Regulation of the human P450scc gene by steroidogenic factor 1 is mediated by CBP/p300

Gene array analysis of the effects of chronic adrenocorticotropic hormone in vivo on immature rat adrenal glands

Development of a mature adrenocortical phenotype is a critical event in the transition of mammals from fetal to postnatal life. We previously reported that the functional maturation of the adrenal glands of newborn rats is accelerated by adrenocorticotropic hormone (ACTH). We report here that chronic exposure of neonatal/juvenile rat pups to ACTH in vivo results in significant changes in expression of over 200 genes in the adrenal glands. ACTH significantly upregulated genes associated with cell signaling, gene transcription, cell migration and tissue remodeling. In addition, ACTH significantly downregulated several genes associated with de novo cholesterol biosynthesis and cholesterol trafficking. Finally, ACTH upregulated genes associated with intracellular metabolism and inactivation of glucocorticoids. The results demonstrate that the developmental effects of ACTH alter expression of a broad range of genes involved not solely in steroid synthesis, but in cellular functions related to growth and differentiation of the glands. In addition, the negative effects of ACTH on genes required for cholesterol synthesis and production of active glucocorticoids, suggests a mechanism whereby excessive production of glucocorticoids, which may have deleterious actions on developing structures like the central nervous system, is prevented.

DNA sequence-dependent regulation of SF-1-mediated transcription

Rat P450c17 gene transcription is regulated by several nuclear factors, including steroidogenic factor-1 (SF-1), nerve growth factor-inducible protein B (NGF-IB, Nurr77), COUP-TF, SET, and Ku autoimmune antigen. A region of this gene, -447/-419, that mediates both basal and cAMP-stimulated transcription, contains two binding sites for orphan nuclear receptors. While SF-1 activates transcription through a single binding site, we show that both binding sites at -447/-419 are required for transcriptional activation by SF-1 and cAMP. Both SF-1 and a novel factor, Steroidogenic Factor-Inducer of Transcription-2 (StF-IT-2) bind to this region, suggesting that a DNA-dependent interaction between StF-IT-2 and SF-1 may be required for full transcriptional activity. Each of the two orphan nuclear receptor sites -429/-424 and at -444/-439 are sufficient for SF-1 binding but are insufficient for SF-1-mediated transcription. Increasing the distance between or changing the orientation of these two sites does not affect basal or SF-1-stimulated activity. Circular permutation analysis, which measures the degree of DNA bending caused by protein binding, indicates that SF-1 binding to -447/-419 induces a different degree of DNA bending than it does at another SF-1-responsive site. However, similar domains of the SF-1 protein are required for its actions at these two regions. Southwestern blots suggest that StF-IT-2 is a approximately 33 kDa protein, and gel shift assays suggest it is expressed primarily in the gonad and brain early in rodent development. These data suggest that the mechanism by which SF-1 stimulates transcription is DNA sequence dependent, and may require additional proteins, such as StF-IT-2, for activation at specific regions of DNA.

Steroidogenic factor-1 interacts with cAMP response element-binding protein to mediate cAMP stimulation of CYP1B1 via a far upstream enhancer

CYP1B1 activates polycyclic aromatic hydrocarbon carcinogens in cAMP-regulated tissues such as the adrenal, ovary, and testis. A 27-fold cAMP stimulation of the CYP1B1-luciferase reporter in Y-1 adrenal cells depends entirely on a far upstream enhancer region (FUER; -5298 to -5110). Cooperative participation of multiple steroidogenic factor 1 (SF-1) elements with the downstream cAMP response element (CRE) in FUER is essential for both basal and cAMP-stimulated activities of FUER. Basal and induced activities were similarly lowered by DAX-1, an SF-1 suppressor, and raised by steroid receptor coactivator 1, an SF-1 coactivator. cAMP response element-binding protein (CREB)-binding protein (CBP) that interacts preferentially with the phosphorylated-CREB increased the cAMP-induced FUER. 10T1/2 cells and human embryonic kidney (HEK)293 cells do not express SF-1. Introduction of exogenous SF-1 generated cAMP stimulation of the FUER in 10T1/2 fibroblasts. The same transfection only increased basal activity of FUER in HEK293 cells, despite presence of active CREB in cells. HEK293 cells therefore remain deficient in additional factor(s) critical to the cAMP stimulation of CYP1B1. Mutations of the protein kinase A (PKA) and the mitogen-activated protein kinase phosphorylation sites (Ser-430 and Ser-203) on SF-1 had no effect on the SF-1-dependent FUER stimulation in Y-1 and 10T1/2 cells. This contrasts with loss of activity with mutation of CREB at PKA phosphorylation site (Ser-133). SF-1 phosphorylation at these sites is therefore not essential for the cAMP stimulation and the cooperation with CREB. cAMP-enhanced activation protein 1 (AP-1) and stimulatory protein 1 (Sp1) complexes in the proximal promoter region contributed substantially to both basal and cAMP-stimulated FUER activity. Chromatin immunoprecipitation from primary rat adrenal cells demonstrated cAMP stimulation of histone acetylation proximal to, respectively, the FUER and AP-1 sites of CYP1B1.

Adrenocortical cell lines

The human adrenal cortex is a complex endocrine organ that secretes mineralocorticoids, glucocorticoids and adrenal androgens. These steroids arise from morphologically and biochemically distinct zones of the adrenal gland. Studying secretion of these distinct steroid hormones can make use of cells isolated from the adrenal gland but this requires animal sacrifice and the need for continued isolation for long-term studies. In addition primary cultures of adrenal cells have a limited life-span in culture and the cultured cells are often contaminated by the presence of non-steroidogenic cells. For that reason in vitro cell culture models have several benefits for research on adrenocortical function. Herein we discuss the available adrenocortical cell lines and their uses as model systems for adrenal studies. Focus is placed on the human NCI-H295 and mouse Y-1 adrenal cell lines, which have been used extensively as adrenocortical model systems. These cell lines have proven to be of considerable value in studying the molecular and biochemical mechanisms controlling adrenal steroidogenesis. The current review will discuss the attributes and limitations of the currently available adrenocortical cell lines as models for adrenal studies.

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.

Testicular dysgenesis without adrenal insufficiency in a 46,XY patient with a heterozygous inactive mutation of steroidogenic factor-1

Steroidogenic factor-1 (SF-1) regulates multiple genes involved in the adrenal and gonadal development and in the biosynthesis of a variety of hormones, including adrenal and gonadal steroids, anti-Mullerian hormone (AMH), and gonadotropins. We identified a novel SF-1 mutation in a 27-yr-old Japanese patient with a 46,XY karyotype. Sequence analysis was performed for all the seven exons of SF-1, revealing a heterozygous single base pair deletion at exon 2 (18delC) that is predicted to cause a frameshift at the sixth codon and resultant termination at the 74th codon. Functional studies showed that the mutation produced no demonstrable protein and had no transcription activity or dominant negative effect. Clinical features included small dysgenetic testes with vasa deferentia and epididymides, absent uterus, blind-ending vagina, clitoromegaly, and psychosexual disturbance. Endocrine studies showed normal adrenal function (cortisol response to ACTH stimulation, 13.4-->25.3 microg/dl) and primary hypogonadism (testosterone response to hCG stimulation, 0.57-->0.76 ng/ml; gonadotropin responses to GnRH stimulation: LH, 10-->59 mIU/ml; FSH, 36-->69 mIU/ml), and urinary steroid hormone profile analysis indicated grossly normal steroidogenic enzyme activities. The results suggest that SF-1 haploinsufficiency can selectively impair testicular development and permit the biosynthesis of AMH and testosterone in dysgenetic testes and the production of gonadotropins in pituitary gonadotropes.

Prospero-Related Homeobox (Prox1) Is a Corepressor of Human Liver Receptor Homolog-1 and Suppresses the Transcription of the Cholesterol 7-α-Hydroxylase Gene

Cholesterol 7-α-hydroxylase (CYP7A1) catalyzes a rate-limiting step in bile acid synthesis in liver, and its gene transcription is under complex regulation by multiple nuclear receptors in response to bile acids, cholesterol derivatives, and hormones. The liver receptor homolog-1 (LRH-1), a member of the fushi tarazu factor 1 subfamily of nuclear receptors, has emerged as an essential regulator for the expression of cyp7a1. In this report, we demonstrate Prox1, a prospero-related homeobox transcription factor, identified through a yeast two-hybrid screening, can directly interact with human LRH-1 (hLRH-1) and suppresses hLRH-1-mediated transcriptional activation of human cyp7a1 gene. Biochemical analysis demonstrates that Prox1 interacts with both the ligand binding domain (LBD) and the DNA binding domain (DBD) of hLRH-1. An LRKLL motif in Prox1 is important for the interaction with the LBD but not the DBD of hLRH-1. In hLRH-1 LBD, helices 2 and 10 are essential for Prox1 recruitment. The suppression by Prox1 on the transcriptional activity of hLRH-1 can be mediated through its interaction with the LBD or the DBD of hLRH-1. Gel shift assays reveal that Prox1 impairs the binding of hLRH-1 to the promoter of human cyp7a1 gene.

SUMO Modification of Repression Domains Modulates Function of Nuclear Receptor 5A1 (Steroidogenic Factor-1)

Steroidogenic factor 1 (SF-1 or NR5A1), is a Ftz-F1 member of the nuclear receptor superfamily that plays essential roles in endocrine development, steroidogenesis, and gonad differentiation. We investigated modifications that control SF-1 function and found that SF-1 could be conjugated by SUMO-1 both in vitro and in vivo. SF-1 was modified predominantly at Lys(194) and much less at Lys(119) when free SUMO-1 was supplied. Mutations of Lys(194) and Lys(119) enhanced transcriptional activity of SF-1, although the DNA binding activity of SF-1 was not affected. Sequences around Lys(194) and Lys(119) both repressed transcription intrinsically. The Lys(194) motif repressed transcription more efficiently than the Lys(119) domain, consistent with its ability to be a better substrate for SUMO conjugation. Thus, SUMO modification of SF-1 correlates with transcriptional repression. Wild-type but not conjugation-deficient SF-1 was localized at the nuclear speckles together with SUMO-1. Thus, SUMO-1 conjugation could also target SF-1 into nuclear speckles. Collectively, these results suggest that SUMO modification at the repression domains targets SF-1 to nuclear speckles; this could be an important mechanism by which SF-1 is regulated.

Negative regulatory effect of an oligodendrocytic bHLH factor OLIG2 on the astrocytic differentiation pathway

In the developing vertebrate nervous system, multipotent neural stem cells produce both neurons and glia. OLIG2 is a basic helix-loop-helix transcription factor that plays critical roles in oligodendrocyte and motor neuron development; however, its role in astrocytic development remains elusive. In this study, we analyzed an effect of OLIG2 on cytokine-induced astrocytic differentiation from mouse telencephalic neuroepithelial cells. We show that the presence of OLIG2 protein leads to inhibition of the promoter activation of astrocyte-specific glial fibrillary acidic protein gene. We found that OLIG2 abolishes complex formation between a transcriptional coactivator p300 and a transcription factor, signal transducer and activator of transcription 3 (STAT3), which is activated by astrocytic differentiation-inducing cytokines, such as leukemia inhibitory factor (LIF). The enforced expression of OLIG2 in neuroepithelial cells inhibits the LIF-induced astrocytic differentiation. We also show that the OLIG2 protein in the nuclei of neural precursor cells disappears in accordance with astrocytic differentiation during culture with LIF. Together, these results reveal a novel molecular function of OLIG2 on the astrocyte development. Cell Death and Differentiation (2004) 11, 196-202. doi:10.1038/sj.cdd.4401332 Published online 24 October 2003

Small ubiquitin-like modifier 1 (SUMO-1) modification of the synergy control motif of Ad4 binding protein/steroidogenic factor 1 (Ad4BP/SF-1) regulates synergistic transcription between Ad4BP/SF-1 and Sox9

An orphan nuclear receptor, Ad4 binding protein/steroidogenic factor 1 (Ad4BP/SF-1), is essential for the development and function of steroidogenic tissues. To examine the transcriptional regulation of Ad4BP/SF-1, two-hybrid screening was performed, and the sumoylation [conjugation of a small ubiqutin-like modifier (SUMO-1)] components Ubc9, protein inhibitor of activated STAT 1 (PIAS1), and protein inhibitor of activated STAT 3 (PIAS3) were isolated. Cultured cell and in vitro studies revealed that Ad4BP/SF-1 is sumoylated at K119 and K194. Because K194 lies within the synergy control (SC) motif defined to repress synergistic transcription from promoters containing multiple binding sites, correlation between the functions of the SC motif and sumoylation was investigated. The K194R mutant of Ad4BP/SF-1, which cannot be sumoylated, showed enhanced synergistic transcription from a promoter containing multiple Ad4/SF-1 sites, suggesting that sumoylation is necessary for repression of transcriptional synergy through the SC motif. It has been established that the Müllerian inhibiting substance gene is transcribed predominantly under the control of Ad4BP/SF-1 and, moreover, its transcription is regulated synergistically with Sox9, Gata4, and Wt1. Interestingly, it was found that all of these factors are sumoylated, and these sumoylation sites occur within SC motifs. Based on the observation that SC motif mutants of Ad4BP/SF-1 and Sox9 resulted in the enhancement of their synergistic transcription, it was concluded that the SC motif regulates synergistic transcription even between distinct types of transcription factors. Considering that both mutants cannot be sumoylated, it is likely that sumoylation is implicated in this regulation. Because it was revealed with an in vitro sumoylated Ad4BP/SF-1 that DNA binding activity and interaction with Sox9 were unaffected, sumoylation may regulate transcription through affecting selective and cooperative interaction among factors constituting transcriptional complexes.

Hepatocyte nuclear factor 4alpha enhances the hepatocyte nuclear factor 1alpha-mediated activation of transcription

Hepatocyte Nuclear Factor 1alpha (HNF1alpha) and Hepatocyte Nuclear Factor 4alpha (HNF4alpha) are two liver-enriched transcription factors coexpressed in specific tissues where they play a crucial role through their involvement in a complex cross-regulatory network. HNF1alpha down regulates HNF4alpha-mediated activation of transcription via a direct protein-protein interaction. Here we show that HNF4alpha enhances the transcriptional activity of HNF1alpha in a DNA binding independent manner, thus indicating that it behaves as a HNF1alpha coactivator. Using mutations in the ligand binding domain (LBD) of HNF4alpha, we confirmed the involvement of the Activation Function 2 module and demonstrated the requirement of the integrity of the LBD for the interaction with HNF1alpha. Moreover, we show that HNF4alpha cooperates with p300 to achieve the highest HNF1alpha-mediated transcription rates. Our findings highlight a new way by which HNF4alpha can regulate gene expression and extend our knowledge of the complexity of the transcriptional network involving HNF4alpha and HNF1alpha.

Regulation of transcription of the steroidogenic acute regulatory protein (StAR) gene: temporal and spatial changes in transcription factor binding and histone modification

We examined the binding of transcription factors and histone modifications associated with induction of expression of the steroidogenic acute regulatory protein (StAR) gene in MA-10 cells using a quantitative chromatin immunoprecipitation (ChIP) assay. GATA-4, SF-1/Ad4BP, and cyclic AMP response element binding protein binding protein (CBP) bind rapidly to the StAR proximal promoter, but in different patterns following 8-Br-cAMP stimulation. Concomitantly, histone modifications occur in a spatial and temporal sequence including increased association of acetylated histone H3 with the proximal promoter region, increased association of dimethylated lysine 4 histone H3 with exonic sequences, a modification that marks actively transcribed regions, and reduced association of a marker linked to gene silencing (lysine 9 dimethylated histone H3). Our findings demonstrate that transcription factors and coactivators are rapidly associated with the StAR proximal promoter, that the patterns of binding differ which has implications for postulated direct interactions among these factors, and that multiple histone modifications are demonstrable in a spatially- and temporally-specific pattern along the StAR gene. These observations suggest that a combinatorial code of transcription factors including reciprocal changes in histone modifications associated with active transcription and gene silencing control StAR gene expression.

Estrogen regulation of vascular endothelial growth factor gene expression in ZR-75 breast cancer cells through interaction of estrogen receptor alpha and SP proteins

Vascular endothelial growth factor (VEGF) is expressed in multiple hormone-dependent cancer cells/tumors. Treatment of ZR-75 breast cancer cells with 17beta-estradiol (E2) induced a greater than fourfold increase of VEGF mRNA levels. ZR-75 breast cancer cells were transfected with pVEGF1, a construct containing a -2018 to +50 VEGF promoter insert, and E2 induced reporter gene (luciferase) activity. Deletion and mutation analysis of the VEGF gene promoter identified a GC-rich region (-66 to -47) which was required for E2-induced transactivation of pVEGF5, a construct containing the minimal promoter (-66 to +54) that exhibited E2-responsiveness. Interactions of nuclear proteins from ZR-75 cells with the proximal GC-rich region of the VEGF gene promoter were investigated by electrophoretic mobility shift and chromatin immunoprecipitation assays. The results demonstrate that both Sp1 and Sp3 proteins bound the GC-rich motif (-66 to -47), and estrogen receptor alpha (ERalpha) interactions were confirmed by chromatin immunoprecipitation. Moreover, E2-dependent activation of constructs containing proximal and distal GC/GT-rich regions of the VEGF promoter was inhibited in ZR-75 cells transfected with small inhibitory RNAs for Sp1 and Sp3. These results were consistent with a mechanism of hormone activation of VEGF through ERalpha/Sp1 and ERalpha/Sp3 interactions with GC-rich motifs.

p300 regulates the synergy of steroidogenic factor-1 and early growth response-1 in activating luteinizing hormone-beta subunit gene

Tight regulation of luteinizing hormone-beta subunit (LHbeta) expression is critical for differentiation and maturation of mammalian sexual organs and reproductive function. Two transcription factors, steroidogenic factor-1 (SF-1) and early growth response-1 (Egr-1), play a central role in activating LHbeta promoter, and the synergy between these two factors is essential in mediating gonadotropin-releasing hormone stimulation of LHbeta promoter. Here we demonstrate that the transcriptional co-activator p300 regulates this synergy. Overexpression of p300 results in strong stimulation of LHbeta promoter but only in the presence of both SF-1 and Egr-1, and not in the presence of other Egr proteins. Mutation of the binding sites for either SF-1 or Egr-1 completely abolishes the synergy between these two factors, as well as the influence of p300. Importantly, LHbeta promoter is precipitated using p300 antibodies in a chromatin immunoprecipitation assay with LbetaT2 gonadotropes, and this effect is enhanced by gonadotropin-releasing hormone. The influence of p300 on LHbeta promoter is potentiated by steroid receptor co-activator, as well as by E1A proteins, and attenuated by Smad nuclear interacting protein 1. Taken together, these results suggest that p300 is recruited to LHbeta promoter where it coordinates the functional synergy between SF-1 and Egr-1.

SF1 in the development of the adrenal gland and gonads

SF1 (steroidogenic factor-1; NR5A1) is an orphan nuclear receptor that is expressed in the adrenal gland, gonads, spleen, ventromedial hypothalamus and pituitary gonadotroph cells. Combined approaches of targeted mutagenesis in mice and examination of the effects of naturally occurring mutations in humans have clarified the role of SF1 in steroidogenesis and development. Targeted disruption of SF1 (FTZF1) in mice prevents gonadal and adrenal development and causes male-to-female sex reversal. A heterozygous loss-of-function human SF1 mutation (G35E) was described in a patient with adrenal failure and complete 46,XY sex reversal, indicating that haploinsufficiency of this transcription factor is sufficient to cause a severe clinical phenotype. In an infant with a similar clinical phenotype, a homozygous SF1 mutation (R92Q) was identified. In functional assays, this mutant SF1 protein exhibited partial loss of DNA binding and transcriptional activity when compared with the more severe G35E P-box mutant. These patients reveal the exquisite sensitivity of SF1-dependent developmental pathways to gene dosage and function in humans.

DAX1 and its network partners: exploring complexity in development

DAX1 encoded by NR0B1, when mutated, is responsible for X-linked adrenal hypoplasia congenita (AHC). AHC is due to failure of the adrenal cortex to develop normally and is fatal if untreated. When duplicated, this gene is associated with an XY sex-reversed phenotype. DAX1 expression is present during development of the steroidogenic hypothalamic-pituitary-adrenal-gonadal (HPAG) axis and persists into adult life. Despite recognition of the crucial role for DAX1, its function remains largely undefined. The phenotypes of patients and animal models are complex and not always in agreement. Investigations using cell lines have proved difficult to interpret, possibly reflecting cell line choices and their limited characterization. We will review the efforts of our group and others to identify appropriate cell lines for optimizing ex vivo analysis of NR0B1 function throughout development. We will examine the role of DAX1 and its network partners in development of the hypothalamic-pituitary-adrenal/gonadal axis (HPAG) using a variety of different types of investigations, including those in model organisms. This network analysis will help us to understand normal and abnormal development of the HPAG. In addition, these studies permit identification of candidate genes for human inborn errors of HPAG development.

Convergence of Wnt signaling and steroidogenic factor-1 (SF-1) on transcription of the rat inhibin alpha gene

The action of a variety of peptide hormones is critical for proper growth and differentiation of the urogenital ridge, which ultimately gives rise to the kidney, adrenal cortex, and gonad. One such class of peptides is the Wnt family of secreted glycoproteins that is classically involved in development of cell polarity and cell fate determination. Notably, alterations in Wnt-4 expression in mice and humans result in profound defects in urogenital ridge development, including dysregulation of kidney, gonadal, and adrenal growth. The nuclear receptor steroidogenic factor-1 (SF-1) has been implicated as a downstream effector of peptide hormone signaling during urogenital ridge development as evidenced by both the activation of SF-1-dependent transcription in the adrenal cortex by signaling molecules such as protein kinase A and by the adrenal and gonadal agenesis in mice with null mutations in SF-1. We hypothesized that Wnt-dependent signaling cascades regulate SF-1-dependent transcription of genes required for adreno-gonadal development. Specifically, the data demonstrate that beta-catenin synergizes with SF-1 to activate the alpha-inhibin promoter through formation of a transcriptional complex. The activation requires an intact SF-1 RE and is independent of TCF/Lef. These data support the recent observation that beta-catenin can participate in nuclear receptor-mediated transcriptional activation and extend the findings to the monomer binding class of orphan nuclear receptors.

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.

Regulation of niemann-pick c1 gene expression by the 3'5'-cyclic adenosine monophosphate pathway in steroidogenic cells

The Niemann Pick-C1 (NPC-1) protein is essential for intracellular transport of cholesterol derived from low-density lipoprotein import in mammalian cells. The role of the protein kinase A (PKA) pathway in regulation of expression of the NPC-1 gene was investigated. NPC-1 promoter activity was induced by treatment with dibutryl cAMP (dbcAMP), alone or in combination with the cAMP response element (CRE) binding protein (CREB) overexpressed in adrenal Y-1 cells. When the catalytic subunit of PKA was overexpressed in Y-1 cells, there were similar increases in NPC-1 promoter activity in the presence of CREB. Responses were attenuated by blockade of the PKA pathway, and in the Kin-8 cell line deficient in PKA. Promoter deletion analysis revealed that this response was present in promoter fragments of 186 bp and larger but not present in the 121-bp fragment. Two promoter regions, one at -430 and one at -120 upstream of the translation initiation site, contained CRE consensus sequences. These bound recombinant CREB in EMSA, confirming their authenticity as CREB response elements. Promoters bearing mutations of both CRE displayed no response to dbcAMP. The orphan nuclear receptor, steroidogenic factor-1 (SF-1), was implicated in NPC-1 transactivation by the presence of SF-1 target sequence that formed a complex with recombinant SF-1 in EMSA. Furthermore, transfection of a plasmid that overexpressed SF-1 into ovarian granulosa cells increased promoter activity in response to dbcAMP, an effect abrogated by mutation of the SF-1 target sequence. Chromatin immunoprecipitation assays demonstrated that the CRE region of the endogenous and transfected NPC-1 promoter associated with both acetylated and phosphorylated histone H-3 and that this association was increased by dbcAMP treatment. Treatment with dbcAMP also increased the association of the CRE region of the promoter with CREB binding protein, which has histone acetyltransferase activity. Together, these results demonstrate a mechanism of regulation of NPC-1 expression by the cAMP-PKA pathway that includes PKA phosphorylation of CREB, recruitment of the coactivator CREB binding protein and the phosphorylation and acetylation of histone H-3 to transactivate the NPC-1 promoter.

LXXLL-related motifs in Dax-1 have target specificity for the orphan nuclear receptors Ad4BP/SF-1 and LRH-1

The orphan receptor Ad4BP/SF-1 (NR5A1) is a constitutive activator, and its activity is repressed by another orphan receptor, Dax-1 (NR0B1). In the present study, we investigated the molecular mechanisms underlying this repression by Dax-1. Yeast two-hybrid and transient-transfection assays confirmed the necessity of three LXXLL-related motifs in Dax-1 for interaction with and repression of Ad4BP/SF-1. In vitro pull-down experiments confirmed that Dax-1 interacts with Ad4BP/SF-1 and also with LRH-1 (NR5A2). The target specificity of the LXXLL-related motifs was indicated by the observations that Ad4BP/SF-1, ERalpha (NR3A1), LRH-1, ERR2 (NR3B2), and fly FTZ-F1 (NR5A3) interacted through their ligand binding domains with all the LXXLL-related motifs in Dax-1 whereas HNF4 (NR2A1) and RORalpha (NR1F1) did not. Transcriptional activities of the receptors whose DNA binding domains (DBDs) were replaced by the GAL4 DBD were repressed by Dax-1 to various levels, which correlated with the strength of interaction. Amino acid substitutions revealed that Ad4BP/SF-1 and LRH-1 preferentially interact with L(+1)XXLL-related motifs containing serine, tyrosine, serine, and threonine at positions -2, +2, +3, and +6, respectively. Taken together, our results indicate that the specificities of LXXLL-related motifs in Dax-1 based on their amino acid sequences play an important role in regulation of orphan receptors.

The orphan nuclear receptor, steroidogenic factor 1, regulates neuronal nitric oxide synthase gene expression in pituitary gonadotropes

Steroidogenic factor 1 (SF-1), an essential nuclear receptor, plays key roles in steroidogenic cell function within the adrenal cortex and gonads. It also contributes to reproductive function at all three levels of the hypothalamic-pituitary-gonadal axis. SF-1 regulates genes in the steroidogenic pathway, such as LHbeta, FSHbeta, and steroid hydroxylase. Abundant evidence suggests that nitric oxide (NO) has an important role in the control of reproduction due to its ability to control GnRH secretion from the hypothalamus and the preovulatory LH surge in pituitary gonadotropes. Recently, we cloned and characterized the promoter of mouse neuronal NO synthase (nNOS). nNOS is localized at all three levels of the hypothalamic-pituitary-gonadal axis to generate NO. We find that its major promoter resides at exon 2 in the pituitary gonadotrope alphaT3-1 cell line and that there is a nuclear hormone receptor binding site in this region, to which SF-1 can bind and regulate nNOS transcription. Mutation of the nuclear hormone receptor binding site dramatically decreases basal promoter activity and abolishes SF-1 responsiveness. A dominant negative of SF-1, in which the transactivation (AF-2) domain of SF-1 was deleted, inhibits nNOS exon 2 promoter activity. Dosage-sensitive reversal- adrenal hypoplasia congenita critical region on the X chromosome, gene 1 (DAX-1), which colocalizes and interferes with SF-1 actions in multiple cell lineages, negatively modulates SF-1 regulation of nNOS transcription. These findings demonstrate that mouse nNOS gene expression is regulated by the SF-1 gene family in pituitary gonadotropes. nNOS, a member of the cytochrome p450 gene family, could be one of the downstream effector genes, which mediates SF-1's reproductive function and developmental patterning.

Function of the transcriptional regulating protein of 132 kDa (TReP-132) on human P450scc gene expression

Cytochrome P450scc catalyzes the important first step in the steroid synthesis pathway; however, it is clear that additional factors regulating the temporal and spacial specific expression of the CYP11A1 gene remain to be identified. To isolate novel transcription factors that regulate this gene, a cis-acting element of the 5'-flanking region from nucleotides -155 to -131 (-155/-131) was used to screen a human placental lambda gt11 cDNA expression library, and an interacting clone was isolated. The open reading frame of the cDNA encodes several domains that are characteristic of transcription factors including an acidic region, a region rich in prolines and three zinc-finger motifs. Expression of the cDNA by in vitro transcription/translation and by transient transfection in HeLa cells yielded a protein of 132 kDa, which concurs with the predicted size. Transfection of the cDNA in placental JEG-3 and adrenal NCI-H295 cells, stimulate expression of a reporter construct controlled by the P450scc gene 5'-flanking region from nucleotides -1676 to +49. This transcriptional regulating protein of 132kDa (TReP-132) when expressed in HeLa cells was demonstrated to interact with the -155/-131 region in bandshift analysis, and tandem copies of this region was shown to confer activation of the heterologous HSV thymidine kinase minimal promoter. Coexpression of CBP/p300 with TReP-132 further increased promoter activity, and the proteins were demonstrated to interact physically. RNA analysis demonstrated the highest levels of expression in the adrenal cortex and testis; and transcript expression is also found in the steroidogenic JEG-3, NCI-H295, and MCF-7 cell lines, but not in non-steroidogenic HepG2 and HK293 cells. Subsequently it has been shown that TReP-132 interacts with steroidogenic factor-1 (SF-1) through specific domains; and along with the interaction with CBP/p300 these factors are postulated to form a complex to regulate expression of the P450scc gene.

The transcriptional regulating protein of 132 kDa (TReP-132) enhances P450scc gene transcription through interaction with steroidogenic factor-1 in human adrenal cells

The human P450scc gene is regulated by the tissue-specific orphan nuclear receptor, steroidogenic factor-1 (SF-1), which plays a key role in several physiologic processes including steroid synthesis, adrenal and gonadal development, and sexual differentiation. Several studies have demonstrated the interaction of SF-1 with different proteins. However, it is clear that additional factors not yet identified are involved with SF-1 to regulate different target genes. Recently, it was demonstrated that a novel transcriptional regulating protein of 132 kDa (TReP-132) regulates expression of the human P450scc gene. The overexpression of TReP-132 in adrenal cells increases the production of pregnenolone, which is associated with the activation of P450scc gene expression. Considering the colocalization of TReP-132 and SF-1 in steroidogenic tissues such as the adrenal and testis, and the presence of two putative LXXLL motifs in TReP-132 that can potentially interact with SF-1, the relationship between these two factors on the P450scc gene promoter was determined. The coexpression of SF-1 and TReP-132 in adrenal NCI-H295 cells cooperates to increase promoter activity. Pull-down experiments demonstrated the interaction between TReP-132 and SF-1, and this was further confirmed in intact cells by coimmunoprecipitation/Western blot and two-hybrid analyses. Deletions and mutations of the TReP-132 cDNA sequence demonstrate that SF-1 interaction requires the LXXLL motif found at the amino-terminal region of the protein. Also, the "proximal activation domain" and the "AF-2 hexamer" motif of SF-1 are involved in interaction with TReP-132. Consistent with previous studies showing interaction between CBP/p300 and SF-1 or TReP-132, the coexpression of these three proteins results in a synergistic effect on P450scc gene promoter activity. Taken together the results in this study identify a novel function of TReP-132 as a partner in a complex with SF-1 and CBP/p300 to regulate gene transcription involved in steroidogenesis.

WT1 and DAX-1 inhibit aromatase P450 expression in human endometrial and endometriotic stromal cells

The orphan nuclear receptor steroidogenic factor-1 (SF-1) induces the expression of Müllerian inhibiting substance (MIS) and many steroidogenic genes, including aromatase P450 (P450arom). Dosage-sensitive sex reversal adrenal hypoplasia congenita critical region on the X chromosome gene 1 (DAX-1) inhibits SF-1-mediated induction of MIS and other steroidogenic genes, whereas Wilms' tumor suppressor gene (WT1) augments SF-1-mediated MIS expression. The effects of WT1 on steroidogenesis or P450arom expression have not been explored to date. In human endometriotic stromal cells, extremely high levels of P450arom mRNA and enzyme activity are present. Prostaglandin E(2) stimulates cAMP formation, SF-1 binding activity, P450arom mRNA levels, and estrogen synthesis in endometriotic stromal cells. Stromal cells of eutopic endometrium from disease-free women, on other hand, do not contain readily detectable levels of P450arom mRNA. Thus, we evaluated herein the possible roles of WT1 and DAX-1 in cAMP/SF-1-mediated regulation of P450arom expression in endometriotic and endometrial stromal cells. We also determined the cellular distribution and levels of these transcription factors in pathological endometriotic vs. normal eutopic endometrial tissues by immunohistochemistry to understand their in vivo roles. In vitro transcriptional regulation studies showed that both WT1 and DAX-1 inhibited cAMP and/or SF-1-induced P450arom promoter activity in a dose-dependent fashion in cultured human endometriotic and endometrial stromal cells. Site-directed disruption of the SF-1 binding site (-136/-124 bp) in the P450arom promoter abolished basal or cAMP/SF-1-induced promoter activity in the presence or absence of WT1 or DAX-1. Immunohistochemistry and H-scoring showed that DAX-1 was ubiquitously present in epithelial and stromal cells of both tissues. WT1, on the other hand, was preferentially expressed in stromal (vs. epithelial) cells. Moreover, WT1 levels in endometriotic stromal cells are significantly down-regulated compared with normal endometrial stromal cells. In summary, WT1 or DAX-1 inhibits cAMP-SF-1 pathway-dependent P450arom expression in cultured human endometriotic and endometrial stromal cells. In vivo down-regulation of WT1 in endometriotic stromal cells (vs. normal endometrial stromal cells) may in part be responsible for aberrantly increased P450arom expression and estrogen formation in this pathological tissue.

Recent insights into organogenesis of the adrenal cortex

The primary endocrine organs responsible for steroid hormone biosynthesis--the adrenal cortex and gonads--are derived from the urogenital ridge. Several recent discoveries in human and mouse genetics have begun to unravel the complex genetic cascade that dictates adrenocortical cell lineage, proliferation and differentiation. The factors that regulate adrenocortical organogenesis and the maintenance of growth promote or block a cascade of transcription factors that differentially coordinate the proliferation and differentiation of the gland. Here, we outline the developmental milestones of the adrenal cortex with recent contributions to the field, focusing on factors that have been shown to play a role in vivo in humans and mice.

Sexually dimorphic expression of Dax-1 in the adrenal cortex

BACKGROUND

The DAX-1 (also known as AHC) gene encodes an unusual member of the nuclear receptor superfamily, and the gene product plays a pivotal role during gonadal and adrenal differentiation. Mutations of the human DAX-1 gene cause X-linked adrenal hypoplasia congenita associated with hypogonadotropic hypogonadism. However, the molecular mechanisms underlying the transcriptional regulation of the gene are not well understood.

RESULTS

Sexually dimorphic expression of Dax-1 (NR0B1) in the adrenal cortex was observed by RT-PCR, Western blotting and immunohistochemistry. The differential expression was abolished by gonadectomy and was restored again by sex steroid replacement. Our results suggested that the Dax-1 gene transcription is suppressed by androgens and androgen receptor (AR/NR3C4). Dax-1 gene transcription is regulated by Ad4BP/SF-1 (NR5A1), therefore we investigated the functional correlation between A4BP/SF-1 and AR. Interestingly, AR down-regulated the Dax-1 gene transcription mediated by Ad4BP/SF-1 in the presence of the ligand. DNA binding by AR was not essential for the suppressive action, however the suppression seemed to be dependent on the promoter contexts. An interaction between Ad4BP/SF-1 and AR was detected in the presence of the ligand for AR.

CONCLUSION

The present study revealed that the expression of Dax-1 in the adrenal cortex is regulated by androgen and the receptor. Interestingly, AR acts as a suppressor in the presence of the ligand through interaction with Ad4BP/SF-1.

The role of SF1 in adrenal and reproductive function: insight from naturally occurring mutations in humans

Steroidogenic factor 1 is a monomeric orphan nuclear receptor and one of several hundreds of transcription factors encoded in the human genome. It regulates the transcription of many genes involved in gonadal development, sexual differentiation, steroidogenesis and reproduction. Recently, mutations in the gene encoding SF1 have been identified in several patients with primary adrenal failure and 46,XY sex-reversal. Interpreting the consequences of these mutations provides further understanding of transcription factor haploinsufficiency in human genetic disease as well as the exquisite sensitivity of humans to gene-dosage effects during adrenal and gonadal development.

Phenotypic spectrum of mutations in DAX-1 and SF-1

SF-1 (steroidogenic factor-1) (NR5A1) and DAX-1 (dosage-sensitive sex-reversal, adrenal hypoplasia congenital, X chromosome) (NR0B1) are orphan nuclear receptors that are expressed in the adrenal gland, gonads, ventromedial hypothalamus (VMH), and pituitary gonadotrope cells. The function of these genes has been clarified by examining the consequences of naturally occurring mutations in humans, as well as targeted disruption of the genes in mice. Mutations in DAX1 cause adrenal hypoplasia congenita (AHC), an X-linked disorder characterized by adrenal insufficiency and failure to undergo puberty because of hypogonadotropic hypogonadism. Most DAX1 mutations introduce frameshifts and/or cause premature termination of the protein. Relatively few missense mutations have been described and all are located within the carboxy-terminal half of the protein. Transfection assays demonstrate that AHC-associated DAX1 mutations abrogate its ability to act as a transcriptional repressor of SF-1. Most boys affected with AHC present with adrenal insufficiency in early infancy, although a significant fraction present in later childhood or even as young adults. The degree of gonadotropin deficiency is also variable. With the exception of one mild missense DAX1 mutation, genotype-phenotype correlations have been elusive, suggesting an important role for modifier genes. Targeted mutagenesis of Dax1 (Ahch) in mice reveals an additional role in testis development and spermatogenesis. Similar abnormalities appear to be present in humans. Targeted mutagenesis of Sf1 (FtzF1) prevents gonadal and adrenal development, and causes male-to-female sex-reversal. A human XY individual with a heterozygous SF1 mutation presented with adrenal insufficiency and complete sex-reversal; this DNA-binding domain mutation prevents SF-1 stimulation of its target genes. In addition to their clinical relevance, studies of SF1 and DAX1 are proving useful for unraveling the genetic pathways that govern adrenal and gonadal development.

Follicle-stimulating hormone stimulates protein kinase A-mediated histone H3 phosphorylation and acetylation leading to select gene activation in ovarian granulosa cells

We examined the phosphorylation and acetylation of histone H3 in ovarian granulosa cells stimulated to differentiate by follicle-stimulating hormone (FSH). We found that protein kinase A (PKA) mediates H3 phosphorylation on serine 10, based on inhibition exclusively by PKA inhibitors. FSH-stimulated H3 phosphorylation in granulosa cells is not downstream of mitogen-activated protein kinase/extracellular signal-regulated kinase, ribosomal S6 kinase-2, mitogen- and stress-activated protein kinase-1, p38 MAPK, phosphatidylinositol-3 kinase, or protein kinase C. Transcriptional activation-associated H3 phosphorylation on serine 10 and acetylation of lysine 14 leads to activation of serum glucocorticoid kinase, inhibin alpha, and c-fos genes. We propose that phosphorylation of histone H3 on serine 10 by PKA in coordination with acetylation of H3 on lysine 14 results in reorganization of the promoters of select FSH responsive genes into a more accessible configuration for activation. The unique role of PKA as the physiological histone H3 kinase is consistent with the central role of PKA in initiating granulosa cell differentiation.

Acetylation of steroidogenic factor 1 protein regulates its transcriptional activity and recruits the coactivator GCN5

Steroidogenic factor-1 (SF-1) is an orphan nuclear receptor that plays an essential role in the development of the hypothalamic-pituitary-gonadal axis in both sexes. SF-1 belongs to the hormone nuclear receptor superfamily and possesses an N-terminal DNA binding domain and a C-terminal ligand binding domain. Activation function domain 2 is located C-terminal of the ligand binding domain of SF-1 and is important for the transactivation of target genes. Coactivators with histone acetyltransferase activity such as cAMP response element-binding protein-binding protein and steroid receptor coactivator 1 interact and increase SF-1-mediated transcriptional activity. In this study we demonstrate that SF-1 is acetylated in vivo. Histone acetyltransferase GCN5 acetylates SF-1 in vitro. Moreover, we found that SF-1 recruited a novel coactivator GCN5, which can be a newly identified coactivator for SF-1. Acetylation of SF-1 stimulates its transcriptional activity. Inhibition of deacetylation by trichostatin A, a histone deacetylase inhibitor, increased SF-1-mediated transactivation and stabilized and induced the nuclear export of the SF-1 protein.

The effect of the arylhydrocarbon receptor on the human steroidogenic acute regulatory gene promoter activity

The steroidogenic acute regulatory (StAR) protein is a rate-limiting factor in steroid hormone production. The StAR protein plays a role in the movement of cholesterol from the outer membrane to the inner membrane, where cholesterol side chain cleavage enzyme exists. Dioxins, which may act as 'endocrine disruptors', mimic and antagonize endogenous hormone actions in vivo. Although the mechanism of endocrine disruption is not clear, the actions of dioxins are known to be mediated by binding to the arylhydrocarbon receptor (AhR), and it is known that dioxins act as transcription factors to endocrine-associated gene expression. In the present study, we examined the effect of the AhR on the human StAR gene promoter, and we clarified the action mechanisms of environmental endocrine disruptors. We transfected constructs containing the human StAR gene promoter sequences pGL(2) 1.3-kb StAR (nt -1293 to +39) into mouse Y-1 adrenal tumor cells and measured the promoter activity of the StAR gene. With the addition of beta-napthoflavone (betaNF), which is a ligand of AhR, to the culture medium, the activity of the StAR gene promoter increased significantly (P<0.05), and with the addition of 1 microM of betaNF, it became maximum (3.1+/-0.6-fold higher than the control value). When the AhR and ARNT were co-transfected together in Y-1 cells or human adrenocortical carcinoma H295R cells, the promoter activity of the StAR gene significantly (P<0.05) increased, to a level 1.4+/-0.01-fold higher in Y-1 cells and to a level 1.6+/-0.04-fold higher in H295R cells than the control level, when 1 microM of betaNF was added. We examined the effect of induction of cAMP with transfection with AhR or ARNT. With the addition of 1 mM 8-Br-cAMP, there were no differences between the StAR gene promoter activities in the group in which AhR and ARNT was introduced and in the group in which they were not introduced. The results suggest that AhR plays a role in the promoter activity of the human StAR gene and that the effect of AhR on StAR gene expression may cause a disturbance to the human endocrine system.

The nuclear receptor Ftz-F1 and homeodomain protein Ftz interact through evolutionarily conserved protein domains

The Drosophila homeodomain protein Fushi Tarazu (Ftz) and its partner, the orphan receptor Ftz-F1, are members of two distinct families of DNA binding transcriptional regulators. Ftz and Ftz-F1 form a novel partnership in vivo as a Hox/orphan receptor heterodimer. Here we show that the murine Ftz-F1 ortholog SF-1 functionally substitutes for Ftz-F1 in vivo, rescuing the defects of ftz-f1 mutants. This finding identified evolutionarily conserved domains of Ftz-F1 as critical for activity of this receptor in vivo. These domains function, at least in part, by mediating direct protein interactions with Ftz. The Ftz-F1 DNA binding domain interacts strongly with Ftz and dramatically facilitates the binding of Ftz to target DNA. This interaction is augmented by a second interaction between the AF-2 domain of Ftz-F1 and the N-terminus of Ftz via an LRALL sequence in Ftz that is reminiscent of LXXLL motifs in nuclear receptor coactivators. We propose that Ftz-F1 serves as a cofactor for Ftz by facilitating the selection of target sites in the genome that contain Ftz/Ftz-F1 composite binding sites. Ftz, on the other hand, influences Ftz-F1 activity by interacting with its AF-2 domain in a manner that mimics a nuclear receptor coactivator.

Expression of FTZ-F1alpha in frog testicular cells

Fushi tarazu transcription factor-1 (FTZ-F1), a member of a nuclear hormone receptor superfamily, is a transcriptional regulator for fushi tarazu gene expression in Drosophila (Ueda et al., '90). We have cloned a homologue (rrFTZ-F1alpha) of the FTZ-F1 gene of the frog Rana rugosa. The gene, in frogs, has been shown to have high expression level in the testis (Nakajima et al., 2000). In this study, the RT-PCR analysis showed that the FTZ-F1alpha mRNA level in adult frogs did not change throughout the year, even during hibernation. However, when immunohistological studies using the anti-rrFTZ-F1alpha antibody were employed to examine which testicular cells expressed this gene, Sertoli cells were found to produce rrFTZ-F1alpha in the two seasons: the breeding season (from March through May) and the pre-hibernating season (from October through November). Interstitial cells, however, did it in only the breeding season (from April through May). Taken together, the results suggest that the rrFTZ-F1alpha expression is regulated at the post-transcriptional step, and that the rrFTZ-F1alpha may play an important role(s) in the seasonal activities of Sertoli and interstitial cells in the frog testis. J. Exp. Zool. 290:182-189, 2001.

Pituitary adenylate cyclase-activating polypeptide and cyclic adenosine 3',5'-monophosphate stimulate the promoter activity of the rat gonadotropin-releasing hormone receptor gene via a bipartite response element in gonadotrope-derived cells

Specific type I receptors for pituitary adenylate cyclase-activating polypeptide (PACAP) are present in gonadotrope cells of the anterior pituitary gland. By transient transfection of mouse gonadotrope-derived alphaT3-1 cells, which are direct targets for PACAP and express gonadotropin-releasing hormone receptor (GnRH-R), a marker of the gonadotrope lineage, we provide the first evidence that PACAP stimulates rat GnRH-R gene promoter activity. The EC(50) of this stimulation is compatible with a mediation via activation of the cyclic AMP-dependent signaling pathway and, consistently, co-transfection of an expression vector expressing the protein kinase A inhibitor causes reduction in PACAP as well as cholera toxin-stimulated promoter activity. Deletion and mutational analyses indicate that PACAP activation necessitates a bipartite response element that consists of a first region (-272/-237) termed PACAP response element (PARE) I that includes a steroidogenic factor-1 (SF-1)-binding site and a second region (-136/-101) referred to as PARE II that contains an imperfect cyclic AMP response element. Gel shift experiments indicate the specific binding of the SF-1 and a potential SF-1-interacting factor to PARE I while a protein immunologically related to the cyclic AMP response element-binding protein interacts with PARE II. These findings suggest that PACAP might regulate the GnRH-R gene at the transcriptional level, providing novel insights into the regulation of pituitary-specific genes by hypothalamic hypophysiotropic signals.

Transcriptional activation of genes by 17 beta-estradiol through estrogen receptor-Sp1 interactions

Estrogen receptor-alpha (ER alpha) is a ligand-activated transcription factor and a member of the nuclear receptor superfamily. The classic mechanism of ER alpha action is associated with estrogen-induced formation of a nuclear ER alpha homodimer, binding to 5'-regulatory estrogen response elements (EREs) in target gene promoters, interaction with other nuclear proteins, and general transcription factors to activate gene expression. ER alpha also interacts with Sp1 protein to transactivate genes through binding Sp1(N)xERE or Sp1(N)xERE half-site (1/2) motifs where both ER alpha and Sp1 bind DNA elements. Activation through Sp1(N)xERE1/2 requires interactions of both proteins with their cognate DNA elements as well as additional nuclear factors to form a functional ER alpha/Sp1-DNA complex. Recent studies also show that ER alpha and Sp1 physically interact and ER alpha preferentially binds to the C-terminal DNA-binding domain of Sp1 protein. Moreover, ER alpha/Sp1 can activate transcription from a consensus GC-rich Sp1 binding site in transient transfection studies in MCF-7 human breast cancer cells, and this response is also observed with ER alpha variants that do not contain the DNA-binding domain. Several genes that are induced by estrogens in MCF-7 cells are activated through one or more GC-rich sites in their regulatory regions and these include the cathepsin D, E2F1, bcl-2, c-fos, adenosine deaminase, insulinlike growth factor binding protein 4, and retinoic acid receptor alpha 1 genes. ER alpha/Sp1 and ER beta/Sp1 action is dependent on ligand structure and cell context and ER beta/Sp1 is primarily associated with decreased ligand-dependent gene expression. ER alpha/Sp1, like ER alpha/AP1, represents a pathway for hormone activation of genes in which the receptor does not bind DNA, and results of ongoing studies suggest that ER alpha/Sp1 plays an important role in transcriptional activation of multiple growth regulatory genes in breast cancer cells.

A novel zinc finger protein TReP-132 interacts with CBP/p300 to regulate human CYP11A1 gene expression

The human CYP11A1 gene is expressed specifically in steroidogenic tissues and encodes cytochrome P450scc, which catalyzes the first step in steroid synthesis. A region of the 5'-flanking DNA of the gene from nucleotides -155 to -131 (-155/-131) is shown to activate transcription in steroidogenic human placental JEG-3 (1) and adrenal NCI-H295 cells. Using this region of the gene as probe, a cDNA clone of 4.4 kilobase pairs was isolated by screening JEG-3 cell and human placental cDNA expression libraries. The open reading frame encodes three zinc fingers of the C(2)H(2) subtype, and separate regions rich in glutamate, proline, and glutamine, which are indicative of a DNA-binding protein involved in gene transcription. Expression of the cDNA in vitro and in HeLa cells yields a protein of 132 kDa, which concurs with the predicted size. Northern blot analysis demonstrate expression of two TReP-132 transcripts of 4.4 and 7.5 kilobase pairs in the thymus, adrenal cortex, and testis; and expression is also found in the steroidogenic JEG-3, NCI-H295, and MCF-7 cell lines. Immunocytochemistry analysis demonstrates localization of the HA-tagged TReP-132 protein in the nucleus. The expression of exogenous TReP-132 in HeLa cells was demonstrated to interact with the -155/-131 region in bandshift analysis. Transfection of the cDNA in placental JEG-3 and adrenal NCI-H295 cells increases expression of a reporter construct controlled by the P450scc gene 5'-flanking region from nucleotides -1676 to +49. Moreover, a chimeric protein generated by fusion of TReP-132 with the Gal4 DNA-binding domain was able to significantly increase promoter activity of a reporter construct via Gal4-binding sites upstream of the E1b minimal promoter. Coexpression of CREB-binding protein (CBP)/p300 with TReP-132 has an additive effect on promoter activity, and the proteins were demonstrated to interact physically. Thus, these results together indicate the isolation of a novel zinc-finger transcriptional regulating protein of 132 kDa (TReP-132) involved in the regulation of P450scc gene expression.

Effects of mutating different steroidogenic factor-1 protein regions on gene regulation

The involvement of cyclic adenosine monophosphate cAMP-dependent protein kinase A (PKA) in the regulation of the steroidogenic acute regulatory protein (StAR) and the high-density lipoprotein receptor (HDL-R) genes by steroidogenic factor-1 (SF-1) and cAMP were examined. Cotransfection studies carried out in Kin 8 cells, a Y1 cell line (mouse adrenal) with a mutation in the type I PKA regulatory subunit, demonstrated that an intact PKA is required for maximal activation and that SF-1 participates in cAMP regulation of these genes. Site-directed mutational analysis was performed to examine which SF-1 regions could be involved in SF-1 transcriptional activation of the StAR and HDL-R genes. SF-1 regions protein analyzed were amino acids Thr 60, Ser 203, Ser 431, Thr 462, and the activation function-2 domain (amino acids 449-462). Plasmids encoding each of the mutated SF-1 proteins were cotransfected with the StAR and HDL-R promoter constructs into human bladder carcinoma (HTB-9) cells in the presence or absence of dibutyryl cAMP. The results of these studies suggest that although SF-1 is required for optimal promoter response to cAMP, transcriptional activation of genes by SF-1 and cAMP are promoter dependent, perhaps resulting from gene-specific interactions of this transcription factor with other regulatory proteins.

Characterization of a steroidogenic factor-1-binding site found in promoter of sterol carrier protein-2 gene

Sterol carrier protein-2 (SCP2) is thought to mediate intracellular cholesterol transport in steroidogenic tissues. To elucidate the mechanism underlying the expression of this gene, a 300-bp fragment of the SCP2 promoter was cloned and analyzed for regulatory motifs. This promoter region contained a SF-1 binding motif, three activator protein-1 elements, an insulin response element, and a peroxisomal proliferator response element. The putative SF-1 binding region reacted with recombinant SF-1 DNA-binding domain in a mobility shift assay. The SCP2 promoter fragment was linked to a luciferase reporter gene and cotransfected in the presence or absence of SF-1 into HTB-9 cells. The results indicated that SF-1 was able to increase SCP2 promoter activity, an effect that was enhanced by cAMP. Similar results were obtained when the SCP2 promoter construct was cotransfected into Y1 cells. Cotransfection studies carried out in Kin 8 cells, a Y1 cell line with a mutation that prevents cAMP activation of PKA, revealed that a functional PKA is required for cAMP induction of SCP2 gene transcription. These results demonstrated that SF-1 confers cAMP responsiveness to the SCP2 promoter suggesting that SF-1 activation may be critical in regulation of this cholesterol transport protein.

Ectopic and abnormal hormone receptors in adrenal Cushing's syndrome

The mechanism by which cortisol is produced in adrenal Cushing's syndrome, when ACTH is suppressed, was previously unknown and was referred to as being "autonomous." More recently, several investigators have shown that some cortisol and other steroid-producing adrenal tumors or hyperplasias are under the control of ectopic (or aberrant, illicit, inappropriate) membrane hormone receptors. These include ectopic receptors for gastric inhibitory polypeptide (GIP), beta-adrenergic agonists, or LH/hCG; a similar outcome can result from altered activity of eutopic receptors, such as those for vasopressin (V1-AVPR), serotonin (5-HT4), or possibly leptin. The presence of aberrant receptors places adrenal cells under stimulation by a trophic factor not negatively regulated by glucocorticoids, leading to increased steroidogenesis and possibly to the proliferative phenotype. The molecular mechanisms responsible for the abnormal expression and function of membrane hormone receptors are still largely unknown. Identification of the presence of these illicit receptors can eventually lead to new pharmacological therapies as alternatives to adrenalectomy, now demonstrated by the long-term control of ectopic P-AR- and LH/hCGR-dependent Cushing's syndrome by propanolol and leuprolide acetate. Further studies will potentially identify a larger diversity of hormone receptors capable of coupling to G proteins, adenylyl cyclase, and steroidogenesis in functional adrenal tumors and probably in other endocrine and nonendocrine tumors.

Proximal cis-acting elements, including steroidogenic factor 1, mediate the efficiency of a distal enhancer in the promoter of the rat gonadotropin-releasing hormone receptor gene

The gonadotrope-specific and regulated expression of the GnRH receptor (GnRH-R) gene is dependent on multiple transcription factors that interact with the noncanonical GnRH-R activating sequence (GRAS), the activator protein-1 (AP-1) element, and the steroidogenic factor-1 (SF-1) binding site. However, these three elements are not sufficient to mediate the complete cell-specific expression of the rat GnRH-R gene. In the present study, we demonstrate, by transient transfection in gonadotrope-derived alphaT3-1 and LssT2 cell lines, the existence of a distal enhancer [GnRH-R- specific enhancer (GnSE)] that is highly active in the context of the GnRH-R gene promoter. We show that the GnSE activity (-1,135/-753) is mediated through a functional interaction with a proximal region (-275/-226) that includes the SF-1 response element. Regions of similar length containing either the AP-1 or GRAS elements are less active or inactive. Transfection assays using an artificial promoter containing two SF-1 elements fused to a minimal PRL promoter indicate that SF-1 is crucial in this interaction. In addition, by altering the promoter with deletion and block- replacement mutations, we have identified the active elements of GnSE within two distinct sequences at positions -983/-962 and -871/-862. Sequence analysis and electrophoretic mobility shift experiments suggest that GnSE response elements interact, in these two regions, with GATA- and LIM-related factors, respectively. Altogether, these data establish the importance of the GnSE in the GnRH-R gene expression and reveal a novel role for SF-1 as a mediator of enhancer activity, a mechanism that might regulate other SF-1 target genes.

Equine P450 cholesterol side-chain cleavage and 3 beta-hydroxysteroid dehydrogenase/delta(5)-delta(4) isomerase: molecular cloning and regulation of their messenger ribonucleic acids in equine follicles during the ovulatory process

The preovulatory LH rise is the physiological trigger of follicular luteinization, a process during which the synthesis of progesterone is markedly increased. To study the control of follicular progesterone biosynthesis in mares, the objectives of this study were to clone and characterize the equine cholesterol side-chain cleavage cytochrome P450 (P450(scc)) and 3 beta-hydroxysteroid dehydrogenase/Delta(5)-Delta(4)-isomerase (3 beta-HSD), and describe the regulation and cellular localization of their transcripts in equine follicles during hCG-induced ovulation. Complementary DNA cloning and primer extension analyses revealed that the equine P450(scc) transcript is composed of a 5'-untranslated region (UTR) of 52 nucleotides, an open reading frame (ORF) of 1560 nucleotides, and a 3'-UTR of 225 nucleotides, whereas the equine 3 beta-HSD mRNA consists of a 5'-UTR of 61 nucleotides, an ORF of 1119 nucleotides, and a 3'-UTR of 432 nucleotides. The equine P450(scc) and 3 beta-HSD ORF encode 520 and 373 amino acid proteins, respectively, that are highly conserved (68-79% identity) when compared to homologs of other mammalian species. Northern blot analyses were performed with preovulatory follicles isolated 0, 12, 24, 30, 33, 36, and 39 h post-hCG, and corpora lutea obtained on day 8 of the cycle. Results showed that levels of P450(scc) mRNA in follicular wall (theca interna with attached granulosa cells) decreased after hCG treatment (30-39 h versus 0 h post-hCG, P: < 0.05), and increased again after ovulation to reach their highest levels in corpora lutea (P: < 0.05). Northern blots on isolated cellular preparations revealed that theca interna was the predominant site of P450(scc) expression in follicles prior to hCG (P: < 0.05). However, transcript levels decreased in theca interna between 30-39 h (P: < 0.05) and increased in granulosa cells at 39 h (P: < 0.05), making the granulosa cell layer the predominant site of P450(scc) expression at the end of the ovulatory process. A different pattern of regulation was observed for 3 beta-HSD, as transcript levels remained constant throughout the luteinization process (P: > 0.05). Also, in contrast to other species, expression of 3 beta-HSD mRNA in equine preovulatory follicles was localized only in granulosa cells and not in theca interna. Thus, this study characterizes for the first time the complete structure of equine P450(scc) and 3 beta-HSD mRNA and identifies novel patterns of expression and regulation of these transcripts in equine follicles prior to ovulation.

Expression and regulation of transcripts encoding two members of the NR5A nuclear receptor subfamily of orphan nuclear receptors, steroidogenic factor-1 and NR5A2, in equine ovarian cells during the ovulatory process

Steroidogenic factor-1 (SF-1, NR5A1a) is a member of the NR5A nuclear receptor subfamily and has been implicated as a key transcriptional regulator of all ovarian steroidogenic genes in vitro. To establish links between the expression of SF-1 and that of the steroidogenic genes in vivo, the objectives of this study were to clone equine SF-1 and examine the regulation of its messenger RNA (mRNA) in follicular cells during human CG (hCG)-induced ovulation. The equine SF-1 primary transcript was cloned by a combination of RT-PCR techniques. Results showed that the transcript was composed of a 5'-untranslated region (UTR) of 161 bp, an open reading frame (ORF) of 1386 bp that encodes a highly-conserved 461-amino acid protein, and a 3'-UTR of 518 bp. The cloning of SF-1 also led to the unexpected and serendipitous isolation of the highly-related orphan nuclear receptor NR5A2, which was shown to include a 5'-UTR of 243 bp, an ORF of 1488 bp, and a 3'-UTR of 1358 bp. The NR5A2 ORF encodes a 495-amino acid protein that is 60% identical to SF-1, including 99%-similar DNA-binding domains. Northern blot analysis revealed that SF-1 and NR5A2 were expressed in all major steroidogenic tissues, with the exception that NR5A2 was not present in the adrenal. Interestingly, NR5A2 was found to be, by far, the major NR5A subfamily member expressed in the preovulatory follicle and the corpus luteum. Using a semiquantitative RT-PCR/Southern blotting approach, the regulation of SF-1 and NR5A2 mRNAs in vivo was studied in equine follicular cells obtained from preovulatory follicles isolated between 0 and 39 h post hCG. Results showed that the theca interna was the predominant site of SF-1 mRNA expression in the follicle, and that hCG caused a significant decrease in SF-1 levels between 12-39 h in theca interna and between 24-39 h post hCG in granulosa cells (P < 0.05). In contrast, the granulosa cell layer was the predominant, if not the sole, site of NR5A2 mRNA expression in the follicle. Importantly, NR5A2 was much more highly expressed in granulosa cells than SF-1. The administration of hCG caused a significant decrease in NR5A2 transcripts in granulosa cells at 30, 36, and 39 h post hCG (P < 0.05). Thus, this study is the first to report the concomitant regulation of SF-1 in theca interna and granulosa cells throughout the ovulation/luteinization process, and to demonstrate the novel expression and hormonal regulation of NR5A2 in ovarian cells. Based on the marked expression of NR5A2 in equine granulosa and luteal cells and on mounting evidence of a functional redundancy between SF-1 and NR5A2 in other species, it is proposed that NR5A2 may play a key role in the regulation of gonadal steroidogenic gene expression.

Apparently normal ovarian differentiation in a prepubertal girl with transcriptionally inactive steroidogenic factor 1 (NR5A1/SF-1) and adrenocortical insufficiency

Steroidogenic factor 1 (NR5A1/SF-1) plays an essential role in the development of the hypothalamic-pituitary-adrenal and hypothalamic-pituitary-gonadal axes, controlling expression of their many important genes. The recent description of a 46,XY patient bearing a mutation in the NR5A1 gene, causing male pseudohermaphroditism and adrenal failure, demonstrated the crucial role of SF-1 in male gonadal differentiation. The role of SF-1 in human ovarian development was, until now, unknown. We describe a phenotypically and genotypically normal girl, with signs and symptoms of adrenal insufficiency and no apparent defect in ovarian maturation, bearing a heterozygote G-->T transversion in exon 4 of the NR5A1 gene that leads to the missense R255L in the SF-1 protein. The exchange does not interfere with protein translation and stability. Consistent with the clinical picture, R255L is transcriptionally inactive and has no dominant-negative activity. The inability of the mutant (MUT) NR5A1/SF-1 to bind canonical DNA sequences might offer a possible explanation for the failure of the mutant protein to transactivate target genes. This is the first report of a mutation in the NR5A1 gene in a genotypically female patient, and it suggests that NR5A1/SF-1 is not necessary for female gonadal development, confirming the crucial role of NR5A1/SF-1 in adrenal gland formation in both sexes.

FTZ-F1alpha is expressed in the developing gonad of frogs

Fushi tarazu transcription factor-1 (FTZ-F1), a member of the nuclear hormone receptor superfamily, is a regulator for fushi tarazu gene expression in Drosophila. Its expression pattern during organogenesis in vertebrates, however, is not known yet. In this study, we cloned a frog FTZ-F1 homologue (rrFTZ-F1alpha) and analyzed its expression and localization during gonadal development of the frog Rana rugosa. Cloned rrFTZ-F1alpha cDNA encoded a protein of 501 amino acids including the regions I-III and FTZ-F1 box that are evolutionally conserved in the FTZ-F1 superfamily. rrFTZ-F1alpha shared high similarity at the amino acid level with mouse LRH-1 (76%), human FTF (92%), chicken OR2.0 (92%), Xenopus laevis FF1rA (94%) and zebrafish FF1A (82%). Northern blot analysis showed that the rrFTZ-F1alpha mRNA at a size of 7.4 kb was the most prominent in the testis among various tissues of adult frogs examined. The RT-PCR analysis revealed that the expression of rrFTZ-F1alpha was weak in the gonad of tadpoles before stage XVI, but it became stronger in the testis of froglets at stage XXV and much higher in the testis of frogs 2 months after metamorphosis. In addition, in situ hybridization analysis revealed that the rrFTZ-F1alpha gene was transcribed in germ cells except for sperm in the testis, and in oocytes at stage A in the ovary of frogs 2 months after metamorphosis. Together, these results suggest that FTZ-F1alpha probably plays an important role in differentiation of germ cells in the gonad of frogs in both sexes.

A naturally occurring steroidogenic factor-1 mutation exhibits differential binding and activation of target genes

Steroidogenic factor-1 (SF-1) is an orphan nuclear receptor that binds DNA as a monomer and regulates the transcription of multiple target genes. A mutation in the proximal (P)-box of the first zinc finger of SF-1 (G35E) has been reported to cause complete XY sex reversal and adrenal insufficiency. Because this P-box region dictates DNA binding specificity, we investigated the effect of this mutation on DNA binding and regulation of target genes. Binding of the P-box mutant was markedly impaired for most native SF-1 response elements. However, mutant SF-1 bound to a subset of response elements containing a CCA AGGTCA motif. Mutagenesis studies of response elements revealed that the first nucleotide position in the 5'-flanking sequence triplet and the central part of the half-site dictate DNA binding specificity by the mutant SF-1. Further, introduction of a mutation into the SF-1 A-box, which has been proposed to bind to the 5'-flanking sequence triplet, eliminated binding by mutant SF-1 to all response elements tested. These data support the idea that the A-box stabilizes monomeric binding by nuclear receptors. This action may be particularly important when P-box binding affinity is compromised either by mutations in SF-1 or by sequence alterations in its binding site.

Sp1 and SF-1 interact and cooperate in the regulation of human steroidogenic acute regulatory protein gene expression

Steroidogenic acute regulatory (StAR) protein plays a critical role in the movement of cholesterol from the outer to the inner mitochondrial membrane. Steroidogenic factor 1 (SF-1) controls basal and cAMP-stimulated transcription of the StAR gene. The 1.3-kb StAR promoter has three SF-1 binding sites, and two consensus transcription factor Spl binding sequences near the two most distal SF-1 binding sites. Spl mediates cAMP-dependent transcription of steroidogenic P450 enzyme genes, raising the possibility of Sp1 involvement in cAMP regulation of the StAR gene. However, the mechanism of Spl-mediated, cAMP-stimulated responsiveness is not known. In this study, we elucidated the roles of Sp1 and SF-1 in the regulation of the human StAR gene promoter. We found that there was negligible promoter activity in a pGL2 StAR construct (-235 to +39) in which Spl and SF-1 binding sites were mutated in Y-1 adrenal tumor cells. An Sp1 binding site mutation (pGL2Sp1M) did not support promoter activity, suggesting that Spl cooperates with SF-1 in regulating StAR promoter function. In gel shift assays, the SF-1 binding site formed a complex with an SF-1-GST fusion protein and Spl. Coimmunoprecipitation cross-linking experiments indicated that SF-1 physically interacts with Sp1 in vitro. Finally, a mammalian two-hybrid system was employed to demonstrate that Spl and SF-1 associate in vivo. In conclusion, our data indicate that Spl and SF-1 physically interact and cooperate in the regulation of human StAR promoter activity.

Inhibition of vascular endothelial growth factor expression in HEC1A endometrial cancer cells through interactions of estrogen receptor alpha and Sp3 proteins

Treatment of HEC1A endometrial cancer cells with 10 nm 17beta-estradiol (E2) resulted in decreased vascular endothelial growth factor (VEGF) mRNA expression, and a similar response was observed using a construct, pVEGF1, containing a VEGF gene promoter insert from -2018 to +50. In HEC1A cells transiently transfected with pVEGF1 and a series of deletion plasmids, it was shown that E2-dependent down-regulation was dependent on wild-type estrogen receptor alpha (ERalpha) and reversed by the anti-estrogen ICI 182, 780, and this response was not affected by progestins. Deletion analysis of the VEGF gene promoter identified an overlapping G/GC-rich site between -66 to -47 that was required for decreased transactivation by E2. Protein-DNA binding studies using electrophoretic mobility shift and DNA footprinting assays showed that both Sp1 and Sp3 proteins bound this region of the VEGF promoter. Coimmunoprecipitation and pull-down assays demonstrated that Sp3 and ERalpha proteins physically interact, and the interacting domains of both proteins are different from those previously observed for interactions between Sp1 and ERalpha proteins. Using a dominant negative form of Sp3 and transcriptional activation assays in Schneider SL-2 insect cells, it was confirmed that ERalpha-Sp3 interactions define a pathway for E2-mediated inhibition of gene expression, and this represents a new mechanism for decreased gene expression by E2.

Sterols and isoprenoids: signaling molecules derived from the cholesterol biosynthetic pathway

Compounds derived from the isoprenoid/cholesterol biosynthetic pathway have recently been shown to have novel biological activities. These compounds include certain sterols, oxysterols, farnesol, and geranylgeraniol, as well as the diphosphate derivatives of isopentenyl, geranyl, farnesyl, geranylgeranyl, and presqualene. They regulate transcriptional and post-transcriptional events that in turn affect lipid synthesis, meiosis, apoptosis, developmental patterning, protein cleavage, and protein degradation.