p53 is required for the inhibitory effect of cAMP on IR-induced apoptosis. (A) Reh cells were transfected with the pXJ-E6 plasmid expressing the HPV16-strain E6-protein, empty vector, siRNA-p53, or control siRNA-A. Cells were then exposed to 10 Gy IR or left untreated. After 12 hours, a portion of the cells was stained with PI for cell death analysis, and the remaining portion was subjected to immunoblotting with the indicated antibodies (n = 3). *P < .05; **P < .01. (B) Reh cells were incubated with or without forskolin for 30 minutes before addition of menadione or staurosporine, and examined for PI uptake after 18 hours. Because menadione interferes with PI fluorescence, the shift in scatter profile was used to discriminate between dead and viable menadione-treated cells (menadione, n = 3; staurosporine, n = 4).