Helicobacter pylori activates the histidine decarboxylase promoter through a mitogen-activated protein kinase pathway independent of pathogenicity island-encoded virulence factors

Helicobacter pylori-controlled c-Abl localization promotes cell migration and limits apoptosis

BACKGROUND

Deregulated c-Abl activity has been intensively studied in a variety of solid tumors and leukemia. The class-I carcinogen Helicobacter pylori (Hp) activates the non-receptor tyrosine kinase c-Abl to phosphorylate the oncoprotein cytotoxin-associated gene A (CagA). The role of c-Abl in CagA-dependent pathways is well established; however, the knowledge of CagA-independent c-Abl processes is scarce.

METHODS

c-Abl phosphorylation and localization were analyzed by immunostaining and immunofluorescence. Interaction partners were identified by tandem-affinity purification. Cell elongation and migration were analyzed in transwell-filter experiments. Apoptosis and cell survival were examined by FACS analyses and MTT assays. In mice experiments and human biopsies, the involvement of c-Abl in Hp pathogenesis was investigated.

RESULTS

Here, we investigated the activity and subcellular localization of c-Abl in vitro and in vivo and unraveled the contribution of c-Abl in CagA-dependent and -independent pathways to gastric Hp pathogenesis. We report a novel mechanism and identified strong c-Abl threonine 735 phosphorylation (pAbl^T735) mediated by the type-IV secretion system (T4SS) effector D-glycero-β-D-manno-heptose-1,7-bisphosphate (βHBP) and protein kinase C (PKC) as a new c-Abl kinase. pAbl^T735 interacted with 14-3-3 proteins, which caused cytoplasmic retention of c-Abl, where it potentiated Hp-mediated cell elongation and migration. Further, the nuclear exclusion of pAbl^T735 attenuated caspase-8 and caspase-9-dependent apoptosis. Importantly, in human patients suffering from Hp-mediated gastritis c-Abl expression and pAbl^T735 phosphorylation were drastically enhanced as compared to type C gastritis patients or healthy individuals. Pharmacological inhibition using the selective c-Abl kinase inhibitor Gleevec confirmed that c-Abl plays an important role in Hp pathogenesis in a murine in vivo model.

CONCLUSIONS

In this study, we identified a novel regulatory mechanism in Hp-infected gastric epithelial cells by which Hp determines the subcellular localization of activated c-Abl to control Hp-mediated EMT-like processes while decreasing cell death.

What We Know and What We Need to Know about Aromatic and Cationic Biogenic Amines in the Gastrointestinal Tract

Biogenic amines derived from basic and aromatic amino acids (B/A-BAs), polyamines, histamine, serotonin, and catecholamines are a group of molecules playing essential roles in many relevant physiological processes, including cell proliferation, immune response, nutrition and reproduction. All these physiological effects involve a variety of tissue-specific cellular receptors and signalling pathways, which conforms to a very complex network that is not yet well-characterized. Strong evidence has proved the importance of this group of molecules in the gastrointestinal context, also playing roles in several pathologies. This work is based on the hypothesis that integration of biomedical information helps to reach new translational actions. Thus, the major aim of this work is to combine scientific knowledge on biomolecules, metabolism and physiology of the main B/A-BAs involved in the pathophysiology of the gastrointestinal tract, in order to point out important gaps in information and other facts deserving further research efforts in order to connect molecular information with pathophysiological observations.

Physiological implications of biased signaling at histamine H2 receptors

Histamine mediates numerous functions acting through its four receptor subtypes all belonging to the large family of seven transmembrane G-protein coupled receptors. In particular, histamine H2 receptor (H2R) is mainly involved in gastric acid production, becoming a classic pharmacological target to treat Zollinger–Ellison disease and gastric and duodenal ulcers. H2 ligands rank among the most widely prescribed and over the counter-sold drugs in the world. Recent evidence indicate that some H2R ligands display biased agonism, selecting and triggering some, but not all, of the signaling pathways associated to the H2R. The aim of the present work is to study whether famotidine, clinically widespread used ligand acting at H2R, exerts biased signaling. Our findings indicate that while famotidine acts as inverse agonist diminishing cAMP basal levels, it mimics the effects of histamine and the agonist amthamine concerning receptor desensitization and internalization. Moreover, the treatment of HEK293T transfected cells with any of the three ligands lead to a concentration dependent pERK increment. Similarly in AGS gastric epithelial cells, famotidine treatment led to both, the reduction in cAMP levels as well as the increment in ERK phosphorylation, suggesting that this behavior could have pharmacological relevant implications. Based on that, histidine decarboxylase expression was studied by quantitative PCR in AGS cells and its levels were increased by famotidine as well as by histamine and amthamine. In all cases, the positive regulation was impeded by the MEK inhibitor PD98059, indicating that biased signaling toward ERK1/2 pathway is the responsible of such enzyme regulation. These results support that ligand bias is not only a pharmacological curiosity but has physiological and pharmacological implications on cell metabolism.

Analysis of T4SS-induced signaling by H. pylori using quantitative phosphoproteomics

Helicobacter pylori is a Gram-negative bacterial pathogen colonizing the human stomach. Infection with H. pylori causes chronic inflammation of the gastric mucosa and may lead to peptic ulceration and/or gastric cancer. A major virulence determinant of H. pylori is the type IV secretion system (T4SS), which is used to inject the virulence factor CagA into the host cell, triggering a wide range of cellular signaling events. Here, we used a phosphoproteomic approach to investigate tyrosine signaling in response to host-pathogen interaction, using stable isotope labeling in cell culture (SILAC) of AGS cells to obtain a differential picture between multiple infection conditions. Cells were infected with wild type H. pylori P12, a P12Δ CagA deletion mutant, and a P12Δ PAI deletion mutant to compare signaling changes over time and in the absence of CagA or the T4SS. Tryptic peptides were enriched for tyrosine (Tyr) phosphopeptides and analyzed by nano-LC-Orbitrap MS. In total, 85 different phosphosites were found to be regulated following infection. The majority of phosphosites identified were kinases of the MAPK family. CagA and the T4SS were found to be key regulators of Tyr phosphosites. Our findings indicate that CagA primarily induces activation of ERK1 and integrin-linked factors, whereas the T4SS primarily modulates JNK and p38 activation.

Complex cellular responses of Helicobacter pylori-colonized gastric adenocarcinoma cells

Helicobacter pylori is an important class I carcinogen that persistently infects the human gastric mucosa to induce gastritis, gastric ulceration, and gastric cancer. H. pylori pathogenesis strongly depends on pathogenic factors, such as VacA (vacuolating cytotoxin A) or a specialized type IV secretion system (T4SS), which injects the oncoprotein CagA (cytotoxin-associated gene A product) into the host cell. Since access to primary gastric epithelial cells is limited, many studies on the complex cellular and molecular mechanisms of H. pylori were performed in immortalized epithelial cells originating from individual human adenocarcinomas. The aim of our study was a comparative analysis of 14 different human gastric epithelial cell lines after colonization with H. pylori. We found remarkable differences in host cell morphology, extent of CagA tyrosine phosphorylation, adhesion to host cells, vacuolization, and interleukin-8 (IL-8) secretion. These data might help in the selection of suitable cell lines to study host cell responses to H. pylori in vitro, and they imply that different host cell factors are involved in the determination of H. pylori pathogenesis. A better understanding of H. pylori-directed cellular responses can provide novel and more balanced insights into the molecular mechanisms of H. pylori-dependent pathogenesis in vivo and may lead to new therapeutic approaches.

Helicobacter pylori induction of the gastrin promoter through GC-rich DNA elements

BACKGROUND

Helicobacter pylori (H. pylori) infection has been linked to the development of chronic gastritis, duodenal ulcer disease, and gastric cancer. Helicobacter pylori- infected patients and animal models develop hypergastrinemia, chronic gastritis, and gastric atrophy. Since gastrin is an important regulator of gastric acid secretion and cell growth, H. pylori regulation of this hormone has been implicated in its pathogenesis.

OBJECTIVES

To investigate the effect of H. pylori on gastrin gene expression in mice and of human bacterial isolates on gastrin mRNA expressed in a human cell line.

METHODS

Gastrin mRNA was measured by qRT-PCR in H. pylori-infected mice. H. pylori were co-cultured with AGS cells to study regulation of human gastrin gene expression. Various MAP kinases were implicated in signal transduction from the bacteria using specific inhibitors. Gastrin reporter constructs and gel shift assays were used to map DNA responsive elements.

RESULTS

In addition to an increase in gastrin mRNA in H. pylori-infected mice, H. pylori induced the endogenous human gastrin gene through MAP kinase-dependent signaling but not NFκB-dependent signaling. Activation of gastrin through MAPK signaling did not require CagA or VacA virulence factors. Transfection studies demonstrated that a GC-rich motif mediated H. pylori-induction of the gastrin promoter and that the motif inducibly binds Sp1 and Sp3 transcription factors.

CONCLUSIONS

Direct contact of live H. pylori bacteria with human cells is sufficient to induce gastrin gene expression.

H. pylori-induced promoter hypermethylation downregulates USF1 and USF2 transcription factor gene expression

Helicobacter pylori infection is associated with the development of gastric adenocarcinoma. Upstream stimulatory factors USF1 and USF2 regulate the transcription of genes related to immune response, cell cycle and cell proliferation. A decrease in their expression is observed in human gastric epithelial cells infected with H. pylori, associated to a lower binding to their DNA E-box recognition site as shown by electrophoretic mobility shift assay. DNA methylation leads to gene silencing. The treatment of cells with 5'-azacytidine, an inhibitor of DNA methylation, restored the USF1 and USF2 gene expression in the presence of infection. Using promoter PCR methylation assay, a DNA hypermethylation was shown in the promoter region of USF1 and USF2 genes, in infected cells. The inhibition of USF1 and USF2 expression by H. pylori and the DNA hypermethylation in their gene promoter region was confirmed in gastric tissues isolated from 12 to 18 months infected mice. Our study demonstrated the involvement of USF1 and USF2 as molecular targets of H. pylori and the key role of DNA methylation in their regulation. These mechanisms occurred in the context of metaplastic lesions, suggesting that alteration of USF1 and USF2 levels could participate in the promotion of neoplastic process during H. pylori infection.

The innate immune molecule, NOD1, regulates direct killing of Helicobacter pylori by antimicrobial peptides

The cytosolic innate immune molecule, NOD1, recognizes peptidoglycan (PG) delivered to epithelial cells via the Helicobacter pylori cag pathogenicity island (cagPAI), and has been implicated in host defence against cagPAI(+)H. pylori bacteria. To further clarify the role of NOD1 in host defence, we investigated NOD1-dependent regulation of human beta-defensins (DEFBs) in two epithelial cell lines. Our findings identify that NOD1 activation, via either cagPAI(+) bacteria or internalized PG, was required for DEFB4 and DEFB103 expression in HEK293 cells. To investigate cell type-specific induction of DEFB4 and DEFB103, we generated stable NOD1'knockdown' (KD) and control AGS cells. Reporter gene assay and RT-PCR analyses revealed that only DEFB4 was induced in an NOD1-/cagPAI-dependent fashion in AGS cells. Moreover, culture supernatants from AGS control, but not AGS NOD1 KD cells, stimulated with cagPAI(+)H. pylori, significantly reduced H. pylori bacterial numbers. siRNA studies confirmed that human beta-defensin 2 (hBD-2), but not hBD-3, contributes to the antimicrobial activity of AGS cell supernatants against H. pylori. This study demonstrates, for the first time, the involvement of NOD1 and hBD-2 in direct killing of H. pylori bacteria by epithelial cells and confirms the importance of NOD1 in host defence mechanisms against cagPAI(+)H. pylori infection.

Prediction of extracellular proteases of the human pathogen Helicobacter pylori reveals proteolytic activity of the Hp1018/19 protein HtrA

Exported proteases of Helicobacter pylori (H. pylori) are potentially involved in pathogen-associated disorders leading to gastric inflammation and neoplasia. By comprehensive sequence screening of the H. pylori proteome for predicted secreted proteases, we retrieved several candidate genes. We detected caseinolytic activities of several such proteases, which are released independently from the H. pylori type IV secretion system encoded by the cag pathogenicity island (cagPAI). Among these, we found the predicted serine protease HtrA (Hp1019), which was previously identified in the bacterial secretome of H. pylori. Importantly, we further found that the H. pylori genes hp1018 and hp1019 represent a single gene likely coding for an exported protein. Here, we directly verified proteolytic activity of HtrA in vitro and identified the HtrA protease in zymograms by mass spectrometry. Overexpressed and purified HtrA exhibited pronounced proteolytic activity, which is inactivated after mutation of Ser205 to alanine in the predicted active center of HtrA. These data demonstrate that H. pylori secretes HtrA as an active protease, which might represent a novel candidate target for therapeutic intervention strategies.

C314T polymorphism in histamine N-methyltransferase gene and susceptibility to duodenal ulcer in Chinese population

BACKGROUND

Histamine is a regulator of gastric acid secretion, which is involved in the development of duodenal ulcer (DU). Histamine is metabolized by both histamine N-methyltransferase (HNMT) and diamine oxidase, and its local action is terminated primarily by methylation which is catalyzed by HNMT.

METHODS

Polymerase chain reaction-restriction fragment length polymorphism assay was used to identify the polymorphism of the point mutation C314T of HNMT gene of 498 Chinese patients with DU and 151 healthy individuals.

RESULTS

In normal controls, the allele frequency of HNMT T314 was 3.3%, which was significantly lower than American Caucasians. The HNMT T314 allele was detected in 3.5% of the DU patients. In cases and controls, the frequency of C/C genotypes were 93.0% and 93.4%, respectively. The HNMT T/T genotype was not found in this population. No significant differences were seen in both genotype frequencies and allele frequencies between DU groups and controls. After stratified by H. pylori infection, they also could not reach significant differences in our current study.

CONCLUSION

The HNMT T314 allele frequency is lower in Chinese population than in American Caucasians. No association can be found in the involvement of HNMT C314T polymorphism in the susceptibility to duodenal ulcer.

An upstream CRE-E-box element is essential for gastrin-dependent activation of the cyclooxygenase-2 gene in human colon cancer cells

Cyclooxygenase-2, the inducible enzyme of arachidonic acid metabolism and prostaglandin synthesis, is over expressed in colorectal cancer. Inhibition of COX-1/-2 by non-steroidal anti-inflammatory drugs is associated with a decreased risk for these malignancies, whereas high serum gastrin levels elevate this risk. As gastrin exhibits trophical effects on colonic epithelium we sought to explore whether it is capable to induce COX-2 expression in a human colon cancer cell line. The aim of this study is the description of the gastrin evoked effects on the transcriptional activity of the COX-2 gene in colorectal cancer cells and the identification of regulatory promoter elements. Reporter gene assays were performed with the gastrin-stimulated human colorectal cancer cell-line Colo-320, which was stable transfected with the human cholecystokinin-B/gastrin receptor cDNA and COX-2-promoter-luciferase constructs containing different segments of the 5'-region of the COX-2 gene or with mutated promoter constructs. Transcription factors were characterized with electrophoretic mobility shift assays. Gastrin-dependent induction of COX-2 mRNA was shown using "real-time" PCR. Resulting elevated Prostaglandin E2-levels were measured using ELISA. Gastrin stimulated the PGE2-generation and COX-2-mRNA expression in human Colo-320-B cells potently, obviously by transactivating the COX-2-promoter using a region between - 68 bp and + 70 bp. Further examinations identified a CRE-E-box element between - 56 bp and - 48 bp mediating the gastrin-effects on the COX-2 gene. Transcription factors binding to this promoter element were USF-1 und -2. These results show the necessity to perform succeeding studies, which could describe possible mechanisms in which gastrin and COX-2 contribute to the induction of colorectal carcinomas.

Tip60 functions as a potential corepressor of KLF4 in regulation of HDC promoter activity

KLF4 is a transcription factor that is highly expressed in the gastrointestinal tract. Previously we have demonstrated that KLF4 represses HDC promoter activity in a gastric cell line through both an upstream Sp1 binding GC box and downstream gastrin responsive elements. However, the mechanism by which KLF4 inhibits HDC promoter is not well defined. In the current study, by using yeast two-hybrid screening, Tip60 was identified as a KLF4 interacting protein. Further coimmunoprecipitation and functional reporter assays support the interaction between these two proteins. In addition, Tip60 and HDAC7, previously shown to interact with each other and repress transcription, inhibited HDC promoter activity in a dose-dependent fashion. Consistently, knock down of Tip60 or HDAC7 gene expression by specific shRNA increased endogenous HDC mRNA level. Co-immunoprecipitation assays showed that HDAC7 was pulled down by KLF4 and Tip60, suggesting that these three proteins form a repressive complex. Further chromatin immuno-precipitation indicated that all three proteins associated with HDC promoter. Two-hour gastrin treatment, known to activate HDC gene expression, significantly decreased the association of KLF4, Tip60 and HDAC7 with HDC promoter, suggesting that gastrin activates HDC gene expression at least partly by decreasing the formation of KLF4/Tip60/HDAC7 repressive complexes at the HDC promoter.

Helicobacter pylori stimulates gastric epithelial cell MMP-1 secretion via CagA-dependent and -independent ERK activation

Because the mechanisms of Helicobacter pylori-induced gastric injury are incompletely understood, we examined the hypothesis that H. pylori induces matrix metalloproteinase-1 (MMP-1) secretion, with potential to disrupt gastric stroma. We further tested the role of CagA, an H. pylori virulence factor, in MMP-1 secretion. Co-incubation of AGS cells with Tx30a, an H. pylori strain lacking the cagA virulence gene, stimulated MMP-1 secretion, confirming cagA-independent secretion. Co-incubation with strain 147C (cagA(+)) resulted in CagA translocation into AGS cells and increased MMP-1 secretion relative to Tx30a. Transfection of cells with the recombinant 147C cagA gene also induced MMP-1 secretion, indicating that CagA can independently stimulate MMP-1 secretion. Co-incubation with strain 147A, containing a cagA gene that lacks an EPIYA tyrosine phosphorylation motif, as well as transfection with 147A cagA, yielded an MMP-1 secretion intermediate between no treatment and 147C, indicating that CagA tyrosine phosphorylation regulates cellular signaling in this model system. H. pylori induced activation of the MAP kinase ERK, with CagA-independent (early) and dependent (later) components. MEK inhibitors UO126 and PD98059 inhibited both CagA-independent and -dependent MMP-1 secretion, whereas p38 inhibition enhanced MMP-1 secretion and ERK activation, suggesting p38 negative regulation of MMP-1 and ERK. These data indicate H. pylori effects on host epithelial MMP-1 expression via ERK, with p38 playing a potential regulatory role.

In-Cell Western analysis of Helicobacter pylori-induced phosphorylation of extracellular-signal related kinase via the transactivation of the epidermal growth factor receptor

Helicobacter pylori activates extracellular-signal related (ERK) kinases in gastric epithelial cells, via transactivation of the EGF receptor (EGFR). H. pylori activation of EGFR may be relevant to epithelial hyperproliferation and gastric carcinogenesis. The aim of this study was to develop an 'In-Cell Western' (ICW) assay for quantitative examination of H. pylori-induced epithelial signalling, to enable the role of the EGFR in H. pylori-induced phosphorylation of ERK in epithelial cells to be ascertained. H. pylori strains were co-incubated with A431 and AGS cells. pERK and total ERK were quantified in situ using ICW analysis. H. pylori strains both with, and without a cag PAI, and Helicobacter felis, significantly increased pERK levels in A431 cells. The EGFR inhibitor EKB-569 dose-dependently reduced H. pylori-induced ERK phosphorylation in A431 and AGS cells. A significantly lower reduction was observed with cag+ strains in A431 but not AGS cells. The cag PAI was not necessary for EGFR signal transactivation. These data suggest that H. pylori induces pERK in epithelial cells partly via the EGFR pathway. Additional signalling mechanisms are likely to be involved in H. pylori-induced ERK phosphorylation. ICW analysis is a rapid quantitative method for evaluating the effects of inhibitors on H. pylori-induced cell signalling pathways of relevance to gastric carcinogenesis.

Functional and intracellular signaling differences associated with the Helicobacter pylori AlpAB adhesin from Western and East Asian strains

Following adhesion of Helicobacter pylori to gastric epithelial cells, intracellular signaling leads to cytokine production, which causes H. pylori-related gastric injury. Two adjacent homologous genes (alpA and alpB), which encode H. pylori outer membrane proteins, are thought to be associated with adhesion and cytokine induction. We co-cultured gastric epithelial cells with wild type H. pylori strains and their corresponding alpA/alpB-deleted mutants (DeltaalpAB). Results were confirmed by complementation. Flow cytometry confirmed that AlpAB was involved in cellular adhesion. Deletion of alpAB reduced interleukin (IL)-6 induction in gastric epithelial cells. Deletion of alpAB reduced IL-8 induction with East Asian but not with Western strains. All AlpAB-positive strains tested activated the extracellular signal-regulated kinase, c-Fos, and cAMP-responsive element-binding protein. Activation of the Jun-N-terminal kinase, c-Jun, and NF-kappaB was exclusive to AlpAB from East Asian strains. DeltaalpAB mutants poorly colonized the stomachs of C57BL/6 mice and were associated with lower mucosal levels of KC and IL-6. Our results suggest that AlpAB may induce gastric injury by mediating adherence to gastric epithelial cells and by modulating proinflammatory intracellular signaling cascades. Known geographical differences in H. pylori-related clinical outcomes may relate to differential effects of East Asian and Western types of AlpAB on NF-kappaB-related proinflammatory signaling pathways.

Phosphorylation of Helicobacter pylori CagA by c-Abl leads to cell motility

Helicobacter pylori induces a strong motogenic response in infected gastric epithelial host cells, which is enhanced by translocation of the pathogenic factor cytotoxin-associated gene A (CagA) into host cells via a specialized type IV secretion system. Once injected into the cytosol CagA is rapidly tyrosine phosphorylated by Src family kinases followed by Src inactivation. Hence, it remained unknown why CagA is constantly phosphorylated in sustained H. pylori infections to induce cell migration, whereas other substrates of Src kinases are dephosphorylated. Here, we identify the non-receptor tyrosine kinase c-Abl as a crucial mediator of H. pylori-induced migration and novel CagA kinase in epithelial cells. Upon H. pylori infection c-Abl directly interacts with CagA and localizes in focal adhesion complexes and membrane ruffles, which are highly dynamic cytoskeletal structures necessary for cell motility. Selective inhibition of c-Abl kinase activity by STI571 or shRNA abrogates sustained CagA phosphorylation and epithelial cell migration, indicating a pivotal role of c-Abl in H. pylori infection and pathogenicity. These results implicate c-Abl as a novel molecular target for therapeutic intervention in H. pylori-related gastric diseases.

Yin yang 1 (YY1) represses histidine decarboxylase gene expression with SREBP-1a in part through an upstream Sp1 site

Histidine decarboxylase (HDC) is the enzyme that converts histidine to histamine, a bioamine that plays an important role in many physiological aspects including allergic responses, inflammation, neurotransmission, and gastric acid secretion. In previous studies, we demonstrated that Kruppel-like factor 4 represses HDC promoter activity in a gastric cell line through both an upstream Sp1-binding GC box (GGGCGG sequence) and downstream gastrin-responsive elements. In the current study, Yin Yang 1 (YY1), a pleiotropic transcriptional factor, was also shown in cotransfection assays to repress HDC promoter activity through the upstream GC box. DNA affinity purification assay demonstrated that YY1 was pulled down specifically by the upstream GC box. In addition, sterol-responsive element-binding protein 1a (SREBP-1a), a transcriptional factor that binds YY1, represses the HDC promoter. Interestingly, deletion analysis and cotransfection assays indicated that mutation of the upstream GC box or truncation of downstream gastrin-responsive elements in the HDC promoter disrupted the inhibitory effect of YY1 and SREBP-1a in an identical fashion. Furthermore, quantitative real-time PCR analysis indicated that gastrin treatment downregulated SREBP-1a gene expression and reduced the DNA binding activity of SREBP in EMSAs. Taken together, these results suggest that YY1 and SREBP-1a form a complex to inhibit HDC gene expression through both the upstream GC box and downstream gastrin-responsive elements and gastrin-induced activation of HDC gene expression is mediated at least partly through downregulation of transcriptional repressors such as SREBPs.

Regulation of RANTES promoter activation in gastric epithelial cells infected with Helicobacter pylori

RANTES, a CC chemokine, plays an important role in the inflammatory response associated with Helicobacter pylori infection. However, the mechanism by which H. pylori induces RANTES expression in the gastric mucosa is unknown. We cocultured gastric epithelial cells with wild-type H. pylori, isogenic oipA mutants, cag pathogenicity island (PAI) mutants, or double knockout mutants. Reverse transcriptase PCR showed that RANTES mRNA was induced by H. pylori and that the expression was both OipA and cag PAI dependent. Luciferase reporter gene assays and electrophoretic mobility shift assays showed that maximal H. pylori-induced RANTES gene transcription required the presence of the interferon-stimulated responsive element (ISRE), the cyclic AMP-responsive element (CRE), nuclear factor-interleukin 6 (NF-IL-6), and two NF-kappaB sites. OipA- and cag PAI-dependent pathways included NF-kappaB-->NF-kappaB/NF-IL-6/ISRE pathways, and cag PAI-dependent pathways additionally included Jun N-terminal kinase-->CRE/NF-kappaB pathways. The OipA-dependent pathways additionally included p38-->CRE/ISRE pathways. We confirmed the in vitro effects in vivo by examining RANTES mRNA levels in biopsy specimens from human gastric antral mucosa. RANTES mRNA levels in the antral mucosa were significantly higher for patients infected with cag PAI/OipA-positive H. pylori than for those infected with cag PAI/OipA-negative H. pylori or uninfected patients. The mucosal inflammatory response to H. pylori infection involves different signaling pathways for activation of the RANTES promoter, with both OipA and the cag PAI being required for full activation of the RANTES promoter.

Helicobacter pylori encoding the pathogenicity island activates matrix metalloproteinase 1 in gastric epithelial cells via JNK and ERK

Helicobacter pylori colonizes the human gastric epithelium and induces an inflammatory response that is a trigger for gastric carcinogenesis. Matrix metalloproteinases (MMPs) have recently been shown to be up-regulated in gastric epithelial cells infected with H. pylori and might contribute to the pathogenesis of peptic ulcer. The aim of this study was to extend the knowledge about the effect of H. pylori infection on MMP-1 expression by gastric epithelial cells, the kinetics of induction, the pathogenetic properties of the bacterium, and the intracellular signaling pathways required for MMP-1 up-regulation. Expression of MMP-1 was induced more than 10-fold by co-culture of AGS+cells with H. pylori strains carrying the pathogenicity island (PAI). H. pylori strains with mutations in the PAI and a defective type IV secretion system had no effect on MMP-1. Double immunofluorescence revealed strong MMP-1 staining in epithelial cells of gastric biopsies at sites of bacterial attachment. In vitro, MMP-1 is up-regulated by interleukin-1beta and tumor necrosis factor-alpha, but these regulatory mechanisms are not operating in H. pylori infection as shown by inhibitory antibodies. Specific inhibitors of JNK kinase and ERK1/2 kinase were found to suppress the H. pylori-induced MMP-1 expression and activity. AGS cells treated with antisense MMP-1 showed a significantly reduced potential to degrade reconstituted basement membrane. Our results suggest that in gastric epithelial cells, H. pylori up-regulates MMP-1 in a type IV secretion system-dependent manner via JNK and ERK1/2. Induction of MMP-1 is further implicated in complex processes induced by H. pylori, resulting in tissue degradation and remodeling of the gastric mucosa.

Regulation of interleukin-6 promoter activation in gastric epithelial cells infected with Helicobacter pylori

The regulation of Helicobacter pylori induced interleukin (IL)-6 in the gastric epithelium remains unclear. Primary gastric epithelial cells and MKN28 cells were cocultured with H. pylori and its isogenic cag pathogenicity island (PAI) mutant and/or oipA mutants. H. pylori infection-induced IL-6 mRNA expression and IL-6 protein production, which was further enhanced by the cag PAI and OipA. Luciferase reporter gene assays and electrophoretic mobility shift assays showed that full IL-6 transcription required binding sites for nuclear factor-kappaB (NF-kappaB), cAMP response element (CRE), CCAAT/enhancer binding protein (C/EBP), and activator protein (AP)-1. The cag PAI and OipA were involved in binding to NF-kappaB, AP-1, CRE, and C/EBP sites. The cag PAI activated the extracellular signal-regulated kinase (ERK) and Jun N-terminal kinase (JNK) pathways; OipA activated the p38 pathway. Transfection of dominant negative G-protein confirmed roles for Raf, Rac1, and RhoA in IL-6 induction. Overall, the cag PAI-related IL-6 signal transduction pathway involved the Ras/Raf/MEK1/2/ERK/AP-1/CRE pathway and the JNK/AP-1/CRE pathway; the OipA-related pathway is p38/AP-1/CRE and both the cag PAI and OipA appear to be involved in the RhoA/Rac1/NF-kappaB pathway. Combination of different pathways by the cag PAI and OipA will lead to the maximum IL-6 induction.

Helicobacter infection and gastric neoplasia

Chronic gastritis induced by Helicobacter pylori is the strongest known risk factor for adenocarcinoma of the distal stomach, yet only a minority of people who harbour this organism ever develop cancer. H. pylori isolates possess substantial genotypic diversity, which engenders differential host inflammatory responses that influence clinical outcome. H. pylori strains that possess the cag pathogenicity island and secrete a functional cytotoxin induce more severe gastric injury and further augment the risk for developing distal gastric cancer. However, carcinogenesis is also influenced by host genetic diversity, particularly involving immune response genes such as IL-1ss and TNF-alpha. It is important to gain insight into the pathogenesis of H. pylori-induced gastritis and adenocarcinoma, not only to develop more effective treatments for gastric cancer, but also because it might serve as a paradigm for the role of chronic inflammation in the genesis of other malignancies that arise within the gastrointestinal tract.

Analysis of the type IV secretion system-dependent cell motility of Helicobacter pylori-infected epithelial cells

The pathogenesis of Helicobacter pylori-associated disorders is strongly dependent on a specialized type IV secretion system (T4SS) encoded by the cag pathogenicity island (PAI). Cytotoxin-associated gene A (CagA) is the only known H. pylori protein translocated into the host cell followed by tyrosine phosphorylation through host protein kinases. H. pylori induces cellular processes which are either PAI- or CagA-dependent (e.g., cell motility), PAI-dependent, but CagA-independent (e.g., interleukin-8 release), or PAI- and CagA-independent (e.g., cyclooxygenase-2 release). Here, we investigated H. pylori strains mutated in single PAI genes of the wild type strain Hp26695 and their effects on cell motility. We found 17 gene products out of 27 PAI genes playing a superordinated role and five PAI-encoded proteins exhibiting a clearly critical role in motogenic host cell responses, whereas the remaining five PAI gene products had no significant influence on the motogenic response in reaction to H. pylori infection. This study clearly demonstrated that H. pylori-induced cell motility and invasive growth involve type IV secretion system-dependent signalling as well as translocated and phosphorylated CagA. These findings reveal a deeper insight in to the meaning of the T4SS of H. pylori for host cell motility.

Helicobacter pylori stimulates host cyclooxygenase-2 gene transcription: critical importance of MEK/ERK-dependent activation of USF1/-2 and CREB transcription factors

Cyclooxygenase-2 (COX-2) represents the inducible key enzyme of arachidonic acid metabolism and contributes to the pathogenesis of gastroduodenal ulcers and gastric cancer. Helicobacter pylori infection is associated with elevated gastric COX-2 levels, but the mechanisms underlying H. pylori-dependent cox-2 gene expression are unclear. H. pylori stimulated cox-2 mRNA and protein abundance in gastric epithelial cells in vitro and in vivo, and functional analysis of the cox-2 gene promoter mapped its H. pylori-responsive region to a proximal CRE/Ebox element at -56 to -48. Moreover, USF1/-2 and CREB transcription factors binding to this site were identified to transmit H. pylori-dependent cox-2 transcription. Activation of MEK/ERK1/-2 signalling by bacterial virulence factors located outside the H. pylori cag pathogenicity island (cagPAI) was found to mediate bacterial effects on the cox-2 promoter. Our study provides a detailed description of the molecular pathways underlying H. pylori-dependent cox-2 gene expression in gastric epithelial cells, and may thus contribute to a better understanding of mechanisms underlying H. pylori pathogenicity.

Kruppel-like factor 4 (KLF4) represses histidine decarboxylase gene expression through an upstream Sp1 site and downstream gastrin responsive elements

Histidine decarboxylase (HDC) is the enzyme that catalyzes the conversion of histidine to histamine, a bioamine that plays an important role in allergic responses, inflammation, neurotransmission, and gastric acid secretion. Previously, we demonstrated that gastrin activates HDC promoter activity in a gastric cancer (AGS-E) cell line through three overlapping downstream promoter elements. In the current study, we used the yeast one-hybrid strategy to identify nuclear factors that bind to these three elements. Among eight positives from the one-hybrid screen, we identified Kruppel-like factor 4 (KLF4) (previously known as gut-enriched Kruppel-like factor (GKLF)) as one factor that binds to the gastrin responsive elements in the HDC promoter. Electrophoretic mobility shift assays confirmed that KLF4 is able to bind all three gastrin responsive elements. In addition, transient cotransfection experiments showed that overexpression of KLF4 dose dependently and specifically inhibited HDC promoter activity. Regulation of HDC transcription by KLF4 was confirmed by changes in the endogenous HDC messenger RNA by KLF4 small interfering RNA and KLF4 overexpression. We further showed that KLF4 inhibits HDC promoter activity by competing with Sp1 at the upstream GC box and also independently by binding the three downstream gastrin responsive elements. Taken together, these results indicate that KLF4 can act to repress HDC gene expression by Sp1-dependent and -independent mechanisms.

Helicobacter pylori stimulates host vascular endothelial growth factor-A (vegf-A) gene expression via MEK/ERK-dependent activation of Sp1 and Sp3

VEGF-A is a key regulator of inflammatory and tumor-associated angiogenesis. H. pylori plays a critical role in the pathogenesis of benign and malignant gastric diseases. It has been suggested that H. pylori infection is associated with activation of host angiogenesis, however, underlying mechanisms as well as angiogenic growth factors activated by the bacterium have not yet been identified. Therefore, we investigated the influence of the bacterium on VEGF-A as a candidate host target gene in vivo and in vitro. We show that H. pylori potently up-regulates production and release of VEGF-A protein as well as vegf-A mRNA levels, and we provide strong evidence that enhanced recruitment of Sp1 and Sp3 transcription factors to two proximal GC-rich vegf-A promoter elements mediates H. pylori-triggered vegf-A gene expression. In addition, H. pylori infection increased the transactivating capacity of both Sp1 and Sp3, which suggests additional mechanism(s) of vegf-A gene regulation by the bacterium. Signaling studies identified the MEK>ERK1/-2 kinase cascade as principal host signaling pathway mediating H. pylori-stimulated vegf-A transcription. By identifying H. pylori as potent activator of vegf-A gene expression and characterization of underlying molecular mechanisms, our results provide novel insights into pathways linking the bacterium to host angiogenesis and may help to develop strategies to influence vegf-A gene expression in the setting of H. pylori infection.

Physiology of gastric enterochromaffin-like cells

Enterochromaffin-like (ECL) cells are neuroendocrine cells in the gastric mucosa that control acid secretion by releasing histamine as a paracrine stimulant. The antral hormone gastrin and the neural messenger pituitary adenylyl cyclase-activating peptide (PACAP) potently stimulate histamine synthesis, storage, and secretion by ECL cells. Histamine is stored in secretory vesicles via V-type ATPases and vesicular monoamine transporters of subtype 2 (VMAT-2). Plasmalemmal calcium entry occurs via L-type calcium channels upon stimulation with secretagogues. K(+) and Cl(-) channels maintain the membrane potential. Calcium-triggered exocytosis of histamine is mediated by interacting SNARE proteins, especially by synaptobrevin and SNAP-25. Dynamins and amphiphysins appear to play a key role in endocytosis. ECL cells are under transcriptional control of various hormones. Gastrin stimulates transcriptional activity of the histidine decarboxylase (HDC), VMAT-2, and chromogranin A promoter by activation of Sp1 elements and CREB. During chronic Helicobacter pylori infection, pro-inflammatory cytokines are released that can also affect ECL cells, thus impairing their secretory function and viability, which can predispose to hypochlorhydria and gastric carcinogenesis.

Helicobacter pylori CagA protein targets the c-Met receptor and enhances the motogenic response

Infection with the human microbial pathogen Helicobacter pylori is assumed to lead to invasive gastric cancer. We find that H. pylori activates the hepatocyte growth factor/scatter factor receptor c-Met, which is involved in invasive growth of tumor cells. The H. pylori effector protein CagA intracellularly targets the c-Met receptor and promotes cellular processes leading to a forceful motogenic response. CagA could represent a bacterial adaptor protein that associates with phospholipase Cgamma but not Grb2-associated binder 1 or growth factor receptor-bound protein 2. The H. pylori-induced motogenic response is suppressed and blocked by the inhibition of PLCgamma and of MAPK, respectively. Thus, upon translocation, CagA modulates cellular functions by deregulating c-Met receptor signaling. The activation of the motogenic response in H. pylori-infected epithelial cells suggests that CagA could be involved in tumor progression.

Intracellular and interstitial expression of Helicobacter pylori virulence genes in gastric precancerous intestinal metaplasia and adenocarcinoma

Gastric intestinal metaplasia (IM) and gastric cancer are associated with Helicobacter pylori, but the bacterium often is undetectable in these lesions. To unravel this apparent paradox, IM, H. pylori presence, and the expression of H. pylori virulence genes were quantified concurrently using histologic testing, in situ hybridization, and immunohistochemistry. H. pylori was detected inside metaplastic, dysplastic, and neoplastic epithelial cells, and cagA and babA2 expression was colocalized. Importantly, expression of cagA was significantly higher in patients with IM and adenocarcinoma than in control subjects. The preneoplastic "acidic" MUC2 mucin was detected only in the presence of H. pylori, and MUC2 expression was higher in patients with IM, dysplasia, and cancer. These novel findings are compatible with the hypothesis that all stages of gastric carcinogenesis are fostered by persistent intracellular expression of H. pylori virulence genes, especially cagA inside MUC2-producing precancerous gastric cells and pleomorphic cancer cells.

Oxidative stress regulates vascular endothelial growth factor-A gene transcription through Sp1- and Sp3-dependent activation of two proximal GC-rich promoter elements

Enhanced VEGF-A (vascular endothelial growth factor A) gene expression is associated with increased tumor growth and metastatic spread of solid malignancies including gastric cancer. Oxidative stress has been linked to tumor-associated neoangiogenesis; underlying mechanisms, however, remained poorly understood. Therefore, we studied the effect of oxidative stress on VEGF-A gene expression in gastric cancer cells. Oxidative stress generated by H(2)O(2) application potently stimulated VEGF-A protein and mRNA levels as determined by enzyme-linked immunosorbent assay and real-time PCR techniques, respectively, and elevated the activity of a transfected (-2018) VEGF-A promoter reporter gene construct in a time- and dose-dependent manner (4-8-fold). These effects were abolished by the antioxidant N-acetylcysteine, demonstrating specificity of oxidative stress responses. Functional 5' deletion analysis mapped the oxidative stress response element of the human VEGF-A promoter to the sequence -88/-50, and a single copy of this element was sufficient to confer basal promoter activity as well as oxidative stress responsiveness to a heterologous promoter system. Combination of EMSA studies, Sp1/Sp3 overexpression experiments in Drosophila SL-2 cells, and systematic promoter mutagenesis identified enhanced Sp1 and Sp3 binding to two GC-boxes at -73/-66 and -58/-52 as the core mechanism of oxidative stress-triggered VEGF-A transactivation. Additionally, in Gal4-Sp1/-Sp3-Gal4-luciferase assays, oxidative stress increased Sp1 but not Sp3 transactivating capacity, indicating additional mechanism(s) of VEGF-A gene regulation. Signaling studies identified a cascade comprising Ras --> Raf --> MEK1 --> ERK1/2 as the main pathway mediating oxidative stress-stimulated VEGF-A transcription. This study for the first time delineates the mechanisms underlying regulation of VEGF-A gene transcription by oxidative stress and thereby further elucidates potential pathways underlying redox control of neoangiogenesis.

Effect of inhibition of extracellular signal-regulated kinase 1 and 2 pathway on apoptosis and bcl-2 expression in Helicobacter pylori-infected AGS cells

Helicobacter pylori induces activation of mitogen-activated protein kinases (MAPKs). However, its effect on H. pylori-induced apoptosis has not been evaluated. Thus, we examined whether H. pylori-induced extracellular signal-regulated kinase 1 and 2 (ERK1/2) and p38 MAPK activation affects gastric epithelial cell apoptosis and bcl-2 family gene expression, especially in relation to the cagA status of an H. pylori strain. In flow cytometric and oligonucleosome-bound DNA enzyme-linked immunosorbent assay analyses, infection with cagA(+) H. pylori strains induced gastric cancer cell apoptosis in AGS cells more prominently than infection with cagA mutants. Activation of ERK1/2 and p38 MAPKs was also more prominent in cagA(+) strains. Pretreatment with a MEK inhibitor (PD98059) inhibited ERK1/2 activation and increased H. pylori-induced apoptosis significantly. This increased apoptosis was accompanied by decreased antiapoptotic bcl-2 mRNA expression among bcl-2-related genes (bcl-2, bax, bak, mcl-1, and bcl-X(L/S)), and the effect was also more prominent in the cagA(+) strains. However, the alteration of bcl-2 gene expression was not accompanied by protein level changes. Inhibition of p38 using specific inhibitor SB203580 decreased H. pylori-induced apoptosis but resulted in little alteration of bcl-2-related gene expression. In conclusion, H. pylori-induced ERK1/2 activation, especially by the cagA(+) H. pylori strain, may play a protective role against gastric epithelial cell apoptosis partially through maintenance of bcl-2 gene expression.

Interaction of early growth response protein 1 (Egr-1), specificity protein 1 (Sp1), and cyclic adenosine 3'5'-monophosphate response element binding protein (CREB) at a proximal response element is critical for gastrin-dependent activation of the chromogranin A promoter

Recently, binding of specific protein 1 (Sp1) and cAMP response element binding protein (CREB) to a GC-rich element at -92/-62 has been identified as a critical step in gastrin-dependent regulation of the chromogranin A (CgA) gene in gastric epithelial cells. Here we demonstrate that binding of early growth response protein 1 (Egr-1) to the distal part of the -92/-62 site is also required for gastrin-dependent CgA transactivation. Gastrin elevated cellular and nuclear Egr-1 levels in a time-dependent manner and also increased Egr-1 binding to the CgA -92/-73 region. Disruption of this site reduced gastrin responsiveness without influencing basal promoter activity, while loss of Sp1 and/or CREB binding sites diminished basal and gastrin-stimulated CgA promoter activity. Ectopic Egr-1 overexpression potently stimulated the CgA promoter, whereas coexpression of Egr-1 with Sp1 and/or CREB resulted in additive effects. Functional analysis of Sp1-, Egr-1-, or CREB-specific promoter mutations in transfection studies confirmed the tripartite organization of the CgA -92/-62 element. Signaling studies revealed that MAPK kinase 1 (MEK1)/ERK1/2 cascades are critical for gastrin-dependent Egr-1 protein accumulation as well as Egr-1 binding to the CgA promoter. Our studies for the first time identify Egr-1 as a nuclear target of gastrin and show that functional interplay of Egr-1, Sp1, and CREB is indispensable for gastrin-dependent CgA transactivation in gastric epithelial cells.

Grb2 is a key mediator of helicobacter pylori CagA protein activities

CagA delivered from Helicobacter pylori into gastric epithelial cells undergoes tyrosine phosphorylation and induces host cell morphological changes. Here we show that CagA can interact with Grb2 both in vitro and in vivo, which results in the activation of the Ras/MEK/ERK pathway and leads to cell scattering as well as proliferation. Importantly, this ability of CagA is independent from the tyrosine phosphorylation, which occurs within the five repeated EPIYA sequences (PY region) of CagA. However, the PY region appears to be indispensable for the Grb2 binding and induction of the cellular responses. Thus, intracellular CagA via its binding to Grb2 may act as a transducer for stimulating growth factor-like downstream signals which lead to cell morphological changes and proliferation, the causes of H. pylori-induced gastric hyperplasia.

Role of the alpAB proteins and lipopolysaccharide in adhesion of Helicobacter pylori to human gastric tissue

The attachment of the bacterial pathogen Helicobacter pylori (H. pylori) to gastric epithelial cells is commonly believed to be required for an efficient and persistent colonization of the human stomach as well as for host cell trans-membrane signaling. In the past, several putative adhesins were postulated, including the outer membrane proteins AlpAB and the bacterial lipopolysaccharide (LPS) presenting oligomeric Lewis x (Le(x)) sugar components. We investigated the AlpAB-mediated and the Le(x)-dependent binding by knockout mutagenesis in one distinct strain, H. pylori P1. We show here that the mutagenesis of either alpA and/or alpB dramatically reduced the adherence of H. pylori P1 to a given gastric biopsy section. None of these mutations influenced the surface exposure of the Le(x) antigen, suggesting that the assembly and/or presentation of LPS is independent of the AlpAB outer membrane proteins. However, a truncation of the LPS O-side chain by a galE mutation abolished the presentation of the Le(x) epitope. This Le(x)-negative strain did not show any significant reduction in its binding capacity to the gastric tissue, when compared with the corresponding wild-type strain. From these data we conclude that the AlpAB-specific adherence is independent of the composition of the LPS and that the oligomeric Le(x) structure does not confer binding to the gastric biopsy material used in this study. As the adhesion properties of our H. pylori strain P1 vary in dependence on the respective biopsy donor it is assumed that the surface-exposed Le(x) epitope recognizes a different host cell receptor than AlpAB, which was probably not present in the tissue sections used in this study.

CagA tyrosine phosphorylation and interleukin-8 induction by Helicobacter pylori are independent from alpAB, HopZ and bab group outer membrane proteins

In several studies Helicobacter pylori type I strains (cag-positive strains) have been described to translocate their CagA protein into epithelial cells, where it is tyrosine-phosphorylated. The intimate contact allows a Cag-dependent bacteria-to-cell signaling inducing the secretion of the chemokine interleukin-8. Although a contact between the bacterial and the eukaryotic cell is known to be necessary for these signal transduction events the bacterial adhesin and the cellular receptor are unknown, so far. In this study, we investigated the influence of several outer membrane proteins associated with adherence on CagA translocation and IL-8 induction. The quantitative assessment of a cag deletion mutant strain binding to epithelial cells revealed that the Cag secretion apparatus is not primarily necessary for attachment. In contrast, the knockout mutation of the adherence-associated alpAB locus significantly reduced the binding capacity in two independent strains. Despite this partial adherence defect, the alpAB mutation did not affect CagA translocation and IL-8 induction. The mutagenesis of the bab group genes hp317, hp896 and hp1243 in H. pylori 26695 did not influence the Cag-dependent signaling either. No causative linkage could be found between the production of the outer membrane proteins HopZ, OipA or seven additional outer membrane proteins and CagA translocation or IL-8 induction.

B-Raf/Rap1 signaling, but not c-Raf-1/Ras, induces the histidine decarboxylase promoter in Helicobacter pylori infection

Histidine decarboxylase (HDC) is the key enzyme for gastric histamine synthesis, and enhanced HDC expression is critically involved in the pathogenesis of gastric disorders, including gastroduodenal ulcer disease. We characterized the pathogenicity mechanism underlying activation of the HDC promoter in H. pylori-infected gastric epithelial cells and performed a detailed analysis of the participating signaling elements. We found that H. pylori infection of gastric epithelial cells activated the MEK1-2/ERK1-2 cascade through cAMP-dependent stimulation of Rap1 and B-Raf, but not Ras/c-Raf-1, leading to potent transactivation of the human HDC promoter. H. pylori-triggered elevation of adenylate cyclase activity was directed by GalphaS-subunits of heterotrimeric G proteins. Stimulation of this signaling cascade was triggered independent of bacterial-cell contact by a small molecular- weight component(s) (approximately 1 kDa) released by H. pylori and did not require a functional type IV secretion system. Thus, our studies demonstrate for the first time to our knowledge that the GalphaS-->cAMP-->Rap1--->B-Raf-->MEK1/2-->ERK1/2 pathway is critical for H. pylori-dependent epithelial gene regulation, which can be induced via a bioactive component(s) apart from the site of bacterial colonization. These results further elucidate the molecular mechanisms underlying interaction of H. pylori with gastric epithelial cells and help to define potential molecular targets for therapeutic interventions in the context of H. pylori-related gastric diseases.

cag+ Helicobacter pylori induce transactivation of the epidermal growth factor receptor in AGS gastric epithelial cells

The gastric pathogen Helicobacter pylori is known to activate epithelial cell signaling pathways that regulate numerous inflammatory response genes. The aim of this study was to elucidate the pathway leading to extracellular signal-regulated kinase (ERK) 1/2 phosphorylation in H. pylori-infected AGS gastric epithelial cells. We find that H. pylori, via activation of the epidermal growth factor (EGF) receptor activates the small GTP-binding protein Ras, which in turn, mediates ERK1/2 phosphorylation. cag+ strains of H. pylori are able to induce greater EGF receptor activation than cag- strains, and studies with isogenic mutants indicate that an intact type IV bacterial secretion system is required for this effect. Blockade of EGF receptor activation using tyrphostin AG1478 prevents H. pylori-mediated Ras activation, inhibits ERK1/2 phosphorylation, and substantially decreases interleukin-8 gene expression and protein production. Investigations into the mechanism of EGF receptor activation, using heparin, a metalloproteinase inhibitor and neutralizing antibodies reveal that H. pylori transactivates the EGF receptor via activation of the endogenous ligand heparin-binding EGF-like growth factor. Transactivation of gastric epithelial cell EGF receptors may be instrumental in regulating both proliferative and inflammatory responses induced by cag+ H. pylori infection.

Phosphorylation of tyrosine 972 of the Helicobacter pylori CagA protein is essential for induction of a scattering phenotype in gastric epithelial cells

Helicobacter pylori colonizes the human stomach and is the causative agent of a variety of gastric diseases. After bacterial attachment, the H. pylori CagA protein is translocated into gastric epithelial cells and tyrosine phosphorylated. This process is associated with characteristic cytoskeletal rearrangements, resulting in a scatter factor-like ('hummingbird') phenotype. In this study, using a cagA mutant complemented with wild-type cagA and transiently expressing CagA in AGS cells, we have demonstrated that translocated CagA is necessary for rearrangements of the actin cytoskeleton to occur. Anti-phosphotyrosine immunoblotting studies and treatment of infected cells with phosphotyrosine kinase inhibitors suggested that not only translocation but also phosphorylation of CagA is important in this process. Transient expression of CagA-green fluorescent protein (GFP) fusion proteins and two-dimensional gel electrophoresis of CagA protein species demonstrated tyrosine phosphorylation in the C-terminus. Site-directed mutagenesis of CagA revealed that tyrosine residue 972 is essential for induction of the cellular phenotype. We have also demonstrated that translocation and phosphorylation of CagA is necessary but not sufficient for induction of the hummingbird phenotype in AGS cells, indicating the involvement of as yet unidentified bacterial factor(s).

Enteropathogenic Escherichia coli infection induces expression of the early growth response factor by activating mitogen-activated protein kinase cascades in epithelial cells

Enteropathogenic Escherichia coli (EPEC) is an extracellular bacterial pathogen that infects the human intestinal epithelium and is a major cause of infantile diarrhea in developing countries. EPEC belongs to the group of attaching and effacing (A/E) pathogens. It uses a type III secretion system to deliver proteins into the host cell that mediate signal transduction events in host cells. We used gene array technology to study epithelial cell responses to EPEC infection at the level of gene expression. We found that EPEC induces the expression of several genes in infected HeLa cells by a lipopolysaccharide (LPS)-independent mechanism, including cytokines and early growth response factor 1 (Egr-1). The transcription factor Egr-1 is an immediate-early-induced gene that is activated in most cell types in response to stress. EPEC-induced upregulation of egr-1 is mediated by the activation of the MEK/extracellular signal-regulated kinase signal transduction pathway and is dependent on the type III secretion system. egr-1 is also induced during infection of mice by the A/E pathogen Citrobacter rodentium, suggesting that both Egr-1 and the activation of this mitogen-activated protein kinase signal transduction pathway may play a role in disease.

Host cell signaling in Helicobacter pylori infection

Helicobacter pylori represents a highly successful human microbial pathogen that has infected approximately half of the world's population. This gram-negative microorganism colonizes the human epithelial layer in the stomach and induces a state of chronic inflammation that does not resolve the underlying infection and often leads to gastric or duodenal ulcers, or more rarely to gastric cancer. Among the reactions in H. pylori-infected epithelial cells the induction of proinflammatory cytokines, cell spreading and movement, as well as a scattered phenotype appear strictly dependent on the expression of pathogenicity island-encoded proteins in H. pylori. This review will discuss the features of the H. pylori-induced signal transduction leading to changes in host cellular function. Topics discussed comprise the signaling and the phenotypes associated with the type IV secretion system, the activation of target genes involved in gastric physiology, and putative mechanisms leading to the development of gastric cancer.

Multiple sites of L-histidine decarboxylase expression in mouse suggest novel developmental functions for histamine

Histamine mediates many types of physiologic signals in multicellular organisms. To clarify the developmental role of histamine, we have examined the developmental expression of L-histidine decarboxylase (HDC) mRNA and the production of histamine during mouse development. The predominant expression of HDC in mouse development was seen in mast cells. The HDC expression was evident from embryonal day 13 (Ed13) until birth, and the mast cells were seen in most peripheral tissues. Several novel sites with a prominent HDC mRNA expression were revealed. In the brain, the choroid plexus showed HDC expression at Ed14 and the raphe neurons at Ed15. Close to the parturition, at Ed19, the neurons in the tuberomammillary (TM) area and the ventricular neuroepithelia also displayed a clear HDC mRNA expression and histamine immunoreactivity (HA-ir). From Ed14 until birth, the olfactory and nasopharyngeal epithelia showed an intense HDC mRNA expression and HA-ir. In the olfactory epithelia, the olfactory receptor neurons (ORN) were shown to have very prominent histamine immunoreactivity. The bipolar nerve cells in the epithelium extended both to the epithelial surface and into the subepithelial layers to be collected into thick nerve bundles extending caudally toward the olfactory bulbs. Also, in the nasopharynx, an extensive subepithelial network of histamine-immunoreactive nerve fibers were seen. Furthermore, in the peripheral tissues, the degenerating mesonephros (Ed14) and the convoluted tubules in the developing kidneys (Ed15) showed HDC expression, as did the prostate gland (Ed15). In adult mouse brain, the HDC expression resembled the neuronal pattern observed in rat brain. The expression was restricted to the TM area in the ventral hypothalamus, with the main expression in the five TM subgroups called E1-E5. A distinct mouse HDC mRNA expression was also seen in the ependymal wall of the third ventricle, which has not been reported in the rat. The tissue- and cell-specific expression patterns of HDC and histamine presented in this work indicate that histamine could have cell guidance or regulatory roles in development.

Pathogenicity island-dependent activation of Rho GTPases Rac1 and Cdc42 in Helicobacter pylori infection

Helicobacter pylori has been identified as the major aetiological agent in the development of chronic gastritis and duodenal ulcer, and it plays a role in the development of gastric carcinoma. Attachment of H. pylori to gastric epithelial cells leads to nuclear and cytoskeletal responses in host cells. Here, we show that Rho GTPases Rac1 and Cdc42 were activated during infection of gastric epithelial cells with either the wild-type H. pylori or the mutant strain cagA. In contrast, no activation of Rho GTPases was observed when H. pylori mutant strains (virB7 and PAI) were used that lack functional type IV secretion apparatus. We demonstrated that H. pylori-induced activation of Rac1 and Cdc42 led to the activation of p21-activated kinase 1 (PAK1) mediating nuclear responses, whereas the mutant strain PAI had no effect on PAK1 activity. Activation of Rac1, Cdc42 and PAK1 represented a very early event in colonization of gastric epithelial cells by H. pylori. Rac1 and Cdc42 were recruited to the sites of bacterial attachment and are therefore probably involved in the regulation of local and overall cytoskeleton rearrangement in host cells. Finally, actin rearrangement and epithelial cell motility in H. pylori infection depended on the presence of a functional type IV secretion system encoded by the cag pathogenicity island (PAI).

Helicobacter pylori resists phagocytosis by macrophages: quantitative assessment by confocal microscopy and fluorescence-activated cell sorting

Helicobacter pylori infection of the stomach epithelium is characterized by an infiltration of polymorphonuclear and mononuclear cells. These immune cells contribute to mucosal damage which may eventually lead to gastritis, peptic ulcer, gastric cancer, and/or MALT-associated gastric lymphoma. Here we show that H. pylori inhibits its own uptake, as well as in trans the phagocytosis of Neisseria gonorrhoeae, by human and murine macrophages. This antiphagocytic activity is dependent on the presence of the cag pathogenicity island in the H. pylori genome. We demonstrate that H. pylori also expresses its antiphagocytic activity towards the myelomonocytic cell line JOSKM, thus providing a potent model for the study of the interaction between H. pylori and phagocytes. Our data were obtained using laser confocal microscopy and flow cytometry after quenching the fluorescence of labeled extracellular bacteria. The antiphagocytic activity of H. pylori may explain the persistence of H. pylori and its pathological consequences. The use of cell lines and flow cytometry will hopefully facilitate progress in our understanding of the immune escape of these persistent bacteria.

Role of virulence factors, cell components and adhesion in Helicobacter pylori-mediated iNOS induction in murine macrophages

To investigate the mechanisms involved in Helicobacter pylori-mediated inducible nitric oxide synthase (iNOS) upregulation in mononuclear cells we cocultivated human THP-1 acute monocytic leukemia cells and murine J774A.1 professional macrophages with different H. pylori wild-type strains and mutants. We have shown that H. pylori-mediated iNOS induction in J774A.1 is independent of established virulence factors but dependent on direct interaction between bacteria and cells. In J774A.1, iNOS was equally upregulated by the wild-type strains J99, 26695, P12, and P1 as well as by mutants lacking the cag pathogenicity island, vacA, katA, alpAB genes and the hp0043 gene taking part in lipopolysaccharide biosynthesis when direct cell contact was allowed but not when bacteria and cells were separated by protein-permeable filter membranes. In contrast, iNOS was not induced in THP-1. This indicates that H. pylori-mediated iNOS induction in J774A.1 is independent of important virulence factors whereas cell contact is crucial which suggests a role of adhesion or phagocytosis.

Helicobacter pylori-induced prostaglandin E(2) synthesis involves activation of cytosolic phospholipase A(2) in epithelial cells

Helicobacter pylori initiates an inflammatory response and gastric diseases, which are more common in patients infected with H. pylori strains carrying the pathogenicity island, by colonizing the gastric epithelium. In the present study we investigated the mechanism of prostaglandin E(2) (PGE(2)) synthesis in response to H. pylori infection. We demonstrate that H. pylori induces the synthesis of PGE(2) via release of arachidonic acid predominately from phosphatidylinositol. In contrast to H. pylori wild type, an isogenic H. pylori strain with a mutation in the pathogenicity island exerts only weak arachidonic acid and PGE(2) synthesis. The H. pylori-induced arachidonic acid release was abolished by phospholipase A(2) (PLA(2)) inhibitors and by pertussis toxin (affects the activity of G alpha(i)/G alpha(o)). The role of phospholipase C, diacylglycerol lipase, or phospholipase D was excluded by using specific inhibitors. An inhibitor of the stress-activated p38 kinase (SB202190), but neither inhibitors of protein kinase C nor an inhibitor of the extracellular-regulated kinase pathway (PD98059), decreased the H. pylori-induced arachidonic acid release. H. pylori-induced phosphorylation of p38 kinase and cytosolic PLA(2) was blocked by SB202190. These results indicate that H. pylori induces the release of PGE(2) from epithelial cells by cytosolic PLA(2) activation via G alpha(i)/G alpha(o) proteins and the p38 kinase pathway.

p21-activated kinase 1 activates the nuclear factor kappa B (NF-kappa B)-inducing kinase-Ikappa B kinases NF-kappa B pathway and proinflammatory cytokines in Helicobacter pylori infection

Helicobacter pylori, the causative agent of several human gastric diseases, induces activation of the immediate early response transcription factor nuclear factor kappaB (NF-kappaB), which subsequently triggers release of proinflammatory cytokines in colonized epithelial cells. Here we report that in H. pylori infection p21-activated kinase 1 (PAK1) activates NF-kappaB. Activated PAK1 associates with NF-kappaB-inducing kinase, which upon activation directs the activity of IkappaB kinases to IkappaBalpha. Our results indicate that in epithelial cells PAK1 participates in a unique pathway that links H. pylori-dependent effector molecules to the activation of NF-kappaB and the induction of the innate immune response.

Helicobacter pylori inhibits phagocytosis by professional phagocytes involving type IV secretion components

Gastric infections by Helicobacter pylori are characteristically associated with an intense inflammation and infiltration of mainly polymorphonuclear lymphocytes (PMNs) and monocytes. The inflammatory response by infiltrated immune cells appears to be a primary cause of the damage to surface epithelial layers and may eventually result in gastritis, peptic ulcer, gastric cancer and/or MALT-associated gastric lymphoma. Our analysis of the interaction between H. pylori and PMNs and monocytes revealed that H. pylori inhibits its own uptake by these professional phagocytes. To some degree, this effect resembles antiphagocytosis by Yersinia enterocolitica. Increasing numbers of bacteria associated per cell are more efficient at blocking their own engulfment. In H. pylori, bacterial protein synthesis is necessary to block phagocytic uptake, as shown by the time and concentration dependence of the bacteriostatic protein synthesis inhibitor chloramphenicol. Furthermore, H. pylori appears broadly to inhibit the phagocytic function of monocytes and PMNs, as infection with H. pylori abrogates the phagocytes' ability to engulf latex beads or adherent Neisseria gonorrhoeae cells. This antiphagocytic phenotype depends on distinct virulence (vir) genes, such as virB7 and virB11, encoding core components of a putative type IV secretion apparatus. Our data indicate that H. pylori exhibits an antiphagocytic activity that may play an essential role in the immune escape of this persistent pathogen.

The immune response against Helicobacter pylori--a direct linkage to the development of gastroduodenal disease

Helicobacter pylori infects about half of the world's population. H. pylori elicits marked immune responses, but the infection is commonly life-long. Some infected individuals remain asymptomatic, while others develop significant gastroduodenal disease. We review the underlying host immune response to H. pylori which programs for persistence and evolution of gastroduodenal disease.