A Genome-Wide RNA Interference Screen Identifies a Role for Wnt/β-Catenin Signaling during Rift Valley Fever Virus Infection

Evaluation of Inactivation Methods for Rift Valley Fever Virus in Mouse Microglia

Rift Valley fever phlebovirus (RVFV) is a highly pathogenic mosquito-borne virus with bioweapon potential due to its ability to be spread by aerosol transmission. Neurological symptoms are among the worst outcomes of infection, and understanding of pathogenesis mechanisms within the brain is limited. RVFV is classified as an overlap select agent by the CDC and USDA; therefore, experiments involving fully virulent strains of virus are tightly regulated. Here, we present two methods for inactivation of live virus within samples derived from mouse microglia cells using commercially available kits for the preparation of cells for flow cytometry and RNA extraction. Using the flow cytometry protocol, we demonstrate key differences in the response of primary murine microglia to infection with fully virulent versus attenuated RVFV.

Wnt3a Facilitates SARS-CoV-2 Pseudovirus Entry into Cells

How ACE2 functions as the major host receptor of SARS-CoV-2 despite having low expression in the lungs is still unknown. To facilitate the development of therapeutic strategies against coronaviruses, gaining a deeper comprehension of the molecular mechanism of SARS-CoV-2 infection is imperative. In our previous study, we identified several potential host factors of SARS-CoV-2 using an shRNA arrayed screen, one of which was Wnt3a. Here, we validated the significance of Wnt3a, a potent activator of the Wnt/β-catenin signaling pathway, for SARS-CoV-2 entry into cells by evaluating the effects of its knockdown and overexpression on SARS-CoV-2 pseudotyped virus entry. Further analysis revealed that SARS-CoV-2 pseudotyped virus infection activates the canonical Wnt/β-catenin signaling pathway, which we found could subsequently stimulate ACE2 transcription. Collectively, our study identified Wnt3a as an important host factor that facilitates ACE2-mediated virus infection. Insight into the virus entry mechanism is impactful as it will aid in developing novel therapeutic strategies against current and future coronavirus pandemics.

Regulation of the WNT-CTNNB1 signaling pathway by severe fever with thrombocytopenia syndrome virus in a cap-snatching manner

IMPORTANCE

One of the conserved mechanisms at the stage of genome transcription of segmented negative-strand RNA viruses (sNSVs) is the cap-snatching process, which is vital for sNSVs transcription and provides drugable targets for the development of antivirals. However, the specificity of RNAs snatched by sNSV is still unclear. By transcriptomics analysis of whole blood samples from SFTS patients, we found WNT-CTNNB1 signaling pathway was regulated according to the course of the disease. We then demonstrated that L protein of severe fever with thrombocytopenia syndrome virus (SFTSV) could interact with mRNAs of WNT-CTNNB1 signaling pathway-related gene, thus affecting WNT-CTNNB1 signaling pathway through its cap-snatching activity. Activation of WNT-CTNNB1 signaling pathway enhanced SFTSV replication, while inhibition of this pathway decreased SFTSV replication in vitro and in vivo. These findings suggest that WNT-associated genes may be the substrate for SFTSV "cap-snatching", and indicate a conserved sNSVs replication mechanism involving WNT-CTNNB1 signaling.

Dishevelled Has Anti-Viral Activity in Rift Valley Fever Virus Infected Aedes aegypti

Mosquitoes in the genera Aedes and Culex are vectors of Rift Valley fever virus (RVFV), which emerges in periodic epidemics in Africa and Saudi Arabia. Factors that influence the transmission dynamics of RVFV are not well characterized. To address this, we interrogated mosquito host-signaling responses through analysis of differentially expressed genes (DEGs) in two mosquito species with marked differences in RVFV vector competence: Aedes aegypti (Aae, low competence) and Culex tarsalis (Cxt, high competence). Mosquito-host transcripts related to three different signaling pathways were investigated. Selected genes from the Wingless (Wg, WNT-beta-catenin) pathway, which is a conserved regulator of cell proliferation and differentiation, were assessed. One of these, dishevelled (DSH), differentially regulates progression/inhibition of the WNT and JNK (c-Jun N-terminal Kinase) pathways. A negative regulator of the JNK-signaling pathway, puckered, was also assessed. Lastly, Janus kinase/signal transducers and activators of transcription (JAK-STAT) are important for innate immunity; in this context, we tested domeless levels. Here, individual Aae and Cxt were exposed to RVFV MP-12 via oral bloodmeals and held for 14 days. Robust decreases in DEGs in both Aae and Cxt were observed. In particular, Aae DSH expression, but not Cxt DSH, was correlated to the presence/absence of viral RNA at 14 days post-challenge (dpc). Moreover, there was an inverse relationship between the viral copy number and aaeDSH expression. DSH silencing resulted in increased viral copy numbers compared to controls at 3 dpc, consistent with a role for aaeDSH in antiviral immunity. Analysis of cis-regulatory regions for the genes of interest revealed clues to upstream regulation of these pathways.

β-catenin facilitates fowl adenovirus serotype 4 replication through enhancing virus-induced autophagy

β-catenin is a key component of the Wnt/β-catenin signal transduction cascade which is a highly conserved signaling pathway in eukaryotes. Increasing evidence suggests that the Wnt/β-catenin signaling pathway is involved in the infection of many viruses. However, its role in fowl adenovirus serotype 4 (FAdV-4) replication remains unclear. In the present study, we showed that FAdV-4 infection increased the expression of β-catenin and promoted the nuclear translocation of β-catenin. Overexpression of β-catenin and LiCl treatment stimulated the accumulation of β-catenin in the nucleus, and then facilitated FAdV-4 replication. Conversely, repression of β-catenin by inhibitors and siRNA significantly inhibited FAdV-4 replication. Furthermore, inhibition of autophagy by 3-Methyladenine (3-MA) suppressed the FAdV-4 replication, and repression of β-catenin inhibited the FAdV-4-triggered autophagy. In conclusion, the nuclear translocation of β-catenin benefits FAdV-4 replication, and suppression of β-catenin limits FAdV-4 production by inhibiting FAdV-4-induced autophagy. These findings indicated that β-catenin is an important regulator of FAdV-4 replication which can serve as a potential target for anti-FAdV-4 agents.

Arm race between Rift Valley fever virus and host

Rift Valley fever (RVF) is a zoonotic disease caused by Rift Valley fever virus (RVFV), an emerging arbovirus within the Phenuiviridae family of Bunyavirales that has potential to cause severe diseases in both humans and livestock. It increases the incidence of abortion or foetal malformation in ruminants and leads to clinical manifestations like encephalitis or haemorrhagic fever in humans. Upon virus invasion, the innate immune system from the cell or the organism is activated to produce interferon (IFN) and prevent virus proliferation. Meanwhile, RVFV initiates countermeasures to limit antiviral responses at transcriptional and protein levels. RVFV nonstructural proteins (NSs) are the key virulent factors that not only perform immune evasion but also impact the cell replication cycle and has cytopathic effects. In this review, we summarize the innate immunity host cells employ depending on IFN signal transduction pathways, as well as the immune evasion mechanisms developed by RVFV primarily with the inhibitory activity of NSs protein. Clarifying the arms race between host innate immunity and RVFV immune evasion provides new avenues for drug target screening and offers possible solutions to current and future epidemics.

Involvement of the Wnt pathway in BVDV cytopathogenic strain replication in primary bovine cells

Background

Bovine viral diarrhea virus 1 (BVDV-1) of the pestivirus genus is an economically crippling virus in the cattle industry; this positive RNA virus causes mucosal disease resulting in reproductive losses and other disease syndromes. The pathogenesis mechanism of the disease caused by BVDV infection is not well understood; for a better understanding of in vivo host BVDV-1 interactions, we conducted a transcriptomic study of infected cells at different times post-infection.

Methods

We compared the permissiveness and cellular response of a BVDV-1 cytopathogenic strain on Madin-Darby Bovine Kidney cells (MDBK) and bovine lung primary cells, a model closer to in vivo infection. Then a RNAseq analysis was realized on the infected bovine lung primary cells, at 10 hpi and 30 hpi (hours post-infection), to identify transcriptomic signatures.

Results

RNAseq analysis on BVDV-1 infected bovine primary cells showed 2,759 and 5,376 differentially expressed genes at respectively 10 hpi and 30 hpi with an absolute Fold Change  ≥ 2. Among the different pathways deregulated, data analysis revealed a deregulation of Wnt signaling pathway, a conserved process that play a critical role in embryogenesis, cellular proliferation, and differentiation as well as in viral responses against viruses such as Influenza or Hepatitis C. We demonstrated here that the deregulation of the Wnt/βcatenin signaling pathway plays a role in viral replication of BVDV cp strain. Interestingly, we showed that the inhibition of this Wnt pathway using two inhibitors, FZM1 and iCRT14, induced a delay in onset of the establishment of a cytopathic effect of primary cells.

Conclusions

Thereby, this study highlighted a role of the Wnt signaling pathway in the BVDV-1 viral replication in bovine cells, suggesting an interesting option to explore as a new therapeutic target.

The canonical Wnt/β-catenin signaling pathway facilitates pseudorabies virus proliferation and enhances virus-induced autophagy

Pseudorabies virus (PRV) is a swine herpesvirus with a broad host range that causes significant economic losses worldwide. The Wnt/β-catenin signaling pathway is reportedly involved in multiple viruses' proliferation. In this study, we demonstrated that PRV infection significantly activated the Wnt/β-catenin signaling and promoted the nuclear translocation of β-catenin. Applying specific chemical inhibitors (FH535 and iCRT14) caused a remarkable decrease in PRV titers in various cell lines. Knockdown of β-catenin by siRNA also reduced the proliferation of PRV. On the contrary, treatment with lithium chloride (LiCl), an inhibitor of GSK3β, stimulated the Wnt/β-catenin signaling pathway and enhanced the PRV proliferation. Similarly, overexpression of β-catenin promoted PRV proliferation and reversed the antiviral effect of FH535. Moreover, LiCl promoted PRV-induced autophagy, whereas FH535 and iCRT14 showed converse effects. These findings suggest that PRV infection stimulates the canonical Wnt/β-catenin signaling pathway, facilitating PRV proliferation and regulating virus-induced autophagy. These data also provide potential targets for developing antiviral agents against PRV.

MAVS mediates a protective immune response in the brain to Rift Valley fever virus

Rift Valley fever virus (RVFV) is a highly pathogenic mosquito-borne virus capable of causing hepatitis, encephalitis, blindness, hemorrhagic syndrome, and death in humans and livestock. Upon aerosol infection with RVFV, the brain is a major site of viral replication and tissue damage, yet pathogenesis in this organ has been understudied. Here, we investigated the immune response in the brain of RVFV infected mice. In response to infection, microglia initiated robust transcriptional upregulation of antiviral immune genes, as well as increased levels of activation markers and cytokine secretion that is dependent on mitochondrial antiviral-signaling protein (MAVS) and independent of toll-like receptors 3 and 7. In vivo, Mavs^-/- mice displayed enhanced susceptibility to RVFV as determined by increased brain viral burden and higher mortality. Single-cell RNA sequence analysis identified defects in type I interferon and interferon responsive gene expression within microglia in Mavs^-/- mice, as well as dysregulated lymphocyte infiltration. The results of this study provide a crucial step towards understanding the precise molecular mechanisms by which RVFV infection is controlled in the brain and will help inform the development of vaccines and antiviral therapies that are effective in preventing encephalitis.

Rift Valley fever virus causes severe disease in humans and livestock and in some cases can be fatal. There is concern about the use of Rift Valley fever virus as a bioweapon since it can be transmitted through the air, and there are no vaccines or antiviral treatments. Airborne transmission of the virus causes severe inflammation of the brain, yet little is known about the immune response against the virus in this organ. Here, we investigated the immune response in the brain to Rift Valley fever virus following intranasal infection. We determined that microglia, the resident immune cells of the brain, initiate a robust response to Rift Valley fever virus infection and identified a key immune pathway that is critical for the ability of microglia to respond to infection. When this immune pathway is rendered non-functional, mice have a dysregulated response to infection in the brain. This study provides insight into how the immune response can control Rift Valley fever virus infection of the brain.

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.

Phosphorylation of Shrimp Tcf by a Viral Protein Kinase WSV083 Suppresses Its Antiviral Effect

Nuclear DNA-binding TCF proteins, which act as the main downstream effectors of Wnt signaling, are essential for the regulation of cell fate and innate immunity. However, their role during viral infection in shrimp remains unknown. Herein, we demonstrated that Litopenaeus vannamei TCF (LvTcf) acts independently of Lvβ-catenin to promote interferon-like protein LvVago1 production, thus mounting the response to WSSV infection. Further, we observed that WSV083, a WSSV serine/threonine protein kinase, bound to LvTcf and phosphorylated it. Phosphorylated LvTcf was then recognized and degraded via the ubiquitin-proteasome pathway. Moreover, mass spectrometry analyses indicated that the T39 and T104 residues of LvTcf were target sites phosphorylated by WSV083. Point mutation analyses suggested that additional sites of LvTcf may undergo phosphorylation via WSV083. Taken together, the current work provides valuable insights into host immunity and viral pathogenesis. LvTcf is not only a modulator of shrimp innate immunity but is also an important target for WSSV immune evasion. Thus, the current findings will help improve disease control in shrimps.

18 Additional Amino Acids of the Signal Peptide of the Bombyx mori Nucleopolyhedrovirus GP64 Activates Immunoglobulin Binding Protein (BiP) Expression by RNA-seq Analysis

GP64 is the key membrane fusion protein of Group I baculovirus, and while the Bombyx mori nucleopolyhedrovirus (BmNPV) GP64 contains a longer n-region (18 amino acid) of the signal peptide than does the Autographa californica multiple nucleopolyhedrovirus (AcMNPV), the function of the n-region has not been determined. In this study, we first showed that n-region is required for membrane protein localization in BmN cells, then the transcriptome sequencing was conducted on proteins guided by different signal peptide regions, and the results were analyzed and validated by quantitative PCR and luciferase assays. The results indicated that 1049 differentially expressed genes (DEGs) were identified among the different region of signal peptides and the control. With the n-region, the protein export pathway was upregulated significantly, the Wnt-1 signaling pathway was downregulated, and BiP was significantly activated by the GP64 full-length signal peptide. Furthermore, RNA interference on BiP efficiently increased luciferase secretion. These results indicate that the GP64 n-region plays a key role in protein expression and regulation.

Wnt/β-catenin signaling pathway inhibits porcine reproductive and respiratory syndrome virus replication by enhancing the nuclear factor-κB-dependent innate immune response

The Wnt/β-catenin signaling pathway is an evolutionarily highly conserved signaling pathway related to the replication of various viruses. However, the interaction between the Wnt/β-catenin pathway and porcine reproductive and respiratory syndrome virus (PRRSV) is unknown. In the present study, we showed that PRRSV-infected Marc-145 and PAM cells expressed high levels of c-myc and cyclinD1 mRNA and accumulation of β-catenin in the nucleus. PRRSV nonstructural proteins (Nsps) 1α, 1β, 3, 4, 7, 10, and 12, and proteins encoded by open reading frames (ORFs) 2b, 3, and 5 induced the activation of the Wnt pathway according to TOP/FOP luciferase reporter assay. But, Nsp5 inhibited the activation of the Wnt pathway. Pre-treatment with Wnt3a inhibited PRRSV replication in Marc-145 cells in a dose-dependent manner. Over-expression of β-catenin also inhibited PRRSV replication, while silencing of β-catenin by small hairpin RNA increased its replication in Marc-145 cells. Over-expression of β-catenin increased interferon regulatory factor (IRF)-3 expression and nuclear factor (NF)-κB phosphorylation, NF-κB and interferon-stimulated response element promoter activities, and interferon-β, DExD/H-box helicase 58 (DDX58), interferon-induced protein with tetratricopeptide repeats 1 (IFIT1), interleukin (IL)-1β, tumor necrosis factor (TNF)-α, and IL-8 mRNA expression. Conversely, silencing β-catenin decreased phosphorylated IRF-3 and NF-κB, NF-κB and IFIT1 promoter activities, and IFN-β, DDX58, IFIT1, IL-1β, TNF-α, and IL-8 mRNA levels in Marc-145 cells. Co-immunoprecipitation and immunofluorescence colocalization analyses confirmed that β-catenin interacted with NF-κB in Marc-145 cells. In conclusion, PRRSV infection activates the Wnt/β-catenin signaling pathway via Nsps 1α, 1β, 3, 4, 7, 10, and 12, and proteins encoded by ORFs 2b, 3, and 5. The Wnt/β-catenin pathway then inhibits PRRSV replication by enhancing the NF-κB-dependent innate immune response. These findings further our understanding of the role of the Wnt/β-catenin signaling pathway in regulating PRRSV replication and provide new insights into virus-host interactions.

Genome-wide CRISPR screening reveals genes essential for cell viability and resistance to abiotic and biotic stresses in Bombyx mori

High-throughput genetic screens are powerful methods to interrogate gene function on a genome-wide scale and identify genes responsible to certain stresses. Here, we developed a piggyBac strategy to deliver pooled sgRNA libraries stably into cell lines. We used this strategy to conduct a screen based on genome-wide clustered regularly interspaced short palindromic repeat technology (CRISPR)-Cas9 in Bombyx mori cells. We first constructed a single guide RNA (sgRNA) library containing 94,000 sgRNAs, which targeted 16,571 protein-coding genes. We then generated knockout collections in BmE cells using the piggyBac transposon. We identified 1006 genes that are essential for cell viability under normal growth conditions. Of the identified genes, 82.4% (829 genes) were homologous to essential genes in seven animal species. We also identified 838 genes whose loss facilitated cell growth. Next, we performed context-specific positive screens for resistance to biotic or nonbiotic stresses using temperature and baculovirus separately, which identified several key genes and pathways from each screen. Collectively, our results provide a novel and versatile platform for functional annotations of B. mori genomes and deciphering key genes responsible for various conditions. This study also shows the effectiveness, practicality, and convenience of genome-wide CRISPR screens in nonmodel organisms.

Crimean-Congo hemorrhagic fever virus infection triggers the upregulation of the Wnt signaling pathway inhibitor genes

Crimean-Congo hemorrhagic fever virus (CCHFV) is a highly pathogenic agent. Thus far, vaccines and specific antiviral therapies are not available against the threat of infection. Our knowledge regarding its pathogenesis is indeed limited, and thus, developing effective antiviral therapies is hampered. Several studies have demonstrated that the CCHFV infection has an impact on numerous signal transduction pathways. In parallel, the Wnt signaling pathway components are responsible for different important biological processes including cell fate determination, cell migration and cell polarity. Moreover, its implication among several virus infections has been proven, yet little is known in reference to which components of the Wnt pathway are being activated/inhibited as a response to the infection. Our aim was to elicit the influence of the CCHFV infection on adenocarcinomic human alveolar basal epithelial cells in vitro regarding the Wnt signaling pathway-related genes. Gene-expression changes of 92 Wnt-associated genes were examined 48 h post-infection. Furthermore, β-catenin levels were compared in the infected and uninfected cells. Significant changes were observed in the case of 13 genes. The majority of the upregulated genes are associated with the inhibition of the Wnt/β-catenin signaling. Additionally, infected cells expressed less β-catenin. Our findings suggest that CCHFV blocks the Wnt/β-catenin pathway. Our study corroborates the link between CCHFV infection and the Wnt signaling pathways. In addition, it broadens our knowledge in the CCHFV pathomechanism.

Immune correlates of postexposure vaccine protection against Marburg virus

Postexposure immunization can prevent disease and reduce transmission following pathogen exposure. The rapid immunostimulatory properties of recombinant vesicular stomatitis virus (rVSV)-based vaccines make them suitable postexposure treatments against the filoviruses Ebola virus and Marburg virus (MARV); however, the mechanisms that drive this protection are undefined. Previously, we reported 60–75% survival of rhesus macaques treated with rVSV vectors expressing MARV glycoprotein (GP) 20–30 minutes after a low dose exposure to the most pathogenic variant of MARV, Angola. Survival in this model was linked to production of GP-specific antibodies and lower viral load. To confirm these results and potentially identify novel correlates of postexposure protection, we performed a similar experiment, but analyzed plasma cytokine levels, frequencies of immune cell subsets, and the transcriptional response to infection in peripheral blood. In surviving macaques (80–89%), we observed induction of genes mapping to antiviral and interferon-related pathways early after treatment and a higher percentage of T helper 1 (Th1) and NK cells. In contrast, the response of non-surviving macaques was characterized by hypercytokinemia; a T helper 2 signature; recruitment of low HLA-DR expressing monocytes and regulatory T-cells; and transcription of immune checkpoint (e.g., PD-1, LAG3) genes. These results suggest dysregulated immunoregulation is associated with poor prognosis, whereas early innate signaling and Th1-skewed immunity are important for survival.

Functions of the WNT Signaling Network in Shaping Host Responses to Infection

It is well-established that aberrant WNT expression and signaling is associated with developmental defects, malignant transformation and carcinogenesis. More recently, WNT ligands have emerged as integral components of host responses to infection but their functions in the context of immune responses are incompletely understood. Roles in the modulation of inflammatory cytokine production, host cell intrinsic innate defense mechanisms, as well as the bridging of innate and adaptive immunity have been described. To what degree WNT responses are defined by the nature of the invading pathogen or are specific for subsets of host cells is currently not well-understood. Here we provide an overview of WNT responses during infection with phylogenetically diverse pathogens and highlight functions of WNT ligands in the host defense against infection. Detailed understanding of how the WNT network orchestrates immune cell functions will not only improve our understanding of the fundamental principles underlying complex immune response, but also help identify therapeutic opportunities or potential risks associated with the pharmacological targeting of the WNT network, as currently pursued for novel therapeutics in cancer and bone disorders.

High-throughput screening for negative-stranded hemorrhagic fever viruses using reverse genetics

Viral hemorrhagic fevers (VHFs) cause thousands of fatalities every year, but the treatment options for their management remain very limited. In particular, the development of therapeutic interventions is restricted by the lack of commercial viability of drugs targeting individual VHF agents. This makes approaches like drug repurposing and/or the identification of broad range therapies (i.e. those directed at host responses or common proviral factors) highly attractive. However, the identification of candidates for such antiviral repurposing or of host factors/pathways important for the virus life cycle is reliant on high-throughput screening (HTS). Recently, such screening work has been increasingly facilitated by the availability of reverse genetics-based approaches, including tools such as full-length clone (FLC) systems to generate reporter-expressing viruses or various life cycle modelling (LCM) systems, many of which have been developed and/or greatly improved during the last years. In particular, since LCM systems are capable of modelling specific steps in the life cycle, they are a valuable tool for both targeted screening (i.e. for inhibitors of a specific pathway) and mechanism of action studies. This review seeks to summarize the currently available reverse genetics systems for negative-sense VHF causing viruses (i.e. arenaviruses, bunyaviruses and filoviruses), and to highlight the recent advancements made in applying these systems for HTS to identify either antivirals or new virus-host interactions that might hold promise for the development of future treatments for the infections caused by these deadly but neglected virus groups.

HSV-1 single-cell analysis reveals the activation of anti-viral and developmental programs in distinct sub-populations

Viral infection is usually studied at the population level by averaging over millions of cells. However, infection at the single-cell level is highly heterogeneous, with most infected cells giving rise to no or few viral progeny while some cells produce thousands. Analysis of Herpes Simplex virus 1 (HSV-1) infection by population-averaged measurements has taught us a lot about the course of viral infection, but has also produced contradictory results, such as the concurrent activation and inhibition of type I interferon signaling during infection. Here, we combine live-cell imaging and single-cell RNA sequencing to characterize viral and host transcriptional heterogeneity during HSV-1 infection of primary human cells. We find extreme variability in the level of viral gene expression among individually infected cells and show that these cells cluster into transcriptionally distinct sub-populations. We find that anti-viral signaling is initiated in a rare group of abortively infected cells, while highly infected cells undergo cellular reprogramming to an embryonic-like transcriptional state. This reprogramming involves the recruitment of β-catenin to the host nucleus and viral replication compartments, and is required for late viral gene expression and progeny production. These findings uncover the transcriptional differences in cells with variable infection outcomes and shed new light on the manipulation of host pathways by HSV-1.

Quantitative Proteomic Analysis Reveals Unfolded-Protein Response Involved in Severe Fever with Thrombocytopenia Syndrome Virus Infection

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging, highly pathogenic, infectious disease caused by infection with a newly discovered tick-borne phlebovirus, SFTS virus (SFTSV). Limited information on the molecular mechanism of SFTSV infection and pathogenesis impedes the development of effective vaccines and drugs for SFTS prevention and treatment. In this study, an isobaric tag for relative and absolute quantification (iTRAQ)-based quantitative proteomic analysis of SFTSV-infected HEK 293 cells was performed to explore dynamic host cellular protein responses toward SFTSV infection. A total of 433 of 5,606 host proteins involved in different biological processes were differentially regulated by SFTSV infection. The proteomic results highlighted a potential role of endoplasmic reticular stress-triggered unfolded-protein response (UPR) in SFTSV infection. Further functional studies confirmed that all three major branches of the UPR, including the PKR-like endoplasmic reticulum kinase (PERK), the activating transcription factor-6 (ATF6), and the inositol-requiring protein-1 (IRE1)/X-box-binding protein 1 (XBP1) pathways, were activated by SFTSV. However, only the former two pathways play a crucial role in SFTSV infection. Furthermore, expression of SFTSV glycoprotein (GP) alone was sufficient to stimulate the UPR, whereas suppression of PERK and ATF6 notably decreased GP expression. Interestingly, two other newly discovered phleboviruses, Heartland virus and Guertu virus, also stimulated the UPR, suggesting a common mechanism shared by these genetically related phleboviruses. This study provides a global view to our knowledge on how host cells respond to SFTSV infection and highlights that host cell UPR plays an important role in phlebovirus infection.IMPORTANCE Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging tick-borne bunyavirus that causes severe fever with thrombocytopenia syndrome in humans, with a mortality rate reaching up to 30% in some outbreaks. There are currently no U.S. Food and Drug Administration-approved vaccines or specific antivirals available against SFTSV. To comprehensively understand the molecular interactions occurring between SFTSV and the host cell, we exploit quantitative proteomic approach to investigate the dynamic host cellular responses to SFTSV infection. The results highlight multiple biological processes being regulated by SFTSV infection. Among these, we focused on exploration of the mechanism of how SFTSV infection stimulates the host cell's unfolded-protein response (UPR) and identified the UPR as a common feature shared by SFTSV-related new emerging phleboviruses. This study, for the first time to our knowledge, provides a global map for host cellular responses to SFTSV infection and highlighted potential host targets for further research.

miR-193b represses influenza A virus infection by inhibiting Wnt/β-catenin signalling

Due to an increasing emergence of new and drug‐resistant strains of the influenza A virus (IAV), developing novel measures to combat influenza is necessary. We have previously shown that inhibiting Wnt/β‐catenin pathway reduces IAV infection. In this study, we aimed to identify antiviral human microRNAs (miRNAs) that target the Wnt/β‐catenin signalling pathway. Using a miRNA expression library, we identified 85 miRNAs that up‐regulated and 20 miRNAs that down‐regulated the Wnt/β‐catenin signalling pathway. Fifteen miRNAs were validated to up‐regulate and five miRNAs to down‐regulate the pathway. Overexpression of four selected miRNAs (miR‐193b, miR‐548f‐1, miR‐1‐1, and miR‐509‐1) that down‐regulated the Wnt/β‐catenin signalling pathway reduced viral mRNA, protein levels in A/PR/8/34‐infected HEK293 cells, and progeny virus production. Overexpression of miR‐193b in lung epithelial A549 cells also resulted in decreases of A/PR/8/34 infection. Furthermore, miR‐193b inhibited the replication of various strains, including H1N1 (A/PR/8/34, A/WSN/33, A/Oklahoma/3052/09) and H3N2 (A/Oklahoma/309/2006), as determined by a viral reporter luciferase assay. Further studies revealed that β‐catenin was a target of miR‐193b, and β‐catenin rescued miR‐193b‐mediated suppression of IAV infection. miR‐193b induced G0/G1 cell cycle arrest and delayed vRNP nuclear import. Finally, adenovirus‐mediated gene transfer of miR‐193b to the lung reduced viral load in mice challenged by a sublethal dose of A/PR/8/34. Collectively, our findings suggest that miR‐193b represses IAV infection by inhibiting Wnt/β‐catenin signalling.

Host-based processes as therapeutic targets for Rift Valley fever virus

Rift Valley fever virus (RVFV) is an enveloped, segmented, negative sense RNA virus that replicates within the host's cytoplasm. To facilitate its replication, RVFV must utilize host cell processes and as such, these processes may serve as potential therapeutic targets. This review summarizes key host cell processes impacted by RVFV infection. Specifically the influence of RVFV on host transcriptional regulation, post-transcriptional regulation, protein half-life and availability, host signal transduction, trafficking and secretory pathways, cytoskeletal modulation, and mitochondrial processes and oxidative stress are discussed. Therapeutics targeted towards host processes that are essential for RVFV to thrive as well as their efficacy and importance to viral pathogenesis are highlighted.

Brucella Downregulates Tumor Necrosis Factor-α to Promote Intracellular Survival via Omp25 Regulation of Different MicroRNAs in Porcine and Murine Macrophages

Brucella spp. impedes the production of pro-inflammatory cytokines by its outer membrane protein Omp25 in order to promote survival and immune evasion. However, how Omp25 regulates tumor necrosis factor (TNF-α) expression in different mammalian macrophages remains unclear. In this study, we investigated the potential mechanisms by which Omp25 regulates TNF-α expression and found that Omp25-deficient mutant of B. suis exhibited an enhanced TNF-α expression compared with wild-type (WT) B. suis, whereas ectopic expression of Omp25 suppressed LPS-induced TNF-α production at both protein and mRNA levels in porcine alveolar macrophages (PAMs) and murine macrophage RAW264.7 cells. We observed that Omp25 protein as well as WT B. suis upregulated miR-146a, -181a, -181b, and -301a-3p and downregulated TRAF6 and IRAK1 in both PAMs and RAW264.7 cells, but separately upregulates miR-130a-3p in PAMs and miR-351-5p in RAW264.7. The upregulation of miR-146a or miR-351-5p attenuated TNF-α transcription by targeting TRAF6 and IRAK1 at the 3' untranslated region (UTR), resulting in inhibition of NF-kB pathway, while upregulation of miR-130a-3p, -181a, or -301a-3p correlated temporally with decreased TNF-α by targeting its 3'UTR in PAMs or RAW264.7 cells. In contrast, inhibition of miR-130a-3p, -146a, -181a, and -301a-3p attenuated the inhibitory effects of Omp25 on LPS-induced TNF-α in PAMs, while inhibition of miR-146a, -181a, -301a-3p, and -351-5p attenuated the inhibitory effects of Omp25 in RAW264.7, resulting in an increased TNF-α production and decreased intracellular bacteria in both cells. Taken together, our results demonstrate that Brucella downregulates TNF-α to promote intracellular survival via Omp25 regulation of different microRNAs in porcine and murine macrophages.

Vaccinia virus protein A49 activates Wnt signalling by targetting the E3 ligase β-TrCP

Vaccinia virus (VACV) encodes multiple proteins inhibiting the NF-κB signalling pathway. One of these, A49, targets the E3 ubiquitin ligase β-TrCP, which is responsible for the ubiquitylation and consequential proteosomal degradation of IκBα and the release of the NF-κB heterodimer. β-TrCP is a pleiotropic enzyme ubiquitylating multiple cellular substrates, including the transcriptional activator β-catenin. Here we demonstrate that A49 can activate the Wnt signalling pathway, a critical pathway that is involved in cell cycle and cell differentiation, and is controlled by β-catenin. The data presented show that the expression of A49 ectopically or during VACV infection causes accumulation of β-catenin, and that A49 triggering of Wnt signalling is dependent on binding β-TrCP. This is consistent with A49 blocking the ability of β-TrCP to recognise β-catenin and IκBα, and possibly other cellular targets. Thus, A49 targetting of β-TrCP affects multiple cellular pathways, including the NF-κB and Wnt signalling cascades.

Recent advances in the development of antiviral therapeutics for Rift Valley fever virus infection

Rift Valley fever virus (RVFV) is a mosquito-borne bunyavirus endemic to sub-Saharan Africa and the Arabian Peninsula and the etiological agent of Rift Valley fever. Rift Valley fever is a disease of major public health and economic concern, affecting livestock and humans. In ruminants, RVFV infection is characterized by high mortality rates in newborns and near 100% abortion rates in pregnant animals. Infection in humans is typically manifested as a self-limiting febrile illness, but can lead to severe and fatal hepatitis, encephalitis, hemorrhagic fever or retinitis with partial or complete blindness. Currently, there are no specific treatment options available for RVFV infection. This review presents a summary of the therapeutic approaches that have been explored on the treatment of RVFV infection.

A MicroRNA Screen Identifies the Wnt Signaling Pathway as a Regulator of the Interferon Response during Flavivirus Infection

The impact of mosquito-borne flavivirus infections worldwide is significant, and many critical aspects of these viruses' biology, including virus-host interactions, host cell requirements for replication, and how virus-host interactions impact pathology, remain to be fully understood. The recent reemergence and spread of flaviviruses, including dengue virus (DENV), West Nile virus (WNV), and Zika virus (ZIKV), highlight the importance of performing basic research on this important group of pathogens. MicroRNAs (miRNAs) are small, noncoding RNAs that modulate gene expression posttranscriptionally and have been demonstrated to regulate a broad range of cellular processes. Our research is focused on identifying pro- and antiflaviviral miRNAs as a means of characterizing cellular pathways that support or limit viral replication. We have screened a library of known human miRNA mimics for their effect on the replication of three flaviviruses, DENV, WNV, and Japanese encephalitis virus (JEV), using a high-content immunofluorescence screen. Several families of miRNAs were identified as inhibiting multiple flaviviruses, including the miRNA miR-34, miR-15, and miR-517 families. Members of the miR-34 family, which have been extensively characterized for their ability to repress Wnt/β-catenin signaling, demonstrated strong antiflaviviral effects, and this inhibitory activity extended to other viruses, including ZIKV, alphaviruses, and herpesviruses. Previous research suggested a possible link between the Wnt and type I interferon (IFN) signaling pathways. Therefore, we investigated the role of type I IFN induction in the antiviral effects of the miR-34 family and confirmed that these miRNAs potentiate interferon regulatory factor 3 (IRF3) phosphorylation and translocation to the nucleus, the induction of IFN-responsive genes, and the release of type I IFN from transfected cells. We further demonstrate that the intersection between the Wnt and IFN signaling pathways occurs at the point of glycogen synthase kinase 3β (GSK3β)-TANK-binding kinase 1 (TBK1) binding, inducing TBK1 to phosphorylate IRF3 and initiate downstream IFN signaling. In this way, we have identified a novel cellular signaling network with a critical role in regulating the replication of multiple virus families. These findings highlight the opportunities for using miRNAs as tools to discover and characterize unique cellular factors involved in supporting or limiting virus replication, opening up new avenues for antiviral research.IMPORTANCE MicroRNAs are a class of small regulatory RNAs that modulate cellular processes through the posttranscriptional repression of multiple transcripts. We hypothesized that individual miRNAs may be capable of inhibiting viral replication through their effects on host proteins or pathways. To test this, we performed a high-content screen for miRNAs that inhibit the replication of three medically relevant members of the flavivirus family: West Nile virus, Japanese encephalitis virus, and dengue virus 2. The results of this screen identify multiple miRNAs that inhibit one or more of these viruses. Extensive follow-up on members of the miR-34 family of miRNAs, which are active against all three viruses as well as the closely related Zika virus, demonstrated that miR-34 functions through increasing the infected cell's ability to respond to infection through the interferon-based innate immune pathway. Our results not only add to the knowledge of how viruses interact with cellular pathways but also provide a basis for more extensive data mining by providing a comprehensive list of miRNAs capable of inhibiting flavivirus replication. Finally, the miRNAs themselves or cellular pathways identified as modulating virus infection may prove to be novel candidates for the development of therapeutic interventions.