Cleavage of a 135 kD cell surface glycoprotein correlates with loss of fibroblast adhesion to fibronectin

Abstract

We have previously described a group of three plasma membrane glycoproteins that are recognized by an adhesion-disrupting antiserum and that are involved in fibronectin-mediated BHK cell adhesion. A peculiar property of these molecules is their resistance to tryptic digestion [1]. We have now extended this study in the attempt to identify the active component within this group of molecules. SR/BALB mouse fibroblasts, used in this work, expose at their surface only two trypsin-resistant glycoproteins, gp1 (150 K) and gp2 (135 K), that are recognized by the adhesion-disrupting anti-BHK serum. Controlled proteolysis of the cell surface in the presence of a reducing agent results in the loss of cell adhesion to fibronectin-coated substratum. gp2 is selectively cleaved under these conditions. Moreover, cells treated with trypsin and reducing agent can no longer adsorb the adhesion-relevant antibodies from the anti-BHK serum. These data indicate that gp2 plays a critical role in the adhesion of SR/BALB fibroblasts to fibronectin-coated substratum, and that disulfide bonds are important in the conformation and function of this molecule.