An ARF6-Exportin-5 axis delivers pre-miRNA cargo to tumour microvesicles.

Tumour-derived microvesicles (TMVs) comprise a class of extracellular vesicles released from tumour cells that are now understood to facilitate communication between the tumour and the surrounding microenvironment. Despite their significance, the regulatory mechanisms governing the trafficking of bioactive cargos to TMVs at the cell surface remain poorly defined. Here we describe a molecular pathway for the delivery of microRNA (miRNA) cargo to nascent TMVs involving the dissociation of a pre-miRNA/Exportin-5 complex from Ran-GTP following nuclear export and its subsequent transfer to a cytoplasmic shuttle comprised of ARF6-GTP and GRP1. As such, ARF6 activation increases the pre-miRNA cargo contained within TMVs through a process that requires the casein kinase 2-mediated phosphorylation of RanGAP1. Furthermore, TMVs were found to contain pre-miRNA processing machinery including Dicer and Argonaute-2, which allow for cell-free pre-miRNA processing within shed vesicles. These findings offer cellular targets to block the loading and processing of pre-miRNAs within TMVs.