Physical interaction between pRb and cdk9/cyclinT2 complex.
Cyclin-dependent kinase 9 (cdk9) is a multifunctional kinase with roles in different cellular pathways such as transcriptional elongation, differentiation and apoptosis. Cdk9/cyclin T differs functionally from other cdk/cyclin complexes that regulate cell cycle progression, but maintains structural affinity with those complexes. In addition, previous reports have demonstrated that the cdk9 complex is able to phosphorylate p56/pRb in vitro. In this report we show in vitro and in vivo interaction between cdk9/cyclinT2 and the protein product of the retinoblastoma gene (pRb) in human cell lines. The interaction involves the region composed of residues 129-195 of cdk9, cyclinT2 (1-642 aa) and the C-terminal domain of pRb (835-928 aa). We located the minimal region of cdk9 phosphorylation on the C-terminus of pRb, by identifying the residues between 793 and 834. This region contains at least three proline-directed serines (sp), S795, S807 and S811, which have been reported to be phosphorylated in vivo and which could be targeted by the cdk9 complex. These data suggest that, in logarithmically growing cells, cdk9/cyclin T2 and pRb are located in a nuclear multiprotein complex probably involved in transduction of cellular signals to the basal transcription machinery and that one of these signals could be the cdk9 phosphorylation of pRb.
Simone
Cristiano
C
Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, PA 19107, USA.
Bagella
Luigi
L
Bellan
Cristiana
C
Giordano
Antonio
A
D000595:Amino Acid Sequence; D001483:Base Sequence; D056906:Cyclin T; D042863:Cyclin-Dependent Kinase 9; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D016213:Cyclins / Q000378:metabolism*; D017931:DNA Primers; D006367:HeLa Cells; D006801:Humans; D019169:Jurkat Cells; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011485:Protein Binding; D016160:Retinoblastoma Protein / Q000737:chemistry / Q000378:metabolism*
C441622:CCNT2 protein, human; D056906:Cyclin T; D016213:Cyclins; D017931:DNA Primers; D016160:Retinoblastoma Protein; C467969:CDK9 protein, human; D042863:Cyclin-Dependent Kinase 9; D018844:Cyclin-Dependent Kinases