Subcellular distribution and metabolic fate of exogenous ceramides taken up by HL-60 cells.

Ceramides (Cer) are key intermediates in the metabolism of sphingomyelin and are also important second messengers. We report that natural long-chain ceramides added to the incubation medium in microgram amounts are internalized in HL-60 cells as well as the short-chain analogue C2-Cer and targeted to various subcellular compartments. No significant difference was detected in the ability of HL-60 cells to metabolize exogenous Cer containing a short (acetyl) versus long (palmitoyl or oleoyl) acyl chain. After a 2-h incubation time with [14C]-C16 ceramides, most of the cell-bound radioactivity was found in free ceramides. Sphingomyelin was the major metabolized sphingolipid containing labeled ceramides and only a small proportion of exogenous ceramides were converted to neutral glycolipids and gangliosides. Up to 20% of the exogenous ceramides taken up by the cells were recovered in mitochondria, mostly as authentic C16 ceramides and C16 sphingomyelin, along with a trace amount of labeled GM3 ganglioside. These results are consistent with the notion that exogenous natural ceramides enter cells, can be further metabolized in situ and partly targeted to mitochondria, which are known to be involved in the control of programmed cell death.