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

Single-nucleus transcriptomics and chromatin accessibility analysis of musk gland development in Chinese forest musk deer (Moschus berezovskii)

Musk secreted by male forest musk deer (Moschus berezovskii) musk glands is an invaluable component of medicine and perfume. Musk secretion depends on musk gland maturation; however, the mechanism of its development remains elusive. Herein, using single cell multiome ATAC + gene expression coupled with several bioinformatic analyses, a dynamic transcriptional cell atlas of musk gland development was revealed, and key genes and transcription factors affecting its development were determined. Twelve cell types, including two different types of acinar cells (Clusters 0 and 10) were identified. Single-nucleus RNA and single-nucleus ATAC sequencing analyses revealed that seven core target genes associated with musk secretion (Hsd17b2, Acacb, Lss, Vapa, Aldh16a1, Aldh7a1, and Sqle) were regulated by 12 core transcription factors (FOXO1, CUX2, RORA, RUNX1, KLF6, MGA, NFIC, FOXO3, ETV5, NR3C1, HSF4, and MITF) during the development of Cluster 0 acinar cells. Kyoto Encyclopedia of Genes and Genomes enrichment showed significant changes in the pathways associated with musk secretion during acinar cell development. Gene set variation analysis also revealed that certain pathways associated with musk secretion were enriched in 6-year-old acinar cells. A gene co-expression network was constructed during acinar cell development to provide a precise understanding of the connections between transcription factors, genes, and pathways. Finally, intercellular communication analysis showed that intercellular communication is involved in musk gland development. This study provides crucial insights into the changes and key factors underlying musk gland development, which serve as valuable resources for studying musk secretion mechanisms and promoting the protection of this endangered species.

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.

17β-hydroxysteroid dehydrogenases in the progression of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) has become a worldwide epidemic and a major public health problem, with a prevalence of approximately 25%. The pathogenesis of NAFLD is complex and may be affected by the environment and susceptible genetic factors, resulting in a highly variable disease course and no approved drugs in the clinic. Notably, 17β-hydroxysteroid dehydrogenase type 13 (HSD17B13), which belongs to the 17β-hydroxysteroid dehydrogenase superfamily (HSD17Bs), is closely related to the clinical outcome of liver disease. HSD17Bs consists of fifteen members, most related to steroid and lipid metabolism, and may have the same biological function as HSD17B13. In this review, we highlight recent advances in basic research on the functional activities, major substrates, and key roles of HSD17Bs in the progression of NAFLD to develop innovative anti-NAFLD drugs targeting HSD17Bs.

New insights into the substrate inhibition of human 17β-hydroxysteroid dehydrogenase type 1

Human type 1 17β-hydroxysteroid dehydrogenase (17β-HSD1),a member of the short-chain dehydrogenase/reductase family, catalyzes the last step in the bioactivation of the most potent estrogen estradiol with high specificity and is thus involved in estrogen-dependent diseases. As an oxidoreductase, 17β-HSD1 can utilize both triphosphate and diphosphate cofactors in reaction at the molecular level, but more specific with triphosphate cofactor. The NADPH is much higher than NADP+ in living cells leading to preliminary reduction action. The enzyme also showed substrate-induced inhibition unprecedented in other members of 17β-HSDs. Our previous study elucidated the structural mechanism of substrate inhibition is due to the reversely bound estrone (E1) in the substrate-binding pocket of the enzyme resulting in a dead-end complex. However, the effect of the cofactor preference on the substrate inhibition of the enzyme is not yet clear. In the present study, we solved the ternary crystal structures of 17β-HSD1 in complex with E1 and cofactor analog NAD+ . Combined with molecular dynamics simulation using the enzyme with NADH/NADPH and different oriented E1 (normally oriented, E1N; reversely oriented, E1R), such ternary structure provides a complete picture of enzyme-substrate-cofactor interactions. The results reveal that different cofactors and substrate binding mode affect the allosteric effect between the two subunits of the enzyme. And the results from MD simulations confirmed that His²²¹ plays a key role in the formation of dead-end complex in NADPH complex, and the absence of stable interaction between His²²¹ and E1R in the NADH complex should be the main reason for its lack of substrate inhibition.

How inversion variants can shape neural circuitry: Insights from the three-morph mating tactics of ruffs

Behavior polymorphisms underlying alternative mating tactics can evolve due to genetic inversions, especially when inversions capture sets of genes involved in hormonal regulation. In the three-morph system of the ruff (Calidris pugnax), two alternative morphs (Satellites and Faeders) with distinct behaviors and low circulating testosterone are genetically determined by an inverted region on an autosomal chromosome. Here, we discuss recent findings on the ruff and present novel insights into how an inversion that poses drastic constraints on testosterone production might lead to morph-specific differences in brain areas that regulate social behavior. A gene responsible for converting testosterone to androstenedione (HSD17B2) is located inside the inverted region and is a promising candidate. We identify a single missense mutation in the HSD17B2 gene of inverted alleles that is responsible for a 350–500% increase in testosterone to androstenedione conversion, when mutated in the human HSD17B2 protein. We discuss new evidence of morph differences in neural HSD17B2 expression in embryos and circulating androgens in sexually-immature juveniles. We suggest processes that shape morph differences in behavior likely begin early in ontogeny. We propose that the organization of behaviorally relevant neuron cell types that are canonically sexually dimorphic, such as subpopulations of aromatase and vasotocin neurons, should be particularly affected due to the life-long condition of low circulating testosterone in inversion morphs. We further emphasize how HSD17B2 catalytic activity extends beyond androgens, and includes estradiol oxidation into estrone and progesterone synthesis. Lastly, we underscore dimerization of HSD17B2 as an additional layer of complexity that merits consideration.

Identification of Diagnostic Genes and Effective Drugs Associated with Osteoporosis Treatment by Single-Cell RNA-Seq Analysis and Network Pharmacology

Background

Osteoporosis is a common bone metabolic disease with increased bone fragility and fracture rate. Effective diagnosis and treatment of osteoporosis still need to be explored due to the increasing incidence of disease.

Methods

Single-cell RNA-seq was acquired from GSE147287 dataset. Osteoporosis-related genes were obtained from chEMBL. Cell subpopulations were identified and characterized by scRNA-seq, t-SNE, clusterProfiler, and other computational methods. “limma” R packages were used to identify all differentially expressed genes. A diagnosis model was build using rms R packages. Key drugs were determined by proteins-proteins interaction and molecular docking.

Results

Firstly, 15,577 cells were obtained, and 12 cell subpopulations were identified by clustering, among which 6 cell subpopulations belong to CD45+ BM-MSCs and the other subpopulations were CD45-BM-MSCs. CD45- BM-MSCs_6 and CD45+ BM-MSCs_5 were consider as key subpopulations. Furthermore, we found 7 genes were correlated with above two subpopulations, and F9 gene had highest AUC. Finally, five compounds were identified, among which DB03742 bound well to F9 protein.

Conclusions

This work discovered that 7 genes were correlated with CD45-BM-MSCs_6 and CD45+ BM-MSCs_5 subpopulations in osteoporosis, among which F9 gene had better research value. Moreover, compound DB03742 was a potential inhibitor of F9 protein.

Homology modeling meets site-directed mutagenesis: An ideal combination to elucidate the topology of 17β-HSD2

17β-Hydroxysteroid dehydrogenase type 2 (17β-HSD2) catalyzes the conversion of highly active estrogens and androgens into their less active forms using NAD⁺ as cofactor. Substrate and cofactor specificities of 17β-HSD2 have been reported and potent 17β-HSD2 inhibitors have been discovered in a ligand-based approach. However, the molecular basis and the amino acids involved in the enzymatic functionality are poorly understood, as no crystal structure of the membrane-associated 17β-HSD2 exists. The functional properties of only few amino acids are known. The lack of topological information impedes structure-based drug design studies and limits the design of biochemical experiments. The aim of this work was the determination of the 17β-HSD2 topology. For this, the first homology model of 17β-HSD2 in complex with NAD⁺ and 17β-estradiol was built, using a multi-fragment "patchwork" approach. To confirm the quality of the model, fifteen selected amino acids were exchanged one by one using site directed mutagenesis. The mutants' functional behavior demonstrated that the generated model was of very good quality and allowed the identification of several key amino acids involved in either ligand or internal structure stabilization. The final model is an optimal basis for further experiments like, for example, lead optimization.

Transcriptome of 17β-hydroxysteroid dehydrogenase type 2 plays both hormone-dependent and hormone-independent roles in MCF-7 breast cancer cells

Breast cancer is a major cause of cancer-related death for women in western countries. 17β-Hydroxysteroid dehydrogenases (17β-HSDs) play important roles in the last step of sex-hormone activation and the first step of sex-hormone inactivation. 17β-HSD2 is responsible for oxidizing the sex hormones. We used microarray technology to analyze the effect of 17β-HSD2 on the MCF-7 cell transcript profile after knocking down 17β-HSD2. Five hundred forty-two genes were regulated 1.5-fold or higher after treatment with 17β-HSD2 siRNA. Knocking down 17β-HSD2 interrupted nucleosome assembly. Pathway-Act-Network analysis showed that the MAPK and apoptosis signaling pathways were most regulated. In the gene-gene interaction network analysis, UGT2B15, which is involved in hormone metabolism, was the most regulated core gene. FOS, GREB1, and CXCL12 were the most regulated genes, and CXCL12 was related to tumor migration. Following 17β-HSD2 knock-down, the cell viability decreased to 75.9%. The S-phase percentage decreased by 19.4%, the Q2-phase percentage in cell apoptosis testing increased by 1.5 times, and cell migration decreased to 66.0%. These results were consistent with our gene chip analysis and indicated that 17β-HSD2 plays both hormone-dependent and hormone-independent enzymatic roles. In-depth investigations of this enzyme on the genomic level will help clarify its related molecular mechanisms.

Design, Synthesis, and Biological Characterization of Orally Active 17β-Hydroxysteroid Dehydrogenase Type 2 Inhibitors Targeting the Prevention of Osteoporosis

Osteoporosis is predominantly treated with drugs that inhibit further bone resorption due to estrogen deficiency. Yet, osteoporosis drugs that not only inhibit bone resorption but also stimulate bone formation, such as potentially inhibitors of 17β-hydroxysteroid dehydrogenase type 2 (17β-HSD2), may be more efficacious in the treatment of osteoporosis. Blockade of 17β-HSD2 is thought to increase intracellular estradiol and testosterone in bone, thereby inhibiting bone resorption by osteoclasts and stimulating bone formation by osteoblasts, respectively. We here describe the design, synthesis, and biological characterization of a novel bicyclic-substituted hydroxyphenylmethanone 17β-HSD2 inhibitor (compound 24). Compound 24 is a nanomolar potent inhibitor of human 17β-HSD2 (IC₅₀ of 6.1 nM) and rodent 17β-HSD2 with low in vitro cellular toxicity, devoid of detectable estrogen receptor α affinity, displays high aqueous solubility and in vitro metabolic stability, and has an excellent oral pharmacokinetic profile for testing in a rat osteoporosis model. Administration of 24 in a rat osteoporosis model demonstrates its bone-sparing efficacy.

Metabolic and Epigenetic Action Mechanisms of Antidiabetic Medicinal Plants

Diabetes is a predominant metabolic disease nowadays due to the off-beam lifestyle of diet and reduced physical activity. Complications of the illness include the gene-environment interactions and the downstream genetic and epigenetic consequences, e.g., cardiovascular diseases, tumor progression, retinopathy, nephropathy, neuropathy, polydipsia, polyphagia, polyuria, and weight loss. This review sheds the light on the mechanistic insights of antidiabetic medicinal plants in targeting key organs and tissues involved in regulating blood glucose homeostasis including the pancreas, liver, muscles, adipose tissues, and glucose absorption in the intestine. Diabetes is also involved in modulating major epigenetic pathways such as DNA methylation and histone modification. In this respect, we will discuss the phytochemicals as current and future epigenetic drugs in the treatment of diabetes. In addition, several proteins are common targets for the treatment of diabetes. Some phytochemicals are expected to directly interact with these targets. We lastly uncover modeling studies that predict such plausible interactions. In conclusion, this review article presents the mechanistic insight of phytochemicals in the treatment of diabetes by combining both the cellular systems biology and molecular modeling.

Targeted Endocrine Therapy: Design, Synthesis, and Proof-of-Principle of 17β-Hydroxysteroid Dehydrogenase Type 2 Inhibitors in Bone Fracture Healing

Current therapies of steroid hormone-dependent diseases predominantly alter steroid hormone concentrations (or their actions) in plasma, in target and nontarget tissues alike, rather than in target organs only. Targeted therapy through the inhibition of steroidogenic enzymes may pose an attractive alternative with much less side effects. Here, we describe the design of a nanomolar potent 17β-hydroxysteroid dehydrogenase type 2 (17β-HSD2) inhibitor (compound 15) and successful targeted intracrine therapy in a mouse bone fracture model. Blockade of 17β-HSD2 in bone is thought to increase intracellular estradiol (E2) and testosterone (T), which thereby inhibits bone resorption by osteoclasts and stimulates bone formation by osteoblasts, respectively. Administration of compound 15 in the mouse fracture model strongly increases the mechanical stability of the healing fractured bone because of a larger periosteal callus with newly formed bone without changing the plasma E2 and T concentrations. Steroidogenic 17β-HSD2 inhibition thus enables targeted intracrine therapy.

Initial characterization of human DHRS1 (SDR19C1), a member of the short-chain dehydrogenase/reductase superfamily

Many enzymes from the short-chain dehydrogenase/reductase superfamily (SDR) have already been well characterized, particularly those that participate in crucial biochemical reactions in the human body (e.g. 11β-hydroxysteroid dehydrogenase 1, 17β-hydroxysteroid dehydrogenase 1 or carbonyl reductase 1). Several other SDR enzymes are completely or almost completely uncharacterized, such as DHRS1 (also known as SDR19C1). Based on our in silico and experimental approaches, DHRS1 is described as a likely monotopic protein that interacts with the membrane of the endoplasmic reticulum. The highest expression level of DHRS1 protein was observed in human liver and adrenals. The recombinant form of DHRS1 was purified using the detergent n-dodecyl-β-D-maltoside, and DHRS1 was proven to be an NADPH-dependent reductase that is able to catalyse the in vitro reductive conversion of some steroids (estrone, androstene-3,17-dione and cortisone), as well as other endogenous substances and xenobiotics. The expression pattern and enzyme activities fit to a role in steroid and/or xenobiotic metabolism; however, more research is needed to fully clarify the exact biological function of DHRS1.

Endometrial Intracrinology: Oestrogens, Androgens and Endometrial Disorders

Peripheral tissue metabolism of steroids (intracrinology) is now accepted as a key way in which tissues, such as the endometrium, can utilise inactive steroids present in the blood to respond to local physiological demands and 'fine-tune' the activation or inhibition of steroid hormone receptor-dependent processes. Expression of enzymes that play a critical role in the activation and inactivation of bioactive oestrogens (E1, E2) and androgens (A4, T, DHT), as well as expression of steroid hormone receptors, has been detected in endometrial tissues and cells recovered during the menstrual cycle. There is robust evidence that increased expression of aromatase is important for creating a local microenvironment that can support a pregnancy. Measurement of intra-tissue concentrations of steroids using liquid chromatography⁻tandem mass spectrometry has been important in advancing our understanding of a role for androgens in the endometrium, acting both as active ligands for the androgen receptor and as substrates for oestrogen biosynthesis. The emergence of intracrinology, associated with disordered expression of key enzymes such as aromatase, in the aetiology of common women's health disorders such as endometriosis and endometrial cancer has prompted renewed interest in the development of drugs targeting these pathways, opening up new opportunities for targeted therapies and precision medicine.

Functional Silencing of HSD17B2 in Prostate Cancer Promotes Disease Progression

PURPOSE

Steroidogenic enzymes are essential for prostate cancer development. Enzymes inactivating potent androgens were not investigated thoroughly, which leads to limited interference strategies for prostate cancer therapy. Here we characterized the clinical relevance, significance, and regulation mechanism of enzyme HSD17B2 in prostate cancer development.

EXPERIMENTAL DESIGN

HSD17B2 expression was detected with patient specimens and prostate cancer cell lines. Function of HSD17B2 in steroidogenesis, androgen receptor (AR) signaling, and tumor growth was investigated with prostate cancer cell lines and a xenograft model. DNA methylation and mRNA alternative splicing were investigated to unveil the mechanisms of HSD17B2 regulation.

RESULTS

HSD17B2 expression was reduced as prostate cancer progressed. 17βHSD2 decreased potent androgen production by converting testosterone (T) or dihydrotestosterone (DHT) to each of their upstream precursors. HSD17B2 overexpression suppressed androgen-induced cell proliferation and xenograft growth. Multiple mechanisms were involved in HSD17B2 functional silencing including DNA methylation and mRNA alternative splicing. DNA methylation decreased the HSD17B2 mRNA level. Two new catalytic-deficient isoforms, generated by alternative splicing, bound to wild-type 17βHSD2 and promoted its degradation. Splicing factors SRSF1 and SRSF5 participated in the generation of new isoforms.

CONCLUSIONS

Our findings provide evidence of the clinical relevance, significance, and regulation of HSD17B2 in prostate cancer progression, which might provide new strategies for clinical management by targeting the functional silencing mechanisms of HSD17B2.See related commentary by Mostaghel, p. 1139.

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.

Role of aldo-keto reductase family 1 (AKR1) enzymes in human steroid metabolism

Human aldo-keto reductases AKR1C1-AKR1C4 and AKR1D1 play essential roles in the metabolism of all steroid hormones, the biosynthesis of neurosteroids and bile acids, the metabolism of conjugated steroids, and synthetic therapeutic steroids. These enzymes catalyze NADPH dependent reductions at the C3, C5, C17 and C20 positions on the steroid nucleus and side-chain. AKR1C1-AKR1C4 act as 3-keto, 17-keto and 20-ketosteroid reductases to varying extents, while AKR1D1 acts as the sole Δ(4)-3-ketosteroid-5β-reductase (steroid 5β-reductase) in humans. AKR1 enzymes control the concentrations of active ligands for nuclear receptors and control their ligand occupancy and trans-activation, they also regulate the amount of neurosteroids that can modulate the activity of GABAA and NMDA receptors. As such they are involved in the pre-receptor regulation of nuclear and membrane bound receptors. Altered expression of individual AKR1C genes is related to development of prostate, breast, and endometrial cancer. Mutations in AKR1C1 and AKR1C4 are responsible for sexual development dysgenesis and mutations in AKR1D1 are causative in bile-acid deficiency.

Estrogen biosynthesis, phase I and phase II metabolism, and action in endometrial cancer

Endometrial cancer is the most common gynecological malignancy in the developed World. Based on their histopathology, clinical manifestation, and epidemiology, the majority of endometrial cancer cases can be divided into two groups: the more prevalent type 1 which is associated with unopposed estrogen exposure; and the less common type 2, which is usually not associated with hyper-estrogenic factors. This manuscript overviews the published data on the expression of genes encoding the estrogen biosynthetic enzymes, the phase I and phase II estrogen metabolic enzymes, and the estrogen receptors in endometrial cancer, at the mRNA, protein and enzyme activity levels. The potential role of altered expression of these enzymes and receptors in cancerous versus control endometrial tissue, and the implication of estrogens in tumor initiation and promotion, are discussed. Finally, based on the published data, a model of estrogen metabolism and actions is proposed for pre-cancerous and cancerous endometrial tissue, and the role of the estrogens in the progression of endometrial cancer from endometrial hyperplasia is suggested.

The contribution of 17beta-hydroxysteroid dehydrogenase type 1 to the estradiol-estrone ratio in estrogen-sensitive breast cancer cells

Estrone and estradiol are both estrogens with estrone being the less potent form and estradiol being the most potent estrogen. The binding of the latter to cellular regulatory elements stimulates the proliferation of breast cancer cells. A high ratio of estradiol/estrone is related to increased cell proliferation, and is of great importance to understanding of breast cancer mechanisms. 17beta-hydroxysteroid dehydrogenase type 1 and type 2 play important roles in the activation of estrone and inactivation of estradiol. Breast cancer cells T47D, MCF-7, BT 20, and JEG 3 as control cells, were chosen to evaluate the contribution of these two enzymes to the ratio. Twenty four hours after addition of different concentrations of estrone and estradiol, the ratio stabilized to around 9/1 in breast cancer cell lines with high expression of type 1 (T47D, BT 20, and JEG 3), whereas it approached 1/5 in cells with low expression of type 1 (MCF-7). The estradiol/estrone concentration ratio was modified to 9/1 in MCF-7 and HEK-293 cells over-expressing type 1. In T47D and BT 20, this ratio was decreased from 9/1 to nearly 1/5 (19/81 and 17/83 respectively) after type 1 knockdown by specific siRNAs. Type 2 is mainly involved in the conversion of estradiol into estrone. This ratio was decreased from 9/1 to 7/3 after over-expression of type 2 in MCF-7 cells already over-expressing type 1. The ratio was further decreased by the addition of the oxidative cofactor, NAD, to the cell culture to facilitate the estradiol to estrone conversion catalyzed by type 2. These results demonstrate that the estradiol/estrone ratio is controlled by both type 1 and type 2 with an additional contribution by NAD, although type 1 is the first determining factor in the cellular environment compared with type 2 and cofactors. Moreover, kinetic studies were carried out in intact cells as a new approach, using HEK-293 cells over-expressing type 1 and T47D breast cancer cells.

Triazole ring-opening leads to the discovery of potent nonsteroidal 17β-hydroxysteroid dehydrogenase type 2 inhibitors

17β-Hydroxysteroid dehydrogenase type 2 (17β-HSD2) catalyzes the oxidation of the highly potent steroids: the estrogen estradiol (E2) and the androgen testosterone (T) to the less active estrone and androstenedione, respectively. Inhibition of this enzyme may help maintain the local E2 level in bone tissue when the circulating E2 level drops and is therefore a novel and promising approach for the treatment of osteoporosis. In this work, a series of new nonsteroidal and achiral 17β-HSD2 inhibitors, namely N-benzyl-diphenyl-3(or 4)-carboxamide and N-benzyl-5-phenyl-thiophene-2-carboxamide was designed and the compounds were synthesized in a two to three steps reaction. A small library was built applying parallel synthesis. Highly potent 17β-HSD2 inhibitors could be identified in the thiophene-2-carboxamide class with IC(50) in the low nanomolar range. These compounds also showed a good selectivity profile toward 17β-HSD1 and toward the estrogen receptors α and β. The most interesting 17β-HSD2 inhibitor identified in this study is the 5-(2-fluoro-3-methoxyphenyl)-N-(3-hydroxybenzyl)-N-methylthiophene-2-carboxamide 6w displaying an IC(50) of 61 nM and a selectivity factor of 73 toward 17β-HSD1.

Biochemical factors governing the steady-state estrone/estradiol ratios catalyzed by human 17beta-hydroxysteroid dehydrogenases types 1 and 2 in HEK-293 cells

Human 17beta-hydroxysteroid dehydrogenase types 1 and 2 (17betaHSD1 and 17betaHSD2) regulate estrogen potency by catalyzing the interconversion of estrone (E1) and estradiol (E2) using nicotinamide adenine dinucleotide (phosphate) cofactors NAD(P)(H). In intact cells, 17betaHSD1 and 17betaHSD2 establish pseudo-equilibria favoring E1 reduction or E2 oxidation, respectively. The vulnerability of these equilibrium steroid distributions to mutations and to altered intracellular cofactor abundance and redox state, however, is not known. We demonstrate that the equilibrium E2/E1 ratio achieved by 17betaHSD1 in intact HEK-293 cell lines is progressively reduced from 94:6 to 10:90 after mutagenesis of R38, which interacts with the 2'-phosphate of NADP(H), and by glucose deprivation, which lowers the NADPH/NADP(+) ratio. The shift to E2 oxidation parallels changes in apparent K(m) values for purified 17betaHSD1 proteins to favor NAD(H) over NADP(H). In contrast, mutagenesis of E116 (corresponding to R38 in 17betaHSD1) and changes in intracellular cofactor ratios do not alter the greater than 90:10 E1/E2 ratio catalyzed by 17betaHSD2, and these mutations lower the apparent K(m) of recombinant 17betaHSD2 for NADP(H) only less than 3-fold. We conclude that the equilibrium E1/E2 ratio maintained by human 17betaHSD1 in intact cells is governed by NADPH saturation, which is strongly dependent on both R38 and high intracellular NADPH/NADP(+) ratios. In contrast, the preference of 17betaHSD2 for E2 oxidation strongly resists alteration by genetic and metabolic manipulations. These findings suggest that additional structural features, beyond the lack of a specific arginine residue, disfavor NADPH binding and thus support E2 oxidation by 17betaHSD2 in intact cells.

Estrogen metabolism and action in endometriosis

Endometriosis is a complex estrogen-dependent disease that is defined as the presence of endometrial glands and stroma outside the uterine cavity. The etiology of endometriosis is multifactorial and includes complex interactions of genetic, immunological, hormonal and environmental factors. Many theories have been proposed, but no single theory can explain all aspects of endometriosis, suggesting that endometriosis is a heterogeneous disease. This review presents the current theories on the pathogenesis of endometriosis, followed by an overview on estrogen metabolism in normal endometrium and diseased endometrium of endometriosis patients. The potential role of aberrant expression of individual estrogen-metabolizing enzymes is discussed, and a model mechanism for increased formation of estradiol is presented separately for different types of endometriosis. The disturbed expression of estrogen receptors in endometriosis is detailed, and the estrogen biosynthetic enzymes and receptors are discussed as novel therapeutic targets for the treatment of endometriosis.

Estrone C15 derivatives--a new class of 17beta-hydroxysteroid dehydrogenase type 1 inhibitors

Lowering local estradiol concentration by inhibition of the estradiol-synthesizing enzyme 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1) has been proposed as a promising new therapeutic option to treat estrogen-dependent diseases like endometriosis and breast cancer. Based on a molecular modelling approach we designed and synthesized novel C15-substituted estrone derivatives. Subsequent biological evaluation revealed that potent inhibitors of human 17beta-HSD1 can be identified in this compound class. The best, compound 21, inhibited recombinant human 17beta-HSD1 with an IC50 of 10nM and had no effect on the activity of recombinant human 17beta-hydroxysteroid dehydrogenase type 2 (17beta-HSD2), the enzyme catalyzing estradiol inactivation. These properties were retained in a cell-based enzyme activity assays. In spite of the estrogen backbone compound 21 did not show estrogen receptor mediated effects in vitro or in vivo. In conclusion, estrone C15 derivative compound 21 can be regarded as a promising lead compound for further development as a 17beta-HSD1 inhibitor.

Aberrant pre-receptor regulation of estrogen and progesterone action in endometrial cancer

Endometrial cancer is related to estrogen stimulation not opposed by progesterone. We have examined expression of the pre-receptor regulatory enzymes aromatase, 17beta-hydroxysteroid dehydrogenases (17beta-HSDs), 20alpha-hydroxysteroid dehydrogenases (20alpha-HSDs), sulfatase and sulfotransferase, and estrogen (ERs) and progesterone (PRs) receptors in samples of endometrial cancer and adjacent normal endometrium. No significant gene up-regulation was seen, although aromatase, AKR1C3, a 17beta-HSD and 20alpha-HSD, and AKR1C1, the major 20alpha-HSD, were up-regulated in 50% of samples. Significant down-regulation was seen for 17beta-HSD types 1 and 7, sulfotransferase, ERalpha, ERbeta, PR-AB. Western blotting revealed higher levels of AKR1C3 and PR-B and lower levels of ERalpha in cancerous endometrium, and immunohistochemistry confirmed expression of AKR1C3, PR-B and ERalpha at the cellular level. Up-regulation of aromatase in concert with AKR1C3 can lead to increased levels of estradiol, which acts via ERalpha. Up-regulation of AKR1C1 and AKR1C3 can result in lower levels of the protective progesterone, which acts mainly via PR-B.

Expression of 17beta-hydroxysteroid dehydrogenases and other estrogen-metabolizing enzymes in different cancer cell lines

Estrogen action is regulated at the receptor level by regulation of expression of estrogen receptors, and at the pre-receptor level by interconversions between the active hormone (estradiol) and its inactive counterparts (estrone, estrone-sulfate). In peripheral tissues, estrogens can be produced via the aromatase or the sulfatase pathways. Aromatase converts androstenedione and testosterone to estrone and estradiol, respectively, and sulfatase releases estrogens from inactive sulfates, while sulfotransferase catalyzes the reverse reaction. In both pathways, 17beta-hydroxysteroid dehydrogenases (17beta-HSDs) are of paramount importance as they catalyze activation of estrone to estradiol and inactivation of estradiol to estrone. These enzymes belong to either the short-chain dehydrogenase/reductase (SDR) or the aldo-keto reductase (AKR) protein superfamilies. Differential expression of these pre-receptor regulatory enzymes can lead to high estradiol concentrations, which have been implicated in the development of different diseases. Here, we have examined gene expression levels of estrogen-metabolizing enzymes, as six SDRs (17beta-HSD types 1, 2, 4, 7, 8, 12) and one AKR (17beta-HSD type 5; AKR1C3), of aromatase, steroid sulfatase (STS) and estrogen sulfotransferase (SULT1E1), and of the alpha and beta estrogen receptors (ERs), in breast cancer (MCF-7), endometrial cancer (Ishikawa), choriocarcinoma (JEG3) and liver cancer (HepG2) cell lines. After RNA isolation and cDNA synthesis, real-time PCR analyses were performed. The expression of AKR1C3 was examined also at the protein level. Our data show that in all four cancer cell lines, estradiol can be synthesized from estrone by the action of 17beta-HSD type 12, or from estrone-sulfate by sulfatase. In JEG3 and HepG2 cells, estradiol can be formed from androgens by aromatase and 17beta-HSD type 1. Also in HepG2 cells, AKR1C3, which converts androstenedione to testosterone, in concert with aromatase might be responsible for estradiol formation. In MCF7 and Ishikawa cells, estradiol exerts its actions through ERalpha, while in JEG3 and HepG2 cells, it may act through non-ER-mediated pathways.

Human 17beta-hydroxysteroid dehydrogenases types 1, 2, and 3 catalyze bi-directional equilibrium reactions, rather than unidirectional metabolism, in HEK-293 cells

Human 17beta-hydroxysteroid dehydrogenases (17betaHSDs) catalyze the interconversion of weak and potent androgen and estrogen pairs. Although the reactions using purified enzymes can be driven in either direction, these enzymes appear to function unidirectionally in intact cells: only reductive reactions for 17betaHSD1 and 17beta HSD3 and only oxidative reactions for 17betaHSD2. We show that, after exhaustive incubations with either 17beta-hydroxy- or 17-ketosteroid, the medium for HEK-293 cells expressing 17betaHSD1 or 17betaHSD3 contains a 92:8 ratio of reduced:oxidized steroid. Similarly, 17betaHSD2 yields a >95:5 ratio of oxidized:reduced steroids for both androgens and estrogens. Dual-isotope kinetic measurements show that the rates of the forward and reverse reactions are identical at these functional equilibrium states in intact cells for all three 17betaHSD isoforms, and these rates are much faster than those estimated from single-isotope flux studies. Mutation L36D converts 17betaHSD1 to an oxidative enzyme in intact cells, reversing the equilibrium distribution of estradiol:estrone to 5:95; however, the rates of the forward and reverse reactions at equilibrium are equal and comparable to those of the wild-type enzymes. The co-expression of 17betaHSD2 paradoxically increases the potency of estrone in transactivation assays, demonstrating the physiological relevance of "backwards" metabolism to estradiol. We conclude that 17betaHSD types 1, 2, and 3 catalyze both oxidative and reductive reactions in HEK-293 cells at intrinsic rates that are much faster than those estimated from single-isotope studies. These 17betaHSD isoforms do not drive steroid flux in one direction but rather may achieve functional equilibria in intact cells, reflecting thermodynamically driven steroid distributions.

Expression and purification of recombinant vesicular glutamate transporter VGLUT1 using PC12 cells and High Five insect cells

In synaptic vesicles, the estimated concentration of the excitatory amino acid glutamate is 100-150 mM. It was recently discovered that VGLUT1, previously characterized as an inorganic phosphate transporter (BNPI) with 9-11 predicted transmembrane spanning domains, is capable of transporting glutamate. The expression and His-tag based purification of recombinant VGLUT1 from PC12 cells and High Five insect cells is described. Significantly better virus and protein expression was obtained using High Five rather than Sf9 insect cells. PC12 cell expressed VGLUT1 is functional but not the Baculovirus expressed protein. The lack of functionality of the Baculovirus expressed VGLUT1 is discussed. The data indicate that VGLUT1 readily oligomerizes/dimerizes. The data are discussed in the context of developing this system further in order to reconstitute vesicular glutamate uptake in vitro using lipid-detergent vesicles.