ISOLATION AND CHARACTERIZATION OF CD47 GLYCOPROTEIN - A MULTISPANNINGMEMBRANE-PROTEIN WHICH IS THE SAME AS INTEGRIN-ASSOCIATED PROTEIN (IAP) AND THE OVARIAN TUMOR-MARKER OA3

The CD47 glycoprotein was isolated from human erythrocytes by immunopr ecipitation using monoclonal antibody (mAb) BRIC-125. Enzymic deglycos ylation of the protein showed it contained N-linked oligosaccharides, and trypsin proteolysis of the protein in situ in the erythrocyte memb rane cleaved it into two portions, one of which was glycosylated. Both the intact protein and the glycosylated fragment had blocked N-termin i. Amino acid sequence was obtained from several proteolytic fragments of CD47. Comparison with the sequence database showed the protein to be very similar to or identical with OA3, a multispanning membrane pro tein. The protein also appears to be the same as the integrin-associat ed protein, which has a role in cell adhesion in non-erythroid cells. CD47 has six potential N-glycosylation sites, five of which are in an Ig superfamily domain. We show that three of these sites carry N-glyca ns in erythrocytes. Immunocytochemical staining of human tissues showe d that CD47 was broadly distributed on mesenchyme and epithelia at mul tiple sites. Reactivity was particularly prominent in surface and duct ular epithelia, and in the brain. The possible roles of the CD47 glyco protein are discussed.