title: Parkinson's disease-associated mutations in α-synuclein and UCH-L1 inhibit the unconventional secretion of UCH-L1.
abstract: Ubiquitin carboxy-terminal hydrolase L1 (UCH-L1) is an intracellular protein abundantly expressed in neurons, and a mutation in UCH-L1 has been identified in familial Parkinson's disease. UCH-L1 has been detected in human cerebrospinal fluid, raising the possibility that UCH-L1 is secreted from neurons. In the present study, we showed that a portion of UCH-L1 is secreted from cultured cells. The secretion of D30K UCH-L1, which lacks ubiquitin binding activity, was decreased compared with that of wild-type UCH-L1, while the secretion of C90S UCH-L1, which lacks hydrolase activity, was not. Treatment with Brefeldin A, an inhibitor of vesicle transport from the endoplasmic reticulum to the Golgi, did not block the secretion of UCH-L1, indicating that UCH-L1 is secreted by an unconventional pathway. The UCH-L1 sequence from Leu-32 to Leu-39 is similar to the unconventional secretory signal sequence of engrailed 2, and substitution of the leucines within this region (L32S/L32A/L34S/L34A/L39S/L39A) reduced the secretion of UCH-L1. We found that the Parkinson's disease-associated mutation I93M in UCH-L1 decreased the secretion of I93M UCH-L1. In addition, Parkinson's disease-linked α-synuclein mutants reduced the secretion of endogenous UCH-L1. Our results indicate that the hydrolase activity is not necessary for the unconventional secretion of UCH-L1, and suggest that the ubiquitin binding activity and the sequence between Leu-32 and Leu-39 are involved in the secretion. Moreover, the secretion of UCH-L1 could be involved in the pathology of Parkinson's disease.
authors.affiliation: Department of Degenerative Neurological Diseases, National Institute of Neuroscience, National Center of Neurology and Psychiatry, 4-1-1 Ogawahigashi, Kodaira, Tokyo 187-8502, Japan.
authors.forename: Chiho
authors.initials: C
authors.lastname: Konya
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Hatanaka
authors.forename: Yuuki
authors.initials: Y
authors.lastname: Fujiwara
authors.forename: Kenko
authors.initials: K
authors.lastname: Uchida
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Nagai
authors.forename: Keiji
authors.initials: K
authors.lastname: Wada
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Kabuta
mesh_terms: D000595:Amino Acid Sequence; D015153:Blotting, Western; D002460:Cell Line; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D010300:Parkinson Disease / Q000235:genetics*; D043222:Ubiquitin Thiolesterase / Q000737:chemistry / Q000235:genetics*; D051844:alpha-Synuclein / Q000235:genetics*
chemical_list: C482860:UCHL1 protein, human; D051844:alpha-Synuclein; D043222:Ubiquitin Thiolesterase