Apoptosis in gastric epithelial cells is induced by Helicobacter pylori and accompanied by increased expression of BAK

Molecular mechanism of Enteroaggregative Escherichia coli induced apoptosis in cultured human intestinal epithelial cells

Background. Enteroaggregative Escherichia coli (EAEC) is an evolving etiological agent of acute and persistent diarrhoea worldwide. The previous study from our laboratory has reported the apoptosis-inducing activity of EAEC in human small intestinal and colonic epithelial cell lines. In the present investigation, we have explored the underlying mechanism of EAEC-induced apoptosis in human intestinal epithelial cell lines.Methods. INT-407 and HCT-15 cells were infected with EAEC-T8 and EAEC-pT8 (plasmid cured strain of EAEC-T8) separately. Cells cultured in the absence of bacteria served as a negative control in all the experiments. For the subsequent experiments, the molecular mechanism(s) of epithelial cell aposptosis was measured in EAEC infecting both the cell lines by flow cytometry, real-time PCR and Western blotting.Results and conclusions. EAEC was found to activate the intrinsic/mitochondrial apoptotic pathway in both the cell lines through upregulation of pro-apoptotic Bax and Bak, un-alteration/reduction in the level of anti-apoptotic Bcl-2 and Bcl-XL, decrease in mitochondrial transmembrane potential, accumulation of cytosolic cytochrome c leading to activation of procaspase-9 and procaspase-3, which ultimately resulted in DNA fragmentation and apoptosis. Further, an increased expression of Fas, activation of procaspase-8 and upregulation of pro-apoptotic Bid in the EAEC-infected cells indicated the involvement of extrinsic apoptotic pathway too in this process. Our finding has undoubtedly led to an increased understanding of EAEC pathogenesis, which may be helpful to develop an improved strategy to combat the infection.

Role of mitochondrial outer membrane permeabilization during bacterial infection

Beyond the initial 'powerhouse' view, mitochondria have numerous functions in their mammalian cell and contribute to many physiological processes, and many of these we understand only partially. The control of apoptosis by mitochondria is firmly established. Many questions remain however how this function is embedded into physiology, and how other signaling pathways regulate mitochondrial apoptosis; the interplay of bacteria with the mitochondrial apoptosis pathway is one such example. The outer mitochondrial membrane regulates both import into mitochondria and the release of intermembrane, and in some situations also matrix components from mitochondria, and these mitochondrial components can have signaling function in the cytosol. One function is the induction of apoptotic cell death. An exciting, more recently discovered function is the regulation of inflammation. Mitochondrial molecules, both proteins and nucleic acids, have inflammatory activity when released from mitochondria, an activity whose regulation is intertwined with the activation of apoptotic caspases. Bacterial infection can have more general effects on mitochondrial apoptosis-regulation, through effects on host transcription and other pathways, such as signals controlled by pattern recognition. Some specialized bacteria have products that more specifically regulate signaling to the outer mitochondrial membrane, and to apoptosis; both pro- and anti-apoptotic mechanisms have been reported. Among the intriguing recent findings in this area are signaling contributions of porins and the sub-lethal release of intermembrane constituents. We will here review the literature and place the new developments into the established context of mitochondrial signaling during the contact of bacterial pathogens with human cells.

The expression of RIPK3 is associated with cell turnover of gastric mucosa in the mouse and human stomach

Necroptosis is a novel manner of programmed cell death and important for tissue development, homeostasis, damage, and repair. Activation of receptor-interacting protein kinase 3 (RIPK3), a key member of receptor-interacting protein family in contributing significantly to necroptosis, in tissues is a hallmark of cells dying by necroptosis. However, there are few studies that examine the expression of RIPK3 in the glandular cells of stomachs under physiological condition. We have therefore conducted this study to immunohistochemically characterize the key element of necroptosis, RIPK3, in the mouse and human stomach. Results showed that RIPK3 positive cells could be observed in the surface mucosal cells, granular cells, and lamina propria cells in both mouse and human stomach tissues. Ratios of PCNA/RIPK3 positive cells in the glandular cells were ~ 2.1 in mouse and ~ 4.15 in human sections respectively. Morphological and double immunofluorescence analysis confirmed that these RIPK3 positive cells were mucous, parietal and lamina propria cells. Our results indicate that the expression of RIPK3 in different cell types might contribute to cell turnover of gastric mucosa in the mouse and human stomach under physiological condition.

Bacterial CagA protein compromises tumor suppressor mechanisms in gastric epithelial cells

Approximately half of the world's population is infected with the stomach pathogen Helicobacter pylori. Infection with H. pylori is the main risk factor for distal gastric cancer. Bacterial virulence factors, such as the oncoprotein CagA, augment cancer risk. Yet despite high infection rates, only a fraction of H. pylori-infected individuals develop gastric cancer. This raises the question of defining the specific host and bacterial factors responsible for gastric tumorigenesis. To investigate the tumorigenic determinants, we analyzed gastric tissues from human subjects and animals infected with H. pylori bacteria harboring different CagA status. For laboratory studies, well-defined H. pylori strain B128 and its cancerogenic derivative strain 7.13, as well as various bacterial isogenic mutants were employed. We found that H. pylori compromises key tumor suppressor mechanisms: the host stress and apoptotic responses. Our studies showed that CagA induces phosphorylation of XIAP E3 ubiquitin ligase, which enhances ubiquitination and proteasomal degradation of the host proapoptotic factor Siva1. This process is mediated by the PI3K/Akt pathway. Inhibition of Siva1 by H. pylori increases survival of human cells with damaged DNA. It occurs in a strain-specific manner and is associated with the ability to induce gastric tumor.

Apoptosis induction in gastric mucous cells in vitro: lesser potency of Helicobacter pylori than Escherichia coli lipopolysaccharide, but positive interaction with ibuprofen

Non-steroidal anti-inflammatory drugs (NSAIDs) cause peptic ulcer disease, but whether they interact with Helicobacter pylori to promote damage is controversial. Moreover, the reported induction of apoptosis in gastric cells by H. pylori lipopolysaccharide (LPS) (10—9 g/ml) contrasts with studies showing low immunological potency of this LPS. Therefore, the effects of LPS from H. pylori NCTC 11637 and Escherichia coli O111:B4 on apoptosis in a primary culture of guinea-pig gastric mucous cells were investigated in the presence and absence of the NSAID, ibuprofen. Cell loss was estimated by a crystal violet assay, and apoptosis determined from caspase activity and from condensation and fragmentation of nuclei. Exposure to E. coli LPS for 24 h caused cell loss and enhanced apoptotic activity at concentrations ≥ 10—9 g/ml, but similar effects were only obtained with H. pylori LPS at concentrations ≥ 10— 6 g/ml. Although ibuprofen (250 µM) caused cell loss and apoptosis, addition of either E. coli or H. pylori LPSs further enhanced these effects. In conclusion, LPS and ibuprofen interact to enhance gastric cell loss and apoptosis. In such interactions, E. coli LPS is more potent than that of H. pylori. The low potency of H. pylori LPS may contribute to a chronic low-grade gastritis that can be enhanced by the use of NSAIDs.

bak deletion stimulates gastric epithelial proliferation and enhances Helicobacter felis-induced gastric atrophy and dysplasia in mice

Helicobacter infection causes a chronic superficial gastritis that in some cases progresses via atrophic gastritis to adenocarcinoma. Proapoptotic bak has been shown to regulate radiation-induced apoptosis in the stomach and colon and also susceptibility to colorectal carcinogenesis in vivo. Therefore we investigated the gastric mucosal pathology following H. felis infection in bak-null mice at 6 or 48 wk postinfection. Primary gastric gland culture from bak-null mice was also used to assess the effects of bak deletion on IFN-γ-, TNF-α-, or IL-1β-induced apoptosis. bak-null gastric corpus glands were longer, had increased epithelial Ki-67 expression, and contained fewer parietal and enteroendocrine cells compared with the wild type (wt). In wt mice, bak was expressed at the luminal surface of gastric corpus glands, and this increased 2 wk post-H. felis infection. Apoptotic cell numbers were decreased in bak-null corpus 6 and 48 wk following infection and in primary gland cultures following cytokine administration. Increased gastric epithelial Ki-67 labeling index was observed in C57BL/6 mice after H. felis infection, whereas no such increase was detected in bak-null mice. More severe gastric atrophy was observed in bak-null compared with C57BL/6 mice 6 and 48 wk postinfection, and 76% of bak-null compared with 25% of C57BL/6 mice showed evidence of gastric dysplasia following long-term infection. Collectively, bak therefore regulates gastric epithelial cell apoptosis, proliferation, differentiation, mucosal thickness, and susceptibility to gastric atrophy and dysplasia following H. felis infection.

Triptolide induces apoptosis of gastric cancer cells via inhibiting the overexpression of MDM2

Triptolide has been reported to exhibit antitumor effects in several cancers. This study investigates the mechanism by which triptolide induces apoptosis of gastric cancer cells. Gastric biopsies were collected for histological evaluation and detection of murine double minute 2 (MDM2) expression. Gastric cancer cells were cultured and treated with different concentrations of triptolide at indicated time points. The expression of MDM2, p53 protein, and target proteins including p21, PUMA, and X-linked inhibitor of apoptosis protein (XIAP) was detected. Apoptosis of cells treated with or without triptolide was evaluated. Our results showed that MDM2 protein was overexpressed in gastric cancer (p < 0.01, resp.). Triptolide induced significant apoptosis of gastric cancer cells in a dose- and time-dependent manner (p < 0.05). In addition, treatment with triptolide strongly inhibited the overexpression of MDM2 in gastric cancer cells, and this MDM2 inhibition led to increased levels of p53 protein and inhibition of XIAP (p < 0.05). However, triptolide failed to increase the expression of p53 target protein p21 and PUMA (p > 0.05). In conclusion, triptolide may induce apoptosis of gastric cancer cells via the inhibition of MDM2 overexpression in a p53-independent manner.

Effects of Helicobacter pylori and Heat Shock Protein 70 on the Proliferation of Human Gastric Epithelial Cells

Infection of Helicobacter pylori (H. pylori) changed the proliferation of gastric epithelial cells and decreased the expression of heat shock protein 70 (HSP70). However, the effects of H. pylori on the proliferation of gastric epithelial cells and the roles of HSP70 during the progress need further investigation. Objective. To investigate the effects of Helicobacter pylori (H. pylori) and heat shock protein 70 (HSP70) on the proliferation of human gastric epithelial cells. Methods. H. pylori and a human gastric epithelial cell line (AGS) were cocultured. The proliferation of AGS cells was quantitated by an MTT assay, and the expression of HSP70 in AGS cells was detected by Western blotting. HSP70 expression in AGS cells was silenced by small interfering RNA (siRNA) to investigate the role of HSP70. The siRNA-treated AGS cells were cocultured with H. pylori and cell proliferation was measured by an MTT assay. Results. The proliferation of AGS cells was accelerated by coculturing with H. pylori for 4 and 8 h, but was suppressed at 24 and 48 h. HSP70 expression was decreased in AGS cells infected by H. pylori for 48 h. The proliferation in HSP70-silenced AGS cells was inhibited after coculturing with H. pylori for 24 and 48 h compared with the control group. Conclusions. Coculture of H. pylori altered the proliferation of gastric epithelial cells and decreased HSP70 expression. HSP70 knockdown supplemented the inhibitory effect of H. pylori on proliferation of epithelial cells. These results indicate that the effects of H. pylori on the proliferation of gastric epithelial cells at least partially depend on the decreased expression of HSP70 induced by the bacterium.

Effect of Di(2-ethylhexyl)phthalate on Helicobacter pylori-Induced Apoptosis in AGS Cells

Plastic products are wildly used in human life. Di(2-ethylhexyl)phthalate (DEHP) is an essential additive in plastic manufacturing and is used as plasticizer for many products including plastic food packaging. DEHP is a teratogenic compound and can cause potent reproductive toxicity. DEHP can also cause liver damage, peroxisome proliferation, and carcinogenesis. DEHP is also strongly associated with peptic ulcers and gastric cancer; however, the underlying effect and mechanism of DEHP on the gastrointestinal tract are not entirely clear. The oral infection route of H. pylori parallels the major ingestion route of DEHP into the human body. Therefore, we wanted to study the effect of DEHP and H. pylori exposure on the human gastric epithelial cell line, AGS (gastric adenocarcinoma). The viability of the AGS cell line was significantly lower in 80  μ M-DEHP and H. pylori (MOI = 100 : 1) coexposure than DEHP or H. pylori alone. DEHP and H. pylori coexposure also induced caspase-3 activation, and increased Bax/Bcl-2 ratio and DNA fragmentation in AGS cells. These results indicate that DEHP can enhance H. pylori cytotoxicity and induce gastric epithelial cell apoptosis. Therefore, it is possible that DEHP and H. pylori coexposure might enhance the disruption of the gastric mucosa integrity and potentially promote the pathogenesis of gastric carcinogenesis.

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

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

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

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

Rebamipide abolishes Helicobacter pylori CagA-induced phospholipase D1 expression via inhibition of NFκB and suppresses invasion of gastric cancer cells

Infection with cagA-positive Helicobacter pylori is a risk factor for the development of severe gastritis and gastric cancer (GC). CagA protein is injected into gastric epithelial cells and deregulates a variety of cellular signaling molecules. Phospholipase D (PLD) is elevated in many different types of human cancers and has been implicated as a critical factor in inflammation and carcinogenesis. In this study, we show that infection with cagA-positive H. pylori in GC cells significantly induces PLD1 expression via CagA-dependent activation of nuclear factor κB (NFκB). Interestingly, the level of PLD1 protein and IκBα phosphorylation is aberrantly upregulated in H. pylori-infected human GC tissues. Infection with cagA-positive H. pylori and expression of CagA enhanced the binding of NFκB to the PLD1 promoter, and two functional NFκB-binding sites were identified within the PLD1 promoter. Rebamipide, a mucosal-protective antiulcer agent, abolished H. pylori cagA-induced PLD1 expression via inhibition of binding of NFκB to the PLD1 promoter, and also inhibited PLD activity. Moreover, rebamipide suppressed H. pylori-induced matrix metalloproteinase-9, interleukin-8 and activation-induced cytidine deaminase expression as well as invasion of GC cells through downregulation of PLD1. Our data suggest that H. pylori cagA targets PLD1 for invasion of GC cells, and rebamipide might contribute to the antitumorigenic effect of GC cells via inhibition of the H. pylori cagA-NFκB-PLD1 signaling pathway.

Regulation of RKIP function by Helicobacter pylori in gastric cancer

Helicobacter pylori (H. pylori) is a gram-negative, spiral-shaped bacterium that infects more than half of the world's population and is a major cause of gastric adenocarcinoma. The mechanisms that link H. pylori infection to gastric carcinogenesis are not well understood. In the present study, we report that the Raf-kinase inhibitor protein (RKIP) has a role in the induction of apoptosis by H. pylori in gastric epithelial cells. Western blot and luciferase transcription reporter assays demonstrate that the pathogenicity island of H. pylori rapidly phosphorylates RKIP, which then localizes to the nucleus where it activates its own transcription and induces apoptosis. Forced overexpression of RKIP enhances apoptosis in H. pylori-infected cells, whereas RKIP RNA inhibition suppresses the induction of apoptosis by H. pylori infection. While inducing the phosphorylation of RKIP, H. pylori simultaneously targets non-phosphorylated RKIP for proteasome-mediated degradation. The increase in RKIP transcription and phosphorylation is abrogated by mutating RKIP serine 153 to valine, demonstrating that regulation of RKIP activity by H. pylori is dependent upon RKIP's S153 residue. In addition, H. pylori infection increases the expression of Snail, a transcriptional repressor of RKIP. Our results suggest that H. pylori utilizes a tumor suppressor protein, RKIP, to promote apoptosis in gastric cancer cells.

Helicobacter pylori interferes with an embryonic stem cell micro RNA cluster to block cell cycle progression

BACKGROUND

MicroRNAs, post-transcriptional regulators of eukaryotic gene expression, are implicated in host defense against pathogens. Viruses and bacteria have evolved strategies that suppress microRNA functions, resulting in a sustainable infection. In this work we report that Helicobacter pylori, a human stomach-colonizing bacterium responsible for severe gastric inflammatory diseases and gastric cancers, downregulates an embryonic stem cell microRNA cluster in proliferating gastric epithelial cells to achieve cell cycle arrest.

RESULTS

Using a deep sequencing approach in the AGS cell line, a widely used cell culture model to recapitulate early events of H. pylori infection of gastric mucosa, we reveal that hsa-miR-372 is the most abundant microRNA expressed in this cell line, where, together with hsa-miR-373, it promotes cell proliferation by silencing large tumor suppressor homolog 2 (LATS2) gene expression. Shortly after H. pylori infection, miR-372 and miR-373 synthesis is highly inhibited, leading to the post-transcriptional release of LATS2 expression and thus, to a cell cycle arrest at the G1/S transition. This downregulation of a specific cell-cycle-regulating microRNA is dependent on the translocation of the bacterial effector CagA into the host cells, a mechanism highly associated with the development of severe atrophic gastritis and intestinal-type gastric carcinoma.

CONCLUSIONS

These data constitute a novel example of host-pathogen interplay involving microRNAs, and unveil the couple LATS2/miR-372 and miR-373 as an unexpected mechanism in infection-induced cell cycle arrest in proliferating gastric cells, which may be relevant in inhibition of gastric epithelium renewal, a major host defense mechanism against bacterial infections.

Down-regulation of Bcl-2 is mediated by NF-κB activation in Helicobacter pylori-induced apoptosis of gastric epithelial cells

OBJECTIVE

Bcl-2 family is involved in the regulation of apoptosis. NF-κB activation is associated with either the expression of Bcl-2 or down-regulation of Bcl-2 depending on cell types and stimuli. Previously, we showed NF-κB activation, decrease in the level of Bcl-2, and apoptosis in Helicobacter pylori (H. pylori)-infected gastric epithelial cells. The present study aims to investigate the relation of Bcl-2 expression and NF-κB activation in H. pylori-induced apoptotic cell death of AGS (gastric adenocarcinoma) cells.

MATERIAL AND METHODS

AGS cells were transfected with mutant IκBα to suppress NF-κB activation or Bcl-2 gene to induce overexpression of Bcl-2. mRNA expression of Bcl-2, p53 and Bax, DNA fragmentation, cell viability, and the numbers of apoptotic cells were determined.

RESULTS

H. pylori induced decrease in Bcl-2, but increase in p53 and Bax at the levels of mRNA and protein in AGS cells. H. pylori-induced increment of apoptotic cells and decrease in Bcl-2 level were inhibited in the cells transfected with mutant IκBα gene as compared with the cells transfected with control vector. H. pylori-induced apoptosis determined by apoptotic cells, DNA fragmentation, and cell viability was inhibited in the cells transfected with Bcl-2 gene.

CONCLUSION

Down-regulation of Bcl-2 is mediated by NF-κB activation, which may be the underlying mechanism of apoptosis in H. pylori-infected gastric epithelial cells.

Helicobacter pylori infection generates genetic instability in gastric cells

The discovery that Helicobacter pylori is associated with gastric cancer has led to numerous studies that investigate the mechanisms by which H. pylori induces carcinogenesis. Gastric cancer shows genetic instability both in nuclear and mitochondrial DNA, besides impairment of important DNA repair pathways. As such, this review highlights the consequences of H. pylori infection on the integrity of DNA in the host cells. By down-regulating major DNA repair pathways, H. pylori infection has the potential to generate mutations. In addition, H. pylori infection can induce direct changes on the DNA of the host, such as oxidative damage, methylation, chromosomal instability, microsatellite instability, and mutations. Interestingly, H. pylori infection generates genetic instability in nuclear and mitochondrial DNA. Based on the reviewed literature we conclude that H. pylori infection promotes gastric carcinogenesis by at least three different mechanisms: (1) a combination of increased endogenous DNA damage and decreased repair activities, (2) induction of mutations in the mitochondrial DNA, and (3) generation of a transient mutator phenotype that induces mutations in the nuclear genome.

Surreptitious manipulation of the human host by Helicobacter pylori

Microbial pathogens contribute to the development of more than 1 million cases of cancer per year. Gastric adenocarcinoma is the second leading cause of cancer-related death in the world, and gastritis induced by Helicobacter pylori is the strongest known risk factor for this malignancy. H. pylori colonizes the stomach for years, not days or weeks, as is usually the case for bacterial pathogens and it always induces inflammation; however, only a fraction of colonized individuals ever develop disease. Identification of mechanisms through which H. pylori co-opts host defenses to facilitate its own persistence will not only improve diagnostic and therapeutic modalities, but may also provide insights into other diseases that arise within the context of long-term pathogen-initiated inflammatory states, such as chronic viral hepatitis and hepatocellular carcinoma.

The Expression of Murine Double Minute 2 (MDM2) on Helicobacter pylori-Infected Intestinal Metaplasia and Gastric Cancer

The overexpression of murine double minute 2 (MDM2) is found in several human tumors, and increased expression of MDM2 inactivates the apoptotic and cell cycle arrest function of p53. Interleukin-16 (IL-16) is a pleiotrophic cytokine and the properties of IL-16 suggest that it involve in the pathophysiological process of chronic inflammatory diseases. In this study, we investigated the expression of MDM2 in intestinal metaplasia and gastric cancer as well as the effect of H. pylori infection and IL-16 on epithelial cell proliferation and MDM2 expression in gastric cells in vitro. The expression of MDM2 on gastric biopsies was studied immunohistochemistry. AGS cells were incubated with a combination of IL-16 and Helicobacter pylori (H. pylori). Gastric epithelial cell proliferation was studied by BrdU uptake and the expressions of MDM2 were studied by ELISA. There was no significant difference on the expression of MDM2 between with and without H. pylori infected chronic gastritis. In H. pylori infected gastric mucosa; the MDM2 expression was higher on intestinal metaplasia and gastric cancer than chronic gastritis. IL-16 administration was increased MDM2 expression and cell proliferation on AGS cells, which was decreased by H. pylori infection. In conclusion, the expression of MDM2 in long-term H. pylori infected gastric mucosa may indicate a risk for carcinogenesis. IL-16 secretion in H. pylori infected mucosa is one of the factors for gastric cancer. The expression of MDM2 on mucosa can be a mediator for gastric cancer.

H. pylori-induced apoptosis in human gastric cancer cells mediated via the release of apoptosis-inducing factor from mitochondria

BACKGROUND AND AIM

Our previous study of Helicobacter pylori-induced apoptosis showed the involvement of Bcl-2 family proteins and cytochrome c release from mitochondria. Here, we examine the release of other factors from mitochondria, such as apoptosis-inducing factor (AIF), and upstream events involving caspase-8 and Bid.

METHODS

Human gastric adenocarcinoma (AGS) cells were incubated with a cagA-positive H. pylori strain for 0, 3, 6, and 24 hours and either total protein or cytoplasmic, nuclear, and mitochondrial membrane fractions were collected.

RESULTS

Proteins were immunoblotted for AIF, Bid, polyadenosine ribose polymerase (PARP), caspase-8, and beta-catenin. H. pylori activated caspase-8, caused PARP cleavage, and attenuated mitochondrial membrane potential. A time-dependent decrease in beta-catenin protein expression was detected in cytoplasmic and nuclear extracts, coupled with a decrease in beta-actin. An increase in the cytoplasmic pool of AIF was seen as early as 3 hours after H. pylori exposure, and a concomitant increase was seen in nuclear AIF levels up to 6 hours. A band corresponding to full-length Bid was seen in both the cytoplasmic and the nuclear fractions of controls, but not after H. pylori exposure. Active AIF staining was markedly increased in gastric mucosa from infected persons, compared to uninfected controls.

CONCLUSION

H. pylori might trigger apoptosis in AGS cells via interaction with death receptors in the plasma membrane, leading to the cleavage of procaspase-8, release of cytochrome c and AIF from mitochondria, and activation of subsequent downstream apoptotic events, as reported previously for chlorophyllin. This is consistent with AIF activation that was found in the gastric mucosa of humans infected with H. pylori. Hence, the balance between apoptosis and proliferation in these cells may be altered in response to injury caused by H. pylori infection, leading to an increased risk of cancer.

Advance in research of genes associated with peptic ulcer

At present, studies about peptic ulcer have developed from cellular level to molecular level. More and more genes associated with peptic ulcer have been discovered, including human leukocyte antigen (HLA) genes, epidermal growth factor (EGF) genes, apoptosis-associated genes, calcitonin genes and trefoil peptide genes. These genes play important roles in the development and healing of peptic ulcer, providing theoretical basis for clinical diagnosis and cure of peptic ulcer.

Evaluation of apoptosis induction using PARP cleavage on gastric adenocarcinoma and fibroblast cell lines by different strains of Helicobacter pylori

Helicobacter pylori is one of the most common pathogens affecting humans and is the major environmental factor in the development of gastric cancer increasing from 4 to 6 folds the risk of its development. Variations in cancer risk among H. pylori infected individuals may correlate to difference in H. pylori strains, variable host characteristics and specific interactions between host and microbial determinants. To determine the effect of different strains of H. pylori on cellular apoptosis this study was designed an in vitro model using AGS and HEF cell lines. After specified time intervals total cell proteins was extracted and subjected to SDS-PAGE and immunoblotting using anti poly ADP-ribose polymerase (PARP) antibody. Decrease in densitometric value of PARP was indicative of higher level of apoptosis. The ability of apoptosis induction in AGS and HEF cell lines by wild type (cagA+/vacA+), cagA-/vacA+, vacA-/cagA+ and double negative (cagA-/vacA-) strains were significantly different. The assessed apoptosis in AGS cell line co-cultured with wild type strain was 3.22 +/- 0.2 in 24 h, 2.8 +/- 0.1 in 48 and 2.1 +/- 0.09 in 72 h of incubation time. Similar assessment with cagA-/vacA+ strains in AGS cells was 4.17 +/- 1.49 in 24 h, 3.32 +/- 0.45 in 48 h and 2.32 +/- 0.61 in 72 h incubation. A variation in apoptotic potential between the H. pylori strains on two cells (AGS and HEF) was observed. Based on present results, it is concluded that H. pylori strains as well as target cell types are important in pathogenesis and induction of apoptosis during a specified time interval.

Radiation-induced gastric epithelial apoptosis occurs in the proliferative zone and is regulated by p53, bak, bax, and bcl-2

Unlike the small intestine and colon where gamma-radiation-induced apoptosis has previously been well characterized, the response of murine gastric epithelium to gamma-radiation has not been investigated in detail. Apoptosis was therefore assessed on a cell positional basis in gastric antral and corpus glands from adult male mice following gamma-radiation. Maximum numbers of apoptotic cells were observed in both antrum and corpus at 48 h and at radiation doses greater than 12 Gy. However, the number of apoptotic cells observed in the gastric epithelium was much lower than observed in the small intestine or colon after similar doses of radiation. Hematoxylin and eosin, caspase 3 immunohistochemistry, and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling detected similar numbers and cell positional distributions of apoptotic cells, hence hematoxylin and eosin was used for subsequent studies. The highest numbers of apoptotic cells were observed at cell positions 5-6 in the antrum and cell positions 15-18 in the corpus. These distributions coincided with the distributions of PCNA-labeled proliferating cells, but not with the distributions of H(+)-K(+)-ATPase-labeled parietal cells or TFF2-labeled mucous neck cells. Decreased numbers of apoptotic gastric epithelial cells were observed in p53-null, bak-null, and bax-null mice compared with wild-type counterparts 6 and 48 h after 12 Gy gamma-radiation. Significantly increased numbers of apoptotic gastric epithelial cells were observed in bcl-2-null mice compared with wild-type littermates 6 h after 12 Gy gamma-radiation. Radiation therefore induces apoptosis in the proliferative zone of mouse gastric epithelium. This response is regulated by the expression of p53, bak, bax, and bcl-2.

Apoptosis in Helicobacter pylori gastritis is related to cagA status

BACKGROUND

Helicobacter pylori infection increases gastric epithelial cell apoptosis; however, the influence of cagA status is still controversial. We aimed to investigate if cagA status is related to apoptosis in H. pylori gastritis at different anatomic sites of the gastric mucosa.

MATERIALS AND METHODS

We studied by immunohistochemistry (streptavidin-biotin method) pro-apoptotic (Bax and Bak) and antiapoptotic (Bcl-2 and Bcl-x) proteins expression, scored from 0 to 4, in gastric biopsies, at the antrum (lesser and greater curvatures), incisura, and corpus (greater curvature) from 50 patients with H. pylori gastritis (22 males, 28 females, median age 40 years) and eight non-infected patients (6 males, median age 39.6 years). H. pylori and cagA status were determined by polymerase chain reaction.

RESULTS

Apoptotic proteins were expressed in a granular pattern, in the cytoplasm of foveolar cells; Bax and Bak expression was higher than Bcl-2 and Bcl-x in most cases and was significantly higher in patients infected by cagA-positive strains than in those infected by cagA-negative strains (p = .001). Bak expression was higher at the lesser curvature (antrum and incisura) than in the other regions (p = .002) and was correlated with atrophy. Anti-apoptotic proteins were significantly more expressed at the antral lesser curvature than in the other regions of the stomach (Bcl-2: p = .02; Bcl-x: p < .001).

CONCLUSIONS

Infection with cagA-positive strains is significantly associated with overexpression of pro-apoptotic proteins in the gastric mucosa, mainly at the antral lesser curvature, which may have a role on atrophy development. Anti-apoptotic proteins were also overexpressed at the lesser curvature, which may occur to keep epithelial cell turnover or might be related to malignant transformation.

Effects of Helicobacter pylori infection on gastric epithelial cell kinetics in patients with chronic renal failure

AIM

To evaluate the effects of Helicobacter pylori infection on gastric epithelial cell kinetics in patients with chronic renal failure (CRF).

METHODS

Forty-four patients were enrolled in this study and divided into four groups with respect to their Helicobacter pylori (H pylori) and CRF status. Groups were labeled as follows: 1a: normal renal function, H pylori negative (n = 12), 1b: normal renal function, H pylori positive (n = 11), 2a: CRF, H pylori negative (n = 10), 2b: CRF, H pylori positive (n = 11). Upper gastrointestinal endoscopy was done in all the patients involved in the study. During endoscopical investigation, antral biopsy specimens were taken from each patient. In order to evaluate the cell apoptosis and proliferation in gastric epithelial cells, Bax and proliferating cell nuclear antigen (PCNA) labeling indexes (LI) were assessed with immunohistochemical staining method.

RESULTS

For groups 1a, 1b, 2a, and 2b, mean Bax LI was identified as 34.4+/-13.7, 44.1+/-16.5, 46.3+/-20.5, 60.7+/-13.8, respectively and mean PCNA LI was identified as 36.2+/-17.2, 53.6+/-25.6, 59.5+/-25.6, 67.2+/-22, respectively. When the one-way ANOVA test was applied, statistically significant differences were detected between the groups for both Bax LI (P = 0.004 <0.01) and PCNA LI (P = 0.009 <0.01). When groups were compared further in terms of Bax LI and PCNA LI with Tukeyos HSD test for multiple pairwise comparisons, statistically significant difference was observed only between groups 1a and 2b (P = 0.006 <0.01).

CONCLUSION

In gastric epithelial cells, expression of both the pre-apoptotic protein Bax and the proliferation marker PCNA increase with H pylori infection. This increase is more evident in patients with uremia. These findings suggest that uremia accelerates apoptosis and proliferation in gastric epithelial cells.

Major histocompatibility complex class II inhibits fas antigen-mediated gastric mucosal cell apoptosis through actin-dependent inhibition of receptor aggregation

Escape from normal apoptotic controls is thought to be essential for the development of cancer. During Helicobacter pylori infection, the leading cause of gastric cancer, activation of the Fas antigen (Fas Ag) apoptotic pathway is responsible for early atrophy and tissue loss. As disease progresses, metaplastic and dysplastic glands arise which express Fas Ag but are resistant to apoptosis and are believed to be the precursor cells for adenocarcinoma. In this report, we show that one mechanism of acquired Fas resistance is inhibition of receptor aggregation via a major histocompatibility complex class II (MHCII)-mediated, actin-dependent mechanism. For these studies we used the well-described C57BL/6 mouse model of Helicobacter pylori and Helicobacter felis infection. Under normal conditions, Fas Ag is expressed at low levels, and MHCII expression on gastric mucosal cells is negligible. With infection and inflammation, both receptors are upregulated, and 6.1% of gastric mucosal cells express MHCII in combination with Fas Ag. Using the rat gastric mucosal cell line RGM-1 transfected with murine Fas Ag and MHCIIalphabeta chains, we demonstrate that MHCII prevents Fas receptor aggregation and inhibits Fas-mediated signaling through its effects on the actin cytoskeleton. Depolymerization of actin with cytochalasin D allows receptors to aggregate and restores Fas sensitivity. These findings offer one mechanism by which gastric mucosal cells acquire Fas resistance.

Interleukin-8 regulates expression of Reg protein in Helicobacter pylori-infected gastric mucosa

BACKGROUND & AIM

Chronic inflammation induced by Helicobacter pylori infection is closely associated with epithelial cell proliferation and apoptosis, which are related to cellular turnover in gastric mucosa. Reg protein is a regenerating gene product and a potent growth factor for gastric mucosal cells, however, little is known regarding its association with the pathogenesis of H. pylori infection. The aim of this study was to investigate Reg protein production and its regulation in H. pylori-associated gastritis.

METHODS

Gastric fundic biopsy samples were taken from patients with and without H. pylori infection. In vivo expression of Reg protein was examined by Western blotting and immunohistochemistry methods. The effects of interleukin (IL)-8 on Reg protein expression and transcriptional activation of the Reg gene in ECC10 cells were investigated by Western blotting and luciferase assays, respectively.

RESULTS

Reg expression was found localized in the deeper part of gastric fundic glands and clearly shown in chromogranin A-positive cells in the gastric corpus. Semiquantitative immunohistochemistry and Western blotting results for Reg expression were significantly associated with polymorphonuclear neutrophil activity and chronic inflammation of gastric mucosa. IL-8 production in the gastric mucosa was significantly augmented by H. pylori infection, while IL-8 dose-dependently stimulated Reg protein production and Reg promoter activity in vitro in cultured ECC10 cells.

CONCLUSION

The present study showed for the first time that Reg protein may be a potent stimulator of gastric epithelial cells in H. pylori-infected human gastric mucosa stimulated by IL-8. Further, our findings provide evidence of a novel link between Reg protein and H. pylori infection, which may help explain the molecular mechanisms underlying H. pylori-associated diseases, including gastric cancer.

Human alphaA- and alphaB-crystallins bind to Bax and Bcl-X(S) to sequester their translocation during staurosporine-induced apoptosis

AlphaA- and alphaB-crystallins are distinct antiapoptotic regulators. Regarding the antiapoptotic mechanisms, we have recently demonstrated that alphaB-crystallin interacts with the procaspase-3 and partially processed procaspase-3 to repress caspase-3 activation. Here, we demonstrate that human alphaA- and alphaB-crystallins prevent staurosporine-induced apoptosis through interactions with members of the Bcl-2 family. Using GST pulldown assays and coimmunoprecipitations, we demonstrated that alpha-crystallins bind to Bax and Bcl-X(S) both in vitro and in vivo. Human alphaA- and alphaB-crystallins display similar affinity to both proapoptotic regulators, and so are true with their antiapoptotic ability tested in human lens epithelial cells, human retina pigment epithelial cells (ARPE-19) and rat embryonic myocardium cells (H9c2) under treatment of staurosporine, etoposide or sorbitol. Two prominent mutants, R116C in alphaA-crystallin and R120G, in alphaB-crystallin display much weaker affinity to Bax and Bcl-X(S). Through the interaction, alpha-crystallins prevent the translocation of Bax and Bcl-X(S) from cytosol into mitochondria during staurosporine-induced apoptosis. As a result, alpha-crystallins preserve the integrity of mitochondria, restrict release of cytochrome c, repress activation of caspase-3 and block degradation of PARP. Thus, our results demonstrate a novel antiapoptotic mechanism for alpha-crystallins.

Roles of Helicobacter pylori infection and cyclooxygenase-2 expression in gastric carcinogenesis

AIM: Cyclooxygenase (COX)-2 is over expressed in gastrointestinal neoplasm. Helicobacter pylori (H pylori) infection is causally linked to gastric cancer. However, the expression of COX-2 in various stages of H pylori-associated gastric carcinogenesis pathway has not been elucidated. Therefore, the aim of this study was to clarify the role of H pylori induced COX-2 expression during carcinogenesis in the stomach.

METHODS: Gastric biopsies from 138 subjects [30 cases of chronic superficial gastritis (CSG), 28 cases of gastric glandular atrophy (GA), 45 cases of gastric mucosal intestinal metaplasia (IM), 12 cases of moderate gastric epithelial dysplasia and 23 cases of gastric cancer] were enrolled. H pylori infection was assessed by a rapid urease test and histological examination (modified Giemsa staining). The expression of COX-1 and COX-2 in human gastric mucosa was detected by immunohistochemical staining.

RESULTS: H pylori infection rate was 64.3% in GA and 69.5% in gastric cancer, which was significantly higher than that (36.7%) in CSG (P < 0.05). The positive expression rates of COX-2 were 10.0%, 35.7%, 37.8%, 41.7% and 69.5% in CSG, GA, IM, dysplasia and gastric cancer, respectively. From CSG to GA, IM, dysplasia and finally to gastric cancer, expression of COX-2 showed an ascending tendency, whereas COX-1 expression did not change significantly in the gastric mucosa. The level of COX-2 expression in IM and dysplasia was significantly higher in H pylori-positive than in H pylori-negative subjects (P < 0.01).

CONCLUSION: COX-2 expression induced by H pylori infection is a relatively early event during carcinogenesis in the stomach.

Induction of apoptosis and expression of apoptosis related genes in human epithelial carcinoma cells by Helicobacter pylori VacA toxin

Virulence factors produced by Helicobacter pylori have been known to be associated with serious gastroduodenal diseases. The aims of this study were to clarify the apoptosis-inducing properties of vacuolating cytotoxin (VacA) and examine the expression of apoptosis related proteins in human epithelial carcinoma cells expressing (AGS) or lacking (Kato III) p53. The midregion VacA homolog from H. pylori strain Q35 (Korean isolate) was cloned, expressed and sequenced. Recombinant VacA (VacA(418-799)) inhibited cell growth and induced apoptosis in gastric epithelial cells. Treatment with VacA(418-799) resulted in morphological changes and DNA fragmentation. Cell cycle analysis revealed subdiploid cells suggesting apoptosis, which was confirmed by the activation of caspase-3 and cleavage of PARP. VacA(418-799) also mediated a prolongation of the cell cycle progression in G1 phase. Furthermore, VacA(418-799) increased the expression of p53, p21(waf1/cip1) and Bax in AGS cells, but not in Kato III cells and did not affect the phosphorylation of Rb in both cell lines. These results indicate that recombinant VacA of H. pylori induces apoptosis in both Kato III and AGS cells, regardless of p53 status and suggest that VacA(418-799) mediate the development of gastric diseases through cell cycle arrest in the G1 phase. VacA(418-799) induction of apoptosis is associated with up-regulation of p53, p21(waf1/cip1), Bax in AGS cells and activation of caspase-3 in both cell lines.

Helicobacter pylori supernatants cause epithelial cytoskeletal disruption that is bacterial strain and epithelial cell line dependent but not toxin VacA dependent

We show here that Helicobacter pylori broth culture supernatants disrupt the actin cytoskeleton of epithelial cell lines, leading to cell rounding and apoptosis through anoikis. We demonstrate that there are marked quantitative differences between strains and that there are different cell line sensitivities. By constructing VacA null isogenic mutants, we show that the effect is not due to the vacuolating cytotoxin.

Effect of inhibition of extracellular signal-regulated kinase 1 and 2 pathway on apoptosis and bcl-2 expression in Helicobacter pylori-infected AGS cells

Helicobacter pylori induces activation of mitogen-activated protein kinases (MAPKs). However, its effect on H. pylori-induced apoptosis has not been evaluated. Thus, we examined whether H. pylori-induced extracellular signal-regulated kinase 1 and 2 (ERK1/2) and p38 MAPK activation affects gastric epithelial cell apoptosis and bcl-2 family gene expression, especially in relation to the cagA status of an H. pylori strain. In flow cytometric and oligonucleosome-bound DNA enzyme-linked immunosorbent assay analyses, infection with cagA(+) H. pylori strains induced gastric cancer cell apoptosis in AGS cells more prominently than infection with cagA mutants. Activation of ERK1/2 and p38 MAPKs was also more prominent in cagA(+) strains. Pretreatment with a MEK inhibitor (PD98059) inhibited ERK1/2 activation and increased H. pylori-induced apoptosis significantly. This increased apoptosis was accompanied by decreased antiapoptotic bcl-2 mRNA expression among bcl-2-related genes (bcl-2, bax, bak, mcl-1, and bcl-X(L/S)), and the effect was also more prominent in the cagA(+) strains. However, the alteration of bcl-2 gene expression was not accompanied by protein level changes. Inhibition of p38 using specific inhibitor SB203580 decreased H. pylori-induced apoptosis but resulted in little alteration of bcl-2-related gene expression. In conclusion, H. pylori-induced ERK1/2 activation, especially by the cagA(+) H. pylori strain, may play a protective role against gastric epithelial cell apoptosis partially through maintenance of bcl-2 gene expression.

Effect of Helicobacter pylori on apoptosis and apoptosis related genes in gastric cancer cells

BACKGROUND/AIMS

Helicobacter pylori induces the apoptosis of gastric epithelial cells in vivo and in vitro. However, the molecular mechanism has not been clarified. The aim of this study was to investigate the effect of H pylori on the apoptosis of gastric epithelial cells and the expression of apoptosis related genes in vitro.

METHODS

Human gastric adenocarcinoma SGC-7901 cells were co-cultured with a cytotoxic H pylori strain, NCTC 11637, at various densities ranging from 3.2 x 10(4) to 1.0 x 10(8) colony forming units (CFU)/ml for 48 hours. Apoptosis in gastric cells was determined by transmission electron microscopy, Hoechst 33258 fluorochrome staining, and flow cytometry. The expression of apoptosis related proteins, Bcl-2, Bax, and c-Myc, was measured by an immunohistochemical method, and c-Myc mRNA expression was determined by the reverse transcription-polymerase chain reaction.

RESULTS

Helicobacter pylori induces morphological changes typical of apoptosis. Both fluorochrome staining and flow cytometry showed that the apoptotic index began to increase when H pylori were at a density of > 1.6 x 10(4) CFU/ml, and in a density dependent manner (p < 0.01; one way ANOVA). The expression of the Bax and c-Myc proteins and of c-Myc mRNA was increased, whereas Bcl-2 expression was decreased after co-culture for 48 hours.

CONCLUSIONS

Helicobacter pylori induced apoptosis in gastric epithelial cells is mediated by altered expression of the products of the Bcl-2, Bax, and c-Myc genes.

A novel apoptosis-inducing protein from Helicobacter pylori

Helicobacter pylori infection induces apoptosis in gastric epithelial cells. Here, we report a novel apoptosis-inducing protein that functions as a leading factor in H. pylori-mediated apoptosis induction. We purified the protein from H. pylori by separating fractions that showed apoptosis-inducing activity. This protein induced apoptosis of AGS cells in a dose-dependent manner. The purified protein consisted of two protein fragments with molecular masses of about 40 and 22 kDa, which combined to constitute a single complex in their natural form. N-terminal sequencing indicated that both these protein fragments were encoded by the HP1118 gene. The purified protein exhibited gamma-glutamyl transpeptidase activity, the inhibition of which by 6-diazo-5-oxo-l-norleucine resulted in a complete loss of apoptosis-inducing activity. To the best of our knowledge, the apoptosis-inducing function is a newly identified physiological role for bacterial gamma-glutamyl transpeptidase. The apoptosis-inducing activity of the isogenic mutant gamma-glutamyl transpeptidase-deficient strain was significantly lower compared with that of the parent strain, demonstrating that gamma-glutamyl transpeptidase plays a significant role in H. pylori-mediated apoptosis. Our findings provide new insights into H. pylori pathogenicity and reveal a novel aspect of the bacterial gamma-glutamyl transpeptidase function.

Topographic association of gastric epithelial expression of Ki-67, Bax, and Bcl-2 with antralization in the gastric incisura, body, and fundus

OBJECTIVES

Helicobacter pylori (H. pylon) infection seems to induce antralization (ie., gastric mucosal transformation from transitional or body type to antral type), which is strongly associated with gastric atrophy and intestinal metaplasia. The aim of this study was to determine the topographic associations of Ki-67 (a protein expressed in proliferative cells), Bax (a pro-apoptotic protein), and Bcl-2 (an antiapoptotic protein) expression with antralization.

METHODS

In each of 104 patients, eight biopsy specimens were taken from the gastric antrum, incisura, body, and fundus for the determination of H. pylori infection, histological changes, and epithelial expression of Ki-67, Bax, and Bcl-2. A labeling index (LI), i.e., the rate of positive cells over total cells counted, was used for Ki-67 and Bax expression. Bcl-2 overexpression was considered to be present if the rate of Bcl-2 positive cells over total cells counted was > or = 5%.

RESULTS

H. pylori infection was present at the gastric antrum, incisura, body, and fundus in 50, 48, 51, and 49 patients, respectively. Ki-67 LI was greater in the presence vs absence) of H. pylori infection at the antrum (51 vs 40), incisura (47 vs 36), body (43 vs 30), and fundus (41 vs 31) (all p < 0.001). At the incisura, Ki-67 LI was greater (47 vs 32, p < 0.001), Bax LI was lower (22 vs 30, p < 0.05), and prevalence of Bcl-2 overexpression was higher (44% vs 18%, p < 0.001) in the presence (vs absence) of antralization. Compared with normal mucosa, gastric atrophy/intestinal metaplasia were associated with an increased Ki-67 LI and decreased Bax LI at the antrum (49 vs 32 and 15 vs 23, respectively), incisura (47 vs 32 and 15 vs 26, respectively) (all p < 0.001). Bcl-2 overexpression was more frequent in gastric atrophy/intestinal metaplasia at the antrum (56% vs 11%, p < 0.001) and incisura (63% vs 19%, p < 0.001) compared with normal mucosa.

CONCLUSIONS

Antralization at the incisura is topographically associated with increased cell proliferation, reduced Bax expression, and Bcl-2 overexpression, which implies that antralization may be an important histological marker for future cancer risk.

Analysis of apoptotic and antiapoptotic signalling pathways induced by Helicobacter pylori

BACKGROUND AND AIMS

Although it is reported that Helicobacter pylori induces apoptosis on gastric epithelial cells, the mechanism remains unknown. Antiapoptotic effects generated by H pylori have not yet been evaluated.

METHODS

(1) H pylori strains (type 1 wild, TN2-deltacagE, TN2-deltavacA) were cocultured with MKN45, TMK1, and HeLa cells, and cell viability and apoptosis were assessed by trypan blue exclusion and DNA laddering, respectively. (2) Activation of caspases-3, 7, and 8, cytochrome c release from the mitochondria, and Fas, Fas associated death domain protein (FADD), Bax, Bak, and Bcl-X expression were evaluated by immunoblot analysis. (3) To investigate whether nuclear factor kappa B (NFkappaB) activation induced by cag pathogenicity island (PAI) positive H pylori affects antiapoptosis, MKN45 cells stably expressing super-repressor IkappaBalpha were cocultured with H pylori, and cell viability and caspase activation were evaluated. NFkappaB regulated gene expression was also evaluated by ribonuclease protection assay.

RESULTS

(1) Wild-type and deltavacA mutant H pylori induced apoptosis more potently than the deltacagE mutant. Inhibition of cell contact between H pylori and cancer cells and heat killing H pylori diminished cell death. (2) Caspases-3, 7, and 8 were activated time dependently by H pylori as well as by the agonist anti-Fas. Cytochrome c release from mitochondria was observed and was not inhibited by caspase-8 inhibitor. Although protein expression of Fas, FADD, Bax, Bak, and Bcl-X in the whole cell lysates was not changed by H pylori, Bax was decreased from mitochondria free cytosol suggesting that Bax was translocated into mitochondria. (3) Cell death and the activities of caspases-3 and 8 were promoted in MKN45 cells stably expressing super-repressor IkappaBalpha that inhibits NFkappaB activation. Antiapoptotic proteins c-IAP1 and c-IAP2 were upregulated by the wild-type strains.

CONCLUSION

cag PAI positive H pylori is capable of inducing apoptotic effects mainly through the mitochondrial pathway. Antiapoptotic effects mediated by NFkappaB activation were also observed.

In vivo and in vitro activation of caspase-8 and -3 associated with Helicobacter pylori infection

In vivo and in vitro studies have shown an increase in apoptosis in gastric epithelial cells in persons infected with Helicobacter pylori. H. pylori-induced activation of caspase-8 and -3 was evaluated using a human gastric adenocarcinoma cell line (AGS) and gastric tissue from humans and monkeys colonized with H. pylori. The enzymatic activity of caspase-8 was detected only in AGS cells exposed to H. pylori up to 24 h. The active form of caspase-8 was present by Western blot after exposure to H. pylori for 3 h and persisted through 24 h. Caspase-3 activity was present in AGS cells exposed to H. pylori for 3 h, reaching a maximum after 24 h (a sevenfold increase in activity). Caspase-8-mediated cleavage of procaspase-3 generated a 20-kDa band (indicative of the presence of active caspase-3) present only in AGS cells exposed to H. pylori. Active caspase-3 staining was markedly increased in gastric mucosa from infected persons and animals, compared to uninfected controls by immunohistochemistry. Stimulation of downstream events leading to apoptosis, such as the cleavage of PARP (poly adenosine-diphosphate-ribose polymerase) and DFF45 (DNA fragmentation factor 45) as a result of activation of caspase-3, was evaluated. PARP was cleaved, resulting in the presence of both an 89- and a 24-kDa band along with DFF45, resulting in the presence of 10- and 12-kDa bands only in gastric cells exposed to H. pylori. Our data show that H. pylori stimulates the activation of caspases and downstream mediators of caspase-induced apoptosis. This suggests that H. pylori-induced apoptosis is mediated through caspase pathways, which include the activation of caspase-8 and subsequent cleavage and activation of caspase-3. This is consistent with caspase-3 activation that was found in the gastric mucosa of humans and monkeys infected with H. pylori.

Role of Helicobacter pylori and p53 in regulation of gastric epithelial cell cycle phase progression

H. pylori disrupts gastric mucosal homeostasis by altering gastric epithelial cell cycle distribution, and this may contribute to the diverse disease outcomes associated with this infection. The effect of H. pylori on gastric epithelial cells and the role of p53 were assessed in this study by incubating H. pylori strains with gastric epithelial cells. During a 72-hr coincubation, H. pylori induced a time- and dose-dependent inhibition of cell growth and induction of apoptosis. However, at low inocula, H. pylori stimulates cell DNA synthesis compared to untreated controls. Although there was no difference in the induction of AGS cell line apoptosis and cell proliferation between cells exposed to cagA+/vacA+ and cagA-/vacA- strains, an interstrain variation on H. pylori-induced cell cycle events was noted. Serum starvation enhanced the sensitivity of gastric epithelial cells to H. pylori-induced apoptosis. H. pylori induced apoptosis in all the cell lines regardless of their p53 status, but cells with wild-type p53 had higher apoptosis rates. Therefore, bacterial density, diversity, local nutrient levels, and host cell p53 status may contribute to the regulation of H. pylori-induced cell cycle events.

T cell-mediated cytotoxicity via Fas/Fas ligand signaling in Helicobacter pylori-infected gastric corpus

BACKGROUND

Helicobacter pylori infection induces T helper-1 immune responses in inflamed mucosa. However, the role of T cell-mediated cytotoxicity in the induction of epithelial apoptosis is still unclear. The aim of this study was to investigate the involvement of the Fas/Fas ligand (Fas/Fas-L) system in the H. pylori-infected gastric corpus.

MATERIALS AND METHODS

Gastric fundic biopsy specimens were taken from patients with and without H. pylori infection. The expression of Fas and Fas-L was examined by immunohistochemistry and RT-PCR. Subsets of gastric infiltrating T cells in the biopsy specimens were studied by immunohistochemistry and flow cytometry. In histological sections, apoptosis was detected by the TUNEL method. We studied the in vitro expression of Fas-L in peripheral T cells after stimulation with H. pylori antigen and interferon-gamma (IFN-gamma). The Fas-mediated in vitro cytotoxicity of activated T cells was assessed by flow cytometry.

RESULTS

The numbers of CD4+ and CD8+ T cells were greater in H. pylori-infected subjects. Fas expression was abundantly increased on fundic gland epithelium, and Fas-L was detected on lamina propria mononuclear cells in H. pylori-infected mucosa. TUNEL-positive epithelial cells were also increased in H. pylori-infected subjects. H. pylori antigen and IFN-gamma induced Fas-L mRNA expression in both CD4+ and CD8+ T cells. In cytotoxic assay, activated T cells induced apoptosis in AGS cells, which could be significantly inhibited by neutralizing Fas-L antibody.

CONCLUSIONS

T cell-mediated cytotoxicity via Fas/Fas-L signaling may contribute to the induction of apoptosis in gastric epithelial cells during H. pylori infection.

Caspase-3 activity and expression of Bcl-2 family in human neutrophils by Helicobacter pylori water-soluble proteins

BACKGROUND

Persistent infiltration of neutrophils is an almost invariable feature of Helicobacter pylori-infected gastric mucosa. A prolongation of neutrophil life-span could contribute to the pathogenesis of H. pylori infection. Recently, we have demonstrated that H. pylori water extracts (HPWE) inhibited neutrophil apoptosis. To elucidate the regulation of intracellular apoptotic signals by HPWE, we examined the activity of caspase-8, -3 and expression of Bcl-2 family in neutrophils.

MATERIALS AND METHODS

Human neutrophils were obtained from the peripheral blood of healthy volunteers by density gradient separation. HPWE was prepared from a supernatant of the H. pylori suspension in distilled water. After neutrophils were incubated with HPWE, expression of Bcl-2 family [antiapoptotic (Bcl-2, Bcl-XL and Mcl-1) and proapoptotic (Bax, Bak and Bcl-XS)] was determined by RT-PCR and Western blotting, respectively. Western blot for Bcl-2 family also performed in neutrophilic differentiated HL-60 cells by all-trans-retinoic acid. The activity of caspase-8, -3 was measured by the detection of p-nitroanilide after cleavage from labeled substrate.

RESULTS

HPWE suppressed the activation of caspase-8 and -3, and upregulated the expression of Bcl-XL mRNA and proteins in neutrophils. The expression of Bax and Bak was upregulated and Bcl-2, Bcl-XL and Mcl-1 downregulated in HL-60 cells during neutrophilic differentiation.

CONCLUSION

Bcl-XL may have an important role in the neutrophilic development and inhibition of neutrophil apoptosis by H. pylori.

Activation of peroxisome proliferator-activated receptor gamma suppresses nuclear factor kappa B-mediated apoptosis induced by Helicobacter pylori in gastric epithelial cells

Helicobacter pylori colonization leads to epithelial cell hyperproliferation within inflamed mucosa, but levels of apoptosis vary, suggesting that imbalances between rates of cell production and loss may contribute to differences in gastric cancer risk among infected populations. Peroxisome proliferator-activated receptor gamma (PPARgamma) regulates inflammatory and growth responses of intestinal epithelial cells. We determined whether activation of PPARgamma modified H. pylori-induced apoptosis in gastric epithelial cells. PPARgamma was expressed and functionally active in gastric epithelial cell lines sensitive to H. pylori-induced apoptosis. PPARgamma ligands 15d-PGJ(2) and BRL-49653 significantly attenuated H. pylomicronri-induced apoptosis, effects that could be reversed by co-treatment with a specific PPARgamma antagonist. Cyclopentanone prostaglandins that do not bind and activate PPARgamma had no effects on H. pylori-induced apoptosis. The ability of H. pylori to activate nuclear factor (NF)-kappaB and increase levels of the NF-kappaB target IL-8 was blocked by co-treatment with PPARgamma agonists, and direct inhibition of NF-kappaB also abolished H. pylori-stimulated apoptosis. These results suggest that activation of the PPARgamma pathway attenuates the ability of H. pylori to induce NF-kappaB-mediated apoptosis in gastric epithelial cells. Because PPARgamma regulates a multitude of host responses, activation of this receptor may contribute to varying levels of cellular turnover as well as the diverse pathologic outcomes associated with chronic H. pylori colonization.

Effects of nonsteroidal anti-inflammatory drugs on Helicobacter pylori-infected gastric mucosae of mice: apoptosis, cell proliferation, and inflammatory activity

Helicobacter pylori and nonsteroidal anti-inflammatory drugs (NSAIDs) are two well-known important causative factors of gastric damage. While H. pylori increases apoptosis and the proliferation of gastric epithelial cells and is an important factor in peptic ulcer and gastric cancer, NSAIDs induce cell apoptosis and have antineoplastic effects. We investigated the effects of NSAIDs (a nonselective cyclooxygenase [COX] inhibitor [indomethacin] and a selective COX-2 inhibitor [NS-398]) on the apoptosis and proliferation of gastric epithelial cells and gastric inflammation in H. pylori-infected mice. C57BL/6 mice were sacrificed 8 weeks after H. pylori SS1 inoculation. Indomethacin (2 mg/kg) or NS-398 (10 mg/kg) was administered subcutaneously once daily for 10 days before sacrifice. The following were assessed: gastric inflammatory activity, gastric COX protein expression by Western blotting; gastric prostaglandin E(2) levels by enzyme immunoassay, apoptosis by terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling, and cell proliferation by Ki67 immunostaining. Compared to the controls, H. pylori infection and/or NSAID treatment increased COX-1 and COX-2 protein expression. Gastric prostaglandin E(2) levels, apoptotic index, cell proliferation index, neutrophil activity, and the degree of chronic inflammation were all increased by H. pylori infection, and these effects were significantly decreased by indomethacin treatment. However, NS-398 treatment after H. pylori infection did not induce a significant reduction, although it did result in a tendency to decrease. These results show that NSAIDs can reverse the increased apoptosis and proliferation of epithelial cells and inflammatory activity in the stomachs of H. pylori-infected mice and that, like COX-2 activation, COX-1 induction contributes to the change of gastric mucosal cell turnover and inflammation induced by H. pylori infection.

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.

An insight into the mechanism of cytotoxicity of ricin to hepatoma cell: roles of Bcl-2 family proteins, caspases, Ca(2+)-dependent proteases and protein kinase C

The ability of ricin, a type II ribosome-inactivating protein, to induce hepatoma cell (BEL7404) to apoptosis in vitro was examined by fluorescence microscopy, flow cytometry, and DNA fragmentation assay. As a Bcl-2 lacking model, BEL7404 bore unique advantage to study the effect of over-expressing Bcl-2 on the apoptosis induced by the inhibitor of protein synthesis. By establishing a Bcl-2 over-expressing cell line (BEL7404/ Bcl-2), we found that Bcl-2 could promote the survival of the hepatoma cell against ricin insult. The ricin-induced apoptosis of BEL7404 was accompanied by increased expression of Bak and decreased levels of Bcl-xl and Bax. Caspases and PARP cleavage activity were found to be implicated in the death process. Through the inhibitor tests, our results excluded the participation of calcium-dependent proteases or protein kinase C in the apoptotic process induced by ricin, though an elevation of intracellular calcium did occur as an immediate response to ricin treatment. Cycloheximide, another protein synthesis inhibitor, did synergistically enhance rather than inhibit the cytotoxicity of ricin to hepatoma cell BEL7404. Actually, cycloheximide alone was able to induce hepatoma cell BEL7404 to death that could also be inhibited by over-expressing Bcl-2. The elevation of apoptotic protein Bak was discussed to challenge the notion that ricin exerted its cytotoxicity through nonspecific inhibition of all the de novo protein synthesis.

Helicobacter pylori infection induced alteration of gene expression in human gastric cells

BACKGROUND

Helicobacter pylori, a human pathogen responsible for many digestive disorders, induces complex changes in patterns of gene expression in infected tissues. cDNA expression arrays provide a useful tool for studying these complex phenomena.

AIM

To identify genes that showed altered expression after H pylori infection of human gastric cells compared with uninfected controls.

METHODS

The gastric adenocarcinoma cell line AGS was cocultivated with H pylori. Growth of infected cells was determined by trypan blue exclusion assay. Complementary DNA probes derived from H pylori treated and untreated cells were hybridised to two identical Atlas human cDNA expression arrays, and those genes with altered expression levels were identified. A real time quantitative reverse transcription-polymerase chain reaction assay was used to better define expression patterns of these genes in endoscopically gastric mucosal biopsies with and without H pylori infection.

RESULTS

Over 24 hours, coincubation with H pylori inhibited AGS cell growth but did not cause a noticeable degree of cell death. H pylori treatment altered the pattern of gene expression in AGS cells. We identified 21 overexpressed genes and 17 suppressed genes from the cDNA expression arrays. The majority of genes were transcription factors such as c-jun, BTEB2, and ETR101. Other genes were involved in signal transduction pathways, such as MAP kinase, interleukin 5, and insulin-like growth factor. Genes involved in cell cycle regulation and differentiation, such as CDC25B and NM23-H2, were also identified. In patients with H pylori infection (n=20), there was a significant difference for ERCC3, Id-2, and NM23-H2 mRNA levels in infected gastric mucosa compared with uninfected gastric mucosa in patients without peptic diseases (n=20) (ERCC3 4.75 molecules/10(4) beta-actin mRNA molecules v 13.65, p<0.001; Id-2 16.1 v 23.4, p<0.05; NM23-H2 17.5 v 45.5, p<0.001). There was no significant difference between mRNA levels of c-jun and CDC25B in H pylori colonised gastric mucosa and uninfected mucosa.

CONCLUSION

We demonstrated that H pylori infection caused alteration of gene expression in AGS cells. The differential hybridisation technique of Atlas human cDNA expression array is a useful method to identify host genes involved in pathogenic mechanisms in H pylori infection.