Nontemplated Nucleotide Additions Distinguish the Small RNA Composition in Cells from Exosomes

TLDR

Small noncoding RNAs are released via extracellular vesicles, yet the mechanisms driving the distinct RNA composition between cells and exosomes remain unclear. The authors profiled small RNAs in human B cells and their exosomes using RNA‑seq. Nonrandom subsets of miRNA species differ between B cells and exosomes, with 3′ adenylated miRNAs enriched in cells and 3′ uridylated isoforms enriched in exosomes, indicating that opposing post‑transcriptional modifications may drive ncRNA sorting into EVs.

Abstract

Functional biomolecules, including small noncoding RNAs (ncRNAs), are released and transmitted between mammalian cells via extracellular vesicles (EVs), including endosome-derived exosomes. The small RNA composition in cells differs from exosomes, but underlying mechanisms have not been established. We generated small RNA profiles by RNA sequencing (RNA-seq) from a panel of human B cells and their secreted exosomes. A comprehensive bioinformatics and statistical analysis revealed nonrandomly distributed subsets of microRNA (miRNA) species between B cells and exosomes. Unexpectedly, 3′ end adenylated miRNAs are relatively enriched in cells, whereas 3′ end uridylated isoforms appear overrepresented in exosomes, as validated in naturally occurring EVs isolated from human urine samples. Collectively, our findings suggest that posttranscriptional modifications, notably 3′ end adenylation and uridylation, exert opposing effects that may contribute, at least in part, to direct ncRNA sorting into EVs.