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 speci es of the ceramides preferentially used in biosynthesis were quite dif ferent in GSLs and SM. When HL-60 cells were stimulated to differentia te into macrophage-like cells by phorbol ester after their sphingolipi ds 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 pathwa y of ganglioside GM3. No significant changes were, however, observed i n the ceramide residues of SM. These results indicate that it is neces sary to consider the overall metabolism of ceramides, including their origin, when investigating the functions of ceramides in signal transd uction systems.