Cofilin Phosphorylation and Actin Cytoskeletal Dynamics Regulated by Rho- and Cdc42-Activated Lim-Kinase 2

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.

Signaling mechanisms that regulate actin‐based motility processes in the nervous system

“…While earlier studies of LIMK indicated that loss of its activity (and thus, increased cofilin activation) inhibits rac and cdc42 actin polymerization (Yang et al 1998;Sumi et al 1999), there is also evidence that LIMK activity/cofilin inactivation inhibits lamellipodium extension . Considering that ADF/cofilin activity is required for actin dynamics (Carlier et al 1997), the function of LIMK in this process, especially downstream of pro-polymerization regulators like growth factors, rac and cdc42, is less clear.…”

“…LIMK is the regulatory link between rho GTPase signaling and cofilin activity. Inactive LIMK blocks rac-and insulin-induced lamellipodium formation (Yang et al 1998), as well as rho-induced stress fibers and cdc42-induced filopodia (Sumi et al 1999). Rac and cdc42 signal to LIMK via PAK, which phosphorylates and activates LIMK on threonine 508 (Edwards et al 1999).…”

Scaffold mediated regulation of MAPK signaling and cytoskeletal dynamics: A perspective

“…Rho-ROCK signaling influences contraction through effects on both the myosin and actin: ROCK elevates myosin light chain phosphorylation by inhibiting myosin phosphatase and/or by directly phosphorylating myosin light chain (MLC) [41][42][43]. ROCK also phosphorylates and activates LIM kinase [64], which in turn phosphorylates and inactivates the actin severing protein, cofilin [36,65].…”

“…While Rac entrains PAK for this function [66,67], Cdc42 signals through MRCK [36,65]. Finally, the recently discovered TESKs can directly phosphorylate cofilin [68], perhaps in response to Rac signaling [69] (Fig.…”

Differentiation-inducing activity of lupane triterpenes on a mouse melanoma cell line

“…Rho up-regulates the formation of stress fibers through the activation of downstream effectors such as Rock. Rock and Rho-kinase activate LIM-kinases, which are responsible for the phosphorylation and inactivation of actin depolymerization factors such as cofilin (Buchan et al 2002;Maekawa et al 1999;Sumi et al 1999). In contrast to the mechanisms of cofilin inactivation by LIMkinases, Slingshot was found to dephosphorylate phospho-cofilin and reactivate cofilin to depolymerize F-actin (Niwa et al 2002).…”