hMLH1 promoter methylation and silencing in primary endometrial cancers are associated with specific alterations in MBDs occupancy and histone modifications

Research Progress of DNA Methylation Markers for Endometrial Carcinoma Diagnosis

Endometrial carcinoma (EC) is the most common malignancies of the female reproductive system in developed countries and areas. Ultrasound-guided and hysteroscopic samplings are commonly used to diagnose EC. However, clinicians question their diagnostic efficacy and the associated patient discomfort. DNA methylation is the widely studied epigenetic alteration in human tumors, and tumor screening and diagnosis. This review summarized common methods for collecting clinical samples for methylation testing. Furthermore, we analyzed the diagnostic evaluation indices of different methylation marker assays in clinical diagnosis and discussed the challenges of methylation testing in the future application of EC diagnosis.

Shining a spotlight on m6A and the vital role of RNA modification in endometrial cancer: a review

RNA modifications are mostly dynamically reversible post-transcriptional modifications, of which m6A is the most prevalent in eukaryotic mRNAs. A growing number of studies indicate that RNA modification can finely tune gene expression and modulate RNA metabolic homeostasis, which in turn affects the self-renewal, proliferation, apoptosis, migration, and invasion of tumor cells. Endometrial carcinoma (EC) is the most common gynecologic tumor in developed countries. Although it can be diagnosed early in the onset and have a preferable prognosis, some cases might develop and become metastatic or recurrent, with a worse prognosis. Fortunately, immunotherapy and targeted therapy are promising methods of treating endometrial cancer patients. Gene modifications may also contribute to these treatments, as is especially the case with recent developments of new targeted therapeutic genes and diagnostic biomarkers for EC, even though current findings on the relationship between RNA modification and EC are still very limited, especially m6A. For example, what is the elaborate mechanism by which RNA modification affects EC progression? Taking m6A modification as an example, what is the conversion mode of methylation and demethylation for RNAs, and how to achieve selective recognition of specific RNA? Understanding how they cope with various stimuli as part of in vivo and in vitro biological development, disease or tumor occurrence and development, and other processes is valuable and RNA modifications provide a distinctive insight into genetic information. The roles of these processes in coping with various stimuli, biological development, disease, or tumor development in vivo and in vitro are self-evident and may become a new direction for cancer in the future. In this review, we summarize the category, characteristics, and therapeutic precis of RNA modification, m6A in particular, with the purpose of seeking the systematic regulation axis related to RNA modification to provide a better solution for the treatment of EC.

Research Progress of DNA Methylation in Endometrial Cancer

Endometrial cancer (EC)) is one of the most common malignant tumors of the female genital system, with an increasing incidence and mortality, worldwide. Although the therapeutic strategy of EC is still complicated and challenging, further understanding of carcinogenesis from a gene perspective would allow an effort to improve therapeutic precision in this complex malignancy. DNA methylation is the most widely studied epigenetic alteration in human tumors. Aberrant DNA methylation events, resulting in altered gene expression, are features of many tumor types. In this review, we provide an update on evidence about the roles of aberrant DNA methylation within some classical tumor suppressor genes and oncogenes in endometrial carcinogenesis, and report on recent advances in the understanding of the contribution of aberrant DNA methylation to EC, as well as opportunities and challenges of DNA methylation in EC management and prevention.

Epigenetics in endometrial carcinogenesis - part 1: DNA methylation

Carcinogenesis is a multistep multifactorial process that involves the accumulation of genetic and epigenetic alterations. In the past two decades, there has been an exponential growth of knowledge establishing the importance of epigenetic changes in cancer. Our work focused on reviewing the main role of epigenetics in the pathogenesis of endometrial carcinoma, highlighting the reported results concerning each epigenetic mechanistic layer. The present review is the first part of this work, in which we examined the contribution of DNA methylation alterations for endometrial carcinogenesis.

MBD2 as a novel marker associated with poor survival of patients with hepatocellular carcinoma after hepatic resection

Methyl-CpG binding domain 2 (MBD2) leads to the silencing of methylated genes in cancer cells and was implicated in the activation of prometastatic genes in hepatocellular carcinoma (HCC). The present study aimed to investigate the expression status of MBD2 in HCC and the correlation with surgical outcomes. The correlation between clinical prognostic factors and MBD2 were also evaluated. MBD2 expression was analyzed by western blotting in 20 paired HCC and paratumor liver (PTL) tissues. In addition, immunohistochemistry was performed on the 159 HCC samples following hepatic resection performed between January 2003 and October 2008. The correlation between clinicopathological factors and MBD2 expression was also evaluated by statistical analysis to determine the prognostic value of MBD2 expression in HCC. Postoperative prognostic factors were evaluated using univariate and multivariate analyses. Compared with PTL tissues, MBD2 expression was shown to be upregulated in 10 of the 20 HCC tissues (50%) by western blotting. The immunohistochemistry data indicated significant increase of the MBD2 expression level in 81 cases (50.94%) compared with the PTL tissues (0/159, 0%, P<0.001). The upregulated MBD2 expression in HCC tissues was correlated with BCLC stage B, tumor size >5 cm and microscopic vascular invasion. Multivariate analysis revealed that MBD2 was an independent prognostic factor for overall survival [HR, 2.089; P=0.001] and disease-free survival (HR, 1.601; P=0.022). In conclusion, MBD2 expression was elevated in HCC tissue, which suggesting MBD2 as a candidate prognostic marker of HCC.

Detection of endometrial cancer via molecular analysis of DNA collected with vaginal tampons

OBJECTIVE

We demonstrate the feasibility of detecting EC by combining minimally-invasive specimen collection techniques with sensitive molecular testing.

METHODS

Prior to hysterectomy for EC or benign indications, women collected vaginal pool samples with intravaginal tampons and underwent endometrial brushing. Specimens underwent pyrosequencing for DNA methylation of genes reported to be hypermethylated in gynecologic cancers and recently identified markers discovered by profiling over 200 ECs. Methylation was evaluated individually across CpGs and averaged across genes. Differences between EC and benign endometrium (BE) were assessed using two-sample t-tests and area under the curve (AUC).

RESULTS

Thirty-eight ECs and 28 BEs were included. We evaluated 97 CpGs within 12 genes, including previously reported markers (RASSF1, HSP2A, HOXA9, CDH13, HAAO, and GTF2A1) and those identified in discovery work (ASCL2, HTR1B, NPY, HS3ST2, MME, ADCYAP1, and additional CDH13 CpG sites). Mean methylation was higher in tampon specimens from EC v. BE for 9 of 12 genes (ADCYAP1, ASCL2, CDH13, HS3ST2, HTR1B, MME, HAAO, HOXA9, and RASSF1) (all p<0.05). Among these genes, relative hypermethylation was observed in EC v. BE across CpGs. Endometrial brush and tampon results were similar. Within tampon specimens, AUC was highest for HTR1B (0.82), RASSF1 (0.75), and HOXA9 (0.74). This is the first report of HOXA9 hypermethylation in EC.

CONCLUSION

DNA hypermethylation in EC tissues can also be identified in vaginal pool DNA collected via intravaginal tampon. Identification of additional EC biomarkers and refined collection methods are needed to develop an early detection tool for EC.

Estrogen and estrogen receptor induce matrix metalloproteinase-26 expression in endometrial carcinoma cells

The human matrix metalloproteinase (MMP)-26, also called matrilysin-2 or endometase, has been isolated as a matrilysin (MMP-7) homolog. Several reports describe that MMP-26 may be related to the development of endometrial carcinomas. Total RNAs were isolated from 51 normal endometrial tissue samples, 6 endometrial hyperplasia tissue samples and 30 endometrial carcinomas. Real-time reverse transcription-polymerase chain reaction (RT-PCR) was performed to evaluate MMP-26 mRNA expression levels. We examined the effect of estrogen and its receptor (ER) on MMP-26 expression in endometrial carcinoma cell lines by real-time RT-PCR, western blot analysis and luciferase assays. To examine protein-DNA binding between ER and MMP-26 promoter, we performed chromatin immunoprecipitation (ChIP) assay. Real-time RT-PCR analysis revealed that MMP-26 mRNA expression was significantly higher in the normal human endometria and hyperplasias compared with that in endometrial carcinomas. Estrogen not only transactivated the MMP-26 promoter activity but also enhanced endogenous MMP-26 expression. The MMP-26 promoter region contains a putative ER response element (ERE). Nuclear ER protein interacted with ERE on the MMP-26 promoter by ChIP assay. We found a significant difference in MMP-26 expression in normal and malignant endometrial tissue samples and that estrogen induced MMP-26 expression. Estrogen may induce endometrial hyperplasia but not endometrial carcinoma. Our results provide evidence that regulation of MMP-26 promoter activity by estrogen may represent a mechanism for endometrial carcinogenesis.

TSA suppresses miR-106b-93-25 cluster expression through downregulation of MYC and inhibits proliferation and induces apoptosis in human EMC

Histone deacetylase (HDAC) inhibitors are emerging as a novel class of anti-tumor agents and have manifested the ability to decrease proliferation and increase apoptosis in different cancer cells. A significant number of genes have been identified as potential effectors responsible for the anti-tumor function of HDAC inhibitor. However, the molecular mechanisms of these HDAC inhibitors in this process remain largely undefined. In the current study, we searched for microRNAs (miRs) that were affected by HDAC inhibitor trichostatin (TSA) and investigated their effects in endometrial cancer (EMC) cells. Our data showed that TSA significantly inhibited the growth of EMC cells and induced their apoptosis. Among the miRNAs that altered in the presence of TSA, the miR-106b-93-25 cluster, together with its host gene MCM7, were obviously down-regulated in EMC cells. p21 and BIM, which were identified as target genes of miR-106b-93-25 cluster, increased in TSA treated tumor cells and were responsible for cell cycle arrest and apoptosis. We further identified MYC as a regulator of miR-106b-93-25 cluster and demonstrated its down-regulation in the presence of TSA resulted in the reduction of miR-106b-93-25 cluster and up-regulation of p21 and BIM. More important, we found miR-106b-93-25 cluster was up-regulated in clinical EMC samples in association with the overexpression of MCM7 and MYC and the down-regulation of p21 and BIM. Thus our studies strongly indicated TSA inhibited EMC cell growth and induced cell apoptosis and cell cycle arrest at least partially through the down-regulation of the miR-106b-93-25 cluster and up-regulation of it's target genes p21 and BIM via MYC.

The endometrial epigenome and its response to steroid hormones

The human endometrium undergoes cyclic morphological and functional changes during the menstrual cycle. These changes are driven mainly by steroid hormones and orchestrated by a myriad of genes - many of which have been identified recently as being epigenetically regulated. Epigenetic modifications, including DNA methylation and histone acetylations, are shown recently to be involved in functional changes in endometrium and endometrial diseases. Since epigenetics itself is a rapidly evolving field, this review starts with an overview of epigenetics and its intrinsic connections with endometrial response to steroid hormones, highlighting its various levels of complexities. This is followed by a review of published and unpublished work on "writers", "erasers", and other players of endometrial epigenome. In the end, areas in need for future research in this area will be exposed.

Hypoxia-induced epigenetic regulation and silencing of the BRCA1 promoter

Disruption of the BRCA1 tumor suppressor can be caused not only by inherited mutations in familial cancers but also by BRCA1 gene silencing in sporadic cancers. Hypoxia, a key feature of the tumor microenvironment, has been shown to downregulate BRCA1 at the transcriptional level via repressive E2F4/p130 complexes. Here we showed that hypoxia also drives epigenetic modification of the BRCA1 promoter, with decreased H3K4 methylation as a key repressive modification produced by the lysine-specific histone demethylase LSD1. We also observed increased H3K9 methylation coupled with decreased H3K9 acetylation. Similar modifications were seen in the RAD51 promoter, which is also downregulated by hypoxia, whereas exactly opposite changes were seen in the promoter of the hypoxia-inducible gene VEGF. In cells containing the BRCA1 promoter driving a selectable HPRT gene, long-term silencing of the promoter was observed following exposure to hypoxic stress. Clones with silenced BRCA1 promoters were detected at frequencies of 2% or more following hypoxia, but at less than 6 × 10(-5) without hypoxia. The silenced clones showed decreased H3K4 methylation and decreased H3K9 acetylation in the BRCA1 promoters, consistent with the acute effects of hypoxic stress. Hypoxia-induced BRCA1 promoter silencing persisted in subsequent normoxic conditions but could be reversed by treatment with a histone deacetylase (HDAC) inhibitor but not with a DNA methylation inhibitor. Interestingly, treatment of cells with inhibitors of poly(ADP-ribose) polymerase (PARP) can cause short-term repression of BRCA1 expression, but such treatment does not produce H3K4 or H3K9 histone modification or BRCA1 promoter silencing. These results suggest that hypoxia is a driving force for long-term silencing of BRCA1, thereby promoting genome instability and tumor progression.

Modulation of histone methylation and MLH1 gene silencing by hexavalent chromium

Hexavalent chromium [Cr(VI)] is a mutagen and carcinogen, and occupational exposure can lead to lung cancers and other adverse health effects. Genetic changes resulting from DNA damage have been proposed as an important mechanism that mediates chromate's carcinogenicity. Here we show that chromate exposure of human lung A549 cells increased global levels of di- and tri-methylated histone H3 lysine 9 (H3K9) and lysine 4 (H3K4) but decreased the levels of tri-methylated histone H3 lysine 27 (H3K27) and di-methylated histone H3 arginine 2 (H3R2). Most interestingly, H3K9 dimethylation was enriched in the human MLH1 gene promoter following chromate exposure and this was correlated with decreased MLH1 mRNA expression. Chromate exposure increased the protein as well as mRNA levels of G9a a histone methyltransferase that specifically methylates H3K9. This Cr(VI)-induced increase in G9a may account for the global elevation of H3K9 dimethylation. Furthermore, supplementation with ascorbate, the primary reductant of Cr(VI) and also an essential cofactor for the histone demethylase activity, partially reversed the H3K9 dimethylation induced by chromate. Thus our studies suggest that Cr(VI) may target histone methyltransferases and demethylases, which in turn affect both global and gene promoter specific histone methylation, leading to the silencing of specific tumor suppressor genes such as MLH1.