Differential Regulation of Retinoblastoma Tumor Suppressor Protein by G1 Cyclin-Dependent Kinase Complexes In Vivo

• DOI: 10.1128/mcb.21.14.4773-4784.2001
• Publication Date: 2002-07-27T10:03:53Z
• Authors: Sergei A. Ezhevsky; Alan Ho; Michelle Becker-H...; Penny K. Davis; Steven F. Dowdy
• Keywords: Retinoblastoma protein; Cyclin-dependent kinase 6; Cyclin E; Cyclin A; Cyclin D; Cyclin A2; E2F; Cyclin-dependent kinase complex; Hyperphosphorylation; Cyclin B

The retinoblastoma tumor suppressor protein (pRB) negatively regulates early-G 1 cell cycle progression, in part, by sequestering E2F transcription factors and repressing E2F-responsive genes.Although pRB is phosphorylated on up to 16 cyclin-dependent kinase (Cdk) sites multiple G cyclin-Cdk complexes, the active form(s) of vivo remains unknown.pRB present as an unphosphorylated 0 quiescent cells becomes hypophosphorylated (ϳ2 mol PO 4 pRB) early hyperphosphorylated (ϳ10 late phase.Here, we report that pRB, , represents biologically form assembled with E2Fs E1A but both fail become E1A.Furthermore, using transducible dominant-negative TAT fusion proteins differentially target cyclin D-Cdk4 or D-Cdk6 (cyclin D-Cdk4/6) E-Cdk2 namely, TAT-p16 TATdominant-negative Cdk2, respectively, found that, vivo, D-Cdk4/6 complexes hypophosphorylate inactivate hyperphosphorylation .Moreover, cycling human expressing deregulated due deletion p16 INK4a gene, contained was bound genes, including those for dihydrofolate reductase E, were transcriptionally repressed.Thus, conclude physiologically, regulated complexes.