TRIMming viral infection: identification and characterization of the novel antiviral TRIM7

Abstract

Abstract Noroviruses (NoVs) are the leading cause of acute viral gastroenteritis worldwide, causing up to 700 million infections and 200,000 deaths annually, and treatment is limited to supportive care as there are currently no targeted antivirals nor vaccines against NoVs. Therefore, it is critical to discover novel antivirals and develop targeted interventions in order to improve outcomes. Here we have used a novel genome-wide CRISPR activation screening approach to identify host genes that can inhibit murine norovirus (MNoV) infection or replication. A substantial number of high scoring gene candidates acted in interferon and immune regulation signaling networks, but several were not previously associated with antiviral activity or immunity. TRIM7, the strongest screen hit, was a little studied E3 ubiquitin ligase associated with metabolism and some cancers, yet its expression served as a powerful antiviral in an MNoV-infected cell. Since our initial screen, TRIM7 has begun to emerge as a strategic player in both positive and negative regulation of the innate immune response during infection. We have since characterized the antiviral mechanism of action of TRIM7 against MNoV in vitro, and have found TRIM7 to be acting early in the viral life cycle to limit viral protein production. Co-immunoprecipitation and in vitro viral evolution experiments have identified MNoV NS6 (viral protease) and NS7 (RNA-dependent RNA polymerase) as important targets of the antiviral activity of TRIM7, and also point to key residues of interest associated with MNoV resistance to TRIM7. Finally, we have investigated the relevance of TRIM7 during in vivo infection using knock-in mouse lines to determine tissue specificity and potency of the antiviral effect.