Transcription and post-transcriptional regulation of luteotropin/chorionic gonadotropin receptor by the agonist in Leydig cells.
Porcine Leydig, cultured in a chemically defined medium, express luteotropin/human chorionic gonadotropin (LH/hCG) receptor and mRNA transcripts of several sizes (7.6, 6.7, 5.6, 4.7, 4, 2.6 and 1.4 kb). Incubation of these cells with hCG results in a concentration-dependent decrease of both LH/hCG receptor number and of all mRNA transcripts with a half-maximal at 0.01 nM. Time-course analysis of the effects of maximal (1 nM) concentration of hCG on both receptor number and mRNA levels results in a lag period of about 6-8 h. Thereafter, the receptor number progressively declines to reach a low point (20% of control) at 36 h, whereas more than 80% of receptor mRNA were lost between 8-12 h after addition of the hormone. By nuclear run-on assays, we showed that hCG caused a slight reduction (13 +/- 2%) in LH/hCG receptor gene transcription, which could not explain the rapid and pronounced mRNA decline observed between 8-12 h. In fact, we estimated that hCG reduced 10-fold (from < 22 h to 2 h) the half-life of LH/hCG receptor mRNA. Both actinomycin D and cycloheximide blocked the hCG-induced decrease in both receptor number and mRNA levels. These results indicate that the main mechanism by which hCG regulates its own receptor is by inducing a decrease in the stability of its own receptor mRNA and this effect requires induction of transcription and translation, presumably leading to synthesis of a labile factor(s) which favors the degradation of LH/hCG mRNA. Most of the effects of hCG are mediated by cAMP since treatment of cells with its 8-bromo derivative leads to a similar reduction in the level of LH/hCG receptor and mRNA. Finally, the effects of hCG are reversible, since after withdrawal of the hormone there was a recovery of receptor mRNA followed by receptor number.
Chuzel
F
F
INSERM-INRA U 307, Hôpital Debrousse, Lyon, France.
Schteingart
H
H
Vigier
M
M
Avallet
O
O
Saez
J M
JM
D000818:Animals; D002478:Cells, Cultured; D006063:Chorionic Gonadotropin / Q000494:pharmacology; D015536:Down-Regulation; D006801:Humans; D007985:Leydig Cells / Q000378:metabolism*; D008297:Male; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000378:metabolism; D011974:Receptors, LH / Q000187:drug effects / Q000378:metabolism*; D013552:Swine; D014158:Transcription, Genetic
D006063:Chorionic Gonadotropin; D012333:RNA, Messenger; D011974:Receptors, LH