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      The calcium-sensing receptor regulates parathyroid hormone gene expression in transfected HEK293 cells

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          Abstract

          Background

          The parathyroid calcium receptor determines parathyroid hormone secretion and the response of parathyroid hormone gene expression to serum Ca 2+ in the parathyroid gland. Serum Ca 2+ regulates parathyroid hormone gene expression in vivo post-transcriptionally affecting parathyroid hormone mRNA stability through the interaction of trans-acting proteins to a defined cis element in the parathyroid hormone mRNA 3'-untranslated region. These parathyroid hormone mRNA binding proteins include AUF1 which stabilizes and KSRP which destabilizes the parathyroid hormone mRNA. There is no parathyroid cell line; therefore, we developed a parathyroid engineered cell using expression vectors for the full-length human parathyroid hormone gene and the human calcium receptor.

          Results

          Co-transfection of the human calcium receptor and the human parathyroid hormone plasmid into HEK293 cells decreased parathyroid hormone mRNA levels and secreted parathyroid hormone compared with cells that do not express the calcium receptor. The decreased parathyroid hormone mRNA correlated with decreased parathyroid hormone mRNA stability in vitro, which was dependent upon the 3'-UTR cis element. Moreover, parathyroid hormone gene expression was regulated by Ca 2+ and the calcimimetic R568, in cells co-transfected with the calcium receptor but not in cells without the calcium receptor. RNA immunoprecipitation analysis in calcium receptor-transfected cells showed increased KSRP-parathyroid hormone mRNA binding and decreased binding to AUF1. The calcium receptor led to post-translational modifications in AUF1 as occurs in the parathyroid in vivo after activation of the calcium receptor.

          Conclusion

          The expression of the calcium receptor is sufficient to confer the regulation of parathyroid hormone gene expression to these heterologous cells. The calcium receptor decreases parathyroid hormone gene expression in these engineered cells through the parathyroid hormone mRNA 3'-UTR cis element and the balanced interactions of the trans-acting factors KSRP and AUF1 with parathyroid hormone mRNA, as in vivo in the parathyroid. This is the first demonstration that the calcium receptor can regulate parathyroid hormone gene expression in heterologous cells.

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          Most cited references46

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          Cloning and characterization of an extracellular Ca(2+)-sensing receptor from bovine parathyroid.

          E M Brown, G Gamba, D. Riccardi … (1993)
          Maintenance of a stable internal environment within complex organisms requires specialized cells that sense changes in the extracellular concentration of specific ions (such as Ca2+). Although the molecular nature of such ion sensors is unknown, parathyroid cells possess a cell surface Ca(2+)-sensing mechanism that also recognizes trivalent and polyvalent cations (such as neomycin) and couples by changes in phosphoinositide turnover and cytosolic Ca2+ to regulation of parathyroid hormone secretion. The latter restores normocalcaemia by acting on kidney and bone. We now report the cloning of complementary DNA encoding an extracellular Ca(2+)-sensing receptor from bovine parathyroid with pharmacological and functional properties nearly identical to those of the native receptor. The novel approximately 120K receptor shares limited similarity with the metabotropic glutamate receptors and features a large extracellular domain, containing clusters of acidic amino-acid residues possibly involved in calcium binding, coupled to a seven-membrane-spanning domain like those in the G-protein-coupled receptor superfamily.
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            Extracellular calcium sensing and signalling.

            M Hofer, Micah Brown (2003)
            Ca2+ is well established as an intracellular second messenger. However, the molecular identification of a detector for extracellular Ca2+--the extracellular calcium-sensing receptor--has opened up the possibility that Ca2+ might also function as a messenger outside cells. Information about the local extracellular Ca2+ concentration is conveyed to the interior of many cell types through this unique G-protein-coupled receptor. Here, we describe new emerging concepts concerning the signalling function of extracellular Ca2+, with particular emphasis on the extracellular calcium-sensing receptor.
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              Mutations in the human Ca(2+)-sensing receptor gene cause familial hypocalciuric hypercalcemia and neonatal severe hyperparathyroidism.

              Martin R. Pollak, Edward M Brown, Yah-Huei Wu Chou … (1993)
              We demonstrate that mutations in the human Ca(2+)-sensing receptor gene cause familial hypocalciuric hypercalcemia (FHH) and neonatal severe hyperparathyroidism (NSHPT), two inherited conditions characterized by altered calcium homeostasis. The Ca(2+)-sensing receptor belongs to the superfamily of seven membrane-spanning G protein-coupled receptors. Three nonconservative missense mutations are reported: two occur in the extracellular N-terminal domain of the receptor; the third occurs in the final intracellular loop. One mutated receptor identified in FHH individuals was expressed in X. laevis oocytes. The expressed wild-type receptor elicited large inward currents in response to perfused polyvalent cations; a markedly attenuated response was observed with the mutated protein. We conclude that the mammalian Ca(2+)-sensing receptor "sets" the extracellular Ca2+ level and is defective in individuals with FHH and NSHPT.
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                Author and article information

                Journal
                Journal ID (nlm-ta): BMC Biol
                Title: BMC Biology
                Publisher: BioMed Central
                ISSN (Electronic): 1741-7007
                Publication date Collection: 2009
                Publication date (Electronic): 27 April 2009
                Volume: 7
                Page: 17
                Affiliations
                [1 ]Minerva Center for Calcium and Bone Metabolism, Nephrology Services, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
                Article
                Publisher ID: 1741-7007-7-17
                DOI: 10.1186/1741-7007-7-17
                PMC ID: 2681451
                PubMed ID: 19397786
                SO-VID: bf249d5e-110d-4253-abb4-689b1bfdc3fd
                Copyright © Copyright © 2009 Galitzer et al; licensee BioMed Central Ltd.
                License:

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                Date received : 3 October 2008
                Date accepted : 27 April 2009
                Categories
                Subject: Research Article

                ScienceOpen disciplines: Life sciences
                Data availability:
                ScienceOpen disciplines: Life sciences

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