Mitogenic responsiveness of caprine mammary epithelial cells to endocrine and cytokine factors.

Mammary cell mitogenic responsiveness was evaluated with an established nontransformed caprine mammary epithelial cell line (CMEC). As expected, the cells responded to insulin-like growth factor 1 (IGF-1), insulin, and hydrocortisone with an increased number of cells after 3 and 5 d in culture. In combination, insulin and hydrocortisone augmented each other. A proliferation response was also observed for transforming growth factor-alpha (TGF-alpha), and epidermal growth factor (EGF), but not for fibroblast growth factor a (FGFa), FGFb, IGF-2, bovine somatotropin, or prolactin. Comparison of mitogenic potential for these growth factors with cells grown on plastic substratum indicated that hydrocortisone was most potent, followed by TGF-alpha in inducing a proliferative response measured by 3H-thymidine incorporation assay. Hydrocortisone augmented proliferation by 149% and TGF-alpha stimulated proliferation by 126% relative to the media control (p < 0.01). EGF, which binds to the same receptor as TGF-alpha in other species, induced a modest 35% increase in proliferation. Comparison of culture conditions with plastic, fibronectin, and type I collagen suggests that extracellular matrix/stroma influences the magnitude and effective concentration for cytokine-mediated growth response. Studies on responsiveness to ovarian steroids estradiol 17-beta (E2) and progesterone (P4) showed a modest proliferation response to E2 only in combination with triiodio-L-thyronine (T3), and no response to P4 or T3 either alone or in combination when grown on plastic.