Our long-term goal is to understand the function of the basal lamina, a component of the basement membrane, in cellulose physiology and in various pathological states. Our studies have shown that mouse mammary epithelial cells cultured on a collagen gel substratum form a proteoglycan-containing basal lamina. Basal lamina formation correlates with reduced glycosaminoglycan degradation and the apparent conversion of a cellular proteoglycan fraction to a slowly degrading extracellular fraction. Similarly cultured neoplastically transformed cells of the same origin show defective lamina formation and lack of proteoglycan processing. Based upon the hypothesis that the presence and interactions of the proteoglycans in the basal lamina are crucial to its structure and function, we will continue these studies. Using mouse mammary epithelial cells in culture, the focus will be on: (1) isolating and purifying the various proteoglycans and determining the structural relationships between them by analyzing their protein and glycosaminglycan components; (2) elucidating the macromolecular organization of the proteoglycan-containing basal lamina by analyzing the interactions of its various extracellular matrix constituents; (3) establishing the steps in the processing and degradation of basal laminar proteoglycans to determine the role of the collagen substratum in facilitating lamina formation; and (4) applying this new information to elucidate the basis for the defective lamina formation shown by the malignant cells. The functional role of proteoglycans in the lamina will be further assessed by comparing laminar proteoglycans of cultured mammary and vascular endothelial cells.
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