The antiviral action of the RIG-I induced pathway of apoptosis (RIPA) is enhanced by its ability to degrade Otulin, which deubiquitinates IRF3
- 20 September 2021
- journal article
- research article
- Published by Springer Science and Business Media LLC in Cell Death & Differentiation
- Vol. 29 (3), 504-513
- https://doi.org/10.1038/s41418-021-00870-4
Abstract
Mammalian innate immune response to virus infection is meditated by many cell-intrinsic pathways. RNA viruses, such as Sendai virus, which replicate in the cytoplasm, trigger the RIG-I-like receptor pathway, which activates the transcription factor, IRF3. Activated IRF3 translocates to the nucleus and induces transcription of the genes which encode interferons, the major antiviral cytokines. Interestingly, IRF3 activates another interferon-independent antiviral pathway, called RIG-I induced pathway of apoptosis (RIPA). For activating RIPA, IRF3 translocates from the cytoplasm to mitochondria. RIPA requires linear polyubiquitination of IRF3 by the enzyme complex, LUBAC; ubiquitinated IRF3 binds to Bax and translocates it to mitochondria causing the release of Cytochrome C, activation of caspases and apoptosis of the infected cell. Here, we report that Otulin, the deubiquitinase that removes linear polyubiquitin chains, inhibits RIPA by deubiquitinating IRF3. Ablation of Otulin expression enhanced RIPA and its overexpression inhibited RIPA. In virus-infected cells, to overcome Otulin-mediated inhibition, RIPA actively degrades Otulin. This degradation required sequential actions of RIPA-activated Caspase 3 and proteasomes. Caspase 3 cleaved Otulin at D31; the D31A mutant was not cleaved at all. The caspase-cleaved fragment was totally degraded by proteasomes, which was preceded by its K48-linked ubiquitination. Mass spectrometric analysis of Otulin identified K64 and K197 as the ubiquitinated residues. Otulin interacted with LUBAC after virus infection and the E3-ubiquitin ligase, HOIP, a component of LUBAC, ubiquitinated Otulin to trigger its proteasome-mediated degradation. To assess the impact of Otulin degradation on RIPA-mediated antiviral action, we expressed, in Otulin-ablated cells, a non-degradable mutant of Otulin, in which D31, K64 and K197 had been mutated. The cells expressing the Otulin mutant were less susceptible to virus-induced apoptosis, because RIPA was less active, and consequently virus replication was more robust. Thus, our study has revealed an important positive feedback loop of RIPA.Funding Information
- National Institutes of Health-Bethesda
This publication has 43 references indexed in Scilit:
- Linear Ubiquitination of NEMO Negatively Regulates the Interferon Antiviral Response through Disruption of the MAVS-TRAF3 ComplexCell Host & Microbe, 2012
- Intrinsic antiviral immunityNature Immunology, 2012
- Structural Insights into RNA Recognition by RIG-ICell, 2011
- RIG-I like receptors and their signaling crosstalk in the regulation of antiviral immunityCurrent Opinion in Virology, 2011
- Immune Signaling by RIG-I-like ReceptorsImmunity, 2011
- Phosphatidylinositol 3-Kinase Signaling Delays Sendai Virus-Induced Apoptosis by Preventing XIAP DegradationJournal of Virology, 2011
- Linear Ubiquitin Assembly Complex Negatively Regulates RIG-I- and TRIM25-Mediated Type I Interferon InductionMolecular Cell, 2011
- Viral apoptosis is induced by IRF-3-mediated activation of BaxThe EMBO Journal, 2010
- The tumour suppressor CYLD is a negative regulator of RIG‐I‐mediated antiviral responseEMBO Reports, 2008
- A ubiquitin ligase complex assembles linear polyubiquitin chainsThe EMBO Journal, 2006