Analysis of progestin effects on hepatocyte growth factor signaling pathways in relation to proliferation and alveolar morphogenesis of normal mammary epithelial cell in vitro

Progestins (P) are major mitogens in the adult human breast and can significantly contribute to breast cancer risk. Using an in vitro, primary culture system we determined that for P-induced proliferation and morphogenesis to occur in normal mouse mammary cells, the presence of hepatocyte growth factor (HGF) is required. HGF induces proliferation and ductal morphogenesis. Addition of P results in increased proliferation and alveolar-like morphogenesis.; The aim was to determine the cell type specific signaling pathways by which P and HGF interact to promote growth and morphology change of mammary epithelial organoids, containing luminal and myoepithelial cells. This was done by immunostaining of HGF signaling intermediates and using biochemical inhibitors of relevant signaling pathways, PI3K, MEK1/2, and matrix metalloproteinases (MMPs). Results showed that increased expression of cyclin D1 and PR B, and decreased expression of PRA in luminal cells was correlated with increased proliferation and alveolar-like morphology response to HGF+P treatment; no changes in c-Met expression were observed in either cell type under any treatment. Both PI3K, and MEK1/2 signaling intermediates were important for the proliferative response of luminal cells and morphologic responses of myoepithelial cell treated with HGF+P. MMPs activity was important for proliferative and morphologic responses of luminal cells only.