SMAD1 and triple-negative breast carcinoma: In addition, they showed that acutely stimulating triple-negative breast cancer cells (MDA-MB-231) and immortalized human mammary epithelial cells (MCF10A-5E) with GDF11 (250 ng/mL) induced the phosphorylation of Smad2/3, while Smad1/5 remained unaffected, suggesting that the Smad2/3 pathway has a central role in the mammary epithelium [20].