Kifor O, Diaz R, Butters R, Kifor I, Brown E M
Endocrine-Hypertension Division and Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA.
J Biol Chem. 1998 Aug 21;273(34):21708-13. doi: 10.1074/jbc.273.34.21708.
Parathyroid cells have an intracellular machinery for parathyroid hormone (PTH) secretion that is inversely regulated by the extracellular calcium concentration (Ca2+o). The recently characterized Ca2+o-sensing receptor (CaR) is a G protein-coupled, seven-transmembrane receptor mediating the inhibitory effects of high Ca2+o on PTH secretion. The CaR's precise cell surface localization and the signal transduction pathway(s) mediating its inhibitory effects on PTH secretion have not been characterized fully. Here, we demonstrate that the CaR resides within caveolin-rich membrane domains in bovine parathyroid cells. Chief cells within bovine parathyroid glands exhibit a similar pattern of staining for caveolin-1 and for alkaline phosphatase, a glucosylphosphatidylinositol-anchored protein often enriched in caveolae. Purified caveolin-enriched membrane fractions (CEMF) from bovine parathyroid cells are highly enriched in the CaR and alkaline phosphatase. Other signaling proteins, including Gq/11, eNOS, and several protein kinase C isoforms (i.e. alpha, delta, and zeta), are also present in CEMF. Activation of the CaR by high Ca2+o increases tyrosine phosphorylation of caveolin-1 in CEMF, suggesting that CaR-mediated signal transduction potentially involved in Ca2+o-regulated processes in parathyroid cells occur in caveolae-like domains.
甲状旁腺细胞具有用于甲状旁腺激素（PTH）分泌的细胞内机制，该机制受细胞外钙浓度（Ca2+o）的反向调节。最近鉴定出的Ca2+o-传感受体（CaR）是一种G蛋白偶联的七跨膜受体，介导高Ca2+o对PTH分泌的抑制作用。CaR在细胞表面的精确定位以及介导其对PTH分泌抑制作用的信号转导途径尚未完全明确。在此，我们证明CaR存在于牛甲状旁腺细胞中富含小窝蛋白的膜结构域内。牛甲状旁腺中的主细胞对小窝蛋白-1和碱性磷酸酶（一种通常在小窝中富集的糖基磷脂酰肌醇锚定蛋白）呈现出相似的染色模式。从牛甲状旁腺细胞中纯化的富含小窝蛋白的膜组分（CEMF）高度富集了CaR和碱性磷酸酶。其他信号蛋白包括Gq/11、内皮型一氧化氮合酶（eNOS）以及几种蛋白激酶C同工型（即α、δ和ζ）也存在于CEMF中。高Ca2+o激活CaR会增加CEMF中小窝蛋白-1的酪氨酸磷酸化，这表明在类小窝结构域中可能发生了CaR介导的、参与甲状旁腺细胞中Ca2+o调节过程的信号转导。
