P25a/PPP expression increases plasma membrane presentation of the dopamine transporter and enhances cellular sensitivity to dopamine toxicity

Parkinsons disease is characterized by preferential degeneration of the dopamine-producing neurons of the brain stem substantia nigra. Imbalances between mechanisms governing dopamine transport across the plasma membrane and cellular storage vesicles increase the level of toxic pro-oxidative cytosolic dopamine. The microtubule-stabilizing protein p25a accumulates in dopaminergic neurons in Parkinsons disease. We hypothesized that p25a modulates the subcellular localization of the dopamine transporter via effects on sorting vesicles, and thereby indirectly affects its cellular activity. Here we show that co-expression of the dopamine transporter with p25a in HEK-293-MSR cells increases dopamine uptake via increased plasma membrane presentation of the transporter. No direct interaction between p25a and the dopamine transporter was demonstrated, but they co-fractionated during subcellular fractionation of brain tissue from striatum, and direct binding of p25a peptides to brain vesicles was demonstrated. Truncations of the p25a peptide revealed that the requirement for stimulating dopamine uptake is located in the central core and were similar to those required for vesicle binding. Co-expression of p25a and the dopamine transporter in HEK-293-MSR cells sensitized them to the toxicity of extracellular dopamine. Neuronal expression of p25a thus holds the potential to sensitize the cells toward dopamine and toxins carried by the dopamine transporter.