β-Adrenergic Receptor Kinase-1 Acutely Regulates PTH/PTHrP Receptor Signalling in Human Osteoblastlike Cells

Abstract

To investigate whether G protein-coupled receptor kinases (GRKs) are involved in the regulation of the PTH/PTHrPR, we have established mutant SaOS-2 cells which stably overexpress (> 10–20-fold) a dominant negative form of the β-adrenergic receptor kinase-1 (βARK-1). Acute (≤ 2 h) incubation with hPTH (1–34) induced significantly less (by up to 50%) downregulation of the PTH/PTHrPR in βARK-1 mutant SaOS-2 cells than observed in wild-type cells. Pretreatment of wild-type cells with PTH for 2 h induced homologous cAMP desensitisation to a second challenge with PTH, while the effect was blunted by up to 60% in βARK-1 mutant cells. We conclude that activation of βARK-1 (or a closely related GRK) is a critical component of the acute phase (≤ 2 h) of PTH-induced receptor downregulation and homologous cAMP desensitisation of the PTH/PTHrPR.