ALS2, a novel guanine nucleotide exchange factor for the small GTPase Rab5, is implicated in endosomal dynamics
ALS2, a novel guanine nucleotide exchange factor for the small GTPase Rab5, is implicated in endosomal dynamics
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DOI：
10.1093/hmg/ddg184
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发表时间：
2003-07-15
影响因子：
3.5
通讯作者：
Ikeda, JE
中科院分区：
文献类型：
--
作者：
Otomo, A;Hadano, S;Ikeda, JE
ALS2突变导致许多隐性运动神经元疾病，包括肌萎缩侧索硬化、原发性侧索硬化和遗传性痉挛性截瘫。尽管计算预测表明ALS2编码一种含有多个鸟嘌呤核苷酸交换因子（GEF）结构域[rcc1样结构域（RLD）， Dbl同源性和pleckstrin同源性（DH/PH）和液泡蛋白分选9 (VPS9)]的蛋白，但ALS2蛋白的功能尚未揭示。本研究表明，ALS2蛋白特异性结合小GTPase Rab5，并作为Rab5的GEF起作用。异位表达的ALS2蛋白与Rab5和早期核内体抗原-1 （EEA1）一起定位于早期核内体腔室，刺激培养皮层神经元核内体的扩大。携带VPS9结构域的ALS2蛋白羧基端不仅通过鸟嘌呤-核苷酸交换反应介导Rab5的激活，而且还介导了ALS2蛋白的内体定位，而含有RLD的氨基端则对其膜质定位起抑制作用。此外，ALS2蛋白中部的DH/PH结构域增强了VPS9结构域介导的内体融合。综上所述，ALS2蛋白作为一种新的Rab5-GEF， ALS2rab5GEF似乎与体内内体动力学有关。值得注意的是，在运动神经元疾病中报道的8种ALS2突变的共同特征是VPS9结构域的丢失，导致Rab5激活失败。因此，由ALS2 rab5GEF活性丧失引起的内体动力学扰动可能是许多运动神经元疾病中神经元功能障碍和变性的基础。
ALS2 mutations account for a number of recessive motor neuron diseases including forms of amyotrophic lateral sclerosis, primary lateral sclerosis and hereditary spastic paraplegia. Although computational predictions suggest that ALS2 encodes a protein containing multiple guanine nucleotide exchange factor (GEF) domains [RCC1-like domain (RLD), the Dbl homology and pleckstrin homology (DH/PH), and the vacuolar protein sorting 9 (VPS9)], the functions of the ALS2 protein have not been revealed as yet. Here we show that the ALS2 protein specifically binds to small GTPase Rab5 and functions as a GEF for Rab5. Ectopically expressed ALS2 protein localizes with Rab5 and early endosome antigen-1 (EEA1) onto early endosomal compartments and stimulates the enlargement of endosomes in cultured cortical neurons. The carboxy-terminus of ALS2 protein carrying a VPS9 domain mediates not only the activation of Rab5 via a guanine-nucleotide exchanging reaction but also the endosomal localization of the ALS2 protein, while the amino-terminal half containing RLD acts suppressive in its membranous localization. Further, the DH/PH domain in the middle portion of ALS2 protein enhances the VPS9 domain-mediated endosome fusions. Taken together, the ALS2 protein as a novel Rab5-GEF, ALS2rab5GEF seems to be implicated in the endosomal dynamics in vivo. Notably, a feature common to eight reported ALS2 mutations among motor neuron diseases is the loss of VPS9 domain, resulting in the failure of Rab5 activation. Thus, a perturbation of endosomal dynamics caused by loss of ALS2 rab5GEF activity might underlie neuronal dysfunction and degeneration in a number of motor neuron diseases.