Department of Molecular and Cell Biology, Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, United States.
Elife. 2021 Nov 12;10:e71982. doi: 10.7554/eLife.71982.
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.
外泌体可以通过向邻近细胞转运各种蛋白质和核酸来介导细胞间通讯。一些蛋白质和 RNA 货物在外泌体中显著富集。细胞如何有效地和选择性地将它们分拣到外泌体中仍未被充分探索。以前，我们报道 YBX1 在 miR-223 分拣到外泌体中是必需的。在这里，我们显示 YBX1 在体外和细胞中经历液-液相分离（LLPS）。YBX1 凝聚物在体外和培养细胞分泌的外泌体中选择性地招募 miR-223。抑制 YBX1 相分离的点突变会损害 YBX1 蛋白掺入细胞中形成的生物分子凝聚物，并扰乱 miR-233 分拣到外泌体中。我们提出，相分离介导的细胞质 RNA 结合蛋白及其同源 RNA 的局部富集，使得它们可以被形成多泡体的小泡靶向和包装。这为细胞质蛋白质和 RNA 被有效和选择性地包裹到腔内小泡中提供了一种可能的机制，然后从小泡中以外泌体的形式分泌到细胞外。
