Cancer-Associated Fibroblasts-Derived Exosomal METTL3 Drives Breast Cancer Malignancy by Eliciting PABPN1 m6A Modification.

BACKGROUND: Cancer-associated fibroblasts (CAFs) drive breast cancer (BC) progression. While N6-methyladenosine (m6A) regulates tumorigenesis, the mechanisms by which CAF-derived exosomes transmit oncogenic m6A signals remain unclear. MATERIALS AND METHODS: Primary CAFs and normal fibroblasts were isolated and exosomes purified via ultracentrifugation. Exosomal impact on BC cell malignancy and T-cell cytotoxicity was evaluated in vitro. Molecular targets were validated using methylated RNA immunoprecipitation and dual-luciferase assays. In vivo tumorigenesis was assessed using xenograft models. RESULTS: CAFs secrete exosomes enriched with the methyltransferase-like 3 (METTL3), which is crucial for BC oncogenic reprogramming, promoting malignancy and immune evasion by suppressing T-cell function. Mechanistically, exosomal METTL3 is internalized by cancer cells, catalyzing m6A modification of poly(A)-binding protein nuclear 1 (PABPN1) mRNA to stabilize and upregulate it. Clinical analyses confirmed a positive correlation between METTL3 and PABPN1 levels in BC tissues. PABPN1 overexpression rescued the effects of exosomal METTL3 depletion in vitro and in vivo. Furthermore, knocking down METTL3 in CAFs-derived exosomes significantly impeded tumor growth in vivo, reducing PABPN1 and Ki-67 expression. CONCLUSION: This study identifies a novel CAFs-to-cancer cell communication axis where exosomal METTL3 promotes BC progression and immune escape via m6A-dependent upregulation of PABPN1, highlighting this pathway as a promising therapeutic target.