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 stimu-lating the stemness and progression of breast cancer (BCa) through mediating N-6-methyladenosine (m(6)A) modification on SOX2 mRNA. Methods: METTL3 levels in 48 paired BCa and adjacent normal ones were examined. Kaplan-Meier method was in-troduced for assessing the prognostic value of METTL3 in BCa. Regulatory effects of METTL3 on invasive and migra- tory 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 MET- TL3 were determined by Western blot. In addition, the poten-tial 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, especial-ly 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 attenu-ated in BCa cells with METTL3 knockdown. Silencing of IGF2BP2 markedly downregulated SOX2. RIP assay con-firmed 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 m(6)A modification on SOX2 mRNA.