Regulation of aromatase activity of rat granulosa cells: induction of synthesis of NADPH-cytochrome P-450 reductase by FSH and dibutyryl cyclic AMP

Abstract

Aromatase is an enzyme complex that is composed of a specific form of cytochrome P-450 and a flavoprotein, NADPH-cytochrome P-450 reductase. Aromatase activity of granulosa cells is increased markedly by follicle-stimulating hormone (FSH) and by analogs of cyclic AMP. It was the objective of the present study to investigate the effects of FSH and dibutyryl cyclic AMP (Bt 2cAMP) on the synthesis of NADPH-cytochrome P-450 reductase in rat granulosa cells maintained in vitro. Granulosa cells were obtained from the ovaries of diethylstilbestrol (DES)-treated immature rats and were incubated in the presence of DES (10 −7 M), DES + FSH (250 ng/ml), or DES + Bt 2cAMP (1 mM) for up to 72 h. After 72 h of incubation, aromatase activity of cells incubated with DES alone was 5 pmoles estrogen formed 2 h −1 mg −1 protein and was increased > 60-fold in cells incubated with FSH or Bt 2cAMP. NADPH-cytochrome P-450 reductase was immunoisolated from [ 35S]methionine-labeled lysates of granulosa cells incubated for 72 h in the absence or presence of stimulatory factors. The rate of synthesis of reductase was found to be increased about 3-fold in cells incubated with DES + FSH or DES + Bt 2cAMP as compared to cells incubated with DES alone. By immunoblot analysis we found that the cellular content of reductase was increased about 2-fold by FSH and Bt 2cAMP treatment. Reductase specific activity was 10 nmoles min −1 mg −1 protein in membrane fractions of DES-treated cells and was increased 1.6-fold by FSH treatment. These findings are indicative that FSH increases the rate of synthesis, cellular content and specific activity of NADPH-cytochrome P-450 reductase in rat granulosa cells in vitro. The finding that Bt 2cAMP causes a similar induction of reductase synthesis is suggestive that the stimulatory effect of FSH on this component of the aromatase enzyme complex is mediated by an increase in cyclic AMP formation.