An adenosine 3'5'-monophosphate-responsive deoxyribonucleic acid element confers forskolin sensitivity on gene expression by primary rat granulosa cells.

The following studies were conducted with the goal of understanding some of the molecular mechanisms by which cAMP alters granulosa cell function. In this regard, we characterized the expression of messages for the cholesterol side-chain cleavage cytochrome P450 (P450scc) enzyme and a type II cAMP-dependent protein kinase subunit (RII beta) in granulosa cells isolated from small antral follicles and cultured in 1% fetal bovine serum-containing medium. Forskolin (FSK) stimulated cAMP production followed by accumulation of RII beta mRNAs, induction of P450scc mRNA, and, finally, progesterone biosynthesis. The regulation of each mRNA displayed a different sensitivity to actinomycin-D treatment. To determine if the modulation of RII beta or the induction of P450scc could be mediated by the enhancer activity of a cAMP-responsive DNA element (CRE), plasmid DNA containing the CRE and TATA box of the human glycoprotein alpha-subunit (alpha G) gene fused to the chloramphenicol acetyl transferase (CAT) gene was introduced into cultured granulosa or interstitial cells, and the ability of FSK to stimulate the expression of the CAT enzyme was measured. When granulosa cells were isolated from preantral/small antral follicles and maintained for at least 5 days in culture, 5 or 10 microM FSK reversibly stimulated expression of the CAT enzyme within 18 h posttransfection. Under similar conditions, interstitial ovarian cells (prepared from the residual ovarian tissue remaining after granulosa cell isolation) were unable to express the template unless the cells were pretreated for 24 h with FSK before transfection. Thereafter, CAT gene expression by interstitial cells was maintained in a FSK-insensitive manner. To determine if cAMP-dependent transcription of the reporter gene required the same sequences that had been characterized for placenta-derived cells, a truncated plasmid lacking the CRE of the alpha G gene was transfected. Under no condition was expression of the CAT gene observed from a CRE-deficient template. The acute transcriptional activation of a CRE/TATA box-containing gene by cAMP in granulosa cells indicated that transcription-activating proteins interacting with the CRE were either present in these cells or were rapidly synthesized after stimulation. To distinguish between these two possibilities, protein synthesis was transiently inhibited after transfection, before the addition of FSK, by incubating the cells for 2 h with 25 micrograms/ml cycloheximide. Cycloheximide treatment alone did not stimulate transcription from the CRE-containing molecule. Incubation with cycloheximide, followed by treatment with FSK, increased CAT activity 2-fold compared to t