Cell biology

how cdk enzyme role in this prb

another question. prb are unphosphorylate that means there is no s phase transcription. and there is no s phase expression that means no chance of cancer?

The retinoblastoma tumor suppressor protein (pRB) negatively regulates early-G1 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 by multiple G1 cyclin-Cdk complexes, the active form(s) of pRB in vivo remains unknown. pRB is present as an unphosphorylated protein in G0 quiescent cells and becomes hypophosphorylated (∼2 mol of PO4 to 1 mol of pRB) in early G1 and hyperphosphorylated (∼10 mol of PO4 to 1 mol of pRB) in late G1 phase. Here, we report that hypophosphorylated pRB, present in early G1, represents the biologically active form of pRB in vivo that is assembled with E2Fs and E1A but that both unphosphorylated pRB in G0 and hyperphosphorylated pRB in late G1 fail to become assembled with E2Fs and E1A. Furthermore, using transducible dominant-negative TAT fusion proteins that differentially target cyclin D-Cdk4 or cyclin D-Cdk6 (cyclin D-Cdk4/6) and cyclin E-Cdk2 complexes, namely, TAT-p16 and TAT–dominant-negative Cdk2, respectively, we found that, in vivo, cyclin D-Cdk4/6 complexes hypophosphorylate pRB in early G1 and that cyclin E-Cdk2 complexes inactivate pRB by hyperphosphorylation in late G1. Moreover, we found that cycling human tumor cells expressing deregulated cyclin D-Cdk4/6 complexes, due to deletion of the p16INK4a gene, contained hypophosphorylated pRB that was bound to E2Fs in early G1 and that E2F-responsive genes, including those for dihydrofolate reductase and cyclin E, were transcriptionally repressed. Thus, we conclude that, physiologically, pRB is differentially regulated by G1 cyclin-Cdk complexes.

some important points are given from reputed article. Hope it will help you. read slowly and draw to understand better.

causing cancer not depends on pRB protein. it is depend upon gene mutation. phosphorylation is cellular process it is not control by gene so there is no relation between phosphorylation of pRB and cancer. if still some problem revise topic again and ask the doubts.