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Identification of distinct signaling pathways leading to the phosphorylation of interferon regulatory factor 3
M J Servant1, B ten Oever, C LePage
1Terry Fox Molecular Oncology Group, Lady Davis Institute for Medical Research, McGill University, Montreal, H3T 1E2 Canada.
Abstract:
Infection of host cells by viruses leads to the activation of multiple signaling pathways, resulting in the expression of host genes involved in the establishment of the antiviral state. Among the transcription factors mediating the immediate response to virus is interferon regulatory factor-3 (IRF-3) which is post-translationally modified as a result of virus infection. Phosphorylation of latent cytoplasmic IRF-3 on serine and threonine residues in the C-terminal region leads to dimerization, cytoplasmic to nuclear translocation, association with the p300/CBP coactivator, and stimulation of DNA binding and transcriptional activities. We now demonstrate that IRF-3 is a phosphoprotein that is uniquely activated via virus-dependent C-terminal phosphorylation. Paramyxoviridae including measles virus and rhabdoviridae, vesicular stomatitis virus, are potent inducers of a unique virus-activated kinase activity. In contrast, stress inducers, growth factors, DNA-damaging agents, and cytokines do not induce C-terminal IRF-3 phosphorylation, translocation or transactivation, but rather activate a MAPKKK-related signaling pathway that results in N-terminal IRF-3 phosphorylation. The failure of numerous well characterized pharmacological inhibitors to abrogate virus-induced IRF-3 phosphorylation suggests the involvement of a novel kinase activity in IRF-3 regulation by viruses.
Insights
Virus infection uniquely activates interferon regulatory factor-3 (IRF-3) through C-terminal phosphorylation, distinct from other cellular stressors. This virus-specific activation involves a novel kinase, crucial for initiating the antiviral state.
Area of Science:
- Virology
- Molecular Biology
- Immunology
Background:
- Viral infections trigger host cell signaling pathways to establish an antiviral state.
- Interferon regulatory factor-3 (IRF-3) is a key transcription factor in the immediate response to viral infection.
- IRF-3 undergoes post-translational modification, specifically phosphorylation, upon virus entry.
Purpose of the Study:
- To investigate the specific mechanism of IRF-3 activation during viral infections.
- To differentiate virus-induced IRF-3 activation from pathways activated by other cellular stressors.
- To identify the kinase responsible for virus-dependent IRF-3 phosphorylation.
Main Methods:
- Analysis of IRF-3 phosphorylation patterns in response to various stimuli, including viruses (Paramyxoviridae, Rhabdoviridae), stress inducers, growth factors, DNA-damaging agents, and cytokines.
- Assessment of IRF-3 translocation from the cytoplasm to the nucleus.
- Evaluation of IRF-3 transcriptional activity and DNA binding.
- Testing the efficacy of pharmacological inhibitors on virus-induced IRF-3 phosphorylation.
Main Results:
- Virus infection, specifically by Paramyxoviridae and Rhabdoviridae, potently induces C-terminal phosphorylation of IRF-3.
- This C-terminal phosphorylation leads to IRF-3 dimerization, nuclear translocation, and transcriptional activation.
- Stress inducers, growth factors, DNA-damaging agents, and cytokines activate IRF-3 via N-terminal phosphorylation through a MAPKKK pathway.
- Common pharmacological inhibitors failed to block virus-induced IRF-3 phosphorylation, indicating a novel kinase activity.
Conclusions:
- IRF-3 activation is uniquely regulated by virus-dependent C-terminal phosphorylation.
- A novel kinase activity, distinct from those activated by other stressors, mediates virus-induced IRF-3 phosphorylation.
- Understanding this unique pathway is critical for comprehending the host antiviral response and developing targeted therapies.