Differential glycosylation and cell surface expression of lysosomal membrane glycoproteins in sublines of a human colon cancer exhibiting distinct metastatic potentials.

Changes in the glycosylation of asparagine-linked oligosaccharides have been shown in various tumor cells, including human colon cancer. Attempts were made to elucidate the difference in Asn-linked oligo-saccharides attached to lysosomal membrane glycoproteins isolated from sublines of human colon carcinoma exhibiting high and low metastatic potentials in nude mice. Lysosomal membrane glycoproteins (lamp) 1 and 2 were immunoprecipitated from the cells after labeling with radioactive sugars, and the glycopeptides prepared were fractionated by serial lectin affinity chromatography employing immobilized concanavalin A, Datura stramonium agglutinin, and tomato lectin. Comparison of Asn-linked oligosaccharides from the different colonic carcinoma cells revealed the following features. First, the highly metastatic carcinoma cells express more poly-N-acetyllactosaminyl side chains with branched galactose residues than cells with low metastatic potential. Second, sialylation is more significant in the highly metastatic carcinoma cells than in the poorly metastatic ones. Conversely, N-acetyllactosamine units are less fucosylated in the highly metastatic cells than in poorly metastatic cells. These structural changes were apparently caused by the increase in sialyltransferase and the decrease in alpha 1----3 fucosyltransferase in the highly metastatic cells. The results also suggest that highly metastatic carcinoma cells express more sialyl Lex structures at the termini of poly-N-acetyllactosaminyl side chains than poorly metastatic carcinoma cells. Further, highly metastatic cells were found to express more lamp-1 and lamp-2 on the cell surface. These results were found to be correlated to the increased expression of sialyl Lex structures with high affinity binding of anti-sialyl Lex antibody on highly metastatic cells. Increased expression of sialyl Lex in the poly-N-acetyllactosamines of the cell surface may contribute to the metastatic behavior of the cells, assuming that this structure can serve as a better ligand for selectins present on endothelial cells and platelets.