Divergent transforming growth factor (TGF)-β gene activation and biological responses in MCF-7 and MDA-MB-231 cell lines. (a,b) The TGF-β induced transcriptional program is almost entirely non-overlapping in the luminal MCF-7 and the mesenchymal MDA-MB-231 breast cancer cell lines. The number of genes (a) induced and (b) repressed greater than 1.5-fold with a p-value < 0.01 after a 24 h exposure to TGF-β are shown. All of the individual genes commonly affected in both control cell lines (MCF-7 CN and MDA-MB-231 CN) are listed below the diagram. (c,d) Model for the differential outcomes of TGF-β stimulation in estrogen receptor (ER) positive luminal breast cells compared to ER-negative mesenchymal cells. (e,f) Model for context specific effects of HER-2 overexpression on TGF-β signaling in ER-positive luminal cells versus ER-negative mesenchymal cells. EMT, epithelial to mesenchymal transition.