A GLYCOPROTEIN EXPRESSED BY HUMAN FIBROUS ASTROCYTES IS A HYALURONATE-BINDING PROTEIN AND A MEMBER OF THE CD44 FAMILY

We have isolated and characterized an antigen from normal human brain called p80, so called because it migrated with an Mr of 80 kDa on SDS PAGE. The Mr of 80 kDa consists of a protein of about 55-60 kDa and ca rbohydrate (20-25 kDa). The carbohydrate is almost entirely of the N-l inked type, although a small amount of O-linked carbohydrate was detec ted. Cross-reactivity with monoclonal antibodies A3D8 and A1G3 showed that p80 could therefore be considered an isoform of the CD44 adhesion molecules. In addition, specific binding to hyaluronate which was not competed for by proteoglycan demonstrated that it involved different sites than the proteoglycan binding sites. We also observed that fucoi dan and dextran sulphate increased the binding by 200-250% while chond roitin sulphate C also increased the binding but to a lesser extent. H eparin, heparan sulphate and chondroitin sulphates A and B did not hav e such an effect. The binding of p80 to hyaluronate was pH dependent w ith a maximum at pH 6.4. We concluded that p80 was an astrocyte specif ic adhesion molecule.