GRANULYSIN-INDUCED APOPTOSIS - I - INVOLVEMENT OF AT LEAST 2 DISTINCTPATHWAYS

Granulysin is a newly described cytolytic molecule released by CTL and NK cells via granule-mediated exocytosis. It shares homology with sap osin-like proteins, including NK-lysin and amoebapores, and has been i mplicated in the lysis of tumor cells and microbes, In the present stu dy we show that recombinant granulysin alone induces apoptosis of Jurk at cells. This apoptosis is associated with a sixfold increase in the ceramide/sphingomyelin ratio, implicating the activation of sphingomye linases. Granulysin- and ceramide-induced apoptosis are similar in tha t they both are only minimally inhibited by the more selective cystein e protease p32 (caspase 3)-like caspase inhibitor N-acetyl-Asp-Glu-Val -Asp aldehyde, while they are significantly inhibited by the more gene ral caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (Z-VAD-fmk), Nevertheless, while Z-VAD-fmk almost completely inhibits ceramide-induced apoptosis, a Z-VAD-fmk-resistant component was obser ved using granulysin. Granulysin also causes apoptosis in cells deplet ed of sphingomyelin by prolonged treatment with the ceramide synthase inhibitor fumonisin B-1. These data indicate that granulysin induces t arget cell death by both ceramide- and caspase-dependent and -independ ent pathways.