m6A methyltransferase METTL3 promotes oral squamous cell carcinoma progression through enhancement of IGF2BP2-mediated SLC7A11 mRNA stability

As the key enzyme of the N6-methyladenosine (m(6)A) in eukaryotic messenger RNA, METTL3 plays an important role in tumor progression, but the exact mechanism by which METTL3 controls oral squamous cell carcinoma (OSCC) progression remains unclear. In this study, METTL3 expression in OSCC samples was analyzed by qPCR and immunohistochemistry. The effects of METTL3 suppression on OSCC cell lines were measured by CCK-8, Ki67 flow cytometry analysis, invasion transwell and wound healing assays. MeRIP-seq and RNA-seq analyses were performed to explore target gene of METTL3. RIP-qPCR and RNA stability assays were performed to explore the mechanism by which METTL3 regulated the target genes. Triptolide was used to evaluate its specific treatment effects on METTL3 in OSCC cells. BALB/c nude mice were used to establish orthotopic and subcutaneous xenograft models to verify the in vitro results. The results showed that METTL3 was upregulated in OSCC tissues compared with OSCC adjacent normal tissues, and its expression was associated with T stage, lymphatic metastasis and prognosis. METTL3 suppression impaired OSCC cells proliferation, invasion, and migration. MeRIP-seq and RNA-seq analysis identified that SLC7A11 mRNA was the m(6)A target of METTL3, which was verified by meRIP-qPCR, qPCR and western blot. METTL3 depletion decreased the stability of SLC7A11 mRNA, and IGF2BP2 as m(6)A reader was involved in this process. Moreover, METTL3 knockdown attenuated the binding between SLC7A11 mRNA and IGF2BP2, finally leading to accelerate SLC7A11 mRNA degradation. Triptolide inhibited METTL3-mediated SLC7A11 expression, thus suppressing malignancy of OSCC cells. In conclusion, the new finding of the manuscript is that METTL3 enhances the mRNA stability of SLC7A11 via m(6)A-mediated binding of IGF2BP2, which thus promotes OSCC progression, and triptolide inhibits OSCC by suppressing METTL3-SLC7A11 axis. Triptolide has a potential to be as an effective anti-OSCC drug targeted to METTL3.