cDNA array analysis of cag pathogenicity island-associated Helicobacter pylori epithelial cell response genes

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.

Epithelial cell responses induced upon adherence of pathogenic Neisseria

Neisseria meningitidis and Neisseria gonorrhoeae colonize human mucosal surfaces and cause sepsis/meningitis and gonorrhoea respectively. The first step in the infection process is pilus-mediated adhesion of the bacteria to epithelial cells, followed by host cell invasion. Adhesion of pathogenic Neisseria elicits multiple responses in host cells, including cellular signalling events, cytokine production and modulation of the eukaryotic cell surface. We used microarrays to assess the respective involvement of 375 human cytokine and adhesion related genes during adhesion of piliated and non-piliated N. gonorrhoeae, and piliated encapsulated N. meningitidis to the epithelial cell line ME-180. We identified 29 differentially regulated genes not previously reported to respond to neisserial infections, many of which encode membrane proteins. Selected genes were further analysed by semiquantitative RT-PCR, and protein expression was examined by flow cytometry. We found that N. gonorrhoeae elicited a different inflammatory response than N. meningitidis and we also demonstrated that early adhesion events are responsible for the induction of specific genes. Our data create a new platform for elucidating the interaction between pathogenic Neisseria and target cells.

Helicobacter pyloriInduces Plasminogen Activator Inhibitor 2 in Gastric Epithelial Cells through Nuclear Factor-κB and RhoA

The gastric pathogen Helicobacter pylori is associated with a progression to gastric cancer. The specific targets of H. pylori that might influence this progression are still unclear. Previous studies indicated that the gastric hormone gastrin, which may be increased in H. pylori infection, stimulates gastric expression of plasminogen activator inhibitor (PAI)-2, which is an inhibitor of the urokinase plasminogen activator and has previously been shown to be increased in gastric adenocarcinoma. Here, we report that H. pylori also increases PAI-2 expression. In gastric biopsies of H. pylori-positive subjects there was increased PAI-2, including subjects with plasma gastrin concentrations in the normal range. PAI-2 was expressed mainly in chief and mucous cells. In a gastric cancer cell line (AGS), H. pylori increased PAI-2 expression, which was associated with inhibition of H. pylori-stimulated cell invasion and apoptosis. The induction of PAI-2 by H. pylori was mediated by release of interleukin-8 and activation of cyclooxygenase-2, and interestingly, gastrin stimulated PAI-2 expression by similar paracrine pathways. The activation of NFkappaB was required for interleukin-8 and cyclooxygenase-2 activation but did not occur in cells responding to these paracrine mediators. The data suggest that induction of PAI-2 is a specific target in H. pylori infection, mediated at least partly by paracrine factors; induction of PAI-2 inhibits cell invasion and apoptosis and is a candidate for influencing the progression to gastric cancer.

A genomics-based approach to biodefence preparedness

Since October 2001, the United States has greatly expanded its commitment to biodefence-related research, with $1.75 billion earmarked for this activity in fiscal year 2003.

The goals of this accelerated research and development effort are to understand better the biology of potential bioterror agents and to use this information in the development of new diagnostics, antibiotics and vaccines to protect the world's population against bioterrorism.

Genomics, proteomics and bioinformatics approaches are considered to be key enabling technologies in the development of these new products.

Genome sequence data for all of the principal human pathogens, including most of the potential bioterror agents on the Center for Disease Control and Prevention (CDC) category A–C lists, are available in public databases and provide a new foundation for follow-up studies.

Comparative genomics approaches, together with large-scale methods for studying gene function, such as DNA microarrays, are providing insights into the molecular basis and evolution of pathogenicity, diversity within closely related isolates of the same pathogen and the molecular determinants of host–pathogen interactions.

Genomics-based approaches have already proven to be of great use in the identification of new targets for antimicrobial compounds and in the identification of new vaccine candidates.

Comparative genomics is also providing important information on the natural variability between closely related isolates that is aiding in the development of the new field of microbial forensics.

The anthrax letter attacks in October 2001, followed by the SARS outbreak in early 2003, dramatically illustrated our vulnerability to both deliberate and natural outbreaks of infectious disease. The availability of pathogen genome sequences and high-throughput methods for studying the biology of both pathogens and their hosts have provided new insights into the mechanisms of pathogenesis and host defence. As infectious disease research expands to include major bioterror agents, genomics-based approaches will provide one of the cornerstones of efforts to develop more accurate diagnostics, new therapeutics and vaccines, and further capabilities for microbial forensics.

Prevention of gastric cancer by Helicobacter pylori eradication

The evidence supporting the important role of Helicobacter pylori causing gastric cancer is getting stronger. The mechanisms by which H. pylori can influence the progression to severe changes in the gastric mucosa are under investigation. An increased gastric epithelial cell proliferation has been observed in individuals infected with H. pylori. This lifelong increased cell turnover is deemed to be a major risk factor for increased mutational changes and may lead to the development of gastric cancer. Successful eradication of H. pylori infection induces the healing of the gastritis and a significant decrease in gastric epithelial cell proliferation. Nevertheless, it is right now unknown at which time the point of no return, meaning at which time an eradication therapy leads to a benefit for the individual to prevent gastric cancer, has been reached. Therefore the major question that arises is to whom an eradication therapy should be offered to prevent gastric cancer. A general elimination of the infection might be worthwhile, but seems to be unrealistic now because of the high prevalence of the infection and the missing of a vaccine. This review reflects possible mechanisms of gastric cancer development induced by chronic H. pylori infection and recent investigational trials for prevention of gastric cancer by H. pylori eradication therapy will be discussed.

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.

Deletion of Helicobacter pylori vacuolating cytotoxin gene by introduction of directed mutagenesis

AIM: To construct a vacA-knockout Helicobacter pylori mutant strain, whose only difference from the wild strain is its disrupted vacA gene.

METHODS AND RESULTS: A clone containing kanamycin resistance gene used for homologous recombination was constructed in a directional cloning procedure into pBluescript II SK, and then transformed into vacA⁺H pylori by electroporation. Colonies growing on the selective media containing kanamycin were harvested for chromosomal DNA extraction, and the allelic exchange was determined by polymerase chain reactions and sequencing. Loss of vacuolating activity of the vacA-knockout strain was confirmed by examining the gastric cells co-cultured with cell-free supernatants from H pylori wild strain or the mutant.

CONCLUSION: We constructed a vacA-knockout strain of H pylori through direct mutagenesis, which creates an important precondition for the future research on virulence comparison with gene expression analysis.

Helicobacter pylori strain-selective induction of matrix metalloproteinase-7 in vitro and within gastric mucosa

BACKGROUND AND AIMS

Helicobacter pylori strains that possess the cag pathogenicity island (cag(+)) augment the risk for distal gastric cancer. Matrix metalloproteinase (MMP)-7, an epithelial cell-derived MMP that is induced by bacterial contact, is overexpressed within human gastric adenocarcinoma specimens and enhances tumor formation in rodents. We determined whether H. pylori alters MMP-7 expression and investigated the molecular pathways required for these events.

METHODS

MMP-7 was detected in human gastric mucosa by immunohistochemistry and in H. pylori/AGS gastric epithelial cell coculture supernatants by Western analysis. AGS cells were cocultured with wild-type H. pylori, or isogenic cagA(-), cagE(-), or vacA(-) mutants, in the absence or presence of inhibitors of nuclear factor kappaB activation, p38, or extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase.

RESULTS

H. pylori cag(+) strains increased MMP-7 expression in AGS cells 5-7-fold, whereas cag(-) isolates had no effect. Inactivation of cagE, but not cagA or vacA, completely attenuated induction of MMP-7, and inhibition of ERK 1/2 decreased MMP-7 production. In vivo, MMP-7 was expressed in gastric epithelial cells in specimens from 80% of cag(+)-colonized persons but in none of the cag(-) or uninfected subjects.

CONCLUSIONS

H. pylori cag(+) strains enhance levels of MMP-7 within inflamed mucosa. In vitro, cag(+) isolates selectively induce MMP-7, and this is dependent on activation of ERK 1/2 by specific components within the cag island. Differential induction of MMP-7 by H. pylori cag(+) isolates may explain in part the augmentation in gastric cancer risk associated with these strains.

Cell adhesion-related gene expression by Helicobacter pylori in gastric epithelial AGS cells

Helicobacter pylori (H. pylori) infection leads to gastroduodenal inflammation, peptic ulceration and gastric carcinoma. H. pylori may induce disease-specific gene expression in gastric epithelial cells. cDNA microarray for 352 cancer-related genes was used to identify the genes altered by H. pylori (cagA positive) in gastric epithelial AGS cells. Expressions of the genes identified on the microarray and other genes closely associated with these genes were determined by reverse transcriptase-polymerase chain reaction (RT-PCR). Western blot analysis and cell adhesion assay were performed to confirm the protein levels of the genes and the role of the genes on cell adhesion in H. pylori-infected AGS cells. As a result, the expression of four genes (galectin 1, aldolase A, integrin alpha5, LIM domain only 7 (LMO7)) were up-regulated by H. pylori in AGS cells, determined by cDNA microarray. RT-PCR analysis showed that the genes up-regulated by H. pylori were the genes regulating cell-cell adhesion and cell-extracellular matrix interaction, such as galectin-1 and galectin-3, integrin alpha5, and LIM domain only 7 (LMO7), and cancer-related glycolytic enzyme aldolase A and C. Cell adhesion to extracellular matrix proteins such as poly-L-lysine and fibronectin was mediated by H. pylori-induced expression of integrin alpha5. RT-PCR and Western blot analysis showed that E-cadherin, regulating cell adhesion and contact cell inhibition, was decreased by H. pylori in AGS cells. In conclusion, the increased expression of cell adhesion molecules and decrease in E-cadherin expression by H. pylori might contribute to cell adhesion, invasion and possibly cell proliferation in gastric epithelial cells.

The effect of rebamipide on Helicobacter pylori extract-mediated changes of gene expression in gastric epithelial cells

BACKGROUND

Recent studies have shown that Helicobacter pylori affects intracellular signal transduction in host cells, leading to the activation of transcriptional factors and the induction of pro-inflammatory cytokines. On the other hand, rebamipide, an anti-gastritis and anti-ulcer agent, could scavenge reactive oxygen species and reduce interleukin-8 (IL-8) expression in gastric epithelial cells induced by H. pylori-stimulation through the attenuated activation of nuclear factor-kappaB (NF-kappaB).

AIMS

In this study, we investigated the effects of rebamipide on gene expression in H. pylori-stimulated epithelial cells using DNA chip.

METHODS

H. pylori water extract (HPE) was prepared from NCTC11637, the type strain of H. pylori. Total RNA was extracted from MKN45 cells, a human gastric cancer cell line, following HPE-stimulation with and without rebamipide for 3 h, and differences in gene expression profiles were observed using GeneChip and Human 6800 probe array.

RESULTS

The GeneChip analysis demonstrated that 132 up-regulated genes and 873 down-regulated genes, such as growth factors, chemokines and transcription factors, were detected in MKN45 cells 3 h after stimulation of H. pylori. Among them, several genes, including bFGF, RANTES and MIP-2beta, were previously unknown to be expressed in H. pylori-stimulated human gastric cells. Rebamipide reduced expression of 119 genes encoding cytokines, growth factors and their receptors and transcription factors.

CONCLUSIONS

These findings suggest that rebamipide could inhibit inflammatory reactions and tumour progression by modifying H. pylori infection-induced gene expression in gastric epithelial cells.

Increased zinc finger protein zFOC1 transcripts in gastric cancer compared with normal gastric tissue

BACKGROUND

Screening of cDNA arrays of the IMAGE library identified human zFOC1 as a differentially expressed cDNA that was upregulated in KATO III gastric cancer cells following stimulation with the gastric pathogen Helicobacter pylori.

AIMS

To determine the expression of zFOC1 in gastric mucosa with and without H pylori infection and in patients with gastric cancer.

RESULTS

zFOC1 is localised on chromosome 12q24.3 and encodes a zinc finger protein. Expression studies in human H pylori infected and uninfected gastric biopsies, gastric tumours, and gastric cancer cell lines revealed that zFOCI gene transcripts are significantly higher in gastric cancer than in non-cancerous gastric tissues.

CONCLUSIONS

The zFOC1 gene appears to be a tumour marker associated with gastric cancer.

Genomics of Helicobacter pylori

During this review period, we have definitely entered into the genomic era. The Helicobacter pylori studies reported here illustrate the use of most of the technologies currently available to globally interrogate the genome of a pathogen. Global analysis of the gene content of H. pylori strains gives insight into the extent of its genetic diversity and its in vivo evolution. Our understanding of the particularities of H. pylori as a gastric pathogen colonizing a unique niche has been improved by studies aimed at: (i) the identification of H. pylori-specific genes; (ii) the establishment of correlations between the presence of one or a group of genes (or proteins) with clinical outcome; and (iii) the analysis of global regulatory circuits or responses to the extracellular signals. The response of host cells to H. pylori infection will be developed in the chapter 'H. pylori and gastric malignancies' by Sepulveda and Coehlo. Despite our knowledge of the H. pylori genome, the function of about one third of its total proteins is still unknown. Functional genomics are straightforward approaches for the identification of new gene functions or metabolic pathways as well as for the understanding of cellular processes and the detection of new virulence factors. In silico studies combined with experimental work will undoubtedly continue to develop. To date, the expansion of proteomics with refinements in mass spectrometry technology has illustrated that through immunoproteomics and comparative studies, relevant novel antigens can be identified. Genomics not only provides invaluable information on H. pylori but also opens new perspectives for diagnostic or therapeutic applications.

Pathogenesis of Helicobacter pylori infection

Five years after publication of the complete genome sequence of Helicobacter pylori, research interest is shifting from the descriptive association of virulence factors with clinical outcome in infected patients to the molecular mechanisms of virulence factor action. This is particularly noticeable for VacA and CagA, for both of which detailed understanding of the interaction with host signalling pathways has accumulated over the last year. The role of H. pylori Lewis antigens for clinical outcome was further substantiated. Various strategies of H. pylori to fool or evade the human immune system are described, which all lead to the dysfunction of specific compartments of the host cellular immune system. Finally, a number of animal models indicate that inflammation is a key factor for gastric carcinogenesis, which is finally supported by a large prospective study identifying corpus atrophy and intestinal metaplasia as precancerous conditions.

Helicobacter pylori and gastric malignancies

The epidemiological link of Helicobacter pylori and gastric carcinoma was confirmed and the reported rate of gastric carcinoma development in the Japanese population with H. pylori gastritis was 2.9% during a 7.8-year period. Studies showed that gastric atrophy and intestinal metaplasia may partially regress after H. pylori eradication, but whether this will result in a decrease in the development of malignant lesions remains to be confirmed in large studies. Little progress was made towards the identification of criteria applicable to individualized populations that would benefit from H. pylori screening and surveillance of gastric malignancy. Studies of low-grade MALT lymphoma reported clinical and molecular features that may be useful to identify cases that may be responsive to H. pylori eradication therapy, namely evaluation of lymphoma stage by EUS and t(11;18). The role of H. pylori eradication therapy in high-grade MALT lymphoma needs to be evaluated in larger prospective studies. The application of methods of global analysis of gene expression (microarray studies) resulted in the explosion of information on the molecular pathways activated by H. pylori in gastric epithelial cells. New pathways that may play an important role in H. pylori carcinogenesis have been discovered in several studies.

Cag pathogenicity island-specific responses of gastric epithelial cells to Helicobacter pylori infection

Helicobacter pylori infects over half the world's population and causes a wide range of diseases, including gastritis, peptic ulcer, and two forms of gastric cancer. H. pylori infection elicits a variety of phenotypic responses in cultured gastric epithelial cells, including the expression of proinflammatory genes and changes in the actin cytoskeleton. Both of these responses are mediated by the type IV secretion system (TFSS) encoded by the cag pathogenicity island (cag PAI). We used human cDNA microarrays to examine the temporal transcriptional profiles of gastric AGS cells infected with H. pylori strain G27 and a panel of isogenic mutants to dissect the contributions of various genes in the cag PAI. Infection with G27 induced expression of genes involved in the innate immune response, cell shape regulation, and signal transduction. A mutant lacking the cagA gene, which encodes an effector molecule secreted by the TFSS and required for the host cell cytoskeletal response, induced the expression of fewer cytoskeletal genes. A mutant lacking cagE, which encodes a structural component of the TFSS, failed to up-regulate a superset of host genes, including the cagA-dependent genes, and many of the immune response genes. A mutant lacking the entire cag PAI failed to induce both the cagE-dependent genes and several transiently expressed cagE independent genes. Host cell transcriptional profiling of infection with isogenic strains offered a detailed molecular picture of H. pylori infection and provided insight into potential targets of individual virulence determinants such as tyrosine kinase and Rho GTPase signaling molecules.

Helicobacter pylori-stimulated EGF receptor transactivation requires metalloprotease cleavage of HB-EGF

Helicobacter pylori has a major aetiological role in human gastric carcinogenesis but the cellular and molecular pathways by which infection promotes transformation remain to be resolved. This study demonstrates that H. pylori exposure to MKN-1, ST42, and MKN-28 gastric epithelial tumour cells results in the activation of HB-EGF gene expression and EGFR tyrosine phosphorylation. These cell responses are induced by both cagPAI positive and cagPAI negative H. pylori strains and are dependent on cell surface expression of the HB-EGF precursor. The induction of HB-EGF gene transcription by H. pylori requires metalloprotease-, EGFR-, and Mek1-activities, indicating the involvement of the "triple membrane passing signal" (TMPS) for EGFR transactivation. Moreover, the release of the inflammatory cytokine IL-8 by cells exposed to H. pylori is significantly impaired by inhibitors of TMPS pathway elements. Our findings support a model in which H. pylori triggers constitutive EGFR signal activation, which enhances IL-8 production, and initiates neoplastic transformation of gastric epithelial cells.

Up-regulation of heparin binding epidermal growth factor-like growth factor and amphiregulin expression in Helicobacter pylori-infected human gastric mucosa

BACKGROUND

Host response plays a major role in pathogenesis of Helicobacter pylori-induced gastroduodenal disease including adenocarcinoma of distal stomach. Epidermal growth factor-related growth factors are important modulators of gastric homeostasis in normal and damaged gastrointestinal mucosa.

AIM

To evaluate expression of heparin binding epidermal growth factor and amphiregulin in antral mucosa of Helicobacter pylori-infected and non-infected dyspeptic patients and to correlate levels of heparin binding-epidermal growth factor and amphiregulin mRNA with mitogenic activity of gastric epithelial cells.

METHODS

A total of 10 Helicobacter pylori-infected and 15 Helicobacter pylori non-infected (10 with and 5 without gastritis) dyspeptic patients were studied. Diagnosis of Helicobacter pylori infection was based on rapid urease test and histology. Heparin binding-epidermal growth factor and amphiregulin mRNA expression in antral mucosa were assessed by reverse transcriptase-polymerase chain reaction. Protein expression and localization of both peptides were determined by immunohistochemistry. Mitogenic activity of antral gastric mucosa was assessed by determination of proliferating cell nuclear antigen labelling index by immunohistochemistry.

RESULTS

Heparin binding-epidermal growth factor and amphiregulin mRNA expression increased in Helicobacter pylori-infected vs Helicobacter pylori non-infected patients. Heparin binding-epidermal growth factor and amphiregulin immunostaining was more intense and deeper in gastric gland compartment in infected mucosa than in non-infected mucosa. Increase in heparin binding-epidermal growth factor and amphiregulin mRNA expression significantly correlated with increase in proliferating cell nuclear antigen labelling index.

CONCLUSIONS

Helicobacter pylori gastritis is associated with up-regulation of heparin binding-epidermal growth factor and amphiregulin which correlates with increased mitogenic activity of gastric mucosa. Increased heparin binding-epidermal growth factor and amphiregulin expression is postulated to contribute to reparative response of gastric mucosa to Helicobacter pylori infection.