Knockout of IRF7 Highlights its Modulator Function of Host Response Against Avian Influenza Virus and the Involvement of MAPK and TOR Signaling Pathways in Chicken

Abstract

Interferon regulatory factor 7 (IRF7) is known as the master transcription factor of the type I interferon response in mammalian species along with IRF3. Yet birds only have IRF7, while they are missing IRF3, with a smaller repertoire of immune-related genes, which leads to a distinctive immune response in chickens compared to in mammals. In order to understand the functional role of IRF7 in the regulation of the antiviral response against avian influenza virus in chickens, we generated IRF7-/- chicken embryonic fibroblast (DF-1) cell lines and respective controls (IRF7wt) by utilizing the CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9) system. IRF7 knockout resulted in increased viral titers of low pathogenic avian influenza viruses. Further RNA-sequencing performed on H6N2-infected IRF7-/- and IRF7wt cell lines revealed that the deletion of IRF7 resulted in the significant down-regulation of antiviral effectors and the differential expression of genes in the MAPK (mitogen-activated protein kinase) and mTOR (mechanistic target of rapamycin) signaling pathways. Dynamic gene expression profiling of the host response between the wildtype and IRF7 knockout revealed potential signaling pathways involving AP1 (activator protein 1), NF-κB (nuclear factor kappa B) and inflammatory cytokines that may complement chicken IRF7. Our findings in this study provide novel insights that have not been reported previously, and lay a solid foundation for enhancing our understanding of the host antiviral response against the avian influenza virus in chickens.

Comparative Investigation of Gene Regulatory Processes Underlying Avian Influenza Viruses in Chicken and Duck

“…Kim et al. [ 87 ] showed that a knockout of IRF7 in chicken DF-1 cells, and subsequent AIV infection, resulted in the altered gene expression pattern of several genes, including key immune response genes such as IL12 , FOS , and AP1 . The authors further suggest that this shift in expression pattern could be a compensation for the absence of IRF7 [ 87 ].…”

“…In chicken trachea, FOS was shown to be upregulated after hydrogen-sulfide-induced oxidative stress, revealing the importance of FOS/IL8 signaling during tracheal inflammation [86]. Kim et al [87] showed that a knockout of IRF7 in chicken DF-1 cells, and subsequent AIV infection, resulted in the altered gene expression pattern of several genes, including key immune response genes such as IL12, FOS, and AP1. The authors further suggest that this shift in expression pattern could be a compensation for the absence of IRF7 [87].…”

Evolution of RNA sensing receptors in birds

“…The absence of IRF3 and key role of chIRF7 were confirmed by analyzing de novo assembled RNA-seq data in response to the dsRNA viral mimic poly (I:C), following IRF7 knockdown or overexpression (Kim and Zhou 2015). Ultimately, knockout of IRF7 in the DF-1 chicken embryonic fibroblast cell line (Cheng et al 2019b;Kim et al 2020) greatly decreased expression of type I interferon. In birds, two serologically distinct types of type I interferon genes have been identified on the Z chromosome (Sick et al 1996).…”

Loss of IRF7 accelerates acute myeloid leukemia progression and induces VCAM1-VLA-4 mediated intracerebral invasion

“…However, IRF7 can be coimmunoprecipitated with Smad3 [ 43 ], which also interact with TGIF1 [ 19 ]. Furthermore, the deletion of IRF7 hinders the upregulation of genes in the MAPK pathway [ 44 ], which is upstream of TGIF1 phosphorylation [ 45 ]. Therefore, although a link between IRF7 and TGIF1 has been observed and the IRF7-TGIF1 axis has been implicated, the molecular mechanism requires further investigation.…”