Bcl-xL inhibits cytochrome c release but not mitochondrial depolarization during the activation of multiple death pathways by tumor necrosis factor-alpha.
Cells can respond differently to anti-CD95 antibody treatment. Type I cells show strong activation of caspase-8 and directly activate caspase-3. Type II cells weakly activate caspase-8 and must amplify their death signal through the mitochondria. These cells can be rescued by Bcl-x(L). Here we show that tumor necrosis factor-alpha induces both Type I and II pathways, which can be inhibited by benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (Z-VAD-fmk) and Bcl-x(L) in a cooperative fashion. Death induced in the presence of Z-VAD-fmk was associated with a partial inhibition of caspase-8, whereas no effects on cytochrome c release, DEVDase activity, and intranucleosomal DNA cleavage were observed. Thus, Z-VAD-fmk is likely weakening the death-inducing signaling complex-mediated activation of caspase-8 and diverting cells to a Type II pathway. Bcl-x(L) cooperates with Z-VAD-fmk by blocking the Type II pathway at the level of cytochrome c release. Surprisingly, although Bcl-x(L) was able to block cytochrome c release, it was unable to block mitochondrial depolarization, suggesting that these are separate events. This suggests that mitochondria occupy two places in apoptotic signaling, as initiators of apoptosis through the release of cytochrome c as well as a target for effector caspases.
Department of Microbiology and Immunology and the Sylvester Comprehensive Cancer Center, University of Miami School of Medicine, Miami, Florida 33101, USA.
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Johnson
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Cepero
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Boise
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis; D001402:B-Lymphocytes / Q000378:metabolism; D015153:Blotting, Western; D053181:Caspase 8; D053453:Caspase 9; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D003513:Cycloheximide / Q000494:pharmacology; D003574:Cytochrome c Group / Q000037:antagonists & inhibitors*; D004247:DNA / Q000378:metabolism; D053938:DNA Fragmentation; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000378:metabolism; D005434:Flow Cytometry; D051379:Mice; D008928:Mitochondria / Q000378:metabolism*; D008954:Models, Biological; D010447:Peptide Hydrolases / Q000378:metabolism; D010641:Phenotype; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism / Q000502:physiology*; D015843:Serpins / Q000378:metabolism; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*; D014764:Viral Proteins; D051020:bcl-X Protein; D019014:fas Receptor / Q000378:metabolism
D000590:Amino Acid Chloromethyl Ketones; C494812:Bcl2l1 protein, mouse; D061945:Caspase Inhibitors; D003574:Cytochrome c Group; D004792:Enzyme Precursors; D011500:Protein Synthesis Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D015843:Serpins; D014409:Tumor Necrosis Factor-alpha; D014764:Viral Proteins; D051020:bcl-X Protein; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D019014:fas Receptor; D004247:DNA; C074641:interleukin-1beta-converting enzyme inhibitor; D003513:Cycloheximide; D010447:Peptide Hydrolases; C505526:Casp8 protein, mouse; C506434:Casp9 protein, mouse; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases; C108711:DEVDase