title: Synphilin-1A inhibits seven in absentia homolog (SIAH) and modulates alpha-synuclein monoubiquitylation and inclusion formation.
abstract: 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.
authors.affiliation: Department of Pharmacology, The B. Rappaport Faculty of Medicine and Institute of Medical Research, Technion-Israel Institute of Technology, Haifa 31096, Israel.
authors.forename: Raymonde
authors.initials: R
authors.lastname: Szargel
authors.forename: Ruth
authors.initials: R
authors.lastname: Rott
authors.forename: Allon
authors.initials: A
authors.lastname: Eyal
authors.forename: Joseph
authors.initials: J
authors.lastname: Haskin
authors.forename: Vered
authors.initials: V
authors.lastname: Shani
authors.forename: Livia
authors.initials: L
authors.lastname: Balan
authors.forename: Herman
authors.initials: H
authors.lastname: Wolosker
authors.forename: Simone
authors.initials: S
authors.lastname: Engelender
mesh_terms: D000818:Animals; D001671:Biochemistry / Q000379:methods; D001921:Brain / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism / Q000502:physiology*; D045744:Cell Line, Tumor; D006801:Humans; D016631:Lewy Bodies / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D009419:Nerve Tissue Proteins / Q000378:metabolism / Q000502:physiology*; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D014162:Transfection; D025801:Ubiquitin / Q000737:chemistry*; D044767:Ubiquitin-Protein Ligases / Q000037:antagonists & inhibitors*; D051844:alpha-Synuclein / Q000737:chemistry*; D000098563:Seven in Absentia Proteins
chemical_list: D002352:Carrier Proteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D034741:RNA, Small Interfering; C118958:SNCAIP protein, human; D025801:Ubiquitin; D051844:alpha-Synuclein; D044767:Ubiquitin-Protein Ligases; D000098563:Seven in Absentia Proteins; D046988:Proteasome Endopeptidase Complex