Receptor selectivity of the cloned opossum G protein-coupled receptor kinase 2 (GRK2) in intact opossum kidney cells: Role in desensitization of endogenous alpha(2C)-adrenergic but not serotonin 1B receptors
Pmc. Lembo et al., Receptor selectivity of the cloned opossum G protein-coupled receptor kinase 2 (GRK2) in intact opossum kidney cells: Role in desensitization of endogenous alpha(2C)-adrenergic but not serotonin 1B receptors, MOL ENDOCR, 13(1), 1999, pp. 138-147
To characterize the specificity of endogenously expressed G protein-coupled
receptor kinases (GRKs) for endogenous Gi-coupled alpha(2C)-adrenergic and
serotonin 1B (5-HT1B) receptors in the opossum kidney (OK) cell line, we h
ave isolated a 3.073-kb OK-GRK2 clone encoding a 689-amino acid protein tha
t shares 94.2% amino acid identity with rat GRK2. Northern blot analysis re
vealed the presence of GRK2 mRNA transcripts of 5.0 and 3.0 kb in OK cells.
In intact OK cells, preincubation (45 min) with agonist (5-HT or UK 14304,
1 mu M) reduced the maximal inhibition of forskolin-induced cAMP accumulat
ion mediated by endogenous 5-HT1B and alpha(2C)-adrenergic receptors by 12
+/- 2% or 17 +/- 4%, respectively. In transfected OK cells overexpressing O
K-GRK2, agonist-induced desensitization of the alpha(2C)-adrenergic recepto
r, but not the 5-HT1B receptor, was enhanced by 2- to 4-fold. Conversely, i
n cells overexpressing the kinase-inactive mutant OK-GRK2-K220R, alpha(2C)-
adrenergic receptor desensitization was selectively abolished, whereas dese
nsitization of the 5-HT1B receptor was slightly enhanced. Similarly, deplet
ion of GRK-2 protein by stable transfection of full-length antisense OK-GRK
2. cDNA blocked the desensitization of alpha(2C)-adrenergic receptors but n
ot of 5-HT1B receptors. These results represent the first evidence of the c
oexistence of GRK2-dependent (for alpha(2C) receptors) and GRK2-independent
(for 5-HT1B receptors) mechanisms of desensitization in intact cells and d
emonstrate the selectivity of GRK2 for distinct Gi-coupled receptors.