Loss-of-function in the Parkin protein is thought to play a part in causing neuronal cell death in patients with Parkinson's disease. This study explores the effect of Parkin degradation, via the overexpression of nucleus accumbens 1 (NAC1), on cell viability. It was found that NAC1 and Parkin are co-localized within the cell and interact with one another, leading to a decrease in Parkin levels. Moreover, NAC1 down-regulates Parkin by presenting it for ubiquitin-dependent proteasome degradation, which causes a decrease in proteasomal activity in neuronal cells. Consequently, this decrease in proteasomal activity leads to an increase in the cells' susceptibility to proteasome inhibition-induced toxicity. It was also found that Parkin and NAC1 are key proteins found to be present mainly in the cytoplasm and are co-localized in neurons of Parkinson's disease patients. Interestingly, mutation in the POZ/BTB domain (Q23L) of NAC1 disrupts the co-localization and interaction of NAC1 with Parkin and it further abrogates the proteasome inhibition-induced toxicity. We further observed that co-transfection of the mutant form of NAC1 with Parkin reversed the proteasome activity and 20S proteasome protein levels. These results indicate a novel interaction between NAC1 and Parkin that leads to neuronal cell death, a main characteristic in Parkinson's disease.
Keywords: 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide; 4′,6-diamidino-2-phenylindole; DAPI; GAPDH; GST; MTT; NAC; PBS; PCR; PD; Parkinson’s disease; SDS–PAGE; UPS; aggregates; co-immunoprecipitation; co-localization; degradation; down-regulation; glutathione S-transferase; glyceraldehyde 3-phosphate dehydrogenase; nucleus accumbens; phosphate-buffered saline; polymerase chain reaction; proteasome; sodium dodecyl sulfate–polyacrylamide gel electrophoresis; ubiquitin–proteasome system.
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