Stress granules in virus infections - Stress granules (SG) are non-membranous, phase-separated complexes of stalled mRNA, translation factors and RNA binding proteins that are formed transiently in the cytoplasm in response to diverse stress signals, including viral infections. SG formed during viral infection, antiviral stress granules (avSG), are distinct from canonical SG in that they recruit antiviral proteins and components of signaling pathways to function as a platform to mount an effective antiviral response. However, the composition, temporal changes and function of avSG during viral infections are still poorly understood. The dynamic nature of SG suggest that host cells use avSG as a signaling hub for antiviral defense. On the other hand, viruses have evolved mechanisms to antagonize SG formation and repurpose SG to facilitate replication highlighting an important role in viral pathogenesis. How the stress-specific differences in SG composition, assembly and dynamics impact the outcome of viral infections remains unclear and represents a critical gap in our understanding of signaling events and host-virus interactions. Our recent work has highlighted a role for avSG as a platform for the activation of pattern recognition receptors (PRRs) by dsRNA pathogen associated molecular patterns (PAMPs) and subsequent interferon (IFN) response during viral infections. DsRNAs produced during viral infections serve as PAMPs to stimulate interferon (IFN) production by binding the cytosolic Rig-like helicases (RLHs), endosomal Toll-like receptors (TLRs), dsRNA-dependent protein kinase (PKR) or 2’-5’oligoadenylate synthetase (OAS). Furthermore, virus infection induces degradation of viral and cellular RNAs by the activity of interferon-induced endoribonuclease, RNase L. We have recently shown that dsRNA products of RNase L activity function as PAMPs and activate PKR, phosphorylate eukaryotic translation initiation factor-2 (eIF2) to suppress translation and induce avSG formation. Our results demonstrate that avSG assembly provides a platform for efficient interaction of RNA ligands with PRRs to enhance interferon production and antiviral effect. Our overarching hypothesis for this proposal is that composition, assembly and disassembly of avSG change during viral infection to allow host cells to respond and clear infection by limiting damage. In preliminary studies we show that activation of RNase L induces avSG formation marked by SG protein, G3BP1 and contain antiviral proteins Rig-I, PKR, OAS and RNase L. We developed a novel method to purify avSG and biochemically characterized protein-protein interactions in avSG that will be used in this proposal. We will test our central hypothesis with the following specific aims. Aim 1: To determine stress-specific differences in SG composition in canonical SG and avSG, Aim 2: To determine the physiological role of dynamic change in avSG composition in virus infections. Completion of these aims will allow us to build on the advances in purifying avSG to dissect the antiviral role of SG by following the dynamics of assembly or disassembly and analyzing the avSG composition to provide correlation of stress response pathways and innate signaling.
