Variations among cell lines in the synthesis of sphingolipids in de novo and recycling pathways

There are several pathways for the incorporation of sugars intoglycosphingolipids (GSL). Sugars can be added to ceramide that containssphinganine (dihydrosphingosine) synthesized de novo (pathway 1), toceramide synthesized from sphingoid bases produced by hydrolysis ofsphingolipids (pathway 2), and into GSL recycling from the endosomalpathway through the Golgi (pathway 3). We reported previously thesurprising observation that SW13 cells, a human adrenal carcinoma cellline, synthesize most of their GSL in pathway 2. We now present data on thesynthesis of GSL in four additional cell lines. Approximately 90% of sugarincorporation took place in pathway 2, and 10% or less in pathway 1, inhuman foreskin fibroblasts and NB41A3 neuroblastoma cells. In contrast,approximately 50-90% of sugar incorporation took place in pathway 1 inC2C12 myoblasts. The C2C12 cells divide more rapidly and synthesize 10-14times as much GSL as the other three cell lines. In C6 glioma cells,approximately 30% of sugar incorporation occurred in pathway 1 and 60% inpathway 2. There was no relation between the utilization of pathways forGSL and sphingomyelin synthesis in foreskin fibroblasts and C2C12 cells. Inboth cells pathways 1 and 2 each accounted for 50% of incorporation ofcholine into sphingomyelin. In five of the six cell lines that we havestudied, most GSL synthesis takes place in pathway 2. We suggest that whenthe need for synthesis is relatively low, as in slowly dividing cells, GSLare synthesized predominantly from sphingoid bases salvaged from thehydrolytic pathway. When cells are dividing more rapidly, the need forincreased synthesis is met by upregulating the de novo pathway.