Expression of DNA methyltransferases in multistep hepatocarcinogenesis

Epigenetic-Based Biomarkers in the Malignant Transformation of BEAS-2B Cells Induced by Coal Tar Pitch Extract

Background and Objectives: The carcinogenicity of coal tar pitch (CTP) to occupational workers has been confirmed by the International Agency for Research on Cancer, especially for lung cancer. Herein, we explored the dynamic changes of epigenetic modifications in the malignant transformation process of CTP-induced BEAS-2B cells and also provided clues for screening early biomarkers of CTP-associated occupational lung cancer. Material and Methods: BEAS-2B cells treated with 3.0 μg/mL CTP extract (CTPE) were cultured to the 30th passage to set up a malignant transformation model, which was confirmed by platelet clone formation assay and xenograft assay. DNA methylation levels were determined by ultraviolet-high performance liquid chromatography. mRNA levels in cells and protein levels in supernatants were respectively detected by Real-Time PCR and enzyme-linked immunosorbent assay. Results: The number of clones and the ability of tumor formation in nude mice of CTPE-exposed BEAS-2B cells at 30th passage were significantly increased compared to vehicle control. Moreover, genomic DNA methylation level was down-regulated. The mRNA levels of DNMT1, DNMT3a and HDAC1 as well as the expression of DNMT1 protein were up-regulated since the 10th passage. From the 20th passage, the transcriptional levels of DNMT3b, let-7a and the expression of DNMT3a, DNMT3b, and HDAC1 proteins were detected to be higher than vehicle control, while the level of miR-21 increased only at the 30th passage. Conclusion: Data in this study indicated that the changes of epigenetic molecules including DNMT1, DNMT3a, DNMT3b, HDAC1, and let-7a occurred at the early stages of BEAS-2B cell malignant transformation after CTPE exposure, which provided critical information for screening early biomarkers of CTP-associated occupational lung cancer.

DNA methyltransferase expression is associated with cell proliferation in salivary mucoepidermoid carcinoma

OBJECTIVES

The present study investigated the correlation between the expression of DNA methyltransferase (DNMT)1, DNMT3A, and DNMT3B and the proliferation of mucoepidermoid carcinomas (MECs) using the molecular markers Ki-67 and cyclin D1. This study also demonstrates the effects of 5-aza-2-deoxycytidine (5AC) on the MEC tumor cell lines in relation to DNMT1 and DNMT3A expression, and cell-cycle arrest.

MATERIALS AND METHODS

The immunohistochemistry of DNMT1, DNMT3A, DNMT3B, Ki-67, and cyclin D1 was analyzed in 40 samples of MEC and 15 samples of healthy minor salivary glands. The effects of 5AC on DNMT1 and DNMT3B expression in MEC cell lines were analyzed by Western blot, and the effects of 5AC on the cell cycle were analyzed using flow cytometry.

RESULTS

The expression of DNMT1 and DNMT3B was more intense in MECs than in healthy salivary glands. A strong correlation was found between the expression of the DNMTs and the proliferation markers. This correlation was validated In Vitro, where treatment with 5AC reduced the expression of the DNMTs and the percentage of cells at the G2/M phase of the cell cycle.

CONCLUSION

The expression of DNMT1, DNMT3A, DNMT3B is correlated significantly with the expression of Ki-67 and cyclin D1. The treatment with 5AC reduces DNMT expression and decreases the percentage of cells at the G2/M phase of the cell cycle, while increasing the cells at the G0/G1 phase.

Radiation-Induced Normal Tissue Damage: Oxidative Stress and Epigenetic Mechanisms

Radiotherapy (RT) is currently one of the leading treatments for various cancers; however, it may cause damage to healthy tissue, with both short-term and long-term side effects. Severe radiation-induced normal tissue damage (RINTD) frequently has a significant influence on the progress of RT and the survival and prognosis of patients. The redox system has been shown to play an important role in the early and late effects of RINTD. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are the main sources of RINTD. The free radicals produced by irradiation can upregulate several enzymes including nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase), lipoxygenases (LOXs), nitric oxide synthase (NOS), and cyclooxygenases (COXs). These enzymes are expressed in distinct ways in various cells, tissues, and organs and participate in the RINTD process through different regulatory mechanisms. In recent years, several studies have demonstrated that epigenetic modulators play an important role in the RINTD process. Epigenetic modifications primarily contain noncoding RNA regulation, histone modifications, and DNA methylation. In this article, we will review the role of oxidative stress and epigenetic mechanisms in radiation damage, and explore possible prophylactic and therapeutic strategies for RINTD.

ZNF479 downregulates metallothionein-1 expression by regulating ASH2L and DNMT1 in hepatocellular carcinoma

Decreased expression of metallothionein-1 (MT-1) is associated with a poor prognosis in hepatocellular carcinoma (HCC). Here, we found that MT-1 expression was suppressed by 14-3-3ε, and MT-1 overexpression abolished 14-3-3ε-induced cell proliferation and tumor growth. We identified that 14-3-3ε induced expression of ZNF479, a novel potential transcriptional regulator by gene expression profiling and ZNF479 contributed to 14-3-3ε-suppressed MT-1 expression. ZNF479 induced the expression of DNMT1, UHRF1, and mixed-lineage leukemia (MLL) complex proteins (ASH2L and Menin), and increased tri-methylated histone H3 (H3K4me3) levels, but suppressed H3K4 (H3K4me2) di-methylation. ZNF479-suppressed MT-1 expression was restored by silencing of ASH2L and DNMT1. Furthermore, ZNF479 expression was higher in HCC tissues than that in the non-cancerous tissues. Expression analyses revealed a positive correlation between the expression of ZNF479 and DNMT1, UHRF1, ASH2L, and Menin, and an inverse correlation with that of ZNF479, ASH2L, Menin, and MT-1 isoforms. Moreover, correlations between the expression of ZNF479 and its downstream factors were more pronounced in HCC patients with hepatitis B. Here, we found that ZNF479 regulates MT-1 expression by modulating ASH2L in HCC. Approaches that target ZNF479/MLL complex/MT-1 or related epigenetic regulatory factors are potential therapeutic strategies for HCC.

Therapeutic approach of Cancer stem cells (CSCs) in gastric adenocarcinoma; DNA methyltransferases enzymes in cancer targeted therapy

Cancer stem cells (CSCs) show a remarkable sub class of cancer cells population which have a potential to organize and regulate stemness properties which possess a main particular responsibility for uncontrolled growth in carcinogenesis, production of different cancers in differentiated situation and also resistancy to radiotherapy and chemotherapy. Correspondingly, gastric cancer (GC) as a very serious type in cancer mortality in the world, has received a deep attention in molecular therapy recently. Besides the main characteristics of CSCs like differentiation, epithelial mesenchymal transition, self-renewal and metastasis, they are so effective in expression of stemness genes resistancy in radiotherapy and chemotherapy. In this way, the regulation of epigenetic elements including DNA methylation and the performance of DNA methyltransferase (DNMT) which is a notable epigenetic trait in GC, is of great importance. Inhibitors of DNA methylation are the first epigenetic drugs in cancer therapy. Considerably, recent studies indicate that low doses of DNMT inhibitors have a high potential in sustaining reduced DNA methylation and related with re-expression of silenced genes in tumorigenesis. Importantly, these certain doses have the ability to decrease the carcinogenesis and tumorigenesis in CSC populations within GC. Meaningly, the inhibition of DNMTs are able to reduce the accumulation of tumorigenic ability of GC CSCs. Furthermore, many epigenetic drugs have a great potential in cancer therapy, including histone methyltransferases, lysine demethylases, histone deacetylasesand, bromodomain and extra-terminal domain proteins and DNA methyltransferases inhibitors. In this review article, we try to focus on the therapeutic mechanism of DNMTs alongside with their impact on CSCs in GC.

Non-coding RNAs, epigenetics, and cancer: tying it all together

While only a small part of the human genome encodes for proteins, biological functions for the so-called junk genome are increasingly being recognized through high-throughput technologies and mechanistic experimental studies. Indeed, novel mechanisms of gene regulation are being discovered that require coordinated interaction between DNA, RNA, and proteins. Therefore, interdisciplinary efforts are still needed to decipher these complex transcriptional networks. In this review, we discuss how non-coding RNAs (ncRNAs) are epigenetically regulated in cancer and metastases and consequently how ncRNAs participate in the sculpting of the epigenetic profile of a cancer cell, thus modulating the expression of other RNA molecules. In the latter case, ncRNAs not only affect the DNA methylation status of certain genomic loci but also interact with histone-modifying complexes, changing the structure of the chromatin itself. We present several examples of epigenetic changes causing aberrant expression of ncRNAs in the context of tumor progression. Interestingly, there are also important epigenetic changes and transcriptional regulatory effects derived from their aberrant expression. As ncRNAs can also be used as biomarkers for diagnosis and prognosis or explored as potential targets, we present insights into the use of ncRNAs for targeted cancer therapy.

Hepatitis B Virus-Associated Hepatocellular Carcinoma and Hepatic Cancer Stem Cells

Chronic Hepatitis B Virus (HBV) infection is linked to hepatocellular carcinoma (HCC) pathogenesis. Despite the availability of a HBV vaccine, current treatments for HCC are inadequate. Globally, 257 million people are chronic HBV carriers, and children born from HBV-infected mothers become chronic carriers, destined to develop liver cancer. Thus, new therapeutic approaches are needed to target essential pathways involved in HCC pathogenesis. Accumulating evidence supports existence of hepatic cancer stem cells (hCSCs), which contribute to chemotherapy resistance and cancer recurrence after treatment or surgery. Understanding how hCSCs form will enable development of therapeutic strategies to prevent their formation. Recent studies have identified an epigenetic mechanism involving the downregulation of the chromatin modifying Polycomb Repressive Complex 2 (PRC2) during HBV infection, which results in re-expression of hCSC marker genes in infected hepatocytes and HBV-associated liver tumors. However, the genesis of hCSCs requires, in addition to the expression of hCSC markers cellular changes, rewiring of metabolism, cell survival, escape from programmed cell death, and immune evasion. How these changes occur in chronically HBV-infected hepatocytes is not yet understood. In this review, we will present the basics about HBV infection and hepatocarcinogenesis. Next, we will discuss studies describing the mutational landscape of liver cancers and how epigenetic mechanisms likely orchestrate cellular reprograming of hepatocytes to enable formation of hCSCs.

EYA4 gene functions as a prognostic marker and inhibits the growth of intrahepatic cholangiocarcinoma

Background

The molecular prognostic markers and carcinogenesis of intrahepatic cholangiocarcinoma (ICC) have not been well documented. The purpose of this study was to investigate the prognostic value of the eyes absent homolog 4 (EYA4) gene in ICC and its biological effects on ICC growth in vitro and in vivo.

Methods

One hundred twelve patients with ICC who underwent hepatectomy were enrolled in the study. EYA4 mRNA and EYA4 protein levels in ICC and adjacent non-tumoral tissues were evaluated using real-time quantitative polymerase chain reaction and immunohistochemical staining, respectively. EYA4 protein levels in ICC cells were determined using western blot analysis. The associations between EYA4 expression and clinicopathologic features of ICC were analyzed. To identify independent prognostic factors, univariate and multivariate analyses were performed. The biological effects of EYA4 on ICC cells were evaluated by establishing stable EYA4-overexpressing transfectants in vitro, and EYA4’s effects on tumor growth were evaluated by intra-tumoral injection of EYA4-expressing plasmids in a NOD/SCID murine model of xenograft tumors.

Results

ICC tissues had significantly lower EYA4 mRNA and protein levels compared with adjacent non-tumoral tissues (both P < 0.001). Univariate and multivariate analyses showed that EYA4 protein level, tumor number, adjacent organ invasion, lymph node metastasis, and tumor differentiation were independent prognostic factors for disease-free survival and overall survival (all P < 0.05). In vitro, EYA4 overexpression inhibited tumor cell growth, foci formation, and cell invasiveness. In vivo, intra-tumoral injection of EYA4-expressing plasmids significantly inhibited ICC growth in the murine xenograft model compared with the control group (P < 0.05).

Conclusion

EYA4 gene functioned as a molecular prognostic marker in ICC, and its overexpression inhibited tumor growth in vitro and in vivo.

DNA Methyltransferase 1: A Potential Gene Therapy Target for Hepatocellular Carcinoma?

BACKGROUND

DNA methyltransferase 1 (DNMT1) mutants display altered methylation patterns that may contribute to oncogenesis. We hypothesized that the silencing or inhibition of DNMT1 may affect the malignancy of hepatocellular carcinoma (HCC) cells.

METHODS

The HCC cell line KYN2 was used to construct 3 experimental groups: i) a DNMT1-siRNA group transfected with a green fluorescent protein (GFP) lentiviral vector to silence endogenous DNMT1 gene expression, which was confirmed by real-time quantitative polymerase chain reaction, ii) a 5-Aza-CdR group transfected with a null GFP lentiviral vector and treated with the DNMT1 inhibitor 5-aza-2'-deoxycytidine (5-Aza-CdR), and iii) a control group transfected with a null GFP lentiviral vector. Cellomics ArrayScan VTI imaging and MTT assays were conducted to assess cell proliferation. Cell cycle phase arrest and apoptosis were assayed by flow cytometry. Colony formation was assessed by fluorescence microscopy.

RESULTS

DNMT1 mRNA expression was significantly inhibited in DNMT1-silenced cells relative to control cells (p < 0.05), indicating successful transfection and gene expression knockdown. Cell proliferation was significantly inhibited in DNMT1-siRNA and 5-Aza-CdR cells relative to control cells (p < 0.05). G1-to-S phase shifts were significantly increased in DNMT1-siRNA and 5-Aza-CdR cells relative to control cells (p < 0.05). Apoptosis was significantly increased in DMNT1-siRNA and 5-Aza-CdR cells relative to control cells (p < 0.05). DMNT1-siRNA and 5-Aza-CdR cells displayed significantly reduced colony formation relative to control cells (p < 0.05). Notably, 5-Aza-CdR had more pronounced effects upon all these parameters than DNMT1 silencing.

CONCLUSION

DNMT1 activity appears to positively contribute to the malignancy of HCC cells.

Burkitt lymphoma beyond MYC translocation: N-MYC and DNA methyltransferases dysregulation

Background

The oncogenic transcription factor MYC is pathologically activated in many human malignancies. A paradigm for MYC dysregulation is offered by Burkitt lymphoma, where chromosomal translocations leading to Immunoglobulin gene-MYC fusion are the crucial initiating oncogenic events. However, Burkitt lymphoma cases with no detectable MYC rearrangement but maintaining MYC expression have been identified and alternative mechanisms can be involved in MYC dysregulation in these cases.

Methods

We studied the microRNA profile of MYC translocation-positive and MYC translocation-negative Burkitt lymphoma cases in order to uncover possible differences at the molecular level. Data was validated at the mRNA and protein level by quantitative Real-Time polymerase chain reaction and immunohistochemistry, respectively.

Results

We identified four microRNAs differentially expressed between the two groups. The impact of these microRNAs on the expression of selected genes was then investigated. Interestingly, in MYC translocation-negative cases we found over-expression of DNA-methyl transferase family members, consistent to hypo-expression of the hsa-miR-29 family. This finding suggests an alternative way for the activation of lymphomagenesis in these cases, based on global changes in methylation landscape, aberrant DNA hypermethylation, lack of epigenetic control on transcription of targeted genes, and increase of genomic instability. In addition, we observed an over-expression of another MYC family gene member, MYCN that may therefore represent a cooperating mechanism of MYC in driving the malignant transformation in those cases lacking an identifiable MYC translocation but expressing the gene at the mRNA and protein levels.

Conclusions

Collectively, our results showed that MYC translocation-positive and MYC translocation-negative Burkitt lymphoma cases are slightly different in terms of microRNA and gene expression. MYC translocation-negative Burkitt lymphoma, similarly to other aggressive B-cell non Hodgkin’s lymphomas, may represent a model to understand the intricate molecular pathway responsible for MYC dysregulation in cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1661-7) contains supplementary material, which is available to authorized users.

Deregulation of DNMT1, DNMT3B and miR-29s in Burkitt lymphoma suggests novel contribution for disease pathogenesis

Methylation of CpG islands in promoter gene regions is frequently observed in lymphomas. DNA methylation is established by DNA methyltransferases (DNMTs). DNMT1 maintains methylation patterns, while DNMT3A and DNMT3B are critical for de novo DNA methylation. Little is known about the expression of DNMTs in lymphomas. DNMT3A and 3B genes can be regulated post-transcriptionally by miR-29 family. Here, we demonstrated for the first time the overexpression of DNMT1 and DNMT3B in Burkitt lymphoma (BL) tumor samples (69% and 86%, respectively). Specifically, the treatment of two BL cell lines with the DNMT inhibitor 5-aza-dC decreased DNMT1 and DNMT3B protein levels and inhibited cell growth. Additionally, miR-29a, miR-29b and miR-29c levels were significantly decreased in the BL tumor samples. Besides, the ectopic expression of miR-29a, miR-29b and miR-29c reduced the DNMT3B expression and miR-29a and miR-29b lead to increase of p16(INK4a) mRNA expression. Altogether, our data suggest that deregulation of DNMT1, DNMT3B and miR29 may be involved in BL pathogenesis.

Detection of epigenetic aberrations in the development of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the third most common cause of cancer death worldwide. Hepatocarcinogenesis is a complex, multistep process. It is now recognized that HCC is a both genetic and epigenetic disease; genetic and epigenetic components cooperate at all stages of hepatocarcinogenesis. Epigenetic changes involve aberrant DNA methylation, posttranslational histone modifications and aberrant expression of microRNAs all of which can affect the expression of oncogenes, tumor suppressor genes and other tumor-related genes and alter the pathways in cancer development. Several risk factors for HCC, including hepatitis B and C virus infections and exposure to the chemical carcinogen aflatoxin B1 have been found to influence epigenetic changes. Their interactions could play an important role in the initiation and progression of HCC. Discovery and detection of biomarkers for epigenetic changes is a promising area for early diagnosis and risk prediction of HCC.

DNA methyltransferases 3a and 3b are differentially expressed in the early stages of a rat liver carcinogenesis model

Carcinogenesis is driven by the accumulation of mutations and abnormal DNA methylation patterns, particularly the hypermethylation of tumor‑suppressor genes. Changes in genomic DNA methylation patterns are established by the DNA methyltransferases (DNMTs) family: DNMT1, DNMT3a and DNMT3b. The DNMTs are known to be overexpressed in tumors. However, when the DNMTs expression profile is altered in earlier stages of carcinogenesis remains to be elucidated. The resistant hepatocyte model (RHM) allows the analysis of the hepatocellular carcinoma (HCC) from the formation of altered cell foci to the appearance of tumors in rats. To investigate the DNMTs expression in this model, we first observed that timp3, rassf1a and p16 genes became methylated during cancer development by methylation‑specific PCR (MSP) and the bisulphate sequencing PCR (BSP) of timp3. The differential expression at the RNA and protein level of the three DNMTs was also assessed. dnmt1 expression was higher in tumors than in normal and early cancer stages. However, no evident overexpression of the enzyme was identified by immunohistochemistry. By contrast, DNMT3a and DNMT3b were consistently subexpressed in tumors. In the present study, we report a carcinogenesis model that does not feature the overexpression of DNMT1 but exhibits a transient expression of DNMT3a and DNMT3b.

Methylation of miR-124a-1, miR-124a-2, and miR-124a-3 genes correlates with aggressive and advanced breast cancer disease

Aberrant DNA methylation on CpG islands is one of the most consistent epigenetic changes in human cancers, and the process of methylation is catalyzed by the DNA methyltransferases DNMT1, DNMT3a, and DNMT3b. Recent reports demonstrate that deregulation of miR-124a, one of the frequently methylated microRNAs in human cancers, is related to carcinogenesis. The aim of this study was to evaluate the frequencies of methylation of the three genomic loci encoding the miR-124a in primary breast cancers and to investigate their relationships with the clinicopathological characteristics of the tumors and with the expression levels of DNMT1, DNMT3a, and DNMT3b. The methylation status of the three genomic loci encoding the miR-124a (miR-124a-1, miR-124a-2, and miR-124a-3) was analyzed in fresh-frozen tumor samples using methylation-specific PCR in a large series of invasive breast ductal carcinomas (n = 60). Results were correlated to several clinicopathological characteristics of the tumors and to the expression levels of DNMT1, DNMT3a, and DNMT3b, determined by immunohistochemistry. Promoter hypermethylation of miR-124a-1, miR-124a-2, and miR-124a-3 was detected in 53.3, 70, and 36.7% of cases, respectively. Methylation of miR-124a-2 correlated to patients with age higher than 45 years (P = 0.008) and to postmenopausal patients (P = 0.03), whereas methylation of miR-124a-3 correlated significantly to tumor size >20 mm (P = 0.03). Interestingly, simultaneous methylation of the three genes encoding miR-124a correlated significantly with the presence of lymph node metastasis (P = 0.01) and high mitotic score (P = 0.03). No significant correlation was found between promoter hypermethylation of miR-124a and expression of hormone receptors or HER2/neu. With regard to DNMT expression, no correlation was found between DNMT1 or DNMT3a expression and promoter methylation of any tested microRNA. However, DNMT3b overexpression correlates significantly with the hypermethylation of miR-124a-3 (P = 0.03). Our data indicates that miR-124a-1, miR-124a-2, and miR-124a-3 genes are frequently methylated in breast cancer and play a role in tumor growth and aggressivity.

DNA methylation profiling identifies EYA4 gene as a prognostic molecular marker in hepatocellular carcinoma

BACKGROUND

DNA hypermethylation plays important roles in carcinogenesis by silencing key genes. This study aims to identify pivotal genes in hepatocellular carcinoma (HCC) by DNA methylation microarray and to assess their prognostic values.

MATERIALS AND METHODS

DNA methylation microarray was performed in 45 pairs of HCC and adjacent nontumorous tissues and six normal liver tissues to identify hypermethylated genes in HCC. Potential prognosis-related genes were selected among hypermethylated genes by analyzing influences of methylation levels on disease-free survival (DFS) and overall survival (OS) in 45 patients. Their prognostic values were validated in 154 patients with HCC (including the initial 45 patients) to determine the independent prognostic gene.

RESULTS

Altogether, 54 CpG islands in 44 genes were hypermethylated in HCC compared with liver tissues. Among them, methylation levels of ERG and HOXA11 were inversely associated with DFS (both P < 0.050), and methylation levels of EYA4 were inversely related to DFS and OS (both P < 0.050). EYA4 expression was inversely related to tumor size (P < 0.050). Lower EYA4 expression and larger tumor size were independent predictors of both shorter DFS and OS, and higher Barcelona Clinic Liver Cancer (BCLC) staging was an independent predictor of shorter OS (all P < 0.050).

CONCLUSIONS

EYA4 functions as a prognostic molecular marker in HCC. Its aberrant hypermethylation and subsequent down-regulation may promote tumor progression.

Expression of DNMTs and genomic DNA methylation in gastric signet ring cell carcinoma

The aim of the present study was to investigate the protein expression of DNA methyltransferases (DNMTs) and genomic DNA methylation status of genomes in gastric signet ring cell carcinoma (SRC). Immunohistochemistry was performed to analyze DNMT expression and methylated DNA immunoprecipitation microarray (MeDIP‑chip) and MeDIP quantitative real‑time PCR (MeDIP‑qPCR) were performed to analyze the genomic DNA methylation status in gastric SRC tissue. An increase in DNMT1 and decrease in DNMT3A expression in SRC tissue was observed compared with matched non‑cancerous tissue. However, expression of other DNMTs, DNMT2, DNMT3B and DNMT3L, was not found to differ significantly between carcinoma and control. The MeDIP‑chip assay revealed that methylation of gene promoters and CpG islands in SRC was higher than those in matched control tissue. However, MeDIP‑qPCR analysis demonstrated that specific tumor‑related genes, including ABL2, FGF18, TRAF2, EGFL7 and RAB33A were aberrantly hypomethylated in SRC tissue. Results of the current study indicate that gastric SRC may produce complex patterns of aberrant DNA methylation and DNMT expression.

Prognostic impact of pERK in advanced hepatocellular carcinoma patients treated with sorafenib

BACKGROUND

Sorafenib represents the standard of care targeted therapy for patients with advanced hepatocellular carcinoma (HCC). However, biomolecules that predict a patient's response to sorafenib treatment for HCC remain largely unknown. Thus, this study was designed to investigate whether phosphorylated ERK (pERK) and members of the sorafenib target or PI3K/Akt/mTOR signaling pathway predict the efficacy of sorafenib in advanced HCC patients.

METHODOLOGY

From December 2008 to October 2011, pathological specimens from 54 advanced HCC patients received sorafenib treatment were obtained. Clinicopathological variables, treatment response, survival and time to progression (TTP) were recorded. Immunophenotypical analysis was carried out using antibodies against pERK, phosphorylated S6K (pS6K), VEGFR2 and PTEN.

RESULTS

The median overall survival (OS) and TTP were 14.2 and 3.4 months, respectively, and the disease control rate (DCR) was 59.3%. Better Eastern Cooperative Oncology Group Performance Status (ECOG PS) (95% CI: 3.27-4.93 m vs. 1.15-2.85 m, p = 0.01), Child-Pugh class A score (95% CI: 3.47-4.53 vs. 1.14-2.06 m, p < 0.01), and higher pERK (3.34-6.66 m vs. 1.33-2.67 m, p = 0.03) and VEGFR2 (3.49-6.52 m vs. 2.15-2.73 m, p = 0.04) immunohistochemical staining score were associated with increased TTP by univariate analysis. The ECOG PS (p = 0.022), Child-Pugh class (p = 0.045) and pERK staining score (p = 0.012) were found to be associated with TTP using multivariate analysis.

CONCLUSION

Sorafenib treatment outcome is favorable in advanced HCC patients who received tumor resection and who have a good ECOG PS and Child-Pugh class A liver function. The pERK immunohistological staining score, ECOG PS and Child-Pugh class may be helpful in determining patients most likely to benefit from sorafenib therapy.

miR-101 is down-regulated by the hepatitis B virus x protein and induces aberrant DNA methylation by targeting DNA methyltransferase 3A

The hepatitis B virus x (HBx) protein has been implicated in HBV-related hepatocellular carcinoma (HCC) pathogenesis. However, whether HBx regulates miRNA expression that plays important roles in gene regulation during hepatocarcinogenesis remains unknown. The expression of microRNA-101 (miR-101) in HBV-related HCC tissues and HCC cells was evaluated by real-time PCR. The direct target of miR-101, DNA methyltransferase 3A (DNMT3A), was identified in silico and validated using a 3'-UTR reporter assay. miR-101 was functionally characterized in cells with transiently altered miR-101 expression. HBx expression was found to have a significant inverse correlation with miR-101 expression in HBx-expressing HepG2 compared to control HepG2 cells. miR-101 expression was frequently down-regulated in HBV-related HCC tissues compared to adjacent noncancerous hepatic tissues and had a significant inverse correlation with DNMT3A expression in HBV-related HCCs. Further characterization of miR-101 revealed that it negatively regulated DNA methylation partly through targeting DNMT3A. HBx-mediated miR-101 down-regulation and DNMT3A up-regulation supported the enhanced DNA methylation of several tumor-suppressor genes in HBx-expressing cells. Our studies demonstrating the deregulation of miR-101 expression by HBx may provide novel mechanistic insights into HBV-mediated hepatocarcinogenesis and identify a potential miRNA-based targeted approach for treating HBV-related HCC.

Clinicopathologic significance of DNA methyltransferase 1, 3a, and 3b overexpression in Tunisian breast cancers

DNA methyltransferase 1, 3a, and 3b affect DNA methylation, and it is thought that they play an important role in the malignant transformation of various cancers. The current study was designed to analyze DNA methyltransferase expression by immunohistochemistry in a series of 94 Tunisian sporadic breast carcinomas. Results were correlated to clinicopathologic parameters and promoter methylation status of 8 tumor suppressor genes (BRCA1, BRCA2, RASSFA1, TIMP3, CDH1, P16, RARβ2, and DAPK). Overexpression of DNA methyltransferase 1, 3a, and 3b was detected in 46.8%, 32%, and 44.7% of cases, respectively. A significant correlation was found between DNA methyltransferase 1 overexpression and Scarff-Bloom-Richardson histologic grade III (P = .01). DNA methyltransferase 3a overexpression was significantly associated with menopausal status (P = .01), Scarff-Bloom-Richardson histologic grade III (P = .0001), estrogen (P = .04) and progesterone (P = .007) receptor negativity, and HER2 overexpression (P = .004). However, DNA methyltransferase 3a overexpression was found less frequently in the luminal A intrinsic breast cancer subtype (9.7%) than in luminal B (53%), HER2 (41%), and triple-negative (50%) subtypes (P = .001). DNA methyltransferase 3b overexpression shows significant correlation with promoter hypermethylation of BRCA1 (P = .03) and RASSFA1 (P = .04) and with the hypermethylator phenotype (more than 4 methylated genes, P = .01). These data suggest that overexpression of various DNA methyltransferases might represent a critical event responsible for the epigenetic inactivation of multiple tumor suppressor genes, leading to the development of aggressive forms of sporadic breast cancer.

Inhibition of DNA methyltransferase activity and expression by treatment with the pan-deacetylase inhibitor panobinostat in hepatocellular carcinoma cell lines

BACKGROUND

Hepatocellular carcinoma (HCC) still represents an unmet medical need. Epigenetic inactivation of tumor suppressor genes like RASSF1A or APC by overexpression of DNA methyltransferases (DNMTs) has been shown to be common in HCC and to be linked to the overall prognosis of patients. Inhibitors of protein and histone deacetylases (DACi) have been demonstrated to possess strong anti-tumor effects in HCC models.

METHODS

We therefore investigated whether DACi also has any influence on the expression and activity of DNMTs and methylated target genes in HepG2 and Hep3B cell culture systems and in a xenograft model by immunohistochemistry, westernblotting, RT-qPCR and methylation-specific PCR.

RESULTS

Our findings demonstrate a rapid inhibition of DNMT activity 6 h after treatment with 0.1 μM of the pan-DACi panobinostat. A downregulation of DNMT mRNAs and protein were also observed at later points in time. This loss of DNMT activity and expression was paralleled by a diminished methylation of the target genes RASSF1A and APC and a concomitant re-expression of APC mRNA and protein. Analysis of HepG2 xenograft specimens confirmed these results in vivo.

CONCLUSION

We suggest a dual mode of action of DACi on DNA methylation status: a rapid inhibition of enzyme activity due to interference with posttranslational acetylation and a delayed effect on transcriptional control of DNMT genes by HDAC or miRNA mechanisms.

MTSS1, a novel target of DNA methyltransferase 3B, functions as a tumor suppressor in hepatocellular carcinoma

DNA methyltransferase 3B (DNMT3B) mediates gene silencing via epigenetic mechanisms during hepatocellular carcinoma (HCC) progression. We aimed to identify novel targets of DNMT3B and their potential regulatory mechanisms in HCC. Metastasis suppressor 1 (MTSS1) was one of the DNMT3B targets and selected for further study. DNMT3B overexpression was detected in 81.25% of clinical HCC specimens and was negatively associated with MTSS1 in HCC cells and clinical samples. The underlying mechanism by which DNMT3B silences MTSS1 was studied using a combination of methylation-specific polymerase chain reaction (PCR) and bisulfite genome sequencing, chromatin immunoprecipitation-PCR and luciferase reporter assays. We found that the MTSS1 promoter region was sparsely methylated, and the methylation inhibitors failed to abolish DNMT3B-mediated MTSS1 silencing. DNMT3B protein bound directly to the 5'-flanking region (-865/-645) of the MTSS1 gene to inhibit its transcription. The functional role of MTSS1 was investigated using in vitro and in vivo tumorigenicity assays. As a result, MTSS1 exerted tumor suppressor effects and arrested cells in the G2/M phase, but not the G1/S phase of the cell cycle when it was depleted or overexpressed in HCC cells. Taken together, MTSS1, a novel target of DNMT3B, is repressed by DNMT3B via a DNA methylation-independent mechanism. MTSS1 was further characterized as a novel tumor suppressor gene in HCC. These findings highlight how DNMT3B regulates MTSS1, and such data may be useful for the development of new treatment options for HCC.

DNA methylation of colon mucosa in ulcerative colitis patients: correlation with inflammatory status

BACKGROUND

Although DNA methylation of colonic mucosa in ulcerative colitis (UC) has been suggested, the majority of published reports indicate the correlation between methylation of colon mucosa and occurrence of UC-related dysplasia or cancer without considering the mucosal inflammatory status. The aim of this study was to verify whether mucosal inflammation-specific DNA methylation occurs in the colon of UC.

METHODS

Of 15 gene loci initially screened, six loci (ABCB1, CDH1, ESR1, GDNF, HPP1, and MYOD1) methylated in colon mucosa of UC were analyzed according to inflammatory status using samples from 28 surgically resected UC patients.

RESULTS

Four of six regions (CDH1, GDNF, HPP1, and MYOD1) were more highly methylated in the active inflamed mucosa than in the quiescent mucosa in each UC patient (P = 0.003, 0.0002, 0.02, and 0.048, respectively). In addition, when the methylation status of all samples taken from examined patients was stratified according to inflammatory status, methylation of CDH1 and GDNF loci was significantly higher in active inflamed mucosa than in quiescent mucosa (P = 0.045 and 0.002, respectively). Multiple linear regression analysis revealed that active inflammation was an independent factor of methylation for CDH1 and GDNF. DNA methyltransferase 1 and 3b were highly expressed in colon epithelial cells with active mucosal inflammation, suggesting their involvement in inflammation-dependent methylation.

CONCLUSIONS

Methylation in colonic mucosa of UC was correlated with mucosal inflammatory status, suggesting the involvement of methylation due to chronic active inflammation in UC carcinogenesis.

Immunohistochemical expression of DNA methyltransferases 1, 3a and 3b in oral leukoplakias and squamous cell carcinomas

Over-expression of DNA methyltransferases DNMT1, DNMT3a and DNMT3b has been reported in various cancers and precancerous lesions.

OBJECTIVE

To investigate DNMT1, DNMT3a and DNMT3b enzymes in oral squamous cell carcinoma (SCC) and leukoplakia, and their relationship with histopathologic/clinical parameters.

STUDY DESIGN

Immunohistochemistry was carried out to evaluate the three DNMTs in 60 samples of oral SCC and 37 samples of oral leukoplakia.

RESULTS

DNMT3a immunoreactivity in the three groups of oral SCC (39.8%) was significantly higher than in control (22.6%) (ANOVA, Student-Newman-Keuls test, P<0.05), but not when compared to oral leukoplakia groups (28.2%). For DNMT1 and DNMT3b, there were no statistically significant differences between oral SCC groups (65% and 74.7%), oral leukoplakia groups (68.3% and 70.9%) and control (65.4% and 76.5%). There was a significantly higher mean percentage of DNMT1 immunoreactivity in non-smokers (ANOVA, P=0.048), and a higher DNMT3a immunoreactivity in alcohol users (ANOVA, P=0.01).

CONCLUSIONS

Higher DNMT3a immunopositivity may be associated with oral SCC and alcohol use, whilst lower levels of DNMT1 may be related with smoking habit. However, there was a significantly higher mean percentage of DNMT1 immunoreactivity in non-smokers (ANOVA, P=0.048), and a higher DNMT3a immunoreactivity in alcohol users (ANOVA, P=0.010).

The role of epigenetic transcription repression and DNA methyltransferases in cancer

Epigenetic alterations such as DNA methylation have been implicated in the development and progression of various cancers. DNA methylation consists of the reversible addition of a methyl group to the carbon 5 position of cytosine in CpG dinucleotides and is considered essential for normal embryonic development. However, global genomic hypomethylation and aberrant hypermethylation of regulatory regions of tumor suppressor genes have been associated with chromosomal instability and transcription repression, respectively, providing neoplastic cells with a selective advantage. DNA methyltransferases are the enzymes responsible for the addition of methyl groups to CpG dinucleotides, which, together with histone modifiers, initiate the events necessary for transcription repression to occur. It has been demonstrated that increased expression of DNA methyltransferases may contribute to tumor progression through methylation-mediated gene inactivation in various human cancers. Given their importance, this article reviews the main epigenetic mechanisms for regulating transcription and its implications in cancer development.

DNA methyltransferase DNMT3b protein overexpression as a prognostic factor in patients with diffuse large B-cell lymphomas

Diffuse large B-cell lymphomas (DLBCL) are the most common type of aggressive lymphomas, with considerable heterogeneity in clinical presentation, molecular characteristics, and outcome. Previous studies have showed significant correlations between DNA methyltransferase (DNMT) overexpression and unfavorable prognosis in human cancers. Therefore, we investigated in this study the biological and prognostic significance of DNMT1, DNMT3a, and DNMT3b protein expression in DLBCL. DNA methyltransferase (DNMT) expression was analyzed by immunohistochemistry in 81 DLBCL cases and correlated with clinicopathological parameters. Kaplan-Meier curves were used to estimate survival rates, and the Cox proportional hazard regression model was used to evaluate the prognostic impact of DNMT expression. Our results showed that overexpression of DNMT1, DNMT3a, and DNMT3b were detected in 48%, 13%, and 45% of investigated cases, respectively. DNA methyltransferase 1 (DNMT1) and DNMT3b overexpression was significantly correlated with advanced clinical stages (P = 0.028 and P = 0.016, respectively). Moreover, concomitant expression of DNMT1 and DNMT3b was significantly correlated with resistance to treatment (P = 0.015). With regard to survival rates, although data was available only for 40 patients, DNMT3b overexpression was significantly correlated with shorter overall survival (P = 0.006) and progression-free survival (P = 0.016). Interestingly, multivariate analysis demonstrated that DNMT3b overexpression was an independent prognostic factor for predicting shortened overall survival (P = 0.004) and progression-free survival (P = 0.024). In conclusion, DNMT3b overexpression was identified as an independent prognostic factor for predicting shortened survival of patients with DLBCL and could be, therefore, useful in identifying patients who would benefit from aggressive therapy.

Down-regulated microRNA-152 induces aberrant DNA methylation in hepatitis B virus-related hepatocellular carcinoma by targeting DNA methyltransferase 1

The hepatitis B virus (HBV) X protein has been implicated as a potential trigger of the epigenetic modifications of some genes during hepatocarcinogenesis, but the underlying mechanisms remain unknown. MicroRNAs (miRNAs), which are noncoding RNAs that regulate gene expression, are involved in diverse biological functions and in carcinogenesis. In this study, we investigated whether some miRNAs are aberrantly expressed and involved in the regulation of the abnormal DNA methylation status in HBV-related hepatocellular carcinoma (HCC). Our results showed that the expression of microRNA-152 (miR-152) was frequently down-regulated in HBV-related HCC tissues in comparison with adjacent noncancerous hepatic tissues and was inversely correlated to DNA methyltransferase 1 (DNMT1) messenger RNA (mRNA) expression in HBV-related HCCs. The forced expression of miR-152 in liver cell lines resulted in a marked reduction of the expression of DNMT1 at both the mRNA and protein levels by directly targeting the 3' untranslated regions of DNMT1. This in turn led to a decrease in global DNA methylation, whereas inhibition of miR-152 caused global DNA hypermethylation and increased the methylation levels of two tumor suppressor genes, glutathione S-transferase pi 1 (GSTP1) and E-cadherin 1 (CDH1).

CONCLUSION

Our findings suggest that miR-152 is frequently down-regulated and regulates DNMT1 in HBV-related HCC. These findings support a tumor-suppressive role of miR-152 in the epigenetic aberration of HBV-related HCC and the potential development of miRNA-based targeted approaches for the treatment of HBV-related HCC.

Depletion of DNMT3A suppressed cell proliferation and restored PTEN in hepatocellular carcinoma cell

Promoter hypermethylation mediated by DNA methyltransferases (DNMTs) is the main reason for epigenetic inactivation of tumor suppressor genes (TSGs). Previous studies showed that DNMT1 and DNMT3B play an important role in CpG island methylation in tumorigenesis. Little is known about the role of DNMT3A in this process, especially in hepatocellular carcinoma (HCC). In the present study, increased DNMT3A expression in 3 out of 6 HCC cell lines and 16/25 (64%) HCC tissues implied that DNMT3A is involved in hepatocellular carcinogenesis. Depletion of DNMT3A in HCC cell line SMMC-7721 inhibited cell proliferation and decreased the colony formation (about 65%). Microarray data revealed that 153 genes were upregulated in DNMT3A knockdown cells and that almost 71% (109/153) of them contain CpG islands in their 5′ region. 13 of them including PTEN, a crucial tumor suppressor gene in HCC, are genes involved in cell cycle and cell proliferation. Demethylation of PTEN promoter was observed in DNMT3A-depleted cells implying that DNMT3A silenced PTEN via DNA methylation. These results provide insights into the mechanisms of DNMT3A to regulate TSGs by an epigenetic approach in HCC.

DNA methyltransferase expression in odontogenic cysts and tumours

Epigenetic silencing of gene expression by promoter CpG island hypermethylation is promoted by the enzymes, DNA methyltransferases (DNMTs). DNMT3a is mainly involved in de novo methylation, whereas DNMT1 acts mainly as a maintenance methyltransferase. The purpose of this study was to investigate the immunoexpression of DNMT1 and DNMT3a in a set of odontogenic cysts and tumours. Formalin-fixed and paraffin-embedded tissue samples of eight radicular cysts, 10 odontogenic keratocysts (OKC), eight adenomatoid odontogenic tumours (AOT), 16 ameloblastomas and eight samples of normal mucosae were included in the study. The DNMT1 and DNMT3a proteins were identified by using a highly sensitive polymer-based system. We found that the normal oral mucosa, OKC, AOT, radicular cyst and ameloblastomas samples showed a widespread nuclear and cytoplasmic immunopositivity for DNMT1. Some radicular cysts, ameloblastomas, AOT and OKC samples presented a positive cytoplasmic reaction for DNMT3a, while negative staining was observed in the normal oral mucosa. Nuclear positivity was found only in the suprabasal cell layers of three OKC samples. Our study shows an increased expression of DNMT3a in odontogenic cysts and tumours, confirming that epigenetic mechanisms are involved in the development of these tumours.

Overexpression of DNA methyltransferase 1 and its biological significance in primary hepatocellular carcinoma

AIM: To explore the relationship between DNA methyltransferase 1 (DNMT1) and hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC) and its biological significance in primary HCC.

METHODS: We carried out an immunohistochemical examination of DNMT1 in both HCC and paired non-neoplastic liver tissues from Chinese subjects. DNMT1 mRNA was further examined in HCC cell lines by real-time PCR. We inhibited DNMT1 using siRNA and detected the effect of depletion of DNMT1 on cell proliferation ability and cell apoptosis in the HCC cell line SMMC-7721.

RESULTS: DNMT1 protein expression was increased in HCCs compared to histologically normal non-neoplastic liver tissues and the incidence of DNMT1 immunoreactivity in HCCs correlated significantly with poor tumor differentiation (P = 0.014). There were more cases with DNMT1 overexpression in HCC with HBV (42.85%) than in HCC without HBV (28.57%). However, no significant difference in DNMT1 expression was found in HBV-positive and HBV-negative cases in the Chinese HCC group. There was a trend that DNMT1 RNA expression increased more in HCC cell lines than in pericarcinoma cell lines and normal liver cell lines. In addition, we inhibited DNMT1 using siRNA in the SMMC-7721 HCC cell line and found depletion of DNMT1 suppressed cells growth independent of expression of proliferating cell nuclear antigen (PCNA), even in HCC cell lines where DNMT1 was stably decreased.

CONCLUSION: The findings implied that DNMT1 plays a key role in HBV-related hepatocellular tumorigenesis. Depletion of DNMT1 mediates growth suppression in SMMC-7721 cells.

Hypermethylation of RAS effector related genes and DNA methyltransferase 1 expression in endometrial carcinogenesis

Epigenetic aberration is known to be important in human carcinogenesis. Promoter methylation status of RAS effector related genes, RASSF1A, RASSF2A, hDAB2IP (m2a and m2b regions) and BLU, was evaluated in 76 endometrial carcinomas and their non-neoplastic endometrial tissue by methylation specific PCR. Hypermethylation of at least one of the 5 genes was detected in 73.7% of carcinomas. There were significant correlations between methylation of hDAB2IP and RASSF1A, RASSF2A (p = 0.042, p = 0.012, respectively). Significantly, more frequent RASSF1A hypermethylation was found in Type I endometrioid carcinomas than Type II carcinomas (p = 0.049). Among endometrioid cancers, significant association between RASSF1A hypermethylation and advanced stage, as well as between methylation of hDAB2IP at m2a region with deep myometrial invasion (p < 0.05) was observed. mRNA expression of RASSF1A, RASSF2A and BLU in endometrial cancer cell lines significantly increased after treatment with the demethylating agent 5-Aza-2'-deoxycytidine supporting the repressive effect of hypermethylation on their transcription. Immunohistochemical study of DNMT1 on eight normal endometrium, 16 hyperplastic endometrium without atypia, 40 atypical complex hyperplasia and 79 endometrial carcinomas showed progressive increase in DNMT1 immunoreactivity from normal endometrium to endometrial hyperplasia and endometrioid carcinomas (p = 0.001). Among carcinomas, distinctly higher DNMT1 expression was observed in Type I endometrioid carcinomas (p < 0.001). DNMT1 immunoreactivity correlated with RASSF1A and RASSF2A methylation (p < 0.05). The data suggested that hypermethylation of RAS related genes, particularly RASSF1A, was involved in endometrial carcinogenesis with possible divergent patterns in different histological types. DNMT1 protein overexpression might contribute to such aberrant DNA hypermethylation of specific tumor suppressor genes in endometrial cancers.

Tumor suppressor and hepatocellular carcinoma

A few signaling pathways are driving the growth of hepatocellular carcinoma. Each of these pathways possesses negative regulators. These enzymes, which normally suppress unchecked cell proliferation, are circumvented in the oncogenic process, either the over-activity of oncogenes is sufficient to annihilate the activity of tumor suppressors or tumor suppressors have been rendered ineffective. The loss of several key tumor suppressors has been described in hepatocellular carcinoma. Here, we systematically review the evidence implicating tumor suppressors in the development of hepatocellular carcinoma.

DNA methylation in hepatocellular carcinoma

As for many other tumors, development of hepatocellular carcinoma (HCC) must be understood as a multistep process with accumulation of genetic and epigenetic alterations in regulatory genes, leading to activation of oncogenes and inactivation or loss of tumor suppressor genes (TSG). In the last decades, in addition to genetic alterations, epigenetic inactivation of (tumor suppressor) genes by promoter hypermethylation has been recognized as an important and alternative mechanism in tumorigenesis. In HCC, aberrant methylation of promoter sequences occurs not only in advanced tumors, it has been also observed in premalignant conditions just as chronic viral hepatitis B or C and cirrhotic liver. This review discusses the epigenetic alterations in hepatocellular carcinoma focusing DNA methylation.

Molecular pathogenesis of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common cancer and the third leading cause of cancer death worldwide. Hepatocarcinogenesis is a multistep process evolving from normal through chronic hepatitis/cirrhosis and dysplastic nodules to HCC. With advances in molecular methods, there is a growing understanding of the molecular mechanisms in hepatocarcinogenesis. Hepatocarcinogenesis is strongly linked to increases in allelic losses, chromosomal changes, gene mutations, epigenetic alterations and alterations in molecular cellular pathways. Some of these alterations are accompanied by a stepwise increase in the different pathological disease stages in hepatocarcinogenesis. Overall, a detailed understanding of the underlying molecular mechanisms involved in the progression of HCC is of fundamental importance to the development of effective prevention and treatment regimes for HCC.

Expression of human DNA methyltransferase 1 in colorectal cancer tissues and their corresponding distant normal tissues

BACKGROUND AND AIM

DNA methylation plays an important role during colorectal cancer (CRC) carcinogenesis. DNA methyltransferase 1 (DNMT1) is responsible for maintaining DNA methylation. We addressed the significance of DNMT1 expression in CRC.

MATERIALS AND METHODS

We measured the expression of DNMT1 in CRC tissues and in their corresponding distal normal colorectal mucosa using reverse transcriptase-polymerase chain reaction and immunohistochemical analysis.

RESULTS

The mean +/- SD of DNMT1 mRNA in CRC tissues was 1.04 +/- 0.36, which was significantly higher than that in their corresponding distal normal colorectal mucosa (0.58 +/- 0.44, P < 0.05). Fifty-eight out of 77 (75.3%) CRC tissues and only 30 out of 77 (39%) corresponding distant normal colorectal mucosa showed immunoreactivity (P < 0.001). We also found that the immunoreactivity of DNMT1 was higher in mucosa adjacent to cancer than in corresponding normal colorectal mucosa; high immunoreactivity was significantly correlated with poor differentiation in CRC tissues (P = 0.008). No significant associations were found between DNMT1 immunoreactivity and the following variables: age, sex, locations of cancer, Duke's phase, and the presence of lymph-node metastasis.

CONCLUSION

These findings suggested that DNMT1 was associated with the malignant phenotype, and dysregulation of DNMT1 expression was present in tumor cells of CRC.

Vitamin A and beta-carotene inhibitory effect during 1,2-dimethylhydrazine induced hepatocarcinogenesis potentiated by 5-azacytidine

5-Azacytidine is being used for reactivation of tumor suppressor genes. However, its administration during DNA repair pontentiates hepatocarcinogenesis. We observed chemopreventive activities by vitamin A and beta-carotene during early hepatocarcinogenesis. Thus, in the present study we evaluated vitamin A and beta-carotene chemopreventive potential during early hepatocarcinogenesis potentiated by 5-azacytidine. Wistar rats received vitamin A (VAA group), beta-carotene (betaCA group) or corn oil (CO and COA groups). After three weeks of treatment, all animals were initiated with 1,2-dimethylhydrazine. Twelve hours later VAA, betaCA and COA groups received a single dose of 5-Azc. Hepatocytes were selected/promoted by 2-acetylaminofluorene and 70% partial hepatectomy. All animals were sacrificed six weeks after initiation. Compared to CO group (without 5-azacytidine), COA group presented higher (p<0.05) nodule multiplicity, larger (p<0.05) gamma-GT positive lesions that occupied a larger (p<0.05) area of liver section. Compared to COA group, VAA group presented decreased (p<0.05) nodule multiplicity while betaCA group tended to present smaller gamma-GT positive lesions and to decrease occupied liver section. These results reinforce vitamin A and beta-carotene chemopreventive potential. Considering that 5-azacytidine potentiates hepatocarcinogenesis, more studies are needed to elucidate the efficacy and safety of this drug for cancer control.

Epigenetic effects of ethanol on liver and gastrointestinal injury

Alcohol consumption causes cellular injury. Recent developments indicate that ethanol induces epigenetic alterations, particularly acetylation, methylation of histones, and hypo- and hypermethylation of DNA. This has opened up a new area of interest in ethanol research and is providing novel insight into actions of ethanol at the nucleosomal level in relation to gene expression and patho-physiological consequences. The epigenetic effects are mainly attributable to ethanol metabolic stress (Emess), generated by the oxidative and non-oxidative metabolism of ethanol, and dysregulation of methionine metabolism. Epigenetic changes are important in ethanol-induced hepatic steatosis, fibrosis, carcinoma and gastrointestinal injury. This editorial highlights these new advances and its future potential.

A folate- and methyl-deficient diet alters the expression of DNA methyltransferases and methyl CpG binding proteins involved in epigenetic gene silencing in livers of F344 rats

Aberrations in methylation profile of the genome occur in human cancers induced by folate deficiency. To elucidate the underlying mechanism, male F344 rats were fed a diet deficient in l-methionine and devoid of folic acid and choline (FMD diet), which is known to induce hepatocellular carcinomas. We investigated changes in the DNA methylation machinery, namely, de novo DNA methyltransferases (Dnmt3a and 3b), maintenance DNA methyltransferase (Dnmt1), and methyl CpG binding proteins (MBDs), in rat livers during early stages of tumorigenesis. RT-PCR and Western blot analyses revealed differential expression of these proteins in the livers of rats fed the FMD diet. Although the hepatic Dnmt1 mRNA level declined with age (P < 0.001), it was elevated (P < 0.001) in deficient rats compared with controls. The changes in hepatic Dnmt1 protein level with the diet correlated with its mRNA levels (r = 0.60, P = 0.002). Similarly, the Dnmt3a mRNA level was elevated in rats fed the FMD diet (P < 0.001), whereas the Dnmt3b level (mRNA and protein) was not affected by diet or age. Compared with controls, hepatic MBD1-3 RNA levels increased (P < 0.001) and the protein levels of MBD1, 2, and 4 were elevated (P < 0.001) in the deficient rats. In both diet groups, hepatic MBD2 protein decreased (P < 0.001), whereas MeCP2 protein increased (P < 0.001) with age. These results demonstrate that a combined folate and methyl deficiency alters components of the DNA methylation machinery by both transcriptional and posttranscriptional mechanisms during early stages of hepatocarcinogenesis.

DNA methyltransferase expression and DNA hypermethylation in human hepatocellular carcinoma

Aberrant DNA methylation and increased expression of DNA methyltransferases (DNMTs) are features of tumor cells. To investigate roles for DNMTs during hepatocarcinogenesis, we examined DNMT expression at both the mRNA and protein level in hepatocellular carcinomas (HCCs) and paired non-neoplastic liver tissues, along with measuring the DNA methylation status of five tumor suppressor genes. Expression of DNMT1, DNMT3a and DNMT3b mRNA was detected in 33.3, 59.3, and 55.6% of HCCs and 40.7, 22.2, and 0% of non-neoplastic liver tissues, respectively. DNMT1 and DNMT3a were immunoreactive in 100 and 48% of HCCs and 52 and 0% of non-neoplastic liver tissues. The DNMT3a mRNA expression profile showed significant correlation with its immunoreactivity (P=0.022). DNA methylation status of five tumor suppressor genes, HIC-1, p16, RASSF1A, p53, and RB1 was detected in 85.2, 48.1, 44.4, 22.2, and 0% of HCCs, respectively. There was no significant correlation between DNMT mRNA expression and DNA methylation (P>0.05). DNMT immunoreactivity was also not associated with DNA methylation except HIC-1 (P=0.036) and p53 methylation (P=0.009). Despite the lack of correlation between DNA methylation status and DNMT expression, the frequency of hypermethylation of tumor suppressor genes remained relatively high in HCCs, suggesting that regional DNA hypermethylation is involved in hepatocarcinogenesis and that there may be other mechanisms for increasing DNA methylation.

Silencing of caspase-8 in murine hepatocellular carcinomas is mediated via methylation of an essential promoter element

BACKGROUND & AIMS

Caspase-8 is the apical caspase essential for triggering Fas-induced apoptosis. In this study, we investigated caspase-8 expression in hepatocellular carcinomas (HCCs) using recently described HCC mouse models (c-myc and IgEGF transgenes).

METHODS

HCCs were isolated from c-myc and IgEGF transgenic animals. Expression of caspase-8 was monitored by reverse-transcription polymerase chain reaction. The murine caspase-8 promoter was characterized by luciferase-reporter analysis and the analysis of promoter methylation was performed by bisulfite genomic sequencing.

RESULTS

In HCCs investigated, we frequently found a lack of caspase-8 messenger RNA expression. Genomic deletions at the caspase-8 locus did not contribute to caspase-8 silencing. We examined tumor-derived promoter sequences and found significant hypermethylation at distinct CpG sites. In parallel, we characterized the murine caspase-8 promoter and identified a 30-bp promoter element that is indispensable for basal promoter activity. This minimal promoter element contained SP1 binding motifs that are colocalized with CpG sites and were methylated in tumor-derived promoter sequences. Electrophoretic mobility shift assay analysis showed that methylation of these SP1 sites is sufficient to prevent SP1 complex formation. To support our data, we mimicked the methylation pattern of a tumor-derived caspase-8 promoter in vitro using CpG methylase and found a strong reduction of promoter activity.

CONCLUSIONS

We show that HCCs are correlated frequently with silencing of caspase-8 expression and provide data suggesting that caspase-8 silencing is a direct consequence of inhibiting SP1-dependent transactivation caused by CpG methylation at its essential binding sites in the promoter region. Our data support the hypothesis that inhibition of apoptosis triggers hepatocarcinogenesis.

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Alcohol in hepatocellular cancer

Hepatocellular cancer accounts for almost half a million cancer deaths a year, with an escalating incidence in the Western world. Alcohol has long been recognized as a major risk factor for cancer of the liver and of other organs including oropharynx, larynx, esophagus, and possibly the breast and colon. There is compelling epidemiologic data confirming the increased risk of cancer associated with alcohol consumption, which is supported by animal experiments. Cancer of the liver associated with alcohol usually occurs in the setting of cirrhosis. Alcohol may act as a cocarcinogen, and has strong synergistic effects with other carcinogens including hepatitis B and C, aflatoxin, vinyl chloride, obesity, and diabetes mellitus. Acetaldehyde, the main metabolite of alcohol, causes hepatocellular injury, and is an important factor in causing increased oxidant stress, which damages DNA. Alcohol affects nutrition and vitamin metabolism, causing abnormalities of DNA methylation. Abnormalities of DNA methylation, a key pathway of epigenetic gene control, lead to cancer. Other nutritional and metabolic effects, for example on vitamin A metabolism, also play a key role in hepatocarcinogenesis. Alcohol enhances the effects of environmental carcinogens directly and by contributing to nutritional deficiency and impairing immunological tumor surveillance. This review summarizes the epidemiologic evidence for the role of alcohol in hepatocellular cancer, and discusses the mechanisms involved in the promotion of cancer.