BAP31 Promotes Epithelial–Mesenchymal Transition Progression Through the Exosomal miR-423-3p/Bim Axis in Colorectal Cancer

This study explores the regulatory function of BAP31 on exosomal miRNA and its impact on the EMT in CRC. Exosomes from BAP31-OE cells promoted recipient cell migration and triggered the EMT, as indicated by decreased E-cadherin and increased N-cadherin and Vimentin levels. By contrast, exosomes derived from shBAP31 cells were observed to inhibit cell migration and revert EMT markers. The administration of shBAP31 exosomes significantly inhibited tumor growth in vivo. miRNA profiling revealed 76 differentially expressed miRNAs in BAP31-OE exosomes. Six miRNA candidates associated with the EMT were identified in the GEO database, miR-423-3p was identified as a key mediator, the candidates from shBAP31 exosomes exhibited the opposite effect. EMT promotion by miR-423-3p was further evidenced by EMT marker expression, enhanced migratory capacity, and accelerated tumor growth. Sixteen potential target genes were identified through bioinformatics analysis. Bim exhibited significant downregulation by the miR-423-3p mimic. Luciferase reporter assays verified the direct interaction between miR-423-3p and the 3'UTR of Bim. Silencing Bim negated the effects of miR-423-3p. It was also revealed that BAP31 does not influence the total exosomal miRNA content but selectively regulates miR-423-3p, which contains an EXOmotif enriched in BAP31-OE exosomes. Mechanistic studies revealed that BAP31 enhances the expression of the RNA export adaptor Alyref, as validated by qRT-PCR and Western blot analyses. RNA immunoprecipitation assays verified that Alyref binds to miR-423-3p in BAP31-OE cells. Our results reveal that BAP31 facilitates the sorting of exosomal miR-423-3p via Alyref, thereby promoting EMT in CRC through the miR-423-3p/Bim signaling axis. This indicates that BAP31 could be a viable therapeutic target for managing the EMT in CRC.