title: Calcitonin-secreting cells of the thyroid express an extracellular calcium receptor gene.
abstract: Calcitonin (CT) secretion by parafollicular cells of the thyroid (C cells) is regulated by small changes in the concentration of extracellular calcium ([Ca2+]e). Elevation of [Ca2+]e elicits a rise in the C cell cytoplasmic calcium concentration and stimulates CT release. The molecular entity through which C cells detect changes in [Ca2+]e and modulate hormone secretion is unknown. Recently, an extracellular calcium-sensing receptor (CaR) complementary DNA was isolated from bovine parathyroid gland. To assess whether parathyroid cells and C cells use similar mechanisms to detect changes in ambient Ca2+, rat, human, and sheep C cells were examined for expression of the parathyroid CaR or a related receptor isoform. Reverse transcription-polymerase chain reaction analysis identified CaR transcripts in rat and human thyroid gland. Northern blot analysis demonstrated CaR messenger RNA (mRNA) in rat thyroid gland, a human medullary thyroid carcinoma (MTC) isolate, and a highly enriched preparation of sheep C cells. Rat MTC 44-2 cells, a cell line responsive to changes in [Ca2+]e, express abundant levels of CaR mRNA. Human TT cells, a C cell line lacking the extracellular calcium-sensing function, have undetectable levels of CaR mRNA by Northern blot analysis. Western blot analysis, using antiserum specific to the parathyroid CaR, detected CaR protein in rMTC 44-2, but not TT cells. Immunostaining of both dispersed sheep C cells and rat thyroid gland sections identified C cell-specific expression of the CaR protein, and in situ hybridization analysis confirmed the C cell-specific expression of CaR mRNA in the intact rat thyroid. The nucleotide sequence of the coding region of the rMTC 44-2 CaR transcripts was found to encode the same CaR protein as that expressed in the parathyroid and kidney. The results demonstrate that C cells express the same extracellular calcium-sensing receptor that is found in parathyroid and kidney, and the presence of this receptor protein in C cell lines correlates with the extracellular calcium-sensing function. This CaR is likely to represent the primary molecular entity through which C cells detect changes in [Ca2+]e and control CT release, suggesting that activation of the same receptor can either stimulate or inhibit hormone secretion in different cell types.
authors.affiliation: Department of Molecular Biology, NPS Pharmaceuticals, Salt Lake City, Utah 84108, USA.
authors.forename: J E
authors.initials: JE
authors.lastname: Garrett
authors.forename: H
authors.initials: H
authors.lastname: Tamir
authors.forename: O
authors.initials: O
authors.lastname: Kifor
authors.forename: R T
authors.initials: RT
authors.lastname: Simin
authors.forename: K V
authors.initials: KV
authors.lastname: Rogers
authors.forename: A
authors.initials: A
authors.lastname: Mithal
authors.forename: R F
authors.initials: RF
authors.lastname: Gagel
authors.forename: E M
authors.initials: EM
authors.lastname: Brown
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D015153:Blotting, Western; D002116:Calcitonin / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D002417:Cattle; D002460:Cell Line; D015870:Gene Expression; D006801:Humans; D007150:Immunohistochemistry; D008969:Molecular Sequence Data; D010280:Parathyroid Glands / Q000737:chemistry; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000032:analysis / Q000737:chemistry; D012194:RNA-Directed DNA Polymerase; D051381:Rats; D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000235:genetics*; D017421:Sequence Analysis; D012756:Sheep; D013961:Thyroid Gland / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism
chemical_list: D012333:RNA, Messenger; D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface; C473605:extracellular calcium cation-sensing receptor, rat; D002116:Calcitonin; D012194:RNA-Directed DNA Polymerase; D002118:Calcium