Synergistic activation of the inhibin alpha-promoter by steroidogenic factor-1 and cyclic adenosine 3',5'-monophosphate

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.

Extracellular Signal-regulated Kinase (ERK)-dependent Phosphorylation of Y-Box-binding Protein 1 (YB-1) Enhances Gene Expression in Granulosa Cells in Response to Follicle-stimulating Hormone (FSH)

Within the ovarian follicle, immature oocytes are surrounded and supported by granulosa cells (GCs). Stimulation of GCs by FSH leads to their proliferation and differentiation, events that are necessary for fertility. FSH activates multiple signaling pathways to regulate genes necessary for follicular maturation. Herein, we investigated the role of Y-box-binding protein-1 (YB-1) within GCs. YB-1 is a nucleic acid binding protein that regulates transcription and translation. Our results show that FSH promotes an increase in the phosphorylation of YB-1 on Ser(102) within 15 min that is maintained at significantly increased levels until ∼8 h post treatment. FSH-stimulated phosphorylation of YB-1(Ser(102)) is prevented by pretreatment of GCs with the PKA-selective inhibitor PKA inhibitor (PKI), the MEK inhibitor PD98059, or the ribosomal S6 kinase-2 (RSK-2) inhibitor BI-D1870. Thus, phosphorylation of YB-1 on Ser(102) is PKA-, ERK-, and RSK-2-dependent. However, pretreatment of GCs with the protein phosphatase 1 (PP1) inhibitor tautomycin increased phosphorylation of YB-1(Ser(102)) in the absence of FSH; FSH did not further increase YB-1(Ser(102)) phosphorylation. This result suggests that the major effect of RSK-2 is to inhibit PP1 rather than to directly phosphorylate YB-1 on Ser(102) YB-1 coimmunoprecipitated with PP1β catalytic subunit and RSK-2. Transduction of GCs with the dephospho-adenoviral-YB-1(S102A) mutant prevented the induction by FSH of Egfr, Cyp19a1, Inha, Lhcgr, Cyp11a1, Hsd17b1, and Pappa mRNAs and estradiol-17β production. Collectively, our results reveal that phosphorylation of YB-1 on Ser(102) via the ERK/RSK-2 signaling pathway is necessary for FSH-mediated expression of target genes required for maturation of follicles to a preovulatory phenotype.

Insulin Receptor Substrate 1, the Hub Linking Follicle-stimulating Hormone to Phosphatidylinositol 3-Kinase Activation

The ubiquitous phosphatidylinositol 3-kinase (PI3K) signaling pathway regulates many cellular functions. However, the mechanism by which G protein-coupled receptors (GPCRs) signal to activate PI3K is poorly understood. We have used ovarian granulosa cells as a model to investigate this pathway, based on evidence that the GPCR agonist follicle-stimulating hormone (FSH) promotes the protein kinase A (PKA)-dependent phosphorylation of insulin receptor substrate 1 (IRS1) on tyrosine residues that activate PI3K. We report that in the absence of FSH, granulosa cells secrete a subthreshold concentration of insulin-like growth factor-1 (IGF-1) that primes the IGF-1 receptor (IGF-1R) but fails to promote tyrosine phosphorylation of IRS1. FSH via PKA acts to sensitize IRS1 to the tyrosine kinase activity of the IGF-1R by activating protein phosphatase 1 (PP1) to promote dephosphorylation of inhibitory Ser/Thr residues on IRS1, including Ser(789). Knockdown of PP1β blocks the ability of FSH to activate PI3K in the presence of endogenous IGF-1. Activation of PI3K thus requires both PKA-mediated relief of IRS1 inhibition and IGF-1R-dependent tyrosine phosphorylation of IRS1. Treatment with FSH and increasing concentrations of exogenous IGF-1 triggers synergistic IRS1 tyrosine phosphorylation at PI3K-activating residues that persists downstream through protein kinase B (AKT) and FOXO1 (forkhead box protein O1) to drive synergistic expression of genes that underlies follicle maturation. Based on the ability of GPCR agonists to synergize with IGFs to enhance gene expression in other cell types, PP1 activation to relieve IRS1 inhibition may be a more general mechanism by which GPCRs act with the IGF-1R to activate PI3K/AKT.

Steroidogenic factor 1 promotes aggressive growth of castration-resistant prostate cancer cells by stimulating steroid synthesis and cell proliferation

The dependence of prostate cancer on androgens provides a targeted means of treating advanced disease. Unfortunately, androgen deprivation therapies eventually become ineffective, leading to deadly castration-resistant prostate cancer (CRPC). One of many factors implicated in the transition to CRPC is the onset of de novo steroidogenesis. Although reactivation of steroid receptors likely plays a pivotal role in aggressive CRPC, little is understood regarding the mechanisms whereby prostate cancer cells initiate and maintain steroidogenesis. We hypothesize that steroidogenic factor 1 (SF1, NR5A1, AD4BP), a key regulator of steroidogenesis in normal endocrine tissues, is expressed in CRPC where it stimulates aberrant steroidogenesis and fuels aggressive growth. Notably, SF1 is not expressed in normal prostate tissue. Our results indicated that SF1 was absent in benign cells but present in aggressive prostate cancer cell lines. Introduction of ectopic SF1 expression in benign human prostate epithelial cells (BPH-1) stimulated increased steroidogenic enzyme expression, steroid synthesis, and cell proliferation. In contrast, data from an aggressive human prostate cancer cell line (BCaPT10) demonstrated that SF1 was required for steroid-mediated cell growth because BCaPT10 cell growth was diminished by abiraterone treatment and short hairpin RNA-mediated knockdown of SF1 (shSF1). SF1-depleted cells also exhibited defective centrosome homeostasis. Finally, whereas xenograft experiments in castrated hosts with BCaPT10 control transplants grew large, invasive tumors, BCaPT10-shSF1 knockdown transplants failed to grow. Therefore, we conclude that SF1 stimulates steroid accumulation and controls centrosome homeostasis to mediate aggressive prostate cancer cell growth within a castrate environment. These findings present a new molecular mechanism and therapeutic target for deadly CRPC.

Novel NR5A1 missense mutation in premature ovarian failure: detection in han chinese indicates causation in different ethnic groups

Background

The etiology of most premature ovarian failure (POF) cases is usually elusive. Although genetic causes clearly exist and a likely susceptible region of 8q22.3 has been discovered, no predominant explanation exists for POF. More recently, evidences have indicated that mutations in NR5A1 gene could be causative for POF. We therefore screened for mutations in the NR5A1 gene in a large cohort of Chinese women with non-syndromic POF.

Methods

Mutation screening of NR5A1 gene was performed in 400 Han Chinese women with well-defined 46,XX idiopathic non-syndromic POF and 400 controls. Subsequently, functional characterization of the novel mutation identified was evaluated in vitro.

Results

A novel heterozygous missense mutation [c.13T>G (p.Tyr5Asp)] in NR5A1 was identified in 1 of 384 patients (0.26%). This mutation impaired transcriptional activation on Amh, Inhibin-a, Cyp11a1 and Cyp19a1 gene, as shown by transactivation assays. However, no dominant negative effect was observed, nor was there impact on protein expression and nuclear localization.

Conclusions

This novel mutation p.Tyr5Asp, in a novel non-domain region, is presumed to result in haploinsufficiency. Irrespectively, perturbation in NR5A1 is not a common explanation for POF in Chinese.

Lhcgr Expression in Granulosa Cells: Roles for PKA-Phosphorylated β-Catenin, TCF3, and FOXO1

Ovarian follicles lacking FSH or FSH receptors fail to progress to a preovulatory stage, resulting in infertility. One hallmark of the preovulatory follicle is the presence of luteinizing hormone/choriogonadotropin receptors (LHCGR) on granulosa cells (GCs). However, the mechanisms by which FSH induces Lhcgr gene expression are poorly understood. Our results show that protein kinase A (PKA) and phosphoinositide 3-kinase (PI3K)/AKT pathways are required for FSH to activate both the murine Lhcgr-luciferase reporter and expression of Lhcgr mRNA in rat GCs. Based on results showing that an adenovirus (Ad) expressing a steroidogenic factor 1 (SF1) mutant that cannot bind β-catenin abolished FSH-induced Lhcgr mRNA, we evaluated the role of β-catenin in the regulation of Lhcgr gene expression. FSH promoted the PKA-dependent, PI3K-independent phosphorylation of β-catenin on Ser552 and Ser665. FSH activated the β-catenin/T-cell factor (TCF) artificial promoter-reporter TOPFlash via a PKA-dependent, PI3K-independent pathway, and dominant-negative (DN) TCF abolished FSH-activated Lhcgr-luciferase reporter and induction of Lhcgr mRNA. Microarray analysis of GCs treated with Ad-DN-TCF and FSH identified the Lhcgr as the most down-regulated gene. Chromatin immunoprecipitation results placed β-catenin phosphorylated on Ser552 and Ser675 and SF1 on the Lhcgr promoter in FSH-treated GCs; TCF3 was constitutively associated with the Lhcgr promoter. Transduction with an Ad-phospho-β-catenin mutant (Ser552/665/Asp) enhanced Lhcgr mRNA expression in FSH-treated cells greater than 3-fold. Finally, we identified a recognized PI3K/AKT target, forkhead box O1, as a negative regulator of Lhcgr mRNA expression. These results provide new understanding of the complex regulation of Lhcgr gene expression in GCs.

Expression of Wnt and TGF-β pathway components and key adrenal transcription factors in adrenocortical tumors: association to carcinoma aggressiveness

Factors controlling benign and malignant adrenocortical tumorigenesis are largely unknown, but several mouse models suggest an important role for inhibin-alpha (INHA). To show that findings in the mouse are relevant to human tumors and clinical outcome, we investigated the expression of signaling proteins and transcription factors involved in the regulation of INHA in human tumor samples⋅ Thirty-one adrenocortical tumor samples, including 13 adrenocortical carcinomas (ACCs), were categorized according to Weiss score, hormonal profile, and patient survival data and analyzed using immunohistochemistry and RT-PCR. Expression of the TGF-β signaling mediator SMAD3 varied inversely with Weiss score, so that SMAD3 expression was lowest in the most malignant tumors. By contrast, SMAD2 expression was upregulated in most malignant tumors. Wnt pathway co-receptors LRP5 and LRP6 were predominantly expressed in benign adrenocortical tumors. In ACCs, expression of transcription factors GATA-6 and SF-1 correlated with that of their target gene INHA. Moreover, the diminished expression of GATA-6 and SF-1 in ACCs correlated with poor outcome. We conclude that the factors driving INHA expression are reduced in ACCs with poor outcome, implicating a role for INHA as a tumor suppressor in humans.

cAMP-stimulated transcription of DGKθ requires steroidogenic factor 1 and sterol regulatory element binding protein 1

Diacylglycerol kinase (DGK)θ is a lipid kinase that phosphorylates diacylglycerol to form phosphatidic acid (PA). We have previously shown that PA is a ligand for the nuclear receptor steroidogenic factor 1 (SF1) and that cAMP-stimulated expression of SF1 target genes requires DGKθ. In this study, we sought to investigate the role of cAMP signaling in regulating DGKθ gene expression. Real time RT-PCR and Western blot analysis revealed that dibutyryl cAMP (Bt2cAMP) increased the mRNA and protein expression, respectively, of DGKθ in H295R human adrenocortical cells. SF1 and sterol regulatory element binding protein 1 (SREBP1) increased the transcriptional activity of a reporter plasmid containing 1.5 kb of the DGKθ promoter fused to the luciferase gene. Mutation of putative cAMP responsive sequences abolished SF1- and SREBP-dependent DGKθ reporter gene activation. Consistent with this finding, chromatin immunoprecipitation assay demonstrated that Bt2cAMP signaling increased the recruitment of SF1 and SREBP1 to the DGKθ promoter. Coimmunoprecipitation assay revealed that SF1 and SREBP1 interact, suggesting that the two transcription factors form a complex on the DGKθ promoter. Finally, silencing SF1 and SREBP1 abolished cAMP-stimulated DGKθ expression. Taken together, we demonstrate that SF1 and SREBP1 activate DGKθ transcription in a cAMP-dependent manner in human adrenocortical cells.

Scavenger receptors mediate the role of SUMO and Ftz-f1 in Drosophila steroidogenesis

SUMOylation participates in ecdysteroid biosynthesis at the onset of metamorphosis in Drosophila melanogaster. Silencing the Drosophila SUMO homologue smt3 in the prothoracic gland leads to reduced lipid content, low ecdysone titers, and a block in the larval–pupal transition. Here we show that the SR-BI family of Scavenger Receptors mediates SUMO functions. Reduced levels of Snmp1 compromise lipid uptake in the prothoracic gland. In addition, overexpression of Snmp1 is able to recover lipid droplet levels in the smt3 knockdown prothoracic gland cells. Snmp1 expression depends on Ftz-f1 (an NR5A-type orphan nuclear receptor), the expression of which, in turn, depends on SUMO. Furthermore, we show by in vitro and in vivo experiments that Ftz-f1 is SUMOylated. RNAi–mediated knockdown of ftz-f1 phenocopies that of smt3 at the larval to pupal transition, thus Ftz-f1 is an interesting candidate to mediate some of the functions of SUMO at the onset of metamorphosis. Additionally, we demonstrate that the role of SUMOylation, Ftz-f1, and the Scavenger Receptors in lipid capture and mobilization is conserved in other steroidogenic tissues such as the follicle cells of the ovary. smt3 knockdown, as well as ftz-f1 or Scavenger knockdown, depleted the lipid content of the follicle cells, which could be rescued by Snmp1 overexpression. Therefore, our data provide new insights into the regulation of metamorphosis via lipid homeostasis, showing that Drosophila Smt3, Ftz-f1, and SR-BIs are part of a general mechanism for uptake of lipids such as cholesterol, required during development in steroidogenic tissues.

Steroid hormones are cholesterol derivates that control many aspects of animal physiology, including development of the adult organisms, growth, energy storage, and reproduction. In insects, pulses of the steroid hormone ecdysone precede molting and metamorphosis, the regulation of hormonal synthesis being a crucial step that determines animal viability and size. Reduced levels of the small ubiquitin-like modifier SUMO in the prothoracic gland block the synthesis of ecdysone, as SUMO is needed for cholesterol intake. Here we show that SUMO is required for the expression of Scavenger Receptors (Class B, type I). These membrane receptors are necessary for lipid uptake by the gland. Strikingly, their expression is sufficient to recover lipid content when SUMO is removed. The expression of the Scavenger Receptors depends on Ftz-f1, a nuclear transcription factor homologous to mammalian Steroidogenic factor 1 (SF-1). Interestingly, the expression of Ftz-f1 also depends on SUMO and, in addition, Ftz-f1 is SUMOylated. This modification modulates its capacity to activate the Scavenger Receptor Snmp1. The role of SUMO, Scavenger Receptors, and Ftz-f1 on lipid intake is conserved in other tissues that synthesize steroid hormones, such as the ovaries. These factors are conserved in vertebrates, with mutations underlying human disease, so this mechanism to regulate lipid uptake could have implications for human health.

Expression of inhibin-alpha is regulated synergistically by Wilms' tumor gene 1 (Wt1) and steroidogenic factor-1 (Sf1) in sertoli cells

Wt1 encodes a zinc finger nuclear transcriptional factor, which is specifically expressed in testicular Sertoli cells and knockdown of Wt1 in Sertoli cells causes male mice subfertility. However, the underlying mechanism is still unclear. In this study, we found that expression of inhibin-α is significantly reduced in Wt1-deficient Sertoli cells. Luciferase assays using the inhibin-α promoter indicated that the inhibin-α promoter is transactivated by the Wt1 A, and B isoforms (−KTS), but not the C, and D isoforms (+KTS). Analysis of the Wt1 responsive element of the inhibin-α promoter region using site-directed mutagenesis showed that the nucleotides between −58 and −49 are essential for Wt1-dependent transactivation of the inhibin-α promoter. ChIP assays indicated that Wt1 directly interacts with the inhibin-α promoter. In addition, the inhibin-α promoter is activated synergistically by Wt1 and Sf1. Mutation of the ligand binding domain (LBD) of Sf1 (residues 235–238) completely abolished the synergistic action between Wt1 and Sf1, but did not affect the physical interaction between these two proteins, suggesting that other factor(s) may also be involved in the regulation of inhibin-α in Sertoli cells. Further studies demonstrated that β-catenin enhances the synergistic activation of Wt1 and Sf1 on the inhibin-α promoter. Given the fact that inhibin-α, a subunit of inhibin, is known to be involved in the regulation of spermatogenesis and testicular steroidogenesis, this study reveals a new regulatory mechanism of inhibin-α in Sertoli cells and also sheds light on the physiological functions of Wt1 in gonad development and spermatogenesis.

Mechanism of CREB recognition and coactivation by the CREB-regulated transcriptional coactivator CRTC2

Basic leucine zipper (bZip) transcription factors regulate cellular gene expression in response to a variety of extracellular signals and nutrient cues. Although the bZip domain is widely known to play significant roles in DNA binding and dimerization, recent studies point to an additional role for this motif in the recruitment of the transcriptional apparatus. For example, the cAMP response element binding protein (CREB)-regulated transcriptional coactivator (CRTC) family of transcriptional coactivators has been proposed to promote the expression of calcium and cAMP responsive genes, by binding to the CREB bZip in response to extracellular signals. Here we show that the CREB-binding domain (CBD) of CRTC2 folds into a single isolated 28-residue helix that seems to be critical for its interaction with the CREB bZip. The interaction is of micromolar affinity on palindromic and variant half-site cAMP response elements (CREs). The CBD and CREB assemble on the CRE with 2:2:1 stoichiometry, consistent with the presence of one CRTC binding site on each CREB monomer. Indeed, the CBD helix and the solvent-exposed residues in the dimeric CREB bZip coiled-coil form an extended protein-protein interface. Because mutation of relevant bZip residues in this interface disrupts the CRTC interaction without affecting DNA binding, our results illustrate that distinct DNA binding and transactivation functions are encoded within the structural constraints of a canonical bZip domain.

DNA methylation and histone modifications are associated with repression of the inhibin α promoter in the rat corpus luteum

The transition from follicle to corpus luteum after ovulation is associated with profound morphological and functional changes and is accompanied by corresponding changes in gene expression. The gene encoding the α subunit of the dimeric reproductive hormone inhibin is maximally expressed in the granulosa cells of the preovulatory follicle, is rapidly repressed by the ovulatory LH surge, and is expressed at only very low levels in the corpus luteum. Although previous studies have identified transient repressors of inhibin α gene transcription, little is known about how this repression is maintained in the corpus luteum. This study examines the role of epigenetic changes, including DNA methylation and histone modification, in silencing of inhibin α gene expression. Bisulfite sequencing reveals that methylation of the inhibin α proximal promoter is low in preovulatory and ovulatory follicles but is elevated in the corpus luteum. Increased methylation during luteinization is observed within the cAMP response element in the promoter, and EMSA demonstrate that methylation of this site inhibits cAMP response element binding protein binding in vitro. Chromatin immunoprecipitation reveals that repressive histone marks H3K9 and H3K27 trimethylation are increased on the inhibin α promoter in primary luteal cells, whereas the activation mark H3K4 trimethylation is decreased. The changes in histone modification precede the alterations in DNA methylation, suggesting that they facilitate the recruitment of DNA methyltransferases. We show that the DNA methyltransferase DNMT3a is present in the ovary and in luteal cells when the inhibin α promoter becomes methylated and observe recruitment of DNMT3a to the inhibin promoter during luteinization.

The LIM domain protein FHL2 interacts with the NR5A family of nuclear receptors and CREB to activate the inhibin-α subunit gene in ovarian granulosa cells

Nuclear receptor transcriptional activity is enhanced by interaction with coactivators. The highly related nuclear receptor 5A (NR5A) subfamily members liver receptor homolog 1 and steroidogenic factor 1 bind to and activate several of the same genes, many of which are important for reproductive function. To better understand transcriptional activation by these nuclear receptors, we sought to identify interacting proteins that might function as coactivators. The LIM domain protein four and a half LIM domain 2 (FHL2) was identified as interacting with the NR5A receptors in a yeast two-hybrid screen of a human ovary cDNA library. FHL2, and the closely related FHL1, are both expressed in the rodent ovary and in granulosa cells. Small interfering RNA-mediated knockdown of FHL1 and FHL2 in primary mouse granulosa cells reduced expression of the NR5A target genes encoding inhibin-α and P450scc. In vitro assays confirmed the interaction between the FHL and NR5A proteins and revealed that a single LIM domain of FHL2 is sufficient for this interaction, whereas determinants in both the ligand binding domain and DNA binding domain of NR5A proteins are important. FHL2 enhances the ability of both liver receptor homolog 1 and steroidogenic factor 1 to activate the inhibin-α subunit gene promoter in granulosa cells and thus functions as a transcriptional coactivator. FHL2 also interacts with cAMP response element-binding protein and substantially augments activation of inhibin gene expression by the combination of NR5A receptors and forskolin, suggesting that FHL2 may facilitate integration of these two signals. Collectively these results identify FHL2 as a novel coactivator of NR5A nuclear receptors in ovarian granulosa cells and suggest its involvement in regulating target genes important for mammalian reproduction.

Mechanisms underlying the tissue-specific and regulated activity of the Gnrhr promoter in mammals

The GnRH receptor (GnRHR) plays a central role in the development and maintenance of reproductive function in mammals. Following stimulation by GnRH originating from the hypothalamus, GnRHR triggers multiple signaling events that ultimately stimulate the synthesis and the periodic release of the gonadotropins, luteinizing-stimulating hormone (LH) and follicle-stimulating hormones (FSH) which, in turn, regulate gonadal functions including steroidogenesis and gametogenesis. The concentration of GnRHR at the cell surface is essential for the amplitude and the specificity of gonadotrope responsiveness. The number of GnRHR is submitted to strong regulatory control during pituitary development, estrous cycle, pregnancy, lactation, or after gonadectomy. These modulations take place, at least in part, at the transcriptional level. To analyze this facet of the reproductive function, the 5' regulatory sequences of the gene encoding the GnRHR have been isolated and characterized through in vitro and in vivo approaches. This review summarizes results obtained with the mouse, rat, human, and ovine promoters either by transient transfection assays or by means of transgenic mice.

Steroidogenic factor-1 (SF-1)-driven differentiation of murine embryonic stem (ES) cells into a gonadal lineage

Steroidogenic factor 1 (SF-1) is essential for the development and function of steroidogenic tissues. Stable incorporation of SF-1 into embryonic stem cells (SF-1-ES cells) has been shown to prime the cells for steroidogenesis. When provided with exogenous cholesterol substrate, and after treatment with retinoic acid and cAMP, SF-1-ES cells produce progesterone but do not produce other steroids such as cortisol, estradiol, or testosterone. In this study, we explored culture conditions that optimize SF-1-mediated differentiation of ES cells into defined steroidogenic lineages. When embryoid body formation was used to facilitate cell lineage differentiation, SF-1-ES cells were found to be restricted in their differentiation, with fewer cells entering neuronal pathways and a larger fraction entering the steroidogenic lineage. Among the differentiation protocols tested, leukemia inhibitory factor (LIF) removal, followed by prolonged cAMP treatment was most efficacious for inducing steroidogenesis in SF-1-ES cells. In this protocol, a subset of SF-1-ES cells survives after LIF withdrawal, undergoes morphologic differentiation, and recovers proliferative capacity. These cells are characterized by induction of steroidogenic enzyme genes, use of de novo cholesterol, and production of multiple steroids including estradiol and testosterone. Microarray studies identified additional pathways associated with SF-1 mediated differentiation. Using biotinylated SF-1 in chromatin immunoprecipitation assays, SF-1 was shown to bind directly to multiple target genes, with induction of binding to some targets after steroidogenic treatment. These studies indicate that SF-1 expression, followed by LIF removal and treatment with cAMP drives ES cells into a steroidogenic pathway characteristic of gonadal steroid-producing cells.

StarD7 gene expression in trophoblast cells: contribution of SF-1 and Wnt-beta-catenin signaling

Steroidogenic acute regulatory protein-related lipid transfer domain containing 7 (StarD7) is a poorly characterized member of the steroidogenic acute regulatory protein-related lipid transfer proteins, up-regulated in JEG-3 cells, involved in intracellular transport and metabolism of lipids. Previous studies dealing with the mechanisms underlying the human StarD7 gene expression led us to define the cis-acting regulatory sequences in the StarD7 promoter using as a model JEG-3 cells. These include a functional T cell-specific transcription factor 4 (TCF4) site involved in Wnt-β-catenin signaling. To understand these mechanisms in more depth, we examined the steroidogenic factor 1 (SF-1) contribution to StarD7 expression. Cotransfection experiments in JEG-3 cells point out that the StarD7 promoter is activated by SF-1, and this effect is increased by forskolin. EMSA using JEG-3 nuclear proteins demonstrated that SF-1 binds to the StarD7 promoter. Additionally, chromatin immunoprecipitation analysis indicated that SF-1 and β-catenin are bound in vivo to the StarD7 promoter. Reporter gene assays in combination with mutations in the SF-1 and TCF4 binding sites revealed that the StarD7 promoter is synergistically activated by SF-1 and β-catenin and that the TCF4 binding site (-614/-608) plays an important role in this activation. SF-1 amino acid mutations involved in the physical interaction with β-catenin abolished this activation; thus demonstrating that the contact between the two proteins is necessary for an efficient StarD7 transcriptional induction. Finally, these data suggest that β-catenin could function as a bridge between SF-1 and TCF4 forming a ternary complex, which would stimulate StarD7 expression. The SF-1 and β-catenin pathway convergence on StarD7 expression may have important implications in the phospholipid uptake and transport, contributing to the normal trophoblast development.

Cushing's syndrome and fetal features resurgence in adrenal cortex-specific Prkar1a knockout mice

Carney complex (CNC) is an inherited neoplasia syndrome with endocrine overactivity. Its most frequent endocrine manifestation is primary pigmented nodular adrenocortical disease (PPNAD), a bilateral adrenocortical hyperplasia causing pituitary-independent Cushing's syndrome. Inactivating mutations in PRKAR1A, a gene encoding the type 1 α-regulatory subunit (R1α) of the cAMP–dependent protein kinase (PKA) have been found in 80% of CNC patients with Cushing's syndrome. To demonstrate the implication of R1α loss in the initiation and development of PPNAD, we generated mice lacking Prkar1a specifically in the adrenal cortex (AdKO). AdKO mice develop pituitary-independent Cushing's syndrome with increased PKA activity. This leads to autonomous steroidogenic genes expression and deregulated adreno-cortical cells differentiation, increased proliferation and resistance to apoptosis. Unexpectedly, R1α loss results in improper maintenance and centrifugal expansion of cortisol-producing fetal adrenocortical cells with concomitant regression of adult cortex. Our data provide the first in vivo evidence that loss of R1α is sufficient to induce autonomous adrenal hyper-activity and bilateral hyperplasia, both observed in human PPNAD. Furthermore, this model demonstrates that deregulated PKA activity favors the emergence of a new cell population potentially arising from the fetal adrenal, giving new insight into the mechanisms leading to PPNAD.

Carney complex is a rare familial disease characterized by a predisposition to develop multiple endocrine tumors and highly morbid syndromes due to endocrine overactivities. Its most frequent endocrine manifestation, hypersecretion of glucocorticoids i.e. Cushing's syndrome, is caused by micronodular adrenal gland hyperplasia, an unusual neoplasia which combines both hyperplastic and atrophic areas. Inactivating mutations of the gene encoding the regulatory subunit 1α (R1α) of the cAMP–dependent protein kinase were frequently found in these patients, but the causal link between loss of R1α and onset of this adrenal disorder had not yet been established. Here, we describe the first mouse model mimicking this disease and provide mechanistic insights into endocrine overactivity and neoplastic transformation. Indeed, we show that lack of R1α induces autonomous expression of genes involved in steroid biosynthesis and resurgence of hyperplastic fetal-like cells with concomitant defects in cell renewal of the adult cortex. Our data therefore represent a substantial conceptual advance on the cellular dynamics involved in adrenal gland homeostasis. They suggest that regression of fetal structures may be important to establish normal endocrine functions and to allow cell renewal in the definitive cortex. Failure to clear out cells of fetal features in R1α-deficient adrenals leads to morbid hyperplasia.

Minireview: steroidogenic factor 1: its roles in differentiation, development, and disease

The orphan nuclear receptor steroidogenic factor 1 (SF-1, also called Ad4BP, encoded by the NR5A1 gene) is an essential regulator of endocrine development and function. Initially identified as a tissue-specific transcriptional regulator of cytochrome P450 steroid hydroxylases, studies of both global and tissue-specific knockout mice have demonstrated that SF-1 is required for the development of the adrenal glands, gonads, and ventromedial hypothalamus and for the proper functioning of pituitary gonadotropes. Many genes are transcriptionally regulated by SF-1, and many proteins, in turn, interact with SF-1 and modulate its activity. Whereas mice with heterozygous mutations that disrupt SF-1 function have only subtle abnormalities, humans with heterozygous SF-1 mutations can present with XY sex reversal (i.e. testicular failure), ovarian failure, and occasionally adrenal insufficiency; dysregulation of SF-1 has been linked to diseases such as endometriosis and adrenocortical carcinoma. The current state of knowledge of this important transcription factor will be reviewed with a particular emphasis on the pioneering work on SF-1 by the late Keith Parker.

In search of adrenocortical stem and progenitor cells

Scientists have long hypothesized the existence of tissue-specific (somatic) stem cells and have searched for their location in different organs. The theory that adrenocortical organ homeostasis is maintained by undifferentiated stem or progenitor cells can be traced back nearly a century. Similar to other organ systems, it is widely believed that these rare cells of the adrenal cortex remain relatively undifferentiated and quiescent until needed to replenish the organ, at which time they undergo proliferation and terminal differentiation. Historical studies examining cell cycle activation by label retention assays and regenerative potential by organ transplantation experiments suggested that the adrenocortical progenitors reside in the outer periphery of the adrenal gland. Over the past decade, the Hammer laboratory, building on this hypothesis and these observations, has endeavored to understand the mechanisms of adrenocortical development and organ maintenance. In this review, we summarize the current knowledge of adrenal organogenesis. We present evidence for the existence and location of adrenocortical stem/progenitor cells and their potential contribution to adrenocortical carcinomas. Data described herein come primarily from studies conducted in the Hammer laboratory with incorporation of important related studies from other investigators. Together, the work provides a framework for the emerging somatic stem cell field as it relates to the adrenal gland.

Impaired follicle development and infertility in female mice lacking steroidogenic factor 1 in ovarian granulosa cells

The nuclear receptor steroidogenic factor 1 (SF-1 [officially designated NR5A1]) is essential for fetal gonadal development, but its roles in postnatal ovarian function are less well defined. Herein, we have extended our analyses of knockout (KO) mice with markedly decreased SF-1 expression in granulosa cells. As described, these SF-1 KO mice had hypoplastic ovaries that contained a decreased number of follicles and lacked corpora lutea. In the present study, we showed that SF-1 KO mice exhibited abnormal estrous cycles, were infertile, and released significantly fewer oocytes in response to a standard superovulation regimen. Moreover, they had blunted induction of plasma estradiol in response to gonadotropins. The granulosa cell-specific SF-1 KO also significantly affected ovarian expression of putative SF-1 target genes. Consistent with their decreased follicle number, these mice had reduced ovarian expression of anti-müllerian hormone (Amh), which correlates with the reserve pool of ovarian follicles, as well as decreased gonadotropin-induced ovarian expression of aromatase (Cyp19a1) and cyclin D2 (Ccnd2). In contrast, perhaps because of their abnormal cyclicity, SF-1 KO ovaries had higher basal expression of inhibin-alpha. They also had decreased immunoreactivity for genes related to proliferation (Ccnd2 and Mki67 [also known as Ki67]) and increased expression of Cdkn1b, also known as p27, which inhibits cyclin-dependent kinases, arguing for a role of SF-1 in granulosa cell proliferation. These findings demonstrate that SF-1 has a key role in female reproduction via essential actions in granulosa cells.

The structures that underlie normal reproductive function

The mechanisms and physiology of reproductive function have fascinated scientists throughout time. Recent cellular and molecular level structural studies have provided unprecedented insights into reproductive systems and signaling networks. This 'cutting edge' editorial provides a recent example in each of these areas, namely, the anatomical integrity of the follicle, the molecular structure of activin with its binding partners and the molecular regulation of inhibin. These three examples of structure informing function help explain reproductive health and may provide solutions to reproductive disease.

Follicle-stimulating hormone/cAMP regulation of aromatase gene expression requires beta-catenin

Estrogens profoundly influence the physiology and pathology of reproductive and other tissues. Consequently, emphasis has been placed on delineating the mechanisms underlying regulation of estrogen levels. Circulating levels of estradiol in women are controlled by follicle-stimulating hormone (FSH), which regulates transcription of the aromatase gene (CYP19A1) in ovarian granulosa cells. Previous studies have focused on two downstream effectors of the FSH signal, cAMP and the orphan nuclear receptor steroidogenic factor-1 (NR5A1). In this report, we present evidence for beta-catenin (CTNNB1) as an essential transcriptional regulator of CYP19A1. FSH induction of select steroidogenic enzyme mRNAs, including Cyp19a1, is enhanced by beta-catenin. Additionally, beta-catenin is present in transcription complexes assembled on the endogenous gonad-specific CYP19A1 promoter, as evidenced by chromatin immunoprecipitation assays. Transient expression and RNAi studies demonstrate that FSH- and cAMP-dependent regulation of this promoter is sensitive to alterations in the level of beta-catenin. The stimulatory effect of beta-catenin is mediated through functional interactions with steroidogenic factor-1 that involve four acidic residues within its ligand-binding domain, mutation of which attenuates FSH/cAMP-induced Cyp19a1 mRNA accumulation. Together, these data demonstrate that beta-catenin is essential for FSH/cAMP-regulated gene expression in the ovary, identifying a central and previously unappreciated role for beta-catenin in estrogen biosynthesis, and a potential broader role in other aspects of follicular maturation.

FSH signaling pathways in immature granulosa cells that regulate target gene expression: branching out from protein kinase A

Follicle-stimulating hormone (FSH) is necessary and sufficient to induce maturation of ovarian follicles to a mature, preovulatory phenotype in the intact animal, resulting in the generation of mature eggs and production of estrogen. FSH accomplishes these actions by inducing a complex pattern of gene expression in target granulosa cells that is regulated by input from many different signaling cascades, including those for the extracellular regulated kinases (ERKs), p38 mitogen-activated protein kinases (MAPKs), and phosphatidylinositol-3 kinase (PI3K). The upstream kinase that appears to be responsible for initiating all of the signaling that regulates gene expression in these epithelial cells is protein kinase A (PKA). PKA not only signals to directly phosphorylate transcription factors like cAMP response element binding protein and to promote chromatin remodeling by phosphorylating histone H3, this versatile kinase also enhances the activity of the p38 MAPK, ERK, and PI3K pathways. Additionally, accumulating evidence suggests that activation of a single signaling cascade downstream of PKA is not sufficient to activate target gene expression. Rather, cross-talk between and among signaling cascades is required. We will review the signaling cascades activated by FSH in granulosa cells and how these cascades contribute to the regulation of select target gene expression.

A FTZ-F1-containing yeast artificial chromosome recapitulates expression of steroidogenic factor 1 in vivo

Steroidogenic factor 1 (SF-1/Nr5a1) is an orphan nuclear receptor encoded by the Ftz-F1 gene and is required for gonad and adrenal development and regulation of hormone production within the reproductive and adrenal axes. To extend our understanding of Ftz-F1 and its role in SF-1 expression, we identified and characterized a yeast artificial chromosome (YAC) containing Ftz-F1. Within this YAC, Ftz-F1 is centrally located and flanked by genes encoding a second orphan nuclear receptor, germ cell nuclear factor, and proteasome (prosome, macropain) subunit beta type 7. Three lines of transgenic mice carrying the YAC were generated and in two lines (lines 7 and 14), RT-PCR and ribonuclease protection analysis showed that expression of transgenic SF-1 mimicked that of endogenous SF-1, both spatially and quantitatively. In the third line (line 15), pituitary and hypothalamic expression were absent. Comparison of the integrated transgenes revealed that line 15 was truncated at the end of intron 4 and revealed a region within the locus that is responsible for SF-1 expression in the pituitary and hypothalamus. The line 14 transgene was introduced into a mouse strain lacking functional SF-1. Examination of SF-1-deficient, transgene-positive mice revealed that the YAC was able to rescue adrenal and gonad development, which normally arrests in the SF-1-null embryos and showed that the 153-kb transgene integrated in line 14 is sufficient to properly direct SF-1 expression and support its biological activity. Thus, the study defines a region of Ftz-F1 that contains the requisite set of regulatory elements to direct SF-1 cell-specific expression and all temporal and quantitative changes need for its biological activity.

The DEAD-box protein DP103 (Ddx20 or Gemin-3) represses orphan nuclear receptor activity via SUMO modification

Structural analysis of nuclear receptor subfamily V orphan nuclear receptors suggests that ligand-independent mechanisms must regulate this subclass of receptors. Here, we report that steroidogenic factor 1 (SF-1) and liver receptor homolog 1 are repressed via posttranslational SUMO modification at conserved lysines within the hinge domain. Indeed, mutating these lysines or adding the SUMO isopeptidase SENP1 dramatically increased both native and Gal4-chimera receptor activities. The mechanism by which SUMO conjugation attenuates SF-1 activity was found to be largely histone deacetylase independent and was unaffected by the AF2 corepressor Dax1. Instead, our data suggest that SUMO-mediated repression involves direct interaction of the DEAD-box protein DP103 with sumoylated SF-1. Of potential E3-SUMO ligase candidates, PIASy and PIASxalpha strongly promoted SF-1 sumoylation, and addition of DP103 enhanced both PIAS-dependent receptor sumoylation and SF-1 relocalization to discrete nuclear bodies. Taken together, we propose that DEAD-box RNA helicases are directly coupled to transcriptional repression by protein sumoylation.

Induction of cyclin D2 in rat granulosa cells requires FSH-dependent relief from FOXO1 repression coupled with positive signals from Smad

Ovarian follicles undergo exponential growth in response to follicle-stimulating hormone (FSH), largely as a result of the proliferation of granulosa cells (GCs). In vitro under serum-free conditions, rat GCs differentiate in response to FSH but do not proliferate unless activin is also present. In the presence of FSH plus activin, GCs exhibit enhanced expression of cyclin D2 as well as inhibin-alpha, aromatase, steroidogenic factor-1 (SF-1), cholesterol side chain (SCC), and epiregulin. In this report we sought to identify the signaling pathways by which FSH and activin promote GC proliferation and differentiation. Our results show that these responses are associated with prolonged Akt phosphorylation relative to time-matched controls and are dependent on phosphatidylinositol 3-kinase (PI 3-kinase) and Smad2/3 signaling, based on the ability of the PI 3-kinase inhibitor LY294002 or infection with adenoviral dominant negative Smad3 (DN-Smad3) mutant to attenuate induction of cyclin D2, inhibin-alpha, aromatase, SCC, SF-1, and epiregulin. The DN-Smad3 mutant also abolished prolonged Akt phosphorylation stimulated by FSH plus activin 24 h post-treatment. Infection with the adenoviral constitutively active forkhead box-containing protein, O subfamily (FOXO)1 mutant suppressed induction of cyclin D2, aromatase, inhibin-alpha, SF-1, and epiregulin. Transient transfections of GCs with constitutively active FOXO1 mutant also suppressed cyclin D2, inhibin-alpha, and epiregulin promoter-reporter activities. Chromatin immunoprecipitation results demonstrate in vivo the association of FOXO1 with the cyclin D2 promoter in untreated GCs and release of FOXO1 from the cyclin D2 promoter upon addition of FSH plus activin. These results suggest that proliferation and differentiation of GCs in response to FSH plus activin requires both removal of FOXO1-dependent repression and positive signaling from Smad2/3.

Follicle-stimulating hormone activation of hypoxia-inducible factor-1 by the phosphatidylinositol 3-kinase/AKT/Ras homolog enriched in brain (Rheb)/mammalian target of rapamycin (mTOR) pathway is necessary for induction of select protein markers of follicular differentiation

We sought to elucidate the role of AKT in follicle-stimulating hormone (FSH)-mediated granulosa cell (GC) differentiation. Our results define a signaling pathway in GCs whereby the inactivating phosphorylation of tuberin downstream of phosphatidylinositol (PI) 3-kinase/AKT activity leads to Rheb (Ras homolog enriched in brain) and subsequent mTOR (mammalian target of rapamycin) activation. mTOR then stimulates translation by phosphorylating p70 S6 kinase and, consequently, the 40 S ribosomal protein S6. Activation of this pathway is required for FSH-mediated induction of several follicular differentiation markers, including luteinizing-hormone receptor (LHR), inhibin-alpha, microtubule-associated protein 2D, and the PKA type IIbeta regulatory subunit. FSH also promotes activation of the transcription factor hypoxia-inducible factor-1 (HIF-1). FSH-stimulated HIF-1 activity is inhibited by the PI 3-kinase inhibitor LY294002, the Rheb inhibitor FTI-277 (farnesyltransferase inhibitor-277), and the mTOR inhibitor rapamycin. Finally, we find that the FSH-mediated up-regulation of reporter activities for LHR, inhibin-alpha, and vascular endothelial growth factor is dependent upon HIF-1 activity, because a dominant negative form of HIF-1alpha interferes with the up-regulation of these genes. These results show that FSH enhances HIF-1 activity downstream of the PI 3-kinase/AKT/Rheb/mTOR pathway in GCs and that HIF-1 activity is necessary for FSH to induce multiple follicular differentiation markers.

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.

Expression of MIS in the testis is downregulated by tumor necrosis factor alpha through the negative regulation of SF-1 transactivation by NF-kappa B

The expression of Mullerian inhibiting substance (MIS), a key molecule in sex differentiation and reproduction, is tightly regulated. It has been suggested that meiotic germ cells repress MIS expression in testicular Sertoli cells, although the substance responsible for this cell-cell communication remains unknown. Here, we present the cytokine tumor necrosis factor alpha (TNF-alpha) as a strong candidate for such a substance and its downstream molecular events. TNF-alpha inhibited MIS expression in testis organ cultures, and TNF-alpha(-/-) testes showed high and prolonged MIS expression. Furthermore, in transient-transfection assays TNF-alpha suppressed the MIS promoter that was activated by steroidogenic factor 1 (SF-1), one of the major transcription factors that regulate MIS expression. The modulation of SF-1 transactivation by TNF-alpha is through the activation of NF-kappa B, which subsequently interacts with SF-1 and represses its transactivation. The physical association of NF-kappa B with SF-1 was shown by yeast two-hybrid protein interaction, glutathione S-transferase pull-down, and coimmunoprecipitation (ChIP) analyses. ChIP assays also revealed that endogenous NF-kappa B, as well as SF-1, is recruited to the MIS promoter upon TNF-alpha signaling. SF-1-bound NF-kappa B subsequently recruits histone deacetylases to inhibit the SF-1-activated gene expression. These results may identify, for the first time, the responsible substance and its action mechanism underlying the repression of MIS expression by meiotic germ cells in the testis.

T-cell factor 4N (TCF-4N), a novel isoform of mouse TCF-4, synergizes with beta-catenin to coactivate C/EBPalpha and steroidogenic factor 1 transcription factors

We have cloned T-cell factor 4N (TCF-4N), an alternative isoform of TCF-4, from developing pituitary and 3T3-L1 preadipocytes. This protein contains the N-terminal interaction domain for beta-catenin but lacks the DNA binding domain. While TCF-4N inhibited coactivation by beta-catenin of a TCF/lymphoid-enhancing factor (LEF)-dependent promoter, TCF-4N potentiated coactivation by beta-catenin of several non-TCF/LEF-dependent promoters. For example, TCF-4N synergized with beta-catenin to activate the alpha-inhibin promoter through functional and physical interactions with the orphan nuclear receptor steroidogenic factor 1 (SF-1). In addition, TCF-4N and beta-catenin synergized with the adipogenic transcription factor CCAAT/enhancer binding protein alpha (C/EBPalpha) to induce leptin promoter activity. The mechanism by which beta-catenin and TCF-4N coactivated C/EBPalpha appeared to involve p300, based upon synergy between these important transcriptional regulators. Consistent with TCF-4N's redirecting the actions of beta-catenin in cells, ectopic expression of TCF-4N in 3T3-L1 preadipocytes partially relieved the block of adipogenesis caused by beta-catenin. Thus, we propose that TCF-4N inhibits coactivation by beta-catenin of TCF/LEF transcription factors and potentiates the coactivation by beta-catenin of other transcription factors, such as SF-1 and C/EBPalpha.

Requirement of the orphan nuclear receptor SF-1 in terminal differentiation of ventromedial hypothalamic neurons

The ventromedial hypothalamic nucleus (VMN) is known to mediate autonomic responses in feeding and reproductive behaviors. To date, the most definitive molecular marker for the VMN is the orphan nuclear receptor steroidogenic factor-1 (SF-1). However, it is unclear whether SF-1 functions in the VMN as it does in peripheral endocrine organ development where loss of SF-1 results in organ agenesis due to apoptosis. Here, we provide evidence that SF-1 has a distinct role in later stages of VMN development by demonstrating the persistence of VMN precursors, the misexpression of an early marker (NKX2-1) concomitant with the absence of a late marker (BDNF neurotrophin), and the complete loss of projections to the bed nucleus of stria terminalis and the amygdala in sf-1 null mice. Our findings demonstrate that SF-1 is required for terminal differentiation of the VMN and suggest that transcriptional targets of SF-1 mediate normal circuitry between the hypothalamus and limbic structures in the telencephalon.

Follicle-stimulating hormone activates extracellular signal-regulated kinase but not extracellular signal-regulated kinase kinase through a 100-kDa phosphotyrosine phosphatase

In this report we sought to elucidate the mechanism by which the follicle-stimulating hormone (FSH) receptor signals to promote activation of the p42/p44 extracellular signal-regulated protein kinases (ERKs) in granulosa cells. Results show that the ERK kinase MEK and upstream intermediates Raf-1, Ras, Src, and L-type Ca(2+) channels are already partially activated in vehicle-treated cells and that FSH does not further activate them. This tonic stimulatory pathway appears to be restrained at the level of ERK by a 100-kDa phosphotyrosine phosphatase that associates with ERK in vehicle-treated cells and promotes dephosphorylation of its regulatory Tyr residue, resulting in ERK inactivation. FSH promotes the phosphorylation of this phosphotyrosine phosphatase and its dissociation from ERK, relieving ERK from inhibition and resulting in its activation by the tonic stimulatory pathway and consequent translocation to the nucleus. Consistent with this premise, FSH-stimulated ERK activation is inhibited by the cell-permeable protein kinase A-specific inhibitor peptide Myr-PKI as well as by inhibitors of MEK, Src, a Ca(2+) channel blocker, and chelation of extracellular Ca(2+). These results suggest that FSH stimulates ERK activity in immature granulosa cells by relieving an inhibition imposed by a 100-kDa phosphotyrosine phosphatase.

Expression of steroidogenic factor 1 in the testis requires an interactive array of elements within its proximal promoter

Steroidogenic factor 1 (SF-1) is an orphan nuclear receptor that is important for expression of genes involved in sexual differentiation, testicular and adrenal development, and hormone synthesis and regulation. To better understand the mechanisms required for SF-1 production, we employed transient transfection analysis and electrophoretic mobility shift assays to characterize the elements and proteins required for transcriptional activity of the SF-1 proximal promoter in testicular Sertoli and Leydig cells and adrenocortical cells. Direct comparison of SF-1-promoter activity in testis and adrenal cell types established that a similar set of regulatory elements (an E box, CCAAT box, and Sp1-binding sites) is required for proximal promoter activity in these cells. Further evaluation of the E box and CCAAT box revealed a novel synergism between the two elements and identified functionally important bases within the elements. Importantly, DNA/protein-binding studies uncovered new proteins interacting with the E box and CCAAT box. Thus, in addition to the previously identified USF and NF-Y proteins, newly described complexes, having migration properties that differed between Sertoli and Leydig cells, were observed bound to the E box and CCAAT box. Transient transfection analysis also identified several Sp1/Sp3-binding elements important for expression of SF-1 in the testis, one of which was previously described for expression in the adrenal gland whereas the other two were newly disclosed elements.

Phosphorylation and intramolecular stabilization of the ligand binding domain in the nuclear receptor steroidogenic factor 1

Steroidogenic factor 1 (SF-1) is an orphan nuclear receptor with no known ligand. We showed previously that phosphorylation at serine 203 located N'-terminal to the ligand binding domain (LBD) enhanced cofactor recruitment, analogous to the ligand-mediated recruitment in ligand-dependent receptors. In this study, results of biochemical analyses and an LBD helix assembly assay suggest that the SF-1 LBD adopts an active conformation, with helices 1 and 12 packed against the predicted alpha-helical bundle, in the apparent absence of ligand. Fine mapping of the previously defined proximal activation function in SF-1 showed that the activation function mapped fully to helix 1 of the LBD. Limited proteolyses demonstrate that phosphorylation of S203 in the hinge region mimics the stabilizing effects of ligand on the LBD. Moreover, similar effects were observed in an SF-1/thyroid hormone LBD chimera receptor, illustrating that the S203 phosphorylation effects are transferable to a heterologous ligand-dependent receptor. Our collective data suggest that the hinge together with helix 1 is an individualized specific motif, which is tightly associated with its cognate LBD. For SF-1, we find that this intramolecular association and hence receptor activity are further enhanced by mitogen-activated protein kinase phosphorylation, thus mimicking many of the ligand-induced changes observed for ligand-dependent receptors.

The expression of the follicle-stimulating hormone receptor in spermatogenesis

Results from experiments using mouse models suggest that the role of follicle-stimulating hormone (FSH) in spermatogenesis is the regulation of Sertoli cell proliferation and, ultimately, the size and spermatogenic capacity of the testis. The regulation of the expression of the FSH receptor (FSHR) gene is very cell specific and plays an initial role in the ultimate response of the Sertoli cells to FSH. The extreme cell specificity and the importance of the FSH response to spermatogenesis have led to an extensive characterization of the promoter of the FSHR gene. Several widely expressed transcription factors - including USF 1 and 2, GATA-1, and SF-1 and potential elements such as an E2F site and an Inr region - have been shown to contribute to the maximal transcription of the transfected FSHR gene. However, these experiments have failed to provide clues as to the cell-specific expression of the FSHR gene. In both cell transfections and in transgenic mice, the promoter can direct expression of transgenes promiscuously. The rodent FSHR promoter contains conserved CpG dinucleotides that were shown to be methylated in nonexpressing cells and tissue but unmethylated in Sertoli cells. The methylated CpG sites could interfere with the binding of general transcription factors and/or lead to a repressive chromatin structure in the nonexpressing cells. While yet-undiscovered cell-specific factors may play a role in the expression of the FSHR gene, repression and activation of local chromatin structure are likely to be involved.

Activation of the rat follicle-stimulating hormone receptor promoter by steroidogenic factor 1 is blocked by protein kinase a and requires upstream stimulatory factor binding to a proximal E box element

The receptor for the pituitary glycoprotein hormone FSH (FSHR) and the nuclear hormone receptor steroidogenic factor 1 (SF-1) play important roles in control of the hypothalamic-pituitary- gonadal axis. FSHR is essential for integrating the pituitary FSH signal to gonadal response, while SF-1 is an important transcriptional regulator of many genes that function within this axis and is essential for the development of gonads and adrenal glands. Given the critical role of SF-1 in regulation of the gonads and the coexpression of FSHR and SF-1 in Sertoli and granulosa cells, we examined the ability of SF-1 to regulate transcription of the FSHR gene. We found that SF-1 stimulated rat FSHR promoter activity in a dose-dependent and promoter-specific manner. Examination of various promoter deletion mutants indicated that SF-1 acts through the proximal promoter region and upstream promoter sequences. An E box element within the proximal promoter is essential for activation of the FSHR promoter by SF-1. This element binds the transcriptional regulators USF1 and USF2 (upstream stimulatory factors 1 and 2) but not SF-1, as shown by electrophoretic mobility shift assays. In addition, functional studies identified a requirement for the USF proteins in SF-1 activation of FSHR and mapped an important regulatory domain within exons 4 and 5 of USF2. Cotransfection studies revealed that activation of protein kinase A leads to inhibition of SF-1-stimulated transcription of FSHR, while it synergized with SF-1 to activate the equine LH beta-promoter (ebeta). Thus, stimulation of the cAMP pathway differentially regulates SF-1 activation of the FSHR and ebeta-promoters.