Progesterone can participate in down-regulation of the luteinizing hormone receptor gene expression and function in cultured murine Leydig cells.
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.
El-Hefnawy
T
T
Department of Physiology, University of Turku, Finland.
Huhtaniemi
I
I
D000616:Aminoglutethimide / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D006063:Chorionic Gonadotropin / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis; D015536:Down-Regulation / Q000187:drug effects; D016758:Genes, jun; D006854:Hydrocortisone / Q000494:pharmacology; D066298:In Vitro Techniques; D007985:Leydig Cells / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D051379:Mice; D011374:Progesterone / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011974:Receptors, LH / Q000235:genetics* / Q000378:metabolism*; D013261:Sterols / Q000096:biosynthesis; D014162:Transfection
D006063:Chorionic Gonadotropin; D012333:RNA, Messenger; D011974:Receptors, LH; D013261:Sterols; D000616:Aminoglutethimide; D011374:Progesterone; D000242:Cyclic AMP; D006854:Hydrocortisone