MicroRNA miR-722 Inhibits Cyprinid Herpesvirus 3 Replication via Targeting the Viral Immune Evasion Protein ORF89, Which Negatively Regulates IFN by Degrading IRF3.

Cyprinid herpesvirus 3 (CyHV-3) has caused severe economic losses to carp culture, but its pathogenicity is far from clear. Our previous study has revealed that microRNA (miR)-722 was upregulated during CyHV-3 infection, indicating that miR-722 might play an important role in CyHV-3 replication. In this study, we found that overexpression of miR-722 inhibited CyHV-3 replication and promoted IFN expression. The putative target gene of miR-722 was searched over the CyHV-3 genome, and ORF89 was identified and validated as a target gene of miR-722. Overexpression of ORF89 markedly reduced the expression of IFN and IFN-stimulated genes. Mechanistically, ORF89 interacted with and degraded IFN regulatory factor 3 (IRF3), and inhibited the entry of IRF3 into the nucleus by suppressing the dimerization of IRF3. Moreover, ORF89-mediated suppression of IFN expression could be restored by adding miR-722. To our knowledge, our findings confirm a novel virus-host combat, in which CyHV-3 evades host antiviral immunity by its ORF89 protein, whereas host miR-722, upregulated on CyHV-3 infection, targets ORF89 to impede CyHV-3 replication.