lncRNA Maternally Expressed Gene 3 Research Articles

Long non-coding RNA MEG3 functions as a competing endogenous RNA to regulate gastric cancer progression.

BackgroundLong noncoding RNAs (lncRNAs) have recently emerged as important regulators in governing fundamental biological processes, and many of which are likely to have functional roles in tumorigenesis. Maternally expressed gene 3 (MEG3) gene encodes a lncRNA whose expression is lost in an expanding list of primary human tumors and tumor cell lines, however its biological role and regulatory mechanism in gastric cancer (GC) development and progression are poorly defined.MethodsQuantitative RT-PCR analysis was used to determine whether aberrant MEG3 expression was associated with GC patients pTNM stage and pM state. Furthermore, the effect of ectopic expression of MEG3 on cell proliferation, migration, invasion and cell apoptosis was assessed by using CCK-8, wound healing, transwell invasion assays and flow cytometric analysis, respectively, in GC cell lines HGC-27 and MGC-803. Moreover, the competing endogenous RNA (ceRNA) activity of MEG3 on miR-181a was investigated via luciferase reporter assay and immunoblot analysis.ResultsMEG3 is decreased in GC patients and cell lines, and its expression was associated with metastatic GC. Furthermore, ectopic expression of MEG3 in HGC-27 and MGC-803 cells inhibited cell proliferation, migration, invasion, and promoted cell apoptosis, which might be due to MEG3 sequestering oncogenic miR-181 s in GC cells. Furthermore, MEG3 could up-regulated Bcl-2 via its competing endogenous RNA (ceRNA) activity on miR-181a.ConclusionsThese findings suggest that lncRNA MEG3, a ceRNA of miR-181 s, could regulate gastric carcinogenesis and may serve as a potential target for antineoplastic therapies.

Identification of lncRNA MEG3 Binding Protein Using MS2-Tagged RNA Affinity Purification and Mass Spectrometry.

Long noncoding RNAs (lncRNAs) are nonprotein coding transcripts longer than 200 nucleotides. Recently in mammals, thousands of long noncoding RNAs have been identified and studied as key molecular players in different biological processes with protein complexes. As a long noncoding RNA, maternally expressed gene 3 (MEG3) plays an important role in many cellular processes. However, the mechanism underlying MEG3 regulatory effects remains enigmatic. By using the specific interaction between MS2 coat protein and MS2 RNA hairpin, we developed a method (MS2-tagged RNA affinity purification and mass spectrometry (MTRAP-MS)) to identify proteins that interact with MEG3. Mass spectrometry and gene ontology (GO) analysis showed that MEG3 binding proteins possess nucleotide binding properties and take part in transport, translation, and other biological processes. In addition, interleukin enhancer binding factor 3 (ILF3) and poly(A) binding protein, cytoplasmic 3 (PABPC3) were validated for their interaction with MEG3. These findings indicate that the newly developed method can effectively enrich lncRNA binding proteins and provides a strong basis for studying MEG3 functions.

Down-regulated long non-coding RNA MEG3 and its effect on promoting apoptosis and suppressing migration of trophoblast cells.

Preeclampsia is characterized by hypertension and proteinuria twenty weeks into pregnancy. Failure of uterine spiral artery remodeling contributes to preeclampsia's development. The development might be associated with trophoblast cells functioning abnormally. Long non-coding RNAs (lncRNAs) are aberrantly expressed in many diseases. Maternally expressed gene 3 (MEG3), one of these lncRNAs, might function as a tumor suppressor. Aberrant expression of MEG3 induces prenatal death, and little is known of MEG3's role in preeclampsia. This study aims to identify the role of lncRNA MEG3 on apoptosis and the migration of human trophoblast cells, and to investigate the involvement of lncRNA MEG3 in pathogenic mechanisms underlying preeclampsia. In this study, we found MEG3 levels were down-regulated by approximately 80% in placental samples collected from preeclamptic patients (n = 30) compared to samples collected from normotensive patients (n = 30) by qRT-PCR analysis. By designing RNA interference species to suppress MEG3 and specific plasmids designed to over-express MEG3, we explored the role of MEG3 on the functions of two trophoblast cell-lines, HTR-8/SVneo and JEG3 cells. Over-expression of MEG3 reduced apoptosis and promoted migration of HTR-8/SVneo and JEG3 cells. Furthermore, inhibition of endogenous MEG3 increased apoptosis and decreased migration of HTR-8/SVneo and JEG3 cells. Additionally, lncRNA MEG3 influenced expression of NF-κB, Caspase-3, and Bax protein expressions in trophoblast cells. Our findings highlight that abnormal levels of lncRNA MEG3 might lead to aberrant conditions in HTR-8/SVneo and JEG3 trophoblast cells, which might be associated with uterine spiral artery remodeling failure and its contribution to preeclampsia.

Downregulated long noncoding RNA MEG3 is associated with poor prognosis and promotes cell proliferation in gastric cancer

Long noncoding RNAs (lncRNAs) have emerged recently as major players in governing fundamental biological processes, and many of which are altered in expression and likely to have a functional role in tumorigenesis. Maternally expressed gene 3 (MEG3) is an imprinted gene located at 14q32 that encodes a lncRNA associated with various human cancers. However, its biological role and clinical significance in gastric cancer development and progression are unknown. In this study, to investigate the lncRNA MEG3 expression in gastric cancer, quantitative reverse-transcription polymerase chain reaction was conducted. We found that MEG3 levels were markedly decreased in gastric cancer tissues compared with adjacent normal tissues. Its expression level was significantly correlated with TNM stages, depth of invasion, and tumor size. Moreover, patients with low levels of MEG3 expression had a relatively poor prognosis. Furthermore, knockdown of MEG3 expression by siRNA could promote cell proliferation, while ectopic expression of MEG3 inhibited cell proliferation, promoted cell apoptosis, and modulated p53 expression in gastric cancer cell lines. By 5-aza-CdR treatment, we also observed that MEG3 expression can be modulated by DNA methylation. Our findings present that MEG3 downexpression can be identified as a poor prognostic biomarker in gastric cancer and regulate cell proliferation and apoptosis in vitro.

MicroRNA-29 can regulate expression of the long non-coding RNA gene MEG3 in hepatocellular cancer

The human genome is replete with long non-coding RNAs (lncRNA), many of which are transcribed and likely to have a functional role. Microarray analysis of >23,000 lncRNAs revealed downregulation of 712 (~3%) lncRNA in malignant hepatocytes, among which maternally expressed gene 3 (MEG3) was downregulated by 210-fold relative to expression in non-malignant hepatocytes. MEG3 expression was markedly reduced in four human hepatocellular cancer (HCC) cell lines compared with normal hepatocytes by real-time PCR. RNA in situ hybridization showed intense cytoplasmic expression of MEG3 in non-neoplastic liver with absent or very weak expression in HCC tissues. Enforced expression of MEG3 in HCC cells significantly decreased both anchorage-dependent and -independent cell growth, and induced apoptosis. MEG3 promoter hypermethylation was identified by methylation-specific PCR and MEG3 expression was increased with inhibition of methylation with either 5-Aza-2-Deoxycytidine, or siRNA to DNA Methyltransferase (DNMT) 1 and 3b in HCC cells. MiRNA-dependent regulation of MEG3 expression was studied by evaluating the involvement of miR-29, which can modulate DNMT 1 and 3. Overexpression of mir-29a increased expression of MEG3. GTL2, the murine homolog of MEG3, was reduced in liver tissues from hepatocyte-specific miR-29a/b1 knock-out mice compared with wild-type controls. These data show that methylation-dependent tissue-specific regulation of the lncRNA MEG3 by miR-29a may contribute to HCC growth and highlight the inter-relationship between two classes of non-coding RNA, miRNAs and lncRNAs, and epigenetic regulation of gene expression.