A cyclin D-Cdk4 activity required for G(2) phase cell cycle progression isinhibited in ultraviolet radiation-induced G(2) phase delay

Cyclin D-Cdk4 complexes have a demonstrated role in G(1) phase, regulating the function of the retinoblastoma susceptibility gene product (Rb). Previo usly, we have shown that following treatment with low doses of UV radiation , cell lines that express wild-type pie and Cdk4 responded with a Gz phase cell. cycle delay. The UV-responsive lines contained elevated levels of p16 posttreatment, and the accumulation of pie correlated with the G(2) delay, Here we report that in UV-irradiated HeLa and A2058 cells, pie bound Cdk4 and Cdk6 complexes with increased avidity and inhibited a cyclin D3-Cdk4 co mpiler normally activated in late S/early G(2) phase. Activation of this co mplex was correlated with the caffeine-induced release from the UV-induced G(2) delay and a decrease in the level of pie bound to Cdk4, Finally, overe xpression of a dominant-negative mutant of Cdk4 blocked cells in G(2) phase . These data indicate that the cyclin D3-Cdk4 activity is necessary for cel l cycle progression through G(2) phase into mitosis and that the increased binding of p16 blocks this activity and G(2), phase progression after UV ex posure.