Glutathione decreases in dopaminergic PC12 cells interfere
with the ubiquitin protein degradation pathway: relevance 
for Parkinson's disease?

• Published in: Journal of neurochemistry 2002-02, Vol.80 (4), p.555-561
• Main Authors: Jha, Nandita, Kumar, M. Jyothi, Boonplueang, Rapee, Andersen, Julie K.
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Cell Line; Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; DNA, Antisense - drug effects; DNA, Antisense - genetics; DNA, Antisense - metabolism; Dopamine - metabolism; Doxycycline - pharmacology; Glutamate-Cysteine Ligase - antagonists & inhibitors; Glutamate-Cysteine Ligase - genetics; Glutathione - metabolism; Hydrogen Peroxide - metabolism; Ligases - metabolism; Macromolecular Substances; Medical sciences; Neurology; Parkinson Disease - etiology; Parkinson Disease - metabolism; Parkinson's disease; PC12 Cells; protein degradation; Protein Processing, Post-Translational - physiology; Proteins - metabolism; Rats; Sulfhydryl Compounds - metabolism; thiol oxidation; total glutathione; Ubiquitin - metabolism; ubiquitin E1 ligase; Ubiquitin-Protein Ligases
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1046/j.0022-3042.2001.00009.x

Parkinson's disease (PD) is characterized by the presence of proteinaceous neuronal inclusions called Lewy bodies in susceptible dopaminergic midbrain neurons. Inhibition of the ubiquitin‐proteasome protein degradation pathway may contribute to protein build‐up and subsequent cell death. Ubiquitin is normally activated for transfer to substrate proteins by interaction with the E1 ubiquitin ligase enzyme via a thiol ester bond. Parkinson's disease is also characterized by decreases in midbrain levels of total glutathione which could impact on E1 enzyme activity via oxidation of the active site sulfhydryl. We have demonstrated that increasing reductions in total glutathione in dopaminergic PC12 cells results in corresponding decreases in ubiquitin‐protein conjugate levels suggesting that ubiquitination of proteins is inhibited in a glutathione‐dependent fashion. Decreased ubiquitinated protein levels appears to be due to inhibition of E1 activity as demonstrated by reductions in endogenous E1‐ubiquitin conjugate levels as well as decreases in the production of de novo E1‐ubiquitin conjugates when glutathione is depleted. This is a reversible process as E1 activity increases upon glutathione restoration. Our data suggests that decreases in cellular glutathione in dopaminergic cells results in decreased E1 activity and subsequent disruption of the ubiquitin pathway. This may have implications for neuronal degeneration in PD.