Interaction between ROCK II and nucleophosmin/B23 in the regulation of centrosome duplication

Nucleophosmin (NPM)/B23 has been implicated in the regulation of centrosorne duplication. NPM/B23 localizes between two centrioles in the unduplicated centrosome. Upon phosphoryllation on Thr(199) by cyclindependent kinase 2 (CDK2)/cyclin E, the majority of centrosomal NPM/B23 dissociates from centrosomes, but some NPM/B23 phosphorylated on Thr(199) remains at centrosomes. It has been shown that Thr(199) phosphorylation of NPM/B23 is critical for the physical separation of the paired centrioles, an initial event of the centrosome duplication process. Here, we identified ROCK 11 kinase, an effector of Rho small GTPase, as a protein that localizes to centrosomes and physically interacts with NPM/B23. Expression of the constitutively active form of ROCK II promotes centrosome duplication, while down-regulation of ROCK II expression results in the suppression of centrosome duplication, especially delaying the initiation of centrosorne duplication during the cell cycle. Moreover, ROCK 11 regulates centrosome duplication in its kinase and centrosome localization activity-dependent manner. We further found that ROCK 11 kinase activity is significantly enhanced by binding to NPM/1323 and that NPM/B23 acquires a higher binding affinity to ROCK II upon phosphorylation on Thr(199). Moreover, physical interaction between ROCK 11 and NPM/B23 in vivo occurs in association with CDK2/cyclin E activation and the emergence of Thr(199)-phosphorylated NPM/B23. All these findings point to ROCK II as the effector of the CDK2/cyclin E-NPM/B23 pathway in the regulation of centrosome duplication.