title: Cdk9 phosphorylates p53 on serine 392 independently of CKII.
abstract: The tumor suppressor p53 is an important cellular protein, which controls cell cycle progression. Phosphorylation is one of the mechanisms by which p53 is regulated. Here we report the interaction of p53 with another key regulator, cdk9, which together with cyclin T1 forms the positive transcription elongation complex, p-TEFb. This complex cooperates with the HIV-1 Tat protein to cause the phosphorylation of the carboxyl terminal domain (CTD) of RNA polymerase II and this facilitates the elongation of HIV-1 transcription. We demonstrate that cdk9 phosphorylates p53 on serine 392 through their direct physical interaction. Results from protein-protein interaction assays revealed that cdk9 interacts with the C-terminal domain (aa 361-393) of p53, while p53 interacts with the N-terminal domain of cdk9. Transfection and protein binding assays (EMSA and ChIP) demonstrated the ability of p53 to bind and activate the cdk9 promoter. Interestingly, cdk9 phosphorylates serine 392 of p53, which could be also phosphorylated by casein kinase II. Kinase assays demonstrated that cdk9 phosphorylates p53 independently of CKII. These studies demonstrate the existence of a feedback-loop between p53 and cdk9, pinpointing a novel mechanism by which p53 regulates the basal transcriptional machinery.
authors.affiliation: Center for Biotechnology, Sbarro Institute for Cancer Research and Molecular Medicine, College of Science and Technology, Temple University, Philadelphia, Pennsylvania 19122, USA. claudio@temple.edu
authors.forename: Pier Paolo
authors.initials: PP
authors.lastname: Claudio
authors.forename: Jianqi
authors.initials: J
authors.lastname: Cui
authors.forename: Mohammad
authors.initials: M
authors.lastname: Ghafouri
authors.forename: Chiara
authors.initials: C
authors.lastname: Mariano
authors.forename: Martyn K
authors.initials: MK
authors.lastname: White
authors.forename: Mahmut
authors.initials: M
authors.lastname: Safak
authors.forename: Joel B
authors.initials: JB
authors.lastname: Sheffield
authors.forename: Antonio
authors.initials: A
authors.lastname: Giordano
authors.forename: Kamel
authors.initials: K
authors.lastname: Khalili
authors.forename: Shohreh
authors.initials: S
authors.lastname: Amini
authors.forename: Bassel E
authors.initials: BE
authors.lastname: Sawaya
mesh_terms: D001932:Brain Neoplasms; D047390:Casein Kinase II / Q000378:metabolism*; D045744:Cell Line, Tumor; D042863:Cyclin-Dependent Kinase 9 / Q000378:metabolism*; D005909:Glioblastoma; D015497:HIV-1 / Q000235:genetics; D006801:Humans; D007700:Kinetics; D008175:Lung Neoplasms; D010766:Phosphorylation; D011994:Recombinant Proteins / Q000378:metabolism; D012694:Serine; D014158:Transcription, Genetic; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
chemical_list: D011994:Recombinant Proteins; D016159:Tumor Suppressor Protein p53; D012694:Serine; D047390:Casein Kinase II; D042863:Cyclin-Dependent Kinase 9