Function of the Calcium Sensing Receptor in the Breast

描述（由申请人提供）：钙敏感受体（CaR）是一种G蛋白偶联的、7跨膜的细胞表面受体（GPCR），可结合钙离子并使细胞对细胞外钙浓度的变化做出反应。它通过调节甲状旁腺激素分泌和肾钙处理在全身矿物质代谢中起核心作用。此外，它也由许多其他细胞类型表达，包括乳腺上皮细胞（MEC）。在妊娠期快速增殖的MEC中，CaR的表达较低，但在泌乳开始时大大上调。这使得乳腺成为一个钙敏感器官，在哺乳期间积极参与全身钙代谢的调节。在正常MEC中，CaR的激活抑制PTHrP分泌，但促进钙转运到乳汁中。因此，如果钙输送到乳腺福尔斯下降，MEC运输更少的钙和分泌更多的PTHrP。循环PTHrP的增加反过来激活骨吸收并从骨骼释放钙用于产奶。因此，在哺乳期，钙-CaR-PTHrP乳腺轴模拟钙-CaR-PTH甲状旁腺轴通常负责全身钙稳态。我们已经观察到，恶性转化改变了CaR和PTHrP之间的关系，这样乳腺癌细胞刺激PTHrP的生产响应钙，而不是抑制PTHrP的生产，因为他们应该。类似地，CaR的激活抑制正常细胞的增殖，但刺激乳腺癌细胞的增殖。我们推测，这些改变在如何钙调节增殖和PTHrP分泌恶性与正常乳腺细胞的乳腺肿瘤的进展和骨转移的发展作出贡献。为了研究这些可能性，我们概述了三个具体目标。目的1将检查是否PKC磷酸化的钙受体改变G蛋白的使用和cAMP和PTHrP的生产在恶性与正常乳腺细胞中响应钙。目的2将检查CaR基因的破坏是否会影响小鼠模型中乳腺肿瘤的发展和进展。它还将确定肿瘤CaR表达是否能预测大型乳腺癌患者队列的结果。目的3将检查CaR刺激PTHrP产生是否有助于体内溶骨性骨转移的发展。

DESCRIPTION (provided by applicant): The calcium-sensing receptor (CaR) is a G protein-coupled, 7 transmembrane-spanning, cell surface receptor (GPCR) that binds calcium ions and allows cells to respond to changes in extracellular calcium concentrations. It plays a central role in systemic mineral metabolism by regulating parathyroid hormone secretion and renal calcium handling. In addition, it is expressed by many other cell types, including mammary epithelial cells (MECs). Expression of the CaR is low in rapidly proliferating MECs during pregnancy, but is greatly upregulated at the start of lactation. This allows the mammary gland to become a calcium-sensing organ that actively participates in the regulation of systemic calcium metabolism during lactation. In normal MECs, activation of the CaR inhibits PTHrP secretion but promotes calcium transport into milk. Therefore, if calcium delivery to the mammary gland falls, MECs transport less calcium and secrete more PTHrP. The increase in circulating PTHrP, in turn, activates bone resorption and liberates calcium from the skeleton for milk production. Thus, during lactation, a calcium-CaR-PTHrP mammary axis mimics the calcium-CaR-PTH parathyroid axis normally responsible for systemic calcium homeostasis. We have observed that malignant transformation alters the relationship between the CaR and PTHrP, such that breast cancer cells stimulate PTHrP production in response to calcium, rather than inhibiting PTHrP production, as they should. Similarly, activation of the CaR inhibits proliferation in normal cells, but stimulates proliferation in breast cancer cells. We hypothesize that these alterations in how the CaR regulates proliferation and PTHrP secretion in malignant versus normal breast cells contribute to the progression of breast tumors and the development of bone metastases. In order to investigate these possibilities, we outline three specific aims. Aim 1 will examine whether PKC phosphorylation of the CaR alters G-protein usage and cAMP and PTHrP production in response to calcium in malignant versus normal breast cells. Aim 2 will examine if disruption of the CaR gene will affect the development and progression of mammary tumors in mouse models. It will also determine if tumor CaR expression predicts outcome in a large cohort of patients with breast cancer. Aim 3 will examine if stimulation of PTHrP production by the CaR contributes to the development of osteolytic bone metastases in vivo.