Assessment of porcine and human 16-ene-synthase, a third activity of P450c17, in the formation of an androstenol precursor. Role of recombinant cytochrome b5 and P450 reductase.
Recently, we have shown that the biosynthesis of androstenol, a potential endogenous ligand for the orphan receptors constitutive androstane receptor and pregnane-X-receptor, requires the presence of enzymes of the steroidogenic pathway, such as 3 beta-hydroxysteroid dehydrogenase, 5 alpha-reductase and 3 alpha-hydroxysteroid dehydrogenase. In this report, we examine at the molecular level whether the enzyme 17 alpha-hydroxylase/17,20-lyase (P450c17), which possesses dual 17 alpha-hydroxylase and 17,20-lyase activities and catalyzes the production of precursors for glucocorticoids and sex steroids, is also able to catalyze the formation of a third class of active steroids, 16-ene steroids (including androstenol). The role of components of the P450 complex is also assessed. We transfected human embryonic kidney (HEK-293) cells with various amounts of vectors expressing P450c17, NADPH-cytochrome P450 reductase, and cytochrome b5. Our results showed that P450c17 possesses a 16-ene-synthase activity able to transform pregnenolone into 5,16-androstadien-3 beta-ol, without the formation of the precursor 17-hydroxypregnenolone. Cytochrome b5 has a much stronger effect on the 16-ene-synthase activity than on the 17 alpha-hydroxylase/17,20-lyase activities. On the other hand, P450reductase has a drastic effect on the latter, but a negligible one on 5,16-androstadien-3 beta-ol synthesis. Our results therefore demonstrate that human P450c17, as other enzymes of the classical steroidogenic pathway, is involved in the biosynthetic pathway leading to the formation of androstenol.
Soucy
Penny
P
Molecular Endocrinology and Oncology Research Center, Laval University Medical Center (CHUL) and Laval University, Québec, Canada.
Lacoste
Lucille
L
Luu-The
Van
V
D000737:Androstenols / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D015786:Cytochromes b5 / Q000235:genetics / Q000378:metabolism; D003687:Dehydroepiandrosterone / Q000378:metabolism; D006801:Humans; D015394:Molecular Structure; D009251:NADPH-Ferrihemoprotein Reductase / Q000235:genetics / Q000378:metabolism; D010088:Oxidoreductases / Q000378:metabolism*; D011284:Pregnenolone / Q000737:chemistry / Q000378:metabolism; D013254:Steroid 17-alpha-Hydroxylase / Q000235:genetics / Q000378:metabolism*; D013552:Swine
D000737:Androstenols; C000152:androsta-5,16-dien-3 beta-ol; D003687:Dehydroepiandrosterone; D011284:Pregnenolone; D015786:Cytochromes b5; D010088:Oxidoreductases; C019701:androsta-5,16-dien-3 beta-ol synthetase; D013254:Steroid 17-alpha-Hydroxylase; D009251:NADPH-Ferrihemoprotein Reductase