Resistance to the cytotoxic effects of tumor necrosis factor alpha can be overcome by inhibition of a FADD/caspase-dependent signaling pathway.
Tumor necrosis factor (TNF) alpha initiates the activation of a pro-apoptotic pathway involving the recruitment of the death domain containing protein FADD and the subsequent activation of specific proteases (caspases). Many cells are resistant, however, to the cytotoxic effects of TNFalpha due to the concurrent activation of pro-survival pathways involving the transcription factor NFkappaB and TRAF2. Here we show that the TNFalpha-activated FADD/caspase pathway can also exert an unexpected pro-survival effect. Inhibition of this pathway in NIH3T3 fibroblasts or U937 leukemic cells by peptide caspase inhibitors or expression of dominant-negative FADD leads to rapid death following treatment with TNFalpha, whereas control cells are TNFalpha-resistant. FADD/caspase-inhibited cells die by a non-apoptotic mechanism caused by increased production of reactive oxygen species which precedes loss of the mitochondrial membrane potential. Cytotoxicity can be prevented by preincubation with antioxidants including reduced glutathione or by expression of a dominant-negative Rac GTP-binding protein. These results indicate that caspase activation in response to TNFalpha has anti-necrotic as well as pro-apoptotic effects and extend our understanding of the biological role of these proteases.
Khwaja
A
A
Department of Haematology, University College London Medical School, 98 Chenies Mews, London WC1E 6HX, United Kingdom. a.khwaja@ucl.ac.uk
Tatton
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L
D016475:3T3 Cells; D000818:Animals; D017209:Apoptosis; D029681:Arabidopsis Proteins; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D044943:Fatty Acid Desaturases / Q000378:metabolism*; D006801:Humans; D051379:Mice; D015398:Signal Transduction / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism* / Q000633:toxicity*; D020298:U937 Cells
D029681:Arabidopsis Proteins; D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; D014409:Tumor Necrosis Factor-alpha; D044943:Fatty Acid Desaturases; C084083:Fad7 protein, Arabidopsis; D020169:Caspases