A role for alpha-synuclein in the regulation of dopamine biosynthesis.
The alpha-synuclein gene is implicated in the pathogenesis of Parkinson's disease. Although alpha-synuclein function is uncertain, the protein has homology to the chaperone molecule 14-3-3. In addition, alpha-synuclein can bind to 14-3-3, and both alpha-synuclein and 14-3-3 bind to many of the same proteins. Because 14-3-3 binds to and activates ... tyrosine hydroxylase, the rate-limiting enzyme in dopamine (DA) biosynthesis, we explored whether alpha-synuclein also bound to tyrosine hydroxylase and influenced its activity. Immunoprecipitation revealed an interaction between alpha-synuclein and tyrosine hydroxylase in brain homogenates and MN9D dopaminergic cells. Colocalization of alpha-synuclein with tyrosine hydroxylase was confirmed by immunoelectron microscopy. To explore the consequences of the interaction, we measured the effect of recombinant alpha-synuclein on tyrosine hydroxylase activity in a cell-free system and observed a dose-dependent inhibition of tyrosine hydroxylase by alpha-synuclein. To measure the impact of alpha-synuclein on tyrosine hydroxylase in dopaminergic cells, we stably transfected MN9D cells with wild-type or A53T mutant alpha-synuclein. Overexpression of wild-type or A53T mutant alpha-synuclein did not significantly alter tyrosine hydroxylase protein levels in our stably transfected cells. However, overexpressing cell lines had significantly reduced tyrosine hydroxylase activity and a corresponding reduction in dopamine synthesis. The reduction in cellular dopamine levels was not caused by increased dopamine catabolism or dopamine efflux. These data suggest that alpha-synuclein plays a role in the regulation of dopamine biosynthesis, acting to reduce the activity of tyrosine hydroxylase. If so, a loss of soluble alpha-synuclein, by reduced expression or aggregation, could increase dopamine synthesis with an accompanying increase in reactive dopamine metabolites.
Mesh Terms:
Amino Acid Substitution, Animals, Brain, Brain Chemistry, Cell Line, Cell Survival, Cell-Free System, Dopamine, Enzyme Activation, Gene Expression, Hybrid Cells, Mice, Mice, Inbred C57BL, Microscopy, Immunoelectron, Models, Biological, Nerve Tissue Proteins, Neurons, Parkinson Disease, Phosphorylation, Precipitin Tests, Protein Binding, Synucleins, Transfection, Tyrosine 3-Monooxygenase, alpha-Synuclein
Amino Acid Substitution, Animals, Brain, Brain Chemistry, Cell Line, Cell Survival, Cell-Free System, Dopamine, Enzyme Activation, Gene Expression, Hybrid Cells, Mice, Mice, Inbred C57BL, Microscopy, Immunoelectron, Models, Biological, Nerve Tissue Proteins, Neurons, Parkinson Disease, Phosphorylation, Precipitin Tests, Protein Binding, Synucleins, Transfection, Tyrosine 3-Monooxygenase, alpha-Synuclein
J. Neurosci.
Date: Apr. 15, 2002
PubMed ID: 11943812
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