Helicobacter pylori culture supernatant interferes with epidermal growth factor-activated signal transduction in human gastric KATO III cells.

The mechanisms by which Helicobacter pylori infection leads to gastroduodenal ulceration remain poorly understood. Previous studies have shown that H. pylori vacuolating cytotoxin (VacA) inhibits proliferation of gastric epithelial cells, which suggests that H pylori may interfere with gastric mucosal repair mechanisms. In this study, we investigated the effects of H. pylori broth culture supernatants on epidermal growth factor (EGF)-mediated signal transduction pathways in a gastric carcinoma cell line (KATO III). Exposure of these cells to EGF resulted in increased expression and phosphorylation of the EGF receptor (EGF-R), increased ERK2 activity and phosphorylation, and increased c-fos protein levels. Preincubation of cells with broth culture supernatant from VacA (+) H. pylori strain 60190 inhibited the capacity of EGF to induce each of these effects. In contrast, preincubation of cells with broth culture supernatant from an isogenic VacA-mutant strain (H. pylori 60190-v1) failed to inhibit the effects of EGF. These results suggest that the H. pylori vacuolating cytotoxin interferes with EGF-activated signal transduction pathways, which are known to be essential for cell proliferation and ulcer healing.     

Helicobacter pylori adherence to gastric epithelial cells: a role for non-adhesin virulence genes

Helicobacter pylori is a major aetiological agent in gastroduodenal disorders and adherence of the bacteria to the gastric mucosa is one of the initial stages of infection. Although a number of specific adhesins has been identified, other H. pylori virulence factors may play a role in adherence to gastric epithelial cells directly or through interaction with other adhesins. This study assessed the effect of 16 H. pylori virulence factors on the adherence of the bacteria to gastric AGS cells and on gastric epithelial cell cycle distribution. Defined isogenic H. pylori SS1 mutants were used. After co-incubation of gastric AGS cells and bacteria, adherence of H. pylori to AGS cells was visualised by immunofluorescence microscopy and quantified by flow cytometry. Cell cycle phase distribution was analysed by flow cytometry with propidium iodide staining. Mutants were tested for their ability to adhere to AGS cells and compared with the wild-type SS1 strain. Mutations in genes in the cag pathogenicity island showed that cagP and cagE mutants adhered less than the wild-type strain to AGS cells, whereas a cagF mutant showed no reduction in adherence. Mutations in genes involved in flagellar biosynthesis showed that the adherence ability of fliQ, fliM and fliS mutants was reduced, but a flhB mutant possessed wild-type levels of adherence. Mutations in genes coding for the urease (ureB) and phospholipase (pldA) enzymes did not affect adherence, but mutation of the tlyA gene encoding an H. pylori haemolysin resulted in a reduced adherence. A fliQ mutant, with reduced adherence to AGS cells, was less able to induce AGS cell apoptosis than SS1. The ability to induce G0G1 cell cycle arrest was also abolished in the fliQ mutant. However, an increased cell number in S phase was observed when AGS cells were exposed to the fliQ mutant compared with SS1, suggesting that unattached bacteria may still be able to stimulate cell proliferation. In addition to known adhesins, other bacterial virulence factors such as CagE, CagP, FliQ, FliM, FliS and TlyA appear to play a role in H. pylori adherence to gastric epithelial cells. Mutations in these genes may affect H. pylori pathogenicity by reducing either the ability of the bacteria to attach to gastric epithelial cells or the intensity of bacteria-host cell interactions.     

Helicobacter pylori Induces Gastric Epithelial Cell Apoptosis in Association with Increased Fas Receptor Expression

The mechanisms involved in mediating the enhanced gastric epithelial cell apoptosis observed during infection with Helicobacter pylori in vivo are unknown. To determine whether H. pylori directly induces apoptosis of gastric epithelial cells in vitro and to define the role of the Fas-Fas ligand signal transduction cascade, human gastric epithelial cells were infected with H. pylori for up to 72 h under microaerophilic conditions. As assessed by both transmission electron microscopy and fluorescence microscopy, incubation with a cagA-positive, cagE-positive, VacA-positive clinical H. pylori isolate stimulated an increase in apoptosis compared to the apoptosis of untreated AGS cells (16.0% +/- 2.8% versus 5.9% +/- 1. 4%, P < 0.05) after 72 h. In contrast, apoptosis was not detected following infection with cagA-negative, cagE-negative, VacA-negative clinical isolates or a Campylobacter jejuni strain. In addition to stimulating apoptosis, infection with H. pylori enhanced Fas receptor expression in AGS cells to a degree comparable to that of treatment with a positive control, gamma interferon (12.5 ng/ml) (148% +/- 24% and 167% +/- 24% of control, respectively). The enhanced Fas receptor expression was associated with increased sensitivity to Fas-mediated cell death. Ligation of the Fas receptor with an agonistic monoclonal antibody resulted in an increase in apoptosis compared to the apoptosis of cells infected with the bacterium alone (38.5% +/- 7.1% versus 16.0% +/- 2.8%, P < 0.05). Incubation with neutralizing anti-Fas antibody did not prevent apoptosis of H. pylori-infected cells. Taken together, these findings demonstrate that the gastric pathogen H. pylori stimulates apoptosis of gastric epithelial cells in vitro in association with the enhanced expression of the Fas receptor. These data indicate a role for Fas-mediated signaling in the programmed cell death that occurs in response to H. pylori infection.     

Helicobacter pylori activates myosin light-chain kinase to disrupt claudin-4 and claudin-5 and increase epithelial permeability

Helicobacter pylori is a spiral, gram-negative bacterium that specifically and persistently infects the human stomach. In some individuals, H. pylori-induced chronic gastritis may progress to gastroduodenal ulcers and gastric cancer. Currently, the host-microbe interactions that determine the clinical outcome of infection are not well defined. H. pylori strains capable of disrupting the gastric epithelial barrier may increase the likelihood of developing serious disease. In this study, H. pylori strain SS1 increased gastric, but not small intestinal, permeability in C57BL/6 mice. H. pylori strain SS1 was able to directly increase paracellular permeability, in the absence of host inflammatory cells, by disrupting the tight-junctional proteins occludin, claudin-4, and claudin-5 in confluent nontransformed epithelial cells. H. pylori SS1 also reduced claudin-4 protein levels in human gastric AGS cells. The ability of H. pylori SS1 to increase permeability appeared to be independent of the well-characterized virulence factors vacuolating cytotoxin and CagA protein. H. pylori activated myosin light-chain kinase in epithelial cells to phosphorylate myosin light chain and increase permeability by disrupting claudin-4 and claudin-5. The bacterial factor responsible for increasing epithelial permeability was heat sensitive, membrane bound, and required apical contact with monolayers. In conclusion, disruptions of the tight junctions observed in this study implicate host cell signaling pathways, including the phosphorylation of myosin light chain and the regulation of tight-junctional proteins claudin-4 and claudin-5, in the pathogenesis of H. pylori infection.     

Helicobacter pylori VacA induces programmed necrosis in gastric epithelial cells

Helicobacter pylori is a Gram-negative bacterium that colonizes the human stomach and contributes to the development of peptic ulcer disease and gastric cancer. The secreted pore-forming toxin VacA is one of the major virulence factors of H. pylori. In the current study, we show that AZ-521 human gastric epithelial cells are highly susceptible to VacA-induced cell death. Wild-type VacA causes death of these cells, whereas mutant VacA proteins defective in membrane channel formation do not. Incubation of AZ-521 cells with wild-type VacA results in cell swelling, poly(ADP-ribose) polymerase (PARP) activation, decreased intracellular ATP concentration, and lactate dehydrogenase (LDH) release. VacA-induced death of these cells is a caspase-independent process that results in cellular release of histone-binding protein high mobility group box 1 (HMGB1), a proinflammatory protein. These features are consistent with the occurrence of cell death through a programmed necrosis pathway and suggest that VacA can be included among the growing number of bacterial pore-forming toxins that induce cell death through programmed necrosis. We propose that VacA augments H. pylori-induced mucosal inflammation in the human stomach by causing programmed necrosis of gastric epithelial cells and subsequent release of proinflammatory proteins and may thereby contribute to the pathogenesis of gastric cancer and peptic ulceration.     

Novel activities of the Helicobacter pylori vacuolating cytotoxin: from epithelial cells towards the immune system

H. pylori has developed a unique set of virulence factors, which allow its survival in a unique ecological niche, the human stomach. The vacuolating cytotoxin (VacA) and the cytotoxin-associated antigen (CagA) are major bacterial factors involved in modulating the host. VacA, so far mainly regarded as a cytotoxin for the gastric epithelial cell layer, apparently has profound effects in modulating the immune response. In this review we discuss some of the classical effects of VacA, such as cell vacuolation, and compare them with more recently identified mechanisms of VacA on immune cells.     

Epithelial Intestinal Cell Apoptosis Induced by Helicobacter pylori Depends on Expression of the cag Pathogenicity Island Phenotype

Helicobacter pylori has been shown to induce chronic active gastritis and peptic ulcer and may contribute to the development of duodenal ulcer. Previous studies have shown that H. pylori mediates apoptosis of gastric epithelial cells via a Fas-dependent pathway. However, evidence for the induction of such a mechanism in intestinal epithelial cells (IEC) by H. pylori infection has not been demonstrated yet. This study was performed (i) to ascertain that H. pylori can induce IEC apoptosis; (ii) to delineate the role of the cag pathogenicity island (PAI), cagE, and vacA gene products in this process; and (iii) to verify whether the Fas-dependent pathway is involved in this phenomenon. When T84 cells were exposed to VacA(+)/cag PAI(+) H. pylori strains (CCUG 17874 and 60190), they exhibited apoptosis hallmarks as assessed by morphological studies, as well as annexin V and 3,3'-dihexyloxacarbocyanine iodide staining. In contrast, few or no apoptotic features could be detected after incubation with an isogenic mutant of strain 60190 in which the cagE gene was disrupted (60190:C(-) strain) or with a VacA(-)/cag PAI(-) H. pylori strain (G21). In addition, activation of caspase-3 during infection with VacA(+)/cag PAI(+) H. pylori strains was inhibited by pretreatment of IEC with an antagonistic anti-Fas antibody (ZB4). Taken together, these findings indicate that H. pylori triggers apoptosis in IEC via a Fas-dependent pathway following a process that depends on the expression of the cag PAI.     

Complex cellular responses of Helicobacter pylori-colonized gastric adenocarcinoma cells

Helicobacter pylori is an important class I carcinogen that persistently infects the human gastric mucosa to induce gastritis, gastric ulceration, and gastric cancer. H. pylori pathogenesis strongly depends on pathogenic factors, such as VacA (vacuolating cytotoxin A) or a specialized type IV secretion system (T4SS), which injects the oncoprotein CagA (cytotoxin-associated gene A product) into the host cell. Since access to primary gastric epithelial cells is limited, many studies on the complex cellular and molecular mechanisms of H. pylori were performed in immortalized epithelial cells originating from individual human adenocarcinomas. The aim of our study was a comparative analysis of 14 different human gastric epithelial cell lines after colonization with H. pylori. We found remarkable differences in host cell morphology, extent of CagA tyrosine phosphorylation, adhesion to host cells, vacuolization, and interleukin-8 (IL-8) secretion. These data might help in the selection of suitable cell lines to study host cell responses to H. pylori in vitro, and they imply that different host cell factors are involved in the determination of H. pylori pathogenesis. A better understanding of H. pylori-directed cellular responses can provide novel and more balanced insights into the molecular mechanisms of H. pylori-dependent pathogenesis in vivo and may lead to new therapeutic approaches.     

Helicobacter pylori -induced apoptosis in gastric epithelial cells is blocked by protein kinase C activation

Apoptosis plays a major role in gastrointestinal epithelial cell turnover. We have examined induction of apoptosis by Helicobacter pylori in gastric AGS cells and the role of protein kinase C (PKC) which has been shown to modulate programmed cell death. Incubation of AGS cells with H. pylori resulted in an activation of caspases 3 and 9 and induced programmed cell death. The PKC activator 12- O -tetradecanoylphorbol-13-acetate (TPA) caused translocation of PKC gamma, delta and var epsilon, prevented H. pylori -induced caspase activation and programmed cell death. Cocultivation of AGS cells with H. pylori resulted in a translocation of the atypical PKC isoform PKC lambda. We suggest that inhibition of H. pylori induced apoptosis by PKC activation can play a role in the process of neoplastic transformation.     

Effect of Helicobacter pylori on polymorphonuclear leukocyte migration across polarized T84 epithelial cell monolayers: role of vacuolating toxin VacA and cag pathogenicity island

Helicobacter pylori infection can induce polymorphonuclear leukocyte (PMNL) infiltration of the gastric mucosa, which characterizes acute chronic gastritis. The mechanisms underlying this process are poorly documented. The lack of an in vitro model has considerably impaired the study of transepithelial migration of PMNL induced by H. pylori. In the present work, we used confluent polarized monolayers of the human intestinal cell line T84 grown on permeable filters to analyze the epithelial PMNL response induced by broth culture filtrates (BCFs) and bacterial suspensions from different strains of H. pylori. We have evaluated the role of the vacuolating cytotoxin VacA and of the cag pathogenicity island (PAI) of H. pylori in PMNL migration via their effects on T84 epithelial cells. We noted no difference in the rates of PMNL transepithelial migration after epithelial preincubation with bacterial suspensions or with BCFs of VacA-negative or VacA-positive H. pylori strains. In contrast, PMNL transepithelial migration was induced after incubation of the T84 cells with cag PAI-positive and cagE-positive H. pylori strains. Finally, PMNL migration was correlated with a basolateral secretion of interleukin-8 by T84 cells, thus creating a subepithelial chemotactic gradient for PMNL. These data provide evidence that the vacuolating cytotoxin VacA is not involved in PMNL transepithelial migration and that the cag PAI, with a pivotal role for the cagE gene, provokes a transcellular signal across T84 monolayers, inducing a subepithelial PMNL response.     

Effects of Helicobacter pylori on the cadherin-catenin complex

BACKGROUND: The cadherin-catenin complex is the key component of the adherens junction in epithelial cells, and changes in this complex are implicated in gastric adenocarcinoma. Germline mutations in E-cadherin have been described in diffuse-type gastric adenocarcinoma. Helicobacter pylori infection is the first stage in gastric carcinogenesis. AIMS: To determine whether H pylori was associated with changes in the complex, and whether this was affected by virulence of the strain. METHODS: Epithelial cell lines were cultured with H pylori using the wild-type pathogenic and non-pathogenic strains and CagE null and VacA null isogenic mutants. Gastric biopsy specimens at endoscopy were obtained from patients with (n = 17) and without (n = 15) H pylori infection, and E-cadherin and beta-catenin expression was assessed by immunohistochemistry. H pylori was typed by polymerase chain reaction from these patients for CagE and VacA. RESULTS: In vitro studies showed that coculture with a pathogenic strain of H pylori led to disruption of epithelial junctional beta-catenin expression, but without evidence of nuclear translocation or signalling. This effect was independent of a functional Cag pathogenicity island and vacuolating activity, but dependent on live bacteria. No marked differences in beta-catenin or E-cadherin expression were seen in gastric biopsy specimens in patients with and without H pylori infection. CONCLUSION: Acute H pylori infection disrupts junctional beta-catenin in vitro, but chronic infection by H pylori has no effect on E-cadherin and beta-catenin expression, as seen in gastric biopsy specimens at the initial gastritis stage of the proposed Correa pathway of gastric carcinogenesis. A later effect at the later stages of atrophy or intestinal metaplasia cannot be ruled out.     

Impairment of glutathione metabolism in human gastric epithelial cells treated with vacuolating cytotoxin from Helicobacter pylori.

Helicobacter pylori vacuolating cytotoxin (VacA) is believed to be one of the factors that induces gastric disease. Our previous study indicated that VacA causes a decrease in the intracellular ATP level in human gastric epithelial cells, suggesting to impair mitochondrial membrane potential followed by a decrease in energy metabolism (Kimura et al., Microb. Pathog., 1999, 26: 45--52). In the present study, we investigated whether the decrease in ATP level affects glutathione metabolism, in which its synthesis and efflux are ATP-dependent. Treatment of AZ-521 human gastric epithelial cells with 120 nM VacA for 6 h suppressed the efflux of oxidized glutathione (GSSG) in a dose- and time-dependent manner. The efflux of GSSG from the cells and glutathione (GSH) synthesis of cells treated with VacA were approximately 50 and 70% of those of the control, respectively. The turnover rate of intracellular GSH was also suppressed by VacA. Viability of the cells pretreated with VacA, then further incubated with H(2)O(2), was decreased by 50% at 6 h and 70% at 12 h. These results suggested that VacA impairs GSH metabolism in the gastric epithelial cells, which weakens the resistance of the cells against oxidative stress or cellular redox regulation by GSH.     

Vacuolating cytotoxin of Helicobacter pylori plays a role during colonization in a mouse model of infection

Helicobacter pylori, the causative agent of gastritis and ulcer disease in humans, secretes a toxin called VacA (vacuolating cytotoxin) into culture supernatants. VacA was initially characterized and purified on the basis of its ability to induce the formation of intracellular vacuoles in tissue culture cells. H. pylori strains possessing different alleles of vacA differ in their ability to express active toxin. Those strains expressing higher toxin levels are correlated with more severe gastric disease. However, the specific role(s) played by VacA during the course of infection and disease is not clear. We have used a mouse model of H. pylori infection to begin to address this role. A null mutation of vacA compromises H. pylori in its ability to initially establish infection. If an infection by a vacA mutant is established, the bacterial load and degree of inflammation are similar to those associated with an isogenic wild-type strain. Thus, in this infection model, vacA plays a role in the initial colonization of the host, suggesting that strains of H. pylori expressing active alleles of vacA may be better adapted for host-to-host transmission.     

Binding and internalization of the Helicobacter pylori vacuolating cytotoxin by epithelial cells.

Many Helicobacter pylori strains produce a cytotoxin (VacA) that induces vacuolation in epithelial cells. In this study, binding and internalization of the cytotoxin by HeLa or AGS (human gastric adenocarcinoma) cells were characterized by indirect fluorescence microscopy. Cells incubated with the cytotoxin at 4 degrees C displayed a uniform fluorescent plasma membrane signal. Preincubation of the cytotoxin with either rabbit antiserum to approximately 90-kDa H. pylori VacA or sera from H. pylori-infected persons inhibited its binding to cells and blocked its capacity to induce cytoplasmic vacuolation. Recombinant VacA fragments (approximately 34 and approximately 58 kDa), corresponding to two proteolytic cleavage products of approximately 90-kDa VacA, each bound to the plasma membrane of HeLa cells. Antiserum reactive with the approximately 58-kDa VacA fragment inhibited the binding of native H. pylori cytotoxin to cells and inhibited cytotoxin activity, whereas antiserum to the approximately 34-kDa fragment had no effect. When incubated with cells at 37 degrees C for > or = 3 h, the H. pylori cytotoxin localized intracellularly in a perinuclear location but did not localize within cytotoxin-induced vacuoles. When cells with previously bound cytotoxin were incubated with anticytotoxin serum at 4 degrees C and then shifted to 37 degrees C, vacuolation was completely inhibited. Bound cytotoxin became inaccessible to the neutralizing effects of antiserum after 60 to 120 min of incubation with cells at 37 degrees C. These data suggest a model in which (i) VacA binds to cells primarily via amino acid sequences in its 58-kDa fragment, (ii) VacA internalization occurs slowly in a temperature-dependent process, and (iii) VacA interacts with an intracellular target.     

Helicobacter pylori Membrane Vesicles Stimulate Innate Pro- and Anti-Inflammatory Responses and Induce Apoptosis in Jurkat T Cells

Persistent Helicobacter pylori infection induces chronic inflammation in the human gastric mucosa, which is associated with development of peptic ulceration, gastric atrophy, and gastric adenocarcinoma. It has been postulated that secretion of immunomodulatory molecules by H. pylori facilitates bacterial persistence, and membrane vesicles (MV), which have the potential to cross the gastric epithelial barrier, may mediate delivery of these molecules to host immune cells. However, bacterial MV effects on human immune cells remain largely uncharacterized to date. In the present study, we investigated the immunomodulatory effects of H. pylori MV with and without the vacuolating cytotoxin, VacA, which inhibits human T cell activity. We show a high degree of variability in the toxin content of vesicles between two H. pylori strains (SS1 and 60190). Vesicles from the more toxigenic 60190 strain contain more VacA (s1i1 type) than vesicles from the SS1 strain (s2i2 VacA), but engineering the SS1 strain to produce s1i1 VacA did not increase the toxin content of its vesicles. Vesicles from all strains tested, including a 60190 isogenic mutant null for VacA, strongly induced interleukin-10 (IL-10) and IL-6 production by human peripheral blood mononuclear cells independently of the infection status of the donor. Finally, we show that H. pylori MV induce T cell apoptosis and that this is enhanced by, but not completely dependent on, the carriage of VacA. Together, these findings suggest a role for H. pylori MV in the stimulation of innate pro- and anti-inflammatory responses and in the suppression of T cell immunity.     

幽门螺杆菌对体外感染胃黏膜上皮细胞TGF-β1 B7-H1表达的影响

目的 探讨适当菌量幽门螺杆菌(H.pylori)对体外感染胃黏膜上皮细胞转化生长因子β1(TGF-β1)、B7-H1 mRNA表达的影响及其诱导TGF-β1表达的菌体因素,为支持H.pylori通过诱导胃黏膜上皮细胞表达TGF-β1及B7-H1,抑制宿主免疫功能,参与H.pylori免疫逃逸提供依据.方法 (1)选用1.0×109CFU/ml(低浓度)、4.0×109 CFU/ml(中浓度)、8.0×109 CFU/ml(高浓度)H.pylori国际标准毒力菌株NCTC 11637活菌悬液分别感染体外培养胃黏膜上皮细胞,建立不同共孵育时间(0 h、0.5 h、1 h、1.5 h、2 h、4 h、8 h、12 h)H.pylori体外感染细胞模型,设立未加H.pylori的胃黏膜上皮细胞对照组,以酶联免疫吸附法(ELISA)检测感染及对照细胞各时间点培养上清TGF-β1含量,原位杂交法检测不同浓度感染及对照细胞共培养12 h B7-H1 mRNA的表达.(2)同时用H.pylori中浓度灭活菌悬液与体外培养胃黏膜细胞共孵育,测定共孵育细胞2 h、12 h培养细胞上清的TGF-β1含量.(3)用超声粉碎并经离心获取的H.pylori菌体成分上清、沉淀以及煮沸后上清、沉淀分别作用体外培养胃黏膜细胞,测定2 h、12 h培养细胞上清TGF-β1含量.结果 (1)H.pylori活菌悬液3种浓度各时间组胃黏膜上皮细胞培养上清TGF-β1含量均较对照组明显增高(P<0.05),各浓度时间组TGF-β1表达量有栩似的动态趋势,但尤以中浓度组TGF-β1表达量最高(P<0.05).(2)中浓度H.pylori灭活菌株组与同浓度活菌组细胞培养上清TGF-β1含量差异无统计学意义(P>0.05).(3)H.pylori菌体成分上清组较对照组和沉淀组细胞培养上清TGF-β1表达增高(P<0.01);上清煮沸组较未煮沸组明显降低(P<0.01);沉淀煮沸组与未煮沸组差异无统计学意义(P>0.05).(4)高、中、低浓度组感染细胞12 h B7-H1 mRNA的表达均较对照组增高(P<0.05),以中浓度组表达最高,并与高、中、低浓度组12 h感染细胞上清TGF-β1含量呈正相关(rs=0.628,P<0.01).结论 H.pylori可直接诱导胃黏膜上皮细胞分泌TGF-β1,其诱导因素为可溶性不耐热菌体成分;H.pylori同样可诱导胃黏膜上皮细胞B7-H1 mRNA表达增高,且B7-H1 mRNA表达与TGF-β1呈正相关.推测H.pylori通过诱导TGF-β1、B7-H1高表达,抑制宿主免疫应答,参与H.pylori免疫逃逸.     

Detoxification of the Helicobacter pylori cytotoxin.

Treatment of the Helicobacter pylori vacuolating cytotoxin with very low concentrations of formaldehyde resulted in abrogation of toxic activity in both a HeLa cell vacuolation assay and an in vivo assay of gastric epithelial damage. Detoxification had only a minimal effect on the integrity of the oligomeric or monomeric structure. The toxoid retained the ability to bind to target cells and to induce high-titer neutralizing antibodies after immunization of rabbits. Furthermore, oral immunization of mice with the toxoid resulted in protection against infective challenge with mouse-adapted strains of H. pylori. The sensitivity of the toxin to formaldehyde treatment suggests that a few lysine residues in the protein may be essential for toxic activity and that VacA detoxified in this manner may be a potential candidate for inclusion in a vaccine against H. pylori infection and disease.     

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.     

Helicobacter pylori organisms induce expression of activation and apoptotic surface markers on human lymphocytes and AGS cells: a cytofluorimetric evaluation

Human peripheral blood mononuclear cells (PBMCs) were treated with Helicobacter pylori (Hp) organisms alone or with Hp-stimulated AGS cells (a gastric adenocarcinoma cell line). Hp organisms were able per se to increase the percentage of CD8+CD95+ cells, while number of CD25+ cells and HLA-DR molecule expression increased following pretreatment with Hp-stimulated AGS cells.

A comparison was made with a test system in which PBMCs were stimulated with Escherichia coli (Ec) organisms and colo-cells (a colon carcinoma cell line). In this case, CD95+ cells and CD25+ cells increased when the combination Ec organisms/colo-cells was present in the culture. On the other hand, Hp bacteria in combination with colo-cells were not able to induce activation and/or apoptotic surface markers on PBMCs, while Ec-stimulated AGS cells increased the expression of CD95 on PBMC.

Finally, the direct interaction of AGS cells with Hp was able to induce higher expression of CD95 on gastric epithelial cells than Hp-stimulated PBMCs. Taken together, these data support the interplay between bacteria and epithelial cells in the course of Hp-mediated gastropathy.