Helicobacter pylori CagL activates ADAM17 to induce repression of the gastric H, K-ATPase alpha subunit

Roles of the components of the cag-pathogenicity island encoded type IV secretion system in Helicobacter pylori

The Helicobacter pylori (H. pylori) cytotoxin-associated gene pathogenicity island (cagPAI) encodes 31 genes that assemble the cag type IV secretion system (T4SS) apparatus, which includes structures such as the outer membrane core complex, periplasmic ring, inner membrane complex and bacterial hairs. These proteins interact with each other to inject CagA into the host gastric epithelium. There are also individual unique functions that help H. pylori interfere with host cellular pathways, modulate the immune response and colonize the host for a long time. However, the functions of some of the proteins remain unclear. This review summarizes what is known about the structure and function of these auxiliary components and discusses their role in H. pylori pathogenesis.

Unveiling the gastric microbiota: implications for gastric carcinogenesis, immune responses, and clinical prospects

High-throughput sequencing has ushered in a paradigm shift in gastric microbiota, breaking the stereotype that the stomach is hostile to microorganisms beyond H. pylori. Recent attention directed toward the composition and functionality of this 'community' has shed light on its potential relevance in cancer. The microbial composition in the stomach of health displays host specificity which changes throughout a person's lifespan and is subject to both external and internal factors. Distinctive alterations in gastric microbiome signature are discernible at different stages of gastric precancerous lesions and malignancy. The robust microbes that dominate in gastric malignant tissue are intricately implicated in gastric cancer susceptibility, carcinogenesis, and the modulation of immunosurveillance and immune escape. These revelations offer fresh avenues for utilizing gastric microbiota as predictive biomarkers in clinical settings. Furthermore, inter-individual microbiota variations partially account for differential responses to cancer immunotherapy. In this review, we summarize current literature on the influence of the gastric microbiota on gastric carcinogenesis, anti-tumor immunity and immunotherapy, providing insights into potential clinical applications.

Infiltration to infection: key virulence players of Helicobacter pylori pathogenicity

PURPOSE

This study aims to comprehensively review the multifaceted factors underlying the successful colonization and infection process of Helicobacter pylori (H. pylori), a prominent Gram-negative pathogen in humans. The focus is on elucidating the functions, mechanisms, genetic regulation, and potential cross-interactions of these elements.

METHODS

Employing a literature review approach, this study examines the intricate interactions between H. pylori and its host. It delves into virulence factors like VacA, CagA, DupA, Urease, along with phase variable genes, such as babA, babC, hopZ, etc., giving insights about the bacterial perspective of the infection The association of these factors with the infection has also been added in the form of statistical data via Funnel and Forest plots, citing the potential of the virulence and also adding an aspect of geographical biasness to the virulence factors. The biochemical characteristics and clinical relevance of these factors and their effects on host cells are individually examined, both comprehensively and statistically.

RESULTS

H. pylori is a Gram-negative, spiral bacterium that successfully colonises the stomach of more than half of the world's population, causing peptic ulcers, gastric cancer, MALT lymphoma, and other gastro-duodenal disorders. The clinical outcomes of H. pylori infection are influenced by a complex interplay between virulence factors and phase variable genes produced by the infecting strain and the host genetic background. A meta-analysis of the prevalence of all the major virulence factors has also been appended.

CONCLUSION

This study illuminates the diverse elements contributing to H. pylori's colonization and infection. The interplay between virulence factors, phase variable genes, and host genetics determines the outcome of the infection. Despite biochemical insights into many factors, their comprehensive regulation remains an understudied area. By offering a panoramic view of these factors and their functions, this study enhances understanding of the bacterium's perspective, i.e. H. pylori's journey from infiltration to successful establishment within the host's stomach.

Immune evasion by proteolytic shedding of natural killer group 2, member D ligands in Helicobacter pylori infection

Background

Helicobacter pylori (H. pylori) uses various strategies that attenuate mucosal immunity to ensure its persistence in the stomach. We recently found evidence that H. pylori might modulate the natural killer group 2, member 2 (NKG2D) system. The NKG2D receptor and its ligands are a major activation system of natural killer and cytotoxic T cells, which are important for mucosal immunity and tumor immunosurveillance. The NKG2D system allows recognition and elimination of infected and transformed cells, however viruses and cancers often subvert its activation. Here we aimed to identify a potential evasion of the NKG2D system in H. pylori infection.

Methods

We analyzed expression of NKG2D system genes in gastric tissues of H. pylori gastritis and gastric cancer patients, and performed cell-culture based infection experiments using H. pylori isogenic mutants and epithelial and NK cell lines.

Results

In biopsies of H. pylori gastritis patients, NKG2D receptor expression was reduced while NKG2D ligands accumulated in the lamina propria, suggesting NKG2D evasion. In vitro, H. pylori induced the transcription and proteolytic shedding of NKG2D ligands in stomach epithelial cells, and these effects were associated with specific H. pylori virulence factors. The H. pylori-driven release of soluble NKG2D ligands reduced the immunogenic visibility of infected cells and attenuated the cytotoxic activity of effector immune cells, specifically the anti-tumor activity of NK cells.

Conclusion

H. pylori manipulates the NKG2D system. This so far unrecognized strategy of immune evasion by H. pylori could potentially facilitate chronic bacterial persistence and might also promote stomach cancer development by allowing transformed cells to escape immune recognition and grow unimpeded to overt malignancy.

The Efficacy of Cancer Immunotherapies Is Compromised by Helicobacter pylori Infection

Helicobacter pylori infects the gastric mucosa of a large number of humans. Although asymptomatic in the vast majority of cases, H pylori infection can lead to the development of peptic ulcers gastric adenocarcinoma and mucosa-associated lymphoid tissue (MALT) lymphoma. Using a variety of mechanisms, H pylori locally suppresses the function of the host immune system to establish chronic infection. Systemic immunomodulation has been observed in both clinical and pre-clinical studies, which have demonstrated that H pylori infection is associated with reduced incidence of inflammatory diseases, such as asthma and Crohn’s disease. The introduction of immunotherapies in the arsenal of anti-cancer drugs has revealed a new facet of H pylori-induced immune suppression. In this review, we will describe the intimate interactions between H pylori and its host, and formulate hypothtyeses describing the detrimental impact of H pylori infection on the efficacy of cancer immunotherapies.

Proteolytic Landscapes in Gastric Pathology and Cancerogenesis

Gastric cancer is a leading cause of cancer-related death, and a large proportion of cases are inseparably linked to infections with the bacterial pathogen and type I carcinogen Helicobacter pylori. The development of gastric cancer follows a cascade of transformative tissue events in an inflammatory environment. Proteases of host origin as well as H. pylori-derived proteases contribute to disease progression at every stage, from chronic gastritis to gastric cancer. In the present article, we discuss the importance of (metallo-)proteases in colonization, epithelial inflammation, and barrier disruption in tissue transformation, deregulation of cell proliferation and cell death, as well as tumor metastasis and neoangiogenesis. Proteases of the matrix metalloproteinase (MMP) and a disintegrin and metalloproteinase domain-containing protein (ADAM) families, caspases, calpain, and the H. pylori proteases HtrA, Hp1012, and Hp0169 cleave substrates including extracellular matrix molecules, chemokines, and cytokines, as well as their cognate receptors, and thus shape the pathogenic microenvironment. This review aims to summarize the current understanding of how proteases contribute to disease progression in the gastric compartment.

Helicobacter pylori-induced reactive oxygen species direct turnover of CSN-associated STAMBPL1 and augment apoptotic cell death

Deubiquitinylases (DUBs) are central regulators of the ubiquitin system involved in protein regulation and cell signalling and are important for a variety of physiological processes. Most DUBs are cysteine proteases, and few other proteases are metalloproteases of the JAB1/MPN +/MOV34 protease family (JAMM). STAM-binding protein like 1 (STAMBPL1), a member of the JAMM family, cleaves ubiquitin bonds and has a function in regulating cell survival, Tax-mediated nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) activation and epithelial-mesenchymal transition. However, the molecular mechanism by which STAMBPL1 influences cell survival is not well defined, especially with regard to its deubiquitinylation function. Here, we show that reactive oxygen species (ROS) induced by chemotherapeutic agents or the human microbial pathogen Helicobacter pylori can induce cullin 1-RING ubiquitin ligase (CRL1) and 26S proteasome-dependent degradation STAMBPL1. Interestingly, STAMBPL1 has a direct interaction with the constitutive photomorphogenic 9 (COP9 or CSN) signalosome subunits CSN5 and CSN6. The interaction with the CSN is required for the stabilisation and function of the STAMBPL1 protein. In addition, STAMBPL1 deubiquitinylates the anti-apoptotic protein Survivin and thus ameliorates cell survival. In summary, our data reveal a previously unknown mechanism by which the deubiquitinylase STAMBPL1 and the E3 ligase CRL1 balance the level of Survivin degradation and thereby determine apoptotic cell death. In response to genotoxic stress, the degradation of STAMBPL1 augments apoptotic cell death. This new mechanism may be useful to develop therapeutic strategies targeting STAMBPL1 in tumours that have high STAMBPL1 and Survivin protein levels.

In Silico Protein-Protein Interaction of Pterois volitans Venom with Cancer Inducers of Helicobacter pylori

Gastric cancer is a pathological condition induced by the bacteria Helicobacter pylori. Targeting the key virulence factors of H. pylori causing gastric cancer is a promising method for treating gastric cancer. Recently, research has been focused on analyzing the adrenergic, cholinergic, and anti-cancer properties of their venom proteins. Testing the anti-cancer activity of the lethal proteins in the venom of P. volitans provides a bioactive compound for cancer treatment. Still, it is also helpful to eliminate the ecological imbalance caused by these fish in the marine environment. This study focuses on an in silico approach using Z-dock to analyze the bioactive prospective of the venom proteins of P. volitans against the essential virulence proteins of H. pylori responsible for inducing cancer. Our in silico docking study using a computational model of the venom proteins and H. pylori proteins has displayed the possible interactions between these proteins. The results revealed that P. volitans hyaluronidase and PV toxin's venom proteins effectively interact with H. pylori proteins Cag A, Cag L, GGT, Cag D, and urease that may be promising proteins in cancer therapy.

Transcriptional alteration of genes linked to gastritis concerning Helicobacter pylori infection status and its virulence factors

BACKGROUND

Helicobacter pylori infection and heterogeneity in its pathogenesis could describe diversity in the expression of inflammatory genes in the gastric tissue. We aimed to investigate transcriptional alteration of genes linked to gastritis concerning the H. pylori infection status and its virulence factors.

METHODS AND RESULTS

Biopsy samples of 12 infected and 12 non-infected patients with H. pylori that showed moderate chronic gastritis were selected for transcriptional analysis. Genotyping of H. pylori strains was done using PCR and relative expression of inflammatory genes was compared between the infected and non-infected patients using relative quantitative real-time PCR. Positive correlations between transcriptional changes of IL8 with TNF-α and Noxo1 in the infected and TNF-α with Noxo1, MMP7, and Atp4A in the non-infected patients were detected. Six distinct genotypes of H. pylori were detected that showed no correlation with gender, ethnicity, age, endoscopic findings, and transcriptional levels of host genes. Irrespective of the characterized genotypes, our results showed overexpression of TNF-α, MMP7, Noxo1, and ATP4A in the infected and IL-8, Noxo1, and ATP4A in the non-infected patients.

CONCLUSIONS

A complexity in transcription of genes respective to the characterized H. pylori genotypes in the infected patients was detected in our study. The observed difference in co-regulation of genes linked to gastritis in the infected and non-infected patients proposed involvement of different regulatory pathways in the inflammation of the gastric tissue in the studied groups.

Helicobacter pylori Infection

Helicobacter pylori infection remains one of the most prevalent infections worldwide, causing significant morbidity and mortality from gastric malignancies and peptic ulcers. This article provides a summary of the microbiology and pathogenesis of this bacterium, emphasizing the complex and protean effects of H pylori on gastric epithelial cells, including stem and progenitor populations, and evasion of host immune defenses. Increasing antibiotic resistance has made management more challenging. This article discusses the appropriate diagnostic modality for different clinical scenarios, and the evolving treatment of H pylori infections, including the use of antibiotic susceptibility testing to aid regimen selection.

A Disintegrin and Metalloproteinase-Control Elements in Infectious Diseases

Despite recent advances in treatment strategies, infectious diseases are still under the leading causes of death worldwide. Although the activation of the inflammatory cascade is one prerequisite of defense, persistent and exuberant immune response, however, may lead to chronicity of inflammation predisposing to a temporal or permanent tissue damage not only of the site of infection but also among different body organs. The initial response to invading pathogens is mediated by the recognition through various pattern-recognition receptors along with cellular engulfment resulting in a coordinated release of soluble effector molecules and cytokines aiming to terminate the external stimuli. Members of the ‘a disintegrin and metalloproteinase’ (ADAM) family have the capability to proteolytically cleave transmembrane molecules close to the plasma membrane, a process called ectodomain shedding. In fact, in infectious diseases dysregulation of numerous ADAM substrates such as junction molecules (e.g., E-cadherin, VE-cadherin, JAM-A), adhesion molecules (e.g., ICAM-1, VCAM-1, L-selectin), and chemokines and cytokines (e.g., CXCL16, TNF-α) has been observed. The alpha-cleavage by ADAM proteases represents a rate limiting step for downstream regulated intramembrane proteolysis (RIPing) of several substrates, which influence cellular differentiation, cell signaling pathways and immune modulation. Both the substrates mentioned above and RIPing crucially contribute to a systematic damage in cardiovascular, endocrine, and/or gastrointestinal systems. This review will summarize the current knowledge of ADAM function and the subsequent RIPing in infectious diseases (e.g., pathogen recognition and clearance) and discuss the potential long-term effect on pathophysiological changes such as cardiovascular diseases.

Thiol switches in membrane proteins - Extracellular redox regulation in cell biology

Redox-mediated signal transduction depends on the enzymatic production of second messengers such as hydrogen peroxide, nitric oxide and hydrogen sulfite, as well as specific, reversible redox modifications of cysteine-residues in proteins. So-called thiol switches induce for instance conformational changes in specific proteins that regulate cellular pathways e.g., cell metabolism, proliferation, migration, gene expression and inflammation. Reduction, oxidation and disulfide isomerization are controlled by oxidoreductases of the thioredoxin family, including thioredoxins, glutaredoxins, peroxiredoxins and protein dsisulfide isomerases. These proteins are located in different cellular compartments, interact with substrates and catalyze specific reactions. Interestingly, some of these proteins are released by cells. Their extracellular functions and generally extracellular redox control have been widely underestimated. Here, we give an insight into extracellular redox signaling, extracellular thiol switches and their regulation by secreted oxidoreductases and thiol-isomerases, a topic whose importance has been scarcely studied so far, likely due to methodological limitations. We focus on the secreted redox proteins and characterized thiol switches in the ectodomains of membrane proteins, such as integrins and the metalloprotease ADAM17, which are among the best-characterized proteins and discuss their underlying mechanisms and biological implications.

Helicobacter pylori Virulence Factor Cytotoxin-Associated Gene A (CagA)-Mediated Gastric Pathogenicity

Helicobacter pylori causes persistent infection in the gastric epithelium of more than half of the world’s population, leading to the development of severe complications such as peptic ulcer diseases, gastric cancer, and gastric mucosa-associated lymphoid tissue (MALT) lymphoma. Several virulence factors, including cytotoxin-associated gene A (CagA), which is translocated into the gastric epithelium via the type 4 secretory system (T4SS), have been indicated to play a vital role in disease development. Although infection with strains harboring the East Asian type of CagA possessing the EPIYA-A, -B, and -D sequences has been found to potentiate cell proliferation and disease pathogenicity, the exact mechanism of CagA involvement in disease severity still remains to be elucidated. Therefore, we discuss the possible role of CagA in gastric pathogenicity.

Distance dependent shedding of IL-6R

Proteolytic processing of membrane proteins by A disintegrin and metalloprotease-17 (ADAM17) is a key regulatory step in many physiological and pathophysiological processes. This so-called shedding is essential for development, regeneration and immune defense. An uncontrolled ADAM17 activity promotes cancer development, chronic inflammation and autoimmune diseases. Consequently, the ADAM17 activity is tightly regulated. As a final trigger for the shedding event a phosphatidylserine (PS) flip to the outer leaflet of the cell membrane was recently described. PS interacts with the extracellular part of ADAM17, which results in the shedding event by shifting the catalytic domain towards the membrane close to the cleavage sites within ADAM17 substrates. Our data indicate that the intrinsic proteolytic activity of the catalytic domain is prerequisite for the shedding activity and constantly present. However, the accessibility for substrate cleavage sites is controlled on several levels. In this report, we demonstrate that the positioning of the catalytic domain towards the cleavage sites is a crucial part of the shedding process. This finding contributes to the understanding of the complex and multilayered regulation of ADAM17 at the cell surface.

Association between polymorphisms in HLA-A, HLA-B, HLA-DR, and DQ genes from gastric cancer and duodenal ulcer patients and cagL among cagA-positive Helicobacter pylori strains: The first study in a Turkish population

Colonization of the human gastric mucosa by H. pylori may cause peptic and duodenal ulcers (DUs), gastric lymphomas, and gastric cancers. The cagL gene is a component of cag T4SS and is involved in cagA translocation into host. An association between the risk of gastric cancer and the type of HLA class II (DR and/or DQ) was suggested in different populations. The aim of this study was to investigate, the clinical association of the cagL gene with host HLA alleles in H. pylori strains that were isolated from patients with gastric cancer, DU, and non-ulcer dyspepsia (NUD) and to determine the HLA allele that confers susceptibility or resistance for the risk of gastric cancer and DU development in Turkish patients. A total of 94 patients (44 gastric cancer and 50 DU patients; 58 male, 36 female; mean age, 49.6 years), and 86 individuals (50 NUD patients and 36 persons with normal gastrointestinal system [NGIS]; 30 male, 56 female; mean age, 47.3 years) were included as the patient and the control groups, respectively. CagA and cagL were determined by PCR method. DNA from peripheral blood samples was obtained by EZ-DNA extraction kit. For HLA SSO typing, LIFECODES SSO Typing kits (HLA-A, HLA-B HLA-C, HLA-DRB1 and HLA-DQA1/B1 kits) were used. The CagL/CagA positivity distribution in the groups were as follows: 42 (95.4%) gastric cancer, 46 (92%) DU and, 34 (68%) NUD and no NGIS cases. The HLA-DQA1*01 (OR: 3.82) allele was significantly different, suggesting that these individuals with H. pylori strains harbouring the CagL/CagA positivity are susceptible to the risk of gastric cancer and DU, and the HLA-DQA1*05 (OR, 0.318) allele was suggested as a protective allele for the risk of gastric cancer and DU using univariate analyses. HLA-DQA1*01 (OR, 2.21), HLA-DQB1*06 (OR, 2.67), sex (male, OR, 2.27), and CagL/CagA/(<2) EPIYA C repeats (OR, 5.72) were detected independent risk factors that increased the risk of gastric cancer and DU using multivariate analyses. However, the HLA-DRB1*04 (OR, 0.28) allele was shown to be a protective allele, which decreased the risk of gastric cancer and DU. Gastric pathologies result from an interaction between bacterial virulence factors, host epigenetic and environmental factors, and H. pylori strain heterogeneity, such as genotypic variation among strains and variations in H. pylori populations within an individual host.

Cortactin: A Major Cellular Target of the Gastric Carcinogen Helicobacter pylori

Cortactin is an actin binding protein and actin nucleation promoting factor regulating cytoskeletal rearrangements in nearly all eukaryotic cell types. From this perspective, cortactin poses an attractive target for pathogens to manipulate a given host cell to their own benefit. One of the pathogens following this strategy is Helicobacter pylori, which can cause a variety of gastric diseases and has been shown to be the major risk factor for the onset of gastric cancer. During infection of gastric epithelial cells, H. pylori hijacks the cellular kinase signaling pathways, leading to the disruption of key cell functions. Specifically, by overruling the phosphorylation status of cortactin, H. pylori alternates the activity of molecular interaction partners of this important protein, thereby manipulating the performance of actin-cytoskeletal rearrangements and cell movement. In addition, H. pylori utilizes a unique mechanism to activate focal adhesion kinase, which subsequently prevents host epithelial cells from extensive lifting from the extracellular matrix in order to achieve chronic infection in the human stomach.

Gastric Peptides-Gastrin and Somatostatin

Gastric acid secretion (i) facilitates digestion of protein as well as absorption of micronutrients and certain medications, (ii) kills ingested microorganisms, including Helicobacter pylori, and (iii) prevents bacterial overgrowth and enteric infection. The principal regulators of acid secretion are the gastric peptides gastrin and somatostatin. Gastrin, the major hormonal stimulant for acid secretion, is synthesized in pyloric mucosal G cells as a 101-amino acid precursor (preprogastrin) that is processed to yield biologically active amidated gastrin-17 and gastrin-34. The C-terminal active site of gastrin (Trp-Met-Asp-Phe-NH₂ ) binds to gastrin/CCK₂ receptors on parietal and, more importantly, histamine-containing enterochromaffin-like (ECL) cells, located in oxyntic mucosa, to induce acid secretion. Histamine diffuses to the neighboring parietal cells where it binds to histamine H₂ -receptors coupled to hydrochloric acid secretion. Gastrin is also a trophic hormone that maintains the integrity of gastric mucosa, induces proliferation of parietal and ECL cells, and is thought to play a role in carcinogenesis. Somatostatin, present in D cells of the gastric pyloric and oxyntic mucosa, is the main inhibitor of acid secretion, particularly during the interdigestive period. Somatostatin exerts a tonic paracrine restraint on gastrin secretion from G cells, histamine secretion from ECL cells, and acid secretion from parietal cells. Removal of this restraint, for example by activation of cholinergic neurons during ingestion of food, initiates and maximizes acid secretion. Knowledge regarding the structure and function of gastrin, somatostatin, and their respective receptors is providing novel avenues to better diagnose and manage acid-peptic disorders and certain cancers. Published 2020. Compr Physiol 10:197-228, 2020.

Helicobacter pylori Virulence Factors Exploiting Gastric Colonization and its Pathogenicity

Helicobacter pylori colonizes the gastric epithelial cells of at least half of the world's population, and it is the strongest risk factor for developing gastric complications like chronic gastritis, ulcer diseases, and gastric cancer. To successfully colonize and establish a persistent infection, the bacteria must overcome harsh gastric conditions. H. pylori has a well-developed mechanism by which it can survive in a very acidic niche. Despite bacterial factors, gastric environmental factors and host genetic constituents together play a co-operative role for gastric pathogenicity. The virulence factors include bacterial colonization factors BabA, SabA, OipA, and HopQ, and the virulence factors necessary for gastric pathogenicity include the effector proteins like CagA, VacA, HtrA, and the outer membrane vesicles. Bacterial factors are considered more important. Here, we summarize the recent information to better understand several bacterial virulence factors and their role in the pathogenic mechanism.

Activity and Functional Importance of Helicobacter pylori Virulence Factors

Helicobacter pylori is a very successful Gram-negative pathogen colonizing the stomach of humans worldwide. Infections with this bacterium can generate pathologies ranging from chronic gastritis and peptic ulceration to gastric cancer. The best characterized H. pylori virulence factors that cause direct cell damage include an effector protein encoded by the cytotoxin-associated gene A (CagA), a type IV secretion system (T4SS) encoded in the cag-pathogenicity island (cag PAI), vacuolating cytotoxin A (VacA), γ-glutamyl transpeptidase (GGT), high temperature requirement A (HtrA, a serine protease) and cholesterol glycosyl-transferase (CGT). Since these H. pylori factors are either surface-exposed, secreted or translocated, they can directly interact with host cell molecules and are able to hijack cellular functions. Studies on these bacterial factors have progressed substantially in recent years. Here, we review the current status in the characterization of signaling cascades by these factors in vivo and in vitro, which comprise the disruption of cell-to-cell junctions, induction of membrane rearrangements, cytoskeletal dynamics, proliferative, pro-inflammatory, as well as, pro-apoptotic and anti-apoptotic responses or immune evasion. The impact of these signal transduction modules in the pathogenesis of H. pylori infections is discussed.

Lactobacillus gasseri Suppresses the Production of Proinflammatory Cytokines in Helicobacter pylori-Infected Macrophages by Inhibiting the Expression of ADAM17

The ability of Helicobacter pylori to evade the host immune system allows the bacterium to colonize the host for a lifetime. Long-term infection with H. pylori causes chronic inflammation, which is the major risk factor for the development of gastric ulcers and gastric cancer. Lactobacilli are part of the human microbiota and have been studied as an adjunct treatment in H. pylori eradication therapy. However, the molecular mechanisms by which lactobacilli act against H. pylori infection have not been fully characterized. In this study, we investigated the anti-inflammatory effects of Lactobacillus strains upon coincubation of host macrophages with H. pylori. We found that Lactobacillus gasseri Kx110A1 (L. gas), a strain isolated from a human stomach, but not other tested Lactobacillus species, blocked the production of the proinflammatory cytokines TNF and IL-6 in H. pylori-infected macrophages. Interestingly, L. gas also inhibited the release of these cytokines in LPS or LTA stimulated macrophages, demonstrating a general anti-inflammatory property. The inhibition of these cytokines did not occur through the polarization of macrophages from the M1 (proinflammatory) to M2 (anti-inflammatory) phenotype or through the altered viability of H. pylori or host cells. Instead, we show that L. gas suppressed the release of TNF and IL-6 by reducing the expression of ADAM17 (also known as TNF-alpha-converting enzyme, TACE) on host cells. Our findings reveal a novel mechanism by which L. gas prevents the production of the proinflammatory cytokines TNF and IL-6 in host macrophages.

Specific high affinity interaction of Helicobacter pylori CagL with integrin αV β6 promotes type IV secretion of CagA into human cells

CagL is an essential pilus surface component of the virulence-associated type IV secretion system (T4SS) employed by Helicobacter pylori to translocate the oncogenic effector protein CagA into human gastric epithelial cells. CagL contains an RGD motif and integrin α₅ β₁ is widely accepted as its host cell receptor. Here, we show that CagL binds integrin α_V β₆ with substantially higher affinity and that this interaction is functionally important. Cell surface expression of α_V β₆ on various cell lines correlated perfectly with cell adhesion to immobilized CagL and with binding of soluble CagL to cells. We found no such correlation for α₅ β₁ . The purified α_V β₆ ectodomain bound CagL with high affinity. This interaction was highly specific, as the affinity of CagL for other RGD-binding integrins was two to three orders of magnitude weaker. Mutation of either conserved leucine in the CagL RGDLXXL motif, a motif that generally confers specificity for integrin α_V β₆ and α_V β₈ , lowered the affinity of CagL for α_V β₆ . Stable expression of α_V β₆ in α_V β₆ -negative but α₅ β₁ -expressing human cells promoted two hallmarks of the functional H. pylori T4SS, namely translocation of CagA into host cells and induction of interleukin-8 secretion by host cells. These findings suggest that integrin α_V β₆ , although not essential for T4SS function, represents an important host cell receptor for CagL.

Gastric Parietal Cell Physiology and Helicobacter pylori-Induced Disease

Acidification of the gastric lumen poses a barrier to transit of potentially pathogenic bacteria and enables activation of pepsin to complement nutrient proteolysis initiated by salivary proteases. Histamine-induced activation of the PKA signaling pathway in gastric corpus parietal cells causes insertion of proton pumps into their apical plasma membranes. Parietal cell secretion and homeostasis are regulated by signaling pathways that control cytoskeletal changes required for apical membrane remodeling and organelle and proton pump activities. Helicobacter pylori colonization of human gastric mucosa affects gastric epithelial cell plasticity and homeostasis, promoting epithelial progression to neoplasia. By intervening in proton pump expression, H pylori regulates the abundance and diversity of microbiota that populate the intestinal lumen. We review stimulation-secretion coupling and renewal mechanisms in parietal cells and the mechanisms by which H pylori toxins and effectors alter cell secretory pathways (constitutive and regulated) and organelles to establish and maintain their inter- and intracellular niches. Studies of bacterial toxins and their effector proteins have provided insights into parietal cell physiology and the mechanisms by which pathogens gain control of cell activities, increasing our understanding of gastrointestinal physiology, microbial infectious disease, and immunology.

Genetic diversity and amino acid sequence polymorphism in Helicobacter pylori CagL hypervariable motif and its association with virulence markers and gastroduodenal diseases

Genetic variability in cagL gene especially within the Helicobacter pylori CagL hypervariable motif (CagLHM) may affect the development of gastric cancer. Therefore, this study was conducted to investigate the association of CagL diversity with clinical outcomes and with H pylori virulence markers. A total of 126 patients with different gastric diseases including non-ulcer dyspepsia (NUD), peptic ulcer disease (PUD), gastric erosion (GE), and gastric cancer (GC) were enrolled. H pylori was cultured from gastric biopsies, and the isolates were screened for the presence of cagL, cagA, vacA, babA2, sabA, and cagPAI integrity by PCR. The amino acid polymorphisms of cagL were analyzed using DNA sequencing. We isolated 61 (48.4%) H pylori strains from 36 NUD, eight PUD, 12 GE, and five GC patients. Almost all isolates were cagL positive (97%), and their RGD, RHS, and SKIIVK motifs were highly conserved. Among 10 CagLHM variants identified, NEIGQ and NKIGQ were detected as the most prevalent sequences. Interestingly, a significant association was found between the presence of NKMGK and PUD (P = 0.002). Notably, the NEIGQ isolates with multiple C-type EPIYA repeat that carried intact cagPAI correlated with disease risk for PUD, GE, and GC (P = 0.021). In conclusion, we identified novel variants of H pylori CagLHM sequences in Iranian population such as NKMGK, which was associated with disease risk for PUD. Further studies using a large number of strains are required to better clarify the function of certain CagLHM motifs in gastric carcinogenesis and disease outcome.

The Possible Role of Helicobacter pylori in Gastric Cancer and Its Management

Helicobacter pylori (HP) is a facultative anaerobic bacterium. HP is a normal flora having immuno-modulating properties. This bacterium is an example of a microorganism inducing gastric cancer. Its carcinogenicity depends on bacteria-host related factors. The proper understanding of the biology of HP inducing gastric cancer offers the potential strategy in the managing of HP rather than eradicating it. In this article, we try to summarize the biology of HP-induced gastric cancer and discuss the current pharmacological approach to treat and prevent its carcinogenicity.

CagL polymorphisms D58/K59 are predominant in Helicobacter pylori strains isolated from Mexican patients with chronic gastritis

Background

Helicobacter pylori is a Gram-negative bacterium that colonizes the gastric mucosa in humans. One of the main virulence factors of H. pylori is the cag pathogenicity island (cagPAI), which encodes a type 4-secretion system (T4SS) and the cytotoxin CagA. Translocation of CagA through the T4SS triggers host-signaling pathways. One of the T4SS proteins is CagL, which is necessary for CagA translocation. CagL is a 26-kDa protein that contains a hypervariable motif, which spans residues 58 to 62. Several polymorphisms in this region have been associated with different disease outcomes, e.g. in Mexico, N58 is associated with a higher risk of gastric cancer. The aim of this work is to analyze the sequence of the hypervariable motif (residues 58 to 62) of clinical isolates from Mexican patients with chronic gastritis, and to correlate these polymorphisms with the vacA genotype.

Results

Of the 164 biopsies analyzed, only 30.5% (50/164) were positive for H. pylori. Thirty-six of the 50 clinical isolates (72%) were cagA positive, and 40 (80%) had the most virulent vacA genotype (s1/m1). Of the cagA positive strains, 94.4% were vacA s1/m1. All the cagA⁺ strains contained the cagL gene. The most prevalent sequence in the polymorphic region (residues 58–62) was DKMGE (75.8%, 25/33), followed by NKMGQ and NEIGQ (6.1%, 2/33), and DEIGQ, NKMGE, DKIGE, and DKIGK (3%, 1/33). Regarding polymorphisms in positions 58 and 59, the most common were D58/K59 (81.8%, 27/33), followed by N58/K59 (9.1%, 3/33), and D58/E59 (3%, 1/33). Only two isolates (6.1%) contained residues N58/E59, which correspond to those found in H. pylori strain ATCC 26695. 92.6% of the clinical isolates having polymorphism D58/K59 had the genotype vacA s1/m1, considered to be the most virulent, while 7.4% had the genotypes vacA s1/m2 and s2/m2.

Conclusions

In Mexican patients, CagL polymorphisms D58, K59, M60, E62, K122, and I134 are more common in patients with chronic gastritis.

Roles of Adhesion to Epithelial Cells in Gastric Colonization by Helicobacter pylori

Helicobacter pylori adherence to host epithelial cells is essential for its survival against the harsh conditions of the stomach and for successful colonization. Adherence of H. pylori is achieved through several related families of outer membrane proteins and proteins of a type IV secretion system (T4SS), which bridge H. pylori to host cells through protein-protein and other protein-ligand interactions. Local environmental conditions such as cell type, available host cell surface proteins and/or ligands, as well as responses by the host immune system force H. pylori to alter expression of these proteins to adapt quickly to the local environment in order to colonize and survive. Some of these host-pathogen interactions appear to function in a "catch-and-release" manner, regulated by reversible binding at varying pH and allowing H. pylori to detach itself from cells or debris sloughed off the gastric epithelial lining in order to return for subsequent productive interactions. Other interactions between bacterial adhesin proteins and host adhesion molecules, however, appear to function as a committed step in certain pathogenic processes, such as translocation of the CagA oncoprotein through the H. pylori T4SS and into host gastric epithelial cells. Understanding these adhesion interactions is critical for devising new therapeutic strategies, as they are responsible for the earliest stage of infection and its maintenance. This review will discuss the expression and regulation of several outer membrane proteins and CagL, how they engage their known host cell protein/ligand targets, and their effects on clinical outcome.

Epidermal growth factor receptor inhibition downregulates Helicobacter pylori-induced epithelial inflammatory responses, DNA damage and gastric carcinogenesis

OBJECTIVE

Gastric cancer is the third leading cause of cancer death worldwide and infection by Helicobacter pylori is the strongest risk factor. We have reported increased epidermal growth factor receptor (EGFR) phosphorylation in the H. pylori-induced human carcinogenesis cascade, and association with DNA damage. Our goal was to determine the role of EGFR activation in gastric carcinogenesis.

DESIGN

We evaluated gefitinib, a specific EGFR inhibitor, in chemoprevention of H. pylori-induced gastric inflammation and cancer development. Mice with genetically targeted epithelial cell-specific deletion of Egfr (Efgr^Δepi mice) were also used.

RESULTS

In C57BL/6 mice, gefitinib decreased Cxcl1 and Cxcl2 expression by gastric epithelial cells, myeloperoxidase-positive inflammatory cells in the mucosa and epithelial DNA damage induced by H. pylori infection. Similar reductions in chemokines, inflammatory cells and DNA damage occurred in infected Egfr^Δepi versus Egfr^fl/fl control mice. In H. pylori-infected transgenic insulin-gastrin (INS-GAS) mice and gerbils, gefitinib treatment markedly reduced dysplasia and carcinoma. Gefitinib blocked H. pylori-induced activation of mitogen-activated protein kinase 1/3 (MAPK1/3) and activator protein 1 in gastric epithelial cells, resulting in inhibition of chemokine synthesis. MAPK1/3 phosphorylation and JUN activation was reduced in gastric tissues from infected wild-type and INS-GAS mice treated with gefitinib and in primary epithelial cells from Efgr^Δepi versus Egfr^fl/fl mice. Epithelial EGFR activation persisted in humans and mice after H. pylori eradication, and gefitinib reduced gastric carcinoma in INS-GAS mice treated with antibiotics.

CONCLUSIONS

These findings suggest that epithelial EGFR inhibition represents a potential strategy to prevent development of gastric carcinoma in H. pylori-infected individuals.

ADAM17 activation and regulation of profibrotic responses by high glucose requires its C-terminus and FAK kinase

Glomerular matrix accumulation is the hallmark of diabetic nephropathy. The metalloprotease ADAM17 mediates high glucose (HG)-induced matrix production by kidney mesangial cells through release of ligands for the epidermal growth factor receptor. Here we study the mechanism by which HG activates ADAM17. We find that the C-terminus is essential for ADAM17 activation and the profibrotic response to HG. In the C-terminus, Src-mediated Y702 phosphorylation and PI3K/MEK/Erk-mediated T735 phosphorylation are critical to ADAM17 activation, but play divergent roles in ADAM17 trafficking in response to HG. While T735 phosphorylation is required for the HG-induced increase in cell surface mature ADAM17, Y702 phosphorylation is dispensable. Src, however, enables trafficking independently of its phosphorylation of ADAM17. The nonreceptor tyrosine kinase FAK is a central mediator of these processes. These data not only support a critical role for the C-terminus in ADAM17 activation and downstream profibrotic responses to HG, but also highlight FAK as a potential alternate therapeutic target for diabetic nephropathy.

Helicobacter pylori controls NLRP3 expression by regulating hsa-miR-223-3p and IL-10 in cultured and primary human immune cells

Inflammasome-mediated production of mature IL-1β and IL-18 cytokines represents an important innate immune response against infecting pathogens. Helicobacter pylori, one of the most successful and persistent human pathogens, induces severe inflammation leading to gastritis and more serious gastric diseases. H. pylori modulates different immune responses for its survival and inflammasome signaling is manipulated by the cag pathogenicity island ( cagPAI), urease and VacA cytotoxin. Here we report that H. pylori regulates NLRP3 expression, an inflammasome forming regulator, in infected THP-1 monocytes. This response was independent of the major H. pylori pathogenicity-associated factors CagA, VacA, Cgt, FlaA and cagPAI. Two NLRP3 expression controlling factors, the NLRP3 mRNA targeting microRNA hsa-miR-223-3p and cytokine IL-10, were found to work in tandem for its regulation. H. pylori infection also induced copious amount of pro-IL-1β in THP-1 monocytes/macrophages but secreted a very low amount of mature IL-1β. Moreover, secreted IL-10 correlated with the down-regulation of nigericin-induced NLRP3 inflammasome activation of LPS-primed THP-1 monocytes and human PBMCs from volunteers. However, H. pylori-treated PBMCs secreted significantly more mature IL-1β throughout the infection period, which suggests a different mode of activation. Taken together, this study demonstrates targeting of inflammasome-forming NLRP3, an important innate immunity component, and crucial manipulation of pro- and anti-inflammatory cytokines in H. pylori infection.

GRP78 protects a disintegrin and metalloprotease 17 against protein-disulfide isomerase A6 catalyzed inactivation

The shedding of ectodomains is a crucial mechanism in many physiological and pathological events. A disintegrin and metalloprotease-17 (ADAM17) is a key sheddase involved in essential processes, such as development, regeneration, and immune defense. ADAM17 exists in two conformations which differ in their disulfide connection in the membrane-proximal domain (MPD). Protein-disulfide isomerases (PDIs) on the cell surface convert the open MPD into a rigid closed form, which corresponds to inactive ADAM17. ADAM17 is expressed in its open activatable form in the endoplasmic reticulum (ER) and consequently must be protected against ER-resident PDI activity. Here, we show that the chaperone 78-kDa glucose-regulated protein (GRP78) protects the MPD against PDI-dependent disulfide-bond isomerization by binding to this domain and, thereby, preventing ADAM17 inhibition.

Overexpression of serine protease HtrA enhances disruption of adherens junctions, paracellular transmigration and type IV secretion of CagA by Helicobacter pylori

BACKGROUND

The serine protease HtrA is an important factor for regulating stress responses and protein quality control in bacteria. In recent studies, we have demonstrated that the gastric pathogen Helicobacter pylori can secrete HtrA into the extracellular environment, where it cleaves-off the ectodomain of the tumor suppressor and adherens junction protein E-cadherin on gastric epithelial cells.

RESULTS

E-cadherin cleavage opens cell-to-cell junctions, allowing paracellular transmigration of the bacteria across polarized monolayers of MKN-28 and Caco-2 epithelial cells. However, rapid research progress on HtrA function is mainly hampered by the lack of ΔhtrA knockout mutants, suggesting that htrA may represent an essential gene in H. pylori. To circumvent this major handicap and to investigate the role of HtrA further, we overexpressed HtrA by introducing a second functional htrA gene copy in the chromosome and studied various virulence properties of the bacteria. The resulting data demonstrate that overexpression of HtrA in H. pylori gives rise to elevated rates of HtrA secretion, cleavage of E-cadherin, bacterial transmigration and delivery of the type IV secretion system (T4SS) effector protein CagA into polarized epithelial cells, but did not affect IL-8 chemokine production or the secretion of vacuolating cytotoxin VacA and γ-glutamyl-transpeptidase GGT.

CONCLUSIONS

These data provide for the first time genetic evidence in H. pylori that HtrA is a novel major virulence factor controlling multiple pathogenic activities of this important microbe.

Regulation and functions of inflammasome-mediated cytokines in Helicobacter pylori infection

Persistent stomach infection with Helicobacter pylori causes chronic mucosal inflammation (gastritis), which is widely recognized as an essential precursor to gastric cancer. The IL-1 interleukin family cytokines IL-1β and IL-18 have emerged as central mediators of mucosal inflammation. Here, we review the regulation and functions of these cytokines in H. pylori-induced inflammation and carcinogenesis.

Helicobacter pylori-Induced Changes in Gastric Acid Secretion and Upper Gastrointestinal Disease

Appropriate management of Helicobacter pylori infection of the human stomach is evolving and remains a significant clinical challenge. Acute infection results in hypochlorhydria, whereas chronic infection results in either hypo- or hyperchlorhydria, depending upon the anatomic site of infection. Acute hypochlorhydria facilitates survival of the bacterium and its infection of the stomach. Interestingly, most patients chronically infected with H. pylori manifest a pangastritis with reduced acid secretion due to bacterial virulence factors, inflammatory cytokines, and various degrees of gastric atrophy. While these patients are predisposed to develop gastric adenocarcinoma (~1%), there is increasing evidence from population studies that they are also protected from gastroesophageal reflux disease (GERD), Barrett's esophagus (BE), and esophageal adenocarcinoma (EAC). Eradication of H. pylori, in these patients, may provoke GERD in predisposed individuals and may be a contributory factor for the rising incidence of refractory GERD, BE, and EAC observed in Westernized societies. Only ~10% of chronically infected patients, mainly the young, manifest an antral predominant gastritis with increased acid secretion due to a decrease in somatostatin and increase in gastrin secretion; these patients are predisposed to develop peptic ulcer disease. H. pylori-induced changes in acid secretion, in particular hypochlorhydria, may allow ingested microorganisms to survive transit through the stomach and colonize the distal intestine and colon. Such perturbation of gut microbiota, i.e. dysbiosis, may influence human health and disease.

Molecular insights into the multilayered regulation of ADAM17: The role of the extracellular region

In contrast to many other signalling mechanisms shedding of membrane-anchored proteins is an irreversible process. A Disintegrin And Metalloproteinase (ADAM) 17 is one of the major sheddases involved in a variety of physiological and pathophysiological processes including regeneration, differentiation, and cancer progression. Due to its central role in signalling the shedding activity of ADAM17 is tightly regulated, especially on the cell surface, where shedding events take place. The activity of ADAM17 can be subdivided into a catalytic activity and the actual shedding activity. Whereas the catalytic activity is constitutively present, the shedding activity has to be induced and is tightly controlled to prevent pathological situations induced by the release of its substrates. The regulation of the shedding activity of ADAM17 is multilayered and different regions of the protease are involved. Intriguingly, its extracellular domains play crucial roles in different regulatory mechanisms. We will discuss the role of these domains in the control of ADAM17 activity. This article is part of a Special Issue entitled: Proteolysis as a Regulatory Event in Pathophysiology edited by Stefan Rose-John.

Proteolysis in Helicobacter pylori-Induced Gastric Cancer

Persistent infections with the human pathogen and class-I carcinogen Helicobacter pylori (H. pylori) are closely associated with the development of acute and chronic gastritis, ulceration, gastric adenocarcinoma and lymphoma of the mucosa-associated lymphoid tissue (MALT) system. Disruption and depolarization of the epithelium is a hallmark of H. pylori-associated disorders and requires extensive modulation of epithelial cell surface structures. Hence, the complex network of controlled proteolysis which facilitates tissue homeostasis in healthy individuals is deregulated and crucially contributes to the induction and progression of gastric cancer through processing of extracellular matrix (ECM) proteins, cell surface receptors, membrane-bound cytokines, and lateral adhesion molecules. Here, we summarize the recent reports on mechanisms how H. pylori utilizes a variety of extracellular proteases, involving the proteases Hp0169 and high temperature requirement A (HtrA) of bacterial origin, and host matrix-metalloproteinases (MMPs), a disintegrin and metalloproteinases (ADAMs) and tissue inhibitors of metalloproteinases (TIMPs). H. pylori-regulated proteases represent predictive biomarkers and attractive targets for therapeutic interventions in gastric cancer.

Type IV Secretion and Signal Transduction of Helicobacter pylori CagA through Interactions with Host Cell Receptors

Helicobacter pylori is a highly successful human bacterium, which is exceptionally equipped to persistently inhabit the human stomach. Colonization by this pathogen is associated with gastric disorders ranging from chronic gastritis and peptic ulcers to cancer. Highly virulent H. pylori strains express the well-established adhesins BabA/B, SabA, AlpA/B, OipA, and HopQ, and a type IV secretion system (T4SS) encoded by the cag pathogenicity island (PAI). The adhesins ascertain intimate bacterial contact to gastric epithelial cells, while the T4SS represents an extracellular pilus-like structure for the translocation of the effector protein CagA. Numerous T4SS components including CagI, CagL, CagY, and CagA have been shown to target the integrin-β₁ receptor followed by translocation of CagA across the host cell membrane. The interaction of CagA with membrane-anchored phosphatidylserine and CagA-containing outer membrane vesicles may also play a role in the delivery process. Translocated CagA undergoes tyrosine phosphorylation in C-terminal EPIYA-repeat motifs by oncogenic Src and Abl kinases. CagA then interacts with an array of host signaling proteins followed by their activation or inactivation in phosphorylation-dependent and phosphorylation-independent fashions. We now count about 25 host cell binding partners of intracellular CagA, which represent the highest quantity of all currently known virulence-associated effector proteins in the microbial world. Here we review the research progress in characterizing interactions of CagA with multiple host cell receptors in the gastric epithelium, including integrin-β₁, EGFR, c-Met, CD44, E-cadherin, and gp130. The contribution of these interactions to H. pylori colonization, signal transduction, and gastric pathogenesis is discussed.

Helicobacter pylori: A Paradigm Pathogen for Subverting Host Cell Signal Transmission

Helicobacter pylori colonizes the gastric mucosa in the human stomach and represents a major risk factor for peptic ulcer disease and gastric cancer. Here, we summarize our current knowledge of the complex impact of H. pylori on manipulating host signalling networks, that is, by the cag pathogenicity island (cagPAI)-encoded type IV secretion system (T4SS). We show that H. pylori infections reflect a paradigm for interspecies contact-dependent molecular communication, which includes the disruption of cell-cell junctions and cytoskeletal rearrangements, as well as proinflammatory, cell cycle-related, proliferative, antiapoptotic, and DNA damage responses. The contribution of these altered signalling cascades to disease outcome is discussed.

Inflammatory signaling pathways induced by Helicobacter pylori in primary human gastric epithelial cells

Inflammatory signaling pathways induced by Helicobacter pylori remain unclear, having been studied mostly on cell-line models derived from gastric adenocarcinoma with potentially altered signaling pathways and nonfunctional receptors. Here, H. pylori-induced signaling pathways were investigated in primary human gastric epithelial cells. Inflammatory response was analyzed on chemokine mRNA expression and production after infection of gastric epithelial cells by H. pylori strains, B128 and B128Δ cagM, a cag type IV secretion system defective strain. Signaling pathway involvement was investigated using inhibitors of epidermal growth factor receptor (EGFR), MAPK, JAK and blocking Abs against TLR2 and TLR4. Inhibitors of EGFR, MAPK and JAK significantly reduced the chemokine mRNA expression and production induced by both H. pylori strains at 3 h and 24 h post-infection. JNK inhibitor reduced chemokine production at 24 h post-infection. Blocking Abs against TLR2 but not TLR4 showed significant reduction of chemokine secretion. Using primary culture of human gastric epithelial cells, our data suggest that H. pylori can be recognized by TLR2, leading to chemokine induction, and that EGFR, MAPK and the JAK/STAT signaling pathways play a key role in the H. pylori-induced CXCL1, CXCL5 and CXCL8 response in a cag pathogenicity island-independent manner.

Use of VacA as a Vaccine Antigen

One of the major toxins secreted by H. pylori is the Vacuolating cytotoxin A (VacA) named after its ability to induce the formation of “vacuole”-like membrane vesicles in the cytoplasm of gastric cells. VacA has been associated with the disruption of mitochondrial functions, stimulation of apoptosis, blockade of T cell proliferation and promotion of regulatory T cells, thereby making it a promising vaccine target. Immunity to bacterial virulence factors is well known to protect humans against bacterial infections; hence, detoxified VacA has been evaluated as a vaccine antigen. Our short review summarizes the pre-clinical and clinical data that have been published on the use of VacA in the development of the H. pylori vaccine.

Composition, structure and function of the Helicobacter pylori cag pathogenicity island encoded type IV secretion system

Many Gram-negative pathogens harbor type IV secretion systems (T4SS) that translocate bacterial virulence factors into host cells to hijack cellular processes. The pathology of the gastric pathogen Helicobacter pylori strongly depends on a T4SS encoded by the cag pathogenicity island. This T4SS forms a needle-like pilus, and its assembly is accomplished by multiple protein-protein interactions and various pilus-associated factors that bind to integrins followed by delivery of the CagA oncoprotein into gastric epithelial cells. Recent studies revealed the crystal structures of six T4SS proteins and pilus formation is modulated by iron and zinc availability. All these T4SS interactions are crucial for deregulating host signaling events and disease progression. New developments in T4SS functions and their importance for pathogenesis are discussed.

Helicobacter pylori CagL Hypervariable Motif: A Global Analysis of Geographical Diversity and Association With Gastric Cancer

Previous studies suggest overrepresentation of particular polymorphisms within the Helicobacter pylori CagL hypervariable motif (CagLHM) in gastric cancer-associated isolates. However, these disease correlations were geographically variable and ambiguous. We compared the disease correlation of several hundred geographically diverse CagL sequences and identified 33 CagLHM sequence combinations with disparate geographical distribution, revealing substantial worldwide CagLHM diversity, particularly within Asian countries. Notably, polymorphisms E59 and I60 were significantly overrepresented, whereas D58 and E62 were underrepresented, in gastric cancer-associated H. pylori isolates worldwide. Thus, CagLHM regional diversity may contribute to the varied prevalence of H. pylori-related gastric cancer observed in diverse populations.

ADAM Proteases and Gastrointestinal Function

A disintegrin and metalloproteinases (ADAMs) are a family of cell surface proteases that regulate diverse cellular functions, including cell adhesion, migration, cellular signaling, and proteolysis. Proteolytically active ADAMs are responsible for ectodomain shedding of membrane-associated proteins. ADAMs rapidly modulate key cell signaling pathways in response to changes in the extracellular environment (e.g., inflammation) and play a central role in coordinating intercellular communication within the local microenvironment. ADAM10 and ADAM17 are the most studied members of the ADAM family in the gastrointestinal tract. ADAMs regulate many cellular processes associated with intestinal development, cell fate specification, and the maintenance of intestinal stem cell/progenitor populations. Several signaling pathway molecules that undergo ectodomain shedding by ADAMs [e.g., ligands and receptors from epidermal growth factor receptor (EGFR)/ErbB and tumor necrosis factor α (TNFα) receptor (TNFR) families] help drive and control intestinal inflammation and injury/repair responses. Dysregulation of these processes through aberrant ADAM expression or sustained ADAM activity is linked to chronic inflammation, inflammation-associated cancer, and tumorigenesis.

Helicobacter pylori virulence factors affecting gastric proton pump expression and acid secretion

Acute Helicobacter pylori infection of gastric epithelial cells and human gastric biopsies represses H,K-ATPase α subunit (HKα) gene expression and inhibits acid secretion, causing transient hypochlorhydria and supporting gastric H. pylori colonization. Infection by H. pylori strains deficient in the cag pathogenicity island (cag PAI) genes cagL, cagE, or cagM, which do not transfer CagA into host cells or induce interleukin-8 secretion, does not inhibit HKα expression, nor does a cagA-deficient strain that induces IL-8. To test the hypothesis that virulence factors other than those mediating CagA translocation or IL-8 induction participate in HKα repression by activating NF-κB, AGS cells transfected with HKα promoter-Luc reporter constructs containing an intact or mutated NF-κB binding site were infected with wild-type H. pylori strain 7.13, isogenic mutants lacking cag PAI genes responsible for CagA translocation and/or IL-8 induction (cagA, cagζ, cagε, cagZ, and cagβ), or deficient in genes encoding two peptidoglycan hydrolases (slt and cagγ). H. pylori-induced AGS cell HKα promoter activities, translocated CagA, and IL-8 secretion were measured by luminometry, immunoblotting, and ELISA, respectively. Human gastric biopsy acid secretion was measured by microphysiometry. Taken together, the data showed that HKα repression is independent of IL-8 expression, and that CagA translocation together with H. pylori transglycosylases encoded by slt and cagγ participate in NF-κB-dependent HKα repression and acid inhibition. The findings are significant because H. pylori factors other than CagA and IL-8 secretion are now implicated in transient hypochlorhydria which facilitates gastric colonization and potential triggering of epithelial progression to neoplasia.

Preservation of Helicobacter pylori CagA Translocation and Host Cell Proinflammatory Responses in the Face of CagL Hypervariability at Amino Acid Residues 58/59

Carriage of the CagA oncoprotein by the human gastric cancer-associated pathogen Helicobacter pylori is significantly associated with this typically benign chronic infection advancing to a potentially fatal outcome. However it remains to be elucidated why only a small subset of individuals infected with H. pylori CagA-positive strains develops gastric cancer. H. pylori translocates CagA into host cells using a type IV secretion apparatus that interacts with host integrin receptors via a three-amino-acid-residue RGD motif on the H. pylori protein CagL. The RGD motif of CagL also plays a major role in the induction of proinflammatory responses. Upstream of this motif is a conserved glycine flanked by four hypervariable amino acid residues (residues 58, 59, 61 and 62). Certain amino acid polymorphisms at 58 and 59 are significantly prevalent in strains from gastric cancer patients in particular geographic regions; Y58E59 is seen in Taiwan and D58K59 in India. In light of the seemingly contradictory findings of recent CagL mutagenesis studies, we have examined the contribution of sequence promiscuity specifically at CagL residues 58 and 59 to CagA translocation and H. pylori-mediated proinflammatory responses of gastric epithelial cells. Using isogenic mutants of H. pylori strains P12 and 26695 with amino acid substitutions at CagL residues 58 and 59, we determined that carriage of the polymorphisms Y58E59, D58K59, D58E59, N58E59 or N58K59 did not significantly alter the capacity of H. pylori to translocate CagA into, or induce IL-8 secretion in, host cells. Our findings, together with other recently published data, suggest that the variation at CagL residues 58 and 59 does not influence type IV secretion system function in isolation, but rather may work in concert with particular polymorphisms elsewhere in CagL to modulate disease progression.