Resistance to CD95/Fas-induced and ceramide-mediated apoptosis of human melanoma cells is caused by a defective mitochondrial cytochrome c release

Intracellular CD95/Fas-signaling pathways have not been investigated in mel anoma yet, Two different CD95 receptor-induced apoptotic pathways are prese ntly known in other cell types: (i) direct activation of caspase-8 and (ii) induction of ceramide-mediated mitochondrial activation, both leading to s ubsequent caspase-3 activation. In the present study, five of II melanoma c ell populations were shown to release cytochrome c from mitochondria, which activates caspase-3 and finally results in DNA fragmentation upon treatmen t with the agonistic monoclonal antibody CH-11. In contrast, this apoptotic pathway was not activated in the remaining six melanoma cell populations, interestingly, the susceptibility of melanoma cells to CD95L/FasL-triggered cell death was clearly correlated with N-acetylsphingosine-mediated apopto sis, Our results are in line with a defect upstream of mitochondrial cytoch rome c release in resistant cells. (C) 2000 Federation of European Biochemi cal Societies.