Molecular biology of the 3beta-hydroxysteroid dehydrogenase/delta5-delta4 isomerase gene family

The 3beta-hydroxysteroid dehydrogenase/Delta(5)-Delta(4) isomerase (3beta-HSD) isoenzymes are responsible for the oxidation and isomerization of Delta(5)-3beta-hydroxysteroid precursors into Delta(4)-ketosteroids, thus catalyzing an essential step in the formation of all classes of active steroid hormones. In humans, expression of the type I isoenzyme accounts for the 3beta-HSD activity found in placenta and peripheral tissues, whereas the type II 3beta-HSD isoenzyme is predominantly expressed in the adrenal gland, ovary, and testis, and its deficiency is responsible for a rare form of congenital adrenal hyperplasia. Phylogeny analyses of the 3beta-HSD gene family strongly suggest that the need for different 3beta-HSD genes occurred very late in mammals, with subsequent evolution in a similar manner in other lineages. Therefore, to a large extent, the 3beta-HSD gene family should have evolved to facilitate differential patterns of tissue- and cell-specific expression and regulation involving multiple signal transduction pathways, which are activated by several growth factors, steroids, and cytokines. Recent studies indicate that HSD3B2 gene regulation involves the orphan nuclear receptors steroidogenic factor-1 and dosage-sensitive sex reversal adrenal hypoplasia congenita critical region on the X chromosome gene 1 (DAX-1). Other findings suggest a potential regulatory role for STAT5 and STAT6 in transcriptional activation of HSD3B2 promoter. It was shown that epidermal growth factor (EGF) requires intact STAT5; on the other hand IL-4 induces HSD3B1 gene expression, along with IL-13, through STAT 6 activation. However, evidence suggests that multiple signal transduction pathways are involved in IL-4 mediated HSD3B1 gene expression. Indeed, a better understanding of the transcriptional factors responsible for the fine control of 3beta-HSD gene expression may provide insight into mechanisms involved in the functional cooperation between STATs and nuclear receptors as well as their potential interaction with other signaling transduction pathways such as GATA proteins. Finally, the elucidation of the molecular basis of 3beta-HSD deficiency has highlighted the fact that mutations in the HSD3B2 gene can result in a wide spectrum of molecular repercussions, which are associated with the different phenotypic manifestations of classical 3beta-HSD deficiency and also provide valuable information concerning the structure-function relationships of the 3beta-HSD superfamily. Furthermore, several recent studies using type I and type II purified enzymes have elegantly further characterized structure-function relationships responsible for kinetic differences and coenzyme specificity.

Structure and expression of a new complementary DNA encoding the almost exclusive 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4-isomerase in human adrenals and gonads

The 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta HSD) enzyme catalyzes the oxidation and isomerization of delta 5-3 beta-hydroxysteroid precursors into delta 4-ketosteroids, thus leading to the formation of all classes of steroid hormones. In addition, 3 beta HSD catalyzes the interconversion of 3 beta-hydroxy- and 3-keto-5 alpha-androstane steroids. Clinical observations in patients with 3 beta HSD deficiency as well as our recent data obtained by Southern blot analysis using a human placental 3 beta HSD cDNA (type I) as probe suggested the existence of multiple related 3 beta HSD isoenzymes. We now report the isolation and characterization of a second type of cDNA clone (arbitrarily designated type II) encoding 3 beta HSD after screening of a human adrenal lambda gt22A library. The nucleotide sequence of 1676 basepairs of human 3 beta HSD type II cDNA predicts a protein of 371 amino acids with a calculated molecular mass of 41,921 daltons, which displays 93.5% and 96.2% homology with human placental type I and rhesus macaque ovary 3 beta HSD deduced proteins, respectively. To characterize and compare the kinetic properties of the two isoenzymes, plasmids derived from pCMV and containing type I or type II 3 beta HSD full-length cDNA inserts were transiently expressed in HeLa human cervical carcinoma cells. In vitro incubation with NAD+ and 3H-labeled pregnenolone or dehydroepiandrosterone shows that the type I protein possesses a 3 beta HSD/delta 5-delta 4 isomerase activity higher than type II, with respective Km values of 0.24 vs. 1.2 microM for pregnenolone and 0.18 vs. 1.6 microM for dihydroepiandrosterone, while the specific activity of both types is equivalent. Moreover, incubation in the presence of NADH of homogenates from cells transfected with type I or type II 3 beta HSD indicates that dihydrotestosterone is converted into 5 alpha-androstane-3 beta, 17 beta-diol, with Km values of 0.26 and 2.7 microM, respectively. Ribonuclease protection assay using type I- and type II-specific cRNA probes revealed that type II transcripts are the almost exclusive 3 beta HSD mRNA species in the human adrenal gland, ovary, and testis, while type I transcripts correspond to the almost exclusive 3 beta HSD mRNA species in the placenta and skin and represent the predominantly expressed species in mammary gland tissue. The present data show for the first time that adrenals and gonads express a type of 3 beta HSD isoenzyme that is distinct from the type expressed in the placenta.(ABSTRACT TRUNCATED AT 400 WORDS)

Gonadal differentiation, sex determination and normalSryexpression in mice require direct interaction between transcription partners GATA4 and FOG2

In mammals, Sry expression in the bipotential, undifferentiated gonad directs the support cell precursors to differentiate as Sertoli cells, thus initiating the testis differentiation pathway. In the absence of Sry, or if Sry is expressed at insufficient levels, the support cell precursors differentiate as granulosa cells, thus initiating the ovarian pathway. The molecular mechanisms upstream and downstream of Sry are not well understood. We demonstrate that the transcription factor GATA4 and its co-factor FOG2 are required for gonadal differentiation. Mouse fetuses homozygous for a null allele of Fog2 or homozygous for a targeted mutation in Gata4 (Gata4ki) that abrogates the interaction of GATA4 with FOG co-factors exhibit abnormalities in gonadogenesis. We found that Sry transcript levels were significantly reduced in XY Fog2–/– gonads at E11.5, which is the time when Sry expression normally reaches its peak. In addition, three genes crucial for normal Sertoli cell function (Sox9, Mis and Dhh) and three Leydig cell steroid biosynthetic enzymes (p450scc, 3βHSD and p450c17) were not expressed in XY Fog2–/– and Gataki/ki gonads, whereas Wnt4, a gene required for normal ovarian development, was expressed ectopically. By contrast, Wt1 and Sf1, which are expressed prior to Sry and necessary for gonad development in both sexes, were expressed normally in both types of mutant XY gonads. These results indicate that GATA4 and FOG2 and their physical interaction are required for normal gonadal development.

Transcriptional regulation of steroidogenic genes: STARD1, CYP11A1 and HSD3B

Expression of the genes that mediate the first steps in steroidogenesis, the steroidogenic acute regulatory protein (STARD1), the cholesterol side-chain cleavage enzyme, cytochrome P450scc (CYP11A1) and 3beta-hydroxysteroid dehydrogenase/Delta5-Delta4 isomerase (HSD3B), is tightly controlled by a battery of transcription factors in the adrenal cortex, the gonads and the placenta. These genes generally respond to the same hormones that stimulate steroid production through common pathways such as cAMP signaling and common actions on their promoters by proteins such as NR5A and GATA family members. However, there are distinct temporal, tissue and species-specific differences in expression between the genes that are defined by combinatorial regulation and unique promoter elements. This review will provide an overview of the hormonal and transcriptional regulation of the STARD1, CYP11A1 and specific steroidogenic HSD3B genes in the adrenal, testis, ovary and placenta and discuss the current knowledge regarding the key transcriptional factors involved.

Genetics of congenital adrenal hyperplasia

Congenital adrenal hyperplasia (CAH) is one of the most common inherited metabolic disorders. It comprises a group of autosomal recessive disorders caused by the deficiency of one of four steroidogenic enzymes involved in cortisol biosynthesis or in the electron donor enzyme P450 oxidoreductase (POR) that serves as electron donor to steroidogenic cytochrome P450 (CYP) type II enzymes. The biochemical and clinical phenotype depends on the specific enzymatic defect and the impairment of specific enzyme activity. Defects of steroid 21-hydroxylase (CYP21A2) and 11beta-hydroxylase (CYP11B1) only affect adrenal steroidogenesis, whereas 17alpha-hydroxylase (CYP17A1) and 3beta-hydroxysteroid dehydrogenase type 2 (HSD3B2) deficiency also impact on gonadal steroid biosynthesis. Inactivating POR gene mutations are the cause of CAH manifesting with apparent combined CYP17A1-CYP21A2 deficiency. P450 oxidoreductase deficiency (ORD) has a complex phenotype including two unique features not observed in any other CAH variant: skeletal malformations and severe genital ambiguity in both sexes.

Human 3 beta-hydroxysteroid dehydrogenase/delta 5----4isomerase from placenta: expression in nonsteroidogenic cells of a protein that catalyzes the dehydrogenation/isomerization of C21 and C19 steroids

The isolation, cloning, and expression of a cDNA insert complementary to mRNA encoding human 3 beta-hydroxysteroid dehydrogenase/delta 5----4isomerase is reported. The insert contains an open reading frame encoding a protein of 372 amino acids, the initial 29 amino acids corresponding to the N-terminal sequence identified from the purified human placental microsomal enzyme. The cDNA was inserted into a modified pCMV vector and expressed in COS-1 monkey kidney tumor cells. The expressed protein was similar in size to human placental microsomal 3 beta-hydroxysteroid dehydrogenase/delta 5----4isomerase, as detected by immunoblot analysis, and catalyzed the conversion of 17 alpha-hydroxypregnenolone to 17 alpha-hydroxyprogesterone, pregnenolone to progesterone, and dehydroepiandrosterone to androstenedione. Transfected COS cell homogenates, supplemented with NAD+, very efficiently oxidized 5 alpha-androstan-3 beta,17 beta-diol to 5 alpha-dihydrotestosterone and, upon addition of NADH, reduced 5 alpha-dihydrotestosterone to 5 alpha-androstan-3 beta,17 beta-diol. Thus, the dehydrogenation/isomerization steps of steroid biosynthesis can be catalyzed by a single polypeptide chain, which can metabolize all of the major physiological substrates.

Synergistic activation of the human type II 3beta-hydroxysteroid dehydrogenase/delta5-delta4 isomerase promoter by the transcription factor steroidogenic factor-1/adrenal 4-binding protein and phorbol ester

Steroidogenic factor-1/adrenal 4-binding protein (SF-1/Ad4BP) is an orphan nuclear receptor/transcription factor known to regulate the P450 steroid hydroxylases; however, mechanisms that regulate the activity of SF-1/Ad4BP are not well defined. In addition, little is known about the mechanisms that regulate the human steroidogenic enzyme, type II 3beta-hydroxysteroid dehydrogenase (3beta-HSD II), the major gonadal and adrenal isoform. Regulation of the 3beta-HSD II promoter was examined using human adrenal cortical (H295R; steroidogenic) and cervical (HeLa; non-steroidogenic) carcinoma cells. H295R cells were transfected with a series of 5' deletions of 1251 base pairs (bp) of the 3beta-HSD II 5'-flanking region fused to a chloramphenicol acetyltransferase (CAT) reporter gene followed by treatment with or without phorbol ester (phorbol 12-myristate 13-acetate; PMA). CAT assay data indicated that the region from -101 to -52 bp of the promoter was required for PMA-induced expression. A putative SF-1/Ad4BP regulatory element, TCAAGGTAA, was identified by sequence homology at -64 to -56 bp of the promoter. Cotransfection of HeLa cells with the -101 3beta-HSD-CAT construct and an expression vector for SF-1/Ad4BP increased CAT activity 49-fold. Subsequent treatment with PMA induced an unexpected synergistic increase in transcriptional activity 540-fold over basal. Mutation of the putative response element (TCAAGGTAA to TCAATTTAA) abolished SF-1-induced CAT activity and the synergistic response to PMA. Gel mobility shift assays confirmed that SF-1/Ad4BP interacts with the putative element and transcripts for SF-1/Ad4BP were detected in H295R cells by Northern analysis. These data are the first to demonstrate 1) regulation of a non-cytochrome P450 steroidogenic enzyme promoter by SF-1/Ad4BP, 2) a powerful synergistic effect of PMA on SF-1/Ad4BP-induced transcription, and 3) the importance of the SF-1/Ad4BP regulatory element in the regulation of the 3beta-HSD II promoter.

HSD3B1 and resistance to androgen-deprivation therapy in prostate cancer: a retrospective, multicohort study

BACKGROUND

HSD3B1 (1245A>C) has been mechanistically linked to castration-resistant prostate cancer because it encodes an altered enzyme that augments dihydrotestosterone synthesis from non-gonadal precursors. We postulated that men inheriting the HSD3B1 (1245C) allele would exhibit resistance to androgen-deprivation therapy (ADT).

METHODS

In this multicohort study, we determined HSD3B1 genotype retrospectively in men treated with ADT for post-prostatectomy biochemical failure and correlated genotype with long-term clinical outcomes. We used data and samples from prospectively maintained prostate cancer registries at the Cleveland Clinic (Cleveland, OH, USA; primary study cohort) and the Mayo Clinic (Rochester, MN, USA; post-prostatectomy and metastatic validation cohorts). In the post-prostatectomy cohorts, patients of any age were eligible if they underwent prostatectomy between Jan 1, 1996, and Dec 31, 2009 (at the Cleveland Clinic; primary cohort), or between Jan 1, 1987, and Dec 31, 2011 (at the Mayo Clinic; post-prostatectomy cohort) and were treated with ADT for biochemical failure or for non-metastatic clinical failure. In the metastatic validation cohort, patients of any age were eligible if they were enrolled at Mayo Clinic between Sept 1, 2009, and July 31, 2013, with metastatic castration-resistant prostate cancer. The primary endpoint was progression-free survival according to HSD3B1 genotype. We did prespecified multivariable analyses to assess the independent predictive value of HSD3B1 genotype on outcomes.

FINDINGS

We included and genotyped 443 patients: 118 in the primary cohort (who underwent prostatectomy), 137 in the post-prostatectomy validation cohort, and 188 in the metastatic validation cohort. In the primary study cohort, median progression-free survival diminished as a function of the number of variant alleles inherited: 6·6 years (95% CI 3·8-not reached) in men with homozygous wild-type genotype, 4·1 years (3·0-5·5) in men with heterozygous variant genotype, and 2·5 years (0·7 to not reached) in men with homozygous variant genotype (p=0·011). Relative to the homozygous wild-type genotype, inheritance of two copies of the variant allele was predictive of decreased progression-free survival (hazard ratio [HR] 2·4 [95% CI 1·1-5·3], p=0·029), as was inheritance of one copy of the variant allele (HR 1·7 [1·0-2·9], p=0·041). Findings were similar for distant metastasis-free survival and overall survival. The effect of the HSD3B1 genotype was independently confirmed in the validation cohorts.

INTERPRETATION

Inheritance of the HSD3B1 (1245C) allele that enhances dihydrotestosterone synthesis is associated with prostate cancer resistance to ADT. HSD3B1 could therefore potentially be a powerful genetic biomarker capable of distinguishing men who are a priori likely to fare favourably with ADT from those who harbour disease liable to behave more aggressively, and who therefore might warrant early escalated therapy.

FUNDING

Prostate Cancer Foundation, National Institutes of Health, US Department of Defense, Howard Hughes Medical Institute, American Cancer Society, Conquer Cancer Foundation of the American Society of Clinical Oncology, Cleveland Clinic Research Programs Committee and Department of Radiation Oncology, Gail and Joseph Gassner Development Funds.

The human 3beta-hydroxysteroid dehydrogenase/Delta5-Delta4 isomerase type 2 promoter is a novel target for the immediate early orphan nuclear receptor Nur77 in steroidogenic cells

The human (h) 3beta-hydroxysteroid dehydrogenase/Delta5-Delta4 isomerase type 2 (3beta-HSD2) enzyme, encoded by the hHSD3B2 gene, is mainly found in gonads and adrenals. This enzyme catalyzes an essential early step in the biosynthesis of all classes of steroid hormones. The critical nature of the enzyme is supported by the occurrence of human syndromes that are associated with insufficient 3beta-HSD2 expression and/or activity. Although the need for a functional 3beta-HSD2 enzyme is indisputable, the molecular mechanisms that regulate HSD3B2 expression (both basal and hormone-induced) in steroidogenic cells remain poorly understood. A role for the Nur77 family of immediate-early orphan nuclear receptors in steroidogenesis has received recent interest. For example, Nur77 is present in gonads and adrenals, where its expression is robustly and rapidly induced by hormones that stimulate steroidogenic gene expression. Moreover, the expression patterns of Nur77 and at least one key steroidogenic gene (hHSD3B2) closely parallel one another. We now report that the hHSD3B2 promoter is indeed a novel target for Nur77 in both testicular Leydig cells and adrenal cells. We have mapped a novel response element located at -130 bp specific for Nur77 and not other orphan nuclear receptors (steroidogenic factor-1 and liver receptor homolog-1) previously shown to regulate hHSD3B2 promoter activity. This Nur77 element is essential and sufficient to confer Nur77 responsiveness to the hHSD3B2 promoter, and its mutation blunts basal and hormone-induced hHSD3B2 promoter activity in steroidogenic cells. We also show that Nur77 synergizes with all members of the steroid receptor coactivator family of coactivators on the hHSD3B2 promoter. Taken together, our identification of Nur77 as an important regulator of HSD3B2 promoter activity helps us to better define the tissue-specific and hormonal regulation of the HSD3B2 gene in steroidogenic cells.

Structure, function and tissue-specific gene expression of 3β-hydroxysteroid dehydrogenase/5-ene-4-ene isomerase enzymes in classical and peripheral intracrine steroidogenic tissues

The membrane-bound enzyme 3β-hydroxysteroid dehydrogenase/5-ene-4-ene isomerase (3β-HSD) catalyses an essential step in the transformation of all 5-pregnen-3β-ol and 5-androsten-3β-ol steroids into the corresponding 3-keto-4-ene-steroids, namely progesterone as well as all the precursors of androgens, estrogens, glucocorticoids and mineralocorticoids. We have recently characterized two types of human 3β-HSD cDNA clones and the corresponding genes which encode type I and II 3β-HSD isoenzymes of 372 and 371 amino acids, respectively, and share 93.5% homology. The human 3β-HSD genes containing 4 exons were assigned by in situ hybridization to the p11-p13 region of the short arm of chromosome 1. Human type I 3β-HSD is the almost exclusive mRNA species present in the placenta and skin while the human type II is the predominant mRNA species in the adrenals, ovaries and testes. The type I protein possesses higher 3β-HSD activity than type II. We elucidated the structures of three types of rat 3β-HSD cDNAs as well that of one type of 3β-HSD from bovine and macaque ovary λgt11 cDNA libraries, which all encode a 372 amino acid protein. The rat type I and II 3β-HSD proteins expressed in the adrenals, gonads and adipose tissue share 93.8% homology. Transient expression of human type I and II as well as rat type I and II 3β-HSD cDNAs in HeLa human cervical carcinoma cells reveals that 3β-ol dehydrogenase and 5-ene-4-ene isomerase activities reside within a single protein. These expressed 3β-HSD proteins convert 3β-hydroxy-5-ene-steroids into 3-keto-4-ene derivatives and catalyze the interconversion of 3β-hydroxy and 3-keto-5α-androstane steroids. By site-directed mutagenesis, we demonstrated that the lower activity of expressed rat type II compared to rat type I 3β-HSD is due to a change of four residues probably involved in a membrane-spanning domain. When homogenates from cells transfected with a plasmid vector containing rat type I 3β-HSD is incubated in the presence of dihydrotestosterone (DHT) using NAD⁺ as co-factor, 5α-androstanedione was formed (A-dione), indicating an intrinsic androgenic 17β-hydroxysteroid dehydrogenase (17β-HSD) activity of this 3β-HSD. We cloned a third type of rat cDNA encoding a predicted type III 3β-HSD specifically expressed in the rat liver, which shares 80% similarity with the two other isoenzymes. Transient expression in human HeLa cells reveals that the type III isoenzyme does not display oxidative activity for the classical substrates of 3β-HSD. However, in common with the type I enzyme, it converts A-dione and DHT to the corresponding 3β-hydroxysteroids, thus showing an exclusive 3-ketosteroid reductase activity. When NADPH is used as co-factor, the affinity for DHT of the type III enzyme becomes 10-fold higher than that of the type I. Rat type III mRNA was below the detection limit in intact female liver. Following hypophysectomy, its concentration increased to 55% of the values measured in intact or hypophysectomized male rats, an increase which can be blocked by administration of ovine prolactin (oPRL). Treatment with oPRL for 10 days starting 15 days after hypophysectomy markedly decreased ovarian 3β-HSD mRNA accumulation accompanied by a similar decrease in 3β-HSD activity and protein levels. Treatment with the gonadotropin hCG reversed the potent inhibitory effect of oPRL on these parameters and stimulated 3β-HSD mRNA levels in ovarian interstitial cells. These data indicate that the presence of multiple 3β-HSD isoenzymes offers the possibility of tissue-specific expression and regulation of this enzymatic activity that plays an essential role in the biosynthesis of all hormonal steroids in classical as well as peripheral intracrine steroidogenic tissues.

Self-sufficient biosynthesis of pregnenolone and progesterone in engineered yeast

The first two steps of the steroidogenic pathway were reproduced in Saccharomyces cerevisiae. Engineering of sterol biosynthesis by disruption of the delta 22-desaturase gene and introduction of the Arabidopsis thaliana delta 7-reductase activity and coexpression of bovine side chain cleavage cytochrome P450, adrenodoxin, and adrenodoxin reductase, lead to pregnenolone biosynthesis from a simple carbon source. Following additional coexpression of human 3 beta-hydroxysteroid dehydrogenase/isomerase, pregnenolone is further metabolized to progesterone. Steroid formation appears to be coupled to yeast sterol biosynthesis.

Structure/function relationships responsible for the kinetic differences between human type 1 and type 2 3beta-hydroxysteroid dehydrogenase and for the catalysis of the type 1 activity

Two distinct genes encode the 93% homologous type 1 (placenta, peripheral tissues) and type 2 (adrenals, gonads) 3beta-hydroxysteroid dehydrogenase/isomerase (3beta-HSD/isomerase) in humans. Mutagenesis studies using the type 1 enzyme have produced the Y154F and K158Q mutant enzymes in the Y(154)-P-H(156)-S-K(158) motif as well as the Y269S and K273Q mutants from a second motif, Y(269)-T-L-S-K(273), both of which are present in the primary structure of the human type 1 3beta-HSD/isomerase. In addition, the H156Y mutant of the type 1 enzyme has created a chimera of the type 2 enzyme motif (Y(154)-P-Y(156)-S-K(158)) in the type 1 enzyme. The mutant and wild-type enzymes have been expressed and purified. The K(m) value of dehydroepiandrosterone is 13-fold greater, and the maximal turnover rate (K(cat)) is 2-fold greater for wild-type 2 3beta-HSD compared with the wild-type 1 3beta-HSD activity. The H156Y mutant of the type 1 enzyme has substrate kinetic constants for 3beta-HSD activity that are very similar to those of the wild-type 2 enzyme. Dixon analysis shows that epostane inhibits the 3beta-HSD activity of the wild-type 1 enzyme with 14-17-fold greater affinity compared with the wild-type 2 and H156Y enzymes. The Y154F and K158Q mutants exhibit no 3beta-HSD activity, have substantial isomerase activity, and utilize substrate with K(m) values similar to those of wild-type 1 isomerase. The Y269S and K273Q mutants have low, pH-dependent 3beta-HSD activity, exhibit only 5% of the maximal isomerase activity, and utilize the isomerase substrate very poorly. From these studies, a structural basis for the profound differences in the substrate and inhibition kinetics of the wild-type 1 and 2 3beta-HSD, plus a catalytic role for the Tyr(154) and Lys(158) residues in the 3beta-HSD reaction have been identified. These advances in our understanding of the structure/function of human type 1 and 2 3beta-HSD/isomerase may lead to the design of selective inhibitors of the type 1 enzyme not only in placenta to control the onset of labor but also in hormone-sensitive breast, prostate, and choriocarcinoma tumors to slow their growth.

Multiple forms of mouse 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase and differential expression in gonads, adrenal glands, liver, and kidneys of both sexes

Observations of patients deficient in the steroidogenic enzyme 3 beta-hydroxy-delta 5-steroid dehydrogenase/isomerase (3 beta HSD) have suggested the presence of distinct 3 beta HSD structural gene(s) that are expressed at peripheral sites, possibly the liver. We now report the isolation of cDNA clones representing three forms of 3 beta HSD from mouse Leydig cell and liver libraries. The three forms share significant identify but differ from each other by 5-10% within their coding regions. RNA that hybridizes to radiolabeled 3 beta HSD probes is present in the gonads, adrenal glands, liver, and kidneys of both sexes. Ribonuclease protection analysis using antisense probes derived from each of the three forms demonstrates that one form, 3 beta HSD I, is restricted to steroidogenic tissues. Two other forms, 3 beta HSD II and III, are expressed in liver and kidney but are not detected in steroidogenic tissues. A polyclonal antibody raised against the human placental form of 3 beta HSD recognizes a 42-kDa protein in gonadal and adrenal tissue and a 45-kDa protein in liver. The antibody recognizes a 42-kDa protein in kidney only weakly. 3 beta HSD enzyme activity is present in testicular, adrenal, hepatic, and renal tissue, with adrenal tissue possessing the highest specific activity. When expressed as total 3 beta HSD activity for whole organ mass, activity is greatest in the liver. The results demonstrate that the mouse liver is a significant site of 3 beta HSD activity and demonstrate the existence of multiple 3 beta HSD structural genes in the mouse.

Characterization, expression, and immunohistochemical localization of 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase in human skin

Three beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD) catalyses an obligatory step in the biosynthesis of all classes of hormonal steroids, namely, the oxidation/isomerization of 3 beta-hydroxy-5-ene steroids into the corresponding 3-keto-4-ene steroids in gonadal as well as in peripheral tissues. Because humans are unique with some primates in having adrenals that secrete large amounts of the steroid precursors dehydropiandrosterone (DHEA) and its sulfate (DHEA-S) and its exceptionally large volume makes the skin an important site of steroid biosynthesis, we have isolated and characterized cDNA clones encoding 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase from a human skin lambda gt11 library. The longest clone obtained contains the entire coding sequence for type I 3 beta-HSD (372 amino acids) as well as an additional 131 nucleotides in the 5'-untranslated region. The insert of 1647 bp containing the entire coding region has been inserted in a pCMV expression vector and transfected into human cervical carcinoma cells (HeLa). The expressed enzyme efficiently catalyzes the transformation of pregnenolone, DHEA, and dihydrotestosterone into progesterone, 4-androstenedione, and 5 alpha-androstane-3 beta, 17 beta-diol, respectively. Using the enzyme expressed in HeLa cells, we have shown cyproterone acetate, a progestin used in the treatment of acne and hirsutism, as well as norgestrel and norethindrone, two steroids widely used as oral contraceptives, to be relatively potent inhibitors, with Ki values of 0.38 microM, 1.3 microM, and 1.2 microM, respectively. Immunohistochemical localization of 3 beta-HSD, illustrated by using an antibody raised against human placental 3 beta-HSD, shows that the enzyme is localized in sebaceous glands.

Structural analysis of the gene encoding human 3 beta-hydroxysteroid dehydrogenase/delta 5----4-isomerase

The structural gene encoding human 3 beta-hydroxysteroid dehydrogenase/delta 5----4-isomerase (3 beta HSD) was isolated from a human EMBL3 genomic library. The gene encompasses approximately 8 kilobases of DNA and is comprised of two large introns and three exons encoding amino acid residues 1-48, 49-103, and 104-373, respectively. The exonic sequence is identical to that of the cDNA that we previously isolated and expressed in COS 1 cells. DNA sequence analysis reveals a putative TATA (TATATAA) motif 26 basepairs up-stream of the beginning of exon I, as determined by S1 nuclease protection analysis. However, primer extension analysis using poly(A)+ RNA isolated from both placenta and corpora lutea indicates that the RNA initiates up-stream of the putative TATA motif, and that an additional 53-basepair exon, which is untranslated, is present 5' to the first coding exon. Southern hybridization analysis of genomic DNA using a single exon probe suggests that there may be more than one copy of the gene in the human genome. In addition, we confirm from Southern analysis of genomic DNA isolated from human x hamster somatic cell hybrids that the gene is located on human chromosome 1. These findings will provide a foundation for the characterization of apparent 3 beta HSD clinical deficiencies when these are due to a mutation in the structural gene.

Sub-acute intravenous administration of silver nanoparticles in male mice alters Leydig cell function and testosterone levels

The aim of this study was to determine whether short-term, in vivo exposure to silver nanoparticles (AgNPs) could be toxic to male reproduction. Low dose (1mg/kg/dose) AgNPs were intravenously injected into male CD1 mice over 12 days. Treatment resulted in no changes in body and testis weights, sperm concentration and motility, fertility indices, or follicle-stimulating hormone and luteinizing hormone serum concentrations; however, serum and intratesticular testosterone concentrations were significantly increased 15 days after initial treatment. Histologic evaluation revealed significant changes in epithelium morphology, germ cell apoptosis, and Leydig cell size. Additionally, gene expression analysis revealed Cyp11a1 and Hsd3b1 mRNA significantly upregulated in treated animals. These data suggest that AgNPs do not impair spermatogonial stem cells in vivo since treatment did not result in significant decreases in testis weight and sperm concentrations. However, AgNPs appear to affect Leydig cell function, yielding increasing testicular and serum testosterone levels.

Metformin inhibits human androgen production by regulating steroidogenic enzymes HSD3B2 and CYP17A1 and complex I activity of the respiratory chain

Metformin is treatment of choice for the metabolic consequences seen in polycystic ovary syndrome for its insulin-sensitizing and androgen-lowering properties. Yet, the mechanism of action remains unclear. Two potential targets for metformin regulating steroid and glucose metabolism are AMP-activated protein kinase (AMPK) signaling and the complex I of the mitochondrial respiratory chain. Androgen biosynthesis requires steroid enzymes 17α-Hydroxylase/17,20 lyase (CYP17A1) and 3β-hydroxysteroid dehydrogenase type 2 (HSD3B2), which are overexpressed in ovarian cells of polycystic ovary syndrome women. Therefore, we aimed to understand how metformin modulates androgen production using NCI-H295R cells as an established model of steroidogenesis. Similar to in vivo situation, metformin inhibited androgen production in NCI cells by decreasing HSD3B2 expression and CYP17A1 and HSD3B2 activities. The effect of metformin on androgen production was dose dependent and subject to the presence of organic cation transporters, establishing an important role of organic cation transporters for metformin's action. Metformin did not affect AMPK, ERK1/2, or atypical protein kinase C signaling. By contrast, metformin inhibited complex I of the respiratory chain in mitochondria. Similar to metformin, direct inhibition of complex I by rotenone also inhibited HSD3B2 activity. In conclusion, metformin inhibits androgen production by mechanisms targeting HSD3B2 and CYP17-lyase. This regulation involves inhibition of mitochondrial complex I but appears to be independent of AMPK signaling.

GATA factors and the nuclear receptors, steroidogenic factor 1/liver receptor homolog 1, are key mutual partners in the regulation of the human 3beta-hydroxysteroid dehydrogenase type 2 promoter

The human HSD3B2 gene encodes the 3beta-hydroxysteroid dehydrogenase/delta5-delta4 isomerase type 2 (3beta-HSD2) enzyme that is required for steroid hormone biosynthesis. Mutations in the hHSD3B2 gene are responsible for a form of congenital adrenal hyperplasia and male pseudohermaphroditism whereas overexpression of hHSD3B2 has been recently associated with polycystic ovarian syndrome. Despite the importance of the hHSD3B2 gene, the molecular mechanisms that regulate its expression remain poorly understood. Transcription factors belonging to the GATA family are emerging as novel regulators of steroidogenesis. Indeed, GATA-4 and GATA-6 are abundantly expressed in steroidogenic cells of the gonads and adrenals. We now report that the human HSD3B2 promoter (hHSD3B2), which contains four consensus GATA elements, constitutes an important target for GATA factors. GATA-4 and GATA-6 by themselves are sufficient to activate transcription (up to 15-fold) from a -1073 bp hHSD3B2 promoter fragment and blockade of endogenous GATA expression and/or activity blunts hHSD3B2 promoter activity in steroidogenic cells. Deletion studies showed that the proximal GATA element located at -196 bp is sufficient to confer GATA responsiveness of the hHSD3B2 promoter and is required for full hHSD3B2 promoter activity in steroidogenic cells. Moreover, we report that GATA-4 and GATA-6 can physically interact with the nuclear receptors, steroidogenic factor 1 and liver receptor homolog 1, to synergistically activate hHSD3B2 promoter activity in both homologous and heterologous cells. Aberrant expression of transcription factors essential for hHSD3B2 expression might also be involved in some pathologies/syndromes associated with deregulated hHSD3B2 expression.

Structure and sexual dimorphic expression of a liver-specific rat 3 beta-hydroxysteroid dehydrogenase/isomerase

The enzyme 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD) catalyzes the obligatory oxidation and isomerization of delta 5-3 beta-hydroxysteroid precursors into delta 4-3-ketosteroids which lead to the formation of all classes of steroid hormones. We report the molecular cloning of a third type of cDNA clone encoding rat 3 beta- HSD isolated from a rat liver lambda gt11 cDNA library. The nucleotide sequence of 1955 bp determined from overlapping cDNA clones predicts a protein of 372 amino acids which displays 80% similarity with that of rat type I and type II 3 beta-HSD proteins. RNA blot analysis reveals the presence of mRNA transcripts of 2.1 kb in male liver in contrast to the 1.7 kb mRNA species detected in adrenal and gonad poly(A)+ RNA. Ribonuclease protection assays using type I, type II and type III specific cRNA probes demonstrate the liver-specific expression of type III mRNA while the two others are expressed in adrenals and gonads. The type III mRNA species was below the detection limit in intact female liver while in hypophysectomized females, its accumulation was restored to 55% of the levels measured in intact or hypophysectomized male rats. The present data describe the presence of a third type of 3 beta-HSD mRNA species and its marked sexual dimorphic gene expression in the liver which apparently results from pituitary hormone-induced gene repression in female rat liver tissue.

Molecular cloning, cDNA structure and predicted amino acid sequence of bovine 3 beta-hydroxy-5-ene steroid dehydrogenase/delta 5-delta 4 isomerase

We have used our recently characterized human 3 beta-hydroxy-5-ene steroid dehydrogenase/delta 5-delta 4-isomerase (3 beta-HSD) cDNA as probe to isolate cDNAs encoding bovine 3 beta-HSD from a bovine ovary lambda gtll cDNA library. Nucleotide sequence analysis of two overlapping cDNA clones of 1362 bp and 1536 bp in length predicts a protein of 372 amino acids with a calculated molecular mass of 42,093 (excluding the first Met). The deduced amino acid sequence of bovine 3 beta-HSD displays 79% homology with human 3 beta-HSD while the nucleotide sequence of the coding region shares 82% interspecies similarity. Hybridization of cloned cDNAs to bovine ovary poly(A)+ RNA shows the presence of an approximately 1.7 kb mRNA species.

Structure and tissue-specific expression of 3 beta-hydroxysteroid dehydrogenase/5-ene-4-ene isomerase genes in human and rat classical and peripheral steroidogenic tissues

The enzyme 3 beta-hydroxysteroid dehydrogenase/5-ene-4-ene isomerase (3 beta-HSD) catalyzes the oxidation and isomerization of 5-ene-3 beta-hydroxypregnene and 5-ene-hydroxyandrostene steroid precursors into the corresponding 4-ene-ketosteroids necessary for the formation of all classes of steroid hormones. We have recently characterized two types of human 3 beta-HSD cDNA clones and the corresponding genes which encode deduced proteins of 371 and 372 amino acids, respectively, and share 93.5% homology. The human 3 beta-HSD genes containing 4 exons were assigned by in situ hybridization to the p11-p13 region of the short arm of chromosome 1. We have also recently elucidated the structure of three types of rat 3 beta-HSD cDNAs as well as that of one type of 3 beta-HSD from bovine and macaque ovary lambda gt11 cDNA libraries which all encode 372 amino acid proteins. The human type I 3 beta-HSD is the almost exclusive mRNA species detected in the placenta and skin, while the human type II is the predominant mRNA species in the adrenals, ovaries and testes. The predicted rat type I and type II 3 beta-HSD proteins expressed in adrenals, gonads and adipose tissue share 94% homology while they share 80% similarity with the liver-specific type III 3 beta-HSD. Transient expression of human type I and type II as well as rat type I and type II 3 beta-HSD cDNAs in HeLa human cervical carcinoma cells reveals that 3 beta-ol dehydrogenase and 5-ene-4-ene isomerase activities reside within a single protein and these cDNAs encode functional 3 beta-HSD proteins that are capable of converting 3 beta-hydroxy-5-ene-steroids into 3-keto-4-ene derivatives as well as the interconversion of 3 beta-hydroxy and 3-keto-5 alpha-androstane steroids. We have found that the rat type III mRNA species was below the detection limit in intact female liver while, following hypophysectomy, its accumulation increased to 55% of the levels measured in intact or HYPOX male rats, an increase which can be blocked by administration of ovine prolactin (oPRL). In addition, in female rats, treatment with oPRL for 10 days starting 15 days after HYPOX, markedly decreased ovarian 3 beta-HSD mRNA accumulation accompanied by a similar decrease in 3 beta-HSD activity and protein levels. Treatment with the gonadotropin hCG reversed the potent inhibitory effect of oPRL on these parameters and stimulated 3 beta-HSD mRNA levels in ovarian interstitial cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Neurosteroids and female reproduction: estrogen increases 3beta-HSD mRNA and activity in rat hypothalamus

A central event in mammalian reproduction is the LH surge that induces ovulation and corpus luteum formation. Typically, the LH surge is initiated in ovariectomized rats by sequential treatment with estrogen and progesterone (PROG). The traditional explanation for this paradigm is that estrogen induces PROG receptors (PR) that are activated by exogenous PROG. Recent evidence suggests that whereas exogenous estrogen is necessary, exogenous PROG is not. In ovariectomized-adrenalectomized rats, estrogen treatment increases hypothalamic PROG levels before an LH surge. This estrogen-induced LH surge was blocked by an inhibitor of 3beta-hydroxysteroid dehydrogenase/delta5-delta4 isomerase (3beta-HSD), the proximal enzyme for PROG synthesis. These data indicate that estrogen induces de novo synthesis of PROG from cholesterol in the hypothalamus, which initiates the LH surge. The mechanism(s) by which estrogen up-regulates neuro-PROG is unknown. We investigated whether estrogen increases 1) mRNA levels for several proteins involved in PROG synthesis and/or 2) activity of 3beta-HSD in the hypothalamus. In ovariectomized-adrenalectomized rats, estrogen treatment increased 3beta-HSD mRNA in the hypothalamus, as measured by relative quantitative RT-PCR. The mRNAs for other proteins involved in steroid synthesis (sterol carrier protein 2, steroidogenic acute regulatory protein, and P450 side chain cleavage) were detectable in hypothalamus but not affected by estrogen. In a biochemical assay, estrogen treatment also increased 3beta-HSD activity. These data support the hypothesis that PROG is a neurosteroid, produced locally in the hypothalamus from cholesterol, which functions in the estrogen positive-feedback mechanism driving the LH surge.

Endogenous ouabain: upregulation of steroidogenic genes in hypertensive hypothalamus but not adrenal

BACKGROUND

Mammalian tissues contain a presumed endogenous Na+, K(+)-ATPase inhibitor that binds reversibly to the Na+ pump with high affinity and specificity. The inhibitor has been linked to the pathogenesis of experimental volume-expanded and human essential hypertension. This compound has been isolated from mammalian hypothalamus and appears to be an isomer of the plant-derived cardiac glycoside ouabain, if not ouabain itself. The objective of this study was to test the hypothesis that a biosynthetic pathway exists in mammalian tissues to produce a steroid derivative closely related to plant cardiac glycosides.

METHODS AND RESULTS

Using bioinformatics and genomic techniques, Milan hypertensive rat tissues were studied because this strain has a 10-fold increase in hypothalamic ouabain-like compound that is linked to the pathogenesis of the hypertension. A putative steroid biosynthetic pathway was constructed and candidate genes encoding enzymes in this pathway were identified from sequence databases. Differential expression of selected genes in the pathway was studied by microarray analysis and quantitative polymerase chain reaction, with functional validation by gene silencing using small interfering RNAs. Marked upregulation of genes coding for P450 side chain cleavage and Delta5-3beta-hydroxysteroid dehydrogenase/Delta5-Delta4- isomerase enzymes in hypertensive hypothalamus but not adrenal was found, compared with normotensive Milan rats. Knockdown of the latter gene decreased production of ouabain-like factor from neural tissue.

CONCLUSIONS

Our findings support the possibility that a unique steroid biosynthetic circuit exists in Milan rat brain, functioning independently from adrenal, which could account for the overproduction of the hypothalamic ouabain-like compound in this species.

Regulation of steroidogenic genes by insulin-like growth factor-1 and follicle-stimulating hormone: differential responses of cytochrome P450 side-chain cleavage, steroidogenic acute regulatory protein, and 3beta-hydroxysteroid dehydrogenase/isomerase in rat granulosa cells

The present study sought to characterize the concerted action of FSH and insulin-like growth factor-1 (IGF-1) on functional differentiation of prepubertal rat ovarian granulosa cells in culture. To this end, we examined the regulation of three key genes encoding pivotal proteins required for progesterone biosynthesis, namely, side-chain cleavage cytochrome P450 (P450(scc)), steroidogenic acute regulatory (StAR) protein, and 3beta-hydroxysteroid dehydrogenase/isomerase (3beta-HSD). Time-dependent expression profiles showed that P450(scc), StAR, and 3beta-HSD gene products accumulate in chronic, acute, and constitutive patterns, respectively. Each of these genes responded to FSH and/or IGF-1 in a characteristic manner: A synergistic action of IGF-1 was indispensable for FSH induction of P450(scc) mRNA and protein; IGF-1 did not affect FSH-mediated upregulation of StAR products; and IGF-1 alone was enough to promote expression of 3beta-HSD. The responsiveness of the genes to IGF-1 correlated well with their apparent susceptibility to the inhibitory impact of tyrphostin AG18, a potent inhibitor of protein tyrosine kinase receptors. Thus, IGF-1-dependent P450(scc) and 3beta-HSD expression was completely arrested in the presence of AG18, whereas StAR expression was unaffected in the presence of tyrphostin. These findings suggest that FSH/cAMP signaling and IGF-1/tyrosine phosphorylation events are interwoven in rat ovarian cells undergoing functional differentiation. We also sought the mechanism of IGF-1 synergy with FSH. In this regard, our studies were unable to demonstrate a stabilizing effect of IGF-1 on P450(scc) mRNA, nor could IGF-1 augment FSH-induced transcription examined using a proximal region of the P450(scc) promoter (-379/+6). Thus, the mechanism of IGF-1 and FSH synergy remains enigmatic and provides a major challenge for future studies.

Structure/function relationships responsible for coenzyme specificity and the isomerase activity of human type 1 3 beta-hydroxysteroid dehydrogenase/isomerase

Human type 1 3 beta-hydroxysteroid dehydrogenase/isomerase (3 beta-HSD/isomerase) catalyzes the two sequential enzyme reactions on a single protein that converts dehydroepiandrosterone or pregnenolone to androstenedione or progesterone, respectively, in placenta, mammary gland, breast tumors, prostate, prostate tumors, and other peripheral tissues. Our earlier studies show that the two enzyme reactions are linked by the coenzyme product, NADH, of the 3 beta-HSD activity. NADH activates the isomerase activity by inducing a time-dependent conformational change in the enzyme protein. The current study tested the hypothesis that the 3 beta-HSD and isomerase activities shared a common coenzyme domain, and it characterized key amino acids that participated in coenzyme binding and the isomerase reaction. Homology modeling with UDP-galactose-4-epimerase predicts that Asp36 is responsible for the NAD(H) specificity of human 3 beta-HSD/isomerase and identifies the Rossmann-fold coenzyme domain at the amino terminus. The D36A/K37R mutant in the potential coenzyme domain and the D241N, D257L, D258L, and D265N mutants in the potential isomerase domain (previously identified by affinity labeling) were created, expressed, and purified. The D36A/K37R mutant shifts the cofactor preference of both 3 beta-HSD and isomerase from NAD(H) to NADP(H), which shows that the two activities utilize a common coenzyme domain. The D257L and D258L mutations eliminate isomerase activity, whereas the D241N and D265N mutants have nearly full isomerase activity. Kinetic analyses and pH dependence studies showed that either Asp257 or Asp258 plays a catalytic role in the isomerization reaction. These observations further characterize the structure/function relationships of human 3 beta-HSD/isomerase and bring us closer to the goal of selectively inhibiting the type 1 enzyme in placenta (to control the timing of labor) or in hormone-sensitive breast tumors (to slow their growth).