The innate immune response is the first line of defense against microbial infection. Virus infection causes rapid induction of interferon (IFN) and IFN-induced genes, which are critical for antiviral defense. IFN regulatory factor 3 (IRF3), expressed ubiquitously, is the key transcription factor for the induction of IFN? and the antiviral genes. Therefore, IRF3 deficiency leads to susceptibility to a wide range of virus infections. We have discovered that IRF3, in addition to its transcriptional activity, has a non-transcriptional (nt) function, to kill the virus-infected cells by a pro-apoptotic pathway, RIPA. Knock-in mice, expressing nt-Irf3 mutant, can mount antiviral protection in the absence of antiviral genes. Recently, we demonstrated that nt-Irf3 functions contribute to alcoholic and non-alcoholic liver diseases, further strengthening the physiological significance of nt-Irf3. In the current proposal, we present a new function for nt-Irf3 to inhibit the NF-?B activity and the inflammatory gene induction. We termed this anti-inflammatory activity of IRF3 as Repression of IRF3- mediated NF-?B Activity, ?RIKA?. Our strong preliminary results demonstrate that: (a) IRF3-/- cells, in response to viral or non-viral stimulation, express elevated levels of NF-?B-induced inflammatory genes compared to the Wt cells, (b) IRF3 interacts with the NF-?B subunit to inhibit its transcriptional activity, and (c) the Irf3-/- mice that are susceptible to respiratory virus infection, exhibit higher levels of NF-?B-induced genes in the lungs. These results led to our central hypothesis that nt-IRF3, activated by either RIPA or transcription-independent pathway, binds to p65, inhibiting the NF-?B-induced genes, and suppressing inflammatory pathogenesis. To address this, using cellular and conditional knockout mouse models and respiratory virus pathogenesis, we formulate two specific aims: (SA1) Investigate the molecular mechanisms by which IRF3 functions in RIKA, and (SA2) Evaluate the contribution of RIKA to prevent inflammatory responses and viral pathogenesis. Successful completion of these aims will delineate a new anti-inflammatory function of Irf3 that contributes to its antiviral functions. Our research is innovative because it uses the novel in vitro and in vivo models to study the molecular mechanism of RIKA, and its cell type-specific contribution to protect against inflammatory pathogenesis. Our results will be significant as delineating a new anti-inflammatory function for IRF3 that contributes to its antiviral innate immune responses will advance the field with a new functional branch of IRF3 that has implications in preventing inflammatory pathogenesis, beyond viral infection.
Viral infection often leads to unregulated inflammatory responses, which contribute to the viral pathogenesis. The proposal will reveal novel anti-inflammatory functions for the host transcription factor IRF3 in modulating immune responses to inflammatory stimulus e.g. respiratory virus infection. The results will lead to deeper understanding of how viral as well as non-viral inflammation is controlled, with potential therapeutic significance.