Rho-kinase/ROCK is involved in cytokinesis through the phosphorylation of myosin light chain and not ezrin/radixin/moesin proteins at the cleavage furrow

The small GTPase Rho and one of its targets, Rho-kinase (also termed ROK or ROCK), are implicated in various cellular functions including stress fiber formation, smooth muscle contraction, tumor cell invasion and cell motilit y, We have previously reported that Rho-kinase accumulates at the cleavage furrow during cytokinesis in several cultured cells. Here, using Rho-kinase inhibitors, Y-27632 and HA1077, we found that Rho-kinase is responsible fo r the phosphorylation of myosin regulatory light chain at Ser(19) in the cl eavage furrow during cytokinesis. On the other hand, phosphorylation of ezr in/radixin/moesin (ERM) proteins at the cleavage furrow was enhanced by the addition of the above Rho-kinase inhibitors, Treatment with Y-27632 strong ly enhanced the accumulation of Rho-kinase but not RhoA and citron kinase a t the cleavage furrow. Furthermore, the furrow ingression in cytokinesis wa s significantly prolonged in the presence of Y-27632, These results suggest that Rho-kinase is involved in the progression of cytokinesis through the phosphorylation of several proteins including myosin light chain at the cle avage furrow.