OTUB1 is a key regulator of RIG-I dependent immune signalling and is targeted for proteasomal degradation by influenza A NS1

Abstract

Running title: OTUB1 activates RIG-I during influenza virus infections Highlights 1. OTUB1 is induced during influenza A virus infections in an IFN-I dependent manner 2. OTUB1 regulates the RIG-I complex by hydrolysing K48-linked polyubiquitin chains and by sequestering UBCH5c to prevent K48 polyubiquitylation 3. Optimal K63 versus K48 polyubiquitin chain concentrations determine RIG-I activation 4. Influenza NS1 targets OTUB1 for proteasomal degradation Summary Deubiquitylases (DUBs) regulate critical signaling pathways at the intersection of host innate immunity and viral pathogenesis. Although RIG-I activation is heavily dependent on ubiquitylation, DUBs that regulate this pathway have not been identified. Using a ubiquitin C-terminal electrophile, we profiled DUBs that function during influenza A virus (IAV) infection, and isolated OTUB1 as a key regulator of RIG-I dependent antiviral responses. OTUB1 was interferon-inducible, and interacted with RIG-I, viral PB2 and NS1. Upon infection, OTUB1 relocalised from the nucleus to mitochondrial membranes, and activated the RIG-I signaling complex via hydrolysis of K48 polyubiquitin chains and by forming a repressive complex with UBCH5c. Using a reconstituted system composed of in vitro translated [ 35 S]IRF3, purified RIG-I, mitochondrial membranes and cytosol expressing OTUB1 variants, we recapitulated the mechanism of OTUB1dependent RIG-I activation. A wide range of IAV NS1 proteins triggered proteasomal degradation of OTUB1, thereby antagonizing the RIG-I signaling cascade and antiviral responses.

Identification and characterization of interactions between Influenza A Virus NS1 protein and the human ubiquitin proteasome system

“…NS1 is described as the main IAV virulence factor, acting by direct interactions with cellular proteins or through the regulation of host genes expression, a process named host shut-off (17)(18)(19)(20)(21)(22)(23)(24)(25). In addition to TRIM25, some other perturbations of UPS factors by NS1 were described, such as the regulation of the MDM2 E3 ligase, OTUB1 DUB, and A20 E3 ligase/DUB (26)(27)(28)(29)(30).…”