title: Species-specific inhibition of RIG-I ubiquitination and IFN induction by the influenza A virus NS1 protein.
abstract: Influenza A viruses can adapt to new host species, leading to the emergence of novel pathogenic strains. There is evidence that highly pathogenic viruses encode for non-structural 1 (NS1) proteins that are more efficient in suppressing the host immune response. The NS1 protein inhibits type-I interferon (IFN) production partly by blocking the TRIM25 ubiquitin E3 ligase-mediated Lys63-linked ubiquitination of the viral RNA sensor RIG-I, required for its optimal downstream signaling. In order to understand possible mechanisms of viral adaptation and host tropism, we examined the ability of NS1 encoded by human (Cal04), avian (HK156), swine (SwTx98) and mouse-adapted (PR8) influenza viruses to interact with TRIM25 orthologues from mammalian and avian species. Using co-immunoprecipitation assays we show that human TRIM25 binds to all tested NS1 proteins, whereas the chicken TRIM25 ortholog binds preferentially to the NS1 from the avian virus. Strikingly, none of the NS1 proteins were able to bind mouse TRIM25. Since NS1 can inhibit IFN production in mouse, we tested the impact of TRIM25 and NS1 on RIG-I ubiquitination in mouse cells. While NS1 efficiently suppressed human TRIM25-dependent ubiquitination of RIG-I 2CARD, NS1 inhibited the ubiquitination of full-length mouse RIG-I in a mouse TRIM25-independent manner. Therefore, we tested if the ubiquitin E3 ligase Riplet, which has also been shown to ubiquitinate RIG-I, interacts with NS1. We found that NS1 binds mouse Riplet and inhibits its activity to induce IFN-β in murine cells. Furthermore, NS1 proteins of human but not swine or avian viruses were able to interact with human Riplet, thereby suppressing RIG-I ubiquitination. In conclusion, our results indicate that influenza NS1 protein targets TRIM25 and Riplet ubiquitin E3 ligases in a species-specific manner for the inhibition of RIG-I ubiquitination and antiviral IFN production.
authors.affiliation: Department of Microbiology, Mount Sinai School of Medicine, New York, New York, United States of America.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Rajsbaum
authors.forename: Randy A
authors.initials: RA
authors.lastname: Albrecht
authors.forename: May K
authors.initials: MK
authors.lastname: Wang
authors.forename: Natalya P
authors.initials: NP
authors.lastname: Maharaj
authors.forename: Gijs A
authors.initials: GA
authors.lastname: Versteeg
authors.forename: Estanislao
authors.initials: E
authors.lastname: Nistal-Villán
authors.forename: Adolfo
authors.initials: A
authors.lastname: García-Sastre
authors.forename: Michaela U
authors.initials: MU
authors.lastname: Gack
mesh_terms: D000818:Animals; D002522:Chlorocebus aethiops; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004285:Dogs; D006367:HeLa Cells; D006801:Humans; D009980:Influenza A virus / Q000235:genetics / Q000378:metabolism*; D007251:Influenza, Human / Q000235:genetics / Q000378:metabolism*; D007372:Interferons / Q000096:biosynthesis* / Q000235:genetics; D051379:Mice; D018345:Mice, Knockout; D011971:Receptors, Immunologic; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D000070584:Tripartite Motif Proteins; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism; D054875:Ubiquitination; D014709:Vero Cells; D017361:Viral Nonstructural Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; C085820:INS1 protein, influenza virus; D011971:Receptors, Immunologic; D014157:Transcription Factors; C490034:Trim25 protein, mouse; D000070584:Tripartite Motif Proteins; D017361:Viral Nonstructural Proteins; D007372:Interferons; C557200:Rnf135 protein, mouse; C084523:TRIM25 protein, human; D044767:Ubiquitin-Protein Ligases; C452820:RIGI protein, human; C503356:Ddx58 protein, mouse; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases