Transcriptional regulation of human 11beta-hydroxylase (hCYP11B1)

Generation of glucocorticoid-producing cells derived from human pluripotent stem cells

Adrenal insufficiency is a life-threatening condition resulting from the inability to produce adrenal hormones in a dose- and time-dependent manner. Establishing a cell-based therapy would provide a physiologically responsive approach for the treatment of this condition. We report the generation of large numbers of human-induced steroidogenic cells (hiSCs) from human pluripotent stem cells (hPSCs). Directed differentiation of hPSCs into hiSCs recapitulates the initial stages of human adrenal development. Following expression of steroidogenic factor 1, activation of protein kinase A signaling drives a steroidogenic gene expression profile most comparable to human fetal adrenal cells, and leads to dynamic secretion of steroid hormones, in vitro. Moreover, expression of the adrenocorticotrophic hormone (ACTH) receptor/co-receptor (MC2R/MRAP) results in dose-dependent ACTH responsiveness. This protocol recapitulates adrenal insufficiency resulting from loss-of-function mutations in AAAS, which cause the enigmatic triple A syndrome. Our differentiation protocol generates sufficient numbers of hiSCs for cell-based therapy and offers a platform to study disorders causing adrenal insufficiency.

Flow-dependent differentiation of cultured adrenal cells under different stimuli

It still remains unclear how the functional organisation of the adrenal cortex arises. One aim of this study was to create a setup which allows for the establishment of a concentration gradient in vitro. This was achieved by a continuous flow of medium through the culture flask which caused differences in glucose and cortisol concentrations as well as in pH values between the sites of inflow and outflow of medium. Using real-time polymerase chain reaction, we found that a continuous supply of 1 ml medium per hour significantly increased the expression of MC2R, CYP11B1 and CYP17A1 genes of NCI-H295R cells in the distal area of the flask as compared with the proximal part. The expression of the AT1R showed a reverse regulation. The addition of dexamethasone to the medium led to an increase in gene expression of MC2R while AT1R was downregulated. Moreover, we detected a higher expression of CYP11B2 and a decreased expression of CYP11B1 when endothelial cell-conditioned medium (ECCM) was added to the inflow. Our experiments show that a directed medium delivery system creates different gradients and affects the functional differentiation of the NCI-H295R cells. Also, our results emphasise that products of endothelial cells have additional effects on the differentiation of the cultured adrenal cortical cells. Our results are in support that the regulation of the adrenal zonation is possible through different concentration gradients.

Activation and expression of endogenous CREB-regulated transcription coactivators (CRTC) 1, 2 and 3 in the rat adrenal gland

The activation and nuclear translocation of cAMP-response element binding protein (CREB)-regulated transcription coactivator (CRTC)2 occurs in the rat adrenal gland, in response to adrenocorticotrophic hormone (ACTH) and stressors, and has been implicated in the transcriptional regulation of steroidogenic acute regulatory protein (StAR). We have recently demonstrated the activation of CRTC isoforms, CRTC1 and CRTC3, in adrenocortical cell lines. In the present study, we aimed to determine the activation and expression of the three CRTC isoforms in vivo in relation to Star transcription, under basal conditions and following a robust endotoxic stress challenge. Rat adrenal glands and blood plasma were collected following i.v. administration of either an ultradian-sized pulse of ACTH or administration of lipopolysaccharide, as well as under unstressed conditions across the 24-hour period. Plasma ACTH and corticosterone (CORT) were measured and the adrenal glands were processed for measurement of protein by western immunoblotting, RNA by a quantitative reverse transcriptase-polymerase chain reaction and association of CRTC2 and CRTC3 with the Star promoter by chromatin immunoprecipitation. An increase in nuclear localisation of CRTC2 and CRTC3 followed increases in both ultradian and endotoxic stress-induced plasma ACTH, and this was associated with increased CREB phosphorylation and corresponding increases in Star transcription. Both CRTC2 and CRTC3 were shown to associate with the Star promoter, with the dynamics of CRTC3 binding corresponding to that of nuclear changes in protein levels. CRTC isoforms show little variation in ultradian expression or variation across 24 hours, although evidence of long-term down-regulation following endotoxic stress was found. We conclude that co-transcription factors CRTC2 and, more clearly, CRTC3 appear to act alongside phosphorylated CREB in the generation of ultradian pulses of Star transcription, essential for the maintenance of basal StAR expression. Similarly, our findings suggest CRTC2 and CRTC3 mediate Star transcriptional initiation following an endotoxic stressor; however, other transcription factors are likely to be responsible for the long-term up-regulation of adrenal Star transcription.

Dog Steroidogenic Factor-1: Molecular cloning and analysis of epigenetic regulation

Steroidogenic factor 1 (SF-1) is a nuclear receptor that is important in steroid hormone production, and adrenal and gonad development. The SF-1 gene is highly conserved among most vertebrates. However, dog SF-1 registered in public databases, such as CanFam3.1, lacks the 5' end compared to other mammals including mouse, human, bovine, and cat. Whether this defect is due to species differences or database error is unclear. Here, we determined the full-length dog SF-1 cDNA sequence and identified the missing 5' end sequence in the databases. The coding region of the dog SF-1 gene has 1,386 base pairs, and the protein has 461 amino acid residues. Sequence alignment analysis among vertebrates revealed that the 5' end sequence of dog SF-1 cDNA is highly conserved compared to other vertebrates. The genomic position of the first exon was determined, and its promoter region sequence was analyzed. The DNA methylation state at the basal promoter and the expression of dog SF-1 in steroidogenic tissues and non-steroidogenic cells were examined. CpG sites at the basal promoter displayed methylation kinetics inversely correlated with gene expression. The promoter was hypomethylated and hypermethylated in SF-1 expressing and non-SF-1 expressing tissues, respectively. In conclusion, we identified the true full sequence of dog SF-1 cDNA and determined the genome sequence around the first exon. The gene is under the control of epigenetic regulation, such as DNA methylation, at the promoter.

Regulation of the KCNJ5 gene by SF-1 in the adrenal cortex: Complete genomic organization and promoter function

Activating mutations in the KCNJ5 gene are responsible for the significant number of aldosterone-producing adenomas. To elucidate the molecular mechanisms underlying KCNJ5 expression, we characterized the entire human KCNJ5 gene. The gene spanned approximately 29.8 kb and contained three exons and two introns. The strongest expression of KCNJ5 mRNA was observed in the adrenal gland. The promoter region contained a putative binding site for SF-1 at -1782 bp. A construct containing -2444 bp of the promoter region exhibited the strongest promoter activity in adrenal H295R cells, and the introduction of a mutation in the SF-1 binding site almost completely abolished promoter activity. Furthermore, deletion mutation, EMSA, and knockdown analyses revealed that SF-1 bound to this element and was functional. Immunochemistry showed that KCNJ5 was predominantly expressed in the zona glomerulosa, while SF-1 was ubiquitously expressed in the adrenal cortex. These results demonstrated that SF-1 mediates the expression of human KCNJ5 in the adrenal cortex.

Transcriptional Regulation of Ovarian Steroidogenic Genes: Recent Findings Obtained from Stem Cell-Derived Steroidogenic Cells

Ovaries represent one of the primary steroidogenic organs, producing estrogen and progesterone under the regulation of gonadotropins during the estrous cycle. Gonadotropins fluctuate the expression of various steroidogenesis-related genes, such as those encoding steroidogenic enzymes, cholesterol deliverer, and electronic transporter. Steroidogenic factor-1 (SF-1)/adrenal 4-binding protein (Ad4BP)/NR5A1 and liver receptor homolog-1 (LRH-1) play important roles in these phenomena via transcriptional regulation. With the aid of cAMP, SF-1/Ad4BP and LRH-1 can induce the differentiation of stem cells into steroidogenic cells. This model is a useful tool for studying the molecular mechanisms of steroidogenesis. In this article, we will provide insight into the transcriptional regulation of steroidogenesis-related genes in ovaries that are revealed from stem cell-derived steroidogenic cells. Using the cells derived from the model, novel SF-1/Ad4BP- and LRH-1-regulated genes were identified by combined DNA microarray and promoter tiling array analyses. The interaction of SF-1/Ad4BP and LRH-1 with transcriptional regulators in the regulation of ovarian steroidogenesis was also revealed.

Extra-adrenal glucocorticoid synthesis at epithelial barriers

Epithelial barriers play an important role in the exchange of nutrients, gases, and other signals between our body and the outside world. However, they protect it also from invasion by potential pathogens. Defective epithelial barriers and associated overshooting immune responses are the basis of many different inflammatory disorders of the skin, the lung, and the intestinal mucosa. The anti-inflammatory activity of glucocorticoids has been efficiently used for the treatment of these diseases. Interestingly, epithelia in these tissues are also a rich source of endogenous glucocorticoids, suggesting that local glucocorticoid synthesis is part of a tissue-specific regulatory circuit. In this review, we summarize current knowledge about the extra-adrenal glucocorticoid synthesis at the epithelial barriers of the intestine, lung and the skin, and discuss their relevance in the pathogenesis of inflammatory diseases and as therapeutic targets.

Cortisol overproduction results from DNA methylation of CYP11B1 in hypercortisolemia

Adrenocortical hormone excess, due to primary aldosteronism (PA) or hypercortisolemia, causes hypertension and cardiovascular complications. In PA, hypomethylation of aldosterone synthase (CYP11B2) is associated with aldosterone overproduction. However, in hypercortisolemia, the role of DNA methylation of 11β-hydroxylase (CYP11B1), which catalyzes cortisol biosynthesis and is highly homologous to CYP11B2, is unclear. The aims of our study were to determine whether the CYP11B1 expression was regulated through DNA methylation in hypercortisolemia with cortisol-producing adenoma (CPA), and to investigate a possible relationship between DNA methylation and somatic mutations identified in CPA. Methylation analysis showed that the CYP11B1 promoter was significantly less methylated in CPA than in adjacent unaffected adrenal tissue and white blood cells. Furthermore, in CPA with somatic mutations in either the catalytic subunit of protein kinase A (PRKACA) or the guanine nucleotide-binding protein subunit alpha (GNAS) gene, the CYP11B1 promoter was significantly hypomethylated. In addition, DNA methylation reduced CYP11B1 promoter activity using a reporter assay. Our study results suggest that DNA methylation at the CYP11B1 promoter plays a role in the regulation of CYP11B1 expression and cortisol production in CPA, and that somatic mutations associated with CPA reduce DNA methylation at the CYP11B1 promoter.

Oxysterol-related-binding-protein related Protein-2 (ORP2) regulates cortisol biosynthesis and cholesterol homeostasis

Oxysterol binding protein-related protein 2 (ORP2) is a lipid binding protein that has been implicated in various cellular processes, including lipid sensing, cholesterol efflux, and endocytosis. We recently identified ORP2 as a member of a protein complex that regulates glucocorticoid biosynthesis. Herein, we examine the effect of silencing ORP2 on adrenocortical function and show that the ORP2 knockdown cells exhibit reduced amounts of multiple steroid metabolites, including progesterone, 11-deoxycortisol, and cortisol, but have increased concentrations of androgens, and estrogens. Moreover, silencing ORP2 suppresses the expression of most proteins required for cortisol production and reduces the expression of steroidogenic factor 1 (SF1). ORP2 silencing also increases cellular cholesterol, concomitant with decreased amounts of 22-hydroxycholesterol and 7-ketocholesterol, two molecules that have been shown to bind to ORP2. Further, we show that ORP2 binds to liver X receptor (LXR) and is required for nuclear LXR expression. LXR and ORP2 are recruited to the CYP11B1 promoter in response to cAMP signaling. Additionally, ORP2 is required for the expression of other LXR target genes, including ABCA1 and the LDL receptor (LDLR). In summary, we establish a novel role for ORP2 in regulating steroidogenic capacity and cholesterol homeostasis in the adrenal cortex.

Expression of steroidogenic enzymes and their transcription factors in cortisol-producing adrenocortical adenomas: immunohistochemical analysis and quantitative real-time polymerase chain reaction studies

Adrenal Cushing syndrome (CS) is caused by the overproduction of cortisol in adrenocortical tumors including adrenal cortisol-producing adenoma (CPA). In CS, steroidogenic enzymes such as 17α-hydroxylase/17, 20-lase (CYP17A1), 3β-hydroxysteroid dehydrogenase (HSD3B), and 11β-hydroxylase (CYP11B1) are abundantly expressed in tumor cells. In addition, several transcriptional factors have been reported to play pivotal roles in the regulation of these enzymes in CPA, but their correlations with those enzymes above have still remained largely unknown. Therefore, in this study, we examined the status of steroidogenic enzymes and their transcriptional factors in 78 and 15 CPA cases by using immunohistochemistry and quantitative real-time polymerase chain reaction (qPCR), respectively. Immunoreactivity of HSD3B2, CYP11B1, CYP17A1, steroidogenic factor-1 (SF1[NR5A1]), GATA6, and nerve growth factor induced-B (NGFIB[NR4A1]) was detected in tumor cells. Results of qPCR analysis revealed that expression of HSD3B2 mRNA was significantly higher than that of HSD3B1, and CYP11B1 mRNA was significantly higher than CYP11B2. In addition, the expression of CYP11B1 mRNA was positively correlated with those of NR5A1, GATA6, and NR4A1. These results all indicated that HSD3B2 but not HSD3B1 was mainly involved in cortisol overproduction in CPA. In addition, NR5A1, GATA6, and NR4A1 were all considered to play important roles in cortisol overproduction through regulating CYP11B1 gene transcription.

High risk of adrenal toxicity of N1-desoxy quinoxaline 1,4-dioxide derivatives and the protection of oligomeric proanthocyanidins (OPC) in the inhibition of the expression of aldosterone synthetase in H295R cells

Quinoxaline 1,4-dioxide derivatives (QdNOs) with a wide range of biological activities are used in animal husbandry worldwide. It was found that QdNOs significantly inhibited the gene expression of CYP11B1 and CYP11B2, the key aldosterone synthases, and thus reduced aldosterone levels. However, whether the metabolites of QdNOs have potential adrenal toxicity and the role of oxidative stress in the adrenal toxicity of QdNOs remains unclear. The relatively new QdNOs, cyadox (CYA), mequindox (MEQ), quinocetone (QCT) and their metabolites, were selected for elucidation of their toxic mechanisms in H295R cells. Interestingly, the results showed that the main toxic metabolites of QCT, MEQ, and CYA were their N1-desoxy metabolites, which were more harmful than other metabolites and evoked dose and time-dependent cell damage on adrenal cells and inhibited aldosterone production. Gene and protein expression of CYP11B1 and CYP11B2 and mRNA expression of transcription factors, such as NURR1, NGFIB, CREB, SF-1, and ATF-1, were down regulated by N1-desoxy QdNOs. The natural inhibitors of oxidant stress, oligomeric proanthocyanidins (OPC), could upregulate the expression of diverse transcription factors, including CYP11B1 and CYP11B2, and elevated aldosterone levels to reduce adrenal toxicity. This study demonstrated for the first time that N1-desoxy QdNOs have the potential to be the major toxic metabolites in adrenal toxicity, which may shed new light on the adrenal toxicity of these fascinating compounds and help to provide a basic foundation for the formulation of safety controls for animal products and the design of new QdNOs with less harmful effects.

Impact of ACTH Signaling on Transcriptional Regulation of Steroidogenic Genes

The trophic peptide hormone adrenocorticotropic (ACTH) stimulates steroid hormone biosynthesis evoking both a rapid, acute response and a long-term, chronic response, via the activation of cAMP/protein kinase A (PKA) signaling. The acute response is initiated by the mobilization of cholesterol from lipid stores and its delivery to the inner mitochondrial membrane, a process that is mediated by the steroidogenic acute regulatory protein. The chronic response results in the increased coordinated transcription of genes encoding steroidogenic enzymes. ACTH binding to its cognate receptor, melanocortin 2 receptor (MC2R), stimulates adenylyl cyclase, thus inducing cAMP production, PKA activation, and phosphorylation of specific nuclear factors, which bind to target promoters and facilitate coactivator protein recruitment to direct steroidogenic gene transcription. This review provides a general view of the transcriptional control exerted by the ACTH/cAMP system on the expression of genes encoding for steroidogenic enzymes in the adrenal cortex. Special emphasis will be given to the transcription factors required to mediate ACTH-dependent transcription of steroidogenic genes.

Adrenal Mitochondria and Steroidogenesis: From Individual Proteins to Functional Protein Assemblies

The adrenal cortex is critical for physiological function as the central site of glucocorticoid and mineralocorticoid synthesis. It possesses a great degree of specialized compartmentalization at multiple hierarchical levels, ranging from the tissue down to the molecular levels. In this paper, we discuss this functionalization, beginning with the tissue zonation of the adrenal cortex and how this impacts steroidogenic output. We then discuss the cellular biology of steroidogenesis, placing special emphasis on the mitochondria. Mitochondria are classically known as the "powerhouses of the cell" for their central role in respiratory adenosine triphosphate synthesis, and attention is given to mitochondrial electron transport, in both the context of mitochondrial respiration and mitochondrial steroid metabolism. Building on work demonstrating functional assembly of large protein complexes in respiration, we further review research demonstrating a role for multimeric protein complexes in mitochondrial cholesterol transport, steroidogenesis, and mitochondria-endoplasmic reticulum contact. We aim to highlight with this review the shift in steroidogenic cell biology from a focus on the actions of individual proteins in isolation to the actions of protein assemblies working together to execute cellular functions.

Regulation of Steroidogenesis, Development, and Cell Differentiation by Steroidogenic Factor-1 and Liver Receptor Homolog-1

Steroidogenic factor-1 (SF-1) and liver receptor homolog-1 (LRH-1) belong to the nuclear receptor superfamily and are categorized as orphan receptors. In addition to other nuclear receptors, these play roles in various physiological phenomena by regulating the transcription of target genes. Both factors share very similar structures and exhibit common functions. Of these, the roles of SF-1 and LRH-1 in steroidogenesis are the most important, especially that of SF-1, which was originally discovered and named to reflect such roles. SF-1 and LRH-1 are essential for steroid hormone production in gonads and adrenal glands through the regulation of various steroidogenesis-related genes. As SF-1 is also necessary for the development of gonads and adrenal glands, it is also considered a master regulator of steroidogenesis. Recent studies have clearly demonstrated that LRH-1 also represents another master regulator of steroidogenesis, which similarly to SF-1, can induce differentiation of non-steroidogenic stem cells into steroidogenic cells. Here, we review the functions of both factors in these steroidogenesis-related phenomena.

Adrenal steroidogenesis and congenital adrenal hyperplasia

Adrenal steroidogenesis is a dynamic process, reliant on de novo synthesis from cholesterol, under the stimulation of ACTH and other regulators. The syntheses of mineralocorticoids (primarily aldosterone), glucocorticoids (primarily cortisol), and adrenal androgens (primarily dehydroepiandrosterone and its sulfate) occur in separate adrenal cortical zones, each expressing specific enzymes. Congenital adrenal hyperplasia (CAH) encompasses a group of autosomal-recessive enzymatic defects in cortisol biosynthesis. 21-Hydroxylase (21OHD) deficiency accounts for more than 90% of CAH cases and, when milder or nonclassic forms are included, 21OHD is one of the most common genetic diseases.

Transcriptional regulation of human ferredoxin 1 in ovarian granulosa cells

Ferredoxin 1 (FDX1; adrenodoxin) is an iron-sulfur protein that is involved in various metabolic processes, including steroid hormone synthesis in mammalian tissues. We investigated the transcriptional regulation of FDX1 in ovarian granulosa cells. Previously, we reported that the NR5A family, including steroidogenic factor-1 (SF-1) and liver receptor homolog-1 could induce differentiation of human mesenchymal stem cells (hMSCs) into steroidogenic cells. A ChIP assay showed that SF-1 could bind to the FDX1 promoter in differentiated hMSCs. Luciferase reporter assays showed that transcription of FDX1 was synergistically activated by the NR5A family and 8Br-cAMP treatment through two SF-1 binding sites and a CRE-like sequence in a human ovarian granulosa cell line, KGN. Knockdown of FDX1 attenuated progesterone production in KGN cells. These results indicate transcription of FDX1 is regulated by the NR5A family and cAMP signaling, and participates in steroid hormone production in ovarian granulosa cells.

Identification of biologically active PDE11-selective inhibitors using a yeast-based high-throughput screen

The biological roles of cyclic nucleotide phosphodiesterase 11 (PDE11) enzymes are poorly understood, in part due to the lack of selective inhibitors. To address the need for such compounds, we completed an ~200,000 compound high-throughput screen (HTS) for PDE11 inhibitors using a yeast-based growth assay, and identified 4 potent and selective PDE11 inhibitors. One compound, along with two structural analogs, elevates cAMP and cortisol levels in human adrenocortical cells, consistent with gene association studies that link PDE11 activity to adrenal function. As such, these compounds can immediately serve as chemical tools to study PDE11 function in cell culture, and as leads to develop therapeutics for the treatment of adrenal insufficiencies. Our results further validate this yeast-based HTS platform for the discovery of potent, selective, and biologically active PDE inhibitors.

Differential effects of down-regulated steroidogenic factor-1 on basal and angiotensin II-induced aldosterone secretion

Aldosterone synthase (CYP11B2) is responsible for the final step in aldosterone synthesis and is importantly regulated by angiotensin-II (Ang II) through diverse pathways. However, under pathological conditions, such as in hyperaldosteronism, the regulation becomes disordered. The transcription factor steroidogenic factor-1 (SF-1) is important in regulating the endocrine system and is overexpressed in aldosterone-producing adenoma (APA), a common cause of hyperaldosteronism. Overexpression of SF-1 has been extensively studied, but little in-depth information is available regarding the effects of inhibitory SF-1 on CYP11B2 and Ang II. In this paper, we have investigated the roles of down-regulated SF-1 in basal and Ang II-induced CYP11B2 expression using SF-1-specific short hairpin RNA. Inhibitory SF-1 was found to decrease the sensitivity of CYP11B2 and aldosterone to Ang II stimulation, whereas a down-regulation of SF-1 enhanced basal CYP11B2 expression and aldosterone production in H295R cells. Considering these differential effects of SF-1 on aldosterone production, these results might provide a new insight into the understanding of hyperaldosteronism.

Coactivation of SF-1-mediated transcription of steroidogenic enzymes by Ubc9 and PIAS1

Steroidogenic factor-1 (SF-1) is a nuclear orphan receptor, which is essential for adrenal development and regulation of steroidogenic enzyme expression. SF-1 is posttranslationally modified by small ubiquitin-related modifier-1 (SUMO-1), thus mostly resulting in attenuation of transcription. We investigated the role of sumoylation enzymes, Ubc9 and protein inhibitors of activated STAT1 (PIAS1), in SF-1-mediated transcription of steroidogenic enzyme genes in the adrenal cortex. Coimmunoprecipitation assays showed that both Ubc9 and PIAS1 interacted with SF-1. Transient transfection assays in adrenocortical H295R cells showed Ubc9 and PIAS1 potentiated SF-1-mediated transactivation of reporter constructs containing human CYP17, CYP11A1, and CYP11B1 but not CYP11B2 promoters. Reduction of endogenous Ubc9 and PIAS1 by introducing corresponding small interfering RNA significantly reduced endogenous CYP17, CYP11A1, and CYP11B1 mRNA levels, indicating that they normally function as coactivators of SF-1. Wild type and sumoylation-inactive mutants of Ubc9 and PIAS1 can similarly enhance the SF-1-mediated transactivation of the CYP17 gene, indicating that the coactivation potency of Ubc9 and PIAS1 is independent of sumoylation activity. Chromatin immunoprecipitation assays demonstrated that SF-1, Ubc9, and PIAS1 were recruited to an endogenous CYP17 gene promoter in the context of chromatin in vivo. Immunohistochemistry and Western blotting showed that SF-1, Ubc9, and PIAS1 were expressed in the nuclei of the human adrenal cortex. In cortisol-producing adenomas, the expression pattern of SF-1 and Ubc9 were markedly increased, whereas that of PIAS1 was decreased compared with adjacent normal adrenals. These results showed the physiological roles of Ubc9 and PIAS1 as SF-1 coactivators beyond sumoylation enzymes in adrenocortical steroidogenesis and suggested their possible pathophysiological roles in human cortisol-producing adenomas.

PPARγ co-activator-1α co-activates steroidogenic factor 1 to stimulate the synthesis of luteinizing hormone and aldosterone

The orphan nuclear receptor SF-1 (steroidogenic factor 1) is highly expressed in the pituitary, gonad and adrenal glands and plays key roles at all levels of the hypothalamic-pituitary-steroidogenic tissue axis. In the present study, we show that PGC-1α [PPARγ (peroxisome-proliferator-activated receptor γ) co-activator 1α] interacts with and co-activates SF-1 to induce LHβ (luteinizing hormone β) and αGSU (α-glycoprotein subunit) gene expression, subsequently leading to the increased secretion of LH in pituitary gonadotrope-derived αT3-1 cells. PGC-1α co-activation of LHβ expression requires an SF-1-binding element [GSE (gonadotrope-specific element)] mapped to the promoter region of LHβ. Mammalian two-hybrid and co-immunoprecipitation assays, as well as GST (glutathione transferase) pull-down experiments demonstrated that PGC-1α interacts with SF-1 in vivo and in vitro. Additionally, PGC-1α stimulates the expression of Cyp11b2 (aldosterone synthase gene), Cyp11b1 (steroid 11β-hydroxylase gene) and P450scc (cholesterol side-chain cleavage enzyme), and the synthesis of aldosterone in adrenal-cortex-derived Y-1 cells. Chromatin immunoprecipitation assays confirmed that endogenous PGC-1α co-localizes with SF-1 in the LHβ and Cyp11b2 promoter region. Knockdown of endogenous SF-1 by siRNA (small interfering RNA) abolished the PGC-1α induction of LHβ and Cyp11b2 gene expression in αT3-1 and Y-1 cells respectively. Finally, we demonstrated that PGC-1α induces SF-1 gene expression in both αT3-1 and Y-1 cells. Taken together, our findings reveal the potential role of PGC-1α and suggest that it may play important roles in steroidogenesis, gonad development and sex differentiation through SF-1.

Stirring up new ideas about the regulation of the hypothalamic-pituitary-interrenal axis in zebrafish (Danio rerio)

The dynamic relationships between the changes in cortisol synthesis during and after a stressor and the expression pattern of the key genes that regulate the different levels of the hypothalamic-pituitary-interrenal (HPI) stress axis are poorly understood. This study established a novel vortex stressor and characterized its impact at all levels of the HPI axis in adult zebrafish. Exposure to a moderate vortex speed for 60 min was associated with a marked 18-fold increase in whole-body cortisol after 10 min followed by a gradual return to basal values 30 min poststress. The changes in whole-body cortisol were paralleled by increases in the expression of preoptic area corticotropin-releasing factor, pituitary prohormone convertase 1, and interrenal melanocortin 2 receptor, steroid acute regulatory protein, 11β-hydroxylase and 11β-hydroxysteroid dehydrogenase 2. The response to the vortex stressor also included delayed increases in preoptic area urotensin I and pituitary pro-opiomelanocortin mRNA levels but no change in the expression of other putative HPI axis regulators. Notably, the expression of several genes was depressed below control values 30 min poststress. These findings suggest that multiple genes at all levels of the HPI axis play an active role in the stimulation and termination of the cortisol stress response in zebrafish.

Regulation of aldosterone synthase by activator transcription factor/cAMP response element-binding protein family members

Aldosterone synthesis is regulated by angiotensin II (Ang II) and K(+) acting in the adrenal zona glomerulosa, in part through the regulation of aldosterone synthase (CYP11B2). Here, we analyzed the role of cAMP response element (CRE)-binding proteins (CREBs) in the regulation of CYP11B2. Expression analysis of activator transcription factor (ATF)/CREB family members, namely the ATF1 and ATF2, the CREB, and the CRE modulator, in H295R cells and normal human adrenal tissue was performed using quantitative real-time PCR. Ang II-induced phosphorylation of ATF/CREB members was analyzed by Western blot analysis, and their subsequent binding to the CYP11B2 promoter using chromatin immunoprecipitation assay. Aldosterone production and CYP11B2 expression were measured in small interfering RNA-transfected cells to knockdown the expression of ATF/CREB members. CYP11B2 promoter activity was measured in H295R cells cotransfected with NURR1 (NR4A2) alone or with constitutively active vectors for ATF/CREB members. Ang II induced phosphorylation of ATF1, ATF2, and CRE modulator in a time-dependent manner. Based on chromatin immunoprecipitation analysis, there was an increased association of these proteins with the CYP11B2 promoter after Ang II and K(+) treatment. Phosphorylated ATF/CREB members also bound the CYP11B2 promoter. Knockdown of ATF/CREB members reduced Ang II and K(+) induction of adrenal cell CYP11B2 mRNA expression and aldosterone production. The constitutively active ATF/CREB vectors increased the promoter activity of CYP11B2 and had a synergistic effect with NURR1. In summary, these results suggest that ATF/CREB and NGFI-B family members play a crucial role in the transcriptional regulation of CYP11B2 and adrenal cell capacity to produce aldosterone.

Regulation of aldosterone and cortisol production by the transcriptional repressor neuron restrictive silencer factor

Aldosterone synthase (CYP11B2) and 11 beta-hydroxylase (CYP11B1) regulate aldosterone and cortisol production, respectively. The expression of these enzymes is promoted by calcium influx through Cav3.2, a T-type calcium channel. Neuron-restrictive silencer factor (NRSF) binds to neuron-restrictive silencer element (NRSE) to suppress the transcription of NRSE-containing genes. We found a NRSE-like sequence in human CYP11B2 and CYP11B1 genes as well as the CACNA1H gene of many mammalian species. The CACNA1H gene encodes the alpha-subunit of Cav3.2. Here we investigated how NRSF/NRSE regulates aldosterone and cortisol synthesis. Inhibition of endogenous NRSF by an adenovirus-expressing dominant-negative NRSF (AD/dnNRSF) increased human CYP11B2 and CYP11B1 mRNA expression, leading to aldosterone and cortisol secretion in human adrenocortical (H295R) cells. In reporter gene experiments, NRSE suppressed luciferase reporters driven by CYP11B2 and CYP11B1 promoters and dnNRSF enhanced them. Moreover, cotransfection of dnNRSF increased luciferase activity of reporter genes after deletion or mutation of NRSE, suggesting that NRSF/NRSE regulates transcription of CYP11B2 and CYP11B1 genes indirectly. AD/dnNRSF augmented mRNA expression of rat CYP11B2 and CYP11B1 genes, neither of which contains a NRSE-like sequence in rat adrenal cells. AD/dnNRSE also significantly increased CACNA1H mRNA in H295R and rat adrenal cells. Efonidipine, a T/L-type calcium channel blocker, significantly suppressed dnNRSF-mediated up-regulation of CYP11B2 and CYP11B1 expression. Moreover, NRSF/NRSE is also involved in angiotensin II- and K(+)-stimulated augmentation of CYP11B2 and CYP11B1 gene transcription. In conclusion, NRSF/NRSE controls aldosterone and cortisol synthesis by regulating CYP11B2 and CYP11B1 gene transcription mainly through NRSF/NRSE-mediated enhancement of the CACNA1H gene.

Role of angiotensin II-induced rapid response genes in the regulation of enzymes needed for aldosterone synthesis

Aldosterone is principally synthesized in the zona glomerulosa of the adrenal by a series of enzymatic reactions leading to the conversion of cholesterol to aldosterone. Angiotensin II (Ang II) is the major physiological regulator of aldosterone production acting acutely to stimulate aldosterone biosynthesis and chronically to increase the capacity of the adrenals to produce aldosterone. We previously defined eight transcription factors that are rapidly induced following Ang II treatment using three in vitro adrenocortical cell models. Herein, we investigated the function of these transcription factors in the regulation of the enzymes needed for aldosterone production. H295R adrenal cells were co-transfected with expression vectors for each transcription factor and promoter/reporter constructs prepared for genes encoding the enzymes needed for aldosterone production. NGFI-B family members induced promoter activity of 3-beta-hydroxysteroid-dehydrogenase type 2 (HSD3B2), 21-hydroxylase (CYP21A2), and aldosterone synthase (CYP11B2). The importance of NGFI-B in the regulation of CYP11B2 was also demonstrated by reduced CYP11B2 transcription in the presence of a dominant-negative-NGFI-B. A pharmacological approach was used to characterize the Ang II pathways regulating transcription of NGFI-B family genes. Transcription of NGFI-B members were decreased following inhibition of Ang II type 1 receptor (AT1R), protein kinase C (PKC), calcium/calmodulin-dependent kinases (CaMK), and Src tyrosine kinase (SRC). Taken together, these results suggest that Ang II binding to the AT1R increases activity of PKC, CaMK, and SRC, which act to increase expression of the family of NGFI-B genes as well as CYP11B2. Ang II induction of the NGFI-B family members represents an important pathway to increase the capacity of adrenal cells to produce aldosterone.

Differential effects of high and low steroidogenic factor-1 expression on CYP11B2 expression and aldosterone production in adrenocortical cells

Steroidogenic factor-1 (SF-1/Ad4BP/NR5A1) plays a major role in regulating steroidogenic enzymes. We have previously shown that SF-1 inhibits aldosterone synthase (CYP11B2) reporter gene activity. Herein, we used the H295R/TR/SF-1 adrenal cells that increase SF-1 in a doxycycline-dependent fashion. Cells were incubated with or without doxycycline to induce SF-1 and then treated with angiotensin II (Ang II). Aldosterone was measured by immunoassay. SF-1 mRNA was silenced by small interfering RNA (siRNA) by Nucleofector technology. mRNA levels were measured by real-time RT-PCR. Ang II treatment without doxycycline increased aldosterone production by 11.3-fold and CYP11B2 mRNA by 116-fold. Doxycycline treatment increased SF-1 mRNA levels by 3.7-fold and inhibited Ang II-induced aldosterone by 84%. Doxycycline treatment inhibited Ang II-stimulated CYP11B2 mRNA levels by 86%. Doxycycline decreased basal CYP11B2 promoter activity by 68%. Doxycycline inhibited Ang II stimulation by 85%. Ang II increased CYP21 mRNA expression by 4.6-fold, whereas doxycycline inhibited induction by 69%. In contrast, doxycycline treatment increased CYP11B1 mRNA by 1.7-fold in basal cells and increased Ang II induction by 3.6-fold. SF-1-specific siRNA significantly reduced SF-1 mRNA expression as compared with cells treated with control siRNA. SF-1 siRNA reversed doxycycline stimulation of CYP B1 and its inhibition of CYP11B2. However, in H295R/TR/SF-1 cells without doxycycline treatment, both CYP11B1 and CYP11B2 mRNAs were significantly decreased, suggesting that both enzymes require a minimal level of SF-1 for basal expression. In summary, SF-1 overexpression dramatically inhibited CYP11B2 expression and decreased aldosterone production. The opposing effects of SF-1 on CYP11B1 and CYP11B2 suggest that the regulation of SF-1 activity may play a role that determines the relative ability to produce mineralocorticoid and glucocorticoid.

Cyp11b1 is induced in the murine gonad by luteinizing hormone/human chorionic gonadotropin and involved in the production of 11-ketotestosterone, a major fish androgen: conservation and evolution of the androgen metabolic pathway

We have shown previously that Cyp11b1, an 11beta-hydroxylase responsible for glucocorticoid biosynthesis in the adrenal gland, was induced by cAMP in androgen-producing Leydig-like cells derived from mesenchymal stem cells. We found that Cyp11b1 was induced in male Leydig cells, or female theca cells, when human chorionic gonadotropin was administered in immature mice. Expression of Cyp11b1 in rodent gonads caused the production of 11-ketotestosterone (11-KT), a major fish androgen, which induces male differentiation or spermatogenesis in fish. As in teleosts, plasma concentrations of 11-KT were elevated in human chorionic gonadotropin-treated mice. In contrast to teleosts, however, plasma concentrations of 11-KT were similar in both sexes, despite levels of testosterone, a precursor substrate, being about 20 times higher in male mice. Because expression of 11beta-hydroxysteroid dehydrogenase type 2, was much higher in the mouse ovary than in the testis, conversion of testosterone into 11-KT may occur more efficiently in the ovary. In a luciferase reporter system that was responsive to and activated by androgens, 11-KT efficiently activated mammalian androgen receptor-mediated transactivation. Our results suggest that the androgen metabolic pathway is conserved between teleosts and mammals, despite sexual dominance and reproductive functions of 11-KT being altered during evolution.

Binding of steroidogenic factor-1 to the regulatory region might not be critical for transcriptional regulation of the human CYP1B1 gene

Cytochrome P450 (CYP) 1B1, which catalyzes 17beta-estradiol 4-hydroxylation, is expressed in steroid-related tissues including ovary, testis, and adrenal gland. Generally, the expressions of steroidogenic CYPs are transcriptionally regulated by steroidogenic factor-1 (SF-1) and cAMP response element (CRE) binding protein (CREB). In the present study, we examined the possibility that the human CYP1B1 gene might be regulated by SF-1 and CREB. Gel shift analyses revealed that in vitro translated SF-1 can bind to the putative SF-1 binding sites, SF-1a (at -1722) and SF-1b (at -2474), on the CYP1B1 gene. In vitro translated CREB barely binds to the putative SF-1 binding sites. Luciferase analysis revealed that a reporter plasmid, pGL3 (-2623/+25), containing the SF-1a and SF-1b elements is transactivated by the concomitant co-expression of SF-1 and protein kinase A (PKA). However, the transcriptional activity is induced by PKA alone. Mutations in the SF-1a and SF-1b elements did not affect the luciferase activity. Thus, the binding of SF-1 to the putative SF-1 binding sites of the human CYP1B1 gene might not be essential for transcriptional regulation. Interestingly, deletion and mutation analyses indicated that the PKA signaling pathway is involved in the xenobiotic responsive element (XRE)-mediated transactivation of the human CYP1B1 gene.

Transcriptional regulation of adrenocortical steroidogenic gene expression

By serving as ligands for nuclear and plasma membrane receptors, steroid hormones are key regulators of a diverse array of physiological processes. These hormones are synthesized from cholesterol in tissues such as the adrenal cortex, ovaries, testes, and placenta. Because steroid hormones control the expression of numerous genes, steroidogenic cells utilize multiple mechanisms that ensure tight control of the synthesis of these molecules. This review will give an overview of the molecular mechanisms by which the expression of steroidogenic genes is regulated in the human adrenal cortex.

Increased steroidogenic factor-1 dosage triggers adrenocortical cell proliferation and cancer

Steroidogenic factor-1 (SF-1/Ad4BP; NR5A1), a nuclear receptor transcription factor, has a pivotal role in adrenal and gonadal development in humans and mice. A frequent feature of childhood adrenocortical tumors is SF-1 amplification and overexpression. Here we show that an increased SF-1 dosage can by itself augment human adrenocortical cell proliferation through concerted actions on the cell cycle and apoptosis. This effect is dependent on an intact SF-1 transcriptional activity. Gene expression profiling showed that an increased SF-1 dosage regulates transcripts involved in steroid metabolism, the cell cycle, apoptosis, and cell adhesion to the extracellular matrix. Consistent with these results, increased SF-1 levels selectively modulate the steroid secretion profile of adrenocortical cells, reducing cortisol and aldosterone production and maintaining dehydroepiandrosterone sulfate secretion. As a model to understand the mechanisms of transcriptional regulation by increased SF-1 dosage, we studied FATE1, coding for a cancer-testis antigen implicated in the control of cell proliferation. Increased SF-1 levels increase its binding to a consensus site in FATE1 promoter and stimulate its activity through modulation of the recruitment of specific cofactors. On the other hand, sphingosine, which can compete with phospholipids for binding to SF-1, had no effect on the SF-1 dosage-dependent increase of adrenocortical cell proliferation and expression of the FATE1 promoter. In mice, increased Sf-1 dosage produces adrenocortical hyperplasia and formation of tumors expressing gonadal markers (Amh, Gata-4), which originate from the subcapsular region of the adrenal cortex. Gene expression profiling revealed that genes involved in cell adhesion and the immune response and transcription factor signal transducer and activator of transcription-3 (Stat3) are differentially expressed in Sf-1 transgenic mouse adrenals compared with wild-type adrenals. Our studies reveal a critical role for SF-1 dosage in adrenocortical tumorigenesis and constitute a rationale for the development of drugs targeting SF-1 transcriptional activity for adrenocortical tumor therapy.

Dephosphorylation of TORC initiates expression of the StAR gene

Cyclic AMP responsive element (CRE) binding protein (CREB) is known to activate transcription when its Ser133 is phosphorylated. However, transducer of regulated CREB activity (TORC), a CREB specific co-activator, upregulates CREB activity in a phospho-Ser133-independent manner. Interestingly, TORC is also regulated by phosphorylation; the phospho-form is inactive, and the dephospho-form active. When PKA phosphorylates CREB, it inhibits TORC kinases simultaneously and accelerates dephosphorylation of TORC. We show in this report that staurosporine, a kinase inhibitor, induces the expression of the StAR gene in Y1 adrenocortical cells, possibly a result of an increase in the population of dephospho-TORC. The expression of the StAR gene is known to be regulated by SF-1 and CREB, and the co-activators CBP/p300 may mediate the actions of both factors. Our experiments using KG501, a disruptor of the interaction between phospho-CREB and CBP/p300, also support the importance of TORC in the regulation of StAR gene expression.

Cyclic AMP stimulates SF-1-dependent CYP11A1 expression through homeodomain-interacting protein kinase 3-mediated Jun N-terminal kinase and c-Jun phosphorylation

Steroids are synthesized in adrenal glands and gonads under the control of pituitary peptides. These peptides bind to cell surface receptors to activate the cyclic AMP (cAMP) signaling pathway leading to an increase of steroidogenic gene expression. Exactly how cAMP activates steroidogenic gene expression is not clear, except for the knowledge that transcription factor SF-1 plays a key role. Investigating the factors participating in SF-1 action, we found that c-Jun and homeodomain-interacting protein kinase 3 (HIPK3) were required for basal and cAMP-stimulated expression of one major steroidogenic gene, CYP11A1. HIPK3 enhanced SF-1 activity, and c-Jun was required for the functional interaction of HIPK3 with SF-1. Furthermore, after cAMP stimulation, both c-Jun and Jun N-terminal kinase (JNK) were phosphorylated through HIPK3. These phosphorylations were important for SF-1 activity and CYP11A1 expression. Thus, we have defined HIPK3-mediated JNK activity and c-Jun phosphorylation as important events that increase SF-1 activity for CYP11A1 transcription in response to cAMP. This finding has linked three common factors, HIPK3, JNK, and c-Jun, to the cAMP signaling pathway leading to increased steroidogenic gene expression.

The nuclear receptor LRH-1 critically regulates extra-adrenal glucocorticoid synthesis in the intestine

The nuclear receptor liver receptor homologue-1 (LRH-1, NR5A2) is a crucial transcriptional regulator of many metabolic pathways. In addition, LRH-1 is expressed in intestinal crypt cells where it regulates the epithelial cell renewal and contributes to tumorigenesis through the induction of cell cycle proteins. We have recently identified the intestinal epithelium as an important extra-adrenal source of immunoregulatory glucocorticoids. We show here that LRH-1 promotes the expression of the steroidogenic enzymes and the synthesis of corticosterone in murine intestinal epithelial cells in vitro. Interestingly, LRH-1 is also essential for intestinal glucocorticoid synthesis in vivo, as LRH-1 haplo-insufficiency strongly reduces the intestinal expression of steroidogenic enzymes and glucocorticoid synthesis upon immunological stress. These results demonstrate for the first time a novel role for LRH-1 in the regulation of intestinal glucocorticoid synthesis and propose LRH-1 as an important regulator of intestinal tissue integrity and immune homeostasis.

Transcriptional regulation of dehydroepiandrosterone sulfotransferase (SULT2A1) by estrogen-related receptor alpha

The estrogen-related receptors (ERRalpha, -beta, and -gamma) are a subfamily of orphan nuclear receptors (designated NR3B1, NR3B2, and NR3B3) that are structurally and functionally related to estrogen receptors alpha and beta. Herein we test the hypothesis that ERRalpha regulates transcription of the genes encoding the enzymes involved in adrenal steroid production. Real-time RT-PCR was first used to determine the levels of ERRalpha mRNA in various human tissues. Adult adrenal levels of ERRalpha transcript were similar to that seen in heart, which is known to highly express ERRalpha. Expression of ERRalpha in the adult adrenal was then confirmed using Western blotting and immunohistochemistry. To examine the effects of ERRalpha on steroidogenic capacity we used reporter constructs with the 5'-flanking regions of steroidogenic acute regulatory protein (StAR), cholesterol side-chain cleavage (CYP11A), 3beta-hydroxysteroid dehydrogenase type II (HSD3B2), 17alpha-hydroxylase/17,20-lyase (CYP17), and dehydroepiandrosterone sulfotransferase (SULT2A1). Cotransfection of these reporter constructs with wild-type ERRalpha or VP16-ERRalpha expression vectors demonstrated ERRalpha enhanced reporter activity driven by flanking DNA from CYP17 and SULT2A1. SULT2A1 promoter activity was most responsive to the ERRalpha and VP16-ERRalpha, increasing activity 2.6- and 79.5-fold, respectively. ERRalpha effects on SULT2A1 were greater than the stimulation seen in response to steroidogenic factor 1 (SF1). Transfection of serial deletions of the 5'-flanking DNA of the SULT2A1 gene and EMSA experiments indicated the presence of three functional regulatory cis-elements which shared sequence similarity to binding sites for SF1. Taken together, the expression of ERRalpha in the adrenal and its regulation of SULT2A1 suggest an important role for this orphan receptor in the regulation of adrenal steroid production.

The orphan nuclear receptor, liver receptor homolog-1, regulates cholesterol side-chain cleavage cytochrome p450 enzyme in human granulosa cells

After ovulation, there is a shift in ovarian steroidogenesis from an estrogen-producing ovarian follicle to a progesterone-producing corpus luteum. The first step in human ovarian steroidogenesis is catalyzed by cholesterol side-chain cleavage cytochrome P450 (CYP11A1) enzyme. Steroidogenic factor-1 is an orphan nuclear receptor that regulates several steroidogenic enzymes, including CYP11A1. Liver receptor homolog-1 (LRH-1) is another orphan nuclear receptor that is expressed in the human ovary. After ovulation there is a down-regulation in steroidogenic factor-1, which is associated with an up-regulation of LRH-1 expression. These changes coincide with increased level of CYP11A1 expression in human corpus luteum. In this study, we examined the role of LRH-1 in the regulation of human granulosa cell CYP11A1 expression. Cotransfection of human granulosa cell tumor cells with CYP11A1 promoter and LRH-1 expression vector resulted in a significant increase in CYP11A1 expression. Deletion analysis revealed two putative LRH-1 binding sites at -1580 and -40, which was confirmed by EMSA. Dosage-sensitive sex-reversal-adrenal hypoplasia congenita critical region on the X chromosome, gene-1 inhibited LRH-1 stimulated CYP11A1 expression, and that was not overcome by the presence of PKA agonist. We conclude that CYP11A1 expression in human granulosa cells is regulated by LRH-1. We propose that LRH-1 could be the major transcription factor for the post-ovulatory surge in human ovarian steroidogenesis.

Steroid Sulfotransferase 2A1 Gene Transcription Is Regulated by Steroidogenic Factor 1 and GATA-6 in the Human Adrenal

Sulfonation is a phase II conjugation reaction responsible for the biotransformation of many compounds including steroids, bile acids, and drugs. Humans are presently known to express at least five cytosolic sulfotransferase (SULT) enzymes, of which only two are hydroxysteroid SULT, SULT2A1, commonly known as steroid sulfotransferase, and the cholesterol sulfotransferase SULT2B1. SULT2A1 is highly expressed in the adrenal where it is responsible for the sulfation of hydroxysteroids including conversion of dehydroepiandrosterone to dehydroepiandrosterone sulfate and in the liver where it is responsible for sulfation of bile acids and circulating hydroxysteroids. Little is known concerning the transcriptional regulation of human SULT2A1 in adrenal. Herein we demonstrate the role of two transcription factors, steroidogenic factor 1 (SF1) and GATA-6, in the regulation of SULT2A1 transcription. These transcription factors were quantified by real-time RT-PCR in normal human adrenal tissue. Transient transfection assays with deleted and mutated SULT2A1 promoter constructs allowed for the determination of specific SF1 and GATA binding cis-regulatory elements necessary for transactivation of SULT2A1 promoter, and binding was confirmed by EMSA analysis. Both SF1 and GATA-6 were positive regulators of SULT2A1 promoter constructs. These data support the hypothesis that adrenal SULT2A1 expression is regulated by SF1 and GATA-6.

Novel action of activin and bone morphogenetic protein in regulating aldosterone production by human adrenocortical cells

We have uncovered a functional bone morphogenetic protein (BMP) and activin system complete with ligands (BMP-6 and activin betaA/betaB), receptors (activin receptor-like kinase receptors 2, 3, and 4; activin type-II receptor; and BMP type-II receptor), and the binding protein follistatin in the human adrenocortical cell line H295R. Administration of activin and BMP-6 to cultures of H295R cells caused concentration-responsive increases in aldosterone production. The mRNA levels of steroidogenic acute regulatory protein or P450 steroid side-chain cleavage enzyme, the rate-limiting steps of adrenocortical steroidogenesis, were enhanced by activin and BMP-6. Activin and BMP-6 also activated the transcription of steroidogenic acute regulatory protein as well as the late-step steriodogenic enzyme CYP11B2. Activin enhanced ACTH-, forskolin-, or dibutyryl-cAMP- but not angiotensin II (Ang II)-induced aldosterone production, whereas BMP-6 specifically augmented Ang II-induced aldosterone production. Activin and ACTH but not BMP-6 increased cAMP production. Follistatin, which inhibits activin actions by binding, suppressed basal and ACTH-induced aldosterone secretion but failed to affect the Ang II-induced aldosterone level. Furthermore, MAPK signaling appeared to be involved in aldosterone production induced by Ang II and BMP-6 because an inhibitor of MAPK activation, U0126, reduced the level of aldosterone synthesis stimulated by Ang II and BMP-6 but not activin. In addition, Ang II reduced the expression levels of BMP-6 but increased that of activin betaB, whereas ACTH had no effect on these levels. Collectively, the present data suggest that activin acts to regulate adrenal aldosterone synthesis predominantly by modulating the ACTH-cAMP-protein kinase A signaling cascade, whereas BMP-6 works primarily by modulating the Ang II-MAPK cascade in human adrenal cortex in an autocrine/paracrine fashion.

The Orphan Nuclear Receptors NURR1 and NGFIB Regulate Adrenal Aldosterone Production

Aldosterone biosynthesis in the zona glomerulosa of the adrenal cortex is regulated by transcription of CYP11B2 (encoding aldosterone synthase). The effects of nerve growth factor-induced clone B (NGFIB) (NR4A1), Nur-related factor 1 (NURR1) (NR4A2), and steroidogenic factor-1 (SF-1) (NR5A1) on transcription of human CYP11B2 (hCYP11B2) and hCYP11B1 (11β-hydroxylase) were compared in human H295R adrenocortical cells. hCYP11B2 expression was increased by NGFIB and NURR1. Although hCYP11B1 was activated by SF-1, cotransfection with SF-1 inhibited activation of hCYP11B2 by NGFIB and NURR1. NGFIB and NURR1 transcript and protein levels were strongly induced by angiotensin (Ang) II, the major regulator of hCYP11B2 expression in vivo. Sequential deletion and mutagenesis of the hCYP11B2 promoter identified two functional NGFIB response elements (NBREs), one located at −766/−759 (NBRE-1) and the previously studied Ad5 element at −129/−114. EMSAs suggested that both elements bound NGFIB and NURR1. In human adrenals, NURR1 immunoreactivity was preferentially localized in the zona glomerulosa and to a lesser degree in the zona fasciculata, whereas NGFIB was detected in both zones. The calmodulin kinase inhibitor KN93 partially blocked K+-stimulated transcription of NGFIB and NURR1. KN93 partially inhibited the effect of Ang II on NURR1 mRNA levels but did not modify the effect on expression of NGFIB. Mutation of the NBRE-1, Ad5, and Ad1/cAMP response element (CRE) cis-elements reduced both basal and Ang II-induced levels of hCYP11B2, demonstrating that all three elements are important for maximal transcriptional activity. Our results suggest that NGFIB and NURR1 are key regulators of hCYP11B2 expression and may partially mediate the regulation of hCYP11B2 by Ang II.

The role of the orphan nuclear receptor, liver receptor homologue-1, in the regulation of human corpus luteum 3beta-hydroxysteroid dehydrogenase type II

After ovulation, ovarian 3beta-hydroxysteroid dehydrogenase type II (HSD3B2) expression increases to enhance the shift of steroidogenesis toward progesterone biosynthesis. Steroidogenic factor-1 (SF-1) is a transcription factor for several genes encoding steroidogenic enzymes. However, the level of SF-1 expression decreases in the human corpus luteum (CL) after ovulation. Liver receptor homolog-1 (LRH-1) is another member of the orphan nuclear receptor family. We hypothesize that LRH-1, rather than SF-1, plays an essential role in the regulation of corpus luteum steroidogenesis. Semiquantitative RT-PCR and real-time PCR were performed to quantify the level of LRH-1 expression and correlate with HSD3B2 level. Cell transfection, mutation analysis, and EMSA were performed to examine the role of LRH-1 in the regulation of HSD3B2. LRH-1 expression was higher in CL, compared with mature ovarian follicles. Cotransfection of granulosa cells with HSD3B2 and LRH-1 resulted in a 10-fold increase of transcription. DAX-1 inhibited LRH-1-stimulated HSD3B2, which was maintained in the presence of dibutyryl cAMP. Mutation of the either of the two putative LRH-1 binding sites, which were confirmed by EMSA, in the HSD3B2 promoter decreased LRH-1 stimulation. Our findings suggest that LRH-1 is highly expressed in CL, and it plays an essential role in the regulation of HSD3B2.

SF-1 a key player in the development and differentiation of steroidogenic tissues

Since its discovery in the early 1990s, the orphan nuclear receptor SF-1 has been attributed a central role in the development and differentiation of steroidogenic tissues. SF-1 controls the expression of all the steroidogenic enzymes and cholesterol transporters required for steroidogenesis as well as the expression of steroidogenesis-stimulating hormones and their cognate receptors. SF-1 is also an essential regulator of genes involved in the sex determination cascade. The study of SF-1 null mice and of human mutants has been of great value to demonstrate the essential role of this factor in vivo, although the complete adrenal and gonadal agenesis in knock-out animals has impeded studies of its function as a transcriptional regulator. In particular, the role of SF-1 in the hormonal responsiveness of steroidogenic genes promoters is still a subject of debate. This extensive review takes into account recent data obtained from SF-1 haploinsufficient mice, pituitary-specific knock-outs and from transgenic mice experiments carried out with SF-1 target gene promoters. It also summarizes the pros and cons regarding the presumed role of SF-1 in cAMP signalling.

Cell selective cAMP induction of rat CYP1B1 in adrenal and testis cells. Identification of a novel cAMP-responsive far upstream enhancer and a second Ah receptor-dependent mechanism

CYP1B1 is unique among P450 cytochromes in exhibiting inductive responses mediated by both the Ah receptor (AhR) and cAMP. cAMP induction was mediated either by a 189bp far upstream enhancer region (FUER, -5110 to -5298) or by a 230bp AhR-responsive enhancer region (AhER) (-797 to -1026). CYP1B1 luciferase reporters respond selectively to cAMP and TCDD in adrenal Y-1 cells (only cAMP), testis MA10 cells (cAMP>TCDD), and C3H10T1/2 mouse embryo fibroblasts (only TCDD). In Y-1 cells, which lack AhR, cAMP induction is totally dependent on the FUER, including absolute requirements for upstream and downstream halves of this region, and for CREB activity at a CRE sequence located at the 3(')-end. cAMP stimulation of the FUER was remarkably high (27-fold) and equally effective when linked to an HSV-TK promoter, indicating direct cAMP activation of the FUER. Binding of CREB to the essential CRE was demonstrated along with dominant negative effects of functionally impaired mutants. cAMP induction in MA10 cells was partially mediated by the FUER mechanism but was regulated additionally by AhER through AhR activity. MA10 cells also exhibit cAMP-dependent AhR down-regulation and AhR/Arnt complex formation. Mutations in AhER including XRE5 were similarly inhibitory to cAMP stimulation in MA10 cells and to TCDD stimulation in C3H10T1/2 cells. Transfection of AhR into the AhR-deficient Y-1 cells did not introduce this second mechanism, which indicated a need for additional components that are present in MA10 cells.

Transcription factor 3',5'-cyclic adenosine 5'-monophosphate-responsive element-binding protein (CREB) is decreased during human adrenal cortex tumorigenesis and fetal development

Various cellular and molecular alterations of the cAMP pathway have been observed in adrenal Cushing syndrome. We recently reported the loss of cAMP-responsive element-binding protein (CREB) expression in the adrenocortical cancer cell line H295R. CREB is the major nuclear target of the cAMP pathway. This study therefore aimed to analyze the status of the CREB protein in various types of human adrenocortical tumors and normal fetal adrenal cortex. CREB protein status was studied by Western blotting in adrenocortical adenomas (AAs, n = 27) and adrenocortical carcinomas (ACs, n = 24). A decrease of CREB protein was noticed in the majority of the adrenocortical tumors. The dramatic decrease in CREB protein levels was more pronounced in ACs than in AAs. Levels of the phosphorylated form of CREB were also low in adrenocortical tumors, with a greater decrease in ACs than in AAs. EMSAs also showed decreases in the amounts of CREB- containing complexes in nuclear extracts from adrenocortical tumors. The secretory status of adenomas was strongly correlated with CREB levels, significantly lower in nonfunctioning AAs (n = 9) than in functioning AAs (n = 9). CREB levels, determined by Western blotting and immunohistochemistry, were very low in the fetal zone of human fetal adrenal cortex, whereas they were normal in the definitive zone. In tumors, adrenocortical cells in several zones were weakly immunohistochemically stained for CREB, whereas CREB was uniformly detected in nonendocrine cell nuclei (e.g. vascular cells, fibroblasts). These results suggest that the absence of CREB may be linked to the development of a highly aggressive tumor with a dedifferentiated benign (nonfunctioning AA) or malignant (AC) phenotype. These findings highlight the similarities between the normal human fetal adrenal gland and adrenal cancers previously observed in terms of parallelism in IGF-II production.

ACTH modulation of transcription factors responsible for steroid hydroxylase gene expression in the adrenal cortex

Steroid hormone biosynthesis in the adrenal cortex and gonads involves the coordinated transcription of the genes encoding the steroid hydroxylases, 3beta-hydroxysteroid dehydrogenase (3betaHSD), the steroidogenic acute regulatory protein (StAR), and adrenodoxin (Adx). Transcriptional regulation of steroidogenic genes is multifactorial, entailing developmental, tissue-specific, constitutive, and cAMP-dependent mechanisms. Optimal steroidogenic capacity is achieved by the actions of ACTH which exerts transcriptional pressure on all steroidogenic genes. The actions of ACTH in the adrenal cortex have been studied in great detail and is mediated by cAMP and protein kinase A (PKA) via two temporally distinct pathways. The acute response leads to mobilization of cholesterol, the initial substrate for all steroidogenic pathways, from cellular stores to the inner mitochondrial membrane where cholesterol sidechain cleavage cytochrome P450 (P45011A1) resides. The slower, chronic response of ACTH in the adrenal cortex directs transcription of the genes encoding the steroidogenic enzymes. Although steroidogenic gene transcription in response to ACTH is cAMP-dependent, the consensus cAMP response pathway (CRE/CREB) is not involved. Instead, each steroidogenic gene utilizes unique cAMP-responsive sequences (CRS) found in the promoters of each gene, which bind a diverse array of transcription factors. Moreover, once specific transcription factors are bound to the promoters of the steroidogenic genes, increased gene expression requires posttranslational modification (phosphorylation/dephosphorylation) of the transcription factors and binding of coactivator proteins. This review provides a general view (with emphasis on the human) of the important factors involved in regulating steroidogenic gene expression and ultimately steroid hormone biosynthesis.

12-lipoxygenase pathway increases aldosterone production, 3',5'-cyclic adenosine monophosphate response element-binding protein phosphorylation, and p38 mitogen-activated protein kinase activation in H295R human adrenocortical cells

Evidence suggests that the 12-lipoxygenase (LO) pathway mediates angiotensin II (Ang II)-induced aldosterone synthesis in adrenal glomerulosa cells. To study the mechanisms of 12-LO pathway on aldosterone synthesis, the human adrenocortical cell line, H295R, was transiently transfected with a mouse leukocyte type of 12-LO. Overexpression of 12-LO stimulated aldosterone production 2.7-fold as well as the reporter gene activity of CYP11B2 gene-encoding human aldosterone synthase by 5-fold over that in mock-transfected cells. Ang II further enhanced aldosterone production, which could be blocked by a 12-LO inhibitor, baicalein, in mock cells and cells overexpressing 12-LO. Ang II stimulated cAMP response element-binding protein (CREB) phosphorylation in a dose- and time-dependent fashion in parent H295R cells. Overexpression of 12-LO increased phosphorylation of CREB/activating transcription factor (ATF)-1 1.5-fold over that in mock cells under basal conditions. Ang II led to a further 5.2- and 7.5-fold increase in mock cells and 12-LO cells, respectively. Overexpression of 12-LO induced p38 MAPK activation. The 12-LO product, 12-hydroxyeicosatetraenoic acid, increased phosphorylation of CREB/ATF-1 3.6-fold and phosphorylation of p38 MAPK 8-fold over basal. The p38 MAPK inhibitor SB203580 inhibited Ang II- and 12-LO pathway-induced phosphorylated CREB/ATF-1, suggesting a role of p38 MAPK in Ang II and 12-LO pathway signaling. These results suggest that 12-LO stimulation leads to aldosterone production in H295R cells in part through activation of CREB/ATF-1 and p38 MAPK pathway.

Role of the PKA-regulated transcription factor CREB in development and tumorigenesis of endocrine tissues

The cAMP pathway plays a major role in the development of endocrine tissues and various molecular defects of key components of this pathway (G protein, receptors, PKA, etc.) have been observed in endocrine tumors. The ubiquitous transcription factor CREB (cAMP-response element binding protein) binds to the cAMP response element (CRE) and stimulates transcription after phosphorylation on Ser(133) by PKA. The CREB family of transcription factors contains three members: CREB, CREM, and ATF-1. Targeted expression of dominant-negative mutants of CREB in transgenic mice leads to somatotrophs or thyroid hypoplasia. GH-secreting adenomas are benign secreting tumors expressing an activated mutant G alpha s protein (Gsp) in about 40% of cases. In GH-secreting adenomas CREB is always expressed and often highly phosphorylated. The CREM isoform ICER is stimulated by cAMP, and its expression is increased in Gsp-harboring tumors. After transfection in pituitary somatotroph cells, activating mutations of Gs protein (Gsp) and overexpression of wild-type G alpha S stimulate transcription of various CRE-containing promoters via CREB in a Ser(133)-specific-dependent manner. Activation of the cAMP pathway by ACTH is required for adrenal cortex (AdCx) maintenance and steroidogenesis. CREB is expressed in normal AdCx. Alterations of CRE binding proteins with loss of CREB expression and compensatory overexpression of CREMtau is observed in the human adrenocortical cancer cell line H295R. Similar alterations are found at the protein level in human malignant adrenocortical tumors. In conclusion, the CREB family of transcription factors plays an important role in the development, differentiation, and proliferation of endocrine tissues. Various alterations of the CREB family of transcription factors can be observed in endocrine tumors.