The interleukin-1 receptor/Toll-like receptor superfamily: signal transduction during inflammation and host defense

Regulation of IGF-I function by proinflammatory cytokines: at the interface of immunology and endocrinology

During the past decade, the immune and endocrine systems have been discovered to interact in controlling physiologic processes as diverse as cell growth and differentiation, metabolism, and even human and animal behavior. The interaction between these two major physiological systems is a bi-directional process. While it has been well documented that hormones, including prolactin (PRL), growth hormone (GH), insulin-like growth factor-I (IGF-I), and thyroid-stimulating hormone (TSH), regulate a variety of immune events, a great deal of data have accumulated supporting the notion that cytokines from the innate immune system also affect the neuroendocrine system. Communication between these two systems coordinates processes that are necessary to maintain homeostasis. Proinflammatory cytokines often act as negative regulatory signals that temper the action of hormones and growth factors. This system of 'checks and balances' is an active, ongoing process, even in healthy individuals. Dysregulation of this process has been implicated as a potential pathogenic factor in the development of co-morbid conditions associated with several chronic inflammatory diseases, including type 2 diabetes, cardiovascular disease, cerebrovascular disease, inflammatory bowel disease, rheumatoid arthritis, major depression, and even normal aging. Over the past decade, research in our laboratory has focused on the ability of the major proinflammatory cytokines, tumor necrosis factor (TNF)alpha and interleukin (IL)-1beta, to induce a state of IGF resistance. This review will highlight these and other new findings by explaining how proinflammatory cytokines induce resistance to the major growth factor, insulin-like growth factor-I (IGF-I). We also highlight that IGF-I can induce resistance or reduce sensitivity to brain TNFalpha and discuss how TNFalpha, IL-1beta, and IGF-I interact to regulate several aspects of behavior and cognition.

Differential expression of pattern recognition receptors in the three pathological forms of sheep paratuberculosis

Paratuberculosis is a chronic inflammatory disease of the gut caused by Mycobacterium avium subspecies paratuberculosis. Three forms have been described in sheep--paucibacillary, multibacillary and asymptomatic. The pauci- and multibacillary forms are characterized by type 1 and type 2 immune responses respectively; asymptomatic animals have no clinical signs or pathology. What determines this polarization is unknown, although pattern recognition receptors (PRR) have been implicated in other mycobacterial diseases. To investigate this in sheep paratuberculosis we used real-time RT-PCR to quantify the expression of fifteen PRR and adaptor genes from forty infected and nine control animals. These data show that there is a relationship between the different pathological forms and PRR transcript profiles. Nine PRRs were up-regulated in asymptomatic animals; with TLR9 being significantly raised in relation to the other three groups. Comparison of the three infected groups showed increases in many PRRs, with CARD15 and Dectin-2 being particularly high in both diseased groups. Significant differences between the pauci- and multibacillary animals included TLR2, CD14 and Dectin-1. Sequence analysis of TLR2 exon 2 and CARD15 exon 11 in the forty animals failed to identify any relationship between SNPs and pathological form.

Sensing of viral infection and activation of innate immunity by toll-like receptor 3

Toll-like receptors (TLRs) form a major group of transmembrane receptors that are involved in the detection of invading pathogens. Double-stranded RNA is a marker for viral infection that is recognized by TLR3. TLR3 triggering activates specific signaling pathways that culminate in the activation of NF-kappaB and IRF3 transcription factors, as well as apoptosis, enabling the host to mount an effective innate immune response through the induction of cytokines, chemokines, and other proinflammatory mediators. In this review, we describe the paradoxical role of TLR3 in innate immunity against different viruses and in viral pathogenesis but also the evidence for TLR3 as a "danger" receptor in nonviral diseases. We also discuss the structure and cellular localization of TLR3, as well as the complex signaling and regulatory events that contribute to TLR3-mediated immune responses.

IL-1R1/MyD88 signaling and the inflammasome are essential in pulmonary inflammation and fibrosis in mice

The molecular mechanisms of acute lung injury resulting in inflammation and fibrosis are not well established. Here we investigate the roles of the IL-1 receptor 1 (IL-1R1) and the common adaptor for Toll/IL-1R signal transduction, MyD88, in this process using a murine model of acute pulmonary injury. Bleomycin insult results in expression of neutrophil and lymphocyte chemotactic factors, chronic inflammation, remodeling, and fibrosis. We demonstrate that these end points were attenuated in the lungs of IL-1R1- and MyD88-deficient mice. Further, in bone marrow chimera experiments, bleomycin-induced inflammation required primarily MyD88 signaling from radioresistant resident cells. Exogenous rIL-1beta recapitulated a high degree of bleomycin-induced lung pathology, and specific blockade of IL-1R1 by IL-1 receptor antagonist dramatically reduced bleomycin-induced inflammation. Finally, we found that lung IL-1beta production and inflammation in response to bleomycin required ASC, an inflammasome adaptor molecule. In conclusion, bleomycin-induced lung pathology required the inflammasome and IL-1R1/MyD88 signaling, and IL-1 represented a critical effector of pathology and therapeutic target of chronic lung inflammation and fibrosis.

Prolonged exposure to IL-1beta and IFNgamma induces necrosis of L929 tumor cells via a p38MAPK/NF-kappaB/NO-dependent mechanism

Interleukin-1beta (IL-1beta) is a cytokine that shares with tumor necrosis factor (TNF) the ability to initiate largely similar signaling pathways, leading to proinflammatory gene expression. In contrast to TNF, however, IL-1beta is not believed to induce tumor cell death. Here we demonstrate that prolonged treatment with IL-1beta, in combination with interferon-gamma (IFNgamma), is cytotoxic for L929 tumor cells. IL-1beta/IFNgamma-induced cytotoxicity requires only minimal amounts of IL-1beta and shows morphological features of necrosis. Although TNF induces a similar response, we could exclude a contribution of endogenous TNF production in the effect of IL-1beta/IFNgamma. Cell death in response to IL-1beta/IFNgamma is independent of caspases, but requires the IL-1beta/IFNgamma-induced production of inducible nitric oxide synthase (iNOS) and NO. Moreover, necrosis and iNOS/NO production could be prevented by treatment of the cells with a p38 mitogen activated protein kinase (p38MAPK) or IkappaB kinase beta inhibitor. Altogether, these findings demonstrate that prolonged exposure to IL-1beta plus IFNgamma induces L929 tumor cell necrosis, via a p38MAPK and nuclear factor-kappaB (NF-kappaB)-dependent signaling pathway, leading to the expression of iNOS and the production of toxic NO levels.

Inflammatory cardiac valvulitis in TAX1BP1-deficient mice through selective NF-kappaB activation

Nuclear factor kappa B (NF-kappaB) is a key mediator of inflammation. Unchecked NF-kappaB signalling can engender autoimmune pathologies and cancers. Here, we show that Tax1-binding protein 1 (TAX1BP1) is a negative regulator of TNF-alpha- and IL-1beta-induced NF-kappaB activation and that binding to mono- and polyubiquitin by a ubiquitin-binding Zn finger domain in TAX1BP1 is needed for TRAF6 association and NF-kappaB inhibition. Mice genetically knocked out for TAX1BP1 are born normal, but develop age-dependent inflammatory cardiac valvulitis, die prematurely, and are hypersensitive to low doses of TNF-alpha and IL-1beta. TAX1BP1-/- cells are more highly activated for NF-kappaB than control cells when stimulated with TNF-alpha or IL-1beta. Mechanistically, TAX1BP1 acts in NF-kappaB signalling as an essential adaptor between A20 and its targets.

Critical involvement of pneumolysin in production of interleukin-1alpha and caspase-1-dependent cytokines in infection with Streptococcus pneumoniae in vitro: a novel function of pneumolysin in caspase-1 activation

Pneumolysin is a pore-forming cytolysin known as a major virulence determinant of Streptococcus pneumoniae. This protein toxin has also been shown to activate the Toll-like receptor 4 (TLR4) signaling pathway. In this study, a mutant S. pneumoniae strain deficient in pneumolysin (Deltaply) and a recombinant pneumolysin protein (rPLY) were constructed. Upon infection of macrophages in vitro, the ability to induce the production of interleukin-1alpha (IL-1alpha), IL-1beta, and IL-18 was severely impaired in the Deltaply mutant, whereas there was no marked difference in the induction of tumor necrosis factor alpha (TNF-alpha) and IL-12p40 between the wild type and the Deltaply mutant of S. pneumoniae. When macrophages were stimulated with rPLY, the production of IL-1alpha, IL-1beta, and IL-18 was strongly induced in a TLR4-dependent manner, whereas lipopolysaccharide, a canonical TLR4 agonist, hardly induced these cytokines. In contrast, lipopolysaccharide was more potent than rPLY in inducing the production of TNF-alpha, IL-6, and IL-12p40, the cytokines requiring no caspase activation. Activation of caspase-1 was observed in macrophages stimulated with rPLY but not in those stimulated with lipopolysaccharide, and the level of activation was higher in macrophages infected with wild-type S. pneumoniae than in those infected with the Deltaply mutant. These results clearly indicate that pneumolysin plays a key role in the host response to S. pneumoniae, particularly in the induction of caspase-1-dependent cytokines.

Molecular architecture of signal complexes regulating immune cell function

Signals transmitted via multichain immunoreceptors control the development, differentiation and activation of hematopoetic cells. The cytoplasmic parts of these receptors contain immunoreceptor tyrosine-based activation motifs (ITAMs) that upon phosphorylation by members of the Src tyrosine kinase family orchestrate a complex set of signaling events involving tyrosine phosphorylation, generation of second messengers like DAG, IP3 and Ca2+, activation of effector molecules like Ras and MAPKs and the translocation and activation of transcription factors like NFAT, API and NF-kB. Spatial and temporal organization of these signaling events is essential both to connect the receptors to downstream cascades as well as to control the functional outcome of the immune activation. Throughout this process control and fine-tuning of the different signals are necessary both for effective immune function and in order to avoid inappropriate or exaggerated immune activation and autoimmunity. This control includes modulating mechanisms that set the threshold for activation and reset the activation status after an immune response has been launched. One immunomodulating pathway is the cAMP-protein kinase A-Csk pathway scaffolded by a supramolecular complex residing in lipid rafts with the A kinase-anchoring protein (AKAP) ezrin, the Csk-binding protein PAG and a linker between the two, EBP50. Failure of correct scaffolding and loss of spatiotemporal control can potentially have severe consequences, leading to immune failure or autoimmunity. The clinical relevance of supramolecular complexes specifically organized by scaffolding proteins in regulating immune activity and the specter of genetic diseases linked to different signaling components suggest that protein-protein contact surfaces can be potential targets for drug intervention. It is also of interest to note that different pathogens have evolved strategies to specifically modulate signal integration, thereby rewiring the signal in a way beneficial for their survival. In addition to demonstrating the importance of different signal processes, these adaptations are elegant illustrations of the potential for drug targeting of protein assembly. This chapter reviews some of the important scaffolding events downstream of immunoreceptors with focus on signaling transduction through the T-cell receptor (TCR).

Systemic inflammation after trauma

Trauma is still one of the main reasons for death among the population worldwide. Mortality occurring early after injury is due to "first hits", including severe organ injury, hypoxia, hypovolaemia or head trauma. Massive injury leads to activation of the immune system and the early inflammatory immune response after trauma has been defined as systemic inflammatory response syndrome (SIRS). "Second hits" such as infections, ischaemia/reperfusion or operations can further augment the pro-inflammatory immune response and have been correlated with the high morbidity and mortality in the latter times after trauma. SIRS can lead to tissue destruction in organs not originally affected by the initial trauma with subsequent development of multi-organ dysfunction (MOD). The initial pro-inflammatory response is followed by an anti-inflammatory response and can result in immune suppression with high risk of infection and sepsis. Trauma causes activation of nearly all components of the immune system. It activates the neuroendocrine system and local tissue destruction and accumulation of toxic byproducts of metabolic respiration leads to release of mediators. Extensive tissue injury may result in spillover of these mediators into the peripheral bloodstream to further maintain and augment the pro-inflammatory response. Hormones like ACTH, corticosteroids and catecholamines as well as cytokines, chemokines and alarmins play important roles in the initiation and persistence of the pro-inflammatory response after severe injury. The purpose of this review is therefore to describe the immunological events after trauma and to introduce important mediators and pathways of the inflammatory immune response.

Pellino proteins: novel players in TLR and IL-1R signalling

Members of the Toll-like receptor (TLR) and interleukin-1 receptor (IL-1R) family play important roles in immunity and inflammation. They initiate common intracellular signalling cascades leading to the activation of nuclear factor-κB (NF-κB) and other transcription factors that stimulate the expression of a variety of genes that shape an appropriate immune response. TLR/IL-1R signalling involves multiple protein–protein interactions, but the mechanisms that regulate these interactions are still largely unclear. In this context, Pellino proteins have been suggested to function as evolutionary conserved scaffold proteins in TLR/IL-1R signalling. However, recently Pellino proteins were also proposed to function as novel ubiquitin ligases for IL-1R associated kinase 1 (IRAK-1). Here we review our current knowledge on the expression, biological role and mechanism of action of Pellino proteins in TLR/IL-1R-induced signalling.

A novel alternatively spliced interleukin-1 receptor accessory protein mIL-1RAcP687

The 570-amino acid membrane form of IL-1RAcP (mIL-1RAcP) plays a pivotal role in the IL-1 signal transduction and response. We have identified another membrane form of IL-1RAcP with 687 amino acids (named as mIL-1RAcP687 hereon). Its except the last amino acid N-terminal 448 amino acid portion, containing three extracellular immunoglobulin domains, one transmembrane domain, and Box 1 and Box 2 of Toll/IL1 Receptor (TIR) domain, is identical to that of mIL-1RAcP. In contrast, the C-terminal 239 amino acid portion of mIL-1RAcP687, containing Box 3 of TIR domain, is unique. The mIL-1RAcP687 splice variant is derived from the first 11 exons except 9b, and a newly identified exon 13 of IL-1RAcP gene, while mIL-1RAcP is derived from the first 12 exons except 9b. Furthermore, mIL-1RAcP687 can associate with proteins involved in the upstream IL-1 signaling pathway such as IL-1RI, Tollip, and MyD88. It thus activates downstream signaling events to activate transcription factor NF-kappaB, and induce the expression of IL-1 responsive genes such as TNF-alpha and GM-CSF. These results demonstrate that like mIL-1RAcP, mIL-1RAcP687 functions in the IL-1 signal transduction and response. Identification of mIL-1RAcP687 adds further complexity to the regulation of IL-1 signaling and its subsequent response.

Constitutive association of MyD88 to IRAK in HTLV-I-transformed T cells

OBJECTIVE

Constitutive activation of nuclear factor (NF)-kappaB is a common feature of human T-cell leukemia virus type I (HTLV-I)-transformed T cells. Inhibition of NF-kappaB activity reduces cell growth and induces apoptosis of HTLV-I-transformed T cells, suggesting a central role of NF-kappaB in their proliferation and survival. In this study, we investigated whether MyD88, an adaptor protein of Toll-like receptor (TLR) signaling, contributes to constitutive NF-kappaB activation in HTLV-I-transformed T cells.

MATERIALS AND METHODS

Activation status of MyD88 and interleukin (IL)-1R-associated kinase 1 (IRAK1) in HTLV-I-transformed human T cells, MT2, MT4, and HUT102 was examined by using Western blot and immunoprecipitation. TLR expression was evaluated with reverse transcription polymerase chain reaction. An expression vector encoding a dominant negative MyD88 with a deletion of its death domain (MyD88dn) was transfected into MT2 cells to evaluate roles of MyD88 in spontaneous activation of cytokine gene promoters and transcription factors, proliferation, and apoptosis in HTLV-I-transformed T cells.

RESULTS

Constitutive association of MyD88 with IRAK1 was observed in all three of HTLV-I-transformed T cells, but not in HTLV-I-negative T cells, such as Jurkat, HUT78, and MOLT4. MT2 cells showed expression of TLR-1, -6, and -10 mRNAs. Constitutive activation of NF-kappaB and NF-IL-6 and cytokine gene promoters, such as IL-1alpha, interferon-gamma, and tumor necrosis factor-alpha in MT2 cells was inhibited by MyD88dn expression. MyD88dn reduced proliferation and induced apoptosis of MT2 cells. HTLV-I Tax enhanced TLR expression and synergistically activated NF-kappaB with wild-type MyD88.

CONCLUSION

Our results show a novel pathway in NF-kappaB activation in HTLV-I-transformed T cells and further demonstrate a critical role of MyD88 in their dysregulated gene activation, survival, and proliferation.

Mechanisms of dexamethasone-mediated inhibition of Toll-like receptor signaling induced by Neisseria meningitidis and Streptococcus pneumoniae

Excessive inflammation contributes to the pathogenesis of bacterial meningitis, which remains a serious disease despite treatment with antibiotics. Therefore, anti-inflammatory drugs have important therapeutic potential, and clinical trials have revealed that early treatment with dexamethasone significantly reduces mortality and morbidity from bacterial meningitis. Here we investigate the molecular mechanisms behind the inhibitory effect of dexamethasone upon the inflammatory responses evoked by Neisseria meningitidis and Streptococcus pneumoniae, two of the major causes of bacterial meningitis. The inflammatory cytokine response was dependent on Toll-like receptor signaling and was strongly inhibited by dexamethasone. Activation of the NF-kappaB pathway was targeted at several levels, including inhibition of IkappaB phosphorylation and NF-kappaB DNA-binding activity as well as upregulation of IkappaB alpha synthesis. Our data also revealed that the timing of steroid treatment relative to infection was important for achieving strong inhibition, particularly in response to S. pneumoniae. Altogether, we describe important targets of dexamethasone in the inflammatory responses evoked by N. meningitidis and S. pneumoniae, which may contribute to our understanding of the clinical effect and the importance of timing with respect to corticosteroid treatment during bacterial meningitis.

Tumor suppressor CYLD acts as a negative regulator for non-typeable Haemophilus influenza-induced inflammation in the middle ear and lung of mice

Non-typeable Haemophilus influenza (NTHi) is an important human pathogen causing respiratory tract infections in both adults and children. NTHi infections are characterized by inflammation, which is mainly mediated by nuclear transcription factor kappaB (NF-κB)-dependent production of inflammatory mediators. The deubiquitinating enzyme cylindromatosis (CYLD), loss of which was originally reported to cause a benign human syndrome called cylindromatosis, has been identified as a key negative regulator for NF-κB in vitro. However, little is known about the role of CYLD in bacteria-induced inflammation in vivo. Here, we provided direct evidence for the negative role of CYLD in NTHi-induced inflammation of the mice in vivo. Our data demonstrated that CYLD is induced by NTHi in the middle ear and lung of mice. NTHi-induced CYLD, in turn, negatively regulates NTHi-induced NF-κB activation through deubiquitinating TRAF6 and 7 and down-regulates inflammation. Our data thus indicate that CYLD acts as a negative regulator for NF-κB-dependent inflammation in vivo, hence protecting the host against detrimental inflammatory response to NTHi infection.

IL-1 receptor accessory protein and ST2 comprise the IL-33 receptor complex

IL-33 (IL-1F11) is a recently described member of the IL-1 family of cytokines that stimulates the generation of cells, cytokines, and Igs characteristic of a type 2 immune response. IL-33 mediates signal transduction through ST2, a receptor expressed on Th2 and mast cells. In this study, we demonstrate that IL-33 and ST2 form a complex with IL-1R accessory protein (IL-1RAcP), a signaling receptor subunit that is also a member of the IL-1R complex. Additionally, IL-1RAcP is required for IL-33-induced in vivo effects, and IL-33-mediated signal transduction can be inhibited by dominant-negative IL-1RAcP. The implications of this shared usage of IL-1RAcP by IL-1(alpha and beta) and IL-33 are discussed.

Differential expression of pattern recognition receptors in sheep tissues and leukocyte subsets

The various members of the different pattern recognition receptor families are now recognized as playing a crucial role in the initial interactions between a pathogen and the host. This paper identifies all 10 members of the TLR family in sheep as well as key members of the C-type lectin and NLR families. Our data show that sheep possess the 'human' and not the 'mouse' pattern of TLRs and confirm the high degree of sequence identity between orthologous genes in the different species. In the absence of definitive antibodies, qRT-PCR assays were developed to quantify PRR transcript expression patterns in a range of normal sheep tissues as well as isolated dendritic cell (DC) and leukocyte subsets. These data show that the lymphoid organs (spleen and lymph nodes) express the widest range of PRRs and that organs such as the lung and kidney have distinctive arrays of PRRs that reflect their potential risk of pathogen exposure. In addition we show that the two DC subsets, defined by the differential expression of CD172a/CD45RA and their cytokine expression profiles, have different and characteristic PRR complements again possibly reflecting their distinctive function. These data are important for future studies on the role of PRRs in disease pathogenesis and control.

Interactions of interleukin-1 with neurotrophic factors in the central nervous system: beneficial or detrimental?

Interleukin (IL)-1 is a multifunctional cytokine that plays a key role in mediating inflammation in the brain. Many different cell types in the brain express the IL-1 receptor and respond to this cytokine by activating cell-type-specific signaling pathways leading to distinct functional responses, which collectively comprise the inflammatory response in the brain. One key effect of IL-1 in the brain is the induction of trophic factor production by glial cells, which has traditionally been considered a neuroprotective response to injury or disease. However, recent studies have shown that nerve growth factor, which is regulated by IL-1, can induce neuronal survival or apoptosis via different receptors. This article examines the interaction of IL-1 with different trophic factors in the brain.

IL-33 and ST2 comprise a critical biomechanically induced and cardioprotective signaling system

ST2 is an IL-1 receptor family member with transmembrane (ST2L) and soluble (sST2) isoforms. sST2 is a mechanically induced cardiomyocyte protein, and serum sST2 levels predict outcome in patients with acute myocardial infarction or chronic heart failure. Recently, IL-33 was identified as a functional ligand of ST2L, allowing exploration of the role of ST2 in myocardium. We found that IL-33 was a biomechanically induced protein predominantly synthesized by cardiac fibroblasts. IL-33 markedly antagonized angiotensin II- and phenylephrine-induced cardiomyocyte hypertrophy. Although IL-33 activated NF-kappaB, it inhibited angiotensin II- and phenylephrine-induced phosphorylation of inhibitor of NF-kappa B alpha (I kappa B alpha) and NF-kappaB nuclear binding activity. sST2 blocked antihypertrophic effects of IL-33, indicating that sST2 functions in myocardium as a soluble decoy receptor. Following pressure overload by transverse aortic constriction (TAC), ST2(-/-) mice had more left ventricular hypertrophy, more chamber dilation, reduced fractional shortening, more fibrosis, and impaired survival compared with WT littermates. Furthermore, recombinant IL-33 treatment reduced hypertrophy and fibrosis and improved survival after TAC in WT mice, but not in ST2(-/-) littermates. Thus, IL-33/ST2 signaling is a mechanically activated, cardioprotective fibroblast-cardiomyocyte paracrine system, which we believe to be novel. IL-33 may have therapeutic potential for beneficially regulating the myocardial response to overload.

Exploitation of eukaryotic ubiquitin signaling pathways by effectors translocated by bacterial type III and type IV secretion systems

The specific and covalent addition of ubiquitin to proteins, known as ubiquitination, is a eukaryotic-specific modification central to many cellular processes, such as cell cycle progression, transcriptional regulation, and hormone signaling. Polyubiquitination is a signal for the 26S proteasome to destroy earmarked proteins, but depending on the polyubiquitin chain topology, it can also result in new protein properties. Both ubiquitin-orchestrated protein degradation and modification have also been shown to be essential for the host's immune response to pathogens. Many animal and plant pathogenic bacteria utilize type III and/or type IV secretion systems to inject effector proteins into host cells, where they subvert host signaling cascades as part of their infection strategy. Recent progress in the determination of effector function has taught us that playing with the host's ubiquitination system seems a general tactic among bacteria. Here, we discuss how bacteria exploit this system to control the timing of their effectors' action by programming them for degradation, to block specific intermediates in mammalian or plant innate immunity, or to target host proteins for degradation by mimicking specific ubiquitin/proteasome system components. In addition to analyzing the effectors that have been described in the literature, we screened publicly available bacterial genomes for mimicry of ubiquitin proteasome system subunits and detected several new putative effectors. Our understanding of the intimate interplay between pathogens and their host's ubiquitin proteasome system is just beginning. This exciting research field will aid in better understanding this interplay, and may also provide new insights into eukaryotic ubiquitination processes.

THE IN VIVO ANTITUMORAL EFFECTS OF LIPOPOLYSACCHARIDE AGAINST GLIOBLASTOMA MULTIFORME ARE MEDIATED IN PART BY TOLL-LIKE RECEPTOR 4

OBJECTIVE

Toll-like receptor 4 (Tlr-4) mediates many biological effects of lipopolysaccharide (LPS), which has antitumoral effects on glioblastoma both in vivo and in vitro. However, the precise role of Tlr-4 in these antitumoral effects remains unknown.

METHODS

The role of Tlr-4 in the antitumoral effect of LPS on glioblastomas was assessed in wild-type BALB/c mice and in Tlr-4 knockout (KO) BALB/c mice. Mice were implanted with DBT glioblastoma cells intracranially or subcutaneously, were treated with intratumoral LPS, and were assessed by histopathological examination for degrees of tumor progression and inflammation. Flow cytometry and Western blotting with antibodies to the Tlr-4 receptor and flow cytometry to the related CD14 moiety were performed to quantitate the expression levels of these two receptors by glioblastoma cells.

RESULTS

For subcutaneous tumors, LPS caused near complete tumor elimination in wild-type mice, but only a 50% reduction in Tlr-4 KO mice. For mice implanted with intracranial glioblastomas, LPS increased survival times modestly in wild-type mice, but showed no benefit in the Tlr-4 KO mice. There were no histological differences among wild-type and Tlr-4 KO mice, except for tumor size. In both models, an early neutrophilic and later macrophage-rich inflammatory infiltrate were seen after LPS administration. Quantitative flow cytometry and Western blotting showed no Tlr-4 receptor or CD14 expression in murine and human glioblastoma cells in vitro, and Western blotting suggested that Tlr-4 effects are mediated by nontumoral elements such as microglia and inflammatory cells.

CONCLUSION

LPS-induced antitumoral effects on glioblastoma multiforme are mediated, in part, by the Tlr-4 receptor. Further understanding of this process may lead to novel treatment strategies for this uniformly fatal disease.

The LIM Protein, LIMD1, Regulates AP-1 Activation through an Interaction with TRAF6 to Influence Osteoclast Development

Increasingly a number of proteins important in the regulation of bone osteoclast development have been shown primarily influence osteoclastogenesis under conditions of physiologic or pathologic stress. Why basal osteoclastogenesis is normal and how these proteins regulate stress osteoclastogenic responses, as opposed to basal osteoclastogenesis, is unclear. LIM proteins of the Ajuba/Zyxin family localize to cellular sites of cell adhesion where they contribute to the regulation of cell adhesion and migration, translocate into the nucleus where they can affect cell fate, but are also found in the cytoplasm where their function is largely unknown. We show that one member of this LIM protein family, Limd1, is uniquely up-regulated during osteoclast differentiation and interacts with Traf6, a critical cytosolic regulator of RANK-L-regulated osteoclast development. Limd1 positively affects the capacity of Traf6 to activate AP-1, and Limd1(-/-) osteoclast precursor cells are defective in the activation of AP-1 and thus induction of NFAT2. Limd1(-/-) mice, although having normal basal bone osteoclast numbers and bone density, are resistant to physiological and pathologic osteoclastogenic stimuli. These results implicate Limd1 as a potentially important regulator of osteoclast development under conditions of stress.

Microbial heat shock protein 70 stimulatory properties have different TLR requirements

Members of the HSP70 family have acquired special significance in immunity. Among other receptors, toll like receptor (TLR)-2 and TLR-4 have been suggested to be involved in HSP70-mediated signalling. We have previously shown that recombinant HSP70 from Trypanosoma cruzi and from Plasmodium falciparum function as adjuvants. In the present study, we have extended the study with other microbial HSPs (mHSPs) and considered of interest to assess the influence of TLR-2 and TLR-4 in mHSP-promoted responses. To test this, we evaluated the adjuvant effect of various mHSP molecules in TLR-2(-/-), TLR-4(-/-) and MyD88(-/-) mice. We show that all the mHSPs tested are strong adjuvants and induced IL-12 production by bone marrow macrophages. However, even within the same family, mHSPs induced different types of immune responses. Furthermore, the mHSPs tested, possess different requirements for signaling through TLRs. Interestingly, Tc70 was found to induce in vivo and in vitro responses in both TLR-2(-/-) and TLR-4(-/-) mice. Possible implications of our findings are taken up in the discussion section.

The interleukin-1 receptor family

The cytokines IL-1 and IL-18 are key molecules both in the innate and in the adaptive immune response. Their activity is mediated by specific receptors present on the membrane of target cells. It has become apparent that these receptors are members of a larger family of related receptors, most of which are apparently involved in the mechanisms of host defense. Thus, the large Toll/IL-1R (TIR) superfamily encompasses the Ig domain family (IL-1 receptors, IL-18 receptors, and IL-1R-like receptors), the leucine-rich domain family [the Toll-like receptors (TLR) and similar receptors], and a series of TIR domain-containing intracellular adapter molecules. The TIR superfamily is defined by a common intracellular TIR domain, involved in the initiation of signaling. A group of TIR domain-containing adapters (MyD88, TIRAP, TRIF, and TRAM) are differentially recruited to the Toll/IL-1 receptors, contributing to the specificity of signaling. Recent studies have also begun to unravel the mechanisms of negative regulation of the Toll/IL-1 receptors. The orphan receptor TIR8/SIGIRR, a member of TIR superfamily, while unable to initiate signaling, can negatively modulate the TIR-mediated responses. Other negative regulators of the Toll/IL-1R family include T1/ST2, some soluble forms of TLR, and MyD88s. The coordinated positive and negative regulation of the TIR activation ensures the appropriate modulation of the innate and inflammatory responses and avoids the risk of pathological derangement. This chapter will consider in detail the characteristics and functional role of the Ig domain receptor subfamily in the regulation of host defense and their possible role in pathology.

MEKK3 is essential for lipopolysaccharide-induced interleukin-6 and granulocyte-macrophage colony-stimulating factor production in macrophages

Mitogen-activated protein/ERK kinase kinase 3 (MEKK3) is a Ser/Thr protein kinase belonging to the MEKK/STE11 subgroup of the MAP3K family. Recently, we found that MEKK3 plays a critical role in interleukin-1 (IL-1) receptor and Toll-like receptor 4 signalling using established primary mouse embryonic fibroblast (MEF) cell lines. However, the function of MEKK3 in immune cells has not been studied because germ-line MEKK3 knockout mice are embryonically lethal between embryonic days 10 and 11. In this study, we used small interference RNA to the mouse Mekk3 gene to specifically knock down MEKK3 expression in the macrophage line Raw264.7. We found that the lipopolysaccharide-induced IL-6 and granulocyte-macrophage colony-stimulating factor (GM-CSF) production was dramatically decreased in MEKK3 knockdown cells whereas the tumour necrosis factor-alpha and IL-1beta production were not affected. We also observed that the ERK1/2, p38 and JNK MAPK induction in MEKK3 knockdown cells were moderately inhibited within the first 60 min of stimulation, while the ERK and p38 were more severely inhibited after 2-4 hr of stimulation. Degradation of IkappaBalpha was also partially blocked in MEKK3 knockdown cells. Notably, the impairment in IL-6 and GM-CSF production in the MEKK3 knockdown cells was restored by reintroducing a human Mekk3 cDNA that could not be targeted by mouse Mekk3-siRNAs. In conclusion, this study showed that MEKK3 is a crucial and specific regulator of the proinflammatory cytokines IL-6 and GM-CSF in macrophages and provided a novel method for investigating MEKK3 function in other immune cells.

Manipulation of the nuclear factor-kappaB pathway and the innate immune response by viruses

Viral and microbial constituents contain specific motifs or pathogen-associated molecular patterns (PAMPs) that are recognized by cell surface- and endosome-associated Toll-like receptors (TLRs). In addition, intracellular viral double-stranded RNA is detected by two recently characterized DExD/H box RNA helicases, RIG-I and Mda-5. Both TLR-dependent and -independent pathways engage the IkappaB kinase (IKK) complex and related kinases TBK-1 and IKKvarepsilon. Activation of the nuclear factor kappaB (NF-kappaB) and interferon regulatory factor (IRF) transcription factor pathways are essential immediate early steps of immune activation; as a result, both pathways represent prime candidates for viral interference. Many viruses have developed strategies to manipulate NF-kappaB signaling through the use of multifunctional viral proteins that target the host innate immune response pathways. This review discusses three rapidly evolving areas of research on viral pathogenesis: the recognition and signaling in response to virus infection through TLR-dependent and -independent mechanisms, the involvement of NF-kappaB in the host innate immune response and the multitude of strategies used by different viruses to short circuit the NF-kappaB pathway.

Toll-like receptor interactions: tolerance of MyD88-dependent cytokines but enhancement of MyD88-independent interferon-beta production

Toll-like receptors (TLRs) signal through two main pathways: a myeloid differentiation factor (MyD)88-dependent pathway that acts via nuclear factor kappaB (NF-kappaB) to induce proinflammatory cytokines such as tumour necrosis factor-alpha (TNF-alpha) and a MyD88-independent pathway that acts via type I interferons to increase the expression of interferon-inducible genes. Repeated signalling through TLR4 and a number of other TLRs has been reported to result in a reduction in the subsequent proinflammatory cytokine response, a phenomenon known as TLR tolerance. In this study we have shown that, whilst NF-kappaB activation and production of TNF-alpha and interleukin-12 by murine RAW264.7 and J774.2 cells in response to stimulation by TLR4, -5, -7 or -9, was reduced by prior stimulation with TLR4, -5, -7 or -9 ligands, the primary stimulation of TLR3, which does not use the MyD88 pathway, did not reduce the TNF-alpha or interleukin-12 responses to subsequent TLR stimulation. The response to TLR3 stimulation was not diminished by prior TLR ligand exposure. Furthermore, the production of interferon-beta (IFN-beta) following stimulation of TLR3 or -4, which is MyD88-independent, was increased by prior activation of TLR4, -5, -7 or -9. In contrast, TLR9 ligand-induced IFN-beta production, which is MyD88-dependent, was tolerized by prior TLR stimulation. These results are consistent with differential regulation of MyD88-dependent and MyD88-independent cytokine production following serial activation of TLRs.

Human hepatitis B viral e antigen interacts with cellular interleukin-1 receptor accessory protein and triggers interleukin-1 response

Human hepatitis B virus (HBV) can cause acute and chronic hepatitis, cirrhosis, and hepatocellular carcinoma. HBV e antigen (HBeAg), a secreted protein and not required for viral replication, is thought to play an immunoregulatory role during viral infection. However, the functional involvement of HBeAg in host immune response has not been fully elucidated. We report in this study that HBeAg can bind to interleukin-1 receptor accessory protein (IL-1RAcP). Interleukin-1 (IL-1) plays an important role in inflammation and regulation of immune response, and membrane form of IL-1RAcP (mIL-1RAcP) is an essential component of trimeric IL-1/IL-1 receptor/mIL-1RAcP complex. We show that glutathione S-transferase- or polyhistidine-tagged recombinant HBeAg can interact with endogenous mIL-1RAcP in vitro. Purified (His)6-HBeAg added in the culture medium can interact with overexpressed FLAG-tagged mIL-1RAcP in vivo. Indirect immunofluorescence and confocal microscopy show that HBeAg colocalizes with mIL-1RAcP on the cell surface. Furthermore, HBeAg is able to induce the interaction of IL-1 receptor I (IL-1RI) with mIL-1RAcP and trigger the recruitment of adaptor protein myeloid differentiation factor 88 (MyD88) to the IL-1RI/mIL-1RAcP complex. Assembly and activation of IL-1RI/mIL-1RAcP signaling complex by HBeAg can activate downstream NF-kappaB pathway through IkappaB degradation, induce NF-kappaB-dependent luciferase expression, and induce the expression of IL-1-responsive genes. Silencing of IL-1RAcP by small interfering RNA dramatically abolishes HBeAg-mediated NF-kappaB activation. These results demonstrate that HBeAg can trigger host IL-1 response by binding to mIL-1RAcP. The interaction of HBeAg with mIL-1RAcP may play an important role in modulating host immune response in acute and chronic HBV infection.

Essential role of TAK1 in thymocyte development and activation

The protein kinase TAK1 mediates the activation of NF-kappaB in response to stimulation by proinflammatory cytokines and microbial pathogens in the innate immunity pathways. However, the physiological function of TAK1 in the adaptive immunity pathways is unclear. By engineering mice lacking TAK1 in T cells, here, we show that TAK1 is essential for thymocyte development and activation in vivo. Deletion of TAK1 prevented the maturation of single-positive thymocytes displaying CD4 or CD8, leading to reduction of T cells in the peripheral tissues. Thymocytes lacking TAK1 failed to activate NF-kappaB and JNK and were prone to apoptosis upon stimulation. Our results provide the genetic evidence that TAK1 is required for the activation of NF-kappaB in thymocytes and suggest that TAK1 plays a central role in both innate and adaptive immunity.

New players in TLR-mediated innate immunity: PI3K and small Rho GTPases

Toll-like receptors (TLRs) play a crucial role in the innate immune system as a first line of defense against pathogens. TLR activation in phagocytes produces pro-inflammatory cytokines and chemokines that contribute directly to elimination of infectious agents and activation of adaptive immune responses. However, a sustained inflammatory response can result in tissue damage and generalized sepsis. This review summarizes the complex and sometimes conflicting links of TLR signaling with two important regulators of immune cells functions: phosphoinositide 3-kinases (PI3Ks) and small GTPases of the Rho family. A unified model of hierarchical organization of these signaling participants is still premature, given that the tools for delineating how control of TLRmediated pathways is achieved are just emerging. Critical progress in our understanding of spatial-temporal propagation of TLR signaling will certainly be provided in the near future by pharmacological targeting of PI3Ks using recently characterized, second-generation PI3K inhibitors in combination with gene-targeting strategies for PI3K subunits and Rho GTPases targeted to the murine myeloid compartment.

Lung epithelium as a sentinel and effector system in pneumonia--molecular mechanisms of pathogen recognition and signal transduction

Pneumonia, a common disease caused by a great diversity of infectious agents is responsible for enormous morbidity and mortality worldwide. The bronchial and lung epithelium comprises a large surface between host and environment and is attacked as a primary target during lung infection. Besides acting as a mechanical barrier, recent evidence suggests that the lung epithelium functions as an important sentinel system against pathogens. Equipped with transmembranous and cytosolic pathogen-sensing pattern recognition receptors the epithelium detects invading pathogens. A complex signalling results in epithelial cell activation, which essentially participates in initiation and orchestration of the subsequent innate and adaptive immune response. In this review we summarize recent progress in research focussing on molecular mechanisms of pathogen detection, host cell signal transduction, and subsequent activation of lung epithelial cells by pathogens and their virulence factors and point to open questions. The analysis of lung epithelial function in the host response in pneumonia may pave the way to the development of innovative highly needed therapeutics in pneumonia in addition to antibiotics.

MyD88 innate immune function in a zebrafish embryo infection model

Innate immunity signaling mechanisms during vertebrate embryogenesis are largely unknown. To study Toll-like receptor (TLR) signaling function in the zebrafish embryo model, we designed an experimental setup for antisense morpholino knockdown under conditions of bacterial infection. Clearance of Salmonella enterica serovar Typhimurium Ra bacteria was significantly impaired after knockdown of myeloid differentiation factor 88 (MyD88), a common adaptor protein in TLR and interleukin-1 receptor signaling. Thereby, we demonstrate for the first time that the innate immune response of the developing embryo involves MyD88-dependent signaling, which further establishes the zebrafish embryo as a model for the study of vertebrate innate immunity.

The myristoylation of TRIF-related adaptor molecule is essential for Toll-like receptor 4 signal transduction

TRIF-related adaptor molecule (TRAM) is the fourth Toll/IL-1 resistance domain-containing adaptor to be described that participates in Toll-like receptor (TLR) signaling. TRAM functions exclusively in the TLR4 pathway. Here we show by confocal microscopy that TRAM is localized in the plasma membrane and the Golgi apparatus, where it colocalizes with TLR4. Membrane localization of TRAM is the result of myristoylation because mutation of a predicted myristoylation site in TRAM (TRAM-G2A) brought about dissociation of TRAM from the membrane and its relocation to the cytosol. Further, TRAM, but not TRAM-G2A, was radiolabeled with [3H]myristate in vivo. Unlike wild-type TRAM, overexpression of TRAM-G2A failed to elicit either IFN regulatory factor 3 or NF-kappaB signaling. Moreover, TRAM-G2A was unable to reconstitute LPS responses in bone marrow-derived macrophages from TRAM-deficient mice. These observations provide clear evidence that the myristoylation of TRAM targets it to the plasma membrane, where it is essential for LPS responses through the TLR4 signal transduction pathway, and suggest a hitherto unappreciated manner in which LPS responses can be regulated.

TRAF6 activation of PI 3-kinase-dependent cytoskeletal changes is cooperative with Ras and is mediated by an interaction with cytoplasmic Src

Interleukin 1 (IL-1) has been implicated in the reorganization of the actin cytoskeleton. An expression vector encoding a PKB/Akt pleckstrin-homology domain fused to a fluorescent protein was used to detect phosphoinositide 3-kinase (PI 3-kinase) products. It was observed that PI 3-kinase was activated either by treatment with IL-1 or by expression of either TRAF6, Src, MyD88 or dominant-positive PI 3-kinase, and resulted in the formation of long filopodia-like cellular protrusions that appeared to branch at membrane sites consisting of clusters of phosphoinositide. This depended upon a TRAF6 polyproline motif and Src catalytic activity, and was blocked by inhibitors of PI 3-kinase, Src and Ras. Using both conventional and split fluorescent protein probes fused to expressed TRAF6 and Src in living cells, the polyproline sequence of TRAF6 and the Src-homology 3 (SH3) domain of Src were shown to be required for interaction between these two proteins. Interaction occurred within the cytoplasm, and not at either the cell membrane or cytoplasmic sequestosomes. In addition, co-transfection of vectors expressing fluorescent-protein-fused TRAF6 and non-fluorescent MyD88, IRAK1 and IRAK2 revealed an inverse correlation between increased sequestosome formation and activation of both PI 3-kinase and NF-kappaB. Although a key factor in TRAF6-dependent activation of PI 3-kinase, ectopic expression of Src was insufficient for NF-kappaB activation and, in contrast to NF-kappaB, was not inhibited by IRAK2.

Automatic pathway building in biological association networks

Background

Scientific literature is a source of the most reliable and comprehensive knowledge about molecular interaction networks. Formalization of this knowledge is necessary for computational analysis and is achieved by automatic fact extraction using various text-mining algorithms. Most of these techniques suffer from high false positive rates and redundancy of the extracted information. The extracted facts form a large network with no pathways defined.

Results

We describe the methodology for automatic curation of Biological Association Networks (BANs) derived by a natural language processing technology called Medscan. The curated data is used for automatic pathway reconstruction. The algorithm for the reconstruction of signaling pathways is also described and validated by comparison with manually curated pathways and tissue-specific gene expression profiles.

Conclusion

Biological Association Networks extracted by MedScan technology contain sufficient information for constructing thousands of mammalian signaling pathways for multiple tissues. The automatically curated MedScan data is adequate for automatic generation of good quality signaling networks. The automatically generated Regulome pathways and manually curated pathways used for their validation are available free in the ResNetCore database from Ariadne Genomics, Inc. [1]. The pathways can be viewed and analyzed through the use of a free demo version of PathwayStudio software. The Medscan technology is also available for evaluation using the free demo version of PathwayStudio software.

Variant IRAK-1 haplotype is associated with increased nuclear factor-kappaB activation and worse outcomes in sepsis

RATIONALE

The IL-1 receptor-associated kinase (IRAK-1) plays a central role in TLR2- and TLR4-induced activation of nuclear factor (NF)-kappaB, a critical event in the transcriptional regulation of many sepsis-associated proinflammatory mediators. There are two haplotypes for the IRAK-1 gene in Caucasians, with the variant haplotype consisting of five intron single-nucleotide polymorphisms (SNPs) and three exon SNPs.

OBJECTIVES

To examine the functional significance of the IRAK-1 variant haplotype in modifying nuclear translocation of NF-kappaB and affecting outcomes from sepsis.

MEASUREMENTS AND MAIN RESULTS

One hundred fifty-five Caucasian patients with sepsis were included. Twenty-one (14%) were homozygous for the IRAK-1 variant haplotype as determined by a SNP in which T is replaced with C at nucleotide 1,595 within exon 12 of the IRAK-1 gene. The IRAK-1 variant haplotype was associated with increased nuclear levels of NF-kappaB in LPS-stimulated peripheral blood neutrophils from patients with sepsis compared with that found in patients with wild-type IRAK-1 haplotype (p=0.0009). There was an increased incidence of shock (p=0.047) (odds ratio [OR], 2.9; 95% confidence interval [CI], 1.1-7.7), greater requirement for more prolonged mechanical ventilator support (p=0.04) (OR, 2.7; 95% CI, 1.05-6.9), and higher 60-d mortality (p=0.05) (OR, 2.7; 95% CI, 1.0-6.8) in patients with the IRAK-1 variant haplotype compared with wild type.

CONCLUSIONS

These results indicate that the IRAK-1 variant haplotype is functionally significant in patients with sepsis, being associated with increased nuclear translocation of NF-kappaB, more severe organ dysfunction, and higher mortality.

Interleukin-1 beta up-regulates tissue inhibitor of matrix metalloproteinase-1 mRNA and phosphorylation of c-jun N-terminal kinase and p38 in hepatic stellate cells

AIM: To study the relationship between interleukin-1beta (IL-1β) up-regulating tissue inhibitor of matrix metalloproteinase-1 (TIMMP-1) mRNA expression and phosphorylation of both c-jun N-terminal kinase (JNK) and p38 in rat hepatic stellate cells (HSC).

METHODS: RT-PCR was performed to measure the expression of TIMMP-1 mRNA in rat HSC. Western blot was performed to measure IL-1β-induced JNK and p38 activities in rat HSC.

RESULTS: TIMMP-1 mRNA expression (1.191 ± 0.079) was much higher after treatment with IL-1β (10 ng/mL) for 24 h than in control group (0.545 ± 0.091) (P<0.01). IL-1β activated JNK and p38 in a time-dependent manner. After stimulation with IL-1β for 0, 5, 15, 30, 60 and 120 min，the JNK activity was 0.982 ± 0.299，1.501 ± 0.720, 2.133 ± 0.882, 3.360 ± 0.452, 2.181 ± 0.789, and 1.385 ± 0.368, respectively. There was a significant difference in JNK activity at 15 min (P < 0.01), 30 min (P < 0.01) and 60 min (P < 0.01) in comparison to that at 0 min. The p38 activity was 1.061 ± 0.310，2.050 ± 0.863，2.380 ± 0.573, 2.973 ± 0.953, 2.421 ± 0.793, and 1.755 ± 0.433 at the 6 time points (0, 5, 15, 30, 60 and 120 min) respectively. There was a significant difference in p38 activity at 5 min (P < 0.05), 15 min (P < 0.01), 30 min (P < 0.01) and 60 min (P < 0.01) compared to that at 0 min. TIMMP-1 mRNA expression trended to decrease in 3 groups pretreated with different concentrations of SP600125 (10 µmol/L, 1.022 ± 0.113; 20 µmol/L, 0.869 ± 0.070; 40 µmol/L, 0.666 ± 0.123). Their decreases were all significant (P < 0.05, P < 0.01, P < 0.01) in comparison to control group (without SP600125 treatment, 1.163 ± 0.107). In the other 3 groups pretreated with different concentrations of SB203580 (10 µmol/L, 1.507 ± 0.099; 20 µmol/L, 1.698 ± 0.107; 40 µmol/L, 1.857 ± 0.054), the expression of TIMMP-1 mRNA increased. Their levels were higher than those in the control group (without SB203580 treatment, 1.027 ± 0.061) with a significant statistical significance (P < 0.01).

CONCLUSION: IL-1β has a direct action on hepatic fibrosis by up-regulating TIMMP-1 mRNA expression in rat HSC. JNK and p38 mitogen-activated protein kinases (MAPKs) are involved in IL-1β-induced TIMMP-1 gene expression, and play a distinct role in this process, indicating that p38 and JNK pathways cooperatively mediate TIMP-1 mRNA expression in rat HSC.

Alternate transcription of the Toll-like receptor signaling cascade

BACKGROUND

Alternate splicing of key signaling molecules in the Toll-like receptor (Tlr) cascade has been shown to dramatically alter the signaling capacity of inflammatory cells, but it is not known how common this mechanism is. We provide transcriptional evidence of widespread alternate splicing in the Toll-like receptor signaling pathway, derived from a systematic analysis of the FANTOM3 mouse data set. Functional annotation of variant proteins was assessed in light of inflammatory signaling in mouse primary macrophages, and the expression of each variant transcript was assessed by splicing arrays.

RESULTS

A total of 256 variant transcripts were identified, including novel variants of Tlr4, Ticam1, Tollip, Rac1, Irak1, 2 and 4, Mapk14/p38, Atf2 and Stat1. The expression of variant transcripts was assessed using custom-designed splicing arrays. We functionally tested the expression of Tlr4 transcripts under a range of cytokine conditions via northern and quantitative real-time polymerase chain reaction. The effects of variant Mapk14/p38 protein expression on macrophage survival were demonstrated.

CONCLUSION

Members of the Toll-like receptor signaling pathway are highly alternatively spliced, producing a large number of novel proteins with the potential to functionally alter inflammatory outcomes. These variants are expressed in primary mouse macrophages in response to inflammatory mediators such as interferon-gamma and lipopolysaccharide. Our data suggest a surprisingly common role for variant proteins in diversification/repression of inflammatory signaling.

MyD88-dependent and -independent signaling by IL-1 in neurons probed by bifunctional Toll/IL-1 receptor domain/BB-loop mimetics

Interleukin (IL)-1beta is a pluripotent proinflammatory cytokine that signals through the type-I IL-1 receptor (IL-1RI), a member of the Toll-like receptor family. In hypothalamic neurons, binding of IL-1beta to IL-1RI mediates transcription-dependent changes that depend on the recruitment of the cytosolic adaptor protein myeloid differentiation primary-response protein 88 (MyD88) to the IL-1RI/IL-1 receptor accessory protein (IL-1RAcP) complex through homomeric Toll/IL-1 receptor (TIR)-TIR interactions. Through design and synthesis of bifunctional TIR mimetics that disrupt the interaction of MyD88 with the IL-1RI/IL-1RAcP complex, we analyzed the involvement of MyD88 in the signaling of IL-1beta in anterior hypothalamic neurons. We show here that IL-1beta-mediated activation of the protein tyrosine kinase Src depended on a MyD88 interaction with the IL-1RI/IL-1RAcP complex. The activation of the protein kinase Akt/PKB depended on the recruitment of the p85 subunit of PI3K to IL-1RI and independent of MyD88 association with the IL-1RI/IL-1RAcP complex. These bifunctional TIR-TIR mimetics represent a class of low-molecular-weight compounds with both an antiinflammatory and neuroprotective potential. These compounds have the potential to inhibit the MyD88-dependent proinflammatory actions of IL-1beta, while permitting the potential neuronal survival supporting actions mediated by the MyD88-independent activation of the protein kinase Akt.

Identification and characterization of a novel bacterial virulence factor that shares homology with mammalian Toll/interleukin-1 receptor family proteins

Many important bacterial virulence factors act as mimics of mammalian proteins to subvert normal host cell processes. To identify bacterial protein mimics of components of the innate immune signaling pathway, we searched the bacterial genome database for proteins with homology to the Toll/interleukin-1 receptor (TIR) domain of the mammalian Toll-like receptors (TLRs) and their adaptor proteins. A previously uncharacterized gene, which we have named tlpA (for TIR-like protein A), was identified in the Salmonella enterica serovar Enteritidis genome that is predicted to encode a protein resembling mammalian TIR domains, We show that overexpression of TlpA in mammalian cells suppresses the ability of mammalian TIR-containing proteins TLR4, IL-1 receptor, and MyD88 to induce the transactivation and DNA-binding activities of NF-kappaB, a downstream target of the TIR signaling pathway. In addition, TlpA mimics the previously characterized Salmonella virulence factor SipB in its ability to induce activation of caspase-1 in a mammalian cell transfection model. Disruption of the chromosomal tlpA gene rendered a virulent serovar Enteritidis strain defective in intracellular survival and IL-1beta secretion in a cell culture infection model using human THP1 macrophages. Bacteria with disrupted tlpA also displayed reduced lethality in mice, further confirming an important role for this factor in pathogenesis. Taken together, our findings demonstrate that the bacterial TIR-like protein TlpA is a novel prokaryotic modulator of NF-kappaB activity and IL-1beta secretion that contributes to serovar Enteritidis virulence.

Limiting inflammatory responses during activation of innate immunity

The idea of the importance of mounting an inflammatory response for effective immunity is supported by a multiplicity of experimental data. It is also well understood that resolution of inflammation is essential for maintaining the balance between health and disease. When the normal regulatory mechanisms are disturbed, the potential for developing chronic inflammatory diseases is increased. Inflammation is a key element in the response of the innate immune system to a variety of challenges, including those provided by bacterial and viral infection as well as by damaged or dying host cells. Here we review elements of innate immunity that lead to inflammation and some of the host mechanisms that allow for the resolution of the inflammatory responses.

The tumor suppressor cylindromatosis (CYLD) acts as a negative regulator for toll-like receptor 2 signaling via negative cross-talk with TRAF6 AND TRAF7

Toll-like receptor 2 (TLR2) plays an important role in host defense against bacterial pathogens. Activation of TLR2 signaling not only induces the activation of innate immunity and instructs the development of the acquired immunity but also leads to the detrimental inflammatory responses in inflammatory and infectious diseases. To avoid detrimental inflammatory responses, TLR2 signaling must be tightly regulated. In contrast to the relative known positive regulation of TLR2 signaling, its negative regulation, however, is largely unknown. In addition the distal signaling components that link TLR2 to its downstream signaling pathways have yet to be further defined. In the present study we have provided direct evidence for the negative regulation of TLR2 signaling by the tumor suppressor cylindromatosis (CYLD). We showed that activation of TLR2 signaling by TLR2 ligands including peptidoglycan (PGN), MALP-2, and Pam3CSK4 induces activation of IKKs-IkappaBalpha and MKK3/6-p38 pathways not only by TRAF6 but also by TRAF7, a recently identified TRAF family member. The activation of both pathways leads to the transcription of TNF-alpha, IL-1beta, and IL-8 as well as CYLD. CYLD in turn leads to the inhibition of TRAF6 and TRAF7 likely via a deubiquitination-dependent mechanism. The present studies thus unveil a novel autoregulatory feedback mechanism that negatively controls TLR2-IKKs-IkappaBalpha/MKK3/6-p38-NF-kappaB-dependent induction of immune and inflammatory responses via negatively cross-talking with both TRAF6 and TRAF7. These findings provide novel insights into autoregulation and negative regulation of TLR signaling.

Innate mechanisms for Bifidobacterium lactis to activate transient pro-inflammatory host responses in intestinal epithelial cells after the colonization of germ-free rats

Bifidobacteria comprise a dominant microbial population group in the human intestinal tract with purported beneficial health effects on the host. In this study, we characterized the molecular mechanisms for the initial interaction of probiotic Bifidobacterium lactis strain BB12 with native and intestinal epithelial cell (IEC) lines. We showed that B. lactis-monoassociated Fisher F344 rats transiently induce phosphorylation/activation of the NF-kappaB transcriptionally active subunit RelA and the mitogen-activated protein kinase (MAPK) p38 in native IEC at day 5 after initial bacterial colonization. In addition, Interleukin 6 (IL-6) gene expression was significantly increased at day 5, demonstrating the physiological relevance of transient transcription factor activation in IEC. In contrast, Bacteroides vulgatus-monoassociated Fisher rats revealed RelA but not p38 MAPK phosphorylation and failed to trigger significant IL-6 gene expression in native IEC. Moreover, we demonstrated that B. lactis triggers NF-kappaB RelA and p38 MAPK phosphorylation in IEC lines. Adenoviral delivery of mutant IKK-beta (Ad5dnIKKbeta) and inhibition of the p38 MAPK pathway through the pharmacological inhibitor SB203580 significantly blocked B. lactis-induced IL-6 gene expression in IEC, suggesting that B. lactis triggers NF-kappaB and MAPK signaling to induce gene expression in the intestinal epithelium. Regarding the mechanisms of bacteria epithelial cell cross-talk, B. lactis-induced IL-6 gene expression was completely inhibited in TLR2 deficient mouse embryogenic fibroblasts (MEF TLR2-/-) as well as TLR2DeltaTIR transfected Mode-K cells. In conclusion, we demonstrated that probiotic bacteria transiently trigger innate signal transduction and pro-inflammatory gene expression in the intestinal epithelium at early stages of bacterial colonization.

LPS induces CD40 gene expression through the activation of NF-kappaB and STAT-1alpha in macrophages and microglia

CD40 is expressed on various immune cells, including macrophages and microglia. Aberrant expression of CD40 is associated with autoimmune inflammatory diseases such as multiple sclerosis and rheumatoid arthritis. Interaction of Toll-like receptor-4 (TLR4) with the Gram-negative bacteria endotoxin lipopolysaccharide (LPS) results in the induction of an array of immune response genes. In this study, we describe that LPS is a strong inducer of CD40 expression in macrophages and microglia, which occurs at the transcriptional level and involves the activation of the transcription factors nuclear factor-kappaB (NF-kappaB) and signal transducer and activator of transcription 1alpha (STAT-1alpha). LPS-induced CD40 expression involves the endogenous production of the cytokine interferon-beta (IFN-beta), which contributes to CD40 expression by the activation of STAT-1alpha. Blocking IFN-beta-induced activation of STAT-1alpha by IFN-beta-neutralizing antibody reduces LPS-induced CD40 gene expression. Furthermore, LPS induces acetylation and phosphorylation of histones H3 and H4 and the recruitment of NF-kappaB, STAT-1alpha, and RNA polymerase II on the CD40 promoter in vivo in a time-dependent manner, all events important for CD40 gene transcription. These results indicate that both LPS-induced NF-kappaB activation and endogenous production of IFN-beta that subsequently induces STAT-1alpha activation play critical roles in the transcriptional activation of the CD40 gene by LPS.

Cytokine-induced sickness behaviour: a neuroimmune response to activation of innate immunity

Sickness refers to a coordinated set of subjective, behavioural and physiological changes that develop in sick individuals during the course of an infection. These changes are due to the effects of interleukin-1 (IL-1) and other proinflammatory cytokines on brain cellular targets. Sickness behaviour is mediated by proinflammatory cytokines that are temporarily expressed in the brain during infection. These centrally produced cytokines are the same as those expressed by innate immune cells and they act on brain receptors that are identical to those characterized on immune cells. Primary afferent nerves represent the main communication pathway between peripheral and central cytokines. Proinflammatory cytokines modulate learning and memory processes. The expression and action of proinflammatory cytokines in the brain in response to peripheral cytokines are regulated by various molecular intermediates including anti-inflammatory cytokines such as interleukin-10 (IL-10) and the IL-1 receptor antagonist (IL-1ra), growth factors such as insulin-like growth factor-1 (IGF-1), hormones such as glucocorticoids and neuropeptides such as vasopressin and alpha-melanotropin.

The LIM protein Ajuba influences interleukin-1-induced NF-kappaB activation by affecting the assembly and activity of the protein kinase Czeta/p62/TRAF6 signaling complex

The Zyxin/Ajuba family of cytosolic LIM domain-containing proteins has the potential to shuttle from sites of cell adhesion into the nucleus and thus can be candidate transducers of environmental signals. To understand Ajuba's role in signal transduction pathways, we performed a yeast two-hybrid screen with the LIM domain region of Ajuba. We identified the atypical protein kinase C (aPKC) scaffold protein p62 as an Ajuba binding partner. A prominent function of p62 is the regulation of NF-kappaB activation in response to interleukin-1 (IL-1) and tumor necrosis factor signaling through the formation of an aPKC/p62/TRAF6 multiprotein signaling complex. In addition to p62, we found that Ajuba also interacted with tumor necrosis factor receptor-associated factor 6 (TRAF6) and PKCzeta. Ajuba recruits TRAF6 to p62 and in vitro activates PKCzeta activity and is a substrate of PKCzeta. Ajuba null mouse embryonic fibroblasts (MEFs) and lungs were defective in NF-kappaB activation following IL-1 stimulation, and in lung IKK activity was inhibited. Overexpression of Ajuba in primary MEFs enhances NF-kappaB activity following IL-1 stimulation. We propose that Ajuba is a new cytosolic component of the IL-1 signaling pathway modulating IL-1-induced NF-kappaB activation by influencing the assembly and activity of the aPKC/p62/TRAF6 multiprotein signaling complex.

A novel negative regulator for IL-1 receptor and Toll-like receptor 4

The Toll-IL-1 receptor (TIR) superfamily, defined by the presence of an intracellular TIR domain, initiates innate immunity via NF-kappaB activation, leading to production of proinflammatory cytokines. ST2 is a member of the TIR family that does not activate NF-kappaB and has been suggested as an important effector molecule of type 2 T helper cell responses. We have recently demonstrated that the membrane bound form of ST2 (ST2L) negatively regulated IL-1RI and TLR4 but not TLR3 signaling by sequestrating the adaptors MyD88 and Mal. In contrast to wild-type mice, ST2 deficient mice failed to develop endotoxin tolerance. Thus, ST2 suppresses IL-1R and TLR4 signaling via MyD88- and Mal-dependent pathways and modulates innate immunity. The results provide a molecular explanation for the role of ST2 in T(H)2 responses since inhibition of TLRs will promote a T(H)2 response and also identify ST2 as a key regulator of endotoxin tolerance.

Increased soluble interleukin-1 receptor type II proteolysis in the endometrium of women with endometriosis

Numerous functional changes were observed in the intrauterine endometrial tissue of women with endometriosis. Our previous studies revealed a marked decrease in the expression of interleukin-1 receptor type 2 (IL-1RII), a decoy receptor known for its ability to buffer IL-1 effects. The aim of the present study was to assess whether post-translational mechanisms such as proteolysis may contribute to the down-regulation of IL-1RII levels. Our data showed that soluble IL-1RII (sIL-1RII) concentrations released by freshly cultured endometrial tissue were significantly lower in women with endometriosis than in normal women (P < 0.01) and further revealed a statistically significant correlation between increased proteolysis and decreased sIL-1RII levels (P < 0.05; r = -0.47). (125)I-labelled soluble recombinant human IL-1RII ([(125)I]srhIL-1RII) was significantly more degraded in culture supernatant of tissues from women with endometriosis compared to normal women (P < 0.05), and natural tissue inhibitor of matrix metalloproteinase (TIMP)-1 inhibited [(125)I]srhIL-1RII degradation. Incubation of srhIL-1RII with active rhMMP-9 resulted in a dose-dependent degradation of srhIL-1RII as analysed by western blotting. Dual immunofluorescence showed an increased immunostaining for matrix metalloproteinase-9 in situ in the endometrial tissue of women with endometriosis compared to normal women and a decreased immunostaining for IL-1RII. The present study showed a reduced release of sIL-1RII by the endometrial tissue of women with endometriosis and revealed a proteolytic post-translational mechanism which may be involved in the down-regulation of IL-1RII levels. This may enhance IL-1-mediated activation of endometrial cells and contribute to the local immuno-inflammatory process observed in endometriosis patients.

A type I interferon autocrine-paracrine loop is involved in Toll-like receptor-induced interleukin-12p70 secretion by dendritic cells

Dendritic cells (DC) produce interleukin-12 (IL-12) in response to Toll-like receptor (TLR) activation. Two major TLR signaling pathways participate in the response to pathogens: the nuclear factor-kappaB (NF-kappaB)-dependent pathway leading to inflammatory cytokine secretion including IL-12 and the interferon (IFN)-dependent pathway inducing type I IFN and IFN-regulated genes. Here we show that the two pathways cooperate and are likely both necessary for inducing an optimal response to pathogens. R-848/Resiquimod (TLR7 ligand in the mouse and TLR7/8 ligand in human) synergized with poly(I:C) (TLR3 ligand) or lipopolysaccharide (LPS; TLR4 ligand) in inducing high levels of bioactive IL-12p70 secretion and IFN-beta mRNA accumulation by mouse bone marrow-derived DC (BM-DC). Strikingly, IL-12p70 but not IL-12p40 secretion was strongly reduced in BM-DC from STAT1(-/-) and IFNAR(-/-) mice. STAT1 tyrosine-phosphorylation, IL-12p35, and IFN-beta mRNA accumulation were strongly inhibited in IFNAR(-/-) BM-DC activated with the TLR ligand combinations. Similar observation were obtained in human TLR8-expressing monocyte-derived DC (moDC) using neutralizing anti-IFNAR2 antibodies, although results also pointed to a possible involvement of IFN-lambda1 (also known as IL-29). This suggests that TLR engagement on DC induces endogenous IFNs that further synergize with the NF-kappaB pathway for optimal IL-12p70 secretion. Moreover, analysis of interferon regulatory factors (IRF) regulation in moDC suggests a role for IRF7/8 in mediating IRF3-independent type I IFN and possibly IL-12p35 synthesis in response to TLR7/8.