Non-coding RNA Maternally Expressed Gene 3 Research Articles

Long non-coding RNA MEG3 functions as a competing endogenous RNA of miR-93 to regulate bladder cancer progression via PI3K/AKT/mTOR pathway.

BackgroundMaternally expressed gene 3 (MEG3) is a long non-coding RNA (lncRNA) and involved in progression of various human tumors. However, its underlying regulatory mechanism in tumorigenesis of bladder cancer (BC) remains unclear. To demonstrate effects of MEG3 on BC cell proliferation and elaborate its regulatory mechanism in BC.MethodsAberrant expressions of MEG3 and miR-93-5p were induced by cell transfection. The mRNA and protein expression were analyzed using qRT-PCR and western blot. Cell proliferation was examined by CCK-8 assay and EdU staining. The targeted regulation effect of MEG3 on miR-93-5p was confirmed by luciferase reporter assay. The number of LC3 punctated cells was detected by immunofluorescence. Xeno-graft mouse model was constructed for in vivo validation.ResultsMEG3 was down-regulated with increased expression of miR-93-5p in BC cells and tissues. Luciferase reporter assay showed that miR-93-5p was a direct target of MEG3 and was negatively regulated by MEG3. MEG3 overexpression inhibited cell proliferation and the expression of proliferation-, apoptosis- and autophagy-related proteins. The activation of PI3K/AKT/mTOR pathway was also suppressed with elevated cell apoptosis. miR-93-5p overexpression counteracted these results. In vivo experiments, we confirmed that miR-93-5p overexpression reversed the MEG3 overexpression-mediated suppression on tumor growth and protein expression.ConclusionslncRNA MEG3 could function as a competing endogenous RNA of miR-93 to regulate the tumorigenesis of BC via PI3K/AKT/mTOR pathway. The present research provided a new perspective to understanding the pathogenic mechanism of BC, and an effective therapeutic target for BC.

Effect of long non-coding RNA maternally expressed gene 3 on proliferation and invasion capacity of glioma cells through the Wnt/human-catenin signal pathway

Objective To investigate the effect of long non-coding RNA maternally expressed gene 3 (MEG3) on the proliferation and invasion capacity of glioma cells through the Wnt/human-catenin signal pathway. Methods Glioma cells were divided into 3 groups: the blank control group (CON), the gene transfection group (MEG3) and the gene inhibition group (siMEG3). The cells in blank group were left untreated and cultured normally. MEG3 gene was transfected in the gene transfection group, and gene interference was conducted in the gene inhibition group. Protein expression was determined by Western blotting, and gene expression was detected by real-time quantitative reverse transcriptase-polymerase chain reaction (RT-qPCR). Results After transfection of MEG3 gene, the apoptosis rate increased to 61.05±2.77 with the prolongation of culture time, which was higher than that of the control group and the gene inhibition group (F=23.543, P<0.05). After MEG3 gene knockout, the apoptosis rate of glioma cells was higher than that of the control group (P<0.05). After 48 hours of transfection, the number of cell migration was 105.36±15.27 (F=33.350, P<0.05). When MEG3 gene was inhibited, the number of cell migration was 989.41±11.06, higher than that of the control group (F=40.667, P<0.05). After MEG3 gene transfection, the number of invasion cells was 251.25±35.85, which was lower than that of the control group and gene knockout group (F=31.167, P<0.05). After MEG3 gene was knocked out, the number of invasion cells was 1 500.00± 84.76, which was higher than that of the blank control group (F=63.762, P<0.05). Compared with the gene inhibition group, the c-Jun gene of the control group and the gene transfection group decreased, and the gene transfection group was lower than the blank control group (F=15.426, P<0.05). Conclusion Long non-coding RNA MEG3 can inhibit the proliferation and invasion of glioma cells through the Wnt/human-catenin signal pathway. Key words: Glioma; Protein; Gene

Transthyretin Upregulates Long Non-Coding RNA MEG3 by Affecting PABPC1 in Diabetic Retinopathy.

The aim of the study was to demonstrate how transthyretin (TTR) could affect long non-coding RNA (lncRNA) of maternally expressed gene 3 (MEG3) and play important roles in diabetic retinopathy (DR). A DR model in C57BL/6 mice was established after intraperitoneal injection of streptozotocin (STZ). After intravitreal injection with TTR pAAV vector, MEG3 short hairpin RNA (shRNA), scrambled shRNA, or MEG3, retinal imaging, retinal trypsin digestion, and fundus vascular permeability tests were performed. Cell counting kit-8 (CCK8), transwell, and Matrigel assays were employed to detect the proliferation and migration of human retinal microvascular endothelial cells (hRECs). The binding between long non-coding RNA of maternally expressed gene 3 (lncRNA-MEG3) and microRNA-223-3p (miR-223-3p) was observed by using luciferase reporter assays, while co-immunoprecipitation (co-IP) was employed to confirm the interaction between TTR and the target. In the DR mice model, retinal vascular leakage and angiogenesis were repressed by overexpressing TTR. In vitro, the added TTR promoted the level of lncRNA-MEG3 by interacting with poly (A) binding protein cytoplasmic 1 (PABPC1), and then repressed proliferation and angiogenesis of hRECs. In vivo, silencing or overexpressing lncRNA-MEG3 significantly affected retinal vascular phenotypes. Additionally, the interaction between lncRNA-MEG3 and miR-223-3p was confirmed, and silencing of miR-223-3p revealed similar effects on hRECs as overexpression of lncRNA-MEG3. In summary, in the DR environment, TTR might affect the lncRNA MEG3/miR-223-3p axis by the direct binding with PABPC1, and finally repress retinal vessel proliferation.

Long non-coding RNA MEG3 promotes cerebral ischemia-reperfusion injury through increasing pyroptosis by targeting miR-485/AIM2 axis

ObjectiveInflammasome contributes to ischemic brain injury by inducing pyroptosis and inflammation. The aim of this study is to unravel the mechanism of long non-coding RNA (lncRNA) maternally expressed gene 3 (MEG3)-mediated regulation of absent in melanoma 2 (AIM2) inflammasome during cerebral ischemia/reperfusion (I/R). MethodsIn vivo middle cerebral artery occlusion (MCAO) rat model and in vitro oxygen-glucose deprivation/reperfusion (OGD/R)-treated neurocytes model were generated. TTC, H&E staining and TUNEL were performed to assess the cerebral ischemic injury. LDH and MTT assays were used to detect cell viability and cytotoxicity. qRT-PCR was used to detect the expression levels of MEG3, miR-485 and AIM2. Immunohistochemistry (IHC) and immunofluorescence were conducted to detect the AIM2 expression. ELISA and Western blotting were performed to determine the secretion and protein levels of inflammasome signaling proteins. Dual luciferase reporter assay and Ago2-RIP were used to validate the direct interaction among MEG3, miR-485 and AIM2. ResultsIn both MCAO rats and OGD/R-treated neurocytes, MEG3 and AIM2 were significantly up-regulated, whereas miR-485 was down-regulated. MCAO induces pyroptosis and release of IL-1β and IL-18 in ischemia brain. MEG3 acted as a molecular sponge to suppress miR-485, and AIM2 was identified as a direct target of miR-485. Knockdown of MEG3 inhibited OGD/R-induced pyroptosis and inflammation, and lack of MEG3 inhibited caspase1 signaling and decreased the expression of AIM2, ASC, cleaved-caspase1 and GSDMD-N. While overexpression of MEG3 exerted opposite effects. ConclusionMEG3/miR-485/AIM2 axis contributes to pyroptosis via activating caspase1 signaling during cerebral I/R, suggesting that this axis may be a potent therapeutic target in ischemic stroke.

Long noncoding RNA MEG3 suppresses podocyte injury in diabetic nephropathy by inactivating Wnt/β-catenin signaling.

BackgroundDiabetic nephropathy (DN) is one of the principal complications of diabetes and podocyte injury plays an important role in the DN pathogenesis. Wnt/β-catenin signaling overactivation confers podocyte injury and promotes multiple types of renal disease. However, the underlying mechanism of Wnt/β-catenin signaling activation in DN progression has not been fully elucidated. Long noncoding RNA (lncRNA) is a large class of endogenous RNA molecules lacking functional code capacity and which participates in the pathogenesis of human disease, including DN.MethodA diabetes model was constructed by intraperitoneal injection of Streptozotocin in rats. The MPC5 cells were used to create the in vitro model. Western blot and Quantitative reverse-transcriptase-PCR were used to examine the expression of protein and mRNA. The migrated capacity was analyzed by Transwell migration assay. The cell viability was detected by CCK8.ResultsIn the present study, we revealed the association of lncRNA Maternally Expressed Gene 3 (MEG3) with aberrant activation of Wnt/β-catenin signaling and the role of MEG3/Wnt axis in podocyte injury. We found that high glucose (HG) treatment suppressed MEG3 expression in cultured podocytes, activated Wnt/β-catenin signaling and caused podocyte injury as indicated by the downregulation of podocyte-specific markers (podocin and synaptopodin) and the upregulation of snail1 and α-smooth muscle actin. Overexpression of MEG3 attenuated HG-induced podocyte injury by reducing Wnt/β-catenin activity, repressing cell migration, reactive oxygen species production and increasing the viability of podocytes. Furthermore, we provided evidences that restoration of Wnt/β-catenin signaling by specific agonist impeded the protective effect of MEG3 on podocyte injury. Current results demonstrated that MEG3/Wnt axis plays an important role in fostering podocyte injury and may serve as a potential therapeutic target for the treatment of DN.ConclusionlncRNA MEG3 ameliorates podocyte injury in DN via inactivating Wnt/β-catenin signaling.

Long non-coding RNA MEG3 regulates CSE-induced apoptosis and inflammation via regulating miR-218 in 16HBE cells

Chronic obstructive pulmonary disease (COPD) is a prevalent disease worldwide, mainly caused by cigarette smoking. Maternally expressed gene 3 (MEG3) functions as the lncRNA and is upregulated in COPD patients and human bronchial epithelial cells after fine particulate matter (PM2.5) treatment. However, the molecular mechanism of MEG3 in COPD remains unknown. The expression of MEG3 and miR-218 in COPD tissues and cigarette smoke extract (CSE)-treated 16HBE cells was detected by RT-qPCR. The effects of MEG3 and miR-218 on proliferation and apoptosis in (CSE)-treated 16HBE cells were analyzed by CCK-8 and flow cytometry assay, respectively. The protein levels of inflammatory cytokines (IL-1β IL-6 and TNF-α) were detected in 16HBE cells by ELISA. MEG3 and miR-218 binding interaction was predicted by LncBase Predicted v.2 and further confirmed by dual luciferase reporter assay and RNA Immunoprecipitation (RIP) assay. MEG3 was upregulated in COPD tissues and inversely related to FEV1%. MEG3 was upregulated in (CSE)-treated 16HBE cells, and knockdown of MEG3 mitigated CSE-repressed proliferation and CSE-triggered apoptosis or inflammation. MiR-218 was demonstrated as a target miRNA of MEG3. MiR-218 was downregulated in COPD tissues and (CSE)-treated or MEG3 overexpressed 16HBE cells. MiR-218 overexpression attenuated CSE-blocked proliferation and CSE-induced apoptosis or inflammation. Deficiency of MEG3 counteracted CSE-blocked proliferation CSE-induced apoptotic rate and inflammatory cytokine (IL-1β IL-6 and TNF-α) levels, while introduction of anti-miR-218 reversed these effects. MEG3 regulated CSE-inhibited proliferation and CSE-induced apoptosis or inflammation by targeting miR-218, providing a possible therapeutic target for treatment of CSE-induced COPD.

Role of long non-coding RNA MEG3 in hyperglycose-induced neurocyte damage in rats: relationship with mitochondrion-dependent apoptosis

Objective To evaluate the role of long non-coding RNA maternally expressed gene 3 (MEG3) in hyperglycose-induced neurocyte damage and the relationship with mitochondrion-dependent apoptosis in rats. Methods Normally cultured PC12 cells were divided into 5 groups (n=18 each) using a random number table method: normal concentration of glucose control group (C group), normal concentration of glucose plus MEG3 group (C+ MEG3 group), high-concentration glucose group (HG group), high-concentration glucose plus MEG3 group(HG+ MEG3 group), and high-concentration glucose plus negative lentiviral vector (LV-NC) group (HG+ NC group). PC12 cells were cultured in DMEM medium with 25 mmol/L glucose in group C. PC12 cells were cultured in DMEM medium with 25 mmol/L glucose after being transfected with MEG3 lentiviral vector (LV-MEG3) in C+ MEG3 group.PC12 cells were cultured in DMEM medium with 250 mmol/L glucose in HG group.PC12 cells were incubated in DMEM medium containing 250 mmol/L glucose after being transfected with LV-MEG3 in HG+ MEG3 group.PC12 cells were incubated in DMEM medium containing 250 mmol/L glucose after being transfected with LV-NC in HG+ NC group.After the cells were cultured or incubated for 1 day, the cell viability was measured by CCK8 assay, the apoptosis rate and level of reactive oxygen species (ROS) were determined by flow cytometry, and the amount of lactic dehydrogenase (LDH) released was measured by DCFH-DA, the expression of Cyt c, caspase-3, caspase-9, Bcl-2, Bax and Apaf-1 was determined by Western blot, and the opening of mitochondrial permeability transition pore (mPTP) was determined by fluorescent method.Blc-2/Bax ratio was calculated. Results Compared with group C, the cell viability was significantly decreased, the amount of LDH released, ROS level and apoptosis rate were increased, the opening of mPTP was increased, and the expression of caspase-3, caspase-9, Cyt c, Bax, Bcl-2 and Apaf-1 was up-regulated in HG, HG+ MEG3 and HG+ NC groups, and Bcl-2/Bax ratio was increased in HG+ MEG3 group and decreased in HG and HG+ NC groups (P<0.05). Compared with HG group and HG+ NC group, the cell activity was significantly increased, the amount of LDH released, ROS level and apoptosis rate were decreased, the opening of mPTP was decreased, the expression of caspase-3, caspase-9, Cyt c, Bax, and Apaf-1 was down-regulated, the expression of Bcl-2 was up-regulated, and Bcl-2/Bax ratio was increased in HG+ MEG3 group (P<0.01). Conclusion MEG3 may be involved in the endogenous protective mechanism during hyperglycose-induced neurocyte damage by inhibiting mitochondrion-dependent apoptosis in rats. Key words: RNA, long noncoding; Diabetes mellitus; Neurons; Apoptosis

Long non-coding RNA MEG3 regulates migration and invasion of lung cancer stem cells via miR-650/SLC34A2 axis

Long non-coding RNA maternally expressed gene 3 (MEG3) is related to the occurrence and development of non-small cell lung cancer (NSCLC). However, the function and underlying molecular mechanisms of MEG3 in lung cancer stem cells (LCSCs) are still unclear. LCSCs were determined in lung cancer cells using fluorescence-activated cell sorting (FACS). qRT-PCR and western blot were performed to examine the expressions of MEG3, miR-650, solute carrier family 34 member 2 (SLC34A2), octamer-binding transcription factor 4 (Oct4), and CD133. Sphere assay was employed to evaluate sphere-forming ability. Cell migration and invasion were analyzed by Transwell assay. The relationships among MEG3, miR-650, and SLC34A2 were validated by luciferase reporter, RIP, and RNA pulldown assays. We found MEG3 was downregulated in LCSCs. MEG3 depletion strengthened stem cell-like characteristics and sphere-forming ability in LCCs. Upregulation of MEG3 suppressed migration and invasion in LCCs and LCSCs. miR-650 was bound to MEG3 and upregulated in LCSCs. miR-650 inhibitor alleviated si-MEG3-induced promotion of stem cell-like characteristics in lung cancer cells (LCCs) H1299. Furthermore, miR-650 mimic attenuated the MEG3 upregulation-mediated inhibition of migration and invasion. In addition, SLC34A2 was a target of miR-650 and downregulated in LCSCs. miR-650 mimic induced stem cell-like characteristics in LCCs, which was weakened by overexpression of SLC34A2. In contrast, the repression of SLC34A2 mitigated the miR-650 silencing-induced inhibition of migration and invasion in LCCs and LCSCs. Besides, MEG3 regulated SLC34A2 expression by sponging miR-650. Importantly, SLC34A2 weakened MEG3-mediated stem cell-like state and cell metastasis. Our data suggested MEG3 was involved in stem cell-like state of LCCs and curbed migration and invasion through miR-650/SLC34A2 axis in NSCLC.

Down-regulation of long non-coding RNA MEG3 suppresses osteogenic differentiation of periodontal ligament stem cells (PDLSCs) through miR-27a-3p/IGF1 axis in periodontitis.

Objective: This study aimed to investigate the roles of long noncoding RNA (lncRNA) maternally expressed gene 3 (MEG3) in osteogenic differentiation of periodontal ligament stem cells (PDLSCs) in periodontitis.Methods: Differentially expressed lncRNAs and mRNAs between periodontitis periodontal ligament tissues and healthy periodontal ligament tissues were selected out using R project. PDLSCs were identified using flow cytometry. Western blot was employed to detect pathway relative proteins. Besides, targeted relationships between lncRNA and miRNA, as well as miRNA and mRNA were verified by dual luciferase reporter gene assay. Osteogenic differentiation of PDLSCs was assessed by alkaline phosphatase (ALP) staining and Alizarin Red Staining (ARS). Markers for osteoblast (Runx2, Osterix, Osteocalcin, Colla1) were detected using western blot.Results: LncRNA MEG3 and IGF1 were both down-regulated, while miR-27a-3p was up-regulated in periodontitis samples compared with healthy samples. Overexpression of MEG3 promoted osteogenic differentiation by enhancing expression of IGF1 yet suppressing expression of miRNA-27a-3p. Meanwhile, the results of ALP and ARS staining indicated that up-regulation of lncRNA MEG3 or IGF1 promoted osteogenic differentiation in PDLSCs, which could be reversed with up-regulation of miRNA-27a-3p.Conclusion: Down-regulation of MEG3 suppressed osteogenic differentiation of PDLSCs through miR-27a-3p/IGF1 axis in periodontitis.

Long noncoding RNA MEG3 silencing protects against hypoxia-induced pheochromocytoma-12 cell injury through inhibition of TIMP2 promoter methylation.

Hypoxia is a common pathological process caused by insufficient oxygen. Long noncoding RNAs (lncRNAs) have been proven to participate in this pathology. Hypoxia is reported to significantly reduce the secretion of tissue inhibitor of metalloproteinase 2 (TIMP2) and TIMP2 induces pheochromocytoma-12 (PC12) cell cycle arrest. Thus, our study aimed to explore the mechanism by which lncRNA maternally expressed gene 3 (MEG3) was implicated in hypoxia-induced PC12 cell injury through TIMP2 promoter methylation. To elucidate the potential biological significance of MEG3 and the regulatory mechanism between MEG3 and TIMP2, a hypoxia-induced PC12 cell injury model was generated. The hypoxia-exposed cells were subjected to a series of overexpression plasmids and short hairpin RNAs, followed by the measurement of levels of MEG3, TIMP2, lactate dehydrogenase (LDH), malondialdehyde (MDA), superoxide dismutase (SOD), reactive oxygen species (ROS), Bcl-2-associated X protein, B-cell lymphoma-2, and caspase-3, as well as the changes in MMP, cell proliferation, apoptosis, and cell cycle progression. On the basis of the findings, MEG3 was upregulated in hypoxia-injured PC12 cells. MEG3 recruited methylation proteins DNMT3a, DNMT3b, and MBD1 and accelerated TIMP2 promoter methylation, which in turn inhibited its expression. Moreover, PC12 cells following MEG3 silencing and TIMP2 overexpression exhibited significantly decreased levels of LDH, MDA, and ROS along with cell apoptosis, yet increased SOD and MMP levels, as well as cell cycle entry to the S phase and cell proliferation. In conclusion, MEG3 silencing suppresses hypoxia-induced PC12 cell injury by inhibiting TIMP2 promoter methylation. This study may provide novel therapeutic targets for hypoxia-induced injury.

Long noncoding RNA MEG3 plays a promoting role in the proliferation, invasion, and angiogenesis of lung adenocarcinoma cells through the AKT pathway.

The role of long noncoding RNA maternally expressed gene 3 (MEG3) in lung adenocarcinoma has not been explored entirely. In this study, it was demonstrated that the expression of MEG3 was enhanced in lung adenocarcinoma tissues from TCGA database and some specific cell lines, while the survival analysis showed that patients with higher MEG3 levels had lower survival probabilities, which suggested that MEG3 might serve as a lung adenocarcinoma promoter. In addition, the results suggested that the overexpression of MEG3 could promote the proliferation and invasion of lung adenocarcinoma cells. Furthermore, increased MEG3 expression could result in a notable increase in angiogenesis-related factors as well as in the capillary tube formation of endothelial cells, which indicates that the overexpression of MEG3 could promote the angiogenesis of lung adenocarcinoma. From a mechanistic perspective, the results obtained revealed that the upregulation of MEG3 could stimulate the AKT signaling pathway and consequently lead to the biological behaviors mentioned above. In summary, all the results obtained from this study indicated that MEG3 plays a promoting role in the tumorigenesis and angiogenesis of lung adenocarcinoma, which deserves special attention when considered as a potential therapeutic target for lung adenocarcinoma.

Long non-coding RNA MEG3 serves as a ceRNA for microRNA-145 to induce apoptosis of AC16 cardiomyocytes under high glucose condition.

Diabetic cardiomyopathy (DCM) is one of the most serious complications of diabetes, but its pathogenesis remains largely unclear. In the present study, we aimed to explore the potential role of long non-coding RNA (lncRNA) maternally expressed gene 3 (MEG3) and to investigate the underlying mechanisms in human AC16 cardiomyocytes under high glucose (HG) condition. The results demonstrated that MEG3 was overexpressed in HG-treated AC16 cells, and MEG3 knockdown suppressed the HG-induced apoptosis in AC16 cells. Mechanistically, MEG3 directly binds to miR-145 in AC16 cells, thereby up-regulating the expression of PDCD4. Rescue experiments showed that the role of MEG3 in HG-treated AC16 cells was partly dependent on its suppression on miR-145. In summary, our findings suggested that the role of MEG3 in HG-treated human cardiomyocytes is to serve as a competing endogenous RNA (ceRNA), which negatively regulates miR-145. These findings may provide a valuable and promising therapeutic target for the treatment of DCM in the future.

Downregulation of long non-coding RNA MEG3 promotes proliferation, migration, and invasion of human hepatocellular carcinoma cells by upregulating TGF-β1.

Hepatocellular carcinoma is a common malignant cancer with high incidence. And long non-coding RNAs (lncRNAs) play pivotal roles in the development of different types of cancers. In this study, we aimed to investigate the role of lncRNA maternally expressed gene 3 (MEG3) in the development and progression of hepatocellular carcinoma. Expression of MEG3 in tumor tissues and adjacent healthy tissues of hepatocellular carcinoma patients, as well as the serum of both hepatocellular carcinoma patients and healthy controls, was detected by quantitative reverse transcriptase-polymerase chain reaction. The results showed that expression level of MEG3 was significantly lower in tumor tissues than in adjacent healthy tissues. Serum level of MEG3 was also significantly lower in hepatocellular carcinoma patients than in normal controls. The receiver operating characteristic curve analysis was used to evaluate the diagnostic value of MEG3 for hepatocellular carcinoma, and the prognostic value of MEG3 for this disease was analyzed using Kaplan-Meier method. The results indicated that serum level of MEG3 was a diagnostic and prognostic marker for hepatocellular carcinoma. We also found that MEG3 small interfering Ribonucleic Acid (siRNA) silencing promoted the proliferation, migration, and invasion of hepatocellular carcinoma cells by CCK-8 assay, transwell migration, and invasion assay, respectively, while TGF-β inhibitor treatment reduced those enhancing effects. MEG3 siRNA silencing also increased the expression level of TGF-β1. These results indicated that downregulation of MEG3 can promote proliferation, migration, and invasion of human hepatocellular carcinoma cells by upregulating TGF-β1 expression.

Long noncoding RNA MEG3 regulates rheumatoid arthritis by targeting NLRC5.

Rheumatoid arthritis (RA) is one of the chronic systemic autoimmune diseases that cardinally affect the joints. Many people all over the world suffer from the disease. Fibroblast-like synoviocytes (FLSs) play a significant role in the occurrence and development of RA. The long noncoding RNA maternally expressed gene 3 (MEG3) is an imprinted gene, which participates in various cancers as a tumor suppressor. Previous studies have shown that nucleotide oligomerization domain (NOD)-like receptors 5 (NLRC5) plays a key role in inflammatory and autoimmune diseases. Nonetheless, we know very little about the biofunctionality of MEG3 during the development of RA. In this paper, we used complete Freund's adjuvant (CFA)-induced rats as RA animal models. The level of MEG3 significantly reduced in CFA-induced synovial tissues and FLSs, whereas the NLRC5 levels were increased. Enforced expression of MEG3 may be responsible for the decreased level of NLRC5 and inflammatory cytokine level. The results of methylation-specific PCR suggested that the MEG3 gene promoter was significantly methylated in CFA-induced synovial tissues and FLSs. More important, hypermethylation of MEG3 promoter could be inhibited by 5-aza-2-deoxycytidine (5-azadC; methylation inhibitor). Besides, the expression of NLRC5 significantly decreased followed by 5-azadc. Furthermore, DNA methyltransferases 1 (DNMT1) increased in CFA-induced synovial tissues and cells. These results indicated that MEG3 regulates RA by targeting NLRC5 potentially.

Long non-coding RNA MEG3 attends to morphine-mediated autophagy of HT22 cells through modulating ERK pathway

Context: Morphine is an alkaloid isolated from the poppy plants. The addiction of morphine is a very serious social issue. Some long non-coding RNAs (lncRNAs) have been proposed to engage in drug addiction.Objective: Whether lncRNA maternally expressed gene 3 (MEG3) attended to morphine-mediated autophagy of mouse hippocampal neuronal HT22 cells was probed.Materials and methods: HT22 cells were subjected to 10 µM morphine for 24 h. Cell autophagy was assessed by measuring LC3-II/LC3-I and Beclin-1 expression. qRT-PCR was carried out to measure MEG3 expression. SiRNA oligoribonucleotides targeting MEG3 (si-MEG3) was transfected to silence MEG3. The orexin1 receptor (OX1R), c-fos, p/t-ERK and p/t-PKC expressions were tested by western blotting. SCH772984 was used as an inhibitor of ERK pathway.Results: Morphine elevated OX1R (2.92 times), c-fos (2.06 times), p/t-ERK (2.04 times) and p/t-PKC (2.4 times), Beclin-1 (3.2 times) and LC3-II/LC3-I (3.96 times) expression in HT22 cells. Moreover, followed by morphine exposure, the MEG3 expression was also elevated in HT22 cells (3.03 times). The silence of MEG3 lowered the Beclin-1 (1.85 times), LC3-II/LC3-I (2.12 times), c-fos (1.39 times) and p/t-ERK (1.44 times) expressions in morphine-treated HT22 cells. Inhibitor of ERK pathway SCH772984 further promoted the influence of MEG3 silence on morphine-caused Beclin-1 (1.97 times) and LC3-II/LC3-I (1.92 times) expressions decreases.Conclusions: Up-regulation of MEG3 attended to the morphine-caused autophagy of HT22 cells might be through elevating c-fos expression and promoting ERK pathway activation. More experiments are also needed in the future to analyse the influence of other lncRNAs in drug addiction.

Retracted Article: Long non-coding RNA MEG3 inhibits cell proliferation, migration, invasion and enhances apoptosis in non-small cell lung cancer cells by regulating the miR-31-5p/TIMP3 axis.

Non-small cell lung cancer (NSCLC) is a malignant lung cancer and accounts for 80% of lung cancer-related deaths. Long non-coding RNA maternally expressed gene 3 (MEG3) has been identified as a tumor suppressor in multiple cancers. However, the regulatory mechanism of MEG3 in NSCLC development is still largely unknown. The expression levels of MEG3, microRNA-31-5p (miR-31-5p) and tissue inhibitor of metalloproteinase 3 (TIMP3) in NSCLC tumors and cells were measured by quantitative real time polymerase chain reaction (qRT-PCR). Cell viability, apoptosis, migration and invasion were detected by cell counting kit-8 (CCK-8), flow cytometry, western blotting and transwell assays, respectively. Xenograft mouse models were established by subcutaneously injecting NSCLC cells stably transfected with Lenti-pcDNA or Lenti-MEG3. The interaction between miR-31-5p and MEG3 or TIMP3 was validated by luciferase reporter and RNA immunoprecipitation (RIP) assays. MEG3 and TIMP3 levels were up-regulated, whereas miR-31-5p expression was down-regulated in NSCLC tumors and cells compared with normal tissues and cells. Overexpression of MEG3 repressed cell proliferation, migration and invasion, but induced apoptosis in NSCLC cells. More importantly, MEG3 effectively hindered tumor growth in vivo. Next, luciferase reporter and RIP assays confirmed the interaction between miR-31-5p and MEG3 or TIMP3. Pearson's correlation coefficient revealed that miR-31-5p was inversely correlated with MEG3 or TIMP3. Rescue experiments indicated that MEG3 regulated TIMP3 expression by sponging miR-31-5p in NSCLC cells. Thus, MEG3 inhibited cell proliferation, migration and invasion, but enhanced apoptosis in NSCLC cells through up-regulating TIMP3 expression by regulating miR-31-5p, indicating novel biomarkers for the therapy of NSCLC.

Retracted: Long noncoding RNA MEG3 inhibits proliferation and migration but induces autophagy by regulation of Sirt7 and PI3K/AKT/mTOR pathway in glioma cells.

Glioma is a common primary brain tumor with high mortality rate and poor prognosis. Long noncoding RNA maternally expressed gene 3 (MEG3) is a tumor suppressor in diverse cancer types. However, the role of MEG3 in glioma remains unclear. We aimed to explore the effects of MEG3 on U251 cells as well as the underlying mechanisms. U251 cells were stably transfected with different recombined plasmids to overexpress or silence MEG3. Effects of aberrantly expressed MEG3 on cell viability, migration, apoptosis, expressions of apoptosis-associated and autophagy-associated proteins, and phosphorylated levels of key kinases in the PI3K/AKT/mTOR pathway were all evaluated. Then, messenger RNA (mRNA) and protein expression of Sirt7 in cells abnormally expressing MEG3 were estimated. In addition, effects of abnormally expressed MEG3 and Sirt7 on U251 cells were determined to reveal the underlying mechanism of MEG3-associated modulation. Cell viability and migration were significantly reduced by MEG3 overexpression whereas cell apoptosis as well as Bax and cleaved caspase-3/-9 proteins were obviously induced. Beclin-1 and LC3-II/LC3-I were upregulated and p62 was downregulated in MEG3 overexpressed cells. In addition, the autophagy pharmacological inhibitor (3-methyladenine, 3-MA) affected the effect of MEG3 overexpression on cell proliferation. Furthermore, the phosphorylated levels of key kinases in the PI3K/AKT/mTOR pathway were all reduced by MEG3 overexpression. Sirt7 was positively regulated by MEG3 expression, and effects of MEG3 overexpression on U251 cells were ameliorated by Sirt7 silence. MEG3 suppressed cell proliferation and migration but promoted autophagy in U251 cells through positively regulating Sirt7, involving in the inhibition of the PI3K/AKT/mTOR pathway.

Interaction of long noncoding RNA MEG3 with miRNAs: A reciprocal regulation.

The competitive endogenous RNA (ceRNA) hypothesis suggests that a long noncoding RNA (lncRNA) can function as sinks for pools of microRNAs (miRNAs); thereby, in the presence of ceRNA, messenger RNAs (mRNAs) targeted by specific miRNAs can liberate and translate to protein. Maternally expressed gene 3 (MEG3) is a lncRNA, which its expression has been detected in various normal tissues, while it is lost or downregulated in human tumors. The MEG3 is an imprinted gene which, is methylated and suppressed by DNA methyltransferases (DNMTs) family. Also, miRNAs are involved in the regulation of MEG3 gene expression. Interestingly, the lncRNA MEG3 (lnc-MEG3), as a ceRNA affects various cell processes such as proliferation, apoptosis, and angiogenesis by sponging miRNAs. These miRNAs, in turn, regulate different mRNAs in different pathways. This review focuses on the interaction between lnc-MEG3 and experimentally validated miRNAs. In addition, the discussion supplemented by some data obtained from mirPath (v.3) and TarBase (v.8) databanks to provide more details about the pathways affected by this ceRNA.

The prognostic value of long noncoding RNA MEG3 expression in the survival of patients with cancer: A meta-analysis.

Long noncoding RNAs (lncRNAs) play an important role in carcinogenesis and cancer progression. lncRNA maternally expressed gene 3 (MEG3) is a tumor suppressor that is downregulated in several cancers. However, its prognostic value in human malignancies remains controversial. We have therefore undertaken a meta-analysis to explore the relationship between cancer survival and the expression of lncRNA MEG3. A systematic literature search identified 13 potentially eligible investigations comprising 1733 patients in nine different cancer types. In the pooled analysis, a low expression of MEG3 was associated with low overall survival (OS) in patients with cancer having a combined hazard ratio (HR) of 0.830 (HR = 0.83; 95% CI: 0.70-0.98; p = 0.03; random effect model). However, subgroup analysis according to cancer type revealed that MEG3 expression was not associated with better OS in gastrointestinal cancer (HR = 0.58, 95% CI = 0.33-1.03; p = 0.06), and patients with breast cancer (HR = 0.85, 95% CI: 0.12-5.88; p = 0.87). In conclusion, our results demonstrate that only in the pooled analysis, there was a significant relationship between MEG3 expression and cancer survival. Further investigation of other molecular biomarkers involved in tumorigenesis-related pathways is necessary.

Long non-coding RNA MEG3 suppresses survival, migration, and invasion of cervical cancer.

BackgroundLong non-coding RNAs nowadays emerge as important biomarkers or potential therapeutic targets discussed in human cancers. Among them, maternally expressed gene 3 (MEG3) is known to be decreased in a variety of malignancies, and this affects tumor cellular proliferation, migration, and invasion.Materials and methodsQuantitative real-time PCR was performed to detect the expression of MEG3 in normal cervical epithelium, cervical intraepithelial neoplasia, and cervical squamous cell carcinoma tissues. Gain-of-function and loss-of-function studies were carried out to determine the effect of MEG3 on cell survival, migration, and invasion, which was evaluated by CCK-8 assay, wound healing assay, and transwell assays. mRNA and protein expression of Rac1 were finally determined by quantitative real-time PCR and immunoblotting, respectively. In addition, rescue experiments were performed by overexpression of Rac1.ResultsThe expression of MEG3 was downregulated in cervical intraepithelial neoplasia and squamous cell carcinoma tissues. Forced expression of MEG3 led to reduced abilities of cell survival. Overexpression of MEG3 also inhibited cell migration and invasion in vitro. Cell proliferation marker and EMT markers were changed consistently with the phenotype. In addition, Rac1 was inhibited by MEG3 overexpression at both transcriptional and translational levels. Also, Rac1 could rescue the phenotype caused by long non-coding RNA MEG3. And, it negatively correlated with MEG3 expression in cervical cancer (CC) tissues and cell lines.ConclusionOur findings revealed that MEG3 could negatively regulate CC cell survival, migration, and invasion. It might serve as an important target for CC treatment.