Abstract
Exosomes may mediate cell-to-cell communication by transporting various proteins and nucleic acids to neighboring cells. Some protein and RNA cargoes are significantly enriched in exosomes. How cells efficiently and selectively sort them into exosomes remains incompletely explored. Previously, we reported that YBX1 is required in sorting of miR-223 into exosomes. Here, we show that YBX1 undergoes liquid-liquid phase separation (LLPS) in vitro and in cells. YBX1 condensates selectively recruit miR-223 in vitro and into exosomes secreted by cultured cells. Point mutations that inhibit YBX1 phase separation impair the incorporation of YBX1 protein into biomolecular condensates formed in cells, and perturb miR-233 sorting into exosomes. We propose that phase separation-mediated local enrichment of cytosolic RNA-binding proteins and their cognate RNAs enables their targeting and packaging by vesicles that bud into multivesicular bodies. This provides a possible mechanism for efficient and selective engulfment of cytosolic proteins and RNAs into intraluminal vesicles which are then secreted as exosomes from cells.
Highlights
Extracellular vesicles (EVs) secreted into the extracellular space appear to mediate some forms of intercellular communication (Colombo et al, 2014; Maia et al., 2018; Song et al, 2021)
A compound previously shown to disrupt liquid-liquid phase separation of biomolecules (1,6-hexanediol, Kroschwald et al, 2017) caused YBX1 puncta to disassemble in a time- and concentration- dependent manner
Several RNA-binding proteins (RBPs) involved in the sorting of miRNAs into exosomes secreted by mammalian cells share a sequence domain, the intrinsically disordered region (IDR), implicated in the association of RNA and proteins in membraneless organelles such as P-bodies (Lee et al, 2020; Luo et al, 2018; Santangelo et al, 2016; Shurtleff et al, 2016; Temoche-Diaz et al, 2019; Xing et al, 2020)
Summary
Extracellular vesicles (EVs) secreted into the extracellular space appear to mediate some forms of intercellular communication (Colombo et al, 2014; Maia et al., 2018; Song et al, 2021). Different sub-populations of EVs bud from the plasma membrane or arise from membrane internalized into endosomes to form multi-vesicular bodies (MVB) that fuse at the cell surface to secrete intralumenal vesicles (ILV). Plasma membrane-derived microvesicles, referred to as shedding vesicles, are more heterogeneous with sizes ranging from 30 to 1,000 nm (Cocucci et al, 2009; Raposo and Stoorvogel, 2013). During their biogenesis, EVs may selectively capture proteins, lipids, metabolites, and nucleic acids which vary according to the cell of origin.
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