Dopamine-induced arrestin recruitment and desensitization of the dopamine D4 receptor is regulated by G protein-coupled receptor kinase-2
The dopamine D 4 receptor (D 4 R) is expressed in the retina, prefrontal cortex, and autonomic nervous system and has been implicated in attention deficit hyperactivity disorder (ADHD), substance use disorders, and erectile dysfunction. D 4 R has also been investigated as a target for antipsychotics due to its high affinity for clozapine. As opposed to the closely related dopamine D 2 receptor (D 2 R), dopamine-induced arrestin recruitment and desensitization at the D 4 R have not been studied in detail. Indeed, some earlier investigations could not detect arrestin recruitment and desensitization of this receptor upon its activation by agonist. Here, we used a novel nanoluciferase complementation assay to study dopamine-induced recruitment of β-arrestin2 (βarr2; also known as arrestin3) and G protein-coupled receptor kinase-2 (GRK2) to the D 4 R in HEK293T cells. We also studied desensitization of D 4 R-evoked G protein-coupled inward rectifier potassium (GIRK; also known as Kir3) current responses in Xenopus oocytes. Furthermore, the effect of coexpression of GRK2 on βarr2 recruitment and GIRK response desensitization was examined. The results suggest that coexpression of GRK2 enhanced the potency of dopamine to induce βarr2 recruitment to the D 4 R and accelerated the rate of desensitization of D 4 R-evoked GIRK responses. The present study reveals new details about the regulation of arrestin recruitment to the D 4 R and thus increases our understanding of the signaling and desensitization of this receptor.