Internalization Determinants of the Parathyroid Hormone Receptor Differentially Regulate β-Arrestin/Receptor Association

Jean-Pierre Vilardaga, Cornelius Krasel, Stéphanie Chauvin, Tom Bambino, Martin J. Lohse, Robert A. Nissenson
2001 Journal of Biological Chemistry  
␤-Arrestins have been implicated in regulating internalization of the parathyroid hormone receptor (PTHR), but the structural features in the receptor required for this effect are unknown. In the present study performed in HEK-293 cells, we demonstrated that different topological domains of PTHR are implicated in agonist-dependent receptor internalization; truncation of the cytoplasmic tail (PTHR-TR), selective mutations of the cytoplasmic tail to remove the sites of parathyroid hormone
more » ... oid hormone (PTH)-stimulated phosphorylation (PTHR-PD), and mutations in the third transmembrane helix (N289A) or in the third cytoplasmic loop (K382A) resulted in a 30 -60% reduction in 125 I-PTH-related protein internalization. To better define the role of these internalization determinants, we have tested the ability of these mutant PTHRs to associate with ␤-arrestins by using three different methodological approaches: 1) ability of overexpression of ␤-arrestins to restore the internalization of 125 I-PTH-related protein for the mutant PTHRs; 2) visualization of PTH-mediated trafficking of ␤-arrestin1 and -2 fused to the green fluorescent protein with receptors by confocal microscopy; 3) quantification of ␤-arrestin1-green fluorescent protein translocation by Western blot. Our data reveal that the receptor' cytoplasmic tail contains determinants of ␤-arrestin interaction that are distinct from the phosphorylation sites and are sufficient for transient association of ␤-ar-restin2, but stable association requires receptor phosphorylation. Determinants in the receptor's core (Asn-289 and Lys-382) appear to regulate internalization of the receptor/␤-arrestin complex toward early endocytic endosomes during the initial step of endocytosis. Agonist binding to most G protein-coupled receptors (GPCRs) 1 is quickly followed by the internalization of the agonist-receptor complex into endocytic vesicles. The model developed from studies of the ␤ 2 -adrenergic receptor views internalization as a process facilitated by binding of ␤-arrestin proteins to agonist-activated receptors after phosphorylation of the receptors by G protein-coupled receptor kinases (GRKs) (1, 2). Phosphorylation of GPCRs by GRKs is a prerequisite for the mobilization of cytosolic ␤-arrestins. Binding of ␤-arrestins to GRK-phosphorylated receptors results in the physical uncoupling of receptors from their cognate G proteins and terminates agonist-mediated signaling (3, 4). It was shown recently that ␤-arrestins bind clathrin, a major component of the clathrinbased endocytic machinery, with high affinity and serve as an adaptor that targets activated and phosphorylated receptors to clathrin-coated pits (5-7). In the case of the ␤ 2 -adrenergic receptor, receptor internalization is the consequence of the formation of a complex between ␤-arrestin2, the clathrin adaptor protein AP2, clathrin, and the activated receptor (8). Internalization has at least two outcomes: directing the receptor to a compartment where the phosphates are removed, allowing resensitization, and movement of the receptor to lysosomes for degradation (2, 9, 10) . Little is known about the structural determinants of GPCRs involved in receptor internalization and/or in arrestin interaction. The current model for the understanding of the arrestinreceptor interaction mechanism is based on various studies of visual arrestin interaction with rhodopsin (11-16). Visual arrestin binding with rhodopsin requires GRK-1 phosphorylated residues, and the contact of phosphorylated residues with a cationic region of arrestin switches it into an active conformation, enabling interaction with an exposed binding site on activated rhodopsin. The receptor for parathyroid hormone (PTH) and PTH-related protein (PTHrP) is involved in the regulation of calcium homeostasis and in bone remodeling (17). Agonist occupancy of the PTH/PTHrP receptor (PTHR) leads to activation of adenylyl cyclase (via G s ), and phosphatidylinositol-specific phospholipase C ␤ (via G q ). PTH-induced activation of the PTHR results in the internalization of the PTH-receptor complex via the clathrin-coated pit pathway and involves ␤-arrestin2 (18, 19) . Recently, we have demonstrated that neither the internalization nor the mobilization of ␤-arrestins (i.e. ␤-arrestin1 and ␤-arrestin2) to PTHR required the receptor activation isoform that is necessary for activation of both G s and G q proteins (i.e.
doi:10.1074/jbc.m110433200 pmid:11726668 fatcat:ciz4jaysvfhbvocrnu5ueqyiuu