CpG island hypermethylation in gastric carcinoma and its premalignant lesions

Genome-wide characterization of extrachromosomal circular DNA in gastric cancer and its potential role in carcinogenesis and cancer progression

Extrachromosomal circular DNAs (eccDNAs) carrying random genomic segments are broadly found across different cancer types, but their molecular functions and impact in gastric cancer (GC) are rarely known. In this study, we aimed to investigate the potential role of eccDNA in GC. Using the Circle-seq strategy, we observed the eccDNA abundance in gastric cancer tissues (GCT) was aberrantly higher than that of normal adjacent tissues (NAT). The high abundance of eccDNAs carrying oncogene-segments in GCT may represent the DNA damage products of amplified oncogenes. Analysis of GCT over-represented eccDNA carrying enhancer (eccEnhancer) based on data from FANTOM5 project combined with TCGA database suggested the GC over-represented eccEnhancers may contribute to development of GC. GC over-represented eccDNAs carrying pre-miRNA (eccMIR) were enriched to multiple cancer-relevant signal pathways by KEGG analysis. We then synthesized the top six GC over-represented eccMIRs and found four of them enabled high expression of miRNAs and down-regulation of miRNA-target genes in MGC803 cells. Furthermore, we observed the inheritance of GC over-represented eccMIRs benefited host cell proliferation and promoted the aggressive features of host cells. Altogether, this study revealed the GC over-represented eccDNAs carrying functional genomic segments were related to the carcinogenesis of GC and presented the capability to facilitate cancer progression, suggesting the cancerous eccDNAs may serve as a dynamic reservoir for genome plasticity and rapid adaptive evolution of cancer. Therefore, blocking the pathways for eccDNAs generation may provide a novel therapeutic strategy for the treatment of gastric cancer.

Helicobacter pylori severely reduces expression of DNA repair proteins PMS2 and ERCC1 in gastritis and gastric cancer

Gastric cancers are the third leading cause of cancer mortality in the world. Helicobacter pylori causes over 60 % of all stomach cancers. Colonization of the gastric mucosa by H. pylori results in increased DNA damage. Repair of DNA damage may also be reduced by H. pylori infection. Reduced DNA repair in combination with increased DNA damage can cause carcinogenic mutations. During progression to gastric cancer, gastric epithelium goes through stages of increasing pathology. Determining the levels of DNA repair enzymes during progression to gastric cancer could illuminate treatment approaches. Our aim is to determine the level of gastric expression of DNA repair proteins ERCC1 (a nucleotide excision repair enzyme) and PMS2 (a mismatch repair enzyme) in the presence of H. pylori infection at successive stages of gastric pathology and in gastric cancers. We analyzed gastric tissues of 300 individuals, including 30 without dyspepsia, 200 with dyspepsia and 70 with gastric cancers. The presence of H. pylori, gastric pathology and expression of DNA repair proteins ERCC1 and PMS2 were evaluated. Infection by H. pylori carrying the common cagA gene reduced median nuclear expression of ERCC1 and PMS2 to less than 20 % and 15 % of normal, respectively, in all pathologic stages preceding cancer. ERCC1 and PMS2 nuclear expression was 0-5 % of normal in gastric cancers. H. pylori can cause deficiency of ERCC1 and PMS2 protein expression. These deficiencies are associated with gastric pathology and cancer. This reduction in DNA repair likely causes carcinogenic mutations. Substantially reduced ERCC1 and PMS2 expression appears to be an early step in progression to H. pylori-induced gastric cancer.

Analysis of DNA methylation in endometrial biopsies to predict risk of endometrial cancer

OBJECTIVE

To determine whether analysis of methylated DNA in benign endometrial biopsy (EB) specimens is associated with risk of endometrial cancer (EC).

METHODS

We identified 23 women with EBs performed at Mayo Clinic diagnosed as normal (n = 14) or hyperplasia (n = 9) and who later developed endometrial cancer after a median interval of 1 year. Cases were matched 1:1 with patients with benign EBs who did not develop EC (controls) by histology of benign EB (normal endometrium vs. endometrial hyperplasia without atypia), date of EB, age at EB, and length of post-biopsy follow-up. DNA extracted from formalin-fixed paraffin-embedded tissues underwent pyrosequencing to determine percent methylation of promoter region CpGs at 26 loci in 4 genes (ADCYAP1, HAND2, MME, RASSF1A) previously reported as methylated in EC.

RESULTS

After pathologic review, 23 matched pairs of cases and controls were identified (14 normal, 9 hyperplasia without atypia per group). Among cases, median time from benign EB to EC was 1 year (range 2 days - 9.2 years). We evaluated 26 CpG sites within 4 genes and found a consistent trend of increasing percentage of methylation from control to case to EC for all CpGs. At the gene-level, mean methylation events of ADCYAP1 and HAND2 in cases were significantly higher than control (p = 0.015 and p = 0.021, respectively). Though the other genes did not reach statistical significance, we observed an increased methylation trend among all genes. Area-under-curve (AUC) calculations (predicting future development of EC in the setting of benign EB) for ADCYAP1 and HAND2 were 0.71 (95% CI 0.55-0.88) and 0.83 (95% CI 0.64-1, respectively).

CONCLUSIONS

This proof-of-principle study provides evidence that specific methylation patterns in benign EB correlate with future development of EC.

Decreased Methylation of IFNAR Gene Promoter from Peripheral Blood Mononuclear Cells Is Associated with Oxidative Stress in Chronic Hepatitis B

Type I interferons (IFNs) play an antiviral effect by binding to type I interferon receptor (IFNAR). Oxidative stress might induce the gene promoter methylation. The purpose of our study was to evaluate the potential relationship between the methylation of IFNAR promoter and the status of oxidative stress in chronic hepatitis B (CHB). The methylation level of the IFNAR promoter in patients with CHB and healthy controls (HCs) was determined by methylation-specific polymerase chain reaction (MS-PCR). The quantitative real-time PCR (RT-qPCR) was used to evaluate the IFNAR mRNA status in peripheral blood mononuclear cells from CHB and HCs. Level of plasma-soluble IFNAR and oxidative stress parameters, including malondialdehyde (MDA) and glutathione (GSH) were determined by enzyme-linked immunosorbent assay (ELISA). The frequency of IFNAR promoter methylation in CHB patients was significantly lower than that of HCs. The IFNAR mRNA level of patients with CHB was higher than HCs. MDA level was higher in CHB patients, whereas GSH level was lower in CHB patients than that of HCs. In CHB patients, plasma MDA level was significantly higher with IFNAR promoter methylation than unmethylation, and soluble IFNAR in the circulation of methylated patients with CHB was decreased than unmethylated patients with CHB. Our results indicated that the IFNAR promoter methylation might have a potential relationship with the status of oxidative stress.

Genomic and Epigenomic Profiling of High-Risk Intestinal Metaplasia Reveals Molecular Determinants of Progression to Gastric Cancer

Intestinal metaplasia (IM) is a pre-malignant condition of the gastric mucosa associated with increased gastric cancer (GC) risk. We performed (epi)genomic profiling of 138 IMs from 148 cancer-free patients, recruited through a 10-year prospective study. Compared with GCs, IMs exhibit low mutational burdens, recurrent mutations in certain tumor suppressors (FBXW7) but not others (TP53, ARID1A), chromosome 8q amplification, and shortened telomeres. Sequencing identified more IM patients with active Helicobacter pylori infection compared with histopathology (11%-27%). Several IMs exhibited hypermethylation at DNA methylation valleys; however, IMs generally lack intragenic hypomethylation signatures of advanced malignancy. IM patients with shortened telomeres and chromosomal alterations were associated with subsequent dysplasia or GC; conversely patients exhibiting normal-like epigenomic patterns were associated with regression.

Hypermethylation of the galectin-3 promoter is associated with poor prognosis of acute-on-chronic hepatitis B liver failure

BACKGROUND AND AIMS

The possible role of galectin-3 in acute-on-chronic hepatitis B liver failure (ACHBLF) remains unknown. This study aimed to determine the methylation status of the galectin-3 promoter in patients with ACHBLF and analyze its prognostic value.

METHODS

The methylation status of the galectin-3 promoter in patients with ACHBLF, chronic hepatitis B (CHB) and healthy controls (HCs) was determined by methylation-specific polymerase chain reaction (MSP). The galectin-3 mRNA level in peripheral blood mononuclear cells (PBMCs) was detected using real-time polymerase chain reaction (RT-PCR).

RESULTS

The methylation frequency of the galectin-3 promoter was significantly higher while galectin-3 mRNA was lower in ACHBLF than in CHB and HCs. Galectin-3 promoter methylation was negatively correlated with the mRNA level in ACHBLF. In addition, ACHBLF patients carrying the methylated promoter showed shorter survival time, higher 3-month mortality, and higher model for end-stage liver disease (MELD) score when compared to ACHBLF patients carrying the unmethylated promoter. Moreover, promoter methylation was a better predictor of 3-week mortality than the MELD score in ACHBLF patients.

CONCLUSION

Our results suggest that hypermethylation of the galectin-3 promoter might be an early biomarker for predicting disease severity and prognosis in patients with ACHBLF.

Helicobacter pylori CagA induces tumor suppressor gene hypermethylation by upregulating DNMT1 via AKT-NFκB pathway in gastric cancer development

Methylation of CpG islands in tumor suppressor gene prompter is one of the most characteristic abnormalities in Helicobacter pylori (HP)-associated gastric carcinoma (GC). Here, we investigated the pathogenic and molecular mechanisms underlying hypermethylation of tumor suppressor genes in HP induced GC development. We found that tumor suppressor genes hypermethylation, represented by MGMT, positively correlated with CagA in clinical specimens, gastric tissues from HP infected C57 mice and GC cell lines transfected by CagA or treated by HP infection. CagA enhanced PDK1 and AKT interaction and increased AKT phosphorylation. The P-AKT subsequent activated NFκB, which then bound to DNMT1 promoter and increased its expression. Finally, the upregulated DNMT1 promoted tumor suppressor genes hypermethylation with MGMT as a representative. In conclusion, CagA increased tumor suppressor genes hypermethylation via stimulating DNMT1 expression through the AKT-NFκB pathway.

Genomic landscape of gastric cancer: molecular classification and potential targets

Gastric cancer imposes a considerable health burden worldwide, and its mortality ranks as the second highest for all types of cancers. The limited knowledge of the molecular mechanisms underlying gastric cancer tumorigenesis hinders the development of therapeutic strategies. However, ongoing collaborative sequencing efforts facilitate molecular classification and unveil the genomic landscape of gastric cancer. Several new drivers and tumorigenic pathways in gastric cancer, including chromatin remodeling genes, RhoA-related pathways, TP53 dysregulation, activation of receptor tyrosine kinases, stem cell pathways and abnormal DNA methylation, have been revealed. These newly identified genomic alterations await translation into clinical diagnosis and targeted therapies. Considering that loss-of-function mutations are intractable, synthetic lethality could be employed when discussing feasible therapeutic strategies. Although many challenges remain to be tackled, we are optimistic regarding improvements in the prognosis and treatment of gastric cancer in the near future.

Lack of Correlation between Aberrant p16, RAR-β2, TIMP3, ERCC1, and BRCA1 Protein Expression and Promoter Methylation in Squamous Cell Carcinoma Accompanying Candida albicans-Induced Inflammation

Hyperplastic candidiasis is characterized by thickening of the mucosal epithelia with Candida albicans infection with occasional progression to squamous cell carcinoma (SCC). C. albicans is a critical factor in tumor development; however, the oncogenic mechanism is unclear. We have previously produced an animal model for hyperplastic candidiasis in the rat forestomach. In the present study, we investigate whether impaired DNA methylation and associated protein expression of tumor suppressor and DNA repair genes are involved in the SCC carcinogenesis process using this hyperplastic candidiasis model. Promoter methylation and protein expression were analyzed by methylation specific PCR and immunohistochemical staining, respectively, of 5 areas in the forestomachs of alloxan-induced diabetic rats with hyperplastic candidiasis: normal squamous epithelia, squamous hyperplasia, squamous hyperplasia adjacent to SCC, squamous hyperplasia transitioning to SCC, and SCC. We observed nuclear p16 overexpression despite increases in p16 gene promoter methylation during the carcinogenic process. TIMP3 and RAR-β2 promoter methylation progressed until the precancerous stage but disappeared upon malignant transformation. In comparison, TIMP3 protein expression was suppressed during carcinogenesis and RAR-β2 expression was attenuated in the cytoplasm but enhanced in nuclei. ERCC1 and BRCA1 promoters were not methylated at any stage; however, their protein expression disappeared beginning at hyperplasia and nuclear protein re-expression in SCC was observed only for ERCC1. These results suggest that aberrant p16, RAR-β2, TIMP3, ERCC1, and BRCA1 expression might occur that is inconsistent with the respective gene promoter methylation status, and that this overexpression might serve to promote the inflammatory carcinogenesis caused by C. albicans infection.

Proteomics-Based Identification and Analysis of Proteins Associated with Helicobacter pylori in Gastric Cancer

Helicobacter pylori (H. pylori) is a spiral-shaped Gram-negative bacterium that causes the most common chronic infection in the human stomach. Approximately 1%-3% of infected individuals develop gastric cancer. However, the mechanisms by which H. pylori induces gastric cancer are not completely understood. The available evidence indicates a strong link between the virulence factor of H. pylori, cytotoxin-associated gene A (CagA), and gastric cancer. To further characterize H. pylori virulence, we established three cell lines by infecting the gastric cancer cell lines SGC-7901 and AGS with cagA⁺H. pylori and transfecting SGC-7901 with a vector carrying the full-length cagA gene. We detected 135 differently expressed proteins from the three cell lines using proteome technology, and 10 differential proteins common to the three cell lines were selected and identified by LC-MS/MS as well as verified by western blot: β-actin, L-lactate dehydrogenase (LDH), dihydrolipoamide dehydrogenase (DLD), pre-mRNA-processing factor 19 homolog (PRPF19), ATP synthase, calmodulin (CaM), p64 CLCP, Ran-specific GTPase-activating protein (RanGAP), P43 and calreticulin. Detection of the expression of these proteins and genes encoding these proteins in human gastric cancer tissues by real-time PCR (RT-qPCR) and western blot revealed that the expression of β-ACTIN, LDH, DLD, PRPF19 and CaM genes were up-regulated and RanGAP was down-regulated in gastric cancer tissues and/or metastatic lymph nodes compared to peri-cancerous tissues. High gene expression was observed for H. pylori infection in gastric cancer tissues. Furthermore, the LDH, DLD and CaM genes were demethylated at the promoter -2325, -1885 and -276 sites, respectively, and the RanGAP gene was highly methylated at the promoter -570 and -170 sites in H. pylori-infected and cagA-overexpressing cells. These results provide new insights into the molecular pathogenesis and treatment targets for gastric cancer with H. pylori infection.

Promoter methylation status and expression of PPAR-γ gene are associated with prognosis of acute-on-chronic hepatitis B liver failure

BACKGROUND

Peroxisome proliferator-activated receptor gamma (PPAR-γ) has been demonstrated to be involved in anti-inflammatory reactions, but its role in acute-on-chronic hepatitis B liver failure (ACHBLF) is unclear. Therefore, DNA methylation patterns and expression level of PPAR-γ gene were detected in peripheral blood mononuclear cells (PBMCs) from 81 patients with ACHBLF, 50 patients with chronic hepatitis B (CHB), and 30 healthy controls, and the possible role of PPAR-γ in ACHBLF was analyzed.

RESULTS

We found that aberrant PPAR-γ promoter methylation was attenuated in ACHBLF patients compared with CHB patients and was responsible for the elevated PPAR-γ expression level, which was negatively correlated with total bilirubin and international normalized ratio. Plasma level of TNF-α and IL-6 in ACHBLF patients were higher than CHB patients and healthy controls and significantly reduced in unmethylated group. ACHBLF patients with PPAR-γ promoter methylation had poorer outcomes than those without. Correspondingly, PPAR-γ messenger RNA (mRNA) level was higher in survivors than non-survivors and gradually increased in survivors with time, while remained low level in non-survivors.

CONCLUSIONS

Aberrant promoter methylation decline and PPAR-γ expression rebound occurred in ACHBLF compared with CHB and could improve prognosis of ACHBLF by negatively regulating cytokines.

Role of epigenetics in EBV regulation and pathogenesis

Epigenetic modifications of the viral and host cell genomes regularly occur in EBV-associated lymphomas and carcinomas. The cell type-dependent usage of latent EBV promoters is determined by the cellular epigenetic machinery. Viral oncoproteins interact with the very same epigenetic regulators and alter the cellular epigenotype and gene-expression pattern: there are common gene sets hypermethylated in both EBV-positive and EBV-negative neoplasms of different histological types. A group of hypermethylated promoters may represent, however, a unique EBV-associated epigenetic signature in EBV-positive gastric carcinomas. By contrast, EBV-immortalized B-lymphoblastoid cell lines are characterized by genome-wide demethylation and loss and rearrangement of heterochromatic histone marks. Early steps of EBV infection may also contribute to reprogramming of the cellular epigenome.

Helicobacter pylori Induces Hypermethylation of CpG Islands Through Upregulation of DNA Methyltransferase: Possible Involvement of Reactive Oxygen/Nitrogen Species

Helicobacter pylori infection has been considered to be one of the major factors implicated in etiology of gastric cancer. Aberrant DNA methylation accounts for epigenetic modifications induced by H. pylori. H. pylori-induced hypermethylation has been linked to enhancement of the rates of metastasis and recurrence in gastric cancer patients. H. pylori-induced gene hypermethylation has been known to be associated with inflammation. However, the molecular mechanisms underlying H. pylori-induced hypermethylation remain largely unknown. This review highlights possible involvement of reactive oxygen/nitrogen species in H. pylori-induced hypermethylation and gastric carcinogenesis.

Mallory-Denk Body (MDB) formation modulates Ufmylation expression epigenetically in alcoholic hepatitis (AH) and non-alcoholic steatohepatitis (NASH)

Promoter CpG island hypermethylation is an important mechanism for inactivating key cellular enzymes that mediate epigenetic processes in hepatitis-related hepatocellular carcinoma (HCC). The ubiquitin-fold modifier 1 (Ufm1) conjugation pathway (Ufmylation) plays an essential role in protein degradation, protein quality control and signal transduction. Previous studies showed that the Ufmylation pathway was downregulated in alcoholic hepatitis (AH), non-alcoholic steatohepatitis (NASH) and in mice fed DDC, resulting in the formation of Mallory-Denk Bodies (MDBs). In this study, we further discovered that betaine, a methyl donor, fed together with DDC significantly prevents the increased expression of Ufmylation in drug-primed mice fed DDC. Betaine significantly prevented transcript silencing of Ufm1, Uba5 and UfSP1 where MDBs developed and also prevented the increased expression of FAT10 and LMP7 caused by DDC re-fed mice. Similar downregulation of Ufmylation was observed in multiple AH and NASH biopsies which had formed MDBs. The DNA methylation levels of Ufm1, Ufc1 and UfSP1 in the promoter CpG region were significantly increased both in AH and NASH patients compared to normal subjects. DNA (cytosine-5-)-methyltransferase 1 (DNMT1) and DNA (cytosine-5-)-methyltransferase 3 beta (DNMT3B) mRNA levels were markedly upregulated in AH and NASH patients, implying that the maintenance of Ufmylation methylation might be mediated by DNMT1 and DNMT3B together. These data show that MDB formation results from Ufmylation expression epigenetically in AH and NASH patients. Promoter CpG methylation may be a major mechanism silencing Ufmylation expression.

Microarray-based DNA methylation study of Ewing's sarcoma of the bone

Alterations in DNA methylation patterns are a hallmark of malignancy. However, the majority of epigenetic studies of Ewing’s sarcoma have focused on the analysis of only a few candidate genes. Comprehensive studies are thus lacking and are required. The aim of the present study was to identify novel methylation markers in Ewing’s sarcoma using microarray analysis. The current study reports the microarray-based DNA methylation study of 1,505 CpG sites of 807 cancer-related genes from 69 Ewing’s sarcoma samples. The Illumina GoldenGate Methylation Cancer Panel I microarray was used, and with the appropriate controls (n=14), a total of 92 hypermethylated genes were identified in the Ewing’s sarcoma samples. The majority of the hypermethylated genes were associated with cell adhesion, cell regulation, development and signal transduction. The overall methylation mean values were compared between patients who survived and those that did not. The overall methylation mean was significantly higher in the patients who did not survive (0.25±0.03) than in those who did (0.22±0.05) (P=0.0322). However, the overall methylation mean was not found to significantly correlate with age, gender or tumor location. GDF10, OSM, APC and HOXA11 were the most significant differentially-methylated genes, however, their methylation levels were not found to significantly correlate with the survival rate. The DNA methylation profile of Ewing’s sarcoma was characterized and 92 genes that were significantly hypermethylated were detected. A trend towards a more aggressive behavior was identified in the methylated group. The results of this study indicated that methylation may be significant in the development of Ewing’s sarcoma.

Exportin 4 gene expression and DNA promoter methylation status in chronic hepatitis B virus infection

Exportin 4 (XPO4) is a novel identified candidate tumour-suppressor gene involved in the pathogenesis of hepatocellular carcinoma (HCC). This study was aimed to determine the clinical features of XPO4 mRNA expression and promoter methylation status in peripheral blood mononuclear cells (PBMCs) of patients with chronic hepatitis B virus (HBV) infection. PBMCs were isolated from 44 HCC, 38 liver cirrhosis (LC), 34 chronic hepatitis B (CHB) patients and 17 healthy controls (HCs). The mRNA level and promoter methylation status of XPO4 were determined by quantitative real-time RT-PCR and methylation-specific PCR, respectively. XPO4 mRNA level of HCC patients was significantly lower compared with LC and CHB patients as well as HCs (all P < 0.01, respectively), and significant differences of the XPO4 mRNA level were found in LC and CHB group than in HCs (LC vs HCs, P < 0.01; CHB vs HCs, P < 0.05). Methylation rate of XPO4 promoter was significantly increased in patients with HCC than in patients with CHB and HCs (both P < 0.05). DNA methylation pattern was responsible for the suppression of XPO4 transcription in the progression of HBV infection (P = 0.000). Furthermore, AFP level was significantly higher in HCC patients with XPO4 methylation than in those without methylation ((8702 ± 15635) μm vs (1052 ± 5370) μm, P < 0.05). In conclusion, transcription of XPO4 gene was gradually decreased and methylation rate of XPO4 promoter was increased with the progression of HBV infection. Methylation status of XPO4 in PBMCs tended to be a noninvasive biomarker to predict HCC and the progression of HBV infection.

Role of p16 gene promoter methylation in gastric carcinogenesis: a meta-analysis

This meta-analysis was performed to evaluate the relationships between promoter DNA methylation in tumor suppressor gene p16 and gastric carcinogenesis. The PubMed, CISCOM, CINAHL, Web of Science, Google Scholar, EBSCO, Cochrane Library and CBM databases were searched for relevant articles published before November 1st, 2013 without any language restrictions. Meta-analysis was conducted using the STATA 12.0 software. Crude odds ratios (ORs) with 95% confidence intervals (95% CI) were calculated. Forty-seven clinical cohort studies that met all inclusion criteria were included in this meta-analysis. A total of 2,813 gastric cancer (GC) patients were assessed. Our meta-analysis results revealed that the frequencies of p16 promoter methylation in the GC tissues were higher than those of normal and adjacent tissues (Normal: OR = 23.04, 95% CI = 13.55-39.15, P < 0.001; Adjacent: OR = 4.42, 95% CI = 1.66-11.76, P = 0.003; respectively). Furthermore, we observed significant associations of p16 promoter methylation with TNM stage, histologic grade, invasive grade, lymph node metastasis of GC (TNM stage: OR = 3.60, 95% CI: 2.17-5.98, P < 0.001; Histologic grade: OR = 2.63, 95% CI: 1.55-4.45, P < 0.001; Invasive grade: OR = 3.44, 95% CI: 1.68-7.06, P = 0.001; Lymph node metastasis: OR = 2.68, 95% CI: 1.66-4.32, P < 0.001; respectively). However, there were no correlations of p16 promoter methylation with the TNM stage and Helicobacter pylori (HP) infection of GC (Tumor size: OR = 0.76, 95% CI: 0.14-4.07, P = 0.746; HP infection: OR = 1.31, 95% CI: 0.75-2.27, P = 0.342; respectively). Our findings provide empirical evidence that p16 promoter methylation may play an important role in gastric carcinogenesis. Thus, p16 promoter methylation may be a promising potential biomarker for the early diagnosis of GC.