Dopamine (DA) metabolism and oxidation produce both reactive oxygen species (ROS) and reactive quinones. These chemical species are implicated in dopamine neurotoxicity and neurodegeneration. In the present studies, human neuroblastoma (SK-N-SH) cells were exposed to toxic concentrations of dopamine (333 μM) in order to investigate molecular pathways involved in dopamine toxicity. cDNA hybridization array (microarray) technology demonstrated that GADD45 and GADD153 (growth arrest and DNA-damage inducible) gene expression was increased in dopamine-treated cells (333 μM for 18 h). Subsequent Northern and Western blot analysis confirmed these changes in GADD45 and GADD153 gene expression. The antioxidant, ascorbic acid, significantly reduced the increase in GADD45 gene expression but did not significantly reduce GADD153 gene expression. Currently, the precise function of the GADD gene products is not known. It is known, however, that these genes are upregulated in response to stress to allow cells time to repair macromolecular damage. In the present case, GADD gene expression (manifested as increased mRNA and protein levels) preceded dopamine-induced cytotoxicity. It appears that dopamine, through the formation of reactive oxygen species and quinones, may damage cellular macromolecules to the point of inducing GADD gene expression. Other genes that displayed changes, but that have not been subjected to post-hoc confirmation, include clusterin (increased), ubiquitin (increased), CD27 ligand (increased), CD27BP (increased), and rac-PK-beta (decreased).
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