Zebrafish IRF1 Regulates IFN Antiviral Response through Binding to IFNϕ1 and IFNϕ3 Promoters Downstream of MyD88 Signaling

Abstract

In mammals, type I IFNs (mainly IFN-α/β) are primarily regulated by transcription factors of the IFN regulatory factor (IRF) family. Fish IFNs do not show a one-to-one orthologous relationship with mammalian type I IFN homologues. Using a bacterial one-hybrid reporter screening system and an overexpression approach to explore the molecular mechanism underlying fish IFN induction, we identified zebrafish Danio rerio IRF (DrIRF)1 as a positive regulator of the fish IFN antiviral response. Among 12 zebrafish IRF family genes, DrIRF1 is most abundant in zebrafish immune tissues, including head kidney and spleen; upon virus infection, it is one of most significantly induced genes. Overexpression of DrIRF1 induces the expression of IFN and IFN-stimulated genes, hence protecting epithelioma papulosum cyprini cells against spring viremia of carp virus infection. As a transcription factor with constitutively nuclear retention, DrIRF1 directly binds to the IFN-stimulated regulatory element/IRF-binding element sites of zebrafish IFN promoters, which are dependent on four conserved amino acids of the N-terminal DNA-binding domain helix α3 motif. Mutation of either residue reveals a differential requirement for DrIRF1-mediated activation of zebrafish IFNϕ1 and IFNϕ3 promoters. Notably, C-terminal phosphorylation of DrIRF1 is observed and is not required for in vitro binding of DrIRF1 to fish IFN promoters. Unlike DrIRF3 and DrIRF7, which are responsible for differential expression of zebrafish IFNϕ1 and IFNϕ3 through the retinoic acid–inducible gene I–like receptor pathway, DrIRF1 works in concert with MyD88 to activate zebrafish IFNϕ3 but not IFNϕ1. These results provide insights into the evolving function of IRF1 as a positive IFN regulator.

Fish IRF6 is a positive regulator of IFN expression and involved in both of the MyD88 and TBK1 pathways

“…A few IRFs are involved in these two signaling pathways. In mammals, IRF5 participates in the MyD88 pathway to activate IFN expression, and fish IRF1 is downstream of MyD88 as a pivotal regulator of IFN [21]. On the other hand, IRF3 is a crucial transcription factor that is phosphorylated by TBK1 in both mammals and fish [15].…”

The kinetics and protection of the antiviral state induced by recombinant iIFN1a in rainbow trout against infectious hematopoietic necrosis virus

“…The response of the liver was delayed, compared to the head kidney and spleen. Fish IRF-1 functions as a transcriptional activator for IFN and IFN-inducible genes (Feng et al, 2015). Compared to other genes, the IRF-1 induced in the head kidney gave long-lasting expression that benefitted the initial potency of the antiviral response.…”

“…The type I IFNs bind to specific cell surface receptors to induce the JAK-STAT signaling pathway that results in the expression of a set of antiviral proteins . Many molecules (MAVS,IRF1 and viperin) have been proven to exert conserved functions in fish (Feng et al, 2015;Wang et al, 2014;Zhang et al, 2014). Additionally, identification of the novel fish-specific antiviral genes (Gig1, Gig2 and DreI) has shown that fish type I IFNs can function in a unique way (Li et al, 2012;Sun et al, 2014).…”

Zebrafish foxo3b Negatively Regulates Antiviral Response through Suppressing the Transactivity of irf3 and irf7

“…Anti-irf7 Ab was obtained from Shun Li (Institute of Hydrobiolgy, Chinese Academy of Science). Dominant-negative (DN) forms of irf3 and irf7 were cloned into pCMVMyc (Clontech) and pCMV-HA (Clontech) as described previously and subcloned into the psp64 vector (38). GFP and myc-tagged foxo3b in the psp64 vector were described previously (35).…”