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Smac/DIABLO is not released from mitochondria during apoptotic signalling in cells deficient in cytochrome c

T M Hansen1, D J Smith, P Nagley

  • 1Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia.

Cell Death and Differentiation
|October 22, 2005
PubMed

Insights

Mitochondria normally release cytochrome c and Smac/DIABLO together during apoptosis. However, cells lacking cytochrome c fail to release Smac/DIABLO, revealing a new link in apoptosis regulation.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Cytochrome c release from mitochondria is a key event in apoptosis.
  • Smac/DIABLO is another mitochondrial protein released during apoptosis, promoting cell death.
  • The coordinated release of these proteins is crucial for the apoptotic pathway.

Purpose of the Study:

  • To investigate the role of cytochrome c in the release of Smac/DIABLO during apoptosis.
  • To characterize the apoptotic defects in cells lacking cytochrome c.
  • To understand the relationship between cytochrome c and Smac/DIABLO release.

Main Methods:

  • Confocal microscopy to visualize protein localization.
  • Western blotting to detect protein levels.
  • Induction of apoptosis using staurosporine (STS).
  • Analysis of cytochrome c-null (cyt c-/-) cells and control cells.

Main Results:

  • Cells lacking cytochrome c (cyt c-/-) showed Bax translocation to mitochondria and activation upon STS treatment.
  • However, cyt c-/- cells failed to release Smac/DIABLO from mitochondria.
  • Control cells expressing cytochrome c successfully released both cytochrome c and Smac/DIABLO.
  • Proteasomal degradation of cytosolic Smac/DIABLO was ruled out as the cause of its absence.

Conclusions:

  • There is an unexpected link between cytochrome c and Smac/DIABLO release from mitochondria.
  • The release of these two proteins, previously thought to be simultaneous, is differentially regulated.
  • The inability of cyt c-/- cells to release Smac/DIABLO highlights distinct regulatory mechanisms for mitochondrial protein release in apoptosis.

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