Frequent CpG island methylation in precursor lesions and early gastric adenocarcinomas

LGR5 as a diagnostic marker for dysplasia in serrated polyps

AIMS

WNT signalling pathway dysregulation is often a critical early component in colorectal neoplasia, particularly the chromosomal instability pathway. Using two WNT reporters, LGR5 and AXIN2, we sought to assess whether these polyps demonstrate predictable expression patterns and if these patterns show diagnostic value.

METHODS

We evaluated 23 adenomas (TA), 23 sessile serrated lesions (SSLs), 14 SSL with dysplasia and 38 traditional serrated adenomas (TSA). Chromogenic in situ hybridisation stains (ISH) for LGR5 and AXIN2 were performed. Reactivity was defined as strong, intermediate or weak. Upper third crypt reactivity was defined as full-thickness staining. Accentuation within ectopic crypts (ECF) was recorded.

RESULTS

TAs (91%) showed strong reactivity and full-thickness staining with LGR5. TSAs showed full-thickness and weak to intermediate LGR5 reactivity (79%) and ECF with LGR5 accentuation was exclusively seen in TSA. SSL showed weak LGR5 reactivity confined to the basal crypt region (100%). SSL with dysplasia also showed weak or intermediate (100%) LGR5 reactivity, but the reactivity pattern was full thickness (88%). AXIN2 expression parallels LGR5 expression (Pearson coefficient=0.63) regarding signal intensity for the examined polyp groups.

CONCLUSIONS

Qualitative and quantitative differences in AXIN2 and LGR5 expression assist in the diagnosis of SSL with dysplasia.

Potent therapeutic strategy in gastric cancer with microsatellite instability-high and/or deficient mismatch repair

Gastric cancer (GC) is a common malignancy that presents challenges in patient care worldwide. The mismatch repair (MMR) system is a highly conserved DNA repair mechanism that protects genome integrity during replication. Deficient MMR (dMMR) results in an increased accumulation of genetic errors in microsatellite sequences, leading to the development of a microsatellite instability-high (MSI-H) phenotype. Most MSI-H/dMMR GCs arise sporadically, mainly due to MutL homolog 1 (MLH1) epigenetic silencing. Unlike microsatellite-stable (MSS)/proficient MMR (pMMR) GCs, MSI-H/dMMR GCs are relatively rare and represent a distinct subtype with genomic instability, a high somatic mutational burden, favorable immunogenicity, different responses to treatment, and prognosis. dMMR/MSI-H status is a robust predictive biomarker for treatment with immune checkpoint inhibitors (ICIs) due to high neoantigen load, prominent tumor-infiltrating lymphocytes, and programmed cell death ligand 1 (PD-L1) overexpression. However, a subset of MSI-H/dMMR GC patients does not benefit from immunotherapy, highlighting the need for further research into predictive biomarkers and resistance mechanisms. This review provides a comprehensive overview of the clinical, molecular, immunogenic, and therapeutic aspects of MSI-H/dMMR GC, with a focus on the impact of ICIs in immunotherapy and their potential as neoadjuvant therapies. Understanding the complexity and diversity of the molecular and immunological profiles of MSI-H/dMMR GC will drive the development of more effective therapeutic strategies and molecular targets for future precision medicine.

Exosomal LINC00853 promotes progression of gastric cancer via the MAP17/PDZK1/AKT signaling pathway

Although rare, there is ongoing research into biomarkers that predict the onset and recurrence of gastric cancer, particularly focusing on substances found in exosomes. Long non-coding RNAs (lncRNAs) have garnered attention for their potential in diagnosing gastric cancer. This study investigates the role of lncRNAs in gastric cancer, focusing on their presence in exosomes as potential biomarkers for the disease's onset and recurrence. We utilized the ArrayStar Human LncRNA array 2.0 to analyze lncRNA expression in tissues from early-stage gastric cancer patients. Our analysis highlighted LINC00853, which was significantly upregulated in cancer tissues and implicated in promoting epithelial-mesenchymal transition via the MAP17/PDZK1/AKT pathway. Functional studies on AGS and MKN74 gastric cancer cell lines demonstrated that LINC00853 facilitates cell proliferation, invasion, and migration. Additionally, RNA immunoprecipitation and electrophoretic mobility shift assays confirmed LINC00853 interaction with MAP17. Importantly, LINC00853 was also detected in exosomes from both patient samples and cell lines, and its downregulation led to decreased tumorigenicity in AGS cells. These findings suggest that both cellular and exosomal LINC00853 contribute to gastric cancer pathogenesis and may serve as valuable biomarkers for the disease.

Identification of Prognostic Biomarkers for Bladder Cancer Based on DNA Methylation Profile

Background: DNA methylation is an important epigenetic modification, which plays an important role in regulating gene expression at the transcriptional level. In tumor research, it has been found that the change of DNA methylation leads to the abnormality of gene structure and function, which can provide early warning for tumorigenesis. Our study aims to explore the relationship between the occurrence and development of tumor and the level of DNA methylation. Moreover, this study will provide a set of prognostic biomarkers, which can more accurately predict the survival and health of patients after treatment.

Methods: Datasets of bladder cancer patients and control samples were collected from TCGA database, differential analysis was employed to obtain genes with differential DNA methylation levels between tumor samples and normal samples. Then the protein-protein interaction network was constructed, and the potential tumor markers were further obtained by extracting Hub genes from subnet. Cox proportional hazard regression model and survival analysis were used to construct the prognostic model and screen out the prognostic markers of bladder cancer, so as to provide reference for tumor prognosis monitoring and improvement of treatment plan.

Results: In this study, we found that DNA methylation was indeed related with the occurrence of bladder cancer. Genes with differential DNA methylation could serve as potential biomarkers for bladder cancer. Through univariate and multivariate Cox proportional hazard regression analysis, we concluded that FASLG and PRKCZ can be used as prognostic biomarkers for bladder cancer. Patients can be classified into high or low risk group by using this two-gene prognostic model. By detecting the methylation status of these genes, we can evaluate the survival of patients.

Conclusion: The analysis in our study indicates that the methylation status of tumor-related genes can be used as prognostic biomarkers of bladder cancer.

Changes at global and site-specific DNA methylation of MLH1 gene promoter induced by waterpipe smoking in blood lymphocytes and oral epithelial cells

Objective: Cigarette tobacco smoking has been shown to cause cancer through different mechanisms that include epigenetic modulation of tumor-suppressor genes. In the present study, the association between global and MLH1 gene promoter methylation and waterpipe tobacco smoking was investigated. Materials and Methods: Blood lymphocytes and oral epithelium were sampled from 150 pure waterpipe smokers and 150 never-smokers from Jordan. Methylation assessment was performed using the methylation-specific PCR technique for MLH1 gene and ELISA for global DNA methylation. Results: Significant increases were shown in global DNA methylation as measured in blood lymphocytes (p < 0.01). In addition, increases in MLH1 gene promoter methylation among waterpipe smokers compared to nonsmokers (p < 0.001) in both oral epithelium and blood lymphocytes was also observed. In addition, strong correlation was found between LWDS-10J dependence score and magnitude of promoter specific methylation of MLH1 (r2 = 0.74-0.78, p < 0.001). Moreover, the percentage of methylated MLH1 promoter was not affected by age or gender (p > 0.05). Discussion and Conclusion: Collectively, the results indicate that waterpipe tobacco use is associated with epigenetic changes that might predispose users to lung and blood cancers. The results highlight the need for actions to discourage waterpipe smoking and can be used in cessation interventions that target this type of smoking.

A four-DNA methylation signature as a novel prognostic biomarker for survival of patients with gastric cancer

Background

Gastric cancer (GC) is the fifth most frequently diagnosed cancer and the third leading cause of cancer-related mortality. Lack of prognostic indicators for patient survival hinders GC treatment and survival.

Methods and results

Methylation profile data of patients with GC obtained from The Cancer Genome Atlas (TCGA) database were analyzed to identify methylation sites as biomarkers for GC prognosis. The cohort was divided into training and validation sets. Univariate Cox, LASSO regression,and multivariate Cox analyses revealed a close correlation of a four-DNA methylation signature as a risk score model with the overall survival of patients with GC. The survival between high-risk and low-risk score patients with GC was significantly different. Analyses of receiver operating characteristics revealed a high prognostic accuracy of the four-DNA methylation signature in patients with GC. The subgroup analysis indicated that the accuracy included that for anatomical region, histologic grade, TNM stage, pathological stage, and sex. The GC prognosis based on the four-DNA methylation signature was more precise than that based on known biomarkers.

Conclusions

The four-DNA methylation signature could serve as a novel independent prognostic factor that could be an important tool to predict the prognostic outcome of GC patients. This potential must be verified in a large-scale population cohort study and through basic research studies.

Downregulation of Friend Leukemia Integration 1 (FLI1) follows the stepwise progression to gastric adenocarcinoma

Gastric adenocarcinoma (GC) is a leading cause of cancer-related deaths worldwide. The transcription factor gene Friend Leukemia Integration 1 (FLI1) is methylated and downregulated in human GC tissues. Using human GC samples, we determined which cells downregulate FLI1, when FLI1 downregulation occurs, if FLI1 downregulation correlates with clinical-pathologic characteristics, and whether FLI1 plays a role in invasion and/or proliferation of cultured cells. We analyzed stomach tissues from 98 patients [8 normal mucosa, 8 intestinal metaplasia (IM), 7 dysplasia, 91 GC] by immunohistochemistry for FLI1. Epithelial cells from normal, IM, and low-grade dysplasia (LGD) showed strong nuclear FLI1 staining. GC epithelial cells showed significantly less nuclear FLI1 staining as compared to normal epithelium, IM and LGD (P=1.2×10^-5, P=1.4×10^-6 and P=0.006, respectively). FLI1 expression did not correlate with tumor stage or differentiation, but was associated with patient survival, depending on tumor differentiation. We tested the functional role of FLI1 by assaying proliferation and invasion in cultured GC cells. Lentiviral-transduced FLI1 overexpression in GC AGS cells inhibited invasion by 73.5% (P = 0.001) and proliferation by 31.5% (P = 0.002), as compared to controls. Our results support a combined role for FLI1 as a suppressor of invasiveness and proliferation in gastric adenocarcinoma, specifically in the transition from pre-cancer lesions and dysplasia to invasive adenocarcinoma, and suggest that FLI1 may be a prognostic biomarker of survival in gastric cancers.

Epigenetic Mechanisms and Events in Gastric Cancer-Emerging Novel Biomarkers

Gastric cancer is one of the most common malignancy worldwide. The various genetic and epigenetic events have been found to be associated with its carcinogenesis. The epigenetic is a heritable and transient/reversible change in the gene expression that is not accompanied by modification in the DNA sequence. This event is characterized by the alteration in the promoter CpG island of the gene or histone modification. These events are associated with silencing of critical tumor suppressor gene and activation of oncogenes leading to carcinogenesis. The DNA methylation is a chemical change in the DNA sequence that most commonly occurs at cytosine moiety of CpG dinucleotide and histone, primarily on N- terminal tail that ultimately effect the interaction of DNA with chromatin modifying protein.Hypermethylation of tumor suppressor genes and global hypomethylation of oncogenes are widely studied epigenetic modifications. There are large number of publish reports regarding epigenetic events involving gastric cancer. These changes are potentially useful in identifying markers for early diagnosis and management of this lethal malignancy. Also, role of specific miRNAs and long non coding RNAs in regulation of gene expression is gaining interest and is a matter of further investigation. In this review, we aimed to summarize major epigenetic events (DNA methylation) in gastric cancer along with alteration in miRNAs and long non coding RNAs which plays an important role in pathology of this poorly understood malignancy.

Matricellular proteins in cancer: a focus on secreted Frizzled-related proteins

Tumours are complex entities, wherein cancer cells interact with myriad soluble, insoluble and cell associated factors. These microenvironmental mediators regulate tumour growth, progression and metastasis, and are produced by cancer cells and by stromal components such as fibroblast, adipocytes and immune cells. Through their ability to bind to extracellular matrix proteins, cell surface receptors and growth factors, matricellular proteins enable a dynamic reciprocity between cancer cells and their microenvironment. Hence, matricellular proteins play a critical role in tumour progression by regulating where and when cancer cells are exposed to key growth factors and regulatory proteins. Recent studies suggest that, in addition to altering Wingless (Wnt) signalling, certain members of the Secreted Frizzled Related Protein (sFRP) family are matricellular in nature. In this review, we outline the importance of matricellular proteins in cancer, and discuss how sFRPs may function to both inhibit and promote cancer progression in a context-dependent manner. By considering the matricellular functionality of sFRPs, we may better understand their apparently paradoxical roles in cancers.

How to stomach an epigenetic insult: the gastric cancer epigenome

Gastric cancer is a deadly malignancy afflicting close to a million people worldwide. Patient survival is poor and largely due to late diagnosis and suboptimal therapies. Disease heterogeneity is a substantial obstacle, underscoring the need for precision treatment strategies. Studies have identified different subgroups of gastric cancer displaying not just genetic, but also distinct epigenetic hallmarks. Accumulating evidence suggests that epigenetic abnormalities in gastric cancer are not mere bystander events, but rather promote carcinogenesis through active mechanisms. Epigenetic aberrations, induced by pathogens such as Helicobacter pylori, are an early component of gastric carcinogenesis, probably preceding genetic abnormalities. This Review summarizes our current understanding of the gastric cancer epigenome, highlighting key advances in recent years in both tumours and pre-malignant lesions, made possible through targeted and genome-wide technologies. We focus on studies related to DNA methylation and histone modifications, linking these findings to potential therapeutic opportunities. Lessons learned from the gastric cancer epigenome might also prove relevant for other gastrointestinal cancers.

Pathogenesis of Gastric Cancer: Genetics and Molecular Classification

Gastric cancer is the fifth most incident and the third most common cause of cancer-related death in the world. Infection with Helicobacter pylori is the major risk factor for this disease. Gastric cancer is the final outcome of a cascade of events that takes decades to occur and results from the accumulation of multiple genetic and epigenetic alterations. These changes are crucial for tumor cells to expedite and sustain the array of pathways involved in the cancer development, such as cell cycle, DNA repair, metabolism, cell-to-cell and cell-to-matrix interactions, apoptosis, angiogenesis, and immune surveillance. Comprehensive molecular analyses of gastric cancer have disclosed the complex heterogeneity of this disease. In particular, these analyses have confirmed that Epstein-Barr virus (EBV)-positive gastric cancer is a distinct entity. The identification of gastric cancer subtypes characterized by recognizable molecular profiles may pave the way for a more personalized clinical management and to the identification of novel therapeutic targets and biomarkers for screening, prognosis, prediction of response to treatment, and monitoring of gastric cancer progression.

Pathogenesis of Gastric Cancer: Genetics and Molecular Classification

Gastric cancer is the fifth most incident and the third most common cause of cancer-related death in the world. Infection with Helicobacter pylori is the major risk factor for this disease. Gastric cancer is the final outcome of a cascade of events that takes decades to occur and results from the accumulation of multiple genetic and epigenetic alterations. These changes are crucial for tumor cells to expedite and sustain the array of pathways involved in the cancer development, such as cell cycle, DNA repair, metabolism, cell-to-cell and cell-to-matrix interactions, apoptosis, angiogenesis, and immune surveillance. Comprehensive molecular analyses of gastric cancer have disclosed the complex heterogeneity of this disease. In particular, these analyses have confirmed that Epstein-Barr virus (EBV)-positive gastric cancer is a distinct entity. The identification of gastric cancer subtypes characterized by recognizable molecular profiles may pave the way for a more personalized clinical management and to the identification of novel therapeutic targets and biomarkers for screening, prognosis, prediction of response to treatment, and monitoring of gastric cancer progression.

Molecular alterations in gastric cancer with special reference to the early-onset subtype

Currently, gastric cancer (GC) is one of the most frequently diagnosed neoplasms, with a global burden of 723000 deaths in 2012. It is the third leading cause of cancer-related death worldwide. There are numerous possible factors that stimulate the pro-carcinogenic activity of important genes. These factors include genetic susceptibility expressed in a single-nucleotide polymorphism, various acquired mutations (chromosomal instability, microsatellite instability, somatic gene mutations, epigenetic alterations) and environmental circumstances (e.g., Helicobcter pylori infection, EBV infection, diet, and smoking). Most of the aforementioned pathways overlap, and authors agree that a clear-cut pathway for GC may not exist. Thus, the categorization of carcinogenic events is complicated. Lately, it has been claimed that research on early-onset gastric carcinoma (EOGC) and hereditary GC may contribute towards unravelling some part of the mystery of the GC molecular pattern because young patients are less exposed to environmental carcinogens and because carcinogenesis in this setting may be more dependent on genetic factors. The comparison of various aspects that differ and coexist in EOGCs and conventional GCs might enable scientists to: distinguish which features in the pathway of gastric carcinogenesis are modifiable, discover specific GC markers and identify a specific target. This review provides a summary of the data published thus far concerning the molecular characteristics of GC and highlights the outstanding features of EOGC.

Effect of coffee consumption on the risk of gastric cancer: a systematic review and meta-analysis of prospective cohort studies

Background and Objectives

Results from observational epidemiologic studies on the relationship between coffee consumption and gastric cancer are inconsistent and inconclusive. To assess the association between coffee consumption and the risk of gastric cancer, we summarized evidence from prospective cohort studies.

Methods

Relevant studies were retrieved through computer searches (PubMed, EmBase and the Cochrane Library) and a review of references up to December 2014. The quality of the included studies was evaluated by Newcastle-Ottawa quality assessment scale. We used a meta-analytic approach to estimate overall hazard ratios (HRs) and 95% confidence intervals (CIs) for regular coffee drinkers versus individuals who seldom drank coffee. Sensitivity analysis and subgroup analysis were performed to assess the reliability of our results. A dose–response analysis was performed to assess the risk of gastric cancer based on the level of coffee consumption.

Results

Nine prospective cohort studies involving 1,250,825 participants and 3027 gastric cancer cases were included in this meta-analysis. The pooled HR of gastric cancer for the study-specific regularly versus seldom coffee drinking categories was 1.05 (95% CI, 0.88 to 1.25) with significant heterogeneity across studies (I² = 74.0%, P = 0.000). After the sensitivity analysis, three studies were deleted; however the association remained insignificant (HR, 0.99; 95% CI, 0.91 to 1.08). Subgroup analysis by anatomic location showed a risk for coffee consumption associated with cardia cancer (HR, 1.23; 95% CI, 1.04 to 1.45; heterogeneity, I² = 36.4, P = 0.207). In the dose–response analysis, there was no significant association between coffee intake (in cups) and the risk of gastric cancer (P for linearity trend and non-linearity > 0.05).

Conclusion

Our meta-analysis demonstrated that coffee consumption was not associated with overall gastric cancer risk; however, coffee consumption may be a risk factor for gastric cardia cancer.

Epigenetic alterations in gastric cancer (Review)

Gastric cancer is one of the most common types of cancer and the second most common cause of cancer-related mortality worldwide. An increasing number of recent studies have confirmed that gastric cancer is a multistage pathological state that arises from environmental factors; dietary factors in particulary are considered to play an important role in the etiology of gastric cancer. Improper dietary habits are one of the primary concerns as they influence key molecular events associated with the onset of gastric carcinogenesis. In the field of genetics, anticancer research has mainly focused on the various genetic markers and genetic molecular mechanisms responsible for the development of this of this disease. Some of this research has proven to be very fruitful, providing insight into the possible mechamisms repsonsible for this disease and into possible treatment modalities. However, the mortality rate associated with gastric cancer remains relatively high. Thus, epigenetics has become a hot topic for research, whereby genetic markers are bypassed and this research is directed towards reversible epigenetic events, such as methylation and histone modifications that play a crucial role in carcinogenesis. The present review focuses on the epigenetic events which play an important role in the development and progression of this deadly disease, gastric cancer.

Is gastric lymphoepithelioma-like carcinoma a special subtype of EBV-associated gastric carcinoma? New insight based on clinicopathological features and EBV genome polymorphisms

BACKGROUND

Gastric lymphoepithelioma-like carcinoma (LELC) is a rare entity that is closely associated with Epstein-Barr virus (EBV). However, the EBV latency pattern and genome polymorphisms in gastric LELC have not been systematically explored.

METHODS

The clinicopathological features, EBV latency pattern and genome polymorphisms of EBV-positive gastric LELC in Guangzhou, southern China were investigated and compared with those of ordinary EBV-associated gastric carcinoma (EBVaGC) in the same area.

RESULTS

Ten (1.42%) of 702 gastric carcinoma cases were identified as gastric LELC, in which eight (80%) cases were EBV-positive. The clinicopathological characteristics and EBV latency pattern of EBV-positive gastric LELC were similar to those of ordinary EBVaGC. In EBV genotype analysis, type A strain, type F, I, mut-W1/I, XhoI- and del-LMP1 variants were predominant among EBV-positive gastric LELCs, accounting for eight (100%), six (75%), eight (100%), seven (87.5%), five (62.5%) and six (75%) cases, respectively, which are similar to those in ordinary EBVaGC. For EBNA1 polymorphisms, the V-leu and P-ala subtypes were predominant in EBV-positive gastric LELC, which is different from the predominant V-val subtype in ordinary EBVaGC. EBV-positive gastric LELC has a favorable prognosis when compared to ordinary EBVaGC (median survival time 43.0 vs. 18.0 months).

CONCLUSIONS

Gastric LELC is strongly associated with EBV and EBV-positive gastric LELC should be regarded as a special subtype of EBVaGC. This, to our best knowledge, is the first time in the world that the EBV latency pattern and genome polymorphisms of EBV-positive gastric LELC are systematically revealed.

ARID1A expression in gastric adenocarcinoma: Clinicopathological significance and correlation with DNA mismatch repair status

AIM: To analyze the mismatch repair (MMR) status and the ARID1A expression as well as their clinicopathological significance in gastric adenocarcinomas.

METHODS: We examined the expressions of MMR proteins and ARID1A by immunohistochemistry in consecutive 489 primary gastric adenocarcinomas. The results were further correlated with clinicopathological variables.

RESULTS: The loss of any MMR protein expression, indicative of MMR deficiency, was observed in 38 cases (7.8%) and was significantly associated with an older age (68.6 ± 9.2 vs 60.4 ± 11.7, P < 0.001), a female sex (55.3% vs 31.3%, P = 0.004), an antral location (44.7% vs 25.7%, P = 0.021), and a differentiated histology (57.9% vs 39.7%, P = 0.023). Abnormal ARID1A expression, including reduced or loss of ARID1A expression, was observed in 109 cases (22.3%) and was significantly correlated with lymphatic invasion (80.7% vs 69.5%, P = 0.022) and lymph node metastasis (83.5% vs 73.7%, P = 0.042). The tumors with abnormal ARID1A expression more frequently indicated MMR deficiency (47.4% vs 20.2%, P < 0.001). A multivariate analysis identified abnormal ARID1A expression as an independent poor prognostic factor (HR = 1.36, 95%CI: 1.01-1.84; P = 0.040).

CONCLUSION: Our observations suggest that the AIRD1A inactivation is associated with lymphatic invasion, lymph node metastasis, poor prognosis, and MMR deficiency in gastric adenocarcinomas.

Clinical Significance of MLH1 Methylation and CpG Island Methylator Phenotype as Prognostic Markers in Patients with Gastric Cancer

BACKGROUND

To improve the outcome of patients suffering from gastric cancer, a better understanding of underlying genetic and epigenetic events in this malignancy is required. Although CpG island methylator phenotype (CIMP) and microsatellite instability (MSI) have been shown to play pivotal roles in gastric cancer pathogenesis, the clinical significance of these events on survival outcomes in patients with gastric cancer remains unknown.

METHODS

This study included a patient cohort with pathologically confirmed gastric cancer who had surgical resections. A cohort of 68 gastric cancers was analyzed. CIMP and MSI statuses were determined by analyzing promoter CpG island methylation status of 28 genes/loci, and genomic instability at 10 microsatellite markers, respectively. A Cox's proportional hazards model was performed for multivariate analysis including age, stage, tumor differentiation, KRAS mutation status, and combined CIMP/MLH1 methylation status in relation to overall survival (OS).

RESULTS

By multivariate analysis, longer OS was significantly correlated with lower pathologic stage (P = 0.0088), better tumor differentiation (P = 0.0267) and CIMP-high and MLH1 3' methylated status (P = 0.0312). Stratification of CIMP status with regards to MLH1 methylation status further enabled prediction of gastric cancer prognosis.

CONCLUSIONS

CIMP and/or MLH1 methylation status may have a potential to be prognostic biomarkers for patients with gastric cancer.

Epigenetic pathogenesis of human papillomavirus in upper aerodigestive tract cancers

Human papillomavirus (HPV) has been recently associated with squamous cell carcinoma of upper aerodigestive tract (SCC of UADT), but its possible role in promoting aberrant methylation in these tumors has largely remained unexplored. Herein, we investigated the association of HPV with aberrant methylation in tumor-related genes/loci consisting of the classical CpG Island Methylator Phenotype (CIMP) panel markers (p16, MLH1, MINT1, MINT2, and MINT31) and other frequently methylated cancer-related genes (DAPK1, GSTP1, BRCA1, ECAD, and RASSF1) and survival of UDAT cancers. The study includes 219 SCC of UADT patients from different hospitals of Northeast India. Detection of HPV and aberrant promoter methylation was performed by PCR and Methylation Specific PCR respectively. Association study was conducted by Logistic regression analysis and overall survival analysis was done by Kaplan-Meier plot. HPV was detected in 37% of cases, with HPV-18 as the major high-risk sub-type. Although HPV presence did not seem to affect survival in overall UADT cancers, but was associated with a favourable prognosis in head and neck squamous cell carcinoma. Hierarchical clustering revealed three distinct clusters with different methylation profile and HPV presence. Among these, the CIMP-high subgroup exhibited the highest HPV positive cases (66%). Furthermore, multivariate analysis revealed a strong synergistic association of HPV and tobacco towards modulating promoter hypermethylation in UADT cancer (OR = 27.50 [95% CI = 11.51-88.03] for CIMP-high vs. CIMP-low). The present study proposes a potential role of HPV in impelling aberrant methylation in specific tumor related loci, which might contribute in the initiation and progression of SCC of UADT.

Occurrence of HHIP gene CpG island methylation in gastric cancer

The present study aimed to observe the methylation status of the CpG islands at the human hedgehog interacting protein (HHIP) gene in gastric cancer tissues, peritumoral tissues and the AGS cell line, to analyze the association between the methylation status of the CpG islands and the tumorigenesis of gastric cancer. The HHIP mRNA expression in 60 human gastric carcinnoma tissues, peritumoral tissues and the gastric carcinoma AGS cell line were detected by reverse transcription polymerase chain reaction (RT-PCR). The HHIP methylation status of the promoter region in the gastric carcinnoma tissues and peritumoral tissues was detected by methylation-specific PCR (MSP). Prior to and following treatment with methyl transferase inhibitor 5-aza-2'-deoxycitydine (5-aza-dc), the HHIP mRNA expression level, the methylation status of the promoter region and the methylation site loci on the CpG islands in the AGS cells were detected by RT-PCR, MSP and bisulfite sequencing PCR (BSP), respectively. The correlation between the methylation status of the CpG islands at the HHIP promoter region and the HHIP mRNA expression level were analyzed. It was found that the expression level of the HHIP mRNA in the gastric carcinoma tissues was significantly lower than that in the adjacent tissues (0.82±0.38 vs. 1.60±0.26, respectively; P<0.001). No significant correlations were observed between the expression of HHIP mRNA and age, gender, tumor-node-metastasis stage, differentiation degree and presence of lymph node metastasis (P>0.05). The degree of methylation of the HHIP gene promotor in the peritumoral tissues (17.7±3.59%) was significantly lower than that in the gastric cancer tissues (62.9±6.14%) and in the AGS cells (99.7±0.67%) (P<0.05). Compared with prior to 5-aza-dc intervention, the HHIP mRNA expression level in the AGS cells was significantly increased subsequent to intervention (0.21±0.12 vs. 4.68±0.22; P<0.01), while the degree of methylation in the AGS cells was significantly decreased (90.2±0.67 vs. 10.1±0.21%; P<0.01), and the methylation sites in CpG islands were significantly reduced. The degree of HHIP methylation showed a negative correlation with the level of mRNA expression (r=-0.693; P<0.01). It can be hypothesized that a high degree of methylation of the HHIP gene promoter CpG islands in gastric cancer tissues and cells causes a decrease in HHIP mRNA expression, which may be involved in the carcinogenesis of gastric cancer.

Methylation status of blood leukocyte DNA and risk of gastric cancer in a high-risk Chinese population

BACKGROUND

To evaluate the relationship between methylation status of blood leukocyte DNA and risk of gastric cancer, a population-based study was conducted in Linqu County.

METHODS

Methylation levels of IGFII and N33 were determined by quantitative methylation-specific PCR. The temporal trend of methylation levels during gastric cancer development was investigated in 133 gastric cancer cases from two cohorts with pre- and/or post-gastric cancer samples. As the references of pre-GCs, 204 intestinal metaplasia (IM) or dysplasia (DYS) subjects who did not progress to gastric cancer during the follow-up period were selected. Meanwhile, 285 subjects with superficial gastritis/chronic atrophic gastritis (SG/CAG) were also selected as controls.

RESULTS

IGFII median methylation level was significantly higher in gastric cancer cases than those with SG/CAG (61.47% vs. 49.73%; P < 0.001). IGFII and N33 methylation levels were elevated at least 5 years ahead of clinical gastric cancer diagnosis comparing with SG/CAG (63.38% vs. 49.73% for IGFII, 9.12% vs. 5.70% for N33; all P < 0.001). Furthermore, the frequency of hypermethylated IGFII was markedly increased in IM or DYS subjects who progressed to gastric cancer in contrast to those who remained with IM and DYS, and adjusted ORs were 12.52 [95% confidence interval (CI), 3.81-41.15] for IM and 10.12 (95% CI, 2.68-38.22) for DYS. Similar results were also found for N33 in subjects with IM (OR, 3.77; 95% CI, 1.20-11.86).

CONCLUSIONS

Our findings suggested that hypermethylated IGFII and N33 in blood leukocyte DNA were associated with risk of gastric cancer in a Chinese population.

IMPACT

IGFII and N33 methylation status may be related to gastric carcinogenesis.

Transmembrane protein 106A is silenced by promoter region hypermethylation and suppresses gastric cancer growth by inducing apoptosis

Inactivation of tumour suppressor genes by promoter methylation plays an important role in the initiation and progression of gastric cancer (GC). Transmembrane 106A gene (TMEM106A) encodes a novel protein of previously unknown function. This study analysed the biological functions, epigenetic changes and the clinical significance of TMEM106A in GC. Data from experiments indicate that TMEM106A is a type II membrane protein, which is localized to mitochondria and the plasma membrane. TMEM106A was down-regulated or silenced by promoter region hypermethylation in GC cell lines, but expressed in normal gastric tissues. Overexpression of TMEM106A suppressed cell growth and induced apoptosis in GC cell lines, and retarded the growth of xenografts in nude mice. These effects were associated with the activation of caspase-2, caspase-9, and caspase-3, cleavage of BID and inactivation of poly (ADP-ribose) polymerase (PARP). In primary GC samples, loss or reduction of TMEM106A expression was associated with promoter region hypermethylation. TMEM106A was methylated in 88.6% (93/105) of primary GC and 18.1% (2/11) in cancer adjacent normal tissue samples. Further analysis suggested that TMEM106A methylation in primary GCs was significantly correlated with smoking and tumour metastasis. In conclusion, TMEM106A is frequently methylated in human GC. The expression of TMEM106A is regulated by promoter hypermethylation. TMEM106A is a novel functional tumour suppressor in gastric carcinogenesis.

Clinical significance of expression and epigenetic profiling of TUSC1 in gastric cancer

BACKGROUND AND OBJECTIVES

The prognosis of advanced gastric cancer (GC) remains dismal. The aim of this study was to identify a novel tumor suppressor gene (TSG) with repressed transcription by aberrant DNA methylation in GC.

METHODS

The expression and methylation status of tumor suppressor candidate 1 (TUSC1) were evaluated in GC cell lines and 112 pairs of surgical specimens. TUSC1 protein expression and distribution in GC tissue were determined by immunohistochemistry.

RESULTS

The majority of GC cell lines (83%) and GC tissues (82%) showed downregulation of TUSC1 mRNA compared with noncancerous tissues. No significant differences were found in TUSC1 mRNA expression between three GC subtypes categorized by tumor locations and morphology. Reduced expression of TUSC1 mRNA in GC tissues was significantly associated with advanced T stage, vessel invasion and lymph node metastasis, leading to poor prognosis. The expression patterns of TUSC1 protein were confirmed to be consistent with those of TUSC1 mRNA. Sixty-three (57%) of 112 patients showed intragenic hypermethylation of TUSC1 in GC tissues.

CONCLUSIONS

Our results suggested that reduced expression of TUSC1 mRNA was related to poor prognosis and TUSC1 is a putative TSG that is suppressed through intragenic hypermethylation in GC.

Epstein-Barr Virus Associated Lymphoepithelioma-like Carcinoma at the Lesser Curvature of the Upper Gastric Body: A Case Report

Lymphoepithelioma-like gastric carcinoma (LELGC) is a rare neoplasm of the stomach with dense lymphocytic infiltration. More than 80% of LELGCs are positive for the Epstein-Barr virus (EBV). Here, we report a 64-year old Chinese man with swallowing discomfort while eating food. Endoscopy and computed tomography both showed a submucosal lesion at the lesser curvature of the upper gastric body. The first diagnostic impression was a gastrointestinal stromal tumour. Subsequently, the patient received a wedge resection of the stomach. On histopathological examination, the tumour was found to consist of small nests of neoplastic cells within dense lymphocytic infiltration. Additionally, most of the neoplastic cells were positive for cytokeratin and Epstein-Barr virus-encoded RNA (EBER). Subsequently, the diagnosis of LELGC was made. We believe that physicians should be aware of the diagnosis of submucosal gastric lesions, particularly in older male patients.

Hypomethylation of long interspersed nuclear element-1 promoter is associated with poor outcomes for curative resected hepatocellular carcinoma

BACKGROUND

Epigenetic alterations are well documented in hepatocarcinogenesis. However, hypomethylation of long interspersed nuclear element 1(LINE-1) promoter and its relationship with clinicopathological features in hepatocellular carcinoma(HCC) remain unknown.

METHODS

The bisulfite-specific PCR and DNA sequencing analysis was performed to assess the methylation status of LINE-1 promoter in a pilot cohort of 71 patients with HCC. Additionally,methylation levels of two hot CpG sites of LINE-1 promoter, site 7 and 18 were measured by real-time PCR and compared with clinicopathological parameters in a cohort of 172 HCC. All the patients included were in BCLC stage A or B.

RESULTS

Most patients with HCC (87.3%) showed hypomethylation of LINE-1 promoter compared with HBV-related cirrhosis and normal controls (P < 0.001). The HCC patients with LINE-1 promoter hypomethylation had a median tumour-free survival (TFS) and overall survival (OS)post-resection of 22.0 (95% CI: 13.3–30.7) months and 35.0 (95% CI: 24.0–46.1) months, respectively, compared with 40 months and ~60 months for those with LINE-1 promoter hypermethylation (P < 0.05). Multivariate analyses showed that the hypomethylation level at CpG site 7 and 18 of LINE-1 promoter, along with tumour size and tumour differentiation, was independently associated with both TFS and OS for patients with HCC after resection.

CONCLUSION

Promoter hypomethylation of LINE-1, especially at the CpG site 7 and 18, was associated with a poor prognosis in HCC.

Lymphoepithelioma-like carcinoma of the stomach: a case report and review of the literature

A lymphoepithelioma-like carcinoma (LLC), characterized by a carcinoma with stromal heavy lymphocyte infiltration, is one of the histological patterns observed in patients with Epstein-Barr virus (EBV)-associated gastric carcinoma. Although this entity is hard to be recognized in the biopsy specimens, pathologists and clinicians should acknowledge this subset of gastric cancer because it generally has a better prognosis than other forms of EBV-associated gastric carcinomas and conventional gastric carcinomas. This might be due to the fact that the patient's inflammatory response may prevent the spread of tumor through the gastric wall and to the lymph nodes or remote organs.

We report a case of EBV-positive, microsatellite stable LLC as a rare morphologic variant of gastric carcinoma.

Disappearance of Serum Methylated p16 Indicates Longer Survival in Patients with Gastric Cancer

Purpose

The aim of this study was to assess clinical correlations with postoperative alteration of p16 DNA methylation, and to clarify whether postoperative changes in the serum DNA methylation status of p16 could be used as a reliable prognostic factor for gastric cancer.

Materials and Methods

Fifty-three consecutive gastric adenocarcinoma patients who underwent gastric resection (Chung-Ang University Hospital, Seoul, Korea) were included. DNA methylation of p16 was evaluated by methylation-specific polymerase chain reaction using serum DNA preoperatively and at the 10th postoperative day. The correlation between changes in methylation status and patients' prognosis was analyzed.

Results

p16 was methylated in 79.2% of preoperative serum DNA and in 54.7% of postoperative serum DNA, respectively. Methylation in p16 disappeared more frequently in patients who underwent standard D2 lymphadenectomy compared to those who underwent modified D1+ lymphadenectomy (P=0.016). Whereas methylation of preoperative serum DNA was not correlated with survival, patients with postoperative disappearance of p16 methylation showed longer survival than those without postoperative disappearance of p16 methylation in the patients who had gastric cancer with lymph node metastasis (P=0.042).

Conclusions

Postoperative disappearance of p16 methylation could be an available prognostic factor for node-positive gastric cancer.

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.

DNA methylation and cancer diagnosis

DNA methylation is a major epigenetic modification that is strongly involved in the physiological control of genome expression. DNA methylation patterns are largely modified in cancer cells and can therefore be used to distinguish cancer cells from normal tissues. This review describes the main technologies available for the detection and the discovery of aberrantly methylated DNA patterns. It also presents the different sources of biological samples suitable for DNA methylation studies. We discuss the interest and perspectives on the use of DNA methylation measurements for cancer diagnosis through examples of methylated genes commonly documented in the literature. The discussion leads to our consideration for why DNA methylation is not commonly used in clinical practice through an examination of the main requirements that constitute a reliable biomarker. Finally, we describe the main DNA methylation inhibitors currently used in clinical trials and those that exhibit promising results.

Gastric cancer pathology and underlying molecular mechanisms

The development of gastric adenocarcinoma is a complex multistep process involving multiple genetic alterations. Based on pathology, four different macroscopic types and at least two major histological types, intestinal and diffuse, have been described. Most gastric cancer (GC) show genetic instability, either microsatellite instability or chromosomal instability, which is considered an early event in gastric carcinogenesis. Molecular studies of alterations of single genes have provided evidence that intestinal and diffuse type GC evolve via different genetic pathways. Recent results from high-throughput whole-genome expression or copy number studies have demonstrated extensive genetic diversity between cases and within individual GC. Sets of commonly up- or downregulated microRNAs have been identified in GC and might be useful in the near future to identify pathways of GC progression. Results from detailed molecular and/or pathological GC studies, although promising, still have limited clinical utility in predicting survival and stratifying GC patients for appropriate treatment.

Helicobacter, Inflammation, and Gastric Cancer

Helicobacter pylori infection leads to long-lasting chronic inflammation and represents the most common risk factor underlying gastric cancer. Recently, new insights into the mechanisms through which H. pylori and mucosal inflammation lead to cancer development have emerged. H. pylori virulence factors, in particular specific CagA genotypes, represent main factors in gastric cancer, inducing altered intracellular signaling in epithelial cells. The chronic nature of H. pylori infection appears to relate to the VacA virulence factor and Th17/Treg mechanisms. A role of H. pylori infection in epigenetic and microRNA deregulation has been shown. Mutation of the epithelial cell genome, a hallmark of cancer, was demonstrated to accumulate in H. pylori infected stomach partly due to inadequate DNA repair. Gastric stem cells were shown to be targets of oxidative injury in the Helicobacter-inflammatory milieu. Recent advances emphasizing the contribution of bacterial factors, inflammatory mediators, and the host epithelial response in gastric carcinogenesis are reviewed.

Early-stage gastric cancers represented as dysplasia in a previous forceps biopsy: the importance of clinical management

BACKGROUND AND AIMS

Because histological examination of gastric lesions by forceps biopsy is of limited accuracy, management on the basis of histological results is occasionally controversial. We examined the characteristics of early gastric cancers that presented as dysplasia resulting from a previous forceps biopsy.

PATIENTS AND METHODS

Between April 2007 and December 2010, 341 gastric adenocarcinoma lesions from 330 patients previously diagnosed histologically via endoscopic submucosal dissection were examined. We retrospectively assessed the characteristics of early gastric cancer according to their initial forceps biopsy results.

RESULTS

In total, 183 EGCs were diagnosed as dysplasia (53.7%; 89 low-grade and 94 high-grade) and 158 (46.3%) as carcinoma by forceps biopsy before endoscopic submucosal dissection. Significant differences were noted with respect to histologic differentiation of carcinomas, Lauren histologic type, depth of invasion, lymphovascular invasion, and en bloc resection between the dysplastic group and carcinoma group, based on forceps biopsy results.

CONCLUSION

A forceps biopsy result is not fully representative of the entire lesion and, thus, endoscopic submucosal dissection should be considered for lesions diagnosed as dysplasia via forceps biopsy in order to avoid the risk of missed carcinomas.

Methylation and Immunoexpression of p16(INK4a) Tumor Suppressor Gene in Primary Breast Cancer Tissue and Their Quantitative p16(INK4a) Hypermethylation in Plasma by Real-Time PCR

Background

The p16^INK4a gene methylation has been reported to be a major tumorigenic mechanism.

Methods

We evaluated the methylation status of the p16^INK4a genes in 231 invasive breast cancer and 90 intraductal carcinoma specimens using a methylation-specific polymerase chain reaction and p16 protein expression using immunohistochemistry. The quantity of cell-free methylated p16^INK4a DNA in the plasma samples of 200 patients with invasive breast cancer was also examined using a fluorescence-based real-time polymerase chain reaction assay.

Results

The frequencies of p16^INK4a methylation in invasive and intraductal tumors were 52.8% (122/231) and 57.8% (52/90), respectively. The p16 protein was overexpressed in 145 of the 231 invasive carcinomas (62.8%) and 63 of the 90 intraductal carcinomas (70%). High p16 expression in invasive carcinomas correlated significantly with a high histologic grade, a negative estrogen receptor and progesterone receptor status, p53 immunoreactivity and high Ki-67 expression with immunohistochemistry. In addition, the methylation index of p16^INK4a was significantly higher in the cancer patients than the normal controls (p<0.001).

Conclusions

High p16 immunoreactivity correlated with a loss of differentiation in breast carcinomas and high frequency of p16^INK4a promoter methylation in both invasive and intraductal carcinomas, suggesting it may be involved in the pathogenesis of breast cancer.

Microsatellite instability is associated with a better prognosis for gastric cancer patients after curative surgery

BACKGROUND

Microsatellite instability (MSI) is one of the leading mechanisms for the carcinogenesis of gastric cancer. Its prognostic value is controversial.

METHODS

Between May 1988 and Oct 2003, a total of 214 gastric cancer patients undergoing curative surgery were enrolled, and their MSI statuses were classified as MSI-H (high) or MSI-L/S (low/stable). The clinicopathologic characteristics of MSI-H and MSI-L/S gastric cancers were compared.

RESULTS

The MSI-H tumors accounted for 11.7 % (n = 25) of the 214 total gastric cancers. Although not statistically significant, the MSI-H gastric cancers were more frequently located in the lower third of the stomach (64 % vs. 49.2 %) and were more often the intestinal type (72 % vs. 61.4 %) compared to the MSI-L/S gastric cancers. The MSI-H gastric cancers had a significantly better 5-year overall survival (OS) rate (68 % vs. 47.6 %, p = 0.030) and a trend of a better 3-year disease-free survival rate (71.8 % vs. 55.2 %, p = 0.076) compared to the MSI-L/S gastric cancers. A multivariate analysis revealed that pathologic TNM stage and MSI status were the independent prognostic factors for OS after curative surgery.

CONCLUSIONS

Compared to MSI-L/S tumors, MSI-H tumors are associated with a better OS rate for gastric cancer patients after R0 resection.

Role of DNA methylation in the development of Epstein-Barr virus-associated gastric carcinoma

The frequencies of DNA methylation of certain tumor-related genes are higher in Epstein-Barr virus (EBV)-associated gastric carcinomas than in EBV-negative gastric carcinomas. EBV-associated gastric carcinomas have distinct clinicopathological features; however, there are no case-control studies comparing methylation frequency between EBV-associated gastric carcinomas and controls that have been adjusted according to the clinicopathological features of EBV-associated gastric carcinomas. This study evaluated 25 EBV-associated gastric carcinomas that were positive for EBV-encoded small RNA 1 (EBER-1) by in situ hybridization and 50 EBV-negative gastric carcinomas that were matched with the EBV-associated gastric carcinomas by age, sex, histology, depth of tumor invasion, and stage. Methylation status of 16 loci associated with tumor-related genes was analyzed by methylation-specific polymerase chain reaction (PCR) to identify genes in which DNA methylation specifically occurred in EBV-associated gastric carcinomas. Methylation frequencies of 12 of the 16 genes were higher in EBV-associated gastric carcinomas than in EBV-negative controls, and the frequency of methylation of 6 specific loci (MINT2, MINT31, p14, p16, p73, and RUNX3) was significantly higher in EBV-associated gastric carcinomas than in EBV-negative controls. There were no significant differences in the methylation frequencies of the other genes. The mean methylation index in EBV-associated gastric carcinomas was significantly higher than that in EBV-negative controls. DNA methylation of tumor suppressor genes that regulate the cell cycle and apoptosis specifically occurred in EBV-associated gastric carcinomas. Aberrant DNA methylation might lead to the development and progression of EBV-associated gastric carcinoma.

DNMT3A rs36012910 A>G polymorphism and gastric cancer susceptibility in a Chinese population

DNA-methyltransferase (DNMT)-3A plays a crucial role in embryonic development and aberrant DNA methylation in carcinogenesis. Polymorphisms of the DNMT3A gene may influence its enzymatic activity and its contribution to susceptibility to cancer. This study evaluated the association of DNMT3A rs36012910 A>G with susceptibility to gastric cancer (GC) in a Chinese population. Genomic DNA was extracted from samples taken from 340 patients with GC and 251 healthy control subjects. The genotype frequency of DNMT3A rs36012910 A>G in all subjects was detected by polymerase chain reaction-restriction fragment length polymorphism and confirmed by sequencing. Stratification analyses were used to study subgroups by age and gender and to evaluate the association of rs36012910 A>G polymorphism with genetic susceptibility to GC. All patients and control individuals were successfully genotyped for the DNMT3A rs36012910 A>G polymorphism. The frequency of DNMT3A rs36012910 allele G is 3.39 % in healthy individuals and 7.78 % in GC patients, respectively. The rs36012910 AG genotype was significantly more common in the GC group than in the controls, although the rs36012910 GG genotype was only one case in GC patients. Further stratification indicated that AG+GG genotypes were associated with susceptibility to GC in males older than 60, but this polymorphism has no significant association with GC susceptibility in females. Male individuals who carried AG+GG genotypes had a 2.362-fold increased risk of GC compared to those who carried the AA genotype. The rs36012910 allele G was associated with an increased risk of GC compared to the rs36012910 allele A. This is the first report to investigate the distribution and evaluate the association of a rare SNP in DNMT3A with genetic susceptibility to GC. DNMT3A rs36012910 A>G might become a potential biomarker for use in GC prediction, although further studies in larger groups and different populations are needed for confirmation.

Understanding the genetic basis of gastric cancer: recent advances

Two major gastric cancer histological subtypes are recognized with distinct morphology, epidemiology, pathogenesis and clinical behavior. Genetically, the intestinal and diffuse subtypes are also characterized by distinct germline susceptibility patterns and somatic aberrations. Helicobacter pylori is strongly associated with both Lauren's subtypes, although the underlying carcinogenic mechanisms are unique. Risk is modulated by strain-specific virulence factors, host responses and specific host-microbe interactions. Somatic aberrations in gastric cancer are driven by three major mechanisms, namely chromosomal instability, microsatellite instability and epigenetic alterations. These processes drive carcinogenesis in both Lauren's subtypes; however, the relative contribution of these processes and the specific genes aberrated differ. Moving beyond Lauren's subtypes, next-generation techniques have identified major genomic subtypes that have prognostic impact and exhibit distinct response patterns to standard cytotoxics.

Zinc-finger protein 331, a novel putative tumor suppressor, suppresses growth and invasiveness of gastric cancer

Zinc-finger protein 331 (ZNF331), a Kruppel-associated box zinc-finger protein gene, was identified as a putative tumor suppressor in our previous study. However, the role of ZNF331 in tumorigenesis remains elusive. We aimed to clarify its epigenetic regulation and biological functions in gastric cancer. ZNF331 was silenced or downregulated in 71% (12/17) gastric cancer cell lines. A significant downregulation was also detected in paired gastric tumors compared with adjacent non-cancer tissues. In contrast, ZNF331 was readily expressed in various normal adult tissues. The downregulation of ZNF331 was closely linked to the promoter hypermethylation as evidenced by methylation-specific PCR, bisulfite genomic sequencing and reexpression by demethylation agent treatment. DNA sequencing showed no genetic mutation/deletion of ZNF331 in gastric cancer cell lines. Ectopic expression of ZNF331 in the silenced cancer cell lines MKN28 and HCT116 significantly reduced colony formation and cell viability, induced cell cycle arrests and repressed cell migration and invasive ability. Concordantly, knockdown of ZNF331 increased cell viability and colony formation ability of gastric cancer cell line MKN45. Two-dimensional gel electrophoresis and mass spectrometry-based comparative proteomic approach were applied to analyze the molecular basis of the biological functions of ZNF331. In all, 10 downstream targets of ZNF331 were identified to be associated with regulation of cell growth and metastasis. The tumor-suppressive effect of ZNF331 is mediated at least by downregulation of genes involved in cell growth promotion (DSTN, EIF5A, GARS, DDX5, STAM, UQCRFS1 and SET) and migration/invasion (DSTN and ACTR3), and upregulation of genome-stability gene (SSBP1) and cellular senescence gene (PNPT1). A novel target of ZNF331 (DSTN) was functionally validated. Overexpression of DSTN in BGC-823 cells increased colony formation and migration ability. In conclusion, our results suggest that ZNF331 possesses important functions for the suppression of gastric carcinogenesis as a novel functional tumor-suppressor gene.

CpG island hypermethylation in gastric carcinoma and its premalignant lesions

Gastric cancers arise through a multistep process characterized by the progressive accumulation of molecular alterations in which genetic and epigenetic mechanisms have been implicated. Gastric cancer is one of the human malignancies in which aberrant promoter CpG island hypermethylation is frequently found. Helicobacter pylori and Epstein-Barr virus, which are known carcinogens for gastric cancer, are closely associated with enhanced hypermethylation of CpG island loci in gastric non-neoplastic epithelial cells and cancer cells, respectively. Aberrant CpG island hypermethylation occurs early in the multistep cascade of gastric carcinogenesis and tends to increase with the step-wise progression of the lesion. Approximately 400 genes that are actively expressed in normal gastric epithelial cells are estimated to be inactivated in gastric cancers as a result of promoter CpG island hypermethylation. In this review, a variety of information is summarized regarding CpG island hypermethylation in gastric cancer.

Epigenetic inactivation of paired box gene 5, a novel tumor suppressor gene, through direct upregulation of p53 is associated with prognosis in gastric cancer patients

Using genome-wide methylation screening, we identified that paired box gene 5 (PAX5) is involved in human cancer development. However, the function of PAX5 in gastric cancer (GC) development is largely unclear. We analyzed its epigenetic inactivation, biological functions and clinical application in GC. PAX5 was silenced in seven out of eight GC cell lines. A significant downregulation was also detected in paired gastric tumors compared with adjacent non-cancerous tissues. The downregulation of PAX5 was closely linked to the promoter hypermethylation status and could be restored with demethylation treatment. Ectopic expression of PAX5 in silenced GC cell lines (AGS and BGC823) inhibited colony formation and cell viability, arrested cell cycle, induced apoptosis, suppressed cell migration and invasion and repressed tumorigenicity in nude mice. Consistent with the induction of apoptosis by PAX5 in vitro, terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick end labeling (TUNEL) staining showed significantly enhanced apoptotic cells in PAX5-expressed tumors compared with the vector control tumors. On the other hand, knockdown of PAX5 by PAX5-short hairpin RNA increased the cell viability and proliferation. The anti-tumorigenic function of PAX5 was revealed to be mediated by upregulating downstream targets of tumor protein 53 (p53), p21, BCL2-associated X protein, metastasis suppressor 1 and tissue inhibitors of metalloproteinase 1, and downregulating BCL2, cyclin D1, mesenchymal-epithelial transition factor (MET) and matrix metalloproteinase 1. Immunoprecipitation assay demonstrated that PAX5 directly bound to the promoters of p53 and MET. Moreover, PAX5 hypermethylation was detected in 77% (144 of 187) of primary GCs compared with 10.5% (2/19) of normal gastric tissues (P<0.0001). GC patients with PAX5 methylation had a significant poor survival compared with the unmethylated cases as demonstrated by Cox regression model and log-rank test. In conclusion, PAX5 is a novel functional tumor suppressor in gastric carcinogenesis. Detection of methylated PAX5 can be utilized as an independent prognostic factor in GC.

Hypermethylated DNA as potential biomarkers for gastric cancer diagnosis

OBJECTIVES

To demonstrate the diagnostic significance of methylation, an important molecular event in gastric carcinogenesis.

DESIGN AND METHODS

We used methylation microarray to determine candidate genes, and performed MSP to evaluate the methylation status of them in tissues and sera. The effect of demethylation on mRNA expression was investigated by rt-PCR after gastric cancer cell lines were treated with 5-Aza-dC for 96 h.

RESULTS

In tissues and sera of gastric cancer patients, a higher prevalence of methylation was observed for BX141696, WT1, CYP26B1, and KCNA4, compared to healthy people (p<0.05, respectively). Detection of the methylation prevalence of KCNA4 and CYP26B1 together in serum demonstrated the good sensitivity (91.3%) and specificity (92.1%). After 5-Aza-dC treatment in gastric cancer cell lines, the mRNA expression level of these genes was restored.

CONCLUSIONS

This study underscores the potential application of measurement of serum DNA methylation of these genes, as promising tool for gastric cancer detection.

Increased frequency of CpG island methylator phenotype and CDH1 methylation in a gastric cancer high-risk region of china

This study aimed to profile the methylation statuses of CDH1/E-cadherin and five CpG island methylator phenotype (CIMP)-associated genes (p16, hMLH1, MINT1, MINT2, and MINT31) in gastric specimens of 47 Dalian long-term residents with and 31 without gastric cancers (GCs). CIMP patterns were classified as CIMP-H with over three methylated genes, CIMP-L with one to two methylated genes, and CIMP-N without methylation. Of 47 GC cases, 24 (51.1%) were CIMP-H, 18 (38.3%) were CIMP-L, and 5 (10.6%) were CIMP-N, whereas 5 of 21 (23.8%) premalignant lesions were CIMP-H and 15 (71.4%) were CIMP-L. CIMP-L was found in 75% (12/16) of GC-adjacent mucosa and in 38.7% (12/31) of mucosa from GC-free patients. CDH1 methylation occurred in 48.9% (23/47) of cancer, in 23.8% (5/21) of premalignant, and in 25% (4/16) of noncancerous tissues and was correlated with patients' age (P = .01), lymph node metastasis, and CIMP severity (P = .000-.028). Our results demonstrated that the frequencies of CIMP-H in Dalian GCs, CIMP-L, and p16 methylation in GC-adjacent tissues and in GC-free mucosa were much higher than those reported previously, indicating the elevated methylation pressure in this GC high-risk region. The close correlation between CDH1 methylation and CIMP severity suggests the necessity of their combination in GC prevention and earlier diagnosis.