Upregulated Akt signaling adjacent to gastric cancers: implications for screening and chemoprevention

Transcriptome changes of Takifugu obscurus liver after acute exposure to phenanthrene

Phenanthrene (Phe) is a model compound in polycyclic aromatic hydrocarbon (PAH) research. Reportedly, Phe treatment induced oxidative stress and histological disorders to Takifugu obscurus liver. In this study, to further explore the molecular responses of T. obscurus liver to Phe exposure, transcriptome sequencing was applied to compare mRNA transcription profiles between Phe treatment and the control. Compared with the control, 1,581 and 1,428 genes were significantly upregulated and downregulated in Phe treatment, respectively. Further analysis revealed that Phe treatment mainly upregulated genes in Ras-MAPK and PI3K-akt signaling pathways, which represented insulin resistance and further activated the FOXO signaling pathway. The triacylglycerol biosynthesis was promoted but the gluconeogenesis process was inhibited in response to Phe treatment, demonstrating that Phe exposure disturbed the sugar and lipid metabolism. Moreover, Phe treatment upregulated the Apelin-APJ and ErbB signaling pathways, promoting angiogenesis in T. obscurus liver. Insulin resistance, promoted triacylglycerol biosynthesis, and angiogenesis might explain the molecular mechanisms underlying carcinogenic toxicity of Phe. Overall, this study provides new insights to understand the environmental risk of Phe to fishes.

Integrated bioinformatics analysis to decipher molecular mechanism of compound Kushen injection for esophageal cancer by combining WGCNA with network pharmacology

Compound Kushen injection (CKI), a medicine in widespread clinical use in China, has proven therapeutic effects on cancer. However, few molecular mechanism analyses have been carried out. To address this problem, bioinformatics approaches combining weighted gene co-expression network analysis with network pharmacology methods were undertaken to elucidate the underlying molecular mechanisms of CKI in the treatment of esophageal cancer (ESCA). First, the key gene modules related to the clinical traits of ESCA were analysed by WCGNA. Based on the results, the hub genes related to CKI treatment for ESCA were explored through network pharmacology. Molecular docking simulation was performed to recognize the binding activity of hub genes with CKI compounds. The results showed that the potential hub targets, including EGFR, ErbB2, CCND1 and IGF1R, are therapeutic targets of CKI for the treatment of ESCA. Moreover, these targets were significantly enriched in many pathways related to cancer and signalling pathways, such as the PI3K-Akt signalling pathway and ErbB signalling pathway. In conclusion, this research partially highlighted the molecular mechanism of CKI in the treatment of ESCA, offering great potential in the identification of the effective compounds in CKI and biomarkers for ESCA treatment.

Identification of the lncRNA-miRNA-mRNA network associated with gastric cancer via integrated bioinformatics analysis

The aim of the present study was to investigate the long non-coding RNA (lncRNA)-microRNA (miRNA)-mRNA regulatory network in gastric cancer (GC) using bioinformatics analysis. Two mRNA gene expression profiles, GSE79973 and GSE54129, and two miRNA expression profiles, GSE93415 and GSE78091, were downloaded from the Gene Expression Omnibus database. The differentially expressed mRNAs (DEMs) and the differentially expressed miRNAs (DEMis) were merged separately. Gene ontology and pathway enrichment analysis were conducted using the Database for Annotation, Visualization and Integrated Discovery. A protein-protein interaction (PPI) network was then constructed and the 10 top hub genes in the network were analyzed using the Search Tool for the Retrieval of Interacting Genes. The lncRNA-miRNA-mRNA networks were visualized using Cytoscape software. As a result, 158 shared DEMs (40 upregulated and 118 downregulated) were identified from two mRNA datasets. A total of 30 upregulated miRNAs and 1 downregulated miRNA functioned as DEMis. The PPI network consisted of 129 nodes and 572 interactions. The 10 top hub genes were selected by degree using Cytohubba, including Jun proto-oncogene, mitogen-activated protein kinase (MAPK)3, transforming growth factor-β1, Fos proto-oncogene, AP-1 transcription factor subunit, interleukin (IL)-8, MAPK1, RELA proto-oncogene nuclear factor-κB subunit, interferon regulatory factor 7, ubiquitin like modifier and vascular endothelial growth factor A. In the lncRNA-miRNA-mRNA network, a total of 1,215 regulatory associations were constructed using Cytoscape. In conclusion, the present study provides a novel perspective of the molecular mechanisms underlying GC by identifying the lncRNA-miRNA-mRNA regulatory network via bioinformatics analysis.

Increased Thioredoxin-1 Expression Promotes Cancer Progression and Predicts Poor Prognosis in Patients with Gastric Cancer

Background

Thioredoxin-1 (Trx-1) is a small redox protein, which plays an important role in many biological processes. Although increased expression of Trx-1 in various solid tumors has been reported, the prognostic significance and function of Trx-1 in human gastric cancer (GC) are still unclear. Here, we investigated the clinical and prognostic significance of Trx-1 expression and the function and mechanism of Trx-1 in human GC.

Methods

We analyzed Trx-1 mRNA expression from the GEO database and Trx-1 protein expression in 144 GC tissues using immunohistochemistry. Effects of Trx-1 on GC cell were assessed in vitro and in vivo through Trx-1 knockdown or overexpression. The antitumor effects of the Trx-1 inhibitor, PX-12, on GC cells were investigated. PTEN and p-AKT expressions were evaluated by Western blotting.

Results

Increased Trx-1 expression was found in GC tissues and associated with poor prognosis and aggressive clinicopathological characteristics in patients with GC. High Trx-1 expression predicted poor prognosis, and its expression was an independent prognostic factor for overall survival of GC patients. Knockdown of Trx-1 expression inhibited GC cell growth, migration, and invasion in vitro and tumor growth and lung metastasis in vivo. Conversely, overexpression of Trx-1 promoted GC cell growth, migration, and invasion. We also found that PX-12 inhibited GC cell growth, migration, and invasion. Overexpression of Trx-1 caused a decrease in PTEN and increase in p-AKT levels whereas silencing Trx-1 caused an increase in PTEN and decrease in p-AKT levels in GC cells. Inhibition of AKT signaling pathway by MK2206 also inhibited GC cell growth, migration, and invasion.

Conclusion

Our results indicate that Trx-1 may be a promising prognostic indicator and therapeutic target for GC patients.

Pan-Pim Kinase Inhibitor AZD1208 Suppresses Tumor Growth and Synergistically Interacts with Akt Inhibition in Gastric Cancer Cells

Purpose

Pim kinases are highly conserved serine/threonine kinases, and different expression patterns of each isoform (Pim-1, Pim-2, and Pim-3) have been observed in various types of human cancers, including gastric cancer. AZD1208 is a potent and selective inhibitor that affects all three isoforms of Pim. We investigated the effects of AZD1208 as a single agent and in combination with an Akt inhibitor in gastric cancer cells.

Materials and Methods

The antitumor activity of AZD1208 with/without an Akt inhibitor was evaluated in a large panel of gastric cancer cell lines through growth inhibition assays. The underlying mechanism was also examined by western blotting, immunofluorescence assay, and cell cycle analysis.

Results

AZD1208 treatment decreased gastric cancer cell proliferation rates and induced autophagy only in long-term culture systems. Light chain 3B (LC3B), a marker of autophagy, was increased in sensitive cells in a dose-dependent manner with AZD1208 treatment, which suggested that the growth inhibition effect of AZD1208 was achieved through autophagy, not apoptosis. Moreover, we found that cells damaged by Pim inhibition were repaired by activation of the DNA damage repair pathway, which promoted cell survival and led the cells to become resistant to AZD1208. We also confirmed that the combination of an Akt inhibitor with AZD1208 produced a highly synergistic effect in gastric cancer cell lines.

Conclusion

Treatment with AZD1208 alone induced considerable cell death through autophagy in gastric cancer cells. Moreover, the combination of AZD1208 with an Akt inhibitor showed synergistic antitumor effects through regulation of the DNA damage repair pathway.

Helicobacter pylori CagA protein activates Akt and attenuates chemotherapeutics-induced apoptosis in gastric cancer cells

Infection with cagA-positive Helicobacter pylori is associated with a higher risk of gastric cancer. The cagA gene product, CagA, is translocated into gastric epithelial cells and perturbs host cellular biological functions. Etoposide, a topoisomerase II inhibitor widely used to couple DNA damage to apoptosis, is a common cytotoxic agent used for advanced gastric cancer. We investigate the effect of CagA on etoposide-induced apoptosis in gastric cancer cells to elucidate whether CagA play a role in gastric carcinogenesis via impairing DNA damage-dependent apoptosis. AGS cell lines stably expressing CagA isolated from H. pylori 26695 strain were established. In the presence of etoposide, viability of parental AGS cells was decreased in a time-and dose-dependent manner, whereas CagA-expressing AGS cells were less susceptible to etoposide induced cell-killing effect. Suppression of etoposide-induced apoptosis was shown in CagA-expressing but not in parental AGS cells by DNA fragmentation, cell cycle, and annexin-V assays. This inhibitory effect of etoposide-induced apoptosis conferred by CagA was also demonstrated in SCM1 and MKN45 gastric cancer cell lines, with two additional chemotherapeutics, 5-FU and cisplatin. The effect of Akt activation on inhibition of etoposide-induced cytotoxicity by CagA was also evaluated. CagA expression and etoposide administration activate Akt in a dose-dependent manner. Enhancement of etoposide cytotoxicity by a PI-3-kinase inhibitor, LY294002, was evident in parental but was attenuated in CagA-expressing AGS cells. CagA may activate Akt, either in the absence or presence of etoposide, potentially contributing to gastric carcinogenesis associated with H. pylori infection and therapeutic resistance by impairing DNA damage-dependent apoptosis.

Combination of cecropinXJ and LY294002 induces synergistic cytotoxicity, and apoptosis in human gastric cancer cells via inhibition of the PI3K/Akt signaling pathway

The aim of the present study was to investigate the cytotoxic and apoptotic effects of cecropinXJ against human gastric cancer BGC823 cells, either alone, or in combination with a specific phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002. Cell viability and the apoptosis rate were measured using flow cytometry with Annexin-V staining. Additionally, the expression levels of several RAC-α serine/threonine kinase (Akt) phosphorylation-associated proteins and apoptosis-regulating proteins were evaluated by western blot analysis. It was observed that the combination of cecropinXJ and LY294002 resulted in significant synergistic cytotoxic and apoptosis effects, as compared with any single agent alone, in a dose-dependent manner. Corresponding to enhanced apoptosis, the expression levels of certain apoptosis-regulating proteins were changed, the most notable being the upregulation of caspase-3, B-cell lymphoma-2 (Bcl-2)-associated death promotor, Bcl-2 homologous antagonist killer, Bcl-2 interacting killer, Bcl-2-like protein 11, Bcl-2-like protein 4 and cytochrome c, and the downregulation of phosphorylated-Bad and Bcl-2 proteins. The present study provided a novel therapeutic regimen for the use of the cecropinXJ in combination with LY294002 for the treatment of gastric cancer.

Gastrokine 1 inhibits the carcinogenic potentials of Helicobacter pylori CagA

Helicobacter pylori CagA directly injected by the bacterium into epithelial cells via a type IV secretion system, leads to cellular changes such as morphology, apoptosis, proliferation and cell motility, and stimulates gastric carcinogenesis. We investigated the effects of cytotoxin-associated gene A (CagA) and gastrokine 1 (GKN1) on cell proliferation, apoptosis, reactive oxygen species (ROS) production, epithelial-mesenchymal transition (EMT) and cell migration in CagA- or GKN1-transfected gastric epithelial cells and mucosal tissues from humans and mice infected with H.pylori. On the molecular level, H.pylori CagA induced increased cell proliferation, ROS production, antiapoptotic activity, cell migration and invasion. Moreover, CagA induced activation of NF-κB and PI3K/Akt signaling pathways and EMT-related proteins. In addition, H.pylori CagA reduced GKN1 gene copy number and expression in gastric cells and mucosal tissues of humans and mice. However, GKN1 overexpression successfully suppressed the carcinogenic effects of CagA through binding to CagA. These results suggest that GKN1 might be a target to inhibit the effects from H.pylori CagA.

Involvement of the Akt signaling pathway in ER-α36/GRP94-mediated signaling in gastric cancer

Glucose-regulated protein 94 (GRP94) has been implicated in the promotion of tumor proliferation and metastasis. Previous studies have found that GRP94 is involved in the malignant growth of gastric carcinoma cells through estrogen receptor-α36 (ER-α36)-mediated estrogen signaling, but the underlying mechanism remains unclear. In the present study, we examined the expression levels of GRP94 and ER-α36 in tumor specimens from gastric cancer patients by immunohistochemistry, and found that both GRP94 and ER-α36 were highly expressed in the cytoplasms of gastric carcinoma cells. Furthermore, treatment with 17β-estradiol at a concentration of 10⁻¹² M for 24 h increased the expression levels of GRP94 and ER-α36, and the phosphorylation levels of Akt at the Ser473 site (Ser473-Akt). In established SGC7901 gastric cancer cells with knockdown of ER-α36 expression, the levels of GRP94 and Ser473-Akt expression were significantly reduced. Thus, the Akt signaling pathway is a potentially important signaling pathway in ER-α36-GRP94-mediated gastric carcinogenesis.

β-lapachone-Induced Apoptosis of Human Gastric Carcinoma AGS Cells Is Caspase-Dependent and Regulated by the PI3K/Akt Pathway

β-lapachone is a naturally occurring quinone that selectively induces apoptotic cell death in a variety of human cancer cells in vitro and in vivo; however, its mechanism of action needs to be further elaborated. In this study, we investigated the effects of β-lapachone on the induction of apoptosis in human gastric carcinoma AGS cells. β-lapachone significantly inhibited cellular proliferation, and some typical apoptotic characteristics such as chromatin condensation and an increase in the population of sub-G1 hypodiploid cells were observed in β-lapachone-treated AGS cells. Treatment with β-lapachone caused mitochondrial transmembrane potential dissipation, stimulated the mitochondria-mediated intrinsic apoptotic pathway, as indicated by caspase-9 activation, cytochrome c release, Bcl-2 downregulation and Bax upregulation, as well as death receptor-mediated extrinsic apoptotic pathway, as indicated by activation of caspase-8 and truncation of Bid. This process was accompanied by activation of caspase-3 and concomitant with cleavage of poly(ADP-ribose) polymerase. The general caspase inhibitor, z-VAD-fmk, significantly abolished β-lapachone-induced cell death and inhibited growth. Further analysis demonstrated that the induction of apoptosis by β-lapachone was accompanied by inactivation of the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway. The PI3K inhibitor LY29004 significantly increased β-lapachone-induced apoptosis and growth inhibition. Taken together, these findings indicate that the apoptotic activity of β-lapachone is probably regulated by a caspase-dependent cascade through activation of both intrinsic and extrinsic signaling pathways, and that inhibition of the PI3K/Akt signaling may contribute to β-lapachone-mediated AGS cell growth inhibition and apoptosis induction.

The Role of PI3K/Akt/mTOR Signaling in Gastric Carcinoma

The phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway is one of the key signaling pathways induced by various receptor-tyrosine kinases. Accumulating evidence shows that this pathway is an important promoter of cell growth, metabolism, survival, metastasis, and resistance to chemotherapy. Genetic alterations in the PI3K/Akt/mTOR pathway in gastric carcinoma have often been demonstrated. Many kinds of molecular targeting therapies are currently undergoing clinical testing in patients with solid tumors. However, with the exception of the ErbB2-targeting antibody, targeting agents, including PI3K/Akt/mTOR inhibitors, have not been approved for treatment of patients with gastric carcinoma. This review summarizes the current knowledge on PI3K/Akt/mTOR signaling in the pathogenesis of gastric carcinoma and the possible therapeutic targets for gastric carcinoma. Improved knowledge of the PI3K/Akt/mTOR pathway in gastric carcinoma will be useful in understanding the mechanisms of tumor development and for identifying ideal targets of anticancer therapy for gastric carcinoma.

Akt-p53-miR-365-cyclin D1/cdc25A axis contributes to gastric tumorigenesis induced by PTEN deficiency

Although PTEN/Akt signaling is frequently deregulated in human gastric cancers, the in vivo causal link between its dysregulation and gastric tumorigenesis has not been established. Here we show that inactivation of PTEN in mouse gastric epithelium initiates spontaneous carcinogenesis with complete penetrance by 2 months of age. Mechanistically, activation of Akt suppresses the abundance of p53, leading to decreased transcription of miR-365, thus causing upregulation of cyclin D1 and cdc25A, which promotes gastric cell proliferation. Importantly, genetic ablation of Akt1 restores miR-365 expression and effectively rescues gastric tumorigenesis in PTEN-mutant mice. Moreover, orthotopic restoration of miR-365 represses PTEN-deficient-induced hyperplasia. In human gastric cancer tissues, miR-365 reduction correlates with poorly differentiated histology, deep invasion and advanced stage, as well as the deregulation of PTEN, phosphorylated Akt, p53, cyclin D1 and cdc25A. These data demonstrate that the PTEN-Akt-p53-miR-365-cyclin D1/cdc25A axis serves as a new mechanism underlying gastric tumorigenesis, providing potential new therapeutic targets.

Gastrokine 1 functions as a tumor suppressor by inhibition of epithelial-mesenchymal transition in gastric cancers

PURPOSE

Gastrokine 1 (GKN1) plays an important role in the gastric mucosal defense mechanism and also acts as a functional gastric tumor suppressor. The specific aim of this study was to determine the molecular mechanisms underlying GKN1 tumor suppressor activity in the progression of gastric cancers.

METHODS

We examined the effect of GKN1 on epithelial-mesenchymal transition (EMT) and cell migration in GKN1-transfected and recombinant GKN1-treated AGS gastric cancer cells using in vitro wound healing, microchemotaxis, and invasion assays.

RESULTS

In GKN1-transfected AGS cells, we observed inhibition of cell migration and invasion in wound healing, transwell and Matrigel assay. Also, GKN1-transfected and recombinant GKN1-treated AGS cells showed decreased levels of ROS and expression of phosphatidylinositol 3-kinase (PI3K)/Akt pathway proteins, concomitant with re-expression of E-cadherin and decreased expression of cytoplasmic and nuclear expression of β-catenin, slug, snail, fibronectin, and vimentin.

CONCLUSIONS

These data suggest that the GKN1 gene may play an important role in the progression of sporadic gastric cancers via inhibition of EMT and cancer cell migration.

Programmed cell death 4 (PDCD4) enhances the sensitivity of gastric cancer cells to TRAIL-induced apoptosis by inhibiting the PI3K/Akt signaling pathway

OBJECTIVE

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is thought to be a promising anti-neoplastic agent because of its ability to selectively induce apoptosis in cancer cells. However, some cancer cells are resistant to TRAIL. The mechanisms underlying this resistance are unclear. The aim of this study was to explore the role of programmed cell death 4 (PDCD4) in regulating TRAIL sensitivity in gastric cancer cells.

METHODS

PDCD4 complementary DNA and PDCD4-specific short-hairpin RNA (shRNA) fragments were transfected into TRAIL-sensitive and -resistant gastric cancer cells. Expression of PDCD4 and Akt was detected via western blot. Cell survival and apoptosis were measured using 3-(4,5-dimethylthiazolyl)-2,5-diphenyltetrazolium bromide (MTT) and flow cytometry (FCM) assays.

RESULTS

We found that upregulation of PDCD4 enhanced TRAIL sensitivity in gastric cancer cells. Downregulation of PDCD4 decreased TRAIL sensitivity. Inhibition of Akt by the phosphoinositide 3-kinase (PI3K) inhibitor LY294002 induced PDCD4 activity and enhanced TRAIL sensitivity in TRAIL-resistant gastric cancer cells.

CONCLUSION

We demonstrated that PDCD4 regulates TRAIL sensitivity in gastric cancer cells by inhibiting the PI3K/Akt signaling pathway.

LY294002 potentiates the anti-cancer effect of oxaliplatin for gastric cancer via death receptor pathway

AIM: To examine the effects of combined treatment of oxaliplatin and phosphatidylinositol 3’-kinase inhibitor, 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002) for gastric cancer.

METHODS: Cell viability was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Apoptotic cells were detected by flow cytometric analysis and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay. Western blotting and immuno-precipitation were used to examine protein expression and recruitment, respectively. Nuclear factor κB (NFκB) binding activities were investigated using electrophoretic mobility shift assay. Nude mice were used to investigate tumor growth.

RESULTS: Treatment with combined oxaliplatin and LY294002 resulted in increased cell growth inhibition and cell apoptosis in vitro, and increased tumor growth inhibition and cell death in the tumor mass in vivo. In MKN45 and AGS cells, oxaliplatin treatment promoted both protein kinase B (Akt) and NFκB activation, while pretreatment with LY294002 significantly attenuated oxaliplatin-induced Akt activity and NFκB binding. LY294002 promoted oxaliplatin-induced Fas ligand (FasL) expression, Fas-associated death domain protein recruitment, caspase-8, Bid, and caspase-3 activation, and the short form of cellular caspase-8/FLICE-inhibitory protein (c-FLIP_S) inhibition. In vivo, LY294002 inhibited oxaliplatin-induced activation of Akt and NFκB, and increased oxaliplatin-induced expression of FasL, inhibition of c-FLIP_S, and activation of caspase-8, Bid, and caspase-3.

CONCLUSION: Combination of oxaliplatin and LY294002 was therapeutically promising for gastric cancer treatment. The enhanced sensitivity of the combined treatment was associated with the activation of the death receptor pathway.

BMP2 accelerates the motility and invasiveness of gastric cancer cells via activation of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway

Up-regulation of bone morphogenetic proteins (BMPs) and their receptors by tumor is an important hallmark in cancer progression, as it contributes through autocrine and paracrine mechanisms to tumor development, invasion, and metastasis. Generally, increased motility and invasion are positively correlated with the epithelial-mesenchymal transition (EMT). The purpose of the present study was to determine whether BMP-2 signaling to induce gastric cancer cells to undergo EMT-mediated invasion might pass through the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. Herein we showed that gastric cancer cell lines express all the components of BMP-2 signaling, albeit to different extents. Moreover, an increased concentration of BMP-2 strongly enhanced motility and invasiveness in gastric cancer cells, whereas no increase was observed in cells treated with either Noggin (a BMP-2 inhibitor) or BMP-2 blocking antibodies. The stimulation of BMP-2 in gastric cancer cells induces a full EMT characterized by Snail induction, E-cadherin delocalization and down-regulation, and up-regulation of mesenchymal and invasiveness markers. Furthermore, blockade of BMP-2 signaling by Noggin or BMP-2 blocking antibodies also restored these changes in EMT markers. In addition, phosphorylation of Akt was also enhanced by treatment with BMP-2, but not Noggin or BMP-2 blocking antibodies. Pretreatment of gastric cancer cells with PI-3 kinase/Akt kinase inhibitor (kinase-dead Akt [DN-Akt], Akt siRNA, or LY294002) significantly inhibited BMP-2-induced EMT and invasiveness. Overall, our studies suggest that BMP-2 promotes motility and invasion of gastric cancer cells by activating PI-3 kinase/Akt and that targeting of this signaling pathway may provide therapeutic opportunities in preventing metastasis mediated by BMP-2.

Application of PI3K/Akt and COX-2 signal pathway blockage in treatment of gastric carcinoma

The abnormal alternation of phosphatidylinositol-3-kinase/Protein Kinase B (PI3K/PKB) and cyclooxygenase-2 (COX-2) signal pathways plays an important role in emergence and development of tumors, which also contributes to a series of biological processes and exerts a tremendous influence on treatment and prognosis of tumors. This review investigates PI3K/Akt and COX-2 signal pathways blockage and their mechanism, and provided a original direction for molecular target therapy of diverse tumors including gastric carcinoma.

Helicobacter pylori activate epidermal growth factor receptor- and phosphatidylinositol 3-OH kinase-dependent Akt and glycogen synthase kinase 3beta phosphorylation

The signalling pathways leading to the development of Helicobacter pylori-induced gastric cancer remain poorly understood. We tested the hypothesis that H. pylori infections involve the activation of Akt signalling in human gastric epithelial cancer cells. Immunoblot, immunofluorescence and kinase assays show that H. pylori infection of gastric epithelial cells induced phosphorylation of Akt at Ser 473 and Thr 308. Mutations in the H. pylori virulence factor OipA dramatically reduced phosphorylation of Ser 473, while the cag pathogenicity island mutants predominantly inhibited phosphorylation of Thr 308. As the downstream of Akt activation, H. pylori infection inactivated the inactivation of glycogen synthase kinase 3beta at Ser 9 by its phosphorylation. As the upstream of Akt activation, H. pylori infection activated epidermal growth factor receptor (EGFR) at Tyr 992, phosphatidylinositol 3-OH kinase (PI3K) p85 subunit and PI3K-dependent kinase 1 at Ser 241. Pharmacologic inhibitors of PI3K or mitogen-activated protein kinase kinase (MEK), Akt knock-down and EGFR knock-down showed that H. pylori infection induced the activation of EGFR-->PI3K-->PI3K-dependent kinase 1-->Akt-->extracellular signal-regulated kinase signalling pathways, the inactivation of glycogen synthase kinase 3beta and interleukin-8 production. The combined functions of cag pathogenicity island and OipA were necessary and sufficient for full activation of signalling at each level. We propose activation of these pathways as a novel mechanism for H. pylori-mediated carcinogenesis.

Helicobacter pylori infection upregulates endothelial nitric oxide synthase expression and induces angiogenesis in gastric mucosa of dyspeptic patients

BACKGROUND

Helicobacter pylori (H. pylori) infection induces nitric acid (NO) overproduction through inducible NO synthase (NOS) expression, subsequent DNA damage and enhanced antiapoptosis signal transduction sequence in the human gastric mucosa, whereas its possible effect on endothelial nitric oxide synthase (eNOS) expression has not as yet been investigated. The aim of this study was to evaluate the effect of H. pylori infection in the expression of eNOS in gastric mucosa.

PATIENTS AND METHODS

We prospectively studied 30 nonsmoking dyspeptic patients (12 men, 18 women, mean age 54.26+/-12.89 years). The diagnosis of H. pylori infection was based mainly on histology. The histological grading of H. pylori infection was evaluated according to the modified Sydney classification. Histological grading of eNOS expression and microvessel density as estimated by CD34 expression were determined by immunohistochemistry (degree 0-3) and correlated with H. pylori infection and histological degree of gastritis.

RESULTS

Twelve patients were H. pylori-positive and 18 patients were H. pylori-negative. The two groups were matched for age (P=0.139), sex (P=0.342) and similar degree of gastritis. Intensity of eNOS and CD34 expression in the corpus and antrum were significantly correlated (P<0.001). eNOS expression was correlated with H. pylori infection in the mucosa of the body and antrum (P=0.013 and 0.037, respectively) but not with gastric inflammation and activity (P=0.848 and 0.871, respectively, for the corpus and P=0.565 and 0.793, respectively, for the antrum). H. pylori-positive patients showed higher expression of CD34-positive blood vessels in the mucosa of the antrum (P=0.048). CD34 expression was correlated with gastric inflammation and activity (P=0.03 and 0.044, respectively) in the mucosa of the antrum of H. pylori-positive patients.

CONCLUSION

H. pylori infection upregulates eNOS, and induces angiogenesis, contributing to H. pylori-associated pathophysiology in gastric mucosa.

Posttranscriptional regulation of the telomerase hTERT by gambogic acid in human gastric carcinoma 823 cells

We previously reported that gambogic acid (GA), a natural product, was an effective telomerase inhibitor by repressing hTERT promoter. In this study, posttranscriptional regulation of the telomerase hTERT by GA was investigated in BGC-823 human gastric carcinoma cells. The telomerase activity was detected by PCR-TRAP assay. RT-PCR assay and Western blot were performed to examine the repression of telomerase hTERT and c-Myc after GA or c-Myc-specific siRNA treatment. The results indicated that GA repressed telomerase activity and hTERT transcriptional activity via down-regulation of c-Myc expression in BGC-823 human gastric carcinoma cells. We further observed that hTERT transcriptional activity was not completely blocked by c-Myc-specific siRNA, suggesting that additional factors are involved in the repression of telomerase activity. The results of Western blot and immunoprecipitation assay revealed that GA inhibits the phosphorylation of Akt. The further results also confirmed that celecoxib, an inhibitor of Akt phosphorylation, could significantly repressed telomerase activity alone and enhance the repression of telomerase activity combined with GA. These data suggested that GA inhibits the posttranslational modification of hTERT by inhibiting the phosphorylation of Akt. Collectively, we suggest that GA represses telomerase activity not only by repressing hTERT transcriptional activity via c-Myc but also by posttranslational modification of hTERT via Akt.

Phosphoinositide 3-kinase/Akt pathway plays an important role in chemoresistance of gastric cancer cells against etoposide and doxorubicin induced cell death

The major obstacle to successful treatment of gastric cancer is chemotherapy resistance. Our study was designed to investigate the role of phosphoinositide 3-kinase (PI3K)/Akt pathway in the development of chemoresistance in gastric cancer. In the present study, elevated Akt expression and Akt phosphorylation (Ser 473), as well as decreased PTEN expression were observed in 28 cases of gastric cancer tissues. Etoposide and doxorubicin stimulated Akt and PI3K activities in 2 gastric cancer cell lines (BGC-823 and SGC-7901), and the activities were concentration and time-dependent. Up-regulation of PTEN expression in BGC-823 cells by PEAK8-PTEN transient transfection obviously decreased the basal and anticancer drugs induced Akt activities, then sensitized BGC-823 cells to etoposide and doxorubicin. Pretreatment of BGC-823 and SGC-7901 cells with wortmannin, a PI3K inhibitor, attenuated cells's resistance to etoposide and doxorubicin. In addition, pretreatment of wortmannin blocked etoposide and doxorubicin induced IkappaB-alpha degradation, NFkappaB activation, phosphorylation of Akt, MDM-2 and forkhead transcription factors. Wortmannin pretreatment also promoted the accumulation of p27/Kip, but inhibited the Mcl-1 expression. Furthermore, wortmannin promoted etoposide and doxorubicin induced caspase-3, caspase-9 activation and poly ADP-ribose polymerase cleavage. Taken together, the observations indicate the PI3K/Akt pathway plays an important role in the chemoresistance of gastric cancer cells. A new strategy for combined chemotherapy of gastric cancer should be designed to more specifically block PI3K/Akt pathway and then decrease the amount of resistant cells.

Field defects in progression to gastrointestinal tract cancers

A field of defective tissue may represent a pre-malignant stage in progression to many cancers. However, field defects are often overlooked in studies of cancer progression through assuming tissue at some distance from the cancer is normal. We indicate, however, the generality of field defects in gastrointestinal cancers, including cancers of the oropharynx, esophagus, stomach, bile duct, pancreas, small intestine and colon/rectum. Common features of these field defects are reduced apoptosis competence, aberrant proliferation and genomic instability. These features are often associated with high bile acid exposure and may explain the association of dietary-related factors with cancer progression.

Celecoxib induces apoptosis in COX-2 deficient human gastric cancer cells through Akt/GSK3beta/NAG-1 pathway

In this study, we analyzed the mechanisms of the apoptotic effects of celecoxib on COX-2 deficient gastric cancer cell line, MGC-803. We found celecoxib treatment induced caspase-dependent apoptosis in MGC-803 cells. Celecoxib inhibited Ser473 Akt and Ser9 GSK3beta phosphorylation and induced upregulation of nonsteroidal anti-inflammatory drugs-activated gene-1 (NAG-1) expression. The effects of celecoxib on NAG-1 expression were abolished by pretreatment with GSK3beta inhibitor, SB216763. Furthermore, GSK3beta gene silencing by siRNA inhibited the celecoxib-induced NAG-1 expression. Our study demonstrated that Akt/GSK3beta/NAG-1 signal pathway may represent as the major mechanism of the COX-2-independent effects of celecoxib on gastric cancer cells.