Isogloboside Biosynthesis in Metastatic R3230AC Cells Results from a Decreased GM3 Synthase Activity

Abstract We have determined that the production of a metastasis-associated neutral glycosphingolipid, isogloboside (iGb 4 Cer, GalNAcβ1-3Galα1-3Galβ1-4Glcβ1- O -ceramide) is associated with the loss of G M3 synthase activity. Assays for neutral glycosphingolipid-forming glycosyltransferases in cells producing various levels of iGb 4 Cer revealed no consistent differences that could account for the difference in iGb 4 Cer biosynthesis. However, comparison of the activity of G M3 synthase in homogenates of these two cell types revealed that cells that did not synthesize iGb 4 Cer had activity significantly greater than that of cells possessing this antigen. Furthermore, somatic cell hybrids generated using clones of the iGb 4 Cer -producing and nonproducing cell lines lacked iGb 4 Cer while possessing high levels of G M3 synthase activity. When iGb 4 Cer-producing cells were transfected with a G M3 synthase expression vector, all of the resultant clones were negative for iGb 4 Cer production. The results of these studies clearly show that the presence of G M3 synthase prevents the formation of iGb 4 Cer in these cells.