Function of the calcium sensing receptor in the breast

描述(申请人提供)：钙敏感受体(CAR)是一种G蛋白偶联的跨膜细胞表面受体(GPCR)，它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的分泌和肾钙的处理，在全身矿物质代谢中发挥中心作用。此外，它由许多其他类型的细胞表达，包括乳腺上皮细胞(MECs)。在妊娠期间快速增殖的微血管内皮细胞中，CAR的表达很低，但在哺乳期开始时显著上调。这使得乳腺成为钙敏感器官，积极参与哺乳期全身钙代谢的调节。在正常的微血管内皮细胞中，CAR的激活抑制了PTHrP的分泌，但促进了钙向牛奶中的运输。因此，如果向乳腺的钙输送减少，微血管内皮细胞运输的钙减少，分泌更多的PTHrP。循环中PTHrP的增加反过来又激活了骨吸收，并从骨骼中释放出钙来生产牛奶。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。我们观察到恶性转化改变了CAR和PTHrP之间的关系，使得乳腺癌细胞对钙的反应刺激PTHrP的产生，而不是像它们应该的那样抑制PTHrP的产生。同样，CAR的激活抑制了正常细胞的增殖，但刺激了乳腺癌细胞的增殖。我们推测，CAR调节恶性乳腺细胞的增殖和PTHrP分泌的这些变化有助于乳腺肿瘤的进展和骨转移的发展。为了调查这些可能性，我们概述了三个具体目标。目的1将检测CAR的PKC磷酸化是否改变G蛋白的使用以及cAMP和PTHrP的产生，以响应钙在恶性乳腺细胞和正常乳腺细胞中的反应。目标2将检查CAR基因的破坏是否会影响小鼠模型乳腺肿瘤的发展和进展。它还将确定肿瘤CAR的表达是否可以预测一大批乳腺癌患者的预后。目的3研究CAR刺激PTHrP的产生是否有助于体内溶骨性骨转移的发生。 与公共卫生相关：乳腺癌是困扰美国和其他发达国家女性的最常见肿瘤。这种疾病造成了许多痛苦，导致了大量的过早死亡，每年给美国经济造成了巨大的损失。乳腺癌的大多数发病率和死亡率的来源不是原发肿瘤本身，而是转移。乳腺癌特别容易扩散到骨骼。据估计，80%-90%的转移性乳腺癌患者会发生骨病变。骨转移导致顽固性疼痛、病理性骨折、高钙血症和脊髓压迫。它们还预示着死亡，因为骨骼损伤目前无法治愈。我们的初步数据表明，钙敏感受体(CAR)可能通过刺激甲状旁腺激素相关蛋白(PTHrP)的产生而参与乳腺癌的发展和/或其骨转移。相反，在哺乳期，正常乳房通过抑制甲状旁腺激素释放蛋白的生成来参与骨代谢的调节。我们在这些研究中的目标是确定恶性转化如何改变CAR对PTHrP产生的调节，并在动物模型中确定CAR是否有助于乳腺癌的发展和/或其向骨骼的扩散。为治疗骨骼和甲状旁腺疾病而开发的控制CAR信号的药物也有可能对乳腺癌有效。

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.