STING Engages Distinct Antiviral Mechanisms to Restrict RNA Virus and DNA Virus Replication

Abstract

In mammalian cells, interferon (IFN) responses that occur during RNA and DNA virus infections are activated by distinct signaling pathways. The RIG-I-like-receptors (RLR) bind viral RNA and engage the adaptor MAVS to promote IFN expression, whereas cGAS binds viral DNA and activates an analogous pathway via the protein STING. While this suggests a simple dichotomy in the control of virus replication, multiple studies have suggested a role for the STING pathway in the control of RNA viruses, in addition to DNA viruses. In this study, we further elucidate the mechanism of the STING-dependent IFN induction as well as identify STING’s role in the control of RNA virus replication. In our first study, we confirm that STING is not necessary to induce IFN expression during RNA virus infection, but also find that STING is required to restrict the replication of diverse RNA viruses. The antiviral activities of STING were not linked to its ability to regulate basal expression of IFN-stimulated genes, activate transcription, or autophagy. Using vesicular stomatitis virus as a model, we identified a requirement of STING to inhibit translation during infection and upon transfection of synthetic RLR ligands. This inhibition occurs at the level of translation initiation, and restricts the production of both viral and host proteins. Genetic analysis linked RNA-sensing by RLRs to STING-dependent translation inhibition, independent of MAVS. Second, we identified a novel mechanism for the induction of STING-dependent IFN. We show that the sensing of transfected DNA in one cell can induce IFN production in an untransfected bystander cell. This signaling is dependent on enzymatically active cGAS in the transfected cell and STING in the bystander cell. We show that the presence of cGAMP, the product of cGAS, in one cell is sufficient to induce signaling in bystander cells. Signaling is dependent on gap junction intercellular communication. Taken together, we construct a model where cGAMP is transferred through gap junctions to bystander cells to induce interferon. Thus, this work establishes dual STING functions in host defense, regulating protein synthesis to prevent RNA virus infection and regulating IFN expression to restrict DNA viruses.