Regulation of Dopamine Transporter Trafficking by Substrates, Rabs, and Shares.

Abstract

The plasmalemmal dopamine transporter (DAT) regulates dopaminergic neurotransmission by facilitating reuptake of extracellular dopamine (DA). The psychostimulant amphetamine (AMPH) is a substrate of DAT which stimulates DA efflux through DAT. DAT undergoes both constitutive and substrate-regulated trafficking and this trafficking further regulates DA action. To date, most trafficking studies focus on DAT endocytosis following prolonged (10 – 60 min) substrate treatment. However, little is known about the mechanisms regulating DAT exocytosis or trafficking to the plasma membrane. The purpose of this thesis was to elucidate the mechanisms by which constitutive and rapid stimulated DAT trafficking occur. Specifically, the role of Rab and SNARE (N-ethylmaleimide sensitive factor attachment protein receptor) proteins in constitutive DAT trafficking was examined. Additionally, the mechanisms of rapid DAT trafficking to the surface in response to substrates were examined. Our results provide a new model whereby (1) Rab 11 and syntaxin 1A (SYN1A) are required for proper tethering and fusion of DAT to the plasma membrane; (2) Rapid substrate treatment induces DAT exocytosis in a PKC-β-dependent, D2R-independent manner and; (3) AMPH and SYN1A regulate one another’s action on DAT trafficking and function. Taken together DAT trafficking and function are rapidly and specifically regulated by intracellular stimuli including protein kinase activation and GTPase protein regulation as well as extracellular stimuli including the physiological substrate DA and the psychostimulant amphetamine. These data confirm the importance of DAT in maintaining proper dopaminergic neurotransmission and demonstrate that homeostatic mechanisms are in place to rapidly modulate DAT function in response to exogenous stimuli.