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Apoptosis-associated release of Smac/DIABLO from mitochondria requires active caspases and is blocked by Bcl-2

C Adrain1, E M Creagh, S J Martin

  • 1Molecular Cell Biology Laboratory, Department of Genetics, The Smurfit Institute, Trinity College, Dublin 2, Ireland.

The EMBO Journal
|December 1, 2001
PubMed

Insights

The mitochondrial protein Smac/DIABLO is released during apoptosis, but its efflux is caspase-dependent and occurs after cytochrome c release. Bcl-2 overexpression inhibits Smac/DIABLO release, suggesting a shared mitochondrial pathway.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Smac/DIABLO is a mitochondrial protein that promotes apoptosis by inhibiting IAP proteins.
  • Smac/DIABLO release from mitochondria into the cytosol is observed during apoptosis induced by various stimuli.
  • The role of Bcl-2 and caspases in Smac/DIABLO mitochondrial efflux is not fully understood.

Purpose of the Study:

  • To investigate the regulation of Smac/DIABLO release from mitochondria during apoptosis.
  • To determine the role of Bcl-2 and caspases in Smac/DIABLO efflux.
  • To compare the mechanisms of Smac/DIABLO and cytochrome c release from mitochondria.

Main Methods:

  • Induction of apoptosis using cytotoxic drugs, DNA damage, and CD95 ligation.
  • Overexpression of Bcl-2 in cells.
  • Treatment with a broad-spectrum caspase inhibitor.
  • Monitoring of Smac/DIABLO and cytochrome c release from mitochondria.

Main Results:

  • Smac/DIABLO release is triggered by cytotoxic drugs, DNA damage, and CD95 ligation.
  • Bcl-2 overexpression significantly inhibits Smac/DIABLO efflux from mitochondria.
  • Smac/DIABLO release is blocked by caspase inhibitors, indicating a caspase-dependent mechanism.
  • Smac/DIABLO release occurs downstream of cytochrome c release and does not share the same mechanism.

Conclusions:

  • Bcl-2 regulates Smac/DIABLO release from mitochondria, potentially via the same pathway as cytochrome c.
  • Smac/DIABLO efflux is a caspase-catalyzed event occurring downstream of cytochrome c release.
  • These findings elucidate the distinct mechanisms governing the release of key apoptotic regulators from mitochondria.

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