EXPRESSION OF AROMATASE CYTOCHROME-P450 IN RAT H540 LEYDIG TUMOR-CELLS

The rat H540 Leydig cell tumor has been shown to express cholesterol s ide-chain cleavage and 17 alpha-hydroxylase cytochrome P450s, 3 beta-h ydroxysteroid dehydrogenase/delta 5-delta 4 isomerase, and steroid 5 a lpha-reductase, making it a useful model in which to study steroidogen esis. In the current studies, we report that cultured H540 cells expre ss high levels of aromatase cytochrome P450 (P450(arom)), which conver ts androgens to estrogens. Levels of aromatase activity varied from 9. 4 to 51.7 pmol/h/mg protein and inhibition of 5 alpha-reductase with f inasteride did not significantly effect aromatase measurements, indica ting that Sa-reductase is not competing for the substrate used in the aromatase assays. Aromatase activity was decreased 95% by preincubatin g the cells with 4-hydroxyandrostenedione, an aromatase inhibitor. Cha racterization of the aromatase mRNA expressed in the H540 cell line de monstrates that, like R2C cells and rat ovarian tissue, three distinct P450(arom) mRNA species are detected by Northern analysis, and that t hese transcripts are derived from the same site of transcription initi ation. Despite these similarities, the regulation of aromatase activit y by 8-bromo-cAMP in H540 cells differs from both R2C cells and rat ov arian tissue. As the H540 and R2C cell Lines appear to have distinct o rigins, H540 is the second rat Leydig tumor cell line characterized th at constitutively expresses high levels of aromatase. (C) 1997 Elsevie r Science Ltd. All rights reserved.