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Cofilin phosphorylation and actin cytoskeletal dynamics regulated by rho- and Cdc42-activated LIM-kinase 2
1Division of Biochemistry, Department of Oncology, Biomedical Research Center, Osaka University Medical School, Suita, Japan.
Abstract:
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.
Insights
Limbic kinase 2 (LIMK2) regulates actin cytoskeleton reorganization by phosphorylating cofilin. LIMK2 is crucial for Rho- and Cdc42-induced actin rearrangements, distinct from LIMK1
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Actin filament dynamics are crucial for cell structure and function.
- Actin-binding proteins, like cofilin, regulate actin turnover.
- Cofilin phosphorylation by LIMK2 inhibits its actin depolymerizing activity.
Purpose of the Study:
- To investigate the role of LIMK2 in actin cytoskeletal reorganization.
- To determine the specific Rho GTPases that regulate LIMK2 activity.
- To elucidate the mechanism by which LIMK2 influences actin dynamics.
Main Methods:
- Expression of wild-type and kinase-dead LIMK2 in cells.
- Co-expression with activated Rho, Cdc42, and Rac.
- Analysis of actin structures such as stress fibers, filopodia, and lamellipodia.
Main Results:
- LIMK2 phosphorylates cofilin, promoting stress fiber and focal complex formation.
- LIMK2 activity is stimulated by activated Rho and Cdc42, but not Rac.
- LIMK2 inhibition abrogates Rho- and Cdc42-induced actin rearrangements.
- LIMK2 does not affect Rac-induced lamellipodia formation.
Conclusions:
- LIMK2 is a key regulator of Rho- and Cdc42-mediated actin cytoskeletal reorganization.
- LIMK2 functions by inhibiting cofilin activity.
- LIMK1 and LIMK2 regulate distinct Rho subfamily GTPase pathways, highlighting their specialized roles.