The PDZ-binding domain is essential for the dendritic targeting of 5-HT_2A serotonin receptors in cortical pyramidal neurons in vitro

The 5-HT_2A serotonin receptor represents an important molecular target for atypical antipsychotic drugs and for most hallucinogens. In the mammalian cerebral cortex, 5-HT_2A receptors are enriched in pyramidal neurons, within which 5-HT_2A receptors are preferentially sorted to the apical dendrites. In primary cortical cultures, 5-HT_2A receptors are sorted to dendrites and not found in the axons of pyramidal neurons. We identified a sorting motif that mediates the preferential targeting of 5-HT_2A receptors to the dendrites of cortical pyramidal neurons in vitro. We constructed green fluorescent protein-tagged 5-HT_2A receptors wherein potential sorting motifs were disrupted, and subsequently employed either the Semliki Forest virus or calcium phosphate for the transient expression of recombinant 5-HT_2A receptors in cultured cortical pyramidal neurons. Using dual-labeling immunofluorescent confocal microscopy, we quantified the axonal and dendritic sorting patterns of endogenous and recombinant 5-HT_2A receptors. We discovered that disruption of the PDZ-binding domain of the 5-HT_2A receptor greatly attenuates the dendritic targeting of 5-HT_2A receptors without inappropriately sorting 5-HT_2A receptors to axons. The PDZ-binding domain is therefore a necessary signal for the preferential targeting of the 5-HT _2A receptor to the dendritic compartment of cultured cortical pyramidal neurons, the first such role ascribed to this protein-protein interaction motif of any G protein-coupled receptor.