title: Expression of aromatase cytochrome P450 in rat H540 Leydig tumor cells.
abstract: The rat H540 Leydig cell tumor has been shown to express cholesterol side-chain cleavage and 17alpha-hydroxylase cytochrome P450s, 3beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase, and steroid 5alpha-reductase, making it a useful model in which to study steroidogenesis. In the current studies, we report that cultured H540 cells express high levels of aromatase cytochrome P450 (P450arom), which converts androgens to estrogens. Levels of aromatase activity varied from 9.4 to 51.7 pmol/h/mg protein and inhibition of 5alpha-reductase with finasteride did not significantly effect aromatase measurements, indicating that 5alpha-reductase is not competing for the substrate used in the aromatase assays. Aromatase activity was decreased 95% by preincubating the cells with 4-hydroxyandrostenedione, an aromatase inhibitor. Characterization of the aromatase mRNA expressed in the H540 cell line demonstrates that, like R2C cells and rat ovarian tissue, three distinct P450arom mRNA species are detected by Northern analysis, and that these transcripts are derived from the same site of transcription initiation. Despite these similarities, the regulation of aromatase activity by 8-bromo-cAMP in H540 cells differs from both R2C cells and rat ovarian tissue. As the H540 and R2C cell lines appear to have distinct origins, H540 is the second rat Leydig tumor cell line characterized that constitutively expresses high levels of aromatase.
authors.affiliation: Department of Internal Medicine, The University of Texas Southwestern Medical Center at Dallas, 75235-8857, USA.
authors.forename: M
authors.initials: M
authors.lastname: Young
authors.forename: E D
authors.initials: ED
authors.lastname: Lephart
authors.forename: M J
authors.initials: MJ
authors.lastname: McPhaul
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D001141:Aromatase / Q000235:genetics / Q000378:metabolism*; D047072:Aromatase Inhibitors; D015152:Blotting, Northern; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D004967:Estrogens / Q000096:biosynthesis; D005260:Female; D007984:Leydig Cell Tumor / Q000201:enzymology*; D008297:Male; D010053:Ovary / Q000201:enzymology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D013736:Testicular Neoplasms / Q000201:enzymology*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
chemical_list: D047072:Aromatase Inhibitors; D004967:Estrogens; D012333:RNA, Messenger; D015124:8-Bromo Cyclic Adenosine Monophosphate; D003577:Cytochrome P-450 Enzyme System; D001141:Aromatase