Depletion of the p53 protein in fibroblasts by RNA interference. (A) Control fibroblasts transfected with p53, non-targeting control, or no siRNA oligonucleotides (mock) were harvested at the indicated times. Levels of p53 mRNA was measured by real-time TaqMan PCR using p53 as the target and gusB as the endogenous control. Statistical analyses (one-way ANOVA) indicate a significant reduction of p53 mRNA by the addition of p53 siRNA at each time point analyzed as compared to mock control (*** p < 0.0001). The data shown here are representative of two independent experiments. (B) A similar experiment was conducted as described for (A), and levels of the p53 protein were detected as described for 2A. (C) Control and SMA fibroblasts were transfected as described for (A). Twenty-four hours after transfection, cells were treated with 25 μM camptothecin for 24 h. Levels of p53 were analyzed as described for (B). NT = non-targeting control, CPT = camptothecin, and ND = non-detected.