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PubMed2003

Inhibitors of 17 beta-hydroxysteroid dehydrogenases.

The 17beta-hydroxysteroid dehydrogenases (17beta-HSDs) play an important role in the regulation of steroid hormones, such as estrogens and androgens, by catalysing the reduction of 17-ketosteroids or the oxidation of 17beta-hydroxysteroids using NAD(P)H or NAD(P)(+) as cofactor. The enzyme activities associated with the different 17beta-HSD isoforms are widespread in human tissues, not only in classic steroidogenic tissues, such as the testis, ovary, and placenta, but also in a large series of peripheral intracrine tissues. In the nineties, several new types of 17beta-HSD were reported, indicating that a fine regulation is carried out. More importantly, each type of 17beta-HSD has a selective substrate affinity, directional (reductive or oxidative) activity in intact cells, and a particular tissue distribution. These findings are important for understanding the mode of action of the 17beta-HSD family. From a therapeutic point of view, this means that selectivity of drug action could be achieved by targeting a particular 17beta-HSD isozyme. Consequently, each study that leads to better knowledge of the inhibition of 17beta-HSDs deserves attention from scientists working in this and related fields. Being involved in the last step of the biosynthesis of sex steroids from cholesterol, the 17beta-HSD family constitutes an interesting target for controlling the concentration of estrogens and androgens. Thus, inhibitors of 17beta-HSDs are useful tools to elucidate the role of these enzymes in particular biological systems or for a therapeutic purpose, especially to block the formation of active hydroxysteroids that stimulate estrogeno-sensitive pathologies (breast, ovarian, and endometrium cancers) and androgeno-sensitive pathologies (prostate cancer, benign prostatic hyperplasia, acne, hirsutism, etc). Few review articles have however focussed on 17beta-HSD inhibitors although this family of steroidogenic enzymes includes interesting therapeutic targets for the control of several diseases. Furthermore, inhibitors of 17beta-HSDs constitute a growing field in biomedical research and there is a need for an exhaustive review on this topic. In addition to giving an up-to-date description of inhibitors of all 17beta-HSD isoforms (types 1-8), the present review will also address, when possible, the isoform selectivity and residual estrogenic or androgenic activity often associated with steroidal inhibitors.

17-Hydroxysteroid Dehydrogenases↗

PubMed1976

Human placental 3beta-hydroxysteroid dehydrogenase: delta5-isomerase. Demonstration of an intermediate in the conversion of 3beta-hydroxypregn-5-en-20-one to pregn-4-ene-3,20-dione.

3beta-Hydroxypregn-5-en-20-one (pregnenolone) and NAD+ were incubated with a solubilized preparation of the coupled enzyme 3beta-hydroxysteroid:NAD(P) oxidoreductase-3-ketosteroid delta4,delta5-isomerase (3beta-hydroxysteroid dehydrogenase: delta5-isomerase) from the mitochondrial fraction of human placenta. Unconverted pregnenolone, pregn-4-ene-3,20-dione (rogesterone), and a small but detectable amount of pregn-5-ene-3,20-dione were isolated from the medium by Sephadex LH-20 chromomatography. The identification of pregn-5-ene-3,20-dione, confirmed by mass fragmentography, has provided the first direct evidence for the formation of the hypothetical delta5,3-ketone intermediate in the conversion of pregnenolone to progesterone. When tritium-labeled pregnenolone and [4-14C]pregnenolone were incubated simultaneously the 3H:14C ratio in isolated pregn-5-ene-3,20-dione was 4.6 times greater than in isolated progesterone and pregnenolone, indicating a kinetic isotope effect in the enzymatic isomerization of tritium-labeled pregn-5-ene-3,20-dione. Exposure of the enzyme to two steroids which inhibit the overall enzyme reaction, 2alpha-cyano-17beta-hydroxy-4,4,17alpha-trimethylandrost-5-en-3-one (cyanoketone) and 3-hydroxyestra-1,3,5(10),6,8-pentaen-17-one (equilenin), increased the relative yield of labeled pregn-5-ene-3,20-dione as well as the recovery of radioactivity remaining as unconverted pregnenolone, suggesting that both the dehydrogenase and isomerase activities were inhibited. Exposure of the enzyme to equilenin increased the ratio of isolated pregn-5-ene-3,20-dione radioactivity to progesterone radioactivity as progesterone synthesis was inhibited. Equilenin also diminished the tritium isotope effect on the isomerase reaction. Both findings suggest that it is possible to inhibit the isomerase to a greater extent than the dehydrogenase. In order to measure the rate of progesterone produced by the coupled enzymes, we have modified a radiochemical method which involves precipitation of pregnenolone by digitonin. Digitonin precipitation proved to be effective in separating unconverted pregnenolone from the steroid products of both enzyme reactions, progesterone and pregn-5-ene-3,20-dione. Neither the steroidal inhibitors nor the kinetic isotope effect altered the accuracy of the method for routine measurement of the overall rate of conversion of delta5,3beta-hydroxysteroid to delta4,3-ketosteroid.

Female↗

PubMed1992

Subunit identity of the dimeric 17 beta-hydroxysteroid dehydrogenase from human placenta.

Human placental 17 beta-hydroxysteroid dehydrogenase has been purified with a new rapid procedure based on fast protein liquid chromatography, yielding quantitatively a homogeneous preparation with high specific activity catalyzing the oxidation of 7.2 mumol of estradiol/min/mg of enzyme protein at 23 degrees C, pH 9.2. This preparation was shown to have a subunit mass of 34.5 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis while having a molecular mass of 68 kDa by both Superose-12 gel-filtration and native pore gradient gel electrophoresis. When 17 beta-hydroxysteroid dehydrogenase was expressed in HeLa cells or overproduced in insect cells using the baculovirus expression system, both from its cDNA encoding a protein of 34 kDa, the enzyme had the same migration in native and sodium dodecyl sulfate-gel electrophoresis as the purified one from human placenta and eluted from the Superose-12 column at the same elution volume. Moreover, all the above forms of this enzyme have similar specific activity. These results clearly demonstrate the identity of the three enzyme forms. The enzyme produced from the cDNA is expressed as a dimer, and its two subunits are identical. 17 beta-Hydroxysteroid dehydrogenase subunit identity is thus proved. The NH2-terminal analysis revealed a unique sequence of Ala-Arg-Thr-Val-Val-Leu-Ile for the purified enzyme from placenta, further confirming the above conclusion.

17-Hydroxysteroid Dehydrogenases↗

PubMed1990

Characterization of human 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4-isomerase gene and its expression in mammalian cells.

Three beta-hydroxysteroid dehydrogenase/delta 5-delta 4-isomerase (3 beta-HSD) catalyze the oxidative conversion of delta 5-3 beta-hydroxysteroids to the delta 4-3-keto configuration and is therefore essential for the biosynthesis of all classes of hormonal steroids, namely progesterone, glucocorticoids, mineralocorticoids, androgens, and estrogens. Using human 3 beta-HSD cDNA as probe, a human 3 beta-HSD gene was isolated from a lambda-EMBL3 library of leucocyte genomic DNA. A fragment of 3 beta-HSD genomic DNA was also obtained by amplification of genomic DNA using the polymerase chain reaction. The 3 beta-HSD gene contains a 5'-untranslated exon of 53 base pairs (bp) and three successive translated exons of 232, 165, and 1218 bp, respectively, separated by introns of 129, 3883, and 2162 bp. The transcription start site is situated 267 nucleotides upstream from the ATG initiating codon. DNA sequence analysis of the 5'-flanking region reveals the existence of a putative TATA box (ATAAA) situated 28 nucleotides upstream from the transcription start site while a putative CAAT binding sequence is located 57 nucleotides upstream from the TATA box. Expression of a cDNA insert containing the coding region of 3 beta-HSD in nonsteroidogenic cells shows that the gene encodes a single 42-kDa protein containing both 3 beta-hydroxysteroid dehydrogenase and delta 5-delta 4-isomerase activities. Moreover, all natural steroid substrates tested are transformed with comparable efficiency by the enzyme. In addition to its importance for studies of the regulation of expression of 3 beta-HSD in gonadal as well as peripheral tissues, knowledge of the structure of the human 3 beta-HSD gene should permit investigation of the molecular defects responsible for 3 beta-HSD deficiency, the second most common cause of adrenal hyperplasia in children.

3-Hydroxysteroid Dehydrogenases↗

PubMed1978

Purification and properties of an NADPH-dependent 21-oxo-20-hydroxysteroid reductase (17beta-aldol reductase) from sheep liver. Isolation of the 20beta-glycol product.

This investigation was undertaken to test the hypothesis that steroidal 20-hydroxy-21-aldehydes are intermediates in an alternative pathway of corticosteroid metabolism leading to steroidal 20,21-diols. A NADPH-dependent 21-oxo-20-hydroxysteroid reductase which catalyzed the reduction of 11beta,17,20beta-trihydroxy-3-keto-4-pregnen-21-al (isocortisol) to 11beta,17,20beta,21-tetrahydroxy-4-pregnen-3-one (Reichstein's compound E) was prepared from sheep liver. Other steroidal 17-aldols were also good substrates. Some steroidal 17-oxoaldehydes, D-, and L-glyceraldehyde were reduced, but less effectively than the steroidal aldols. Steroidal ketols and 21-oic acids were not substrates. The enzyme contains--SH groups, has a pH optimum of 6.9 to 7.5 and a molecular weight of about 28,000. Reversibility of the enzymic reaction could not be demonstrated. The reduction product obtained from isocortisol was isolated and characterized. Other 17-glycols were derived from their respective steroid aldols. Reductase activity was also present in hamster and rat liver. From a comparison of 21-oxo-20-hydroxysteroid reductase and 21-hydroxysteroid dehydrogenase with respect to pH optima, substrate specificity, stability to heat, and kinetic constants, we conclude that the two enzymes are distinct.

Animals↗

PubMed1989

A quantitative histochemical study of delta 5-3 beta-hydroxysteroid dehydrogenase and succinate dehydrogenase activities in the bovine corpus luteum of pregnancy.

In corpora lutea of pregnancy of dairy cows delta 5-3 beta-hydroxysteroid dehydrogenase and succinate dehydrogenase were demonstrated histochemically and evaluated densitometrically. Serum progesterone was determined radioimmunologically. Activities per volume unit of delta 5-3 beta-hydroxysteroid dehydrogenase and succinate dehydrogenase in large and small luteal cells as well as progesterone concentrations, exhibited no typical and correlated pattern during pregnancy. Large luteal cells in regressive tissue regions showed weaker delta 5-3 beta-hydroxysteroid dehydrogenase activities than in maturing or well-developed tissue regions. Succinate dehydrogenase activities of small luteal cells were highest in regressive luteal tissue. The results indicate that structural development of bovine luteal tissue during pregnancy is reflected by corresponding enzyme activities.

3-Hydroxysteroid Dehydrogenases↗

PubMed1985

Short-term effects of tamoxifen, medroxyprogesterone acetate, and their combination on receptor kinetics and 17 beta-hydroxysteroid dehydrogenase in human endometrium.

The interactions of an antiestrogen (tamoxifen) and a progestin (medroxyprogesterone acetate) on endometrial 17 beta-hydroxysteroid dehydrogenase activities were studied in short-term experiments (four to 96 hours) in normally menstruating women at the follicular phase and were related to simultaneously measured concentrations of cytosol and nuclear estrogen and progestin receptors. Tamoxifen effected a decrease in the activity of 17 beta-hydroxysteroid dehydrogenase. This was associated with an apparent translocation to and retention of estrogen receptor in the nucleus without any significant changes in cellular progestin receptor. Medroxyprogesterone acetate administration led to a rapid increase in endometrial 17 beta-hydroxysteroid dehydrogenase activity, and depletion of cytosol and total cellular progestin receptor. Combination of the drugs led to effects that could be addressed to the individual drugs separately, and under the experimental conditions the effects of medroxyprogesterone acetate were uninfluenced by simultaneous tamoxifen administration. Put together with the authors' previous findings on the same parameters during long-term (three-week) medroxyprogesterone acetate administration, it seems possible that potentiation of progestin effects on endometrial carcinoma is not to be expected during long-term simultaneous antiestrogen-progestin treatment. It is therefore likely that the favorable effects of combining these two drugs in long-term treatment are due to their different endocrine action mechanisms.

17-Hydroxysteroid Dehydrogenases↗

PubMed1978

Immunological detection of 20beta-hydroxysteroid dehydrogenase-synthesizing polysomes from Streptomyces hydrogenans.

Immunoprecipitation of polyribosomes from Streptomyces hydrogenans synthesizing 20beta-hydroxysteroid dehydrogenase was performed by immunoelectrophoresis. Only polyribosomes from cells induced by 11beta, 21-dihydroxy-4, 11(20)-pregnadien-3-one in vivo were precipitated by immunoglobulins specific for 20beta-hydroxysteroid dehydrogenase. No unspecific precipitations with polysomes from control cells cultivated in the absence of steroids were observed. Therefore, 11beta, 21-dihydroxy-4, 17(20)-pregnadien-3-one increases the number of biological active polyribosomes involved in 20beta-hydroxysteroid dehydrogenase synthesis, presumably by specific stimulation of mRNA synthesis in Streptomyces hydrogenans.

20-Hydroxysteroid Dehydrogenases↗

PubMed1983

Cytosol and nuclear estrogen and progestin receptors and 17 beta-hydroxysteroid dehydrogenase activity in normal and carcinomatous endometrium.

Endometrial estrogen and progestin receptors were quantitatively measured in the cytosol (ERc, PRc) and nuclear (ERn, PRn) fractions, the activity of 17 beta-hydroxysteroid dehydrogenase measured in 13 normal women in the late proliferative phase of the cycle (control group), in 33 patients with adenocarcinoma, and in 6 patients with other malignancies of the endometrium. The parameters measured had relatively small variations in the control group, whereas the opposite was true for the malignant endometrium. ERc and PRc were present in significantly higher concentrations in normal endometrial tissue (167 and 1697 fmol/mg cytosol protein, respectively) than in malignant endometrial tissue (45 and 116 fmol/mg cytosol protein, respectively), and the ratios of ERc/ERn and PRc/PRn were higher (P much less than .001 in both cases) in the normal group. The activities of 17 beta-hydroxysteroid dehydrogenase were identical in normal and adenocarcinoma tissue and correlated with PRc in carcinomatous endometrium. The present results support previous findings that the great majority of endometrial adenocarcinoma specimens have significant concentrations of ERc and PRc and that these concentrations are lower than in normal endometrium. In addition, they demonstrate that nuclear location of the female sex steroid receptors is favored in the malignant tissue. Despite these differences, the 17 beta-hydroxysteroid dehydrogenase activities were identical in proliferative endometrium and in endometrial adenocarcinoma.

17-Hydroxysteroid Dehydrogenases↗

PubMed1982

Enzymatic estimation of steroids in subpicomole quantities by hydroxysteroid dehydrogenases and nicotinamide nucleotide cycling.

Extremely sensitive methods are described for the measurement of 3 alpha- and 3 beta-hydroxysteroids, as well as 3-ketosteroids, based on their reaction with highly purified bacterial hydroxysteroid dehydrogenases and the amplification of the accompanying changes in nicotinamide nucleotides by enzymatic cycling procedures. Conditions have been devised under which the steroid oxidation and reduction reactions lead to the formation of stoichiometric quantities of NADH or NAD+, respectively, even in the presence of large excesses of reaction products. The scope of these methods is illustrated by application to the analysis of minute volumes of human pregnancy urine, high pressure liquid chromatography fractions derived from such urine samples, and human serum. The steroid contents of milligram quantities of rat prostate have been determined. The methods have been applied also to the measurement of the activities of steroid-transforming enzymes, such as the 3 alpha-hydroxysteroid dehydrogenase of prostate microsomes. At the present time the sensitivity of the described methods allows the accurate determination of 0.2-0.4 pmol of steroids.

Animals↗

PubMed1982

Comparison of the multiple forms of the soluble 3(17) alpha-hydroxysteroid dehydrogenases of female rabbit kidney and liver.

Multiple forms of the soluble 17 alpha-hydroxysteroid dehydrogenases of female rabbit liver and kidney having similar purification characteristics and isoelectric points were compared with regard to their relative rates of oxidation and reduction of estrogen and androgen substrates, their kinetic parameters and their primary structures. All of the enzyme forms exhibited both 3 alpha- and 17 alpha-enzyme activity toward androgen substrates and the oxidation of the 17 alpha-hydroxysteroid epitestosterone was competitively inhibited by the 3 alpha-hydroxysteroid androsterone. The most basic enzyme forms from liver and kidney had similar relative activities toward estrogen and androgen substrates in the oxidative direction but differed in their activities in the reductive direction. Major differences in the peptide maps of these enzymes were observed. The less basic enzyme forms from the two tissues had similar activities toward estrogen substrates but differed considerably in their relative activities toward androgens. Only minor differences were observed in the peptide maps of these enzymes.

Androgens↗

PubMed1994

[Late onset hyperandrogenism caused by 3-beta-hydroxysteroid dehydrogenase deficiency].

OBJECTIVES: Clinical manifestations of hyperandrogenism, including hirsutism and acne with or without dysmenorrhoea are well recognized in late onset hyperandrogenism due to deficiency in 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD), yet the frequency of this deficiency in patients with post-puberty hirsutism is not well established. We therefore evaluated retrospectively this deficiency state in women who consulted our unit for manifestations suggestive of hyperandrogenism from 1990 to 1992. METHODS: We included 32 women with clinical manifestations of hyperandrogenism for whom a partial deficit in 3 beta-HSD could be searched for on the basis of hormone assays. Their mean age was 27.5 years (range 14 to 46) and the clinical manifestation was hirsutism in 21 cases, acne in 13, alopecia in 5 and dysmenorrhoea in 11. Diagnostic tests included adrenal stimulation with 0.25 mg beta 1-24 corticotrophin and immunoradioassay of plasma levels of 17-hydroxypregnenolone (17-OHPreg), 17-hydroxyprogesterone (17-OHP), dehydroepiandrosterone (DHA) and cortisol (F). Pang's criteria for the diagnosis of partial deficiency in 3 beta-HSD were retained. We defined deficiency in 3 beta-HSD as certain when the 4 following criteria were present 60 minutes after stimulation: 17-OHPreg > 17.5 ng/ml; DHA > 20 mg/ml; 17-OHPreg/17-OHP > 9; 17-OHPreg/F.10(-3) > 53. Diagnosis was considered probable when only 3 criteria were met and was excluded in all other cases. RESULTS: Positive diagnosis of deficiency in 3 beta-hydroxysteroid dehydrogenase was made in 4 of the 32 patients and probable in 4 others. CONCLUSION: Based on our series of patients, late onset hyperandrogenism due to 3 beta-hydroxysteroid dehydrogenase deficiency would thus appear to be a relative frequent deficiency state. Since therapeutic measures can be taken, this deficiency should be carefully searched for in all young patients presenting with manifestations suggesting hyperandrogenism.

3-Hydroxysteroid Dehydrogenases↗

PubMed2003

Structure-function relationships in 3alpha-hydroxysteroid dehydrogenases: a comparison of the rat and human isoforms.

3alpha-Hydroxysteroid dehydrogenases (3alpha-HSDs) inactivate steroid hormones in the liver, regulate 5alpha-dihydrotestosterone (5alpha-DHT) levels in the prostate, and form the neurosteroid, allopregnanolone in the CNS. Four human 3alpha-HSD isoforms exist and correspond to AKR1C1-AKR1C4 of the aldo-keto reductase (AKR) superfamily. Unlike the related rat 3alpha-HSD (AKR1C9) which is positional and stereospecific, the human enzymes display varying ratios of 3-, 17-, and 20-ketosteroid reductase activity as well as 3alpha-, 17beta-, and 20alpha-hydroxysteroid oxidase activity. Their k(cat) values are 50-100-fold lower than that observed for AKR1C9. Based on their product profiles and discrete tissue localization, the human enzymes may regulate the levels of active androgens, estrogens, and progestins in target tissues. The X-ray crystal structures of AKR1C9 and AKR1C2 (human type 3 3alpha-HSD, bile acid binding protein and peripheral 3alpha-HSD) reveal that the AKR1C2 structure can bind steroids backwards (D-ring in the A-ring position) and upside down (beta-face inverted) relative to the position of a 3-ketosteroid in AKR1C9 and this may account for its functional plasticity. Stopped-flow studies on both enzymes indicate that the conformational changes associated with binding cofactor (the first ligand) are slow; they are similar in both enzymes but are not rate-determining. Instead the low k(cat) seen in AKR1C2 (50-fold less than AKR1C9) may be due to substrate "wobble" at the plastic active site.

20-Hydroxysteroid Dehydrogenases↗

PubMed2003

Purification, characterization and NNK carbonyl reductase activities of 11beta-hydroxysteroid dehydrogenase type 1 from human liver: enzyme cooperativity and significance in the detoxification of a tobacco-derived carcinogen.

11beta-Hydroxysteroid dehydrogenase type 1 (11beta-HSD 1) physiologically catalyzes the interconversion of receptor-active 11-hydroxy glucocorticoids (cortisol) to their receptor-inactive 11-oxo metabolites (cortisone), thereby acting as important pre-receptor control device in regulating access of glucocorticoid hormones to the glucocorticoid receptor. Evidence is emerging that 11beta-HSD 1 fulfills an additional role in the detoxification of non-steroidal carbonyl compounds, by catalyzing their reduction to the corresponding hydroxy derivatives that are easier to conjugate and eliminate. Whereas a number of methods were ineffective in purifying 11beta-HSD 1 from human liver, this membrane-bound enzyme was successfully obtained in an active state by a purification procedure that took advantage of a gentle solubilization method as well as providing a favourable detergent surrounding during the various chromatographic steps. We could demonstrate that 11beta-HSD 1 is active as a dimeric enzyme which exhibits cooperativity with cortisone and dehydrocorticosterone (11-oxoreducing activity) as substrates. Accordingly, this enzyme dynamically adapts to low (nanomolar) as well as to high (micromolar) substrate concentrations, thereby providing the fine tuning required as a consequence of great variations in circadian plasma glucocorticoid levels. Due to this kinetic peculiarity, 11beta-HSD 1 is also able to even metabolize nanomolar concentrations of the tobacco-specific nitrosamine 4-methylnitrosamino-1-(3-pyridyl)-1-butanone (NNK), a fact which is important in view of the relatively low levels of this carcinogen observed in smokers. Finally, 11beta-HSD 1 is potently (in nM concentrations) inhibited by glycyrrhetinic acid, the main constituent of licorice. Licorice, however, in addition to being a confectionary, serves as a major cigarette additive, which is used in cigarette manufacturing as a taste and flavour intensifier. Hence, licorice exposure may affect NNK detoxification by inhibition of 11beta-HSD 1, a condition which may advance lung cancer incidence, especially in smokers expressing low levels of this enzyme. Collectively, our data expand insights into the multifunctional nature of hydroxysteroid dehydrogenases/carbonyl reductases and emphasize the importance of 11beta-HSD 1 in the detoxification of a tobacco-derived carcinogen, in addition to its endocrinological functions.

11-beta-Hydroxysteroid Dehydrogenase Type 1↗

PubMed2001

Structure-function aspects and inhibitor design of type 5 17beta-hydroxysteroid dehydrogenase (AKR1C3).

17beta-Hydroxysteroid dehydrogenase (17beta-HSD) type 5 has been cloned from human prostate and is identical to type 2 3alpha-HSD and is a member of the aldo-keto reductase (AKR) superfamily; it is formally AKR1C3. In vitro the homogeneous recombinant enzyme expressed in Escherichia coli functions as a 3-keto-, 17-keto- and 20-ketosteroid reductase and as a 3alpha-, 17beta- and 20alpha-hydroxysteroid oxidase. The enzyme will reduce 5alpha-DHT, Delta(4)-androstene-3,17-dione, estrone and progesterone to produce 3alpha-androstanediol, testosterone, 17beta-estradiol and 20alpha-hydroxprogesterone, respectively. It will also oxidize 3alpha-androstanediol, testosterone, 17beta-estradiol and 20alpha-hydroxyprogesterone to produce 5alpha-androstane-3,17-dione, Delta(4)-androstene-3,17-dione, and progesterone, respectively. Many of these properties are shared by the related AKR1C1, AKR1C2 and AKR1C4 isoforms. RT-PCR shows that AKR1C3 is dominantly expressed in the human prostate and mammary gland. Examination of k(cat)/K(m) for these reactions indicates that as a reductase it prefers 5alpha-dihydrotestosterone and 5alpha-androstane-3,17-dione as substrates to Delta(4)-androstene-3,17-dione, suggesting that in the prostate it favors the formation of inactive androgens. Its concerted reductase activity may, however, lead to a pro-estrogenic state in the breast since it will convert estrone to 17beta-estradiol; convert Delta(4)-androstene-3,17-dione to testosterone (which can be aromatized to 17beta-estradiol); and it will reduce progesterone to its inactive metabolite 20alpha-hydroxyprogesterone. Drawing on detailed structure-function analysis of the related rat 3alpha-HSD (AKR1C9), which shares 69% sequence identity with AKR1C3, it is predicted that AKR1C3 catalyzes an ordered bi bi mechanism, that the rate determining step is k(chem), and that an oxyanion prevails in the transition state. Based on these relationships steroidal-based inhibitors that compete with the steroid product would be desirable since they would act as uncompetitive inhibitors. With regards to transition state analogs steroid carboxylates and pyrazoles may be preferred while 3alpha, 17beta or 20alpha-spiro-oxiranes may act as mechanism-based inactivators.

17-Hydroxysteroid Dehydrogenases↗

PubMed1999

Genomic structure of rat 3alpha-hydroxysteroid/dihydrodiol dehydrogenase (3alpha-HSD/DD, AKR1C9).

Rat liver 3alpha-hydroxysteroid/dihydrodiol dehydrogenase (3alpha-HSD/DD) is a member of the aldo-keto reductase (AKR) superfamily. It is involved in the inactivation of steroid hormones and the metabolic activation of polycyclic aromatic hydrocarbons (PAH) by converting trans-dihydrodiols into reactive and redox-active o-quinones. The structure of the 5'-flanking region of the gene and factors involved in the constitutive and regulated expression of this gene have been reported [H.-K. Lin, T.M. Penning, Cloning, sequencing, and functional analysis of the 5'-flanking region of the rat 3alpha-hydroxysteroid/dihydrodiol dehydrogenase gene, Cancer Res. 55 (1995) 4105-4113]. We now describe the complete genomic structure of the rat type 1 3alpha-HSD/DD gene. Charon 4A and P1 genomic clones contained at least three rat genes (type 1, type 2 and type 3 3alpha-HSD/DD) each of which encoded for the same open reading frame (ORF) but differed in their exon-intron organization. 5'-RACE confirmed that the type 1 3alpha-HSD/DD gene encodes for the dominant transcript in rat liver and it was the regulation of this gene that was previously studied. The rat type 1 3alpha-HSD/DD gene is 30 kb in length and consists of nine exons and eight introns. Exon 9 encodes +931 to 966 bp of the ORF and the 1292 bp 3'-UTR implicated in mRNA stability. This genomic structure is nearly identical to the homologous human genes, type 1 3alpha-HSD (chlordecone reductase/DD4, AKR1C4), type 2 3alpha-HSD (AKR1C3) and type 3 3alpha-HSD (bile-acid binding protein, AKR1C2) genes. Three different cDNA's containing identical ORFs for 3alpha-HSD have been reported suggesting that all three genes may be expressed in rat liver. Using 5' primers corresponding to the 5'-UTR's of the three different cDNA's only one PCR fragment was obtained and corresponded to the type 1 3alpha-HSD/DD gene. These data suggested that the type 2 and type 3 3alpha-HSD/DD genes are not abundantly expressed in rat liver. It is unknown whether the type 2 and type 3 3alpha-HSD/DD genes represent pseudo-genes or whether they represent genes that are differentially expressed in other rat tissues.

3' Untranslated Regions↗

PubMed1997

Expression cloning and characterization of oxidative 17beta- and 3alpha-hydroxysteroid dehydrogenases from rat and human prostate.

Intracellular levels of active steroid hormones are determined by their relative rates of synthesis and breakdown. In the case of the potent androgen dihydrotestosterone, synthesis from the precursor testosterone is mediated by steroid 5alpha-reductase, whereas breakdown to the inactive androgens 5alpha-androstane-3alpha, 17beta-diol (3alpha-adiol), and androsterone is mediated by reductive 3alpha-hydroxysteroid dehydrogenases (3alpha-HSD) and oxidative 17beta-hydroxysteroid dehydrogenases (17beta-HSD), respectively. We report the isolation by expression cloning of a cDNA encoding a 17beta-HSD6 isozyme that oxidizes 3alpha-adiol to androsterone. 17beta-HSD6 is a member of the short chain dehydrogenase/reductase family and shares 65% sequence identity with retinol dehydrogenase 1 (RoDH1), which catalyzes the oxidation of retinol to retinal. Expression of rat and human RoDH cDNAs in mammalian cells is associated with the oxidative conversion of 3alpha-adiol to dihydrotestosterone. Thus, 17beta-HSD6 and RoDH play opposing roles in androgen action; 17beta-HSD6 inactivates 3alpha-adiol by conversion to androsterone and RoDH activates 3alpha-adiol by conversion to dihydrotestosterone. The synthesis of an active steroid hormone by back conversion of an inactive metabolite represents a potentially important mechanism by which the steady state level of a transcriptional effector can be regulated.

17-Hydroxysteroid Dehydrogenases↗

PubMed2003

Human type 3 3alpha-hydroxysteroid dehydrogenase (aldo-keto reductase 1C2) and androgen metabolism in prostate cells.

Human aldo-keto reductases (AKRs) of the AKR1C subfamily function in vitro as 3-keto-, 17-keto-, and 20-ketosteroid reductases or as 3alpha-, 17beta-, and 20alpha-hydroxysteroid oxidases. These AKRs can convert potent sex hormones (androgens, estrogens, and progestins) into their cognate inactive metabolites or vice versa. By controlling local ligand concentration AKRs may regulate steroid hormone action at the prereceptor level. AKR1C2 is expressed in prostate, and in vitro it will catalyze the nicotinamide adenine dinucleotide (NAD(+))-dependent oxidation of 3alpha-androstanediol (3alpha-diol) to 5alpha-dihydrotestosterone (5alpha-DHT). This reaction is potently inhibited by reduced NAD phosphate (NADPH), indicating that the NAD(+): NADPH ratio in cells will determine whether AKR1C2 makes 5alpha-DHT. In transient COS-1-AKR1C2 and in stable PC-3-AKR1C2 transfectants, 5alpha-DHT was reduced by AKR1C2. However, the transfected AKR1C2 oxidase activity was insufficient to surmount the endogenous 17beta-hydroxysteroid dehydrogenase (17beta-HSD) activity, which eliminated 3alpha-diol as androsterone. PC-3 cells expressed retinol dehydrogenase/3alpha-HSD and 11-cis-retinol dehydrogenase, but these endogenous enzymes did not oxidize 3alpha-diol to 5alpha-DHT. In stable LNCaP-AKR1C2 transfectants, AKR1C2 did not alter androgen metabolism due to a high rate of glucuronidation. In primary cultures of epithelial cells, high levels of AKR1C2 transcripts were detected in prostate cancer, but not in cells from normal prostate. Thus, in prostate cells AKR1C2 acts as a 3-ketosteroid reductase to eliminate 5alpha-DHT and prevents activation of the androgen receptor. AKR1C2 does not act as an oxidase due to either potent product inhibition by NADPH or because it cannot surmount the oxidative 17beta-HSD present. Neither AKR1C2, retinol dehydrogenase/3alpha-HSD nor 11-cis-retinol dehydrogenase is a source of 5alpha-DHT in PC-3 cells.

17-Hydroxysteroid Dehydrogenases↗