Anti-inflammatory functions for non-transcriptional IRF3

Project Summary/Abstract
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 IFNβ 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-κB activity and the
inflammatory gene induction. We termed this anti-inflammatory activity of IRF3 as Repression of IRF3-
mediated NF-κB Activity, “RIKA”. Our strong preliminary results demonstrate that: (a) IRF3-/- cells, in response
to viral or non-viral stimulation, express elevated levels of NF-κB-induced inflammatory genes compared to the
Wt cells, (b) IRF3 interacts with the NF-κB subunit to inhibit its transcriptional activity, and (c) the Irf3-/- mice
that are susceptible to respiratory virus infection, exhibit higher levels of NF-κB-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-κB-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.

Grant Number: 5R01AI155545-04
NIH Institute/Center: NIH
Principal Investigator: Saurabh Chattopadhyay