8-bromoadenosine cyclic 3',5'-phosphate rapidly increases 3-hydroxy-3-methylglutaryl coenzyme A reductase mRNA in human granulosa cells: role of cellular sterol balance in controlling the response to tropic stimulation.
Exposure of cultured human granulosa cells to 8-bromoadenosine cyclic 3',5'-phosphate (8-bromo-cAMP) resulted in a rapid increase in the content of the mRNA for 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, a rate-limiting enzyme in the de novo synthesis of cholesterol. HMG-CoA reductase mRNA levels increased within 2 h of stimulation and remained elevated for at least 6 h. Treatment of granulosa cells with 25-hydroxycholesterol, a soluble cholesterol analogue, in combination with aminoglutethimide to block conversion of cellular sterols to pregnenolone, resulted in suppression of HMG-CoA reductase mRNA. When cells were stimulated with 8-bromo-cAMP in the presence of 25-hydroxycholesterol and aminoglutethimide, the increase in HMG-CoA reductase mRNA provoked by the tropic agent was markedly attenuated. This indicates that 8-bromo-cAMP raises HMG-CoA reductase mRNA levels indirectly by accelerating steroidogenesis and depleting cellular sterol pools, thus relieving sterol-mediated negative feedback of HMG-CoA reductase gene expression. 25-Hydroxycholesterol in the presence of aminoglutethimide suppressed low-density lipoprotein (LDL) receptor mRNA, but 8-bromo-cAMP effected a significant stimulation of LDL receptor mRNA levels when added with hydroxysterol and aminoglutethimide. These findings reveal differential regulation of HMG-CoA reductase and LDL receptor mRNAs in the presence of sterol negative feedback.
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*; D002478:Cells, Cultured; D005260:Female; D005796:Genes / Q000187:drug effects; D006107:Granulosa Cells / Q000187:drug effects / Q000201:enzymology*; D006801:Humans; D006903:Hydroxymethylglutaryl CoA Reductases / Q000235:genetics*; D007700:Kinetics; D009693:Nucleic Acid Hybridization; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics*; D013261:Sterols / Q000502:physiology*
D012333:RNA, Messenger; D013261:Sterols; D015124:8-Bromo Cyclic Adenosine Monophosphate; D006903:Hydroxymethylglutaryl CoA Reductases