title: A role for alpha-synuclein in the regulation of dopamine biosynthesis.
abstract: 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.
authors.affiliation: Department of Neurology and Center for Biological Imaging, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213, USA. perezrg@pitt.edu
authors.forename: Ruth G
authors.initials: RG
authors.lastname: Perez
authors.forename: Jack C
authors.initials: JC
authors.lastname: Waymire
authors.forename: Eva
authors.initials: E
authors.lastname: Lin
authors.forename: Jen J
authors.initials: JJ
authors.lastname: Liu
authors.forename: Fengli
authors.initials: F
authors.lastname: Guo
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Zigmond
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001921:Brain / Q000378:metabolism; D001923:Brain Chemistry; D002460:Cell Line; D002470:Cell Survival; D002474:Cell-Free System / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism*; D004789:Enzyme Activation / Q000502:physiology; D015870:Gene Expression; D006822:Hybrid Cells / Q000378:metabolism / Q000648:ultrastructure; D051379:Mice; D008810:Mice, Inbred C57BL; D016253:Microscopy, Immunoelectron; D008954:Models, Biological; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism / Q000648:ultrastructure; D010300:Parkinson Disease / Q000209:etiology / Q000378:metabolism; D010766:Phosphorylation; D011233:Precipitin Tests; D011485:Protein Binding / Q000502:physiology; D051843:Synucleins; D014162:Transfection; D014446:Tyrosine 3-Monooxygenase / Q000737:chemistry / Q000378:metabolism; D051844:alpha-Synuclein
chemical_list: D009419:Nerve Tissue Proteins; C497605:Snca protein, mouse; D051843:Synucleins; D051844:alpha-Synuclein; D014446:Tyrosine 3-Monooxygenase; D004298:Dopamine