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Apoptotic protease activating factor 1 (Apaf-1)-independent cell death suppression by Bcl-2

M Haraguchi1, S Torii, S i Matsuzawa

  • 1Burnham Institute Program on Apoptosis and Cell Death Regulation, La Jolla, California 92037, USA.

The Journal of Experimental Medicine
|May 17, 2000
PubMed

Insights

Bcl-2 protects cells from death independently of Apaf-1 by maintaining mitochondrial function. This antiapoptotic protein preserves cell viability through a caspase-independent pathway, even in Apaf-1 deficient cells.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Antiapoptotic Bcl-2 proteins are known to inhibit apoptosis by interacting with CED-4 family caspase activators.
  • Apoptotic Protease Activating Factor 1 (Apaf-1) is a homologue of CED-4 and a key component of the apoptosome.
  • The precise mechanism by which Bcl-2 exerts its antiapoptotic effects, particularly in relation to Apaf-1, requires further elucidation.

Purpose of the Study:

  • To investigate the role of Apaf-1 in mediating the antiapoptotic effects of Bcl-2.
  • To determine whether Bcl-2's cytoprotective functions are dependent on its interaction with Apaf-1.
  • To explore the mechanisms underlying Bcl-2-mediated cell survival in the absence of functional Apaf-1.

Main Methods:

  • Generation of Apaf-1 heterozygous (+/-) and homozygous (-/-) knockout embryonic stem (ES) cells.
  • Overexpression of Bcl-2 in these engineered ES cell lines.
  • Induction of apoptosis using various stimuli including serum withdrawal, staurosporine (STS), UVB irradiation, etoposide (VP16), and cisplatin.
  • Assessment of apoptosis, caspase activation, mitochondrial membrane potential (DeltaPsi) loss, and cell death.
  • Co-immunoprecipitation assays to examine protein-protein interactions between Bcl-2, Bax, and Apaf-1.

Main Results:

  • Apaf-1 knockout ES cells exhibited significantly reduced caspase activation and apoptosis in response to death stimuli.
  • Apaf-1-deficient cells underwent nonapoptotic cell death associated with DeltaPsi loss.
  • Overexpression of Bcl-2 preserved DeltaPsi, reduced cell death, and increased survival in both Apaf-1 heterozygous and homozygous knockout cells.
  • Bcl-2 co-immunoprecipitated with Bax, but not with Apaf-1, under conditions where Apaf-1 interacted with procaspase-9.
  • Bcl-2 provided significant cytoprotection independent of Apaf-1 presence.

Conclusions:

  • Bcl-2 exerts cytoprotective functions that are independent of Apaf-1.
  • Bcl-2 preserves mitochondrial function through a caspase-independent mechanism.
  • These findings reveal a novel pathway for Bcl-2-mediated cell survival that does not rely on the canonical Apaf-1-dependent apoptotic pathway.

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