A number of enzymes possessing 17beta-hydroxysteroid dehydrogenase/17-ketosteroid reductase (17HSD/KSR) activities have been described and cloned, but their nomenclature needs specification. To clarify the present situation, descriptions of the eight cloned 17HSD/KSRs are given and guidelines for the classification of novel 17HSD/KSR enzymes are presented.
H Peltoketo, V Luu-The, J Simard, and J Adamski
Y Zhang, I Dufort, P Rheault, and V Luu-The
It has been suggested that 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD) is a T-cell differentiation marker in mice. In the human, this enzyme has generally been associated with types 1 and 2 17beta-HSDs, which belong to the short-chain alcohol dehydrogenase family, whereas the rat, rabbit, pig and bovine 20alpha-HSDs are members of the aldoketo reductase superfamily, which also includes the 3alpha-HSD family. In this study, we report the cloning, from a human skin cDNA library, of a cDNA that shows, after transfection into human embryonic kidney (HEK-293) cells, high 20alpha-HSD activity but negligible 3alpha- and 17beta-hydroxysteroid dehydrogenase activities. A comparison of the amino acid sequence of the human 20alpha-HSD with those of other related 20alpha- and 3alpha-HSDs indicates that the human 20alpha-HSD shares 79.9, 68.7 and 52.3% identity with rabbit, rat and bovine 20alpha-HSDs, whereas it shows 97, 84 and 65% identity with human type 3, type 1 and rat 3alpha-HSDs. In contrast, the enzyme shares only 15.2 and 15.0% identity with type 1 and type 2 human 17beta-HSDs. DNA analysis predicts a protein of 323 amino acids, with a calculated molecular weight of 36 767 Da. In intact transfected cells, the human 20alpha-HSD preferentially catalyzes the reduction of progesterone to 20alpha-hydroxyprogesterone with a K(m) value of 0.6 microM, the reverse reaction (oxidation) being negligible. In a cell cytosolic preparation, the enzyme could use both NADPH and NADH as cofactors, but NADPH, which gave 4-fold lower K(m) values, was preferred. We detected the expression of 20alpha-HSD mRNA in liver, prostate, testis, adrenal, brain, uterus and mammary-gland tissues and in human keratinocyte (HaCaT) cells. The present study clearly indicates that the genuine human 20alpha-HSD belongs to the aldoketo reductase family, like the 20alpha-HSDs from other species.
R K Srivastava, V Luu-The, B L Marrone, and R Sridaran
LHRH and its analogues are known to exert direct effects on the ovary. Herein we have described a direct inhibitory effect of an LHRH antagonist (Nal-Lys antagonist: antide) on the basal progesterone (P4) and pregnenolone (P5) production by luteal cells obtained from the day-8 pregnant rat. Luteal cells incubated with two doses of antide (10−4 and 10−7 m) for 24 or 48 h showed suppression of P4 production. P5 production was suppressed by both doses of antide within 12 h of incubation. Neither dose of antide interfered with P5 production when the duration of incubation was extended beyond 12 h. The 20α-dihydroprogesterone yield from the luteal cells treated with these doses of antide remained unaffected. We estimated the activities of the cholesterol side-chain cleavage (P450scc) enzyme (which is a key enzyme involved in the conversion of cholesterol to P5) and 3β-hydroxysteroid dehydrogenase (3β-HSD) (which catalyses the conversion of P5 to P4) in the luteal cells treated with different doses of antide. Both doses of antide suppressed the activity of the P450scc enzyme after 12 h of incubation and the 3β-HSD content of the luteal cells after 48 h of incubation. These observations indicate that antide exerts a direct inhibitory effect at the level of the corpus luteum, that differential suppression of P5 and P4 during different periods of incubation with antide is due to a defect in either the P450scc or the 3β-HSD enzyme system, or both.
G Pelletier, V Luu-The, M El-Alfy, S Li, and F Labrie
The subcellular distribution of steroidogenic enzymes has so far been studied mostly in classical endocrine glands and in the placenta. In the peripheral intracrine organs which synthesize sex steroids there is no indication about the organelles which contain the enzymes involved in steroid biosynthesis. We have thus investigated the subcellular localization of two enzymes involved in the production of sex steroids, namely 3beta-hydroxysteroid dehydrogenase (3beta-HSD) and type 5 17beta-hydroxysteroid dehydrogenase (17beta-HSD). Using specific antibodies to these enzymes, we conducted immunoelectron microscopic studies in two peripheral tissues, namely the human prostate and mammary gland. In the prostate, immunolabelling for both 3beta-HSD and type 5 17beta-HSD was detected in the basal cells of the tube-alveoli as well as in fibroblasts and endothelial cells lining the blood vessels. In all the labelled cell types, the gold particles were distributed throughout the cytoplasm. No obvious association with any specific organelle could be observed, although some concentration of gold particles was occasionally found over bundles of microfilaments. In mammary gland sections immunolabelled for 3beta-HSD or type 5 17beta-HSD localization, labelling was observed in the cytoplasm of the secretory epithelial cells in both the acini and terminal ducts. Immunolabelling was also found in the endothelial cells as well as in fibroblasts in stroma and blood vessels. The gold particles were not detected over any organelles, except with the occasional accumulation of gold particles over microfilaments. The present data on the localization of two steroidogenic enzymes leading to the synthesis of testosterone indicate that these enzymes are located not only in epithelial cells but also in stromal and endothelial cells in both tissues studied. The absence of any association of the enzymes with membrane-bound organelles appears as a common finding in the reactive cell types of two peripheral tissues.
F Gizard, E Teissier, I Dufort, G Luc, V Luu-The, B Staels, and DW Hum
Steroid hormones synthesized from cholesterol in the adrenal gland are important regulators of many physiological processes. It is now well documented that the expression of many genes required for steroid biosynthesis is dependent on the coordinated expression of the nuclear receptor steroidogenic factor-1 (SF-1). However, transcriptional mechanisms underlying the species-specific, developmentally programmed and hormone-dependent modulation of the adrenal steroid pathways remain to be elucidated. Recently, we demonstrated that the transcriptional regulating protein of 132 kDa (TReP-132) acts as a coactivator of SF-1 to regulate human P450scc gene transcription in human adrenal NCI-H295 cells. The present study shows that overexpression of TReP-132 increases the level of active steroids produced in NCI-H295 cells. The conversion of pregnenolone to downstream steroids following TReP-132 expression showed increased levels of glucocorticoids, C(19) steroids and estrogens. Correlating with these data, TReP-132 increases P450c17 activities via the induction of transcript levels and promoter activity of the P450c17 gene, an effect that is enhanced in the presence of cAMP or SF-1. In addition, P450aro activity and mRNA levels are highly induced by TReP-132, whereas 3beta-hydroxysteroid dehydrogenase type II and P450c11aldo transcript levels are only slightly modulated. Taken together, these results demonstrate that TReP-132 is a trans-acting factor of genes involved in adrenal glucocorticoid, C(19) steroid and estrogen production.
G Pelletier, V Luu-The, S Li, L Ren, and F Labrie
The enzyme 17β-hydroxysteroid dehydrogenase (17β-HSD) type 1 catalyzes the conversion of estrone (E1) into 17β estradiol (E2). To gain information about the cellular localization of 17β-HSD mRNA type 1 expression, we performed in situ hybridization using a 35S-labeled cRNA probe in several tissues of adult mice of both sexes. In the ovary, high expression was found in granulosa cells of growing follicles. No specific labeling could be observed in corpora lutea or interstitial cells. In the pituitary gland of animals of both sexes, 17β-HSD type 1 mRNA was expressed in the intermediate lobe melanotrophs while no specific signal could be detected in the anterior or posterior lobes of the pituitary. In the prostate, 17β-HSD type 1 mRNA was exclusively found in the epithelial cells. In both male and female mouse dorsal skin, a specific hybridization signal was seen in the sebaceous glands while the epidermis, stroma, hair follicles and sweat glands were unlabeled. In the testis, a hybridization signal was detected in germ cells of the seminiferous tubules, Leydig cells being unlabeled. The present data indicate that E2 can be formed through the action of 17β-HSD type 1 in specific cells of the gonads and peripheral tissues. In the testes and peripheral tissues, the action of E2 is probably limited to the cells involved in its formation in an intracrine fashion.
F Labrie, V Luu-The, SX Lin, J Simard, C Labrie, M El-Alfy, G Pelletier, and A Belanger
In women and men, an important proportion of estrogens and androgens are synthesized locally at their site of action in peripheral target tissues. This new field of endocrinology has been called intracrinology. In postmenopausal women, 100% of active sex steroids are synthesized in peripheral target tissues from inactive steroid precursors while, in adult men, approximately 50% of androgens are made locally in intracrine target tissues. The last and key step in the formation of all estrogens and androgens is catalyzed by members of the family of 17beta-hydroxysteroid dehydrogenases (17 beta-HSDs) while different 17 beta-HSDs inactivate these steroids in the same cell where synthesis takes place. To date, seven human 17 beta-HSDs have been cloned, sequenced and characterized. The 17 beta-HSDs provide each cell with the means of precisely controlling the intracellular concentration of each sex steroid according to local needs.