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Bcl-2 down-regulates the activity of transcription factor NF-kappaB induced upon apoptosis
S Grimm1, M K Bauer, P A Baeuerle
1Institute of Biochemistry and Molecular Biology, Albert-Ludwigs-University, Freiburg, Germany.
Abstract:
Among the many target genes of the transcription factor NF-kappaB are p53 and c-myc, both of which are involved in apoptosis. This prompted us to investigate the role of NF-kappaB in this process. We report that NF-kappaB is potently activated upon serum starvation, a condition leading to apoptosis in 293 cells. Similar to Bcl-2, a transdominant-negative mutant of the NF-kappaB p65 subunit partially inhibited apoptosis, indicating a direct involvement of the transcription factor in induction of cell death. As expected, the p65 mutant suppresses kappaB-dependent gene expression. Surprisingly, transiently or stably overexpressed Bcl-2 had the same effect. The transcription inhibitory activity of the two proteins correlated with their cell death protective potential. Like Bcl-2, the related protein Bcl-xL but not Bcl-xS was able to suppress kB-dependent transcription. Bcl-2 inhibited NF-kappaB activity by an unusual mechanism. It did not prevent the release of IkappaB in the cytoplasm but down-modulated the transactivating potential of nuclear p65. These data show that NF-kappaB can participate in apoptosis. We suggest that at least part of the anti-apoptotic potential of Bcl-2 may be explained from a hitherto undiscovered activity of Bcl-2 in controlling nuclear gene expression.
Insights
Nuclear factor-kappaB (NF-kappaB) activation promotes apoptosis. Bcl-2 and Bcl-xL proteins inhibit NF-kappaB activity, suggesting a novel mechanism for their cell death protective effects.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Nuclear factor-kappaB (NF-kappaB) is a transcription factor regulating genes involved in apoptosis, such as p53 and c-myc.
- Serum starvation induces apoptosis in 293 cells and activates NF-kappaB.
Purpose of the Study:
- To investigate the role of NF-kappaB in apoptosis.
- To explore the relationship between NF-kappaB activity and the anti-apoptotic proteins Bcl-2 and Bcl-xL.
Main Methods:
- Activation of NF-kappaB by serum starvation in 293 cells.
- Utilizing a transdominant-negative mutant of the NF-kappaB p65 subunit to inhibit NF-kappaB activity.
- Overexpression of Bcl-2 and Bcl-xL to assess their effects on NF-kappaB-dependent gene expression and apoptosis.
- Investigating the mechanism by which Bcl-2 inhibits NF-kappaB activity.
Main Results:
- NF-kappaB is activated during serum starvation-induced apoptosis.
- Inhibition of NF-kappaB by a p65 mutant partially suppressed apoptosis.
- Overexpression of Bcl-2 and Bcl-xL (but not Bcl-xS) inhibited NF-kappaB-dependent gene expression and protected against apoptosis.
- Bcl-2 inhibited NF-kappaB by down-modulating the transactivating potential of nuclear p65, not by affecting IkappaB release.
Conclusions:
- NF-kappaB plays a role in the induction of apoptosis.
- Bcl-2 and Bcl-xL possess transcription inhibitory activity against NF-kappaB.
- Bcl-2's anti-apoptotic function may involve a novel mechanism of controlling nuclear gene expression by modulating NF-kappaB activity.