Unraveling the Independent Role of METTL3 in m6A Modification and Tumor Progression in Esophageal Squamous Cell Carcinoma

METTL3 and METTL14 are considered to faithfully form the m6A writing complex in a 1:1 ratio, regulating the fate of mRNA by adding m6A modifications. However, recent studies have shown inconsistent expression and prognostic value of METTL3 and METTL14 in some tumors, suggesting that they may not be faithful in tumors. Pan-cancer analysis based on TCGA data reveals significant differences in expression, function, tumor burden correlation, and immune correlation between METTL3 and METTL14, especially in esophageal squamous cell carcinoma (ESCC). Knockdown of METTL3 significantly inhibits the cell proliferation in vitro and in vivo in ESCC EC109 cells, while the impact of METTL14 knockdown on proliferation is limited, and it cannot abolish the expression of METTL3 protein. mRNA-seq results indicate that METTL3 independently regulates the expression of 1615 genes, while only 776 genes are co-regulated by METTL3 and METTL14. Furthermore, through immunofluorescence co-localization, it is observed that METTL3 and METTL14 have certain inconsistencies in cellular localization. HPLC-MS results show that METTL3 independently binds to the Nop56p-associated pre-rRNA complex and mRNA splicing complex, separate from METTL14. Through bioinformatics and various omics studies, we have preliminarily discovered that METTL3 independently regulating tumor cell proliferation, and the participation in mRNA splicing may be a critical molecular mechanism. Our study provides an experimental basis and theoretical foundation for further understanding of the m6A writing complex and tumor therapy targeting METTL3.