Singapore grouper iridovirus VP128 inhibits STING-TBK1 mediated signaling to evade antiviral immunity.

Singapore grouper iridovirus (SGIV) belongs to the family Iridoviridae and the genus Ranavirus, which is a large cytoplasmic DNA virus. Infection of grouper with SGIV can cause hemorrhage and swelling of the spleen of the fish. Previous work on genome annotation demonstrated that SGIV contained numerous uncharacterized or hypothetical open reading frames (ORFs), whose functions remained largely unknown. In the present study, the protein encoded by SGIV ORF128 (VP128) was identified. VP128 is predominantly localized within the endoplasmic reticulum (ER). Overexpression of VP128 significantly promoted SGIV replication. VP128 inhibited the interferon (IFN)-3 promoter activity and mRNA level of IFN-related genes induced by poly(I:C), Epinephelus coioides cyclic GMP/AMP synthase (EccGAS)/stimulator of IFN genes (EcSTING), and TANK-binding kinase 1 (EcTBK1). Moreover, VP128 interacted with EcSTING and EcTBK1. The interaction between VP128 and EcSTING was independent of any specific structural domain of EcSTING. Together, our results demonstrated that SGIV VP128 negatively regulated the IFN response by inhibiting EcSTING-EcTBK1 signaling for viral evasion.