Functional Studies of Ubiquilin

描述(由研究人员提供)：从神经退行性疾病的研究中出现的一个共同主题是认识到许多神经退行性疾病与涉及泛素-蛋白酶体系统或自噬的蛋白质降解途径的缺陷有关或由其引起。泛素-蛋白酶体降解途径是细胞中使用的主要途径，在该途径中，错误折叠、损坏和不需要的蛋白质首先被四个或更多泛素分子链标记，然后被蛋白酶体识别和降解。自噬途径在许多方面类似于泛素-蛋白酶体降解途径，不同的是蛋白质和细胞器针对的是溶酶体而不是蛋白酶体。目前还不知道细胞如何选择这两条途径中的一条或两条来降解特定的蛋白质。我们的实验室发现了泛素，它是一类新的蛋白质的创始成员，似乎可以调节细胞中的蛋白质降解。在上一个资助阶段，我们发现泛素与一种新的内质网(ER)和核膜定位的蛋白质相互作用，我们将其命名为Erasin。我们发现，Erasin促进内质网相关蛋白降解(ERAD)，这是一种调节途径，内质网中错误折叠的蛋白质被蛋白酶体以泛素依赖的方式提取和降解。我们发现，内质网应激增加了Erasin的水平，在阿尔茨海默病神经纤维变性的神经元中，泛素和Erasin蛋白的水平都增加了。在其他研究中，我们发现泛素和擦除素在ERAD中功能上相互作用，并且在自噬过程中它们是共同定位的，是自噬形成自噬小体所必需的。这项建议的目的是描述泛素和擦除素蛋白在细胞中的功能作用，特别强调它们在ERAD和自噬中的作用。我们提出了三个目标。在目标1中，我们将确定泛素-erasin相互作用在ERAD中的作用。在目标2中，我们将确定泛素-erasin相互作用在自噬中的作用。最后，在目标3中，我们将对与擦除素相互作用的蛋白质进行表征，并确定擦除素的ER膜定位序列的靶向结构和机制。总之，这些研究应该有助于更好地理解泛素和擦除素在蛋白质降解途径中的功能，以及这些蛋白质在健康和病理过程中的作用。 蛋白质在生物体中执行许多重要功能，但要做到这一点，它们需要正确折叠。不幸的是，蛋白质往往会错误折叠，要么是因为它们含有基因突变，要么是因为环境影响。事实上，错误折叠蛋白质的积累现在已知会导致许多人类疾病，特别是神经退行性疾病，如阿尔茨海默病、亨廷顿病、卢·格里克病和帕金森氏病。这项建议是针对泛素和擦除素的研究，这两种我们发现的新蛋白质参与了细胞中错误折叠蛋白质的去除。从这一提议中获得的结果不仅将有助于更好地了解错误折叠的蛋白质是如何从细胞中清除的，还可能导致治疗蛋白质错误折叠导致的人类疾病的新疗法。

DESCRIPTION (provided by investigator): A common theme that is emerging from studies of neurodegenerative disorders is the realization that many of them are associated, or caused, by defects in protein degradation pathways involving either the ubiquitin-proteasome system or autophagy. The ubiquitin-proteasome degradation pathway is the major pathway used in cells in which misfolded, damaged, and unwanted proteins are first tagged with a chain of four or more ubiquitin molecules and is then recognized and degraded by the proteasome. The autophagy pathway is similar in many respects to the ubiquitin-proteasome degradation pathway, except that proteins as well as organelles are targeted to the lysosome instead of the proteasome. At present it is not known how cells select one or both of these pathways to degrade a particular protein. Our laboratory identified ubiquilin, the founding member of a new class of proteins that appears to regulate protein degradation in cells. During the last funding period, we discovered that ubiquilin interacts with a novel endoplasmic reticulum (ER)- and nuclear envelope-localized protein that we named erasin. We found that erasin promotes endoplasmic reticulum- associated protein degradation (ERAD), a regulated pathway in which misfolded proteins in the ER are extracted and degraded in a ubiquitin-dependent manner by the proteasome. We found that erasin levels are increased by ER stress and that both ubiquilin and erasin protein levels are increased in neurons undergoing neurofibrillary degeneration in Alzheimer's disease. In other studies we found that ubiquilin and erasin interact functionally in ERAD and that they colocalize and are required for autophagosome formation during autophagy. The goal of this proposal is to characterize the functional role of ubiquilin and erasin proteins in cells, with particular emphasis of their roles in ERAD and autophagy. We propose three aims. In Aim 1, we will determine the role of ubiquilin-erasin interaction in ERAD. In Aim 2, we will determine the role of ubiquilin-erasin interaction in autophagy. Finally in Aim 3 we will characterize erasin-interacting proteins and determine the structure and mechanism of targeting of the ER-membrane-localization sequence of erasin. Together these studies should lead to a better understanding of the function of ubiquilin and erasin in protein degradation pathways and the role of the proteins in health and pathological processes. Proteins carry out many vital functions in organisms, but to do so, they need to be correctly folded. Unfortunately proteins tend to misfold, either because they contain genetic mutations or because of environmental influences. In fact, accumulation of misfolded proteins is now known to cause many human diseases, particularly neurodegenerative diseases like Alzheimer's disease, Huntingtons's disease, Lou Gehrig's disease, and Parkinson's disease. This proposal is directed towards studies of ubiquilin and erasin, two new proteins that we discovered that are involved in the removal of misfolded proteins in cells. The results obtained from this proposal will not only lead to a better understanding of how misfolded proteins are cleared from cells, but also could lead to new therapies to treat human diseases caused by protein misfolding.