METTL3-mediated N6-methyladenosine modification is critical for epithelial-mesenchymal transition and metastasis of gastric cancer

Abstract

Background As one of the most frequent chemical modifications in eukaryotic mRNAs, N6-methyladenosine (m6A) modification exerts important effects on mRNA stability, splicing, and translation. Recently, the regulatory role of m6A in tumorigenesis has been increasingly recognized. However, dysregulation of m6A and its functions in tumor epithelial-mesenchymal transition (EMT) and metastasis remain obscure. Methods qRT-PCR and immunohistochemistry were used to evaluate the expression of methyltransferase-like 3 (METTL3) in gastric cancer (GC). The effects of METTL3 on GC metastasis were investigated through in vitro and in vivo assays. The mechanism of METTL3 action was explored through transcriptome-sequencing, m6A-sequencing, m6A methylated RNA immunoprecipitation quantitative reverse transcription polymerase chain reaction (MeRIP qRT-PCR), confocal immunofluorescent assay, luciferase reporter assay, co-immunoprecipitation, RNA immunoprecipitation and chromatin immunoprecipitation assay. Results Here, we show that METTL3, a major RNA N6-adenosine methyltransferase, was upregulated in GC. Clinically, elevated METTL3 level was predictive of poor prognosis. Functionally, we found that METTL3 was required for the EMT process in vitro and for metastasis in vivo. Mechanistically, we unveiled the METTL3-mediated m6A modification profile in GC cells for the first time and identified zinc finger MYM-type containing 1 (ZMYM1) as a bona fide m6A target of METTL3. The m6A modification of ZMYM1 mRNA by METTL3 enhanced its stability relying on the “reader” protein HuR (also known as ELAVL1) dependent pathway. In addition, ZMYM1 bound to and mediated the repression of E-cadherin promoter by recruiting the CtBP/LSD1/CoREST complex, thus facilitating the EMT program and metastasis. Conclusions Collectively, our findings indicate the critical role of m6A modification in GC and uncover METTL3/ZMYM1/E-cadherin signaling as a potential therapeutic target in anti-metastatic strategy against GC.

Multiple Functions and Mechanisms Underlying the Role of METTL3 in Human Cancers

“…METTL3 and m 6 A were upregulated in human osteosarcoma (46), gastric cancer (23,47,48), melanoma (49), ovarian carcinoma (50), and hepatocellular carcinoma (51). Its expression level gradually increased with the increasing tumor stage and grade.…”

“…Its expression level gradually increased with the increasing tumor stage and grade. METTL3 was an indicator of poor prognosis and METTL3 silencing inhibited the proliferation, migration, and invasion abilities of cells, colony formation, and motility (24,(47)(48)(49)(50)(51)(52), demonstrating that METTL3 plays an oncogenic role in these cancers. Taketo et al reported that a METTL3-knockdown pancreatic cancer cell line showed higher sensitivity to anticancer agents such as gemcitabine, 5-fluorouracil, cisplatin, and irradiation, suggesting that METTL3 is a potential target for the enhancement of therapeutic efficacy (25).…”

Functions of N6-methyladenosine and its role in cancer

“…Loss of METTL3 results in higher level of BCL-XS isoform and NCOR2α isoform and inhibition of GSC growth and self-renewal [41]. In gastric cancer, upregulated METTL3 promotes stability of ZMYM1, thus enhancing EMT process in vitro and metastasis in vivo [42]. Moreover, METTL3 can also participate in regulation of target mRNA in a post-modification way, therefore partially acting as a reader [43,44].…”

m6A-binding proteins: the emerging crucial performers in epigenetics

“…Firstly, a few of non-classic m 6 A readers are found through RNA sequencing, such as HuR and SND1. ZMYM1 mRNA, which could facilitate the process of EMT and the metastasis of GC, was modified by m 6 A and its stability was enhanced relying on the recognition by HuR [116]. Another novel m 6 A reader SND1 bound to the m 6 A sites of ORF50 transcript and promoted its stability.…”

“…Increasing the expression of β-catenin, WNT6 and FZD9A to activate Wnt/β-catenin pathway [49] YTHDF3 GAS5 Enhancing the degradation of lncRNA GAS5 [50] YTHDC1 circNSUN2 Facilitating circNSUN2 export from nucleus to cytoplasm [51] IGF2BP2 HMGA2 Forming a circNSUN2/IGF2BP2 complex to fortify the stability of HMGA2 [51] IGF2BP2 SOX2 Stabilizing SOX2 mRNA [52] Gastric cancer IGF2BP1 SEC62 Augmenting SEC62 mRNA translation [53] IGF2BP3 HDGF Facilitating HDGF mRNA expression [54] HuR ZMYM1 Fortifying the stability of ZMYM1 mRNA [116] Lung cancer YTHDF1 CDK2, CDK4, cyclinD1…”