Chemical-controlled Activation of Antiviral Myxovirus Resistance Protein 1

Genome-wide siRNA library screening identifies human host factors that influence the replication of the highly pathogenic H5N1 influenza virus

The global dissemination of H5 avian influenza viruses represents a significant threat to both human and animal health. In this study, we conducted a genome-wide siRNA library screening against the highly pathogenic H5N1 influenza virus, leading us to the identification of 457 cellular cofactors (441 proviral factors and 16 antiviral factors) involved in the virus replication cycle. Gene Ontology term enrichment analysis revealed that the candidate gene data sets were enriched in gene categories associated with mRNA splicing via spliceosome in the biological process, integral component of membrane in the cellular component, and protein binding in the molecular function. Reactome pathway analysis showed that the immune system (up to 63 genes) was the highest enriched pathway. Subsequent comparisons with four previous siRNA library screenings revealed that the overlapping rates of the involved pathways were 8.53%-62.61%, which were significantly higher than those of the common genes (1.85%-6.24%). Together, our genome-wide siRNA library screening unveiled a panorama of host cellular networks engaged in the regulation of highly pathogenic H5N1 influenza virus replication, which may provide potential targets and strategies for developing novel antiviral countermeasures.

The effects of GCRV on various tissues of grass carp (Ctenopharyngodon idella) and identification of differential interferon-stimulating genes (ISGs) through muscle transcriptome analysis

Grass carp hemorrhagic disease is caused by the grass carp reovirus (GCRV). The disease spreads rapidly and has a high fatality rate, which seriously affects grass carp culture. Moreover, the molecular mechanisms underlying grass carp hemorrhagic disease remain unclear. To decipher the effects of GCRV on grass carp tissues, resistant grass carp A (GA) and susceptible grass carp B (GB) were selected through GCRV treatment, and control grass carp C (GC) was also established. The gill, liver, and muscle tissues exhibited different onset symptoms under the influence of GCRV by histological observation. We selected muscle samples with significant differences in symptoms for Illumina RNA sequencing. Analyses using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes revealed 3512, 3074, and 1853 differentially expressed genes between "GC vs. GB," "GC vs. GA," and "GA vs. GB," respectively. Additionally, 40 differential immune-related genes and 28 differential interferon-stimulating genes (ISGs) related to the interferon (IFN) pathway were identified. The expression of immunogene-related genes of GB and GA, such as MDA5, IL-34, NF-KB, TRIM25, SOCS3, CEBPB, and BCL2, and genes associated with the JAK-STAT signaling pathway, such as IRF4, STAT1, STAT3, JAK 1, and JAK 2, was significantly upregulated. The IFN and JAK-STAT signaling pathways were closely related to anti-GCRV infection. The transcriptome data and predicted immune genes and ISGs in this study provide novel insights into the treatment of GCRV.

Host factor MxA restricts Dabie bandavirus infection by targeting the viral NP protein to inhibit NP-RdRp interaction and ribonucleoprotein activity

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with high case mortality rates, which is caused by Dabie bandavirus (DBV), a novel pathogen also termed as SFTS virus (SFTSV). Currently, no specific therapeutic drugs or vaccines are available for SFTS. Myxovirus resistance protein A (MxA) has been shown to inhibit multiple viral pathogens; however, the role of MxA in DBV infection is unknown. Here, we demonstrated that DBV stimulates MxA expression which, in turn, restricts DBV infection. Mechanistic target analysis revealed that MxA specifically interacts with the viral nucleocapsid protein (NP) in a manner independent of RNA. Minigenome reporter assay showed that in agreement with its targeting of NP, MxA inhibits DBV ribonucleoprotein (RNP) activity. In detail, MxA interacts with the NP N-terminal and disrupts the interaction of NP with the viral RNA-dependent RNA polymerase (RdRp) but not NP multimerization, the critical activities of NP for RNP formation and function. Furthermore, MxA N-terminal domain was identified as the functional domain inhibiting DBV infection, and, consistently, then was shown to interact with NP and obstruct the NP-RdRp interaction. Additionally, threonine 103 within the N-terminal domain is important for MxA inhibition to DBV, and its mutation (T103A) attenuates MxA binding to NP and obstruction of the NP-RdRp interaction. This study uncovers MxA inhibition of DBV with a series of functional and mechanistical analyses, providing insights into the virus-host interactions and probably helping inform the development of antiviral agents in the future.IMPORTANCEDBV/SFTSV is an emerging high-pathogenic virus. Since its first identification in China in 2009, cases of DBV infection have been reported in many other countries, posing a significant threat to public health. Uncovering the mechanisms of DBV-host interactions is necessary to understand the viral pathogenesis and host response and may advance the development of antiviral therapeutics. Here, we found that host factor MxA whose expression is induced by DBV restricts the virus infection. Mechanistically, MxA specifically interacts with the viral NP and blocks the NP-RdRp interaction, inhibiting the viral RNP activity. Further studies identified the key domain and amino acid residue required for MxA inhibition to DBV. Consistently, they were then shown to be important for MxA targeting of NP and obstruction of the NP-RdRp association. These findings unravel the restrictive role of MxA in DBV infection and the underlying mechanism, expanding our knowledge of the virus-host interactions.

The host transcriptome change involved in the inhibitory effect of exogenous interferon-γ on Getah virus replication

Introduction

Getah virus (GETV) has become a growing potential threat to the global livestock industry and public health. However, little is known about the viral pathogenesis and immune escape mechanisms, leading to ineffective control measures.

Methods

In this study, the antiviral activity of exogenous interferons (IFNs) was assessed by using western blotting (WB), real-time quantitative PCR (RT-qPCR) and indirect immunofluorescence assay (IFA). The comparative transcriptomics among mock- and GETV-infected (MOI = 0.1) ST cells with or without IFN-γ was performed by RNA-seq, and then the transcriptome profiling of GETV-infected ST cells and key pathways and putative factors involved in inhibitory effect of IFN-γ on GETV replication were analyzed by bioinformatics methods and RT-qPCR.

Results

The results showed that treatment with IFN-γ could suppress GETV replication, and the inhibitory effect lasted for at least 48 h, while the exogenous IFN-α/ω and IFN-λ3 treatments failed to inhibit the viral infection and early replication in vitro. Furthermore, the blueprint of virus-host interaction was plotted by RNA-seq and RT-qPCR, showing systemic activation of inflammatory, apoptotic, and antiviral pathways in response to GETV infection, indicating viral hijacking and inhibition of innate host immunity such as IFN-I/III responses. Last and most importantly, activation of the JAK-STAT signaling pathway and complement and coagulation cascades may be a primary driver for IFN-γ-mediated inhibition of GETV replication.

Discussion

These findings revealed that GETV possessed the capability of viral immune escape and indicated that IFN-γ aided in the prevention and control of GETV, implying the potential molecular mechanism of suppression of GETV by IFN-γ, all of which warrant emphasis or further clarification.

The primitive interferon-like system and its antiviral function in molluscs

The phylum mollusca is a very important group in the animal kingdom for the large number and diversified species. Recently, interest in molluscan immunity has increased due to their phylogenetic position and importance in worldwide aquaculture and aquatic environment. As the main aquaculture animal, most molluscs live in the water environment and they have to cope with many pathogen challenges, in which virus is one of the primary causes for the mass mortality. In vertebrates, interferon (IFN) system is generally recognized as the first line of defence against viral infection, while the antiviral mechanisms in molluscs remain to be clearly illuminated. Recently, some IFN-like proteins and IFN-related components have been characterized from molluscs, such as pattern recognition receptors (PRRs), interferon regulatory factors (IRFs), IFN-like receptors, JAK/STAT and IFN-stimulated genes (ISGs), which reinforce the existence of IFN-like system in molluscs. This system can be activated by virus or poly (I:C) challenges and further regulate the antiviral response of haemocytes in molluscs. This review summarizes the research progresses of IFN-like system in molluscs with the emphases on the uniformity and heterogeneity of IFN-like system of molluscs compared to that of other animals, which will be helpful for elucidating the antiviral modulation in molluscs and understanding the origin and evolution of IFN system.

Role of the Host Genetic Susceptibility to 2009 Pandemic Influenza A H1N1

Influenza A virus (IAV) is the most common infectious agent in humans, and infects approximately 10-20% of the world's population, resulting in 3-5 million hospitalizations per year. A scientific literature search was performed using the PubMed database and the Medical Subject Headings (MeSH) "Influenza A H1N1" and "Genetic susceptibility". Due to the amount of information and evidence about genetic susceptibility generated from the studies carried out in the last influenza A H1N1 pandemic, studies published between January 2009 to May 2020 were considered; 119 papers were found. Several pathways are involved in the host defense against IAV infection (innate immune response, pro-inflammatory cytokines, chemokines, complement activation, and HLA molecules participating in viral antigen presentation). On the other hand, single nucleotide polymorphisms (SNPs) are a type of variation involving the change of a single base pair that can mean that encoded proteins do not carry out their functions properly, allowing higher viral replication and abnormal host response to infection, such as a cytokine storm. Some of the most studied SNPs associated with IAV infection genetic susceptibility are located in the FCGR2A, C1QBP, CD55, and RPAIN genes, affecting host immune responses through abnormal complement activation. Also, SNPs in IFITM3 (which participates in endosomes and lysosomes fusion) represent some of the most critical polymorphisms associated with IAV infection, suggesting an ineffective virus clearance. Regarding inflammatory response genes, single nucleotide variants in IL1B, TNF, LTA IL17A, IL8, IL6, IRAK2, PIK3CG, and HLA complex are associated with altered phenotype in pro-inflammatory molecules, participating in IAV infection and the severest form of the disease.

Mx1 in Hematopoietic Cells Protects against Thogoto Virus Infection

Myxovirus resistance 1 (Mx1) is an interferon-induced gene that encodes a GTPase that plays an important role in the defense of mammalian cells against influenza A and other viruses. The Mx1 protein can restrict a number of viruses independently of the expression of other interferon-induced genes. Mx genes are therefore considered to be an important part of the innate antiviral immune response. However, the possible impact of Mx expression in the hematopoietic cellular compartment has not been investigated in detail in the course of a viral infection. To address this, we performed bone marrow chimera experiments using congenic B6.A2G Mx1 ^+/+ and B6.A2G Mx1^-/- mice to study the effect of Mx1 expression in cells of hematopoietic versus nonhematopoietic origin. Mx1^+/+ mice were protected and Mx1^-/- mice were susceptible to influenza A virus challenge infection, regardless of the type of bone marrow cells (Mx1 ^+/+ or Mx1^-/- ) the animals had received. Infection with Thogoto virus, however, revealed that Mx1^-/- mice with a functional Mx1 gene in the bone marrow compartment showed reduced liver pathology compared with Mx1^-/- mice that had been grafted with Mx1 ^-/- bone marrow. The reduced pathology in these mice was associated with a reduction in Thogoto virus titers in the spleen, lung, and serum. Moreover, Mx1 ^+/+ mice with Mx1 ^-/- bone marrow failed to control Thogoto virus replication in the spleen. Mx1 in the hematopoietic cellular compartment thus contributes to protection against Thogoto virus infection.IMPORTANCE Mx proteins are evolutionarily conserved in vertebrates and can restrict a wide range of viruses in a cell-autonomous way. The contribution to antiviral defense of Mx1 expression in hematopoietic cells remains largely unknown. We show that protection against influenza virus infection requires Mx1 expression in the nonhematopoietic cellular compartment. In contrast, Mx1 in bone marrow-derived cells is sufficient to control disease and virus replication following infection with a Thogoto virus. This indicates that, in addition to its well-established antiviral activity in nonhematopoietic cells, Mx1 in hematopoietic cells can also play an important antiviral function. In addition, cells of hematopoietic origin that lack a functional Mx1 gene contribute to Thogoto virus dissemination and associated disease.

The Discovery of the Antiviral Resistance Gene Mx: A Story of Great Ideas, Great Failures, and Some Success

The discovery of the Mx gene-dependent, innate resistance of mice against influenza virus was a matter of pure chance. Although the subsequent analysis of this antiviral resistance was guided by straightforward logic, it nevertheless led us into many blind alleys and was full of surprising turns and twists. Unexpectedly, this research resulted in the identification of one of the first interferon-stimulated genes and provided a new view of interferon action. It also showed that in many species, MX proteins have activities against a broad range of viruses. To this day, Mx research continues to flourish and to provide insights into the never-ending battle between viruses and their hosts.