PGE₂ inhibits IR-induced cell death and p53 accumulation in BCP-ALL cells. (A) BCP-ALL blasts from ALL5 were cultured in the presence or absence of 200 µM PGE₂ for 45 min prior to treatment with 2 Gy of IR. Subsequent cell death analysis by fluorescence-activated cell sorter 20 h after irradiation was performed as described in Figure 1A (n = 5, error bars = SEM; *P < .05 by paired samples t test). (B) A portion of cells from the experiments presented in panel 4A were harvested 4 h after irradiation, lysed, and subjected to immunoblot analysis with antibodies against p53 and GAPDH. The immunoblot shows 1 representative experiment of 5. Vertical division lines have been inserted to mark sites where the picture file has been cut and repositioned to remove lanes of intervening samples. Densitometric analyses of the immunoblots were performed as described in Materials and Methods, and calculated fold change in p53 intensity is presented as a histogram (n = 5, error bars = SEM; *P < .05 by paired samples t test). (C) BCP-ALL blasts from ALL5 were cultured in the presence or absence of 60 µM forskolin, 200 µM 8-CPT-cAMP, or 200 µM PGE₂ for 45 min prior to treatment with 2 Gy of IR as indicated. At 4 h after irradiation, 500 000 cells/sample were harvested and subjected to immunocytochemistry as described in Materials and Methods.