scholarly journals GRKs as Modulators of Neurotransmitter Receptors

Cells ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 52
Author(s):  
Eugenia V. Gurevich ◽  
Vsevolod V. Gurevich
Keyword(s):  
G Protein ◽  
General Model ◽  
G Protein Coupled Receptors ◽  
Receptor Internalization ◽  
Neurotransmitter Receptors ◽  
Receptor Subtype ◽  
Receptor Subtypes ◽  
Receptor Kinase ◽  
G Protein Coupled ◽  
Homologous Desensitization

Many receptors for neurotransmitters, such as dopamine, norepinephrine, acetylcholine, and neuropeptides, belong to the superfamily of G protein-coupled receptors (GPCRs). A general model posits that GPCRs undergo two-step homologous desensitization: the active receptor is phosphorylated by kinases of the G protein-coupled receptor kinase (GRK) family, whereupon arrestin proteins specifically bind active phosphorylated receptors, shutting down G protein-mediated signaling, facilitating receptor internalization, and initiating distinct signaling pathways via arrestin-based scaffolding. Here, we review the mechanisms of GRK-dependent regulation of neurotransmitter receptors, focusing on the diverse modes of GRK-mediated phosphorylation of receptor subtypes. The immediate signaling consequences of GRK-mediated receptor phosphorylation, such as arrestin recruitment, desensitization, and internalization/resensitization, are equally diverse, depending not only on the receptor subtype but also on phosphorylation by GRKs of select receptor residues. We discuss the signaling outcome as well as the biological and behavioral consequences of the GRK-dependent phosphorylation of neurotransmitter receptors where known.

CCK receptor phosphorylation exposes regulatory domains affecting phosphorylation and receptor trafficking

2000 ◽  
Vol 279 (6) ◽  
pp. C1986-C1992 ◽  
Author(s):  
Rammohan V. Rao ◽  
Eileen L. Holicky ◽  
Susan M. Kuntz ◽  
Laurence J. Miller
Keyword(s):  
G Protein ◽  
Chinese Hamster ◽  
G Protein Coupled Receptors ◽  
Receptor Internalization ◽  
Ovary Cell ◽  
Guanine Nucleotide Binding Protein ◽  
Receptor Phosphorylation ◽  
Regulatory Domains ◽  
Ovary Cell Line ◽  
G Protein Coupled

Agonist-stimulated phosphorylation of guanine nucleotide-binding protein (G protein)-coupled receptors has been recognized as an important mechanism for desensitization by interfering with coupling of the activated receptor with its G protein. We recently described a mutant of the CCK receptor that modified two of five key sites of phosphorylation (S260,264A) and eliminated agonist-stimulated receptor phosphorylation, despite normal ligand binding and signaling (20). As expected, this nonphosphorylated mutant had impaired rapid desensitization but was ultimately able to be desensitized by normal receptor internalization. Here we demonstrate that this mutant receptor is also defective in resensitization, with abnormal recycling to the cell surface. To explore this, another receptor mutant was prepared, replacing the same serines with aspartates to mimic the charge of serine-phosphate (S260,264D). This mutant was expressed in a Chinese hamster ovary cell line and shown to bind CCK normally. It had accelerated kinetics of signaling and desensitization and was phosphorylated in response to agonist occupation, with all other normal sites of phosphorylation modified. It was internalized like wild-type receptors and was resensitized and trafficked normally. This provides evidence for an additional important function for phosphorylation of G protein-coupled receptors. Phosphorylation may induce a conformational change in the receptor to expose other potential sites of phosphorylation and to expose domains involved in the targeting and trafficking of endosomes. The hierarchical phosphorylation of these sites may play a key role in receptor regulation.

scholarly journals Mammalian Type I Gonadotropin-Releasing Hormone Receptors Undergo Slow, Constitutive, Agonist-Independent Internalization

Endocrinology ◽  
2007 ◽  
Vol 149 (3) ◽  
pp. 1415-1422 ◽  
Author(s):  
Adam J. Pawson ◽  
Elena Faccenda ◽  
Stuart Maudsley ◽  
Zhi-Liang Lu ◽  
Zvi Naor ◽  
...  
Keyword(s):  
G Protein ◽  
Regulatory Elements ◽  
Gnrh Receptor ◽  
G Protein Coupled Receptors ◽  
Receptor Internalization ◽  
Type I ◽  
Receptor Desensitization ◽  
Gnrh Receptors ◽  
Carboxyl Terminal ◽  
G Protein Coupled

Regulatory elements present in the cytoplasmic carboxyl-terminal tails of G protein-coupled receptors contribute to agonist-dependent receptor desensitization, internalization, and association with accessory proteins such as β-arrestin. The mammalian type I GnRH receptors are unique among the rhodopsin-like G protein-coupled receptors because they lack a cytoplasmic carboxyl-terminal tail. In addition, they do not recruit β-arrestin, nor do they undergo rapid desensitization. By measuring the internalization of labeled GnRH agonists, previous studies have reported that mammalian type I GnRH receptors undergo slow agonist-dependent internalization. In the present study, we have measured the internalization of epitope-tagged GnRH receptors, both in the absence and presence of GnRH stimulation. We demonstrate that mammalian type I GnRH receptors exhibit a low level of constitutive agonist-independent internalization. Stimulation with GnRH agonist did not significantly enhance the level of receptor internalization above the constitutive level. In contrast, the catfish GnRH and rat TRH receptors, which have cytoplasmic carboxyl-terminal tails, displayed similar levels of constitutive agonist-independent internalization but underwent robust agonist-dependent internalization, as did chimeras of the mammalian type I GnRH receptor with the cytoplasmic carboxyl-terminal tails of the catfish GnRH receptor or the rat TRH receptor. When the carboxyl-terminal Tyr325 and Leu328 residues of the mammalian type I GnRH receptor were replaced with alanines, these two mutant receptors underwent significantly impaired internalization, suggesting a function for the Tyr-X-X-Leu sequence in mediating the constitutive agonist-independent internalization of mammalian type I GnRH receptors. These findings provide further support for the underlying notion that the absence of the cytoplasmic carboxyl-terminal tail of the mammalian type I GnRH receptors has been selected for during evolution to prevent rapid receptor desensitization and internalization to allow protracted GnRH signaling in mammals.

scholarly journals Clathrin and GRK2/3 inhibitors block δ-opioid receptor internalization in myenteric neurons and inhibit neuromuscular transmission in the mouse colon

2019 ◽  
Vol 317 (2) ◽  
pp. G79-G89 ◽  
Author(s):  
Jesse J. DiCello ◽  
Pradeep Rajasekhar ◽  
Emily M. Eriksson ◽  
Ayame Saito ◽  
Arisbel B. Gondin ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
G Protein ◽  
Opioid Receptor ◽  
Neuromuscular Transmission ◽  
G Protein Coupled Receptors ◽  
Receptor Internalization ◽  
Enteric Neurons ◽  
Myenteric Neurons ◽  
Gut Function ◽  
G Protein Coupled

Endocytosis is a major mechanism through which cellular signaling by G protein-coupled receptors (GPCRs) is terminated. However, recent studies demonstrate that GPCRs are internalized in an active state and continue to signal from within endosomes, resulting in effects on cellular function that are distinct to those arising at the cell surface. Endocytosis inhibitors are commonly used to define the importance of GPCR internalization for physiological and pathophysiological processes. Here, we provide the first detailed examination of the effects of these inhibitors on neurogenic contractions of gastrointestinal smooth muscle, a key preliminary step to evaluate the importance of GPCR endocytosis for gut function. Inhibitors of clathrin-mediated endocytosis (Pitstop2, PS2) or G protein-coupled receptor kinase-2/3-dependent phosphorylation (Takeda compound 101, Cmpd101), significantly reduced GPCR internalization. However, they also attenuated cholinergic contractions through different mechanisms. PS2 abolished contractile responses by colonic muscle to SNC80 and morphine, which strongly and weakly internalize δ-opioid and μ-opioid receptors, respectively. PS2 did not affect the increased myogenic contractile activity following removal of an inhibitory neural influence (tetrodotoxin) but suppressed electrically evoked neurogenic contractions. Ca2+ signaling by myenteric neurons in response to exogenous ATP was unaffected by PS2, suggesting inhibitory actions on neurotransmitter release rather than neurotransmission. In contrast, Cmpd101 attenuated contractions to the cholinergic agonist carbachol, indicating direct effects on smooth muscle. We conclude that, although PS2 and Cmpd101 are effective blockers of GPCR endocytosis in enteric neurons, these inhibitors are unsuitable for the study of neurally mediated gut function due to their inhibitory effects on neuromuscular transmission and smooth muscle contractility. NEW & NOTEWORTHY Internalization of activated G protein-coupled receptors is a major determinant of the type and duration of subsequent downstream signaling events. Inhibitors of endocytosis effectively block opioid receptor internalization in enteric neurons. The clathrin-dependent endocytosis inhibitor Pitstop2 blocks effects of opioids on neurogenic contractions of the colon in an internalization-independent manner. These inhibitors also significantly impact cholinergic neuromuscular transmission. We conclude that these tools are unsuitable for examination of the contribution of neuronal G protein-coupled receptor endocytosis to gastrointestinal motility.

G-protein-coupled receptor allosterism: the promise and the problem(s)

2004 ◽  
Vol 32 (5) ◽  
pp. 873-877 ◽  
Author(s):  
A. Christopoulos ◽  
L.T. May ◽  
V.A. Avlani ◽  
P.M. Sexton
Keyword(s):  
G Protein ◽  
Binding Sites ◽  
G Protein Coupled Receptors ◽  
Receptor Activity ◽  
Screening Methods ◽  
Receptor Subtype ◽  
Allosteric Modulators ◽  
Physiological Regulation ◽  
Subtype Selectivity ◽  
G Protein Coupled

Allosteric modulators of G-protein-coupled receptors interact with binding sites that are topographically distinct from the orthosteric site recognized by the receptor's endogenous agonist. Allosteric ligands offer a number of advantages over orthosteric drugs, including the potential for greater receptor subtype selectivity and a more ‘physiological’ regulation of receptor activity. However, the manifestations of allosterism at G-protein-coupled receptors are quite varied, and significant challenges remain for the optimization of screening methods to ensure the routine detection and validation of allosteric ligands.

scholarly journals Involvement of G Protein-coupled Receptor Kinase 5 in Homologous Desensitization of the Thyrotropin Receptor

1996 ◽  
Vol 271 (17) ◽  
pp. 10143-10148 ◽  
Author(s):  
Yuji Nagayama ◽  
Kunihiko Tanaka ◽  
Takeshi Hara ◽  
Hiroyuki Namba ◽  
Shunichi Yamashita ◽  
...  
Keyword(s):  
G Protein ◽  
Thyrotropin Receptor ◽  
Receptor Kinase ◽  
G Protein Coupled Receptor ◽  
G Protein Coupled ◽  
Homologous Desensitization

scholarly journals GRK2 promotes growth of medulloblastoma cells and protects them from chemotherapy-induced apoptosis

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Anup S. Pathania ◽  
Xiuhai Ren ◽  
Min Y. Mahdi ◽  
Gregory M. Shackleford ◽  
Anat Erdreich-Epstein
Keyword(s):  
G Protein ◽  
Cell Lines ◽  
G Protein Coupled Receptors ◽  
Receptor Kinase ◽  
Medulloblastoma Cell ◽  
Chemotherapy Drugs ◽  
Erk Phosphorylation ◽  
Induced Apoptosis ◽  
G Protein Coupled ◽  
Medulloblastoma Cell Lines

Abstract G-protein coupled receptor kinase 2 (GRK2; ADRBK1, BARK1) is most known as a regulator of G-protein coupled receptors. However, GRK2 also has other functions. Medulloblastomas are the most common malignant brain cancers in children. GRK2 has not been implicated in medulloblastoma biology. Here we report that GRK2 knockdown slowed cell growth, diminished proliferation, and enhanced cisplatin- and etoposide-induced apoptosis in medulloblastoma cell lines UW228-2 and Daoy. Reciprocally, GRK2 overexpression attenuated apoptosis induced by these chemotherapy drugs. Cisplatin and etoposide increased phosphorylation of AKT (S473) and GRK2 knockdown mitigated this increase. Cisplatin and etoposide attenuated ERK phosphorylation, but GRK2 knockdown did not alter this effect. Wildtype GRK2 reversed the increase in cisplatin- and etoposide-induced apoptosis caused by GRK2 knockdown. GRK2-K220R (kinase dead) and GRK2-S670A (unphosphorylated, constitutively active) conferred protection from cisplatin that was similar to wildtype GRK2, suggesting that this protection may be mediated though a kinase-independent activity of GRK2. These data demonstrate that GRK2 contributes to proliferation and survival of these medulloblastoma cell lines and to their protection from cisplatin- and etoposide-induced apoptosis.

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