title: Proteasomal inhibition by misfolded mutant superoxide dismutase 1 induces selective motor neuron death in familial amyotrophic lateral sclerosis.
abstract: Accumulating evidence indicates that abnormal conformation of mutant superoxide dismutase 1 (SOD1) is an essential feature underlying the pathogenesis of mutant SOD1-linked familial amyotrophic lateral sclerosis (ALS). Here we investigated the role of ubiquitin-proteasome pathway in the mutant SOD1-related cell death and the effect of oxidative stress on the misfolding of mutant SOD1. Transient overexpression of ubiquitin with human SOD1 (wild-type, ala4val, gly85arg, gly93ala) in Neuro2A cells decreased the amount of mutant SOD1, but not of wild-type, while only mutants were co-immunoprecipitated with poly-ubiquitin. Proteasome inhibition by lactacystin augmented accumulation of mutant SOD1 in the non-ionic detergent-insoluble fraction. The spinal cord lysates from mutant SOD1 transgenic mice showed multiple carbonylated proteins, including mutant SOD1 with SDS-resistant dimer formation. Furthermore, the treatment of hSOD1-expressing cells with hydrogen peroxide promoted the oligomerization, and detergent-insolubility of mutant SOD1 alone, and the oxidized mutant SOD1 proteins were more heavily poly-ubiquitinated. In Neuro2A cells stably expressing human SOD1 protein, the proteasome function measured by chymotrypsin-like activity, was decreased over time without a quantitative alteration of the 20S proteasomal component. Finally, primary motor neurons from the mouse embryonic spinal cord were more vulnerable to lactacystin than non-motor neurons. These results indicate that the sustained expression of mutant SOD1 leads to proteasomal inhibition and motor neuronal death, which in part explains the pathogenesis of mutant SOD1-linked ALS.
authors.affiliation: Laboratory for Motor System Neurodegeneration, Brain Science Institute (BSI), RIKEN, Saitama, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Urushitani
authors.forename: Junko
authors.initials: J
authors.lastname: Kurisu
authors.forename: Kayoko
authors.initials: K
authors.lastname: Tsukita
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Takahashi
mesh_terms: D019943:Amino Acid Substitution; D000690:Amyotrophic Lateral Sclerosis / Q000201:enzymology* / Q000209:etiology; D000818:Animals; D016923:Cell Death; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004195:Disease Models, Animal; D004789:Enzyme Activation; D015870:Gene Expression; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D046911:Macromolecular Substances; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009046:Motor Neurons / Q000166:cytology / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors* / Q000378:metabolism; D009447:Neuroblastoma / Q000378:metabolism; D018384:Oxidative Stress; D046988:Proteasome Endopeptidase Complex; D011489:Protein Denaturation; D017510:Protein Folding; D012995:Solubility; D013482:Superoxide Dismutase / Q000235:genetics / Q000378:metabolism*; D000072105:Superoxide Dismutase-1; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D046911:Macromolecular Substances; D009097:Multienzyme Complexes; C000606290:SOD1 protein, human; D025801:Ubiquitin; C109415:SOD1 G93A protein; C000606291:Sod1 protein, mouse; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex