The human dopamine transporter (hDAT) was transiently expressed in N2A neuroblastoma cells. Confocal fluorescence microscopy revealed efficient surface targeting of the transporter in undifferentiated cells as well as in differentiated cells. In the differentiated cells the hDAT displayed a characteristic cluster-like expression pattern in the neuronal processes. This was not dependent of PDZ domain interactions since C-terminal mutations disrupting binding of PDZ-domain containing scaffolding proteins such as PICK1 did not alter the expression pattern of the transporter. By employment of a surface strip-biotinylation assay we obtained evidence that the hDAT does not reside statically in the plasma membrane of the N2A cells but undergoes rapid constitutive internalization. Using the strip-biotinylation assay we could also show increased intracellular accumulation of the hDAT both in the presence of amphetamine and upon activation of protein kinase C (PKC) with phorbol esters. Inhibition of lysosomal degradation by chloroquine increased the amount of intracellularly accumulated transporter suggesting that the enhanced intracellular accumulation of the hDAT observed both in response to amphetamine and to PKC activation targets the transporter for degradation. Because PDZ domain interactions appeared to be of less importance for transporter targeting we are currently exploring the putative role of such interactions for regulating constitutive internalization, recycling and lysosomal degradation using N2A cells as a model system. Furthermore, we are investigating the role of N-terminal phosphorylation of the hDAT for the same processes, since this phosphorylation surprisingly is not critical for the enhanced intracellular accumulation of the hDAT observed in response to PKC activation.
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Society for Neuroscience 33th annual meeting, 2003