DAUNORUBICIN-INDUCED APOPTOSIS - TRIGGERING OF CERAMIDE GENERATION THROUGH SPHINGOMYELIN HYDROLYSIS

The nature of the signaling pathway(s) which initiate drug-triggered a poptosis remains largely unknown and is of fundamental importance in u nderstanding cell death induced by chemotherapeutic agents, Here we sh ow that in the leukemic cell lines U937 and HL-60, daunorubicin, at co ncentrations which trigger apoptosis, stimulated two distinct cycles o f sphingomyelin hydrolysis (similar to 20% decrease at 1 mu M) within 4-10 min and 60-75 min with concomitant ceramide generation, We demons trate 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 dauno rubicin-triggered apoptosis is mediated by a signaling pathway which i s initiated by an early sphingomyelin-derived ceramide production.