The calcium-sensing receptor (CaSR) is a Class CG-protein coupled receptor which senses extracellular levels of calcium ion. It is primarily expressed in the parathyroid gland and the renal tubules of the kidney. In the parathyroid gland, the calcium-sensing receptor controls calcium homeostasis by regulating the release of parathyroid hormone (PTH).[1] In the kidney it has an inhibitory effect on the reabsorption of calcium, potassium, sodium, and water depending on which segment of the tubule is being activated.[2]
The release of PTH is inhibited in response to elevations in plasma calcium concentrations and activation of the calcium receptor. Increased calcium binding on the extracellular side gives a conformational change in the receptor, which, on the intracellular side, initiates the phospholipase C pathway,[3][4] presumably through a Gqα type of G protein, which ultimately increases intracellular concentration of calcium, which inhibits vesicle fusion and exocytosis of parathyroid hormone. It also inhibits (not stimulates, as some[5] sources state) the cAMP dependent pathway.[4]
Pathology
Mutations that inactivate a CaSR gene cause familial hypocalciuric hypercalcemia (FHH) (also known as familial benign hypercalcemia because it is generally asymptomatic and does not require treatment),[6] when present in heterozygotes. Patients who are homozygous for CaSR inactivating mutations have more severe hypercalcemia.[7] Other mutations that activate CaSR are the cause of autosomal dominant hypocalcemia[8] or Type 5 Bartter syndrome. An alternatively spliced transcript variant encoding 1088 aa has been found for this gene, but its full-length nature has not been defined.[9]
Therapeutic application
The drugs cinacalcet and etelcalcetide are allosteric modifiers of the calcium-sensing receptor.[10] They are classified as a calcimimetics, binding to the calcium-sensing receptor and decreasing parathyroid hormone release.
Calcilytic drugs, which block CaSR, produce increased bone density in animal studies and have been researched for the treatment of osteoporosis. Unfortunately clinical trial results in humans have proved disappointing, with sustained changes in bone density not observed despite the drug being well tolerated.[11][12] More recent research has shown the CaSR receptor to be involved in numerous other conditions including Alzheimer's disease, asthma and some forms of cancer,[13][14][15][15][16] and calcilytic drugs are being researched as potential treatments for these. Recently it has been shown that biomimetic bone like apatite inhibits formation of bone through endochondral ossification pathway via hyperstimulation of extracellular calcium sensing receptor[17].
↑D'Souza-Li L (Aug 2006). "The calcium-sensing receptor and related diseases". Arquivos Brasileiros de Endocrinologia e Metabologia. 50 (4): 628–39. doi:10.1590/S0004-27302006000400008. PMID17117288.
↑Vezzoli, Giuseppe; Soldati, Laura; Gambaro, Giovanni (2009-04-01). "Roles of calcium-sensing receptor (CaSR) in renal mineral ion transport". Current Pharmaceutical Biotechnology. 10 (3): 302–310. doi:10.2174/138920109787847475. ISSN1873-4316. PMID19355940.
↑Pidasheva S, Canaff L, Simonds WF, Marx SJ, Hendy GN (Jun 2005). "Impaired cotranslational processing of the calcium-sensing receptor due to signal peptide missense mutations in familial hypocalciuric hypercalcemia". Human Molecular Genetics. 14 (12): 1679–90. doi:10.1093/hmg/ddi176. PMID15879434.
↑Torres PU (Jul 2006). "Cinacalcet HCl: a novel treatment for secondary hyperparathyroidism caused by chronic kidney disease". Journal of Renal Nutrition. 16 (3): 253–8. doi:10.1053/j.jrn.2006.04.010. PMID16825031.
↑Nemeth EF, Shoback D (Jun 2013). "Calcimimetic and calcilytic drugs for treating bone and mineral-related disorders". Best Practice & Research. Clinical Endocrinology & Metabolism. 27 (3): 373–84. doi:10.1016/j.beem.2013.02.008. PMID23856266.
↑John MR, Harfst E, Loeffler J, Belleli R, Mason J, Bruin GJ, Seuwen K, Klickstein LB, Mindeholm L, Widler L, Kneissel M (Jul 2014). "AXT914 a novel, orally-active parathyroid hormone-releasing drug in two early studies of healthy volunteers and postmenopausal women". Bone. 64: 204–10. doi:10.1016/j.bone.2014.04.015. PMID24769332.
↑Hjälm G, MacLeod RJ, Kifor O, Chattopadhyay N, Brown EM (Sep 2001). "Filamin-A binds to the carboxyl-terminal tail of the calcium-sensing receptor, an interaction that participates in CaR-mediated activation of mitogen-activated protein kinase". The Journal of Biological Chemistry. 276 (37): 34880–7. doi:10.1074/jbc.M100784200. PMID11390380.
↑Awata H, Huang C, Handlogten ME, Miller RT (Sep 2001). "Interaction of the calcium-sensing receptor and filamin, a potential scaffolding protein". The Journal of Biological Chemistry. 276 (37): 34871–9. doi:10.1074/jbc.M100775200. PMID11390379.
Further reading
Hendy GN, D'Souza-Li L, Yang B, Canaff L, Cole DE (Oct 2000). "Mutations of the calcium-sensing receptor (CASR) in familial hypocalciuric hypercalcemia, neonatal severe hyperparathyroidism, and autosomal dominant hypocalcemia". Human Mutation. 16 (4): 281–96. doi:10.1002/1098-1004(200010)16:4<281::AID-HUMU1>3.0.CO;2-A. PMID11013439.
Fukumoto S (Mar 2002). "[Calcium-sensing receptor in bone cells]". Nihon Rinsho. Japanese Journal of Clinical Medicine. 60 Suppl 3: 57–63. PMID11979955.
Tfelt-Hansen J, Schwarz P, Brown EM, Chattopadhyay N (May 2003). "The calcium-sensing receptor in human disease". Frontiers in Bioscience. 8: s377–90. doi:10.2741/1068. PMID12700051.
Hu J, Spiegel AM (Aug 2003). "Naturally occurring mutations of the extracellular Ca2+-sensing receptor: implications for its structure and function". Trends in Endocrinology and Metabolism. 14 (6): 282–8. doi:10.1016/S1043-2760(03)00104-8. PMID12890593.
Aida K, Koishi S, Inoue M, Nakazato M, Tawata M, Onaya T (Sep 1995). "Familial hypocalciuric hypercalcemia associated with mutation in the human Ca(2+)-sensing receptor gene". The Journal of Clinical Endocrinology and Metabolism. 80 (9): 2594–8. doi:10.1210/jc.80.9.2594. PMID7673400.
Aida K, Koishi S, Tawata M, Onaya T (Sep 1995). "Molecular cloning of a putative Ca(2+)-sensing receptor cDNA from human kidney". Biochemical and Biophysical Research Communications. 214 (2): 524–9. doi:10.1006/bbrc.1995.2318. PMID7677761.
Garrett JE, Capuano IV, Hammerland LG, Hung BC, Brown EM, Hebert SC, Nemeth EF, Fuller F (May 1995). "Molecular cloning and functional expression of human parathyroid calcium receptor cDNAs". The Journal of Biological Chemistry. 270 (21): 12919–25. doi:10.1074/jbc.270.21.12919. PMID7759551.
Pollak MR, Brown EM, Estep HL, McLaine PN, Kifor O, Park J, Hebert SC, Seidman CE, Seidman JG (Nov 1994). "Autosomal dominant hypocalcaemia caused by a Ca(2+)-sensing receptor gene mutation". Nature Genetics. 8 (3): 303–7. doi:10.1038/ng1194-303. PMID7874174.
Pollak MR, Brown EM, Chou YH, Hebert SC, Marx SJ, Steinmann B, Levi T, Seidman CE, Seidman JG (Dec 1993). "Mutations in the human Ca(2+)-sensing receptor gene cause familial hypocalciuric hypercalcemia and neonatal severe hyperparathyroidism". Cell. 75 (7): 1297–303. doi:10.1016/0092-8674(93)90617-Y. PMID7916660.
Janicic N, Soliman E, Pausova Z, Seldin MF, Rivière M, Szpirer J, Szpirer C, Hendy GN (Nov 1995). "Mapping of the calcium-sensing receptor gene (CASR) to human chromosome 3q13.3-21 by fluorescence in situ hybridization, and localization to rat chromosome 11 and mouse chromosome 16". Mammalian Genome. 6 (11): 798–801. doi:10.1007/BF00539007. PMID8597637.
Bai M, Quinn S, Trivedi S, Kifor O, Pearce SH, Pollak MR, Krapcho K, Hebert SC, Brown EM (Aug 1996). "Expression and characterization of inactivating and activating mutations in the human Ca2+o-sensing receptor". The Journal of Biological Chemistry. 271 (32): 19537–45. doi:10.1074/jbc.271.32.19537. PMID8702647.
Baron J, Winer KK, Yanovski JA, Cunningham AW, Laue L, Zimmerman D, Cutler GB (May 1996). "Mutations in the Ca(2+)-sensing receptor gene cause autosomal dominant and sporadic hypoparathyroidism". Human Molecular Genetics. 5 (5): 601–6. doi:10.1093/hmg/5.5.601. PMID8733126.
Freichel M, Zink-Lorenz A, Holloschi A, Hafner M, Flockerzi V, Raue F (Sep 1996). "Expression of a calcium-sensing receptor in a human medullary thyroid carcinoma cell line and its contribution to calcitonin secretion". Endocrinology. 137 (9): 3842–8. doi:10.1210/en.137.9.3842. PMID8756555.
Chattopadhyay N, Ye C, Singh DP, Kifor O, Vassilev PM, Shinohara T, Chylack LT, Brown EM (Apr 1997). "Expression of extracellular calcium-sensing receptor by human lens epithelial cells". Biochemical and Biophysical Research Communications. 233 (3): 801–5. doi:10.1006/bbrc.1997.6553. PMID9168937.
Cole DE, Janicic N, Salisbury SR, Hendy GN (Aug 1997). "Neonatal severe hyperparathyroidism, secondary hyperparathyroidism, and familial hypocalciuric hypercalcemia: multiple different phenotypes associated with an inactivating Alu insertion mutation of the calcium-sensing receptor gene". American Journal of Medical Genetics. 71 (2): 202–10. doi:10.1002/(SICI)1096-8628(19970808)71:2<202::AID-AJMG16>3.0.CO;2-I. PMID9217223.
Ward BK, Stuckey BG, Gutteridge DH, Laing NG, Pullan PT, Ratajczak T (1997). "A novel mutation (L174R) in the Ca2+-sensing receptor gene associated with familial hypocalciuric hypercalcemia". Human Mutation. 10 (3): 233–5. doi:10.1002/(SICI)1098-1004(1997)10:3<233::AID-HUMU9>3.0.CO;2-J. PMID9298824.
Quinn SJ, Kifor O, Trivedi S, Diaz R, Vassilev P, Brown E (Jul 1998). "Sodium and ionic strength sensing by the calcium receptor". The Journal of Biological Chemistry. 273 (31): 19579–86. doi:10.1074/jbc.273.31.19579. PMID9677383.
Magno AL, Ward BK, Ratajczak T (Feb 2011). "The calcium-sensing receptor: a molecular perspective". Endocrine Reviews. 32 (1): 3–30. doi:10.1210/er.2009-0043. PMID20729338.
External links
"Calcium-Sensing Receptors". IUPHAR Database of Receptors and Ion Channels. International Union of Basic and Clinical Pharmacology.