Ray Arpita, Zhang Siyuan, Rentas Courtney, Caldwell Kim A, Caldwell Guy A
Department of Biological Sciences, The University of Alabama, Tuscaloosa, Alabama 35487, and.
Department of Biological Sciences, The University of Alabama, Tuscaloosa, Alabama 35487, and Departments of Neurobiology and Neurology and Center for Neurodegeneration and Experimental Therapeutics, University of Alabama at Birmingham, Birmingham, Alabama 35294.
J Neurosci. 2014 Nov 26;34(48):16076-85. doi: 10.1523/JNEUROSCI.1945-14.2014.
Parkinson's disease (PD), the second most prevalent neurodegenerative disorder, is characterized by the degeneration of dopamine (DA) neurons and age-dependent formation of protein inclusions that contain the α-synuclein (α-syn) protein. RNA interference (RNAi) screening using Caenorhabditis elegans identified RTCB-1, an uncharacterized gene product, as one of several significant modifiers of α-syn protein misfolding. RTCB-1 is the worm ortholog of the human HSPC117 protein, a component of RNA trafficking granules in mammalian neurons. Here we show that RTCB-1 protects C. elegans DA neurons from age-dependent degeneration induced by human α-syn. Moreover, neuronal-specific RNAi depletion of rtcb-1 enhanced α-syn-induced degeneration. Similar results were obtained when worms were exposed to the DA neurotoxin 6-hydroxydopamine. HSPC117 has been characterized recently as an essential subunit of the human tRNA splicing ligase complex. tRNA ligases have alternative functions in RNA repair and nonconventional mRNA splicing events. For example, in yeast, unconventional splicing of HAC1, a transcription factor that controls the unfolded protein response (UPR), is mediated by a tRNA ligase. In C. elegans, we demonstrate that RTCB-1 is necessary for xbp-1 (worm homolog of HAC1) mRNA splicing. Moreover, using a RNA ligase-dead mutant, we determine that the ligase activity of worm RTCB-1 is required for its neuroprotective role, which, in turn, is mediated through XBP-1 in the UPR pathway. Collectively, these studies highlight the mechanistic intersection of RNA processing and proteostasis in mediating neuroprotection.
帕金森病（PD）是第二常见的神经退行性疾病，其特征是多巴胺（DA）神经元变性以及与年龄相关的富含α-突触核蛋白（α-syn）的蛋白包涵体形成。利用秀丽隐杆线虫进行的RNA干扰（RNAi）筛选确定了RTCB-1（一种未鉴定的基因产物）是α-syn蛋白错误折叠的几个重要调节因子之一。RTCB-1是人类HSPC117蛋白的线虫直系同源物，HSPC117是哺乳动物神经元中RNA转运颗粒的一个组成部分。在此我们表明，RTCB-1可保护秀丽隐杆线虫的DA神经元免受人类α-syn诱导的年龄依赖性变性。此外，rtcb-1的神经元特异性RNAi缺失增强了α-syn诱导的变性。当线虫暴露于DA神经毒素6-羟基多巴胺时也获得了类似结果。HSPC117最近被鉴定为人类tRNA剪接连接酶复合物的一个必需亚基。tRNA连接酶在RNA修复和非常规mRNA剪接事件中具有其他功能。例如，在酵母中，控制未折叠蛋白反应（UPR）的转录因子HAC1的非常规剪接由一种tRNA连接酶介导。在秀丽隐杆线虫中，我们证明RTCB-1是xbp-1（HAC1的线虫同源物）mRNA剪接所必需的。此外，使用一种RNA连接酶失活突变体，我们确定线虫RTCB-1的连接酶活性是其神经保护作用所必需的，而这种神经保护作用反过来是通过UPR途径中的XBP-1介导的。总的来说，这些研究突出了RNA加工和蛋白质稳态在介导神经保护中的机制交叉点。
