scholarly journals Insights into calcium-sensing receptor trafficking and biased signalling by studies of calcium homeostasis

2018 ◽  
Vol 61 (1) ◽  
pp. R1-R12 ◽  
Author(s):  
Caroline M Gorvin
Keyword(s):  
G Protein ◽  
Calcium Homeostasis ◽  
Calcium Release ◽  
Transmembrane Domain ◽  
Hormone Secretion ◽  
Adaptor Protein ◽  
Structural Motif ◽  
Calcium Excretion ◽  
Calcium Sensing Receptor ◽  
Calcium Sensing

The calcium-sensing receptor (CASR) is a class C G-protein-coupled receptor (GPCR) that detects extracellular calcium concentrations, and modulates parathyroid hormone secretion and urinary calcium excretion to maintain calcium homeostasis. The CASR utilises multiple heterotrimeric G-proteins to mediate signalling effects including activation of intracellular calcium release; mitogen-activated protein kinase (MAPK) pathways; membrane ruffling; and inhibition of cAMP production. By studying germline mutations in the CASR and proteins within its signalling pathway that cause hyper- and hypocalcaemic disorders, novel mechanisms governing GPCR signalling and trafficking have been elucidated. This review focusses on two recently described pathways that provide novel insights into CASR signalling and trafficking mechanisms. The first, identified by studying a CASR gain-of-function mutation that causes autosomal dominant hypocalcaemia (ADH), demonstrated a structural motif located between the third transmembrane domain and the second extracellular loop of the CASR that mediates biased signalling by activating a novel β-arrestin-mediated G-protein-independent pathway. The second, in which the mechanism by which adaptor protein-2 σ-subunit (AP2σ) mutations cause familial hypocalciuric hypercalcaemia (FHH) was investigated, demonstrated that AP2σ mutations impair CASR internalisation and reduce multiple CASR-mediated signalling pathways. Furthermore, these studies showed that the CASR can signal from the cell surface using multiple G-protein pathways, whilst sustained signalling is mediated only by the Gq/11 pathway. Thus, studies of FHH- and ADH-associated mutations have revealed novel steps by which CASR mediates signalling and compartmental bias, and these pathways could provide new targets for therapies for patients with calcaemic disorders.

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 Molecular and clinical insights from studies of calcium-sensing receptor mutations

2019 ◽  
Vol 63 (2) ◽  
pp. R1-R16 ◽  
Author(s):  
Caroline M Gorvin
Keyword(s):  
G Protein ◽  
Structural Integrity ◽  
Elevated Serum ◽  
Failure To Thrive ◽  
Receptor Activation ◽  
Urinary Calcium ◽  
Signalling Pathways ◽  
Calcium Excretion ◽  
Calcium Sensing Receptor ◽  
Calcium Sensing

Twenty-five years have elapsed since the calcium-sensing receptor (CaSR) was first identified in bovine parathyroid and the receptor is now recognized as a fundamental contributor to extracellular Ca2+ (Ca2+ e) homeostasis, regulating parathyroid hormone release and urinary calcium excretion. The CaSR is a class C G-protein-coupled receptor (GPCR) that is functionally active as a homodimer and couples to multiple G-protein subtypes to activate intracellular signalling pathways. The importance of the CaSR in the regulation of Ca2+ e has been highlighted by the identification of >400 different germline loss- and gain-of-function CaSR mutations that give rise to disorders of Ca2+ e homeostasis. CaSR-inactivating mutations cause neonatal severe hyperparathyroidism, characterised by marked hypercalcaemia, skeletal demineralisation and failure to thrive in early infancy; and familial hypocalciuric hypercalcaemia, an often asymptomatic disorder associated with mild-moderately elevated serum calcium concentrations. Activating mutations are associated with autosomal dominant hypocalcaemia, which is occasionally associated with a Bartter’s-like phenotype. Recent elucidation of the CaSR extracellular domain structure enabled the locations of CaSR mutations to be mapped and has revealed clustering in locations important for structural integrity, receptor dimerisation and ligand binding. Moreover, the study of disease-causing mutations has demonstrated that CaSR signals in a biased manner and have revealed specific residues important for receptor activation. This review presents the current understanding of the genetic landscape of CaSR mutations by summarising findings from clinical and functional studies of disease-associated mutations. It concludes with reflections on how recently uncovered signalling pathways may expand the understanding of calcium homeostasis disorders.

scholarly journals Mutations of calcium-sensing receptor gene: two novel mutations and overview of impact on calcium homeostasis

2011 ◽  
Vol 165 (2) ◽  
pp. 353-358 ◽  
Author(s):  
Elena Livadariu ◽  
Renata S Auriemma ◽  
Catherine Rydlewski ◽  
Silvia Vandeva ◽  
Etienne Hamoir ◽  
...  
Keyword(s):  
Calcium Homeostasis ◽  
Genetic Disorders ◽  
Receptor Gene ◽  
Correct Diagnosis ◽  
Gene Mutations ◽  
Calcium Excretion ◽  
Coding Region ◽  
Calcium Sensing Receptor ◽  
Calcium Sensing ◽  
Exon 4

ObjectiveGenetic disorders of calcium metabolism arise in a familial or sporadic setting. The calcium-sensing receptor (CASR) plays a key role in maintaining calcium homeostasis and study of theCASRgene can be clinically useful in determining etiology and appropriate therapeutic approaches. We report two cases of novelCASRgene mutations that illustrate the varying clinical presentations and discuss these in terms of the current understanding of CASR function.Patients and methodsA 16-year-old patient had mild hypercalcemia associated with low-normal urinary calcium excretion and normal-to-high parathyroid hormone (PTH) levels. Because of negative family history, familial hypocalciuric hypercalcemia was originally excluded. The second patient was a 54-year-old man with symptomatic hypocalcemia, hyperphosphatemia, low PTH, and mild hypercalciuria. Familial investigation revealed the same phenotype in the patient's sister. The coding region of theCASRgene was sequenced in both probands and their available first-degree relatives.ResultsThe first patient had a novel heterozygous inactivatingCASRmutation in exon 4, which predicted a p.A423K change; genetic analysis was negative in the parents. The second patient had a novel heterozygous activatingCASRmutation in exon 6, which predicted a p.E556K change; the affected sister of the proband was also positive.ConclusionsWe reported two novel heterozygous mutations of theCASRgene, an inactivating mutation in exon 4 and the first activating mutation reported to date in exon 6. These cases illustrate the importance of genetic testing ofCASRgene to aid correct diagnosis and to assist in clinical management.

scholarly journals Structural basis for activation and allosteric modulation of full-length calcium-sensing receptor

2021 ◽  
Vol 7 (23) ◽  
pp. eabg1483
Author(s):  
Tianlei Wen ◽  
Ziyu Wang ◽  
Xiaozhe Chen ◽  
Yue Ren ◽  
Xuhang Lu ◽  
...  
Keyword(s):  
Conformational Changes ◽  
Bound States ◽  
Hormone Secretion ◽  
Allosteric Modulation ◽  
Full Length ◽  
Structural Basis ◽  
Endocrine Disorders ◽  
Calcium Sensing Receptor ◽  
Calcium Sensing ◽  
Class C

Calcium-sensing receptor (CaSR) is a class C G protein–coupled receptor (GPCR) that plays an important role in calcium homeostasis and parathyroid hormone secretion. Here, we present multiple cryo–electron microscopy structures of full-length CaSR in distinct ligand-bound states. Ligands (Ca2+ and l-tryptophan) bind to the extracellular domain of CaSR and induce large-scale conformational changes, leading to the closure of two heptahelical transmembrane domains (7TMDs) for activation. The positive modulator (evocalcet) and the negative allosteric modulator (NPS-2143) occupy the similar binding pocket in 7TMD. The binding of NPS-2143 causes a considerable rearrangement of two 7TMDs, forming an inactivated TM6/TM6 interface. Moreover, a total of 305 disease-causing missense mutations of CaSR have been mapped to the structure in the active state, creating hotspot maps of five clinical endocrine disorders. Our results provide a structural framework for understanding the activation, allosteric modulation mechanism, and disease therapy for class C GPCRs.

scholarly journals Relationship between parathyroid calcium-sensing receptor expression and potency of the calcimimetic, cinacalcet, in suppressing parathyroid hormone secretion in an in vivo murine model of primary hyperparathyroidism

2005 ◽  
Vol 153 (4) ◽  
pp. 587-594 ◽  
Author(s):  
Takehisa Kawata ◽  
Yasuo Imanishi ◽  
Keisuke Kobayashi ◽  
Takao Kenko ◽  
Michihito Wada ◽  
...  
Keyword(s):  
Parathyroid Hormone ◽  
Primary Hyperparathyroidism ◽  
Secondary Hyperparathyroidism ◽  
Murine Model ◽  
Hormone Secretion ◽  
Suppressive Effect ◽  
Receptor Expression ◽  
Parathyroid Glands ◽  
Calcium Sensing Receptor ◽  
Calcium Sensing

Cinacalcet HCl, an allosteric modulator of the calcium-sensing receptor (CaR), has recently been approved for the treatment of secondary hyperparathyroidism in patients with chronic kidney disease on dialysis, due to its suppressive effect on parathyroid hormone (PTH) secretion. Although cinacalcet’s effects in patients with primary and secondary hyperparathyroidism have been reported, the crucial relationship between the effect of calcimimetics and CaR expression on the parathyroid glands requires better understanding. To investigate its suppressive effect on PTH secretion in primary hyperparathyroidism, in which hypercalcemia may already have stimulated considerable CaR activity, we investigated the effect of cinacalcet HCl on PTH-cyclin D1 transgenic mice (PC2 mice), a model of primary hyperparathyroidism with hypo-expression of CaR on their parathyroid glands. A single administration of 30 mg/kg body weight (BW) of cinacalcet HCl significantly suppressed serum calcium (Ca) levels 2 h after administration in 65- to 85-week-old PC2 mice with chronic biochemical hyperparathyroidism. The percentage reduction in serum PTH was significantly correlated with CaR hypo-expression in the parathyroid glands. In older PC2 mice (93–99 weeks old) with advanced hyperparathyroidism, serum Ca and PTH levels were not suppressed by 30 mg cinacalcet HCl/kg. However, serum Ca and PTH levels were significantly suppressed by 100 mg/kg of cinacalcet HCl, suggesting that higher doses of this compound could overcome severe hyperparathyroidism. To conclude, cinacalcet HCl demonstrated potency in a murine model of primary hyperparathyroidism in spite of any presumed endogenous CaR activation by hypercalcemia and hypo-expression of CaR in the parathyroid glands.

scholarly journals The Calcium Sensing Receptor: From Understanding Parathyroid Calcium Homeostasis to Bone Metastases

2008 ◽  
Vol 90 (4) ◽  
pp. 271-277 ◽  
Author(s):  
Radu Mihai
Keyword(s):  
Breast Cancer ◽  
Bone Metastases ◽  
Intracellular Calcium ◽  
Calcium Homeostasis ◽  
Membrane Trafficking ◽  
Calcium Concentration ◽  
Fluorescent Microscopy ◽  
Calcium Sensing Receptor ◽  
Calcium Sensing ◽  
Parathyroid Adenomas

The cloning of the calcium sensing receptor (CaR) confirmed that parathyroid cells monitor extracellular calcium concentration ([Ca2+]ext) via a receptor-type mechanism. This lead to the hypothesis that abnormalities in the expression and/or function of the CaR could explain the biochemical abnormalities in primary hyperparathyroidism (PHPT). Cultured cells from parathyroid adenomas of patients operated for PHPT were used to monitor real-time changes in intracellular calcium concentration ([Ca2+]i) as measured by fluorescent microscopy using the Fura-2/AM dye. We found that CaR agonists trigger release of intracellular calcium pools and such responses are amplified by increasing the affinity of IP3 receptors. Using confocal microscopy to monitor membrane trafficking in living parathyroid cells labelled with the fluorescent dye FM1-43, we found that a decrease in [Ca2+]i rather than an absolute change in [Ca2+]ext is the main stimulus for exocytosis from human parathyroid cells. These data suggest that, in PHPT, a defective signalling mechanism from the CaR allows cells from parathyroid adenomas to maintain low [Ca2+]i with uninhibited PTH secretion in the face of hypercalcaemia. Over longer periods of time, CaR controls parathyroid proliferation via changes in tyrosine phosphorylation. We found that multiple proteins of molecular weight 20–65 kDa are phosphorylated within 10–60 min in response to CaR agonists. Further work demonstrated that high [Ca2+]i stimulates the expression of bcl-2 oncoprotein in cultured human parathyroid cells and that, in parathyroid adenomas, predominant expression of bcl-2 rather than bax oncoprotein might prevent apoptosis and explain the slow growth rate of these tumours. More recently, it became apparent that CaR stimulates cell proliferation in several cell types not involved in calcium homeostasis. Using archived histological material from 65 patients who died with metastatic breast cancer, we identified CaR expression predominantly in tumours from patients who developed bone rather than visceral metastases (35 of 49 versus 7 of 16; P < 0.01, chi-squared test). These data suggest that CaR expression has the potential to become a new biological marker predicting the risk of bone metastases in patients with breast cancer. A prospective study should investigate if patients with CaR-positive tumours are more likely to develop bone metastases and whether they could benefit more from prophylactic treatment with bisphosphonates or the newly developed CaR antagonists.

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.

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