GRKs as Modulators of Neurotransmitter Receptors (original) (raw)
Related papers
Desensitization of G Protein–Coupled Receptors and Neuronal Functions
Annual Review of Neuroscience, 2004
I Abstract G protein-coupled receptors (GPCRs) have proven to be the most highly favorable class of drug targets in modern pharmacology. Over 90% of nonsensory GPCRs are expressed in the brain, where they play important roles in numerous neuronal functions. GPCRs can be desensitized following activation by agonists by becoming phosphorylated by members of the family of G protein-coupled receptor kinases (GRKs). Phosphorylated receptors are then bound by arrestins, which prevent further stimulation of G proteins and downstream signaling pathways. Discussed in this review are recent progress in understanding basics of GPCR desensitization, novel functional roles, patterns of brain expression, and receptor specificity of GRKs and βarrestins in major brain functions. In particular, screening of genetically modified mice lacking individual GRKs or βarrestins for alterations in behavioral and biochemical responses to cocaine and morphine has revealed a functional specificity in dopamine and µ-opioid receptor regulation of locomotion and analgesia. An important and specific role of GRKs and βarrestins in regulating physiological responsiveness to psychostimulants and morphine suggests potential involvement of these molecules in certain brain disorders, such as addiction, Parkinson's disease, mood disorders, and schizophrenia. Furthermore, the utility of a pharmacological strategy aimed at targeting this GPCR desensitization machinery to regulate brain functions can be envisaged.
G protein-coupled receptor kinases of the GRK4 subfamily phosphorylate inactive GPCRs
The Journal of biological chemistry, 2015
G protein-coupled receptor (GPCR) kinases (GRKs) play key role in homologous desensitization of GPCRs. It is widely assumed that most GRKs selectively phosphorylate only active GPCRs. Here we show that although this seems to be the case for GRK2/3 subfamily, GRK5/6 effectively phosphorylate inactive forms of several GPCRs, including β2-adrenergic and M2 muscarinic receptors, which are commonly used as representative model GPCRs. Agonist-independent GPCR phosphorylation cannot be explained by constitutive activity of the receptor or membrane association of the GRK, suggesting that it is an inherent ability of GRK5/6. Importantly, phosphorylation of inactive β2-adrenergic receptor enhanced its interactions with arrestins. Arrestin-3 was able to discriminate between phosphorylation of the same receptor by GRK2 and GRK5, demonstrating preference for the latter. Arrestin recruitment to inactive phosphorylated GPCRs suggests that not only agonist activation, but also the complement of GRK...
Biomolecules
The D2 dopamine receptor (D2R) signals through both G proteins and β-arrestins to regulate important physiological processes, such as movement, reward circuitry, emotion, and cognition. β-arrestins are believed to interact with G protein-coupled receptors (GPCRs) at the phosphorylated C-terminal tail or intracellular loops. GPCR kinases (GRKs) are the primary drivers of GPCR phosphorylation, and for many receptors, receptor phosphorylation is indispensable for β-arrestin recruitment. However, GRK-mediated receptor phosphorylation is not required for β-arrestin recruitment to the D2R, and the role of GRKs in D2R–β-arrestin interactions remains largely unexplored. In this study, we used GRK knockout cells engineered using CRISPR-Cas9 technology to determine the extent to which β-arrestin recruitment to the D2R is GRK-dependent. Genetic elimination of all GRK expression decreased, but did not eliminate, agonist-stimulated β-arrestin recruitment to the D2R or its subsequent internalizat...
Cell Reports, 2013
G-protein-coupled receptors (GPCRs) are typically present in a basal, inactive state but, when bound to an agonist, activate downstream signaling cascades. In studying arrestin regulation of opioid receptors in dorsal root ganglia (DRG) neurons, we find that agonists of delta opioid receptors (dORs) activate cofilin through Rho-associated coiled-coilcontaining protein kinase (ROCK), LIM domain kinase (LIMK), and b-arrestin 1 (b-arr1) to regulate actin polymerization. This controls receptor function, as assessed by agonist-induced inhibition of voltage-dependent Ca 2+ channels in DRGs. Agonists of opioid-receptor-like receptors (ORL1) similarly influence the function of this receptor through ROCK, LIMK, and b-arr1. Functional evidence of this cascade was demonstrated in vivo, where the behavioral effects of dOR or ORL1 agonists were enhanced in the absence of b-arr1 or prevented by inhibiting ROCK. This pathway allows dOR and ORL1 agonists to rapidly regulate receptor function.
G protein-coupled receptor kinases as regulators of dopamine receptor functions
Pharmacological Research, 2016
Actions of the neurotransmitter dopamine in the brain are mediated by dopamine receptors that belong to the superfamily of G protein-coupled receptors (GPCRs). Mammals have five dopamine receptor subtypes, D1 through D5. D1 and D5 couple to G s/olf and activate adenylyl cyclase, whereas D2, D3, and D4 couple to G i/o and inhibit it. Most GPCRs upon activation by an agonist are phosphorylated by GPCR kinases (GRKs). The GRK phosphorylation makes receptors highaffinity binding partners for arrestin proteins. Arrestin binding to active phosphorylated receptors stops further G protein activation and promotes receptor internalization, recycling or degradation, thereby regulating their signaling and trafficking. Four non-visual GRKs are expressed in striatal neurons. Here we describe known effects of individual GRKs on dopamine receptors in cell culture and in the two in vivo models of dopamine-mediated signaling: behavioral response to psychostimulants and L-DOPA-induced dyskinesia. Dyskinesia, associated with dopamine supersensitivity of striatal neurons, is a debilitating side effect of L-DOPA therapy in Parkinson's disease. In vivo, GRK subtypes show greater receptor specificity than in vitro or in cultured cells. Overexpression, knockdown, and knockout of individual GRKs, particularly GRK2 and GRK6, have differential effects on signaling of dopamine receptor subtypes in the brain. Furthermore, deletion of GRK isoforms in select striatal neuronal types differentially affects psychostimulantinduced behaviors. In addition, anti-dyskinetic effect of GRK3 does not require its kinase activity: it is mediated by the binding of its RGS-like domain to G αq/11 , which suppresses G q/11 signaling. The data demonstrate that the dopamine signaling in defined neuronal types in vivo is regulated by specific and finely orchestrated actions of GRK isoforms.
Frontiers in Pharmacology
The dopamine D4 receptor (D4R) is expressed in the retina, prefrontal cortex, and autonomic nervous system and has been implicated in attention deficit hyperactivity disorder (ADHD), substance use disorders, and erectile dysfunction. D4R has also been investigated as a target for antipsychotics due to its high affinity for clozapine. As opposed to the closely related dopamine D2 receptor (D2R), dopamine-induced arrestin recruitment and desensitization at the D4R have not been studied in detail. Indeed, some earlier investigations could not detect arrestin recruitment and desensitization of this receptor upon its activation by agonist. Here, we used a novel nanoluciferase complementation assay to study dopamine-induced recruitment of β-arrestin2 (βarr2; also known as arrestin3) and G protein-coupled receptor kinase-2 (GRK2) to the D4R in HEK293T cells. We also studied desensitization of D4R-evoked G protein-coupled inward rectifier potassium (GIRK; also known as Kir3) current respons...
Targeting G protein–coupled receptor kinases to G protein–coupled receptors
Current Opinion in Endocrine and Metabolic Research, 2021
G protein-coupled receptors (GPCRs) interact with three protein families following agonist binding: heterotrimeric G proteins, G protein-coupled receptor kinases (GRKs) and arrestins. GRK-mediated phosphorylation of GPCRs promotes arrestin binding to uncouple the receptor from G protein, a process called desensitization, and for many GPCRs, arrestin binding also promotes receptor endocytosis and intracellular signaling. Thus, GRKs play a central role in modulating GPCR signaling and localization. Here we review recent advances in this field which include additional insight into how GRKs target GPCRs and bias signaling, and the development of specific inhibitors to dissect GRK function in model systems.
GPCR Signaling Regulation: The Role of GRKs and Arrestins
Frontiers in Pharmacology
Every animal species expresses hundreds of different G protein-coupled receptors (GPCRs) that respond to a wide variety of external stimuli. GPCRs-driven signaling pathways are involved in pretty much every physiological function and in many pathologies. Therefore, GPCRs are targeted by about a third of clinically used drugs. The signaling of most GPCRs via G proteins is terminated by the phosphorylation of active receptor by specific kinases (GPCR kinases, or GRKs) and subsequent binding of arrestin proteins, that selectively recognize active phosphorylated receptors. In addition, GRKs and arrestins play a role in multiple signaling pathways in the cell, both GPCR-initiated and receptor-independent. Here we focus on the mechanisms of GRK-and arrestin-mediated regulation of GPCR signaling, which includes homologous desensitization and redirection of signaling to additional pathways by bound arrestins.
Journal of Biological Chemistry, 2001
The D 2 and D 3 receptors (D 2 R and D 3 R), which are potential targets for antipsychotic drugs, have a similar structural architecture and signaling pathway. Furthermore, in some brain regions they are expressed in the same cells, suggesting that differences between the two receptors might lie in other properties such as their regulation. In this study we investigated, using COS-7 and HEK-293 cells, the mechanism underlying the intracellular trafficking of the D 2 R and D 3 R. Activation of D 2 R caused G protein-coupled receptor kinase-dependent receptor phosphorylation, a robust translocation of -arrestin to the cell membrane, and profound receptor internalization. The internalization of the D 2 R was dynamin-dependent, suggesting that a clathrin-coated endocytic pathway is involved. In addition, the D 2 R, upon agonist-mediated internalization, localized to intracellular compartments distinct from those utilized by the  2 -adrenergic receptor. However, in the case of the D 3 R, only subtle agonist-mediated receptor phosphorylation, -arrestin translocation to the plasma membrane, and receptor internalization were observed. Interchange of the second and third intracellular loops of the D 2 R and D 3 R reversed their phenotypes, implicating these regions in the regulatory properties of the two receptors. Our studies thus indicate that functional distinctions between the D 2 R and D 3 R may be found in their desensitization and cellular trafficking properties. The differences in their regulatory properties suggest that they have distinct physiological roles in the brain.
G protein–coupled receptor kinases (GRKs) orchestrate biased agonism at the β2-adrenergic receptor
Science Signaling
Biased agonists of G protein-coupled receptors (GPCRs), which selectively activate either G protein-or -arrestinmediated signaling pathways, are of major therapeutic interest because they have the potential to show improved efficacy and specificity as drugs. Efforts to understand the mechanistic basis of this phenomenon have focused on the hypothesis that G proteins and -arrestins preferentially couple to distinct GPCR conformations. However, because GPCR kinase (GRK)-dependent receptor phosphorylation is a critical prerequisite for the recruitment of -arrestins to most GPCRs, GRKs themselves may play an important role in establishing biased signaling. We showed that an alanine mutant of the highly conserved residue tyrosine 219 (Y219A) in transmembrane domain five of the 2-adrenergic receptor ( 2 AR) was incapable of -arrestin recruitment, receptor internalization, and -arrestin-mediated activation of extracellular signal-regulated kinase (ERK), whereas it retained the ability to signal through G protein. We found that the impaired -arrestin recruitment in cells was due to reduced GRKmediated phosphorylation of the 2 AR Y219A C terminus, which was recapitulated in vitro with purified components. Furthermore, in vitro ligation of a synthetically phosphorylated peptide onto the C terminus of 2 AR Y219A rescued both the initial recruitment of -arrestin and its engagement with the intracellular core of the receptor. These data suggest that the Y219A mutation generates a G protein-biased state primarily by conformational selection against GRK coupling, rather than against -arrestin. Together, these findings highlight the importance of GRKs in modulating the biased agonism of GPCRs.