Glycosylation-dependent collagen-binding activities of two membrane glycoproteins in MDAY-D2 tumor cells.

Two highly glycosylated membrane sialoglycoproteins designated P2A and P2B were isolated from the lymphoreticular tumor cell line called MDAY-D2 and shown to be structurally similar to the lymphocyte glycoprotein called leukosialin and to lysosome-associated membrane glycoprotein termed LAMP-1, respectively. The loss of sialic acid and polylactosamine sequences in glycosylation mutants of MDAY-D2 has been correlated previously with enhanced cell adhesion on extracellular matrix proteins. Since these two glycoproteins bear the majority of the sialylated oligosaccharides found in membrane fractions of MDAY-D2, they were tested for binding activity on extracellular matrix proteins. Both isolated glycoproteins bound to immobilized collagen type I with affinities that were dependent on their glycosylation. Enzymatic removal of sialic acid, polylactosamine, or complete asparagine-linked chains from purified P2B enhanced its binding to collagen, laminin, and fibronectin. In contrast, P2A bound specifically to collagen type I and the interaction required the presence of sialic acid residues which were sensitive to neuraminidase digestion but not to endoglycosidase F. The results suggest that oncodevelopmental regulation of oligosaccharide expression on P2A and P2B glycoproteins may modulate their binding to extracellular matrix glycoproteins.