Dopamine Transporter Activity Is Modulated by α-Synuclein

The duration and strength of the dopaminergic signal are regulated by the dopamine transporter (DAT). Drug addiction and neurodegenerative and neuropsychiatric diseases have all been associated with altered DAT activity. The membrane localization and the activity of DAT are regulated by a number of intracellular proteins. α-Synuclein, a protein partner of DAT, is implicated in neurodegenerative disease and drug addiction. Little is known about the regulatory mechanisms of the interaction between DAT and α-synuclein, the cellular location of this interaction, and the functional consequences of this interaction on the basal, amphetamine-induced DAT-mediated dopamine efflux, and membrane microdomain distribution of the transporter. Here, we found that the majority of DAT·α-synuclein protein complexes are found at the plasma membrane of dopaminergic neurons or mammalian cells and that the amphetamine-mediated increase in DAT activity enhances the association of these proteins at the plasma membrane. Further examination of the interaction of DAT and α-synuclein revealed a transient interaction between these two proteins at the plasma membrane. Additionally, we found DAT-induced membrane depolarization enhances plasma membrane localization of α-synuclein, which in turn increases dopamine efflux and enhances DAT localization in cholesterol-rich membrane microdomains.

Dopamine Transporter Activity Is Modulated by α-synuclein

The duration and strength of the dopaminergic signal is regulated by the dopamine transporter (DAT). Drug addiction, neurodegenerative and neuropsychiatric diseases have all been associated with altered DAT activity. The membrane localization and the activity of DAT are regulated by a number of intracellular proteins. α-synuclein, a protein partner of DAT, is implicated in neurodegenerative disease and drug addiction. Little is known about the regulatory mechanisms of the interaction between DAT and α-synuclein, the cellular location of this interaction, and the functional consequences of this interaction on the basal, amphetamine (AMPH) induced DAT-meditated DA efflux and membrane microdomain distribution of the transporter. Here, we found that the majority of DAT/α-synuclein protein complexes are found at the plasma membrane of dopaminergic neurons or mammalian cells, and that AMPH-mediated increase in DAT activity enhances the association of these proteins at the plasma membrane. Further examination of the interaction of DAT and α-synuclein revealed a transient interaction between these two proteins at the plasma membrane. Additionally, we found DAT-induced membrane depolarization enhances plasma membrane localization of α-synuclein, which in turn increases DA efflux and enhances DAT localization in cholesterol rich membrane microdomains.

Differential regulation of dopamine transporter function and location by low concentrations of environmental estrogens and 17beta-estradiol

BACKGROUND

The effects of 17beta-estradiol (E2) and xenoestrogens (XEs) on dopamine transport may have important implications for the increased incidence of neurologic disorders, especially in women during life stages characterized by frequent hormonal fluctuations.

OBJECTIVE

We examined low concentrations of XEs [dieldrin, endosulfan, o', p'-dichlorodiphenyl-ethylene (DDE), nonylphenol (NP), and bisphenol A (BPA)] for nongenomic actions via action of membrane estrogen receptors (ERs).

METHODS

We measured activity of the dopamine transporter (DAT) by the efflux of 3H-dopamine in nontransfected nerve growth factor-differentiated PC12 rat pheochromocytoma cells expressing membrane DAT, ER-alpha, ER-beta, and G-protein-coupled receptor 30. We used a plate immunoassay to monitor trafficking of these proteins.

RESULTS

All compounds at 1 nM either caused efflux or inhibited efflux, or both; each compound evoked a distinct oscillatory pattern. At optimal times for each effect, we examined different concentrations of XEs. All XEs were active at some concentration < 10 nM, and dose responses were all nonmonotonic. For example, 10(-14) to 10(-11) M DDE caused significant efflux inhibition, whereas NP and BPA enhanced or inhibited efflux at several concentrations. We also measured the effects of E2/XE combinations; DDE potentiated E(2)-mediated dopamine efflux, whereas BPA inhibited it. In E2-induced efflux, 15% more ER-alpha trafficked to the membrane, whereas ER-beta waned; during BPA-induced efflux, 20% more DAT was trafficked to the plasma membrane.

CONCLUSIONS

Low levels of environmental estrogen contaminants acting as endocrine disruptors via membrane ERs can alter dopamine efflux temporal patterning and the trafficking of DAT and membrane ERs, providing a cellular mechanism that could explain the disruption of physiologic neurotransmitter function.