Helicobacter pylori CagA targets PAR1/MARK kinase to disrupt epithelial cell polarity

CD44 plays a functional role in Helicobacter pylori-induced epithelial cell proliferation

The cytotoxin-associated gene (Cag) pathogenicity island is a strain-specific constituent of Helicobacter pylori (H. pylori) that augments cancer risk. CagA translocates into the cytoplasm where it stimulates cell signaling through the interaction with tyrosine kinase c-Met receptor, leading cellular proliferation. Identified as a potential gastric stem cell marker, cluster-of-differentiation (CD) CD44 also acts as a co-receptor for c-Met, but whether it plays a functional role in H. pylori-induced epithelial proliferation is unknown. We tested the hypothesis that CD44 plays a functional role in H. pylori-induced epithelial cell proliferation. To assay changes in gastric epithelial cell proliferation in relation to the direct interaction with H. pylori, human- and mouse-derived gastric organoids were infected with the G27 H. pylori strain or a mutant G27 strain bearing cagA deletion (∆CagA::cat). Epithelial proliferation was quantified by EdU immunostaining. Phosphorylation of c-Met was analyzed by immunoprecipitation followed by Western blot analysis for expression of CD44 and CagA. H. pylori infection of both mouse- and human-derived gastric organoids induced epithelial proliferation that correlated with c-Met phosphorylation. CagA and CD44 co-immunoprecipitated with phosphorylated c-Met. The formation of this complex did not occur in organoids infected with ∆CagA::cat. Epithelial proliferation in response to H. pylori infection was lost in infected organoids derived from CD44-deficient mouse stomachs. Human-derived fundic gastric organoids exhibited an induction in proliferation when infected with H. pylori that was not seen in organoids pre-treated with a peptide inhibitor specific to CD44. In the well-established Mongolian gerbil model of gastric cancer, animals treated with CD44 peptide inhibitor Pep1, resulted in the inhibition of H. pylori-induced proliferation and associated atrophic gastritis. The current study reports a unique approach to study H. pylori interaction with the human gastric epithelium. Here, we show that CD44 plays a functional role in H. pylori-induced epithelial cell proliferation.

A specific A/T polymorphism in Western tyrosine phosphorylation B-motifs regulates Helicobacter pylori CagA epithelial cell interactions

Helicobacter pylori persistently colonizes the human stomach, with mixed roles in human health. The CagA protein, a key host-interaction factor, is translocated by a type IV secretion system into host epithelial cells, where its EPIYA tyrosine phosphorylation motifs (TPMs) are recognized by host cell kinases, leading to multiple host cell signaling cascades. The CagA TPMs have been described as type A, B, C or D, each with a specific conserved amino acid sequence surrounding EPIYA. Database searching revealed strong non-random distribution of the B-motifs (including EPIYA and EPIYT) in Western H. pylori isolates. In silico analysis of Western H. pylori CagA sequences provided evidence that the EPIYT B-TPMs are significantly less associated with gastric cancer than the EPIYA B-TPMs. By generating and using a phosphorylated CagA B-TPM-specific antibody, we demonstrated the phosphorylated state of the CagA B-TPM EPIYT during H. pylori co-culture with host cells. We also showed that within host cells, CagA interaction with phosphoinositol 3-kinase (PI3-kinase) was B-TPM tyrosine-phosphorylation-dependent, and the recombinant CagA with EPIYT B-TPM had higher affinity to PI3-kinase and enhanced induction of AKT than the isogenic CagA with EPIYA B-TPM. Structural modeling of the CagA B-TPM motif bound to PI3-kinase indicated that the threonine residue at the pY+1 position forms a side-chain hydrogen bond to N-417 of PI3-kinase, which cannot be formed by alanine. During co-culture with AGS cells, an H. pylori strain with a CagA EPIYT B-TPM had significantly attenuated induction of interleukin-8 and hummingbird phenotype, compared to the isogenic strain with B-TPM EPIYA. These results suggest that the A/T polymorphisms could regulate CagA activity through interfering with host signaling pathways related to carcinogenesis, thus influencing cancer risk.

Cell Polarity: A Key Defence Mechanism Against Infection and Cancer Cell Invasion?

It is now emerging that a number of cellular targets of pathogens are involved in the establishment and/or maintenance of epithelial cell polarity. Increasing evidence also suggests that cancer-causing pathogens such as Helicobacter pylori (H. pylori) and human papilloma virus (HPV) may induce oncogenesis by disrupting cell polarity. This is mainly achieved through their ability to deregulate the function of cell polarity components and/or regulators. Hence cell polarity represents the first line of defence against infection. Interestingly, EGFR/RAS oncogenic signals also induce cancer cell invasion by inducing epithelial to mesenchymal transition (EMT). Since the loss of cell polarity is a prerequisition of EMT, cell polarity also represents the last line of defence against cancer cell invasion. As such we argue that cell polarity may be a key defence mechanism against infection and cancer cell invasion. The potential role of cell polarity as a gatekeeper against cancer through its ability to regulate asymmetric cell division and tumour suppression has been discussed in a number of recent reviews. In this review we will focus on the role of cell polarity as a potential target of infection and cancer cell invasion.

Clinical relevance of Helicobacter pylori vacA and cagA genotypes in gastric carcinoma

Helicobacter pylori infection is the major etiological factor of gastric carcinoma. This disease is the result of a long, multistep, and multifactorial process, which occurs only in a small proportion of patients infected with H. pylori. Gastric carcinoma development is influenced by host genetic susceptibility factors, environmental factors, and H. pylori virulence. H. pylori is genetically highly variable, and variability that affects H. pylori virulence factors may be useful to identify strains with different degrees of pathogenicity. This review will focus on VacA and CagA that have polymorphic regions that impact their functional properties. The characterization of H. pylori vacA and cagA-associated could be useful for identifying patients at highest risk of disease, who could be offered H. pylori eradication therapy and who could be included in programs of more intensive surveillance in an attempt to reduce gastric carcinoma incidence.

Systems biology of cancer: entropy, disorder, and selection-driven evolution to independence, invasion and "swarm intelligence"

Our knowledge of the biology of solid cancer has greatly progressed during the last few years, and many excellent reviews dealing with the various aspects of this biology have appeared. In the present review, we attempt to bring together these subjects in a general systems biology narrative. It starts from the roles of what we term entropy of signaling and noise in the initial oncogenic events, to the first major transition of tumorigenesis: the independence of the tumor cell and the switch in its physiology, i.e., from subservience to the organism to its own independent Darwinian evolution. The development after independence involves a constant dynamic reprogramming of the cells and the emergence of a sort of collective intelligence leading to invasion and metastasis and seldom to the ultimate acquisition of immortality through inter-individual infection. At each step, the probability of success is minimal to infinitesimal, but the number of cells possibly involved and the time scale account for the relatively high occurrence of tumorigenesis and metastasis in multicellular organisms.

Intestinal permeability--a new target for disease prevention and therapy

Data are accumulating that emphasize the important role of the intestinal barrier and intestinal permeability for health and disease. However, these terms are poorly defined, their assessment is a matter of debate, and their clinical significance is not clearly established. In the present review, current knowledge on mucosal barrier and its role in disease prevention and therapy is summarized. First, the relevant terms 'intestinal barrier' and 'intestinal permeability' are defined. Secondly, the key element of the intestinal barrier affecting permeability are described. This barrier represents a huge mucosal surface, where billions of bacteria face the largest immune system of our body. On the one hand, an intact intestinal barrier protects the human organism against invasion of microorganisms and toxins, on the other hand, this barrier must be open to absorb essential fluids and nutrients. Such opposing goals are achieved by a complex anatomical and functional structure the intestinal barrier consists of, the functional status of which is described by 'intestinal permeability'. Third, the regulation of intestinal permeability by diet and bacteria is depicted. In particular, potential barrier disruptors such as hypoperfusion of the gut, infections and toxins, but also selected over-dosed nutrients, drugs, and other lifestyle factors have to be considered. In the fourth part, the means to assess intestinal permeability are presented and critically discussed. The means vary enormously and probably assess different functional components of the barrier. The barrier assessments are further hindered by the natural variability of this functional entity depending on species and genes as well as on diet and other environmental factors. In the final part, we discuss selected diseases associated with increased intestinal permeability such as critically illness, inflammatory bowel diseases, celiac disease, food allergy, irritable bowel syndrome, and--more recently recognized--obesity and metabolic diseases. All these diseases are characterized by inflammation that might be triggered by the translocation of luminal components into the host. In summary, intestinal permeability, which is a feature of intestinal barrier function, is increasingly recognized as being of relevance for health and disease, and therefore, this topic warrants more attention.

Helicobacter pylori CagA and gastric cancer: a paradigm for hit-and-run carcinogenesis

Helicobacter pylori is a gastric bacterial pathogen that is etiologically linked to human gastric cancer. The cytotoxin-associated gene A (CagA) protein of H. pylori, which is delivered into gastric epithelial cells via bacterial type IV secretion, is an oncoprotein that can induce malignant neoplasms in mammals. Upon delivery, CagA perturbs multiple host signaling pathways by acting as an extrinsic scaffold or hub protein. On one hand, signals aberrantly raised by CagA are integrated into a direct oncogenic insult, whereas on the other hand, they engender genetic instability. Despite its decisive role in the development of gastric cancer, CagA is not required for the maintenance of a neoplastic phenotype in established cancer cells. Therefore, CagA-conducted gastric carcinogenesis progresses through a hit-and-run mechanism in which pro-oncogenic actions of CagA are successively taken over by a series of genetic and/or epigenetic alterations compiled in cancer-predisposing cells during long-standing infection with cagA-positive H. pylori.

Helicobacter pylori dwelling on the apical surface of gastrointestinal epithelium damages the mucosal barrier through direct contact

BACKGROUND

Epithelial junctions and mucins compose a major portion of the mucosal barrier. Helicobacter pylori (H. pylori) infections induce alterations of the tight junctions and adherens junctions in epithelial cells, although the precise mechanisms underlying this process are not fully understood.

METHODS

The expression of adhesion molecules and MUC1 was systematically investigated in gastrointestinal epithelial cells infected with H. pylori in vitro and in vivo. Furthermore, we developed several new in vitro methods to study the relationships between the bacterium and the dysfunction of tight junctions using Boyden Chambers.

RESULTS

The expression of a series of junctional molecules and MUC1 decreased in the cultured cells that were infected with H. pylori. According to the degree of damage at the tight junctions, direct contact of H. pylori with the apical membrane of the cells resulted in the greatest increase in permeability compared to basal membrane binding or non-binding of H. pylori to the cells. Similarly, we noted that H. pylori infection could reduce the expression and glycosylation of MUC1.

CONCLUSIONS

Helicobacter pylori dwelling on the apical surface of the gastrointestinal epithelium could directly induce serious injury of the mucosal barrier, and the new methods outlined here, based on the Boyden Chamber system, could be very useful for studying the relationships between bacteria and their target cells.

Effect of Helicobacter pylori on gastric epithelial cells

The gastrointestinal epithelium has cells with features that make them a powerful line of defense in innate mucosal immunity. Features that allow gastrointestinal epithelial cells to contribute in innate defense include cell barrier integrity, cell turnover, autophagy, and innate immune responses. Helicobacter pylori (H. pylori) is a spiral shape gram negative bacterium that selectively colonizes the gastric epithelium of more than half of the world’s population. The infection invariably becomes persistent due to highly specialized mechanisms that facilitate H. pylori’s avoidance of this initial line of host defense as well as adaptive immune mechanisms. The host response is thus unsuccessful in clearing the infection and as a result becomes established as a persistent infection promoting chronic inflammation. In some individuals the associated inflammation contributes to ulcerogenesis or neoplasia. H. pylori has an array of different strategies to interact intimately with epithelial cells and manipulate their cellular processes and functions. Among the multiple aspects that H. pylori affects in gastric epithelial cells are their distribution of epithelial junctions, DNA damage, apoptosis, proliferation, stimulation of cytokine production, and cell transformation. Some of these processes are initiated as a result of the activation of signaling mechanisms activated on binding of H. pylori to cell surface receptors or via soluble virulence factors that gain access to the epithelium. The multiple responses by the epithelium to the infection contribute to pathogenesis associated with H. pylori.

A model to explain specific cellular communications and cellular harmony:- a hypothesis of coupled cells and interactive coupling molecules

BACKGROUND

The various cell types and their relative numbers in multicellular organisms are controlled by growth factors and related extracellular molecules which affect genetic expression pathways. However, these substances may have both/either inhibitory and/or stimulatory effects on cell division and cell differentiation depending on the cellular environment. It is not known how cells respond to these substances in such an ambiguous way. Many cellular effects have been investigated and reported using cell culture from cancer cell lines in an effort to define normal cellular behaviour using these abnormal cells.A model is offered to explain the harmony of cellular life in multicellular organisms involving interacting extracellular substances.

METHODS

A basic model was proposed based on asymmetric cell division and evidence to support the hypothetical model was accumulated from the literature. In particular, relevant evidence was selected for the Insulin-Like Growth Factor system from the published data, especially from certain cell lines, to support the model. The evidence has been selective in an attempt to provide a picture of normal cellular responses, derived from the cell lines.

RESULTS

The formation of a pair of coupled cells by asymmetric cell division is an integral part of the model as is the interaction of couplet molecules derived from these cells. Each couplet cell will have a receptor to measure the amount of the couplet molecule produced by the other cell; each cell will be receptor-positive or receptor-negative for the respective receptors. The couplet molecules will form a binary complex whose level is also measured by the cell. The hypothesis is heavily supported by selective collection of circumstantial evidence and by some direct evidence. The basic model can be expanded to other cellular interactions.

CONCLUSIONS

These couplet cells and interacting couplet molecules can be viewed as a mechanism that provides a controlled and balanced division-of-labour between the two progeny cells, and, in turn, their progeny. The presence or absence of a particular receptor for a couplet molecule will define a cell type and the presence or absence of many such receptors will define the cell types of the progeny within cell lineages.

Phospholipid binding residues of eukaryotic membrane-remodelling F-BAR domain proteins are conserved in Helicobacter pylori CagA

Background

Cytotoxin associated gene product A (CagA) is an oncogenic protein secreted by the gastric bacterium Helicobacter pylori. Internalization of CagA by human epithelial cells occurs by an unknown mechanism that requires interaction with the host membrane lipid phosphatidylserine.

Findings

Local homology at the level of amino acid sequence and secondary structure has been identified between the membrane-tethering region of CagA and the lipid-binding Fes-CIP4 homology-Bin/Amphiphysin/Rvs (F-BAR) domains of eukaryotic proteins. The F-BAR proteins are major components of the endocytic machinery. In addition to the membrane-binding F-BAR domains, they contain other domains that interact with actin-regulatory networks and mediate interplay between membrane dynamics and cytoskeleton re-arrangements. Positively charged residues found on the lipid binding face of the F-BAR domains are conserved in CagA and represent residues involved in CagA binding to lipids.

Conclusions

The homologies with F-BAR proteins extend to lipid binding specificities and involvement in reorganization of the actin cytoskeleton. CagA and F-BAR domains share binding specificity for phosphatidylserine and phosphoinositides. Similar to the F-BAR proteins, CagA has a membrane-binding module and a module that shares structural homology with actin-binding proteins, and, like eukaryotic F-BAR domain proteins, CagA function is linked to actin dynamics. The uncovered similarities between the bacterial effector protein and eukaryotic F-BAR proteins suggest convergent evolution of CagA towards a similar function.

Electronic supplementary material

The online version of this article (doi:10.1186/1756-0500-7-525) contains supplementary material, which is available to authorized users.

An Update on Helicobacter pylori as the Cause of Gastric Cancer

BACKGROUND

Gastric cancer is the second most common cause of cancer deaths worldwide. The vast majority of gastric cancers are inflammation-related cancers caused by infection with Helicobacter pylori. H. pylori-induced oxidative stress damages DNA, resulting in genetic instability. In addition, H. pylori itself can cause DNA damage and epigenetic changes that trigger genetic instability and neoplastic transformation.

SUMMARY

H. pylori strain-specific components act in combination with host factors and environmental and dietary factors to greatly enhance the inflammatory response and thus the cancer risk. Variations in several key factors, such as the cag pathogenicity island and the VacA protein, can trigger a greater inflammatory response in host cells. Genetic polymorphisms in the host such as in the IL-1β gene, and chromosomes 9p21.3 and 10q23 also play a contributing role. Finally, diet is a major external factor that modulates the risk of gastric cancer.

KEY MESSAGE

The majority of gastric cancers are inflammation-related cancers caused by infection with H. pylori. Eradication of H. pylori is important for the prevention and treatment of gastric cancer.

PRACTICAL IMPLICATIONS

H. pylori eradication results in healing of gastritis and prevention of further H. pylori-induced genetic damage. Eradication of H. pylori prior to development of atrophic gastritis can prevent the development of gastric cancer. Japan has undertaken a nationwide program to identify and eliminate H. pylori, along with surveillance for those who underwent H. pylori eradication too late to eliminate cancer risk. Population-wide eradication of H. pylori will result in gastric cancer becoming a vanishingly rare disease.

Helicobacter pylori cytotoxin-associated gene A protein upregulates α-enolase expression via Src/MEK/ERK pathway: implication for progression of gastric cancer

Persistent infection with Helicobacter pylori confers an increased risk for the development of gastric cancer. In our previous investigations, we found that ENO1 was overexpression in cagA-positive H. pylori-infected gastric epithelial AGS cells by proteomic method, in contrast to the isogenic cagA knock out mutant H. pylori-infected cells. ENO1 is a newly identified oncoprotein overexpressed in some cancer. However, the relationship between H. pylori infection and ENO1 expression still remains undefined. The AGS gastric cancer cells were transfected with WT-cagA plasmid and PR-cagA plasmids. Expression of ENO1 mRNA and protein were measured by real-time quantitative PCR and western blot analysis. Signal protein inhibitor treatment was used to investigate the signal pathways. It was found that the ENO1 mRNA and protein overexpression levels were dependent on cagA gene expression and CagA protein phosphorylation. Further analysis revealed that the Src, MEK and ERK pathway was involved in this upregulation effect. Our data suggest that ENO1 was upregulated by CagA protein through activating the Src and MEK/ERK signal pathways, thereby providing a novel mechanism underlying H. pylori-mediated gastric diseases.

Helicobacter pylori CagA promotes Snail-mediated epithelial-mesenchymal transition by reducing GSK-3 activity

Cytotoxin-associated gene A (CagA) is an oncoprotein and a major virulence factor of H. pylori. CagA is delivered into gastric epithelial cells via a type IV secretion system and causes cellular transformation. The loss of epithelial adhesion that accompanies the epithelial-mesenchymal transition (EMT) is a hallmark of gastric cancer. Although CagA is a causal factor in gastric cancer, the link between CagA and the associated EMT has not been elucidated. Here, we show that CagA induces the EMT by stabilizing Snail, a transcriptional repressor of E-cadherin expression. Mechanistically we show that CagA binds GSK-3 in a manner similar to Axin and causes it to shift to an insoluble fraction, resulting in reduced GSK-3 activity. We also find that the level of Snail protein is increased in H. pylori infected epithelium in clinical samples. These results suggest that H. pylori CagA acts as a pathogenic scaffold protein that induces a Snail-mediated EMT via the depletion of GSK-3.

The role of epithelial tight junctions involved in pathogen infections

Tight junctions (TJs) are sealing complexes between adjacent epithelial cells, functioning by controlling paracellular passage and maintaining cell polarity. These functions of TJs are primarily based on structural integrity as well as dynamic regulatory balance, indicating plasticity of TJ in response to external stimuli. An indispensable role of TJs involved in pathogen infection has been widely demonstrated since disruption of TJs leads to a distinct increase in paracellular permeability and polarity defects which facilitate viral or bacterial entry and spread. In addition to pathological changes in TJ integrity, TJ proteins such as occludin and claudins can either function as receptors for pathogen entry or interact with viral/bacterial effector molecules as an essential step for characterizing an infective stage. This suggests a more complicated role for TJ itself and especially specific TJ components. Thus, this review surveys the role of the epithelial TJs involved in various pathogen infections, and extends TJ targeted therapeutic and pharmacological application prospects.

Gastrointestinal malignancy and the microbiome

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

Helicobacter pylori and gastric cancer

Infection with Helicobacter pylori is established as the major risk factor for gastric cancer development. Damage of the mucosal barrier due to H. pylori-induced inflammation enhances the carcinogenic effect of other risk factors such as salt intake or tobacco smoking. The genetic disposition of both the bacterial strain and the host can increase the potential towards gastric cancer formation. Genetic variance of the bacterial proteins CagA and VacA is associated with a higher gastric cancer risk, as are polymorphisms and epigenetic changes in host gene coding for interleukins (IL1β, IL8), transcription factors (CDX2, RUNX3) and DNA repair enzymes. Application of high-throughput assays for genome-wide assessment of either genetic structural variance or gene expression patterns may lead to a better understanding of the pathobiological background of these processes, including the underlying signaling pathways. Understanding of the stepwise alterations that take place in the transition from chronic atrophic gastritis, via metaplastic changes, to invasive neoplasia is vital to define the 'point of no return' before which eradication of H. pylori has the potential to prevent gastric cancer. Currently, eradication as preventive strategy is only recommended for high-incidence regions in Asia; large population studies with an adequate follow-up are required to demonstrate the effectiveness of such an approach in Western populations.

Exploring alternative treatments for Helicobacter pylori infection

Helicobacter pylori (H. pylori) is a successful pathogen that can persist in the stomach of an infected person for their entire life. It provokes chronic gastric inflammation that leads to the development of serious gastric diseases such as peptic ulcers, gastric cancer and Mucosa associated lymphoid tissue lymphoma. It is known that these ailments can be avoided if the infection by the bacteria can be prevented or eradicated. Currently, numerous antibiotic-based therapies are available. However, these therapies have several inherent problems, including the appearance of resistance to the antibiotics used and associated adverse effects, the risk of re-infection and the high cost of antibiotic therapy. The delay in developing a vaccine to prevent or eradicate the infection has furthered research into new therapeutic approaches. This review summarises the most relevant recent studies on vaccine development and new treatments using natural resources such as plants, probiotics and nutraceuticals. In addition, novel alternatives based on microorganisms, peptides, polysaccharides, and intragastric violet light irradiation are presented. Alternative therapies have not been effective in eradicating the bacteria but have been shown to maintain low bacterial levels. Nevertheless, some of them are useful in preventing the adverse effects of antibiotics, modulating the immune response, gastroprotection, and the general promotion of health. Therefore, those agents can be used as adjuvants of allopathic anti-H. pylori eradication therapy.

Natural variant of the Helicobacter pylori CagA oncoprotein that lost the ability to interact with PAR1

Helicobacter pylori strains carrying the cagA gene are associated with severe disease outcomes, most notably gastric cancer. CagA protein is delivered into gastric epithelial cells by a type IV secretion system. The translocated CagA undergoes tyrosine phosphorylation at the C-terminal EPIYA motifs by host cell kinases. Tyrosine-phosphorylated CagA acquires the ability to interact with and activate SHP2, thereby activating mitogenic signaling and inducing cell morphological transformation (hummingbird phenotype). CagA also interacts with PAR1b via the CM sequence, resulting in induction of junctional and polarity defects. Furthermore, CagA-PAR1b interaction stabilizes the CagA-SHP2 complex. Because transgenic mice systemically expressing CagA develop gastrointestinal and hematological malignancies, CagA is recognized as a bacterium-derived oncoprotein. Interestingly, the C-terminal region of CagA displays a large diversity among H. pylori strains, which influences the ability of CagA to bind to SHP2 and PAR1b. In the present study, we investigated the biological activity of v225d CagA, an Amerindian CagA of H. pylori isolated from a Venezuelan Piaroa Amerindian subject, because the variant CagA does not possess a canonical CM sequence. We found that v225d CagA interacts with SHP2 but not PAR1b. Furthermore, SHP2-binding activity of v225d CagA was much lower than that of CagA of H. pylori isolated from Western countries (Western CagA). v225d CagA also displayed a reduced ability to induce the hummingbird phenotype than that of Western CagA. Given that perturbation of PAR1b and SHP2 by CagA underlies the oncogenic potential of CagA, the v225d strain is considered to be less oncogenic than other well-studied cagA-positive H. pylori strains.

Structure of the Helicobacter pylori CagA oncoprotein bound to the human tumor suppressor ASPP2

The Cytotoxin associated gene A (CagA) protein of Helicobacter pylori is associated with increased virulence and risk of cancer. Recent proteomic studies have demonstrated an association of CagA with the human tumor suppressor Apoptosis-stimulating Protein of p53-2 (ASPP2). We present here a genetic, biochemical, and structural analysis of CagA with ASPP2. Domain delineation of the 120-kDa CagA protein revealed a stable N-terminal subdomain that was used in a yeast two-hybrid screen that identified the proline-rich domain of ASPP2 as a host cellular target. Biochemical experiments confirm this interaction. The cocrystal structure to 2.0-Å resolution of this N-terminal subdomain of CagA with a 7-kDa proline-rich sequence of ASPP2 reveals that this domain of CagA forms a highly specialized three-helix bundle, with large insertions in the loops connecting the helices. These insertions come together to form a deep binding cleft for a highly conserved 20-aa peptide of ASPP2. ASPP2 forms an extended helix in this groove of CagA, burying more than 1,000 Å(2) of surface area. This interaction is disrupted in vitro and in vivo by structure-based, loss-of-contact point mutations of key residues in either CagA or ASPP2. Disruption of CagA and ASPP2 binding alters the function of ASPP2 and leads to the decreased survival of H. pylori-infected cells.

Par1b links lumen polarity with LGN-NuMA positioning for distinct epithelial cell division phenotypes

Columnar epithelia establish their luminal domains and their mitotic spindles parallel to the basal surface and undergo symmetric cell divisions in which the cleavage furrow bisects the apical domain. Hepatocyte lumina interrupt the lateral domain of neighboring cells perpendicular to two basal domains and their cleavage furrow rarely bifurcates the luminal domains. We determine that the serine/threonine kinase Par1b defines lumen position in concert with the position of the astral microtubule anchoring complex LGN-NuMA to yield the distinct epithelial division phenotypes. Par1b signaling via the extracellular matrix (ECM) in polarizing cells determined RhoA/Rho-kinase activity at cell-cell contact sites. Columnar MDCK and Par1b-depleted hepatocytic HepG2 cells featured high RhoA activity that correlated with robust LGN-NuMA recruitment to the metaphase cortex, spindle alignment with the substratum, and columnar organization. Reduced RhoA activity at the metaphase cortex in HepG2 cells and Par1b-overexpressing MDCK cells correlated with a single or no LGN-NuMA crescent, tilted spindles, and the development of lateral lumen polarity.

Helicobacter and salmonella persistent infection strategies

Some host-adapted bacterial pathogens are capable of causing persistent infections in humans. For example, Helicobacter pylori inhabits the human gastric mucosa and persistence can be lifelong. Salmonella enterica serovar Typhi causes systemic infections that involve colonization of the reticuloendothelial system and some individuals become lifelong carriers. In this review, I compare and contrast the different lifestyles of Helicobacter and Salmonella within the host and the strategies they have evolved to persist in mammalian hosts. Persistently infected carriers serve as the reservoirs for these pathogens, and the carrier state is an essential feature that is required for survival of the bacteria within a restricted host population. Therefore, investigating the chronic carrier state should provide insight into bacterial survival strategies, as well as new therapeutic approaches for treatments.

Strain-specific suppression of microRNA-320 by carcinogenic Helicobacter pylori promotes expression of the antiapoptotic protein Mcl-1

Helicobacter pylori is the strongest risk factor for gastric cancer, and strains harboring the cag pathogenicity island, which translocates the oncoprotein CagA into host cells, further augment cancer risk. We previously reported that in vivo adaptation of a noncarcinogenic H. pylori strain (B128) generated a derivative strain (7.13) with the ability to induce adenocarcinoma, providing a unique opportunity to define mechanisms that mediate gastric carcinogenesis. MicroRNAs (miRNAs) are small noncoding RNAs that regulate expression of oncogenes or tumor suppressors and are frequently dysregulated in carcinogenesis. To identify miRNAs and their targets involved in H. pylori-mediated carcinogenesis, miRNA microarrays were performed on RNA isolated from gastric epithelial cells cocultured with H. pylori strains B128, 7.13, or a 7.13 cagA(-) isogenic mutant. Among 61 miRNAs differentially expressed in a cagA-dependent manner, the tumor suppressor miR-320 was significantly downregulated by strain 7.13. Since miR-320 negatively regulates the antiapoptotic protein Mcl-1, we demonstrated that H. pylori significantly induced Mcl-1 expression in a cagA-dependent manner and that suppression of Mcl-1 results in increased apoptosis. To extend these results, mice were challenged with H. pylori strain 7.13 or its cagA(-) mutant; consistent with cell culture data, H. pylori induced Mcl-1 expression in a cagA-dependent manner. In human subjects, cag(+) strains induced significantly higher levels of Mcl-1 than cag(-) strains, and Mcl-1 expression levels paralleled the severity of neoplastic lesions. Collectively, these results indicate that H. pylori suppresses miR-320, upregulates Mcl-1, and decreases apoptosis in a cagA-dependent manner, which likely confers an increased risk for gastric carcinogenesis.

H. pylori-encoded CagA disrupts tight junctions and induces invasiveness of AGS gastric carcinoma cells via Cdx2-dependent targeting of Claudin-2

Helicobacter pylori encoded CagA is presently the only known virulence factor that is injected into gastric epithelial cells where it destroys apical junctional complexes and induces dedifferentiation of gastric epithelial cells, leading to H. pylori-related gastric carcinogensis. However, little is known about the molecular mechanisms by which CagA mediates these changes. Caudal-related homeobox 2 (Cdx2) is an intestine-specific transcription factor highly expressed in multistage tissues of dysplasia and cancer. One specific target of Cdx2, Claudin-2, is involved in the regulation of tight junction (TJ) permeability. In this study, our findings showed that the activity of Cdx2 binding to Cdx binding sites of CdxA (GTTTATG) and CdxB (TTTTAGG) of probes corresponding to claudin-2 flanking region increased in AGS cells, infected with CagA positive wild-type strain of H. pylori, compared to CagA negative isogenic mutant-type strain. Moreover, Cdx2 upregulated claudin-2 expression at transcriptional level and translational level. In the meantime, we found that TJs of AGS cells, infected with CagA positive wild-type strain of H. pylori, compared to CagA negative isogenic mutant-type strain, were more severely destroyed, leading to wider cell gap, interference of contact, scattering and highly elevated migration of cells. Herein, this study is firstly demonstrated that H. pylori-encoded CagA disrupts TJs and induces invasiveness of AGS gastric carcinoma cells via Cdx2-dependent targeting of Claudin-2. This provides a new mechanism whereby CagA induced dedifferentiation of AGS cells, leading to malignant behavior of biology.

Conformational analysis of isolated domains of Helicobacter pylori CagA

The CagA protein of Helicobacter pylori is associated with increased virulence and gastric cancer risk. CagA is translocated into the host cell by a H. pylori type IV secretion system via mechanisms that are poorly understood. Translocated CagA interacts with numerous host factors, altering a variety of host signalling pathways. The recently determined crystal structure of C-terminally-truncated CagA indicated the presence of two domains: the smaller, flexible N-terminal domain and the larger, middle domain. In this study, we have investigated the conformation, oligomeric state and stability of the N-terminal, middle and glutamate-proline-isoleucine-tyrosine-alanine (EPIYA)-repeats domains. All three domains are monomeric, suggesting that the multimerisation of CagA observed in infected cells is likely to be mediated not by CagA itself but by its interacting partners. The middle and the C-terminal domains, but not the N-terminal domain, are capable of refolding spontaneously upon heat denaturation, lending support to the hypothesis that unfolded CagA is threaded C-terminus first through the type IV secretion channel with its N-terminal domain, which likely requires interactions with other domains to refold, being threaded last. Our findings also revealed that the C-terminal EPIYA-repeats domain of CagA exists in an intrinsically disordered premolten globule state with regions in PPII conformation - a feature that is shared by many scaffold proteins that bind multiple protein components of signalling pathways. Taken together, these results provide a deeper understanding of the physicochemical properties of CagA that underpin its complex cellular and oncogenic functions.

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

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

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

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

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

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

Gastric cancer prevention by demethylation

Niwa and colleagues report in this issue that treatment with the DNA demethylation agent 5-aza-2'-deoxycytidine decreases the incidence of gastric cancers in an animal model of Helicobacter pylori-promoted gastric cancer. This provocative study underscores the importance of changes in DNA methylation that contribute to the origin of inflammation-related cancers. The findings also raise the exciting possibility of cancer prevention by altering DNA methylation events early during tumorigenesis.

Helicobacter pylori CagA: From Pathogenic Mechanisms to Its Use as an Anti-Cancer Vaccine

Helicobacter pylori colonizes the gastric mucosa of more than 50% of the human population, causing chronic inflammation, which however is largely asymptomatic. Nevertheless, H. pylori-infected subjects can develop chronic gastritis, peptic ulcer, gastric mucosa-associated lymphoid tissue lymphoma, and gastric cancer. Chronic exposure to the pathogen and its ability to induce epithelial to mesenchymal transition (EMT) through the injection of cytotoxin-associated gene A into gastric epithelial cells may be key triggers of carcinogenesis. By deregulating cell-cell and cell-matrix interactions as well as DNA methylation, histone modifications, expression of micro RNAs, and resistance to apoptosis, EMT can actively contribute to early stages of the cancer formation. Host response to the infection significantly contributes to disease development and the concomitance of particular genotypes of both pathogen and host may turn into the most severe outcomes. T regulatory cells (Treg) have been recently demonstrated to play an important role in H. pylori-related disease development and at the same time the Treg-induced tolerance has been proposed as a possible mechanism that leads to less severe disease. Efficacy of antibiotic therapies of H. pylori infection has significantly dropped. Unfortunately, no vaccine against H. pylori is currently licensed, and protective immunity mechanisms against H. pylori are only partially understood. In spite of promising results obtained in animal models of infection with a number of vaccine candidates, few clinical trials have been conducted so far and with no satisfactory outcomes. However, prophylactic vaccination may be the only means to efficiently prevent H. pylori-associated cancers.

Phosphatase regulation of intercellular junctions

Intercellular junctions represent the key contact points and sites of communication between neighboring cells. Assembly of these junctions is absolutely essential for the structural integrity of cell monolayers, tissues and organs. Disruption of junctions can have severe consequences such as diarrhea, edema and sepsis, and contribute to the development of chronic inflammatory diseases. Cell junctions are not static structures, but rather they represent highly dynamic micro-domains that respond to signals from the intracellular and extracellular environments to modify their composition and function. This review article will focus on the regulation of tight junctions and adherens junctions by phosphatase enzymes that play an essential role in preserving and modulating the properties of intercellular junction proteins.

Expression and clinical significance of SHP2 in gastric cancer

OBJECTIVES

To investigate the expression and clinical significance of the protein tyrosine phosphatase, nonreceptor type 11 (PTPN11 or SHP2) gene, which encodes Src homology 2 domain-containing phosphatase (SHP-2) in gastric cancer.

METHODS

SHP2 expression was detected by immunohistochemical staining and real-time quantitative reverse transcription-polymerase chain reaction in tissue samples of normal gastric mucosa and different grades of gastric cancer. Correlation between SHP2 expression and standard clinico pathological parameters was analysed.

RESULTS

Immunohistochemical staining revealed significantly higher rates of SHP2 expression in gastric cancer tissues (72.5%) versus normal gastric mucosa (21.9%). SHP-2 mRNA levels were also significantly higher in gastric cancer tissues versus normal gastric mucosa. SHP2 expression correlated significantly with tumour differentiation, clinical classification and lymph node metastases, but was independent of sex and age.

CONCLUSIONS

SHP-2 is upregulated in gastric cancer and may be related to the development of gastric cancer. SHP-2 may be a potential prognostic marker of, or a therapeutic target for, gastric cancer.

Breaking the epithelial polarity barrier in cancer: the strange case of LKB1/PAR-4

The PAR clan of polarity regulating genes was initially discovered in a genetic screen searching for genes involved in asymmetric cell divisions in the Caenorhabditis elegans embryo. Today, investigations in worms, flies and mammals have established PAR proteins as conserved and fundamental regulators of animal cell polarization in a broad range of biological phenomena requiring cellular asymmetries. The human homologue of invertebrate PAR-4, a serine-threonine kinase LKB1/STK11, has caught attention as a gene behind Peutz-Jeghers polyposis syndrome and as a bona fide tumour suppressor gene commonly mutated in sporadic cancer. LKB1 functions as a master regulator of AMP-activated protein kinase (AMPK) and 12 other kinases referred to as the AMPK-related kinases, including four human homologues of PAR-1. The role of LKB1 as part of the energy sensing LKB1-AMPK module has been intensively studied, whereas the polarity function of LKB1, in the context of homoeostasis or cancer, has gained less attention. Here, we focus on the PAR-4 identity of LKB1, discussing the weight of evidence indicating a role for LKB1 in regulation of cell polarity and epithelial integrity across species and highlight recent investigations providing new insight into the old question: does the PAR-4 identity of LKB1 matter in cancer?

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

Background/Aims

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

Methods

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

Results

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

Conclusions

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

Dynamics of the Cag-type IV secretion system of Helicobacter pylori as studied by bacterial co-infections

Many pathogenic Gram-negative bacteria possess type IV secretion systems (T4SS) to inject effector proteins directly into host cells to modulate cellular processes to their benefit. The human bacterial pathogen Helicobacter pylori, a major aetiological agent in the development of chronic gastritis, duodenal ulcer and gastric carcinoma, harbours the cag-T4SS to inject the cytotoxin associated Antigen (CagA) into gastric epithelial cells. This results in deregulation of major signalling cascades, actin-cytoskeletal rearrangements and eventually gastric cancer. We show here that a pre-infection with live H. pylori has a dose-dependent negative effect on the CagA translocation efficiency of a later infecting strain. This effect of the 'first' strain was independent of any of its T4SS, the vacuolating cytotoxin (VacA) or flagella. Other bacterial pathogens, e.g. pathogenic Escherichia coli, Campylobacter jejuni, Staphylococcus aureus, or commensal bacteria, such as lactobacilli, were unable to interfere with H. pylori's CagA translocation capacity in the same way. This interference was independent of the β1 integrin receptor availability for H. pylori, but certain H. pylori outer membrane proteins, such as HopI, HopQ or AlpAB, were essential for the effect. We suggest that the specific interference mechanism induced by H. pylori represents a cellular response to restrict and control CagA translocation into a host cell to control the cellular damage.

The involvement of Helicobacter pylori thioredoxin-1 in gastric carcinogenesis

Helicobacter pylori infection is related to the development of gastric diseases. Various virulence factors are responsible for the pathogenic mechanisms of H. pylori infection. Our previous studies using two-dimensional gel electrophoresis showed that H. pylori thioredoxin-1 (Trx1) is overexpressed in gastric carcinomas. Here, we examined whether H. pylori Trx1 is a novel virulence factor associated with gastric tumorigenesis. We found that Trx1 expression in H. pylori isolated from gastric cancer tissues was significantly higher than that from tissues exhibiting gastritis. In the gastric epithelial cell line GES-1, infection of H. pylori with high Trx1 expression significantly induced cell apoptosis, decreased the expression of cyclin D1 and upregulated p21. However, in the gastric cancer cell line BGC823, high Trx1 expression in H. pylori significantly increased cell proliferation, and upregulated cyclin D1. The effects on cell lines were confirmed using the H. pylori Trx1-knockout mutant strain. Our observations indicate that high Trx1 expression in H. pylori is associated with gastric carcinogenesis. In H. pylori, Trx1 likely participates in the pathogenesis of gastric cancer and H. pylori expressing high levels of Trx1 would be expected to be highly pathogenic in gastric diseases in China.

Helicobacter pylori CagA: a critical destroyer of the gastric epithelial barrier

The destruction of the integrity of the gastric epithelial barrier underlies the pathology of many gastric diseases, including gastric tumors. The Helicobacter pylori virulence factor CagA is one of the main destroyers of the gastric epithelial barrier. There are differences among CagA proteins that originate from different isolates. CagA translocated into the gastric epithelial cells causes significant changes in cell signaling pathways in phosphorylation-dependent and phosphorylation-independent manners, leading to cell morphological changes and host cell epithelial barrier injury, which lay the foundation for the occurrence of related diseases. As a newly identified pathogenic mechanism of CagA, miRNA is involved in the remodeling of the gastric epithelial barrier. Both the eradication of H. pylori infection and interventions against CagA-induced gastric epithelial barrier lesions may contribute to the prevention of the development of gastric tumors.

Concepts and mechanisms: crossing host barriers

The human body is bordered by the skin and mucosa, which are the cellular barriers that define the frontier between the internal milieu and the external nonsterile environment. Additional cellular barriers, such as the placental and the blood-brain barriers, define protected niches within the host. In addition to their physiological roles, these host barriers provide both physical and immune defense against microbial infection. Yet, many pathogens have evolved elaborated mechanisms to target this line of defense, resulting in a microbial invasion of cells constitutive of host barriers, disruption of barrier integrity, and systemic dissemination and invasion of deeper tissues. Here we review representative examples of microbial interactions with human barriers, including the intestinal, placental, and blood-brain barriers, and discuss how these microbes adhere to, invade, breach, or compromise these barriers.

Neisseria gonorrhoeae breaches the apical junction of polarized epithelial cells for transmigration by activating EGFR

Neisseria gonorrhoeae initiates infection at the apical surface of columnar endocervical epithelial cells in the female reproductive tract. These cells provide a physical barrier against pathogens by forming continuous apical junctional complexes between neighbouring cells. This study examines the interaction of gonococci (GC) with polarized epithelial cells. We show that viable GC preferentially localize at the apical side of the cell-cell junction in polarized endometrial and colonic epithelial cells, HEC-1-B and T84. In GC-infected cells, continuous apical junctional complexes are disrupted, and the junction-associated protein β-catenin is redistributed from the apical junction to the cytoplasm and to GC adherent sites; however, overall cellular levels remain unchanged. This redistribution of junctional proteins is associated with a decrease in the 'fence' function of the apical junction but not its 'gate' function. Disruption of the apical junction by removing calcium increases GC transmigration across the epithelial monolayer. GC inoculation induces the phosphorylation of both epidermal growth factor receptor (EGFR) and β-catenin, while inhibition of EGFR kinase activity significantly reduces both GC-induced β-catenin redistribution and GC transmigration. Therefore, the gonococcus is capable of weakening the apical junction and polarity of epithelial cells by activating EGFR, which facilitates GC transmigration across the epithelium.

A mutagenesis method for the addition and deletion of highly repetitive DNA regions: the paradigm of EPIYA motifs in the cagA gene of Helicobacter pylori

BACKGROUND

CagA protein of Western origin Helicobacter pylori isolates contains at its carboxyl-terminal end repeating types of EPIYA motifs, depending on the surrounding sequence, which dictate hierarchic tyrosine phosphorylation. To produce, in an isogenic background, mutant strains expressing CagA protein with variable numbers of EPIYA-C terminal motifs, we have adopted a mutagenesis assay using a megaprimer approach.

MATERIALS AND METHODS

The H. pylori P12 reference strain containing two terminal EPIYA-C motifs was utilized. Initially, we cloned, full-length cagA gene, next to the Campylobacter jejuni kanamycin-resistance cassette, followed by the 1200-bp region located immediately after cagA gene (metacagA region). Then, we generated a megaprimer consisting of three consecutive copies of the EPIYA-C coding sequence of cagA gene, followed by the 140-bp region of the cagA genomic sequence present immediately after the second EPIYA-C repeat. We utilized these two products to perform a QuikChange mutagenesis assay and were able to obtain all desired combinations of EPIYA-C motifs, followed by Kan(r) cassette and metacagA region. These constructions were used to perform natural transformation of the P12 parental strain, by directional homologous recombination.

RESULTS

We produced isogenic H. pylori strains that express CagA with variable number of EPIYA-C motifs (AB, ABC, ABCCC) and their phosphorylation-deficient counterparts. They exhibited similar growth characteristics to the parental strain, adhered equally well to gastric cells and successfully translocated CagA, following pilus induction.

CONCLUSIONS

Our method can be used in other cases where highly repetitive sequences need to be reproduced.

Helicobacter pylori in gastric carcinogenesis: mechanisms

Helicobacter pylori infection induces chronic inflammation and is the strongest known risk factor for gastric cancer. The genomes of H pylori are highly diverse and therefore bacterial virulence factors play an important role in determining the outcome of H pylori infection, in combination with host responses that are augmented by environmental and dietary risk factors. It is important to gain further understanding of the pathogenesis of H pylori infection to develop more effective treatments for this common but deadly malignancy. This review focuses on the specific mechanisms used by H pylori to drive gastric carcinogenesis.

Biochemical characterization and functional analysis of fructose-1,6-bisphosphatase from Clonorchis sinensis

Fructose-1,6-bisphosphatase (FBPase), a key regulatory enzyme of gluconeogenesis, plays an essential role in metabolism and development of most organisms. To the wealth of available knowledge about FBPase from Clonorchis sinensis (CsFBPase), in this study, the characteristics of CsFBPase and its potential role in pathogenesis of clonorchiasis were investigated. The Km value of CsFBPase was calculated to be 41.9 uM. The optimal temperature and pH of CsFBPase were 37 °C and pH 7.5-8.0, respectively. In addition, Mg(2+) or K(+) played a regulatory role in enzyme activity of CsFBPase. Both transcriptional and translational level of CsFBPase were higher in metacercariae (one of larva stages) than those in adult worm (P < 0.05). CsFBPase were observed to extensively express in the intestine, vitellaria and tegument of adult worms and ubiquitously in metacercariae. Moreover, CsFBPase was confirmed as a component of excretory/secretory products. Consequently, the translocation of CsFBPase could be detected on epithelial cells of bile duct in liver of C. sinensis infected rat. Recombinant CsFBPase can specifically bind to the membrane of human hepatic stellate cell line LX-2 by immunofluorescence analysis and stimulated proliferation and activation of LX-2 which demonstrated by Cell Counting Kit-8 and upregulation of key fibrosis-related factors, such as α-smooth muscle actin, collagen I and collagen III using qRT-PCR. Thus, we predicated that CsFBPase might be a multifunctional enzyme which played as both regulatory enzyme and virulence factor in pathogenesis of C. sinensis infection.

Epstein Barr virus and Helicobacter pylori co-infection are positively associated with severe gastritis in pediatric patients

Background

H. pylori infection is acquired during childhood and causes a chronic inflammatory response in the gastric mucosa, which is considered the main risk factor to acquire gastric cancer (GC) later in life. More recently, infection by Epstein-Barr virus (EBV) have also been associated with GC. The role of EBV in early inflammatory responses and its relationship with H. pylori infection remains poorly studied. Here, we assessed whether EBV infection in children correlated with the stage of gastritis and whether co-infection with H. pylori affected the severity of inflammation.

Methodology/Principal Findings

333 pediatric patients with chronic abdominal pain were studied. From them, gastric biopsies were taken and inflammation graded according to the Sydney system; peripheral blood was drawn and antibodies against EBV (IgG and IgM anti-VCA) and H. pylori (IgG anti-whole bacteria and anti-CagA) were measured in sera. We found that children infected only by EBV presented mild mononuclear (MN) and none polymorphonuclear (PMN) cell infiltration, while those infected by H. pylori presented moderate MN and mild PMN. In contrast, patients co-infected with both pathogens were significantly associated with severe gastritis. Importantly, co-infection of H. pylori CagA+/EBV+ had a stronger association with severe MN (PR 3.0) and PMN (PR 7.2) cells than cases with single H. pylori CagA+ infection.

Conclusions/Significance

Co-infection with EBV and H. pylori in pediatric patients is associated with severe gastritis. Even single infections with H. pylori CagA+ strains are associated with mild to moderate infiltration arguing for a cooperative effect of H. pylori and EBV in the gastric mucosa and revealing a critical role for EBV previously un-appreciated. This study points out the need to study both pathogens to understand the mechanism behind severe damage of the gastric mucosa, which could identified children with increased risk to present more serious lesions later in life.

A 5'-flanking region polymorphism in toll-like receptor 4 is associated with gastric cancer in a Chinese population

Objective

Inflammation induced by H.pylori colonization in the stomach is related to the development of gastric cancer and the genetic variations of the genes involved in the immune responses modify the host response to the infection. The aim of this study was to evaluate whether polymorphisms in the toll-like receptor 4 (TLR4) gene, a key regulator of both innate and adaptive immunity, were related to the susceptibility to gastric cancer in a Chinese population.

Methods

Two variations in the 5′-flanking region of TLR4 (rs1927914 T > C and rs10759932 T > C) were genotyped by using the PCR-restriction fragment length polymorphism (RFLP) assay in a case-control study of 1,053 incident gastric cancer cases and 1,100 cancer-free controls in a Chinese population.

Results

Individuals carrying the C allele of rs10759932 had a significantly reduced risk of gastric cancer (adjusted OR = 0.81; 95%CI = 0.67-0.96), compared with the wild-type homozygote (TT), and the protective effect was not significantly different among subgroups stratified by age, sex, smoking, drinking and H.pylori infection status (P for heterogeneity > 0.05). No significant association was observed between rs1927914 and gastric cancer risk in this study population.

Conclusion

The T to C allele substitution of rs10759932 may play a protective role in gastric carcinogenesis in a Chinese population. Large studies with different ethnic populations are warranted to confirm these findings.

Polymorphism in the Helicobacter pylori CagA and VacA toxins and disease

Half of the world's population is infected with Helicobacter pylori and approximately 20% of infected individuals develop overt clinical disease such as ulcers and stomach cancer. Paradoxically, despite its classification as a class I carcinogen, H. pylori has been shown to be protective against development of asthma, allergy, and esophageal disease. Given these conflicting roles for H. pylori, researchers are attempting to define the environmental, host, and pathogen interactions that ultimately result in severe disease in some individuals. From the bacterial perspective, the toxins, CagA and VacA, have each been shown to be polymorphic and to contribute to disease in an allele-dependent manner. Based on the notable advances that have recently been made in the CagA field, herein we review recent studies that have begun to shed light on the role of CagA polymorphism in H. pylori disease. Moreover, we discuss the potential interaction of CagA and VacA as a mediator of gastric disease.

Functional plasticity in the type IV secretion system of Helicobacter pylori

Helicobacter pylori causes clinical disease primarily in those individuals infected with a strain that carries the cytotoxin associated gene pathogenicity island (cagPAI). The cagPAI encodes a type IV secretion system (T4SS) that injects the CagA oncoprotein into epithelial cells and is required for induction of the pro-inflammatory cytokine, interleukin-8 (IL-8). CagY is an essential component of the H. pylori T4SS that has an unusual sequence structure, in which an extraordinary number of direct DNA repeats is predicted to cause rearrangements that invariably yield in-frame insertions or deletions. Here we demonstrate in murine and non-human primate models that immune-driven host selection of rearrangements in CagY is sufficient to cause gain or loss of function in the H. pylori T4SS. We propose that CagY functions as a sort of molecular switch or perhaps a rheostat that alters the function of the T4SS and “tunes” the host inflammatory response so as to maximize persistent infection.

Helicobacter pylori is a bacterium that colonizes the stomach of about half the world's population, most of whom are asymptomatic. However, some strains of H. pylori express a bacterial secretion system, a sort of molecular syringe that injects a bacterial protein inside the gastric cells and causes inflammation that can lead to peptic ulcer disease or gastric cancer. One of the essential components of the H. pylori secretion system is CagY, which is unusual because it contains a series of repetitive amino acid motifs that are encoded by a very large number of direct DNA repeats. Here we have shown that DNA recombination in cagY changes the protein motif structure and alters the function of the secretion system—turning it on or off. Using mouse and non-human primate models, we have demonstrated that CagY is a molecular switch that “tunes” the host inflammatory response, and likely contributes to persistent infection. Determining the mechanism by which CagY functions will enhance our understanding of the effects of H. pylori on human health, and could lead to novel applications for the modulation of host cell function.

Lkb1 regulates organogenesis and early oncogenesis along AMPK-dependent and -independent pathways

A combination of ex vivo embryonic tissue culture, genetic manipulation, and chemical genetics reveals novel details of Lkb1-mediated regulation of tissue morphogenesis.

The tumor suppressor Lkb1/STK11/Par-4 is a key regulator of cellular energy, proliferation, and polarity, yet its mechanisms of action remain poorly defined. We generated mice harboring a mutant Lkb1 knockin allele that allows for rapid inhibition of Lkb1 kinase. Culturing embryonic tissues, we show that acute loss of kinase activity perturbs epithelial morphogenesis without affecting cell polarity. In pancreas, cystic structures developed rapidly after Lkb1 inhibition. In lung, inhibition resulted in cell-autonomous branching defects. Although the lung phenotype was rescued by an activator of the Lkb1 target adenosine monophosphate–activated kinase (AMPK), pancreatic cyst development was independent of AMPK signaling. Remarkably, the pancreatic phenotype evolved to resemble precancerous lesions, demonstrating that loss of Lkb1 was sufficient to drive the initial steps of carcinogenesis ex vivo. A similar phenotype was induced by expression of mutant K-Ras with p16/p19 deletion. Combining culture of embryonic tissues with genetic manipulation and chemical genetics thus provides a powerful approach to unraveling developmental programs and understanding cancer initiation.