Differential response to growth factor by rat mammary epithelium plated on different collagen substrata in serum-free medium.

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Abstract
Primary cultures of rat mammary epithelial cells proliferate and synthesize basement membrane collagen (type IV collagen) in a serum-free medium supplemented with epidermal growth factor (EGF), hydrocortisone or dexamethasone, insulin, transferrin and Pedersen fetuin. The growth response of the cells to EGF and glucocorticoids, but not to insulin or transferrin, varies depending on the substratum on which the cells are plated. Cell growth is 4 times more sensitive to omission of EGF or glucocorticoid on type I collagen or plastic substratum than on type IV collagen substratum. The mechanism by which these 2 growth factors differentially affect cell growth appears to be linked to an increase in type IV collagen synthesis, and a stabilization of secreted type IV collagen in the extracellular matrix. Glucocorticoids suppress the elaboration of type IV collagenolytic activity by the cells, whereas EGF stimulates amino acid incorporation into type IV collagen. The results suggest that EGF and glucocorticoids affect mammary epithelial cell growth by facilitating the accumulation of the appropriate cell substratum.