Clustering seems to be employed by many receptors for transmembrane signali
ng. Here, we show that acid sphingomyelinase (ASM)-released ceramide is ess
ential for clustering of CD95, In vitro and in vivo, extracellularly orient
ated ceramide, released upon CD95-triggered translocation of ASM to the pla
sma membrane outer surface, enabled clustering of CD95 in sphingo lipid-ric
h membrane rafts and apoptosis induction. Whereas ASM deficiency, destructi
on of rafts, or neutralization of surface ceramide prevented CD95 clusterin
g and apoptosis, natural ceramide only rescued ASM-deficient cells. The dat
a suggest CD95-mediated clustering by ceramide is prerequisite for signalin
g and death.