Effect of type 1 transforming growth factor-beta on the level of aromatase cytochrome P-450 in human fetal hepatocytes.
Aromatase cytochrome P-450 (P-450AROM) is the enzyme in the steroidogenic pathway controlling the formation of oestrogens from 19 carbon steroid precursors. Aromatase is present in various tissues of the human fetus. The liver is second only to the placenta in the level of P-450AROM activity in the fetus. In this study we examined the effects of type 1 transforming growth factor-beta (TGF beta) on P-450AROM expression in human fetal (HF) hepatocytes. The HF hepatocytes were dispersed into single cells which were placed into monolayer cell culture until confluent. Cells were then rinsed and treated in serum-free media with dibutyryl cyclic AMP (Bu2cAMP) for 72 h. Treatment with Bu2cAMP (2 mmol/l) caused a fivefold increase in aromatase activity in hepatocytes. The increase in aromatase activity apparently represented an increase in P-450AROM enzyme as determined by immunoblotting using an antibody directed against human placental aromatase. TGF beta blocked basal, as well as Bu2cAMP increases, in aromatase activity by over 50%. The effect of TGF beta was dose-dependent with maximal inhibition observed using 2-5 ng TGF beta/ml. Immunodetectable P-450AROM decreased in parallel with activity following TGF beta treatment. The mechanism of TGF beta action was not through increasing phosphodiesterase (PDE) breakdown of cAMP since inhibition of PDE had no effect on TGF beta action. Finally we examined the level of P-450AROM mRNA using competitive polymerase chain reaction amplification. Bu2cAMP increased mRNA levels of P-450AROM by 2.5-fold, while TGF beta inhibited this induction by 35%. The results of this investigation demonstrated that TGF beta is a potent regulator of P-450AROM expression in HF hepatocytes.
Rainey, WE; Price, TM; Means, GD; Carr, BR
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