DOK3 is required for IFN-β production by enabling TRAF3/TBK1 complex formation and IRF3 activation

DOK3 promotes proliferation and inhibits apoptosis of prostate cancer via the NF-κB signaling pathway

BACKGROUND

DOK3 (Downstream of kinase 3) is involved primarily with immune cell infiltration. Recent research reported the role of DOK3 in tumor progression, with opposite effects in lung cancer and gliomas; however, its role in prostate cancer (PCa) remains elusive. This study aimed to explore the role of DOK3 in PCa and to determine the mechanisms involved.

METHODS

To investigate the functions and mechanisms of DOK3 in PCa, we performed bioinformatic and biofunctional analyses. Samples from patients with PCa were collected from West China Hospital, and 46 were selected for the final correlation analysis. A lentivirus-based short hairpin ribonucleic acid (shRNA) carrier was established for silencing DOK3. A series of experiments involving the cell counting kit-8, bromodeoxyuridine, and flow cytometry assays were performed to identify cell proliferation and apoptosis. Changes in biomarkers from the nuclear factor kappa B (NF-κB) signaling pathway were detected to verify the relationship between DOK3 and the NF-κB pathway. A subcutaneous xenograft mouse model was performed to examine phenotypes after knocking down DOK3 in vivo . Rescue experiments with DOK3 knockdown and NF-κB pathway activation were designed to verify regulating effects.

RESULTS

DOK3 was up-regulated in PCa cell lines and tissues. In addition, a high level of DOK3 was predictive of higher pathological stages and worse prognoses. Similar results were observed with PCa patient samples. After silencing DOK3 in PCa cell lines 22RV1 and PC3, cell proliferation was significantly inhibited while apoptosis was promoted. Gene set enrichment analysis revealed that DOK3 function was enriched in the NF-κB pathway. Mechanism experiments determined that knockdown of DOK3 suppressed activation of the NF-κB pathway, increased the expressions of B-cell lymphoma-2 like 11 (BIM) and B-cell lymphoma-2 associated X (BAX), and decreased the expression of phosphorylated-P65 and X-linked inhibitor of apoptosis (XIAP). In the rescue experiments, pharmacological activation of NF-κB by tumor necrosis factor-α (TNF-α) partially recovered cell proliferation after the knockdown of DOK3.

CONCLUSION

Our findings suggest that overexpression of DOK3 promotes PCa progression by activating the NF-κB signaling pathway.

Molecular Characterization, Expression, and Regulatory Signal Pathway Analysis of Inflammasome Component Apoptosis-Associated Speck-like Protein Containing a CARD Domain (ASC) in Large Yellow Croaker (Larimichthys crocea)

ASC (apoptosis-associated speck-like protein containing a caspase recruitment domain (CARD)) is the only adaptor involved in the formation of multiple types of inflammasomes. Accumulating evidence demonstrates that ASC plays a critical role in the protection of the host against pathogen infection. In this study, we identified an ASC gene in the large yellow croaker (Larimichthys crocea), namely LcASC, and then investigated the expression characteristics and related signal pathways. On one hand, LcASC has several conserved protein modules, i.e., an N-terminal PYD region, a C-terminal CARD region, and twelve α-helix structures. On the other hand, it has a high variable linker between PYD and CARD domains. Moreover, LcASC has varying degrees of expression in different tissues, among which the highest expression is observed in the spleen followed by the gills and skin. It also shows induced expressions in the head kidney, liver, and spleen following immune stimulation, especially Vibrio Parahaemolyticus infection. Further subcellular localization analysis showed that LcASC formed a clear aggregated speck in the cytoplasm close to the nucleus. In addition, we found 46 DEGs in a comparative transcriptome analysis between the LcASC overexpression group and the control vector group. Notedly, the up-regulated gene Fos and down-regulated gene DOK3 in LcASC overexpressed cells play important roles in the immune system. How ASC contacts these two genes needs to be clarified in upcoming studies. These findings collectively provide new insights into finfish ASC and its potential regulatory signaling pathway as well.

TBK1 and IRF3 are potential therapeutic targets in Enterovirus A71-associated diseases

BACKGROUND

Enterovirus A71 (EV-A71) is an important causative agent of hand-foot-and-mouth disease (HFMD) associated with enormous healthcare and socioeconomic burden. Although a range of studies about EV-A71 pathogenesis have been well described, the underlying molecular mechanism in terms of innate immune response is still not fully understood, especially the roles of TANK-binding kinase 1 (TBK1) and interferon-regulatory factor 3 (IRF3).

METHODOLOGY/PRINCIPAL FINDINGS

Here, we applied TBK1 inhibitor and IRF3 agonist, for the first time, to evaluate the antiviral activities of TBK1 and IRF3 in vivo. We found that, through regulating EV-A71-induced type I interferon (IFN) response, IRF3 agonist effectively alleviated EV-A71-induced illness, while TBK1 inhibitor aggravated disease progression. In addition, EV-A71 replication was suppressed in EVA-71-infected mice administrated with IRF3 agonist. On the other hand, more severe pathological alterations of neuronal degeneration, muscle fiber breaks, fractured or fused alveolar walls, and diffuse congestion occurred in EVA-71-infected mice treated with TBK1 inhibitor administration. Furthermore, we determined the concentrations of interleukin (IL)-6, tumor necrosis factor-alpha (TNF-α), IL-1β, monocyte chemotactic protein-1 (MCP-1), and IL-10 in both lungs and brains of mice and found that TBK1 inhibitor promoted EV-A71-induced inflammatory response, while IRF3 agonist alleviated it, which was consistent with clinical manifestations and pathological alterations.

CONCLUSIONS

Collectively, our findings suggest that TBK1 and IRF3 are potential therapeutic targets in EV-A71-induced illness.

3',4'-Dihydroxyflavone mitigates inflammatory responses by inhibiting LPS and TLR4/MD2 interaction

BACKGROUND

We previously reported the potential inhibitory activity of 3',4'-dihydroxyflavone (DHF) on nitric oxide (NO) and prostaglandin E₂ (PGE₂) production in lipopolysaccharide (LPS)-stimulated macrophages.

PURPOSE

We investigated the underlying molecular mechanisms of DHF in LPS-activated macrophages and evaluated its effect on LPS-induced septic shock in mice.

METHODS

To explore the anti-inflammatory effect of DHF, nitrite, PGE₂, and cytokines were measured in vitro and in vivo experiments. In addition, to verify the molecular signaling pathway, quantitative real time-PCR, luciferase assay, nuclear extraction, electrophoretic mobility shift assay, immunocytochemistry, immunoprecipitation, molecular docking analysis, and myeloid differentiation 2 (MD2)-LPS binding assay were conducted.

RESULTS

DHF suppressed the LPS-induced expression of proinflammatory mediators through nuclear factor-κB (NF-κB), activator protein-1 (AP-1), and interferon regulatory factor 3 (IRF3) inactivation pathways in RAW 264.7 macrophages. Importantly, molecular docking analysis and in vitro binding assays showed that DHF interacts with the hydrophobic pocket of MD2 and then interferes with the interaction between LPS and toll-like receptor 4 (TLR4). DHF inhibited LPS-induced oxidative stress by upregulating nuclear factor erythroid 2-related factor 2 (Nrf2). Treatment of LPS-induced endotoxemia mice with DHF reduced the expression levels of pro-inflammatory mediators via the inactivation of NF-κB, AP-1, and signal transducer and activator of transcription 1 (STAT1) in the lung tissue, thus increasing the survival rate.

CONCLUSION

Taken together, our data first time revealed the underlying mechanism of the DHF-dependent anti-inflammatory effect by preventing LPS from binding to the TLR4/MD2 complex. Therefore, DHF may be a possible anti-inflammatory agent for the treatment of LPS-mediated inflammatory diseases.

Bruton’s Tyrosine Kinase phosphorylates scaffolding and RNA-binding protein G3BP1 to induce stress granule aggregation during host sensing of foreign ribonucleic acids

The Ras-GTPase activating protein SH3 domain-binding protein 1 (G3BP1) plays a critical role in the formation of classical and antiviral stress granules in stressed and virus-infected eukaryotic cells, respectively. While G3BP1 is known to be phosphorylated at serine residues which could affect stress granule assembly, whether G3BP1 is phosphorylated at tyrosine residues and how this posttranslational modification might affect its functions is less clear. Here, we show using immunoprecipitation and immunoblotting studies with 4G10 antibody that G3BP1 is tyrosine-phosphorylated when cells are stimulated with the synthetic double-stranded RNA analog polyinosinic:polycytidylic acid to mimic viral infection. We further demonstrate via co-immunoprecipitation and inhibitor studies that Bruton’s tyrosine kinase (BTK) binds and phosphorylates G3BP1. The nuclear transport factor 2–like domain of G3BP1 was previously shown to be critical for its self-association to form stress granules. Our mass spectrometry, mutational and biochemical cross-linking analyses indicate that the tyrosine-40 residue in this domain is phosphorylated by BTK and critical for G3BP1 oligomerization. Furthermore, as visualized via confocal microscopy, pretreatment of cells with the BTK inhibitor LFM-A13 or genetic deletion of the btk gene or mutation of G3BP1-Y40 residue to alanine or phenylalanine all significantly attenuated the formation of antiviral stress granule aggregates upon polyinosinic:polycytidylic acid treatment. Taken together, our data indicate that BTK phosphorylation of G3BP1 induces G3BP1 oligomerization and facilitates the condensation of ribonucleoprotein complexes into macromolecular aggregates.

Grass Carp Reovirus Nonstructural Proteins Avoid Host Antiviral Immune Response by Targeting the RLR Signaling Pathway

Grass carp reovirus (GCRV) is a highly virulent RNA virus that mainly infects grass carp and causes hemorrhagic disease. The roles of nonstructural proteins NS38 and NS80 of GCRV-873 in the viral replication cycle and viral inclusion bodies have been established. However, the strategies that NS38 and NS80 used to avoid host antiviral immune response are still unknown. In this study, we report the negative regulations of NS38 and NS80 on the RIG-I-like receptors (RLRs) antiviral signaling pathway and the production of IFNs and IFN-stimulated genes. First, both in the case of overexpression and GCRV infection, NS38 and NS80 inhibited the IFN promoter activation induced by RIG-I, MDA5, MAVS, TBK1, IRF3, and IRF7 and mRNA abundance of key antiviral genes involved in the RLR-mediated signaling. Second, both in the case of overexpression and GCRV infection, NS38 interacted with piscine TBK1 and IRF3, but not with piscine RIG-I, MDA5, MAVS, and TNF receptor-associated factor (TRAF) 3. Whereas NS80 interacted with piscine MAVS, TRAF3, and TBK1, but not with piscine RIG-I, MDA5, and IRF3. Finally, both in the case of overexpression and GCRV infection, NS38 inhibited the formation of the TBK1-IRF3 complex, but NS80 inhibited the formation of the TBK1-TRAF3 complex. Most importantly, NS38 and NS80 could hijack piscine TBK1 and IRF3 into the cytoplasmic viral inclusion bodies and inhibit the translocation of IRF3 into the nucleus. Collectively, all of these data demonstrate that GCRV nonstructural proteins can avoid host antiviral immune response by targeting the RLR signaling pathway, which prevents IFN-stimulated gene production and facilitates GCRV replication.

Regulation of antiviral innate immune signaling and viral evasion following viral genome sensing

A harmonized balance between positive and negative regulation of pattern recognition receptor (PRR)-initiated immune responses is required to achieve the most favorable outcome for the host. This balance is crucial because it must not only ensure activation of the first line of defense against viral infection but also prevent inappropriate immune activation, which results in autoimmune diseases. Recent studies have shown how signal transduction pathways initiated by PRRs are positively and negatively regulated by diverse modulators to maintain host immune homeostasis. However, viruses have developed strategies to subvert the host antiviral response and establish infection. Viruses have evolved numerous genes encoding immunomodulatory proteins that antagonize the host immune system. This review focuses on the current state of knowledge regarding key host factors that regulate innate immune signaling molecules upon viral infection and discusses evidence showing how specific viral proteins counteract antiviral responses via immunomodulatory strategies.

Dok3 is involved in cisplatin-induced acute kidney injury via regulation of inflammation and apoptosis

Cisplatin-induced acute kidney injury (AKI) is associated with high morbidity and mortality worldwide, but the underlying mechanisms are not fully understood. Downstream-of-kinase 3 (Dok3), a member of the Dok family of adaptor proteins plays a critical role in inflammatory response and immune regulation; however, the role of Dok3 in cisplatin-induced AKI remains unclear. This study explored the effect and potential molecular mechanisms of Dok3 in cisplatin-induced AKI using Dok3 knockout (Dok3-/-) and control mice (129S) with or without administration of a single intraperitoneal injection of cisplatin. Apoptosis was assessed by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, lactate dehydrogenase (LDH) release, and Hoechst staining. Inflammatory factors were measured using ELISA kits. Protein and gene expression levels were measured by western blot analysis and real-time PCR, respectively. The results showed that Dok3 was expressed in renal tubular epithelial cells. Dok3 expression was decreased in kidneys of mice treated with cisplatin and cisplatin-treated HK2 cells. Dok3-/- mice showed lower creatinine levels and NGAL expression, and increased survival rates compared to 129S mice. Cisplatin-induced production of TNF-α and IL-6, and renal tubular cell apoptosis was attenuated in Dok3-/- mice. In vitro experiments demonstrated that HK2 cells overexpressing Dok3 exhibited exacerbated cisplatin-induced apoptosis and production of TNF-α and IL-6. These findings demonstrate that Dok3 regulates cisplatin-induced AKI by regulating apoptosis and inflammation.

DOK3 is involved in microglial cell activation in neuropathic pain by interacting with GPR84

Adaptor molecule downstream of kinase-3 (DOK3) is a vital regulator of innate immune responses in macrophages and B cells, and G-protein-coupled receptor 84 (GPR84) is significant in mediating the biosynthesis and maintenance of inflammatory mediators that are induced by neuropathic pain in microglia. In the present study, we determined the role of DOK3 in activating microglia-induced neuropathic pain and investigated the underlying mechanisms associated with GPR84. We found that knockdown of DOK3 in microglial cells dramatically reduced the levels of inflammatory factors, and we uncovered a physical association between DOK3 and GPR84 in the induction of inflammatory responses. We also observed that neuropathic pain and inflammatory responses induced by chronic constriction injury (CCI) of the sciatic nerve or intrathecal injection of a GPR84 agonist were compromised in DOK3^-/- mice in vivo. Finally, enforced expression of DOK3 provoked inflammatory responses, and administration of pregabalin relieved neuropathic pain via inhibition of DOK3 expression. In conclusion, DOK3 induced neuropathic pain in mice by interacting with GPR84 in microglia. We hypothesize that targeting the adaptor protein DOK3 may open new avenues for pharmaceutical approaches to the alleviation of neuropathic pain in the spinal cord.

Emerging Roles of Downstream of Kinase 3 in Cell Signaling

Downstream of kinase (Dok) 3 is a member of the Dok family of adaptor proteins known to regulate signaling pathways downstream of various immunoreceptors. As Dok-3 lacks intrinsic catalytic activity, it functions primarily as a molecular scaffold to facilitate the nucleation of protein complexes in a regulated manner and hence, achieve specificity in directing signaling cascades. Since its discovery, considerable progress has been made toward defining the role of Dok-3 in limiting B cell-receptor signaling. Nonetheless, Dok-3 has since been implicated in the signaling of Toll-like and C-type lectin receptors. Emerging data further demonstrate that Dok-3 can act both as an activator and inhibitor, in lymphoid and non-lymphoid cell types, suggesting Dok-3 involvement in a plethora of signal transduction pathways. In this review, we will focus on the structure and expression profile of Dok-3 and highlight its role during signal transduction in B cells, innate cells as well as in bone and lung tissues.

Toll-like Receptors as a Novel Therapeutic Target for Natural Products Against Chronic Diseases

Toll-like receptors (TLR) are one among the initial responders of the immune system which participate in the activation inflammatory processes. Several different types of TLR such as TLR2, TLR4, TLR7 and TLR9 have been identified in various cell types, each having distinct ligands like lipids, lipoproteins, nucleic acids and proteins. Though its prime concern is xenobiotic defences, TLR signalling has also recognized as an activator of inflammation and associated development of chronic degenerative disorders (CDDs) including obesity, type 2 diabetes mellitus (T2DM), fatty liver disease, cardiovascular and neurodegenerative disorders as well as various types of cancers. Numerous drugs are in use to prevent these disorders, which specifically inhibit different pathways associated with the development of CDDs. Compared to these drug targets, inhibition of TLR, which specifically responsible for the inflammatory insults has proven to be a better drug target. Several natural products have emerged as inhibitors of CDDs, which specifically targets TLR signalling, among these, many are in the clinical trials. This review is intended to summarize the recent progress on TLR association with CDDs and to list possible use of natural products, their combinations and their synthetic derivative in the prevention of TLR-driven CDD development.

SHP-1 suppresses the antiviral innate immune response by targeting TRAF3

Type I interferons play a pivotal role in innate immune response to virus infection. The protein tyrosine phosphatase SHP‐1 was reported to function as a negative regulator of inflammatory cytokine production by inhibiting activation of NF‐κB and MAPKs during bacterial infection, however, the role of SHP‐1 in regulating type I interferons remains unknown. Here, we demonstrated that knockout or knockdown of SHP‐1 in macrophages promoted both HSV‐1‐ and VSV‐induced antiviral immune response. Conversely, overexpression of SHP‐1 in L929 cells suppressed the HSV‐1‐ and VSV‐induced immune response; suppression was directly dependent on phosphatase activity. We identified a direct interaction between SHP‐1 and TRAF3; the association between these two proteins resulted in diminished recruitment of CK1ε to TRAF3 and inhibited its K63‐linked ubiquitination; SHP‐1 inhibited K63‐linked ubiquitination of TRAF3 by promoting dephosphorylation at Tyr116 and Tyr446. Taken together, our results identify SHP‐1 as a negative regulator of antiviral immunity and suggest that SHP‐1 may be a target for intervention in acute virus infection.

Elevated expression of DOK3 indicates high suppressive immune cell infiltration and unfavorable prognosis of gliomas

Docking protein 3 has been implicated in immune response, including interferon-β production in macrophage and plasma cell differentiation. And its importance in lung adenocarcinoma has been reported. However, studies about its role in gliomas are rare. In this study, we explored the clinical and prognostic characteristics of DOK3 expression in 921 glioma samples. Kaplan-Meier survival analysis and Cox regression analysis verified the independent unfavorable prognostic value and high prognostic accuracy of DOK3 expression for overall survival. Functional analysis with Database for Annotation, Visualization and Integrated Discovery (DAVID) and Gene Set Enrichment Analysis (GSEA) implied the involvement of DOK3 in immune related responses. Immune cell infiltration analysis with online tools, CIBERSORT and EPIC, showed that samples with higher DOK3 expression were infiltrated with much more macrophages. DOK3 was also found to be strongly positively correlated with marker genes of tumor-associated macrophages and M2 macrophages, not M1. Results of immunohistochemical staining also demonstrated that samples with higher DOK3 expression level were infiltrated with more microglia/macrophages and immunosuppressive M2 macrophages. In summary, our results demonstrated the correlation between high DOK3 expression level and malignant progression of gliomas, and the possible involvement of DOK3 in immunosuppressive responses in gliomas.

Regulation of 8-Hydroxydaidzein in IRF3-Mediated Gene Expression in LPS-Stimulated Murine Macrophages

Cytokines and chemokines are transcriptionally regulated by inflammatory transcription factors such as nuclear factor-κB (NF-κB), activator protein-1 (AP-1), and interferon regulatory factor (IRF)-3. A daidzein derivative compound, 8-hydroxydaidzein (8-HD), isolated from soy products, has recently gained attention due to various pharmacological benefits, including anti-inflammatory activities. However, regulation of the inflammatory signaling mechanism for 8-HD is still poorly understood, particularly with respect to the IRF-3 signaling pathway. In this study, we explored the molecular mechanism of 8-HD in regulating inflammatory processes, with a focus on the IRF-3 signaling pathway using a lipopolysaccharide (LPS) and polyinosinic:polycytidylic acid [Poly (I:C)] stimulated murine macrophage cell line (RAW264.7). The 8-HD downregulated the mRNA expression level of IRF-3-dependent genes by inhibiting phosphorylation of the IRF-3 transcription factor. The inhibitory mechanism of 8-HD in the IRF-3 signaling pathway was shown to inhibit the kinase activity of IKKε to phosphorylate IRF-3. This compound can also interfere with the TRIF-mediated complex formation composed of TRAF3, TANK, and IKKε leading to downregulation of AKT phosphorylation and reduction of IRF-3 activation, resulted in inhibition of IRF-3-dependent expression of genes including IFN-β, C-X-C motif chemokine 10 (CXCL10), and interferon-induced protein with tetratricopeptide repeats 1 (IFIT1). Therefore, these results strongly suggest that 8-HD can act as a promising compound with the regulatory function of IRF-3-mediated inflammatory responses.

Docking protein-1 promotes inflammatory macrophage signaling in gastric cancer

Docking protein-1 (DOK1) is a tumor suppressor frequently lost in malignant cells, however, it retains the ability to control activities of immune receptors in adjacent stroma cells of the tumor microenvironment. We therefore hypothesized that addressing DOK1 may be useful for cancer immunotherapy. DOK1 mRNA and DOK1 protein expression were downregulated in tumor cells of gastric cancer patients (n = 249). Conversely, its expression was up-regulated in cases positive for Epstein Barr Virus (EBV+) together with genes related to macrophage biology and targets of clinical immunotherapy such as programmed-cell-death-ligand-1 (PD-L1). Notably, high DOK1 positivity in stroma cells conferred poor prognosis in patients and correlated with high levels of inducible nitric oxide synthase in CD68+ tumor-associated macrophages. In macrophages derived from human monocytic leukemia cell lines, DOK1 (i) was inducible by agonists of the anti-diabetic transcription factor peroxisome proliferator-activated receptor-gamma (PPARγ), (ii) increased polarization towards an inflammatory phenotype, (iii) augmented nuclear factor-κB-dependent transcription of pro-inflammatory cytokines and (iv) reduced PD-L1 expression. These properties empowered DOK1+ macrophages to decrease the viability of human gastric cancer cells in contact-dependent co-cultures. DOK1 also reduced PD-L1 expression in human primary blood monocytes. Our data propose that the drugability of DOK1 may be exploited to reprogram myeloid cells and enforce the innate immune response against EBV+ human gastric cancer.

Dok-3 deficient mice display different immune clustering and Tim-3 expression

Background

Dok-3 has been shown to play an important role in immune system. Tim-3 also has been recognized as an important immune regulator which involves in many diseases. The relationship of them is still unclear.

Methods

We detected the expression of Tim-3 on spleen immune cells from Dok-3 deficient mice and control mice by flow cytometry.

Results

In this article, we found that Dok-3^−/− mice display almost entirely different immune clustering characteristics compared with wild type 129 mice. The CD4 T cells and CD8 T cells decreased and DC cells, macrophages, MDSCs increased when the Dok-3 gene knocked-out. The Tim-3 expression on CD4 T cells, CD8 T cells, NK cells, DC cells increased when the Dok-3 gene knocked-out. The macrophages and MDSCs just display the opposite results.

Conclusions

Although Dok-3^−/− mice display different immune clustering and Tim-3 expression, the mechanism still needs further study.

Electronic supplementary material

The online version of this article (10.1186/s40001-019-0384-7) contains supplementary material, which is available to authorized users.

Dok3-protein phosphatase 1 interaction attenuates Card9 signaling and neutrophil-dependent antifungal immunity

Invasive fungal infection is a serious health threat with high morbidity and mortality. Current antifungal drugs only demonstrate partial success in improving prognosis. Furthermore, mechanisms regulating host defense against fungal pathogens remain elusive. Here, we report that the downstream of kinase 3 (Dok3) adaptor negatively regulates antifungal immunity in neutrophils. Our data revealed that Dok3 deficiency increased phagocytosis, proinflammatory cytokine production, and netosis in neutrophils, thereby enhancing mutant mouse survival against systemic infection with a lethal dose of the pathogenic fungus Candida albicans. Biochemically, Dok3 recruited protein phosphatase 1 (PP1) to dephosphorylate Card9, an essential player in innate antifungal defense, to dampen downstream NF-κB and JNK activation and immune responses. Thus, Dok3 suppresses Card9 signaling, and disrupting Dok3-Card9 interaction or inhibiting PP1 activity represents therapeutic opportunities to develop drugs to combat candidaemia.

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

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

An ethanolic extract of the aerial part of Siegesbeckia orientalis L. inhibits the production of inflammatory mediators regulated by AP-1, NF-κB and IRF3 in LPS-stimulated RAW 264.7 cells

Herba Siegesbeckiae (HS, the dried aerial part of Siegesbeckia orientalis L.) is a commonly used traditional Chinese medicinal herb for treating inflammatory diseases. HS has been reported to exert anti-inflammatory effects by inhibiting the MAPKs and NF-κB pathways, the downstream effectors of TLR4 signalling. This study aims to further investigate the involvement of TLR4 signalling cascades in the effects of an ethanolic extract of HS (HS for short) on inflammatory mediators in murine macrophages. HS was extracted using 50% ethanol. Lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages were used as the cell model. ELISA was used to detect cytokine/chemokine secretion. Real time-PCR and immunoblotting were used to examine mRNA and protein levels, respectively. We observed that HS dose-dependently inhibited the secretion of PGE₂, MCP-1, MIP-1α and RANTES, and down-regulated mRNA levels of iNOS, COX-2, IL-1β, IL-6, TNF-α, mPGES-1, MCP-1, MIP-1α and RANTES in LPS-stimulated RAW264.7 cells. HS did not affect the protein levels of TAK1, TBK1, PI3K, Akt, IKK, c-Jun, c-Fos and IRF3, while, dose-dependently decreased levels of their phosphorylated forms. The protein levels of IRAK1 and IRAK4 were upregulated, while those of TRAF6 and TRAF3 were downregulated by HS. Moreover, the nuclear protein levels of AP-1, NF-κB and IRF3 were dose-dependently decreased by HS. These results indicate that suppression of the IRAK4/MAPKs/AP-1, IRAK4/MAPKs/NF-κB, IRAK4/PI3K/NF-κB and TRAF3/TBK1/IRF3 pathways is associated with the inhibitory effects of HS on inflammatory mediators in LPS-stimulated RAW264.7 cells. This study provides a pharmacological basis for the clinical application of this herb in the treatment of inflammatory disorders.

Genetic Alterations of TRAF Proteins in Human Cancers

The tumor necrosis factor receptor (TNF-R)-associated factor (TRAF) family of cytoplasmic adaptor proteins regulate the signal transduction pathways of a variety of receptors, including the TNF-R superfamily, Toll-like receptors (TLRs), NOD-like receptors (NLRs), RIG-I-like receptors (RLRs), and cytokine receptors. TRAF-dependent signaling pathways participate in a diverse array of important cellular processes, including the survival, proliferation, differentiation, and activation of different cell types. Many of these TRAF-dependent signaling pathways have been implicated in cancer pathogenesis. Here we analyze the current evidence of genetic alterations of TRAF molecules available from The Cancer Genome Atlas (TCGA) and the Catalog of Somatic Mutations in Cancer (COSMIC) as well as the published literature, including copy number variations and mutation landscape of TRAFs in various human cancers. Such analyses reveal that both gain- and loss-of-function genetic alterations of different TRAF proteins are commonly present in a number of human cancers. These include pancreatic cancer, meningioma, breast cancer, prostate cancer, lung cancer, liver cancer, head and neck cancer, stomach cancer, colon cancer, bladder cancer, uterine cancer, melanoma, sarcoma, and B cell malignancies, among others. Furthermore, we summarize the key in vivo and in vitro evidence that demonstrates the causal roles of genetic alterations of TRAF proteins in tumorigenesis within different cell types and organs. Taken together, the information presented in this review provides a rationale for the development of therapeutic strategies to manipulate TRAF proteins or TRAF-dependent signaling pathways in different human cancers by precision medicine.

PLA1A Participates in the Antiviral Innate Immune Response by Facilitating the Recruitment of TANK-Binding Kinase 1 to Mitochondria

As a key molecule in the antiviral innate immune response, the activation of TANK-binding kinase 1 (TBK1) is under tight regulation. In this report, we identified phosphatidylserine-specific phospholipase PLA1A as a host factor that modulates the TBK1 activation. Knockdown of PLA1A expression suppressed the innate immune signaling induced by RNA viruses, while PLA1A overexpression enhanced the signaling. PLA1A functioned at the TBK1 level of the signaling pathway, as PLA1A silencing blocked TBK1, but not interferon regulatory factor 3 (IRF3) induced interferon-β (IFN-β) promoter activity. The phosphorylation and kinase activity of TBK1 was reduced in PLA1A knockdown cells. Mechanistically, PLA1A was required in TBK1-mitochondrial antiviral signaling protein (MAVS) interactions but not the interactions of TBK1 with other adaptor proteins. Furthermore, PLA1A knockdown reduced the recruitment of TBK1 and IRF3 to mitochondria, concomitant with altered mitochondria morphology.

TANK-Binding Kinase 1 (TBK1) Isoforms Negatively Regulate Type I Interferon Induction by Inhibiting TBK1-IRF3 Interaction and IRF3 Phosphorylation

TANK-binding kinase 1 (TBK1) is an important serine/threonine-protein kinase that mediates phosphorylation and nuclear translocation of IRF3, which contributes to induction of type I interferons (IFNs) in the innate antiviral response. In mammals, TBK1 spliced isoform negatively regulates the virus-triggered IFN-β signaling pathway by disrupting the interaction between retinoic acid-inducible gene I (RIG-I) and mitochondria antiviral-signaling protein (MAVS). However, it is still unclear whether alternative splicing patterns and the function of TBK1 isoform(s) exist in teleost fish. In this study, we identify two alternatively spliced isoforms of TBK1 from zebrafish, termed TBK1_tv1 and TBK1_tv2. Both TBK1_tv1 and TBK1_tv2 contain an incomplete STKc_TBK1 domain. Moreover, the UBL_TBK1_like domain is also missing for TBK1_tv2. TBK1_tv1 and TBK1_tv2 are expressed in zebrafish larvae. Overexpression of TBK1_tv1 and TBK1_tv2 inhibits RIG-I-, MAVS-, TBK1-, and IRF3-mediated activation of IFN promoters in response to spring viremia of carp virus infection. Also, TBK1_tv1 and TBK1_tv2 inhibit expression of IFNs and IFN-stimulated genes induced by MAVS and TBK1. Mechanistically, TBK1_tv1 and TBK1_tv2 competitively associate with TBK1 and IRF3 to disrupt the formation of a functional TBK1-IRF3 complex, impeding the phosphorylation of IRF3 mediated by TBK1. Collectively, these results demonstrate that TBK1 spliced isoforms are dominant negative regulators in the RIG-I/MAVS/TBK1/IRF3 antiviral pathway by targeting the functional TBK1-IRF3 complex formation. Identification and functional characterization of piscine TBK1 spliced isoforms may contribute to understanding the role of TBK1 expression in innate antiviral response.

Genetic Alterations of TRAF Proteins in Human Cancers

The tumor necrosis factor receptor (TNF-R)-associated factor (TRAF) family of cytoplasmic adaptor proteins regulate the signal transduction pathways of a variety of receptors, including the TNF-R superfamily, Toll-like receptors (TLRs), NOD-like receptors (NLRs), RIG-I-like receptors (RLRs), and cytokine receptors. TRAF-dependent signaling pathways participate in a diverse array of important cellular processes, including the survival, proliferation, differentiation, and activation of different cell types. Many of these TRAF-dependent signaling pathways have been implicated in cancer pathogenesis. Here we analyze the current evidence of genetic alterations of TRAF molecules available from The Cancer Genome Atlas (TCGA) and the Catalog of Somatic Mutations in Cancer (COSMIC) as well as the published literature, including copy number variations and mutation landscape of TRAFs in various human cancers. Such analyses reveal that both gain- and loss-of-function genetic alterations of different TRAF proteins are commonly present in a number of human cancers. These include pancreatic cancer, meningioma, breast cancer, prostate cancer, lung cancer, liver cancer, head and neck cancer, stomach cancer, colon cancer, bladder cancer, uterine cancer, melanoma, sarcoma, and B cell malignancies, among others. Furthermore, we summarize the key in vivo and in vitro evidence that demonstrates the causal roles of genetic alterations of TRAF proteins in tumorigenesis within different cell types and organs. Taken together, the information presented in this review provides a rationale for the development of therapeutic strategies to manipulate TRAF proteins or TRAF-dependent signaling pathways in different human cancers by precision medicine.

A functional genomics predictive network model identifies regulators of inflammatory bowel disease

A major challenge in inflammatory bowel disease (IBD) is the integration of diverse IBD data sets to construct predictive models of IBD. We present a predictive model of the immune component of IBD that informs causal relationships among loci previously linked to IBD through genome-wide association studies (GWAS) using functional and regulatory annotations that relate to the cells, tissues, and pathophysiology of IBD. Our model consists of individual networks constructed using molecular data generated from intestinal samples isolated from three populations of patients with IBD at different stages of disease. We performed key driver analysis to identify genes predicted to modulate network regulatory states associated with IBD, prioritizing and prospectively validating 12 of the top key drivers experimentally. This validated key driver set not only introduces new regulators of processes central to IBD but also provides the integrated circuits of genetic, molecular, and clinical traits that can be directly queried to interrogate and refine the regulatory framework defining IBD.

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.

TRAF3: a novel tumor suppressor gene in macrophages

Tumor necrosis factor receptor-associated factor 3 (TRAF3), a member of the TRAF family of cytoplasmic adaptor proteins with E3 ligase activity, is ubiquitously expressed in various cell types of the immune system. It is shared for signaling by a variety of adaptive and innate immune receptors as well as cytokine receptors. Previous studies examining conditional TRAF3-deficient mouse models that have the Traf3 gene specifically deleted in B lymphocytes or T lymphocytes have revealed the diverse and critical in vivo functions of TRAF3 in adaptive immunity. Although in vitro evidence points to a pivotal and indispensable role for TRAF3 in type I interferon production induced by pattern recognition receptors in macrophages and dendritic cells, the in vivo functions of TRAF3 in the innate immune system had long remained unclear. Three laboratories have recently addressed this gap in knowledge by investigating myeloid cell-specific TRAF3-deficient (genotype: TRAF3^flox/floxLysM^+/Cre) mice. The new evidence together demonstrates that specific ablation of TRAF3 in myeloid cells leads to inflammatory diseases, altered progression of diabetes, and spontaneous development of different types of tumors and infections in mice. These new findings indicate that TRAF3 acts as an anti-inflammatory factor and is required for optimal innate immunity in myeloid cells. Strikingly, the new evidence also identifies TRAF3 as a novel tumor suppressor gene in macrophages and other myeloid cells. In this review, we discuss and summarize the new findings and current knowledge about the multi-faceted regulatory roles and complex signaling mechanisms of myeloid cell TRAF3 in inflammation, innate immunity, and tumor development.

TBK1 inhibitors: a review of patent literature (2011 - 2014)

INTRODUCTION

TANK-binding kinase 1 (TBK1) is a noncanonical IκB kinase family member that regulates the innate immune response. Misregulation of TBK1 activity can promote inflammatory disorders and oncogenesis; therefore, TBK1 inhibitors are considered a promising therapy for inflammation and cancer.

AREAS COVERED

In this review, the authors provide information on the role of TBK1 in human health and on recently developed inhibitors from patents granted from 2011 to 2014. The reader will gain an understanding of the mechanisms of TBK1 function as well as the structure and biological activity of recently developed TBK1 inhibitors. Google and NCBI search engines were used to find relevant patents and clinical information using "TBK1 inhibitor" as the search term.

EXPERT OPINION

The role of TBK1 in various diseases has prompted the further investigation of significant targets. Although research on TBK1 inhibitors has increased over the last few years, only a few inhibitors of this kinase have been identified. In addition, almost all of the chemical inhibitors are modified from different scaffolds and/or chemotypes of pyrimidine. Specifically, compound BX795 is the representative one, which was first patented as a potent TBK1 inhibitor. Even though some compounds have displayed interesting potential inhibition and selectivity of TBK1 in vitro and in in vivo trials, the development of more efficient and selective TBK1 inhibitors is still required.