Collagen reduces glycosaminoglycan degradation by cultured mammary epithelial cells: possible mechanism for basal lamina formation.

Collagenous substrates are reported to promote the accumulation of extracellular matrix materials by epithelia in culture. Glycosaminoglycan (GAG) metabolism is compared in secondary cultures of mouse mammary epithelial cells maintained on plastic or type I collagen gel substrates. The incorporation of 35SO42- into GAG during brief labeling indicates no difference between substrates in the rate of GAG synthesis. During prolonged labeling, however, accumulation of [35S]GAG in cultures on colllagen exceeds that of cultures on plastic. This increased accumulation is due to a markedly reduced rate of GAG degradation. GAG degradation does not occur in the medium, indicating that degradation is localized to the cells. The cultures on collagen contain a slowly degrading cell-associated [35S]GAG pool and a ruthenium red-stained basal lamina, neither of which is present in cultures on plastic. The cell-associated [35S]GAG in cultures on collagen is, in part, localized to the site of the ultrastructurally identified basal lamina. Formation of the basal lamina, therefore, may result from collagen-mediated reduction in the degradation of GAG-containing molecules.