Centre for Cellular and Molecular Biology, Council of Scientific and Industrial Research, Uppal Road, Hyderabad 500 007, India.
J Cell Sci. 2012 Nov 1;125(Pt 21):5026-39. doi: 10.1242/jcs.102327. Epub 2012 Aug 1.
Rab GTPases regulate various membrane trafficking pathways but the mechanisms by which GTPase-activating proteins recognise specific Rabs are not clear. Rab8 is involved in controlling several trafficking processes, including the trafficking of transferrin receptor from the early endosome to the recycling endosome. Here, we provide evidence to show that TBC1D17, a Rab GTPase-activating protein, through its catalytic activity, regulates Rab8-mediated endocytic trafficking of transferrin receptor. Optineurin, a Rab8-binding effector protein, mediates the interaction and colocalisation of TBC1D17 with Rab8. A non-catalytic region of TBC1D17 is required for direct interaction with optineurin. Co-expression of Rab8, but not other Rabs tested, rescues the inhibition of transferrin receptor trafficking by TBC1D17. The activated GTP-bound form of Rab8 is localised to the tubules emanating from the endocytic recycling compartment. Through its catalytic activity, TBC1D17 inhibits recruitment of Rab8 to the tubules and reduces colocalisation of transferrin receptor and Rab8. Knockdown of optineurin or TBC1D17 results in enhanced recruitment of Rab8 to the tubules. A glaucoma-associated mutant of optineurin, E50K, causes enhanced inhibition of Rab8 by TBC1D17, resulting in defective endocytic recycling of transferrin receptor. Our results show that TBC1D17, through its interaction with optineurin, regulates Rab8-mediated endocytic recycling of transferrin receptor and recruitment of Rab8 to the endocytic recycling tubules. We describe a mechanism of regulating a Rab GTPase by an effector protein (optineurin) that acts as an adaptor to bring together a Rab (Rab8) and its GTPase-activating protein (TBC1D17).
Rab GTPases 调节各种膜运输途径，但 GTPase 激活蛋白识别特定 Rab 的机制尚不清楚。Rab8 参与控制几种运输过程，包括转铁蛋白受体从早期内体到再循环内体的运输。在这里，我们提供证据表明，Rab GTPase 激活蛋白 TBC1D17 通过其催化活性调节 Rab8 介导的转铁蛋白受体的内吞运输。Optineurin，一种 Rab8 结合效应蛋白，介导 TBC1D17 与 Rab8 的相互作用和共定位。TBC1D17 与 optineurin 直接相互作用需要非催化区域。TBC1D17 与 Rab8 的共表达可挽救 TBC1D17 对转铁蛋白受体运输的抑制。激活的 GTP 结合形式的 Rab8 定位于从内吞再循环隔室发出的小管。通过其催化活性，TBC1D17 抑制 Rab8 向小管的募集，并减少转铁蛋白受体和 Rab8 的共定位。Optineurin 或 TBC1D17 的敲低导致 Rab8 向小管的募集增加。Optineurin 的青光眼相关突变体 E50K 导致 TBC1D17 对 Rab8 的抑制增强，从而导致转铁蛋白受体的内吞再循环缺陷。我们的结果表明，TBC1D17 通过与 optineurin 的相互作用，调节 Rab8 介导的转铁蛋白受体内吞再循环和 Rab8 向内吞再循环小管的募集。我们描述了一种效应蛋白（optineurin）通过作为衔接蛋白将 Rab（Rab8）与其 GTPase 激活蛋白（TBC1D17）聚集在一起来调节 Rab GTPase 的机制。
