein's ability to interact
catalytically with actin in a fashion promoting exchange of the bound
nucleotide and divalent cation. It was noted early on that Acanthamoeba
profilin interacts with G-actin to increase the rate of exchange of the
bound nucleotide (Mockrin & Korn, 1980). This is consistent with


CHAPTER 3
PURIFICATION AND IDENTIFICATION OF CAPZ AS THE PMN ACTIN
POLYMERIZATION INHIBITOR
Introduction
The viscosity lowering activity of PMN actin polymerization
inhibitor, as originally published, was thought to be composed of two
related polypeptides of 62,000 and 65,000 daltons (Southwick & Stossel,
1981). The polypeptides purified with this activity, although, were not
identified. This chapter outlines the efforts to identify the PMN inhibitor,
and my eventual discovery that the ~65 kDa, heterodimeric-protein capZ
is solely responsible for the actin viscosity-lowering activity.
Results
Identification Of The Two Major Polypeptides (~ 66 And 68 kDa)
Copurified With The Neutrophil Actin Polymerization Inhibitor
The calcium independent activity called human neutrophil actin
polymerization inhibitor was purified using ion exchange chromatography
and gel filtration (see methods) (Figure 3-1, lane 2). Yields and purity
were identical to the previously reported purifications (Southwick &
Stossel, 1981). The two polypeptides copurified with the inhibitor were
noted to have Mr of 66,000 and 68,000 when fractionated through a
discontinuous pH, 10 % SDS-PAGE. Similar to previous reports, highly
52


141
proteins are phosphorylated in response to fMLP activation (Andrews &
Babior, 1983). Although PKC does not appear important in the regulation
of the rapid actin filament response in fMLP stimulated PMN (Chapter 1),
phosphorylation by any of the other cellular kinases may indirectly
regulate this response through phosphorylation of those proteins directly
involved in regulating the actin polymerization. Additionally,
immunodepletion of capZ from PMN extracts would enable an estimation
of its contribution to the calcium independent capping activity found in
PMN extracts. Lastly, this technique could be used as an alternative
method to purify capZ from cells.
When PMN are stimulated by fMLP and subsequently lysed, the actin
nucleating activity in the detergent insoluble fraction (cytoskeleton)
increases (presumably due to uncapping of filaments). If capZ blocks
filament ends in resting PMN and loses this ability upon stimulation, a
shift from the triton insoluble to the soluble fraction would be detectable
by Western analysis.
If the cDNA's for the two subunits of capZ were obtained, a variety
of studies could be developed to further analyze the in vivo role of capZ in
cells. Antisense RNA studies inhibiting the translation of one or both
subunits in cells would enable one to address two major questions. First,
is capZ vital for maintaining the cytoarchitecture in cells. The effects of
antisense transfections would be monitored by light microscopy and
indirect immunofluorescence microscopy probing for known cytoskeletal
elements such as actin. Secondly, if a morphological change is observed,
the necessity of each subunit can be tested. Overexpression of capZ can
also be monitored as described above for antisense RNA studies.
Additionally, transgenic mouse studies can be done. This technique has


Activity
A
B
Std 16 24 30 34 38 42 50 58 66 74 86
12 20 28 32 37 40 46 54 62 70 78 82
^1
K>
C
Fraction U


124
Immunolocalization Of Annexin VI In Mveloid Cells
PMN and monocytes were isolated from peripheral blood and
allowed to adhere to glass coverslips (Chapter 2). A diffuse cytoplasmic
distribution was observed by indirect immunofluorescence when fixed and
permeabilized PMN were stained with the monoclonal anti-annexin VI
antibody (Figure 5-4A). Additionally, annexin VI appears to be absent
from the nucleus. The specificity of this stain is supported by the positive
and negative controls (Chapter 2) processed simultaneously (Figure 5-4 C
& D). When peripheral monocytes were similarly stained, a specific
cytoplasmic pattern was also observed. The stain, although, did not
appear as intense as in PMN (data not shown). Interestingly, there
appeared to be an enhancement of the immunofluorescent signal at the
peripheral margins of monocytes stained with the anti-annexin VI
antibody.
To explore the possibility that annexin VI concentrates in certain
regions of the cell, confocal microscopy was performed (Figure 5-5 &
Figure 5-6). Figure 5-5 demonstrates that annexin VI in adherence-
stimulated PMN has a diffuse cytoplasmic distribution, and is not
concentrated in the membrane rich periphery of these cells. Surprisingly,
annexin VI appears concentrated at the periphery of adherent monocytes
(Figure 5-6). Panel B of Figure 5-5 and Figure 5-6 depicts control cells
stained with the anti-yeast antibody (Chapter 2).
Quantitation Of Annexin VI In PMN Extracts
Each of the preceding studies as well as our purification of annexin
VI (Chapter 3), suggests annexin VI is an abundant protein in PMN.
Freshly prepared human PMN extract was isolated from cells treated with


CD
<
CM
i ni i i
CM
! Ilium I -


83
antibody to annexin VI, the polyclonal antisera only recognized the 68 kDa
polypeptide. These Findings suggested that the 66 kDa protein was not a
degradation product of annexin VI.
To determine the identity of this protein, active fractions were again
prepared for amino acid sequence determination as described earlier (see
Results), and sent to our collaborator D. W. Speicher at The Wistar
Institute. Utilizing improved techniques, the 68 kDa band was once more
identified as annexin VI while the 66 kDa band was identified as L-plastin.
Based on previously published cDNA sequences, the predicted molecular
weights of annexin VI and L-plastin are 75,901 and 70,306 respectively
(Sudhof et al., 1988; Lin et al., 1988).
There have been no prior reports of annexin VI and L-plastin
copurified, probably a reflection of the abundance of both proteins in
neutrophils and the tissue specific expression of L-plastin (limited to
transformed and hematopoetic cells) (Lin et al. 1988). I was unable to
detect a complex formation between these proteins as evidenced by the
inability of annexin VI and L-plastin antibodies to recognize a common
band in active fractions resolved by native acrylamide gel electrophoresis.
Biochemical analysis reported by several laboratories repeatedly
demonstrates Mr between 64,000 70,000 and pi between 5.3 and 5.6 for
both proteins. The shared physical properties explains why we
consistently copurified these two proteins.
Earlier reports have implicated both annexin VI and L-plastin as
cytoskeletal regulatory proteins. They therefore remained likely
candidates responsible for the activity of neutrophil actin polymerization
inhibitor. Annexin VI isolated from bovine hepatic tissue was recently
observed to cosediment with actin filaments in a calcium dependent (>


92
efforts to maintain the critical concentration of G-actin. Since the off rate
constant is several fold greater at the barbed end (k- = 3.5 s~l) than at the
pointed end (k- = 0.5 s'l), this assay is largely a reflection of monomer
loss at the barbed end (Bonder et al., 1983). If the filaments are composed
predominantly of ADP-actin, the difference in the off rate constants (k- of
ADP-actin) is increased to greater than one order of magnitude (Pollard,
1986; Korn et al., 1987). The steady state fluorescence values of each
sample reflected complete depolymerization, even at concentrations of
capZ causing maximal inhibition of depolymerization.
The ability of the neutrophil actin depolymerization inhibitor to
decrease the viscosity of actin filament solutions was previously reported
to be inhibited by increasing salt concentrations from 0.1 M KC1 to 0.6 M
KC1 (Southwick & Stossel, 1981). Therefore the effect of increasing salt
concentration on capZ barbed-end capping activity was also assessed by
the depolymerization assay. The capping activity of capZ was
progressively inhibited as the KC1 concentration in buffer P was raised to
0.6 M. This highest salt concentration caused near complete inhibition of
capZ capping activity (data not shown).
In addition to examining human PMN capZ's effects on the release of
actin monomers from the barbed filament ends, this protein's effects on
barbed end monomer addition were also examined using a complex
isolated from red blood cells composed of actin, band 4.1, and spectrin.
This membrane associated complex contains short actin filaments which
are thought to be capped at the pointed ends, and has been previously
used in the study of chicken skeletal muscle capZ's capping function
(Casella et al., 1986). As shown in Figure 4-2, capZ also blocked barbed
end actin filament assembly in a concentration dependent manner. The


1 23456789
1 23456789


142
proved helpful in clarifying gelsolin's in vivo function (Witke et al., 1993).
In a similar fashion, the gene/genes for capZ can be knocked out. If a
homozygote lacking capZ expression appears grossly normal, phenotypical
differences in this transgenic mouse and the gelsolin-minus mouse can be
studied. Would the motile function of PMN be altered? Would the PMN be
able to produce a rapid doubling of F-actin in response to
chemoattractants? If it is found that transgenic mice are never produced,
suggesting inviability, knock outs for each particular subunit can be
attempted. Because chemoattractant stimulated actin assembly is Ca^+-
independent, loss of capZ may have profound effects on chemotaxis. Each
of the studies described above would greatly enhance the proposal that
capZ is a key regulator in the actin-based motility of PMN.
PMN Annexin VI
Future studies regarding the function of annexin VI in PMN include
the search for membrane compartments which this protein may
specifically bind. Neutrophils have two major types of intracellular
vesicles (azurophil and specific granules). The killing and digestion of
phagocytosed organisms by PMN is dependent upon the fusion of
phagocytic vesicle membranes with the granules. Additionally, the
secretion of vesicle contents into the extracellular milieu necessitates a
regulated interaction with the cytoplasmic membrane.
Immunolocalization of annexin VI during such processes may suggest an
in vivo role for this abundant PMN protein.
The differential expression of annexin VI in HL-60 induced to
differentiate must be further explored. Treating cells on the third day of
differentiation (maximal difference in annexin VI mRNA observed) with


84
100 pM) fashion (Hosoya et al., 1992). L-plastin has been shown to bundle
actin filaments in a calcium dependent manner (Namba et al., 1992). This
group was able to demonstrate by electron microscopy that L-plastin
induces actin bundle formation in vitro in the presence of low free calcium
concentrations (10 100 nM), and this property is lost as the calcium
concentration is elevated (1-10 pM). A separate group (Pacaud et al.,
1993) was able to demonstrate that L-plastin increases the viscosity of
actin solutions at low free calcium concentrations (< 0.1 pM), but the
viscosity of L-plastin/actin solutions was progressively lowered to control
levels (actin polymerized alone) as the free calcium concentration was
elevated (> 10 pM). The reported interactions of annexin VI or L-plastin
with actin, although, could not readily explain the calcium-independent
viscosity-lowering effect of the neutrophil actin polymerization inhibitor.
Annexin VI purified by either the phospholipid affinity column or
the High S cation exchange chromatography did not possess the
neutrophil inhibitory activity. Additionally, L-plastin could also be
separated from the neutrophil actin polymerization inhibitor (see Results)
by Mono Q.-anion exchange chromatography. The ability to separate both
proteins from the activity proves the activity of PMN actin polymerization
inhibitor is not due to annexin VI or L-plastin.
It was subsequently discovered that capZ was responsible for the
inhibitory activity. Utilizing three additional chromatography columns,
the neutrophil actin polymerization inhibitor was successfully separated
from annexin VI and L-plastin (Figures 3-7, 3-8, and 3-9). Silver stained
polyacrylamide gels of the various purification steps reveal that active
fractions consistently correlate with the presence of the 36 and 32 kDa
capZ bands. My purification of the activity to these bands, and their


149
Gallagher, R., Collins, S., Trujillo, J., McCredie, K., Aheam, M., Tsai,
S., Metzgar, R., Aulakh, G., Ting, R., Ruscetti, F., and Gallo, R. 1979.
Characterization of the continuous differentiating myeloid cell line (HL-
60) from a patient with acute promyelocytic leukemia. Blood 54: 713-733
Gallin, J. I. 1988. The Neutrophil. In: Immunological diseases, 4th
Ed., Eds: Samter, M., Talmage, D. W., Frank, M. M., Austen, K. F., and
Claman, H. N. Little Brown & Co., Boston
Garrels, J. I., and Gibson, W. 1976. Identification and
characterization of multiple forms of actin. Cell 9: 793-805
Geisow, M. J., and Burgoyne, R. D. 1982. Calcium-dependent binding
of cytosolic proteins by chromaffin granules from adrenal medulla. J.
Neurochem. 38: 1735-1741
Glenney, J. R., Tack, B., and Powell, M. A. 1987. Calpactins: two
distinct Ca++-regulated phospholipid- and actin-binding proteins isolated
from lung and placenta. J. Cell Biol. 104: 503-511
Golde, D.W. 1990. Production, distribution, and fate of neutrophils.
In: Hematology, 4th Ed., McGraw-Hill, Inc., Ohio
Goldschmidt-Clermont, P. J., Machesky, L. M., Doberstein, S. K., and
Pollard, T. D. 1991. Mechanism of the interaction of human platelet
profilin with actin. J. Cell Biol. 113: 1081-1089
Hartwig, J. H., and Kwiatkowski, D. J. 1991. Actin-binding proteins.
Cum Opin. Cell Biol. 3: 87-97
Hatano, S., and Oosawa, F. 1966. Extraction of an actin-like protein
from the plasmodium of a myxomycete and its interaction with myosin. A.
J. Cell. Physiol. 68: 197-202
Haus, U., Hartmann, H., Trommler, P., Noegel, A. A., and Schleicher,
M. 1991. F-actin capping by cap32/34 requires heterodimeric
conformation and can be inhibited with PIP2. Biochem. Biophys. Res.
Comm. 181: 833-839
Hayashi, H., Owada, M. K., Sonobe, S., and Kakunaga, T. 1989.
Characterizations of two distinct Ca^+ -dependent phospholipid-binding
proteins of 68-kDa isolated from human placenta. J. Biol. Chem. 264:
17222-17230.




128


Relative Fluorescence
100
Time (min)




137
independently of calcium in vitro, suggests this protein is a key
component of the PMN model for actin assembly. In support of this,
transgenic mice lacking gelsolin (the only other barbed-end capping
protein in animal cells which is capable of blocking actin monomer
exchange in vitro at calcium concentrations found in resting cells, i. e.
submicromolar Ca2+) appear grossly normal and retain the ability to
interbreed (Witke et al., 1993). Additionally, the presence of capZ was
recently noted in human platelets (Barkalow & Hartwig 1994; Nachmias et
al., 1994). PMN, macrophages, and platelets are the mammalian model
cells for understanding the signal transduction mechanisms leading to
rapid actin assembly.
Purification Of PMN CapZ
Three major conclusions can be drawn from the work described in
Chapter 3. First of all, capZ is present in highly motile mammalian cells.
Secondly, capZ is responsible for the activity originally purified as PMN
actin polymerization inhibitor. This conclusion is supported by the
finding that when the PMN actin filament shortening activity was followed
through 5 consecutive column chromatography separations, the activity
localized solely to the 36 and 32 kDa bands (as detected by silver stained
SDS-polyacrylamide gels) which appeared stoichiometrically equivalent.
Additionally, when peak active fractions from Mono Q.column separations
(immediately precedes our final column) are probed with chicken,
skeletal-muscle capZ antisera the 36 and 32 kD polypeptides are
specifically detected by Western analysis. Although we were unable to
immunoprecipitate the capZ and/or the activity from final purified
fractions, the apparent affinity measured (Chapter 4) for the binding of


18
structural data obtained by chemical cross-linking and X-ray
crystallography which suggests profilin binds to actin in subdomain 3, a
region opposite the cleft wherein the adenosine nucleotide and divalent
cation bind (Vandekerckhove et al., 1989). The binding of DNase I to
subdomain 1 inhibits the nucleotide exchange rate, most likely by blocking
its exit from the cleft (Hitchcock, 1980; Mannherz et ah, 1980). It is
foreseeable that conformational changes induced upon the binding of
profilin may alter the nucleotide and divalent cation binding sites within
the cleft. It was recently demonstrated that profilin, when bound to actin,
increases the off rate constant (k-) of the bound nucleotide by 1,000-fold
(Goldschmidt-Clermont et al., 1991). More importantly, kinetic modeling
of the nucleotide exchange rates revealed that at substoichiometric
amounts profilin is still able to accelerate the nucleotide exchange of the
whole actin population. In this model, the catalytic mechanism is possible
because the rate of profilin's exchange between actin monomers is
relatively rapid (sub-second), but slower than the rapid dissociation of
actin ligands (nucleotide, divalent cation) which occurs during the
transient binding of profilin to each actin molecule (Goldschmidt-
Clermont et al., 1991). As discussed earlier, the kinetics of actin
polymerization are highly dependent upon the type of nucleotide bound.
Therefore, this mechanism may be central to the cell's ability to rapidly
"recharge" actin molecules which are continuously being cycled through
polymerization in highly motile regions of the cell.
Capping Proteins
Experimental evidence suggests the assembly of actin in nonmuscle
cells occurs by addition of monomers to the barbed ends of actin filaments


I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of Doctor
of Philosophy.
and Molecular Biology
Daniel L. Punch, Chair
Professor of Biochemistry -
I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of Doctor
of Philosophy.
Frederick S. Southwick, Cochair
Professor of Molecular Genetics
and Microbiology
I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of Doctor
of Philosophy.
Henry V. Baker, II
Associate Professor of Molecular
Genetics and Microbiology
I certify that I have read this
conforms to acceptable standards of
adequate, in scope and quality, as a
of Philosophy.
study and that in my opinion it
scholarly presentation and is fully
dissertation for the degree of Doctor
Associate Professor of
Biochemistry and Molecular
Biology


PURIFICATION AND FUNCTIONAL CHARACTERIZATION OF HUMAN
POLYMORPHONUCLEAR LEUKOCYTE ACTIN POLYMERIZATION INHIBITOR
By
NOEL ANTHONY MAUN
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE
UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
1995

This dissertation is dedicated to all the teachers who have guided
my education at the University of Florida.

ACKNOWLEDGMENTS
I would like to thank the members of my graduate committee for
their assistance and willingness to be a part of my education. Drs. Purich,
Baker, Driscoll, and Nick's constant support throughout my graduate work
enabled me to carry the project forward. I am especially indebted to my
mentor, Dr. Frederick Southwick, for his continued encouragement and
constant scientific guidance. His traits of perpetual enthusiasm, sincerity,
willingness to learn and dedication to basic science and clinical medicine
have provided a model I hope to equal someday. I would also like to
thank Dr. Purich for always being available when advice was needed. Our
discussions were always enjoyable, and 1 hope someday to be able to
explain complicated topics as simply and elegantly as he always does.
Special thanks also goes out to Dr. Mary Jo Koroly for a wonderful
introduction to the basic sciences. My tenure in the lab would not have
been as enjoyable if it were not for the many friends that I have made
during graduate school.
Finally, 1 would like to thank my family for their love, patience, and
support throughout my education.
iii

TABLE OF CONTENTS
ACKNOWLEDGMENTS iii
LIST OF FIGURES vi
ABSTRACT viii
CHAPTERS
1 INTRODUCTION 1
Overview 1
The Human Neutrophil 2
Actin 4
Actin Binding Proteins 14
Actin Dynamics in PMN 21
Calcium Independent Model For Polymerization 31
PMN Actin Polymerization Inhibitor 35
2 MATERIALS AND METHODS 37
Isolation Of Human Polymorphonuclear Leukocytes
(PMN) 37
Purification Of CapZ From Human PMN 37
Purification of Muscle Actin 40
Amino Acid Sequence Analysis 40
Polyacrylamide Gel Electrophoresis And Western Blot
Analysis 41
Actin Binding Studies 43
Lipid-Binding And Capping-Inhibition Studies 45
Promyelocyte Differentiation Studies 47
Fluorescence Microscopy 50
tv

3 PURIFICATION AND IDENTIFICATION OF CAPZ AS THE PMN
ACTIN POLYMERIZATION INHIBITOR 52
Introduction 52
Results 52
Discussion 75
4 FUNCTIONAL CHARACTERIZATION OF PMN CAPZ 8 8
Introduction 88
Results 89
Discussion 103
5 DEVELOPMENTAL EXPRESSION AND INTRACELLULAR
LOCALIZATION OF ANNEXIN VI IN PMN 113
Introduction 113
Results 115
Discussion 131
6 CONCLUSIONS AND FUTURE DIRECTIONS 136
Conclusions 136
Future Directions 139
REFERENCES 144
BIOGRAPHICAL SKETCH 160
v

LIST OF FIGURES
Figure page
1-1 Actin and its spontaneous polymerization in salt 8
1-2 Rate constants for the association and dissociation
of ATP-actin and ADP-actin at filament ends 11
1-3 fMet-Leu-Phe induced phospholipase C signaling
pathway 26
1-4 Regulation of actin assembly in PMN 34
3-1 PMN actin polymerization inhibitor 54
3-2 Amino-terminal sequence analysis of PMN actin
polymerization inhibitor 57
3-3 Nondenaturing polyacrylamide gel electrophoresis 61
3-4 SDS-PAGE of phospholipid affinity chromatography,
and anti-annexin VI western analysis 64
3-5 Western blot analysis of PMN inhibitory fractions
probed with capZ antisera 67
3-6 DEAE-anion exchange chromatography of PMN extract 70
3-7 High S-cation exchange chromatography of PMN
actin polymerization inhibitor 72
3-8 Mono Q-anion exchange chromatography of PMN
actin polymerization inhibitor 74
3-9 Western blot analysis of PMN actin polymerization
inhibitor purified to Mono Q chromatography 77
3-10 Hydroxylapatite column chromatography 79
vi

3-11 Silver stained peak fractions from Mono Q
and HA chromatography 81
4-1 Effects of purified capZ on actin filament
depolymerization 91
4-2 Effects of purified capZ on actin filament polymerization
from spectrin/band 4.1/actin nuclei 94
4-3 Effects of neutrophil capZ on the extent of
actin polymerization 97
4-4 Effects of neutrophil capZ on G-actin nucleation 100
4-5 Actin filament severing assay 102
4-6 Effects of capZ on polymerization from
gelsolimactin nuclei 105
4-7 Effects of PIP2 on capZ barbed-end
capping activity 107
5-1 Northern analysis of PMN and U937 117
5-2 Northern analysis of HL-60 differentiated to
neutrophil-like or macrophage-like cells 120
5-3 Western analysis of HL-60 differentiated to
neutrophil-like or macrophage-like cells 123
5-4 Indirect immunofluorescence microscopy of PMN 126
5-5 Confocal microscopy of PMN stained with
anti-annexin VI antibodies 128
5-6 Confocal microscopy of peripheral blood
monocytes stained with anti-annexin VI
antibodies 130
5-7 Quantitation of annexin VI in human
neutrophil cytoplasmic extracts 133
vii

Abstract of Dissertation Presented to the Graduate School of the University
of Florida in Partial Fulfillment of the Requirements for the Degree of
Doctor of Philosophy
PURIFICATION AND FUNCTIONAL CHARACTERIZATION OF HUMAN
POLYMORPHONUCLEAR LEUKOCYTE ACTIN POLYMERIZATION INHIBITOR
By
NOEL ANTHONY MAUN
May, 1995
Chairperson: Daniel L. Purich, Ph.D.
Cochairperson: Frederick S. Southwick, M.D.
Major Department: Biochemistry and Molecular Biology
Actin polymerization inhibitor, an activity from human
polymorphonuclear leukocytes (PMN) which lowers the viscosity of actin
filament solutions, was previously purified by our laboratory. The calcium
independent nature of the activity suggests it may be involved in the
motile behavior of PMN based on the current theories regarding the
regulation of actin filament assembly. This activity has been found by
additional column chromatography steps and Western blot analysis to be
the heterodimeric capping protein capZ. The actin regulatory activity of
this non-muscle capZ was assessed utilizing pyrenylactin. Similar to
skeletal muscle capZ and other members of the capping protein family, I
report that non-muscle capZ purified from PMN blocks monomer exchange
at the barbed ends of actin filaments under both polymerizing and
depolymerizing conditions with an apparent disassociation constant for
capping of 3 nM. Similar to the activity reported for actin polymerization
viii

inhibitor, PMN capZ's capping activity is independent of Ca^+ and is
inhibited by increasing the KC1 concentration from 0.1 M to 0.6 M. As
observed in all previously studied barbed-end capping proteins, PMN
capZ's capping function is inhibited by phosphatidylinositol 4,5-
bisphosphate (PIP2) micelles, 1/2 maximal inhibition being observed at
5.5 pg ml'l. Phosphatidylcholine, phosphatidylserine, or
phosphatidylinositol (11 pg ml'l) fan t0 inhibit capping function. The
PMN capZ's effects on actin assembly are confined to an interaction with
the barbed ends of actin filaments. This protein does not cap actin
filament pointed ends, does not sever preformed filaments, and fails to
interact significantly with actin monomers. Kinetic studies reveal no
enhancement of the nucleation step in actin assembly. This first report of
a capZ-related protein isolated from mammalian phagocytes suggests that
capZ is likely to play an important role in the regulation of actin filament
assembly in phagocytic cells.
IX

CHAPTER 1
INTRODUCTION
Overview
Cellular motility is a complex process which mandates the ability of
a cell to change its shape. In response to an external stimulus, outer
membrane receptors receive motivational signals and transmit this
information intracellularly. Subsequently, a cascade of events is initiated
which allow the cell to change its morphology and generate force for
motion towards the extracellular signal. A likely candidate which appears
central to this behavior is the self-assembling protein actin. Actin is the
most highly conserved and abundant protein in eukaryotic cells; and, in
addition, is the predominant filament of the cytoskeletal network. Unlike
in the sarcomere of muscle cells, non-muscle actin filaments are randomly
arranged in a fashion which enables the generation of force in three
dimensions rather than two dimensions. It is becoming increasingly
apparent that actin filament assembly/disassembly is vital to the process
of cell motility and shape change, and that the randomness of this
assembly is prevented by a group of regulatory proteins known
collectively as "actin binding proteins." This is a very exciting time for the
field of cellular motility and cell shape change. Amoebae, tumor cells,
leukocytes, fibroblasts, epithelial cells, and many other different cell types
share the ability to move by crawling across solid substrates utilizing a
1

2
similar process (Stossel, 1993). Our deeper understanding of the
molecular events involved may lead to a better understanding of the
biological processes which rely on cellular motility such as embryonic
development, inflammation, wound healing, tumor invasion, and host
defense. The work entailed in this dissertation centers around an actin
binding activity purified from human polymorphonuclear leukocytes
(PMN), one of the most highly motile animal cell types (10-20 pm/min)
(Howard & Meyer, 1984).
The Human Neutrophil
The neutrophil is one of the most motile cell types in the human
body; its primary purpose is to engulf and kill invading pathogens.
Histologically, polymorphonuclear granulocytes can be subdivided into
three distinct cell types named according to their staining characteristics;
the neutrophil (> 90 %), basophil, and eosinophil. Despite originating
from the same progenitor stem cell, each has a functionally distinct
immunological role (Williams et al., 1990). For the purposes of this
dissertation, the terms neutrophil, polymorphonuclear leukocyte (PMN),
and granulocyte will be used synonymously to denote neutrophil
leukocytes. In the normal human adult, the life span of the PMN is spent
in three environments: marrow, blood, and tissues (Bainton, 1992).
Proliferation and terminal differentiation occur primarily in the marrow
compartment over a period of approximately 10 days (Gallin, 1988). They
are subsequently released into the blood. This intravascular pool of
granulocytes representing only 5 % of the total number in the body is
equally divided between a freely circulating pool and a marginated pool

3
that is adherent to, or closely associated with, the lining of the blood
vessels (Golde, 1990). Individual cells move back and forth behaving
kinetically as a single pool. The neutrophils' stay in the blood is short,
with an approximate half-life of 6 - 7 hours, from where they subsequently
enter the extravascular space (Dancey et al., 1976). It is estimated that
approximately 100 billion PMN enter and leave the circulation daily
(Walker & Willemze, 1980). Despite this number, their fate after
migrating to tissues is unknown. Based on in vitro survivability of
peripheral PMN, it is thought that they probably remain functional for 1-2
days, and are then cleared (Golde, 1990).
Neutrophils are first-line defenders against invading
microorganisms. The frequent and severe infections that occur in persons
whose neutrophils are deficient quantitatively (neutropenia) or
qualitatively (e.g. chronic granulomatous disease or neutrophil actin
dysfunction) attest to the central role of this cell in host defense
mechanisms. They are the predominant leukocyte in peripheral blood
comprising two-thirds to three-fourths (4,000 - 8,000/mm3) of the
peripheral white blood cell count.
It is estimated that the bone marrow compartment houses PMN
reserves in excess of 100-fold the quantity found in peripheral blood.
These stores are readily discharged in response to bodily invasion.
Neutrophils are commissioned to seek, attack, and destroy pathogens and
so are endowed with the facility to rapidly advance and engage the enemy.
The major functions through which neutrophils carry out this mission
include chemotaxis, adherence, aggregation, phagocytosis, degranulation,
and generation of toxic metabolites. In part, these properties are
dependent upon an extensive rearrangement of the actin filament system

4
in certain parts of or throughout the cell (Stossel, 1992). The properties
of PMN chemotaxis, phagocytosis, adherence, and degranulation (the
principle movements) have gained the most attention in regards to the
relationship to cytoplasmic actin assembly.
In attempts to familiarize itself to the environment, the neutrophil
(and all animal cells to a certain extent) constantly forms and dissolves
diverse protrusions from its surface. Dependent upon external signals,
these protrusions take on particular shapes known as veils, ruffles, pleats,
filopodia, microvilli, and pseudopodia. Evidence suggests actin is
responsible for the elasticity of this organelle-deplete, actin-enriched
cortical region (Bretscher, 1991). The predominance of an agonistic signal
in certain regions allows for the formation of peripheral protrusions which
eventually lead to the motile properties of the neutrophil.
Actin
Actin Isoforms
In 1942 Bruno Straub discovered and isolated actin from rabbit
skeletal muscle (Straub, 1942). Nonmuscle cell actin was first purified
from Physarium by Hatano and Oosawa (1966). It has since been realized
that actin is ubiquitous (prokaryotic, plant, and animal cells), and often
the most abundant protein component in cells. Initially, it was thought
there were three major isoforms of actin in mammalian cells (Carrels &
Gibson, 1976). One muscle (a) and two non-muscle isoforms (p,
predominant non-muscle form, and y, second non-muscle form) could be
distinguished by isoelectric focusing; each with apparently distinct pis
between 5.40 and 5.44. It has since been demonstrated in mammals and

5
birds that at least six actin isoforms exist (three a, one (3, and two 7) and
are expressed in a tissue specific manner (Vandekerckhove & Weber, 1978;
Vandekerckhove & Weber, 1984). They differ from one another by only a
few amino acid residues, mainly in the first 20 N-terminal amino acids.
Utilizing near physiologic conditions, no major differences in the
polymerization characteristics of muscle vs. non-muscle isoforms of actin
are noted (Korn, 1982). As reviewed by Herman (1993), recent
compelling evidence suggests there are functional differences amongst the
muscle and non-muscle isoforms. Based on this evidence which includes
isoform-specific antibody localization and gene replacement studies, he
proposes a model cell wherein the nonmuscle isoforms are found in
regions of moving cytoplasm/cell cortex, and the muscle isoforms compose
the static microfilament bundles (stress fibers or myofibrils). Curiously, it
was recently noted that the cytoplasmic mRNAs for the p and y actin
isoforms are differentially segregated in myoblasts (Hill & Gunning, 1993),
and overexpression of either differentially impacts the cytoarchitecture of
these cells (Schevzov et ah, 1992). This suggests subtle functional
differences exist even amongst the nonmuscle isoforms.
Actin Structure
Actin consists of a single polypeptide chain of 375 amino acid
residues, with a molecular weight of about 42 kDa (G-actin). It has long
been known that G-actin contains a divalent cation and an adenine
nucleotide binding site. Both sites are occupied in all forms of purified
actin. Due to its tendency to polymerize, the formation of actin crystals
and thus its atomic structure had eluded researchers for many years.
Utilizing the ability of deoxyribonuclease 1 (DNase I) to inhibit

6
polymerization, Kabash et al. (1990) were finally able to solve the
structure of the actin (muscle isoform) molecule to atomic (2.8 and 3.0 Á)
resolution. Using this atomic structure along with lower resolution
analyses, the G-actin molecule can be described as an oblate sphere
(overall dimensions of 5.5 X 5.5 X 3.5 nm) composed of two major
domains (small and large) which are separated by a pronounced cleft. The
small and large domains are further divided into subdomains 1 & 2, and
subdomains 3 & 4 respectively. The four subdomains are stabilized
mainly by interactions with the nucleotide and divalent cation bound
within the cleft formed between the major domains. The crystalline
structure of beta-actin (non-muscle isoform) complexed with profilin was
recently solved to 2.55 Á. When compared to the a-actin structure of
Kabash et al., they appeared structurally similar with a notable 5° rotation
between the major domains.
The polar actin monomers can polymerize to form a polar actin
filament (F-actin). Geometrically, the filament can be described as a two-
start, double-stranded, right-handed helix with approximately 13 subunits
per turn. The precise orientation of the actin subunits is uncertain, but it
is thought that subdomain 2 of the monomer represents the end (see
"Polymerization" below), and "+" end (see below) is within subdomain 3.
Multiple inter- and intrastrand contacts between the subunits exist. The
structure of the filament is very complicated and has yet to be directly
characterized at the atomic level. Holmes et al. (1990) have proposed an
atomic model of the actin filament which they derived from the atomic
model of the G-actin molecule and low resolution (8 Á) F-actin structural
data. The intermolecular contact points in this model were recently
reviewed by Mannherz (1992).

Figure 1-1. Actin and its spontaneous polymerization in salt. The filament
shown here is decorated with heavy meromyosin which binds at a 45°
angle distinguishing the 2 ends of the filament. The barbed-end (+) is the
fast-growing end, and the pointed end (-) is the slow-growing end of the
filament


9
Polymerization
The 42,000 dalton actin monomer (G-actin) can non-covalently self¬
associate and polymerize to form filaments (F-actin) in the presence of
monovalent (KC1) or divalent (MgCl2, CaCl2) salts, and hence increase the
solution viscosity. The theory of actin polymerization has been reviewed
extensively by several authors (Korn, 1982; Stossel et al., 1985; Pollard &
Cooper 1986; Pollard, 1990), and will be briefly discussed. Actin
polymerization is at least a two-step process: nucleation followed by
elongation. Nucleation, the rate-limiting, thermodynamically-unfavorable
step, occurs when 3 molecules of actin associate to form the nucleus for
further assembly. Polymerization/elongation cannot proceed unless the G-
actin concentration is above a critical concentration (Cc), which is defined
as the minimum concentration of G-actin required to form a polymer
(Pollard & Cooper, 1986). The Cc value is sensitive to the ionic conditions,
pH, temperature, and nucleotide content of the reaction solution
(Zimmerle & Frieden, 1986; Zimmerle & Frieden, 1988). Despite the
minimal requirements, many groups have simulated physiologic
conditions (0.1 M KC1, ImM MgCl2, EGTA-to chelate Ca2+, ImM ATP, and
pH 7.4) during their analysis of polymerization kinetics. As alluded to
earlier, at near physiologic conditions the critical concentrations for
assembly of muscle and non-muscle actin isoforms are virtually
indistinguishable. Under defined conditions, actin filament assembly
reaches a steady-state as a result of actin molecules continually being
exchanged between actin filaments and the critical concentration of
monomers without affecting the overall F-actin content.
The actin filament has two kinetically different ends (barbed "+"
and pointed "-") defined by the arrowhead pattern produced when an

Figure 1-2. Rate constants for the association and dissociation of ATP-
actin and ADP-actin at filament ends. Adapted from Pollard (Curr. Opin.
Cell Biol. 1990. 2: 33-40)

11
Unit K+ = iimol'1 s_1
K. = s-1

12
actin filament is labeled with heavy meromyosin ("rigor" conformation)
and visualized by electron microscopy (Huxley, 1963). The barbed (+)
ends have a greater exchange rate and a lower critical concentration (Cc+
= 0.1 pM) for monomer binding than the pointed (-) ends (Cc- = 0.6 pM)
(Bonder et al., 1983). Thus, the barbed ends are the more kinetically
active and preferred ends for filament growth. At steady-state, i. e. when
the association rate equals the dissociation rate, the apparent critical
concentration for the entire filament (Cc = 0.15 pM) is closer to that of the
barbed end (Korn, 1982). As a result, a steady-state condition termed
"treadmilling" occurs in which monomers slowly dissociate from the
pointed ends allowing new monomers to rapidly add on to the barbed
ends (Neuhaus et al., 1983; Wanger et al., 1985).
Actin polymerization is more rapid in the presence of ATP than in
the presence of ADP (Carlier et al., 1984; Pollard, 1984). This is not due to
energy made available through ATP-hydrolysis since polymerization can
occur faster than ATP-hydrolysis (Carlier et al., 1984). The differential
polymerization rates could be explained by the fact that ATP-G-actin has a
higher affinity and a lower dissociation rate than ADP-G-actin (Pollard &
Cooper, 1986). The hydrolysis of the ATP within the actin molecule
consists of two temporally distinct steps: the chemical cleavage of ATP
resulting in an ADP-Pj-actin followed by the slower release of P¡ into the
medium (Korn et al., 1987). Additionally, it has been shown that the
cleavage of ATP occurs vectorally (Carlier et al., 1987). This suggests that
if one examines a filament during the polymerization of ATP-actin, the
newly added actin molecules are ATP-actin followed by ADP-Pi-actin, and
most internally, ADP-actin (Carlier, 1991). Since the dissociation rate of
ATP-actin is slower than ADP-actin, the delayed ATP hydrolysis promotes

13
actin filament assembly. Under these conditions, the extent of this "ATP-
cap" is dependent upon the polymerization rate. In contrast,
depolymerization is facilitated by the exposure of these internal ADP-actin
molecules. In this model, the presence of ATP and its hydrolysis may
partially regulate the rapid reorganization of actin structures.
Using electron microscopy to monitor the elongation rates of
preformed filaments as a function of added G-actin has enabled the
determination of the rate constants for the "elongation" reactions (Bonder
et al., 1983; Pollard, 1986). The differences between ATP-actin and ADP-
actin result in eight main reactions (Figure 1-2). Several labs have
determined various rate constants, and at least two labs have generated all
eight (Pollard, 1986; Korn et al., 1987). There is general agreement (at
least within an order of magnitude) regarding the values of these rate
constants.
The different affinities of the various forms of nucleotide-bound
actin monomers for filaments may be due to conformational changes. In
Kabsch's atomic models comparing ATP- and ADP-actin, there are direct
interactions between the calcium ion and the (5- and y- phosphates of ATP
(P alone with ADP) within the cleft, and subtle differences in the hydrogen
bonds formed between the phosphate groups with neighboring amino
acids (Kabsch et al., 1990). The atomic structure of Mg2+-ATP-actin,
although, may be quite different, as suggested by the fluorescence
difference seen when AEDANS (N-acetyl-N'-[sulfo-l-
napthyljethylenediamine) labeled actin is in a Mg2+ verses a Ca2+
environment (Selden et al., 1986). Despite the literature available on the
effects of calcium or magnesium binding to actin (Estes, 1992), this

14
complicated topic will not be covered. Additionally, it is generally
accepted that Mg2+ is the divalent cation bound to actin in the cell.
Actin Rinding Proteins
Background
It was recognized early on that at least 50 % of the actin in extracts
from various non-muscle cells is nonpolymerized, in stark contrast to
muscle cells in which nearly 100 % of the actin is polymerized (Korn,
1982). Based on the earlier findings that nonmuscle isoforms of actin
share the same polymerization kinetics and critical concentrations as
muscle isoforms, it was hypothesized that the polymerization of actin in
nonmuscle cells was regulated through the interaction of actin with other
cellular components. This hypothesis was amply supported by the
identification of nonmuscle cell proteins that have specific interactions
with G-actin and/or F-actin.
On the basis of their ability to interact with actin in vitro, these
proteins were collectively termed "actin-binding proteins" (Stossel et al.,
1985; Pollard & Cooper, 1986; Hartwig & Kwiatkowski, 1991). Today, over
100 such nonmuscle proteins have been described. They are felt to be
responsible for the coordinated regulation of nonmuscle cell actin
polymerization considered necessary for motile activities as well as the
maintenance of structural integrity. Actin-binding proteins can be
subdivided into groups that either control the three-dimensional
arrangement of actin filaments (cross-linking and bundling proteins),
apply force to the actin-filament network (myosins), or regulate actin -
filament number and length (capping, severing, nucleating, and monomer-

15
binding proteins). Although the groups that control the three-dimensional
arrangement of actin filaments (gelation to solution or gel-sol reaction)
and those that apply force (contraction of actin gels) to the network are
almost certainly involved with the motile behavior of PMN (Condeelis,
1993), this discussion on actin-binding proteins will be limited to the
subset controlling actin-filament number and length.
The regulation of actin filament number and length is achieved by
four principle mechanisms. First, capping describes the ability of a
regulatory protein to bind to either the barbed ("+") or pointed ("-") end
of an actin filament preventing further addition or loss of monomers at
the particular end "capped." Severing is the mechanism whereby an actin-
binding protein is able to interact with the side of a filament and disrupt
the intermolecular interactions at that site, thus breaking the filament in
two. This is usually achieved by binding a "barbed" region within the
filament, and thus one of the newly severed fragments is capped at their
barbed end (Weeds & Maciver, 1993). The third mechanism, nucleation,
describes the ability of a protein to initiate elongation of actin filaments
without a lag phase. This may be achieved by either the rapid induction
of a polymerization-favorable conformation or stabilization of
intermediates in the formation of the trimeric nucleus. The forth
mechanism describes the ability of an actin binding protein to sequester
monomers in a 1:1 complex and inhibit their incorporation into filaments.
Therefore, if monomer-binding proteins are added to a solution of actin
monomers in stoichiometric amounts, the final extent of polymerization
upon the addition of salts will be decreased. The decrease will be
dependent upon the critical concentration of actin and the dissociation
constant of the interaction with actin monomers. It must be noted that the

16
in vitro analysis and in vivo interpretation of function of actin binding
proteins is often complicated by their ability to utilize more than one
mechanism to regulate actin filaments.
Monomer Sequestering Proteins
A high concentration of actin, well above the Cc necessary for
assembly at both ends of the filament, is stored in an unpolymerized form
in nonmuscle cells (100 - 200 pM or greater in PMN, assuming a uniform
distribution) and becomes available for assembly into filaments upon cell
activation. Monomer sequestering proteins are felt to account for a
majority of the unpolymerized actin found in these cells. The two major
families of proteins in this class are the profilins and the thymosins.
Mammalian profilins are low-molecular-weight proteins with Mr
around 15,000. Initially purified from spleen (Carlsson et al., 1977), it
has since been found in almost all mammalian cell types including PMN,
macrophages, and platelets (Southwick & Young, 1990; DiNubile &
Southwick, 1985; Markey et al., 1978). Purified profilin is able to
reversibly bind actin monomers with an apparent dissociation constant
(Kd) in the range of 1 to 10 pM (Larsson & Lindberg, 1988; Goldschmidt-
Clermont et al., 1991). For many years, profilin was thought to be the
major sequestering protein in nonmuscle cells, and simple sequestration
was its primary function. Estimations of profilin concentrations made
initially in platelets and subsequently in PMN suggested the concentration
of profilin (~40 pM) present within these cells is insufficient, when using
the simple model of sequestration, to account for the amount of
nonpolymerized actin (~100 - 200 pM) in resting states (Lind et al., 1987;
Southwick & Young, 1990).

17
In search for additional monomer sequestering proteins, a 5 kD
peptide was discovered in high concentrations in human platelets (Safer et
al., 1990). Sequence analysis revealed identity to a peptide believed to be
a thymic hormone, thymosin 84 (TK4) (Safer et ah, 1991). Based on its
wide distribution pattern and lack of secretory activity, this protein is no
longer believed to be a hormone. The dissociation constant (Kd) for the
TJk4-actin complex has been reported to be in the 0.4 - 2.0 pM range
(Nachmias, 1993). It is calculated that in human PMN the cytoplasmic
concentration of TK4 is -150 pM, and together with profilin can account
for the sequestration of a majority of the G-actin in resting PMN
(Cassimeris et ah, 1992). The amount of actin sequestered can be
estimated using the following equation for the dissociation constant (Kd)
of the sequestered monomer (Stossel et ah, 1985):
Kd = [sequestering proteinjfree [Cc actin]/[sequestered G-actin]
Note that the concentration of sequestered actin is quite sensitive to the
critical concentration of actin.
With the recent suggestions that thymosin 15,4 alone is capable of
sequestering a majority of the G-actin in resting cells (platelets -560 pM;
Weber et ah, 1992), the question arose as to the role of the ubiquitous
protein profilin. Still controversial, several different actin regulatory
functions for profilin besides its ability to sequester monomers have been
proposed (Theriot & Mitchison, 1993). In the writer's opinion, the most
fascinating proposed mechanism is this protein's ability to interact
catalytically with actin in a fashion promoting exchange of the bound
nucleotide and divalent cation. It was noted early on that Acanthamoeba
profilin interacts with G-actin to increase the rate of exchange of the
bound nucleotide (Mockrin & Korn, 1980). This is consistent with

18
structural data obtained by chemical cross-linking and X-ray
crystallography which suggests profilin binds to actin in subdomain 3, a
region opposite the cleft wherein the adenosine nucleotide and divalent
cation bind (Vandekerckhove et ah, 1989). The binding of DNase I to
subdomain 1 inhibits the nucleotide exchange rate, most likely by blocking
its exit from the cleft (Hitchcock, 1980; Mannherz et ah, 1980). It is
foreseeable that conformational changes induced upon the binding of
profilin may alter the nucleotide and divalent cation binding sites within
the cleft. It was recently demonstrated that profilin, when bound to actin,
increases the off rate constant (k-) of the bound nucleotide by 1,000-fold
(Goldschmidt-Clermont et al., 1991). More importantly, kinetic modeling
of the nucleotide exchange rates revealed that at substoichiometric
amounts profilin is still able to accelerate the nucleotide exchange of the
whole actin population. In this model, the catalytic mechanism is possible
because the rate of profilin's exchange between actin monomers is
relatively rapid (sub-second), but slower than the rapid dissociation of
actin ligands (nucleotide, divalent cation) which occurs during the
transient binding of profilin to each actin molecule (Goldschmidt-
Clermont et ah, 1991). As discussed earlier, the kinetics of actin
polymerization are highly dependent upon the type of nucleotide bound.
Therefore, this mechanism may be central to the cell's ability to rapidly
"recharge" actin molecules which are continuously being cycled through
polymerization in highly motile regions of the cell.
Capping Proteins
Experimental evidence suggests the assembly of actin in nonmuscle
cells occurs by addition of monomers to the barbed ends of actin filaments

19
(Wallace et al., 1984; Carson et al., 1986). All capping proteins purified
from non-muscle cells thus far cap (in vitro) the barbed ends of F-actin
filaments. Inhibiting exchange at the high affinity, barbed end effectively
raises the Cc to that of the pointed end. The steady-state result of the
interaction of these capping proteins with actin is increasing the
concentration of the G-actin pool and creating a large number of relatively
short filaments. Two proteins, accumentin and S-actinin, were originally
reported to cap the pointed end of F-actin filaments, but their activities
have since been shown to actually be barbed end capping of filaments
(acumentin) (Young, Maun, and Southwick unpublished data; Maruyama
et al., 1990). Barbed-end capping proteins are grouped based on their
functional and structural characteristics (Hartwig & Kwiatkowski, 1991;
Weeds & Maciver, 1993). The two major families of capping proteins are
the gelsolin family and the capZ family. The major functional difference
between these families is that proteins in the gelsolin family require
calcium to initiate the interaction with actin whereas the capping activity
of the capZ family occurs independently of calcium.
The gelsolin family of capping proteins is composed of the
structurally related mammalian (gelsolin, villin, capG, and scinderin) and
invertebrate proteins (fragmin and severin) (Mishra et al., 1994). Each
member is able to nucleate filament assembly and sever preformed
filaments (except capG; Southwick & DiNubile, 1986) in addition to their
collective ability to cap the barbed end. The founding and best
characterized member is gelsolin. Originally purified from rabbit alveolar
macrophages as a 91 kDa protein, gelsolin is now known to be widely
distributed (including muscle cells) (Yin & Stossel, 1979; Yin et al., 1981).

20
As reviewed by Stossel et al., (1985), the three in vitro effects of
gelsolin on actin are differentially dependent upon the Ca2+
concentration. Severing has the most stringent calcium requirement, and
does not occur in the presence of submicromolar Ca2+. Barbed-end
capping occurs to a small extent in the presence of submicromolar Ca2+,
but this activity is markedly enhanced at higher calcium concentrations.
Gelsolin is able to nucleate filament assembly in the presence of calcium
by forming a complex (1 gelsolin : 2 actin) with two molecules of actin
(Janmey et al., 1985). Removal of calcium by EGTA dissociates one of the
actin monomers leaving behind a stable 1:1 gelsolin-actin complex. This
EGTA-resistant complex is unable to sever filaments, but can now bind the
barbed ends of filaments with high affinity even at submicromolar calcium
concentrations. Gelsolin has also been isolated as an alternatively spliced,
93 kDa, plasma form differing from the cytoplasmic form by the presence
of an additional 25 N-terminal amino acids (Kwiatkowski et al., 1986).
The secreted gelsolin is hypothesized to maintain and buffer a low plasma
actin filament content even when the cytoplasmic components of cells are
spilled into the vasculature during processes such as injury.
The capZ family includes heterodimeric proteins with subunits of
30-35 kDa which are able to bind the barbed end of actin filaments
independently of calcium. Most members described can nucleate filament
assembly, but all lack the ability to sever filaments. CapZ, a heterodimeric
protein with subunits of Mr = 36,000 (a-subunit) and 32,000 (p-subunit)
daltons, is the best characterized member of this family (Casella et al.,
1986). Purified skeletal-muscle capZ caps the barbed end of filaments
with an apparent dissociation constant of approximately 0.5 - 1 nM
(Caldwell et al., 1989a). It was originally purified from skeletal muscle

21
and localized to the sarcomeric Z-line (Casella et al., 1987). CapZ has
subsequently been recognized in nonmuscle cells as well (Caldwell et al.,
1989b; Schafer et al., 1992). It has recently been recognized that barbed-
end capping proteins purified from Acanthamoeba (Isenberg et al., 1980),
Dictyostelium (Schleicher et al., 1984), Xenopus (Ankenbauer et al., 1989),
Saccharomyces (Amatruda & Cooper, 1992) and bovine brain (Kilimann &
Isenberg, 1982) are indeed analogues of capZ. The presence of
mammalian capZ in highly motile cell types such as PMN and macrophages
has yet to be noted. It was recently reported to be present in human
platelets (Barkalow& Hartwig, 1994; Nachmias et al., 1994).
Actin Dynamics In PMN
PMN Chemoattractants
Chemoattractants are substances which have the ability to induce
directed migration. The three major groups of neutrophil
chemoattractants are described as complement-derived (C5a), leukocyte-
derived (LTB4, PAF, 11-8), and bacterial-derived (formylated peptides, e.g.
fMet-Leu-Phe). Neutrophils can sense a chemotactic concentration
gradient as small as 1 % across their dimension (Zigmond, 1977). As
discussed below, the rapid, chemoattractant-induced polymerization of
actin is probably the best understood transduction mechanism involved in
regulating the actin microfilament network. Overall, the transduction
mechanisms which regulate cellular actin assembly, although, remain
poorly understood.
Curiously, nanomolar concentrations of chemoattractants are
enough to induce shape change and locomotion in neutrophils, whereas it

22
takes much higher (micromolar) concentrations to induce the microbicidal
mechanisms of PMN (Gallin, 1988). Chemoattractants transmit their signal
through specific surface receptors, and many appear to utilize a common
signal transduction pathway. The "bimodal" response of PMN to
chemoattractants (differential triggering of motile verses microbicidal
functions) is currently thought to result from the activation of additional
transduction pathways dependent upon the extent of the chemotactic
stimulus (Snyderman & Uhing, 1992). The remaining discussion in this
chapter will focus on the rapid actin assembly occurring during the initial
phase as the transductional events of the second phase are poorly
understood. The fMet-Leu-Phe peptide has been termed the neutrophil
"pan-activator" for its ability to induce almost all major PMN functions in
addition to chemotaxis (Becker, 1987), and consequently its signal
transduction mechanisms have been extensively studied (for review see
Snyderman & Uhing, 1992).
Rapid Polymerization In Response To fMet-Leu-Phe
The overall morphology of PMN dramatically changes in response to
chemotactic stimulation (Fechheimer & Zigmond, 1983; Howard & Oresajo,
1985). At rest the cells are spherical, and upon stimulation form
peripheral ruffles or lamellipodia at their surface which have been shown
microscopically to be highly concentrated in F-actin (Fechheimer &
Zigmond, 1983; Sheterline, et al., 1984a). Neutrophils contain
approximately 5 pg actin/cell, which correlates to roughly 10 % of the
total cellular protein in these cells (Sheterline et ah, 1984b). Others have
calculated that actin represents as high as 20 % of PMN extracts
(Southwick & Young, 1990). Probably the best evidence suggesting actin

23
dynamics is important in PMN cell motility are the changes in the ratios of
monomeric to filamentous actin seen when cells are stimulated to undergo
motility. The rapid, chemoattractant-induced actin polymerization
response occurs in many eukaryotic cells, in addition to PMN, which are
able to undergo "amoeboid-like" motility (Stossel, 1992; Caterina &
Devreotes, 1991).
In resting PMN approximately 30 - 40 % of the total actin
concentration is F-actin (Feichheimer & Zigmond, 1983; Sheterline et al.,
1984b; Bengtsson et al., 1986). Assuming a uniform distribution, this
corresponds to roughly 100 pM F-actin and 200 pM G-actin (Southwick &
Young, 1990). Remarkably, several laboratories have demonstrated that
within 30 seconds or less of fMet-Leu-Phe stimulation, the actin filament
content doubles (F-actin: ~100 —> 200 pM) (Shalit et al., 1987; Howard &
Meyer, 1984; Fechheimer & Zigmond, 1983; Omann et al., 1987; Lofgren et
al., 1993). Cytochalasins, in vitro inhibitors of actin polymerization,
inhibit the morphological changes associated with neutrophil motility
(Zigmond & Hirsch, 1972) as well as the induced rise in polymerized actin
(Southwick et al., 1989; Cassimeris et al., 1990; White et al., 1983).
Furthermore, the dose dependency of the fMet-Leu-Phe-induced
chemotaxis and the rapid, actin-polymerization response are similar
(Howard & Meyer, 1984).
Dynamic changes in actin filament content occur during other PMN
motile events such as phagocytosis, degranulation, and adherence. A
nearly twofold rise in actin filament content is also observed during these
neutrophil functions (Boyles & Bainton, 1981; Fechheimer & Zigmond,
1983; Southwick et al., 1989), but the dissection of the transduction
cascade is complicated by the activation of multiple pathways. Although

24
these functions can be initiated by fMLP stimulation, their predominant
signal transduction pathways appear to be different (Southwick et al.,
1989; Rosales et al., 1994).
fMet-l.eu-Phe Signal Transduction Pathway
The N-formylated methionyl peptides such as fMet-Leu-Phe activate
neutrophils by binding to a specific cell surface receptor. The primary
structure of the fMet-Leu-Phe receptor has been deduced from its cDNA
sequence, revealing it belongs to the G-protein-coupled receptor family
(Boulay et al., 1990). Nearly all G-protein-coupled receptors share a
similar sequence motif which allows for seven-transmembrane-segments
(7-TMS motif) that span the lipid bilayer (Dohlman et al., 1991). The
recent sequence data only confirmed what had been suspected about the
fMet-Leu-Phe signal transduction cascade based on biochemical studies.
Pertussis toxin, a well known inhibitor of some G-proteins, inhibits
many chemotactic responses in a concentration dependent fashion (Brandt
et al., 1985; Becker et al., 1985; Bengtsson et al., 1986). Guanine
nucleotides, and not adenine compounds, regulate the affinity state of the
plasma purified f-Met-Leu-Phe receptors (Sklar et al., 1987). Chemotactic
factors stimulate membrane associated GTPase-activity and guanine
nucleotides can potentiate fMet-Leu-Phe induced activation (Feltner et al.,
1986; Verghese et al., 1986). Additionally, a GTP-binding, 40 kDa
pertussis-toxin-substrate complex copurifies with the fMet-Leu-Phe
receptor after several chromatographic steps. Immunochemical
identification and cDNA sequence analysis reveal the PMN G-protein
coupled to the fMet-Leu-Phe receptor is of the G¡2 (pertussis toxin

Figure 1-3. fMet-Leu-Phe induced phospholipase C signaling pathway. Stimulation of PMN results in the
doubling of intracellular F-actin in < 30 sec.

Calciosome

27
sensitive, phospholipase C activator) subtype (Snyderman & Uhing, 1992;
Kaziro et al., 1991).
The kinetics and dose-dependency of the fMet-Leu-Phe-induced
actin polymerization burst coincides with the rapid, initial phase of the
fMet-Leu-Phe response (discussed under "PMN chemoattractants"). The
following sequence of major intracellular events comprise this initial
phase. In short, binding of fMet-Leu-Phe to its receptor results in the
dissociation of a membrane-bound, heterotrimeric, GTP-binding protein
(G-protein). This activated G-protein (Gj2-alpha subunit) transiently
activates phospholipase C to produce two second messengers, 1,2-
diacylglycerol (DAG) and inositol (1,4,5) triphosphate (IP3) from
phosphatidylinositol(4,5) bisphosphate (PIP2) hydrolysis. Inositol
triphosphate releases intracellular stores of calcium, while DAG activates
protein kinase C. The rapid cleavage of PIP2 by PKC results in the
conversion of other phosphoinositides such as PIP and PIP3 to PIP2- The
conversion of phosphoinositides is regulated by a large number of kinases
and phosphatases that add or remove phosphates on the inositol ring
(Janmey, 1994). Temporal studies show rapid (< 5 sec) elevations in
phosphoinositide metabolism and cytosolic calcium levels following fMet-
Leu-Phe stimulation. The molecular mechanisms responsible for the
cytochalasin-sensitive, rapid (< 15-30 sec) and dramatic increase in actin
polymerization in response to fMet-Leu-Phe remain unknown, but are
thought to involve these molecules.
Calcium And Protein Kinase C-Independent, Phosphoinositide-Deoendent
IMLP-Induced Actin Polymerization Response
Modulation of the transductional cascade using traditional
pharmacological agents demonstrates that neither calcium or protein

28
kinase C (PKC) are primarily associated with the rapid polymerization of
actin in PMN stimulated with fMet-Leu-Phe. Since this fMet-Leu-Phe-
induced increase in F-actin content in PMN is totally abolished if cells are
pretreated with pertussis toxin (Bengtsson et al., 1986; Omann et al.,
1991), investigators have actively pursued potential signals distal to the G-
protein, but proximal to calcium release and protein kinase C activation.
In addition to calcium, the in vitro actin regulatory activities of various
actin binding proteins are modulated by phosphoinositides. These in vitro
findings in combination with the observation that phosphoinositides are
rapidly turned over in PMN stimulated with fMet-Leu-Phe has led to the
hypothesis that phosphoinositides are primarily involved in the regulation
of the rapid, actin-polymerization response (Stossel, 1989; Janmey, 1994).
Phorbol esters, exemplified by phorbol myristate acetate (PMA),
have been shown to bind, translocate, and activate PKC in human
neutrophils (Castagna et al., 1982; Nishihira et al., 1986), and are
consequently utilized as specific PKC activators. Only minor increases in
F-actin content are noted when resting human neutrophils are stimulated
with levels of PMA that phosphorylate much more effectively than fMLP
(Bengtsson et al., 1986; Howard & Wang, 1987). Conversely, several
protein kinase inhibitors with relative specificity for PKC (i.e.,
staurosporine, CGP 41251, and H7), when used at functional
concentrations, do not significantly alter the rapid, 2-fold increase in F-
actin seen within 30 seconds of fMet-Leu-Phe stimulation of neutrophils
(Niggli & Keller, 1991; Keller & Niggli, 1993; Sham et al., 1993).
Additionally, neutrophil chemotaxis induced by fMet-Leu-Phe is only
slightly inhibited by staurosporine (Boonen et al., 1993).

29
Chemotactic stimulation increases the intracellular free calcium
concentration, [Ca2+], from the 100 nM level at rest to micromolar levels
(Janmey, 1994). Despite buffering resting neutrophil [Ca^+fi with calcium
chelators (e.g., EGTA, quin-2, BAPTA), the cells are still capable of
migrating at normal rates (Elferink & Deierkauf, 1985; Meshulam et al.,
1986; Zigmond et al., 1988). The fMLP-induced rise in [Ca^+] involves
both the release of calcium from intracellular stores (via IP3) and influx
across the membrane. The use of fluorescent calcium indicators (quin2 or
fura2) reveals the "biphasic" nature of this fMLP-induced increase (Lew et
al., 1984; Lew et al., 1986; Anderson et al., 1986). The prolonged second
phase is eliminated by removal of extracellular calcium, while the rapid
first phase remains unaffected. The rapid doubling of F-actin in response
to fMet-Leu-Phe stimulation is temporally associated with the initial rise in
[Ca2+]¡ caused by IP3 (Snyderman & Uhing, 1992). Preventing the fMet-
Leu-Phe-induced rise in calcium with calcium chelators has no effect on
the neutrophil's ability to double its F-actin content within 15-30 seconds
(Sha'afi et al., 1986; Downey et al., 1990; Sham et al., 1993). Neutrophil
migration is a complex process that involves the continuous cycling of
polymerization and depolymerization. It is possible that the repetitive
increases in intracellular calcium in migrating PMN (Marks & Maxfield,
1990; Jaconi et al., 1990) may actually enhance depolymerization of actin
filaments by activating the severing activity of proteins like gelsolin
(Downey et al., 1990).
With increasing evidence suggesting neither calcium nor protein
kinase C activation were necessary for the chemoattractant-induced actin
polymerization seen in PMN, the signaling role of phosphoinositides was
actively investigated. It has been known for over 30 years that

30
phosphoinositide phospholipids such as PIP2 can form complexes with
certain proteins (Janmey, 1994). Since phosphoinositide turnover via
phospholipase C hydrolysis of PIP2 is one of the major intracellular events
occurring proximal to either the increase in calcium or activation of
protein kinase C in activated PMN, the proposal that phosphoinositides
might regulate actin assembly seems plausible (Lassing & Lindberg, 1985;
Stossel, 1993). With the finding that phosphoinositides modulate the in
vitro interaction of profilin with actin, Lassing and Lindberg proposed
phosphoinositides may regulate actin assembly in cells. They were able to
demonstrate that actin sequestered by profilin can be dissociated by PIP2,
thus leading to actin polymerization (Lassing & Lindberg, 1985). Since
that time, numerous other actin-binding proteins have been shown to
interact with phosphoinositides (Isenberg, 1991; Janmey, 1994).
Interestingly, the interaction of barbed-end capping proteins with actin is
also specifically inhibited in the presence of polyphosphoinositide
phospholipids (Janmey, 1994).
Stossel has recently proposed a model that integrates motile signal
transduction events with the modulation of actin binding proteins in
attempts to explain how animal cells are able to crawl in response to a
stimulus (Stossel, 1993). The motile behavior of certain animal cells is
partly explained by the rapid polymerization of actin. In this model, a
motile stimulus results in the rapid turnover of intracellular
phosphoinositides. This in turn causes release of sequestered monomers
of actin, and prevention of barbed-end cap formation. The net result
would be a rapid polymerization of monomeric actin onto the barbed-ends
of actin filaments.

31
Utilizing fluorescent actin probes, it can be demonstrated that
fibroblasts undergo actin filament assembly and disassembly. The
lamellipodium of a cultured fibroblasts includes a dense network of actin
filaments (Wang, 1985). Fluorescence photobleaching of a discrete region
within the lamellipodium demonstrates centripetal movement and
eventual disappearance at the proximal edge of the actin band, a process
not unlike treadmilling. Their finding suggests actin filaments within the
lamellipodium are undergoing net assembly at their distal, membrane-
directed barbed ends and net disassembly at their proximal pointed ends
(Wang, 1985). Electron micrographs of neutrophils whose actin filaments
are decorated with heavy meromyosin reveal the barbed ends of actin
filaments are directed peripherally towards the membrane (Pryzwansky et
al., 1983). In addition, when PMN are stimulated with fMet-Leu-Phe, the
number of nucleation sites for actin polymerization is increased
transiently (Carson et al., 1986). These nucleation sites are sensitive to
cytochalasin, a drug whose actin inhibitory activity is partly explained by
its ability to cap the barbed-end of filaments, and they sediment with the
detergent insoluble actin cytoskeleton (Carson et al., 1986). These
findings suggests that neutrophils rapidly increase their F-actin content by
increasing the number of free barbed-ends upon chemotactic stimulation.
Calcium Independent Model For Polymerization
The two mammalian cell types which undergo a rapid (< 30 sec.)
doubling of actin in response to stimulation are phagocytes (neutrophils
and macrophages) and platelets. Profilin and thymosin 84 have both been
purified in these cell types. The only capping proteins that have been

32
purified from phagocytes are members of the calcium-dependent/gelsolin
capping-protein family. CapZ was recently noted in platelets (see
"Capping Proteins")
A simple model integrating what is currently known about
neutrophils and other motile cells is suggested by Stossel (1993). At rest,
a majority of the actin filaments are capped at their membrane-proximal
barbed-ends. This leads to a critical concentration of free actin monomers
close to the dissociation constant of the freely-exchanging minus-end (~1.0
pM). As discussed earlier, the concentrations of monomer sequestering
proteins (profilin and thymosin IL4) and their affinities for actin
monomers (Kd ~0.5 - 5 pM) can explain the high amounts of
unpolymerized actin in resting neutrophils (> 60 %). Stimulation of
neutrophils with chemotactic peptide causes an increased
phosphoinositide turnover (Snyderman & Uhing, 1992; Janmey, 1994).
Based on the findings that profilin and the barbed-end capping proteins
bind the phosphoinositides PIP and PIP2 thereby inhibiting their ability to
bind to actin, it is thought that phosphoinositides mediate the signal
transduction between the surface receptors and actin assembly (Stossel,
1993). In this model it is explained that phosphoinositides cause the
uncapping of membrane-proximal barbed-ends, thus lowering the critical
concentration of actin monomers in that region closer to that of the
barbed-end (0.1 - 0.3 pM). Since the critical concentration of free actin
monomers is lowered, a majority of the sequestered actin can be released
into the polymerizable pool (see "Monomer Sequestering Proteins").
Stimulation of neutrophils may activate profilin's ability to increase the
nucleotide exchange rate of actin molecules, thus ensuring a continuous
supply of ATP-actin available for rapid polymerization (Goldschmidt-

Figure 1-4. Regulation of actin assembly in PMN. This simple model attempts to explain the rapid
assembly of actin in fMet-Leu-Phe stimulated PMN.

Rest
+
|CAP
DOCOOCÓ
ED
ED
\
O
ED
ED
BO
ED
fMLP < 30 sec
(^Phosphoinositide Turnover)
Gelsolin/Ca2+
Ú.
ccccccco
t
[El o o o
\T\
E
ADP
X)
1
SO
o
ATP

35
Clermont et al., 1991). The role of profilin in activated PMN remains
controversial since the PIP2 effect would theoretically prevent ATP/ADP
exchange.
There have been no reports of calcium-independent capping
proteins in neutrophils or macrophages. Two abstracts were recently
presented at the ASCB (American Society for Cell Biology) meeting
December, 1994 noting the presence of capZ in platelets (Barkalow &
Hartwig, 1994; Nachmias et al., 1994). These three cells are the
mammalian model cells for understanding the signal transduction
mechanisms leading to rapid actin assembly. As discussed above, the
rapid polymerization response in neutrophils can occur independently of
calcium. It is upon these premises that we have further investigated the
calcium insensitive activity of PMN Actin Polymerization Inhibitor, an
activity originally purified by my mentor Dr. Southwick.
PMN Actin Polymerization Inhibitor
A Major Calcium-Independent Activity In PMN Extracts
Approximately 15 years ago, Southwick and Stossel isolated an actin
binding activity from human neutrophils thought to account for much of
the unpolymerized actin in granulocyte extracts (Southwick & Stossel,
1981). This activity, PMN actin polymerization inhibitor, was shown to
decrease the viscosity of purified skeletal-muscle actin under polymerizing
conditions in the presence of 1 mM EGTA and absence of added calcium.
Substoichiometric concentrations of the inhibitor were still able to
decrease the viscosity of purified actin allowed to polymerize in the
presence of 0.1 M KC1. PMN Actin Polymerization Inhibitor was purified

36
from granulocyte extracts by DEAE-ion exchange chromatography and gel-
filtration chromatography. The viscosity lowering activity of the column
fractions was monitored using a Cannon-Manning semi-microviscometer.
The purified inhibitor was noted to contain polypeptides of 65,000 and
62,000 daltons by SDS-PAGE. The Stokes radius of the inhibitor was
reportedly 32 Á and the S20,w was 4.8. These data were felt to be
compatible with the inhibitor being a globular monomer with a native
molecular weight similar to that of the 65,000 and 62,000-dalton peptides
resolved by SDS-Page. Increasing KC1 concentrations from 0.1 - 0.6 M KC1
reversed the inhibition.
All activity studies were done in the absence of added calcium and
presence of 1 mM EGTA to avoid the potential contaminating activity of
the calcium dependent protein gelsolin. The PMN actin polymerization
inhibitor is hence a major calcium-independent actin filament regulatory
protein. The recent findings that the PMN actin polymerization-burst in
response to fMet-Leu-Phe occurs independently of calcium has prompted
my further examination of this inhibitor's actin regulatory role.

CHAPTER 2
MATERIALS AND METHODS
Isolation Of Human Polymorphonuclear Leukocytes (PMN)
Fresh leukocyte enriched fractions from the whole blood of healthy
donors were obtained from the community blood bank. For each
preparation, 15-45 buffy coat units were used. Further isolation of
leukocytes was accomplished using a variation of the technique described
by Southwick and Stossel (1981). Briefly, leukocyte enriched fractions
were pooled and sedimented through Dextran T-500 (Pharmacia Biotech
Inc., Piscataway, NJ). This procedure yielded on average 85 % PMN the
remainder of the cells representing lymphocytes (12 96) and monocytes (3
%). In some cases this procedure was followed by Ficoll-sodium diatrizoate
sedimentation. This procedure increased the purity of PMN to 95 %. CapZ
obtained from granulocytes isolated with or without a Ficoll-sodium
diatrizoate sedimentation resulted in purified protein with identical actin
binding activity. Higher yields of PMN capZ were achieved using dextran
alone.
Purification Of CapZ From Human PMN
All steps were done at 4 °C whenever feasible. The initial
procedures used were nearly identical to those described previously
37

38
(Southwick & Stossel, 1981). Briefly, cells were cooled to 4 °C and washed
twice in normal saline, treated with 5 mM diisopropylfluorophosphate
(DFP) for 15 min and then resuspended in 3 volumes of a solution
containing 5 mM dithiothreitol (DTT), 2 mM ATP, 20 mM EGTA, 20 mM
imidazole-HCL, pH 7.5, 1 mM phenylmethylsulfonyl fluoride (PMSF), 1
g/100 ml leupeptin, 4 g/100 ml aprotonin, and 7.8 g/100 ml benzamidine
(homogenization solution). Cells were broken by nitrogen cavitation at
900 psi. This procedure ruptured greater than 95 % of all cells, as
monitored by phase microscopy. The homogenates were centrifuged at
12,100 Xg for 60 min. The supernatant was dialyzed against 500
volumes of S2 buffer (10 mM Imidazole pH 7.8, 5 mM DTT, 1 mM MgCl2,
1 mM ATP, 1 mM EGTA) for 3 hrs, then diluted 1:1 with S2 buffer and
applied to a 1.5 cm X 16.5 cm DEAE-Sepharose CL-6B anion exchange
column (Pharmacia Biotech Inc. Piscataway, NJ) equilibrated with 120-200
ml of S2 buffer. After application of the supernatant, the column was
washed with 60 ml of 0.08 M KC1 in S2 buffer, followed by 250 ml linear,
0.08-0.4 M KC1, gradient in S2 buffer. Eluted fractions were analyzed by
coomassie blue stained SDS-PAGE and by falling ball microviscometry
(MacLean-Fletcher & Pollard, 1980). Fractions that lowered the viscosity
of F-actin under low Ca^+ conditions were pooled and concentrated to a
volume of 0.5-3.0 ml (< 10 mg/ml) in a nitrogen pressure concentrator
using an Amicon PM-30 ultrafiltration membrane (Amicon Corp.,
Lexington, Mass.). The concentrated sample was then subjected to gel
filtration using a protein-pak 125 (Waters Associates, Milford, MA) column
equilibrated, and eluted with 0.1 M KC1 in S2 buffer. Several precautions
were taken to limit activation of the abundant proteases present in PMN.
Isolation of PMN was performed using plastic to avoid generalized

39
activation by adherence to glass, Purified PMN were treated with the
potent neutral serine protease inhibitor DFP, cells were homogenized in
the presence of EGTA and a protease inhibitor cocktail, and efforts were
made to maintain the purification at 4 °C. As originally reported
(Southwick & Stossel, 1981), the PMN viscosity lowering activity at this
stage copurified with two polypeptides in the 60 - 68 kDa range.
In efforts to further purify this activity, three additional columns
were utilized in the following order; High S (Bio-Rad Laboratories, Inc.,
Hercules, CA), Mono Q.(Pharmacia Biotech Inc., Piscataway, NJ), and
HTP/hydroxylapatite (Bio-Rad Laboratories, Inc., Hercules, CA). To
minimize protein loss during screening activity of these additional
columns, the Band 4.1 capping assay was substituted for the falling-ball
microviscometry assay (see "Actin Binding Studies" below). For the High
S cation exchange chromatography, active fractions were pooled and
dialyzed against a buffer containing 8 mM MES pH 6.0, ImM sodium azide,
and 0.1 mM PMSF (buffer S). The dialyzed fractions were then applied to
a 5 ml Econo-Pac High S cation exchange column which had been
equilibrated with buffer S. The column was washed with 5 ml of buffer S,
followed by a 30 ml (1 ml/min) linear salt gradient to 0.150 M KC1 in
buffer S. Active fractions from the High S column were pooled then
dialyzed against S2 buffer. After preclearing the fractions by
centrifugation at 10,000 X g for 5 minutes, they were applied to a Mono Q.
HR 5/5 anion exchange column equilibrated with S2 buffer. The column
was then washed with 5 ml (1 ml/min) of 0.1 M KC1 in S2 buffer, and
followed by a 12 ml linear gradient, 0.1 - 0.3 M KC1, gradient in S2 buffer.
Similar to the purification step described by Casella et al. (1986), our final
step entailed pooling and dialyzing Mono Q.active fractions against a 10

40
mM potassium phosphate buffer pH 7.0 containing 0.1 mM DTT. This
sample was then applied to a 1 ml hydroxylapatite (Econo-Pac HTP)
column equilibrated with the same buffer, and eluted with a linear
gradient to 75 mM potassium phosphate pH 7.0, and 0.1 mM DTT. Active
fractions were quantified using the Quantigold assay (Diversified Biotech)
and then stored at -20 °C in 30 % ethylene glycol (under these storage
conditions the specific activity of the protein remained stable for >3
months).
Purification Of Muscle Actin
Actin was purified from rabbit skeletal-muscle by the method of
Spudich and Watt (1971). Monomeric actin was gel filtered through a
Superdex 200 16/60 (Pharmacia Biotech Inc., Piscataway, NJ) column for
polymerization kinetic studies. Pyrenylactin was prepared according to
Kouyama and Mihashi (1981) with the modifications described previously
(Young et al., 1990). Actin concentrations were calculated using the
extinction coefficient of 24.9 mM"' cm'l at 290 nm with the correction for
pyrenyl absorption according to Selden and colleagues (1983).
Amino Acid Sequence Analysis
Peptides were electroblotted from SDS-polyacrylamide gels onto
polyvinylidene difluoride (PVDF) membranes using a transfer buffer
containing 12.5 mM Tris, 96 mM glycine, 10 % ethanol, pH 8.3 as
previously described (Mozdzanowski et al., 1992). The samples were
blotted, stained, and sent to our collaborator Dr. David W. Speicher at The

41
Wistar Institute Philadelphia, PA for amino acid sequence analysis.
Coomassie blue stained bands were excised and sequenced on an Applied
Biosystems model 475A sequencer using gas phase TFA delivery and an
on-line model 120A PTH analyzer with modifications as previously
described (Reim et al., 1992). Acetonitrile and tetrahydrofuran were from
J. T. Baker. All other sequencer solvents and reagents were from Applied
Biosystems.
Polyacrylamide Gel Electrophoresis And Western Blot Analysis
SDS-PAGE
Protein samples were subjected to electrophoresis on 10 %
discontinuous pH mini (Bio-Rad Laboratories, Inc., Hercules,
CA) or mid-sized (Hoefer Scientific Instruments, San Francisco, CA) SDS-
PAGE. Molecular weights (Mr) of proteins of interest were determined by
simultaneous electrophoresis of other polypeptides of known molecular
weights, and plotting their relative mobility verses log Mr- Proteins were
visualized by staining the gels with Coomassie brilliant blue R-250 or
Silver (Silver stain plus kit, Bio-Rad Laboratories, Inc., Hercules, CA).
Immunoblotting
The electrophoresed proteins were then transferred to nitrocellulose
paper (graphite electroblotter, Millipore) using standard protocols
(Towbin et al., 1979). The transferred blots were subjected to a blocking
step in 3 - 5 % non-fat dry milk in phosphate-buffered saline (PBS) and 0.3
% tween-20 for at least three hours. The primary antibodies were diluted
appropriately in the blocking solution (anti human annexin VI at 1:4000

42
(monoclonal) & 1:7500 (polyclonal), anti human L-plastin at 1:500, anti
chicken capZ alpha and beta 1:300) and incubated with the blot for 1 hour
at room temperature. After subsequent washes with PBS-tween, the blots
were incubated with the appropriate alkaline phosphatase-conjugated
secondary antibody for 40 - 60 minutes. The detection was in an alkaline
phosphatase buffer (0.1 M Tris, 5 mM MgCl2, 0.1 M NaCl) containing 30
pg/ml nitro blue tetrazolium (Sigma Chemical Company, Saint Louis, MO)
and 20 pg/ml BCIP (5-bromo-4-chloro-3-indolyl phosphate, Sigma).
The annexin VI concentration in neutrophil extracts was determined
using a method similar to that described by Dabiri et al. (1992). The
immuno-reactivities of the polypeptides in neutrophil extracts were
compared to known concentrations of purified annexin VI using a
scanning laser densitometer (Zeineh Model SLR-2D/1D, Biomed
Instruments, Inc.). A linear standard curve could be generated relating
densitometry integration units to protein concentration.
Nondenaturing Polyacrylamide Gel Electrophoresis
Neutrophil actin polymerization inhibitor containing predominantly
annexin VI and L-plastin were subjected to 7.5 % nondenaturing
polyacrylamide gel electrophoresis (mid-sized gel, Hoefer Scientific
Instruments, San Francisco, CA) according to the method of Safer (1989).
Samples were added 1:1 (volume:volume) with 10 % glycerol in the
running buffer with <1 mg of bromophenol blue (tracking dye). A
heterogeneous population of monomers, dimers, and trimers of bovine
serum albumin (BSA) are formed when placed in solution, and therefore
15 pg of BSA (fraction V, Sigma Chemical Company, Saint Louis, MO; 1

43
mg/ml in water) was run simultaneously to the proteins of interest as
evidence of nondenaturing resolution of proteins.
Actin Binding Studies
Pyrene actin was used for all kinetic studies. Fluorescence intensity
was monitored using a Perkin-Elmer LS-5 fluorescence spectrophotometer
with excitation and emission wavelengths of 364 nm and 407 nm
respectively.
Denolvmerization Assay
Pyrene labeled actin (2 pM) was allowed to polymerize to steady
state in the presence of 1 mM EGTA or 1 mM calcium. The F-actin was
then diluted to 50 nM into a buffer containing 10 mM Imidazole pH 7.5,
0.5 mM ATP, 0.1 M KC1, 1 mM MgCl2, 1 mM DTT (Buffer P) in the presence
of varying concentrations of capZ (Southwick & DiNubile, 1986). The
reaction was observed for 30 min at 25 °C.
Actin-Spectrin Nuclei Elongation Assay
Red blood cell derived spectrin/band 4.1/actin nuclei (rbc nuclei)
were isolated according to the methods of Casella et al. (1986). Pyrene-
labeled G-actin (0.55 pM) was added to a mixture of 1.25 pg/ml of rbc
nuclei, varying concentrations of capZ and buffer P containing 1 mM
EGTA. In the absence of rbc nuclei, this concentration of pyrene actin
(0.55 pM) failed to spontaneously polymerize during the time course of
our experiments (15 min). The capZ and rbc nuclei were allowed to
incubate for 2 min prior to the addition of the pyrene actin.

44
Steady-State Assay
Pyrene-labeled actin in buffer P with 1 mM EGTA was allowed to
polymerize at room temperature for 18 hours (steady-state), and the
critical concentration was determined by plotting the total actin
concentration verses the steady-state fluorescence (correcting for
fluorescence values at t = 0). The effects of various concentrations
(substoichiometric relative to actin) of capZ on the steady-state
fluorescence of pyrene actin (0.9 pM or 3 pM) was measured. The steady-
state G-actin concentration (apparent critical concentration) of the
solutions was calculated from the decrease in steady-state fluorescence
relative to pyrene actin controls. The fluorescent signal of pyrene actin is
proportional to polymer weight concentration (Cooper et al., 1983).
Nucleation Assay
For this assay, 1.5 pM pyrene labeled G-actin was allowed to
polymerize in buffer P in the presence of varying concentrations of capZ.
The effects of capZ on this polymerization rate were assessed by
fluorimetry (Southwick & DiNubile, 1986).
Severing Assay
Gelsolin (0.01 pM) and pyrene actin (2 pM) were copolymerized
(molar ratio 1:200) to steady-state, forming barbed-end capped filaments
(Casella et al., 1986). These filaments were then diluted to 100 nM in
buffer P containing 1 mM calcium and varying concentrations of capZ.

45
Monomer Sequestration Assay
Gelsolin and non-pyrene labeled actin were copolymerized at high
molar ratios (1:16) in buffer P forming nuclei for pointed end
polymerization. Pyrene labeled G-actin (final of 0.8 pM) was added to
buffer P containing gelsolin/actin nuclei (15 nM/0.24 pM) and varying
concentrations of capZ (Young et al., 1990). This assay was repeated in
the presence of G-actin that was 50 % labeled to examine the possibility
that capZ binds pyrenylactin with lower affinity. These reactions were
performed in the presence of either 1 mM EGTA or 0.5 mM calcium.
Falling Ball Microviscometrv
The falling ball assay of MacLean-Fletcher and Pollard (1980) was
used to follow the relative activities of individual elution fractions at
various stages during the purification of neutrophil capZ. Rabbit skeletal
muscle actin (final concentration of 10 pM) was polymerized in the
presence of sample. After 2 hours at room temperature, the solutions
were drawn into glass capillary tubes. Relative viscosities are reflected by
the speed of steel balls traversing the tube (angled at 15°).
Lipid-Binding And Capping-Inhibition Studies
Phosphatidylcholine (PC), phosphatidylinositol (PI),
Phosphatidylserine (PS) were purchased from Sigma (St. Louis, MO) and
used without further purification. Phosphatidylinositol 4,5-bisphosphate
(PIP2) was obtained from Calbiochem.

46
Annexin VI Binding To Multilamellar Vesicles
For the annexin VI lipid binding studies PC and PS were treated as
previously described by Blackwood, et al. (1990). Partially purified
neutrophil annexin VI was incubated at 25 °C for 15 minutes with either PS
or PC in buffer P containing 0.2 mM EGTA and varying concentrations of
calcium. Each mixture was then centrifuged at 12,000 X g in a table top
microfuge for 15 min at 25 °C. Supernatants and pellets were subjected to
SDS-PAGE and stained with Coomassie brilliant blue. The relative amounts
of annexin VI in the pellets and supernatants were determined by laser
densitometry.
Phospholipid Column
A 3.5 ml sepharose-4B phospholipid column composed of PS/PC/PE
(2:2:1) was built in attempts to separate annexin VI and L-plastin, the two
predominant proteins copurified with the PMN actin polymerization
inhibitor after gel-filtration chromatography. The phospholipid column,
which exploits the ability of annexin proteins to bind acidic phospholipids,
was constructed according to the methods of Meers and colleagues (1987).
Modulation Of Capping Activity Bv Phosphoinositides
The ability of various lipids to block capZ filament end capping was
also examined. The phospholipids PIP2, PI, PC and PS were treated as
previously described (Janmey & Stossel, 1989). The modulation of capZ
actin binding function was assessed using the depolymerization assay (see
above). CapZ (36 nM final concentration) was first added to
polymerization buffer, followed by the addition of phospholipids from
previously sonicated stock solutions and resonicated in a water bath

47
sonicator at room temperature for 15 sec. After 1 min to allow the lipid-
capZ mixture to equilibrate, pyrene labeled F-actin was added (25 pi of 2
pM F-actin to a final volume of 1 ml). The inhibition of capZ capping was
assessed by measuring the initial slopes of depolymerization in the
presence of varying amounts of PIP2-
Promyelocyte Differentiation Studies
RNA Isolation And Northern Blots
Total RNA was extracted by a guanidinium thiocyanate (G1TC)
method (Chomczynski & Sacchi, 1987). The cells of interest were lysed in
a GITC buffer (4 M guanidinium isothiocyanate, 25 mM sodium acetate, pH
7.0, 0.5 % sarcosyl, and 0.1 M R-mercaptoethanol) with vigorous pipetting
and vortexing. Two milliliters (2 ml) of GITC buffer was added to 0.5- 1.0
X 107 cells. The following was sequentially added to the extract with
thorough mixing by inversion in between: 0.07 volume 3 M sodium
acetate pH 5.2, 1 volume cold water-saturated phenol, and 0.2 volume of
chloroform/ alcohol (49:1). The mixture was shaken vigorously for 10 sec
and kept on ice for 15 in and centrifuged in a Beckman JA-20 rotor at
10,000 X g for 20 min. The aqueous phase was carefully removed and
precipitated with 1:1 volume of cold for 1 hour to overnight at -20 °C.
After another 10,000 X g spin, the RNA pellet was resuspended in 300 pi of
GITC buffer and precipitated another time with 2.5 volumes of cold 95 %
ethanol at -20 °C. The final pellet was washed with 70 % ethanol, dried
and resuspended in 0.5 % SDS in diethylpyrocarbonate (DEPC) treated
water. To eliminate any contaminating proteins and to remove the SDS,
the samples were heated at 65 °C for 15 min, kept on ice for 15 min (to

48
precipitate the SDS), and microfuged for 5 min. The clear supernatant was
transferred into a clean tube and the concentration and purity of the
sample was analyzed by a spectrophotometer.
The RNA samples were prepared for electrophoresis as follows. The
RNA (10 pg/sample) was completely lyophilized and resuspended in 10 pi
of a sample mix containing 250 pi deionized formamide, 90 pi 37 %
formaldehyde, 26 pi 10 X MOPS (3-[N-morpholino]propanesulfonic acid)
buffer (1 X MOPS buffer = 0.2 M MOPS, 0.05 M sodium acetate, 0.01 M
Na2EDTA, pH 7.0), 10 pi of ethidium bromide (10 mg/ml stock solution)
and 30 pi of loading dye. The samples were heated at 67 °C for 15 min,
cooled on ice and were electrophoresed in 1.2 % agarose gels with 2.2 M
formaldehyde in 1 X MOPS buffer. The gel was transferred to
nitrocellulose membrane in 20 X SSC (IX SSC = 0.15 M NaCl and 0.015 M
sodium citrate) by standard capillary blotting. The blots were hybridized
with random-primed probes (1 X 10^ cpm/ml) at 42 °C in 5 X Denhardt's
solution, 5 X SSPE (IX SSPE = 0.15 M NaCl, 0.01 M NaH2P04'H20, and
0.001 M EDTA), 50 % formamide (Fluka), 0.1 % SDS, and 150 pg/ml
salmon sperm DNA. After a room temperature rinse in 2 X SSC, 0.1 % SDS,
the filter was washed at 65 °C in 2 X SSC, 0.1 % SDS for 30 min followed by
a brief wash in 0.2 X SSC, 0.1 % SDS until the background was low by a
Geiger counter survey.
Generation Of Annexin VI cDNA Probe
Total RNA was isolated from human neutrophils as described above.
Using the published cDNA sequence for human annexin VI, upstream and
downstream oligonucleotide (25 base-pairs each) primers were
synthesized (I.C.B.R. DNA synthesis laboratory, University of Florida). The

49
Perkin-Elmer Cetus R.T.-P.C.R. kit was utilized to generate a 1057 base-pair
(bp) annexin VI DNA fragment from neutrophil total RNA via a reverse
transcription reaction immediately followed by initiation of the
polymerase chain reaction (Perkin-Elmer Cetus DNA Thermal Cycler model
480). The ends of the 1057 bp DNA fragment were blunt-ended with the
Klenow fragment of DNA polymerase, and ligated into the E. coli vector
pBluescript II SK + (Stratagene Cloning Systems, Lajolla, CA) at the Sma I
polylinker site. The 1057 bp, subcloned, annexin Vl-cDNA-fragment (bp #
32 - 1088) was verified by sequencing (I.C.B.R. DNA sequencing facility,
University of Florida).
Cell Culture And Induction Of Differentiation
The human promyeloblast leukemic cell line HL-60 (Gallagher et al.,
1979) was obtained from ATCC (American Type Culture Collection,
Rockville, MD) and maintained in RPM1 1640 medium supplemented with
10 % iron-supplemented calf serum (Gibco BRL, Gaithersburg, MD) and 2
mM glutamine. This cell line can be induced to differentiate towards the
neutrophil lineage or macrophage lineage depending upon the
pharmacologic exposure (Collins, 1987). Differentiation of HL-60 cells was
induced according to the methods previously described by Dabiri et al.
(1992) Briefly, exponentially growing HL-60 cells (> 1 X 10® cells/ml)
were plated at 0.5 X 10® cells/ml and treated at time zero with the
appropriate pharmacologic agents. For macrophage differentiation, HL-60
cells were treated with phorbal 12-myristate-13 acetate (PMA, Sigma) at 10
nM (6.2 ng/ml), and for granulocyte differentiation the HL-60 cells were
treated with 1.5 % dimethyl sulfoxide (DMSO, Sigma Chemical Company,
Saint Louis, MO). At appropriate time points after differentiation, RNA or

50
cellular protein was isolated and analyzed by Northern or Western blots as
described earlier. For Western studies, the total protein concentrations
were calculated on the last day of the experiment using the same standard
curve. Samples from earlier time points were rapidly collected (saving an
aliquot for determination of protein concentration), placed in gel sample
buffer, and stored at -70° C until the final sample was processed.
Fluorescence Microscopy
Human neutrophils and monocytes were isolated from peripheral
blood by sedimentation through PolymorphprepTM, a sodium-metrizoate,
dextran 500 solution (Nycomed Pharma As, distributed by Gibco BRL,
Gaithersburg, MD). The cells were resuspended in Hank's balanced salt
solution (Gibco BRL, Gaithersburg, MD), and allowed to adhere to glass
coverslips for 15 - 20 min in a 37 °C C02 incubator. The adherent cells
were treated for immunofluorescence by fixation for 20 min at room
temperature in 3 % formaldehyde (prepared from paraformaldehyde)
made in standard salt (0.1 M KC1, 0.01 M KPO4 buffer, 0.001 M MgCl2, pH
7.0), permeabilization in 0.1 % Triton-X 100 in standard salt, 5 min
overlay with 50 mM ammonium chloride in standard salt, and rinses with
standard salt between steps (Sanger et al., 1980). The following reactions
were carried out in a moist chamber in a 37 °C CO2 incubator, the cells
were then blocked with 10 % goat serum in standard salt for 30 min,
followed by 45 min incubation with monoclonal antibodies (0.01 pg/pl
anti-human annexin VI, control antibodies were a kind gift from Maurice
Swanson, Univ. of Fla., College of Medicine: anti-human hnRNP-M protein
& anti-yeast polyadenylated RNA-binding protein, Nab-1) (Datar et al.,

51
1993; Wilson et al., 1994) and used at concentrations greater than the
anti-annexin VI as determined by immunoblots of the antibodies run on
SDS-PAGE, rinses in standard salt, incubation with fluorescein
isothiocyanate (FITC)-conjugated goat anti-mouse IgGl (heavy chain
specific; Fisher Scientific, Pittsburgh, PA) for 30 min, followed with rinses
in standard salt. The coverslips were mounted in glycerol containing an
antioxidant to prevent fluorescence quenching (90 % glycerol, 10 % 0.25
M Tris pH 8.0, 2.3 % 1,4 l,4-diazabicyclo-[2.2.2] octane obtained from
Sigma). The cells were observed and photographed using a Nikon Diaphot
inverted microscope (Nikon, Tokyo, Japan) set up for epifluorescence.
Photographs were taken through the camera port using Tri-X Pan film
(Kodak). The film exposure lengths and print development times were
kept identical to photographs of PMN stained with anti-annexin VI.
Confocal microscopy was conducted with the assistance of Michael Paddy
(l.C.B.R. Confocal microscopy facility, University of Florida).
Approximately 30 images 1 pm thick were taken with a z-increment of 0.3
pm. Digitized images were obtained using Dr. Paddy's microscope and
processed with an Image-1 video image analyzer (Universal Imaging Corp.,
West Chester, PA), and finally stored on a Panasonic laser disk recorder.

CHAPTER 3
PURIFICATION AND IDENTIFICATION OF CAPZ AS THE PMN ACTIN
POLYMERIZATION INHIBITOR
Introduction
The viscosity lowering activity of PMN actin polymerization
inhibitor, as originally published, was thought to be composed of two
related polypeptides of 62,000 and 65,000 daltons (Southwick & Stossel,
1981). The polypeptides purified with this activity, although, were not
identified. This chapter outlines the efforts to identify the PMN inhibitor,
and my eventual discovery that the ~65 kDa, heterodimeric-protein capZ
is solely responsible for the actin viscosity-lowering activity.
Results
Identification Of The Two Major Polypeptides (~ 66 And 68 kDa)
Copurified With The Neutrophil Actin Polymerization Inhibitor
The calcium independent activity called human neutrophil actin
polymerization inhibitor was purified using ion exchange chromatography
and gel filtration (see methods) (Figure 3-1, lane 2). Yields and purity
were identical to the previously reported purifications (Southwick &
Stossel, 1981). The two polypeptides copurified with the inhibitor were
noted to have Mr of 66,000 and 68,000 when fractionated through a
discontinuous pH, 10 % SDS-PAGE. Similar to previous reports, highly
52

Figure 3-1. PMN actin polymerization inhibitor. The PMN inhibitor
purified by DEAE-anion exchange and gel-filtration chromatography. Lane
2 represents the PMN inhibitor subjected to 10 % SDS-PAGE with standards
(lane 1; Mr = X 103) and stained with Coomassie blue. Fractions were
subjected to Western analysis and probed with antibodies to annexin VI
(lane 3) or L-plastin (lane 4).

54
4

55
purified fractions (> 90 % composed of the 66 and 68 kDa polypeptides as
assessed by densitometry scanning of Coomassie blue stained SDS-PAGE)
lowered the viscosity of actin filament solutions as measured by falling-
ball microviscometry. The minor proteins, if present, (usually < 10 %)
were composed of a 42 kDa polypeptide believed to be actin (rabbit
skeletal muscle actin comigrates with this band) and a 55 kDa polypeptide
later found to be an L-plastin degradation product (see below). Active
fractions, composed predominantly of the 66 and 68 kDa polypeptides,
were separated on SDS-PAGE, transferred onto polyvinylidene difluoride
(PVDF), stained and sent to our collaborator Dr. David W. Speicher (The
Wistar Institute, Philadelphia, PA) for amino-acid sequence analysis. The
original analysis performed after BNPS-Skatole digestion (the amino-
termini of the polypeptides were blocked) resulted in sequence
information solely from the 68 kDa polypeptide. As shown in Figure 3-2A,
two fragments from the 68 kDa polypeptide yielded sequences of 18 and
23 amino acids which were identical to amino acids 193 - 210 and 344 -
366 respectively of human annexin VI (Crompton et al., 1988; Sudhof et
al., 1988). Immunoblots probed with a monoclonal antibody to human
placental annexin VI (Zymed Laboratories, Inc., South San Francisco, CA)
only revealed the 68 kDa polypeptide (Figure 3-1, lane 3). Polyclonal
antibodies to human annexin VI (rabbit antisera was a kind gift from Dr.
Joel D. Ernst, University of California, San Francisco) detected the 68 kDa
annexin VI, but also failed to recognize the 66 kDa polypeptide (data not
shown).
Amino acid sequence analysis of the 66 and 68 kDa polypeptides
containing neutrophil activity was repeated. Samples were prepared as
described above, and sent to The Wistar Institute (Protein

Figure 3-2. Amino-terminal sequence analysis of PMN actin
polymerization inhibitor. Since the amino termini were blocked,
microsequence analysis was performed on the predominant cleavage
products of the upper peptide (Skatole) or lower peptide (Trypsin)
component. The 68 kDa upper band is identical to annexin VI and the 66
kDa peptide is identical to L-plastin.

57
A. UPPER BAND (SKATOLE cleavage)
human Anx VI
pep 1
GELKWGTDEAQFIYILGNRSKQH
GTDEAQFIYILGNRSKQF
• 213
LRL
human Anx VI
pep 2
ayqm w
369
ELSAVARVELKGTVRPANDFNPDADA
ELSAVARVELKGTVRPANDFNPD
B. LOWER BAND (TRYPSIN cleavage)
human L-Plastin
pep 1
62
SEEEK
YAFVNWINK
VAFVNWINK
79
ALEN
human L-Plastin
pep 2
512
GGQKVNDDIIVNWVNETLR
/NDDIIVNWVNETLR
534
EAEK

58
Microsequencing Facility). For this analysis, the two polypeptide bands
were digested with trypsin. Comparative HPLC peptide maps (post-trypsin
digestion) with a trypsin control demonstrated that almost all major peaks
in the 68 kDa sample were different from those generated from the 66 kDa
sample. The masses of the major trypsin cleavage peptides were
determined by MALD1 mass spectrometry. Most major peak masses from
the 68 kDa sample agreed with expected masses of limit tryptic peptides of
annexin VI. In contrast, only a few major peaks in the 66 kDa sample
could possibly fit with annexin peptides. Two of the major peptides
generated by trypsin digestion of the 66 kDa band were sequenced, and
revealed a perfect match with the protein L-plastin. As shown in Figure 3-
2B, N-terminal sequence analysis of these two major peptides yielded
sequences of 9 and 15 amino acids which were identical to amino acids 67
- 75 and 516 - 530 respectively of human L-plastln (Lin et al., 1988). To
further confirm the identity of the 66 kDa polypeptide western blot
analysis was performed using a mouse monoclonal anti-human L-plastin (a
kind gift from Dr. Yuziro Namba, Kyoto University, Japan). As shown in
Figure 3-1 (lane 4), the antibody specifically cross-reacts with the lower,
66 kDa polypeptide. The antibody also cross-reacts with a polypeptide
with approximate Mr of 55,000. This band is felt to be a degradation
product of the neutrophil L-plastin, as it is absent in fresh PMN extract and
increases with storage of the PMN inhibitor fractions (data not shown). A
similar molecular weight L-plastin degradation product has been
previously reported (Pacaud & Derancourt, 1993).

59
Separation Of Annexin VI From L-Plastin
The following experiments were conducted in attempts to correlate
the neutrophil actin polymerization inhibitory activity with one of the two
proteins or a complex formed between them. Additional chromatography
steps were added in attempts to separate annexin VI from L-plastin.
Neither phenylsepharose (Pharmacia Biotech, Inc., Piscataway, NJ) or Affi-
Gel blue (Bio-Rad Laboratories, Inc., Hercules, CA) chromatography
separated the two proteins. The viscosity lowering activity was noted to
coelute with the annexin VI and L-plastin proteins during Affi-Gel blue
chromatography (the viscosity lowering activity was not monitored in the
fractions obtained from phenylsepharose chromatography).
The difficulty in separating these two proteins raised the possibility
that annexin VI and L-plastin were forming a complex. Nondenaturing
polyacrylamide gel electrophoresis was used to test this possibility (Figure
3-3). Active fractions containing both annexin VI and L-plastin (Figure 3-
3, lane 2), purified annexin VI (lane 1) (via liposome purification, see
below), recombinant human L-plastin (lane 3) (purified from E. coli by Dr.
Clarence Young for unrelated studies in our laboratory), and bovine
albumin (lane *) (indicator of the nondenaturing conditions of the assay)
were each subjected to nondenaturing electrophoresis. If a complex was
formed by annexin VI and L-plastin in active fractions, one might expect a
migration pattern different from lanes containing the purified annexin VI
(Figure 3-3, lane 1) or purified L-plastin (Figure 3-3, lane 3). This
difference would most likely appear as a slower migrating band in
fractions where a complex is formed (analogous to the decreasing
mobilities of monomer, dimer, and trimer species of native bovine
albumin seen in Figure 3-3A lane *). The samples were run in triplicate

Figure 3-3. Nondenaturing polyacrylamide gel electrophoresis. PMN inhibitor (lane 2; 12pg) was
subjected to native gel electrophoresis in search of evidence suggesting complex formation between L-
plastin & annexin VI. Purified annexin VI (lane 1; 6 pg) and purified L-plastin (lane 2; 6 pg) were run to
enable the determination of a mobility shift when the two proteins are present. Panel A is a Coomassie
stained gel of the various fractions (starred lane contains 15 pg of albumin/BSA). Gels were run in
triplicate for western analysis with antibodies to annexin VI (Panel B) or L-plastin (Panel C).

1
O'
★ 1
2
3
1

62
for Coomassie blue staining and immunoblot analysis. As shown in Figure
3-3B, antibodies to annexin VI (Zymed Laboratories, Inc., South San
Francisco, CA) reveal one band in the active fraction. The similar
migration pattern shared by annexin VI in purified and active fractions
(Figure 3-3B, lane 1 and lane 2), suggests annexin VI does not take part in
complex formation. Although the L-plastin antibody reveals two closely
spaced reactive bands in the active fraction (Figure 3-3C, lane 2), they
both migrate separately from annexin VI. The detection of two L-plastin
bands in active fractions (Figure 3-3C, lane 2) and only one in the purified
(recombinant L-plastin) fractions (lane 3) most likely results from post-
translational modification of the PMN isolated L-plastin. Furthermore, L-
plastin is a known phosphoprotein (Zu et al., 1990). It is well established
that bacteria are incapable of many of the post-translational modifications
seen in eukaryotes, and thus could explain the appearance of one band
with L-plastin recombinantly expressed and purified from E. coli. It is
notable that recombinant L-plastin does not decrease the viscosity of actin
solutions (Dr. C. Young, unpublished data). These data derived from
nondenaturing polyacrylamide gel-electrophoresis suggest no complex is
formed between the annexin VI and L-plastin present in the neutrophil
actin polymerization inhibitory activity.
To further clarify which protein was responsible for the actin
viscosity lowering activity, attempts were made to separate annexin VI by
methods previously developed for studying the membrane binding
properties of annexins (Blackwood & Ernst, 1990). In this assay,
phosphatidylserine liposomes were prepared as described, and added to
active fractions. After incubation in the presence of calcium, the
liposomes were separated from the fractions by centrifugation. This

Figure 3-4. SDS-PAGE of phospholipid affinity chromatography, and anti-
annexin VI western analysis. PMN inhibitor was exposed to a mixed-lipid-
vesicle column in the presence of calcium. The activity remained in the
fall through (lane 2). Annexin VI (> 95 % pure) was eluted with ImM
excess EGTA. Fractions were transferred to nitrocellulose and probed with
antibodies to annexin VI. The same molecular weight standards in Figure
3-1 were used (HMW Std).

CD
O
in I I
C\J
*
i i i
i
i
i

65
method was able to remove > 60 % of annexin VI from those fractions
purified by DEAE-ion exchange and gel-filtration chromatography.
Phospholipid affinity chromatography (Chapter 2), as well, incompletely
separated annexin VI from the neutrophil activity (Figure 3-4, lane 2).
The neutrophil actin polymerization inhibitory activity remained in
fractions partially depleted of annexin VI and predominantly composed of
L-plastin, and was not associated with the highly purified annexin VI (> 90
%) (Figure 3-4, lane 1).
Purification And Identification Of PMN Actin Polymerization Inhibitor As
CapZ
In efforts to avoid phospholipid contamination and the addition of
calcium, other chromatographic methods were tested. After DEAE-anion
exchange chromatography and gel-filtration, the neutrophil inhibitory
activity was applied to a Mono Q.anion exchange column and eluted with a
KC1 gradient (Chapter 2). Surprisingly, the activity coeluted with annexin
VI and not L-plastin (data not shown). The peak activity, although,
correlated with a fraction in which no protein was seen by Coomassie
staining of the fractions run on SDS-PAGE (no predominant band was seen
by silver staining as well). However, Western blots of this and three other
active fractions from previous purifications probed with antisera from a
goat immunized with chicken, skeletal-muscle capZ (kindly provided by
Dr. J. Cooper, Washington University, St. Louis, MO) revealed two
immunoreactive bands (Figure 3-5) in the appropriate molecular weight
range of the heterodimeric, skeletal-muscle protein capZ (Mr between
30,000 - 40,000). The DEAE-anion exchange fractions from the
subsequent purification were subjected to immunoblot analysis and
probed with the capZ antisera as well (Figure 3-6). Peak capZ

Figure 3-5. Western blot analysis of PMN inhibitory fractions probed with
capZ antisera. Fractions from the four most recently purified PMN actin
polymerization inhibitor purified by DEAE-ion exchange and gel-filtration
chromatography each had detectable levels of both subunits (a and |3) of
capZ.

67
12 3 4

68
immunoreactive peptides (Figure 3-6C fraction # 36 - 42) were found to
correlate with the neutrophil actin polymerization inhibitory activity. As
seen in Figure 3-6, the viscosity lowering activity was maximal in fractions
36 - 42 (panel C). These fractions also represented the peak capZ, annexin
VI (68 kDa), and L-plastin (66 kDa) fractions.
A scheme utilizing three additional columns was empirically devised
to separate annexin VI and L-plastin and further purify the neutrophil
actin polymerization inhibitor (High S, Mono Q, and hydroxylapatite).
Active fractions composed predominantly of annexin VI and L-plastin were
further separated by High S-cation exchange chromatography (Figure 3-7)
under similar conditions utilized during the purification of skeletal muscle
capZ. Figure 3-7A represents the typical separation achieved by this
method. The polymerization inhibitory activity correlates with L-plastin
(fraction # 28 - 42). Fractions #62 -86 are composed of annexin VI
(Figure 3-7B) as detected by Western analysis. Similar to the
phospholipid-purified annexin VI, no activity was detected for fractions of
annexin VI separated by High S-ion exchange chromatography (Figure 3-
7C, fraction # 62 - 70).
Active fractions after High S chromatography were applied to a
Mono Q.anion exchange column and eluted with KC1 (Figure 3-8A) as
described earlier (Chapter 2). Despite the presence of PMSF in dialysis
solutions and maintenance of all procedures at 4 °C, the 55 kDa L-plastin
degradation product was formed in significant amounts by this stage of
the purification (Figure 3-8C, fraction # 28 - 34: lower band). Mono Q.
chromatography separated the peak L-plastin fractions (Figure 3-8C
fraction # 29 - 32), but not its degradation product (see fraction # 26 - 28)
from the neutrophil actin polymerization inhibitor. The purification was

Figure 3-6. DEAE-anion exchange chromatography of PMN extract.
Extracts were eluted with a linear KC1 gradient as described (Chapter 2).
Eluted proteins were subjected to 10 % SDS-PAGE (with HMW stds) and
stained with Coomassie (Panel A) or transferred to nitrocellulose and
probed with antisera to chicken skeletal-muscle capZ (Panel B). Relative
activities (Panel C) were reported as the ability of fractions to decrease the
viscosity of actin solutions (10 pM) as measured by falling ball
microviscometry.

Activity
70
c
1.0
0.5
0.0
C 24 3 0 3 2 3 4 3 6 3 8 4 0 4 2 4 4 5 2
Fraction #

Figure 3-7. High S-cation exchange chromatography of PMN actin polymerization inhibitor. PMN
inhibitor consisting predominantly of annexin VI and L-plastin was bound to a High S column (Chapter 2)
and eluted with a 0 - 0.15 M linear KC1 gradient. Fractions were subjected to 10 % SDS-PAGE (with HMW
stds) and stained with Coomassie (Panel A). Fractions were trasferred to nitrocellulose and probed with
antibodies to annexin VI (Panel B). Relative activities are reported as the ability to prevent actin
polymerization from actin filament nuclei isolated from red blood cells (Panel C).

Activity
A
B
Std 16 24 30 34 38 42 50 58 66 74 86
12 20 28 32 37 40 46 54 62 70 78 82
â– ^1
K>
C
Fraction tt

Figure 3-8. Mono Q.-anion exchange chromatography of PMN actin
polymerization inhibitor. Peak activities from High S chromatography
were pooled and allowed to adhere to a Mono Q. column. The proteins
were eluted with a 0.1 - 0.3 M linear KC1 gradient, and subjected to 10 %
SDS-PAGE (with HMW stds). The 10 % SDS-PAGE gel shown was first
stained with Coomassie blue (Panel A), and then silver stained (Panel A').
The relative activities (Panel B) were measured as in Figure 3-7. Fractions
were also transferred to nitrocellulose and probed with antibodies to L-
plastin (Panel C).

Activity
74
A
A'
i*1 J
<*r
I
w
t
-
*
•- *
. r
if?- • *i»** •
1
t
#
-
f
f
14 18 22 24 26 28 30 34 38 Std
12 16 20 23 25 27 29 32 36 40
14 18 22 24 26 28 30 34 38 Std
12 16 20 23 25 27 29 32 36 40
Anti-L-piastin
-m
—
26 27
28 29 30 31
32
C

75
carried out to this extent on three separate occasions, each resulting in the
isolation of polypeptides with approximate Mr of 55,000 (L-plastin
degradation product), 36,000, and 32,000 seen upon silver staining (for
examples see Figure 3-8A' lanes 26 and 27 or Figure 3-11, lane 3).
Western analysis identified the 36 and 32 kDa bands as capZ (Figure
3-9A & B, lane 2). As shown in Figure 3-8 (panel A verses panel A, lanes
26 & 27), the presence of these peptides after Mono Q. chromatography is
revealed by silver staining. Hydroxylapatite chromatography of these
fractions successfully separated the L-plastin degradation product from
the actin-filament-shortening activity (Figure 3-10, fraction 21 verses
fraction 22). The activity was strictly associated with capZ (Figure 3-10).
Although several minor bands were seen below the 36 and 32 kDa
polypeptides in Figure 3-10, they were not seen when fraction 21 was
separated on other occasions (Figure 3-11, lane 4). Several possibilities
including degradation, resolution of isomers or an artifact of the
procedure can explain this finding.
Discussion
Proteins that bind to actin and modulate actin filament assembly are
also hypothesized to regulate the finely coordinated assembly and
disassembly of the microfilament network in motile cells. Based on
viscometric studies, actin polymerization inhibitor is thought to play an
important role in the regulation of actin filament length in PMN.
Originally, my purifications focused on the 62 and 65 kDa proteins, and so
the identity of these polypeptides was pursued.

Figure 3-9. Western blot analysis of PMN actin polymerization inhibitor
purified to Mono Q. chromatography. Peak fractions from Mono Q_
chromatography (lane 2) (see Figure 3-8) were separated by 10 % SDS-
PAGE (with HMW stds), and either stained (Panel A) with Coomassie or
subjected to Western analysis (Panel B) probing with antisera to chicken
skeletal-muscle capZ. Lane 1 is 30 pg PMN extract, while a total of 3 pg of
protein was loaded in lane 2.

CD
<
CM
i ni i i
CM
: mini i i ^

Figure 3-10. Hydroxylapatite column chromatography. As a final
purification step, peak active fractions from Mono Q.chromatography were
subjected to hydroxylapatite (HA) column chromatography as described
(Chapter 2). Fractions were subjected to 10 % SDS-PAGE and silver stained
(Panel A). Relative activities were measured as in Figure 3-7.

Fraction
Relative Activity
o o —
o Ln o

Figure 3-11. Silver stained peak fractions from Mono Q. and HA
chromatography. PMN extract (14 pg; lane 2), Mono Qpeak activity (2pg;
lane 3), HA peak activity (0.25 pg; lane 4), and HMW std (lane 1) were
subjected to 10 % SDS-PAGE and silver stained. Arrowheads point to the
36 kDa and 32 kDa subunits of capZ.

81
12 3 4

82
The molecular weights of the polypeptides copurified with the
viscosity lowering activity were currently found to be 66,000 and 68,000
when separated by 10 % SDS-PAGE (originally determined with 5 - 15 %
SDS-PAGE). Initial sequence analysis of the polypeptides resulted solely in
the identification of the 68 kDa upper band as annexin VI. Their shared
physical properties (Mr and pi) suggested the 66 kDa polypeptide was
related. It was speculated that the 68 kDa protein was susceptible to
known neutral proteolytic activity in human granulocytes (Southwick &
Stossel, 1981).
Despite the recognition of only the upper band by anti-annexin VI
immunoblot analysis, it was thought that the epitope recognized by this
monoclonal antibody (Zymed Laboratories, Inc., South San Francisco, CA)
was not present in the 66 kDa polypeptide. The annexins are a large
family of related proteins (Chapter 5). The structural similarity amongst
the annexin proteins limits the number of epitopes specific to each
member. The annexins have divergent sequences at their amino termini
(Creutz, 1992), and therefore it is likely that the monoclonal anti-annexin
VI-speciflc antibody recognizes an epitope in this region. It seemed
plausible that the 66 kDa polypeptide was a partially degraded form of
annexin VI that had lost the epitope recognized by the monoclonal
antibody. Alternative explanations included the possibility the 66 kDa
peptide was an alternatively spliced annexin VI lacking the epitope
(Crompton et al., 1988), the 66 kDa peptide was annexin VI post-
translationally modified in a manner preventing recognition of the
epitope, or the 66 kDa peptide was an unrelated peptide. To test these
possible explanations, the peptides were probed with a polyclonal antisera
specific to human annexin VI (Dr. Joel Ernst). Similar to the monoclonal

83
antibody to annexin VI, the polyclonal antisera only recognized the 68 kDa
polypeptide. These Findings suggested that the 66 kDa protein was not a
degradation product of annexin VI.
To determine the identity of this protein, active fractions were again
prepared for amino acid sequence determination as described earlier (see
Results), and sent to our collaborator D. W. Speicher at The Wistar
Institute. Utilizing improved techniques, the 68 kDa band was once more
identified as annexin VI while the 66 kDa band was identified as L-plastin.
Based on previously published cDNA sequences, the predicted molecular
weights of annexin VI and L-plastin are 75,901 and 70,306 respectively
(Sudhof et al., 1988; Lin et al., 1988).
There have been no prior reports of annexin VI and L-plastin
copurified, probably a reflection of the abundance of both proteins in
neutrophils and the tissue specific expression of L-plastin (limited to
transformed and hematopoetic cells) (Lin et al. 1988). I was unable to
detect a complex formation between these proteins as evidenced by the
inability of annexin VI and L-plastin antibodies to recognize a common
band in active fractions resolved by native acrylamide gel electrophoresis.
Biochemical analysis reported by several laboratories repeatedly
demonstrates Mr between 64,000 - 70,000 and pi between 5.3 and 5.6 for
both proteins. The shared physical properties explains why we
consistently copurified these two proteins.
Earlier reports have implicated both annexin VI and L-plastin as
cytoskeletal regulatory proteins. They therefore remained likely
candidates responsible for the activity of neutrophil actin polymerization
inhibitor. Annexin VI isolated from bovine hepatic tissue was recently
observed to cosediment with actin filaments in a calcium dependent (>

84
100 pM) fashion (Hosoya et al., 1992). L-plastin has been shown to bundle
actin filaments in a calcium dependent manner (Namba et al., 1992). This
group was able to demonstrate by electron microscopy that L-plastin
induces actin bundle formation in vitro in the presence of low free calcium
concentrations (10 - 100 nM), and this property is lost as the calcium
concentration is elevated (1-10 pM). A separate group (Pacaud et al.,
1993) was able to demonstrate that L-plastin increases the viscosity of
actin solutions at low free calcium concentrations (< 0.1 pM), but the
viscosity of L-plastin/actin solutions was progressively lowered to control
levels (actin polymerized alone) as the free calcium concentration was
elevated (> 10 pM). The reported interactions of annexin VI or L-plastin
with actin, although, could not readily explain the calcium-independent
viscosity-lowering effect of the neutrophil actin polymerization inhibitor.
Annexin VI purified by either the phospholipid affinity column or
the High S cation exchange chromatography did not possess the
neutrophil Inhibitory activity. Additionally, L-plastin could also be
separated from the neutrophil actin polymerization inhibitor (see Results)
by Mono Q.-anion exchange chromatography. The ability to separate both
proteins from the activity proves the activity of PMN actin polymerization
inhibitor is not due to annexin VI or L-plastin.
It was subsequently discovered that capZ was responsible for the
inhibitory activity. Utilizing three additional chromatography columns,
the neutrophil actin polymerization inhibitor was successfully separated
from annexin VI and L-plastin (Figures 3-7, 3-8, and 3-9). Silver stained
polyacrylamide gels of the various purification steps reveal that active
fractions consistently correlate with the presence of the 36 and 32 kDa
capZ bands. My purification of the activity to these bands, and their

85
recognition by antibodies to capZ proves this protein is responsible for the
PMN actin polymerization inhibitor.
CapZ is a heterodimeric protein with subunits of Mr 36,000 la-
subunit) and 32,000 (p-subunit) (Casella et al., 1986). Members of this
family are capable of binding the barbed end of actin filaments with high
affinity (~ 0.5 - 10 nM) independently of calcium. Binding to the barbed
end of actin filaments effectively decreases the apparent viscosity of actin
solutions by two mechanisms. First, this interaction results in the
shortening of the average filament length, and secondly it raises the
critical concentration to that of the pointed end. The elucidation that
PMN actin polymerization inhibitor is identical to capZ was complicated by
several factors. The limited number of human PMN available for
purification, capZ's high affinity interaction with actin, its decreased
sensitivity to Coomassie staining, the predominance of annexin VI and L-
plastin in active fractions, and most notably the physical properties shared
by these three proteins each added to my difficulties in identifying capZ as
the PMN inhibitor.
The use of the human neutrophil system greatly limits the starting
material. These immune cells have developed an effective antimicrobial
repertoire which includes a diverse collection of proteolytic molecules. A
packed cell volume of ~ 20 - 25 ml (derived from > 20 liters of peripheral
blood) was isolated during the largest preparations. With this amount of
cells, less than 1 gram of protein remains after clarification of the
homogenized cells. This is in stark contrast to the two previous published
purifications of capZ from animal cells (chicken skeletal muscle and
bovine brain). With the purification from chicken skeletal muscle, 1000 g
of chicken breast muscle are typically utilized to purify ~1 mg capZ

86
(Casella et al., 1986, Caldwell et al., 1989). Purification of capZ from
bovine brain similarly requires ~ 1000 g starting material (4 brains)
(Kilimann and Isenberg, 1982). Our final yield of PMN capZ after
hydroxylapatite chromatography (~ 10 pg) was about one-tenth of those in
chicken muscle capZ preparations. This finding is not surprising
considering the abundant proteolytic activity commonly seen in extracts
made from these phagocytes. Secondly, the ability of capZ to interact with
actin with such high affinity (s 250 ng/ml, based on Kd ~3 nM) (see
Chapter 4) allowed for detection of activity with minimal protein as seen
by stained polyacrylamide gels. The problem was further complicated by
the identification of the two major polypeptides copurified with the
activity as previously studied actin binding proteins.
Lastly, the elusiveness of capZ resulted primarily from its physical
properties and staining characteristics. The consistent purification of
annexin VI and L-plastin with capZ is currently explained by the similar
native molecular weights and isoelectric points shared by these three
proteins (annexin VI/L-plastin: Mr 64,000 - 70,000 and pi 5.3 - 5.6 for
both proteins). The molecular weights of bovine brain and chicken
skeletal muscle capZ were reported as 63,000 (pi 5.75) and 61,000
respectively (Kilimann and Isenberg, 1982; Casella et al., 1986). A Stokes
radius of 32 Á was determined for the PMN actin polymerization inhibitor
by analytical gel filtration following the viscosity lowering activity
(Southwick & Stossel, 1981). This closely resembles the Stokes radii
determined for bovine brain (35.5 Á) and chicken skeletal muscle (37 Á)
(Kilimann and Isenberg, 1982; Casella et al., 1986). Many
chromatographic techniques rely on variations of MW or pi to separate
proteins. The physical properties shared by these three proteins

87
necessitates the use of several columns to purify the neutrophil inhibitory
activity.
In summary, the exhaustive purification protocols have
demonstrated human neutrophil actin polymerization inhibitor is capZ, a
heterodimeric protein consisting of two subunits with Mr of 36,000 and
32,000 as detected by silver staining active fractions separated by SDS-
PAGE. Western blot analysis of peak inhibitory activity from Mono Q.
chromatography fractions reveals immunoreactivity of the 36 and 32 kDa
polypeptides with antisera made to chicken skeletal-muscle capZ,
supporting my conclusion that the 36 and 32 kDa polypeptides further
purified by hydroxylapatite were identical to the capZ immunoreactive
peptides. Together these findings presented in Chapter 3 indicate that the
previously published neutrophil actin polymerization inhibitor is indeed
related, if not identical, to the skeletal muscle form of capZ. In addition,
neither of the polypeptides originally identified as the neutrophil inhibitor
(currently identified in this work as annexin VI and L-plastin) contributes
to the activity of PMN actin polymerization inhibitor.

CHAPTER 4
FUNCTIONAL CHARACTERIZATION OF PMN CAPZ
Introduction
The PMN actin polymerization inhibitor was originally isolated in
the presence of EGTA primarily to distinguish it from the calcium-
dependent viscosity-lowering activity of gelsolin (Yin & Stossel, 1979).
The importance of this characteristic is suggested by the recent findings of
calcium-independent actin assembly in PMN (reviewed in Chapter 1).
Based on the current theories of actin regulatory proteins (Pollard &
Cooper, 1986), several interactions with actin could explain the actin
viscosity lowering effect originally reported for PMN actin polymerization
inhibitor (Southwick & Stossel, 1981). Proteins that sequester actin
molecules away from the polymerizable pool would lower the viscosity of
actin solutions. Additionally, interactions which shorten the average
length of actin filaments such as severing or capping (barbed or pointed
end) would also lead to a relative decrease in the final viscosity.
Conversely, actin binding proteins that cross-link or bundle actin
filaments would be expected to raise the viscosity of actin solutions. The
identification of the neutrophil activity as capZ suggests the viscosity
lowering effect results from the ability of this protein to cap the barbed-
end of actin filaments.
88

89
The characterization of the specific interactions of proteins with
actin was at first limited to those expert in the techniques of electron
microscopy. By this method the lengths of filaments can be directly
visualized, the kinetics of assembly at each end of the actin filament can
be simultaneously analyzed (using morphologically identifiable nuclei
such as heavy-meromyosin-labeled actin oligomers or Limulus sperm
acrosomal actin bundles), and the three-dimensional configuration of
actin solutions can be monitored. With the development of fluorescent
labels covalently attached to actin, most notably pyrene-labeled actin,
spectrophometric analysis of actin polymerization has become an
alternative, more accessible technique to study specific interactions and
kinetics of actin filament assembly (Kouyama & Mihashi, 1981; Cooper et
al., 1983). In efforts to further characterize the viscosity lowering activity
of PMN capZ, its effects on actin polymerization were studied utilizing
pyrene actin.
Results
Barbed-End Capping Activity
As shown in Figure 4-1A, capZ slowed the rate of actin filament
disassembly in a concentration dependent fashion. The marked slowing in
the depolymerization rate was most consistent with blocking of monomer
release from the barbed end of actin filaments. The apparent dissociation
constant for the interaction of capZ with the barbed end (Kd app) was
approximately 3 nM. CapZ inhibited actin depolymerization to a similar
extent in the presence as well as in the absence of Ca2+ (Figure 4-1B).
When filaments are diluted, they rapidly depolymerize from their ends in

Figure 4-1. Effects of purified capZ on actin filament depolymerization. Pyrene actin (2pM) was allowed
to polymerize to steady state in the presence of 1 mM EGTA (Panel A) or 1 mM CaCl2 (Panel B). At time
zero, aliquots of the F-actin were diluted 1/40 (final concentration 50 nM) into varying concentrations of
purified neutrophil capZ in buffer P containing EGTA (Panel A) or 1 mM CaCl2 (Panel B). Fluorescence
intensity was monitored over time. Numbers next to symbols represent the final concentrations of capZ.

Relative Fluorescence
>
Relative Fluorescence
©ooooooooo
16
EGTA Calcium

92
efforts to maintain the critical concentration of G-actin. Since the off rate
constant is several fold greater at the barbed end (k- = 3.5 s~l) than at the
pointed end (k- = 0.5 s'l), this assay is largely a reflection of monomer
loss at the barbed end (Bonder et al., 1983). If the filaments are composed
predominantly of ADP-actin, the difference in the off rate constants (k- of
ADP-actin) is increased to greater than one order of magnitude (Pollard,
1986; Korn et al., 1987). The steady state fluorescence values of each
sample reflected complete depolymerization, even at concentrations of
capZ causing maximal inhibition of depolymerization.
The ability of the neutrophil actin depolymerization inhibitor to
decrease the viscosity of actin filament solutions was previously reported
to be inhibited by increasing salt concentrations from 0.1 M KC1 to 0.6 M
KC1 (Southwick & Stossel, 1981). Therefore the effect of increasing salt
concentration on capZ barbed-end capping activity was also assessed by
the depolymerization assay. The capping activity of capZ was
progressively inhibited as the KC1 concentration in buffer P was raised to
0.6 M. This highest salt concentration caused near complete inhibition of
capZ capping activity (data not shown).
In addition to examining human PMN capZ's effects on the release of
actin monomers from the barbed filament ends, this protein's effects on
barbed end monomer addition were also examined using a complex
isolated from red blood cells composed of actin, band 4.1, and spectrin.
This membrane associated complex contains short actin filaments which
are thought to be capped at the pointed ends, and has been previously
used in the study of chicken skeletal muscle capZ's capping function
(Casella et al., 1986). As shown in Figure 4-2, capZ also blocked barbed
end actin filament assembly in a concentration dependent manner. The

Figure 4-2. Effects of purified capZ on actin filament polymerization from
spectrin/band 4.1/actin nuclei. To a constant (1.25 pg/ml) amount of
spectrin/band 4.1/actin nuclei (rbc nuclei), 0.55 pM pyrene labeled G-
actin was allowed to polymerize in the presence of varying concentrations
of capZ in buffer P containing 1 mM EGTA. The capZ and rbc nuclei were
allowed to incubate for 2 min prior to the addition of the pyrene actin. At
this concentration of pyrene actin, nucleation of filament assembly was
prolonged so that the fluorescence increases detected were due primarily
to growth at the barbed ends of the actin filament complexes.

Relative Fluorescence
94
Time (min)

95
apparent dissociation constant (Kd app) ~ 3.0 nM, was identical to that
determined from our depolymerization studies. The ability to block
monomer exchange at the barbed end of actin filaments was not affected
by changing the Ca^+ concentration (data not shown).
The concentration of added capZ producing 50 % inhibition of actin
filament polymerization or depolymerization (the number of free barbed
ends equals the number of capped ends) represents the upper limit for the
Kd since the number of filaments initially present with both assays is
unknown. Our logic is as follows. The fluorescence change is proportional
to the depolymerization/polymerization of pyrene-labeled actin filaments.
Although the total number of filaments is unknown, the 1/2 maximal rate
change caused by capZ represents the condition where 50 % of the
filaments are capped and 50 % are freely exchanging actin monomers.
As the dissociation constant (Kd) equals [capZ]free X [filaments]free /
[capZ-capped filaments], the condition where 1/2 maximal fluorescence
change is observed relates Kd to the total capZ added to the reaction since
the ratio of free to capped filaments equals one. If the initial
concentration of filaments added is «< than the total capZ added, then
this concentration is equivalent to Kd- Therefore, the Kd measured for
PMN capZ capping the barbed end is at least 3 nM, but could theoretically
be much lower (i. e. greater affinity).
Substoichiometric concentrations of capZ decreased the steady-state
filament content of actin solutions polymerized in buffer P with 1 mM
EGTA as reflected by the decrease in pyrenyl fluorescence. The G-actin
concentration was maximally elevated to ~0.8 pM in the presence of capZ.
Similar elevations were seen when the total actin concentration was either

Figure 4-3. Effects of neutrophil capZ on the extent of actin
polymerization. Actin (3.0 pM or 0.9 pM) was allowed to polymerize to
steady state in the presence of varying concentrations of capZ. The G-
actin concentration was calculated from the steady state fluorescence
difference in actin solutions without capZ.

97
=L
C
u
<
6
1.0
0.9-
0.8-
0.7-
0.6-
0.5-
0.4-
0.3 is
0.2-
o.i-
o.o —
0
Ú
A
â–¡
1 0
A
â–¡
2 0
â–¡
â–¡
A 0.9 |iM Total Actin
â–¡ 3.0 |iM Total Actin
—i ■ 1 ■ 1
3 0 4 0 5 0
CapZ (nM)

98
0.9 or 3 pM (Figure 4-3). A similar increase in G-actin was seen when capZ
was added to actin solutions in the presence of calcium (data not shown).
Nucleation Assay
CapZ nucleation activity was also tested in the presence and absence
of calcium. Concentrations of capZ up to 219 nM (Figure 4-4, closed
squares) failed to stimulate the polymerization of actin as compared to
actin monomers alone (open squares). Addition of unlabeled actin
filaments 10 min after addition of salt caused a rapid rise in pyrenylactin
fluorescence indicating the actin was capable of assembling (open
triangles). Figure 4-4 is representative of multiple assays all of which
demonstrated a failure to stimulate actin assembly. In two instances capZ
prolonged the lag phase and was associated with assembly rates that were
slower than actin alone (data not shown).
Severing Assay
To examine the ability of capZ to break apart preformed actin
filaments, gelsolin-capped filaments were diluted into a buffer containing
varying concentrations of capZ. As seen in Figure 4-5, capZ at
concentrations as high as 215 nM did not accelerate the depolymerization
rate (closed squares) as compared to filaments diluted into buffer (open
squares). Dilution of gelsolin-capped actin filaments into a buffer
containing free gelsolin (100 nM) caused a marked acceleration in the
depolymerization rate (closed triangles).

Figure 4-4. Effects of neutrophil capZ on G-actin nucleation. At time zero,
a final concentration of 0.1 M KCI and ImM MgCl2 was added to 1.5 pM
gel-filtered, pyrene-labeled G-actin combined with a final concentration of
215 nM capZ (closed squares) or in buffer P alone (open squares). These
two curves virtually overlie each other, and control points were taken
corresponding to every experimental point. Identical effects were seen in
the presence of 1 mM CaCl2- The ability of the pyrene labeled actin to
polymerize was assessed by adding a final concentration of 1.4 pM
unlabeled F-actin to the control reaction 10 minutes after initiation of
actin assembly by the addition of salt (closed triangles).

Relative Fluorescence
100
Time (min)

Figure 4-5. Actin filament severing assay. Gelsolin and pyrene actin
(2 pM) were copolymerized (molar ratio 1:200 gelsolin to G-actin) to
steady state in buffer P and ImM CaCl2 forming filaments capped at the
barbed ends. These filaments were then diluted to a final actin
concentration of 100 nM in buffer alone (open squares), buffer containing
a final concentration of 215 nM capZ (closed squares), and buffer
containing a final concentration of 100 nM gelsolin (closed triangles).

Relative Fluorescence
KÍ -U ON 00 o
O O O O O o
102

103
Monomer Sequestration Assay
The ability of capZ to sequester monomeric actin was examined
using gelsolin-actin nuclei (Chapter 2). These nuclei containing free
pointed ends were added to a mixture containing a fixed concentration of
actin monomers and increasing concentrations of capZ. A monomer
sequestering protein would be expected to slow the rate of actin assembly
in a dose dependent manner (Young et al., 1990). In the presence of 1
mM EGTA or 0.5 mM calcium, at final concentrations as high as 360 nM,
capZ failed to alter the polymerization rate of gelsolin-actin nuclei (see
Figure 4-6). Identical effects were observed with both 100 % and 50 %
pyrene-labeled monomeric actin.
Effect Of P1P2 On The Ability Of CapZ To Bind The Barbed-Ends Of Actin
Filaments
As seen in Figure 4-7, the capping ability of 36 nM capZ was
decreased in a concentration dependent fashion by the addition of PIP2
micelles. The 1/2 maximal inhibition of capZ capping activity was
observed at approximately 5.5 pg/ml (5 pM). At concentrations of up to
11 pg/ml, the anionic phospholipids phosphatidylserine and
phosphatidylinositol as well as the neutral phospholipid
phosphatidylcholine failed to elicit a detectable decrease in capZ capping
activity (see figure 4-7).
Discussion
My discovery that PMN capZ binds the barbed ends of actin
filaments in vitro, suggests its involvement in the regulation of the
microfilament network in highly motile animal cells. Although this

Figure 4-6. Effects of capZ on polymerization from gelsolimactin nuclei. Pyrene labeled G-actin (final of
0.8 pM; 100 % labeled) was polymerized in the presence of gelsolimactin nuclei (molar ratio 1:16), and
assembly rates monitored in the presence of final concentrations of 290 nM capZ (closed squares) or 360
nM capZ (closed triangles) or in the presence of buffer alone (open circles). The same concentration of
pyrene G-actin alone failed to polymerize during the time period of our assay (open squares). The
reaction was performed in the presence of either 1 mM EGTA (Panel A) or 0.5 mM calcium (Panel B).
Similar results were obtained when this assay was repeated in the presence of G-actin that was 50 %
labeled.

Time (min)
Relative Fluorescence
>
Relative Fluorescence
CXJ
SOI

Figure 4-7. Effects of PIP2 on capZ barbed-end capping activity. Panel A). The effects of equivalent
amounts (llpg/ml) of various phospholipids PIP2-Phosphatidylinositol 4,5-bisphosphate, PC-
Phosphatidylcholine, PS-Phosphatidylserine, and PI-Phosphatidylinositol on capZ capping activity was
tested. Two micromolar (2 pM) pyrene F-actin was diluted in buffer P + EGTA to 50 nM in the presence of
36 nM capZ and the various phospholipids. Panel B). Barbed-end capping activity of 36 nM capZ was
measured in the presence of varying amounts of PIP2. One hundred percent capping activity was defined
as the inhibition of depolymerization observed with 36 nM capZ in the absence of PIP2-

Time (min)
Relative Fluorescence
>
g £
§
Capping Activity (%) gg
¿01

108
protein has been previously purified and characterized in muscle and
brain, its presence and interaction with actin in highly motile animal cells
has yet to be described. The majority of actin filaments present in resting
neutrophils are thought to be capped at their kinetically active barbed
end. This cap is partially responsible for maintaining the high levels of
unpolymerized actin found in these cells. Upon chemotactic stimulation,
the amount of actin in neutrophils doubles (see Chapter 1). Uncapping of
the high-affinity barbed-ends in response to chemoattractant stimulation
may be responsible for the rapid conversion of monomeric actin to
filamentous actin. Unlike gelsolin or capG, the other major barbed-end
blocking proteins found in the cytoplasm of PMN, capZ's capping function
is independent of the free calcium concentration. This characteristic may
partly explain the findings that changes in intracellular Ca^+ are not
required for chemoattractant-stimulated actin assembly (see Chapter 1).
Using three separate assays I was able to demonstrate that PMN capZ
interacts specifically at the barbed end. The interaction of capZ with
polymerizing or depolymerizing filaments suggests this protein binds with
high affinity (Kd ~3 nM) to the barbed-end of actin filaments. This is
similar to the Kd (0.5 - 1 nM) reported for capZ purified from chicken
skeletal muscle (Caldwell et al., 1989). As further evidence for barbed-end
capping, capZ was shown to maximally elevate the critical concentration of
actin at steady-state (~ 0.8 pM) to levels resembling that of the pointed
end.
My detailed analysis of the interaction of PMN capZ with actin
suggests the calcium-independent viscosity lowering effect of this protein
is due primarily to the formation of short actin filaments capped at the
barbed end. The ability of capZ to inhibit the depolymerization of

109
filaments argues against a severing activity. In addition, I was unable to
demonstrate severing of filaments by capZ (as high as 215 nM) at
concentrations and conditions where the severing activity of gelsolin is
readily detected. The lack of any reduction in the rate of growth from
gelsolin-actin nuclei suggests that capZ does not sequester actin monomers
with high affinity. These assays could not detect low affinity sequestering
(micromolar Kd) as the purification of PMN capZ limits the studies to
substoichiometric ratios of capZ to actin. This assay, however, proves that
capZ has no effect on monomer exchange at the pointed ends of actin
filaments. This finding is consistent with the steady-state analysis
revealing an elevation of the critical concentration in the presence of capZ.
An interaction with the pointed end would be expected to lower the
critical concentration of actin closer to that of the barbed end.
Similar to aginactin, an activity from Dictyostelium containing the
capZ-related protein cap 32/34 (Eddy et al., 1993; Sauterer et al., 1991), I
was unable to demonstrate nucleation of filament assembly by PMN capZ.
Additionally, when the polymerization of actin was studied in the presence
of the capZ-related protein purified from Xenopus, a prolongation of the
lag phase and a reduction in the extent of polymerization was observed
(Ankenbauer et al., 1989). These findings were explained by an
interaction with polymerizing-actin limited to capping of the barbed end.
A similar prolongation of the lag phase was noted for the calcium-sensitive
barbed-end capping protein capG (Young et al., 1990). 1 cannot
completely exclude the possibility that PMN capZ may weakly interact with
monomeric actin and cause low levels of nucleation. Because this protein
blocks the barbed ends and fails to produce more pointed ends by
severing, low levels of nucleation activity may not be readily measurable.

Figure 4-5. Actin filament severing assay. Gelsolin and pyrene actin
(2 pM) were copolymerized (molar ratio 1:200 gelsolin to G-actin) to
steady state in buffer P and ImM CaCl2 forming filaments capped at the
barbed ends. These filaments were then diluted to a final actin
concentration of 100 nM in buffer alone (open squares), buffer containing
a final concentration of 215 nM capZ (closed squares), and buffer
containing a final concentration of 100 nM gelsolin (closed triangles).

110
A modest increase in nuclei with free pointed ends could be canceled out
by the loss of nuclei with free barbed ends.
The capZ purified from brain or skeletal muscle, although, has been
demonstrated to nucleate filament assembly (Kilimann & Isenberg, 1982;
Caldwell et al., 1989). The capZ nucleation reaction is quite complicated,
and is not completely understood (Caldwell et al., 1989). The cellular
importance of the capZ nucleating activity, as well, is unknown. If the
capZ concentration in cells is greater than the concentration of barbed
ends, free capZ would likely exist. A substantial portion of capZ in
epithelial cells is present in the supernatants of ultra-speed cellular
fractions as detected by Western analysis, suggesting the abundance of
soluble capZ in these cells (Schafer et al., 1992). The ability of free capZ to
nucleate assembly would be highly dependent upon the critical
concentration of actin in cells. As the majority of the unpolymerized actin
in PMN is most likely sequestered by thymosin 84 and profilin (Cassimeris
et al., 1992), the free G-actin concentration is probably close to the critical
concentrations determined in vitro for capped (~1 pM or ~0.1 pM
respectively for barbed- or pointed-end capped filaments) or uncapped
filaments (~0.15 pM). With the nucleation studies, the effects of PMN capZ
on the polymerization of 1.5 pM G-actin in 0.1 M KC1 and 1 mM Mg2+
were monitored. These conditions are closer to the physiologic ionic
conditions and presumed critical concentration in PMN than those used in
similar assays to detect nucleating activity by capZ isolated from brain (12
pM actin, 20 mM KC1) or skeletal muscle (5 pM, 2 mM Mg2+).
Additionally, the nucleating activity for skeletal muscle capZ is inhibited in
the presence of P1P2, a phospholipid thought to interact with actin binding
proteins in a manner promoting polymerization (Heiss & Cooper, 1991).

Ill
The ability of gelsolin to cap the barbed end is dependent upon an
initial interaction with calcium (Stossel et al., 1985). Its proposed barbed
end capping function in resting cells stems from the isolation of a 1:1
complex of actin and gelsolin which blocks acdn filaments with high
affinity even at submicromolar concentrations (Janmey et al., 1985). The
recent generation of transgenic mice lacking the expression of functional
gelsolin suggests other calcium-independent capping proteins exist in
mammalian non-muscle cells (Witke et al., 1993). This finding in
combination with my studies suggests capZ is the predominant calcium-
independent capping protein in PMN. The other capping protein
identified in mammalian phagocytes, capG, requires calcium for its
capping activity (Southwick & DiNubile, 1986).
Similar to skeletal-muscle capZ and the related protein cap 32/34 of
Dictyostelium I have found that the barbed-end capping function of PMN
capZ is inhibited in the presence of PIP2 (Heiss & Cooper, 1991; Haus et
al., 1991). Chemoattractant receptor occupancy is associated with rapid
polyphosphoinositide turnover (Cockcroft et al., 1985; Eberle et al., 1990),
and the activities of several actin-binding proteins are inhibited by these
phospholipids (Janmey, 1994). Polyphosphoinositides, therefore, may
switch on actin assembly during chemoattractant stimulation by causing
the release of actin subunits from sequestering proteins, and uncapping of
the barbed ends of actin filaments (Stossel, 1993).
The present findings confirm the ability of PMN capZ to interact
specifically with the barbed end of actin filaments. There have been no
previous reports of capZ in neutrophils or macrophages, and it was only
recently noted in platelets (Barkalow & Hartwig, 1994; Nachmias et al.,
1994). These cells, although, are the mammalian model cells for

112
understanding the signal transduction mechanisms leading to rapid actin
assembly. The calcium-independent, phospholipid-regulated nature of
this activity suggests capZ is an important regulator of actin assembly in
highly motile animal cells such as the PMN.

CHAPTER 5
DEVELOPMENTAL EXPRESSION AND INTRACELLULAR LOCALIZATION OF
ANNEXIN VI IN PMN
Introduction
The studies presented in this chapter were initiated by the initial
findings that the 68 kDa polypeptide purified with the PMN actin
polymerization inhibitor (Chapter 3) is annexin VI. Although it was
eventually discovered that capZ and not annexin VI was responsible for
the PMN viscosity lowering activity, further studies were pursued to
characterize annexin VI as a potential cytoskeletal protein in PMN. This
protein belongs to a family of structurally and functionally related
proteins known as the annexins which possess a characteristic sequence
motif consisting of 70 - 80 amino acids that is repeated four to eight times
depending on the individual annexin (Pepinsky et al., 1988). Each
annexin exhibits the ability in vitro to bind anionic phospholipids found
in cell membranes in a calcium dependent fashion (Klee, 1988). Many
investigators postulate that the annexins play a key role in regulating
membrane interactions (Creutz, 1992).
Several annexins, as well, bind actin microfilaments. Both annexin I
and annexin II bundle actin filaments at high (ImM) Ca^+ concentrations
(Glenney et al., 1987). Annexin VI from bovine liver cosediments with
actin in ¿ 10 pM Ca2+ solutions (Hosoya et al., 1992), and a 68 kDa
annexin from human placenta cosediments with actin in solutions
113

114
containing 1 mM Ca2+ (Hayashi et al., 1989). My studies of PMN annexin
VI (Chapter 3) do not exclude the possibility of a calcium-regulated actin-
filament bundling or cross-linking activity by this protein. At least seven
annexins, including a 68 kDa protein, are present in human PMN (Meers et
al., 1987; Ernst, 1990).
In response to various stimuli, the intracellular calcium
concentration in PMN transiently elevates. This rise is thought to be
important for degranulation (Lew et al., 1986). Blocking this increase can
prevent superoxide anion production and exocytosis (Lew et al., 1984). In
neutrophils, intracellular calcium levels have been observed as high as
1,586 nM during phagocytosis (Jaconi et al., 1990). In this same study,
however, phagosome-lysosome fusion could be inhibited by buffering
intracellular Ca2+ to < 20 nM. Annexin VI in vitro binds phospholipids in
the micromolar calcium range (Geisow & Burgoyne, 1982). Chemotaxis,
phagocytosis, and degranulation are quintessential functions for PMN. In
part, these properties are dependent upon a coordinated rearrangement of
cellular membranes and the surrounding cytoskeleton. It is possible that
annexin VI from human neutrophils may play a role in this process.
As PMN differentiate from myeloblasts they develop more
prominent intracellular vesicles termed granules, hence earning the
designation granulocytes. There are at least two major (azurophilic and
specific) and two minor populations of granules in PMN whose distinct
role in the inflammatory process is evidenced by the different proteins
stored in each granule. Azurophilic granules store molecules necessary for
non-oxidative killing of microorganisms, while the constituents of specific
granules include, in addition to antimicrobial agents, a collection of
receptors and other proteins involved in functional activation of PMN

115
processes. The azurophilc granules and their constituents are formed
earlier in the differentiation of PMN than are the specific granules
(Bainton, 1992). As PMN mature, they also attain functions specific to
these cells such as superoxide generation, and effective non-oxidative
killing capabilities. I was interested in examining the developmentally-
associated changes on PMN as well as examining the intracellular
localization of annexin VI in PMN.
Results
Northern Analysis
The expression of annexin VI was examined in human PMN (isolated
from peripheral blood) and the human monocyte-like cell line U937
(ATCC, Rockville, Maryland) by Northern blot analysis. Using the 1057 bp
cDNA clone from human PMN annexin VI (Chapter 2), a prominent mRNA
of about 2.5 kb was detected (Figure 5-1). Although a lower band
migrating below the 18 S RNA was often seen, only the 2.5 kb mRNA was
detected under more stringent conditions. This is not surprising
considering the structural similarities shared by the annexin proteins.
Annexin VI mRNA from transformed human fibroblasts is similar in size to
the prominent band detected by our probe (Sudhof et al., 1988). Despite
the identical protocols used in the isolation of RNA and an equivalent
loading of 10 pg of total RNA (as judged by ethidium bromide staining of
gels) from both cell types, the levels of annexin VI mRNA detected were
much higher in PMN compared to U937 (Figure 5-1).

Figure 5-1. Northern analysis of PMN and U937. Total RNA (10 pg per
lane) was isolated from PMN or U937. Blots were probed using the partial
cDNA of annexin VI (Chapter 2) labeled with 3 2p by random primer
extension.

117
28S—
18S—
0
1 2

118
Northern Analysis Of Annexin VI During Differentiation Of Promyelocytes
The results from the analysis of annexin VI mRNA expression in PMN
and U937 cells suggest neutrophils have higher annexin VI niRNA levels
than monocytes/macrophages. This finding is curious as both these cell
types originate from promyelocytes. Currently used as a model for
differentiation is the human promyeloblast leukemic cell line HL-60
(Gallagher et ah, 1979). The ability of the HL-60 cells to differentiate
towards neutrophils by DMSO treatment or macrophages by phorbal
diester treatment was used as an in vitro model to study the
developmental regulation of annexin VI mRNA. The HL-60 cells were
grown in suspension cultures with a doubling time of approximately 24 -
48 hours. When induced to differentiate by PMA, these cells ceased to
proliferate and began to acquire characteristics of mature macrophages.
By 1 - 2 days, when a majority of the cells were adhered to the plates, they
developed many pseudopodial extensions. Similar to previous reports, I
found the HL-60 cells induced to differentiate by DMSO continued to
proliferate, but gained many of the morphological characteristics of
peripheral blood PMN (multilobular nuclei, and increased granules by
light microscopy). In all, the differentiation patterns observed were as
previously documented for HL-60 cells (Collins, 1987).
Total RNA was prepared from these cells at different time points
after the induction of differentiation with DMSO or PMA and analyzed on
Northern blots using the 1057 bp annexin VI cDNA fragment as a probe.
As shown in Figure 5-2, annexin Vi mRNA levels appears maximal by 3
days in HL-60 cells differentiated towards the neutrophil lineage. In
contrast the mRNA levels in HL-60 cells differentiated towards the
macrophage lineage had no detectable annexin VI mRNA by day 3. This

Figure 5-2. Northern analysis of HL-60 differentiated to neutrophil-like or
macrophage-like cells. Total RNA was isolated at various time points and
subjected to Northern analysis probing with the partial cDNA sequence to
annexin VI. This same blot was probed with random primer labeled
fragments of the F-actin cDNA sequence.

120
DMSO P M A
AN X VI
08 16 12345 08 16 1234
HOURS DAYS HOURS DAYS
B-ACTIN

121
analysis was repeated for a total of 3 separate differentiation experiments.
By laser scanning densitometry of the autoradiograms the changes in the
mRNA levels were quantified. All three DMSO induced differentiations
revealed a similar trend in that the annexin VI mRNA levels slowly
increased relative to HL-60 controls (t = 0), but the differences were not
statistically significant. It is notable that in each instance the annexin VI
mRNA levels followed to 3 days never dropped below the levels seen at
time zero. In contrast, annexin VI mRNA rapidly declined by day 3 to
about 12 % (12.1 ± 15.5, n = 3) the levels at time zero. In contrast to the
developmental changes in annexin VI, the level of actin remained
essentially unchanged (Figure 5-2).
Western Analysis Of Annexin VI During Differentiation Of Promyelocytes
The annexin VI protein levels were measured during myeloid
differentiation as well to determine whether the differences in annexin VI
mRNA expression correlate with the apparent levels of protein translated.
The identical differentiation protocols used for our Northern analysis were
performed, and equivalent amounts of proteins (60 pg total protein) were
separated on SDS-PAGE. Using the monoclonal anti-annexin VI antibody
(Chapter 2), Western blots of extracts from HL-60 differentiation studies
were probed and quantitated by laser scanning densitometry. This
experiment was performed twice, and the results of both experiments are
shown in Figure 5-3. We found that annexin VI levels maximally increased
3.4-fold by day three in cells differentiated towards the neutrophil lineage.
In contrast, the levels of annexin VI protein in PMA treated cells was
maximally reduced by day three to 28 % the time zero level.

Figure 5-3. Western analysis of HL-60 differentiated to neutrophil-like or
macrophage-like cells. Total protein was collected at various time points
and subjected to Western analysis with the antibody to annexin VI.
Relative annexin VI amounts were obtained by laser scanning
densitometry of reactive bands on the nitrocellulose blots

Area Relative to T-0 Area Relative to T=0
123
Western Blot HL-60 Differentiation #1
Time (hrs)
Western Blot HL-60 Differentiation #2
Time (hrs)

124
Immunolocalization Of Annexin VI In Mveloid Cells
PMN and monocytes were isolated from peripheral blood and
allowed to adhere to glass coverslips (Chapter 2). A diffuse cytoplasmic
distribution was observed by indirect immunofluorescence when fixed and
permeabilized PMN were stained with the monoclonal anti-annexin VI
antibody (Figure 5-4A). Additionally, annexin VI appears to be absent
from the nucleus. The specificity of this stain is supported by the positive
and negative controls (Chapter 2) processed simultaneously (Figure 5-4 C
& D). When peripheral monocytes were similarly stained, a specific
cytoplasmic pattern was also observed. The stain, although, did not
appear as intense as in PMN (data not shown). Interestingly, there
appeared to be an enhancement of the immunofluorescent signal at the
peripheral margins of monocytes stained with the anti-annexin VI
antibody.
To explore the possibility that annexin VI concentrates in certain
regions of the cell, confocal microscopy was performed (Figure 5-5 &
Figure 5-6). Figure 5-5 demonstrates that annexin VI in adherence-
stimulated PMN has a diffuse cytoplasmic distribution, and is not
concentrated in the membrane rich periphery of these cells. Surprisingly,
annexin VI appears concentrated at the periphery of adherent monocytes
(Figure 5-6). Panel B of Figure 5-5 and Figure 5-6 depicts control cells
stained with the anti-yeast antibody (Chapter 2).
Quantitation Of Annexin VI In PMN Extracts
Each of the preceding studies as well as our purification of annexin
VI (Chapter 3), suggests annexin VI is an abundant protein in PMN.
Freshly prepared human PMN extract was isolated from cells treated with

Figure 5-4. Indirect immunofluorescence microscopy of PMN. PMN were
allowed to adhere to glass coverslips. They were then fixed, permeabilized
and probed with the monoclonal antibody to annexin VI (Panel A) or
control monoclonal antibodies (Panel C, anti human hnRNP-M & Panel D,
anti yeast nab-1). Secondary antibodies used were identical (FITC-
conjugated anti mouse IgGl-heavy chain specific). Panel B is the phase
contrast image of panel A.

126

Figure 5-5. Confocal microscopy of PMN stained with anti-annexin VI
antibodies. Digitized images representing 1 pm cuts were obtained in
adherent PMN probed with annexin VI antibodies (Panel A) or control
antibodies (anti-nab-1; Panel B). Cells were fixed and stained identically to
Figure 5-4.

128

Figure 5-6. Confocal microscopy of peripheral blood monocytes stained
with anti-annexin VI antibodies. These experiments were done in tandem
to Figure 5-5. Panel A is stained with anti-annexin VI antibodies, and
Panel B is stained with anti-nab-1 antibodies.

130
A
B

131
the serine protease inhibitor diisopropylfluorophosphate and subjected to
Western blot analysis (Figure 5-7). A linear standard curve was generated
using highly purified annexin VI. Comparisons of these values to the 68
kDa reactive band in 3 (Figure 5-7, lanes 2-4) different dilutions of PMN
extract demonstrated that annexin VI represents 0.8 - 0.9 % of the total
protein in human PMN extracts. The concentration of annexin VI in
human PMN is ~7 pM when calculated relative to the actin in PMN (300
pM, 15 - 20 % of extracts; Southwick & Young, 1990).
Discussion
1 have found that annexin VI, a member of the annexin family of
Ca2+- and phospholipid-binding proteins, is present in the cytoplasm of
human PMN at high concentrations. The northern and western analyses
suggest the levels of annexin VI mRNA and protein is differentially
regulated in myeloid cells of the monocyte/macrophage lineage verses
those of the neutrophil lineage. The data presented indicate that
differentiation of HL-60 cells towards macrophages results in a marked
decrease in annexin VI mRNA levels, while the level in cells differentiated
to neutrophils is at least maintained if not elevated. Moderate increases in
annexin VI, although, may be masked during DMSO treatment since
incomplete induction (a population continues to proliferate) is common.
A moderate difference was also seen when annexin VI protein levels were
examined during differentiation of HL-60 cells. Consistent with mRNA
levels, the annexin VI protein content was elevated in cells treated with
DMSO, and appeared to decrease with PMA treatment. Changes in mRNA
levels upon differentiation are not limited to regulation at the

Figure 5-7. Quantitation of annexin VI in human neutrophil cytoplasmic extracts. Extracts were obtained
from PMN purified > 95 % (Chapter 2). A. Coomassie blue-stained and B. Nitrocellulose transfers. Lanes
1-4, decreasing concentrations of human neutrophil extracts 100, 75, 50, and 25 pg, respectively. Lanes
5-9, decreasing concentrations of purified human annexin VI: 1.0, 0.8, 0.6, 0.4, and 0.2 pg respectively.
The relative intensity of each nitrocellulose band was measured by laser densitometry, generating a linear
standard curve and allowing quantification of annexin VI in neutrophil extracts.

205
1 23456789
1 23456789

134
transcriptional level. Several other levels of regulation, including
alterations in the stability of mRNA, the sequestering in cellular
compartments, and the interaction with proteins can also explain changes
in the expression of mRNAs.
The abundance of annexin VI in fully differentiated PMN, isolated
from peripheral blood, is in agreement with the differentiation studies.
When the annexin VI intracellular distribution was analyzed in peripheral
blood PMN and monocytes, the fluorescent signal was consistently more
intense in PMN compared to monocytes. Additionally, it was found that
annexin VI comprises roughly 0.8 - 0.9 % of PMN extracts.
There are several functional differences between PMN and
macrophages. It is possible that the differential expression of annexin VI
is a direct reflection of a PMN-specific activity. Since annexin proteins
have been repeatedly demonstrated to bind phospholipids in vitro, it
seems reasonable to speculate they may retain this calcium regulated
function in cells. The killing and digestion of phagocytosed pathogens by
PMN is critically dependent upon fusion of their azurophilic and specific
granules with the membranes of the phagocytic vesicle. Additionally, the
regulated degranulation of constituents into the extracellular environment
is vital to the inflammatory role of this cell. Regulation of PMN
membrane-membrane interactions by annexin proteins has been
previously proposed (Meers et al., 1987). Annexin III is able to promote
the aggregation of specific granules in vitro upon the addition of calcium
(Ernst et al., 1990; Ernst, 1991). Additionally, annexin III, the most
abundant annexin in their preparations (> 1 %), was found to concentrate
in the peri-phagosomal region of cells ingesting yeast. My discovery that
annexin VI is abundant in the cytoplasm of PMN suggests this protein may

135
similarly interact with various membrane formed vesicles or granule
populations in PMN.

CHAPTER 6
CONCLUSIONS AND FUTURE DIRECTIONS
Conclusions
Cellular motility is a complex process which, as a whole, is still
poorly understood. Actin microfilaments, the predominant cytoskeletal
component, are constantly remodeled in non-muscle cells. It is generally
accepted that the dynamic rearrangements of this network are vital to
movement. As the kinetics of actin assembly in vitro have been elegantly
dissected over the past 15-20 years, many investigators are currently
exploring the cellular implications of these findings. Several models
including the fMLP-induced, rapid actin assembly in PMN (Chapter 1) and
the actin-based intracellular motility of the bacterial pathogen Listeria
monocytogenes in host cells (Southwick & Purich, 1994), are leading to
better insights as to how the cell regulates the assembly of actin. Findings
based on these models, therefore, would have direct implications towards
the mechanism of cellular motility.
The studies presented in this dissertation were pursued in the
context of what is currently understood about the regulation of actin
assembly in PMN. A calcium-independent, barbed-end, actin-filament,
capping activity is critical to current models explaining the rapid actin
filament formation in PMN and other cells capable of receiving
motivational signals. My discovery that capZ purified from human PMN
interacts with actin, specifically regulating assembly at the barbed end
136

137
independently of calcium in vitro, suggests this protein is a key
component of the PMN model for actin assembly. In support of this,
transgenic mice lacking gelsolin (the only other barbed-end capping
protein in animal cells which is capable of blocking actin monomer
exchange in vitro at calcium concentrations found in resting cells, i. e.
submicromolar Ca2+) appear grossly normal and retain the ability to
interbreed (Witke et al., 1993). Additionally, the presence of capZ was
recently noted in human platelets (Barkalow & Hartwig 1994; Nachmias et
al., 1994). PMN, macrophages, and platelets are the mammalian model
cells for understanding the signal transduction mechanisms leading to
rapid actin assembly.
Purification Of PMN CapZ
Three major conclusions can be drawn from the work described in
Chapter 3. First of all, capZ is present in highly motile mammalian cells.
Secondly, capZ is responsible for the activity originally purified as PMN
actin polymerization inhibitor. This conclusion is supported by the
finding that when the PMN actin filament shortening activity was followed
through 5 consecutive column chromatography separations, the activity
localized solely to the 36 and 32 kDa bands (as detected by silver stained
SDS-polyacrylamide gels) which appeared stoichiometrically equivalent.
Additionally, when peak active fractions from Mono Q.column separations
(immediately precedes our final column) are probed with chicken,
skeletal-muscle capZ antisera the 36 and 32 kD polypeptides are
specifically detected by Western analysis. Although we were unable to
immunoprecipitate the capZ and/or the activity from final purified
fractions, the apparent affinity measured (Chapter 4) for the binding of

138
PMN capZ to the barbed end of filaments is consistent with those
previously described for skeletal muscle capZ and the related
heterodimeric capping protein of Dictyostelium. Thirdly, it can be
concluded that annexin VI and L-plastin purified from PMN do not
decrease the viscosity of actin solutions or cap the barbed end of filaments
in the absence of calcium, proving they are not the activity of PMN actin
polymerization inhibitor as previously thought.
In Vitro Interaction Of PMN CapZ With Actin
By careful in vitro analysis utilizing the fluorescent actin probe,
pyrenlyactin, I was able to study the mechanisms regarding the viscosity
lowering activity of PMN capZ. First of all, it can be stated that PMN capZ
binds the barbed end of actin filaments with high affinity (3 nM) in vitro.
Secondly, this affinity is unchanged in the presence or absence of calcium.
Thirdly, based on the studies testing for pointed end capping, severing, or
monomer sequestering activity, the viscosity lowering activity of PMN capZ
is due solely to an interaction with the barbed end of filaments.
Developmental Regulation And Intracellular Localization Of PMN
Annexin VI
Annexin VI is an abundant intracellular protein comprising about
0.8 - 0.9 % of human PMN extracts. A relative increase in annexin VI is
seen in human promyelocytes differentiated towards the neutrophil
lineage versus those differentiated towards the macrophage lineage. We
conclude this difference is partly responsible for distinguishing these
developmentally related phagocytes. Based on the indirect
immunofluorescence analysis of annexin VI in PMN, I conclude that this
protein has a diffuse cytoplasmic distribution and is not present in the

139
nuclei of these cells. The relevance of these findings may become more
apparent once an in vivo role for annexin VI and other annexins is
established. I was unable to reproduce the actin binding properties
previously reported for annexin VI. These studies, although, were limited
as the primary focus was aimed at studying capZ. PMN annexin VI is able
to bind membrane phospholipids in a calcium regulated fashion as
demonstrated by my purifications of annexin VI with phosphatidylserine
multilammelar vesicles or with our phospholipid affinity column. Based
on its abundance and cytoplasmic distribution in PMN, it remains possible
that annexin VI may be involved in the regulation of membrane-
membrane interactions specific to these cells including those occurring
during degranulation, phagocytosis, phagolysosome fusion, and motility.
Future Directions
PMN CapZ
The physiological relevance of the Kd determined for capZ's
interaction with the barbed end is limited unless the concentration and
intracellular localization of this protein in PMN is established. Future
studies are directed at quantifying the amount of this protein in PMN.
Several approaches can be used to attain this value. With thymosin f>4,
the cytoplasmic concentration in PMN was estimated by the quantity of
protein purified from a known packed cell volume using a previously
established cytoplasmic volume for PMN (Cassimeris et al., 1992). The
purification of capZ, although, involves many more chromatographic steps
allowing ample opportunity for proteolytic degradation. Additionally, the
purified capZ would represent a small fraction of the amount originally

140
present in extracts if my purification scheme were used (degradation and
selection of highly pure fractions at each stage). The most practical
estimation of capZ concentrations can be achieved using an analysis
similar to that employed for annexin VI (Chapter 5). This experiment is
currently being conducted by Dr. Mark DiNubile (Cooper Hospital /
University Medical Center, Camden, NJ) with the purified PMN capZ due to
the limited availability of antisera. Once the concentration of capZ in PMN
is established, the physiological relevance of the in vitro capping function
can be further addressed.
The development of antibodies with higher affinity to human capZ
would be beneficial, as the antibodies currently available have poor inter-
species reactivities and their quantities are limited. The cDNA sequences
coding both subunits of human capZ were recently isolated from a human
retinal cDNA library (Barron-Casella & Casella, 1993). Sufficient quantities
of pure capZ necessary for the production of high affinity antisera can
easily be obtained through recombinant expression of this protein in £
coii.
Monoclonal antibodies can be generated, selecting for hybridoma
clones producing antibodies suitable for immunoprecipitation or
immunolocalization studies. The intracellular localization and relative
distribution of capZ in resting and stimulated PMN can be followed by
indirect immunofluorescence microscopy. Colocalization with actin would
support an in vivo actin function of capZ. The presence of capZ in actin
rocket tails formed by Listeria can also be evaluated by the same
technique. Immunoprecipitation of capZ from extracts would be useful in
monitoring potential post-translation modifications that may occur as a
result of stimulation of PMN. It has been previously established that many

141
proteins are phosphorylated in response to fMLP activation (Andrews &
Babior, 1983). Although PKC does not appear important in the regulation
of the rapid actin filament response in fMLP stimulated PMN (Chapter 1),
phosphorylation by any of the other cellular kinases may indirectly
regulate this response through phosphorylation of those proteins directly
involved in regulating the actin polymerization. Additionally,
immunodepletion of capZ from PMN extracts would enable an estimation
of its contribution to the calcium independent capping activity found in
PMN extracts. Lastly, this technique could be used as an alternative
method to purify capZ from cells.
When PMN are stimulated by fMLP and subsequently lysed, the actin
nucleating activity in the detergent insoluble fraction (cytoskeleton)
increases (presumably due to uncapping of filaments). If capZ blocks
filament ends in resting PMN and loses this ability upon stimulation, a
shift from the triton insoluble to the soluble fraction would be detectable
by Western analysis.
If the cDNA's for the two subunits of capZ were obtained, a variety
of studies could be developed to further analyze the in vivo role of capZ in
cells. Antisense RNA studies inhibiting the translation of one or both
subunits in cells would enable one to address two major questions. First,
is capZ vital for maintaining the cytoarchitecture in cells. The effects of
antisense transfections would be monitored by light microscopy and
indirect immunofluorescence microscopy probing for known cytoskeletal
elements such as actin. Secondly, if a morphological change is observed,
the necessity of each subunit can be tested. Overexpression of capZ can
also be monitored as described above for antisense RNA studies.
Additionally, transgenic mouse studies can be done. This technique has

142
proved helpful in clarifying gelsolin's in vivo function (Witke et al., 1993).
In a similar fashion, the gene/genes for capZ can be knocked out. If a
homozygote lacking capZ expression appears grossly normal, phenotypical
differences in this transgenic mouse and the gelsolin-minus mouse can be
studied. Would the motile function of PMN be altered? Would the PMN be
able to produce a rapid doubling of F-actin in response to
chemoattractants? If it is found that transgenic mice are never produced,
suggesting inviability, knock outs for each particular subunit can be
attempted. Because chemoattractant stimulated actin assembly is Ca^+-
independent, loss of capZ may have profound effects on chemotaxis. Each
of the studies described above would greatly enhance the proposal that
capZ is a key regulator in the actin-based motility of PMN.
PMN Annexin VI
Future studies regarding the function of annexin VI in PMN include
the search for membrane compartments which this protein may
specifically bind. Neutrophils have two major types of intracellular
vesicles (azurophil and specific granules). The killing and digestion of
phagocytosed organisms by PMN is dependent upon the fusion of
phagocytic vesicle membranes with the granules. Additionally, the
secretion of vesicle contents into the extracellular milieu necessitates a
regulated interaction with the cytoplasmic membrane.
Immunolocalization of annexin VI during such processes may suggest an
in vivo role for this abundant PMN protein.
The differential expression of annexin VI in HL-60 induced to
differentiate must be further explored. Treating cells on the third day of
differentiation (maximal difference in annexin VI mRNA observed) with

143
the transcriptional inhibitor actinomycin D should delineate in each
differentiation pathway if the changes in annexin VI mRNA expression is
due to regulation at the transcriptional level. If one finds that such
changes are transcriptionally regulated, the necessity of protein synthesis
for this level of regulation can be addressed with transient treatment of
the induced cells with translational inhibitors. Conversely, if actinomycin
D treatment does not affect the levels of mRNA seen in differentiated cells
it can be speculated that the expression of annexin VI mRNA is regulated
by other mechanisms (e. g. stabilization or compartmentalization of
mRNA). The precise regulatory mechanisms involved in the
differentiation of HL-60 cells are important to our understanding of how
stem cells cease to proliferate and go on to differentiate. These
mechanisms have obvious implications in terms of the pathogenesis and
evolution of cancer, particularly myeloid leukemias. A deeper
understanding of the regulation of annexin VI mRNA expression in HL-60
cells is therefore worthy of further pursuit.

REFERENCES
Amatruda, J. F., and Cooper, J. A. 1992. Purification,
characterization, and immunofluorescence localization of Saccharomyces
cerevisiae capping protein. J. Cell Biol. 117: 1067-1076
Anderson, T., Dahlgren, C., Pozzan, T., Stendahl, O., and Lew, D. P.
1986. Characterization of fMet-Leu-Phe receptor-mediated Ca^+ influx
across the plasma membrane of human neutrophils. Mol. Pharm. 30: 437
Andrews, P. C., and Babior, B. M. 1983. Endogenous protein
phosphorylation by resting and activated human neutrophils. Blood 61:
333-340
Ankenbauer, T., Kleinschmidt, J. A., Walsh, M. J., Weiner, O. H., and
Franke, W. W. 1989. Identification of a widespread nuclear actin binding
protein. Nature 342: 822-826
Bainton, D. F. 1992. Developmental biology of neutrophils and
eosinophils. In: Inñammation: basic principles and clinical correlates, 2nd
Ed., Eds: Gallin, J. I., Goldstein, I. M., and Snyderman, R. Raven Press, New
York
Barkalow, K., and Hartwig, J. H. 1994. Identification of a calcium
independent actin filament capping activity in human platelets. Mol. Biol.
Cell Vol. 5, abstract 1580
Barron-Casella, E. A., and Casella, J. F. 1993. Sequence analysis of
human capZ. Mol. Biol. Cell Vol. 4, abstract 1496
Becker, E. L. 1987. The formyl peptide receptor of the neutrophil. A
search and conserve operation. Am. J. Pathol. 129: 16-24
Becker, E. L., Kermode, J. C., Naccache, P. H., Yassin, R., Marsh, M. L.,
Munoz, J. J., and Sha'afi, R. I. 1985. The inhibition of neutrophils granule
enzyme secretion and chemotaxis by pertussis toxin. J. Cell Biol. 100:
1641-1646
144

145
Bengtsson, T., Stendahl, 0., and Anderson, T. 1986. The role of the
cytosolic free Ca^+ transient for fMet-Leu-Phe induced actin
polymerization in human neutrophils. Eur. J. Cell Biol. 422: 338-343
Blackwood, R. A., and Ernst, J. D. 1990. Characterization of Ca^+-
dependent phospholipid binding, vesicle aggregation and membrane
fusion by annexins. Biochem. J. 266: 195-200
Bonder, E. M., Fishkind, D. J., and Mooseker, M. S. 1983. Direct
measurement of critical concentrations and assembly rate constants at the
two ends of actin filaments. Cell 34: 491-501
Boonen, G. J., deKoster, B. M., Vansteveninck, J., and Elferink., J. G.
1993. Neutrophil chemotaxis induced by the diacylglycerol kinase
inhibitor R59022. Biochim. Biophys. Acta. 1178: 97-102
Boulay, F., Tardif, M., Brouchon, L., and Vignais, P. 1990. Synthesis
and use of a novel N-formyl peptide derivative to isolate a human N-
formyl peptide receptor cDNA. Biochem. Biophys. Res. Commun. 29:
11123-11133
Boyles, J., and Bainton, D. F. 1981. Changes in plasma-membrane-
associated filaments during endocytosis and exocytosis in
polymorphonuclear leukocytes. Cell. 24: 905-914
Brandt, S. J., Dougherty, R. W., Lapetina, E. G., and Niedel, J. E. 1985.
Pertussis toxin inhibits chemotactic peptide-stimulated generation of
inositol phosphates and lysosomal enzyme secretion in human leukemic
(HL-60) cells. Proc. Natl. Acad. Sci. 82: 3277-3280
Bretscher, A. 1991. Microfilament structure and function in the
cortical cytoskeleton. Annu. Rev. Cell Biol. 7: 337-374
Caldwell, J. E., Heiss, S. G., Mermall, V., and Cooper, J. A. 1989a.
Effects of capZ, an actin capping protein of muscle, on the polymerization
of actin. Biochemistry 28: 8506-8514
Caldwell, J. E., Waddle, J. A., Cooper, J. A., Hollands, J. A., Casella, S.
J., and Casella, J. F. 1989b. cDNAs encoding the 13 subunit of capZ, the
actin-capping protein of the Z line of muscle. J. Biol. Chem. 264: 12648-
12652
Carlier, M. F. 1991. Actin: protein structure and filament dynamics.
J. Biol. Chem. 266: 1-4

146
Carlier, M. F., and Pantaloni, D. 1986. Direct evidence for ADP-Pi-F-
actin as the major intermediate in ATP-actin polymerization. Rate of
dissociation of Pi from actin filaments. Biochemistry 25: 7789-7792
Carlier, M. F., Pantaloni, D., and Korn, E. D. 1984. Evidence for an
ATP cap at the ends of actin filaments and its regulation of the F-actin
steady state. J. Biol. Chem. 259: 9983-9986
Carlier, M. F., Pantaloni, D., and Korn, E. D. 1987. The mechanisms
of ATP hydrolysis accompanying the polymerization of Mg-actin and Ca-
actin. J. Biol. Chem. 262: 3052-3059
Carlsson, L, Nystrom, L. E., Sundkvist, I., Markey, F., and Lindberg,
U. 1977. Actin polymerizability is influenced by profilin, a low molecular
weight protein in non-muscle cells. J. Mol. Biol. 115: 465-483.
Carson, M., Weber, A., and Zigmond, S. 1986. An actin-nucleating
activity in polymorphonuclear leukocytes is modulated by chemotactic
peptides. J. Cell Biol. 103: 2707-2714
Casella, J. F., Craig, S. W., Maack, D. J., and Brown, A. E. 1987. CapZ
(36/32), a barbed end actin-capping protein, is a component of the Z-line
of skeletal muscle. J. Cell Biol. 105: 371-379
Casella, J. F., Maack, D. J., and Lin S. 1986. Purification and initial
characterization of a protein from skeletal muscle that caps the barbed
ends of actin filaments. J. Biol. Chem. 261: 10915-10921
Cassimeris, L., McNeill, H., and Zigmond, S. H. 1990.
Chemoattractant-stimulated polymorphonuclear leukocytes contain two
populations of actin filaments that differ in their spatial distributions and
relative stabilities. J. Cell Biol. 110: 1067-1075
Cassimeris, L., Safer, D., Nachmias, V. T., and Zigmond, S. H. 1992.
Thymosin R4 sequesters the majority of G-actin in resting human
polymorphonuclear leukocytes. J. Cell Biol. 119: 1261-1270
Castagna, M., Yoshima, T., Kaibachi, S., Kikkawa, U., and Nishizuka,
Y. 1982. Direct activation of calcium-activated , phospholipid-dependent
protein kinase by tumour-promoting phorbol esters. J. Biol. Chem., 257:
7847-7851
Caterina, M. J., and Devreotes, P. N. 1991. Molecular insights into
eukaryotic chemotaxis. FASEB. 5: 3078-3085

147
Chomczynski, P., and Sacchi, N. 1987. Single-step method of RNA
isolation by acid guanidinium thiocyanate-phenol-chloroform extraction.
Anal. Biochem. 162: 156-159
Cockcroft, S., Barrowman, M. M., and Gomperts, B. D., 1985.
Breakdown and synthesis of polyphosphoinositides in fMet-Leu-Phe
stimulated neutrophils. FEBS Lett. 181: 259-263
Collins, S. J. 1987. The HL-60 promyelocytic leukemia cell line:
proliferation, differentiation, and cellular oncogene expression. Blood 70:
1233-1244
Condeelis, J. 1993. Life at the leading edge: The formation of cell
protrusions. Annu. Rev. Cell Biol. 9: 411-44
Cooper, J. A., Walker, S. B., and Pollard, T. D. 1983. Pyrene actin:
documentation of the validity of a sensitive assay for actin polymerization.
J. Muscle Res. Cell Mot. 4: 253-262
Creutz, C. E., 1992. The annexins and exocytosis. Science 258: 924-
930
Crompton, M. R., Owens, R. J., Totty, N. F., Moss, S. E., Waterfield, M.
D., and Crumpton, M. J. 1988. Primary structure of the human, membrane-
associated Ca2+-binding protein p68: a novel member of a protein family.
EMBOJ. 7: 21-27
Dabiri, G. A., Young, C. L., Rosenbloom, J., and Southwick, F. S. 1992.
Molecular cloning of human macrophage capping protein cDNA. J. Biol.
Chem. 267: 16545-16552
Dancey, J. T., Deubelbeiss, K. A., Harker, L. A., and Finch, C. A. 1976.
Neutrophil kinetics in man. J. Clin. Invest., 58: 705-715
Datar, K. V., Dreyfuss, G., and Swanson, M. S. 1993. The human
hnRNP M proteins: identification of a methionine/arginine-rich repeat
motif in ribonucleoproteins. Nucleic Acids Res. 21: 439-446
DiNubile, M. J., and Southwick, F. S. 1985. Effects of macrophage
profilin on actin in the presence and absence of acumentin and gelsolin. J.
Biol. Chem. 260: 7402-7409
Dohlman, H. G., Thorner, J., Caron, M. G., and Lefkowitz, R. J. 1991.
Model systems for the study of seven-transmembrane-segment receptors.
Annu. Rev. Biochem. 60: 653-688

148
Downey, G. P., Chan, C. K., Trudel, S., and Grinstein, S. 1990. Actin
assembly in electropermeabilized neutrophils: role of intracellular
calcium. J. Cell Biol. 110: 1975-1982
Eberle, M., Traynor-Kaplan, A. E., Sklar, L. A., and Norgauer, J. 1990
Is there a relationship between phosphatidylinositol triphosphate and F-
actin polymerization in human neutrophils? J. Biol. Chem. 265: 16725-
16728
Eddy, R. J., Sauterer, R. A., Hug, C., Cooper, J. A., and Condeelis, J. S.
1993. Aginactin contains a 2:1 complex of HSC70 and cap 32/34 and is
dependent on HSC70 through its ATP binding domain. Mol. Biol. CellVol.
4, abstract 1492
Elferink, J. G. R., and Deierkauf, M., 1985. The effect of quin2 on
chemotaxis by polymorphonuclear leukocytes. Biochim. Biophys. Acta.
846: 364-369
Ernst, J. D. 1991. Annexin III translocates to the periphagosomal
region when neutrophils ingest opsonized yeast. J. Immunol. 146: 3110-
3114
Ernst, J. D., Hoye, E., Blackwood, A.,and Jaye, D. 1990. Purification
and characterization of an abundant cytosolic protein from human
neutrophils that promotes Ca2+-dependent aggregation of isolated specific
granules. J. Clin. Invest. 85: 1065-1071
Estes, J. E. 1992. Tightly bound divalent cation of actin. J. Muscle
Res. Cell. Mot. 13: 272-284.
Fechheimer, M., and Zigmond, S. H. 1983. Changes in cytoskeletal
proteins of polymorphonuclear leukocytes induced by chemotactic
peptides. Cell Motility. 3: 349-361
Feltner, D. E., Smith, R. H., and Marasco, W. A. 1986.
Characterization of the plasma membrane GTPase from rabbit neutrophils.
I. Evidence for an Ni-like protein coupled to the formyl peptide, C5a, and
leukotriene B4 chemotaxis receptors. J. Immunol. 137: 1961-1970
Frieden 1982. The Mg2+-induced conformation change in rabbit
skeletal muscle G-actin. J. Biol. Chem. 257: 2882-2886

149
Gallagher, R., Collins, S., Trujillo, J., McCredie, K., Aheam, M., Tsai,
S., Metzgar, R., Aulakh, G., Ting, R., Ruscetti, F., and Gallo, R. 1979.
Characterization of the continuous differentiating myeloid cell line (HL-
60) from a patient with acute promyelocytic leukemia. Blood 54: 713-733
Gallin, J. I. 1988. The Neutrophil. In: Immunological diseases, 4th
Ed., Eds: Samter, M., Talmage, D. W., Frank, M. M., Austen, K. F., and
Claman, H. N. Little Brown & Co., Boston
Garrels, J. I., and Gibson, W. 1976. Identification and
characterization of multiple forms of actin. Cell 9: 793-805
Geisow, M. J., and Burgoyne, R. D. 1982. Calcium-dependent binding
of cytosolic proteins by chromaffin granules from adrenal medulla. J.
Neurochem. 38: 1735-1741
Glenney, J. R., Tack, B., and Powell, M. A. 1987. Calpactins: two
distinct Ca++-regulated phospholipid- and actin-binding proteins isolated
from lung and placenta. J. Cell Biol. 104: 503-511
Golde, D.W. 1990. Production, distribution, and fate of neutrophils.
In: Hematology, 4th Ed., McGraw-Hill, Inc., Ohio
Goldschmidt-Clermont, P. J., Machesky, L. M., Doberstein, S. K., and
Pollard, T. D. 1991. Mechanism of the interaction of human platelet
profilin with actin. J. Cell Biol. 113: 1081-1089
Hartwig, J. H., and Kwiatkowski, D. J. 1991. Actin-binding proteins.
Cum Opin. Cell Biol. 3: 87-97
Hatano, S., and Oosawa, F. 1966. Extraction of an actin-like protein
from the plasmodium of a myxomycete and its interaction with myosin. A.
J. Cell. Physiol. 68: 197-202
Haus, U., Hartmann, H., Trommler, P., Noegel, A. A., and Schleicher,
M. 1991. F-actin capping by cap32/34 requires heterodimeric
conformation and can be inhibited with PIP2. Biochem. Biophys. Res.
Comm. 181: 833-839
Hayashi, H., Owada, M. K., Sonobe, S., and Kakunaga, T. 1989.
Characterizations of two distinct Ca^+ -dependent phospholipid-binding
proteins of 68-kDa isolated from human placenta. J. Biol. Chem. 264:
17222-17230.

150
Heiss, S. G., and Cooper, J. A. 1991. Regulation of capZ, an actin
capping protein of chicken muscle, by anionic phospholipids. Biochemistry
30: 8753-8758
Herman, I. M., 1993. Actin isoforms. Curr. Opin. Cell Biol. 5, 48-55
Hill, M. A., and Gunning, P., 1993. Beta and gamma actin mRNAs are
differentially located within myoblasts. J. Cell Biol. 122: 825-832
Hitchcock, S. E. 1980. Actin-deoxyribonuclease I interaction.
Depolymerization and nucleotide exchange. J. Biol. Chem. 255: 5668-5673
Holmes, K. C., Popp, D., Gebhard, W., and Kabsch, W. 1990. Atomic
model of the actin filament. Nature 347: 44-49
Hosoya, H., Kobayashi, R., Tsukita, S., and Matsumura, F. 1992.
Ca2+-regulated actin and phospholipid binding protein (68kD-protein)
from bovine liven identification as a homologue for annexin VI and
intracellular localization. Cell Motil. Cyto. 22: 200-210
Howard, T. H. and Meyer, W. H. 1984. Chemotactic peptide
modulation of actin assembly and locomotion in neutrophils. J. Cell Biol.
98: 1265-1271
Howard, T. H., and Oresajo, C. O. 1985. The kinetics of chemotactic
peptide-induced changes in F-actin content, F-actin distribution, and the
shape of neutrophils. J. Cell Biol. 101: 1078-1085
Howard, T. H., and Wang, D. 1987. Calcium ionophore, phorbol
ester, and chemotactic peptide-induced cytoskeleton reorganization in
human neutrophils. J. Clin. Invest. 79: 1359-1364
Huxley, H. E. 1963. Electron microscope studies on the structure of
natural and synthetic protein filaments from striated muscle. J. Mol. Biol.
7: 281-308
Isenberg, G. 1991. Actin-binding protein-lipid interactions. Cell
Motil. Cytoskeleton 12: 136-44
Isenberg, G., Aebi, U., and Pollard, T. 1980. An actin-binding protein
from Acanthamoeba regulates actin filament polymerization and
interactions. Nature 288: 455-459

151
Jaconi, M. E., Lew, D. P., Carpentier, J. L., Magnusson, K. E., Sjogren,
M., and Stendahl, 0. 1990. Cytosolic free calcium elevation mediates the
phagosome-lysosome fusion during phagocytosis in human neutrophils. J.
Cell Biol. 110: 1555-1564
Janmey, P. A. 1994. Phosphoinositides and calcium as regulators of
cellular actin assembly and disassembly. Annu. Rev. Physiol. 56: 169-191
Janmey, P. A., and Stossel, T. P. 1989. Gelsolin-polyphosphoinositide
interaction. J. Biol. Chem. 264: 4825-4831
Janmey, P. A., Chaponnier, C, Lind, S. E., Zaner, R. S., Stossel, T. P.
and Yin, H. L. 1985. Interaction of gelsolin and gelsolin-actin complexes
with actin. Effects of calcium on actin nucleation, filament severing, and
end blocking. Biochemistry. 24: 3714-3723
Kabsch, W., Mannherz, H. G., Suck, D., Pai, E. F., and Holmes, K. C.
1990. Atomic structure of the actin:DNase I complex. Nature 347: 37-44
Kaziro, Y., Itoh, H., Kozasa, T., Nakafuku, M., and Satoh, T. 1991.
Structure and function of signal-transducing GTP-binding proteins. Annu.
Rev. Biochem. 60: 349-400
Keller, H. U., and Niggli, V. 1993. The PKC-inhibitor Ro 31-9220
selectively surpresses PMA- and diacyglycerol-induced fluid pinocytosis
and actin polymerization in PMNs. Biochem. Biophys. Res. Commun. 194:
1111-1116
Kilimann, M. W., and Isenberg, G. 1982. Actin filament capping
protein from bovine brain. EMBO J. 1: 889-894
Klee, C. B. 1988. Ca2+-dependent phospholipid- (and membrane-)
binding proteins. Biochemistry 27: 6645-6653
Korn, E. D., 1982. Actin polymerization and its regulation by
proteins from nonmuscle cells Physiol. Rev. 62: 612-Til
Korn, E. D., Carlier, M. F., and Pantaloni, D. 1987. Actin
polymerization and ATP hydrolysis. Science 238: 638-644
Kouyama, T., and Mihashi, K. 1981. Fluorimetry Study of N-(l-
Pyrenyl)iodoacetamide-labelled F-actin. Fur. J. Biochem. 114: 33-38
Kwiatkowski, D. J., and Bruns, G. A. P. 1988. Human profilin:
molecular cloning, sequence comparison, and chromosomal analysis. J.
Biol. Chem. 263: 5910-5915

152
Kwiatkowski, D. J., Stossel, T. P., Orkin, S. H., Mole, J. E., Colten, H. R.,
and Yin, H. L. 1986. Plasma and cytoplasmic gelsolins are encoded by a
single gene and contain a duplicated acdn-binding domain. Nature 323:
455-457.
Larsson, H., and Lindberg, U. 1988. The effect of divalent cations on
the interaction between calf spleen profilin and different actins. Biochim.
Biophys. Acta. 953: 95-105
Lassing, L, and Lindberg, U. 1985. Specific interaction between
phosphatidylinositol 4,5-bisphosphate and profilactin. Nature 314: 472-
474
Lew, P. D., Monod, A., Waldvogel, F. A., Dewald, B., Baggiolini, M.,
and Pozzan, T. 1986. Quantitative analysis of the cytosolic free calcium
dependency of exocytosis from three subcellular compartments in intact
neutrophils. J. Cell Biol. 102: 2197-2204
Lew, P., Wollheim, F., Waldvogel, F., and Pozzan, T. 1984.
Modulation of cytosolic free-calcium transients by changes in intracellular
calcium-buffering. Correlation with exocytosis and 02' production in
human neutrophils. J. Cell Biol. 99: 1212-1220
Lin, S. C., Aebersold, R. H., Kent, S. B., Varma, M., and Leavitt, J.
1988. Molecular cloning and characterization of plastin, a human
leukocyte protein expressed in transformed human fibroblasts. Mol. Cell.
Biol. 8: 4659-4668
Lind, S. E., Janmey, P. A., Chaponnier, C., Herbert, T. J., and Stossel,
T. P. 1987. Reversible binding of actin to gelsolin and profilin in human
platelet extracts. J. Cell Biol. 105: 833-842
Lofgren, R., Ng-Sikorski, J., Sjolander, A., and Andersson, T. 1993. 82
integrin engagement triggers actin polymerization and
phosphatidylinositol triphosphate formation in non-adherent human
neutrophils. J. Cell Biol. 123: 1597-1605
MacLean-Fletcher, S. D., and Pollard, T. D. 1980. Viscometric
analysis of gelation of Acanthamoeba extracts. J. Cell Biol. 85: 414-428
Mannherz, H. G. 1992. Crystallization of actin in complex with acdn-
binding proteins. J. Biol. Chem. 267: 11661-11664
Mannherz, H. G., Goody, R. S., Konrad, M., and Nowak, E. 1980. The
interaction of bovine pancreatic deoxyribonuclease I and skeletal muscle
actin. Eur. J. Biochem. 14: 367-379

153
Markey, F., Lindberg, U., and Eriksson, L. 1978. Human platelets
contain profilin, a potential regulator of actin polymerisability. FEBS Lett.
88: 75-79
Marks, P. W., and Maxfield, F. R. 1990. Transient increases in
cytosolic free calcium appear to be required for the migration of adherent
human neutrophils. J. Cell Biol. 110: 43-52
Maruyama, K., Kurokawa, H., Oosawa, M., Shimaoka, S., Yamamoto,
H., Ito, M., and Maruyama, K. 1990. K-actinin is equivalent to capZ protein.
J. Biol. Chem. 265: 8712-8715
Meers, P., Ernst, J. D., Duzgunes, N., Hong, K., Fedor, J., Goldstein, 1.
M., and Papahadjopoulos, D. 1987. Synexin-like proteins from human
polymorphonuclear leukocytes. J. Biol. Chem. 262: 7850-7858
Meshulam, T., Proto, P., Diamond, R. D., and Melnick, D. A. 1986.
Calcium modulation and chemotactic response: divergent stimulation of
neutrophil chemotaxis and cytosolic calcium response by the chemotactic
peptide receptor. J. Immunol. 137: 1954-1960
Mishra, V. S., Henske, E. P., Kwiatkowski, D. J., and Southwick, F. S.
1994. The human actin-regulatory protein cap G: gene structure and
chromosome location. Genomics 23: 560-565
Mockrin, S. C., and Korn, E. D. 1980. Acanthamoeba profilin
interacts with G-actin to increase the rate of exchange of actin-bound
adenosine 5'-triphosphate. Biochemistry 19: 5359-5362
Mozdzanowski, J., Hembach, P., and Speicher, D. W. 1992. High yield
electroblotting onto polyvinlidene difluoride membranes from
polyacrylamide gels. Electrophoresis 13: 59-64
Nachmias, V. T. 1993. Small actin-binding proteins: the 8-thymosin
family. Curr. Opin. Cell Biol. 5: 56-62
Nachmias, V. T., Golla, R., Casella, J. F., and Barron-Casella, E. 1994.
CapZ in human platelets. Mol. Biol. CellVol. 5, abstract 1579
Namba, Y., Ito, M., Zu, Y., Shigesada, K., and Maruyama, K. 1992.
Human T cell L-plastin bundles actin filaments in a calcium-dependent
manner. J. Biochem. 112: 503-507
Neuhaus, J. M., Wanger, M., Keisler, T., and Wegner, A. 1983.
Treadmilling of actin. J. Muscle Res. Cell Motil. 4: 507-527

154
Niggli, V., and Keller, H., 1991. On the role of protein kinases in
regulating neutrophil actin association with the cytoskeleton. J. Biol.
Chem. 266: 7927-7932
Nishihira, J., McPhail, L. C., and O'Flaherty, J. T. 1986. Stimulus
dependent mobilization of protein kinase C. Biochem. Biophys. Res.
Commun. 134: 587-594
Omann, G. M, and Porasik-Lowes, M. M. 1991. Graded G-protein
uncoupling by pertussis toxin treatment of human polymorphonuclear
leukocytes. J. Immunol. 146: 1303-1308
Omann, G. M., Allen, R. A., Bokoch, G. M., Painter, R. G., Traynor, A.
E., and Sklar, L. A. 1987. Signal transduction and cytoskeletal activation in
the neutrophil. Physiol. Rev. 67: 285-322
Pacaud, M., and Derancourt, J. 1993. Purification and further
characterization of macrophage 70-kDa protein, a calcium-regulated,
actin-binding protein identical to L-plastin. Biochemistry 32: 3449-3455
Pepinsky, R. B., Tizard, R., Mattaliano, R. J., Sinclair, L. K., Miller, G.
T., Browining, J. L., Chow, E., Burne, C., Huang, K. S., Pratt, D., Wachter, L.,
Hession, C., Frey, A. Z., and Wallner, B. P. 1988. Five distinct calcium and
phospholipid binding proteins share homology with lipocortin I. J. Biol.
Chem. 263: 10799-10811
Pollard, T. D. 1984. Polymerization of ADP-actin. J. Cell Biol. 99:
769-777
Pollard, T. D., 1990. Actin. Curr. Opin. Ceil Biol. 2: 33-40
Pollard, T. D., and Cooper, J. A., 1986. Actin and actin-binding
proteins. A critical evaluation of mechanisms and functions. Ann. Rev.
Biochem. 55: 987-1035
Pollard, T. P. 1986. Rate constants for the reactions of ATP- and
ADP-actin with the ends of actin filaments. J. Cell Biol. 103: 2747-2754
Pryzwansky, K. B., Schliwa, M., and Porter, K. R. 1983. Comparison of
the three-dimensional organization of unextracted and triton-extracted
human neutrophilic polymorphonuclear leukocytes. Eur. J. Cell Biol. 30:
112-125
Reim, D. F., Hembach, P., and Speicher, D. W. 1992. Techniques in
Protein Chemistry III, Academic Press, NY, 53-60

155
Rosales, C., Jones, S. L, McCourt, D., and Brown, E. J. 1994.
Bromophenacyl bromide binding to the actin-bundling protein 1-plastin
inhibits inositol triphosphate-independent increase in Ca^+ in human
neutrophils. Proc. Natl. Acad. Sci. 91: 3534-3538
Safer, D. 1989. An electrophoretic procedure for detecting proteins
that bind actin monomers. Anal. Biochem. 178: 32-37
Safer, D., Elzinga, M., and Nachmias, V. T. 1991. Thymosin M and
Fx, an actin-sequestering peptide, are indistinguishable. J. Biol. Chem. 268:
4029-4032
Safer, D., Golla, R., and Nachmias, V. 1990. Isolation of a 5-
kilodalton actin-sequestering peptide from human blood platelets. Proc.
Natl. Acad. Sci. 87: 2536-2540
Sanger, J. W., Sanger, J. M., Kreis, T. E., and Jockusch, B. M. 1980.
Reversible translocation of cytoplasmic actin into the nucleus caused by
dimethyl sulfoxide. Proc. Natl. Acad. Sci. 77: 5268-5272
Sauterer, R. A., Eddy, R. J., Hall, A. L, and Condeelis, J. S. 1991.
Purification and characterization of aginactin, a newly identified agonist-
regulated actin-capping protein from Dictyostelium amoebae. J. Biol.
Chem. 266: 24533-24539
Schafer, D. A., Mooseker, M. S., and Cooper, J. A. 1992. Localization
of capping protein in chicken epithelial cells by immunofluorescence and
biochemical fractionation. J. Cell Biol. 118: 335-346
Schevzov, G., Lloyd, C., and Gunning, P., 1992. High level expression
of transfected B- and gamma-actin genes differentially impacts on
myoblast cytoarchitecture. J. Cell Biol. 117: 775-785
Schleicher, M., Gerisch, G., and Isenberg, G. 1984. New actin-binding
proteins from Dictyostelium discoideum. EMBOJ. 3: 2095-2100
Schutt, C. E., Myslik, J. C., Rozycki, M. D., Goonesekere, N. C. W., and
Lindberg, U. 1993. The structure of crystalline profilin-13-actin. Nature
365: 810-816
Selden, L. A., Estes, J. E., and Gershman, L. C. 1983. Biochem
Biophys. Res., Commun. 116: 478-485
Selden, L. A., Gershman, L. C., and Estes, J. E. 1986. A kinetic
comparison between Mg-actin and Ca-actin. J. Muscle Res. Cell Mot. 7: 215-
224

156
Sha'afi, R. I., Shefcyk, J., Yassin, R., Molski, T. F. P., Volpi, M.,
Naccache, P. H., White, J. R., Feinstein, M. B., and Becker, E. L. 1986. Is a
rise in intracellular concentration of free calcium necessary or sufficient
for stimulated cytoskeletal-associated actin? J. Cell Biol. 102: 1459-1463
Shalit, M., Dabiri, G. A., and Southwick, F. S. 1987. Platelet-activating
factor both stimulates and "primes" human polymorphonuclear leukocyte
actin filament assembly. Blood. 70: 1921-1927
Sham, R. L., Phatak, P. D., Ihne, T. P., Abboud, C. N., and Packman, C.
H. 1993. Signal pathway regulation of interleukin-8-induced actin
polymerization in neutrophils. Blood. 82: 2546-2551
Sheterline, P., Rickard, J. E., and Richards, R. C. 1984a. Fc receptor-
directed phagocytic stimuli induce transient actin assembly at an early
stage of phagocytosis in neutrophil leukocytes. Eur. J. Cell Biol. 34: 80
Sheterline, P., Rickard, J. E., and Richards, R. C. 1984b. Involvement
of the cortical actin filament network of neutrophil leukocytes during
phagocytosis. Biochem. Soc. Transac. 12: 983-987
Sklar, L. A., Bokoch, G. M, Button, D., and Smolen, J. E. 1987.
Regulation of ligand-receptor dynamics by guanine nucleotides: real-time
analysis of interconverting states for the neutrophil formylpeptide
receptor. J. Biol. Chem. 262: 135-139
Snyderman, R., and Uhing, R. J. 1992. Chemoattractant stimulus-
response coupling. In: Inflammation: basic principles and clinical
correlates 2nd Ed., Eds: Gallin, J. I., Goldstein, I. M., and Snyderman, R.
Raven Press, New York
Southwick, F. S., Dabiri, G. A., Paschetto, M., and Zigmond, S. H.
1989. Polymorphonuclear leukocyte adherence induces actin
polymerization by a transduction pathway which differs from that used by
chemoattractants. J. Cell Biol. 109: 1561-1569
Southwick, F. S., and DiNubile, M. J. 1986. Rabbit alveolar
macrophages contain a Ca2+-sensitive, 41,000-dalton protein which
reversibly blocks the "barbed" ends of actin filaments but does not sever
them. J. Biol. Chem. 261: 14191-14195
Southwick, F. S., and Purich, D. L. 1994. Dynamic remodeling of the
actin cytoskeleton: Lessons learned from Listeria locomotion. BioEssays 16:
885-891

157
Southwick, F. S., and Young, C. L. 1990. The actin released from
profilin-actin complexes is insufficient to account for the increase in F-
actin in chemoattractant-stimulated polymorphonuclear leukocytes. J. Cell
Biol. 110: 1965-1973
Spudich, J. A., and Watt, S. 1971. J. Biol. Chem. 246: 4866-4871
Stossel, T. P. 1989. From signal to pseudopod. J. Biol. Chem. 264:
18261-18264
Stossel, T. P. 1992. The mechanical responses of white blood cells.
In: lnfíammation: Basic principles and clinical correlates, 2nd Ed., Eds:
Gallin, J. I., Goldstein, J. M, and Snyderman, R. Raven Press, Ltd., New York
Stossel, T. P. 1993. On the crawling of animal cells. Science 260,
1086-1094
Stossel, T. P., Chaponnier, C., Ezzell, R. M., Hartwig, J. H., Janmey, P.
A., Kwiatkowski, D. J., Lind, S. E., Smith, D. B., Southwick, F. S., Yin, H. L.,
and Zaner, K. S. 1985. Nonmuscle actin-binding proteins. Ann. Rev. Cell
Biol. 1: 353-402
Straub, F. B. 1942. Actin Studies, University of Szeged II: 3-15
Sudhof, T. C., Slaughter, C. A., Leznicki, L, Barjon, P., and Reynolds,
G. 1988. Human 67-kDa calelectrin contains a duplication of four repeats
found in 35-kDa lipocortins. Proc. Natl. Acad. Sci. 85: 664-668
Theriot, J. A., and Mitchison, T. J. 1993. The three faces of profilin.
Cell 75: 835-838
Towbin, H., Staehelin, T., and Gordon, J. 1979. Electrophoretic
transfer of proteins from polyacrylamide gels to nitrocellulose sheets:
procedures and some applications. Proc. Natl. Acad. Sci. 76: 4350-4354
Vandekerckhove, J., and Weber, K. 1978. At least six different actins
are expressed in higher mammals: An analysis based on the amino acid
sequence of the amino-terminal tryptic peptide. J. Mol. Biol. 122: 783 -
802
Vandekerckhove, J., and Weber, K. 1984. Chordate muscle actins
differ distinctly from invertebrate muscle actins. J. Mol. Biol. 179, 391-413
Vandekerckhove, J., Kaiser, D. A., and Pollard, T. D. 1989.
Acanthamoeba actin and profilin can be crosslinked between glutamic acid
364 of actin and lysine 115 of profilin J. Cell Biol. 109: 619-626

158
Verghese, M. W., Uhing, R. J., and Snyderman, R. 1986. A
pertussis/cholera toxin-sensitive N protein may mediate chemoattractant
receptor signal transduction. Biochem. Biophys. Res. Commun. 138: 887-
894
Walker, R. I., and Willemze, R. 1980. Neutrophil kinetics and the
regulation of granulopoiesis. Rev. Infect. Dis. 2: 282-292
Wallace, P. J., Westo, R. P., Packman, C. H., and Lichtman, M. A.
1984. Chemotactic peptide-induced changes in neutrophil actin
conformation. J. Cell Biol. 98: 214-221
Wang, Y. L. 1985. Exchange of actin subunits at the leading edge of
living fibroblasts: Possible role of treadmilling. J. Cell Biol. 101: 597-602
Wanger, M., Keiser, T., Neuhaus, J. M., and Wegner, A. 1985. The
actin treadmill. Can. J. Biochem. Cell. Biol. 63: 414-421
Weber, A., Nachmias, V. T., Pennise, C., Pring, M., and Safer, D. 1992.
Interaction of thymosin 84 with muscle and platelet actin: implications for
actin sequestration in resting platelets. Biochemistry 32: 6179-6185
Weeds, A., and Maciver, S. 1993. F-acdn capping proteins. Curr.
Opin. Cell Biol. 5: 63-69
White, J. R., Naccache, P. H., and Sha'afi, R. I. 1983. Stimulation by
chemotactic factor of actin association with the cytoskeleton in rabbit
neutrophils. J. Biol. Chem. 258: 14041-14047
Williams, W. J., Beutler, E., Erslev, A. J., and Lichtman, M. A. 1990.
Neutrophils, eosinophils, and basophils. In: Hematology, 4th Ed., McGraw-
Hill, Inc., Ohio
Wilson, S. M., Datar, K. V., Paddy, M. R., Swedlow, J. R., and Swanson,
M. S. 1994. Characterization of nuclear polyadenylated RNA-binding
proteins in Saccharomyces cerevisiae. J. Cell Biol. 127: 1173-1184
Witke, W., Sharpe, A. H., Hartwig, J., Azumi, T., Stossel, T. and
Kwiatkowski, D. J. 1993. Transgenic mice lacking gelsolin. Mol. Biol. Cell
Vol. 4, abstract 1483
Yin, H. L., Albrecht, J. H., and Fattoum, A. 1981. Identification of
gelsolin, a Ca++-dependent regulatory protein of actin gel-sol
transformation, and its intracellular distribution in a variety of cells and
tissues. J. Cell Biol. 91: 901-906

159
Yin, H. L, and Stossel, T. P. 1979. Control of cytoplasmic actin gel-
sol transformation by gelsolin, a calcium-dependent regulatory protein.
Nature. 281: 583-586
Young, C. L., Southwick, F. S., and Weber, A. 1990. Kinetics of the
interaction of a 41-kilodalton macrophage capping protein with actin:
promotion of nucleation during prolongation of the lag period.
Biochemistry 29: 2232-2240
Zigmond, S. H. 1977. The ability of polymorphonuclear leukocytes
to orient in gradients of chemotactic factors. J. Ceil Biol. 75: 606-616
Zigmond, S. H., and Hirsch, J. G. 1972. Effects of cytochalasin B on
polymorphonuclear leukocyte locomotion, phagocytosis and glycolysis.
Exp. Cell Res. 73: 383-393
Zigmond, S. H., Slonczewski, J. L, Wilde, M. W., and Carson, M. 1988.
Polymorphonuclear leukocyte locomotion is insensitive to lowered
cytoplasmic calcium levels. Cell Motil. Cytoskeleton. 9: 184-189
Zimmerle, C. T., and Frieden, C. 1986. Effect of temperature on the
mechanism of actin polymerization. Biochemistry 25: 6432-6438
Zimmerle, C. T., and Frieden, C. 1988. Effect of pH on the
mechanism of actin polymerization. Biochemistry 27: 7766-7772
Zu, Y., Shigesada, K., Nishida, E., Kubota, I., Kohno, M., Hanaoka, M.,
and Namba, Y. 1990. 65-kilodalton protein phosphorylated by interleukin
2 stimulation bears two putative actin-binding sites and two calcium¬
binding sites. Biochemistry 29: 8319-8324

BIOGRAPHICAL SKETCH
Noel Anthony Maun was born on October 14, 1968, in Belleville, IL.
He is married to Erica Boysen Maun, his high school sweetheart. After
graduating from Buchholz High School in 1986 (Gainesville, FL), he
attended the University of Florida. Noel was admitted to the Junior
Honors Medical Program, and subsequently went on to the UF College of
Medicine MD/PhD program. He joined Dr. Frederick S. Southwick's
laboratory in 1991 where the work described in this dissertation was
conducted. After graduating from the program, Noel will continue his
training in academic medicine at Yale University as a resident in Internal
Medicine.
160

I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of Doctor
of Philosophy.
and Molecular Biology
Daniel L. Punch, Chair
Professor of Biochemistry -
I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of Doctor
of Philosophy.
Frederick S. Southwick, Cochair
Professor of Molecular Genetics
and Microbiology
I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of Doctor
of Philosophy.
Henry V. Baker, II
Associate Professor of Molecular
Genetics and Microbiology
I certify that I have read this
conforms to acceptable standards of
adequate, in scope and quality, as a
of Philosophy.
study and that in my opinion it
scholarly presentation and is fully
dissertation for the degree of Doctor
Associate Professor of
Biochemistry and Molecular
Biology

I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertatipn for the degree of Doctor
of Philosophy.
Daniel J. Driscoll
Assistant Professor of Molecular
Genetics and Microbiology
This dissertation was submitted to the Graduate Faculty of the
College of Medicine and to the Graduate School and was accepted as
partial fulfillment of the requirements for the degree of Doctor of
Philosophy
May, 1995
/fy/i4&7í!7Á/¿
Dean, College of Medicine
Dean, Graduate School




2
similar process (Stossel, 1993). Our deeper understanding of the
molecular events involved may lead to a better understanding of the
biological processes which rely on cellular motility such as embryonic
development, inflammation, wound healing, tumor invasion, and host
defense. The work entailed in this dissertation centers around an actin
binding activity purified from human polymorphonuclear leukocytes
(PMN), one of the most highly motile animal cell types (10-20 pm/min)
(Howard & Meyer, 1984).
The Human Neutrophil
The neutrophil is one of the most motile cell types in the human
body; its primary purpose is to engulf and kill invading pathogens.
Histologically, polymorphonuclear granulocytes can be subdivided into
three distinct cell types named according to their staining characteristics;
the neutrophil (> 90 %), basophil, and eosinophil. Despite originating
from the same progenitor stem cell, each has a functionally distinct
immunological role (Williams et al., 1990). For the purposes of this
dissertation, the terms neutrophil, polymorphonuclear leukocyte (PMN),
and granulocyte will be used synonymously to denote neutrophil
leukocytes. In the normal human adult, the life span of the PMN is spent
in three environments: marrow, blood, and tissues (Bainton, 1992).
Proliferation and terminal differentiation occur primarily in the marrow
compartment over a period of approximately 10 days (Gallin, 1988). They
are subsequently released into the blood. This intravascular pool of
granulocytes representing only 5 % of the total number in the body is
equally divided between a freely circulating pool and a marginated pool


BIOGRAPHICAL SKETCH
Noel Anthony Maun was born on October 14, 1968, in Belleville, IL.
He is married to Erica Boysen Maun, his high school sweetheart. After
graduating from Buchholz High School in 1986 (Gainesville, FL), he
attended the University of Florida. Noel was admitted to the Junior
Honors Medical Program, and subsequently went on to the UF College of
Medicine MD/PhD program. He joined Dr. Frederick S. Southwick's
laboratory in 1991 where the work described in this dissertation was
conducted. After graduating from the program, Noel will continue his
training in academic medicine at Yale University as a resident in Internal
Medicine.
160


14
complicated topic will not be covered. Additionally, it is generally
accepted that Mg2+ is the divalent cation bound to actin in the cell.
Artin Rinding Proteins
Background
It was recognized early on that at least 50 % of the actin in extracts
from various non-muscle cells is nonpolymerized, in stark contrast to
muscle cells in which nearly 100 % of the actin is polymerized (Korn,
1982). Based on the earlier findings that nonmuscle isoforms of actin
share the same polymerization kinetics and critical concentrations as
muscle isoforms, it was hypothesized that the polymerization of actin in
nonmuscle cells was regulated through the interaction of actin with other
cellular components. This hypothesis was amply supported by the
identification of nonmuscle cell proteins that have specific interactions
with G-actin and/or F-actin.
On the basis of their ability to interact with actin in vitro, these
proteins were collectively termed "actin-binding proteins" (Stossel et al.,
1985; Pollard & Cooper, 1986; Hartwig & Kwiatkowski, 1991). Today, over
100 such nonmuscle proteins have been described. They are felt to be
responsible for the coordinated regulation of nonmuscle cell actin
polymerization considered necessary for motile activities as well as the
maintenance of structural integrity. Actin-binding proteins can be
subdivided into groups that either control the three-dimensional
arrangement of actin filaments (cross-linking and bundling proteins),
apply force to the actin-filament network (myosins), or regulate actin -
filament number and length (capping, severing, nucleating, and monomer-


Relative Fluorescence
-U ON 00 o
O O O O O o
102


157
Southwick, F. S., and Young, C. L. 1990. The actin released from
profilin-actin complexes is insufficient to account for the increase in F-
actin in chemoattractant-stimulated polymorphonuclear leukocytes. J. Cell
Biol. 110: 1965-1973
Spudich, J. A., and Watt, S. 1971. J. Biol. Chem. 246: 4866-4871
Stossel, T. P. 1989. From signal to pseudopod. J. Biol. Chem. 264:
18261-18264
Stossel, T. P. 1992. The mechanical responses of white blood cells.
In: lnfammation: Basic principles and clinical correlates, 2nd Ed., Eds:
Gallin, J. I., Goldstein, J. M, and Snyderman, R. Raven Press, Ltd., New York
Stossel, T. P. 1993. On the crawling of animal cells. Science 260,
1086-1094
Stossel, T. P., Chaponnier, C., Ezzell, R. M., Hartwig, J. H., Janmey, P.
A., Kwiatkowski, D. J., Lind, S. E., Smith, D. B., Southwick, F. S., Yin, H. L.,
and Zaner, K. S. 1985. Nonmuscle actin-binding proteins. Ann. Rev. Cell
Biol. 1: 353-402
Straub, F. B. 1942. Actin Studies, University of Szeged II: 3-15
Sudhof, T. C., Slaughter, C. A., Leznicki, L, Barjon, P., and Reynolds,
G. 1988. Human 67-kDa calelectrin contains a duplication of four repeats
found in 35-kDa lipocortins. Proc. Natl. Acad. Sci. 85: 664-668
Theriot, J. A., and Mitchison, T. J. 1993. The three faces of profilin.
Cell 75: 835-838
Towbin, H., Staehelin, T., and Gordon, J. 1979. Electrophoretic
transfer of proteins from polyacrylamide gels to nitrocellulose sheets:
procedures and some applications. Proc. Natl. Acad. Sci. 76: 4350-4354
Vandekerckhove, J., and Weber, K. 1978. At least six different actins
are expressed in higher mammals: An analysis based on the amino acid
sequence of the amino-terminal tryptic peptide. J. Mol. Biol. 122: 783 -
802
Vandekerckhove, J., and Weber, K. 1984. Chordate muscle actins
differ distinctly from invertebrate muscle actins. J. Mol. Biol. 179, 391-413
Vandekerckhove, J., Kaiser, D. A., and Pollard, T. D. 1989.
Acanthamoeba actin and profilin can be crosslinked between glutamic acid
364 of actin and lysine 115 of profilin J. Cell Biol. 109: 619-626


9
Polymerization
The 42,000 dalton actin monomer (G-actin) can non-covalently self
associate and polymerize to form filaments (F-actin) in the presence of
monovalent (KC1) or divalent (MgCl2, CaCl2) salts, and hence increase the
solution viscosity. The theory of actin polymerization has been reviewed
extensively by several authors (Korn, 1982; Stossel et al., 1985; Pollard &
Cooper 1986; Pollard, 1990), and will be briefly discussed. Actin
polymerization is at least a two-step process: nucleation followed by
elongation. Nucleation, the rate-limiting, thermodynamically-unfavorable
step, occurs when 3 molecules of actin associate to form the nucleus for
further assembly. Polymerization/elongation cannot proceed unless the G-
actin concentration is above a critical concentration (Cc), which is defined
as the minimum concentration of G-actin required to form a polymer
(Pollard & Cooper, 1986). The Cc value is sensitive to the ionic conditions,
pH, temperature, and nucleotide content of the reaction solution
(Zimmerle & Frieden, 1986; Zimmerle & Frieden, 1988). Despite the
minimal requirements, many groups have simulated physiologic
conditions (0.1 M KC1, ImM MgCl2, EGTA-to chelate Ca2+, ImM ATP, and
pH 7.4) during their analysis of polymerization kinetics. As alluded to
earlier, at near physiologic conditions the critical concentrations for
assembly of muscle and non-muscle actin isoforms are virtually
indistinguishable. Under defined conditions, actin filament assembly
reaches a steady-state as a result of actin molecules continually being
exchanged between actin filaments and the critical concentration of
monomers without affecting the overall F-actin content.
The actin filament has two kinetically different ends (barbed "+"
and pointed "-") defined by the arrowhead pattern produced when an


11
Unit K+ = iimol'1 S'1
K. = s-1


Abstract of Dissertation Presented to the Graduate School of the University
of Florida in Partial Fulfillment of the Requirements for the Degree of
Doctor of Philosophy
PURIFICATION AND FUNCTIONAL CHARACTERIZATION OF HUMAN
POLYMORPHONUCLEAR LEUKOCYTE ACTIN POLYMERIZATION INHIBITOR
By
NOEL ANTHONY MAUN
May, 1995
Chairperson: Daniel L. Purich, Ph.D.
Cochairperson: Frederick S. Southwick, M.D.
Major Department: Biochemistry and Molecular Biology
Actin polymerization inhibitor, an activity from human
polymorphonuclear leukocytes (PMN) which lowers the viscosity of actin
filament solutions, was previously purified by our laboratory. The calcium
independent nature of the activity suggests it may be involved in the
motile behavior of PMN based on the current theories regarding the
regulation of actin filament assembly. This activity has been found by
additional column chromatography steps and Western blot analysis to be
the heterodimeric capping protein capZ. The actin regulatory activity of
this non-muscle capZ was assessed utilizing pyrenylactin. Similar to
skeletal muscle capZ and other members of the capping protein family, I
report that non-muscle capZ purified from PMN blocks monomer exchange
at the barbed ends of actin filaments under both polymerizing and
depolymerizing conditions with an apparent disassociation constant for
capping of 3 nM. Similar to the activity reported for actin polymerization
viii


118
Northern Analysis Of Annexin VI During Differentiation Of Promyelocytes
The results from the analysis of annexin VI mRNA expression in PMN
and U937 cells suggest neutrophils have higher annexin VI niRNA levels
than monocytes/macrophages. This finding is curious as both these cell
types originate from promyelocytes. Currently used as a model for
differentiation is the human promyeloblast leukemic cell line HL-60
(Gallagher et ah, 1979). The ability of the HL-60 cells to differentiate
towards neutrophils by DMSO treatment or macrophages by phorbal
diester treatment was used as an in vitro model to study the
developmental regulation of annexin VI mRNA. The HL-60 cells were
grown in suspension cultures with a doubling time of approximately 24 -
48 hours. When induced to differentiate by PMA, these cells ceased to
proliferate and began to acquire characteristics of mature macrophages.
By 1 2 days, when a majority of the cells were adhered to the plates, they
developed many pseudopodial extensions. Similar to previous reports, I
found the HL-60 cells induced to differentiate by DMSO continued to
proliferate, but gained many of the morphological characteristics of
peripheral blood PMN (multilobular nuclei, and increased granules by
light microscopy). In all, the differentiation patterns observed were as
previously documented for HL-60 cells (Collins, 1987).
Total RNA was prepared from these cells at different time points
after the induction of differentiation with DMSO or PMA and analyzed on
Northern blots using the 1057 bp annexin VI cDNA fragment as a probe.
As shown in Figure 5-2, annexin Vi mRNA levels appears maximal by 3
days in HL-60 cells differentiated towards the neutrophil lineage. In
contrast the mRNA levels in HL-60 cells differentiated towards the
macrophage lineage had no detectable annexin VI mRNA by day 3. This


5
birds that at least six actin isoforms exist (three a, one (3, and two 7) and
are expressed in a tissue specific manner (Vandekerckhove & Weber, 1978;
Vandekerckhove & Weber, 1984). They differ from one another by only a
few amino acid residues, mainly in the first 20 N-terminal amino acids.
Utilizing near physiologic conditions, no major differences in the
polymerization characteristics of muscle vs. non-muscle isoforms of actin
are noted (Korn, 1982). As reviewed by Herman (1993), recent
compelling evidence suggests there are functional differences amongst the
muscle and non-muscle isoforms. Based on this evidence which includes
isoform-specific antibody localization and gene replacement studies, he
proposes a model cell wherein the nonmuscle isoforms are found in
regions of moving cytoplasm/cell cortex, and the muscle isoforms compose
the static microfilament bundles (stress fibers or myofibrils). Curiously, it
was recently noted that the cytoplasmic mRNAs for the p and y actin
isoforms are differentially segregated in myoblasts (Hill & Gunning, 1993),
and overexpression of either differentially impacts the cytoarchitecture of
these cells (Schevzov et ah, 1992). This suggests subtle functional
differences exist even amongst the nonmuscle isoforms.
Actin Structure
Actin consists of a single polypeptide chain of 375 amino acid
residues, with a molecular weight of about 42 kDa (G-actin). It has long
been known that G-actin contains a divalent cation and an adenine
nucleotide binding site. Both sites are occupied in all forms of purified
actin. Due to its tendency to polymerize, the formation of actin crystals
and thus its atomic structure had eluded researchers for many years.
Utilizing the ability of deoxyribonuclease 1 (DNase I) to inhibit


32
purified from phagocytes are members of the calcium-dependent/gelsolin
capping-protein family. CapZ was recently noted in platelets (see
"Capping Proteins")
A simple model integrating what is currently known about
neutrophils and other motile cells is suggested by Stossel (1993). At rest,
a majority of the actin filaments are capped at their membrane-proximal
barbed-ends. This leads to a critical concentration of free actin monomers
close to the dissociation constant of the freely-exchanging minus-end (~1.0
pM). As discussed earlier, the concentrations of monomer sequestering
proteins (profilin and thymosin IL4) and their affinities for actin
monomers (Kd ~0.S 5 pM) can explain the high amounts of
unpolymerized actin in resting neutrophils (> 60 %). Stimulation of
neutrophils with chemotactic peptide causes an increased
phosphoinositide turnover (Snyderman & Uhing, 1992; Janmey, 1994).
Based on the findings that profilin and the barbed-end capping proteins
bind the phosphoinositides PIP and PIP2 thereby inhibiting their ability to
bind to actin, it is thought that phosphoinositides mediate the signal
transduction between the surface receptors and actin assembly (Stossel,
1993). In this model it is explained that phosphoinositides cause the
uncapping of membrane-proximal barbed-ends, thus lowering the critical
concentration of actin monomers in that region closer to that of the
barbed-end (0.1 0.3 pM). Since the critical concentration of free actin
monomers is lowered, a majority of the sequestered actin can be released
into the polymerizable pool (see "Monomer Sequestering Proteins").
Stimulation of neutrophils may activate profilin's ability to increase the
nucleotide exchange rate of actin molecules, thus ensuring a continuous
supply of ATP-actin available for rapid polymerization (Goldschmidt-


20
As reviewed by Stossel et al., (1985), the three in vitro effects of
gelsolin on actin are differentially dependent upon the Ca2+
concentration. Severing has the most stringent calcium requirement, and
does not occur in the presence of submicromolar Ca2+. Barbed-end
capping occurs to a small extent in the presence of submicromolar Ca2+,
but this activity is markedly enhanced at higher calcium concentrations.
Gelsolin is able to nucleate filament assembly in the presence of calcium
by forming a complex (1 gelsolin : 2 actin) with two molecules of actin
(Janmey et al., 1985). Removal of calcium by EGTA dissociates one of the
actin monomers leaving behind a stable 1:1 gelsolin-actin complex. This
EGTA-resistant complex is unable to sever filaments, but can now bind the
barbed ends of filaments with high affinity even at submicromolar calcium
concentrations. Gelsolin has also been isolated as an alternatively spliced,
93 kDa, plasma form differing from the cytoplasmic form by the presence
of an additional 25 N-terminal amino acids (Kwiatkowski et al., 1986).
The secreted gelsolin is hypothesized to maintain and buffer a low plasma
actin filament content even when the cytoplasmic components of cells are
spilled into the vasculature during processes such as injury.
The capZ family includes heterodimeric proteins with subunits of
30-35 kDa which are able to bind the barbed end of actin filaments
independently of calcium. Most members described can nucleate filament
assembly, but all lack the ability to sever filaments. CapZ, a heterodimeric
protein with subunits of Mr = 36,000 (a-subunit) and 32,000 (p-subunit)
daltons, is the best characterized member of this family (Casella et al.,
1986). Purified skeletal-muscle capZ caps the barbed end of filaments
with an apparent dissociation constant of approximately 0.5 1 nM
(Caldwell et al., 1989a). It was originally purified from skeletal muscle


87
necessitates the use of several columns to purify the neutrophil inhibitory
activity.
In summary, the exhaustive purification protocols have
demonstrated human neutrophil actin polymerization inhibitor is capZ, a
heterodimeric protein consisting of two subunits with Mr of 36,000 and
32,000 as detected by silver staining active fractions separated by SDS-
PAGE. Western blot analysis of peak inhibitory activity from Mono Q.
chromatography fractions reveals immunoreactivity of the 36 and 32 kDa
polypeptides with antisera made to chicken skeletal-muscle capZ,
supporting my conclusion that the 36 and 32 kDa polypeptides further
purified by hydroxylapatite were identical to the capZ immunoreactive
peptides. Together these findings presented in Chapter 3 indicate that the
previously published neutrophil actin polymerization inhibitor is indeed
related, if not identical, to the skeletal muscle form of capZ. In addition,
neither of the polypeptides originally identified as the neutrophil inhibitor
(currently identified in this work as annexin VI and L-plastin) contributes
to the activity of PMN actin polymerization inhibitor.


126


3
that is adherent to, or closely associated with, the lining of the blood
vessels (Golde, 1990). Individual cells move back and forth behaving
kinetically as a single pool. The neutrophils' stay in the blood is short,
with an approximate half-life of 6 7 hours, from where they subsequently
enter the extravascular space (Dancey et al., 1976). It is estimated that
approximately 100 billion PMN enter and leave the circulation daily
(Walker & Willemze, 1980). Despite this number, their fate after
migrating to tissues is unknown. Based on in vitro survivability of
peripheral PMN, it is thought that they probably remain functional for 1-2
days, and are then cleared (Golde, 1990).
Neutrophils are first-line defenders against invading
microorganisms. The frequent and severe infections that occur in persons
whose neutrophils are deficient quantitatively (neutropenia) or
qualitatively (e.g. chronic granulomatous disease or neutrophil actin
dysfunction) attest to the central role of this cell in host defense
mechanisms. They are the predominant leukocyte in peripheral blood
comprising two-thirds to three-fourths (4,000 8,000/mm3) of the
peripheral white blood cell count.
It is estimated that the bone marrow compartment houses PMN
reserves in excess of 100-fold the quantity found in peripheral blood.
These stores are readily discharged in response to bodily invasion.
Neutrophils are commissioned to seek, attack, and destroy pathogens and
so are endowed with the facility to rapidly advance and engage the enemy.
The major functions through which neutrophils carry out this mission
include chemotaxis, adherence, aggregation, phagocytosis, degranulation,
and generation of toxic metabolites. In part, these properties are
dependent upon an extensive rearrangement of the actin filament system


Figure 3-3. Nondenaturing polyacrylamide gel electrophoresis. PMN inhibitor (lane 2; 12pg) was
subjected to native gel electrophoresis in search of evidence suggesting complex formation between L-
plastin & annexin VI. Purified annexin VI (lane 1; 6 pg) and purified L-plastin (lane 2; 6 pg) were run to
enable the determination of a mobility shift when the two proteins are present. Panel A is a Coomassie
stained gel of the various fractions (starred lane contains 15 pg of albumin/BSA). Gels were run in
triplicate for western analysis with antibodies to annexin VI (Panel B) or L-plastin (Panel C).


Relative Fluorescence
>
Relative Fluorescence
ooooooooo
16
EGTA Calcium


65
method was able to remove > 60 % of annexin VI from those fractions
purified by DEAE-ion exchange and gel-filtration chromatography.
Phospholipid affinity chromatography (Chapter 2), as well, incompletely
separated annexin VI from the neutrophil activity (Figure 3-4, lane 2).
The neutrophil actin polymerization inhibitory activity remained in
fractions partially depleted of annexin VI and predominantly composed of
L-plastin, and was not associated with the highly purified annexin VI (> 90
%) (Figure 3-4, lane 1).
Purification And Identification Of PMN Actin Polymerization Inhibitor As
CapZ
In efforts to avoid phospholipid contamination and the addition of
calcium, other chromatographic methods were tested. After DEAE-anion
exchange chromatography and gel-filtration, the neutrophil inhibitory
activity was applied to a Mono Q.anion exchange column and eluted with a
KC1 gradient (Chapter 2). Surprisingly, the activity coeluted with annexin
VI and not L-plastin (data not shown). The peak activity, although,
correlated with a fraction in which no protein was seen by Coomassie
staining of the fractions run on SDS-PAGE (no predominant band was seen
by silver staining as well). However, Western blots of this and three other
active fractions from previous purifications probed with antisera from a
goat immunized with chicken, skeletal-muscle capZ (kindly provided by
Dr. J. Cooper, Washington University, St. Louis, MO) revealed two
immunoreactive bands (Figure 3-5) in the appropriate molecular weight
range of the heterodimeric, skeletal-muscle protein capZ (Mr between
30,000 40,000). The DEAE-anion exchange fractions from the
subsequent purification were subjected to immunoblot analysis and
probed with the capZ antisera as well (Figure 3-6). Peak capZ


29
Chemotactic stimulation increases the intracellular free calcium
concentration, [Ca2+], from the 100 nM level at rest to micromolar levels
(Janmey, 1994). Despite buffering resting neutrophil [Ca^+fi with calcium
chelators (e.g., EGTA, quin-2, BAPTA), the cells are still capable of
migrating at normal rates (Elferink & Deierkauf, 1985; Meshulam et al.,
1986; Zigmond et al., 1988). The fMLP-induced rise in [Ca^+] involves
both the release of calcium from intracellular stores (via IP3) and influx
across the membrane. The use of fluorescent calcium indicators (quin2 or
fura2) reveals the "biphasic" nature of this fMLP-induced increase (Lew et
al., 1984; Lew et al., 1986; Anderson et al., 1986). The prolonged second
phase is eliminated by removal of extracellular calcium, while the rapid
first phase remains unaffected. The rapid doubling of F-actin in response
to fMet-Leu-Phe stimulation is temporally associated with the initial rise in
[Ca2+]¡ caused by IP3 (Snyderman & Uhing, 1992). Preventing the fMet-
Leu-Phe-induced rise in calcium with calcium chelators has no effect on
the neutrophil's ability to double its F-actin content within 15-30 seconds
(Sha'afi et al., 1986; Downey et al., 1990; Sham et al., 1993). Neutrophil
migration is a complex process that involves the continuous cycling of
polymerization and depolymerization. It is possible that the repetitive
increases in intracellular calcium in migrating PMN (Marks & Maxfield,
1990; Jaconi et al., 1990) may actually enhance depolymerization of actin
filaments by activating the severing activity of proteins like gelsolin
(Downey et al., 1990).
With increasing evidence suggesting neither calcium nor protein
kinase C activation were necessary for the chemoattractant-induced actin
polymerization seen in PMN, the signaling role of phosphoinositides was
actively investigated. It has been known for over 30 years that


Figure 5-5. Confocal microscopy of PMN stained with anti-annexin VI
antibodies. Digitized images representing 1 pm cuts were obtained in
adherent PMN probed with annexin VI antibodies (Panel A) or control
antibodies (anti-nab-1; Panel B). Cells were fixed and stained identically to
Figure 5-4.


49
Perkin-Elmer Cetus R.T.-P.C.R. kit was utilized to generate a 1057 base-pair
(bp) annexin VI DNA fragment from neutrophil total RNA via a reverse
transcription reaction immediately followed by initiation of the
polymerase chain reaction (Perkin-Elmer Cetus DNA Thermal Cycler model
480). The ends of the 1057 bp DNA fragment were blunt-ended with the
Klenow fragment of DNA polymerase, and ligated into the E. coli vector
pBluescript II SK + (Stratagene Cloning Systems, Lajolla, CA) at the Sma I
polylinker site. The 1057 bp, subcloned, annexin VI-cDNA-fragment (bp #
32 1088) was verified by sequencing (I.C.B.R. DNA sequencing facility,
University of Florida).
Cell Culture And Induction Of Differentiation
The human promyeloblast leukemic cell line HL-60 (Gallagher et al.,
1979) was obtained from ATCC (American Type Culture Collection,
Rockville, MD) and maintained in RPM1 1640 medium supplemented with
10 % iron-supplemented calf serum (Gibco BRL, Gaithersburg, MD) and 2
mM glutamine. This cell line can be induced to differentiate towards the
neutrophil lineage or macrophage lineage depending upon the
pharmacologic exposure (Collins, 1987). Differentiation of HL-60 cells was
induced according to the methods previously described by Dabiri et al.
(1992) Briefly, exponentially growing HL-60 cells (> 1 X 10 cells/ml)
were plated at 0.5 X 10 cells/ml and treated at time zero with the
appropriate pharmacologic agents. For macrophage differentiation, HL-60
cells were treated with phorbal 12-myristate-13 acetate (PMA, Sigma) at 10
nM (6.2 ng/ml), and for granulocyte differentiation the HL-60 cells were
treated with 1.5 % dimethyl sulfoxide (DMSO, Sigma Chemical Company,
Saint Louis, MO). At appropriate time points after differentiation, RNA or


Figure 4-4. Effects of neutrophil capZ on G-actin nucleation. At time zero,
a final concentration of 0.1 M KC1 and ImM MgCl2 was added to 1.5 pM
gel-filtered, pyrene-labeled G-actin combined with a final concentration of
215 nM capZ (closed squares) or in buffer P alone (open squares). These
two curves virtually overlie each other, and control points were taken
corresponding to every experimental point. Identical effects were seen in
the presence of 1 mM CaCl2- The ability of the pyrene labeled actin to
polymerize was assessed by adding a final concentration of 1.4 pM
unlabeled F-actin to the control reaction 10 minutes after initiation of
actin assembly by the addition of salt (closed triangles).


Figure 3-7. High S-cation exchange chromatography of PMN actin polymerization inhibitor. PMN
inhibitor consisting predominantly of annexin VI and L-plastin was bound to a High S column (Chapter 2)
and eluted with a 0 0.15 M linear KC1 gradient. Fractions were subjected to 10 % SDS-PAGE (with HMW
stds) and stained with Coomassie (Panel A). Fractions were trasferred to nitrocellulose and probed with
antibodies to annexin VI (Panel B). Relative activities are reported as the ability to prevent actin
polymerization from actin filament nuclei isolated from red blood cells (Panel C).


59
Separation Of Annexin VI From L-Plastin
The following experiments were conducted in attempts to correlate
the neutrophil actin polymerization inhibitory activity with one of the two
proteins or a complex formed between them. Additional chromatography
steps were added in attempts to separate annexin VI from L-plastin.
Neither phenylsepharose (Pharmacia Biotech, Inc., Piscataway, NJ) or Affi-
Gel blue (Bio-Rad Laboratories, Inc., Hercules, CA) chromatography
separated the two proteins. The viscosity lowering activity was noted to
coelute with the annexin VI and L-plastin proteins during Affi-Gel blue
chromatography (the viscosity lowering activity was not monitored in the
fractions obtained from phenylsepharose chromatography).
The difficulty in separating these two proteins raised the possibility
that annexin VI and L-plastin were forming a complex. Nondenaturing
polyacrylamide gel electrophoresis was used to test this possibility (Figure
3-3). Active fractions containing both annexin VI and L-plastin (Figure 3-
3, lane 2), purified annexin VI (lane 1) (via liposome purification, see
below), recombinant human L-plastin (lane 3) (purified from E. coli by Dr.
Clarence Young for unrelated studies in our laboratory), and bovine
albumin (lane *) (indicator of the nondenaturing conditions of the assay)
were each subjected to nondenaturing electrophoresis. If a complex was
formed by annexin VI and L-plastin in active fractions, one might expect a
migration pattern different from lanes containing the purified annexin VI
(Figure 3-3, lane 1) or purified L-plastin (Figure 3-3, lane 3). This
difference would most likely appear as a slower migrating band in
fractions where a complex is formed (analogous to the decreasing
mobilities of monomer, dimer, and trimer species of native bovine
albumin seen in Figure 3-3A lane *). The samples were run in triplicate


42
(monoclonal) & 1:7500 (polyclonal), anti human L-plastin at 1:500, anti
chicken capZ alpha and beta 1:300) and incubated with the blot for 1 hour
at room temperature. After subsequent washes with PBS-tween, the blots
were incubated with the appropriate alkaline phosphatase-conjugated
secondary antibody for 40 60 minutes. The detection was in an alkaline
phosphatase buffer (0.1 M Tris, 5 mM MgCl2, 0.1 M NaCl) containing 30
pg/ml nitro blue tetrazolium (Sigma Chemical Company, Saint Louis, MO)
and 20 pg/ml BCIP (5-bromo-4-chloro-3-indolyl phosphate, Sigma).
The annexin VI concentration in neutrophil extracts was determined
using a method similar to that described by Dabiri et al. (1992). The
immuno-reactivities of the polypeptides in neutrophil extracts were
compared to known concentrations of purified annexin VI using a
scanning laser densitometer (Zeineh Model SLR-2D/1D, Biomed
Instruments, Inc.). A linear standard curve could be generated relating
densitometry integration units to protein concentration.
Nondenaturing Polyacrylamide Gel Electrophoresis
Neutrophil actin polymerization inhibitor containing predominantly
annexin VI and L-plastin were subjected to 7.5 % nondenaturing
polyacrylamide gel electrophoresis (mid-sized gel, Hoefer Scientific
Instruments, San Francisco, CA) according to the method of Safer (1989).
Samples were added 1:1 (volume:volume) with 10 % glycerol in the
running buffer with <1 mg of bromophenol blue (tracking dye). A
heterogeneous population of monomers, dimers, and trimers of bovine
serum albumin (BSA) are formed when placed in solution, and therefore
15 pg of BSA (fraction V, Sigma Chemical Company, Saint Louis, MO; 1


54
4


3-11 Silver stained peak fractions from Mono Q
and HA chromatography 81
4-1 Effects of purified capZ on actin filament
depolymerization 91
4-2 Effects of purified capZ on actin filament polymerization
from spectrin/band 4.1/actin nuclei 94
4-3 Effects of neutrophil capZ on the extent of
actin polymerization 97
4-4 Effects of neutrophil capZ on G-actin nucleation 100
4-5 Actin filament severing assay 102
4-6 Effects of capZ on polymerization from
gelsolimactin nuclei 105
4-7 Effects of PIP2 on capZ barbed-end
capping activity 107
5-1 Northern analysis of PMN and U937 117
5-2 Northern analysis of HL-60 differentiated to
neutrophil-like or macrophage-like cells 120
5-3 Western analysis of HL-60 differentiated to
neutrophil-like or macrophage-like cells 123
5-4 Indirect immunofluorescence microscopy of PMN 126
5-5 Confocal microscopy of PMN stained with
anti-annexin VI antibodies 128
5-6 Confocal microscopy of peripheral blood
monocytes stained with anti-annexin VI
antibodies 130
5-7 Quantitation of annexin VI in human
neutrophil cytoplasmic extracts 133
vii


143
the transcriptional inhibitor actinomycin D should delineate in each
differentiation pathway if the changes in annexin VI mRNA expression is
due to regulation at the transcriptional level. If one finds that such
changes are transcriptionally regulated, the necessity of protein synthesis
for this level of regulation can be addressed with transient treatment of
the induced cells with translational inhibitors. Conversely, if actinomycin
D treatment does not affect the levels of mRNA seen in differentiated cells
it can be speculated that the expression of annexin VI mRNA is regulated
by other mechanisms (e. g. stabilization or compartmentalization of
mRNA). The precise regulatory mechanisms involved in the
differentiation of HL-60 cells are important to our understanding of how
stem cells cease to proliferate and go on to differentiate. These
mechanisms have obvious implications in terms of the pathogenesis and
evolution of cancer, particularly myeloid leukemias. A deeper
understanding of the regulation of annexin VI mRNA expression in HL-60
cells is therefore worthy of further pursuit.


155
Rosales, C., Jones, S. L, McCourt, D., and Brown, E. J. 1994.
Bromophenacyl bromide binding to the actin-bundling protein 1-plastin
inhibits inositol triphosphate-independent increase in Ca^+ in human
neutrophils. Proc. Natl. Acad. Sci. 91: 3534-3538
Safer, D. 1989. An electrophoretic procedure for detecting proteins
that bind actin monomers. Anal. Biochem. 178: 32-37
Safer, D., Elzinga, M., and Nachmias, V. T. 1991. Thymosin M and
Fx, an actin-sequestering peptide, are indistinguishable. J. Biol. Chem. 268:
4029-4032
Safer, D., Golla, R., and Nachmias, V. 1990. Isolation of a 5-
kilodalton actin-sequestering peptide from human blood platelets. Proc.
Natl. Acad. Sci. 87: 2536-2540
Sanger, J. W., Sanger, J. M., Kreis, T. E., and Jockusch, B. M. 1980.
Reversible translocation of cytoplasmic actin into the nucleus caused by
dimethyl sulfoxide. Proc. Natl. Acad. Sci. 77: 5268-5272
Sauterer, R. A., Eddy, R. J., Hall, A. L, and Condeelis, J. S. 1991.
Purification and characterization of aginactin, a newly identified agonist-
regulated actin-capping protein from Dictyostelium amoebae. J. Biol.
Chem. 266: 24533-24539
Schafer, D. A., Mooseker, M. S., and Cooper, J. A. 1992. Localization
of capping protein in chicken epithelial cells by immunofluorescence and
biochemical fractionation. J. Cell Biol. 118: 335-346
Schevzov, G., Lloyd, C., and Gunning, P., 1992. High level expression
of transfected 13- and gamma-actin genes differentially impacts on
myoblast cytoarchitecture. J. Cell Biol. 117: 775-785
Schleicher, M., Gerisch, G., and Isenberg, G. 1984. New actin-binding
proteins from Dictyostelium discoideum. EMBOJ. 3: 2095-2100
Schutt, C. E., Myslik, J. C., Rozycki, M. D., Goonesekere, N. C. W., and
Lindberg, U. 1993. The structure of crystalline profilin-13-actin. Nature
365: 810-816
Selden, L. A., Estes, J. E., and Gershman, L. C. 1983. Biochem
Biophys. Res., Commun. 116: 478-485
Selden, L. A., Gershman, L. C., and Estes, J. E. 1986. A kinetic
comparison between Mg-actin and Ca-actin. J. Muscle Res. Cell Mot. 7: 215-
224


Time (min)
Relative Fluorescence
>
Relative Fluorescence
CXJ
SOI


27
sensitive, phospholipase C activator) subtype (Snyderman & Uhing, 1992;
Kaziro et al., 1991).
The kinetics and dose-dependency of the fMet-Leu-Phe-induced
actin polymerization burst coincides with the rapid, initial phase of the
fMet-Leu-Phe response (discussed under "PMN chemoattractants"). The
following sequence of major intracellular events comprise this initial
phase. In short, binding of fMet-Leu-Phe to its receptor results in the
dissociation of a membrane-bound, heterotrimeric, GTP-binding protein
(G-protein). This activated G-protein (Gj2-alpha subunit) transiently
activates phospholipase C to produce two second messengers, 1,2-
diacylglycerol (DAG) and inositol (1,4,5) triphosphate (IP3) from
phosphatidylinositol(4,5) bisphosphate (PIP2) hydrolysis. Inositol
triphosphate releases intracellular stores of calcium, while DAG activates
protein kinase C. The rapid cleavage of PIP2 by PKC results in the
conversion of other phosphoinositides such as PIP and PIP3 to PIP2- The
conversion of phosphoinositides is regulated by a large number of kinases
and phosphatases that add or remove phosphates on the inositol ring
(Janmey, 1994). Temporal studies show rapid (< 5 sec) elevations in
phosphoinositide metabolism and cytosolic calcium levels following fMet-
Leu-Phe stimulation. The molecular mechanisms responsible for the
cytochalasin-sensitive, rapid (< 15-30 sec) and dramatic increase in actin
polymerization in response to fMet-Leu-Phe remain unknown, but are
thought to involve these molecules.
Calcium And Protein Kinase C-Independent, Phosphoinositide-Deoendent
fMLP-lnduced Actin Polymerization Response
Modulation of the transductional cascade using traditional
pharmacological agents demonstrates that neither calcium or protein


Figure 5-1. Northern analysis of PMN and U937. Total RNA (10 pg per
lane) was isolated from PMN or U937. Blots were probed using the partial
cDNA of annexin VI (Chapter 2) labeled with 3 2p by random primer
extension.


Figure 3-9. Western blot analysis of PMN actin polymerization inhibitor
purified to Mono Q. chromatography. Peak fractions from Mono Q_
chromatography (lane 2) (see Figure 3-8) were separated by 10 % SDS-
PAGE (with HMW stds), and either stained (Panel A) with Coomassie or
subjected to Western analysis (Panel B) probing with antisera to chicken
skeletal-muscle capZ. Lane 1 is 30 pg PMN extract, while a total of 3 pg of
protein was loaded in lane 2.


89
The characterization of the specific interactions of proteins with
actin was at first limited to those expert in the techniques of electron
microscopy. By this method the lengths of filaments can be directly
visualized, the kinetics of assembly at each end of the actin filament can
be simultaneously analyzed (using morphologically identifiable nuclei
such as heavy-meromyosin-labeled actin oligomers or Limulus sperm
acrosomal actin bundles), and the three-dimensional configuration of
actin solutions can be monitored. With the development of fluorescent
labels covalently attached to actin, most notably pyrene-labeled actin,
spectrophometric analysis of actin polymerization has become an
alternative, more accessible technique to study specific interactions and
kinetics of actin filament assembly (Kouyama & Mihashi, 1981; Cooper et
al., 1983). In efforts to further characterize the viscosity lowering activity
of PMN capZ, its effects on actin polymerization were studied utilizing
pyrene actin.
Results
Barbed-End Capping Activity
As shown in Figure 4-1A, capZ slowed the rate of actin filament
disassembly in a concentration dependent fashion. The marked slowing in
the depolymerization rate was most consistent with blocking of monomer
release from the barbed end of actin filaments. The apparent dissociation
constant for the interaction of capZ with the barbed end (Kd app) was
approximately 3 nM. CapZ inhibited actin depolymerization to a similar
extent in the presence as well as in the absence of Ca2+ (Figure 4-1B).
When filaments are diluted, they rapidly depolymerize from their ends in


This dissertation is dedicated to all the teachers who have guided
my education at the University of Florida.


120
DMSO P M A
AN X VI
08 16 12345 08 16 1234
HOURS DAYS HOURS DAYS
B-ACTIN


158
Verghese, M. W., Uhing, R. J., and Snyderman, R. 1986. A
pertussis/cholera toxin-sensitive N protein may mediate chemoattractant
receptor signal transduction. Biochem. Biophys. Res. Commun. 138: 887-
894
Walker, R. I., and Willemze, R. 1980. Neutrophil kinetics and the
regulation of granulopoiesis. Rev. Infect. Dis. 2: 282-292
Wallace, P. J., Westo, R. P., Packman, C. H., and Lichtman, M. A.
1984. Chemotactic peptide-induced changes in neutrophil actin
conformation. J. Cell Biol. 98: 214-221
Wang, Y. L. 1985. Exchange of actin subunits at the leading edge of
living fibroblasts: Possible role of treadmilling. J. Cell Biol. 101: 597-602
Wanger, M., Keiser, T., Neuhaus, J. M., and Wegner, A. 1985. The
actin treadmill. Can. J. Biochem. Cell. Biol. 63: 414-421
Weber, A., Nachmias, V. T., Pennise, C., Pring, M., and Safer, D. 1992.
Interaction of thymosin 84 with muscle and platelet actin: implications for
actin sequestration in resting platelets. Biochemistry 32: 6179-6185
Weeds, A., and Maciver, S. 1993. F-acdn capping proteins. Curr.
Opin. Cell Biol. 5: 63-69
White, J. R., Naccache, P. H., and Sha'afi, R. I. 1983. Stimulation by
chemotactic factor of actin association with the cytoskeleton in rabbit
neutrophils. J. Biol. Chem. 258: 14041-14047
Williams, W. J., Beutler, E., Erslev, A. J., and Lichtman, M. A. 1990.
Neutrophils, eosinophils, and basophils. In: Hematology, 4th Ed., McGraw-
Hill, Inc., Ohio
Wilson, S. M., Datar, K. V., Paddy, M. R., Swedlow, J. R., and Swanson,
M. S. 1994. Characterization of nuclear polyadenylated RNA-binding
proteins in Saccharomyces cerevisiae. J. Cell Biol. 127: 1173-1184
Witke, W., Sharpe, A. H., Hartwig, J., Azumi, T., Stossel, T. and
Kwiatkowski, D. J. 1993. Transgenic mice lacking gelsolin. Mol. Biol. Cell
Vol. 4, abstract 1483
Yin, H. L., Albrecht, J. H., and Fattoum, A. 1981. Identification of
gelsolin, a Ca++-dependent regulatory protein of actin gel-sol
transformation, and its intracellular distribution in a variety of cells and
tissues. J. Cell Biol. 91: 901-906


75
carried out to this extent on three separate occasions, each resulting in the
isolation of polypeptides with approximate Mr of 55,000 (L-plastin
degradation product), 36,000, and 32,000 seen upon silver staining (for
examples see Figure 3-8A' lanes 26 and 27 or Figure 3-11, lane 3).
Western analysis identified the 36 and 32 kDa bands as capZ (Figure
3-9A & B, lane 2). As shown in Figure 3-8 (panel A verses panel A, lanes
26 & 27), the presence of these peptides after Mono Q. chromatography is
revealed by silver staining. Hydroxylapatite chromatography of these
fractions successfully separated the L-plastin degradation product from
the actin-filament-shortening activity (Figure 3-10, fraction 21 verses
fraction 22). The activity was strictly associated with capZ (Figure 3-10).
Although several minor bands were seen below the 36 and 32 kDa
polypeptides in Figure 3-10, they were not seen when fraction 21 was
separated on other occasions (Figure 3-11, lane 4). Several possibilities
including degradation, resolution of isomers or an artifact of the
procedure can explain this finding.
Discussion
Proteins that bind to actin and modulate actin filament assembly are
also hypothesized to regulate the finely coordinated assembly and
disassembly of the microfilament network in motile cells. Based on
viscometric studies, actin polymerization inhibitor is thought to play an
important role in the regulation of actin filament length in PMN.
Originally, my purifications focused on the 62 and 65 kDa proteins, and so
the identity of these polypeptides was pursued.


13
actin filament assembly. Under these conditions, the extent of this "ATP-
cap" is dependent upon the polymerization rate. In contrast,
depolymerization is facilitated by the exposure of these internal ADP-actin
molecules. In this model, the presence of ATP and its hydrolysis may
partially regulate the rapid reorganization of actin structures.
Using electron microscopy to monitor the elongation rates of
preformed filaments as a function of added G-actin has enabled the
determination of the rate constants for the "elongation" reactions (Bonder
et al., 1983; Pollard, 1986). The differences between ATP-actin and ADP-
actin result in eight main reactions (Figure 1-2). Several labs have
determined various rate constants, and at least two labs have generated all
eight (Pollard, 1986; Korn et al., 1987). There is general agreement (at
least within an order of magnitude) regarding the values of these rate
constants.
The different affinities of the various forms of nucleotide-bound
actin monomers for filaments may be due to conformational changes. In
Kabsch's atomic models comparing ATP- and ADP-actin, there are direct
interactions between the calcium ion and the (i- and y- phosphates of ATP
((3 alone with ADP) within the cleft, and subtle differences in the hydrogen
bonds formed between the phosphate groups with neighboring amino
acids (Kabsch et al., 1990). The atomic structure of Mg2+-ATP-actin,
although, may be quite different, as suggested by the fluorescence
difference seen when AEDANS (N-acetyl-N'-[sulfo-l-
napthyljethylenediamine) labeled actin is in a Mg2+ verses a Ca2+
environment (Selden et al., 1986). Despite the literature available on the
effects of calcium or magnesium binding to actin (Estes, 1992), this


Figure 5-7. Quantitation of annexin VI in human neutrophil cytoplasmic extracts. Extracts were obtained
from PMN purified > 95 % (Chapter 2). A. Coomassie blue-stained and B. Nitrocellulose transfers. Lanes
1-4, decreasing concentrations of human neutrophil extracts 100, 75, 50, and 25 pg, respectively. Lanes
5-9, decreasing concentrations of purified human annexin VI: 1.0, 0.8, 0.6, 0.4, and 0.2 pg respectively.
The relative intensity of each nitrocellulose band was measured by laser densitometry, generating a linear
standard curve and allowing quantification of annexin VI in neutrophil extracts.


147
Chomczynski, P., and Sacchi, N. 1987. Single-step method of RNA
isolation by acid guanidinium thiocyanate-phenol-chloroform extraction.
Anal. Biochem. 162: 156-159
Cockcroft, S., Barrowman, M. M., and Gomperts, B. D., 1985.
Breakdown and synthesis of polyphosphoinositides in fMet-Leu-Phe
stimulated neutrophils. FEBS Lett. 181: 259-263
Collins, S. J. 1987. The HL-60 promyelocytic leukemia cell line:
proliferation, differentiation, and cellular oncogene expression. Blood 70:
1233-1244
Condeelis, J. 1993. Life at the leading edge: The formation of cell
protrusions. Annu. Rev. Cell Biol. 9: 411-44
Cooper, J. A., Walker, S. B., and Pollard, T. D. 1983. Pyrene actin:
documentation of the validity of a sensitive assay for actin polymerization.
J. Muscle Res. Cell Mot. 4: 253-262
Creutz, C. E., 1992. The annexins and exocytosis. Science 258: 924-
930
Crompton, M. R., Owens, R. J., Totty, N. F., Moss, S. E., Waterfield, M.
D., and Crumpton, M. J. 1988. Primary structure of the human, membrane-
associated Ca2+-binding protein p68: a novel member of a protein family.
EMBOJ. 7: 21-27
Dabiri, G. A., Young, C. L., Rosenbloom, J., and Southwick, F. S. 1992.
Molecular cloning of human macrophage capping protein cDNA. J. Biol.
Chem. 267: 16545-16552
Dancey, J. T., Deubelbeiss, K. A., Harker, L. A., and Finch, C. A. 1976.
Neutrophil kinetics in man. J. Clin. Invest., 58: 705-715
Datar, K. V., Dreyfuss, G., and Swanson, M. S. 1993. The human
hnRNP M proteins: identification of a methionine/arginine-rich repeat
motif in ribonucleoproteins. Nucleic Acids Res. 21: 439-446
DiNubile, M. J., and Southwick, F. S. 1985. Effects of macrophage
profilin on actin in the presence and absence of acumentin and gelsolin. J.
Biol. Chem. 260: 7402-7409
Dohlman, H. G., Thorner, J., Caron, M. G., and Lefkowitz, R. J. 1991.
Model systems for the study of seven-transmembrane-segment receptors.
Annu. Rev. Biochem. 60: 653-688


156
Sha'afi, R. I., Shefcyk, J., Yassin, R., Molski, T. F. P., Volpi, M.,
Naccache, P. H., White, J. R., Feinstein, M. B., and Becker, E. L. 1986. Is a
rise in intracellular concentration of free calcium necessary or sufficient
for stimulated cytoskeletal-associated actin? J. Cell Biol. 102: 1459-1463
Shalit, M., Dabiri, G. A., and Southwick, F. S. 1987. Platelet-activating
factor both stimulates and "primes" human polymorphonuclear leukocyte
actin filament assembly. Blood. 70: 1921-1927
Sham, R. L., Phatak, P. D., Ihne, T. P., Abboud, C. N., and Packman, C.
H. 1993. Signal pathway regulation of interleukin-8-induced actin
polymerization in neutrophils. Blood. 82: 2546-2551
Sheterline, P., Rickard, J. E., and Richards, R. C. 1984a. Fc receptor-
directed phagocytic stimuli induce transient actin assembly at an early
stage of phagocytosis in neutrophil leukocytes. Eur. J. Cell Biol. 34: 80
Sheterline, P., Rickard, J. E., and Richards, R. C. 1984b. Involvement
of the cortical actin filament network of neutrophil leukocytes during
phagocytosis. Biochem. Soc. Transac. 12: 983-987
Sklar, L. A., Bokoch, G. M., Button, D., and Smolen, J. E. 1987.
Regulation of ligand-receptor dynamics by guanine nucleotides: real-time
analysis of interconverting states for the neutrophil formylpeptide
receptor. J. Biol. Chem. 262: 135-139
Snyderman, R., and Uhing, R. J. 1992. Chemoattractant stimulus-
response coupling. In: Inflammation: basic principles and clinical
correlates 2nd Ed., Eds: Gallin, J. I., Goldstein, I. M., and Snyderman, R.
Raven Press, New York
Southwick, F. S., Dabiri, G. A., Paschetto, M., and Zigmond, S. H.
1989. Polymorphonuclear leukocyte adherence induces actin
polymerization by a transduction pathway which differs from that used by
chemoattractants. J. Cell Biol. 109: 1561-1569
Southwick, F. S., and DiNubile, M. J. 1986. Rabbit alveolar
macrophages contain a Ca2+-sensitive, 41,000-dalton protein which
reversibly blocks the "barbed" ends of actin filaments but does not sever
them. J. Biol. Chem. 261: 14191-14195
Southwick, F. S., and Purich, D. L. 1994. Dynamic remodeling of the
actin cytoskeleton: Lessons learned from Listeria locomotion. BioEssays 16:
885-891


21
and localized to the sarcomeric Z-line (Casella et al., 1987). CapZ has
subsequently been recognized in nonmuscle cells as well (Caldwell et al.,
1989b; Schafer et al., 1992). It has recently been recognized that barbed-
end capping proteins purified from Acanthamoeba (Isenberg et al., 1980),
Dictyostelium (Schleicher et al., 1984), Xenopus (Ankenbauer et al., 1989),
Saccharomyces (Amatruda & Cooper, 1992) and bovine brain (Kilimann &
Isenberg, 1982) are indeed analogues of capZ. The presence of
mammalian capZ in highly motile cell types such as PMN and macrophages
has yet to be noted. It was recently reported to be present in human
platelets (Barkalow& Hartwig, 1994; Nachmias et al., 1994).
Actin Dynamics In PMN
PMN Chemoattractants
Chemoattractants are substances which have the ability to induce
directed migration. The three major groups of neutrophil
chemoattractants are described as complement-derived (C5a), leukocyte-
derived (LTB4, PAF, 11-8), and bacterial-derived (formylated peptides, e.g.
fMet-Leu-Phe). Neutrophils can sense a chemotactic concentration
gradient as small as 1 % across their dimension (Zigmond, 1977). As
discussed below, the rapid, chemoattractant-induced polymerization of
actin is probably the best understood transduction mechanism involved in
regulating the actin microfilament network. Overall, the transduction
mechanisms which regulate cellular actin assembly, although, remain
poorly understood.
Curiously, nanomolar concentrations of chemoattractants are
enough to induce shape change and locomotion in neutrophils, whereas it


85
recognition by antibodies to capZ proves this protein is responsible for the
PMN actin polymerization inhibitor.
CapZ is a heterodimeric protein with subunits of Mr 36,000 la-
subunit) and 32,000 (p-subunit) (Casella et al., 1986). Members of this
family are capable of binding the barbed end of actin filaments with high
affinity (~ 0.5 10 nM) independently of calcium. Binding to the barbed
end of actin filaments effectively decreases the apparent viscosity of actin
solutions by two mechanisms. First, this interaction results in the
shortening of the average filament length, and secondly it raises the
critical concentration to that of the pointed end. The elucidation that
PMN actin polymerization inhibitor is identical to capZ was complicated by
several factors. The limited number of human PMN available for
purification, capZ's high affinity interaction with actin, its decreased
sensitivity to Coomassie staining, the predominance of annexin VI and L-
plastin in active fractions, and most notably the physical properties shared
by these three proteins each added to my difficulties in identifying capZ as
the PMN inhibitor.
The use of the human neutrophil system greatly limits the starting
material. These immune cells have developed an effective antimicrobial
repertoire which includes a diverse collection of proteolytic molecules. A
packed cell volume of ~ 20 25 ml (derived from > 20 liters of peripheral
blood) was isolated during the largest preparations. With this amount of
cells, less than 1 gram of protein remains after clarification of the
homogenized cells. This is in stark contrast to the two previous published
purifications of capZ from animal cells (chicken skeletal muscle and
bovine brain). With the purification from chicken skeletal muscle, 1000 g
of chicken breast muscle are typically utilized to purify ~1 mg capZ


28
kinase C (PKC) are primarily associated with the rapid polymerization of
actin in PMN stimulated with fMet-Leu-Phe. Since this fMet-Leu-Phe-
induced increase in F-actin content in PMN is totally abolished if cells are
pretreated with pertussis toxin (Bengtsson et al., 1986; Omann et al.,
1991), investigators have actively pursued potential signals distal to the G-
protein, but proximal to calcium release and protein kinase C activation.
In addition to calcium, the in vitro actin regulatory activities of various
actin binding proteins are modulated by phosphoinositides. These in vitro
findings in combination with the observation that phosphoinositides are
rapidly turned over in PMN stimulated with fMet-Leu-Phe has led to the
hypothesis that phosphoinositides are primarily involved in the regulation
of the rapid, actin-polymerization response (Stossel, 1989; Janmey, 1994).
Phorbol esters, exemplified by phorbol myristate acetate (PMA),
have been shown to bind, translocate, and activate PKC in human
neutrophils (Castagna et al., 1982; Nishihira et al., 1986), and are
consequently utilized as specific PKC activators. Only minor increases in
F-actin content are noted when resting human neutrophils are stimulated
with levels of PMA that phosphorylate much more effectively than fMLP
(Bengtsson et al., 1986; Howard & Wang, 1987). Conversely, several
protein kinase inhibitors with relative specificity for PKC (i.e.,
staurosporine, CGP 41251, and H7), when used at functional
concentrations, do not significantly alter the rapid, 2-fold increase in F-
actin seen within 30 seconds of fMet-Leu-Phe stimulation of neutrophils
(Niggli & Keller, 1991; Keller & Niggli, 1993; Sham et al., 1993).
Additionally, neutrophil chemotaxis induced by fMet-Leu-Phe is only
slightly inhibited by staurosporine (Boonen et al., 1993).


45
Monomer Sequestration Assay
Gelsolin and non-pyrene labeled actin were copolymerized at high
molar ratios (1:16) in buffer P forming nuclei for pointed end
polymerization. Pyrene labeled G-actin (final of 0.8 pM) was added to
buffer P containing gelsolin/actin nuclei (15 nM/0.24 pM) and varying
concentrations of capZ (Young et al., 1990). This assay was repeated in
the presence of G-actin that was 50 % labeled to examine the possibility
that capZ binds pyrenylactin with lower affinity. These reactions were
performed in the presence of either 1 mM EGTA or 0.5 mM calcium.
Falling Ball Microviscometrv
The falling ball assay of MacLean-Fletcher and Pollard (1980) was
used to follow the relative activities of individual elution fractions at
various stages during the purification of neutrophil capZ. Rabbit skeletal
muscle actin (final concentration of 10 pM) was polymerized in the
presence of sample. After 2 hours at room temperature, the solutions
were drawn into glass capillary tubes. Relative viscosities are reflected by
the speed of steel balls traversing the tube (angled at 15).
Lipid-Binding And Capping-Inhibition Studies
Phosphatidylcholine (PC), phosphatidylinositol (PI),
Phosphatidylserine (PS) were purchased from Sigma (St. Louis, MO) and
used without further purification. Phosphatidylinositol 4,5-bisphosphate
(PIP2) was obtained from Calbiochem.


Time (min)
Relative Fluorescence
>
g £
Capping Activity (%) QO
01


ACKNOWLEDGMENTS
I would like to thank the members of my graduate committee for
their assistance and willingness to be a part of my education. Drs. Purich,
Baker, Driscoll, and Nick's constant support throughout my graduate work
enabled me to carry the project forward. I am especially indebted to my
mentor, Dr. Frederick Southwick, for his continued encouragement and
constant scientific guidance. His traits of perpetual enthusiasm, sincerity,
willingness to learn and dedication to basic science and clinical medicine
have provided a model I hope to equal someday. I would also like to
thank Dr. Purich for always being available when advice was needed. Our
discussions were always enjoyable, and I hope someday to be able to
explain complicated topics as simply and elegantly as he always does.
Special thanks also goes out to Dr. Mary Jo Koroly for a wonderful
introduction to the basic sciences. My tenure in the lab would not have
been as enjoyable if it were not for the many friends that I have made
during graduate school.
Finally, 1 would like to thank my family for their love, patience, and
support throughout my education.
iii


82
The molecular weights of the polypeptides copurified with the
viscosity lowering activity were currently found to be 66,000 and 68,000
when separated by 10 % SDS-PAGE (originally determined with 5 15 %
SDS-PAGE). Initial sequence analysis of the polypeptides resulted solely in
the identification of the 68 kDa upper band as annexin VI. Their shared
physical properties (Mr and pi) suggested the 66 kDa polypeptide was
related. It was speculated that the 68 kDa protein was susceptible to
known neutral proteolytic activity in human granulocytes (Southwick &
Stossel, 1981).
Despite the recognition of only the upper band by anti-annexin VI
immunoblot analysis, it was thought that the epitope recognized by this
monoclonal antibody (Zymed Laboratories, Inc., South San Francisco, CA)
was not present in the 66 kDa polypeptide. The annexins are a large
family of related proteins (Chapter 5). The structural similarity amongst
the annexin proteins limits the number of epitopes specific to each
member. The annexins have divergent sequences at their amino termini
(Creutz, 1992), and therefore it is likely that the monoclonal anti-annexin
VI-speciflc antibody recognizes an epitope in this region. It seemed
plausible that the 66 kDa polypeptide was a partially degraded form of
annexin VI that had lost the epitope recognized by the monoclonal
antibody. Alternative explanations included the possibility the 66 kDa
peptide was an alternatively spliced annexin VI lacking the epitope
(Crompton et al., 1988), the 66 kDa peptide was annexin VI post-
translationally modified in a manner preventing recognition of the
epitope, or the 66 kDa peptide was an unrelated peptide. To test these
possible explanations, the peptides were probed with a polyclonal antisera
specific to human annexin VI (Dr. Joel Ernst). Similar to the monoclonal


Figure 5-3. Western analysis of HL-60 differentiated to neutrophil-like or
macrophage-like cells. Total protein was collected at various time points
and subjected to Western analysis with the antibody to annexin VI.
Relative annexin VI amounts were obtained by laser scanning
densitometry of reactive bands on the nitrocellulose blots


3 PURIFICATION AND IDENTIFICATION OF CAPZ AS THE PMN
ACTIN POLYMERIZATION INHIBITOR 52
Introduction 52
Results 52
Discussion 75
4 FUNCTIONAL CHARACTERIZATION OF PMN CAPZ 8 8
Introduction 88
Results 89
Discussion 103
5 DEVELOPMENTAL EXPRESSION AND INTRACELLULAR
LOCALIZATION OF ANNEXIN VI IN PMN 113
Introduction 113
Results 115
Discussion 131
6 CONCLUSIONS AND FUTURE DIRECTIONS 136
Conclusions 136
Future Directions 139
REFERENCES 144
BIOGRAPHICAL SKETCH 160
v


19
(Wallace et al., 1984; Carson et al., 1986). All capping proteins purified
from non-muscle cells thus far cap (in vitro) the barbed ends of F-actin
filaments. Inhibiting exchange at the high affinity, barbed end effectively
raises the Cc to that of the pointed end. The steady-state result of the
interaction of these capping proteins with actin is increasing the
concentration of the G-actin pool and creating a large number of relatively
short filaments. Two proteins, accumentin and S-actinin, were originally
reported to cap the pointed end of F-actin filaments, but their activities
have since been shown to actually be barbed end capping of filaments
(acumentin) (Young, Maun, and Southwick unpublished data; Maruyama
et al., 1990). Barbed-end capping proteins are grouped based on their
functional and structural characteristics (Hartwig & Kwiatkowski, 1991;
Weeds & Maciver, 1993). The two major families of capping proteins are
the gelsolin family and the capZ family. The major functional difference
between these families is that proteins in the gelsolin family require
calcium to initiate the interaction with actin whereas the capping activity
of the capZ family occurs independently of calcium.
The gelsolin family of capping proteins is composed of the
structurally related mammalian (gelsolin, villin, capG, and scinderin) and
invertebrate proteins (fragmin and severin) (Mishra et al., 1994). Each
member is able to nucleate filament assembly and sever preformed
filaments (except capG; Southwick & DiNubile, 1986) in addition to their
collective ability to cap the barbed end. The founding and best
characterized member is gelsolin. Originally purified from rabbit alveolar
macrophages as a 91 kDa protein, gelsolin is now known to be widely
distributed (including muscle cells) (Yin & Stossel, 1979; Yin et al., 1981).


Figure 1-4. Regulation of actin assembly in PMN. This simple model attempts to explain the rapid
assembly of actin in fMet-Leu-Phe stimulated PMN.


15
binding proteins). Although the groups that control the three-dimensional
arrangement of actin filaments (gelation to solution or gel-sol reaction)
and those that apply force (contraction of actin gels) to the network are
almost certainly involved with the motile behavior of PMN (Condeelis,
1993), this discussion on actin-binding proteins will be limited to the
subset controlling actin-filament number and length.
The regulation of actin filament number and length is achieved by
four principle mechanisms. First, capping describes the ability of a
regulatory protein to bind to either the barbed ("+") or pointed ("-") end
of an actin filament preventing further addition or loss of monomers at
the particular end "capped." Severing is the mechanism whereby an actin-
binding protein is able to interact with the side of a filament and disrupt
the intermolecular interactions at that site, thus breaking the filament in
two. This is usually achieved by binding a "barbed" region within the
filament, and thus one of the newly severed fragments is capped at their
barbed end (Weeds & Maciver, 1993). The third mechanism, nucleation,
describes the ability of a protein to initiate elongation of actin filaments
without a lag phase. This may be achieved by either the rapid induction
of a polymerization-favorable conformation or stabilization of
intermediates in the formation of the trimeric nucleus. The forth
mechanism describes the ability of an actin binding protein to sequester
monomers in a 1:1 complex and inhibit their incorporation into filaments.
Therefore, if monomer-binding proteins are added to a solution of actin
monomers in stoichiometric amounts, the final extent of polymerization
upon the addition of salts will be decreased. The decrease will be
dependent upon the critical concentration of actin and the dissociation
constant of the interaction with actin monomers. It must be noted that the


39
activation by adherence to glass, Purified PMN were treated with the
potent neutral serine protease inhibitor DFP, cells were homogenized in
the presence of EGTA and a protease inhibitor cocktail, and efforts were
made to maintain the purification at 4 C. As originally reported
(Southwick & Stossel, 1981), the PMN viscosity lowering activity at this
stage copurified with two polypeptides in the 60 68 kDa range.
In efforts to further purify this activity, three additional columns
were utilized in the following order; High S (Bio-Rad Laboratories, Inc.,
Hercules, CA), Mono Q.(Pharmacia Biotech Inc., Piscataway, NJ), and
HTP/hydroxylapatite (Bio-Rad Laboratories, Inc., Hercules, CA). To
minimize protein loss during screening activity of these additional
columns, the Band 4.1 capping assay was substituted for the falling-ball
microviscometry assay (see "Actin Binding Studies" below). For the High
S cation exchange chromatography, active fractions were pooled and
dialyzed against a buffer containing 8 mM MES pH 6.0, ImM sodium azide,
and 0.1 mM PMSF (buffer S). The dialyzed fractions were then applied to
a 5 ml Econo-Pac High S cation exchange column which had been
equilibrated with buffer S. The column was washed with 5 ml of buffer S,
followed by a 30 ml (1 ml/min) linear salt gradient to 0.150 M KC1 in
buffer S. Active fractions from the High S column were pooled then
dialyzed against S2 buffer. After preclearing the fractions by
centrifugation at 10,000 X g for 5 minutes, they were applied to a Mono Q.
HR 5/5 anion exchange column equilibrated with S2 buffer. The column
was then washed with 5 ml (1 ml/min) of 0.1 M KC1 in S2 buffer, and
followed by a 12 ml linear gradient, 0.1 0.3 M KC1, gradient in S2 buffer.
Similar to the purification step described by Casella et al. (1986), our final
step entailed pooling and dialyzing Mono Q.active fractions against a 10


30
phosphoinositide phospholipids such as PIP2 can form complexes with
certain proteins (Janmey, 1994). Since phosphoinositide turnover via
phospholipase C hydrolysis of PIP2 is one of the major intracellular events
occurring proximal to either the increase in calcium or activation of
protein kinase C in activated PMN, the proposal that phosphoinositides
might regulate actin assembly seems plausible (Lassing & Lindberg, 1985;
Stossel, 1993). With the finding that phosphoinositides modulate the in
vitro interaction of profilin with actin, Lassing and Lindberg proposed
phosphoinositides may regulate actin assembly in cells. They were able to
demonstrate that actin sequestered by profilin can be dissociated by PIP2,
thus leading to actin polymerization (Lassing & Lindberg, 1985). Since
that time, numerous other actin-binding proteins have been shown to
interact with phosphoinositides (Isenberg, 1991; Janmey, 1994).
Interestingly, the interaction of barbed-end capping proteins with actin is
also specifically inhibited in the presence of polyphosphoinositide
phospholipids (Janmey, 1994).
Stossel has recently proposed a model that integrates motile signal
transduction events with the modulation of actin binding proteins in
attempts to explain how animal cells are able to crawl in response to a
stimulus (Stossel, 1993). The motile behavior of certain animal cells is
partly explained by the rapid polymerization of actin. In this model, a
motile stimulus results in the rapid turnover of intracellular
phosphoinositides. This in turn causes release of sequestered monomers
of actin, and prevention of barbed-end cap formation. The net result
would be a rapid polymerization of monomeric actin onto the barbed-ends
of actin filaments.


Figure 5-2. Northern analysis of HL-60 differentiated to neutrophil-like or
macrophage-like cells. Total RNA was isolated at various time points and
subjected to Northern analysis probing with the partial cDNA sequence to
annexin VI. This same blot was probed with random primer labeled
fragments of the F-actin cDNA sequence.


Figure 4-5. Actin filament severing assay. Gelsolin and pyrene actin
(2 pM) were copolymerized (molar ratio 1:200 gelsolin to G-actin) to
steady state in buffer P and ImM CaCl2 forming filaments capped at the
barbed ends. These filaments were then diluted to a final actin
concentration of 100 nM in buffer alone (open squares), buffer containing
a final concentration of 215 nM capZ (closed squares), and buffer
containing a final concentration of 100 nM gelsolin (closed triangles).


Figure 5-4. Indirect immunofluorescence microscopy of PMN. PMN were
allowed to adhere to glass coverslips. They were then fixed, permeabilized
and probed with the monoclonal antibody to annexin VI (Panel A) or
control monoclonal antibodies (Panel C, anti human hnRNP-M & Panel D,
anti yeast nab-1). Secondary antibodies used were identical (FITC-
conjugated anti mouse IgGl-heavy chain specific). Panel B is the phase
contrast image of panel A.


130
A


150
Heiss, S. G., and Cooper, J. A. 1991. Regulation of capZ, an actin
capping protein of chicken muscle, by anionic phospholipids. Biochemistry
30: 8753-8758
Herman, I. M., 1993. Actin isoforms. Curr. Opin. Cell Biol. 5, 48-55
Hill, M. A., and Gunning, P., 1993. Beta and gamma actin mRNAs are
differentially located within myoblasts. J. Cell Biol. 122: 825-832
Hitchcock, S. E. 1980. Actin-deoxyribonuclease I interaction.
Depolymerization and nucleotide exchange. J. Biol. Chem. 255: 5668-5673
Holmes, K. C., Popp, D., Gebhard, W., and Kabsch, W. 1990. Atomic
model of the actin filament. Nature 347: 44-49
Hosoya, H., Kobayashi, R., Tsukita, S., and Matsumura, F. 1992.
Ca2+-regulated actin and phospholipid binding protein (68kD-protein)
from bovine liven identification as a homologue for annexin VI and
intracellular localization. Cell Motil. Cyto. 22: 200-210
Howard, T. H. and Meyer, W. H. 1984. Chemotactic peptide
modulation of actin assembly and locomotion in neutrophils. J. Cell Biol.
98: 1265-1271
Howard, T. H., and Oresajo, C. O. 1985. The kinetics of chemotactic
peptide-induced changes in F-actin content, F-actin distribution, and the
shape of neutrophils. J. Cell Biol. 101: 1078-1085
Howard, T. H., and Wang, D. 1987. Calcium ionophore, phorbol
ester, and chemotactic peptide-induced cytoskeleton reorganization in
human neutrophils. J. Clin. Invest. 79: 1359-1364
Huxley, H. E. 1963. Electron microscope studies on the structure of
natural and synthetic protein filaments from striated muscle. J. Mol. Biol.
7: 281-308
Isenberg, G. 1991. Actin-binding protein-lipid interactions. Cell
Motil. Cytoskeleton 12: 136-44
Isenberg, G., Aebi, U., and Pollard, T. 1980. An actin-binding protein
from Acanthamoeba regulates actin filament polymerization and
interactions. Nature 288: 455-459


Figure 1-1. Actin and its spontaneous polymerization in salt. The filament
shown here is decorated with heavy meromyosin which binds at a 45
angle distinguishing the 2 ends of the filament. The barbed-end (+) is the
fast-growing end, and the pointed end (-) is the slow-growing end of the
filament


Relative Fluorescence
94
Time (min)


35
Clermont et al., 1991). The role of profilin in activated PMN remains
controversial since the PIP2 effect would theoretically prevent ATP/ADP
exchange.
There have been no reports of calcium-independent capping
proteins in neutrophils or macrophages. Two abstracts were recently
presented at the ASCB (American Society for Cell Biology) meeting
December, 1994 noting the presence of capZ in platelets (Barkalow &
Hartwig, 1994; Nachmias et al., 1994). These three cells are the
mammalian model cells for understanding the signal transduction
mechanisms leading to rapid actin assembly. As discussed above, the
rapid polymerization response in neutrophils can occur independently of
calcium. It is upon these premises that we have further investigated the
calcium insensitive activity of PMN Actin Polymerization Inhibitor, an
activity originally purified by my mentor Dr. Southwick.
PMN Actin Polymerization Inhibitor
A Major Calcium-Independent Activity In PMN Extracts
Approximately 15 years ago, Southwick and Stossel isolated an actin
binding activity from human neutrophils thought to account for much of
the unpolymerized actin in granulocyte extracts (Southwick & Stossel,
1981). This activity, PMN actin polymerization inhibitor, was shown to
decrease the viscosity of purified skeletal-muscle actin under polymerizing
conditions in the presence of 1 mM EGTA and absence of added calcium.
Substoichiometric concentrations of the inhibitor were still able to
decrease the viscosity of purified actin allowed to polymerize in the
presence of 0.1 M KC1. PMN Actin Polymerization Inhibitor was purified


38
(Southwick & Stossel, 1981). Briefly, cells were cooled to 4 C and washed
twice in normal saline, treated with 5 mM diisopropylfluorophosphate
(DFP) for 15 min and then resuspended in 3 volumes of a solution
containing 5 mM dithiothreitol (DTT), 2 mM ATP, 20 mM EGTA, 20 mM
imidazole-HCL, pH 7.5, 1 mM phenylmethylsulfonyl fluoride (PMSF), 1
g/100 ml leupeptin, 4 g/100 ml aprotonin, and 7.8 g/100 ml benzamidine
(homogenization solution). Cells were broken by nitrogen cavitation at
900 psi. This procedure ruptured greater than 95 % of all cells, as
monitored by phase microscopy. The homogenates were centrifuged at
12,100 Xg for 60 min. The supernatant was dialyzed against 500
volumes of S2 buffer (10 mM Imidazole pH 7.8, 5 mM DTT, 1 mM MgCl2,
1 mM ATP, 1 mM EGTA) for 3 hrs, then diluted 1:1 with S2 buffer and
applied to a 1.5 cm X 16.5 cm DEAE-Sepharose CL-6B anion exchange
column (Pharmacia Biotech Inc. Piscataway, NJ) equilibrated with 120-200
ml of S2 buffer. After application of the supernatant, the column was
washed with 60 ml of 0.08 M KC1 in S2 buffer, followed by 250 ml linear,
0.08-0.4 M KC1, gradient in S2 buffer. Eluted fractions were analyzed by
coomassie blue stained SDS-PAGE and by falling ball microvlscometry
(MacLean-Fletcher & Pollard, 1980). Fractions that lowered the viscosity
of F-actin under low Ca2+ conditions were pooled and concentrated to a
volume of 0.5-3.0 ml (< 10 mg/ml) in a nitrogen pressure concentrator
using an Amicon PM-30 ultrafiltration membrane (Amicon Corp.,
Lexington, Mass.). The concentrated sample was then subjected to gel
filtration using a protein-pak 125 (Waters Associates, Milford, MA) column
equilibrated, and eluted with 0.1 M KC1 in S2 buffer. Several precautions
were taken to limit activation of the abundant proteases present in PMN.
Isolation of PMN was performed using plastic to avoid generalized


97
=L
C
v
<
6
l.o-
0.9-
0.8-
0.7-
0.6-
0.5-
0.4-
0.3 is
0.2-
o.i-
o.o
0

A

1 0
A

2 0


A 0.9 jiM Total Actin
3.0 |iM Total Actin
i 1 1
3 0 4 0 5 0
CapZ (nM)


REFERENCES
Amatruda, J. F., and Cooper, J. A. 1992. Purification,
characterization, and immunofluorescence localization of Saccharomyces
cerevisiae capping protein. J. Cell Biol. 117: 1067-1076
Anderson, T., Dahlgren, C., Pozzan, T., Stendahl, O., and Lew, D. P.
1986. Characterization of fMet-Leu-Phe receptor-mediated Ca^+ influx
across the plasma membrane of human neutrophils. Mol. Pharm. 30: 437
Andrews, P. C., and Babior, B. M. 1983. Endogenous protein
phosphorylation by resting and activated human neutrophils. Blood 61:
333-340
Ankenbauer, T., Kleinschmidt, J. A., Walsh, M. J., Weiner, O. H., and
Franke, W. W. 1989. Identification of a widespread nuclear actin binding
protein. Nature 342: 822-826
Bainton, D. F. 1992. Developmental biology of neutrophils and
eosinophils. In: Inammation: basic principles and clinical correlates, 2nd
Ed., Eds: Gallin, J. I., Goldstein, I. M., and Snyderman, R. Raven Press, New
York
Barkalow, K., and Hartwig, J. H. 1994. Identification of a calcium
independent actin filament capping activity in human platelets. Mol. Biol.
Cell Vol. 5, abstract 1580
Barron-Casella, E. A., and Casella, J. F. 1993. Sequence analysis of
human capZ. Mol. Biol. Cell Vol. 4, abstract 1496
Becker, E. L. 1987. The formyl peptide receptor of the neutrophil. A
search and conserve operation. Am. J. Pathol. 129: 16-24
Becker, E. L., Kermode, J. C., Naccache, P. H., Yassin, R., Marsh, M. L.,
Munoz, J. J., and Sha'afi, R. I. 1985. The inhibition of neutrophils granule
enzyme secretion and chemotaxis by pertussis toxin. J. Cell Biol. 100:
1641-1646
144


Activity
70
c
1.0
0.5
0.0
C 24 3 0 3 2 3 4 3 6 3 8 4 0 4 2 4 4 5 2
Fraction #


xml version 1.0 encoding UTF-8
REPORT xmlns http:www.fcla.edudlsmddaitss xmlns:xsi http:www.w3.org2001XMLSchema-instance xsi:schemaLocation http:www.fcla.edudlsmddaitssdaitssReport.xsd
INGEST IEID EL7XQ7RKC_D4W9PY INGEST_TIME 2012-12-07T21:04:49Z PACKAGE AA00012900_00001
AGREEMENT_INFO ACCOUNT UF PROJECT UFDC
FILES


114
containing 1 mM Ca2+ (Hayashi et al., 1989). My studies of PMN annexin
VI (Chapter 3) do not exclude the possibility of a calcium-regulated actin-
filament bundling or cross-linking activity by this protein. At least seven
annexins, including a 68 kDa protein, are present in human PMN (Meers et
al., 1987; Ernst, 1990).
In response to various stimuli, the intracellular calcium
concentration in PMN transiently elevates. This rise is thought to be
important for degranulation (Lew et al., 1986). Blocking this increase can
prevent superoxide anion production and exocytosis (Lew et al., 1984). In
neutrophils, intracellular calcium levels have been observed as high as
1,586 nM during phagocytosis (Jaconi et al., 1990). In this same study,
however, phagosome-lysosome fusion could be inhibited by buffering
intracellular Ca2+ to < 20 nM. Annexin VI in vitro binds phospholipids in
the micromolar calcium range (Geisow & Burgoyne, 1982). Chemotaxis,
phagocytosis, and degranulation are quintessential functions for PMN. In
part, these properties are dependent upon a coordinated rearrangement of
cellular membranes and the surrounding cytoskeleton. It is possible that
annexin VI from human neutrophils may play a role in this process.
As PMN differentiate from myeloblasts they develop more
prominent intracellular vesicles termed granules, hence earning the
designation granulocytes. There are at least two major (azurophilic and
specific) and two minor populations of granules in PMN whose distinct
role in the inflammatory process is evidenced by the different proteins
stored in each granule. Azurophilic granules store molecules necessary for
non-oxidative killing of microorganisms, while the constituents of specific
granules include, in addition to antimicrobial agents, a collection of
receptors and other proteins involved in functional activation of PMN


Figure 3-6. DEAE-anion exchange chromatography of PMN extract.
Extracts were eluted with a linear KC1 gradient as described (Chapter 2).
Eluted proteins were subjected to 10 % SDS-PAGE (with HMW stds) and
stained with Coomassie (Panel A) or transferred to nitrocellulose and
probed with antisera to chicken skeletal-muscle capZ (Panel B). Relative
activities (Panel C) were reported as the ability of fractions to decrease the
viscosity of actin solutions (10 pM) as measured by falling ball
microviscometry.


Area Relative to T-0 Area Relative to T=0
123
Western Blot HL-60 Differentiation #1
Time (hrs)
Western Blot HL-60 Differentiation
4t
Time (hrs)
#2


110
A modest increase in nuclei with free pointed ends could be canceled out
by the loss of nuclei with free barbed ends.
The capZ purified from brain or skeletal muscle, although, has been
demonstrated to nucleate filament assembly (Kilimann & Isenberg, 1982;
Caldwell et al., 1989). The capZ nucleation reaction is quite complicated,
and is not completely understood (Caldwell et al., 1989). The cellular
importance of the capZ nucleating activity, as well, is unknown. If the
capZ concentration in cells is greater than the concentration of barbed
ends, free capZ would likely exist. A substantial portion of capZ in
epithelial cells is present in the supernatants of ultra-speed cellular
fractions as detected by Western analysis, suggesting the abundance of
soluble capZ in these cells (Schafer et al., 1992). The ability of free capZ to
nucleate assembly would be highly dependent upon the critical
concentration of actin in cells. As the majority of the unpolymerized actin
in PMN is most likely sequestered by thymosin 84 and profilin (Cassimeris
et al., 1992), the free G-actin concentration is probably close to the critical
concentrations determined in vitro for capped (~1 pM or ~0.1 pM
respectively for barbed- or pointed-end capped filaments) or uncapped
filaments (~0.15 pM). With the nucleation studies, the effects of PMN capZ
on the polymerization of 1.5 pM G-actin in 0.1 M KC1 and 1 mM Mg2+
were monitored. These conditions are closer to the physiologic ionic
conditions and presumed critical concentration in PMN than those used in
similar assays to detect nucleating activity by capZ isolated from brain (12
pM actin, 20 mM KC1) or skeletal muscle (5 pM, 2 mM Mg2+).
Additionally, the nucleating activity for skeletal muscle capZ is inhibited in
the presence of P1P2, a phospholipid thought to interact with actin binding
proteins in a manner promoting polymerization (Heiss & Cooper, 1991).


16
in vitro analysis and in vivo interpretation of function of actin binding
proteins is often complicated by their ability to utilize more than one
mechanism to regulate actin filaments.
Monomer Sequestering Proteins
A high concentration of actin, well above the Cc necessary for
assembly at both ends of the filament, is stored in an unpolymerized form
in nonmuscle cells (100 200 pM or greater in PMN, assuming a uniform
distribution) and becomes available for assembly into filaments upon cell
activation. Monomer sequestering proteins are felt to account for a
majority of the unpolymerized actin found in these cells. The two major
families of proteins in this class are the profilins and the thymosins.
Mammalian profilins are low-molecular-weight proteins with Mr
around 15,000. Initially purified from spleen (Carlsson et al., 1977), it
has since been found in almost all mammalian cell types including PMN,
macrophages, and platelets (Southwick & Young, 1990; DiNubile &
Southwick, 1985; Markey et al., 1978). Purified profilin is able to
reversibly bind actin monomers with an apparent dissociation constant
(Kd) in the range of 1 to 10 pM (Larsson & Lindberg, 1988; Goldschmidt-
Clermont et al., 1991). For many years, profilin was thought to be the
major sequestering protein in nonmuscle cells, and simple sequestration
was its primary function. Estimations of profilin concentrations made
initially in platelets and subsequently in PMN suggested the concentration
of profilin (~40 pM) present within these cells is insufficient, when using
the simple model of sequestration, to account for the amount of
nonpolymerized actin (~100 200 pM) in resting states (Lind et al., 1987;
Southwick & Young, 1990).


Figure 3-5. Western blot analysis of PMN inhibitory fractions probed with
capZ antisera. Fractions from the four most recently purified PMN actin
polymerization inhibitor purified by DEAE-ion exchange and gel-filtration
chromatography each had detectable levels of both subunits (a and |3) of
capZ.


108
protein has been previously purified and characterized in muscle and
brain, its presence and interaction with actin in highly motile animal cells
has yet to be described. The majority of actin filaments present in resting
neutrophils are thought to be capped at their kinetically active barbed
end. This cap is partially responsible for maintaining the high levels of
unpolymerized actin found in these cells. Upon chemotactic stimulation,
the amount of actin in neutrophils doubles (see Chapter 1). Uncapping of
the high-affinity barbed-ends in response to chemoattractant stimulation
may be responsible for the rapid conversion of monomeric actin to
filamentous actin. Unlike gelsolin or capG, the other major barbed-end
blocking proteins found in the cytoplasm of PMN, capZ's capping function
is independent of the free calcium concentration. This characteristic may
partly explain the findings that changes in intracellular Ca^+ are not
required for chemoattractant-stimulated actin assembly (see Chapter 1).
Using three separate assays I was able to demonstrate that PMN capZ
interacts specifically at the barbed end. The interaction of capZ with
polymerizing or depolymerizing filaments suggests this protein binds with
high affinity (Kd ~3 nM) to the barbed-end of actin filaments. This is
similar to the Kd (0.5 1 nM) reported for capZ purified from chicken
skeletal muscle (Caldwell et al., 1989). As further evidence for barbed-end
capping, capZ was shown to maximally elevate the critical concentration of
actin at steady-state (~ 0.8 pM) to levels resembling that of the pointed
end.
My detailed analysis of the interaction of PMN capZ with actin
suggests the calcium-independent viscosity lowering effect of this protein
is due primarily to the formation of short actin filaments capped at the
barbed end. The ability of capZ to inhibit the depolymerization of


86
(Casella et al., 1986, Caldwell et al., 1989). Purification of capZ from
bovine brain similarly requires ~ 1000 g starting material (4 brains)
(Kilimann and Isenberg, 1982). Our final yield of PMN capZ after
hydroxylapatite chromatography (~ 10 pg) was about one-tenth of those in
chicken muscle capZ preparations. This finding is not surprising
considering the abundant proteolytic activity commonly seen in extracts
made from these phagocytes. Secondly, the ability of capZ to interact with
actin with such high affinity (s 250 ng/ml, based on Kd ~3 nM) (see
Chapter 4) allowed for detection of activity with minimal protein as seen
by stained polyacrylamide gels. The problem was further complicated by
the identification of the two major polypeptides copurified with the
activity as previously studied actin binding proteins.
Lastly, the elusiveness of capZ resulted primarily from its physical
properties and staining characteristics. The consistent purification of
annexin VI and L-plastin with capZ is currently explained by the similar
native molecular weights and isoelectric points shared by these three
proteins (annexin VI/L-plastin: Mr 64,000 70,000 and pi 5.3 5.6 for
both proteins). The molecular weights of bovine brain and chicken
skeletal muscle capZ were reported as 63,000 (pi 5.75) and 61,000
respectively (Kilimann and Isenberg, 1982; Casella et al., 1986). A Stokes
radius of 32 was determined for the PMN actin polymerization inhibitor
by analytical gel filtration following the viscosity lowering activity
(Southwick & Stossel, 1981). This closely resembles the Stokes radii
determined for bovine brain (35.5 ) and chicken skeletal muscle (37 )
(Kilimann and Isenberg, 1982; Casella et al., 1986). Many
chromatographic techniques rely on variations of MW or pi to separate
proteins. The physical properties shared by these three proteins


145
Bengtsson, T., Stendahl, 0., and Anderson, T. 1986. The role of the
cytosolic free Ca^+ transient for fMet-Leu-Phe induced actin
polymerization in human neutrophils. Eur. J. Cell Biol. 422: 338-343
Blackwood, R. A., and Ernst, J. D. 1990. Characterization of Ca^+-
dependent phospholipid binding, vesicle aggregation and membrane
fusion by annexins. Biochem. J. 266: 195-200
Bonder, E. M., Fishkind, D. J., and Mooseker, M. S. 1983. Direct
measurement of critical concentrations and assembly rate constants at the
two ends of actin filaments. Cell 34: 491-501
Boonen, G. J., deKoster, B. M., Vansteveninck, J., and Elferink., J. G.
1993. Neutrophil chemotaxis induced by the diacylglycerol kinase
inhibitor R59022. Biochim. Biophys. Acta. 1178: 97-102
Boulay, F., Tardif, M., Brouchon, L., and Vignais, P. 1990. Synthesis
and use of a novel N-formyl peptide derivative to isolate a human N-
formyl peptide receptor cDNA. Biochem. Biophys. Res. Commun. 29:
11123-11133
Boyles, J., and Bainton, D. F. 1981. Changes in plasma-membrane-
associated filaments during endocytosis and exocytosis in
polymorphonuclear leukocytes. Cell. 24: 905-914
Brandt, S. J., Dougherty, R. W., Lapetina, E. G., and Niedel, J. E. 1985.
Pertussis toxin inhibits chemotactic peptide-stimulated generation of
inositol phosphates and lysosomal enzyme secretion in human leukemic
(HL-60) cells. Proc. Natl. Acad. Sci. 82: 3277-3280
Bretscher, A. 1991. Microfilament structure and function in the
cortical cytoskeleton. Anriu. Rev. Cell Biol. 7: 337-374
Caldwell, J. E., Heiss, S. G., Mermall, V., and Cooper, J. A. 1989a.
Effects of capZ, an actin capping protein of muscle, on the polymerization
of actin. Biochemistry 28: 8506-8514
Caldwell, J. E., Waddle, J. A., Cooper, J. A., Hollands, J. A., Casella, S.
J., and Casella, J. F. 1989b. cDNAs encoding the 13 subunit of capZ, the
actin-capping protein of the Z line of muscle. J. Biol. Chem. 264: 12648-
12652
Carlier, M. F. 1991. Actin: protein structure and filament dynamics.
J. Biol. Chem. 266: 1-4


Figure 4-5. Actin filament severing assay. Gelsolin and pyrene actin
(2 pM) were copolymerized (molar ratio 1:200 gelsolin to G-actin) to
steady state in buffer P and ImM CaCl2 forming filaments capped at the
barbed ends. These filaments were then diluted to a final actin
concentration of 100 nM in buffer alone (open squares), buffer containing
a final concentration of 215 nM capZ (closed squares), and buffer
containing a final concentration of 100 nM gelsolin (closed triangles).


40
mM potassium phosphate buffer pH 7.0 containing 0.1 mM DTT. This
sample was then applied to a 1 ml hydroxylapatite (Econo-Pac HTP)
column equilibrated with the same buffer, and eluted with a linear
gradient to 75 mM potassium phosphate pH 7.0, and 0.1 mM DTT. Active
fractions were quantified using the Quantigold assay (Diversified Biotech)
and then stored at -20 C in 30 % ethylene glycol (under these storage
conditions the specific activity of the protein remained stable for >3
months).
Purification Of Muscle Actin
Actin was purified from rabbit skeletal-muscle by the method of
Spudich and Watt (1971). Monomeric actin was gel filtered through a
Superdex 200 16/60 (Pharmacia Biotech Inc., Piscataway, NJ) column for
polymerization kinetic studies. Pyrenylactin was prepared according to
Kouyama and Mihashi (1981) with the modifications described previously
(Young et al., 1990). Actin concentrations were calculated using the
extinction coefficient of 24.9 mM"' cm'l at 290 nm with the correction for
pyrenyl absorption according to Selden and colleagues (1983).
Amino Acid Sequence Analysis
Peptides were electroblotted from SDS-polyacrylamide gels onto
polyvinylidene difluoride (PVDF) membranes using a transfer buffer
containing 12.5 mM Tris, 96 mM glycine, 10 % ethanol, pH 8.3 as
previously described (Mozdzanowski et al., 1992). The samples were
blotted, stained, and sent to our collaborator Dr. David W. Speicher at The


4
in certain parts of or throughout the cell (Stossel, 1992). The properties
of PMN chemotaxis, phagocytosis, adherence, and degranulation (the
principle movements) have gained the most attention in regards to the
relationship to cytoplasmic actin assembly.
In attempts to familiarize itself to the environment, the neutrophil
(and all animal cells to a certain extent) constantly forms and dissolves
diverse protrusions from its surface. Dependent upon external signals,
these protrusions take on particular shapes known as veils, ruffles, pleats,
filopodia, microvilli, and pseudopodia. Evidence suggests actin is
responsible for the elasticity of this organelle-deplete, actin-enriched
cortical region (Bretscher, 1991). The predominance of an agonistic signal
in certain regions allows for the formation of peripheral protrusions which
eventually lead to the motile properties of the neutrophil.
Actin
Actin Isoforms
In 1942 Bruno Straub discovered and isolated actin from rabbit
skeletal muscle (Straub, 1942). Nonmuscle cell actin was first purified
from Physarium by Hatano and Oosawa (1966). It has since been realized
that actin is ubiquitous (prokaryotic, plant, and animal cells), and often
the most abundant protein component in cells. Initially, it was thought
there were three major isoforms of actin in mammalian cells (Carrels &
Gibson, 1976). One muscle (a) and two non-muscle isoforms (p,
predominant non-muscle form, and y, second non-muscle form) could be
distinguished by isoelectric focusing; each with apparently distinct pis
between 5.40 and 5.44. It has since been demonstrated in mammals and


Figure 3-10. Hydroxylapatite column chromatography. As a final
purification step, peak active fractions from Mono Q.chromatography were
subjected to hydroxylapatite (HA) column chromatography as described
(Chapter 2). Fractions were subjected to 10 % SDS-PAGE and silver stained
(Panel A). Relative activities were measured as in Figure 3-7.


I
I
I I I
*
N>
I rim
I
>
GO


Activity
74
A
14 18 22 24 26 28 30 34 38 Std
12 16 20 23 25 27 29 32 36 40
A'
12 16 20 23 25 27 29 32 36 40
Anti-L-plastin
-
*' **-1
26 27
28 29 30 31
32
C


CHAPTER 2
MATERIALS AND METHODS
Isolation Of Human Polymorphonuclear Leukocytes (PMN)
Fresh leukocyte enriched fractions from the whole blood of healthy
donors were obtained from the community blood bank. For each
preparation, 15-45 buffy coat units were used. Further isolation of
leukocytes was accomplished using a variation of the technique described
by Southwick and Stossel (1981). Briefly, leukocyte enriched fractions
were pooled and sedimented through Dextran T-500 (Pharmacia Biotech
Inc., Piscataway, NJ). This procedure yielded on average 85 % PMN the
remainder of the cells representing lymphocytes (12 96) and monocytes (3
%). In some cases this procedure was followed by Ficoll-sodium diatrizoate
sedimentation. This procedure increased the purity of PMN to 95 %. CapZ
obtained from granulocytes isolated with or without a Ficoll-sodium
diatrizoate sedimentation resulted in purified protein with identical actin
binding activity. Higher yields of PMN capZ were achieved using dextran
alone.
Purification Of CapZ From Human PMN
All steps were done at 4 C whenever feasible. The initial
procedures used were nearly identical to those described previously
37


153
Markey, F., Lindberg, U., and Eriksson, L. 1978. Human platelets
contain profilin, a potential regulator of actin polymerisability. FEBS Lett.
88: 75-79
Marks, P. W., and Maxfield, F. R. 1990. Transient increases in
cytosolic free calcium appear to be required for the migration of adherent
human neutrophils. J. Cell Biol. 110: 43-52
Maruyama, K., Kurokawa, H., Oosawa, M., Shimaoka, S., Yamamoto,
H., Ito, M., and Maruyama, K. 1990. 8-actinin is equivalent to capZ protein.
J. Biol. Chem. 265: 8712-8715
Meers, P., Ernst, J. D., Duzgunes, N., Hong, K., Fedor, J., Goldstein, 1.
M., and Papahadjopoulos, D. 1987. Synexin-like proteins from human
polymorphonuclear leukocytes. J. Biol. Chem. 262: 7850-7858
Meshulam, T., Proto, P., Diamond, R. D., and Melnick, D. A. 1986.
Calcium modulation and chemotactic response: divergent stimulation of
neutrophil chemotaxis and cytosolic calcium response by the chemotactic
peptide receptor. J. Immunol. 137: 1954-1960
Mishra, V. S., Henske, E. P., Kwiatkowski, D. J., and Southwick, F. S.
1994. The human actin-regulatory protein cap G: gene structure and
chromosome location. Genomics 23: 560-565
Mockrin, S. C., and Korn, E. D. 1980. Acanthamoeba profilin
interacts with G-actin to increase the rate of exchange of actin-bound
adenosine 5'-triphosphate. Biochemistry 19: 5359-5362
Mozdzanowski, J., Hembach, P., and Speicher, D. W. 1992. High yield
electroblotting onto polyvinlidene difluoride membranes from
polyacrylamide gels. Electrophoresis 13: 59-64
Nachmias, V. T. 1993. Small actin-binding proteins: the 8-thymosin
family. Curr. Opin. Cell Biol. 5: 56-62
Nachmias, V. T., Golla, R., Casella, J. F., and Barron-Casella, E. 1994.
CapZ in human platelets. Mol. Biol. CellVol. 5, abstract 1579
Namba, Y., Ito, M., Zu, Y., Shigesada, K., and Maruyama, K. 1992.
Human T cell L-plastin bundles actin filaments in a calcium-dependent
manner. J. Biochem. 112: 503-507
Neuhaus, J. M., Wanger, M., Keisler, T., and Wegner, A. 1983.
Treadmilling of actin. J. Muscle Res. Cell Motil. 4: 507-527


103
Monomer Sequestration Assay
The ability of capZ to sequester monomeric actin was examined
using gelsolin-actin nuclei (Chapter 2). These nuclei containing free
pointed ends were added to a mixture containing a fixed concentration of
actin monomers and increasing concentrations of capZ. A monomer
sequestering protein would be expected to slow the rate of actin assembly
in a dose dependent manner (Young et al., 1990). In the presence of 1
mM EGTA or 0.5 mM calcium, at final concentrations as high as 360 nM,
capZ failed to alter the polymerization rate of gelsolin-actin nuclei (see
Figure 4-6). Identical effects were observed with both 100 % and 50 %
pyrene-labeled monomeric actin.
Effect Of P1P2 On The Ability Of CapZ To Bind The Barbed-Ends Of Actin
Filaments
As seen in Figure 4-7, the capping ability of 36 nM capZ was
decreased in a concentration dependent fashion by the addition of PIP2
micelles. The 1/2 maximal inhibition of capZ capping activity was
observed at approximately 5.5 pg/ml (5 pM). At concentrations of up to
11 pg/ml, the anionic phospholipids phosphatidylserine and
phosphatidylinositol as well as the neutral phospholipid
phosphatidylcholine failed to elicit a detectable decrease in capZ capping
activity (see figure 4-7).
Discussion
My discovery that PMN capZ binds the barbed ends of actin
filaments in vitro, suggests its involvement in the regulation of the
microfilament network in highly motile animal cells. Although this


68
immunoreactive peptides (Figure 3-6C fraction # 36 42) were found to
correlate with the neutrophil actin polymerization inhibitory activity. As
seen in Figure 3-6, the viscosity lowering activity was maximal in fractions
36 42 (panel C). These fractions also represented the peak capZ, annexin
VI (68 kDa), and L-plastin (66 kDa) fractions.
A scheme utilizing three additional columns was empirically devised
to separate annexin VI and L-plastin and further purify the neutrophil
actin polymerization inhibitor (High S, Mono Q, and hydroxylapatite).
Active fractions composed predominantly of annexin VI and L-plastin were
further separated by High S-cation exchange chromatography (Figure 3-7)
under similar conditions utilized during the purification of skeletal muscle
capZ. Figure 3-7A represents the typical separation achieved by this
method. The polymerization inhibitory activity correlates with L-plastin
(fraction # 28 42). Fractions #62 -86 are composed of annexin VI
(Figure 3-7B) as detected by Western analysis. Similar to the
phospholipid-purified annexin VI, no activity was detected for fractions of
annexin VI separated by High S-ion exchange chromatography (Figure 3-
7C, fraction # 62 70).
Active fractions after High S chromatography were applied to a
Mono Q.anion exchange column and eluted with KC1 (Figure 3-8A) as
described earlier (Chapter 2). Despite the presence of PMSF in dialysis
solutions and maintenance of all procedures at 4 C, the 55 kDa L-plastin
degradation product was formed in significant amounts by this stage of
the purification (Figure 3-8C, fraction # 28 34: lower band). Mono Q.
chromatography separated the peak L-plastin fractions (Figure 3-8C
fraction # 29 32), but not its degradation product (see fraction # 26 28)
from the neutrophil actin polymerization inhibitor. The purification was


41
Wistar Institute Philadelphia, PA for amino acid sequence analysis.
Coomassie blue stained bands were excised and sequenced on an Applied
Biosystems model 475A sequencer using gas phase TFA delivery and an
on-line model 120A PTH analyzer with modifications as previously
described (Reim et al., 1992). Acetonitrile and tetrahydrofuran were from
J. T. Baker. All other sequencer solvents and reagents were from Applied
Biosystems.
Polyacrylamide Gel Electrophoresis And Western Blot Analysis
SDS-PAGE
Protein samples were subjected to electrophoresis on 10 %
discontinuous pH mini (Bio-Rad Laboratories, Inc., Hercules,
CA) or mid-sized (Hoefer Scientific Instruments, San Francisco, CA) SDS-
PAGE. Molecular weights (Mr) of proteins of interest were determined by
simultaneous electrophoresis of other polypeptides of known molecular
weights, and plotting their relative mobility verses log Mr- Proteins were
visualized by staining the gels with Coomassie brilliant blue R-250 or
Silver (Silver stain plus kit, Bio-Rad Laboratories, Inc., Hercules, CA).
Immunoblotting
The electrophoresed proteins were then transferred to nitrocellulose
paper (graphite electroblotter, Millipore) using standard protocols
(Towbin et al., 1979). The transferred blots were subjected to a blocking
step in 3 5 % non-fat dry milk in phosphate-buffered saline (PBS) and 0.3
% tween-20 for at least three hours. The primary antibodies were diluted
appropriately in the blocking solution (anti human annexin VI at 1:4000


109
filaments argues against a severing activity. In addition, I was unable to
demonstrate severing of filaments by capZ (as high as 215 nM) at
concentrations and conditions where the severing activity of gelsolin is
readily detected. The lack of any reduction in the rate of growth from
gelsolin-actin nuclei suggests that capZ does not sequester actin monomers
with high affinity. These assays could not detect low affinity sequestering
(micromolar Kd) as the purification of PMN capZ limits the studies to
substoichiometric ratios of capZ to actin. This assay, however, proves that
capZ has no effect on monomer exchange at the pointed ends of actin
filaments. This finding is consistent with the steady-state analysis
revealing an elevation of the critical concentration in the presence of capZ.
An interaction with the pointed end would be expected to lower the
critical concentration of actin closer to that of the barbed end.
Similar to aginactin, an activity from Dictyostelium containing the
capZ-related protein cap 32/34 (Eddy et al., 1993; Sauterer et al., 1991), I
was unable to demonstrate nucleation of filament assembly by PMN capZ.
Additionally, when the polymerization of actin was studied in the presence
of the capZ-related protein purified from Xenopus, a prolongation of the
lag phase and a reduction in the extent of polymerization was observed
(Ankenbauer et al., 1989). These findings were explained by an
interaction with polymerizing-actin limited to capping of the barbed end.
A similar prolongation of the lag phase was noted for the calcium-sensitive
barbed-end capping protein capG (Young et al., 1990). 1 cannot
completely exclude the possibility that PMN capZ may weakly interact with
monomeric actin and cause low levels of nucleation. Because this protein
blocks the barbed ends and fails to produce more pointed ends by
severing, low levels of nucleation activity may not be readily measurable.


inhibitor, PMN capZ's capping activity is independent of Ca^+ and is
inhibited by increasing the KC1 concentration from 0.1 M to 0.6 M. As
observed in all previously studied barbed-end capping proteins, PMN
capZ's capping function is inhibited by phosphatidylinositol 4,5-
bisphosphate (PIP2) micelles, 1/2 maximal inhibition being observed at
5.5 pg ml'l. Phosphatidylcholine, phosphatidylserine, or
phosphatidylinositol (11 pg ml'l) fan t0 inhibit capping function. The
PMN capZ's effects on actin assembly are confined to an interaction with
the barbed ends of actin filaments. This protein does not cap actin
filament pointed ends, does not sever preformed filaments, and fails to
interact significantly with actin monomers. Kinetic studies reveal no
enhancement of the nucleation step in actin assembly. This first report of
a capZ-related protein isolated from mammalian phagocytes suggests that
capZ is likely to play an important role in the regulation of actin filament
assembly in phagocytic cells.
IX


Figure 1-2. Rate constants for the association and dissociation of ATP-
actin and ADP-actin at filament ends. Adapted from Pollard (Curr. Opin.
Cell Biol. 1990. 2: 33-40)


55
purified fractions (> 90 % composed of the 66 and 68 kDa polypeptides as
assessed by densitometry scanning of Coomassie blue stained SDS-PAGE)
lowered the viscosity of actin filament solutions as measured by falling-
ball microviscometry. The minor proteins, if present, (usually < 10 %)
were composed of a 42 kDa polypeptide believed to be actin (rabbit
skeletal muscle actin comigrates with this band) and a 55 kDa polypeptide
later found to be an L-plastin degradation product (see below). Active
fractions, composed predominantly of the 66 and 68 kDa polypeptides,
were separated on SDS-PAGE, transferred onto polyvinylidene difluoride
(PVDF), stained and sent to our collaborator Dr. David W. Speicher (The
Wistar Institute, Philadelphia, PA) for amino-acid sequence analysis. The
original analysis performed after BNPS-Skatole digestion (the amino-
termini of the polypeptides were blocked) resulted in sequence
information solely from the 68 kDa polypeptide. As shown in Figure 3-2A,
two fragments from the 68 kDa polypeptide yielded sequences of 18 and
23 amino acids which were identical to amino acids 193 210 and 344 -
366 respectively of human annexin VI (Crompton et al., 1988; Sudhof et
al., 1988). Immunoblots probed with a monoclonal antibody to human
placental annexin VI (Zymed Laboratories, Inc., South San Francisco, CA)
only revealed the 68 kDa polypeptide (Figure 3-1, lane 3). Polyclonal
antibodies to human annexin VI (rabbit antisera was a kind gift from Dr.
Joel D. Ernst, University of California, San Francisco) detected the 68 kDa
annexin VI, but also failed to recognize the 66 kDa polypeptide (data not
shown).
Amino acid sequence analysis of the 66 and 68 kDa polypeptides
containing neutrophil activity was repeated. Samples were prepared as
described above, and sent to The Wistar Institute (Protein


23
dynamics is important in PMN cell motility are the changes in the ratios of
monomeric to filamentous actin seen when cells are stimulated to undergo
motility. The rapid, chemoattractant-induced actin polymerization
response occurs in many eukaryotic cells, in addition to PMN, which are
able to undergo "amoeboid-like" motility (Stossel, 1992; Caterina &
Devreotes, 1991).
In resting PMN approximately 30 40 % of the total actin
concentration is F-actin (Feichheimer & Zigmond, 1983; Sheterline et al.,
1984b; Bengtsson et al., 1986). Assuming a uniform distribution, this
corresponds to roughly 100 pM F-actin and 200 pM G-actin (Southwick &
Young, 1990). Remarkably, several laboratories have demonstrated that
within 30 seconds or less of fMet-Leu-Phe stimulation, the actin filament
content doubles (F-actin: ~100 > 200 pM) (Shalit et al., 1987; Howard &
Meyer, 1984; Fechheimer & Zigmond, 1983; Omann et al., 1987; Lofgren et
al., 1993). Cytochalasins, in vitro inhibitors of actin polymerization,
inhibit the morphological changes associated with neutrophil motility
(Zigmond & Hirsch, 1972) as well as the induced rise in polymerized actin
(Southwick et al., 1989; Cassimeris et al., 1990; White et al., 1983).
Furthermore, the dose dependency of the fMet-Leu-Phe-induced
chemotaxis and the rapid, actin-polymerization response are similar
(Howard & Meyer, 1984).
Dynamic changes in actin filament content occur during other PMN
motile events such as phagocytosis, degranulation, and adherence. A
nearly twofold rise in actin filament content is also observed during these
neutrophil functions (Boyles & Bainton, 1981; Fechheimer & Zigmond,
1983; Southwick et al., 1989), but the dissection of the transduction
cascade is complicated by the activation of multiple pathways. Although


148
Downey, G. P., Chan, C. K., Trudel, S., and Grinstein, S. 1990. Actin
assembly in electropermeabilized neutrophils: role of intracellular
calcium. J. Cell Biol. 110: 1975-1982
Eberle, M., Traynor-Kaplan, A. E., Sklar, L. A., and Norgauer, J. 1990
Is there a relationship between phosphatidylinositol triphosphate and F-
actin polymerization in human neutrophils? J. Biol. Chem. 265: 16725-
16728
Eddy, R. J., Sauterer, R. A., Hug, C., Cooper, J. A., and Condeelis, J. S.
1993. Aginactin contains a 2:1 complex of HSC70 and cap 32/34 and is
dependent on HSC70 through its ATP binding domain. Mol. Biol. CellVol.
4, abstract 1492
Elferink, J. G. R., and Deierkauf, M., 1985. The effect of quin2 on
chemotaxis by polymorphonuclear leukocytes. Biochim. Biophys. Acta.
846: 364-369
Ernst, J. D. 1991. Annexin III translocates to the periphagosomal
region when neutrophils ingest opsonized yeast. J. Immunol. 146: 3110-
3114
Ernst, J. D., Hoye, E., Blackwood, A.,and Jaye, D. 1990. Purification
and characterization of an abundant cytosolic protein from human
neutrophils that promotes Ca2+-dependent aggregation of isolated specific
granules. J. Clin. Invest. 85: 1065-1071
Estes, J. E. 1992. Tightly bound divalent cation of actin. J. Muscle
Res. Cell. Mot. 13: 272-284.
Fechheimer, M., and Zigmond, S. H. 1983. Changes in cytoskeletal
proteins of polymorphonuclear leukocytes induced by chemotactic
peptides. Cell Motility. 3: 349-361
Feltner, D. E., Smith, R. H., and Marasco, W. A. 1986.
Characterization of the plasma membrane GTPase from rabbit neutrophils.
I. Evidence for an Ni-like protein coupled to the formyl peptide, C5a, and
leukotriene B4 chemotaxis receptors. J. Immunol. 137: 1961-1970
Frieden 1982. The Mg2+-induced conformation change in rabbit
skeletal muscle G-actin. J. Biol. Chem. 257: 2882-2886


CHAPTER 1
INTRODUCTION
Overview
Cellular motility is a complex process which mandates the ability of
a cell to change its shape. In response to an external stimulus, outer
membrane receptors receive motivational signals and transmit this
information intracellularly. Subsequently, a cascade of events is initiated
which allow the cell to change its morphology and generate force for
motion towards the extracellular signal. A likely candidate which appears
central to this behavior is the self-assembling protein actin. Actin is the
most highly conserved and abundant protein in eukaryotic cells; and, in
addition, is the predominant filament of the cytoskeletal network. Unlike
in the sarcomere of muscle cells, non-muscle actin filaments are randomly
arranged in a fashion which enables the generation of force in three
dimensions rather than two dimensions. It is becoming increasingly
apparent that actin filament assembly/disassembly is vital to the process
of cell motility and shape change, and that the randomness of this
assembly is prevented by a group of regulatory proteins known
collectively as "actin binding proteins." This is a very exciting time for the
field of cellular motility and cell shape change. Amoebae, tumor cells,
leukocytes, fibroblasts, epithelial cells, and many other different cell types
share the ability to move by crawling across solid substrates utilizing a
1


Figure 3-2. Amino-terminal sequence analysis of PMN actin
polymerization inhibitor. Since the amino termini were blocked,
microsequence analysis was performed on the predominant cleavage
products of the upper peptide (Skatole) or lower peptide (Trypsin)
component. The 68 kDa upper band is identical to annexin VI and the 66
kDa peptide is identical to L-plastin.


134
transcriptional level. Several other levels of regulation, including
alterations in the stability of mRNA, the sequestering in cellular
compartments, and the interaction with proteins can also explain changes
in the expression of mRNAs.
The abundance of annexin VI in fully differentiated PMN, isolated
from peripheral blood, is in agreement with the differentiation studies.
When the annexin VI intracellular distribution was analyzed in peripheral
blood PMN and monocytes, the fluorescent signal was consistently more
intense in PMN compared to monocytes. Additionally, it was found that
annexin VI comprises roughly 0.8 0.9 % of PMN extracts.
There are several functional differences between PMN and
macrophages. It is possible that the differential expression of annexin VI
is a direct reflection of a PMN-specific activity. Since annexin proteins
have been repeatedly demonstrated to bind phospholipids in vitro, it
seems reasonable to speculate they may retain this calcium regulated
function in cells. The killing and digestion of phagocytosed pathogens by
PMN is critically dependent upon fusion of their azurophilic and specific
granules with the membranes of the phagocytic vesicle. Additionally, the
regulated degranulation of constituents into the extracellular environment
is vital to the inflammatory role of this cell. Regulation of PMN
membrane-membrane interactions by annexin proteins has been
previously proposed (Meers et al., 1987). Annexin III is able to promote
the aggregation of specific granules in vitro upon the addition of calcium
(Ernst et al., 1990; Ernst, 1991). Additionally, annexin III, the most
abundant annexin in their preparations (> 1 %), was found to concentrate
in the peri-phagosomal region of cells ingesting yeast. My discovery that
annexin VI is abundant in the cytoplasm of PMN suggests this protein may


151
Jaconi, M. E., Lew, D. P., Carpentier, J. L., Magnusson, K. E., Sjogren,
M., and Stendahl, 0. 1990. Cytosolic free calcium elevation mediates the
phagosome-lysosome fusion during phagocytosis in human neutrophils. J.
Cell Biol. 110: 1555-1564
Janmey, P. A. 1994. Phosphoinositides and calcium as regulators of
cellular actin assembly and disassembly. Annu. Rev. Physiol. 56: 169-191
Janmey, P. A., and Stossel, T. P. 1989. Gelsolin-polyphosphoinositide
interaction. J. Biol. Chem. 264: 4825-4831
Janmey, P. A., Chaponnier, C, Lind, S. E., Zaner, R. S., Stossel, T. P.
and Yin, H. L. 1985. Interaction of gelsolin and gelsolin-actin complexes
with actin. Effects of calcium on actin nucleation, filament severing, and
end blocking. Biochemistry. 24: 3714-3723
Kabsch, W., Mannherz, H. G., Suck, D., Pai, E. F., and Holmes, K. C.
1990. Atomic structure of the actin:DNase I complex. Nature 347: 37-44
Kaziro, Y., Itoh, H., Kozasa, T., Nakafuku, M., and Satoh, T. 1991.
Structure and function of signal-transducing GTP-binding proteins. Annu.
Rev. Biochem. 60: 349-400
Keller, H. LL, and Niggli, V. 1993. The PKC-inhibitor Ro 31-9220
selectively surpresses PMA- and diacyglycerol-induced fluid pinocytosis
and actin polymerization in PMNs. Biochem. Biophys. Res. Commun. 194:
1111-1116
Kilimann, M. W., and Isenberg, G. 1982. Actin filament capping
protein from bovine brain. EMBO J. 1: 889-894
Klee, C. B. 1988. Ca2+-dependent phospholipid- (and membrane-)
binding proteins. Biochemistry 27: 6645-6653
Korn, E. D., 1982. Actin polymerization and its regulation by
proteins from nonmuscle cells Physiol. Rev. 62: 672-737
Korn, E. D., Carlier, M. F., and Pantaloni, D. 1987. Actin
polymerization and ATP hydrolysis. Science 238: 638-644
Kouyama, T., and Mihashi, K. 1981. Fluorimetry Study of N-(l-
Pyrenyl)iodoacetamide-labelled F-actin. Fur. J. Biochem. 114: 33-38
Kwiatkowski, D. J., and Bruns, G. A. P. 1988. Human profilin:
molecular cloning, sequence comparison, and chromosomal analysis. J.
Biol. Chem. 263: 5910-5915


PURIFICATION AND FUNCTIONAL CHARACTERIZATION OF HUMAN
POLYMORPHONUCLEAR LEUKOCYTE ACTIN POLYMERIZATION INHIBITOR
By
NOEL ANTHONY MAUN
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE
UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
1995




CHAPTER 6
CONCLUSIONS AND FUTURE DIRECTIONS
Conclusions
Cellular motility is a complex process which, as a whole, is still
poorly understood. Actin microfilaments, the predominant cytoskeletal
component, are constantly remodeled in non-muscle cells. It is generally
accepted that the dynamic rearrangements of this network are vital to
movement. As the kinetics of actin assembly in vitro have been elegantly
dissected over the past 15-20 years, many investigators are currently
exploring the cellular implications of these findings. Several models
including the fMLP-induced, rapid actin assembly in PMN (Chapter 1) and
the actin-based intracellular motility of the bacterial pathogen Listeria
monocytogenes in host cells (Southwick & Purich, 1994), are leading to
better insights as to how the cell regulates the assembly of actin. Findings
based on these models, therefore, would have direct implications towards
the mechanism of cellular motility.
The studies presented in this dissertation were pursued in the
context of what is currently understood about the regulation of actin
assembly in PMN. A calcium-independent, barbed-end, actin-filament,
capping activity is critical to current models explaining the rapid actin
filament formation in PMN and other cells capable of receiving
motivational signals. My discovery that capZ purified from human PMN
interacts with actin, specifically regulating assembly at the barbed end
136


48
precipitate the SDS), and microfuged for 5 min. The clear supernatant was
transferred into a clean tube and the concentration and purity of the
sample was analyzed by a spectrophotometer.
The RNA samples were prepared for electrophoresis as follows. The
RNA (10 pg/sample) was completely lyophilized and resuspended in 10 pi
of a sample mix containing 250 pi deionized formamide, 90 pi 37 %
formaldehyde, 26 pi 10 X MOPS (3-[N-morpholino]propanesulfonic acid)
buffer (1 X MOPS buffer = 0.2 M MOPS, 0.05 M sodium acetate, 0.01 M
Na2EDTA, pH 7.0), 10 pi of ethidium bromide (10 mg/ml stock solution)
and 30 pi of loading dye. The samples were heated at 67 C for 15 min,
cooled on ice and were electrophoresed in 1.2 % agarose gels with 2.2 M
formaldehyde in 1 X MOPS buffer. The gel was transferred to
nitrocellulose membrane in 20 X SSC (IX SSC = 0.15 M NaCl and 0.015 M
sodium citrate) by standard capillary blotting. The blots were hybridized
with random-primed probes (1 X 10^ cpm/ml) at 42 C in 5 X Denhardt's
solution, 5 X SSPE (IX SSPE = 0.15 M NaCl, 0.01 M NaH2P04'H20, and
0.001 M EDTA), 50 % formamide (Fluka), 0.1 % SDS, and 150 pg/ml
salmon sperm DNA. After a room temperature rinse in 2 X SSC, 0.1 % SDS,
the filter was washed at 65 C in 2 X SSC, 0.1 % SDS for 30 min followed by
a brief wash in 0.2 X SSC, 0.1 % SDS until the background was low by a
Geiger counter survey.
Generation Of Annexin VI cDNA Probe
Total RNA was isolated from human neutrophils as described above.
Using the published cDNA sequence for human annexin VI, upstream and
downstream oligonucleotide (25 base-pairs each) primers were
synthesized (I.C.B.R. DNA synthesis laboratory, University of Florida). The


Figure 4-6. Effects of capZ on polymerization from gelsolimactin nuclei. Pyrene labeled G-actin (final of
0.8 pM; 100 % labeled) was polymerized in the presence of gelsolimactin nuclei (molar ratio 1:16), and
assembly rates monitored in the presence of final concentrations of 290 nM capZ (closed squares) or 360
nM capZ (closed triangles) or in the presence of buffer alone (open circles). The same concentration of
pyrene G-actin alone failed to polymerize during the time period of our assay (open squares). The
reaction was performed in the presence of either 1 mM EGTA (Panel A) or 0.5 mM calcium (Panel B).
Similar results were obtained when this assay was repeated in the presence of G-actin that was 50 %
labeled.


95
apparent dissociation constant (Kd app) ~ 3.0 nM, was identical to that
determined from our depolymerization studies. The ability to block
monomer exchange at the barbed end of actin filaments was not affected
by changing the Ca^+ concentration (data not shown).
The concentration of added capZ producing 50 % inhibition of actin
filament polymerization or depolymerization (the number of free barbed
ends equals the number of capped ends) represents the upper limit for the
Kd since the number of filaments initially present with both assays is
unknown. Our logic is as follows. The fluorescence change is proportional
to the depolymerization/polymerization of pyrene-labeled actin filaments.
Although the total number of filaments is unknown, the 1/2 maximal rate
change caused by capZ represents the condition where 50 % of the
filaments are capped and 50 % are freely exchanging actin monomers.
As the dissociation constant (Kd) equals [capZ]free X [filaments]free /
[capZ-capped filaments], the condition where 1/2 maximal fluorescence
change is observed relates Kd to the total capZ added to the reaction since
the ratio of free to capped filaments equals one. If the initial
concentration of filaments added is < than the total capZ added, then
this concentration is equivalent to Kd- Therefore, the Kd measured for
PMN capZ capping the barbed end is at least 3 nM, but could theoretically
be much lower (i. e. greater affinity).
Substoichiometric concentrations of capZ decreased the steady-state
filament content of actin solutions polymerized in buffer P with 1 mM
EGTA as reflected by the decrease in pyrenyl fluorescence. The G-actin
concentration was maximally elevated to ~0.8 pM in the presence of capZ.
Similar elevations were seen when the total actin concentration was either


115
processes. The azurophilc granules and their constituents are formed
earlier in the differentiation of PMN than are the specific granules
(Bainton, 1992). As PMN mature, they also attain functions specific to
these cells such as superoxide generation, and effective non-oxidative
killing capabilities. I was interested in examining the developmentally-
associated changes on PMN as well as examining the intracellular
localization of annexin VI in PMN.
Results
Northern Analysis
The expression of annexin VI was examined in human PMN (isolated
from peripheral blood) and the human monocyte-like cell line U937
(ATCC, Rockville, Maryland) by Northern blot analysis. Using the 1057 bp
cDNA clone from human PMN annexin VI (Chapter 2), a prominent mRNA
of about 2.5 kb was detected (Figure 5-1). Although a lower band
migrating below the 18 S RNA was often seen, only the 2.5 kb mRNA was
detected under more stringent conditions. This is not surprising
considering the structural similarities shared by the annexin proteins.
Annexin VI mRNA from transformed human fibroblasts is similar in size to
the prominent band detected by our probe (Sudhof et al., 1988). Despite
the identical protocols used in the isolation of RNA and an equivalent
loading of 10 pg of total RNA (as judged by ethidium bromide staining of
gels) from both cell types, the levels of annexin VI mRNA detected were
much higher in PMN compared to U937 (Figure 5-1).


Figure 3-1. PMN actin polymerization inhibitor. The PMN inhibitor
purified by DEAE-anion exchange and gel-filtration chromatography. Lane
2 represents the PMN inhibitor subjected to 10 % SDS-PAGE with standards
(lane 1; Mr = X 103) and stained with Coomassie blue. Fractions were
subjected to Western analysis and probed with antibodies to annexin VI
(lane 3) or L-plastin (lane 4).


12
actin filament is labeled with heavy meromyosin ("rigor" conformation)
and visualized by electron microscopy (Huxley, 1963). The barbed (+)
ends have a greater exchange rate and a lower critical concentration (Cc+
= 0.1 pM) for monomer binding than the pointed (-) ends (Cc- = 0.6 pM)
(Bonder et al., 1983). Thus, the barbed ends are the more kinetically
active and preferred ends for filament growth. At steady-state, i. e. when
the association rate equals the dissociation rate, the apparent critical
concentration for the entire filament (Cc = 0.15 pM) is closer to that of the
barbed end (Korn, 1982). As a result, a steady-state condition termed
"treadmilling'' occurs in which monomers slowly dissociate from the
pointed ends allowing new monomers to rapidly add on to the barbed
ends (Neuhaus et al., 1983; Wanger et al., 1985).
Actin polymerization is more rapid in the presence of ATP than in
the presence of ADP (Carlier et al., 1984; Pollard, 1984). This is not due to
energy made available through ATP-hydrolysis since polymerization can
occur faster than ATP-hydrolysis (Carlier et al., 1984). The differential
polymerization rates could be explained by the fact that ATP-G-actin has a
higher affinity and a lower dissociation rate than ADP-G-actin (Pollard &
Cooper, 1986). The hydrolysis of the ATP within the actin molecule
consists of two temporally distinct steps: the chemical cleavage of ATP
resulting in an ADP-Pj-actin followed by the slower release of P¡ into the
medium (Korn et al., 1987). Additionally, it has been shown that the
cleavage of ATP occurs vectorally (Carlier et al., 1987). This suggests that
if one examines a filament during the polymerization of ATP-actin, the
newly added actin molecules are ATP-actin followed by ADP-Pi-actin, and
most internally, ADP-actin (Carlier, 1991). Since the dissociation rate of
ATP-actin is slower than ADP-actin, the delayed ATP hydrolysis promotes


Ill
The ability of gelsolin to cap the barbed end is dependent upon an
initial interaction with calcium (Stossel et al., 1985). Its proposed barbed
end capping function in resting cells stems from the isolation of a 1:1
complex of actin and gelsolin which blocks acdn filaments with high
affinity even at submicromolar concentrations (Janmey et al., 1985). The
recent generation of transgenic mice lacking the expression of functional
gelsolin suggests other calcium-independent capping proteins exist in
mammalian non-muscle cells (Witke et al., 1993). This finding in
combination with my studies suggests capZ is the predominant calcium-
independent capping protein in PMN. The other capping protein
identified in mammalian phagocytes, capG, requires calcium for its
capping activity (Southwick & DiNubile, 1986).
Similar to skeletal-muscle capZ and the related protein cap 32/34 of
Dictyostelium I have found that the barbed-end capping function of PMN
capZ is inhibited in the presence of PIP2 (Heiss & Cooper, 1991; Haus et
al., 1991). Chemoattractant receptor occupancy is associated with rapid
polyphosphoinositide turnover (Cockcroft et al., 1985; Eberle et al., 1990),
and the activities of several actin-binding proteins are inhibited by these
phospholipids (Janmey, 1994). Polyphosphoinositides, therefore, may
switch on actin assembly during chemoattractant stimulation by causing
the release of actin subunits from sequestering proteins, and uncapping of
the barbed ends of actin filaments (Stossel, 1993).
The present findings confirm the ability of PMN capZ to interact
specifically with the barbed end of actin filaments. There have been no
previous reports of capZ in neutrophils or macrophages, and it was only
recently noted in platelets (Barkalow & Hartwig, 1994; Nachmias et al.,
1994). These cells, although, are the mammalian model cells for


62
for Coomassie blue staining and immunoblot analysis. As shown in Figure
3-3B, antibodies to annexin VI (Zymed Laboratories, Inc., South San
Francisco, CA) reveal one band in the active fraction. The similar
migration pattern shared by annexin VI in purified and active fractions
(Figure 3-3B, lane 1 and lane 2), suggests annexin VI does not take part in
complex formation. Although the L-plastin antibody reveals two closely
spaced reactive bands in the active fraction (Figure 3-3C, lane 2), they
both migrate separately from annexin VI. The detection of two L-plastin
bands in active fractions (Figure 3-3C, lane 2) and only one in the purified
(recombinant L-plastin) fractions (lane 3) most likely results from post-
translational modification of the PMN isolated L-plastin. Furthermore, L-
plastin is a known phosphoprotein (Zu et al., 1990). It is well established
that bacteria are incapable of many of the post-translational modifications
seen in eukaryotes, and thus could explain the appearance of one band
with L-plastin recombinantly expressed and purified from E. coli. It is
notable that recombinant L-plastin does not decrease the viscosity of actin
solutions (Dr. C. Young, unpublished data). These data derived from
nondenaturing polyacrylamide gel-electrophoresis suggest no complex is
formed between the annexin VI and L-plastin present in the neutrophil
actin polymerization inhibitory activity.
To further clarify which protein was responsible for the actin
viscosity lowering activity, attempts were made to separate annexin VI by
methods previously developed for studying the membrane binding
properties of annexins (Blackwood & Ernst, 1990). In this assay,
phosphatidylserine liposomes were prepared as described, and added to
active fractions. After incubation in the presence of calcium, the
liposomes were separated from the fractions by centrifugation. This


112
understanding the signal transduction mechanisms leading to rapid actin
assembly. The calcium-independent, phospholipid-regulated nature of
this activity suggests capZ is an important regulator of actin assembly in
highly motile animal cells such as the PMN.


135
similarly interact with various membrane formed vesicles or granule
populations in PMN.


67
12 3 4


57
A. UPPER BAND (SKATOLE cleavage)
human Anx VI
pep 1
human Anx VI
pep 2
B. LOWER BAND (TRYPSIN cleavage)
human L-Plastin
pep 1
62
SEEEK
YAFVNWINK
YAFVNWINK
79
ALEN
human L-Plastin
pep 2
512
GGQKVNDDIIVNWVNETLR
/NDDIIVNWVNETLR
534
EAEK


154
Niggli, V., and Keller, H., 1991. On the role of protein kinases in
regulating neutrophil actin association with the cytoskeleton. J. Biol.
Chem. 266: 7927-7932
Nishihira, J., McPhail, L. C., and O'Flaherty, J. T. 1986. Stimulus
dependent mobilization of protein kinase C. Biochem. Biophys. Res.
Commun. 134: 587-594
Omann, G. M, and Porasik-Lowes, M. M. 1991. Graded G-protein
uncoupling by pertussis toxin treatment of human polymorphonuclear
leukocytes. J. Immunol. 146: 1303-1308
Omann, G. M., Allen, R. A., Bokoch, G. M., Painter, R. G., Traynor, A.
E., and Sklar, L. A. 1987. Signal transduction and cytoskeletal activation in
the neutrophil. Physiol. Rev. 67: 285-322
Pacaud, M., and Derancourt, J. 1993. Purification and further
characterization of macrophage 70-kDa protein, a calcium-regulated,
actin-binding protein identical to L-plastin. Biochemistry 32: 3449-3455
Pepinsky, R. B., Tizard, R., Mattaliano, R. J., Sinclair, L. K., Miller, G.
T., Browining, J. L., Chow, E., Burne, C., Huang, K. S., Pratt, D., Wachter, L.,
Hession, C., Frey, A. Z., and Wallner, B. P. 1988. Five distinct calcium and
phospholipid binding proteins share homology with lipocortin 1. J. Biol.
Chem. 263: 10799-10811
Pollard, T. D. 1984. Polymerization of ADP-actin. J. Cell Biol. 99:
769-777
Pollard, T. D., 1990. Actin. Curr. Opin. Ceil Biol. 2: 33-40
Pollard, T. D., and Cooper, J. A., 1986. Actin and actin-binding
proteins. A critical evaluation of mechanisms and functions. Ann. Rev.
Biochem. 55: 987-1035
Pollard, T. P. 1986. Rate constants for the reactions of ATP- and
ADP-actin with the ends of actin filaments. J. Cell Biol. 103: 2747-2754
Pryzwansky, K. B., Schliwa, M., and Porter, K. R. 1983. Comparison of
the three-dimensional organization of unextracted and triton-extracted
human neutrophilic polymorphonuclear leukocytes. Eur. J. Cell Biol. 30:
112-125
Reim, D. F., Hembach, P., and Speicher, D. W. 1992. Techniques in
Protein Chemistry III, Academic Press, NY, 53-60


138
PMN capZ to the barbed end of filaments is consistent with those
previously described for skeletal muscle capZ and the related
heterodimeric capping protein of Dictyostelium. Thirdly, it can be
concluded that annexin VI and L-plastin purified from PMN do not
decrease the viscosity of actin solutions or cap the barbed end of filaments
in the absence of calcium, proving they are not the activity of PMN actin
polymerization inhibitor as previously thought.
in Vitro Interaction Of PMN CapZ With Actin
By careful in vitro analysis utilizing the fluorescent actin probe,
pyrenlyactin, I was able to study the mechanisms regarding the viscosity
lowering activity of PMN capZ. First of all, it can be stated that PMN capZ
binds the barbed end of actin filaments with high affinity (3 nM) in vitro.
Secondly, this affinity is unchanged in the presence or absence of calcium.
Thirdly, based on the studies testing for pointed end capping, severing, or
monomer sequestering activity, the viscosity lowering activity of PMN capZ
is due solely to an interaction with the barbed end of filaments.
Developmental Regulation And Intracellular Localization Of PMN
Annexin VI
Annexin VI is an abundant intracellular protein comprising about
0.8 0.9 % of human PMN extracts. A relative increase in annexin VI is
seen in human promyelocytes differentiated towards the neutrophil
lineage versus those differentiated towards the macrophage lineage. We
conclude this difference is partly responsible for distinguishing these
developmentally related phagocytes. Based on the indirect
immunofluorescence analysis of annexin VI in PMN, I conclude that this
protein has a diffuse cytoplasmic distribution and is not present in the


CHAPTER 5
DEVELOPMENTAL EXPRESSION AND INTRACELLULAR LOCALIZATION OF
ANNEXIN VI IN PMN
Introduction
The studies presented in this chapter were initiated by the initial
findings that the 68 kDa polypeptide purified with the PMN actin
polymerization inhibitor (Chapter 3) is annexin VI. Although it was
eventually discovered that capZ and not annexin VI was responsible for
the PMN viscosity lowering activity, further studies were pursued to
characterize annexin VI as a potential cytoskeletal protein in PMN. This
protein belongs to a family of structurally and functionally related
proteins known as the annexins which possess a characteristic sequence
motif consisting of 70 80 amino acids that is repeated four to eight times
depending on the individual annexin (Pepinsky et al., 1988). Each
annexin exhibits the ability in vitro to bind anionic phospholipids found
in cell membranes in a calcium dependent fashion (Klee, 1988). Many
investigators postulate that the annexins play a key role in regulating
membrane interactions (Creutz, 1992).
Several annexins, as well, bind actin microfilaments. Both annexin I
and annexin II bundle actin filaments at high (ImM) Ca^+ concentrations
(Glenney et al., 1987). Annexin VI from bovine liver cosediments with
actin in 10 pM Ca2+ solutions (Hosoya et al., 1992), and a 68 kDa
annexin from human placenta cosediments with actin in solutions
113


159
Yin, H. L, and Stossel, T. P. 1979. Control of cytoplasmic actin gel-
sol transformation by gelsolin, a calcium-dependent regulatory protein.
Nature. 281: 583-586
Young, C. L., Southwick, F. S., and Weber, A. 1990. Kinetics of the
interaction of a 41-kilodalton macrophage capping protein with actin:
promotion of nucleation during prolongation of the lag period.
Biochemistry 29: 2232-2240
Zigmond, S. H. 1977. The ability of polymorphonuclear leukocytes
to orient in gradients of chemotactic factors. J. Ceil Biol. 75: 606-616
Zigmond, S. H., and Hirsch, J. G. 1972. Effects of cytochalasin B on
polymorphonuclear leukocyte locomotion, phagocytosis and glycolysis.
Exp. Cell Res. 73: 383-393
Zigmond, S. H., Slonczewski, J. L, Wilde, M. W., and Carson, M. 1988.
Polymorphonuclear leukocyte locomotion is insensitive to lowered
cytoplasmic calcium levels. Cell Motil. Cytoskeleton. 9: 184-189
Zimmerle, C. T., and Frieden, C. 1986. Effect of temperature on the
mechanism of actin polymerization. Biochemistry 25: 6432-6438
Zimmerle, C. T., and Frieden, C. 1988. Effect of pH on the
mechanism of actin polymerization. Biochemistry 27: 7766-7772
Zu, Y., Shigesada, K., Nishida, E., Kubota, I., Kohno, M., Hanaoka, M.,
and Namba, Y. 1990. 65-kilodalton protein phosphorylated by interleukin
2 stimulation bears two putative actin-binding sites and two calcium
binding sites. Biochemistry 29: 8319-8324


LIST OF FIGURES
Figure page
1-1 Actin and its spontaneous polymerization in salt 8
1-2 Rate constants for the association and dissociation
of ATP-actin and ADP-actin at filament ends 11
1-3 fMet-Leu-Phe induced phospholipase C signaling
pathway 26
1-4 Regulation of actin assembly in PMN 34
3-1 PMN actin polymerization inhibitor 54
3-2 Amino-terminal sequence analysis of PMN actin
polymerization inhibitor 57
3-3 Nondenaturing polyacrylamide gel electrophoresis 61
3-4 SDS-PAGE of phospholipid affinity chromatography,
and anti-annexin VI western analysis 64
3-5 Western blot analysis of PMN inhibitory fractions
probed with capZ antisera 67
3-6 DEAE-anion exchange chromatography of PMN extract 70
3-7 High S-cation exchange chromatography of PMN
actin polymerization inhibitor 72
3-8 Mono Q-anion exchange chromatography of PMN
actin polymerization inhibitor 74
3-9 Western blot analysis of PMN actin polymerization
inhibitor purified to Mono Q chromatography 77
3-10 Hydroxylapatite column chromatography 79
vi


36
from granulocyte extracts by DEAE-ion exchange chromatography and gel-
filtration chromatography. The viscosity lowering activity of the column
fractions was monitored using a Cannon-Manning semi-microviscometer.
The purified inhibitor was noted to contain polypeptides of 65,000 and
62,000 daltons by SDS-PAGE. The Stokes radius of the inhibitor was
reportedly 32 and the S20,w was 4.8. These data were felt to be
compatible with the inhibitor being a globular monomer with a native
molecular weight similar to that of the 65,000 and 62,000-dalton peptides
resolved by SDS-Page. Increasing KC1 concentrations from 0.1 0.6 M KC1
reversed the inhibition.
All activity studies were done in the absence of added calcium and
presence of 1 mM EGTA to avoid the potential contaminating activity of
the calcium dependent protein gelsolin. The PMN actin polymerization
inhibitor is hence a major calcium-independent actin filament regulatory
protein. The recent findings that the PMN actin polymerization-burst in
response to fMet-Leu-Phe occurs independently of calcium has prompted
my further examination of this inhibitor's actin regulatory role.


58
Microsequencing Facility). For this analysis, the two polypeptide bands
were digested with trypsin. Comparative HPLC peptide maps (post-trypsin
digestion) with a trypsin control demonstrated that almost all major peaks
in the 68 kDa sample were different from those generated from the 66 kDa
sample. The masses of the major trypsin cleavage peptides were
determined by MALD1 mass spectrometry. Most major peak masses from
the 68 kDa sample agreed with expected masses of limit tryptic peptides of
annexin VI. In contrast, only a few major peaks in the 66 kDa sample
could possibly fit with annexin peptides. Two of the major peptides
generated by trypsin digestion of the 66 kDa band were sequenced, and
revealed a perfect match with the protein L-plastin. As shown in Figure 3-
2B, N-terminal sequence analysis of these two major peptides yielded
sequences of 9 and 15 amino acids which were identical to amino acids 67
- 75 and 516 530 respectively of human L-plastln (Lin et al., 1988). To
further confirm the identity of the 66 kDa polypeptide western blot
analysis was performed using a mouse monoclonal anti-human L-plastin (a
kind gift from Dr. Yuziro Namba, Kyoto University, Japan). As shown in
Figure 3-1 (lane 4), the antibody specifically cross-reacts with the lower,
66 kDa polypeptide. The antibody also cross-reacts with a polypeptide
with approximate Mr of 55,000. This band is felt to be a degradation
product of the neutrophil L-plastin, as it is absent in fresh PMN extract and
increases with storage of the PMN inhibitor fractions (data not shown). A
similar molecular weight L-plastin degradation product has been
previously reported (Pacaud & Derancourt, 1993).


146
Carlier, M. F., and Pantaloni, D. 1986. Direct evidence for ADP-Pi-F-
actin as the major intermediate in ATP-actin polymerization. Rate of
dissociation of Pi from actin filaments. Biochemistry 25: 7789-7792
Carlier, M. F., Pantaloni, D., and Korn, E. D. 1984. Evidence for an
ATP cap at the ends of actin filaments and its regulation of the F-actin
steady state. J. Biol. Chem. 259: 9983-9986
Carlier, M. F., Pantaloni, D., and Korn, E. D. 1987. The mechanisms
of ATP hydrolysis accompanying the polymerization of Mg-actin and Ca-
actin. J. Biol. Chem. 262: 3052-3059
Carlsson, L, Nystrom, L. E., Sundkvist, I., Markey, F., and Lindberg,
U. 1977. Actin polymerizability is influenced by profilin, a low molecular
weight protein in non-muscle cells. J. Mol. Biol. 115: 465-483.
Carson, M., Weber, A., and Zigmond, S. 1986. An actin-nucleating
activity in polymorphonuclear leukocytes is modulated by chemotactic
peptides. J. Cell Biol. 103: 2707-2714
Casella, J. F., Craig, S. W., Maack, D. J., and Brown, A. E. 1987. CapZ
(36/32), a barbed end actin-capping protein, is a component of the Z-line
of skeletal muscle. J. Cell Biol. 105: 371-379
Casella, J. F., Maack, D. J., and Lin S. 1986. Purification and initial
characterization of a protein from skeletal muscle that caps the barbed
ends of actin filaments. J. Biol. Chem. 261: 10915-10921
Cassimeris, L., McNeill, H., and Zigmond, S. H. 1990.
Chemoattractant-stimulated polymorphonuclear leukocytes contain two
populations of actin filaments that differ in their spatial distributions and
relative stabilities. J. Cell Biol. 110: 1067-1075
Cassimeris, L., Safer, D., Nachmias, V. T., and Zigmond, S. H. 1992.
Thymosin I?>4 sequesters the majority of G-actin in resting human
polymorphonuclear leukocytes. J. Cell Biol. 119: 1261-1270
Castagna, M., Yoshima, T., Kaibachi, S., Kikkawa, U., and Nishizuka,
Y. 1982. Direct activation of calcium-activated phospholipid-dependent
protein kinase by tumour-promoting phorbol esters. J. Biol. Chem., 257:
7847-7851
Caterina, M. J., and Devreotes, P. N. 1991. Molecular insights into
eukaryotic chemotaxis. FASEB. 5: 3078-3085


6
polymerization, Kabash et al. (1990) were finally able to solve the
structure of the actin (muscle isoform) molecule to atomic (2.8 and 3.0 )
resolution. Using this atomic structure along with lower resolution
analyses, the G-actin molecule can be described as an oblate sphere
(overall dimensions of 5.5 X 5.5 X 3.5 nm) composed of two major
domains (small and large) which are separated by a pronounced cleft. The
small and large domains are further divided into subdomains 1 & 2, and
subdomains 3 & 4 respectively. The four subdomains are stabilized
mainly by interactions with the nucleotide and divalent cation bound
within the cleft formed between the major domains. The crystalline
structure of beta-actin (non-muscle isoform) complexed with profilin was
recently solved to 2.55 . When compared to the a-actin structure of
Kabash et al., they appeared structurally similar with a notable 5 rotation
between the major domains.
The polar actin monomers can polymerize to form a polar actin
filament (F-actin). Geometrically, the filament can be described as a two-
start, double-stranded, right-handed helix with approximately 13 subunits
per turn. The precise orientation of the actin subunits is uncertain, but it
is thought that subdomain 2 of the monomer represents the end (see
"Polymerization" below), and "+" end (see below) is within subdomain 3.
Multiple inter- and intrastrand contacts between the subunits exist. The
structure of the filament is very complicated and has yet to be directly
characterized at the atomic level. Holmes et al. (1990) have proposed an
atomic model of the actin filament which they derived from the atomic
model of the G-actin molecule and low resolution (8 ) F-actin structural
data. The intermolecular contact points in this model were recently
reviewed by Mannherz (1992).


98
0.9 or 3 pM (Figure 4-3). A similar increase in G-actin was seen when capZ
was added to actin solutions in the presence of calcium (data not shown).
Nucleation Assay
CapZ nucleation activity was also tested in the presence and absence
of calcium. Concentrations of capZ up to 219 nM (Figure 4-4, closed
squares) failed to stimulate the polymerization of actin as compared to
actin monomers alone (open squares). Addition of unlabeled actin
filaments 10 min after addition of salt caused a rapid rise in pyrenylactin
fluorescence indicating the actin was capable of assembling (open
triangles). Figure 4-4 is representative of multiple assays all of which
demonstrated a failure to stimulate actin assembly. In two instances capZ
prolonged the lag phase and was associated with assembly rates that were
slower than actin alone (data not shown).
Severing Assay
To examine the ability of capZ to break apart preformed actin
filaments, gelsolin-capped filaments were diluted into a buffer containing
varying concentrations of capZ. As seen in Figure 4-5, capZ at
concentrations as high as 215 nM did not accelerate the depolymerization
rate (closed squares) as compared to filaments diluted into buffer (open
squares). Dilution of gelsolin-capped actin filaments into a buffer
containing free gelsolin (100 nM) caused a marked acceleration in the
depolymerization rate (closed triangles).


Rest
+
|CAP
DOCOOO
ED
ED
\
O
ED
ED
BO
ED
fMLP < 30 sec
(^Phosphoinositide Turnover)
Gelsolin/Ca2+
.
ccccccco
t
[El o o o
\T\
E
ADP
X)
1
[ID
O
ATP


Figure 4-7. Effects of PIP2 on capZ barbed-end capping activity. Panel A). The effects of equivalent
amounts (llpg/ml) of various phospholipids PIP2-Phosphatidylinositol 4,5-bisphosphate, PC-
Phosphatidylcholine, PS-Phosphatidylserine, and PI-Phosphatidylinositol on capZ capping activity was
tested. Two micromolar (2 pM) pyrene F-actin was diluted in buffer P + EGTA to 50 nM in the presence of
36 nM capZ and the various phospholipids. Panel B). Barbed-end capping activity of 36 nM capZ was
measured in the presence of varying amounts of PIP2. One hundred percent capping activity was defined
as the inhibition of depolymerization observed with 36 nM capZ in the absence of PIP2-


Figure 4-1. Effects of purified capZ on actin filament depolymerization. Pyrene actin (2pM) was allowed
to polymerize to steady state in the presence of 1 mM EGTA (Panel A) or 1 mM CaCl2 (Panel B). At time
zero, aliquots of the F-actin were diluted 1/40 (final concentration 50 nM) into varying concentrations of
purified neutrophil capZ in buffer P containing EGTA (Panel A) or 1 mM CaCl2 (Panel B). Fluorescence
intensity was monitored over time. Numbers next to symbols represent the final concentrations of capZ.


CHAPTER 4
FUNCTIONAL CHARACTERIZATION OF PMN CAPZ
Introduction
The PMN actin polymerization inhibitor was originally isolated in
the presence of EGTA primarily to distinguish it from the calcium-
dependent viscosity-lowering activity of gelsolin (Yin & Stossel, 1979).
The importance of this characteristic is suggested by the recent findings of
calcium-independent actin assembly in PMN (reviewed in Chapter 1).
Based on the current theories of actin regulatory proteins (Pollard &
Cooper, 1986), several interactions with actin could explain the actin
viscosity lowering effect originally reported for PMN actin polymerization
inhibitor (Southwick & Stossel, 1981). Proteins that sequester actin
molecules away from the polymerizable pool would lower the viscosity of
actin solutions. Additionally, interactions which shorten the average
length of actin filaments such as severing or capping (barbed or pointed
end) would also lead to a relative decrease in the final viscosity.
Conversely, actin binding proteins that cross-link or bundle actin
filaments would be expected to raise the viscosity of actin solutions. The
identification of the neutrophil activity as capZ suggests the viscosity
lowering effect results from the ability of this protein to cap the barbed-
end of actin filaments.
88


117
28S
18S
\
1 2


22
takes much higher (micromolar) concentrations to induce the microbicidal
mechanisms of PMN (Gallin, 1988). Chemoattractants transmit their signal
through specific surface receptors, and many appear to utilize a common
signal transduction pathway. The "bimodal" response of PMN to
chemoattractants (differential triggering of motile verses microbicidal
functions) is currently thought to result from the activation of additional
transduction pathways dependent upon the extent of the chemotactic
stimulus (Snyderman & Uhing, 1992). The remaining discussion in this
chapter will focus on the rapid actin assembly occurring during the initial
phase as the transductional events of the second phase are poorly
understood. The fMet-Leu-Phe peptide has been termed the neutrophil
"pan-activator" for its ability to induce almost all major PMN functions in
addition to chemotaxis (Becker, 1987), and consequently its signal
transduction mechanisms have been extensively studied (for review see
Snyderman & Uhing, 1992).
Rapid Polymerization In Response To fMet-Leu-Phe
The overall morphology of PMN dramatically changes in response to
chemotactic stimulation (Fechheimer & Zigmond, 1983; Howard & Oresajo,
1985). At rest the cells are spherical, and upon stimulation form
peripheral ruffles or lamellipodia at their surface which have been shown
microscopically to be highly concentrated in F-actin (Fechheimer &
Zigmond, 1983; Sheterline, et al., 1984a). Neutrophils contain
approximately 5 pg actin/cell, which correlates to roughly 10 % of the
total cellular protein in these cells (Sheterline et ah, 1984b). Others have
calculated that actin represents as high as 20 % of PMN extracts
(Southwick & Young, 1990). Probably the best evidence suggesting actin


I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of Doctor
of Philosophy. '
oUr,
Daniel J. Driscoll
Assistant Professor of Molecular
Genetics and Microbiology
This dissertation was submitted to the Graduate Faculty of the
College of Medicine and to the Graduate School and was accepted as
partial fulfillment of the requirements for the degree of Doctor of
Philosophy
May, 1995
Dean, College of Medicine
Dean, Graduate School


50
cellular protein was isolated and analyzed by Northern or Western blots as
described earlier. For Western studies, the total protein concentrations
were calculated on the last day of the experiment using the same standard
curve. Samples from earlier time points were rapidly collected (saving an
aliquot for determination of protein concentration), placed in gel sample
buffer, and stored at -70 C until the final sample was processed.
Fluorescence Microscopy
Human neutrophils and monocytes were isolated from peripheral
blood by sedimentation through PolymorphprepTM, a sodium-metrizoate,
dextran 500 solution (Nycomed Pharma As, distributed by Gibco BRL,
Gaithersburg, MD). The cells were resuspended in Hank's balanced salt
solution (Gibco BRL, Gaithersburg, MD), and allowed to adhere to glass
coverslips for 15 20 min in a 37 C C02 incubator. The adherent cells
were treated for immunofluorescence by fixation for 20 min at room
temperature in 3 % formaldehyde (prepared from paraformaldehyde)
made in standard salt (0.1 M KC1, 0.01 M KPO4 buffer, 0.001 M MgCl2, pH
7.0), permeabilization in 0.1 % Triton-X 100 in standard salt, 5 min
overlay with 50 mM ammonium chloride in standard salt, and rinses with
standard salt between steps (Sanger et al., 1980). The following reactions
were carried out in a moist chamber in a 37 C CO2 incubator, the cells
were then blocked with 10 % goat serum in standard salt for 30 min,
followed by 45 min incubation with monoclonal antibodies (0.01 pg/pl
anti-human annexin VI, control antibodies were a kind gift from Maurice
Swanson, Univ. of Fla., College of Medicine: anti-human hnRNP-M protein
& anti-yeast polyadenylated RNA-binding protein, Nab-1) (Datar et al.,


Figure 4-3. Effects of neutrophil capZ on the extent of actin
polymerization. Actin (3.0 pM or 0.9 pM) was allowed to polymerize to
steady state in the presence of varying concentrations of capZ. The G-
actin concentration was calculated from the steady state fluorescence
difference in actin solutions without capZ.


Figure 1-3. fMet-Leu-Phe induced phospholipase C signaling pathway. Stimulation of PMN results in the
doubling of intracellular F-actin in < 30 sec.


121
analysis was repeated for a total of 3 separate differentiation experiments.
By laser scanning densitometry of the autoradiograms the changes in the
mRNA levels were quantified. All three DMSO induced differentiations
revealed a similar trend in that the annexin VI mRNA levels slowly
increased relative to HL-60 controls (t = 0), but the differences were not
statistically significant. It is notable that in each instance the annexin VI
mRNA levels followed to 3 days never dropped below the levels seen at
time zero. In contrast, annexin VI mRNA rapidly declined by day 3 to
about 12 % (12.1 15.5, n = 3) the levels at time zero. In contrast to the
developmental changes in annexin VI, the level of actin remained
essentially unchanged (Figure 5-2).
Western Analysis Of Annexin VI During Differentiation Of Promyelocytes
The annexin VI protein levels were measured during myeloid
differentiation as well to determine whether the differences in annexin VI
mRNA expression correlate with the apparent levels of protein translated.
The identical differentiation protocols used for our Northern analysis were
performed, and equivalent amounts of proteins (60 pg total protein) were
separated on SDS-PAGE. Using the monoclonal anti-annexin VI antibody
(Chapter 2), Western blots of extracts from HL-60 differentiation studies
were probed and quantitated by laser scanning densitometry. This
experiment was performed twice, and the results of both experiments are
shown in Figure 5-3. We found that annexin VI levels maximally increased
3.4-fold by day three in cells differentiated towards the neutrophil lineage.
In contrast, the levels of annexin VI protein in PMA treated cells was
maximally reduced by day three to 28 % the time zero level.


Figure 3-11. Silver stained peak fractions from Mono Q. and HA
chromatography. PMN extract (14 pg; lane 2), Mono Qpeak activity (2pg;
lane 3), HA peak activity (0.25 pg; lane 4), and HMW std (lane 1) were
subjected to 10 % SDS-PAGE and silver stained. Arrowheads point to the
36 kDa and 32 kDa subunits of capZ.


Figure 4-2. Effects of purified capZ on actin filament polymerization from
spectrin/band 4.1/actin nuclei. To a constant (1.25 pg/ml) amount of
spectrin/band 4.1/actin nuclei (rbc nuclei), 0.55 pM pyrene labeled G-
actin was allowed to polymerize in the presence of varying concentrations
of capZ in buffer P containing 1 mM EGTA. The capZ and rbc nuclei were
allowed to incubate for 2 min prior to the addition of the pyrene actin. At
this concentration of pyrene actin, nucleation of filament assembly was
prolonged so that the fluorescence increases detected were due primarily
to growth at the barbed ends of the actin filament complexes.


Figure 3-8. Mono Q.-anion exchange chromatography of PMN actin
polymerization inhibitor. Peak activities from High S chromatography
were pooled and allowed to adhere to a Mono Q. column. The proteins
were eluted with a 0.1 0.3 M linear KC1 gradient, and subjected to 10 %
SDS-PAGE (with HMW stds). The 10 % SDS-PAGE gel shown was first
stained with Coomassie blue (Panel A), and then silver stained (Panel A').
The relative activities (Panel B) were measured as in Figure 3-7. Fractions
were also transferred to nitrocellulose and probed with antibodies to L-
plastin (Panel C).


51
1993; Wilson et al., 1994) and used at concentrations greater than the
anti-annexin VI as determined by immunoblots of the antibodies run on
SDS-PAGE, rinses in standard salt, incubation with fluorescein
isothiocyanate (FITC)-conjugated goat anti-mouse IgGl (heavy chain
specific; Fisher Scientific, Pittsburgh, PA) for 30 min, followed with rinses
in standard salt. The coverslips were mounted in glycerol containing an
antioxidant to prevent fluorescence quenching (90 % glycerol, 10 % 0.25
M Tris pH 8.0, 2.3 % 1,4 l,4-diazabicyclo-[2.2.2] octane obtained from
Sigma). The cells were observed and photographed using a Nikon Diaphot
inverted microscope (Nikon, Tokyo, Japan) set up for epifluorescence.
Photographs were taken through the camera port using Tri-X Pan film
(Kodak). The film exposure lengths and print development times were
kept identical to photographs of PMN stained with anti-annexin VI.
Confocal microscopy was conducted with the assistance of Michael Paddy
(l.C.B.R. Confocal microscopy facility, University of Florida).
Approximately 30 images 1 pm thick were taken with a z-increment of 0.3
pm. Digitized images were obtained using Dr. Paddy's microscope and
processed with an Image-1 video image analyzer (Universal Imaging Corp.,
West Chester, PA), and finally stored on a Panasonic laser disk recorder.


47
sonicator at room temperature for 15 sec. After 1 min to allow the lipid-
capZ mixture to equilibrate, pyrene labeled F-actin was added (25 pi of 2
pM F-actin to a final volume of 1 ml). The inhibition of capZ capping was
assessed by measuring the initial slopes of depolymerization in the
presence of varying amounts of PIP2-
Promyelocyte Differentiation Studies
RNA Isolation And Northern Blots
Total RNA was extracted by a guanidinium thiocyanate (G1TC)
method (Chomczynski & Sacchi, 1987). The cells of interest were lysed in
a GITC buffer (4 M guanidinium isothiocyanate, 25 mM sodium acetate, pH
7.0, 0.5 % sarcosyl, and 0.1 M R-mercaptoethanol) with vigorous pipetting
and vortexing. Two milliliters (2 ml) of GITC buffer was added to 0.5- 1.0
X 107 cells. The following was sequentially added to the extract with
thorough mixing by inversion in between: 0.07 volume 3 M sodium
acetate pH 5.2, 1 volume cold water-saturated phenol, and 0.2 volume of
chloroform/ alcohol (49:1). The mixture was shaken vigorously for 10 sec
and kept on ice for 15 in and centrifuged in a Beckman JA-20 rotor at
10,000 X g for 20 min. The aqueous phase was carefully removed and
precipitated with 1:1 volume of cold for 1 hour to overnight at -20 C.
After another 10,000 X g spin, the RNA pellet was resuspended in 300 pi of
GITC buffer and precipitated another time with 2.5 volumes of cold 95 %
ethanol at -20 C. The final pellet was washed with 70 % ethanol, dried
and resuspended in 0.5 % SDS in diethylpyrocarbonate (DEPC) treated
water. To eliminate any contaminating proteins and to remove the SDS,
the samples were heated at 65 C for 15 min, kept on ice for 15 min (to


140
present in extracts if my purification scheme were used (degradation and
selection of highly pure fractions at each stage). The most practical
estimation of capZ concentrations can be achieved using an analysis
similar to that employed for annexin VI (Chapter 5). This experiment is
currently being conducted by Dr. Mark DiNubile (Cooper Hospital /
University Medical Center, Camden, NJ) with the purified PMN capZ due to
the limited availability of antisera. Once the concentration of capZ in PMN
is established, the physiological relevance of the in vitro capping function
can be further addressed.
The development of antibodies with higher affinity to human capZ
would be beneficial, as the antibodies currently available have poor inter-
species reactivities and their quantities are limited. The cDNA sequences
coding both subunits of human capZ were recently isolated from a human
retinal cDNA library (Barron-Casella & Casella, 1993). Sufficient quantities
of pure capZ necessary for the production of high affinity antisera can
easily be obtained through recombinant expression of this protein in £
coii.
Monoclonal antibodies can be generated, selecting for hybridoma
clones producing antibodies suitable for immunoprecipitation or
immunolocalization studies. The intracellular localization and relative
distribution of capZ in resting and stimulated PMN can be followed by
indirect immunofluorescence microscopy. Colocalization with actin would
support an in vivo actin function of capZ. The presence of capZ in actin
rocket tails formed by Listeria can also be evaluated by the same
technique. Immunoprecipitation of capZ from extracts would be useful in
monitoring potential post-translation modifications that may occur as a
result of stimulation of PMN. It has been previously established that many


24
these functions can be initiated by fMLP stimulation, their predominant
signal transduction pathways appear to be different (Southwick et al.,
1989; Rosales et al., 1994).
fMet-l.eu-Phe Signal Transduction Pathway
The N-formylated methionyl peptides such as fMet-Leu-Phe activate
neutrophils by binding to a specific cell surface receptor. The primary
structure of the fMet-Leu-Phe receptor has been deduced from its cDNA
sequence, revealing it belongs to the G-protein-coupled receptor family
(Boulay et al., 1990). Nearly all G-protein-coupled receptors share a
similar sequence motif which allows for seven-transmembrane-segments
(7-TMS motif) that span the lipid bilayer (Dohlman et al., 1991). The
recent sequence data only confirmed what had been suspected about the
fMet-Leu-Phe signal transduction cascade based on biochemical studies.
Pertussis toxin, a well known inhibitor of some G-proteins, inhibits
many chemotactic responses in a concentration dependent fashion (Brandt
et al., 1985; Becker et al., 1985; Bengtsson et al., 1986). Guanine
nucleotides, and not adenine compounds, regulate the affinity state of the
plasma purified f-Met-Leu-Phe receptors (Sklar et al., 1987). Chemotactic
factors stimulate membrane associated GTPase-activity and guanine
nucleotides can potentiate fMet-Leu-Phe induced activation (Feltner et al.,
1986; Verghese et al., 1986). Additionally, a GTP-binding, 40 kDa
pertussis-toxin-substrate complex copurifies with the fMet-Leu-Phe
receptor after several chromatographic steps. Immunochemical
identification and cDNA sequence analysis reveal the PMN G-protein
coupled to the fMet-Leu-Phe receptor is of the G¡2 (pertussis toxin


TABLE OF CONTENTS
ACKNOWLEDGMENTS iii
LIST OF FIGURES vi
ABSTRACT viii
CHAPTERS
1 INTRODUCTION 1
Overview 1
The Human Neutrophil 2
Actin 4
Actin Binding Proteins 14
Actin Dynamics in PMN 21
Calcium Independent Model For Polymerization 31
PMN Actin Polymerization Inhibitor 35
2 MATERIALS AND METHODS 37
Isolation Of Human Polymorphonuclear Leukocytes
(PMN) 37
Purification Of CapZ From Human PMN 37
Purification of Muscle Actin 40
Amino Acid Sequence Analysis 40
Polyacrylamide Gel Electrophoresis And Western Blot
Analysis 41
Actin Binding Studies 43
Lipid-Binding And Capping-Inhibition Studies 45
Promyelocyte Differentiation Studies 47
Fluorescence Microscopy 50
tv


152
Kwiatkowski, D. J., Stossel, T. P., Orkin, S. H., Mole, J. E., Colten, H. R.,
and Yin, H. L. 1986. Plasma and cytoplasmic gelsolins are encoded by a
single gene and contain a duplicated acdn-binding domain. Nature 323:
455-457.
Larsson, H., and Lindberg, U. 1988. The effect of divalent cations on
the interaction between calf spleen profilin and different actins. Biochim.
Biophys. Acta. 953: 95-105
Lassing, I., and Lindberg, U. 1985. Specific interaction between
phosphatidylinositol 4,5-bisphosphate and profilactin. Nature 314: 472-
474
Lew, P. D., Monod, A., Waldvogel, F. A., Dewald, B., Baggiolini, M.,
and Pozzan, T. 1986. Quantitative analysis of the cytosolic free calcium
dependency of exocytosis from three subcellular compartments in intact
neutrophils. J. Cell Biol. 102: 2197-2204
Lew, P., Wollheim, F., Waldvogel, F., and Pozzan, T. 1984.
Modulation of cytosolic free-calcium transients by changes in intracellular
calcium-buffering. Correlation with exocytosis and 02' production in
human neutrophils. J. Cell Biol. 99: 1212-1220
Lin, S. C., Aebersold, R. H., Kent, S. B., Varma, M., and Leavitt, J.
1988. Molecular cloning and characterization of plastin, a human
leukocyte protein expressed in transformed human fibroblasts. Mol. Cell.
Biol. 8: 4659-4668
Lind, S. E., Janmey, P. A., Chaponnier, C., Herbert, T. J., and Stossel,
T. P. 1987. Reversible binding of actin to gelsolin and profilin in human
platelet extracts. J. Cell Biol. 105: 833-842
Lofgren, R., Ng-Sikorski, J., Sjolander, A., and Andersson, T. 1993. 82
integrin engagement triggers actin polymerization and
phosphatidylinositol triphosphate formation in non-adherent human
neutrophils. J. Cell Biol. 123: 1597-1605
MacLean-Fletcher, S. D., and Pollard, T. D. 1980. Viscometric
analysis of gelation of Acanthamoeba extracts. J. Cell Biol. 85: 414-428
Mannherz, H. G. 1992. Crystallization of actin in complex with acdn-
binding proteins. J. Biol. Chem. 267: 11661-11664
Mannherz, H. G., Goody, R. S., Konrad, M., and Nowak, E. 1980. The
interaction of bovine pancreatic deoxyribonuclease I and skeletal muscle
actin. Eur. J. Biochem. 14: 367-379


139
nuclei of these cells. The relevance of these findings may become more
apparent once an in vivo role for annexin VI and other annexins is
established. I was unable to reproduce the actin binding properties
previously reported for annexin VI. These studies, although, were limited
as the primary focus was aimed at studying capZ. PMN annexin VI is able
to bind membrane phospholipids in a calcium regulated fashion as
demonstrated by my purifications of annexin VI with phosphatidylserine
multilammelar vesicles or with our phospholipid affinity column. Based
on its abundance and cytoplasmic distribution in PMN, it remains possible
that annexin VI may be involved in the regulation of membrane-
membrane interactions specific to these cells including those occurring
during degranulation, phagocytosis, phagolysosome fusion, and motility.
Future Directions
PMN CapZ
The physiological relevance of the Kd determined for capZ's
interaction with the barbed end is limited unless the concentration and
intracellular localization of this protein in PMN is established. Future
studies are directed at quantifying the amount of this protein in PMN.
Several approaches can be used to attain this value. With thymosin f>4,
the cytoplasmic concentration in PMN was estimated by the quantity of
protein purified from a known packed cell volume using a previously
established cytoplasmic volume for PMN (Cassimeris et al., 1992). The
purification of capZ, although, involves many more chromatographic steps
allowing ample opportunity for proteolytic degradation. Additionally, the
purified capZ would represent a small fraction of the amount originally


131
the serine protease inhibitor diisopropylfluorophosphate and subjected to
Western blot analysis (Figure 5-7). A linear standard curve was generated
using highly purified annexin VI. Comparisons of these values to the 68
kDa reactive band in 3 (Figure 5-7, lanes 2-4) different dilutions of PMN
extract demonstrated that annexin VI represents 0.8 0.9 % of the total
protein in human PMN extracts. The concentration of annexin VI in
human PMN is ~7 pM when calculated relative to the actin in PMN (300
pM, 15 20 % of extracts; Southwick & Young, 1990).
Discussion
I have found that annexin VI, a member of the annexin family of
Ca2+- and phospholipid-binding proteins, is present in the cytoplasm of
human PMN at high concentrations. The northern and western analyses
suggest the levels of annexin VI mRNA and protein is differentially
regulated in myeloid cells of the monocyte/macrophage lineage verses
those of the neutrophil lineage. The data presented indicate that
differentiation of HL-60 cells towards macrophages results in a marked
decrease in annexin VI mRNA levels, while the level in cells differentiated
to neutrophils is at least maintained if not elevated. Moderate increases in
annexin VI, although, may be masked during DMSO treatment since
incomplete induction (a population continues to proliferate) is common.
A moderate difference was also seen when annexin VI protein levels were
examined during differentiation of HL-60 cells. Consistent with mRNA
levels, the annexin VI protein content was elevated in cells treated with
DMSO, and appeared to decrease with PMA treatment. Changes in mRNA
levels upon differentiation are not limited to regulation at the