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. 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 Ser33 in vivo and the phosphorylation could be inhibited by YN968D1 a dominant negative Cdk9 mutant YN968D1 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 Mouse monoclonal to ERK3 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. Kaposi’s sarcoma-associated herpesvirus (KSHV) or human being herpesvirus 8 can be a DNA tumor disease and etiologic agent of Kaposi’s sarcoma (KS) major effusion lymphoma (PEL) and multicentric Castleman’s disease (MCD) (13 53 72 YN968D1 KS is among the most common malignancies in Helps patients as well as the 4th most common tumor caused by disease world-wide (4). PEL can be a high-grade non-Hodgkin B-cell lymphoma with poor prognosis and brief survival period (6). MCD can be a lymphoproliferative disorder which has a high threat of developing into PEL (58). Nearly all tumor cells in these neoplasms are latently contaminated with KSHV recommending that viral latent genes are essential for KSHV-associated malignancies (5 29 79 K-cyclin encoded by for 20 min at 4°C. Regular Traditional western blotting was performed utilizing the TCL as well as the targeted protein had been visualized with an enhanced chemiluminescence detection system. The primary antibodies used in the Western blots were purchased from the following companies: anti-Flag-horseradish peroxidase (HRP) (M2) antibody and antitubulin monoclonal antibody (MAb) Sigma; rabbit antibodies against p53 phospho-p53 (Ser33) phospho-p53 (Ser315) and phospho-p53 (Ser392) Cell Signaling Technology; and anti-Cdk9 (D-7) MAb Santa Cruz Biotechnology. Anti-myc MAb was produced from the MYC 1-9E10.2 hybridoma cell line (American Tissue Culture Collection). HRP-conjugated secondary antibodies were purchased from Rockland Immunochemicals (Gilbertsville PA). Coimmunoprecipitation. For the transfected 293FT cells TCL was prepared as described above and then was gently mixed with an appropriate antibody on a rotator for 2 h at 4°C. Five microliters of Protein G Plus-agarose beads (Santa Cruz Biotechnology) was then added and samples were continuously mixed for an additional 2 h at 4°C. The agarose beads were washed three times with cold total cell lysis buffer and the immunoprecipitated protein complexes were eluted in sodium dodecyl sulfate (SDS) sample buffer for Western blot analysis. For the KSHV-infected BCBL-1 and control BJAB cells 107 cells were treated with 1 mM of butyric acid for 48 h and then lysed in total cell lysis buffer containing 1% NP-40. Five hundred microliters of the lysates was diluted with 1 0 μl of PBS containing protease inhibitors. Coimmunoprecipitation was performed in two steps. First 5 μl of rat anti-K-cyclin antibody (Santa Cruz Biotechnology) was added and the samples were mixed on a rotator at 4°C for 3 h. Second 1 μl of rabbit anti-rat antibody (Santa Cruz Biotechnology) was added followed by mixing for another 3 h. Ten microliters of protein A-agarose beads (Sigma) was then added and the coimmunoprecipitation was performed overnight at 4°C. The YN968D1 immune complexes were analyzed by Western blotting as described above. In vitro kinase assay. Transfected 293FT cells were lysed on ice for 10 min in 500 μl of kinase lysis buffer (50 mM Tris-HCl pH 8.0 120 mM NaCl 5 mM dithiothreitol 0.5% NP-40 1 μg/ml pepstatin A 0.5 μg/ml leupeptin 0.5 μg/ml aprotinin 0.5 mM phenylmethylsulfonyl fluoride 0.3 μg/ml E-64 20 mM sodium pyrophosphate and 1 mM NaF). The cell lysates were clarified by centrifugation and subjected to immunoprecipitation with anti-Flag or anti-Cdk9 antibody as described above. The agarose beads were rinsed three times with the kinase lysis buffer and once with a kinase reaction buffer (100 mM Tris-HCl pH 7.5 20 mM MgCl2 10 mM dithiothreitol and 5 μM ATP). The beads were resuspended in 20 μl of the kinase reaction buffer containing 0.5 μCi of [γ-32P]ATP (PerkinElmer Life Sciences) and purified glutathione for 5 min and used for transduction. To generate Cdk9 knockdown cells 2 × 105 SaOS2.