Department of Tumor Cell Biology, University Hospital of Surgery, Heidelberg, Germany.
Int J Biochem Cell Biol. 2011 Jan;43(1):106-19. doi: 10.1016/j.biocel.2010.10.002. Epub 2010 Oct 16.
Exosomes are most important intercellular communicators and tetraspanins/tetraspanin-complexes have been suggested to play an important role in exosomal target cell selection. We have shown that only exosomes expressing a Tspan8-CD49d complex preferentially bind endothelial cells, which initiates angiogenesis. This finding was unexpected as in the exosome donor cell Tspan8 is associated with CD49c and the tetraspanins CD9 and CD151. In view of the discussed therapeutic power of exosomes as message/drug transporter, it became important to clarify the mechanisms accounting for the distinct Tspan8-web in the cell membrane versus exosomes. We therefore compared the route of Tspan8 and Tspan8-chimera internalization, where the N- and/or C-terminal regions were exchanged with the corresponding regions of CD9 or CD151. Activation-induced Tspan8-internalization proceeds more rapidly than CD9 internalization and is accompanied by disassembly of the Tspan8-CD9-CD151 membrane complex in resting cells. Tspan8-internalization relies on the association of the Tspan8 N-terminal region with intersectin-2, a multimodular complex involved in clathrin-coated pit internalization. Internalization and recovery of Tspan8 in early endosomes is further promoted by the recruitment of CD49d such that only in PMA-activated cells a Tspan8-INS2-CD49d-clathrin complex is recovered in cholesterol-depletion-resistant membrane microdomains. PMA-induced Tspan8-internalization promotes cell migration, but reduces matrix and cell adhesion. Thus, stimulation initiates tetraspanin-web rearrangements, which have strong functional consequences for the cell, exosome-delivery and exosome target selection. This knowledge will be essential for generating tailored therapeutic exosomes.
外泌体是最重要的细胞间通讯者，四跨膜蛋白/四跨膜蛋白复合物被认为在选择外泌体的靶细胞中发挥重要作用。我们已经表明，只有表达 Tspan8-CD49d 复合物的外泌体优先结合内皮细胞，从而启动血管生成。这一发现出乎意料，因为在供体细胞中，Tspan8 与 CD49c 以及四跨膜蛋白 CD9 和 CD151 相关。鉴于外泌体作为信使/药物转运体的治疗潜力，阐明导致细胞膜与外泌体中独特 Tspan8 网络的机制变得非常重要。因此，我们比较了 Tspan8 和 Tspan8 嵌合体内化的途径，其中 N-和/或 C-末端与 CD9 或 CD151 的相应区域交换。激活诱导的 Tspan8 内化比 CD9 内化更快，并伴随着静止细胞中 Tspan8-CD9-CD151 膜复合物的解体。Tspan8 内化依赖于 Tspan8 N 末端区域与 intersectin-2 的结合，后者是一种参与网格蛋白包被凹陷内化的多模块复合物。Tspan8 在早期内体中的内化和恢复进一步受到 CD49d 的募集的促进，因此只有在 PMA 激活的细胞中，Tspan8-INS2-CD49d-网格蛋白复合物才会在胆固醇耗竭抗性膜微区中恢复。PMA 诱导的 Tspan8 内化促进细胞迁移，但减少基质和细胞黏附。因此，刺激引发四跨膜蛋白网络重排，这对细胞、外泌体传递和外泌体靶细胞选择具有强烈的功能后果。这些知识对于生成定制的治疗性外泌体至关重要。
