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Bax is present as a high molecular weight oligomer/complex in the mitochondrial membrane of apoptotic cells
B Antonsson1, S Montessuit, B Sanchez
1Serono Pharmaceutical Research Institute, Serono International S.A., 14 chemin des Aulx, CH-1228 Plan-les Ouates, Geneva, Switzerland. bruno.antonsson@serono.com
Abstract:
Bax is a Bcl-2 family protein with proapoptotic activity, which has been shown to trigger cytochrome c release from mitochondria both in vitro and in vivo. In control HeLa cells, Bax is present in the cytosol and weakly associated with mitochondria as a monomer with an apparent molecular mass of 20,000 Da. After treatment of the HeLa cells with the apoptosis inducer staurosporine or UV irradiation, Bax associated with mitochondria is present as two large molecular weight oligomers/complexes of 96,000 and 260,000 Da, which are integrated into the mitochondrial membrane. Bcl-2 prevents Bax oligomerization and insertion into the mitochondrial membrane. The outer mitochondrial membrane protein voltage-dependent anion channel and the inner mitochondrial membrane protein adenosine nucleotide translocator do not coelute with the large molecular weight Bax oligomers/complexes on gel filtration. Bax oligomerization appears to be required for its proapoptotic activity, and the Bax oligomer/complex might constitute the structural entirety of the cytochrome c-conducting channel in the outer mitochondrial membrane.
Insights
Bax protein oligomerization is essential for apoptosis. This process involves Bax forming large complexes integrated into the mitochondrial membrane, leading to cytochrome c release.
Area of Science:
- Biochemistry
- Cell Biology
- Molecular Biology
Background:
- Bax is a proapoptotic protein in the Bcl-2 family.
- Bax induces cytochrome c release from mitochondria.
- In HeLa cells, Bax exists as a monomer in the cytosol and weakly associated with mitochondria.
Purpose of the Study:
- To investigate the molecular mechanism of Bax-mediated apoptosis.
- To characterize Bax oligomerization and its role in cytochrome c release.
Main Methods:
- Apoptosis induction in HeLa cells using staurosporine or UV irradiation.
- Analysis of Bax molecular weight and mitochondrial association using gel filtration.
- Investigating the interaction of Bax with mitochondrial membrane proteins.
Main Results:
- Staurosporine or UV irradiation treatment induced Bax oligomerization into 96,000 and 260,000 Da complexes.
- These Bax oligomers integrated into the mitochondrial membrane.
- Bcl-2 inhibited Bax oligomerization and mitochondrial insertion.
- Specific mitochondrial proteins did not coelute with Bax oligomers.
Conclusions:
- Bax oligomerization is a critical step for its proapoptotic activity.
- Bax oligomers/complexes may form the cytochrome c-conducting channel in the outer mitochondrial membrane.