Isolation and characterization of a heterodimeric surface antigen on human melanoma cells and evidence that it is the 4f2 cell activation/proliferation molecule

Murine monoclonal antibody (MAb) LS109 was one of a series of MAbs produced by hyperimmunization of mice with detergent extracts of pooled melanoma cell lines and metastatic melanoma patient tumors. ELISA screening of extracts of individual cultured melanoma cell lines and single patient tumors with MAb LS109 gave an interesting pattern of reactivity. The antibody was strongly positive with some of these extracts, yet negative or weakly positive with others. In addition, there was strong reactivity with a restricted set of normal necropsy tissues and certain non‐melanoma tumor extracts. Taken together, our data suggest that MAb LS109 recognizes a normal differentiation antigen which is perhaps aberrantly expressed or over‐produced during certain stages of melanoma tumor progression. The antigen recognized by LS109 is a heterodimeric surface glycoprotein molecule, consisting of an 89‐kDa “heavy” chain linked by disulfide bonds to an 83‐kDa “light” chain. Under non‐reducing SDS‐PAGE conditions, the intact dimer migrates with an M of approximately 140kDa. The 89‐kDa component appears to be heavily N‐glycosylated whereas the 38‐kDa component has little, if any, covalently attached carbohydrate. Our data show the biosynthesis, glycosylation and turnover of the LS109 antigen, as well as evidence of its surface localization. In addition, evidence is presented that the LS109 antigen is identical to the 4F2 cell activation/proliferation molecule previously described on a variety of normal and neoplastic cells.