The m6A methyltransferase METTL3 promotes the stemness and malignant progression of breast cancer by mediating m6A modification on SOX2.

Purpose We aimed to uncover the role of METTL3 in stimulating the stemness and progression of breast cancer (BCa) through mediating N6-methyladenosine (m6A) modification on SOX2 mRNA. Methods METTL3 levels in 48 paired BCa and adjacent normal ones were examined. Kaplan-Meier method was introduced for assessing the prognostic value of METTL3 in BCa. Regulatory effects of METTL3 on invasive and migratory abilities in MCF-7 cells were evaluated by Transwell assay. Besides, the protein levels of SOX2 and tumor stem cell markers CD133 and CD44 in MCF-7 cells affected by METTL3 were determined by Western blot. In addition, the potential interaction between METTL3 and SOX2 was ascertained through RIP (RNA-Binding Protein Immunoprecipitation) assay. Moreover, the interaction between IGF2BP2 and SOX2 influenced by METTL3 was verified by RIP assay as well. Results METTL3 was upregulated in BCa tissues, especially in T3-T4 or those accompanied with lymphatic metastasis. BCa patients expressing a high level of METTL3 suffered worse prognosis. Knockdown of METTL3 downregulated protein levels of SOX2, CD133 and CD44 in MCF-7 cells. Moreover, invasive and migratory abilities were attenuated in BCa cells with METTL3 knockdown. Silencing of IGF2BP2 markedly downregulated SOX2. RIP assay confirmed the binding between METTL3 and SOX2 mRNA, and knockdown of METTL3 decreased the enrichment of SOX2 in anti-IGF2BP2. Interestingly, overexpression of SOX2 partially reversed the regulatory effects of downregulated METTL3 on MCF-7 cells. Conclusions METTL3 is upregulated in BCa, and it promotes the stemness and malignant progression of BCa through mediating m6A modification on SOX2 mRNA.