SagA of CagA in Helicobacter pylori pathogenesis

CagI is an essential component of the Helicobacter pylori Cag type IV secretion system and forms a complex with CagL

Helicobacter pylori, the causative agent of type B gastritis, peptic ulcers, gastric adenocarcinoma and MALT lymphoma, uses the Cag type IV secretion system to induce a strong proinflammatory response in the gastric mucosa and to inject its effector protein CagA into gastric cells. CagA translocation results in altered host cell gene expression profiles and cytoskeletal rearrangements, and it is considered as a major bacterial virulence trait. Recently, it has been shown that binding of the type IV secretion apparatus to integrin receptors on target cells is a crucial step in the translocation process. Several bacterial proteins, including the Cag-specific components CagL and CagI, have been involved in this interaction. Here, we have examined the localization and interactions of CagI in the bacterial cell. Since the cagI gene overlaps and is co-transcribed with the cagL gene, the role of CagI for type IV secretion system function has been difficult to assess, and conflicting results have been reported regarding its involvement in the proinflammatory response. Using a marker-free gene deletion approach and genetic complementation, we show now that CagI is an essential component of the Cag type IV secretion apparatus for both CagA translocation and interleukin-8 induction. CagI is distributed over soluble and membrane-associated pools and seems to be partly surface-exposed. Deletion of several genes encoding essential Cag components has an impact on protein levels of CagI and CagL, suggesting that both proteins require partial assembly of the secretion apparatus. Finally, we show by co-immunoprecipitation that CagI and CagL interact with each other. Taken together, our results indicate that CagI and CagL form a functional complex which is formed at a late stage of secretion apparatus assembly.

c-Src and c-Abl kinases control hierarchic phosphorylation and function of the CagA effector protein in Western and East Asian Helicobacter pylori strains

Many bacterial pathogens inject into host cells effector proteins that are substrates for host tyrosine kinases such as Src and Abl family kinases. Phosphorylated effectors eventually subvert host cell signaling, aiding disease development. In the case of the gastric pathogen Helicobacter pylori, which is a major risk factor for the development of gastric cancer, the only known effector protein injected into host cells is the oncoprotein CagA. Here, we followed the hierarchic tyrosine phosphorylation of H. pylori CagA as a model system to study early effector phosphorylation processes. Translocated CagA is phosphorylated on Glu-Pro-Ile-Tyr-Ala (EPIYA) motifs EPIYA-A, EPIYA-B, and EPIYA-C in Western strains of H. pylori and EPIYA-A, EPIYA-B, and EPIYA-D in East Asian strains. We found that c-Src only phosphorylated EPIYA-C and EPIYA-D, whereas c-Abl phosphorylated EPIYA-A, EPIYA-B, EPIYA-C, and EPIYA-D. Further analysis revealed that CagA molecules were phosphorylated on 1 or 2 EPIYA motifs, but never simultaneously on 3 motifs. Furthermore, none of the phosphorylated EPIYA motifs alone was sufficient for inducing AGS cell scattering and elongation. The preferred combination of phosphorylated EPIYA motifs in Western strains was EPIYA-A and EPIYA-C, either across 2 CagA molecules or simultaneously on 1. Our study thus identifies a tightly regulated hierarchic phosphorylation model for CagA starting at EPIYA-C/D, followed by phosphorylation of EPIYA-A or EPIYA-B. These results provide insight for clinical H. pylori typing and clarify the role of phosphorylated bacterial effector proteins in pathogenesis.

Identification of genetic modifiers of CagA-induced epithelial disruption in Drosophila

Helicobacter pylori strains containing the CagA protein are associated with high risk of gastric diseases including atrophic gastritis, peptic ulcers, and gastric cancer. CagA is injected into host cells via a Type IV secretion system where it activates growth factor-like signaling, disrupts cell-cell junctions, and perturbs host cell polarity. Using a transgenic Drosophila model, we have shown that CagA expression disrupts the morphogenesis of epithelial tissues such as the adult eye. Here we describe a genetic screen to identify modifiers of CagA-induced eye defects. We determined that reducing the copy number of genes encoding components of signaling pathways known to be targeted by CagA, such as the epidermal growth factor receptor (EGFR), modified the CagA-induced eye phenotypes. In our screen of just over half the Drosophila genome, we discovered 12 genes that either suppressed or enhanced CagA's disruption of the eye epithelium. Included in this list are genes involved in epithelial integrity, intracellular trafficking, and signal transduction. We investigated the mechanism of one suppressor, encoding the epithelial polarity determinant and junction protein Coracle, which is homologous to the mammalian Protein 4.1. We found that loss of a single copy of coracle improved the organization and integrity of larval retinal epithelia expressing CagA, but did not alter CagA's localization to cell junctions. Loss of a single copy of the coracle antagonist crumbs enhanced CagA-associated disruption of the larval retinal epithelium, whereas overexpression of crumbs suppressed this phenotype. Collectively, these results point to new cellular pathways whose disruption by CagA are likely to contribute to H. pylori-associated disease pathology.

J-Western forms of Helicobacter pylori cagA constitute a distinct phylogenetic group with a widespread geographic distribution

Chronic infection with Helicobacter pylori strains expressing the bacterial oncoprotein CagA confers an increased risk of gastric cancer. While much is known about the ancestry and molecular evolution of Western, East Asian, and Amerindian cagA sequences, relatively little is understood about a fourth group, known as "J-Western," which has been detected mainly in strains from Okinawa, Japan. We show here that J-Western cagA sequences have a more widespread global distribution than previously recognized, occur in strains with multiple different ancestral origins (based on multilocus sequence typing [MLST] analysis), and did not arise recently. As shown by comparisons of Western and J-Western forms of CagA, there are 45 fixed or nearly fixed amino acid differences, and J-Western forms contain a unique 4-amino-acid insertion. The mean nucleotide diversity of synonymous sites (π(s)) is slightly lower in the J-Western group than in the Western and East Asian groups (0.066, 0.086, and 0.083, respectively), which suggests that the three groups have comparable, but not equivalent, effective population sizes. The reduced π(s) of the J-Western group is attributable to ancestral recombination events within the 5' region of cagA. Population genetic analyses suggest that within the cagA region encoding EPIYA motifs, the East Asian group underwent a marked reduction in effective population size compared to the Western and J-Western groups, in association with positive selection. Finally, we show that J-Western cagA sequences are found mainly in strains producing m2 forms of the secreted VacA toxin and propose that these functionally interacting proteins coevolved to optimize the gastric colonization capacity of H. pylori.

Characterization of CagI in the cag pathogenicity island of Helicobacter pylori

Helicobacter pylori is a highly successful human-specific gastric pathogen that infects up to 50% of the world's population. Virulent H. pylori isolates harbor the cytotoxin-associated genes pathogenicity island (cag-PAI), which encodes a type IV secretion system that translocates bacterial effector (e.g., CagA oncoprotein) molecules into host cells. Although some cag-PAI genes are shown to be required for CagA delivery or localization, the majority have no known function. In the current study, the authors performed a cell components fractionation assay and showed that CagI, one of the cag-PAI proteins located in the bacterial membrane, was not translocated into host cells. The homologous recombination method then was used to construct the isogenic mutant of H. pylori cagI, and the translocation assay was performed. The results showed that the isogenic mutant of H. pylori NCTC 11637 cagI could cause a reduction in the degree of CagA translocation. Overall, the results suggested that CagI might be an accessory component of the CagA secretion system not translocated into host cells and that it is located in the bacterial membrane.

Molecular mechanisms of gastric epithelial cell adhesion and injection of CagA by Helicobacter pylori

Helicobacter pylori is a highly successful pathogen uniquely adapted to colonize humans. Gastric infections with this bacterium can induce pathology ranging from chronic gastritis and peptic ulcers to gastric cancer. More virulent H. pylori isolates harbour numerous well-known adhesins (BabA/B, SabA, AlpA/B, OipA and HopZ) and the cag (cytotoxin-associated genes) pathogenicity island encoding a type IV secretion system (T4SS). The adhesins establish tight bacterial contact with host target cells and the T4SS represents a needle-like pilus device for the delivery of effector proteins into host target cells such as CagA. BabA and SabA bind to blood group antigen and sialylated proteins respectively, and a series of T4SS components including CagI, CagL, CagY and CagA have been shown to target the integrin β₁ receptor followed by injection of CagA across the host cell membrane. The interaction of CagA with membrane-anchored phosphatidylserine may also play a role in the delivery process. While substantial progress has been made in our current understanding of many of the above factors, the host cell receptors for OipA, HopZ and AlpA/B during infection are still unknown. Here we review the recent progress in characterizing the interactions of the various adhesins and structural T4SS proteins with host cell factors. The contribution of these interactions to H. pylori colonization and pathogenesis is discussed.

Mammalian Pragmin regulates Src family kinases via the Glu-Pro-Ile-Tyr-Ala (EPIYA) motif that is exploited by bacterial effectors

Several pathogenic bacteria have adopted effector proteins that, upon delivery into mammalian cells, undergo tyrosine phosphorylation at the Glu-Pro-Ile-Tyr-Ala (EPIYA) or EPIYA-like sequence motif by host kinases such as Src family kinases (SFKs). This EPIYA phosphorylation triggers complex formation of bacterial effectors with SH2 domain-containing proteins that results in perturbation of host cell signaling and subsequent pathogenesis. Although the presence of such an anomalous protein interaction suggests the existence of a mammalian EPIYA-containing protein whose function is mimicked or subverted by bacterial EPIYA effectors, no molecule that uses the EPIYA motif for biological function has so far been reported in mammals. Here we show that mammalian Pragmin/SgK223 undergoes tyrosine phosphorylation at the EPIYA motif by SFKs and thereby acquires the ability to interact with the SH2 domain of the C-terminal Src kinase (Csk), a negative regulator of SFKs. The Pragmin-Csk interaction prevents translocalization of Csk from the cytoplasm to the membrane and subsequent inactivation of membrane-associated SFKs. As a result, SFK activity is sustained in cells where Pragmin is phosphorylated at the EPIYA motif. Because EPIYA phosphorylation of Pragmin is mediated by SFKs, cytoplasmic sequestration of Csk by Pragmin establishes a positive feedback regulation of SFK activation. Remarkably, the Helicobacter pylori EPIYA effector CagA binds to the Csk SH2 domain in place of Pragmin and enforces membrane recruitment of Csk and subsequent inhibition of SFKs. This work identifies Pragmin as a mammalian EPIYA effector and suggests that bacterial EPIYA effectors target Pragmin to subvert SFKs for successful infection.

The Human Gastric Pathogen Helicobacter pylori and Its Association with Gastric Cancer and Ulcer Disease

With the momentous discovery in the 1980's that a bacterium, Helicobacter pylori, can cause peptic ulcer disease and gastric cancer, antibiotic therapies and prophylactic measures have been successful, only in part, in reducing the global burden of these diseases. To date, ~700,000 deaths worldwide are still attributable annually to gastric cancer alone. Here, we review H. pylori's contribution to the epidemiology and histopathology of both gastric cancer and peptic ulcer disease. Furthermore, we examine the host-pathogen relationship and H. pylori biology in context of these diseases, focusing on strain differences, virulence factors (CagA and VacA), immune activation and the challenges posed by resistance to existing therapies. We consider also the important role of host-genetic variants, for example, in inflammatory response genes, in determining infection outcome and the role of H. pylori in other pathologies—some accepted, for example, MALT lymphoma, and others more controversial, for example, idiopathic thrombocytic purpura. More recently, intriguing suggestions that H. pylori has protective effects in GERD and autoimmune diseases, such as asthma, have gained momentum. Therefore, we consider the basis for these suggestions and discuss the potential impact for future therapeutic rationales.

Attenuated CagA oncoprotein in Helicobacter pylori from Amerindians in Peruvian Amazon

Population genetic analyses of bacterial genes whose products interact with host tissues can give new understanding of infection and disease processes. Here we show that strains of the genetically diverse gastric pathogen Helicobacter pylori from Amerindians from the remote Peruvian Amazon contain novel alleles of cagA, a major virulence gene, and reveal distinctive properties of their encoded CagA proteins. CagA is injected into the gastric epithelium where it hijacks pleiotropic signaling pathways, helps Hp exploit its special gastric mucosal niche, and affects the risk that infection will result in overt gastroduodenal diseases including gastric cancer. The Amerindian CagA proteins contain unusual but functional tyrosine phosphorylation motifs and attenuated CRPIA motifs, which affect gastric epithelial proliferation, inflammation, and bacterial pathogenesis. Amerindian CagA proteins induced less production of IL-8 and cancer-associated Mucin 2 than did those of prototype Western or East Asian strains and behaved as dominant negative inhibitors of action of prototype CagA during mixed infection of Mongolian gerbils. We suggest that Amerindian cagA is of relatively low virulence, that this may have been selected in ancestral strains during infection of the people who migrated from Asia into the Americas many thousands of years ago, and that such attenuated CagA proteins could be useful therapeutically.

Role of cagA-positive Helicobacter pylori on cell proliferation, apoptosis, and inflammation in biliary cells

BACKGROUND AND AIMS

The pathogenesis of Helicobacter pylori in the human hepatobiliary system has not been clearly elucidated. We compared the effects of H. pylori cagA(+) and cagA(-) mutant strains on cell proliferation, apoptosis, and inflammation in a cholangiocarcinoma (CCA) cell line (KKU-100).

METHODS

MTT and BrdU were used to determine cell viability and DNA synthesis, respectively. The results were further investigated by RT-PCR and Western-blot analysis. The production of interleukin-8 (IL-8) was measured by ELISA assay.

RESULTS

At low H. pylori inocula (cell-bacteria ratio of 1:1), the H. pylori cagA(+) strain showed a significant stimulation in KKU-100 cell growth (109 ± 1.79%) and DNA synthesis (131 ± 3.39%) than did the H. pylori cagA(-) strain (95 ± 3.06% and 120 ± 2.32%, respectively), through activation of the anti-apoptotic bcl-2 gene, MAP kinase and NF- κB cascade. By contrast, at high H. pylori inocula (cell-bacteria ratio of 1:200), the H. pylori cagA(+) strain showed a significant reduction in KKU-100 cell survival (49 ± 2.47%) and DNA synthesis (49 ± 1.14%) than did the H. pylori cagA(-) strain (60 ± 1.30% and 75 ± 4.00%, respectively), by increased iNOS, p53 and bax, while decreased bcl-2. Additionally, caspase-8 and -3 protein were activated. The H. pylori cagA (+) strain had significantly stronger effect on IL-8 production than did the cagA(-) strain.

CONCLUSIONS

These results suggest that the H. pylori cagA(+) strain may play an important role in the development of biliary cancer by disturbing cell proliferation, apoptosis, and promoting cell inflammation in the CCA cell line.

Induction of TLR-2 and TLR-5 expression by Helicobacter pylori switches cagPAI-dependent signalling leading to the secretion of IL-8 and TNF-α

Helicobacter pylori is the causative agent for developing gastritis, gastric ulcer, and even gastric cancer. Virulent strains carry the cag pathogenicity island (cagPAI) encoding a type-IV secretion system (T4SS) for injecting the CagA protein. However, mechanisms of sensing this pathogen through Toll-like receptors (TLRs) and downstream signalling pathways in the development of different pathologies are widely unclear. Here, we explored the involvement of TLR-2 and TLR-5 in THP-1 cells and HEK293 cell lines (stably transfected with TLR-2 or TLR-5) during infection with wild-type H. pylori and isogenic cagPAI mutants. H. pylori triggered enhanced TLR-2 and TLR-5 expression in THP-1, HEK293-TLR2 and HEK293-TLR5 cells, but not in the HEK293 control. In addition, IL-8 and TNF-α cytokine secretion in THP-1 cells was induced in a cagPAI-dependent manner. Furthermore, we show that HEK293 cells are not competent for the uptake of T4SS-delivered CagA, and are therefore ideally suited for studying TLR signalling in the absence of T4SS functions. HEK293 control cells, which do not induce TLR-2 and TLR-5 expression during infection, only secreted cytokines in small amounts, in agreement with T4SS functions being absent. In contrast, HEK293-TLR2 and HEK293-TLR5 cells were highly competent for inducing the secretion of IL-8 and TNF-α cytokines in a cagPAI-independent manner, suggesting that the expression of TLR-2 or TLR-5 has profoundly changed the capability to trigger pro-inflammatory signalling upon infection. Using phospho-specific antibodies and luciferase reporter assays, we further demonstrate that H. pylori induces IRAK-1 and IκB phosphorylation in a TLR-dependent manner, and this was required for activation of transcription factor NF-κB. Finally, NF-κB activation in HEK293-TLR2 and HEK293-TLR5 cells was confirmed by expressing p65-GFP which was translocated from the cytoplasm into the nucleus. These data indicate that H. pylori-induced expression of TLR-2 and TLR-5 can qualitatively shift cagPAI-dependent to cagPAI-independent pro-inflammatory signalling pathways with possible impact on the outcome of H. pylori-associated diseases.

Role of the cag-pathogenicity island encoded type IV secretion system in Helicobacter pylori pathogenesis

Helicobacter pylori is a very successful human-specific bacterium worldwide. Infections of the stomach with this pathogen can induce pathologies, including chronic gastritis, peptic ulcers and even gastric cancer. Highly virulent H. pylori strains encode the cytotoxin-associated gene (cag)-pathogenicity island, which expresses a type IV secretion system (T4SS). This T4SS forms a syringe-like pilus structure for the injection of virulence factors such as the CagA effector protein into host target cells. This is achieved by a number of T4SS proteins, including CagI, CagL, CagY and CagA, which by itself binds the host cell integrin member β(1) followed by delivery of CagA across the host cell membrane. A role of CagA interaction with phosphatidylserine has also been shown to be important for the injection process. After delivery, CagA becomes phosphorylated by oncogenic tyrosine kinases and mimics a host cell factor for the activation or inactivation of some specific intracellular signalling pathways. We review recent progress aiming to characterize the CagA-dependent and CagA-independent signalling capabilities of the T4SS, which include the induction of membrane dynamics, disruption of cell-cell junctions and actin-cytoskeletal rearrangements, as well as pro-inflammatory, cell cycle-related and anti-apoptotic transcriptional responses. The contribution of these signalling pathways to pathogenesis during H. pylori infections is discussed.

Molecular cross-talk between Helicobacter pylori and human gastric mucosa

Helicobacter pylori (H. pylori) has co-evolved with humans to be transmitted from person to person and to colonize the stomach persistently. A well-choreographed equilibrium between the bacterial effectors and host responses permits microbial persistence and health of the host, but confers a risk for serious diseases including gastric cancer. During its long coexistence with humans, H. pylori has developed complex strategies to limit the degree and extent of gastric mucosal damage and inflammation, as well as immune effector activity. The present editorial thus aims to introduce and comment on major advances in the rapidly developing area of H. pylori/human gastric mucosa interaction (and its pathological sequelae), which is the result of millennia of co-evolution of, and thus of reciprocal knowledge between, the pathogen and its human host.

Helicobacter pylori CagA disrupts epithelial patterning by activating myosin light chain

Helicobacter pylori infection is a leading cause of ulcers and gastric cancer. We show that expression of the H. pylori virulence factor CagA in a model Drosophila melanogaster epithelium induces morphological disruptions including ectopic furrowing. We find that CagA alters the distribution and increases the levels of activated myosin regulatory light chain (MLC), a key regulator of epithelial integrity. Reducing MLC activity suppresses CagA-induced disruptions. A CagA mutant lacking EPIYA motifs (CagA^EPISA) induces less epithelial disruption and is not targeted to apical foci like wild-type CagA. In a cell culture model in which CagA^EPISA and CagA have equivalent subcellular localization, CagA^EPISA is equally potent in activating MLC. Therefore, in our transgenic system, CagA is targeted by EPIYA motifs to a specific apical region of the epithelium where it efficiently activates MLC to disrupt epithelial integrity.

Integrin-mediated type IV secretion by Helicobacter: what makes it tick?

Helicobacter pylori (Hp) employs a multi-component type IV secretion system (T4SS) to secrete the effector protein CagA into the cytosol of infected host cells. A longstanding challenge has been to identify the host cell receptor(s) involved. Two recent studies have independently unveiled human β(1) integrin as the receptor but are divided over which T4SS proteins bind to β(1) integrin. Here we revisit the two models in light of previous findings and recent progress in the field. More concerted efforts are required to fully understand the complex T4SS mechanisms that underpin Hp pathogenesis.

Architecture of the Helicobacter pylori Cag-type IV secretion system

Type IV secretion systems (T4SS) are macromolecular assemblies used by bacteria to transport material across their membranes. T4SS are generally composed of a set of twelve proteins (VirB1-11 and VirD4). This represents a dynamic machine powered by three ATPases. T4SS are widespread in pathogenic bacteria where they are often used to deliver effectors into host cells. For example, the human pathogen Helicobacter pylori encodes a T4SS, the Cag-T4SS, which mediates the injection of the toxin CagA. We review the progress made in the past decade in our understanding of T4SS architecture. We translate this new knowledge to derive an understanding of the structure of the H. pylori Cag system, and use recent protein-protein interaction data to refine this model.

Assembly and molecular mode of action of the Helicobacter pylori Cag type IV secretion apparatus

Bacterial type IV secretion systems (T4SS) form supramolecular protein complexes that are capable of transporting DNA or protein substrates across the bacterial cell envelope and, in many cases, also across eukaryotic target cell membranes. Because of these characteristics, they are often used by pathogenic bacteria for the injection of host cell-modulating virulence factors. One example is the human pathogen Helicobacter pylori, which uses the Cag-T4SS to induce a pro-inflammatory response and multiple cytoskeletal and gene regulatory effects in gastric epithelial cells. Work in recent years has shown that the Cag-T4SS exhibits marked differences in relation to other systems, both with respect to the composition of its secretion apparatus and the molecular details of its secretion mechanisms. This review describes the molecular properties of the Cag-T4SS and compares these with prototypical systems of this family of protein transporters.

A novel inhibitory domain of Helicobacter pylori protein CagA reduces CagA effects on host cell biology

The Helicobacter pylori protein CagA (cytotoxin-associated gene A) is associated with an increased risk for gastric cancer formation. After attachment to epithelial cells, the bacteria inject CagA via a type IV secretion apparatus into host cells, where it exerts its biological activity. Host cell responses to intracellular CagA have been linked exclusively to signaling motifs in the C terminus of the CagA protein. Little is known about the functional role of the remaining CagA protein. Using transgenic expression of CagA mutants in epithelial cells, we were able to identify a novel CagA inhibitory domain at the N terminus consisting of the first 200 amino acids. This domain localizes to cell-cell contacts and increases the rate and strength of cell-cell adhesion in epithelial cells. Thus, it compensates for the loss of cell-cell adhesion induced by the C terminus of the CagA protein. Consistent with its stabilizing role on cell-cell adhesion, the CagA N terminus domain reduces the CagA-induced β-catenin transcriptional activity in the nucleus. Furthermore, it inhibits apical surface constriction and cell elongations, host cell phenotypes induced by the C terminus in polarized epithelia. Therefore, our study suggests that CagA contains an intrinsic inhibitory domain that reduces host cell responses to CagA, which have been associated with the formation of cancer.

The origin of non-H. pylori-related positive Giemsa staining in human gastric biopsy specimens: A prospective study

BACKGROUND

Upper gastrointestinal endoscopically biopsied specimens are usually sent for the diagnosis of Helicobacter pylori infection. The study aimed to determine the relationship between the origin of positive Giemsa staining and the grade of gastritis based on the updated Sydney system.

METHODS

Gastric biopsy specimens taken at the lesser curvature and greater curvature sides of the corpus and greater curvature side of the antrum were stained with H&E, Giemsa, anti-East Asian-specific antibody and anti-H. pylori antibody stains. Pyrosequencing analysis was performed in cases that showed discrepancy between the Giemsa and anti-H. pylori antibody staining.

RESULTS

Seventy-two out of 150 cases (48%) stained positive for anti-H. pylori antibody, of which 68 (94.4%) stained positive for anti-East Asian-specific antibody stain. Twelve of the 20 cases with discrepant results for Giemsa and anti-H. pylori antibody stains exhibited Campylobacter hyointestinalis infection. The grades of neutrophil activity (p<0.001) and chronic inflammation (p<0.001) were lower for Campylobacter infection than for East Asian CagA H. pylori-related infection.

CONCLUSION

C. hyointestinalis is the most common cause of non-H. pylori-related Giemsa positive infection, and is associated with lower grades of neutrophil activity and chronic inflammation than East Asian CagA H. pylori-related infection.

Anthropological and clinical implications for the structural diversity of the Helicobacter pylori CagA oncoprotein

Helicobacter pylori CagA is the first bacterial oncoprotein to be identified in relation to human cancer. CagA is delivered into gastric epithelial cells through a bacterial type IV secretion system and localizes to the plasma membrane, where it undergoes tyrosine phosphorylation by host cell kinases. Membrane-localized CagA then mimics mammalian scaffold proteins and perturbs a number of host signaling pathways in both tyrosine phosphorylation-dependent and -independent manners, thereby promoting transformation of gastric epithelial cells. Helicobacter pylori CagA is noted for structural diversity in its C-terminal region, with which CagA interacts with numerous host cell proteins. This CagA polymorphism is primarily due to differential combination and alignment of the four distinct EPIYA segments and the two different CagA-multimerization sequences in making the C-terminal region. The structural diversity substantially influences the pathophysiological action of CagA. This review focuses on the molecular basis for the structural polymorphism that determines the degrees of virulence and oncogenic potential of individual CagA. The pylogeographic distribution of differential CagA isoforms is also discussed in the context of human migration history, which may underlie large geographical variations in the incidence of gastric cancer in different parts of the world.

Promoter DNA hypermethylation in gastric biopsies from subjects at high and low risk for gastric cancer

Gene promoter CpG island hypermethylation is associated with Helicobacter pylori (H. pylori) infection and may be an important initiator of gastric carcinogenesis. To examine factors influencing methylation, we utilized bisulfite Pyrosequencing® technology for quantitative analysis of promoter DNA methylation in RPRM, APC, MGMT and TWIST1 genes using DNA from 86 gastric biopsies from Colombian residents of areas with high and low incidence of gastric cancer. H. pylori colonies were cultured from the same subjects, and gastric pathology was evaluated. Virulence factors cagA (including segments of the 3' end, encoding EPIYA polymorphisms) and vacA s and m regions were characterized in the H. pylori strains. Using univariate analysis, we found significantly elevated levels of RPRM and TWIST1 promoter DNA methylation in biopsies from residents of the high-risk region compared to those from residents of the low-risk region. The presence of cagA and vacA s1m1 alleles were independently associated with elevated levels of promoter DNA methylation of RPRM and MGMT. Using multivariate analysis, DNA methylation of RPRM was associated with location of residence, cagA and vacA s1m1 status and methylation of TWIST1. We conclude that cagA and vacA virulence determinants are significantly associated with quantitative differences in promoter DNA methylation in these populations, but that other as yet undefined factors that differ between the populations may also contribute to variation in methylation status.

Effector prediction in host-pathogen interaction based on a Markov model of a ubiquitous EPIYA motif

Background

Effector secretion is a common strategy of pathogen in mediating host-pathogen interaction. Eight EPIYA-motif containing effectors have recently been discovered in six pathogens. Once these effectors enter host cells through type III/IV secretion systems (T3SS/T4SS), tyrosine in the EPIYA motif is phosphorylated, which triggers effectors binding other proteins to manipulate host-cell functions. The objectives of this study are to evaluate the distribution pattern of EPIYA motif in broad biological species, to predict potential effectors with EPIYA motif, and to suggest roles and biological functions of potential effectors in host-pathogen interactions.

Results

A hidden Markov model (HMM) of five amino acids was built for the EPIYA-motif based on the eight known effectors. Using this HMM to search the non-redundant protein database containing 9,216,047 sequences, we obtained 107,231 sequences with at least one EPIYA motif occurrence and 3115 sequences with multiple repeats of the EPIYA motif. Although the EPIYA motif exists among broad species, it is significantly over-represented in some particular groups of species. For those proteins containing at least four copies of EPIYA motif, most of them are from intracellular bacteria, extracellular bacteria with T3SS or T4SS or intracellular protozoan parasites. By combining the EPIYA motif and the adjacent SH2 binding motifs (KK, R4, Tarp and Tir), we built HMMs of nine amino acids and predicted many potential effectors in bacteria and protista by the HMMs. Some potential effectors for pathogens (such as Lawsonia intracellularis, Plasmodium falciparum and Leishmania major) are suggested.

Conclusions

Our study indicates that the EPIYA motif may be a ubiquitous functional site for effectors that play an important pathogenicity role in mediating host-pathogen interactions. We suggest that some intracellular protozoan parasites could secrete EPIYA-motif containing effectors through secretion systems similar to the T3SS/T4SS in bacteria. Our predicted effectors provide useful hypotheses for further studies.

Genetic predisposition to Helicobacter pylori-induced gastric precancerous conditions

Gastric cancer is the most common malignancy of the gastrointestinal tract in East Asian populations and the second most frequent cause of cancer-related mortality in the world. While previous studies have investigated the genetic factors involved in gastric carcinogenesis, there still exist relatively few studies that have investigated the genetic traits associated with the risk of gastric precancerous conditions. In this paper we will review the biology and genetic polymorphisms involved in the genesis of gastric precancerous conditions reported to date and discuss the future prospects of this field of study. The associations of gastric precancerous conditions with polymorphisms in the cytotoxin-associated gene A-related genes (e.g. PTPN11 G/A at intron 3, rs2301756), those in the genes involved in host immunity against Helicobacter pylori (H. pylori) infection (e.g. TLR4 +3725G/C, rs11536889) or polymorphisms of the genes essential for the development/ differentiation of the gastric epithelial cells (e.g. RUNX3 T/A polymorphism at intron 3, rs760805) have been reported to date. Genetic epidemiological studies of the associations between H. pylori-induced gastric precancerous conditions and other gene polymorphisms in these pathways as well as polymorphisms of the genes involved in other pathways like oxidative DNA damage repair pathways would provide useful evidence for the individualized prevention of these H. pylori-induced gastric precancerous conditions.

Helicobacter pylori CagA targets gastric tumor suppressor RUNX3 for proteasome-mediated degradation

Chronic infection with cagA-positive Helicobacter pylori is the strongest risk factor for the development of gastric adenocarcinoma. The cagA gene product CagA is injected into gastric epithelial cells and disturbs cellular functions by physically interacting with and deregulating a variety of cellular signaling molecules. RUNX3 is a tumor suppressor in many tissues, and it is frequently inactivated in gastric cancer. In this study, we show that H. pylori infection inactivates the gastric tumor suppressor RUNX3 in a CagA-dependent manner. CagA directly associates with RUNX3 through a specific recognition of the PY motif of RUNX3 by a WW domain of CagA. Deletion of the WW domains of CagA or mutation of the PY motif in RUNX3 abolishes the ability of CagA to induce the ubiquitination and degradation of RUNX3, thereby extinguishing its ability to inhibit the transcriptional activation of RUNX3. Our studies identify RUNX3 as a novel cellular target of H. pylori CagA and also reveal a mechanism by which CagA functions as an oncoprotein by blocking the activity of gastric tumor suppressor RUNX3.

Conversion of Helicobacter pylori CagA from senescence inducer to oncogenic driver through polarity-dependent regulation of p21

The Helicobacter pylori CagA bacterial oncoprotein plays a critical role in gastric carcinogenesis. Upon delivery into epithelial cells, CagA causes loss of polarity and activates aberrant Erk signaling. We show that CagA-induced Erk activation results in senescence and mitogenesis in nonpolarized and polarized epithelial cells, respectively. In nonpolarized epithelial cells, Erk activation results in oncogenic stress, up-regulation of the p21(Waf1/Cip1) cyclin-dependent kinase inhibitor, and induction of senescence. In polarized epithelial cells, CagA-driven Erk signals prevent p21(Waf1/Cip1) expression by activating a guanine nucleotide exchange factor-H1-RhoA-RhoA-associated kinase-c-Myc pathway. The microRNAs miR-17 and miR-20a, induced by c-Myc, are needed to suppress p21(Waf1/Cip1) expression. CagA also drives an epithelial-mesenchymal transition in polarized epithelial cells. These findings suggest that CagA exploits a polarity-signaling pathway to induce oncogenesis.

A global overview of the genetic and functional diversity in the Helicobacter pylori cag pathogenicity island

The Helicobacter pylori cag pathogenicity island (cagPAI) encodes a type IV secretion system. Humans infected with cagPAI–carrying H. pylori are at increased risk for sequelae such as gastric cancer. Housekeeping genes in H. pylori show considerable genetic diversity; but the diversity of virulence factors such as the cagPAI, which transports the bacterial oncogene CagA into host cells, has not been systematically investigated. Here we compared the complete cagPAI sequences for 38 representative isolates from all known H. pylori biogeographic populations. Their gene content and gene order were highly conserved. The phylogeny of most cagPAI genes was similar to that of housekeeping genes, indicating that the cagPAI was probably acquired only once by H. pylori, and its genetic diversity reflects the isolation by distance that has shaped this bacterial species since modern humans migrated out of Africa. Most isolates induced IL-8 release in gastric epithelial cells, indicating that the function of the Cag secretion system has been conserved despite some genetic rearrangements. More than one third of cagPAI genes, in particular those encoding cell-surface exposed proteins, showed signatures of diversifying (Darwinian) selection at more than 5% of codons. Several unknown gene products predicted to be under Darwinian selection are also likely to be secreted proteins (e.g. HP0522, HP0535). One of these, HP0535, is predicted to code for either a new secreted candidate effector protein or a protein which interacts with CagA because it contains two genetic lineages, similar to cagA. Our study provides a resource that can guide future research on the biological roles and host interactions of cagPAI proteins, including several whose function is still unknown.

Most humans are infected with Helicobacter pylori. The H. pylori cag pathogenicity island (cagPAI) encodes a secretion apparatus that can translocate the CagA protein into host cells. Humans infected with cagPAI–carrying H. pylori are at increased risk of severe disease, including gastric cancer. We analyzed the nucleotide sequences and functional diversity of the cagPAI in a globally representative collection of isolates. Complete cagPAI sequences were obtained for 29 strains from all known H. pylori biogeographic populations. The gene content and arrangement of the cagPAI and its function were highly conserved. Diversity in most cag genes consisted in large part of synonymous polymorphisms. However some genes—in particular those that encode proteins predicted to be secreted or located on the outside of the bacterial cell—had particularly high frequencies of non-synonymous polymorphisms, suggesting that they were under diversifying selection. Our study provides evidence that the cagPAI was only acquired once and provides an important resource that can guide future research on the biological roles and host interactions of cagPAI proteins, including several whose function is still unknown.

Helicobacter pylori exploits host membrane phosphatidylserine for delivery, localization, and pathophysiological action of the CagA oncoprotein

When delivered into gastric epithelial cells via type IV secretion, Helicobacter pylori CagA perturbs host cell signaling and thereby promotes gastric carcinogenesis. However, the mechanisms of CagA delivery, localization, and action remain poorly understood. We show that direct contact of H. pylori with epithelial cells induces externalization of the inner leaflet enriched host phospholipid, phosphatidylserine, to the outer leaflet of the host plasma membrane. CagA, which is exposed on the bacterial surface via type IV secretion, interacts with the externalized phosphatidylserine to initiate its entry into cells. CagA delivery also requires energy-dependent host cell processes distinct from known endocytic pathways. Within polarized epithelial cells, CagA is tethered to the inner leaflet of the plasma membrane through interaction with phosphatidylserine and binds the polarity-regulating host kinase PAR1/MARK to induce junctional and polarity defects. Thus, host membrane phosphatidylserine plays a key role in the delivery, localization, and pathophysiological action of CagA.

Biochemical and functional characterization of Helicobacter pylori vesicles

Helicobacter pylori can cause peptic ulcer disease and/or gastric cancer. Adhesion of bacteria to the stomach mucosa is an important contributor to the vigour of infection and resulting virulence. H. pylori adheres primarily via binding of BabA adhesins to ABO/Lewis b (Leb) blood group antigens and the binding of SabA adhesins to sialyl-Lewis x/a (sLex/a) antigens. Similar to most Gram-negative bacteria, H. pylori continuously buds off vesicles and vesicles derived from pathogenic bacteria often include virulence-associated factors. Here we biochemically characterized highly purified H. pylori vesicles. Major protein and phospholipid components associated with the vesicles were identified with mass spectroscopy and nuclear magnetic resonance. A subset of virulence factors present was confirmed by immunoblots. Additional functional and biochemical analysis focused on the vesicle BabA and SabA adhesins and their respective interactions to human gastric epithelium. Vesicles exhibit heterogeneity in their protein composition, which were specifically studied in respect to the BabA adhesin. We also demonstrate that the oncoprotein, CagA, is associated with the surface of H. pylori vesicles. Thus, we have explored mechanisms for intimate H. pylori vesicle–host interactions and found that the vesicles carry effector-promoting properties that are important to disease development.

LnaB: a Legionella pneumophila activator of NF-kappaB

Legionella pneumophila possesses a large arsenal of type IV translocated substrates. Over 100 such proteins have been identified, but the functions of most are unknown. Previous studies have demonstrated that L. pneumophila activates NF-kappaB, a master transcriptional regulator of the mammalian innate immune response. Activation of NF-kappaB is dependent on the Legionella Icm/Dot type IV protein translocation system, consistent with the possibility that translocated bacterial proteins contribute to this response. To test this hypothesis, an expression library of 159 known and putative translocated substrates was created to evaluate whether ectopic production of a single L. pneumophila protein could activate NF-kappaB in mammalian cells. Expression of two of these proteins, LnaB (Legionella NF-kappaB activator B) and LegK1, resulted in approximately 150-fold induction of NF-kappaB activity in HEK293T cells, levels similar to the strong induction that occurs with ectopic expression of the known activator Nod1. LnaB is a substrate of the Icm/Dot system, and in the absence of this protein, a partial reduction of NF-kappaB activation in host cells occurs after challenge by post-exponential phase bacteria. These data indicate that LnaB is an Icm/Dot substrate that contributes to NF-kappaB activation during L. pneumophila infection in host cells.

Tarp regulates early Chlamydia-induced host cell survival through interactions with the human adaptor protein SHC1

Many bacterial pathogens translocate effector proteins into host cells to manipulate host cell functions. Here, we used a protein microarray comprising virtually all human SRC homology 2 (SH2) and phosphotyrosine binding domains to comprehensively and quantitatively assess interactions between host cell proteins and the early phase Chlamydia trachomatis effector protein translocated actin-recruiting phosphoprotein (Tarp), which is rapidly tyrosine phosphorylated upon host cell entry. We discovered numerous novel interactions between human SH2 domains and phosphopeptides derived from Tarp. The adaptor protein SHC1 was among Tarp's strongest interaction partners. Transcriptome analysis of SHC1-dependent gene regulation during infection indicated that SHC1 regulates apoptosis- and growth-related genes. SHC1 knockdown sensitized infected host cells to tumor necrosis factor-induced apoptosis. Collectively, our findings reveal a critical role for SHC1 in early C. trachomatis-induced cell survival and suggest that Tarp functions as a multivalent phosphorylation-dependent signaling hub that is important during the early phase of chlamydial infection.

The versatility of Helicobacter pylori CagA effector protein functions: The master key hypothesis

Several bacterial pathogens inject virulence proteins into host target cells that are substrates of eukaryotic tyrosine kinases. One of the key examples is the Helicobacter pylori CagA effector protein which is translocated by a type-IV secretion system. Injected CagA becomes tyrosine-phosphorylated on EPIYA sequence motifs by Src and Abl family kinases. CagA then binds to and activates/inactivates multiple signaling proteins in a phosphorylation-dependent and phosphorylation-independent manner. A recent proteomic screen systematically identified eukaryotic binding partners of the EPIYA phosphorylation sites of CagA and similar sites in other bacterial effectors by high-resolution mass spectrometry. Individual phosphorylation sites recruited a surprisingly high number of interaction partners suggesting that each phosphorylation site can interfere with many downstream pathways. We now count 20 reported cellular binding partners of CagA, which represents the highest quantitiy among all yet known virulence-associated effector proteins in the microbial world. This complexity generates a highly remarkable and puzzling scenario. In addition, the first crystal structure of CagA provided us with new information on the function of this important virulence determinant. Here we review the recent advances in characterizing the multiple binding signaling activities of CagA. Injected CagA can act as a 'master key' that evolved the ability to highjack multiple host cell signalling cascades, which include the induction of membrane dynamics, actin-cytoskeletal rearrangements and the disruption of cell-to-cell junctions as well as proliferative, pro-inflammatory and anti-apoptotic nuclear responses. The discovery that different pathogens use this common strategy to subvert host cell functions suggests that more examples will emerge soon.

The cag PAI is intact and functional but HP0521 varies significantly in Helicobacter pylori isolates from Malaysia and Singapore

Helicobacter pylori-related disease is at least partially attributable to the genotype of the infecting strain, particularly the presence of specific virulence factors. We investigated the prevalence of a novel combination of H. pylori virulence factors, including the cag pathogenicity island (PAI), and their association with severe disease in isolates from the three major ethnicities in Malaysia and Singapore, and evaluated whether the cag PAI was intact and functional in vitro. Polymerase chain reaction (PCR) was used to detect dupA, cagA, cagE, cagT, cagL and babA, and to type vacA, the EPIYA motifs, HP0521 alleles and oipA ON status in 159 H. pylori clinical isolates. Twenty-two strains were investigated for IL-8 induction and CagA translocation in vitro. The prevalence of cagA, cagE, cagL, cagT, babA, oipA ON and vacA s1 and i1 was >85%, irrespective of the disease state or ethnicity. The prevalence of dupA and the predominant HP0521 allele and EPIYA motif varied significantly with ethnicity (p < 0.05). A high prevalence of an intact cag PAI was found in all ethnic groups; however, no association was observed between any virulence factor and disease state. The novel association between the HP0521 alleles, EPIYA motifs and host ethnicity indicates that further studies to determine the function of this gene are important.

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

Background

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

Findings

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

Conclusion

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

the versatility of the Helicobacter pylori vacuolating cytotoxin vacA in signal transduction and molecular crosstalk

By modulating important properties of eukaryotic cells, many bacterial protein toxins highjack host signalling pathways to create a suitable niche for the pathogen to colonize and persist. Helicobacter pylori VacA is paradigm of pore-forming toxins which contributes to the pathogenesis of peptic ulceration. Several cellular receptors have been described for VacA, which exert different effects on epithelial and immune cells. The crystal structure of VacA p55 subunit might be important for elucidating details of receptor interaction and pore formation. Here we discuss the multiple signalling activities of this important toxin and the molecular crosstalk between VacA and other virulence factors.

PKA-mediated phosphorylation of EPEC-Tir at serine residues 434 and 463: A novel pathway in regulating Rac1 GTPase function

Type-III or type-IV secretion systems of many Gram-negative bacterial pathogens inject effector proteins into host cells that modulate cellular functions in their favour. A preferred target of these effectors is the actin-cytoskeleton as shown by studies using the gastric pathogens Helicobacter pylori (H. pylori) and enteropathogenic Escherichia coli (EPEC). We recently developed a co-infection approach to study effector protein function and molecular mechanisms by which they highjack cellular signalling cascades. This is exemplified by our observation that EPEC profoundly blocks H. pylori-induced epithelial cell scattering and elongation, a disease-related event requiring the activity of small Rho GTPase Rac1. While this suppressive effect is dependent on the effector protein Tir and the outer-membrane protein Intimin, it unexpectedly revealed evidence for Tir-signalling independent of phosphorylation of Tir at tyrosine residues 454 and 474. Instead, our studies revealed a previously unidentified function for protein kinase A (PKA)-mediated phosphorylation of Tir at serine residues 434 and 463. We demonstrated that EPEC infection activates PKA for Tir phosphorylation. Activated PKA then phosphorylates Rac1 at its serine residue 71 associated with reduced GTP-load and inhibited cell elongation. Phosphorylation of Rho GTPases such as Rac1 might be an interesting novel strategy in microbial pathogenesis.

Helicobacter pylori CagA activates NF-kappaB by targeting TAK1 for TRAF6-mediated Lys 63 ubiquitination

Helicobacter pylori-initiated chronic gastritis is characterized by the cag pathogenicity island-dependent upregulation of proinflammatory cytokines, which is largely mediated by the transcription factor nuclear factor (NF)-kappaB. However, the cag pathogenicity island-encoded proteins and cellular signalling molecules that are involved in H. pylori-induced NF-kappaB activation and inflammatory response remain unclear. Here, we show that H. pylori virulence factor CagA and host protein transforming growth factor-beta-activated kinase 1 (TAK1) are essential for H. pylori-induced activation of NF-kappaB. CagA physically associates with TAK1 and enhances its activity and TAK1-induced NF-kappaB activation through the tumour necrosis factor receptor-associated factor 6-mediated, Lys 63-linked ubiquitination of TAK1. These findings show that polyubiquitination of TAK1 regulates the activation of NF-kappaB, which in turn is used by H. pylori CagA for the H. pylori-induced inflammatory response.

Helicobacter pylori counteracts the apoptotic action of its VacA toxin by injecting the CagA protein into gastric epithelial cells

Infection with Helicobacter pylori is responsible for gastritis and gastroduodenal ulcers but is also a high risk factor for the development of gastric adenocarcinoma and lymphoma. The most pathogenic H. pylori strains (i.e., the so-called type I strains) associate the CagA virulence protein with an active VacA cytotoxin but the rationale for this association is unknown. CagA, directly injected by the bacterium into colonized epithelium via a type IV secretion system, leads to cellular morphological, anti-apoptotic and proinflammatory effects responsible in the long-term (years or decades) for ulcer and cancer. VacA, via pinocytosis and intracellular trafficking, induces epithelial cell apoptosis and vacuolation. Using human gastric epithelial cells in culture transfected with cDNA encoding for either the wild-type 38 kDa C-terminal signaling domain of CagA or its non-tyrosine-phosphorylatable mutant form, we found that, depending on tyrosine-phosphorylation by host kinases, CagA inhibited VacA-induced apoptosis by two complementary mechanisms. Tyrosine-phosphorylated CagA prevented pinocytosed VacA to reach its target intracellular compartments. Unphosphorylated CagA triggered an anti-apoptotic activity blocking VacA-induced apoptosis at the mitochondrial level without affecting the intracellular trafficking of the toxin. Assaying the level of apoptosis of gastric epithelial cells infected with wild-type CagA⁺/VacA⁺H. pylori or isogenic mutants lacking of either CagA or VacA, we confirmed the results obtained in cells transfected with the CagA C-ter constructions showing that CagA antagonizes VacA-induced apoptosis. VacA toxin plays a role during H. pylori stomach colonization. However, once bacteria have colonized the gastric niche, the apoptotic action of VacA might be detrimental for the survival of H. pylori adherent to the mucosa. CagA association with VacA is thus a novel, highly ingenious microbial strategy to locally protect its ecological niche against a bacterial virulence factor, with however detrimental consequences for the human host.

The gram-negative bacterium Helicobacter pylori is the main causative agent of peptic ulcer and gastric cancer in humans. Our work sheds light on a new molecular mechanism by which H. pylori would exert its highly efficient colonization strategy of the human host. In this paper, we show that the H. pylori CagA protein counteracts, by two distinct non-overlapping mechanisms, the apoptotic activity of the H. pylori VacA toxin on human gastric epithelial cells so as to allow a protection of the bacterium niche against VacA, giving a rationale for the association of these two virulence factors in the most pathogenic H. pylori strains. This is a new, highly ingenious mechanism by which a bacterium locally protects its ecological niche against the action of one of its own virulence factors. However, while exerting a beneficial role for survival and growth of the bacterium by counteracting VacA toxin, CagA injection in the gastric epithelial cells triggers proinflammatory and anti-apoptotic responses which are detrimental for the human host in the long-term and favor the development of ulcer and cancer.

Development of vaccines against Helicobacter pylori

Helicobacter pylori is a Gram-negative, microaerophilic bacterium adapted to survive in the stomach of humans where it can cause peptide ulcers and gastric cancer. Although effective antibiotic treatment exists, there is a consensus that vaccines are necessary to limit the severity of this infection. Great progress has been made since its discovery 25 years ago in understanding the virulence factors and several aspects of the pathogenesis of the H. pylori gastric diseases. Several key bacterial factors have been identified: urease, vacuolating cytotoxin, cytotoxin-associated antigen, the pathogenicity island, neutrophil-activating protein, and among others. These proteins, in their native or recombinant forms, have been shown to confer protection against infectious challenge with H. pylori in experimental animal models. It is not known, however, through which effector mechanisms this protection is achieved. Nevertheless, a number of clinical trials in healthy volunteers have been conducted using urease given orally as a soluble protein or expressed in bacterial vectors with limited results. Recently, a mixture of H. pylori antigens was reported to be highly immunogenic in H. pylori-negative volunteers following intramuscular administration of the vaccine with aluminium hydroxide as an adjuvant. These data show that vaccination against this pathogen is feasible. More research is required to understand the immunological mechanisms underlying immune-mediate protection.

Gastric helicobacters in domestic animals and nonhuman primates and their significance for human health

Helicobacters other than Helicobacter pylori have been associated with gastritis, gastric ulcers, and gastric mucosa-associated lymphoid tissue lymphoma in humans. These very fastidious microorganisms with a typical large spiral-shaped morphology were provisionally designated "H. heilmannii," but in fact they comprise at least five different Helicobacter species, all of which are known to colonize the gastric mucosa of animals. H. suis, which has been isolated from the stomachs of pigs, is the most prevalent gastric non-H. pylori Helicobacter species in humans. Other gastric non-H. pylori helicobacters colonizing the human stomach are H. felis, H. salomonis, H. bizzozeronii, and the still-uncultivable "Candidatus Helicobacter heilmannii." These microorganisms are often detected in the stomachs of dogs and cats. "Candidatus Helicobacter bovis" is highly prevalent in the abomasums of cattle but has only occasionally been detected in the stomachs of humans. There are clear indications that gastric non-H. pylori Helicobacter infections in humans originate from animals, and it is likely that transmission to humans occurs through direct contact. Little is known about the virulence factors of these microorganisms. The recent successes with in vitro isolation of non-H. pylori helicobacters from domestic animals open new perspectives for studying these microorganisms and their interactions with the host.

Advances in research on Helicobacter pylori virulence factors

Helicobacter pylori (H. pylori) infection is a common chronic infectious disease in the world. It can lead to several divergent clinical diseases, such as chronic gastritis, duodenal ulcer, mucosa-associated lymphoid tissue lymphoma and gastric adenocarcinoma. These divergent clinical diseases are caused through complex mechanisms involving interaction between the bacterium and host. Recent investigations of virulence pathogenic factors have provided more information to reveal the pathogenic mechanism of H. pylori infection. Here, we will review the recent advances in research on various H. pylori virulence factors, such as CagA, VacA, BabA, SabA, OipA and DupA.

Stability of Helicobacter pylori CagA oncoprotein in human gastric epithelial cells

Upon delivery into gastric epithelial cells, Helicobacter pylori cytotoxin-associated gene A (CagA) binds and deregulates cellular proteins such as Src homology 2 domain-containing protein tyrosine phosphatase 2 and partitioning-defective 1 (PAR1), thereby acting as an epigenetic oncoprotein that promotes early phases of gastric cancer development. To elucidate the spatial and temporal contribution of CagA to carcinogenesis, it is crucial to know the stability of CagA in host cells. Here we show that the biological half-life of CagA is about 200 min in gastric epithelial cells. Furthermore, deletion of the PAR1-binding sequence accelerates CagA degradation. Thus, CagA is a relatively short half-life protein whose stability may be modulated through complex formation with PAR1.

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

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

Protein scaffolds in MAP kinase signalling

The mitogen-activated protein kinase (MAPK) pathway allows cells to interpret external signals and respond in an appropriate way. Diverse cellular functions, ranging from differentiation and proliferation to migration and inflammation, are regulated by MAPK signalling. Therefore, cells have developed mechanisms by which this single pathway modulates numerous cellular responses from a wide range of activating factors. This specificity is achieved by several mechanisms, including temporal and spatial control of MAPK signalling components. Key to this control are protein scaffolds, which are multidomain proteins that interact with components of the MAPK cascade in order to assemble signalling complexes. Studies conducted on different scaffolds, in different biological systems, have shown that scaffolds exert substantial control over MAPK signalling, influencing the signal intensity, time course and, importantly, the cellular responses. Protein scaffolds, therefore, are integral elements to the modulation of the MAPK network in fundamental physiological processes.