MP1 silencing induces apoptosis of MCF-7 but not of MDA-MB-231 cells. MCF-7 or MDA-MB-231 cells were transfected for 24 or 48 h with 30 nM control or MP1 siRNA. (A) Immunoblot of Bcl-2 protein levels in extracts of MCF-7 cells. Numbers represent the Bcl-2/Actin ratios expressed as percentage of control samples for a single experiment (24 h)or the average ± SD of 3 independent experiments (48 h, p < 0.05). (B) Immunoblot of PARP in extracts of MCF-7 and MDA-MB-231 cells at 48 h. (C) Transfected MCF-7 cells were harvested at 48 h, stained with Annexin V and propidium iodide, and analyzed by flow cytometry as described in the methods section. Numbers in the 4 quadrants represent the percentage of cells that are PI-/Annexin- (lower left), PI+/Annexin- (upper left), PI-/Annexin+ (lower right) and PI+/Annexin+ (upper right). The immunoblot of MP1 expression is also shown. (D) Photographs of MCF-7 cells transfected with MP1 siRNA in the absence or presence of 50 μM z-VAD-FMK at 48 h. Scale bar = 100 μm. (E) Immunoblot and quantification of PARP cleavage at 48 h under the indicated conditions.