Disruption of interferon-β production by the Npro of atypical porcine pestivirus

The host protein CALCOCO2 interacts with bovine viral diarrhoea virus Npro, inhibiting type I interferon production and thereby promoting viral replication

Bovine viral diarrhoea-mucosal disease caused by bovine viral diarrhoea virus (BVDV) is a major infectious disease that affects the cattle industry. The nonstructural protein Npro of BVDV antagonizes the type I interferon (IFN-I) pathway, thereby escaping the host immune response. The exact mechanism by which Npro uses host proteins to inhibit IFN-I production is unclear. The host protein CALCOCO2 was identified as a binding partner of Npro using a yeast two-hybrid screen. The interaction between Npro and CALCOCO2 was confirmed by yeast co-transformation, co-immunoprecipitation assays, and GST pull-down assays. The stable overexpression of CALCOCO2 markedly promoted BVDV propagation, while the knockdown of CALCOCO2 significantly inhibited BVDV replication in MDBK cells. Interestingly, CALCOCO2 inhibited IFN-I and IFN-stimulated gene production in BVDV-infected cells. Ectopic expression of CALCOCO2 effectively reduced IRF3 protein levels via the proteasome pathway. CALCOCO2 was found to promote Npro-mediated ubiquitination degradation of IRF3 by interacting with IRF3. Our results demonstrate the molecular mechanism by which Npro recruits the CALCOCO2 protein to regulate IRF3 degradation to inhibit IFN-I production.

Current progress on innate immune evasion mediated by Npro protein of pestiviruses

Interferon (IFN), the most effective antiviral cytokine, is involved in innate and adaptive immune responses and is essential to the host defense against virus invasion. Once the host was infected by pathogens, the pathogen-associated molecular patterns (PAMPs) were recognized by the host pattern recognition receptors (PRRs), which activates interferon regulatory transcription factors (IRFs) and nuclear factor-kappa B (NF-κB) signal transduction pathway to induce IFN expression. Pathogens have acquired many strategies to escape the IFN-mediated antiviral immune response. Pestiviruses cause massive economic losses in the livestock industry worldwide every year. The immune escape strategies acquired by pestiviruses during evolution are among the major difficulties in its control. Previous experiments indicated that Erns, as an envelope glycoprotein unique to pestiviruses with RNase activity, could cleave viral ss- and dsRNAs, therefore inhibiting the host IFN production induced by viral ss- and dsRNAs. In contrast, Npro, the other envelope glycoprotein unique to pestiviruses, mainly stimulates the degradation of transcription factor IRF-3 to confront the IFN response. This review mainly summarized the current progress on mechanisms mediated by Npro of pestiviruses to antagonize IFN production.

Avian Metapneumovirus Subgroup C Phosphoprotein Suppresses Type I Interferon Production by Blocking Interferon Regulatory Factor 3 Nuclear Translocation

Avian metapneumovirus subgroup C (aMPV/C) is an important pathogen that causes upper respiratory symptoms and egg production decline in turkeys and chickens. aMPV/C infection leads to inhibition of the host antiviral immune response. However, our understanding of the molecular mechanisms underlying host immune response antagonized by aMPV/C infection is limited. In this study, we demonstrated that the aMPV/C phosphoprotein (P) inhibits the IFN antiviral signaling pathway triggered by melanoma differentiation gene 5 (MDA5) and reduces interferon β (IFN-β) production and IFN-stimulated genes (ISGs) by targeting IFN regulatory factor 7 (IRF7) but not nuclear factor κB (NF-κB) in DF-1 cells. Moreover, we found that aMPV/C P protein only blocks the nuclear translocation of IRF3 by interacting with IRF3 in HEK-293T cells, instead of affecting IRF3 phosphorylation and inducing IRF3 degradation, which suppresses IRF3 signaling activation and results in a decrease in IFN-β production. Collectively, these results reveal a novel mechanism by which aMPV/C infection disrupts IFN-β production in the host. IMPORTANCE The innate immune response is the first defense line of host cells and organisms against viral infections. When RNA viruses infect cells, viral RNA induces activation of retinoic acid-induced gene I and melanoma differentiation gene 5, which initiates downstream molecules and finally produces type I interferon (IFN-I) to regulate antiviral immune responses. The mechanism for avian metapneumovirus (aMPV) modulating IFN-I production to benefit its replication remains unknown. Here, we demonstrate that phosphoprotein of aMPV subgroup C (aMPV/C) selectively inhibits the nuclear translocation of interferon regulatory 3 (IRF3), instead of affecting the expression and phosphorylation of IRF3, which finally downregulates IFN-I production. This study showed a novel mechanism for aMPV/C infection antagonizing the host IFN response.

Genetic characterization of atypical porcine pestivirus from neonatal piglets with congenital tremor in Hubei province, China

Background

Atypical porcine pestivirus (APPV) is a single-stranded RNA virus with high genetic variation that causes congenital tremor (CT) in newborn piglets, belonging to the genus Pestivirus of the family Flaviviridae. Increasing cases of APPV infection in China in the past few years would pose severe challenges to the development of pig production. In view of the high genetic variability of APPV, the genetic characteristics of APPV in Hubei province was determined.

Methods

52 tissue samples from 8 CT-affected newborn piglets were collected at two different periods in the same pig farm in Hubei province. Viral nucleic acid was extracted to detect pathogens that can cause CT in piglets or other common clinical pathogens by RT-PCR. Haematoxylin and eosin (HE) staining, immunohistochemical (IHC) analysis, and qRT-PCR were performed to observe histopathological changes and histological distribution, and detect the viral load of APPV in CT-affected piglets. The full-length genome of APPV was obtained and sequence analysis was conducted to determine the phylogenetic relationship.

Results

Histopathological observation and histological distribution analysis showed that the histological lesions and distribution of APPV were mainly in central nervous system (CNS) tissues and immune tissues. Viral load analysis revealed that the viral copy number was higher in the cerebellum, submaxillary lymph nodes, tonsil, and serum than in other tissues. Phylogenetic analysis showed that CH-HB2020 and CH-HB2021 belonged to Clade I.3, and is most closely related to APPV_CH-GX2016. Sequence alignment based on APPV encoding sequences (CDS) showed that the nucleotide identities of CH-HB2020 or CH-HB2021 with Clade I, Clade II, and Clade III strains were 83.5–98.6%, 83.1–83.5%, and 81.1–81.4%, respectively, while the amino acid identities were 91.9–99.2%, 91.2–95.3%, and 90.77–91.4%, respectively. No recombination event was observed in CH-HB2020 or CH-HB2021 strains.

Conclusions

These findings enhance our understanding of the pathogenesis of APPV and may provide potential molecular evidence for its prevalence and transmission.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12985-022-01780-8.

Cloning and codon optimization of a novel feline interferon omega gene for production by Pichia pastoris and its antiviral efficacy in polyethylene glycol-modified form

Feline viral diseases, such as feline panleukopenia, feline infectious peritonitis, and feline coronaviral enteritis, seriously endanger the health of cats, and restrict the development of pet industry. Meanwhile, there is a current lack of effective vaccines to protect against feline viral diseases. Thus, effective therapeutic agents are highly desirable. Interferons (IFNs) are important mediators of the antiviral host defense in animals, particularly type I IFNs. In this study, a novel feline IFN omega (feIFN-ω) gene was extracted from the cat stimulated with feline parvovirus (FPV) combined with poly(I:C), and following codon optimization encoding the feIFN-ω, the desired gene (feIFN-ω’) fragment was inserted into plasmid pPICZαA, and transformed into Pichia pastoris GS115, generating a recombinant P. pastoris GS115 strain expressing the feIFN-ω’. After induction, we found that the expression level of the feIFN-ω’ was two times more than that of feIFN-ω (p < 0.01). Subsequently, the feIFN-ω’ was purified and modified with polyethylene glycol, and its antiviral efficacy was evaluated in vitro and in vivo, using vesicular stomatitis virus (VSV) and FPV as model virus. Our results clearly demonstrated that the feIFN-ω’ had significant antiviral activities on both homologous and heterologous animal cells in vitro. Importantly, the feIFN-ω’ can effectively promote the expression of antiviral proteins IFIT3, ISG15, Mx1, and ISG56, and further enhance host defense to eliminate FPV infection in vivo, suggesting a potential candidate for the development of therapeutic agent against feline viral diseases.

Atypical Porcine Pestiviruses: Relationships and Conserved Structural Features

For two decades, the genus pestivirus has been expanding and the host range now extends to rodents, bats and marine mammals. In this review, we focus on one of the most diverse pestiviruses, atypical porcine pestivirus or pestivirus K, comparing its special traits to what is already known at the structural and functional level from other pestiviruses.