Characterization of molecular and catalytic properties of intact and truncated human 17beta-hydroxysteroid dehydrogenase type 2 enzymes: intracellular localization of the wild-type enzyme in the endoplasmic reticulum

Hydroxysteroid 17-β dehydrogenase 14 (HSD17B14) is an L-fucose dehydrogenase, the initial enzyme of the L-fucose degradation pathway

L-Fucose (6-deoxy-L-galactose), a monosaccharide abundant in glycolipids and glycoproteins produced by mammalian cells, has been extensively studied for its role in intracellular biosynthesis and recycling of GDP-L-fucose for fucosylation. However, in certain mammalian species, L-fucose is efficiently broken down to pyruvate and lactate in a poorly understood metabolic pathway. In the 1970s, L-fucose dehydrogenase, an enzyme responsible for the initial step of this pathway, was partially purified from pig and rabbit livers and characterized biochemically. However, its molecular identity remained elusive until recently. This study reports the purification, identification, and biochemical characterization of the mammalian L-fucose dehydrogenase. The enzyme was purified from rabbit liver approximately 340-fold. Mass spectrometry analysis of the purified protein preparation identified mammalian hydroxysteroid 17-β dehydrogenase 14 (HSD17B14) as the sole candidate enzyme. Rabbit and human HSD17B14 were expressed in HEK293T and Escherichia coli, respectively, purified, and demonstrated to catalyze the oxidation of L-fucose to L-fucono-1,5-lactone, as confirmed by mass spectrometry and NMR analysis. Substrate specificity studies revealed that L-fucose is the preferred substrate for both enzymes. The human enzyme exhibited a catalytic efficiency for L-fucose that was 359-fold higher than its efficiency for estradiol. Additionally, recombinant rat HSD17B14 exhibited negligible activity towards L-fucose, consistent with the absence of L-fucose metabolism in this species. The identification of the gene-encoding mammalian L-fucose dehydrogenase provides novel insights into the substrate specificity of enzymes belonging to the 17-β-hydroxysteroid dehydrogenase family. This discovery also paves the way for unraveling the physiological functions of the L-fucose degradation pathway, which remains enigmatic.

Systemwide effects of ER-intracellular membrane contact site disturbance in primary endothelial cells

Membrane contact sites (MCS) make up a crucial route of inter-organelle non-vesicular transport within the cell. Multiple proteins are involved in this process, which includes the ER-resident proteins vesicle associated membrane protein associated protein A and -B (VAPA/B) that form MCS between the ER and other membrane compartments. Currently most functional data on VAP depleted phenotypes have shown alterations in lipid homeostasis, induction of ER stress, dysfunction of UPR and autophagy, as well as neurodegeneration. Literature on concurrent silencing of VAPA/B is still sparse; therefore, we investigated how it affects the macromolecule pools of primary endothelial cells. Our transcriptomics results showed significant upregulation in genes related to inflammation, ER and Golgi dysfunction, ER stress, cell adhesion, as well as Coat Protein Complex-I and -II (COP-I, COP-II) vesicle transport. Genes related to cellular division were downregulated, as well as key genes of lipid and sterol biosynthesis. Lipidomics analyses revealed reductions in cholesteryl esters, very long chain highly unsaturated and saturated lipids, whereas increases in free cholesterol and relatively short chain unsaturated lipids were evident. Furthermore, the knockdown resulted in an inhibition of angiogenesis in vitro. We speculate that ER MCS depletion has led to multifaceted outcomes, which include elevated ER free cholesterol content and ER stress, alterations in lipid metabolism, ER-Golgi function and vesicle transport, which have led to a reduction in angiogenesis. The silencing also induced an inflammatory response, consistent with upregulation of markers of early atherogenesis. To conclude, ER MCS mediated by VAPA/B play a crucial role in maintaining cholesterol traffic and sustain normal endothelial functions.

17β-Hydroxysteroid dehydrogenases types 1 and 2: Enzymatic assays based on radiometric and mass-spectrometric detection

The 17β-hydroxysteroid dehydrogenase type 1 (HSD17B1) has a key role in estrogen biosynthesis as it catalyzes the reduction of estrone to the most potent estrogen, estradiol. Estradiol has a high affinity for estrogen receptors and thus stimulates their transactivation, which leads to cell proliferation and numerous other effects. HSD17B2 catalyzes the oxidation of estradiol to the less potent estrone, thereby decreasing estrogen receptor activation, which results in reduction of estrogen-associated effects. HSD17B1 and HSD17B2 overexpressing E.coli homogenates or recombinant enzymes can be used for screening and development of drugs against various pathologies such as cancer, endometriosis or osteoporosis. Here we describe the preparation of HSD17B1 and HSD17B2 bacterial homogenates and purified recombinant HSD17B1 protein as enzyme sources as well as enzymatic assays based on radiometric and mass-spectrometric detection for enzyme characterization.

Role of hydroxysteroid (17beta) dehydrogenase type 1 in reproductive tissues and hormone-dependent diseases

Abnormal synthesis and metabolism of sex steroids is involved in the pathogenesis of various human diseases, such as endometriosis and cancers arising from the breast and uterus. Steroid biosynthesis is a multistep enzymatic process proceeding from cholesterol to highly active sex steroids via different intermediates. Human Hydroxysteroid (17beta) dehydrogenase 1 (HSD17B1) enzyme shows a high capacity to produce the highly active estrogen, estradiol, from a precursor hormone, estrone. However, the enzyme may also play a role in other steps of the steroid biosynthesis pathway. In this article, we have reviewed the literature on HSD17B1, and summarize the role of the enzyme in hormone-dependent diseases in women as evidenced by preclinical studies.

Subcellular localization and membrane topology of 17β-hydroxysteroid dehydrogenases

The 17β-hydroxysteroid dehydrogenases (17β-HSDs) comprise enzymes initially identified by their ability to interconvert active and inactive forms of sex steroids, a vital process for the tissue-specific control of estrogen and androgen balance. However, most 17β-HSDs have now been shown to accept substrates other than sex steroids, including bile acids, retinoids and fatty acids, thereby playing unanticipated roles in cell physiology. This functional divergence is often reflected by their different subcellular localization, with 17β-HSDs found in the cytosol, peroxisome, mitochondria, endoplasmic reticulum and in lipid droplets. Moreover, a subset of 17β-HSDs are integral membrane proteins, with their specific topology dictating the cellular compartment in which they exert their enzymatic activity. Here, we summarize the present knowledge on the subcellular localization and membrane topology of the 17β-HSD enzymes and discuss the correlation with their biological functions.

Virtual screening applications in short-chain dehydrogenase/reductase research

Several members of the short-chain dehydrogenase/reductase (SDR) enzyme family play fundamental roles in adrenal and gonadal steroidogenesis as well as in the metabolism of steroids, oxysterols, bile acids, and retinoids in peripheral tissues, thereby controlling the local activation of their cognate receptors. Some of these SDRs are considered as promising therapeutic targets, for example to treat estrogen-/androgen-dependent and corticosteroid-related diseases, whereas others are considered as anti-targets as their inhibition may lead to disturbances of endocrine functions, thereby contributing to the development and progression of diseases. Nevertheless, the physiological functions of about half of all SDR members are still unknown. In this respect, in silico tools are highly valuable in drug discovery for lead molecule identification, in toxicology screenings to facilitate the identification of hazardous chemicals, and in fundamental research for substrate identification and enzyme characterization. Regarding SDRs, computational methods have been employed for a variety of applications including drug discovery, enzyme characterization and substrate identification, as well as identification of potential endocrine disrupting chemicals (EDC). This review provides an overview of the efforts undertaken in the field of virtual screening supported identification of bioactive molecules in SDR research. In addition, it presents an outlook and addresses the opportunities and limitations of computational modeling and in vitro validation methods.

Potential Antiosteoporotic Natural Product Lead Compounds That Inhibit 17β-Hydroxysteroid Dehydrogenase Type 2

17β-Hydroxysteroid dehydrogenase type 2 (17β-HSD2) converts the active steroid hormones estradiol, testosterone, and 5α-dihydrotestosterone into their weakly active forms estrone, Δ⁴-androstene-3,17-dione, and 5α-androstane-3,17-dione, respectively, thereby regulating cell- and tissue-specific steroid action. As reduced levels of active steroids are associated with compromised bone health and onset of osteoporosis, 17β-HSD2 is considered a target for antiosteoporotic treatment. In this study, a pharmacophore model based on 17β-HSD2 inhibitors was applied to a virtual screening of various databases containing natural products in order to discover new lead structures from nature. In total, 36 hit molecules were selected for biological evaluation. Of these compounds, 12 inhibited 17β-HSD2 with nanomolar to low micromolar IC₅₀ values. The most potent compounds, nordihydroguaiaretic acid (1), IC₅₀ 0.38 ± 0.04 μM, (-)-dihydroguaiaretic acid (4), IC₅₀ 0.94 ± 0.02 μM, isoliquiritigenin (6), IC₅₀ 0.36 ± 0.08 μM, and ethyl vanillate (12), IC₅₀ 1.28 ± 0.26 μM, showed 8-fold or higher selectivity over 17β-HSD1. As some of the identified compounds belong to the same structural class, structure-activity relationships were derived for these molecules. Thus, this study describes new 17β-HSD2 inhibitors from nature and provides insights into the binding pocket of 17β-HSD2, offering a promising starting point for further research in this area.

Type 2 17-β hydroxysteroid dehydrogenase as a novel target for the treatment of osteoporosis

Low estradiol level in postmenopausal women is implicated in osteoporosis, which occurs because of the high bone resorption rate. Estrogen formation is controlled by 17-β hydroxysteroid dehydrogenase 17-β HSD enzymes, where 17-β HSD type 1 contributes in the formation of estradiol, while type 2 catalyzes its catabolism. Inhibiting 17-β HSD2 can help in increasing estradiol concentration. Several promising 17-β HSD2 inhibitors that can act at low nanomolar range have been identified. However, there are some specific challenges associated with the application of these compounds. Our review provides an up-to-date summary of the current status and recent progress in the production of 17-β HSD2 inhibitors as well as the future challenges in their clinical application.

Pharmacophore Models and Pharmacophore-Based Virtual Screening: Concepts and Applications Exemplified on Hydroxysteroid Dehydrogenases

Computational methods are well-established tools in the drug discovery process and can be employed for a variety of tasks. Common applications include lead identification and scaffold hopping, as well as lead optimization by structure-activity relationship analysis and selectivity profiling. In addition, compound-target interactions associated with potentially harmful effects can be identified and investigated. This review focuses on pharmacophore-based virtual screening campaigns specifically addressing the target class of hydroxysteroid dehydrogenases. Many members of this enzyme family are associated with specific pathological conditions, and pharmacological modulation of their activity may represent promising therapeutic strategies. On the other hand, unintended interference with their biological functions, e.g., upon inhibition by xenobiotics, can disrupt steroid hormone-mediated effects, thereby contributing to the development and progression of major diseases. Besides a general introduction to pharmacophore modeling and pharmacophore-based virtual screening, exemplary case studies from the field of short-chain dehydrogenase/reductase (SDR) research are presented. These success stories highlight the suitability of pharmacophore modeling for the various application fields and suggest its application also in futures studies.

Determination of the topology of endoplasmic reticulum membrane proteins using redox-sensitive green-fluorescence protein fusions

Membrane proteins of the endoplasmic reticulum (ER) are involved in a wide array of essential cellular functions. Identification of the topology of membrane proteins can provide significant insight into their mechanisms of action and biological roles. This is particularly important for membrane enzymes, since their topology determines the subcellular site where a biochemical reaction takes place and the dependence on luminal or cytosolic co-factor pools and substrates. The methods currently available for the determination of topology of proteins are rather laborious and require post-lysis or post-fixation manipulation of cells. In this work, we have developed a simple method for defining intracellular localization and topology of ER membrane proteins in living cells, based on the fusion of the respective protein with redox-sensitive green-fluorescent protein (roGFP). We validated the method and demonstrated that roGFP fusion proteins constitute a reliable tool for the study of ER membrane protein topology, using as control microsomal 11β-hydroxysteroid dehydrogenase (11β-HSD) proteins whose topology has been resolved, and comparing with an independent approach. We then implemented this method to determine the membrane topology of six microsomal members of the 17β-hydroxysteroid dehydrogenase (17β-HSD) family. The results revealed a luminal orientation of the catalytic site for three enzymes, i.e. 17β-HSD6, 7 and 12. Knowledge of the intracellular location of the catalytic site of these enzymes will enable future studies on their biological functions and on the role of the luminal co-factor pool.

Ligand-based pharmacophore modeling and virtual screening for the discovery of novel 17β-hydroxysteroid dehydrogenase 2 inhibitors

17β-Hydroxysteroid dehydrogenase 2 (17β-HSD2) catalyzes the inactivation of estradiol into estrone. This enzyme is expressed only in a few tissues, and therefore its inhibition is considered as a treatment option for osteoporosis to ameliorate estrogen deficiency. In this study, ligand-based pharmacophore models for 17β-HSD2 inhibitors were constructed and employed for virtual screening. From the virtual screening hits, 29 substances were evaluated in vitro for 17β-HSD2 inhibition. Seven compounds inhibited 17β-HSD2 with low micromolar IC50 values. To investigate structure-activity relationships (SAR), 30 more derivatives of the original hits were tested. The three most potent hits, 12, 22, and 15, had IC50 values of 240 nM, 1 μM, and 1.5 μM, respectively. All but 1 of the 13 identified inhibitors were selective over 17β-HSD1, the enzyme catalyzing conversion of estrone into estradiol. Three of the new, small, synthetic 17β-HSD2 inhibitors showed acceptable selectivity over other related HSDs, and six of them did not affect other HSDs.

Hydroxybenzothiazoles as new nonsteroidal inhibitors of 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD1)

17β-estradiol (E2), the most potent estrogen in humans, known to be involved in the development and progession of estrogen-dependent diseases (EDD) like breast cancer and endometriosis. 17β-HSD1, which catalyses the reduction of the weak estrogen estrone (E1) to E2, is often overexpressed in breast cancer and endometriotic tissues. An inhibition of 17β-HSD1 could selectively reduce the local E2-level thus allowing for a novel, targeted approach in the treatment of EDD. Continuing our search for new nonsteroidal 17β-HSD1 inhibitors, a novel pharmacophore model was derived from crystallographic data and used for the virtual screening of a small library of compounds. Subsequent experimental verification of the virtual hits led to the identification of the moderately active compound 5. Rigidification and further structure modifications resulted in the discovery of a novel class of 17β-HSD1 inhibitors bearing a benzothiazole-scaffold linked to a phenyl ring via keto- or amide-bridge. Their putative binding modes were investigated by correlating their biological data with features of the pharmacophore model. The most active keto-derivative 6 shows IC₅₀-values in the nanomolar range for the transformation of E1 to E2 by 17β-HSD1, reasonable selectivity against 17β-HSD2 but pronounced affinity to the estrogen receptors (ERs). On the other hand, the best amide-derivative 21 shows only medium 17β-HSD1 inhibitory activity at the target enzyme as well as fair selectivity against 17β-HSD2 and ERs. The compounds 6 and 21 can be regarded as first benzothiazole-type 17β-HSD1 inhibitors for the development of potential therapeutics.

Sex steroid-dependent and -independent action of hydroxysteroid (17beta) Dehydrogenase 2: evidence from transgenic female mice

We have recently generated transgenic (TG) mice overexpressing human hydroxysteroid (17beta) dehydrogenase 2 enzyme (HSD17B2TG mice) under the ubiquitous chicken beta-actin promoter. As shown in the present study, the HSD17B2TG female mice presented with slower gain of body weight as compared with the wild-type (WT) littermates and suffered from ovarian dysfunction and mammary gland hyperplasia associated with increased expression of multiple pregnancy-associated genes. The macroscopic phenotype observed in the mammary gland was likely to be dependent on the increased progesterone and prolactin secretion, and a normal histological appearance was observed in HSD17B2TG mammary gland transplanted into a WT host. However, a significant suppression of several known estrogen target genes in the HSD17B2TG mammary transplants in WT females was observed, suggesting that HSD17B2 modulates estrogen action in vivo. Interestingly, the growth retardation of HSD17B2TG females was not efficiently rescued in the bi-TG mice expressing both HSD17B2 and HSD17B1 enzymes, and the bi-TG mice presented with certain masculinized phenotypes, including lack of nipples and closed vagina, recently reported for HSD17B1TG females. The present data suggest that HSD17B2 expression affects both sex steroid-independent and steroid-dependent pathways.

Prepubertal healthy children's urinary androstenediol predicts diaphyseal bone strength in late puberty

CONTEXT

During the physiological process of adrenarche, the adrenal glands of healthy children secrete increasing amounts of weak androgenic steroids partly metabolized to potent sex steroids.

OBJECTIVE

The aim of the study was to examine whether adrenal androgen metabolite excretion rates before the onset of puberty may be prospectively associated with late-pubertal diaphyseal bone strength.

SETTING

We conducted the study in an auxological and metabolic child nutrition research facility.

STUDY POPULATION AND DESIGN

The sample included 45 healthy adolescents who underwent proximal forearm bone and muscle area measurements by peripheral quantitative computed tomography at the age of 16 yr (SD 1.5) and who had collected a 24-h urine sample 8 yr earlier, allowing to quantify the prepubertal urine metabolome. Prepubertal hormonal predictors quantified by gas chromatography-mass spectrometry were: dehydroepiandrosterone, its 16-hydroxylated downstream metabolites, 5-androstene-3beta,17beta-diol (androstenediol), sums of total androgen and glucocorticoid metabolites, cortisol, and 6beta-hydroxycortisol.

MAIN OUTCOMES

Proximal forearm radius was measured.

RESULTS

Of all prepubertal hormones analyzed, only sex- and age-specific androstenediol levels significantly predicted pubertal stage-, height-, and muscularity-adjusted diaphyseal bone modeling (periosteal circumference, beta = 0.67, P = 0.002; cortical area, beta = 2.15, P = 0.02), bone mineral content (beta = 2.2; P = 0.04), and polar strength strain index (beta = 12.2; P = 0.002). Androstenediol explained 5-10% of the late-pubertal diaphyseal radius variability.

CONCLUSIONS

Our prospective profiling of urinary steroid metabolites in 24-h urine samples collected before puberty suggests that androstenediol is an early predictor of the diaphyseal bone strength in late puberty. This predominantly peripheral conversion product of adrenarchal dehydroepiandrosterone by 17beta-hydroxysteroid dehydrogenase may hence be involved in a sustained improvement of radial bone accretion during growth.

Direct protein-protein interaction of 11beta-hydroxysteroid dehydrogenase type 1 and hexose-6-phosphate dehydrogenase in the endoplasmic reticulum lumen

Hexose-6-phosphate dehydrogenase (H6PDH) has been shown to stimulate 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1)-dependent local regeneration of active glucocorticoids. Here, we show that coexpression with H6PDH results in a dramatic shift from 11beta-HSD1 oxidase to reductase activity without affecting the activity of the endoplasmic reticular enzyme 17beta-HSD2. Immunoprecipitation experiments revealed coprecipitation of H6PDH with 11beta-HSD1 but not with the related enzymes 11beta-HSD2 and 17beta-HSD2, suggesting a specific interaction between H6PDH and 11beta-HSD1. The use of the 11beta-HSD1/11beta-HSD2 chimera indicates that the N-terminal 39 residues of 11beta-HSD1 are sufficient for interaction with H6PDH. An important role of the N-terminus was indicated further by the significantly stronger interaction of 11beta-HSD1 mutant Y18-21A with H6PDH compared to wild-type 11beta-HSD1. The protein-protein interaction and the involvement of the N-terminus of 11beta-HSD1 were confirmed by Far-Western blotting. Finally, fluorescence resonance energy transfer (FRET) measurements of HEK-293 cells expressing fluorescently labeled proteins provided evidence for an interaction between 11beta-HSD1 and H6PDH in intact cells. Thus, using three different methods, we provide strong evidence that the functional coupling between 11beta-HSD1 and H6PDH involves a direct physical interaction of the two proteins.

The role of 17beta-hydroxysteroid dehydrogenases in modulating the activity of 2-methoxyestradiol in breast cancer cells

The bis-sulfamoylated derivative of 2-methoxyestradiol (2-MeOE2), 2-methoxyestradiol-3,17-O,O-bis-sulfamate (2-MeOE2bisMATE), has shown potent antiproliferative and antiangiogenic activity in vitro and inhibits tumor growth in vivo. 2-MeOE2bisMATE is bioavailable, in contrast to 2-MeOE2 that has poor bioavailability. In this study, we have examined the role of 17beta-hydroxysteroid dehydrogenase (17beta-HSD) type 2 in the metabolism of 2-MeOE2. In MDA-MB-231 cells, which express high levels of 17beta-HSD type 2, and in MCF-7 cells transfected with 17beta-HSD type 2, high-performance liquid chromatography analysis showed that a significant proportion of 2-MeOE2 was metabolized to inactive 2-methoxyestrone. Furthermore, MCF-7 cells transfected with 17beta-HSD type 2 were protected from the cytotoxic effects of 2-MeOE2. In contrast, no significant metabolism of 2-MeOE2bisMATE was detected in transfected cells and 17beta-HSD type 2 transfection did not offer protection against 2-MeOE2bisMATE cytotoxicity. This study may go some way to explaining the poor bioavailability of 2-MeOE2, as the gastrointestinal mucosa expresses high levels of 17beta-HSD type 2. In addition, this study shows the value of synthesizing sulfamoylated derivatives of 2-MeOE2 with C17-position modifications as these compounds have improved bioavailability and potency both in vitro and in vivo.

The relationship between physical activity and 2-hydroxyestrone, 16alpha-hydroxyestrone, and the 2/16 ratio in premenopausal women (United States)

OBJECTIVES

Estrogen is metabolized in the body through two mutually exclusive pathways yielding metabolites with different biological activities: the low estrogenic 2-hydroxyestrone (2-OHE1) and the highly estrogenic 16alpha-hydroxyestrone (16alpha-OHE1). The ratio of these metabolites (2/16) may be predictive of risk for developing breast cancer. Early evidence has demonstrated that exercise may alter estrogen metabolism to favor the weak estrogen, 2-OHE1.

METHODS

Seventy-seven eumenorrheic females completed physical activity logs for two weeks prior to providing a luteal phase urine sample. Concentrations of 2-OHE1 and 16alpha-OHE1 were measured and the 2/16 ratio computed. Hierarchical regression, controlling for age and body mass index (BMI), was used to determine relationships between estrogen metabolites and daily physical activity.

RESULTS

Regression analyses indicated significant positive relationships between physical activity and 2-OHE1 and the 2/16 ratio (p < 0.05) that appears to be independent of BMI. 16alpha-OHE1 was not significantly related to physical activity.

CONCLUSION

These results indicate that physical activity may modulate estrogen metabolism to favor the weak estrogen, 2-OHE1, thus producing a higher 2/16 ratio. This alteration in estrogen metabolism may represent one of the mechanisms by which increased physical activity reduces breast cancer risk.

Selective insensitivity of ZR-75-1 human breast cancer cells to 2-methoxyestradiol: evidence for type II 17beta-hydroxysteroid dehydrogenase as the underlying cause

2-Methoxyestradiol (2-MeO-E2), a nonpolar endogenous metabolite of 17beta-estradiol, has strong antiproliferative, apoptotic, and antiangiogenic actions. Among the four human breast cancer cell lines tested (MCF-7, T-47D, ZR-75-1, and MDA-MB-435s), the ZR-75-1 cells were selectively insensitive to the antiproliferative actions of 2-MeO-E2, although these cells had a similar sensitivity as other cell lines to several other anticancer agents (5-fluorouracil, mitomycin C, doxorubicin, colchicine, vinorelbine, and paclitaxel). Mechanistically, this insensitivity is largely attributable to the presence of high levels of a steroid-selective metabolizing enzyme, the type II 17beta-hydroxysteroid dehydrogenase (17beta-HSD), in the ZR-75-1 cells, which rapidly converts 2-MeO-E2 to the inactive 2-methoxyestrone, but this enzyme does not metabolically inactivate other nonsteroidal anticancer agents. The type II 17beta-HSD-mediated conversion of 2-MeO-E2 to 2-methoxyestrone in ZR-75-1 cells followed the first-order kinetics, with a very short half-life (approximately 2 hours). In comparison, the T-47D, MCF-7, and MDA-MB-435s human breast cancer cells, which were highly sensitive to 2-MeO-E2, had very low or undetectable catalytic activity for the conversion of 2-MeO-E2 to 2-methoxyestrone. Reverse transcription-PCR analysis of the mRNA levels of three known oxidative 17beta-HSD isozymes (types II, IV, and VIII) revealed that only the type II isozyme was selectively expressed in the ZR-75-1 cells, whereas the other two isozymes were expressed in all four cell lines. Taken together, our results showed, for the first time, that the high levels of type II 17beta-HSD present in ZR-75-1 cells were largely responsible for the facile conversion of 2-MeO-E2 to 2-methoxyestrone and also for the selective insensitivity to the antiproliferative actions of 2-MeO-E2.

Estrogen receptors and estrogen-metabolizing enzymes in human ovaries during fetal development

Estrogen action plays a crucial role in many processes throughout the human life span, including development. Estrogens are pivotal in the regulation of female reproduction, but little is known about their role during ovarian development. To better understand estrogen action during ovarian development, the expression of estrogen receptors (ERs)-alpha and -beta and key enzymes regulating estradiol production, 17beta-hydroxysteroid dehydrogenases (17HSDs) types 1, 2, and 7, were analyzed in human fetal ovaries. The expression of ERs was related to the development of ovarian follicles. Before the 26th week of fetal life ERalpha was only occasionally detected, but from then onward, its expression was detected in ovarian follicles. Consistent expression of ERbeta was seen from the 20th week until term. Both ERalpha and ERbeta were localized to the granulosa cells and oocytes. Expression of 17HSD1 and 17HSD7 enzymes, catalyzing the conversion of estrone to more active estradiol, was detected as early as at the 17th week of fetal life. The expression of 17HSD1 displayed a pattern similar to that of ERs and increased toward term, whereas that of 17HSD7 decreased and was negative by the 36th week. 17HSD1 was localized to the granulosa cells, whereas 17HSD7 expression was more diffuse and was found in both granulosa and stromal cells. 17HSD2, converting estradiol to less potent estrone, was negative in all samples studied. The simultaneous appearance of estrogen-converting enzymes and ERs at the time of follicle formation indicates that the machinery for estrogen action exists in fetal ovaries and suggests a possible role for estrogens in the developing ovary.

17beta-hydroxysteroid dehydrogenase type 1 is an independent prognostic marker in breast cancer

Estrogens have an important role in the development and progression of breast cancer. 17beta-Hydroxysteroid dehydrogenase type 1 (17HSD1), type 2 (17HSD2), and type 5 (17HSD5) are associated with sex steroid metabolism in normal and cancerous breast tissue. The mRNA expressions of the 17HSD1, 17HSD2, and 17HSD5 enzymes were analyzed in 794 breast carcinoma specimens by using tissue microarrays and normal histologic sections. The results were correlated with the estrogen receptor alpha (ER-alpha) and beta (ER-beta), progesterone receptor, Ki67, and c-erbB-2 expressions analyzed by immunohistochemical techniques and with the Tumor-Node-Metastasis classification, tumor grade, disease-free interval, and survival of the patients. Signals for 17HSD1 mRNA were detected in 16%, 17HSD2 in 25%, and 17HSD5 in 65% of the breast cancer specimens. No association between the 17HSD1, 17HSD2, and 17HSD5 expressions was detected. A significant association was observed between ER-alpha and ER-beta (P = 0.02; odds ratio, 1.96) expressions. There was also a significant inverse association between ER-alpha and 17HSD1 (P = 0.04; odds ratio, 0.53), as well as ER-alpha and 17HSD5 (P = 0.001; odds ratio, 0.35). Patients with tumors expressing 17HSD1 mRNA or protein had significantly shorter overall and disease-free survival than the other patients (P = 0.0010 and 0.0134, log rank). The expression of 17HSD5 was significantly higher in breast tumor specimens than in normal tissue (P = 0.033; odds ratio, 5.56). The group with 17HSD5 overexpression had a worse prognosis than the other patients (P = 0.0146). ER-alpha also associated with survival (P = 0.045). Cox multivariate analyses showed that 17HSD1 mRNA, tumor size, and ER-alpha had independent prognostic significance.

Production, purification, and functional analysis of recombinant human and mouse 17beta-hydroxysteroid dehydrogenase type 7

17beta-Hydroxysteroid dehydrogenases (17HSDs) have a central role in the regulation of the biological activity of sex steroid hormones. There is increasing evidence that in addition to their importance in gonads, these hormones also have substantial metabolic roles in a variety of peripheral tissues. In the present study, the cDNA of human 17HSD type 7 was cloned. In silico, the gene corresponding to the cDNA was localized on chromosome 1q23, close to the locus of hereditary prostate cancer 1 (HPC1) (1q24-25) and primary open-angle glaucoma (GLC1A) (1q23-25). Further, a pseudogene was found on chromosome 1q44, close to the locus of predisposing for early-onset prostate cancer (PCaP) (1q42.2-43). Both human (h17HSD7) and mouse 17HSD type 7 (m17HSD7) were for the first time produced as recombinant proteins and purified for functional analyses. Further, kinetic parameters and specific activities were described. h17HSD7 converted estrone (E1) to a more potent estrogen, estradiol (E2), and dihydrotestosterone (DHT), a potent androgen, to an estrogenic metabolite 5alpha-androstane-3beta, 17beta-diol (3betaA-diol) equally, thereby catalyzing the reduction of the keto group in either 17- or 3-position of the substrate. Minor 3betaHSD-like activity towards progesterone (P) and 20-hydroxyprogesterone (20-OH-P), leading to the inactivation of P by h17HSD7, was also detected. m17HSD7 efficiently catalyzed the reaction from E1 to E2 and moderately converted DHT to an inactive metabolite 5alpha-androstane-3alpha,17beta-diol (3alphaA-diol) and to an even lesser degree 3betaA-diol. The mouse enzyme did not metabolize P or 20-OH-P. The expression of 17HSD type 7 was observed widely in human tissues, most distinctly in adrenal gland, liver, lung, and thymus. Based on the enzymatic characteristics and tissue distribution, we conclude that h17HSD7 might be an intracrine regulator of steroid metabolism, fortifying the estrogenic milieu in peripheral tissues.

Dehydroepiandrosterone (DHEA) metabolism in Saccharomyces cerevisiae expressing mammalian steroid hydroxylase CYP7B: Ayr1p and Fox2p display 17beta-hydroxysteroid dehydrogenase activity

We have engineered recombinant yeast to perform stereospecific hydroxylation of dehydroepiandrosterone (DHEA). This mammalian pro-hormone promotes brain and immune function; hydroxylation at the 7alpha position by P450 CYP7B is the major pathway of metabolic activation. We have sought to activate DHEA via yeast expression of rat CYP7B enzyme. Saccharomyces cerevisiae was found to metabolize DHEA by 3beta-acetylation; this was abolished by mutation at atf2. DHEA was also toxic, blocking tryptophan (trp) uptake: prototrophic strains were DHEA-resistant. In TRP(+) atf2 strains DHEA was then converted to androstene-3beta,17beta-diol (A/enediol) by an endogenous 17beta-hydroxysteroid dehydrogenase (17betaHSD). Seven yeast polypeptides similar to human 17betaHSDs were identified: when expressed in yeast, only AYR1 (1-acyl dihydroxyacetone phosphate reductase) increased A/enediol accumulation, while the hydroxyacyl-CoA dehydrogenase Fox2p, highly homologous to human 17betaHSD4, oxidized A/enediol to DHEA. The presence of endogenous yeast enzymes metabolizing steroids may relate to fungal pathogenesis. Disruption of AYR1 eliminated reductive 17betaHSD activity, and expression of CYP7B on the combination background (atf2, ayr1, TRP(+)) permitted efficient (>98%) bioconversion of DHEA to 7alpha-hydroxyDHEA, a product of potential medical utility.

Purification, reconstitution, and steady-state kinetics of the trans-membrane 17 beta-hydroxysteroid dehydrogenase 2

Human membrane 17 beta-hydroxysteroid dehydrogenase 2 is an enzyme essential in the conversion of the highly active 17beta-hydroxysteroids into their inactive keto forms in a variety of tissues. 17 beta-hydroxysteroid dehydrogenase 2 with 6 consecutive histidines at its N terminus was expressed in Sf9 insect cells. This recombinant protein retained its biological activity and facilitated the enzyme purification and provided the most suitable form in our studies. Dodecyl-beta-D-maltoside was found to be the best detergent for the solubilization, purification, and reconstitution of this enzyme. The overexpressed integral membrane protein was purified with a high catalytic activity and a purity of more than 90% by nickel-chelated chromatography. For reconstitution, the purified protein was incorporated into dodecyl-beta-D-maltoside-destabilized liposomes prepared from l-alpha-phosphatidylcholine. The detergent was removed by adsorption onto polystyrene beads. The reconstituted enzyme had much higher stability and catalytic activity (2.6 micromol/min/mg of enzyme protein with estradiol) than the detergent-solubilized and purified protein (0.9 micromol/min/mg of enzyme protein with estradiol). The purified and reconstituted protein (with a 2-kDa His tag) was proved to be a homodimer, and its functional molecular mass was calculated to be 90.4 +/- 1.2 kDa based on glycerol gradient analytical ultracentrifugation and chemical cross-linking study. The kinetic studies demonstrated that 17 beta-hydroxysteroid dehydrogenase 2 was an NAD-preferring dehydrogenase with the K(m) of NAD being 110 +/- 10 microM and that of NADP 9600 +/- 100 microM using estradiol as substrate. The kinetic constants using estradiol, testosterone, dihydrotestosterone, and 20 alpha-dihydroprogesterone as substrates were also determined.

Downregulation of estrogen-metabolizing 17 beta-hydroxysteroid dehydrogenase type 2 expression correlates inversely with Ki67 proliferation marker in colon-cancer development

The 17HSDs are a group of isozymes that catalyze the interconversion between high-activity 17 beta-hydroxysteroids and low-activity 17-ketosteroids. In the present study, we characterized the expression of 17HSD types 1 and 2 in normal and malignant gastrointestinal tissues and cells. Using the colon as a model for cancer of the gastrointestinal tract, expression of the 17HSD enzymes in cancer development was studied and correlated with proliferation and differentiation markers as assessed by Ki67 and mucin staining, respectively. In normal colon and small intestine, 17HSD type 2 mRNA was expressed in the surface epithelial cells and, to a lesser extent, in the cryptal epithelial cells. In colon-cancer specimens, 17HSD type 2 expression was downregulated both in the tissues and in the cell lines and correlated inversely with the proliferation marker. No expression for the 17HSD type 1 enzyme was observed in normal or cancerous gastrointestinal tract tissues. In line with the expression studies, 17HSD activity measurements with colon cells showed that only the oxidative conversion of E2 to E1 was present, and Northern blot analysis showed the signal only for 17HSD type 2. Localization of the ERs alpha and beta, assessed by immunohistochemistry and in situ hybridization, showed the presence of ER beta in the lamina propria of the colon. Our study shows that 17HSD type 2 expression is associated with the functional integrity of the gastrointestinal tract. The decrease in expression of the type 2 enzyme may increase estrogen influence in colon cancer.

Oestrogen inactivation in the colon: analysis of the expression and regulation of 17beta-hydroxysteroid dehydrogenase isozymes in normal colon and colonic cancer

Epidemiological data suggest that oestrogen contributes to the aetiology of colonic cancer. Furthermore, recent studies have suggested that local hormone metabolism may play a key role in determining colonic responsiveness to oestrogen. To further clarify this mechanism we have characterized the expression and regulation of isozymes of 17beta-hydroxysteroid dehydrogenase (17beta-HSD) in vitro and in situ. Immunohistochemistry was used to confirm expression of the type 2 and 4 isozymes of 17beta-HSD (17beta-HSD2 and 4) in normal colonic epithelial cells. Parallel studies suggested that both isozymes were abnormally expressed in colonic tumours and this was confirmed by Western blot analyses. Abnormal expression of 17beta-HSD2 and 4 proteins was also observed in Caco-2, HT-29 and SW620 colonic cancer cell lines, although the overall pattern of oestrogen metabolism in these cells was similar to that seen in primary colonic mucosal tissue. The predominant activity (conversion of oestradiol to oestrone) was highest in Caco-2>SW620>HT-29, which correlated inversely with the rate of proliferation of the cell lines. Regulatory studies using SW620 cells indicated that the most potent stimulator of oestradiol to oestrone inactivation was the antiproliferative agent 1,25-dihydroxyvitamin D3 (1,25D3), whilst oestradiol itself inhibited 17beta-HSD activity. Both oestradiol and 1,25D3 decreased mRNA for 17beta-HSD2 and 4. Data indicate that the high capacity for inactivation of oestrogens in the colon is associated with the presence of 17beta-HSD2 and 4 in epithelial cells. Abnormal expression of both isozymes in colonic cancer cells and the stimulation of oestrogen inactivation by the antiproliferative agent 1,25D3 highlights a possible role for 17beta-HSD isozymes as modulators of colonic cell proliferation.