Augmented gp130-mediated cytokine signalling accompanies human gastric cancer progression

Inhibition of the JAK2/STAT3 pathway reduces gastric cancer growth in vitro and in vivo

Signal Transducer and Activator of Transcription-3 (STAT3) is constitutively activated in many cancers where it promotes growth, inflammation, angiogenesis and inhibits apoptosis. We have shown that STAT3 is constitutively activated in human gastric cancer, and that chronic IL-11-driven STAT3 transcriptional activity induces gastric tumourigenesis in the gp130^757FF mouse model of gastric cancer development. Here we show that treatment of human AGS gastric cancer cells with the Janus Kinase (JAK) inhibitor WP1066 dose-, and time-dependently inhibits STAT3 phosphorylation, in conjunction with reduced JAK2 phosphorylation, reduced proliferation and increased apoptosis. In addition, application of intraperitoneal WP1066 for 2 weeks, reduced gastric tumour volume by 50% in the gp130^757FF mouse coincident with reduced JAK2 and STAT3 activation compared with vehicle-treated, littermate controls. Gastric tumours from WP1066- treated mice had reduced polymorphonuclear inflammation, coincident with inhibition of numerous proinflammatory cytokines including IL-11, IL-6 and IL-1β, as well as the growth factors Reg1 and amphiregulin. These results show that WP1066 can block proliferation, reduce inflammation and induce apoptosis in gastric tumour cells by inhibiting STAT3 phosphorylation, and that many cytokines and growth factors that promote gastric tumour growth are regulated by STAT3-dependent mechanisms. WP1066 may form the basis for future therapeutics against gastric cancer.

Obesity accelerates Helicobacter felis-induced gastric carcinogenesis by enhancing immature myeloid cell trafficking and TH17 response

OBJECTIVE

To investigate the role of obesity-associated inflammation and immune modulation in gastric carcinogenesis during Helicobacter-induced chronic gastric inflammation.

DESIGN

C57BL/6 male mice were infected with H felis and placed on a high-fat diet (45% calories from fat). Study animals were analysed for gastric and adipose pathology, inflammatory markers in serum, stomach and adipose tissue, and immune responses in blood, spleen, stomach and adipose tissue.

RESULTS

H felis-induced gastric carcinogenesis was accelerated in diet-induced obese mice compared with lean controls. Obesity increased bone marrow-derived immature myeloid cells in blood and gastric tissue of H felis-infected mice. Obesity also led to elevations in CD4 T cells, IL-17A, granulocyte macrophage colony-stimulating factor, phosphorylated STAT3 and prosurvival gene expression in gastric tissue of H felis-infected mice. Conversely, in adipose tissue of obese mice, H felis infection increased macrophage accumulation and expression of IL-6, C-C motif ligand 7 (CCL7) and leptin. Finally, the combination of obesity and gastric inflammation synergistically increased serum proinflammatory cytokines, including IL-6.

CONCLUSIONS

Here, we have established a model to study the molecular mechanism by which obesity predisposes individuals to gastric cancer. In H felis-infected mice, obesity increased proinflammatory immune responses and accelerated gastric carcinogenesis. Interestingly, gastric inflammation augmented obesity-induced adipose inflammation and production of adipose-derived factors in obese, but not lean, mice. Our findings suggest that obesity accelerates Helicobacter-associated gastric cancer through cytokine-mediated cross-talk between inflamed gastric and adipose tissues, augmenting immune responses at both tissue sites, and thereby contributing to a protumorigenic gastric microenvironment.

IL-6 and related cytokines as the critical lynchpins between inflammation and cancer

Inflammatory responses play pivotal roles in cancer development, including tumor initiation, promotion, progression, and metastasis. Cytokines are now recognized as important mediators linking inflammation and cancer, and are therefore potential therapeutic and preventive targets as well as prognostic factors. The interleukin (IL)-6 family of cytokines, especially IL-6 and IL-11, is highly up-regulated in many cancers and considered as one of the most important cytokine families during tumorigenesis and metastasis. This review discusses molecular mechanisms linking the IL-6 cytokine family to solid malignancies and their treatment.

Helicobacter pylori infection: host immune response, implications on gene expression and microRNAs

Helicobacter pylori (H. pylori) infection is the most common bacterial infection worldwide. Persistent infection of the gastric mucosa leads to inflammatory processes and may remain silent for decades or progress causing more severe diseases, such as gastric adenocarcinoma. The clinical consequences of H. pylori infection are determined by multiple factors, including host genetic predisposition, gene regulation, environmental factors and heterogeneity of H. pylori virulence factors. After decades of studies of this successful relationship between pathogen and human host, various mechanisms have been elucidated. In this review, we have made an introduction on H. pylori infection and its virulence factors, and focused mainly on modulation of host immune response triggered by bacteria, changes in the pattern of gene expression in H. pylori-infected gastric mucosa, with activation of gene transcription involved in defense mechanisms, inflammatory and immunological response, cell proliferation and apoptosis. We also highlighted the role of bacteria eradication on gene expression levels. In addition, we addressed the recent involvement of different microRNAs in precancerous lesions, gastric cancer, and inflammatory processes induced by bacteria. New discoveries in this field may allow a better understanding of the role of major factors involved in the pathogenic mechanisms of H. pylori.

Genetic regulation of MUC1 expression by Helicobacter pylori in gastric cancer cells

Helicobacter pylori infection of the stomach is associated with the development of gastritis, peptic ulcers, and gastric adenocarcinomas, but the mechanisms are unknown. MUC1 is aberrantly overexpressed by more than 50% of stomach cancers, but its role in carcinogenesis remains to be defined. The current studies were undertaken to identify the genetic mechanisms regulating H. pylori-dependent MUC1 expression by gastric epithelial cells. Treatment of AGS cells with H. pylori increased MUC1 mRNA and protein levels, and augmented MUC1 gene promoter activity, compared with untreated cells. H. pylori increased binding of STAT3 and MUC1 itself to the MUC1 gene promoter within a region containing a STAT3 binding site, and decreased CpG methylation of the MUC1 promoter proximal to the STAT3 binding site, compared with untreated cells. These results suggest that H. pylori upregulates MUC1 expression in gastric cancer cells through STAT3 and CpG hypomethylation.

Roles of proinflammatory cytokines in precancerous lesions of gastric cancer

Precancerous lesions of gastric cancer, including intestinal metaplasia and dysplasia, are important stages in the evolution from normal gastric tissue to gastric cancer. Gastric cancer has a very high mortality rate, mainly due to post-metastasis diagnosis. Therefore, diagnosis of precancerous lesions of gastric cancer is of great clinical significance. In recent years, it has been reported that some proinflammatory cytokines such as interleukin 1β (IL-1β), IL-8, IL-11, tumor necrosis factor α (TNF-α) and interferon-gamma (IFN-γ) play important roles in the development of precancerous lesions of gastric cancer. A more detailed understanding of the roles of proinflammatory cytokines may provide new therapeutic targets for precancerous lesions of gastric cancer. Here, we summarize the roles of some proinflammatory cytokines in the progression of precancerous lesions of gastric cancer.

Activation of STAT3 in human gastric cancer cells via interleukin (IL)-6-type cytokine signaling correlates with clinical implications

Background

The signal transducers and activators of transcription 3 (STAT3) signaling pathway plays important roles in oncogenesis, angiogenesis, immunity, and tumor cell invasion. In the present study, we investigated the association of interleukin (IL)-6/STAT3 signaling pathway with T lymphocytes and clinical implication in patients with gastric cancer.

Methods

Seventy one patients who underwent gastrectomy due to gastric adenocarcinoma were studied. Blood samples were collected before and after surgical gastrectomy to quantify the levels of IL-6, IL-10 and VEGF using an enzyme-linked immunosorbent assay, as well as T lymphocyte subsets (CD3⁺, CD4⁺, CD8⁺, CD4⁺/CD8⁺) and natural killer (NK) cells by a flow cytometry. Furthermore, the expression of IL-6, survivin, STAT3, STAT3 phosphorylation (p-STAT3), and VEGF were determined in human gastric cancer and adjacent normal mucosa through Western blot and immunohistochemistry.

Results

Postoperative levels of IL-6, IL-10 and VEGF in serum were significantly lower than preoperative levels. Percentages of T-cell subsets and NK cells in blood were significantly increased after postoperative-week 1 as compared to preoperative group, which was further augmented at 1 month after gastrectomy. In addition, the expression of IL-6, survivin, STAT3, p-STAT3, and VEGF were increased in human gastric cancer tissues as compared to adjacent normal mucosa. Their expression was associated with TNM stage of gastric cancer. The level of STAT3 activation in clinical samples was correlated with IL-6 expression. All gastric tumor samples, which expressed p-STAT3, also expressed IL-6 with weak expression detected in adjacent normal mucosa.

Conclusion

Increased IL-6-induced activation of STAT3 was observed in neoplastic gastric tissue, which positively correlated with tumor progression. Moreover, IL-6 and STAT3 downstream signals such as IL-10 and VEGF were reduced in patients after removal of gastric cancer as compared to pre-operation. Therefore, inhibition of the IL-6/STAT3 signaling pathway may provide a new therapeutic strategy against gastric cancer.

Lymph node metastasis is mediated by suppressor of cytokine signaling-3 in gastric cancer

Suppressor of cytokine signaling-3 (SOCS-3), a multifunctional cytokine, is able to inhibit cell growth and migration by blocking the Janus kinase signal transducers and activators of transcription signaling (JAK/STAT) activation in oncogenesis. Although the STAT-3 expression was associated with lymph node metastasis from gastric cancer (GC), the implication of SOCS-3 expression in GC is not clearly elucidated. In this study, SOCS-3, STAT-3, and pSTAT-3 were evaluated in GC tissues and adjacent non-tumor tissues of 107 patients who underwent curative surgery by immunohistochemistry. Further, SOCS-3 and STAT-3 mRNA levels were also detected simultaneously. In addition, survival analysis was performed between clinicopathologic variables and prognosis of GC patients. Finally, correlative analysis was adopted for demonstration the best predicator of the survival independent factor. From the results, we demonstrated that only the lymph node metastasis was the independent predictor of the overall survival (OS) of GC patients, although SOCS-3, STAT-3, and other variables were significantly relative to OS. With multivariate logistical regression analysis, SOCS-3, STAT-3, and the status of extragastric nodal metastasis were identified to be the independent factors of the lymph node metastasis from GC. Ultimately, the SOCS-3 was the best predicator of lymph node metastasis from GC identified with the nominal regression analysis. Therefore, SOCS-3 should be considered as a potential indicator for prediction the lymph node metastasis from GC.

Autoimmune gastritis mediated by CD4+ T cells promotes the development of gastric cancer

Chronic inflammation is a major risk factor for cancer, including gastric cancers and other gastrointestinal cancers. For example, chronic inflammation caused by autoimmune gastritis (AIG) is associated with an increased risk of gastric polyps, gastric carcinoid tumors, and possibly adenocarcinomas. In this study, we characterized the progression of gastric cancer in a novel mouse model of AIG. In this model, disease was caused by CD4(+) T cells expressing a transgenic T-cell receptor specific for a peptide from the H(+)/K(+) ATPase proton pump, a protein expressed by parietal cells in the stomach. AIG caused epithelial cell aberrations that mimicked most of those seen in progression of human gastric cancers, including chronic gastritis followed by oxyntic atrophy, mucous neck cell hyperplasia, spasmolytic polypeptide-expressing metaplasia, dysplasia, and ultimately gastric intraepithelial neoplasias. Our work provides the first direct evidence that AIG supports the development of gastric neoplasia and provides a useful model to study how inflammation drives gastric cancer.

Mouse models of gastric cancer

Animal models have greatly enriched our understanding of the molecular mechanisms of numerous types of cancers. Gastric cancer is one of the most common cancers worldwide, with a poor prognosis and high incidence of drug-resistance. However, most inbred strains of mice have proven resistant to gastric carcinogenesis. To establish useful models which mimic human gastric cancer phenotypes, investigators have utilized animals infected with Helicobacter species and treated with carcinogens. In addition, by exploiting genetic engineering, a variety of transgenic and knockout mouse models of gastric cancer have emerged, such as INS-GAS mice and TFF1 knockout mice. Investigators have used the combination of carcinogens and gene alteration to accelerate gastric cancer development, but rarely do mouse models show an aggressive and metastatic gastric cancer phenotype that could be relevant to preclinical studies, which may require more specific targeting of gastric progenitor cells. Here, we review current gastric carcinogenesis mouse models and provide our future perspectives on this field.

The novel focal adhesion gene kindlin-2 promotes the invasion of gastric cancer cells mediated by tumor-associated macrophages

Kindlin-2 is a novel focal adhesion gene mediating the cell-extracellular matrix (ECM) adhesion. Tumor-associated macrophages (TAMs) play an important role in linking chronic inflammation to cancer progression. Both kindlin-2 and TAMs have been found to promote the invasion of gastric cancer cells in our previous studies. However, the correlation between kindlin-2 and TAMs remains unclear. Real-time RT-PCR was used to investigate kindlin-2 expression in the AGS, NCI and Hs-746T gastric cancer cell lines co-cultured with TAMs under normal or hypoxic conditions. IL8, IL10, IL11, IL17b, IL18, IL22 and IL24 expressions were measured by real-time RT-PCR in the gastric cancer lines with varying levels of kindlin-2 expression, as well as after downregulation of kindlin-2 mRNA expression by the siRNA method. We found that kindlin-2 was upregulated in all three gastric cancer cell lines when co-cultured with TAMs under normal conditions. Under hypoxic conditions, the induction of kindlin-2 expression induced by macrophages was significantly downregulated in the Hs-746T cell line. IL8, IL11, IL17b, IL22 and IL24 expression was significantly higher in gastric cell lines with high kindlin-2 expression. Downregulation of kindlin-2 mRNA decreased IL10, IL11, IL17b, IL22 and IL24 expression but IL8 and IL18 expression was upregulated. Therefore, the novel focal adhesion gene kindlin-2 may play an important role in promoting the invasion of gastric cancer cells mediated by TAMs through regulating interleukin expression.

Transgenic expression of interferon-γ in mouse stomach leads to inflammation, metaplasia, and dysplasia

Gastric adenocarcinoma is one of the leading causes of cancer mortality worldwide. It arises through a stepwise process that includes prominent inflammation with expression of interferon-γ (IFN-γ) and multiple other pro-inflammatory cytokines. We engineered mice expressing IFN-γ under the control of the stomach-specific H(+)/K(+) ATPase β promoter to test the potential role of this cytokine in gastric tumorigenesis. Stomachs of H/K-IFN-γ transgenic mice exhibited inflammation, expansion of myofibroblasts, loss of parietal and chief cells, spasmolytic polypeptide expressing metaplasia, and dysplasia. Proliferation was elevated in undifferentiated and metaplastic epithelial cells in H/K-IFN-γ transgenic mice, and there was increased apoptosis. H/K-IFN-γ mice had elevated levels of mRNA for IFN-γ target genes and the pro-inflammatory cytokines IL-6, IL-1β, and tumor necrosis factor-α. Intracellular mediators of IFN-γ and IL-6 signaling, pSTAT1 and pSTAT3, respectively, were detected in multiple cell types within stomach. H/K-IFN-γ mice developed dysplasia as early as 3 months of age, and 4 of 39 mice over 1 year of age developed antral polyps or tumors, including one adenoma and one adenocarcinoma, which expressed high levels of nuclear β-catenin. Our data identified IFN-γ as a pivotal secreted factor that orchestrates complex changes in inflammatory, epithelial, and mesenchymal cell populations to drive pre-neoplastic progression in stomach; however, additional alterations appear to be required for malignant conversion.

Targeting STAT3 in gastric cancer

INTRODUCTION

STAT3 is a key transcription factor for many regulatory factors that modulate gene transcription. Particularly important are cytokines and growth factors that maintain homeostasis by regulating immunocytes, stromal and epithelial cells. Dysregulation of STAT3 by constitutive activation plays an important role in the initiation of inflammation and cellular transformation in numerous cancers, especially of epithelial origin. This review focuses on STAT3 drive in gastric cancer initiation and progression, with emphasis on its activation by cytokines, and how targeting the primary drivers or gastric STAT3 therapeutically may prevent or slow stomach cancer development.

AREAS COVERED

This review will discuss the mechanics of STAT3 signalling, how constitutive STAT3 activation promotes gastric tumourigenesis in both human adenocarcinomas and mouse models, the nature of the upstream regulators of STAT3, and their association with chronic Helicobacter pylori infection, STAT3-activated genes that promote transformation and progression, and finally the development and use of STAT3 and upstream cytokine inhibitors as therapeutics.

EXPERT OPINION

Chronic STAT3 activation is a key event in gastric cancer induction and progression. Specific targeting of stomach epithelial STAT3 or blocking IL-11Rα/gp130 and/or EGFR signal transduction in chronic gastric inflammation and metaplasia may be therapeutically effective in preventing gastric carcinogenesis.

IL10, IL11, IL18 are differently expressed in CD14+ TAMs and play different role in regulating the invasion of gastric cancer cells under hypoxia

BACKGROUND

Recent evidence shows that chronic inflammation mediated by tumor-associated macrophage (TAM) play an important role in malignant tumor formation and progression. Interleukins expressed in TAMs regulate this progress. Hypoxia is a salient feature of solid tumors and has a profound influence on the biology of TAMs However, the role of interleukins in the gastric cancer progression under hypoxia is not clear.

METHODS

Realtime RT-PCR was used to quantitatively investigate the IL10, IL11 and IL18 expression in CD14(-) normal macrophages and CD14(+) TAMs co-cultured with four gastric cancer cell lines including non-metastatic cell line AGS and metastatic cell lines HGC-27, Hs-746T and NCI-N87 under normal or hypoxic conditions. In addition, the correlation between IL10, IL11, IL18 expression in TAMs under hypoxia and mobility of gastric cancer cells were analyzed.

RESULTS

Under normal conditions, the IL10 and IL18 expressions were significantly higher in CD14(+) TAMs co-cultured with non-metastatic cell line than with metastatic cell lines. IL11 expression was significantly higher in CD14(+) TAMs co-cultured with distant metastasis cell lines. Hypoxia induced IL10, IL11 and IL18 expression up regulated significantly in TAMs co-cultured with AGS, Hs-746T and NCI-N87 cell line. There was a significant negative correlation between IL11 expression in CD14(+) TAMs and gastric cancer cell invasion speed under hypoxic conditions (r=0.861, P<0.001).

CONCLUSION

The up-regulation of IL10, IL11 and IL18 expression in TAMs by hypoxia differed in gastric cancer cell lines. IL11 expression in TAMs might play more important role than IL10 and IL18 expression in regulating the invasion of gastric cancer cells under hypoxia.

Helicobacter pylori in First Nations and recent immigrant populations in Canada

The diminishing prevalence of Helicobacter pylori infection among most segments of the Canadian population has led to changes in the etiologies and patterns of associated upper gastrointestinal diseases, including fewer peptic ulcers and their complications. Canadian Aboriginals and recent immigrants are among populations in which the prevalence of H pylori infection remains high and, therefore, the health risks imposed by H pylori remain a significant concern. Population-based strategies for H pylori eradication in groups with a low prevalence of infection are unlikely to be cost effective, but such measures are attractive in groups in which the prevalence rates of infection remain substantial. In addition to a lower prevalence of peptic ulcers and dyspepsia, the public health value of eradication may be particularly important if this leads to a reduction in the prevalence of gastric cancer in high prevalence groups. Therefore The Canadian Helicobacter Study Group held a conference that brought together experts in the field to address these issues, the results of which are reviewed in the present article. Canadians with the highest prevalence of H pylori infection are an appropriate focus for considering the health advantages of eradicating persistent infection. In Canadian communities with a high prevalence of both H pylori and gastric cancer, there remains an opportunity to test the hypothesis that H pylori infection is a treatable risk factor for malignancy.

Interleukin-11 promotes the progress of gastric carcinoma via abnormally expressed versican

Versican, a ubiquitous component of the extracellular matrix (ECM), accumulates both in tumor stroma and cancer cells and is highly regulated by various cytokines. The aberrant expression of versican and its isoforms is known to modulate cell proliferation, differentiation, and migration, all of which are features of the invasion and metastasis of cancer; versican is also known to favour the homeostasis of the ECM. Interleukin-11 (IL-11) is an important cytokine that exhibits a wide variety of biological effects in gastric cancer development. Here, we analysed the expression of versican isoforms and found that the major isoforms expressed by both gastric carcinoma tissue and gastric cell lines were V0 and V1, and V1 was significantly higher in gastric carcinoma tissue. The treatment of the gastric cell lines AGS and MKN45 with rhIL-11 resulted in a significant increase in the expression of V0 and V1. Exogenous IL-11 increased migration in AGS and MKN45 cells, whereas these effects were reversed when the expression of V0 and V1 were abolished by siRNA targeting versican V0/V1. Collectively, these findings suggest that the abnormally expressed versican and its isoforms participate, at least in part, in the progress of gastric carcinoma triggered by IL-11.

Helicobacter pylori CagA triggers expression of the bactericidal lectin REG3γ via gastric STAT3 activation

BACKGROUND

Most of what is known about the Helicobacter pylori (H. pylori) cytotoxin, CagA, pertains to a much-vaunted role as a determinant of gastric inflammation and cancer. Little attention has been devoted to potential roles of CagA in the majority of H. pylori infected individuals not showing oncogenic progression, particularly in relation to host tolerance. Regenerating islet-derived (REG)3γ encodes a secreted C-type lectin that exerts direct bactericidal activity against Gram-positive bacteria in the intestine. Here, we extend this paradigm of lectin-mediated innate immunity, showing that REG3γ expression is triggered by CagA in the H. pylori-infected stomach.

METHODOLOGY/PRINCIPAL FINDINGS

In human gastric mucosal tissues, REG3γ expression was significantly increased in CagA-positive, compared to CagA-negative H. pylori infected individuals. Using transfected CagA-inducible gastric MKN28 cells, we recapitulated REG3γ induction in vitro, also showing that tyrosine phosphorylated, not unphosphorylated CagA triggers REG3γ transcription. In concert with induced REG3γ, pro-inflammatory signalling downstream of the gp130 cytokine co-receptor via the signal transducer and activator of transcription (STAT)3 and transcription of two cognate ligands, interleukin(IL)-11 and IL-6, were significantly increased. Exogenous IL-11, but not IL-6, directly stimulated STAT3 activation and REG3γ transcription. STAT3 siRNA knockdown or IL-11 receptor blockade respectively abrogated or subdued CagA-dependent REG3γ mRNA induction, thus demonstrating a requirement for uncompromised signalling via the IL-11/STAT3 pathway. Inhibition of the gp130-related SHP2-(Ras)-ERK pathway did not affect CagA-dependent REG3γ induction, but strengthened STAT3 activation as well as augmenting transcription of mucosal innate immune regulators, IL-6, IL-8 and interferon-response factor (IRF)1.

CONCLUSIONS/SIGNIFICANCE

Our results support a model of CagA-directed REG3γ expression in gastric epithelial cells via activation of the IL-11/gp130/STAT3 pathway. This response might allow Gram-negative H. pylori to manipulate host immunity to favour its own survival, by reducing the fitness of co-habiting Gram-positive bacteria with which it competes for resources in the gastric mucosal niche.

Smad4 deficiency in T cells leads to the Th17-associated development of premalignant gastroduodenal lesions in mice

While there is evidence that specific T cell populations can promote the growth of established tumors, instances where T cell activity causes neoplasms to arise de novo are infrequent. Here, we employed two conditional mutagenesis systems to delete the TGF-β signaling pathway component Smad4 in T cells and observed the spontaneous development of massive polyps within the gastroduodenal regions of mice. The epithelial lesions contained increased levels of transcripts encoding IL-11, IL-6, TGF-β, IL-1β, and TNF-α, and lamina propria cells isolated from lesions contained abundant IL-17A+CD4+ T cells. Furthermore, we found that Smad4 deficiency attenuated TGF-β-mediated in vitro polarization of FoxP3+CD4+ T cells, but not IL-17A+CD4+ T cells, suggesting that the epithelial lesions may have arisen as a consequence of unchecked Th17 cell activity. Proinflammatory cytokine production likely accounted for the raised levels of IL-11, a cytokine known to promote gastric epithelial cell survival and hyperplasia. Consistent with IL-11 having a pathogenic role in this model, we found evidence of Stat3 activation in the gastric polyps. Thus, our data indicate that a chronic increase in gut Th17 cell activity can be associated with the development of premalignant lesions of the gastroduodenal region.

Helicobacter pylori infection promotes methylation and silencing of trefoil factor 2, leading to gastric tumor development in mice and humans

BACKGROUND & AIMS

Trefoil factors (TFFs) regulate mucosal repair and suppress tumor formation in the stomach. Tff1 deficiency results in gastric cancer, whereas Tff2 deficiency increases gastric inflammation. TFF2 expression is frequently lost in gastric neoplasms, but the nature of the silencing mechanism and associated impact on tumorigenesis have not been determined.

METHODS

We investigated the epigenetic silencing of TFF2 in gastric biopsy specimens from individuals with Helicobacter pylori-positive gastritis, intestinal metaplasia, gastric cancer, and disease-free controls. TFF2 function and methylation were manipulated in gastric cancer cell lines. The effects of Tff2 deficiency on tumor growth were investigated in the gp130(F/F) mouse model of gastric cancer.

RESULTS

In human tissue samples, DNA methylation at the TFF2 promoter began at the time of H pylori infection and increased throughout gastric tumor progression. TFF2 methylation levels were inversely correlated with TFF2 messenger RNA levels and could be used to discriminate between disease-free controls, H pylori-infected, and tumor tissues. Genome demethylation restored TFF2 expression in gastric cancer cell lines, so TFF2 silencing requires methylation. In Tff2-deficient gp130(F/F)/Tff2(-/-) mice, proliferation of mucosal cells and release of T helper cell type-1 (Th-1) 1 cytokines increased, whereas expression of gastric tumor suppressor genes and Th-2 cytokines were reduced, compared with gp130(F/F)controls. The fundus of gp130(F/F)/Tff2(-/-) mice displayed glandular atrophy and metaplasia, indicating accelerated preneoplasia. Experimental H pylori infection in wild-type mice reduced antral expression of Tff2 by increased promoter methylation.

CONCLUSIONS

TFF2 negatively regulates preneoplastic progression and subsequent tumor development in the stomach, a role that is subverted by promoter methylation during H pylori infection.

STAT-3 correlates with lymph node metastasis and cell survival in gastric cancer

AIM: To investigate the correlation between gastric cancer growth and signal transducer and activator of transcription-3 (STAT3) expression.

METHODS: We assessed the expressions of STAT3, phosphor-STAT3 (pSTAT3), suppressor of cytokine signaling-1 (SOCS-1), survivin and Bcl-2 in gastric cancer patients after gastrectomy by immunohistochemical method. In addition, in situ hybridization was used to further demonstrate the mRNA expression of STAT3 in gastric cancer.

RESULTS: With the univariate analysis, expressions of STAT3, pSTAT3, SOCS-1, survivin and Bcl-2, the size of primary tumor and the lymph node metastasis were found to be associated with the overall survival (OS) of gastric cancer patients. However, only pSTAT3 expression and the lymph node metastasis were identified as the independent factors of OS of gastric cancer with multivariate analysis. STAT3 expression was correlated with the lymph node metastasis. There were positive correlations between expressions of STAT3, survivin, Bcl-2 and pSTAT3 in gastric cancer, whereas there was negative correlation between STAT3 expression and SOCS-1 expression in gastric cancer.

CONCLUSION: STAT3 can transform into pSTAT3 to promote the survival and inhibit the apoptosis of gastric cancer cells. SOCS-1 might be the valid molecular antagonist to inhibit the STAT3 expression in gastric cancer.

Inflammation modulates the expression of the intestinal mucins MUC2 and MUC4 in gastric tumors

Infection of gastric mucosa by Helicobacter pylori induces an inflammatory response with increased levels of proinflammatory cytokines. Among them, tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta and IL-6 induce the activation of signaling pathways that regulate genes expression, such as MUC2 and MUC4 intestinal mucins ectopically detected in gastric tumors. This study evaluated if the predominant inflammatory cell type correlates with MUC2 and MUC4 expression in human intestinal gastric tumors (n=78). In addition, we analyzed the regulatory effects of the associated inflammatory signaling pathways on their expression in gastric cancer cell lines, and in a mouse model with hyperactivated STAT3 signaling pathway. Tumors with predominant lymphoplasmocytic infiltrate (chronic inflammation), presented higher levels of MUC2 and were more differentiated than tumors with predominant polymorphonuclear infiltrate (acute inflammation). These differences can be attributed to specific cytokines, because TNF-alpha and IL-1beta induced MUC2 but no MUC4 expression in gastric cancer cell lines. The two groups of tumors expressed similar levels of MUC4 that correlated with the expression of STAT3 transcription factor, implicated in the activation of genes through the IL-6 pathway. In gastric tissues from gp130(+/+), gp130(Y757F/Y757F) and gp130(Y757F/Y757F) Stat3(-/+) mice, Muc2 was not detected, whereas Muc4 was found in the gastric tumors developed in the gp130(Y757F/Y757F) mice, with hyperactivated STAT3. These data indicate that the signaling pathways associated with the inflammatory response can modulate the expression of MUC2 and MUC4 intestinal mucin genes, in human and mouse gastric tumors.

Induction of cytokine gene expression in human thyroid epithelial cells irradiated with HZE particles (iron ions)

Gene expression profiles were examined using cDNA microarray technology in human thyroid epithelial (Htori-3) cells exposed to a low, non-toxic dose (10 cGy) of radiation from HZE particles in the form of iron ions in the absence or presence of selenomethionine (SeM). A total of 215 genes were differentially regulated 2 h after exposure to a 10-cGy dose of iron-ion radiation. In the microarray analysis, SeM had profound effects on the radiation-induced expression of several specific genes, which includes PLAU, IGFBP3, FOLR1, B4GALT1 and COL1A1. Of particular interest to us was a gene cluster, "secreted proteins", that was up-regulated after radiation exposure. Seven up-regulated genes of this gene cluster fall within the chemokine/cytokine gene cluster, namely, CXCL1, CXCL2, IL6, IL11, IL8, IL24 and TGFbeta2. In microarray studies, the radiation-induced up-regulated expression of some these genes encoding cytokine/chemokine proteins was significantly decreased by SeM treatment. For IL8, TGFbeta2, CXCL1 and CXCL2, these observations were validated by qPCR techniques. It is concluded that SeM can regulate ionizing radiation-induced gene expression and may serve as an effective countermeasure for some of the acute inflammatory/immune responses induced by low-dose HZE-particle radiation.

Cytokine signalling via gp130 in gastric cancer

Cytokine signalling pathways that depend on gp130 are dysregulated in several epithelial cancers including gastric cancer. It has been established that blockade of SHP2 activation of MAPK signalling results in hyperactivation of STAT3 resulting in increased cell proliferation, angiogenesis, inflammation and inhibition of both immunocyte and epithelial cell apoptosis. Additionally, key genes regulated downstream of gp130 via MAPK activation such as the stomach-specific tumor suppressor gene tff1 are suppressed, contributing to the oncogenic outcome. The main cytokine driver of gp130 signalling in the stomach is IL-11, with IL-6 having little activity in the antral stomach in which most pathology initiates. IL-11 is up-regulated in both mouse and human gastric cancer and in pre-neoplastic mucosa. A characteristic gene signature specifically associated with IL-11 drive has been observed, although the prognostic value of the signature has not yet been assessed. Infection of human or mouse stomach with Helicobacter pylori, especially that expressing the CagA cytotoxin, produces constitutive MAPK activation, but also activated STAT3 and increases IL-11 expression. The possibility of designing and utilising small molecule inhibitors of either IL-11 or STAT3 activation may be worthwhile in developing new cancer therapeutics.

Activation of DNA methyltransferase 1 by EBV latent membrane protein 2A leads to promoter hypermethylation of PTEN gene in gastric carcinoma

CpG island promoter methylation of tumor suppressor genes is one of the most characteristic abnormalities in EBV-associated gastric carcinoma (GC). Aberrant promoter methylation and expression loss of PTEN were evaluated in cancer tissues of GC by methylation-specific PCR and immunohistochemistry, respectively, showing that both abnormalities occurred concurrently in EBV-associated GC. PTEN abnormalities were reiterated in GC cell lines MKN-1 and MKN-7 infected with recombinant EBV, and DNA methyltransferase 1 (DNMT1) was commonly overexpressed in both cell lines. Stable and transient transfection systems in MKN-1 similarly showed that viral latent membrane protein 2A (LMP2A) up-regulated DNMT1, leading to an increase in methylation of the PTEN promoter. Importantly, the level of phosphorylated signal transducer and activator of transcription 3 (pSTAT3) increased in the nuclei of LMP2A-expressing GC cells, and knockdown of STAT3 counteracted LMP2A-mediated DNMT1 overexpression. Immunohistochemistry for both pSTAT3 and DNMT1 showed diffuse labeling in the nuclei of the cancer cells in GC tissues, especially in EBV-associated GC. Taken together, LMP2A induces the phosphorylation of STAT3, which activates DNMT1 transcription and causes PTEN expression loss through CpG island methylation of the PTEN promoter in EBV-associated GC. LMP2A plays an essential role in the epigenetic abnormalities in host stomach cells and in the development and maintenance of EBV-associated cancer.

Cytokine signalling by gp130 regulates gastric mucosal healing after ulceration and, indirectly, antral tumour progression

The cytokines IL-6 and IL-11, which signal via the receptor gp130, have been implicated in various gut pathologies, including inflammation and wound healing. We used mouse cytokine signalling mutants to evaluate the role of gp130 pathways in gastric ulceration and healing and the effect of spatially remote fundic ulceration on antral tumour progression, since compromised wound healing may impact tumourigenesis. Glacial acetic acid applied to the serosal surface of stomachs from wild-type, gp130(757FF), IL-6(-/-) and IL-11 receptor (R)alpha(-/-) mice was used to induce discrete haemostasis/necrosis and resultant mucosal ulceration. Wound pathology and mRNA expression of key cytokine target genes were examined 2 and 14 weeks after ulcer induction. The outcome of fundic ulceration on antral tumour development in gp130(757FF) mice was also examined. Chemical haemostasis in gp130(7575FF) mice produces more severe gastric ulcers than in wild-type mice. Lack of IL-6 produces more severe ulceration, while loss of IL-11Ralpha less severe ulcers, suggesting a role for IL-11 in ulcer induction. Increased expression of ulcer-associated IL-11 and its established mitogenic target genes RegI, IIIbeta and IIIgamma paralleled severe ulceration in gp130(757FF) mice. In this model, coincident with fundic ulceration, antral tumour development was inhibited and correlated with decreased RegI, IIIbeta and IIIgamma and reduced MMP9 and 13 expression. IL-11-driven transcription via gp130 contributes to the gastric mucosal response to ulceration. Fundic mucosal ulceration modulates antral growth factor and metalloproteinase gene expression, thereby contributing to restricted tumour growth.

The interleukin-6 family cytokine interleukin-11 regulates homeostatic epithelial cell turnover and promotes gastric tumor development

BACKGROUND & AIMS

Gastric cancer is the second most common cause of cancer-related mortality worldwide, mainly as a result of late-stage detection. Interleukin (IL)-11 is a multifunctional cytokine reported to be up-regulated in human gastric cancer.

METHODS

We investigated the importance of IL-11 in gastric cancer progression by examining its role in a variety of mouse gastric tumor models, as well as in nonneoplastic and tumor tissues taken from gastric cancer patients. We then determined the transcriptional and translational outcomes of IL-11 overexpression in normal gastric mucosa and identified a novel gene signature important early in the progression toward gastric tumorigenesis.

RESULTS

IL-11 was up-regulated significantly in 4 diverse mouse models of gastric pathology as well as in human biopsy specimens adjacent to and within gastric cancer. Removal of IL-11 co-receptor alpha significantly reduced HKbeta-/- mouse fundic hyperplasia and ablated gp130(757F/F) mouse tumorigenesis. Exogenous IL-11 but not IL-6 activated oncogenic signal transducer and activator of transcription-3, and altered expression of novel proliferative and cytoprotective genes RegIII-beta, RegIII-gamma, gremlin-1, clusterin, and growth arrest specific-1 in wild-type gastric mucosa, a gene signature common in gp130(757F/F) and HKbeta-/- tumors as well as nonneoplastic mucosa of gastric cancer patients. One week of chronic IL-11 administration in wild-type mice sustained the gene signature, causing pretumorigenic changes in both antrum and fundus.

CONCLUSIONS

Increased gastric IL-11 alters expression of proliferative and cytoprotective genes and promotes pretumorigenic cellular changes.

Helicobacter pylori cytotoxin-associated gene A activates the signal transducer and activator of transcription 3 pathway in vitro and in vivo

Persistent infection with Helicobacter pylori confers an increased risk for the development of gastric cancer. However, the exact mechanisms whereby this bacterium causes carcinogenesis have not been completely elucidated. Recent evidence indicates that aberrant activation of the signal transducers and activators of transcription 3 (STAT3) signaling pathway may play a role in gastric carcinogenesis. Therefore, we hypothesized that H. pylori infection modulates STAT3 signaling, favoring gastric cancer development. In epithelial cells infected with H. pylori, STAT3 was activated, as assessed by immunoblotting for phosphorylated STAT3, immunofluorescence of translocated STAT3, fluorescence recovery after photobleaching, and luciferase activation in transfected cells. Activation was dependent on translocation but not phosphorylation of cytotoxin-associated gene A (CagA) in host cells. Activation seemed to be receptor-mediated because preincubation of cells with the interleukin-6 (IL-6) receptor superantagonist sant7 or inhibition of gp130 by a monoclonal antibody prevented H. pylori-mediated STAT3 activation. However, activation was not related to autocrine activation by IL-6 or IL-11. CagA+ wild-type H. pylori, but not the noncarcinogenic cagA- mutant, activated STAT3 in gastric epithelial cells in vivo in the gerbil model of H. pylori-mediated gastric carcinogenesis. Collectively, these results indicate that H. pylori CagA activates the STAT3 signaling pathway in vitro and in vivo, providing a potential mechanism by which chronic H. pylori infection promotes the development of gastric cancer.

Helicobacter and gastric malignancies

Individuals infected with Helicobacter pylori, a stomach colonizing bacteria, have an increased risk of developing gastric malignancies. The risk for developing cancer relates to the physiologic and histologic changes that H. pylori infection induces in the stomach. In the last year numerous studies have been conducted in order to characterize the association between H. pylori infection and gastric cancer. These studies range from epidemiologic approaches aiming at the identification of environmental, host genetic, and bacterial factors associated with risk of gastric cancer, to molecular and cell biology approaches aiming at understanding the interaction between H. pylori and the transforming epithelial cell. In this review an account of the last year's research activity on the relationship between H. pylori and gastric cancer will be given.

Mechanism for gastric cancer development by Helicobacter pylori infection

Helicobacter pylori (H. pylori) infection plays a crucial role in the development of gastric cancer. There are two major pathways for the development of gastric cancer by H. pylori infection: the indirect action of H. pylori on gastric epithelial cells through inflammation, and the direct action of the bacteria on epithelial cells through the induction of protein modulation and gene mutation. Both pathways work together to promote gastric carcinogenesis.

Transgenic cyclooxygenase-2 expression and high salt enhanced susceptibility to chemical-induced gastric cancer development in mice

Cyclooxoygenase (COX)-2 overexpression is involved in gastric carcinogenesis. While high-salt intake is a known risk factor for gastric cancer development, we determined the effects of high salt on gastric chemical carcinogenesis in COX-2 transgenic (TG) mice. COX-2 TG mice were developed in C57/BL6 strain using the full-length human cox-2 complementary DNA construct. Six-week-old COX-2 TG and wild-type (WT) littermates were randomly allocated to receive alternate week of N-methyl-N-nitrosourea (MNU, 240 p.p.m.) in drinking water or control for 10 weeks. Two groups of mice were further treated with 10% NaCl during the initial 10 weeks. All mice were killed at the end of week 50. Both forced COX-2 overexpression and high-salt intake significantly increased the frequency of gastric cancer development in mice as compared with WT littermates treated with MNU alone. However, no additive effect was observed on the combination of high salt and COX-2 expression. We further showed that MNU and high-salt treatment increased chronic inflammatory infiltrates and induced prostaglandin E(2) (PGE(2)) production in the non-cancerous stomach. Whereas high-salt treatment markedly increased the expression of inflammatory cytokines (tumor necrosis factor-alpha, interferon-gamma, interleukin (IL)-1 beta and IL-6) in the gastric mucosa, COX-2 overexpression significantly altered the cell kinetics in the MNU-induced gastric cancer model. In conclusion, both high salt and COX-2 overexpression promote chemical-induced gastric carcinogenesis, possibly related to chronic inflammation, induction of PGE(2), disruption of cell kinetics and induction of inflammatory cytokines.

Effects of different Helicobacter pylori culture filtrates on growth of gastric epithelial cells

AIM

To study the effects of different Helicobacter pylori (H pylori) culture filtrates on growth of gastric epithelial cells.

METHODS

Broth culture filtrates of H pylori were prepared. Gastric epithelial cells were treated with the filtrates, and cell growth was determined by growth curve and flow cytometry. DNA damage of gastric epithelial cells was measured by single-cell microgel electrophoresis.

RESULTS

Gastric epithelial cells proliferated actively when treated by CagA-gene-positive broth culture filtrates, and colony formation reached 40%. The number of cells in S phase increased compared to controls. Comet assay showed 41.2% comet cells in GES-1 cells treated with CagA-positive filtrates (P < 0.05).

CONCLUSION

CagA-positive filtrates enhance the changes in morphology and growth characteristics of human gastric epithelial tumor cells. DNA damage maybe one of the mechanisms involved in the growth changes.