Effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin on the expression of follicle-stimulating hormone receptors during cell differentiation in cultured granulosa cells

Dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin; TCDD) is a common environmenta l pollutant causing public concern. Using a cell culture system derived fro m rat granulosa cells that provides unique advantages for studying the mole cular mechanisms underlying the action of TCDD, the influences of TCDD on F SH receptor (FSH-R) induction were examined. The treatment with FSH produce d, as expected, a substantial increase in specific FSH-R expression, wherea s concurrent treatment with the environmental amount of TCDD (10 pM) result ed in a significant decrease in FSH-R after being cultured from 24-72 h. Co treatment with FSH (30 ng/ml) and increasing doses of TCDD inhibited the le vels of FSH-induced FSH-R messenger RNA (mRNA) in a dose-dependent manner. Treatment with 8-Br-cAMP (1 mM) produced a significant increase in FSH-R mR NA; concurrent treatment with TCDD (10 pM) produced a significant attenuati on of 8-Br-cAMP action. These findings suggest that the ability of TCDD to interfere with FSH action, as regards the induction of FSH-Rs, is exerted a t sites distal to those involved in cAMP generation. Because a single trans cript of 5.2 kb was seen for the Ah receptor in this granulosa cell system, the effects of TCDD may be mediated by this specific receptor. The rates o f FSH-R mRNA gene transcription, assessed by nuclear run-on transcription a ssay, were decreased by the addition of TCDD. The effect of TCDD on FSH-R m RNA stability was determined by measuring the decay of FSH-R mRNA under con ditions known to inhibit transcription. The decay curve for the 2.4-kb FSH- R mRNA transcript was not significantly changed after the addition of TCDD. These findings showed that the effect of TCDD on FSH-R mRNA was, at least in part, the result of decreased transcription.