[Source: PLoS Pathogens, full text: (LINK). Abstract, edited.]
Species-Specific Inhibition of RIG-I Ubiquitination and IFN Induction by the Influenza A Virus NS1 Protein
Ricardo Rajsbaum1,2, Randy A. Albrecht1,2, May K. Wang3, Natalya P. Maharaj3, Gijs A. Versteeg1,2, Estanislao Nistal-Villán1¤, Adolfo García-Sastre1,2,4*, Michaela U. Gack3*
1 Department of Microbiology, Mount Sinai School of Medicine, New York, New York, United States of America, 2 Global Health and Emerging Pathogens Institute, Mount Sinai School of Medicine, New York, New York, United States of America, 3 Department of Microbiology and Immunobiology, New England Primate Research Center, Harvard Medical School, Southborough, Massachusetts, United States of America, 4 Department of Medicine, Mount Sinai School of Medicine, New York, New York, United States of America
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.
Influenza viruses cause annual epidemics and occasionally, major global pandemics. To establish productive infection these viruses have mechanisms to evade host immune responses, including the type-I interferon (IFN) response. An important component of the IFN system is the helicase RIG-I that recognizes viral RNA, and is subsequently ubiquitinated by TRIM25 ubiquitin E3 ligase to induce downstream signaling resulting in IFN-α/β production. The NS1 protein of influenza A viruses binds to human TRIM25 and inhibits TRIM25-dependent RIG-I ubiquitination and downstream RIG-I signaling. An important unresolved question is how viruses can inhibit the RIG-I pathway when infecting new hosts. Here we show that while human TRIM25 is able to bind to different NS1 proteins, chicken TRIM25 binds preferentially to the NS1 from an avian virus. Strikingly, mouse TRIM25 was unable to bind NS1. We found that NS1 blocks RIG-I signaling in mouse and human cells by different mechanisms. While NS1 inhibits human TRIM25-mediated RIG-I ubiquitination, in mouse cells NS1 suppresses RIG-I signaling by binding to and inhibiting the ubiquitin E3 ligase Riplet. These results help understand the immune evasion strategies used by influenza virus in different species, and may partly explain the ability of this virus to adapt to different host species.
Citation: Rajsbaum R, Albrecht RA, Wang MK, Maharaj NP, Versteeg GA, et al. (2012) Species-Specific Inhibition of RIG-I Ubiquitination and IFN Induction by the Influenza A Virus NS1 Protein. PLoS Pathog 8(11): e1003059. doi:10.1371/journal.ppat.1003059
Editor: Andrew Pekosz, Johns Hopkins University - Bloomberg School of Public Health, United States of America
Received: September 16, 2012; Accepted: October 13, 2012; Published: November 29, 2012
Copyright: © 2012 Rajsbaum et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This study was supported by U.S. Public Health Service grants RO1 AI087846 and RR00168 (M.U.G.), RO1 AI046954, U19 AI083025 and CRIP (Center for Research on Influenza Pathogenesis, NIAID CEIRS contract HHSN266200700010C) (A.G.-S.). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
¤Current address: Center for Applied Medical Research (CIMA), Universidad de Navarra, Pamplona, Spain.