Dataset Information

Porcine deltacoronavirus nucleocapsid protein antagonizes IFN-? production by impairing dsRNA and PACT binding to RIG-I.

ABSTRACT: Porcine deltacoronavirus (PDCoV) is an emerging swine enteropathogenic coronavirus that causes watery diarrhea, vomiting and mortality in newborn piglets. Previous studies have suggested that PDCoV infection antagonizes RIG-I-like receptor (RLR)-mediated IFN-? production to evade host innate immune defense, and PDCoV-encoded nonstructural protein nsp5 and accessory protein NS6 are associated with this process. However, whether the structural protein(s) of PDCoV also antagonize IFN-? production remains unclear. In this study, we found that PDCoV nucleocapsid (N) protein, the most abundant viral structural protein, suppressed Sendai virus (SEV)-induced IFN-? production and transcription factor IRF3 activation, but did not block IFN-? production induced by overexpressing RIG-I/MDA5. Furthermore, study revealed that PDCoV N protein interacted with RIG-I and MDA5 in an in vitro overexpression system and evident interactions between N protein and RIG-I could be detected in the context of PDCoV infection, which interfered with the binding of dsRNA and protein activator of protein kinase R (PACT) to RIG-I. Together, our results demonstrate that PDCoV N protein is an IFN antagonist and utilizes diverse strategies to attenuate RIG-I recognition and activation.

SUBMITTER: Chen J

PROVIDER: S-EPMC7088841 | biostudies-literature | 2019 Aug

REPOSITORIES: biostudies-literature

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Porcine deltacoronavirus nucleocapsid protein antagonizes IFN-β production by impairing dsRNA and PACT binding to RIG-I.

Chen Jun J Fang Puxian P Wang Mohan M Peng Qi Q Ren Jie J Wang Dang D Peng Guiqing G Fang Liurong L Xiao Shaobo S Ding Zhen Z

Virus genes 20190525 4

Porcine deltacoronavirus (PDCoV) is an emerging swine enteropathogenic coronavirus that causes watery diarrhea, vomiting and mortality in newborn piglets. Previous studies have suggested that PDCoV infection antagonizes RIG-I-like receptor (RLR)-mediated IFN-β production to evade host innate immune defense, and PDCoV-encoded nonstructural protein nsp5 and accessory protein NS6 are associated with this process. However, whether the structural protein(s) of PDCoV also antagonize IFN-β production r ...[more]

PMID: 31129785

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Project description:Porcine deltacoronavirus (PDCoV) has recently emerged as an enteric pathogen that can cause serious vomiting and diarrhea in suckling piglets. The first outbreak of PDCoV occurred in the United States in 2014 and was followed by reports of PDCoV in South Korea, China, Thailand, Lao People's Democratic Republic, and Vietnam, leading to economic losses for pig farms and posing a considerable threat to the swine industry worldwide. Our previous studies have shown that PDCoV encodes three accessory proteins, NS6, NS7, and NS7a, but the functions of these proteins in viral replication, pathogenesis, and immune regulation remain unclear. Here, we found that ectopic expression of accessory protein NS6 significantly inhibits Sendai virus-induced interferon beta (IFN-?) production as well as the activation of transcription factors IRF3 and NF-?B. Interestingly, NS6 does not impede the IFN-? promoter activation mediated via key molecules in the RIG-I-like receptor (RLR) signaling pathway, specifically RIG-I, MDA5, and their downstream molecules MAVS, TBK1, IKK?, and IRF3. Further analyses revealed that NS6 is not an RNA-binding protein; however, it interacts with RIG-I/MDA5. This interaction attenuates the binding of double-stranded RNA by RIG-I/MDA5, resulting in the reduction of RLR-mediated IFN-? production. Taken together, our results demonstrate that ectopic expression of NS6 antagonizes IFN-? production by interfering with the binding of RIG-I/MDA5 to double-stranded RNA, revealing a new strategy employed by PDCoV accessory proteins to counteract the host innate antiviral immune response.IMPORTANCE Coronavirus accessory proteins are species specific, and they perform multiple functions in viral pathogenicity and immunity, such as acting as IFN antagonists and cell death inducers. Our previous studies have shown that PDCoV encodes three accessory proteins. Here, we demonstrated for the first time that PDCoV accessory protein NS6 antagonizes IFN-? production by interacting with RIG-I and MDA5 to impede their association with double-stranded RNA. This is an efficient strategy of antagonizing type I IFN production by disrupting the binding of host pattern recognition receptors (PRRs) and pathogen-associated molecular patterns (PAMPs). These findings deepen our understanding of the function of accessory protein NS6, and they may direct us toward novel therapeutic targets and lead to the development of more effective vaccines against PDCoV infection.

Project description:Porcine deltacoronavirus (PDCoV) is an emerging swine enteropathogenic coronavirus. The first outbreak of PDCoV was announced from the United States in 2014, followed by reports in Asia. The nonstructural protein nsp5 is a 3C-like protease of coronavirus, and our previous study showed that PDCoV nsp5 inhibits type I interferon (IFN) production. In this study, we found that PDCoV nsp5 significantly inhibited IFN-stimulated response element (ISRE) promoter activity and transcription of IFN-stimulated genes (ISGs), suggesting that PDCoV nsp5 also suppresses IFN signaling. Detailed analysis showed that nsp5 cleaved signal transducer and activator of transcription 2 (STAT2) but not Janus kinase 1 (JAK1), tyrosine kinase 2 (TYK2), STAT1, and interferon regulatory factor 9 (IRF9), key molecules of the JAK-STAT pathway. STAT2 cleavage was dependent on the protease activity of nsp5. Interestingly, nsp5 cleaved STAT2 at two sites, glutamine 685 (Q685) and Q758, and similar cleavage was observed in PDCoV-infected cells. As expected, cleaved STAT2 impaired the ability to induce ISGs, demonstrating that STAT2 cleavage is an important mechanism utilized by PDCoV nsp5 to antagonize IFN signaling. We also discussed the substrate selection and binding mode of PDCoV nsp5 by homologous modeling of PDCoV nsp5 with the two cleaved peptide substrates. The results of our study demonstrate that PDCoV nsp5 antagonizes type I IFN signaling by cleaving STAT2 and provides structural insights for comprehending the cleavage mechanism of PDCoV nsp5, revealing a potential new function for PDCoV nsp5 in type I IFN signaling.IMPORTANCE The 3C-like protease encoded by nsp5 is a major protease of coronaviruses; thus, it is an attractive target for development of anticoronavirus drugs. Previous studies have revealed that the 3C-like protease of coronaviruses, including PDCoV and porcine epidemic diarrhea virus (PEDV), antagonizes type I IFN production by targeting the NF-κB essential modulator (NEMO). Here, for the first time, we demonstrate that overexpression of PDCoV nsp5 also antagonizes IFN signaling by cleaving STAT2, an essential component of transcription factor complex ISGF3, and that PDCoV infection reduces the levels of STAT2, which may affect the innate immune response.

Dataset Information

Porcine deltacoronavirus nucleocapsid protein antagonizes IFN-? production by impairing dsRNA and PACT binding to RIG-I.

Publications

Porcine deltacoronavirus nucleocapsid protein antagonizes IFN-β production by impairing dsRNA and PACT binding to RIG-I.

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