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

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

Mouse 17alpha-hydroxysteroid dehydrogenase (AKR1C21) binds steroids differently from other aldo-keto reductases: identification and characterization of amino acid residues critical for substrate binding

The mouse 17alpha-hydroxysteroid dehydrogenase (m17alpha-HSD) is the unique known member of the aldo-keto reductase (AKR) superfamily able to catalyze efficiently and in a stereospecific manner the conversion of androstenedione (Delta4) into epi-testosterone (epi-T), the 17alpha-epimer of testosterone. Structural and mutagenic studies had already identified one of the residues delineating the steroid-binding cavity, A24, as the major molecular determinant for the stereospecificity of m17alpha-HSD. We report here a ternary complex crystal structure (m17alpha-HSD:NADP(+):epi-T) determined at 1.85 A resolution that confirms this and reveals a unique steroid-binding mode for an AKR enzyme. Indeed, in addition to the interactions found in all other AKRs (van der Waals contacts stabilizing the core of the steroid and the hydrogen bonds established at the catalytic site by the Y55 and H117 residues with the oxygen atom of the ketone group to be reduced), m17alpha-HSD establishes with the other extremity of the steroid nucleus an additional interaction involving K31. By combining direct mutagenesis and kinetic studies, we found that the elimination of this hydrogen bond did not affect the affinity of the enzyme for its steroid substrate but led to a slight but significant increase of its catalytic efficiency (k(cat)/K(m)), suggesting a role for K31 in the release of the steroidal product at the end of the reaction. This previously unobserved steroid-binding mode for an AKR is similar to that adopted by other steroid-binding proteins, the hydroxysteroid dehydrogenases of the short-chain dehydrogenases/reductases (SDR) family and the steroid hormone nuclear receptors. Mutagenesis and structural studies made on the human type 3 3alpha-HSD, a closely related enzyme that shares 73% amino acids identity with the m17alpha-HSD, also revealed that the residue at position 24 of these two enzymes directly affects the binding and/or the release of NADPH, in addition to its role in their 17alpha/17beta stereospecificity.

Expression of sulfotransferase 1E1 in human prostate as studied by in situ hybridization and immunocytochemistry

BACKGROUND

Estrogen is recognized to play a role in the development and function of the prostate. Estrogen sulfotransferase (EST) 1E1 catalyzes the sulfoconjugation of estrogen and is thus involved in the metabolism of estrogen. We have recently shown that EST 1E1 is highly expressed in male mouse reproductive organs, including prostate. It appeared of interest to study the expression of EST 1E1 in human prostate.

METHODS

EST 1E1 mRNA and protein expression was evaluated in benign prostatic hyperplasia (BPH) using in situ hybridization and immunocytochemistry, respectively.

RESULTS

EST 1E1 mRNA and protein were found to be expressed in epithelial cells bordering alveola lumen (luminal cells) as well as stroma cells.

CONCLUSION

The enzyme EST may play a physiological role in regulating local estrogen levels in human prostate.

Localization and glucocorticoid regulation of 11β-hydroxysteroid dehydrogenase type 1 mRNA in the male mouse forebrain

The enzyme 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) converts the inactive 11-dehydrocorticosterone into the active glucocorticoid corticosterone. There is accumulating evidence indicating widespread expression of 11beta-HSD1 in the brain. However, there is little information about regulation of 11beta-HSD1 expression in this tissue. Using in situ hybridization involving use of 35S-labeled cRNA probe, we have studied the distribution of cells expressing 11beta-HSD1 mRNA in the male mouse forebrain as well as the effects of adrenalectomy (ADX) and acute administration of corticosterone (3 and 24 h) on 11beta-HSD1 mRNA levels. Cells expressing 11beta-HSD1 mRNA were mostly detected in the cerebral cortex, hippocampus, amygdala and medial preoptic area, with the highest expression in the cerebral cortex (retrosplenial granular area) and hippocampus (CA3 and granular layer of the gyrus dentatus). Seven days following ADX, 11beta-HSD mRNA levels were increased by 50% in the gyrus dentatus, by 100% in the CA3 area, and 105% in the cerebral cortex. Administration of corticosterone to ADX mice induced a significant decrease in mRNA, in both the hippocampus and cerebral cortex so that, at the 24 h time interval, the levels were similar to those observed in intact mice. These results clearly indicate that circulating corticosterone is downregulating the expression of 11beta-HSD1 mRNA in the two forebrain areas studied. This downregulation might contribute to maintain low intracellular corticosterone levels in central regions and then prevent the deleterious effects induced by high glucocorticoid levels.

Immunohistochemical localization and biological activity of the steroidogenic enzyme cytochrome P450 17α-hydroxylase/C17, 20-lyase (P450C17) in the frog brain and pituitary

It is now clearly established that the brain has the capability of synthesizing various biologically active steroids including 17-hydroxypregnenolone (17OH-Delta(5)P), 17-hydroxyprogesterone (17OH-P), dehydroepiandrosterone (DHEA) and androstenedione (Delta(4)). However, the presence, distribution and activity of cytochrome P450 17alpha-hydroxylase/C17, 20-lyase (P450(C17)), a key enzyme required for the conversion of pregnenolone (Delta(5)P) and progesterone (P) into these steroids, are poorly documented. Here, we show that P450(C17)-like immunoreactivity is widely distributed in the frog brain and pituitary. Prominent populations of P450(C17)-containing cells were observed in a number nuclei of the telencephalon, diencephalon, mesencephalon and metencephalon, as well as in the pars distalis and pars intermedia of the pituitary. In the brain, P450(C17)-like immunoreactivity was almost exclusively located in neurons. In several hypothalamic nuclei, P450(C17)-positive cell bodies also contained 3beta-hydroxysteroid dehydrogenase-like immunoreactivity. Incubation of telencephalon, diencephalon, mesencephalon, metencephalon or pituitary explants with [(3)H]Delta(5)P resulted in the formation of several tritiated steroids including 17OH-Delta(5)P, 17OH-P, DHEA and Delta(4). De novo synthesis of C(21) 17-hydroxysteroids and C(19) ketosteroids was reduced in a concentration-dependent manner by ketoconazole, a P450(C17) inhibitor. This is the first detailed immunohistochemical mapping of P450(C17) in the brain and pituitary of any vertebrate. Altogether, the present data provide evidence that CNS neurons and pituitary cells can synthesize androgens.

C6-(N,N-butyl-methyl-heptanamide) derivatives of estrone and estradiol as inhibitors of type 1 17β-hydroxysteroid dehydrogenase: Chemical synthesis and biological evaluation

A series of estrone and estradiol derivatives having an N-butyl,methyl heptanamide side chain at C6-position were synthesized, tested as inhibitors of type 1 17beta-HSD and assessed for their possible estrogenic activity. A better type 1 17beta-HSD inhibition was obtained for the 6beta-side chain orientation over 6alpha; the C17-alcohols are more potent inhibitors than the corresponding ketones; introducing a 2-methoxy group decreased the inhibitory potency; and the replacement of a C-S bond by a C-C bond in the C6beta-side chain is not detrimental to inhibition. Interestingly, the new inhibitors were also found less estrogenic than the lead compound in two breast cancer cell lines, T-47D and MCF-7.

Structure-based inhibitor design for an enzyme that binds different steroids: a potent inhibitor for human type 5 17beta-hydroxysteroid dehydrogenase

Human type 5 17beta-hydroxysteroid dehydrogenase plays a crucial role in local androgen formation in prostate tissue. Several chemicals were synthesized and tested for their ability to inhibit this enzyme, and a series of estradiol derivatives bearing a lactone on the D-ring were found to inhibit its activity efficiently. The crystal structure of the type 5 enzyme in complex with NADP and such a novel inhibitor, EM1404, was determined to a resolution of 1.30 A. Significantly more hydrogen bonding and hydrophobic interactions were defined between EM1404 and the enzyme than in the substrate ternary complex. The lactone ring of EM1404 accounts for important interactions with the enzyme, whereas the amide group at the opposite end of the inhibitor contributes to the stability of three protein loops involved in the construction of the substrate binding site. EM1404 has a strong competitive inhibition, with a Ki of 6.9+/-1.4 nM, demonstrating 40 times higher affinity than that of the best inhibitor previously reported. This is observed despite the fact that the inhibitor occupies only part of the binding cavity. Attempts to soak the inhibitor into crystals of the binary complex with NADP were unsuccessful, yielding a structure with a polyethylene glycol fragment occupying the substrate binding site. The relative crystal packing is discussed. Combined studies of small molecule inhibitor synthesis, x-ray crystallography, enzyme inhibition, and molecular modeling make it possible to analyze the plasticity of the substrate binding site of the enzyme, which is essential for developing more potent and specific inhibitors for hormone-dependent cancer therapy.

Androgen inactivation and steroid-converting enzyme expression in abdominal adipose tissue in men

We examined 5alpha-dihydrotestosterone (5alpha-DHT) inactivation and the expression of several steroid-converting enzymes with a focus on aldoketoreductases 1C (AKR1C), especially AKR1C2, in abdominal adipose tissue in men. AKR1C2 is mainly involved in the conversion of the potent androgen 5alpha-DHT to its inactive forms 5alpha-androstane-3alpha/beta,17beta-diol (3alpha/beta-diol). Subcutaneous (s.c.) and omental (Om) adipose tissue biopsies were obtained from 21 morbidly obese men undergoing biliopancreatic derivation surgery and 11 lean to obese men undergoing general abdominal surgery. AKR1C2 mRNA and 5alpha-DHT inactivation were detected in both s.c. and Om adipose tissue. After incubation of preadipocytes with 5alpha-DHT, both 3alpha-diol and 3beta-diol were produced through 3alpha/beta-ketosteroid reductase (3alpha/beta-HSD) activity. In preadipocyte cultures, 3alpha-reductase activity was significantly predominant over 3beta-reductase activity in cells from both the s.c. and Om compartments. Expression levels of AKR1C1, AKR1C3 and of the androgen receptor were significantly higher in s.c. versus Om adipose tissue while mRNA levels of 17beta-HSD-2 (hydroxysteroid dehydrogenase type 2) and 3(alpha-->beta)-hydroxysteroid epimerase were significantly higher in Om fat. 3Alpha/beta-HSD activity was mainly detected in the cytosolic fraction, suggesting that AKR1C may be responsible for this reaction. Experiments with isoform-specific AKR1C inhibitors in preadipocytes showed that AKR1C2 inhibition significantly decreased 3alpha-HSD and 3beta-HSD activities (3alpha-HSD: 30 +/- 24% of control for s.c. and 32 +/- 9% of control for Om, 3beta-HSD: 44 +/- 12% of control for s.c.). When cells were incubated with both AKR1C2 and AKR1C3 inhibitors, no significant additional inhibition was observed. 5Alpha-DHT inactivation was significantly higher in mature adipocytes compared with preadipocyte cultures in s.c. adipose tissue, as expressed per microgram total protein (755 +/- 830 versus 245 +/- 151 fmol 3alpha/beta-diol per microg protein over 24 h, P < 0.05 n = 10 cultures). 5Alpha-DHT inactivation measured in tissue homogenates was significantly higher in the s.c. depot compared with Om fat (117 +/- 39 versus 79 +/- 38 fmol 3alpha/beta-diol per microg prot over 24 h, P < 0.0001). On the other hand, Om 3alpha/beta-HSD activity was significantly higher in obese men (body mass index (BMI) >or= 30 kg/m2) compared with lean and overweight men (84 +/- 37 versus 52 +/- 30 fmol 3alpha/beta-diol per microg protein over 24 h, P < 0.03). No difference was found in s.c. 3alpha/beta-HSD activity between these groups. Positive correlations were found between s.c. 5alpha-DHT inactivation rate and circulating levels of the androgen metabolites androsterone-glucuronide (r = 0.41, P < 0.02) and 3alpha-diol-glucuronide (r = 0.38, P < 0.03) and with the adrenal precursor androstenedione (r = 0.42, P < 0.02). In conclusion, androgen inactivation was detected in abdominal adipose tissue in men, with higher 3alpha/beta-HSD activity in the s.c. versus Om depot. Higher Om 5alpha-DHT inactivation rates were found in obese compared with lean men. Further studies are required to elucidate whether local androgen inactivation in abdominal adipose tissue is involved in the modulation of adipocyte metabolism and regional fat distribution in men.

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

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

Crystal structures of mouse 17alpha-hydroxysteroid dehydrogenase (apoenzyme and enzyme-NADP(H) binary complex): identification of molecular determinants responsible for the unique 17alpha-reductive activity of this enzyme

Very recently, the mouse 17alpha-hydroxysteroid dehydrogenase (m17alpha-HSD), a member of the aldo-keto reductase (AKR) superfamily, has been characterized and identified as the unique enzyme able to catalyze efficiently and in a stereospecific manner the conversion of androstenedione (Delta4) into epitestosterone (epi-T), the 17alpha-epimer of testosterone. Indeed, the other AKR enzymes that significantly reduce keto groups situated at position C17 of the steroid nucleus, the human type 3 3alpha-HSD (h3alpha-HSD3), the human and mouse type 5 17beta-HSD, and the rabbit 20alpha-HSD, produce only 17beta-hydroxy derivatives, although they possess more than 70% amino acid identity with m17alpha-HSD. Structural comparisons of these highly homologous enzymes thus offer an excellent opportunity of identifying the molecular determinants responsible for their 17alpha/17beta-stereospecificity. Here, we report the crystal structure of the m17alpha-HSD enzyme in its apo-form (1.9 A resolution) as well as those of two different forms of this enzyme in binary complex with NADP(H) (2.9 A and 1.35 A resolution). Interestingly, one of these binary complex structures could represent a conformational intermediate between the apoenzyme and the active binary complex. These structures provide a complete picture of the NADP(H)-enzyme interactions involving the flexible loop B, which can adopt two different conformations upon cofactor binding. Structural comparison with binary complexes of other AKR1C enzymes has also revealed particularities of the interaction between m17alpha-HSD and NADP(H), which explain why it has been possible to crystallize this enzyme in its apo form. Close inspection of the m17alpha-HSD steroid-binding cavity formed upon cofactor binding leads us to hypothesize that the residue at position 24 is of paramount importance for the stereospecificity of the reduction reaction. Mutagenic studies have showed that the m17alpha-HSD(A24Y) mutant exhibited a completely reversed stereospecificity, producing testosterone only from Delta4, whereas the h3alpha-HSD3(Y24A) mutant acquires the capacity to metabolize Delta4 into epi-T.

Role of androgens and glucocorticoids in the regulation of diazepam-binding inhibitor mRNA levels in male mouse hypothalamus

In peripheral organs, gonadal and adrenal steroids regulate diazepam-binding inhibitor (DBI) mRNA expression. In order to further investigate the involvement of peripheral steroid hormones in the modulation of brain DBI mRNA expression, we studied by semiquantitative in situ hybridization the effect of adrenalectomy (ADX) and castration (CX) and short-term replacement therapy on DBI mRNA levels in the male mouse hypothalamus. Cells expressing DBI mRNA were mostly observed in the arcuate nucleus, the median eminence and the ependyma bordering the third ventricle. In the median eminence and the ependyma bordering the third ventricule, the DBI gene expression was decreased in ADX rats and a single injection of corticosterone to ADX rats induced a significant increase in DBI gene expression at 3 and 12 h time intervals without completely restoring the basal DBI mRNA expression observed in intact mice. In the arcuate nucleus, ADX and corticosterone administration did not modify DBI mRNA expression. CX down-regulated DBI gene expression in the ependyma bordering the third ventricle. The administration of dihydrotestosterone (3-24 h) completely reversed the inhibitory effect of CX. In the median eminence and arcuate nucleus, neither CX or dihydrotestosterone administration modified DBI mRNA levels. These results suggest that the effects of glucocorticoids on the hypothalamo-pituitary-adrenocortical axis and androgens on the hypothalamo-pituitary-gonadal axis are mediated by DBI.

Visceral adiposity and endothelial lipase

CONTEXT

Overexpression of endothelial lipase (EL) has been shown to reduce plasma high-density lipoprotein cholesterol levels in animal models. However, the extent to which EL contributes to modulate the deteriorated high-density lipoprotein profile observed in obesity in humans is less clear.

OBJECTIVES

The objectives of this study were to investigate the association between levels of obesity and visceral adiposity in particular and plasma EL concentrations.

METHODS

Postheparin plasma EL concentrations were measured by ELISA and visceral adiposity by computed tomography in a sample of 80 sedentary men in good health. EL mRNA levels in abdominal sc and omental adipose tissues obtained during abdominal hysterectomies were measured in another sample of 14 women.

RESULTS

Plasma EL levels were positively correlated with body mass index (R = 0.46, P < 0.0001), visceral adipose tissue accumulation (R = 0.44, P < 0.0001), and a proatherogenic lipid profile including increased plasma cholesterol and triglycerides. However, EL mRNA levels were similar in sc and omental AT and were 10,000-fold lower than lipoprotein lipase mRNA levels in those tissues.

CONCLUSIONS

Increased visceral adiposity is significantly correlated with elevated plasma EL levels, but this association is unlikely to be causal and may reflect other common metabolic alterations.

Vasotocin and mesotocin stimulate the biosynthesis of neurosteroids in the frog brain

The neurohypophysial nonapeptides vasopressin (VP) and oxytocin (OT) modulate a broad range of cognitive and social activities. Notably, in amphibians, vasotocin (VT), the ortholog of mammalian VP, plays a crucial role in the control of sexual behaviors. Because several neurosteroids also regulate reproduction-related behaviors, we investigated the possible effect of VT and the OT ortholog mesotocin (MT) in the control of neurosteroid production. Double immunohistochemical labeling of frog brain sections revealed the presence of VT/MT-positive fibers in close proximity of neurons expressing the steroidogenic enzymes 3beta-hydroxysteroid dehydrogenase/delta5-delta4 isomerase (3beta-HSD) and cytochrome P450 17alpha-hydroxylase/c17, 20-lyase (P450(C17)). High concentrations of VT and MT receptor mRNAs were observed in diencephalic nuclei containing the 3beta-HSD and P450(C17) neuronal populations. Exposure of frog hypothalamic explants to graded concentrations of VT or MT produced a dose-dependent increase in the formation of progesterone, 17-hydroxypregnenolone, 17-hydroxyprogesterone, and dehydroepiandrosterone. The stimulatory effect of VT and MT on neurosteroid biosynthesis was mimicked by VP and OT, as well as by a selective V1b receptor agonist, whereas V2 and OT receptor agonists had no effect. VT-induced neurosteroid production was completely suppressed by selective V1a receptor antagonists and was not affected by V2 and OT receptor antagonists. Concurrently, the effect of MT on neurosteroidogenesis was markedly attenuated by selective OT and V1a receptor antagonists but not by a V2 antagonist. The present study provides the first evidence for a regulatory effect of VT and MT on neurosteroid biosynthesis. These data suggest that neurosteroids may mediate some of the behavioral actions of VT and MT.

Dehydroepiandrosterone (DHEA) is an anabolic steroid like dihydrotestosterone (DHT), the most potent natural androgen, and tetrahydrogestrinone (THG)

We have recently taken advantage of the unique power of DNA microarrays to compare the genomic expression profile of tetrahydrogestrinone (THG) with that of dihydrotestosterone (DHT), the most potent natural androgen, thus clearly demonstrating that THG is an anabolic steroid. In 2004, the U.S. Controlled Substances Act has been modified to include androstenedione (4-dione) as an anabolic steroid. However, despite the common knowledge that dehydroepiandrosterone (DHEA) is the precursor of testosterone, DHEA has been excluded from the list of anabolic steroids. We thus used the same DNA microarray technology to analyze the expression profile of practically all the 30,000 genes of the mouse genome modulated by DHEA and DHT in classical androgen-sensitive tissues. Daily subcutaneous injections of DHT (0.1mg) or DHEA (3mg) for 1 month in gonadectomized C57BL6/129 SV mice increased ventral prostate, dorsal prostate, seminal vesicle and preputial gland weight (p<0.01 for all tissues). As early as 24h after single injection of the two steroids, 878, 2681 and 14 probe sets were commonly stimulated or inhibited (p<0.01, change> or =30%), in the prostate (ventral+dorsal), seminal vesicles and preputial glands, respectively, compared to tissues from gonadectomized control animals. After 7 days of daily treatment with DHEA and DHT, 629, 919 and 562 probe sets were commonly modulated in the same tissues while after 27 days of treatment, 1195, 5127 and 2883 probe sets were modulated, respectively. In analogy with the data obtained with THG, the present microarray data provide an extremely precise and unquestionable genomic signature and proof of the androgenic/anabolic activity of DHEA. Such data add to the literature showing that DHEA is transformed into androgens in the human peripheral tissues as well as in laboratory animal species, including the monkey, thus exerting potent androgenic/anabolic activity. The present microarray approach to identify anabolic compounds is applicable to all potential androgenic/anabolic compounds.

Expression of enzymes involved in estrogen metabolism in human prostate

There is evidence that estrogens can directly modulate human prostate cell activity. It has also been shown that cultured human prostate cancer LNCaP can synthesize the active estrogen estradiol (E2). To elucidate the metabolism of estrogens in the human prostate, we have studied the expression of enzymes involved in the formation and inactivation of estrogens at the cellular level. 17beta-Hydroxysteroid dehydrogenase (17beta-HSD) types 1, 2, 4, 7, and 12, as well as aromatase mRNA and protein expressions, were studied in benign prostatic hyperplasia (BPH) specimens using in situ hybridization and immunohistochemistry. For 17beta-HSD type 4, only in situ hybridization studies were performed. Identical results were obtained with in situ hybridization and immunohistochemistry. All the enzymes studied were shown to be expressed in both epithelial and stromal cells, with the exception of 17beta-HSD types 4 and 7, which were detected only in the epithelial cells. On the basis of our previous results, showing that 3beta-HSD and 17beta-HSD type 5 are expressed in human prostate, and of the present data, it can be concluded that the human prostate expresses all the enzymes involved in the conversion of circulating dehydroepiandrosterone (DHEA) to E2. The local biosynthesis of E2 might be involved in the development and/or progression of prostate pathology such as BPH and prostate cancer through modulation of estrogen receptors, which are also expressed in epithelial and stromal cells.

3Beta-alkyl-androsterones as inhibitors of type 3 17beta-hydroxysteroid dehydrogenase: inhibitory potency in intact cells, selectivity towards isoforms 1, 2, 5 and 7, binding affinity for steroid receptors, and proliferative/antiproliferative activities on AR+ and ER+ cell lines

Type 3 17beta-hydroxysteroid dehydrogenase (17beta-HSD) is involved in the biosynthesis of the potent androgen testosterone (T), which plays an important role in androgen-sensitive diseases. In an attempt to design compounds to lower the level of T, we designed androsterone (ADT) derivatives substituted at the position 3beta as inhibitors of type 3 17beta-HSD, and then selected the eight most potent ones (compounds 1-8) for additional studies. In an intact cell assay, they inhibited efficiently the conversion of natural substrate 4-androstene-3,17-dione into T, although they were less active in intact cells (IC50 approximately 1 microM) than in homogenated cells (IC50=57-100 nM). A study of the inhibitory potency with four other 17beta-HSDs revealed they were selective, since they do not inhibit reductive types 1, 5 and 7, nor oxidative type 2. Interestingly, they did not show any binding affinity for steroid receptors (androgen, estrogen, glucocorticoid and progestin). Only two inhibitors, 3beta-phenyl-ADT (5) and 3beta-phenylmethyl-ADT (6) showed some proliferative activities on an AR+ cell line and on an ER+ cell line, but their effects were not mediated through the androgen or estrogen receptors. This study identified selective inhibitors of type 3 17beta-HSD acting through a mixed-type inhibition, and devoid of non-suitable androgenic and estrogenic proliferative activities. The more potent inhibitors were 3beta-hexyl-ADT (2), 3beta-cyclohexylethyl-ADT (4) and 3beta-phenylethyl-ADT (7).

Ontogeny of 3β-Hydroxysteroid Dehydrogenase and 5α-Reductase in the Frog Brain

The distribution of 3beta-hydroxysteroid dehydrogenase (3beta-HSD) and 5alpha-reductase (5alpha-R) has been studied in the frog brain during development. Soon after hatching, 3beta-HSD- and 5alpha-R-immunoreactive (ir) cells appeared first in the olfactory bulb and in the rhombencephalon. Subsequently, 3beta-HSD-ir cells were seen in the hypothalamus and cerebellum, whereas 5alpha-R-ir cells were visualized in the pallium, preoptic nucleus, posterocentral nucleus, cerebellum, and pituitary gland. At stages XIII-XVIII, additional 3beta-HSD- and 5alpha-R-ir cells appeared in several regions of the telencephalon, diencephalon, and mesencephalon. At stages XIX-XXI, the number of 5alpha-R-ir cells increased in the preoptic nucleus. These observations indicate that biosynthesis of biologically active steroids occurs in the brain of tadpoles, suggesting that neurosteroids may play a role in brain development.

Isolation and characterization of a cDNA encoding mouse 3alpha-hydroxysteroid dehydrogenase: an androgen-inactivating enzyme selectively expressed in female tissues

3alpha-Hydroxysteroid dehydrogenase catalyzes the transformation of 3-ketosteroids into 3alpha-hydroxysteroids, thus playing an important role in androgen and progesterone metabolism. So far, mouse cDNA and gene encoding 3alpha-HSD has not been reported. In this report, we describe the isolation of a mouse 3alpha-HSD cDNA and the characterization of its substrate specificity and tissue distribution. Sequence analysis indicates that m3alpha-HSD shares 87% amino acid identity with rat 3alpha-HSD. Cells stably transfected with this enzyme catalyze the transformation of dihydrotestosterone (DHT), 5alpha-androstanedione (5alpha-dione) and dihydroprogesterone (DHP) into 5alpha-androstane-3alpha,17beta-diol (3alpha-diol), androsterone (ADT) and 5alpha-pregnan-3alpha-ol-20-one (allopregnanolone), respectively. Quantification of mRNA expression levels of this enzyme was determined in male and female mouse sex-specific tissues using quantitative Realtime PCR. We show that this enzyme is mainly expressed in female-specific tissues while being almost absent from male-specific tissues. In the liver, the same expression level is seen in both male and female, while there is 6-fold higher expression level in female pituitary than in male. These results strongly suggest that m3alpha-HSD could play an important role in the female mouse physiology similar to that of type 1 5alpha-reductase with which it works in tandem. This role could be related to the inactivation of excess of androgen and progesterone that are more severely regulated than in man.

Is dehydroepiandrosterone a hormone?

Dehydroepiandrosterone (DHEA) is not a hormone but it is a very important prohormone secreted in large amounts by the adrenals in humans and other primates, but not in lower species. It is secreted in larger quantities than cortisol and is present in the blood at concentrations only second to cholesterol. All the enzymes required to transform DHEA into androgens and/or estrogens are expressed in a cell-specific manner in a large series of peripheral target tissues, thus permitting all androgen-sensitive and estrogen-sensitive tissues to make locally and control the intracellular levels of sex steroids according to local needs. This new field of endocrinology has been called intracrinology. In women, after menopause, all estrogens and almost all androgens are made locally in peripheral tissues from DHEA which indirectly exerts effects, among others, on bone formation, adiposity, muscle, insulin and glucose metabolism, skin, libido and well-being. In men, where the secretion of androgens by the testicles continues for life, the contribution of DHEA to androgens has been best evaluated in the prostate where about 50% of androgens are made locally from DHEA. Such knowledge has led to the development of combined androgen blockade (CAB), a treatment which adds a pure anti-androgen to medical (GnRH agonist) or surgical castration in order to block the access of the androgens made locally to the androgen receptor. In fact, CAB has been the first treatment demonstrated to prolong life in advanced prostate cancer while recent data indicate that it can permit long-term control and probably cure in at least 90% of cases of localized prostate cancer. The new field of intracrinology or local formation of sex steroids from DHEA in target tissues has permitted major advances in the treatment of the two most frequent cancers, namely breast and prostate cancer, while its potential use as a physiological HRT could well provide a physiological balance of androgens and estrogens, thus offering exciting possibilities for women's health at menopause.

Bone microenvironment-related growth factors, zoledronic acid and dexamethasone differentially modulate PTHrP expression in PC-3 prostate cancer cells

Bone metastasis microenvironment-related growth factors such as insulin-like growth factor 1 (IGF-1), transforming growth factor beta 1 (TGF-beta1), basic fibroblast growth factor (bFGF) and interleukin 6 (IL-6) show survival factor activity, thereby inhibiting chemotherapy-induced apoptosis of PC-3 prostate cancer cells in vitro. Recently, zoledronic acid has been shown to induce apoptosis in PC-3 prostate cancer cells while overexpression of parathyroid hormone-related protein (PTHrP) inhibits serum deprivation-induced apoptosis in PC-3 cells. Consequently, we have investigated whether IGF-1, TGF-beta1, bFGF, IL-6, zoledronic acid and/or dexamethasone affect the expression of the PTHrP and type I PTH/PTHrP receptor (PTH.1R) in PC-3 prostate cancer cells using relative quantitative PCR and real-time PCR (expression at mRNA level) and immunocytochemical and immunofluorescence analysis (expression at protein level). Our data show that IGF-1, TGF-beta1, bFGF and IL-6 increase PTHrP mRNA expression and its perinuclear localization, while zoledronic acid (50 muM, 100 muM for 24 h and 48 h) and dexamethasone suppress PTHrP expression in PC-3 cells. We did not detect any appreciable change of the PTH.1R expression due to IGF-1, TGF- beta1, bFGF, IL-6, zoledronic acid or dexamethasone in PC-3 cells. Therefore, it is conceivable that bone metastasis microenvironment-related survival factor/anti-apoptotic activity and zoledronic acid anticancer action/pro-apoptotic activity on PC-3 cells is mediated, at least in part, by differential modulation of PTHrP expression.

Androsterone 3alpha-ether-3beta-substituted and androsterone 3beta-substituted derivatives as inhibitors of type 3 17beta-hydroxysteroid dehydrogenase: chemical synthesis and structure-activity relationship

Type 3 17beta-hydroxysteroid dehydrogenase (17beta-HSD) is involved in the biosynthesis of androgen testosterone. To produce potent inhibitors of this key steroidogenic enzyme, we prepared a series of androsterone (ADT) derivatives by adding a variety of substituents at position 3. The 3beta-substituted ADT derivatives proved to be good inhibitors (IC(50) = 57-147 nM) with better inhibitory activities obtained for compounds bearing a propyl, s-butyl, cyclohexylalkyl, or phenylalkyl group. With an IC(50) value of 57 nM, the 3beta-phenylmethyl-ADT was 6-fold more potent than ADT, the lead compound, and 13-fold more potent than 4-androstene-3,17-dione, the natural enzyme substrate used itself as inhibitor. The 3alpha-ether-3beta-substituted ADT derivatives had a lower inhibitory activity compared to the 3beta-substituted ADT analogues except for the 3beta-phenylethyl-3alpha-methl-O-ADT (IC(50) = 73 nM), which proved to be a more potent inhibitor than 3beta-phenylethyl-ADT (IC(50) = 99 nM). The results of our study identified potent type 3 17beta-HSD inhibitors for potential use in the treatment of androgen-sensitive diseases.

Comparison of crystal structures of human type 3 3alpha-hydroxysteroid dehydrogenase reveals an "induced-fit" mechanism and a conserved basic motif involved in the binding of androgen

The aldo-keto reductase (AKR) human type 3 3alpha-hydroxysteroid dehydrogenase (h3alpha-HSD3, AKR1C2) plays a crucial role in the regulation of the intracellular concentrations of testosterone and 5alpha-dihydrotestosterone (5alpha-DHT), two steroids directly linked to the etiology and the progression of many prostate diseases and cancer. This enzyme also binds many structurally different molecules such as 4-hydroxynonenal, polycyclic aromatic hydrocarbons, and indanone. To understand the mechanism underlying the plasticity of its substrate-binding site, we solved the binary complex structure of h3alpha-HSD3-NADP(H) at 1.9 A resolution. During the refinement process, we found acetate and citrate molecules deeply engulfed in the steroid-binding cavity. Superimposition of this structure with the h3alpha-HSD3-NADP(H)-testosterone/acetate ternary complex structure reveals that one of the mobile loops forming the binding cavity operates a slight contraction movement against the citrate molecule while the side chains of many residues undergo numerous conformational changes, probably to create an optimal binding site for the citrate. These structural changes, which altogether cause a reduction of the substrate-binding cavity volume (from 776 A(3) in the presence of testosterone/acetate to 704 A(3) in the acetate/citrate complex), are reminiscent of the "induced-fit" mechanism previously proposed for the aldose reductase, another member of the AKR superfamily. We also found that the replacement of residues Arg(301) and Arg(304), localized near the steroid-binding cavity, significantly affects the 3alpha-HSD activity of this enzyme toward 5alpha-DHT and completely abolishes its 17beta-HSD activity on 4-dione. All these results have thus been used to reevaluate the binding mode of this enzyme for androgens.

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

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

Characterization of 17alpha-hydroxysteroid dehydrogenase activity (17alpha-HSD) and its involvement in the biosynthesis of epitestosterone

BACKGROUND

Epi-testosterone (epiT) is the 17alpha-epimer of testosterone. It has been found at similar level as testosterone in human biological fluids. This steroid has thus been used as a natural internal standard for assessing testosterone abuse in sports. EpiT has been also shown to accumulate in mammary cyst fluid and in human prostate. It was found to possess antiandrogenic activity as well as neuroprotective effects. So far, the exact pathway leading to the formation of epiT has not been elucidated.

RESULTS

In this report, we describe the isolation and characterization of the enzyme 17alpha-hydroxysteroid dehydrogenase. The name is given according to its most potent activity. Using cells stably expressing the enzyme, we show that 17alpha-HSD catalyzes efficienty the transformation of 4-androstenedione (4-dione), dehydroepiandrosterone (DHEA), 5alpha-androstane-3,17-dione (5alpha-dione) and androsterone (ADT) into their corresponding 17alpha-hydroxy-steroids : epiT, 5-androstene-3beta,17alpha-diol (epi5diol), 5alpha-androstane-17alpha-ol-3-one (epiDHT) and 5alpha-androstane-3alpha,17alpha-diol (epi3alpha-diol), respectively. Similar to other members of the aldo-keto reductase family that possess the ability to reduce the keto-group into hydroxyl-group at different position on the steroid nucleus, 17alpha-HSD could also catalyze the transformation of DHT, 5alpha-dione, and 5alpha-pregnane-3,20-dione (DHP) into 3alpha-diol, ADT and 5alpha-pregnane-3alpha-ol-20-one (allopregnanolone) through its less potent 3alpha-HSD activity. We also have over-expressed the 17alpha-HSD in Escherichia coli and have purified it by affinity chromatography. The purified enzyme exhibits the same catalytic properties that have been observed with cultured HEK-293 stably transfected cells. Using quantitative Realtime-PCR to study tissue distribution of this enzyme in the mouse, we observed that it is expressed at very high levels in the kidney.

CONCLUSION

The present study permits to clarify the biosynthesis pathway of epiT. It also offers the opportunity to study gene regulation and function of this enzyme. Further study in human will allow a better comprehension about the use of epiT in drug abuse testing; it will also help to clarify the importance of its accumulation in breast cyst fluid and prostate, as well as its potential role as natural antiandrogen.

Localization of Type 8 17β-hydroxysteroid Dehydrogenase mRNA in Mouse Tissues as Studied by In Situ Hybridization

The enzyme type 8 17β-hydroxysteroid dehydrogenase (17β-HSD) selectively catalyzes the conversion of estradiol (E2) to estrone (E1). To obtain detailed information on the sites of action of type 8 17β-HSD, we have studied the cellular localization of type 8 17β-HSD mRNA in mouse tissues using in situ hybridization. In the ovary, hybridization signal was detected in granulosa cells of growing follicles and luteal cells. In the uterus, type 8 17β-HSD mRNA was found in the epithelial (luminal and glandular) and stromal cells. In the female mammary gland, the enzyme mRNA was seen in ductal epithelial cells and stromal cells. In the testis, hybridization signal was observed in the seminiferous tubule. In the prostate, type 8 17β-HSD was detected in the epithelial cells of the acini and stromal cells. In the clitoral and preputial glands, labeling was detected in the epithelial cells of acini and small ducts. The three lobes of the pituitary gland were labeled. In the adrenal gland, hybridization signal was observed in the three zones of the cortex, the medulla being unlabeled. In the kidney, the enzyme mRNA was found to be expressed in the epithelial cells of proximal convoluted tubules. In the liver, all the hepatocytes exhibited a positive signal. In the lung, type 8 17β-HSD mRNA was detected in bronchial epithelial cells and walls of pulmonary arteries. The present data suggest that type 8 17β-HSD can exert its action to downregulate E2 levels in a large variety of tissues.