Interplay between the RBP SYNCRIP and RNA methylation in determining sEV miRNA-cargo and function in cell-to-cell communication.

Small extracellular vesicles (sEVs) are critical mediators of tumor microenvironment communication, largely through the selective transfer of microRNAs (miRNAs) that reprogram recipient cells. Active miRNA sorting into sEVs depends on RNA‑binding proteins (RBPs), sequence determinants, and RNA modifications. Here, a functional interplay between the RBP SYNCRIP and N6‑methyladenosine (m6A) RNA methylation controlling miRNA loading into hepatocellular carcinoma (HCC)‑derived sEVs has been disclosed. It is reported that (i) METTL3 (Methyltransferase-like-3)‑dependent m6A modification is required for efficient binding of SYNCRIP to specific miRNAs, thereby enabling their selective incorporation into sEVs; (ii) silencing of SYNCRIP markedly reshapes the sEV miRNA-cargo and impairs the ability of HCC‑derived sEVs to induce epithelial-to-mesenchymal transition (EMT) in non‑tumorigenic hepatocytes. Notably, (iii) depletion of METTL3 produces an even stronger effect, indicating that m6A methylation represents an upstream and essential determinant of SYNCRIP‑mediated miRNA export. Mechanistically, the data identify SYNCRIP as an m6A‑dependent miRNA reader, adding epitranscriptomic regulation to sequence‑based miRNA sorting into sEVs. Functionally, disruption of this interaction attenuates sEV‑driven EMT and pro‑tumorigenic signaling. Collectively, these findings uncover a novel regulatory axis governing sEV miRNA cargo selection and highlight the m6A-SYNCRIP interplay as a potential therapeutic target to interfere with sEV‑mediated tumor progression and metastasis.