Abstract
Porcine deltacoronavirus (PDCoV) is a newly detected porcine coronavirus causing serious vomiting and diarrhea in piglets, especially newborn piglets. There has been an outbreak of PDCoV in worldwide since 2014, causing significant economic losses in the pig industry. The interferon (IFN)-mediated antiviral response is an important component of virus-host interactions and plays an essential role in inhibiting virus infection. However, the mechanism of PDCoV escaping the porcine immune surveillance is unclear. In the present study, we demonstrated that the PDCoV nucleocapsid (N) protein antagonizes porcine IFN-β production after vesicular stomatitis virus (VSV) infection or poly(I:C) stimulation. PDCoV N protein also suppressed the activation of porcine IFN-β promoter when it was stimulated by porcine RLR signaling molecules. PDCoV N protein targeted porcine retinoic acid-inducible gene I (pRIG-I) and porcine TNF receptor associated factor 3 (pTRAF3) by directly interacting with them. The N-terminal region (1–246 aa) of PDCoV N protein was important for interacting with pRIG-I and interfere its function. We confirmed that PDCoV N antagonizes IFN-β production by associating with pRIG-I to impede it from binding double-stranded RNA. Furthermore, porcine Riplet (pRiplet) was an important activator for pRIG-I by mediating the K63-linked polyubiquitination. However, PDCoV N protein restrained the pRiplet binding pRIG-I to inhibit pRIG-I K63-linked polyubiquitination. Taken together, our results revealed a novel mechanism by which PDCoV N protein interferes with the early activation of pRIG-I in the host antiviral response. The novel findings provide a new insight into PDCoV on evading the host innate immune response and may provide new therapeutic targets and more efficacious vaccines strategies for PDCoV infections.
Highlights
Porcine deltacoronavirus (PDCoV), a newly detected porcine coronavirus, as well as porcine transmissible gastroenteritis virus (TGEV), porcine rotavirus (PRV), and porcine epidemic diarrhea virus (PEDV) are the major pathogens of the porcine epidemic diarrhea disease
The results showed that the vesicular stomatitis virus (VSV)-GFP or poly(I:C) induced porcine IFN-β-luc promoter activation was significantly suppressed by PDCoV-N protein in PK-15 cells (Figures 1A,C)
The results showed that PDCoV N overexpression could significantly suppress poly(I:C)-induced porcine IFNB1, porcine OAS1, and porcine ISG15 mRNA expression in PK-15 cells (Figure 1D)
Summary
Porcine deltacoronavirus (PDCoV), a newly detected porcine coronavirus, as well as porcine transmissible gastroenteritis virus (TGEV), porcine rotavirus (PRV), and porcine epidemic diarrhea virus (PEDV) are the major pathogens of the porcine epidemic diarrhea disease. They cause microscopic intestinal lesions leading to serious diarrhea and often dehydration to death [1, 2]. Until now PDCoV strains have been isolated from a few regions and countries, including the United States, China, South Korea, Laos, and Thailand [4,5,6,7]. PDCoV is an enveloped, singlestranded, positive-sense RNA virus with the genome length of approximately 25 kb. PDCoV could use the aminopeptidase N (APN) of mammalian and avian species to efficiently infect cells of an unusual abroad species range, including humans and chickens [10]
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