El-Hefnawy T, Huhtaniemi I
Department of Physiology, University of Turku, Finland.
Mol Cell Endocrinol. 1998 Feb;137(2):127-38. doi: 10.1016/s0303-7207(98)00002-1.
The intratesticular concentration of progesterone (P) rises up to the micromolar range during high-dose luteinizing hormone (LH)/hCG stimulation. The aim of this study was to examine whether P is involved in the concomitant down-regulation of the LH receptor (R) function. The effects were tested in a mouse Leydig tumor cell line (mLTC-1) and in Percoll-purified adult mouse Leydig cells. Pre-incubation of the mLTC-1 cells for 48 h with P (1-10 micromol/l) decreased in dose-dependent fashion their specific binding of [125I]iodo-hCG as well as the hCG-induced cAMP production (down to 65 and 40% respectively, of controls, P < 0.01). Similar effect of P on hCG-induced cAMP production was observed in adult mouse Leydig cells following a 24 h incubation in the presence of P (0.3-10 micromol/l). In addition, P treatment significantly inhibited the expression of a transiently transfected murine LHR promoter (715 or 950 bp of the 5' untranslated region)-luciferase fusion constructs in mLTC-1 cells (down to 50% of control, P < 0.01). In accordance, a 6-12 h culture in the presence of 5-10 micromol/l of P showed significant down-regulatory effects on the steady state levels of LHR-mRNA in mLTC-1 cells. These inhibitory effects of P on the LHR expression and function were mimicked by similar concentrations of cortisol, but not by testosterone or estradiol. Blocking the steroid synthesis of mLTC-1 cells with 86 micromol/l of aminoglutethimide (AMG) partially reversed the down-regulating effect of hCG on the LHR-mRNA. Moreover, a 24 h culture in the presence of AMG showed an up-regulating effect on expression of the LHR promoter-luciferase constructs, and including hCG (50 microg/l) in the culture medium enhanced this effect. Hence, in the absence of steroidogenesis, hCG up-regulates the LHR promoter expression. In conclusion, we present here a novel short-loop regulatory mechanism in murine Leydig cells where P exerts a negative effect on LHR expression and function. Since Leydig cell P production is dramatically increased during high-dose stimulation with LH/hCG, due to blockade of C21 steroid side chain cleavage, the present findings offer a function for this steroid in the LHR down-regulation.
在高剂量促黄体生成素（LH）/人绒毛膜促性腺激素（hCG）刺激期间，睾丸内孕酮（P）浓度升高至微摩尔范围。本研究的目的是检测P是否参与LH受体（R）功能的伴随性下调。在小鼠睾丸间质细胞瘤细胞系（mLTC-1）和经Percoll纯化的成年小鼠睾丸间质细胞中测试了其作用。用P（1 - 10微摩尔/升）预孵育mLTC-1细胞48小时，以剂量依赖性方式降低了它们对[125I]碘-hCG的特异性结合以及hCG诱导的cAMP产生（分别降至对照的65%和40%，P < 0.01）。在成年小鼠睾丸间质细胞中，在P（0.3 - 10微摩尔/升）存在下孵育24小时后，观察到P对hCG诱导的cAMP产生有类似作用。此外，P处理显著抑制了mLTC-1细胞中瞬时转染的小鼠LHR启动子（5'非翻译区的715或950碱基对）-荧光素酶融合构建体的表达（降至对照的50%，P < 0.01）。相应地，在5 - 10微摩尔/升P存在下培养6 - 12小时对mLTC-1细胞中LHR-mRNA的稳态水平显示出显著的下调作用。P对LHR表达和功能的这些抑制作用可被类似浓度的皮质醇模拟，但不能被睾酮或雌二醇模拟。用86微摩尔/升氨鲁米特（AMG）阻断mLTC-1细胞的类固醇合成部分逆转了hCG对LHR-mRNA的下调作用。此外，在AMG存在下培养24小时对LHR启动子-荧光素酶构建体的表达显示出上调作用，并且在培养基中加入hCG（50微克/升）可增强这种作用。因此，在没有类固醇生成的情况下，hCG上调LHR启动子表达。总之，我们在此提出了一种小鼠睾丸间质细胞中的新型短环调节机制，其中P对LHR表达和功能发挥负性作用。由于在LH/hCG高剂量刺激期间，由于C21类固醇侧链裂解的阻断，睾丸间质细胞P产生显著增加，本研究结果为该类固醇在LHR下调中的作用提供了依据。
