Biochemical and Biophysical Research Communications
Regular ArticleMolecular Cloning of a Putative Ca2+-Sensing Receptor cDNA from Human Kidney
Abstract
A cDNA that encodes a putative Ca2+-sensing receptor (HuKCaSR) was cloned from human kidney with the use of the polymerase chain reaction. The predicted HuKCaSR protein consists of 1078 amino acids and shares 93.1 and 93.8% overall identity with the bovine parathyroid Ca2+-sensing receptor (BoPCaR1) and rat kidney Ca2+-sensing receptor (RaKCaR), respectively, with least similarity in the carboxyl-terminal regions. The HuKCaSR gene was mapped by fluorescence in situ hybridization to chromosome 3q21, at which region the gene responsible for familial hypocalciuric hypercalcemia has previously been localized by genetic linkage analysis. RNA blot analysis revealed HuKCaSR mRNA in human kidney, but not in brain, lung, liver, heart, skeletal muscle, or placenta.
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Hypoparathyroidism Associated with the DNA Variants in Non-Coding Sequence Region of Calcium-Sensing Receptor
2021, Endocrine and Metabolic ScienceA stable narrow range of extracellular calcium concentration in the blood is essential for life. The calcium-sensing receptor (CaSR), a member of the G protein-coupled receptors family, is required to adjust the set point of blood extracellular calcium concentration, thus regulate parathyroid hormone (PTH) secretion and renal calcium excretion. Loss or gain function of CaSR mutations may result in either hyper- or hypocalcaemia. The CaSR activating mutations increase its sensitivity to extracellular ionized calcium (Ca2+). As consequence, PTH synthesis and secretion are suppressed continuously at normal ionized calcium concentrations. Patients display hypocalcaemia, hyperphosphatemia and lower levels of PTH. Urinary calcium excretion is increased due to the decreased circulating inappropriately PTH level and the activation of the renal tubular CaSR. Therefore, CaSR becomes a good potential clinical therapeutic target for hypoparathyroidism treatment. In order to define new drugs and improve medical management of hypoparathyroidism patients, this study attempts to identify new CaSR variants and analyse in detail the functional change of these CaSR variants, thus better understand the molecular mechanism involved. The study is based on collected hypoparathyroidism patients in our clinical site. In the study we enrolled in 10 patients, obtained all their clinical results and DNA results from seven patients. Our results indicated that the effect of serum intact PTH level correlated to change of serum Ca2+ and phosphate level. The CaSR carrying newly identified DNA variants displayed strong phosphorylation of phospholipase C and mitogen-activated protein kinases. Although the size of clinical cases need to be accumulated, current cases have showed a tendency that the identified multiple DNA variants in CaSR gene revealed an effect on the diagnostic criterion of the hypocalcaemic syndrome. It is undeniable that our research has certain limitations. So far, we tested several DNA variants at the same time, further functional examination for individual DNA variant would largely help to be better understand the mechanisms of CaSR regulation on extracellular calcium concentration.
Parathyroid Hormones
2020, Hormonal Signaling in Biology and Medicine: Comprehensive Modern EndocrinologyThis chapter focuses on the hormone produced by the parathyroid gland, parathyroid hormone (PTH), its structure, regulation, action through its known receptors, physiologic functions, and diseases. The parathyroid glands were discovered in the late 19th century and were found to be distinct from the thyroid glands and to regulate Ca2+ metabolism. The hormone was purified in 1959 and found to be an 84 amino acid peptide, which was later synthesized. Its biologic activity is contained within the first 34 amino acids. Release of PTH from the gland is regulated by extracellular Ca2+ through the calcium-sensing receptor (high inhibits, low stimulates), by phosphate (high stimulates) and by 1,25-dihydroxyvitamin D3 (negative feedback inhibition). In this manner, the hormone regulates the levels or synthesis of these three components, by action primarily on bone and kidney. It acts through its receptor, PTHR1 (a G protein–coupled receptor), in the kidney and on cells of the osteoblast lineage in bone. PTH induces the synthesis of 1,25-dihydroxyvitamin D3 by the kidney, which acts on the intestine to increase uptake of Ca2+. PTH-PTHR1 binding facilitates increased renal reabsorption of Ca2 and causes phosphaturia by downregulation of sodium/phosphate transporters. In bone, it causes many changes in gene expression through a number of signal transduction pathways in cells of the osteoblastic lineage, resulting in either catabolic or anabolic effects on bone. Because of the latter effects, PTH (1–34; teriparatide) was approved for treatment of osteoporosis. There are many diseases associated with each of these constituent parts, and these are described in the chapter. There are still gaps in our knowledge, and we have attempted to point these out.
Parathyroid Hormones
2019, Hormonal Signaling in Biology and Medicine: Comprehensive Modern EndocrinologyThis chapter focuses on the hormone produced by the parathyroid gland, parathyroid hormone (PTH), its structure, regulation, action through its known receptors, physiologic functions, and diseases. The parathyroid glands were discovered in the late 19th century and were found to be distinct from the thyroid glands and to regulate Ca2+ metabolism. The hormone was purified in 1959 and found to be an 84 amino acid peptide, which was later synthesized. Its biologic activity is contained within the first 34 amino acids. Release of PTH from the gland is regulated by extracellular Ca2+ through the calcium-sensing receptor (high inhibits, low stimulates), by phosphate (high stimulates) and by 1,25-dihydroxyvitamin D3 (negative feedback inhibition). In this manner, the hormone regulates the levels or synthesis of these three components, by action primarily on bone and kidney. It acts through its receptor, PTHR1 (a G protein–coupled receptor), in the kidney and on cells of the osteoblast lineage in bone. PTH induces the synthesis of 1,25-dihydroxyvitamin D3 by the kidney, which acts on the intestine to increase uptake of Ca2+. PTH-PTHR1 binding facilitates increased renal reabsorption of Ca2 and causes phosphaturia by downregulation of sodium/phosphate transporters. In bone, it causes many changes in gene expression through a number of signal transduction pathways in cells of the osteoblastic lineage, resulting in either catabolic or anabolic effects on bone. Because of the latter effects, PTH (1–34; teriparatide) was approved for treatment of osteoporosis. There are many diseases associated with each of these constituent parts, and these are described in the chapter. There are still gaps in our knowledge, and we have attempted to point these out.
Biology of the extracellular calcium-sensing receptor
2019, Principles of Bone BiologyCalcium-sensing receptors (CaSRs) were postulated long before receptor cDNA clones became available in the 1990s and definitively identified this molecule as a G-protein-coupled receptor superfamily member and a member of subfamily C. Unsuspected was the CaSR's moderate homology with metabotropic glutamate, type B gamma aminobutyric acid receptors, and taste and pheromone receptors. Rapid progress was made with molecular probes in hand in identifying this essential sensing and signaling molecule as the basis for human disorders of extracellular calcium sensing—namely familial hypocalcemia hypercalcemia, neonatal severe primary hyperparathyroidism, and autosomal dominant hypocalcemia—and as playing a role in the more common form of hyperparathyroidism accompanying renal failure and in primary hyperparathyroidism due to adenomas or hyperplasia. Rapidly, lead compounds were studied in human clinical trials and became key compounds in the treatment of renal secondary hyperparathyroidism, parathyroid cancer, and primary hyperparathyroidism. A large body of evidence accumulated in subsequent years showing that the CaSR plays essential modulatory roles in both calciotropic and noncalciotropic actions in vivo. Many of these key tissues and the roles of CaSRs and their signaling pathways are described in this chapter. It has become clear that CaSRs are important not only in controlling parathyroid hormone secretion and renal calcium excretion but also in skeletal homeostasis, cancer, epidermal differentiation, and lactation, to name just a few functions. Therapeutics targeted to the unique receptor-coupled signaling pathways in these divergent cell systems are a goal for further research and potential drug development.
Calcium-sensing receptor
2018, Encyclopedia of Endocrine DiseasesExtracellular calcium is essential to assure metabolic functions in different cells. Cellular response to its changes is achieved through the calcium-sensing receptor (CaSR) localized on the plasma membrane. Its presence in parathyroid glands and kidney tubules is recognized as a key factor for the homeostasis of calcium, because it enables these cells to regulate parathyroid hormone secretion and tubular calcium reabsorption. CaSR is also crucial for bone cell activity in skeleton development and bone remodeling. Activating or inactivating CaSR mutations cause hypercalcemic or hypocalcemic disorders, whereas CaSR polymorphic variants may contribute to individual variability of serum calcium concentrations.
Familial disorders of parathyroid glands
2017, Diagnostic HistopathologyCitation Excerpt :The extracellular calcium sensing receptor (CASR) detects alterations in calcium levels and modulates secretion of PTH and urinary calcium excretion. Loss of function or inactivating CASR mutation causes decreased calcium sensitivity of parathyroid and kidney and PTH-dependent hypercalcaemia.21 Heterozygous inactivating CASR mutation causes familial hypocalciuric hypercalcaemia (FHH) type 1.22
The molecular mechanisms underlying familial parathyroid diseases continue to be elucidated. The mechanisms of familial parathyroid diseases are better understood than many sporadic parathyroid diseases. Familial parathyroid disease is associated with multiple endocrine neoplasia type 1 which is associated with MEN1 mutation, multiple endocrine neoplasia type 2A caused by RET mutation, and multiple endocrine neoplasia type 4 is caused with CDKN1B mutation. Sporadic parathyroid tumours are identified with mutations of MEN1 but generally not of RET. CDKN1B mutations are also identified in sporadic forms of primary hyperparathyroidism, although very rarely. Calcium sensing receptor gene mutations are involved in familial hyperparathyroidism and hypoparathyroidism, but are generally not identified in sporadic parathyroid tumours. However, the HPRT2 (CDC73) gene, which is mutated in hyperparathyroidism jaw-tumour syndrome and a subset of cases of familial isolated hyperparathyroidism, is frequently mutated in sporadic parathyroid carcinomas. Germline activating GCM2 mutations were recently found associated with a subset of familial isolated hyperparathyroidism. Parafibromin, a protein encoded by HPRT2, has been used in the diagnostic setting. The understanding and pathogenesis of parathyroid disease continues to evolve.