In vivo footprinting of the human 11beta-hydroxysteroid dehydrogenase type 2 promoter: evidence for cell-specific regulation by Sp1 and Sp3

Differential expression of placental 11β-HSD2 induced by high maternal glucocorticoid exposure mediates sex differences in placental and fetal development

A variety of adverse environmental factors during pregnancy cause maternal chronic stress. Caffeine is a common stressor, and its consumption during pregnancy is widespread. Our previous study showed that prenatal caffeine exposure (PCE) increased maternal blood glucocorticoid levels and caused abnormal development of offspring. However, the placental mechanism for fetal development inhibition caused by PCE-induced high maternal glucocorticoid has not been reported. This study investigated the effects of PCE-induced high maternal glucocorticoid level on placental and fetal development by regulating placental 11β-hydroxysteroid dehydrogenase 2 (11β-HSD2) expression and its underlying mechanism. First, human placenta and umbilical cord blood samples were collected from women without prenatal use of synthetic glucocorticoids. We found that placental 11β-HSD2 expression was significantly correlated with umbilical cord blood cortisol level and birth weight in male newborns but not in females. Furthermore, we established a rat model of high maternal glucocorticoids induced by PCE (caffeine, 60 mg/kg·d, ig), and found that the expression of 11β-HSD2 in male PCE placenta was decreased and negatively correlated with the maternal/fetal/placental corticosterone levels. Meanwhile, we found abnormal placental structure and nutrient transporter expression. In vitro, BeWo cells were used and confirm that 11β-HSD2 mediated inhibition of placental nutrient transporter expression induced by high levels of glucocorticoid. Finally, combined with the animal and cell experiments, we further confirmed that high maternal glucocorticoid could activate the GR-C/EBPα-Egr1 signaling pathway, leading to decreased expression of 11β-HSD2 in males. However, there was no significant inhibition of placental 11β-HSD2 expression, placental and fetal development in females. In summary, we confirmed that high maternal glucocorticoids could regulate placental 11β-HSD2 expression in a sex-specific manner, leading to differences in placental and fetal development. This study provides the theoretical and experimental basis for analyzing the inhibition of fetoplacental development and its sex difference caused by maternal stress.

cAMP regulates 11β-hydroxysteroid dehydrogenase-2 and Sp1 expression in MLO-Y4/MC3T3-E1 cells

11β-hydroxysteroid dehydrogenase-2 (11β-HSD2) is one of the key enzymes in glucocorticoid metabolism, which can inactivate local corticosterone and regulate the level of active glucocorticoid in tissues. The expression of 11β-HSD2 and its regulatory pathway serve an important role in the apoptosis of steroid induced osteonecrosis of the femoral head (SANFH). The present study aimed to identify the regulatory effects of cAMP on the expression of Sp1 transcription factor (Sp1) and 11β-HSD2 in osteocytes at the cellular level. Murine long bone osteocyte Y4 (MLO-Y4) clone cells and mouse embryo osteoblast-like (MC3T3-E1) cells were cultured in vitro with adenylate cyclase activator or inhibitor (forskolin and SQ22536, respectively) to investigate the effects of alterations to intracellular cAMP levels. mRNA and protein expression levels of Sp1 and 11β-HSD2 were detected by reverse transcription-quantitative PCR and western blotting, respectively. Compared with the negative control group, the mRNA and protein expression levels of Sp1 were significantly increased in the activation group, whereas Sp1 expression levels were significantly decreased in the inhibition group. Similarly, compared with the negative control group, the mRNA and protein expression levels of 11β-HSD2 were significantly increased in the activator group, but significantly decreased in the inhibitor group. The aforementioned results indicated that intracellular cAMP levels significantly regulated the expression of Sp1 and 11β-HSD2 in mouse osteocytes and osteoblasts. Therefore, the present study suggested a potential therapeutic strategy for the prevention of osteonecrosis of the femoral head.

Impaired 11β-Hydroxysteroid Dehydrogenase Type 2 in Glucocorticoid-Resistant Patients

CONTEXT

Six patients carrying heterozygous loss-of-function mutations of glucocorticoid (GC) receptor (GR) presented with hypercortisolism, associated with low kalemia, low plasma renin, and aldosterone levels, with or without hypertension, suggesting a pseudohypermineralocorticism whose mechanisms remain unclear. We hypothesize that an impaired activity of the 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2; encoded by the HSD11B2 gene), catalyzing cortisol (F) inactivation, may account for an inappropriate activation of a renal mineralocorticoid signaling pathway in these GC-resistant patients.

OBJECTIVE

We aim at studying the GR-mediated regulation of HSD11B2.

DESIGN

The HSD11B2 promoter was subcloned and luciferase reporter assays evaluated GR-dependent HSD11B2 regulation, and 11β-HSD2 expression/activity was studied in human breast cancer MCF7 cells, endogenously expressing this enzyme.

RESULTS

Transfection assays revealed that GR transactivated the long (2.1-kbp) HSD11B2 promoter construct, whereas a defective 501H GR mutant was unable to stimulate luciferase activity. GR-mediated transactivation of the HSD11B2 gene was inhibited by the GR antagonist RU486. A threefold increase in HSD11B2 mRNA levels was observed after dexamethasone (DXM) treatment of MCF7 cells, inhibited by RU486 or by actinomycin, supporting a GR-dependent transcription. Chromatin immunoprecipitation further demonstrated a DXM-dependent GR recruitment onto the HSD11B2 promoter. 11β-HSD2 activity, evaluated by the cortisone/F ratio, quantified by liquid chromatography/tandem mass spectrometry, was 10-fold higher in the supernatant of DXM-treated cells than controls, consistent with a GR-dependent stimulation of 11β-HSD2 catalytic activity.

CONCLUSION

Collectively, we demonstrate that 11β-HSD2 expression and activity are transcriptionally regulated by GR. In the context of GR haploinsufficiency, these findings provide evidence that defective GR signaling may account for apparent mineralocorticoid excess in GC-resistant patients.

Chemistry, biochemistry, metabolic fate and mechanism of action of 6-oxo-cholestan-3β,5α-diol (OCDO), a tumor promoter and cholesterol metabolite

Oxygenation products of cholesterol, named oxysterols, were suspected since the 20th century to be involved in carcinogenesis. Among the family of oxysterol molecules, cholesterol-5,6-epoxides (5,6-EC) retained the attention of scientists because they contain a putative alkylating epoxide group. However, studies failed into demonstrating that 5,6-EC were direct carcinogens and revealed a surprising chemical stability and unreactivity towards nucleophiles in standard conditions. Analyses of 5,6-EC metabolism in normal cells showed that they were extensively transformed into cholestane-3β,5α,6β-triol (CT) by the cholesterol-5,6-epoxide hydrolase (ChEH). Studies performed in cancer cells showed that CT was additionally metabolized into an oxysterol identified as the 6-oxo-cholestan-3β,5α-diol (OCDO), by the 11β-hydroxysteroid dehydrogenase of type 2 (HSD2), the enzyme which inactivates cortisol into cortisone. Importantly, OCDO was shown to display tumor promoter properties in breast cancers, by binding to the glucocorticoid receptor, and independently of their estrogen receptor status, revealing the existence of a new tumorigenic pathway centered on 5,6-EC. In breast tumors from patients, OCDO production as well as the expression of the enzymes involved in the pathway producing OCDO, namely ChEH subunits and HSD2, were higher compared to normal tissues, and overexpression of these enzymes correlate with a higher risk of patient death, indicating that this onco-metabolism is of major importance to breast cancer pathology. Herein, we will review the actual knowledge and the future trends in OCDO chemistry, biochemistry, metabolism and mechanism of action and will discuss the impact of OCDO discovery on new anticancer therapeutic strategies.

Fructose intake during gestation and lactation differentially affects the expression of hippocampal neurosteroidogenic enzymes in rat offspring

Neurosteroids, steroidal hormones synthesized de novo from cholesterol within the brain, stimulate hippocampal functions such as neuron protection and synapse formation. Previously, we examined the effect of maternal fructose on the transcriptional regulation of neurosteroidogenic enzymes. We found that the mRNA expression level of the steroidogenic acute regulatory protein (StAR), peripheral benzodiazepine receptor (PBR), cytochrome P450(11β), 11β-hydroxysteroid dehydrogenase (HSD), and 17β-HSD was altered. However, we could not determine whether maternal fructose intake played a role in the gestation or lactation period because the dam rats were fed fructose solution during both periods. Thus, in this study, we analyzed the hippocampi of the offspring of dams fed fructose during the gestation or lactation period. Maternal fructose consumption during either the gestation or lactation period did not affect the mRNA levels of StAR, P450(17α), 11β-HSD-2, and 17β-HSD-1. PBR expression was down-regulated, even when rats consumed fructose during the lactation period only, while fructose consumption during gestation tended to activate the expression of P450(11β)-2. We found that maternal fructose intake during gestation and lactation differentially affected the expression of hippocampal neurosteroidogenic enzymes in the offspring.

Nutritional marginal zinc deficiency disrupts placental 11β-hydroxysteroid dehydrogenase type 2 modulation

This paper investigated if marginal zinc nutrition during gestation could affect fetal exposure to glucocorticoids as a consequence of a deregulation of placental 11βHSD2 expression. Placenta 11β-hydroxysteroid dehydrogenase type 2 (11βHSD2) plays a central role as a barrier protecting the fetus from the deleterious effects of excess maternal glucocorticoids. Rats were fed control (25 μg zinc per g diet) or marginal (10 μg zinc per g diet, MZD) zinc diets from day 0 through day 19 (GD19) of gestation. At GD19, corticosterone concentration in plasma, placenta, and amniotic fluid was similar in both groups. However, protein and mRNA levels of placenta 11βHSD2 were significantly higher (25% and 58%, respectively) in MZD dams than in controls. The main signaling cascades modulating 11βHSD2 expression were assessed. In MZD placentas the activation of ERK1/2 and of the downstream transcription factor Egr-1 was low, while p38 phosphorylation and SP-1-DNA binding were low compared to the controls. These results point to a central role of ERK1/Egr-1 in the regulation of 11βHSD2 expression under the conditions of limited zinc availability. In summary, results show that an increase in placenta 11βHSD2 expression occurs as a consequence of gestational marginal zinc nutrition. This seems to be due to a low tissue zinc-associated deregulation of ERK1/2 rather than to exposure to high maternal glucocorticoid exposure. The deleterious effects on brain development caused by diet-induced marginal zinc deficiency in rats do not seem to be due to fetal exposure to excess glucocorticoids.

Cross-talk between cAMP and MAPK pathways in HSD11B2 induction by hCG in placental trophoblasts

Overexposure of the fetus to glucocorticoids in gestation is detrimental to fetal development. The passage of maternal glucocorticoids into the fetal circulation is governed by 11beta-Hydroxysteroid Dehydrogenase Type 2 (HSD11B2) in the placental syncytiotrophoblasts. Human chorionic gonadotropin (hCG) plays an important role in maintaining placental HSD11B2 expression via activation of the cAMP pathway. In this study, we investigated the relationship between the activation of the cAMP pathway by hCG and subsequent phosphorylation of extracellular signal-regulated kinase1/2 (ERK1/2) or p38 mitogen-activated protein kinase (MAPK) pathways in the regulation of placental HSD11B2 expression in human placental syncytiotrophoblasts. We found that treatment of the placental syncytiotrophoblasts with either hCG or dibutyl cAMP (dbcAMP) could promote the phosphorylation of p38 and ERK1/2. Inhibition of p38 MAPK with SB203580 not only reduced the basal HSD11B2 mRNA and protein levels but also attenuated HSD11B2 levels induced by either hCG or dbcAMP. By contrast, inhibition of ERK1/2 with PD98059 increased the basal mRNA and protein levels of HSD11B2 and had no effect on HSD11B2 mRNA and protein levels induced by either hCG or dbcAMP. These data suggest that p38 MAPK is involved in both basal and hCG/cAMP-induced expression of HSD11B2, and ERK1/2 may play a role opposite to p38 MAPK at least in the basal expression of HSD11B2 in human placental syncytiotrophoblasts and that there is complicated cross-talk between hCG/cAMP and MAPK cascades in the regulation of placental HSD11B2 expression.

Insulin, CCAAT/enhancer-binding proteins and lactate regulate the human 11β-hydroxysteroid dehydrogenase type 2 gene expression in colon cancer cell lines

11β-Hydroxysteroid dehydrogenases (11beta-HSD) modulate mineralocorticoid receptor transactivation by glucocorticoids and regulate access to the glucocorticoid receptor. The isozyme 11beta-HSD2 is selectively expressed in mineralocorticoid target tissues and its activity is reduced in various disease states with abnormal sodium retention and hypertension, including the apparent mineralocorticoid excess. As 50% of patients with essential hypertension are insulin resistant and hyperinsulinemic, we hypothesized that insulin downregulates the 11beta-HSD2 activity. In the present study we show that insulin reduced the 11beta-HSD2 activity in cancer colon cell lines (HCT116, SW620 and HT-29) at the transcriptional level, in a time and dose dependent manner. The downregulation was reversible and required new protein synthesis. Pathway analysis using mRNA profiling revealed that insulin treatment modified the expression of the transcription factor family C/EBPs (CCAAT/enhancer-binding proteins) but also of glycolysis related enzymes. Western blot and real time PCR confirmed an upregulation of C/EBP beta isoforms (LAP and LIP) with a more pronounced increase in the inhibitory isoform LIP. EMSA and reporter gene assays demonstrated the role of C/EBP beta isoforms in HSD11B2 gene expression regulation. In addition, secretion of lactate, a byproduct of glycolysis, was shown to mediate insulin-dependent HSD11B2 downregulation. In summary, we demonstrate that insulin downregulates HSD11B2 through increased LIP expression and augmented lactate secretion. Such mechanisms are of interest and potential significance for sodium reabsorption in the colon.

Regulation of 11β-hydroxysteroid dehydrogenase type 2 by microRNA

The enzyme 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) is selectively expressed in aldosterone target tissues, conferring aldosterone selectivity for the mineralocorticoid receptor. A diminished activity causes salt-sensitive hypertension. The mechanism of the variable and distinct 11β-hydroxysteroid dehydrogenase type 2 gene (HSD11B2) expression in the cortical collecting duct is poorly understood. Here, we analyzed for the first time whether the 11β-HSD2 expression is modulated by microRNAs (miRNAs). In silico analysis revealed 53 and 27 miRNAs with potential binding sites on human or rat HSD11B2 3'-untranslated region. A reporter assay demonstrated 3'-untranslated region-dependent regulation of human and rodent HSD11B2. miRNAs were profiled from cortical collecting ducts and proximal convoluted tubules. Bioinformatic analyses showed a distinct clustering for cortical collecting ducts and proximal convoluted tubules with 53 of 375 miRNAs, where 13 were predicted to bind to the rat HSD11B2 3'-untranslated region. To gain insight into potentially relevant miRNAs in vivo, we investigated 2 models with differential 11β-HSD2 activity linked with salt-sensitive hypertension. (1) Comparing Sprague-Dawley with low and Wistar rats with high 11β-HSD2 activity revealed rno-miR-20a-5p, rno-miR-19b-3p, and rno-miR-190a-5p to be differentially expressed. (2) Uninephrectomy lowered 11β-HSD2 activity in the residual kidney with differentially expressed rno-miR-19b-3p, rno-miR-29b-3p, and rno-miR-26-5p. In conclusion, miRNA-dependent mechanisms seem to modulate 11β-HSD2 dosage in health and disease states.

11β-hydroxysteroid dehydrogenases: intracellular gate-keepers of tissue glucocorticoid action

Glucocorticoid action on target tissues is determined by the density of "nuclear" receptors and intracellular metabolism by the two isozymes of 11β-hydroxysteroid dehydrogenase (11β-HSD) which catalyze interconversion of active cortisol and corticosterone with inert cortisone and 11-dehydrocorticosterone. 11β-HSD type 1, a predominant reductase in most intact cells, catalyzes the regeneration of active glucocorticoids, thus amplifying cellular action. 11β-HSD1 is widely expressed in liver, adipose tissue, muscle, pancreatic islets, adult brain, inflammatory cells, and gonads. 11β-HSD1 is selectively elevated in adipose tissue in obesity where it contributes to metabolic complications. Similarly, 11β-HSD1 is elevated in the ageing brain where it exacerbates glucocorticoid-associated cognitive decline. Deficiency or selective inhibition of 11β-HSD1 improves multiple metabolic syndrome parameters in rodent models and human clinical trials and similarly improves cognitive function with ageing. The efficacy of inhibitors in human therapy remains unclear. 11β-HSD2 is a high-affinity dehydrogenase that inactivates glucocorticoids. In the distal nephron, 11β-HSD2 ensures that only aldosterone is an agonist at mineralocorticoid receptors (MR). 11β-HSD2 inhibition or genetic deficiency causes apparent mineralocorticoid excess and hypertension due to inappropriate glucocorticoid activation of renal MR. The placenta and fetus also highly express 11β-HSD2 which, by inactivating glucocorticoids, prevents premature maturation of fetal tissues and consequent developmental "programming." The role of 11β-HSD2 as a marker of programming is being explored. The 11β-HSDs thus illuminate the emerging biology of intracrine control, afford important insights into human pathogenesis, and offer new tissue-restricted therapeutic avenues.

Fetal growth restriction alters transcription factor binding and epigenetic mechanisms of renal 11beta-hydroxysteroid dehydrogenase type 2 in a sex-specific manner

Intrauterine growth restriction (IUGR) increases the risk of serious adult morbidities such as hypertension. In an IUGR rat model of hypertension, we reported a persistent decrease in kidney 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) mRNA and protein levels from birth through postnatal (P) day 21. This enzyme deficiency can lead to hypertension by limiting renal glucocorticoid deactivation. In the present study, we hypothesized that IUGR affects renal 11beta-HSD2 epigenetic determinants of chromatin structure and alters key transcription factor binding to the 11beta-HSD2 promoter in association with persistent downregulation of its mRNA expression. To test this hypothesis, we performed bilateral uterine artery ligation on embryonic day 19.5 pregnant rats and harvested kidneys at day 0 (P0) and P21. Key transcription factors that can affect 11beta-HSD2 expression include transcriptional enhancers specificity protein 1 (SP1) and NF-kappaB p65 and transcriptional repressors early growth response factor (Egr-1) and NF-kappaB p50. Our most important findings were as follows: 1) IUGR significantly decreased SP1 and NF-kappaB (p65) binding to the 11beta-HSD2 promoter in males, while it increased Egr-1 binding in females and NF-kappaB (p50) binding in males; 2) IUGR increased CpG methylation status, as well as modified the pattern of methylation in several CpG sites of 11beta-HSD2 promoter at P0 also in a sex-specific manner; and 3) IUGR decreased trimethylation of H3K36 in exon 5 of 11beta-HSD2 at P0 and P21 in both genders. We conclude that IUGR is associated with altered transcriptional repressor/activator binding in connection with increased methylation in the 11beta-HSD2 promoter region in a sex-specific manner, possibly leading to decreased transcriptional activity. Furthermore, IUGR decreased trimethylation of H3K36 of the 11beta-HSD2 gene in both genders, which is associated with decreased transcriptional elongation. We speculate that alterations in transcription factor binding and chromatin structure play a role in in utero reprogramming.

Sp1 regulates chromatin looping between an intronic enhancer and distal promoter of the human heme oxygenase-1 gene in renal cells

HO-1 (heme oxygenase-1) is an inducible microsomal enzyme that catalyzes the degradation of pro-oxidant heme. The goal of this study was to characterize a minimal enhancer region within the human HO-1 gene and delineate its role in modulating HO-1 expression by participation with its promoter elements in renal epithelial cells. Deletion analysis and site-directed mutagenesis identified a 220-bp minimal enhancer in intron 1 of the HO-1 gene, which regulates hemin-mediated HO-1 gene expression. Small interfering RNA, decoy oligonucleotides, site-directed mutagenesis, and chromatin immunoprecipitation assays confirmed the functional interaction of Sp1 with a consensus binding sequence within the 220-bp region. Mutations of regulatory elements within the -4.5 kb promoter region (a cyclic AMP response and a downstream NF-E2/AP-1 element, both located at -4.0 kb, and/or an E-box sequence located at -44 bp) resulted in the loss of enhancer activity. A chromosome conformation capture assay performed in human renal epithelial (HK-2) cells demonstrated hemin-inducible chromatin looping between the intronic enhancer and the -4.0 kb promoter region in a time-dependent manner. Restriction digestion with ApaLI (which cleaves the 220-bp enhancer) led to a loss of stimulus-dependent chromatin looping. Sp1 small interfering RNA and mithramycin A, a Sp1 binding site inhibitor, resulted in loss of the loop formation between the intronic enhancer and the distal HO-1 promoter by the chromosome conformation capture assay. These results provide novel insight into the complex molecular interactions that underlie human HO-1 regulation in renal epithelial cells.

The p38 mitogen-activated protein kinase regulates 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) expression in human trophoblast cells through modulation of 11beta-HSD2 messenger ribonucleic acid stability

The placental 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2; encoded by the HSD11B2 gene) has emerged as a key player in controlling fetal development, but its regulation is incompletely understood. Here we identified p38 MAPK as an important regulator of placental 11beta-HSD2. We showed that inhibition of p38 MAPK with the pharmacological inhibitor SB202190 led to an approximately 50% reduction in 11beta-HSD2 activity, protein, and mRNA in primary human placental trophoblast cells. Furthermore, the effect of SB202190 was confirmed by the use of two additional p38 inhibitors, SB203580 and SB220025. In addition, SB202190 decreased the half-life of 11beta-HSD2 mRNA without altering the HSD11B2 promoter activity, indicating that p38 MAPK regulates placental 11beta-HSD2 expression through modulation of 11beta-HSD2 mRNA stability. Importantly, small interfering RNA-mediated knockdown of p38alpha caused a 50% reduction in 11beta-HSD2 activity, suggesting that p38alpha is the primary p38 isoform involved. Taken together, these findings suggest a novel pathway controlling placental 11beta-HSD2 expression resulting from the activation of p38 MAPK. Given that p38alpha is abundantly expressed in the human placenta in which its function is largely unknown, our present study also reveals 11beta-HSD2 as an important target through which p38alpha may regulate human placental function and consequently fetal growth and development.

Glycyrrhetinic acid food supplementation lowers serum potassium concentration in chronic hemodialysis patients

Hyperkalemia is a common life-threatening problem in hemodialysis patients. Because glycyrrhetinic acid (GA) inhibits the enzyme 11beta-hydroxy-steroid dehydrogenase II and thereby increases cortisol availability to the colonic mineralocorticoid receptor, it has the potential to lower serum potassium concentrations. To test this, 10 patients in a 6 month prospective, double-blind, placebo-controlled crossover study were given cookies or bread rolls supplemented with glycyrrhetinic acid or placebo. Twenty-four-hour blood pressure measurements were performed at baseline and week 6 and 12 of each treatment period. The ratio of plasma cortisol/cortisone was significantly increased in all patients on GA as compared to baseline or placebo, indicating appropriate enzyme inhibition. Nine of the 10 patients had a persistent decrease in predialysis serum potassium concentration. On GA, mean predialysis serum potassium was significantly lower than at baseline or on placebo. On placebo, serum potassium was significantly elevated above the upper limit of normal in 76% compared to 30% of measurements during GA treatment. Furthermore, on this treatment the frequency of severe hyperkalemia significantly decreased from 9% to 0.6%. No differences were found in parameters reflecting sodium retention. Although these studies show that prolonged GA supplementation persistently lowers serum potassium in dialysis patients, a long-term toxicity study will be mandatory before we recommend the routine use of this treatment.

Progesterone induction of the 11beta-hydroxysteroid dehydrogenase type 2 promoter in breast cancer cells involves coordinated recruitment of STAT5A and progesterone receptor to a distal enhancer and polymerase tracking

Steroid hormone receptors regulate gene expression, interacting with target DNA sequences but also activating cytoplasmic signaling pathways. Using the human 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) gene as a model, we have investigated the contributions of both effects on a human progesterone-responsive promoter in breast cancer cells. Chromatin immunoprecipitation has identified two different mechanisms of hormone-induced progesterone receptor (PR) recruitment to the 11beta-HSD2 promoter: (i) direct PR binding to DNA at the proximal promoter, abrogated when PR contains a mutated DNA binding domain (DBD), and (ii) STAT5A (signal transducer and activator of transcription 5A)-mediated recruitment of PR to an upstream distal region, impaired by AG490, a JAK/STAT pathway inhibitor. The JAK/STAT inhibitor, as well as expression of dominant-negative STAT5A, impairs hormone induction of 11beta-HSD2. On the other hand, the DBD-mutated PR fully supports 11beta-HSD2 expression. These results, along with data from a deletion analysis, indicate that the distal region is crucial for hormone regulation of 11beta-HSD2. We show active RNA polymerase II tracking from the distal region upon PR and STAT5A binding, concomitant with synthesis of noncoding, hormone-dependent RNAs, suggesting that this region works as a hormone-dependent transcriptional enhancer. In conclusion, coordination of PR transcriptional effects and cytoplasmic signaling activation, in particular the JAK/STAT pathway, are critical in regulating progestin-induced endogenous 11beta-HSD2 gene expression in breast cancer cells. This is not unique to this promoter, as AG490 also alters the expression of other progesterone-regulated genes.

Identification of polymorphisms in the human 11beta-hydroxysteroid dehydrogenase type 2 gene promoter: functional characterization and relevance for salt sensitivity

Reduced activity of 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) plays a role in essential hypertension and the sensitivity of blood pressure to dietary salt. Nonconservative mutations in the coding region are extremely rare and do not explain the variable 11beta-HSD2 activity. We focused therefore on the 5'-regulatory region and identified and characterized the first promoter polymorphisms. Transfections of variants G-209A and G-126A into SW620 cells reduced promoter activity and affinity for activators nuclear factor 1 (NF1) and Sp1. Chromatin immunoprecipitation revealed Sp1, NF1, and glucocorticoid receptor (GR) binding to the HSD11B2 promoter. Dexamethasone induced expression of mRNA and activity of HSD11B2. GR and/or NF1 overexpression increased endogenous HSD11B2 mRNA and activity. GR complexes cooperated with NF1 to activate HSD11B2, an effect diminished in the presence of the G-209A variant. When compared to salt-resistant subjects (96), salt-sensitive volunteers (54) more frequently had the G-209A variant, higher occurrence of alleles A4/A7 of polymorphic microsatellite marker, and higher urinary ratios of cortisol to cortisone metabolites. First, we conclude that the mechanism of glucocorticoid-induced HSD11B2 expression is mainly mediated by cooperation between GR and NF1 on the HSD11B2 promoter and, second, that the newly identified promoter variants reduce activity and cooperation of cognate transcription factors, resulting in diminished HSD11B2 transcription, an effect favoring salt sensitivity.

Impaired 11 beta-hydroxysteroid dehydrogenase contributes to renal sodium avidity in cirrhosis: hypothesis or fact?

Exaggerated renal sodium retention with concomitant potassium loss is a hallmark of cirrhosis and contributes to the accumulation of fluid as ascites, pleural effusion, or edema. This apparent mineralocorticoid effect is only partially explained by increased aldosterone concentrations. I present evidence supporting the hypothesis that cortisol confers mineralocorticoid action in cirrhosis. The underlying molecular pathology for this mineralocorticoid receptor (MR) activation by cortisol is a reduced activity of the 11 beta-hydroxysteroid dehydrogenase type 2, an enzyme protecting the MR from promiscuous activation by cortisol in healthy mammalians.

Caveolin-1 is required for signaling and membrane targeting of EphB1 receptor tyrosine kinase

Eph receptor tyrosine kinases are key players during the development of the embryonic vasculature; however, their role and regulation in adult angiogenesis remain to be defined. Caveolae are flask-shaped invaginations of the cell membrane; their major structural protein, caveolin-1, has been shown to regulate signaling molecules localized in these micro-domains. The interaction of caveolin-1 with several of these proteins is mediated by the binding of its scaffolding domain to a region containing hydrophobic amino acids within these proteins. The presence of such a motif within the EphB1 kinase domain prompted us to investigate the caveolar localization and regulation of EphB1 by caveolin-1. We report that EphB1 receptors are localized in caveolae, and directly interact with caveolin-1 upon ligand stimulation. This interaction, as well as EphB1-mediated activation of extracellular-signal-regulated kinase (ERK), was abrogated by overexpression of a caveolin-1 mutant lacking a functional scaffolding domain. Interaction between Ephs and caveolin-1 is not restricted to the B-subclass of receptors, since we show that EphA2 also interacts with caveolin-1. Furthermore, we demonstrate that the caveolin-binding motif within the kinase domain of EphB1 is primordial for its correct membrane targeting. Taken together, our findings establish caveolin-1 as an important regulator of downstream signaling and membrane targeting of EphB1.

Ligand-controlled interaction of histone acetyltransferase binding to ORC-1 (HBO1) with the N-terminal transactivating domain of progesterone receptor induces steroid receptor coactivator 1-dependent coactivation of transcription

Modulators of cofactor recruitment by nuclear receptors are expected to play an important role in the coordination of hormone-induced transactivation processes. To identify such factors interacting with the N-terminal domain (NTD) of the progesterone receptor (PR), we used this domain as bait in the yeast Sos-Ras two-hybrid system. cDNAs encoding the C-terminal MYST (MOZ-Ybf2/Sas3-Sas2-Tip60 acetyltransferases) domain of HBO1 [histone acetyltransferase binding to the origin recognition complex (ORC) 1 subunit], a member of the MYST acetylase family, were thus selected from a human testis cDNA library. In transiently transfected CV1 cells, the wild-type HBO1 [611 amino acids (aa)] enhanced transcription mediated by steroid receptors, notably PR, mineralocorticoid receptor, and glucocorticoid receptor, and strongly induced PR and estrogen receptor coactivation by steroid receptor coactivator 1a (SRC-1a). As assessed by two-hybrid and glutathione-S-transferase pull-down assays, the HBO1 MYST acetylase domain (aa 340-611) interacts mainly with the NTD, and also contacts the DNA-binding domain and the hinge domains of hormone-bound PR. The HBO1 N-terminal region (aa 1-340) associates additionally with PR ligand-binding domain (LBD). HBO1 was found also to interact through its NTD with SRC-1a in the absence of steroid receptor. The latter coassociation enhanced specifically activation function 2 activation function encompassed in the LBD. Conversely, the MYST acetylase domain specifically enhanced SRC-1 coupling with PR NTD, through a hormone-dependent mechanism. In human embryonic kidney 293 cells expressing human PRA or PRB, HBO1 raised selectively an SRC-1-dependent response of PRB but failed to regulate PRA activity. We show that HBO1 acts through modification of an LBD-controlled structure present in the N terminus of PRB leading to the modulation of SRC-1 functional coupling with activation function 3-mediated transcription. Importantly, real-time RT-PCR analysis also revealed that HBO1 enhanced SRC-1 coactivation of PR-dependent transcription of human endogenous genes such as alpha-6 integrin and 11beta-hydroxydehydrogenase 2 but not that of amphiregulin. Immunofluorescence and confocal microscopy of human embryonic kidney-PRB cells demonstrated that the hormone induces the colocalization of HBO1 with PR-SRC-1 complex into nuclear speckles characteristic of PR-mediated chromatin remodeling. Our results suggest that HBO1 might play an important physiological role in human PR signaling.

Cadmium reduces 11 beta-hydroxysteroid dehydrogenase type 2 activity and expression in human placental trophoblast cells

Cadmium, a common environmental pollutant and a major constituent of tobacco smoke, has been identified as a new class of endocrine disruptors with a wide range of detrimental effects on mammalian reproduction. During human pregnancy, maternal cadmium exposure, via the environment and/or cigarette smoking, leads to fetal growth restriction (FGR), but the underlying mechanisms are unknown. Although a substantial amount of evidence suggests that cadmium may affect fetal growth indirectly via the placenta, the molecular targets remain to be identified. Given that reduced placental 11 beta-hydroxysteroid dehydrogenase type 2 (11 beta-HSD2, encoded by HSD11B2 gene) is causally linked to FGR, the present study was undertaken to examine the hypothesis that cadmium induces FGR in part by targeting placental HSD11B2. Using cultured human trophoblast cells as a model system, we showed that cadmium exposure resulted in a time- and concentration-dependent decrease in 11 beta-HSD2 activity, such that an 80% reduction was observed after 24-h treatment at 1 microM. It also led to a similar decrease in levels of 11 beta-HSD2 protein and mRNA, suggesting that cadmium reduced 11 beta-HSD2 expression. Furthermore, cadmium diminished HSD11B2 promoter activity, indicative of repression of HSD11B2 gene transcription. In addition, the effect of cadmium was highly specific, in that other divalent metals (Zn(2+), Mg(2+), and Mn(2+)) as well as nicotine and cotinine (a major metabolite of nicotine) did not alter 11 beta-HSD2 activity. Taken together, these findings demonstrate that cadmium reduces human placental 11 beta-HSD2 expression and activity by suppressing HSD11B2 gene transcription. Thus the present study identifies placental 11 beta-HSD2 as a novel molecular target of cadmium. It also reveals a molecular mechanism by which this endocrine disruptor may affect human placental function and, consequently, fetal growth and development.

RFX-1, a putative alpha Adducin interacting protein in a human kidney library

Adducin regulates tubular absorption of sodium by modulating the expression levels of the sodium-potassium-ATPase in renal tubular cells. Adducin is a candidate gene in the pathogenesis of hypertension. Yeast two hybrid screen showed a specific interaction between human alpha Adducin and the regulatory factor for X box (RFX-1), a nuclear protein that down regulates the expression of several proteins in non neuronal cells. The interaction was confirmed in cells through co-immunoprecipitation and colocalization experiments. The binding of alpha Adducin to RFX-I and their nuclear co-localization suggests that Adducin can have a role in modulating the transcriptional regulating activity of RFX-I.

Extracellular ATP determines 11beta-hydroxysteroid dehydrogenase type 2 activity via purinergic receptors

Hypertension and sodium retention are features of a diminished 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2). The activity of this enzyme is reduced in various disease states with abnormal renal sodium retention and hypertension, including preeclampsia. ATP release to the extracellular compartment is observed with shear stress, inflammation, and placental ischemia. It was hypothesized that ATP downregulates 11beta-HSD2 activity. For that purpose, cell lines from different tissues that previously were used to study the regulation of 11beta-HSD2 were investigated: JEG-3, a vascular trophoblastic; LLCPK1, a renal tubular; and SW620, a colonic epithelial cell line. The 11beta-HSD2 activity, assessed by the conversion of 3H-cortisol to cortisone, was reversibly reduced during incubation with ATP or its stable analogue ATPgammaS in intact JEG-3 and LLCPK1, but not in SW620 cells. In JEG-3 cells, the purinergic antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid but not suramin reversed the inhibition. Incubation with UTP and ADP and their degradation products including adenosine and alpha,beta-methylene-ATP did not inhibit 11beta-HSD2 activity. In contrast, 11beta-HSD2 activity increased almost 2.5-fold after incubation with 2'-methylthio-ATP. This indicates a bidirectional regulation by nucleotides via purinergic receptors. In JEG-3 cells, ATP/ATPgammaS did not alter 11beta-HSD2 promoter activity but reduced 11beta-HSD2 protein and mRNA concentration and half-life, suggesting a posttranscriptional regulation. In conclusion, ATP inhibits cell type specifically via purinergic receptors the expression and activity of the 11beta-HSD2 by a posttranscriptional mechanism.

Hypoxia up-regulates expression of Eph receptors and ephrins in mouse skin

Eph receptor tyrosine kinases and their ligands (ephrins) are key players during the development of the embryonic vasculature; however, their role and regulation in adult angiogenesis remain to be defined. Both receptors and ligands have been shown to be up-regulated in a variety of tumors. To address the hypothesis that hypoxia is an important regulator of Ephs/ephrins expression, we developed a mouse skin flap model of hypoxia. We demonstrate that our model truly represents segmental skin hypoxia by applying four independent methods: continuous measurement of partial cutaneous oxygen tension, monitoring of tissue lactate/pyruvate ratio, time course of hypoxia-inducible factor-1alpha (HIF-1alpha) induction, and localization of stabilized HIF-1alpha by immunofluorescence in the hypoxic skin flap. Our experiments indicate that hypoxia up-regulates not only HIF-1alpha and vascular endothelial growth factor (VEGF) expression, but also Ephs and ephrins of both A and B subclasses in the skin. In addition, we show that in Hep3B and PC-3 cells, the hypoxia-induced up-regulation of Ephs and ephrins is abrogated by small interfering RNA-mediated down-regulation of HIF-1alpha. These novel findings shed light on the role of this versatile receptor/ligand family in adult angiogenesis. Furthermore, our model offers considerable potential for analyzing distinct mechanisms of neovascularization in gene-targeted mice.

Biochemical and genetic characterization of 11 beta-hydroxysteroid dehydrogenase type 2 in low-renin essential hypertensives

BACKGROUND

The 11beta-hydroxysteroid dehydrogenase type 2 (11betaHSD2) catalyzes the conversion of cortisol (F) to cortisone (E), avoiding the interaction of cortisol with the mineralocorticoid receptor. If it fails, cortisol will stimulate sodium and water reabsorption, increasing the intravascular volume that suppresses renin and secondarily increase the blood pressure.

OBJECTIVE

To look for the possible contribution of a decreased ability of 11betaHSD2 to convert cortisol to its inactive metabolite cortisone in the pathogenesis of low renin hypertension (LREH).

PATIENTS AND METHODS

We studied 64 LREH patients (plasma renin activity, PRA < 1 ng/ml per h), eighty normo-renin essential hypertensives (NREH) (PRA: 1-2.5 ng/ml per h) and 74 normotensives. Serum aldosterone (SA), F, E and serum F/E ratio was determined in all patients. A serum F/E ratio was considered high when it was higher than X + 2SD from the normotensive value. Cytosine-adenine (CA)-repeat microsatellite region in intron 1 of HSD11B2 gene was genotyped in all patients and normotensives volunteers. In 13 LREH with high F/E ratio we performed HSD11B2 gene sequencing.

RESULTS

LREH had serum F/E ratio higher than NREH and normotensive controls (3.6 (2.9-4.3) versus 2.9 (2.2-4.3) versus 3.0 (2.4-3.7) (P = 0.004), respectively). We observed an inverse relation between F/E ratio and SA and PRA. In NREH and normotensives we did not find correlation between these variables. In the LREH subset the longer 155 bp CA-allele showed the highest serum F/E ratio. No mutations in coding region or short introns were found in LREH patients.

CONCLUSION

In this study we show that low-renin essential hypertensives had increased serum cortisol/cortisone ratios as compared with normotensive subjects. This suggest that some essential hypertensives, with suppressed renin activity, may have an impairment in the cortisol inactivation catalyzed by the enzyme 11betaHSD2, whose low activity in LREH patients could be associated with the length of CA-repeat microsatellite in intron 1 of the HSD11B2 gene.

Peroxisome proliferator-activated receptor delta suppresses 11beta-hydroxysteroid dehydrogenase type 2 gene expression in human placental trophoblast cells

Accumulating evidence suggests that the human placental enzyme 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) plays a key role in fetal development by controlling fetal exposure to maternal glucocorticoids. Recently, the nuclear peroxisome proliferator-activated receptor delta (PPAR delta) has been found to be the most abundantly expressed PPAR subtype in the human placenta, but its function in this organ is unknown. Given that PPAR delta-null mice exhibited placental defects and consequent intrauterine growth restriction, the present study was undertaken to examine the hypothesis that PPAR delta regulates human placental function in part by targeting 11beta-HSD2. Using cultured human trophoblast cells as a model system, we demonstrated that 1) the putative PPAR delta agonist carbaprostacyclin (cPGI2) reduced 11beta-HSD2 activity as well as 11beta-HSD2 expression at both protein and mRNA levels; 2) GW610742 (a selective PPAR delta agonist) mimicked the effect of cPGI2, whereas indomethacin (a known ligand for PPARalpha and PPAR gamma) had no effect; 3) the cPGI2-induced down-regulation of 11beta-HSD2 mRNA did not require de novo protein synthesis; 4) cPGI2 suppressed HSD11B2 promoter activity, but did not alter the half-life of 11beta-HSD2 mRNA; and 5) the inhibitory effect of cPGI2 on HSD11B2 promoter activity was abrogated in trophoblast cells cotransfected with a dominant negative PPAR delta mutant. Taken together, these findings suggest that activation of PPAR delta down-regulates HSD11B2 gene expression in human trophoblast cells, and that this effect is mediated primarily at the transcriptional level. Thus, the present study reveals 11beta-HSD2 as an additional target for PPAR delta and identifies a molecular mechanism by which this nuclear receptor may regulate human placental function.

Identification of two candidate collecting duct cell-specific cis-acting elements in the Hoxb-7 promoter region

HOX genes encode highly conserved transcription factors responsible for developmental patterning and postnatal tissue homeostasis. Previous studies have shown that a 1.4-kb segment of the Hoxb-7 proximal promoter drives renal expression of reporter genes specifically in the ureteric bud and collecting ducts. In this study using stably transfected renal tubule cell lines, we have identified three short cis-acting sequences within this promoter segment that cooperate to induce high-level expression specifically in collecting duct cells. In addition to an inverted CCAAT box (-71/-67) that acts as an ubiquitous enhancer and binds the transcription factor CBF/NF-Y, two different cis-acting sequences, named CDSE-1 and CDSE-2 (for Collecting Duct Specific Element 1 and 2), allow collecting duct cell-specific promoter activation. CDSE-1 (-56/-34) is composed of two E-boxes separated by a 9-bp GC-rich sequence. Only the latter sequence enhances reporter gene expression specifically in collecting duct cells. CDSE-2 (-34/-13) contains sequence bears high homology with a segment of the Pax-2 promoter. CDSE-2 also conveys cell specificity but has no enhancer activity by itself.

Adrenal gland involvement in the regulation of renal 11beta-hydroxysteroid dehydrogenase 2

Renal 11beta-hydroxysteroid dehydrogenase 2 (HSD2) catalyzes the conversion of active glucocorticoids to inert 11beta-keto compounds, thereby preventing the illicit binding of these hormones to mineralocorticoid receptors (MRs) and, thus, conferring aldosterone specificity. Absence or inhibition of HSD2 activity, originates a hypertensive syndrome with sodium retention and increased potassium elimination. Recent studies from our laboratory reported an increment of HSD2 activity in intact-stressed rats. To evaluate the adrenal involvement in this increase, we analyzed HSD2 activity and protein abundance in Intact, Sham-operated, and adrenalectomized rats under stress situations (gavage with an overload of 200 mM HCl (10 ml) and simulated gavage) or with corticosterone replacement. HSD2 activity was assessed in renal microsomal preparations obtained from different groups of animals. HSD2 protein abundance was measured by Western-blot. Circulating corticosterone was determined by radioimmunoassay. Sham-operated animals showed an increase in HSD2 activity and abundance compared to Intact and adrenalectomized rats suggesting the involvement of stress-related adrenal factors in HSD2 regulation. In the case of acidotic adrenalectomized animals, there was an increase in renal HSD2 activity when, along with the HCl overload, the rats were injected with corticosterone. This increment occurred without an increase in enzyme abundance. These results suggest the importance of circulating levels of glucocorticoids to respond to a metabolic acidosis, through regulation of HSD2 stimulation. The group subjected to a simulated gavage showed an increase in enzyme activity and protein abundance, thus demonstrating the need for both adrenal and extra-factors in the modulation of renal HSD2. The adrenalectomized animals injected with different doses of corticosterone, produced a progressive increase in enzyme activity and abundance, being significant for the dose of 68 microg corticosterone/100 g body weight. The highest dose (308 microg/100 g body weight) did not show any variation in activity and abundance compared to the control group. This biphasic effect of glucocorticoids could be explained taking into account their permissive and suppressive actions, depending on their blood levels. Knowing that stress induces multifactorial responses, it should not be surprising to observe a differential regulation in renal HSD2, confirming that different stressors act through different factors of both, adrenal and extra-adrenal origin.

Epigenetic regulation of 11 beta-hydroxysteroid dehydrogenase type 2 expression

The enzyme 11 beta-hydroxysteroid dehydrogenase type 2 (11 beta HSD2) is selectively expressed in aldosterone target tissues, where it confers aldosterone selectivity for the mineralocorticoid receptor by inactivating 11 beta-hydroxyglucocorticoids. Variable activity of 11 beta HSD2 is relevant for blood pressure control and hypertension. The present investigation aimed to elucidate whether an epigenetic mechanism, DNA methylation, accounts for the rigorous control of expression of the gene encoding 11 beta HSD2, HSD11B2. CpG islands covering the promoter and exon 1 of HSD11B2 were found to be densely methylated in tissues and cell lines with low expression but not those with high expression of HSD11B2. Demethylation induced by 5-aza-2'-deoxycytidine and procainamide enhanced the transcription and activity of the 11 beta HSD2 enzyme in human cells in vitro and in rats in vivo. Methylation of HSD11B2 promoter-luciferase constructs decreased transcriptional activity. Methylation of recognition sequences of transcription factors, including those for Sp1/Sp3, Arnt, and nuclear factor 1 (NF1) diminished their DNA-binding activity. Herein NF1 was identified as a strong HSD11B2 stimulatory factor. The effect of NF1 was dependent on the position of CpGs and the combination of CpGs methylated. A methylated-CpG-binding protein complex 1 transcriptional repression interacted directly with the methylated HSD11B2 promoter. These results indicate a role for DNA methylation in HSD11B2 gene repression and suggest an epigenetic mechanism affecting this gene causally linked with hypertension.

Glucocorticoid-mediated mineralocorticoid receptor activation and hypertension

PURPOSE OF REVIEW

Traditionally, the mineralocorticoid receptor was thought to be activated by the mineralocorticoid hormone aldosterone, and to exhibit its main action on epithelia by promoting renal sodium retention, potassium excretion and inducing hypertension upon excessive activation. Recently, evidence appeared that mineralocorticoid receptors are expressed in nonepithelial cells and activated by endogenous glucocorticoids including cortisol. Therefore, the prereceptor regulation of cortisol access to the mineralocorticoid receptors by 11beta-hydroxysteroid dehydrogenase enzymes (11beta-HSDs), a mechanism absent in most nonepithelial cells, appears to be relevant for disease states with cortisol-induced mineralocorticoid action. The present review focuses on direct and indirect effects attributable to mineralocorticoid receptor activation by glucocorticoids.

RECENT FINDINGS

The determination of the intracellular topology of 11beta-HSD1, facing the endoplasmic reticulum lumen, and 11beta-HSD2, facing the cytoplasm, suggests that 11beta-HSD1 acts as a prereceptor mechanism in the local activation of glucocorticoid receptors, whereas 11beta-HSD2 controls mineralocorticoid receptors by interacting with the receptor in the absence of aldosterone. Downregulation of 11beta-HSD2 was observed with various stimuli including hypoxia, shear stress, angiotensin II and tumor necrosis factor alpha. The corresponding signal transcription pathways and some relevant transcription factors have been identified. Renal sodium retention in liver cirrhosis, nephrotic syndrome and hypoxia have been linked to 11beta-HSD2 reduced activity. Overexpression of 11beta-HSD1 specifically in adipose tissue in mice caused central obesity, a metabolic syndrome and hypertension due to increased intracellular cortisol concentrations. Peroxisome proliferator-activated receptor gamma agonists reduce 11beta-HSD1 activity and diminish the intracellular availability of cortisol, an effect accompanied by a decline in blood pressure. Three individuals with loss-of-function mutations of peroxisome proliferator-activated receptor gamma developed early hypertension. A potential mechanism might be glucocorticoid dependent mineralocorticoid receptor-mediated downregulation of endothelial nitric oxide synthase.

SUMMARY

Recently, mineralocorticoid receptor antagonists have been used in the randomized aldactone evaluation study (RALES) with spironolactone, the eplerenone post-AMI heart failure efficacy and survival study (EPHESUS), and in severe and postmyocardial infarct heart failure, respectively. These investigations cannot be understood on the basis of the present physiological knowledge and underscore the relevance of focusing on mineralocorticoid receptor activation by ligands other than aldosterone.

Angiotensin II regulates 11beta-hydroxysteroid dehydrogenase type 2 via AT2 receptors

BACKGROUND

In preeclampsia, cortisol degradation by the enzyme 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) is compromised, which enhances intracellular cortisol availability. This leads to vasoconstriction and renal sodium retention with volume expansion, thus increasing blood pressure. An augmented availability of angiotensin II (Ang II) predisposes to preeclampsia. Some effects of Ang II are mediated by the mitogen-activated protein kinase (MAPK) cascade, which also regulates 11beta-HSD2 activity. Therefore, we hypothesized that Ang II regulates 11beta-HSD2.

METHODS

The human choriocarcinoma cell line JEG-3, which expresses the 11beta-HSD2 isoenzyme, was used. 3H-cortisol/cortisone conversion assays and mRNA analyses by reverse transcription-polymerase chain reaction (RT-PCR) were performed. Cells were stimulated with Ang II and the effect was modulated by Ang II type 1 (AT1) and AT2 receptor blockers DUP753 or L-158809 and PD-123319, respectively. In order to elucidate the signaling cascade, the MAPK kinase inhibitors PD-098059 and U-0126 were probed. The impact of a modulated 11beta-HSD2 activity was assessed by determining the effect of cortisol on AT1 receptor mRNA.

RESULTS

Ang II reduced mRNA and activity of 11beta-HSD2 mainly by a post-transcriptional mechanism. This Ang II effect was abrogated by AT2, but not by AT1 receptor blockade. Mitogen-activated protein (MAP) kinase kinase (MAPKK) inhibitors reversed the Ang II effect. Dexamethasone augmented the mRNA expression of AT1 receptors. Cortisol enhanced AT1 receptor mRNA expression when the 11beta-HSD2 activity was reduced either by Ang II or by glycyrrhetinic acid, an 11beta-HSD2 inhibitor.

CONCLUSION

Ang II decreases the activity of 11beta-HSD2 by an AT2 receptor- and MAPK-dependent mechanism. The decreased activity of 11beta-HSD2 increases the intracellular availability of cortisol, which might be relevant for the pathogenesis of hypertension and preeclampsia.

11beta-hydroxysteroid dehydrogenases, cell proliferation and malignancy

The enzymes 11beta-hydroxysteroid dehydrogenase type 1 and 2 (11beta-HSD1 and 2) have well-defined roles in the tissue-specific metabolism of glucocorticoids which underpin key endocrine mechanisms such as adipocyte differentiation (11beta-HSD1) and mineralocorticoid action (11beta-HSD2). However, in recent studies we have shown that the effects of 11beta-HSD1 and 2 are not restricted to distinct tissue-specific hormonal functions. Studies of normal fetal and adult tissues, as well as their tumor equivalents, have shown a further dichotomy in 11beta-HSD expression and activity. Specifically, most normal glucocorticoid receptor (GR)-rich tissues such as adipose tissue, bone, and pituitary cells express 11beta-HSD1, whereas their fetal equivalents and tumors express 11beta-HSD2. We have therefore postulated that the ability of 11beta-HSD1 to generate cortisol acts as an autocrine anti-proliferative, pro-differentiation stimulus in normal adult tissues. In contrast, the cortisol-inactivating properties of 11beta-HSD2 lead to pro-proliferative effects, particularly in tumors. This proposal is supported by experiments in vitro which have demonstrated divergent effects of 11beta-HSD1 and 2 on cell proliferation. Current studies are aimed at (1) characterizing the underlying mechanisms for a "switch" in 11beta-HSD isozyme expression in tumors; (2) defining the molecular targets for glucocorticoids as regulators of cell proliferation; (3) evaluating the potential for targeting glucocorticoid metabolism as therapy for some cancers. These and other issues are discussed in the present review.

Abnormal expression of 11 beta-hydroxysteroid dehydrogenase type 2 in human pituitary adenomas: a prereceptor determinant of pituitary cell proliferation

The physiological effects of glucocorticoids (GCs) are, at least in part, mediated by inhibition of cell proliferation. Two isozymes of 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) interconvert cortisol (F) and inactive cortisone (E), and are thus able to modulate GC action at an autocrine level. Previously, we have demonstrated absent expression of 11 beta-HSD2 in normal pituitaries; however, in a small number of pituitary tumors analysed, 11 beta-HSD2 was readily demonstrable. Here we have used real-time RT-PCR to quantify expression of mRNA for 11 beta-HSD1 and 2 in 105 human pituitary tumors and have performed enzyme expression and activity studies in primary pituitary cultures. Overall, pituitary tumors expressed lower levels of 11 beta-HSDl mRNA compared with normals (0.2-fold, P<0.05). In contrast, expression of 11 beta-HSD2 mRNA was 9.8-fold greater in tumors than in normals (P<0.001). Enzyme assays showed significant 11 beta-HSD2 activity (71.9+/-22.3 pmol/h/mg protein (mean+/-s.d.)) but no detectable 11 beta-HSDl activity. Proliferation assays showed that addition of glycyrrhetinic acid (an 11 beta-HSD2 inhibitor) resulted in a 30.3+/-7.7% inhibition of cell proliferation. In summary, we describe a switch in expression from 11 beta-HSDl to 11 beta-HSD2 in neoplastic pituitary tissue. We propose that abnormal expression of 11 beta-HSD2 acts as a proproliferative prereceptor determinant of pituitary cell growth, and may provide a novel target for future tumor therapy.