Nucleotide-binding Oligomerization Domain Protein Research Articles

CARD6 Is Interferon Inducible but Not Involved in Nucleotide-Binding Oligomerization Domain Protein Signaling Leading to NF-κB Activation

We have previously reported the cloning and characterization of CARD6, a caspase recruitment domain (CARD)-containing protein that is structurally related to the interferon (IFN)-inducible GTPases. CARD6 associates with microtubules and with receptor-interacting protein 2 (RIP2). RIP2 mediates NF-kappaB activation induced by the intracellular nucleotide-binding oligomerization domain (NOD) receptors that sense bacterial peptidoglycan. Here we report that the expression of CARD6 and RIP2 in bone marrow-derived macrophages is rapidly induced by beta IFN and gamma IFN. This IFN-induced upregulation of CARD6 is suppressed by lipopolysaccharide (LPS), in contrast to LPS's enhancement of IFN-induced RIP2 upregulation. We generated CARD6-deficient (CARD6(-/-)) mice and carried out extensive analyses of signaling pathways mediating innate and adaptive immune responses, including the NOD pathways, but did not detect any abnormalities. Moreover, CARD6(-/-) mice were just as susceptible as wild-type mice to infection by Salmonella enterica serovar Typhimurium, Listeria monocytogenes, Candida albicans, lymphocytic choriomeningitis virus, or mouse adenovirus type 1. Thus, although structural and in vitro analyses strongly suggest an important role for CARD6 in immune defense, the physiological function of CARD6 remains obscure.

Blau syndrome‐associated mutations in exon 4 of the caspase activating recruitment domain 15 (CARD 15) gene are not found in ethnic Danes with sarcoidosis

Distinct mutations of the caspase activating recruitment domain 15 (CARD15) gene (also known as nucleotide-binding oligomerisation domain protein 2) on chromosome 16q are associated with the chronic granulomatous disease called Blau syndrome. Sarcoidosis is a systemic granulomatous disease, which has features in common with Blau syndrome. The aim of this study was to evaluate whether ethnic Danes with sarcoidosis have CARD15 mutations associated with Blau syndrome. Analysis of exon 4 of the CARD15 gene containing mutations associated with Blau syndrome was performed by polymerase chain reaction and sequencing of genomic DNA from 52 patients with histologically verified sarcoidosis. None of the patients had mutations in CARD15 associated with Blau syndrome. Eight other variations were found in exon 4: single nucleotide polymorphism (SNP)6 in 40% of the 104 alleles examined, SNP7 in 26%, c. 1833 C > T and SNP8 in 4%, c. 2107 C > T in 2%, and c. 931 C > T, c. 1292 C > T and c. 2377 G > A in 1%. One variation was found in intron 4 (IVS4 + 10 A > C) in 3% of the alleles. The frequencies of the variations in sarcoidosis patients were not statistically significant compared with frequencies in a control group of 103 healthy subjects. The course of disease was not significantly different in patients with or without variations in CARD15 or in the 46 patients with SNP6 and/or SNP7. Danish sarcoidosis patients have frequent variations in CARD15 exon 4, but do not present any mutation associated with Blau syndrome. The variations found had no influence on the course of disease.

ADP for ATP Exchange Mechanism

The signal transduction ATPases with numerous domains (STAND) family of proteins can be subdivided, according to the characteristics of the nucleotide-binding oligomerization domain (NOD), into three groups: the AP subfamily that includes APAF-1, an apoptotic mediator; the NACHT subfamily members that are involved in mammalian innate immunity; and the MalT subfamily of bacterial transcription factors. Although the presence of ATP is critical for the activation of these proteins, which are generally monomeric in the inactive state and oligomerize upon activation, it has been unclear what role ATP plays in this process and whether ATP hydrolysis was involved. Marquenet and Richet determined that the Escherichia coli MalT transcription factor cycles between an ADP-bound inactive form and an ATP-bound active form and that intrinsic ATP hydrolysis was required to return the protein to the inactive state. This is quite similar to the mechanism by which heterotrimeric guanine nucleotide-binding proteins (G proteins) and small guanosine triphosphatases (GTPases) function, except that the latter bind guanine nucleotides instead of adenosine nucleotides. Endogenous inhibitors of MalT--MalY, Aes, and MalK--bind and stabilize the monomeric form and, in the presence of ATP, maltotriose stimulates the oligomerization and formation of active MalT. The authors compared the activities of mutant MalT proteins that bound, but could not hydrolyze ATP, with the activity of wild-type MalT in vivo. MalT-D129A was most extensively studied. In vivo, MalT-D129A was hyperactive, stimulating transcription of a reporter to higher levels than the wild-type protein, and the activity of the ATP hydrolysis mutant was also not inhibited by MalK or MalY. Gel filtration assays showed that MalT-D129A did not bind effectively to MalY and that MalT-D129A existed in an oligomeric state with no detectable monomers in the presence or absence of added maltotriose or ATP. The wild-type protein bound MalY and existed as only monomers in the absence of maltotriose and ATP and as both oligomeric and monomeric forms in the presence of maltotriose and ATP. Assays to detect the bound nucleotide showed that MalT-D129A was bound to ATP in a 1:1 stoichometry, suggesting that it purified in an ATP-bound state. In contrast, wild-type MalT in the absence of ATP and maltotriose, either alone or when bound to MalY, was bound to ADP. Maltotriose stimulated the exchange of ADP for ATP on wild-type MalT, which was detected either using nonhydrolyzable analogs of ATP or with radiolabeled ATP. Thus, maltotriose appears to switch MalT from an inactive ADP-bound form to an activated ATP-bound form, and hydrolysis of ATP is necessary for MalT cycling and regulation. It will be interesting to see if other NOD proteins show similar adenine nucleotide exchange and hydrolysis as part of their signaling mechanism. E. Marquenet, E. Richet, How integration pf positive and negative regulatory signals by a STAND signaling protein depends on ATP hydrolysis. Mol. Cell 28 , 187-199 (2007). [PubMed]

Muramylpeptide shedding modulates cell sensing of Shigella flexneri

Bacterial infections trigger the activation of innate immunity through the interaction of pathogen-associated molecular patterns (PAMPs) with pattern recognition molecules (PRMs). The nucleotide-binding oligomerization domain (Nod) proteins are intracellular PRMs that recognize muramylpeptides contained in peptidoglycan (PGN) of bacteria. It is still unclear how Nod1 physically interacts with PGN, a structure internal to the Gram-negative bacterial envelope. To contribute to the understanding of this process, we demonstrate that, like Escherichia coli, Bordetella pertussis and Neisseria gonorrheae, the Gram-negative pathogen Shigella spontaneously releases PGN fragments and that this process can be increased by inactivating either ampG or mppA, genes involved in PGN recycling. Both Shigella mutants, but especially the strain carrying the mppA deletion, trigger Nod1-mediated NF-kappaB activation to a greater extent than the wild-type strain. Likewise, muramylpeptides spontaneously shed by Shigella are able per se to trigger a Nod1-mediated response consistent with the relative amount. Finally, we found that qualitative changes in muramylpeptide shedding can alter in vivo host responses to Shigella infection. Our findings support the idea that muramylpeptides released by pathogens during infection could modulate the immune response through Nod proteins and thereby influence the outcome of disease.

Mammalian NLR proteins; discriminating foe from friend

Eukaryotic organisms of the plant and animal kingdoms have developed evolutionarily conserved systems of defence against microbial pathogens. These systems depend on the specific recognition of microbial products or structures by molecules of the host innate immune system. The first mammalian molecules shown to be involved in innate immune recognition of, and defence against, microbial pathogens were the Toll-like receptors (TLRs). These proteins are predominantly but not exclusively located in the transmembrane region of host cells. Interestingly, mammalian hosts were subsequently found to also harbour cytosolic proteins with analogous structures and functions to plant defence molecules. The members of this protein family exhibit a tripartite domain structure and are characterized by a central nucleotide-binding oligomerization domain (NOD). Moreover, in common with TLRs, most NOD proteins possess a C-terminal leucine-rich repeat (LRR) domain, which is required for the sensing of microbial products and structures. Recently, the name 'nucleotide-binding domain and LRR' (NLR) was coined to describe this family of proteins. It is now clear that NLR proteins play key roles in the cytoplasmic recognition of whole bacteria or their products. Moreover, it has been demonstrated in animal studies that NLRs are important for host defence against bacterial infection. This review will particularly focus on two subfamilies of NLR proteins, the NODs and 'NALPs', which specifically recognize bacterial products, including cell wall peptidoglycan and flagellin. We will discuss the downstream signalling events and host cell responses to NLR recognition of such products, as well as the strategies that bacterial pathogens employ to trigger NLR signalling in host cells. Cytosolic recognition of microbial factors by NLR proteins appears to be one mechanism whereby the innate immune system is able to discriminate between pathogenic bacteria ('foe') and commensal ('friendly') members of the host microflora.

The pattern recognition receptor Nod1 activates CCAAT/enhancer binding protein β signalling in lung epithelial cells

The innate immune receptor nucleotide-binding oligomerisation domain protein 1 (Nod1) recognises peptidoglycan containing meso-diaminopimelic acid found in all Gram-negative and some Gram-positive bacteria. Nod1 has been shown to activate nuclear factor (NF)-kappaB. The aim of the present study was to examine the expression of Nod1 in the lung, particularly in lung epithelial cells, and to investigate the activation of CCAAT/enhancer binding protein (C/EBP) transcription factors downstream of the Nod1 receptor in these cells. The expression of Nod1 in mouse lung was examined using immunohistochemistry. A tissue array was used to determine the expression pattern in the human lung. Signalling downstream of Nod1 was examined in the human lung epithelial cell type, BEAS-2B, by electrophoretic mobility shift assay and reporter gene activation. Nod1 expression was seen in various cell types in the lung, including epithelial cells. Activation of Nod1 in these cells resulted in modest activation of NF-kappaB, together with strong activation of the C/EBP transcription factors, particularly C/EBPbeta. This activation appears to be independent of de novo protein synthesis. The present study showed that nucleotide-binding oligomerisation domain protein 1 is expressed in lung epithelial cells. The results demonstrate a novel pathway downstream of the nucleotide-binding oligomerisation domain protein 1 receptor in these cells and suggest that C/EBPbeta may play a role in immune responses to meso-diaminopimelic acid-containing bacteria in the lung.

A major role for intestinal epithelial nucleotide oligomerization domain 1 (NOD1) in eliciting host bactericidal immune responses to Campylobacter jejuni

Campylobacter jejuni is the foremost cause of bacterial-induced diarrhoeal disease worldwide. Although it is well established that C. jejuni infection of intestinal epithelia triggers host innate immune responses, the mechanism(s) involved remain poorly defined. Innate immunity can be initiated by families of structurally related pattern-recognition receptors (PRRs) that recognize specific microbial signature motifs. Here, we demonstrated maximal induction of epithelial innate responses during infection with live C. jejuni cells. In contrast when intestinal epithelial cells (IECs) were exposed to paraformaldehyde-fixed bacteria, host responses were minimal and a marked reduction in the number of intracellular bacteria was noted in parallel. These findings suggested a role for intracellular host-C. jejuni interactions in eliciting early innate immunity. We therefore investigated the potential involvement of a family of intracellular, cytoplasmic PRRs, the nucleotide-binding oligomerization domain (NOD) proteins in C. jejuni recognition. We identified NOD1, but not NOD2, as a major PRR for C. jejuni in IEC. We also found that targeting intestinal epithelial NOD1 with small interfering RNA resulted in an increase in number of intracellular C. jejuni, thus highlighting a critical role for NOD1-mediated antimicrobial defence mechanism(s) in combating this infection at the gastrointestinal mucosal surface.

NOD蛋白質の機能から考える『自己炎症疾患』発症の分子メカニズム

The latest decade, our understanding of pattern-recognizing receptors involved in innate immune system has been accumulated. One class of the pattern recognizing receptors, the toll-like receptors (TLRs) are well known to detect extracellular pathogens on the cell surface membrane. On the other hand, recently discovered the nucleotide-binding oligomerization domain proteins (NODs) are involved in recognizing intracellular pathogens. Since Nod2, one of the NODs, mutations were found to associate with susceptibility of Crohn's disease, the NODs have been highlighted. For example, cryopyrin mutations have been reported to associate with Familial cold urticaria (FCU)/Familial cold autoinflammatory syndrome (FCAS), Muckle-Wells syndrome (MWS), Neonatal onset multisystem inflammatory disease (NOMID)/Chronic infantile neurologic cutaneous and articular syndrome (CINCA). Here, we summarize the discovery of the NODs and related molecules, and also discuss the function of the NODs and molecular mechanisms of the autoinflammatory diseases.

NOD Protein Expression and Function in First Trimester Trophoblast Cells

Through the expression of pattern recognition receptors, the trophoblast can recognize and respond to infectious microorganisms and, therefore, participate in the control of pathogens that may compromise fetal well-being. We hypothesize that the trophoblast has the ability to sense invasive intracellular bacteria through the cytoplasmic-based nucleotide-binding oligomerization domain (NOD) proteins. The aim of this study was to characterize the expression and function of NOD proteins in first trimester trophoblast cells. NOD1 and NOD2 expressions by first trimester trophoblast cells were evaluated by immunohistochemistry, Western blot analysis and reverse transcription-polymerase chain reaction. The effect of NOD2 activation on trophoblast cells was determined by analyzing the cytokine response following treatment with muramyl dipeptide (MDP). Both NOD1 and NOD2 were expressed by first trimester placental villi and localized to trophoblast cells. Moreover, NOD1, NOD2 and the signaling effector protein, RIP-like interacting CLARP kinase (RICK), were all expressed by isolated trophoblast cells. Following exposure to the NOD2 ligand, MDP, trophoblast cells generated a pro-inflammatory cytokine response. This response was confirmed to be specific, as an NOD2-deficient trophoblast cell line failed to respond to MDP unless transfected with NOD2. These findings suggest that, through the expression and function of NOD proteins, first trimester trophoblast cells are able to recognize and respond to invasive intracellular pathogens that may have evaded other forms of pattern recognition.

Modification of the Structure of Peptidoglycan Is a Strategy To Avoid Detection by Nucleotide-Binding Oligomerization Domain Protein 1

Nucleotide-binding oligomerization domain (NOD) protein 1 (NOD1) and NOD2 are pathogen recognition receptors that sense breakdown products of peptidoglycan (PGN) (muropeptides). It is shown that a number of these muropeptides can induce tumor necrosis factor alpha (TNF-alpha) gene expression without significant TNF-alpha translation. This translation block is lifted when the muropeptides are coincubated with lipopolysaccharide (LPS), thereby accounting for an apparently synergistic effect of the muropeptides with LPS on TNF-alpha protein production. The compounds that induced synergistic effects were also able to activate NF-kappaB in a NOD1- or NOD2-dependent manner, implicating these proteins in synergistic TNF-alpha secretion. It was found that a diaminopimelic acid (DAP)-containing muramyl tetrapeptide could activate NF-kappaB in a NOD1-dependent manner, demonstrating that an exposed DAP is not essential for NOD1 sensing. The activity was lost when the alpha-carboxylic acid of iso-glutamic acid was modified as an amide. However, agonists of NOD2, such as muramyl dipeptide and lysine-containing muramyl tripeptides, were not affected by amidation of the alpha-carboxylic acid of iso-glutamic acid. Many pathogens modify the alpha-carboxylic acid of iso-glutamic acid of PGN, and thus it appears this is a strategy to avoid recognition by the host innate immune system. This type of immune evasion is in particular relevant for NOD1.

Legionella pneumophila Induces IFNβ in Lung Epithelial Cells via IPS-1 and IRF3, Which Also Control Bacterial Replication

Legionella pneumophila, a Gram-negative facultative intracellular bacterium, causes severe pneumonia (Legionnaires' disease). Type I interferons (IFNs) were so far associated with antiviral immunity, but recent studies also indicated a role of these cytokines in immune responses against (intracellular) bacteria. Here we show that wild-type L. pneumophila and flagellin-deficient Legionella, but not L. pneumophila lacking a functional type IV secretion system Dot/Icm, or heat-inactivated Legionella induced IFNbeta expression in human lung epithelial cells. We found that factor (IRF)-3 and NF-kappaB-p65 translocated into the nucleus and bound to the IFNbeta gene enhancer after L. pneumophila infection of lung epithelial cells. RNA interference demonstrated that in addition to IRF3, the caspase recruitment domain (CARD)-containing adapter molecule IPS-1 (interferon-beta promoter stimulator 1) is crucial for L. pneumophila-induced IFNbeta expression, whereas other CARD-possessing molecules, such as RIG-I (retinoic acid-inducible protein I), MDA5 (melanoma differentiation-associated gene 5), Nod27 (nucleotide-binding oligomerization domain protein 27), and ASC (apoptosis-associated speck-like protein containing a CARD) seemed not to be involved. Finally, bacterial multiplication assays in small interfering RNA-treated cells indicated that IPS-1, IRF3, and IFNbeta were essential for the control of intracellular replication of L. pneumophila in lung epithelial cells. In conclusion, we demonstrated a critical role of IPS-1, IRF3, and IFNbeta in Legionella infection of lung epithelium.

Circadian oscillation of innate immunity components in mouse small intestine

The digestive system is a major port of entry for pathogens. To detect and combat pathogens, the innate immunity in the gut utilizes pattern recognition receptors, such as Toll-like receptors (TLRs) and nucleotide-binding oligomerization domain (NOD) proteins, and broad-spectrum anti-bacterial polypeptides, such as defensins. We have previously shown that mouse enteric defensins (cryptdins) oscillate around the circadian cycle and peak at the end of the dark phase suggesting control by the biological clock. As the core mechanism of the biological clock has never been studied in the small intestine, our objective was to determine whether the biological clock is functional in mouse jejunum and examine whether mTlr and mNod2 mRNAs, similarly to cryptdins, oscillate throughout the circadian cycle. Mouse jejunum and Paneth-enriched crypt base cells were isolated around the circadian day and the levels of clock ( mClock, mBmal1, mPer1, mPer2, mCry1) and innate immunity component ( mTlr2, mTlr3, mTlr4, mTlr5, mTlr9, mNod2) genes were measured by real-time PCR. Analysis of mouse jejunum and Paneth-enriched crypt base cells revealed that all clock genes exhibited circadian oscillation. Similarly to cryptdins, mTlr2, mTlr3, mTlr4, mTlr5 displayed circadian rhythmicity in mouse jejunum. Although no circadian oscillation could be detected for mTlr9 and mNod2 in the whole jejunum, these genes oscillated in Paneth-enriched crypt base cells. In addition, mTlr3 exhibited the highest expression level. As the clock regulates intestinal motility and function, resetting of the clock in the small intestine may help not only to restore activity but also to gain better protection against pathogens.

Expression of functionally active NOD1 and NOD2 in folliculostellate TtT/GF pituitary cells

The follicullostellate (FS) cells of the pituitary share properties with dendritic cells and also with macrophages. A contingent of FS cells express MHC class I and MHC class II molecules and also several lymphoid markers and lymphatic markers. Therefore, FS cells were found to regulate the secretion of hormones by endocrine cells inside of the pituitary and to be a source of growth factors such as basic fibroblast growth factor (bFGF), vascular endothelial growth factors (VEGF), as well as, cytokines as leukaemia inhibitor factor (LIF) and interleukin-6 (IL-6). Functionally, it was suggested that FS cells are capable of initiating immune responses and act as part of a neuroendocrine immune regulation system. Understanding of the way macrophages and/others cells respond to endotoxins and development of innate immunity, a major step was archived with the discovery of Toll-like receptors (TLRs). Toll receptors are members of a membrane-anchored proteins that upon stimulation recruits proteins kinases via a adaptor MyD88 inducing the activation of nuclear factor κB (NF-κB). Recently, nucleotide-binding oligomerization domain (NOD) proteins, NOD1 and NOD2 were found to represent an intracellular pathogen sensing system identified in both immune and non-immune cell types. The ligand of NOD2 is muramyl dipeptide (MDP), a component of bacterial cell-wall peptidoglycan present in most bacterial species. NOD2 oligomerization after bind in MDP activates RICK, an effector molecule that leads to phosphorylation of IKB and release of NF-κB for translocation in the nucleus. Considering characteristics of FS cells and the function of NOD molecules, we decided to investigate the expression and function of NOD in FS cells. Our preliminary RT-PCR data demonstrated the presence of NOD1 and NOD2 transcripts in FS cells. Moreover, NOD2 protein expression was increased in FS cells after 24 hours stimulation with MDP. We also observed significantly enhanced IL-6 secretion in the supernatant of FS cell cultures after stimulation with MDP. The MDP-induced and NOD-mediated IL-6 secretion by FS cells may play a role in modulating hormone secretion (e.g. stimulation of ACTH) during bacterial infections.

Characterization of nucleotide-binding oligomerization domain (NOD) protein expression in primary murine microglia

We demonstrate that primary microglia express nucleotide-binding oligomerization domain (NOD) proteins that are thought to serve as novel pattern recognition receptors for bacterial peptidoglycan motifs. NOD2 is constitutively present in microglia and is upregulated following exposure to Borrelia burgdorferi or Neisseria meningitidis. Its expression is also elevated following exposure to Toll-like receptor (TLR) ligands and muramyl dipeptide (MDP), a putative ligand for NOD2. Microglia express essential downstream effector molecules for NOD2-mediated cell responses, and MDP augments TLR ligand-induced inflammatory cytokine production. Together these data suggest that NOD2 may contribute to microglial immune responses to bacterial pathogens.

Tweaking Innate Immunity: The Promise of Innate Immunologicals as Anti‐Infectives

New and exciting insights into the importance of the innate immune system are revolutionizing our understanding of immune defense against infections, pathogenesis, and the treatment and prevention of infectious diseases. The innate immune system uses multiple families of germline-encoded pattern recognition receptors (PRRs) to detect infection and trigger a variety of antimicrobial defense mechanisms. PRRs are evolutionarily highly conserved and serve to detect infection by recognizing pathogen-associated molecular patterns that are unique to microorganisms and essential for their survival. Toll-like receptors (TLRs) are transmembrane signalling receptors that activate gene expression programs that result in the production of proinflammatory cytokines and chemokines, type I interferons and antimicrobial factors. Furthermore, TLR activation facilitates and guides activation of adaptive immune responses through the activation of dendritic cells. TLRs are localized on the cell surface and in endosomal/lysosomal compartments, where they detect bacterial and viral infections. In contrast, nucleotide-binding oligomerization domain proteins and RNA helicases are located in the cell cytoplasm, where they serve as intracellular PRRs to detect cytoplasmic infections, particularly viruses. Due to their ability to enhance innate immune responses, novel strategies to use ligands, synthetic agonists or antagonists of PRRs (also known as 'innate immunologicals') can be used as stand-alone agents to provide immediate protection or treatment against bacterial, viral or parasitic infections. Furthermore, the newly appreciated importance of innate immunity in initiating and shaping adaptive immune responses is contributing to our understanding of vaccine adjuvants and promises to lead to improved next-generation vaccines.

NOD2/CARD15 Mediates Induction of the Antimicrobial Peptide Human Beta-defensin-2

Production of inducible antimicrobial peptides offers a first and rapid defense response of epithelial cells against invading microbes. Human beta-defensin-2 (hBD-2) is an antimicrobial peptide induced in various epithelia upon extracellular as well as intracellular bacterial challenge. Nucleotide-binding oligomerization domain protein 2 (NOD2/CARD15) is a cytosolic protein involved in intracellular recognition of microbes by sensing peptidoglycan fragments (e.g. muramyl dipeptide). We used luciferase as a reporter gene for a 2.3-kb hBD-2 promoter to test the hypothesis that NOD2 mediates the induction of hBD-2. Activation of NOD2 in NOD2-overexpressing human embryonic kidney 293 cells through its ligand muramyl dipeptide (MDP) induced hBD-2 expression. In contrast, overexpression of NOD2 containing the 3020insC frame-shift mutation, the most frequent NOD2 variant associated with Crohn disease, resulted in defective induction of hBD-2 through MDP. Luciferase gene reporter analyses and site-directed mutagenesis experiments demonstrated that functional binding sites for NF-kappaB and AP-1 in the hBD-2 promoter are required for NOD2-mediated induction of hBD-2 through MDP. Moreover, the NF-kappaB inhibitor Helenalin as well as a super-repressor form of the NF-kappaB inhibitor IkappaB strongly inhibited NOD2-mediated hBD-2 promoter activation. Expression of NOD2 was detected in primary keratinocytes, and stimulation of these cells with MDP induced hBD-2 peptide release. In contrast, small interference RNA-mediated down-regulation of NOD2 expression in primary keratinocytes resulted in a defective induction of hBD-2 upon MDP treatment. Together, these data suggest that NOD2 serves as an intracellular pattern recognition receptor to enhance host defense by inducing the production of antimicrobial peptides such as hBD-2.

Analysis of NOD2-mediated Proteome Response to Muramyl Dipeptide in HEK293 Cells

NOD2, a cytosolic receptor for the bacterial proteoglycan fragment muramyl dipeptide (MDP), plays an important role in the recognition of intracellular pathogens. Variants in the bacterial sensor domain of NOD2 are genetically associated with an increased risk for the development of Crohn disease, a human chronic inflammatory bowel disease. In the present study, global protein expression changes after MDP stimulation were analyzed by two-dimensional PAGE of total protein extracts of human cultured cells stably transfected with expression constructs encoding for wild type NOD2 (NOD2(WT)) or the disease-associated NOD2 L1007fsinsC (NOD2(SNP13)) variant. Differentially regulated proteins were identified by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) peptide mass fingerprinting and MALDI MS/MS. The limited overlap in the responses of the NOD2-overexpressing cell lines to MDP included a down-regulation of heat shock 70-kDa protein 4. A complex pro-inflammatory program regulated by NOD2(WT) that encompasses a regulation of key genes involved in protein folding, DNA repair, cellular redox homeostasis, and metabolism was observed both under normal growth conditions and after stimulation with MDP. By using the comparison of NOD2(WT) and disease-associated NOD2(SNP13) variant, we have identified a proteomic signature pattern that may further our understanding of the influence of genetic variations in the NOD2 gene in the pathophysiology of chronic inflammatory bowel disease.

Elicitor-Mediated Oligomerization of the Tobacco N Disease Resistance Protein

Plant nucleotide binding site-leucine-rich repeat (NBS-LRR) proteins are similar to the nucleotide binding oligomerization domain (NOD) protein family in their domain structure. It has been suggested that most NOD proteins rely on ligand-mediated oligomerization for function, and we have tested this possibility with the N protein of tobacco (Nicotiana tabacum). The N gene for resistance to Tobacco mosaic virus (TMV) is a member of the Toll-interleukin receptor (TIR)-NBS-LRR class of plant disease resistance (R) genes that recognizes the helicase domain from the TMV replicase. Using transient expression followed by immunoprecipitation, we show that the N protein oligomerizes in the presence of the elicitor. The oligomerization was not affected by silencing Nicotiana benthamiana ENHANCED DISEASE SUSCEPTIBILITY1 and N REQUIREMENT GENE1 cofactors of N-mediated resistance, but it was abolished by a mutation in the P-loop motif. However, loss-of-function mutations in the RNBS-A motif and in the TIR domain retain the ability to oligomerize. From these results, we conclude that oligomerization is an early event in the N-mediated resistance to TMV.

Signalling pathways and molecular interactions of NOD1 and NOD2

The NOD (nucleotide-binding oligomerization domain) proteins NOD1 and NOD2 have important roles in innate immunity as sensors of microbial components derived from bacterial peptidoglycan. The importance of these molecules is underscored by the fact that mutations in the gene that encodes NOD2 occur in a subpopulation of patients with Crohn's disease, and NOD1 has also been shown to participate in host defence against infection with Helicobacter pylori. Here, we focus on the molecular interactions between these NOD proteins and other intracellular molecules to elucidate the mechanisms by which NOD1 and NOD2 contribute to the maintenance of mucosal homeostasis and the induction of mucosal inflammation.

Generation of inflammatory stimuli: how bacteria set up inflammatory responses in the gingiva

The primary aetiologic factor of periodontal disease is the bacterial biofilm. Gram-positive and gram-negative bacteria possess a plethora of structural or secreted components that may cause direct destruction to periodontal tissues or stimulate host cells to activate a wide range of inflammatory responses. These responses are intended to eliminate the microbial challenge, but may often cause further tissue damage. This review has been divided into three parts: (a) bacterial virulence factors, which includes basic information on bacterial virulence factors, and the principle inflammatory responses that host cells elicit against these factors, (b) main receptors and signalling pathways, which includes basic information about the main receptors that interact with the bacterial virulence factors, the nature of these interactions, and the activated signalling pathways that lead to inflammatory responses, and (c) initiation of inflammation, which includes a model by which the virulence factors may interact with host cells and lead to inflammatory responses in the gingiva. Bacterial components/virulence factors may be involved in modulating inflammatory responses and include: lipopolysaccharides (LPS), peptidoglycans, lipotechoic acids, fimbriae, proteases, heat-shock proteins, formyl-methionyl peptides, and toxins. Potential host cell receptors involved in recognizing bacterial components and initiating signalling pathways that lead to inflammatory responses include: Toll-like receptors (TLRs), CD14, nucleotide-binding oligomerization domain proteins (Nod) and G-protein-coupled receptors, including formyl-methionyl peptide receptors and protease-activated receptors. Of the above bacterial and host molecules, evidence from experimental animal studies implicate LPS, fimbriae, proteases, TLRs, and CD14 in periodontal tissue or alveolar bone destruction. However, evidence verifying the involvement of any of the above molecules in periodontal tissue destruction in humans does not exist.