Function of the calcium sensing receptor in the breast

描述（由申请人提供）：钙感应受体（CaR）是一种G蛋白偶联，7跨膜，细胞表面受体（GPCR），结合钙离子并允许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中心作用。此外，它在许多其他细胞类型中表达，包括乳腺上皮细胞（MECs）。在妊娠期快速增殖的mec中，CaR的表达水平较低，但在哺乳期开始时，CaR的表达水平大幅上调。这使得乳腺成为钙感知器官，在哺乳期积极参与调节全身钙代谢。在正常的mec中，CaR的激活抑制PTHrP的分泌，但促进钙转运到乳汁中。因此，如果向乳腺输送的钙减少，mec转运的钙减少，分泌的PTHrP增多。循环PTHrP的增加，反过来，激活骨吸收，从骨骼中释放钙，用于产奶。因此，在哺乳期，钙- car - pthrp乳腺轴模仿钙- car - pth甲状旁腺轴通常负责全身钙稳态。我们观察到，恶性转化改变了CaR和PTHrP之间的关系，因此乳腺癌细胞对钙的反应是刺激PTHrP的产生，而不是抑制PTHrP的产生，它们应该抑制PTHrP的产生。同样，CaR的激活抑制正常细胞的增殖，但刺激乳腺癌细胞的增殖。我们假设这些CaR调节恶性乳腺细胞与正常乳腺细胞的增殖和PTHrP分泌的改变有助于乳腺肿瘤的进展和骨转移的发展。为了研究这些可能性，我们概述了三个具体目标。目的1将检验PKC磷酸化的CaR是否会改变g蛋白的使用以及cAMP和PTHrP的产生，以响应恶性乳腺细胞与正常乳腺细胞对钙的反应。目的2将在小鼠模型中检查CaR基因的破坏是否会影响乳腺肿瘤的发生和进展。它还将确定肿瘤CaR表达是否能预测大量乳腺癌患者的预后。目的3将研究CaR刺激PTHrP的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. PUBLIC HEALTH RELEVANCE: Breast cancer is the most common neoplasm afflicting women in the US and other developed countries. This disease causes much suffering, is responsible for a large number of premature deaths and costs the US economy a great amount each year. The source of most morbidity and mortality from breast cancer is not the primary tumor itself, but rather metastases. Breast cancer is particularly prone to spread to the skeleton. It is estimated that 80% - 90% of patients with metastatic breast cancer will develop bone lesions. Bone metastases cause intractable pain, pathological fracture, hypercalcemia and spinal cord compression. They also herald mortality, as skeletal lesions cannot be cured at present. Our preliminary data suggest that the calcium sensing receptor (CaR) may contribute to the development of breast cancer and/or its bone metastases by stimulating parathyroid hormone-related protein (PTHrP) production. In contrast, during lactation, the normal breast participates in the regulation of bone metabolism by inhibiting PTHrP production. Our goal in these studies is to determine how malignant transformation alters the regulation of PTHrP production by the CaR and to determine if the CaR contributes to the development of breast cancer and/or its spread to the skeleton in animal models. It is possible that drugs developed to manipulate CaR signaling for bone and parathyroid diseases may also be effective for breast cancer.