Identification and functional characterization of an interferon regulatory factor 7-like (IRF7-like) gene from orange-spotted grouper, Epinephelus coioides

Interferon regulatory factor (IRF) 7 plays a crucial role in modulating cellular responses to viral infection and cytokines, including interferons (IFNs). In the present study, a novel IRF7 gene (designated as EcIRF7) was cloned and characterized from orange-spotted grouper, Epinephelus coioides. The full-length EcIRF7 cDNA is composed of 2089 bp and encodes a polypeptide of 433 amino acids with 81% identity to IRF7 of Siniperca chuatsi, and the genomic DNA of EcIRF7 consists of 9 exons and 8 introns, with a length of approximately 5629 bp. EcIRF7 contains three conserved domains including a DNA-binding domain (DBD), an IRF associated domain (IAD) and a serine-rich domain, all of which are highly conserved across species. Recombinant EcIRF7 was expressed in Escherichia coli BL21 (DE3) and purified for mouse anti-EcIRF7 serum preparation. Realtime quantitative PCR (RT-qPCR) analysis revealed a broad expression of EcIRF7, with a relative strong expression in spleen, kidney, skin and intestine. The expression of EcIRF7 was differentially up-regulated after stimulation with Vibrio vulnificus, Staphylococcus aureus and Singapore grouper iridovirus (SGIV). EcIRF7 showed similar intracellular localization pattern to those of mammalian and chicken, and translocated into nucleus after SGIV infection. Further more, EcIRF7 was proved to be capable of activating zebrafish type I IFN promoter and inhibiting the replication of SGIV in grouper spleen (GS) cells. These results suggest that EcIRF7 is potentially involved in grouper immune responses to invasion of viral and bacterial pathogens.