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Inhibition of Bax channel-forming activity by Bcl-2
B Antonsson1, F Conti, A Ciavatta
1Geneva Biomedical Research Institute, Glaxo Wellcome R&D S. A., 1288 Plan les Ouates, Geneva, Switzerland. beau6063@ggr.co.uk
Abstract:
Proteins of the Bcl-2 family are intracellular membrane-associated proteins that regulate programmed cell death (apoptosis) either positively or negatively by as yet unknown mechanisms. Bax, a pro-apoptotic member of the Bcl-2 family, was shown to form channels in lipid membranes. Bax triggered the release of liposome-encapsulated carboxyfluorescein at both neutral and acidic pH. At physiological pH, release could be blocked by Bcl-2. Bcl-2, in contrast, triggered carboxyfluorescein release at acidic pH only. In planar lipid bilayers, Bax formed pH- and voltage-dependent ion-conducting channels. Thus, the pro-apoptotic effects of Bax may be elicited through an intrinsic pore-forming activity that can be antagonized by Bcl-2.
Insights
The Bcl-2 family proteins regulate cell death. Bax forms membrane channels, potentially causing apoptosis, while Bcl-2 can block this effect, suggesting a pore-forming mechanism in programmed cell death.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Proteins of the Bcl-2 family regulate programmed cell death (apoptosis).
- The precise mechanisms by which Bcl-2 family proteins control apoptosis are not fully understood.
- Bax, a pro-apoptotic member, has been implicated in membrane permeabilization.
Purpose of the Study:
- To investigate the pore-forming activity of Bax in lipid membranes.
- To determine the influence of pH and voltage on Bax channel formation.
- To explore the antagonistic role of Bcl-2 in Bax-mediated membrane disruption.
Main Methods:
- Liposome-based assays to measure carboxyfluorescein release.
- Planar lipid bilayer electrophysiology to study ion channel formation.
- Experiments conducted at neutral, acidic, and physiological pH.
Main Results:
- Bax formed channels in lipid membranes, triggering carboxyfluorescein release at neutral and acidic pH.
- Bcl-2 inhibited Bax-induced release at physiological pH.
- Bcl-2 alone induced carboxyfluorescein release only at acidic pH.
- Bax formed pH- and voltage-dependent ion-conducting channels in planar lipid bilayers.
Conclusions:
- Bax exhibits intrinsic pore-forming activity that may mediate its pro-apoptotic effects.
- Bcl-2 can antagonize the pore-forming activity of Bax.
- The interaction between Bax and Bcl-2, modulated by pH, is crucial in regulating apoptosis.