title: CYP7B1-mediated metabolism of dehydroepiandrosterone and 5alpha-androstane-3beta,17beta-diol--potential role(s) for estrogen signaling.
abstract: CYP7B1, a cytochrome P450 enzyme, metabolizes several steroids involved in hormonal signaling including 5alpha-androstane-3beta,17beta-diol (3beta-Adiol), an estrogen receptor agonist, and dehydroepiandrosterone, a precursor for sex hormones. Previous studies have suggested that CYP7B1-dependent metabolism involving dehydroepiandrosterone or 3beta-Adiol may play an important role for estrogen receptor beta-mediated signaling. However, conflicting data are reported regarding the influence of different CYP7B1-related steroids on estrogen receptor beta activation. In the present study, we investigated CYP7B1-mediated conversions of dehydroepiandrosterone and 3beta-Adiol in porcine microsomes and human kidney cells. As part of these studies, we compared the effects of 3beta-Adiol (a CYP7B1 substrate) and 7alpha-hydroxy-dehydroepiandrosterone (a CYP7B1 product) on estrogen receptor beta activation. The data obtained indicated that 3beta-Adiol is a more efficient activator, thus lending support to the notion that CYP7B1 catalysis may decrease estrogen receptor beta activation. Our data on metabolism indicate that the efficiencies of CYP7B1-mediated hydroxylations of dehydroepiandrosterone and 3beta-Adiol are very similar. The enzyme catalyzed both reactions at a similar rate and the K(cat)/K(m) values were in the same order of magnitude. A high dehydroepiandrosterone/3beta-Adiol ratio in the incubation mixtures, similar to the ratio of these steroids in many human tissues, strongly suppressed CYP7B1-mediated 3beta-Adiol metabolism. As the efficiencies of CYP7B1-mediated hydroxylation of dehydroepiandrosterone and 3beta-Adiol are similar, we propose that varying steroid concentrations may be the most important factor determining the rate of CYP7B1-mediated metabolism of dehydroepiandrosterone or 3beta-Adiol. Consequently, tissue-specific steroid concentrations may have a strong impact on CYP7B1-dependent catalysis and thus on the levels of different CYP7B1-related steroids that can influence estrogen receptor beta signaling.
authors.affiliation: Department of Pharmaceutical Biosciences, Division of Biochemistry, University of Uppsala, Sweden.
authors.forename: Hanna
authors.initials: H
authors.lastname: Pettersson
authors.forename: Lisa
authors.initials: L
authors.lastname: Holmberg
authors.forename: Magnus
authors.initials: M
authors.lastname: Axelson
authors.forename: Maria
authors.initials: M
authors.lastname: Norlin
mesh_terms: D000375:Aging / Q000502:physiology; D015113:Androstane-3,17-diol / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D003687:Dehydroepiandrosterone / Q000378:metabolism*; D047629:Estrogen Receptor beta / Q000378:metabolism; D004967:Estrogens / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D006900:Hydroxylation; D007700:Kinetics; D008297:Male; D009928:Organ Specificity; D015398:Signal Transduction
chemical_list: D047629:Estrogen Receptor beta; D004967:Estrogens; D015113:Androstane-3,17-diol; D003687:Dehydroepiandrosterone; D003577:Cytochrome P-450 Enzyme System