Differential subcellular localization of two dopamine D₂ receptor isoforms in transfected NG108-15 cells

The dopamine D₂ receptor (D2R) is target for antipsychotic drugs and associated with several neuropsychiatric disorders. D2R has a long third cytoplasmic loop and a short carboxylterminal cytoplasmic tail. It exists as two alternatively spliced isoforms, termed D2LR and D2SR, which differ in the presence and absence, respectively, of a 29 amino acid insert in the third cytoplasmic loop. To evaluate the differential roles of the two D2R isoforms, we transfected both isoforms into NG108-15 cells and observed their subcellular localization by a confocal laser scanning light microscope. D2SR was predominantly localized at the plasma membrane, whereas D2LR was mostly retained in the perinuclear region around the Golgi apparatus. Using a yeast two hybrid system with a mouse brain cDNA library and coimmunoprecipitation assay, we found that heart-type fatty acid binding protein (H-FABP) interacts with D2LR but not with D2SR. H-FABP is a cytosolic protein involved in binding and transport of fatty acids. Over-expressed H-FABP and endogenous H-FABP were colocalized with the intracellular D2LR in NG108-15 cells. Furthermore, in the rat striatum, H-FABP was detected in the D2R-expressing neurons. From these results, H-FABP is associated with D2LR, and may thereby modulate the subcellular localization and function of D2LR.