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Competing G protein-coupled receptor kinases balance G protein and ?-arrestin signaling.

ABSTRACT: Seven-transmembrane receptors (7TMRs) are involved in nearly all aspects of chemical communications and represent major drug targets. 7TMRs transmit their signals not only via heterotrimeric G proteins but also through ?-arrestins, whose recruitment to the activated receptor is regulated by G protein-coupled receptor kinases (GRKs). In this paper, we combined experimental approaches with computational modeling to decipher the molecular mechanisms as well as the hidden dynamics governing extracellular signal-regulated kinase (ERK) activation by the angiotensin II type 1A receptor (AT(1A)R) in human embryonic kidney (HEK)293 cells. We built an abstracted ordinary differential equations (ODE)-based model that captured the available knowledge and experimental data. We inferred the unknown parameters by simultaneously fitting experimental data generated in both control and perturbed conditions. We demonstrate that, in addition to its well-established function in the desensitization of G-protein activation, GRK2 exerts a strong negative effect on ?-arrestin-dependent signaling through its competition with GRK5 and 6 for receptor phosphorylation. Importantly, we experimentally confirmed the validity of this novel GRK2-dependent mechanism in both primary vascular smooth muscle cells naturally expressing the AT(1A)R, and HEK293 cells expressing other 7TMRs.

SUBMITTER: Heitzler D

PROVIDER: S-EPMC3397412 | biostudies-literature | 2012 Jun

REPOSITORIES: biostudies-literature

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Competing G protein-coupled receptor kinases balance G protein and β-arrestin signaling.

Heitzler Domitille D Durand Guillaume G Gallay Nathalie N Rizk Aurélien A Ahn Seungkirl S Kim Jihee J Violin Jonathan D JD Dupuy Laurence L Gauthier Christophe C Piketty Vincent V Crépieux Pascale P Poupon Anne A Clément Frédérique F Fages François F Lefkowitz Robert J RJ Reiter Eric E

Molecular systems biology 20120626

Seven-transmembrane receptors (7TMRs) are involved in nearly all aspects of chemical communications and represent major drug targets. 7TMRs transmit their signals not only via heterotrimeric G proteins but also through β-arrestins, whose recruitment to the activated receptor is regulated by G protein-coupled receptor kinases (GRKs). In this paper, we combined experimental approaches with computational modeling to decipher the molecular mechanisms as well as the hidden dynamics governing extracel ...[more]

PMID: 22735336

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Project description:Activated Gq protein-coupled receptors (GqPCRs) can be desensitized by phosphorylation and β-arrestin binding. The kinetics and individual contributions of these two mechanisms to receptor desensitization have not been fully distinguished. Here, we describe the shut off of protease-activated receptor 2 (PAR2). PAR2 activates Gq and phospholipase C (PLC) to hydrolyze phosphatidylinositol 4,5-bisphosphate (PIP2) into diacylglycerol and inositol trisphosphate (IP3). We used fluorescent protein-tagged optical probes to monitor several consequences of PAR2 signaling, including PIP2 depletion and β-arrestin translocation in real time. During continuous activation of PAR2, PIP2 was depleted transiently and then restored within a few minutes, indicating fast receptor activation followed by desensitization. Knockdown of β-arrestin 1 and 2 using siRNA diminished the desensitization, slowing PIP2 restoration significantly and even adding a delayed secondary phase of further PIP2 depletion. These effects of β-arrestin knockdown on PIP2 recovery were prevented when serine/threonine phosphatases that dephosphorylate GPCRs were inhibited. Thus, PAR2 may continuously regain its activity via dephosphorylation when there is insufficient β-arrestin to trap phosphorylated receptors. Similarly, blockers of protein kinase C (PKC) and G protein-coupled receptor kinase potentiated the PIP2 depletion. In contrast, an activator of PKC inhibited receptor activation, presumably by augmenting phosphorylation of PAR2. Our interpretations were strengthened by modeling. Simulations supported the conclusions that phosphorylation of PAR2 by protein kinases initiates receptor desensitization and that recruited β-arrestin traps the phosphorylated state of the receptor, protecting it from phosphatases. Speculative thinking suggested a sequestration of phosphatidylinositol 4-phosphate 5 kinase (PIP5K) to the plasma membrane by β-arrestin to explain why knockdown of β-arrestin led to secondary depletion of PIP2. Indeed, artificial recruitment of PIP5K removed the secondary loss of PIP2 completely. Altogether, our experimental and theoretical approaches demonstrate roles and dynamics of the protein kinases, β-arrestin, and PIP5K in the desensitization of PAR2.

Project description:G-protein-coupled receptors (GPCRs) are critically regulated by ?-arrestins, which not only desensitize G-protein signalling but also initiate a G-protein-independent wave of signalling. A recent surge of structural data on a number of GPCRs, including the ?2 adrenergic receptor (?2AR)-G-protein complex, has provided novel insights into the structural basis of receptor activation. However, complementary information has been lacking on the recruitment of ?-arrestins to activated GPCRs, primarily owing to challenges in obtaining stable receptor-?-arrestin complexes for structural studies. Here we devised a strategy for forming and purifying a functional human ?2AR-?-arrestin-1 complex that allowed us to visualize its architecture by single-particle negative-stain electron microscopy and to characterize the interactions between ?2AR and ?-arrestin 1 using hydrogen-deuterium exchange mass spectrometry (HDX-MS) and chemical crosslinking. Electron microscopy two-dimensional averages and three-dimensional reconstructions reveal bimodal binding of ?-arrestin 1 to the ?2AR, involving two separate sets of interactions, one with the phosphorylated carboxy terminus of the receptor and the other with its seven-transmembrane core. Areas of reduced HDX together with identification of crosslinked residues suggest engagement of the finger loop of ?-arrestin 1 with the seven-transmembrane core of the receptor. In contrast, focal areas of raised HDX levels indicate regions of increased dynamics in both the N and C domains of ?-arrestin 1 when coupled to the ?2AR. A molecular model of the ?2AR-?-arrestin signalling complex was made by docking activated ?-arrestin 1 and ?2AR crystal structures into the electron microscopy map densities with constraints provided by HDX-MS and crosslinking, allowing us to obtain valuable insights into the overall architecture of a receptor-arrestin complex. The dynamic and structural information presented here provides a framework for better understanding the basis of GPCR regulation by arrestins.

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Competing G protein-coupled receptor kinases balance G protein and ?-arrestin signaling.

Publications

Competing G protein-coupled receptor kinases balance G protein and β-arrestin signaling.

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