β-arrestin-dependent parathyroid hormone-stimulated extracellular signal-regulated kinase activation and parathyroid hormone type 1 receptor internalization

PTH regulates renal calcium homeostasis by actions on the distal nephron. PTH-induced calcium transport in mouse distal convoluted tubule (DCT) cells requires activation of ERK1/2. ERK activation by beta-adrenergic receptors occurs in a biphasic manner and involves receptor internalization. An early rapid phase is beta-arrestin (beta Ar) independent, whereas prolonged activation is beta Ar dependent. We characterized PTH-stimulated ERK activation and the involvement of receptor internalization and beta Ar dependence. In DCT cells, PTH transiently activated ERK maximally at 5 min and then returned to baseline. beta Ar dependence of PTH receptor (PTH1R)mediated ERK stimulation was assessed using mouse embryonic fibroblasts (MEFs) from beta Ar1-and-2-null mice. In wildtype MEFs, PTH(1-34)-stimulated ERK activation peaked after 5 min, was 50% maximal after 15 min, and then recovered to 80% of maximal stimulation by 30 min. In MEFs null for beta Ar1 and-2, PTH-stimulated ERK activation peaked by 5 min and returned to baseline. The effect was identical in beta Ar2-null MEFs. In beta Ar1-null MEFs, ERK exhibited delayed activation and remained elevated. PTH-stimulated ERK activation and receptor endocytosis were not inhibited by the clathrin-binding domain of beta Ar1 [Ar(319-418)]. Coexpression of the sodium proton exchanger regulatory factor 1 (NHERF1) with Ar(319 418) blocked PTH1R internalization. We conclude that PTH-stimulated ERK activation in DCT cells proceeds with a rapid but transient phase that may involve beta Ar1. Furthermore, the beta Ar-dependent late phase of ERK activation by PTH requires the participation of beta Ar2 and PTH1R internalization.