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Characterization of direct ERK‐mediated activation of the Dopamine Transporter

Primarily localized in the substantia nigra and tegmental areas of animal brain tissue, the neurotransmitter dopamine (DA) mediates numerous CNS functions including motor activity, emotion, and reward. Synaptic and extracellular DA concentrations are controlled by the dopamine transporter (DAT), which is activated or down‐regulated in response to both allosteric and feedback mechanisms including protein kinase pathways and dopamine receptor feedback signals from adjacent neuronal membrane surfaces. Many mechanisms that play a role in DAT regulation have been characterized, such as PKC‐dependent DAT trafficking. However, physiological DAT activity is likely to be mediated by other Ser/Thr‐kinases, such as ERK. For this study, polyclonal antibodies against ERK phosphorylated rDAT N‐terminus were raised against the N‐terminus tail of recombinant DAT and phospho‐DAT peptides. To examine the effect of ERK on DAT activation, ERK phosphorylation was consistently reduced in rDAT‐LLC‐PK cells through the application of specifically defined culture conditions including optimum confluency, media, and culture serum starvation length. To verify phospho‐ERK levels, control and stimulated rDAT‐LLC‐PK lysate was prepared and subjected to immunoanalysis by p‐rDAT antibodies. Follow‐on studies investigated the effects of expressing dominant negative MEK on DAT activity and ERK phosphorylation of rDAT. These studies indicate the involvement of ERK in DA metabolism and suggest a novel role for ERK in CNS functions.