Helicobacter pylori VacA, acting through receptor protein tyrosine phosphatase α, is crucial for CagA phosphorylation in human duodenum carcinoma cell line AZ-521.

Helicobacter pylori, a major cause of gastroduodenal diseases, produces vacuolating cytotoxin (VacA) and cytotoxin-associated gene A (CagA), which seem to be involved in virulence. VacA exhibits pleiotropic actions in gastroduodenal disorders via its specific receptors. Recently, we found that VacA induced the phosphorylation of cellular Src kinase (Src) at Tyr418 in AZ-521 cells. Silencing of receptor protein tyrosine phosphatase (RPTP)α, a VacA receptor, reduced VacA-induced Src phosphorylation. Src is responsible for tyrosine phosphorylation of CagA at its Glu-Pro-Ile-Tyr-Ala (EPIYA) variant C (EPIYA-C) motif in Helicobacter pylori-infected gastric epithelial cells, resulting in binding of CagA to SHP-2 phosphatase. Challenging AZ-521 cells with wild-type H. pylori induced phosphorylation of CagA, but this did not occur when challenged with a vacA gene-disrupted mutant strain. CagA phosphorylation was observed in cells infected with a vacA gene-disrupted mutant strain after addition of purified VacA, suggesting that VacA is required for H. pylori-induced CagA phosphorylation. Following siRNA-mediated RPTPα knockdown in AZ-521 cells, infection with wild-type H. pylori and treatment with VacA did not induce CagA phosphorylation. Taken together, these results support our conclusion that VacA mediates CagA phosphorylation through RPTPα in AZ-521 cells. These data indicate the possibility that Src phosphorylation induced by VacA is mediated through RPTPα, resulting in activation of Src, leading to CagA phosphorylation at Tyr972 in AZ-521 cells.

Identification of Helicobacter pylori VacA in human lung and its effects on lung cells.

OBJECTIVE: Prior reports suggested that infection with Helicobacter pylori was associated with respiratory diseases; pathogenetic mechanisms however, were not defined. We tested the hypothesis that VacA, an exotoxin of H. pylori, a gastric pathogen, was aspirated into the lung and could stimulate secretion of inflammatory cytokines by lung epithelial cells. METHODS: The presence of VacA was determined by immunohistochemistry in surgical lung biopsy tissue samples from 72 patients with interstitial pneumonia. The effects of VacA on A549 human alveolar epithelial adenocarcinoma cells and normal human bronchial epithelial cells were determined. After incubation with VacA, the secretions of cytokines were measured by Multiplex Luminex(®) Assays. RESULTS: VacA was detected with anti-VacA antibodies in bronchial epithelial cells and alveolar epithelial cells from 10 of 72 patients with interstitial pneumonia. VacA was more prevalent in lungs of patients with collagen vascular disease-associated interstitial pneumonia than in those of patients with idiopathic pulmonary fibrosis, nonspecific interstitial pneumonia and cryptogenic organizing pneumonia. Incubation of A549 cells and normal human bronchial epithelial cells with VacA for 24 h was cytotoxic, and resulted in vacuolation. VacA induced interleukin-8 production by A549 cells and normal human bronchial epithelial cells and interleukin-6 production by A549 cells. Based on multiplex screening, interleukin-8 and interleukin-6 were the primary secretory products induced by VacA. CONCLUSIONS: H. pylori VacA is present in human lung and can induce interleukin-8 and interleukin-6 production by human lung cells. VacA could have a role in the pathogenesis of respiratory diseases by its cytotoxic effects and by inducing the secretion of interleukin-8 and interleukin-6 by targeted airway epithelial cells.

Endoplasmic reticulum stress contributes to Helicobacter pylori VacA-induced apoptosis.

Vacuolating cytotoxin A (VacA) is one of the important virulence factors produced by H. pylori. VacA induces apoptotic cell death, which is potentiated by ammonia. VacA also causes cell death by mitochondrial damage, via signaling pathways that are not fully defined. Our aim was to determine whether endoplasmic reticulum (ER) stress is associated with VacA-induced mitochondrial dysfunction and apoptosis. We found that C/EBP homologous protein (CHOP), a key signaling protein of ER stress-induced apoptosis, was transcriptionally up-regulated following incubation of gastric epithelial cells with VacA. The effect of VacA on CHOP induction was significantly enhanced by co-incubation with ammonium chloride. Phosphorylation of eukaryotic initiation factor 2 (eIF2)-alpha, which is known to occur downstream of the ER stress sensor PKR-like ER-localized eIF2-alpha kinase (PERK) and to regulate CHOP expression, was also observed following incubation with VacA in the presence of ammonium chloride. Knockdown of CHOP by siRNA resulted in inhibition of VacA-induced apoptosis. Further studies showed that silencing of the PERK gene with siRNA attenuated VacA-mediated phosphorylation of eIF2-alpha, CHOP induction, expression of BH3-only protein Bim and Bax activation, and cell death induced by VacA with ammonium chloride, indicating that ER stress may lead to mitochondrial dysfunction during VacA-induced toxicity. Activation of ER stress and up-regulation of BH3-only proteins were also observed in human H. pylori-infected gastric mucosa. Collectively, this study reveals a possible association between VacA-induced apoptosis in gastric epithelial cells, and activation of ER stress in H. pylori-positive gastric mucosa.

Reactive oxygen species-induced autophagic degradation of Helicobacter pylori CagA is specifically suppressed in cancer stem-like cells.

Sustained expression of CagA, the type IV secretion effector of Helicobacter pylori, is closely associated with the development of gastric cancer. However, we observed that after translocation, CagA is degraded by autophagy and therefore short lived. Autophagy and CagA degradation are induced by the H. pylori vacuolating cytotoxin, VacA, which acted via decreasing intracellular glutathione (GSH) levels, causing reactive oxygen species (ROS) accumulation and Akt activation. Investigating this further, we found that CagA specifically accumulated in gastric cells expressing CD44, a cell-surface marker associated with cancer stem cells. The autophagic pathway in CD44-positive gastric cancer stem-like cells is suppressed because of their resistance to ROS, which is supported by increased intracellular GSH levels. These findings provide a molecular link between H. pylori and gastric carcinogenesis through the specific accumulation of CagA in gastric cancer stem-like cells.

Low-density lipoprotein receptor-related protein-1 (LRP1) mediates autophagy and apoptosis caused by Helicobacter pylori VacA.

In Helicobacter pylori infection, vacuolating cytotoxin (VacA)-induced mitochondrial damage leading to apoptosis is believed to be a major cause of cell death. It has also been proposed that VacA-induced autophagy serves as a host mechanism to limit toxin-induced cellular damage. Apoptosis and autophagy are two dynamic and opposing processes that must be balanced to regulate cell death and survival. Here we identify the low-density lipoprotein receptor-related protein-1 (LRP1) as the VacA receptor for toxin-induced autophagy in the gastric epithelial cell line AZ-521, and show that VacA internalization through binding to LRP1 regulates the autophagic process including generation of LC3-II from LC3-I, which is involved in formation of autophagosomes and autolysosomes. Knockdown of LRP1 and Atg5 inhibited generation of LC3-II as well as cleavage of PARP, a marker of apoptosis, in response to VacA, whereas caspase inhibitor, benzyloxycarbonyl-VAD-fluoromethylketone (Z-VAD-fmk), and necroptosis inhibitor, Necrostatin-1, did not inhibit VacA-induced autophagy, suggesting that VacA-induced autophagy via LRP1 binding precedes apoptosis. Other VacA receptors such as RPTPα, RPTPß, and fibronectin did not affect VacA-induced autophagy or apoptosis. Therefore, we propose that the cell surface receptor, LRP1, mediates VacA-induced autophagy and apoptosis.

Interweaving microRNAs and proinflammatory cytokines in gastric mucosa with reference to H. pylori infection.

Using endoscopic biopsies, gastric mucosal expression levels of interleukin (IL)-1ß, IL-6, IL-8, and tumor necrosis factor-alpha (TNF-α) messenger RNA (mRNA) and microRNAs (miRNAs) that were differentially expressed in association with Helicobacter pylori were assessed by quantitative reverse-transcriptase polymerase chain reaction. Among the H. pylori-positive mucosa, 17 out of 29 miRNAs had significant correlations with at least one of the four proinflammatory cytokines in expression. Among the 17 miRNAs, 15 were associated with the degree of neutrophil infiltration and, more prominently, the degree of mononuclear cell infiltration, according to the updated Sydney system. Persistent H. pylori infection may affect the mucosal expression profiles of miRNAs via chronic inflammation mediated by proinflammatory cytokines. There were significant positive correlations between certain miRNAs including the microRNA-200 family and IL-1ß, IL-6, or TNF-α mRNA in H. pylori-negative gastric mucosa. Underscoring the causal association between miRNAs and proinflammatory cytokines may provide insights into the pathogenesis of H. pylori-associated gastritis linking to gastric carcinogenesis.

Enhanced expression of CXCL13 in human Helicobacter pylori-associated gastritis.

BACKGROUND AND AIMS: Chemokine CXC ligand 13 (CXCL13) and CXC receptor type 5 (CXCR5) are constitutively expressed in tertiary lymphoid follicles where the CXCL13/CXCR5 system regulates B lymphocytes homing. In this study, we sought to examine CXCL13 expression in the H. pylori-infected and -uninfected gastric mucosa and to elucidate the implication in the pathogenesis of HAG in humans. METHODS: Using endoscopic biopsies taken from the gastric antrum of 29 subjects infected with Helicobacter pylori and 22 uninfected subjects, mucosal CXCL13 mRNA and protein levels were measured by real-time polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. RESULTS: The CXCL13 expression levels were significantly more elevated in H. pylori-positive patients than uninfected ones. The CXCL13 expression levels correlated with the degree of chronic gastritis and bacterial colonization. Immunohistochemistry and in vitro infection assay showed that CXCL13 was not produced by the gastric epithelium, but the α-smooth muscle antigen expressing mesenchymal cells were the possible source of CXCL13 within H. pylori-infected gastric mucosa. CXCR5 immunostaining was seen in the CD20-positive lymphoid aggregates. CONCLUSIONS: The enhanced induction of CXCL13 may be involved in the pathogenesis of H. pylori-associated gastritis.

MicroRNA signatures in Helicobacter pylori-infected gastric mucosa.

The study was conducted to determine expression patterns of microRNA (miRNA), a non-coding RNA that controls gene expression mainly through translational repression, in gastric mucosa infected with Helicobacter pylori. Using endoscopic biopsy specimens, miRNA expression patterns in H. pylori-infected gastric mucosa were determined by microarray. The differentially expressed miRNAs were quantitated by real-time reverse-transcriptase polymerase chain reaction (RT-PCR). An in vitro infection model was assessed to monitor the regulation of miRNAs in gastric epithelium in response to H. pylori. The comprehensive method unraveled the expression profiles; among 470 human miRNAs loaded, 55 were differentially expressed between H. pylori-positive and -negative subjects. The expression levels were significantly decreased in 30 miRNAs, whereas hsa-miRNA-223 was the only miRNA to be overexpressed on quantitative RT-PCR. Eight miRNAs enabled discrimination of H. pylori status with acceptable accuracy. Gastritis scores of activity and chronic inflammation according to the updated Sydney system correlated significantly with the expression levels of diverse miRNAs. Cure of the infection with an anti-H. pylori regimen restored decreased expression in 14 of the 30 miRNAs. Expression levels of some miRNAs, including let-7 family members, were significantly altered following infection with a virulent H. pylori strain carrying intact cag pathogenicity island including cagA but not isogenic mutants. These results provide insights into miRNA involvement in the pathogenesis of H. pylori-associated gastritis. cagA may be involved in cellular regulation of certain miRNAs in the gastric epithelium.

Helicobacter pylori VacA reduces the cellular expression of STAT3 and pro-survival Bcl-2 family proteins, Bcl-2 and Bcl-XL, leading to apoptosis in gastric epithelial cells.

BACKGROUND: Helicobacter pylori vacuolating cytotoxin, VacA, stimulates apoptosis via a mitochondria-dependent pathway. VacA induces apoptosis via activation of the pro-apoptotic B-cell lymphoma (Bcl)-2 family proteins, Bcl-2-associated X protein (Bax) and Bcl-2 homologous antagonist/killer (Bak), while the implication of such pro-survival Bcl-2 family members as Bcl-2 and Bcl-XL in the VacA-induced apoptosis remains unknown. Signal transduction and activator of transcription 3 (STAT3) is a pivotal transcription factor that upregulates Bcl-2 and Bcl-XL. AIMS: This study was conducted to elicit the implication of STAT3 and pro-survival Bcl-2 and Bcl-XL in the intrinsic apoptosis. METHODS: Immunoblot and reverse transcriptase real-time polymerase chain reaction (RT-PCR) were employed to assess the cellular expression of STAT3, Bcl-2, and Bcl-XL in response to purified VacA in gastric adenocarcinoma cell lines. VacA-induced apoptosis was quantitated morphologically following knockdown by each specific small interfering RNA (siRNA) or in the presence of pharmacological inhibitors. RESULTS: VacA reduced STAT3, Bcl-2, and Bcl-XL expression in a dose-dependent manner. Knockdown of STAT3, Bcl-2, and Bcl-XL by siRNA induced apoptosis to a similar extent in the case of sufficient VacA inoculation. The VacA-mediated reduction of STAT3 expression was independent of cellular vacuolization, since a vacuolar-type ATPase inhibitor, bafilomycin A1, did not inhibit VacA-induced reduction of STAT3, Bcl-2, and Bcl-XL expression. Instead, a c-JUN NH2-terminal kinase (JNK) inhibitor, SP600125, restored the VacA-induced reduction of STAT3 expression to the basal level. CONCLUSIONS: VacA-induced apoptosis may be, in part, implicated in the reduction of STAT3 linking to the downregulation of Bcl-2 and Bcl-XL, in association with JNK activity.

Conversion of Helicobacter pylori CagA from senescence inducer to oncogenic driver through polarity-dependent regulation of p21.

The Helicobacter pylori CagA bacterial oncoprotein plays a critical role in gastric carcinogenesis. Upon delivery into epithelial cells, CagA causes loss of polarity and activates aberrant Erk signaling. We show that CagA-induced Erk activation results in senescence and mitogenesis in nonpolarized and polarized epithelial cells, respectively. In nonpolarized epithelial cells, Erk activation results in oncogenic stress, up-regulation of the p21(Waf1/Cip1) cyclin-dependent kinase inhibitor, and induction of senescence. In polarized epithelial cells, CagA-driven Erk signals prevent p21(Waf1/Cip1) expression by activating a guanine nucleotide exchange factor-H1-RhoA-RhoA-associated kinase-c-Myc pathway. The microRNAs miR-17 and miR-20a, induced by c-Myc, are needed to suppress p21(Waf1/Cip1) expression. CagA also drives an epithelial-mesenchymal transition in polarized epithelial cells. These findings suggest that CagA exploits a polarity-signaling pathway to induce oncogenesis.

Helicobacter pylori CagA inhibits endocytosis of cytotoxin VacA in host cells.

Helicobacter pylori, a common pathogen that causes chronic gastritis and cancer, has evolved to establish persistent infections in the human stomach. Epidemiological evidence suggests that H. pylori with both highly active vacuolating cytotoxin A (VacA) and cytotoxin-associated gene A (CagA), the major virulence factors, has an advantage in adapting to the host environment. However, the mechanistic relationship between VacA and CagA remains obscure. Here, we report that CagA interferes with eukaryotic endocytosis, as revealed by genome-wide screening in yeast. Moreover, CagA suppresses pinocytic endocytosis and the cytotoxicity of VacA in gastric epithelial cells without affecting clathrin-dependent endocytosis. Our data suggest that H. pylori secretes VacA to attack distant host cells while injecting CagA into the gastric epithelial cells to which the bacteria are directly attached, thereby protecting these attached host cells from the cytotoxicity of VacA and creating a local ecological niche. This mechanism might allow H. pylori to balance damage to one population of host cells with the preservation of another, allowing for persistent infection.

Pleiotropic actions of Helicobacter pylori vacuolating cytotoxin, VacA.

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

Helicobacter pylori-induced interleukin-12 p40 expression.

Interleukin-12 (IL-12) is a heterodimeric cytokine produced by antigen-presenting cells that promotes the development of T-helper lymphocyte 1 (Th1). Chronic gastritis induced by Helicobacter pylori is considered a Th1-mediated process. IL-12 levels in gastric biopsy samples of H. pylori-infected patients are higher than in those of uninfected individuals, but the cellular source of IL-12 remains elusive. IL-12 staining was detected in mucosal epithelial cells, lymphocytes, and macrophages in specimens of patients with H. pylori-positive gastritis. Therefore, we investigated IL-12 p40 mRNA induction by H. pylori in gastric epithelial cells and T cells. Although cag pathogenicity island (PAI)-positive H. pylori induced IL-12 p40 mRNA expression, an isogenic mutant of the cag PAI failed to induce it in both cell types. Supernatants from H. pylori cultures and H. pylori VacA induced IL-12 p40 mRNA expression in T cells but not in epithelial cells. The activation of the IL-12 p40 promoter by H. pylori was mediated through NF-kappaB. The transfection of IkappaB kinase and NF-kappaB-inducing kinase dominant-negative mutants inhibited H. pylori-induced IL-12 p40 activation. Inhibitors of NF-kappaB, phosphatidylinositol 3-kinase, p38 mitogen-activated protein kinase, and Hsp90 suppressed H. pylori- and VacA-induced IL-12 p40 mRNA expression. The results indicate that H. pylori induces IL-12 p40 expression by the activation of NF-kappaB, phosphatidylinositol 3-kinase, and p38 mitogen-activated protein kinase. Hsp90 is also a crucial regulator of H. pylori-induced IL-12 p40 expression. In addition to the cag PAI, VacA might be relevant in the induction of IL-12 expression and a Th1-polarized response only in T cells.

Enhanced expression of CCL20 in human Helicobacter pylori-associated gastritis.

CC chemokine ligand 20 (CCL20) attracts CC chemokine receptor 6 (CCR6)-expressing cells. Using endoscopic biopsies taken from the gastric antrum of 42 subjects infected with H. pylori and 42 uninfected subjects, mucosal CCL20 mRNA and protein levels were measured by real-time polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. CCL19 mRNA and protein levels, as well as CCL21 mRNA levels, were also measured. The CCL20 mRNA and protein levels were significantly elevated in H. pylori-positive patients and substantially decreased after successful eradication. CCL19 and CCL21 expression levels were comparable in the H. pylori-infected and the uninfected groups. The CCL20 concentrations correlated with the degree of chronic gastritis. Immunohistochemistry and the in vitro infection assay showed that CCL20 was principally produced by the gastric epithelium. CCR6-expressing cells, including CD45RO(+) memory T lymphocytes and fascin(+)-CD1a(+) immature dendritic cells, infiltrated close to the CCL20-expressing epithelial cells. The CCL20/CCR6 interaction may be involved in the development of H. pylori-associated gastritis.

Helicobacter pylori VacA-induced inhibition of GSK3 through the PI3K/Akt signaling pathway.

Helicobacter pylori VacA toxin contributes to the pathogenesis and severity of gastric injury. We found that incubation of AZ-521 cells with VacA resulted in phosphorylation of protein kinase B (Akt) and glycogen synthase kinase-3beta (GSK3beta) through a PI3K-dependent pathway. Following phosphorylation and inhibition of GSK3beta,beta-catenin was released from a GSK3beta/beta-catenin complex, with subsequent nuclear translocation. Methyl-beta-cyclodextrin (MCD) and phosphatidylinositol-specific phospholipase C (PI-PLC), but not 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) and bafilomycin A1, inhibited VacA-induced phosphorylation of Akt, indicating that it does not require VacA internalization and is independent of vacuolation. VacA treatment of AZ-521 cells transfected with TOPtkLuciferase reporter plasmid or control FOPtkLucifease reporter plasmid resulted in activation of TOPtkLuciferase, but not FOPtkLucifease. In addition, VacA transactivated the beta-catenin-dependent cyclin D1 promoter in a luciferase reporter assay. Infection of AZ-521 cells by a vacA mutant strain of H. pylori failed to induce phosphorylation of Akt and GSK3beta, or release of beta-catenin from a GSK3beta/beta-catenin complex. Taken together, these results support the conclusion that VacA activates the PI3K/Akt signaling pathway, resulting in phosphorylation and inhibition of GSK3beta, and subsequent translocation ofbeta-catenin to the nucleus, consistent with effects of VacA on beta-catenin-regulated transcriptional activity. These data introduce the possibility that Wnt-dependent signaling might play a role in the pathogenesis of H. pylori infection, including the development of gastric cancer.

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

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

Unexpected expression of Hsp47, a replacement of one amino acid (Val 7 Leu) in the amino terminal region, in cultured human tumorigenic cell lines.

BACKGROUND: In general, it has been stated that keratin (K) molecules are glycosylated. During biochemical studies of K subunits, we encountered a glycoprotein that does not judge K subunits. OBJECTIVE: This study was intended to elucidate how the above glycoprotein co-exists in the K fraction prepared from ISO-HAS (cultured angiosarcoma cell line). METHODS: We analyzed and sequenced a remarkable spot, which was shown as a glycoprotein by periodic acid Sciff's (PAS) staining, in the K fraction prepared from ISO-HAS. RESULTS: The glycoprotein was identified as an N-terminal amino acid sequence covering 10 residues of the spot. A homology search showed that it was identical to that of Hsp47 (matured type), except for one amino acid (seventh amino acid: Val 7 Leu). Similar results were confirmed for four other tumorigenic cell line types. Subsequent PAS staining using the same samples after 2D-PAGE revealed no glycosylated Ks. CONCLUSION: No glycosylated Ks were found by PAS staining in the K fraction prepared from four tumorigenic cell line types. During K preparation from cultured human tumor cell lines, Hsps might be associated with K expression in tumor cells.

Helicobacter pylori VacA enhances prostaglandin E2 production through induction of cyclooxygenase 2 expression via a p38 mitogen-activated protein kinase/activating transcription factor 2 cascade in AZ-521 cells.

Treatment of AZ-521 cells with Helicobacter pylori VacA increased cyclooxygenase 2 (COX-2) mRNA in a time- and dose-dependent manner. A p38 mitogen-activated protein kinase (MAPK) inhibitor, SB203580, blocked elevation of COX-2 mRNA levels, whereas PD98059, which blocks the Erk1/2 cascade, partially suppressed the increase. Consistent with involvement of p38 MAPK, VacA-induced accumulation of COX-2 mRNA was reduced in AZ-521 cells overexpressing a dominant-negative p38 MAPK (DN-p38). Phosphatidylinositol-specific phospholipase C, which inhibits VacA-induced p38 MAPK activation, blocked VacA-induced COX-2 expression. In parallel with COX-2 expression, VacA increased prostaglandin E(2) (PGE(2)) production, which was inhibited by SB203580 and NS-398, a COX-2 inhibitor. VacA-induced PGE(2) production was markedly attenuated in AZ-521 cells stably expressing DN-p38. VacA increased transcription of a COX-2 promoter reporter gene and activated a COX-2 promoter containing mutated NF-kappaB or NF-interleukin-6 sites but not a mutated cis-acting replication element (CRE) site, suggesting direct involvement of the activating transcription factor 2 (ATF-2)/CREB-binding region in VacA-induced COX-2 promoter activation. The reduction of ATF-2 expression in AZ-521 cells transformed with ATF-2-small interfering RNA duplexes resulted in suppression of COX-2 expression. Thus, VacA enhances PGE(2) production by AZ-521 cells through induction of COX-2 expression via the p38 MAPK/ATF-2 cascade, leading to activation of the CRE site in the COX-2 promoter.