METTL3 promotes the progression of nasopharyngeal carcinoma through mediating M6A modification of EZH2

Q.-Z. Meng, C.-H. Cong, X.-J. Li, F. Zhu, X. Zhao, F.-W. Chen

Department of Head and Neck Surgery, Linyi Cancer Hospital, Linyi, China. lyfangwen001@126.com

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• Oncology

OBJECTIVE: The aim of this study was to investigate whether METTL3 promoted the progression of nasopharyngeal carcinoma (NPC) by silencing CDKN1C through EZH2.
PATIENTS AND METHODS: Quantitative Real Time-Polymerase Chain Reaction (qRT-PCR) was performed to examine the expression level of METTL3 in 48 pairs of NPC tissues and adjacent normal tissues. METTL3 expression in patients with different tumor lymph node metastasis (TNM) stages was detected by qRT-PCR as well. The Kaplan-Meier method was used to analyze the interplay between METTL3 expression and the prognosis of patients with NPC. At the same time, METTL3 expression in normal epithelial cell line (BEAS-2B) and NPC cell lines (SUNE-1 and C666-1) was examined using qRT-PCR. After METTL3 was knocked down in SUNE-1 cells, cell viability and migration abilities were analyzed by cell counting kit-8 (CCK-8) test and wound healing assay, respectively. The mRNA and protein expressions of EZH2 were detected by qRT-PCR and Western blot, respectively. RNA immunoprecipitation (RIP) assay was applied to detect the binding of METTL3 to EZH2 mRNA and the m6A modification on EZH2 mRNA. After knockdown of EZH2 in SUNE-1 cells, qRT-PCR was used to detect the mRNA expression of CDKN1C. Meanwhile, chromatin immunoprecipitation (ChIP) assay was conducted to analyze the binding of EZH2 to the CDKN1C promoter region. After down-regulation of METTL3 in SUNE-1 cells, the protein expressions of EZH2 and CDKN1C were detected using Western blot. After simultaneous knockdown of METTL3 and CDKN1C in SUNE-1 cells, CCK8 assay and wound healing assay were applied to examine cell viability and migration abilities.
RESULTS: METTL3 expression in NPC tissues was remarkably higher than that of adjacent normal tissues. Meanwhile, METTL3 expression in T3 and T4 tumors was significantly higher than that of T1 and T2 tumors. In patients with lymph node metastasis, the expression of METTL3 was remarkably higher than those without metastasis. Survival analysis demonstrated that patients with higher expression of METTL3 exhibited significantly longer overall survival time than those with lower METTL3 expression. QRT-PCR revealed that METTL3 was highly expressed in NPC cell lines, including SUNE-1 and C666-1. After knock-down of METTL3 in SUNE-1 cells, cell viability and migration abilities were both markedly weakened. Meanwhile, the protein expression of EZH2 was remarkably reduced. However, no significant changes were observed in EZH2 mRNA level. RIP assay revealed that METTL3 could bind to EZH2 mRNA, and a m6A modification was verified on EZH2 mRNA. After knockdown of EZH2, the mRNA level of CDKN1C in SUNE-1 cells was significantly up-regulated. CHIP assay indicated that EZH2 could bind to CDKN1C. Western blot showed that, after interfering with METTL3 in SUNE-1 cells, the protein expression of EZH2 decreased significantly, while CDKN1C was up-regulated. In addition, simultaneous downregulation of METTL3 and CDKN1C in SUNE-1 cells reversed the influence of METTL3 on cell viability and migration abilities.
CONCLUSIONS: METTL3 was highly expressed in NPC tissues, which might inhibit EZH2 expression by mediating M6A modification of EZH2 mRNA. Furthermore, CDKN1C could increase the malignancy of NPC cells and promote the progression of NPC.

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