How cells tell the difference between their own mRNAs and RNA species of potential viral origin is an essential part of the first line of defence in mammals. TRIM25 is a member of the Tripartite Motif family of E3 ubiquitin ligases that plays a central role in innate intracellular immunity to a wide range of RNA viruses. In turn, a variety of these viruses have evolved countermeasures that inhibit TRIM25. While TRIM25 was thought to be the main regulator of the RIG-I pattern recognition receptor for cytoplasmic viral RNA species, this has now been shown to be untrue.
So what does TRIM25 actually do?
We have worked extensively on how TRIM25 regulates RNA-binding proteins that target and degrade viral RNAs. Of note, we have recently shown TRIM25 targets the Ebola virus ribonucleoprotein (vRNP) complex to dissociate viral proteins from the viral genome and expose it to the antiviral protein ZAP (see figure). In this project, the student will elucidate the mechanism of action of TRIM25 against diverse medically important negative strand RNA viruses (influenza A virus, measles virus, respiratory syncytial virus as well a safe replication defective Ebola virus system). Techniques may include: infecting cells with viruses, whole cell proteomic analyses, global identification of ubiquitinated proteins, CRISPR/RNAi screens, confocal imaging and RNA virus reverse genetics.
Year 1: Establish cell and virological assays to identify and understand the role of cellular RNA species that regulate TRIM25 antiviral activity against negative-strand RNA viruses.
Year 2: Determine how RNA-binding by TRIM25 allows it to ubiquitinate viral and cellular proteins with K63- and K27-linked chains and how this exposes viral genomes to ZAP and other antiviral RNA-binding proteins.
Year 3: Use live cell imaging to understand where and when these antiviral processes happen in the cell.