Abstract
Innate immunity plays a pivotal role in virus infection. RIG-I senses viral RNA and initiates an effective innate immune response for type I interferon production. To transduce RIG-I-mediated antiviral signalling, a mitochondrial protein MAVS forms prion-like aggregates to activate downstream kinases and transcription factors. However, the activation mechanism of RIG-I is incompletely understood. Here we identify two ubiquitin enzymes Ube2D3 and Ube2N through chromatographic purification as activators for RIG-I on virus infection. We show that together with ubiquitin ligase Riplet, Ube2D3 promotes covalent conjugation of polyubiquitin chains to RIG-I, while Ube2N preferentially facilitates production of unanchored polyubiquitin chains. In the presence of these polyubiquitin chains, RIG-I induces MAVS aggregation directly on the mitochondria. Our data thus reveal two essential polyubiquitin-mediated mechanisms underlying the activation of RIG-I and MAVS for triggering innate immune signalling in response to viral infection in cells.
Highlights
Innate immunity plays a pivotal role in virus infection
To mimic viral infection-induced innate immune signalling in cells, the genomic RNA was extracted from vesicular stomatitis virus (VSV) and used as a stimulus
In the cell-free assay, MAVS aggregation was dependent on RIG-I, as VSV RNA (vRNA) could not induce MAVS aggregation in Rig-i À / À cell lysate under the same condition
Summary
Innate immunity plays a pivotal role in virus infection. RIG-I senses viral RNA and initiates an effective innate immune response for type I interferon production. Our data reveal two essential polyubiquitin-mediated mechanisms underlying the activation of RIG-I and MAVS for triggering innate immune signalling in response to viral infection in cells. Other E3 ubiquitin ligases such as Riplet ( known as RNF135/REUL), MEX3C and TRIM4, were reported to regulate RIG-I pathway positively, through a covalent conjugation of polyubiquitin chains to RIG-I21–24 Both the relative contributions of these E3 ubiquitin ligases to RIG-I activation and the coordination of their functions in RIG-I-mediated antiviral signalling are poorly understood. With loss-of-function analysis in both human and mouse cells, we determine that Riplet, rather than other E3 ubiquitin ligases, such as TRIM25 as previously reported, is the only E3 ubiquitin ligase that is required for RIG-I to activate MAVS in the early phase production of type I IFN. The Ube2N-Riplet pair could catalyse the formation of unanchored polyubiquitin chains, which is potent in facilitating MAVS aggregation and activation by RIG-I
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
