Activity-dependent regulation of the dopamine transporter is mediated by Cam Kinase II signaling

Abstract

Dopamine signaling in the brain governs a variety of functions such as locomotor activity, reward, attention and working memory. The dopamine transporter (DAT) plays a crucial role in the clearance of extracellular dopamine and thus helps terminate dopamine neurotransmission. DAT is also the target for psychostimulant drugs of abuse and therapeutic agents. Changes in DAT expression occur in neuropsychiatric disorders such as attention deficit hyperactivity disorder (ADHD) and chro_nic psychostimulant use, and variability in DAT abundance is associated with differences in working memory. However, mechanisms regulating DAT expression are poorly understood. We tested the hypothesis that neuronal activity is one of the non-genetic determinants of DAT abundance. Chronic perturbations in neuronal firing, caused by pharmacological agents, significantly altered DAT expression and function in primary cultures of mesencephalic neurons. Pharmacological experiments showed that calcium entry through L-type voltage-gated calcium channels and calcium/calmodulindependent protein kinase II (CaMKII) activity played a role in activity-dependent changes in DAT expression. In order to further evaluate the role of CaMKII in DAT regulation, the effect of sustained depolarization, a stimulus often used to study activity-dependent changes in gene expression, on DAT expression was tested. Surprisingly, chronic KCl-induced depolarization decreased DAT expression and function. Measurement of CaMKII activity in dopam·ine neurons showed that chronic depolarization led to a decrease in CaMKI I activity, even in the presence of elevated intracellular calcium, due to activation of the serine/threonine protein phosphatase 2A. Moreover, increasing CaMKII activity in dopamine neurons by introducing a constitutively active CaMKII mutant caused a significant increase in DAT abundance while inhibiting CaMKII activity in dopamine neurons using a dominant-negative CaMKII mutant decreased DAT abundance suggesting that CaMKII activity is both sufficient and required to cause changes in DAT expression in a cell autonomous fashion. Taken together, our data demonstrate that CaMKI I activity can govern DAT expression and may play an important role in dopamine neurotransmission in the brain.