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

Abstract

Caspase activation is currently proposed as a common feature of apoptosis. However, although the apoptotic events triggered by Fas ligation are well documented, the terminal effectors of the ceramide-induced pathway are not completely identified. In this work, we found that C2-ceramide (Cer)-induced apoptosis was antagonised by leupeptin while Fas-triggered cell death occurred in the presence of this protease inhibitor. Nevertheless, this Cer-induced apoptosis could not be attributed to chymotrypsin, calpain or proteasome 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 whereas an anti-Fas IgM (7C11) treatment was inefficient. Moreover, Cer induced apoptosis without DEVDase activation in U937 cell line. Finally, Cer induced 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.