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 either Fas ligand or agonistic antibody (Fas antibody). The Fas-Fas ligand system has an important role in the immune system where it is involved in the downregulation of immune responses and the deletion of peripheral autoreactive T lymphocytes. The intracellular domain of Fas interacts with several proteins including FADD (MORT-1), DAXX, RIP, FAF-1, FAP-1 and Sentrin. The adaptor protein FADD can, in turn, interact with the cysteine protease caspase-8 (FLICE/MACH/Mch5).


RESULTS
In a genetic screen for essential components of the Fas-mediated apoptotic cascade, we isolated a Jurkat T lymphocyte cell line deficient in caspase-8 that was completely resistant to Fas-induced apoptosis. Complementation of this cell line with wild-type caspase-8 restored Fas-mediated apoptosis. Fas activation of multiple caspases and of the stress kinase p38 and c-Jun NH2-terminal kinase (JNK) was completely blocked in the caspase-8-deficient cell line. Furthermore, the cell line was severely deficient in cell death induced by TNF-alpha and was partially deficient in cell death induced by ultraviolet irradiation, adriamycin and etoposide.


CONCLUSIONS
This study provides the first genetic evidence that caspase-8 occupies an essential and apical position in the Fas signaling pathway and suggests that caspase-8 may participate broadly in multiple apoptotic pathways.
Juo
P
P
Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Kuo
C J
CJ
Yuan
J
J
Blenis
J
J
D017209:Apoptosis / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism*; D004317:Doxorubicin / Q000494:pharmacology; D005047:Etoposide / Q000494:pharmacology; D053222:Fas Ligand Protein; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases; D019169:Jurkat Cells; D008562:Membrane Glycoproteins / Q000502:physiology*; D020928:Mitogen-Activated Protein Kinases; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D019311:Staurosporine / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology / Q000502:physiology; D014466:Ultraviolet Rays; D019014:fas Receptor / Q000502:physiology*; D048051:p38 Mitogen-Activated Protein Kinases
C505661:FASLG protein, human; D053222:Fas Ligand Protein; D008562:Membrane Glycoproteins; D014409:Tumor Necrosis Factor-alpha; D019014:fas Receptor; D005047:Etoposide; D004317:Doxorubicin; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases; D019311:Staurosporine