title: Actinomycin D-mediated sensitization of AIDS-Kaposi's sarcoma cells to Fas-mediated apoptosis: involvement of the mitochondrion-dependent pathway.
abstract: Fas engagement rapidly induces formation of the death-inducing signaling complex (DISC) that consists of Fas, FADD and pro-caspase-8. Activated caspase-8 at the DISC directly activates downstream caspases, resulting in induction of apoptosis of the independent mitochondria. In this study, we have obtained evidence demonstrating that Fas-mediated apoptosis in AIDS-KS cells takes place in a mitochondria-dependent manner. FADD and pro-caspase-8 were detected in immunoprecipitates with anti-Fas antibody in anti-Fas mAb (CH-11)-treated Hut 78, a typical Fas-sensitive cell line. On the other hand, DISC formation by CH-11 was markedly reduced in AIDS-KS cells. In addition, CH-11-induced activation of caspase-8-like protease in AIDS-KS cells was much less pronounced compared with that in Hut 78; however, a caspase-8 inhibitor, zIETD-fmk, completely blocked the apoptosis. Further, a caspase-9 inhibitor, zLEHD-fmk, markedly inhibited Fas-mediated apoptosis in AIDS-KS cells. Several apoptotic stimuli induce mitochondria activation allowing cytochrome c release from the mitochondria. In the apoptosome, cytochrome c and Apaf-1 activate caspase-9 which subsequently leads to the activation of caspase-3. In AIDS-KS cells, CH-11 triggered cytochrome c release, an event which was inhibited by zIETD-fmk. Further, a caspase-3 inhibitor, zDEVD-fmk completely inhibited the apoptosis. Altogether, the present data provide evidence that the Fas signal in AIDS-KS cells is preferentially transduced through the mitochondria-dependent pathway, which is initiated by caspase-8 activation.
authors.affiliation: Department of Microbiology, Immunology, and Molecular Genetics, UCLA School of Medicine, University of California, Los Angeles, CA 90095, USA.
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Mori
authors.forename: Kaoru
authors.initials: K
authors.lastname: Murakami-Mori
authors.forename: Shuji
authors.initials: S
authors.lastname: Nakamura
authors.forename: Benjamin
authors.initials: B
authors.lastname: Bonavida
mesh_terms: D000163:Acquired Immunodeficiency Syndrome / Q000378:metabolism* / Q000473:pathology; D048868:Adaptor Proteins, Signal Transducing; D017209:Apoptosis; D015153:Blotting, Western; D002352:Carrier Proteins / Q000378:metabolism; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D003574:Cytochrome c Group / Q000378:metabolism; D003609:Dactinomycin / Q000494:pharmacology*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D053200:Fas-Associated Death Domain Protein; D006801:Humans; D008928:Mitochondria / Q000378:metabolism*; D012514:Sarcoma, Kaposi / Q000378:metabolism* / Q000473:pathology; D015398:Signal Transduction / Q000502:physiology; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D019014:fas Receptor / Q000502:physiology*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D003574:Cytochrome c Group; D004791:Enzyme Inhibitors; C505533:FADD protein, human; D053200:Fas-Associated Death Domain Protein; D019014:fas Receptor; D003609:Dactinomycin; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases