Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.1.1.3 (HSD)
3,464 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The isoenzymes of the 3 beta-hydroxysteroid dehydrogenase/5-ene-4-ene-isomerase (3 beta-HSD) gene family catalyse the transformation of all 5-ene-3 beta-hydroxysteroids into the corresponding 4-ene-3-keto-steroids and are responsible for the interconversion of 3 beta-hydroxy- and 3-keto-5 alpha-androstane steroids. The two human 3 beta-HSD genes and the three related pseudogenes are located on the chromosome 1p13.1 region, close to the centromeric marker D1Z5. The 3 beta-HSD isoenzymes prefer NAD+ to NADP+ as cofactor with the exception of the rat liver type III and mouse kidney type IV, which both prefer NADPH as cofactor for their specific 3-ketosteroid reductase activity due to the presence of Tyr36 in the rat type III and of Phe36 in mouse type IV enzymes instead of Asp36 found in other 3 beta-HSD isoenzymes. The rat types I and IV, bovine and guinea pig 3 beta-HSD proteins possess an intrinsic 17 beta-HSD activity specific to 5 alpha-androstane 17 beta-ol steroids, thus suggesting that such "secondary" activity is specifically responsible for controlling the bioavailability of the active androgen DHT. To elucidate the molecular basis of classical form of 3 beta-HSD deficiency, the structures of the types I and II 3 beta-HSD genes in 12 male pseudohermaphrodite 3 beta-HSD deficient patients as well as in four female patients were analyzed. The 14 different point mutations characterized were all detected in the type II 3 beta-HSD gene, which is the gene predominantly expressed in the adrenals and gonads, while no mutation was detected in the type I 3 beta-HSD gene predominantly expressed in the placenta and peripheral tissues. The mutant type II 3 beta-HSD enzymes carrying mutations detected in patients affected by the salt-losing form exhibit no detectable activity in intact transfected cells, at the exception of L108W and P186L proteins, which have some residual activity (approximately 1%). Mutations found in nonsalt-loser patients have some residual activity ranging from approximately 1 to approximately 10% compared to the wild-type enzyme. Characterization of mutant proteins provides unique information on the structure-function relationships of the 3 beta-HSD superfamily.
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PMID:Structure-function relationships and molecular genetics of the 3 beta-hydroxysteroid dehydrogenase gene family. 854 74

Rat liver 3 alpha-hydroxysteroid/dihydrodiol dehydrogenase (3 alpha-HSD) inactivates circulating steroid hormones and is involved in polycyclic aromatic hydrocarbon (PAH) carcinogenesis. It is the only HSD of known structure in the aldo-keto reductase (AKR) superfamily and may provide a paradigm for other mammalian HSDs in this family. The structure of the 3 alpha-HSD.NADP+ binary complex has been determined at 2.7 A resolution and refined to a crystallographic R-factor of 23.4% with good geometry. The model is similar to other binary complexes in the AKR superfamily in that NADP+ binds at the C-terminal end of an alpha/beta barrel. However, it is unique in that NADP+ is bound in two alternate conformations, probably because of the lack of a salt-linked "safety belt" over the pyrophosphate bridge. The structure supports a previously proposed catalytic mechanism for carbonyl reduction in which Tyr 55 is the general acid, and its effective pKa is lowered by the adjacent Lys 84. We present evidence that the structurally distinct short-chain dehydrogenase/reductase (SDR) superfamily may have convergently evolved a similar catalytic mechanism. Insight into substrate binding is offered by a crystal packing contact in which a neighboring molecule inserts a tryptophan residue (Trp 227) into an apolar cleft in 3 alpha-HSD. This cleft is proximal to the bound NADP+ cofactor and contains a surface of apolar residues (Leu 54, Trp 86, Leu 122, Phe 128, Phe 129, Leu 137, Phe 139), making it a likely candidate for the substrate-binding site. Thus, in forming this crystal contact, Trp 227 may mimic a portion of a bound steroid. In addition, we propose that a water molecule in the active site indicates the position of the hydroxyl oxygen in a 3 alpha-hydroxysteroid substrate. Knowledge of the position of this water molecule, combined with the stereochemistry of hydride transfer, suggests that the alpha face of a bound steroid will be oriented toward the side of the apolar cleft containing Trp 86.
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PMID:Structure of 3 alpha-hydroxysteroid/dihydrodiol dehydrogenase complexed with NADP+. 871 59

The type 2 isoform of 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD2), which catalyzes the conversion of cortisol to hormonally inactive cortisone in man, is principally expressed in the placenta and mineralocorticoid target tissues, kidney and colon. To date, few studies have addressed the regulation of this novel 11 beta-HSD2 isoform. We have characterized the nature and regulation of the 11 beta-HSD activity expressed in a human cytotrophoblastic cell line, the JEG-3 choriocarcinoma cell. The 11 beta-HSD activity in JEG-3 cell homogenates required NAD+ as cofactor with NADP+ ineffective and demonstrated a high affinity for cortisol (apparent Km 31 nM). Incubation of JEG-3 cells with forskolin and dibutyryl cyclic AMP increased 11 beta-HSD2 activity several-fold in a time-dependent manner, while treatment with phorbol ester had little, if any, effect on 11 beta-HSD2 activity. Northern blot analysis of RNA isolated from JEG-3 cells after these treatments demonstrated a marked increase in a 1.9 kb 11 beta-HSD2 mRNA species in cells treated with forskolin for 24 h. We conclude that 11 beta-HSD2 is regulated by activation of the protein kinase A pathway, but not the protein kinase C pathway in human choriocarcinoma cells, and that this regulation occurs at a pretranslational level. JEG-3 cells provide an excellent model for further studies on the regulation of 11 beta-HSD2 gene expression in human trophoblast tissue.
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PMID:Regulation of 11 beta-hydroxysteroid dehydrogenase type 2 activity and mRNA in human choriocarcinoma cells. 878 85

Benign meningioma tumors possess significant levels of 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) activity. Two different 17 beta-HSDs were discovered in human placenta: one highly estrogen specific and using NADP+/NADPH as cofactors (type-1 17 beta-HSD), and a second one that utilizes both androgens and estrogens as substrates with NAD+/NADH (type-2 17 beta-HSD). Recently, two further human 17 beta-HSDs were isolated. A testis-specific 17 beta-HSD (type-3 17 beta-HSD) favors the reduction of delta 4-androstenedione to testosterone, and a ubiquitously expressed type-4 17 beta-HSD preferentially catalyzes the oxidation of estradiol and delta 5-androstenediol. In this study we characterize the expression levels of different types of 17 beta-HSD in a wide series of tumors. Using the Northern blotting method we show that type-1, -3, and -4 17 beta-HSDs are not detectable in meningiomas. In contrast, the type-2 17 beta-HSD RNA is present in 6 of 17 meningiomas and its abundance is directly correlated with estrogenic 17 beta-HSD activity (r2 = 0.74). The presence of type-2 17 beta-HSD is also demonstrated by in situ hybridization. RT-PCR and Western blots show that type-4 17 beta-HSD is also present, though at much lower levels. The progesterone receptor level, the epidermal growth factor receptor level, and the age of the patients are not correlated with the estrogenic 17 beta-HSD activity or type-2 17 beta-HSD mRNA expression level.
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PMID:17 beta-Hydroxysteroid dehydrogenase activity correlates with the type-2 17 beta-hydroxysteroid dehydrogenase mRNA abundance in human meningioma tumors. 881 69

Mammalian 3 alpha-hydroxysteroid dehydrogenases (3 alpha-HSDs) inactivate circulating steroid hormones, and in target tissues regulate the occupancy of steroid hormone receptors. Molecular cloning indicates that 3 alpha-HSDs are members of the aldo-keto reductase (AKR) superfamily and display high sequence identity (> 60%). Of these, the most extensively characterized is rat liver 3 alpha-HSD. X-ray crystal structures of the apoenzyme and the E.NADP+ complex have been determined and serve as structural templates for other 3 alpha-HSDs. These structures reveal that rat liver 3 alpha-HSD adopts an (alpha/beta)8-barrel protein fold. NAD(P)(H) lies perpendicular to the barrel axis in an extended conformation, with the nicotinamide ring at the core of the barrel, and the adenine ring at the periphery of the structure. The nicotinamide ring is stabilized by interaction with Y216, S166, D167, and Q190, so that the A-face points into the vacant active site. The 4-pro-(R) hydrogen transferred in the oxidoreduction of steroids is in close proximity to a catalytic tetrad that consists of D50, Y55, K84, and H117. A water molecule is within hydrogen bond distance of H117 and Y55, and its position may mimic the position of the carbonyl of a 3-ketosteroid substrate. The catalytic tetrad is conserved in members of the AKR superfamily and resides at the base of an apolar cleft implicated in binding steroid hormone. The apolar cleft consists of a side of apolar residues (L54, W86, F128, and F129), and opposing this side is a flexible loop that contains W227. These constraints suggest that the alpha-face of the steroid would orient itself along that side of the cleft containing W86. Site-directed mutagenesis of the catalytic tetrad indicates that Y55 and K84 are essential for catalysis. Y55S and Y55F mutants are catalytically inactive, but still form binary (E.NADPH) and ternary (E.NADH.Testosterone) complexes; by contrast K84R and K84M mutants are catalytically inactive, but do not bind steroid hormone. The reliance on a Tyr/Lys pair is reminiscent of catalytic mechanisms proposed for other AKR members as well as for HSDs that belong to the short-chain dehydrogenase/reductase (SDR) family, in which Tyr is the general acid, with its pKa being lowered by Lys. Superimposition of the nicotinamide rings in the structures of 3 alpha-HSD (an AKR) and 3 alpha, 20 beta-HSD (an SDR) show that the Tyr/Lys pairs are positionally conserved, suggesting convergent evolution across protein families to a common mechanism for HSD catalysis. W86Y and W227Y mutants bind testosterone to the E.NADH complex, with effective increases in Kd of 8- and 20-fold. These data provide the first evidence that the side of the apolar cleft containing W86 and the opposing flexible loop containing W227 are parts of the steroid-binding site. Detailed mutagenesis studies of the apolar cleft and elucidation of a ternary complex structure will ultimately provide details of the determinants that govern steroid hormone recognition. These determinants could provide a rational basis for structure-based inhibitor design.
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PMID:Structure and function of 3 alpha-hydroxysteroid dehydrogenase. 902 23

Whereas aldosterone is normally a much stronger mineralocorticoid than cortisol in vivo, mineralocorticoid receptors have identical in vitro affinities for these hormones. The in vivo specificity of the receptors is, at least in part, the result of activity of 11-HSD, an enzyme located in most mineralocorticoid target tissues that converts cortisol to cortisone. Cortisone is not a ligand for the receptor, whereas aldosterone is not a substrate of the enzyme. The syndrome of AME is a rare form of juvenile hypertension in which 11-HSD is defective. This deficiency allows mineralocorticoid receptors to be occupied by cortisol, leading to hypertension, because plasma concentrations of cortisol are much higher than those of aldosterone. Licorice, which contains 11-HSD inhibitors, causes a similar syndrome. There are two known isozymes of 11-HSD. The liver or type I isozyme is expressed at high levels in the liver, has a relatively low affinity for steroids (micromolar Km), catalyzes both dehydrogenation and the reverse reductase reaction, and utilizes NADP+ or NADPH as cofactors. The kidney or type 2 isozyme is expressed at high levels in the kidney and placenta, has a high affinity (nanomolar Km) for steroids, catalyzes only dehydrogenation, and utilizes NAD+ as a cofactor. Mutations in the HSD11B2 (HSD11K) gene encoding the kidney isozyme of 11-HSD have been detected in all kindreds with AME studied thus far. This gene represents a candidate locus for the common, "essential" form of hypertension.
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PMID:11 beta-Hydroxysteroid dehydrogenase and the syndrome of apparent mineralocorticoid excess. 903 89

We have previously reported that 5 alpha and 5 beta pathways of steroid metabolism are controlled in vivo by dietary Na+ and glycyrrhetinic acid, see Gorsline et al. 1988; Latif et al. 1990. The present investigations provide evidence supporting the suggestion that endogenous substances may regulate the glucocorticoid inactivating isoenzymes, 11 beta-HSD (hydroxysteroid dehydrogenase) 1 (liver) and 11 beta-HSD2 (kidney). The activity of 11 beta-HSD is impaired in essential hypertension, following licorice ingestion, and in patients with apparent mineralocorticoid excess where 11 beta-HSD2 is particularly affected. In all three conditions, excretion of the less common 5 alpha metabolites is elevated in urine. We now report on the differential abilities of a series of Ring A reduced (5 alpha and 5 beta) adrenocorticosteroid and progesterone metabolites to inhibit these isoenzymes. Using liver microsomes with NADP+ as co-factor (11 beta-HSD1), and sheep kidney microsomes with NAD+ as co-factor (11 beta-HSD2), we have systematically investigated the abilities of a number of adrenocorticosteroids and their derivatives to inhibit the individual isoforms of 11 beta-HSD. A striking feature is the differential sensitivity of the two isoenzymes to inhibition by 5 alpha and 5 beta derivatives. 11 beta-HSD1 is inhibited by both 5 alpha and certain 5 beta derivatives. 11 beta-HSD-2 was selectively inhibited only by 5 alpha derivatives: 5 beta derivatives were without inhibitory activity toward this isoform of 11 beta-HSD. These results indicate the importance of the structural conformation of the A and B Rings in conferring specific inhibitory properties on these compounds. In addition, we discuss the effects of additions or substitutions of other functional groups on the inhibitory potency of these steroid molecules against 11 beta-HSD1 and 11 beta-HSD2.
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PMID:Selective inhibition of sheep kidney 11 beta-hydroxysteroid dehydrogenase isoform 2 activity by 5 alpha-reduced (but not 5 beta) derivatives of adrenocorticosteroids. 905 82

Endogenous glucocorticoids are converted to their biologically inert 11-dehydroderivatives by isoforms of the enzyme 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD). The low-K(m), NAD(+)-dependent renal isoform (Type 2) identified in the distal nephron protects mineralocorticoid receptors from activation by endogenous glucocorticoids. The function of high-K(m), NADP(+)-dependent renal isoform (Type 1) is less well understood. Since glucocorticoids may modulate sodium transport in renal proximal tubules (PT), we hypothesized that Type 1 activity in this segment may be regulated by dietary Na(+)-11 beta-HSD activity was assessed in homogenates of canine PT by the conversion of cortisol to cortisone in the presence of NADP+ 200 microM. A high-Na+ diet for 4 days increased the Vmax 4-fold, with no change in the Type 1 K(m) (40 mEq/day Na+ diet: K(m) 0.959 microM, Vmax 3.40 pmoles/min/mg protein versus 150 mEq/day Na+ diet: K(m) 0.962 microM, Vmax 14.8 pmoles/min/mg protein). Type 1 mRNA also rose in the salt repleted animals. The high-Na+ diet produced no detectable change in the Type 2 isoform enzyme kinetics and mRNA level. No reverse oxo-reductase activity was noted with either renal isoform. Thus, renal Type 1 11 beta-HSD can be regulated by dietary Na+ independent of changes in the renal Type 2 isoform.
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PMID:Influence of dietary sodium on the renal isoforms of 11 beta-hydroxysteroid dehydrogenase. 911 24

Dexamethasone is used in the clinic to test the sensitivity of the hypothalamic-pituitary-adrenal axis to negative feedback. It has also been proposed that metabolism of dexamethasone might differentiate between the activities of the two isozymes of 11 beta-hydroxysteroid dehydrogenase (11 beta HSD1 and 11 beta HSD2). We have developed a gas chromatographic mass spectrometric assay for dexamethasone and 11-dehydrodexamethasone and have confirmed in vitro that dexamethasone is a substrate for 11 beta-HSD2 but not 11 beta-HSD1 (conversion to 11-dehydrodexamethasone 0.6 +/- 0.3% in homogenates of rat liver with NADP+ for 11 beta-HSD1, and 29.4 +/- 10.3% and 40.0 +/- 2.0% in homogenates of rat and human kidney respectively with NAD+ for 11 beta-HSD2). However, we have also made the novel observation that 11-dehydrodexamethasone is a substrate for both isozymes (conversion to dexamethasone 65.0 +/- 20.4% for 11 beta HSD1 and 53.5 +/- 20.8% and 69.0 +/- 4.5% for 11 beta HSD2, rat and human respectively). In healthy humans, the concentrations of 11-dehydrodexamethasone in plasma after an intravenous bolus of dexamethasone were less than 10% of those of dexamethasone, and 11-dehydrodexamethasone was detected (at 0.8-65.0 nM) in plasma from only 11 of 20 subjects at 0900 h on the morning after oral dexamethasone (0.1-1 mg taken at 2400 h). Concentrations of 11-dehydrodexamethasone did not correlate with the degree of suppression of plasma cortisol. Thus dexamethasone is not useful in differentiating the activities of the isozymes of 11 beta-HSD in vivo and variations in 11 beta-HSD activity do not explain the interindividual variability in suppression of plasma cortisol by low doses of dexamethasone.
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PMID:Dexamethasone and 11-dehydrodexamethasone as tools to investigate the isozymes of 11 beta-hydroxysteroid dehydrogenase in vitro and in vivo. 913 68

In the human and in rodents like the rat and mouse, the liver enzyme 11 beta-hydroxysteroid dehydrogenase type I (11 beta-HSD-I) is a functional oxidoreductase preferring NADP+/NADPH as cosubstrate, while the renal isoenzyme (11 beta-HSD-II) prefers NAD+ as cosubstrate, and seems to be a pure oxidase and protects the tubular, mineralocorticoid (MC) receptor from occupancy by cortisol and corticosterone. We studied the enzyme kinetics of 11 beta-HSDs in kidney and liver microsomes of the guinea pig, a species whose zoological classification is still a matter of debate. With a fixed concentration of 10(-6) mol/l cortisol, liver and kidney microsomes preferred NAD+ to NADP+ (10(-3) mol/l) for the conversion to cortisone. Kidney microsomes converted cortisol to cortisone with K(m) values of 0.64 mumol/l and 9.8 mumol/l with NAD+ and NADP+ as cosubstrates respectively. The reduction of cortisone to cortisol was slow with kidney microsomes, but could be markedly enhanced by adding an NADH/NADPH regenerating system: with NADPH as preferred cosubstrate, the approximate K(m) was 7.2 mumol/l. This indicated the existence of both isoenzymes in the guinea pig kidney. Liver microsomes oxidized cortisol to cortisone with similar K(m) and Vmax values for NAD+ to NADP+ as cosubstrates (K(m) of 4.3 mumol/l and 5.0 mumol/l respectively). The NAD+ preference for the oxidation of 10(-6) mol/l cortisol described above may be due to a second, NAD(+)-preferring 11 beta-HSD with a K(m) of 1.4 mumol/l. In contrast to the kidney, liver microsomes actively converted cortisone to cortisol with a preference for NADPH (K(m): 1.2 mumol/l; Vmax: 467 nmol/min per mg protein). Thus, the main liver enzyme is similar to the oxidoreductase of other species (11 beta-HSD-I) and is also present in the kidney, while the main kidney enzyme is clearly NAD(+)-preferring. This kidney enzyme (analogous to 11 beta-HSD-II of other species) seems to be suitable for the protection of the MC receptor from the high free plasma cortisol levels of the guinea pig.
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PMID:Evidence for isoforms of 11 beta-hydroxysteroid dehydrogenase in the liver and kidney of the guinea pig. 916 19


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