β-TrCP-mediated IRAK1 degradation releases TAK1-TRAF6 from the membrane to the cytosol for TAK1-dependent NF-κB activation

Increased expression of miR146a dysregulates TLR2-induced HBD2 in airway epithelial cells from patients with COPD

Background

Airway epithelial cells from patients with COPD show suboptimal innate immune responses to nontypeable Haemophilus influenzae (NTHi) and Toll-like receptor (TLR)2 ligands despite expressing TLR2 similar to normal airway epithelial cells, but the underlying mechanisms are poorly understood.

Methods

Normal or COPD mucociliary-differentiated airway epithelial cells were treated with TLR2 agonists or infected with NTHi and expression of β-defensin (HBD)2 was examined. Interleukin-1 receptor-associated kinase (IRAK)-1 and microRNA (miR)146a were genetically inhibited in normal and COPD airway epithelial cell cultures, respectively, and HBD2 responses to TLR2 ligands were determined. IRAK-1 expression in lung sections was determined by immunofluorescence microscopy.

Results

Compared to normal, COPD airway epithelial cell cultures showed impaired expression of HBD2 in response to TLR2 agonists or NTHi infection. Apical secretions from TLR2 agonist-treated normal, but not COPD, airway epithelial cells efficiently killed NTHi. Knockdown of HBD2 significantly reduced NTHi killing by apical secretions of normal airway epithelial cells. Compared to normal, COPD cells showed significantly reduced expression of IRAK-1 and this was associated with increased expression of miR146a. Inhibition of miR146a increased the expression of IRAK-1, improved the expression of HBD2 in response to TLR2 agonists in COPD cells and enhanced the killing of bacteria by apical secretions obtained from TLR2 agonist-treated COPD cells. Bronchial epithelium of COPD patients showed reduced expression of IRAK-1.

Conclusions

These results suggest that reduced levels of IRAK-1 due to increased expression of miR146a may contribute to impaired expression of TLR2-induced HBD2 in COPD airway epithelial cells.

IRAK1 inhibition blocks the HIV-1 RNA mediated pro-inflammatory cytokine response from microglia

Human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) are a common source of morbidity in people living with HIV (PLWH). Although antiretroviral therapy (ART) has lessened the severity of neurocognitive disorders, cognitive impairment still occurs in PLWH receiving ART. The pathogenesis of HAND is likely multifaceted, but common factors include the persistence of HIV transcription within the central nervous system, higher levels of pro-inflammatory cytokines in the cerebrospinal fluid, and the presence of activated microglia. Toll-like receptor (TLR) 7 and TLR8 are innate pathogen recognition receptors located in microglia and other immune and non-immune cells that can recognise HIV RNA and trigger pro-inflammatory responses. IL-1 receptor-associated kinase (IRAK) 1 is key to these signalling pathways. Here, we show that IRAK1 inhibition inhibits the TLR7 and TLR8-dependent pro-inflammatory response to HIV RNA. Using genetic and pharmacological inhibition, we demonstrate that inhibition of IRAK1 prevents IRAK1 phosphorylation and ubiquitination, and the subsequent recruitment of TRAF6 and the TAK1 complex to IRAK1, resulting in the inhibition of downstream signalling and the suppression of pro-inflammatory cytokine and chemokine release.

Inter-Fighting between Influenza A Virus NS1 and β-TrCP: A Novel Mechanism of Anti-Influenza Virus

Influenza A virus (IAV) prevents innate immune signaling during infection. In our previous study, the production of pro-inflammatory cytokines was associated with Cullin-1 RING ligase (CRL1), which was related to NF-κB activation. However, the underlying mechanism is unclear. Here, an E3 ligase, β-transducin repeat-containing protein (β-TrCP), was significantly downregulated during IAV infection. Co-IP analysis revealed that non-structural 1 protein (NS1) interacts with β-TrCP. With co-transfection, an increase in NS1 expression led to a reduction in β-TrCP expression, affecting the level of IκBα and then resulting in repression of the activation of the NF-κB pathway during IAV infection. In addition, β-TrCP targets the viral NS1 protein and significantly reduces the replication level of influenza virus. Our results provide a novel mechanism for influenza to modulate its immune response during infection, and β-TrCP may be a novel target for influenza virus antagonism.

Viperin impairs the innate immune response through the IRAK1-TRAF6-TAK1 axis to promote Mtb infection

Mycobacterium tuberculosis (Mtb) infection is a long-standing public health threat, and the development of host-directed therapy for eradicating Mtb infection requires better insights into Mtb-host interactions. Viperin [virus-inhibitory protein, endoplasmic reticulum-associated, interferon (IFN) inducible] is an IFN-inducible protein with broad antiviral activities. Here, we demonstrated that Viperin was increased in abundance in patients with lymphatic and pulmonary tuberculosis (TB). Viperin-deficient mice had decreased Mtb bacterial loads and enhanced macrophage responses compared with their wild-type counterparts. Viperin suppressed the formation of a complex containing interleukin-1 receptor-associated kinase 1, TNF receptor-associated factor 6, and transforming growth factor β-activated kinase 1 (TAK1) and inhibited the TAK1-dependent activation of IκB kinase α/β, thereby impairing the production of nitric oxide and proinflammatory cytokines. These results suggest that Viperin promotes Mtb infection by inhibiting host innate immune responses in macrophages, suggesting that Viperin may be a candidate target for adjunct host-directed therapy in patients with TB.

Nonhematopoietic IRAK1 drives arthritis via neutrophil chemoattractants

IL-1 receptor-activated kinase 1 (IRAK1) is involved in signal transduction downstream of many TLRs and the IL-1R. Its potential as a drug target for chronic inflammatory diseases is underappreciated. To study its functional role in joint inflammation, we generated a mouse model expressing a functionally inactive IRAK1 (IRAK1 kinase deficient, IRAK1KD), which also displayed reduced IRAK1 protein expression and cell type–specific deficiencies of TLR signaling. The serum transfer model of arthritis revealed a potentially novel role of IRAK1 for disease development and neutrophil chemoattraction exclusively via its activity in nonhematopoietic cells. Consistently, IRAK1KD synovial fibroblasts showed reduced secretion of neutrophil chemoattractant chemokines following stimulation with IL-1β or human synovial fluids from patients with rheumatoid arthritis (RA) and gout. Together with patients with RA showing prominent IRAK1 expression in fibroblasts of the synovial lining, these data suggest that targeting IRAK1 may be therapeutically beneficial. As pharmacological inhibition of IRAK1 kinase activity had only mild effects on synovial fibroblasts from mice and patients with RA, targeted degradation of IRAK1 may be the preferred pharmacologic modality. Collectively, these data position IRAK1 as a central regulator of the IL-1β–dependent local inflammatory milieu of the joints and a potential therapeutic target for inflammatory arthritis.

Pacritinib Inhibition of IRAK1 Blocks Aberrant TLR8 Signalling by SARS-CoV-2 and HIV-1-Derived RNA

Macrophages promote an early host response to infection by releasing pro-inflammatory cytokines such as interleukin (IL) 1β (IL-1β), tumour necrosis factor (TNF), and IL-6. One of the mechanisms through which cells sense pathogenic microorganisms is through Toll-like receptors (TLRs). IL-1 receptor-associated kinase (IRAK) 1, IRAK2, IRAK3, and IRAK4 are integral to TLR and IL-1 receptor signalling pathways. Recent studies suggest a role for aberrant TLR8 and NLRP3 inflammasome activation during both COVID-19 and HIV-1 infection. Here, we show that pacritinib inhibits the TLR8-dependent pro-inflammatory cytokine response elicited by GU-rich single-stranded RNA derived from SARS-CoV-2 and HIV-1. Using genetic and pharmacologic inhibition, we demonstrate that pacritinib inhibits IRAK1 phosphorylation and ubiquitination which then inhibits the recruitment of the TAK1 complex to IRAK1, thus inhibiting the activation of downstream signalling and the production of pro-inflammatory cytokines.

TRIM67 Suppresses TNFalpha-Triggered NF-kB Activation by Competitively Binding Beta-TrCP to IkBa

The transcription factor NF-κB plays an important role in modulation of inflammatory pathways, which are associated with inflammatory diseases, neurodegeneration, apoptosis, immune responses, and cancer. Increasing evidence indicates that TRIM proteins are crucial role in the regulation of NF-κB signaling pathways. In this study, we identified TRIM67 as a negative regulator of TNFα-triggered NF-κB activation. Ectopic expression of TRIM67 significantly represses TNFα-induced NF-κB activation and the expression of pro-inflammatory cytokines TNFα and IL-6. In contrast, Trim67 depletion promotes TNFα-induced expression of TNFα, IL-6, and Mcp-1 in primary mouse embryonic fibroblasts. Mechanistically, we found that TRIM67 competitively binding β-transducin repeat-containing protein (β-TrCP) to IκBα results inhibition of β-TrCP-mediated degradation of IκBα, which finally caused inhibition of TNFα-triggered NF-κB activation. In summary, our findings revealed that TRIM67 function as a novel negative regulator of NF-κB signaling pathway, implying TRIM67 might exert an important role in regulation of inflammation disease and pathogen infection caused inflammation.

Antioxidant and Anti-Inflammatory Effects of Bischofia javanica (Blume) Leaf Methanol Extracts through the Regulation of Nrf2 and TAK1

Bischofia javanica (Blume) has been traditionally used to treat inflammatory diseases such as tonsillitis and ulcers throughout Asia, including China, Indonesia, and the Philippines: however, the molecular mechanisms by which B. javanica exerts its antioxidant and anti-inflammatory properties remain largely unknown. In this study, we analyzed the antioxidant and anti-inflammatory mechanisms of methanol extracts of B. javanica leaves (MBJ) in vitro and in vivo. MBJ decreased nitric oxide (NO) production and the expression of pro-inflammatory cytokines, including interleukin (IL)-1β, IL-6, and tumor necrosis factor-α, in lipopolysaccharide (LPS)-treated RAW 264.7 cells. The observed suppression of inflammatory responses by MBJ was correlated with an inhibition of the nuclear factor-κB (NF-κB) and the mitogen-activated protein kinase (MAPK) pathways. Additionally, MBJ induced nuclear translocation of the nuclear factor erythroid 2-related factor 2 (Nrf2), a transcription factor that upregulates the expression of anti-inflammatory and antioxidant genes. Furthermore, MBJ exhibited antioxidant and anti-inflammatory effects in an acute hepatitis mouse model. In conclusion, our results confirm the medicinal properties of B. javanica, and therefore MBJ could be applied to improve inflammatory and redox imbalances in different types of pathologies.

Establishing and Validating Cellular Functional Target Engagement Assay for Selective IRAK4 Inhibitor Discovery

One of the main reasons for the lack of drug efficacy in late-stage clinical trials is the lack of specific and selective target engagement. To increase the likelihood of success of new therapeutics, one approach is to conduct proximal target engagement testing during the early phases of preclinical drug discovery. To identify and optimize selective IRAK4 inhibitors, a kinase that has been implicated in multiple inflammatory and autoimmune diseases, we established an electrochemiluminescence (ECL)-based cellular endogenous IRAK1 activation assay as the most proximal functional evaluation of IRAK4 engagement to support structure-activity relationship (SAR) studies. Since IRAK1 activation is dependent on both the IRAK4 scaffolding function in Myddosome formation and IRAK4 kinase activity for signal transduction, this assay potentially captures inhibitors with different mechanisms of action. Data from this IRAK1 assay with compounds representing different structural classes showed statistically significant correlations when compared with results from both IRAK4 biochemical kinase activity and functional peripheral blood mononuclear cell (PBMC)-derived tumor necrosis factor α (TNFα) secretion assays, validating the biological relevancy of the IRAK1 target engagement as a biomarker of the IRAK4 activity. Plate uniformity and potency reproducibility evaluations demonstrated that this assay is amenable to high throughput. Using Bland-Altman assay agreement analysis, we demonstrated that incorporating such proximal pharmacological assessment of cellular target engagement to an in vitro screening funnel for SAR studies can prevent compound optimization toward off-target activity.

The deubiquitinase OTUB1 augments NF-κB-dependent immune responses in dendritic cells in infection and inflammation by stabilizing UBC13

Dendritic cells (DCs) are indispensable for defense against pathogens but may also contribute to immunopathology. Activation of DCs upon the sensing of pathogens by Toll-like receptors (TLRs) is largely mediated by pattern recognition receptor/nuclear factor-κB (NF-κB) signaling and depends on the appropriate ubiquitination of the respective signaling molecules. However, the ubiquitinating and deubiquitinating enzymes involved and their interactions are only incompletely understood. Here, we reveal that the deubiquitinase OTU domain, ubiquitin aldehyde binding 1 (OTUB1) is upregulated in DCs upon murine Toxoplasma gondii infection and lipopolysaccharide challenge. Stimulation of DCs with the TLR11/12 ligand T. gondii profilin and the TLR4 ligand lipopolysaccharide induced an increase in NF-κB activation in OTUB1-competent cells, resulting in elevated interleukin-6 (IL-6), IL-12, and tumor necrosis factor (TNF) production, which was also observed upon the specific stimulation of TLR2, TLR3, TLR7, and TLR9. Mechanistically, OTUB1 promoted NF-κB activity in DCs by K48-linked deubiquitination and stabilization of the E2-conjugating enzyme UBC13, resulting in increased K63-linked ubiquitination of IRAK1 (IL-1 receptor-associated kinase 1) and TRAF6 (TNF receptor-associated factor 6). Consequently, DC-specific deletion of OTUB1 impaired the production of cytokines, in particular IL-12, by DCs over the first 2 days of T. gondii infection, resulting in the diminished production of protective interferon-γ (IFN-γ) by natural killer cells, impaired control of parasite replication, and, finally, death from chronic T. encephalitis, all of which could be prevented by low-dose IL-12 treatment in the first 3 days of infection. In contrast, impaired OTUB1-deficient DC activation and cytokine production by OTUB1-deficient DCs protected mice from lipopolysaccharide-induced immunopathology. Collectively, these findings identify OTUB1 as a potent novel regulator of DCs during infectious and inflammatory diseases.

Manifold role of ubiquitin in Helicobacter pylori infection and gastric cancer

Infection with H. pylori induces a strong host cellular response represented by induction of a set of molecular signaling pathways, expression of proinflammatory cytokines and changes in proliferation. Chronic infection and inflammation accompanied by secretory dysfunction can result in the development of gastric metaplasia and gastric cancer. Currently, it has been determined that the regulation of many cellular processes involves ubiquitinylation of molecular effectors. The binding of ubiquitin allows the substrate to undergo a change in function, to interact within multimolecular signaling complexes and/or to be degraded. Dysregulation of the ubiquitinylation machinery contributes to several pathologies, including cancer. It is not understood in detail how H. pylori impacts the ubiquitinylation of host substrate proteins. The aim of this review is to summarize the existing literature in this field, with an emphasis on the role of E3 ubiquitin ligases in host cell homeodynamics, gastric pathophysiology and gastric cancer.

Dipterocarpus tuberculatus Roxb. Ethanol Extract Has Anti-Inflammatory and Hepatoprotective Effects In Vitro and In Vivo by Targeting the IRAK1/AP-1 Pathway

Dipterocarpus tuberculatus Roxb. has been used traditionally as a remedy for many diseases, especially inflammation. Therefore, we analyzed and explored the mechanism of the anti-inflammatory effect of a Dipterocarpus tuberculatus Roxb. ethanol extract (Dt-EE). Dt-EE clearly and dose-dependently inhibited the expression of pro-inflammatory cytokines such as IL-6, TNF-α, and IL-1β in lipopolysaccharide (LPS)-treated RAW264.7 cells. Also, Dt-EE suppressed the activation of the MyD88/TRIF-mediated AP-1 pathway and the AP-1 pathway related proteins JNK2, MKK4/7, and TAK1, which occurred as a result of inhibiting the kinase activity of IRAK1 and IRAK4, the most upstream factors of the AP-1 pathway. Finally, Dt-EE displayed hepatoprotective activity in a mouse model of hepatitis induced with LPS/D-galactosamine (D-GalN) through decreasing the serum levels of alanine aminotransferase and suppressing the activation of JNK and IRAK1. Therefore, our results strongly suggest that Dt-EE could be a candidate anti-inflammatory herbal medicine with IRAK1/AP-1 inhibitory and hepatoprotective properties.

Inhibition of IRAK4 kinase activity improves ethanol-induced liver injury in mice

BACKGROUNDS & AIMS

Alcohol-related liver disease (ALD) is a major cause of chronic liver disease worldwide with limited therapeutic options. Interleukin-1 receptor associated kinase 4 (IRAK4), the master kinase of Toll-like receptor (TLR)/IL-1R-mediated signalling activation, is considered a novel therapeutic target in inflammatory diseases, but has not been investigated in the context of ALD.

METHODS

IRAK4 phosphorylation and IRAK1 protein were analysed in liver from alcohol-related hepatitis patients and healthy controls. IRAK4 kinase activity-inactive knock-in (Irak4 KI) mice and bone marrow chimeric mice were exposed to chronic ethanol-induced liver injury. IL-1β-induced IRAK4-mediated signalling and acute phase response were investigated in cultured hepatocytes. IRAK1/4 inhibitor was used to test the therapeutic potential for ethanol-induced liver injury in mice.

RESULTS

Increased IRAK4 phosphorylation and reduced IRAK1 protein were found in livers of patients with alcoholic hepatitis. In the chronic ethanol-induced liver injury mouse model, hepatic inflammation and hepatocellular damage were attenuated in Irak4 KI mice. IRAK4 kinase activity promotes expression of acute phase proteins in response to ethanol exposure, including C-reactive protein and serum amyloid A1 (SAA1). SAA1 and IL-1β synergistically exacerbate ethanol-induced cell death ex vivo. Pharmacological blockage of IRAK4 kinase abrogated ethanol-induced liver injury, inflammation, steatosis, as well as acute phase gene expression and protein production in mice.

CONCLUSIONS

Our data elucidate the critical role of IRAK4 kinase activity in the pathogenesis of ethanol-induced liver injury in mice and provide preclinical validation for use of an IRAK1/4 inhibitor as a new potential therapeutic strategy for the treatment of ALD.

LAY SUMMARY

Herein, we have identified the role of IRAK4 kinase activity in the development of alcohol-induced liver injury in mice. Hepatocyte-specific IRAK4 is associated with an acute phase response and release of proinflammatory cytokines/chemokines, which synergistically exacerbate alcohol-induced hepatocyte cell death ex vivo. Pharmacological inhibition of IRAK4 kinase activity effectively attenuates alcohol-induced liver injury in mice and could have therapeutic implications.

The characteristics and roles of β-TrCP1/2 in carcinogenesis

β-transducin repeat-containing protein (β-TrCP), one of the well-characterized F-box proteins, acts as a substrate receptor and constitutes an active SCF^β-TrCP E3 ligase with a scaffold protein CUL1, a RING protein RBX1, and an adaptor protein SKP1. β-TrCP plays a critical role in the regulation of various physiological and pathological processes, including signal transduction, cell cycle progression, cell migration, DNA damage response, and tumorigenesis, by governing burgeoning amounts of key regulators for ubiquitination and proteasomal degradation. Given that a variety of β-TrCP substrates are well-known oncoproteins and tumor suppressors, and dysregulation of β-TrCP is frequently identified in human cancers, β-TrCP plays a vital role in carcinogenesis. In this review, we first briefly introduce the characteristics of β-TrCP1, β-TrCP2, and SCF^β-TrCP ubiquitin ligase, and then discuss SCF^β-TrCP ubiquitin ligase regulated biological processes by targeting its substrates for degradation. Moreover, we summarize the regulation of β-TrCP1 and β-TrCP2 at multiple layers and further discuss the various roles of β-TrCP1 and β-TrCP2 in human cancer, functioning as either an oncoprotein or a tumor suppressor in a manner dependent of cellular context. Finally, we provide novel insights for future perspectives on the potential of targeting β-TrCP1 and β-TrCP2 for cancer therapy.

Regulation of NFκB Signalling by Ubiquitination: A Potential Therapeutic Target in Head and Neck Squamous Cell Carcinoma?

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide, with over 600,000 cases per year. The primary causes for HNSCC include smoking and alcohol consumption, with an increasing number of cases attributed to infection with Human Papillomavirus (HPV). The treatment options for HNSCC currently include surgery, radiotherapy, and/or platinum-based chemotherapeutics. Cetuximab (targeting EGFR) and Pembrolizumab (targeting PD-1) have been approved for advanced stage, recurrent, and/or metastatic HNSCC. Despite these advances, whilst HPV+ HNSCC has a 3-year overall survival (OS) rate of around 80%, the 3-year OS for HPV- HNSCC is still around 55%. Aberrant signal activation of transcription factor NFκB plays an important role in the pathogenesis and therapeutic resistance of HNSCC. As an important mediator of inflammatory signalling and the immune response to pathogens, the NFκB pathway is tightly regulated to prevent chronic inflammation, a key driver of tumorigenesis. Here, we discuss how NFκB signalling is regulated by the ubiquitin pathway and how this pathway is deregulated in HNSCC. Finally, we discuss the current strategies available to target the ubiquitin pathway and how this may offer a potential therapeutic benefit in HNSCC.

Myeloid Differentiation Primary Response 88-Cyclin D1 Signaling in Breast Cancer Cells Regulates Toll-Like Receptor 3-Mediated Cell Proliferation

Toll-like receptor 3 (TLR3)-mediated apoptotic changes in cancer cells are well-documented, and hence, several synthetic ligands of TLR3 are being used for adjuvant therapy, but there are reports showing a contradictory effect of TLR3 signaling, which include our previous report that had shown cell proliferation following surface localization of TLR 3. However, the underlying mechanism of cell surface localization of TLR3 and subsequent cell proliferation lacks clarity. This study addresses the TLR3 ligand-mediated signaling cascade that regulates a proliferative effect in breast cancer cells (MDA-MB-231 and T47D) challenged with TLR3 ligand in the presence of myeloid differentiation primary response 88 (MyD88) inhibitor. Evidences were obtained using immunoblotting, coimmunoprecipitation, confocal microscopy, immunocytochemistry, ELISA, and flow cytometry. Results had revealed that TLR3 ligand treatment significantly enhanced breast cancer cell proliferation marked by an upregulated expression of cyclinD1, but the same was suppressed by the addition of MyD88 inhibitor. Also, expression of interleukin 1 receptor-associated kinase 1 (IRAK1)-TNF receptor-associated factor 6 (TRAF6)-transforming growth factor beta-activated kinase 1 (TAK1) was altered in the given TLR3-signaling pathway. Inhibition of MyD88 disrupted the downstream adaptor complex and mediated signaling through the TLR3-MyD88-NF-κB (p65)-IL-6-cyclin D1 pathway. TLR3-mediated alternative signaling of the TLR3-MyD88-IRAK1-TRAF6-TAK1-TAB1-NF-κB axis leads to upregulation of IL6 and cyclin D1. This response is hypothesized to be via the MyD88 gateway that culminates in the proliferation of breast cancer cells. Overall, this study provides first comprehensive evidence on the involvement of canonical signaling of TLR3 using MyD88-cyclin D1-mediated breast cancer cell proliferation. The findings elucidated herein will provide valuable insights into understanding the TLR3-mediated adjuvant therapy in cancer.

Interleukin-1 Receptor-Associated Kinase (IRAK) Signaling in Kaposi Sarcoma-Associated Herpesvirus-Induced Primary Effusion Lymphoma

Kaposi sarcoma-associated herpesvirus (KSHV) is necessary but not sufficient for primary effusion lymphoma (PEL) development. Alterations in cellular signaling pathways are also a characteristic of PEL. Other B cell lymphomas have acquired an oncogenic mutation in the myeloid differentiation primary response 88 (MYD88) gene. The MYD88 L265P mutant results in the activation of interleukin-1 receptor associated kinase (IRAK). To probe IRAK/MYD88 signaling in PEL, we employed CRISPR/Cas9 technology to generate stable deletion clones in BCBL-1Cas9 and BC-1Cas9 cells. To look for off-target effects, we determined the complete exome of the BCBL-1Cas9 and BC-1Cas9 cells. Deletion of either MYD88, IRAK4, or IRAK1 abolished interleukin-1 beta (IL-1β) signaling; however, we were able to grow stable subclones from each population. Transcriptome sequencing (RNA-seq) analysis of IRAK4 knockout cell lines (IRAK4 KOs) showed that the IRAK pathway induced cellular signals constitutively, independent of IL-1β stimulation, which was abrogated by deletion of IRAK4. Transient complementation with IRAK1 increased NF-κB activity in MYD88 KO, IRAK1 KO, and IRAK4 KO cells even in the absence of IL-1β. IL-10, a hallmark of PEL, was dependent on the IRAK pathway, as IRAK4 KOs showed reduced IL-10 levels. We surmise that, unlike B cell receptor (BCR) signaling, MYD88/IRAK signaling is constitutively active in PEL, but that under cell culture conditions, PEL rapidly became independent of this pathway.IMPORTANCE One hundred percent of primary effusion lymphoma (PEL) cases are associated with Kaposi sarcoma-associated herpesvirus (KSHV). PEL cell lines, such as BCBL-1, are the workhorse for understanding this human oncovirus and the host pathways that KSHV dysregulates. Understanding their function is important for developing new therapies as well as identifying high-risk patient groups. The myeloid differentiation primary response 88 (MYD88)/interleukin-1 receptor associated kinase (IRAK) pathway, which has progrowth functions in other B cell lymphomas, has not been fully explored in PEL. By performing CRISPR/Cas9 knockout (KO) studies targeting the IRAK pathway in PEL, we were able to determine that established PEL cell lines can circumvent the loss of IRAK1, IRAK4, and MYD88; however, the deletion clones are deficient in interleukin-10 (IL-10) production. Since IL-10 suppresses T cell function, this suggests that the IRAK pathway may serve a function in vivo and during early-stage development of PEL.

BAP31 regulates IRAK1-dependent neuroinflammation in microglia

BACKGROUND

Microglia, the mononuclear immune cells of the central nervous system (CNS), are essential for the maintenance of CNS homeostasis. BAP31, a resident and ubiquitously expressed protein of the endoplasmic reticulum, serves as a sorting factor for its client proteins, mediating the subsequent export, retention, and degradation or survival. Recently, BAP31 has been defined as a regulatory molecule in the CNS, but the function of BAP31 in microglia has yet to be determined. In the present study, we investigated whether BAP31 is involved in the inflammatory response of microglia.

METHODS

This study used the BV2 cell line and BAP31 conditional knockdown mice generated via the Cre/LoxP system. A BAP31 knockdown experiment was performed to elucidate the role of BAP31 in the endogenous inflammatory cytokine production by microglial BV2 cells. A mouse model of lipopolysaccharide (LPS)-induced cognitive impairment was established to evaluate the neuroprotective effect of BAP31 against neuroinflammation-induced memory deficits. Behavioral alterations were assessed with the open field test (OFT), Y maze, and Morris water maze. The activation of microglia in the hippocampus of mice was observed by immunohistochemistry. Western blot, enzyme-linked immunosorbent assay (ELISA), immunofluorescence staining, and reverse transcription quantitative real-time polymerase chain reaction (RT-PCR) were used to clarify the mechanisms.

RESULTS

BAP31 deficiency upregulates LPS-induced proinflammatory cytokines in BV2 cells and mice by upregulating the protein level of IRAK1, which in turn increases the translocation and transcriptional activity of NF-κB p65 and c-Jun, and moreover, knockdown of IRAK1 or use of an IRAK1 inhibitor reverses these functions. In the cognitive impairment animal model, the BAP31 knockdown mice displayed increased severity in memory deficiency accompanied by an increased expression of proinflammatory factors in the hippocampus.

CONCLUSIONS

These findings indicate that BAP31 may modulate inflammatory cytokines and cognitive impairment induced by neuroinflammation through IRAK1, which demonstrates that BAP31 plays an essential role in microglial inflammation and prevention of memory deficits caused by neuroinflammation.

Anti-Inflammatory Effects of Licania macrocarpa Cuatrec Methanol Extract Target Src- and TAK1-Mediated Pathways

In this study, we investigated the anti-inflammatory effects of Licania macrocarpa Cuatrec methanol extract (Lm-ME) in vitro and in vivo and found pharmacological target proteins of Lm-ME in TLR4-mediated inflammatory signaling. This extract reduced NO production and mRNA expression of inflammatory cytokines such as iNOS, COX-2, IL-6, and IL-1β. In the NF-κB- and AP-1-mediated luciferase reporter gene assay, transcription factor activities decreased under cotransfection with MyD88 or TRIF. Phosphorylated protein levels of Src, PI3K, IKKα/β, and IκBα as well as p50 and p65 in the NF-κB signal pathway were downregulated, and phosphorylation of TAK1, MEK1/2, MKK4/7, and MKK3/6 as well as ERK, JNK, and p38 was decreased in the AP-1 signal pathway. Through overexpression of HA-Src and HA-TAK1, respectively, Lm-ME inhibited autophosphorylation of overexpressed proteins and thereby activated fewer downstream signaling molecules. Lm-ME also attenuated stomach ulcers in an HCl/EtOH-induced acute gastritis model mice, and COX-2 mRNA expression and phosphorylated TAK1 levels in gastric tissues were diminished. The flavonoids kaempferol and quercetin were identified in the HPLC analysis of Lm-ME; both are actively anti-inflammatory. Therefore, these results suggest that Lm-ME can be used for anti-inflammatory remedy by targeting Src and TAK1.

Geranylgeraniol Suppresses the Expression of IRAK1 and TRAF6 to Inhibit NFκB Activation in Lipopolysaccharide-Induced Inflammatory Responses in Human Macrophage-Like Cells

Geranylgeraniol (GGOH), a natural isoprenoid found in plants, has anti-inflammatory effects via inhibiting the activation of nuclear factor-kappa B (NFκB). However, its detailed mechanism has not yet been elucidated. Recent studies have revealed that isoprenoids can modulate signaling molecules in innate immune responses. We found that GGOH decreased the expression of lipopolysaccharide (LPS)-induced inflammatory genes in human macrophage-like THP-1 cells. Furthermore, we observed that the suppression of NFκB signaling proteins, in particular interleukin-1 receptor-associated kinase 1 (IRAK1) and tumor necrosis factor receptor-associated factor 6 (TRAF6), occurred in GGOH-treated cells prior to LPS stimulation, suggesting an immunomodulatory effect. These results indicate that GGOH may modulate and help prevent excessive NFκB activation that can lead to numerous diseases.

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

Background

Dingchuan tang (asthma-relieving decoction), a formula of nine herbs, has been used for treating respiratory inflammatory diseases for >400 years in the People’s Republic of China. However, the mechanisms underlying the anti-inflammatory action of dingchuan tang is not fully understood. This study aims to investigate the effects of Dingchuan tang essential oil (DCEO) on inflammatory mediators and the underlying mechanism of action.

Materials and methods

DCEO was extracted by steam distillation. Lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages were used as the cell model. Production of nitric oxide (NO) was determined by the Griess test. Protein secretion and mRNA levels of inflammatory mediators were measured by the enzyme-linked immunosorbent assay (ELISA) and quantitative real-time polymerase chain reaction (qRT-PCR), respectively. Protein levels were examined by Western blot. Nuclear localization of nuclear factor-kappa B (NF-κB) was detected using immunofluorescence analyses.

Results

DCEO significantly reduced LPS-triggered production of NO and prostaglandin E2 (PGE2) and decreased protein and mRNA levels of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). LPS induced upregulation of protein and mRNA levels of cytokines (interleukin-1β [IL-1β], interleukin-6 [IL-6], tumor necrosis factor-α [TNF-α]), and chemokines (monocyte chemoattractant protein-1 [MCP-1], chemokine [C-C motif] ligand 5 [CCL-5], and macrophage inflammatory protein [MIP]-1α) were suppressed by DCEO treatment. Phosphorylation and nuclear protein levels of transcription factors (activator protein-1 [AP-1], NF-κB, interferon regulatory factor 3 [IRF3]) were decreased by DCEO. Protein levels of phosphorylated IκB-α, IκB kinase α/β (IKKα/β), phosphatidylinositol 3-kinase (PI3K), protein kinase B (Akt), TGF β-activated kinase 1 (TAK1), TANK-binding kinase 1 (TBK1), extracellular signal-regulated kinase (ERK), p38 mitogen-activated protein kinase (p38), and c-Jun N-terminal kinase (JNK) were lowered by DCEO. Moreover, degradation of interleukin-1 receptor-associated kinase 1 (IRAK1) and IRAK4 induced by LPS was inhibited by DCEO treatment.

Conclusion

Suppression of the interleukin-1 receptor-associated kinase (IRAK)/NF-κB, IRAK/AP-1 and TBK1/IRF3 pathways was associated with the inhibitory effects of DCEO on inflammatory mediators in LPS-stimulated RAW264.7 macrophages. This study provides a pharmacological justification for the use of dingchuan tang in managing inflammatory disorders.

The Many Roles of Ubiquitin in NF-κB Signaling

The nuclear factor κB (NF-κB) signaling pathway ubiquitously controls cell growth and survival in basic conditions as well as rapid resetting of cellular functions following environment changes or pathogenic insults. Moreover, its deregulation is frequently observed during cell transformation, chronic inflammation or autoimmunity. Understanding how it is properly regulated therefore is a prerequisite to managing these adverse situations. Over the last years evidence has accumulated showing that ubiquitination is a key process in NF-κB activation and its resolution. Here, we examine the various functions of ubiquitin in NF-κB signaling and more specifically, how it controls signal transduction at the molecular level and impacts in vivo on NF-κB regulated cellular processes.

Inhibition of IRAK1 Ubiquitination Determines Glucocorticoid Sensitivity for TLR9-Induced Inflammation in Macrophages

Inflammatory responses are controlled by signaling mediators that are regulated by various posttranslational modifications. Recently, transcription-independent functions for glucocorticoids (GC) in restraining inflammation have emerged, but the underlying mechanisms are unknown. In this study, we report that GC receptor (GR)-mediated actions of GC acutely suppress TLR9-induced inflammation via inhibition of IL-1R-associated kinase 1 (IRAK1) ubiquitination. β-TrCP-IRAK1 interaction is required for K48-linked ubiquitination of IRAK1 at Lys¹³⁴ and subsequent membrane-to-cytoplasm trafficking of IRAK1 interacting partners TNFR-associated factor 6 and TAK1 that facilitates NF-κB and MAPK activation. Upon costimulation of macrophages with GC and TLR9-engaging ligand, GR physically interacts with IRAK1 and interferes with protein-protein interactions between β-TrCP and IRAK1. Ablation of GR in macrophages prevents GC-dependent suppression of β-TrCP-IRAK1 interactions. This GC-mediated suppression of IRAK1 activation is unique to TLR9, as GC treatment impairs TLR9 but not TLR4 ligand-induced K48-linked IRAK1 ubiquitination and trafficking of IRAK1 interacting partners. Furthermore, mutations in IRAK1 at Lys¹³⁴ prevent TLR9 ligand-induced activation of inflammatory signaling mediators and synthesis of proinflammatory cytokines to an extent comparable to GC-mediated inhibition. Collectively, these findings identify a transcription-independent, rapid, and nongenomic GC suppression of TLR9 ligand-mediated IRAK1 ubiquitination as a novel mechanism for restraining acute inflammatory reactions.

IRAK2 directs stimulus-dependent nuclear export of inflammatory mRNAs

Expression of inflammatory genes is determined in part by post-transcriptional regulation of mRNA metabolism but how stimulus- and transcript-dependent nuclear export influence is poorly understood. Here, we report a novel pathway in which LPS/TLR4 engagement promotes nuclear localization of IRAK2 to facilitate nuclear export of a specific subset of inflammation-related mRNAs for translation in murine macrophages. IRAK2 kinase activity is required for LPS-induced RanBP2-mediated IRAK2 sumoylation and subsequent nuclear translocation. Array analysis showed that an SRSF1-binding motif is enriched in mRNAs dependent on IRAK2 for nuclear export. Nuclear IRAK2 phosphorylates SRSF1 to reduce its binding to target mRNAs, which promotes the RNA binding of the nuclear export adaptor ALYREF and nuclear export receptor Nxf1 loading for the export of the mRNAs. In summary, LPS activates a nuclear function of IRAK2 that facilitates the assembly of nuclear export machinery to export selected inflammatory mRNAs to the cytoplasm for translation.

The innate immune system is the body’s first line of defense against invading microbes. Some immune cells carry specific receptor proteins called Toll-like receptors that can identify microbes and the signals they emit. As soon as the receptors have detected a threat – for example through sensing oily molecules that make up the cell membranes of microbes – they produce signaling proteins called cytokines and chemokines to alert other immune cells.

The DNA in the cell’s nucleus carries the instructions needed to make proteins. To produce proteins, including cytokines and chemokines, the information first has to be transferred into mRNA templates, which carry the instructions to the sites in the cell where the proteins are made. Cytokine and chemokine mRNAs are generally short-lived, but previous studies in 2009 and 2011 have shown that an enzyme called IRAK2 can stabilize them to make them last longer. IRAK enzymes are activated by the Toll-like receptors after a threat has been detected. However, until now it was not known whether IRAK2 also helps to transport the mRNAs of cytokines and chemokines out of the cell nucleus.

Using immune cells of mice, Zhou et al. – including some of the researchers involved in the previous studies – discovered that IRAK2 helped to export the mRNAs of cytokines and chemokines from the immune cell nucleus into the surrounding cell fluid. The Toll-like receptors recognized the oily molecules of the microbes and consequently activated IRAK2, which lead to IRAK2 being moved into the cell nucleus.

Once activated, IRAK2 helped to assemble the export machinery that moved selected mRNAs out of the nucleus to build the proteins. To do so, IRAK2 stopped a destabilizing protein from binding to the mRNA, so that instead the export machinery could transport the mRNA of the cytokines and chemokines out of the cell nucleus.

A next step will be to test whether IRAK2 is required to guide exported mRNA tothe sites in the cell where the proteins are made. This new insight could help to develop new treatments for various diseases. For example, diseases in which the immune system attacks the cells of the body, rather than invaders, can be caused by too many cytokines and chemokines. Since IRAK2 helps to control the availability of cytokines and chemokines it may in future be used as a new drug target.

Leucine-Rich Repeat Kinase 2 (LRRK2) Stimulates IL-1β-Mediated Inflammatory Signaling through Phosphorylation of RCAN1

Leucine-rich repeat kinase 2 (LRRK2) is a Ser/Thr kinase having mixed lineage kinase-like and GTPase domains, controlling neurite outgrowth and neuronal cell death. Evidence suggests that LRRK2 is involved in innate immune response signaling, but the underlying mechanism is yet unknown. A novel protein inhibitor of phosphatase 3B, RCAN1, is known to positively regulate inflammatory signaling through modulation of several intracellular targets of interleukins in immune cells. In the present study, we report that LRRK2 phosphorylates RCAN1 (RCAN1-1S) and is markedly up-regulated during interleukin-1β (IL-1β) treatment. During IL-1β treatment, LRRK2-mediated phosphorylation of RCAN1 promoted the formation of protein complexes, including that between Tollip and RCAN1. LRRK2 decreased binding between Tollip and IRAK1, which was accompanied by increased formation of the IRAK1-TRAF6 complex. TAK1 activity was significantly enhanced by LRRK2. Furthermore, LRRK2 enhanced transcriptional activity of NF-κB and cytokine IL-8 production. These findings suggest that LRRK2 might be important in positively modulating IL-1β-mediated signaling through selective phosphorylation of RCAN1.

Thymoquinone: An IRAK1 inhibitor with in vivo and in vitro anti-inflammatory activities

Thymoquinone (TQ) is a bioactive component of black seed (Nigella sativa) volatile oil and has been shown to have anti-oxidative, anti-inflammatory, and anti-cancer properties. In the present study, we explored the molecular mechanisms that underlie the anti-inflammatory effect of TQ and its target proteins using lipopolysaccharide (LPS)-stimulated murine macrophage-like RAW264.7 and human monocyte-like U937 cells, together with LPS/D-galactosamine (GalN)-induced acute hepatitis and HCl/EtOH-induced gastritis mouse models. TQ strongly inhibited the production of nitric oxide (NO) and repressed NO synthase (iNOS), tumor necrosis factor (TNF)-α, cyclooxygenase (COX)−2, interleukin (IL)−6, and IL-1β expression in LPS-activated RAW264.7 cells. Treatment of LPS/D-GalN–induced hepatitis and EtOH/HCl–induced gastritis mouse models with TQ significantly ameliorated disease symptoms. Using luciferase reporter gene assays, we also showed that the nuclear levels of transcription factors and phosphorylation patterns of signaling proteins, activator protein (AP)−1, and nuclear factor (NF)-κB pathways were all affected by TQ treatment. Finally, we used additional kinase and luciferase validation assays with interleukin-1 receptor-associated kinase 1 (IRAK1) to show that IRAK1 is directly suppressed by TQ treatment. Together, these findings strongly suggest that the anti-inflammatory actions of TQ are caused by suppression of IRAK-linked AP-1/NF-κB pathways.

IRAKM-Mincle axis links cell death to inflammation: Pathophysiological implications for chronic alcoholic liver disease

Lipopolysaccharide (LPS)-mediated activation of Toll-like receptors (TLRs) in hepatic macrophages and injury to hepatocytes are major contributors to the pathogenesis of alcoholic liver disease. However, the mechanisms by which TLR-dependent inflammatory responses and alcohol-induced hepatocellular damage coordinately lead to alcoholic liver disease are not completely understood. In this study, we found that mice deficient in interleukin-1 receptor-associated kinase M (IRAKM), a proximal TLR pathway molecule typically associated with inhibition of TLR signaling, were actually protected from chronic ethanol-induced liver injury. In bone marrow-derived macrophages challenged with low concentrations of LPS, which reflect the relevant pathophysiological levels of LPS in both alcoholic patients and ethanol-fed mice, the IRAKM Myddosome was preferentially formed. Further, the IRAKM Myddosome mediated the up-regulation of Mincle, a sensor for cell death. Mincle-deficient mice were also protected from ethanol-induced liver injury. The endogenous Mincle ligand spliceosome-associated protein 130 (SAP130) is a danger signal released by damaged cells; culture of hepatocytes with ethanol increased the release of SAP130. Ex vivo studies in bone marrow-derived macrophages suggested that SAP130 and LPS synergistically activated inflammatory responses, including inflammasome activation.

CONCLUSION

This study reveals a novel IRAKM-Mincle axis that contributes to the pathogenesis of ethanol-induced liver injury. (Hepatology 2016;64:1978-1993).

IinQ attenuates systemic inflammatory responses via selectively impairing the Myddosome complex formation upon TLR4 ligation

A specific small-molecule inhibitor of the TLR4 signaling complex upstream of the IKK would likely provide therapeutic benefit for NF-κB-mediated inflammatory disease. We previously identified brazilin as a selective upstream IKK inhibitor targeting the Myddosome complex. In this study, using a cell-based ubiquitination assay for IRAK1 and a chemical library comprising a series of structural analogues of brazilin, a novel small molecule, 2-hydroxy-5,6-dihydroisoindolo[1,2-a]isoquinoline-3,8-dione (IinQ), was identified as a selective and potent inhibitor of IRAK1-dependent NF-κB activation upon TLR4 ligation. In RAW264.7 macrophages, IinQ drastically suppressed activation of upstream IKK signaling events including membrane-bound IRAK1 ubiquitination and IKK phosphorylation by the TLR4 ligand, resulting in reduced expression of proinflammatory mediators including IL-6, TNF-α, and nitric oxide. Interestingly, IinQ did not suppress NF-κB activation via the TLR3 ligand, DNA damaging agents, or a protein kinase C activator, indicating IinQ is specific for TLR4 signaling. Analysis of upstream signaling events further confirmed that IinQ disrupts the MyD88-IRAK1-TRAF6 complex formation induced by LPS treatment, without affecting TLR4 oligomerization. Moreover, intravenous administration of IinQ significantly reduced lethality and attenuated systemic inflammatory responses in an in vivo mouse model of endotoxin shock following LPS challenge. Thus, IinQ represents a novel class of brazilin analogues with improved potency and specificity toward disruption of Myddosome complex formation in TLR4 signaling, indicating that IinQ may be a promising therapeutic candidate for the treatment of systemic inflammatory diseases.

Rotavirus Strategies Against the Innate Antiviral System

"Rotaviruses represent the most important etiological agents of acute, severe gastroenteritis in the young of many animal species, including humans." This statement, variations of which are a common beginning in articles about rotaviruses, reflects the fact that these viruses have evolved efficient strategies for evading the innate immune response of the host and for successfully replicating in the population. In this review, we summarize what is known about the defense mechanisms that host cells employ to prevent rotavirus invasion and the countermeasures that these viruses have successfully developed to surpass cellular defenses. Rotaviruses use at least two viral multifunctional proteins to directly interact with, and prevent the activation of, the interferon system, and they use at least one other protein to halt the protein synthesis machinery and prevent the expression of most of the transcriptional antiviral program of the cell. Characterization of the confrontation between rotaviruses and their host cells has allowed us to learn about the virus-host coevolution that prevents the damaging effects of the innate immune response.

Regulation of Transforming Growth Factor β-Activated Kinase Activation by Epigallocatechin-3-Gallate in Rheumatoid Arthritis Synovial Fibroblasts: Suppression of K(63) -Linked Autoubiquitination of Tumor Necrosis Factor Receptor-Associated Factor 6

OBJECTIVE

Transforming growth factor β-activated kinase 1 (TAK1) is a key MAPKKK family protein in interleukin-1β (IL-1β), tumor necrosis factor (TNF), and Toll-like receptor signaling. This study was undertaken to examine the posttranslational modification of TAK1 and its therapeutic regulation in rheumatoid arthritis (RA).

METHODS

The effect of TAK1, IL-1 receptor-associated kinase 1 (IRAK-1), and TNF receptor-associated factor 6 (TRAF6) inhibition was evaluated in IL-1β-stimulated human RA synovial fibroblasts (RASFs). Western blotting, immunoprecipitation, and 20S proteasome assay were used to study the ubiquitination process in RASFs. The efficacy of epigallocatechin-3-gallate (EGCG), a potent antiinflammatory molecule, in regulating these processes in RASFs was evaluated. Molecular docking was performed to examine the interaction of EGCG with human TAK1, IRAK-1, and TRAF6. These findings were confirmed using a rat model of adjuvant-induced arthritis (AIA).

RESULTS

Inhibition of TAK1, but not IRAK-1 or TRAF6, completely abrogated IL-1β-induced IL-6 and IL-8 synthesis in RASFs. EGCG inhibited TAK1 phosphorylation at Thr(184/187) and occupied the C(174) position, an ATP-binding site, to inhibit its kinase activity. EGCG pretreatment also inhibited K(63) -linked autoubiquitination of TRAF6, a posttranslational modification essential for TAK1 autophosphorylation, by forming a stable H bond at the K(124) position on TRAF6. Furthermore, EGCG enhanced proteasome-associated deubiquitinase expression to rescue proteins from proteasomal degradation. Western blot analyses of joint homogenates from rats with AIA showed a significant increase in K(48) -linked polyubiquitination, TAK1 phosphorylation, and TRAF6 expression when compared to naive rats. Administration of EGCG (50 mg/kg/day) for 10 days ameliorated AIA in rats by reducing TAK1 phosphorylation and K(48) -linked polyubiquitination.

CONCLUSION

Our findings provide a rationale for targeting TAK1 for the treatment of RA with EGCG.

A herbal formula comprising Rosae Multiflorae Fructus and Lonicerae Japonicae Flos inhibits the production of inflammatory mediators and the IRAK-1/TAK1 and TBK1/IRF3 pathways in RAW 264.7 and THP-1 cells

ETHNOPHARMACOLOGICAL RELEVANCE

As documented in the Chinese Materia Medica Grand Dictionary (), a herbal formula (RL) consisting of Rosae Multiflorae Fructus (multiflora rose hips) and Lonicerae Japonicae Flos (Japanese honeysuckle flowers) has traditionally been used in treating inflammatory disorders. RL was previously reported to inhibit the expression of various inflammatory mediators regulated by NF-κB and MAPKs that are components of the TLR4 signalling pathways.

AIM OF THE STUDY

This study aims to provide further justification for clinical application of RL in treating inflammatory disorders by further delineating the involvement of the TLR4 signalling cascades in the effects of RL on inflammatory mediators.

MATERIALS AND METHODS

RL consisting of Rosae Multiflorae Fructus and Lonicerae Japonicae Flos (in 5:3 ratio) was extracted using absolute ethanol. We investigated the effect of RL on the production of cytokines and chemokines that are regulated by three key transcription factors of the TLR4 signalling pathways AP-1, NF-κB and IRF3 in LPS-stimulated RAW264.7 cells using the multiplex biometric immunoassay. Phosphorylation of AP-1, NF-κB, IRF3, IκB-α, IKKα/β, Akt, TAK1, TBK1, IRAK-1 and IRAK-4 were examined in LPS-stimulated RAW264.7 cells and THP-1 cells using Western blotting. Nuclear localizations of AP-1, NF-κB and IRF3 were also examined using Western blotting.

RESULTS

RL reduced the secretion of various pro-inflammatory cytokines and chemokines regulated by transcription factors AP-1, NF-κB and IRF3. Phosphorylation and nuclear protein levels of these transcription factors were decreased by RL treatment. Moreover, RL inhibited the activation/phosphorylation of IκB-α, IKKα/β, TAK1, TBK1 and IRAK-1.

CONCLUSIONS

Suppression of the IRAK-1/TAK1 and TBK1/IRF3 signalling pathways was associated with the effect of RL on inflammatory mediators in LPS-stimulated RAW264.7 and THP-1 cells. This provides further pharmacological basis for the clinical application of RL in the treatment of inflammatory disorders.

Pellino-3 promotes endotoxin tolerance and acts as a negative regulator of TLR2 and TLR4 signaling

Development of endotoxin tolerance in macrophages during sepsis reprograms Toll-like receptor 4 signaling to inhibit proinflammatory cytokines without suppressing anti-inflammatory and antimicrobial mediators and protects the host from excessive inflammation and tissue damage. However, endotoxin tolerance renders septic patients immunocompromised and unable to control secondary infections. Although previous studies have revealed the importance of several negative regulators of Toll-like receptor signaling in endotoxin tolerance, the role of Pellino proteins has not been addressed. The present report shows that the induction of endotoxin tolerance in vivo in mice and in vitro in human monocytes and THP-1 and MonoMac-6 macrophages increases the expression of Pellino-3. Overexpression of Pellino-3 in human embryonic kidney 293/Toll-like receptor 2 or 293/Toll-like receptor 4/myeloid differentiation factor-2 cells inhibited Toll-like receptor 2/4-mediated activation of nuclear factor-κB and induction of CXCL-8 mRNA, and Pellino-3 ablation increased these responses. Pellino-3-deficient THP-1 cells had elevated Toll-like receptor 2/4-driven tumor necrosis factor-α, interleukin-6 mRNA, and Toll-like receptor 4-driven CCL5 gene expression in response to Toll-like receptor agonists and heat-killed Escherichia coli and Staphylococcus aureus, cytokines controlled by the MyD88 and Toll-interleukin-1R domain-containing protein inducing interferon-β-mediated pathways, respectively. In addition, deficiency in Pellino-3 slightly increased phagocytosis of heat-killed bacteria. Transfected Pellino-3 inhibited nuclear factor-κB activation driven by overexpression of MyD88, TIR domain-containing adapter inducing interferon-β, interleukin-1R-associated kinase-1, and tumor necrosis factor receptor activator of nuclear factor-κB-binding kinase-1, TGF-β-activated kinase 1, and tumor necrosis factor receptor-associated factor-6, and inhibited interleukin-1R-associated kinase 1 modifications and tumor necrosis factor receptor activator of nuclear factor-κB-binding kinase 1 phosphorylation. Finally, Pellino-3 ablation in THP-1 decreased the extent of endotoxin tolerization. Thus, Pellino-3 is involved in endotoxin tolerance and functions as a negative regulator of Toll-like receptor 2/4 signaling.

Interleukin-1 receptor associated kinase inhibitors: potential therapeutic agents for inflammatory- and immune-related disorders

The various cells of innate immune system quickly counter-attack invading pathogens, and mount up "first line" defense through their trans-membrane receptors including Toll-like receptors (TLRs) and interleukin receptors (IL-Rs) that result in the secretion of pro-inflammatory cytokines. Albeit such inflammatory responses are beneficial in pathological conditions, their overstimulation may cause severe inflammatory damage; thus, make this defense system a "double edged sword". IRAK-4 has been evaluated as an indispensable element of IL-Rs and TLR pathways that can regulate the abnormal levels of cytokines, and therefore could be employed to manage immune- and inflammation-related disorders. Historically, the identification of selective and potent inhibitors has been challenging; thus, a limited number of small molecule IRAK-4 inhibitors are available in literature. Recently, IRAK-4 achieved great attention, when Ligand® pharmaceutical and Nimbus Discovery® reported the beneficial potentials of IRAK-4 inhibitors in the pre-clinical evaluation for various inflammatory- and immune-related disorders, but not limited to, such as rheumatoid arthritis, inflammatory bowel disease, psoriasis, gout, asthma and cancer.

Putative E3 ubiquitin ligase of human rotavirus inhibits NF-κB activation by using molecular mimicry to target β-TrCP

NF-κB plays a critical role in the induction and maintenance of innate and adaptive immune transcriptional programs. An associated inhibitor of κB protein (IκB) regulates NF-κB activation and contains a degron motif (DSGΦxS) that undergoes phosphorylation following pathogen recognition or other proinflammatory signals. The E3 ubiquitin ligase SCF^β-TrCP recognizes this phosphodegron through its β-transducin repeat-containing protein (β-TrCP) subunit and induces IκB degradation, allowing NF-κB to translocate to the nucleus and modulate gene expression. Rotavirus (RV), a major cause of pediatric gastroenteritis, can block NF-κB activation through the action of its nonstructural protein NSP1, a putative E3 ubiquitin ligase that mediates the degradation of β-TrCP or other immunomodulatory proteins in a virus strain-specific manner. Here, we show that NSP1 targets β-TrCP by mimicking the IκB phosphodegron. The NSP1 proteins of most human and porcine RV strains conserve a C-terminal phosphodegron-like (PDL) motif, DSGΦS. Deletion of this motif or mutation of its serine residues disrupts NSP1-mediated degradation of β-TrCP and inhibition of NF-κB activation. Additionally, a point mutation within the phosphodegron-binding pocket protects β-TrCP from NSP1-mediated turnover. Fusion of the PDL motif to an NSP1 protein known to target other immunomodulatory proteins generates a chimeric NSP1 protein that can induce β-TrCP degradation and block NF-κB activation. Other viral proteins (Epstein-Barr virus LMP1, HIV-1 Vpu, and vaccinia virus A49) also contain a PDL motif and interact with β-TrCP to inhibit NF-κB activation. Taken together, these data suggest that targeting β-TrCP by molecular mimicry may be a common strategy used by human viruses to evade the host immune response.

IMPORTANCE   The transcription factor NF-κB, a central regulator of the host response to infection, is a frequent target of viral antagonism. Pathogen detection activates NF-κB by inducing the phosphorylation of an associated inhibitor protein (IκB), which targets IκB for degradation by the E3 ubiquitin ligase β-TrCP. Rotavirus, a significant cause of childhood gastroenteritis, antagonizes NF-κB through the activity of its NSP1 protein, a putative E3 ubiquitin ligase that mediates β-TrCP turnover. Here, we show that NSP1 functions by mimicking the IκB phosphodegron recognized by β-TrCP. Nearly all human rotavirus strains conserve this motif at the NSP1 C terminus, and its removal disrupts NSP1 antagonist activity. This sequence conserves the biochemical properties of the IκB phosphodegron and can rescue antagonist activity when fused to an NSP1 protein otherwise inactive against β-TrCP. Other viral proteins also mimic IκB to disrupt NF-κB activation, indicating that this is an important immune evasion strategy.

The transcription factor NF-κB, a central regulator of the host response to infection, is a frequent target of viral antagonism. Pathogen detection activates NF-κB by inducing the phosphorylation of an associated inhibitor protein (IκB), which targets IκB for degradation by the E3 ubiquitin ligase β-TrCP. Rotavirus, a significant cause of childhood gastroenteritis, antagonizes NF-κB through the activity of its NSP1 protein, a putative E3 ubiquitin ligase that mediates β-TrCP turnover. Here, we show that NSP1 functions by mimicking the IκB phosphodegron recognized by β-TrCP. Nearly all human rotavirus strains conserve this motif at the NSP1 C terminus, and its removal disrupts NSP1 antagonist activity. This sequence conserves the biochemical properties of the IκB phosphodegron and can rescue antagonist activity when fused to an NSP1 protein otherwise inactive against β-TrCP. Other viral proteins also mimic IκB to disrupt NF-κB activation, indicating that this is an important immune evasion strategy.

The pellino e3 ubiquitin ligases recognize specific phosphothreonine motifs and have distinct substrate specificities

The four mammalian Pellinos (Pellinos 1, 2, 3a, and 3b) are E3 ubiquitin ligases that are emerging as critical mediators for a variety of immune signaling pathways, including those activated by Toll-like receptors, the T-cell receptor, and NOD2. It is becoming increasingly clear that each Pellino has a distinct role in facilitating immune receptor signaling. However, the underlying mechanisms by which these highly homologous proteins act selectively in these signaling pathways are not clear. In this study, we investigate whether Pellino substrate recognition contributes to the divergent functions of Pellinos. Substrate recognition of each Pellino is mediated by its noncanonical forkhead-associated (FHA) domain, a well-characterized phosphothreonine-binding module. Pellino FHA domains share very high sequence identity, so a molecular basis for differences in substrate recognition is not immediately apparent. To explore Pellino substrate specificity, we first identify a high-affinity Pellino2 FHA domain-binding motif in the Pellino substrate, interleukin-1 receptor-associated kinase 1 (IRAK1). Analysis of binding of the different Pellinos to a panel of phosphothreonine-containing peptides derived from the IRAK1-binding motif reveals that each Pellino has a distinct phosphothreonine peptide binding preference. We observe a similar binding specificity in the interaction of Pellinos with a number of known Pellino substrates. These results argue that the nonredundant roles that Pellinos play in immune signaling are in part due to their divergent substrate specificities. This new insight into Pellino substrate recognition could be exploited for pharmacological advantage in treating inflammatory diseases that have been linked to the aberrant regulation of Pellinos.

Anti-inflammatory activities and mechanisms of Artemisia asiatica ethanol extract

ETHNOPHARMACOLOGICAL RELEVANCE

Artemisia asiatica Nakai (Compositae) is a representative herbal plant used to treat infection and inflammatory diseases. Although Artemisia asiatica is reported to have immunopharmacological activities, the mechanisms of these activities and the effectiveness of Artemisia asiatica preparations in use are not known.

MATERIALS AND METHODS

To evaluate the anti-inflammatory activities of Artemisia asiatica ethanol extract (Aa-EE), we assayed nitric oxide (NO), tumor necrosis factor (TNF)-α, and prostaglandin E2 (PGE2) in macrophages and measured the extent of tissue injury in a model of gastric ulcer induced in mice by treatment with HCl in EtOH. Putative enzymatic mediators of Aa-EE activities were identified by nuclear fractionation, reporter gene assay, immunoprecipitation, immunoblotting, and kinase assay. Active compound in Aa-EE was identified using HPLC.

RESULTS

Treatment of RAW264.7 cells and peritoneal macrophages with Aa-EE suppressed the production of NO, PGE2, and TNF-α in response to lipopolysaccharide (LPS) and induced heme oxygenase-1 expression. The Aa-EE also ameliorated symptoms of gastric ulcer in HCl/EtOH-treated mice. These effects were associated with the inhibition of nuclear translocation of nuclear factor (NF)-κB and activator protein (AP)-1, implying that the anti-inflammatory action of the Aa-EE occurred through transcriptional inhibition. The upstream regulatory signals Syk and Src for translocation of NF-κB and TRAF6 for AP-1 were identified as targets of this effect. Analysis of Aa-EE by HPLC revealed the presence of luteolin, known to inhibit NO and PGE2 activity.

CONCLUSION

The anti-inflammatory activities attributed to Artemisia asiatica Nakai in traditional medicine may be mediated by luteolin through inhibition of Src/Syk/NF-κB and TRAF6/JNK/AP-1 signaling pathways.

MEK1 promotes YAP and their interaction is critical for tumorigenesis in liver cancer

Mitogen-activated protein kinase kinase 1 (MAP2K1/MEK1) as well as Yes-associated protein (YAP), the downstream effector of Hippo signaling pathway, is linked to hepatocarcinogenesis. However, little is known about whether and how MEK1 interacts with YAP. In this study, we find that MEK1-YAP interaction is critical for liver cancer cell proliferation and maintenance of transformed phenotypes both in vitro and in vivo. Moreover, MEK1 and YAP proteins are closely correlated in human liver cancer samples. Mechanistically, inhibition of MEK1 by both PD98059 and U0126 as well as RNAi reduces beta-transducin repeat containing E3 ubiquitin protein ligase (BTRC), which acts as a potential endogenous YAP protector.

Methanol extract of Hopea odorata suppresses inflammatory responses via the direct inhibition of multiple kinases

ETHNOPHARMACOLOGICAL RELEVANCE

Hopea odorata Roxb. (Dipterocarpaceae) is a representative Thai ethnopharmacological herbal plant used in the treatment of various inflammation-related diseases. In spite of its traditional use, systematic studies of its anti-inflammatory action have not been performed.

MATERIALS AND METHODS

The inhibitory activities of a Hopea odorata methanol extract (Ho-ME) on the production of nitric oxide (NO), tumour necrosis factor (TNF)-α, and prostaglandin E(2) (PGE(2)) in RAW264.7 cells and peritoneal macrophages were investigated. The effects of Ho-ME on the gastritis symptoms induced by HCl/EtOH and on ear oedemas induced by arachidonic acid were also examined. Furthermore, to identify the immunopharmacological targets of this extract, nuclear fractionation, a reporter gene assay, immunoprecipitation, immunoblot analysis, and a kinase assay were employed.

RESULTS

Ho-ME strongly inhibited the release of NO, PGE(2), and TNF-α in RAW264.7 cells and peritoneal macrophages stimulated by lipopolysaccharide (LPS). Ho-ME also clearly suppressed the gene expression of pro-inflammatory cytokines and chemokines, such as interferon (IFN)-β, interleukin (IL)-12, and monocyte chemotactic protein-1 (MCP-1). By analysing the inhibited target molecules, Syk and Src were found to be suppressed in the inhibition of nuclear factor (NF)-κB pathway. In addition, the observed downregulation of activator protein (AP)-1 and cAMP response element-binding (CREB) was due to the direct inhibition of interleukin-1 receptor-associated kinase (IRAK)1 and IRAK4, which was also linked to the suppression of c-Jun N-terminal kinase (JNK) and p38. In agreement with the in vitro observations, this extract also ameliorated the inflammatory symptoms in EtOH/HCl-induced gastritis and arachidonic acid-induced ear oedemas in mice.

CONCLUSION

Ho-ME has potential as a functional herbal remedy targeting Syk- and Src-mediated anti-inflammatory mechanisms. Future pre-clinical studies will be needed to investigate this possibility.