Extracellular matrix regulation of cell-cell communication and tissue-specific gene expression in primary liver cultures.

Epithelial-mesenchymal interactions are effected, in part, by extracellular matrix components. We have spent many years analyzing the influence of extracellular matrix, both as extracts of matrix and as purified matrix components, on the growth and differentiation of normal and neoplastic liver cells. Currently we are focused on analyzing the influence of the extracellular matrix components, glycosaminoglycans and proteoglycans. We have found that these factors induce dramatic morphological changes, are potent inducers of gap junction synthesis and can regulate tissue-specific gene expression. With respect to gap junctions: intercellular communication via gap junctions, as measured by dye and electrical coupling, disappears within 12 hrs in primary rat hepatocytes cultured in serum supplemented media or within 24 hrs in cells in a serum free, hormonally defined medium designed for hepatocytes. Glucagon and linoleic acid/BSA were the primary factors in the HDM responsible for the extended life span of the electrical coupling. Addition of proteoglycans or glycosaminoglycans to hormonally defined medium after 24 hrs resulted in reexpression of electrical and dye coupling when assayed at 96 hrs of culture. The incidence of coupling was less than 5% in hormonally defined medium alone. Coupling incidence increased to 10-30% with the addition of 10 micrograms/ml of glycosaminoglycans (i.e., hyaluronic acid, dermatan sulfate, chondroitin 4- or 6-sulfate, and iota- or kappa-carrageenan) to hormonally defined medium. By contrast, the same concentrations of chondroitin sulfate proteoglycan, dermatan sulfate proteoglycan, or lambda-carrageenan resulted in dye coupling in more than 70% of the cells, with numerous cells showing dye spread from a single injected cell (in the case of the proteoglycans). The greatest effect of those tested was elicited by the dermatan sulfate proteoglycans, which induced cell-cell communication in 90-100% of the cells. Heparins gave intermediate responses (30-50%). Western blots demonstrated that the amounts of the main intrinsic gap junction polypeptide (27 KDa) extractable from cells correlated with the degree of electrical and dye coupling. Thus, proteoglycans and glycosaminoglycans appear to elicit the formation and function of gap junctions and may thus play a role in the regulation of intercellular communication under normal and pathological conditions. With respect to gene expression: normal rat hepatocytes maintained in culture on tissue culture plastic and in serum supplemented medium lose their tissue-specific functions within hours to a few days due to loss of synthesis and to rapid degradation of tissue-specific mRNAs.(ABSTRACT TRUNCATED AT 400 WORDS)