The kinase activities of interleukin-1 receptor associated kinase (IRAK)-1 and 4 are redundant in the control of inflammatory cytokine expression in human cells

Geraniin from the methanol extract of Pilea mongolica suppresses LPS-induced inflammatory responses by inhibiting IRAK4/MAPKs/NF-κB/AP-1 pathway in HaCaT cells

The skin acts as a vital barrier, shielding the body from external threats that can trigger dryness, itching, and inflammation. Pilea mongolica, a traditional Chinese medicinal herb, holds promise for various ailments, yet its anti-inflammatory properties remain understudied. This study aimed to explore the potential anti-inflammatory effects of the methanol extract of P. mongolica (MEPM) and its underlying molecular mechanisms and active compounds in LPS-stimulated human keratinocytes. MEPM treatment, at concentrations without cytotoxicity, significantly decreased NO productions and the iNOS, IL-6, IL-1β, and TNF-α levels in LPS-induced HaCaT cells. Moreover, MEPM suppressed IRAK4 expression and phosphorylation of JNK, ERK, p38, p65, and c-Jun, suggesting that the anti-inflammatory effects of MEPM result from the inhibition of IRAK4/MAPK/NF-κB/AP-1 signaling pathway. Through LC/MS/MS analysis, 30 compounds and 24 compounds were estimated in negative and positive modes, respectively, including various anti-inflammatory compounds, such as corilagin and geraniin. Through HPLC analysis, geraniin was found to be present in MEPM at a concentration of 18.87 mg/g. Similar to MEPM, geraniin reduced iNOS mRNA expression and inhibited NO synthesis. It also decreased mRNA and protein levels of inflammatory cytokines, including IL-6 and TNF-α, and inhibited IRAK4 expression and the phosphorylation of MAPKs, NF-κB, and AP-1 pathways. Therefore, it can be inferred that the anti-inflammatory effects of MEPM are attributable to geraniin. Thus, MEPM and its active compound geraniin are potential candidates for use in natural functional cosmetics.

A small molecule potent IRAK4 inhibitor abrogates lipopolysaccharide-induced macrophage inflammation in-vitro and in-vivo

Increasing evidence supports vanillin and its analogs as potent toll-like receptor signaling inhibitors that strongly attenuate inflammation, though, the underlying molecular mechanism remains elusive. Here, we report that vanillin inhibits lipopolysaccharide (LPS)-induced toll-like receptor 4 activation in macrophages by targeting the myeloid differentiation primary-response gene 88 (MyD88)-dependent pathway through direct interaction and suppression of interleukin-1 receptor-associated kinase 4 (IRAK4) activity. Moreover, incubation of vanillin in cells expressing constitutively active forms of different toll-like receptor 4 signaling molecules revealed that vanillin could only able to block the ligand-independent constitutively activated IRAK4/1 or its upstream molecules-associated NF-κB activation and NF-κB transactivation along with the expression of various proinflammatory cytokines. A significant inhibition of LPS-induced IRAK4/MyD88, IRAK4/IRAK1, and IRAK1/TRAF6 association was evinced in response to vanillin treatment. Furthermore, mutations at Tyr262 and Asp329 residues in IRAK4 or modifications of 3-OMe and 4-OH side groups in vanillin, significantly reduced IRAK4 activity and vanillin function, respectively. Mice pretreated with vanillin followed by LPS challenge markedly impaired LPS-induced IRAK4 activation and inflammation in peritoneal macrophages. Thus, the present study posits vanillin as a novel and potent IRAK4 inhibitor and thus providing an opportunity for its therapeutic application in managing various inflammatory diseases.

IRAK1 and IRAK4 as emerging therapeutic targets in hematologic malignancies

PURPOSE OF REVIEW

Cell intrinsic and extrinsic perturbations to inflammatory signaling pathways are a hallmark of development and progression of hematologic malignancies. The interleukin 1 receptor-associated kinases (IRAKs) are a family of related signaling intermediates (IRAK1, IRAK2, IRAK3, IRAK4) that operate at the nexus of multiple inflammatory pathways implicated in the hematologic malignancies. In this review, we explicate the oncogenic role of these kinases and review recent therapeutic advances in the dawning era of IRAK-targeted therapy.

RECENT FINDINGS

Emerging evidence places IRAK signaling at the confluence of adaptive resistance and oncogenesis in the hematologic malignancies and solid tissue tumors. Preclinical investigations nominate the IRAK kinases as targetable molecular dependencies in diverse cancers.

SUMMARY

IRAK-targeted therapies that have matriculated to early phase trials are yielding promising preliminary results. However, studies of IRAK kinase signaling continue to defy conventional signaling models and raise questions as to the design of optimal treatment strategies. Efforts to refine IRAK signaling mechanisms in the malignant context will inspire deliberate IRAK-targeted drug development and informed combination therapy.

Multiscale interactome analysis coupled with off-target drug predictions reveals drug repurposing candidates for human coronavirus disease

The COVID-19 pandemic has highlighted the urgent need for the identification of new antiviral drug therapies for a variety of diseases. COVID-19 is caused by infection with the human coronavirus SARS-CoV-2, while other related human coronaviruses cause diseases ranging from severe respiratory infections to the common cold. We developed a computational approach to identify new antiviral drug targets and repurpose clinically-relevant drug compounds for the treatment of a range of human coronavirus diseases. Our approach is based on graph convolutional networks (GCN) and involves multiscale host-virus interactome analysis coupled to off-target drug predictions. Cell-based experimental assessment reveals several clinically-relevant drug repurposing candidates predicted by the in silico analyses to have antiviral activity against human coronavirus infection. In particular, we identify the MET inhibitor capmatinib as having potent and broad antiviral activity against several coronaviruses in a MET-independent manner, as well as novel roles for host cell proteins such as IRAK1/4 in supporting human coronavirus infection, which can inform further drug discovery studies.

The Interleukin-1 Receptor-Associated Kinase 4 Inhibitor PF-06650833 Blocks Inflammation in Preclinical Models of Rheumatic Disease and in Humans Enrolled in a Randomized Clinical Trial

OBJECTIVE

To investigate the role of PF-06650833, a highly potent and selective small-molecule inhibitor of interleukin-1-associated kinase 4 (IRAK4), in autoimmune pathophysiology in vitro, in vivo, and in the clinical setting.

METHODS

Rheumatoid arthritis (RA) inflammatory pathophysiology was modeled in vitro through 1) stimulation of primary human macrophages with anti-citrullinated protein antibody immune complexes (ICs), 2) RA fibroblast-like synoviocyte (FLS) cultures stimulated with Toll-like receptor (TLR) ligands, as well as 3) additional human primary cell cocultures exposed to inflammatory stimuli. Systemic lupus erythematosus (SLE) pathophysiology was simulated in human neutrophils, dendritic cells, B cells, and peripheral blood mononuclear cells stimulated with TLR ligands and SLE patient ICs. PF-06650833 was evaluated in vivo in the rat collagen-induced arthritis (CIA) model and the mouse pristane-induced and MRL/lpr models of lupus. Finally, RNA sequencing data generated with whole blood samples from a phase I multiple-ascending-dose clinical trial of PF-06650833 were used to test in vivo human pharmacology.

RESULTS

In vitro, PF-06650833 inhibited human primary cell inflammatory responses to physiologically relevant stimuli generated with RA and SLE patient plasma. In vivo, PF-06650833 reduced circulating autoantibody levels in the pristane-induced and MRL/lpr murine models of lupus and protected against CIA in rats. In a phase I clinical trial (NCT02485769), PF-06650833 demonstrated in vivo pharmacologic action pertinent to SLE by reducing whole blood interferon gene signature expression in healthy volunteers.

CONCLUSION

These data demonstrate that inhibition of IRAK4 kinase activity can reduce levels of inflammation markers in humans and provide confidence in the rationale for clinical development of IRAK4 inhibitors for rheumatologic indications.

Role of Inflammation in the Development of Colorectal Cancer

Chronic inflammation can lead to the development of many diseases, including cancer. Inflammatory bowel disease (IBD) that includes both ulcerative colitis (UC) and Crohnmp's disease (CD) are risk factors for the development of colorectal cancer (CRC). Many cytokines produced primarily by the gut immune cells either during or in response to localized inflammation in the colon and rectum are known to stimulate the complex interactions between the different cell types in the gut environment resulting in acute inflammation. Subsequently, chronic inflammation, together with genetic and epigenetic changes, have been shown to lead to the development and progression of CRC. Various cell types present in the colon, such as enterocytes, Paneth cells, goblet cells, and macrophages, express receptors for inflammatory cytokines and respond to tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), IL-6, and other cytokines. Among the several cytokines produced, TNF-α and IL-1β are the key pro-inflammatory molecules that play critical roles in the development of CRC. The current review is intended to consolidate the published findings to focus on the role of pro-inflammatory cytokines, namely TNF-α and IL-1β, on inflammation (and the altered immune response) in the gut, to better understand the development of CRC in IBD, using various experimental model systems, preclinical and clinical studies. Moreover, this review also highlights the current therapeutic strategies available (monotherapy and combination therapy) to alleviate the symptoms or treat inflammation-associated CRC by using monoclonal antibodies or aptamers to block pro-inflammatory molecules, inhibitors of tyrosine kinases in the inflammatory signaling cascade, competitive inhibitors of pro-inflammatory molecules, and the nucleic acid drugs like small activating RNAs (saRNAs) or microRNA (miRNA) mimics to activate tumor suppressor or repress oncogene/pro-inflammatory cytokine gene expression.

Nck1 is a critical adaptor between proatherogenic blood flow, inflammation, and atherosclerosis

Atherosclerosis is an inflammatory condition of the arteries that has profound incidence and increasing prevalence. Although endothelial cells detect changes in blood flow, how endothelial activation contributes to atherogenic inflammation is not well understood. In this issue of the JCI, Alfaidi et al. used mouse models to explore flow-induced endothelial activation. The authors revealed a role for Nck1 and a specific activator of the innate immune response, the downstream interleukin receptor-associated kinase-1 (IRAK-1) in NF-κB-mediated inflammation and atherosclerosis susceptibility. These results link disturbed blood flow to NF-κB-mediated inflammation, which promotes atherosclerosis, and provide Nck1 as a potential target for the treatment of atherosclerosis.

Central IRAK-4 kinase inhibition for the treatment of pain following nerve injury in rats

There is ample evidence for the role of the immune system in developing chronic pain following peripheral nerve injury. Especially Toll-like receptors (TLRs) and their associated signaling components and pro-inflammatory cytokines such as IL-1β, induced after injury, are involved in nociceptive processes and believed to contribute to the manifestation of chronic neuropathic pain states. Whereas the inhibition of the kinase function of IRAK-4, a central kinase downstream of TLRs and IL-1 receptors (IL-1Rs), seems efficacious in various chronic inflammatory and autoimmune models, it's role in regulating chronic neuropathic pain remained elusive to date. Here, we examined whether pharmacological inhibition of IRAK-4 kinase activity using PF-06650833 and BMS-986147, two clinical-stage kinase inhibitors, is effective for controlling persistent pain following nerve injury. Both inhibitors potently inhibited TLR-triggered cytokine release in human peripheral blood mononuclear cell (PBMC) as well as human and rat whole blood cultures. BMS-986147 showing favorable pharmacokinetic (PK) properties, significantly inhibited R848-triggered plasma TNF levels in a rat in vivo cytokine release model after single oral dosing. However, BMS-986147 dose dependently reversed cold allodynia in a rat chronic constriction injury (CCI) model following intrathecal administration only, supporting the notion that central neuro-immune modulation is beneficial for treating chronic neuropathic pain. Although both inhibitors were efficacious in inhibiting IL-1β- or TLR-triggered cytokine release in rat dorsal root ganglion cultures, only partial efficacy was reached in IL-1β-stimulated human glial cultures indicating that inhibiting IRAK-4́'s kinase function might be partially dispensable for human IL-1β driven neuroinflammation. Overall, our data demonstrate that IRAK-4 inhibitors could provide therapeutic benefit in chronic pain following nerve injury, and the central driver for efficacy in the neuropathic pain model as well as potential side effects of centrally available IRAK-4 inhibitors warrant further investigation to develop effective analgesia for patients in high unmet medical need.

Molecular characterization, expression and functional analysis of IRAK1 and IRAK4 in Nile tilapia (Oreochromis niloticus)

Interleukin-1 receptor-associated kinase 1 (IRAK1) and IRAK4 are critical signalling mediators and play pivotal roles in the innate immune and inflammatory responses mediated by TLR/IL-1R. In the present study, two IRAK family members, OnIRAK1 and OnIRAK4, were identified in the Nile tilapia Oreochromis niloticus with a conserved N-terminal death domain and a protein kinase domain, similar to those of other fishes and mammals. The gene structures of OnIRAK1 and OnIRAK4 are organized into fifteen exons split by fourteen introns and ten exons split by nine introns. OnIRAK1 and OnIRAK4 were broadly expressed in all of the tissues tested, with the highest expression levels being observed in the blood and the lowest expression levels being observed in the liver. Both genes could be detected from 2 d post-fertilization (dpf) to 8 dpf during embryonic development. Moreover, the expression levels of OnIRAK1 and OnIRAK4 were clearly altered in all five tissues after Streptococcus agalactiae infection in vivo and could be induced by LPS, Poly I: C, S. agalactiae WC1535 and △CPS in Nile tilapia macrophages. The overexpression of OnIRAK1 and OnIRAK4 in 293T cells showed that they were both distributed in the cytoplasm and could significantly increase NF-κB activation. Interestingly, after transfection, OnIRAK1 significantly upregulated OnMyd88-induced NF-κB activation, while OnIRAK4 had no effect on OnMyd88-induced NF-κB activation. Co-immunoprecipitation (Co-IP) assays showed that OnMyd88 did not interact with either OnIRAK1 or OnIRAK4 and that OnIRAK1 did not interact with OnIRAK4. Taken together, these findings suggest that OnIRAK1 and OnIRAK4 could play important roles in TLR/IL-1R signalling pathways and the immune response to pathogen invasion.

Dexamethasone sodium phosphate attenuates lipopolysaccharide-induced neuroinflammation in microglia BV2 cells

Abnormal neuroinflammation ignited by overproduction of chemokines and cytokines via microglial cells can induce the occurrence and development of neurodegenerative disorders. The aim of this study is to investigate the effects of dexamethasone sodium phosphate (Dex-SP) on chemokine and cytokine secretion in lipopolysaccharide (LPS)-activated microglial cells. LPS markedly enhanced the secretion of pro-inflammatory factors such as regulated on activation, normal T cell expressed and secreted (RANTES), transforming growth factor beta-β1 (TGF-β1) and nitric oxide (NO), but decreased the production of macrophage inflammatory protein-1α (MIP-1α) and interleukin 10 (IL-10) in BV-2 microglial cells. Furthermore, LPS increased BV-2 microglial cell migration. However, Dex-SP treatment had the opposite effect, dampening the secretion of RANTES, TGF-β1, and NO, while increasing the production of MIP-1α and IL-10 and blocking migration of LPS-stimulated BV-2 microglial cells. Furthermore, Dex-SP markedly suppressed the LPS-induced degradation of IRAK-1 and IRAK-4, and blocked the activation in TRAF6, p-TAK1, and p-JNK in BV-2 microglial cells. These results showed that Dex-SP inhibited the neuroinflammatory response and migration in LPS-activated BV-2 microglia by inhibiting the secretion of RANTES, TGF-β1, and NO and increasing the production of MIP-1α and IL-10. The molecular mechanism of Dex-SP may be associated with inhibition of TRAF6/TAK-1/JNK signaling pathways mediated by IRAK-1 and IRAK-4.

Mechanism of dysfunction of human variants of the IRAK4 kinase and a role for its kinase activity in interleukin-1 receptor signaling

Interleukin-1 receptor (IL1R)-associated kinase 4 (IRAK4) is a central regulator of innate immune signaling, controlling IL1R and Toll-like receptor (TLR)-mediated responses and containing both scaffolding and kinase activities. Humans deficient in IRAK4 activity have autosomal recessive primary immune deficiency (PID). Here, we characterized the molecular mechanism of dysfunction of two IRAK4 PID variants, G298D and the compound variant R12C (R12C/R391H/T458I). Using these variants and the kinase-inactive D329A variant to delineate the contributions of IRAK4's scaffolding and kinase activities to IL1R signaling, we found that the G298D variant is kinase-inactive and expressed at extremely low levels, acting functionally as a null mutation. The R12C compound variant possessed WT kinase activity, but could not interact with myeloid differentiation primary response 88 (MyD88) and IRAK1, causing impairment of IL-1-induced signaling and cytokine production. Quantitation of IL-1 signaling in IRAK4-deficient cells complemented with either WT or the R12C or D329A variant indicated that the loss of MyD88 interaction had a greater impact on IL-1-induced signaling and cytokine expression than the loss of IRAK4 kinase activity. Importantly, kinase-inactive IRAK4 exhibited a greater association with MyD88 and a weaker association with IRAK1 in IRAK4-deficient cells expressing kinase-inactive IRAK4 and in primary cells treated with a selective IRAK4 inhibitor. Loss of IRAK4 kinase activity only partially inhibited IL-1-induced cytokine and NF-κB signaling. Therefore, the IRAK4-MyD88 scaffolding function is essential for IL-1 signaling, but IRAK4 kinase activity can control IL-1 signal strength by modulating the association of IRAK4, MyD88, and IRAK1.

Interleukin-1 receptor-associated kinase 4 (IRAK4) plays a dual role in myddosome formation and Toll-like receptor signaling

Toll-like receptors (TLRs) form part of the host innate immune system, in which they act as sensors of microbial and endogenous danger signals. Upon TLR activation, the intracellular Toll/interleukin-1 receptor domains of TLR dimers initiate oligomerization of a multiprotein signaling platform comprising myeloid differentiation primary response 88 (MyD88) and members of the interleukin-1 receptor–associated kinase (IRAK) family. Formation of this myddosome complex initiates signal transduction pathways, leading to the activation of transcription factors and the production of inflammatory cytokines. To date, little is known about the assembly and disassembly of the myddosome and about the mechanisms by which these complexes mediate multiple downstream signaling pathways. Here, we isolated myddosome complexes from whole-cell lysates of TLR-activated primary mouse macrophages and from IRAK reporter macrophages to examine the kinetics of myddosome assembly and disassembly. Using a selective inhibitor of IRAK4's kinase activity, we found that whereas TLR cytokine responses were ablated, myddosome formation was stabilized in the absence of IRAK4's kinase activity. Of note, IRAK4 inhibition had only a minimal effect on NF-κB and mitogen-activated protein kinase (MAPK) signaling. In summary, our results indicate that IRAK4 has a critical scaffold function in myddosome formation and that its kinase activity is dispensable for myddosome assembly and activation of the NF-κB and MAPK pathways but is essential for MyD88-dependent production of inflammatory cytokines. Our findings suggest that the scaffold function of IRAK4 may be an attractive target for treating inflammatory and autoimmune diseases.

Small molecule inhibitors reveal an indispensable scaffolding role of RIPK2 in NOD2 signaling

RIPK2 mediates inflammatory signaling by the bacteria‐sensing receptors NOD1 and NOD2. Kinase inhibitors targeting RIPK2 are a proposed strategy to ameliorate NOD‐mediated pathologies. Here, we reveal that RIPK2 kinase activity is dispensable for NOD2 inflammatory signaling and show that RIPK2 inhibitors function instead by antagonizing XIAP‐binding and XIAP‐mediated ubiquitination of RIPK2. We map the XIAP binding site on RIPK2 to the loop between β2 and β3 of the N‐lobe of the kinase, which is in close proximity to the ATP‐binding pocket. Through characterization of a new series of ATP pocket‐binding RIPK2 inhibitors, we identify the molecular features that determine their inhibition of both the RIPK2‐XIAP interaction, and of cellular and in vivoNOD2 signaling. Our study exemplifies how targeting of the ATP‐binding pocket in RIPK2 can be exploited to interfere with the RIPK2‐XIAP interaction for modulation of NOD signaling.

The Role of Toll-Like Receptors in Autoimmune Diseases through Failure of the Self-Recognition Mechanism

Toll-like receptors (TLRs), part of the innate immune system that recognises molecular signatures, are important in the recognition of pathogenic components. However, when specific cellular contexts develop in which TLRs are inappropriately activated by self-components, this may lead to sterile inflammation and result in the occurrence of autoimmunity. This review analyses the available data regarding TLR biochemistry, the specific mechanisms which are brought about by TLR activation, and the importance of these mechanisms in the light of any existing and potential therapies in the field of autoimmunity.

Inherited human IRAK-1 deficiency selectively impairs TLR signaling in fibroblasts

Most members of the Toll-like receptor (TLR) and interleukin-1 receptor (IL-1R) families transduce signals via a canonical pathway involving the MyD88 adapter and the interleukin-1 receptor-associated kinase (IRAK) complex. This complex contains four molecules, including at least two (IRAK-1 and IRAK-4) active kinases. In mice and humans, deficiencies of IRAK-4 or MyD88 abolish most TLR (except for TLR3 and some TLR4) and IL-1R signaling in both leukocytes and fibroblasts. TLR and IL-1R responses are weak but not abolished in mice lacking IRAK-1, whereas the role of IRAK-1 in humans remains unclear. We describe here a boy with X-linked MECP2 deficiency-related syndrome due to a large de novo Xq28 chromosomal deletion encompassing both MECP2 and IRAK1 Like many boys with MECP2 null mutations, this child died very early, at the age of 7 mo. Unlike most IRAK-4- or MyD88-deficient patients, he did not suffer from invasive bacterial diseases during his short life. The IRAK-1 protein was completely absent from the patient's fibroblasts, which responded very poorly to all TLR2/6 (PAM2CSK4, LTA, FSL-1), TLR1/2 (PAM3CSK4), and TLR4 (LPS, MPLA) agonists tested but had almost unimpaired responses to IL-1β. By contrast, the patient's peripheral blood mononuclear cells responded normally to all TLR1/2, TLR2/6, TLR4, TLR7, and TLR8 (R848) agonists tested, and to IL-1β. The death of this child precluded long-term evaluations of the clinical consequences of inherited IRAK-1 deficiency. However, these findings suggest that human IRAK-1 is essential downstream from TLRs but not IL-1Rs in fibroblasts, whereas it plays a redundant role downstream from both TLRs and IL-1Rs in leukocytes.

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.

Toll-Like Receptors in the Pathogenesis of Autoimmune Diseases

Human Toll-like receptors (TLRs) are a family of transmembrane receptors, which play a key role in both innate and adaptive immune responses. Beside of recognizing specific molecular patterns that associated with different types of pathogens, TLRs may also detect a number of self-proteins and endogenous nucleic acids. Activating TLRs lead to the heightened expression of various inflammatory genes, which have a protective role against infection. Data rising predominantly from human patients and animal models of autoimmune disease indicate that, inappropriate triggering of TLR pathways by exogenous or endogenous ligands may cause the initiation and/or perpetuation of autoimmune reactions and tissue damage. Given their important role in infectious and non-infectious disease process, TLRs and its signaling pathways emerge as appealing targets for therapeutics. In this review, we demonstrate how TLRs pathways could be involved in autoimmune disorders and their therapeutic application.

The IRAK-ERK-p67phox-Nox-2 axis mediates TLR4, 2-induced ROS production for IL-1β transcription and processing in monocytes

In monocytic cells, Toll-like receptor 4 (TLR4)- and TLR2-induced reactive oxygen species (ROS) cause oxidative stress and inflammatory response; however, the mechanism is not well understood. The present study investigated the role of interleukin-1 receptor-associated kinase (IRAK), extracellular signal-regulated kinase (ERK), p67phox and Nox-2 in TLR4- and TLR2-induced ROS generation during interleukin-1 beta (IL-1β) transcription, processing, and secretion. An IRAK1/4 inhibitor, U0126, PD98059, an NADPH oxidase inhibitor (diphenyleneiodonium (DPI)), and a free radical scavenger (N-acetyl cysteine (NAC))-attenuated TLR4 (lipopolysaccharide (LPS))- and TLR2 (Pam3csk4)-induced ROS generation and IL-1β production in THP-1 and primary human monocytes. An IRAK1/4 inhibitor and siRNA-attenuated LPS- and Pam3csk4-induced ERK-IRAK1 association and ERK phosphorylation and activity. LPS and Pam3csk4 also induced IRAK1/4-, ERK- and ROS-dependent activation of activator protein-1 (AP-1), IL-1β transcription, and IL-1β processing because significant inhibition in AP-1 activity, IL-1β transcription, Pro- and mature IL-β expression, and caspase-1 activity was observed with PD98059, U0126, DPI, NAC, an IRAK1/4 inhibitor, tanshinone IIa, and IRAK1 siRNA treatment. IRAK-dependent ERK-p67phox interaction, p67phox translocation, and p67phox-Nox-2 interaction were observed. Nox-2 siRNA significantly reduced secreted IL-1β, IL-1β transcript, pro- and mature IL-1β expression, and caspase-1 activity indicating a role for Nox-2 in LPS- and Pam3csk4-induced IL-1β production, transcription, and processing. In the present study, we demonstrate that the TLR4- and TLR2-induced IRAK-ERK pathway cross-talks with p67phox-Nox-2 for ROS generation, thus regulating IL-1β transcription and processing in monocytic cells.

Discovery and Structure Enabled Synthesis of 2,6-Diaminopyrimidin-4-one IRAK4 Inhibitors

We report the identification and synthesis of a series of aminopyrimidin-4-one IRAK4 inhibitors. Through high throughput screening, an aminopyrimidine hit was identified and modified via structure enabled design to generate a new, potent, and kinase selective pyrimidin-4-one chemotype. This chemotype is exemplified by compound 16, which has potent IRAK4 inhibition activity (IC50 = 27 nM) and excellent kinase selectivity (>100-fold against 99% of 111 tested kinases), and compound 31, which displays potent IRAK4 activity (IC50 = 93 nM) and good rat bioavailability (F = 42%).

Toll-like receptors: Activation, signalling and transcriptional modulation

Families of innate immune receptors serve as the bodies primary defence system by recognising and rapidly responding to infection by microorganisms or to endogenous danger signals and initiating inflammatory processes. Whilst Toll-like receptors (TLRs) were the first family to be discovered, important and exciting discoveries continue to emerge into the molecular mechanisms that control their activation and regulation. Herein, I will provide an overview of TLR activation and their downstream signalling cascades, and discuss some of the recent findings concerning the assembly of a TLR oligomeric signalling platform, known as the Myddosome. Further, a brief examination of the importance of crosstalk between multiple TLRs or between TLRs and other innate immune receptors for appropriate and coordinated immune responses will be presented. Finally, I will discuss the importance of mechanisms that regulate TLRs with a focus on the role of activating transcription factor 3 (ATF3) in modulating transcriptional responses downstream of TLRs.

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.

Receptor proximal kinases in NF-κB signaling as potential therapeutic targets in cancer and inflammation

Many signaling pathways leading to activation of transcription factors and gene expression are characterized by phosphorylation events mediated by specific kinases. The transcription factor NF-κB plays a key role in multiple cellular processes, including immune signaling, inflammation, development, proliferation and survival. Dysregulated NF-κB activation is associated with autoimmunity, chronic inflammation and cancer. Activation of NF-κB requires IκB kinase (IKK)α or β, the activity of which is regulated via phosphorylation by specific IKK kinases and by autophosphorylation. Receptor specificity is further obtained by the use of multiple upstream receptor proximal kinases. We review the identities of several IKK regulatory kinases as well as the proposed molecular mechanisms. In addition, we discuss the potential for therapeutic targeting of some of these kinases in the context of inflammatory diseases and cancer.

Protective effect of diallyl trisulfide on liver in rats with sepsis and the mechanism

The protective effects of diallyl trisulfide on liver were examined in rats with sepsis. Sepsis was reproduced in rats by cecum ligation and puncture (CLP). Fifty-six male Wistar rats were randomly divided into sham-operated group (group S, n=8), sepsis model group (group C, n=24), diallyl trisulfide (DATS)-treated group (group D, n=24). Animals in groups C and D were further divided into three subgroups according to different observation time points, with 8 rats in each subgroup· Rats in group D and C were intravenously injected with normal saline or DATS respectively at a dose of 20 mg/kg after the establishment of sepsis model. Eight rats in groups C and D were sacrificed at 3, 6 and 24 h post-CLP and their livers were harvested for detection of interleukin (IL)-1 receptor associated kinase-4 (IRAK-4), nuclear factor-κB (NF-κB), c-fos, c-jun, malondialdehydethhe (MDA) and superoxide dismutase (SOD), tumor necrosis factor alpha (TNF-α) and for pathological examination. The results showed that the levels of serum IRAK-4, NF-κB and TNF-α in hepatic tissues were higher in group C than group S (control group) (P<0.05). After DATS treatment, the levels of IRAK-4 and NF-κB in the hepatic tissues and serum TNF-α in group D were lower than those in group C (P<0.05). The levels of c-fos and c-jun and MDA in the hepatic tissues were higher in group C than in group S (P<0.05). After DATS treatment, the levels of c-fos and c-jun and MDA in the hepatic tissues were significantly lower in group D than in group C (P<0.05). When compared with group S group, concentration of SOD in the hepatic tissues in group C was significantly lower (P<0.05). After DATS treatment, the concentration of SOD in the hepatic tissues was higher in group D than in group C (P<0.05). These findings suggested that treatment with DATS could ameliorate sepsis-induced liver injury in rats. The protective effect might be related to its ability to inhibit the signal pathway of IRAK-4 and NF-κB, thereby decreasing the production of oxygen free radicals and down-regulating the expression of c-fos and c-jun.

Identification of IRAK-4 in grouper (Epinephelus coioides) that impairs MyD88-dependent NF-κB activation

Interleukin 1 (IL-1) receptor-associated kinase (IRAK) family members are crucial signal transducer in the Toll-like receptor/IL-1R signal pathway, which mediates downstream signal cascades involved in the innate and adaptive immune responses. In this study, we identified an IRAK-4 protein (EcIRAK-4) in the orange-spotted grouper (Epinephelus coioides), with an N-terminal death domain, a proST domain, and a central kinase domain, similar to that of other fishes and mammals. A sequence alignment and phylogenic analysis demonstrated that full-length EcIRAK-4 shares a high degree of sequence identity with those of other fishes, especially the roughskin sculpin, and their death domains and kinase domains share greater identity than their proST domains. A conservation analysis indicated that most of the functional sites in mammalian IRAK-4 are conserved in IRAK-4 of the grouper and other fishes, with the exception of the sites of interaction with IRAK-2 and one autophosphorylation site within the activation loop. EcIRAK-4 is broadly expressed in all the tissues examined, with highest expression in the head kidney and liver. After infection with Cryptocaryon irritans, EcIRAK-4 expression was significantly upregulated, especially in the skin, which suggests that this molecule is involved in the host's defense against parasitic infection. Surprisingly, after cotransfection with grouper MyD88, EcIRAK-4 significantly impaired the NF-κB activity induced by MyD88. EcIRAK-4 was uniformly distributed throughout the cytoplasm in HeLa cells. These findings suggest that although IRAK-4 is evolutionarily conserved between fish and mammals, its signal transduction function is markedly different.

Isomerase-catalyzed binding of interleukin-1 receptor-associated kinase 1 to the EVH1 domain of vasodilator-stimulated phosphoprotein

Interleukin-1 receptor-associated kinase 1 (IRAK1) is a crucial signaling kinase in the immune system, involved in Toll-like receptor signaling. Vasodilator-stimulated phosphoprotein (VASP) is a central player in cell migration that regulates actin polymerization and connects signaling events to cytoskeletal remodeling. A VASP–IRAK1 interaction is thought to be important in controlling macrophage migration in response to protein kinase C-ε activation. We show that the monomeric VASP EVH1 domain directly binds to the 168WPPPP172 motif in the IRAK1 undefined domain (IRAK1-UD) with moderate affinity (KDApp = 203 ± 3 μM). We further show that this motif adopts distinct cis and trans isomers for the Trp168–Pro169 peptide bond with nearly equal populations, and that binding to the VASP EVH1 domain is specific for the trans isomer, coupling binding to isomerization. Nuclear magnetic resonance line shape analysis and tryptophan fluorescence experiments reveal the complete kinetics and thermodynamics of the binding reaction, showing diffusion-limited binding to the trans isomer followed by slow, isomerization-dependent binding. We further demonstrate that the peptidyl-prolyl isomerase cyclophilin A (CypA) catalyzes isomerization of the Trp168–Pro169 peptide bond and accelerates binding of the IRAK1-UD to the VASP EVH1 domain. We propose that binding of IRAK1 to tetrameric VASP is regulated by avidity through the assembly of IRAK1 onto receptor-anchored signaling complexes and that an isomerase such as CypA may modulate IRAK1 signaling in vivo. These studies demonstrate a direct interaction between IRAK1 and VASP and suggest a potential mechanism for how this interaction might be regulated by both assembly of IRAK1 onto an activated signaling complex and PPIase enzymes.

Interleukin 1/Toll-like receptor-induced autophosphorylation activates interleukin 1 receptor-associated kinase 4 and controls cytokine induction in a cell type-specific manner

IRAK4 is a central kinase in innate immunity, but the role of its kinase activity is controversial. The mechanism of activation for IRAK4 is currently unknown, and little is known about the role of IRAK4 kinase in cytokine production, particularly in different human cell types. We show IRAK4 autophosphorylation occurs by an intermolecular reaction and that autophosphorylation is required for full catalytic activity of the kinase. Phosphorylation of any two of the residues Thr-342, Thr-345, and Ser-346 is required for full activity, and the death domain regulates the activation of IRAK4. Using antibodies against activated IRAK4, we demonstrate that IRAK4 becomes phosphorylated in human cells following stimulation by IL-1R and Toll-like receptor agonists, which can be blocked pharmacologically by a dual inhibitor of IRAK4 and IRAK1. Interestingly, in dermal fibroblasts, although complete inhibition of IRAK4 kinase activity does not inhibit IL-1-induced IL-6 production, NF-κB, or MAPK activation, there is complete ablation of these processes in IRAK4-deficient cells. In contrast, the inhibition of IRAK kinase activity in primary human monocytes reduces R848-induced IL-6 production with minimal effect on NF-κB or MAPK activation. Taken together, these studies define the mechanism of IRAK4 activation and highlight the differential role of IRAK4 kinase activity in different human cell types as well as the distinct roles IRAK4 scaffolding and kinase functions play.

Interleukin 1 receptor 1 and interleukin 1β regulate megakaryocyte maturation, platelet activation, and transcript profile during inflammation in mice and humans

OBJECTIVE

Interleukin 1 Receptor 1 (IL1R1) and its ligand, IL1β, are upregulated in cardiovascular disease, obesity, and infection. Previously, we reported a higher level of IL1R1 transcripts in platelets from obese individuals of the Framingham Heart Study (FHS), but its functional effect in platelets has never been described. Additionally, IL1β levels are increased in atherosclerotic plaques and in bacterial infections. The aim of this work is to determine whether IL1β, through IL1R1, can activate platelets and megakaryocytes to promote atherothrombosis.

APPROACH AND RESULTS

We found that IL1β-related genes from platelets, as measured in 1819 FHS participants, were associated with increased body mass index, and a direct relationship was shown in wild-type mice fed a high-fat diet. Mechanistically, IL1β activated nuclear factor-κB and mitogen-activated protein kinase signaling pathways in megakaryocytes. IL1β, through IL1R1, increased ploidy of megakaryocytes to 64+ N by 2-fold over control. IL1β increased agonist-induced platelet aggregation by 1.2-fold with thrombin and 4.2-fold with collagen. IL1β increased adhesion to both collagen and fibrinogen, and heterotypic aggregation by 1.9-fold over resting. High fat diet-enhanced platelet adhesion was absent in IL1R1(-/-) mice. Wild-type mice infected with Porphyromonas gingivalis had circulating heterotypic aggregates (1.5-fold more than control at 24 hours and 6.2-fold more at 6 weeks) that were absent in infected IL1R1(-/-) and IL1β(-/-) mice.

CONCLUSIONS

In summary, IL1R1- and IL1β-related transcripts are elevated in the setting of obesity. IL1R1/IL1β augment both megakaryocyte and platelet functions, thereby promoting a prothrombotic environment during infection and obesity; potentially contributing to the development of atherothrombotic disease.

Role of innate immunity in the development of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common form of liver cancer worldwide. It is caused by a variety of risk factors, most common ones being infection with hepatitis viruses, alcohol, and obesity. HCC often develops in the background of underlying cirrhosis, and even though a number of interventional treatment methods are currently in use, recurrence is fairly common among patients who have had a resection. Therefore, whole liver transplantation remains the most practical treatment option for HCC. Due to the growing incidence of HCC, intense research efforts are being made to understand cellular and molecular mechanisms of the disease so that novel therapeutic strategies can be developed to combat liver cancer. In recent years, it has become clear that innate immunity plays a critical role in the development of a number of liver diseases, including HCC. In particular, the activation of Toll-like receptor signaling results in the generation of immune responses that often results in the production of pro-inflammatory cytokines and chemokines, and could cause acute inflammation in the liver. In this review, the current knowledge on the role of innate immune responses in the development and progression of HCC is examined, and emerging therapeutic strategies based on molecular mechanisms of HCC are discussed.

IRAK4 kinase activity is not required for induction of endotoxin tolerance but contributes to TLR2-mediated tolerance

Prior exposure to LPS induces "endotoxin tolerance" that reprograms TLR4 responses to subsequent LPS challenge by altering expression of inflammatory mediators. Endotoxin tolerance is thought to limit the excessive cytokine storm and prevent tissue damage during sepsis but renders the host immunocompromised and susceptible to secondary infections. Tolerance initiated via one TLR can affect cellular responses to challenge via the same TLR ("homotolerance") or through different TLRs ("heterotolerance"). IRAK4, an essential component of the MyD88-dependent pathway, functions as a kinase and an adapter, activating subsets of divergent signaling pathways. In this study, we addressed mechanistically the role of IRAK4 kinase activity in TLR4- and TLR2-induced tolerance using macrophages from WT versus IRAK4(KDKI) mice. Whereas IRAK4 kinase deficiency decreased LPS signaling, it did not prevent endotoxin tolerance, as endotoxin pretreatment of WT and IRAK4(KDKI) macrophages inhibited LPS-induced MAPK phosphorylation, degradation of IκB-α and recruitment of p65 to the TNF-α promoter, expression of proinflammatory cytokines, and increased levels of A20 and IRAK-M. Pretreatment of WT macrophages with Pam3Cys, a TLR2-TLR1 agonist, ablated p-p38 and p-JNK in response to challenge with Pam3Cys and LPS, whereas IRAK4(KDKI) macrophages exhibited attenuated TLR2-elicited homo- and heterotolerance at the level of MAPK activation. Thus, IRAK4 kinase activity is not required for the induction of endotoxin tolerance but contributes significantly to TLR2-elicited homo- and heterotolerance.

Complete dependence on IRAK4 kinase activity in TLR2, but not TLR4, signaling pathways underlies decreased cytokine production and increased susceptibility to Streptococcus pneumoniae infection in IRAK4 kinase-inactive mice

IRAK4 is critical for MyD88-dependent TLR signaling, and patients with Irak4 mutations are extremely susceptible to recurrent bacterial infections. In these studies, mice homozygous for a mutant IRAK4 that lacks kinase activity (IRAK4(KDKI)) were used to address the role of IRAK4 in response to TLR agonists or bacterial infection. IRAK4(KDKI) macrophages exhibited diminished responsiveness to the TLR4 agonist LPS and little to no response to the TLR2 agonist Pam3Cys compared with wild-type macrophages as measured by cytokine mRNA, cytokine protein expression, and MAPK activation. Importantly, we identified two kinases downstream of the MAPKs, MNK1 and MSK1, whose phosphorylation is deficient in IRAK4(KDKI) macrophages stimulated through either TLR2 or TLR4, suggesting that IRAK4 contributes to TLR signaling beyond the initial phosphorylation of MAPKs. Additionally, IRAK4(KDKI) macrophages produced minimal cytokine mRNA expression in response to the Gram-positive bacteria Streptococcus pneumoniae and Staphylococcus aureus compared with WT cells, and IRAK4(KDKI) mice exhibited increased susceptibility and decreased cytokine production in vivo upon S. pneumoniae infection. Treatment of infected mice with a complex of polyinosinic-polycytidylic acid with poly-L-lysine and carboxymethyl cellulose (Hiltonol), a potent TLR3 agonist, significantly improved survival of both WT and IRAK4(KDKI) mice, thereby providing a potential treatment strategy in both normal and immunocompromised patients.

T granules in human platelets function in TLR9 organization and signaling

TLR9 localizes to a novel intracellular compartment called the T granule to promote immune signaling by platelets.

Human and murine platelets (PLTs) variably express toll-like receptors (TLRs), which link the innate and adaptive immune responses during infectious inflammation and atherosclerotic vascular disease. In this paper, we show that the TLR9 transcript is specifically up-regulated during pro-PLT production and is distributed to a novel electron-dense tubular system-related compartment we have named the T granule. TLR9 colocalizes with protein disulfide isomerase and is associated with either VAMP 7 or VAMP 8, which regulates its distribution in PLTs on contact activation (spreading). Preincubation of PLTs with type IV collagen specifically increased TLR9 and CD62P surface expression and augmented oligodeoxynucleotide (ODN) sequestration and PLT clumping upon addition of bacterial/viral ODNs. Collectively, this paper (a) tracks TLR9 to a new intracellular compartment in PLTs and (b) describes a novel mechanism of TLR9 organization and signaling in human PLTs.

Membrane-bound toll-like receptors are overexpressed in peripheral blood and synovial fluid mononuclear cells of enthesitis-related arthritis category of juvenile idiopathic arthritis (JIA–ERA) patients and lead to secretion of inflammatory mediators

We examined expression and function of TLRs in enthesitis-related arthritis (ERA) patients. RNA levels of TLR1, TLR3, and TLRs 5–8 were measured in 24 ERA peripheral blood mononuclear cells (PBMC), 18 synovial fluid mononuclear cells (SFMC), and IRAK1, IRAK4, TRIF, TRAF3, and TRAF6 in 18 PBMC and 10 SFMC. IL-6 and IL-8 were measured in supernatants from ERA PBMC (n=7), SFMC (n=3), and healthy PBMC (n=5) cultured with ligands for TLR1/2 (Pam 3-cys), TLR3 (polyI:C), TLR5 (flagellin), and TLR2/6 (zymosan). TLRs 1, 3, 5, and 6 were measured in whole blood (n=20 ERA, seven healthy) and SFMC (n=2) by flow cytometry. ERA PBMC compared to healthy PBMC and SFMC compared to ERA PBMC had higher RNA expression of TLR1, TLR3, TLR5, TLR6, IRAK1, IRAK4, TRIF, TRAF3, and TRAF6. TLR7 and TLR8 RNA expression was similar in all study groups. IL-6 and IL-8 levels were higher in stimulated ERA SFMC compared to ERA PBMC and in ERA PBMC compared to control PBMC. TLRs 1, 3, and 6 were also overexpressed at the protein level.

Kaposi's sarcoma-associated herpesvirus microRNAs target IRAK1 and MYD88, two components of the toll-like receptor/interleukin-1R signaling cascade, to reduce inflammatory-cytokine expression

Kaposi's sarcoma (KS)-associated herpesvirus (KSHV) is the causative agent of KS, an important AIDS-associated malignancy. KSHV expresses at least 18 different mature microRNAs (miRNAs). We identified interleukin-1 receptor (IL-1R)-associated kinase 1 (IRAK1) as a potential target of miR-K12-9 (miR-K9) in an array data set examining changes in cellular gene expression levels in the presence of KSHV miRNAs. Using 3'-untranslated region (3'UTR) luciferase reporter assays, we confirmed that miR-K9 and other miRNAs inhibit IRAK1 expression. In addition, IRAK1 expression is downregulated in cells transfected with miR-K9 and during de novo KSHV infection. IRAK1 is an important component of the Toll-like receptor (TLR)/IL-1R signaling cascade. The downregulation of IRAK1 by miR-K9 resulted in the decreased stimulation of NF-κB activity in endothelial cells treated with IL-1α and in B cells treated with a TLR7/8 agonist. Interestingly, miR-K9 had a greater effect on NF-κB activity than did a small interfering RNA (siRNA) targeting IRAK1 despite the more efficient downregulation of IRAK1 expression with the siRNA. We hypothesized that KSHV miRNAs may also be regulating a second component of the TLR/IL-1R signaling cascade, resulting in a stronger phenotype. Reanalysis of the array data set identified myeloid differentiation primary response protein 88 (MYD88) as an additional potential target. 3'UTR luciferase reporter assays and Western blot analysis confirmed the targeting of MYD88 by miR-K5. The presence of miR-K9 and miR-K5 inhibited the production of IL-6 and IL-8 upon the IL-1α stimulation of endothelial cells. These results demonstrate KSHV-encoded miRNAs regulating the TLR/IL-1R signaling cascade at two distinct points and suggest the importance of these pathways during viral infection.

Interleukin-1 receptor associated kinases-1/4 inhibition protects against acute hypoxia/ischemia-induced neuronal injury in vivo and in vitro

Neuronal Toll-like receptors (TLRs)-2 and -4 have been shown to play a pivotal role in ischemic brain injury, and the interleukin-1 receptor associated kinases (IRAKs) are considered to be the key signaling molecules involved downstream of TLRs. Here, we investigated the expression levels of IRAK-1 and -4 and the effects of IRAK-1/4 inhibition on brain ischemic insult and neuronal hypoxia-induced injury. Male Sprague-Dawley (SD) rats and the rat neuroblastoma B35 cell line were used in these experiments. Permanent middle cerebral artery occlusion (MCAO) was induced by the intraluminal filament technique, and B35 cells were stimulated with the hypoxia-mimetic, cobalt chloride (CoCl(2)). Following induction of hypoxia/ischemia (H/I), B35 cells and cerebral cortical neurons expressed higher levels of IRAK-1 and -4. Furthermore, IRAK-1/4 inhibition decreased the mortality rate, functional deficits, and ischemic infarct volume by 7 days after MCAO. Similarly, IRAK-1/4 inhibition attenuated CoCl(2)-induced cytotoxicity and apoptosis in B35 cells in vitro. Our results show that IRAK-1/4 inhibition decreased the nuclear translocation of the nuclear factor-kappaB (NF-κB) p65 subunit, the levels of activated (phosphorylated) c-jun N-terminal kinase (JNK) and cleaved caspase-3, and the secretion of TNF-α and IL-6 in B35 cells at 6 h after CoCl(2) treatment. These data suggest that IRAK-1/4 inhibition plays a neuroprotective role in H/I-induced brain injury.

Role of Toll-like receptors in liver health and disease

TLRs (Toll-like receptors), as evolutionarily conserved germline-encoded pattern recognition receptors, have a crucial role in early host defence by recognizing so-called PAMPs (pathogen-associated molecular patterns) and may serve as an important link between innate and adaptive immunity. In the liver, TLRs play an important role in the wound healing and regeneration processes, but they are also involved in the pathogenesis and progression of various inflammatory liver diseases, including autoimmune liver disease, alcoholic liver disease, non-alcoholic steatohepatitis, fibrogenesis, and chronic HBV (hepatitis B virus) and HCV (hepatitis C virus) infection. Hepatitis viruses have developed different evading strategies to subvert the innate immune system. Thus recent studies have suggested that TLR-based therapies may represent a promising approach in the treatment in viral hepatitis. The present review focuses on the role of the local innate immune system, and TLRs in particular, in the liver.

Immune complex-mediated cell activation from systemic lupus erythematosus and rheumatoid arthritis patients elaborate different requirements for IRAK1/4 kinase activity across human cell types

IL-1R-associated kinases (IRAKs) are important mediators of MyD88-dependent signaling by the TLR/IL-1R superfamily and facilitate inflammatory responses. IRAK4 and IRAK1 function as active kinases and as scaffolds for protein-protein interactions. We report that although IRAK1/4 kinase activity is essential for human plasmacytoid dendritic cell (pDC) activation, it is dispensable in B, T, dendritic, and monocytic cells, which is in contrast with an essential active kinase role in comparable mouse cell types. An IRAK1/4 kinase inhibitor abrogated TLR7/9-induced IFN-α responses in both mouse and human pDCs, but other human immune cell populations activated via TLR7/9 or IL-1R were refractory to IRAK4 kinase inhibition. Gene ablation experiments using small interfering RNA demonstrated an essential scaffolding role for IRAK1 and IRAK4 in MyD88-dependent signaling. Finally, we demonstrate that autoimmune patient (systemic lupus erythematosus and rheumatoid arthritis) serum activates both pDC and B cells, but IRAK1/4 kinase inhibition affects only the pDC response, underscoring the differential IRAK1/4 functional requirements in human immune cells. These data reveal important species differences and elaborate cell type requirements for IRAK1/4 kinase activity.

Toll-like receptor signaling pathways--therapeutic opportunities

Toll-like receptors (TLRs) are transmembrane proteins acting mainly as sensors of microbial components. Triggering TLRs results in increased expression of multiple inflammatory genes, which then play a protective role against infection. However, aberrant activation of TLR signaling has a significant impact on the onset of cancer, allergy, sepsis and autoimmunity. Various adaptor proteins, including MyD88, IRAKs, TIRAP, TRIF, and TRAM, are involved in specific TLR signaling pathways. This article reviews the role of these molecules in TLR signaling, and discusses the impact of this pathway on various disease scenarios. Given their important role in infectious and non-infectious disease settings, TLRs and their signaling pathways emerge as attractive targets for therapeutics.

Gene signatures in wound tissue as evidenced by molecular profiling in the chick embryo model

BACKGROUND

Modern functional genomic approaches may help to better understand the molecular events involved in tissue morphogenesis and to identify molecular signatures and pathways. We have recently applied transcriptomic profiling to evidence molecular signatures in the development of the normal chicken chorioallantoic membrane (CAM) and in tumor engrafted on the CAM. We have now extended our studies by performing a transcriptome analysis in the "wound model" of the chicken CAM, which is another relevant model of tissue morphogenesis.

RESULTS

To induce granulation tissue (GT) formation, we performed wounding of the chicken CAM and compared gene expression to normal CAM at the same stage of development. Matched control samples from the same individual were used. We observed a total of 282 genes up-regulated and 44 genes down-regulated assuming a false-discovery rate at 5% and a fold change > 2. Furthermore, bioinformatics analysis lead to the identification of several categories that are associated to organismal injury, tissue morphology, cellular movement, inflammatory disease, development and immune system. Endothelial cell data filtering leads to the identification of several new genes with an endothelial cell signature.

CONCLUSIONS

The chick chorioallantoic wound model allows the identification of gene signatures and pathways involved in GT formation and neoangiogenesis. This may constitute a fertile ground for further studies.

The interleukin-1 receptor-associated kinases: critical regulators of innate immune signalling

The interleukin receptor-associated kinase (IRAK) family are involved in regulating Toll-like receptor (TLR) and interleukin-1 (IL-1) signalling pathways. TLRs are pattern recognition receptors of the innate immune response that are responsible for sensing pathogens and initiating immunity, while IL-1 is one of the key cytokines that mediates inflammation. As such, IL-1/TLR signalling pathways and the IRAK family are critical in anti-pathogen responses, inflammation and autoimmunity. The family comprises of four members, IRAK-1, IRAK-2, IRAK-M (IRAK-3) and IRAK-4, and has a role in both positive and negative regulation of signal transduction. While it was once thought that the family displayed some redundancy, each member of the family is emerging as a distinct and vital contributor to IL-1/TLR signalling mechanisms. Knockout mouse studies have explored the relative contribution of each of the IRAKs in IL-1/TLR signalling, while the recent generation of kinase-inactive knock-in IRAK-4 mice have revealed which of IRAK-4 functions require its kinase activity. IRAK-2, previously thought of as a pseudokinase, has recently been proposed to have kinase activity that is essential for TLR signalling. Not surprisingly given their critical role in IL-1/TLR signalling, the IRAK family members have been implicated in certain disease models including human immunodeficiencies. Thus the potential targeting of these essential protein kinases therapeutically is also discussed.

IRAK1 and IRAK4 promote phosphorylation, ubiquitination, and degradation of MyD88 adaptor-like (Mal)

Signal transduction by Toll-like receptor 2 (TLR2) and TLR4 requires the adaptors MyD88 and Mal (MyD88 adaptor-like) and serine/threonine kinases, interleukin-1 receptor-associated kinases IRAK1 and IRAK4. We have found that both IRAK1 and IRAK4 can directly phosphorylate Mal. In addition, co-expression of Mal with either IRAK resulted in depletion of Mal from cell lysates. This is likely to be due to Mal phosphorylation by the IRAKs because kinase-inactive forms of either IRAK had no effect. Furthermore, lipopolysaccharide stimulation resulted in ubiquitination and degradation of Mal, which was inhibited using an IRAK1/4 inhibitor or by knocking down expression of IRAK1 and IRAK4. MyD88 is not a substrate for either IRAK and did not undergo degradation. We therefore conclude that Mal is a substrate for IRAK1 and IRAK4 with phosphorylation promoting ubiquitination and degradation of Mal. This process may serve to negatively regulate signaling by TLR2 and TLR4.

Steady-state kinetic characterization of kinase activity and requirements for Mg2+ of interleukin-1 receptor-associated kinase-4

Interleukin-1 receptor-associated kinase-4 (IRAK-4) is a Ser/Thr-specific protein kinase that plays a critical role in intracellular signaling cascades mediated by Toll-like and interleukin-1 (IL-1) receptors. Despite a growing body of information on the physiological functions of IRAK-4, its kinase activity remains poorly studied. The present study entails characterization of the steady-state kinetic properties and Mg(2+) requirements of full-length, recombinant human IRAK-4 preactivated by incubation with MgATP. In the presence of 20 mM Mg(2+), activated IRAK-4 herein is demonstrated to phosphorylate a peptide substrate (IRAK-1 peptide), derived from the activation loop of IRAK-1, with a k(cat) of 30 +/- 2.9 s(-1) and K(m) values of 668 +/- 120 and 852 +/- 273 microM for ATP and the peptide, respectively. Two-substrate, dead-end and product inhibition data, using analogues of ATP, are consistent with both a sequential ordered kinetic mechanism with ATP binding to the enzyme prior to the peptide and a sequential random mechanism. Investigation of the Mg(2+) requirements for phosphoryl transfer activity of IRAK-4 revealed that more than one Mg(2+) ion interacts with the enzyme and that the enzyme is maximally active in the presence of 5-10 mM free Mg(2+). While one divalent metal, as part of a chelate complex with ATP, is essential for catalysis, kinetic evidence is provided to show that uncomplexed Mg(2+) further enhances the catalytic activity of IRAK-4 by bringing about an approximately 3-fold increase in k(cat) and an approximately 6-fold reduction in the K(m) for ATP and by rendering the interaction between the nucleotide and peptide substrate binding sites less antagonistic.

Deregulation of microRNA expression in the different genetic subtypes of multiple myeloma and correlation with gene expression profiling

Specific microRNA (miRNA) signatures have been associated with different cytogenetic subtypes in acute leukemias. This finding prompted us to investigate potential associations between genetic abnormalities in multiple myeloma (MM) and singular miRNA expression profiles. Moreover, global gene expression profiling was also analyzed to find correlated miRNA gene expression and select miRNA target genes that show such correlation. For this purpose, we analyzed the expression level of 365 miRNAs and the gene expression profiling in 60 newly diagnosed MM patients, selected to represent the most relevant recurrent genetic abnormalities. Supervised analysis showed significantly deregulated miRNAs in the different cytogenetic subtypes as compared with normal PC. It is interesting to note that miR-1 and miR-133a clustered on the same chromosomal loci, were specifically overexpressed in the cases with t(14;16). The analysis of the relationship between miRNA expression and their respective target genes showed a conserved inverse correlation between several miRNAs deregulated in MM cells and CCND2 expression level. These results illustrate, for the first time, that miRNA expression pattern in MM is associated with genetic abnormalities, and that the correlation of the expression profile of miRNA and their putative mRNA targets is useful to find statistically significant protein-coding genes in MM pathogenesis associated with changes in specific miRNAs.

IRAK-4 inhibitors for inflammation

Interleukin-1 receptor-associated kinases (IRAKs) are key components in the signal transduction pathways utilized by interleukin-1 receptor (IL-1R), interleukin-18 receptor (IL-18R), and Toll-like receptors (TLRs). Out of four members in the mammalian IRAK family, IRAK-4 is considered to be the “master IRAK”, the only family member indispensable for IL-1R/TLR signaling. In humans, mutations resulting in IRAK-4 deficiency have been linked to susceptibility to bacterial infections, especially recurrent pyogenic bacterial infections. Furthermore, knock-in experiments by several groups have clearly demonstrated that IRAK-4 requires its kinase activity for its function. Given the critical role of IRAK-4 in inflammatory processes, modulation of IRAK-4 kinase activity presents an attractive therapeutic approach for the treatment of immune and inflammatory diseases. The recent success in the determination of the 3-dimensional structure of the IRAK-4 kinase domain in complex with inhibitors has facilitated the understanding of the mechanistic role of IRAK-4 in immunity and inflammation as well as the development of specific IRAK-4 kinase inhibitors. In this article, we review the biological function of IRAK-4, the structural characteristics of the kinase domain, and the development of small molecule inhibitors targeting the kinase activity. We also review the key pharmacophores required for several classes of inhibitors as well as important features for optimal protein/inhibitor interactions. Lastly, we summarize how these insights can be translated into strategies to develop potent IRAK-4 inhibitors with desired properties as new anti-inflammatory therapeutic agents.

A modeling-derived hypothesis on chronicity in respiratory diseases: desensitized pathogen recognition secondary to hyperactive IRAK/TRAF6 signaling

Several chronic respiratory diseases exhibit hyperactive immune responses in the lung: abundant inflammatory mediators; infiltrating neutrophils, macrophages, lymphocytes and other immune cells; and increased level of proteases. Such diseases include cystic fibrosis (CF), chronic obstructive pulmonary disease (COPD) and severe/neutrophilic asthma. Paradoxically, patients with these diseases are also susceptible to detrimental bacterial infection and colonization. In this paper, we seek to explain how a positive feedback mechanism via IL-8 could lead to desensitization of epithelial cells to pathogen recognition thus perpetuating bacterial colonization and chronic disease states in the lung. Such insight was obtained from mathematical modeling of the IRAK/TRAF6 signaling module, and is consistent with existing clinical evidence. The potential implications for targeted treatment regimes for these persistent respiratory diseases are explored.