Research Article: IRF-3, IRF-5, and IRF-7 Coordinately Regulate the Type I IFN Response in Myeloid Dendritic Cells Downstream of MAVS Signaling

Date Published: January 3, 2013

Publisher: Public Library of Science

Author(s): Helen M. Lazear, Alissa Lancaster, Courtney Wilkins, Mehul S. Suthar, Albert Huang, Sarah C. Vick, Lisa Clepper, Larissa Thackray, Margaret M. Brassil, Herbert W. Virgin, Janko Nikolich-Zugich, Ashlee V. Moses, Michael Gale, Klaus Früh, Michael S. Diamond, Christopher F. Basler.


Although the transcription factors IRF-3 and IRF-7 are considered master regulators of type I interferon (IFN) induction and IFN stimulated gene (ISG) expression, Irf3−/−×Irf7−/− double knockout (DKO) myeloid dendritic cells (mDC) produce relatively normal levels of IFN-β after viral infection. We generated Irf3−/−×Irf5−/−×Irf7−/− triple knockout (TKO) mice to test whether IRF-5 was the source of the residual induction of IFN-β and ISGs in mDCs. In pathogenesis studies with two unrelated positive-sense RNA viruses (West Nile virus (WNV) and murine norovirus), TKO mice succumbed at rates greater than DKO mice and equal to or approaching those of mice lacking the type I IFN receptor (Ifnar−/−). In ex vivo studies, after WNV infection or exposure to Toll-like receptor agonists, TKO mDCs failed to produce IFN-β or express ISGs. In contrast, this response was sustained in TKO macrophages following WNV infection. To define IRF-regulated gene signatures, we performed microarray analysis on WNV-infected mDC from wild type (WT), DKO, TKO, or Ifnar−/− mice, as well as from mice lacking the RIG-I like receptor adaptor protein MAVS. Whereas the gene induction pattern in DKO mDC was similar to WT cells, remarkably, almost no ISG induction was detected in TKO or Mavs−/− mDC. The relative equivalence of TKO and Mavs−/− responses suggested that MAVS dominantly regulates ISG induction in mDC. Moreover, we showed that MAVS-dependent induction of ISGs can occur through an IRF-5-dependent yet IRF-3 and IRF-7-independent pathway. Our results establish IRF-3, -5, and -7 as the key transcription factors responsible for mediating the type I IFN and ISG response in mDC during WNV infection and suggest a novel signaling link between MAVS and IRF-5.

Partial Text

The type I interferon (IFN) signaling network is an essential component of the innate immune response against viral infections, and also functions to shape adaptive immunity [1]–[4]. Infected cells initiate an antiviral response upon recognition of non-self pathogen-associated molecular patterns (PAMPs), which are detected by host pattern recognition receptors (PRRs) [2], . PRRs that recognize RNA viruses include members of the Toll-like receptor (TLR3 and TLR7) and the RIG-I-like receptor (RLR; RIG-I and MDA5) families. TLRs and RLRs recognize distinct PAMPs in different locations (extracellular/endosomes and cytoplasm, respectively) and activate signaling cascades to initiate antiviral and inflammatory responses. TLR3 binds to double-stranded RNA and recruits the adaptor molecule TRIF to activate the kinases TRAF and IKK-ε, which in turn activates the latent transcription factors IRF-3, IRF-7, and NF-κB. Single-stranded RNA is recognized by TLR7, which uses the adaptor molecule MyD88 to activate TRAF and IKK-ε, and subsequently NF-κB- and IRF-7-dependent transcription. RLRs interact with the mitochondria-associated adapter molecule MAVS (also called IPS-1, VISA, or CARDIF), which signals through the kinases TBK1 and IKK-ε to activate IRF-3, IRF-7, and NF-κB and initiate type I IFN production.

In the present study, we generated Irf3−/−×Irf5−/−×Irf7−/− TKO mice to establish that these three IRF family transcription factors coordinately regulate IFN-β production and ISG expression in mDC. We found that antiviral gene induction was ablated almost entirely in mDC from TKO or Mavs−/− mice, suggesting a dominant role for MAVS in initiating the antiviral response and pointing to a novel signaling interaction between IRF-5 and the RLR signaling pathway.




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