title: Kaposi's sarcoma-associated herpesvirus K-cyclin interacts with Cdk9 and stimulates Cdk9-mediated phosphorylation of p53 tumor suppressor.
abstract: K-cyclin, encoded by Kaposi's sarcoma-associated herpesvirus, has previously been demonstrated to activate cyclin-dependent kinase 6 (Cdk6) to induce the phosphorylation of various cell cycle regulators. In this study, we identified Cdk9 as a new K-cyclin-associated Cdk and showed that K-cyclin interacted with Cdk9 through its basic domain. We hypothesized that K-cyclin served as a regulatory subunit for the activity of Cdk9. Recent reports show that Cdk9 phosphorylates tumor suppressor p53, and we found that the K-cyclin/Cdk9 interaction greatly enhanced the kinase activity of Cdk9 toward p53. The phosphorylation site(s) of K-cyclin/Cdk9 kinase complexes was mapped in the transactivation domain of p53. We showed that the ectopic expression of K-cyclin led to a sustained increase of p53 phosphorylation on Ser(33) in vivo, and the phosphorylation could be inhibited by a dominant negative Cdk9 mutant, dn-Cdk9. Using p53-positive U2OS and p53-null SaOS2 cells, we demonstrated that K-cyclin-induced growth arrest was associated with the presence of p53. In addition, K-cyclin-induced p53-dependent growth arrest was rescued by the dn-Cdk9- or Cdk9-specific short hairpin RNA in SaOS2 cells. Together, our findings for the first time demonstrated the interaction of K-cyclin and Cdk9 and revealed a new molecular link between K-cyclin and p53.
authors.affiliation: Center for Oral Health Research, University of Kentucky College of Dentistry, Lexington, Kentucky 40536, USA.
authors.forename: Pei-Ching
authors.initials: PC
authors.lastname: Chang
authors.forename: Mengtao
authors.initials: M
authors.lastname: Li
mesh_terms: D002453:Cell Cycle / Q000502:physiology; D002460:Cell Line; D042863:Cyclin-Dependent Kinase 9 / Q000378:metabolism*; D016213:Cyclins / Q000378:metabolism*; D019288:Herpesvirus 8, Human / Q000378:metabolism*; D006801:Humans; D010766:Phosphorylation; D011485:Protein Binding; D025941:Protein Interaction Mapping; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D014764:Viral Proteins / Q000378:metabolism*
chemical_list: D016213:Cyclins; C483104:K cyclin protein, Herpesvirus 8, Human; D016159:Tumor Suppressor Protein p53; D014764:Viral Proteins; C467969:CDK9 protein, human; D042863:Cyclin-Dependent Kinase 9