CCAAT enhancer-binding protein beta and GATA-4 binding regions within the promoter of the steroidogenic acute regulatory protein (StAR) gene are required for transcription in rat ovarian cells

FSH and ApoE4 contribute to Alzheimer's disease-like pathogenesis via C/EBPβ/δ-secretase in female mice

Alzheimer's disease (AD) is the most common dementia. It is known that women with one ApoE4 allele display greater risk and earlier onset of AD compared with men. In mice, we previously showed that follicle-stimulating hormone (FSH), a gonadotropin that rises in post-menopausal females, activates its receptor FSHR in the hippocampus, to drive AD-like pathology and cognitive impairment. Here we show in mice that ApoE4 and FSH jointly trigger AD-like pathogenesis by activating C/EBPβ/δ-secretase signaling. ApoE4 and FSH additively activate C/EBPβ/δ-secretase pathway that mediates APP and Tau proteolytic fragmentation, stimulating Aβ and neurofibrillary tangles. Ovariectomy-provoked AD-like pathologies and cognitive defects in female ApoE4-TR mice are ameliorated by anti-FSH antibody treatment. FSH administration facilitates AD-like pathologies in both young male and female ApoE4-TR mice. Furthermore, FSH stimulates AD-like pathologies and cognitive defects in ApoE4-TR mice, but not ApoE3-TR mice. Our findings suggest that in mice, augmented FSH in females with ApoE4 but not ApoE3 genotype increases vulnerability to AD-like process by activating C/EBPβ/δ-secretase signalling.

C/EBPβ/AEP Signaling Drives Alzheimer's Disease Pathogenesis

Alzheimer's disease (AD) is the most common type of dementia. Almost two-thirds of patients with AD are female. The reason for the higher susceptibility to AD onset in women is unclear. However, hormone changes during the menopausal transition are known to be associated with AD. Most recently, we reported that follicle-stimulating hormone (FSH) promotes AD pathology and enhances cognitive dysfunctions via activating the CCAAT-enhancer-binding protein (C/EBPβ)/asparagine endopeptidase (AEP) pathway. This review summarizes our current understanding of the crucial role of the C/EBPβ/AEP pathway in driving AD pathogenesis by cleaving multiple critical AD players, including APP and Tau, explaining the roles and the mechanisms of FSH in increasing the susceptibility to AD in postmenopausal females. The FSH-C/EBPβ/AEP pathway may serve as a novel therapeutic target for the treatment of AD.

Insulin-like growth factor 1 enhances follicle-stimulating hormone-induced phosphorylation of GATA4 in rat granulosa cells

Preovulatory granulosa cell (GC) differentiation is essential for the maturation and release of oocytes from the ovary. We have previously demonstrated that follicle-stimulating hormone (FSH) and insulin-like growth factors (IGFs) closely interact to control GC function. Similarly, we showed that GATA4 mediates FSH actions and it is required for preovulatory follicle formation. This report aimed to determine in vivo the effect of FSH on GATA4 phosphorylation and to investigate whether FSH and IGF1 interact to regulate GATA4 activity. In rat ovaries, treatment with equine chorionic gonadotropin (eCG) increased the phosphorylation of GATA4, which was confined to the nucleus of GCs. Using primary rat GCs, we observed that GATA4 phosphorylation at serine 105 increases the transcriptional activity of this transcription factor. Like FSH, IGF1 stimulated GATA4 phosphorylation at serine 105. Interestingly, GATA4 phosphorylation was significantly higher in cells cotreated with FSH and IGF1 when compared to FSH or IGF1 alone, suggesting that IGF1 augments the effects of FSH on GATA4. It was also found that the enhancing effect of IGF1 requires AKT activity and is mimicked by the inhibition of glycogen synthase kinase-3 β (GSK3β), suggesting that AKT inhibition of GSK3β may play a role in the regulation of GATA4 phosphorylation. The data support an important role of the IGF1/AKT/GSK3β signaling pathway in the regulation of GATA4 transcriptional activity and provide new insights into the mechanisms by which FSH and IGF1 regulate GC differentiation. Our findings suggest that GATA4 transcriptional activation may, at least partially, mediate AKT actions in GCs.

A Short Promoter Region Containing Conserved Regulatory Motifs Is Required for Steroidogenic Acute Regulatory Protein (Star) Gene Expression in the Mouse Testis

In the testis, Leydig cells produce steroid hormones that are needed to masculinize typical genetic males during fetal development and to initiate and maintain spermatogenesis at puberty and adulthood, respectively. Steroidogenesis is initiated by the transfer of cholesterol from the outer to the inner mitochondrial membrane through the action of steroidogenic acute regulatory protein (STAR). Given its importance for the steroidogenic process, the regulation of STAR gene expression has been the subject of numerous studies. These studies have involved the characterization of key promoter sequences through the identification of relevant transcription factors and the nucleotide motifs (regulatory elements) that they bind. This work has traditionally relied on in vitro studies carried out in cell cultures along with reconstructed promoter sequences. While this approach has been useful for developing models of how a gene might be transcriptionally regulated, one must ultimately validate that these modes of regulation occur in an endogenous context. We have used CRISPR/Cas9 genome editing to modify a short region of the mouse Star promoter (containing a subset of regulatory elements, including conserved CRE, C/EBP, AP1, and GATA motifs) that has been proposed to be critical for Star transcription. Analysis of the resultant mutant mice showed that this short promoter region is indeed required for maximal STAR mRNA and protein levels in the testis. Analysis also showed that both basal and hormone-activated testosterone production in mature mice was unaffected despite significant changes in Star expression. Our results therefore provide the first in vivo validation of regulatory sequences required for Star gene expression.

FSH blockade improves cognition in mice with Alzheimer's disease

Alzheimer's disease has a higher incidence in older women, with a spike in cognitive decline that tracks with visceral adiposity, dysregulated energy homeostasis and bone loss during the menopausal transition1,2. Inhibiting the action of follicle-stimulating hormone (FSH) reduces body fat, enhances thermogenesis, increases bone mass and lowers serum cholesterol in mice3-7. Here we show that FSH acts directly on hippocampal and cortical neurons to accelerate amyloid-β and Tau deposition and impair cognition in mice displaying features of Alzheimer's disease. Blocking FSH action in these mice abrogates the Alzheimer's disease-like phenotype by inhibiting the neuronal C/EBPβ-δ-secretase pathway. These data not only suggest a causal role for rising serum FSH levels in the exaggerated Alzheimer's disease pathophysiology during menopause, but also reveal an opportunity for treating Alzheimer's disease, obesity, osteoporosis and dyslipidaemia with a single FSH-blocking agent.

Mechanisms of MEHP Inhibitory Action and Analysis of Potential Replacement Plasticizers on Leydig Cell Steroidogenesis

Steroid production in Leydig cells is stimulated mainly by the pituitary luteinizing hormone, which leads to increased expression of genes involved in steroidogenesis, including the gene encoding the steroidogenic acute regulatory (STAR) protein. Mono(2-ethylhexyl)phthalate (MEHP), the active metabolite of the widely used plasticizer DEHP, is known to disrupt Leydig steroidogenesis but its mechanisms of action remain poorly understood. We found that MEHP caused a significant reduction in hormone-induced steroid hormone production in two Leydig cell lines, MA-10 and MLTC-1. Consistent with disrupted cholesterol transport, we found that MEHP represses cAMP-induced Star promoter activity. MEHP responsiveness was mapped to the proximal Star promoter, which contains multiple binding sites for several transcription factors. In addition to STAR, we found that MEHP also reduced the levels of ferredoxin reductase, a protein essential for electron transport during steroidogenesis. Finally, we tested new plasticizers as alternatives to phthalates. Two plasticizers, dioctyl succinate and 1,6-hexanediol dibenzoate, had no significant effect on hormone-induced steroidogenesis. Our current findings reveal that MEHP represses steroidogenesis by affecting cholesterol transport and its conversion into pregnenolone. We also found that two novel molecules with desirable plasticizer properties have no impact on Leydig cell steroidogenesis and could be suitable phthalate replacements.

In Silico Prediction of Transcription Factor Collaborations Underlying Phenotypic Sexual Dimorphism in Zebrafish (Danio rerio)

The transcriptional regulation of gene expression in higher organisms is essential for different cellular and biological processes. These processes are controlled by transcription factors and their combinatorial interplay, which are crucial for complex genetic programs and transcriptional machinery. The regulation of sex-biased gene expression plays a major role in phenotypic sexual dimorphism in many species, causing dimorphic gene expression patterns between two different sexes. The role of transcription factor (TF) in gene regulatory mechanisms so far has not been studied for sex determination and sex-associated colour patterning in zebrafish with respect to phenotypic sexual dimorphism. To address this open biological issue, we applied bioinformatics approaches for identifying the predicted TF pairs based on their binding sites for sex and colour genes in zebrafish. In this study, we identified 25 (e.g., STAT6-GATA4; JUN-GATA4; SOX9-JUN) and 14 (e.g., IRF-STAT6; SOX9-JUN; STAT6-GATA4) potentially cooperating TFs based on their binding patterns in promoter regions for sex determination and colour pattern genes in zebrafish, respectively. The comparison between identified TFs for sex and colour genes revealed several predicted TF pairs (e.g., STAT6-GATA4; JUN-SOX9) are common for both phenotypes, which may play a pivotal role in phenotypic sexual dimorphism in zebrafish.

Effects of TG interaction factor 1 on synthesis of estradiol and progesterone in granulosa cells of goats through SMAD2/3-SP1 signaling pathway

The TG interaction factor 1 (TGIF1) is of the TALE homologue domain protein family and is considered as a transcriptional repressor of SMAD protein that interacts with DNA through a specific consensus-binding site for TG and recruits mSin3A and histone deacetylases to the SMAD complex. In this study, there is the first detailed description of TGIF1 on steroidogenesis in goat granulosa cells. When there is a relatively greater expression of the TGIF1 gene, there is a lesser abundance of CYP11A1, CYP19A1, and StAR mRNA transcript and protein and 3β-HSD mRNA transcript in granulosa cells of goats. Furthermore, there were lesser concentrations of 17β-estradiol (E₂) and progesterone (P₄) in culture medium when there was greater TGIF1 gene expression and there were greater concentrations of these hormones in the culture medium when there was lesser TGIF1 gene expression. There may be functions of TGIF1, therefore, in suppression of SMAD-induced E₂ and P₄ production and in decreasing the phosphorylation of SMAD2/3 in granulosa cells of goats and relative abundance of the SMAD2/3 protein transcription factor, SP1. With suppression of TGIF1 gene expression, there was a reversal of SP1-induced suppression of steroidogenesis-related genes. Results of the present study provide insights about the potential mechanism underlying the regulation of granulosa cell steroidogenesis of goats by TGIF1.

Granulosa cells from human primordial and primary follicles show differential global gene expression profiles

STUDY QUESTION

Can novel genetic candidates involved in follicle dormancy, activation and integrity be identified from transcriptomic profiles of isolated granulosa cells from human primordial and primary follicles?

SUMMARY ANSWER

The granulosa cell compartment of the human primordial and primary follicle was extensively enriched in signal transducer and activator of transcription 3 (STAT3) and cAMP-response element binding protein (CREB) signalling, and several other putative signalling pathways that may also be mediators of follicle growth and development were identified.

WHAT IS KNOWN ALREADY

Mechanistic target of rapamycin kinase (mTOR) signalling and the factors Forkhead Box L2 (FOXL2) and KIT proto-oncogene receptor tyrosine kinase (KITL) may be involved in defining the early steps of mammalian follicular recruitment through complex bidirectional signalling between the oocyte and granulosa cells. cAMP/protein kinase K (PKA)/CREB signalling is a feature of FSH-induced regulation of granulosa cell steroidogenesis that is essential to normal human fertility.

STUDY DESIGN, SIZE, DURATION

A class comparison study was carried out on primordial follicles (n = 539 follicles) and primary follicles (n = 261) follicles) donated by three women having ovarian tissue cryopreserved before chemotherapy.

PARTICIPANTS/MATERIALS, SETTING, METHODS

RNA samples from isolates of laser capture micro-dissected oocytes and follicles from the primordial and primary stage, respectively, were sequenced on the HiSeq Illumina platform. Data mapping, quality control, filtering, FPKM (fragments per kilobase of exon per million) normalization and comparisons were performed. The granulosa cell contribution in whole follicle isolates was extracted in silico. Modelling of complex biological systems was performed using Ingenuity Pathway Analysis (IPA). For validation of transcriptomic findings, we performed quantitative RT-PCR of selected candidate genes. Furthermore, we interrogated the in situ localization of selected corresponding proteins using immunofluorescence.

MAIN RESULTS AND THE ROLE OF CHANCE

Our differentially expressed gene analysis revealed a number of transcripts in the granulosa cells to be significantly down- (736 genes) or up- (294 genes) regulated during the human primordial-to-primary follicle transition. The IPA analysis revealed enriched canonical signalling pathways not previously associated with granulosa cells from human primordial and primary follicles. Immunofluorescent staining of human ovarian tissue explored the intra-ovarian localization of FOG2, and FOXL2, which revealed the presence of forkhead box L2 (FOXL2) in both oocytes and granulosa cells in primary follicles, with a more enriched staining in the granulosa cells in primary follicles. Friend of GATA 2 (FOG2) stained strongly in oocytes in primordial follicles, with a shift towards granulosa cell as follicle stage advanced.

LARGE SCALE DATA

http://users-birc.au.dk/biopv/published_data/ernst_et_al_GC_2017/.

LIMITATIONS REASONS FOR CAUTION

This is a descriptive study, and no functional assays were employed. The study was based on a limited number of patients, and it is acknowledged that natural biological variance exists in human samples. Strict filters were applied to accommodate the in silico extraction of the granulosa cell contribution. In support of this, quantitative RT-PCR was used to confirm selected candidate genes, and immunofluorescent staining was employed to interrogate the intra-ovarian distribution of selected corresponding proteins. Moreover, it is unknown whether the primordial follicles analysed represent those still in the resting pool, or those from the cohort that have entered the growing pool.

WIDER IMPLICATIONS OF THE FINDINGS

We present, for the first time, a detailed description of global gene activity in the human granulosa cell compartment of primordial and primary follicles. These results may be utilized in the development of novel clinical treatment strategies aimed at improving granulosa cell function.

STUDY FUNDING/COMPETING INTEREST(S)

E.H.E. was supported by the Health Faculty, Aarhus University and Kong Christian Den Tiendes Fond. K.L.H. was supported by a grant from Fondens til Lægevidenskabens Fremme and Kong Christian Den Tiendes Fond. No authors have competing interests to declare.

C/EBPβ Promotes STAT3 Expression and Affects Cell Apoptosis and Proliferation in Porcine Ovarian Granulosa Cells

Previous studies suggest that signal transducer and activator of transcription 3 (STAT3) and CCAAT/enhancer binding protein beta (C/EBPβ) play an essential role in ovarian granulosa cells (GCs) for mammalian follicular development. Several C/EBPβ putative binding sites were previously predicted on the STAT3 promoter in mammals. However, the molecular regulation of C/EBPβ on STAT3 and their effects on cell proliferation and apoptosis remain virtually unexplored in GCs. Using porcine GCs as a model, the 5′-deletion, luciferase report assay, mutation, chromatin immunoprecipitation, Annexin-V/PI staining and EdU assays were applied to investigate the molecular mechanism for C/EBPβ regulating the expression of STAT3 and their effects on the cell proliferation and apoptosis ability. We found that over and interfering with the expression of C/EBPβ significantly increased and decreased the messenger RNA (mRNA) and protein levels of STAT3, respectively. The dual luciferase reporter assay showed that C/EBPβ directly bound at −1397/−1387 of STAT3 to positively regulate the mRNA and protein expressions of STAT3. Both C/EBPβ and STAT3 were observed to inhibit cell apoptosis and promote cell proliferation. Furthermore, C/EBPβ might enhance the antiapoptotic and pro-proliferative effects of STAT3. These results would be of great insight in further exploring the molecular mechanism of C/EBPβ and STAT3 on the function of GCs and the development of ovarian follicles in mammals.

GATA Regulation and Function During the Ovarian Life Cycle

GATA4 and GATA6 are the sole GATA factors expressed in the ovary during embryonic development and adulthood. Up today, GATA4 and GATA6 are the only transcription factors that have been conditionally deleted during ovarian development and at each major stage of follicle maturation. The evidence from these transgenic mice revealed that GATA4 and GATA6 are crucial for follicles assembly, granulosa cell differentiation, postnatal follicle growth, and luteinization. Thus, conditional knockdown of both factors in the granulosa cells at any stage of development leads to female infertility. GATA targets impacting female reproduction include genes involved in steroidogenesis, hormone signaling, ovarian hormones, extracellular matrix organization, and apoptosis/cell division.

Systemic analysis of gene expression profiles in porcine granulosa cells during aging

Current studies have revealed that aging is a negative factor that suppresses granulosa cell functions and causes low fertility in women. However, the difference in gene expression between normal and aging granulosa cells remains undefined. Therefore, the aim of this study was to investigate the gene expression profiles of granulosa cells during aging. Granulosa cells from young healthy porcine ovaries were aged in vitro by prolonging the culture time (for 48h). First, the extracellular ultrastructure was observed by scanning electron microscopy followed by RNA-seq and KEGG pathway analysis. The results showed that the extracellular ultrastructure was significantly altered by aging; cell membranes were rough, and cavitations were found. Moreover, the formations of filopodia were greatly reduced. RNA-seq data revealed that 3411 genes were differentially expressed during aging, of which 2193 genes were up-regulated and 1218 genes were down-regulated. KEGG pathway analysis revealed that 25 pathways including pathway in cancer, PI3K-Akt signaling pathway, focal adhesion, proteoglycans in cancer, and cAMP signaling pathway were the most changed. Moreover, several high differentially expressed genes (CEBPB, CXCL12, ANGPT2, IGFBP3, and BBOX1) were identified in aging granulosa cells, The expressions of these genes and genes associated with extracellular matrix remodeling associated genes (TIMP3, MMP2, MMP3, and CTGF), energy metabolism associated genes (SLC2A1, PPARγ) and steroidogenesis associated genes (StAR, CYP11A1 and LHCGR) were confirmed by quantitative PCR. This study identifies the differently changed pathways and their related genes, contributes to the understanding of aging in granulosa cells, and provides an important foundation for further studies.

Role of CYP51 in the Regulation of T3 and FSH-Induced Steroidogenesis in Female Mice

Cytochrome P450 lanosterol 14α-demethylase (CYP51) is a key enzyme in sterol and steroid biosynthesis that is involved in folliculogenesis and oocyte maturation, which is regulated by follicle-stimulating hormone (FSH), as a key reproductive hormone during follicular development. Thyroid hormone (TH) is also important for normal reproductive function. Although 3,5,3'-triiodothyronine (T3) enhances FSH-induced preantral follicle growth, whether and how TH combines with FSH to regulate CYP51 expression during the preantral to early antral transition stage is unclear. The objective of this study was to determine the cellular and molecular mechanisms by which T3 and FSH regulate CYP51 expression and steroid biosynthesis during preantral follicle growth. Our results indicated that CYP51 expression was upregulated in granulosa cells by FSH, and this response was enhanced by T3. Moreover, knockdown CYP51 decreased cell viability. Meanwhile, gene knockdown also blocked T3 and FSH-induced estradiol (E2) and progesterone (P4) synthesis. These changes were accompanied by upregulation of phospho-GATA-4 content. Results of small interfering RNA analysis showed that knockdown of GATA-4 significantly diminished CYP51 gene expression as well as E2/P4 levels. Furthermore, thyroid hormone receptor β was necessary to the activation of phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt), which was required for the regulation of CYP51 expression; activated GATA-4 was also involved these processes. Our data demonstrate that T3 and FSH cotreatment potentiates cellular development and steroid biosynthesis via CYP51 upregulation, which is mediated through the activation of the PI3K/Akt pathway. Meanwhile, activated GATA-4 is also involved in this regulatory system. These findings suggest that CYP51 is a mediator of T3 and FSH-induced follicular development.

Steroidogenic effect of Erxian decoction for relieving menopause via the p-Akt/PKB pathway in vitro and in vivo

ETHNOPHARMACOLOGICAL RELEVANCE

Erxian decoction (EXD), an empirical Chinese medicine formula, is effectively used in the clinical treatment of menopause-related symptoms in China. Previous data from our group show that EXD has steroidogenic effect on natural menopausal Sprague-Dawley-rats (SD-rats) as an animal model of menopause. However, the mechanistic studies on steroidogenic effects of EXD are still inadequate. Hence, the mechanisms of steroidogenic effects of EXD were studied in vitro and in vivo in this study.

MATERIALS AND METHODS

Menopause causes a decline of endocrine function and a series of symptoms. In this study, 16-20-month-old female SD rats with a low serum estradiol level were employed. Their endocrine functions after treatment with EXD (4.1g/kg) were assessed by determination of their serum estradiol level. Proteins involved in the steroidogenic pathway including StAR, 17βHSD, 3βHSD, aromatase, and activation of phosphorylated Protein Kinase B (p-Akt/PKB), as well as estradiol receptor proteins (ERα & ERβ) after EXD treatment were analyzed. Kinase inhibition assay was conducted to confirm the mechanism of steroidogenic effects of EXD in vitro. MCF-7 and BT-483 cells were used to investigate whether EXD stimulated breast cancer cell proliferation.

RESULTS

Results revealed a significantly ameliorated serum estradiol level, and a significantly increased expression of ovarian aromatase and PKB in the EXD-treated rats. EXD attenuated 17β-estradiol stimulated proliferation of breast cancer cells.

CONCLUSIONS

The results obtained from immunoblotting and measurements of serum estradiol level of the present investigation revealed that EXD may relieve the menopausal syndrome through an upregulation of ovarian aromatase and p-PKB expression without stimulating the growth of breast cancer cells.

The Role of GATA in Mammalian Reproduction

GATA transcription factors are emerging as critical players in mammalian reproductive development and function. GATA-4 contributes to fetal male gonadal development by regulating genes mediating Müllerian duct regression and the onset of testosterone production. GATA-2 expression appears to be sexually dimorphic being transiently expressed in the germ cell lineage of the fetal ovary but not the fetal testis. In the reproductive system, GATA-1 is exclusively expressed in Sertoli cells at specific seminiferous tubule stages. In addition, GATA-4 and GATA-6 are localized primary to ovarian and testicular somatic cells. The majority of cell transfection studies demonstrate that GATA-1 and GATA-4 can stimulate inhibin subunit gene promoter constructs. Other studies provide strong evidence that GATA-4 and GATA-6 can activate genes mediating gonadal cell steroidogenesis. GATA-2 and GATA-3 are found in pituitary and placental cells and can regulate alpha-glycoprotein subunit gene expression. Gonadal expression and activation of GATAs appear to be regulated in part by gonadotropin signaling via the cyclic AMP-protein kinase A pathway. This review will cover the current knowledge regarding GATA expression and function at all levels of the reproductive axis.

Impact of ACTH Signaling on Transcriptional Regulation of Steroidogenic Genes

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

GATA4 and GATA6 Knockdown During Luteinization Inhibits Progesterone Production and Gonadotropin Responsiveness in the Corpus Luteum of Female Mice

The surge of luteinizing hormone triggers the genomic reprogramming, cell differentiation, and tissue remodeling of the ovulated follicle, leading to the formation of the corpus luteum. During this process, called luteinization, follicular granulosa cells begin expressing a new set of genes that allow the resulting luteal cells to survive in a vastly different hormonal environment and to produce the extremely high amounts of progesterone (P4) needed to sustain pregnancy. To better understand the molecular mechanisms involved in the regulation of luteal P4 production in vivo, the transcription factors GATA4 and GATA6 were knocked down in the corpus luteum by crossing mice carrying Gata4 and Gata6 floxed genes with mice carrying Cre recombinase fused to the progesterone receptor. This receptor is expressed exclusively in granulosa cells after the luteinizing hormone surge, leading to recombination of floxed genes during follicle luteinization. The findings demonstrated that GATA4 and GATA6 are essential for female fertility, whereas targeting either factor alone causes subfertility. When compared to control mice, serum P4 levels and luteal expression of key steroidogenic genes were significantly lower in conditional knockdown mice. The results also showed that GATA4 and GATA6 are required for the expression of the receptors for prolactin and luteinizing hormone, the main luteotropic hormones in mice. The findings demonstrate that GATA4 and GATA6 are crucial regulators of luteal steroidogenesis and are required for the normal response of luteal cells to luteotropins.

Identification of novel steroidogenic factor 1 (SF-1)-target genes and components of the SF-1 nuclear complex

Steroidogenic factor 1 (SF-1) is a master regulator of adrenal and reproductive development and function. Although SF-1 was identified as a transcriptional regulator for steroid metabolic enzymes, it has been shown that SF-1 also regulates other genes that are involved in various cellular processes. Previously, we showed that introduction of SF-1 into mesenchymal stem cells resulted in the differentiation of these cells to the steroidogenic lineage. By using this method of differentiation, we performed comprehensive analyses to identify the novel SF-1-target genes and components of the SF-1 nuclear complex. Genome-wide analyses with promoter tiling array and DNA microarray identified 10 genes as novel SF-1-target genes including glutathione S-transferase A family, 5-aminolevulinic acid synthase 1 and ferredoxin reductase. Using SF-1 immuno-affinity chromatography of nuclear proteins followed by MS/MS analysis, we identified 24 proteins including CCAAT/enhancer-binding protein β as components of SF-1 nuclear complex. In this review, we will describe novel roles of the newly identified genes for steroidogenesis.

Transcriptional regulation of genes related to progesterone production

Steroid hormones are synthesized from cholesterol in various tissues, mainly in the adrenal glands and gonads. Because these lipid-soluble steroid hormones immediately diffuse through the cells in which they are produced, their secretion directly reflects the activity of the genes related to their production. Progesterone is important not only for luteinization and maintenance of pregnancy, but also as a substrate for most other steroids. Steroidogenic acute regulatory protein (STAR), cytochrome P450 cholesterol side-chain cleavage enzyme (P450scc), and 3β-hydroxysteroid dehydrogenase/Δ(5)-Δ(4) isomerase (3β-HSD) are well-known proteins essential for progesterone production. In addition to them, glutathione S-transferase A1-1 and A3-3 are shown to exert Δ(5)-Δ(4) isomerization activity to produce progesterone in a cooperative fashion with 3β-HSD. 5-Aminolevulinic acid synthase 1, ferredoxin 1, and ferredoxin reductase also play a role in steroidogenesis as accessory factors. Members of the nuclear receptor 5A (NR5A) family (steroidogenic factor 1 and liver receptor homolog 1) play a crucial role in the transcriptional regulation of these genes. The NR5A family activates these genes by binding to NR5A responsive elements present within their promoter regions, as well as to the elements far from their promoters. In addition, various NR5A-interacting proteins including peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), nuclear receptor subfamily 0, group B, member 1 (DAX-1), and CCAAT/enhancer-binding proteins (C/EBP) are involved in the transcription of NR5A target genes and regulate the transcription either positively or negatively under both basal and tropic hormone-stimulated conditions. In this review, we describe the transcriptional regulation of genes related to progesterone production.

GATA4 knockdown in MA-10 Leydig cells identifies multiple target genes in the steroidogenic pathway

GATA4 is an essential transcription factor required for the initiation of genital ridge formation, for normal testicular and ovarian differentiation at the time of sex determination, and for male and female fertility in adulthood. In spite of its crucial roles, the genes and/or gene networks that are ultimately regulated by GATA4 in gonadal tissues remain to be fully understood. This is particularly true for the steroidogenic lineages such as Leydig cells of the testis where many in vitro (promoter) studies have provided good circumstantial evidence that GATA4 is a key regulator of Leydig cell gene expression and steroidogenesis, but formal proof is still lacking. We therefore performed a microarray screening analysis of MA-10 Leydig cells in which Gata4 expression was knocked down using an siRNA strategy. Analysis identified several GATA4-regulated pathways including cholesterol synthesis, cholesterol transport, and especially steroidogenesis. A decrease in GATA4 protein was associated with decreased expression of steroidogenic genes previously suspected to be GATA4 targets such as Cyp11a1 and Star. Gata4 knockdown also led to an important decrease in other novel steroidogenic targets including Srd5a1, Gsta3, Hsd3b1, and Hsd3b6, as well as genes known to participate in cholesterol metabolism such as Scarb1, Ldlr, Soat1, Scap, and Cyp51. Consistent with the decreased expression of these genes, a reduction in GATA4 protein compromised the ability of MA-10 cells to produce steroids both basally and under hormone stimulation. These data therefore provide strong evidence that GATA4 is an essential transcription factor that sits atop of the Leydig cell steroidogenic program.

Transgenic mouse models in the study of reproduction: insights into GATA protein function

For the past 2 decades, transgenic technology in mice has allowed for an unprecedented insight into the transcriptional control of reproductive development and function. The key factor among the mouse genetic tools that made this rapid advance possible is a conditional transgenic approach, a particularly versatile method of creating gene deletions and substitutions in the mouse genome. A centerpiece of this strategy is an enzyme, Cre recombinase, which is expressed from defined DNA regulatory elements that are active in the tissue of choice. The regulatory DNA element (either genetically engineered or natural) assures Cre expression only in predetermined cell types, leading to the guided deletion of genetically modified (flanked by loxP or ‘floxed’ byloxP) gene loci. This review summarizes and compares the studies in which genes encoding GATA family transcription factors were targeted either globally or by Cre recombinases active in the somatic cells of ovaries and testes. The conditional gene loss experiments require detailed knowledge of the spatial and temporal expression of Cre activity, and the challenges in interpreting the outcomes are highlighted. These studies also expose the complexity of GATA-dependent regulation of gonadal gene expression and suggest that gene function is highly context dependent.

The nuclear receptor NR2F2 activates star expression and steroidogenesis in mouse MA-10 and MLTC-1 Leydig cells

Testosterone production is dependent on cholesterol transport within the mitochondrial matrix, an essential step mediated by a protein complex containing the steroidogenic acute regulatory (STAR) protein. In steroidogenic Leydig cells, Star expression is hormonally regulated and involves several transcription factors. NR2F2 (COUP-TFII) is an orphan nuclear receptor that plays critical roles in cell differentiation and lineage determination. Conditional NR2F2 knockout prior to puberty leads to male infertility due to insufficient testosterone production, suggesting that NR2F2 could positively regulate steroidogenesis and Star expression. In this study we found that NR2F2 is expressed in the nucleus of some peritubular myoid cells and in interstitial cells, mainly in steroidogenically active adult Leydig cells. In MA-10 and MLTC-1 Leydig cells, small interfering RNA (siRNA)-mediated NR2F2 knockdown reduces basal steroid production without affecting hormone responsiveness. Consistent with this, we found that STAR mRNA and protein levels were reduced in NR2F2-depleted MA-10 and MLTC-1 cells. Transient transfections of Leydig cells revealed that a -986 bp mouse Star promoter construct was activated 3-fold by NR2F2. Using 5' progressive deletion constructs, we mapped the NR2F2-responsive element between -131 and -95 bp. This proximal promoter region contains a previously uncharacterized direct repeat 1 (DR1)-like element to which NR2F2 is recruited and directly binds. Mutations in the DR1-like element that prevent NR2F2 binding severely blunted NR2F2-mediated Star promoter activation. These data identify an essential role for the nuclear receptor NR2F2 as a direct activator of Star gene expression in Leydig cells, and thus in the control of steroid hormone biosynthesis.

C/EBPβ (CCAAT/enhancer-binding protein β) mediates progesterone production through transcriptional regulation in co-operation with SF-1 (steroidogenic factor-1)

CCAAT/enhancer-binding protein β (C/EBPβ) was identified as a component of the SF-1 nuclear complex. C/EBPβ regulates expression of progesterone production-related genes (STAR, CYP11A1 and HSD3B2) by co-operation with SF-1. Our findings reveal a novel molecular mechanism of progesterone production.

Fetal programming of adult Leydig cell function by androgenic effects on stem/progenitor cells

Fetal growth plays a role in programming of adult cardiometabolic disorders, which in men, are associated with lowered testosterone levels. Fetal growth and fetal androgen exposure can also predetermine testosterone levels in men, although how is unknown, because the adult Leydig cells (ALCs) that produce testosterone do not differentiate until puberty. To explain this conundrum, we hypothesized that stem cells for ALCs must be present in the fetal testis and might be susceptible to programming by fetal androgen exposure during masculinization. To address this hypothesis, we used ALC ablation/regeneration to identify that, in rats, ALCs derive from stem/progenitor cells that express chicken ovalbumin upstream promoter transcription factor II. These stem cells are abundant in the fetal testis of humans and rodents, and lineage tracing in mice shows that they develop into ALCs. The stem cells also express androgen receptors (ARs). Reduction in fetal androgen action through AR KO in mice or dibutyl phthalate (DBP) -induced reduction in intratesticular testosterone in rats reduced ALC stem cell number by ∼40% at birth to adulthood and induced compensated ALC failure (low/normal testosterone and elevated luteinizing hormone). In DBP-exposed males, this failure was probably explained by reduced testicular steroidogenic acute regulatory protein expression, which is associated with increased histone methylation (H3K27me3) in the proximal promoter. Accordingly, ALCs and ALC stem cells immunoexpressed increased H3K27me3, a change that was also evident in ALC stem cells in fetal testes. These studies highlight how a key component of male reproductive development can fundamentally reprogram adult hormone production (through an epigenetic change), which might affect lifetime disease risk.

CCAAT/enhancer-binding protein β is involved in the breed-dependent transcriptional regulation of 3β-hydroxysteroid dehydrogenase/Δ(5)-Δ(4)-isomerase in adrenal gland of preweaning piglets

The enzyme 3β-hydroxysteroid dehydrogenase/Δ(5)-Δ(4)-isomerase (3β-HSD) catalyzes the biosynthesis of all steroid hormones. The molecular mechanisms regulating porcine adrenal 3β-HSD expression in different breeds are still poorly understood. In this study, we aimed to compare the expression of 3β-HSD between preweaning purebred Large White (LW) and Erhualian (EHL) piglets and to explore the potential factors regulating 3β-HSD transcription. EHL had significantly higher serum levels of cortisol (P<0.01) and testosterone (P<0.01), which were associated with significantly higher expression of 3β-HSD mRNA (P<0.01) and protein (P<0.05) in the adrenal gland, compared with LW piglets. The 5' flanking region of the porcine 3β-HSD gene showed significant sequence variations between breeds, and the sequence of EHL demonstrated an elevated promoter activity (P<0.05) in luciferase reporter gene assay. Higher adrenal expression of 3β-HSD in EHL was accompanied with higher CCAAT/enhancer binding protein β (C/EBPβ) expression (P<0.05), enriched histone H3 acetylation (P<0.05) and C/EBPβ binding to 3β-HSD promoter (P<0.05). In addition, higher androgen receptor (AR) (P=0.06) and lower glucocorticoid receptor (GR) (P<0.05) were detected in EHL. Co-immunoprecipitation analysis revealed interactions of C/EBPβ with both AR and GR. These results indicate that the C/EBPβ binding to 3β-HSD promoter is responsible, at least in part, for the breed-dependent 3β-HSD expression in adrenal gland of piglets. The sequence variations of 3β-HSD promoter and the interactions of AR and/or GR with C/EBPβ may also participate in the regulation.

Low-dose monobutyl phthalate stimulates steroidogenesis through steroidogenic acute regulatory protein regulated by SF-1, GATA-4 and C/EBP-beta in mouse Leydig tumor cells

BACKGROUND

The ubiquitous use of dibutyl phthalate (DBP), one of the most widely used plasticizers, results in extensive exposure to humans and the environment. DBP and its major metabolite, monobutyl phthalate (MBP), may alter steroid biosynthesis and their exposure may lead to damage to male reproductive function. Low-doses of DBP/MBP may result in increased steroidogenesis in vitro and in vivo. However, the mechanisms of possible effects of low-dose MBP on steroidogenesis remain unclear. The aim of present study was to elaborate the role of transcription factors and steroidogenic acute regulatory protein in low-dose MBP-induced distruption of steroidogenesis in mouse Leydig tumor cells (MLTC-1 cells).

METHODS

In the present study, MLTC-1 cells were cultured in RPMI 1640 medium supplemented with 2 g/L sodium bicarbonate. Progesterone level was examined by I125-pregesterone Coat-A-Count radioimmunoassay (RIA) kits. mRNA and protein levels were assessed by reverse transcription-polymerase chain reaction (RT-PCR) and western blot, respectively. DNA-binding of several transcription factors was examined by electrophoretic mobility shift assay (EMSA).

RESULTS

In this study, various doses of MBP (0, 10(-9), 10(-8), 10(-7), or 10(-6) M) were added to the medium followed by stimulation of MLTC-1 cells with human chorionic gonadotrophin (hCG). The results showed that MBP increased progesterone production and steroidogenic acute regulatory protein (StAR) mRNA and protein levels. However, the protein levels of cytochrome P450scc and 3 beta-hydroxy-steroid dehydrogenase (3 beta-HSD) were unchanged after MBP treatment. EMSA assay showed that DNA-binding of steroidogenic factors 1(SF-1), GATA-4 and CCAAT/enhancer binding protein-beta (C/EBP-beta) was increased in a dose-dependent manner after MBP exposure. Western blot tests were next employed and confirmed that the protein levels of SF-1, GATA-4 and C/EBP-beta were also increased. Additionally, western blot tests confirmed the expression of DAX-1, negative factor of SF-1, was dose-dependently down regulated after MBP exposure, which further confirmed the role of SF-1 in MBP-stimulated steroid biosynthesis.

CONCLUSIONS

In conclusion, we firstly delineated the regulation of StAR by transcription factors including SF-1, GATA-4 and C/EBP-beta maybe critical mechanism involved in low-dose MBP-stimulated steroidogenesis.

StAR enhances transcription of genes encoding the mitochondrial proteases involved in its own degradation

Steroidogenic acute regulatory protein (StAR) is essential for steroid hormone synthesis in the adrenal cortex and the gonads. StAR activity facilitates the supply of cholesterol substrate into the inner mitochondrial membranes where conversion of the sterol to a steroid is catalyzed. Mitochondrial import terminates the cholesterol mobilization activity of StAR and leads to mounting accumulation of StAR in the mitochondrial matrix. Our studies suggest that to prevent mitochondrial impairment, StAR proteolysis is executed by at least 2 mitochondrial proteases, ie, the matrix LON protease and the inner membrane complexes of the metalloproteases AFG3L2 and AFG3L2:SPG7/paraplegin. Gonadotropin administration to prepubertal rats stimulated ovarian follicular development associated with increased expression of the mitochondrial protein quality control system. In addition, enrichment of LON and AFG3L2 is evident in StAR-expressing ovarian cells examined by confocal microscopy. Furthermore, reporter studies of the protease promoters examined in the heterologous cell model suggest that StAR expression stimulates up to a 3.5-fold increase in the protease gene transcription. Such effects are StAR-specific, are independent of StAR activity, and failed to occur upon expression of StAR mutants that do not enter the matrix. Taken together, the results of this study suggest the presence of a novel regulatory loop, whereby acute accumulation of an apparent nuisance protein in the matrix provokes a mitochondria to nucleus signaling that, in turn, activates selected transcription of genes encoding the enrichment of mitochondrial proteases relevant for enhanced clearance of StAR.

Changes in histone modification and DNA methylation of the StAR and Cyp19a1 promoter regions in granulosa cells undergoing luteinization during ovulation in rats

The ovulatory LH surge induces rapid up-regulation of steroidogenic acute regulatory (StAR) protein and rapid down-regulation of aromatase (Cyp19a1) in granulosa cells (GCs) undergoing luteinization during ovulation. This study investigated in vivo whether epigenetic mechanisms including histone modifications are involved in the rapid changes of StAR and Cyp19a1 gene expression. GCs were obtained from rats treated with equine chorionic gonadotropin (CG) before (0 h) and after human (h)CG injection. StAR mRNA levels rapidly increased after hCG injection, reached a peak at 4 h, and then remained higher compared with 0 h until 12 h. Cyp19a1 mRNA levels gradually decreased after hCG injection and reached their lowest level at 12 h. A chromatin immunoprecipitation assay revealed that levels of histone-H4 acetylation (Ac-H4) and trimethylation of histone-H3 lysine-4 (H3K4me3) increased whereas H3K9me3 and H3K27me3 decreased in the StAR promoter after hCG injection. On the other hand, the levels of Ac-H3 and -H4 and H3K4me3 decreased, and H3K27me3 increased in the Cyp19a1 promoter after hCG injection. Chromatin condensation, which was analyzed using deoxyribonuclease I, decreased in the StAR promoter and increased in the Cyp19a1 promoter after hCG injection. A chromatin immunoprecipitation assay also showed that binding activities of CAATT/enhancer-binding protein β to the StAR promoter increased and binding activities of phosphorylated-cAMP response element binding protein to the Cyp19a1 promoter decreased after hCG injection. These results provide in vivo evidence that histone modifications are involved in the rapid changes of StAR and Cyp19a1 gene expression by altering chromatin structure of the promoters in GCs undergoing luteinization during ovulation.

Loss of GATA-6 and GATA-4 in granulosa cells blocks folliculogenesis, ovulation, and follicle stimulating hormone receptor expression leading to female infertility

Single GATA-6 (G6(gcko)), GATA-4 (G4(gcko)), and double GATA-4/6 (G4/6(gcko)) granulosa cell-specific knockout mice were generated to further investigate the role of GATA transcription factors in ovarian function in vivo. No reproductive defects were found in G6(gcko) animals. G4(gcko) animals were subfertile as indicated by the reduced number of pups per litter and the release of significantly fewer oocytes at ovulation. In marked contrast, G4/6(gcko) females fail to ovulate and are infertile. Furthermore, G4/6(gcko) females had irregular estrous cycles, which correlate with the abnormal ovarian histology found in unstimulated adult G4/6(gcko) females showing lack of follicular development and increased follicular atresia. Moreover, treatment with exogenous gonadotropins did not rescue folliculogenesis or ovulation in double-knockout G4/6(gcko) mice. In addition, ovary weight and estradiol levels were significantly reduced in G4(gcko) and G4/6(gcko) animals when compared with control and G6(gcko) mice. Aromatase, P450scc, and LH receptor expression was significantly lower in G4(gcko) and G4/6(gcko) mice when compared with control animals. Most prominently, FSH receptor (FSHR) protein was undetectable in granulosa cells of G4(gcko) and G4/6(gcko). Accordingly, gel shift and reporter assays revealed that GATA-4 binds and stimulates the activity of the FSHR promoter. These results demonstrate that GATA-4 and GATA-6 are needed for normal ovarian function. Our data are consistent with a role for GATA-4 in the regulation of the FSHR gene and provide a possible molecular mechanism to explain the fertility defects observed in animals with deficient GATA expression in the ovary.

Luteinizing hormone (LH) regulates production of androstenedione and progesterone via control of histone acetylation of StAR and CYP17 promoters in ovarian theca cells

Although luteinizing hormone (LH) affects androstenedione (A4) and progesterone (P4) production in theca cells, it is still unknown how LH influences molecular mechanism of A4 and P4 production. To examine the relationship between LH and transcription factors involved in A4 and P4 production, ovarian theca cells were cultured in the presence or absence of high concentrations of LH for 24 h (pre-treatment with high concentration of LH) and then cultured in the presence or absence of low concentration of LH for 48 h. Low LH enhanced production of A4 and P4, and expressions of CYP17 and StAR mRNA in theca cells without pre-treatment with high LH. In addition, low LH stimulated the expression of SF-1 protein in nuclear fractions from theca cells with or without pre-treatment with high LH. The binding of SF-1 to the CYP17 and StAR promoter regions increased in theca cells treated with low LH. Although GATA-4 and GATA-6 are both found in the nuclear fraction but not in the cytosol of theca cells, low LH enhanced the binding of GATA-6, but not of GATA-4, to the CYP17 promoter region without pre-treatment with high LH. Acetylation histone H3 in StAR and CYP17 promoter regions were changed by different LH-dosage. Overall, we showed that LH regulates the production of A4 and P4 by affecting the nuclear localization and switching of transcription factors in theca cells and that target transcription factors involved in steroid production in theca cells are changed by different LH concentration.

Angiotensin II-dependent transcriptional activation of human steroidogenic acute regulatory protein gene by a 25-kDa cAMP-responsive element modulator protein isoform and Yin Yang 1

Transcriptional activation of the steroidogenic acute regulatory protein (STAR) gene is a critical component in the angiotensin II (Ang II)-dependent increase in aldosterone biosynthesis in the adrenal gland. The purpose of this study was to define the molecular mechanisms that mediate the Ang II-dependent increase in STARD1 gene (STAR) expression in H295R human adrenocortical cells. Mutational analysis of the STAR proximal promoter revealed that a nonconsensus cAMP-responsive element located at -78 bp relative to the transcription start site (-78CRE) is required for the Ang II-stimulated STAR reporter gene activity. DNA immunoaffinity chromatography identified a 25-kDa cAMP-responsive element modulator isoform and Yin Yang 1 (YY1) as -78CRE DNA-binding proteins, and Ang II treatment of H295R cells increased expression of that 25-kDa CREM isoform. Small interfering RNA silencing of CREM and YY1 attenuated the Ang II-dependent increases in STAR reporter gene activity and STAR mRNA levels. Conversely, overexpression of CREM and YY1 in COS-1 cells resulted in transactivation of STAR reporter gene activity. Chromatin immunoprecipitation analysis demonstrated recruitment of CREM and YY1 to the STAR promoter along with increased association of the coactivator cAMP response element-binding protein-binding protein (CBP) and increased phosphorylated RNA polymerase II after Ang II treatment. Together our data reveal that the Ang II-stimulated increase in STAR expression in H295R cells requires 25 kDa CREM and YY1. The recruitment of these transcription factors to the STAR proximal promoter results in association of CBP and activation of RNA polymerase II leading to increased STAR transcription.

GATA transcription factors in the developing reproductive system

Previous work has firmly established the role for both GATA4 and FOG2 in the initial global commitment to sexual fate, but their (joint or individual) function in subsequent steps remained unknown. Hence, gonad-specific deletions of these genes in mice were required to reveal their roles in sexual development and gene regulation. The development of tissue-specific Cre lines allowed for substantial advances in the understanding of the function of GATA proteins in sex determination, gonadal differentiation and reproductive development in mice. Here we summarize the recent work that examined the requirement of GATA4 and FOG2 proteins at several critical stages in testis and ovarian differentiation. We also discuss the molecular mechanisms involved in this regulation through the control of Dmrt1 gene expression in the testis and the canonical Wnt/ß-catenin pathway in the ovary.

Identification of a novel distal control region upstream of the human steroidogenic acute regulatory protein (StAR) gene that participates in SF-1-dependent chromatin architecture

StAR (steroidogenic acute regulatory protein) mediates the transport of cholesterol from the outer to the inner mitochondrial membrane, the process of which is the rate-limiting step for steroidogenesis. Transcriptional regulation of the proximal promoter of the human StAR gene has been well characterized, whereas analysis of its distal control region has not. Recently, we found that SF-1 (steroidogenic factor 1) induced the differentiation of mesenchymal stem cells (MSCs) into steroidogenic cells with the concomitant strong induction of StAR expression. Here, we show, using differentiated MSCs, that StAR expression is regulated by a novel distal control region. Using electrophoretic mobility shift (EMSA) and chromatin immunoprecipitation (ChIP) assays, we identified novel SF-1 binding sites between 3,000 and 3,400 bp upstream of StAR. A luciferase reporter assay revealed that the region worked as a strong regulator to exert maximal transcription of StAR. ChIP analysis of histone H3 revealed that upon SF-1 expression, nucleosome eviction took place at the SF-1 binding sites, not only in the promoter but also in the distal SF-1 binding sites. Chromosome conformation capture analysis revealed that the region upstream of StAR formed a chromatin loop both in the differentiated MSCs and in KGN cells, a human granulosa cell tumor cell line, where SF-1 is endogenously expressed. Finally, SF-1 knockdown resulted in disrupted formation of this chromatin loop in KGN cells. These results indicate that the novel distal control region participate in StAR activation through SF-1 dependent alterations of chromatin structure, including histone eviction and chromatin loop formation.

IGF1 induces up-regulation of steroidogenic and apoptotic regulatory genes via activation of phosphatidylinositol-dependent kinase/AKT in bovine granulosa cells

IGF1, a potent stimulator of cellular proliferation, differentiation and development, regulates granulosa cell steroidogenesis and apoptosis during follicular development. Depending upon species and stage of follicular growth, IGF1 acts on granulosa cell steroidogenesis either alone or together with FSH. We examined the mechanism of action of IGF1 in bovine granulosa cells in serum-free culture without insulin to determine its potential role in the regulation of steroidogenic and apoptotic regulatory gene expression and to investigate the interaction of FSH with IGF1 on this mechanism. Bovine granulosa cells treated with IGF1 demonstrated a significant increase in 17beta-oestradiol (OE(2)) production, cell number and in mRNA expression of CYP11A1, HSD3B1, CYP19A1, BAX, type 1 IGF receptor (IGF1R) and FSHR, while FSH alone had no significant effects. IGF1 or FSH alone or both together had no effect on BCL2 expression. IGF1 with FSH resulted in a synergistic increase in granulosa cell number and in mRNA expression of CYP19A1 and IGF1R without altering OE(2) production. IGF1 stimulated the phosphoinositide 3'-OH kinase (PI3K) but not the MAPK pathway in granulosa cells, as evidenced by increased phosphorylation of AKT but not extracellular-regulated kinase 1/2. Addition of the PI3K pathway inhibitor LY294002 (but not the MAPK pathway inhibitor PD98059) abrogated the increased expression of genes induced by IGF1. IGF1 therefore up-regulates the steroidogenic and apoptotic regulatory genes via activation of PI3K/AKT in bovine granulosa cells. The synergistic action of IGF1 with FSH is of likely key importance for the development of small antral follicles before selection; subsequently, other factors such as LH may also become necessary for continued cell survival.

cAMP-dependent regulation of CYP19 gene in rabbit preovulatory granulosa cells and corpus luteum

Transcription of the CYP19 gene encoding the aromatase P450 enzyme in ovarian cells is under the control of the two gonadotropins, follicle stimulating hormone (FSH) and luteinizing hormone (LH), via modulation of intracellular cyclic 3',5'-adenosine monophosphate (cAMP) levels. Primary cultures of rabbit ovarian cells were used to identify the functional regions of the ovarian promoter (PII) that are responsive to the gonadotropic secondary messenger and to estradiol. Transfection experiments in granulosa and luteal cells with deleted constructs of the PII promoter show that the region between -274 and -193bp is critical for cAMP-dependent transcriptional activity. A comparison of PII activities in granulosa and small luteal cells highlights a 50% decrease consecutive to the LH surge. Sequence analysis of the above mentioned region revealed the presence of a cAMP responsive element like sequence (CLS) and of a nuclear receptor element A (NREA). Binding of CREB to CLS has been shown using granulosa and luteal cells nuclear extracts. In addition, we identified the expression of NR5A1 (Steroidogenic Factor 1) and NR5A2 (Liver Receptor Homologue 1) in granulosa and luteal cells. However, the binding to NREA is observed only with granulosa cells nuclear extracts. Data suggest that the NR5A factors are not the main regulators of CYP19 gene, in contrast with the others genes of streroidogenesis enzymes, and additional sites may play an important role during the post-LH surge down-regulation of CYP19 transcription.

Transcriptional regulation of steroidogenic genes: STARD1, CYP11A1 and HSD3B

Expression of the genes that mediate the first steps in steroidogenesis, the steroidogenic acute regulatory protein (STARD1), the cholesterol side-chain cleavage enzyme, cytochrome P450scc (CYP11A1) and 3beta-hydroxysteroid dehydrogenase/Delta5-Delta4 isomerase (HSD3B), is tightly controlled by a battery of transcription factors in the adrenal cortex, the gonads and the placenta. These genes generally respond to the same hormones that stimulate steroid production through common pathways such as cAMP signaling and common actions on their promoters by proteins such as NR5A and GATA family members. However, there are distinct temporal, tissue and species-specific differences in expression between the genes that are defined by combinatorial regulation and unique promoter elements. This review will provide an overview of the hormonal and transcriptional regulation of the STARD1, CYP11A1 and specific steroidogenic HSD3B genes in the adrenal, testis, ovary and placenta and discuss the current knowledge regarding the key transcriptional factors involved.

Role of basic leucine zipper proteins in transcriptional regulation of the steroidogenic acute regulatory protein gene

The regulation of steroidogenic acute regulatory protein (StAR) gene transcription by cAMP-dependent mechanisms occurs in the absence of a consensus cAMP response element (CRE, TGACGTGA). This regulation is coordinated by multiple transcription factors that bind to sequence-specific elements located approximately 150 bp upstream of the transcription start site. Among the proteins that bind within this region, the basic leucine zipper (bZIP) family of transcription factors, i.e. CRE binding protein (CREB)/CRE modulator (CREM)/activating transcription factor (ATF), activator protein 1 (AP-1; Fos/Jun), and CCAAT enhancer binding protein beta (C/EBPbeta), interact with an overlapping region (-81/-72 bp) in the StAR promoter, mediate stimulus-transcription coupling of cAMP signaling and play integral roles in regulating StAR gene expression. These bZIP proteins are structurally similar and bind to DNA sequences as dimers; however, they exhibit discrete transcriptional activities, interact with several transcription factors and other properties that contribute in their regulatory functions. The 5'-flanking -81/-72 bp region of the StAR gene appears to function as a key element within a complex cAMP response unit by binding to different bZIP members, and the StAR promoter displays variable states of cAMP responsivity contingent upon the occupancy of these cis-elements with these transcription factors. The expression and activities of CREB/CREM/ATF, Fos/Jun and C/EBPbeta have been demonstrated to be mediated by a plethora of extracellular signals, and the phosphorylation of these proteins at several Ser and Thr residues allows recruitment of the transcriptional coactivator CREB binding protein (CBP) or its functional homolog p300 to the StAR promoter. This review will focus on the current level of understanding of the roles of selective bZIP family proteins within the complex series of processes involved in regulating StAR gene transcription.

Regulation of the steroidogenic acute regulatory protein gene expression: present and future perspectives

Steroid hormones are synthesized in the adrenal gland, gonads, placenta and brain and are critical for normal reproductive function and bodily homeostasis. The steroidogenic acute regulatory (StAR) protein regulates the rate-limiting step in steroid biosynthesis, i.e. the delivery of cholesterol from the outer to the inner mitochondrial membrane. The expression of the StAR protein is predominantly regulated by cAMP-dependent mechanisms in the adrenal and gonads. Whereas StAR plays an indispensable role in the regulation of steroid biosynthesis, a complete understanding of the regulation of its expression and function in steroidogenesis is not available. It has become clear that the regulation of StAR gene expression is a complex process that involves the interaction of a diversity of hormones and multiple signaling pathways that coordinate the cooperation and interaction of transcriptional machinery, as well as a number of post-transcriptional mechanisms that govern mRNA and protein expression. However, information is lacking on how the StAR gene is regulated in vivo such that it is expressed at appropriate times during development and is confined to the steroidogenic cells. Thus, it is not surprising that the precise mechanism involved in the regulation of StAR gene has not yet been established, which is the key to understanding the regulation of steroidogenesis in the context of both male and female development and function.

Transcription of steroidogenic acute regulatory protein in the rodent ovary and placenta: alternative modes of cyclic adenosine 3', 5'-monophosphate dependent and independent regulation

Steroid hormone synthesis is a vital function of the adrenal cortex, serves a critical role in gonadal function, and maintains pregnancy if normally executed in the placenta. The substrate for the synthesis of all steroid hormones is cholesterol, and its conversion to the first steroid, pregnenolone, by the cholesterol side-chain cleavage cytochrome P450 (CYP11A1) enzyme complex takes place in the inner mitochondrial membranes. Steroidogenic acute regulatory protein (STAR) facilitates the rate-limiting transfer of cholesterol from the outer mitochondrial membrane to CYP11A1 located in the inner organelle membranes. The current study explored the mechanisms controlling transcription of the Star gene in primary cell cultures of mouse placental trophoblast giant cells and rat ovarian granulosa cells examined throughout the course of their functional differentiation. Our findings show that the cis-elements required for Star transcription in the rodent placenta and the ovary are centered in a relatively small proximal region of the promoter. In placental trophoblast giant cells, cAMP is required for activation of the Star promoter, and the cis-elements mediating a maximal response were defined as cAMP response element 2 and GATA. EMSA studies show that placental cAMP-responsive element binding protein (CREB)-1 and activating transcription factor-2 (ATF2) bind to a -81/-78 sequence, whereas GATA-2 binds to a -66/-61 sequence. In comparison, patterns of Star regulation in the ovary suggested tissue-specific and developmental controlled modes of Star transcription. During the follicular phase, FSH/cAMP induced CREB-1 dependent activity, whereas upon luteinization STAR expression becomes cAMP and CREB independent, a functional shift conferred by FOS-related antigen-2 displacement of CREB-1 binding, and the appearance of a new requirement for CCAAT enhancer-binding protein beta and steroidogenic factor 1 that bind to upstream elements (-117/-95). These findings suggest that during evolution, the promoters of the Star gene acquired nonconsensus sequence elements enabling expression of a single gene in different organs, or allowing dynamic temporal changes corresponding to progressing phases of differentiation in a given cell type.

Role of dosage-sensitive sex reversal, adrenal hypoplasia congenita, critical region on the X chromosome, gene 1 in protein kinase A- and protein kinase C-mediated regulation of the steroidogenic acute regulatory protein expression in mouse Leydig tumor cells: mechanism of action

Dosage-sensitive sex reversal, adrenal hypoplasia congenita, critical region on the X chromosome, gene 1 (DAX-1) is an orphan nuclear receptor that has been demonstrated to be instrumental to the expression of the steroidogenic acute regulatory (StAR) protein that regulates steroid biosynthesis in steroidogenic cells. However, its mechanism of action remains obscure. The present investigation was aimed at exploring the molecular involvement of DAX-1 in protein kinase A (PKA)- and protein kinase C (PKC)-mediated regulation of StAR expression and its concomitant impact on steroid synthesis using MA-10 mouse Leydig tumor cells. We demonstrate that activation of the PKA and PKC pathways, by a cAMP analog dibutyryl (Bu)2cAMP [(Bu)2cAMP] and phorbol 12-myristate 13-acetate (PMA), respectively, markedly decreased DAX-1 expression, an event that was inversely correlated with StAR protein, StAR mRNA, and progesterone levels. Notably, the suppression of DAX-1 requires de novo transcription and translation, suggesting that the effect of DAX-1 in regulating StAR expression is dynamic. Chromatin immunoprecipitation studies revealed the association of DAX-1 with the proximal but not the distal region of the StAR promoter, and both (Bu)2cAMP and PMA decreased in vivo DAX-1-DNA interactions. EMSA and reporter gene analyses demonstrated the functional integrity of this interaction by showing that DAX-1 binds to a DNA hairpin at position -44/-20 bp of the mouse StAR promoter and that the binding of DAX-1 to this region decreases progesterone synthesis by impairing transcription of the StAR gene. In support of this, targeted silencing of endogenous DAX-1 elevated basal, (Bu)2cAMP-, and PMA-stimulated StAR expression and progesterone synthesis. Transrepression of the StAR gene by DAX-1 was tightly associated with expression of the nuclear receptors Nur77 and steroidogenic factor-1, demonstrating these factors negatively modulate the steroidogenic response. These findings provide insight into the molecular events by which DAX-1 influences the PKA and PKC signaling pathways involved in the regulation of the StAR protein and steroidogenesis in mouse Leydig tumor cells.

GATA4 reduction enhances 3',5'-cyclic adenosine 5'-monophosphate-stimulated steroidogenic acute regulatory protein messenger ribonucleic acid and progesterone production in luteinized porcine granulosa cells

Previous studies with cultured granulosa cells implicated GATA4 in gonadotropin regulation of the steroidogenic acute regulatory protein (STAR) gene. Caveats to these prior studies exist. First, GATA4 levels are reduced in granulosa-luteal cells after the LH surge when GATA6 expression is relatively high. Second, STAR mRNA expression is negligible in granulosa cells until after the LH surge. Both exogenous GATA4 and GATA6 can transactivate STAR gene promoter constructs. We used an RNA interference (RNAi) approach to determine the contributions of GATA4 and GATA6 to cAMP analog regulation of the endogenous STAR gene in luteinizing granulosa cells. STAR mRNA was stimulated by cAMP under control RNAi conditions. Surprisingly, GATA4 reduction by its respective RNAi approximately doubled the cAMP induction of STAR mRNA. At 24 h cAMP treatment, this augmentation was abolished by co-down-regulation of GATA4+GATA6. GATA6 down-regulation by itself did not alter STAR mRNA levels. GATA4+GATA6 co-down-regulation elevated basal CYP11A mRNA at 24 h treatment but did not affect its induction by cAMP. Basal levels of HSD3B mRNA were reduced by GATA4 RNAi conditions leading to a greater fold induction of its mRNA by cAMP. Fold cAMP-stimulated progesterone production was enhanced by GATA4 down-regulation but not by GATA4+GATA6 co-down-regulation. These data implicate GATA6 as the facilitator in cAMP-stimulated STAR mRNA and downstream progesterone accumulation under reduced GATA4 conditions. Data also demonstrate that basal levels of GATA4/6 are not required for cAMP induction of the STAR gene. The altered ratio of GATA4 to GATA6 after ovulation may allow GATA6 to enhance STAR mRNA accumulation.

Cyclic adenosine 3',5'-monophosphate response element-binding protein and CCAAT/enhancer-binding protein mediate prostaglandin E2-induced steroidogenic acute regulatory protein expression in endometriotic stromal cells

Aberrant expression of the steroidogenic acute regulatory (StAR) protein in human endometriotic stromal cells plays an important role in the development of endometriosis. Prostaglandin E(2) (PGE(2)) is a potent inducer of StAR expression in these cells; however, the mechanisms responsible for the transcriptional regulation of StAR remain to be elucidated. Herein we report that PGE(2)-induced StAR expression is independent of the transcriptional suppressor DAX-1 but is regulated by the transcriptional activator cyclic adenosine 3',5'-monophosphate (cAMP) response element-binding protein (CREB). A promoter activity assay revealed that the cis-element needed for the binding of the CCAAT/enhancer-binding protein (C/EBP) was critical for PGE(2)-induced StAR expression. Electrophoretic mobility shift assay demonstrated that this region of the StAR promoter was bound by C/EBPalpha, C/EBPbeta, and CREB. Forced expression of either C/EBPalpha or C/EBPbeta alone was sufficient to up-regulate StAR promoter activity whereas PGE(2) was needed to induce StAR promoter activity in CREB-overexpressed cells. Results from a chromatin immunoprecipitation assay demonstrated that the binding of C/EBPbeta to the StAR promoter was increased whereas CREB binding was unchanged after PGE(2) treatment. Taken together, PGE(2)-induced StAR promoter activity appears to be regulated by CREB and C/EBPbeta in a cooperative manner in ectopic human endometriotic stromal cells, providing a molecular framework for the etiology of endometriosis.

Positive regulation of steroidogenic acute regulatory protein gene expression through the interaction between Dlx and GATA-4 for testicular steroidogenesis

Split hand/foot malformation (SHFM) is syndromic ectrodactyly often associated with mental retardation and/or craniofacial defects. Several clinical reports previously described urogenital dysplasia such as micropenis, hypospadias, and small testis in SHFM patients. Genetic lesions in the Dlx5 and Dlx6 (Dlx5/6) locus are associated with the human genetic disorder SHFM type 1. Although Dlx5/6 are expressed in the testis, their possible function of Dlx5/6 during testis differentiation has not been described. In this study, we show that Dlx5/6 are expressed in the fetal Leydig cells during testis development. We examined the effect of Dlx5 expression on the promoter activation of the steroidogenic acute regulatory protein (StAR) gene, which is essential for gonadal and adrenal steroidogenesis, in a Leydig cell line. Dlx5 efficiently activates the StAR promoter when GATA-4, another transcription factor essential for testicular steroidogenesis, was coexpressed. The transcriptional activation required the GATA-4-recognition element in the StAR promoter region and Dlx5 can physically interact with GATA-4. Furthermore, we herein show that the double inactivation of Dlx5 and Dlx6 in the mouse leads to decreased testosterone level and abnormal masculinization phenotype. These results suggest that Dlx5 and Dlx6 participate in the control of steroidogenesis during testis development. The findings of this study may open the way to analyze human congenital birth defects.

Role of the GATA family of transcription factors in endocrine development, function, and disease

The WGATAR motif is a common nucleotide sequence found in the transcriptional regulatory regions of numerous genes. In vertebrates, these motifs are bound by one of six factors (GATA1 to GATA6) that constitute the GATA family of transcriptional regulatory proteins. Although originally considered for their roles in hematopoietic cells and the heart, GATA factors are now known to be expressed in a wide variety of tissues where they act as critical regulators of cell-specific gene expression. This includes multiple endocrine organs such as the pituitary, pancreas, adrenals, and especially the gonads. Insights into the functional roles played by GATA factors in adult organ systems have been hampered by the early embryonic lethality associated with the different Gata-null mice. This is now being overcome with the generation of tissue-specific knockout models and other knockdown strategies. These approaches, together with the increasing number of human GATA-related pathologies have greatly broadened the scope of GATA-dependent genes and, importantly, have shown that GATA action is not necessarily limited to early development. This has been particularly evident in endocrine organs where GATA factors appear to contribute to the transcription of multiple hormone-encoding genes. This review provides an overview of the GATA family of transcription factors as they relate to endocrine function and disease.

CCAAT/enhancer binding protein beta, but not steroidogenic factor-1, modulates the phthalate-induced dysregulation of rat fetal testicular steroidogenesis

Prolonged in utero exposure of fetal male rats to dibutyl phthalate (DBP) can result in a feminized phenotype characterized by malformed epididymides, hypospadias, cryptorchidism, and retained thoracic nipples, among others. These symptoms likely result, in part, from decreased expression of steroidogenic enzymes and, therefore, reduced testosterone biosynthesis. However, the molecular mechanisms involved in these changes in gene expression profiles are unknown. To understand these mechanisms in rats, in vivo DNase footprinting was adapted to provide a semiquantitative map of changes in DNA-protein interactions in the promoter region of steroidogenic genes, including steroidogenic acute regulatory, scavenger receptor B-1, cytochrome P450 side chain cleavage, and cytochrome P450 17A1, that are down-regulated after an in utero DBP exposure. Regions with altered DNase protection were coordinated with a specific DNA binding protein event by EMSA, and binding activity confirmed with chromatin immunoprecipitation. Results demonstrated altered DNase protection at regions mapping to CCAAT/enhancer binding protein beta (c/ebp beta) and steroidogenic factor-1 (SF-1). Chromatin immunoprecipitation confirmed declines in DNA-protein interactions of c/ebp beta in DBP treated animals, whereas SF-1 was reduced in both diethyl phthalate (nontoxic) and DBP (toxic) treatments. These results suggest that inhibition of c/ebp beta, and not SF-1, is critical in DBP induced inhibition of steroidogenic genes. In addition, these observations suggest a pathway redundancy in the regulation of steroidogenesis in fetal testis. In conclusion, this study presents a snapshot of changes in the structure of transcriptional machinery and proposes a mechanism of action resulting from DBP exposure.

An intronic locus control region plays an essential role in the establishment of an autonomous hepatic chromatin domain for the human vitamin D-binding protein gene

The human vitamin D-binding protein (hDBP) gene exists in a cluster of four liver-expressed genes. A minimal hDBP transgene, containing a defined set of liver-specific DNase I hypersensitive sites (HSs), is robustly expressed in mouse liver in a copy-number-dependent manner. Here we evaluate these HSs for function. Deletion of HSI, located 5' to the promoter (kb -2.1) had no significant effect on hDBP expression. In contrast, deletion of HSIV and HSV from intron 1 repressed hDBP expression and eliminated copy number dependency without a loss of liver specificity. Chromatin immunoprecipitation analysis revealed peaks of histone H3 and H4 acetylation coincident with HSIV in the intact hDBP locus. This region contains a conserved array of binding sites for the liver-enriched transcription factor C/EBP. In vitro studies revealed selective binding of C/EBPalpha to HSIV. In vivo occupancy of C/EBPalpha at HSIV was demonstrated in hepatic chromatin, and depletion of C/EBPalpha in a hepatic cell line decreased hDBP expression. A nonredundant role for C/EBPalpha was confirmed in vivo by demonstrating a reduction of hDBP expression in C/EBPalpha-null mice. Parallel studies revealed in vivo occupancy of the liver-enriched factor HNF1alpha at HSIII (at kb 0.13) within the hDBP promoter. These data demonstrate a critical role for elements within intron 1 in the establishment of an autonomous and productive hDBP chromatin locus and suggest that this function is dependent upon C/EBPalpha. Cooperative interactions between these intronic complexes and liver-restricted complexes within the target promoter are likely to underlie the consistency and liver specificity of the hDBP activation.

The steroidogenic acute regulatory protein as a target of endocrine disruption in male reproduction

Development of the adult male reproductive tract requires proper spatial-temporal expression of the sex hormones testosterone and estrogen during fetal developmental stages and at puberty. Exogenous agents that disrupt the production and/or actions of the testosterone and estrogen and cause aberrant reproductive tract development can be thought of as endocrine disruptors (ED). This review will focus on the impact of ED on testosterone production by Leydig cells during fetal development and in the adult. In particular, the genes encoding the steroidogenic acute regulatory protein (StAR) and cytochrome P450 17 alpha hydroxylase/17,20 lyase (CYP17A1) within the steroid hormone biosynthetic pathway are highlighted as ED targets. We begin with an overview of steroidogenesis and regulation of StAR then summarize the published literature on the effects of diethylstibesterol, phthalate esters, and arsenite on male reproduction with a focus on the expression and function of StAR.