Insights into Gordon Holmes syndrome by substrate profiling of Triad3A and Chip using Orthogonal Ubiquitin Transfer

摘要：在神经系统中，蛋白质泛素化伴随着多种细胞过程， 利用由泛素激活酶(E1)、泛素 结合酶(E2)和泛素连接酶(E3)。E3在这一途径中的主要作用 是将一种名为泛素的76个残基的小蛋白质共价连接到已知的选定蛋白质靶点上 作为底物。据估计，E3代表了人类基因组中的500-1000个基因。我们 在70种不同类型的神经系统疾病中发现了83种不同的E3突变 支持证据表明泛素信号的中断是人类的诱发因素 神经方面的情况。尽管大量的E3基因在许多神经系统中发生了突变 关于疾病的功能和底物，人们仍然缺乏了解- 大脑中相关的E3。在这个提案中，我们将阐明两个E3的关键功能，TRIAD3A 和芯片，它们在一种名为戈登·霍姆斯的异质性神经疾病中突变 综合征(GHS)。GHS的主要病理生理包括下丘脑功能障碍、痴呆 和神经退化。携带RNF216/TRIAD3和CHIP/STUB1突变的个体也 表现出性腺激素减退症，这被认为是由功能失调引起的 促性腺激素释放不足所致的下丘脑-垂体-性腺(HPG)轴 下丘脑GnRH阳性神经元的释放激素(GnRH)。在这里，我们 脑表达的RNF216/TRIAD3、TRIAD3A和CHIP异构体调控假说 一组底物，其泛素化导致观察到的表型多样性 GHS。在目标1中，我们将开发一个名为“Orthogonal”的泛素底物捕获平台 “泛素转移”法研究海马区TRIAD3A和CHIP的底物特异性 神经元。在目标2中，我们将验证TRIAD3A和CHIP在神经元发育中的协同作用。 综上所述，我们的研究将首次全面概述大脑特异的TRIAD3A 和芯片底物，改变选定大脑区域的生理功能，并将识别新的 弥补GHS患者这两种酶缺陷的分子靶点。更多 概括地说，我们的工作将为E3的故障如何导致 神经系统疾病。通过确定TRIAD3A和CHIP的通用基板配置文件，我们将 能够揭示与全球统一制度相关的关键机制缺陷，最终可能是 有效地指导GHS和类似神经退行性疾病的治疗。

Abstract: In the nervous system, protein ubiquitination subserves multiple cellular processes, utilizing an enzymatic cascade that consists of ubiquitin activating enzymes (E1), ubiquitin conjugating enzymes (E2), and ubiquitin ligases (E3). The main function of the E3 in this pathway is to covalently link a small 76 residue protein called ubiquitin on to selected protein targets known as substrates. It is estimated that E3s represent 500 – 1000 genes in the human genome. We found 83 different E3s that are mutated in 70 different types of neurological disease providing supporting evidence that disruptions in ubiquitin signaling is a precipitating factor in human neurological conditions. Although a multitude of E3s are mutated in numerous neurological disorders, there is still a paucity of knowledge regarding the function and substrates of disease- relevant E3s in the brain. In this proposal, we will elucidate key functions for two E3s, TRIAD3A and CHIP, which are mutated in a heterogenous neurological disorder called Gordon Holmes syndrome (GHS). Major pathophysiologies of GHS include hypothalamic dysfunction, dementia and neurodegeneration. Individuals with RNF216/TRIAD3 and CHIP/STUB1 mutations also exhibit hypogonadotropic hypogonadism, which is thought to be caused by a dysfunctional hypothalamic-pitiutary-gonadal (HPG) axis due to deficiencies in the release of gonadotropin- releasing hormone (GnRH) within GnRH positive neurons in the hypothalamus. Here, we hypothesize that the brain-expressed isoform of RNF216/TRIAD3, TRIAD3A and CHIP regulate a suite of substrates, whose ubiquitination gives rise to the diversity of phenotypes observed in GHS. In Aim 1, we will develop a ubiquitin substrate capture platform known as “Orthogonal Ubiquitin Transfer” to profile the substrate specificities of TRIAD3A and CHIP in hippocampal neurons. In Aim 2, we will verify the synergy between TRIAD3A and CHIP in neuron development. Taken together, our study will provide the first comprehensive overview of brain-specific TRIAD3A and CHIP substrates that alter physiological functions in select brain regions, and will identify new molecular targets to compensate for the deficiency of these two enzymes in GHS patients. More broadly, our work will provide a mechanistic perspective of how malfunctions of E3s cause neurological diseases. By identifying common substrate profiles for TRIAD3A and CHIP, we will be able to reveal key mechanistic deficiencies associated with GHS, which may ultimately be effective in guiding the treatment of GHS and similar neurodegenerative diseases.