Vacuoles induced by Helicobacter pylori toxin contain both late endosomal and lysosomal markers

There Are No Insurmountable Barriers: Passage of the Helicobacter pylori VacA Toxin from Bacterial Cytoplasm to Eukaryotic Cell Organelle

The Gram-negative bacterium Helicobacter pylori is a very successful pathogen, one of the most commonly identified causes of bacterial infections in humans worldwide. H. pylori produces several virulence factors that contribute to its persistence in the hostile host habitat and to its pathogenicity. The most extensively studied are cytotoxin-associated gene A (CagA) and vacuolating cytotoxin A (VacA). VacA is present in almost all H. pylori strains. As a secreted multifunctional toxin, it assists bacterial colonization, survival, and proliferation during long-lasting infections. To exert its effect on gastric epithelium and other cell types, VacA undergoes several modifications and crosses multiple membrane barriers. Once inside the gastric epithelial cell, VacA disrupts many cellular-signaling pathways and processes, leading mainly to changes in the efflux of various ions, the depolarization of membrane potential, and perturbations in endocytic trafficking and mitochondrial function. The most notable effect of VacA is the formation of vacuole-like structures, which may lead to apoptosis. This review focuses on the processes involved in VacA secretion, processing, and entry into host cells, with a particular emphasis on the interaction of the mature toxin with host membranes and the formation of transmembrane pores.

ER-phagy: mechanisms, regulation and diseases connected to the lysosomal clearance of the endoplasmic reticulum

ER-phagy (reticulo-phagy) defines the degradation of portions of the endoplasmic reticulum (ER) within lysosomes or vacuoles. It is part of the self-digestion (i.e., auto-phagic) programs recycling cytoplasmic material and organelles, which rapidly mobilize metabolites in cells confronted with nutrient shortage. Moreover, selective clearance of ER subdomains participates to the control of ER size and activity during ER stress, the re-establishment of ER homeostasis after ER stress resolution and the removal of ER parts, in which aberrant and potentially cytotoxic material has been segregated. ER-phagy relies on the individual and/or concerted activation of the ER-phagy receptors, ER peripheral or integral membrane proteins that share the presence of LC3/Atg8-binding motifs in their cytosolic domains. ER-phagy involves the physical separation of portions of the ER from the bulk ER network, and their delivery to the endolysosomal/vacuolar catabolic district. This last step is accomplished by a variety of mechanisms including macro-ER-phagy (in which ER fragments are sequestered by double-membrane autophagosomes that eventually fuse with lysosomes/vacuoles), micro-ER-phagy (in which ER fragments are directly engulfed by endosomes/lysosomes/vacuoles), or direct fusion of ER-derived vesicles with lysosomes/vacuoles. ER-phagy is dysfunctional in specific human diseases and its regulators are subverted by pathogens, highlighting its crucial role for cell and organism life.

Helicobacter pylori: an up-to-date overview on the virulence and pathogenesis mechanisms

Helicobacter pylori is an organism associated with ulcer disease and gastric cancer. The latter is one of the most prevalent malignancies and currently the fourth major cause of cancer-related deaths globally. The pathogen infects about 50% of the world population, and currently, no treatment ensures its total elimination. There has been an increase in our understanding of the pathophysiology and pathogenesis mechanisms of H. pylori over the years. H. pylori can induce several genetic alterations, express numerous virulence factors, and trigger diverse adaptive mechanisms during its adherence and colonization. For successful colonization and infection establishment, several effector proteins/toxins are released by the organism. Evidence is also available reporting spiral to coccoid transition as a unique tactic H. pylori uses to survive in the host’s gastrointestinal tract (GIT). Thus, the virulence and pathogenicity of H. pylori are under the control of complex interplay between the virulence factors, host, and environmental factors. Expounding the role of the various virulence factors in H. pylori pathogenesis and clinical outcomes is crucial for vaccine development and in providing and developing a more effective therapeutic intervention. Here we critically reflect on H. pylori infection and delineate what is currently known about the virulence and pathogenesis mechanisms of H. pylori.

Helicobacter pylori-Derived Outer Membrane Vesicles (OMVs): Role in Bacterial Pathogenesis?

Persistent infections with the human pathogen Helicobacter pylori (H. pylori) have been closely associated with the induction and progression of a wide range of gastric disorders, including acute and chronic gastritis, ulceration in the stomach and duodenum, mucosa-associated lymphoid tissue (MALT) lymphoma, and gastric adenocarcinoma. The pathogenesis of H. pylori is determined by a complicated network of manifold mechanisms of pathogen–host interactions, which involves a coordinated interplay of H. pylori pathogenicity and virulence factors with host cells. While these molecular and cellular mechanisms have been intensively investigated to date, the knowledge about outer membrane vesicles (OMVs) derived from H. pylori and their implication in bacterial pathogenesis is not well developed. In this review, we summarize the current knowledge on H. pylori-derived OMVs.

Loss of MYO5B expression deregulates late endosome size which hinders mitotic spindle orientation

Recycling endosomes regulate plasma membrane recycling. Recently, recycling endosome–associated proteins have been implicated in the positioning and orientation of the mitotic spindle and cytokinesis. Loss of MYO5B, encoding the recycling endosome–associated myosin Vb, is associated with tumor development and tissue architecture defects in the gastrointestinal tract. Whether loss of MYO5B expression affects mitosis is not known. Here, we demonstrate that loss of MYO5B expression delayed cytokinesis, perturbed mitotic spindle orientation, led to the misorientation of the plane of cell division during the course of mitosis, and resulted in the delamination of epithelial cells. Remarkably, the effects on spindle orientation, but not cytokinesis, were a direct consequence of physical hindrance by giant late endosomes, which were formed in a chloride channel–sensitive manner concomitant with a redistribution of chloride channels from the cell periphery to late endosomes upon loss of MYO5B. Rab7 availability was identified as a limiting factor for the development of giant late endosomes. In accordance, increasing rab7 availability corrected mitotic spindle misorientation and cell delamination in cells lacking MYO5B expression. In conclusion, we identified a novel role for MYO5B in the regulation of late endosome size control and identify the inability to control late endosome size as an unexpected novel mechanism underlying defects in cell division orientation and epithelial architecture.

Loss of the recycling endosome-associated motor protein myosin Vb causes the formation of giant late endo-lysosomes; these in turn hinder the orientation of the mitotic spindle and chromosome segregation. Deregulated endosome size thus hampers faithful cell division.

Intracellular Degradation of Helicobacter pylori VacA Toxin as a Determinant of Gastric Epithelial Cell Viability

Helicobacter pylori VacA is a secreted pore-forming toxin that induces cell vacuolation in vitro and contributes to the pathogenesis of gastric cancer and peptic ulcer disease. We observed that purified VacA has relatively little effect on the viability of AGS gastric epithelial cells, but the presence of exogenous weak bases such as ammonium chloride (NH₄Cl) enhances the susceptibility of these cells to VacA-induced vacuolation and cell death. Therefore, we tested the hypothesis that NH₄Cl augments VacA toxicity by altering the intracellular trafficking of VacA or inhibiting intracellular VacA degradation. We observed VacA colocalization with LAMP1- and LC3-positive vesicles in both the presence and absence of NH₄Cl, indicating that NH₄Cl does not alter VacA trafficking to lysosomes or autophagosomes. Conversely, we found that supplemental NH₄Cl significantly increases the intracellular stability of VacA. By conducting experiments using chemical inhibitors, stable ATG5 knockdown cell lines, and ATG16L1 knockout cells (generated using CRISPR/Cas9), we show that VacA degradation is independent of autophagy and proteasome activity but dependent on lysosomal acidification. We conclude that weak bases like ammonia, potentially generated during H. pylori infection by urease and other enzymes, enhance VacA toxicity by inhibiting toxin degradation.

Helicobacter pylori VacA, a distinct toxin exerts diverse functionalities in numerous cells: An overview

BACKGROUND

Helicobacter pylori, gastric cancer-causing bacteria, survive in their gastric environment of more than 50% of the world population. The presence of H. pylori in the gastric vicinity promotes the development of various diseases including peptic ulcer and gastric carcinoma. H. pylori produce and secret Vacuolating cytotoxin A (VacA), a major toxin facilitating the bacteria against the host defense system. The toxin causes multiple effects in epithelial cells and immune cells, especially T cells, B cells, and Macrophages.

METHODS

This review describes the diverse functionalities of protein toxin VacA. The specific objective of this review is to address the overall structure, mechanism, and functions of VacA in various cell types. The recent advancements are summarized and discussed and thus conclusion is drawn based on the overall reported evidences.

RESULTS

The searched articles on H. pylori VacA were evaluated and limited up to 66 articles for this review. The articles were divided into four major categories including articles on vacA gene, VacA toxin, distinct effects of VacA toxin, and their effects on various cells. Based on these studies, the review article was prepared.

CONCLUSIONS

This review describes an overview of how VacA is secreted by H. pylori and contributes to colonization and virulence in multiple ways by affecting epithelial cells, T cells, Dendritic cells, B cells, and Macrophages. The reported evidence suggests that the comprehensive outlook need to be developed for understanding distinctive functionalities of VacA.

Sequestration inside the yeast vacuole may enhance Helicobacter pylori survival against stressful condition

Vacuole of eukaryotic cells, beyond intracellular digestion plays additional roles such as storage of nutrients that provide favorable conditions for bacterial survival. In this study, occurrence of H. pylori inside the vacuole of Candida yeast was studied and the role of vacuolating cytotoxin A (VacA) in constructing the vacuole was discussed. One gastric Candida yeast was used for Live/Dead stain and fluorescence in situ hybridization (FISH) with universal bacterial probe. Yeast total DNA was used for amplification of full-length bacterial 16S rDNA as well as H. pylori-specific 16S rDNA and vacA alleles. Vacuoles were isolated from yeast cells and stained with fluorescent yeast vacuole membrane marker MDY-64. DNA extracted from vacuoles was used for amplification of H. pylori-specific 16S rDNA. Fluorescent microscopy showed occurrence of viable bacteria inside the vacuole of intact Candida yeast cells. FISH showed intracellular bacteria as fluorescent spots inside the vacuole of mother and daughter yeast cells, suggesting bacterial transmission to next generations of yeast. Sequencing of amplified products of bacterial 16S rDNA and amplification of H. pylori 16S rDNA and vacA confirmed the identity of intracellular bacteria as H. pylori. Isolated vacuoles were stained with membrane-specific marker and H. pylori 16S rDNA was amplified from their DNA content. Results of this study suggest yeast vacuole as a specialized niche for H. pylori. It appears that sequestration inside the vacuole may enhance bacterial survival.

Natural history of Helicobacter pylori VacA toxin in human gastric epithelium in vivo: vacuoles and beyond

Uptake, intracellular trafficking and pathologic effects of VacA toxin from Helicobacter pylori have been widely investigated in vitro. However, no systematic analysis investigated VacA intracellular distribution and fate in H. pylori-infected human gastric epithelium in vivo, using ultrastructural immunocytochemistry that combines precise toxin localization with analysis of the overall cell ultrastructure and intercompartimental/interorganellar relationships. By immunogold procedure, in this study we investigated gastric biopsies taken from dyspeptic patients to characterize the overall toxin’s journey inside human gastric epithelial cells in vivo. Endocytic pits were found to take up VacA at sites of bacterial adhesion, leading to a population of peripheral endosomes, which in deeper (juxtanuclear) cytoplasm enlarged and fused each other to form large VacA-containing vacuoles (VCVs). These directly opened into endoplasmic reticulum (ER) cisternae, which in turn enveloped mitochondria and contacted the Golgi apparatus. In all such organelles we found toxin molecules, often coupled with structural damage. These findings suggest direct toxin transfer from VCVs to other target organelles such as ER/Golgi and mitochondria. VacA-induced cytotoxic changes were associated with the appearance of auto(phago)lysosomes containing VacA, polyubiquitinated proteins, p62/SQSTM1 protein, cathepsin D, damaged mitochondria and bacterial remnants, thus leading to persistent cell accumulation of degradative products.

Helicobacter pylori Vacuolating Toxin and Gastric Cancer

Helicobacter pylori VacA is a channel-forming toxin unrelated to other known bacterial toxins. Most H. pylori strains contain a vacA gene, but there is marked variation among strains in VacA toxin activity. This variation is attributable to strain-specific variations in VacA amino acid sequences, as well as variations in the levels of VacA transcription and secretion. In this review, we discuss epidemiologic studies showing an association between specific vacA allelic types and gastric cancer, as well as studies that have used animal models to investigate VacA activities relevant to gastric cancer. We also discuss the mechanisms by which VacA-induced cellular alterations may contribute to the pathogenesis of gastric cancer.

Giant Cellular Vacuoles Induced by Rare Earth Oxide Nanoparticles are Abnormally Enlarged Endo/Lysosomes and Promote mTOR-Dependent TFEB Nucleus Translocation

Many nanomaterials are reported to disrupt lysosomal function and homeostasis, but how cells sense and then respond to nanomaterial-elicited lysosome stress is poorly understood. Nucleus translocation of transcription factor EB (TFEB) plays critical roles in lysosome biogenesis following lysosome stress induced by starvation. The authors previously reported massive cellular vacuolization, along with autophagy induction, in cells treated with rare earth oxide (REO) nanoparticles. Here, the authors identify these giant cellular vacuoles as abnormally enlarged and alkalinized endo/lysosomes whose formation is dependent on macropinocytosis. This vacuolization causes deactivation of mammalian target of rapamycin (mTOR), a TFEB-interacting kinase that resides on the lysosome membrane. Subsequently, TFEB is dephosphorylated at serine 142 and translocated into cell nucleus. This nucleus translocation of TFEB is observed only in vacuolated cells and it is critical for maintaining lysosome homeostasis after REO nanoparticle treatment, as knock-down of TFEB gene significantly compromises lysosome function and enhances cell death in nanoparticle-treated cells. Our results reveal that cellular vacuolization, which is commonly observed in cells treated with REOs and other nanomaterials, represents a condition of profound lysosome stress, and cells sense and respond to this stress by facilitating mTOR-dependent TFEB nucleus translocation in an effort to restore lysosome homeostasis.

"Non-Toxic" Proteins of the Botulinum Toxin Complex Exert In-vivo Toxicity

The botulinum neurotoxin (BoNT) causes muscle paralysis and is the most potent toxin in nature. BoNT is associated with a complex of auxiliary “Non-Toxic” proteins, which constitute a large-sized toxin complex (L-TC). However, here we report that the “Non-Toxic” complex of serotype D botulinum L-TC, when administered to rats, exerts in-vivo toxicity on small-intestinal villi. Moreover, Serotype C and D of the “Non-Toxic” complex, but not BoNT, induced vacuole-formation in a rat intestinal epithelial cell line (IEC-6), resulting in cell death. Our results suggest that the vacuole was formed in a manner distinct from the mechanism by which Helicobacter pylori vacuolating toxin (VacA) and Vibrio cholerae haemolysin induce vacuolation. We therefore hypothesise that the serotype C and D botulinum toxin complex is a functional hybrid of the neurotoxin and vacuolating toxin (VT) which arose from horizontal gene transfer from an ancestral BoNT-producing bacterium to a hypothetical VT-producing bacterium.

Relationship between VacA Toxin and Host Cell Autophagy in Helicobacter pylori Infection of the Human Stomach: A Few Answers, Many Questions

Helicobacter pylori is a Gram-negative bacterium that colonizes the stomach of about half the global population and represents the greatest risk factor for gastric malignancy. The relevance of H. pylori for gastric cancer development is equivalent to that of tobacco smoking for lung cancer. VacA toxin seems to play a pivotal role in the overall strategy of H. pylori towards achieving persistent gastric colonization. This strategy appears to involve the modulation of host cell autophagy. After an overview of autophagy and its role in infection and carcinogenesis, I critically review current knowledge about the action of VacA on host cell autophagy during H. pylori infection of the human stomach. Although VacA is a key player in modulation of H. pylori-induced autophagy, a few discrepancies in the data are also evident and many questions remain to be answered. We are thus still far from a definitive understanding of the molecular mechanisms through which VacA affects autophagy and the consequences of this toxin action on the overall pathogenic activity of H. pylori.

VacA's Induction of VacA-Containing Vacuoles (VCVs) and Their Immunomodulatory Activities on Human T Cells

Vacuolating cytotoxin A (VacA) is a secreted pore-forming toxin and one of the major virulence factors of Helicobacter pylori (H. pylori), which actively supports the persistence and survival of the bacteria in the special ecological niche of the human stomach. H. pylori genomes harbor different allelic forms of the vacA gene, which translate into functionally distinct VacA toxin types. VacA internalizes into various cell types via membrane or specific receptor interactions finally forming acidic endocytic VacA-containing vacuoles (VCVs). In this review, we focus on different characteristics of VacA, its interaction with host cells, the formation and protein content of VCVs and their intracellular transport into human T cells, which finally leads to the immunosuppressive phenotype of VacA. Immunomodulatory activities of VacA on human T cells are discussed with a focus on T-cell proliferation and calcium signaling.

An Overview of Helicobacter pylori VacA Toxin Biology

The VacA toxin secreted by Helicobacter pylori enhances the ability of the bacteria to colonize the stomach and contributes to the pathogenesis of gastric adenocarcinoma and peptic ulcer disease. The amino acid sequence and structure of VacA are unrelated to corresponding features of other known bacterial toxins. VacA is classified as a pore-forming toxin, and many of its effects on host cells are attributed to formation of channels in intracellular sites. The most extensively studied VacA activity is its capacity to stimulate vacuole formation, but the toxin has many additional effects on host cells. Multiple cell types are susceptible to VacA, including gastric epithelial cells, parietal cells, T cells, and other types of immune cells. This review focuses on the wide range of VacA actions that are detectable in vitro, as well as actions of VacA in vivo that are relevant for H. pylori colonization of the stomach and development of gastric disease.

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

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

V-ATPase and osmotic imbalances activate endolysosomal LC3 lipidation

Recently a noncanonical activity of autophagy proteins has been discovered that targets lipidation of microtubule-associated protein 1 light chain 3 (LC3) onto macroendocytic vacuoles, including macropinosomes, phagosomes, and entotic vacuoles. While this pathway is distinct from canonical autophagy, the mechanism of how these nonautophagic membranes are targeted for LC3 lipidation remains unclear. Here we present evidence that this pathway requires activity of the vacuolar-type H(+)-ATPase (V-ATPase) and is induced by osmotic imbalances within endolysosomal compartments. LC3 lipidation by this mechanism is induced by treatment of cells with the lysosomotropic agent chloroquine, and through exposure to the Heliobacter pylori pore-forming toxin VacA. These data add novel mechanistic insights into the regulation of noncanonical LC3 lipidation and its associated processes, including LC3-associated phagocytosis (LAP), and demonstrate that the widely and therapeutically used drug chloroquine, which is conventionally used to inhibit autophagy flux, is an inducer of LC3 lipidation.

A novel role of transient receptor potential mucolipin1 (TRPML1) in protecting against imidazole-induced cytotoxicity

Lysosomotropic amines cause serious side effects such as cytoplasmic vacuolation and cell death. TRPML1 (also known as mucolipin1), a member of the transient receptor potential (TRP) protein family, may regulate fusion/fission of vesicles along the endocytic pathway and some aspects of lysosomal ion homeostasis. Nevertheless, it is still unknown whether TRPML1 is involved in death of mammalian cells induced by lysosomotropic agents. In this study, imidazole was used as a model to investigate the role of TRPML1 in the cytotoxicity of lysosomotropic agents. Overexpression of wild-type TRPML1 inhibited imidazole-induced vacuole formation and cell death in human endometrial adenocarcinoma (HEC-1B) cells. In contrast, siRNA-mediated TRPML1 knockdown increased the cell death induced by imidazole. Bafilomycin A1 raises the pH of acidic organelles and therefore suppresses accumulation of weak bases in them. Similarly, lysosomal pH was raised in TRPML1-overexpressing cells; therefore, we inferred that TRPML1 protected against imidazole toxicity by regulating the pH of acidic organelles. We concluded that TRPML1 had a novel role in protecting against lysosomotropic amine toxicity.

Autotransporter secretion: varying on a theme

Autotransporters are widely distributed among Gram-negative bacteria. They can have a large variety of functions and many of them have a role in virulence. They are synthesized as large precursors with an N-terminal signal sequence that mediates transport across the inner membrane via the Sec machinery and a translocator domain that mediates the transport of the connected passenger domain across the outer membrane to the bacterial cell surface. Like integral outer membrane proteins, the translocator domain folds in a β-barrel structure and requires the Bam machinery for its insertion into the outer membrane. After transport across the outer membrane, the passenger may stay connected via the translocator domain to the bacterial cell surface or it is proteolytically released into the extracellular milieu. Based on the size of the translocator domain and its position relative to the passenger in the precursor, autotransporters are divided into four sub-categories. We review here the current knowledge of the biogenesis, structure and function of various autotransporters.

Bacterial pathogens commandeer Rab GTPases to establish intracellular niches

Intracellular bacterial pathogens deploy virulence factors termed effectors to inhibit degradation by host cells and to establish intracellular niches where growth and differentiation take place. Here, we describe mechanisms by which human bacterial pathogens (including Chlamydiae; Coxiella burnetii; Helicobacter pylori; Legionella pneumophila; Listeria monocytogenes; Mycobacteria; Pseudomonas aeruginosa, Salmonella enterica) modulate endocytic and exocytic Rab GTPases in order to thrive in host cells. Host cell Rab GTPases are critical for intracellular transport following pathogen phagocytosis or endocytosis. At the molecular level bacterial effectors hijack Rab protein function to: evade degradation, direct transport to particular intracellular locations and monopolize host vesicles carrying molecules that are needed for a stable niche and/or bacterial growth and differentiation. Bacterial effectors may serve as specific receptors for Rab GTPases or as enzymes that post-translationally modify Rab proteins or endosomal membrane lipids required for Rab function. Emerging data indicate that bacterial effector expression is temporally and spatially regulated and multiple virulence factors may act concertedly to usurp Rab GTPase function, alter signaling and ensure niche establishment and intracellular bacterial growth, making this field an exciting area for further study.

Remodeling the host environment: modulation of the gastric epithelium by the Helicobacter pylori vacuolating toxin (VacA)

Virulence mechanisms underlying Helicobacter pylori persistence and disease remain poorly understood, in part, because the factors underlying disease risk are multifactorial and complex. Among the bacterial factors that contribute to the cumulative pathophysiology associated with H. pylori infections, the vacuolating cytotoxin (VacA) is one of the most important. Analogous to a number of H. pylori genes, the vacA gene exhibits allelic mosaicism, and human epidemiological studies have revealed that several families of toxin alleles are predictive of more severe disease. Animal model studies suggest that VacA may contribute to pathogenesis in several ways. VacA functions as an intracellular-acting protein exotoxin. However, VacA does not fit the current prototype of AB intracellular-acting bacterial toxins, which elaborate modulatory effects through the action of an enzymatic domain translocated inside host cells. Rather, VacA may represent an alternative prototype for AB intracellular acting toxins that modulate cellular homeostasis by forming ion-conducting intracellular membrane channels. Although VacA seems to form channels in several different membranes, one of the most important target sites is the mitochondrial inner membrane. VacA apparently take advantage of an unusual intracellular trafficking pathway to mitochondria, where the toxin is imported and depolarizes the inner membrane to disrupt mitochondrial dynamics and cellular energy homeostasis as a mechanism for engaging the apoptotic machinery within host cells. VacA remodeling of the gastric environment appears to be fine-tuned through the action of the Type IV effector protein CagA which, in part, limits the cytotoxic effects of VacA in cells colonized by H. pylori.

Alzheimer's Disease: APP, Gamma Secretase, APOE, CLU, CR1, PICALM, ABCA7, BIN1, CD2AP, CD33, EPHA1, and MS4A2, and Their Relationships with Herpes Simplex, C. Pneumoniae, Other Suspect Pathogens, and the Immune System

Alzheimer's disease susceptibility genes, APP and gamma-secretase, are involved in the herpes simplex life cycle, and that of other suspect pathogens (C. pneumoniae, H. pylori, C. neoformans, B. burgdorferri, P. gingivalis) or immune defence. Such pathogens promote beta-amyloid deposition and tau phosphorylation and may thus be causative agents, whose effects are conditioned by genes. The antimicrobial effects of beta-amyloid, the localisation of APP/gamma-secretase in immunocompetent dendritic cells, and gamma secretase cleavage of numerous pathogen receptors suggest that this network is concerned with pathogen disposal, effects which may be abrogated by the presence of beta-amyloid autoantibodies in the elderly. These autoantibodies, as well as those to nerve growth factor and tau, also observed in Alzheimer's disease, may well be antibodies to pathogens, due to homology between human autoantigens and pathogen proteins. NGF or tau antibodies promote beta-amyloid deposition, neurofibrillary tangles, or cholinergic neuronal loss, and, with other autoantibodies, such as anti-ATPase, are potential agents of destruction, whose formation is dictated by sequence homology between pathogen and human proteins, and thus by pathogen strain and human genes. Pathogen elimination in the ageing population and removal of culpable autoantibodies might reduce the incidence and offer hope for a cure in this affliction.

Helicobacter pylori vacuolating toxin A and apoptosis

VacA, the vacuolating cytotoxin A of Helicobacter pylori, induces apoptosis in epithelial cells of the gastic mucosa and in leukocytes. VacA is released by the bacteria as a protein of 88 kDa. At the outer surface of host cells, it binds to the sphingomyelin of lipid rafts. At least partially, binding to the cells is facilitated by different receptor proteins. VacA is internalized by a clathrin-independent mechanism and initially accumulates in GPI-anchored proteins-enriched early endosomal compartments. Together with early endosomes, VacA is distributed inside the cells. Most of the VacA is eventually contained in the membranes of vacuoles. VacA assembles in hexameric oligomers forming an anion channel of low conductivity with a preference for chloride ions. In parallel, a significant fraction of VacA can be transferred from endosomes to mitochondria in a process involving direct endosome-mitochondria juxtaposition. Inside the mitochondria, VacA accumulates in the mitochondrial inner membrane, probably forming similar chloride channels as observed in the vacuoles. Import into mitochondria is mediated by the hydrophobic N-terminus of VacA. Apoptosis is triggered by loss of the mitochondrial membrane potential, recruitment of Bax and Bak, and release of cytochrome c.

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.

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.

Sphingomyelin is important for the cellular entry and intracellular localization of Helicobacter pylori VacA

Plasma membrane sphingomyelin (SM) binds the Helicobacter pylori vacuolating toxin (VacA) to the surface of epithelial cells. To evaluate the importance of SM for VacA cellular entry, we characterized toxin uptake and trafficking within cells enriched with synthetic variants of SM, whose intracellular trafficking properties are strictly dependent on the acyl chain lengths of their sphingolipid backbones. While toxin binding to the surface of cells was independent of acyl chain length, cells enriched with 12- or 18-carbon acyl chain variants of SM (e.g. C12-SM or C18-SM) were more sensitive to VacA, as indicated by toxin-induced cellular vacuolation, than those enriched with shorter 2- or 6-carbon variants (e.g. C2-SM or C6-SM). In C18-SM-enriched cells, VacA was taken into cells by a previously described Cdc42-dependent pinocytic mechanism, localized initially to GPI-enriched vesicles, and ultimately trafficked to Rab7/Lamp1 compartments. In contrast, within C2-SM-enriched cells, VacA was taken up at a slower rate by a Cdc42-independent mechanism and trafficked to Rab11 compartments. VacA-associated predominantly with detergent-resistant membranes (DRMs) in cells enriched with C18-SM, but predominantly with non-DRMs in C2-SM-enriched cells. These results suggest that SM is required for targeting VacA to membrane rafts important for subsequent Cdc42-dependent pinocytic cellular entry.

Role of virulence factors and host cell signaling in the recognition of Helicobacter pylori and the generation of immune responses

Helicobacter pylori colonizes a large proportion of the world's population, with infection invariably leading to chronic, lifelong gastritis. While the infection often persists undiagnosed and without causing severe pathology, there are a number of host, bacterial and environmental factors that can influence whether infection provokes a mild inflammatory response or results in significant morbidity. Intriguingly, the most virulent H. pylori strains appear to deliberately induce the epithelial signaling cascades responsible for activating the innate immune system. While the reason for this remains unclear, the resulting adaptive immune responses are largely ineffective in clearing the bacterium once infection has become established and, as a result, inflammation likely causes more damage to the host itself.

A Tale of Two Toxins: Helicobacter Pylori CagA and VacA Modulate Host Pathways that Impact Disease

Helicobacter pylori is a pathogenic bacterium that colonizes more than 50% of the world's population, which leads to a tremendous medical burden. H. pylori infection is associated with such varied diseases as gastritis, peptic ulcers, and two forms of gastric cancer: gastric adenocarcinoma and mucosa-associated lymphoid tissue lymphoma. This association represents a novel paradigm for cancer development; H. pylori is currently the only bacterium to be recognized as a carcinogen. Therefore, a significant amount of research has been conducted to identify the bacterial factors and the deregulated host cell pathways that are responsible for the progression to more severe disease states. Two of the virulence factors that have been implicated in this process are cytotoxin-associated gene A (CagA) and vacuolating cytotoxin A (VacA), which are cytotoxins that are injected and secreted by H. pylori, respectively. Both of these virulence factors are polymorphic and affect a multitude of host cellular pathways. These combined facts could easily contribute to differences in disease severity across the population as various CagA and VacA alleles differentially target some pathways. Herein we highlight the diverse types of cellular pathways and processes targeted by these important toxins.

Suppression of expression of endoplasmic reticulum chaperones by Helicobacter pylori and its role in exacerbation of non-steroidal anti-inflammatory drug-induced gastric lesions

Both the use of non-steroidal anti-inflammatory drugs (NSAIDs), such as indomethacin, and infection with Helicobacter pylori are major causes of gastric ulcers. Although some clinical studies suggest that infection with H. pylori increases the risk of developing NSAID-induced gastric lesions, the molecular mechanism governing this effect is unknown. We recently found that in cultured gastric cells, expression of endoplasmic reticulum (ER) chaperones (such as 150-kDa oxygen-regulated protein (ORP150) and glucose-regulated protein 78 (GRP78)) is induced by NSAIDs and confers protection against NSAID-induced apoptosis, which is important in the development of NSAID-induced gastric lesions. In this study we have found that co-culture of gastric cells with H. pylori suppresses the expression of ER chaperones. This suppression was regulated at the level of transcription and accompanied by a reduction in the level of activating transcription factor 6 (ATF6), one of the transcription factors for ER chaperone genes. In vivo, inoculation of mice with H. pylori suppressed the expression of ER chaperones at gastric mucosa both with and without administration of indomethacin. Inoculation with H. pylori also stimulated formation of indomethacin-induced gastric lesions and mucosal cell death. In addition, we found that heterozygous ORP150-deficient mice are sensitive to the development of indomethacin-induced gastric lesions and mucosal cell death. The results of this study suggest that H. pylori exacerbates NSAID-induced gastric lesions through suppression of expression of ER chaperones, which stimulates NSAID-induced mucosal cell death.

Role of innate immunity in Helicobacter pylori-induced gastric malignancy

Helicobacter pylori colonizes the majority of persons worldwide, and the ensuing gastric inflammatory response is the strongest singular risk factor for peptic ulceration and gastric cancer. However, only a fraction of colonized individuals ever develop clinically significant outcomes. Disease risk is combinatorial and can be modified by bacterial factors, host responses, and/or specific interactions between host and microbe. Several H. pylori constituents that are required for colonization or virulence have been identified, and their ability to manipulate the host innate immune response will be the focus of this review. Identification of bacterial and host mediators that augment disease risk has profound ramifications for both biomedical researchers and clinicians as such findings will not only provide mechanistic insights into inflammatory carcinogenesis but may also serve to identify high-risk populations of H. pylori-infected individuals who can then be targeted for therapeutic intervention.

Induction of nonapoptotic cell death by activated Ras requires inverse regulation of Rac1 and Arf6

Methuosis is a unique form of nonapoptotic cell death triggered by alterations in the trafficking of clathrin-independent endosomes, ultimately leading to extreme vacuolization and rupture of the cell. Methuosis can be induced in glioblastoma cells by expression of constitutively active Ras. This study identifies the small GTPases, Rac1 and Arf6, and the Arf6 GTPase-activating protein, GIT1, as key downstream components of the signaling pathway underlying Ras-induced methuosis. The extent to which graded expression of active H-Ras(G12V) triggers cytoplasmic vacuolization correlates with the amount of endogenous Rac1 in the active GTP state. Blocking Rac1 activation with the specific Rac inhibitor, EHT 1864, or coexpression of dominant-negative Rac1(T17N), prevents the accumulation of vacuoles induced by H-Ras(G12V). Coincident with Rac1 activation, H-Ras(G12V) causes a decrease in the amount of active Arf6, a GTPase that functions in the recycling of clathrin-independent endosomes. The effect of H-Ras(G12V) on Arf6 is blocked by EHT 1864, indicating that the decrease in Arf6-GTP is directly linked to the activation of Rac1. Constitutively active Rac1(G12V) interacts with GIT1 in immunoprecipitation assays. Ablation of GIT1 by short hairpin RNA prevents the decrease in active Arf6, inhibits vacuolization, and prevents loss of cell viability in cells expressing Rac1(G12V). Together, the results suggest that perturbations of endosome morphology associated with Ras-induced methuosis are due to downstream activation of Rac1 combined with reciprocal inactivation of Arf6. The latter seems to be mediated through Rac1 stimulation of GIT1. Further insights into this pathway could suggest opportunities for the induction of methuosis in cancers that are resistant to apoptotic cell death.

Endosome-mitochondria juxtaposition during apoptosis induced by H. pylori VacA

The vacuolating cytotoxin (VacA) is an important virulence factor of Helicobacter pylori with pleiotropic effects on mammalian cells, including the ability to trigger mitochondria-dependent apoptosis. However, the mechanism by which VacA exerts its apoptotic function is unclear. Using a genetic approach, in this study we show that killing by VacA requires the proapoptotic Bcl-2 family members BAX and BAK at the mitochondrial level, but not adequate endoplasmic reticulum Ca²(+) levels, similarly controlled by BAX and BAK. A combination of subcellular fractionation and imaging shows that wild-type VacA, but not mutants in its channel-forming region, induces the accumulation of BAX on endosomes and endosome-mitochondria juxtaposition that precedes the retrieval of active BAX on mitochondria. It is noteworthy that in Bax- and Bak-deficient cells, VacA is unable to cause endosome-mitochondria juxtaposition and is not retrieved in mitochondria. Thus, VacA causes BAX/BAK-dependent juxtaposition of endosomes and mitochondria early in the process of cell death, revealing a new function for these proapoptotic proteins in the regulation of relative position of organelles.

Pleiotropic actions of Helicobacter pylori vacuolating cytotoxin, VacA

Helicobacter pylori produces a vacuolating cytotoxin, VacA, and most virulent H. pylori strains secrete VacA. VacA binds to two types of receptor-like protein tyrosine phosphatase (RPTP), RPTPalpha and RPTPbeta, on the surface of host cells. VacA bound to RPTPbeta, relocates and concentrates in lipid rafts in the plasma membrane. VacA causes vacuolization, membrane anion-selective channel and pore formation, and disruption of endosomal and lysosomal activity in host cells. Secreted VacA is processed into p33 and p55 fragments. The p55 domain not only plays a role in binding to target cells but also in the formation of oligomeric structures and anionic membrane channels. Oral administration of VacA to wild-type mice, but not to RPTPbeta knockout mice, resulted in gastric ulcers, in agreement with the clinical effect of VacA. VacA with s1/m1 allele has more potent cytotoxic activity in relation to peptic ulcer disease and appears to be associated with human gastric cancer. VacA activates pro-apoptotic Bcl-2 family proteins, and induces apoptosis via a mitochondria-dependent pathway. VacA can disrupt other signal transduction pathways; VacA activates p38 MAPK, enhancing production of IL-8 and PGE(2), and PI3K/Akt, suppressing GSK-3beta activity. VacA has immunomodulatory actions on T cells and other immune cells, possibly contributing to the chronic infection seen with this organism. H. pylori virulence factors including VacA and CagA, which is encoded by cytotoxin-associated gene A, along with host genetic and environmental factors, constitute a complex network to regulate chronic gastric injury and inflammation, which is involved in a multistep process leading to gastric carcinogenesis.

Direct binding of gangliosides to Helicobacter pylori vacuolating cytotoxin (VacA) neutralizes its toxin activity

Gangliosides are target receptors for bacterial entry, yet those present in human milk exhibit a protective role against bacterial infection. Here, we show that treatment with ganglioside mixture at a concentration of 100 microg/mL resulted in significant inhibition of the vacuole formation activity of Helicobacter pylori vacuolating cytotoxin (VacA) in gastric epithelial cancer AZ-521 cells. All gangliosides (GM1, GM2, GM3, GD1a, GD1b, GD3 and GT1b) examined showed good neutralizing capacity against VacA. A pull-down assay was performed using lyso-GM1 coupled to Sepharose as the tagged polysaccharide polymer to capture VacA from H. pylori culture supernatant. GM1-VacA complexes were successfully precipitated, suggesting that GM1 binds directly to VacA. The hydrodynamic binding of lyso-GM1 and VacA measured by fluorescence correlation spectroscopy had a K(d) value of 190 nM. VacA also bound to lyso-GM1 at pH 2 corresponding to the physiological pH of human stomach. Collectively, these results showed that direct binding of H. pylori VacA to free gangliosides neutralizes the toxin activity of VacA. These findings offer an alternative insight into the role of gangliosides in VacA toxicity and the pathogenesis of H. pylori.

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.

Meningococcal porin PorB prevents cellular apoptosis in a toll-like receptor 2- and NF-kappaB-independent manner

Meningococcal porin PorB is an inhibitor of apoptosis induced via the intrinsic pathway in various cell types. This effect is attributed to prevention of mitochondrial depolarization and of subsequent release of proapoptotic mitochondrial factors. To determine whether apoptosis is globally inhibited by PorB, we compared the intrinsic and extrinsic pathways in HeLa cells. Interestingly, PorB does not prevent extrinsic apoptosis induced by tumor necrosis factor alpha plus cycloheximide, suggesting a unique mitochondrial pathway specificity. Several intracellular factors regulated by NF-kappaB, including members of the Bcl-2 family and of the inhibitor of apoptosis (IAP) family, play major roles in controlling apoptosis, and some of them are thought to contribute to the antiapoptotic effect of the gonococcal porin, PIB. However, most of the members of the Bcl-2 family and the IAP family are not induced by meningococcal PorB in HeLa cells, with the exception of Bfl-1/A1. Interestingly, PorB does not induce NF-kappaB activation in HeLa cells, likely due to a lack of Toll-like receptor 2 (TLR2) expression in these cells. Bfl-1/A1 expression is also regulated by CBF1, a nuclear component of the Notch signaling pathway, independent of NF-kappaB activation. Since HeLa cells are protected by PorB from intrinsic apoptosis events, regardless of TLR2 and NF-kappaB expression, the possibility of a contribution of alternative signaling pathways to this effect cannot be excluded. In this paper, we describe an initial dissection of the cascade of cellular events involved in the antiapoptotic effect of PorB in the absence of TLR2.

Characterizing the polymeric status of Helicobacter pylori heat shock protein 60

Helicobacter pylori heat shock protein 60 (HpHsp60) was first identified as an adhesion molecule associated with H. pylori infection. Here we have analyzed the structure of HpHsp60 via amino acid BLAST, circular dichroism, and electrophoresis and the results indicate that most recombinant HpHsp60 molecules exist as dimers or tetramers, which is quite different from Escherichia coli Hsp60. Treatment of human monocytic cells THP-1 with HpHsp60 was found to up-regulate a panel of cytokines including IL-1alpha, IL-8, IL-10, IFN-gamma, TNF-alpha, TGF-beta, GRO, and RANTES. Carboxymethylated HpHsp60 molecules with a switched oligomeric status were able to further enhance NF-kappaB-mediated IL-8 and TNF-alpha secretion in THP-1 cells compared to unmodified HpHsp60 molecules. These results indicated that the oligomeric status of HpHsp60s might have an important role in regulating host inflammation and thus help facilitate H. pylori persistent infection.

Rab7: roles in membrane trafficking and disease

The endocytosis pathway controls multiple cellular and physiological events. The lysosome is the destination of newly synthesized lysosomal hydrolytic enzymes. Internalized molecules or particles are delivered to the lysosome for degradation through sequential transport along the endocytic pathway. The endocytic pathway is also emerging as a signalling platform, in addition to the well-known role of the plasma membrane for signalling. Rab7 is a late endosome-/lysosome-associated small GTPase, perhaps the only lysosomal Rab protein identified to date. Rab7 plays critical roles in the endocytic processes. Through interaction with its partners (including upstream regulators and downstream effectors), Rab7 participates in multiple regulation mechanisms in endosomal sorting, biogenesis of lysosome [or LRO (lysosome-related organelle)] and phagocytosis. These processes are closely related to substrates degradation, antigen presentation, cell signalling, cell survival and microbial pathogen infection. Consistently, mutations or dysfunctions of Rab7 result in traffic disorders, which cause various diseases, such as neuropathy, cancer and lipid metabolism disease. Rab7 also plays important roles in microbial pathogen infection and survival, as well as in participating in the life cycle of viruses. Here, we give a brief review on the central role of Rab7 in endosomal traffic and summarize the studies focusing on the participation of Rab7 in disease pathogenesis. The underlying mechanism governed by Rab7 and its partners will also be discussed.

Importance of EGF receptor, HER2/Neu and Erk1/2 kinase signalling for host cell elongation and scattering induced by the Helicobacter pylori CagA protein: antagonistic effects of the vacuolating cytotoxin VacA

Helicobacter pylori is the causative agent of gastric pathologies ranging from chronic gastritis to peptic ulcers and even cancer. Virulent strains carrying both the cag pathogenicity island (cagPAI) and the vacuolating cytotoxin VacA are key players in disease development. The cagPAI encodes a type IV secretion system (T4SS) which forms a pilus for injection of the CagA protein into gastric epithelial cells. Injected CagA undergoes tyrosine phosphorylation and induces actin-cytoskeletal rearrangements involved in host cell scattering and elongation. We show here that the CagA-induced responses can be inhibited in strains expressing highly active VacA. Further investigations revealed that VacA does not interfere with known activities of phosphorylated CagA such as inactivation of Src kinase and cortactin dephosphorylation. Instead, we demonstrate that VacA exhibits inactivating activities on the epidermal growth factor receptor EGFR and HER2/Neu, and subsequently Erk1/2 MAP kinase which are important for cell scattering and elongation. Inactivation of vacA gene, downregulation of the VacA receptor RPTP-alpha, addition of EGF or expression of constitutive-active MEK1 kinase restored the capability of H. pylori to induce the latter phenotypes. These data demonstrate that VacA can downregulate CagA's effects on epithelial cells, a novel molecular mechanism showing how H. pylori can avoid excessive cellular damage.

Recombination-based in vivo expression technology identifies Helicobacter pylori genes important for host colonization

Here we undertook to identify colonization and gastric disease-promoting factors of the human gastric pathogen Helicobacter pylori as genes that were induced in response to the stomach environment. Using recombination-based in vivo expression technology (RIVET), we identified six promoters induced in the host compared to laboratory conditions. Three of these promoters, designated Pivi10, Pivi66, and Pivi77, regulate genes that H. pylori may use to interact with other microbes or the host. Pivi10 likely regulates the mobA, mobB, and mobD genes, which have potential roles in horizontal gene transfer through plasmid mobilization. Pivi66 occurs in the cytotoxin-associated gene pathogenicity island, a genomic region known to be associated with more severe disease outcomes, and likely regulates cagZ, virB11, and virD4. Pivi77 likely regulates HP0289, an uncharacterized paralogue of the vacA cytotoxin gene. We assessed the roles of a subset of these genes in colonization by creating deletion mutants and analyzing them in single-strain and coinfection experiments. We found that a mobABD mutant was defective for murine host colonization and that a cagZ mutant outcompeted the wild-type strain in a coinfection analysis. Our work supports the conclusion that RIVET is a valuable tool for identifying H. pylori factors with roles in host colonization.

Outer membrane vesicles enhance the carcinogenic potential of Helicobacter pylori

Chronic Helicobacter pylori infection is associated with an increased risk of gastric carcinogenesis. These non-invasive bacteria colonize the gastric mucosa and constitutively shed small outer membrane vesicles (OMV). In this study, we investigated the direct effect of H.pylori OMV on cellular events associated with carcinogenesis. We observed increased micronuclei formation in AGS human gastric epithelial cells treated with OMV isolated from a toxigenic H.pylori strain (60190). This effect was absent in OMV from strain 60190v:1 that has a mutant vacA, indicating VacA-dependent micronuclei formation. VacA induces intracellular vacuolation, and reduced acridine orange staining indicated disruption in the integrity of these vacuoles. This was accompanied by an alteration in iron metabolism and glutathione (GSH) loss, suggesting a role for oxidative stress in genomic damage. Increasing intracellular GSH levels with a GSH ester abrogated the VacA-mediated increase in micronuclei formation. In conclusion, OMV-mediated delivery of VacA to the gastric epithelium may constitute a new mechanism for H.pylori-induced gastric carcinogenesis.

Involvement of vesicle-associated membrane protein 7 in human gastric epithelial cell vacuolation induced by Helicobacter pylori-produced VacA

Helicobacter pylori-produced cytotoxin VacA induces intracellular vacuolation. The VacA-induced vacuole is assumed to represent the pathological status of intracellular trafficking. The fusion mechanism of the endosomes requires the formation of a tight complex between the Q-SNAREs and the R-SNAREs. We recently reported that syntaxin 7, a family member of the Q-SNARE protein, is involved in VacA-induced vacuole formation. In order to further elucidate the molecular mechanism, we identified the participation of vesicle-associated membrane protein 7 (VAMP7) as a partner of syntaxin 7. Immunocytochemistry revealed endogenous VAMP7 to be localized to the vacuoles induced by VacA. A Northern blotting study demonstrated that VacA intoxication increased VAMP7 mRNA in a time-dependent manner. VAMP7 was coimmunoprecipitated with syntaxin 7, and the amounts of endogenous VAMP7 and syntaxin 7 bound to syntaxin 7 and VAMP7, respectively, increased in response to VacA. The down-regulation of VAMP7 using small interfering RNA inhibited VacA-induced vacuolation, and the transient transfection of dominant-negative mutant VAMP7, the N-terminal domain of VAMP7, also inhibited the vacuolation. We therefore conclude that R-SNARE VAMP7 plays an important role in VacA-induced vacuolation as a partner of Q-SNARE syntaxin 7.

Manipulation of rab GTPase function by intracellular bacterial pathogens

Intracellular bacterial pathogens have evolved highly specialized mechanisms to enter and survive within their eukaryotic hosts. In order to do this, bacterial pathogens need to avoid host cell degradation and obtain nutrients and biosynthetic precursors, as well as evade detection by the host immune system. To create an intracellular niche that is favorable for replication, some intracellular pathogens inhibit the maturation of the phagosome or exit the endocytic pathway by modifying the identity of their phagosome through the exploitation of host cell trafficking pathways. In eukaryotic cells, organelle identity is determined, in part, by the composition of active Rab GTPases on the membranes of each organelle. This review describes our current understanding of how selected bacterial pathogens regulate host trafficking pathways by the selective inclusion or retention of Rab GTPases on membranes of the vacuoles that they occupy in host cells during infection.

A new Helicobacter pylori vacuolating cytotoxin determinant, the intermediate region, is associated with gastric cancer

BACKGROUND & AIMS

Helicobacter pylori is the main cause of peptic ulceration and gastric adenocarcinoma. The vacuolating cytotoxin gene, vacA, is a major determinant of virulence. Two naturally polymorphic sites in vacA, the signal region and midregion, are well-characterized determinants of toxicity and markers of pathogenesis. The aim of this study was to characterize a new vacA polymorphic site, the intermediate (i) region.

METHODS

The vacA i-region was identified and characterized by constructing isogenic vacA exchange mutants and determining their vacuolating activity on HeLa, AGS, and RK13 cell lines. The vacA i-region types of H pylori isolates from patients undergoing routine endoscopy were determined by nucleotide sequencing and allele-specific polymerase chain reaction.

RESULTS

Two i-region types were identified, i1 and i2, and both were common among 42 Western clinical isolates. Interestingly, only naturally occurring s1/m2 strains varied in i-type; s1/m1 and s2/m2 strains were exclusively i1 and i2, respectively. Vacuolation assays showed that i-type determined vacuolating activity among these s1/m2 strains, and exchange mutagenesis confirmed that the i-region itself was directly responsible. Using a simple i-region polymerase chain reaction-based typing system, it was shown for 73 Iranian patients that i1-type strains were strongly associated with gastric adenocarcinoma (P < 10(-3)). Finally, logistic regression analysis showed this association to be independent of, and larger than, associations of vacA s- or m-type or cag status with gastric adenocarcinoma.

CONCLUSIONS

Together these data show that the vacA i-region is an important determinant of H pylori toxicity and the best independent marker of VacA-associated pathogenicity.

Phagocytosis and persistence of Helicobacter pylori

Helicobacter pylori is a spiral-shaped, flagellated, microaerophilic Gram-negative bacterium that colonizes the gastric epithelium of humans. All persons infected with H. pylori have gastritis, and some will develop severe disease such as peptic ulcers or gastric cancer. A characteristic feature of this infection is the pronounced accumulation of phagocytes, particularly neutrophils, in the gastric mucosa. H. pylori thrives in a phagocyte-rich environment, and we describe here how this organism uses an array of novel virulence factors to manipulate chemotaxis, phagocytosis, membrane trafficking and the respiratory burst as a means to evade elimination by the innate immune response.