Gene silencing of MDM 2 by siRNA potentiates p53 transactivation in the presence of estrogen. MCF-7 cells were transfected with 100 nM non-specific or mdm2 siRNA. 24 hours following transfection, cells were treated with 10 nM estrogen (E2) for 24 hours and 50 μM etoposide (ETOP) for 3 hours. (a) Western blot analysis of Mdm2, p53, p21 and Actin protein levels from whole cell lysates. (b) Quantitative real-time RT-PCR for mRNA levels of puma, p21 and mdm2 genes in MCF-7 cells. Results were normalized to control samples and actin values. Graphs show means and standard errors of two independent experiments.