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Suppression of steady-state, but not stimulus-induced NF-kappaB activity inhibits alphavirus-induced apoptosis
K I Lin1, J A DiDonato, A Hoffmann
1Department of Molecular Microbiology and Immunology, The Johns Hopkins University School of Public Health, Baltimore, Maryland 21205, USA.
Abstract:
Recent studies have established cell type- specific, proapoptotic, or antiapoptotic functions for the transcription factor NF-kappaB. In each of these studies, inhibitors of NF-kappaB activity have been present before the apoptotic stimulus, and so the role of stimulus- induced NF-kappaB activation in enhancing or inhibiting survival could not be directly assessed. Sindbis virus, an alphavirus, induces NF-kappaB activation and apoptosis in cultured cell lines. To address whether Sindbis virus- induced NF-kappaB activation is required for apoptosis, we used a chimeric Sindbis virus that expresses a superrepressor of NF-kappaB activity. Complete suppression of virus-induced NF-kappaB activity neither prevents nor potentiates Sindbis virus-induced apoptosis. In contrast, inhibition of NF-kappaB activity before infection inhibits Sindbis virus-induced apoptosis. Our results demonstrate that suppression of steady-state, but not stimulus-induced NF-kappaB activity, regulates expression of gene products required for Sindbis virus-induced death. Furthermore, we show that in the same cell line, NF-kappaB can be proapoptotic or antiapoptotic depending on the death stimulus. We propose that the role of NF-kappaB in regulating apoptosis is determined by the death stimulus and by the timing of modulating NF-kappaB activity relative to the death stimulus.
Insights
The transcription factor nuclear factor-kappa B (NF-kappaB) has dual roles in cell death. This study reveals NF-kappaB
Area of Science:
- Molecular Biology
- Virology
- Cell Biology
Background:
- Nuclear factor-kappa B (NF-kappaB) transcription factor exhibits context-dependent pro- or anti-apoptotic functions.
- Previous studies inhibited NF-kappaB before apoptotic stimuli, preventing assessment of stimulus-induced activation's role in cell survival.
Purpose of the Study:
- To investigate whether Sindbis virus-induced NF-kappaB activation is essential for apoptosis.
- To determine if NF-kappaB's role in apoptosis is stimulus-dependent and timing-sensitive.
Main Methods:
- Utilized a chimeric Sindbis virus expressing a superrepressor to completely suppress NF-kappaB activity.
- Assessed apoptosis in cultured cell lines with inhibited or suppressed NF-kappaB activity.
- Compared the effects of pre-infection inhibition versus suppression of stimulus-induced NF-kappaB activity.
Main Results:
- Complete suppression of virus-induced NF-kappaB activation did not alter Sindbis virus-induced apoptosis.
- Inhibition of NF-kappaB activity prior to infection significantly reduced Sindbis virus-induced apoptosis.
- NF-kappaB's role in regulating gene expression for Sindbis virus-induced cell death depends on steady-state, not stimulus-induced, activity.
- NF-kappaB demonstrated both proapoptotic and antiapoptotic roles in the same cell line, contingent on the death stimulus.
Conclusions:
- Steady-state NF-kappaB activity, not stimulus-induced activity, is critical for Sindbis virus-induced apoptosis.
- The function of NF-kappaB in apoptosis is dictated by the specific death stimulus and the timing of NF-kappaB modulation.
- NF-kappaB's role in cell death is dynamic, influenced by both the trigger and the temporal manipulation of its activity.