CLEAR DIFFERENCES IN CERAMIDE METABOLISM BETWEEN GLYCOSPHINGOLIPIDS AND SPHINGOMYELIN IN A HUMAN PROMYELOCYTIC LEUKEMIA-CELL LINE HL-60 STIMULATED BY A DIFFERENTIATION INDUCER

Although the ceramide components of both glycosphingolipids (GSLs) and sphingomyelin (SM) in HL-60 cells were identical, the molecular species of the ceramides preferentially used in biosynthesis were quite different in GSLs and SM. When HL-60 cells were stimulated to differentiate into macrophage-like cells by phorbol ester after their sphingolipids had been metabolically labeled with L-[3-C-14]serine to saturation point, marked changes in the radioactivities of the ceramide residues were observed in GSLs, showing the activation of a biosynthetic pathway of ganglioside GM3. No significant changes were, however, observed in the ceramide residues of SM. These results indicate that it is necessary to consider the overall metabolism of ceramides, including their origin, when investigating the functions of ceramides in signal transduction systems.