Epidermal growth factor, a phorbol ester, and 3',5'-cyclic adenosine monophosphate decrease the transcription of the luteinizing hormone/chorionic gonadotropin receptor gene in MA-10 Leydig tumor cells.
In a recent series of experiments we have shown that the previously recognized ability of mouse epidermal growth factor (mEGF), cAMP, or phorbol 12-myristate 13-acetate (PMA) to reduce the density of LH/CG receptors in MA-10 cells is secondary to a reduction in receptor messenger RNA (mRNA). As a follow-up to these studies we now present experiments designed to determine if the reduction in LH/CG receptor mRNA is due to a decrease in transcription of the receptor gene and/or an increase in the rate of degradation of the mRNA. The potential effects of mEGF, cAMP, or PMA on the degradation of the LH/CG receptor mRNA were measured in MA-10 cells treated with Actinomycin D or in kidney cells permanently transfected with the LH/CG receptor complementary DNA driven by a heterologous promoter. Both experimental strategies revealed that none of these compounds increase the rate of degradation of the receptor mRNA. If anything, a stabilizing effect was noted. The potential effects of mEGF, cAMP, or PMA on the transcription of the LH/CG receptor gene in MA-10 cells were measured using nuclear run-off assays. All three compounds induced a rapid decrease in the transcription of the LH/CG receptor gene. The time course of these effects is similar, and by 2 h all of the stimuli had decreased transcription to 15-30% of control. Our studies show that the mEGF-, cAMP- and PMA-induced down-regulation of the LH/CG receptor in MA-10 cells is primarily (if not entirely) due to a decrease in the transcription of the receptor gene.
Nelson
S
S
Department of Pharmacology, The University of Iowa College of Medicine, Iowa City, Iowa 52242.
Ascoli
M
M
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology*; D004247:DNA / Q000235:genetics; D003609:Dactinomycin / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D007984:Leydig Cell Tumor / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D011974:Receptors, LH / Q000235:genetics*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014158:Transcription, Genetic / Q000187:drug effects*; D014162:Transfection; D014407:Tumor Cells, Cultured
D012333:RNA, Messenger; D011974:Receptors, LH; D003609:Dactinomycin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D004815:Epidermal Growth Factor; D004247:DNA; D000242:Cyclic AMP; D013755:Tetradecanoylphorbol Acetate