Caspases Induce Cytochrome c Release from Mitochondria by Activating Cytosolic Factors*
- From the Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, San Diego, California 92121
Abstract
We investigated the ability of caspases (cysteine proteases with aspartic acid specificity) to induce cytochromec release from mitochondria. When Jurkat cells were induced to undergo apoptosis by Fas receptor ligation, cytochrome cwas 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 cytochromec 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 cytochromec 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.
Footnotes
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↵* This work was supported by National Institutes of Health Grants AI40646 and CA69381 (to D. R. G.) and by Fellowship 823A-046638 from the Swiss National Science Foundation (to E. B.-W.). This is La Jolla Institute for Allergy and Immunology Publication No. 263.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ To whom correspondence should be addressed: Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, 10355 Science Center Dr., San Diego, CA 92121. Tel.: 619-558-3500; Fax: 619-558-3526; E-mail:dgreen5240{at}aol.com.
- Abbreviations:
- Apaf-1
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apoptotic protease activating factor-1
- PAGE
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polyacrylamide gel electrophoresis
- PBS
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phosphate-buffered saline
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- Received August 19, 1998.
- Revision received April 7, 1999.
- The American Society for Biochemistry and Molecular Biology, Inc.
