α-Synuclein activation of protein phosphatase 2A reduces tyrosine hydroxylase phosphorylation in dopaminergic cells

Abstract

α-Synuclein is an abundant presynaptic protein implicated in neuronal plasticity and neurodegenerative diseases. Although the function of α-synuclein is not thoroughly elucidated, we found that α-synuclein regulates dopamine synthesis by binding to and inhibiting tyrosine hydroxylase, the rate limiting enzyme in dopamine synthesis. Understanding α-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 α-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 α-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 α-synuclein overexpression on levels and activity of PKA and PP2A in our cells. PKA was unaffected by α-synuclein. PP2A protein levels also were unchanged, however, the activity of PP2A increased in parallel with α-synuclein expression. Inhibition of PP2A dramatically increased Ser40 phosphorylation only in α-synuclein overexpressors in which α-synuclein was also found to co-immunoprecipitate with PP2A. Together the data reveal a functional interaction between α-synuclein and PP2A that leads to PP2A activation and underscores a key role for α-synuclein in protein phosphorylation.

α-Synuclein Overexpression in PC12 and Chromaffin Cells Impairs Catecholamine Release by Interfering with a Late Step in Exocytosis

“…Previous studies report that ␣-syn can interfere with catecholamine synthesis and vesicular and plasma membrane uptake (Lee et al, 2001;Lotharius et al, 2002;Perez et al, 2002;Wersinger et al, 2003;Peng et al, 2005), and regulation of each of these processes is known to affect the quantal size of transmitter release (Sulzer and Pothos, 2000). Effects of ␣-syn on quantal size, however, have not been studied directly.…”

α-Synuclein Expression Modulates Microglial Activation Phenotype

“…It is found in presynaptic terminals of neurons (Maroteaux et al, 1988;McLean et al, 2000), but also in other regions of neurons as well as within astrocytes and oligodendroglia (Richter-Landsberg et al, 2000;Mori et al, 2002). ␣-Synuclein binds a variety of proteins (Jenco et al, 1998;Peng et al, 2005) and lipid vesicles , and is involved in lipid metabolism (Cabin et al, 2002;Castagnet et al, 2005;Golovko et al, 2005Golovko et al, , 2006. Absence of ␣-synuclein expression is associated with striatal dysfunction (Abeliovich et al, 2000).…”

The phosphorylation state of Ser-129 in human α-synuclein determines neurodegeneration in a rat model of Parkinson disease

“…Furthermore, ␣-syn can interact with presynaptic membranes, indicating that one of its functions may be in the regulation of DA release and reuptake (8)(9)(10). There is also evidence that ␣-syn can modulate expression of genes involved in DA synthesis (11) and can affect enzymes involved in chromatin remodeling (12) and signal transduction (13).…”