Characterization of ganglioside expression in human melanoma cells: immunological and biochemical analysis.

The expression of N-glycolylneuraminic acid (NeuGc)-containing gangliosides in human melanoma cells grown both in culture and as xenografts in athymic (nu/nu) mice was analyzed extensively with specific mouse monoclonal antibodies (MAbs). Three MAbs (GMR8, GMR14, and GMR3) specific for GM3(NeuGc), GM2(NeuGc), and GD3(NeuGc-NeuGc-), respectively, were used. Significant differences were observed in the ganglioside compositions between the cultured cells in vitro and the tumors grown in vivo. The major difference was that the cells cultured in serum-free medium did not express any NeuGc-containing gangliosides, whereas those grown in nude mice expressed a number of NeuGc-containing gangliosides, namely GM3(NeuGc), GM2(NeuGc), GD3(NeuAc-NeuGc-), GD3(NeuGc-NeuAc-), and GD3(NeuGc-NeuGc-). The structures of these gangliosides were also determined chemically. No activity of CMP-NeuAc hydroxylase was demonstrated either in the melanoma cells cultured in vitro or in those grown in nude mice, suggesting that these cells incorporated NeuGc-containing glycoconjugates from the mouse sera and converted them to other NeuGc-containing gangliosides. The mouse sera contained only GM2(NeuGc), but not the other NeuGc-containing gangliosides or any NeuAc-containing gangliosides.