Induction and superinduction of messenger ribonucleic acid specific for aromatase cytochrome P-450 in cultured human skin fibroblasts

Abstract

Aromatase cytochrome P-450 (cytochrome P-450AROM) catalyzes the formation of aromatic C18 estrogenic steroids from C19 androgens. Several studies indicate that cytochrome P-450AROM activity is induced by glucocorticoids such as dexamethasone (DEX) and superinduced by DEX plus cycloheximide (CHX). We have used cultured human skin fibroblasts as a model system to investigate the regulation of aromatase gene expression. Whereas Northern blot analysis of total cellular RNA or poly (A)+ RNA from untreated strains of normal human skin fibroblasts failed to demonstrate any hybridization with a specific human placental cytochrome P-450AROM complementary DNA, analysis of RNA from cells treated with DEX demonstrated hybridization of the cytochrome P-450AROM complementary DNA to two transcripts of about 2.5 and 3.0 kilobases. Incubation of cells with DEX plus CHX resulted in a further increase in levels of cytochrome P-450AROM messenger RNA (mRNA) when compared to cells treated with DEX alone, suggesting that inhibition of protein synthesis superinduces transcription of the cytochrome P-450AROM gene. By contrast, levels of beta-actin mRNA were not affected by treatment with DEX and CHX. Treatment of cells with CHX alone did not produce a change in either aromatase activity or levels of cytochrome P-450AROM mRNA transcripts. These results indicate that aromatase activity is regulated by changes in the concentration of cytochrome P-450AROM mRNA, and imply that control of cytochrome P-450AROM gene expression is at the level of gene transcription. We conclude that the cytochrome P-450AROM gene is regulated by a complex mechanism that includes both positive and negative transcription factors.