Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan.
Mol Biol Cell. 2010 Aug 1;21(15):2746-55. doi: 10.1091/mbc.e10-01-0074. Epub 2010 Jun 9.
The small GTPase Rab14 localizes to early endosomes and the trans-Golgi network, but its cellular functions on endosomes and its functional relationship with other endosomal Rab proteins are poorly understood. Here, we report that Rab14 binds in a GTP-dependent manner to RUFY1/Rabip4, which had been originally identified as a Rab4 effector. Rab14 colocalizes well with Rab4 on peripheral endosomes. Depletion of Rab14, but not Rab4, causes dissociation of RUFY1 from endosomal membranes. Coexpression of RUFY1 with either Rab14 or Rab4 induces clustering and enlargement of endosomes, whereas a RUFY1 mutant lacking the Rab4-binding region does not induce a significant morphological change in the endosomal structures even when coexpressed with Rab14 or Rab4. These findings suggest that Rab14 and Rab4 act sequentially, together with RUFY1; Rab14 is required for recruitment of RUFY1 onto endosomal membranes, and subsequent RUFY1 interaction with Rab4 may allow endosomal tethering and fusion. Depletion of Rab14 or RUFY1, as well as Rab4, inhibits efficient recycling of endocytosed transferrin, suggesting that Rab14 and Rab4 regulate endosomal functions through cooperative interactions with their dual effector, RUFY1.
小分子 GTP 酶 Rab14 定位于早期内体和反式高尔基体网络，但它在内体上的细胞功能及其与其他内体 Rab 蛋白的功能关系知之甚少。在这里，我们报告 Rab14 以 GTP 依赖性方式与 RUFY1/Rabip4 结合，RUFY1/Rabip4 最初被鉴定为 Rab4 效应物。Rab14 与 Rab4 在外周内体上很好地共定位。Rab14 的耗竭会导致 RUFY1 从内体膜解离，但 Rab4 的耗竭不会导致这种情况。RUFY1 与 Rab14 或 Rab4 的共表达会诱导内体的聚集和增大，而缺乏 Rab4 结合区的 RUFY1 突变体即使与 Rab14 或 Rab4 共表达也不会导致内体结构发生显著的形态变化。这些发现表明 Rab14 和 Rab4 与 RUFY1 一起依次作用；Rab14 被招募到内体膜上需要 RUFY1，随后 RUFY1 与 Rab4 的相互作用可能允许内体的连接和融合。Rab14 或 RUFY1 的耗竭以及 Rab4 的耗竭抑制了内吞转铁蛋白的有效再循环，这表明 Rab14 和 Rab4 通过与它们的双重效应物 RUFY1 的协同相互作用调节内体功能。
