Regulation of dopamine D1 receptor trafficking and desensitization by oligomerization with glutamate N-methyl-D-aspartate receptors

Activation of dopamine D-1 receptors is critical for the generation of glutamate-induced long-term potentiation at corticostriatal synapses. In this study, we report that, in striatal neurons, D-1 receptors are co-localized with N-methyl-D-aspartate ( NMDA) receptors in the postsynaptic density and that they co-immunoprecipitate with NMDA receptor subunits from postsynaptic density preparations. Using modified bioluminescence resonance energy transfer, we demonstrate that D-1 and NMDA receptor clustering reflects the existence of direct interactions. The tagged D-1 receptor and NR1 subunit cotransfected in COS-7 cells generated a significant bioluminescence resonance energy transfer signal that was insensitive to agonist stimulation and that did not change in the presence of the NR2B subunit, suggesting that the D-1 receptor constitutively and selectively interacts with the NR1 subunit of the NMDA channel. Oligomerization with the NR1 subunit substantially modified D-1 receptor trafficking. In individually transfected HEK293 cells, NR1 was localized in the endoplasmic reticulum, whereas the D-1 receptor was targeted to the plasma membrane. In cotransfected cells, both the D-1 receptor and NR1 subunit were retained in cytoplasmic compartments. In the presence of the NR2B subunit, the NR1-D-1 receptor complex was translocated to the plasma membrane. These data suggest that D-1 and NMDA receptors are assembled within intracellular compartments as constitutive heteromeric complexes that are delivered to functional sites. Coexpression with NR1 and NR2B subunits also abolished agonist-induced D-1 receptor cytoplasmic sequestration, indicating that oligomerization with the NMDA receptor could represent a novel regulatory mechanism modulating D-1 receptor desensitization and cellular trafficking.