Actin polymerization and depolymerization during apoptosis in hl-60
cells.
Levee, Minette G., Milena I. Dabrowska, Joseph L. Lelli, Jr., and
Daniel B. Hinshaw.
Sections of General and Pediatric Surgery, University of Michigan
Medical School and Surgical Service, VA Medical Center, Ann Arbor,
MI
APStracts 3:0216C, 1996.
Little is known about the biochemical "machinery" responsible
for the morphologic features of apoptosis, although the cytoskeleton
is presumed to be involved. Using flow cytometry, polyacrylamide gel
electrophoresis, and fluorescence microscopy, we show that apoptosis
induced by UV irradiation or 80 [mu]g/ml etoposide (VP16) correlates
with early transient polymerization and later depolymerization of
filamentous (F)-actin and dramatic changes in visible microfilament
organization. Depolymerization of F-actin began before the formation
of apoptotic bodies, and was ultimately composed of decreases in both
the detergent-insoluble (40%) and detergent-soluble (50%) pools of F
-actin. Dihydrocytochalasin B (H2CB), which blocked apoptotic body
formation, depolymerized F-actin in the detergent-insoluble pool
only. Visually, H2CB treatment disrupted microfilament organization,
resulting in short, brightly stained microfilaments dispersed
throughout the cytoplasm. In contrast, apoptotic cells contained a
network of fine microfilaments with bright staining concentrated at
the site of apoptotic body formation. Together, these results suggest
that reorganization of the microfilament network is necessary for the
formation of apoptotic bodies and that depolymerization of F-actin
may also be a necessary component of the process of apoptosis.
Received 24 January 1996; accepted in final form 26 June 1996.
APS Manuscript Number C52-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 July 1996