Characterization of type 12 17beta-hydroxysteroid dehydrogenase, an isoform of type 3 17beta-hydroxysteroid dehydrogenase responsible for estradiol formation in women

A novel 17beta-hydroxysteroid dehydrogenase (17beta-HSD) chronologically named type 12 17beta-HSD (17beta-HSD12), that transforms estrone (E1) into estradiol (E2) was identified by sequence similarity with type 3 17beta-HSD (17beta-HSD3) that catalyzes the formation of testosterone from androstenedione in the testis. Both are encoded by large genes spanning 11 exons, most of them showing identical size. Using human embryonic kidney-293 cells stably expressing 17beta-HSD12, we have found that the enzyme catalyzes selectively and efficiently the transformation of E1 into E2, thus identifying its role in estrogen formation, in contrast with 17beta-HSD3, the enzyme involved in the biosynthesis of the androgen testosterone in the testis. Using real-time PCR to quantify mRNA in a series of human tissues, the expression levels of 17beta-HSD12 as well as two other enzymes that perform the same transformation of E1 into E2, namely type 1 17beta-HSD and type 7 17beta-HSD, it was found that 17beta-HSD12 mRNA is the most highly expressed in the ovary and mammary gland. To obtain a better understanding of the structural basis of the difference in substrate specificity between 17beta-HSD3 and 17beta-HSD12, we have performed tridimensional structure modelization using the coordinates of type 1 17beta-HSD and site-directed mutagenesis. The results show the potential role of bulky amino acid F234 in 17beta-HSD12 that blocks the entrance of androstenedione. Overall, our results strongly suggest that 17beta-HSD12 is the major estrogenic 17beta-HSD responsible for the conversion of E1 to E2 in women, especially in the ovary, the predominant source of estrogens before menopause.     

Androgens, androgen receptors, and male gender role behavior

Studies of genetic males with single gene mutations that impair testosterone formation or action and consequently prevent development of the normal male phenotype provide unique insight into the control of gender role behavior. 46,XY individuals with either of two autosomal recessive mutations [17 beta-hydroxysteroid dehydrogenase 3 (17 beta-HSD3) deficiency or steroid 5 alpha-reductase 2 (5 alpha-R2) deficiency] have a female phenotype at birth and are raised as females but frequently change gender role behavior to male after the expected time of puberty. In contrast, genetic males with mutations that impair profoundly the function of the androgen receptor are also raised as females and have consistent female behavior as adults. Furthermore, the rare men with mutations that impair estrogen synthesis or the estrogen receptor have male gender role behavior. These findings indicate that androgens are important determinants of gender role behavior (and probably of gender identity) and that this action is mediated by the androgen receptor and not the result of conversion of androgen to estrogen. The fact that all genetic males with 17 beta-HSD3 or 5 alpha-R2 deficiency do not change gender role behavior indicates that other factors are also important determinants of this process.     

Male pseudohermaphroditism due to nonsalt-losing 3 beta-hydroxysteroid dehydrogenase deficiency: gender role change and absence of gynecomastia at puberty

Adrenal and gonadal functions were evaluated on two adult cousins with male pseudohermaphroditism due to congenital 3 beta-hydroxysteroid dehydrogenase deficiency (3 beta-HSD) without clinical salt-losing. Both patients had been reared as females since birth. Case 1 presented at age 17 with perineal hypospadias virilization without gynecomastia and a female to male gender role change at puberty. Case 2 had previously undergone bilateral orchidectomy in childhood and presented "primary amenorrhea", absence of virilization and a female gender role at the age of 24. In the basal state, as well as after ACTH and hCG stimulation, 3 beta-hydroxy-5-ene-steroid levels were disproportionately elevated, resulting in abnormal 3 beta-hydroxy-5-ene: 3-oxi-4-ene steroids ratios. Normal basal serum cortisol with inadequate cortisol response to ACTH was observed in both patients. Elevated basal plasma renin activity (PRA) and normal basal serum aldosterone (ALDO) were present in both subjects. After ACTH stimulation serum ALDO rose adequately in Case 1 but subnormally in Case 2. Salt restriction resulted in an increase in serum ALDO and no salt loss in Case 1 whereas in Case 2 the substantial rise in PRA and serum ALDO were unable to prevent slight urinary sodium loss. Case 1 had normal basal serum testosterone with subnormal response to hCG stimulation. Incubation of testicular tissue in vitro with [3H]DHEA resulted in large Androstenediol production but diminished testosterone conversion confirming the 3 beta-HSD deficiency in the testes. We conclude that (1) absence of gynecomastia and a female to male gender role change may be observed in the male pubertal presentation of nonsalt-losing 3 beta-HSD deficiency and (2) the different functional behavior of zona glomerulosa in our patients suggests the presence of variable degrees of 3 beta-HSD deficiency in the zona glomerulosa of the nonsalt-losing form.     

Estradiol formation by human osteoblasts via multiple pathways: relation with osteoblast function.

The importance of estrogens in bone metabolism is illustrated by the accelerated bone loss and increase in osteoporotic fractures associated with postmenopausal estrogen deficiency. In this study, the expression and activity of the enzymes involved in estrogen metabolism in human osteoblastic cells were investigated in relation to differentiation of these cells. PCR reactions using mRNA from an in vitro differentiating human cell line (SV-HFO) were performed to assess mRNA expression of the enzymes aromatase, different subtypes of 17beta-hydroxysteroid dehydrogenase (17beta-HSD), and steroid sulfatase. Aromatase, sulfatase, and 17beta-HSD type 2 and 4 were found to be expressed throughout differentiation. Expression of 17beta-HSD type 3, however, was relatively weak, except for early time points in differentiation. Type 1 17beta-HSD expression was not detected. Aromatase activity decreased during differentiation, as was demonstrated by the conversion of androstenedione (A) and testosterone (T) into estrone (E(1)) and estradiol (E(2)), respectively. The 17beta-HSD isozymes catalysing a reductive reaction convert androstenedione and estrone into testosterone and estradiol, respectively. Their activity declined with differentiation. Analysis of 17beta-HSD activity indicated both oxidative (E(2) to E(1); T to A) and reductive (E(1) to E(2); A to T) metabolism at all stages of osteoblast differentiation. Both activities declined as cells moved toward a differentiating mineralizing phenotype. However, the oxidative reaction was increasingly in favor of the reductive reaction at all times during differentiation. Sulfatase activity, as demonstrated by the conversion of estrone-sulfate into estrone, was constant during differentiation. In conclusion, we have demonstrated that all enzymes necessary for estrogen metabolism are expressed and biologically active in differentiating human osteoblasts. The activity of aromatase and 17beta-HSD was found to be dependent on the stage of cell differentiation. In addition, human osteoblasts effectively convert estradiol into estrone. The efficacy of osteoblasts to synthesize estradiol may determine the ultimate change in rate of bone turnover after menopause, as well as the development of osteoporosis. Moreover, the enzymes involved in the metabolism of estradiol may form a target for intervention.     

Identification of mutations in the arylsulfatase B gene in Russian mucopolysaccharidosis type VI patients

Molecular genetic analysis of the gene for arylsulfatase B (ASB) was conducted in ten Russian patients with type VI mucopolysaccharidosis (MPS VI) of different severity. Eight exons from the translated region of the ASB gene of each patient were amplified and sequenced using the nonradioactive method. Fourteen mutant alleles were identified in the sample studied by means of DNA analysis; 13 of them had not been described before. All patients except for one, who was an offspring of a consanguineous marriage, were genetic compounds with respect to the mutations found. Polymorphic sites A/G 1072 and A/G 1126, which were earlier revealed in exon 5 of the ASB gene, were found in five out of ten patients studied. The spectrum of mutant alleles of the ASB gene was highly specific and agreed with the characteristics of the population genetic load.     

Steroid metabolism in testes of patients with incomplete masculinization due to androgen insensitivity or 17 beta-hydroxysteroid dehydrogenase deficiency and normally differentiated males

For purposes of establishing suitable controls in studies of patients with a suspected enzyme deficiency, activities of enzymes involved in the biosynthesis of testosterone were compared in testes of patients with androgen insensitivity syndrome (AIS) and normally differentiated males with carcinoma of the prostate (Ca prostate) or testis (Ca testis). Activities of 17,20-desmolase and of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) were higher in the testes of pre-, peri- or postpubertal patients with AIS than in elderly men (58-80 yr) with Ca prostate. Activities of 17 beta-HSD (reductive direction) and 3 beta-HSD tended to be higher in peri- or postpubertal than in prepubertal patients with AIS. Activity of 3 beta-HSD was low in the patient with Ca testis. In a peripubertal (12 yr) patient with incomplete masculinization due to a severe deficiency of 17 beta-HSD, reductive activity of 17 beta-HSD was very low compared with that of patients with Ca prostate, Ca testis or AIS. In contrast, in testes from the younger sibling (4 yr), in whom the deficiency of 17 beta-HSD was less severe, 17 beta-HSD reduction of dehydroepiandrosterone was as high as that of men with Ca prostate, yet deficient in comparison with that of more closely age-matched patients with AIS. This emphasizes the desirability of using age-matched tissue for control purposes in enzyme studies.     

Cloning and characterization of human form 2 type 7 17beta-hydroxysteroid dehydrogenase, a primarily 3beta-keto reductase and estrogen activating and androgen inactivating enzyme

Type 7 17beta-HSD catalyzes the transformation of estrone (E1) into estradiol (E2) and dihydrotestosterone (DHT) into 5alpha -androstane-3beta,17beta-diol (3beta-diol) as well as zymosterone into zymosterol. This suggests that in addition to cholesterol metabolism, the enzyme could play a critical role in estrogen-sensitive cells, since it inactivates DHT that generally shows antagonistic effect in the cells, while producing active E2 for cell proliferation. In this report, we describe the cloning and characterization of a second form of type 7 17beta-HSD (17beta-HSD7_2) that shares 95.6% identity with 17beta-HSD7_1. Using a 7.5kb genomic DNA fragment of 17beta-HSD7_1 as probe, we have obtained 7 BAC clones: three clones containing the 17beta-HSD7_1 gene and four containing the 17beta-HSD7_2 gene. The corresponding 17beta-HSD7_2 cDNA fragments of the coding region were obtained by amplification using RT-PCR and subcloned into pCMV expression vector and stably transfected into human embryonic kidney (HEK-293) cells. The overexpressed 17beta-HSD7_2 catalyzes efficiently the transformation of E1 into E2 and of DHT into 3beta-diol. Ribonuclease protection assays (RPA) indicate that 17beta-HSD7_2 is expressed in the liver, prostate, uterus and placenta. FISH mapping using the 7.5kb genomic DNA fragment as well as 2 BAC clones of each form allowed us to map the 17beta-HSD7_1 gene on chromosome band 1q23, and 17beta-HSD7_2 on band 10p11.2. These results contrast with a previous report that the 17beta-HSD7_1 gene was mapped to chromosomal band 10p11.2. This newly identified form of 17beta-HSD7 could have a significant role by modulating active hormone levels in estrogen-sensitive cells or tissues.     

Synthesis, biochemical evaluation and rationalisation of the inhibitory activity of a range of 4-hydroxyphenyl ketones as potent and specific inhibitors of the type 3 of 17beta-hydroxysteroid dehydrogenase (17beta-HSD3)

We report the synthesis and biochemical evaluation of a number of 4-hydroxyphenyl ketones as potential inhibitors of the enzyme 17beta-hydroxysteroid dehydrogenase (17beta-HSD). In particular, we evaluated compounds against the catalysis of the conversion of androstenedione (AD) to testosterone (T) [17beta-HSD type 3 (17beta-HSD3)], furthermore, in an effort to determine the specificity of our compounds, we evaluated the ability of the compounds to inhibit the catalysis of the conversion of estrone (E1) to estradiol (E2) [17beta-HSD type 1 (17beta-HSD1)] as well as the conversion of dehydroepiandrosterone (DHEA) to AD [by 3beta-hydroxysteroid dehydrogenase (3beta-HSD)]. The results of our study suggest that the synthesised compounds are, in general, able to inhibit 17beta-HSD3 whilst being weak inhibitors of 17beta-HSD1. Against 3beta-HSD, we discovered that all of the synthesised compounds were weak inhibitors (all were found to possess less than 50% inhibition at [I]=500 microM). More specifically, we discovered that 1-(4-hydroxy-phenyl)-nonan-1-one (15) was the most potent against 17beta-HSD3 (IC(50)=2.9 microM) whilst possessing poor inhibitory activity against 17beta-HSD1 ( approximately 36% inhibitory activity against this reaction at [I]=100 microM) and less than 10% inhibition for the conversion of DHEA to AD. We have therefore provided good lead compounds in the design and synthesis of novel non-steroidal inhibitors of 17beta-HSD3.     

A new mutation of 5-alpha-reductase type 2 (A62E) in a large Egyptian kindred

OBJECTIVE: To describe the clinical, biological and molecular data in a large Egyptian kindred with 5alpha-reductase deficiency. PATIENTS AND METHODS: Three patients with ambiguous genitalia were referred at the ages of 20, 9 and 2 years, respectively. In all cases, parents were first cousins. Basal and post-HCG stimulation plasma levels of testosterone and dihydrotestosterone were determined. Direct sequencing and restriction site analysis were applied for patient and family study. RESULTS: A homozygous alanine to glutamic acid substitution at position 62 (A62E) was found in the three patients. The parents and two XX sisters were heterozygous while a third XX sibling was normal. CONCLUSION: We report a new mutation of the 5alpha-reductase type 2 gene. The presence of this mutation in all studied patients and their parents suggests its causative role in 5alpha-reductase deficiency. Identification of the mutation enabled genetic counselling for three XX individuals.     

Identification of novel mutations of the human N-acetylglutamate synthase gene and their functional investigation by expression studies

The mitochondrial enzyme N-acetylglutamate synthase (NAGS) produces N-acetylglutamate serving as an allosteric activator of carbamylphosphate synthetase 1, the first enzyme of the urea cycle. Autosomal recessively inherited NAGS deficiency (NAGSD) leads to severe neonatal or late-onset hyperammonemia. To date few patients have been described and the gene involved was described only recently. In this study, another three families affected by NAGSD were analyzed for NAGS gene mutations resulting in the identification of three novel missense mutations (C200R [c.598T > C], S410P [c.1228T > C], A518T [c.1552G > A]). In order to investigate the effects of these three and two additional previously published missense mutations on enzyme activity, the mutated proteins were overexpressed in a bacterial expression system using the NAGS deficient E. coli strain NK5992. All mutated proteins showed a severe decrease in enzyme activity providing evidence for the disease-causing nature of the mutations. In addition, we expressed the full-length NAGS wild type protein including the mitochondrial leading sequence, the mature protein as well as a highly conserved core protein. NAGS activity was detected in all three recombinant proteins but varied regarding activity levels and response to stimulation by l-arginine. In conclusion, overexpression of wild type and mutated NAGS proteins in E. coli provides a suitable tool for functional analysis of NAGS deficiency.     

Spironolactone-related inhibitors of type II 17beta-hydroxysteroid dehydrogenase: chemical synthesis, receptor binding affinities, and proliferative/antiproliferative activities.

The family of 17beta-hydroxysteroid dehydrogenases (17beta-HSDs) catalyzes the formation and inactivation of testosterone (T), dihydrotestosterone (DHT), and estradiol (E2), thus playing a crucial role in the regulation of active steroid hormones in target tissues. Among the five known 17beta-HSD enzymes, type II catalyzes the oxidation of E2 into estrone (E1), T into androstenedione, DHT into androstanedione, and 20alpha-dihydroprogesterone into progesterone. Specific inhibitors are thus an interesting means to study the regulation and to probe the structure of type II 17beta-HSD. In this context, we have efficiently synthesized a series of 7alpha-thioalkyl and 7alpha-thioaryl derivatives of spironolactone that inhibit type II 17beta-HSD. These new C19-steroidal inhibitors possess two important pharmacophores, namely 17-spiro-gamma-lactone and a bulky side-chain at the 7alpha-position. It was found that a para-substituted benzylthio group at the 7alpha-position enhances the inhibitory potency of spironolactone derivatives on type II 17beta-HSD. In fact, the compound with a para-hydroxy-benzylthio group showed an IC50 value of 0.5 microM against type II 17beta-HSD, whereas the compound with a para-[2-(1-piperidinyl)-ethoxy]-benzylthio group inhibited this enzyme with an IC50 value of 0.7 microM. The latter inhibitor is more selective than the former because it did not show any inhibitory potency against P450 aromatase as well as any affinity towards four steroid receptors (AR, PR, GR, ER). As a result, this inhibitor did not show any proliferative effect on androgen-sensitive Shionogi cells and estrogen-sensitive ZR-75-1 cells. These findings contribute to a better knowledge of the structure of type II 17beta-HSD and offer an interesting tool to study the regulation of this enzyme in several biological systems.     

Expression of aromatase and 17beta-hydroxysteroid dehydrogenase types 1, 7 and 12 in breast cancer. An immunocytochemical study

It is known that there is a local biosynthesis of estradiol (E2) in breast carcinoma. The steroidogenic enzymes involved in E2 formation are aromatase which transforms testosterone into E2 and androstenedione into estrone (E1) and reductive 17beta-hydroxysteroid dehydrogenases (17beta-HSDs) which convert E1 into E2. Using immunocytochemistry, we have studied the expression of aromatase and the three reductive 17beta-HSDs 17beta-HSD types 1, 7 and 12 in 41 specimens of female human breast carcinoma and adjacent non-malignant tissues. These results were correlated with the estrogen receptor alpha (ERalpha) and beta (ERbeta), progesterone receptor, androgen receptor, CDC47 and c-erb B-2 expressions and with the tumor stages. Aromatase was found in 58%, 17beta-HSD type 7 in 47% and 17beta-HSD type 12 in 83% of the breast cancer specimens. The 17beta-HSD type 1 could be detected in only one tumor. A significant correlation was observed between the aromatase, 17beta-HSD type 7 and 17beta-HSD type 12 expression, as well as between each of the two enzymes 17beta-types 7 and 12 and the ERbeta expression. The expression of 17beta-HSD type 12 was significantly higher in breast carcinoma specimens than in normal tissue. There was also a significant association of CDC 47 expression with ERbeta, AR and 17beta-HSD type 12. The results indicate that aromatase, 17beta-HSD type 7 and 17beta-HSD type 12, but not 17beta-HSD type 1, are commonly expressed in human breast cancer. Moreover, the high expression of both 17beta-HSD type 12 and ERbeta in breast carcinoma cells may play a role in the development and/or progression of breast cancer.     

Disorders of the aldosterone synthase and steroid 11beta-hydroxylase deficiencies

The most potent corticosteroids are 11beta-hydroxylated compounds. In humans, two cytochrome P450 isoenzymes with 11beta-hydroxylase activity, catalysing the biosynthesis of cortisol and aldosterone, are present in the adrenal cortex. CYP11B1, the gene encoding 11beta-hydroxylase (P450c11), is expressed on high levels in the zona fasciculata and is regulated by ACTH. CYP11B2, the gene encoding aldosterone synthase (P450c11Aldo), is expressed in the zona glomerulosa under primary control of the renin-angiotensin system. Aldosterone synthase has 11beta-hydroxylase activity as well as 18-hydroxylase activity and 18-oxidase activity. The substrate for CYP11B2 is 11-deoxycorticosterone, that of CYP11B1 is 11-deoxycortisol. Mutations in CYP11B1 cause congenital adrenal hyperplasia (CAH) due to 11beta-hydroxylase deficiency. This disorder is characterized by androgen excess and hypertension. Mutations in CYP11B2 cause congenital hypoaldosteronism (aldosterone synthase deficiency) which is characterized by life-threatening salt loss, failure to thrive, hyponatraemia and hyperkalaemia in early infancy. Both disorders have an autosomal recessive inheritance. Classical and nonclassical forms of 11beta-hydroxylase deficiency can be distinguished. Studies in heterozygotes for classical 11beta-hydroxylase deficiency show inconsistent results with no or only mild hormonal abnormalities (elevated plasma levels of 11-deoxycortisol after ACTH stimulation). In infants with congenital hypoaldosteronism, a comparable frequency of 18-hydroxylase deficiency (aldosterone synthase deficiency type I) and of 18-oxidase deficiency (aldosterone synthase deficiency type II) can be found. Molecular genetic studies of the CYP11B1 and CYP11B2 genes in 11beta-hydroxylase deficiency or aldosterone synthase deficiency have led to the identification of several mutations. Transfection experiments showed loss of enzyme activity in vitro. In some of the patients with 18-oxidase deficiency (aldosterone synthase deficiency type II) no mutations in the CYP11B2 gene were identified. Refined methods for steroid determination are the basis for the diagnosis of inborn errors of steroidogenesis. Molecular genetic studies are complementary; on the one hand, they have practical importance for the prenatal diagnosis of virilizing CAH forms and on the other hand, they are of theoretical importance in terms of our understanding of the functioning of cytochrome P450 enzymes. Copyrightz1999S.KargerAG, Basel     

Molecular characterization of the cynomolgus monkey Macaca fascicularis steroidogenic enzymes belonging to the aldo-keto reductase family

Steroidogenic enzymes belonging to the aldo-keto reductase family (AKR) possess highly homologous sequences while having different activities. To gain further knowledge about the function as well as the regulation of these enzymes in the monkey, we have isolated cDNA sequences encoding monkey type 5 17beta-hydroxysteroid dehydrogenase, 20alpha-hydroxysteroid dehydrogenase and 3alpha-hydroxysteroid dehydrogenase, and characterized their enzymatic activity and mRNA tissue distribution. Sequence analysis indicates that these enzymes share approximately 94 and 76% amino acid identity with human and mouse homologs, respectively. Monkey type 5 17beta-HSD possesses 95.9% amino acid sequence identity with human type 5 17beta-HSD. It catalyzes the transformation of 4-androstenedione into testosterone, but it lacks 20alpha-hydroxysteroid dehydrogenase activity that is present in the human enzyme. This activity seems to be specific to human, since mouse type 5 17beta-HSD does not show significant 20alpha-HSD activity. In addition, monkey and mouse 20alpha-HSD possess relatively high 20alpha-, 3alpha-, and 17beta-HSD activities, while their human counterpart is confined to 20alpha-HSD activity. The monkey 3alpha-HSD possesses relatively high 3alpha-, 17beta-, and 20alpha-HSD activities; human type 1 3alpha-HSD exerts 3alpha- and 20alpha-HSD activities; the mouse 3alpha-HSD displays a unique 3alpha-HSD activity. Quantification of mRNA expression shows that the monkey 3alpha-HSD is exclusively expressed in the liver, while the type 5 17beta-HSD is predominately found in the kidney, with lower levels observed in the stomach, liver, and colon. Monkey 20alpha-HSD mRNA is highly expressed in the kidney, stomach, and liver. Our study provides the basis for future investigations on the regulation and function of these enzymes in the monkey.     

Structure/function of the inhibition of human 3beta-hydroxysteroid dehydrogenase type 1 and type 2 by trilostane

The human type 1 (placenta, breast tumors) and type 2 (gonads, adrenals) isoforms of 3beta-hydroxysteroid dehydrogenase/isomerase (3beta-HSD) are key enzymes in biosynthesis of all active steroid hormones. Human 3beta-HSD1 is a critical enzyme in the conversion of DHEA to estradiol in breast tumors and may be a major target enzyme for the treatment of breast cancer. 3beta-HSD2 participates in the production of cortisol and aldosterone in the human adrenal gland. The goals of this project are to evaluate the role of the 2alpha-cyano group on trilostane (2alpha-cyano-4alpha,5alpha-epoxy-17beta-ol-androstane-3-one) and determine which amino acids may be critical for 3beta-HSD1 specificity. Trilostane without the 2alpha-cyano group, 4alpha,5alpha-epoxy-testosterone, was synthesized. Using our structural model of 3beta-HSD1, trilostane or 4alpha,5alpha-epoxy-testosterone was docked in the active site using Autodock 3.0, and the potentially critical residues (Met187 and Ser124) were identified. The M187T and S124T mutants of 3beta-HSD1 were created, expressed and purified. Dixon analyses of the inhibition of wild-type 3beta-HSD1, 3beta-HSD2, M187T and S124T by trilostane and 4alpha,5alpha-epoxy-testosterone suggest that the 2alpha-cyano group of trilostane is anchored by Ser124 in both isoenzymes. Kinetic analyses of cofactor and substrate utilization as well as the inhibition kinetics of M187T and the wild-type enzymes suggest that the 16-fold higher-affinity inhibition of 3beta-HSD1 by trilostane may be related to the presence of Met187 in 3beta-HSD1 and Thr187 in 3beta-HSD2. This structure/function information may lead to the production of more highly specific inhibitors of 3beta-HSD1 to block the hormone-dependent growth of breast tumors.