Activation of duck RIG-I by TRIM25 is independent of anchored ubiquitin.
Retinoic acid inducible gene I (RIG-I) is a viral RNA sensor crucial in defense against several viruses including measles, influenza A and hepatitis C. RIG-I activates type-I interferon signalling through the adaptor for mitochondrial antiviral signaling (MAVS). The E3 ubiquitin ligase, tripartite motif containing protein 25 (TRIM25), activates human RIG-I through generation of anchored K63-linked polyubiquitin chains attached to lysine 172, or alternatively, through the generation of unanchored K63-linked polyubiquitin chains that interact non-covalently with RIG-I CARD domains. Previously, we identified RIG-I of ducks, of interest because ducks are the host and natural reservoir of influenza viruses, and showed it initiates innate immune signaling leading to production of interferon-beta (IFN-β). We noted that K172 is not conserved in RIG-I of ducks and other avian species, or mouse. Because K172 is important for both mechanisms of activation of human RIG-I, we investigated whether duck RIG-I was activated by TRIM25, and if other residues were the sites for attachment of ubiquitin. Here we show duck RIG-I CARD domains are ubiquitinated for activation, and ubiquitination depends on interaction with TRIM25, as a splice variant that cannot interact with TRIM25 is not ubiquitinated, and cannot be activated. We expressed GST-fusion proteins of duck CARD domains and characterized TRIM25 modifications of CARD domains by mass spectrometry. We identified two sites that are ubiquitinated in duck CARD domains, K167 and K193, and detected K63 linked polyubiquitin chains. Site directed mutagenesis of each site alone, does not alter the ubiquitination profile of the duck CARD domains. However, mutation of both sites resulted in loss of all attached ubiquitin and polyubiquitin chains. Remarkably, the double mutant duck RIG-I CARD still interacts with TRIM25, and can still be activated. Our results demonstrate that anchored ubiquitin chains are not necessary for TRIM25 activation of duck RIG-I.
Department of Biological Sciences and the Li Ka Shing Institute of Virology, University of Alberta, Edmonton, Alberta, Canada.
Domingo
D
Miranzo-Navarro
Department of Biological Sciences and the Li Ka Shing Institute of Virology, University of Alberta, Edmonton, Alberta, Canada.
Katharine E
KE
Magor
D017398:Alternative Splicing / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D053468:CARD Signaling Adaptor Proteins / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D002645:Chickens; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases / Q000235:genetics / Q000378:metabolism*; D004372:Ducks / Q000821:virology; D006801:Humans; D007113:Immunity, Innate; D047468:Immunoprecipitation; D009980:Influenza A virus / Q000502:physiology; D016899:Interferon-beta / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009976:Orthomyxoviridae Infections / Q000235:genetics / Q000378:metabolism / Q000821:virology; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D011971:Receptors, Immunologic; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D053719:Tandem Mass Spectrometry; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D000070584:Tripartite Motif Proteins; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination
D053468:CARD Signaling Adaptor Proteins; D012333:RNA, Messenger; D011971:Receptors, Immunologic; D014157:Transcription Factors; D000070584:Tripartite Motif Proteins; D025801:Ubiquitin; D016899:Interferon-beta; C084523:TRIM25 protein, human; D044767:Ubiquitin-Protein Ligases; C452820:RIGI protein, human; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases