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© The Rockefeller University Press, 0021-9525/1999/12/1519/ $5.00
The Journal of Cell Biology, Volume 147, Number 7, December 27, 1999 1519-1532

Original Article

Cofilin Phosphorylation and Actin Cytoskeletal Dynamics Regulated by Rho- and Cdc42-activated LIM-kinase 2

Tomoyuki Sumia, Kunio Matsumotoa, Yoshimi Takaib, and Toshikazu Nakamuraa
a Division of Biochemistry, Department of Oncology
b Department of Molecular Biology and Biochemistry, Biomedical Research Center, Osaka University Medical School, Suita, Osaka 565-0871, Japan

Correspondence to: Toshikazu Nakamura, Division of Biochemistry, Department of Oncology, Biomedical Research Center, Osaka University Medical School, Suita, Osaka 565-0871, Japan. Tel:81-6-6879-3783 Fax:81-6-6879-3789 E-mail:nakamura{at}onbich.med.osaka-u.ac.jp.

The rapid turnover of actin filaments and the tertiary meshwork formation are regulated by a variety of actin-binding proteins. Protein phosphorylation of cofilin, an actin-binding protein that depolymerizes actin filaments, suppresses its function. Thus, cofilin is a terminal effector of signaling cascades that evokes actin cytoskeletal rearrangement. When wild-type LIMK2 and kinase-dead LIMK2 (LIMK2/KD) were respectively expressed in cells, LIMK2, but not LIMK2/KD, phosphorylated cofilin and induced formation of stress fibers and focal complexes. LIMK2 activity toward cofilin phosphorylation was stimulated by coexpression of activated Rho and Cdc42, but not Rac. Importantly, expression of activated Rho and Cdc42, respectively, induced stress fibers and filopodia, whereas both Rho- induced stress fibers and Cdc42-induced filopodia were abrogated by the coexpression of LIMK2/KD. In contrast, the coexpression of LIMK2/KD with the activated Rac did not affect Rac-induced lamellipodia formation. These results indicate that LIMK2 plays a crucial role both in Rho- and Cdc42-induced actin cytoskeletal reorganization, at least in part by inhibiting the functions of cofilin. Together with recent findings that LIMK1 participates in Rac-induced lamellipodia formation, LIMK1 and LIMK2 function under control of distinct Rho subfamily GTPases and are essential regulators in the Rho subfamilies-induced actin cytoskeletal reorganization.

Key Words: cytoskeleton, actin depolymerization, LIM-kinase, Rho family GTPases, stress fibers


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