ESSENTIAL REQUIREMENT FOR CASPASE-8 FLICE IN THE INITIATION OF THE FAS-INDUCED APOPTOTIC CASCADE/

Background: Fas (APO-1/CD95) is a member of the tumor necrosis factor receptor (TNF-R) family and induces apoptosis when crosslinked with ei ther Fas ligand or agonistic antibody (Fas antibody), The Fas-Fas liga nd system has an important role in the immune system where it is invol ved in the downregulation of immune responses and the deletion of peri pheral autoreactive T lymphocytes. The intracellular domain of Fas int eracts with several proteins including FADD (MORT-I), DAXX, RIP, FAF-1 , FAP-I and Sentrin, The adaptor protein FADD can, in turn, interact w ith the cysteine protease caspase-8 (FLICE/MACH/Mch5). Results: In a g enetic screen for essential components of the Fas-mediated apoptotic c ascade, we isolated a Jurkat T lymphocyte cell line deficient in caspa se-8 that was completely resistant to Fas-induced apoptosis. Complemen tation of this cell line with wild-type caspase-8 restored Fas-mediate d apoptosis, Fas activation of multiple caspases and of the stress kin ases p38 and c-Jun NH2-terminal kinase (JNK) was completely blocked in the caspase-8-deficient cell line. Furthermore, the cell line was sev erely deficient in cell death induced by TNF-alpha and was partially d eficient in cell death induced by ultraviolet irradiation, adriamycin and etoposide. Conclusions: This study provides the first genetic evid ence that caspase-8 occupies an essential and apical position in the F as signaling pathway and suggests that caspase-8 may participate broad ly in multiple apoptotic pathways.