Inactivation of Imprinted Genes Induced by Cellular Stress and Tumorigenesis

lncRNA MEG3 modified epithelial-mesenchymal transition of ovarian cancer cells by sponging miR-219a-5p and regulating EGFR

This study was aimed to verify whether there existed any associations between long noncoding RNA MEG3/miR-219a-5p/EGFR axis and the development of ovarian cancer (OC). As a whole, we gathered 317 pairs of OC tissues and surgical marginal normal tissues and simultaneously acquired four OC cell lines (ie, A2780, Caov-3, OVCAR-3, and SKOV-3) and human normal ovarian surface epithelial cell line. Moreover, pcDNA3.1-MEG3, si-MEG3, miR-219a-5p mimic, miR-219a-5p inhibitor, pcDNA3.1-EGFR, and si-EGFR were, respectively, transfected into the OC cells, and their impacts on viability, proliferation, apoptosis, invasion, and migration of OC cells were assessed via conduction of MTT assay, colony formation assay, flow cytometry assay, transwell assay, and scratch assay. Ultimately, dual-luciferase reporter gene assay was performed to testify the targeted relationships among maternally expressed gene 3 (MEG3), miR-219a-5p, and estimated glomerular filtration rate (EGFR). It was indicated that underexpressed MEG3 and miR-219a-5p were significantly associated with unfavorable prognosis of patients with OC when compared with overexpressed MEG3 and miR-219a-5p (P < .05). In addition, the OC cells transfected with si-MEG3 or miR-219a-5p inhibitor exhibited stronger viability, proliferation, invasion, and migration than untreated cells (P < .05). Correspondingly, the apoptotic percentage of OC cells was reduced observably under treatments of si-MEG3 and miR-219a-5p inhibitor (P < .05). Moreover, MEG3 exerted modulatory effects on the expression of miR-219a-5p (P < .05), and there was a sponging relationship between them (P < .05). Finally, EGFR expression was modified by both MEG3 and miR-219a-5p significantly (P < .05), and raising EGFR expression could changeover the impacts of MEG3 and miR-219a-5p on the above-mentioned activity of OC cells (P < .05). Conclusively, MEG3 could serve as a promising biomarker for diagnosis and treatment of OC, considering its involvement with OC etiology via regulation of miR-219a-5p/EGFR axis.

TET2 and MEG3 promoter methylation is associated with acute myeloid leukemia in a Hainan population

The promoter of MEG3, which encodes the long non-coding RNA (lncRNA) MEG3, is often hypermethylated in acute myeloid leukemia (AML). Additionally, the Tet methylcytosine dioxygenase 2 gene (TET2) is frequently inactivated, which can lead to impaired DNA methylation and promote AML development. We examined the association between TET2 and MEG3 promoter hypermethylation in Hainan patients with AML. The expression of MEG3, TET2, miR-22-3p, and miR-22-5p was assessed in bone marrow samples from AML patients and healthy controls using real-time quantitative PCR. Using Sequenom MassARRAY technology, we compared MEG3 promoter methylation in AML patients and healthy controls. MEG3 expression was lower in AML patients than in the controls (P = 0.136). Moreover, there was greater methylation of MEG3 promoter in the AML patients than the controls (P < 0.05). Methylation of the MEG3 promoter correlated negatively with TET2 expression (P < 0.05, r < 0). Likewise there was a negative correlation between TET2 activity and MEG3 promoter methylation (P < 0.05, r < 0). These results suggest that hypermethylation of the MEG3 promoter in AML may result from decreased TET2 activity. These data provide insight into the molecular mechanisms underlying AML development and progression.

Integrative analysis reveals clinical phenotypes and oncogenic potentials of long non-coding RNAs across 15 cancer types

Long non-coding RNAs (lncRNAs) have been shown to contribute to tumorigenesis. However, surprisingly little is known about the comprehensive clinical and genomic characterization of lncRNAs across human cancer. In this study, we conducted comprehensive analyses for the expression profile, clinical outcomes, somatic copy number alterations (SCNAs) profile of lncRNAs in ~7000 clinical samples from 15 different cancer types. We identified significantly differentially expressed lncRNAs between tumor and normal tissues from each cancer. Notably, we characterized 47 lncRNAs which were extensively dysregulated in at least 10 cancer types, suggesting a conserved function in cancer development. We also analyzed the associations between lncRNA expressions and patient survival, and identified sets of lncRNAs that possessed significant prognostic values in specific cancer types. Our combined analysis of SCNA data and expression data uncovered 116 dysregulated lncRNAs are strikingly genomic altered across 15 cancer types, indicating their oncogenic potentials. Our study may lay the groundwork for future functional studies of lncRNAs and help facilitate the discovery of novel clinical biomarkers.

HOTTIP and HOXA13 are oncogenes associated with gastric cancer progression

A long non-coding RNA named HOTTIP (HOXA transcript at the distal tip) coordinates the activation of various 5' HOXA genes which encode master regulators of development through targeting the WDR5/MLL complex. HOTTIP acts as an oncogene in several types of cancers, whereas its biological function in gastric cancer has never been studied. In the present study, we investigated the role of HOTTIP in gastric cancer. We found that HOTTIP was upregulated in gastric cancer cell lines. Knockdown of HOTTIP in gastric cancer cells inhibited cell proliferation, migration and invasion. Moreover, downregulation of HOTTIP led to decreased expression of homeobox protein Hox-A13 (HOXA13) in gastric cancer cell lines. HOXA13 was involved in HOTTIP‑induced malignant phenotypes of gastric cancer cells. Our data showed that the levels of HOTTIP and HOXA13 were both markedly upregulated in gastric cancer tissues compared with their counterparts in non-tumorous tissues. Furthermore, the expression levels of HOTTIP and HOXA13 were both higher in gastric cancer which was poorly differentiated, at advanced TNM stages and exhibited lymph node-metastasis. Spearman analyses indicated that HOTTIP and HOXA13 had a highly positive correlation both in non-tumor mucosae and cancer lesions. Collectively, these findings suggest that HOTTIP and HOXA13 play important roles in gastric cancer progression and provide a new insight into therapeutic treatment for the disease.

Maternally expressed gene 3, an imprinted noncoding RNA gene, is associated with meningioma pathogenesis and progression

Meningiomas are common tumors, representing 15% to 25% of all central nervous system tumors. NF2 gene inactivation on chromosome 22 has been shown as an early event in tumorigenesis; however, few factors underlying tumor growth and progression have been identified. The chromosomal abnormalities of 14q32 are often associated with meningioma pathogenesis and progression; therefore, it has been proposed that an as yet unidentified tumor suppressor is present at this locus. Maternally expressed gene 3 (MEG3) is an imprinted gene located at 14q32 which encodes a noncoding RNA with an antiproliferative function. We found that MEG3 mRNA is highly expressed in normal arachnoidal cells. However, MEG3 is not expressed in the majority of human meningiomas or the human meningioma cell lines IOMM-Lee and CH157-MN. There is a strong association between loss of MEG3 expression and tumor grade. Allelic loss at the MEG3 locus is also observed in meningiomas, with increasing prevalence in higher grade tumors. In addition, there is an increase in CpG methylation within the promoter and the imprinting control region of MEG3 gene in meningiomas. Functionally, MEG3 suppresses DNA synthesis in both IOMM-Lee and CH157-MN cells by approximately 60% in bromodeoxyuridine incorporation assays. Colony-forming efficiency assays show that MEG3 inhibits colony formation in CH157-MN cells by approximately 80%. Furthermore, MEG3 stimulates p53-mediated transactivation in these cell lines. Therefore, these data are consistent with the hypothesis that MEG3, which encodes a noncoding RNA, may be a tumor suppressor gene at chromosome 14q32 involved in meningioma progression via a novel mechanism.

Colorectal cancer epigenetics: the role of environmental factors and the search for molecular biomarkers

This review presents an evenhanded evaluation of the role of epigenetics in the development of colorectal cancer, and investigates the extent of environmental influences on modulating this disease. Advances in our understanding of chromatin structure, histone modification, transcriptional activity and DNA methylation have lead to an integrated approach to the role of epigenetics in carcinogenesis. Epigenetic mechanisms appear to permit response of individuals to environment through change in gene expression and are involved in inactivating one of the two X chromosomes in women. Epigenetic changes play an important role in development and can also arise stochastically as individuals age. Because epigenetic alterations are potentially reversible, thereby allowing malignant cells to revert to the normal state, there is potential to develop effective strategies to prevent or even reverse this curable cancer. Moreover, because the methylation status of a specific sequence or the pattern of methylation across the genome can now be measured accurately, molecular biomarkers of screening, diagnosis, prognosis, prediction of treatment and those related to risk assessment can be developed using sophisticated molecular genetic technologies. Although in many cases a high sensitivity and specificity of the detection assays has been achieved, there still remains ample room for improvement in areas of sample preparation, assay design and marker selection.

Large-Scale CpG Methylation Analysis Identifies Novel Candidate Genes and Reveals Methylation Hotspots in Acute Lymphoblastic Leukemia

This study examined DNA methylation associated with acute lymphoblastic leukemia (ALL) and showed that selected molecular targets can be pharmacologically modulated to reverse gene silencing. A CpG island (CGI) microarray containing more than 3,400 unique clones that span all human chromosomes was used for large-scale discovery experiments and led to 262 unique CGI loci being statistically identified as methylated in ALL lymphoblasts. The methylation status of 10 clones encompassing 11 genes (DCC, DLC-1, DDX51, KCNK2, LRP1B, NKX6-1, NOPE, PCDHGA12, RPIB9, ABCB1, and SLC2A14) identified as differentially methylated between ALL patients and controls was independently verified. Consequently, the methylation status of DDX51 was found to differentiate patients with B- and T-ALL subtypes (P = 0.011, Fisher's exact test). Next, the relationship between methylation and expression of these genes was examined in ALL cell lines (NALM-6 and Jurkat) before and after treatments with 5-aza-2-deoxycytidine and trichostatin A. More than a 10-fold increase in mRNA expression was observed for two previously identified tumor suppressor genes (DLC-1 and DCC) and also for RPIB9 and PCDHGA12. Although the mechanisms that lead to the CGI methylation of these genes are unknown, bisulfite sequencing of the promoter of RPIB9 suggests that expression is inhibited by methylation within SP1 and AP2 transcription factor binding motifs. Finally, specific chromosomal methylation hotspots were found to be associated with ALL. This study sets the stage for acquiring a better biological understanding of ALL and for the identification of epigenetic biomarkers useful for differential diagnosis, therapeutic monitoring, and the detection of leukemic relapse.