GLYCOSYLATION OF A NOVEL MEMBER OF THE IMMUNOGLOBULIN GENE SUPERFAMILY EXPRESSED IN RAT CARCINOMA CELL-LINES

MAb E4 recognizes a 66-kDa glycoprotein, pE4, which is a member of the immunoglobulin gene superfamily. This protein is expressed at the cel l surface in vat colon and mammary carcinomas, but only in trace amoun ts in normal adult vat tissues. Since expression of aberrant carbohydr ate structures is often associated with malignant transformation, glyc osylation of pE4 was analyzed. Reactivity of lectins with pE4 suggeste d the absence of N-acetylneuraminic acid, terminal galactose and O-lin ked glycan, and the presence of N-linked glycans. Tunicamycin treatmen t reduced the binding of MAb E4 to cancer cells suggesting that the E4 epitope is at least partially glycosylated. Digestions with neuramini dases, O-glycosidase and peptide-N-glycosidase F confirmed these resul ts. Pronase treatment abolished the binding of MAb E4, indicating that E4 epitope involves not only a carbohydrate determinant but also a pe ptide moiety. Mild periodate oxidation abolished the binding of MAb E4 , indicating that non-reducing terminus carbohydrates are part of the E4 epitope. Neutral sugar analysis revealed the absence of galactose a nd the presence of fucose. Since fucose is sensitive to periodate oxid ation, this sugar could be the carbohydrate part of the determinant re cognized by MAb E4. Reactivity of lectins specific for fucose indicate d the presence of alpha(1-6)fucose on pE4. (C) 1995 Wiley Liss, Inc.