Fibronectins (FNs), a group of high molecular weight glycoproteins present in the extracellular matrix and body fluids, affect a large variety of cellular properties through cell-cell and cell-substrate adhesion. Loss of FNs from the cell surface is a widely observed phenotypic change in many transformed cells and may correlate with their tumorigenic and metastatic ability. FNs are produced by normal and transformed fibroblasts and many other cell types. FNs isolated from different sources are very similar in many properties but differ slightly from each other in subunit sizes, domain structure, carbohydrate structure, and some other molecular and biological properties. Even in a single molecule, plasma FN consists of two subunit chains that are slightly different in their molecular weights and protease susceptibility. It is not clear whether the heterogeneous FNs are encoded by separate genes or generated by different splicing of a common mRNA or post-translational modification. This work entails study of the molecular basis of the heterogeneity of FNs by comparing the domain structure and functions of various types of human FNs and by isolation and characterization of FN cDNAs. Different types of cellular FNs, i.e., matrix-form FN from normal fibroblasts and from various tissues and released-form FNs from normal, transformed, and teratocarcinoma cells, will be studied along with plasma FN, whose domain structure has been most extensively characterized. 1. Domain structure of different types of FNs, particularly cellular FNs in tissues and in the pericellular matrices of cultured cells, will be analyzed by a combination of limited proteolysis and domain-specific antibodies. 2. Binding of intact FNs as well as domain fragments to three cell surface molecules, i.e., glycosaminoglycans, gangliosides, and FN itself, will be compared. 3. Subunit heterogeneity of plasma FN will be studied in detail by isolation and characterization FN cDNAs obtained from a human liver cDNA library. (A)
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