Expression of the NS3 protease of cytopathogenic bovine viral diarrhea virus results in the induction of apoptosis but does not block activation of the beta interferon promoter

Immune evasion strategies of bovine viral diarrhea virus

Bovine viral diarrhea virus (BVDV) is a significant pathogen that causes great economic losses in the global livestock industry. During the long-term interactions between BVDV and its hosts, the virus has evolved multiple strategies to evade the host's innate immunity and adaptive immunity, thereby promoting viral survival and replication. This review focuses on the most recent research on immune evasion strategies employed by BVDV, including evading type I IFN signaling pathway, evading host adaptive immunity, mediating NF-κB signaling pathway, mediating cell apoptosis and inducing autophagy. Unraveling BVDV's immune evasion strategies will enhance our understanding of the pathogenesis of BVDV and contribute to the development of more effective therapies for the prevention, control and eradication of BVDV.

Pestiviruses infection: Interferon-virus mutual regulation

Pestiviruses are a class of viruses that in some cases can cause persistent infection of the host, thus posing a threat to the livestock industry. Interferons (IFNs) are a group of secreted proteins that play a crucial role in antiviral defense. In this review, on the one hand, we elaborate on how pestiviruses are recognized by the host retinoic acid-inducible gene-I (RIG-I), melanoma-differentiation-associated protein 5 (MDA5), and Toll-like receptor 3 (TLR3) proteins to induce the synthesis of IFNs. On the other hand, we focus on reviewing how pestiviruses antagonize the production of IFNs utilizing various strategies mediated by self-encoded proteins, such as the structural envelope protein (E^rns) and non-structural protein (N^pro). Hence, the IFN signal transduction pathway induced by pestiviruses infection and the process of pestiviruses blockade on the production of IFNs intertwines into an intricate regulatory network. By reviewing the interaction between IFN and pestiviruses (based on studies on BVDV and CSFV), we expect to provide a theoretical basis and reference for a better understanding of the mechanisms of induction and evasion of the innate immune response during infection with these viruses.

Bovine viral diarrhea virus in China: A comparative genomic and phylogenetic analysis with complete genome sequences

Bovine viral diarrhea virus (BVDV), causing bovine viral diarrhea (BVD) in cattle, is one of the highly contagious and devastating diseases of cattle. Since 1980, BVDV has been identified all-over China in a variety of animal species including cattle, camels, yaks, sheep, water buffalo, goats, Sika deer and pigs. In this study, 31 BVDV complete genomes reported in China (from 2004 to 2020) with other 112 genomes reported around the world were comparatively analyzed. Phylogenetic analysis shows that BVDV genomes reported worldwide clustered in three major clades i.e., BVDV-1, BVDV-2, and BVDV-3. The BVDV-1 is genetically the most diverged genotype and phylogenetically classified into 7 sub-clades in our study based on full-length genomes. The China BVDV genomes fall into all three major clades, e.g., BVDV-1, BVDV-2 and BVDV-3. China BVDV-1 clustered into five sub-clades, e.g., 1, 2, 3, 6 and 7, where sub-clade 7 clustered as a separate sub-clade. Full-length genome recombination analysis reveals that the BVDV-1 reported in China appears to be mainly involved in recombination events. In addition, comparative analysis of E2 proteins between BVDV-1, BVDV-2, and BVDV-3 reveals that the amino acid variations could affect 12 potential linear B cell epitopes, demonstrating a dramatic antigen drift in the E2 protein. These results provide a thorough view of the information about the genetic and antigenic diversity of BVDVs circulating in China and therefore could benefit the development of suitable strategies for disease control.

Prevalence characteristic of BVDV in some large scale dairy farms in Western China

The aim of this study was to analyze the prevalence characteristic of Bovine viral diarrhea virus (BVDV) in some large scale dairy farms in Western China. BVDV was detected in 30 samples of bulk tank milk (BTM) collected from 30 large dairy farms in 7 provinces of western China, 93.33% (28/30) of the farms were infected with BVDV, and S/P ratio was over 0.3 in 28 positive farms. The individual status was further estimated in the dairy farm (No. 10) with the highest positive rate (S/P ratio = 1.37) and the dairy farm (No. 17) with the lowest positive rate (S/P ratio = 0.39). Two hundred cows were, respectively, selected from calf, young cows and lactating cows in farm No. 10 and farm No. 17 and the serum sample of each enrolled cow was collected. The individual positive rate of serum antibody (Ab) was 87.17% (523/600) in farm No. 10 and 31.33% (188/600) in farm No. 17. The individual positive ratio of serum antibody in calves, young cows and lactating cows were 41.75 % (167/400), 58.75% (235/400) and 77.25% (309/400), respectively. BTM Ab of farm No. 10 has an S/P ratio more than 1.0, which indicated there were emergent or persistent infection (PI) cases, and further test showed that PI cases were 0.51% in farm No. 10. Pathogens were positive in 42.34% (163/385) of nasal mucus samples collected from cows with respiratory symptom, and BVDV cases were 57 in 163 positive samples. Three strains of NCP BVDV-1, one strain of CP BVDV-1, one strain of NCP BVDV-2 and one strain of CP BVDV-2 were successfully isolated. Phylogenetic analysis revealed that the subtypes of BVDV currently prevalent in western China were BVDV-1a, BVDV-1m, BVDV-1q and BVDV-2. The findings suggested that the BVDV infection is serious in some Large Scale Dairy Farms in Western China.

Non-structural proteins of bovine viral diarrhea virus

Bovine viral diarrhea virus (BVDV) belongs to the family Flaviviridae genus pestivirus. The viral genome is a single-stranded, positive-sense RNA that encodes four structural proteins (i.e., C, Erns, E1, and E2) and eight non-structural proteins (NSPs) (i.e., Npro, p7, NS2, NS3, NS4A, NS4B, NS5A, and NS5B). Cattle infected with BVDV exhibit a number of different clinical signs including diarrhea, abortion, and other reproductive disorders which have a serious impact on the cattle industry worldwide. Research on BVDV mainly focuses on its structural protein, however, progress in understanding the functions of the NSPs of BVDV has also been made in recent decades. The knowledge gained on the BVDV non-structural proteins is helpful to more fully understand the viral replication process and the molecular mechanism of viral persistent infection. This review focuses on the functions of BVDV NSPs and provides references for the identification of BVDV, the diagnosis and prevention of Bovine viral diarrhea mucosal disease (BVD-MD), and the development of vaccines.

Identification of differentially expressed gene pathways between cytopathogenic and non-cytopathogenic BVDV-1 strains by analysis of the transcriptome of infected primary bovine cells

The bovine viral diarrhea virus 1 (BVDV-1), belonging to the Pestivirus genus, is characterized by the presence of two biotypes, cytopathogenic (cp) or non-cytopathogenic (ncp). For a better understanding of the host pathogen interactions, we set out to identify transcriptomic signatures of bovine lung primary cells (BPCs) infected with a cp or a ncp strain. For this, we used both a targeted approach by reverse transcription droplet digital PCR and whole genome approach using RNAseq. Data analysis showed 3571 differentially expressed transcripts over time (Fold Change >2) and revealed that the most deregulated pathways for cp strain are signaling pathways involved in responses to viral infection such as inflammatory response or apoptosis pathways. Interestingly, our data analysis revealed a deregulation of Wnt signaling pathway, a pathway described in embryogenesis, that was specifically seen with the BVDV-1 cp but not the ncp suggesting a role of this pathway in viral replication.

Th17 cell differentiation induced by cytopathogenic biotype BVDV-2 in bovine PBLCs

Background

Bovine viral diarrhea virus (BVDV) is a major pathogen that causes bovine viral diarrhea/mucosal disease (BVD-MD), which has become a global infectious disease due to its wide spread and the lack of effective treatment. The process of BVDV infection is complex. Once infected, host immune cells are activated and modulated. As a major immune cell, peripheral blood lymphocyte cells (PBLCs) are the primary target of BVDV. In order to further understand the mechanism of BVDV- host interaction, the expression profiles of host lymphocytes mRNAs associated with BVDV infection were investigated by transcriptomic sequencing analysis.

Results

The transcriptomic sequencing analysis was performed on bovine PBLCs infected with CP BVDV-2 GS2018 after 12 h of infection. Gene expression profiling demonstrated that 1052 genes were differentially expressed in GS2018 infected PBLCs compared with the control group. Of these genes, 485 genes were up-regulated and 567 were down-regulated. The 19 differential expressed genes (DEGs) were selected for validation using quantitative real-time PCR and the results were consistent with the results of RNA-Seq. Gene ontology enrichment and KEGG pathway analysis showed that 1052 DEGs were significantly enriched in 16 pathways, including cytokine-cytokine receptor interaction, IL17, PI3K-Akt, MAPK and TNF signaling pathway. PPI network analysis showed that IL17A, IFN-γ and TNF-α interacted with various proteins and may play crucial roles in BVDV-2 infection. Of note, we confirmed that GS2018 induced Th17 cell differentiation in PBLCs and persistently increased the expression levels of IL17A. In turn, the replication of GS2018 was inhibited by IL17A.

Conclusion

In this study, the transcription changes of DEGs related to host immune responses in bovine PBLCs were caused by CP BVDV-2 infection. In particular, the effector molecules IL17A of Th17 cells were significantly up-regulated, which inhibited viral replication. These results will contribute to exploration and further understanding of the host immune response mechanism and interaction between host and BVDV-2.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08194-w.

Mechanisms linking bovine viral diarrhea virus (BVDV) infection with infertility in cattle

Bovine viral diarrhea virus (BVDV) is an important infectious disease agent that causes significant reproductive and economic losses in the cattle industry worldwide. Although BVDV infection is known to cause poor fertility in cattle, a greater part of the underlying mechanisms particularly associated with early reproductive losses are not clearly understood. Previous studies reported viral compromise of reproductive function in infected bulls. In females, BVDV infection is thought to be capable of killing the oocyte, embryo or fetus directly, or to induce lesions that result in fetal abortion or malformation. BVDV infections may also induce immune dysfunction, and predispose cattle to other diseases that cause poor health and fertility. Other reports also suggested BVDV-induced disruption of the reproductive endocrine system, and a disruption of leukocyte and cytokine functions in the reproductive organs. More recent studies have provided evidence of viral-induced suppression of endometrial innate immunity that may predispose to uterine disease. Furthermore, there is new evidence that BVDV may potentially disrupt the maternal recognition of pregnancy or the immune protection of the conceptus. This review brings together the previous reports with the more recent findings, and attempts to explain some of the mechanisms linking this important virus to infertility in cattle.

The PP4R1 sub-unit of protein phosphatase PP4 is essential for inhibition of NF-κB by merkel polyomavirus small tumour antigen

Merkel cell carcinoma (MCC) is a highly aggressive skin cancer with a high metastatic potential. The majority of MCC cases are caused by the Merkel cell polyomavirus (MCPyV), through expression of the virus-encoded tumour antigens. Whilst mechanisms attributing tumour antigen expression to transformation are being uncovered, little is known of the mechanisms by which MCPyV persists in the host. We previously identified the MCPyV small T antigen (tAg) as a novel inhibitor of nuclear factor kappa B (NF-kB) signalling and a modulator of the host anti-viral response. Here we demonstrate that regulation of NF-kB activation involves a previously undocumented interaction between tAg and regulatory sub-unit 1 of protein phosphatase 4 (PP4R1). Formation of a complex with PP4R1 and PP4c is required to bridge MCPyV tAg to the NEMO adaptor protein, allowing deactivation of the NF-kB pathway. Mutations in MCPyV tAg that fail to interact with components of this complex, or siRNA depletion of PP4R1, prevents tAg-mediated inhibition of NF-kB and pro-inflammatory cytokine production. Comparison of tAg binding partners from other human polyomavirus demonstrates that interactions with NEMO and PP4R1 are unique to MCPyV. Collectively, these data identify PP4R1 as a novel target for virus subversion of the host anti-viral response.

Human papillomavirus type 18 E5 oncogene supports cell cycle progression and impairs epithelial differentiation by modulating growth factor receptor signalling during the virus life cycle

Deregulation of proliferation and differentiation-dependent signalling pathways is a hallmark of human papillomavirus (HPV) infection. Although the manipulation of these pathways by E6 and E7 has been extensively studied, controversies surround the role of the E5 oncoprotein during a productive virus life cycle. By integrating primary keratinocytes harbouring wild type or E5 knockout HPV18 genomes with pharmacological and gain/loss of function models, this study aimed to provide molecular information about the role of E5 in epithelial proliferation and differentiation. We show that E5 contributes to cell cycle progression and unscheduled host DNA synthesis in differentiating keratinocytes. E5 function correlates with increased EGFR activation in differentiating cells and blockade of this pathway impairs differentiation-dependent cell cycle progression of HPV18 containing cells. Our findings provide a functional requirement of enhanced EGFR signalling for suprabasal cellular DNA synthesis during the virus life cycle. They also reveal an unrecognised contribution of E5 towards the impaired keratinocyte differentiation observed during a productive HPV infection. E5 suppresses a signalling axis consisting of the keratinocyte growth factor receptor (KGFR) pathway. Inhibition of this pathway compensates for the loss of E5 in knockout cells and re-instates the delay in differentiation. The negative regulation of KGFR involves suppression by the EGFR pathway. Thus our data reveal an unappreciated role for E5-mediated EGFR signalling in orchestrating the balance between proliferation and differentiation in suprabasal cells.

Analyses of long non-coding RNAs and mRNA profiling through RNA sequencing of MDBK cells at different stages of bovine viral diarrhea virus infection

BACKGROUND

Bovine viral diarrhea virus (BVDV) infection is a dynamic and complex process that leads to significant economic losses in the dairy and cattle industries. However, our understanding of the protective and pathological mechanism underlying host infection is limited.

METHODS

To determine whether BVDV regulates specific activities of the host cell, the expression of long non-coding RNA (lncRNA) during BVDV NADL infection was studied by deep sequencing.

RESULTS

A total of 1236 lncRNA transcripts and 3261 mRNA transcripts were differentially regulated at 2h, 6h, and 18h post-infection. The lncRNAs shared same characteristics with other mammals in terms of exon length, number, expression level, and conservation. The Gene Ontology (GO) enrichment and KEGG pathway analyses showed that lncRNAs regulate immune reaction during BVDV infection. Thirteen differentially expressed genes in 18 hpi were selected and independently validated by reverse-transcription qPCR.

CONCLUSIONS

The present study is the first to provide insights into the biological connection of lncRNAs and BVDV, which can be further explored for the development of antiviral prevention strategies and in understanding persistent infection between viral and host components.

Transcriptomic analysis of responses to cytopathic bovine viral diarrhea virus-1 (BVDV-1) infection in MDBK cells

The bovine viral diarrhea virus (BVDV) is responsible for significant economic losses in the dairy and cattle industry; however, little is known about the protective and pathological responses of hosts to infection. The present study determined the principal molecular markers implicated in viral infection through meta-transcriptomic analysis using MDBK cells infected for two hours with a field isolate of BVDV-1. While several immune regulator genes were induced, genes involved in cell signaling, metabolic processes, development, and integrity were down-regulated, suggesting an isolation of infected cells from cell-to-cell interactions and responses to external signals. Analysis through RT-qPCR confirmed the expression of more than one hundred markers. Interestingly, there was a significant up-regulation of two negative NF-κB regulators, IER3 and TNFAIP3, indicating a possible blocking of this signaling pathway mediated by BVDV-1 infection. Additionally, several genes involved in the metabolism of reactive oxygen species were down-regulated, suggesting increased oxidative stress. Notably, a number of genes involved in cellular growth and development were also regulated during infection, including MTHFD1L, TGIF1, and Brachyury. Moreover, there was an increased expression of the genes β-catenin, caprin-2, GSK3β, and MMP-7, all of which are crucial to the Wnt signaling pathway that is implicated in the embryonic development of a variety of organisms. This meta-transcriptomic analysis provides the first data towards understanding the infection mechanisms of cytopathic BVDV-1 and the putative molecular relationship between viral and host components.

Bovine Viral Diarrhea Virus in Zoos: A Perspective from the Veterinary Team

The many different species in close proximity make zoological collections a unique environment for disease transmission. Bovine Viral Diarrhea Virus (BVDV) is of special concern with zoos due to the numerous exotic ruminant species that this virus can infect. BVDV occurs as both a non-cytopathic and a cytopathic strain both of which are capable of infecting exotic ruminants. The cytopathic strain causes mucosal disease (MD) and death. Infection with the non-cytopathic strain may produce persistently infected (PI) animals. PI individuals may show vague clinical signs, including abortion. Management of BVDV in zoos should focus on identification of PI individuals and prevention of infection of other animals of the collection. Variability makes serological testing as the sole method of screening for BVDV infection undesirable in exotic ruminants. Combination testing provides a definitive answer, especially in sensitive wildlife. Use of a combination of antigen-capture ELISA (ACE) with haired skin, Real Time-PCR (RT-PCR) on whole blood, and antibody detection via serum neutralization has the greatest potential to identify PI animals. An animal that is positive on both ACE and RT-PCR, but is negative on serology should be considered highly suspicious of being a PI, and should be isolated and undergo repeat testing 4–6 weeks later to confirm positive status. This testing methodology also allows screening of pregnant and newborn animals. Isolation or culling may need to be considered in animals determined to be positive via combination testing. These decisions should only be made after careful consideration and evaluation, especially with endangered species.

A Cell-based Fluorescence Resonance Energy Transfer (FRET) Sensor Reveals Inter- and Intragenogroup Variations in Norovirus Protease Activity and Polyprotein Cleavage

The viral protease represents a key drug target for the development of antiviral therapeutics. Because many protease inhibitors mimic protease substrates, differences in substrate recognition between proteases may affect their sensitivity to a given inhibitor. Here we use a cell-based FRET sensor to investigate the activity of different norovirus proteases upon cleavage of various norovirus cleavage sites inserted into a linker region separating cyan fluorescent protein and yellow fluorescent protein. Using this system, we demonstrate that differences in substrate processing exist between proteases from human noroviruses (genogroups I (GI) and II) and the commonly used murine norovirus (MNV, genogroup V) model. These altered the cleavage efficiency of specific cleavage sites both within and between genogroups. The differences observed between these proteases may affect sensitivity to protease inhibitors and the suitability of MNV as a model system for testing such molecules against the human norovirus protease. Finally, we demonstrate that replacement of MNV polyprotein cleavage sites with the GI or GII equivalents, with the exception of the NS6–7 junction, leads to the production of infectious virus when the MNV NS6 protease, but not the GI or GII proteases, are present.

Characterization of the Determinants of NS2-3-Independent Virion Morphogenesis of Pestiviruses

A peculiarity of the Flaviviridae is the critical function of nonstructural (NS) proteins for virus particle formation. For pestiviruses, like bovine viral diarrhea virus (BVDV), uncleaved NS2-3 represents an essential factor for virion morphogenesis, while NS3 is an essential component of the viral replicase. Accordingly, in natural pestivirus isolates, processing at the NS2-3 cleavage site is not complete, to allow for virion morphogenesis. Virion morphogenesis of the related hepatitis C virus (HCV) shows a major deviation from that of pestiviruses: while RNA replication also requires free NS3, virion formation does not depend on uncleaved NS2-NS3. Recently, we described a BVDV-1 chimera based on strain NCP7 encompassing the NS2-4B*-coding region of strain Osloss (E. Lattwein, O. Klemens, S. Schwindt, P. Becher, and N. Tautz, J Virol 86:427-437, 2012, doi:10.1128/JVI.06133-11). This chimera allowed for the production of infectious virus particles in the absence of uncleaved NS2-3. The Osloss sequence deviates in the NS2-4B* part from NCP7 in 48 amino acids and also has a ubiquitin insertion between NS2 and NS3. The present study demonstrates that in the NCP7 backbone, only two amino acid exchanges in NS2 (E1576V) and NS3 (V1721A) are sufficient and necessary to allow for efficient NS2-3-independent virion morphogenesis. The adaptation of a bicistronic virus encompassing an internal ribosomal entry site element between the NS2 and NS3 coding sequences to efficient virion morphogenesis led to the identification of additional amino acids in E2, NS2, and NS5B that are critically involved in this process. The surprisingly small requirements for approximating the packaging schemes of pestiviruses and HCV with respect to the NS2-3 region is in favor of a common mechanism in an ancestral virus.

IMPORTANCE

For positive-strand RNA viruses, the processing products of the viral polyprotein serve in RNA replication as well as virion morphogenesis. For bovine viral diarrhea virus, nonstructural protein NS2-3 is of critical importance to switch between these processes. While free NS3 is essential for RNA replication, uncleaved NS2-3, which accumulates over time in the infected cell, is required for virion morphogenesis. In contrast, the virion morphogenesis of the related hepatitis C virus is independent from uncleaved NS2-NS3. Here, we demonstrate that pestiviruses can adapt to virion morphogenesis in the absence of uncleaved NS2-3 by just two amino acid exchanges. While the mechanism behind this gain of function remains elusive, the fact that it can be achieved by such minor changes is in line with the assumption that an ancestral virus already used this mechanism but lost it in the course of adapting to a new host/infection strategy.

Global transcriptomic profiling of bovine endometrial immune response in vitro. II. Effect of bovine viral diarrhea virus on the endometrial response to lipopolysaccharide

Infection with noncytopathic bovine viral diarrhea virus (ncpBVDV) is associated with uterine disease and infertility. This study investigated the influence of ncpBVDV on immune functions of the bovine endometrium by testing the response to bacterial lipopolysaccharide (LPS). Primary cultures of mixed epithelial and stromal cells were divided into four treatment groups (control [CONT], BVDV, CONT+LPS, and BVDV+LPS) and infected with ncpBVDV for 4 days followed by treatment with LPS for 6 h. Whole-transcriptomic gene expression was measured followed by Ingenuity Pathway Analysis. Differential expression of 184 genes was found between CONT and BVDV treatments, showing interplay between induction and inhibition of responses. Up-regulation of TLR3, complement, and chemotactic and TRIM factors by ncpBVDV all suggested an ongoing immune response to viral infection. Down-regulation of inflammatory cytokines, chemokines, CXCR4, and serine proteinase inhibitors suggested mechanisms by which ncpBVDV may simultaneously counter the host response. Comparison between BVDV+LPS and CONT+LPS treatments showed 218 differentially expressed genes. Canonical pathway analysis identified the key importance of interferon signaling. Top down-regulated genes were RSAD2, ISG15, BST2, MX2, OAS1, USP18, IFIT3, IFI27, SAMD9, IFIT1, and DDX58, whereas TRIM56, C3, and OLFML1 were most up-regulated. Many of these genes are also regulated by IFNT during maternal recognition of pregnancy. Many innate immune genes that typically respond to LPS were inhibited by ncpBVDV, including those involved in pathogen recognition, inflammation, interferon response, chemokines, tissue remodeling, cell migration, and cell death/survival. Infection with ncpBVDV can thus compromise immune function and pregnancy recognition, thereby potentially predisposing infected cows to postpartum bacterial endometritis and reduced fertility.

The human papillomavirus (HPV) E7 protein antagonises an Imiquimod-induced inflammatory pathway in primary human keratinocytes

High-risk human papillomaviruses (HPV) are the etiological pathogen of cervical and a number of ano-genital cancers. How HPVs overcome the significant barriers of the skin immune system has been the topic of intensive research. The E6 and E7 oncoproteins have emerged as key players in the deregulation of host innate immune pathways that are required for the recruitment of effector cells of the immune response. Here we demonstrate that E7, and to a lesser extend E6, strongly reduce NFκB activation in response to the inflammatory mediator imiquimod. Moreover, we establish that undifferentiated keratinocytes do not express the putative receptor for imiquimod, TLR7, and as such are stimulated by imiquimod through a novel pathway. Inhibition of imiquimod induced cytokine production required residues in the CR1 and CR3 regions of E7 and resulted in reduced nuclear translocation and acetylation of the p65 sub-unit of NFκB. The results provide further evidence for a TLR7-independent role of imiquimod in the epithelial immune response and reinforce the ability of the HPV oncoproteins to disrupt the innate immune response, which may have important consequences for establishment of a chronic infection.

The Molecular Biology of Pestiviruses

Pestiviruses are among the economically most important pathogens of livestock. The biology of these viruses is characterized by unique and interesting features that are both crucial for their success as pathogens and challenging from a scientific point of view. Elucidation of these features at the molecular level has made striking progress during recent years. The analyses revealed that major aspects of pestivirus biology show significant similarity to the biology of human hepatitis C virus (HCV). The detailed molecular analyses conducted for pestiviruses and HCV supported and complemented each other during the last three decades resulting in elucidation of the functions of viral proteins and RNA elements in replication and virus-host interaction. For pestiviruses, the analyses also helped to shed light on the molecular basis of persistent infection, a special strategy these viruses have evolved to be maintained within their host population. The results of these investigations are summarized in this chapter.

Bovine Viral Diarrhea Virus Infections

Bovine viral diarrhea virus (BVDV) continues to be of economic significance to the livestock industry in terms of acute disease and fetal loss. Many of the lesions relating to BVDV infection have been well described previously. The virus is perpetuated in herds through the presence of calves that are persistently infected. Relationships between various species and biotypes of BVDV and host defenses are increasingly understood. Understanding of the host defense mechanisms of innate immunity and adaptive immunity continues to improve, and the effects of the virus on these immune mechanisms are being used to explain how persistent infection develops. The noncytopathic biotype of BVDV plays the major role in its effects on the host defenses by inhibiting various aspects of the innate immune system and creation of immunotolerance in the fetus during early gestation. Recent advances have allowed for development of affordable test strategies to identify and remove persistently infected animals. With these improved tests and removal strategies, the livestock industry can begin more widespread effective control programs.

Human papillomavirus E7 oncoprotein increases production of the anti-inflammatory interleukin-18 binding protein in keratinocytes

Human papillomavirus (HPV) can successfully evade the host immune response to establish a persistent infection. We show here that expression of the E7 oncoprotein in primary human keratinocytes results in increased production of interleukin-18 (IL-18) binding protein (IL-18BP). This anti-inflammatory cytokine binding protein is a natural antagonist of IL-18 and is necessary for skin homeostasis. We map increased IL-18BP production to the CR3 region of E7 and demonstrate that this ability is shared among E7 proteins from different HPV types. Furthermore, mutagenesis shows that increased IL-18BP production is mediated by a gamma-activated sequence (GAS) in the IL-18BP promoter. Importantly, the increased IL-18BP levels seen in E7-expressing keratinocytes are capable of diminishing IL-18-mediated CD4 lymphocyte activation. This study provides the first evidence for a virus protein that targets IL-18BP and further validates E7 as a key component of the HPV immune evasion armor.

IMPORTANCE

Infection with human papillomavirus is a leading cause of morbidity and mortality worldwide. This study demonstrates that the E7 protein increases production of the anti-inflammatory IL-18BP, a major regulator of epithelial homeostasis. A number of E7 proteins can increase IL-18BP production, and a region within the CR3 of E7 is necessary for mediating the increase. A consequence of increased IL-18BP production is a reduction in CD4-positive lymphocyte activation in response to IL-18 costimulation. These findings may shed light on the immune evasion abilities of HPV.

The NS3 protease and helicase domains of Japanese encephalitis virus trigger cell death via caspase‑dependent and ‑independent pathways

Japanese encephalitis virus (JEV), a mosquito‑borne flavivirus, causes acute encephalitis and nervous damage. Previous studies have demonstrated that JEV induces apoptosis in infected cells. However, to date the mechanisms of JEV‑induced apoptosis are unclear. In order to identify the viral proteins associated with JEV‑induced apoptosis, pEGFP‑non‑structural protein 3 (NS3) 1‑619 (expressing the JEV NS3 intact protein, including the protease and helicase domains), pEGFP‑NS3 1‑180 (expressing the protease domain) and pEGFP‑NS3 163‑619 (expressing the helicase domain) were transfected into target cells to study cell death. Results demonstrate that the JEV NS3 intact protein and protease and helicase domains induce cell death. In addition, cell death was identified to be significantly higher in cells transfected with the NS3 protease domain compared with the intact protein and helicase domain. Caspase activation was also analyzed in the current study. NS3 intact protein and NS3 protease and helicase domains activated caspase‑9/‑3‑dependent and ‑independent pathways. However, caspase‑8 activity was not found to be significantly different in NS3‑transfected cells compared with control. In summary, the present study demonstrates that the NS3 helicase and protease domains of JEV activate caspase‑9/‑3‑dependent and ‑independent cascades and trigger cell death.

Apoptosis in Bovine viral diarrhea virus (BVDV)-induced mucosal disease lesions: a histological, immunohistological, and virological investigation

Cattle persistently infected with a noncytopathic Bovine viral diarrhea virus (BVDV) are at risk of developing fatal "mucosal disease" (MD). The authors investigated the role of various apoptosis pathways in the pathogenesis of lesions in animals suffering from MD. Therefore, they compared the expression of caspase-3, caspase-8, caspase-9, and Bcl-2L1 (Bcl-x) in tissues of 6 BVDV-free control animals, 7 persistently infected (PI) animals that showed no signs of MD (non-MD PI animals), and 11 animals with MD and correlated the staining with the localization of mucosal lesions. Caspase-3 and -9 staining were markedly stronger in MD cases and were associated with mucosal lesions, even though non-MD PI animals and negative controls also expressed caspase-9. Conversely, caspase-8 was not elevated in any of the animals analyzed. Interestingly, Bcl-x also colocalized with mucosal lesions in the MD cases. However, Bcl-x was similarly expressed in tissues from all 3 groups, and thus, its role in apoptosis needs to be clarified. This study clearly illustrates ex vivo that the activation of the intrinsic, but not the extrinsic, apoptosis pathway is a key element in the pathogenesis of MD lesions observed in cattle persistently infected with BVDV. However, whether direct induction of apoptosis in infected cells or indirect effects induced by the virus are responsible for the lesions observed remains to be established.

High-risk human papillomavirus E5 oncoprotein displays channel-forming activity sensitive to small-molecule inhibitors

High-risk human papillomavirus type 16 (HPV16) is the primary causative agent of cervical cancer and therefore is responsible for significant morbidity and mortality worldwide. Cellular transformation is mediated directly by the expression of viral oncogenes, the least characterized of which, E5, subverts cellular proliferation and immune recognition processes. Despite a growing catalogue of E5-specific host interactions, little is understood regarding the molecular basis of its function. Here we describe a novel function for HPV16 E5 as an oligomeric channel-forming protein, placing it within the virus-encoded "viroporin" family. The development of a novel recombinant E5 expression system showed that E5 formed oligomeric assemblies of a defined luminal diameter and stoichiometry in membranous environments and that such channels mediated fluorescent dye release from liposomes. Hexameric E5 channel stoichiometry was suggested by native PAGE studies. In lieu of high-resolution structural information, established de novo molecular modeling and design methods permitted the development of the first specific small-molecule E5 inhibitor, capable of both abrogating channel activity in vitro and reducing E5-mediated effects on cell signaling pathways. The identification of channel activity should enhance the future understanding of the physiological function of E5 and could represent an important target for antiviral intervention.

Norovirus regulation of the innate immune response and apoptosis occurs via the product of the alternative open reading frame 4

Small RNA viruses have evolved many mechanisms to increase the capacity of their short genomes. Here we describe the identification and characterization of a novel open reading frame (ORF4) encoded by the murine norovirus (MNV) subgenomic RNA, in an alternative reading frame overlapping the VP1 coding region. ORF4 is translated during virus infection and the resultant protein localizes predominantly to the mitochondria. Using reverse genetics we demonstrated that expression of ORF4 is not required for virus replication in tissue culture but its loss results in a fitness cost since viruses lacking the ability to express ORF4 restore expression upon repeated passage in tissue culture. Functional analysis indicated that the protein produced from ORF4 antagonizes the innate immune response to infection by delaying the upregulation of a number of cellular genes activated by the innate pathway, including IFN-Beta. Apoptosis in the RAW264.7 macrophage cell line was also increased during virus infection in the absence of ORF4 expression. In vivo analysis of the WT and mutant virus lacking the ability to express ORF4 demonstrated an important role for ORF4 expression in infection and virulence. STAT1-/- mice infected with a virus lacking the ability to express ORF4 showed a delay in the onset of clinical signs when compared to mice infected with WT virus. Quantitative PCR and histopathological analysis of samples from these infected mice demonstrated that infection with a virus not expressing ORF4 results in a delayed infection in this system. In light of these findings we propose the name virulence factor 1, VF1 for this protein. The identification of VF1 represents the first characterization of an alternative open reading frame protein for the calicivirus family. The immune regulatory function of the MNV VF1 protein provide important perspectives for future research into norovirus biology and pathogenesis.

This report describes the identification and characterization of a novel protein of unknown function encoded by a mouse virus genetically similar to human noroviruses. This gene is unique to the mouse virus and occupies the same part of the genome that codes for the major capsid protein. The protein that we have described as virulence factor 1 (VF1) is found in all murine norovirus isolates, absent in all human strains but is indeed expressed during infection. Its expression enables MNV-1 to establish efficient infection of its natural host through interference with interferon-mediated response pathways and apoptosis. Our data would indicate that the VF1 protein is multi-functional with an ability to modulate the host's response to infection. Murine noroviruses are frequently used firstly as a model to study human norovirus replication and pathogenesis, studies hampered by their inability to replicate in cell culture. Secondly, persistent infection of laboratory animals with murine norovirus may affect other models of disease using experimental mice. The role of VF1 in infection and pathology in the differential outcome of infection is the source of continued research in our laboratory.

[Pestivirus]

Members of the genus Pestivirus, are causative agents of economically important diseases for livestock and wild animals that occur worldwide, such as bovine viral diarrhea, classical swine fever, and border disease of sheep. Pestivirus have novel insertions of host genes in the viral genome and functions of unique viral proteins, N(pro) and E(rns), related to the pathogenicity although genomic structure is closely related to the other viruses of Flaviviridae family, especially hepatitis C virus. In this review, recent studies on the molecular basis of pathogenicity of pestivirus infections were summarized.

Pestivirus virion morphogenesis in the absence of uncleaved nonstructural protein 2-3

The family Flaviviridae contains three genera of positive-strand RNA viruses, namely, Flavivirus, Hepacivirus (e.g., hepatitis C virus [HCV]), and Pestivirus. Pestiviruses, like bovine viral diarrhea virus (BVDV), bear a striking degree of similarity to HCV concerning polyprotein organization, processing, and function. Along this line, in both systems, release of nonstructural protein 3 (NS3) is essential for viral RNA replication. However, both viruses differ significantly with respect to processing efficiency at the NS2/3 cleavage site and abundance as well as functional relevance of uncleaved NS2-3. In BVDV-infected cells, significant amounts of NS2-3 accumulate at late time points postinfection and play an essential but ill-defined role in the production of infectious virions. In contrast, complete cleavage of the HCV NS2-3 counterpart has been reported, and unprocessed NS2-3 is not required throughout the life cycle of HCV, at least in cell culture. Here we describe the selection and characterization of the first pestiviral genome with the capability to complete productive infection in the absence of uncleaved NS2-3. Despite the insertion of a ubiquitin gene or an internal ribosomal entry site between the NS2 and NS3 coding sequences, the selected chimeric BVDV-1 genomes gave rise to infectious virus progeny. In this context, a mutation in the N-terminal third of NS2 was identified as a critical determinant for efficient production of infectious virions in the absence of uncleaved NS2-3. These findings challenge a previously accepted dogma for pestivirus replication and provide new implications for virion morphogenesis of pestiviruses and HCV.