Nontranscriptional Activity of Interferon Regulatory Factor 3 Protects Mice From High‐Fat Diet‐Induced Liver Injury

Abstract

Interferon regulatory factor 3 (IRF3) has both transcriptional and nontranscriptional functions. Transcriptional activity is dependent on serine phosphorylation of IRF3, while transcription‐independent IRF3‐mediated apoptosis requires ubiquitination. IRF3 also binds to inhibitor of nuclear factor kappa B kinase (IKKβ) in the cytosol, restricting nuclear translocation of p65. IRF3‐deficient mice are highly sensitive to high‐fat diet (HFD)‐induced liver injury; however, it is not known if transcriptional and/or nontranscriptional activity of IRF3 confers protection. Using a mouse model only expressing nontranscriptional functions of IRF3 (Irf3S1/S1), we tested the hypothesis that nontranscriptional activity of IRF3 protects mice from HFD‐induced liver injury. C57BL/6, Irf3−/−, and Irf3S1/S1 mice were fed an HFD for 12 weeks. In C57BL/6 mice, the HFD increased expression of interferon (IFN)‐dependent genes, despite a decrease in IRF3 protein in the liver. The HFD had no impact on IFN‐dependent gene expression Irf3−/− or Irf3S1/S1 mice, both lacking IRF3 transcriptional activity. Liver injury, apoptosis, and fibrosis were exacerbated in Irf3−/− compared to C57BL/6 mice following the HFD; this increase was ameliorated in Irf3S1/S1 mice. Similarly, expression of inflammatory cytokines as well as numbers of neutrophils and infiltrating monocytes was increased in Irf3−/− mice compared to C57BL/6 and Irf3S1/S1 mice. While the HFD increased the ubiquitination of IRF3, a response associated with IRF3‐mediated apoptosis, in Irf3S1/S1 mice, protection from liver injury was not due to differences in apoptosis of hepatocytes or immune cells. Instead, protection from HFD‐induced liver injury in Irf3S1/S1 mice was primarily associated with retardation of nuclear translocation of p65 and decreased expression of nuclear factor kappa B (NFκB)‐dependent inflammatory cytokines. Conclusion: Taken together, these data identify important contributions of the nontranscriptional function of IRF3, likely by reducing NFκB signaling, in dampening the hepatic inflammatory environment in response to an HFD.

Classical Swine Fever Virus NproAntagonizes IRF3 To Prevent Interferon-Independent TLR3- and RIG-I-Mediated Apoptosis

“…IRF3 is best known for its function as a transcription factor, mediating the upregulation of not only type I IFN but also a small subset of “IFN-independent” ISGs ( 28 – 30 ). In order to determine whether apoptosis requires IRF3 transcriptional activity, IRF3 −/− PK-15 cells stably expressing a FLAG-tagged transcriptionally inactive IRF3 mutant (S394A S396A) termed “S1” ( 31 , 40 ) were generated using lentivirus ( Fig. 4D ).…”

Transcriptional and Non-Transcriptional Activation, Posttranslational Modifications, and Antiviral Functions of Interferon Regulatory Factor 3 and Viral Antagonism by the SARS-Coronavirus

“…All three of these inducers contribute to liver injury, implicating IRF3 in the development of liver disease pathology. Studies through our work revealed that RIPA in restorative hepatic monocytes contributes to ethanol-induced liver injury in an acute-on-chronic hepatitis model [ 59 ]. In contrast, we further showed that the non-transcriptional RIPA activity of IRF3 plays a protective role in high-fat diet-induced liver injury [ 59 ].…”

“…Studies through our work revealed that RIPA in restorative hepatic monocytes contributes to ethanol-induced liver injury in an acute-on-chronic hepatitis model [ 59 ]. In contrast, we further showed that the non-transcriptional RIPA activity of IRF3 plays a protective role in high-fat diet-induced liver injury [ 59 ]. Therefore, while we have shown the activation of IRF3-driven apoptosis in virus infections benefits the host, the role of IRF3 in liver disease still remains somewhat unclear.…”

Autophagic degradation of IRF3 induced by the small-molecule auranofin inhibits its transcriptional and proapoptotic activities

“…DMSO was used as vehicle control for auranofin. For palmitic acid treatment, palmitic acid was prepared in BSA-containing DMEM, as described before (15), at the final indicated concentrations and added directly to the culture media for the indicated length of treatment.…”

“…In a recent study using nontranscriptional IRF3 expressing mice, we demonstrated that the nontranscriptional activity of IRF3 is sufficient to induce numerous markers of hepatocellular damage in response to ethanol, including increased ALT/AST, triglycerides, and inflammatory cytokine expression ( 14 ). In contrast, nontranscriptional IRF3 activity plays a protective role in mice from HFD-induced liver injury partially through the suppression of NF-κB signaling ( 15 ).…”