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Bcl-x(L) prevents the initial decrease in mitochondrial membrane potential and subsequent reactive oxygen species
E Gottlieb1, M G Vander Heiden, C B Thompson
1Abramson Family Cancer Research Institute, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Abstract:
The Bcl-2 family of proteins are involved in regulating the redox state of cells. However, the mode of action of Bcl-2 proteins remains unclear. This work analyzed the effects of Bcl-x(L) on the cellular redox state after treatment with tumor necrosis factor alpha (TNF-alpha) or exogenous oxidants. We show that in cells that undergo TNF-alpha-induced apoptosis, TNF-alpha induces a partial decrease in mitochondrial membrane potential (DeltaPsi(m)) followed by high levels of reactive oxygen species (ROS). ROS scavengers delay the progression of mitochondrial depolarization and apoptotic cell death. This indicates that ROS are important mediators of mitochondrial depolarization. However, ROS scavengers fail to prevent the initial TNF-alpha-induced decrease in DeltaPsi(m). In contrast, expression of Bcl-x(L) prevents both the initial decrease in DeltaPsi(m) following TNF-alpha treatment and the subsequent induction of ROS. Bcl-x(L) itself does not act as a ROS scavenger. In addition, Bcl-x(L) does not block the initial decrease in DeltaPsi(m) following treatment with the oxidant hydrogen peroxide. However, unlike control-transfected cells, Bcl-x(L)-expressing cells can recover their mitochondrial membrane potential following the initial drop in DeltaPsi(m) induced by hydrogen peroxide. These data suggest that Bcl-x(L) plays a regulatory role in controlling the membrane potential of and ROS production by mitochondria rather than acting as a direct antioxidant.
Insights
The Bcl-x(L) protein regulates mitochondrial function and reactive oxygen species (ROS) production, preventing cell death. It maintains mitochondrial membrane potential, unlike direct antioxidants.
Area of Science:
- Cellular Biology
- Biochemistry
- Apoptosis Research
Background:
- The Bcl-2 protein family influences cellular redox balance, but their precise mechanisms are not fully understood.
- Reactive oxygen species (ROS) play a role in mitochondrial dysfunction and apoptosis.
Purpose of the Study:
- To investigate the role of Bcl-x(L) in regulating cellular redox state and mitochondrial membrane potential.
- To elucidate the mechanism by which Bcl-x(L) affects TNF-alpha-induced apoptosis and oxidant-induced mitochondrial changes.
Main Methods:
- Treatment of cells with tumor necrosis factor alpha (TNF-alpha) and exogenous oxidants (hydrogen peroxide).
- Measurement of mitochondrial membrane potential (DeltaPsi(m)) and reactive oxygen species (ROS) levels.
- Comparison of Bcl-x(L)-expressing cells with control cells.
Main Results:
- TNF-alpha induced a decrease in DeltaPsi(m) and increased ROS, which were partially mitigated by ROS scavengers.
- Bcl-x(L) expression prevented both the initial DeltaPsi(m) decrease and subsequent ROS induction by TNF-alpha.
- Bcl-x(L) did not prevent initial DeltaPsi(m) drop from hydrogen peroxide but enabled recovery, indicating a regulatory role, not direct antioxidant activity.
Conclusions:
- Bcl-x(L) plays a crucial role in maintaining mitochondrial membrane potential and controlling ROS production.
- Bcl-x(L) acts as a regulator of mitochondrial function during cellular stress, rather than a direct ROS scavenger.
- These findings offer insights into the complex interplay between Bcl-2 proteins, mitochondria, and apoptosis.