Switching of G-protein usage by the calcium-sensing receptor reverses its effect on parathyroid hormone-related protein secretion in normal versus malignant breast cells
Switching of G-protein usage by the calcium-sensing receptor reverses its effect on parathyroid hormone-related protein secretion in normal versus malignant breast cells
复制标题
DOI：
10.1074/jbc.m801738200
复制
发表时间：
2008-09-05
影响因子：
4.8
通讯作者：
Wysolmerski, John
中科院分区：
文献类型：
--
作者：
Mamillapalli, Ramanaiah;VanHouten, Joshua;Wysolmerski, John
钙敏感受体(CAR)是一种G蛋白偶联受体，对细胞外钙作出反应并调节甲状旁腺激素的分泌。CAR也在正常乳腺上皮细胞(MMECs)上表达，它被证明可以抑制甲状旁腺激素相关蛋白(PTHrP)的分泌，并参与哺乳期钙和骨代谢的调节。与正常的乳腺细胞不同，CAR被报道能刺激乳腺癌细胞产生PTHrP。在这项研究中，我们证实了CAR抑制MMEC产生PTHrP，但刺激Comma-D细胞(永生化小鼠乳腺细胞)和MCF-7人乳腺癌细胞产生PTHrP。我们发现，细胞内cAMP的变化，而不是磷脂酶C或MAPK信号的变化，与CAR对PTHrP产生的相反作用有关。药物刺激cAMP的积累增加了正常和转化的乳腺细胞的甲状旁腺素释放。抑制蛋白激酶A活性类似于CAR激活抑制MMECs分泌PTHrP的作用，并阻断CAR刺激Comma-D和MCF-7细胞分泌PTHrP的作用。我们发现，在MMEC中，CAR与Gα(I)偶联，而在Comma-D和MCF7细胞中，CAR与Gα(S)偶联。因此，CAR对甲状旁腺素rP产生的相反影响是由于正常和转化的乳腺细胞中受体的交替G蛋白偶联。由于PTHrP导致高钙血症和骨转移，CAR改变G蛋白的使用可能有助于乳腺癌的发病。
The calcium-sensing receptor (CaR) is a G-protein-coupled receptor that signals in response to extracellular calcium and regulates parathyroid hormone secretion. The CaR is also expressed on normal mammary epithelial cells (MMECs), where it has been shown to inhibit secretion of parathyroid hormone-related protein (PTHrP) and participate in the regulation of calcium and bone metabolism during lactation. In contrast to normal breast cells, the CaR has been reported to stimulate PTHrP production by breast cancer cells. In this study, we confirmed that the CaR inhibits PTHrP production by MMECs but stimulates PTHrP production by Comma-D cells (immortalized murine mammary cells) and MCF-7 human breast cancer cells. We found that changes in intracellular cAMP, but not phospholipase C or MAPK signaling, correlated with the opposing effects of the CaR on PTHrP production. Pharmacologic stimulation of cAMP accumulation increased PTHrP production by normal and transformed breast cells. Inhibition of protein kinase A activity mimicked the effects of CaR activation on inhibiting PTHrP secretion by MMECs and blocked the effects of the CaR on stimulating PTHrP production in Comma-D and MCF-7 cells. We found that the CaR coupled to G alpha(i) in MMECs but coupled to G alpha(s) in Comma-D and MCF-7 cells. Thus, the opposing effects of the CaR on PTHrP production are because of alternate G-protein coupling of the receptor in normal versus transformed breast cells. Because PTHrP contributes to hypercalcemia and bone metastases, switching of G-protein usage by the CaR may contribute to the pathogenesis of breast cancer.