TBC1D18, a novel Rab5-GAP, coordinates endosome maturation together with Mon1
TBC1D18, a novel Rab5-GAP, coordinates endosome maturation together with Mon1
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DOI：
10.1101/2021.11.11.468194
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发表时间：
2021-11
期刊：
影响因子：
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通讯作者：
Shu Hiragi;Takahide Matsui;Y. Sakamaki;M. Fukuda
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文献类型：
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作者：
Shu Hiragi;Takahide Matsui;Y. Sakamaki;M. Fukuda
内体成熟对于内化细胞外分子和质膜蛋白的有效降解至关重要。已知两种 Rab GTP 酶 Rab5 和 Rab7 可以调节内体成熟，并且由 Rab7 激活剂 Mon1-Ccz1 介导的 Rab5 到 Rab7 的转换对于成熟过程的进展至关重要。然而，在内体成熟过程中 Rab5 失活的重要性和机制尚不清楚。在这里，我们报道了一种新型 Rab5 灭活剂（Rab5-GTPase 激活蛋白 [Rab5-GAP]）TBC1D18，它与 Mon1 相关并介导内体成熟。我们发现，在没有 Mon1 的情况下，除了 Rab7 失活之外，还会发生 Rab5 过度激活。我们提供的证据表明，在 Mon1-KO 细胞中观察到的内体成熟的严重缺陷可归因于 Rab5 过度激活，而不是 Rab7 失活。然后，我们通过全面筛选含有 TBC 结构域的 Rab-GAP，将 TBC1D18 鉴定为 Rab5-GAP。 Mon1-KO 细胞中 TBC1D18 的表达挽救了内体成熟的缺陷，而其耗尽则减弱了内体的形成和内吞物质的降解。此外，TBC1D18被发现能够与Mon1相互作用，并且它以Mon1依赖性方式定位在靠近溶酶体的位置。因此，TBC1D18 是内体成熟的关键调节因子，与 Mon1 一起发挥作用。
Endosome maturation is essential for efficient degradation of internalized extracellular molecules and plasma membrane proteins. Two Rab GTPases, Rab5 and Rab7, are known to regulate endosome maturation, and a Rab5-to-Rab7 conversion mediated by a Rab7 activator, Mon1–Ccz1, is essential for progression of the maturation process. However, the importance and mechanism of Rab5 inactivation during endosome maturation is poorly understood. Here we report a novel Rab5 inactivator (Rab5-GTPase activating protein [Rab5-GAP]), TBC1D18, which is associated with Mon1 and mediates endosome maturation. We found that Rab5 hyperactivation in addition to Rab7 inactivation occurs in the absence of Mon1. We present evidence showing that the severe defects in endosome maturation observed in Mon1-KO cells are attributable to Rab5 hyperactivation rather than to Rab7 inactivation. We then identified TBC1D18 as a Rab5-GAP by comprehensive screening of TBC-domain-containing Rab-GAPs. Expression of TBC1D18 in Mon1-KO cells rescued the defects in endosome maturation, whereas its depletion attenuated endosome formation and degradation of endocytosed cargos. Moreover, TBC1D18 was found to be able to interact with Mon1, and it localized in close proximity to lysosomes in a Mon1-dependent manner. Thus, TBC1D18 is a crucial regulator of endosome maturation that functions together with Mon1.