CHANGES IN COMPOSITION OF NEWLY SYNTHESIZED SPHINGOLIPIDS OF HELA-CELLS DURING THE CELL-CYCLE - SUPPRESSION OF SPHINGOMYELIN AND HIGHER-GLYCOSPHINGOLIPID SYNTHESIS AND ACCUMULATION OF CERAMIDE AND GLUCOSYLCERAMIDE IN MITOTIC CELLS

Sphingolipid biosynthesis in synchronized HeLa cells was studied by pu lse labeling with [C-14]Ser or [C-14]Gal and a simple TLC method, The major HeLa cell sphingolipids are ceramide (Cer), sphingo-myelin, gluc osylceramide (GlcCer), lactosylceramide (LacCer), globotriaosylceramid e (Gb(3)Cer), N-acetylneuraminosylgangliotriaosylceramide (G(M2)) and sialylparagloboside (G(M1-GlcNAc)). The sphingolipid biosynthetic prof iles of HeLa cells in the G1, G1/S boundary S and G2 phases were simil ar, but significant changes occurred during M phase, when incorporatio n of radioactivity into sphingomyelin, Gb(3)Cer and a mixture of G(M2) and G(M1-GlcNAc) decreased, and those of Cer and GlcCer increased, Th ese data indicate that transfer of phosphocholine and galactose to Cer and GlcCer, respectively, decreased ill mitotic cells, resulting in a ccumulation of Cer and GlcCer, Analysis of LacCer synthase activity re vealed that GlcCer accumulation was not due to reduced activity of thi s enzyme, The results suggest that Cer and GlcCer accumulation in mito tic cells resulted from suppression of sphingomyelin and LacCer synthe sis, probably caused by vesiculation of membranous organelles, such as the endoplasmic reticulum and Golgi apparatus.