6-Hydroxydopamine increases ubiquitin-conjugates and protein degradation: implications for the pathogenesis of Parkinson's disease.
One of the hallmarks of Parkinson's disease (PD) is pathological structure, termed Lewy body, containing inclusions of ubiquitinated proteins in the dopaminergic neurons in the substantia nigra. The mechanism leading to the formation of these aggregates is unclear, although it has been shown that mutations in alpha-synuclein or in the ubiquitin-related enzyme UCH-L1 might induce such protein aggregation. We, therefore, examined the possible role of 6-hydroxydopamine (6-OHDA), a dopaminergic neurotoxin used in PD experimental models, in causing protein degradation and its association with the ubiquitin system. Using antiubiquitin antibodies we found that exposure of SH-SY5Y neuroblastoma and PC-12 cell lines to 6-OHDA increased the levels of free ubiquitin and ubiquitin-conjugated proteins, in a dose-dependent manner. Furthermore, metabolic labeling with 35S-methionine, demonstrated that 6-OHDA markedly increased protein degradation, as indicated by the secretion of protein metabolites to the medium. Inhibition of the proteasome activity by the specific inhibitor MG132, attenuated the protein degradation induced by 6-OHDA and potentiated its toxicity. Administration of the antioxidant N-acetylcysteine to the 6-OHDA-treated cells, increased cell survival and reduced protein degradation. In conclusion, our findings suggest that 6-OHDA toxicity is associated with protein degradation and ubiquitin-proteasome system activation.
Elkon
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Felsenstein Medical Research Center and the Department of Neurology, Rabin Medical Center, Tel Aviv University, Petah Tikva, Israel.
Melamed
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Offen
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D
D000111:Acetylcysteine / Q000494:pharmacology; D000818:Animals; D003546:Cysteine Endopeptidases / Q000187:drug effects / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D016166:Free Radical Scavengers / Q000494:pharmacology; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D016631:Lewy Bodies / Q000378:metabolism; D008715:Methionine; D008959:Models, Neurological; D009097:Multienzyme Complexes / Q000187:drug effects / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D016627:Oxidopamine / Q000633:toxicity*; D016716:PC12 Cells; D010300:Parkinson Disease / Q000378:metabolism* / Q000503:physiopathology; D046988:Proteasome Endopeptidase Complex; D051381:Rats; D013378:Substantia Nigra / Q000378:metabolism* / Q000503:physiopathology; D013462:Sulfur Radioisotopes; D013565:Sympatholytics / Q000633:toxicity*; D014452:Ubiquitins / Q000187:drug effects / Q000378:metabolism*
D015853:Cysteine Proteinase Inhibitors; D016166:Free Radical Scavengers; D007976:Leupeptins; D009097:Multienzyme Complexes; D009419:Nerve Tissue Proteins; D013462:Sulfur Radioisotopes; D013565:Sympatholytics; D014452:Ubiquitins; D016627:Oxidopamine; D008715:Methionine; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde; D000111:Acetylcysteine