Helicobacter pylori VacA, a paradigm for toxin multifunctionality

Role of Helicobacter pylori infection in gastric carcinogenesis: Current knowledge and future directions

Helicobacter pylori (H. pylori) plays a role in the pathogenesis of gastric cancer. The outcome of the infection depends on environmental factors and bacterial and host characteristics. Gastric carcinogenesis is a multistep process that is reversible in the early phase of mucosal damage, but the exact point of no return has not been identified. Therefore, two main therapeutic strategies could reduce gastric cancer incidence: (1) eradication of the already present infection; and (2) immunization (prior to or during the course of the infection). The success of a gastric cancer prevention strategy depends on timing because the prevention strategy must be introduced before the point of no return in gastric carcinogenesis. Although the exact point of no return has not been identified, infection should be eradicated before severe atrophy of the gastric mucosa develops. Eradication therapy rates remain suboptimal due to increasing H. pylori resistance to antibiotics and patient noncompliance. Vaccination against H. pylori would reduce the cost of eradication therapies and lower gastric cancer incidence. A vaccine against H. pylori is still a research challenge. An effective vaccine should have an adequate route of delivery, appropriate bacterial antigens and effective and safe adjuvants. Future research should focus on the development of rescue eradication therapy protocols until an efficacious vaccine against the bacterium becomes available.

Helicobacter pylori outer membrane protein Q allele distribution is associated with distinct pathologies in Pakistan

Helicobacter pylori (H. pylori) strains expressing outer membrane protein Q (HopQ) promote adherence to the gastric epithelial cell. We characterized HopQ alleles in relation to H. pylori-related disease, histology and virulence markers. Gastric biopsies were obtained at esophagogastroduodenoscopy from patients with upper gastrointestinal symptoms. H. pylori culture, histology and polymerase chain reaction (PCR) for HopQ types, cagA, cagA-promoter and vacA alleles were performed. DNA extracted was used for PCR. Sequencing of PCR products of HopQ types 1 and 2 was followed by BLAST query. We examined 241 H. pylori isolates. HopQ type 1 was positive in 70 (29%) isolates, type 2 in 60 (25%) isolates, while both type 1 and type 2 in 111 (46%) H. pylori isolates, respectively. Nonulcer dyspepsia (NUD) was associated with HopQ type 2 in 48 (41%) isolates, while gastric carcinoma (GC) in 37 (53%) (P<0.001) with type 1 isolates. Gastric ulcers (GU) were 39 (46%) (P<0.001) in H. pylori infection with multiple HopQ alleles compared to 6 (23%) in HopQ type 1. Multivariate analysis demonstrated that multiple HopQ alleles were associated with GU OR 2.9 (1.07-7.8) (P=0.03). HopQ type 1 was associated with cagA 58 (84%) (P<0.001) and cagA-promoter 58 (83%) (P<0.001) compared to 14 (23%) and 17 (28%) respectively, in type 2. VacAs1a was associated with HopQ type 1 in 59 (84%) isolates compared to HopQ type 2 in 35 (58%) (P=0.002) isolates. VacAm1 was associated with HopQ type 1 in 53 (76%) isolates compared to HopQ type 2 in 32 (53%) (P=0.004) isolates. H. pylori infection with multiple HopQ alleles was predominant. H. pylori infection with single HopQ type 1 was associated with GC in the presence of other H. pylori virulence markers.

Helicobacter pylori VacA induces apoptosis by accumulation of connexin 43 in autophagic vesicles via a Rac1/ERK-dependent pathway

Helicobacter pylori (H. pylori) produces vacuolating cytotoxin (VacA), a potent protein toxin, which is associated with gastric inflammation and ulceration. Recent studies demonstrated that connexins (Cxs), which are responsible for intracellular communication at gap junctions (GJs) as well as cell homeostasis, participate in VacA-induced cell death. We now demonstrate in AZ-521 cells that VacA increased cytoplasmic Cx43, accompanied by LC3-II generation in a time- and dose-dependent manner without induction of Cx43 mRNA expression. Inhibition of VacA-induced Rac1 activity prevented ERK phosphorylation and the increase in Cx43. Suppression of ERK activity and addition of N-acetyl-cysteine inhibited VacA-dependent increase in Cx43 and LC3-II. DIDS, an anion-selective inhibitor, suppressed VacA-dependent increase in Cx43, suggesting that VacA channel activity was involved in this pathway. By confocal microscopy, Cx43 increased by VacA was predominately localized in cholesterol-rich, detergent-resistant membranes including GJs, and a fraction of Cx43 was incorporated in endocytotic vesicles and autophagolysosomes. Accumulation of Cx43 was also observed in gastric mucosa from H. pylori-infected patients compared with healthy controls, suggesting that the pathogen caused a similar effect in vivo. Our findings show that VacA-mediated effects on autophagy inhibits turnover of Cx43, resulting in increased levels in the cytoplasm, leading eventually to apoptotic cell death.

Helicobacter pullorum isolated from fresh chicken meat: antibiotic resistance and genomic traits of an emerging foodborne pathogen

Meat and meat products are important sources of human intestinal infections. We report the isolation of Helicobacter pullorum strains from chicken meat. Bacteria were isolated from 4 of the 17 analyzed fresh chicken meat samples, using a membrane filter method. MIC determination revealed that the four strains showed acquired resistance to ciprofloxacin; one was also resistant to erythromycin, and another one was resistant to tetracycline. Whole-genome sequencing of the four strains and comparative genomics revealed important genetic traits within the H. pullorum species, such as 18 highly polymorphic genes (including a putative new cytotoxin gene), plasmids, prophages, and a complete type VI secretion system (T6SS). The T6SS was found in three out of the four isolates, suggesting that it may play a role in H. pullorum pathogenicity and diversity. This study suggests that the emerging pathogen H. pullorum can be transmitted to humans by chicken meat consumption/contact and constitutes an important contribution toward a better knowledge of the genetic diversity within the H. pullorum species. In addition, some genetic traits found in the four strains provide relevant clues to how this species may promote adaptation and virulence.

Alteration of the Helicobacter pylori membrane proteome in response to changes in environmental salt concentration

PURPOSE

Helicobacter pylori infection and a high dietary salt intake are each risk factors for the development of gastric cancer. We hypothesize that changes in environmental salt concentrations lead to alterations in the H. pylori membrane proteome.

EXPERIMENTAL DESIGN

Label-free and iTRAQ methods were used to identify H. pylori proteins that change in abundance in response to alterations in environmental salt concentrations. In addition, we biotinylated intact bacteria that were grown under high- or low-salt conditions, and thereby analyzed salt-induced changes in the abundance of surface-exposed proteins.

RESULTS

Proteins with increased abundance in response to high salt conditions included CagA, the outer membrane protein HopQ, and fibronectin domain-containing protein HP0746. Proteins with increased abundance in response to low salt conditions included VacA, two VacA-like proteins (ImaA and FaaA), outer-membrane iron transporter FecA3, and several proteins involved in flagellar activity. Consistent with the proteomic data, bacteria grown in high salt conditions exhibited decreased motility compared to bacteria grown in lower salt conditions.

CONCLUSION AND CLINICAL RELEVANCE

Alterations in the H. pylori membrane proteome in response to high salt conditions may contribute to the increased risk of gastric cancer associated with a high salt diet.

Helicobacter pylori virulence factors in development of gastric carcinoma

Helicobacter pylori plays a vital role in the pathogenesis of gastric carcinoma. However, only a relatively small proportion of individuals infected with H. pylori develop gastric carcinoma. Differences in the incidence of gastric carcinoma among infected individuals can be explained, at least partly, by the different genotypes of H. pylori virulence factors. Thus far, many virulence factors of H. pylori, such as Cag PAI, VacA, OMPs and DupA, have been reported to be involved in the development of gastric cancer. The risk of developing gastric cancer during H. pylori infection is affected by specific host-microbe interactions that are independent of H. pylori virulence factors. In this review, we discuss virulence factors of H. pylori and their role in the development of gastric carcinoma that will provide further understanding of the biological interactions of H. pylori with the host.

Histological variety of gastric carcinoma and Helicobacter pylori cagA and vacA polymorphism

BACKGROUND

Helicobacter pylori infection may increase the risk of both histotypes of gastric carcinoma (GC): intestinal (IGC) and diffuse (DGC). Polymorphism of the main H. pylori virulence factors, cagA and vacA, could have a different impact on the histological variety of GC.

METHODS

Two hundred and twenty-six H. pylori colonies were examined from 28 GC patients: 15 with IGC and 13 with DGC. DNA was extracted from bacteria and a PCR was performed using primers specific for cagA, the 3' cagA variable region and s and m regions of vacA.

RESULTS

There were 214 cagA+ strains and 55.61% of them were isolated from IGC cases; there were 12 cagA- colonies and they were all isolated from DGC (P<0.001). Most patients were infected by strains with more than one cagA structural type. No strains with a particular cagA type were found to be significantly more frequent in either histological variety of GC. A percentage of 43.90 of strains with vacA subtype s1/m1 were isolated from IGC, whereas 80.95% of vacA subtype s1/m2 strains were isolated from DGC cases (P<0.001).

CONCLUSION

Polymorphism of the main virulence genes of H. pylori may play different roles in the pathogenesis of IGC and DGC.

Molecular Pathogenesis of Helicobacter pylori-Related Gastric Cancer

Helicobacter pylori infection plays a crucial role in gastric carcinogenesis. H pylori exerts oncogenic effects on gastric mucosa through complex interaction between bacterial virulence factors and host inflammatory responses. On the other hand, gastric cancer develops via stepwise accumulation of genetic and epigenetic alterations in H pylori-infected gastric mucosa. Recent comprehensive analyses of gastric cancer genomes indicate a multistep process of genetic alterations as well as possible molecular mechanisms of gastric carcinogenesis. Both genetic processes of gastric cancer development and molecular oncogenic pathways related to H pylori infection are important to completely understand the pathogenesis of H pylori-related gastric cancer.

Effect of bacterial and host factors on Helicobacter pylori eradication therapy

INTRODUCTION

A clearer understanding of the factors affecting the cure rate of Helicobacter pylori infection might lead to the development of novel prevention strategies and therapeutic targets.

AREAS COVERED

This review covers two important issues that affect the eradication of H. pylori: bacterial and host factors. Several virulence factors have been shown to be predictors for gastroduodenal diseases. Successful treatment of H. pylori infection also depends on host genetic factors such as CYP2C19 and IL-1B. The latest evidence on host genetic factors is discussed.

EXPERT OPINION

The authors identify three main targets for achieving effective eradication therapy. The first therapeutic target is to identify counter measures for antibiotic-resistant H. pylori strains. Thus, antibiotic susceptibility should be checked in all patients, ideally, before the start of eradication treatment. The second therapeutic target is the inhibition of acid suppression. Maintaining a high intragastric pH for 24 h increases the effectiveness of some antibiotics and the eradication effects for H. pylori. The third therapeutic target is to identify high-risk groups; the CYP2C19 and IL-1B polymorphisms are candidates for significant risk factors. A personalized medical approach will likely increase the cure rate of H. pylori infection.

Characterization of Helicobacter pylori VacA-containing vacuoles (VCVs), VacA intracellular trafficking and interference with calcium signalling in T lymphocytes

The human pathogen Helicobacter pylori colonizes half of the global population. Residing at the stomach epithelium, it contributes to the development of diseases such as gastritis, duodenal and gastric ulcers, and gastric cancer. A major factor is the secreted vacuolating toxin VacA, which forms anion-selective channels in the endosome membrane that cause the compartment to swell, but the composition and purpose of the resulting VacA-containing vacuoles (VCVs) are still unknown. VacA exerts influence on the host immune response in various ways, including inhibition of T-cell activation and proliferation and suppression of the host immune response. In this study, for the first time the composition of VCVs from T cells was comprehensively analysed to investigate VCV function. VCVs were successfully isolated via immunomagnetic separation, and the purified vacuoles were analysed by mass spectrometry. We detected a set of 122 VCV-specific proteins implicated among others in immune response, cell death and cellular signalling processes, all of which VacA is known to influence. One of the individual proteins studied further was stromal interaction molecule (STIM1), a calcium sensor residing in the endoplasmic reticulum (ER) that is important in store-operated calcium entry. Live cell imaging microscopy data demonstrated colocalization of VacA with STIM1 in the ER and indicated that VacA may interfere with the movement of STIM1 towards the plasma membrane-localized calcium release activated calcium channel protein ORAI1 in response to Ca(2+) store depletion. Furthermore, VacA inhibited the increase of cytosolic-free Ca(2+) in the Jurkat E6-1 T-cell line and human CD4(+) T cells. The presence of VacA in the ER and its trafficking to the Golgi apparatus was confirmed in HeLa cells, identifying these two cellular compartments as novel VacA target structures.

Instrumental Role of Helicobacter pylori γ-Glutamyl Transpeptidase in VacA-Dependent Vacuolation in Gastric Epithelial Cells

Helicobacter pylori causes cellular vacuolation in host cells, a cytotoxic event attributed to vacuolating cytotoxin (VacA) and the presence of permeant weak bases such as ammonia. We report here the role of γ-glutamyl transpeptidase (GGT), a constitutively expressed secretory enzyme of H. pylori, in potentiating VacA-dependent vacuolation formation in H. pylori-infected AGS and primary gastric cells. The enhancement is brought about by GGT hydrolysing glutamine present in the extracellular medium, thereby releasing ammonia which accentuates the VacA-induced vacuolation. The events of vacuolation in H. pylori wild type (WT)- and Δggt-infected AGS cells were first captured and visualized by real-time phase-contrast microscopy where WT was observed to induce more vacuoles than Δggt. By using semi-quantitative neutral red uptake assay, we next showed that Δggt induced significantly less vacuolation in AGS and primary gastric epithelial cells as compared to the parental strain (P<0.05) indicating that GGT potentiates the vacuolating effect of VacA. Notably, vacuolation induced by WT was significantly reduced in the absence of GGT substrate, glutamine (P<0.05) or in the presence of a competitive GGT inhibitor, serine-borate complex. Furthermore, the vacuolating ability of Δggt was markedly restored when co-incubated with purified recombinant GGT (rGGT), although rGGT itself did not induce vacuolation independently. Similarly, the addition of exogenous ammonium chloride as a source of ammonia also rescued the ability of Δggt to induce vacuolation. Additionally, we also show that monoclonal antibodies against GGT effectively inhibited GGT activity and successfully suppressed H. pylori-induced vacuolation. Collectively, our results clearly demonstrate that generation of ammonia by GGT through glutamine hydrolysis is responsible for enhancing VacA-dependent vacuolation. Our findings provide a new perspective on GGT as an important virulence factor and a promising target in the management of H. pylori-associated gastric diseases.

Recombinant human lactoferrin enhances the efficacy of triple therapy in mice infected with Helicobacter pylori

Helicobacter pylori (H. pylori) is a life-threatening pathogen which causes chronic gastritis, gastric ulcers and even stomach cancer. Treatment normally involves bacterial eradication; however, this type of treatment only has a rate of effectiveness of <80%. Thus, it is a matter of some urgency to develop new therapeutic strategies. Lactoferrin, a member of the transferrin family of iron-binding proteins, has been proven to be effective in removing a vast range of pathogens, including H. pylori. In the present study, we examined the effectiveness of recombinant human lactoferrin (rhLf) isolated from transgenic goats as a treatment for H. pylori in vitro and in vivo. For the in vivo experiments, BALB/c mice received an intragastric administration of 0.1 ml of a suspension of H. pylori. The mice were then divided into 4 groups: group A, treated with saline; group B, treated with 1.5 g of rhLF; group C, treated with the standard triple therapy regimen; and group D, treated with the standard triple therapy regimen plus.5 g of rhLF. Following sacrifice, the stomach tissues of the mice were histologically examined for the presence of bacteria. For the in vitro experiments, the bacteria were cultured in BHI broth and RT-qPCR and western blot analysis were carried out to determine the mRNA and protein levels of virulence factors (CagA and VacA) in the cultures. Our results revealed that rhLf not only inhibited the growth of H. pylori, but also suppressed the expression of two major virulence factors. Moreover, rhLf markedly increased bacterial eradication and effectively reduced the inflammatory response when combined with the standard triple therapy regimen. These results provide evidence supporting the use of rhLF as an adjuvant to traditional therapeutic strategies in the treatment of H. pylori.

Helicobacter pylori TlyA Forms Amyloid-like Aggregates with Potent Cytotoxic Activity

Helicobacter pylori is a potent human gastric pathogen. It is known to be associated with several gastroenteric disorders, including gastritis, peptic ulcer, and gastric cancer. The H. pylori genome encodes a gene product TlyA that has been shown to display potent membrane damaging properties and cytotoxic activity. On the basis of such properties, TlyA is considered as a potential virulence factor of H. pylori. In this study, we show that the H. pylori TlyA protein has a strong propensity to convert into the amyloid-like aggregated assemblies, upon exposure to elevated temperatures. Even at the physiological temperature of 37 °C, TlyA shows a strong amyloidogenic property. TlyA aggregates that are generated upon exposure at temperatures of ≥37 °C show prominent binding to dyes like thioflavin T and Nile Red. Transmission electron microscopy also demonstrates the presence of typical amyloid-like fibrils in the TlyA aggregates generated at 37 °C. Conversion of TlyA into the amyloid-like aggregates is found to be associated with major alterations in the secondary and tertiary structural organization of the protein. Finally, our study shows that the preformed amyloid-like aggregates of TlyA are capable of exhibiting potent cytotoxic activities against human gastric adenocarcinoma cells. Altogether, such a propensity of H. pylori TlyA to convert into the amyloid-like aggregated assemblies with cytotoxic activity suggests potential implications for the virulence functionality of the protein.

Morphological changes in human gastric epithelial cells induced by nuclear targeting of Helicobacter pylori urease subunit A

Nuclear targeting of bacterial proteins and their pathological effects on host cells are an emerging pathogenic mechanism in bacteria. We have previously reported that urease subunit A (UreA) of Helicobacter pylori targets the nuclei of COS-7 cells through nuclear localization signals (NLSs). This study further investigated whether UreA of H. pylori targets the nuclei of gastric epithelial cells and then induces molecular and cellular changes in the host cells. H. pylori 26695 strain produced and secreted outer membrane vesicles (OMVs). UreA was translocated into gastric epithelial AGS cells through outer membrane vesicles (OMVs) and then targeted the nuclei of AGS cells. Nuclear targeting of rUreA did not induce host cell death, but resulted in morphological changes, such as cellular elongation, in AGS cells. In contrast, AGS cells treated with rUreA?NLS proteins did not show this morphological change. Next generation sequencing revealed that nuclear targeting of UreA differentially regulated 102 morphogenesis- related genes, of which 67 and 35 were up-regulated and down-regulated, respectively. Our results suggest that nuclear targeting of H. pylori UreA induces both molecular and cellular changes in gastric epithelial cells.

Role of the Wnt/β-catenin pathway in gastric cancer: An in-depth literature review

Gastric cancer remains one of the most common cancers worldwide and one of the leading cause for cancer-related deaths. Gastric adenocarcinoma is a multifactorial disease that is genetically, cytologically and architecturally more heterogeneous than other gastrointestinal carcinomas. The aberrant activation of the Wnt/β-catenin signaling pathway is involved in the development and progression of a significant proportion of gastric cancer cases. This review focuses on the participation of the Wnt/β-catenin pathway in gastric cancer by offering an analysis of the relevant literature published in this field. Indeed, it is discussed the role of key factors in Wnt/β-catenin signaling and their downstream effectors regulating processes involved in tumor initiation, tumor growth, metastasis and resistance to therapy. Available data indicate that constitutive Wnt signalling resulting from Helicobacter pylori infection and inactivation of Wnt inhibitors (mainly by inactivating mutations and promoter hypermethylation) play an important role in gastric cancer. Moreover, a number of recent studies confirmed CTNNB1 and APC as driver genes in gastric cancer. The identification of specific membrane, intracellular, and extracellular components of the Wnt pathway has revealed potential targets for gastric cancer therapy. High-throughput “omics” approaches will help in the search for Wnt pathway antagonist in the near future.

Lysinibacillus sphaericus binary toxin induces apoptosis in susceptible Culex quinquefasciatus larvae

During sporulation, a Gram-positive bacterium Lysinibacillus sphaericus (Ls) produces the mosquito larvicidal binary toxin composed of 2 subunits, BinA and BinB. Full toxicity against Culex and Anopheles mosquito larvae is achieved when both subunits are administered together at equimolar amounts. Although cellular responses to Bin toxin have been reported in previous studies, it remains essential to extensively examine the cytopathic effects in vivo to define the underlying mechanism of larval death. In this study, 4th instar Culex quinquefasciatus larvae fed with different doses of Bin toxin were analyzed both for ultrastructural as well as biochemical effects. Typical morphological changes consistent with apoptosis were observed in mosquito larvae exposed to Bin toxin, including mitochondrial swelling, chromatin condensation, cytoplasmic vacuolization and apoptotic cell formation. Bin toxin also induced the activation of caspase-9 and caspase-3 in larval midgut cells. Our current observations thus suggest that Bin toxin triggers apoptosis via an intrinsic or mitochondrial pathway in vivo, possibly contributing to larval death.

Interplay of the Gastric Pathogen Helicobacter pylori with Toll-Like Receptors

Toll-like receptors (TLRs) are crucial for pathogen recognition and downstream signaling to induce effective immunity. The gastric pathogen Helicobacter pylori is a paradigm of persistent bacterial infections and chronic inflammation in humans. The chronicity of inflammation during H. pylori infection is related to the manipulation of regulatory cytokines. In general, the early detection of H. pylori by TLRs and other pattern recognition receptors (PRRs) is believed to induce a regulatory cytokine or chemokine profile that eventually blocks the resolution of inflammation. H. pylori factors such as LPS, HSP-60, NapA, DNA, and RNA are reported in various studies to be recognized by specific TLRs. However, H. pylori flagellin evades the recognition of TLR5 by possessing a conserved N-terminal motif. Activation of TLRs and resulting signal transduction events lead to the production of pro- and anti-inflammatory mediators through activation of NF-κB, MAP kinases, and IRF signaling pathways. The genetic polymorphisms of these important PRRs are also implicated in the varied outcome and disease progression. Hence, the interplay of TLRs and bacterial factors highlight the complexity of innate immune recognition and immune evasion as well as regulated processes in the progression of associated pathologies. Here we will review this important aspect of H. pylori infection.

Prevalence of Helicobacter pylori vacA, cagA, and iceA Genotypes in Cuban Patients with Upper Gastrointestinal Diseases

Virulence factors of Helicobacter pylori can predict the development of different gastroduodenal diseases. There are scarce reports in Cuba about H. pylori isolates genotyping. The aim of the present investigation was to identify allelic variation of the virulence genes vacA, cagA, and iceA in sixty-eight patients diagnosed as H. pylori positive by culture. In seven out of 68 patients, strains from both gastric regions were obtained and considered independent. DNA was extracted from all the H. pylori strains and evaluated by PCR-genotyping. The vacA s1 allele, cagA gene, and iceA2 allele were the most prevalent (72.0%, 56.0%, and 57.3%, respectively). Alleles from m-region showed a similar frequency as s1a and s1b subtypes. The presence of multiple H. pylori genotypes in a single biopsy and two gastric region specimens were found. Significant statistical association was observed between iceA2 allele and patients with non-peptic ulcer dyspepsia (NUD) (P = 0.037) as well as virulence genotypes (s1, s1m2) and patients over 40 years old (P < 0.05). In conclusion, the results demonstrated a high prevalence of H. pylori virulent genotypes in Cuban patients over 40 years old while iceA2 alleles demonstrated a good specificity in patients with NUD.

Helicobacter pylori cag pathogenicity island's role in B7-H1 induction and immune evasion

During Helicobacter pylori (H. pylori) infection CD4⁺ T cells in the gastric lamina propria are hyporesponsive and polarized by Th1/Th17 cell responses controlled by T_reg cells. We have previously shown that H. pylori upregulates B7-H1 expression on GEC, which, in turn, suppress T cell proliferation, effector function, and induce T_reg cells in vitro. In this study, we investigated the underlying mechanisms and the functional relevance of B7-H1 induction by H. pylori infection to chronic infection. Using H. pylori wild type (WT), cag pathogenicity island (cag PAI^-) and cagA^- isogenic mutant strains we demonstrated that H. pylori requires its type 4 secretion system (T4SS) as well as its effector protein CagA and peptidoglycan (PG) fragments for B7-H1 upregulation on GEC. Our study also showed that H. pylori uses the p38 MAPK pathway to upregulate B7-H1 expression in GEC. In vivo confirmation was obtained when infection of C57BL/6 mice with H. pylori PMSS1 strain, which has a functional T4SS delivery system, but not with H. pylori SS1 strain lacking a functional T4SS, led to a strong upregulation of B7-H1 expression in the gastric mucosa, increased bacterial load, induction of T_reg cells in the stomach, increased IL-10 in the serum. Interestingly, B7-H1^-/- mice showed less T_reg cells and reduced bacterial loads after infection. These studies demonstrate how H. pylori T4SS components activate the p38 MAPK pathway, upregulate B7-H1 expression by GEC, and cause T_reg cell induction; thus, contribute to establishing a persistent infection characteristic of H. pylori.

Relationship between tobacco, cagA and vacA i1 virulence factors and bacterial load in patients infected by Helicobacter pylori

Background and Aim

Several biological and epidemiological studies support a relationship between smoking and Helicobacter pylori (H. pylori) to increase the risk of pathology. However, there have been few studies on the potential synergistic association between specific cagA and vacA virulence factors and smoking in patients infected by Helicobacter pylori. We studied the relationship between smoking and cagA, vacA i1 virulence factors and bacterial load in H. pylori infected patients.

Methods

Biopsies of the gastric corpus and antrum from 155 consecutive patients in whom there was clinical suspicion of infection by H. pylori were processed. In 106 patients H. pylori infection was detected. Molecular methods were used to quantify the number of microorganisms and presence of cagA and vacA i1 genes. A standardized questionnaire was used to obtain patients’ clinical data and lifestyle variables, including tobacco and alcohol consumption. Adjusted Odds Ratios (OR_adjusted) were estimated by unconditional logistic regression.

Results

cagA was significantly associated with active-smoking at endoscope: OR_adjusted 4.52. Evidence of association was found for vacA i1 (OR_adjusted 3.15). Bacterial load was higher in active-smokers, although these differences did not yield statistical significance (median of 262.2 versus 79.4 copies of H. pylori per cell).

Conclusions

The association between smoking and a higher risk of being infected by a virulent bacterial population and with higher bacterial load, support a complex interaction between H. pylori infection and environmental factors.

Relationship between Helicobacter pylori infection and gastric cancer

Gastric cancer is one of the most common malignancies worldwide, and Helicobacter pylori (H. pylori) infection is the most important risk factor. More than 50% of the world population is infected by H. pylori, but less than 2% develop gastric cancer. Other risk factors like host and environmental factors also play a role in the occurrence of gastric cancer. The pathogenesis of gastric cancer is a multi-factorial and multi-step process, and its outcome is influenced by a combination of host, bacterial, and environmental factors.

Gastric cancer review

Gastric cancer is an aggressive disease that continues to have a daunting impact on global health. Despite an overall decline in incidence over the last several decades, gastric cancer remains the fourth most common type of cancer and is the second leading cause of cancer-related death worldwide. This review aims to discuss the global distribution of the disease and the trend of decreasing incidence of disease, delineate the different pathologic subtypes and their immunohistochemical (IHC) staining patterns and molecular signatures and mutations, explore the role of the pathogen H. pylori in tumorgenesis, discuss the increasing incidence of the disease in the young, western populations and define the role of biologic agents in the treatment of the disease.

Helicobacter pylori induces vascular endothelial growth factor production in gastric epithelial cells through hypoxia-inducible factor-1α-dependent pathway

BACKGROUND

Although Helicobacter pylori have been known to induce vascular endothelial growth factor (VEGF) production in gastric epithelial cells, the precise mechanism for cellular signaling is incompletely understood. In this study, we investigated the role of bacterial virulence factor and host cellular signaling in VEGF production of H. pylori-infected gastric epithelial cells.

MATERIALS AND METHODS

We evaluated production of VEGF, activation of nuclear factor nuclear factor-kappaB (NF-κB) and mitogen-activated protein kinases (MAPKs) and hypoxia-inducible factor-1α (HIF-1α) stabilization in gastric epithelial cells infected with H. pylori WT or isogenic mutants deficient in type IV secretion system (T4SS).

RESULTS

H. pylori induced VEGF production in gastric epithelial cells via both T4SS-dependent and T4SS-independent pathways, although T4SS-independent pathway seems to be the dominant signaling. The inhibitor assay implicated that activation of NF-κB and MAPKs is dispensable for H. pylori-induced VEGF production in gastric epithelial cells. H. pylori led to HIF-1α stabilization in gastric epithelial cells independently of T4SS, NF-κB, and MAPKs, which was essential for VEGF production in these cells. N-acetyl-cysteine (NAC), a reactive oxygen species (ROS) inhibitor, treatment impaired H. pylori-induced HIF-1α stabilization and VEGF production in gastric epithelial cells.

CONCLUSION

We defined the important role of ROS-HIF-1α axis in VEGF production of H. pylori-infected gastric epithelial cells, and bacterial T4SS has a minor role in H. pylori-induced VEGF production of gastric epithelial cells.

Beyond the stomach: An updated view of Helicobacter pylori pathogenesis, diagnosis, and treatment

Helicobacter pylori (H. pylori) is an extremely common, yet underappreciated, pathogen that is able to alter host physiology and subvert the host immune response, allowing it to persist for the life of the host. H. pylori is the primary cause of peptic ulcers and gastric cancer. In the United States, the annual cost associated with peptic ulcer disease is estimated to be $6 billion and gastric cancer kills over 700000 people per year globally. The prevalence of H. pylori infection remains high (> 50%) in much of the world, although the infection rates are dropping in some developed nations. The drop in H. pylori prevalence could be a double-edged sword, reducing the incidence of gastric diseases while increasing the risk of allergies and esophageal diseases. The list of diseases potentially caused by H. pylori continues to grow; however, mechanistic explanations of how H. pylori could contribute to extragastric diseases lag far behind clinical studies. A number of host factors and H. pylori virulence factors act in concert to determine which individuals are at the highest risk of disease. These include bacterial cytotoxins and polymorphisms in host genes responsible for directing the immune response. This review discusses the latest advances in H. pylori pathogenesis, diagnosis, and treatment. Up-to-date information on correlations between H. pylori and extragastric diseases is also provided.

Helicobacter pylori cell translocating kinase (CtkA/JHP0940) is pro-apoptotic in mouse macrophages and acts as auto-phosphorylating tyrosine kinase

The Helicobacter pylori gene JHP0940 has been shown to encode a serine/threonine kinase which can induce cytokines in gastric epithelial cells relevant to chronic gastric inflammation. Here we demonstrate that JHP0940 can be secreted by the bacteria, triggers apoptosis in cultured mouse macrophages and acts as an auto-phosphorylating tyrosine kinase. Recombinant JHP0940 protein was found to decrease the viability of RAW264.7 cells (a mouse macrophage cell line) up to 55% within 24h of co-incubation. The decreased cellular viability was due to apoptosis, which was confirmed by TUNEL assay and Fas expression analysis by flow-cytometry. Further, we found that caspase-1 and IL-1beta were activated upon treatment with JHP0940. These results point towards possible action through the host inflammasome. Our in vitro studies using tyrosine kinase assays further demonstrated that JHP0940 acts as auto-phosphorylating tyrosine kinase and induces pro-inflammatory cytokines in RAW264.7 cells. Upon exposure with JHP0940, these cells secreted IL-1beta, TNF-alpha and IL-6, in a dose- and time-dependent manner, as detected by ELISA and transcript profiling by q-RT-PCR. The pro-inflammatory, pro-apoptotic and other regulatory responses triggered by JHP0940 lead to the assumption of its possible role in inducing chronic inflammation for enhanced bacterial persistence and escape from host innate immune responses by apoptosis of macrophages.

Xenophagy in Helicobacter pylori- and Epstein-Barr virus-induced gastric cancer

Helicobacter pylori and Epstein-Barr virus (EBV) account for roughly 80% and 10%, respectively, of gastric carcinomas worldwide. Autophagy is an evolutionarily conserved and intricately regulated cellular process that involves the sequestration of cytoplasmic proteins and organelles into double-membrane autophagosomes that eventually fuse with lysosomes for degradation of the engulfed content. Emerging evidence indicates that xenophagy, a form of selective autophagy, plays a crucial role in the pathogenesis of H. pylori- and EBV-induced gastric cancer. Xenophagy specifically recognizes intracellular H. pylori and EBV and physically targets these pathogens to the autophagosomal-lysosomal pathway for degradation. In this connection, H. pylori or EBV-induced dysregulation of autophagy may be causally linked to gastric tumourigenesis and therefore can be exploited as therapeutic targets. This review will discuss how H. pylori and EBV infection activate autophagy and how these pathogens evade recognition and degradation by the autophagic pathway. Elucidating the molecular aspects of H. pylori- and EBV-induced autophagy will help us better understand the pathogenesis of gastric cancer and promote the development of autophagy modulators as antimicrobial agents.

Inhibiting Helicobacter pylori HtrA protease by addressing a computationally predicted allosteric ligand binding site

Helicobacter pylori is associated with inflammatory diseases and can cause gastric cancer and mucosa-associated lymphoma. One of the bacterium's key proteins is high temperature requirement A (HpHtrA) protein, an extracellular serine protease that cleaves E-cadherin of gastric epithelial cells, which leads to loss of cell-cell adhesion. Inhibition of HpHtrA may constitute an intervention strategy against H. pylori infection. Guided by the computational prediction of hypothetical ligand binding sites on the surface of HpHtrA, we performed residue mutation experiments that confirmed the functional relevance of an allosteric region. We virtually screened for potential ligands addressing this surface cleft located between the catalytic and PDZ1 domains. Our receptor-based computational method represents protein surface pockets in terms of graph frameworks and retrieves small molecules that satisfy the constraints given by the pocket framework. A new chemical entity was identified that blocked E-cadherin cleavage in vitro by direct binding to HpHtrA, and efficiently blocked pathogen transmigration across the gastric epithelial barrier. A preliminary crystal structure of HpHtrA confirms the validity of a comparative "homology" model of the enzyme, which we used for the computational study. The results of this study demonstrate that addressing orphan protein surface cavities of target macromolecules can lead to new bioactive ligands.

Helicobacter pylori TlyA agglutinates liposomes and induces fusion and permeabilization of the liposome membranes

Helicobacter pylori TlyA is a pore-forming hemolysin with potent cytotoxic activity. To explore the potential membrane-damaging activity of H. pylori TlyA, we have studied its interaction with the synthetic liposome vesicles. In our study, H. pylori TlyA shows a prominent ability to associate with the liposome vesicles without displaying an obligatory requirement for any protein receptor on the liposome membranes. Interaction of TlyA triggers agglutination of the liposome vesicles. Such agglutinating activity of TlyA could also be observed with erythrocytes before the induction of its pore-forming hemolytic activity. In addition to its agglutinating activity against liposomes, TlyA also induces fusion and disruption of the liposome membranes. Altogether, our study highlights novel membrane-damaging properties of H. pylori TlyA that have not been documented previously with any other TlyA family protein.

The focal complex of epithelial cells provides a signalling platform for interleukin-8 induction in response to bacterial pathogens

Bacterial pathogens can induce an inflammatory response from epithelial tissues due to secretion of the pro-inflammatory chemokine interleukin-8 (IL-8). Many bacterial pathogens manipulate components of the focal complex (FC) to induce signalling events in host cells. We examined the interaction of several bacterial pathogens with host cells, including Campylobacter jejuni, to determine if the FC is required for induction of chemokine signalling in response to bacterial pathogens. Our data indicate that secretion of IL-8 is triggered by C. jejuni, Helicobacter pylori and Salmonella enterica serovar Typhimurium in response to engagement of β1 integrins. Additionally, we found that the secretion of IL-8 from C. jejuni infected epithelial cells requires FAK, Src and paxillin, which in turn are necessary for Erk 1/2 recruitment and activation. Targeting the FC component paxillin with siRNA prevented IL-8 secretion from cells infected with several bacterial pathogens, including C. jejuni, Helicobacter pylori, Salmonella enterica serovar Typhimurium, Staphylococcus aureus, Pseudomonas aeruginosa, and Vibrio parahaemolyticus. Our findings indicate that maximal IL-8 secretion from epithelial cells in response to bacterial infection is dependent on the FC. Based on the commonality of the host response to bacterial pathogens, we propose that the FC is a signalling platform for an epithelial cell response to pathogenic organisms.

Role of γ-glutamyltranspeptidase in the pathogenesis of Helicobacter pylori infection

γ-Glutamyltranspeptidase and asparaginase have been shown to play important roles in Helicobacter pylori colonization and cell death induced by H. pylori infection. In this study, the association of γ-glutamyltranspeptidase and asparaginase was elucidated by comparing activities of both deamidases in H. pylori strains from patients with chronic gastritis, gastric and duodenal ulcers, and gastric cancer. γ-Glutamyltranspeptidase activities in H. pylori strains from patients with gastric cancer were significantly higher than in those from patients with chronic gastritis or gastric ulcers. There was a wide range of asparaginase activities in H. pylori strains from patients with gastric cancer and these were not significantly than those from patients with other diseases. To identify the contributions of γ-glutamyltranspeptidase and asparaginase to gastric cell inflammation, human gastric epithelial cells (AGS line) were infected with H. pylori wild-type and knockout strains and inflammatory responses evaluated by induction of interleukin-8 (IL-8). IL-8 response was significantly decreased by knockout of the γ-glutamyltranspeptidase-encoding gene but not by knockout of the asparaginase-encoding gene. Additionally, IL-8 induction by infection with the H. pylori wild-type strain was significantly decreased by adding glutamine during infection. These findings indicate that IL-8 induction caused by γ-glutamyltranspeptidase activity in H. pylori is mainly attributable to depletion of glutamine. These data suggest that γ-glutamyltranspeptidase plays a significant role in the chronic inflammation caused by H. pylori infection.

Gastrointestinal malignancy and the microbiome

Microbial species participate in the genesis of a substantial number of malignancies-in conservative estimates, at least 15% of all cancer cases are attributable to infectious agents. Little is known about the contribution of the gastrointestinal microbiome to the development of malignancies. Resident microbes can promote carcinogenesis by inducing inflammation, increasing cell proliferation, altering stem cell dynamics, and producing metabolites such as butyrate, which affect DNA integrity and immune regulation. Studies in human beings and rodent models of cancer have identified effector species and relationships among members of the microbial community in the stomach and colon that increase the risk for malignancy. Strategies to manipulate the microbiome, or the immune response to such bacteria, could be developed to prevent or treat certain gastrointestinal cancers.

Analysis of surface-exposed outer membrane proteins in Helicobacter pylori

More than 50 Helicobacter pylori genes are predicted to encode outer membrane proteins (OMPs), but there has been relatively little experimental investigation of the H. pylori cell surface proteome. In this study, we used selective biotinylation to label proteins localized to the surface of H. pylori, along with differential detergent extraction procedures to isolate proteins localized to the outer membrane. Proteins that met multiple criteria for surface-exposed outer membrane localization included known adhesins, as well as Cag proteins required for activity of the cag type IV secretion system, putative lipoproteins, and other proteins not previously recognized as cell surface components. We identified sites of nontryptic cleavage consistent with signal sequence cleavage, as well as C-terminal motifs that may be important for protein localization. A subset of surface-exposed proteins were highly susceptible to proteolysis when intact bacteria were treated with proteinase K. Most Hop and Hom OMPs were susceptible to proteolysis, whereas Hor and Hof proteins were relatively resistant. Most of the protease-susceptible OMPs contain a large protease-susceptible extracellular domain exported beyond the outer membrane and a protease-resistant domain at the C terminus with a predicted β-barrel structure. These features suggest that, similar to the secretion of the VacA passenger domain, the N-terminal domains of protease-susceptible OMPs are exported through an autotransporter pathway. Collectively, these results provide new insights into the repertoire of surface-exposed H. pylori proteins that may mediate bacterium-host interactions, as well as the cell surface topology of these proteins.

Methuosis: nonapoptotic cell death associated with vacuolization of macropinosome and endosome compartments

Apoptosis is the most widely recognized form of physiological programmed cell death. During the past three decades, various nonapoptotic forms of cell death have gained increasing attention, largely because of their potential importance in pathological processes, toxicology, and cancer therapy. A recent addition to the panoply of cell death phenotypes is methuosis. The neologism is derived from the Greek methuo (to drink to intoxication) because the hallmark of this form of cell death is displacement of the cytoplasm by large fluid-filled vacuoles derived from macropinosomes. The demise of the cell resembles many forms of necrosis, insofar as there is a loss of metabolic capacity and plasma membrane integrity, without the cell shrinkage and nuclear fragmentation associated with apoptosis. Methuosis was initially defined in glioblastoma cells after ectopic expression of activated Ras, but recent reports have described small molecules that can induce the features of methuosis in a broad spectrum of cancer cells, including those that are resistant to conventional apoptosis-inducing drugs. This review summarizes the available information about the distinguishing morphological characteristics and underlying mechanisms of methuosis. We compare and contrast methuosis with other cytopathological conditions in which accumulation of clear cytoplasmic vacuoles is a prominent feature. Finally, we highlight key questions that need to be answered to determine whether methuosis truly represents a unique form of regulated cell death.

Connexins in respiratory and gastrointestinal mucosal immunity

The mucosal lining forms the physical and chemical barrier that protects against pathogens and hostile particles and harbors its own population of bacteria, fungi and archea, known as the microbiota. The immune system controls tolerance of this population of microorganisms that have proven to be beneficial for its host. Keeping its physical integrity and a correct balance with the microbiota, the mucosa preserves its homeostasis and its protective function and maintains host's health. However, in some conditions, pathogens may succeed in breaching mucosal homeostasis and successfully infecting the host. In this review we will discuss the role the mucosa plays in the defense against bacterial pathogens by considering the gap junction protein connexins. We will detail their implication in mucosal homeostasis and upon infection with bacteria in the respiratory and the gastrointestinal tracts.

Susceptibility to Helicobacter pylori infection: results of an epidemiological investigation among gastric cancer patients

The aim of this study was to identify the clinical, demographic, lifestyle factors and selected genetic polymorphisms that affect the susceptibility towards Helicobacter pylori (H. pylori) infection in gastric cancer patients. Histological confirmed gastric adenocarcinoma cases that underwent curative gastrectomy between 2002 and 2012 were included. Gastric biopsy samples were obtained to determine the H. pylori status, and further cagA status and vacA m and s genotypes by polymerase chain reaction. Patients were interviewed with structured questionnaires, and blood samples were collected for EPHX1, GSTM1, GSTT1, IL1B, IL1-RN, MTHFR and p53 genotyping. Proportions were compared in univariate analysis, while the relation between putative risk factors and H. pylori status and genotype were measured using logistic regression analysis. One hundred forty-nine gastric cancer patients were included, of which 78.5% were H. pylori positive. Among positive patients 50% were cagA+, 72.5% vacA m1 and 80.7% vacA s1. The presence of cagA was less frequent among vacA m1 (p = 0.031) and vacA s1 (p = 0.052) subtypes. The presence of father history for any cancer was a significant risk factor for H. pylori infection [adjusted odds ratio (OR) = 8.18, 95% confidence interval (CI) 1.04-64.55]. EPHX1 exon 3 T > C (OR = 0.35, CI 95% 0.13-0.94), IL1B-511 T > C (OR = 0.38, CI 95% 0.15-0.97) and IL1-RN VNTR (OR = 0.19, CI 95% 0.06-0.58) polymorphisms were protective towards H. pylori infection in the univariate analysis. Wine consumption was associated with higher risk of carrying the H. pylori vacA m1 virulent subtype (p = 0.034). Lastly, cardiovascular diseases were less common among cagA positive subjects (p = 0.023). Father history of any cancer is a risk factor for H. pylori infection. Polymorphisms in IL1B-511, IL1-RN and EPHX1 exon 3 genes might be protective towards H. pylori infection.

Helicobacter pylori and pregnancy-related disorders

Helicobacter pylori (H. pylori) infection is investigated in gastric diseases even during pregnancy. In particular, this Gram-negative bacterium seems to be associated with hyperemesis gravidarum, a severe form of nausea and vomiting during pregnancy. During the last decade, the relationship among H. pylori and several extra-gastric diseases strongly emerged in literature. The correlation among H. pylori infection and pregnancy-related disorders was mainly focused on iron deficiency anemia, thrombocytopenia, fetal malformations, miscarriage, pre-eclampsia and fetal growth restriction. H. pylori infection may have a role in the pathogenesis of various pregnancy-related disorders through different mechanisms: depletion of micronutrients (iron and vitamin B₁₂) in maternal anemia and fetal neural tube defects; local or systemic induction of pro-inflammatory cytokines release and oxidative stress in gastrointestinal disorders and pre-eclampsia; cross-reaction between specific anti-H. pylori antibodies and antigens localized in placental tissue and endothelial cells (pre-eclampsia, fetal growth restriction, miscarriage). Since H. pylori infection is most likely acquired before pregnancy, it is widely believed that hormonal and immunological changes occurring during pregnancy could activate latent H. pylori with a negative impact not only on maternal health (nutritional deficiency, organ injury, death), but also on the fetus (insufficient growth, malformation, death) and sometime consequences can be observed later in life. Another important issue addressed by investigators was to determine whether it is possible to transmit H. pylori infection from mother to child and whether maternal anti-H. pylori antibodies could prevent infant’s infection. Studies on novel diagnostic and therapeutic methods for H. pylori are no less important, since these are particularly sensitive topics in pregnancy conditions. It could be interesting to study the possible correlation between H. pylori infection and other pregnancy-related diseases of unknown etiology, such as gestational diabetes mellitus, obstetric cholestasis and spontaneous preterm delivery. Since H. pylori infection is treatable, the demonstration of its causative role in pregnancy-related disorders will have important social-economic implications.

Functional characterization of Helicobacter pylori TlyA: pore-forming hemolytic activity and cytotoxic property of the protein

Helicobacter pylori is a human specific gastric pathogen. H. pylori pathogenesis process involves a number of well-studied virulence factors that include the 'vacuolating cytotoxin' and the 'cytotoxin associated gene A'. Analysis of the H. pylori genome, however, indicates presence of additional virulence factors that are yet to be characterized in molecular detail. For example, H. pylori genome harbors a gene that has potential to encode a protein with sequence similarity to those of the TlyA-like proteins of several pathogenic bacteria. Earlier studies have indicated potential association of this H. pylori tlyA gene in the virulence mechanism of the organism. Despite such notions, however, the TlyA-like protein of H. pylori has not been studied previously in molecular detail. In particular, purified form of H. pylori TlyA has never been studied before toward exploring its functional properties. Here, we report characterization of the H. pylori TlyA protein purified from the recombinant over-expression system in Escherichia coli. Purified form of the recombinant TlyA exhibits prominent hemolytic activity against human erythrocytes, presumably via formation of pores of specific diameter in the cell membrane. Purified TlyA also triggers prominent cytotoxic responses in human gastric adenocarcinoma cells. Altogether, our study establishes H. pylori TlyA as a potential virulence factor of the organism.

Cyanidin 3-O-glucoside reduces Helicobacter pylori VacA-induced cell death of gastric KATO III cells through inhibition of the SecA pathway

Two key virulence factors of Helicobacter pylori are the secreted virulent proteins of vacuolating toxin A (VacA) and cytotoxin associated protein A (CagA) which lead to damages of gastric epithelial cells. We previously identified that the cyanidin 3-O-glucoside (C3G) inhibits the secretion of both VacA and CagA. In the current report, we show that C3G inhibits VacA secretion in a dose-dependent manner by inhibiting secretion system subunit protein A (SecA) synthesis. As SecA is involved in translocation of bacterial proteins, we predicted that inhibition of the SecA pathway by C3G should decrease H. pylori-induced cell death. To test this hypothesis, the human gastric cell line KATO III cells were co-cultured with H. pylori 60190 (VacA(+)/CagA(+)) and C3G. We found that C3G treatment caused a decrease in activation of the pro-apoptotic proteins caspase-3/-8 in H. pylori-infected cells leading to a decrease in cell death. Our data suggest that consumption of foods containing anthocyanin may be beneficial in reducing cell damage due to H. pylori infection.

Sequence divergence and conservation in genomes of Helicobacter cetorum strains from a dolphin and a whale

Background and Objectives

Strains of Helicobacter cetorum have been cultured from several marine mammals and have been found to be closely related in 16 S rDNA sequence to the human gastric pathogen H. pylori, but their genomes were not characterized further.

Methods

The genomes of H. cetorum strains from a dolphin and a whale were sequenced completely using 454 technology and PCR and capillary sequencing.

Results

These genomes are 1.8 and 1.95 mb in size, some 7–26% larger than H. pylori genomes, and differ markedly from one another in gene content, and sequences and arrangements of shared genes. However, each strain is more related overall to H. pylori and its descendant H. acinonychis than to other known species. These H. cetorum strains lack cag pathogenicity islands, but contain novel alleles of the virulence-associated vacuolating cytotoxin (vacA) gene. Of particular note are (i) an extra triplet of vacA genes with ≤50% protein-level identity to each other in the 5′ two-thirds of the gene needed for host factor interaction; (ii) divergent sets of outer membrane protein genes; (iii) several metabolic genes distinct from those of H. pylori; (iv) genes for an iron-cofactored urease related to those of Helicobacter species from terrestrial carnivores, in addition to genes for a nickel co-factored urease; and (v) members of the slr multigene family, some of which modulate host responses to infection and improve Helicobacter growth with mammalian cells.

Conclusions

Our genome sequence data provide a glimpse into the novelty and great genetic diversity of marine helicobacters. These data should aid further analyses of microbial genome diversity and evolution and infection and disease mechanisms in vast and often fragile ocean ecosystems.

Endoplasmic reticulum stress contributes to Helicobacter pylori VacA-induced apoptosis

Vacuolating cytotoxin A (VacA) is one of the important virulence factors produced by H. pylori. VacA induces apoptotic cell death, which is potentiated by ammonia. VacA also causes cell death by mitochondrial damage, via signaling pathways that are not fully defined. Our aim was to determine whether endoplasmic reticulum (ER) stress is associated with VacA-induced mitochondrial dysfunction and apoptosis. We found that C/EBP homologous protein (CHOP), a key signaling protein of ER stress-induced apoptosis, was transcriptionally up-regulated following incubation of gastric epithelial cells with VacA. The effect of VacA on CHOP induction was significantly enhanced by co-incubation with ammonium chloride. Phosphorylation of eukaryotic initiation factor 2 (eIF2)-alpha, which is known to occur downstream of the ER stress sensor PKR-like ER-localized eIF2-alpha kinase (PERK) and to regulate CHOP expression, was also observed following incubation with VacA in the presence of ammonium chloride. Knockdown of CHOP by siRNA resulted in inhibition of VacA-induced apoptosis. Further studies showed that silencing of the PERK gene with siRNA attenuated VacA-mediated phosphorylation of eIF2-alpha, CHOP induction, expression of BH3-only protein Bim and Bax activation, and cell death induced by VacA with ammonium chloride, indicating that ER stress may lead to mitochondrial dysfunction during VacA-induced toxicity. Activation of ER stress and up-regulation of BH3-only proteins were also observed in human H. pylori-infected gastric mucosa. Collectively, this study reveals a possible association between VacA-induced apoptosis in gastric epithelial cells, and activation of ER stress in H. pylori-positive gastric mucosa.

Nanoparticle-detained toxins for safe and effective vaccination

Toxoid vaccines--vaccines based on inactivated bacterial toxins--are routinely used to promote antitoxin immunity for the treatment and prevention of bacterial infections. Following chemical or heat denaturation, inactivated toxins can be administered to mount toxin-specific immune responses. However, retaining faithful antigenic presentation while removing toxin virulence remains a major challenge and presents a trade-off between efficacy and safety in toxoid development. Here, we show a nanoparticle-based toxin-detainment strategy that safely delivers non-disrupted pore-forming toxins for immune processing. Using erythrocyte membrane-coated nanoparticles and staphylococcal α-haemolysin, we demonstrate effective virulence neutralization via spontaneous particle entrapment. Compared with vaccination with heat-denatured toxin, mice vaccinated with the nanoparticle-detained toxin showed superior protective immunity against toxin-mediated adverse effects. We find that the non-disruptive detoxification approach benefited the immunogenicity and efficacy of toxoid vaccines. We anticipate that this study will open new possibilities in the preparation of antitoxin vaccines against the many virulence factors that threaten public health.

Role of connexin 43 in Helicobacter pylori VacA-induced cell death

Helicobacter pylori colonizes the human stomach and confers an increased risk for the development of peptic ulceration, noncardia gastric adenocarcinoma, and gastric lymphoma. A secreted H. pylori toxin, VacA, can cause multiple alterations in gastric epithelial cells, including cell death. In this study, we sought to identify host cell factors that are required for VacA-induced cell death. To do this, we analyzed gene trap and short hairpin RNA (shRNA) libraries in AZ-521 human gastric epithelial cells and selected for VacA-resistant clones. Among the VacA-resistant clones, we identified multiple gene trap library clones and an shRNA library clone with disrupted expression of connexin 43 (Cx43) (also known as gap junction protein alpha 1 [GJA1]). Further experiments with Cx43-specific shRNAs confirmed that a reduction in Cx43 expression results in resistance to VacA-induced cell death. Immunofluorescence microscopy experiments indicated that VacA did not colocalize with Cx43. We detected production of the Cx43 protein in AZ-521 cells but not in AGS, HeLa, or RK-13 cells, and correspondingly, AZ-521 cells were the most susceptible to VacA-induced cell death. When Cx43 was expressed in HeLa cells, the cells became more susceptible to VacA. These results indicate that Cx43 is a host cell constituent that contributes to VacA-induced cell death and that variation among cell types in susceptibility to VacA-induced cell death is attributable at least in part to cell type-specific differences in Cx43 production.

Diet, microbial virulence, and Helicobacter pylori-induced gastric cancer

Gastric adenocarcinoma is a leading cause of cancer-related death worldwide, and Helicobacter pylori infection is one of the strongest known risk factors for this malignancy. H. pylori strains exhibit a high level of genetic diversity, and the risk of gastric cancer is higher in persons carrying certain strain types (for example, those that contain a cag pathogenicity island or type s1 vacA alleles) than in persons carrying other strain types. Additional risk factors for gastric cancer include specific human genetic polymorphisms and specific dietary preferences (for example, a high-salt diet or a diet deficient in fruits and vegetables). Finally, iron-deficiency anemia is a risk factor for gastric cancer. Recent studies have provided evidence that several dietary risk factors for gastric cancer directly impact H. pylori virulence. In this review article, we discuss mechanisms by which diet can modulate H. pylori virulence and thereby influence gastric cancer risk.

Role of childhood infection in the sequelae of H. pylori disease

The persistence of Helicobacter pylori infection plays a fundamental role in the development of H. pylori-associated complications. Since the majority of infected persons acquire the bacteria during early childhood, an examination of the immunobiology of H. pylori infection in children compared with that of adults may help identify host factors that contribute to persistent infection. Therefore, we begin our review of the role of persistence in H. pylori disease with an assessment of the clinical features of H. pylori infection in children. We next review the bacterial factors that promote colonization and evasion of host defense mechanisms. We then focus our attention on the early host immunological factors that promote persistence of the infection and its complications in humans and mouse models. We also highlight topics in which further research is needed. An examination of how immunological factors cause divergent manifestations of H. pylori infection in children compared with adults may provide new insight for therapeutic modification or prevention of persistent H. pylori infection and its complications.

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

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

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

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

The Effect of Helicobacter pylori on Epidermal Growth Factor Receptor-Induced Signal Transduction and the Preventive Effect of Celecoxib in Gastric Cancer Cells

Background/Aims

Helicobacter pylori infection induces cyclooxygenase-2 (COX-2) and epidermal growth factor receptor (EGFR) overexpression, and these factors may engage in cross-talk. The aim of the present study was to evaluate the effect of H. pylori on EGFR signaling pathways and to determine whether celecoxib has an inhibitory effect on this pathway.

Methods

The AGS cell line was cocultured with H. pylori G27 and the isogenic cagE- mutant. The expression of COX-2, EGFR, heparin binding-epidermal growth factor (HB-EGF), and transforming growth factor-β (TGF-β) was measured by real time-polymerase chain reaction (RT-PCR). Next, Western blot analyses of COX-2, EGFR, total Akt, phosphorylated Akt (pAkt), and phosphorylated glycogen synthase kinase-3β (pGSK3β) were performed after incubating H. pylori-treated AGS cells for 24 hours with various concentrations of celecoxib (0, 10, 20, and 30 µmol/L).

Results

H. pylori infection upregulated the mRNA levels of COX-2, EGFR, HB-EGF, and TGF-β, as detected by RT-PCR. However, AGS cells treated with cagE- mutants, which have a defective type IV secretion system, did not exhibit EGFR upregulation. Celecoxib had inhibitory effects on the H. pylori-induced overexpression of COX-2 (p=0.015), EGFR (p=0.025), pAkt (p=0.025), and pGSK3β (p=0.029) by Western blot analysis.

Conclusions

H. pylori with an intact type IV secretion system activated the COX-2 and EGFR-Akt pathways in the AGS cell line. As celecoxib exhibited inhibitory effects on the EGFR signaling pathway, the cross-talk of COX-2 and EGFR likely mediates H. pylori-induced gastric cancer.