Signaling from rho to the actin cytoskeleton through protein kinases ROCK and LIM-kinase

The actin cytoskeleton undergoes extensive remodeling during cell morphogen esis and motility. The small guanosine triphosphatase Rho regulates such re modeling, but the underlying mechanisms of this regulation remain unclear. Cofilin exhibits actin-depolymerizing activity that is inhibited as a resul t of its phosphorylation by LIM-kinase. Cofilin was phosphorylated in N1E-1 15 neuroblastoma cells during lysophosphatidic acid-induced, Rho-mediated n eurite retraction. This phosphorylation was sensitive to Y-27632, a specifi c inhibitor of the Rho-associated kinase ROCK. ROCK, which is a downstream effector of Rho, did not phosphorylate cofilin directly but phosphorylated LIM-kinase, which in turn was activated to phosphorylate cofilin, Overexpre ssion of LIM-kinase in HeLa cells induced the formation of actin stress fib ers in a Y-27632-sensitive manner. These results indicate that phosphorylat ion of LIM-kinase by ROCK and consequently increased phosphorylation of cof ilin by LIM-kinase contribute to Rho-induced reorganization of the actin cy toskeleton.