Effect of PTEN on AIB1-induced cell proliferation. (A) Western blot analysis comparing the endogenous AIB1 and PTEN protein levels in several breast cancer cells. (B) MCF-7 Cells transfected with siRNA against AIB1 or/and PTEN were stained with crystal violet after 8 days of growth (left panel). The right graph shows the relative cell density obtained from three plates estimated by the software Imagepro-pus. Each bar represents the mean ± S.D. from three plates *, P < 0.05; **, P < 0.01. (C) MCF-7 cells were transfected with siRNA against AIB1 or/and PTEN for different time points and the cell proliferation status was assessed by MTT assay. Each bar represents the mean ± S.D. from five independent experiments. *, P < 0.05 (control versus cells with knockdown of PTEN). (D) Flow cytometry analysis on cell-cycle distribution of MCF-7 cells after 2 days of transfection.