Szargel Raymonde, Rott Ruth, Eyal Allon, Haskin Joseph, Shani Vered, Balan Livia, Wolosker Herman, Engelender Simone
Department of Pharmacology, The B. Rappaport Faculty of Medicine and Institute of Medical Research, Technion-Israel Institute of Technology, Haifa 31096, Israel.
J Biol Chem. 2009 Apr 24;284(17):11706-16. doi: 10.1074/jbc.M805990200. Epub 2009 Feb 17.
Parkinson disease (PD) is characterized by the presence of ubiquitylated inclusions and the death of dopaminergic neurons. Seven in absentia homolog (SIAH) is a ubiquitin-ligase that ubiquitylates alpha-synuclein and synphilin-1 and is present in Lewy bodies of PD patients. Understanding the mechanisms that regulate the ubiquitylation of PD-related proteins might shed light on the events involved in the formation of Lewy bodies and death of neurons. We show in this study that the recently described synphilin-1 isoform, synphilin-1A, interacts in vitro and in vivo with the ubiquitin-protein isopeptide ligase SIAH and regulates its activity toward alpha-synuclein and synphilin-1. SIAH promotes limited ubiquitylation of synphilin-1A that does not lead to its degradation by the proteasome. SIAH also increases the formation of synphilin-1A inclusions in the presence of proteasome inhibitors, supporting the participation of ubiquitylated synphilin-1A in the formation of Lewy body-like inclusions. Synphilin-1A/SIAH inclusions recruit PD-related proteins, such as alpha-synuclein, synphilin-1, Parkin, PINK1, and UCH-L1. We found that synphilin-1A robustly increases the steady-state levels of SIAH by decreasing its auto-ubiquitylation and degradation. In addition, synphilin-1A blocks the ubiquitylation and degradation of the SIAH substrates synphilin-1 and deleted in colon cancer protein. Furthermore, synphilin-1A strongly decreases the monoubiquitylation of alpha-synuclein by SIAH and the formation of alpha-synuclein inclusions, supporting a role for monoubiquitylation in alpha-synuclein inclusion formation. Our results suggest a novel function for synphilin-1A as a regulator of SIAH activity and formation of Lewy body-like inclusions.
帕金森病（PD）的特征是存在泛素化包涵体以及多巴胺能神经元死亡。无七同源物（SIAH）是一种泛素连接酶，可使α-突触核蛋白和突触结合蛋白-1泛素化，且存在于PD患者的路易小体中。了解调节PD相关蛋白泛素化的机制可能有助于揭示路易小体形成和神经元死亡所涉及的事件。我们在本研究中表明，最近描述的突触结合蛋白-1异构体突触结合蛋白-1A在体外和体内与泛素-蛋白质异肽连接酶SIAH相互作用，并调节其对α-突触核蛋白和突触结合蛋白-1的活性。SIAH促进突触结合蛋白-1A的有限泛素化，这不会导致其被蛋白酶体降解。在蛋白酶体抑制剂存在的情况下，SIAH还会增加突触结合蛋白-1A包涵体的形成，支持泛素化的突触结合蛋白-1A参与路易小体样包涵体的形成。突触结合蛋白-1A/SIAH包涵体募集PD相关蛋白，如α-突触核蛋白、突触结合蛋白-1、帕金蛋白、PINK1和UCH-L1。我们发现，突触结合蛋白-1A通过减少SIAH的自身泛素化和降解，有力地提高了SIAH的稳态水平。此外，突触结合蛋白-1A阻断了SIAH底物突触结合蛋白-1和结肠癌缺失蛋白的泛素化和降解。此外，突触结合蛋白-1A强烈降低SIAH对α-突触核蛋白的单泛素化以及α-突触核蛋白包涵体的形成，支持单泛素化在α-突触核蛋白包涵体形成中的作用。我们的结果表明，突触结合蛋白-1A作为SIAH活性和路易小体样包涵体形成的调节剂具有新功能。
