Abstract 484: Role of GRK4 Variants in Renal Dopamine D3 Receptor Expression and Function
In the kidney, dopamine promotes natriuresis by inhibiting both proximal and distal tubule NaCl reabsorption through its action on renal dopamine receptors, namely dopamine D3 receptor (DRD3). DRD3 promotes natriuresis, especially during salt-replete states. The involvement of DRD3 dysfunction in the etiology of hypertension has been demonstrated through pharmacologic and genetic interventions. While its gene locus at 3q13.3 has been linked to hypertension, the signal transduction pathway of DRD3 has not been fully ascertained. The physiological effects of the GRK4 sequence variants on DRD3 function in vitro remain to be determined, therefore, the present study aimed to elucidate whether GRK4 sequence variants (142V and 486V) promote DRD3 hyper-phosphorylation that results in receptor dysfunction. For this purpose, Chinese hamster ovary cells heterologously expressing GRK4γ variants (A142V and A486V) were co-transfected with human DRD3. Stimulation with the highly selective D3R agonist PD128907 resulted in an increase in receptor phosphorylation in CHO cells expressing GRK4-A142 and GRK4γ-A486V variants. PD128907 treatment increased the phosphorylation of p44/42 MAP kinases and their downstream target p90RSK n both GRK4γ variants and wild type. Contrasting, S6 ribosomal protein showed a decrease in phosphorylation upon D3R activation. The abundance of active-Gαo was decreased in wild type and GRK4γ-A486V after stimulation with PD128907, but not in CHO cells expressing GRK4-A142. In conclusion, these results indicate that these GRK4 variants phosphorylate and possible desensitize DRD3, suggesting an impairment of its function. Supported by grant PIC/IC/83204/2007.
- © 2012 by American Heart Association, Inc.