HRI of Epinephelus coioides is a critical factor in the grouper immune response to RGNNV infection.

Phosphorylation of eukaryotic initiation factor 2 alpha subunit (eIF2α) occurs under a variety of conditions, including viral infection. Heme-regulated inhibitor (HRI) is an eIF2α kinase that modifies this phosphorylation. In this study, a HRI homologue (EcHRI) from the orange-spotted grouper (Epinephelus coioides) was cloned and its roles during fish viral infection were characterized. EcHRI encodes a 664-amino acid polypeptide that shares a high degree of similarity with HRIs from other species. Quantitative real-time polymerase chain reaction analysis indicated that EcHRI was distributed in all examined tissues. Expression of EcHRI in the spleen of E. coioides was up-regulated when challenged with the synthetic analog of double-stranded RNA (dsRNA) of polyinosine-polycytidylic acid (poly I:C). EcHRI was significantly increased in red-spotted grouper nervous necrosis virus (RGNNV) infected cells. EcHRI was abundantly distributed in the nucleus of grouper spleen (GS) cells. Overexpression of EcHRI inhibited the expression of red-spotted grouper nervous necrosis virus (RGNNV) genes in GS cells. Furthermore, our results showed that EcHRI overexpression significantly increased the expression of interferon (IFN)-related cytokines and enhanced activation of IFN-β, interferon-sensitive response element (ISRE), and nuclear factor κB (NF-κB). Taken together, these results suggest that EcHRI is involved in the fish immune response to virus challenge.