Cell Surface Carbohydrates in Adhesion and Migration
Cell surface sugar chains extend away from the cell membrane and offer a first line of contact with approaching cells and substrates. These sugars are candidates for mediating cell-cell adhesion and migration. Here, I review experiments that implicate carbohydrate-containing molecules in cell-cell adhesion of ascites tumor and embryonic cells and that correlate the mobility of carbohydrate-containing receptor sites in the membrane with cellular migratory activity. The experiments show that L-glutamine is required to form complex carbohydrates implicated in mediating intercellular adhesion and that a controlling factor in determining cellular adhesiveness may be the specific activity of intracellular glutamme synthetase. Molecules that promote ascites tumor cell adhesion have been isolated. These molecules are large, appear to contain terminal D-galactose residues that bind to cell surface receptor sites and consist of more than one component on DEAE cellulose. Studies with sea urchin embryonic cells, utilizing plant lectins that bind to surface carbohydrates, indicate that cell surface sugar-containing receptor sites change during development. In addition only the micromeres, that become actively migratory, possess mobile cell surface lectin receptor sites. Other sea urchin embryonic cell populations (mesonieres and macromeres) do not exhibit lectin receptor site mobility. Cell surface sugar-containing receptor sites potentially mediate adhesion and migration in embryos and tumors.