Dual inhibition of Notch and PEA3 inhibits cell proliferation and induces apoptosis. MDA-MB-231 cells were transfected with scrambled or PEA3 siRNA alone or were treated with vehicle (DMSO) or a γ-secretase inhibitor (MRK-003 GSI), or a combination thereof, for 48 hours. Cell cycle analysis (A) and annexin V staining (B) were performed by using flow cytometry. (C) Percentages of viable cells were measured by the trypan blue exclusion method using a standard light microscope (×10 original magnification). The mean percentage and standard deviation of cells in each experiment were plotted. Statistical significance was determined by performing analysis of variance for multiple comparisons. The error bars represent standard deviations of the mean for three independent experiments.