Epigenetic repression of long non-coding RNA MEG3 mediated by DNMT1 represses the p53 pathway in gliomas

Epigenetic mechanisms of nicotine dependence

Smoking continues to be a leading cause of preventable disease and death worldwide. Nicotine dependence generates a lifelong propensity towards cravings and relapse, presenting an ongoing challenge for the development of treatments. Accumulating evidence supports a role for epigenetics in the development and maintenance of addiction to many drugs of abuse, however, the involvement of epigenetics in nicotine dependence is less clear. Here we review evidence that nicotine interacts with epigenetic mechanisms to enable the maintenance of nicotine-seeking across time. Research across species suggests that nicotine increases permissive histone acetylation, decreases repressive histone methylation, and modulates levels of DNA methylation and noncoding RNA expression throughout the brain. These changes are linked to the promoter regions of genes critical for learning and memory, reward processing and addiction. Pharmacological manipulation of enzymes that catalyze core epigenetic modifications regulate nicotine reward and associative learning, demonstrating a functional role of epigenetic modifications in nicotine dependence. These findings are consistent with nicotine promoting an overall permissive chromatin state at genes important for learning, memory and reward. By exploring these links through next-generation sequencing technologies, epigenetics provides a promising avenue for future interventions to treat nicotine dependence.

The expression and function of long noncoding RNAs in hepatocellular carcinoma

With the deepening of the genome project study, attention on noncoding RNAs is increasing. Long noncoding RNAs (lncRNAs) have become a new research hotspot. A growing number of studies have revealed that lncRNAs are involved in tumorigenesis and tumor suppressor pathways. Aberrant expressions of lncRNAs have been found in a variety of human tumors including hepatocellular carcinoma (HCC). In this review, we provide a brief introduction to lncRNA and highlight recent research on the functions and clinical significance of lncRNAs in HCC.

Novel Immune-Related LncRNA Pairs are Associated with Immunol Infiltration and Survival Status in Glioblastoma

Background

Immune-related lncRNA is involved in tumor initiation and progression, while its effect in glioblastoma (GBM) is still unknown.

Objective

We sought to investigate the association between immune-related lncRNA (ir-lncRNA) and GBM.

Methods

Transcriptomic and clinical data were obtained from the TCGA dataset, and we found 2008 ir-lncRNA differentially expressed between GBM and adjacent brain tissues.

Results

Appling the univariate Cox and Lasso regression model, we found 30 prognosis-related ir-lncRNA pairs to construct a Cox regression risk model to associate the outcome of GBM patients. Furthermore, with this risk model, we can identify the tumor immune infiltration status, the expression of immunosuppressive biomarkers, and chemical sensitivity in GBM patients.

Conclusions

We constructed an immunologic risk model with lncRNA to associate the survival outcome of GBM patients, which can provide useful biomarkers.

Silencing of the MEG3 gene promoted anti-cancer activity and drug sensitivity in glioma

Aberrant expression of MEG3 has been shown in various cancers. The purpose of this study is to evaluate the effect of MEG3 on glioma cells and the use of potential chemotherapeutics in glioma by modulating MEG3 expression. Cell viability, migration and chemosensitivity were assayed. Cell death was evaluated in MEG3 overexpressing and MEG3 suppressed cells. MEG3 expression was compared in patient-derived glioma cells concerning IDH1 mutation and WHO grades. Silencing of MEG3 inhibited cell proliferation and reduced cell migration while overexpression of MEG3 promoted proliferation in glioma cells. MEG3 inhibition improved the chemosensitivity of glioma cells to 5-fluorouracil (5FU) but not to navitoclax. On the other hand, there is no significant effect of MEG3 expression on temozolamide (TMZ) treatment which is a standard chemotherapeutic agent in glioma. Suppression of the MEG3 gene in patient-derived oligodendroglioma cells also showed the same effect whereas glioblastoma cell proliferation and chemosensitivity were not affected by MEG3 inhibition. Further, as a possible cell death mechanism of action apoptosis was investigated. Although MEG3 is a widely known tumour suppressor gene and its loss is associated with several cancer types, here we reported that MEG3 inhibition can be used for improving the efficiency of known chemotherapeutic drug sensitivity. We propose that the level of MEG3 should be evaluated in the treatment of different glioma subtypes that are resistant to effective drugs to increase the potential effective drug applications.

Emerging roles of noncoding RNAs in human cancers

Studies have found that RNA encoding proteins only account for a small part of the total number, most RNA is non-coding RNA, and non-coding RNA may affect the occurrence and development of human cancers by affecting gene expression, therefore play an important role in human pathology. At present, ncRNAs studied include miRNA, circRNA, lncRNA, piRNA, and snoRNA, etc. After decades of research, the basic role of these ncRNAs in many cancers has been clear. As far as we know, the role of miRNAs in cancer is one of the hottest research directions, however, it is also found that the imbalance of ncRNAs will affect the occurrence of gastric cancer, breast cancer, lung cancer, meanwhile, it may also affect the prognosis of these cancers. Therefore, the study of ncRNAs in cancers may help to find new cancer diagnostic and treatment methods. Here, we reviewed the biosynthesis and characteristics of miRNA, cricRNA, and lncRNA etc., their roles in human cancers, as well as the mechanism through which these ncRNAs affect human cancers.

Super-enhancer-driven lncRNA LIMD1-AS1 activated by CDK7 promotes glioma progression

Long non-coding RNAs (lncRNAs) are tissue-specific expression patterns and dysregulated in cancer. How they are regulated still needs to be determined. We aimed to investigate the functions of glioma-specific lncRNA LIMD1-AS1 activated by super-enhancer (SE) and identify the potential mechanisms. In this paper, we identified a SE-driven lncRNA, LIMD1-AS1, which is expressed at significantly higher levels in glioma than in normal brain tissue. High LIMD1-AS1 levels were significantly associated with a shorter survival time of glioma patients. LIMD1-AS1 overexpression significantly enhanced glioma cells proliferation, colony formation, migration, and invasion, whereas LIMD1-AS1 knockdown inhibited their proliferation, colony formation, migration, and invasion, and the xenograft tumor growth of glioma cells in vivo. Mechanically, inhibition of CDK7 significantly attenuates MED1 recruitment to the super-enhancer of LIMD1-AS1 and then decreases the expression of LIMD1-AS1. Most importantly, LIMD1-AS1 could directly bind to HSPA5, leading to the activation of interferon signaling. Our findings support the idea that CDK7 mediated-epigenetically activation of LIMD1-AS1 plays a crucial role in glioma progression and provides a promising therapeutic approach for patients with glioma.

Mutual interaction of lncRNAs and epigenetics: focusing on cancer

Long noncoding RNAs are characterized as noncoding transcripts longer than 200 nucleotides in response to a variety of functions within the cells. They are involved in almost all cellular mechanisms so as epigenetics. Given that epigenetics is an important phenomenon, which participates in the biology of complex diseases, many valuable studies have been performed to demonstrate the control status of lncRNAs and epigenetics. DNA methylation and histone modifications as epigenetic mechanisms can regulate the expression of lncRNAs by affecting their coding genes. Reciprocally, the three-dimensional structure of lncRNAs could mechanistically control the activity of epigenetic-related enzymes. Dysregulation in the mutual interaction between epigenetics and lncRNAs is one of the hallmarks of cancer. These mechanisms are either directly or indirectly involved in various cancer properties such as proliferation, apoptosis, invasion, and metastasis. For instance, lncRNA HOTAIR plays a role in regulating the expression of many genes by interacting with epigenetic factors such as DNA methyltransferases and EZH2, and thus plays a role in the initiation and progression of various cancers. Conversely, the expression of this lncRNA is also controlled by epigenetic factors. Therefore, focusing on this reciprocated interaction can apply to cancer management and the identification of prognostic, diagnostic, and druggable targets. In the current review, we discuss the reciprocal relationship between lncRNAs and epigenetic mechanisms to promote or prevent cancer progression and find new potent biomarkers and targets for cancer diagnosis and therapy.

MiRNA Differences Related to Treatment-Resistant Schizophrenia

Schizophrenia (SZ) is a serious mental disorder that is typically treated with antipsychotic medication. Treatment-resistant schizophrenia (TRS) is the condition where symptoms remain after pharmacological intervention, resulting in long-lasting functional and social impairments. As the identification and treatment of a TRS patient requires previous failed treatments, early mechanisms of detection are needed in order to quicken the access to effective therapy, as well as improve treatment adherence. In this study, we aim to find a microRNA (miRNA) signature for TRS, as well as to shed some light on the molecular pathways potentially involved in this severe condition. To do this, we compared the blood miRNAs of schizophrenia patients that respond to medication and TRS patients, thus obtaining a 16-miRNA TRS profile. Then, we assessed the ability of this signature to separate responders and TRS patients using hierarchical clustering, observing that most of them are grouped correctly (~70% accuracy). We also conducted a network, pathway analysis, and bibliography search to spot molecular pathways potentially altered in TRS. We found that the response to stress seems to be a key factor in TRS and that proteins p53, SIRT1, MDM2, and TRIM28 could be the potential mediators of such responses. Finally, we suggest a molecular pathway potentially regulated by the miRNAs of the TRS profile.

Regulation of temozolomide resistance via lncRNAs: Clinical and biological properties of lncRNAs in gliomas (Review)

Gliomas are a primary types of intracranial malignancies and are characterized by a poor prognosis due to aggressive recurrence profiles. Temozolomide (TMZ) is an auxiliary alkylating agent that is extensively used in conjunction with surgical resection and forms the mainstay of clinical treatment strategies for gliomas. However, the frequent occurrence of TMZ resistance in clinical practice limits its therapeutic efficacy. Accumulating evidence has demonstrated that long non‑coding RNAs (lncRNAs) can play key and varied roles in glioma progression. lncRNAs have been reported to inhibit glioma progression by targeting various signaling pathways. In addition, the differential expression of lncRNAs has also been found to mediate the resistance of glioma to several chemotherapeutic agents, particularly to TMZ. The present review article therefore summarizes the findings of previous studies in an aim to report the significance and function of lncRNAs in regulating the chemoresistance of gliomas. The present review may provide further insight into the clinical treatment of gliomas.

RP11-552D4.1: a novel m6a-related LncRNA associated with immune status in glioblastoma

Glioblastoma (GBM) is the most malignant form of brain cancer in the world. Nevertheless, the survival rate of patients with GBM is extremely low. N6-methyladenosine (m6A) and long noncoding RNAs (lncRNAs) conduct important biological functions in patients’ survival status and the immunotherapeutic response. Here, m6A-related lncRNAs were identified by a co-expression method. Univariate and multivariate Cox regression together with LASSO were applied to establish the risk model. Kaplan-Meier and ROC analysis were applied to evaluate the prediction power of this risk model. Finally, the related immune profiling and chemical sensitivity targets were also investigated. The risk model holding three m6A-related lncRNAs was confirmed as an independent predictor for the prognosis. Furthermore, we found the risk model based on m6A-related lncRNAs is associated with the immune status, immunosuppressive biomarkers, and chemo-sensitivity in GBM patients. The RP11-552D4.1 is found to facilitate neuronal proliferation. This risk model consisted of m6A-related lncRNAs may be available for the clinical interventions in GBM patients.

DNMT1-mediated demethylation of lncRNA MEG3 promoter suppressed breast cancer progression by repressing Notch1 signaling pathway

Breast carcinoma is one of the common causes of cancer-related mortality in women. Maternally expressed gene 3 (MEG3), a lncRNA located at 14q32, can be involved in carcinogenesis. In this study, we discovered that MEG3 was downregulated by CpG hypermethylation within its gene promoter. Functionally, treatment of breast cancer cells with the DNA methylation inhibitor 5-AzadC as well as silencing of DNA methyltransferase-1 (DNMT1) could decrease the abnormal hypermethylation of the MEG3 promoter, reverse MEG3 expression, inhibit cell proliferation and promote cell apoptosis. In addition, we found that MEG3 expression was negatively correlated with DNMT1. Mechanistically, MEG3 knockdown combined with 5-AzadC or sh-DNMT1 treatment restored the expression of Notch1 receptor, leading to the Notch1 pathway activation, and promoted the progression of epithelial mesenchymal transformation (EMT). Finally, the mice tumor model experiments showed that DNMT1 knockdown can increase MEG3 expression and inhibit tumor growth. Collectively, our findings uncovered that DNMT1-mediated MEG3 demethylation leads to MEG3 upregulation, which in turn inhibits the Notch1 pathway and EMT process in breast cancer.

miR-887-3p Inhibits the Progression of Colorectal Cancer via Downregulating DNMT1 Expression and Regulating P53 Expression

Colorectal cancer (CRC) is the third most diagnosed cancer worldwide and the second leading cause of cancer-related deaths. Many researchers have reported that abnormal microRNAs (miRs) were expressed in CRC and participated in the occurrence and progression of CRC. However, there are few reports of miR-887-3p regulating CRC development. In the current study, we investigated the abnormal expression of miR-887-3p and also demonstrated its regulatory role and detailed molecular mechanism in CRC. Initially, miRNA expression data were obtained from TCGA-COAD that consisted of 453 CRC samples and 8 normal tissue samples. These were downloaded and analyzed to compare the expression level of miR-887-3p in CRC tissues to that in normal tissues. Moreover, 32 pairs of surgically resected CRC tumors and para-cancer tissues from our hospital were collected. Quantitative real-time PCR (qRT-PCR) was performed to detect miR-887-3p expression levels in CRC tissues, para-cancer tissues, several CRC cell lines, and an intestinal epithelial cell line. Following miR-887-3p mimic transfection in colon cancer SW480 cell line, the regulatory roles of miR-887-3p on cell proliferation, apoptosis, invasion, migration, and epithelial-mesenchymal transition (EMT) were detected through CCK-8, flow cytometry, transwell assay, and Western blot. After potential targeting protein was predicted by bioinformatic websites, the luciferase reporter assay and Western blot were used to confirm the target of miR-887-3p. The targeting protein expressions were detected by Western blot and qRT-PCR. The relationship between miR-887-3p level and the effect of miR-887-3p on P53 expression was evaluated by Western blot and qRT-PCR. The effects of miR-887-3p on CRC cell growth in vivo by xenograft tumor experiments were investigated, and Ki-67 in tumor tissue was determined by immunohistochemistry. Results. The COAD data demonstrated that the expression levels of miR-887-3p in CRC clinical sample tissues and cell line cultures were remarkably lower than para-cancer normal tissues and NCM460 cells (normal colonic epithelial cell line). Functional experiments demonstrated that overexpression of miR-887-3p in SW480 cells significantly reduced proliferation, migration, invasion, and EMT, and promoted cancer cell apoptosis. Additionally, Western blot, qRT-PCR, and luciferase reporter assays confirmed that DNMT1 was a downstream target of miR-887-3p. Moreover, the blocking of DNMT1 by miR-887-3p mimics also promoted P53 expression. Finally, overexpression of DNMT1 in SW480 cells could partially reverse the regulatory effect of miR-887-3p mimics on CRC cell development. From in vivo experiments, overexpression of miR-887-3p could inhibit tumor growth in CRC xenograft mice and reduce the Ki-67 level. Conclusion. The microRNA miR-887-3p is a potential biomarker of CRC. It inhibited CRC cell proliferation, invasion, and EMT, and promoted cell apoptosis through targeting and downregulating DNMT1 and promoting P53 expression. Therefore, miR-887-3p may be a good biomarker and therapeutic target for CRC treatment.

Long Noncoding RNAs in Lung Cancer: From Disease Markers to Treatment Roles

There is an urgent need to identify reliable biomarkers that can be used in early diagnosis, prognostication prediction and as possible therapeutic targets for lung cancer due to its current poor prognosis. Long noncoding RNAs (lncRNAs) have recently attracted additional attention due to their potential role in carcinogenesis, invasion and metastasis. Issues involved in the biofunctions and regulatory mechanisms of oncogenic and tumor-suppressive lncRNAs in lung cancer are discussed. Some lncRNAs have shown good diagnostic value, especially in combination with conventional serum protein markers. The use of antisense oligonucleotides, small molecules and RNA interference techniques have shown promise as direct therapeutic tools for targeting lncRNAs in preclinical studies. The biomarker function of lncRNAs may also indirectly involved in tumor therapy as a reference to conventional therapy. Overall, the concept of using lncRNAs as biomarkers for prognostication and intervention in lung cancer is still in its infancy, and only with more in-depth studies could they have a significant impact.

DNMT1 facilitates growth of breast cancer by inducing MEG3 hyper-methylation

Background

To understand the effect of DNMT1-mediated MEG3 promoter methylation on breast cancer progression.

Methods

Expression of DNMT1, MEG3 and miR-494-3p was assayed by qRT-PCR and western blot. Methylation-specific PCR was used to examine MEG3 promoter methylation level. ChIP, RNA binding protein immunoprecipitation assay and dual-luciferase reporter gene assay were applied to verify interaction between DNMT1 and MEG3, miR-494-3p and MEG3 and OTUD4. CCK-8, wound healing and Transwell assays were used to detect biological functions of breast cancer cells. Tumor growth was observed by tumor xenograft model.

Results

DNMT1 and miR-494-3p were highly expressed while MEG3 and OTUD4 were lowly expressed in breast cancer cells. Knockdown of DNMT1 inhibited progression of breast cancer cells by enhance MEG3 expression through demethylation. MEG3 could downregulate miR-494-3p expression, and OTUD4 was a target of miR-494-3p. Upregulation of MEG3 and downregulation of miR-494-3p both inhibited malignant behavior of cells in vitro. In addition, high MEG3 expression restrained growth of breast cancer in vivo.

Conclusion

Briefly, our results demonstrated that, DNMT1 induced methylation of MEG3 promoter, and played a key role in breast cancer growth throughmiR-494-3p/OTUD4 axis. These findings provide new insights into molecular therapeutic targets for breast cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-022-02463-8.

Emerging role of long non-coding RNAs in endothelial dysfunction and their molecular mechanisms

Long non-coding RNAs (lncRNAs) are the novel class of transcripts involved in transcriptional, post-transcriptional, translational, and post-translational regulation of physiology and the pathology of diseases. Studies have evidenced that the impairment of endothelium is a critical event in the pathogenesis of atherosclerosis and its complications. Endothelial dysfunction is characterized by an imbalance in vasodilation and vasoconstriction, oxidative stress, proinflammatory factors, and nitric oxide bioavailability. Disruption of the endothelial barrier permeability, the first step in developing atherosclerotic lesions is a consequence of endothelial dysfunction. Though several factors interfere with the normal functioning of the endothelium, intrinsic epigenetic mechanisms governing endothelial function are regulated by lncRNAs and perturbations contribute to the pathogenesis of the disease. This review comprehensively addresses the biogenesis of lncRNA and molecular mechanisms underlying and regulation in endothelial function. An insight correlating lncRNAs and endothelial dysfunction-associated diseases can positively impact the development of novel biomarkers and therapeutic targets in endothelial dysfunction-associated diseases and treatment strategies.

Role of mammalian long non-coding RNAs in normal and neuro oncological disorders

Long non-coding RNAs (lncRNAs) are expressed at lower levels than protein-coding genes but have a crucial role in gene regulation. LncRNA is distinct, they are being transcribed using RNA polymerase II, and their functionality depends on subcellular localization. Depending on their niche, they specifically interact with DNA, RNA, and proteins and modify chromatin function, regulate transcription at various stages, forms nuclear condensation bodies and nucleolar organization. lncRNAs may also change the stability and translation of cytoplasmic mRNAs and hamper signaling pathways. Thus, lncRNAs affect the physio-pathological states and lead to the development of various disorders, immune responses, and cancer. To date, ~40% of lncRNAs have been reported in the nervous system (NS) and are involved in the early development/differentiation of the NS to synaptogenesis. LncRNA expression patterns in the most common adult and pediatric tumor suggest them as potential biomarkers and provide a rationale for targeting them pharmaceutically. Here, we discuss the mechanisms of lncRNA synthesis, localization, and functions in transcriptional, post-transcriptional, and other forms of gene regulation, methods of lncRNA identification, and their potential therapeutic applications in neuro oncological disorders as explained by molecular mechanisms in other malignant disorders.

Long Non-Coding RNAs in Diagnosis, Treatment, Prognosis, and Progression of Glioma: A State-of-the-Art Review

Glioma is the most common malignant central nervous system tumor with significant mortality and morbidity. Despite considerable advances, the exact molecular pathways involved in tumor progression are not fully elucidated, and patients commonly face a poor prognosis. Long non-coding RNAs (lncRNAs) have recently drawn extra attention for their potential roles in different types of cancer as well as non-malignant diseases. More than 200 lncRNAs have been reported to be associated with glioma. We aimed to assess the roles of the most investigated lncRNAs in different stages of tumor progression and the mediating molecular pathways in addition to their clinical applications. lncRNAs are involved in different stages of tumor formation, invasion, and progression, including regulating the cell cycle, apoptosis, autophagy, epithelial-to-mesenchymal transition, tumor stemness, angiogenesis, the integrity of the blood-tumor-brain barrier, tumor metabolism, and immunological responses. The well-known oncogenic lncRNAs, which are upregulated in glioma, are H19, HOTAIR, PVT1, UCA1, XIST, CRNDE, FOXD2-AS1, ANRIL, HOXA11-AS, TP73-AS1, and DANCR. On the other hand, MEG3, GAS5, CCASC2, and TUSC7 are tumor suppressor lncRNAs, which are downregulated. While most studies reported oncogenic effects for MALAT1, TUG1, and NEAT1, there are some controversies regarding these lncRNAs. Expression levels of lncRNAs can be associated with tumor grade, survival, treatment response (chemotherapy drugs or radiotherapy), and overall prognosis. Moreover, circulatory levels of lncRNAs, such as MALAT1, H19, HOTAIR, NEAT1, TUG1, GAS5, LINK-A, and TUSC7, can provide non-invasive diagnostic and prognostic tools. Modulation of expression of lncRNAs using antisense oligonucleotides can lead to novel therapeutics. Notably, a profound understanding of the underlying molecular pathways involved in the function of lncRNAs is required to develop novel therapeutic targets. More investigations with large sample sizes and increased focus on in-vivo models are required to expand our understanding of the potential roles and application of lncRNAs in glioma.

DNA methylation mediated RSPO2 to promote follicular development in mammals

In female mammals, the proliferation, apoptosis, and estradiol-17β (E2) secretion of granulosa cells (GCs) have come to decide the fate of follicles. DNA methylation and RSPO2 gene of Wnt signaling pathway have been reported to involve in the survival of GCs and follicular development. However, the molecular mechanisms for how DNA methylation regulates the expression of RSPO2 and participates in the follicular development are not clear. In this study, we found that the mRNA and protein levels of RSPO2 significantly increased during follicular development, but the DNA methylation level of RSPO2 promoter decreased gradually. Inhibition of DNA methylation or DNMT1 knockdown could decrease the methylation level of CpG island (CGI) in RSPO2 promoter and upregulate the expression level of RSPO2 in porcine GCs. The hypomethylation of -758/-749 and -563/-553 regions in RSPO2 promoter facilitated the occupancy of transcription factor E2F1 and promoted the transcriptional activity of RSPO2. Moreover, RSPO2 promoted the proliferation of GCs with increasing the expression level of PCNA, CDK1, and CCND1 and promoted the E2 secretion of GCs with increasing the expression level of CYP19A1 and HSD17B1 and inhibited the apoptosis of GCs with decreasing the expression level of Caspase3, cleaved Caspase3, cleaved Caspase8, cleaved Caspase9, cleaved PARP, and BAX. In addition, RSPO2 knockdown promoted the apoptosis of GCs, blocked the development of follicles, and delayed the onset of puberty with decreasing the expression level of Wnt signaling pathway-related genes (LGR4 and CTNNB1) in vivo. Taken together, the hypomethylation of -758/-749 and -563/-553 regions in RSPO2 promoter facilitated the occupancy of E2F1 and enhanced the transcription of RSPO2, which further promoted the proliferation and E2 secretion of GCs, inhibited the apoptosis of GCs, and ultimately ameliorated the development of follicles through Wnt signaling pathway. This study will provide useful information for further exploration on DNA-methylation-mediated RSPO2 pathway during follicular development.

Prognostic Value of MEG3 and Its Correlation With Immune Infiltrates in Gliomas

Accumulating evidence has revealed that dysregulated lncRNA expression contributes to the onset and progression of cancer. However, the mechanistic role of lncRNA in glioma progression and tumor immunology remains largely unknown. This study aimed to evaluate the significance of maternally expressed gene 3 (MEG3) in the prognosis of and its immune-related roles in gliomas. The expression levels of MEG3 were analyzed using Oncomine and TIMER database. As an important imprinted gene, the copy number variation (CNV) of MEG3 in both glioblastoma multiforme (GBM) and low-grade glioma (LGG) were analyzed using GSCALite database, whereas its prognostic significance was assessed using PrognoScan and GEPIA databases. The relationship between MEG3 and tumor-infiltrated immune cells was analyzed using TIMER. Results showed that MEG3 expression was lower in most of the human cancer tissues than in the normal tissues. We also found that heterozygous deletion of MEG3 occurred more frequent than heterozygous amplification in gliomas, and mRNA expression of MEG3 was significantly positively correlated with its CNV in both the GBM and LGG group. Survival analysis showed that the CNV level of MEG3 had significant correlation with overall survival (OS) and progression-free survival (PFS) compared with wild type in LGG. Lower MEG3 expression was related with poor prognosis. Further analysis showed that in GBM, MEG3 expression level was significantly positively correlated with that of infiltrating CD8⁺ T cells and significantly negatively correlated with that of infiltrating dendritic cells. In LGG, MEG3 expression level was significantly negatively correlated with levels of infiltrating B cells, CD8⁺ T cells, CD4⁺ T cells, macrophages, neutrophils, and dendritic cells. Univariate Cox survival analysis demonstrated that only the level of infiltrating dendritic cells significantly affected the survival time of patients with GBM, while all six types of immune cells had a significant effect on the survival time of patients with LGG. Furthermore, MEG3 expression showed strong correlations with multiple immune markers in gliomas, especially in LGG. The current findings suggest that MEG3 expression might serve as a possible prognostic marker and potential immunotherapeutic target for gliomas.

A Signature of Nine lncRNA Methylated Genes Predicts Survival in Patients With Glioma

Glioma is one of the most common malignant tumors of the central nervous system, and its prognosis is extremely poor. Aberrant methylation of lncRNA promoter region is significantly associated with the prognosis of glioma patients. In this study, we investigated the potential impact of methylation of lncRNA promoter region in glioma patients to establish a signature of nine lncRNA methylated genes for determining glioma patient prognosis. Methylation data and clinical follow-up data were obtained from The Cancer Genome Atlas (TCGA). The multistep screening strategy identified nine lncRNA methylated genes that were significantly associated with the overall survival (OS) of glioma patients. Subsequently, we constructed a risk signature that containing nine lncRNA methylated genes. The risk signature successfully divided the glioma patients into high-risk and low-risk groups. Compared with the low-risk group, the high-risk group had a worse prognosis, higher glioma grade, and older age. Furthermore, we identified two lncRNAs termed PCBP1-AS1 and LINC02875 that may be involved in the malignant progression of glioma cells by using the TCGA database. Loss-of-function assays confirmed that knockdown of PCBP1-AS1 and LINC02875 inhibited the proliferation, migration, and invasion of glioma cells. Therefore, the nine lncRNA methylated genes signature may provide a novel predictor and therapeutic target for glioma patients.

Curcumin suppresses tumor growth of gemcitabine-resistant non-small cell lung cancer by regulating lncRNA-MEG3 and PTEN signaling

BACKGROUND

Lung cancer is one of the most aggressive malignancies and the efficacy of chemotherapy or concurrent chemoradiation is limited in clinical application. Curcumin has been reported to block cancer development by modulating multiple signaling pathways. However, whether curcumin can inhibit gemcitabine-resistant non-small cell lung cancer through regulation of lncRNA and the involved molecular mechanisms are rarely reported.

MATERIALS AND METHODS

MTT assay, clonogenic assay, apoptosis assay, qRT-PCR, Western blotting, immunohistochemistry, xenograft experiment were carried out in the present study.

RESULTS

The results showed that curcumin suppressed gemcitabine-resistant non-small cell lung cancer cell proliferation and induced apoptosis. Curcumin upregulated the expression of lncRNA-MEG3 and PTEN, and MEG3 overexpression could increase the level of PTEN expression, while MEG3 knockdown decreased the level of PTEN expression in gemcitabine-resistant non-small cell lung cancer cells. Curcumin treatment failed to inhibit the proliferation and induce apoptosis in MEG3 knockdown or PTEN knockdown cells.

CONCLUSIONS

These findings show the antitumor activity of curcumin for potential clinical application in gemcitabine-resistant non-small cell lung cancer treatment.

[Overexpression of lncRNA MEG3 inhibits proliferation and invasion of glioblastoma U251 cells in vitro by suppressing HIF1α expression]

OBJECTIVE

To investigate the effects of overexpression of long noncoding RNA (lncRNA) MEG3 on the proliferation and invasion of glioblastoma U251 cells by suppressing the expression of hypoxia inducible factor 1α(HIF1α).

METHODS

The expression of lncRNA MEG3 and HIF1α mRNA were examined in human fetal glial cells (HFGCs) and U251 cells using realtime quantitative PCR (qRT-PCR), and the expression of HIF1α protein was detected with Western blotting.U251 cells in normal culture or transfected with pcDNA3.1 vector (NC group) or pcDNA3.1-MEG3 vector via lipofectamine2000 were exposed to hypoxia for 12h, and the expressions of HIF1α mRNA and protein were detected with qRT-PCR and Western blotting, respectively.MTT assay and Transwell assay were employed to examine the influence of MEG3 overexpression on the proliferation and invasion of U251 cells.

RESULTS

The expression of MEG3 was significantly lower and HIF1α mRNA and protein expressions were significantly higher in U251 cells than in HFGCs (P < 0.05).In U251 cells, overexpression of MEG3 significantly decreased the mRNA and protein expressions of HIF1α(P < 0.05).Hypoxic exposure for 12h also resulted in significantly lowered expression of HIF1α protein in U251 cells (P < 0.05).Overexpression of MEG3 obviously suppressed the proliferation and invasiveness of U251 cells (P < 0.05).

CONCLUSIONS

MEG3 overexpression inhibits the proliferation and invasion of U251 cells through suppressing the expression of HIF1α mRNA and protein, suggesting that MEG3 may serve as a potential therapeutic target for glioblastomas.

Long non-coding RNAs in brain tumors

Long non-coding RNAs (lncRNAs) have been found to be central players in the epigenetic, transcriptional and post-transcriptional regulation of gene expression. There is an accumulation of evidence on newly discovered lncRNAs, their molecular interactions and their roles in the development and progression of human brain tumors. LncRNAs can have either tumor suppressive or oncogenic functions in different brain cancers, making them attractive therapeutic targets and biomarkers for personalized therapy and precision diagnostics. Here, we summarize the current state of knowledge of the lncRNAs that have been implicated in brain cancer pathogenesis, particularly in gliomas and medulloblastomas. We discuss their epigenetic regulation as well as the prospects of using lncRNAs as diagnostic biomarkers and therapeutic targets in patients with brain tumors.

Coordinated silencing of the Sp1-mediated long noncoding RNA MEG3 by EZH2 and HDAC3 as a prognostic factor in pancreatic ductal adenocarcinoma

Objective:

Pancreatic ductal adenocarcinoma (PDAC) is a disease with high mortality. Many so-called “junk” noncoding RNAs need to be discovered in PDAC. The purpose of this study was therefore to investigate the function and regulatory mechanism of the long noncoding RNA MEG3 in PDAC.

Methods:

The Gene Expression Omnibus database (GEO database) was used to determine the differential expression of long noncoding RNAs in PDAC, and MEG3 was selected for subsequent verification. Tissue and cell samples were used to verify MEG3 expression, followed by functional detection in vitro and in vivo. Microarrays were used to characterize long noncoding RNA and mRNA expression profiles. Competing endogenous RNA analyses were used to detect differential MEG3 and relational miRNA expression in PDAC. Finally, promoter analyses were conducted to explain the downregulation of MEG3 PDAC.

Results:

We generated a catalogue of PDAC-associated long noncoding RNAs in the GEO database. The ectopic expression of MEG3 inhibited PDAC growth and metastasis in vitro and in vivo, which was statistically significant (P < 0.05). Microarray analysis showed that multiple microRNAs interacted with MEG3. We also showed that MEG3, as a competing endogenous RNA, directly sponged miR-374a-5p to regulate PTEN expression. The transcription factor, Sp1, recruited EZH2 and HDAC3 to the promoter and transcriptionally repressed MEG3 expression. Finally, clinical data showed that MEG3 and miR-374a-5p expressions were correlated with clinicopathological features. Statistically, Sp1, EZH2, HDAC3, and miR-374a-5p were negatively correlated with MEG3 (P < 0.05).

Conclusions:

Reduced MEG3 levels played a crucial role in the PDAC malignant phenotype, which provided insight into novel and effective molecular targets of MEG3 for pancreatic cancer treatment.

Long noncoding RNA MEG3 blocks telomerase activity in human liver cancer stem cells epigenetically

BACKGROUND

MEG3 downregulated the expression in several tumors and inhibits human tumorigenesis. But so far, the mechanism of MEG3 in tumorigenesis is still unclear.

METHODS

In gene infection, cellular and molecular technologies and tumorigenesis test in vitro and in vivo were performed, respectively.

RESULTS

Our results indicate that MEG3 enhances the P53 expression by triggering the loading of P300 and RNA polymerase II onto its promoter regions dependent on HP1α. Moreover, MEG3 increases the methylation modification of histone H3 at the 27th lysine via P53. Furthermore, MEG3 inhibits the expression of TERT by increasing the H3K27me3 in TERT promoter regions, thereby inhibiting the activity of telomerase by reducing the binding of TERT to TERC. Furthermore, MEG3 also increases the expression of TERRA; therefore, the interaction between TERC and TERT was competitively attenuated by increasing the interaction between TERRA and TERT, which inhibits the activity of telomerase in hLCSCs. Strikingly, MEG3 reduces the length of telomere by blocking the formation of complex maintaining telomere length (POT1-Exo1-TRF2-SNM1B) and decreasing the binding of the complex to telomere by increasing the interplay between P53 and HULC. Ultimately, MEG3 inhibits the growth of hLCSCs by reducing the activity of telomerase and attenuating telomeric repeat binding factor 2(TRF2).

CONCLUSIONS

Our results demonstrates MEG3 inhibits the occurrence of human liver cancer by blocking telomere, and these findings provide an important insight into the prevention and treatment of human liver cancer.

Long non-coding maternally expressed gene 3 regulates cigarette smoke extract-induced apoptosis, inflammation and cytotoxicity by sponging miR-181a-2-3p in 16HBE cells

Accumulating evidence has suggested that long non-coding (lnc)RNAs are widely involved in the progression of multiple diseases, including chronic obstructive pulmonary disease (COPD). The aim of the present study was to explore the function and molecule mechanism of maternally expressed gene 3 (MEG3) in cigarette smoke extract (CSE)-treated 16HBE cells. Cell viability and apoptosis were evaluated using Cell Counting Kit-8 analysis and flow cytometry, respectively. Western blot analysis was carried out to determine the protein levels of Bcl-2, Bax and cleaved caspase-3. ELISA assays were utilized to measure the protein levels of IL-1β and IL-6 and TNF-α. Cytotoxicity was assessed using a lactate dehydrogenase release assay. The expression levels of MEG3 and microRNA (miR)-181a-2-3p were detected using reverse transcription-quantitative PCR. The interaction between miR-181a-2-3p and MEG3 was predicted using DIANA tools and verified by a dual-luciferase reporter assay and RNA Immunoprecipitation assay. MEG3 expression was enhanced while miR-181a-2-3p abundance was reduced in the serum of patients with COPD and CSE-treated 16HBE cells. MEG3-knockdown or miR-181a-2-3p-overexpression inhibited CSE-induced apoptosis, inflammation and cytotoxicity in 16HBE cells. Moreover, miR-181a-2-3p directly bind to MEG3 and its knockdown reversed the inhibitory effect of MEG3 interference on apoptosis, inflammation and cytotoxicity in CSE-treated 16HBE cells. Overall, MEG3-knockdown suppressed CSE-induced apoptosis, inflammation and cytotoxicity in 16HBE cells by upregulating miR-181a-2-3p, providing a promising therapeutic target for treatment of CSE-induced COPD.

Long noncoding RNA FGF14-AS2 inhibits breast cancer metastasis by regulating the miR-370-3p/FGF14 axis

Long noncoding RNAs (lncRNAs) have emerged as important regulators in cancers, including breast cancer. However, the overall biological roles and clinical significance of most lncRNAs are not fully understood. This study aimed to elucidate the potential role of a novel lncRNA FGF14-AS2 and the mechanisms underlying metastasis in breast cancer. The lncRNA FGF14-AS2 was significantly downregulated in breast cancer tissues; patients with lower FGF14-AS2 expression had advanced clinical stage. In vitro and in vivo assays of FGF14-AS2 alterations revealed a complex integrated phenotype affecting breast cancer cell migration, invasion, and tumor metastasis. Mechanistically, FGF14-AS2 functioned as a competing endogenous RNA of miR-370-3p, thereby leading to the activation of its coding counterpart, FGF14. Clinically, we observed increased miR-370-3p expression in breast cancer tissues, whereas FGF14 expression was decreased in breast cancer tissues compared to the adjacent normal breast tissues. FGF14-AS2 expression was significantly negatively correlated with miR-370-3p expression, and correlated positively to FGF14 expression. Collectively, our findings support a model in which the FGF14-AS2/miR-370-3p/FGF14 axis is a critical regulator in breast cancer metastasis, suggesting a new therapeutic direction in breast cancer.

MicroRNA-21-Enriched Exosomes as Epigenetic Regulators in Melanomagenesis and Melanoma Progression: The Impact of Western Lifestyle Factors

DNA mutation-induced activation of RAS-BRAF-MEK-ERK signaling associated with intermittent or chronic ultraviolet (UV) irradiation cannot exclusively explain the excessive increase of malignant melanoma (MM) incidence since the 1950s. Malignant conversion of a melanocyte to an MM cell and metastatic MM is associated with a steady increase in microRNA-21 (miR-21). At the epigenetic level, miR-21 inhibits key tumor suppressors of the RAS-BRAF signaling pathway enhancing proliferation and MM progression. Increased MM cell levels of miR-21 either result from endogenous upregulation of melanocytic miR-21 expression or by uptake of miR-21-enriched exogenous exosomes. Based on epidemiological data and translational evidence, this review provides deeper insights into environmentally and metabolically induced exosomal miR-21 trafficking beyond UV-irradiation in melanomagenesis and MM progression. Sources of miR-21-enriched exosomes include UV-irradiated keratinocytes, adipocyte-derived exosomes in obesity, airway epithelium-derived exosomes generated by smoking and pollution, diet-related exosomes and inflammation-induced exosomes, which may synergistically increase the exosomal miR-21 burden of the melanocyte, the transformed MM cell and its tumor environment. Several therapeutic agents that suppress MM cell growth and proliferation attenuate miR-21 expression. These include miR-21 antagonists, metformin, kinase inhibitors, beta-blockers, vitamin D, and plant-derived bioactive compounds, which may represent new options for the prevention and treatment of MM.

Current advances of long non-coding RNAs mediated by wnt signaling in glioma

Glioma is the most common and aggressive brain tumor in the central nervous system (CNS), in which Wnt signaling pathway has been verified to play a pivotal role in regulating the initiation and progression. Currently, numerous studies have indicated that long non-coding RNAs (lncRNAs) have critical functions across biological processes including cell proliferation, colony formation, migration, invasion and apoptosis via Wnt signaling pathway in glioma. This review depicts canonical and non-canonical Wnt/β-catenin signaling pathway properties and relative processing mechanisms in gliomas, and summarizes the function and regulation of lncRNAs mediated by Wnt signaling pathway in the development and progression of glioma. Ultimately, we hope to seek out promising biomarkers and reliable therapeutic targets for glioma.

Non-coding RNA in bladder cancer

Bladder cancer is the tenth most common cancer worldwide and has been associated with high mortality and morbidity. Although the treatment of bladder cancer is based on well-defined tumor classifications and gradings, patients still experience different clinical response. The heterogeneity of this disease calls for substantial research with more in-depth molecular characterization, with the hope of identifying new diagnostic and treatment options. In recent years, non-coding RNAs (ncRNAs), particularly, microRNAs (miRNAs), long non-coding RNA (lncRNAs), and circular RNAs (circRNAs) were found to be associated with bladder cancer occurrence and development. This review highlights the recent findings concerning ncRNAs and their relevance to the pathogenesis of bladder cancer. This may provide a foundation for developing highly specific diagnostic tools and more robust therapeutic strategies in the future.

Promoter hypermethylation influences the suppressive role of long non-coding RNA MEG3 in the development of multiple myeloma

Methylation is a fundamental regulator of gene transcription. Long non-coding RNA maternally expressed 3 (MEG3) inhibits cell proliferation in various types of cancer. However, the molecular mechanisms of MEG3 methylation in the regulation of multiple myeloma (MM) are unknown. In the present study, MEG3 upregulation was negatively associated with the International Staging System (ISS) status of the bone marrow samples of 39 patients with MM. MEG3 overexpression in an MM cell line resulted in elevated p53 expression. Furthermore, the results of methylation-specific PCR revealed that the abnormal methylation status of the MEG3 promoter region was present in eight of the 39 bone marrow samples collected. Treatment of the MM cell line with the DNA methylation inhibitor 5-Aza-2'-deoxycytidine (5-Aza-CdR) resulted in tumor cell proliferation inhibition, apoptosis induction and G₀/G₁ cell cycle arrest. Furthermore, 5-Aza-CdR decreased aberrant hypermethylation of the MEG3 promoter and increased the expression of MEG3. However, 5-Aza-CdR exerted no effect on p53 expression. To the best of our knowledge, the present study is the first to report that the demethylation reagent 5-Aza-CdR may serve as a therapeutic agent in MM by upregulating MEG3 expression. However, the mechanism of action was independent of p53 expression.

Emerging Roles and Potential Applications of Non-Coding RNAs in Glioblastoma

Non-coding RNAs (ncRNAs) comprise a diversity of RNA species, which do not have the potential to encode proteins. Non-coding RNAs include two classes of RNAs, namely: short regulatory ncRNAs and long non-coding RNAs (lncRNAs). The short regulatory RNAs, containing up to 200 nucleotides, include small RNAs, such as microRNAs (miRNA), short interfering RNAs (siRNAs), piwi-interacting RNAs (piRNAs), and small nucleolar RNAs (snoRNAs). The lncRNAs include long antisense RNAs and long intergenic RNAs (lincRNAs). Non-coding RNAs have been implicated as master regulators of several biological processes, their expression being strictly regulated under physiological conditions. In recent years, particularly in the last decade, substantial effort has been made to investigate the function of ncRNAs in several human diseases, including cancer. Glioblastoma is the most common and aggressive type of brain cancer in adults, with deregulated expression of small and long ncRNAs having been implicated in onset, progression, invasiveness, and recurrence of this tumor. The aim of this review is to guide the reader through important aspects of miRNA and lncRNA biology, focusing on the molecular mechanism associated with the progression of this highly malignant cancer type.

Long Noncoding RNA LINC00467 Promotes Glioma Progression through Inhibiting P53 Expression via Binding to DNMT1

Purpose: This study aimed to investigate whether long noncoding RNA (lncRNA) LINC00467 could regulate proliferative and invasive abilities of glioma cells via p53 and DNA methyltransferase 1 (DNMT1), so as to participate in the occurrence and progression of glioma. Methods: LINC00467 expression in glioma was analyzed by GEPIA database and LINC00467 expression in glioma cell lines was detected by qRT-PCR. The regulatory effects of LINC00467 and p53 on proliferative, invasive capacities and cell cycle were conducted by CCK-8 and EdU assays, transwell assay and flow cytometry, respectively. The binding conditions between LINC00467, DNMT1 and p53 were determined by RNA immunoprecipitation (RIP) and Chromatin immunoprecipitation (ChIP) assays. Western blot was conducted to determine whether LINC00467 could regulate p53 in glioma cells. Finally, rescue experiments were carried out to evaluate whether LINC00467 regulates proliferative and invasive abilities of glioma cells through p53. Results: The expression of LINC00467 was significantly up-regulated in tumor samples than that in normal samples, which was not correlated with patient survival time. Besides, expression of LINC00467 was higher in glioma cells than that of negative control cells. Upregulation of LINC00467 promoted proliferative and invasive abilities, and accelerated cell cycle in G0/G1 phase of U87 and LN229 cells. The results of RIP and ChIP assays demonstrated that LINC00467 could bind to DNMT1 and inhibit p53 expression. Overexpression of p53 partially reversed the enhancement of LINC00467 on proliferative and invasive abilities of glioma cells. Conclusion: These results indicated that high expression of LINC00467 could promote proliferative and invasive abilities of glioma cells through targeting inhibition of p53 expression by binding to DNMT1.

Meg3 Induces EMT and Invasion of Glioma Cells via Autophagy

Background

Glioma is one of the most common malignant tumors. Glioblastoma (grade IV) is considered the most malignant form of human brain tumors. Maternal expression gene 3 (Meg3) encodes a non-coding RNA (ncRNA) that plays an important role in the development and progression of cancer. However, the role of Meg3 in glioma cells remains largely unclear.

Methods

Reverse transcription-quantitative (RT-q) PCR was conducted to evaluate the mRNA expression related to cell autophagy and EMT while protein expression was detected by Western blotting. Staining of acidic vacuoles and immunofluorescence staining were used to detect autophagy. The ability of cells to migrate and invade was detected by Transwell migration and invasion assays.

Results

In the present study, it was found that the overexpression of Meg3 induced EMT, migration and invasion of glioma cells, whereas Meg3 overexpression induced autophagy of glioma cells. More importantly, the inhibition of autophagy impaired the EMT of glioma cells. In addition, Meg3-induced EMT, migration and invasion could be partially reversed by autophagy inhibitors, chloroquine (CQ) and Lys05, in glioma cells.

Conclusion

All data suggest that Meg3 induces EMT and invasion of glioma cells via autophagy. Overall, the findings of the present study demonstrate the importance of Meg3 in the molecular etiology of glioma, which also indicate its potential applications in the treatment of glioma.

LncRNA MEG3 Reduces Hippocampal Neuron Apoptosis via the PI3K/AKT/mTOR Pathway in a Rat Model of Temporal Lobe Epilepsy

PURPOSE

Temporal lobe epilepsy (TLE) is a common neurological disorder, which is characterized by recurrent spontaneous seizures. Exploring the mechanisms of epileptogenesis has been considered as a priority. The aim of this study is to investigate the effects of LncRNA MEG3 in spontaneous recurrent epileptiform discharges (SREDs) and rats with TLE.

METHODS

Rat model of TLE was produced by intraperitoneal injection of lithium chloride and pilocarpine. Rat hippocampal neuronal model of SREDs was established by Mg²⁺-free treatment. MEG3 was overexpressed by transfection of AAV-MEG3 in TLE and SREDs model. The expression of MEG3, interleukin-1β (IL-1β), interleukin-6 (IL-6) and recombinant human tumor necrosis factor-alpha (TNF-α) was detected by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Malondialdehyde (MDA) content and superoxide dismutase (SOD) activity were detected by corresponding kit. The apoptosis of hippocampal neurons was detected by terminal deoxynucleotidyl transferase transfer‑mediated dUTP nick end‑labeling (TUNEL) assay and flow cytometry. The expression of proteins related to apoptosis (Caspase-3, Bax, and Bcl-2) and the PI3K/AKT/mTOR pathway was detected by Western blot.

RESULTS

MEG3 expression was downregulated in SREDs and rats with TLE. Overexpression of MEG3 reduced the expression of IL-1β, IL-6, and TNF-α, MDA content, apoptosis rate of hippocampal neuron, increased SOD activity, and inhibited the PI3K/AKT/mTOR pathway in rats with TLE. In addition, overexpression of MEG3 enhanced cell viability and inhibited apoptosis through the activation of the PI3K/AKT/mTOR pathway in SREDs.

CONCLUSION

MEG3 reduced proinflammatory cytokines, oxidative stress, and apoptosis rate of hippocampal neuron and enhanced cell viability through the activation of the PI3K/AKT/mTOR pathway in SREDs and rats with TLE. Our findings may contribute to find a new therapeutic target for the treatment of epilepsy.

Long Non-Coding RNA: Dual Effects on Breast Cancer Metastasis and Clinical Applications

As a highly heterogeneous malignancy, breast cancer (BC) has become the most significant threat to female health. Distant metastasis and therapy resistance of BC are responsible for most of the cases of mortality and recurrence. Distant metastasis relies on an array of processes, such as cell proliferation, epithelial-to-mesenchymal transition (EMT), mesenchymal-to-epithelial transition (MET), and angiogenesis. Long non-coding RNA (lncRNA) refers to a class of non-coding RNA with a length of over 200 nucleotides. Currently, a rising number of studies have managed to investigate the association between BC and lncRNA. In this study, we summarized how lncRNA has dual effects in BC metastasis by regulating invasion, migration, and distant metastasis of BC cells. We also emphasize that lncRNA has crucial regulatory effects in the stemness and angiogenesis of BC. Clinically, some lncRNAs can regulate chemotherapy sensitivity in BC patients and may function as novel biomarkers to diagnose or predict prognosis for BC patients. The exact impact on clinical relevance deserves further study. This review can be an approach to understanding the dual effects of lncRNAs in BC, thereby linking lncRNAs to quasi-personalized treatment in the future.

Long noncoding RNAs in cancer: From discovery to therapeutic targets

Long noncoding RNAs (lncRNAs) have recently gained considerable attention as key players in biological regulation; however, the mechanisms by which lncRNAs govern various disease processes remain mysterious and are just beginning to be understood. The ease of next-generation sequencing technologies has led to an explosion of genomic information, especially for the lncRNA class of noncoding RNAs. LncRNAs exhibit the characteristics of mRNAs, such as polyadenylation, 5' methyl capping, RNA polymerase II-dependent transcription, and splicing. These transcripts comprise more than 200 nucleotides (nt) and are not translated into proteins. Directed interrogation of annotated lncRNAs from RNA-Seq datasets has revealed dramatic differences in their expression, largely driven by alterations in transcription, the cell cycle, and RNA metabolism. The fact that lncRNAs are expressed cell- and tissue-specifically makes them excellent biomarkers for ongoing biological events. Notably, lncRNAs are differentially expressed in several cancers and show a distinct association with clinical outcomes. Novel methods and strategies are being developed to study lncRNA function and will provide researchers with the tools and opportunities to develop lncRNA-based therapeutics for cancer.

Participation of tumor suppressors long non-coding RNA MEG3, microRNA-377 and PTEN in glioma cell invasion and migration

PURPOSE

Glioma is a common and fatal intracranial tumor. Both miR-377 and lncRNA MEG3 are tumor suppressors. This study was performed to investigate the association between miR-377 and lncRNA MEG3 in glioma cells.

METHODS

U118 and U251 cell lines were incubated in Dulbecco's modified Eagle's medium supplemented with miR-377 mimics, MEG3 siRNA (si-MEG3) and/or MEG3 overexpression plasmids (pc-MEG3) for 48 h. Cell migration, invasion, apoptosis, cell cycle distribution and the expression of E26 tansformation-specific-1 (ETS-1), phosphatase and tensin homologue (PTEN), E-cadherin, N-cadherin and β-catenin were detected.

RESULTS

MiR-377 mimics increased MEG3 expression and decreased the number of migrated and invaded U118 and U251 cells, without influence on apoptosis in both cell lines. Si-MEG3 transfection increased U118 cell migration and invasion and rescued miR-377 mimics-induced inhibitory in cell migration and invasion. Si-MEG3 decreased U118 cell apoptosis and induced G0/G1 cell cycle arrest, and pc-MEG3 increased U251 cell apoptosis via arresting cell cycle at G2/M phage. MiR-377 mimics and si-MEG3 increased the relative expression level of N-cadherin mRNA, and both si-MEG3 and pc-MEG3 increased E-cadherin in glioma cells. MiR-377 mimics increased ETS-1 mRNA in U118 cells, but decreased it in U251 cells. PTEN was increased by miR-377 mimics and si-MEG3 and decreased by pc-MEG3 in glioma cells.

CONCLUSIONS

These results suggested the link interaction of MEG3 with miR-377 and PTEN, but not functioning as the competing endogenous RNA. MiR-377 mimics and MEG3 were tumor suppressors in glioma cells through regulating PTEN expression.

LncRNA MEG3 inhibits cell proliferation and induces apoptosis in laryngeal cancer via miR-23a/APAF-1 axis

Long non‐coding RNA (LncRNA) MEG3 serves a regulatory role in the progression of several types of cancer, but the role of MEG3 in laryngeal cancer is still unknown. The aim of this study was to explore the regulatory role and mechanism of MEG3 in laryngeal cancer. MEG3 expression in 50 laryngeal cancer tissue samples was detected by reverse transcription‐quantitative polymerase chain reaction (RT‐qPCR). The effects of MEG3 overexpression on laryngeal cancer cells were investigated in vitro and in vivo. The mechanism of competitive endogenous RNA (ceRNA) was validated through luciferase reporter assay, RT‐qPCR and Western blotting. MEG3 was down‐regulated in laryngeal cancer tissues, and the low MEG3 expression was associated with advanced clinical stage. Additionally, MEG3 overexpression inhibited the proliferation and induced the apoptosis of laryngeal cancer cells in vitro and in vivo. Particularly, MEG3 bound to miR‐23a specifically and a reciprocal negative regulation existed between miR‐23a and MEG3. Moreover, MEG3 up‐regulated apoptotic protease activating factor‐1 (APAF‐1), a known miR‐23a's target, thereby leading to the activation of caspase‐9 and caspase‐3. Meanwhile, these activated effects were rescued by miR‐23a overexpression. In conclusion, the present study demonstrated that MEG3 functions as a novel tumour suppressive LncRNA in laryngeal cancer for the first time. Furthermore, MEG3 may act as a ceRNA to regulate APAF‐1 expression by competitive binding to miR‐23a, thereby regulating the progression of laryngeal cancer.

Maternally expressed gene 3 (MEG3): A tumor suppressor long non coding RNA

Maternally expressed gene 3 (MEG3) is a long non-coding RNA (lncRNA) located on chromosome 14q32.3. Direct sequencing experiments have shown monoallelic expression of this lncRNA. Several studies have shown down-regulation of this lncRNA in human cancers. In some cases, hypermethylation of the promoter region has been suggested as the underlying mechanism. Functional studies have shown that this lncRNA controls expression of several tumor suppressor genes and oncogenes among them are p53, RB, MYC and TGF-β. Through regulation of Wnt-β-catenin pathway, it also affects epithelial-mesenchymal transition. In vitro studies have demonstrated contribution of MEG3 in defining response to chemotherapeutic agents such as paclitaxel, cisplatin and oxaliplatin. Certain polymorphisms within MEG3 are implicated in cancer risk (rs7158663, rs4081134 and rs11160608) or therapeutic response of cancer patients (rs10132552). Taken together, this lncRNA is regarded as a putative cancer biomarker and treatment target. In the current review, several aspects of the participation of MEG3 in carcinogenesis are discussed.

LncRNA Linc00511 promotes osteosarcoma cell proliferation and migration through sponging miR-765

Long noncoding RNA (lncRNA) Linc00511 is a novel lncRNA, and it was reported to play important roles in the progression and carcinogenesis of several tumors. However, the expression and biological roles of Linc00511 in osteosarcoma were still unknown. In this research, we showed that the expression of Linc00511 was upregulated in osteosarcoma samples and cell lines. Ectopic expression of Linc00511 promoted osteosarcoma cell growth, colony formation, and migration. Moreover, overexpression of Linc00511 enhanced the epithelial-mesenchymal transition progression in osteosarcoma cell. In addition, we showed that elevated expression of Linc00511 suppressed microRNA-765 (miR-765) expression and promoted apurinic/apyrimidinic endonuclease 1 (APE1) expression in osteosarcoma cell. The expression of miR-765 was downregulated in osteosarcoma cells and samples and was negatively related to Linc00511 expression in osteosarcoma tissues. Ectopic expression of miR-765 inhibited osteosarcoma cell growth and migration. Furthermore, we showed that Linc00511 overexpression promoted MG-63 cells proliferation, colony formation, and migration via downregulation of miR-765. These results suggested that Linc00511 played as an oncogene in the development of osteosarcoma.

Long non-coding RNA CDKN2B-AS1 reduces inflammatory response and promotes cholesterol efflux in atherosclerosis by inhibiting ADAM10 expression

INTRODUCTION

Long non-coding RNAs (lncRNAs) play key roles in the development of atherosclerosis through the inflammatory pathway. This study aimed to investigate the role of lncRNA cyclin-dependent kinase inhibitor 2B antisense RNA 1 (CDKN2B-AS1) in atherosclerosis via its function in A disintegrin and metalloprotease 10 (ADAM10).

METHODS

Initially, the expression of CDKN2B-AS1 and ADAM10 in atherosclerotic plaque tissues and THP-1 macrophage-derived foam cells was determined, after which the cholesterol efflux rate of macrophages was calculated. Interaction between CDKN2B-AS1 and ADAM10 was analyzed, after which, expression of CDKN2B-AS1 and ADAM10 were altered to explore their effects on inflammatory response and cholesterol efflux. The aforementioned findings were further intended to be validated by the atherosclerosis mouse model experiments.

RESULTS

Atherosclerotic plaque tissue and THP-1 macrophage-derived foam cells exhibited downregulated CDKN2B-AS1 and upregulated ADAM10. Upon overexpressing CDKN2B-AS1 or silencing ADAM10, lipid accumulation was reduced and cholesterol efflux was increased. CDKN2B-AS1 located in the nucleus could bind to DNA methyltransferase 1 (DNMT1) to enhance methylation of ADAM10 promoter, leading to suppressed atherosclerotic inflammatory response and promoted cholesterol efflux.

CONCLUSION

Altogether, lncRNA CDKN2B-AS1 can inhibit the transcription of ADAM10 via DNMT1-mediated ADAM10 DNA methylation, consequently preventing inflammatory response of atherosclerosis and promoting cholesterol efflux.

Mycobacterium smegmatis But Not Mycobacterium avium subsp. hominissuis Causes Increased Expression of the Long Non-Coding RNA MEG3 in THP-1-Derived Human Macrophages and Associated Decrease of TGF-β

Pathogenic mycobacteria are able to persist intracellularly in macrophages, whereas non-pathogenic mycobacteria are effectively combated and eliminated after their phagocytosis. It is known that TGF-β plays an important role in this context. Infection with pathogenic mycobacteria such as Mycobacterium tuberculosis or M. avium leads to production of active TGF-β, which blocks the ability of IFN-γ and TNF-α to inhibit intracellular replication. On the other hand, it is known that the long non-coding RNA (lncRNA) maternally expressed 3 (MEG3) is involved in the regulation of TGF-β. In this study, we show how the infection of THP-1-derived human macrophages with the saprophytic M. smegmatis but not with the facultatively pathogenic M. avium subsp. hominissuis leads to increased MEG3 expression. This is associated with the downregulation of DNA methyltransferases (DNMT) 1 and 3b, which are known to regulate MEG3 expression via promoter hypermethylation. Consequently, we observe a significant downregulation of TGF-β in M. smegmatis-infected macrophages but not in M. avium subsp. hominissuis pointing to lncRNAs as novel mediators of host cell response during mycobacterial infections.

Downregulation of KLF13 through DNMT1-mediated hypermethylation promotes glioma cell proliferation and invasion

Background

Recent evidence indicates that Kruppel-like factor 13 (KLF13) has critical roles in regulating cell differentiation, proliferation and may function as a tumor suppressor. However, its role in glioma progression is poorly understood.

Methods

Public database was used to explore the expression and prognostic value of KLF13 in glioma. Cell proliferation and invasion assays were used to explore the role of KLF13. Bisulfite sequencing and ChIP assay were used to determine the methylation of KLF13 promoter in glioma and the regulation of KLF13 by DNMT1.

Results

We found that KLF13 inhibited glioma cell proliferation and invasion, which could be reversed by AKT activation. DNMT1-mediated hypermethylation was responsible for downregulation of KLF13. Knocking down of DNMT1 restored KFL13 expression and inhibited cell proliferation and invasion as well. Patients with high expression of KLF13 might have a better prognosis.

Conclusion

KLF13 suppressed glioma aggressiveness and the regulation of KLF13 could be a potential therapeutic target.

MEG3: an Oncogenic Long Non-coding RNA in Different Cancers

Long noncoding RNAs (lncRNAs) have recently considered as central regulators in diverse biological processes and emerged as vital players controlling tumorigenesis. Several lncRNAs can be classified into oncogenes and tumor suppressor genes depending on their function in cancer. A maternally expressed gene 3 (MEG3) gene transcripts a 1.6 kb lncRNA whose act as an antitumor component in different cancer cells, such as breast, liver, glioma, colorectal, cervical, gastric, lung, ovarian and osteosarcoma cancer cells. The present review highlights biological function of MEG3 to repress tumor through regulating the major tumor suppressor genes p53 and Rb, inhibiting angiogenesis-related factor, or controlling miRNAs. On the other hand, previous studies have also suggested that MEG3 mediates epithelial-mesenchymal transition (EMT). However, deregulation of MEG3 is associated with the  development and progression of cancer, suggesting that MEG3 may function as a potential biomarker and therapeutic target for human cancers.

Long Non-coding RNA MEG3 Attenuates the Angiotensin II-Induced Injury of Human Umbilical Vein Endothelial Cells by Interacting With p53

Angiotensin II (Ang II)-induced damage to endothelial cells (ECs) plays a crucial role in the pathogenesis of cardiovascular disease. This study aimed to investigate the role of maternally expressed gene 3 (Meg3) in endothelial cell injury. A lncRNA human gene expression microarray analysis was used to identify differentially expressed lncRNAs in human umbilical vein endothelial cell (HUVECs). Cell viability, apoptosis, and migration were then assessed Ang II-treated HUVECs. qRT-PCR and western blotting were performed to detect the expression level of p53 after Meg3 knockdown and overexpression. We observed that Ang II treatment decreased the Meg3 level in HUVECs. Next, both knockdown of Meg3 and Ang II decreased cell viability, increased apoptotic cell rate and impair migration function in HUVECs. Furthermore, overexpression of Meg3 inhibited cell apoptosis, and increased cell migration by enhancing p53 transcription on its target genes, including CRP, ICAM-1, VEGF, and HIF-1α. Our findings indicate that Meg3 might be associated with cardiovascular disease development.

Long noncoding RNA ATB participates in the development of renal cell carcinoma by downregulating p53 via binding to DNMT1

Long noncoding RNA (lncRNA) exerts an essential role in the pathological processes of many diseases. Our previous study found that lncRNA ATB was highly expressed in renal cell carcinoma (RCC). Cell Counting Kit-8 (CCK-8), 5-ethynyl-2'-deoxyuridine (EdU), and migration-related assays were conducted to access the regulatory effects of lncRNA ATB on proliferative and migratory capacities of RCC cells. Flow cytometry was carried out to determine cell cycle and apoptosis influenced by lncRNA ATB. The interaction among lncRNA ATB, DNMT1, and p53 was evaluated through RNA immunoprecipitation (RIP), chromatin immunoprecipitation (ChIP), and western blot analyses. The results showed that lncRNA ATB knockdown in RCC cell line ACHN inhibited proliferative and migratory capacities and promoted apoptosis. Meanwhile, overexpression of lncRNA ATB in RCC cell line A-498 promoted proliferative and migratory capacities but inhibited apoptosis. RIP and ChIP assays confirmed that lncRNA ATB can bind to DNMT1 and stabilize its expression; meanwhile, it can promote the binding of DNMT1 to p53. Overexpression of p53 partially reversed the proliferative and migratory changes caused by lncRNA ATB. To sum up, our study revealed that high expression of lncRNA ATB could accelerate the proliferative and migratory rates of RCC cells and inhibit cell apoptosis through downregulating p53 via binding to DNMT1.

LincRNA-p21 enhances the sensitivity of radiotherapy for gastric cancer by targeting the β-catenin signaling pathway

Long noncoding RNAs (lncRNAs) are a large and diverse class of transcribed RNA molecules with a length of more than 200 nucleotides that modulate the gene expression at the posttranscriptional or transcriptional level. LncRNAs played crucial roles in many biological processes, such as cell proliferation, metastasis, and migraton. In this study, we evaluated the role of lincRNA-p21 in the gastric cancer (GC). We demonstrated that the expression level of lincRNA-p21 was downregulated in the GC tissues and cell lines. Moreover, ectopic expression of lincRNA-p21 suppressed the GC cell growth, cell cycle, and migration. Furthermore, we demonstrated that the X-ray increased the expression level of lincRNA-p21 in both the HCG-27 and SGC7901 cells and elevated expression of lincRNA-p21 increased the radiotherapy sensitivity of the GC cell. In addition, we showed that ectopic expression of lincRNA-p21 suppressed the β-catenin and c-myc expression. Overexpression of lincRNA-p21 inhibited the GC cell proliferation and increased the radiosensitivity of GC cells by regulating the β-catenin signaling pathway. These data suggested that lincRNA-p21 acted as a tumor suppressor gene in the development of GC.

miR-506 attenuates methylation of lncRNA MEG3 to inhibit migration and invasion of breast cancer cell lines via targeting SP1 and SP3

Background

Breast cancer has been the first death cause of cancer in women all over the world. Metastasis is believed to be the most important process for treating breast cancer. There is evidence that lncRNA MEG3 functions as a tumor suppressor in breast cancer metastasis. However, upstream regulation of MEG3 in breast cancer remain elusive. Therefore, it is critical to elucidate the underlying mechanism upstream MEG3 to regulate breast cancer metastasis.

Methods

We employed RT-qPCR and Western blot to examine expression level of miR-506, DNMT1, SP1, SP3 and MEG3. Besides, methylation-specific PCR was used to determine the methylation level of MEG3 promoter. Wound healing assay and transwell invasion assay were utilized to measure migration and invasion ability of breast cancer cells, respectively.

Results

SP was upregulated while miR-506 and MEG3 were downregulated in breast tumor tissue compared to adjacent normal breast tissues. In addition, we found that miR-506 regulated DNMT1 expression in an SP1/SP3-dependent manner, which reduced methylation level of MEG3 promoter and upregulated MEG3 expression. SP3 knockdown or miR-506 mimic suppressed migration and invasion of MCF-7 and MDA-MB-231 cells whereas overexpression of SP3 compromised miR-506-inhibited migration and invasion.

Conclusions

Our data reveal a novel axis of miR-506/SP3/SP1/DNMT1/MEG3 in regulating migration and invasion of breast cancer cell lines, which provide rationales for developing effective therapies to treating metastatic breast cancers.