Carcinogenetic risk estimation based on quantification of DNA methylation levels in liver tissue at the precancerous stage

Aberrant cell adhesiveness due to DNA hypermethylation of KLF11 in papillary urothelial carcinomas

PURPOSE

The aim of this study was to clarify DNA methylation profiles determining the clinicopathological diversity of urothelial carcinomas.

METHODS

Genome-wide DNA methylation analysis was performed using the Infinium HumanMethylation450 BeadChip in 46 paired samples of non-cancerous urothelium (N) and corresponding cancerous tissue (T), and 26 samples of normal control urothelium obtained from patients without urothelial carcinomas (C). For genes of interest, correlation between DNA methylation and mRNA expression was examined using the Cancer Genome Atlas database. In addition, the role of a selected target for cancer-relevant endpoints was further examined in urothelial carcinoma cell lines.

RESULTS

The genes showing significant differences in DNA methylation levels between papillary carcinomas and more aggressive non-papillary (nodular) carcinomas were accumulated in signaling pathways participating in cell adhesion and cytoskeletal remodeling. Five hundred ninety-six methylation sites showed differences in DNA methylation levels between papillary and nodular carcinomas. Of those sites, that were located in CpG-islands around transcription start site, 5'-untranslated region or 1st exon, 16 genes exhibited inverse correlations between DNA methylation and mRNA expression levels. Among the latter, only the KLF11 gene showed papillary T sample-specific DNA hypermethylation in comparison to C and N samples. The DNA methylation levels of KLF11 were not significantly different between T samples and N samples or T samples and C samples for patients with papillo-nodular or nodular carcinomas. Knockdown experiments using the urothelial carcinoma cell lines HT1376 and 5637, which are considered models for papillary carcinoma, revealed that KLF11 participates in altering the adhesiveness of cells to laminin-coated dishes, although cell growth was not affected.

CONCLUSION

These data indicate that DNA hypermethylation of KLF11 may participate in the generation of papillary urothelial carcinomas through induction of aberrant cancer cell adhesion to the basement membrane.

Molecular pathological approach to cancer epigenomics and its clinical application

Careful microscopic observation of histopathological specimens, accumulation of large numbers of high-quality tissue specimens, and analysis of molecular pathology in relation to morphological features are considered to yield realistic data on the nature of multistage carcinogenesis. Since the morphological hallmark of cancer is disruption of the normal histological structure maintained through cell-cell adhesiveness and cellular polarity, attempts have been made to investigate abnormalities of the cadherin-catenin cell adhesion system in human cancer cells. It has been shown that the CDH1 tumor suppressor gene encoding E-cadherin is silenced by DNA methylation, suggesting that a "double hit" involving DNA methylation and loss of heterozygosity leads to carcinogenesis. Therefore, in the 1990s, we focused on epigenomic mechanisms, which until then had not received much attention. In chronic hepatitis and liver cirrhosis associated with hepatitis virus infection, DNA methylation abnormalities were found to occur frequently, being one of the earliest indications that such abnormalities are present even in precancerous tissue. Aberrant expression and splicing of DNA methyltransferases, such as DNMT1 and DNMT3B, was found to underlie the mechanism of DNA methylation alterations in various organs. The CpG island methylator phenotype in renal cell carcinoma was identified for the first time, and its therapeutic targets were identified by multilayer omics analysis. Furthermore, the DNA methylation profile of nonalcoholic steatohepatitis (NASH)-related hepatocellular carcinoma was clarified in groundbreaking studies. Since then, we have developed diagnostic markers for carcinogenesis risk in NASH patients and noninvasive diagnostic markers for upper urinary tract cancer, as well as developing a new high-performance liquid chromatography-based diagnostic system for DNA methylation diagnosis. Research on the cancer epigenome has revealed that DNA methylation alterations occur from the precancerous stage as a result of exposure to carcinogenic factors such as inflammation, smoking, and viral infections, and continuously contribute to multistage carcinogenesis through aberrant expression of cancer-related genes and genomic instability. DNA methylation alterations at the precancerous stages are inherited by or strengthened in cancers themselves and determine the clinicopathological aggressiveness of cancers as well as patient outcome. DNA methylation alterations have applications as biomarkers, and are expected to contribute to diagnosis, as well as preventive and preemptive medicine.

DNA methylation alterations of ADCY5, MICAL2, and PLEKHG2 during the developmental stage of cryptogenic hepatocellular carcinoma

AIM

The aim of this study was to clarify the significance of DNA methylation alterations of cryptogenic hepatocellular carcinomas (HCCs).

METHODS

Using the Infinium assay, we performed genome-wide DNA methylation analysis of 250 liver tissue samples, including noncancerous liver tissue (U-N) and corresponding cancerous tissue (U-T) from patients with cryptogenic HCC without a history of excessive alcohol use and hepatitis virus infection, and whose U-N samples showed no remarkable histological features (no microscopic evidence of simple steatosis, any form of hepatitis including nonalcoholic steatohepatitis, or liver cirrhosis).

RESULTS

We identified 3272 probes that showed significant differences of DNA methylation levels between U-N and normal liver tissue samples from patients without HCC, indicating that a distinct DNA methylation profile had already been established at the precancerous U-N stage. U-Ns have a DNA methylation profile differing from that of noncancerous liver tissue of patients with nonalcoholic steatohepatitis-related, viral hepatitis-related, and alcoholic liver disease-related HCCs. Such DNA methylation alterations in U-Ns were inherited by U-Ts. The U-Ns showed DNA methylation alteration of ADCY5, resulting in alteration of its mRNA expression, whereas noncancerous liver tissue of patients with nonalcoholic steatohepatitis-, viral hepatitis-, or alcoholic liver disease-related HCCs did not. DNA methylation levels of MICAL2 and PLEKHG2 in U-Ts were correlated with larger tumor diameter and portal vein involvement, respectively.

CONCLUSIONS

U-N-specific DNA hypermethylation of ADCY5 may have significance, even from the precancerous stage in liver showing no remarkable histological features. DNA hypomethylation of MICAL2 and PLEKHG2 may determine the clinicopathological features of cryptogenic HCC.

DNA methylation in cell plasticity and malignant transformation in liver diseases

The liver possesses extraordinary regenerative capacity mainly attributable to the ability of hepatocytes (HCs) and biliary epithelial cells (BECs) to self-replicate. This ability is left over from their bipotent parent cell, the hepatoblast, during development. When this innate regeneration is compromised due to the absence of proliferative parenchymal cells, such as during cirrhosis, HCs and BEC can transdifferentiate; thus, adding another layer of complexity to the process of liver repair. In addition, dysregulated lineage maintenance in these two cell populations has been shown to promote malignant growth in experimental conditions. Here, malignant transformation, driven in part by insufficient maintenance of lineage reprogramming, contributes to end-stage liver disease. Epigenetic changes are key drivers for cell fate decisions as well as transformation by finetuning overall transcription and gene expression. In this review, we address how altered DNA methylation contributes to the initiation and progression of hepatic cell fate conversion and cancer formation. We also discussed the diagnostic and therapeutic potential of targeting DNA methylation in liver cancer, its current limitations, and what future research is necessary to facilitate its contribution to clinical translation.

Quantification of DNA methylation for carcinogenic risk estimation in patients with non-alcoholic steatohepatitis

BACKGROUND

In recent years, non-alcoholic steatohepatitis (NASH) has become the main cause of hepatocellular carcinoma (HCC). As a means of improving the treatment of NASH-related HCCs based on early detection, this study investigated the feasibility of carcinogenic risk estimation in patients with NASH.

RESULTS

Normal liver tissue (NLT), non-cancerous liver tissue showing histological findings compatible with non-alcoholic fatty liver from patients without HCC (NAFL-O), non-cancerous liver tissue showing NASH from patients without HCC (NASH-O), non-cancerous liver tissue showing non-alcoholic fatty liver from patients with HCC (NAFL-W), non-cancerous liver tissue showing NASH from patients with HCC (NASH-W) and NASH-related HCC were analyzed. An initial cohort of 171 tissue samples and a validation cohort of 55 tissue samples were used. Genome-wide DNA methylation screening using the Infinium HumanMethylation450 BeadChip and DNA methylation quantification using high-performance liquid chromatography (HPLC) with a newly developed anion-exchange column were performed. Based on the Infinium assay, 4050 CpG sites showed alterations of DNA methylation in NASH-W samples relative to NLT samples. Such alterations at the precancerous NASH stage were inherited by or strengthened in HCC samples. Receiver operating characteristic curve analysis identified 415 CpG sites discriminating NASH-W from NLT samples with area under the curve values of more than 0.95. Among them, we focused on 21 CpG sites showing more than 85% specificity, even for discrimination of NASH-W from NASH-O samples. The DNA methylation status of these 21 CpG sites was able to predict the coincidence of HCC independently from histopathological findings such as ballooning and fibrosis stage. The methylation status of 5 candidate marker CpG sites was assessed using a HPLC-based system, and for 3 of them sufficient sensitivity and specificity were successfully validated in the validation cohort. By combining these 3 CpG sites including the ZC3H3 gene, NAFL-W and NASH-W samples from which HCCs had already arisen were confirmed to show carcinogenic risk with 95% sensitivity in the validation cohort.

CONCLUSIONS

After a further prospective validation study using a larger cohort, carcinogenic risk estimation in liver biopsy specimens of patients with NASH may become clinically applicable using this HPLC-based system for quantification of DNA methylation.

DNA methylation status of the SPHK1 and LTB genes underlies the clinicopathological diversity of non-alcoholic steatohepatitis-related hepatocellular carcinomas

Purpose

This study was performed to identify the DNA methylation profiles underlying the clinicopathological diversity of non-alcoholic steatohepatitis (NASH)-related hepatocellular carcinomas (HCCs). 

Methods

Genome-wide DNA methylation analysis of 88 liver tissue samples was performed using the Infinium assay.

Results

Principal component analysis revealed that distinct DNA methylation profiles differing from such profiles in normal control liver tissue had already been established in non-cancerous liver tissue showing NASH, which is considered to be a precancerous condition. Hierarchical clustering separated 26 NASH-related HCCs into Cluster I (n = 8) and Cluster II (n = 18). Such epigenetic clustering was significantly correlated with histopathological diversity, i.e. poorer tumor differentiation, tumor steatosis and development of a scirrhous HCC component. Significant differences in DNA methylation levels between the two clusters were accumulated in molecular pathways participating in cell adhesion and cytoskeletal remodeling, as well as cell proliferation and apoptosis. Among tumor-related genes characterizing Clusters I and II, differences in the levels of DNA methylation and mRNA expression for the SPHK1, INHBA, LTB and PDE3B genes were correlated with poorer tumor differentiation. 5-Aza-2′-deoxycytidine treatment of HCC cells revealed epigenetic regulation of the SPHK1 and LTB genes. Knockdown experiments showed that SPHK1 promotes cell proliferation, represses apoptosis and enhances migration, whereas LTB enhances migration of HCC cells. DNA hypomethylation resulting in increased expression of SPHK1 and LTB in poorly differentiated HCCs may underlie the aggressive phenotype of such HCCs.

Conclusion

These data indicate that DNA methylation profiles may determine the clinicopathological heterogeneity of NASH-related HCCs via alterations of tumor-related gene expression.

Clinicopathological impacts of DNA methylation alterations on pancreatic ductal adenocarcinoma: prediction of early recurrence based on genome-wide DNA methylation profiling

PURPOSE

The present study was conducted to clarify the clinicopathological impacts of DNA methylation alterations on pancreatic ductal adenocarcinoma (PDAC).

METHODS

Genome-wide DNA methylation screening was performed using the Infinium HumanMethylation450 BeadChip, and DNA methylation quantification was verified using pyrosequencing. We analyzed fresh-frozen tissues from an initial cohort (17 samples of normal control pancreatic tissue [C] from 17 patients without PDAC, and 34 samples of non-cancerous pancreatic tissue [N] and 82 samples of cancerous tissue [T] both obtained from 82 PDAC patients) and formalin-fixed paraffin-embedded T samples from 34 patients in a validation cohort.

RESULTS

The DNA methylation profiles of N samples tended to differ from those of C samples, and 91,907 probes showed significant differences in DNA methylation levels between C and T samples. Epigenetic clustering of T samples was significantly correlated with a larger tumor diameter and early recurrence (ER), defined as relapse within 6 months after surgery. Three marker CpG sites, applicable to formalin-fixed paraffin-embedded surgically resected materials regardless of their tumor cell content, were identified for prediction of ER. The sensitivity and specificity for detection of patients belonging to the ER group using a panel combining these three marker CpG sites, including a CpG site in the CDK14 gene, were 81.8% and 71.7% and 88.9% and 70.4% in the initial and validation cohorts, respectively.

CONCLUSION

These findings indicate that DNA methylation alterations may have a clinicopathological impact on PDAC. Application of our criteria will ultimately allow prediction of ER after surgery to improve the outcome of PDAC patients.

Epigenetic Biomarkers for the Diagnosis and Treatment of Liver Disease

Research in the last decades has demonstrated the relevance of epigenetics in controlling gene expression to maintain cell homeostasis, and the important role played by epigenome alterations in disease development. Moreover, the reversibility of epigenetic marks can be harnessed as a therapeutic strategy, and epigenetic marks can be used as diagnosis biomarkers. Epigenetic alterations in DNA methylation, histone post-translational modifications (PTMs), and non-coding RNA (ncRNA) expression have been associated with the process of hepatocarcinogenesis. Here, we summarize epigenetic alterations involved in the pathogenesis of chronic liver disease (CLD), particularly focusing on DNA methylation. We also discuss their utility as epigenetic biomarkers in liquid biopsy for the diagnosis and prognosis of hepatocellular carcinoma (HCC). Finally, we discuss the potential of epigenetic therapeutic strategies for HCC treatment.

DNA methyltransferase 3B plays a protective role against hepatocarcinogenesis caused by chronic inflammation via maintaining mitochondrial homeostasis

Most hepatocellular carcinomas (HCCs) develop on the basis of chronic hepatitis, but the mechanism of epigenetic regulation in inflammatory hepatocarcinogenesis has yet to be elucidated. Among de novo DNA methyltransferases (DNMTs), DNMT3B has lately been reported to act specifically on actively transcribed genes, suggesting the possibility that it plays a role in the pathogenesis of cancer. We confirmed that DNMT3B isoforms lacking its catalytic domain were highly expressed in HCCs compared with non-tumorous liver tissue. To elucidate the role of DNMT3B in hepatocarcinogenesis, we generated a genetically engineered mouse model with hepatocyte-specific Dnmt3b deletion. The liver of the Dnmt3b-deficient mice exhibited an exacerbation of thioacetamide-induced hepatitis, progression of liver fibrosis and a higher incidence of HCC compared with the liver of the control mice. Whole-genome bisulfite sequencing verified a lower CG methylation level in the Dnmt3b-deficient liver, demonstrating differentially methylated regions throughout the genome. Transcriptome analysis revealed decreased expression of genes related to oxidative phosphorylation in the Dnmt3b-deficient liver. Moreover, primary hepatocytes isolated from the Dnmt3b-deficient mice showed reduced mitochondrial respiratory capacity, leading to the enhancement of oxidative stress in the liver tissue. Our findings suggest the protective role of DNMT3B against chronic inflammation and HCC development via maintaining mitochondrial homeostasis.

Epigenetics in hepatocellular carcinoma development and therapy: The tip of the iceberg

Hepatocellular carcinoma (HCC) is a deadly tumour whose causative agents are generally well known, but whose pathogenesis remains poorly understood. Nevertheless, key genetic alterations are emerging from a heterogeneous molecular landscape, providing information on the tumorigenic process from initiation to progression. Among these molecular alterations, those that affect epigenetic processes are increasingly recognised as contributing to carcinogenesis from preneoplastic stages. The epigenetic machinery regulates gene expression through intertwined and partially characterised circuits involving chromatin remodelers, covalent DNA and histone modifications, and dedicated proteins reading these modifications. In this review, we summarise recent findings on HCC epigenetics, focusing mainly on changes in DNA and histone modifications and their carcinogenic implications. We also discuss the potential drugs that target epigenetic mechanisms for HCC treatment, either alone or in combination with current therapies, including immunotherapies.

Establishment of diagnostic criteria for upper urinary tract urothelial carcinoma based on genome-wide DNA methylation analysis

The aim of this study was to develop a less invasive and accurate diagnostic system for upper urinary tract urothelial carcinoma (UTUC) based on genome-wide DNA methylation profiling. Genome-wide DNA methylation screening was performed using the Infinium HumanMethylation450 BeadChip, and DNA methylation quantification was verified using pyrosequencing. We analysed 26 samples of normal control urothelial tissue (C), an initial cohort of 62 samples (31 samples of non-cancerous urothelium [N] from UTUC patients and 31 samples of the corresponding UTUCs), a validation cohort of 82 samples (41 N and 41 UTUC samples), and 14 samples of urinary bladder urothelial carcinoma (BUC). In the initial cohort, we identified 2,448 CpG sites showing significant differences in DNA methylation levels between both C and UTUC and N and UTUC, but not showing differences between C and N. Among these CpG sites, 10 were located within CpG islands or their shores and shelves included in genomic domains where DNA methylation levels are stably controlled, allowing discrimination of UTUC even from BUC. Receiver operating characteristic curve analysis for discrimination of UTUC from N in these 10 CpG and neighbouring sites (37 diagnostic panels in total) yielded area under the curve values of 0.959-1.000, with a sensitivity and specificity of 86.6-100% and 93.5-100%, respectively. The diagnostic impact was successfully confirmed in the validation cohort. Our criteria were useful for diagnosis of UTUC, regardless of its clinicopathological features. Application of our criteria to voided urine samples will ultimately allow non-invasive DNA methylation diagnosis of UTUC.

Establishment of permutation for cancer risk estimation in the urothelium based on genome-wide DNA methylation analysis

The aim of this study was to establish permutation for cancer risk estimation in the urothelium. Twenty-six samples of normal control urothelium obtained from patients without urothelial carcinomas (C), 47 samples of non-cancerous urothelium without noticeable morphological changes obtained from patients with urothelial carcinomas (N), and 46 samples of the corresponding cancerous tissue (T) in the learning cohort and 64 N samples in the validation cohort, i.e. 183 tissue samples in total, were analyzed. Genome-wide DNA methylation analysis was performed using the Infinium HumanMethylation 450K BeadChip, and DNA methylation levels were verified using pyrosequencing and MassARRAY. Amplicon sequencing was performed using the GeneRead DNAseq Targeted Panels V2. Although N samples rarely showed genetic mutations or copy number alterations, they showed DNA methylation alterations at 2502 CpG sites compared to C samples, and such alterations were inherited by or strengthened in T samples, indicating that DNA methylation alterations may participate in field cancerization in the urothelium. Receiver operating characteristic curve analysis confirmed the feasibility of cancer risk estimation to identify urothelium at the precancerous stage by DNA methylation quantification. Cancer risk estimation permutation was established using a combination of two marker CpG loci on the HOXC4, TENM3 and TLR1 genes (sensitivity and specificity 96-100%). Among them, the diagnostic impact of 10 patterns of permutation was successfully validated in the validation cohort (sensitivity and specificity 94-98%). These data suggest that cancer risk estimation using procedures such as urine tests during health checkups might become applicable for clinical use.

Multiple gene promoter methylation and clinical stage in adjacent normal tissues: Effect on prognosis of colorectal cancer in Taiwan

This study provide an insight that the panel genes methylation status in different clinical stage tended to reflect a different prognosis even in matched normal tissues, to clinical recommendation. We enrolled 153 colorectal cancer patients from a medical center in Taiwan and used the candidate gene approach to select five genes involved in carcinogenesis pathways. We analyzed the relationship between DNA methylation with different cancer stages and the prognostic outcome. There were significant trends of increasing risk of 5-year time to progression and event-free survival of subjects with raising number of hypermethylation genes both in normal tissue and tumor tissue. The group with two or more genes with aberrant methylation in the advanced cancer stages (Me/advanced) had lower 5-year event-free survival among patients with colorectal cancer in either normal or tumor tissue. The adjusted hazard ratios in the group with two or more genes with aberrant methylation with advanced cancer stages (Me/advanced) were 8.04 (95% CI, 2.80–23.1; P for trend <0.01) and 8.01 (95% CI, 1.92–33.4; P for trend <0.01) in normal and tumor tissue, respectively. DNA methylation status was significantly associated with poor prognosis outcome. This finding in the matched normal tissues of colorectal cancer patients could be an alternative source of prognostic markers to assist clinical decision making.

Analysis of the clinical significance of DNA methylation in gastric cancer based on a genome-wide high-resolution array

BACKGROUND

Aberrant DNA methylation is involved in gastric carcinogenesis and may serve as a useful biomarker in the diagnosis and detection of gastric cancer (GC) recurrence.

RESULTS

A total of 157 patients who received surgery for GC were enrolled in the present study. A genome-wide methylation analysis was performed in tumor and adjacent normal tissues for the discovery set of 16 GC patients; the top three hypermethylated CpG sites of DNA promoters were selected for validation in tissue and plasma samples for the validation set of 141 GC patients. The frequencies of the top three hypermethylated genes in available patient tissues (n = 141) and plasma samples (n = 106) were 41.8% and 38.7%, respectively, for ADAM19; 40.4% and 42.5%, respectively, for FLI1; and 56.7% and 50.9%, respectively, for MSC. In both tissue and plasma samples, FLI1 hypermethylation was associated with more advanced GC and liver and distant lymphatic metastasis, and ADAM19 hypermethylation was associated with more stage IV GC. In plasma samples, MSC hypermethylation was more common in non-superficial type GC than samples without MSC hypermethylation. In both tissue and plasma samples, patients with methylation of all the three genes had significantly more liver metastases, distant lymphatic metastases, and paraaortic lymph node metastases than patients with two or fewer hypermethylated genes. The survival analysis showed that only for stage III GC, patients with hypermethylation of two or three genes had a worse 5-year disease-free survival rate than those with hypermethylation of one or none of the three genes. Subgroup analysis showed that FLI1 hypermethylation in both tissue and plasma samples was associated with liver metastasis in MSI-/EBV- GC, and MSC hypermethylation in tissue samples was correlated with liver metastasis in MSI+ or EBV+ GC. Patients with FLI1 hypermethylation in plasma samples had a significantly worse 5-year disease-free survival rate than those without FLI1 hypermethylation in MSI-/EBV- GC. FLI1 hypermethylation was an independent prognostic factor affecting the overall survival and disease-free survival in both tissue and plasma samples.

CONCLUSIONS

DNA methylation is a useful biomarker for predicting tumor recurrence patterns and GC patient survival.

Epigenome mapping of human normal purified hepatocytes: personal epigenome variation and genome-epigenome correlation

AIM

The aim of this study was to reveal the epigenome landscape of human normal hepatocytes.

MATERIALS & METHODS

Cells purified from partial hepatectomy specimens of Japanese patients were subjected to whole-genome bisulfite sequencing using postbisulfite adaptor tagging, chromatin immunoprecipitation sequencing, RNA sequencing and whole-genome sequencing.

RESULTS

CHG and CHH methylations were inversely associated with gene expression. Histone modification profiles of personal differentially methylated regions (pDMRs) differed considerably among samples. pDMRs were observed around the transcription start sites of genes whose expression is reportedly regulated by CpG methylation. pDMRs were frequently observed in the vicinity of single-nucleotide variations and insertions/deletions.

CONCLUSION

Genetic variations may induce epigenetic variations, generating individual differences in the phenotypes of normal hepatocytes through variations in expression.

Novel method for DNA methylation analysis using high-performance liquid chromatography and its clinical application

The aim of this study was to develop a new methodology that is suitable for DNA methylation diagnostics and to demonstrate its clinical applicability. We developed a new anion-exchange column for high-performance liquid chromatography (HPLC) with electrostatic and hydrophobic properties. Both cytosine and thymine, corresponding to methylated and unmethylated cytosine after bisulfite modification, respectively, are captured by electrostatic interaction and then discriminated from each other by their hydrophobic interactions. The DNA methylation levels of synthetic DNA were quantified accurately and reproducibly within 10 minutes without time-consuming pretreatment of PCR products, and the measured values were unaffected by the distribution of methylated CpG within the synthetic DNA fragments. When the DNA methylation status of the FAM150A gene, a marker of the CpG island methylator phenotype specific to clear cell renal cell carcinoma (ccRCC), was examined in 98 patients with ccRCC, bulk specimens of tumorous tissue including cancer cells showing DNA methylation of the FAM150A gene were easily identifiable by simply viewing the differentiated chromatograms, even when the cancer cell content was low. Sixteen ccRCC showing DNA methylation more frequently exhibited clinicopathological parameters reflecting tumor aggressiveness (ie, a larger diameter, higher histological grade, vascular involvement, renal vein tumor thrombi, infiltrating growth, tumor necrosis, renal pelvis invasion and higher pathological TNM stage), and had significantly lower recurrence-free and overall survival rates. These data indicate that HPLC analysis using this newly developed anion-exchange column could be a powerful tool for DNA methylation diagnostics, including prognostication of patients with cancers, in a clinical setting.

The role of enhancer of zeste homolog 2: From viral epigenetics to the carcinogenesis of hepatocellular carcinoma

Nowadays, epigenetics covers a crucial role in different fields of science. The enhancer of zeste homolog 2 (EZH2), the catalytic subunit of the Polycomb Repressive Complex 2 (PRC2), is a big proponent of how epigenetic changes can affect the initiation and progression of several diseases. Through its catalytic activity, responsible for the tri-methylation of lysine 27 of the histone H3 (H3K27me3), EZH2 is a good target for both diagnosis and therapy of different pathologies. A large number of studies have demonstrated its crucial role in cancer initiation and progression. Nevertheless, only recently its function in virus diseases has been uncovered; therefore, EZH2 can be an important promoter of viral carcinogenesis. This review explores the role of EZH2 in viral epigenetics based on recent progress that demonstrated the role of this protein in virus environment. In particular, the review focuses on EZH2 behavior in Hepatitis B Virus, analyzing its role in the rise of Hepatocellular Carcinoma.

Diagnostic Value of the Methylation of Multiple Gene Promoters in Serum in Hepatitis B Virus-Related Hepatocellular Carcinoma

This study sought to evaluate the diagnostic value of the methylation of multiple gene promoters in serum in hepatitis B virus- (HBV-) related hepatocellular carcinoma (HCC). A total of 343 participants were enrolled, including 98 patients with HCC, 75 patients with liver cirrhosis (LC), 90 patients with chronic hepatitis B (CHB), and 80 healthy individuals. RASSF1A, APC, BVES, TIMP3, GSTP1, and HOXA9 were selected as the candidate genes. The MethyLight method was used to assay promoter methylation statuses. The diagnostic performances of markers were assessed by constructing receiver operating characteristic (ROC) curves. The prevalences of methylation for RASSF1A, APC, BVES, HOXA9, GSTP1, and TIMP3 were 52.04%, 36.73%, 29.59%, 20.41%, 17.35%, and 11.22%, respectively. APC methylation completely overlapped with RASSF1A methylation. The area under the curve (AUC) for RASSF1A methylation (0.718) was better than the corresponding AUC for AFP (0.609) in distinguishing HCC from CHB. When RASSF1A, BVES, HOXA9, and AFP were combined, the AUC was 0.852 (95% CI = 0.796–0.908, P = 0.028), and the sensitivity and specificity were 83.7% and 78.9%, respectively. In conclusion, an assay that combines methylation of the RASSF1A, BVES, and HOXA9 gene promoters in serum and AFP could significantly improve HBV-related HCC diagnoses.

Genes involved in development and differentiation are commonly methylated in cancers derived from multiple organs: a single-institutional methylome analysis using 1007 tissue specimens

The aim of this study was to clarify the significance of DNA methylation alterations shared by cancers derived from multiple organs. We analyzed single-institutional methylome data by single-CpG-resolution Infinium assay for 1007 samples of non-cancerous tissue (N) and corresponding cancerous tissue (T) obtained from lung, stomach, kidney, breast and liver. Principal component analysis revealed that N samples of each organ showed distinct DNA methylation profiles, DNA methylation profiles of N samples of each organ being inherited by the corresponding T samples and DNA methylation profiles of T samples being more similar to those of N samples in the same organ than those of T samples in other organs. In contrast to such organ and/or carcinogenetic factor-specificity of DNA methylation profiles, when compared with the corresponding N samples, 231 genes commonly showed DNA hypermethylation in T samples in four or more organs. Gene ontology enrichment analysis showed that such commonly methylated genes were enriched among “transcriptional factors” participating in development and/or differentiation, which reportedly show bivalent histone modification in embryonic stem cells. Pyrosequencing and quantitative reverse transcription-PCR revealed an inverse correlation between DNA methylation levels and mRNA expression levels of representative commonly methylated genes, such as ALX1, ATP8A2, CR1 and EFCAB1, in tissue samples. These data suggest that disruption of the differentiated state of precancerous cells via alterations of expression, independent of differences in organs and/or carcinogenetic factors, may be a common feature of DNA methylation alterations during carcinogenesis in multiple organs.

Genome-wide DNA methylation analysis during non-alcoholic steatohepatitis-related multistage hepatocarcinogenesis: comparison with hepatitis virus-related carcinogenesis

The aim of this study was to clarify the significance of DNA methylation alterations during non-alcoholic steatohepatitis (NASH)-related hepatocarcinogenesis. Single-CpG-resolution genome-wide DNA methylation analysis was performed on 264 liver tissue samples using the Illumina Infinium HumanMethylation450 BeadChip. After Bonferroni correction, 3331 probes showed significant DNA methylation alterations in 113 samples of non-cancerous liver tissue showing NASH (NASH-N) as compared with 55 samples of normal liver tissue (NLT). Principal component analysis using the 3331 probes revealed distinct DNA methylation profiles of NASH-N samples that were different from those of NLT samples and 37 samples of non-cancerous liver tissue showing chronic hepatitis or cirrhosis associated with hepatitis B virus (HBV) or hepatitis C virus (HCV) infection (viral-N). Receiver operating characteristic curve analysis identified 194 probes that were able to discriminate NASH-N samples from viral-N samples with area under the curve values of more than 0.95. Jonckheere-Terptsra trend test revealed that DNA methylation alterations in NASH-N samples from patients without hepatocellular carcinoma (HCC) were inherited by or strengthened in NASH-N samples from patients with HCC, and then inherited by or further strengthened in 22 samples of NASH-related HCC (NASH-T) themselves. NASH- and NASH-related HCC-specific DNA methylation alterations, which were not evident in viral-N samples and 37 samples of HCC associated with HBV or HCV infection, were observed in tumor-related genes, such as WHSC1, and were frequently associated with mRNA expression abnormalities. These data suggested that NASH-specific DNA methylation alterations may participate in NASH-related multistage hepatocarcinogenesis.

New Insights into the Epigenetics of Hepatocellular Carcinoma

Hepatocellular Carcinoma (HCC) is one of the most predominant malignancies with high fatality rate. This deadly cancer is rising at an alarming rate because it is quite resistant to radio- and chemotherapy. Different epigenetic mechanisms such as histone modifications, DNA methylation, chromatin remodeling, and expression of noncoding RNAs drive the cell proliferation, invasion, metastasis, initiation, progression, and development of HCC. These epigenetic alterations because of potential reversibility open way towards the development of biomarkers and therapeutics. The contribution of these epigenetic changes to HCC development has not been thoroughly explored yet. Further research on HCC epigenetics is necessary to better understand novel molecular-targeted HCC treatment and prevention. This review highlights latest research progress and current updates regarding epigenetics of HCC, biomarker discovery, and future preventive and therapeutic strategies to combat the increasing risk of HCC.

High-risk oral leukoplakia is associated with aberrant promoter methylation of multiple genes

Background

Early detection of oral squamous cell carcinomas (OSCCs) is urgently needed to improve the prognosis and quality of life (QOL) of patients. Oral leukoplakias (OLs), known as the most common premalignant lesions in the oral cavity, often precede OSCCs. Especially, OLs with dysplasia are known to have a high risk of malignant transformation. Here, we searched for the promoter methylation characteristic of high-risk OLs.

Methods

To identify methylation-silenced genes, a combined analysis of methylated DNA immunoprecipitation (MeDIP) − CpG island (CGI) microarray analysis and expression microarray analysis after treatment with a demethylating agent was performed in two OSCC cell lines (Ca9–22 and HSC-2). The methylation statuses of each gene were examined by methylation-specific PCR.

Results

A total of 52 genes were identified as candidates for methylation-silenced genes in Ca9-22 or HSC-2. The promoter regions of 13 genes among the 15 genes randomly selected for further analysis were confirmed to be methylated in one or more of five cell lines. In OSCC tissues (n = 26), 8 of the 13 genes, TSPYL5, EGFLAM, CLDN11, NKX2-3, RBP4, CMTM3, TRPC4, and MAP6, were methylated. In OL tissues (n = 24), seven of the eight genes, except for EGFLAM, were found to be methylated in their promoter regions. There were significantly greater numbers of methylated genes in OLs with dysplasia than in those without dysplasia (p < 0.0001).

Conclusions

OLs at high risk for malignant transformation were associated with aberrant promoter methylation of multiple genes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2371-5) contains supplementary material, which is available to authorized users.

Identification of Epigenetic Biomarkers of Lung Adenocarcinoma through Multi-Omics Data Analysis

Epigenetic mechanisms such as DNA methylation or histone modifications are essential for the regulation of gene expression and development of tissues. Alteration of epigenetic modifications can be used as an epigenetic biomarker for diagnosis and as promising targets for epigenetic therapy. A recent study explored cancer-cell specific epigenetic biomarkers by examining different types of epigenetic modifications simultaneously. However, it was based on microarrays and reported biomarkers that were also present in normal cells at a low frequency. Here, we first analyzed multi-omics data (including ChIP-Seq data of six types of histone modifications: H3K27ac, H3K4me1, H3K9me3, H3K36me3, H3K27me3, and H3K4me3) obtained from 26 lung adenocarcinoma cell lines and a normal cell line. We identified six genes with both H3K27ac and H3K4me3 histone modifications in their promoter regions, which were not present in the normal cell line, but present in ≥85% (22 out of 26) and ≤96% (25 out of 26) of the lung adenocarcinoma cell lines. Of these genes, NUP210 (encoding a main component of the nuclear pore complex) was the only gene in which the two modifications were not detected in another normal cell line. RNA-Seq analysis revealed that NUP210 was aberrantly overexpressed among the 26 lung adenocarcinoma cell lines, although the frequency of NUP210 overexpression was lower (19.3%) in 57 lung adenocarcinoma tissue samples studied and stored in another database. This study provides a basis to discover epigenetic biomarkers highly specific to a certain cancer, based on multi-omics data at the cell population level.

Genomic-Wide Analysis with Microarrays in Human Oncology

DNA microarray technologies have advanced rapidly and had a profound impact on examining gene expression on a genomic scale in research. This review discusses the history and development of microarray and DNA chip devices, and specific microarrays are described along with their methods and applications. In particular, microarrays have detected many novel cancer-related genes by comparing cancer tissues and non-cancerous tissues in oncological research. Recently, new methods have been in development, such as the double-combination array and triple-combination array, which allow more effective analysis of gene expression and epigenetic changes. Analysis of gene expression alterations in precancerous regions compared with normal regions and array analysis in drug-resistance cancer tissues are also successfully performed. Compared with next-generation sequencing, a similar method of genome analysis, several important differences distinguish these techniques and their applications. Development of novel microarray technologies is expected to contribute to further cancer research.

Multidisciplinary perspective of hepatocellular carcinoma: A Pacific Northwest experience

Hepatocellular carcinoma (HCC) is the most rapidly increasing type of cancer in the United States. HCC is a highly malignant cancer, accounting for at least 14000 deaths in the United States annually, and it ranks third as a cause of cancer mortality in men. One major difficulty is that most patients with HCC are diagnosed when the disease is already at an advanced stage, and the cancer cannot be surgically removed. Furthermore, because almost all patients have cirrhosis, neither chemotherapy nor major resections are well tolerated. Clearly there is need of a multidisciplinary approach for the management of HCC. For example, there is a need for better understanding of the fundamental etiologic mechanisms that are involved in hepatocarcinogenesis, which could lead to the development of successful preventive and therapeutic modalities. It is also essential to define the cellular and molecular bases for malignant transformation of hepatocytes. Such knowledge would: (1) greatly facilitate the identification of patients at risk; (2) prompt efforts to decrease risk factors; and (3) improve surveillance and early diagnosis through diagnostic imaging modalities. Possible benefits extend also to the clinical management of this disease. Because there are many factors involved in pathogenesis of HCC, this paper reviews a multidisciplinary perspective of recent advances in basic and clinical understanding of HCC that include: molecular hepatocarcinogenesis, non-invasive diagnostics modalities, diagnostic pathology, surgical modality, transplantation, local therapy and oncological/target therapeutics.

Chronic liver inflammation modifies DNA methylation at the precancerous stage of murine hepatocarcinogenesis

Chronic liver inflammation precedes the majority of hepatocellular carcinomas (HCC). Here, we explore the connection between chronic inflammation and DNA methylation in the liver at the late precancerous stages of HCC development in Mdr2(-/-) (Mdr2/Abcb4-knockout) mice, a model of inflammation-mediated HCC. Using methylated DNA immunoprecipitation followed by hybridization with "CpG islands" (CGIs) microarrays, we found specific CGIs in 76 genes which were hypermethylated in the Mdr2(-/-) liver compared to age-matched healthy controls. The observed hypermethylation resulted mainly from an age-dependent decrease of methylation of the specific CGIs in control livers with no decrease in mutant mice. Chronic inflammation did not change global levels of DNA methylation in Mdr2(-/-) liver, but caused a 2-fold decrease of the global 5-hydroxymethylcytosine level in mutants compared to controls. Liver cell fractionation revealed, that the relative hypermethylation of specific CGIs in Mdr2(-/-) livers affected either hepatocyte, or non-hepatocyte, or both fractions without a correlation between changes of gene methylation and expression. Our findings demonstrate that chronic liver inflammation causes hypermethylation of specific CGIs, which may affect both hepatocytes and non-hepatocyte liver cells. These changes may serve as useful markers of an increased regenerative activity and of a late precancerous stage in the chronically inflamed liver.

Epigenetic clustering of gastric carcinomas based on DNA methylation profiles at the precancerous stage: its correlation with tumor aggressiveness and patient outcome

Single-CpG resolution genome-wide DNA methylation analysis indicated that distinct DNA methylation profiles are established during field cancerization in gastric mucosae, and such profiles at the precancerous stage are inherited by gastric cancers, thus determining tumor aggressiveness and patient outcome.

The aim of this study was to clarify the significance of DNA methylation alterations during gastric carcinogenesis. Single-CpG resolution genome-wide DNA methylation analysis using the Infinium assay was performed on 109 samples of non-cancerous gastric mucosa (N) and 105 samples of tumorous tissue (T). DNA methylation alterations in T samples relative to N samples were evident for 3861 probes. Since N can be at the precancerous stage according to the field cancerization concept, unsupervised hierarchical clustering based on DNA methylation levels was performed on N samples (β_N) using the 3861 probes. This divided the 109 patients into three clusters: A (n = 20), B1 (n = 20), and B2 (n = 69). Gastric carcinomas belonging to Cluster B1 showed tumor aggressiveness more frequently than those belonging to Clusters A and B2. The recurrence-free and overall survival rates of patients in Cluster B1 were lower than those of patients in Clusters A and B2. Sixty hallmark genes for which β_N characterized the epigenetic clustering were identified. We then focused on DNA methylation levels in T samples (β_T) of the 60 hallmark genes. In 48 of them, including the ADAM23, OLFM4, AMER2, GPSM1, CCL28, DTX1 and COL23A1 genes, β_T was again significantly correlated with tumor aggressiveness, and the recurrence-free and/or overall survival rates. Multivariate analyses revealed that β_T was a significant prognostic factor, being independent of clinicopathological parameters. These data indicate that DNA methylation profiles at the precancerous stage may be inherited by gastric carcinomas themselves, thus determining tumor aggressiveness and patient outcome.

DNA methylation of microRNA-124a is a potential risk marker of colitis-associated cancer in patients with ulcerative colitis

BACKGROUND

Colitis-associated cancer (CAC) is the serious complication of ulcerative colitis (UC), and molecular markers to evaluate the individual risk are required. MicroRNA-124a (miR - 124a) is known to have tumor-suppressive function and be methylation-silenced during exposure to chronic inflammation.

AIM

We analyzed whether higher methylation levels of miR-124a genes correlated with the higher epidemiologic risk of CAC development in UC patients.

METHODS

Forty UC patients without CAC, four patients with CAC or dysplasia, eight sporadic colorectal cancer (S-CRC) patients, and 12 healthy volunteers (HV) were studied. Methylation status of miR-124a genes (miR-124a-1, -2, and -3) was analyzed by methylation-specific polymerase chain reaction (MSP), and methylation levels were quantified by real-time MSP. Expression of cyclin-dependent kinase 6 (CDK6), a target of miR-124a, was analyzed by immunohistochemistry.

RESULTS

Three miR-124a genes were methylated in all neoplastic tissues (CAC, dysplasia, and S-CRC), and CDK6 was highly expressed in those tissues. Regarding disease extent, mean methylation levels of miR-124a-3 in HV, non-pancolitis, and pancolitis were 2.0, 5.3, and 12.3%, respectively, and were significantly higher in pancolitis than in HV (p < 0.01). Regarding disease duration, mean methylation levels in short-term and long-standing UC patients were 2.5 and 13.2%, respectively. Long-standing UC patients had significantly higher methylation levels than HV (p < 0.01). Moreover, UC patients with both pancolitis and long-standing had 7.4-fold higher methylation levels than those without these risk factors.

CONCLUSIONS

MiR-124a genes are methylated during carcinogenesis in UC patients. The methylation level of miR-124a-3 is a promising marker for estimating individual risk for CAC.

Alteration of Epigenetic Profile in Human Hepatocellular Carcinoma and Its Clinical Implications

Hepatocellular carcinoma (HCC) is a common cancer worldwide and develops against a background of chronic liver damage. A variety of HCC-related genes are known to be altered by genetic and epigenetic mechanisms. Therefore, information regarding alteration of the genetic and epigenetic profiles in HCC is essential for understanding the biology of this type of tumor. Methylation at CpG sites in gene promoters is known to affect the transcription of the corresponding genes. Abnormal regional hypermethylation is observed in the 5' region of several tumor suppressor genes (TSGs) in HCC, and this hypermethylation may promote carcinogenesis through the transcriptional inactivation of downstream TSGs. The DNA damage induced by oxidation is a trigger of abnormal DNA methylation and inactivation of TSGs through recruitment of the polycomb repressive complex to the promoter sequence. Thus, oxidative stress may be responsible for the emergence of HCC from chronic hepatitis and liver cirrhosis through the epigenetic alteration of TSGs. There have been several attempts to apply epigenetic information to the diagnosis and treatment of HCC. The predictive value of selected methylation events on survival in HCC patients has been reported, and the methylation profile of background liver could be associated with recurrence-free survival of HCC patients who have undergone hepatectomy. Another study detected methylated DNA from HCC cells in serum, and the circulating tumor DNA was regarded as a potential tumor marker. In addition, several trials of HCC therapy have targeted the epigenetic machinery and were based upon comprehensive analyses of DNA methylation of this type of tumor. Here, we present an overview of research regarding DNA methylation status in human HCC and describe the clinical application of epigenetic information to HCC.

Epigenetic clustering of lung adenocarcinomas based on DNA methylation profiles in adjacent lung tissue: Its correlation with smoking history and chronic obstructive pulmonary disease

The aim of this study was to clarify the significance of DNA methylation alterations during lung carcinogenesis. Infinium assay was performed using 139 paired samples of non-cancerous lung tissue (N) and tumorous tissue (T) from a learning cohort of patients with lung adenocarcinomas (LADCs). Fifty paired N and T samples from a validation cohort were also analyzed. DNA methylation alterations on 1,928 probes occurred in N samples relative to normal lung tissue from patients without primary lung tumors, and were inherited by, or strengthened in, T samples. Unsupervised hierarchical clustering using DNA methylation levels in N samples on all 26,447 probes subclustered patients into Cluster I (n = 32), Cluster II (n = 35) and Cluster III (n = 72). LADCs in Cluster I developed from the inflammatory background in chronic obstructive pulmonary disease (COPD) in heavy smokers and were locally invasive. Most patients in Cluster II were non-smokers and had a favorable outcome. LADCs in Cluster III developed in light smokers were most aggressive (frequently showing lymphatic and blood vessel invasion, lymph node metastasis and an advanced pathological stage), and had a poor outcome. DNA methylation levels of hallmark genes for each cluster, such as IRX2, HOXD8, SPARCL1, RGS5 and EI24, were again correlated with clinicopathological characteristics in the validation cohort. DNA methylation profiles reflecting carcinogenetic factors such as smoking and COPD appear to be established in non-cancerous lung tissue from patients with LADCs and may determine the aggressiveness of tumors developing in individual patients, and thus patient outcome.

Promoter hypermethylation of Wnt pathway inhibitors in hepatitis C virus - induced multistep hepatocarcinogenesis

Background

Aberrant DNA methylation profiles are a characteristic feature of almost all types of cancers including hepatocellular carcinoma (HCC) and play an important role in carcinogenesis. In spite of the accumulating evidence that suggests appearance of such aberrations at precancerous stages, very little effort has been invested to investigate such possible methylation events in patients at risk of developing HCC i.e. those suffering from chronic hepatitis C virus (HCV) infection and liver cirrhosis (LC). We reasoned that such an analysis could lead to the identification of novel predictive biomarkers as well as potential drug targets.

Methods

Promoter methylation status of two Wnt inhibitors SFRP2 and DKK1 was quantitatively analyzed by bisulfite pyrosequencing in a series of liver biopsy samples. These biopsies were collected from HCV-infected individuals suffering from chronic hepatitis (CH; n = 15), liver cirrhosis (LC; n = 13) and hepatocellular carcinoma (HCC; n = 41). DNA isolated from infection free normal livers (N; n =10) was used as control.

Results

Our analysis revealed that both of the genomic loci were significantly hypermethylated in CH patients’ livers as compared to normal controls (p = 0.0136 & 0.0084 for SFRP2 and DKK1, respectively; Mann–Whitney U test). DNA methylation levels for both loci were also significantly higher in all the diseased cohorts as compared to normal controls (p < 0.0001 and = 0.0011 for SFRP2 and DKK1, respectively; Kruskal-Wallis test). However, a comparison between three disease cohorts (CH, LC & HCC) revealed no significant difference in levels of DNA methylation at DKK1 promoter. In contrast, a progressive increase in DNA methylation levels was observed at the SFRP2 promoter (i.e. N < CH & LC < HCC).

Conclusion

This study demonstrated that in HCV infected liver tissues hypermethylation at promoter regions of key cancer related genes SFRP2 and DKK1, appears early at CH and LC stages, long before the appearance of HCC.

Specific molecular signatures of non-tumor liver tissue may predict a risk of hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is one of the most common human cancers and a major cause of cancer-related death worldwide. The bleak outcomes of HCC patients even after curative treatment have been, at least partially, attributed to its multicentric origin. Therefore, it is necessary to examine not only tumor tissue but also non-tumor liver tissue to investigate the molecular mechanisms operating during hepatocarcinogenesis based on the concept of "field cancerization". Several studies previously investigated the association of molecular alterations in non-tumor liver tissue with clinical features and prognosis in HCC patients on a genome-wide scale. In particular, specific alterations of DNA methylation profiles have been confirmed in non-tumor liver tissue. This review focuses on the possible clinical value of array-based comprehensive analyses of molecular alterations, especially aberrant DNA methylation, in non-tumor liver tissue to clarify the risk of hepatocarcinogenesis. Carcinogenetic risk estimation based on specific methylation signatures may be advantageous for close follow-up of patients who are at high risk of HCC development. Furthermore, epigenetic therapies for patients with chronic liver diseases may be helpful to reduce the risk of HCC development because epigenetic alterations are potentially reversible, and thus provide promising molecular targets for therapeutic intervention.

Multilayer-omics analysis of renal cell carcinoma, including the whole exome, methylome and transcriptome

The aim of this study was to identify pathways that have a significant impact during renal carcinogenesis. Sixty-seven paired samples of both noncancerous renal cortex tissue and cancerous tissue from patients with clear cell renal cell carcinomas (RCCs) were subjected to whole-exome, methylome and transcriptome analyses using Agilent SureSelect All Exon capture followed by sequencing on an Illumina HiSeq 2000 platform, Illumina Infinium HumanMethylation27 BeadArray and Agilent SurePrint Human Gene Expression microarray, respectively. Sanger sequencing and quantitative reverse transcription-PCR were performed for technical verification. MetaCore software was used for pathway analysis. Somatic nonsynonymous single-nucleotide mutations, insertions/deletions and intragenic breaks of 2,153, 359 and 8 genes were detected, respectively. Mutations of GCN1L1, MED12 and CCNC, which are members of CDK8 mediator complex directly regulating β-catenin-driven transcription, were identified in 16% of the RCCs. Mutations of MACF1, which functions in the Wnt/β-catenin signaling pathway, were identified in 4% of the RCCs. A combination of methylome and transcriptome analyses further highlighted the significant role of the Wnt/β-catenin signaling pathway in renal carcinogenesis. Genetic aberrations and reduced expression of ERC2 and ABCA13 were frequent in RCCs, and MTOR mutations were identified as one of the major disrupters of cell signaling during renal carcinogenesis. Our results confirm that multilayer-omics analysis can be a powerful tool for revealing pathways that play a significant role in carcinogenesis.

Characteristic patterns of altered DNA methylation predict emergence of human hepatocellular carcinoma

We aimed to identify the specific subset of tumor suppressor genes (TSGs) that are methylation-silenced during the earliest steps of hepatocarcinogenesis, and to further evaluate whether these genes can serve as predictive biomarkers of hepatocellular carcinoma (HCC) emergence. A total of 482 liver tissues including 177 pairs of HCCs and matched nontumor livers and 128 liver biopsies from chronic hepatitis C (CHC) patients were analyzed for quantitative methylation analysis in 24 TSG promoters and three MINT loci. The tumors were classified as early, less-progressed, and highly progressed HCCs using histology and radiological approaches. A subset of TSGs that harbored distinctly high levels of methylation in early HCCs were selected. Based on the methylation profiles of these genes, Kaplan-Meier analyses were performed to determine time-to-HCC occurrence in CHC patients. Subsequently, multivariate analysis was performed using age, gender, fibrosis stage, and number of methylated TSGs as covariates. Among TSGs analyzed, a subset of eight TSGs (HIC1, GSTP1, SOCS1, RASSF1, CDKN2A, APC, RUNX3, and PRDM2) demonstrated a distinct cluster by hierarchical clustering and receiver operating characteristic analyses. This subset of TSGs showed significantly higher methylation levels in the early HCCs (P < 0.0001). In the CHC patients, methylation frequencies in these TSGs were associated with shorter time-to-HCC occurrence (P < 0.0001), and number of methylated genes was an independent risk factor for HCC (hazard ratio = 5.21, 95% confidence interval = 2.25-11.76, P = 0.0002).

CONCLUSION

Epigenetic inactivation of a subset of TSGs plays a critical role in the earliest steps of hepatocarcinogenesis. Furthermore, epigenetic inactivation of these genes in CHC provides a prognostic value for determining the risk for developing HCC later in life.

Single-CpG-resolution methylome analysis identifies clinicopathologically aggressive CpG island methylator phenotype clear cell renal cell carcinomas

To clarify the significance of DNA methylation alterations during renal carcinogenesis, methylome analysis using single-CpG-resolution Infinium array was performed on 29 normal renal cortex tissue (C) samples, 107 non-cancerous renal cortex tissue (N) samples obtained from patients with clear cell renal cell carcinomas (RCCs) and 109 tumorous tissue (T) samples. DNA methylation levels at 4830 CpG sites were already altered in N samples compared with C samples. Unsupervised hierarchical clustering analysis based on DNA methylation levels at the 801 CpG sites, where DNA methylation alterations had occurred in N samples and were inherited by and strengthened in T samples, clustered clear cell RCCs into Cluster A (n = 90) and Cluster B (n = 14). Clinicopathologically aggressive tumors were accumulated in Cluster B, and the cancer-free and overall survival rates of patients in this cluster were significantly lower than those of patients in Cluster A. Clear cell RCCs in Cluster B were characterized by accumulation of DNA hypermethylation on CpG islands and considered to be CpG island methylator phenotype (CIMP)-positive cancers. DNA hypermethylation of the CpG sites on the FAM150A, GRM6, ZNF540, ZFP42, ZNF154, RIMS4, PCDHAC1, KHDRBS2, ASCL2, KCNQ1, PRAC, WNT3A, TRH, FAM78A, ZNF671, SLC13A5 and NKX6-2 genes became hallmarks of CIMP in RCCs. On the other hand, Cluster A was characterized by genome-wide DNA hypomethylation. These data indicated that DNA methylation alterations at precancerous stages may determine tumor aggressiveness and patient outcome. Accumulation of DNA hypermethylation on CpG islands and genome-wide DNA hypomethylation may each underlie distinct pathways of renal carcinogenesis.

Abbreviations:

BAMCA

bacterial artificial chromosome array-based methylated CpG island amplification

C

normal renal cortex tissue obtained from patients without any primary renal tumor

CIMP

CpG island methylator phenotype

HCC

hepatocellular carcinoma

N

non-cancerous renal cortex tissue obtained from patients with clear cell renal cell carcinomas

NCBI

National Center for Biotechnology Information

RCC

renal cell carcinoma

T

tumorous tissue

TNM

Tumor-Node-Metastasis

Role of epigenetic aberrations in the development and progression of human hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most lethal and prevalent cancers in humans. The molecular mechanisms leading to the development of HCC are extremely complicated and consist of prominent genetic, genomic, and epigenetic alterations. This review summarizes the current knowledge of the role of epigenetic aberrations, including changes in DNA methylation, histone modifications, and expression of microRNAs in the pathogenesis of HCC. It also emphasizes that identification of the underlying epigenetic alterations that drive cell transformation and promote development and progression of HCC is crucially important for understanding mechanisms of hepatocarcinogenesis, its detection, therapeutic intervention, and prevention.