Differential Contribution of G‐protein Coupled Receptor Kinase 2 and 3 in Regulating Structurally Related Human Dopamine D1 and D5 Receptors

Abstract

Dopamine (DA) D1‐like receptors (D1R and D5R) are seven‐transmembrane proteins regulating important brain and peripheral functions. Impairment in D1‐like responsiveness may play a crucial role in the phenotypic expression of several brain disorders such as schizophrenia and Parkinson's disease. Agonist‐induced receptor phosphorylation mediated by G‐protein coupled receptor kinase isoforms (GRK1–GRK6) curtails G‐protein signaling and target receptors for internalization. Here we investigated the role of GRK2 and GRK3 in regulating D1R and D5R desensitization in a subtype‐specific manner. Human embryonic kidney 293 cells expressing the D1R or D5R alone or with either GRK2 or GRK3 were analyzed for DA‐mediated receptor activation using whole cell cAMP assays. We demonstrate that GRK2 shows little effect in promoting desensitization of D1R and D5R, whereas GRK3 promotes a significantly more robust desensitization of D1R than D5R as assessed by the extent of DA‐induced maximal stimulation of adenylyl cyclase. However, expression of GRK2 and GRK3 leads to a more reduced DA potency for D5R than for D1R. These findings point to the existence of marked differences in the ability of GRKs to promote D1R and D5R desensitization. Our studies thus provide insight into potential distinct GRK2 and GRK3 molecular mechanisms through which D1‐like receptor signaling is regulated. Supported by a CIHR grant (MOP‐81341) to MT.