Collagen metabolism and basement membrane formation in cultures of mouse mammary epithelial cells : Induction of ‘Assembly’ on fibrillar type I collagen substrata

Collagen metabolism was compared in cultures of mouse mammary epithelial cells maintained on plastic or fibrillar type I collagen gel substrata. The accumulation of dialysable and non-dialysable 3H]hydroxyproline and the identification of the collagens produced suggest no difference between substrata in the all over rates of collagen synthesis and degradation. The proportion of the 3H]collagen which accumulates in the monolayers of cultures on collagen, however, markedly exceeds that of cultures on plastic. Cultures on collagen deposit a sheet-like layer of extracellular matrix materials on the surface of the collagen fibres. Immunoprecipitation of the labelled extracts, electrophoresis, indirect immunofluorescence and immunoperoxidase techniques reveal the presence of type IV collagen, along with laminin and heparan sulfate proteoglycan in this layer, in excess over the amounts detectable on cells cultured on plastic. Transformed cells on collagen produce and accumulate more 3H]collagen, yet are less effective in basement membrane formation than normal cells, indicating that the accumulation of collagen alone and the effect of interstitial collagen thereupon do not suffice. Thus, exogenous fibrillar collagen appears to enhance, but is not sufficient for proper assembly of collagenous basement membrane components near the basal epithelial cell surface.