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    ADAR1 is a new target of METTL3 and plays a pro-oncogenic role in glioblastoma by an editing-independent mechanism. Tassinari Valentina,Cesarini Valeriana,Tomaselli Sara,Ianniello Zaira,Silvestris Domenico Alessandro,Ginistrelli Lavinia Ceci,Martini Maurizio,De Angelis Biagio,De Luca Gabriele,Vitiani Lucia Ricci,Fatica Alessandro,Locatelli Franco,Gallo Angela Genome biology BACKGROUND:N-methyladenosine (m6A) and adenosine-to-inosine (A-to-I) RNA editing are two of the most abundant RNA modification events affecting adenosines in mammals. Both these RNA modifications determine mRNA fate and play a pivotal role in tumor development and progression. RESULTS:Here, we show that METTL3, upregulated in glioblastoma, methylates ADAR1 mRNA and increases its protein level leading to a pro-tumorigenic mechanism connecting METTL3, YTHDF1, and ADAR1. We show that ADAR1 plays a cancer-promoting role independently of its deaminase activity by binding CDK2 mRNA, underlining the importance of ADARs as essential RNA-binding proteins for cell homeostasis as well as cancer progression. Additionally, we show that ADAR1 knockdown is sufficient to strongly inhibit glioblastoma growth in vivo. CONCLUSIONS:Hence, our findings underscore METTL3/ADAR1 axis as a novel crucial pathway in cancer progression that connects m6A and A-to-I editing post-transcriptional events. 10.1186/s13059-021-02271-9
    Dysregulated N6-methyladenosine methylation writer METTL3 contributes to the proliferation and migration of gastric cancer. Liu Tong,Yang Sheng,Sui Jing,Xu Si-Yi,Cheng Yan-Ping,Shen Bo,Zhang Yan,Zhang Xiao-Mei,Yin Li-Hong,Pu Yue-Pu,Liang Ge-Yu Journal of cellular physiology Accumulating evidence implies that N6-methyladenosine (m6A) methylation participated in the tumorigenesis of gastric cancer (GC). Here we synthetically analyzing the prognostic value and expression profile of seven m6A methylation-relevant genes through silico analysis of sequencing data downloaded from The Cancer Genome Atlas, Kaplan-Meier plotter, and Gene Expression Omnibus database. We explored the methyltransferase-like 3 (METTL3) expression in GC cell line and tumor tissues by reverse transcription quantitative polymerase chain reaction and western blot analysis. The m6A methylation status of total RNA was measured by m6A RNA methylation quantification kit. Small interfering RNA was used to establish METTL3 knockdown cell lines. We also measure the proliferation and migration capability GC cell. Furthermore, we detect the epithelial cell mesenchymal transition marker and m6A methylation level after METTL3 knock down. Our result revealed that METTL3 was significantly increased in GC tissues compared with control in big crowd data sets. Survival analysis showed that METTL3 serve as a poor prognostic factor for GC patients. The expression level of METTL3 gradually increased with the progress of tumor stage and grade. GFI1 is an important transcription factor associated with METTL3. We verified the up-trend of METTL3 in messenger RNA and protein expression and observed a significant increase in the m6A methylation status of total RNA in the GC cells and tissues. METTL3 knockdown inhibited total RNA m6A methylation level, as well as cell proliferation and migration capacity. Moreover, METTL3 knockdown decreased α-smooth muscle actin. Taken together, our finding revealed that m6A methylation writer METTL3 serve as an oncogene in tumorigenesis of GC. 10.1002/jcp.28994
    METTL3 May Regulate Testicular Germ Cell Tumors Through EMT and Immune Pathways. Luo Yang,Sun Yuan,Li Lei,Mao Yuling Cell transplantation Testicular germ cell tumors (TGCTs) are highly prevalent in young men aged 20-40 years and are one of the most common lethal solid tumors in men of this age. Due to the current unclear mechanism of tumor development, there is a lack of effective treatment, and therefore in-depth research of the molecular mechanism of the occurrence and development of TGCT and the search for suitable and effective therapeutic targets and molecular markers are of great significance for achieving effective treatment. METTL3 is a very important methylase, which has been implicated in the progression of many cancers, but the role of METTL3 in TGCT has not been fully elucidated. In this article, we found that METTL3 expression was significantly downregulated in TGCT tissues, and patients with low expression levels had lower overall survival and relapse-free survival rates. After overexpressing METTL3, cell proliferation, invasion, and migration ability significantly increased, while influencing the expression of epithelial-mesenchymal transition (EMT)-related proteins. In addition, we observed that the expression level of METTL3 positively correlated with molecular markers and infiltration level of CD8+ and CD4+ T cells and natural killer cells. In sum, our findings identified that METTL3 can be used as an independent prognostic marker in patients with TGCT. METTL3 participates in the proliferation, migration, and invasion of TGCT cells by regulating the expression of EMT-related genes and may also play a role in activating the tumor immune response in TGCT. 10.1177/0963689720946653
    RNA N-Methyladenosine Methyltransferase METTL3 Facilitates Colorectal Cancer by Activating the mA-GLUT1-mTORC1 Axis and Is a Therapeutic Target. Chen Huarong,Gao Shanshan,Liu Weixin,Wong Chi-Chun,Wu Jianfeng,Wu Jingtong,Liu Dabin,Gou Hongyan,Kang Wei,Zhai Jianning,Li Chuangen,Su Hao,Wang Shiyan,Soares Fraser,Han Jiahuai,He Housheng Hansen,Yu Jun Gastroenterology BACKGROUND & AIMS:RNA N-methyladenosine (mA) modification has recently emerged as a new regulatory mechanism in cancer progression. We aimed to explore the role of the mA regulatory enzyme METTL3 in colorectal cancer (CRC) pathogenesis and its potential as a therapeutic target. METHODS:The expression and clinical implication of METTL3 were investigated in multiple human CRC cohorts. The underlying mechanisms of METTL3 in CRC were investigated by integrative mA sequencing, RNA sequencing, and ribosome profiling analyses. The efficacy of targeting METTL3 in CRC treatment was elucidated in CRC cell lines, patient-derived CRC organoids, and Mettl3-knockout mouse models. RESULTS:Using targeted clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 dropout screening, we identified METTL3 as the top essential mA regulatory enzyme in CRC. METTL3 was overexpressed in 62.2% (79/127) and 88.0% (44/50) of primary CRCs from 2 independent cohorts. High METTL3 expression predicted poor survival in patients with CRC (n = 374, P < .01). Functionally, silencing METTL3 suppressed tumorigenesis in CRC cells, human-derived primary CRC organoids, and Mettl3-knockout mouse models. We discovered the novel functional mA methyltransferase domain of METTL3 in CRC cells by domain-focused CRISPR screening and mutagenesis assays. Mechanistically, METTL3 directly induced the mA-GLUT1-mTORC1 axis as identified by integrated mA sequencing, RNA sequencing, ribosome sequencing, and functional validation. METTL3 induced GLUT1 translation in an mA-dependent manner, which subsequently promoted glucose uptake and lactate production, leading to the activation of mTORC1 signaling and CRC development. Furthermore, inhibition of mTORC1 potentiated the anticancer effect of METTL3 silencing in CRC patient-derived organoids and METTL3 transgenic mouse models. CONCLUSIONS:METTL3 promotes CRC by activating the mA-GLUT1-mTORC1 axis. METTL3 is a promising therapeutic target for the treatment of CRC. 10.1053/j.gastro.2020.11.013
    METTL3 regulates heterochromatin in mouse embryonic stem cells. Xu Wenqi,Li Jiahui,He Chenxi,Wen Jing,Ma Honghui,Rong Bowen,Diao Jianbo,Wang Liyong,Wang Jiahua,Wu Feizhen,Tan Li,Shi Yujiang Geno,Shi Yang,Shen Hongjie Nature METTL3 (methyltransferase-like 3) mediates the N-methyladenosine (mA) methylation of mRNA, which affects the stability of mRNA and its translation into protein. METTL3 also binds chromatin, but the role of METTL3 and mA methylation in chromatin is not fully understood. Here we show that METTL3 regulates mouse embryonic stem-cell heterochromatin, the integrity of which is critical for silencing retroviral elements and for mammalian development. METTL3 predominantly localizes to the intracisternal A particle (IAP)-type family of endogenous retroviruses. Knockout of Mettl3 impairs the deposition of multiple heterochromatin marks onto METTL3-targeted IAPs, and upregulates IAP transcription, suggesting that METTL3 is important for the integrity of IAP heterochromatin. We provide further evidence that RNA transcripts derived from METTL3-bound IAPs are associated with chromatin and are mA-methylated. These mA-marked transcripts are bound by the mA reader YTHDC1, which interacts with METTL3 and in turn promotes the association of METTL3 with chromatin. METTL3 also interacts physically with the histone 3 lysine 9 (H3K9) tri-methyltransferase SETDB1 and its cofactor TRIM28, and is important for their localization to IAPs. Our findings demonstrate that METTL3-catalysed mA modification of RNA is important for the integrity of IAP heterochromatin in mouse embryonic stem cells, revealing a mechanism of heterochromatin regulation in mammals. 10.1038/s41586-021-03210-1
    METTL3 expression is associated with glycolysis metabolism and sensitivity to glycolytic stress in hepatocellular carcinoma. Lin Ye,Wei Xiangling,Jian Zhixiang,Zhang Xuewen Cancer medicine METTL3 is an RNA methyltransferase implicated in the control of cell differentiation and proliferation in embryonic development and cancer. The current study was aimed to explore the function and underlying mechanism of METTL3 in hepatocellular carcinoma (HCC). We evaluated the expression and prognostic significance of METTL3 in 100 HCC cases and TCGA dataset. In HCC cases, both the RNA and protein expression of METTL3 were significantly upregulated and associated with poor prognosis. Gene set enrichment analysis of transcriptional profiles in HCC specimens revealed that METTL3 expression was associated with impaired glucose metabolism and mTOR signal pathway. In Huh-7 and SMMC-7721 HCC cells, downregulation of METTL3 by siRNA interference inhibited glycolytic capacity, which was proved by the decreased intracellular glucose uptake and lactate production. In terms of mechanism, we found mTORC1 activity was impaired by downregulation of METTL3, additional silencing of METTL3 cannot further decrease the phosphorylation level of mTORC1 and glycolysis activity in Rapamycin-treated HCC cells. At last, we observed that downregulation of METTL3 synergizes with the glycolysis inhibitor 2-deoxyglucose (2-DG) to inhibit tumor growth in vitro. Our study provided evidence that METTL3 is involved in the regulation of glycolysis activity in HCC, suggesting that suppression of glycolysis via METTL3 inhibition was a potential treating strategy against HCC. 10.1002/cam4.2918
    METTL3 Facilitates Oral Squamous Cell Carcinoma Tumorigenesis by Enhancing c-Myc Stability via YTHDF1-Mediated mA Modification. Zhao Wei,Cui Yameng,Liu Lina,Ma Xiaozhou,Qi Xiaoqian,Wang Yue,Liu Zihao,Ma Shiqing,Liu Jingwen,Wu Jie Molecular therapy. Nucleic acids N-Methyladenosine (mA) is the most common internal modification of eukaryotic messenger RNA (mRNA) that occurred on the N nitrogen of adenosine. However, the roles of mA in oral squamous cell carcinoma (OSCC) are still elusive. Here, we investigate the function and mechanism of methyltransferase-like 3 (METTL3) in OSCC tumorigenesis. Clinically, METTL3 was significantly upregulated in tissue samples and correlated with the poor prognosis of OSCC patients. Functionally, loss and gain studies illustrated that METTL3 promoted the proliferation, invasion, and migration of OSCC cells in vitro, and METTL3 knockdown inhibited tumor growth in vivo. Mechanistically, methylated RNA immunoprecipitation sequencing (MeRIP-seq) illustrated that METTL3 targeted the 3' UTR (near to stop codon) of the c-Myc transcript to install the mA modification, thereby enhancing its stability. Furthermore, results revealed that YTH N-methyladenosine RNA binding protein 1 (YTH domain family, member 1 [YTHDF1]) mediated the mA-increased stability of c-Myc mRNA catalyzed by METTL3. In conclusion, our findings herein identify that METTL3 accelerates the c-Myc stability via YTHDF1-mediated mA modification, thereby giving rise to OSCC tumorigenesis. 10.1016/j.omtn.2020.01.033
    METTL3-mediated mA modification of HDGF mRNA promotes gastric cancer progression and has prognostic significance. Wang Qiang,Chen Chen,Ding Qingqing,Zhao Yan,Wang Zhangding,Chen Junjie,Jiang Zerun,Zhang Yan,Xu Guifang,Zhang Jingjing,Zhou Jianwei,Sun Beicheng,Zou Xiaoping,Wang Shouyu Gut OBJECTIVE:N-methyladenosine (mA) RNA methylation and its associated methyltransferase METTL3 are involved in tumour initiation and progression via the regulation of RNA function. This study explored the biological function and clinical significance of METTL3 in gastric cancer (GC). DESIGN:The prognostic value of METTL3 expression was evaluated using tissue microarray and immunohistochemical staining analyses in a human GC cohort. The biological role and mechanism of METTL3 in GC tumour growth and liver metastasis were determined in vitro and in vivo. RESULTS:The level of mA RNA was significantly increased in GC, and METTL3 was the main regulator involved in the abundant mA RNA modification. METTL3 expression was significantly elevated in GC tissues and associated with poor prognosis. Multivariate Cox regression analysis revealed that METTL3 expression was an independent prognostic factor and effective predictor in human patients with GC. Moreover, METTL3 overexpression promoted GC proliferation and liver metastasis in vitro and in vivo. Mechanistically, P300-mediated H3K27 acetylation activation in the promoter of METTL3 induced METTL3 transcription, which stimulated mA modification of HDGF mRNA, and the mA reader IGF2BP3 then directly recognised and bound to the mA site on HDGF mRNA and enhanced HDGF mRNA stability. Secreted HDGF promoted tumour angiogenesis, while nuclear HDGF activated GLUT4 and ENO2 expression, followed by an increase in glycolysis in GC cells, which was correlated with subsequent tumour growth and liver metastasis. CONCLUSIONS:Elevated METTL3 expression promotes tumour angiogenesis and glycolysis in GC, indicating that METTL3 expression is a potential prognostic biomarker and therapeutic target for human GC. 10.1136/gutjnl-2019-319639
    METTL3 regulates the malignancy of cervical cancer via post-transcriptional regulation of RAB2B. Hu Yingying,Li Youjiang,Huang Yiping,Jin Zujian,Wang Caifeng,Wang Hongsheng,Xu Jian European journal of pharmacology Cervical cancer is one of the leading causes of cancer death in women worldwide. While molecular mechanisms of initiation and cervical carcinogenesis are not well studied. Our data showed that the expression of Methyltransferase-like 3 (METTL3) was upregulated in cervical tumor tissues as compared with normal tissues. Its expression was associated with poor prognosis of cervical cancer. Knockdown of METTL3 can suppress the proliferation of cervical cancer cells. The expression of METTL3 was significantly correlated with the expression of RAB2B, one member of RAS oncogene family. Over expression of RAB2B can significantly attenuate sh-METTL3-suppressed cell proliferation. Mechanistically, METTL3 can increase the mRNA stability of RAB2B via an IGF2BP3-dependent manner. Collectively, METTL3 can trigger growth of cervical cancer cells via upregulation of RAB2B. It indicated that METTL3 might be a potential target for cervical cancer therapy. 10.1016/j.ejphar.2020.173134
    Upregulation of METTL3 Expression Predicts Poor Prognosis in Patients with Esophageal Squamous Cell Carcinoma. Xia Tian-Liang,Yan Shu-Mei,Yuan Li,Zeng Mu-Sheng Cancer management and research Background:The N-methyladenosine (mA) RNA modification of mRNA mediates various cellular functions and cancer progression. However, the roles of mA RNA modification in the regulation of esophageal squamous cell carcinoma (ESCC), the dominant subtype of esophageal cancer in Asia, were unclear. Materials and Methods:Here, we analyzed the mRNA expression level of methyltransferase like 3 (METTL3) in the public available datasets of ESCC tissues and matched adjacent normal tissues. We also performed immunohistochemistry (IHC) assays to detect the protein expression of METTL3 in human ESCC tissue specimen. In our study, we also analyzed the association between METTL3 expression and prognosis using Cox proportional hazard regression in 207 ESCC patients. Results:The results of public available datasets and IHC assays showed that METTL3 was upregulated in tumor compared with adjacent nonmalignant esophageal mucosal tissues. The IHC results indicated that higher expression level of METTL3 was associated with worse survival. We also found that METTL3 expression level was an independent predictor for disease-free survival and overall survival of ESCC patients. Conclusion:Our results revealed that the METTL3 expression level could be used as an independent prognostic biomarker for ESCC prognosis. 10.2147/CMAR.S245019
    METTL3 and N6-Methyladenosine Promote Homologous Recombination-Mediated Repair of DSBs by Modulating DNA-RNA Hybrid Accumulation. Zhang Canfeng,Chen Liping,Peng Di,Jiang Ao,He Yunru,Zeng Yanru,Xie Chen,Zhou Haoxian,Luo Xiaotong,Liu Haiying,Chen Liang,Ren Jian,Wang Wengong,Zhao Yong Molecular cell Double-strand breaks (DSBs) are the most deleterious DNA lesions, which, if left unrepaired, may lead to genome instability or cell death. Here, we report that, in response to DSBs, the RNA methyltransferase METTL3 is activated by ATM-mediated phosphorylation at S43. Phosphorylated METTL3 is then localized to DNA damage sites, where it methylates the N6 position of adenosine (m6A) in DNA damage-associated RNAs, which recruits the m6A reader protein YTHDC1 for protection. In this way, the METTL3-m6A-YTHDC1 axis modulates accumulation of DNA-RNA hybrids at DSBs sites, which then recruit RAD51 and BRCA1 for homologous recombination (HR)-mediated repair. METTL3-deficient cells display defective HR, accumulation of unrepaired DSBs, and genome instability. Accordingly, depletion of METTL3 significantly enhances the sensitivity of cancer cells and murine xenografts to DNA damage-based therapy. These findings uncover the function of METTL3 and YTHDC1 in HR-mediated DSB repair, which may have implications for cancer therapy. 10.1016/j.molcel.2020.06.017
    Roles of METTL3 in cancer: mechanisms and therapeutic targeting. Zeng Chengwu,Huang Wanxu,Li Yangqiu,Weng Hengyou Journal of hematology & oncology N-methyladenosine (mA) is the most abundant mRNA modification and is catalyzed by the methyltransferase complex, in which methyltransferase-like 3 (METTL3) is the sole catalytic subunit. Accumulating evidence in recent years reveals that METTL3 plays key roles in a variety of cancer types, either dependent or independent on its mA RNA methyltransferase activity. While the roles of mA modifications in cancer have been extensively reviewed elsewhere, the critical functions of METTL3 in various types of cancer, as well as the potential targeting of METTL3 as cancer treatment, have not yet been highlighted. Here we summarize our current understanding both on the oncogenic and tumor-suppressive functions of METTL3, as well as the underlying molecular mechanisms. The well-documented protein structure of the METTL3/METTL14 heterodimer provides the basis for potential therapeutic targeting, which is also discussed in this review. 10.1186/s13045-020-00951-w
    Connecting METTL3 and intratumoural CD33 MDSCs in predicting clinical outcome in cervical cancer. Ni Huan-He,Zhang Lin,Huang He,Dai Shu-Qin,Li Jiang Journal of translational medicine BACKGROUND:Methyltransferase-like 3 (METTL3) is a member of the mA methyltransferase family and acts as an oncogene in cancers. Recent studies suggest that host innate immunity is regulated by the enzymes controlling mA epitranscriptomic changes. Here, we aim to explore the associations between the levels of METTL3 and CD33 myeloid-derived suppressor cells (MDSCs) in tumour tissues and the survival of patients with cervical cancer (CC). METHODS:Specimens of paraffin embedded tumour from 197 CC patients were collected. The expression levels of METTL3 and CD33 were measured by immunohistochemical (IHC) staining. The clinical associations of the IHC variants were analysed by Pearson's or Spearman's chi-square tests. Overall survival (OS) and disease-free survival (DFS) were estimated by the Kaplan-Meier method and log-rank test. Hazard ratios (HRs) and independent significance were obtained via Cox proportional hazards models for multivariate analyses. METTL3 in CD33 cells or CC-derived cells was knocked down by METTL3-specific siRNA, and MDSC induction in vitro was performed in a co-culture system in the presence of METTL3-siRNA and METTL3-knockdown-CC-derived cells compared with that of the corresponding controls. RESULTS:We found that tumour tissues displayed increased levels of METTL3 and CD33 MDSCs compared with tumour-adjacent tissues from the same CC patients. Importantly, METTL3 expression was positively related to the density of CD33 cells in tumour tissues (P = 0.011). We further found that the direct CD33CD11bHLA-DR MDSC induction and tumour-derived MDSC induction in vitro were decreased in the absence of METTL3. The level of METTL3 in tumour microenvironments was significantly related to advanced tumour stage. The levels of METTL3 and CD33 MDSCs in tumour tissues were notably associated with reduced DFS or OS. Cox model analysis revealed that the level of METTL3 in tumour cells was an independent factor for patient survival, specifically for DFS (HR = 3.157, P = 0.022) and OS (HR = 3.271, P = 0.012), while the CD33 MDSC number was an independent predictor for DFS (HR: 3.958, P = 0.031). Interestingly, in patients with advanced-disease stages (II-IV), METTL3 in tumour cells was an independent factor for DFS (HR = 6.725, P = 0.010) and OS (HR = 5.140, P = 0.021), while CD33 MDSC density was an independent factor for OS (HR = 8.802, P = 0.037). CONCLUSION:Our findings suggest that CD33 MDSC expansion is linked to high levels of METTL3 and that METTL3 and CD33 MDSCs are independent prognostic factors in CC. 10.1186/s12967-020-02553-z
    mA methyltransferase METTL3 promotes retinoblastoma progression via PI3K/AKT/mTOR pathway. Zhang Han,Zhang Ping,Long Chongde,Ma Xinqi,Huang Hao,Kuang Xielan,Du Han,Tang Han,Ling Xiangtian,Ning Jie,Liu Huijun,Deng Xizhi,Zou Yuxiu,Wang Renchun,Cheng Hao,Lin Shuibin,Zhang Qingjiong,Yan Jianhua,Shen Huangxuan Journal of cellular and molecular medicine Retinoblastoma (RB) is a common intraocular malignancy in children. Due to the poor prognosis of RB, it is crucial to search for efficient diagnostic and therapeutic strategies. Studies have shown that methyltransferase-like 3 (METTL3), a major RNA N (6)-adenosine methyltransferase, is closely related to the initiation and development of cancers. Nevertheless, whether METTL3 is associated with RB remains unexplored. Therefore, we investigated the function and mechanisms of METTL3 in the regulation of RB progression. We manipulated METTL3 expression in RB cells. Then, cell proliferation, apoptosis, migration and invasion were analysed. We also analysed the expression of PI3K/AKT/mTOR pathway members. Finally, we incorporated subcutaneous xenograft mouse models into our studies. The results showed that METTL3 is highly expressed in RB patients and RB cells. We found that METTL3 knockdown decreases cell proliferation, migration and invasion of RB cells, while METTL3 overexpression promotes RB progression in vitro and in vivo. Moreover, two downstream members of the PI3K/AKT/mTOR pathway, P70S6K and 4EBP1, were affected by METTL3. Our study revealed that METTL3 promotes the progression of RB through PI3K/AKT/mTOR pathways in vitro and in vivo. Targeting the METTL3/PI3K/AKT/mTOR signalling axis could be a promising therapeutic strategy for the treatment of RB. 10.1111/jcmm.15736