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Minimal BH3 peptides promote cell death by antagonizing anti-apoptotic proteins
Carole Moreau1, Pierre-François Cartron, Abigail Hunt
1INSERM U419, Nantes, France.
Abstract:
The pro-apoptotic "BH3 domain-only" proteins of the Bcl-2 family (e.g. Bid and Bad) transduce multiple death signals to the mitochondrion. They interact with the anti-apoptotic Bcl-2 family members and induce apoptosis by a mechanism that requires the presence of at least one of the multidomain pro-apoptotic proteins Bax or Bak. Although the BH3 domain of Bid can promote the pro-apoptotic assembly and function of Bax/Bak by itself, other BH3 domains do not function as such. The latter point raises the question of whether, and how, these BH3 domains induce apoptosis. We show here that a peptide comprising the minimal BH3 domain from Bax induces apoptosis but is unable to stimulate the apoptotic activity of microinjected recombinant Bax. This relies on the inability of the peptide to directly induce Bax translocation to mitochondria or a change in its conformation. This peptide nevertheless interferes with Bax/Bcl-xL interactions in vitro and stimulates the apoptotic activity of Bax when combined with Bcl-xL. Similarly, a peptide derived from the BH3 domain of Bad stimulates Bax activity only in the presence of Bcl-xL. Thus, BH3 domains do not necessarily activate multidomain pro-apoptotic proteins directly but promote apoptosis by releasing active multidomain pro-apoptotic proteins from their anti-apoptotic counterparts.
Insights
BH3 domain-only proteins signal cell death to mitochondria. Some BH3 domains activate apoptosis indirectly by releasing pro-apoptotic proteins from inhibitors, rather than direct activation.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- The Bcl-2 family regulates apoptosis, with pro-apoptotic BH3-only proteins initiating death signals.
- Apoptosis induction by BH3-only proteins requires Bax or Bak and involves interactions with anti-apoptotic Bcl-2 proteins.
- While Bid's BH3 domain directly activates Bax/Bak, other BH3 domains' mechanisms remain unclear.
Purpose of the Study:
- To investigate the mechanism by which BH3 domains, other than Bid's, induce apoptosis.
- To determine if BH3 domains activate multidomain pro-apoptotic proteins directly or indirectly.
Main Methods:
- Utilized synthetic peptides representing minimal BH3 domains from Bax and Bad.
- Performed in vitro interaction assays to study Bax/Bcl-xL binding.
- Assessed apoptosis induction and Bax activity modulation in cellular models.
Main Results:
- A Bax BH3 peptide induced apoptosis but did not directly activate recombinant Bax.
- This peptide interfered with Bax/Bcl-xL interactions and enhanced Bax activity in the presence of Bcl-xL.
- A Bad BH3 peptide also stimulated Bax activity only when Bcl-xL was present.
Conclusions:
- BH3 domains do not always directly activate multidomain pro-apoptotic proteins like Bax.
- Apoptosis is promoted by BH3 domains that displace active Bax/Bak from anti-apoptotic Bcl-2 proteins.
- This indirect activation mechanism is crucial for BH3-only protein function in apoptosis.