Abstract
CD44 is a polymorphic family of cell surface glycoproteins expressed by a variety of cells. The CD44 proteins mediate cell-cell and cell-substrate adhesion as well as lymphocyte activation. Here we review the recent isolation and characterization of cDNAs encoding two CD44 proteins, CD44H and CD44E. CD44H is an 80-90kD glycoprotein expressed by cells of both mesodermal and neuro-ectodermal origin. Adhesion studies have shown that CD44H specifically binds hyaluronan. This observation, in conjunction with the finding that the hamster CD44H protein reacts with a monoclonal antibody directed against the hamster hyaluronan receptor indicates that CD44H and the hyaluronan receptor are the same molecule. CD44E is a 150kD glycoprotein expressed by a subset of epithelial cells and contains an additional segment of 134 amino acids intercalated within the extracellular domain of CD44H. Adhesion studies indicate that unlike CD44H, CD44E does not mediate attachment to surface bound hyaluronate.
