The cGAS/STING–TBK1–IRF Regulatory Axis Orchestrates a Primitive Interferon-Like Antiviral Mechanism in Oyster

Abstract

Interferon (IFN) system is considered as the first defense line against viral infection, and it has been extensively studied in vertebrates from fish to mammals. In invertebrates, Vagos from arthropod and IFN-like protein (<i>Cg</i>IFNLP) from <i>Crassostrea gigas</i> appeared to function as IFN-like antiviral cytokines. In the present study, the <i>Cg</i>IFNLP protein in hemocytes was observed to increase after Poly (I:C) stimulation. After <i>Cg</i>IFNLP was knocked down by RNAi, the mRNA expression of IFN-stimulated genes (<i>Cg</i>ISGs) was significantly inhibited. Both cyclic GMP-AMP synthase (<i>Cg</i>cGAS) and stimulator of interferon gene (<i>Cg</i>STING) identified from oyster were able to recognize the double-stranded nucleic acid [Poly (I:C) and dsDNA] and expressed at high level after Poly (I:C) stimulation. The expression of <i>Cg</i>IFNLP and interferon regulatory factors (<i>Cg</i>IRF1/8) and the nuclear translocation of <i>Cg</i>IRF8 were all suppressed in <i>Cg</i>cGAS-RNAi or <i>Cg</i>STING-RNAi oysters after Poly (I:C) stimulation. The expression level of <i>Cg</i>STING and TANK binding kinase1 (<i>Cg</i>TBK1) did not decrease in <i>Cg</i>cGAS-RNAi oysters. After <i>Cg</i>STING was knocked down, the high expression of <i>Cg</i>TBK1 induced by Poly (I:C) was prevented significantly. These results indicated that there was a primitive IFN-like antiviral mechanism dependent on the cGAS/STING-TBK1-IRFs regulatory axis in mollusks, which was different from the classic cGAS-STING-TBK1 signal pathway in mammals.