The overall, long term goal of this project is to gain a greater understanding of the molecular basis of cell matrix adhesion. Cell-extracellular matrix contact can effect cytoskeletal organization, cell proliferation and the expression of differentiated cell products. Cells can in turn modify the matrix in response to contact. Such remodelling of matrix by cells is an important feature of normal development and the maintenance of normal tissue renewal. Alterations in the mechanisms that control normal cell-matrix communication can lead to developmental defects or metastasis. Cells have more than one receptor for some matrix ligands, such as fibronectin and laminin. These molecules also have more than one binding site for cells. This raises the question as to what kinds of signals are being transmitted to the interior of the cell as a result of a particular type of surface receptor-extracellular matrix contact. A large family of structurally related heterodimeric cell surface adhesion receptor complexes, called integrins, are able to interact with several extracellular matrix ligands. Previous studies have shown these receptors to be required for several important migratory processes such as neurite outgrowth, mammalian blastocyst-matrix interactions, neural crest migration and attachment of tumor cells to basement membrane. The ability of integrin to transmit signals across the cell surface will be studied in a system in which the binding by a specific antibody against the integrin fibronectin receptor, which causes cytoskeletal reorganization, induces the expression by the cell of matrix degrading metalloendoproteinases. A similar effect is found if adherent cells are exposed to short peptides containing the arg-gly-asp cell recognition sequence present in matrix ligands that are recognized by integrins. Efforts will focus on determining if the binding of other integrins by specific antibodies can induce these proteases, whether induction of protease requires cytoskeletal reorganization, whether transmission of this signal is regulated by G proteins and whether there is coordinate alteration in the expression of protease inhibitors, extracellular matrix ligands or the integrin receptors themselves as a result of this binding. C-DNA probes and specific antibodies will be used to detect these aspects of the cellular response. In a separate study, adhesion variants will be used whose expression of integrins can be modulated over a 20 fold range by 5-bromodeoxyuridine. Specific antibodies that recognize individual subunits of the regulated integrin dimeric complexes will be used in pulse chase studies to determine the nature of the defect at the protein level. C-DNA probes against individual subunits will be used to compare the levels of mRNA expression in the adherent and non adherent states. Taken together, these studies should enhance our understanding of the biological role and regulation of expression of this very important class of cell matrix adhesion receptors.
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