AN APPROACH TO THE CHARACTERIZATION OF FIBRONECTIN-INTERACTION WITH MAMMALIAN CELLS

Cell adhesion is a fundamentally important process which has been implicated in morphogenesis, metastasis and wound healing. Fibronectin (Fn), a large glycoprotein present in body fluids, the extracellular matrix, and on the cell surface, mediates adhesion of fibroblastic cells. To study the interaction of Fn with Chinese Hamster Cell (CHO) cell membranes, latex beads coated with H('3)-Fn (Fn-beads) were used as surface probes. Binding of Fn-beads was independent of temperature, divalent cations, and metabolic activity. Identification of fibronectin-receptors has been problematical. To study Fn binding components, Fn-beads were pre-incubated with purified glycosaminoglycans (GAGs) and glycolipids. Among the GAGs tested, heparin and heparan sulfate blocked bead binding. Only sialylated glycolipids, GT(,1) and GD(,1) were inhibitory; however, neuraminidase treatment of cells had no effect. It was further shown that Fn-bead binding could be blocked by pre-treating cells with papain. Furthermore, papain digestion releases cellular material which blocks Fn-bead-cell binding. Beads coated with a fragment of Fn which binds to cells but not heparin (F105) were also blocked by soluble papain digests. It was observed that the ability of F105-beads to bind to CHO cells was dependent on surface charge as F105 on uncharged beads did not bind to cells; whereas, F105 on positive or negative beads displayed cell binding activity. The active component in the papain digests was apparently macromolecular (i.e. non-dialysable) and heat stable (i.e. 100(DEGREES)C for 15 min.). This suggested the inhibitory factor is more likely a glycopeptide, rather than a GAG or glycolipid. The findings of this research can be summarized as follows: (1) the expression of cell binding of Fn and Fn fragments can be modulated by the chemical nature of the surface used for adsorption; (2) factors can be released by proteolytic digestion which block Fn and Fn-fragment bead binding; and (3) since bead binding can be done under conditions which reflect initial Fn-cell interaction, it seems likely that the component(s) identified in this way may play a direct role in the recognition phases of cell adhesion to Fn. ^