Chandipura virus changes cellular miRNome in human microglial cells.

Chandipura virus (CHPV) is a neurotropic virus, known to cause encephalitis in humans. The microRNAs (miRNA/miR) play an important role in the pathogenesis of viral infection. The present study is focused on the role of miRNAs during CHPV (strain 1653514) infection in human microglial cells. The deep sequencing of CHPV-infected human microglial cells identified a total of 12 differentially expressed miRNA (DEMs). To elucidate the role of DEMs, the target gene prediction, Gene Ontology term (GO Term), pathway enrichment analysis, and miRNA-messenger RNA (mRNA) interaction network analysis was performed. The GO terms and pathway enrichment analysis provided 146 enriched genes; which were involved in interferon response, cytokine and chemokine signaling. Further, the WGCNA (weighted gene coexpression network analysis) of the enriched genes were discretely categorized into three modules (blue, brown, and turquoise). The hub genes in the blue module may correlate to CHPV induced neuroinflammation. Altogether, the miRNA-mRNA interaction network and WGCNA study revealed the following pairs, hsa-miR-542-3p and FAF1, hsa-miR-92a-1-5p and MYD88, and hsa-miR-3187-3p and TNFRSF21, which may contribute to neuroinflammation during CHPV infection in human microglial cells.

Comparative transcriptome analysis of long non coding RNA (lncRNA) in RTG-2 cells infected by infectious hematopoietic necrosis virus.

Infectious hematopoietic necrosis virus (IHNV) is the vital pathogen that has caused the great economic loss in salmonid fisheries. To date, there is limited information concerning the changes of lncRNAs in RTG-2 cells infected by IHNV. In this study, a comparative transcriptome analysis of lncRNAs was performed in RTG-2 cells with and without IHNV infection to determine their changes and the effects on IHNV infection. The results showed that IHNV infection significantly changed the expression levels of lncRNAs and mRNAs, including 3693 differentially expressed lncRNAs (DE-lncRNAs) and 3503 differentially expressed mRNAs (DE-mRNAs) respectively. These DE-lncRNAs and DE-mRNAs induced by IHNV were mostly associated with immune response, RNA processing, and viral diseases related pathways. Further analysis found that some DE-lncRNAs might participate in the regulation of extracellular matrix metabolism, apoptosis, lipid synthesis, autophagy, and immune responses referring to the functions of their target genes. Afterwards, 349 co-expression relationships were constructed by 223 DE-lncRNAs and 271 DE-mRNAs, of which LTCONS_00146935 was the pivotal node in the interaction networks, and was together with its target genes modulated the immune responses under the IHNV infection. RT-qPCR results showed that the changes of the selected immune-related DEGs were in consistent with the RNA-seq data, suggesting that the sequencing data was relatively reliable. In summary, this is the first study to determine the changes and interactions of lncRNA-mRNA in RTG-2 cells under the IHNV infection. The results provided the valuable information concerning the lncRNAs in salmonid fish, which will benefit for future study on uncovering the roles of lncRNAs-mRNAs during the viral infection.

Zebrafish prmt3 negatively regulates antiviral responses.

Arginine methylation catalyzed by protein arginine methyltransferases (PRMT) is a common post-translational modification in histone and nonhistone proteins, which regulates many cellular functions. Protein arginine methyltransferase 3 (prmt3), a type I arginine methyltransferase, has been shown to carry out the formation of stable monomethylarginine as an intermediate before the establishment of asymmetric dimethylarginine. To date, however, the role of PRMT3 in antiviral innate immunity has not been elucidated. This study showed that zebrafish prmt3 was upregulated by virus infection and that the overexpression of prmt3 suppressed cellular antiviral response. The PRMT3 inhibitor, SGC707, enhanced antiviral capability. Consistently, prmt3-null zebrafish were more resistant to Spring Viremia of Carp Virus (SVCV) and Grass Carp Reovirus (GCRV) infection. Further assays showed that the overexpression of prmt3 diminished the phosphorylation of irf3 and prmt3 interacted with rig-i. In addition, both zinc-finger domain and catalytic domain of prmt3 were required for the suppressive function of prmt3 on IFN activation. Our findings suggested that zebrafish prmt3 negatively regulated the antiviral responses, implicating the vital role of prmt3-or even arginine methylation-in antiviral innate immunity.

Effect of the Viral Hemorrhagic Septicemia Virus Nonvirion Protein on Translation via PERK-eIF2α Pathway.

Viral hemorrhagic septicemia virus (VHSV) is one of the most deadly infectious fish pathogens, posing a serious threat to the aquaculture industry and freshwater ecosystems worldwide. Previous work showed that VHSV sub-genotype IVb suppresses host innate immune responses, but the exact mechanism by which VHSV IVb inhibits antiviral response remains incompletely characterized. As with other novirhabdoviruses, VHSV IVb contains a unique and highly variable nonvirion (NV) gene, which is implicated in viral replication, virus-induced apoptosis and regulating interferon (IFN) production. However, the molecular mechanisms underlying the role of IVb NV gene in regulating viral or cellular processes is poorly understood. Compared to the wild-type recombinant (rWT) VHSV, mutant VHSV lacking a functional IVb NV reduced IFN expression and compromised innate immune response of the host cells by inhibiting translation. VHSV IVb infection increased phosphorylated eukaryotic initiation factor 2α (p-eIF2α), resulting in host translation shutoff. However, VHSV IVb protein synthesis proceeds despite increasing phosphorylation of eIF2α. During VHSV IVb infection, eIF2α phosphorylation was mediated via PKR-like endoplasmic reticulum kinase (PERK) and was required for efficient viral protein synthesis, but shutoff of host translation and IFN signaling was independent of p-eIF2α. Similarly, IVb NV null VHSV infection induced less p-eIF2α, but exhibited decreased viral protein synthesis despite increased levels of viral mRNA. These findings show a role for IVb NV in VHSV pathogenesis by utilizing the PERK-eIF2α pathway for viral-mediated host shutoff and interferon signaling to regulate host cell response.

Development of a minigenome cassette for Lettuce necrotic yellows virus: A first step in rescuing a plant cytorhabdovirus.

Rhabdoviruses are enveloped negative-sense RNA viruses that have numerous biotechnological applications. However, recovering plant rhabdoviruses from cDNA remains difficult due to technical difficulties such as the need for concurrent in planta expression of the viral genome together with the viral nucleoprotein (N), phosphoprotein (P) and RNA-dependent RNA polymerase (L) and viral genome instability in E. coli. Here, we developed a negative-sense minigenome cassette for Lettuce necrotic yellows virus (LNYV). We introduced introns into the unstable viral ORF and employed Agrobacterium tumefaciens to co-infiltrate Nicotiana with the genes for the N, P, and L proteins together with the minigenome cassette. The minigenome cassette included the Discosoma sp. red fluorescent protein gene (DsRed) cloned in the negative-sense between the viral trailer and leader sequences which were placed between hammerhead and hepatitis delta ribozymes. In planta DsRed expression was demonstrated by western blotting while the appropriate splicing of introduced introns was confirmed by sequencing of RT-PCR product.

Cellular, humoral and molecular responses in rainbow trout (Oncorhynchus mykiss) exposed to a herbicide and subsequently infected with infectious hematopoietic necrosis virus.

Aquatic ecosystems are now chronically polluted by a cocktail of many chemical substances. There is now clear evidence of associations between exposure to pollutants and greater susceptibility to pathogens. The aim of the present study was to characterize the defense capacities of rainbow trout (Oncorhynchus mykiss), chronically exposed to pendimethalin (PD), to subsequent experimental challenge with the infectious hematopoietic necrosis virus (IHNV). Immunological responses were examined at different organizational levels, from individuals to gene expression. No negative effects of PD were noted on the Fulton index nor on the liver or spleen somatic indices (LSI; SSI) before viral infection, but the infectious stress seems to generate a weak but significant decrease in Fulton and LSI values, which could be associated with consumption of energy reserves. During the viral challenges, the distribution of cumulative mortality was slightly different between infected groups. The impact of the virus on fish previously contaminated by PD started earlier and lasted longer than controls. The proportion of seropositive fish was lower in the fish group exposed to PD than in the control group, with similar quantities of anti-IHNV antibodies secreted in positive fish, regardless of the treatment. While no significant differences in C3-1 expression levels were detected throughout the experiment, TNF1&2, TLR3, Il-1ß and IFN expression levels were increased in all infected fish, but the difference was more significant in fish groups previously exposed to herbicide. On the other hand, ß-def expression was decreased in the pendimethalin-IHNV group compared to that in fish only infected by the virus (control-IHNV group).

Genome-wide association analysis and accuracy of genome-enabled breeding value predictions for resistance to infectious hematopoietic necrosis virus in a commercial rainbow trout breeding population.

BACKGROUND: Infectious hematopoietic necrosis (IHN) is a disease of salmonid fish that is caused by the IHN virus (IHNV). Under intensive aquaculture conditions, IHNV can cause significant mortality and economic losses. Currently, there is no proven and cost-effective method for IHNV control. Clear Springs Foods, Inc. has been applying selective breeding to improve genetic resistance to IHNV in their rainbow trout breeding program. The goals of this study were to elucidate the genetic architecture of IHNV resistance in this commercial population by performing genome-wide association studies (GWAS) with multiple regression single-step methods and to assess if genomic selection can improve the accuracy of genetic merit predictions over conventional pedigree-based best linear unbiased prediction (PBLUP) using cross-validation analysis. RESULTS: Ten moderate-effect quantitative trait loci (QTL) associated with resistance to IHNV that jointly explained up to 42% of the additive genetic variance were detected in our GWAS. Only three of the 10 QTL were detected by both single-step Bayesian multiple regression (ssBMR) and weighted single-step GBLUP (wssGBLUP) methods. The accuracy of breeding value predictions with wssGBLUP (0.33-0.39) was substantially better than with PBLUP (0.13-0.24). CONCLUSIONS: Our comprehensive genome-wide scan for QTL revealed that genetic resistance to IHNV is controlled by the oligogenic inheritance of up to 10 moderate-effect QTL and many small-effect loci in this commercial rainbow trout breeding population. Taken together, our results suggest that whole genome-enabled selection models will be more effective than the conventional pedigree-based method for breeding value estimation or the marker-assisted selection approach for improving the genetic resistance of rainbow trout to IHNV in this population.

TLR7 Controls VSV Replication in CD169+ SCS Macrophages and Associated Viral Neuroinvasion.

Vesicular stomatitis virus (VSV) is an insect-transmitted rhabdovirus that is neurovirulent in mice. Upon peripheral VSV infection, CD169+ subcapsular sinus (SCS) macrophages capture VSV in the lymph, support viral replication, and prevent CNS neuroinvasion. To date, the precise mechanisms controlling VSV infection in SCS macrophages remain incompletely understood. Here, we show that Toll-like receptor-7 (TLR7), the main sensing receptor for VSV, is central in controlling lymph-borne VSV infection. Following VSV skin infection, TLR7-/- mice display significantly less VSV titers in the draining lymph nodes (dLN) and viral replication is attenuated in SCS macrophages. In contrast to effects of TLR7 in impeding VSV replication in the dLN, TLR7-/- mice present elevated viral load in the brain and spinal cord highlighting their susceptibility to VSV neuroinvasion. By generating novel TLR7 floxed mice, we interrogate the impact of cell-specific TLR7 function in anti-viral immunity after VSV skin infection. Our data suggests that TLR7 signaling in SCS macrophages supports VSV replication in these cells, increasing LN infection and may account for the delayed onset of VSV-induced neurovirulence observed in TLR7-/- mice. Overall, we identify TLR7 as a novel and essential host factor that critically controls anti-viral immunity to VSV. Furthermore, the novel mouse model generated in our study will be of valuable importance to shed light on cell-intrinsic TLR7 biology in future studies.

The stress granule protein G3BP1 binds viral dsRNA and RIG-I to enhance interferon-ß response.

RIG-I senses viral RNA in the cytosol and initiates host innate immune response by triggering the production of type 1 interferon. A recent RNAi knockdown screen yielded close to hundred host genes whose products affected viral RNA-induced IFN-ß production and highlighted the complexity of the antiviral response. The stress granule protein G3BP1, known to arrest mRNA translation, was identified as a regulator of RIG-I-induced IFN-ß production. How G3BP1 functions in RIG-I signaling is not known, however. Here, we overexpress G3BP1 with RIG-I in HEK293T cells and found that G3BP1 significantly enhances RIG-I-induced ifn-b mRNA synthesis. More importantly, we demonstrate that G3BP1 binds RIG-I and that this interaction involves the C-terminal RGG domain of G3BP1. Confocal microscopy studies also show G3BP1 co-localization with RIG-I and with infecting vesicular stomatitis virus in Cos-7 cells. Interestingly, immunoprecipitation studies using biotin-labeled viral dsRNA or poly(I·C) and cell lysate-derived or in vitro translated G3BP1 indicated that G3BP1 could directly bind these substrates and again via its RGG domain. Computational modeling further revealed a juxtaposed interaction between G3BP1 RGG and RIG-I RNA-binding domains. Together, our data reveal G3BP1 as a critical component of RIG-I signaling and possibly acting as a co-sensor to promote RIG-I recognition of pathogenic RNA.

Released Tryptophanyl-tRNA Synthetase Stimulates Innate Immune Responses against Viral Infection.

Tryptophanyl-tRNA synthetase (WRS) is one of the aminoacyl-tRNA synthetases (ARSs) that possesses noncanonical functions. Full-length WRS is released during bacterial infection and primes the Toll-like receptor 4 (TLR4)-myeloid differentiation factor 2 (MD2) complex to elicit innate immune responses. However, the role of WRS in viral infection remains unknown. Here, we show that full-length WRS is secreted by immune cells in the early phase of viral infection and functions as an antiviral cytokine. Treatment of cells with recombinant WRS protein promotes the production of inflammatory cytokines and type I interferons (IFNs) and curtails virus replication in THP-1 and Raw264.7 cells but not in TLR4-/- or MD2-/- bone marrow-derived macrophages (BMDMs). Intravenous and intranasal administration of recombinant WRS protein induces an innate immune response and blocks viral replication in vivo These findings suggest that secreted full-length WRS has a noncanonical role in inducing innate immune responses to viral infection as well as to bacterial infection.IMPORTANCE ARSs are essential enzymes in translation that link specific amino acids to their cognate tRNAs. In higher eukaryotes, some ARSs possess additional, noncanonical functions in the regulation of cell metabolism. Here, we report a novel noncanonical function of WRS in antiviral defense. WRS is rapidly secreted in response to viral infection and primes the innate immune response by inducing the secretion of proinflammatory cytokines and type I IFNs, resulting in the inhibition of virus replication both in vitro and in vivo Thus, we consider WRS to be a member of the antiviral innate immune response. The results of this study enhance our understanding of host defense systems and provide additional information on the noncanonical functions of ARSs.

Nitrosporeusine analogue ameliorates Chandipura virus induced inflammatory response in CNS via NFκb inactivation in microglia.

Chandipura Virus (CHPV), a negative-stranded RNA virus belonging to the Rhabdoviridae family, has been previously reported to bring neuronal apoptosis by activating several factors leading to neurodegeneration. Following virus infection of the central nervous system, microglia, the ontogenetic and functional equivalents of macrophages in somatic tissues gets activated and starts secreting chemokines, thereby recruiting peripheral leukocytes into the brain parenchyma. In the present study, we have systemically examined the effect of CHPV on microglia and the activation of cellular signalling pathways leading to chemokine expression upon CHPV infection. Protein and mRNA expression profiles of chemokine genes revealed that CHPV infection strongly induces the expression of CXC chemokine ligand 10 (CXCL10) and CC chemokine ligand 5 (CCL5) in microglia. CHPV infection triggered the activation of signalling pathways mediated by mitogen-activated protein kinases, including p38, JNK 1 and 2, and nuclear factor κB (NF-kappaB). CHPV-induced expression of CXCL10 and CCL5 was achieved by the activation of p38 and NF-kappaB pathways. Considering the important role of inflammation in neurodegeneration, we have targeted NF-kappaB using a newly synthesised natural product nitrosporeusine analogue and showed incapability of microglial supernatant of inducing apoptosis in neurons after treatment.

RNAi-mediated treatment of two vertically transmitted rhabdovirus infecting the salmon louse (Lepeophtheirus salmonis).

Rhabdoviruses are a family of enveloped negative-sense single-stranded RNA viruses infecting a variety of hosts. Recently, two vertically transmitted salmon louse (Lepeophtheirus salmonis) rhabdoviruses (LsRV) have been identified. The prevalence of these viruses was measured along the Norwegian coast and found to be close to 100%, and with the present lack of suitable cell lines to propagate these viruses, it is challenging to obtain material to study their host impact and infection routes. Thus, virus free lice strains were established from virus infected lice carrying one or both LsRVs by treating them with N protein dsRNA twice during development. The viral replication of the N protein was specifically down-regulated following introduction of virus-specific dsRNA, and virus-free lice strains were maintained for several generations. A preliminary study on infection routes suggested that the LsRV-No9 is maternally transmitted, and that the virus transmits from males to females horizontally. The ability to produce virus free strains allows for further studies on transmission modes and how these viruses influences on the L.salmonis interaction with its salmonid host. Moreover, this study provides a general fundament for future studies on how vertically transmitted rhabdoviruses influence the biology of their arthropod hosts.

Construction & establishment of two minigenome rescue systems for Chandipura virus driven by recombinant vaccinia virus expressing T7 polymerase.

BACKGROUND & OBJECTIVES: Chandipura virus (CHPV) is an emerging pathogenic rhabdovirus with a high case fatality rate. There are no reports of a minigenome system for CHPV, which could help its study without having to use the infectious agent. This study was, therefore, undertaken for the establishment of T7 polymerase-driven minigenome system for CHPV. METHODS: The minigenome rescue system for CHPV consists of three helper plasmids expressing the nucleocapsid protein (N), phosphoprotein (P) and large protein (L) based on a recombinant vaccinia virus expressing bacteriophage T7 polymerase (vTF7-3). The minigenome construct is composed of a reporter gene, flanked by the non-coding regions of CHPV. Two minigenomes were constructed in an antigenome or complimentary sense, expressing luciferase or green fluorescent protein (GFP). The minigenome system was evaluated by co-transfection of the minigenome construct and three helper plasmids into CV-1 cells and analysis of the reporter gene activity. RESULTS: All the helper proteins were expressed from the helper plasmids confirmed by Western blotting. Expression of reporter genes was observed from both the GFP and luciferase-based minigenomes. Green fluorescence could be visualized directly in live CV-1 cells. Luciferase activity was found to be significantly different from control. INTERPRETATION & CONCLUSIONS: The results showed that the helper plasmids provided all the necessary viral structural proteins required for the production of minigenome mRNA template, which in turn could rescue the expression of reporter genes. Thus, these minigenomes can be applied to mimic the manifestation of CHPV life cycle.

Comparative transcriptome analysis of zebrafish (Danio rerio) brain and spleen infected with spring viremia of carp virus (SVCV).

Spring viremia of carp virus (SVCV) is the pathogen of spring viremia of carp (SVC) and often causes acute hemorrhagic symptoms in various kinds of cyprinids and induces serious environmental and economic losses. However, the molecular mechanisms of infection remain poorly understood, especially at the individual level. In this study, zebrafish was employed as the infection model to explore the pathogenesis of SVCV. 4 groups of zebrafish tissues were set and RNA sequencing (RNA-Seq) technology was employed to analyze the differentially expressed genes (DEGs) after SVCV-infection. A total of 360,971,498 clean reads were obtained from 12 samples, 382 DEGs in the brain and 926 DEGs in the spleen were identified. These DEGs were annotated into three ontologies after gene ontology (GO) enrichment analysis. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that these DEGs were primarily related to Influenza A pathway and Herpes simplex infection pathway in brain and Tuberculosis and Toxoplasmosis pathways in spleen, and all of these pathways may be involved in response to pathogen invasion. At the same time, 3' and 5' alternative splicing (AS) events were significantly up-regulated in the spleen. The transcriptome analysis results demonstrated changes and tissue-specific influences caused by SVCV in vivo, which provided us with more information to understand the complex relationships between SVCV and its host.

The influence of temperature on viral replication and antiviral-related genes response in hirame rhabdovirus-infected flounder (Paralichthys olivaceus).

Hirame rhabdovirus (HIRRV) is a rhabdovirus that causes severe disease in fish. The mortality due to HIRRV infection occurs at temperatures below 15 °C, but no mortality is observed over 20 °C. In this study, Japanese flounder (Paralichthys olivaceus) was artificially infected with the HIRRV CNPo2015 strain at 10 °C or 20 °C. Absolute quantitative real-time PCR was employed to examine the viral replication in spleens after HIRRV infection. Expression profiles of four interferon-related genes (type I IFN, Mx, ISG15, MDA5) and two proinflammatory genes (TNF-α and IL-1ß) were also investigated by quantitative real-time PCR. Results showed that viral copies in spleens increased gradually over time and peaked at 72 h post infection (hpi) in the 10 °C group, while viral copies in the 20 °C group increased within 24 hpi, but afterwards decreased to very low levels. Moreover, the expressions of IFNs in the 10 °C group reached the highest levels at 72 hpi, whereas their peak levels appeared much earlier in the 20 °C group, at 12 hpi. The expression levels of TNF-α and IL-1ß in the 10 °C group peaked at 12 hpi and then quickly declined. However, the two genes were highly expressed during 6-24 hpi in the 20 °C group. Based on these findings, we concluded that HIRRV infection induced an efficient antiviral immune response at 20 °C, which might inhibit the viral transcription at early stages and finally prevent HIRRV infection.

Analysis of the expression patterns of the novel large multigene TRIM gene family (finTRIM) in zebrafish.

Tripartite motif (TRIM) proteins are receiving increased research interest because of their roles in a wide range of cellular biological processes in innate immunity. In zebrafish (Danio rerio), the functions of the finTRIM (ftr) family are unclear. In the present study, we investigated the expression pattern of ftr12, ftr51, ftr67, ftr82, ftr83, and ftr84 in zebrafish for the first time. The results showed that ftr12, ftr67, and ftr84 are maternally expressed in the oocyte and highly expressed at the early stage (0-4 hpf) of embryo (P < 0.05), suggesting their involvement in the embryonic innate defense system. The ftr82 gene was highly expressed at 8 hpf (P < 0.05), which implied that the embryos could synthesize their own immunity-related mRNAs. However, ftr51 and ftr83 were highest at 8 hpf (2.33 and 51.53 relative to ß-actin respectively) and might mediate embryonic development. The expression levels of ftr12, ftr51, and ftr67 were highest in the gill, intestines, and liver, respectively. Ftr82, ftr83, and ftr84 were predominantly expressed in the kidney, suggesting that these finTRIMs might play roles in both immunity and non-immunity-related tissue compartments. Zebrafish embryonic fibroblast (ZF4) cells were infected with Grass carp reovirus (GCRV) and Spring viremia of carp virus (SVCV). During GCRV infection, the expression of ftr12 was significantly upregulated from 12 h to 24 h; and ftr51 and ftr67 increased from 3 h to 12 h. The expressions of ftr82, ftr83, and ftr84 were only upregulated at 12 h, 12 h, and 24 h, respectively. All of these genes were significantly downregulated at 48 h (P < 0.05). Challenge with SVCV upregulated the expressions of ftr12 and ftr51 at 12 h and 48 h (P < 0.05), respectively, and ftr67 reached its highest expression level at 3 h. ftr82 showed only a slight upregulation at 6 h and 48 h, and ftr83 and ftr84 were consecutively increased, reaching their highest levels at 12 h (P < 0.05). Meanwhile, ftr67 and ftr83 were significantly downregulated at 48 h (P < 0.05). Our research demonstrated that ftr12, ftr51, ftr67, ftr82, ftr83, and ftr84 probably have important roles in innate immune responses and in non-immunity-related tissues.

The antiviral signaling mediated by black carp MDA5 is positively regulated by LGP2.

Melanoma differentiation-associated gene 5 (MDA5) belongs to RIG-I like receptor (RLR) family, which detects cytosolic viral RNA component in immune response. In this study, MDA5 orthologue of black carp (Mylopharyngodon piceus) has been cloned and characterized. The full-length cDNA of black carp MDA5 (bcMDA5) comprises 3244 nucleotides and the predicted bcMDA5 protein contains 984 amino acids. The constitutive transcription of bcMDA5 was extremely low in all the tested tissues, which included gill, skin, muscle, intestine, kidney, spleen, liver and heart. However, bcMDA5 mRNA level was much enhanced in most selected tissues in response to GCRV or SVCV infection. bcMDA5 migrated around 120 KDa in immunoblot and was identified as a cytosolic protein by immunofluorescent staining in both EPC and HeLa cells. Expressing bcMDA5 in EPC cells resulted in the induction of promoter activity of zebrafish IFN3 or fathead minnow IFN. The EPC cells expressing bcMDA5 obtained improved antiviral ability against both SVCV and GCRV. When EPC cells were co-transfected with plasmids expressing bcMDA5 and bcLGP2, the induced IFN expression by bcMDA5 was obviously enhanced. EPC cells expressing both bcMDA5 and bcLGP2 owned much improved antiviral ability than those cells expressing only bcMDA5 or bcLGP2. In general, our data support the conclusion that bcMDA5 plays an important role in the antiviral innate immune response of black carp and bcLGP2 acts as a positive regulator in bcMDA5 mediated signaling.

The role of infectious hematopoietic necrosis virus (IHNV) proteins in the modulation of NF-κB pathway during IHNV infection.

Viral infections frequently lead to the activation of host innate immune signaling pathways involved in the defense against invading pathogens. To ensure their survival, viruses have evolved sophisticated mechanisms to overcome the host immune responses. The present study demonstrated for the first time that infectious hematopoietic necrosis virus (IHNV) activated NF-κB pathway in fish cells. We further identified that the IHNV L protein could activate the NF-κB signaling pathway and that IHNV NV functioned as an inhibitor of NF-κB activation. Further results demonstrated that the NV protein blocked the degradation of the inhibitor of NF-κB (IκBα) and suppressed the SeV-induced NF-κB nuclear translocation. In conclusion, our study explored the functions of different IHNV proteins on NF-κB activation, and revealed a potential mechanism by which IHNV evades innate immune responses.

NV Proteins of Fish Novirhabdovirus Recruit Cellular PPM1Bb Protein Phosphatase and Antagonize RIG-I-Mediated IFN Induction.

Non virion (NV) protein expression is critical for fish Novirhabdovirus, viral hemorrhagic septicemia virus (VHSV) and infectious hematopoietic necrosis virus (IHNV), in vivo pathogenesis. However, the mechanism by which NV promotes the viral replication is still unclear. We developed an approach based on reverse genetics and interactomic and identified several NV-associated cellular partners underlying cellular pathways as potential viral targets. Among these cell partners, we showed that NV proteins specifically interact with a protein phosphatase, Mg2+/Mn2+-dependent, 1Bb (PPM1Bb) and recruit it in the close vicinity of mitochondria, a subcellular compartment important for retinoic acid-inducible gene-I- (RIG-I)-mediated interferon induction pathway. PPM1B proteins belong to the PP2C family of serine/threonine (Ser/Thr) protein phosphatase and have recently been shown to negatively regulate the host antiviral response via dephosphorylating Traf family member-associated NF-κB activator (TANK)-binding kinase 1 (TBK1). We demonstrated that NV proteins and PPM1Bb counteract RIG-I- and TBK1-dependent interferon (IFN) and IFN-stimulated gene promoter induction in fish cells and, hence, the establishment of an antiviral state. Furthermore, the expression of VHSV NV strongly reduced TBK1 phosphorylation and thus its activation. Our findings provide evidence for a previously undescribed mechanism by which a viral protein recruits PPM1Bb protein phosphatase to subvert innate immune recognition.

The BAFF / APRIL axis plays an important role in virus-induced peritoneal responses in rainbow trout.

IgM+ B cells have been recently demonstrated to be key regulators of peritoneal inflammation in teleost, as a large number of them occupy the peritoneal cavity after 48 h of antigenic stimulation. Despite this, the number of studies addressing the mechanism through which this cell population expands and differentiates in response to stimuli has been scarcely addressed. Because the BAFF/APRIL axis is known to play a major role in B cell survival and differentiation in mammals, we hypothesized that it could be affected in the peritoneal cavity in response to an inflammatory stimulus. To verify this hypothesis, we studied how BAFF, APRIL and the fish-specific related cytokine BALM as well as their putative receptors are regulated in rainbow trout after intraperitoneal (i.p.) injection of viral hemorrhagic septicemia virus (VHSV). When the transcriptional analysis was performed in total cells from the peritoneum, we observed that VHSV provoked an up-regulation of both BAFF and BAFF receptor (BAFF-R) mRNA levels. However, when we examined how isolated peritoneal IgM+ B cells were transcriptionally affected by VHSV i.p. injection, we found that APRIL, BALM and the transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI) were also up-regulated in response to the virus. IgM- cells, on the other hand, only up-regulated BALM transcription in response to VHSV. Finally, to gain further insight on the role that these cytokines play in the peritoneum, we have studied their effect on the survival of peritoneal IgM+ B cells. This work demonstrates a key role for the BAFF/APRIL axis in the peritoneal inflammatory response and contributes to further understanding how IgM+ B cells are regulated at this specific peripheral site.