The N-terminal 34 kDa fragment of Helicobacter pylori vacuolating cytotoxin targets mitochondria and induces cytochrome c release

The concerted action of the Helicobacter pylori cytotoxin VacA and of the v-ATPase proton pump induces swelling of isolated endosomes

The vacuolating cytotoxin (VacA) is a major virulence factor of Helicobacter pylori, the bacterium associated to gastroduodenal ulcers and stomach cancers. VacA induces formation of cellular vacuoles that originate from late endosomal compartments. VacA forms an anion-selective channel and its activity has been suggested to increase the osmotic pressure in the lumen of these acidic compartments, driving their swelling to vacuoles. Here, we have tested this proposal on isolated endosomes that allow one to manipulate at will the medium. We have found that VacA enhances the v-ATPase proton pump activity and the acidification of isolated endosomes in a Cl- dependent manner. Other counter-anions such as pyruvate, Br-, I- and SCN- can be transported by VacA with stimulation of the v-ATPase. The VacA action on isolated endosomes is associated with their increase in size. Single amino acid substituted VacA with no channel-forming and vacuolating activity is unable to induce swelling of endosomes. These data provide a direct evidence that the transmembrane VacA channel mediates an influx of anions into endosomes that stimulates the electrogenic v-ATPase proton pump, leading to their osmotic swelling and transformation into vacuoles.

Clostridium difficile toxin B causes apoptosis in epithelial cells by thrilling mitochondria. Involvement of ATP-sensitive mitochondrial potassium channels

Targeting to mitochondria is emerging as a common strategy that bacteria utilize to interact with these central executioners of apoptosis. Several lines of evidence have in fact indicated mitochondria as specific targets for bacterial protein toxins, regarded as the principal virulence factors of pathogenic bacteria. This work shows, for the first time, the ability of the Clostridium difficile toxin B (TcdB), a glucosyltransferase that inhibits the Rho GTPases, to impact mitochondria. In living cells, TcdB provokes an early hyperpolarization of mitochondria that follows a calcium-associated signaling pathway and precedes the final execution step of apoptosis (i.e. mitochondria depolarization). Importantly, in isolated mitochondria, the toxin can induce a calcium-dependent mitochondrial swelling, accompanied by the release of the proapoptogenic factor cytochrome c. This is consistent with a mitochondrial targeting that does not require the Rho-inhibiting activity of the toxin. Of interest, the mitochondrial ATP-sensitive potassium channels are also involved in the apoptotic response to TcdB and appear to be crucial for the cell death execution phase, as demonstrated by using specific modulators of these channels. To our knowledge, the involvement of these mitochondrial channels in the ability of a bacterial toxin to control cell fate is a hitherto unreported finding.

Helicobacter pylori VacA toxin inhibits human immunodeficiency virus infection of primary human T cells

Human CD4(+) T cells are major targets for human immunodeficiency virus (HIV) infection. Resting T cells are resistant to HIV infection unless activated through the T-cell receptor (TCR) or by cytokine signals. How T-cell signaling promotes susceptibility of T cells to HIV infection remains poorly understood. Here we demonstrate that the VacA toxin produced by Helicobacter pylori can inhibit HIV infection of primary T cells, stimulated through the TCR or by cytokines alone. This activity of VacA was dependent on its ability to form membrane channels. VacA suppressed HIV infection of T cells at a stage after viral entry, post-reverse transcription and pre-two-long-terminal-repeat circle formation, similar to the cytokine signaling inhibitor rapamycin. Mechanistically, neither VacA nor rapamycin inhibited the activation of cytokine signal transduction components (STAT5, p42/44 mitogen-activated protein kinase, or p38), but both blocked activation of key regulatory proteins required for G(1) cell cycle transition. In contrast to rapamycin, VacA did not suppress phosphorylation of p70 S6 kinase but caused mitochondrial depolarization and ATP depletion within primary T cells. These results suggest that VacA inhibits T-cell activation and HIV infection via a novel mechanism. Identifying the host cell targets of VacA could be useful for elucidating the HIV life cycle within primary T cells.

Human polymorphonuclear leukocytes are sensitive in vitro to Helicobacter pylori vaca toxin

BACKGROUND

Interactions between bacterial components and polymorphonuclear leukocytes (PMNL) play a major pathogenic role in Helicobacter pylori-associated diseases. Activation of PMNL can be induced by contact with whole bacteria or by different H. pylori products released in the extracellular space either by active secretion or by bacterial autolysis. Among these products, H. pylori VacA is a secreted toxin inducing vacuolation and apoptosis of epithelial cells.

METHODS AND RESULTS

We found that non-opsonic human PMNL were sensitive to the vacuolating effect of VacA+ broth culture filtrate (BCF) and of purified VacA toxin. PMNL incubated with VacA+ BCF showed Rab7-positive large intracytoplasmic vacuoles. PMNL preincubation with H. pylori BCF of different phenotypes dramatically potentialized the oxidative burst induced by zymosan, increased phagocytosis of opsonized fluorescent beads, and up-regulated CD11b cell surface expression, but independently of the BCF VacA phenotype. Moreover, by using purified VacA toxin we showed that vacuolation induced in PMNL did not modify the rate of spontaneous PMNL apoptosis measured by caspase 3 activity.

CONCLUSIONS

Taken together, these data showed that human PMNL is a sensitive cell population to H. pylori VacA toxin. However, activation of PMNL (i.e., oxidative burst, phagocytosis, CD11b up-regulation) and PMNL apoptosis are not affected by VacA, raising question about the role of VacA toxin on PMNL in vivo.

Clustering of Helicobacter pylori VacA in lipid rafts, mediated by its receptor, receptor-like protein tyrosine phosphatase beta, is required for intoxication in AZ-521 Cells

Helicobacter pylori vacuolating cytotoxin, VacA, induces multiple effects on epithelial cells through different cellular events: one involves pore formation, leading to vacuolation, mitochondrial damage, and apoptosis, and the second involves cell signaling, resulting in stimulation of proinflammatory responses and cell detachment. Our recent data demonstrated that VacA uses receptor-like protein tyrosine phosphatase beta (RPTPbeta) as a receptor, of which five residues (QTTQP) at positions 747 to 751 are involved in binding. In AZ-521 cells, which mainly express RPTPbeta, VacA, after binding to RPTPbeta in non-lipid raft microdomains on the cell surface, is localized with RPTPbeta in lipid rafts in a temperature- and VacA concentration-dependent process. Methyl-beta-cyclodextrin (MCD) did not block binding to RPTPbeta but inhibited translocation of VacA with RPTPbeta to lipid rafts and all subsequent events. On the other hand, 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), which disrupts anion channels, did not inhibit translocation of VacA to lipid rafts or VacA-induced activation of p38 mitogen-activated protein (MAP) kinase, but inhibited VacA internalization followed by vacuolation. Thus, p38 MAP kinase activation did not appear to be required for internalization. In contrast, phosphatidylinositol-specific phospholipase C (PI-PLC) inhibited translocation, as well as p38 MAP kinase/ATF-2 activation, internalization, and VacA-induced vacuolation. Neither NPPB nor PI-PLC affected VacA binding to cells and to its receptor, RPTPbeta. Thus, receptor-dependent translocation of VacA to lipid rafts is critical for signaling pathways leading to p38 MAP kinase/ATF-2 activation and vacuolation.

External membrane vesicles from Helicobacter pylori induce apoptosis in gastric epithelial cells

The Helicobacter pylori infection of gastric mucosa is one of the most common infectious diseases and is associated with a variety of clinical outcomes, including peptic ulcer disease and gastric cancer. Helicobacter pylori-induced damage to gastric mucosal cells is controlled by bacterial virulence factors, which include VacA and CagA. Outer membrane vesicles are constantly shed by the bacteria and can provide an additional mechanism for pathogenicity by releasing non-secretable factors which can then interact with epithelial cells. The present report shows that external membrane vesicles are able to induce apoptosis not mediated by mitochondrial pathway in gastric (AGS) epithelial cells, as demonstrated by the lack of cytochrome c release with an activation of caspase 8 and 3. Apoptosis induced by these vesicles does not require a classic VacA+ phenotype, as a negative strain with a truncated and therefore non-secretable form of this protein can also induce cell death. These results should be taken into account in future studies of H. pylori pathogenicity in strains apparently VacA-.

Helicobacter pylori VacA toxin promotes bacterial intracellular survival in gastric epithelial cells

Helicobacter pylori colonizes the gastric epithelium of at least 50% of the world's human population, playing a causative role in the development of chronic gastritis, peptic ulcers, and gastric adenocarcinoma. Current evidence indicates that H. pylori can invade epithelial cells in the gastric mucosa. However, relatively little is known about the biology of H. pylori invasion and survival in host cells. Here, we analyze both the nature of and the mechanisms responsible for the formation of H. pylori's intracellular niche. We show that in AGS cells infected with H. pylori, bacterium-containing vacuoles originate through the fusion of late endocytic organelles. This process is mediated by the VacA-dependent retention of the small GTPase Rab7. In addition, functional interactions between Rab7 and its downstream effector, Rab-interacting lysosomal protein (RILP), are necessary for the formation of the bacterial compartment since expression of mutant forms of RILP or Rab7 that fail to bind each other impaired the formation of this unique bacterial niche. Moreover, the VacA-mediated sequestration of active Rab7 disrupts the full maturation of vacuoles as assessed by the lack of both colocalization with cathepsin D and degradation of internalized cargo in the H. pylori-containing vacuole. Based on these findings, we propose that the VacA-dependent isolation of the H. pylori-containing vacuole from bactericidal components of the lysosomal pathway promotes bacterial survival and contributes to the persistence of infection.

Paired cysteine residues are required for high levels of the Helicobacter pylori autotransporter VacA

The Helicobacter pylori vacuolating cytotoxin VacA shares homology in its C-terminal domain with many autotransporter proteins, suggesting a similar mechanism of secretion. Like most autotransporters, VacA contains a single pair of cysteine residues located near the C-terminus of the passenger domain. This study aimed to investigate the role of these conserved cysteine residues. This involved changing each cysteine in the VacA passenger domain to serine, quantifying the effect on VacA levels and assessing toxin activity in H. pylori. It was shown that both cysteine residues were required for high VacA levels, although mutation of each cysteine reduced toxin amounts to differing extents, implying that their importance was not simply for intramolecular disulphide bond formation. Although less VacA was observed for the cysteine mutants, vacuolating activity was detected, showing that the cysteines were not required for VacA function.

About lipids and toxins

Many mono or multicellular organisms secrete soluble proteins, referred to as protein toxins, which alter the behavior of foreign, or target cells, possibly leading to their death. These toxins affect either the cell membrane by forming pores or modifying lipids, or some intracellular target. To reach this target, they must cross one of the cellular membranes, generally that of an intracellular organelle. As described in this minireview, lipids play crucial roles in the intoxication process of most if not all toxins, by allowing/promoting binding, endocytosis, trafficking and/or translocation into the cytoplasm.

Pathogenesis of Helicobacter pylori Infection

SUMMARY

Helicobacter pylori is the first formally recognized bacterial carcinogen and is one of the most successful human pathogens, as over half of the world's population is colonized with this gram-negative bacterium. Unless treated, colonization usually persists lifelong. H. pylori infection represents a key factor in the etiology of various gastrointestinal diseases, ranging from chronic active gastritis without clinical symptoms to peptic ulceration, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue lymphoma. Disease outcome is the result of the complex interplay between the host and the bacterium. Host immune gene polymorphisms and gastric acid secretion largely determine the bacterium's ability to colonize a specific gastric niche. Bacterial virulence factors such as the cytotoxin-associated gene pathogenicity island-encoded protein CagA and the vacuolating cytotoxin VacA aid in this colonization of the gastric mucosa and subsequently seem to modulate the host's immune system. This review focuses on the microbiological, clinical, immunological, and biochemical aspects of the pathogenesis of H. pylori .

Pathogenesis of Helicobacter pylori Infection

SUMMARY

Helicobacter pylori is the first formally recognized bacterial carcinogen and is one of the most successful human pathogens, as over half of the world's population is colonized with this gram-negative bacterium. Unless treated, colonization usually persists lifelong. H. pylori infection represents a key factor in the etiology of various gastrointestinal diseases, ranging from chronic active gastritis without clinical symptoms to peptic ulceration, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue lymphoma. Disease outcome is the result of the complex interplay between the host and the bacterium. Host immune gene polymorphisms and gastric acid secretion largely determine the bacterium's ability to colonize a specific gastric niche. Bacterial virulence factors such as the cytotoxin-associated gene pathogenicity island-encoded protein CagA and the vacuolating cytotoxin VacA aid in this colonization of the gastric mucosa and subsequently seem to modulate the host's immune system. This review focuses on the microbiological, clinical, immunological, and biochemical aspects of the pathogenesis of H. pylori .

Pathogenesis of Helicobacter pylori Infection

SUMMARY

Helicobacter pylori is the first formally recognized bacterial carcinogen and is one of the most successful human pathogens, as over half of the world's population is colonized with this gram-negative bacterium. Unless treated, colonization usually persists lifelong. H. pylori infection represents a key factor in the etiology of various gastrointestinal diseases, ranging from chronic active gastritis without clinical symptoms to peptic ulceration, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue lymphoma. Disease outcome is the result of the complex interplay between the host and the bacterium. Host immune gene polymorphisms and gastric acid secretion largely determine the bacterium's ability to colonize a specific gastric niche. Bacterial virulence factors such as the cytotoxin-associated gene pathogenicity island-encoded protein CagA and the vacuolating cytotoxin VacA aid in this colonization of the gastric mucosa and subsequently seem to modulate the host's immune system. This review focuses on the microbiological, clinical, immunological, and biochemical aspects of the pathogenesis of H. pylori .

Pathogenesis of Helicobacter pylori infection

Helicobacter pylori is the first formally recognized bacterial carcinogen and is one of the most successful human pathogens, as over half of the world's population is colonized with this gram-negative bacterium. Unless treated, colonization usually persists lifelong. H. pylori infection represents a key factor in the etiology of various gastrointestinal diseases, ranging from chronic active gastritis without clinical symptoms to peptic ulceration, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue lymphoma. Disease outcome is the result of the complex interplay between the host and the bacterium. Host immune gene polymorphisms and gastric acid secretion largely determine the bacterium's ability to colonize a specific gastric niche. Bacterial virulence factors such as the cytotoxin-associated gene pathogenicity island-encoded protein CagA and the vacuolating cytotoxin VacA aid in this colonization of the gastric mucosa and subsequently seem to modulate the host's immune system. This review focuses on the microbiological, clinical, immunological, and biochemical aspects of the pathogenesis of H. pylori.

Citrobacter rodentium infection causes both mitochondrial dysfunction and intestinal epithelial barrier disruption in vivo: role of mitochondrial associated protein (Map)

Enteropathogenic Escherichia coli (EPEC) and enterohaemorrhagic E. coli are non-invasive attaching/effacing (A/E) bacterial pathogens that infect their host's intestinal epithelium, causing severe diarrhoeal disease. These bacteria utilize a type III secretion apparatus to deliver effector molecules into host cells, subverting cellular function. Mitochondrial associated protein (Map) is a multifunctional effector protein that targets host cell mitochondria and contributes to infection-induced epithelial barrier dysfunction in vitro. Unfortunately, the relevance of these actions to the pathogenesis of EPEC-induced disease is uncertain. Using Citrobacter rodentium, a mouse-adapted A/E bacterium, we found that Map colocalized with host cell mitochondria, and that in vivo infection led to a disruption of mitochondrial morphology in infected colonocytes as assessed by electron microscopy. Histochemical staining for the mitochondrial enzyme succinate dehydrogenase also revealed a significant loss of mitochondrial respiratory function in the infected intestinal epithelium; however, both pathologies were attenuated in mice infected with a Deltamap strain. C. rodentium Map was also implicated in the disruption of epithelial barrier function both in vitro and in vivo. These studies thus advance our understanding of how A/E pathogens subvert host cell functions and cause disease, demonstrating that Map contributes to the functional disruption of the intestinal epithelium during enteric infection by C. rodentium.

A Helicobacter pylori vacuolating toxin mutant that fails to oligomerize has a dominant negative phenotype

Most Helicobacter pylori strains secrete a toxin (VacA) that causes massive vacuolization of target cells and which is a major virulence factor of H. pylori. The VacA amino-terminal region is required for the induction of vacuolization. The aim of the present study was a deeper understanding of the critical role of the N-terminal regions that are protected from proteolysis when VacA interacts with artificial membranes. Using a counterselection system, we constructed an H. pylori strain, SPM 326-Delta49-57, that produces a mutant toxin with a deletion of eight amino acids in one of these protected regions. VacA Delta49-57 was correctly secreted by H. pylori but failed to oligomerize and did not have any detectable vacuolating cytotoxic activity. However, the mutant toxin was internalized normally and stained the perinuclear region of HeLa cells. Moreover, the mutant toxin exhibited a dominant negative effect, completely inhibiting the vacuolating activity of wild-type VacA. This loss of activity was correlated with the disappearance of oligomers in electron microscopy. These findings indicate that the deletion in VacA Delta49-57 disrupts the intermolecular interactions required for the oligomerization of the toxin.

Oxidative phosphorylation and its coupling to mitochondrial creatine and adenylate kinases in human gastric mucosa

Energy metabolism in gastrobiopsy specimens of the antral and corpus mucosa, treated with saponin to permeabilize the cells, was studied in patients with gastric diseases. The results show twice lower oxidative capacity in the antral mucosa than in the corpus mucosa and the relative deficiency of antral mitochondria in complex I. The mucosal cells expressed mitochondrial and cytosolic isoforms of creatine kinase and adenylate kinase (AK). Creatine (20 mM) and AMP (2 mM) markedly stimulated mitochondrial respiration in the presence of submaximal ADP or ATP concentrations, and creatine reduced apparent Km for ADP in stimulation of respiration, which indicates the functional coupling of mitochondrial kinases to oxidative phosphorylation. Addition of exogenous cytochrome c increased ADP-dependent respiration, and the large-scale cytochrome c effect (>or=20%) was associated with suppressed stimulation of respiration by creatine and AMP in the mucosal preparations. These results point to the impaired mitochondrial outer membrane, probably attributed to the pathogenic effects of Helicobacter pylori. Compared with the corpus mucosa, the antral mucosa exhibited greater sensitivity to such type of injury as the prevalence of the large-scale cytochrome c effect was twice higher among the latter specimens. Active chronic gastritis was associated with decreased respiratory capacity of the corpus mucosa but with its increase in the antral mucosa. In conclusion, human gastric mucosal cells express the mitochondrial and cytosolic isoforms of CK and AK participating in intracellular energy transfer systems. Gastric mucosa disease is associated with the altered functions of these systems and oxidative phosphorylation.

The enteropathogenic Escherichia coli (EPEC) Map effector is imported into the mitochondrial matrix by the TOM/Hsp70 system and alters organelle morphology

Enteropathogenic Escherichia coli (EPEC) is a human intestinal pathogen and a major cause of diarrhoea, particularly among infants in developing countries. EPEC target the Map and EspF multifunctional effector proteins to host mitochondria - organelles that play crucial roles in regulating cellular processes such as programmed cell death (apoptosis). While both molecules interfere with the organelles ability to maintain a membrane potential, EspF plays the predominant role and is responsible for triggering cell death. To learn more about the Map-mitochondria interaction, we studied Map localization to mitochondria with purified mitochondria (from mammalian and yeast cells) and within intact yeast. This revealed that (i) Map targeting is dependent on the predicted N-terminal mitochondrial targeting sequence, (ii) the N-terminal 44 residues are sufficient to target proteins to mitochondria and (iii) Map import involves the mitochondrial outer membrane translocase (Tom22 and Tom40), the mitochondrial membrane potential, and the matrix chaperone, mtHsp70. These results are consistent with Map import into the mitochondria matrix via the classical import mechanism. As all known, Map-associated phenotypes in mammalian cells are independent of mitochondrial targeting, this may indicate that import serves as a mechanism to remove Map from the cytoplasm thereby regulating cytoplasmic function. Intriguingly, Map, but not EspF, alters mitochondrial morphology with deletion analysis revealing important roles for residues 101-152. Changes in mitochondrial morphology have been linked to alterations in the ability of these organelles to regulate cellular processes providing a possible additional role for Map import into mitochondria.

Gene expression and protein profiling of AGS gastric epithelial cells upon infection with Helicobacter pylori

Helicobacter pylori, one of the most common bacterial pathogens, colonizes the human stomach and causes a variety of gastric diseases. This pathogen elicits a range of phenotypic responses in infected cultured AGS gastric epithelial cells, including expression of proinflammatory genes and changes in the actin cytoskeleton. Some of these responses are mediated by the type IV secretion system (T4SS) encoded by the cag pathogenicity island. We have used two global approaches, namely 2-DE combined with PMF and cDNA expression array analyses, to study in both a comprehensive and quantitative manner the protein profile and the temporal patterns of mRNA accumulation in AGS cells upon infection with H. pylori and isogenic T4SS mutants. We identified 140 transcripts and detected 190 protein species that were differentially regulated upon infection. Infection with wild-type H. pylori induced expression of a variety of host genes and changes in protein pattern involved in transcriptional responses, cell shape regulation and signal transduction. Among them, some were differentially regulated in a cag PAI-dependent manner, as shown by both the proteomic and cDNA expression array approaches. While 2-DE and PMF allowed us to examine the protein profiles in the infected host, array analysis enabled us to demonstrate dynamic temporal changes in host gene expression profile. In conclusion, our combined application of the two global approaches provides further molecular details on how the host cell responds to infection by H. pylori and its isogenic T4SS mutants on both transcriptional and protein levels. The findings pinpoint host proteins such as serine/threonine and tyrosine kinases, transcription factors, cell cycle related components and actin cytoskeletal signaling molecules as potential targets of individual H. pylori virulence determinants. This study serves as a basis for future work on transcription and proteome analyses of the H. pylori infection model.

Helicobacter pylori induces apoptosis of T- and B-cell lines and translocates mitochondrial apoptosis-inducing factor to nucleus

Immune cell apoptosis may play a role in human persistent Helicobacter pylori infection. We planned to study the apoptosis of T and B cells by H. pylori strains. T (Jurkat) and B (Raji) cell lines were co-cultured with cagA-positive H. pylori strains carrying different vacA genotypes (s1a/m1, s1a/m2, and s2/m2). Apoptosis was detected by microscopy, DNA fragmentation assay, and flow cytometry. Apoptosis-inducing factor (AIF) transfer from mitochondria to nucleus was studied by immunoblot analysis. Apoptosis of T and B cells was significantly higher in H. pylori-infected cells than in uninfected controls (s1a/m1 80%, s1a/m2 78%, s2m2 69% vs. control 16% for T cells, P < 0.001; s1 a/m1 78%, s1a/m2 73%, s2m2 62% vs. control 24% for B cells, P < 0.001 by flow cytometry) with no difference among the genotypes. AIF transfer from mitochondria to nucleus was demonstrated in both apoptotic cell lines. Thus, H. pylori induces apoptosis in T- and B-cell lines and translocates AIF. T and B cells deletion through apoptosis may explain the persistence of H. pylori infection; its role in pathogenesis needs further research.

Staphylococcus aureus Panton-Valentine leukocidin directly targets mitochondria and induces Bax-independent apoptosis of human neutrophils

Panton-Valentine leukocidin (PVL) is a pore-forming toxin secreted by Staphylococcus aureus that has recently been associated with necrotizing pneumonia. In the present study, we report that in vitro, PVL induces polymorphonuclear cell death by necrosis or by apoptosis, depending on the PVL concentration. PVL-induced apoptosis was associated with a rapid disruption of mitochondrial homeostasis and activation of caspase-9 and caspase-3, suggesting that PVL-induced apoptosis is preferentially mediated by the mitochondrial pathway. Polymorphonuclear cell exposure to PVL leads to mitochondrial localization of the toxin, whereas Bax, 1 of the 2 essential proapoptotic members of the Bcl-2 family, was still localized in the cytosol. Addition of PVL to isolated mitochondria induced the release of the apoptogenic proteins cytochrome c and Smac/DIABLO. Therefore, we suggest that PVL, which belongs to the pore-forming toxin family, could act at the mitochondrion level by creating pores in the mitochondrial outer membrane. Furthermore, LukS-PV, 1 of the 2 components of PVL, was detected in lung sections of patients with necrotizing pneumonia together with DNA fragmentation, suggesting that PVL induces apoptosis in vivo and thereby is directly involved in the pathophysiology of necrotizing pneumonia.

Helicobacter pylori vacuolating cytotoxin induces activation of the proapoptotic proteins Bax and Bak, leading to cytochrome c release and cell death, independent of vacuolation

Helicobacter pylori vacuolating cytotoxin, VacA, which causes vacuolation of gastric epithelial cells and other types of cultured cells, is known to stimulate apoptosis via a mitochondria-dependent pathway. In the present study, we examined the mechanisms of VacA-induced mitochondrial damage. Intracellular VacA localization was monitored by immunostaining and confocal microscopy; in AZ-521 cells in which cytochrome c release was stimulated, most of VacA was localized to vacuoles rather than mitochondria. VacA reduced the membrane potential of isolated mitochondria without inducing cytochrome c release, suggesting that it did not act directly to induce cytochrome c release from mitochondria and that in intact cells, VacA-induced cytochrome c release involved apoptosis-related factor(s), such as a proapoptotic Bcl-2 family protein. In agreement, flow cyto-metric analyses using antibodies specific for activated Bax revealed that intracellular Bax was activated by VacA in a concentration- and time-dependent manner. Using active form-specific antibodies, we also observed that the Bcl-2 family protein, Bak, was activated. By confocal microscopy, Bax and Bak were activated in AZ-521 cells in which cyto-chrome c release was induced by VacA. In addition, small interfering RNA-induced silencing of the bax gene resulted in reduction of VacA-stimulated cytochrome c release, consistent with a contribution of VacA-induced Bax activation to cytochrome c release. NH4Cl enhanced both VacA-induced vacuolation and Bax activation, whereas Bax activation was not inhibited by bafilomycin A1, which inhibited vacuolation caused by VacA. These results suggest that VacA acts through different signaling pathways to induce apoptosis via Bax activation, independent of vacuolation.

High resolution structural analysis of Helicobacter pylori VacA toxin oligomers by cryo-negative staining electron microscopy

Helicobacter pylori secretes a vacuolating toxin (VacA) that can assemble into water-soluble oligomeric complexes and insert into membranes to form anion-selective channels. Previous studies have described multiple types of oligomeric VacA structures, including single-layered astral arrays, bilayered forms, and two-dimensional crystalline arrays. In the current study, vitrified VacA complexes were examined by cryo-negative staining electron microscopy, views of the different oligomeric structures in multiple orientations were classified and analyzed, and three-dimensional models of the bilayered forms of VacA were constructed with a resolution of about 19 angstroms. These bilayered forms of VacA have a "flower"-like structure, consisting of a central ring surrounded by symmetrically arranged peripheral "petals." Further structural insights were obtained by analyzing a mutant form of VacA (VacADelta6-27), which lacks a unique amino-terminal hydrophobic segment and is defective in the capacity to form membrane channels. Bilayered oligomeric complexes formed by wild-type VacA contained a visible density within the central ring, whereas bilayered complexes formed by VacADelta6-27 lacked this density. These results indicate that deletion of the VacA amino-terminal hydrophobic region causes a structural alteration in the central ring within VacA oligomers, and suggest that the central ring plays an important role in the process by which VacA forms membrane channels.

Pathogenicity of Helicobacter pylori infection

Numerous Helicobacter pylori virulence factors, including various enzymes (urease, catalase, lipase, phospholipase and proteases), vacuolating cytotoxin (a product of expression of the vacA gene), and the immunogenic protein CagA, encoded by the cagA gene localised in the H. pylori pathogenicity island, are involved in the pathomechanism of infection caused by these organisms. This review presents the current state of knowledge concerning the molecular mechanisms and epidemiology of H. pylori infection, based on the published literature and recent unpublished observations.

Correlation of the Helicobacter pylori adherence factor BabA with duodenal ulcer disease in four European countries

Helicobacter pylori strains harboring the vacAs1, cagA and babA2 have been associated with ulcer disease (UD). We compared the prevalence of these different genotypes and adhesive properties in H. pylori infected patients with UD in four European countries. Genomic DNA was isolated from 314 H. pylori strains: Germany (GER; n=92), Sweden (SWE, n=74), Portugal (POR, n=91) and Finland (FIN, n=57). The frequencies of babA2 genotype varied from 35% to 60%. Triple-positive strains (vacAs1+, cagA+ and babA2+) were significantly associated with UD in GER and POR and were closely correlated with UD in FIN, but not in SWE. Classification as triple-positive strains had a higher specificity for detection of UD in GER, POR and FIN than type1 or cagA+ strains. In vitro adhesion assays revealed that Swedish strains showed high adhesion properties and were thus correlated with the diagnosis of UD, although PCR detected the babA2 gene at lower frequencies and failed to show a correlation with UD. This finding appears to reflect allelic variations of the babA2 gene in SWE, although adhesive properties of the strains are retained.

Etiology of Gastric Cancer: What Is New?

Recent advances in understanding of risk factors for gastric cancer have focused attention on genetic polymorphisms in both the human host and in Helicobacter pylori. Variation in genes for cytokines such as interleukin-1beta and its receptor antagonist may allow identification of those individuals predisposed to mount an immune response that puts them at elevated risk for gastric cancer. Likewise, analysis of how genetic variation in the genome of H. pylori may modulate the action of virulence factors like CagA may prove useful in identification of persons for whom H. pylori eradication efforts would be most important. This review examines recent studies on interleukin-1beta polymorphisms and H. pylori CagA variation with respect to their modulation of risk for gastric cancer.

Helicobacter pylori VacA cytotoxin: a probe for a clathrin-independent and Cdc42-dependent pinocytic pathway routed to late endosomes

The vacuolating cytotoxin VacA is a major virulence factor of Helicobacter pylori, a bacterium responsible for gastroduodenal ulcers and cancer. VacA associates with lipid rafts, is endocytosed, and reaches the late endocytic compartment where it induces vacuolation. We have investigated the endocytic and intracellular trafficking pathways used by VacA, in HeLa and gastric AGS cells. We report here that VacA was first bound to plasma-membrane domains localized above F-actin structures that were controlled by the Rac1 GTPase. VacA was subsequently pinocytosed by a clathrin-independent mechanism into cell peripheral early endocytic compartments lacking caveolin 1, the Rab5 effector early endosomes antigen-1 (EEA1) and transferrin. These compartments took up fluid-phase (as evidenced by the accumulation of fluorescent dextran) and glycosylphosphatidylinositol-anchored proteins (GPI-APs). VacA pinocytosis was controlled by Cdc42 and did not require cellular tyrosine kinases, dynamin 2, ADP-ribosylating factor 6, or RhoA GTPase activities. VacA was subsequently routed to EEA1-sorting endosomes and then sorted to late endosomes. During all these different endocytic steps, VacA was continuously associated with detergent resistant membrane domains. From these results we propose that VacA might be a valuable probe to study raft-associated molecules, pinocytosed by a clathrin-independent mechanism, and routed to the degradative compartment.

All subtypes of the cytotoxin VacA adsorb to the surface of Helicobacter pylori post-secretion

The major secreted virulence factor of Helicobacter pylori, the vacuolating cytotoxin VacA, is known to insert into eukaryotic membranes and has been observed in association with the surface of H. pylori cells that are actively producing it. Here, it is demonstrated that VacA is capable of interacting with the surface of H. pylori and Escherichia coli after secretion. It is shown that this interaction is resistant to disruption of electrostatic and hydrophobic forces, and that it appears to occur despite truncation of LPS and the removal of trypsin-accessible surface proteins. Adsorption to bacterial cell surfaces was independent of the VacA subtype, suggesting that it is not mediated through recognition of a known receptor by the VacA p58 subunit. Similarly, adsorption to bacterial cell surfaces is unlikely to be instigated by the extreme N-terminus of VacA, since a hydrophilic extension at this location that is known to disrupt VacA-induced vacuolation did not interfere with adsorption to H. pylori cells.

The Salmonella translocated effector SopA is targeted to the mitochondria of infected cells

This study investigates the Salmonella effector protein SopA. We show that in Salmonella enterica serovar Dublin-infected cells, SopA(1-347) fused to two carboxy-terminal hemagglutinin tags partially colocalized with mitochondria. Transfection of eukaryotic cells with a panel of constructs encoding truncated versions of SopA identified that amino acids 100 to 347 were sufficient to target SopA to the mitochondria.

Inhibitory effects of polyphenols on gastric injury by Helicobacter pylori VacA toxin

BACKGROUND

Helicobacter pylori induces gastric damage and may be involved in the pathogenesis of gastric cancer. H. pylori-vacuolating cytotoxin, VacA, is one of the important virulence factors, and is responsible for H. pylori-induced gastritis and ulceration. The aim of this study is to assess whether several naturally occurring polyphenols inhibit VacA activities in vitro and in vivo.

MATERIALS AND METHODS

Effects of polyphenols on VacA were quantified by the inhibition of: 1, vacuolation; 2, VacA binding to AZ-521 or G401 cells or its receptors; 3, VacA internalization. Effects of hop bract extract (HBT) containing high molecular weight polymerized catechin on VacA in vivo were investigated by quantifying gastric damage after oral administration of toxins to mice.

RESULTS

HBT had the strongest inhibitory activity among the polyphenols investigated. HBT inhibited, in a concentration-dependent manner: 1, VacA binding to its receptors, RPTP(alpha) and RPTP(beta); 2, VacA uptake; 3, VacA-induced vacuolation in susceptible cells. In addition, oral administration of HBT with VacA to mice reduced VacA-induced gastric damage at 48 hours. In vitro, VacA formed a complex with HBT.

CONCLUSIONS

HBT may suppress the development of inflammation and ulceration caused by H. pylori VacA, suggesting that HBT may be useful as a new type of therapeutic agent for the prevention of gastric ulcer and inflammation caused by VacA.

A secreted low-molecular-weight protein from Helicobacter pylori induces cell-cycle arrest of T cells

BACKGROUND & AIMS

Although Helicobacter pylori is recognized by the human immune system, the bacteria are not eliminated and lead to a chronic inflammation of the gastric mucosa.

METHODS

We investigated the interaction of H. pylori with human lymphocytes. T and B lymphocytes were isolated from H. pylori-infected patients and stimulated with anti-CD3/CD28 or interleukin-6.

RESULTS

Proliferation of lymphocytes was abolished on co-incubation with different H. pylori strains (1-5 bacteria/cell) or with protein extracts of culture supernatants. Inhibition of proliferation was independent of known virulence factors. The factor is a protein or protein complex with an apparent molecular weight between 30 and 60 kilodaltons, clearly distinct from VacA. Although antigen-specific activation of T cells (as shown by nuclear factor of activated T cells [NFAT]-activation, interferon-gamma production, and CD25 or CD69 up-regulation) remained intact, cell-cycle analysis showed that S-phase entry of T cells was inhibited completely by H. pylori. Consequently, stimulated T cells arrested in the G1 phase of the cell cycle. Western blot analysis showed markedly reduced phosphorylation of the retinoblastoma protein (pRb), suggesting inhibition of G1 cyclin-dependent kinase activity. In line with this, activities of cyclin D3 and cyclin E were down-regulated, and levels of the cyclin-dependent kinase inhibitor p27Kip1 were increased. Mouse embryonic fibroblasts deficient in p27 showed a decrease in H. pylori-induced inhibition of cell proliferation, suggesting a central role for p27 in mediating H. pylori-induced G1 arrest.

CONCLUSIONS

Induction of cell-cycle arrest in lymphocytes may be of major significance for the chronic persistence of bacteria in the human stomach.

Helicobacter pylori VacA, a paradigm for toxin multifunctionality

Bacterial protein toxins alter eukaryotic cellular processes and enable bacteria to successfully colonize their hosts. In recent years, there has been increased recognition that many bacterial toxins are multifunctional proteins that can have pleiotropic effects on mammalian cells and tissues. In this review, we examine a multifunctional toxin (VacA) that is produced by the bacterium Helicobacter pylori. The actions of H. pylori VacA represent a paradigm for how bacterial secreted toxins contribute to colonization and virulence in multiple ways.

Opinion: Bacterial toxins and cancer--a case to answer?

Since the discovery that Helicobacter pylori infection leads to gastric cancer, other chronic bacterial infections have been shown to cause cancer. The bacterial and host molecular mechanisms remain unclear. However, many bacteria that cause persistent infections produce toxins that specifically disrupt cellular signalling to perturb the regulation of cell growth or to induce inflammation. Other bacterial toxins directly damage DNA. Such toxins mimic carcinogens and tumour promoters and might represent a paradigm for bacterially induced carcinogenesis.

Micro-managing the executioner: pathogen targeting of mitochondria

Eukaryotic cell viability is largely regulated at the level of mitochondria, with cell death executed by endogenous proteins that act to increase the permeability of the inner and/or outer membranes of these organelles. The gastric pathogen, Helicobacter pylori, can mimic this mechanism by producing the pro-apoptotic toxin, VacA, which was recently demonstrated to (i) localize to mitochondria within epithelial cells, (ii) rapidly transport into mitochondria in vitro, and (iii) induce changes consistent with permeabilization of mitochondrial membranes by a mechanism dependent on cellular entry and toxin membrane channel activity. The targeting of mitochondrial membranes is emerging as a strategy used by pathogenic microbes to control cell viability while circumventing upstream pathways and checkpoints of cell death.

Maspin mediates increased tumor cell apoptosis upon induction of the mitochondrial permeability transition

Maspin is a unique serpin with the ability to suppress certain types of malignant tumors. It is one of the few p53-targeted genes involved in tumor invasion and metastasis. With this in mind, we attempted to study the molecular mechanism behind this tumor suppression. Maspin-expressing mammary tumors are more susceptible to apoptosis in both implanted mammary tumors in vivo, a three-dimensional spheroid culture system, as well as in monolayer cell culture under lowered growth factors. Subcellular fractionation shows that a fraction of maspin (in both TM40D-Mp and mutant maspinDeltaN cells) translocates to the mitochondria. This translocation of maspin to the mitochondria is linked to the opening of the permeability transition pore, which in turn causes the loss of transmembrane potential, thus initiating apoptotic degradation. This translocation is absent in the other mutant, maspinDeltaRSL. It fails to cause any loss of membrane potential and also shows decreased caspase 3 levels, proving that translocation to the mitochondria is a key event for this increase in apoptosis by maspin. Suppression of maspin overexpression by RNA interference desensitizes cells to apoptosis. Our data indicate that maspin inhibits tumor progression through the mitochondrial apoptosis pathway. These findings will be useful for maspin-based therapeutic interventions against breast cancer.

The relation of Helicobacter pylori to gastric adenocarcinoma and lymphoma: pathophysiology, epidemiology, screening, clinical presentation, treatment, and prevention

Helicobacter pylori infection may be the most common chronic bacterial infection worldwide; however, the prevalence varies between countries and is usually linked to socioeconomic conditions. Gastric cancer is one of the most frequent cancers in developing countries and usually about the seventh most common in developed countries. This article explores the relation of H. pylori to gastric adenocarcinoma and lymphoma. The pathophysiology, epidemiology, screening, clinical presentation, treatment, and prevention are discussed.

Helicobacter pylori eradication: novel therapy for immune thrombocytopenic purpura? A review of the literature

Eradication of Helicobacter pylori (H. pylori ) from the gastric mucosa has been associated with improvement of several systemic diseases, including immune thrombocytopenic purpura (ITP). Over the last 5 years, several studies have reported improved platelet counts in H. pylori-positive ITP patients following standard triple H. pylori eradication therapy. Review of published studies in which eradication of H. pylori has been performed in the ITP population indicates an overall response rate of 52% in 193 subjects in whom H. pylori was eradicated. Cohorts from Japan and Italy report higher response rates. There is no established mechanism to explain how this organism, which does not invade the gastric mucosa, could be implicated in the pathogenesis of this immune-based platelet disorder. Several theories including molecular mimicry, platelet aggregation, and immunomodulatory effects of macrolides have been proposed to explain the platelet response to anti-H. pylori therapy. Large randomized-controlled studies enrolling patients from various ethnic backgrounds will be necessary to determine the response rate and mechanism of response and to gain a better understanding of the pathogenesis of ITP.

Ecabet sodium inhibits Helicobacter pylori lipopolysaccharide-induced activation of NADPH oxidase 1 or apoptosis of guinea pig gastric mucosal cells

Helicobacter pylori LPS activates a homolog of gp91(phox), NADPH oxidase 1 (Nox1), in guinea pig gastric mucosal cells cultured in 10% FBS-containing medium. RT-PCR and Northern hybridization demonstrated that H. pylori LPS stimulated expression of Nox1 and a novel p47(phox) homolog (Noxo1) mRNAs with a peak at 4 h, followed by upregulation of superoxide anion (O2-) generation. Pretreatment with 10 mg/ml of a nonabsorbable antigastric ulcer drug, ecabet sodium (ecabet), completely blocked these two mRNA expressions and the upregulation of O2- production. Under low (0.1%)-FBS conditions, H. pylori LPS predominantly caused apoptosis of the cells. Ecabet completely blocked the LPS-triggered phosphorylation of transforming growth factor-beta-activated kinase 1 (TAK1) and TAK1-binding protein 1, activation of caspase 8, loss of mitochondrial membrane potential, release of cytochrome c, activation of caspase 3, and appearance of apoptotic cells. In contrast, ecabet had no effect on ethanol- or etoposide-initiated apoptosis. The ecabet-pretreated cells exhibited the responsiveness to H. pylori LPS, similarly as untreated control cells did, when ecabet was removed by washing before the addition of H. pylori LPS. Incubation of H. pylori LPS with ecabet eliminated the toxic effects of the LPS, and nondenatured polyacrylamide gel electrophoresis indicated the formation of higher molecular mass complexes between H. pylori LPS and ecabet, suggesting that ecabet may interact with H. pylori LPS and block the activation of Toll-like receptor 4 (TLR4). Our results suggest that ecabet may suppress TLR4-mediated inflammation or accelerated apoptosis caused H. pylori infection.

Molecular biology of gastric cancer: Helicobacter infection and gastric adenocarcinoma: bacterial and host factors responsible for altered growth signaling

Gastric cancer remains the second most common cause of cancer-related mortality worldwide. The single most common cause of gastric cancer is chronic infection with the gram-negative microaerophilic spiral bacterium: Helicobacter pylori. Recent advances in this field have identified host factors which predispose to gastric cancer formation via modulation of the host immune response. In addition, recent work has explored bacterial virulence factors which may directly cause tissue damage, and lead to gastric carcinogenesis, as well as factors responsible for enhanced immune response. Environmental factors, long associated with a predilection for gastric cancer, are recognized as modifiers of key growth signalling pathways within the gastric mucosa and as such lead to growth alterations. This review focuses on exploring new advances in our understanding of bacterial factors, host genetic polymorphisms and the interaction between the bacterium and host at the level of the immune response and the regulation of proliferative and apoptotic signal transduction cascades. Modulation of the pivotal balance between cell growth and cell death leads to the formation of gastric adenocarcinoma.

Helicobacter infection and gastric neoplasia

Chronic gastritis induced by Helicobacter pylori is the strongest known risk factor for adenocarcinoma of the distal stomach, yet only a minority of people who harbour this organism ever develop cancer. H. pylori isolates possess substantial genotypic diversity, which engenders differential host inflammatory responses that influence clinical outcome. H. pylori strains that possess the cag pathogenicity island and secrete a functional cytotoxin induce more severe gastric injury and further augment the risk for developing distal gastric cancer. However, carcinogenesis is also influenced by host genetic diversity, particularly involving immune response genes such as IL-1ss and TNF-alpha. It is important to gain insight into the pathogenesis of H. pylori-induced gastritis and adenocarcinoma, not only to develop more effective treatments for gastric cancer, but also because it might serve as a paradigm for the role of chronic inflammation in the genesis of other malignancies that arise within the gastrointestinal tract.

Helicobacter pylori infection and gastric cancer: host, bug, environment, or all three?

Helicobacter pylori is a common bacterial pathogen that colonizes the gastric mucosa of over 50% of the world's population. All infected individuals exhibit chronic gastric inflammation, and approximately 1% of patients develop gastric cancers, including adenocarcinomas and mucosal-associated lymphoid tissue lymphomas. In 1994, the World Health Organization International Agency for Research on Cancer classified H. pylori as a type I, or definite carcinogen. Because the prevalence of gastric cancers among H. pylori-infected patients varies between individuals, countries, and geographic areas, H. pylori disease-related outcomes are believed to be determined by an interplay between host factors, bacterial factors, and their interaction with the environment. This review highlights recent advances in our knowledge on H. pylori disease pathogenesis, focusing on the role of the host, bacteria, and environment in the development of gastric carcinoma.

Enteropathogenic Escherichia coli EspF is targeted to mitochondria and is required to initiate the mitochondrial death pathway

Enteropathogenic Escherichia coli (EPEC) is a causative agent of infant diarrhoea in developing countries. The EspF protein is the product of the espF gene found on the locus of enterocyte effacement, the key pathogenicity island carried by EPEC and enterohemorrhagic E. coli. EspF is injected from adherent EPEC into host cells via a type III secretion system and was previously shown to induce apoptotic cell death and to be required for disruption of host intestinal barrier function. In this work, we show by immunofluorescence and fractionation studies that EspF is targeted to host mitochondria. The N-terminal region of EspF serves as a mitochondrial import signal and, when expressed within cells, can target hybrid green fluorescent protein to mitochondria. Assessment of mitochondrial membrane potential in infected epithelial cells indicated that EspF plays a role in the mitochondrial membrane permeabilization induced by EPEC infection. Furthermore, EspF was associated with the release of cytochrome c from mitochondria into the cytoplasm and with caspase-9 and caspase-3 cleavage. These findings indicate a role for EspF in initiating the mitochondrial death pathway.

Type V protein secretion pathway: the autotransporter story

Gram-negative bacteria possess an outer membrane layer which constrains uptake and secretion of solutes and polypeptides. To overcome this barrier, bacteria have developed several systems for protein secretion. The type V secretion pathway encompasses the autotransporter proteins, the two-partner secretion system, and the recently described type Vc or AT-2 family of proteins. Since its discovery in the late 1980s, this family of secreted proteins has expanded continuously, due largely to the advent of the genomic age, to become the largest group of secreted proteins in gram-negative bacteria. Several of these proteins play essential roles in the pathogenesis of bacterial infections and have been characterized in detail, demonstrating a diverse array of function including the ability to condense host cell actin and to modulate apoptosis. However, most of the autotransporter proteins remain to be characterized. In light of new discoveries and controversies in this research field, this review considers the autotransporter secretion process in the context of the more general field of bacterial protein translocation and exoprotein function.

Targeting of enteropathogenic Escherichia coli EspF to host mitochondria is essential for bacterial pathogenesis: critical role of the 16th leucine residue in EspF

The attachment of enteropathogenic Escherichia coli (EPEC) to host cells and the induction of attaching and effacing (A/E) lesions are prominent pathogenic features. EPEC infection also leads to host cell death and damage to the intestinal mucosa, which is partly dependent upon EspF, one of the effectors. In this study, we demonstrate that EspF is a mitochondrial import protein with a functional mitochondrial targeting signal (MTS), because EspF activity for importing into the mitochondria was abrogated by MTS deletion mutants. Substitution of the 16th leucine with glutamic acid (EspF(L16E)) completely abolished EspF activity. Infection of HeLa cells with wild type but not the espF mutant (DeltaespF) decreased mitochondrial membrane potential (DeltaPsi(m)), leading to cell death. The DeltaPsi(m) decrease and cell death were restored in cells infected with DeltaespF/pEspF but not DeltaespF/pEspF(L16E), suggesting that the 16th leucine in the MTS is a critical amino acid for EspF function. To demonstrate the impact of EspF in vivo, we exploited Citrobacter rodentium by infecting C3H/HeJ mice with DeltaespF(CR), DeltaespF(CR)/pEspF(CR), or DeltaespF(CR)/pEspF(L16E)(CR). These results indicate that EspF activity contributes to bacterial pathogenesis, as judged by murine lethality and intestinal histopathology, and promotion of bacterial colonization of the intestinal mucosa.

Susceptibility of Helicobacter pylori with diversified genotypes to allitridi

AIM: To study the susceptibility of Helicobacter pylori strains with diversified genotypes to allitridi.

METHODS: Fifty-one strains of H. pylori were isolated and cultured from the fresh gastric mucosal specimens. CagA and vacA (s1, m1b, m2) genotypes of H. pylori were determined by PCR method. Minimal inhibitory concentrations (MICs) of allitridi on 51 H. pylori strains were determined by agar dilution methods. MIC50 was also calculated.

RESULTS: Fifty-one strains of H. pylori were satisfactorily susceptible to allitridi. The gross bacteriostatic rate of allitridi on 51 H. pylori strains was 92.2% (47/51), and MIC50 was 7.97 mg/L. MIC was in a range of 1.25 mg/L to 40 mg/L. H. pylori with vacAm1b+ genotype was more susceptible to allitridi than that with vacAm1b- genotype (relative median potential = 0.55, 95% credible range from 0.30 to 0.89). H. pylori with vacAm2+ genotype was more susceptible to allitridi than that with vacAm2- genotype (relative median potential= 0.67, 95% credible range from 0.44 to 0.98). H. pylori with cagA+ vacAs1+ m1b+, cagA+ vacAs1+ m2+ genotypes were more susceptible to allitridi than those with cagA+vacAs1-m1b- genotypes (relative median potential = 0.38/0.37, 95% Credible Range from 0.10 to 0.78/from 0.11 to 0.81).

CONCLUSION: H. pylori is satisfactorily susceptible to allitridi. The bacteriostatic effect increases with the concentration of allitridi. The MIC₅₀ is 7.97 mg/L and MIC range between 1.25 mg/L and 40 mg/L. Diversified genotypes or genotype combinations of H. pylori show different susceptibilities to allitridi.

Effect of H. pylori on the expression of TRAIL, FasL and their receptor subtypes in human gastric epithelial cells and their role in apoptosis

BACKGROUND AND AIMS

In the human stomach expression of TNF-related apoptosis inducing ligand (TRAIL) and its receptors and the modulatory role of Helicobacter pylori are not well described. Therefore, we investigated the effect of H. pylori on the expression of TRAIL, FasL and their receptors (TRAIL-R1-R4, Fas) in gastric epithelial cells and examined their role in apoptosis.

MATERIALS AND METHODS

mRNA and protein expression of TRAIL, FasL and their receptors were analyzed in human gastric epithelial cells using RT-PCR, Western blot, and immunohistochemistry. Gastric epithelial cells were incubated with FasL, TRAIL and/or H. pylori, and effects on expression, cell viability and epithelial apoptosis were monitored. Apoptosis was analyzed by histone ELISA, DAPI staining and immunohistochemistry.

RESULTS

TRAIL, FasL and their receptor subtypes were expressed in human gastric mucosa, gastric epithelial cell primary cultures and gastric cancer cells. TRAIL, FasL and H. pylori caused a time- and concentration-dependent induction of DNA fragmentation in gastric cancer cells with synergistic effects. In addition, H. pylori caused a selective up-regulation of TRAIL, TRAIL-R1 and Fas mRNA and protein expression in gastric cancer cells.

CONCLUSIONS

Next to FasL and Fas, TRAIL and all of its receptor subtypes are expressed in the human stomach and differentially modulated by H. pylori. TRAIL, FasL and H. pylori show complex interaction mediating apoptosis in human gastric epithelial cells. These findings might be important for the understanding of gastric epithelial cell kinetics in patients with H. pylori infection.

Chlamydia and apoptosis: life and death decisions of an intracellular pathogen

The chlamydiae are important obligate intracellular prokaryotic pathogens that, each year, are responsible for millions of human infections involving the eye, genital tract, respiratory tract, vasculature and joints. The chlamydiae grow in cytoplasmic vesicles in susceptible host cells, which include the mucosal epithelium, vascular endothelium, smooth muscle cells, circulating monocytes and recruited or tissue-specific macrophages. One important pathogenic strategy that chlamydiae have evolved to promote their survival is the modulation of programmed cell death pathways in infected host cells. The chlamydiae can elicit the induction of host cell death, or apoptosis, under some circumstances and actively inhibit apoptosis under others. This subtle pathogenic mechanism highlights the manner in which these highly successful pathogens take control of infected cells to promote their own survival - even under the most adverse circumstances.

Essential domain of receptor tyrosine phosphatase beta (RPTPbeta) for interaction with Helicobacter pylori vacuolating cytotoxin

Helicobacter pylori produces a potent exotoxin, VacA, which causes progressive vacuolation as well as gastric injury. Although VacA was able to interact with two receptor-like protein tyrosine phosphatases, RPTPbeta and RPTPalpha, RPTPbeta was found to be responsible for gastric damage caused by VacA. To define the region of RPTPbeta involved in VacA binding, we made mutants of human cDNA RPTPbeta-B, a short receptor form of RPTPbeta. Immunoprecipitation experiments to assess VacA binding to RPTPbeta-B mutants indicated that five residues (QTTQP) at positions 747-751 of the extracellular domain of RPTPbeta-B (which is commonly retained in RPTPbeta-A, a long form of RPTPbeta) play a crucial role in its interaction with VacA, resulting in vacuolation as well as Git-1 phosphorylation. Transfected cells expressing deletion mutant Delta752, which lacks QTTQP, or the double point mutant Delta747 (T748A,T749A) had diminished vacuolation in response to VacA. Treatment of RPTPbeta-B and Delta747 (which have QTTQP at 747-751) with neuraminidase and O-glycosidase diminished their VacA binding, whereas chondroitinase ABC did not have an effect. No inhibitory effect of pleiotrophin, a natural RPTPbeta ligand, on VacA binding to RPTPbeta-B or Delta747 was observed, supporting the conclusion that the extracellular region of RPTPbeta-B responsible for VacA binding is different from that involved in binding pleiotrophin. These data define the region in the RPTPbeta extracellular domain critical for VacA binding, in particular the sequence QTTQP at positions 747-751 with crucial threonines at positions 748 and 749 and are consistent with a role for terminal sialic acids possibly because of threonine glycosylation.

Molecular mechanism of action of major Helicobacter pylori virulence factors

Although Helicobacter pylori infects 50% of the total human population, only a small fraction of the infected people suffer from severe diseases like peptic ulcers and gastric adenocarcinoma. H. pylori strains, host genotypes and environmental factors play important role in deciding the extent and severity of the gastroduodenal diseases. The bacteria has developed a unique set of virulence factors to survive in the extreme ecological niche of human stomach. Together these virulence factors make H. pylori one of the most successful human pathogenic bacteria colonizing more than half of the human population. Understanding the mechanism of action of the major H. pylori virulence factors will shed light into the molecular basis of its pathogenicity.