Analyses of the cag pathogenicity island of Helicobacter pylori

Clinical relevance of cagPAI intactness in Helicobacter pylori isolates from Vietnam

The purpose of this paper is to investigate the relationship between clinical outcome and the intactness of cagPAI in Helicobacter pylori strains from Vietnam. The presence or absence of 30 cagPAI genes was investigated by polymerase chain reaction (PCR) and dot-blotting. H. pylori-induced interleukin-8 secretion and hummingbird phenotype, and H. pylori adhesion to gastric epithelial cells were examined. The serum concentration of pepsinogen 1, pepsinogen 2, and gastrin was also measured in all patients. cagPAI was present in all 103 Vietnamese H. pylori isolates, of which 91 had intact cagPAI and 12 contained only a part of cagPAI. Infection with the partial cagPAI strains was less likely to be associated with peptic ulcer and chronic gastric mucosal inflammation than infection with strains possessing intact cagPAI. The partial cagPAI strains lacked almost all ability to induce interleukin-8 secretion and the hummingbird phenotype in gastric cells. Their adhesion to epithelial cells was significantly decreased in comparison with intact cagPAI strains. Moreover, for the first time, we found an association between cagPAI status and the serum concentration of pepsinogens 1 and 2 in infected patients. H. pylori strains with internal deletion within cagPAI are less virulent and, thus, less likely to be associated with severe clinical outcomes.

Helicobacter pylori-induced histone modification, associated gene expression in gastric epithelial cells, and its implication in pathogenesis

Histone modifications are critical in regulating gene expression, cell cycle, cell proliferation, and development. Relatively few studies have investigated whether Helicobacter pylori, the major cause of human gastric diseases, affects histone modification. We therefore investigated the effects of H. pylori infection on histone modifications in a global and promoter-specific manner in gastric epithelial cells. Infection of gastric epithelial cells by wild-type H. pylori induced time- and dose-dependent dephosphorylation of histone H3 at serine 10 (H3 Ser10) and decreased acetylation of H3 lysine 23, but had no effects on seven other specific modifications. Different cag pathogenicity island (PAI)-containing-clinical isolates showed similar abilities to induce H3 Ser10 dephosphorylation. Mutation of cagA, vacA, nonphosphorylateable CagA mutant cagA_EPISA, or disruption of the flagella showed no effects, while deletion of the entire cagPAI restored the H3 Ser10 phosphorylation to control levels. Analysis of 27 cagPAI mutants indicated that the genes that caused H3 Ser10 dephosphorylation were similar to those that were previously found to induce interleukin-8, irrespective of CagA translocation. This effect was independent of ERK or p38 pathways and type I interferon signaling. Additionally, c-Jun and hsp70 gene expression was associated with this histone modification. These results demonstrate that H. pylori alters histone modification and host response via a cagA-, vacA-independent, but cagPAI-dependent mechanisms, which contribute to its persistent infection and pathogenesis.

p27KIP1 expression in gastric cancer: differential pathways in the histological subtypes associated with Helicobacter pylori infection

OBJECTIVE

Decreases in p27(KIP1) and C-MYC expression have been associated with Helicobacter pylori infection. Furthermore, C-MYC seems to be a transcriptional repressor of p27(KIP1). Therefore, in a series of gastric adenocarcinomas we studied the association of p27(KIP1) expression with H. pylori genotype (vacA, cagA, cagE and virB11) and the involvement of C-MYC in this process.

MATERIAL AND METHODS

Expression of p27(KIP1) and C-MYC was determined by immunohistochemistry in 84 gastric adenocarcinoma samples and H. pylori infection and genotype were determined by polymerase chain reaction.

RESULTS

Most p27(KIP1)-negative cases (94.0%) were H. pylori-positive and 44.8% were C-MYC-positive. In the diffuse gastric cancer subtype, p27-negative-C-MYC-positive was the most frequent combination (cluster II), and was associated with the more pathogenic H. pylori strains. Although an association with p27(KIP1) and H. pylori strain was found in the intestinal gastric cancer subtype, negativity for p27(KIP1) and C-MYC markers was the most frequent cluster, followed by cluster II, and both were present, independent of the H. pylori genotype.

CONCLUSIONS

Reduced expression of p27(KIP1) was closely linked to H. pylori infection, and was dependent on the more pathogenic strains. Moreover, intestinal and diffuse subtypes showed distinct carcinogenic pathways influenced by H. pylori strains. These data add insight to the differential influence and relevance of H. pylori genotype in gastric cancer development.

alphaPix interacts with Helicobacter pylori CagA to induce IL-8 expression in gastric epithelial cells

OBJECTIVE

Helicobacter pylori CagA, translocated into gastric epithelial cells, induces IL-8 expression through the signalling pathways, including extracellular signal-regulated kinase (ERK) and nuclear factor-kappaB (NF-kappaB). We previously demonstrated that CagA interacts with host alphaPix. The present study was purposed to determine the role of the interaction of alphaPix with CagA on the signalling pathways for IL-8 expression in H. pylori-infected gastric epithelial cells.

MATERIAL AND METHODS

H. pylori HP99 strain (CagA+, VacA+) was infected to gastric epithelial AGS cells transfected with non-targeting (NT) or alphaPix- targeting siRNA. Activation of signalling molecules including p21-activated kinase (PAK), ERK and NF-kappaB, and expression of IL-8 in the cells were assessed.

RESULTS

H. pylori CagA was delivered into AGS cells and then interacted with alphaPix at 4 h following H. pylori infection. PAK1, ERK and NF-kappaB were activated in the cells containing NT and alphaPix siRNA at 1-2 h following H. pylori infection. However, after 4 h, the time when CagA was delivered into the cells, the activations of PAK1, ERK and NF-kappaB were inhibited by down-regulation of alphaPix using siRNA but not by NT siRNA. The results indicate that alphaPix is required for H. pylori-mediated signalling of PAK1, ERK and NF-kappaB. Additionally, alphaPix siRNA suppressed IL-8 induction after translocation of CagA into the cells, indicating that interaction of CagA with alphaPix is critical for CagA-mediating signalling for IL-8 expression.

CONCLUSIONS

The interaction of alphaPix with CagA activates PAK1, ERK and NF-kappaB, which induces IL-8 expression in H. pylori-infected gastric epithelial cells.

Application of PCR amplicon sequencing using a single primer pair in PCR amplification to assess variations in Helicobacter pylori CagA EPIYA tyrosine phosphorylation motifs

Background

The presence of various EPIYA tyrosine phosphorylation motifs in the CagA protein of Helicobacter pylori has been suggested to contribute to pathogenesis in adults. In this study, a unique PCR assay and sequencing strategy was developed to establish the number and variation of cagA EPIYA motifs.

Findings

MDA-DNA derived from gastric biopsy specimens from eleven subjects with gastritis was used with M13- and T7-sequence-tagged primers for amplification of the cagA EPIYA motif region. Automated capillary electrophoresis using a high resolution kit and amplicon sequencing confirmed variations in the cagA EPIYA motif region. In nine cases, sequencing revealed the presence of AB, ABC, or ABCC (Western type) cagA EPIYA motif, respectively. In two cases, double cagA EPIYA motifs were detected (ABC/ABCC or ABC/AB), indicating the presence of two H. pylori strains in the same biopsy.

Conclusion

Automated capillary electrophoresis and Amplicon sequencing using a single, M13- and T7-sequence-tagged primer pair in PCR amplification enabled a rapid molecular typing of cagA EPIYA motifs. Moreover, the techniques described allowed for a rapid detection of mixed H. pylori strains present in the same biopsy specimen.

In situ expression of cagA and risk of gastroduodenal disease in Helicobacter pylori-infected children

BACKGROUND AND AIM

Gastroduodenal disease is more common among adults and children with cagA+ Helicobacter pylori infection, but disease severity varies among those infected with cagA+ strains. We examined whether cagA in situ expression can predict disease manifestations among H pylori-infected children.

PATIENTS AND METHODS

Fifty-one children were selected from 805 patients with abdominal symptoms who underwent esophagogastroduodenoscopy with gastric biopsies. Endoscopic and histologic gastritis were scored and H pylori colonization was quantified by Genta stain and in situ hybridization expression of 16S rRNA and cagA.

RESULTS

Endoscopy was either normal (n = 14) or demonstrated nodularity (n = 18), gastric ulcer (n = 8) or duodenal ulcer (n = 11). H pylori was present in 7, 18, 6, and 10 children, respectively. Expression of 16S rRNA and cagA were significantly higher in children with ulcer compared with normal children. The fraction of H pylori bacteria expressing cagA in situ was higher in children with ulcer compared to those with endoscopic nodularity (P < 0.05).

CONCLUSIONS

Thus, cagA in situ expression is increased in H pylori-infected children with peptic ulcers and may play a role in the pathogenesis of peptic ulcer disease during childhood. Determination of in situ expression of cagA complements traditional isolation and in vitro testing of single-colony isolates.

The relationship between Helicobacter pylori genes cagE and virB11 and gastric cancer

BACKGROUND

The association between Helicobacter pylori gene diversity and gastric cancer has been poorly reported, although it is one of the important ways to explain the gastric pathogenesis. The aim of this study was to investigate the frequency of cagE and virB11 genes in H. pylori isolated from patients with gastric cancer and to analyze the histology profiles.

MATERIALS AND METHODS

The presence of H. pylori and subtypes (cagE and virB11) was detected by PCR from the genomic DNA of 101 patients who had been diagnosed with gastric cancer. The cases were grouped according to the presence/absence of the genes studied and were analyzed in relation to histopathological parameters.

RESULTS

H. pylori infection was detected in 94 out of 101 (93.1%) gastric carcinomas. The cases were categorized into the following groups: cagE+/virB11+, cagE+/virB11-, cagE-/virB11+, and cagE-/virB11-. Frequencies were: 50% (47/94) cagE+/virB11+, 3.2% (3/94) cagE+/virB11-, 10.6% (10/94) cagE-/virB11+, and 36.2% (34/94) cagE-/virB11-. Tumors in the gastric antrum were predominant. An exception was the cagE-/virB11- group, in which tumors had a tendency to be located in the gastric cardia; the majority of the cardia tumors (56% (14/25)) were in this group. Intestinal histology type was the most frequent, but the cagE+/virB11- group only had diffuse tumors. H. pyloricagE+/virB11+ occurred most frequently (except at stage III), and was present at all gastric cancer stages.

CONCLUSIONS

This study is the first to include a relevant number of gastric cancer cases with H. pylori infection, reporting the frequency and relationship of cagE and virB11 genes and the genesis of this tumor. The presence of these cag pathogenicity island genes shows that they are important factors for the pathogenesis and malignancy of gastric cancer related to H. pylori.

Diversity of VacA intermediate region among Helicobacter pylori strains from several regions of the world

Helicobacter pylori is known to be a major cause of gastric carcinoma and peptic ulceration. cagA positivity and vacA's signal regions and mid-regions are well-characterized markers of H. pylori's virulence. Recently, an intermediate region has been identified as another strong marker of H. pylori-associated disease, and its i1 allele has been linked with severe diseases in colonized hosts. The goal of this study was to determine the prevalence of the intermediate alleles in H. pylori isolates from China, Turkey, and Uruguay and from U.S. Africans and to compare their distribution with other well-characterized virulence factors. Originally, 123 H. pylori strains were studied, but 3 were excluded due to the failure to amplify the intermediate region in these samples. Therefore, a total of 120 strains were analyzed: 30 Chinese isolates, 35 Turkish isolates, 30 Uruguayan isolates, and 25 U.S. African isolates. The s type and the m type were determined by PCR amplification. The i type was identified by PCR amplification and DNA sequencing. CagA status was determined by PCR methodology. There was a strong correlation among CagA positivity, s1, and i1 in Chinese, U.S. African, and Uruguayan isolates, but less correlation among these markers in Turkish isolates. A new intermediate variant (i3) was identified in 25.7% of Turkish strains and 3.3% of the Chinese strains. In summary, the distribution of CagA positivity and s1 correlated with the i1 in the three populations, except in the Turkish population, which showed a disproportionate representation of the i3 allele. Phylogenetic mapping confirmed the i-typing method previously defined and adopted for this study. The phylogenetic tree showed country-specific correlation with the intermediate region. Our results showed that the i1 allele is strongly associated with CagA positivity and the vacA s1 allele, suggesting its role as a virulence marker and potential predictor for clinical outcome.

Examination of geographical, clinical and intrahost variations in the 3' repeat region of cagA gene in Helicobacter pylori

The size variation of the cytoxin-associated protein (cagA), which is dependent on the 3' repeat region (3'RR) of the cagA gene, is known to play a crucial role in the pathogenesis of Helicobacter pylori infection. The present study evaluated the relationship between the 3'RR variation and the geographic distribution, clinical manifestations, and locations of colonization in the stomach. We evaluated the 3'RR of H. pylori isolates from 78 patients with gastric cancer, peptic ulcer, and non-ulcer dyspepsia from Japan, Hong Kong, India, and the United States and assessed the variations of 3'RR according to the geographical and clinical characteristics. Sixty eight (87.2%) patients had the same 650 bp band without geographical differences. The frequency of polymorphisms in the 3'RR did not differ when compared to the clinical manifestations (P=0.868). The length of 3'RR did not differ by location of colonization. In conclusion, the 3'RR variation of cagA gene is not associated with the geographical and clinical characteristics of the patients studied.

Helicobacter pylori CagA upregulation of CIP2A is dependent on the Src and MEK/ERK pathways

Helicobacter pylori is classified as a class I carcinogenic factor and its persistent colonization in the stomach induces gastric cancer. Cancerous Inhibitor of PP2A (CIP2A) is a newly identified oncoprotein overexpressed in gastric cancer. Serving as a key oncoprotein, CIP2A also participates in regulation of senescence and proliferation of gastric cells. The combination of aberrant CIP2A expression inducing unlimited cell proliferation, and H. pylori infection eliciting aberrant expression of some key proteins, results in the onset of gastric tumorigenesis. However, the relationship between H. pylori infection and CIP2A expression still remains undefined. The aim of our study was to verify the effect of H. pylori infection on CIP2A expression levels and identify H. pylori signalling molecules and corresponding pathways influencing CIP2A expression. Following plasmid-mediated expression of CagA in human gastric cell lines, the cells were infected with H. pylori and CIP2A expression levels were examined by immunoblotting. Signal inhibitors were used to verify which signal pathways were involved. We also performed CIP2A depletion and H. pylori infection after depletion in AGS cells. H. pylori infection-induced CIP2A expression was dependent on cagA gene expression and CagA phosphorylation. Bacterial oncoprotein CagA upregulated CIP2A expression and this upregulation effect was dependent on Src and Ras/mitogen-activated protein kinase kinase/extracellular signal-regulated kinase pathways. H. pylori infection-induced Myc stabilization was partially attenuated by CIP2A depletion. The results of our study provide further information for understanding the mechanism of H. pylori carcinogenesis.

Cag3 is a novel essential component of the Helicobacter pylori Cag type IV secretion system outer membrane subcomplex

Helicobacter pylori strains harboring the cag pathogenicity island (PAI) have been associated with more severe gastric disease in infected humans. The cag PAI encodes a type IV secretion (T4S) system required for CagA translocation into host cells as well as induction of proinflammatory cytokines, such as interleukin-8 (IL-8). cag PAI genes sharing sequence similarity with T4S components from other bacteria are essential for Cag T4S function. Other cag PAI-encoded genes are also essential for Cag T4S, but lack of sequence-based or structural similarity with genes in existing databases has precluded a functional assignment for the encoded proteins. We have studied the role of one such protein, Cag3 (HP0522), in Cag T4S and determined Cag3 subcellular localization and protein interactions. Cag3 is membrane associated and copurifies with predicted inner and outer membrane Cag T4S components that are essential for Cag T4S as well as putative accessory factors. Coimmunoprecipitation and cross-linking experiments revealed specific interactions with HpVirB7 and CagM, suggesting Cag3 is a new component of the Cag T4S outer membrane subcomplex. Finally, lack of Cag3 lowers HpVirB7 steady-state levels, further indicating Cag3 makes a subcomplex with this protein.

CagA and VacA polymorphisms do not correlate with severity of histopathological lesions in Helicobacter pylori-infected Greek children

The presence of various numbers of EPIYA tyrosine phosphorylation motifs in the CagA protein of Helicobacter pylori has been suggested to contribute to pathogenesis in adults. In this prospective study, we characterized H. pylori isolates from symptomatic children, with reference to the diversity of functional EPIYA motifs in the CagA protein and vacA isotypes, and assessed the potential correlation with the histopathological manifestations of the infection. We analyzed 105 H. pylori isolates from 98 children and determined the diversity of EPIYA motifs in CagA by amplification and sequencing of the 3' variable region of the cagA gene as well as vacA isotypes for the signal, middle, and intermediate regions. CagA phosphorylation and levels of secreted IL-8 were determined following in vitro infection of AGS gastric epithelial cells. Histopathological evaluation of H. pylori colonization, activity, and severity of the associated gastritis was performed according to the updated Sydney criteria. EPIYA A (GLKN[ST]EPIYAKVNKKK), EPIYA B (Q[V/A]ASPEPIY[A/T]QVAKKVNAKI), and EPIYA C (RS[V/A]SPEPIYATIDDLG) motifs were detected in the ABC (46.6%) and ABCC (17.1%) combinations. No isolates harboring more than two EPIYA C motifs in CagA were found. The presence of isogenic strains with variable numbers of CagA EPIYA C motifs within the same patient was detected in seven cases. Occurrence of increasing numbers of EPIYA C motifs correlated strongly with presence of a high-vacuolation (s1 or s2/i1/m1) phenotype and age. A weak positive correlation was observed between vacuolating vacA genotypes and presence of nodular gastritis. However, CagA- and VacA-dependent pathogenicities were not found to contribute to severity of histopathology manifestations in H. pylori-infected children.

Helicobacter pylori and gastric carcinogenesis

Gastric carcinoma is the second leading cause of cancer-related deaths in the world, accounting for more than 700,000 deaths each year. Recent studies have revealed that infection with cagA-positive Helicobacter pylori plays an essential role in the development of gastric carcinoma. The cagA-encoded CagA protein is delivered into gastric epithelial cells via the bacterial type IV secretion system, where it undergoes tyrosine phosphorylation by Src and Abl kinases. Tyrosine-phosphorylated CagA then acquires the ability to interact with and deregulate SHP-2 phosphatase, a bona-fide oncoprotein, deregulation of which is involved in a variety of human malignancies. CagA also binds to and inhibits PAR1b/MARK2 polarity-regulating kinase to disrupt tight junctions and epithelial apical-basolateral polarity. These CagA activities may collectively contribute to the transformation of gastric epithelial cells. Indeed, transgenic expression of CagA in mice results in the development of gastrointestinal and hematological malignancies, indicating that CagA is the first bacterial oncoprotein that acts in mammalian cells. The oncogenic potential of CagA may be further potentiated in the presence of chronic inflammation, which aberrantly induces activation-induced cytidine deaminase (AID), a member of the DNA/RNA-editing enzyme family. Ectopically expressed AID may contribute to H. pylori-initiated gastric carcinogenesis by increasing the risk of likelihood of epithelial cells acquiring mutations in cancer-related genes.

Pediatric Helicobacter pylori isolates display distinct gene coding capacities and virulence gene marker profiles

Helicobacter pylori strains display remarkable genetic diversity, and the presence of strains bearing the toxigenic vacA s1 allele, a complete cag pathogenicity island (PAI), cagA alleles containing multiple EPIYA phosphorylation sites, and expressing the BabA adhesin correlates with development of gastroduodenal disease in adults. To better understand the genetic variability present among pediatric strains and its relationship to disease, we characterized H. pylori strains infecting 47 pediatric North American patients. Prevalence of mixed infection was assessed by random amplified polymorphic DNA analysis of multiple H. pylori clones from each patient. Microarray-based comparative genomic hybridization was used to examine the genomic content of the pediatric strains. The cagA and vacA alleles were further characterized by allele-specific PCR. A range of EPIYA motif configurations were observed for the cagA gene, which was present in strains from 22 patients (47%), but only 19 (41%) patients contained a complete cag PAI. Thirty patients (64%) were infected with a strain having the vacA s1 allele, and 28 patients (60%) had the babA gene. The presence of a functional cag PAI was correlated with ulcer disease (P = 0.0095). In spite of declining rates of H. pylori infection in North America, at least 11% of patients had mixed infection. Pediatric strains differ in their spectrum of strain-variable genes and percentage of absent genes in comparison to adult strains. Most children were infected with H. pylori strains lacking the cag PAI, but the presence of a complete cag PAI, in contrast to other virulence markers, was associated with more severe gastroduodenal disease.

NF-kappaB activation by Helicobacter pylori requires Akt-mediated phosphorylation of p65

Background

The inflammatory response in Helicobacter pylori-infected gastric tissue is mediated by cag pathogenicity island (PAI)-dependent activation of nuclear factor-κB (NF-κB). Phosphatidylinositol 3-kinase (PI3K)/Akt signaling is known to play a role in NF-κB activation, but little information is available on the relationship between H. pylori and PI3K/Akt signaling in gastric epithelial cells. We examined whether H. pylori activates Akt in gastric epithelial cells, the role of cag PAI in this process and the role of Akt in regulating H. pylori-induced NF-κB activation.

Results

Phosphorylated Akt was detected in epithelial cells of H. pylori-positive gastric tissues. Although Akt was activated in MKN45 and AGS cells by coculture with cag PAI-positive H. pylori strains, a cag PAI-negative mutant showed no activation of Akt. H. pylori also induced p65 phosphorylation. PI3K inhibitor suppressed H. pylori-induced p65 phosphorylation and NF-κB transactivation, as well as interleukin-8 expression. Furthermore, transfection with a dominant-negative Akt inhibited H. pylori-induced NF-κB transactivation. Transfection with small interference RNAs for p65 and Akt also inhibited H. pylori-induced interleukin-8 expression.

Conclusion

The results suggest that cag PAI-positive H. pylori activates Akt in gastric epithelial cells and this may contribute to H. pylori-mediated NF-κB activation associated with mucosal inflammation and carcinogenesis.

Helicobacter pylori-induced interleukin-12 p40 expression

Interleukin-12 (IL-12) is a heterodimeric cytokine produced by antigen-presenting cells that promotes the development of T-helper lymphocyte 1 (Th1). Chronic gastritis induced by Helicobacter pylori is considered a Th1-mediated process. IL-12 levels in gastric biopsy samples of H. pylori-infected patients are higher than in those of uninfected individuals, but the cellular source of IL-12 remains elusive. IL-12 staining was detected in mucosal epithelial cells, lymphocytes, and macrophages in specimens of patients with H. pylori-positive gastritis. Therefore, we investigated IL-12 p40 mRNA induction by H. pylori in gastric epithelial cells and T cells. Although cag pathogenicity island (PAI)-positive H. pylori induced IL-12 p40 mRNA expression, an isogenic mutant of the cag PAI failed to induce it in both cell types. Supernatants from H. pylori cultures and H. pylori VacA induced IL-12 p40 mRNA expression in T cells but not in epithelial cells. The activation of the IL-12 p40 promoter by H. pylori was mediated through NF-kappaB. The transfection of IkappaB kinase and NF-kappaB-inducing kinase dominant-negative mutants inhibited H. pylori-induced IL-12 p40 activation. Inhibitors of NF-kappaB, phosphatidylinositol 3-kinase, p38 mitogen-activated protein kinase, and Hsp90 suppressed H. pylori- and VacA-induced IL-12 p40 mRNA expression. The results indicate that H. pylori induces IL-12 p40 expression by the activation of NF-kappaB, phosphatidylinositol 3-kinase, and p38 mitogen-activated protein kinase. Hsp90 is also a crucial regulator of H. pylori-induced IL-12 p40 expression. In addition to the cag PAI, VacA might be relevant in the induction of IL-12 expression and a Th1-polarized response only in T cells.

Linking epithelial polarity and carcinogenesis by multitasking Helicobacter pylori virulence factor CagA

Loss of cell polarity and tissue architecture is a hallmark of carcinomas that arise from epithelial cells. Recent studies on Drosophila tumor suppressors have provided evidence that epithelial polarity and cell proliferation are functionally coupled, suggesting a function for polarity defects in the development of carcinomas. This notion is supported by the findings that mammalian orthologs of these Drosophila tumor suppressors are targeted by a number of viral oncoproteins. Chronic infection with Helicobacter pylori is causally associated with gastric carcinoma. H. pylori virulence factor CagA (cytotoxin-associated gene A), which is delivered into gastric epithelial cells through a bacterial type IV secretion system, has an important function in cell transformation through interacting with and deregulating SHP-2 phosphatase, a bona fide oncoprotein that is associated with human malignancies. Recent studies have further revealed that CagA specifically binds and inhibits PAR1/MARK polarity-regulating kinase, thereby causing junctional and polarity defects in epithelial cells. Thus, the bacterial oncoprotein simultaneously targets the polarity-regulating system and growth-regulatory system. These findings indicate that loss of cell polarity underlies the abnormal proliferation of epithelial cells that directs carcinogenesis.

Evaluation of the clinical significance of homB, a novel candidate marker of Helicobacter pylori strains associated with peptic ulcer disease

BACKGROUND

homB codes for a putative Helicobacter pylori outer membrane protein and has previously been associated with peptic ulcer disease (PUD) in children.

METHODS

A total of 190 H. pylori strains isolated from children and adults were studied to evaluate the clinical importance of the homB gene. In vitro experiments were performed to identify HomB mechanisms of bacterial pathogenicity.

RESULTS

Characterization of the isolates demonstrated that homB was significantly associated with PUD in 86 children (odds ratio [OR], 7.64 [95% confidence interval {CI}, 2.65-22.05]) and in 32 adults < or =40 years of age (OR, 11.25 [95% CI, 1.86-68.13]). homB was correlated with the presence of cagA, babA2, vacAs1, hopQI, and oipA "on" genotype (P< .001) The HomB protein was found to be expressed in the H. pylori outer membrane and was noted to be antigenic in humans. H. pylori homB knockout mutant strains presented reduced ability to induce interleukin-8 secretion from human gastric epithelial cells, as well as reduced capacity to bind to these cells. Both of these functions correlated with the number of homB copies present in a strain.

CONCLUSION

homB can be considered a comarker of H. pylori strains associated with PUD. Moreover, results strongly suggest that HomB is involved in the inflammatory response and in H. pylori adherence, constituting a novel putative virulence factor.

H. pylori selectively blocks EGFR endocytosis via the non-receptor kinase c-Abl and CagA

Helicobacter pylori infection is a primary cause of peptic ulcers and is associated with gastric carcinogenesis. The H. pylori-induced pathophysiology may be linked to the deregulation of EGFR signalling. Elevated mucosal levels of EGF and the EGFR have been found in antral gastric biopsies of H. pylori-infected patients. A critical mechanism for regulating EGFR signalling is ligand-induced endocytosis. The internalized receptor recycles back to the plasma membrane for continued signalling or is targeted for degradation terminating receptor signalling. Here, we show that H. pylori blocks EGFR endocytosis and receptor degradation upon prolonged infection of gastric epithelial cells. Moreover, this inhibition occurs via a CagA-dependent, but CagA phosphorylation-independent activation of the non-receptor kinase c-Abl, which in turn phosphorylates the EGFR target site pY1173. This suggests a novel CagA-induced host cell response that is independent of CagA tyrosine phosphorylation. Our data indicate an intriguing strategy of H. pylori in host cell manipulations by altering selective receptor populations via a CagA-dependent endocytic mechanism. Furthermore, we identified a new role for c-Abl in phosphorylation of the EGFR target site pY1173 during H. pylori infection.

Helicobacter pylori AddAB helicase-nuclease and RecA promote recombination-related DNA repair and survival during stomach colonization

Helicobacter pylori colonization of the human stomach is characterized by profound disease-causing inflammation. Bacterial proteins that detoxify reactive oxygen species or recognize damaged DNA adducts promote infection, suggesting that H. pylori requires DNA damage repair for successful in vivo colonization. The molecular mechanisms of repair remain unknown. We identified homologues of the AddAB class of helicase-nuclease enzymes, related to the Escherichia coli RecBCD enzyme, which, with RecA, is required for repair of DNA breaks and homologous recombination. H. pylori mutants lacking addA or addB genes lack detectable ATP-dependent nuclease activity, and the cloned H. pylori addAB genes restore both nuclease and helicase activities to an E. coli recBCD deletion mutant. H. pylori addAB and recA mutants have a reduced capacity for stomach colonization. These mutants are sensitive to DNA damaging agents and have reduced frequencies of apparent gene conversion between homologous genes encoding outer membrane proteins. Our results reveal requirements for double-strand break repair and recombination during both acute and chronic phases of H. pylori stomach infection.

Helicobacter pylori and mitogen-activated protein kinases mediate activator protein-1 (AP-1) subcomponent protein expression and DNA-binding activity in gastric epithelial cells

Emerging evidence has suggested a critical role for activator protein-1 (AP)-1 in regulating various cellular functions. The goal of this study was to investigate the effects of Helicobacter pylori and mitogen-activated protein kinases (MAPK) on AP-1 subcomponents expression and AP-1 DNA-binding activity in gastric epithelial cells. We found that H. pylori infection resulted in a time- and dose-dependent increase in the expression of the proteins c-Jun, JunB, JunD, Fra-1, and c-Fos, which make up the major AP-1 DNA-binding proteins in AGS and MKN45 cells, while the expression levels of Fra-2 and FosB remained unchanged. Helicobacter pylori infection and MAPK inhibition altered AP-1 subcomponent protein expression and AP-1 DNA-binding activity, but did not change the overall subcomponent composition. Different clinical isolates of H. pylori showed various abilities to induce AP-1 DNA binding. Mutation of cagA, cagPAI, or vacA, and the nonphosphorylateable CagA mutant (cagA(EPISA)) resulted in less H. pylori-induced AP-1 DNA-binding activity, while mutation of the H. pylori flagella had no effect. extracellular signal-related kinase (ERK), p38, and c-Jun N-terminal kinase (JNK) each selectively regulated AP-1 subcomponent expression and DNA-binding activity. These results provide more insight into how H. pylori and MAPK modulate AP-1 subcomponents in gastric epithelial cells to alter the expression of downstream target genes and affect cellular functions.

Helicobacter pylori and mitogen-activated protein kinases regulate the cell cycle, proliferation and apoptosis in gastric epithelial cells

BACKGROUND AND AIMS

Helicobacter pylori infection activates mitogen-activated protein kinases (MAPK) and modulates cell proliferation and apoptosis. However, the relationship between H. pylori infection and MAPK signaling in controlling cell proliferation and apoptosis is not clear, nor has the role of MAPK on the gastric epithelial cell cycle and proliferation been established. Therefore, we investigated the effects of H. pylori infection and MAPK inhibition on these processes.

METHODS

Gastric epithelial cell lines (AGS and MKN45) were infected with H. pylori and/or treated with MAPK inhibitors. Cell cycle and apoptosis were measured by flow cytometry. Cell cycle proteins and proliferation were monitored by western blot and cell count, respectively.

RESULTS

Infection with H. pylori resulted in dose-dependent MAPK activation, cell cycle arrest, reduced proliferation and increased apoptosis. The effect of H. pylori and MAPK at various cell cycle checkpoints was noted: MEK1/2 and p38 inhibition increased H. pylori-induced cell cycle G(1) arrest, while JNK inhibition reduced G(1) arrest. MEK1/2 inhibition increased p21, p27 and cyclin E and JNK inhibition additionally increased cyclin D1 expression. Both inhibitors decreased cell proliferation. All inhibitors enhanced apoptosis after H. pylori infection. We also detected MAPK cross-talk in AGS cells: p38 and JNK inhibitors increased ERK activation. The p38 inhibitor increased JNK and the MEK1/2 inhibitor decreased JNK activation only during H. pylori infection.

CONCLUSIONS

These results suggest H. pylori and MAPK differentially regulate the cell cycle, proliferation and apoptosis in gastric epithelial cells. The imbalance between H. pylori infection and MAPK activation likely contributes to the H. pylori-induced pathogenesis.

Involvement of the Helicobacter pylori plasticity region and cag pathogenicity island genes in the development of gastroduodenal diseases

Infection by Helicobacter pylori is associated with the development of several gastroduodenal diseases, including gastritis, peptic ulcer disease (gastric ulcers and duodenal ulcers), and gastric adenocarcinoma. Although a number of putative virulence factors have been reported for H. pylori, there are conflicting results regarding their association with specific H. pylori-related diseases. In this work, we investigated the presence of virB11 and cagT, located in the left half of the cag pathogenicity island (cagPAI), and the jhp917-jhp918 sequences, components of the dupA gene located in the plasticity zone of H. pylori, in Brazilian isolates of H. pylori. We also examined the association between these genes and H. pylori-related gastritis, peptic ulcer disease, and gastric and duodenal ulcers in an attempt to identify a gene marker for clinical outcomes related to infection by H. pylori. The cagT gene was associated with peptic ulcer disease and gastric ulcers, whereas the virB11 gene was detected in nearly all of the samples. The dupA gene was not associated with duodenal ulcers or any gastroduodenal disease here analyzed. These results suggest that cagT could be a useful prognostic marker for the development of peptic ulcer disease in the state of São Paulo, Brazil. They also indicate that cagT is associated with greater virulence and peptic ulceration, and that this gene is an essential component of the type IV secretion system of H. pylori.

Helicobacter pylori genotyping and sequencing using paraffin-embedded biopsies from residents of colombian areas with contrasting gastric cancer risks

BACKGROUND

cagA-positive and vacA s1 and m1 genotypes of Helicobacter pylori are associated with an elevated risk of gastric cancer (GC). We determined these genotypes using paraffin-embedded gastric biopsy specimens harvested from infected individuals and compared genotype distributions in two Colombian populations residing in geographic regions with a high and low incidence of GC.

METHODS

DNA from paraffin-embedded gastric biopsies from 107 adults was amplified using primers specific for cagA, for the cag'empty site', for the s and m alleles of vacA, and for H. pylori 16S rRNA.

RESULTS

H. pylori infection was detected by molecular assays in 97 (90.7%) biopsies. Complete genotyping of cagA and vacA was achieved in 94 (96.9%) cases. The presence of cagA was detected in 78 of 97 cases (80.4%); when considered separately, cagA and vacA s regions were not significantly associated with a particular geographic area. The vacA m1 allele and s1m1 genotypes were more common in the area of high risk for GC (p = .037 and p = .044, respectively), while the vacA m2 allele and s2m2 genotypes were more prevalent in the low-risk area. The prevalence of the combination of cagA-positive, vacA s1m1 genotypes was 84.3% and 60.5% for high and low risk areas, respectively (p = .011).

CONCLUSIONS

H. pylori cagA and vacA genotyping from paraffin-embedded gastric biopsies permitted reliable typability and discrimination. The more virulent cagA-positive s1m1 strains, as well as vacA m1 genotype, were more prevalent in high risk than in low risk areas, which may contribute to the difference in GC risk between those two regions.

Helicobacter pylori induces an antimicrobial response in rhesus macaques in a cag pathogenicity island-dependent manner

BACKGROUND & AIMS

We used the rhesus macaque model to study the effects of the cag pathogenicity island (cag PAI) on the H pylori host-pathogen interaction.

METHODS

H pylori-specific pathogen-free (SPF) monkeys were experimentally challenged with wild-type (WT) H pylori strain J166 (J166WT, n = 4) or its cag PAI isogenic knockout (J166Deltacag PAI, n = 4). Animals underwent endoscopy before and 1, 4, 8, and 13 weeks after challenge. Gastric biopsies were collected for quantitative culture, histopathology, and host gene expression analysis.

RESULTS

Quantitative cultures showed that all experimentally challenged animals were infected with J166WT or its isogenic J166Deltacag PAI. Histopathology demonstrated that inflammation and expansion of the lamina propria were attenuated in animals infected with J166Deltacag PAI compared with J166WT. Microarray analysis showed that of the 119 up-regulated genes in the J166WT-infected animals, several encode innate antimicrobial effector proteins, including elafin, siderocalin, DMBT1, DUOX2, and several novel paralogues of human-beta defensin-2. Quantitative RT-PCR confirmed that high-level induction of each of these genes depended on the presence of the cag PAI. Immunohistochemistry confirmed increased human-beta defensin-2 epithelial cell staining in animals challenged with J166WT compared with either J166Deltacag PAI-challenged or uninfected control animals.

CONCLUSIONS

We propose that one function of the cag PAI is to induce an antimicrobial host response that may serve to increase the competitive advantage of H pylori in the gastric niche and could even provide a protective benefit to the host.

Differences in virulence markers between Helicobacter pylori strains from Iraq and those from Iran: potential importance of regional differences in H. pylori-associated disease

Helicobacter pylori causes peptic ulceration and gastric adenocarcinoma; the latter is common in Iran but not in Iraq. We hypothesized that more virulent H. pylori strains may be found in Iran than in Iraq and so compared established and newly described virulence factors in strains from these countries. We studied 59 unselected dyspeptic patients from Iran and 49 from Iraq. cagA was found in similar proportions of strains from both countries (76% in Iran versus 71% in Iraq) and was significantly associated with peptic ulcer disease in Iraq (P <or= 0.01) but not in Iran. cagA alleles encoding four or more tyrosine phosphorylation motifs were found in 12% of the Iranian strains but none of the Iraqi strains (P = 0.02). There were no significant differences in the vacA signal-, middle-, or intermediate-region types between Iranian and Iraqi strains. Among the strains from Iran, vacA genotypes showed no specific peptic ulcer associations, but among the strains from Iraq, vacA i1 strains were associated with gastric ulcer (P <or= 0.02), mimicking their previously demonstrated association with gastric cancer in Iran. dupA was found in similar proportions of Iranian and Iraqi strains (38% and 32%, respectively) and was associated with peptic ulceration in Iraqi patients (P <or= 0.01) but not Iranian patients. H. pylori strains from Iraq and Iran possess virulence factors similar to those in Western countries. The presence of cagA with more phosphorylation motifs in Iranian strains may contribute to the higher incidence of gastric cancer. However, the association between strain virulence markers and disease in Iraq but not Iran suggests that other host and environmental factors may be more important in the disease-prone Iranian population.

The highly repetitive region of the Helicobacter pylori CagY protein comprises tandem arrays of an alpha-helical repeat module

The cag-pathogenicity-island-encoded type IV secretion system of Helicobacter pylori functions to translocate the effector protein CagA directly through the plasma membrane of gastric epithelial cells. Similar to other secretion systems, the Cag type IV secretion system elaborates a surface filament structure, which is unusually sheathed by the large cag-pathogenicity-island-encoded protein CagY. CagY is distinguished by unusual amino acid composition and extensive repetitive sequence organised into two defined repeat regions. The second and major repeat region (CagY_rpt2) has a regular disposition of six repetitive motifs, which are subject to deletion and duplication, facilitating the generation of CagY size and phenotypic variants. In this study, we show CagY_rpt2 to comprise two highly thermostable and acid-stable α-helical structural motifs, the most abundant of which (motif A) occurs in tandem arrays of one to six repeats terminally flanked by single copies of the second repeat (motif B). Isolated motifs demonstrate hetero- and homomeric interactions, suggesting a propensity for uniform assembly of discrete structural subunit motifs within the larger CagY_rpt2 structure. Consistent with this, CagY proteins comprising substantially different repeat 2 motif organisations demonstrate equivalent CagA translocation competence, illustrating a remarkable structural and functional tolerance for precise deletion and duplication of motif subunits. We provide the first insight into the structural basis for CagY_rpt2 assembly that accommodates both the variable motif sequence composition and the extensive contraction/expansion of repeat modules within the CagY_rpt2 region.

Protein subassemblies of the Helicobacter pylori Cag type IV secretion system revealed by localization and interaction studies

Type IV secretion systems are possibly the most versatile protein transport systems in gram-negative bacteria, with substrates ranging from small proteins to large nucleoprotein complexes. In many cases, such as the cag pathogenicity island of Helicobacter pylori, genes encoding components of a type IV secretion system have been identified due to their sequence similarities to prototypical systems such as the VirB system of Agrobacterium tumefaciens. The Cag type IV secretion system contains at least 14 essential apparatus components and several substrate translocation and auxiliary factors, but the functions of most components cannot be inferred from their sequences due to the lack of similarities. In this study, we have performed a comprehensive sequence analysis of all essential or auxiliary Cag components, and we have used antisera raised against a subset of components to determine their subcellular localization. The results suggest that the Cag system contains functional analogues to all VirB components except VirB5. Moreover, we have characterized mutual stabilization effects and performed a comprehensive yeast two-hybrid screening for potential protein-protein interactions. Immunoprecipitation studies resulted in identification of a secretion apparatus subassembly at the outer membrane. Combining these data, we provide a first low-resolution model of the Cag type IV secretion apparatus.

Current management of Helicobacter pylori infections in the elderly

Helicobacter pylori infection is a chronic gastric gram-negative infection that increases with age worldwide. However, the percentage age of H. pylori-positive elderly patients who are tested and treated for their infection remains very low. It is now demonstrated that H. pylori infection induces a whole cascade of events leading to gastric pathologies, such as peptic ulcer diseases, gastric precancerous lesions and gastric cancer. Recent data also demonstrated that H. pylori chronic infection can play a role in gastric aging, appetite regulation and extradigestive diseases, such as Alzheimer's disease, in the elderly. The diagnosis of H. pylori infection remains difficult to realize in the very old population, and the urea breath test obtains the best performance in this population. 1-week proton pump inhibitor-based triple therapy regimens are highly effective and well tolerated in elderly patients, and antibiotic resistance remains very low. Low compliance is the main factor related to treatment failure in this population.

Helicobacter pylori infection induces oxidative stress and programmed cell death in human gastric epithelial cells

Helicobacter pylori infection is associated with altered gastric epithelial cell turnover. To evaluate the role of oxidative stress in cell death, gastric epithelial cells were exposed to various strains of H. pylori, inflammatory cytokines, and hydrogen peroxide in the absence or presence of antioxidant agents. Increased intracellular reactive oxygen species (ROS) were detected using a redox-sensitive fluorescent dye, a cytochrome c reduction assay, and measurements of glutathione. Apoptosis was evaluated by detecting DNA fragmentation and caspase activation. Infection with H. pylori or exposure of epithelial cells to hydrogen peroxide resulted in apoptosis and a dose-dependent increase in ROS generation that was enhanced by pretreatment with inflammatory cytokines. Basal levels of ROS were greater in epithelial cells isolated from gastric mucosal biopsy specimens from H. pylori-infected subjects than in cells from uninfected individuals. H. pylori strains bearing the cag pathogenicity island (PAI) induced higher levels of intracellular oxygen metabolites than isogenic cag PAI-deficient mutants. H. pylori infection and hydrogen peroxide exposure resulted in similar patterns of caspase 3 and 8 activation. Antioxidants inhibited both ROS generation and DNA fragmentation by H. pylori. These results indicate that bacterial factors and the host inflammatory response confer oxidative stress to the gastric epithelium during H. pylori infection that may lead to apoptosis.

Heterogeneity in the activity of Mexican Helicobacter pylori strains in gastric epithelial cells and its association with diversity in the cagA gene

Helicobacter pylori CagA is translocated into gastric epithelial cells by a type IV secretion system and interacts with the Src homology 2 phosphatase, altering cell morphology. Multiple EPIYA motifs in CagA are associated with increased activity in cells and with gastric cancer. The aim of this work was to study the heterogeneity in activity in cells of multiple H. pylori single colonies isolated from a single patient and its association with polymorphism in cagA. The presence of cagA, cagE, cagT, and cag10 was studied with 318 H. pylori isolates from the antra and corpora of 18 patients. AGS gastric epithelial cells were infected with 75 isolates, and interleukin-8 (IL-8) secretion, cytoskeletal changes, CagA translocation, and tyrosine phosphorylation were measured. The cagA 3'-variable region was sequenced for 30 isolates to determine the number and types of EPIYA motifs. Isolates from an individual stomach were usually genetically related and had quantitatively similar phenotypic effects on cells (IL-8 induction and cytoskeletal changes). However, strains from different patients with similar CagA EPIYA motif patterns varied widely in these phenotypes. Among isolates with an EPIYA-ABC pattern, the phenotype was variable: IL-8 induction ranged from 200 to 1,200 pg/ml, and morphological changes occurred in 20 to 70% of cells. In several cases, cagA sequence diversity appeared to explain the lack of CagA activity, as isolates with an EPIYA-ACC pattern or a modified B motif had reduced cell activity. cag pathogenicity island-positive H. pylori isolates displayed a high level of heterogeneity in the capacity to induce IL-8 secretion and morphological changes; an absent or modified B motif was associated with low activity.

Helicobacter pylori cag pathogenicity island genes: clinical relevance for peptic ulcer disease development in Brazil

The purpose of this study was to verify whether the presence of any of the Helicobacter pylori cagPAI genes or segments--cagA, cagA promoter, cagE, cagM, tnpB, tnpA, cagT and the left end of the cag II (LEC) region--would be a useful marker for the risk of peptic ulcer disease development. H. pylori DNA extracted from positive urease tests of 150 peptic ulcer patients and 65 dyspeptic controls was analysed by PCR. Duodenal ulcers were present in 110, gastric ulcers in 23 and both gastric and duodenal ulcers in 17 patients. A significant association (P <0.001) was found between a conserved cagPAI and peptic ulcer disease (34 %). The positivity of the cagA gene varied according to the region of the gene that was amplified. The region near to the promoter was present in almost all of the H. pylori isolates (97.2 %). The segment from nt 1764 to 2083 and the extreme right end were frequently deleted in the isolates from the controls (P <0.01). The positivity of the promoter region of cagA and cagT, cagE, cagM and LEC showed a significant difference between the isolates from peptic ulcer patients and from the controls (P <0.01). Patients usually had moderate gastritis; however, the intensity of the active inflammation was higher in the peptic ulcer group (P <0.001). cagT, cagM, LEC and the right end terminus of the cagA-positive H. pylori isolates were associated with a 27-fold, 8-fold, 4-fold and 4-fold risk of peptic ulcer disease, respectively, and may be useful markers to identify individuals at higher risk of peptic ulcer disease development in Brazil.

East Asian-type Helicobacter pylori cytotoxin-associated gene A protein has a more significant effect on growth of rat gastric mucosal cells than the Western type

BACKGROUND AND AIM

Cytotoxin-associated gene A (CagA) protein from H. pylori was reported to be injected into host gastric epithelial cells via a bacterial type IV secretion system, thereby modifying signal transduction. It is classified into two major subtypes, Western and East Asian. The present study aimed to compare the effects of East Asian-type and Western-type CagA on host cell growth.

METHODS

A tetracycline (tet)-off system and cagA genes from Western and East Asian-type H. pylori (NCTC 11637 and F32) were transfected into untransformed rat gastric mucosal (RGM1) cells to establish RGM1-CagA cell lines in which CagA expression could be controlled by tetracycline. These cell lines were used to investigate the effect of CagA protein expression on cell growth with BrdU and water-soluble tetrazolium reagent (WST-8) assays. CagA expression, phosphorylation and extracellular signal-regulated kinase (ERK) activation were examined with immunoprecipitation and Western blotting analysis.

RESULTS

5-Bromo-2'deoxyuridine (BrdU) and WST-8 assays demonstrated significant increases in DNA replication and RGM1 cell growth after CagA protein expression. ERK phosphorylation was enhanced when CagA protein was expressed in RGM1-CagA cells. Moreover, the East Asian-type CagA showed a significantly greater effect on ERK activation and host cell growth than the Western type. PD98059, a mitogen-activated protein kinase kinase (MEK) inhibitor, suppressed ERK phosphorylation and the CagA protein-induced increase in RGM1-CagA cell growth.

CONCLUSIONS

CagA protein expression induces an increase in RGM1-CagA cell proliferation via the mitogen-activated protein kinase (MAPK) signal pathway. The East Asian-type CagA showed a significantly greater effect on cell growth than the Western type, suggesting that the East Asian CagA-positive strain may have an important role in pathogenesis.

The role of Helicobacter pylori CagA in gastric carcinogenesis

Gastric carcinoma is the second most common cause of cancer-related deaths in the world, accounting for more than 400,000 deaths each year. Infection with cagA-positive Helicobacter pylori plays a pivotal role in the development of gastric adenocarcinoma. The cagA gene product CagA is directly delivered into gastric epithelial cells via the type IV secretion system. Following membrane localization and subsequent tyrosine phosphorylation by Src family kinases, CagA interacts with a variety of host cell proteins that are involved in the regulation of cell growth and motility in both phosphorylation-dependent and -independent manners. Of special interest is the interaction of CagA with the SH2 domain-containing tyrosine phosphatase SHP-2, gain-of-function mutations of which have recently been found in human malignancies. CagA binds to and activates SHP-2 in a tyrosine phosphorylation-dependent manner, thereby provoking abnormal activation of Erk MAP kinase while inducing elevated cell motility. Perturbation of SHP-2 and other signaling molecules by H pylori CagA may predispose cells to accumulate multiple genetic and epigenetic changes that promote multistep gastric carcinogenesis. Intriguingly, the structural polymorphism of CagA accounts for the differences in pathophysiological activity of individual CagA proteins, raising the possibility of subclassification of H pylori strains into benign and malignant strains.

Interleukin-8 induction by Helicobacter pylori in gastric epithelial cells is dependent on apurinic/apyrimidinic endonuclease-1/redox factor-1

Helicobacter pylori infection causes inflammation and increases the expression of IL-8 in human gastric epithelial cells. H. pylori activates NF-kappaB and AP-1, essential transcriptional factors in H. pylori-induced IL-8 gene transcription. Although colonization creates a local oxidative stress, the molecular basis for the transition from infection to the expression of redox-sensitive cytokine genes is unknown. We recently reported that the expression of apurinic/apyrimidinic endonuclease-1/redox factor-1 (APE-1/Ref-1), which repairs oxidative DNA damage and reductively activates transcription factors including AP-1 and NF-kappaB, is increased in human gastric epithelia during H. pylori infection. In this study, we examine whether APE-1/Ref-1 functions in the modulation of IL-8 gene expression in H. pylori-infected human gastric epithelial cells. Small interfering RNA-mediated silencing of APE-1/Ref-1 inhibited basal and H. pylori-induced AP-1 and NF-kappaB DNA-binding activity without affecting the nuclear translocation of these transcription factors and also reduced H. pylori-induced IL-8 mRNA and protein. In contrast, overexpression of APE-1/Ref-1 enhanced basal and H. pylori-induced IL-8 gene transcription, and the relative involvement of AP-1 in inducible IL-8 promoter activity was greater in APE-1/Ref-1 overexpressing cells than in cells with basal levels of APE-1/Ref-1. APE-1/Ref-1 inhibition also reduced other H. pylori-induced chemokine expression. By implicating APE-1/Ref-1 as an important regulator of gastric epithelial responses to H. pylori infection, these data elucidate a novel mechanism controlling transcription and gene expression in bacterial pathogenesis.

Strategy to characterize the number and type of repeating EPIYA phosphorylation motifs in the carboxyl terminus of CagA protein in Helicobacter pylori clinical isolates

Cytotoxin-associated gene A (CagA) diversity with regard to EPIYA-A, -B, -C, or -D phosphorylation motifs may play an important role in Helicobacter pylori pathogenesis, and therefore determination of these motifs in H. pylori clinical isolates can become a useful prognostic tool. We propose a strategy for the accurate determination of CagA EPIYA motifs in clinical strains, based upon one-step PCR amplification using primers that flank the EPIYA coding region. We thus analyzed 135 H. pylori isolates derived from 75 adults and 60 children Greek patients. A total of 34 cases were found to be EPIYA PCR negative and were consequently verified as cagA negative by cagA-specific PCR, empty-site cagA PCR, and Western blotting. Sequencing of the remaining 101 PCR-positive amplicons confirmed that an accurate prediction of the number of EPIYA motifs on the basis of size distribution of the PCR products was feasible in all cases. Furthermore, our assay could identify closely related H. pylori subclones within the same patient, harboring different numbers of EPIYA repeats. The prevalence of CagA proteins with three EPIYA motifs (ABC) or four EPIYA motifs (ABCC) was the same within the adult and children groups. However, CagA species with more than four EPIYA motifs were observed exclusively within adults (8.6%), suggesting that CagA-positive strains may acquire additional EPIYA-C motifs throughout adulthood. Our strategy requires no initial cagA screening of the clinical isolates and can accurately predict the number of EPIYA repeats in single or multiple closely related subclones bearing different numbers of EPIYA motifs in their CagA, which may coexist within the same patient.

Helicobacter pylori persistence: an overview of interactions between H. pylori and host immune defenses

Helicobacter pylori is a gram-negative bacterium that persistently colonizes more than half of the global human population. In order to successfully colonize the human stomach, H. pylori must initially overcome multiple innate host defenses. Remarkably, H. pylori can persistently colonize the stomach for decades or an entire lifetime despite development of an acquired immune response. This review focuses on the immune response to H. pylori and the mechanisms by which H. pylori resists immune clearance. Three main sections of the review are devoted to (i) analysis of the immune response to H. pylori in humans, (ii) analysis of interactions of H. pylori with host immune defenses in animal models, and (iii) interactions of H. pylori with immune cells in vitro. The topics addressed in this review are important for understanding how H. pylori resists immune clearance and also are relevant for understanding the pathogenesis of diseases caused by H. pylori (peptic ulcer disease, gastric adenocarcinoma, and gastric lymphoma).

Increased seropositivity of Helicobacter pylori cytotoxin-associated gene-A in Behçet's disease

Behçet's disease is a systemic vasculitic syndrome with unknown etiology. The aim of the present study was to compare the Helicobacter pylori seropositivity and cytotoxin associated gene-A status in patients with Behçet's disease. Ninety-one patients with Behçet's disease and 83 age- and sex-matched persons with or without any gastrointestinal complaints were included in the study. Demographic characteristics and H. pylori IgG, IgM, and cytotoxin-associated gene-A IgG status of the Behçet's disease and the control groups were analyzed. The influence of eradication therapy on clinical findings was also determined. The prevalence of H. pylori IgG seropositivity was slightly but not significantly higher in patients with Behçet's disease compared to the controls [72 (79.1%) vs 56 (67.5%), (p = 0.082)]. The prevalence of cytotoxin-associated gene A positivity was significantly higher in Behçet's disease compared to the controls [59 (64.8.%) vs 32 (38.5%), respectively, (p = 0.002)]. Eradication of H. pylori has significantly decreased clinical manifestations such as oral and genital ulceration, arthritis/arthralgia, and cutaneous findings of Bahçet's disease. Our study indicates that H. pylori may be involved in the pathogenesis of Behçet's disease or disease activity might be enhanced due to induced inflammation or altered immunity.

Inhibitors of Helicobacter pylori ATPase Cagα block CagA transport and cag virulence

With the steadily increasing occurrence of antibiotic resistance in bacteria, there is a great need for new antibacterial compounds. The approach described here involves targeting virulence-related bacterial type IV secretion systems (TFSSs) with small-molecule inhibitors. The cag TFSS of Helicobacter pylori was chosen as a model, and novel inhibitors directed against the cag VirB11-type ATPase Cagα were identified. The cag genes encode proteins that are components of a contact-dependent secretion system used by the bacterium to translocate the effector molecule CagA into host cells. Translocated CagA is associated with severe gastritis, and carcinoma. Furthermore, functional TFSSs and immunodominant CagA play a role in interleukin (IL)-8 induction, which is an important factor for chronic inflammation. Inhibitors of Cagα were identified by high-throughput screening of chemical libraries that comprised 524 400 small molecules. The ATPase activity of Cagα was inhibited by the selected compounds in an in vitro enzymic assay using the purified enzyme. The most active compound, CHIR-1, reduced TFSS function to an extent that cellular effects on AGS cells mediated by CagA were virtually undetectable, while reduced levels of IL-8 induction were observed. Gastric colonization by CHIR-1-pre-treated bacteria was found to be impaired in a dose-dependent manner using a mouse model of infection. Small-molecule Cagα inhibitors, the first described inhibitors of a TFSS, are potential candidates for the development of new antibacterial compounds that may lead to alternative medical treatments. The compounds are expected to impose weak selective pressure, since they target virulence functions. Moreover, the targeted virulence protein is conserved in a variety of bacterial pathogens. Additionally, TFSS inhibitors are potent tools to study the biology of TFSSs.

Characterization of the pilin ortholog of the Helicobacter pylori type IV cag pathogenicity apparatus, a surface-associated protein expressed during infection

The Helicobacter pylori cag pathogenicity island (cag PAI) encodes components of a type IV secretion system (T4SS) involved in host interaction and pathogenicity. Previously, seven cag PAI proteins were identified as homologs of Agrobacterium tumefaciens Vir proteins, which form a paradigm T4SS. The T pilus composed of the processed VirB2 pilin is an external structural part of the A. tumefaciens T4SS. In H. pylori, cag-dependent assembly of pili has not been observed so far, nor has a pilin (VirB2) ortholog been characterized. We have here identified, using a motif-based search, an H. pylori cag island protein (HP0546) that possesses sequence and predicted structural similarities to VirB2-like pilins of other T4SSs. The HP0546 protein displays interstrain variability in its terminal domains. HP0546 was expressed as a FLAG-tagged fusion protein in Escherichia coli, A. tumefaciens, and H. pylori and was detected as either two or three bands of different molecular masses in the insoluble fraction, indicating protein processing. As reported previously, isogenic H. pylori mutants in the putative cag pilin gene had reduced abilities to induce cag PAI-dependent interleukin-8 secretion in gastric epithelial cells. Fractionation analysis of H. pylori, using a specific antiserum raised against an N-terminal HP0546 peptide, showed that the protein is partially surface exposed and that its surface localization depended upon an intact cag system. By immunoelectron microscopy, HP0546 was localized in surface appendages, with surface exposure of an N-terminal epitope. Pronounced strain-to-strain variability of this predicted surface-exposed part of HP0546 indicates a strong selective pressure for variation in vivo.

Helicobacter pylori CagA -- a bacterial intruder conspiring gastric carcinogenesis

Infection with cagA-positive Helicobacter pylori (H. pylori) is associated with the development of gastric adenocarcinoma. The cagA gene product CagA is delivered from the bacterium into the cytoplasm of the bacterium-attached gastric epithelial cell via the type-IV secretion system. Upon membrane localization and subsequent tyrosine phosphorylation by Src family kinases, translocated CagA functions as a scaffolding adaptor that interacts with a number of host proteins involved in cell signaling in both tyrosine phosphorylation-dependent and -independent manners. Of special interest is the interaction of CagA with the SHP-2 tyrosine phosphatase, of which gain-of-function mutations have recently been found in human malignancies. Through the complex formation, SHP-2 is catalytically activated and induces morphological transformation that is associated with increased cell motility. In addition to the perturbation of intracellular signaling, CagA disrupts the apical junctional complex that regulates the cell-cell contact and maintains the integrity of the epithelial structure. These CagA activities may collectively cause cellular dysfunctions that promote accumulation of multiple genetic changes involved in malignant transformation. Further elucidation of host cell signaling targeted by CagA should provide a new paradigm for 'bacterial carcinogenesis' and also give insights into general understanding of inflammation-mediated cancers. Clinically, detailed studies on the relationship between structural diversity and degree of pathogenic activity of CagA should make it possible to identify a high-risk group for gastric carcinoma among H. pylori-infected populations through cagA genotyping.