FIG. 8.

Dephosphorylation of pRB during p53 regulation of the G₂ checkpoint. (A) HIp53 cells were treated with 525 nM ADR for 17 h, the drug was washed out, and the cells were cultured for the indicated times in the presence or absence of PonA. (A) Cells were harvested and analyzed by Western blot analysis for pRB protein levels and phosphorylation state (upper blot) and for Cdk2 kinase activity using histone H1 as a substrate (lower blot). (B) HCT116, HCT116 p53^−/−, and HCT116 p21^−/− cells were treated with 350 nM ADR for the times indicated, and the cells were harvested and analyzed by Western blot analysis for pRB protein levels and phosphorylation state (upper blot) and for Cdk2 kinase activity using histone H1 as a substrate (lower blot). Results are representative of three independent experiments. C and Con, control.