State Key Laboratory of Chemical Resource Engineering, College of Life Science and Technology, Beijing University of Chemical Technology, Beijing, China.
Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing, China.
Cell Prolif. 2024 Oct;57(10):e13645. doi: 10.1111/cpr.13645. Epub 2024 Apr 11.
The biogenesis of exosomes that mediate cell-to-cell communication by transporting numerous biomolecules to neighbouring cells is an essential cellular process. The interaction between the transmembrane protein syndecan-4 (SDC4) and cytosolic protein syntenin plays a key role in the biogenesis of exosomes. However, how the relatively weak binding of syntenin to SDC4 efficiently enables syntenin sorting for packaging into exosomes remains unclear. Here, we demonstrate for the first time that SDC4 can undergo liquid-liquid phase separation (LLPS) to form condensates both in vitro and in the cell membrane and that, the SDC4 cytoplasmic domain (SDC4-CD) is a key contributor to this process. The phase separation of SDC4 greatly enhances the recruitment of syntenin to the plasma membrane (PM) despite the weak SDC4-syntenin interaction, facilitating syntenin sorting for inclusion in exosomes. Interestingly, phosphorylation at the only serine (179) in the SDC4-CD (Ser179) disrupts SDC4 LLPS, and inhibited phosphorylation or dephosphorylation restores the SDC4 LLPS to promote its recruitment of syntenin to the PM and syntenin inclusion into exosomes. This research reveals a novel phosphorylation-regulated phase separation property of SDC4 in the PM through which SDC4 efficiently recruits cytosolic syntenin and facilitates the biogenesis of exosomes, providing potential intervention targets for exosome-mediated biomedical events.
外泌体通过将众多生物分子运输到邻近细胞来介导细胞间通讯，其生物发生是一种重要的细胞过程。跨膜蛋白 syndecan-4（SDC4）和细胞质蛋白 syntenin 之间的相互作用在 exosomes 的生物发生中起着关键作用。然而，syntenin 与 SDC4 的相对较弱的结合如何有效地使 syntenin 分选并包装到 exosomes 中仍不清楚。在这里，我们首次证明 SDC4 可以在体外和细胞膜中发生液-液相分离（LLPS）以形成凝聚物，并且 SDC4 细胞质结构域（SDC4-CD）是该过程的关键贡献者。尽管 SDC4-syntenin 相互作用较弱，但 SDC4 的相分离大大增强了 syntenin 向质膜（PM）的募集，从而促进了 syntenin 的分选以包含在 exosomes 中。有趣的是，SDC4-CD 中唯一丝氨酸（179）的磷酸化（Ser179）破坏了 SDC4 的 LLPS，抑制磷酸化或去磷酸化恢复了 SDC4 的 LLPS，从而促进其将 syntenin 募集到 PM 并将 syntenin 包含在 exosomes 中。这项研究揭示了 SDC4 在 PM 中通过一种新的磷酸化调节相分离特性，该特性有效地招募细胞质 syntenin 并促进 exosomes 的生物发生，为外泌体介导的生物医学事件提供了潜在的干预靶点。
