Distinct mechanisms of microRNA sorting into cancer cell-derived extracellular vesicle subtypes

Extracellular vesicles (EVs) encompass a variety of vesicles secreted into the extracellular space. EVs have been implicated in promoting tumor metastasis, but the molecular composition of tumor derived EV subtypes and the mechanisms by which molecules are sorted into EVs remain mostly unknown. We report the separation of two EV sub-populations from a metastatic cancer cell line, with biochemical features consistent with different sub-cellular origins. These EV subtypes use different mechanisms of miRNA sorting, suggesting that sorting occurs via fundamentally distinct processes, possibly dependent on EV origin. Using biochemical and genetic tools, we identified the Lupus La protein as mediating sorting of some selectively packaged miRNAs.We found that two motifs embedded in miR-122 are responsible for high affinity binding to Lupus La and sorting into vesicles formed in vitro. Thus, tumor cells can simultaneously deploy multiple EV species using distinct sorting mechanisms that may enable diverse functions in cancer biology.