Caspases induce cytochrome c release from mitochondria by activating cytosolic factors.
We investigated the ability of caspases (cysteine proteases with aspartic acid specificity) to induce cytochrome c release from mitochondria. When Jurkat cells were induced to undergo apoptosis by Fas receptor ligation, cytochrome c was released from mitochondria, an event that was prevented by the caspase inhibitor, zVAD-fmk (zVal-Ala-Asp-CH2F). Purified caspase-8 triggered rapid cytochrome c release from isolated mitochondria in vitro. The effect was indirect, as the presence of cytosol was required, suggesting that caspase-8 cleaves and activates a cytosolic substrate, which in turn is able to induce cytochrome c release from mitochondria. The cytochrome c releasing activity was not blocked by caspase inhibition, but was antagonized by Bcl-2 or Bcl-xL. Caspase-8 and caspase-3 cleaved Bid, a proapoptotic Bcl-2 family member, which gains cytochrome c releasing activity in response to caspase cleavage. However, caspase-6 and caspase-7 did not cleave Bid, although they initiated cytochrome c release from mitochondria in the presence of cytosol. Thus, effector caspases may cleave and activate another cytosolic substrate (other than Bid), which then promotes cytochrome c release from mitochondria. Mitochondria significantly amplified the caspase-8 initiated DEVD-specific cleavage activity. Our data suggest that cytochrome c release, initiated by the action of caspases on a cytosolic substrates, may act to amplify a caspase cascade during apoptosis.
Bossy-Wetzel
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Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, San Diego, California 92121, USA.
Green
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DR
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis; D051023:BH3 Interacting Domain Death Agonist Protein; D002352:Carrier Proteins / Q000378:metabolism; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism*; D003574:Cytochrome c Group / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D019169:Jurkat Cells; D051379:Mice; D008930:Mitochondria, Liver / Q000201:enzymology / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism; D014462:Ultrafiltration; D051020:bcl-X Protein; D019014:fas Receptor
D000590:Amino Acid Chloromethyl Ketones; C494811:BCL2L1 protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; C494812:Bcl2l1 protein, mouse; C494815:Bid protein, mouse; D002352:Carrier Proteins; D003574:Cytochrome c Group; D004791:Enzyme Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D018124:Receptors, Tumor Necrosis Factor; D051020:bcl-X Protein; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D019014:fas Receptor; C505407:CASP3 protein, human; C505530:CASP8 protein, human; C506433:CASP9 protein, human; C505409:Casp3 protein, mouse; C505526:Casp8 protein, mouse; C506434:Casp9 protein, mouse; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases