Aurora‐B and Rho‐kinase/ROCK, the two cleavage furrow kinases, independently regulate the progression of cytokinesis: possible existence of a novel cleavage furrow kinase phosphorylates ezrin/radixin/moesin (ERM)

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Abstract
Cytokinesis is regulated by several protein kinases, such as Aurora-B and Rho-kinase/ROCK. We have indicated that these two kinases are the cleavage furrow (CF) kinases that accumulate at the cleavage furrow and phosphorylate several intermediate filament (IF) proteins into two daughter cells. It has been reported that Aurora-B phosphorylates MgcRacGAP to functionally convert to a RhoGAP during cytokinesis. Therefore, we investigated here the relationship between Aurora-B and Rho-kinase/ROCK in cytokinesis, by using small interfering RNA (siRNA) technique. Aurora-B depletion did not alter the cleavage furrow-specific localization of Rho-kinase/ROCK and vice versa. Treatment of Aurora-B or Rho-kinase/ROCK siRNA increased multinucleate cells, and the effect of double depletion was additive. Aurora-B depletion induced the reduction of cleavage furrow-specific phosphorylation of vimentin at Ser72 but not vimentin at Ser71, myosin light chain (MLC) at Ser19, and myosin binding subunit of myosin phosphatase (MBS) at Ser852. In contrast, Rho-kinase/ROCK depletion led to the reduction of cleavage furrow-specific phosphorylation of MLC at Ser19, MBS at Ser852, and vimentin at Ser71 but not vimentin at Ser72. Cleavage furrow-specific ezrin/radixin/moesin (ERM) phosphorylation was not altered in the Aurora-B- and/or Rho-kinase/ROCK-depleted cells. In addition, C3 or toxin B treatment did not abolish ERM phosphorylation at the cleavage furrow in cells attaining cytokinesis. These results suggest that Aurora-B and Rho-kinase/ROCK regulate the progression of cytokinesis without communicating to each other, and there may exist a novel protein kinase which phosphorylates ERM at the cleavage furrow.