Regulation of bimodal p53 dynamics by Mdm2 expression. (a) Comparison of kinetics of selected proteins/protein modifications by western blot analysis for U-2 OS cells treated with 100 and 1 μmol/l etoposide, respectively. Actin served as a loading control. (b) Mdm2 and p53 expression levels with the indicated RNA interference (RNAi) treatment after 0 and 24 hours of 1 μmol/l etoposide treatment. +: With etoposide; −: without etoposide. (c) Distribution of the four response phenotypes for the indicated treatments: control (no small interfering (si)RNA), control siRNA, Mdm2 siRNA, and 10 μmol/l nutlin-3, in combination with 1 μmol/l etoposide in U-2 OS cells. The total number of cells analyzed for each treatment ranged from 69 to 99. Error bars show standard deviations of data from two independent experiments. (d) Real-time quantitative (q)PCR analysis of Mdm2 transcript level at 1 μmol/l (filled column) and 100 μmol/l etoposide (empty columns). Error bars show standard deviations of data from three independent experiments.