Mechanisms of rotenone-induced proteasome inhibition

The etiology of Parkinson's disease is unclear but appears to involve mitochondrial dysfunction, proteasome inhibition, and environmental toxins. It has been shown that pesticides, including the complex I inhibitor rotenone, cause proteasome inhibition but the mechanism of rotenone-induced proteasome dysfunction remains largely unknown. In this study, we examined the role of mitochondrial inhibition, oxidative stress, and microtubule dysfunction as potential mediators of rotenone-induced proteasome inhibition. Proteasome activity (26S) was measured in HEK and SK-N-MC cells expressing an EGFP-U degron fusion protein that is selectively degraded by the proteasome. We found that complexes I and III inhibition led to the production of peroxides and decreased proteasome activity. We also found that rotenone increased nitric oxide production and nitric oxide and peroxynitrites led to proteasome inhibition. The effects of rotenone were attenuated by anti-oxidants and nitric oxide synthase inhibition. Since rotenone can also inhibit microtubule assembly, we tested a specific MT inhibitor and found it led to proteasome dysfunction. Rotenone also led to a decrease in 20S proteasome activity and 20S proteasome subunit immunoreactivity without a change in subunit mRNA. Together, these data suggest that rotenone-induced decreases in proteasome activity are due to increased degradation of proteasome components secondary to oxidative damage and possibly microtubule dysfunction.