Epigenetic mechanisms in gastric cancer

Epigenome-based personalized medicine in human cancer

Cancer genome sequencing has created an opportunity for precision medicine. Thus far, genetic alterations can only be used to guide treatment for small subsets of certain cancer types with these key alterations. Similar to mutations, epigenetic events are equally suitable for personalized medicine. DNA methylation alterations have been used to identify tumor-specific drug responsive markers. Methylation of MGMT sensitizes gliomas to alkylating agents is an example of epigenetic personalized medicine. Recent studies have revealed that 5-azacytidine and decitabine show activity in myelodysplasia, lung and other cancers. There are currently at least 20 kinds of histone deacetylase inhibitors in clinical testing. Inhibitors targeting other epigenetic regulators are being clinically tested, such as EZH2 inhibitor EPZ-6438.

The role of piRNA and its potential clinical implications in cancer

Epigenetic mechanisms work in an orchestrated fashion to control gene expression in both homeostasis and diseases. Among small noncoding RNAs, piRNAs seem to meet the necessary requirements to be included in this epigenetic network due to their role in both transcriptional and post-transcriptional regulation. piRNAs and PIWI proteins might play important roles in cancer occurrence, prognosis and treatment as reported previously. Nevertheless, the potential clinical relevance of these molecules has yet been elucidated. A brief overview of piRNA biogenesis and their potential roles as part of an epigenetic network that is possibly involved in cancer is provided. Moreover, potential strategies based on the use of piRNAs and PIWI proteins as diagnostic and prognostic biomarkers as well as for cancer therapeutics are discussed.

Microsatellite instability: an update

Deficient DNA mismatch repair (MMR) results in a strong mutator phenotype known as microsatellite instability (MSI), which is a hallmark of Lynch syndrome-associated cancers. MSI is characterized by length alterations within simple repeated sequences that are called microsatellites. Lynch syndrome is primarily caused by mutations in the MMR genes, mainly MLH1 and MSH2, and less frequently in MSH6, and rarely PMS2, and large genomic rearrangements account for 5-20 % of all mutations. Germ line hemiallelic methylations of MLH1 or MSH2 are termed as epimutations and have been identified as causative of Lynch syndrome. Moreover, germ line 3' deletions of EPCAM gene is involved in MSH2 methylation. MSI is also observed in about 15 % of sporadic colorectal cancer (CRC), gastric cancer (GC), and endometrial cancer (EC), and at lower frequencies in other cancers, often in association with hypermethylation of the MLH1 gene. Trimethylation of histone H3 on Lys36 (H3K36 me3) is an epigenetic histone mark that was required for DNA MMR in vivo. Thus, mutations in the H3K36 trimethyltransferase SETD2 have been reported as a potential cause of MSI. Genetic, epigenetic, and transcriptomic differences have been identified between cancers with and without MSI. Recent comprehensive molecular characterizations of CRC, EC, and GC by The Cancer Genome Atlas indicate that MSI+ cancers are distinct biological entities. The BRAF V600E mutation is specifically associated with sporadic MSI+ CRCs with methylated MLH1, but is not associated with Lynch syndrome-related CRCs. Accumulating evidence indicates a role of interactions between MSI and microRNA (miRNA) in the pathogenesis of MSI-positive (MSI+) cancer. As another new mechanism underlying MSI, overexpression of miR-155 or miR-21 has been shown to downregulate the expression of the MMR genes. Gene targets of frameshift mutations caused by MSI are involved in various cellular functions, including DNA repair (MSH3 and MSH6), cell signaling (TGFBR2 and ACVR2A), apoptosis (BAX), epigenetic regulation (HDAC2 and ARID1A), and miRNA processing (TARBP2 and XPO5), and a subset of MSI+ CRCs reportedly shows the mutated miRNA machinery phenotype. Moreover, microsatellite repeats in miRNA genes, such as hsa-miR-1273c, may be novel MSI targets for CRC, and mutations in noncoding regulatory regions of MRE11, BAX (BaxΔ2), and HSP110 (HSP110ΔE9) may affect the efficiency of chemotherapy. Thus, analyses of MSI and its related molecular alterations in cancers are increasingly relevant in clinical settings, and MSI is a useful screening marker for identifying patients with Lynch syndrome and a prognostic factor for chemotherapeutic interventions. In this review, we summarize recent advances in the pathogenesis of MSI and focus on genome-wide analyses that indicate the potential use of MSI and related alterations as biomarkers and novel therapeutic targets.

Cancer type-specific epigenetic changes: gastric cancer

Gastric cancer (GC) remains a major cause of mortality despite declining rate in the world. Epigenetic alterations contribute significantly to the development and progression of gastric tumors. Epigenetic refers to the number of modifications of the chromatin structure that affect gene expression without altering the primary sequence of DNA, and these changes lead to transcriptional activation or silencing of the gene. Over the years, the study of epigenetic processes has increased, and novel therapeutic approaches have emerged. This chapter summarizes the main epigenomic mechanisms described recently involved in gastric carcinogenesis, focusing on the roles that aberrant DNA methylation, histone modifications (histone acetylation and methylation), and miRNAs (oncogenic and tumor suppressor function of miRNA) play in the onset and progression of gastric tumors. Clinical implications of these epigenetic alterations in GC are also discussed.

Epigenetics of gastric cancer

Epigenetic changes frequently occur in human gastric cancer. Gene promoter region hypermethylation, genomic global hypomethylation, histone modifications, and alterations of noncoding RNAs are major epigenetic changes in gastric cancer. As a key risk factor of gastric cancer, H. pylori infection is an independent predictive indicator of gene methylation. A growing number of epigenetic studies in gastric cancer have provided lots of potential diagnostic and prognostic markers and therapeutic targets.

MicroRNA-503 acts as a tumor suppressor in osteosarcoma by targeting L1CAM

Deregulated microRNAs and their roles in tumorigenesis have attracted much attention in recent years. Although miR-503 was shown to be important in tumorigenesis, its role in osteosarcoma remains unknown. In this study, we focused on the expression and mechanisms of miR-503 in osteosarcoma development. We found that miR-503 was down-regulated in osteosarcoma cell lines and primary tumor samples, and the restoration of miR-503 reduced cell proliferation, migration and invasion. Low level of miR-503 in patients with osteosarcoma was associated with considerably shortened disease-free survival. Furthermore, bioinformatic prediction and experimental validation revealed that the anti-tumor effect of miR-503 was probably exerted through targeting and repressing of L1CAM expression. L1CAM was up-regulated in osteosarcoma cell lines and primary tumor samples and the expression level of L1CAM were negatively correlated with miR-503 levels in osteosarcoma tissues. Collectively, our data identify the important roles of miR-503 in osteosarcoma pathogenesis, indicating its potential application in cancer therapy.

MicroRNA-103a inhibits gastric cancer cell proliferation, migration and invasion by targeting c-Myb

OBJECTIVES

There have been no previous reports concerning functions of miR-103a in gastric cancer (GC) cells. Thus the aim of the study was to investigate its expression and role in development of this tumour.

MATERIALS AND METHODS

Real-time RT-PCR was performed to detect expression of miR-103a in GC cell lines and clinical cancer specimens. To further understand its role, we restored expression of miR-103a in MGC-803 cell line by transfection with miR-103a mimics or inhibitors. Effects of miR-103a on cell proliferation, migration and invasion on targets were also determined.

RESULTS

miR-103a was down-regulated in both GC cell lines and clinical cancer specimens. Meanwhile, its level was closely associated with pM or pTNM stage of GC. Overexpression of miR-103a markedly suppressed proliferation, migration, and invasion of GC cells, while its inhibition significantly accelerated cell proliferation, migration and invasion. Moreover, c-Myb was identified to be a functional downstream target of miR-103a, ectopic expression of which partially reversed suppression of cell proliferation and invasion.

CONCLUSIONS

Thus our observations suggest that miR-103a functioned as a tumour suppressor by targeting c-Myb. These findings indicate that miR-103a might play a significant role in pathogenesis of GC.

Individual risk stratification of gastric cancer: evolving concepts and their impact on clinical practice

Gastric cancer (GC) is the third leading cause of cancer-related death worldwide and it mostly develops in long-standing inflammatory conditions, and Helicobacter pylori-gastritis, in particular. Despite the increasing understanding of both the phenotypic alterations and the molecular mechanisms occurring during GC multi-step carcinogenesis, no reliable biomarker is available to be reliably implemented into GC secondary prevention strategies. Multidisciplinary diagnostic approaches integrating endoscopy, serology, histology and molecular profiling currently appears as the most appropriate approach for patients' stratification into different GC risk classes.

Epidermal growth factor receptor-coamplified and overexpressed protein (VOPP1) is a putative oncogene in gastric cancer

MicroRNAs are found to play an important role in gastric cancer. Reduced expression of microRNA-218 (miR-218) is of key interest. The target gene of microRNA-218, epidermal growth factor receptor-coamplified and overexpressed protein (ECOP) encoded by the VOPP1 gene, has been implicated in tumorigenesis. However, few studies on expression and function of ECOP in gastric cancer have been reported. ECOP expression was determined in matched normal and gastric adenocarcinoma tissue specimens by immunohistochemistry and western blot. Subsequently, ectopic overexpression and RNAi-mediated silencing of VOPP1 was effected in the human gastric cancer cell line, AGS. Proliferation and migration of parental, VOPP1 overexpressing and VOPP1-silenced AGS cells were evaluated by cell proliferation assay and scratch wound-healing motility assay. Finally, intracellular localization of ECOP in AGS cells was assessed by green fluorescent protein tagging and fluorescent microscopy. Western blot and immunohistochemistry showed overexpression of ECOP in gastric adenocarcinoma tissues compared to matched normal tissue specimens. Ectopic overexpression and RNAi-mediated silencing of VOPP1 promoted and inhibited, respectively, cell proliferation and migration in AGS cells. Intracellular localization of ECOP in perinuclear lysosomes mimicked colocalization earlier reported for other cancerous cells. VOPP1 is overexpressed in gastric adenocarcinoma, which is involved in promoting cell proliferation and migration and thus might serve as a putative oncogene.

HDAC6 sustains growth stimulation by prolonging the activation of EGF receptor through the inhibition of rabaptin-5-mediated early endosome fusion in gastric cancer

The aberrant regulation of histone deacetylase 6 (HDAC6) contributes to malignant progression in various types of cancer, but the mechanism underlying gastric carcinogenesis remains unknown. Aberrant HDAC6 overexpression was observed in a subset of human gastric cancer cells. HDAC6 knockdown caused the significant inhibition of gastric cancer cell growth without affecting the transition of cell cycles or the processing of cell death. We demonstrate that an increase in epidermal growth factor receptor (EGFR) signaling through decreased EGFR degradation was mediated by HDAC6 in gastric carcinogenesis. These results establish a molecular mechanism responsible for oncogenic HDAC6, explaining how EGFR signaling induced by the growth factor is sustained during the malignant progression of gastric cancer.

Genetics of gastric cancer

Gastric cancer remains highly prevalent and accounts for a notable proportion of global cancer mortality. This cancer is also associated with poor survival rates. Understanding the genetic basis of gastric cancer will offer insights into its pathogenesis, help identify new biomarkers and novel treatment targets, aid prognostication and could be central to developing individualized treatment strategies in the future. An inherited component contributes to <3% of gastric cancers; the majority of genetic changes associated with gastric cancer are acquired. Over the past few decades, advances in technology and high-throughput analysis have improved understanding of the molecular aspects of the pathogenesis of gastric cancer. These aspects are multifaceted and heterogeneous and represent a wide spectrum of several key genetic influences, such as chromosomal instability, microsatellite instability, changes in microRNA profile, somatic gene mutations or functional single nucleotide polymorphisms. These genetic aspects of the pathogenesis of gastric cancer will be addressed in this Review.

DNA methylation and microRNA biomarkers for noninvasive detection of gastric and colorectal cancer

Cancer initiation and progression is controlled by both genetic and epigenetic events. Epigenetics refers to the study of mechanisms that alter gene expression without permanently altering the DNA sequence. Epigenetic alterations are reversible and heritable, and include changes in histone modifications, DNA methylation, and non-coding RNA-mediated gene silencing. Disruption of epigenetic processes can lead to altered gene function and malignant cellular transformation. Aberrant epigenetic modifications occur at the earliest stages of neoplastic transformation and are now believed to be essential players in cancer initiation and progression. Recent advances in epigenetics have not only offered a deeper understanding of the underlying mechanism(s) of carcinogenesis, but have also allowed identification of clinically relevant putative biomarkers for the early detection, disease monitoring, prognosis and risk assessment of cancer patients. At this moment, DNA methylation and non-coding RNA including with microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) represent the largest body of available literature on epigenetic biomarkers with the highest potential for cancer diagnosis. Following identification of cell-free nucleic acids in systematic circulation, increasing evidence has demonstrated the potential of cell-free epigenetic biomarkers in the blood or other body fluids for cancer detection. In this article, we summarize the current state of knowledge on epigenetic biomarkers - primarily DNA methylation and non-coding RNAs - as potential substrates for cancer detection in gastric and colorectal cancer, the two most frequent cancers within the gastrointestinal tract. We also discuss the obstacles that have limited the routine use of epigenetic biomarkers in the clinical settings and provide our perspective on approaches that might help overcome these hurdles, so that these biomarkers can be readily developed for clinical management of cancer patients.

RKIP suppresses gastric cancer cell proliferation and invasion and enhances apoptosis regulated by microRNA-224

The purposes of this study were to determine the expression profile of Raf kinase inhibitor protein (RKIP) in human gastric cancer cells and its effect on the biological characteristics of SGC-7901 cell lines, to examine the modulatory effect of microRNA-224 (miR-224) on RKIP. The research will provide novel strategies for gastric cancer treatment in the future. Quantitative real-time reverse transcription PCR (qRT-PCR) was employed to determine the expression profile of RKIP in gastric cancer cell lines (SGC-7901, MGC80-3, and MKN45). A eukaryotic expression vector, pcDNA3.1-RKIP, was constructed and transfected into SGC-7901 cells. Changes in RKIP protein expression were examined by Western blot assays, and the effect of RKIP overexpression on SCG-7901 cell viability was determined by 3-(4,5)-dimethylthiahiazo(-z-y1)-3,5-diphenytetrazoliumromide (MTT) assays. The effect of RKIP overexpression on SGC-7901 cell proliferation and apoptosis was analyzed by flow cytometry and that on the migration of SGC-7901 cells was investigated by Transwell migration assays. RKIP was identified to be a regulatory target gene of miR-224 using a luciferase reporter gene system, and the effect of miR-224 on intracellular RKIP protein expression was examined by Western blot assays. The regulatory effect of miR-224 on the biological characteristics of RKIP was investigated by MTT, flow cytometry, and Transwell invasion chamber assays. The expression of RKIP in gastric cancer cells was decreased significantly in comparison to that of normal gastric mucosal epithelial cells (GES-1) (p < 0.01), as demonstrated by qRT-PCR assays. Compared with the control group, the up-regulation of RKIP intracellular expression was observed in SGC-7901 cells after transfection of pcDNA3.1-RKIP for 48 h (p < 0.01). There were significant decreases in cell viability and the S-phase fraction (p < 0.05), concomitant with a significant increase in apoptosis (p < 0.01), as well as a significant reduction in cells migrating through Transwell chambers (p < 0.05), as shown by MTT, flow cytometry, and Transwell invasion chamber assays. A significant decrease in luciferase activities in cells transfected with a miR-224 mimic was observed compared with that of the control group (p < 0.05), as suggested by the luciferase reporter gene system. As shown by Western blot assays, there was a significant decrease in RKIP expression in SGC-7901 cells transfected with the miR-224 mimic for 48 h compared with the control group (p < 0.05). As shown by MTT, flow cytometry, and Transwell invasion chamber assays, the changes in biological characteristics induced by RKIP overexpression could be suppressed in SGC-7901 cells after transfection of the miR-224 mimic. In conclusion, the down-regulation of RKIP expression was observed in human gastric cell lines, and miR-224 could negatively regulate the expression and biological characteristics of RKIP, contributing to suppress the proliferation and invasion of gastric cells.

Galectin-7 is epigenetically-regulated tumor suppressor in gastric cancer

Gastric cancer is the second leading cause of cancer death and remains a major clinical challenge due to poor prognosis and limited treatment options. Therefore, the basic mechanisms underlying gastric tumorigenesis deserve investigation. Although regulation of the galactoside-binding lectin galectin-7 in cancer has been studied, its role in tumor formation and progression remains controversial. In this study, we investigated galectin-7 expression and its role in gastric cancer. Immunohistochemical staining using a tissue microarray of gastric cancer patients revealed significantly low expression levels of galectin-7 in malignant tissues compared with matched normal tissues, and decreased expression of galectin-7 in malignant tissues was associated with advanced TMN stage disease (p =0.034). Importantly, low expression of galectin-7 in normal tissues was associated with a poor survival rate (p =0.0561). Over-expression of galectin-7 in AGS gastric adenocarcinoma cells suppressed cell proliferation, migration, and invasion, whereas ablation of galectin-7 in KATO III gastric carcinoma cells reversed these properties. AGS cells that overexpressed galectin-7 could not form gastric tumors in xenografted mice. More than 70% hypermethylation was observed in 7 of 9 gastric cancer cell lines tested and 5-aza-cytidine treatment lowered galectin-7 expression by reducing methylation in 24 cancer cell lines from five different organ origins. We analyzed CpG islands in the galectin-7 genomic region and detected hypermethylation at +1566bp of exon 2, the predicted p53 binding region. DNA hypermethylation of this region was also detected in gastric cancer tissues from 20 patients. Taken together, our data indicate that galectin-7 has a tumor suppressive function, and that the gene is epigenetically modified by DNA methylation and significantly down-regulated in gastric cancer. Further study of galectin-7 regulation may lead to improved gastric cancer diagnosis and therapy.

MicroRNA-212 inhibits proliferation of gastric cancer by directly repressing retinoblastoma binding protein 2

Retinoblastoma binding protein 2 (RBP2), a newly found histone demethylase, is overexpressed in gastric cancer. We examined the upstream regulatory mechanism of RBP2 at the microRNA (miRNA) level and the role in gastric carcinogenesis. We used bioinformatics to predict that microRNA-212 (miR-212) might be a direct upstream regulator of RBP2 and verified the regulation in gastric epithelial-derived cell lines. Overexpression of miR-212 significantly inhibited the expression levels of RBP2, whereas knockdown of miR-212 promoted RBP2 expression. Furthermore, we identified the putative miR-212 targeting sequence in the RBP2 3' UTR by luciferase assay. MiR-212 inhibited the colony formation ability of cells by repressing RBP2 expression and increasing that of P21(CIP1) and P27(kip1), both critical in cell cycle arrest. In addition, the expression of RBP2 and miR-212 in tumor tissue and matched normal tissue from 18 patients further supported the results in vivo. MiR-212 directly regulates the expression of RBP2 and inhibits cell growth in gastric cancer, which may provide new clues to treatment.

An updated review of gastric cancer in the next-generation sequencing era: Insights from bench to bedside and vice versa

Gastric cancer (GC) is one of the most common malignancies and remains the second leading cause of cancer-related death worldwide. There is an increasing understanding of the roles that genetic and epigenetic alterations play in GCs. Recent studies using next-generation sequencing (NGS) have revealed a number of potential cancer-driving genes in GC. Whole-exome sequencing of GC has identified recurrent somatic mutations in the chromatin remodeling gene ARID1A and alterations in the cell adhesion gene FAT4, a member of the cadherin gene family. Mutations in chromatin remodeling genes (ARID1A, MLL3 and MLL) have been found in 47% of GCs. Whole-genome sequencing and whole-transcriptome sequencing analyses have also discovered novel alterations in GC. Recent studies of cancer epigenetics have revealed widespread alterations in genes involved in the epigenetic machinery, such as DNA methylation, histone modifications, nucleosome positioning, noncoding RNAs and microRNAs. Recent advances in molecular research on GC have resulted in the introduction of new diagnostic and therapeutic strategies into clinical settings. The anti-human epidermal growth receptor 2 (HER2) antibody trastuzumab has led to an era of personalized therapy in GC. In addition, ramucirumab, a monoclonal antibody targeting vascular endothelial growth factor receptor (VEGFR)-2, is the first biological treatment that showed survival benefits as a single-agent therapy in patients with advanced GC who progressed after first-line chemotherapy. Using NGS to systematically identify gene alterations in GC is a promising approach with remarkable potential for investigating the pathogenesis of GC and identifying novel therapeutic targets, as well as useful biomarkers. In this review, we will summarize the recent advances in the understanding of the molecular pathogenesis of GC, focusing on the potential use of these genetic and epigenetic alterations as diagnostic biomarkers and novel therapeutic targets.

MicroRNAs in gastrointestinal cancer: prognostic significance and potential role in chemoresistance

INTRODUCTION

Although chemotherapy is an important therapeutic strategy for gastrointestinal cancer, its clinical effect remains unsatisfied due to drug resistance. Drug resistance is a complex multistep process resulting from deregulated expression of many molecules, including tumor suppressor genes, oncogenes and microRNAs (miRNAs). A better understanding of drug resistance-related miRNAs may eventually lead to optimized therapeutic strategies for cancer patients.

AREAS COVERED

This review summarizes the recent advances of drug resistance-related miRNAs in esophageal, gastric and colorectal cancer. Furthermore, this study envisages future developments toward the clinical applications of these miRNAs to cancer therapy.

EXPERT OPINION

Drug resistance-related miRNAs may be potentially predicting biomarkers that help guide individualized chemotherapy. Specific miRNAs and their target genes can be used as therapeutic targets by reversing drug resistance. More investigations should be performed to promote the translational bridging of the latest research into clinical application.

Decreased expression of ten-eleven translocation 1 protein is associated with some clinicopathological features in gastric cancer

A decrease in ten-eleven translocation 1 (TET1) transcript and 5-Hydroxymethylcytosine (5hmC) levels has recently been demonstrated in primary gastric cancer (GC). However, little is known about TET1 protein levels in gastric tumoral and nontumoral tissue. Therefore, using reverse transcription, real-time quantitative polymerase chain reaction and western blotting analysis, we determined the TET1 transcript and protein levels in tumoral and nontumoral tissue from 38 patients with GC. We also assessed the association between the decrease in TET1 transcript and protein levels and some clinicopathological features in primary GC. We found significantly decreased levels of TET1 transcript (P=0.0023) and protein (P=0.00024) in primary tumoral tissues as compared to nontumoral tissues in patients with GC. Moreover, we also observed significantly lower amounts of TET1 transcript (P=0.03) and protein (P=0.00018) in tumoral tissues in patients aged>60. We also found significant lowered TET1 protein levels in male patients (P=0.0014), stomach (P=0.044) and cardia (P=0.013) tumor localization, T3 depth of invasion (P=0.019), N1 (P=0.012) and N3 lymph node metastasis (P=0.013) and G3 histological grade (P=0.0012). There were also significant decreases in TET1 transcript levels in female patients (P=0.042), intestinal histological types (P=0.0079) and T4 depth of invasion (P=0.037). Our results demonstrated that a decrease in TET1 transcript and protein levels is associated with some clinicopathological features in GC.

MicroRNAs in gastric cancer: from benchtop to bedside

Gastric carcinogenesis represents a stepwise progression from chronic inflammation to invasive adenocarcinomas and distant metastasis. It has been widely accepted that these pathologic changes are contributed by aberrant activation or inactivation of protein-coding proto-oncogenes and tumor suppressor genes. However, recent discoveries in microRNA research have reshaped our understanding of the role of non-protein-coding genes in carcinogenesis. MicroRNAs (miRNAs) are a family of 18-25-nucleotide small RNAs that negatively regulate gene expression at the post-transcriptional level during various crucial cell processes such as apoptosis, differentiation and development. Changes in miRNA expression profiles have been observed in a variety of human tumors, including gastric cancer. Further studies demonstrated that miRNAs may function as tumor suppressors and oncogenes. These findings have shown great potential of miRNAs as a novel class of therapeutic targets. In addition, it was found that some miRNAs were directly involved in patients with gastric cancer, including prognosis prediction, treatment selection, and in the search for unknown primary sites. MiRNAs have also been proved to be detectable in serum and plasma. In this review, we summarize the function of miRNAs in gastric cancer. Furthermore, we describe the pathophysiological roles of these miRNAs and their clinical potential as diagnostic biomarkers and therapeutic targets.

Inhibition of mTOR signalling potentiates the effects of trichostatin A in human gastric cancer cell lines by promoting histone acetylation

Deregulation of the mammalian target of rapamycin pathway (mTOR pathway) is associated with human cancer. The relationship between mTOR pathway and histone acetylation is still unclear in gastric cancer (GC). Immunohistochemistry was used to examine the phosphorylation of mTOR and eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) in GC tissues. MKN45 and SGC7901 cells were treated with the mTOR inhibitor rapamycin (RAPA) alone or in combination with the phosphatidylinositol 3-kinase inhibitor LY294002 and the histone deacetylase (HDAC) inhibitor trichostatin A (TSA). Small interfering RNA (siRNA) technology was also used to knockdown mTOR. Phosphorylated mTOR and phosphorylated 4E-BP1 were expressed in 71.1% and 68.4% of the human GC tissues tested, respectively; significantly higher than the levels in para-cancerous tissues (50% and 57.9%) and normal tissues (44.6% and 29%). RAPA markedly inhibited cell proliferation, induced G1 cell cycle arrest, and reduced phosphorylation of p70 S6 protein kinase (p70S6K) and 4E-BP1 in GC cells, particularly when used in combination with LY294002 or TSA. The mRNA expression of the tumour suppressor gene p21(WAF1) increased significantly in GC cells treated with both RAPA and TSA. Histone acetylation also increased after RAPA and TSA treatment or siRNA knockdown of mTOR. Our findings suggest that the mTOR pathway is activated in GC, and also that inhibition of mTOR enhances the ability of TSA to suppress cell proliferation and lead to cell cycle arrest via increasing histone acetylation and p21(WAF1) transcription in human MKN45 and SGC7901 GC cells.

VEZT, a novel putative tumor suppressor, suppresses the growth and tumorigenicity of gastric cancer

Vezatin (VEZT), an adherens junctions transmembrane protein, was identified as a putative tumor suppressor in our previous study. However, the role of VEZT in tumorigenesis remains elusive. We aimed to clarify its epigenetic regulation and biological functions in gastric cancer. In this study, we show that the expression level of VEZT is involved in lymphatic metastasis, depth of cancer invasion and TNM stage in 104 gastric cancer patients. Bisulfate sequencing polymerase chain reaction (BSP) methods showed that VEZT was hypermethylated in tissues and corresponding blood of gastric cancer patients compared with healthy controls. Helicobacter pylori (H. pylori) infection induces the methylation and silencing of VEZT in GES-1 cells. Restoring VEZT expression in MKN-45 and NCI-N87 gastric cancer cells inhibited growth, invasion and tumorigenesis in vitro and in vivo. Global microarray analysis was applied to analyze the molecular basis of the biological functions of VEZT after VEZT transfection combined with real-time PCR and chromatin immunoprecipitation assay. G protein-coupled receptor 56(GPR56), cell growth, cell division cycle 42(CDC42), migration/invasion and transcription factor 19(TCF19), cell cycle progression, were identified as direct VEZT target genes. TCF19, a novel target of VEZT, was functionally validated. Overexpression of TCF19 in MKN-45 cells increased cell cycle progress and growth ability. This study provides novel insight into the regulation of the VEZT gene, which could represent a potential target for therapeutic anti-cancer strategies.

Association of COX2 gene hypomethylation with intestinal type gastric cancer in samples of patients from northern Brazil

To verify the methylation status of THBS1, GPX3, and COX2 genes and to evaluate their association with Helicobacter pylori in gastric adenocarcinomas. Methylation-sensitive restriction enzyme PCR assay was performed in 16 diffuse type gastric cancer samples, 23 intestinal type, and 15 normal stomach tissue. The presence of H. pylori was performed by amplification of the fragment of the 16S rRNA. Statistical analyses were performed using Fisher's exact test. The hypermethylation of GPX3, THBS1, and COX2 occurred in 18 (n = 7), 5 (n = 2), and 36 % (n = 14) of gastric cancer samples, respectively, whereas in normal samples, it was found in 13, 7, and 67 %. The presence of H. pylori was detected in 67 % of gastric cancer samples and 67 % in normal gastric samples. The methylation of THBS1 and GPX3 was not significantly different between the types of tumors, normal sample, the presence of H. pylori, or clinicopathological variables studied (P > 0.05). However, the methylation status of the gene COX2 is significantly different between normal tissue and intestinal type gastric cancer (P = 0.02). Therefore, our results suggest that the methylation status of the gene COX2 is associated with the intestinal type of gastric cancer.

Association of RASSF1A promoter methylation with gastric cancer risk: a meta-analysis

Ras-association domain family 1A (RASSF1A), a candidate tumor suppressor gene, is frequently silenced and inactivated by hypermethylation of its promoter region in several human tumors. However, the association between RASSF1A promoter methylation and gastric cancer risk remains conflicting. The aim of this study was to assess the association of RASSF1A promoter methylation with gastric cancer risk by a comprehensive meta-analysis. Relevant studies were identified by searches of PubMed and Web of Science databases with no restrictions. Combined odds ratio (OR) and 95 % confidence interval (CI) were used to assess the strength of the association between RASSF1A promoter methylation and gastric cancer risk. A chi-square-based Q test and sensitivity analyses were performed to test the between-study heterogeneity and the contributions of single studies to the final results, respectively. Funnel plots were carried out to evaluate publication bias. Overall, a significant association was observed between RASSF1A promoter methylation and gastric cancer risk (OR, 12.67; 95 % CI, 8.12-19.78; p < 0.001) with no between-study heterogeneity. Subgroup analyses further revealed that gastric cancer risk was increased for individuals carrying the methylated RASSF1A compared with those with unmethylated RASSF1A. In addition, no publication bias was detected in the overall and subgroup analyses. This study identified a strong association between RASSF1A promoter methylation and risk of gastric cancer and highlighted a promising potential for RASSF1A promoter methylation in gastric cancer risk prediction.

Regulation of UHRF1 by miR-146a/b modulates gastric cancer invasion and metastasis

Epigenetic changes play significant roles in the development of cancer. UHRF1, as an epigenetic regulator, has been shown to be overexpressed and to coordinate tumor suppressor gene silencing in several cancers. However, the role and underlying mechanism of UHRF1 in gastric cancer (GC) progression remain largely unknown. In this study, we investigated the expression and function of UHRF1 in GC metastasis and explored its upstream regulatory mechanisms at the microRNA level. UHRF1 was overexpressed in GC tissues, especially in metastatic ones, and a high level of UHRF1 expression predicted poor survival. The down-regulation of UHRF1 suppressed GC invasion and metastasis in vitro and in vivo. We identified and verified miR-146a and miR-146b as direct upstream regulators of UHRF1. Furthermore, the restoration of miR-146a/b dramatically reduced the expression of UHRF1 through the direct targeting of its 3'-UTR, and this effect in turn reactivated the slit homologue 3 (Slit3), cadherin 4 (CDH4), and runt-related transcription factor 3 (RUNX3) genes via promoter demethylation. Finally, analyses of miR-146a/b and UHRF1 levels in human GC tissues revealed that miR-146a/b correlated inversely with UHRF1 expression. These findings describe a new mechanism for the regulation of UHRF1 and aberrant DNA hypermethylation in GC. The newly identified miR-146a/b/UHRF1 axis provides insight into the GC metastasis process, and targeting this novel axis represents a therapeutic approach to blocking GC metastasis.

Involvement of miR-20a in promoting gastric cancer progression by targeting early growth response 2 (EGR2)

Gastric cancer (GC) is one of the most common cancers, with high incidences in East Asia. microRNAs (miRNAs) play essential roles in the carcinogenesis of GC. miR-20a was elevated in GC, while the potential function of miR-20a was poorly understood. miR-20a expression was examined in GC tissues and cell lines. The effects of miR-20a on the growth, migration, invasion, and chemoresistance of GC cells were examined. Luciferase reporter assay and Western blot were used to screen the target of miR-20a. miR-20a was increased in GC tissues and cell lines. miR-20a promoted the growth, migration and invasion of GC cells, enhanced the chemoresistance of GC cells to cisplatin and docetaxel. Luciferase activity and Western blot confirmed that miR-20a negatively regulated EGR2 expression. Overexpression of EGR2 significantly attenuated the oncogenic effect of miR-20a. miR-20a was involved in the carcinogenesis of GC through modulation of the EGR2 signaling pathway.

Helicobacter pylori-Induced Chronic Gastritis and Assessing Risks for Gastric Cancer

Chronic gastritis is an inflammation of the gastric mucosa and has multiple etiologies. Here we discuss the pathological alterations induced by Helicobacter pylori (HP) leading to chronic gastritis and the epigenetic bases underlying these changes. We review the histology of the normal gastric mucosa and overview the role of HP in the multistep cascade of GC. We attempt to define the role of the Operative Link for Gastritis Assessment (OLGA) staging system in assessing the risk of GC. The epigenetic bases of chronic gastritis, mainly DNA methylation, are presented through examples such as (i) the methylation of the promoter region of E-cadherin in HP-induced chronic gastritis and its reversion after HP eradication and (ii) the association of methylation of the promoter region of Reprimo, a p53-mediated cell cycle arrest gene, with aggressive HP strains in high risk areas for GC. In addition, we discuss the finding of RPRM as a circulating cell-free DNA, offering the opportunity for noninvasive risk assessment of GC. Finally, the integration of OLGA and tissue biomarkers, by systems pathology approach, suggests that severe atrophy has a greater risk for GC development if, in addition, overexpressed p73. This trial is registered with ClinicalTrials.gov NCT01774266.

DNA and histone methylation in gastric carcinogenesis

Epigenetic alterations contribute significantly to the development and progression of gastric cancer, one of the leading causes of cancer death worldwide. Epigenetics refers to the number of modifications of the chromatin structure that affect gene expression without altering the primary sequence of DNA, and these changes lead to transcriptional activation or silencing of the gene. Over the years, the study of epigenetic processes has increased, and novel therapeutic approaches that target DNA methylation and histone modifications have emerged. A greater understanding of epigenetics and the therapeutic potential of manipulating these processes is necessary for gastric cancer treatment. Here, we review recent research on the effects of aberrant DNA and histone methylation on the onset and progression of gastric tumors and the development of compounds that target enzymes that regulate the epigenome.

Defective DNA repair systems and the development of breast and prostate cancer (review)

Genetic defects in DNA repair and DNA damage response genes often lead to an increase in cancer incidence. The role of defects is also associated with the modulation of hormone signaling pathways. A number of studies have suggested a role for estrogen in the regulation of DNA repair activity. Furthermore, mutations or epigenetic silencing in DNA repair genes have been associated with the sensitivity of cancers to hormonal therapy. The molecular basis for the progression of cancers from hormone-dependent to hormone-independent remains a critical issue in the management of these types of cancer. In the present review, we aimed to summarize the function of DNA repair molecules from the viewpoint of carcinogenesis and hormone-related cell modulation, providing a comprehensive view of the molecular mechanisms by which hormones may exert their effects on the regulation of tumor progression.