Spliceosome SNRNP200 promotes viral RNA sensing and IRF3 activation of antiviral response
The innate immune system is the first line of defense against invading pathogens of many kind such as bacteria, viruses, parasites and fungi. Its role is straightforward: it acts within minutes of a pathogenic engagement to control and restrict the microscopic invasion using non-specific mechanisms while the host mounts an induced, and specific, innate and adaptive response. To identify new regulators of antiviral innate immunity, we have completed the first genome-wide gene RNAi screen assessing the transcriptional response at the interferon-β (IFNB1) promoter following Sendai virus (SeV) infection. Interestingly, a Gene Set Enrichment Analysis (GSEA) of the 114 gene hits revealed that many of these proteins were spliceosome-associated. Among them, we further prioritized the characterization of SNRNP200, a core and unique spliceosomal member of the Ski2-like RNA helicase family based on its structural similarities to other antiviral RNA helicase like RIG-I and MDA5. In this thesis, we provide evidence for a role of the spliceosomal SNRNP200 that is clearly distinguishable of the one in pre-mRNA splicing. Indeed, the depletion of SNRNP200 in human cells resulted in a reduced antiviral response and increased susceptibility to viral infection. We specifically showed that SNRNP200 positively regulates activation of the key antiviral transcriptional factor IRF3 via a protein-protein interaction with the serine/threonine-protein kinase TBK1. Additionally, we showed that upon infection, SNRNP200 binds viral RNA and relocalizes into TBK1-containing cytoplasmic structures to promote innate signaling. Of clinical relevance, we observed a significantly hindered antiviral response of PBMCs from patients carrying a dominant SNRNP200 mutation associated to the retina pigmentosa type 33 (RP33), an inherited degenerative eye disease. We showed that expression of the RP33-associated mutant has lost the ability to bind RNA and to rescue antiviral response in SNRNP200 silenced cells. Thus, this thesis provides new insights into an immunoregulatory role of spliceosome SNRNP200 acting as an RNA sensor and adaptor of TBK1 to promote IRF3 signaling in antiviral response.
RIG-I SNRNP200 IRF3 TBK1 RNAi screen Innate Antiviral Immunity Sendai Virus Type I Interferon RLR Pathway Signalling Viral RNA Sensor Adaptor Protein Retinitis Pigmentosa