Estrogen provokes increased Mdm2 and compromised transactivation of the p53 apoptotic target puma. MCF-7 and ZR75-1 cells were treated with 10 nM estrogen (E2) for five days and 50 μM etoposide (ETOP) for 48 hours. Western blot analysis of p53, Mdm2, and Actin protein levels from whole cell lysates of MCF-7 (a) and ZR75-1 (b) cells respectively. (c) Protein levels of Puma, Bcl-2 and Actin from whole cell lysates analyzed by Western blot. Quantitative real-time PCR (RT-PCR) was carried out for mRNA levels of puma, mdm2 and p21 genes in MCF-7 (d) and ZR75-1 (e) cells respectively. Results were normalized to control samples and actin values. Graphs show means and standard errors of two independent experiments. * P < 0.05 (Student t-test with * to indicate estrogen significantly influenced the transactivation of a p53 target gene).