The role of DNA methyltransferase 1 in growth control

MicroRNA-148a Targets DNMT1 and PPARGC1A to Regulate the Viability, Proliferation, and Milk Fat Synthesis of Ovine Mammary Epithelial Cells

In this study, the expression profiles of miR-148a were constructed in eight different ovine tissues, including mammary gland tissue, during six different developmental periods. The effect of miR-148a on the viability, proliferation, and milk fat synthesis of ovine mammary epithelial cells (OMECs) was investigated, and the target relationship of miR-148a with two predicted target genes was verified. The expression of miR-148a exhibited obvious tissue-specific and temporal-specific patterns. miR-148a was expressed in all eight ovine tissues investigated, with the highest expression level in mammary gland tissue (p < 0.05). Additionally, miR-148a was expressed in ovine mammary gland tissue during each of the six developmental periods studied, with its highest level at peak lactation (p < 0.05). The overexpression of miR-148a increased the viability of OMECs, the number and percentage of Edu-labeled positive OMECs, and the expression levels of two cell-proliferation marker genes. miR-148a also increased the percentage of OMECs in the S phase. In contrast, transfection with an miR-148a inhibitor produced the opposite effect compared to the miR-148a mimic. These results indicate that miR-148a promotes the viability and proliferation of OMECs in Small-tailed Han sheep. The miR-148a mimic increased the triglyceride content by 37.78% (p < 0.01) and the expression levels of three milk fat synthesis marker genes in OMECs. However, the miR-148a inhibitor reduced the triglyceride level by 87.11% (p < 0.01). These results suggest that miR-148a promotes milk fat synthesis in OMECs. The dual-luciferase reporter assay showed that miR-148a reduced the luciferase activities of DNA methyltransferase 1 (DNMT1) and peroxisome proliferator-activated receptor gamma coactivator 1-A (PPARGC1A) in wild-type vectors, suggesting that they are target genes of miR-148a. The expression of miR-148a was highly negatively correlated with PPARGC1A (r = -0.789, p < 0.001) in ovine mammary gland tissue, while it had a moderate negative correlation with DNMT1 (r = -0.515, p = 0.029). This is the first study to reveal the molecular mechanisms of miR-148a underlying the viability, proliferation, and milk fat synthesis of OMECs in sheep.

LncRNA MIR210HG promotes the proliferation, migration, and invasion of lung cancer cells by inhibiting the transcription of SH3GL3

Lung cancer (LCa), the most frequent malignancy worldwide, causes millions of mortalities each year. Overexpression of the long noncoding RNA MIR210HG in LCa has been established; however, a more comprehensive investigation into its biological role within LCa is imperative. This study aimed to validate the MIR210H levels in LCa tissues and cells. The expression of indicated genes was evaluated using quantitative real-time polymerase chain reaction (qRT-PCR) and/or Western blotting. The viability, proliferation, migration, and invasion of LCa cells were measured using the 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT), colony formation, wound healing, and transwell assays, respectively. The methylation levels of LCa cells were determined via methylation-specific PCR; additionally, chromatin immunoprecipitation or RNA immunoprecipitation assays were performed to determine the targeting relationship between DNA methyltransferase 1 (DNMT1) and the SH3-domain containing CRB2 like 3 (SH3GL3) promoters and the interaction between DNMT1 and MIR210HG, respectively. Our findings revealed the upregulation of MIR210HG, coupled with a diminished expression of SH3GL3 in LCa tissues and cells. Knockdown of MIR210HG or overexpression of SH3GL3 suppressed the proliferative, migratory, and invasive capacities of the cells. DNMT1 bound to the SH3GL3 promoter region, and MIR210HG inhibited the transcription of SH3GL3 by recruiting DNMT1. These findings indicate that MIR210HG facilitates LCa cell growth and metastasis by repressing SH3GL3 transcription via the recruitment of DNMT1 to the SH3GL3 promoter region.

Epigenetic Differences Arise in Endothelial Cells Responding to Cobalt–Chromium

Cobalt–chromium (Co-Cr)-based alloys are emerging with important characteristics for use in dentistry, but the knowledge of epigenetic mechanisms in endothelial cells has barely been achieved. In order to address this issue, we have prepared a previously Co-Cr-enriched medium to further treat endothelial cells (HUVEC) for up to 72 h. Our data show there is important involvement with epigenetic machinery. Based on the data, it is believed that methylation balance in response to Co-Cr is finely modulated by DNMTs (DNA methyltransferases) and TETs (Tet methylcytosine dioxygenases), especially DNMT3B and both TET1 and TET2. Additionally, histone compaction HDAC6 (histone deacetylase 6) seems to develop a significant effect in endothelial cells. The requirement of SIRT1 seems to have a crucial role in this scenario. SIRT1 is associated with a capacity to modulate the expression of HIF-1α in response to hypoxia microenvironments, thus presenting a protective effect. As mentioned previously, cobalt is able to prevent HIF1A degradation and maintain hypoxia-related signaling in eukaryotic cells. Together, our results show, for the first time, a descriptive study reporting the relevance of epigenetic machinery in endothelial cells responding to cobalt–chromium, and it opens new perspectives to better understand their repercussions as prerequisites for driving cell adhesion, cell cycle progression, and angiogenesis surrounding this Co-Cr-based implantable device.

Epigenetic Regulation (Including Micro-RNAs, DNA Methylation and Histone Modifications) of Rheumatoid Arthritis: A Systematic Review

The inflammatory reaction in rheumatoid arthritis (RA) is controlled by major epigenetic modifications that modulate the phenotype of synovial and immune cells. The aim of this work was to perform a systematic review focusing on miR expression, DNA methylation and histone modifications in RA. We demonstrated that, in human samples, the expressions of miR-155, miR-146a and miR-150 were significantly decreased while the expression of miR-410-3p was significantly increased in the RA group. Moreover, miR-146a significantly decreased pro-autoimmune IL-17 cytokine expression in RA. In a murine model, miR-34a inhibition can ameliorate the arthritis score. However, this evidence remain critically insufficient to support current therapeutic applications in RA patients.

The molecular pathway triggered by zirconia in endothelial cells involves epigenetic control

The requirement to achieve natural looking restorations is one of the most challenging aspects in dentistry. Although zirconia has provided new opportunities for achieving superior aesthetics and physicochemical outcomes, very little has been achieved for its cellular and molecular performance, especially considering angiogenesis and osteogenesis. As angiogenesis is a secondary event and concomitant to osteogenesis, an indirect effect of dental implant on endothelial cells could be the release of active molecules such as those already reported affecting osteoblasts. To better address this issue, we challenged human endothelial cells (HUVECs) with zirconia-conditioned medium up to 72 h to allow analysis specific gene expression and protein pattern of mediators of epigenetic machinery in full. Our data shows involvement of zirconia in triggering intracellular signaling through MAPK-ERK activation, leading the signal to activate histone deacetylase HDAC6 likely with concomitant well-modulated DNA methylation profile by DNMTs and TETs. These signaling pathways seem to culminate in cytoskeleton rearrangement of endothelial cells, an important prerequisite to cell migration expected in angiogenesis. Collectively, this study demonstrates for the first time epigenetic-related molecular mechanism involved in endothelial cells responding to zirconia, revealing a repertoire of signaling molecules capable of executing the reprogramming process of gene expression, which are necessary to drive cell proliferation, migration, and consequently angiogenesis. This set of data can further studies using gene editing approaches to better elucidate functional roles.

Prenatal and ancestral exposure to di(2-ethylhexyl) phthalate alters gene expression and DNA methylation in mouse ovaries

Di(2-ethylhexyl) phthalate (DEHP) is a commonly used plasticizer and known endocrine disrupting chemical, which causes transgenerational reproductive toxicity in female rodents. However, the mechanisms of action underlying the transgenerational toxicity of DEHP are not understood. Therefore, this study determined the effects of prenatal and ancestral DEHP exposure on various ovarian pathways in the F1, F2, and F3 generations of mice. Pregnant CD-1 dams were orally exposed to corn oil (vehicle control) or DEHP (20 μg/kg/day-750 mg/kg/day) from gestation day 10.5 until birth. At postnatal day 21 for all generations, ovaries were removed for gene expression analysis of various ovarian pathways and for 5-methyl cytosine (5-mC) quantification. In the F1 generation, prenatal DEHP exposure disrupted the expression of cell cycle regulators, the expression of peroxisome-proliferator activating receptors, and the percentage of 5-mC compared to control. In the F2 generation, exposure to DEHP decreased the expression of steroidogenic enzymes, apoptosis factors, and ten-eleven translocation compared to controls. It also dysregulated the expression of phosphoinositide 3-kinase (PI3K) factors. In the F3 generation, ancestral DEHP exposure decreased the expression of steroidogenic enzymes, PI3K factors, cell cycle regulators, apoptosis factors, Esr2, DNA methylation mediators, and the percentage of 5-mC compared to controls. Overall, the data show that prenatal and ancestral DEHP exposure greatly suppress gene expression of pathways required for folliculogenesis and steroidogenesis in the ovary in a transgenerational manner and that gene expression may be influenced by DNA methylation. These results provide insight into some of the mechanisms of DEHP-mediated toxicity in the ovary across generations.

LncRNA MIR210HG promotes proliferation and invasion of non-small cell lung cancer by upregulating methylation of CACNA2D2 promoter via binding to DNMT1

Background: In recent years, a large number of studies have shown that differentially expressed lncRNAs are capable of promoting the occurrence and development of tumors by regulating cell proliferation and differentiation. However, the biological effects of lncRNAs in non-small cell lung cancer (NSCLC) are still needed to be further investigated.

Methods: The differentially expressed lncRNAs in NSCLC tissues in the downloaded profiles from GEO database were analyzed and further verified in 100 pairs of NSCLC samples collected in our hospital. After identification of the target gene MIR210HG, the relationship between MIR210HG expression and clinical data of NSCLC patients was analyzed. Regulatory effects of MIR210HG on proliferation, migration, and invasion of NSCLC cells were detected by CCK-8, colony formation, and transwell assay, respectively. The binding condition of MIR210HG and DNA methyltransferase 1 (DNMT1) was detected by RNA binding protein immunoprecipitation. Subsequently, chromatin immunoprecipitation assay assessed the promoter binding of DNMT1 to CACNA2D2. Rescue experiments were conducted to assess whether CACNA2D2 can reverse the function of MIR210HG.

Results: MIR210HG was highly expressed in NSCLC tissues not only in GSE30219 dataset but also in our collected NSCLC tissues. MIR210HG expression was correlated to tumor stage and lymph node metastasis of NSCLC patients. Besides, lower disease-free survival (DFS) and overall survival (OS) were found in NSCLC patients with high-level MIR210HG compared with those with low-level MIR210HG. Regression analysis indicated that MIR210HG was the independent risk factor for DFS and OS of NSCLC patients. In vitro experiments demonstrated that MIR210HG knockdown remarkably inhibited proliferation and migration of NSCLC cells. MIR210HG could recruit DNMT1, thereafter promoting methylation of CACNA2D2 promoter region. CACNA2D2 overexpression remarkably inhibited cell proliferation. Moreover, inhibited proliferation induced by MIR210HG knockdown was reversed by CACNA2D2 knockdown.

Conclusion: MIR210HG can promote the tumorigenesis of NSCLC by inhibiting the expression of CACNA2D2. Our findings provide new therapeutic strategies for the future treatment of NSCLC.

DNA methyltransferase expression in triple-negative breast cancer predicts sensitivity to decitabine

Triple-negative breast cancer (TNBC) is a heterogeneous disease with poor prognosis that lacks targeted therapies, especially in patients with chemotherapy-resistant disease. Since DNA methylation-induced silencing of tumor suppressors is common in cancer, reversal of promoter DNA hypermethylation by 5-aza-2'-deoxycytidine (decitabine), an FDA-approved DNA methyltransferase (DNMT) inhibitor, has proven effective in treating hematological neoplasms. However, its antitumor effect varies in solid tumors, stressing the importance of identifying biomarkers predictive of therapeutic response. Here, we focused on the identification of biomarkers to select decitabine-sensitive TNBC through increasing our understanding of the mechanism of decitabine action. We showed that protein levels of DNMTs correlated with response to decitabine in patient-derived xenograft (PDX) organoids originating from chemotherapy-sensitive and -resistant TNBCs, suggesting DNMT levels as potential biomarkers of response. Furthermore, all 3 methytransferases, DNMT1, DNMT3A, and DNMT3B, were degraded following low-concentration, long-term decitabine treatment both in vitro and in vivo. The DNMT proteins could be ubiquitinated by the E3 ligase, TNF receptor-associated factor 6 (TRAF6), leading to lysosome-dependent protein degradation. Depletion of TRAF6 blocked decitabine-induced DNMT degradation, conferring resistance to decitabine. Our study suggests a potential mechanism of regulating DNMT protein degradation and DNMT levels as response biomarkers for DNMT inhibitors in TNBCs.

Milk disrupts p53 and DNMT1, the guardians of the genome: implications for acne vulgaris and prostate cancer

There is accumulating evidence that milk shapes the postnatal metabolic environment of the newborn infant. Based on translational research, this perspective article provides a novel mechanistic link between milk intake and milk miRNA-regulated gene expression of the transcription factor p53 and DNA methyltransferase 1 (DNMT1), two guardians of the human genome, that control transcriptional activity, cell survival, and apoptosis. Major miRNAs of milk, especially miRNA-125b, directly target TP53 and complex p53-dependent gene regulatory networks. TP53 regulates the expression of key genes involved in cell homeostasis such as FOXO1, PTEN, SESN1, SESN2, AR, IGF1R, BAK1, BIRC5, and TNFSF10. Nuclear interaction of p53 with DNMT1 controls gene silencing. The most abundant miRNA of milk and milk fat, miRNA-148a, directly targets DNMT1. Reduced DNMT1 expression further attenuates the activity of histone deacetylase 1 (HDAC1) involved in the regulation of chromatin structure and access to transcription. The presented milk-mediated miRNA-p53-DNMT1 pathway exemplified at the promoter regulation of survivin (BIRC5) provides a novel explanation for the epidemiological association between milk consumption and acne vulgaris and prostate cancer. Notably, p53- and DNMT1-targeting miRNAs of bovine and human milk survive pasteurization and share identical seed sequences, which theoretically allows the interaction of bovine miRNAs with the human genome. Persistent intake of milk-derived miRNAs that attenuate p53- and DNMT1 signaling of the human milk consumer may thus present an overlooked risk factor promoting acne vulgaris, prostate cancer, and other p53/DNMT1-related Western diseases. Therefore, bioactive miRNAs of commercial milk should be eliminated from the human food chain.

DNMT1 Regulates Epithelial-Mesenchymal Transition and Cancer Stem Cells, Which Promotes Prostate Cancer Metastasis

Cancer metastasis is a multistep process associated with the induction of an epithelial-mesenchymal transition (EMT) and cancer stem cells (CSCs). Although significant progress has been made in understanding the molecular mechanisms regulating EMT and the CSC phenotype, little is known of how these processes are regulated by epigenetics. Here we demonstrate that reduced expression of DNA methyltransferase 1 (DNMT1) plays an important role in the induction of EMT and the CSC phenotype by prostate cancer (PCa) cells, with enhanced tumorigenesis and metastasis. First, we observed that reduction of DNMT1 by 5-azacitidine (5-Aza) promotes EMT induction as well as CSCs and sphere formation in vitro. Reduced expression of DNMT1 significantly increased PCa migratory potential. We showed that the increase of EMT and CSC activities by reduction of DNMT1 is associated with the increase of protein kinase C. Furthermore, we confirmed that silencing DNMT1 is correlated with enhancement of the induction of EMT and the CSC phenotype in PCa cells. Additionally, chromatin immunoprecipitation assay reveals that reduction of DNMT1 promotes the suppression of H3K9me3 and H3K27me3 on the Zeb2 and KLF4 promoter region in PCa cells. Critically, we found in an animal model that significant tumor growth and more disseminated tumor cells in most osseous tissues were observed following injection of 5-Aza pretreated-PCa cells compared with vehicle-pretreated PCa cells. Our results suggest that epigenetic alteration of histone demethylation regulated by reduction of DNMT1 may control induction of EMT and the CSC phenotype, which facilitates tumorigenesis in PCa cells and has important therapeutic implications in targeting epigenetic regulation.

MicroRNAs: Milk's epigenetic regulators

Our perception of milk has changed from a "simple food" to a highly sophisticated maternal-neonatal nutrient and communication system orchestrating early programming of the infant. Milk miRNAs delivered by exosomes and milk fat globules derived from mammary gland epithelial cells play a key role in this process. Exosomes resist the harsh intestinal environment, are taken up by intestinal cells via endocytosis, and reach the systemic circulation of the milk recipient. The most abundant miRNA found in exosomes and milk fat globules of human and cow's milk, miRNA-148a, attenuates the expression of DNA methyltransferase 1, which is critically involved in epigenetic regulation. Another important miRNA of milk, miRNA-125b, targets p53, the guardian of the genome, and its diverse transcriptional network. The deficiency of exosomal miRNAs in infant formula and the persistent uptake of milk miRNAs after the nursing period via consumption of cow's milk are two epigenetic aberrations that may induce adverse long-term effects on human health.

In Ovo injection of betaine affects hepatic cholesterol metabolism through epigenetic gene regulation in newly hatched chicks

Betaine is reported to regulate hepatic cholesterol metabolism in mammals. Chicken eggs contain considerable amount of betaine, yet it remains unknown whether and how betaine in the egg affects hepatic cholesterol metabolism in chicks. In this study, eggs were injected with betaine at 2.5 mg/egg and the hepatic cholesterol metabolism was investigated in newly hatched chicks. Betaine did not affect body weight or liver weight, but significantly increased the serum concentration (P < 0.05) and the hepatic content (P < 0.01) of cholesterol. Accordingly, the cholesterol biosynthetic enzyme HMGCR was up-regulated (P < 0.05 for both mRNA and protein), while CYP7A1 which converts cholesterol to bile acids was down-regulated (P < 0.05 for mRNA and P = 0.07 for protein). Moreover, hepatic protein content of the sterol-regulatory element binding protein 1 which regulates cholesterol and lipid biosynthesis, and the mRNA abundance of ATP binding cassette sub-family A member 1 (ABCA1) which mediates cholesterol counter transport were significantly (P < 0.05) increased in betaine-treated chicks. Meanwhile, hepatic protein contents of DNA methyltransferases 1 and adenosylhomocysteinase-like 1 were increased (P < 0.05), which was associated with global genomic DNA hypermethylation (P < 0.05) and diminished gene repression mark histone H3 lysine 27 trimethylation (P < 0.05). Furthermore, CpG methylation level on gene promoters was found to be increased (P < 0.05) for CYP7A1 yet decreased (P < 0.05) for ABCA1. These results indicate that in ovo betaine injection regulates hepatic cholesterol metabolism in chicks through epigenetic mechanisms including DNA and histone methylations.

Preoperative low dose NSAID treatment influences the genes for stemness, growth, invasion and metastasis in colorectal cancer

Preclinical data, and an increasing list of clinical investigations, show anti-inflammatory agents to favourably influence the biology of colorectal tumor. We have earlier reported on re-expression of activated immune cells after three days preoperative treatment of patients with colorectal carcinoma, randomized to receive oral NSAID (indomethacin or celebrex). Antisecretory prophylaxis (esomeprasol) was provided to all patients and served as sham treatment. Concomittant to MHC locus activation, Prominin1/CD133, a marker associated with stemness and poor prognosis in several solid tumors, was downregulated. The aim of the present study was to evaluate expression of additional regulators belonging to the stem cell niche, OCT4, SOX2 and BMP7, as well as some microRNAs, reported to act as tumor suppressors or oncomiRs. Peroperative tumor biopsies were analyzed by microarrays, quantitative real-time PCR and immunohistochemistry (IHC). The stem cell master regulator SOX2 was increased by NSAIDs (p<0.01), as well as the tumor suppressor miR-630 (p<0.01), while BMP7, a marker for poor prognosis in CRC, was downregulated by NSAID (indomethacin, p<0.02). The upregulation of SOX2, but not of its heterodimer binding partner OCT4, could imply a negative feed-back loop, with a switch‑off for stemness preservation of tumor cells. This is supported by the overall evaluation of gene expression profiles with subsequent events, indicating less aggressive tumors following NSAID treatment.

DNA methyltransferases: a novel target for prevention and therapy

Cancer is the second leading cause of death in US. Despite the emergence of new, targeted agents, and the use of various therapeutic combinations, none of the available treatment options are curative in patients with advanced cancer. Epigenetic alterations are increasingly recognized as valuable targets for the development of cancer therapies. DNA methylation at the 5-position of cytosine, catalyzed by DNA methyltransferases (DNMTs), is the predominant epigenetic modification in mammals. DNMT1, the major enzyme responsible for maintenance of the DNA methylation pattern is located at the replication fork and methylates newly biosynthesized DNA. DNMT2 or TRDMT1, the smallest mammalian DNMT is believed to participate in the recognition of DNA damage, DNA recombination, and mutation repair. It is composed solely of the C-terminal domain, and does not possess the regulatory N-terminal region. The levels of DNMTs, especially those of DNMT3B, DNMT3A, and DNMT3L, are often increased in various cancer tissues and cell lines, which may partially account for the hypermethylation of promoter CpG-rich regions of tumor suppressor genes in a variety of malignancies. Moreover, it has been shown to function in self-renewal and maintenance of colon cancer stem cells and need to be studied in several cancers. Inhibition of DNMTs has demonstrated reduction in tumor formation in part through the increased expression of tumor suppressor genes. Hence, DNMTs can potentially be used as anti-cancer targets. Dietary phytochemicals also inhibit DNMTs and cancer stem cells; this represents a promising approach for the prevention and treatment of many cancers.

Class I HDACs are mediators of smoke carcinogen-induced stabilization of DNMT1 and serve as promising targets for chemoprevention of lung cancer

DNA methylation is an early event in bronchial carcinogenesis and increased DNA methyltransferase (DNMT)1 protein expression is a crucial step in the oncogenic transformation of epithelia. Here, we investigate the role of class I histone deacetylases (HDAC) 1 to 3 in the stabilization of DNMT1 protein and as a potential therapeutic target for lung cancer chemoprevention. Long-term exposure of immortalized bronchial epithelial cells (HBEC-3KT) to low doses of tobacco-related carcinogens led to oncogenic transformation, increased HDAC expression, cell-cycle independent increased DNMT1 stability, and DNA hypermethylation. Overexpression of HDACs was associated with increased DNMT1 stability and knockdown of HDACs reduced DNMT1 protein levels and induced DNMT1 acetylation. This suggests a causal relationship among increased class I HDACs levels, upregulation of DNMT1 protein, and subsequent promoter hypermethylation. Targeting of class I HDACs with valproic acid (VPA) was associated with reduced HDAC expression and a profound reduction of DNMT1 protein level. Treatment of transformed bronchial epithelial cells with VPA resulted in reduced colony formation, demethylation of the aberrantly methylated SFRP2 promoter, and derepression of SFRP2 transcription. These data suggest that inhibition of HDAC activity may reverse or prevent carcinogen-induced transformation. Finally, immunohistochemistry on human lung cancer specimens revealed a significant increase in DNMT1, HDAC1, HDAC2, and HDAC3 expression, supporting our hypotheses that class I HDACs are mediators of DNMT1 stability. In summary, our study provides evidence for an important role of class I HDACs in controlling the stability of DNMT1 and suggests that HDAC inhibition could be an attractive approach for lung cancer chemoprevention.

DNA methylation: new therapeutic implications for hepatic fibrosis

DNA methylation refers to a heritable alteration in the pattern of gene expression that is regulated by a mechanism specifically not owing to changes in the primary nucleotide sequence. The transcriptional silencing caused by DNA methylation affects genes involved in the main cellular pathways: cell cycle control, Ras signaling, apoptosis, and detoxification. Recent studies have shown that methylation modifications orchestrate the activation of hepatic stellate cells (HSCs) characterized by excessive accumulation of extracellular matrices (ECMs). The activation of HSCs is mediated by multiple signal transduction pathways and is generally regarded as the major ECM producer responsible for liver fibrosis. In addition, aberrant methylation of specific gene involved in the activation of multiple signal transduction pathways in liver fibrosis. The aim of this review is to compile recent information on aberrant DNA methylation in hepatic fibrosis and to highlight key genes and molecular pathways in hepatic fibrosis formation.

Effects of DNMT1 silencing on malignant phenotype and methylated gene expression in cervical cancer cells

Background

DNA methylation has been widely used in classification, early diagnosis, therapy and prediction of metastasis as well as recurrence of cervical cancer. DNMT methyltransferase 1 (DNMT1), which plays a significant role in maintaining DNA methylation status and regulating the expression of tumor suppressor genes. The aim of this research was to investigate the relationship between DNMT1 and abnormal methylation of tumor suppressor genes and malignant phenotype in cervical cancer.

Methods

Levels of DNMT1 mRNA and protein were detected using qPCR and Western blot, respectively. Cell proliferation was analyzed by MTT and apoptosis was performed by Annexin V-FITC/PI double staining flow cytometry, respectively. MeDIP-qPCR and qPCR were performed to measure demethylation status and mRNA re-expression level of 7 tumor-suppressor genes (CCNA1, CHFR, FHIT, PAX1, PTEN, SFRP4, TSLC1) in Hela and Siha cells after silencing DNMT1.

Results

The average expression levels of DNMT1 mRNA and protein in Hela and Siha cells were decreased significantly compared with control group. The flow cytometry and MTT results showed that Hela and Siha cells apoptosis rates and cell viabilities were 19.4 ± 2.90%, 25.7 ± 3.92% as well as 86.7 ± 3.12%, 84.16 ± 2.67% respectively 48 h after transfection (P < 0.01). Furthermore, the promoter methylation of five tumor suppressor genes was decreased with the increased mRNA expression after silencing DNMT1, whereas there were no significant changes in PTEN and FHIT genes in Hela cells, and CHFR and FHIT genes in Siha cells.

Conclusions

Our experimental results demonstrate that methylation status of DNMT1 can influence several important tumor suppressor genes activity in cervical tumorigenesis and may have the potential to become an effective target for treatment of cervical cancer.

Epigenetic therapeutics in autoimmune disease

Several lines of evidence suggest the involvement of disturbance in epigenetic processes in autoimmune disease. Most noteworthy is the global DNA hypomethylation seen in lupus. Epigenetic states in difference from genetic lesions are potentially reversible and hence candidates for pharmacological intervention. Potential targets for drug development are histone modification and DNA methylating and demethylating enzymes. The most advanced set of drugs in clinical development are histone deacetylase (HDAC) inhibitors. However, the prevalence of DNA hypomethylation in lupus suggests that we should shift our attention from HDAC inhibitors to DNA demethylation inhibitors. MBD2 was recently proposed to be involved in demethylation in T cells in lupus and is, therefore, a candidate target. Although this field is at its infancy, it carries great promise.

The epigenetics of suicide: explaining the biological effects of early life environmental adversity

A number of recent studies have shown epigenetic alterations associated with suicidal behavior. These epigenetic mechanisms, which alter gene expression via alternative mechanisms to the coding DNA sequence, result from environmental effects acting on the genome. Studies in rodents indicate that variation in the early environment will trigger these epigenetic modifications and recent human data suggest the same may be true in humans.The expression of a number of genes, which are involved in normal brain functions and that have been shown to be under epigenetic control, seem to be dysregulated in suicide. The present review briefly describes the main epigenetic mechanisms involved in the regulation of gene expression and discusses recent findings of epigenetic alterations in suicidal behavior.

Promoter polymorphisms of DNMT3B and the risk of head and neck squamous cell carcinoma in Taiwan: a case-control study

Three single nucleotide polymorphisms (SNPs) of the DNMT3B promoter region, C46359T (-149C>T), -283T>C, and -579G>T might be a cancer susceptible factor for several cancers. In this study, we genotyped 226 head-and-neck squamous-cell carcinoma (HNSCC) patients and 249 controls to examine the association between three SNPs of the DNMT3B promoter and the associated risk of the development and/or metastasizing tendency of HNSCC for the population of Taiwan. We observed that only the T/T genotype (C46359T) was found to be present in both patient and control groups (100% frequency). The alleles frequency of -283CC, -283CT and -283TT among patients and controls was, respectively, 88.1% versus 84.3%, 11.9% versus 15.3%, and 0% versus 0.4%. The allele -597GG was not found in both groups, whereas the allele frequency of -597TT and -597GT for patients and controls was, respectively, 88.1% versus 85.5%, and 11.9% versus 14.5%. For both DNMT3B SNPs, inter-group comparison of the allele frequency between patients and controls and distribution of SNPs among cancer patients either featuring or not featuring cervical metastasis did not reveal any significant difference. In conclusion, the relative distribution of three DNMT3B SNPs among a Taiwanese population can not be used as a stratification marker to predict either an individual's susceptibility to HNSCC and/or the likelihood of cervical metastasis of HNSCC.

DNA methyltransferase 1 knockdown activates a replication stress checkpoint

DNA methyltransferase 1 (DNMT1) is an important component of the epigenetic machinery and is responsible for copying DNA methylation patterns during cell division. Coordination of DNA methylation and DNA replication is critical for maintaining epigenetic programming. Knockdown of DNMT1 leads to inhibition of DNA replication, but the mechanism has been unclear. Here we show that depletion of DNMT1 with either antisense or small interfering RNA (siRNA) specific to DNMT1 activates a cascade of genotoxic stress checkpoint proteins, resulting in phosphorylation of checkpoint kinases 1 and 2 (Chk1 and -2), gammaH2AX focus formation, and cell division control protein 25a (CDC25a) degradation, in an ataxia telangiectasia mutated-Rad3-related (ATR)-dependent manner. siRNA knockdown of ATR blocks the response to DNMT1 depletion; DNA synthesis continues in the absence of DNMT1, resulting in global hypomethylation. Similarly, the response to DNMT1 knockdown is significantly attenuated in human mutant ATR fibroblast cells from a Seckel syndrome patient. This response is sensitive to DNMT1 depletion, independent of the catalytic domain of DNMT1, as indicated by abolition of the response with ectopic expression of either DNMT1 or DNMT1 with the catalytic domain deleted. There is no response to short-term treatment with 5-aza-deoxycytidine (5-aza-CdR), which causes demethylation by trapping DNMT1 in 5-aza-CdR-containing DNA but does not cause disappearance of DNMT1 from the nucleus. Our data are consistent with the hypothesis that removal of DNMT1 from replication forks is the trigger for this response.

The methyl donor S-Adenosylmethionine inhibits active demethylation of DNA: a candidate novel mechanism for the pharmacological effects of S-Adenosylmethionine

S-Adenosylmethionine (AdoMet) is the methyl donor of numerous methylation reactions. The current model is that an increased concentration of AdoMet stimulates DNA methyltransferase reactions, triggering hypermethylation and protecting the genome against global hypomethylation, a hallmark of cancer. Using an assay of active demethylation in HEK 293 cells, we show that AdoMet inhibits active demethylation and expression of an ectopically methylated CMV-GFP (green fluorescent protein) plasmid in a dose-dependent manner. The inhibition of GFP expression is specific to methylated GFP; AdoMet does not inhibit an identical but unmethylated CMV-GFP plasmid. S-Adenosylhomocysteine (AdoHcy), the product of methyltransferase reactions utilizing AdoMet does not inhibit demethylation or expression of CMV-GFP. In vitro, AdoMet but not AdoHcy inhibits methylated DNA-binding protein 2/DNA demethylase as well as endogenous demethylase activity extracted from HEK 293, suggesting that AdoMet directly inhibits demethylase activity, and that the methyl residue on AdoMet is required for its interaction with demethylase. Taken together, our data support an alternative mechanism of action for AdoMet as an inhibitor of intracellular demethylase activity, which results in hypermethylation of DNA.

Epigenomic stress response. Knockdown of DNA methyltransferase 1 triggers an intra-S-phase arrest of DNA replication and induction of stress response genes

The DNA methylation pattern is an important component of the epigenome that regulates and maintains gene expression programs. In this paper, we test the hypothesis that vertebrate cells possess mechanisms protecting them from epigenomic stress similar to DNA damage checkpoints. We show that knockdown of DNMT1 (DNA methyltransferase 1) by an antisense oligonucleotide triggers an intra-S-phase arrest of DNA replication that is not observed with control oligonucleotide. The cells are arrested at different positions throughout the S-phase of the cell cycle, suggesting that this response is not specific to distinct classes of origins of replication. The intra-S-phase arrest of DNA replication is proposed to protect the genome from extensive DNA demethylation that could come about by replication in the absence of DNMT1. This protective mechanism is not induced by 5-aza-2'-deoxycytidine, a nucleoside analog that inhibits DNA methylation by trapping DNMT1 in the progressing replication fork, but does not reduce de novo synthesis of DNMT1. Our data therefore suggest that the intra-S-phase arrest is triggered by a reduction in DNMT1 and not by demethylation of DNA. DNMT1 knockdown also leads to an induction of a set of genes that are implicated in genotoxic stress response such as NF-kappaB, JunB, ATF-3, and GADD45beta (growth arrest DNA damage 45beta gene). Based on these data, we suggest that this stress response mechanism evolved to guard against buildup of DNA methylation errors and to coordinate inheritance of genomic and epigenomic information.

Regulation of DNA methylation in human breast cancer. Effect on the urokinase-type plasminogen activator gene production and tumor invasion

Urokinase-type plasminogen activator (uPA) is a member of the serine protease family and can break down various components of the extracellular matrix to promote growth, invasion, and metastasis of several malignancies including breast cancer. In the current study we examined the role that the DNA methylation machinery might be playing in regulating differential uPA gene expression in breast cancer cell lines. uPA mRNA is expressed in the highly invasive, hormone-insensitive human breast cancer cell line MDA-MB-231 but not in hormone-responsive cell line MCF-7. Using methylation-sensitive PCR, we show that 90% of CpG dinucleotides in the uPA promoter are methylated in MCF-7 cells, whereas fully demethylated CpGs were detected in MDA-MB-231 cells. uPA promoter activity, which is directly regulated by the Ets-1 transcription factor, is inhibited by methylation as determined by uPA promoter-luciferase reporter assays. We then tested whether the state of expression and methylation of the uPA promoter correlates with the global level of DNA methyltransferase and demethylase activities in these cell lines. We show that maintenance DNA methyltransferase activity is significantly higher in MCF-7 cells than in MDA-MB-231 cells, whereas demethylase activity is higher in MDA-MB-231 cells. We suggest that the combination of increased DNA methyltransferase activity with reduced demethylase activity contributes to the methylation and silencing of uPA expression in MCF-7 cells. The converse is true in MDA-MB-231 cells, which represents a late stage highly invasive breast cancer. The histone deacetylase inhibitor, Trichostatin A, induces the expression of the uPA gene in MDA-MB-231 cells but not in MCF-7 cells. This supports the hypothesis that DNA methylation is the dominant mechanism involved in the silencing of uPA gene expression. Taken together, these results provide insight into the mechanism regulating the transcription of the uPA gene in the complex multistep process of breast cancer progression.

Senescence and epigenetic dysregulation in cancer

Mammalian cells have a finite proliferative lifespan, at the end of which they are unable to enter S phase in response to mitogenic stimuli. They undergo morphological changes and synthesize an altered repertoire of cell type-specific proteins. This non-proliferative state is termed replicative senescence and is regarded as a major tumor suppressor mechanism. The ability to overcome senescence and obtain a limitless replicative potential is called immortalization, and considered to be one of the prerequisites of cancer formation. While senescence mainly represents a genetically governed process, epigenetic changes in cancer have received increasing attention as an alternative mechanism for mediating gene expression changes in transformed cells. DNA methylation of promoter-containing CpG islands has emerged as an epigenetic mechanism of silencing tumor suppressor genes. New insights are being gained into the mechanisms causing aberrant methylation in cancer and evidence suggests that aging is accompanied by accumulation of cells with aberrant CpG island methylation. Aberrant methylation may contribute to many of the physiological and pathological changes associated with aging including tumor development. Finally, we describe how genes involved in promoting longevity might inhibit pathways promoting tumorigenesis.

Utilization of antisense oligonucleotides to study the role of 5-cytosine DNA methyltransferase in cellular transformation and oncogenesis

A large body of data point toward 5-cytosine DNA methyltransferase 1 (DNMT1) as a critical component of oncogenic programs. The study of the role of DNMT1 in cancer has been hindered by the lack of specific inhibitors. A different approach to study the role of DNMT1 in cancer is to use sequence-specific antisense oligonucleotides against DNMT1 mRNA. This paper discusses methods used to identify sequence-specific antisense oligonucleotides and to assess their DNA methylation inhibitory properties. Antisense oligonucleotides are applied to determine whether DNMT1 plays a causal role in specific cancer models ex vivo as well as in vivo.