Regulation of low density lipoprotein receptor gene expression in cultured human granulosa cells: roles of human chorionic gonadotropin, 8-bromo-3',5'-cyclic adenosine monophosphate, and protein synthesis.
Treatment of human granulosa cells with human CG (hCG) or an analog of its second messenger, cAMP, promotes a rapid increase in low density lipoprotein (LDL) receptor mRNA content. After 1 h of treatment with 8-bromo-cAMP, an appreciable increase in hybridizable LDL receptor mRNA was found which increased to apparently maximal levels within 4-6 h. Treatment of the granulosa cells with 25-hydroxycholesterol, in the presence of aminoglutethimide, resulted in a reduction in LDL receptor mRNA content within 6 h of treatment. However, hCG or 8-bromo-cAMP were able to stimulate an increase in LDL receptor mRNA content in the presence of this inhibitory signal. We further investigated the mechanism by which tropic agents increased mRNA content. While inhibition of RNA synthesis with actinomycin D blocked the hCG or cAMP-induced rise in LDL receptor mRNA content, inhibition of protein synthesis with cycloheximide augmented basal or hCG- or cAMP-stimulated LDL receptor mRNA levels. We conclude that human steroidogenic cells possess a cAMP-mediated mechanism for rapid upregulation of LDL receptor mRNA which is distinct from, and supercedes, cholesterol negative feedback of LDL receptor gene expression. The actions of hCG and 8-bromo-cAMP do not require ongoing protein synthesis. Indeed, a cycloheximide-sensitive mechanism modulates receptor mRNA levels in these cells such that the effects of hCG and 8-bromo-cAMP are enhanced when cells are pretreated with this drug.
Golos
T G
TG
Department of Obstetrics and Gynecology, University of Pennsylvania, Philadelphia 19104.
Strauss
J F
JF
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000616:Aminoglutethimide / Q000494:pharmacology; D002478:Cells, Cultured; D006063:Chorionic Gonadotropin / Q000494:pharmacology*; D000242:Cyclic AMP / Q000502:physiology*; D003513:Cycloheximide / Q000494:pharmacology; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects; D005796:Genes / Q000187:drug effects; D006107:Granulosa Cells / Q000378:metabolism*; D006801:Humans; D006888:Hydroxycholesterols / Q000494:pharmacology; D010957:Plasmids; D014176:Protein Biosynthesis / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics; D011973:Receptors, LDL / Q000235:genetics*; D014158:Transcription, Genetic / Q000187:drug effects
D006063:Chorionic Gonadotropin; D006888:Hydroxycholesterols; D012333:RNA, Messenger; D011973:Receptors, LDL; D000616:Aminoglutethimide; D015124:8-Bromo Cyclic Adenosine Monophosphate; C007997:25-hydroxycholesterol; D003513:Cycloheximide; D000242:Cyclic AMP