PML modulates the apoptotic response to UV radiation in a p53-independent manner. (A) Pml^+/+ (▦) and Pml^-/- (▪) MEFs were UV-irradiated with 60 J/m², and apoptosis was measured at 0, 12, and 24 hours by propidium iodide staining and subdiploid peak analysis. Average of 3 independent experiments ± standard deviation (SD) is shown. (B) p53 Function upon UV radiation is unaltered in Pml^-/- MEFs. Pml^+/+ and Pml^-/- MEFs were UV-treated (60 J/m2) and lysed at 0, 1, 3, 6, 12, and 24 hours. Total extracts were probed with antibodies against p53, phospho (P)–p53 (Ser 18), p21, and Bax. HSP90 levels were measured as loading control. Levels of p53 expression and phosphorylation are represented as fold of induction over untreated controls. (C) Bax and p21 mRNA levels in Pml^+/+ and Pml^-/- MEFs were analyzed by Northern blot at 0, 6, 12, and 18 hours upon UV irradiation (60 J/m²). Ethidium bromide staining of 28S rRNA is shown as loading control.