Interactions of cells with the extracellular matrix are critically important events in normal tissue organization, repair and remodeling. Such interactions are generally considered to be mediated by multiple mechanisms. We will continue our studies demonstrating that receptor molecules embedded in the plasma membrane are involved in interacting with fibronectin outside the cell and microfilaments inside the cell. These molecules are expected to undergo modulation in quantity or position at the cell surface during expression of specialized cell functions. Our goals are to characterize these cell surface moleucles, to define their functional roles and cell biological properties in their interactions with the matrix, and to examine in vivo whether modulation of these cell surface molecules plays a particularly important regulative role in lung cell function by anchoring cells to the matrix, controlling cell migration and phagocytosis, and altering cytoskeletal organization and function. Specifically, (1) monoclonal and polyclonal antibodies directed against a putative fibronectin receptor (the 140K complex), and its copurified subunit polypeptides will continue to be generated. These antibodies, in conjunction with affinity purification, electron microscopy, and limited proteolysis will provide the basis for facile isolation and analysis of active domains of the 140K polypeptides and of their interactions with the matrix. (2) We will use a combined morphological and biochemical assay to examine extracellular fibroenctin-degrading activities of normal tissue cells, and their involvement in lung cell migration and phagocytosis. When the proteases are identified, their functional relationships with the 140K polypeptides in these cells will also be examined. (3) We will extend the recently developed technology of ultrathin-frozen-sectioning of lung tissues, and in conjunction with microinjection and labeling by monoclonal antibodies or other ligands, examine the expression of these cell surface molecules and their interactions with cytoskeletal and matrix components in normal and diseased lungs. Similar to in vitro studies using isolated cells, we will also look for the binding of exogeneous fibronectin to cells in situ and its subsequent degradation within lung tissue sections.
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