The miR-338-5p/METTL3 axis regulates m6A modification to inhibit tumor progression in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is a highly aggressive subtype of breast cancer characterized by poor prognosis and limited therapeutic options. METTL3, a critical m6A RNA methyltransferase, has been implicated in tumor progression. However, its molecular mechanisms in TNBC remain to be fully elucidated.

METTL3 expression was analyzed using public databases, cell lines, and clinical samples. Functional assays were performed on TNBC cells following METTL3 knockdown or overexpression. RNA m6A levels were quantified to assess the methyltransferase activity of METTL3. MiR-338-5p was identified as a potential upstream regulator of METTL3 via prediction tools, and validated by luciferase assays. In vivo relevance was assessed using xenograft mouse models.

METTL3 was upregulated in TNBC cell lines and tumor tissues, correlating with larger tumor size and poorer prognosis. METTL3 knockdown suppressed proliferation, migration, invasion, and EMT, and reduced global RNA m6A modification. METTL3 overexpression enhanced these malignant traits and increased m6A levels. MiR-338-5p directly bound to the 3'UTR of METTL3 and suppressed METTL3 protein expression without affecting mRNA levels. Overexpression of miR-338-5p decreased RNA m6A levels and attenuated TNBC aggressiveness, effects that were reversed by METTL3 restoration, confirming a functional miR-338-5p/METTL3/m6A axis. In vivo, METTL3 overexpression promoted tumor growth and proliferation in xenograft models, whereas knockdown suppressed these effects.

METTL3 functions as an oncogenic driver in TNBC by promoting proliferation, invasion, and EMT through an m6A-dependent mechanism. This study reveals post-transcriptional regulation of METTL3 by miR-338-5p in TNBC. Targeting this distinct regulatory axis represents a promising therapeutic strategy for TNBC.