Carbohydrates and soluble lectins in the regulation of cell adhesion and proliferation

There is a large body of suggestions that complex carbohydrates play a role in the regulation of cell adhesion and cell proliferation. Many reports have emphasized that proteoglycans, glycoproteins or glycolipids are participating to cell adhesion mechanisms. The use of polyvalent anti-carbohydrate antibodies and plant lectins as well as the use of glycosylation inhibitors suggested that cell proliferation can be modulated by surface carbohydrates. The dating experiment of Burger and Noonan (1970) showing restoration of contact inhibition of malignant cells by monovalent concanavalin A was a determining experiment. However, in the latter as in the others, no precise mechanism was demonstrated how carbohydrates can be involved in adhesion and proliferation. New insights were opened with the discovery of vertebrate membrane-bound and soluble lectins. The latter generally display agglutinating activities in in vitro systems, suggesting that they were potential cell adhesion molecules, by forming bridges between cell surface carbohydrates. These polyvalent molecules may be also considered as clustering agents for their cell surface ligands, consequently generating signals for cell proliferation and/or differentiation.