Zebrafish IRF1, IRF3, and IRF7 Differentially Regulate IFNΦ1 and IFNΦ3 Expression through Assembly of Homo- or Heteroprotein Complexes

Abstract

In mammals, IFN regulatory factor (IRF)1, IRF3, and IRF7 are three critical transcription factors that are pivotal for cooperative regulation of the type I IFN response. In this study, we explored the relative contribution of zebrafish (Danio rerio) IRF1 (DrIRF1), IRF3 (DrIRF3), and IRF7 (DrIRF7) (DrIRF1/3/7) to zebrafish IFNΦ1 (DrIFNΦ1) and IFNΦ3 (DrIFNΦ3) (DrIFNΦ1/3) activation. Following spring viremia of carp virus infection, DrIFNΦ1/3 and DrIRF1/3/7 transcripts are significantly induced in zebrafish tissues, which correlates with the replication of spring viremia of carp virus. DrIRF1/3/7 selectively bind to the IRF-binding element/IFN-stimulated regulatory element sites of DrIFNΦ1/3 promoters, with the exception that DrIRF3 has no preference for two IRF-binding element/IFN-stimulated regulatory element motifs within the DrIFNΦ3 promoter. Consistently, DrIRF3 alone activates DrIFNΦ1, but not DrIFNΦ3; DrIRF7 predominantly stimulates DrIFNΦ3; and DrIRF1 has similar potential to DrIFNΦ1 and DrIFNΦ3. Strikingly, DrIRF3 facilitates the binding of DrIRF1 and DrIRF7 to both zebrafish IFN promoters, and so does DrIRF7 for the binding of DrIRF1, particularly to the DrIFNΦ3 promoter. These binding properties correlate with differential responses of DrIFNΦ1 and DrIFNΦ3 to the combinatory stimulation of DrIRF1/3/7, depending on their relative amounts. Similar to the dual roles of human IRF3 in regulating IRF7-activated IFNα genes, DrIRF3 exerts dual effects on DrIRF1-mediated DrIFNΦ3 gene expression: an inhibitory effect at lower concentrations and a synergistic effect at higher concentrations. These data provide evidence that fish and mammals have evolved a similar IRF-dependent regulatory mechanism fine-tuning IFN gene activation.

Beta-glucan enhances the response to SVCV infection in zebrafish

“…infected cells. In the zebrafish ZFL cell line, SVCV rapidly activates ifnphi1 and ifnphi3 expression from 12 to 24 hpi (Feng, 2016) although times of SVCV infection later than 24 hpi were not examined in that study.…”

Zebrafish RPZ5 Degrades Phosphorylated IRF7 To Repress Interferon Production

“…Fish IRF7 is a true ortholog of mammalian IRF7. A recent study showed that fish IRF7 is also involved in regulating IFN expression and undergoes phosphorylation (33). Nevertheless, little is known about the regulation mechanisms of IRF7 activity in fish.…”

The Peculiar Characteristics of Fish Type I Interferons

“…A transgenic reporter zebrafish identified hepatocytes and neutrophils as the two main cell types expressing IFNφ1 (group I) in larvae upon alphavirus infection [34]; a more recent IFNφ3 (group II) reporter line suggests a completely non-overlapping pattern of expression, including fibroblasts (Briolat, Lutfalla, and Levraud, unpublished result). The contributions of IRF1/3/7 to the induction of IFNφ1 and IFNφ3 have been studied in vitro, providing first insights for anatomical complementarity of different IFN [35], as detailed below. In grass carp ( Ctenopharyngodon idella ), four type I IFN were also identified, CiIFN1 and four with two cysteines (group I) and CiIFN2 and three with four cysteines (group II); group II IFNs were transiently induced in gills and spleen by GCRV infection in adult fish, while CiIFN1 was constitutively expressed in gills, spleen, liver and gut, and CiIFN4 was never detectable in any condition tested [36].…”

“…When the reporters were activated by an “upstream” trigger (such as overexpression of TBK-1), expression of a dominant negative version of either IRF3 or IRF7 (but not IRF1) inhibited luciferase production [40,42]. Further biochemical studies indicated that these three IRFs can either homo- or hetero-dimerize and suggested that IRF3 facilitates the binding of IRF1 or IRF7 to the promoters [35]. In summary, the zebrafish IFNφ1 promoter is predominantly controlled by IRF3, and IFNφ3 by IRF7, like IFNβ and IFNα, respectively.…”