BIOSYNTHESIS OF GLYCOSPHINGOLIPIDS IS REDUCED IN THE ABSENCE OF A VIMENTIN INTERMEDIATE FILAMENT NETWORK

Our previous observations on the immunocytochemical colocalization of intermediate filaments and glycosphingolipids led us to analyze the ro le of filaments in the biosynthesis and intracellular transport of gly cosphingolipids. Cells with (vim(+)) and without (vim(-)) vimentin int ermediate filaments were cloned from the adrenal carcinoma cell line S W13. There was no difference between vim(+) and vim(-) cells in the pr oportion of newly synthesized C6-NBD-glucosylceramide transported to t he plasma membrane. The vim(+) cells synthesized glycosphingolipids, e specially lactosylceramide and globotriosylceramide, and to a lesser e xtent G(M)3 ganglioside, more rapidly than vim(-) cells. The altered r ate of biosynthesis did not result from differences in the levels of t he glycosyltransferases that synthesize those compounds. To determine whether the presence of a vimentin network was responsible for the dif ferences in biosynthesis, mouse vimentin cDNA was transfected into vim (-) cells. Transfected cells that expressed a mouse vimentin network d emonstrated a twofold or greater increase in the rate of biosynthesis of neutral glycosphingolipids and gangliosides. There was no differenc e between vim(+) and vim(-) cells in the synthesis of ceramide or sphi ngomyelin, or in their content of phospholipids or cholesterol. The na ture of the biochemical defect(s) underlying the diminished incorporat ion of radiolabeled sugars into glycosphingolipids is unclear. Possibi lities include alterations in the ultrastructure of the Golgi and/or a bnormalities in a portion of the endocytic pathway, .