Insulin-like growth factor 2 hypomethylation of blood leukocyte DNA is associated with gastric cancer risk

TUSC3 Methylation in Peripheral Blood Cells as a Biomarker for Diagnosis of Colorectal Cancer

Background

Several case-control studies have suggested that global and loci-specific deoxyribonucleic acid (DNA) methylation in peripheral blood mononuclear cells (PBMCs) of DNA might be potential biomarkers of cancer diagnosis and prognosis. In this study, for the first time, we intended to assess the diagnostic power of the methylation level of tumor suppressor candidate 3 (TUSC3) gene promoter in patients with colorectal cancer (CRC).

Materials and Methods

In the current study, we quantitatively assessed the promoter methylation level of TUSC3 in PBMCs of 70 CRC cases and 75 non-cancerous subjects via methylation quantification of endonuclease-resistant DNA (MethyQESD) method.

Results

The methylation level of the TUSC3 was meaningfully higher in CRC cases than in non-CRC subjects (43.55 ± 21.80% vs. 16.07 ± 13.63%, respectively; P < 0.001). The sensitivity and specificity of this gene for the detection of CRC were 88.6% and 76.0%, respectively. The receiver operating characteristic (ROC) curve examination discovered an area under the curve (AUC) of 0.880, representing a very high accuracy of the TUSC3 methylation marker in distinguishing CRC subjects from healthy individuals. However, there was no substantial diversity in methylation level between various CRC stages (P: 0.088).

Conclusion

For CRC screening, PBMCs are a reliable source for DNA methylation analysis and TUSC3 promoter methylation can be utilized as a hopeful biomarker for early and non-invasive diagnosis of CRC.

Effects of methylation and imprinting expression of Insulin-like growth factor 2 gene in gastric cancer

BACKGROUND

Epstein-Barr virus (EBV)-associated gastric cancer (EBVaGC) is a common malignant tumor associated with EBV infection. Insulin-like growth factor 2 (IGF2) is an imprinted gene and a key protein that regulates growth, especially during normal fetal development. Loss of imprinting (LOI), is a common epigenetic anomaly in a variety of human cancers. However, the promoter methylation, imprinting status and function of IGF2 gene in GC are unclear.

OBJECTIVE

To explore the role of IGF2 in the occurrence and development of gastric cancer.

METHODS

The biological function of IGF2 in gastric cancer was investigated by Transwell, wound healing, CCK-8 and flow cytometry assays. IGF2 imprinting status and gene promoter methylation in gastric cancer tissues were detected by PCR-RFLP and BGS.

RESULTS

The results showed that the expression of IGF2 was higher in GC tissues than adjacent tissues. IGF2 gene promoter methylation and LOI were significantly higher in EBVaGC tissues than in EBV-negative gastric cancer (EBVnGC) tissues. The high expression of IGF2 in gastric cancer can promote the migration and proliferation of gastric cancer cells.

CONCLUSION

Our data suggest that IGF2 is involved in the occurrence and development of gastric cancer. Targeting IGF2 may be a potential therapeutic target for gastric cancer.

The LncRNA MIR503HG/miR-224-5p/TUSC3 Signaling Cascade Suppresses Gastric Cancer Development via Modulating ATF6 Branch of Unfolded Protein Response

Background

Unfolded protein response (UPR)-mediated tumor-promoting functions have been identified in multiple cancers, and this study focused on investigating the role and molecular mechanisms of UPR in modulating gastric cancer (GC) pathogenesis.

Methods

The bioinformatics analysis was performed to examine the expression status of cancer associated genes in patients with stomach adenocarcinoma (STAD) and predict the targeting sites of miR-224-5p with LncRNA MIR503HG and TUSC3. Genes expressions were quantified by Real-Time qPCR, Western Blot and immunohistochemistry (IHC). Cell proliferation, viability, apoptosis and mobility were evaluated by MTT assay, trypan blue staining assay, flow cytometer and transwell assay, respectively. The binding sites were validated by dual-luciferase reporter gene system assay.

Results

LncRNA MIR503HG and TUSC3 were downregulated, but miR-224-5p was upregulated in GC tissues and cells, in contrast with their normal counterparts. Further gain- and loss-of-function experiments validated that the malignant phenotypes in GC cells, including cell proliferation, invasion, epithelial-mesenchymal transition (EMT) and tumorigenesis, were negatively regulated by LncRNA MIR503HG. Mechanistically, LncRNA MIR503HG upregulated TUSC3 in GC cells through sponging miR-224-5p, resulting in the repression of GC progression. Finally, we validated that knock-down of ATF6, but not other two branches of UPR (PERK1 and IRE1), partially rescued cell proliferation and EMT in the GC cells with LncRNA MIR503HG overexpression.

Conclusions

Targeting the LncRNA MIR503HG/miR-224-5p/TUSC3 signaling cascade suppressed ATF6-mediated UPR, resulting in the blockage of GC development.

Association of ZNF331 and WIF1 methylation in peripheral blood leukocytes with the risk and prognosis of gastric cancer

Background

Peripheral blood leukocyte (PBL) DNA methylation may serve as a surrogate marker to evaluate the susceptibility to and prognosis of gastric cancer (GC). In this study, blood-derived DNA methylation levels of two tumour-related genes, namely, ZNF331 and WIF1, and their impacts on the risk and prognosis of GC were evaluated.

Methods

In total, 398 GC cases and 397 controls were recruited for the study. Then, all cases were followed up for 5 years. ZNF331 and WIF1 promoter methylation status in PBLs was measured using a methylation-sensitive high-resolution melting method. Logistic and Cox regression models were used to analyse the correlation between gene methylation and the risk and prognosis of GC. Confounders were balanced through propensity score (PS) matching.

Results

High ZNF331 methylation significantly decreased GC risk after PS adjustment (OR = 0.580, 95% CI: 0.375–0.898, P = 0.015), which also presented in males (OR = 0.577, 95% CI: 0.343–0.970, P = 0.038). However, WIF1 methylation was not associated with GC risk. Additionally, significant combined effects between ZNF331 methylation and the intake of green vegetables and garlic were observed (OR = 0.073, 95% CI: 0.027–0.196, P < 0.001 and OR = 0.138, 95% CI: 0.080–0.238, P < 0.001, respectively). Furthermore, ZNF331 and WIF1 methylation had no impact on the prognosis of GC.

Conclusion

ZNF331 methylation in PBLs may affect GC risk in combination with the consumption of green vegetables and garlic and may act as a potential biomarker of GC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08199-4.

IL10 hypomethylation is associated with the risk of gastric cancer

Interleukin-10 (IL10), a pleiotropic cytokine secreted by type-2 helper (Th2) T cells, contributes to the oncogenic activation or inactivation of tumor-suppressor genes. The present study investigated whether hypomethylation of IL10 CpG island (CGI) was associated with the risk of developing gastric cancer (GC) and the prognosis of patients with GC. A fragment (hg18, chr1: 206945638-206945774) at the CGI of IL10 was selected for the present methylation assay. Quantitative methylation-specific PCR was used to evaluate the methylation of IL10 CGI in 117 tumor samples from patients with GC. The results demonstrated that IL10 CGI methylation was significantly lower in the tumor tissues compared with that in the paired adjacent non-tumor tissues (median percentage of methylated reference, 29.16 vs. 42.82%, respectively; P=4×10⁻⁸). Furthermore, results from receiver operating characteristic curve analysis identified a significant area under the curve of 0.706, with a sensitivity and a specificity of 77.8 and 58.1%, respectively, between cancer tissues and paired adjacent non-tumor tissues. Furthermore, the methylation of IL10 CGI was significantly associated with patients' age at diagnosis (r=−0.201; P=0.03). Subgroup analyses demonstrated that the association between IL10 CGI hypomethylation and the risk of GC was specific for patients with low differentiation (P=1×10⁻⁷) and Borrmann types III+IV (P=1×10⁻⁷). In addition, IL10 CGI hypomethylation was significantly associated with the risk of GC for patients without smoking history (P=3×10⁻⁷) or a family history of cancer (P=2×10⁻⁷). The results from Kaplan-Meier survival analysis demonstrated that IL10 CGI hypomethylation was associated with a significantly shorter overall survival of patients with GC (P=0.041). Similar results were identified for patients with GC who did not have smoking history (P=0.037) or a family history of cancer (P=0.049). The results from this study demonstrated that IL10 CGI hypomethylation may be considered as a potential biomarker for the diagnosis and prognosis of patients with GC in the Chinese population.

Role of DNA Methylation in the Resistance to Therapy in Solid Tumors

Despite the recent advances in chemotherapeutic treatments against cancer, some types of highly aggressive and invasive cancer develop drug resistance against conventional therapies, which continues to be a major problem in the fight against cancer. In recent years, studies of alterations of DNA methylome have given us a better understanding of the role of DNA methylation in the development of tumors. DNA methylation (DNAm) is an epigenetic change that promotes the covalent transfer of methyl groups to DNA. This process suppresses gene expression through the modulation of the transcription machinery access to the chromatin or through the recruitment of methyl binding proteins. DNAm is regulated mainly by DNA methyltransferases. Aberrant DNAm contributes to tumor progression, metastasis, and resistance to current anti-tumoral therapies. Aberrant DNAm may occur through hypermethylation in the promoter regions of tumor suppressor genes, which leads to their silencing, while hypomethylation in the promoter regions of oncogenes can activate them. In this review, we discuss the impact of dysregulated methylation in certain genes, which impact signaling pathways associated with apoptosis avoidance, metastasis, and resistance to therapy. The analysis of methylome has revealed patterns of global methylation, which regulate important signaling pathways involved in therapy resistance in different cancer types, such as breast, colon, and lung cancer, among other solid tumors. This analysis has provided gene-expression signatures of methylated region-specific DNA that can be used to predict the treatment outcome in response to anti-cancer therapy. Additionally, changes in cancer methylome have been associated with the acquisition of drug resistance. We also review treatments with demethylating agents that, in combination with standard therapies, seem to be encouraging, as tumors that are in early stages can be successfully treated. On the other hand, tumors that are in advanced stages can be treated with these combination schemes, which could sensitize tumor cells that are resistant to the therapy. We propose that rational strategies, which combine specific demethylating agents with conventional treatment, may improve overall survival in cancer patients.

Combined effect between WT1 methylation and Helicobacter pylori infection, smoking, and alcohol consumption on the risk of gastric cancer

BACKGROUND

Peripheral blood leukocyte DNA methylation status has been proposed to be a surrogate marker for evaluating susceptibility to gastric cancer (GC). Helicobacter pylori (H pylori) infection, smoking, and alcohol consumption are known to induce gene methylation. A case-control study was performed to investigate the interactions between the methylation of two candidate genes and H pylori infection, smoking, and alcohol consumption in the risk of GC.

METHODS

A total of 400 GC cases and 402 controls were included in this study. The methylation status of WT1 and IGF2 was semiquantitatively determined by using methylation-sensitive high-resolution melting assays. H pylori IgG antibodies were detected by ELISA method.

RESULTS

Based on the area under the curve (AUC), 0% methylated DNA and 0.5% methylated DNA were used as the cutoff values for WT1 and IGF2, respectively. WT1 methylation was significantly associated with increased GC risk (OR = 1.65, 95% CI = 1.09-2.51, P = .019), especially in males (OR = 1.80, 95% CI: 1.10-2.95, P = .019) and older individuals (≥60 years) (OR = 2.03, 95% CI: 1.15-3.57, P = .014). A significant combination was observed between WT1 methylation and H pylori infection, alcohol consumption, and smoking for the risk of GC (OR_c  = 2.28, 95% CI = 1.47-3.55, P = .003, OR_c  = 2.19, 95% CI = 1.37-3.51, P = .001, OR_c  = 2.21, 95% CI = 1.39-3.51, P = .001, respectively). However, no association between IGF2 methylation and the risk of GC was found in this study.

CONCLUSIONS

WT1 methylation may serve as a new potential biomarker for GC susceptibility and can combine with H pylori infection, smoking, and alcohol consumption to influence GC risk.

Epigenetic biomarkers in gastrointestinal cancers: The current state and clinical perspectives

Each year, almost 4.1 million people are diagnosed with gastrointestinal (GI) cancers. Due to late detection of this disease, the mortality is high, causing approximately 3 million cancer-related deaths annually, worldwide. Although the incidence and survival differs according to organ site, earlier detection and improved prognostication have the potential to reduce overall mortality burden from these cancers. Epigenetic changes, including aberrant promoter DNA methylation, are common events in both cancer initiation and progression. Furthermore, such changes may be identified non-invasively with the use of PCR based methods, in bodily fluids of cancer patients. These features make aberrant DNA methylation a promising substrate for the development of disease biomarkers for early detection, prognosis and for predicting response to therapy. In this article, we will provide an update and current clinical perspectives for DNA methylation alterations in patients with colorectal, gastric, pancreatic, liver and esophageal cancers, and discuss their potential role as cancer biomarkers.

Association of peripheral blood leukocyte KIBRA methylation with gastric cancer risk: a case-control study

KIBRA was reported to be involved in various types of cancer and can be detected in blood. The purpose of this study was to investigate the relationship between the status of KIBRA methylation in peripheral blood leukocytes and gastric cancer (GC) risk. A case-control study was carried out to evaluate the association of blood cell-derived KIBRA methylation with the risk of GC using methylation-sensitive high-resolution melting analysis. A total of 393 cases and 393 controls were detected, respectively. Compared with the subjects in the KIBRA negative methylation (NM) group, positive methylation (PM) subjects exhibited a 1.52-fold (95% CI: 1.030-2.251, P = 0.035) increased risk for GC. Stratified analyses demonstrated that the significant association of KIBRA methylation with GC risk existed in the older group (≥ 60 years; ORa  = 1.846, 95% CI: 1.037-3.287, P = 0.037) and Helicobacter pylori (H. pylori) positive subjects (ORa  = 1.933, 95% CI: 1.103-3.386, P = 0.021). Statistically significant combination effects between the environmental factors and KIBRA methylation on the GC risk were observed except for storing food under refrigeration. KIBRA methylation derived from blood cells and combinations thereof with environmental factors may be associated with the risk of GC.

TUSC3: functional duality of a cancer gene

Two decades ago, following a systematic screening of LOH regions on chromosome 8p22, TUSC3 has been identified as a candidate tumor suppressor gene in ovarian, prostate and pancreatic cancers. Since then, a growing body of evidence documented its clinical importance in various other types of cancers, and first initial insights into its molecular function and phenotypic effects have been gained, though the precise role of TUSC3 in different cancers remains unclear. As a part of the oligosaccharyltransferase complex, TUSC3 localizes to the endoplasmic reticulum and functions in final steps of N-glycosylation of proteins, while its loss evokes the unfolded protein response. We are still trying to figure out how this mechanistic function is reconcilable with its varied effects on cancer promotion. In this review, we focus on cancer-related effects of TUSC3 and envisage a possible role of TUSC3 beyond endoplasmic reticulum.

Genome-wide DNA methylation profiles altered by Helicobacter pylori in gastric mucosa and blood leukocyte DNA

Purpose

To investigate Helicobacter pylori (H.pylori) associated genome-wide aberrant methylation patterns in gastric mucosa and blood leukocyte DNA, a population-based study was conducted in Linqu County.

Results

A total of 3000 and 386 CpGs were differentially methylated after successful H.pylori eradication in gastric mucosa and blood leukocyte DNA respectively, and 17 were the same alteration trend in the both tissues. The differentially methylated CpGs were located more frequently in promoters or CpG islands for gastric mucosa and gene body or open sea for blood leukocyte DNA. In eradicated gastric mucosa, the hypermethylated CpGs were enriched across inflammatory pathways, while the hypomethylated CpGs in tube morphogenesis, development and so on. The final validation found lower SPI1, PRIC285 and S1PR4 methylation levels in H.pylori positive subjects by case-control comparison, and increased methylation levels in H.pylori eradicated gastric mucosa by self-comparison. The Cancer Genome Atlas (TCGA) database analysis suggested that the up-regulation of the three genes by hypomethylation might be associated with gastric carcinogenesis.

Experimental Design

Infinium HumanMethylation 450K BeadChip was used to compare methylation profiles prior to and after eradication treatment. The methylation levels of identified candidate differentially methylated genes before and after H.pylori eradication were further validated by two stages (Stage I: self-comparison of 16 subjects before and after anti-H.pylori treatment; Stage II: case-control comparison of 25 H.pylori positive and 25 negative subjects and self-comparison of 50 anti-H.pylori treated subjects).

Conclusions

Novel H.pylori associated aberrant methylated genes were identified across the whole genome both in gastric mucosa and blood leukocyte DNA.

TUSC3: a novel tumour suppressor gene and its functional implications

The tumour suppressor candidate 3 (TUSC3) gene is located on chromosome region 8p22 and encodes the 34 kD TUSC3 protein, which is a subunit of the oligosaccharyl transferase responsible for the N‐glycosylation of nascent proteins. Known to be related to autosomal recessive mental retardation for several years, TUSC3 has only recently been identified as a potential tumour suppressor gene. Based on the structure and function of TUSC3, specific mechanisms in various diseases have been investigated. Several studies have demonstrated that TUSC3 is an Mg²⁺‐transporter involved in magnesium transport and homeostasis, which is important for learning and memory, embryonic development and testis maturation. Moreover, dysfunction or deletion of TUSC3 exerts its oncological effects as a modulator by inhibiting glycosylation efficiency and consequently inducing endoplasmic reticulum stress and malignant cell transformation. In this study, we summarize the advances in the studies of TUSC3 and comment on the potential roles of TUSC3 in diagnosis and treatment of TUSC3‐related diseases, especially cancer.

Detection and Clinical Significance of COX-2 Gene SNPs in Gastric Cancer

Gastric cancer has high morbidity and mortality. Identification of patients with high gastric cancer risk at early stage will improve patient prognosis. In this study, we examined two single nucleotide polymorphism (SNP) sites of COX-2 gene in gastric cancer patients and explored the effect of the SNPs on the morbidity of gastric cancer. We found that the SNPs COX-2-1195G/A and COX-2-8473T/C are correlated with the occurrence of gastric cancer, and the patients with variants A and C of the SNPs are liable to have gastric cancer. Our study provides a potential method for screening of susceptible population of gastric cancer for early-stage intervention in patients.

Effects of RNAi-mediated TUSC3 silencing on radiation-induced autophagy and radiation sensitivity of human lung adenocarcinoma cell line A549 under hypoxic condition

This study examined the effects of RNAi-mediated TUSC3 silencing on radiation-induced autophagy and radiation sensitivity of human lung adenocarcinoma cell line A549 under hypoxic condition. Different CoCl2 concentrations were used to treat A549 cells and establish a CoCl2-induced hypoxic model of A549 cells. MTT and clone formation assays were used to determine the effects of different concentrations of CoCl2 on the growth and proliferation of A549 cells treated by different doses of X-ray irradiation. The siRNA-expressing vector was transfected by liposomes and for silencing of TUSC3. Flow cytometry was used to measure cell cycle changes and apoptosis rate. Real-time quantitative polymerase chain reaction (qRT-PCR) assay was performed to detect the expression of TUSC3 mRNA. Western blotting was applied to detect the changes of TUSC3, LC3, and p62 proteins under different CoCl2 concentrations and after siRNA silencing of TUSC3. The TUSC3 levels in A549 cells increased under hypoxic conditions in a dose-dependent manner (P < 0.05). Hypoxia inhibited the growth and proliferation of A549 cells and promoted apoptosis (P < 0.05). With an increasing dose of X-ray irradiation, A549 cells showed significantly increased growth and proliferation and decreased apoptosis (P < 0.05). After siRNA-TUSC3 was transfected by liposome, the TUSC3 level was substantially inhibited (P < 0.05). Silencing TUSC3 inhibited A549 cell growth and proliferation after radiotherapy under hypoxic condition, promoted apoptosis, increased G0/G1 phase cells, and reduced S phase cells (all P < 0.05). Hypoxia and radiation along with different CoCl2 concentrations could induce cell autophagy, which increased with concentration and dose, while silencing the TUSC3 gene inhibited autophagy (all P < 0.05). RNAi silencing of TUSC3 inhibited growth and proliferation, while enhanced apoptosis and radiation sensitivity of hypoxic A549 lung adenocarcinoma cells.

TUSC3 suppresses glioblastoma development by inhibiting Akt signaling

Glioblastoma multiform is one of the most common and most aggressive brain tumors in humans. The molecular and cellular mechanisms responsible for the onset and progression of GBM are elusive and controversial. The function of tumor suppressor candidate 3 (TUSC3) has not been previously characterized in GBM. TUSC3 was originally identified as part of an enzyme complex involved in N-glycosylation of proteins, but was recently implicated as a potential tumor suppressor gene in a variety of cancer types. In this study, we demonstrated that the expression levels of TUSC3 were downregulated in both GBM tissues and cells, and also found that overexpression of TUSC3 inhibits GBM cell proliferation and invasion. In addition, the effects of increased levels of methylation on the TUSC3 promoter were responsible for decreased expression of TUSC3 in GBM. Finally, we determined that TUSC3 regulates proliferation and invasion of GBM cells by inhibiting the activity of the Akt signaling pathway.

Methylation status of COX-2 in blood leukocyte DNA and risk of gastric cancer in a high-risk Chinese population

Background

Methylation is a common epigenetic modification which may play a crucial role in cancer development. To investigate the association between methylation of COX-2 in blood leukocyte DNA and risk of gastric cancer (GC), a nested case–control study was conducted in Linqu County, Shandong Province, a high risk area of GC in China.

Methods

Association between blood leukocyte DNA methylation of COX-2 and risk of GC was investigated in 133 GCs and 285 superficial gastritis (SG)/ chronic atrophic gastritis (CAG). The temporal trend of COX-2 methylation level during GC development was further explored in 74 pre-GC and 95 post-GC samples (including 31 cases with both pre- and post-GC samples). In addition, the association of DNA methylation and risk of progression to GC was evaluated in 74 pre-GC samples and their relevant intestinal metaplasia (IM)/dysplasia (DYS) controls. Methylation level was determined by quantitative methylation-specific PCR (QMSP). Odds ratios (ORs) and 95 % confidence intervals (CIs) were calculated by unconditional logistic regression analysis.

Results

The medians of COX-2 methylation levels were 2.3 % and 2.2 % in GC cases and controls, respectively. No significant association was found between COX-2 methylation and risk of GC (OR, 1.15; 95 % CI: 0.70-1.88). However, the temporal trend analysis showed that COX-2 methylation levels were elevated at 1–4 years ahead of clinical GC diagnosis compared with the year of GC diagnosis (3.0 % vs. 2.2 %, p = 0.01). Further validation in 31 GCs with both pre- and post-GC samples indicated that COX-2 methylation levels were significantly decreased at the year of GC diagnosis compared with pre-GC samples (1.5 % vs. 2.5 %, p = 0.02). No significant association between COX-2 methylation and risk of progression to GC was found in subjects with IM (OR, 0.50; 95 % CI: 0.18–1.42) or DYS (OR, 0.70; 95 % CI: 0.23–2.18). Additionally, we found that elder people had increased risk of COX-2 hypermethylation (OR, 1.55; 95 % CI: 1.02–2.36) and subjects who ever infected with H. pylori had decreased risk of COX-2 hypermethylation (OR, 0.54; 95 % CI: 0.34–0.88).

Conclusions

COX-2 methylation exists in blood leukocyte DNA but at a low level. COX-2 methylation levels in blood leukocyte DNA may change during GC development.

DNA methylation as a molecular biomarker in gastric cancer

DNA methylation plays a significant role in gastric carcinogenesis. The CpG island methylator phenotype (CIMP) characterizes distinct subtypes of gastric cancer (GC) and the relationship between specific methylation patterns and clinicopathological features has been evaluated. Altered DNA methylation is also observed in Helicobacter pylori-infected gastric mucosa, and its potential utility for GC risk estimation has been suggested. The ability to detect small amounts of methylated DNA among tissues allows us to use DNA methylation as a molecular biomarker in GC in a variety of samples, including serum, plasma and gastric washes. The DNA methylation status of nontargeted tissue, particularly blood, has been associated with predisposition to GC. We focus on the recent development of DNA methylation-based biomarkers in GC.

Somatic DNA Hypomethylation in H. pylori-Associated High-Risk Gastritis and Gastric Cancer: Enhanced Somatic Hypomethylation Associates with Advanced Stage Cancer

Objectives:

Helicobacter pylori-related high-risk gastritis (HRG) is a severe risk factor for gastric cancer (GC). The link between HRG and long-term risk for GC may involve genetic and epigenetic alterations underlying a field defect, i.e. a region of the mucosa prone to cancer development. Global DNA hypomethylation is a pervasive alteration in GC that associates with chromosomal instability and poor prognosis. The aim of this study was to determine the chronology of this alteration along the progression of HRG to GC, to test the hypothesis that it occurs early in the chronology of this pathway and plays a mechanistic role in the long-term cancer risk.

Methods:

We comparatively measured the genomic methylation level in gastric biopsies from 94 GC patients and 16 of their cancer-free relatives, 38 HRG patients, and 17 GERD patients, using a quantitative enzymatic method.

Results:

GC biopsies were hypomethylated compared to their matching non-tumor mucosa (P=9.4 × 10⁻¹²), irrespective of the tumor location or patients' country of origin. Genome-wide hypomethylation was also found in gastric mucosa of GC (P=1.5 × 10⁻⁵) and HRG (P=0.004) patients compared with healthy donors and GC relatives, regardless of the biopsy location within the stomach or previous H. pylori eradication therapy. An enhanced hypomethylation, distinguished by a bi-slope distribution of the differences in methylation between tumor and normal tissues, associated with a more invasive (P=0.005) and advanced stage (P=0.017) type of GC.

Conclusions:

Universal DNA demethylation in normal gastric mucosa in GC patients appears sporadic rather than familial. Genomic hypomethylation in HRG possibly contributes to a field defect for cancerization that is not reversed by bacterial eradication. Enhanced somatic hypomethylation may stratify GC for prognostic purposes.

Methylation-mediated gene silencing as biomarkers of gastric cancer: A review

Despite a decline in the overall incidence of gastric cancer (GC), the disease remains the second most common cause of cancer-related death worldwide and is thus a significant global health problem. The best means of improving the survival of GC patients is to screen for and treat early lesions. However, GC is often diagnosed at an advanced stage and is associated with a poor prognosis. Current diagnostic and therapeutic strategies have not been successful in decreasing the global burden of the disease; therefore, the identification of reliable biomarkers for an early diagnosis, predictive markers of recurrence and survival and markers of drug sensitivity and/or resistance is urgently needed. The initiation and progression of GC depends not only on genetic alterations but also epigenetic changes, such as DNA methylation and histone modification. Aberrant DNA methylation is the most well-defined epigenetic change in human cancers and is associated with inappropriate gene silencing. Therefore, an increasing number of genes methylated at the promoter region have been targeted as possible biomarkers for different purposes, including early detection, classification, the assessment of the tumor prognosis, the development of therapeutic strategies and patient follow-up. This review article summarizes the current understanding and recent evidence regarding DNA methylation markers in GC with a focus on the clinical potential of these markers.

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.

Tumor suppressor candidate TUSC3 expression during rat testis maturation

Analysis of microarray data obtained by comparing gene expression between 2-week-old infant and 7-week-old mature SD rat testes revealed novel targets involved in tumor suppression. Reverse-transcription polymerase chain reaction and Northern blotting indicated that Tusc3 gene expression was upregulated in the normal maturing testis and prostate and other organs such as the cerebrum and ovary. Tumor suppressor candidate 3 protein expression was detected in these same organs at a size of about 40 kDa, in accord with the predicted molecular size. In situ hybridization and immunohistochemistry showed that mRNA and protein localization were prevalent in the testis spermatocytes and interstitial cells such as the Leydig cells, as well as prostate epithelial cells. These data suggest that TUSC3 is deeply involved in spermatogenesis in the testis, inducing sperm differentiation and maturation, and plays a role in normal prostate development and tumor suppression.

Examination of whole blood DNA methylation as a potential risk marker for gastric cancer

Whole blood DNA methylation analysis has been proposed to be a risk marker for cancer that can be used to target patients for preventive interventions. To test this, we examined whole blood DNA methylation of 16 CpG island promoters and LINE1 repetitive element in patients with gastric cancer and control subjects. Bisulfite pyrosequencing was used to quantify the methylation of 14 CpG island promoters (MINT25, RORA, GDNF, CDH1, RARAB2, ER, CDH13, MYOD1, SFRP1, P2RX7, SLC16A12, IGF2, DPYS, and N33) and LINE1 from 72 patients with gastric cancer, 67 control, and 52 healthy young individuals. Quantitative methylation-specific real-time PCR was also conducted for 3 CpG island promoters (MINT25, MYO3A, and SOX11). Among all sites tested, only a marginal increase in the methylation of the SFRP1 promoter was observed in the blood of patients with gastric cancer when compared with the control group (11.3 % vs 10.5%; age-adjusted P value: P = 0.009), and this association was also seen in a validation set of 91 patients with gastric cancer (11.5% vs 10.5%; age-adjusted P value: P = 0.001). The methylation of 9 sites (GDNF, CDH1, RARAB2, CDH13, MYOD1, SFRP1, SLC16A12, DPYS, N33, and LINE1) and their mean Z score was correlated with higher age (R = 0.41, P < 0.0001) and marginally with telomere shortening (R = -0.18, P = 0.01) but not with gastric cancer risk (other than SFRP1 methylation). Variability in whole blood DNA methylation of cancer markers is primarily associated with aging, reflecting turnover of white blood cells, and has no direct link to gastric cancer predisposition. SFRP1 methylation in whole blood may be associated with gastric cancer risk.

Cancer as a dysregulated epigenome allowing cellular growth advantage at the expense of the host

Although at the genetic level cancer is caused by diverse mutations, epigenetic modifications are characteristic of all cancers, from apparently normal precursor tissue to advanced metastatic disease, and these epigenetic modifications drive tumour cell heterogeneity. We propose a unifying model of cancer in which epigenetic dysregulation allows rapid selection for tumour cell survival at the expense of the host. Mechanisms involve both genetic mutations and epigenetic modifications that disrupt the function of genes that regulate the epigenome itself. Several exciting recent discoveries also point to a genome-scale disruption of the epigenome that involves large blocks of DNA hypomethylation, mutations of epigenetic modifier genes and alterations of heterochromatin in cancer (including large organized chromatin lysine modifications (LOCKs) and lamin-associated domains (LADs)), all of which increase epigenetic and gene expression plasticity. Our model suggests a new approach to cancer diagnosis and therapy that focuses on epigenetic dysregulation and has great potential for risk detection and chemoprevention.