Three melanomas of C57BL/6 mice (BL6, JB/MS, and JB/RH) share several phenotypic properties. All these cells contain melanoma-specific ecotropic C-type retrovirus that encodes melanoma-associated antigen recognizable by MM2-9B6 mAb. They do not express H-2Kb molecules, and the α-galactosyl epitopes (Galα1-3Galβ1-4GlcNAc-R) they fail to react with soybean agglutinin (SBA), peanut agglutinin (PNA), and vicia villosa (VV) lectins. Previously, we found that failure of BL6 melanoma cells to express α-galactosyl epitopes is due to down-regulation of α1,3 galactosyltransferase (α1,3GT) gene expression. To evaluate the possible role of α-galactosyl cell membrane carbohydrates in regulation of metastatic properties, individual clones isolated from BL6, JB/MS, and JB/RH melanomas were transfected with α1,3GT cDNA. This resulted in appearance of α-galactosyl epitopes, as well as of carbohydrates reacting with SBA, PNA, or VV lectins, but did not affect expression of H-2 class I molecules or melanoma-associated antigen. Appearance of SBA, PNA, and VV lectin binding carbohydrates in the α1,3GT gene-transfected melanoma cells is a result of reduction of cell membrane sialylation and unmasking of these carbohydrates. Reduction in cell membrane sialylation in the α1,3GT gene-transfected melanoma cells is probably due to the competition between α1,3GT with α2,3 sialyltransferase or α2,6 sialyltransferase for the common acceptor N-acetyllactosamine in the Golgi apparatus. As a result of this competition, cell membranes of α1,3GT gene-transfected melanoma cells became galactosylated and less sialylated. In parallel with alteration of cell membrane carbohydrates, transfection of the α1,3GT gene leads to the loss of metastatic properties of the transfected melanoma cells in the immunocompetent and immunosuppressed C57BL/6 mice. Thus, the use of specific glycosyltransferase cDNA transfection presents direct experimental confirmation of the importance of cell membrane carbohydrates in the regulation of metastatic properties of tumor cells.
This study was supported by NIH Grant CA59903.