Extracellular Vesicles: Mechanisms of Cargo Selection and Cell-Cell Communication

Abstract

Extracellular vesicles (EVs) are mediators of cell-cell communication and play important roles in many physiological processes including cancer and drug resistance. EVs are nanosized particles secreted from every cell, and contain protein, lipid, and RNA cargo. miRNAs are secreted from cells and a number of different mechanisms regulating miRNA cargo content have been suggested to play a role in export. However, to date there is no universal mechanism responsible for RNA export to EVs. I created stable shRNA-expressing cell lines against factors hypothesized to be involved in miRNA sorting or required for RNA base modifications, and discovered a role for RNA base modifications in miRNA export to EVs in KRAS mutant colorectal cancer cells. Six of the knockdown lines altered extracellular transfer of miR-100, with 4 of those lines involving proteins implicated in N6-methyladenosine (m6A) modification. Knockdown of Mettl3, an m6A writer, led to a significant decrease in the export of miRNAs containing m6A consensus sequences. When tested for functional effects, EVs derived from Mettl3 knockdown cells were not able to confer colony growth in 3D compared to EVs from parental cells. Thus, my data suggest an important role for m6A modifications in selective miRNA export to EVs, and that altered cargo content can affect cell-cell communication.