Characterization of a human melanosome-associated antigen recognized by monoclonal antibody, HMSA-2

This study elucidates the nature of antigens recognized by monoclonal antibody (MoAb) HMSA-2, which was developed against human melanosome-associated antigen (HMSA) of malignant melanoma (Maeda and Jimbow, Cancer 59:415-423, 1987). Through flow cytometry analyses, indirect immunoprecipitation of antigen biosynthetically labeled with 35S-methionine, enzyme-linked immunosorbent assays and immunoelectron microscopy, we found that a) the antigens recognized by MoAb HMSA-2 were melanosomal matrix glycoproteins; b) these antigens were expressed mainly in the cytoplasm, although they could also be detected on the cell surface; c) the cytoplasmic expression of MoAb HMSA-2 was cell-cycle dependent; d) large amounts of these antigens were released into culture supernatants; e) MoAb HMSA-2 immunoprecipitated two major glycoproteins with molecular weights of 94 and 53 kDa from culture supernatants, and f) both components have complex N-linked oligosaccharide chains with sialic acid, suggesting that these melanosomal proteins are derived from the trans-cisternae of the Golgi. These human melanosome-associated antigens may prove useful not only for studying the immunobiology of melanogenesis, but also for the immunodiagnosis of melanocytic disorders.