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Oncology and Molecular Endocrinology Research Center, Laval University Hospital Research Center (CRCHUL) and Laval University, 2705 Laurier Boulevard, Quebec, G1V 4G2, Canada
(Requests for offprints should be addressed to V Luu-The; Email: van.luu-the{at}crchul.ulaval.ca)
Recently, we have shown that human and monkey type 12 17ß-hydroxysteroid dehydrogenases (17ß-HSD12) are estrogen-specific enzymes catalyzing the transformation of estrone (E1) into estradiol (E2). To further characterize this novel steroidogenic enzyme in an animal model, we have isolated a cDNA fragment encoding mouse 17ß-HSD12 and characterized its enzymatic activity. Using human embryonic kidney cells (HEK)-293 cells stably expressing mouse 17ß-HSD12, we found that in contrast with the human and monkey enzymes, which are specific for the transformation of E1 to E2, mouse 17ß-HSD12 also catalyzes the transformation of 4-androstenedione into testosterone (T), dehydroepiandroster-one (DHEA) into 5-androstene-3ß,17ß-diol (5-diol), as well as androsterone into 5
-androstane-3
,17ß-diol (3
-diol). Previously, we have shown that the specificity of human and monkey 17ß-HSD12s for C18-steroid is due to the presence of a bulky phenylalanine (F) at position 234 creating steric hindrance, preventing the entrance of C19-steroids into the active site. To determine whether the smaller size of the corresponding leucine (L) in the mouse sequence is responsible for the entrance of androgenic substrates, we performed site-directed mutagenesis to substitute Leu 234 for Phe in the mouse enzyme. In agreement with our hypothesis, the mutated enzyme has a highly reduced ability to metabolize androgens. mRNA quantification in several mouse tissues using real-time PCR shows that mouse 17ß-HSD12 mRNA is highly expressed in the female clitoral gland, male preputial gland, as well as in retroperitoneal fat and adrenal of both sexes. The differential androgenic/estrogenic substrate specificity of type 12 17ß-HSD in the mouse and primates seems to agree with the observation that androgen and estrogen in the mouse are provided almost exclusively by gonads, while in primates an important part of these steroid hormones are produced locally from adrenal precursors.
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