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.

Activation of p53 Transcriptional Activity by SMRT: a Histone Deacetylase 3-Independent Function of a Transcriptional Corepressor

“…The luciferase (Luc) reporter vectors p21-Luc and p2-mdm2-Luc, as well as the wild-type and mutant 14-3-3 luciferase reporter genes (32), were kind gifts of Larry Donehower (Baylor College of Medicine), and the SMRT DAD mutant (DADm; Y470A) was obtained from Mitch Lazar (19). Wild-type p53 was obtained from Addgene (Cambridge, MA) and cloned into pGEX-4T, while pGEX-4T-p53(1-300) and pGEX-4T-p53(300-393) were kinds gifts of Mengtao Li (33). The expression vectors for deletions in the SMRT N terminus, namely, SMRT-NT⌬36-312, SMRT-NT⌬36-388, and SMRT-NT⌬36-480, were generated by overlap extension PCR following a standard protocol.…”

Role of cdk9 in the Optimization of Expression of the Genes Regulated by ICP22 of Herpes Simplex Virus 1

“…This same group has also shown that the addition of cdk inhibitors at the start of infection alters the levels and localization of cdk9 and cdk7 (15). More recently, the Kaposi's sarcoma-associated herpesvirus K-cyclin protein has been shown to interact with cdk9 (6).…”

Viral Cyclin promotes KSHV-induced cellular transformation and tumorigenesis by overriding contact inhibition

“…5,6 vCyclin binds to several Cyclin-dependent kinases (CDK) including CDK2, CDK4, CDK6, and CDK9 in vitro. [5][6][7][8][9] However, only vCyclin interactions with CDK6 and CDK9 have been shown to be functional in cells so far. The vCyclin-CDK6 complex has a large range of substrates including pRb, Bcl-2, histone Kaposi sarcoma-associated herpesvirus (KSHV) is a tumor virus encoding several proto-oncogenes.…”

“…5,7,[9][10][11][12][13][14] In PEL cell lines, phosphorylation by the vCyclin-CDK6 complex leads to p21 inactivation as well as p27 inactivation, cytoplasmic sequestration, and degradation, resulting in accelerated G 1 /S phase transition. 11,15,16 Single gene overexpression also causes vCyclin-dependent p27 degradation.…”