Detection and partial characterization of collagen synthesis stimulating activities in rat mammary adenocarcinomas

Rat mammary epithelium and adenocarcinomas derived from it synthesize type IV collagen, a structural protein of basement membranes. In cultures of cells, net production of collagen is stimulated 2-fold more than total cell protein by epidermal growth factor. Mammary adenocarcinoma cells also respond to epidermal growth factor but to a much reduced extent. This difference in growth factor responsiveness appears to be due to the production of collagen synthesis stimulating factors by the mammary tumor cells. Such factors have been partially purified and shown to differentially stimulate the incorporation of proline into collagenase-sensitive protein by 2.5-10-fold in normal rat mammary epithelium, normal rat kidney, and mouse 3T3 cells. The tumor factors do not stimulate net collagen production in cultures of tumor cells from which the factors are derived, suggesting that tumor cells produce sufficient stimulatory factors for optimal synthesis of collagen. Pulse-chase studies indicate that the tumor factors stimulate collagen synthesis rather than block collagen turnover. The activities in the extract have been partially purified by gel filtration, ion exchange column chromatography, and isoelectric focusing. The major species has a molecular weight of about 68,000 and a pI of 5.9. A smaller peak of activity with a molecular weight of 6,000 is also present. Since collagen synthesis appears to be necessary for the growth of mammary adenocarcinomas in vivo, production of these collagen synthesis stimulating factors may be important for tumor growth.