Specific accumulation of Rho-associated kinase at the cleavage furrow during cytokinesis: cleavage furrow-specific phosphorylation of intermediate filaments.

The small GTPase Rho and one of its targets, Rho-associated kinase (Rho-kinase), are implicated in a wide spectrum of cellular functions, including cytoskeletal rearrangements, transcriptional activation and smooth muscle contraction. Since Rho also plays an essential role in cytokinesis, Rho-kinase may possibly mediate some biological aspects of cytokinesis. Here, using a series of monoclonal antibodies that can specifically recognize distinct phosphorylated sites on glial fibrillary acidic protein (GFAP) and vimentin, phosphorylation sites by Rho-kinase in vitro were revealed to be identical to in vivo phosphorylation sites on these intermediate filament (IF) proteins at the cleavage furrow in dividing cells. We then found, by preparing two types of anti-Rho-kinase antibodies, that Rho-kinase accumulated highly and circumferentially at the cleavage furrow in various cell lines. This subcellular distribution during cytokinesis was very similar to that of ezrin/radixin/moesin (ERM) proteins and Ser19-phosphorylated myosin light chain. These results raise the possibility that Rho-kinase might be involved in the formation of the contractile ring by modulating these F-actin-binding proteins during cytokinesis and in the phosphorylation and regulation of IF proteins at the cleavage furrow.