title: Parkin facilitates the elimination of expanded polyglutamine proteins and leads to preservation of proteasome function.
abstract: Parkin, the most commonly mutated gene in familial Parkinson's disease, encodes an E3 ubiquitin ligase. A number of candidate substrates have been identified for parkin ubiquitin ligase action including CDCrel-1, o-glycosylated alpha-synuclein, Pael-R, and synphilin-1. We now show that parkin promotes the ubiquitination and degradation of an expanded polyglutamine protein. Overexpression of parkin reduces aggregation and cytotoxicity of an expanded polyglutamine ataxin-3 fragment. Using a cellular proteasome indicator system based on a destabilized form of green fluorescent protein, we demonstrate that parkin reduces proteasome impairment and caspase-12 activation induced by an expanded polyglutamine protein. Parkin forms a complex with the expanded polyglutamine protein, heat shock protein 70 (Hsp70) and the proteasome, which may be important for the elimination of the expanded polyglutamine protein. Hsp70 enhances parkin binding and ubiquitination of expanded polyglutamine protein in vitro suggesting that Hsp70 may help to recruit misfolded proteins as substrates for parkin E3 ubiquitin ligase activity. We speculate that parkin may function to relieve endoplasmic reticulum stress by preserving proteasome activity in the presence of misfolded proteins. Loss of parkin function and the resulting proteasomal impairment may contribute to the accumulation of toxic aberrant proteins in neurodegenerative diseases including Parkinson's disease.
authors.affiliation: Department of Biomedical Engineering, The Johns Hopkins University, Baltimore, MD 21205, USA.
authors.forename: Yien Che
authors.initials: YC
authors.lastname: Tsai
authors.forename: Paul S
authors.initials: PS
authors.lastname: Fishman
authors.forename: Nitish V
authors.initials: NV
authors.lastname: Thakor
authors.forename: George A
authors.initials: GA
authors.lastname: Oyler
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D053454:Caspase 12; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D002470:Cell Survival; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D049452:Green Fluorescent Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D008025:Ligases / Q000378:metabolism / Q000502:physiology*; D008164:Luminescent Proteins / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D009097:Multienzyme Complexes / Q000378:metabolism*; D010455:Peptides / Q000737:chemistry*; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D051381:Rats; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases
chemical_list: D018840:HSP70 Heat-Shock Proteins; D008164:Luminescent Proteins; D009097:Multienzyme Complexes; D010455:Peptides; D025801:Ubiquitin; D049452:Green Fluorescent Proteins; C097188:polyglutamine; D044767:Ubiquitin-Protein Ligases; C111567:parkin protein; C506444:CASP12 protein, human; C506440:Casp12 protein, mouse; C506443:Casp12 protein, rat; D053454:Caspase 12; D020169:Caspases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D008025:Ligases