Retinoic acids increase 17 beta-hydroxysteroid dehydrogenase type 1 expression in JEG-3 and T47D cells, but the stimulation is potentiated by epidermal growth factor, 12-O-tetradecanoylphorbol-13-acetate, and cyclic adenosine 3',5'-monophosphate only in JEG-3 cells

Conversion of Estrone to 17β-Estradiol: A Potential Confounding Factor in Assessing Risks of Environmental Estrogens to Fish

Feminization of male fish and the role of endocrine-active chemicals in this phenomenon has been an area of intense study for many years. Estrone (E1), a natural steroid, is found in aquatic environments sometimes at high concentrations relative to the estrogenic steroids 17β-estradiol (E2) and 17α-ethynylestradiol. However, E1 has been less thoroughly studied than E2 or 17α-ethynylestradiol due in part to a relatively lower potency in metabolically limited estrogen receptor (ER) binding/activation assays. Recent evidence suggests that in vivo biotransformation of E1 to E2 may occur in fathead minnows (Pimephales promelas) residing in environments with high concentrations of E1, such as near wastewater treatment plants. The enzymes likely responsible for this biotransformation, 17β-hydroxysteroid dehydrogenases (17βHSDs), have been well characterized in mammals but to a lesser extent in fish species. In the present study, a novel systematic analysis of amino acid sequence data from the National Center for Biotechnology Information database demonstrated that multiple 17βHSD isoforms are conserved across different fish species. Experimentally, we showed that metabolically active hepatic cytosolic preparations from 2 commercially important salmonid species, rainbow trout and lake trout, biotransformed E1 to E2 to a degree sufficient to alter results of competitive ER binding assays. These results from in silico and in vitro analyses indicate that E1 and biotransformation may play a significant role in adverse effects on development and reproduction of a variety of fish species in contaminated aquatic environments. Environ Toxicol Chem 2020;39:2028-2040. Published 2020. This article is a US Government work and is in the public domain in the USA.

Role of hydroxysteroid (17beta) dehydrogenase type 1 in reproductive tissues and hormone-dependent diseases

Abnormal synthesis and metabolism of sex steroids is involved in the pathogenesis of various human diseases, such as endometriosis and cancers arising from the breast and uterus. Steroid biosynthesis is a multistep enzymatic process proceeding from cholesterol to highly active sex steroids via different intermediates. Human Hydroxysteroid (17beta) dehydrogenase 1 (HSD17B1) enzyme shows a high capacity to produce the highly active estrogen, estradiol, from a precursor hormone, estrone. However, the enzyme may also play a role in other steps of the steroid biosynthesis pathway. In this article, we have reviewed the literature on HSD17B1, and summarize the role of the enzyme in hormone-dependent diseases in women as evidenced by preclinical studies.

The impact of testosterone, tibolone and black cohosh on purified mammary and placental 17β-hydroxysteroid dehydrogenase type 1

CONTEXT

Mammary and placental 17β-hydroxysteroid dehydrogenase type 1 (17βHSD1).

OBJECTIVE

To assess the impact of testosterone, tibolone, and black cohosh on purified mammary and placental 17βHSD1.

MATERIALS AND METHODS

17βHSD1 was purified from human mammary gland and placenta by column chromatography, its activity was monitored by a radioactive activity assay, and the degree of purification was determined by gel electrophoresis. Photometric cofactor transformation analysis was performed to assess 17βHSD1 activity without or in presence of testosterone, tibolone and black cohosh.

RESULTS

17βHSD1 from both sources displayed a comparable basal activity. Testosterone and tibolone metabolites inhibited purified mammary and placental 17βHSD1 activity to a different extent, whereas black cohosh had no impact.

DISCUSSION

Studies on purified enzymes reveal the individual action of drugs on local regulatory mechanisms thus helping to develop more targeted therapeutic intervention.

CONCLUSION

Testosterone, tibolone and black cohosh display a beneficial effect on local mammary estrogen metabolism by not affecting or decreasing local estradiol exposure.

Heterocyclic aromatic hydrocarbons show estrogenic activity upon metabolization in a recombinant transactivation assay

Heterocyclic aromatic hydrocarbons (hetero-PAHs) are increasingly studied at contaminated sites; especially at former industrial facilities where coal tar-oil was handled, e.g., wood treatment plants, high concentrations of hetero-PAHs are frequently detected in groundwater plumes. In previous studies, fractions of groundwater with high estrogenic activity contained hetero-PAHs and their hydroxylated metabolites. To evaluate this preliminary evidence, selected hetero-PAHs were screened for their estrogenic activity in lyticase yeast estrogen screen (LYES) and ER CALUX. All tested substances were inactive in the LYES. Hetero-PAHs such as acridine, xanthene, indole, 2-methylbenzofuran, 2,3-dimethylbenzofuran, dibenzofuran, dibenzothiophene, quinoline, and 6-methylquinoline were positive in the ER CALUX, with estradiol equivalence factors (EEFs) from 2.85 × 10(-7) to 3.18 × 10(-5). The EEF values of these substances were comparable to those of other xenoestrogens (e.g., alkylphenols or bisphenol A) that are sometimes found in surface water. Chemical analyses revealed that T47Dluc cells could metabolize most of the substances. Among the metabolites (tentatively) identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS) were hydroxides and their keto tautomers, sulfates, sulfoxides, and N-oxides. Because of their high concentrations measured in groundwater, we conclude that hetero-PAHs and metabolites may be a potential risk and should be the subject of further research.

Gender, sex hormones and pulmonary hypertension

Most subtypes of pulmonary arterial hypertension (PAH) are characterized by a greater susceptibility to disease among females, although females with PAH appear to live longer after diagnosis. While this "estrogen paradoxȍ of enhanced female survival despite increased female susceptibility remains a mystery, recent progress has begun to shed light upon the interplay of sex hormones, the pathogenesis of pulmonary hypertension, and the right ventricular response to stress. For example, emerging data in humans and experimental models suggest that estrogens or differential sex hormone metabolism may modify disease risk among susceptible subjects, and that estrogens may interact with additional local factors such as serotonin to enhance the potentially damaging chronic effects of estrogens on the pulmonary vasculature. Regardless, it remains unclear why not all estrogenic compounds behave equally, nor why estrogens appear to be protective in certain settings but detrimental in others. The contribution of androgens and other compounds, such as dehydroepiandrosterone, to pathogenesis and possibly treatment must be considered as well. In this review, we will discuss the recent understandings on how estrogens, estrogen metabolism, dehydroepiandrosterone, and additional susceptibility factors may all contribute to the pathogenesis or potentially to the treatment of pulmonary hypertension, by evaluating current human, cell-based, and experimental model data.

Estrogens and development of pulmonary hypertension: interaction of estradiol metabolism and pulmonary vascular disease

Severe pulmonary arterial hypertension (PAH) is characterized by clustered proliferation of endothelial cells (ECs) in the lumina of small size pulmonary arteries resulting in concentric obliteration of the lumina and formation of complex vascular structures known as plexiform lesions. This debilitating disease occurs more frequently in women, yet both animal studies in classical models of PAH and limited clinical data suggest protective effects of estrogens: the estrogen paradox in pulmonary hypertension. Little is known about the role of estrogens in PAH, but one line of evidence strongly suggests that the vascular protective effects of 17β-estradiol (estradiol; E2) are mediated largely by its downstream metabolites. Estradiol is metabolized to 2-hydroxyestradiol (2HE) by CYP1A1/CYP1B1, and 2HE is converted to 2-methoxyestradiol (2ME) by catechol-O-methyl transferase. 2ME is extensively metabolized to 2-methoxyestrone, a metabolite that lacks biologic activity, but which may be converted back to 2ME. 2ME has no estrogenic activity, and its effects are mediated by estrogen receptors–independent mechanism(s). Notably, in systemic and pulmonary vascular ECs, smooth muscle cells, and fibroblasts, 2ME exerts stronger antimitotic effects than E2 itself. E2 and 2ME, despite having similar effects on other cardiovascular cells, have opposing effects on ECs; that is, in ECs, E2 is promitogenic, proangiogenic, and antiapoptotic, whereas 2ME is antimitogenic, antiangiogenic, and proapoptotic. This may have significant ramifications in severe PAH that involves uncontrolled proliferation of monoclonal apoptosis-resistant ECs. Based on its cellular effects, 2ME should be expected to attenuate the progression of disease and provide protection in severe PAH. In contrast, E2, due to its mitogenic, angiogenic, and antiapoptotic effects (otherwise desirable in normal quiescent ECs), may even adversely affect endothelial remodeling in PAH, and this may be even more significant if the E2's effects on injured endothelium are not opposed by 2ME (eg, in the event of reduced E2 conversion to 2ME due to hypoxia, inflammation, drugs, environmental factors, or genetic polymorphism of metabolizing enzymes). This review focuses on the effects of estrogens and their metabolites on pulmonary vascular pathobiology and the development of experimental PAH and offers potential explanation for the estrogen paradox in PAH. Furthermore, we propose that unbalanced estradiol metabolism may lead to the development of PAH. Recent animal data and studies in patients with PAH support this concept.

Retinoid-mediated stimulation of steroid sulfatase activity in myeloid leukemic cell lines requires RARalpha and RXR and involves the phosphoinositide 3-kinase and ERK-MAP kinase pathways

All-trans retinoic acid and 9-cis-retinoic acid stimulate the activity of steroid sulfatase in HL60 acute myeloid leukemia cells in a concentration- and time-dependent manner. Neither of these 'natural retinoids' augmented steroid sulfatase activity in a HL60 sub-line that expresses a dominant-negative retinoic acid receptor alpha (RARalpha). Experiments with synthetic RAR and RXR agonists and antagonists suggest that RARalpha/RXR heterodimers play a role in the retinoid-stimulated increase in steroid sulfatase activity. The retinoid-driven increase in steroid sulfatase activity was attenuated by inhibition of phospholipase D (PLD), but not by inhibitors of phospholipase C. Experiments with inhibitors of protein kinase C (PKC) show that PKCalpha and PKCdelta play an important role in modulating the retinoid-stimulation of steroid sulfatase activity in HL60 cells. Furthermore, we show that pharmacological inhibition of the RAF-1 and ERK MAP kinases blocked the retinoid-stimulated increase in steroid sulfatase activity in HL60 cells and, by contrast, inhibition of the p38-MAP kinase or JNK-MAP kinase had no effect. Pharmacological inhibitors of the phosphatidylinositol 3-kinase, Akt, and PDK-1 also abrogated the retinoid-stimulated increase in steroid sulfatase activity in HL60 cells. These results show that crosstalk between the retinoid-stimulated genomic and non-genomic pathways is necessary to increase steroid sulfatase activity in HL60 cells.

Effects of 9-cis-retinoic acid on the insulin-like growth factor axis in former smokers

PURPOSE

Insulin-like growth factor (IGF) axis has been associated with the risk of lung cancer. 9-cis-retinoic acid (9-cis-RA) has shown potential chemopreventive activities in former smokers. This study was designed to evaluate the effects of 9-cis-RA on IGF axis in former smokers to identify any benefit the retinoid may have in preventing lung cancer.

PATIENTS AND METHODS

Serum concentrations of IGF-I, IGF binding protein (IGFBP)-3, and their molar ratio (IGF-I/IGFBP-3) were measured with radioimmunoassay kits in stored blood samples from the participants of an original chemoprevention trial. The participants had ceased smoking for at least 12 months and were randomly assigned to receive 3 months of daily oral 9-cis-RA (100 mg) or placebo. All statistical tests were two-sided.

RESULTS

A total of 111 samples from the study's baseline and 84 samples from the 3 months treatment were analyzed. The serum concentrations of IGF-I and IGF-I/IGFBP-3 at baseline were significantly lower in female than in male participants. After 3 months of treatment, the serum level of IGF-I and IGF-I/IGFBP-3 were significantly lower in the 9-cis-RA group than in the placebo group (P = .03 and P < .01, respectively), but the IGFBP-3 level was significantly higher (P = .03).

CONCLUSION

9-cis-RA treatment modulated the IGF axis in former smokers, suggesting that the IGF axis is a potential target for the chemopreventive activities of 9-cis-RA and that the serum concentrations of IGF, IGFBP-3, and IGF-I/IGFBP-3 could serve as surrogate end point biomarkers of 9-cis-RA treatment.

Overview of steroidogenic enzymes in the pathway from cholesterol to active steroid hormones

Significant advances have taken place in our knowledge of the enzymes involved in steroid hormone biosynthesis since the last comprehensive review in 1988. Major developments include the cloning, identification, and characterization of multiple isoforms of 3beta-hydroxysteroid dehydrogenase, which play a critical role in the biosynthesis of all steroid hormones and 17beta-hydroxysteroid dehydrogenase where specific isoforms are essential for the final step in active steroid hormone biosynthesis. Advances have taken place in our understanding of the unique manner that determines tissue-specific expression of P450aromatase through the utilization of alternative promoters. In recent years, evidence has been obtained for the expression of steroidogenic enzymes in the nervous system and in cardiac tissue, indicating that these tissues may be involved in the biosynthesis of steroid hormones acting in an autocrine or paracrine manner. This review presents a detailed description of the enzymes involved in the biosynthesis of active steroid hormones, with emphasis on the human and mouse enzymes and their expression in gonads, adrenal glands, and placenta.

Divergent effects of retinoic acids on the expression of ERalpha and 17beta-hydroxysteroid dehydrogenase type 2 in endometrial carcinoma cells (RL 95-2)

The effects of E2 are dependent on ERs and local E2 concentration in target cells. Modulation of intracellular E2 concentration involves the action of 17beta-hydroxysteroid dehydrogenase (17HSD) type 2, the enzyme converting E2 to estrone. In the present study, the influence of RAs on the growth of endometrial cancer cell line RL 95-2 as well as the expression of ERs and 17HSD type 2 have been investigated. It was found that RAs repress the growth of RL 95-2 cells, which express all subtypes of RXR and RAR, as examined by RT-PCR. Also, quantitative RT-PCR analysis showed that both ERalpha and ERbeta are present in RL 95-2 cells, and Western blot assay further revealed that ERalpha expression was decreased by all trans-RA treatment. In contrast, RAs induced 17HSD type 2 mRNA expression in a dose- and time-dependent fashion. This stimulatory effect was also detected at the level of in vivo oxidative 17HSD activity in cultured cells. On the other hand, the abundance of 17HSD type 2 mRNA was not altered by RAs in cultured normal epithelial cells isolated from human early- and late-secretory endometrium. The data indicate that RAs have an inhibitory effect on the growth of RL 95-2 cells and a cross-talk with the estrogen pathway in estrogen-responsive endometrial cancer cells.

Effect of retinoic acid and palm oil carotenoids on oestrone sulphatase and oestradiol-17beta hydroxysteroid dehydrogenase activities in MCF-7 and MDA-MB-231 breast cancer cell lines

Oestrogen is important in the development of breast cancer. Oestrogen receptor positive breast cancers are associated with a better prognosis than oestrogen-receptor negative breast cancers since they are more responsive to hormonal treatment. Oestrone sulphate acts as a huge reservoir for oestrogens in the breast. It is converted to the potent oestrogen, oestradiol (E(2)) by the enzymes oestrone sulphatase and oestradiol-17beta hydroxysteroid dehydrogenase (E(2)DH). Retinoic acid and carotenoids have been shown to have chemopreventive activity against some cancers. The aim of our study was to determine and compare the effects of retinoic acid and palm oil carotenoids on growth of and oestrone sulphatase and E(2)DH activities in the oestrogen receptor positive, MCF-7 and oestrogen receptor negative, MDA-MB-231 breast cancer cell lines. Retinoic acid and carotenoids inhibited MCF-7 cell growth but had no effect on MDA-MB-231 cell growth. Both retinoic acid and carotenoids stimulated oestrone sulphatase activity in the MCF-7 cell line. E(1) to E(2) conversion was inhibited by 10(-7) M carotenoids but was stimulated at 10(-6) M in the MCF-7 cell line. Retinoic acid had no effect on E(1) to E(2) conversion at 10(-7) M but stimulated E(1) to E(2) conversion at 10(-6) M. Retinoic acid and carotenoids had no effect on E(2) to E(1) conversion in the MCF-7 cell line. Retinoic acid stimulated E(1) to E(2) conversion in the MDA-MB-231 cell line but had no effect on oestrone sulphatase activity or E(2) to E(1) conversion in this cell line. Both oestrone sulphatase and E(2)DH activity were not affected by carotenoids in the MDA-MB-231 cell line. In conclusion, retinoic acid and carotenoids may prevent the development of hormone-dependent breast cancers since they inhibit the growth of the MCF-7 cell line.

The expression of nuclear retinoid receptors in human implantation

Vitamin A and retinoids play an important role during development. They affect morphogenesis, cell growth and differentiation by interacting with two types of receptor, the RARs and the RXRs. Despite the well known established teratogenic effects of retinoids during human pregnancy, little is known about the effect of retinoids on human placental development. We studied the possible involvement of retinoids during the implantation process by investigating the spatial distribution of retinoid receptors in the human implantation site by in situ hybridization and immunohistochemistry. For in situ hybridization, we used digoxigenin-labelled antisense riboprobes. Immunochemical staining was performed with specific antibodies against the various retinoid receptors and a streptavidin-alkaline phosphatase immunostaining kit. We found that only two types of receptors were expressed at the implantation site: RARalpha and RXRalpha. Both types of receptors were present in the proliferative intermediate trophoblast, the invasive extravillous trophoblast and decidual cells. Both receptors were also present in the villous cytotrophoblasts. The presence of this retinoid receptor in the cytotrophoblasts suggests a key role for all-trans retinoic acid and/or 9-cis retinoic acid in the development of human placenta.

Estrogen metabolism as a regulator of estrogen action in the mammary gland

Estrogen action in the target cells is dependent on estrogen receptor activity and intracellular estrogen concentration, which, in turn, is affected by the serum concentration and local metabolism in these cells. During the reproductive years the main source of estrogens is the ovarian follicles, but in postmenopausal women most of the estrogens are formed in peripheral tissues. 17Beta-hydroxysteroid dehydrogenases (17HSDs) catalyze the reaction between 17beta-hydroxysteroids and 17-ketosteroids, and several distinct 17HSD isoenzymes have been characterized. 17HSD type 1 catalyzes the reaction from low-activity estrone to high-activity estradiol. The type 2 enzyme has an opposite activity, thereby reducing the exposure of tissues to estrogen action. 17HSD type 1 is expressed both in steroidogenic tissues and in the target tissues of steroid action, such as normal and malignant breast tissue, where it may be responsible for maintaining the high intracellular estradiol concentration seen in breast cancer specimens. Therefore, 17HSD type 1 inhibitors may be useful in the treatment and/or prevention of estrogen-dependent malignancies, such as breast cancer. This article deals mainly with 17HSD types 1 and 2 and their role in estrogen action in breast tissue.

Identification of essential subelements in the hHSD17B1 enhancer: difference in function of the enhancer and that of the hHSD17BP1 analog is due to -480C and -486G

The function of the gene encoding human 17beta-hydroxysteroid dehydrogenase (17HSD) type 1, the hHSD17B1 gene, is regulated by a cell-specific enhancer at position -662 to -392. The adjacent hHSD17BP1 gene, whose function is not known, contains an analogous region in its 5'-flanking region. The identity between the hHSD17B1 enhancer and the hHSD17BP1 equivalent is as high as 98%, i.e. they differ by only five nucleotides. Results from reporter gene analyses showed that the hHSD17BP1 analog, a pseudoenhancer, has only 10% the activity of the hHSD17B1 enhancer. Furthermore, the results indicate that the reduced function of the pseudoenhancer is a consequence of the presence of G and A at positions -480 and -486, whereas the hHSD17B1 enhancer contains -480C and -486G. In addition, three protected areas were localized to regions -495/-485 (FP1), -544/-528 (FP2), and -589/-571 (FP3) in deoxyribonuclease I footprinting analysis of the hHSD17B1 enhancer. Replacement of the footprinted regions with a nonsense sequence demonstrated that the FP2 region is the most critical for enhancer activity. Mutations of FP2 or a short palindromic region within it led to almost complete abolishment of enhancer activity. We have identified several subelements that are essential for appropriate function of the hHSD17B1 enhancer. The results also show that the hHSD17B1 and hHSD17BP1 genes operate differently despite the high homology between them.

Prostaglandins and leukotriene B4 are potent inhibitors of 11beta-hydroxysteroid dehydrogenase type 2 activity in human choriocarcinoma JEG-3 cells

The 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) is responsible for the inactivation of glucocorticoids. This is the predominant isozyme in the human placenta, where it is proposed to protect the fetus from high levels of maternal cortisol. In the present study, we examined the effects of eicosanoids on the activity of 11beta-HSD2 in human choriocarcinoma JEG-3 cells, a well-established model for placental trophoblasts. Treatment of JEG-3 cells for 24 h with either prostaglandin (PG) E2 or F2alpha attenuated 11beta-HSD2 activity ( approximately 40%). Paradoxically, indomethacin, an inhibitor of cyclooxygenases, inhibited (approximately 40%) rather than stimulated the activity of this enzyme. This indicated that the arachidonic acid metabolism may be diverted to other pathway(s), the products of which may inhibit 11beta-HSD2 activity. To determine whether the lipoxygenase pathways were involved, the cells were treated with nordihydroguaretic acid (NDGA), a blocker of all three (5-, 12-, and 15-) lipoxygenases. NDGA caused a 3-fold increase in 11beta-HSD2 activity. To further delineate which specific lipoxygenase pathway was involved, the cells were incubated with zileuton, a selective inhibitor of 5-lipoxygenase. This resulted in a similar increase in 11beta-HSD2 activity, suggesting that the products of this pathway (e.g., leukotrienes) may be involved. Given that leukotriene B4 (LTB4) is the most biologically active product of the 5-lipoxygenase pathway, we treated the cells with LTB4, which inhibited 11beta-HSD2 activity in a time- and dose-dependent manner with a maximal effect (60% reduction) at 10 nM for 9 h. Semiquantitative reverse transcription-polymerase chain reaction analysis revealed that 11beta-HSD2 mRNA levels were not altered by the addition of LTB4, PGE2, or PGF2alpha, indicating an effect at the posttranscriptional level. In conclusion, these results demonstrate that prostaglandins and LTB4 are potent inhibitors of 11beta-HSD2 activity in JEG-3 cells, suggesting that placental 11beta-HSD2 activity is modulated by these locally produced eicosanoids. This is the first time that the products of arachidonic acid metabolism have been found to regulate the activity of 11beta-HSD2.

Retinoic acid stimulates the expression of 11beta-hydroxysteroid dehydrogenase type 2 in human choriocarcinoma JEG-3 cells

The syncytiotrophoblasts of the human placenta express high levels of 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2), the enzyme responsible for the inactivation of glucocorticoids. It has been proposed that the placental 11beta-HSD2 serves as a barrier to protect the fetus from high levels of maternal cortisol. To examine the hypothesis that nutritional signals regulate the expression of 11beta-HSD2 in placental syncytiotrophoblasts, we investigated the effects of retinoic acids (RAs), the major metabolites of vitamin A, on the expression of 11beta-HSD2 using human choriocarcinoma JEG-3 cells as a model. This trophoblast-like cell line displays a number of functional similarities to the syncytiotrophoblast. Treatment for 24 h with all-trans RA (1-1000 nM) resulted in a dose-dependent increase in 11beta-HSD2 activity with a maximal effect (increase to 3-fold) at 100 nM. The effect of all-trans RA (100 nM) was also time-dependent in that the effect was detectable at 6 h and reached its maximum by 48 h. Similar increases in 11beta-HSD2 activity were observed when the cells were treated with 9-cis RA. Results from semi-quantitative reverse transcription-polymerase chain reaction demonstrated that there was a corresponding increase in 11beta-HSD2 mRNA after RA treatment. Moreover, treatment with actinomycin D (100 ng/ml) abrogated the increase in 11beta-HSD2 mRNA induced by RA, indicating an effect on transcription. In conclusion, the present study has demonstrated for the first time that RA, at physiological concentrations, induces 11beta-HSD2 gene expression and enzyme activity in JEG-3 cells. If this occurs in vivo, the present finding suggests that high expression of 11beta-HSD2 in the human placenta may be maintained, at least in part, by dietary intake of vitamin A.

1,25-dihydroxyvitamin D3 regulates estrogen metabolism in cultured keratinocytes

Local estrogen metabolism may play an important role in modulating cell development in peripheral tissues such as breast, adipose, and bone. C19 androgens are converted to C18 estrogens by the enzyme aromatase, overexpression of which is associated with breast cancer. Interconversion of active estradiol (E2) to inactive estrone is controlled by various isoforms of the enzyme 17beta-hydroxysteroid dehydrogenase (17betaHSD). We have studied the expression of these two enzymes in human keratinocytes and report rapid changes in 17betaHSD activity in response to treatment with 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. Keratinocytes cultured in serum-free medium showed aromatase activity of 2.5 fmol/h x mg cell protein, which was unaffected by any culture treatment. A much higher level of 17betaHSD activity was observed in the keratinocytes, predominantly conversion of E2 to estrone (approximately 120 pmol/h x mg cell protein). This inactivation of E2 increased in a dose-dependent fashion after treatment of the cells with antiproliferative doses of 1,25-(OH)2D3 (0.1-200 nM). The effect of 1,25-(OH)2D3 on 17betaHSD activity was enhanced by simultaneous treatment with dexamethasone, which also increased the antiproliferative action of 1,25-(OH)2D3. Reverse transcription-PCR and Northern analysis showed that keratinocytes expressed messenger RNA for three 17betaHSD isoenzymes (types I, II, and IV). Treatment with 1,25-(OH)2D3 (10 nM for 20 h) resulted in the up-regulation of messenger RNA levels for type 2 17betaHSD. Further RNA studies combined with E2 binding experiments demonstrated the presence of estrogen receptors in the cultured keratinocytes. These data indicate that keratinocytes are potential targets for systemically or locally produced estrogens, which may, in turn, play a key role in the development of normal skin. In particular, we propose that 17betaHSD isoenzymes are key target genes for 1,25-(OH)2D3 in keratinocytes and may be an important feature of the antipsoriatic effects of vitamin D and its analogs.

The proximal promoter region of the gene encoding human 17beta-hydroxysteroid dehydrogenase type 1 contains GATA, AP-2, and Sp1 response elements: analysis of promoter function in choriocarcinoma cells

The 5'-flanking region from -78 to +9 in the HSD17B1 gene serves as a promoter, and an HSD17B1 silencer element is located in position -113 to -78. In the present studies, we have characterized three regulatory elements in the proximal 5'-flanking regions of the gene, using electrophoretic mobility shift assays and reporter gene analysis. First, nuclear factors recognized by antibodies against Sp1 and Sp3 were found to bind the Sp1 motif in the region from -52 to -43. Mutation of the Sp1-binding site decreased the promoter activity to 30% in JEG-3 cells and to 60% in JAR cells, suggesting that binding to the Sp1 motif has a substantial role in the complete functioning of the HSD17B1 promoter. Second, the binding of AP-2 to its motif in the region from -62 to -53 led to reduced binding of Sp1 and Sp3, and furthermore, mutation of the AP-2 element increased promoter activity to 260% in JEG-3 cells. The data thus implied that AP-2 can repress the function of the HSD17B1 promoter by preventing binding to the Sp1 motif. Finally, GATA factors, GATA-3 in particular, were demonstrated to bind their cognate sequence in the HSD17B1 silencer region, and mutations introduced into the GATA-binding site increased transcriptional activity to the level seen in constructs not containing the silencer element. Thus, GATA-3 seems to prevent transcription in the constructs, and hence, the GATA motif also may operate as a negative control element for HSD17B1 transcription.