Ubiquitin-Dependent Sorting in Endosomes and the TGN

描述（由申请人提供）：将蛋白质送至溶酶体进行降解是细胞用于控制细胞表面蛋白质活性的主要机制之一。膜蛋白的泛素化是其分选到溶酶体的主要信号。泛素（ubiquitin，Ub）与靶蛋白的翻译后连接启动了靶蛋白从细胞表面的内化，并转运到多泡内体（multiple-esicular endosomes/multiple-esicular bodies，MVB）的腔内囊泡中。已知一系列ESCRT（转运所需的内体分选复合物：例如ESCRT-0、I、II、III））协调泛素化膜蛋白货物（Ub-货物）的分选与MVB内腔囊泡的形成，因此在溶酶体降解过程中发挥关键作用。然而，ESCRT蛋白如何识别和移动Ub货物以及它们如何参与协调Ub连接酶和Ub肽酶的活性以修饰并因此调节Ub货物的命运尚不清楚。这里提出的工作有两个主要目标：第一个是确定哪些蛋白质作为内体Ub分选受体，以及它们如何与其他功能协调移动Ub货物。第二个目标集中在新兴的概念，因为泛素化是动态的，有许多情况下，其中Ub连接酶和肽酶可以竞争货物的最终处置。我们现在提出，作为“ESCRT-0样”蛋白平行工作的其他蛋白质复合物，以及其他内体分选复合物，与DUb和连接酶相关联，以急剧影响特定Ub货物的分选命运。具体目的是：通过ESCRT-I和-II研究Ub结合的作用。测试交替的“ESCRT-0样”复合物的功能。测试去核酶在从核内体回收蛋白质中的作用 公共卫生相关性：未能将特定的膜蛋白靶向溶酶体导致通道、转运蛋白或信号传导受体不适当地过度活跃，这反过来导致许多疾病，包括癌症、代谢紊乱、发育异常、心脏病和高血压。这里提出的工作将调查的生化和细胞生物学过程，确保适当的识别和分类的膜蛋白标记的泛素在溶酶体中降解。我们相信，这样的理解将打开新的途径，治疗干预，操纵溶酶体降解的过程，以针对一系列的生物过程。

DESCRIPTION (provided by applicant): Sending proteins to the lysosome for degradation is one of the chief mechanisms cells use to control the activity of cell-surface proteins. Ubiquitination of membrane proteins serves as a major signal for their sorting to lysosomes. The post-translational ligation of ubiquitin (Ub) to target proteins initiates their internalization from the cell surface and their transport into lumenal vesicles of multivesicular endosomes/multivesicular bodies (MVBs). A series of ESCRTs (Endosomal Sorting Complex Required for Transport: e.g. ESCRT-0,I,II,III)) are known to coordinate the sorting of ubiquitinated membrane protein cargo (Ub-cargo) with the formation of MVB lumenal vesicles and thus play critical roles in the process of lysosomal degradation. Yet, how ESCRT proteins recognize and move Ub-cargo as well as how they might participate in coordinating the activity of Ub ligases and Ub peptidases to modify and thus regulate the fate of Ub-cargo are unclear. The work proposed here has two main objectives: The first is to establish which proteins serve as endosomal Ub sorting receptors, and how they move Ub-cargo in coordination with their other functions. The second objective centers on the emerging concept that since ubiquitination is dynamic, there are many instances in which Ub ligases and peptidases can compete for the final disposition of cargo. We now propose that other protein complexes that work in parallel as "ESCRT-0- like" proteins, as well as other endosomal sorting complexes, associate with DUbs and ligases to acutely influence the sorting fate of specific Ub-cargo. The Specific Aims are to: Investigate the roles of Ub-binding by ESCRT-I and -II. Test the function of alternate "ESCRT-0-like" complexes. Test the role of Deubqiutinating enzymes in recycling proteins from endosomes PUBLIC HEALTH RELEVANCE: Failure to target particular membrane proteins to lysosomes leads to inappropriately hyperactive channels, transporters, or signaling receptors, which in turn contribute to a number of diseases including cancer, metabolic disorders, developmental abnormalities, heart disease, and hypertension. The work proposed here will investigate the biochemical and cell biological processes that ensure proper recognition and sorting of membrane proteins that are marked by ubiquitin for degradation in lysosomes. We believe that such understanding will open new avenues for therapeutic interventions that manipulate the process of lysosomal degradation to target a range of biological processes.