Western blot analysis for HER2 and HER3 and phosphorylated- HER2 (P-HER2), HER3 (P-HER3), AKT (P-AKT), S6 (P-S6) and ERK (P-ERK) in serum starved MCF-7 cells treated with vehicle (C), tamoxifen [100 nM] (TAM), heregulin [10 ng/mL] (HRG) or tamoxifen and heregulin (HRG-TAM). (A) SK-BR3 cells were a positive control for HER2 overexpression. Compared with the SK-BR3 cells, the MCF7 cells do not overexpress HER2. (B) HRG alone or in combination with tamoxifen stimulates HER2, HER3, AKT, S6 and ERK phosphorylation as compared to vehicle and tamoxifen alone. These figures shows a representative blot from three separate western blots.