What a disorder: proinflammatory signaling pathways induced by Helicobacter pylori

Novel role of toll-like receptors in Helicobacter pylori - induced gastric malignancy

Helicobacter pylori (H. pylori) infects the human stomach during infancy and develops into chronic active inflammation. The majority of H. pylori tend to colonize within the mucous gel layer of the stomach. The stomach lacks its own immune function, thus innate immunity as the first line of defense is vital for specific immunity against H. pylori. We review recent discoveries in the pathophysiologic roles of toll-like receptors (TLRs), mainly TLR2 and TLR4, in H. pylori-induced inflammation. In addition, the TLR pathways activated by H. pylori-induced inflammation have been shown to be closely associated not only with gastric carcinogenesis, but also with formation of the tumor microenvironment through the production of pro-inflammatory cytokines, chemokines, and reactive oxygen species. Although the correlation between single nucleotide polymorphisms of TLRs and gastric cancer risk remains unclear, a recent study demonstrated that STAT3-driven up-regulation of TLR2 might promote gastric tumorigenesis independent of inflammation. Further research on the regulation of TLRs in H. pylori-associated gastric carcinogenesis will uncover diagnostic/predictive biomarkers and therapeutic targets for gastric cancer.

Chemokines and antimicrobial peptides have a cag-dependent early response to Helicobacter pylori infection in primary human gastric epithelial cells

Helicobacter pylori infection systematically causes chronic gastric inflammation that can persist asymptomatically or evolve toward more severe gastroduodenal pathologies, such as ulcer, mucosa-associated lymphoid tissue (MALT) lymphoma, and gastric cancer. The cag pathogenicity island (cag PAI) of H. pylori allows translocation of the virulence protein CagA and fragments of peptidoglycan into host cells, thereby inducing production of chemokines, cytokines, and antimicrobial peptides. In order to characterize the inflammatory response to H. pylori, a new experimental protocol for isolating and culturing primary human gastric epithelial cells was established using pieces of stomach from patients who had undergone sleeve gastrectomy. Isolated cells expressed markers indicating that they were mucin-secreting epithelial cells. Challenge of primary epithelial cells with H. pylori B128 underscored early dose-dependent induction of expression of mRNAs of the inflammatory mediators CXCL1 to -3, CXCL5, CXCL8, CCL20, BD2, and tumor necrosis factor alpha (TNF-α). In AGS cells, significant expression of only CXCL5 and CXCL8 was observed following infection, suggesting that these cells were less reactive than primary epithelial cells. Infection of both cellular models with H. pylori B128ΔcagM, a cag PAI mutant, resulted in weak inflammatory-mediator mRNA induction. At 24 h after infection of primary epithelial cells with H. pylori, inflammatory-mediator production was largely due to cag PAI substrate-independent virulence factors. Thus, H. pylori cag PAI substrate appears to be involved in eliciting an epithelial response during the early phases of infection. Afterwards, other virulence factors of the bacterium take over in development of the inflammatory response. Using a relevant cellular model, this study provides new information on the modulation of inflammation during H. pylori infection.

Helicobacter pylori activates NF-κB by inducing Ubc13-mediated ubiquitination of lysine 158 of TAK1

The Helicobacter pylori virulence factor CagA targets a variety of host proteins to alter different cellular responses, including the induction of pro-inflammatory cytokines. We have previously shown that CagA-facilitated lysine 63-linked ubiquitination of TAK1 is essential for the H. pylori-induced NF-κB activation and the expression of proinflammatory cytokines. However, the molecular mechanism for TAK1 ubiquitination and activation in H. pylori-mediated NF-κB activation remains elusive. Here, we identify lysine 158 of TAK1 as the key residue undergoing lysine 63-linked ubiquitination in response to H. pylori infection. Mutation of lysine 158 to arginine prevents the ubiquitination of TAK1 and impairs H. pylori-induced TAK1 and NF-κB activation. Moreover, we demonstrate that E2 ubiquitin conjugating enzyme Ubc13 is involved in H. pylori-mediated TAK1 ubiquitination. Suppressing the activity of Ubc13 by a dominant-negative mutant or siRNA abolishes CagA-facilitated and H. pylori-induced TAK1 and NF-κB activation. These findings further underscore the importance of lysine 63-linked ubiquitination of TAK1 in H. pylori-induced NF-κB activation and NF-κB-mediated inflammatory response.

MEKK3 and TAK1 synergize to activate IKK complex in Helicobacter pylori infection

Helicobacter pylori colonises the gastric epithelial cells of half of the world's population and represents a risk factor for gastric adenocarcinoma. In gastric epithelial cells H. pylori induces the immediate early response transcription factor nuclear factor of kappa light polypeptide gene enhancer in B-cells (NF-κB) and the innate immune response. We show that H. pylori induces in a type IV secretion system-dependent (T4SS) and cytotoxin associated gene A protein (CagA)-independent manner a transient activation of the inhibitor of NF-κB (IκBα) kinase (IKK)-complex. IKKα and IKKβ expression stabilises the regulatory IKK complex subunit NF-κB essential modulator (NEMO). We provide evidence for an intimate mutual control of the IKK complex by mitogen-activated protein kinase kinase kinase 3 (MEKK3) and transforming growth factor β activated kinase 1 (TAK1). TAK1 interacts transiently with the E3 ubiquitin ligase tumor necrosis factor receptor-associated factor 6 (TRAF6). Protein modifications in the TAK1 molecule, e.g. TAK1 autophosphorylation and K63-linked ubiquitinylation, administer NF-κB signalling including transient recruitment of the IKK-complex. Overall, our data uncover H. pylori-induced interactions and protein modifications of the IKK complex, and its upstream regulatory factors involved in NF-κB activation.

Helicobacter pylori and interleukin-8 in gastric cancer

Helicobacter pylori (H. pylori) is a major etiological factor in the development of gastric cancer. Large-scale epidemiological studies have confirmed the strong association between H. pylori infection and both cancer development and progression. Interleukin-8 (IL-8) is overexpressed in gastric mucosa exposed to H. pylori. The expression of IL-8 directly correlates with a poor prognosis in gastric cancer. IL-8 is multifunctional. In addition to its potent chemotactic activity, it can induce proliferation and migration of cancer cells. In this review, we focus on recent insights into the mechanisms of IL-8 signaling associated with gastric cancer. The relationship between IL-8 and H. pylori is discussed. We also summarize the current therapeutics against IL-8 in gastric cancer.

Signal transduction of Helicobacter pylori during interaction with host cell protein receptors of epithelial and immune cells

Helicobacter pylori infections can induce pathologies ranging from chronic gastritis, peptic ulceration to gastric cancer. Bacterial isolates harbor numerous well-known adhesins, vacuolating cytotoxin VacA, protease HtrA, urease, peptidoglycan, and type IV secretion systems (T4SS). It appears that H. pylori targets more than 40 known host protein receptors on epithelial or immune cells. A series of T4SS components such as CagL, CagI, CagY, and CagA can bind to the integrin α 5β 1 receptor. Other targeted membrane-based receptors include the integrins αvβ 3, αvβ 5, and β 2 (CD18), RPTP-α/β, GP130, E-cadherin, fibronectin, laminin, CD46, CD74, ICAM1/LFA1, T-cell receptor, Toll-like receptors, and receptor tyrosine kinases EGFR, ErbB2, ErbB3, and c-Met. In addition, H. pylori is able to activate the intracellular receptors NOD1, NOD2, and NLRP3 with important roles in innate immunity. Here we review the interplay of various bacterial factors with host protein receptors. The contribution of these interactions to signal transduction and pathogenesis is discussed.

Rapid interaction of Helicobacter pylori with microvilli of the polar human gastric epithelial cell line NCI-N87

Infection with Helicobacter pylori results often in chronic gastritis, gastric ulcers or even gastric tumor development. Little is known about the initial interaction between gastric epithelial cells and H. pylori. The aim of the present study was to analyze the initial host contact to the bacteria. Monolayers of the human gastric epithelial cell line NCI-N87 grown on porous membranes were used and the apical side of the epithelium was exposed to the H. pylori wild-type strain P1 for 1 hr. Many epithelial cells were colonized by bacteria within the period of 60 min. Using scanning electron microscopy we detected that the bacteria were in close contact with the epithelia via microvilli. Further, transmission electron microscopy of the contact sites revealed no difference in the morphology of the microvilli in comparison to those not attached to the bacteria. The present study demonstrates the importance of microvilli on apical epithelial cells during the initial contact of the host by colonizing H. pylori. Anat Rec, 296:1800–1805, 2013. © 2013 The Authors. The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology published by Wiley Periodicals, Inc. on behalf of the American Association of Anatomists.

Helicobacter pylori cag pathogenicity island (cagPAI) involved in bacterial internalization and IL-8 induced responses via NOD1- and MyD88-dependent mechanisms in human biliary epithelial cells

Helicobacter pylori infection has been proposed to be associated with various diseases of the hepatobiliary tract, including cancer of the bile duct epithelial cells (cholangiocarcinoma, CCA). The ability of H. pylori bacteria to cause pathogenic effects in these cells has, however, yet to be investigated. Given that the cag pathogenicity island (cagPAI) is required for H. pylori pathogenesis in gastric epithelial cells, we investigated wild-type and cag mutant strains for their ability to adhere, be internalized and induce pro-inflammatory responses in two bile duct epithelial cell lines derived from cases of CCA. The findings from these experiments were compared to results obtained with the well-characterized AGS gastric cancer cell line. We showed that the cagPAI encodes factors involved in H. pylori internalization in CCA cells, but not for adhesion to these cells. Consistent with previous studies in hepatocytes, actin polymerization and α5β1 integrin may be involved in H. pylori internalization in CCA cells. As for AGS cells, we observed significantly reduced levels of NF-κB activation and IL-8 production in CCA cells stimulated with either cagA, cagL or cagPAI bacteria, when compared with wild-type bacteria. Importantly, these IL-8 responses could be inhibited via either pre-treatment of cells with antibodies to α5β1 integrins, or via siRNA-mediated knockdown of the innate immune signaling molecules, nucleotide oligomerization domain 1 (NOD1) and myeloid differentiation response gene 88 (MyD88). Taken together, the data demonstrate that the cagPAI is critical for H. pylori pathogenesis in bile duct cells, thus providing a potential causal link for H. pylori in biliary tract disease.

Effects of EGFR Inhibitor on Helicobacter pylori Induced Gastric Epithelial Pathology in Vivo

Helicobacter pylori transactivates the Epidermal Growth Factor Receptor (EGFR) and predisposes to gastric cancer development in humans and animal models. To examine the importance of EGFR signalling to gastric pathology, this study investigated whether treatment of Mongolian gerbils with a selective EGFR tyrosine kinase inhibitor, EKB-569, altered gastric pathology in chronic H. pylori infection. Gerbils were infected with H. pylori and six weeks later received either EKB-569-supplemented, or control diet, for 32 weeks prior to sacrifice. EKB-569-treated H. pylori-infected gerbils had no difference in H. pylori colonisation or inflammation scores compared to infected animals on control diet, but showed significantly less corpus atrophy, mucous metaplasia and submucosal glandular herniations along with markedly reduced antral and corpus epithelial proliferation to apoptosis ratios. EKB-569-treated infected gerbils had significantly decreased abundance of Cox-2, Adam17 and Egfr gastric transcripts relative to infected animals on control diet. EGFR inhibition by EKB-569 therefore reduced the severity of pre-neoplastic gastric pathology in chronically H. pylori-infected gerbils. EKB-569 increased gastric epithelial apoptosis in H. pylori-infected gerbils which counteracted some of the consequences of increased gastric epithelial cell proliferation. Similar chemopreventative strategies may be useful in humans who are at high risk of developing H. pylori- induced gastric adenocarcinoma.

The functional interplay of Helicobacter pylori factors with gastric epithelial cells induces a multi-step process in pathogenesis

Infections with the human pathogen Helicobacter pylori (H. pylori) can lead to severe gastric diseases ranging from chronic gastritis and ulceration to neoplastic changes in the stomach. Development and progress of H. pylori-associated disorders are determined by multifarious bacterial factors. Many of them interact directly with host cells or require specific receptors, while others enter the host cytoplasm to derail cellular functions. Several adhesins (e.g. BabA, SabA, AlpA/B, or OipA) establish close contact with the gastric epithelium as an important first step in persistent colonization. Soluble H. pylori factors (e.g. urease, VacA, or HtrA) have been suggested to alter cell survival and intercellular adhesions. Via a type IV secretion system (T4SS), H. pylori also translocates the effector cytotoxin-associated gene A (CagA) and peptidoglycan directly into the host cytoplasm, where cancer- and inflammation-associated signal transduction pathways can be deregulated. Through these manifold possibilities of interaction with host cells, H. pylori interferes with the complex signal transduction networks in its host and mediates a multi-step pathogenesis.

Differential roles of ASK1 and TAK1 in Helicobacter pylori-induced cellular responses

The mitogen-activated protein kinase (MAPK) signaling pathway regulates various cellular functions, including those induced by Helicobacter pylori. TAK1 is an upstream MAPK kinase kinase (MAP3K) required for H. pylori-induced MAPK and NF-κB activation, but it remains unclear whether other MAP3Ks are involved in H. pylori-induced cellular responses. In this study, we focused on the MAP3K ASK1, which plays a critical role in gastric tumorigenesis. In gastric epithelial cells, H. pylori activates ASK1 in a reactive oxygen species (ROS)- and cag pathogenicity island-dependent manner, and ASK1 regulates sustained JNK activation and apoptosis induced by H. pylori. In contrast, TAK1 regulates H. pylori-mediated early JNK activation and cytokine production. We also found reciprocal regulation between ASK1 and TAK1 in H. pylori-related responses, whereby inhibition of TAK1 or downstream p38 MAPK activates ASK1 through ROS production, and ASK1 suppresses TAK1 and downstream NF-κB activation. We identified ROS/ASK1/JNK as a new signaling pathway induced by H. pylori, which regulates apoptotic cell death. The balance of ASK1-induced apoptosis and TAK1-induced antiapoptotic or inflammatory responses may determine the fate of epithelial cells infected with H. pylori and thus be involved in the pathogenesis of gastritis and gastric cancer.

Role of ghrelin-induced phosphatidylinositol 3-kinase activation in modulation of gastric mucosal inflammatory responses to Helicobacter pylori

A peptide hormone, ghrelin, is recognized as an important modulator of gastric mucosal inflammatory responses to Helicobacter pylori through the regulation of Src/Akt-dependent activation of constitutive nitric oxide synthase (cNOS) by phosphorylation. In this study, we report on the role of phosphatidylinositol 3-kinase (PI3K) in the processes of Src/Akt activation in gastric mucosal cells exposed to H. pylori LPS. We demonstrate that cNOS activation through phosphorylation induced by ghrelin is associated with PI3K activation which occurs upstream of cSrc, and that PI3K is required for cSrc activation of Akt. We show further that ghrelin-induced activation of PI3K, as well as that of Src and Akt, was susceptible to suppression by the inhibitors of phospholipase C (U73122) and protein kinase C (BIM). Both these inhibitors also blocked the ghrelin-induced membrane translocation of PI3K and cSrc, whereas the inhibitor of PI3K (LY294002) blocked only the membrane translocation of cSrc. Collectively, our findings suggest that the modulatory influence of ghrelin in countering gastric mucosal responses to H. pylori LPS relies on PI3K activation that depends on PLC/PKC signaling pathway, and that PI3K activity is required for the induction of cSrc/Akt activation.

Inflammation, immunity, vaccines for Helicobacter pylori infection

Over the last decades, it has become evident that chronic infection by Helicobacter pylori is achieved by colonizing an almost exclusive niche and hiding from many of the host's cellular immune defense mechanisms. Although recent years have seen progress in our understanding of the innate and adaptive immune response against H. pylori, it is still uncertain how to promote the development of immunity with the final goal of a successful vaccine. Research published in the last year revealed an intriguing mutual regulation of innate response mechanisms of mucosal epithelial cells by the host and H. pylori, respectively. A further focus was put on the interaction between H. pylori and dendritic cells, with some emphasis on the inflammasome and the resulting T-cell responses. Moreover, the function of microRNAs in macrophages and gastric MALT lymphoma development has been studied in more detail. Several novel antigens and adjuvants have been tested as vaccination strategies, primarily in mice. In this review, we present a concise summary of advances in the area of inflammation, immunity, and vaccines during the last twelve months.

Helicobacter bilis gamma-glutamyltranspeptidase enhances inflammatory stress response via oxidative stress in colon epithelial cells

Helicobacter bilis (H. bilis) infection is associated with cases of inflammatory bowel Disease, thyphlocolitis, hepatitis and cholecystitis. However, little is known about the bacterial virulence determinants or the molecular mechanisms involved. Recently, H. bilis γ-glutamyltranspeptidase (HBgGT) was shown to be a virulence factor decreasing host cell viability. Bacterial gGTs play a key role in synthesis and degradation of glutathione and enables the bacteria to utilize extracellular glutamine and glutathione as sources of glutamate. gGT-mediated loss of cell viability has so far been linked to DNA damage via oxidative stress, but the signaling cascades involved herein have not been described. In this study, we identified enhanced ROS production induced by HBgGT as a central factor involved in the activation of the oxidative stress response cascades, which finally activate CREB, AP-1 and NF-κB in H. bilis infected colon cancer cells. IL-8, an important pro-inflammatory chemokine that is a common downstream target of these transcription factors, was up-regulated upon H. bilis infection in an HBgGT dependent manner. Moreover, the induction of these signaling responses and inflammatory cytokine production in host cells could be linked to HBgGT-mediated glutamine deprivation. This study implicates for the first time HBgGT as an important regulator of signaling cascades regulating inflammation in H. bilis infected host epithelial cells that could be responsible for induction of inflammatory disorders by the bacterium.

Helicobacter pylori induces type 4 secretion system-dependent, but CagA-independent activation of IκBs and NF-κB/RelA at early time points

Colonization of the gastric epithelium by Helicobacter pylori induces the transcription factor nuclear factor of kappa light polypeptide gene enhancer in B-cells (NF-κB) and the innate immune response. Virulent strains of H. pylori carry a cag pathogenicity island (cagPAI), which encodes a type IV secretion system (T4SS). Recent publications have shown controversial data regarding the role of the T4SS and the effector protein cytotoxin associated gene A (CagA), which becomes translocated by the T4SS into the eukaryotic epithelial cell, in H. pylori-induced NF-κB activation. Thus, this study analyses by using three different H. pylori strains (P1, B128 and G27) whether CagA is required to initiate activation of different molecules of inhibitors of kappa B (IκB) and the NF-κB transcription factor RelA. We provide experimental evidence that H. pylori induces phosphorylation of NF-κB inhibitors IκBα, IκBβ and IκBɛ, and degradation of IκBα. Further, H. pylori stimulates phosphorylation of RelA at amino acids S536, S468 and S276, promotes DNA binding of RelA, and interleukin 8 (IL-8) gene expression in a T4SS-, but CagA-independent manner at early time points.

Helicobacter pylori outer membrane protein HopQ identified as a novel T4SS-associated virulence factor

Helicobacter pylori is a bacterial pathogen that colonizes the gastric niche of ∼ 50% of the human population worldwide and is known to cause peptic ulceration and gastric cancer. Pathology of infection strongly depends on a cag pathogenicity island (cagPAI)-encoded type IV secretion system (T4SS). Here, we aimed to identify as yet unknown bacterial factors involved in cagPAI effector function and performed a large-scale screen of an H. pylori transposon mutant library using activation of the pro-inflammatory transcription factor NF-κB in human gastric epithelial cells as a measure of T4SS function. Analysis of ∼ 3000 H. pylori mutants revealed three non-cagPAI genes that affected NF-κB nuclear translocation. Of these, the outer membrane protein HopQ from H. pylori strain P12 was essential for CagA translocation and for CagA-mediated host cell responses such as formation of the hummingbird phenotype and cell scattering. Besides that, deletion of hopQ reduced T4SS-dependent activation of NF-κB, induction of MAPK signalling and secretion of interleukin 8 (IL-8) in the host cells, but did not affect motility or the quantity of bacteria attached to host cells. Hence, we identified HopQ as a non-cagPAI-encoded cofactor of T4SS function.

Role of the Helicobacter pylori-induced inflammatory response in the development of gastric cancer

Helicobacter pylori (H. pylori) infection causes chronic gastritis and peptic ulceration and is the strongest risk factor for the development of gastric cancer. The pathogenesis of H. pylori is believed to be associated with infection-initiated chronic gastritis, which is characterized by enhanced expression of many inflammatory genes. H. pylori utilizes various virulence factors, targeting different cellular proteins, to modulate the host inflammatory response. In this review, we explore the many different ways by which H. pylori initiates inflammation, leveling many "hits" on the gastric mucosa which can lead to the development of cancer. We also discuss some recent findings in understanding the pathogen-host interactions and the role of transcription factor NF-κB in H. pylori-induced inflammation.

Role of energy sensor TlpD of Helicobacter pylori in gerbil colonization and genome analyses after adaptation in the gerbil

Helicobacter pylori maintains colonization in its human host using a limited set of taxis sensors. TlpD is a proposed energy taxis sensor of H. pylori and dominant under environmental conditions of low bacterial energy yield. We studied the impact of H. pylori TlpD on colonization in vivo using a gerbil infection model which closely mimics the gastric physiology of humans. A gerbil-adapted H. pylori strain, HP87 P7, showed energy-dependent behavior, while its isogenic tlpD mutant lost it. A TlpD-complemented strain regained the wild-type phenotype. Infection of gerbils with the complemented strain demonstrated that TlpD is important for persistent infection in the antrum and corpus and suggested a role of TlpD in horizontal navigation and persistent corpus colonization. As a part of the full characterization of the model and to gain insight into the genetic basis of H. pylori adaptation to the gerbil, we determined the complete genome sequences of the gerbil-adapted strain HP87 P7, two HP87 P7 tlpD mutants before and after gerbil passage, and the original human isolate, HP87. The integrity of the genome, including that of a functional cag pathogenicity island, was maintained after gerbil adaptation. Genetic and phenotypic differences between the strains were observed. Major differences between the gerbil-adapted strain and the human isolate emerged, including evidence of recent recombination. Passage of the tlpD mutant through the gerbil selected for gain-of-function variation in a fucosyltransferase gene, futC (HP0093). In conclusion, a gerbil-adapted H. pylori strain with a stable genome has helped to establish that TlpD has important functions for persistent colonization in the stomach.

Induction in gastric mucosal prostaglandin and nitric oxide by Helicobacter pylori is dependent on MAPK/ERK-mediated activation of IKK-β and cPLA2: modulatory effect of ghrelin

Among the key factors defining the extent of gastric mucosal inflammatory involvement in response to Helicobacter pylori is the excessive generation of prostaglandin (PGE2) and nitric oxide (NO), caused by the overexpression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS), and triggered by the activation of mitogen-activated protein kinase (MAPK)/c-Jun N-terminal kinase, p38 and ERK, and nuclear translocation of the cognate transcription factors. In this study, we report on the role of MAPK/ERK in the regulation of H. pylori LPS-induced gastric mucosal expression of COX-2 and iNOS. We show that ERK activation by the LPS leads to phosphorylation of the inhibitory κB kinase-β (IKK-β) and cytosolic phospholipase A2 (cPLA2), and is reflected in the upsurge in NF-κB nuclear translocation, induction in COX-2 and iNOS expression, and up-regulation in cPLA2 activity. The modulatory effect of peptide hormone, ghrelin, on the LPS-induced changes, although associated with further enhancement in ERK, IKK-β, and cPLA2 phosphorylation, was reflected in the suppression of IKK-β and cPLA2 activity through S-nitrosylation. While the effect of ghrelin on S-nitrosylation was susceptible to suppression by the inhibitors of Src/Akt pathway, the inhibition of ERK activation caused the blockage in IKK-β and cPLA2 phosphorylation as well as S-nitrosylation. Taken together, our data show that H. pylori-induced ERK activation plays a critical role in up-regulation of gastric mucosal PGE2 and NO generation at the level of IKK-β and cPLA2 activation, and that ghrelin counters these proinflammatory consequences of the LPS through Src/Akt-dependent S-nitrosylation.

Bacteroides fragilis enterotoxin upregulates lipocalin-2 expression in intestinal epithelial cells

Enterotoxigenic Bacteroides fragilis (ETBF) produces an ≈ 20 kDa B. fragilis enterotoxin (BFT), which plays an essential role in mucosal inflammation. Lipocalin (Lcn)-2, a siderophore-binding antimicrobial protein, is critical for control of bacterial infection; however, expression of Lcn-2 in BFT-exposed intestinal epithelial cells has not been elucidated. In the present study, stimulation of human intestinal epithelial cells with BFT resulted in the upregulation of Lcn-2 expression that was a relatively late response of intestinal epithelial cells compared with human β-defensin (hBD)-2 expression. The upregulation of Lcn-2 was dependent on AP-1 but not on NF-κB signaling. Lcn-2 induction via AP-1 was regulated by mitogen-activated protein kinases (MAPKs) including ERK and p38. Lcn-2 was secreted from the apical and basolateral surfaces in BFT-treated cells. These results suggest that a signaling pathway involving MAPKs and AP-1 is required for Lcn-2 induction in intestinal epithelial cells exposed to BFT, after which the secreted Lcn-2 may facilitate antimicrobial activity within ETBF-infected mucosa.

Ca2+/calmodulin-dependent kinase II contributes to inhibitor of nuclear factor-kappa B kinase complex activation in Helicobacter pylori infection

Helicobacter pylori, a class I carcinogen, induces a proinflammatory response by activating the transcription factor nuclear factor-kappa B (NF-κB) in gastric epithelial cells. This inflammatory condition could lead to chronic gastritis, which is epidemiologically and biologically linked to the development of gastric cancer. So far, there exists no clear knowledge on how H. pylori induces the NF-κB-mediated inflammatory response. In our study, we investigated the role of Ca(2+) /calmodulin-dependent kinase II (CAMKII), calmodulin, protein kinases C (PKCs) and the CARMA3-Bcl10-MALT1 (CBM) complex in conjunction with H. pylori-induced activation of NF-κB via the inhibitor of nuclear factor-kappa B kinase (IKK) complex. We use specific inhibitors and/or RNA interference to assess the contribution of these components. Our results show that CAMKII and calmodulin contribute to IKK complex activation and thus to the induction of NF-κB in response to H. pylori infection, but not in response to TNF-α. Thus, our findings are specific for H. pylori infected cells. Neither the PKCs α, δ, θ, nor the CBM complex itself is involved in the activation of NF-κB by H. pylori. The contribution of CAMKII and calmodulin, but not PKCs/CBM to the induction of an inflammatory response by H. pylori infection augment the understanding of the molecular mechanism involved and provide potential new disease markers for the diagnosis of gastric inflammatory diseases including gastric cancer.

Helicobacter, Inflammation, and Gastric Cancer

Helicobacter pylori infection leads to long-lasting chronic inflammation and represents the most common risk factor underlying gastric cancer. Recently, new insights into the mechanisms through which H. pylori and mucosal inflammation lead to cancer development have emerged. H. pylori virulence factors, in particular specific CagA genotypes, represent main factors in gastric cancer, inducing altered intracellular signaling in epithelial cells. The chronic nature of H. pylori infection appears to relate to the VacA virulence factor and Th17/Treg mechanisms. A role of H. pylori infection in epigenetic and microRNA deregulation has been shown. Mutation of the epithelial cell genome, a hallmark of cancer, was demonstrated to accumulate in H. pylori infected stomach partly due to inadequate DNA repair. Gastric stem cells were shown to be targets of oxidative injury in the Helicobacter-inflammatory milieu. Recent advances emphasizing the contribution of bacterial factors, inflammatory mediators, and the host epithelial response in gastric carcinogenesis are reviewed.

Functional plasticity in the type IV secretion system of Helicobacter pylori

Helicobacter pylori causes clinical disease primarily in those individuals infected with a strain that carries the cytotoxin associated gene pathogenicity island (cagPAI). The cagPAI encodes a type IV secretion system (T4SS) that injects the CagA oncoprotein into epithelial cells and is required for induction of the pro-inflammatory cytokine, interleukin-8 (IL-8). CagY is an essential component of the H. pylori T4SS that has an unusual sequence structure, in which an extraordinary number of direct DNA repeats is predicted to cause rearrangements that invariably yield in-frame insertions or deletions. Here we demonstrate in murine and non-human primate models that immune-driven host selection of rearrangements in CagY is sufficient to cause gain or loss of function in the H. pylori T4SS. We propose that CagY functions as a sort of molecular switch or perhaps a rheostat that alters the function of the T4SS and “tunes” the host inflammatory response so as to maximize persistent infection.

Helicobacter pylori is a bacterium that colonizes the stomach of about half the world's population, most of whom are asymptomatic. However, some strains of H. pylori express a bacterial secretion system, a sort of molecular syringe that injects a bacterial protein inside the gastric cells and causes inflammation that can lead to peptic ulcer disease or gastric cancer. One of the essential components of the H. pylori secretion system is CagY, which is unusual because it contains a series of repetitive amino acid motifs that are encoded by a very large number of direct DNA repeats. Here we have shown that DNA recombination in cagY changes the protein motif structure and alters the function of the secretion system—turning it on or off. Using mouse and non-human primate models, we have demonstrated that CagY is a molecular switch that “tunes” the host inflammatory response, and likely contributes to persistent infection. Determining the mechanism by which CagY functions will enhance our understanding of the effects of H. pylori on human health, and could lead to novel applications for the modulation of host cell function.

Presence of terminal EPIYA phosphorylation motifs in Helicobacter pylori CagA contributes to IL-8 secretion, irrespective of the number of repeats

CagA protein contributes to pro-inflammatory responses during H. pylori infection, following its intracellular delivery to gastric epithelial cells. Here, we report for the first time in an isogenic background, on the subtle role of CagA phosphorylation on terminal EPIYA-C motifs in the transcriptional activation and expression of IL-8. We utilized isogenic H. pylori mutants of P12 reference strain, expressing CagA with varying number of EPIYA-C motifs and the corresponding phosphorylation defective EPIFA-C motifs while preserving intact the CM multimerization motifs. These mutants had been previously closely scrutinized in terms of type IV secretion system functionality, CagA translocation and its subsequent phosphorylation. Following infection of gastric epithelial cell lines, transcriptional activation of IL-8 gene and secreted IL-8 levels were found to be strictly dependent upon the functionality of the EPIYA-C phosphorylation motifs, as EPIFA-C phosphorylation-deficient CagA expression failed to induce full IL-8 transcriptional activity. Interestingly, levels of IL-8 gene activation and of secreted IL-8 were the same, irrespective of the number of EPIYA-C terminal repeats. We monitored IkBα phosphorylation and confirmed CagA involvement in NF-kB activation. Furthermore, we observed that presence of EPIYA-C functional phosphorylation motifs contributed to NF-kB activation. NF-kB upstream signaling events, such as early ERK1/2 and AKT activation were confirmed to be independent of EPIYA-C phosphorylation. On the contrary, use of TAK1 specific inhibitor 5Z-7-Oxozeaenol resulted in complete arrest of IL-8 secretion, in a dose-dependent manner, irrespective of CagA status. H. pylori-infected TAK1^-/- mouse embryonic fibroblasts (MEFs) failed to induce NF-kB activity, unlike the respective control MEFs. CagA and TAK1 were found to immunoprecipitate together, irrespective of CagA EPIYA-C status, thus confirming earlier reports of TAK1 and CagA protein interaction. Our data suggest that CagA may potentially interfere with TAK1 activity during NF-kB activation for IL-8 induction in early H. pylori infection.

Role of interleukin-32 in Helicobacter pylori-induced gastric inflammation

Helicobacter pylori infection is associated with gastritis and gastric cancer. An H. pylori virulence factor, the cag pathogenicity island (PAI), is related to host cell cytokine induction and gastric inflammation. Since elucidation of the mechanisms of inflammation is important for therapy, the associations between cytokines and inflammatory diseases have been investigated vigorously. Levels of interleukin-32 (IL-32), a recently described inflammatory cytokine, are increased in various inflammatory diseases, such as rheumatoid arthritis and Crohn's disease, and in malignancies, including gastric cancer. In this report, we examined IL-32 expression in human gastric disease. We also investigated the function of IL-32 in activation of the inflammatory cytokines in gastritis. IL-32 expression paralleled human gastric tissue pathology, with low IL-32 expression in H. pylori-uninfected gastric mucosa and higher expression levels in gastritis and gastric cancer tissues. H. pylori infection increased IL-32 expression in human gastric epithelial cell lines. H. pylori-induced IL-32 expression was dependent on the bacterial cagPAI genes and on activation of nuclear factor κB (NF-κB). IL-32 expression induced by H. pylori was not detected in the supernatant of AGS cells but was found in the cytosol. Expression of the H. pylori-induced cytokines CXCL1, CXCL2, and IL-8 was decreased in IL-32-knockdown AGS cell lines compared to a control AGS cell line. We also found that NF-κB activation was decreased in H. pylori-infected IL-32-knockdown cells. These results suggest that IL-32 has important functions in the regulation of cytokine expression in H. pylori-infected gastric mucosa.

A role for altered phagosome maturation in the long-term persistence of Helicobacter pylori infection

The vigorous host immune response that is mounted against Helicobacter pylori is unable to eliminate this pathogenic bacterium from its niche in the human gastric mucosa. This results in chronic inflammation, which can develop into gastric or duodenal ulcers in 10% of infected individuals and gastric cancer in 1% of infections. The determinants for these more severe pathologies include host (e.g., high IL-1β expression polymorphisms), bacterial [e.g., cytotoxicity-associated gene (cag) pathogenicity island], and environmental (e.g., dietary nitrites) factors. However, it is the failure of host immune effector cells to eliminate H. pylori that underlies its persistence and the subsequent H. pylori-associated disease. Here we discuss the mechanisms used by H. pylori to survive the host immune response and, in particular, the role played by altered phagosome maturation.

Involvement of p38 MAPK-dependent activator protein (AP-1) activation in modulation of gastric mucosal inflammatory responses to Helicobacter pylori by ghrelin

A peptide hormone, ghrelin, plays an important role in modulation of gastric mucosal inflammatory responses to Helicobacter pylori infection by controlling the cross-talk between nitric oxide synthase (NOS) and cyclooxygenase (COX) enzyme systems. In this study, we report that H. pylori LPS-elicited induction in gastric mucosal COX-2 and inducible (i) iNOS protein expression, and the impairment in constitutive (c) cNOS phosphorylation, was associated with mitogen-activated protein kinase, c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase and p38 activation, and occurred with the involvement of transcription factors, CCATT/enhancer-binding protein (C/EBP) δ, cAMP response element-binding protein, activator protein-1 (AP-1), and NF-κB. The modulatory effect of ghrelin on the LPS-induced changes was manifested in the inhibition of nuclear translocation of p65 NF-κB and C/EBPδ, and suppression in AP-1 activation, and the inhibition in phosphorylation of JNK and p38, as well as their respective downstream targets, c-Jun and ATF-2. However, only the inhibition of p38-mediated ATF-2 phosphorylation was reflected in the reduced expression of COX-2 protein. Further, the effect of ghrelin of the LPS-induced changes was reflected in the increase in Src/Akt-dependent cNOS activation through phosphorylation and the inhibition of cNOS-mediated IKK-β S-nitrosylation. Our findings indicate ghrelin counters the proinflammatory consequences of H. pylori by interfering with the p38/ATF-2-induced AP-1 activation in association with concurrent up-regulation in Src/Akt-dependent cNOS phosphorylation.

Induction of microRNA-155 is TLR- and type IV secretion system-dependent in macrophages and inhibits DNA-damage induced apoptosis

Helicobacter pylori is a gastric pathogen responsible for a high disease burden worldwide. Deregulated inflammatory responses, possibly involving macrophages, are implicated in H. pylori-induced pathology, and microRNAs, such as miR-155, have recently emerged as crucial regulators of innate immunity and inflammatory responses. miR-155 is regulated by Toll-like receptor (TLR) ligands in monocyte-derived cells and has been shown to be induced in macrophages during H. pylori infection. Here, we investigated the regulation of miR-155 expression in primary murine bone marrow-derived macrophages (BMMs) during H. pylori infection and examined the downstream mRNA targets of this microRNA using microarray analysis. We report TLR2/4- and NOD1/2-independent up-regulation of miR-155, which was found to be dependent on the major H. pylori pathogenicity determinant, the type IV secretion system (T4SS). miR-155 expression was dependent on NF-κB signaling but was independent of CagA. Microarray analysis identified known gene targets of miR-155 in BMMs during H. pylori infection that are proapoptotic. We also identified and validated miR-155 binding sites in the 3' UTRs of the targets, Tspan14, Lpin1, and Pmaip1. We observed that H. pylori-infected miR-155(-/-) BMMs were significantly more susceptible to cisplatin DNA damage-induced apoptosis than were wild-type BMMs. Thus, our data suggest a function for the prototypical H. pylori pathogenicity factor, the T4SS, in the up-regulation of miR-155 in BMMs. We propose the antiapoptotic effects of miR-155 could enhance macrophage resistance to apoptosis induced by DNA damage during H. pylori infection.

Tannins, peptic ulcers and related mechanisms

This review of the current literature aims to study correlations between the chemical structure and gastric anti-ulcer activity of tannins. Tannins are used in medicine primarily because of their astringent properties. These properties are due to the fact that tannins react with the tissue proteins with which they come into contact. In gastric ulcers, this tannin-protein complex layer protects the stomach by promoting greater resistance to chemical and mechanical injury or irritation. Moreover, in several experimental models of gastric ulcer, tannins have been shown to present antioxidant activity, promote tissue repair, exhibit anti Helicobacter pylori effects, and they are involved in gastrointestinal tract anti-inflammatory processes. The presence of tannins explains the anti-ulcer effects of many natural products.

Protease-activated receptor-2 (PAR2) in human gastric mucosa as mediator of proinflammatory effects in Helicobacter pylori infection

INTRODUCTION

Protease-activated receptors (PAR) are seven transmembrane receptors that are expressed throughout the gastrointestinal tract. In vitro experiments using gastric tumor cell lines, murine models and one clinical study provided evidence for a potential role of PAR2 in Helicobacter pylori-induced gastritis.

AIM

To investigate PAR2 expression in H. pylori-infected patients and correlation with proinflammatory IL-8, IL-1β as well as histologic changes of the mucosa. Furthermore, PAR2 expression was studied in context to mucosal amounts of secretory leukocyte protease inhibitor (SLPI), a putative regulator of PAR2.

METHODS

Twenty-two H. pylori-infected patients and 72 H. pylori-negative subjects underwent upper GI endoscopy. In antrum-derived mucosal biopsies, PAR2, IL-1β, IL-8, and SLPI expression was analyzed by quantitative RT-PCR, and in part by ELISA and immunohistochemistry. Histopathologic evaluation of gastritis was performed according to the updated Sydney classification.

RESULTS

IL-8 gene expression was 5-fold increased in the mucosa of H. pylori-infected patients compared with non-infected (p < .0001), whereas no differences for PAR2 and IL-1β mRNA amounts were observed between both groups. PAR2 gene expression correlated positively with transcript levels of IL-8, IL-1β as well mucosal SLPI levels in H. pylori-infected patients (r: 0.47-0.84; p < .0001), whereas no correlation was found with the degree of gastritis.

CONCLUSIONS

PAR2 represents an additive pathway of IL-8 secretion and proinflammatory effects in H. pylori-induced gastritis. Reduced SLPI levels leading to higher serine protease activities in the mucosa of infected subjects might regulate PAR2 activation.

Helicobacter pylori oipA genetic diversity and its associations with both disease and cagA, vacA s, m, and i alleles among Bulgarian patients

Prevalence of outer inflammatory protein (oipA) gene functional status in Helicobacter pylori strains from Southeastern Europe is still unclear. H. pylori strains from 70 symptomatic patients were polymerase chain reaction (PCR) assessed for cagA and vacA types, and oipA gene functional status was evaluated by PCR and sequencing. Our results demonstrated a high prevalence of strains with oipA status "on" genes (81%) and strong association between them and peptic ulcers, cagA, and vacA s1 and s1/m1 genotypes, regardless of the patient gender, place of residence, and age. Importantly, most vacA i1 strains (93%) harbored oipA status "on" versus only 57% of those with vacA i2 type. The vacA i1 genotype was less frequent (66%) than both cagA and vacA s1 types. The virulent strains with cagA(+) and vacA s1, m1, and i1 were detected in 35% as a predominant genotype and almost all (96%) of these strains harbored oipA status "on". In conclusion, the high prevalence of in-frame oipA gene strains (81%), associated with peptic ulcers and cagA(+), vacA s1, m1, m2, and, importantly, i1 genotypes, indicates a strong synergistic activity of H. pylori virulence factors.

Pathogenesis of Helicobacter pylori infection

Helicobacter pylori infections and clinical outcome are dependent on sophisticated interactions between the bacteria and its host. Crucial bacterial factors associated with pathogenicity comprise a type IV secretion system encoded by the cag pathogenicity island, the effector protein CagA, the vacuolating cytotoxin (VacA), peptidoglycan, lipopolysaccharide (LPS), γ-glutamyl transpeptidase (GGT), protease HtrA, and the adhesins BabA, SabA, and others. The high number of these factors and allelic variation of the involved genes generates a highly complex scenario and reveals the difficulties in testing the contribution of each individual factor. Much effort has been put into identifying the molecular mechanisms associated with H. pylori-associated pathogenesis using human primary tissues, Mongolian gerbils, transgenic, knockout, and other mice as well as in vitro cell model systems. Interactions between bacterial factors and host signal transduction pathways seem to be critical for mediating the induction of pathogenic downstream processes and disease development. In this review article, we discuss the most recent progress in this research field.

BabA-mediated adherence is a potentiator of the Helicobacter pylori type IV secretion system activity

Chronic infection of Helicobacter pylori in the stomach mucosa with translocation of the bacterial cytotoxin-associated gene A (CagA) effector protein via the cag-Type IV secretion system (TFSS) into host epithelial cells are major risk factors for gastritis, gastric ulcers, and cancer. The blood group antigen-binding adhesin BabA mediates the adherence of H. pylori to ABO/Lewis b (Le(b)) blood group antigens in the gastric pit region of the human stomach mucosa. Here, we show both in vitro and in vivo that BabA-mediated binding of H. pylori to Le(b) on the epithelial surface augments TFSS-dependent H. pylori pathogenicity by triggering the production of proinflammatory cytokines and precancer-related factors. We successfully generated Le(b)-positive cell lineages by transfecting Le(b)-negative cells with several glycosyltransferase genes. Using these established cell lines, we found increased mRNA levels of proinflammatory cytokines (CCL5 and IL-8) as well as precancer-related factors (CDX2 and MUC2) after the infection of Le(b)-positive cells with WT H. pylori but not with babA or TFSS deletion mutants. This increased mRNA expression was abrogated when Le(b)-negative cells were infected with WT H. pylori. Thus, H. pylori can exploit BabA-Le(b) binding to trigger TFSS-dependent host cell signaling to induce the transcription of genes that enhance inflammation, development of intestinal metaplasia, and associated precancerous transformations.

Induction of TLR-2 and TLR-5 expression by Helicobacter pylori switches cagPAI-dependent signalling leading to the secretion of IL-8 and TNF-α

Helicobacter pylori is the causative agent for developing gastritis, gastric ulcer, and even gastric cancer. Virulent strains carry the cag pathogenicity island (cagPAI) encoding a type-IV secretion system (T4SS) for injecting the CagA protein. However, mechanisms of sensing this pathogen through Toll-like receptors (TLRs) and downstream signalling pathways in the development of different pathologies are widely unclear. Here, we explored the involvement of TLR-2 and TLR-5 in THP-1 cells and HEK293 cell lines (stably transfected with TLR-2 or TLR-5) during infection with wild-type H. pylori and isogenic cagPAI mutants. H. pylori triggered enhanced TLR-2 and TLR-5 expression in THP-1, HEK293-TLR2 and HEK293-TLR5 cells, but not in the HEK293 control. In addition, IL-8 and TNF-α cytokine secretion in THP-1 cells was induced in a cagPAI-dependent manner. Furthermore, we show that HEK293 cells are not competent for the uptake of T4SS-delivered CagA, and are therefore ideally suited for studying TLR signalling in the absence of T4SS functions. HEK293 control cells, which do not induce TLR-2 and TLR-5 expression during infection, only secreted cytokines in small amounts, in agreement with T4SS functions being absent. In contrast, HEK293-TLR2 and HEK293-TLR5 cells were highly competent for inducing the secretion of IL-8 and TNF-α cytokines in a cagPAI-independent manner, suggesting that the expression of TLR-2 or TLR-5 has profoundly changed the capability to trigger pro-inflammatory signalling upon infection. Using phospho-specific antibodies and luciferase reporter assays, we further demonstrate that H. pylori induces IRAK-1 and IκB phosphorylation in a TLR-dependent manner, and this was required for activation of transcription factor NF-κB. Finally, NF-κB activation in HEK293-TLR2 and HEK293-TLR5 cells was confirmed by expressing p65-GFP which was translocated from the cytoplasm into the nucleus. These data indicate that H. pylori-induced expression of TLR-2 and TLR-5 can qualitatively shift cagPAI-dependent to cagPAI-independent pro-inflammatory signalling pathways with possible impact on the outcome of H. pylori-associated diseases.

Role of the cag-pathogenicity island encoded type IV secretion system in Helicobacter pylori pathogenesis

Helicobacter pylori is a very successful human-specific bacterium worldwide. Infections of the stomach with this pathogen can induce pathologies, including chronic gastritis, peptic ulcers and even gastric cancer. Highly virulent H. pylori strains encode the cytotoxin-associated gene (cag)-pathogenicity island, which expresses a type IV secretion system (T4SS). This T4SS forms a syringe-like pilus structure for the injection of virulence factors such as the CagA effector protein into host target cells. This is achieved by a number of T4SS proteins, including CagI, CagL, CagY and CagA, which by itself binds the host cell integrin member β(1) followed by delivery of CagA across the host cell membrane. A role of CagA interaction with phosphatidylserine has also been shown to be important for the injection process. After delivery, CagA becomes phosphorylated by oncogenic tyrosine kinases and mimics a host cell factor for the activation or inactivation of some specific intracellular signalling pathways. We review recent progress aiming to characterize the CagA-dependent and CagA-independent signalling capabilities of the T4SS, which include the induction of membrane dynamics, disruption of cell-cell junctions and actin-cytoskeletal rearrangements, as well as pro-inflammatory, cell cycle-related and anti-apoptotic transcriptional responses. The contribution of these signalling pathways to pathogenesis during H. pylori infections is discussed.

Helicobacter pylori-induced tyrosine phosphorylation of IKKβ contributes to NF-κB activation

Helicobacter pylori, the etiological agent of several human gastric diseases, induces the transcription factor nuclear factor-κB (NF-κB) in colonized epithelial cells leading to the release of proinflammatory mediators. Activation of NF-κB involves the IκB kinase (IKK)-complex composed of two catalytic subunits, IKKα and IKKβ, and a regulatory scaffold protein, IKKγ. IKKβ was shown to be essential for NF-κB activation in response to a variety of stimuli including H. pylori. In addition to the phosphorylation of serine residues, tyrosine phosphorylation could be crucial for IKKβ activation. Here we provide evidence that IKKβ phosphorylation is induced in lipid rafts (DRM fractions) of H. pylori-infected cells, but not TNFα-stimulated cells. Furthermore, H. pylori transiently induces binding of IKKβ to c-Src kinase. Inhibition of c-Src by specific inhibitors as well as knockdown of c-Src by small interfering RNA reduced phosphorylation of IκBα as well as of p65. Thus, tyrosine-phosphorylated IKKβ contributes at least in part to NF-κB activation in response to H. pylori infection.