Gudermann T, Birnbaumer M, Birnbaumer L
Department of Cell Biology, Baylor College of Medicine, Houston, Texas 77030.
J Biol Chem. 1992 Mar 5;267(7):4479-88.
The murine receptor for luteinizing hormone (LHR) was cloned and expressed in L cells. This LHR (mature protein of 674 amino acids) is very similar to that of the rat (same length, 36 amino acid differences) but differs significantly more from that of man (673 amino acids, 109 differences). Expression of the murine LHR in L cells led to the appearance of binding sites for human chorionic gonadotropin (hCG) with a Kd of 150 pM and an LH- and hCG-stimulable adenylyl cyclase activity (EC50 = 50-100 pM hCG). Upon labeling pools of phosphoinositides with [3H]myo-inositol, L cells expressing the murine LHR responded to hCG with an increase in their rate of phosphoinositide hydrolysis (EC50 = 2,400 pM hCG). This was accompanied by an increase in intracellular Ca2+ [( Ca2+]i), as determined by the Fura2 method. This increase in [Ca2+]i in response to hCG was dependent on the LHR, for HCG did not affect [Ca2+]i in L cells not expressing the LHR. The effect was not due to the cAMP-forming activity of the LH receptor, for neither forskolin nor prostaglandin E1, which both increase cAMP levels in L cells, had a similar effect in either control or LHR-expressing cells and isoproterenol had no effect in L cells expressing a functionally active hamster beta-adrenergic receptor. The effect was also not due to overexpression of a Gs-coupled receptor, for L cells expressing 8-fold higher levels of the human V2 vasopressin receptor did not mimic the Ca(2+)-mobilizing response of the LH receptor. We conclude that the LH receptor has the capability of activating two intracellular signaling pathways: one leading to stimulation of adenylyl cyclase and resulting in increases in cAMP and a second leading to stimulation of phospholipase C and resulting in formation of inositol phosphates and elevations in [Ca2+]i. These data correlate positively with and provide a mechanistic explanation for previous reports on the ability of hCG to mobilize phosphoinositides and increasing [Ca2+]i in luteal and granulosa cells (e.g. Davis, J. S., West, L. A., and Farese, R. V. (1984) J. Biol. Chem. 259, 15028-15034).
促黄体生成素（LHR）的小鼠受体被克隆并在L细胞中表达。这种LHR（674个氨基酸的成熟蛋白）与大鼠的LHR非常相似（长度相同，有36个氨基酸差异），但与人类的LHR差异更大（673个氨基酸，109个差异）。小鼠LHR在L细胞中的表达导致出现了人绒毛膜促性腺激素（hCG）的结合位点，解离常数（Kd）为150 pM，且具有LH和hCG刺激的腺苷酸环化酶活性（半数有效浓度（EC50）= 50 - 100 pM hCG）。在用[3H]肌醇标记磷酸肌醇库后，表达小鼠LHR的L细胞对hCG的反应是磷酸肌醇水解速率增加（EC50 = 2400 pM hCG）。这伴随着细胞内Ca2+浓度（[Ca2+]i）的增加，这是通过Fura2方法测定的。hCG引起的[Ca2+]i增加依赖于LHR，因为hCG对未表达LHR的L细胞中的[Ca2+]i没有影响。这种效应不是由于LH受体的cAMP形成活性，因为无论是福斯可林还是前列腺素E1（两者都能增加L细胞中的cAMP水平）在对照细胞或表达LHR的细胞中都没有类似的效应，而异丙肾上腺素对表达功能性活性仓鼠β - 肾上腺素能受体的L细胞没有影响。这种效应也不是由于Gs偶联受体的过表达，因为表达人类V2血管加压素受体水平高8倍的L细胞并没有模拟LH受体的Ca(2+)动员反应。我们得出结论，LH受体有能力激活两条细胞内信号通路：一条导致腺苷酸环化酶的刺激并导致cAMP增加，另一条导致磷脂酶C的刺激并导致肌醇磷酸的形成和[Ca2+]i升高。这些数据与之前关于hCG在黄体细胞和颗粒细胞中动员磷酸肌醇和增加[Ca2+]i能力的报道呈正相关，并为其提供了一个机制解释（例如Davis, J. S., West, L. A., and Farese, R. V. (1984) J. Biol. Chem. 259, 15028 - 15034）。
