FUNCTION OF THE CALCIUM SENSING RECEPTOR IN THE BREAST

描述(申请人提供)：细胞外钙敏感受体(CAR)结合和信号响应钙离子。通过协调甲状旁腺激素(PTH)的分泌和肾钙的处理，以应对细胞外钙的波动，CAR对维持全身钙平衡至关重要。这种受体在乳腺组织和乳腺癌中也有表达。我们发现，CAR在哺乳期正常小鼠乳腺中高表达，但在妊娠期不表达。在体外和体内，CAR的激活抑制了乳房上皮细胞(MEC)甲状旁腺激素相关蛋白(PTHrP)的产生。此外，我们还表明，CAR信号促进了钙和水进入牛奶的跨上皮运输。基于这些数据，我们提出了一种新的范式：乳腺在哺乳期成为钙敏感器官，并积极参与全身钙和骨稳态的调节。我们认为，CAR在向乳腺的钙供应减少时增加PTHrP的分泌，以增加母体的骨吸收，防止母体低钙血症，并恢复供乳汁生产的钙供应。我们还提出，乳房车将钙输送到牛奶中与母亲的钙供应相匹配。如果钙的供应变得有限，这将通过减少需求来防止母亲发生严重的低钙血症。最后，考虑到在MEC高度增殖的妊娠期CAR表达的丧失，我们假设CAR信号抑制MEC的增殖并促进MEC的分化。为了检验这些假设，我们提出了4个具体目标。目的1将检测乳腺特异CAR基因缺失的小鼠的乳腺甲状旁腺素释放、水和钙运输以及母体骨骼和矿物质代谢。目的研究CAR信号对微血管内皮细胞质膜Ca++/ATPase 2(PMCA2)的调节作用。目标3将研究介导乳房车调节PTHrP产生的信号通路。目的4将通过在转基因小鼠的乳腺中表达CAR的激活突变体来检测CAR信号对MEC增殖的影响。我们相信，这些研究将加深我们对CAR生理学的理解，并将有助于理解乳腺癌患者的骨质疏松和骨转移。

DESCRIPTION (provided by applicant): The extracellular calcium-sensing receptor (CaR) binds and signals in response to Ca++ ions. By coordinating parathyroid hormone (PTH) secretion and renal calcium handling in response to fluctuations in extracellular Ca++, the CaR is critical to maintaining systemic calcium homeostasis. This receptor is also expressed in breast tissue and in breast cancers. We have found that the CaR is highly expressed in the normal mouse mammary gland during lactation, but is not expressed during pregnancy. Activation of the CaR inhibits the production of parathyroid hormone-related protein (PTHrP) by lactating mammary epithelial cells (MECs) both in vitro and in vivo. Furthermore, we have shown that CaR signaling promotes the transepithelial transport of calcium and water into milk. Based on these data, we propose a new paradigm: that the mammary gland becomes a calcium-sensing organ during lactation and actively participates in the regulation of systemic calcium and bone homeostasis. We propose that the CaR increases PTHrP secretion when calcium delivery to the mammary gland falls in order to increase maternal bone resorption, protect against maternal hypocalcemia and restore the supply of calcium for milk production. We also propose that the mammary CaR matches the transport of calcium into milk with the maternal supply of calcium. This would protect against severe hypocaclemia in the mother by reducing demand if supplies of calcium became limiting. Finally, given the loss of CaR expression during pregnancy, a time of intense MEC proliferation, we hypothesize that CaR signaling inhibits MEC proliferation and promotes MEC differentiation. In order to test these hypotheses we propose 4 Specific Aims. Aim 1 will examine mammary PTHrP production, water and calcium transport and maternal bone and mineral metabolism in a mouse model of mammary-specific CaR gene deletion. Aim 2 will examine the regulation of the plasma membrane Ca++/ATPase 2 (PMCA2) by CaR signaling in MECs. Aim 3 will examine the signaling pathways that mediate the mammary CaR's regulation of PTHrP production. Aim 4 will examine the effects of CaR signaling on MEC proliferation by expressing an activated mutant of the CaR in the mammary gland during pregnancy in transgenic mice. We believe that these studies will deepen our understanding of the physiology of the CaR and will contribute to an understanding of both osteoporosis and bone metastases in patients with breast cancer.