Statins attenuate antiviral IFN-ß and ISG expression via inhibition of IRF3 and JAK/STAT signaling in poly(I:C)-treated hyperlipidemic mice and macrophages.

Viral infection is a significant burden to health care worldwide. Statins, 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase inhibitors, are widely used as cholesterol-lowering drugs. Recently, long-term statin therapy was shown to reduce the antiviral immune response; however, the underlying molecular mechanisms are unclear. Here, we found that simvastatin decreased polyinosinic-polycytidylic acid [poly(I:C)]-induced expression of antiviral interferon (IFN)-ß and IFN-stimulated genes (ISGs) in the bronchoalveolar lavage fluid (BALF) and lungs of mice with high-fat diet-induced hyperlipidemia. Macrophages were the dominant cell type in the BALF of poly(I:C)-treated mice. We examined the effects of simvastatin in primary lung macrophages and found that simvastatin suppressed poly(I:C)-induced expression of IFN-ß and ISGs. We examined the molecular mechanisms of statin-mediated inhibition of antiviral gene expression using murine macrophage-like cell line, J774.1/JA-4. Simvastatin and pitavastatin decreased poly(I:C)-induced expression of IFN-ß and ISGs. Moreover, they repressed poly(I:C)-induced phosphorylation of IFN regulatory factor (IRF) 3 and signal transducers and activators of transcription (STAT) 1, which is involved in Janus kinase (JAK)/STAT signaling. Mevalonate and geranylgeranyl pyrophosphate (GGPP), but not cholesterol, counteracted the negative effect of statins on IFN-ß and ISG expression and phosphorylation of IRF3 and STAT1. The geranylgeranyltransferase inhibitor suppressed poly(I:C)-induced expression of IFN-ß and ISGs and phosphorylation of IRF3 and STAT1. These results suggest that statins suppressed the expression of IFN-ß and ISGs in poly(I:C)-treated hyperlipidemic mice and murine macrophages and that these effects occurred through the inhibition of IRF3 and JAK/STAT signaling in macrophages. Furthermore, GGPP recovered the statin-suppressed IRF3 and JAK/STAT signaling in poly(I:C)-treated macrophages.

Zika Virus Proteins NS2A and NS4A Are Major Antagonists that Reduce IFN-ß Promoter Activity Induced by the MDA5/RIG-I Signaling Pathway.

Zika virus (ZIKV) is a mosquito-transmitted, emerging Flavivirus that causes Guillain-Barré syndrome and microcephaly in adults and fetuses, respectively. Since ZIKV was first isolated in 1947, severe outbreaks have occurred at various places worldwide, including Yap Island in 2007, French Polynesia in 2013, and Brazil in 2015. Although incidences of ZIKV infection and dissemination have drastically increased, the mechanisms underlying the pathogenesis of ZIKV have not been sufficiently studied. In addition, despite extensive research, the exact roles of individual ZIKV genes in the viral evasion of the host innate immune responses remain elusive. Besides, it is still possible that more than one ZIKV-encoded protein may negatively affect type I interferon (IFN) induction. Hence, in this study, we aimed to determine the modulations of the IFN promoter activity, induced by the MDA5/RIG-I signaling pathway, by over-expressing individual ZIKV genes. Our results show that two nonstructural proteins, NS2A and NS4A, significantly down-regulated the promoter activity of IFN-ß by inhibiting multiple signaling molecules involved in the activation of IFN-ß. Interestingly, while NS2A suppressed both full-length and constitutively active RIG-I, NS4A had inhibitory activity only on full-length RIG-I. In addition, while NS2A inhibited all forms of IRF3 (full-length, regulatory domain-deficient, and constitutively active), NS4A could not inhibit constitutively active IRF3-5D. Taken together, our results showed that NS2A and NS4A play major roles as antagonists of MDA5/RIG-I-mediated IFN-ß induction and more importantly, these two viral proteins seem to inhibit induction of the type I IFN responses in differential mechanisms. We believe this study expands our understanding regarding the mechanisms via which ZIKV controls the innate immune responses in cells and may pave the way to development of ZIKV-specific therapeutics.

Inhibition of TLR4/TRIF/IRF3 Signaling Pathway by Curcumin in Breast Cancer Cells.

PURPOSE: Toll-like receptor 4 (TLR4) is over-expressed in breast tumors and thus contributing to the tumor progression and metastasis. Natural products have drawn attention in cancer immunotherapy due to their various biological activities. Curcumin is well investigated in different types of cancer. However, the mechanisms underlying its anti-inflammatory actions have not been extensively elucidated.  For this purpose, we explored the inhibitory effects of curcumin on lipopolysaccharide (LPS)-induced TLR4 dependent TRIF signaling pathway in two subtypes of breast cancer cell lines (MCF-7 and MDA-MB-231) in this study. METHODS: In this context, the cytotoxicity of curcumin and LPS alone and the combination of curcumin with LPS on these cells was evaluated by WST-1 assay.  The expression level of TLR4 and the release of type I interferon (IFN) levels were determined after treatment with curcumin and/or LPS by RT-PCR and ELISA analysis, respectively. Furthermore, the subcellular localization of TLR4 and interferon regulatory factor 3 (IRF3) were detected by immunofluorescence analysis. RESULTS: Curcumin treatment suppressed breast cancer cells viabilities and the activation of TLR4-mediated TRIF signaling pathway by the downregulation of TLR4 and IRF3 expression levels and the inhibition of type I IFN (IFN-α/ß) levels induced by LPS. However, curcumin was more efficient in MDA- MB-231 cells than MCF-7 cells owing to its greater inhibitory efficacy in the LPS- enhanced TLR4 signaling pathway. Furthermore, IFN-α/ß levels induced by TLR4 and IRF3 were decreased in these cells following curcumin treatment. CONCLUSIONS: Consequently, these results demonstrated that the activation of LPS stimulated TLR4/TRIF/IRF3 signaling pathway was mediated by curcumin in breast cancer cells, in vitro. However, more studies are necessary to examine the curcumin's anti-inflammatory activities on TLR4/MyD88/NF-κB as well as other signaling pathways downstream of TLRs in breast cancer.

Establishment and Characterization of a New Cell Line Permissive for Hepatitis C Virus Infection.

Hepatitis C virus (HCV) cell culture systems have facilitated the development of efficient direct-acting antivirals against HCV. Huh-7.5, a subline of the human hepatoma cell line Huh-7, has been used widely to amplify HCV because HCV can efficiently replicate in these cells due to a defect in innate antiviral signalling. Recently, we established a novel cell line, KH, derived from human hepatocellular carcinoma, which showed atypical uptake of gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) in a Gd-EOB-DTPA-enhanced magnetic resonance imaging study. KH cells expressed hepatocyte markers including microRNA-122 (miR-122) at a lower level than Huh-7.5 cells. We demonstrated that KH cells could support the entire life cycle of HCV; however, HCV replicated at a lower rate in KH cells compared to Huh-7.5 cells, and virus particles produced from KH cells seemed to have some disadvantages in viral assembly compared with those produced from Huh-7.5 cells. KH cells had more robust interferon-stimulated gene expression and induction upon HCV RNA transfection, interferon-α2b addition, and HCV infection than Huh-7.5 cells. Interestingly, both miR-122 supplementation and IRF3 knockout in KH cells boosted HCV replication to a similar level as in Huh-7.5 cells, suggesting that intact innate antiviral signalling and lower miR-122 expression limit HCV replication in KH cells. KH cells will enable a deeper understanding of the role of the innate immune response in persistent HCV infection.

Porcine deltacoronavirus nucleocapsid protein antagonizes IFN-ß production by impairing dsRNA and PACT binding to RIG-I.

Porcine deltacoronavirus (PDCoV) is an emerging swine enteropathogenic coronavirus that causes watery diarrhea, vomiting and mortality in newborn piglets. Previous studies have suggested that PDCoV infection antagonizes RIG-I-like receptor (RLR)-mediated IFN-ß production to evade host innate immune defense, and PDCoV-encoded nonstructural protein nsp5 and accessory protein NS6 are associated with this process. However, whether the structural protein(s) of PDCoV also antagonize IFN-ß production remains unclear. In this study, we found that PDCoV nucleocapsid (N) protein, the most abundant viral structural protein, suppressed Sendai virus (SEV)-induced IFN-ß production and transcription factor IRF3 activation, but did not block IFN-ß production induced by overexpressing RIG-I/MDA5. Furthermore, study revealed that PDCoV N protein interacted with RIG-I and MDA5 in an in vitro overexpression system and evident interactions between N protein and RIG-I could be detected in the context of PDCoV infection, which interfered with the binding of dsRNA and protein activator of protein kinase R (PACT) to RIG-I. Together, our results demonstrate that PDCoV N protein is an IFN antagonist and utilizes diverse strategies to attenuate RIG-I recognition and activation.

TRIM27 Promotes Hepatitis C Virus Replication by Suppressing Type I Interferon Response.

Type I interferon (IFN) response is central for host defense against viral infection. Tripartite motif 27 (TRIM27) is implicated in antiviral innate immune response; however, whether it affects the replication of hepatitis C virus (HCV) and the underlying mechanisms remain uncharacterized. Here, we show that TRIM27 expression is induced in Huh7.5 human hepatoma cells infected with HCV or stimulated with type I IFNs in vitro. In addition, TRIM27 overexpression increases and its knockdown decreases viral RNA and protein levels, suggesting that TRIM27 positively regulates HCV replication. Mechanistically, TRIM27 inhibits type I IFN response against HCV infection through inhibiting IRF3 and NF-κB pathways, since TRIM27 mutant unable to inhibit these two inflammatory pathways fails to promote HCV replication. Taken together, this study identifies TRIM27 as a novel positive regulator of HCV replication, and also implicates that targeting TRIM27 may serve as a therapeutic strategy for controlling HCV replication.

Identification of an IKBKE inhibitor with antitumor activity in cancer cells overexpressing IKBKE.

BACKGROUND: The serine/threonine kinase IKBKE is frequently overexpressed or activated in a variety of human cancers. Ectopic expression of IKBKE induces malignant transformation, cell migration, invasion and chemoresistance. Thus, IKBKE is an attractive target for anti-cancer drug development. METHODS: By screening of NCI Diversity Set and Clinical Collection I and II compound libraries using cell-based assay, we identified several candidates of IKBKE inhibitors, which directly inhibited IKBKE kinase activity in vitro and in vivo. One of them, malachite green oxalate (MCCK1), was further characterized. The mechanism was examined by western blot, immunoprecipitation (IP) and Immunofluorescence. We also evaluated in a mouse xenograft model. In vitro kinase assay and luciferase reporter assay were also performed in our experiments. RESULTS: MCCK1 inhibits IKBKE kinase as well as its downstream targets such as IκBα, p65 and IRF3. MCCK1 is a selective inhibitor for IKBKE, with moderate effect on TBK1, but does not inhibit the activation of IKKα/ß, STAT3, Erk-1/2, p38 or JNK. The inhibition of IKBKE by MCCK1 resulted in induction of cell growth arrest and apoptosis selectively in human cancer cells that harbor aberrant expression of IKBKE. Furthermore, MCCK1 inhibits tumor growth in nude mice of human cancer cells in which IKBKE is elevated but not of those cancer cells in which it is not. CONCLUSION: These data indicate that MCCK1 is an IKBKE inhibitor with anti-tumor activity in vitro and in vivo and could be a potential anti-cancer agent for patients with tumors over expressing IKBKE.

Dingchuan tang essential oil inhibits the production of inflammatory mediators via suppressing the IRAK/NF-κB, IRAK/AP-1, and TBK1/IRF3 pathways in lipopolysaccharide-stimulated RAW264.7 cells.

BACKGROUND: Dingchuan tang (asthma-relieving decoction), a formula of nine herbs, has been used for treating respiratory inflammatory diseases for >400 years in the People's Republic of China. However, the mechanisms underlying the anti-inflammatory action of dingchuan tang is not fully understood. This study aims to investigate the effects of Dingchuan tang essential oil (DCEO) on inflammatory mediators and the underlying mechanism of action. MATERIALS AND METHODS: DCEO was extracted by steam distillation. Lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages were used as the cell model. Production of nitric oxide (NO) was determined by the Griess test. Protein secretion and mRNA levels of inflammatory mediators were measured by the enzyme-linked immunosorbent assay (ELISA) and quantitative real-time polymerase chain reaction (qRT-PCR), respectively. Protein levels were examined by Western blot. Nuclear localization of nuclear factor-kappa B (NF-κB) was detected using immunofluorescence analyses. RESULTS: DCEO significantly reduced LPS-triggered production of NO and prostaglandin E2 (PGE2) and decreased protein and mRNA levels of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). LPS induced upregulation of protein and mRNA levels of cytokines (interleukin-1ß [IL-1ß], interleukin-6 [IL-6], tumor necrosis factor-α [TNF-α]), and chemokines (monocyte chemoattractant protein-1 [MCP-1], chemokine [C-C motif] ligand 5 [CCL-5], and macrophage inflammatory protein [MIP]-1α) were suppressed by DCEO treatment. Phosphorylation and nuclear protein levels of transcription factors (activator protein-1 [AP-1], NF-κB, interferon regulatory factor 3 [IRF3]) were decreased by DCEO. Protein levels of phosphorylated IκB-α, IκB kinase α/ß (IKKα/ß), phosphatidylinositol 3-kinase (PI3K), protein kinase B (Akt), TGF ß-activated kinase 1 (TAK1), TANK-binding kinase 1 (TBK1), extracellular signal-regulated kinase (ERK), p38 mitogen-activated protein kinase (p38), and c-Jun N-terminal kinase (JNK) were lowered by DCEO. Moreover, degradation of interleukin-1 receptor-associated kinase 1 (IRAK1) and IRAK4 induced by LPS was inhibited by DCEO treatment. CONCLUSION: Suppression of the interleukin-1 receptor-associated kinase (IRAK)/NF-κB, IRAK/AP-1 and TBK1/IRF3 pathways was associated with the inhibitory effects of DCEO on inflammatory mediators in LPS-stimulated RAW264.7 macrophages. This study provides a pharmacological justification for the use of dingchuan tang in managing inflammatory disorders.

Role of miR-148a in Mitigating Hepatic Ischemia-Reperfusion Injury by Repressing the TLR4 Signaling Pathway via Targeting CaMKIIα in Vivo and in Vitro.

BACKGROUND/AIMS: Hepatic ischemia-reperfusion (I/R) injury, which is mainly induced by inflammation and unstable intracellular ions, is a major negative consequence of surgery that compromises hepatic function. However, the exact mechanisms of liver I/R injury have not been determined. Positive crosstalk with the Ca2+/CaMKII pathway is required for complete activation of the TLR4 pathway and inflammation. We previously found that miR-148a, which decreased in abundance with increasing reperfusion time, targeted and repressed the expression of CaMKIIα. In the present study, we examined the role of the miR-148a machinery in I/R-induced Ca2+/CaMKII and TLR4 signaling changes, inflammation, and liver dysfunction in vivo and in vitro. METHODS: Liver function was evaluated by serum aminotransferase levels and hematoxylin-eosin (HE) staining. Inflammatory factors were detected by enzyme-linked immunosorbent assay. Gene and protein expression were assessed by RT-PCR and western blot. Small interfering RNA was used to silence target gene expression. HE staining and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling were used to measure hepatic tissue apoptosis. These assays were performed to identify factors upregulated in hepatic I/R injury and downregulated by miR-148a. RESULTS: We manifested that expression of CaMKIIα and phosphorylation of TAK1 and IRF3 were elevated in hypoxia/reoxygenation (H/R)-treated primary Kupffer cells (KCs) and liver tissue of I/R-treated mice, but these effects were attenuated by treatment with miR-148a mimic and were accompanied by the alleviation of liver dysfunction and hepatocellular apoptosis. Luciferase reporter experiments showed that miR148a suppressed luciferase activity by almost 60%. Moreover, knockdown of CaMKIIα in H/R KCs led to significant deficiencies in p-TAK1, P-IRF3, IL-6, and TNF-α, which was consistent with the effects of miR-148a overexpression. Otherwise, the same trend of activation of TAK1 and IRF3 and inflammatory factors in vitro was observed in the siTAK1 + siIRF3 group compared with the siCaMKIIα group. CONCLUSION: Taken together, we conclude that miR-148a may mitigate hepatic I/R injury by ameliorating TLR4-mediated inflammation via targeting CaMKIIα in vitro and in vivo.

C6orf106 is a novel inhibitor of the interferon-regulatory factor 3-dependent innate antiviral response.

Host recognition of intracellular viral RNA and subsequent induction of cytokine signaling are tightly regulated at the cellular level and are a target for manipulation by viruses and therapeutics alike. Here, we characterize chromosome 6 ORF 106 (C6orf106) as an evolutionarily conserved inhibitor of the innate antiviral response. C6orf106 suppresses the synthesis of interferon (IFN)-α/ß and proinflammatory tumor necrosis factor (TNF) α in response to the dsRNA mimic poly(I:C) and to Sendai virus infection. Unlike canonical inhibitors of antiviral signaling, C6orf106 blocks interferon-regulatory factor 3 (IRF3) and, to a lesser extent, NF-κB activity without modulating their activation, nuclear translocation, cellular expression, or degradation. Instead, C6orf106 interacts with IRF3 and inhibits IRF3 recruitment to type I IFN promoter sequences while also reducing the nuclear levels of the coactivator proteins p300 and CREB-binding protein (CBP). In summary, we have defined C6orf106 as a negative regulator of antiviral immunity that blocks IRF3-dependent cytokine production via a noncanonical and poorly defined mechanism. This work presents intriguing implications for antiviral immunity, autoimmune disorders, and cancer.

A High Content Screen in Macrophages Identifies Small Molecule Modulators of STING-IRF3 and NFkB Signaling.

We screened a library of bioactive small molecules for activators and inhibitors of innate immune signaling through IRF3 and NFkB pathways with the goals of advancing pathway understanding and discovering probes for immunology research. We used high content screening to measure the translocation from the cytoplasm to nucleus of IRF3 and NFkB in primary human macrophages; these transcription factors play a critical role in the activation of STING and other pro-inflammatory pathways. Our pathway activator screen yielded a diverse set of hits that promoted nuclear translocation of IRF3 and/or NFkB, but the majority of these compounds did not cause activation of downstream pathways. Screening for antagonists of the STING pathway yielded multiple kinase inhibitors, some of which inhibit kinases not previously known to regulate the activity of this pathway. Structure-activity relationships (SARs) and subsequent chemical proteomics experiments suggested that MAPKAPK5 (PRAK) is a kinase that regulates IRF3 translocation in human macrophages. Our work establishes a high content screening approach for measuring pro-inflammatory pathways in human macrophages and identifies novel ways to inhibit such pathways; among the targets of the screen are several molecules that may merit further development as anti-inflammatory drugs.

Identification of a small molecule that primes the type I interferon response to cytosolic DNA.

The type I interferon response plays a pivotal role in host defense against infectious agents and tumors, and promising therapeutic approaches rely on small molecules designed to boost this system. To identify such compounds, we developed a high-throughput screening assay based on HEK-293 cells expressing luciferase under the control of Interferon-Stimulated Response Elements (ISRE). An original library of 10,000 synthetic compounds was screened, and we identified a series of 1H-benzimidazole-4-carboxamide compounds inducing the ISRE promoter sequence, specific cellular Interferon-Stimulated Genes (ISGs), and the phosphorylation of Interferon Regulatory Factor (IRF) 3. ISRE induction by ChX710, a prototypical member of this chemical series, was dependent on the adaptor MAVS and IRF1, but was IRF3 independent. Although it was unable to trigger type I IFN secretion per se, ChX710 efficiently primed cellular response to transfected plasmid DNA as assessed by potent synergistic effects on IFN-ß secretion and ISG expression levels. This cellular response was dependent on STING, a key adaptor involved in the sensing of cytosolic DNA and immune activation by various pathogens, stress signals and tumorigenesis. Our results demonstrate that cellular response to cytosolic DNA can be boosted with a small molecule, and potential applications in antimicrobial and cancer therapies are discussed.

Encephalomyocarditis virus 3C protease attenuates type I interferon production through disrupting the TANK-TBK1-IKKε-IRF3 complex.

TRAF family member-associated NF-κB activator (TANK) is a scaffold protein that assembles into the interferon (IFN) regulator factor 3 (IRF3)-phosphorylating TANK-binding kinase 1 (TBK1)-(IκB) kinase ε (IKKε) complex, where it is involved in regulating phosphorylation of the IRF3 and IFN production. However, the functions of TANK in encephalomyocarditis virus (EMCV) infection-induced type I IFN production are not fully understood. Here, we demonstrated that, instead of stimulating type I IFN production, the EMCV-HB10 strain infection potently inhibited Sendai virus- and polyI:C-induced IRF3 phosphorylation and type I IFN production in HEK293T cells. Mechanistically, EMCV 3C protease (EMCV 3C) cleaved TANK and disrupted the TANK-TBK1-IKKε-IRF3 complex, which resulted in the reduction in IRF3 phosphorylation and type I IFN production. Taken together, our findings demonstrate that EMCV adopts a novel strategy to evade host innate immune responses through cleavage of TANK.

Crude Ecklonia cava Flake Extracts Attenuate Inflammation through the Regulation of TLR4 Signaling Pathway in LPS-Induced RAW264.7 Cells.

We investigated the beneficial effects of the crude Ecklonia cava flake (CEF), which is a residual product after polyphenol extraction from Ecklonia cava, on inflammation in LPS-stimulated RAW264.7 cells. A group of five different CEF extracts was obtained by a preparation process using water, hydrochloric acid or temperature. We observed that large-size (>19 kDa) CEF extract, which was extracted with water at 95 °C (CEF-W, 95 °C), suppressed the production of inflammatory cytokines by inhibiting its mRNA expression in LPS-induced RAW264.7 cells. TLR4 signaling involvements were negatively regulated by CEF-W, 95 °C. CEF-W, 95 °C repressed the translocation of NF-κB from cytoplasm into nucleus in LPS-induced RAW264.7 cells. CEF-W, 95 °C attenuated the phosphorylation of TBK1 and IRF3 by inhibiting the phosphorylation of ERK. Taken together, we demonstrated that large-size CEF-W, 95 °C may act as a negative regulator of inflammation through the suppression of TLR4 signaling constituents in LPS-induced RAW264.7 cells.

Ablation of Interferon Regulatory Factor 3 Protects Against Atherosclerosis in Apolipoprotein E-Deficient Mice.

The secretion of adhesion molecules by endothelial cells, as well as the subsequent infiltration of macrophages, determines the initiation and progression of atherosclerosis. Accumulating evidence suggests that IRF3 (interferon regulatory factor 3) is required for the induction of proinflammatory cytokines and for endothelial cell proliferation. However, the effect and underlying mechanism of IRF3 on atherogenesis remain unknown. Our results demonstrated a moderate-to-strong immunoreactivity effect associated with IRF3 in the endothelium and macrophages of the atherosclerotic plaques in patients with coronary heart disease and in hyperlipidemic mice. IRF3-/-ApoE-/- mice showed significantly decreased atherosclerotic lesions in the whole aorta, aortic sinus, and brachiocephalic arteries. The bone marrow transplantation further suggested that the amelioration of atherosclerosis might be attributed to the effects of IRF3 deficiency mainly in endothelial cells, as well as in macrophages. The enhanced stability of atherosclerotic plaques in IRF3-/-ApoE-/- mice was characterized by the reduction of necrotic core size, macrophage infiltration, and lipids, which was accompanied by increased collagen and smooth muscle cell content. Furthermore, multiple proinflammatory cytokines showed a marked decrease in IRF3-/-ApoE-/- mice. Mechanistically, IRF3 deficiency suppresses the secretion of VCAM-1 (vascular cell adhesion molecule 1) and the expression of ICAM-1 (intercellular adhesion molecule 1) by directly binding to the ICAM-1 promoter, which subsequently attenuates macrophage infiltration. Thus, our study suggests that IRF3 might be a potential target for the treatment of atherosclerosis development.

In Vitro and In Vivo Anti-Allergic and Anti-Inflammatory Effects of eBV, a Newly Developed Derivative of Bee Venom, through Modulation of IRF3 Signaling Pathway in a Carrageenan-Induced Edema Model.

BACKGROUND: Bee venom (BV), a type of toxin extracted from honeybees (Apis mellifera), has been empirically and widely used to treat inflammatory diseases throughout Asia. Essential BV (eBV) was developed by removing phospholipase A2 (PLA2) and histamine to lower occurrence of allergic reaction. This study investigated the anti-allergic and anti-inflammatory activities of eBV in vitro and in vivo and its underlying mechanism of action. METHODS: The anti-inflammatory potential of eBV was assessed in vivo using a carrageenan-induced paw edema model. To further investigate the mechanism by which eBV exerts anti-allergic and anti-inflammatory effects, compound 48/80-stimulated RBL-2H3 cells and lipopolysaccharide (LPS)-stimulated RAW 264.7 murine macrophage cells were studied in vitro. RESULTS: Release of ß-hexosaminidase and histamine was increased by eBV in a dose-dependent manner, but these levels were lower in eBV compared to original BV at the same concentration. In addition, eBV suppressed compound 48/80-induced expression of tumor necrosis factor-α (TNF-α) and interleukin-1ß (IL-1ß) in RBL-2H3 cells. eBV was also shown to suppress nitric oxide (NO) production by down-regulating mRNA expression and subsequent protein expression of inflammatory mediators in LPS-induced RAW 264.7 cells. Phosphorylation of activators and signal transducers of transcription 1/interferon regulatory factor 3 (STAT1/IRF3) was attenuated by eBV treatment. eBV significantly inhibited carrageenan-induced acute edema in vivo. Serum levels of prostaglandin E2 (PGE2), TNF-α, and IL-1ß were also down-regulated by eBV. CONCLUSIONS: These results demonstrate that eBV inhibits allergic and inflammatory response by reducing inflammatory mediator production via regulation of the STAT1/IRF3 signaling pathway, suggesting that eBV is a feasible candidate for regulation of allergic-inflammatory response in complementary and alternative medicine.

Dengue virus infection induces interferon-lambda1 to facilitate cell migration.

A marked increase in the rate of dengue virus (DENV) infection has resulted in more than 212 deaths in Taiwan since the beginning of 2015, mostly from fatal outcomes such as dengue hemorrhagic fever and dengue shock syndrome. The pathogenic mechanisms of these fatal manifestations are poorly understood. Cytokines induce an overwhelming immune reaction and thus have crucial roles. Interferon-lambda (IFN-λ), a newly identified IFN subtype, has antiviral effects, but its immunologic effects in DENV infection have not been investigated. In the present study, we show that DENV infection preferentially induced production of IFN-λ1 in human dendritic cells (DCs) and human lung epithelial cells. Virus nonstructural 1 (NS1) glycoprotein was responsible for the effect. DENV-induced production of IFN-λ1 was dependent on signaling pathways involving toll-like receptor (TLR)-3, interferon regulation factor (IRF)-3, and nuclear factor-kappaB (NF-κB). Blocking interaction between IFN-λ1 and its receptor IFN-λR1 through siRNA interference reduced DENV-induced DC migration towards the chemoattractants CCL19 and CCL21, by inhibiting CCR7 expression. Furthermore, IFN-λ1 itself induced CCR7 expression and DC migration. Our study presents the first evidence of the mechanisms and effects of IFN-λ1 induction in DENV-infected DCs and highlights the role of this cytokine in the immunopathogenesis of DENV infection.

Dengue Virus Subverts Host Innate Immunity by Targeting Adaptor Protein MAVS.

UNLABELLED: Dengue virus (DENV) is the most common mosquito-borne virus infecting humans and is currently a serious global health challenge. To establish infection in its host cells, DENV must subvert the production and/or antiviral effects of interferon (IFN). The aim of this study was to understand the mechanisms by which DENV suppresses IFN production. We determined that DENV NS4A interacts with mitochondrial antiviral signaling protein (MAVS), which was previously found to activate NF-κB and IFN regulatory factor 3 (IRF3), thus inducing type I IFN in the mitochondrion-associated endoplasmic reticulum membranes (MAMs). We further demonstrated that NS4A is associated with the N-terminal CARD-like (CL) domain and the C-terminal transmembrane (TM) domain of MAVS. This association prevented the binding of MAVS to RIG-I, resulting in the repression of RIG-I-induced IRF3 activation and, consequently, the abrogation of IFN production. Collectively, our findings illustrate a new molecular mechanism by which DENV evades the host immune system and suggest new targets for anti-DENV strategies. IMPORTANCE: Type I interferon (IFN) constitutes the first line of host defense against invading viruses. To successfully establish infection, dengue virus (DENV) must counteract either the production or the function of IFN. The mechanism by which DENV suppresses IFN production is poorly understood and characterized. In this study, we demonstrate that the DENV NS4A protein plays an important role in suppressing interferon production through binding MAVS and disrupting the RIG-I-MAVS interaction in mitochondrion-associated endoplasmic reticulum membranes (MAMs). Our study reveals that MAVS is a novel host target of NS4A and provides a molecular mechanism for DENV evasion of the host innate immune response. These findings have important implications for understanding the pathogenesis of DENV and may provide new insights into using NS4A as a therapeutic and/or prevention target.

Suppression of Type I Interferon Production by Human T-Cell Leukemia Virus Type 1 Oncoprotein Tax through Inhibition of IRF3 Phosphorylation.

UNLABELLED: Infection with human T-cell leukemia virus type 1 (HTLV-1) is associated with adult T-cell leukemia (ATL) and tropical spastic paraparesis. Type I interferons (IFNs) are key effectors of the innate antiviral response, and IFN-α combined with the nucleoside reverse transcriptase inhibitor zidovudine is considered the standard first-line therapy for ATL. HTLV-1 oncoprotein Tax is known to suppress innate IFN production and response but the underlying mechanisms remain to be fully established. In this study, we report on the suppression of type I IFN production by HTLV-1 Tax through interaction with and inhibition of TBK1 kinase that phosphorylates IRF3. Induced transcription of IFN-ß was severely impaired in HTLV-1-transformed ATL cells and freshly infected T lymphocytes. The ability to suppress IRF3 activation was ascribed to Tax. The expression of Tax alone sufficiently repressed the induction of IFN production by RIG-I plus PACT, cGAMP synthase plus STING, TBK1, IKKε, IRF3, and IRF7, but not by IRF3-5D, a dominant-active phosphomimetic mutant. This suggests that Tax perturbs IFN production at the step of IRF3 phosphorylation. Tax mutants deficient for CREB or NF-κB activation were fully competent in the suppression of IFN production. Coimmunoprecipitation experiments confirmed the association of Tax with TBK1, IKKε, STING, and IRF3.In vitrokinase assay indicated an inhibitory effect of Tax on TBK1-mediated phosphorylation of IRF3. Taken together, our findings suggested a new mechanism by which HTLV-1 oncoprotein Tax circumvents the production of type I IFNs in infected cells. Our findings have implications in therapeutic intervention of ATL. IMPORTANCE: Human T-cell leukemia virus type 1 (HTLV-1) is the cause of adult T-cell leukemia (ATL), an aggressive and fatal blood cancer, as well as another chronic disabling disease of the spinal cord. Treatments are unsatisfactory, and options are limited. A combination of antiviral cellular protein alpha interferon and zidovudine, which is an inhibitor of a viral enzyme called reverse transcriptase, has been recommended as the standard first-line therapy for ATL. Exactly how HTLV-1 interacts with the cellular machinery for interferon production and action is not well understood. Our work sheds light on the mechanism of action for the inhibition of interferon production by an HTLV-1 oncogenic protein called Tax. Our findings might help to improve interferon-based anti-HTLV-1 and anti-ATL therapy.

Contribution of the interaction between the rabies virus P protein and I-kappa B kinase ϵ to the inhibition of type I IFN induction signalling.

The P protein of rabies virus (RABV) is known to interfere with the phosphorylation of the host IFN regulatory factor 3 (IRF-3) and to consequently inhibit type I IFN induction. Previous studies, however, have only tested P proteins from laboratory-adapted fixed virus strains, and to the best of our knowledge there is no report about the effect of P proteins from street RABV strains or other lyssaviruses on the IRF-3-mediated type I IFN induction system. In this study, we evaluated the inhibitory effect of P proteins from several RABV strains, including fixed and street virus strains and other lyssaviruses (Lagos bat, Mokola and Duvenhage viruses), on IRF-3 signalling. All P proteins tested inhibited retinoic acid-inducible gene-1 (RIG-I)- and TANK binding kinase 1 (TBK1)-mediated IRF-3-dependent IFN-ß promoter activities. On the other hand, the P proteins from the RABV street strains 1088 and HCM-9, but not from fixed strains Nishigahara (Ni) and CVS-11 and other lyssaviruses tested, significantly inhibited I-kappa B kinase ϵ (IKKϵ)-inducible IRF-3-dependent IFN-ß promoter activity. Importantly, we revealed that the P proteins from the 1088 and HCM-9 strains, but not from the remaining viruses, interacted with IKKϵ. By using expression plasmids encoding chimeric P proteins from the 1088 strain and Ni strain, we found that the C-terminal region of the P protein is important for the interaction with IKKϵ. These findings suggest that the P protein of RABV street strains may contribute to efficient evasion of host innate immunity.