FIG. 5.

p53 expression after IR or ADR inhibits cyclin B1-Cdc2 kinase activity. (A) Cells were treated with IR (8, 12, and 20 Gy) and incubated for 15 h, after which time cells were cultured for an additional 24, 48, or 72 h in the presence or absence of PonA. Protein lysates were analyzed by Western blotting for the indicated proteins. (B) Cells were treated with ADR (90, 175, 350, or 525 nM) for 17 h, the drug was washed out, and the cells were cultured an additional 24, 48, or 72 h in the presence or absence of PonA. (C and D) Protein lysates were analyzed by cyclin B1 immunoprecipitation-based assays for Cdc2 kinase activity using histone H1 as a substrate (C) and for immunoprecipitable cyclin B1, Cdc2, and p21 proteins by Western blotting (D). HIp53 cells were treated with 525 nM ADR for the data presented in panels C and D. Results are representative of two independent experiments. Con, control; IP, immunoprecipitation.