SIKE is an IKK epsilon/TBK1-associated suppressor of TLR3- and virus-triggered IRF-3 activation pathways

PWWP3A disrupts the assembly of VISA/MAVS signalosome to inhibit innate immune response against RNA viruses

VISA/MAVS is crucial in antiviral innate immunity. Upon RNA virus infection, VISA recruits TBK1 via TRAFs to mitochondria, inducing IRF3 phosphorylation and type I interferons. However, TBK1 recruitment mechanisms via individual TRAFs are unclear. Here, we reveal that PWWP domain-containing 3A (PWWP3A) serves as a negative regulator of RNA virus-triggered signaling. During viral infection, PWWP3A translocates from nucleus to the mitochondria, competing with TRAF6 for binding to VISA, thereby impeding the recruitment of TBK1 and inhibiting IRF3 activation. However, the extent of PWWP3A-mediated inhibition is regulated by the E3 ligase PJA2, which induces PWWP3A degradation post-infection, highlighting the intricate regulatory network in antiviral immunity. Consistently, PWWP3A deficiency enhances antiviral responses, and Pwwp3a-/- mice exhibit elevated levels of type I interferons and displayed greater resistance following RNA virus infection. Together, our findings unveil the inhibitory role of PWWP3A in virus-triggered signaling, which provides insights into preventing excessive immune responses.

STRIPAK, a fundamental signaling hub of eukaryotic development

SUMMARYThe striatin-interacting phosphatase and kinase (STRIPAK) complex is involved in the regulation of many developmental processes in eukaryotic microorganisms and all animals, including humans. STRIPAK is a component of protein phosphatase 2A (PP2A), a highly conserved serine-threonine phosphatase composed of catalytic subunits (PP2Ac), a scaffolding subunit (PP2AA) and various substrate-directing B regulatory subunits. In particular, the B''' regulatory subunit called striatin has evoked major interest over the last 20 years. Studies in fungal systems have contributed substantially to our current knowledge about STRIPAK composition, assembly, and cellular localization, as well as its regulatory role in autophagy and the morphology of fungal development. STRIPAK represents a signaling hub with many kinases and thus integrates upstream and downstream information from many conserved eukaryotic signaling pathways. A profound understanding of STRIPAK's regulatory role in fungi opens the gateway to understanding the multifarious functions carried out by STRIPAK in higher eukaryotes, including its contribution to malignant cell growth.

Characterization of the impact of dietary immunostimulant CpG on the expression of mRNA biomarkers involved in the immune responses in Atlantic salmon (Salmo salar)

Infectious diseases have significantly impacted Atlantic salmon aquaculture worldwide. Modulating fish immunity with immunostimulant-containing functional feeds could be an effective strategy in mitigating disease problems. Previously, we characterized the impact of polyriboinosinic polyribocytidylic acid (pIC) and formalin-killed typical Aeromonas salmonicida bacterin on miRNA expression in Atlantic salmon fed a commercial diet with and without immunostimulant CpG. A set of miRNA biomarkers of Atlantic salmon head kidney responding to pIC and/or bacterin immune stimulations was identified (Xue et al., 2019) [1]. Herein, we report a complementary qPCR study that investigated the impact of the pIC, bacterin and dietary CpG on the expression of immune-relevant mRNAs (n = 31) using the same samples as in the previous study (Xue et al., 2019) [1]. Twenty-six of these genes were predicted target transcripts of the pIC- and/or bacterin-responsive miRNAs identified in the earlier study. The current data showed that pIC and/or bacterin stimulations significantly modulated the majority of the qPCR-analyzed genes involved in various immune pathways. Some genes responded to both stimulations (e.g. tnfa, il10rb, ifng, irf9, cxcr3, campb) while others appeared to be stimulation specific [e.g. irf3, irf7a, il1r1, mxa, mapk3 (pIC only); clra (bacterin only)]. A. salmonicida bacterin stimulation produced a strong inflammatory response (e.g. higher expression of il1b, il8a and tnfa), while salmon stimulated with pIC showed robust interferon responses (both type I and II). Furthermore, the current data indicated significant down-regulation of immune-relevant transcripts (e.g. tlr9, irf5, il1r1, hsp90ab1, itgb2) by dietary immunostimulant CpG, especially among pre-injection and PBS-injected fish. Together with our prior miRNA study, the present research provided complementary information on Atlantic salmon anti-viral and anti-bacterial immune responses and on how dietary CpG may modulate these responses.

Black carp A20 inhibits interferon signaling through de-ubiquitinating IKKβ

IkappaB kinase beta (IKKβ) is a key member of IκB kinases and functions importantly in interferon (IFN) signaling. Phosphorylation and ubiquitination are involved in the activation of IKKβ. A20 is a de-ubiquitin enzyme and functions as a suppressor in inflammation signaling, which has been reported to be phosphorylated and activated by IKKβ. However, the role and relationship of IKKβ and A20 in teleost remains unclear. In this study, IKKβ (bcIKKβ) and A20 (bcA20) of black carp (Mylopharyngodon piceus) have been cloned and characterized. Overexpressed bcIKKβ in EPC cells showed strong anti-viral ability by activating both NF-κB and IFN signaling. EPC cells stable expressing bcIKKβ presented improved anti-viral activity as well. The interaction between bcA20 and bcIKKβ was identified, and overexpression of bcA20 was able to suppress bcIKKβ-mediated activation of NF-κB and IFN signaling. Meanwhile, knock-down of A20 increased host the antiviral ability of host cells. Importantly, it has been identified that bcA20 was able to remove K27-linked ubiquitination and decrease the phosphorylation of bcIKKβ. Thus, our data conclude that bcA20 suppresses the anti-viral activity of bcIKKβ and removes its K27-linked ubiquitination, which presents a new mechanism of IKKβ regulation.

Multispecies transcriptomics identifies SIKE as a MAPK repressor that prevents NASH progression

Nonalcoholic fatty liver (NAFL) remains relatively benign, but high-risk to end-stage liver diseases become highly prevalent when it progresses into nonalcoholic steatohepatitis (NASH). Our current understanding of the development of NAFL to NASH remains insufficient. In this study, we revealed MAP kinase (MAPK) activation as the most notable molecular signature associated with NASH progression across multiple species. Furthermore, we identified suppressor of IKKε (SIKE) as a conserved and potent negative controller of MAPK activation. Hepatocyte-specific overexpression of Sike prevented NASH progression in diet- and toxin-induced mouse NASH models. Mechanistically, SIKE directly interacted with TGF-β-activated kinase 1 (TAK1) and TAK1-binding protein 2 (TAB2) to interrupt their binding and subsequent TAK1-MAPK signaling activation. We found that indobufen markedly up-regulated SIKE expression and effectively improved NASH features in mice and macaques. These findings identify SIKE as a MAPK suppressor that prevents NASH progression and provide proof-of-concept evidence for targeting the SIKE-TAK1 axis as a potential NASH therapy.

Factor inhibiting HIF negatively regulates antiviral innate immunity via hydroxylation of IKKϵ

Activation of type I interferon (IFN-1) signaling is essential to protect host cells from viral infection. The full spectrum of IFN-I induction requires the activation of a number of cellular factors, including IκB kinase epsilon (IKKϵ). However, the regulation of IKKϵ activation in response to viral infection remains largely unknown. Here, we show that factor inhibiting hypoxia-inducible factor (HIF) (FIH), an asparaginyl hydroxylase, interacts with IKKϵ and catalyzes asparagine hydroxylation of IKKϵ at Asn-254, Asn-700, and Asn-701, resulting in the suppression of IKKϵ activation. FIH-mediated hydroxylation of IKKϵ prevents IKKϵ binding to TBK1 and TRAF3 and attenuates the cIAP1/cIAP2/TRAF2 E3 ubiquitin ligase complex-catalyzed K63-linked polyubiquitination of IKKϵ at Lys-416. In addition, Fih-deficient mice and zebrafish are more resistant to viral infection. This work uncovers a previously unrecognized role of FIH in suppressing IKKϵ activation for IFN signaling and antiviral immune responses.

TRIM25 negatively regulates IKKε-mediated interferon signaling in black carp

IKKε plays an important role in the activation of IRF3/IRF7 and the production of interferon (IFN), however, its regulation remains obscure in human. E3 ligase TRIM25 has been reported to manipulate the K63-linked ubiquitination of RIG-I, leading to the activation of RIG-I/IFN signaling. To elucidate the role of TRIM25 in teleost, a TRIM25 homolog (bcTRIM25) was cloned and characterized from black carp (Mylopharyngodon piceus). bcTRIM25 contains 653 amino acids, possessing conservative RING, B-box and SPRY domain, which is highly expressed in muscle, spleen and skin. bcTRIM25 knock-down enhanced the antiviral ability of host cells. bcTRIM25 over-expression alone in EPC cells attenuated bcIFNa promoter transcription in the reporter assays and impeded PKR and MX1 expression in qRT-PCR. Interestingly, co-IP assays indicated that bcTRIM25 interacted with bcIKKε and the induced bcIFNa promoter transcription by bcIKKε was notably hindered by bcTRIM25. Furthermore, bcIKKε-induced expression of interferon stimulated genes (ISGs) and antiviral activity were dampened by bcTRIM25. Further exploration showed that bcTRIM25 visibly enhanced the ubiquitination of bcIKKε but significantly attenuated the phosphorylation of bcIKKε. Thus, our data demonstrate for the first time in vertebrate that TRIM25 negatively regulates IKKε through enhancing its ubiquitination, which sheds a light on the regulation of IKKε/IFN signaling.

SERPINB1 promotes Senecavirus A replication by degrading IKBKE and regulating the IFN pathway via autophagy

IMPORTANCE

Senecavirus A (SVA) is an emerging picornavirus associated with vesicular disease, which wide spreads around the world. It has evolved multiple strategies to evade host immune surveillance. The mechanism and pathogenesis of the virus infection remain unclear. In this study, we show that SERPINB1, a member of the SERPINB family, promotes SVA replication, and regulates both innate immunity and the autophagy pathway. SERPINB1 catalyzes K48-linked polyubiquitination of IκB kinase epsilon (IKBKE) and degrades IKBKE through the proteasome pathway. Inhibition of IKBKE expression by SERPINB1 induces autophagy to decrease type I interferon signaling, and ultimately promotes SVA proliferation. These results provide importantly the theoretical basis of SVA replication and pathogenesis. SERPINB1 could be a potential therapeutic target for the control of viral infection.

Combinatorial targeting of Hippo-STRIPAK and PARP elicits synthetic lethality in gastrointestinal cancers

The striatin-interacting phosphatase and kinase (STRIPAK) complexes integrate extracellular stimuli that result in intracellular activities. Previously, we discovered that STRIPAK is a key machinery responsible for loss of the Hippo tumor suppressor signal in cancer. Here, we identified the Hippo-STRIPAK complex as an essential player in the control of DNA double-stranded break (DSB) repair and genomic stability. Specifically, we found that the mammalian STE20-like protein kinases 1 and 2 (MST1/2), independent of classical Hippo signaling, directly phosphorylated zinc finger MYND type-containing 8 (ZMYND8) and hence resulted in the suppression of DNA repair in the nucleus. In response to genotoxic stress, the cyclic GMP-AMP synthase/stimulator of IFN genes (cGAS/STING) pathway was determined to relay nuclear DNA damage signals to the dynamic assembly of Hippo-STRIPAK via TANK-binding kinase 1-induced (TBK1-induced) structural stabilization of the suppressor of IKBKE 1- sarcolemma membrane-associated protein (SIKE1-SLMAP) arm. As such, we found that STRIPAK-mediated MST1/2 inactivation increased the DSB repair capacity of cancer cells and endowed these cells with resistance to radio- and chemotherapy and poly(ADP-ribose)polymerase (PARP) inhibition. Importantly, targeting the STRIPAK assembly with each of 3 distinct peptide inhibitors efficiently recovered the kinase activity of MST1/2 to suppress DNA repair and resensitize cancer cells to PARP inhibitors in both animal- and patient-derived tumor models. Overall, our findings not only uncover what we believe to be a previously unrecognized role for STRIPAK in modulating DSB repair but also provide translational implications of cotargeting STRIPAK and PARP for a new type of synthetic lethality anticancer therapy.

ID2 inhibits innate antiviral immunity by blocking TBK1- and IKKε-induced activation of IRF3

The transcription regulator ID2 plays an essential role in the development and differentiation of immune cells. Here, we report that ID2 also negatively regulates antiviral innate immune responses. During viral infection of human epithelial cells, ID2 bound to TANK-binding kinase 1 (TBK1) and to inhibitor of nuclear factor κB kinase ε (IKKε). These interactions inhibited the recruitment and activation of interferon (IFN) regulatory factor 3 (IRF3) by TBK1 or IKKε, leading to a reduction in the expression of IFN-β1 (IFNB1). IFN-β induced the nuclear export of ID2 to form a negative feedback loop. Knocking out ID2 in human cells enhanced innate immune responses and suppressed infection by different viruses, including SARS-CoV-2. Mice with a myeloid-specific deficiency of ID2 produced more IFN-α in response to viral infection and were more resistant to viral infection than wild-type mice. Our findings not only establish ID2 as a modulator of IRF3 activation induced by TBK1 and/or IKKε but also introduce a mechanism for cross-talk between innate immunity and cell development and differentiation.

DAK inhibits MDA5-mediated signaling in the antiviral innate immunity of black carp

Dihydroxyacetone kinase (DAK) functions as a negative regulator of melanoma differentiation-associated gene 5 (MDA5)-mediated interferon (IFN) production in human. To explore its role in teleost fish, DAK homologue of black carp (Mylopharyngodon piceus) has been cloned and characterized in this paper. The transcription of black carp DAK (bcDAK) variated in host cells in response to LPS, poly (I:C) and virus stimulation, and bcDAK was majorly distributed in the cytoplasm. Overexpressed bcDAK in EPC cells showed little IFN promoter-inducing ability in the reporter assay and no antiviral activity in plaque assay. When co-expressed with black carp MDA5 (bcMDA5) in EPC cells, bcDAK obviously inhibited bcMDA5-mediated IFN promoter transcription in reporter assay and the antiviral activity in plaque assay. The knockdown of bcDAK enhanced the antiviral activity of the host cells. The association between bcDAK and bcMDA5 has been identified through immunofluorescent staining and co-immunoprecipitation (co-IP) assay. Thus, the data generated in this study support the conclusion that black carp DAK interacts with MDA5 and negatively regulates MDA5-mediated antiviral signaling.

Peroxiredoxin 1 Interacts with TBK1/IKKε and Negatively Regulates Pseudorabies Virus Propagation by Promoting Innate Immunity

Peroxiredoxin 1 (PRDX1) is a cellular antioxidant enzyme that is crucial for diverse fundamental biological processes, such as autophagy, inflammation, and carcinogenesis. However, molecular mechanisms underpinning its diverse roles are not well understood. Here, we report that PRDX1 positively regulates interferon (IFN) induction and that pseudorabies virus (PRV) targets PRDX1 to evade IFN induction. PRV UL13 encodes a serine/threonine kinase important for PRV infection, although its biological function remains obscure. We identified PRDX1 as a UL13-interacting protein. Virological and biochemical assays demonstrate that PRDX1 promotes IFN induction by interacting with TANK-binding kinase 1 (TBK1) and IκB kinase ε (IKKε). Conversely, UL13 accelerates PRDX1 degradation via the ubiquitin-proteosome pathway in a kinase-dependent manner. In doing so, PRV inhibits IFN induction during productive infection, which requires PRDX1 expression. This study uncovers an essential role of PRDX1 in the innate immune response and reveals a new viral immune evasion strategy to counteract cellular defenses. IMPORTANCE PRV interacts with numerous cellular proteins during productive infection. Here, we demonstrated the interaction of viral protein UL13 with the antioxidant enzyme PRDX1, which functions in multiple signal transduction pathways. We found that PRDX1 participates in the type I IFN pathway by interacting with TBK1 and IKKε, thereby negatively regulating PRV propagation. However, UL13 ubiquitinates PRDX1, which routes PRDX1 into proteasomes for degradation and effectively reduces its expression. These results illuminate the fundamental role that PRDX1 plays in the IFN pathway, and they identify a potential target for the control of PRV infection.

Analysis of miRNA and mRNA reveals core interaction networks and pathways of dexamethasone-induced immunosuppression in chicken bursa of Fabricius

Stress-induced immunosuppression is a serious problem affecting the production value of poultry, but its specific molecular mechanism has not yet been elucidated. We selected 7-day-old Gushi cocks as test animals and successfully established a stress-induced immunosuppression model by injecting 2.0 mg/kg (body weight) dexamethasone (Dex). We then constructed six cDNA libraries and two small RNA libraries of Bursa of Fabricius from the control group and the Dex group. RNA-seq results revealed 21,028 transcripts including 3920 novel transcripts; 500 miRNAs including 68 novel miRNAs were identified. Correlation analysis of miRNA, target genes and mRNA results indicated that the gga-miR-15 family, gga-miR-103-3p, gga-miR-456-3p, and gga-miR-27b-3p, as core differentially expressed miRNAs, may potentially regulate multiple genes which are involved in immune-related pathways; and that the core genes Suppressor of IKBKE 1 (SIKE1) and high mobility group AT-hook 2 (HMGA2) are associated with the miR-17 family (gga-miR-20a-5p, gga-miR-20b-5p, gga-miR-106-5p, and gga-miR-17-5p) and gga-let -7 family (gga-let-7b, gga-let-7i, gga-let-7c-5p, and gga-let-7f-5p). The interaction networks of mRNAs of significantly enrichment pathways and PPI (protein-protein interaction) networks showed that IL6, IL1B, IL8L1, CCL5, SOCS3, SOCS1, ITGB5, GSTA3, SQLE, FDFT1, FN1, IL18, IL10, MAPK11 and MAPK12 are network core nodes and that most of them are strongly associated with immune response. One of the candidate miRNAs, gga-miR-20b-5p, may play an important role in stress-induced immunosuppression. Luciferase assay and over-expression experiments suggested that gga-miR-20b-5p negatively regulated the expression of target gene SIKE1. These results provide better understanding of the mechanism of stress-induced immunosuppression in Gushi chicken bursa, and provide novel targets for subsequent research to improve poultry anti-stress capability.

Identification and expression analysis of MicroRNAs in chicken spleen in a corticosterone-induced stress model

For investigating the effects of stress on the immune response of chickens, we established a corticosterone (CORT)-induced stress model by exogenous intake of CORT. Control group was fed with a basal diet and the stress model group was fed with a 30 mg/Kg CORT-treated diet in ad libitum conditions for 7 days. Then, we used RNA-seq technology to identify the expression pattern of miRNAs, target genes, and relevant pathways in chicken spleen. Results showed that 71 differentially expressed miRNAs (DEMs) were determined, 9 of which were significantly differentially expressed miRNAs (SDEMs), and 241 target genes of DEMs were predicted. GO annotation and KEGG pathway analysis were carried out to understand the role of the DEMs. Out of 287 significantly enriched GO terms, 37 were stress- or immune-related, such as response to light stimulus, detection of oxidative stress, and immune response in mucosal-associated lymphoid tissue. Out of 85 KEGG pathways, 8 were related to stress or immunity, such as cytokine-cytokine receptor interaction, JAK-STAT signaling pathway, and RLR signaling pathway. We then constructed the interaction networks between target genes from immune-related pathways and their DEMs. The analysis results suggested that some DEMs (gga-miR-17 family, gga-miR-15/16 family, gga-miR-2954 and gga-miR-34b-5p) and target genes (SIKE1, CX3CL1, IL11Ra, PIGR, and CDKN1A) were core miRNAs and genes. This study revealed the dynamic miRNA transcriptome, target genes and related pathways in chicken spleen under CORT-induced stress model, which provided a basis for studying the molecular mechanism of stress affecting immune function.

A novel role of Zebrafish TMEM33 in negative regulation of interferon production by two distinct mechanisms

The transmembrane protein 33 (TMEM33) was originally identified as an endoplasmic reticulum (ER) protein that influences the tubular structure of the ER and modulates intracellular calcium homeostasis. However, the role of TMEM33 in antiviral immunity in vertebrates has not been elucidated. In this article, we demonstrate that zebrafish TMEM33 is a negative regulator of virus-triggered interferon (IFN) induction via two mechanisms: mitochondrial antiviral signaling protein (MAVS) ubiquitination and a decrease in the kinase activity of TANK binding kinase 1 (TBK1). Upon stimulation with viral components, tmem33 was remarkably upregulated in the zebrafish liver cell line. The IFNφ1 promoter (IFNφ1pro) activity and mRNA level induced by retinoic acid-inducible gene (RIG)-I-like receptors (RLRs) were significantly inhibited by TMEM33. Knockdown of TMEM33 increased host ifn transcription. Subsequently, we found that TMEM33 was colocalized in the ER and interacted with the RLR cascades, whereas MAVS was degraded by TMEM33 during the K48-linked ubiquitination. On the other hand, TMEM33 reduced the phosphorylation of mediator of IFN regulatory factor 3 (IRF3) activation (MITA)/IRF3 by acting as a decoy substrate of TBK1, which was also phosphorylated. A functional domain assay revealed that the N-terminal transmembrane domain 1 (TM1) and TM2 regions of TMEM33 were necessary for IFN suppression. Finally, TMEM33 significantly attenuated the host cellular antiviral capacity by blocking the IFN response. Taken together, our findings provide insight into the different mechanisms employed by TMEM33 in cellular IFN-mediated antiviral process.

Accelerator or Brake: Immune Regulators in Malaria

Malaria is a life-threatening infectious disease, affecting over 250 million individuals worldwide each year, eradicating malaria has been one of the greatest challenges to public health for a century. Growing resistance to anti-parasitic therapies and lack of effective vaccines are major contributing factors in controlling this disease. However, the incomplete understanding of parasite interactions with host anti-malaria immunity hinders vaccine development efforts to date. Recent studies have been unveiling the complexity of immune responses and regulators against Plasmodium infection. Here, we summarize our current understanding of host immune responses against Plasmodium-derived components infection and mainly focus on the various regulatory mechanisms mediated by recent identified immune regulators orchestrating anti-malaria immunity.

Plasmodium yoelii Uses a TLR3-Dependent Pathway to Achieve Mammalian Host Parasitism

Malaria is associated with complicated immunopathogenesis. In this study, we provide evidence for an unexpected role of TLR3 in promoting the establishment of Plasmodium yoelii infection through delayed clearance of parasitemia in wild type C57BL/6jRj (B6) compared with TLR3 knockout mice. In this study, we confirmed an increased expression of Tlr3, Trif, Tbk1, and Irf7/Irf3 in the liver 42 h postinfection and the initiation of an early burst of proinflammatory response such as Ifng, NF-kB, and Tnfa in B6 mice that may promote parasite fitness. Interestingly, in the absence of TLR3, we showed the involvement of high IFN-γ and lower type I IFN response in the early clearance of parasitemia. In parallel, we observed an increase in splenic NK and NKT cells expressing TLR3 in infected B6 mice, suggesting a role for TLR sensing in the innate immune response. Finally, we find evidence that the increase in the frequency of CD19⁺TLR3⁺ B cells along with reduced levels of total IgG in B6 mice possibly suggests the initiation of TLR3-dependent pathway early during P. yoelii infection. Our results thus reveal a new mechanism in which a parasite-activated TLR3 pathway promotes blood stage infection along with quantitative and qualitative differences in Ab responses.

miRNAs Predicted to Regulate Host Anti-viral Gene Pathways in IPNV-Challenged Atlantic Salmon Fry Are Affected by Viral Load, and Associated With the Major IPN Resistance QTL Genotypes in Late Infection

Infectious pancreatic necrosis virus (IPNV) infection has been a major problem in salmonid aquaculture. Marker-assisted selection of individuals with resistant genotype at the major IPN quantitative trait locus (IPN-QTL) has significantly reduced mortality in recent years. We have identified host miRNAs that respond to IPNV challenge in salmon fry that were either homozygous resistant (RR) or homozygous susceptible (SS) for the IPN-QTL. Small RNA-sequenced control samples were compared to samples collected at 1, 7, and 20 days post challenge (dpc). This revealed 72 differentially expressed miRNAs (DE miRNAs). Viral load (VL) was lower in RR vs. SS individuals at 7 and 20 dpc. However, analysis of miRNA expression changes revealed no differences between RR vs. SS individuals in controls, at 1 or 7 dpc, while 38 "high viral load responding" miRNAs (HVL-DE miRNAs) were identified at 20 dpc. Most of the HVL-DE miRNAs showed changes that were more pronounced in the high VL SS group than in the low VL RR group when compared to the controls. The absence of differences between QTL groups in controls, 1 and 7 dpc indicates that the QTL genotype does not affect miRNA expression in healthy fish or their first response to viral infections. The miRNA differences at 20 dpc were associated with the QTL genotype and could, possibly, contribute to differences in resistance/susceptibility at the later stage of infection. In silico target gene predictions revealed that 180 immune genes were putative targets, and enrichment analysis indicated that the miRNAs may regulate several major immune system pathways. Among the targets of HVL-DE miRNAs were IRF3, STAT4, NFKB2, MYD88, and IKKA. Interestingly, TNF-alpha paralogs were targeted by different DE miRNAs. Most DE miRNAs were from conserved miRNA families that respond to viral infections in teleost (e.g., miR-21, miR-146, miR-181, miR-192, miR-221, miR-462, miR-731, and miR-8159), while eight were species specific. The miRNAs showed dynamic temporal changes implying they would affect their target genes differently throughout disease progression. This shows that miRNAs are sensitive to VL and disease progression, and may act as fine-tuners of both immediate immune response activation and the later inflammatory processes.

TBK1, a central kinase in innate immune sensing of nucleic acids and beyond

Sensing of intracellular and extracellular environments is one of the fundamental processes of cell. Surveillance of aberrant nucleic acids, derived either from invading pathogens or damaged organelle, is conducted by pattern recognition receptors (PRRs) including RIG-I-like receptors, cyclic GMP-AMP synthase, absent in melanoma 2, and a few members of toll-like receptors. TANK-binding kinase 1 (TBK1), along with its close analogue I-kappa-B kinase epsilon, is a central kinase in innate adaptor complexes linking activation of PRRs to mobilization of transcriptional factors that transcribe proinflammatory cytokines, type I interferon (IFN-α/β), and myriads interferon stimulated genes. However, it still remains elusive for the precise mechanisms of activation and execution of TBK1 in signaling platforms formed by innate adaptors mitochondrial antiviral signaling protein (MAVS), stimulator of interferon genes protein (STING), and TIR-domain-containing adapter-inducing interferon-β (TRIF), as well as its complex regulations. An atlas of TBK1 substrates is in constant expanding, setting TBK1 as a key node of signaling network and a dominant player in contexts of cell biology, animal models, and human diseases. Here, we review recent advancements of activation, regulations, and functions of TBK1 under these physiological and pathological contexts.

The E3 ubiquitin ligase MARCH1 regulates antimalaria immunity through interferon signaling and T cell activation

Malaria infection induces complex and diverse immune responses. To elucidate the mechanisms underlying host-parasite interaction, we performed a genetic screen during early (24 h) Plasmodium yoelii infection in mice and identified a large number of interacting host and parasite genes/loci after transspecies expression quantitative trait locus (Ts-eQTL) analysis. We next investigated a host E3 ubiquitin ligase gene (March1) that was clustered with interferon (IFN)-stimulated genes (ISGs) based on the similarity of the genome-wide pattern of logarithm of the odds (LOD) scores (GPLS). March1 inhibits MAVS/STING/TRIF-induced type I IFN (IFN-I) signaling in vitro and in vivo. However, in malaria-infected hosts, deficiency of March1 reduces IFN-I production by activating inhibitors such as SOCS1, USP18, and TRIM24 and by altering immune cell populations. March1 deficiency increases CD86⁺DC (dendritic cell) populations and levels of IFN-γ and interleukin 10 (IL-10) at day 4 post infection, leading to improved host survival. T cell depletion reduces IFN-γ level and reverse the protective effects of March1 deficiency, which can also be achieved by antibody neutralization of IFN-γ. This study reveals functions of MARCH1 (membrane-associated ring-CH-type finger 1) in innate immune responses and provides potential avenues for activating antimalaria immunity and enhancing vaccine efficacy.

Immunoregulatory properties of mesenchymal stem cells: Micro-RNAs

Mesenchymal stem cells (MSCs) are multipotent cells that are excellent candidates for different cellular therapies due to their physiological properties such as immunoregulatory function. whetheare currently utilized for regenerative medication and treatment of a number of inflammatory illnesses given their ability to considerably impact tissue microenvironments via extracellular vesicles or toll-like receptor pathway modulation. MicroRNAs (miRNAs) are small noncoding RNAs that target the messenger RNA and play a critical role in different biological procedures, such as the development and reaction of the immune system. Moreover, miRNAs have recently been revealed to have serious functions in MSCs to regulate immunomodulatory properties. In this review, we study how the miRNAs pathway can modulate the immunoregulatory activity of MSCs by counting their interactions with immune cells and also discuss the possibility of using miRNA-based implications for MSC-based therapies.

Deciphering the pathways to antiviral innate immunity and inflammation

The antiviral innate immune and inflammatory responses are critical for host defense against viral infection. How these antiviral responses are initiated and regulated has been intensively investigated. Viral nucleic acids are sensed by pattern-recognition receptors (PRRs), which trigger various signaling pathways by utilizing distinct adaptor proteins, kinases and regulatory proteins. These pathways lead to activation of the transcriptional factors NF-κB and IRF3 and ultimate induction of antiviral effector proteins including type I interferons (IFNs), TNF and IL-1β, which are critical mediators of antiviral innate immune and inflammatory responses. For the past 20 years, our groups at Peking University and Wuhan University have made restless efforts in deciphering the molecular mechanisms of antiviral innate immune and inflammatory responses. Here, we summarize the major discoveries from our groups, including the identifications of the critical adaptors VISA/MAVS and MITA/STING, regulatory mechanisms of these adapter-mediated signaling, and regulation of TNF- and IL1β-triggered inflammatory responses.

Interferon-Induced Protein 44 Interacts with Cellular FK506-Binding Protein 5, Negatively Regulates Host Antiviral Responses, and Supports Virus Replication

Using multiple viral systems, and performing silencing approaches, overexpression approaches, and experiments in knockout cells, we report, for the first time, that interferon (IFN)-induced protein 44 (IFI44) positively affects virus production and negatively modulates innate immune responses induced after viral infections. Moreover, IFI44 is able to rescue poly(I·C)- and IFN-mediated inhibition of virus growth. Furthermore, we report a novel interaction of IFI44 with the cellular factor FK506-binding protein 5 (FKBP5), which binds to cellular kinases such as the inhibitor of nuclear factor kappa B (IκB) kinases (IKKα, IKKβ, and IKKε). Importantly, in the presence of FKBP5, IFI44 decreases the ability of IKKβ to phosphorylate IκBα and the ability of IKKε to phosphorylate interferon regulatory factor 3 (IRF-3), providing a novel mechanism for the function of IFI44 in negatively modulating IFN responses. Remarkably, these new IFI44 functions may have implications for diseases associated with excessive immune signaling and for controlling virus infections mediated by IFN responses.IMPORTANCE Innate immune responses mediated by IFN and inflammatory cytokines are critical for controlling virus replication. Nevertheless, exacerbated innate immune responses could be detrimental for the host and feedback mechanisms are needed to maintain the cellular homeostasis. In this work, we describe a completely novel function for IFI44 in negatively modulating the innate immune responses induced after viral infections. We show that decreasing IFI44 expression by using small interfering RNAs (siRNAs) or by generating knockout (KO) cells impairs virus production and increases the levels of IFN responses. Moreover, we report a novel interaction of IFI44 with the cellular protein FKBP5, which in turn interacts with kinases essential for type I and III IFN induction and signaling, such as the inhibitor of nuclear factor kappa B (IκB) kinases IKKα, IKKβ, and IKKε. Our data indicate that binding of IFI44 to FKBP5 decreased the phosphorylation of IRF-3 and IκBα mediated by IKKε and IKKβ, respectively, providing a likely explanation for the function of IFI44 in negatively modulating IFN responses. These results provide new insights into the induction of innate immune responses and suggest that IFI44 is a new potential antiviral target for reducing virus replication.

Predicting and validating a model of suppressor of IKKepsilon through biophysical characterization

Suppressor of IKKepsilon (SIKE) is a 207 residue protein that is implicated in the TLR3-TANK-binding kinase-1-mediated response to viral infection. SIKE's function in this pathway is unknown, but SIKE forms interactions with two distinct cytoskeletal proteins, α-actinin and tubulin, and SIKE knockout reduces cell migration. As structure informs function and in the absence of solved structural homologs, our studies were directed toward creating a structural model of SIKE through biochemical and biophysical characterization to probe and interrogate SIKE function. Circular dichroism revealed a primarily (73%) helical structure of minimal stability ( =32°C) but reversibly denatured. Limited proteolysis (LP) and chemical modification identified the N-terminal 2/3 of the protein as dynamic and accessible, whereas size exclusion chromatography (SEC) confirmed three homo-oligomeric species. SEC coupled to chemical crosslinking characterized the primary species as dimeric, a secondary hexameric species, and a higher order aggregate/polymer. Fluorescence polarization using intrinsic tryptophan fluorescence contextualized the anisotropy value for the SIKE dimer (molecular weight 51.8 kDa) among proteins of known structure, bovine serum albumin (BSA; 66 kDa), and glutamate dehydrogenase (GDH; 332 kDa). Radii of gyration for BSA and GDH provided exclusionary values for SIKE tertiary and dimeric quaternary models that otherwise conformed to secondary structure, LP, and modification data. Dimeric quaternary models were further culled using acrylamide quenching data of SIKE's single tryptophan that showed a single, protected environment. The low cooperativity of folding and regions of dynamic and potentially disordered structure advance the hypothesis that SIKE forms a conformational ensemble of native states that accommodate SIKE's interactions with multiple, distinct protein-binding partners.

Suppression of CpG-ODN-mediated IFNα and TNFα response in human plasmacytoid dendritic cells (pDC) by cannabinoid receptor 2 (CB2)-specific agonists

Plasmacytoid dendritic cells (pDC) compose 0.2-0.5% of circulating leukocytes but play a significant role in mounting host immune responses. Elevated and chronic activation of pDC are implicated in autoimmune disease like systemic lupus erythematosus and rheumatoid arthritis. Δ⁹-tetrahydrocannabinol (THC) is a well characterized cannabinoid with potent anti-inflammatory activity, but acceptance of THC as a treatment for autoimmune disorders has been hindered due to psychotropic activity. The psychotropic effects of THC are mediated through cannabinoid receptor 1 (CB1) expressed in the central nervous system while the immunomodulatory effects of THC result from THC binding to CB1 and CB2 on immune cells. Synthetic CB2-selective agonists have been developed to explore immune modulation by cannabinoids in the absence of psychotropic effects. The goal of these studies was to determine if the CB2-selective agonists, JWH-015 and JWH-133, have comparable efficacy to THC in modulating IFNα and TNFα responses by primary human pDC. Treatment with JWH-133 and JWH-015 inhibited CpG-induced IFNα and TNFα responses by pDC. Further, the phosphorylation of IRF7, TBK1, NFκB, and IKKγ, key events in pDC activation, were suppressed by THC, JWH-133, and JWH-015. Likewise, the phosphorylation of AKT at the S473 and T308 residues were differentially modulated by treatment with THC and both JWH compounds. Collectively, these results demonstrate the potential for CB2 targeted therapeutics for treatment of inflammatory conditions involving aberrant pDC activity.

Architecture, substructures, and dynamic assembly of STRIPAK complexes in Hippo signaling

Striatin-interacting phosphatases and kinases (STRIPAKs) are evolutionarily conserved supramolecular complexes, which have been implicated in the Hippo signaling pathway. Yet the topological structure and dynamic assembly of STRIPAK complexes remain elusive. Here, we report the overall architecture and substructures of a Hippo kinase-containing STRIPAK complex. PP2Aa/c-bound STRN3 directly contacts the Hippo kinase MST2 and also controls the loading of MST2 via two “arms” in a phosphorylation-dependent manner, one arm being STRIP1 and the other SIKE1-SLMAP. A decreased cell density triggered the dissociation of the STRIP1 arm from STRIPAK, reflecting the dynamic assembly of the complex upon sensing upstream signals. Crystallographic studies defined at atomic resolution the interface between STRN3 and SIKE1, and that between SIKE1 and SLMAP. Disrupting the complex assembly abrogated the regulatory effect of STRIPAK towards Hippo signaling. Collectively, our study revealed a “two-arm” assembly of STRIPAK with context-dependent dynamics, offering a framework for further studies on Hippo signaling and biological processes involving MST kinases.

SIKE of black carp is a substrate of TBK1 and suppresses TBK1-mediated antiviral signaling

RIG-I like receptor (RLR) signaling functions importantly in host innate immune response against RNA virus, which is tightly regulated by a number of mechanisms to prevent aberrant interferon production. The suppressor of IKKε (SIKE) has been identified as a suppressor of IKKε and TBK1, which are key components of RLR signaling. In this study, SIKE homologue (bcSIKE) of black carp (Mylopharyngodon piceus) has been cloned and characterized. The transcription of bcSIKE varied in host cells in response to the stimulation of LPS, poly (I:C) and viruses. bcSIKE migrated around 27 KDa in immunoblot assay and distributed in both cytoplasm and nucleus of host cell in immunofluorescent (IF) staining test. bcSIKE showed no IFN-inducing ability in reporter assay and EPC cells expressing bcSIKE showed no enhanced antiviral ability against either grass carp reovirus (GCRV) or spring viremia of carp virus (SVCV). However, bcSIKE obviously dampened the IFN-inducing ability of RLR signaling members in reporter assay when bcSIKE was co-expressed with these molecules in EPC cells. The association between bcSIKE and bcTBK1 has been identified through IF and co-immunoprecipitation (co-IP) assay. The plaque assay demonstrated clearly that bcTBK1-mediated antiviral activity in EPC cells against both GCRV and SVCV was down regulated by bcSIKE. All the data generated in this paper support the conclusion that bcSIKE interacts with bcTBK1 and inhibits bcTBK1-mediated antiviral signaling during host innate immune activation, which is reported in teleost for the first time.

Zebrafish NDRG1a Negatively Regulates IFN Induction by Promoting the Degradation of IRF7

Viral infection activates the transcription factor IFN regulatory factor 7 (IRF7), which plays a critical role in the induction of IFNs and innate antiviral immune response. How virus-induced IFN signaling is controlled in fish is not fully understood. In this study, we demonstrate that N-myc downstream-regulated gene 1a (NDRG1a) in zebrafish plays a role as a negative regulator for virus-triggered IFN induction. First, the activation of the IFN promoter stimulated by the polyinosinic-polycytidylic acid or spring viremia of carp virus was decreased by the overexpression of NDRG1a. Second, NDRG1a interacted with IRF7 and blocked the IFN transcription activated by IRF7. Furthermore, NDRG1a was phosphorylated by TANK-binding kinase 1 (TBK1) and promoted the K48-linked ubiquitination and degradation of IRF7. Finally, the overexpression of NDRG1a blunted the transcription of several IFN-stimulated genes, resulting in the host cells becoming susceptible to spring viremia of carp virus infection. Our findings suggest that fish NDRG1a negatively regulates the cellular antiviral response by targeting IRF7 for ubiquitination and degradation, providing insights into the novel role of NDRG1a on the innate antiviral immune response in fish.

A novel STRIPAK complex component mediates hyphal fusion and fruiting-body development in filamentous fungi

The STRIPAK complex is involved in growth, cell fusion, development and signaling pathways, and thus malfunctions in the human STRIPAK complex often result in severe neuronal diseases and cancer. Despite the high degree of general conservation throughout the complex, several STRIPAK complex-associated small coiled-coil proteins of animals and yeasts are not conserved across species. As there are no data for filamentous ascomycetes, we addressed this through affinity purification with HA-tagged striatin ortholog PRO11 in Sordaria macrospora. Combining the method with liquid chromatography-mass spectrometry, we were able to co-purify STRIPAK complex interactor 1 (SCI1), the first STRIPAK-associated small coiled-coil protein in filamentous ascomycetes. Using yeast two-hybrid experiments, we identified SCI1 protein regions required for SCI1-PRO11 interaction, dimerization of SCI1 and interaction with other STRIPAK components. Further, both proteins PRO11 and SCI1 co-localize with the nuclear basket protein SmPOM152 at the nuclear envelope. Expression of the gene sci1 occurs during early developmental stages of S. macrospora, and the protein SCI1 in combination with PRO11 is required for cell fusion, vegetative growth and sexual development. The results of the present study will help to understand the underlying molecular mechanisms of STRIPAK signaling and function in cellular development and diseases in higher eukaryotes.

Concise Review: TLR Pathway-miRNA Interplay in Mesenchymal Stromal Cells: Regulatory Roles and Therapeutic Directions

Mesenchymal stromal cells (MSCs) deploy Toll-like receptors (TLRs) to respond to exogenous and endogenous signals. Activation of TLR pathways in MSCs alters their inflammatory profile and immunomodulatory effects on cells from both the innate and adaptive immune systems. Micro-RNAs (miRNAs), whose expression is modulated by TLR activation, can regulate inflammatory responses by targeting components of the TLR signaling pathways either in MSCs or in the cells with which they interact. Here, we review how the miRNA-TLR pathway axis can regulate the immunomodulatory functions of MSCs, including their interactions with monocytes/macrophages and natural killer cells, and discuss the therapeutic implications for MSC-based therapies. Stem Cells 2018;36:1655-1662.

Suppressor of IKKepsilon forms direct interactions with cytoskeletal proteins, tubulin and α-actinin, linking innate immunity to the cytoskeleton

Suppressor of IKKepsilon (SIKE) is associated with the type I interferon response of the innate immune system through TANK-binding kinase 1 (TBK1). Originally characterized as an endogenous inhibitor of TBK1 when overexpressed in viral infection and pathological cardiac hypertrophic models, a mechanistic study revealed that SIKE acts as a high-affinity substrate of TBK1, but its function remains unknown. In this work, we report that scratch assay analysis of parental and SIKE CRISPR/Cas9 knockout HAP1 cells showed an ~ 20% decrease in cell migration. Investigation of the SIKE interaction network through affinity purification/mass spectrometry showed that SIKE formed interactions with cytoskeletal proteins. In immunofluorescence assays, endogenous SIKE localized to cytosolic puncta in both epithelial and myeloid cells and to nuclear puncta in myeloid cells, while in epithelial cells additional staining occurred in stress fiber-like structures and adjacent to the plasma membrane. Using cellular markers, co-occurrence of SIKE fluorescence with actin, α-actinin, and ezrin was detected. Reciprocal immunoprecipitation revealed a SIKE:tubulin interaction sensitive to the phosphorylation state of SIKE, but a SIKE:α-actinin interaction was unchanged by SIKE phosphorylation. In vitro precipitation assays confirmed a direct SIKE interaction with tubulin and α-actinin. These results indicate that SIKE may promote cell migration by directly associating with the cytoskeleton. In this role, SIKE may mediate cytoskeletal rearrangement necessary in innate immunity, but also link a key catalytic hub, TBK1, to the cytoskeleton.

DATABASE

The mass spectrometry proteomics data have been deposited to the ProteomeXchange Consortium via the PRIDE [1] partner repository with the dataset identifier PXD007262.

Harnessing RIG-I and intrinsic immunity in the tumor microenvironment for therapeutic cancer treatment

Cancer immunotherapies that remove checkpoint restraints on adaptive immunity are gaining clinical momentum. Approaches aimed at intrinsic cellular immunity in the tumor microenvironment are less understood, but are of intense interest, based on their ability to induce tumor cell apoptosis while orchestrating innate and adaptive immune responses against tumor antigens. The intrinsic immune response is initiated by ancient, highly conserved intracellular proteins that detect viral infection. For example, the RIG-I-like receptors (RLRs), a family of related RNA helicases, detect viral oligonucleotide patterns of certain RNA viruses. RLR activation induces immunogenic cell death of virally infected cells, accompanied by increased inflammatory cytokine production, antigen presentation, and antigen-directed immunity against virus antigens. Approaches aimed at non-infectious RIG-I activation in cancers are being tested as a treatment option, with the goal of inducing immunogenic tumor cell death, stimulating production of pro-inflammatory cytokines, enhancing tumor neoantigen presentation, and potently increasing cytotoxic activity of tumor infiltrating lymphocytes. These studies are finding success in several pre-clinical models, and are entering early phases of clinical trial. Here, we review pre-clinical studies of RLR agonists, including the successes and challenges currently faced RLR agonists on the path to clinical translation.

Induction of INKIT by Viral Infection Negatively Regulates Antiviral Responses through Inhibiting Phosphorylation of p65 and IRF3

The transcription factors p65 and IRF3 play key roles in the induction of cellular antiviral responses. Phosphorylation of p65 and IRF3 is required for their activity and constitutes a key checkpoint. Here we report that viral infection induced upregulation of INKIT, an inhibitor for NF-κB and IRF3 that restricted innate antiviral responses by blocking phosphorylation of p65 and IRF3. INKIT overexpression inhibited virus-induced phosphorylation of p65 and IRF3 and expression of downstream genes. In contrast, knockdown or knockout of INKIT had the opposite effect: Inkit^-/- mice produced elevated levels of type I interferons and proinflammatory cytokines and were more resistant to lethal viral infection compared to wild-type. INKIT interacted with IKKα/β and TBK1/IKKɛ, impairing the recruitment and phosphorylation of p65 and IRF3. Viral infection induced IKK-mediated phosphorylation of INKIT at Ser58, resulting in its dissociation from the IKKs. Our findings thus uncover INKIT as a regulator of innate antiviral responses.

WITHDRAWN: SIKE1 deficiency accelerates hepatic ischemia/reperfusion (IR) injury through enhancing Toll-like receptor-3-regulated inflammation

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MST kinases in innate immune signaling

The mammalian STE20-like (MST) protein kinases are composed of MST1, MST2, MST3, MST4 and YSK1. They play crucial roles in cell growth, migration, polarity and apoptosis. Dysfunction of these kinases often leads to diseases. MST kinases are extensively involved in development and function of immune system. Here, we review recent progresses on the regulatory function of MST kinases in innate immune signaling.

TBK1 of black carp plays an important role in host innate immune response against SVCV and GCRV

Tank-binding kinase 1 (TBK1) plays a pivotal role in the induction of type I IFNs in higher vertebrates. To explore the function of TBK1 in teleost, TBK1 of black carp (Mylopharyngodon Piceus) was cloned and characterized in this paper. The full-length cDNA of black carp TBK1 (bcTBK1) consists of 2857 nucleotides and the predicted bcTBK1 protein contains 727 amino acids, which includes an N-terminal kinase domain (KD), an ubiquitin-like domain (ULD) and two C-terminal coiled-coils. The transcription of bcTBK1 was constitutively detected in all the selected tissues and bcTBK1 mRNA level was increased in all selected tissues in response to SVCV or GCRV infection except that in muscle post GCRV invasion. The transcription of bcTBK1 in Mylopharyngodon Piceus fin (MPF) cells was up-regulated by the stimulation of SVCV, GCRV or poly (I:C) but not by LPS treatment. bcTBK1 migrated around 80 kDa in immunoblot assay and was identified as a cytosolic protein by immunofluorescence staining. bcTBK1 showed strong IFN-inducing ability in reporter assay and presented strong antiviral activity against both GCRV and SVCV in EPC cells. The reporter assay demonstrated that TRAF6 of black carp (bcTRAF6) up-regulated bcTBK1-induced IFN expression and the subcellular distribution of bcTBK1 overlapped with that of bcTRAF6 when these two proteins were co-expressed in EPC cells. Taken together, our study support the conclusion that bcTBK1 plays an important role in the antiviral innate immune response of black carp against SVCV and GCRV, in which its activity was positively regulated by bcTRAF6.

Overexpression of suppressor of IKBKE 1 is associated with vincristine resistance in colon cancer cells

In a previous study, the suppressor of IKBKE 1 expression level was confirmed to be higher in vincristine (VCR)-resistant HCT-8 (HCT-8/V) colon cancer cells than in non-VCR-resistant HCT-8 cells. In the current study, IKBKE 1 expression in VCR-resistant colon cancer cells was investigated further. HCT-8 and HCT-8/V human colon cancer cells were used, and polymerase chain reaction (PCR) primers were designed to amplify the IKBKE 1 gene. Fluorescence reverse transcription-quantitative PCR (RT-qPCR) was performed to detect differences in IKBKE 1 expression between sensitive and drug-resistant colon cancer cell lines. Western blotting was performed to further observe IKBKE 1 expression. Based on the RT-qPCR and western blot results, IKBKE 1 expression was observed to be markedly higher in the HCT-8/V cells, and this difference was significant (P<0.05). Thus, IKBKE 1 expression was identified to be associated with the resistance of colon cancer cells to VCR.

MSX1 Modulates RLR-Mediated Innate Antiviral Signaling by Facilitating Assembly of TBK1-Associated Complexes

Recognition of viral dsRNA by the retinoic acid-inducible gene-1-like receptors (RLRs) triggers signaling cascades that lead to activation of the TBK1 kinase and transcription factor IFN regulatory factor 3, induction of downstream antiviral genes, and innate antiviral responses. In this study, we identified muscle segment homeobox1 (MSX1) as an important modulator of RLR-mediated signaling pathways. Knockdown or knockout of MSX1 significantly impaired Sendai virus-triggered activation of TBK1 and IFN regulatory factor 3, induction of downstream antiviral genes, and cellular antiviral responses. Interestingly, MSX1 was translocated from the nucleus to cytoplasm, particularly mitochondria upon infection of Sendai virus. Biochemcially, MSX1 was important for assembly of TBK1/IKK-related kinase-associated protein 1/TNFR-associated factor-associated NF-κB activator complexes. Our results suggest that MSX1 is an important component of RLR-mediated signaling and reveal mechanisms on innate immune responses against RNA viruses.

Suppressor of IKKɛ is an essential negative regulator of pathological cardiac hypertrophy

Although pathological cardiac hypertrophy represents a leading cause of morbidity and mortality worldwide, our understanding of the molecular mechanisms underlying this disease is still poor. Here, we demonstrate that suppressor of IKKɛ (SIKE), a negative regulator of the interferon pathway, attenuates pathological cardiac hypertrophy in rodents and non-human primates in a TANK-binding kinase 1 (TBK1)/AKT-dependent manner. Sike-deficient mice develop cardiac hypertrophy and heart failure, whereas Sike-overexpressing transgenic (Sike-TG) mice are protected from hypertrophic stimuli. Mechanistically, SIKE directly interacts with TBK1 to inhibit the TBK1-AKT signalling pathway, thereby achieving its anti-hypertrophic action. The suppression of cardiac remodelling by SIKE is further validated in rats and monkeys. Collectively, these findings identify SIKE as a negative regulator of cardiac remodelling in multiple animal species due to its inhibitory regulation of the TBK1/AKT axis, suggesting that SIKE may represent a therapeutic target for the treatment of cardiac hypertrophy and heart failure.

Identifying pathways that cause pathological cardiac hypertrophy holds great therapeutic potential. Here the authors discover one such pathway and show that SIKE, an inhibitor of interferon signalling, prevents pathological but not physiological cardiac hypertrophy by interacting with TBK1 and modulating the TBK1/AKT signalling in rodents and monkeys.

Specific IgA Enhances the Transcytosis and Excretion of Hepatitis A Virus

Hepatitis A virus (HAV) replicates in the liver, and is excreted from the body in feces. However, the mechanisms of HAV transport from hepatocytes to the gastrointestinal tract are poorly understood, mainly due to lack of suitable in vitro models. Here, we use a polarized hepatic cell line and in vivo models to demonstrate vectorial transport of HAV from hepatocytes into bile via the apical cell membrane. Although this transport is specific for HAV, the rate of fecal excretion in inefficient, accounting for less than 1% of input virus from the bloodstream per hour. However, we also found that the rate of HAV excretion was enhanced in the presence of HAV-specific IgA. Using mice lacking the polymeric IgA receptor (pIgR^−/−), we show that a proportion of HAV:IgA complexes are transported via the pIgR demonstrating a role for specific antibody in pathogen excretion.

Foot-and-mouth disease virus non-structural protein 3A inhibits the interferon-β signaling pathway

Foot-and-mouth disease virus (FMDV) is the etiological agent of FMD, which affects cloven-hoofed animals. The pathophysiology of FMDV has not been fully understood and the evasion of host innate immune system is still unclear. Here, the FMDV non-structural protein 3A was identified as a negative regulator of virus-triggered IFN-β signaling pathway. Overexpression of the FMDV 3A inhibited Sendai virus-triggered activation of IRF3 and the expressions of RIG-I/MDA5. Transient transfection and co-immunoprecipitation experiments suggested that FMDV 3A interacts with RIG-I, MDA5 and VISA, which is dependent on the N-terminal 51 amino acids of 3A. Furthermore, 3A also inhibited the expressions of RIG-I, MDA5, and VISA by disrupting their mRNA levels. These results demonstrated that 3A inhibits the RLR-mediated IFN-β induction and uncovered a novel mechanism by which the FMDV 3A protein evades the host innate immune system.

STRIPAK complexes in cell signaling and cancer

Striatin-interacting phosphatase and kinase (STRIPAK) complexes are striatin-centered multicomponent supramolecular structures containing both kinases and phosphatases. STRIPAK complexes are evolutionarily conserved and have critical roles in protein (de)phosphorylation. Recent studies indicate that STRIPAK complexes are emerging mediators and regulators of multiple vital signaling pathways including Hippo, MAPK (mitogen-activated protein kinase), nuclear receptor and cytoskeleton remodeling. Different types of STRIPAK complexes are extensively involved in a variety of fundamental biological processes ranging from cell growth, differentiation, proliferation and apoptosis to metabolism, immune regulation and tumorigenesis. Growing evidence correlates dysregulation of STRIPAK complexes with human diseases including cancer. In this review, we summarize the current understanding of the assembly and functions of STRIPAK complexes, with a special focus on cell signaling and cancer.

The VP3 structural protein of foot-and-mouth disease virus inhibits the IFN-β signaling pathway

Foot-and-mouth disease is a frequently occurring disease of cloven-hoofed animals that is caused by infection with the foot-and-mouth virus (FMDV). FMDV circumvents the type-I IFN response by expressing proteins that antagonize cellular innate immunity, such as leader protease and 3C protease. We identified the FMDV structural protein VP3 as a negative regulator of the virus-triggered IFN-β signaling pathway. Expression of FMDV VP3 inhibited the Sendai virus-triggered activation of IFN regulatory factor-3 and the expression of retinoic acid-inducible gene-I/melanoma differentiation-associated protein-5. Transient transfection and coimmunoprecipitation confirmed that the structural protein VP3 interacts with virus-induced signaling adapter (VISA), which is dependent on the C-terminal aa 111-220 of VP3. In addition, we found that FMDV VP3 inhibits the expression of VISA by disrupting its mRNA. Taken together, our findings reveal a novel strategy used by the structural VP3 protein of FMDV to evade host innate immunity.-Li, D., Yang, W., Yang, F., Liu, H., Zhu, Z., Lian, K., Lei, C., Li, S., Liu, X., Zheng, H., Shu, H. The VP3 structural protein of foot-and-mouth disease virus inhibits the IFN-β signaling pathway.

The interferon regulatory factors as novel potential targets in the treatment of cardiovascular diseases

The family of interferon regulatory factors (IRFs) consists of nine members (IRF1-IRF9) in mammals. They act as transcription factors for the interferons and thus exert essential regulatory functions in the immune system and in oncogenesis. Recent clinical and experimental studies have identified critically important roles of the IRFs in cardiovascular diseases, arising from their participation in divergent and overlapping molecular programmes beyond the immune response. Here we review the current knowledge of the regulatory effects and mechanisms of IRFs on the immune system. The role of IRFs and their potential molecular mechanisms as novel stress sensors and mediators of cardiovascular diseases are highlighted.

DYRK2 Negatively Regulates Type I Interferon Induction by Promoting TBK1 Degradation via Ser527 Phosphorylation

Viral infection activates the transcription factors NF-κB and IRF3, which contribute to the induction of type I interferons (IFNs) and cellular antiviral responses. Protein kinases play a critical role in various signaling pathways by phosphorylating their substrates. Here, we identified dual-specificity tyrosine-(Y)-phosphorylation-regulated kinase 2 (DYRK2) as a negative regulator of virus-triggered type I IFN induction. DYRK2 inhibited the virus-triggered induction of type I IFNs and promoted the K48-linked ubiquitination and degradation of TANK-binding kinase 1 (TBK1) in a kinase-activity-dependent manner. We further found that DYRK2 phosphorylated Ser527 of TBK1, which is essential for the recruitment of NLRP4 and for the E3 ubiquitin ligase DTX4 to degrade TBK1. These findings suggest that DYRK2 negatively regulates virus-triggered signaling by targeting TBK1 for phosphorylation and priming it for degradation, and these data provide new insights into the molecular mechanisms that dictate the cellular antiviral response.