Antiviral Pathways Research Articles

A novel protein encoded by circVPS13D attenuates antiviral innate immunity by targeting MAVS in teleost fish.

The expression of circVPS13D was upregulated with SCRV invasion, which proved that circVPS13D was involved in the regulation of the antiviral immune response. Our study revealed that the existence of circVPS13D promoted the replication of SCRV. Functionally, circVPS13D negatively regulates the antiviral responses of fish. Mechanistically, we confirmed that circVPS13D inhibited RLRs antiviral signaling pathway via the encoded protein VPS13D-170aa by targeting MAVS. Our study provided novel insights into the roles of protein-coding circRNAs and supported VPS13D-170aa as a negative regulator in the antiviral immune responses of teleost fish.

The poxvirus F17 protein counteracts mitochondrially orchestrated antiviral responses

Poxviruses are unusual DNA viruses that replicate in the cytoplasm. To do so, they encode approximately 100 immunomodulatory proteins that counteract cytosolic nucleic acid sensors such as cGAMP synthase (cGAS) along with several other antiviral response pathways. Yet most of these immunomodulators are expressed very early in infection while many are variable host range determinants, and significant gaps remain in our understanding of poxvirus sensing and evasion strategies. Here, we show that after infection is established, subsequent progression of the viral lifecycle is sensed through specific changes to mitochondria that coordinate distinct aspects of the antiviral response. Unlike other viruses that cause extensive mitochondrial damage, poxviruses sustain key mitochondrial functions including membrane potential and respiration while reducing reactive oxygen species that drive inflammation. However, poxvirus replication induces mitochondrial hyperfusion that independently controls the release of mitochondrial DNA (mtDNA) to prime nucleic acid sensors and enables an increase in glycolysis that is necessary to support interferon stimulated gene (ISG) production. To counter this, the poxvirus F17 protein localizes to mitochondria and dysregulates mTOR to simultaneously destabilize cGAS and block increases in glycolysis. Our findings reveal how the poxvirus F17 protein disarms specific mitochondrially orchestrated responses to later stages of poxvirus replication.

3β-hydroxysteroid-Δ24 reductase dampens anti-viral innate immune responses by targeting K27 ubiquitination of MAVS and STING.

The precise regulation of the innate immune response is essential for the maintenance of homeostasis. MAVS and STING play key roles in immune signaling pathways activated by RNA and DNA viruses, respectively. Here, we showed that DHCR24 impaired the antiviral response by targeting MAVS and STING. Notably, DHCR24 interacts with MAVS and STING and inhibits TRIM21-triggered K27-linked ubiquitination of MAVS and AMFR-triggered K27-linked ubiquitination of STING, restraining the activation of MAVS and STING, respectively. Together, this study elucidates how one cholesterol key enzyme orchestrates two antiviral signal transduction pathways.

Mitochondrial dsRNA from B-Precursor Acute Lymphoblastic Leukemia Cells Induce Formation of Cancer Associated Fibroblast in the Bone Marrow Leading to Formation of a Chemoprotective Bone Marrow Niche

Precursor B-cell Acute Lymphoblastic Leukemia (B-ALL) is typically a highly chemosensitive malignancy with the majority of children being cured by chemotherapy alone. Adult ALL is often chemosensitive at initial treatment, but long term disease free survival is less common. It is widely accepted that outcome in ALL closely relates to underlying genetic lesion (Moorman, Hematologica 2016) but no specific mechanisms by which ALL genetics influence outcome have been identified. We have previously demonstrated that an ‘activated mesenchymal stromal cell (MSC) niche’ develops in response to reactive oxygen species (ROS) -inducing chemotherapy in which mitochondria are actively transferred along tunnelling nanotubes to ‘rescue’ B-ALL cells from chemotherapy (Burt, et al Blood 2019). According to recent evidence that chemotherapy resistant ALL sub-clones may exist at diagnosis (Dobson et al Cancer Discovery 2020), we hypothesised that B-ALL cells may themselves directly activate bone marrow stromal cells to generate cancer associated fibroblasts (CAF) from MSC. To test this hypothesis, we first used our previously described in vitro niche model wherein either the HS27a MSC cell line or healthy donor (HD) MSCs are co-cultured with either B-ALL cell lines or primary patient B-ALL cells. Three of five B-ALL cell lines and 3 of 4 primary B-ALL samples tested, induced activation of the MSCs, as characterised by cytomorphological changes identified by confocal microscopy, up-regulation of CAF-relevant gene expression and increased IL6, IL8 and CCL2 protein secretion. The ability of the B-ALL cell lines to induce CAF correlated directly with the intrinsic ROS levels of the cell as determined by CellROX assay. In vivo, the CAF-inducing ALL cell lines also activated murine MSCs when established as xenografts in NOD-SCID gamma (NSG) mice. Immunohistochemistry of NSG murine femora revealed a very significant expansion in nestin+ cells after exposure to CAF-induing ALL cells compared to non-CAF-inducing controls. We established that the ALL cells activated MSC without contact, both from exposure of MSC to ALL cells in transwell and from exposure to B-ALL cell conditioned media (CM). RNA sequencing of HS27a stromal cells exposed to CAF-inducing B-ALL cell CM compared with non-CAF inducing controls unexpectedly showed that the most highly upregulated pathways were those involved in RNA sensing. Using a smaller gene panel selected from among the RNA-sensing pathway genes, we confirmed that this was also the case for primary, HD MSCs upon exposure to primary ALL patient samples. As a result, we sought evidence for the role of mitochondrial dsRNA, which has been shown to activate the anti-viral signalling pathway (Dhir et al, Nature 2018). Using the J2 anti-dsRNA monoclonal antibody in both confocal and flow cytometric assays, we observed very significantly higher levels of dsRNA in MSC which had been exposed to CAF inducing B-ALL cell CM than in non-CAF inducing B-ALL or MSC alone controls. We confirmed by RT-PCR for mitochondrial genes on dsRNA immunoprecipitated from CAF inducing B-ALL cell CM that the dsRNA was of mitochondrial origin. Using ELISA, we quantified dsRNA from total cell RNA extracted from paired primary B-ALL patient samples at diagnosis and in remission. We found significantly higher levels of dsRNA at diagnosis than in remission, with it being undetectable in most remission samples. Moreover, we confirmed by flow cytometry the presence of dsRNA in 6 B-ALL patient derived xenografts which was absent in the control NSG mice without leukemia. We used DMSO to degrade dsRNA from CAF inducing B-ALL cell CM, as is often done in Sanger sequencing and confirmed the degradation by ELISA. We then quantified gene expression of a selection of stromal cell activation marker genes, as well as genes in the RNA sensing pathway after exposure to either DMSO-treated B-ALL cell CM or non-treated control. There was a 2 to 4-fold reduction in expression of IL6, IL8 as well as of RIG-I, MX2, IFIH1, MAVS and OAS1 expression in DMSO-treated condition compared to control. We confirmed that IL6, IL8 and CCL2 protein secretion was also significantly abrogated in the test but not the control condition. We propose a model in which ROS-induced mitochondrial dysfunction in ALL cells leads to release of dsRNA which in turn activates bone marrow stromal cells leading to protective niche formation, despite lack of prior exposure to cytotoxic agents.

Tuning the Innate Immune Multiple Myeloma Microenvironment By Modulating IRF4

The tumor microenvironment (TME) has emerged as a key contributor to cancer progression in numerous solid tumors as well as blood cancers that evolve in the bone marrow (BM). In the context of multiple myeloma (MM), survival of malignant plasma cells is supported by interactions with the BM microenvironment, which is comprised of various components including cells, extracellular matrix, and soluble factors. Therefore, the development of strategies that specifically target the MM BM microenvironment is crucial for improving current disease prognosis. Within the BM niche, M2-like myeloma-associated macrophages (MAMs) play a significant role in cancer cell survival and progression and have been implicated in producing an immune-suppressive TME by generating inflammatory mediators, growth factors, cytokines, chemokines, etc. Macrophages exhibit plasticity with regard to their polarization state, which enable them to dynamically respond and adapt to different environmental stimuli in order to fulfill important immune functions. Thus, the reprogramming of M2-like, pro-tumoral MAMs toward a M1-like, anti-tumoral phenotype represents a promising therapeutic strategy. In MM, inflammatory and anti-viral pathways promote disease progression. Interferon regulatory factor 4 (IRF4) is a transcription factor that has previously been shown to promote MM progression through enhanced survival of malignant plasma cells. Under physiological conditions, IRF4 also regulates macrophage polarization, where its expression drives alternative activation of macrophages primarily to M2-like (anti-inflammatory) phenotypes. However, the extent to which IRF4 activation or direct inhibition governs the polarization status and pro-tumoral activity of macrophages in the MM microenvironment has not been fully elucidated. In this study, we sought to further explore the role of IRF4 in macrophage polarization and investigated the potential of modulating IRF4 expression to reprogram myeloma-associated macrophages (MAMs) as a novel therapeutic strategy. First, we developed myeloma-tailored macrophage polarization models using primary human peripheral blood-derived monocytes and the THP1 monocyte cell line. Our M1 and M2 polarization models utilize a customized cocktail of myeloid growth factors and cytokines, supplemented with interleukin (IL)-6 to mimic the IL-6-enriched MM microenvironment. Characterization of M1 (CD80, TNFα, and CXCL10) and M2 (MRC1, FN1, and CCL22) markers confirmed the presence of distinct macrophage subpopulations, as well as upregulated expression of IRF4 in M2-like progeny and IRF5 in M1-like macrophages. To investigate the extent to which IRF4 activation or direct inhibition governs macrophage polarization and function, overexpression and knockdown experiments on macrophages were performed in vitro, along with whole transcriptome sequencing of IRF4-overexpressing THP1 monocytes compared to vector-transduced controls. Gene expression analyses revealed that genetic down-modulation of IRF4 in M2-like macrophages shifts the polarization status toward a hybrid phenotype that displays enhanced M1-like properties, while still retaining M2-like characteristics. This shift in polarization state was further amplified when monocytes were transduced to overexpress IRF4 prior to differentiation into M2-like macrophages and subsequent IRF4 knockdown, suggesting that IRF4 plays a key regulatory role in tuning macrophage polarization. Taken together, our preclinical findings provide groundwork for future studies on MAMs and suggest that an IRF4-mediated macrophage reprogramming strategy is a promising therapeutic approach for patients with MM and a variety of other malignancies typified by an anti-inflammatory TME.

C5aR2 Regulates STING-Mediated Interferon Beta Production in Human Macrophages.

The complement system mediates diverse regulatory immunological functions. C5aR2, an enigmatic receptor for anaphylatoxin C5a, has been shown to modulate PRR-dependent pro-inflammatory cytokine secretion in human macrophages. However, the specific downstream targets and underlying molecular mechanisms are less clear. In this study, CRISPR-Cas9 was used to generate macrophage models lacking C5aR2, which were used to probe the role of C5aR2 in the context of PRR stimulation. cGAS and STING-induced IFN-β secretion was significantly increased in C5aR2 KO THP-1 cells and C5aR2-edited primary human monocyte-derived macrophages, and STING and IRF3 expression were increased, albeit not significantly, in C5aR2 KO cell lines implicating C5aR2 as a regulator of the IFN-β response to cGAS-STING pathway activation. Transcriptomic analysis by RNAseq revealed that nucleic acid sensing and antiviral signalling pathways were significantly up-regulated in C5aR2 KO THP-1 cells. Altogether, these data suggest a link between C5aR2 and nucleic acid sensing in human macrophages. With further characterisation, this relationship may yield therapeutic options in interferon-related pathologies.

Single-nucleus sequencing of silkworm larval midgut reveals the immune escape strategy of BmNPV in the midgut during the late stage of infection

The midgut is an important barrier against microorganism invasion and proliferation, yet is the first tissue encountered when a baculovirus naturally invades the host. However, only limited knowledge is available how different midgut cell types contribute to the immune response and the clearance or promotion of viral infection. Here, single-nucleus RNA sequencing (snRNA seq) was employed to analyze the responses of various cell subpopulations in the silkworm larval midgut to B. mori nucleopolyhedrovirus (BmNPV) infection. We identified 22 distinct clusters representing enteroendocrine cells (EEs), enterocytes (ECs), intestinal stem cells (ISCs), Goblet cell-like and muscle cell types in the BmNPV-infected and uninfected silkworm larvae midgut at 72 h post infection. Further, our results revealed that the strategies for immune escape of BmNPV in the midgut at the late stage of infection include (1) inhibiting the response of antiviral pathways; (2) inhibiting the expression of antiviral host factors; (3) stimulating expression levels of genes promoting BmNPV replication. These findings suggest that the midgut, as the first line of defense against the invasion of the baculovirus, has dual characteristics of "resistance" and "tolerance". Our single-cell dataset reveals the diversity of silkworm larval midgut cells, and the transcriptome analysis provides insights into the interaction between host and virus infection at the single-cell level.

DLG1 promotes the antiviral innate immune response by inhibiting p62-mediated autophagic degradation of IKKε.

The type-I interferon (IFN-I) signaling pathway is the first line of antiviral innate immunity. It must be precisely regulated against virus-induced damage. The tightly regulated mechanisms of action of host genes in the antiviral innate immune signaling pathway are still worth studying. Here, we report a novel role of DLG1 in positively regulating the IκB kinase epsilon (IKKε)-mediated IFN-I signaling response against negative-stranded RNA virus replication, whereas the RNA virus inhibits the expression of DLG1 for immune escape. Importantly, the E3 ligase March2 interacts with and promotes K27-linked polyubiquitination of IKKε, and p62 is a cargo receptor that recognizes ubiquitinated IKKε for eventual autophagic degradation. Together, the current findings elucidate the role of DLG1 in the antiviral IFN-I signaling pathway and viral infection repression.

Bacterial cGAS senses a viral RNA to initiate immunity

Cyclic oligonucleotide-based antiphage signalling systems (CBASS) protect prokaryotes from viral (phage) attack through the production of cyclic oligonucleotides, which activate effector proteins that trigger the death of the infected host1,2. How bacterial cyclases recognize phage infection is not known. Here we show that staphylococcal phages produce a structured RNA transcribed from the terminase subunit genes, termed CBASS-activating bacteriophage RNA (cabRNA), which binds to a positively charged surface of the CdnE03 cyclase and promotes the synthesis of the cyclic dinucleotide cGAMP to activate the CBASS immune response. Phages that escape the CBASS defence harbour mutations that lead to the generation of a longer form of the cabRNA that cannot activate CdnE03. Since mammalian oligoadenylate synthetases also bind viral double-stranded RNA during the interferon response, our results reveal a conserved mechanism for the activation of innate antiviral defence pathways.

Cellular nucleic acid-binding protein restricts SARS-CoV-2 by regulating interferon and disrupting RNA-protein condensates.

A detailed understanding of the innate immune mechanisms involved in restricting SARS-CoV-2 infection and how the virus disrupts these processes could reveal new strategies to boost antiviral mechanisms and develop therapeutics for COVID-19. Here, we identify cellular nucleic acid-binding protein (CNBP) as a key host factor controlling SARS-CoV-2 infection. In response to RNA-sensing pathways, CNBP is phosphorylated and translocates from the cytosol to the nucleus where it binds to the interferon-β enhancer to initiate transcription. Because SARS-CoV-2 evades immune detection by the host's RNA-sensing pathways, CNBP is largely retained in the cytosol where it restricts SARS-CoV-2 directly, leading to a battle between the host and SARS-CoV-2 that extends beyond antiviral immune signaling pathways. We further demonstrated that CNBP binds SARS-CoV-2 viral RNA directly and competes with the viral nucleocapsid protein to prevent viral RNA and nucleocapsid protein from forming liquid-liquid phase separation (LLPS) condensates critical for viral replication. Consequently, cells and animals lacking CNBP have higher viral loads, and CNBP-deficient mice succumb rapidly to infection. Altogether, these findings identify CNBP as a key antiviral factor for SARS-CoV-2, functioning both as a regulator of antiviral IFN gene expression and a cell-intrinsic restriction factor that disrupts LLPS to limit viral replication and spread. In addition, our studies also highlight viral condensates as important targets and strategies for the development of drugs to combat COVID-19.

IMMU-35. G-AMINOBUTYRIC ACID DRIVES GLIOBLASTOMA IN FEMALES BY ACTIVATING THE COMPLEMENT SYSTEM

Abstract Interaction between tumor and neural cells drives the progression of glioblastoma (GBM), which is characterized by enhanced immunosuppressive myeloid cell accumulation. Our previous results revealed that myeloid-derived suppressor cell subsets (MDSCs) play a central role in tumorigenesis in a sex-specific manner, with monocytic MDSCs (mMDSCs) accumulating in male tumors and granulocytic MDSCs (gMDSCs) correlating with a worse outcome in females. However, host factors governing sex differences in MDSC subset activity remained unknown. Here, we report that g-aminobutyric acid (GABA) receptor expression by gMDSCs informs their sex-specific behavior. We observed that only female gMDSCs but not male gMDSCs or mMDSCs from either sex respond to GABA by upregulating the antiviral innate immune pathway. As part of this signature, GABA-stimulated female gMDSCs had higher complement 1qa (C1qa) expression. To test the potential role of the GABA pathway on GBM outcome, we tested the GABA analogue pregabalin in preclinical models. Female mice treated with pregabalin succumbed to disease earlier, consistent with our previous observation that gMDSCs have a central role in GBM progression in females. In contrast, pregabalin treatment had no effect in male mice with tumors or immunocompromised female mice. To further evaluate whether C1q is a relevant physiological target, we performed single-cell sequencing of tumor-infiltrating versus circulating MDSC subsets and detected high levels of C1q expression in gMDSCs from tumors. C1q KO transgenic female mice had significantly better outcomes compared to wild-type littermates upon implantation with syngeneic mouse GBM lines, while C1q expression status did not impact the outcome in males. Correspondingly, only in female patients C1q expression correlated with poor prognosis. Collectively, these results identify a neuron-immune-cancer communication axis and indicate that GABA and C1q alter anti-tumor immune responses in a sex-specific manner. These results support the future assessment of the GABA pathway and complement inhibitors as potential immunotherapy agents.

Smyd3 negatively regulates the anti-viral pathway by promoting TAK1 degradation in teleost fish.

In this study, we have found that the existence of Smyd3 promoted the replication of SCRV. Additionally, we report that Smyd3 negatively regulates the NF-κB and IRF3 signaling pathway by facilitating the degradation of TAK1 in fish. Our findings suggest that Smyd3 interacts with TAK1. Further investigations have revealed that Smyd3 specifically mediates K48-linked ubiquitination of TAK1 and enhances TAK1 degradation, resulting in a significant inhibition of the NF-κB and IRF3 signaling pathway. These results not only contribute to the advancement of fish anti-viral immunity but also provide new evidence for understanding the mechanism of TAK1 in mammals.

Adenovirus E1B-55K controls SUMO-dependent degradation of antiviral cellular restriction factors.

Human adenoviruses (HAdVs) generally cause mild and self-limiting diseases of the upper respiratory and gastrointestinal tracts but pose a serious risk to immunocompromised patients and children. Moreover, they are widely used as vectors for vaccines and vector-based gene therapy approaches. It is therefore vital to thoroughly characterize HAdV gene products and especially HAdV virulence factors. Early region 1B 55 kDa protein (E1B-55K) is a multifunctional HAdV-encoded oncoprotein involved in various viral and cellular pathways that promote viral replication and cell transformation. We analyzed the E1B-55K dependency of SUMOylation, a post-translational protein modification, in infected cells using quantitative proteomics. We found that HAdV increases overall cellular SUMOylation and that this increased SUMOylation can target antiviral cellular pathways that impact HAdV replication. Moreover, we showed that E1B-55K orchestrates the SUMO-dependent degradation of certain cellular antiviral factors. These results once more emphasize the key role of E1B-55K in the regulation of viral and cellular proteins in productive HAdV infections.

Serum RNase L levels in patients with chronic hepatitis B virus infection.

Chronic hepatitis B virus (HBV) infection still poses a major threat to global health. Oligoadenylate synthetase-ribonuclease L (RNase L) antiviral pathway is one of interferon-induced antiviral effectors. The relationship between RNase L and HBV has never been investigated and we aim to examine the serum RNase L levels in patients with different stages of chronic HBV infection. The patients were enrolled from 1985 to 2000, who had been HBsAg positive for longer than 6months, at the National Taiwan University Hospital. In total, 426 patients with chronic HBV infection were included in this study, including 135 inactive carriers, 148 cirrhosis, and 143 hepatocellular carcinoma (HCC) cases. The RNase L levels increase as the disease severity increases. Higher RNase L levels were associated with higher HBV viral load, and the HBV-RNase L relationship was replaced by the disease severity status when adding disease status into the model. Compared with inactive carriers, the risk of liver cirrhosis was 60-fold (odds ratio=60.8, 95% confidence interval=3.49-1061) with the highest quintile of RNase L levels, after the adjustment of HBV DNA. The dose-response trend was statistically significant with quintiles and one increment of RNase L level in relation to liver cirrhosis. Similar results were found when HCC was compared with inactive carriers, while there was no association when compared between liver cirrhosis and HCC. A positive relationship between serum RNase L and HBV viral titers or advanced disease status is uncovered in this study. Further investigation in this area may provide more details of an innate immune response for HBV and opportunity for novel therapeutic strategy.

Global genomic diversity and conservation of SARS-CoV-2 since the COVID-19 outbreak.

Global sequencing of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has enabled researchers to monitor the genetic information of new pathogenic variants. However, the integrity and accuracy of most genomic information cannot be guaranteed due to limited sample quality and sequencing technology. This restricts researchers from tracking the latest changes in the virus genome. In this study, we aimed to characterize the diversity and conservation balance of complete SARS-CoV-2 genomes worldwide since the outbreak. To achieve this goal, we collected 5,966,490 genome sequences from various parts of the world, excluding those with incomplete or unknown/degenerate sequences. Our methodology included comparing sequences using BLASTN and BLASTP, analyzing RNA secondary structure, and calculating entropy. Our findings provide insights into the characteristics of SARS-CoV-2 and potential mechanisms of pathogenesis. We found that uracil had the highest proportion of all bases among various coronaviruses and cytosine to uracil mutations had the highest proportion among all point mutations. The consistency in the front part (1-26,599 nt) was significantly higher than that in the back part (26,600-29,903 nt) of the genome. For most genes, the similar consistency characteristics were also observed in their protein families. IMPORTANCE Our results indicate that most severe acute respiratory syndrome coronavirus 2 genomes sampled from patients had a mutation rate ≤1.07 ‰ and genome-tail proteins (including S protein) were the main sources of genetic polymorphism. The analysis of the virus-host interaction network of genome-tail proteins showed that they shared some antiviral signaling pathways, especially the intracellular protein transport pathway.

Interferon-stimulated gene TDRD7 interacts with AMPK and inhibits its activation to suppress viral replication and pathogenesis.

Virus infection triggers induction of interferon (IFN)-stimulated genes (ISGs), which ironically inhibit viruses themselves. We identified Tudor domain-containing 7 (TDRD7) as a novel antiviral ISG, which inhibits viral replication by interfering with autophagy pathway. Here, we present a molecular basis for autophagy inhibitory function of TDRD7. TDRD7 interacted with adenosine monophosphate (AMP)-activated protein kinase (AMPK), the kinase that initiates autophagy, to inhibit its activation. We identified domains required for the interaction; deleting AMPK-interacting domain blocked antiAMPK and antiviral activities of TDRD7. We used primary cells and mice to evaluate the TDRD7-AMPK antiviral pathway. TDRD7-deficient primary mouse cells exhibited enhanced AMPK activation and viral replication. Finally, TDRD7 knockout mice showed increased susceptibility to respiratory virus infection. Therefore, our study revealed a new antiviral pathway of IFN and its contribution to host response. Our results have therapeutic potential; a TDRD7-derived peptide may be an effective AMPK inhibitor with application as antiviral agent.

TRAF family member-associated NF-κB activator (TANK) regulates the antiviral function and NF-κB activation in red-spotted grouper (Epinephelus akaara)

The TRAF family member-associated nuclear factor kappa B (NF-κB) activator (TANK) regulates the NF-κB activation through the TRAF-mediated signaling pathway and is involved in the antiviral pathway by inducing the interferon (IFN) production. In the present study, we identified a TANK ortholog from the red-spotted grouper (Epinephelus akaara) and analyzed its immunological functions. The coding sequence of EaTANK consists of 1047 base pairs and encodes a 348 amino acids protein. The predicted molecular weight and theoretical isoelectric point (pI) were 38.92 kDa and 5.39, respectively. According to the phylogenetic analysis, EaTANK was closely clustered with fish TANK orthologs, exhibiting the highest identity (97.1 %) and similarity (97.1 %) to that of Epinephelus lanceolatus. A highly conserved TBK1/IKKi binding domain (TBD) was identified between 110 and 164 residues. Our tissue distribution analysis showed that EaTANK mRNA was ubiquitously expressed in 12 tested tissues, with the highest expression in the spleen and peripheral blood cells (PBCs). According to the immune challenge experiments, EaTANK mRNA expression in PBCs was significantly elevated following stimulation with polyinosinic:polycytidylic acid [poly (I:C)], lipopolysaccharide (LPS), or nervous necrosis virus (NNV). We also observed a significant elevation in the mRNA expression of downstream antiviral pathway-related genes (ISG15, IRF3, and IRF7) in EaTANK-overexpressing fathead minnow (FHM) cells against poly (I:C) stimulation. Moreover, the replication of 6 genes in the VHSV genome was inhibited by the overexpression of EaTANK. Finally, we confirmed that the expression of NFKB1 mRNA and promoter binding activity of NF-κB was significantly increased in poly (I:C)-stimulated EaTANK-overexpressing FHM cells. In conclusion, the results of this study suggest that TANK significantly contributes to the antiviral response and regulation of NF-κB activity in red-spotted grouper.

TLR7 neo-functionalizes to sense dsRNA and trigger antiviral and antibacterial immunity in non-tetrapod vertebrates

TLR7 plays a crucial role in sensing viral ssRNA and initiating immune responses. Piscine TLR7 also responds to dsRNA challenge. dsRNA exists in almost all the viruses at specific stages. However, the mechanism on sensing dsRNA by TLR7 remains unknown. In the present study, we employed Ctenopharyngodon idella TLR7 (CiTLR7) to systematically explore the immune functions and mechanisms in teleost. CiTLR7 can directly bind not only ssRNA but also dsRNA at different patches in lysosome, recruit MyD88 as adaptor, and activate the downstream IFN pathway via SLC15A4/TASLa/TASLb/IRF5/IRF7 complex for antiviral and antibacterial infections and AP-1 pathway for pro-inflammatory cytokines. The key binding sites for dsRNA are L29 and L811 in CiTLR7. Further, we found that the function on recognizing dsRNA by TLR7 emerges in pisciformes and loses in tetrapods in evolution. This is the first report on sensing both ssRNA and dsRNA by a TLR member.

EBV-Encoded MicroRNA-BART17-3p Targets DDX3X and Promotes EBV Infection in EBV-Associated T/Natural Killer-Cell Lymphoproliferative Diseases.

Epstein-Barr virus (EBV) persistently infects T/natural killer (NK) cells causing an array of refractory EBV-associated T/NK-cell lymphoproliferative disorders. EBV-encoded microRNAs are important regulators for EBV latent infection and tumorigenesis. However, the roles of most EBV microRNAs in EBV-infected T/NK cells remain poorly understood. On the basis of a search of the doRiNA database and the BiBiServ2-RNAhybrid website, we predicted that EBV-miR-BART17-3p targeted DDX3X, and we verified the hypothesis by dual-luciferase reporter assay and cell function experiments. In addition, we collected 50 EBV-positive T-, B-, and NK-cell samples from the peripheral blood of EBV-positive cases to examine the role of EBV-miR-BART17-3p in the disease. We found that EBV-miR-BART17-3p directly targeted DDX3X and downregulated DDX3X expression. By analyzing EBV-positive cell samples from cell lines and patients, we found that EBV-miR-BART17-3p was highly expressed only in EBV-positive NK cells and that the overexpression was significantly related to high EBV loads in EBV-infected NK cells. Furthermore, we found that EBV-miR-BART17-3p downregulated the RIG-I-like receptor antiviral pathway and promoted the expression of EBV-encoded proteins in EBV-infected NK cells by targeting DDX3X. Our study showed that EBV-miR-BART17-3p was abundantly expressed in EBV-infected NK cells and inhibited the important antivirus immune responses of hosts by targeting DDX3X of the RIG-I-like receptor pathway. These findings could help us gain insights into the pathogenic mechanisms underlying EBV-associated T/NK-cell lymphoproliferative disorders and find the potential therapeutic target.

Salicylic acid and RNA interference mediate antiviral immunity of plant stem cells

Stem cells are essential for the development and organ regeneration of multicellular organisms, so their infection by pathogenic viruses must be prevented. Accordingly, mammalian stem cells are highly resistant to viral infection due to dedicated antiviral pathways including RNA interference (RNAi). In plants, a small group of stem cells harbored within the shoot apical meristem generate all postembryonic above-ground tissues, including the germline cells. Many viruses do not proliferate in these cells, yet the molecular bases of this exclusion remain only partially understood. Here, we show that a plant-encoded RNA-dependent RNA polymerase, after activation by the plant hormone salicylic acid, amplifies antiviral RNAi in infected tissues. This provides stem cells with RNA-based virus sequence information, which prevents virus proliferation. Furthermore, we find RNAi to be necessary for stem cell exclusion of several unrelated RNA viruses, despite their ability to efficiently suppress RNAi in the rest of the plant. This work elucidates a molecular pathway of great biological and economic relevance and lays the foundations for our future understanding of the unique systems underlying stem cell immunity.