Transcriptional regulation of type I interferon gene expression by interferon regulatory factor-3 in Japanese flounder, Paralichthys olivaceus

► Japanese flounder type I IFN gene was cloned and clustered with Acanthopterygii. ► The poly I:C-responsible region (−634 to −179bp) was found in IFN promoter. ► Transcriptional activity of IFN promoter was enhanced by the flounder IRF3. ► The activity of IFN promoter was induced by RLRs after poly I:C-stimulation. Type I interferon (IFN) induces the antiviral response in innate immunity. The type I IFN gene cloned from Japanese flounder (Paralichthys olivaceus) has a length of 1189bp and consisting of 5 exons and 4 introns. In a phylogenetic tree of type I IFNs, Japanese flounder grouped with other Acanthopterygii. To gain insight into the transcriptional regulation of IFN gene, the 1.36kb 5′-upstream region including numerous canonical motifs to bind transcription factors [for example, IFN regulatory factor (IRF)] was analyzed. In HINAE cells using a luciferase reporter assay, poly I:C-responsive transcriptional activity was found in the region from −634 to −179bp. This region includes several IRF motifs. In the presence of poly I:C, overexpression of IRF3 and RLR strongly enhanced transcriptional activity. These results suggest that the transcriptional regulation of Japanese flounder type I IFN is regulated by IRF3 after triggering with dsRNA sensors.