The liver contains an extracellular matrix that is localized to the perisinusoidal (Disse) space and similar in composition to the basal lamina of epithelial tissues generally. Recent studies of hepatocytes in primary culture suggest that the matrix, or its constituent proteins, play a major role in modulating the expression of liver-specific functions. Hepatocytes appear to interact with matrix proteins in a saturable manner, suggesting the presence of specific receptors. In this application, we propose to isolate hepatocyte surface receptors for the major proteins of the basal lamina (fibronectin, collagen IV and laminin) using a recently described method for in situ cross-linking of receptors on cultured hepatocytes to the matrix protein serving as culture substratum. The cross-linking is accomplished by means of the cleavable photoactivable heterobifunctional reagent 4'-azidoazobenzene-4-oxysuccinimide ester. Preliminary studies by the Principal Investigator have demonstrated that hepatocyte proteins of distinct molecular size, potentially representing receptors for individual matrix proteins, can be isolated by this approach. Antibodies (both polyvalent and monoclonal) will be raised to these proteins, both for characterizing them and for manipulating cell-matrix interaction in culture. They will be used also to develop an immunoassay for receptor concentration in the liver. The possibility exists that hepatocellular dysfunction accompanying hepatic inflammation reflects not only a matrix of abnormal composition in the Disse space but also altered expression of matrix receptors. The experiments are expected to provide detailed new insight into cell-matrix interaction and its regulation of liver-specific functions.
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