Figure 4.

Analysis of mRNA and protein expression of p53 target genes in response to etoposide. HCT116/wt and HCT116/p53^−/− cells were treated with 10 μM, 50 μM, and 100 μM etoposide for 48 h and expression of Bak (a), Bax (b), Puma (c), and p21 (d) mRNA was analyzed by qRT-PCR. Expression of Bak and Puma mRNA increases with concentration of etoposide, whereas induction of Bax and p21 mRNA expression is independent of the concentration of etoposide. (e) The HCT116/wt and HCT116/p53^−/− cells were incubated with 50 μM etoposide for 24 h, 48 h and 72 h, and expression of p53, Bak, Bax, and p21 was analyzed by western blotting. (f) The HCT116/wt and HCT116/p53^−/− cells were incubated with the indicated concentrations etoposide for 48 h and expression of p53, Bak, Bax, and p21 protein was analyzed likewise. In HCT116/wt and to a lesser extent also in HCT116/p53^−/− cells, the level of Bak expression rises in a time- (e) and concentration- (f) dependent manner. Values are means±S.D. from three independent experiments