Alpha-synuclein activation of protein phosphatase 2A reduces tyrosine hydroxylase phosphorylation in dopaminergic cells.
alpha-Synuclein is an abundant presynaptic protein implicated in neuronal plasticity and neurodegenerative diseases. Although the function of alpha-synuclein is not thoroughly elucidated, we found that alpha-synuclein regulates dopamine synthesis by binding to and inhibiting tyrosine hydroxylase, the rate limiting enzyme in dopamine synthesis. Understanding alpha-synuclein function in dopaminergic cells should add to our knowledge of this key protein, which is implicated in Parkinson's disease and other disorders. Herein, we report a mechanism by which alpha-synuclein diminishes tyrosine hydroxylase phosphorylation and activity in stably transfected dopaminergic cells. Short-term regulation of tyrosine hydroxylase depends on the phosphorylation of key seryl residues in the amino-terminal regulatory domain of the protein. Of these, Ser40 contributes significantly to tyrosine hydroxylase activation and dopamine synthesis. We observed that alpha-synuclein overexpression caused reduced Ser40 phosphorylation in MN9D cells and inducible PC12 cells. Ser40 is phosphorylated chiefly by the cyclic AMP-dependent protein kinase PKA and dephosphorylated almost exclusively by the protein phosphatase, PP2A. Therefore, we measured the impact of alpha-synuclein overexpression on levels and activity of PKA and PP2A in our cells. PKA was unaffected by alpha-synuclein. PP2A protein levels also were unchanged, however, the activity of PP2A increased in parallel with alpha-synuclein expression. Inhibition of PP2A dramatically increased Ser40 phosphorylation only in alpha-synuclein overexpressors in which alpha-synuclein was also found to co-immunoprecipitate with PP2A. Together the data reveal a functional interaction between alpha-synuclein and PP2A that leads to PP2A activation and underscores a key role for alpha-synuclein in protein phosphorylation.
Peng
Xiangmin
X
Department of Neurology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA.
Peng
Xiangmin M
XM
Tehranian
Roya
R
Dietrich
Paula
P
Stefanis
Leonidas
L
Perez
Ruth G
RG
D000818:Animals; D002460:Cell Line; D004298:Dopamine / Q000096:biosynthesis / Q000378:metabolism*; D005786:Gene Expression Regulation; D051379:Mice; D008810:Mice, Inbred C57BL; D019319:Okadaic Acid / Q000494:pharmacology; D016716:PC12 Cells; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation; D054648:Protein Phosphatase 2; D051381:Rats; D012694:Serine / Q000187:drug effects / Q000378:metabolism; D014446:Tyrosine 3-Monooxygenase / Q000037:antagonists & inhibitors* / Q000378:metabolism*
D019319:Okadaic Acid; D012694:Serine; D014446:Tyrosine 3-Monooxygenase; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D004298:Dopamine