This research focuses on routine use of the extracellular matrix (ECM) produced by cultured bovine endothelial cells as a naturally produced substrate adequate for sustaining adhesion, growth, and differentiation of human epithelial cells. Using this substrate and serum-free medium supplemented with HDL, we have developed conditions for the initiation and maintenance in monolayer culture of normal and carcinomatous human breast, bladder, and ovarian epithelial cells, as well as of normal human upper respiratory tract epithelium and first trimester decidual cells. The ECM has been used for screening the efficiency of various cytotoxic drugs in preventing the reimplantation of tumor cells to exposed areas of the bladder submucosa following transurethral resection of the primary tumor. Various chemical modifications of the ECM specifically affected its induction of cell attachment, proliferation, and differentiation, and various cell types responded differently to a given modification of the ECM. Different constituents of the ECM may therefore be held responsible for its induction of specific biological activities. The ECM produced by corneal endothelial cells and chicken embryo fibroblasts was compared. Vascular endothelial cells were stimulated to proliferate by both matrices but when cultured on the fibroblastic matrix they grew on top of each other and failed to adopt the monolayer configuration characteristic of endothelial cells cultured on a basement membrane-like ECM. A highly metastatic subline (ESb) of mouse lymphoma cells exhibited a much higher ability to degrade heparan sulfate than its non-metastatic parental subline (Eb). Degradation of ECM-bound, but not soluble, heparan sulfate proteoglycan proceeded in a sequential manner and was greatly facilitated in the presence of a serine protease which produced a more accessible substrate for further cleavage by the heparanase. Such a role was fulfilled by the ESb plasminogen activator via the generation of plasmin from plasminogen. A similar cascade mechanism was observed with other cell types whether normal or malignant. Heparanase activity was elaborated by normal platelets and granulocytes, and upon specific or nonspecific activation of normal macrophages and T lymphocytes. Antibasic protein (BP) lymphocytes responded to BP presented by ECM by a markedly enhanced heparanase activity, in correlation with their ability to extravasate the blood brain barrier. (A)
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