Middle East Respiratory Syndrome Coronavirus Nucleocapsid Protein Suppresses Type I and Type III Interferon Induction by Targeting RIG-I Signaling.
Type I and type III interferons (IFNs) are the frontline of antiviral defense mechanisms that trigger hundreds of downstream antiviral genes. In this study, we observed that MERS-CoV nucleocapsid (N) protein suppresses type I and type III IFN gene expression. The N protein suppresses Sendai virus-induced IFN-? and IFN-?1 by ... reducing their promoter activity and mRNA levels, as well as downstream IFN-stimulated genes (ISGs). Retinoic acid-inducible gene I (RIG-I) is known to recognize viral RNA and induce IFN expression through tripartite motif-containing protein 25 (TRIM25)-mediated ubiquitination of RIG-I caspase activation and recruitment domains (CARDs). We discovered that MERS-CoV N protein suppresses RIG-I-CARD-induced, but not MDA5-CARD-induced, IFN-? and IFN-?1 promoter activity. By interacting with TRIM25, N protein impedes RIG-I ubiquitination and activation and inhibits the phosphorylation of transcription factors IFN-regulatory factor 3 (IRF3) and NF-?B that are known to be important for IFN gene activation. By employing a recombinant Sindbis virus-EGFP replication system, we showed that viral N protein downregulated the production of not only IFN mRNA but also bioactive IFN proteins. Taken together, MERS-CoV N protein functions as an IFN antagonist. It suppresses RIG-I-induced type I and type III IFN production by interfering with TRIM25-mediated RIG-I ubiquitination. Our study sheds light on the pathogenic mechanism of how MERS-CoV causes disease.IMPORTANCE MERS-CoV causes death of about 35% of patients. Published studies showed that some coronaviruses are capable of suppressing interferon (IFN) expression in the early phase of infection and MERS-CoV proteins can modulate host immune response. In this study, we demonstrated that MERS-CoV nucleocapsid (N) protein suppresses the production of both type I and type III IFNs via sequestering TRIM25, an E3 ubiquitin ligase that is essential for activating the RIG-I signaling pathway. Ectopic expression of TRIM25 rescues the suppressive effect of the N protein. In addition, the C-terminal domain of the viral N protein plays a pivotal role in the suppression of IFN-? promoter activity. Our findings reveal how MERS-CoV evades innate immunity and provide insights into the interplay between host immune response and viral pathogenicity.
Mesh Terms:
CARD Signaling Adaptor Proteins, Cell Line, Coronavirus Infections, DEAD Box Protein 58, Gene Expression Regulation, Host-Pathogen Interactions, Humans, Interferon Lambda, Interferon Regulatory Factor-3, Interferon Type I, Interferons, Middle East Respiratory Syndrome Coronavirus, Nucleocapsid Proteins, Promoter Regions, Genetic, Protein Binding, Receptors, Immunologic, Signal Transduction, Transcription Factors, Tripartite Motif Proteins, Ubiquitin-Protein Ligases
CARD Signaling Adaptor Proteins, Cell Line, Coronavirus Infections, DEAD Box Protein 58, Gene Expression Regulation, Host-Pathogen Interactions, Humans, Interferon Lambda, Interferon Regulatory Factor-3, Interferon Type I, Interferons, Middle East Respiratory Syndrome Coronavirus, Nucleocapsid Proteins, Promoter Regions, Genetic, Protein Binding, Receptors, Immunologic, Signal Transduction, Transcription Factors, Tripartite Motif Proteins, Ubiquitin-Protein Ligases
J Virol
Date: Jun. 16, 2020
PubMed ID: 32295922
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