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J. Cell Biol.,
Volume 141, Number 3, May 4, 1998 647-662


* Division of Hematology and Oncology, Tupper Research Institute, Department of Medicine, New England Medical Center,
Boston, Massachusetts; Previous studies suggest that the Ca2+-dependent proteases, calpains, participate in remodeling of
the actin cytoskeleton during wound healing and are
active during cell migration. To directly test the role
that calpains play in cell spreading, several NIH-3T3- derived clonal cell lines were isolated that overexpress
the biological inhibitor of calpains, calpastatin. These
cells stably overexpress calpastatin two- to eightfold
relative to controls and differ from both parental and
control cell lines in morphology, spreading, cytoskeletal
structure, and biochemical characteristics. Morphologic characteristics of the mutant cells include failure to extend lamellipodia, as well as abnormal filopodia, extensions, and retractions. Whereas wild-type cells extend
lamellae within 30 min after plating, all of the calpastatin-overexpressing cell lines fail to spread and assemble
actin-rich processes. The cells genetically altered to
overexpress calpastatin display decreased calpain activity as measured in situ or in vitro. The ERM protein
ezrin, but not radixin or moesin, is markedly increased
due to calpain inhibition. To confirm that inhibition of
calpain activity is related to the defect in spreading,
pharmacological inhibitors of calpain were also analyzed. The cell permeant inhibitors calpeptin and MDL 28, 170 cause immediate inhibition of spreading. Failure
of the intimately related processes of filopodia formation and lamellar extension indicate that calpain is intimately involved in actin remodeling and cell spreading.
Department of Biochemistry, ¶ Department of Physiology, Tufts University School of Medicine, Boston,
Massachusetts 02111; § Department of Biochemistry, Microbiology, and Molecular Biology, University of Maine, Orono, Maine
04469-5735; and
Department of Applied Biological Sciences, School of Agricultural Sciences, Nagoya University, 464-8601 Nagoya, Japan
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