Human placental 3 beta-hydroxy-5-ene-steroid dehydrogenase and steroid 5----4-ene-isomerase: purification from mitochondria and kinetic profiles, biophysical characterization of the purified mitochondrial and microsomal enzymes

Substrate specificity and kinetic mechanism of 3β-hydroxy-Δ5-C27-steroid oxidoreductase

Cholesterol is a key sterol whose homeostasis is primarily maintained through bile acid metabolism. Proper bile acid formation is vital for nutrient and fat-soluble vitamin absorption and emulsification of lipids. Synthesis of bile acids occurs through two main pathways, both of which rely on 3β-hydroxy-Δ5-C27-steroid oxidoreductase (HSD3B7) to begin epimerization of the 3β hydroxyl of cholesterol into its active 3α conformation. In this sequence, HSD3B7 catalyzes the dehydrogenation of the 3β-hydroxy group followed by isomerization of the Δ5-cholestene-3-one. These reactions are some of the many steps that transform cholesterol for either storage or secretion. HSD3B7 has distinct activity from other 3β-HSD family members leaving significant gaps in our understanding of its mode of catalysis and substrate specificity. In addition, the role of HSD3B7 in health and disease positions it as a metabolic vulnerability that could be harnessed as a therapeutic target. To this end, we evaluated the mechanism of HSD3B7 catalysis and reveal that HSD3B7 displays activity toward diverse 7α-hydroxylated oxysterols. HSD3B7 retains its catalytic efficiency toward these substrates, suggesting that its substrate binding pocket can withstand changes in polarity upon alterations to this hydrocarbon tail. Experiments aimed at determining substrate order are consistent with HSD3B7 catalyzing a sequential ordered bi-bi reaction mechanism with the binding of NAD+ followed by 7α-hydroxycholesterol to form a central complex. HSD3B7 bifunctional activity is dependent on membrane localization through a putative membrane-associated helix giving insight into potential regulation of enzyme activity. We found strong binding of the NADH product thought to activate the isomerization reaction. Homology models of HSD3B7 reveal a potential substrate pocket that allows for oxysterol binding, and mutagenesis was utilized to support this model. Together, these studies offer an understanding of substrate specificity and kinetic mechanism of HSD3B7, which can be exploited for future drug development.

Serum progesterone is lower in ovarian stimulation with highly purified HMG compared to recombinant FSH owing to a different regulation of follicular steroidogenesis: a randomized controlled trial

STUDY QUESTION

Does ovarian stimulation with highly purified (hp)-HMG protect from elevated progesterone in the follicular phase compared to recombinant FSH (r-FSH) cycles through a different regulation of follicular steroidogenesis?

SUMMARY ANSWER

hp-HMG enhanced the Δ4 pathway from pregnenolone to androstenodione leading to lower serum progesterone at the end of the cycle, while r-FSH promoted the conversion of pregnenolone to progesterone causing higher follicular phase progesterone levels.

WHAT IS KNOWN ALREADY

Elevated progesterone in the follicular phase has been related to lower clinical outcome in fresh IVF cycles. Progesterone levels are positively correlated to ovarian response, and some studies have shown that when r-FSH alone is used for ovarian stimulation serum progesterone levels on the day of triggering are higher than when hp-HMG is given. Whether this is caused by a lower ovarian response in hp-HMG cycles or to a difference in follicular steroidogenesis in the two ovarian stimulation regimens has not been well characterized.

STUDY DESIGN, SIZE, DURATION

A randomized controlled trial including 112 oocyte donors undergoing ovarian stimulation with GnRH antagonists and 225 IU/day of r-FSH (n = 56) or hp-HMG (n = 56) was carried out in a university-affiliated private infertility clinic. Subjects were recruited between October 2016 and June 2018.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The women were aged 18-35 years with a regular menstrual cycle (25-35 days) and normal ovarian reserve (serum anti-Müllerian hormone (AMH) = 10-30 pMol/l) undergoing ovarian stimulation for oocyte donation. FSH, LH, estradiol (E2), estrone, progesterone, pregnenolone, 17-OH-progesterone, androstenodione, dehidroepiandrostenodione, and testosterone were determined on stimulation Days 1, 4, 6, and 8 and on day of triggering in serum and in follicular fluid. Samples were frozen at -20°C until assay. Total exposures across the follicular phase were compared by polynomic extrapolation.

MAIN RESULTS AND THE ROLE OF CHANCE

Subjects in both groups were comparable in terms of age, BMI, and AMH levels. Ovarian response was also similar: 17.5 ± 7.9 (mean ± SD) versus 16.5 ± 7.5 oocytes with r-FSH and hp-HMG, respectively (P = 0.49). Serum progesterone (ng/ml) on day of trigger was 0.46 ± 0.27 in the hp-HMG group versus 0.68 ± 0.50 in the r-FSH group (P = 0.010). Differences for progesterone were also significant on stimulation days 6 and 8. The pregnenolone: progesterone ratio was significantly increased in the r-FSH group from stimulation day 8 to the day of trigger (P = 0.019). Serum androstenodione (ng/ml) on day of trigger was 3.0 ± 1.4 in the hp-HMG group versus 2.4 ± 1.1 in the r-FSH group (P = 0.015). Differences in adrostenodione were also significant on stimulation Day 8. The pregnenolone:androstenodione ratio was significantly higher in the hp-HMG group (P = 0.012) on Days 6 and 8 and trigger. There were no other significant differences between groups. Follicular fluid E2, FSH, LH, dehidroepioandrostenodione, androstenodione, and testosterone were significantly higher in the hp-HMG than r-FSH group. No differences were observed for progesterone, estrone, 17-OH-progesterone, and pregnenolone in follicular fluid.

LIMITATIONS, REASONS FOR CAUTION

All women included in the study were young, not infertile, and had a normal BMI and a good ovarian reserve. The findings might be different in other patient subpopulations. Hormone analyses with immunoassays are subject to intra-assay variations that may influence the results.

WIDER IMPLICATIONS OF THE FINDINGS

Stimulation with hp-HMG may prevent progesterone elevation at the end of the follicular phase because of a different follicular steroidogenesis pathway, regardless of ovarian response. This should be considered, particularly in patients at risk of having high progesterone levels at the end of the follicular phase when a fresh embryo transfer is planned.

STUDY FUNDING/COMPETING INTEREST(S)

Roche Diagnostics provided unrestricted funding for all serum and follicular fluid hormone determinations. J.L.R., M.M., and A.P. have nothing to declare. E.B. has received consulting fees from Ferring, Merck, Gedeon Richter, and Roche and has participated in a research cooperation with Gedeon-Richter. In addition, the author has participated in speakers' bureau and received fees from Ferring, Gedeon Richter, Merck, and Roche. P.A. has received consulting fees from MSD and has participated in speakers' bureau and received fees from Ferring. P.A. also declares travel/meeting support from MSD. E.L. has received consulting fees from Ferring and MSD. In addition, the author has participated in a research cooperation with Gedeon-Richter. Also, the author has participated in speakers' bureau and received fees from Ferring and IBSA, as well as travel/meeting support from IBSA and Gedeon Richter. E.B., P.A., and E.L. also own stocks in IVIRMA Valencia.

TRIAL REGISTRATION NUMBER

NCT: NCT02738580.

TRIAL REGISTER DATE

19 February 2016.

DATE OF FIRST PATIENT’S ENROLMENT

03 October 2016.

3βHSD activity saturates at physiological substrate concentrations in intact cells

BACKGROUND

Conversion of adrenally produced dehydroepiandrosterone (DHEA) to the potent androgen dihydrotestosterone (DHT) is an important mechanism by which prostate cancer reaches castration resistance. At the start of this pathway is a branch point at which DHEA can be converted to Δ4 -androstenedione by the enzyme 3β-hydroxysteroid dehydrogenase (3βHSD) or to Δ5 -androstenediol by 17βHSD. To better understand this process, we studied the kinetics of these reactions in cells.

METHODS

Prostate cancer cells (LNCaP cell line) were incubated with steroids (DHEA and Δ5 -androstenediol) over a range of concentrations and the steroid metabolism reaction products were measured by mass spectrometry or by high-performance liquid chromatography to determine reaction kinetics. To confirm the generalizability of results, experiments were also performed in JEG-3 placental choriocarcinoma cells.

RESULTS

The two reactions displayed very different saturation profiles, with only the 3βHSD-catalyzed reaction beginning to saturate within a physiological substrate concentration range. Strikingly, incubating LNCaP cells with low (in the ~10 nM range) concentrations of DHEA resulted in a large majority of the DHEA undergoing 3βHSD-catalyzed conversion to Δ4 -androstenedione, whereas high concentrations of DHEA (in the 100s of nM range) resulted in most of the DHEA undergoing 17βHSD-catalyzed conversion to Δ5 -androstenediol.

CONCLUSION

Contrary to expectations from previous studies that used purified enzyme, cellular metabolism of DHEA by 3βHSD begins to saturate in the physiological concentration range, suggesting that fluctuations in DHEA concentrations could be buffered at the downstream active androgen level.

Luteal Lipid Droplets: A Novel Platform for Steroid Synthesis

Progesterone is an essential steroid hormone that is required to initiate and maintain pregnancy in mammals and serves as a metabolic intermediate in the synthesis of endogenously produced steroids, including sex hormones and corticosteroids. Steroidogenic luteal cells of the corpus luteum have the tremendous capacity to synthesize progesterone. These specialized cells are highly enriched with lipid droplets that store lipid substrate, which can be used for the synthesis of steroids. We recently reported that hormone-stimulated progesterone synthesis by luteal cells requires protein kinase A-dependent mobilization of cholesterol substrate from lipid droplets to mitochondria. We hypothesize that luteal lipid droplets are enriched with steroidogenic enzymes and facilitate the synthesis of steroids in the corpus luteum. In the present study, we analyzed the lipid droplet proteome, conducted the first proteomic analysis of lipid droplets under acute cyclic adenosine monophosphate (cAMP)-stimulated conditions, and determined how specific lipid droplet proteins affect steroidogenesis. Steroidogenic enzymes, cytochrome P450 family 11 subfamily A member 1 and 3 beta-hydroxysteroid dehydrogenase (HSD3B), were highly abundant on lipid droplets of the bovine corpus luteum. High-resolution confocal microscopy confirmed the presence of active HSD3B on the surface of luteal lipid droplets. We report that luteal lipid droplets have the capacity to synthesize progesterone from pregnenolone. Lastly, we analyzed the lipid droplet proteome following acute stimulation with cAMP analog, 8-Br-cAMP, and report increased association of HSD3B with luteal lipid droplets following stimulation. These findings provide novel insights into the role of luteal lipid droplets in steroid synthesis.

Recent Updates on Corticosteroid-Induced Neuropsychiatric Disorders and Theranostic Advancements through Gene Editing Tools

The vast use of corticosteroids (CCSs) globally has led to an increase in CCS-induced neuropsychiatric disorders (NPDs), a very common manifestation in patients after CCS consumption. These neuropsychiatric disorders range from depression, insomnia, and bipolar disorders to panic attacks, overt psychosis, and many other cognitive changes in such subjects. Though their therapeutic importance in treating and improving many clinical symptoms overrides the complications that arise after their consumption, still, there has been an alarming rise in NPD cases in recent years, and they are seen as the greatest public health challenge globally; therefore, these potential side effects cannot be ignored. It has also been observed that many of the neuronal functional activities are regulated and controlled by genomic variants with epigenetic factors (DNA methylation, non-coding RNA, and histone modeling, etc.), and any alterations in these regulatory mechanisms affect normal cerebral development and functioning. This study explores a general overview of emerging concerns of CCS-induced NPDs, the effective molecular biology approaches that can revitalize NPD therapy in an extremely specialized, reliable, and effective manner, and the possible gene-editing-based therapeutic strategies to either prevent or cure NPDs in the future.

History of Adrenal Research: From Ancient Anatomy to Contemporary Molecular Biology

The adrenal is a small, anatomically unimposing structure that escaped scientific notice until 1564 and whose existence was doubted by many until the 18th century. Adrenal functions were inferred from the adrenal insufficiency syndrome described by Addison and from the obesity and virilization that accompanied many adrenal malignancies, but early physiologists sometimes confused the roles of the cortex and medulla. Medullary epinephrine was the first hormone to be isolated (in 1901), and numerous cortical steroids were isolated between 1930 and 1949. The treatment of arthritis, Addison's disease, and congenital adrenal hyperplasia (CAH) with cortisone in the 1950s revolutionized clinical endocrinology and steroid research. Cases of CAH had been reported in the 19th century, but a defect in 21-hydroxylation in CAH was not identified until 1957. Other forms of CAH, including deficiencies of 3β-hydroxysteroid dehydrogenase, 11β-hydroxylase, and 17α-hydroxylase were defined hormonally in the 1960s. Cytochrome P450 enzymes were described in 1962-1964, and steroid 21-hydroxylation was the first biosynthetic activity associated with a P450. Understanding of the genetic and biochemical bases of these disorders advanced rapidly from 1984 to 2004. The cloning of genes for steroidogenic enzymes and related factors revealed many mutations causing known diseases and facilitated the discovery of new disorders. Genetics and cell biology have replaced steroid chemistry as the key disciplines for understanding and teaching steroidogenesis and its disorders.

Identification of unusual oxysterols biosynthesised in human pregnancy by charge-tagging and liquid chromatography - mass spectrometry

The aim of this study was to identify oxysterols and any down-stream metabolites in placenta, umbilical cord blood plasma, maternal plasma and amniotic fluid to enhance our knowledge of the involvement of these molecules in pregnancy. We confirm the identification of 20S-hydroxycholesterol in human placenta, previously reported in a single publication, and propose a pathway from 22R-hydroxycholesterol to a C27 bile acid of probable structure 3β,20R,22R-trihydroxycholest-5-en-(25R)26-oic acid. The pathway is evident not only in placenta, but pathway intermediates are also found in umbilical cord plasma, maternal plasma and amniotic fluid but not non-pregnant women.

Through the Looking-Glass: Reevaluating DHEA Metabolism Through HSD3B1 Genetics

Dehydroepiandrosterone (DHEA) and DHEA sulfate together are abundant adrenal steroids whose physiological effects are mediated through their conversion to potent downstream androgens. 3β-Hydroxysteroid dehydrogenase isotype 1 (3βHSD1) facilitates the rate-limiting step of DHEA metabolism and gates the flux of substrate into the distal portion of the androgen synthesis pathway. Notably, a germline, missense-encoding change, HSD3B1(1245C), results in expression of 3βHSD1 protein that is resistant to degradation, yielding greater potent androgen production in the periphery. In contrast, HSD3B1(1245A) encodes 3βHSD1 protein that is easily degraded, limiting peripheral androgen synthesis. These adrenal-permissive (AP) and adrenal-restrictive (AR) alleles have recently been associated with divergent outcomes in androgen-sensitive disease states, underscoring the need to reevaluate DHEA metabolism using HSD3B1 genetics.

Serum and tissue pregnanes and pregnenes after dexamethasone treatment of cows in late gestation

Dexamethasone (DEX) initiates parturition by inducing progesterone withdrawal and affecting placental steroidogenesis, but the effects of DEX in fetal and maternal tissue steroid synthetic capacity remains poorly investigated. Blood was collected from cows at 270 days of gestation before DEX or saline (SAL) treatment, and blood and tissues were collected at slaughter 38 h later. Steroid concentrations were determined by liquid chromatography tandem mass spectrometry to detect multiple steroids including 5α-reduced pregnane metabolites of progesterone. The activities of 3β-hydroxysteroid dehydrogenase (3βHSD) in cotyledonary and luteal microsomes and mitochondria and cotyledonary microsomal 5α-reductase were assessed. Quantitative PCR was used to further assess transcripts encoding enzymes and factors supporting steroidogenesis in cotyledonary and luteal tissues. Serum progesterone, pregnenolone, 5α-dihydroprogesterone (DHP) and allopregnanolone (3αDHP) concentrations (all <5 ng/mL before treatment) decreased in cows after DEX. However, the 20α-hydroxylated metabolite of DHP, 20αDHP, was higher before treatment (≈100 ng/mL) than at slaughter but not affected by DEX. Serum, cotyledonary and luteal progesterone was lower in DEX- than SAL-treated cows. Progesterone was >100-fold higher in luteal than cotyledonary tissues, and serum and luteal concentrations were highly correlated in DEX-treated cows. 3βHSD activity was >5-fold higher in luteal than cotyledonary tissue, microsomes had more 3βHSD than mitochondria in luteal tissue but equal in cotyledonary sub-cellular fractions. DEX did not affect either luteal or cotyledonary 3βHSD activity but luteal steroidogenic enzyme transcripts were lower in DEX-treated cows. DEX induced functional luteal regression and progesterone withdrawal before any changes in placental pregnene/pregnane synthesis and/or metabolism were detectable.

11-Oxygenated androgens in health and disease

The adrenal gland is a source of sex steroid precursors, and its activity is particularly relevant during fetal development and adrenarche. Following puberty, the synthesis of androgens by the adrenal gland has been considered of little physiologic importance. Dehydroepiandrosterone (DHEA) and its sulfate, DHEAS, are the major adrenal androgen precursors, but they are biologically inactive. The second most abundant unconjugated androgen produced by the human adrenals is 11β-hydroxyandrostenedione (11OHA4). 11-Ketotestosterone, a downstream metabolite of 11OHA4 (which is mostly produced in peripheral tissues), and its 5α-reduced product, 11-ketodihydrotestosterone, are bioactive androgens, with potencies equivalent to those of testosterone and dihydrotestosterone. These adrenal-derived androgens all share an oxygen atom on carbon 11, so we have collectively termed them 11-oxyandrogens. Over the past decade, these androgens have emerged as major components of several disorders of androgen excess, such as congenital adrenal hyperplasia, premature adrenarche and polycystic ovary syndrome, as well as in androgen-dependent tumours, such as castration-resistant prostate cancer. Moreover, in contrast to the more extensively studied, traditional androgens, circulating concentrations of 11-oxyandrogens do not demonstrate an age-dependent decline. This Review focuses on the rapidly expanding knowledge regarding the implications of 11-oxyandrogens in human physiology and disease.

Extra-adrenal glucocorticoid biosynthesis: implications for autoimmune and inflammatory disorders

Glucocorticoid synthesis is a complex, multistep process that starts with cholesterol being delivered to the inner membrane of mitochondria by StAR and StAR-related proteins. Here its side chain is cleaved by CYP11A1 producing pregnenolone. Pregnenolone is converted to cortisol by the enzymes 3-βHSD, CYP17A1, CYP21A2 and CYP11B1. Glucocorticoids play a critical role in the regulation of the immune system and exert their action through the glucocorticoid receptor (GR). Although corticosteroids are primarily produced in the adrenal gland, they can also be produced in a number of extra-adrenal tissue including the immune system, skin, brain, and intestine. Glucocorticoid production is regulated by ACTH, CRH, and cytokines such as IL-1, IL-6 and TNFα. The bioavailability of cortisol is also dependent on its interconversion to cortisone which is inactive, by 11βHSD1/2. Local and systemic glucocorticoid biosynthesis can be stimulated by ultraviolet B, explaining its immunosuppressive activity. In this review, we want to emphasize that dysregulation of extra-adrenal glucocorticoid production can play a key role in a variety of autoimmune diseases including multiple sclerosis (MS), lupus erythematosus (LE), rheumatoid arthritis (RA), and skin inflammatory disorders such as psoriasis and atopic dermatitis (AD). Further research on local glucocorticoid production and its bioavailability may open doors into new therapies for autoimmune diseases.

Human steroid biosynthesis, metabolism and excretion are differentially reflected by serum and urine steroid metabolomes: A comprehensive review

Advances in technology have allowed for the sensitive, specific, and simultaneous quantitative profiling of steroid precursors, bioactive steroids and inactive metabolites, facilitating comprehensive characterization of the serum and urine steroid metabolomes. The quantification of steroid panels is therefore gaining favor over quantification of single marker metabolites in the clinical and research laboratories. However, although the biochemical pathways for the biosynthesis and metabolism of steroid hormones are now well defined, a gulf still exists between this knowledge and its application to the measured steroid profiles. In this review, we present an overview of steroid hormone biosynthesis and metabolism by the liver and peripheral tissues, specifically highlighting the pathways linking and differentiating the serum and urine steroid metabolomes. A brief overview of the methodology used in steroid profiling is also provided.

Rapid and structure-specific cellular uptake of selected steroids

Steroid hormones and their respective nuclear receptors are essential mediators in numerous physiologic and pathophysiologic processes, ranging from regulation of metabolism, immune function, and reproductive processes to the development of hormone-dependent cancers such as those of the breast and prostate. Because steroids must enter cells before activating nuclear receptors, understanding the mechanisms by which cellular uptake occurs is critical, yet a clear understanding of these mechanisms has been elusive. It is generally assumed that diffusion-driven uptake is similar across various steroids whereas an elevated cellular concentration is thought to reflect active uptake, but these assumptions have not been directly tested. Here we show that intact cells rapidly accumulate free steroids to markedly elevated concentrations. This effect varies widely depending on steroid structure; more lipophilic steroids reach more elevated concentrations. Strong preferences exist for 3β-OH, Δ5-steroids vs. 3-keto, Δ4-structural features and for progestogens vs. androgens. Surprisingly, steroid-structure-specific preferences do not require cell viability, implying a passive mechanism, and occur across cells derived from multiple tissue types. Physiologic relevance is suggested by structure-specific preferences in human prostate tissue compared with serum. On the other hand, the presence of serum proteins in vitro blocks much, but not all, of the passive accumulation, while still permitting a substantial amount of active accumulation for certain steroids. Our findings suggest that both passive and active uptake mechanisms make important contributions to the cellular steroid uptake process. The role of passive, lipophilicity-driven accumulation has previously been largely unappreciated, and its existence provides important context to studies on steroid transport and action both in vitro and in vivo.

The Adrenal Lipid Droplet is a New Site for Steroid Hormone Metabolism

Steroid hormones play essential roles for living organisms. It has been long and well established that the endoplasmic reticulum (ER) and mitochondria are essential sites for steroid hormone biosynthesis because several steroidogenic enzymes are located in these organelles. The adrenal gland lipid droplet (LD) proteomes from human, macaque monkey, and rodent are analyzed, revealing that steroidogenic enzymes are also present in abundance on LDs. The enzymes found include 3β-hydroxysteroid dehydrogenase (HSD3B) and estradiol 17β-dehydrogenase 11 (HSD17B11). Analyses by Western blot and subcellular localization consistently demonstrate that HSD3B2 is localized on LDs. Furthermore, in vitro experiments confirm that the isolated LDs from HeLa cell stably expressing HSD3B2 or from rat adrenal glands have the capacity to convert pregnenolone to progesterone. Collectively, these data suggest that LDs may be important sites of steroid hormone metabolism. These findings may bring novel insights into the biosynthesis and metabolism of steroid hormones and the development of treatments for adrenal disorders.

Updates on the Effect of Mycotoxins on Male Reproductive Efficiency in Mammals

Mycotoxins are ubiquitous and unavoidable harmful fungal products with the ability to cause disease in both animals and humans, and are found in almost all types of foods, with a greater prevalence in hot humid environments. These mycotoxins vary greatly in structure and biochemical effects; therefore, by better understanding the toxicological and pathological aspects of mycotoxins, we can be better equipped to fight the diseases, as well as the biological and economic devastations, they induce. Multiple studies point to the association between a recent increase in male infertility and the increased occurrence of these mycotoxins in the environment. Furthermore, understanding how mycotoxins may induce an accumulation of epimutations during parental lifetimes can shed light on their implications with respect to fertility and reproductive efficiency. By acknowledging the diversity of mycotoxin molecular function and mode of action, this review aims to address the current limited knowledge on the effects of these chemicals on spermatogenesis and the various endocrine and epigenetics patterns associated with their disruptions.

Human placental 3β-hydroxysteroid dehydrogenase/steroid Δ5,4-isomerase 1: Identity, regulation and environmental inhibitors

Human placental 3β-hydroxysteroid dehydrogenase/steroid Δ5, 4-isomerase 1 (HSD3B1), a high-affinity type I enzyme, uses pregnenolone to make progesterone, which is critical for maintenance of pregnancy. HSD3B1 is located in the mitochondrion and the smooth endoplasmic reticulum of placental cells and is encoded by HSD3B1 gene. HSD3B1 contains GATA and TEF-5 regulatory elements. Many endocrine disruptors, including phthalates, methoxychlor and its metabolite, organotins, and gossypol directly inhibit placental HSD3B1 thus blocking progesterone production. In this review, we discuss the placental HSD3B1, its gene regulation, biochemistry, subcellular location, and inhibitors from the environment.

Monogenic Disorders of Adrenal Steroidogenesis

Disorders of adrenal steroidogenesis comprise autosomal recessive conditions affecting steroidogenic enzymes of the adrenal cortex. Those are located within the 3 major branches of the steroidogenic machinery involved in the production of mineralocorticoids, glucocorticoids, and androgens. This mini review describes the principles of adrenal steroidogenesis, including the newly appreciated 11-oxygenated androgen pathway. This is followed by a description of pathophysiology, biochemistry, and clinical implications of steroidogenic disorders, including mutations affecting cholesterol import and steroid synthesis, the latter comprising both mutations affecting steroidogenic enzymes and co-factors required for efficient catalysis. A good understanding of adrenal steroidogenic pathways and their regulation is crucial as the basis for sound management of these disorders, which in the majority present in early childhood.

Characterization of equine GST A3-3 as a steroid isomerase

Glutathione transferases (GSTs) comprise a superfamily of enzymes prominently involved in detoxication by making toxic electrophiles more polar and therefore more easily excretable. However some GSTs have developed alternative functions. Thus, a member of the Alpha class GSTs in pig and human tissues is involved in steroid hormone biosynthesis, catalyzing the obligatory double-bond isomerization of Δ⁵-androstene-3,17-dione to Δ⁴-androstene-3,17-dione and of Δ⁵-pregnene-3,20-dione to Δ⁴-pregnene-3,20-dione on the biosynthetic pathways to testosterone and progesterone. The human GST A3-3 is the most efficient steroid double-bond isomerase known so far in mammals. The current work extends discoveries of GST enzymes that act in the steroidogenic pathways in large mammals. The mRNA encoding the steroid isomerase GST A3-3 was cloned from testis of the horse (Equus ferus caballus). The concentrations of GSTA3 mRNA were highest in hormone-producing organs such as ovary, testis and adrenal gland. EcaGST A3-3 produced in E. coli has been characterized and shown to have highly efficient steroid double-bond isomerase activity, exceeding its activities with conventional GST substrates. The enzyme now ranks as one of the most efficient steroid isomerases known in mammals and approaches the activity of the bacterial ketosteroid isomerase, one of the most efficient enzymes of all categories known today. The high efficiency and the tissue distribution of EcaGST A3-3 support the view that the enzyme plays a physiologically significant role in the biosynthesis of steroid hormones.

Structure-function relationships for the selective inhibition of human 3β-hydroxysteroid dehydrogenase type 1 by a novel androgen analog

3β-Hydroxysteroid dehydrogenase type 1 (3β-HSD1) is selectively expressed in human placenta, mammary glands and breast tumors in women. Human 3β-HSD2 is selectively expressed in adrenal glands and ovaries. Based on AutoDock 3 and 4 results, we have exploited key differences in the amino acid sequences of 3β-HSD1 (Ser194, Arg195) and 3β-HSD2 (Gly194, Pro195) by designing a selective inhibitor of 3β-HSD1. 2,16-Dicyano-4,5-epoxy-androstane-3,17-dione (16-cyano-17-keto-trilostane or DiCN-AND) was synthesized in a 4-step procedure from androstenedione. In purified 3β-HSD inhibition studies, DiCN-AND competitively inhibited 3β- HSD1 with K_i=4.7μM and noncompetitively inhibited 3β-HSD2 with a 6.5-fold higher K_i=30.7μM. We previously reported similar isoenzyme-specific inhibition profiles for trilostane. Based on our docking results, we created, expressed and purified the chimeric S194G-1 mutant of 3β-HSD1. Trilostane inhibited S194G-1 (K_i=0.67μM) with a noncompetitive mode compared to its 6.7-fold higher affinity, competitive inhibition of 3β-HSD1 (K_i=0.10μM). DiCN-AND inhibited S194G-1 with a 6.3-fold higher K_i (29.5μM) than measured for 3β-HSD1 (K_i=4.7μM) but with the same competitive mode for both enzyme species. Since DiCN-AND noncompetitively inhibits 3β-HSD2, which has the Gly194 and Pro195 of 3β-HSD2 in place of the Ser194 and Arg195 in 3β-HSD1, this suggests that Arg195 alone in 3β-HSD1 or S194G-1 is required to bind DiCN-AND in the substrate binding site (competitive inhibition). However, both Ser194 and Arg195 are required to bind trilostane in the 3β-HSD1 substrate site based on its noncompetitive inhibition of S194G-1 and 3β-HSD2. In support of this hypothesis, DiCN-AND inhibited our chimeric R195P-1 mutant noncompetitively with a K_i=41.3μM (similar to the 3β-HSD2 inhibition profile). Since DiCN-AND competitively inhibited S194G-1 that still contains R195 but noncompetitively inhibited R195P-1 that still contains S194, our data provides strong evidence that the Arg195 being mutated to Pro195 (as present in 3β-HSD2) shifts the inhibition mode from competitive to noncompetitive in 3β-HSD1. This supports the key role of Arg195 in 3β-HSD1 for the high affinity, competitive binding of the trilostane analogs. Our new structure/function information for the design of targeted 3β-HSD1 inhibitors may lead to important new treatments for the prevention of spontaneous premature birth.

A New Homozygous Frameshift Mutation in the HSD3B2 Gene in an Apparently Nonconsanguineous Italian Family

BACKGROUND

3β-Hydroxysteroid dehydrogenase (3β-HSD) deficiency is a rare cause of congenital adrenal hyperplasia (CAH) caused by inactivating mutations in the HSD3B2 gene.

PATIENT AND METHODS

We report the molecular and structural analysis of the HSD3B2 gene in a 46,XY child born to apparently nonconsanguineous parents and presenting ambiguous genitalia and salt wasting. The steroid profile showed elevated concentrations of 17-hydroxyprogesterone, androstenedione, ACTH and plasma renin, but normal values of cortisol and dehydroepiandrosterone sulfate. Unexpectedly, plasma aldosterone was high. For structural and functional analyses, the three-dimensional structure of 3β-HSD2 was modeled using the crystal structure of the short-chain dehydrogenase Gox2253 from Gluconobacter oxydans as a template.

RESULTS

The direct DNA sequence of the child revealed a new homozygous frameshift mutation in exon 4 of the HSD3B2 gene, a single nucleotide deletion at codon 319 [GTC(Val)x2192;GC], yielding premature stop codon in position 367. Molecular homology modeling and secondary structure predictions suggested that the variant sequence might both alter the substrate-binding cleft and compromise the overall stability of the enzyme.

CONCLUSION

We have described the first HSD3B2 gene mutation in the Italian population and analyzed its effect in the context of the 3β-HSD2 structure and function.

The cellular membrane as a mediator for small molecule interaction with membrane proteins

The cellular membrane constitutes the first element that encounters a wide variety of molecular species to which a cell might be exposed. Hosting a large number of structurally and functionally diverse proteins associated with this key metabolic compartment, the membrane not only directly controls the traffic of various molecules in and out of the cell, it also participates in such diverse and important processes as signal transduction and chemical processing of incoming molecular species. In this article, we present a number of cases where details of interaction of small molecular species such as drugs with the membrane, which are often experimentally inaccessible, have been studied using advanced molecular simulation techniques. We have selected systems in which partitioning of the small molecule with the membrane constitutes a key step for its final biological function, often binding to and interacting with a protein associated with the membrane. These examples demonstrate that membrane partitioning is not only important for the overall distribution of drugs and other small molecules into different compartments of the body, it may also play a key role in determining the efficiency and the mode of interaction of the drug with its target protein. This article is part of a Special Issue entitled: Biosimulations edited by Ilpo Vattulainen and Tomasz Róg.

Urinary cysteinyl progestogens: Occurrence and origin

The presence of two cysteinyl progestogens, 16-cysteinyl-progesterone (16-Cys-Prog) and 16-cysteinyl-pregnenolone (16-Cys-Preg), in human urine is described for the first time. Their occurrence was unequivocally confirmed by comparison with synthesized material by using mass spectrometric detectors. Several experiments were performed in order to clarify their origin. The adrenal origin of both 16-Cys-Prog and 16-Cys-Preg can be inferred from the increase in their concentrations after ACTH stimulatory test, together with their circadian variation similar to the one observed for cortisol. Moreover, the notable increase in excretions of 16-Cys-Prog during the luteal phase of the menstrual cycle points towards an ovarian production for this progestogen. However, the analysis of samples during the course of two pregnancies revealed that, in spite of the large amounts of progesterone produced during gestation, the human placenta lacks the capacity to make 16-Cys-Prog. The adrenal and ovarian origin has been further indicated by the absence of both metabolites in samples collected from a subject with bilateral adrenalectomy and hypogonadotrophyic hypogonadism. Regarding liver action, in vitro studies with hepatocytes and progesterone indicate that, although the liver is able to metabolize progesterone to 6-dehydroprogesterone, it has not the enzymatic machinery for the generation of 16-dehydroprogesterone. Taken together, these results open the possibility for a noninvasive test for the simultaneous evaluation of progesterone biosynthesis in different organs.

Cytochrome b5 modulates multiple reactions in steroidogenesis by diverse mechanisms

Cytochrome b5 (cyt-b5) is a relatively small haemoprotein which plays an important role in the regulation of mammalian steroidogenesis. This unique protein has the ability to modulate the activity of key steroidogenic enzymes via a number of diverse reaction mechanisms. Cyt-b5 can augment the 17,20-lyase activity of CYP17A1 by promoting the interaction of CYP17A1 and POR; enhance the 16-ene-synthase activity of CYP17A1 by acting as an electron donor; and enhance the activity of 3βHSD by increasing the affinity of 3βHSD for its cofactor NAD(+). We review the modulation of CYP17A1 and 3βHSD activity by cyt-b5 and discuss the reaction mechanisms associated with each activity. The physiological importance of cyt-b5 in regulating mammalian steroidogenesis is presented and the impact of inactivating cyt-b5 mutations are reviewed. This article is part of a Special Issue entitled 'Steroid/Sterol signaling'.

Regulation of human 3-beta-hydroxysteroid dehydrogenase type-2 (3βHSD2) by molecular chaperones and the mitochondrial environment affects steroidogenesis

Human 3-β-hydroxysteroid dehydrogenase/isomerase types 1 and 2 (3βHSD1 and 3βHSD2, respectively) are expressed in a tissue-specific pattern by different genes. Site-directed mutagenesis studies have confirmed the function of the catalytic amino acids (Tyr154, Lys 158, Ser124 in both isoenzymes), substrate/inhibitor isoform-specific residues (His156 and Arg195 in 3βHSD1) and cofactor binding residues (Asp36 provides NAD(+) specificity in both isoenzymes). However, detailed analysis of isoform-specific organelle localization and characterization is difficult due to the 93% amino acid identity between the two isoforms. With recent advances in the knowledge of mitochondrial architecture and localization of the various translocases, our laboratory has studied the mechanisms regulating mitochondrial 3βHSD2 localization. The mitochondrial N-terminal leader sequence of 3βHSD2 directs its entry into the mitochondria where it is localized to the intermembrane space (IMS). Unlike other mitochondrial proteins, the N-terminal signal sequence of 3βHSD2 is not cleaved upon mitochondrial import. 3βHSD2 interacts with the mitochondrial translocase, Tim50, to regulate progesterone and androstenedione formation. Our studies suggest that its activity at the IMS is facilitated in a partially unfolded "molten globule" conformation by the proton pump between the matrix and IMS. The unfolded protein is refolded by the mitochondrial chaperones. The protons at the IMS are absorbed by the lipid vesicles, to maintain the proton pump and recycle 3βHSD2. As a result, one molecule of 3βHSD2 may participate in multiple catalytic reactions. In summary, the steroidogenic cell recycles 3βHSD2 to catalyze the reactions needed to produce androstenedione, progesterone and 17α-hydroxyprogesterone on demand in coordination with the mitochondrial translocase, Tim50. This article is part of a Special Issue entitled 'Steroid/Sterol signaling'.

Regulation of human 3β-hydroxysteroid dehydrogenase type 2 by adrenal corticosteroids and product-feedback by androstenedione in human adrenarche

In human adrenarche during childhood, the secretion of dehydroepiandrosterone (DHEA) from the adrenal gland increases due to its increased synthesis and/or decreased metabolism. DHEA is synthesized by 17α-hydroxylase/17,20-lyase, and is metabolized by 3β-hydroxysteroid dehydrogenase type 2 (3βHSD2). In this study, the inhibition of purified human 3βHSD2 by the adrenal steroids, androstenedione, cortisone, and cortisol, was investigated and related to changes in secondary enzyme structure. Solubilized, purified 3βHSD2 was inhibited competitively by androstenedione with high affinity, by cortisone at lower affinity, and by cortisol only at very high, nonphysiologic levels. When purified 3βHSD2 was bound to lipid vesicles, the competitive Ki values for androstenedione and cortisone were slightly decreased, and the Ki value of cortisol was decreased 2.5-fold, although still at a nonphysiologic level. The circular dichroism spectrum that measured 3βHSD2 secondary structure was significantly altered by the binding of cortisol, but not by androstenedione and cortisone. Our import studies show that 3βHSD2 binds in the intermitochondrial space as a membrane-associated protein. Androstenedione inhibits purified 3βHSD2 at physiologic levels, but similar actions for cortisol and cortisone are not supported. In summary, our results have clarified the mechanisms for limiting the metabolism of DHEA during human adrenarche.

Mitochondrial proteases act on STARD3 to activate progesterone synthesis in human syncytiotrophoblast

BACKGROUND

STARD1 transports cholesterol into mitochondria of acutely regulated steroidogenic tissue. It has been suggested that STARD3 transports cholesterol in the human placenta, which does not express STARD1. STARD1 is proteolytically activated into a 30-kDa protein. However, the role of proteases in STARD3 modification in the human placenta has not been studied.

METHODS

Progesterone determination and Western blot using anti-STARD3 antibodies showed that mitochondrial proteases cleave STARD3 into a 28-kDa fragment that stimulates progesterone synthesis in isolated syncytiotrophoblast mitochondria. Protease inhibitors decrease STARD3 transformation and steroidogenesis.

RESULTS

STARD3 remained tightly bound to isolated syncytiotrophoblast mitochondria. Simultaneous to the increase in progesterone synthesis, STARD3 was proteolytically processed into four proteins, of which a 28-kDa protein was the most abundant. This protein stimulated mitochondrial progesterone production similarly to truncated-STARD3. Maximum levels of protease activity were observed at pH7.5 and were sensitive to 1,10-phenanthroline, which inhibited steroidogenesis and STARD3 proteolytic cleavage. Addition of 22(R)-hydroxycholesterol increased progesterone synthesis, even in the presence of 1,10-phenanthroline, suggesting that proteolytic products might be involved in mitochondrial cholesterol transport.

CONCLUSION

Metalloproteases from human placental mitochondria are involved in steroidogenesis through the proteolytic activation of STARD3. 1,10-Phenanthroline inhibits STARD3 proteolytic cleavage. The 28-kDa protein and the amino terminal truncated-STARD3 stimulate steroidogenesis in a comparable rate, suggesting that both proteins share similar properties, probably the START domain that is involved in cholesterol binding.

GENERAL SIGNIFICANCE

Mitochondrial proteases are involved in syncytiotrophoblast-cell steroidogenesis regulation. Understanding STARD3 activation and its role in progesterone synthesis is crucial to getting insight into its action mechanism in healthy and diseased syncytiotrophoblast cells.

Adrenal androgens and androgen precursors-definition, synthesis, regulation and physiologic actions

The human adrenal produces more 19 carbon (C19) steroids, by mass, than either glucocorticoids or mineralocorticoids. However, the mechanisms regulating adrenal C19 steroid biosynthesis continue to represent one of the most intriguing mysteries of endocrine physiology. This review will discuss the C19 steroids synthesized by the human adrenal and the features within the adrenal that allow production of these steroids. Finally, we consider the effects of these steroids in normal physiology and disorders of adrenal C19 steroid excess.

Ochratoxin A: developmental and reproductive toxicity-an overview

Ochratoxin A (OTA) is nephrotoxic, hepatotoxic, reprotoxic, embryotoxic, teratogenic, neurotoxic, immunotoxic, and carcinogenic for laboratory and farm animals. Male and female reproductive health has deteriorated in many countries during the last few decades. A number of toxins in environment are suspected to affect reproductive system in male and female. OTA is one of them. OTA has been found to be teratogenic in several animal models including rat, mouse, hamster, quail, and chick, with reduced birth weight and craniofacial abnormalities being the most common signs. The presence of OTA also results in congenital defects in the fetus. Neither the potential of OTA to cause malformations in human nor its teratogenic mode of action is known. Exposure to OTA leads to increased embryo lethality manifested as resorptions or dead fetuses. The mechanism of OTA transfer across human placenta (e.g., which transporters are involved in the transfer mechanism) is not fully understood. Some of the toxic effects of OTA are potentiated by other mycotoxins or other contaminants. Therefore, OTA exposure of pregnant women should be minimized. OTA has been shown to be an endocrine disruptor and a reproductive toxicant, with abilities of altering sperm quality. Other studies have shown that OTA is a testicular toxin in animals. Thus, OTA is a biologically plausible cause of testicular cancer in man.

Environmental pollutants and hydroxysteroid dehydrogenases

Hydroxysteroid dehydrogenases (HSD) are a group of steroidogenic enzymes that are involved in the steroid biosynthesis and metabolism. Four classes of HSDs, namely, 3β-, 11β-, 17β-, and 20α-HSDs, are discussed. 3β-HSDs catalyze the conversion of pregnenolone, 17α-hydroxypregnenolone, and dehydroepiandrosterone to progesterone, 17α-hydroxyprogesterone, and androstenedione, respectively. 11β-HSDs catalyze the interconversion between active cortisol and inactive cortisone. 17β-HSDs catalyze the interconversion between 17β-hydroxyl steroids and 17-ketoandrogens and estrogens. 20α-HSDs catalyze the conversion of progesterone into 20α-hydroxyprogesterone. Many environmental pollutants directly inhibit one or more enzymes of these HSDs, thus interfering with endogenous active steroid hormone levels. These chemicals include industrial materials (perfluoroalkyl compounds, phthalates, bisphenol A, and benzophenone), pesticides/biocides (methoxychlor, organotins, 1,2-dibromo-3-chloropropane, and prochloraz), and plant constituents (genistein, gossypol, and licorice). This chapter reviews these inhibitors targeting on HSDs.

Steroid hormone synthesis in mitochondria

Mitochondria are essential sites for steroid hormone biosynthesis. Mitochondria in the steroidogenic cells of the adrenal, gonad, placenta and brain contain the cholesterol side-chain cleavage enzyme, P450scc, and its two electron-transfer partners, ferredoxin reductase and ferredoxin. This enzyme system converts cholesterol to pregnenolone and determines net steroidogenic capacity, so that it serves as the chronic regulator of steroidogenesis. Several other steroidogenic enzymes, including 3β-hydroxysteroid dehydrogenase, 11β-hydroxylase and aldosterone synthase also reside in mitochondria. Similarly, the mitochondria of renal tubular cells contain two key enzymes participating in the activation and degradation of vitamin D. The access of cholesterol to the mitochondria is regulated by the steroidogenic acute regulatory protein, StAR, serving as the acute regulator of steroidogenesis. StAR action requires a complex multi-component molecular machine on the outer mitochondrial membrane (OMM). Components of this machine include the 18 kDa translocator protein (TSPO), the voltage-dependent anion chanel (VDAC-1), TSPO-associated protein 7 (PAP7, ACBD3), and protein kinase A regulatory subunit 1α (PKAR1A). The precise fashion in which these proteins interact and move cholesterol from the OMM to P450scc, and the means by which cholesterol is loaded into the OMM, remain unclear. Human deficiency diseases have been described for StAR and for all the mitochondrial steroidogenic enzymes, but not for the electron transfer proteins or for the components of the cholesterol import machine.

Cytochrome b5: novel roles in steroidogenesis

Cytochrome b(5) (cyt-b(5)) is essential for the regulation of steroidogenesis and as such has been implicated in a number of clinical conditions. It is well documented that this small hemoprotein augments the 17,20-lyase activity of cytochrome P450 17α-hydroxylase/17,20-lyase (CYP17A1). Studies have revealed that this augmentation is accomplished by cyt-b(5) enhancing the interaction between cytochrome P450 reductase (POR) and CYP17A1. In this paper we present evidence that cyt-b(5) induces a conformational change in CYP17A1, in addition to facilitating the interaction between CYP17A1 and POR. We also review the recently published finding that cyt-b(5) allosterically augments the activity of 3β-hydroxysteroid dehydrogenase/Δ(5)-Δ(4) isomerase (3βHSD), a non cytochrome P450 enzyme, by increasing the enzymes affinity for its cofactor, NAD(+). The physiological importance of this finding, in terms of understanding adrenal androstenedione production, is examined. Finally, evidence that cyt-b(5) is able to form homomeric complexes in living cells is presented and discussed.

Allosteric interaction between 3β-hydroxysteroid dehydrogenase/Δ⁵-Δ⁴ isomerase and cytochrome b5 influences cofactor binding

The biosynthesis of steroid hormones, essential to the survival of all mammals, is dependent on the activity of 3β-hydroxysteroid dehydrogenase/Δ(5)-Δ(4) isomerase (3βHSD). 3βHSD activity is, in turn, influenced by cytochrome-b(5) (Cyt-b(5)). However, the mechanism through which this occurs is unknown. In this study, we investigated this mechanism by evaluating the influence of Cyt-b(5) on the dehydrogenase and isomerase activities of 3βHSD. Capra hircus 3βHSD was overexpressed in SF-9 cells, using a baculovirus expression system, and purified. Substrate and cofactor kinetics were determined spectrophotometrically in the presence and absence of purified Ovis aries liver Cyt-b(5). Nonspecific enzyme activity was evaluated by zero-enzyme, -substrate, and -cofactor blanks. Fusion proteins, 3βHSD-eCFP, and Cyt-b(5)-eYFP were subsequently coexpressed in COS-1 cells and analyzed for FRET. A CFP-YFP fusion protein served as positive control, while coexpression of 3βHSD-eCFP and cytochrome P450 17α-hydroxylase/17,20 lyase-eYFP (CYP17A1-eYFP) served as negative control. Results showed Cyt-b(5) to decrease the K(m,)(NAD(+)) value of 3βHSD ≈3.5-fold while increasing the V(max,app) of the dehydrogenase reaction ≈17%. FRET analysis showed COS-1 cells coexpressing 3βHSD-eCFP and Cyt-b(5)-eYFP to exhibit a FRET signal ≈9-fold greater than that of the negative control. These results indicate that Cyt-b(5) augments 3βHSD activity via an allosteric mechanism by increasing the affinity of the enzyme toward NAD(+).

Mitochondrial 3β-hydroxysteroid dehydrogenase enzyme activity requires reversible pH-dependent conformational change at the intermembrane space

The inner mitochondrial membrane protein 3β-hydroxysteroid dehydrogenase 2 (3βHSD2) synthesizes progesterone and androstenedione through its dehydrogenase and isomerase activities. This bifunctionality requires 3βHSD2 to undergo a conformational change. Given its proximity to the proton pump, we hypothesized that pH influences 3βHSD2 conformation and thus activity. Circular dichroism (CD) showed that between pH 7.4 and 4.5, 3βHSD2 retained its primarily α-helical character with a decrease in α-helical content at lower pH values, whereas the β-sheet content remained unchanged throughout. Titrating the pH back to 7.4 restored the original conformation within 25 min. Metabolic conversion assays indicated peak 3βHSD2 activity at pH 4.5 with ~2-fold more progesterone synthesized at pH 4.5 than at pH 3.5 and 7.4. Increasing the 3βHSD2 concentration from 1 to 40 μg resulted in a 7-fold increase in progesterone at pH 4.5, but no change at pH 7.4. Incubation with guanidinum hydrochloride (GdmHCl) showed a three-step cooperative unfolding of 3βHSD2 from pH 7.4 to 4.5, possibly due to the native state unfolding to the intermediate ion core state. With further decreases in pH, increasing concentrations of GdmHCl led to rapid two-step unfolding that may represent complete loss of structure. Between pH 4 and 5, the two intermediate states appeared stable. Stopped-flow kinetics showed slower unfolding at around pH 4, where the protein is in a pseudostable state. Based on our data, we conclude that at pH 4-5, 3βHSD2 takes on a molten globule conformation that promotes the dual functionality of the enzyme.

Steroidogenic enzyme histochemistry in the testis of Sprague Dawley rats following the administration the water extracts from Carica papaya seed

Water extracts from pawpaw seed have been reported to reversibly decrease the testicular weight and to suppress spermatogenesis, and fertility of Wistar rats. The reversible changes become evident, 30 - 45 days after the withdrawal of the extract. The possible effect of this extract on the activities of steroidogenic enzymes of the testis has not been investigated. Water extract of papaya seeds was administered to male Sprague Dawley rats ad libitum for 84 days. Following the discontinuation of the extracts, ten rats each were sacrificed on days 0, 10, 20 and 30 after the withdrawal. Their testes were quickly dissected out and frozen. Cryostat sections, 10µm thick were cut. These sections were used for immunohistochemical stains for side chain cleavage enzyme and aromatase, and for histochemical stains for 17-β Hydroxysteroid dehydrogenase, 3-β Hydroxysteroid dehydrogenase. We conclude that the water extract of papaya seed suppresses the activities of steroidogenic enzymes in the testis of Sprague Dawley rats, and that this may contribute to reversible suppression of spermatogenesis, a property that gives a possible male contraceptive potential.

Lipid-mediated unfolding of 3β-hydroxysteroid dehydrogenase 2 is essential for steroidogenic activity

For inner mitochondrial membrane (IMM) proteins that do not undergo N-terminal cleavage, the activity may occur in the absence of a receptor present in the mitochondrial membrane. One such protein is human 3β-hydroxysteroid dehydrogenase 2 (3βHSD2), the IMM resident protein responsible for catalyzing two key steps in steroid metabolism: the conversion of pregnenolone to progesterone and dehydroepiandrosterone to androstenedione. Conversion requires that 3βHSD2 serve as both a dehydrogenase and an isomerase. The dual functionality of 3βHSD2 results from a conformational change, but the trigger for this change remains unknown. Using fluorescence resonance energy transfer, we found that 3βHSD2 interacted strongly with a mixture of dipalmitoylphosphatidylglycerol (DPPG) and dipalmitoylphosphatidylcholine (DPPC). 3βHSD2 became less stable when incubated with the individual lipids, as indicated by the decrease in thermal denaturation (T(m)) from 42 to 37 °C. DPPG, alone or in combination with DPPC, led to a decrease in α-helical content without an effect on the β-sheet conformation. With the exception of the 20 N-terminal amino acids, mixed vesicles protected 3βHSD2 from trypsin digestion. However, protein incubated with DPPC was only partially protected. The lipid-mediated unfolding completely supports the model in which a cavity forms between the α-helix and β-sheet. As 3βHSD2 lacks a receptor, opening the conformation may activate the protein.

Cytochrome b5 augments 3β-hydroxysteroid dehydrogenase/Δ5-Δ4 isomerase activity

During adrenal steroidogenesis the competition between 3β-hydroxysteroid dehydrogenase/Δ(5)-Δ(4) isomerase (3βHSD) and cytochrome P450 17α-hydroxylase/17,20 lyase (CYP17A1) for Δ(5) steroid intermediates greatly influences steroidogenic output. Cytochrome-b(5) (Cyt-b(5)), a small electron transfer hemoprotein, known to augment the lyase activity of CYP17A1, has been shown to alter the steroidogenic outcome of this competition. In this study, the influence of Cyt-b(5) on 3βHSD activity was investigated. In COS-1 cells, Cyt-b(5) was shown to significantly increase the activity of both caprine and ovine 3βHSD towards pregnenolone, 17-OH pregnenolone and dehydroepiandrosterone in a substrate and species specific manner. Furthermore, kinetic studies revealed Cyt-b(5) to have no influence on the K(m) values while significantly increasing the V(max) values of ovine 3βHSD for all its respective substrates. In addition, the activity of ovine 3βHSD in microsomal preparations was significantly influenced by the addition of either purified Cyt-b(5) or anti-Cyt-b(5) IgG. The results presented in this study indicate that Cyt-b(5) augments 3βHSD activity and represents the first documentation of such augmentation in any species.

Inner mitochondrial translocase Tim50 interacts with 3β-hydroxysteroid dehydrogenase type 2 to regulate adrenal and gonadal steroidogenesis

In the adrenals, testes, and ovaries, 3β-hydroxysteroid dehydrogenase type 2 (3βHSD2) catalyzes the conversion of pregnenolone to progesterone and dehydroepiandrostenedione to androstenedione. Alterations in this pathway can have deleterious effects, including sexual development impairment, spontaneous abortion, and breast cancer. 3βHSD2, synthesized in the cytosol, is imported into the inner mitochondrial membrane (IMM) by translocases. Steroidogenesis requires that 3βHSD2 acts as both a dehydrogenase and isomerase. To achieve this dual functionality, 3βHSD2 must undergo a conformational change; however, what triggers that change remains unknown. We propose that 3βHSD2 associates with IMM or outer mitochondrial membrane translocases facing the intermembrane space (IMS) and that this interaction promotes the conformational change needed for full activity. Fractionation assays demonstrate that 3βHSD2 associated with the IMM but did not integrate into the membrane. Through mass spectrometry and Western blotting of mitochondrial complexes and density gradient ultracentrifugation, we show that that 3βHSD2 formed a transient association with the translocases Tim50 and Tom22 and with Tim23. This association occurred primarily through the interaction of Tim50 with the N terminus of 3βHSD2 and contributed to enzymatic activity. Tim50 knockdown inhibited catalysis of dehydroepiandrostenedione to androstenedione and pregnenolone to progesterone. Although Tim50 knockdown decreased 3βHSD2 expression, restoration of expression via proteasome and protease inhibition did not rescue activity. In addition, protein fingerprinting and CD spectroscopy reveal the flexibility of 3βHSD2, a necessary characteristic for forming multiple associations. In summary, Tim50 regulates 3βHSD2 expression and activity, representing a new role for translocases in steroidogenesis.

Selective inhibition of human 3β-hydroxysteroid dehydrogenase type 1 as a potential treatment for breast cancer

Human 3β-hydroxysteroid dehydrogenase/isomerase type 1 (3β-HSD1) is a critical enzyme in the conversion of DHEA to estradiol in breast tumors and may be a target enzyme for inhibition in the treatment of breast cancer in postmenopausal women. Human 3β-HSD2 participates in the production of cortisol and aldosterone in the human adrenal gland in this population. In our recombinant human breast tumor MCF-7 Tet-off cells that express either 3β-HSD1 or 3β-HSD2, trilostane and epostane inhibit the DHEA-induced proliferation of MCF-7 3β-HSD1 cells with 12-16-fold lower IC(50) values compared to the MCF-7 3β-HSD2 cells. Trilostane and epostane also competitively inhibit purified human 3β-HSD1 with 12-16-fold lower K(i) values compared to the noncompetitive K(i) values measured for human 3β-HSD2. Using our structural model of 3β-HSD1, trilostane was docked in the active site of 3β-HSD1, and Arg195 in 3β-HSD1 or Pro195 in 3β-HSD2 was identified as a potentially critical residue. The R195P-1 mutant of 3β-HSD1 and the P195R-2 mutant of 3β-HSD2 were created, expressed and purified. Kinetic analyses of enzyme inhibition suggest that the high-affinity, competitive inhibition of 3β-HSD1 by trilostane may be related to the presence of Arg195 in 3β-HSD1 versus Pro195 in 3β-HSD2. In addition, His156 in 3β-HSD1 may play a role in the higher affinity of 3β-HSD1 for substrates and inhibitors compared to 3β-HSD2 containing Try156. Structural modeling of the 3β-HSD1 dimer identified a possible interaction between His156 on one subunit and Gln105 on the other. Kinetic analyses of the H156Y-1, Q105M-1 and Q105M-2 support subunit interactions that contribute to the higher affinity of 3β-HSD1 for the inhibitor, epostane, compared to 3β-HSD2. Article from the Special issue on Targeted Inhibitors.

Homology modeling and molecular dynamics simulation studies of human type 1 3β-hydroxysteroid dehydrogenase: Toward the understanding of cofactor specificity

The human type 1 isoform of 3β-hydroxysteroid dehydrogenase is a member of short-chain oxidoreductase family that catalyzes the conversion of dehydroepiandrosterone to androstenedione. To compare the molecular events underlying cofactor specificity in the wild-type and D35A/K36R mutant enzymes, molecular dynamics (MD) simulations of fully solvated cofactor-3β-HSD1 (wild-type and mutant) complex are performed. Molecular modeling methods are applied to construct three-dimensional models of cofactor-3β-HSD1 complexes based on Uridine diphosphate (UDP)-galactose 4-epimerase crystal structure from Escherichia coli. The binding mode and binding energy analysis between four different complexes indicate that Asp35 and Lys36 are key residues for the cofactor specificity of 3β-HSD1, which is in agreement with mutagenesis studies results obtained by Thomas et al.8 The MD results also display that the residue Glu41 may be another important residue except Asp35 and Lys36 for the cofactor specificity and that this result needs further mutational experiment for validation.

The molecular biology, biochemistry, and physiology of human steroidogenesis and its disorders

Steroidogenesis entails processes by which cholesterol is converted to biologically active steroid hormones. Whereas most endocrine texts discuss adrenal, ovarian, testicular, placental, and other steroidogenic processes in a gland-specific fashion, steroidogenesis is better understood as a single process that is repeated in each gland with cell-type-specific variations on a single theme. Thus, understanding steroidogenesis is rooted in an understanding of the biochemistry of the various steroidogenic enzymes and cofactors and the genes that encode them. The first and rate-limiting step in steroidogenesis is the conversion of cholesterol to pregnenolone by a single enzyme, P450scc (CYP11A1), but this enzymatically complex step is subject to multiple regulatory mechanisms, yielding finely tuned quantitative regulation. Qualitative regulation determining the type of steroid to be produced is mediated by many enzymes and cofactors. Steroidogenic enzymes fall into two groups: cytochrome P450 enzymes and hydroxysteroid dehydrogenases. A cytochrome P450 may be either type 1 (in mitochondria) or type 2 (in endoplasmic reticulum), and a hydroxysteroid dehydrogenase may belong to either the aldo-keto reductase or short-chain dehydrogenase/reductase families. The activities of these enzymes are modulated by posttranslational modifications and by cofactors, especially electron-donating redox partners. The elucidation of the precise roles of these various enzymes and cofactors has been greatly facilitated by identifying the genetic bases of rare disorders of steroidogenesis. Some enzymes not principally involved in steroidogenesis may also catalyze extraglandular steroidogenesis, modulating the phenotype expected to result from some mutations. Understanding steroidogenesis is of fundamental importance to understanding disorders of sexual differentiation, reproduction, fertility, hypertension, obesity, and physiological homeostasis.

Porcine glutathione transferase Alpha 2-2 is a human GST A3-3 analogue that catalyses steroid double-bond isomerization

A primary role of GSTs (glutathione transferases) is detoxication of electrophilic compounds. In addition to this protective function, hGST (human GST) A3-3, a member of the Alpha class of soluble GSTs, has prominent steroid double-bond isomerase activity. The isomerase reaction is an obligatory step in the biosynthesis of steroid hormones, indicating a special role of hGST A3-3 in steroidogenic tissues. An analogous GST with high steroid isomerase activity has so far not been found in any other biological species. In the present study, we characterized a Sus scrofa (pig) enzyme, pGST A2-2, displaying high steroid isomerase activity. High levels of pGST A2-2 expression were found in ovary, testis and liver. In its functional properties, other than steroid isomerization, pGST A2-2 was most similar to hGST A3-3. The properties of the novel porcine enzyme lend support to the notion that particular GSTs play an important role in steroidogenesis.

The functions of key residues in the inhibitor, substrate and cofactor sites of human 3beta-hydroxysteroid dehydrogenase type 1 are validated by mutagenesis

In postmenopausal women, human 3beta-hydroxysteroid dehydrogenase type 1 (3beta-HSD1) is a critical enzyme in the conversion of DHEA to estradiol in breast tumors, while 3beta-HSD2 participates in the production of cortisol and aldosterone in the human adrenal gland. The goals of this project are to determine if Arg195 in 3beta-HSD1 vs. Pro195 in 3beta-HSD2 in the substrate/inhibitor binding site is a critical structural difference responsible for the higher affinity of 3beta-HSD1 for inhibitor and substrate steroids compared to 3beta-HSD2 and whether Asp61, Glu192 and Thr8 are fingerprint residues for cofactor and substrate binding using site-directed mutagenesis. The R195P-1 mutant of 3beta-HSD1 and the P195R-2 mutant of 3beta-HSD2 have been created, expressed, purified and characterized kinetically. Dixon analyses of the inhibition of the R195P-1 mutant, P195R-2 mutant, wild-type 3beta-HSD1 and wild-type 3beta-HSD2 by trilostane has produced kinetic profiles that show inhibition of 3beta-HSD1 by trilostane (K(i)=0.10microM, competitive) with a 16-fold lower K(i) and different mode than measured for 3beta-HSD2 (K(i)=1.60microM, noncompetitive). The R195P-1 mutation shifts the high-affinity, competitive inhibition profile of 3beta-HSD1 to a low-affinity (trilostane K(i)=2.56microM), noncompetitive inhibition profile similar to that of 3beta-HSD2 containing Pro195. The P195R-2 mutation shifts the low-affinity, noncompetitive inhibition profile of 3beta-HSD2 to a high-affinity (trilostane K(i)=0.19microM), competitive inhibition profile similar to that of 3beta-HSD1 containing Arg195. Michaelis-Menten kinetics for DHEA, 16beta-hydroxy-DHEA and 16alpha-hydroxy-DHEA substrate utilization by the R195P-1 and P195R-2 enzymes provide further validation for higher affinity binding due to Arg195 in 3beta-HSD1. Comparisons of the Michaelis-Menten values of cofactor and substrate for the targeted mutants of 3beta-HSD1 (D61N, D61V, E192A, T8A) clarify the functions of these residues as well.

Hypocortisolism in the South African angora goat: the role of 3betaHSD

South African Angora goats are susceptible to cold stress, due to their inability to produce sufficient levels of cortisol. During adrenal steroidogenesis the production of cortisol relies on the activity of two key enzymes, namely cytochrome P450 17alpha-hydroxylase and 3beta-hydroxysteroid dehydrogenase. Cytochrome P450 17alpha-hydroxylase has previously been identified as a factor contributing to hypocortisolism in the South African Angora goat. In this comparative study, the catalytic activity of Angora and ovine 3beta-hydroxysteroid dehydrogenase, which differ by five amino acid residues, was characterized. The conversion of 17-hydroxypregnenolone and dehydroepiandosterone to their corresponding products, 17-hydroxyprogesterone and androstenedione, by the two enzymes differed significantly. The enzymes were subsequently co-expressed with Angora P450 17alpha-hydroxylase. Major differences were observed in pregnenolone metabolism with a significant reduction in the formation of the cortisol precursor, 17-hydroxyprogesterone, by cells expressing Angora 3beta-hydroxysteroid dehydrogenase, implicating 3beta-hydroxysteroid dehydrogenase as an additional factor contributing to hypocortisolism in the South African Angora goat.

Structural basis for the selective inhibition of human 3beta-hydroxysteroid dehydrogenase 1 in human breast tumor MCF-7 cells

Human 3beta-hydroxysteroid dehydrogenase/isomerase type 1 (3beta-HSD1) is a critical enzyme in the conversion of DHEA to estradiol in breast tumors and may be a target enzyme for inhibition in the treatment of breast cancer in postmenopausal women. Human 3beta-HSD2 participates in the production of cortisol and aldosterone in the human adrenal gland in this population. In our recombinant human breast tumor MCF-7 Tet-off cells that express either 3beta-HSD1 or 3beta-HSD2, trilostane and epostane inhibit the DHEA-induced proliferation of MCF-7 3beta-HSD1 cells with 12- to 16-fold lower IC(50) values compared to the MCF-7 3beta-HSD2 cells. The compounds also competitively inhibit purified human 3beta-HSD1 with 12- to 16-fold lower K(i) values compared to the noncompetitive K(i) values measured for human 3beta-HSD2. Using our structural model of 3beta-HSD1, trilostane or 17beta-acetoxy-trilostane was docked in the active site of 3beta-HSD1, and Arg195 in 3beta-HSD1 or Pro195 in 3beta-HSD2 was identified as a potentially critical residue (one of 23 non-identical residues in the two isoenzymes). The P195R mutant of 3beta-HSD2 were created, expressed and purified. Kinetic analyses of enzyme inhibition suggest that the high affinity, competitive inhibition of 3beta-HSD1 by trilostane and epostane may be related to the presence of Arg195 in 3beta-HSD1 vs. Pro195 in 3beta-HSD2.

3beta-Hydroxysteroid dehydrogenases and pre-receptor steroid metabolism in the human ovarian surface epithelium

Ovulation-associated inflammation with accompanied cytokines and reproductive hormones impact upon the human ovarian surface epithelium (hOSE) and probably have a role in the aetiology of ovarian cancer. Progesterone and progestin-related events, i.e. pregnancy and oral contraception, protect from the disease. We have investigated the pre-receptor metabolism of progesterone in primary hOSE cells and an immortalised hOSE cell line, OSE-C2, focusing on transcriptional regulation of 3beta-hydroxysteroid dehydrogenase (3beta-HSD) by inflammatory, anti-inflammatory and apoptotic factors. In hOSE cells, we show that anti-inflammatory effects of IL-1alpha and IL-4 on 3beta-HSD2 mRNA involve a p38 MAPK signalling pathway, whereas pro-inflammatory response of IL-1alpha to 3beta-HSD1 mRNA involves a NF-kappaB inflammatory pathway. In OSE-C2 cells, retinoic acid and transforming growth factor-beta1 massively induce 3beta-HSD1 mRNA levels. In conclusion, we elaborate several mechanisms for intracrine formation of progesterone in hOSE that could contribute in the development of novel strategies to prevent, diagnose and/or treat ovarian cancer.

Androgen synthesis in adrenarche

The enzymes and pathways of steroidogenesis are central to an understanding of adrenarche. The quantitative regulation of steroidogenesis occurs at the first step, the conversion of cholesterol to pregnenolone. Chronic quantitative regulation is principally at the level of transcription of the CYP11A1 gene encoding P450scc, which is the enzymatically rate-limiting step. Acute regulation is mediated by the steroidogenic acute regulatory protein (StAR), which facilitates the rapid influx of cholesterol into mitochondria, where P450scc resides. Qualitative regulation, which determines the type of steroid produced in a cell, is principally at the level of P450c17 (CYP17). In the absence of P450c17 in the zona glomerulosa, C21 deoxy steroids are produced, leading to the mineralocorticoid, aldosterone. In the presence of the 17alpha-hydroxylase but not the 17,20 lyase activity of P450c17 in the zona fasciculata, C21, 17-hydroxy steroids are produced, leading to the glucocorticoid, cortisol. When both the 17alpha-hydroxylase and 17,20 lyase activities of P450c17 are present in the zona reticularis, the androgen precursor DHEA is produced. The discrimination between 17alpha-hydroxylase and 17,20 lyase activities is regulated by two post-translational events, the serine phosphorylation of P450c17 and the allosteric action of cytochrome b5, both of which act to optimize the interaction of P450c17 with its obligatory electron donor, P450 oxidoreductase. In the adrenal zona reticularis, the abundant expression of P450 oxidoreductase and cytochrome b5, and the low expression of 3beta-hydroxysteroid dehydrogenase (HSD3B2) result in the production of the large amounts of DHEA that characterize adrenarche.