Figure 2. PCAF is required for p53-dependent p21 expression. U2OS (B–E) or H1299 (A) cells were transfected with p53 (+) or vector (-) cDNA (A) along with indicated siRNA (A–E) and harvested for immunoblot (A–D) or stained with propidium iodide and subjected to flow cytometric cell cycle profile analysis (E). Nutlin 3a-treated U2OS cells (B and E) were exposed to 5 µM Nutlin-3 for 16 h prior to lysis or fixation. Doxorubicin-treated U2OS cells (C) were exposed to 1 µM doxorubicin for 16 h prior to lysis. UV-irradiated U2OS (D) cells were treated with 20 J/m² UV-C 24 h prior to lysis.