A double-stranded RNA fish reovirus activates cGAS-STING signaling and evades antiviral immunity through autophagy-mediated degradation

Abstract Background Double-stranded RNA (dsRNA) reoviruses are primarily sensed by the RIG-I-like receptor (RLRs) signaling pathway. However, whether these viruses can also activate the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway, a central DNA-sensing system, remains poorly understood. Grass carp reovirus (GCRV), a highly virulent aquareovirus in the family Spinareoviridae , is the causative agent of hemorrhagic disease in grass carp, an economically important fish species in China. GCRV serves as an ideal model for investigating host-virus interactions during dsRNA reovirus infection. Methods Using GCRV as a reovirus model, we systematically examined the interaction between GCRV and cGAS-STING signaling pathways and investigated the mechanism underlying cGAS-STING activation. Functional analyses were performed to evaluate the antiviral role of cGAS-STING signaling and the viral immune evasion strategies used to counteract this response. Moreover, the involvement of viral proteins and host selective autophagy factors in immune evasion was further characterized. Results We show that GCRV infection activates both RLRs and cGAS-STING signaling pathways. GCRV infection induced mitochondrial membrane depolarization and cytosolic release of mitochondrial DNA, which was sensed by cGAS and triggered activation of the cGAS-STING pathway. Activation of the cGAS-STING pathway restricts GCRV replication, whereas the virus counteracts this antiviral response by inducing degradation of cGAS and STING. Mechanistically, the GCRV nonstructural protein NS26 hijacks the autophagy receptors Tollip and Parkin to promote lysosomal degradation of cGAS and STING via the autophagy-lysosome pathway. Functionally, NS26 enhances viral replication and suppresses host antiviral responses. Conclusions Our findings uncover a previously unrecognized mechanism by which a dsRNA fish reovirus manipulates host selective autophagy to antagonize cGAS-STING-mediated antiviral immunity. These results expand current understanding of cGAS-STING activation during dsRNA fish reovirus infection and highlight a potentially conserved immune evasion strategy shared by both RNA and DNA viruses.