The Severe Acute Respiratory Syndrome Coronavirus Nucleocapsid Inhibits Type I Interferon Production by Interfering with TRIM25-Mediated RIG-I Ubiquitination

Abstract

Severe acute respiratory syndrome (SARS) is a respiratory disease, caused by a coronavirus (SARS-CoV), that is characterized by atypical pneumonia. The nucleocapsid protein (N protein) of SARS-CoV plays an important role in inhibition of type I interferon (IFN) production via an unknown mechanism. In this study, the SARS-CoV N protein was found to bind to the SPRY domain of the tripartite motif protein 25 (TRIM25) E3 ubiquitin ligase, thereby interfering with the association between TRIM25 and retinoic acid-inducible gene I (RIG-I) and inhibiting TRIM25-mediated RIG-I ubiquitination and activation. Type I IFN production induced by poly I·C or Sendai virus (SeV) was suppressed by the SARS-CoV N protein. SARS-CoV replication was increased by overexpression of the full-length N protein but not N amino acids 1 to 361, which could not interact with TRIM25. These findings provide an insightful interpretation of the SARS-CoV-mediated host innate immune suppression caused by the N protein.IMPORTANCE The SARS-CoV N protein is essential for the viral life cycle and plays a key role in the virus-host interaction. We demonstrated that the interaction between the C terminus of the N protein and the SPRY domain of TRIM25 inhibited TRIM25-mediated RIG-I ubiquitination, which resulted in the inhibition of IFN production. We also found that the Middle East respiratory syndrome CoV (MERS-CoV) N protein interacted with TRIM25 and inhibited RIG-I signaling. The outcomes of these findings indicate the function of the coronavirus N protein in modulating the host's initial innate immune response.

Nucleocapsid protein of porcine reproductive and respiratory syndrome virus antagonizes the antiviral activity of TRIM25 by interfering with TRIM25-mediated RIG-I ubiquitination

“…For example, the non-structural protein 1 (NS1) of influenza A virus interacts with the CC domain of TRIM25 preventing its dimerization and the K63-linked ubiquitination of RIG-I CARDs, thereby suppressing RIG-I signal transduction (Gack et al, 2009). Further, TRIM25 interacts with the N protein of SARS-CoV, thereby inhibiting the activation of RIG-I (Hu et al, 2017). In the current study, we found that the N protein of PRRSV inhibits the ubiquitination of RIG-I by competitively interfering with the interaction between RIG-I and TRIM25.…”

“…However, other mechanisms through which N protein inhibits IFN-β production are not clear. The nucleocapsid protein of severe acute respiratory syndrome (SARS) inhibits type I IFN production by interfering with TRIM25mediated RIG-I ubiquitination (Hu et al, 2017). Whereas PRRSV and SARS both belong to the Nidovirales order, whether PRRSV N protein inhibits the host innate immune response by interfering with TRIM25mediated RIG-I ubiquitination is not clear.…”

Molecular Characteristics, Functions, and Related Pathogenicity of MERS-CoV Proteins

“…A comparison of homology between MERS-CoV and other CoVs shows that although the N protein has low homology over the entire amino acid sequence, certain local amino acid sequences-especially the N-terminal amino acid sequence-are highly conserved. The SARS-CoV N protein can increase replication by overexpression [29]. The nucleocapsid structure not only requires the recognition of the characteristic sequences of the viral RNA, but also must recognize binding to other structural viral proteins.…”

“…The N protein of CoV may inhibit type I IFN production by interfering with the interaction between the triple motif protein 25 (TRIM25) and retinoic acid-inducible gene I (RIG-I), and by binding to the E3 ubiquitin ligase of TRIM25. Thus, inhibiting the ubiquitination and activation of RIG-I mediated by TRIM25 ultimately leads to the inhibition of IFN production, suggesting that the N protein of a CoV regulates the host's immune response against the virus [29].…”

Improving immunological insights into the ferret model of human viral infectious disease

“…However, for many viruses, alternative animal models better recapitulate human physiology and disease. Ferrets ( Mustela putorius furo ) have been employed to study the pathogenesis of a variety of human pathogens, including human and avian influenzas, coronaviruses including severe acute respiratory syndrome (SARS‐CoV), human respiratory syncytial virus (HRSV), human metapneumovirus (HMPV), Ebola virus and henipavirus (Nipah virus and Hendra virus) . While ferrets can be productively infected with many of these viruses, a lack of some tools to interrogate ferret immunological responses to infection limits insights that might impact the development of vaccines and/or therapeutics.…”