TRANSCRIPTIONAL AND POSTTRANSCRIPTIONAL REGULATION OF FSH RECEPTOR INRAT GRANULOSA-CELLS BY CYCLIC-AMP AND ACTIVIN

The effect of FSH on the induction of FSH receptors in granulosa cells is believed to be mediated, at least in part, by the cAMP second mess enger system. We examined the effect of activin and cAMP on FSH recept or expression in this culture system. Steady-state levels of FSH recep tor mRNA, analysed by Northern blot hybridization, increased 3.5-fold in response to 24-h incubation with activin and 1.7-fold with 12-h inc ubation with 8-bromoadenosine 3.5-cyclic monophosphate (8-Br-cAMP; 0.2 mM). We have investigated whether 8-Br-cAMP- and/or activin-induced i ncreases in FSH receptor mRNA levels are the result of increased trans cription and/or altered mRNA stability. The rates of FSH receptor mRNA gene transcription, assessed by nuclear run-on transcription assay, i ncreased 3-fold in cells treated with activin and 1.5-fold in cells tr eated with 8-Br-cAMP for 2 h. To examine the degradation rates of FSH receptor mRNA transcripts, granulosa cells were preincubated with 8-Br -cAMP, activin, or medium alone for 6 h. After the preincubation perio d, 5 mu M actinomycin-D or 200 mu M 5,6-dichloro-1-beta-ribofuranosyl benzimidazole were added to arrest new RNA synthesis. The decay curves fr the 2.4 kb FSH receptor mRNA transcript in granulosa cells were no t significantly different in the absence or presence oi 8-Br-cAMP. Act ivin, on the other hand, significantly altered the slope of the FSH re ceptor mRNA decay curve and increased the half-life of the 2.4 kb FSH receptor mRNA transcript. These data provide evidence that cAMP induce s FSH receptor mRNA levels by stimulating the transcription rate and t hat activin increases FSH receptor mRNA levels both by stimulating tra nscription rates and by stabilizing the FSH receptor mRNA transcripts.