Daunorubicin-induced apoptosis: Triggering of ceramide generation through sphingomyelin hydrolysis

The nature of the signaling pathway(s) which initiate drug-triggered apoptosis remains largely unknown and is of fundamental importance in understanding cell death induced by chemotherapeutic agents, Here we show that in the leukemic cell lines U937 and HL-60, daunorubicin, at concentrations which trigger apoptosis, stimulated two distinct cycles of sphingomyelin hydrolysis (similar to 20% decrease at 1 mu M) within 4-10 min and 60-75 min with concomitant ceramide generation, We demonstrate that the increase in ceramide levels, which precedes apoptosis, is mediated by a neutral sphingomyelinase and not by ceramide synthase, Indeed, potent ceramide synthase inhibitors such as fumonisin B1 did not affect daunorubicin-triggered sphingomyelin hydrolysis, ceramide generation or apoptosis, In conclusion, we provide evidence that daunorubicin-triggered apoptosis is mediated by a signaling pathway which is initiated by an early sphingomyelin-derived ceramide production.