scholarly journals Functional Desensitization of the Extracellular Calcium-Sensing Receptor Is Regulated via Distinct Mechanisms: Role of G Protein-Coupled Receptor Kinases, Protein Kinase C and β-Arrestins

Endocrinology ◽  
2007 ◽  
Vol 148 (5) ◽  
pp. 2398-2404 ◽  
Author(s):  
Stephan Lorenz ◽  
Romy Frenzel ◽  
Ralf Paschke ◽  
Gerda E. Breitwieser ◽  
Susanne U. Miedlich
Keyword(s):  
G Protein ◽  
Inositol Phosphate ◽  
Phosphorylation Site ◽  
Extracellular Calcium ◽  
Receptor Internalization ◽  
Calcium Sensing Receptor ◽  
Calcium Sensing ◽  
Kinase C ◽  
Inositol Phosphate Accumulation ◽  
G Protein Coupled

The extracellular calcium-sensing receptor (CaR) senses small fluctuations of the extracellular calcium (Ca2+e) concentration and translates them into potent changes in parathyroid hormone secretion. Dissecting the regulatory mechanisms of CaR-mediated signal transduction may provide insights into the physiology of the receptor and identify new molecules as potential drug targets for the treatment of osteoporosis and/or hyperparathyroidism. CaR can be phosphorylated by protein kinase C (PKC) and G protein-coupled receptor kinases (GRKs), and has been shown to bind to β-arrestins, potentially contributing to desensitization of CaR, although the mechanisms by which CaR-mediated signal transduction is terminated are not known. We used a PKC phosphorylation site-deficient CaR, GRK and β-arrestin overexpression or down-regulation to delineate CaR-mediated desensitization. Fluorescence-activated cell sorting was used to determine whether receptor internalization contributed to desensitization. Overexpression of GRK 2 or 3 reduced Ca2+e-dependent inositol phosphate accumulation by more than 70%, whereas a GRK 2 mutant deficient in Gαq binding (D110A) was without major effect. Overexpression of GRK 4–6 did not reduce Ca2+e-dependent inositol phosphate accumulation. Overexpression of β-arrestin 1 or 2 revealed a modest inhibitory effect on Ca2+e-dependent inositol phosphate production (20–30%), which was not observed for the PKC phosphorylation site-deficient CaR. Agonist-dependent receptor internalization (10–15%) did not account for the described effects. Thus, we conclude that PKC phosphorylation of CaR contributes to β-arrestin-dependent desensitization of CaR coupling to G proteins. In contrast, GRK 2 predominantly interferes with G protein-mediated inositol-1,4,5-trisphosphate formation by binding to Gαq.

The calcium-sensing receptor as a nutrient sensor

2005 ◽  
Vol 33 (1) ◽  
pp. 316-320 ◽  
Author(s):  
D. Riccardi ◽  
D. Maldonado-Perez
Keyword(s):  
G Protein ◽  
Cell Fate ◽  
Aromatic Amino Acids ◽  
Cell Types ◽  
Extracellular Calcium ◽  
Calcium Sensing Receptor ◽  
Calcium Sensing ◽  
Sense And Respond ◽  
Acute Changes ◽  
G Protein Coupled

Critical to cell fate in many cell types is the ability to sense and respond to acute changes in free ionized extracellular calcium concentration ([Ca2+]o). Such tight control is mediated by the activation of a protein known as the extracellular-calcium-sensing receptor (CaR). CaR belongs to the ‘family C’ of G-protein-coupled receptors and was the first G-protein-coupled receptor to be identified to have an inorganic cation, calcium, as its ligand. While calcium is the physiological agonist of the receptor, several other polyvalent cations and polycations can also modulate CaR function as do certain L-aromatic amino acids, polyamines, salinity and pH. This feature renders the CaR uniquely capable of generating cell- and tissue-specific responses, and of integrating inputs deriving from changes in the Ca2+o concentration with signals deriving from the local metabolic environment. Here we address the role of the CaR in physiology and disease, the range of CaR modulators and the potential roles of the CaR as a metabolic sensor in a variety of physiological (and pathological) scenarios.

scholarly journals Recent advances in understanding the extracellular calcium-sensing receptor

F1000Research ◽  
2016 ◽  
Vol 5 ◽  
pp. 2535 ◽  
Author(s):  
Matilde Colella ◽  
Andrea Gerbino ◽  
Aldebaran M. Hofer ◽  
Silvana Curci
Keyword(s):  
G Protein ◽  
Calcium Homeostasis ◽  
Body Fluids ◽  
Extracellular Calcium ◽  
G Protein Coupled Receptor ◽  
Calcium Sensing Receptor ◽  
Endogenous Ligands ◽  
Calcium Sensing ◽  
Intracellular Signals ◽  
G Protein Coupled

The extracellular calcium-sensing receptor (CaR), a ubiquitous class C G-protein-coupled receptor (GPCR), is responsible for the control of calcium homeostasis in body fluids. It integrates information about external Ca2+ and a surfeit of other endogenous ligands into multiple intracellular signals, but how is this achieved? This review will focus on some of the exciting concepts in CaR signaling and pharmacology that have emerged in the last few years.

scholarly journals OR07-06 The Roles of GNAQ and GNA11 in Calcium-Sensing Receptor (CaSR) Signalling

2020 ◽  
Vol 4 (Supplement_1) ◽  
Author(s):  
Anna K Gluck ◽  
Mark Stevenson ◽  
Sara Falcone ◽  
Asuka Inoue ◽  
Gerda E Breitwieser ◽  
...  
Keyword(s):  
Protein Expression ◽  
G Protein ◽  
Extracellular Calcium ◽  
Luciferase Reporter ◽  
Reporter Construct ◽  
Calcium Sensing Receptor ◽  
Luciferase Reporter Construct ◽  
Response Element ◽  
Calcium Sensing

Abstract The G-protein subunits Gα 11 and Gα q, which share >90% peptide sequence identity and are encoded by the GNA11 and GNAQ genes, respectively, mediate signalling by the calcium-sensing receptor (CaSR), a class C G-protein coupled receptor (GPCR) that regulates extracellular calcium (Ca2+e) homeostasis. Germline Gα 11 inactivating and activating mutations cause familial hypocalciuric hypercalcaemia type-2 (FHH2) and autosomal dominant hypocalcaemia type-2 (ADH2), respectively, but such Gα q mutations have not been reported. We therefore investigated the DiscovEHR cohort database, which has exomes from 51,289 patients with matched phenotyping data, for such GNAQ mutations. The DiscovEHR cohort was examined for rare GNAQ variants, which were transiently expressed in CaSR-expressing HEK293A Gα q/11 knockout cells, and their effects on CaSR-mediated intracellular calcium (Ca2+i) release and MAPK activity, in response to increasing concentrations of extracellular calcium were assessed using a nuclear factor of activated T-cells response element (NFAT-RE) luciferase reporter construct and a serum response element (SRE) luciferase reporter construct, respectively. Responses were compared to those of wild-type (WT), inactivating FHH2-associated GNA11 mutations (Leu135Gln and Phe220Ser), and engineered GNAQ mutations that were equivalent to the FHH2-causing GNA11 mutations. Gα q/11 protein expression was confirmed by Western blot analysis. Six rare missense GNAQ variants (Arg19Trp, Ala110Val, Gln299His, Ala302Ser, Ala331Thr, Val344Ile) were identified in DiscovEHR individuals, all of whom had mean plasma calcium values in the normal range (8.30–10.00 mg/dL). Functional characterisation of all six Gα q variants showed no significant difference to WT Gα q responses, thereby indicating that these variants are unlikely to be disease-causing mutations. In addition, the FHH2-causing GNA11 mutations (Leu135Gln and Phe220Ser) had significantly reduced responses, compared to WT Gα 11; however, this could be compensated by WT Gα q. GNAQ Leu135Gln and Phe220Ser, in contrast to their Gα 11 counterparts, showed no differences in protein expression or signalling responses when compared to WT Gα q. Our study, which provides mechanistic insights into the differences between Gα q and Gα 11, indicates that Gα q, unlike Gα 11, does not play a major role in the pathogenesis of FHH2 or ADH2.

Calcium receptor is functionally expressed in rat neonatal ventricular cardiomyocytes

2006 ◽  
Vol 290 (3) ◽  
pp. H1165-H1171 ◽  
Author(s):  
Jacob Tfelt-Hansen ◽  
Jakob Lerche Hansen ◽  
Sanela Smajilovic ◽  
Ernest F. Terwilliger ◽  
Stig Haunso ◽  
...  
Keyword(s):  
Cardiac Myocytes ◽  
Messenger Rna ◽  
Cardiac Development ◽  
Inositol Phosphate ◽  
Tritiated Thymidine ◽  
Extracellular Calcium ◽  
Dominant Negative ◽  
Calcium Sensing Receptor ◽  
Calcium Sensing ◽  
Ventricular Cardiomyocytes

Both intra- and extracellular calcium play multiple roles in the physiology and pathophysiology of cardiomyocytes, especially in stimulus-contraction coupling. The intracellular calcium level is closely controlled through the concerted actions of calcium channels, exchangers, and pumps; however, the expression and function(s) of the so-called calcium-sensing receptor (CaR) in the heart remain less well characterized. The CaR is a seven-transmembrane receptor, which, in response to noncovalent binding of extracellular calcium, activates intracellular effectors, including G proteins and extracellular signal-regulated kinases (ERK1/2). We have shown that cultured neonatal cardiomyocytes express the CaR messenger RNA and the CaR protein. Furthermore, increasing concentrations of extracellular calcium and a type II CaR activator “calcimimetic” caused inositol phosphate (IP) accumulation, downregulated tritiated thymidine incorporation, and supported ERK1/2 phosphorylation, suggesting that the CaR protein is functionally active. Interestingly, the calcimimetic induced a more rapid ERK1/2 phosphorylation than calcium and left-shifted the IP concentration-response curve for extracellular calcium, supporting the hypothesis that CaR is functionally expressed in cardiac myocytes. This notion was underscored by studies using a virus containing a dominant-negative CaR construct, because this protein blunted the calcium-induced IP response. In conclusion, we have shown that the CaR is functionally expressed in neonatal ventricular cardiomyocytes and that the receptor activates second messenger pathways, including IP and ERK, and decreases DNA synthesis. A specific calcium-sensing receptor on cardiac myocytes could play a role in regulating cardiac development, function, and homeostasis.

G protein-coupled calcium-sensing receptor is a crucial mediator of MTA-induced biological activities

Biomaterials ◽  
2017 ◽  
Vol 127 ◽  
pp. 107-116 ◽  
Author(s):  
Jin Man Kim ◽  
Seulki Choi ◽  
Kyu Hwan Kwack ◽  
Sun-Young Kim ◽  
Hyeon-Woo Lee ◽  
...  
Keyword(s):  
G Protein ◽  
Biological Activities ◽  
Calcium Sensing Receptor ◽  
Calcium Sensing ◽  
G Protein Coupled

scholarly journals Eliminating phosphorylation sites of the parathyroid hormone receptor type 1 differentially affects stimulation of phospholipase C and receptor internalization

2008 ◽  
Vol 295 (3) ◽  
pp. E665-E671 ◽  
Author(s):  
Susanne U. Miedlich ◽  
Abdul B. Abou-Samra
Keyword(s):  
Parathyroid Hormone ◽  
Phospholipase C ◽  
G Protein ◽  
Phosphorylation Site ◽  
Receptor Internalization ◽  
Phosphorylation Sites ◽  
G Protein Coupled Receptor ◽  
Parathyroid Hormone Receptor ◽  
Direct Binding ◽  
G Protein Coupled

The parathyroid hormone (PTH)/PTH-related peptide (PTHrP) receptor (PTH1R) belongs to family B of seven-transmembrane-spanning receptors and is activated by PTH and PTHrP. Upon PTH stimulation, the rat PTH1R becomes phosphorylated at seven serine residues. Elimination of all PTH1R phosphorylation sites results in prolonged cAMP accumulation and impaired internalization in stably transfected LLC-PK1 cells. The present study explores the role of individual PTH1R phosphorylation sites in PTH1R signaling through phospholipase C, agonist-dependent receptor internalization, and regulation by G protein-coupled receptor kinases. By means of transiently transfected COS-7 cells, we demonstrate that the phosphorylation-deficient (pd) PTH1R confers dramatically enhanced coupling to Gq/11 proteins upon PTH stimulation predominantly caused by elimination of Ser491/492/493, Ser501, or Ser504. Reportedly, impaired internalization of the pd PTH1R, however, is not dependent on a specific phosphorylation site. In addition, we show that G protein-coupled receptor kinase 2 interferes with pd PTH1R signaling to Gq/11 proteins at least partially by direct binding to Gq/11 proteins.

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