Ceramide-induced apoptosis occurs independently of caspases and is decreased by leupeptin

Caspase activation is currently proposed as a common feature of apoptosis. However, although the apoptotic events triggered by Fas ligation are well d ocumented, the terminal effecters of the ceramide-induced pathway are not c ompletely identified. In this work, we found that C2-ceramide (Cer)-induced apoptosis was antagonised by leupeptin while Fas-triggered cell death occu rred in the presence of this protease inhibitor. Nevertheless, this Cer-ind uced apoptosis could not be attributed to chymotrypsin, calpain or proteaso me activation. In addition, the caspase inhibitor Z-VAD-fmk suppressed Fas- triggered death but did not prevent ceramide-induced apoptosis. In MCF7, a caspase-3-deficient cell line, Cer has been found to induce cell death wher eas an anti-Fas IgM (7C11) treatment was inefficient. Moreover, Cer induced apoptosis without DEVDase activation in U937 cell line, Finally, Cer induc ed an intracytoplasmic calcium release while Fas ligation remained without effect These results are consistent with the notion that Cer acts, at least in part, independently of Fas signalling, and sheds light on a new caspase 3-free apoptotic pathway triggered by ceramide.