Mechanisms of dopamine transporter regulation in normal and disease states

Abstract

The dopamine (DA) transporter (DAT) controls the spatial and temporal dynamics of DA neurotransmission by driving reuptake of extracellular transmitter into presynaptic neurons. Many diseases such as depression, bipolar disorder, Parkinson's disease (PD), and attention deficit hyperactivity disorder (ADHD) are associated with abnormal DA levels, implicating DAT as a factor in their etiology. Medications used to treat these disorders and many addictive drugs target DAT and enhance dopaminergic signaling by suppressing transmitter reuptake. We now understand that the transport and binding properties of DAT are regulated by complex and overlapping mechanisms that provide neurons with the ability to modulate DA clearance in response to physiological demands. These processes are controlled by endogenous signaling pathways and affected by exogenous transporter ligands, demonstrating their importance for normal neurotransmission, drug abuse, and disease treatments. Increasing evidence supports the disruption of these mechanisms in DA disorders, implicating dysregulation of transport in disease etiologies and suggesting these processes as potential points for therapeutic manipulation of DA availability.

Keywords: Parkinson's disease; amphetamine; attention deficit hyperactivity disorder; bipolar disorder; cocaine; drug addiction.

Figure 1. Regulatory elements of rat dopamine transporter N- and C-terminal domains

A 3D model of rat DAT based on the A. aeolicus LeuT transporter was generated using PyMol (Schrödinger, LLC), with TM helices shown as barrels and light shading indicating semitransparent Connolly surfaces. The structure was positioned in a membrane bilayer with schematic depictions of N- and C-terminal tails extending into the cytoplasm. Posttranslational modifications shown are Ser7, Ser13, and Thr53 phosphorylation (blue, P), Lys19 and Lys35 ubiquitylation (light green, Ub), and Cys580 palmitoylation (red, Pal). Motifs and sequences indicated are intracellular gate residue Arg60 (R, purple), putative Src homology domain epitope (mauve, SH3), PKC endocytosis motif (blue, FREK), and domains for interactions with Syntaxin 1A (Syn1A, yellow), D2 DA receptor (D2R, green) Ras-like GTPase Rin 1 (Rin, blue), Calcium-Calmodulin-Dependent Protein Kinase (CaMK, green), and α-synuclein (α-Syn, orange) and Parkin (Park, dark blue-lavender). Flotillin 1 (Flot 1, olive green) is shown with palmitic acid modification (red line) but without a known DAT interaction site.

Figure 2. Selected coding variants and potential CRAC motifs in DAT

(a) Coding variants known to alter DAT function (numbered yellow circles) and helical topological 2D architecture of DAT depicting essential cholesterol interacting residues in putative CRAC motifs (black circles with white letters). (b) Sequence alignment of human DAT, NET, and SERT showing homology within putative CRAC motifs. Residues that are key components of the motifs are shown in red; the numbers above the sequence correspond to hDAT.