Protein kinase A potentiates adrenal 4 binding protein/steroidogenic factor 1 transactivation by reintegrating the subcellular dynamic interactions of the nuclear receptor with its cofactors, general control nonderepressed-5/transformation/transcription domain-associated protein, and suppressor, dosage-sensitive sex reversal-1: a laser confocal imaging study in living KGN cells

Steroidogenic Factor 1, a Goldilocks Transcription Factor from Adrenocortical Organogenesis to Malignancy

Steroidogenic factor-1 (SF-1, also termed Ad4BP; NR5A1 in the official nomenclature) is a nuclear receptor transcription factor that plays a crucial role in the regulation of adrenal and gonadal development, function and maintenance. In addition to its classical role in regulating the expression of P450 steroid hydroxylases and other steroidogenic genes, involvement in other key processes such as cell survival/proliferation and cytoskeleton dynamics have also been highlighted for SF-1. SF-1 has a restricted pattern of expression, being expressed along the hypothalamic-pituitary axis and in steroidogenic organs since the time of their establishment. Reduced SF-1 expression affects proper gonadal and adrenal organogenesis and function. On the other hand, SF-1 overexpression is found in adrenocortical carcinoma and represents a prognostic marker for patients' survival. This review is focused on the current knowledge about SF-1 and the crucial importance of its dosage for adrenal gland development and function, from its involvement in adrenal cortex formation to tumorigenesis. Overall, data converge towards SF-1 being a key player in the complex network of transcriptional regulation within the adrenal gland in a dosage-dependent manner.

FXRα modulates leydig cell endocrine function in mouse

The hypothalamic-pituitary axis exert a major control over endocrine and exocrine testicular functions. The hypothalamic-pituitary axis corresponds to a cascade with the Gonadotropin Releasing Hormone secreted by the hypothalamus, which stimulates the synthesis and the release of Luteinizing Hormone (LH) and Follicle Stimulating Hormone by the gonadotropic cells of the anterior pituitary. The LH signaling pathway controls the steroidogenic activity of the Leydig cells via the activation of the luteinizing hormone/choriogonadotropin receptor. In order to avoid a runaway system, sex steroids exert a negative feedback within hypothalamus and pituitary. Testicular steroidogenesis is locally controlled within Leydig cells. The present work reviews some local regulations of steroidogenesis within the Leydig cells focusing mainly on the roles of the Farnesoid-X-Receptor-alpha and its interactions with several orphan members of the nuclear receptor superfamily. Further studies are required to reinforce our knowledge of the regulation of testicular endocrine function, which is necessary to ensure a better understanding of fertility disorders and then proposed an adequate treatment of the diseases.

Extension of Survival in Bilaterally Adrenalectomized Mice by Implantation of SF-1/Ad4BP-Induced Steroidogenic Cells

Mesenchymal stroma/stem cells (MSCs) exist in adult tissues, such as adipose tissue and bone marrow, and differentiate into cells of multiple lineages. In previous studies, we found that MSCs differentiate into steroidogenic cells by forced expression of steroidogenic factor 1 (SF-1)/adrenal 4 binding protein (Ad4BP), the master regulator of steroidogenesis and differentiation of pituitary gonadotrophs, adrenal glands, and gonads. In this study, SF-1/Ad4BP-induced steroidogenic cells derived from mouse adipose tissue-derived MSCs (ADSCs) were implanted under the kidney capsule of bilateral adrenalectomized (bAdx) mice. bAdx mice did not survive after 7 days. However, 4 of 9 bAdx mice implanted with SF-1/Ad4BP-induced steroidogenic cells, 1 of 10 bAdx mice transplanted with control ADSCs, and bAdx mice transplanted with an adrenal gland survived for 30 days. Plasma corticosterone levels in bAdx mice implanted with SF-1/Ad4BP-induced steroidogenic cells and control ADSCs were 5.41 ± 2.26 ng/mL (mean ± SEM) and undetectable at 7 days after implantation, respectively. After removal of the kidney bearing the graft from the surviving mice at 30 days after implantation, plasma corticosterone was not detected in any of the samples. Immunohistochemical staining revealed SF-1/Ad4BP-positive cells under the capsule of the kidney. Although we performed an adrenocorticotropin (ACTH) loading test on bAdx mice implanted with SF-1/Ad4BP-induced steroidogenic cells, ACTH responsiveness was not observed. Implantation of steroidogenic cells derived from ADSCs into bAdx mice increased the basal plasma corticosterone level and extended the survival of bAdx mice, suggesting the capability of restoring steroidogenic cells by cell transplantation therapy for adrenal insufficiency.

Circular IRE-type RNAs of the NR5A1 gene are formed in adrenocortical cells

The recently discovered circular RNAs (circRNAs) are mostly formed by back-splicing where the downstream 5' splice site splices to the upstream 3' splice site by conventional pre-mRNA splicing. These circRNAs regulate gene expression by acting as sponges for micro-RNAs or RNA-binding proteins. Here we show that the NR5A1 (previously called Ad4BP or SF-1) gene which is exclusively expressed in the adrenal cortex and steroidogenic tissue can form atypical circRNAs by unconventional splicing. Two stem loops with inositol-requiring protein-1α (IRE1α) cleavage sites are connected by an IRE1α cleavage site to form a circRNA (circIRE RNA). From total RNA of normal human adrenal cortex, we detected a circIRE RNA with connected ends by IRE1α cleavage sites in exon 6 and exon 1 (circIRE NR5A1 ex6-1 RNA). circIRE NR5A1 ex6-1 RNA was not detected in the adrenocortical cancer cell line, H295R. When IRE1α was expressed in H295R cells a different circIRE NR5A1 RNA connecting IRE1-cleavage sites in exon 7 and exon 1 was detected (circIRE NR5A1 ex7-1 RNA). The expression of this circIRE RNA was inhibited by the IRE1 inhibitor 1, STF-083010, implicating that it was formed via the ER stress pathway, where IRE1α is a major factor. This is the first report of this type of circular RNA connected by IRE1-cleavage sites found to be expressed in mammalian cells in a tissue-specific manner. To our surprise, the concomitant expression of NR5A1 was increased by IRE1α implicating that NR5A1 was not subjected to IRE1-dependent decay of mRNA (RIDD) but rather activating a transcriptional regulatory network to cope with ER stress in steroidogenic tissue reminiscent to XBP1 in other tissue. We believe this is the first report of such tissue-specific transcriptional cascade responding to ER stress as well as the novel finding of circular RNAs connected by IRE1α cleavage sites expressed in mammalian tissue.

The Orphan Nuclear Receptors Steroidogenic Factor-1 and Liver Receptor Homolog-1: Structure, Regulation, and Essential Roles in Mammalian Reproduction

Nuclear receptors are intracellular proteins that act as transcription factors. Proteins with classic nuclear receptor domain structure lacking identified signaling ligands are designated orphan nuclear receptors. Two of these, steroidogenic factor-1 (NR5A1, also known as SF-1) and liver receptor homolog-1 (NR5A2, also known as LRH-1), bind to the same DNA sequences, with different and nonoverlapping effects on targets. Endogenous regulation of both is achieved predominantly by cofactor interactions. SF-1 is expressed primarily in steroidogenic tissues, LRH-1 in tissues of endodermal origin and the gonads. Both receptors modulate cholesterol homeostasis, steroidogenesis, tissue-specific cell proliferation, and stem cell pluripotency. LRH-1 is essential for development beyond gastrulation and SF-1 for genesis of the adrenal, sexual differentiation, and Leydig cell function. Ovary-specific depletion of SF-1 disrupts follicle development, while LRH-1 depletion prevents ovulation, cumulus expansion, and luteinization. Uterine depletion of LRH-1 compromises decidualization and pregnancy. In humans, SF-1 is present in endometriotic tissue, where it regulates estrogen synthesis. SF-1 is underexpressed in ovarian cancer cells and overexpressed in Leydig cell tumors. In breast cancer cells, proliferation, migration and invasion, and chemotherapy resistance are regulated by LRH-1. In conclusion, the NR5A orphan nuclear receptors are nonredundant factors that are crucial regulators of a panoply of biological processes, across multiple reproductive tissues.

Differentiation of human induced pluripotent stem cells into Leydig-like cells with molecular compounds

Leydig cells (LCs) play crucial roles in producing testosterone, which is critical in the regulation of male reproduction and development. Low levels of testosterone will lead to male hypogonadism. LC transplantation is a promising alternative therapy for male hypogonadism. However, the source of LCs limits this strategy for clinical applications. Thus far, others have reported that LCs can be derived from stem cells by gene transfection, but the safe and effective induction method has not yet been reported. Here, we report that Leydig-like cells can be derived from human induced pluripotent stem cells (iPSCs) using a novel differentiation protocol based on molecular compounds. The iPSCs-derived Leydig-like cells (iPSC-LCs) acquired testosterone synthesis capabilities, had the similar gene expression profiles with LCs, and positively expressed Leydig cell lineage-specific protein markers LHCGR, STAR, SCARB1, SF-1, CYP11A1, HSD3B1, and HSD17B3 as well as negatively expressed iPSC-specific markers NANOG, OCT4, and SOX2. When iPSC-LCs labeled with lipophilic red dye (PKH26) were transplanted into rat testes that were selectively eliminated endogenous LCs using EDS (75 mg/kg), the transplanted iPSC-LCs could survive and function in the interstitium of testes, and accelerate the recovery of serum testosterone levels and testis weights. Collectively, these findings demonstrated that the iPSCs were able to be differentiated into Leydig-like cells by few defined molecular compounds, which may lay the safer groundwork for further clinical application of iPSC-LCs for hypogonadism.

Dynamic responses of the adrenal steroidogenic regulatory network

The hypothalamic-pituitary-adrenal axis is a dynamic system regulating glucocorticoid hormone synthesis in the adrenal glands. Many key factors within the adrenal steroidogenic pathway have been identified and studied, but little is known about how these factors function collectively as a dynamic network of interacting components. To investigate this, we developed a mathematical model of the adrenal steroidogenic regulatory network that accounts for key regulatory processes occurring at different timescales. We used our model to predict the time evolution of steroidogenesis in response to physiological adrenocorticotropic hormone (ACTH) perturbations, ranging from basal pulses to larger stress-like stimulations (e.g., inflammatory stress). Testing these predictions experimentally in the rat, our results show that the steroidogenic regulatory network architecture is sufficient to respond to both small and large ACTH perturbations, but coupling this regulatory network with the immune pathway is necessary to explain the dissociated dynamics between ACTH and glucocorticoids observed under conditions of inflammatory stress.

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.

Kisspeptin induces expression of gonadotropin-releasing hormone receptor in GnRH-producing GT1-7 cells overexpressing G protein-coupled receptor 54

Kisspeptin signaling through its receptor is crucial for many reproductive functions. However, the molecular mechanisms and biomedical significance of the regulation of GnRH neurons by kisspeptin have not been adequately elucidated. In the present study, we found that kisspeptin increases GnRH receptor (GnRHR) expression in a GnRH-producing cell line (GT1-7). Because cellular activity of G protein-coupled receptor 54 (GPR54) and GnRHR was limited in GT1-7 cells, we overexpressed these receptors to clarify receptor function. Using luciferase reporter constructs, the activity of both the serum response element (Sre) promoter, a target for extracellular signal-regulated kinase (ERK), and the cyclic AMP (cAMP) response element (Cre) promoter were increased by kisspeptin. Although GnRH increased Sre promoter activity, the Cre promoter was not significantly activated by GnRH. Kisspeptin, but not GnRH, increased cAMP accumulation in these cells. Kisspeptin also increased the transcriptional activity of GnRHR; however, the effect of GnRH on the GnRHR promoter was limited and not significant. Transfection of GT1-7 cells with constitutively active MEK kinase (MEKK) and protein kinase A (PKA) increased GnRHR expression. In addition, GnRHR expression was further increased by co-overexpression of MEKK and PKA. The Cre promoter, but not the Sre promoter, was also further activated by co-overexpression of MEKK and PKA. GnRH significantly increased the activity of the GnRHR promoter in the presence of cAMP. The present findings suggest that kisspeptin is a potent stimulator of GnRHR expression in GnRH-producing neurons in association with ERK and the cAMP/PKA pathways.

Phenotype and steroidogenic potential of PDGFRα-positive rat neonatal peritubular cells

Platelet-derived growth factor receptor α (PDGFRα)-positive peritubular cells (PTCs) are suggested to be putative stem Leydig cells. At present little is known about their phenotype and steroidogenic potential. We isolated highly purified PDGFRα-positive neonatal PTCs by magnetic cell sorting (MACS) from 8dpp rat testes and characterized them in vitro. We have demonstrated that PDGFRα-positive PTCs have a mixed phenotype. They expressed PTC-specific genes (αSma, Myh11), pluripotency markers (Pou5f1, nestin, Lifr) and genes encoding steroidogenic enzymes. Treatment with the cAMP-analog (Bu)2cAMP for 7 days upregulated steroidogenic enzyme gene expression and significantly increased their steroidogenic potential. The main end-point steroid was progesterone due to rapid inactivation of CYP17 and 17βHSD. Long-term culturing of PDGFRα-positive PTCs increased the expression of Myh11, and treatment with (Bu)2cAMP attenuated this process. All together, our findings support the hypothesis that neonatal PDGFRα-positive PTCs are steroidogenic competent progeny of stem Leydig cells (SLCs) which give rise to the adult Leydig cell lineage.

Distinct functions of steroidogenic factor-1 (NR5A1) in the nucleus and the centrosome

Steroidogenic Factor 1 (SF-1, Ad4bp, NR5A1) is a nuclear receptor expressed mainly in the adrenals and gonads. It activates the transcription of genes in steroidogenesis, reproduction, and energy metabolism. In addition, it also regulates the growth and differentiation of adrenogonadal primodial cells. SF-1 resides in the nucleus and the centrosome. SF-1 moves dynamically in the nucleus, and SF-1 location and activity are dynamically regulated by post-translational modifications. In the centrosome, SF-1 maintains genomic integrity by controlling centrosome homeostasis. SF-1 prevents centrosome amplification by restricting aberrant activation of centrosomal DNA-PK. Upon SF-1 removal, DNA-PK is activated and centrosomes are amplified. This leads to genomic instability and cell growth defects. These data indicate that SF-1 at both the nucleus and the centrosome contributes to cell growth control, but the mechanisms of SF-1 action in different locations are different.

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

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

Molecular aspects of steroidogenic factor 1 (SF-1)

Steroidogenic factor 1 (SF-1, also called Ad4BP and NR5A1) is a nuclear receptor with critical roles in steroidogenic tissues, as well as in the brain and pituitary. In particular, SF-1 has emerged as an essential regulator of adrenal and gonadal functions and development. In the last few years, our knowledge on SF-1 has increased considerably at all levels, from the gene to the protein, and on its specific roles in different physiological processes. In this review, we discuss the current understanding on SF-1 with focus on the parameters that control the transcriptional capacity of SF-1 and the mechanisms that ensure proper stage- and tissue-specific expression of the gene encoding SF-1.

FOXO1 transrepresses peroxisome proliferator-activated receptor gamma transactivation, coordinating an insulin-induced feed-forward response in adipocytes

The transcriptional factor FoxO1 plays an important role in metabolic homeostasis. Herein we identify a novel transrepressional function that converts FoxO1 from an activator of transcription to a promoter-specific repressor of peroxisome proliferator-activated receptor gamma (PPARgamma) target genes that regulate adipocyte biology. FoxO1 transrepresses PPARgamma via direct protein-protein interactions; it is recruited to PPAR response elements (PPRE) on PPARgamma target genes by PPARgamma bound to PPRE and interferes with promoter DNA occupancy of the receptor. The FoxO1 transrepressional function, which is independent and dissectible from the transactivational effects, does not require a functional FoxO1 DNA binding domain, but dose require an evolutionally conserved 31 amino acids LXXLL-containing domain. Insulin induces FoxO1 phosphorylation and nuclear exportation, which prevents FoxO1-PPARgamma interactions and rescues transrepression. Adipocytes from insulin resistant mice show reduced phosphorylation and increased nuclear accumulation of FoxO1, which is coupled to lowered expression of endogenous PPARgamma target genes. Thus the innate FoxO1 transrepression function enables insulin to augment PPARgamma activity, which in turn leads to insulin sensitization, and this feed-forward cycle represents positive reinforcing connections between insulin and PPARgamma signaling.

Modification of androgen receptor function by IGF-1 signaling implications in the mechanism of refractory prostate carcinoma

The androgen-androgen receptor (AR) system plays important roles in a variety of biological processes, including prostate cancer (PC) development and progression. Insulin and Insulin-like growth factor-1 (IGF-1) signaling negatively regulate a member of the forkhead box-containing protein O subfamily (FoxO), Foxo-1, and associated biological functions. IGF-1 can potentiate androgen signaling through AR activation. Foxo-1, phosphorylated and inactivated by phosphatidylinositol-3-kinase (PI3K)/Akt kinase induced by IGF-1 or insulin, suppresses ligand-mediated AR transactivation. Foxo-1 reduces expression of androgen-induced AR target genes and suppresses in vitro growth of PC cells. These inhibitory effects of Foxo-1 are attenuated by IGF-1, but enhanced when it was rendered Akt-non-phosphorylatable. Foxo-1 directly interacts with the C-terminus of AR in a ligand-dependent manner, and disrupts ligand-induced AR subnuclear compartmentalization. Foxo-1 is recruited by liganded AR to the chromatin of the AR target gene promoter, while IGF-1 or insulin abolishes the Foxo-1 occupancy on the promoter. Liganded AR stimulates IGF-1 receptor expression, suggesting the presence of local positive feedback between IGF-1 and AR signaling in PC cells, presumably resulting in higher IGF-1 signaling tension and further enhancing the functions of the receptor itself. Thus, Foxo-1 is a novel corepressor for AR and IGF-1/insulin signaling may confer stimulatory effects on AR by attenuating Foxo-1 inhibition. Positive feedback between the growth factor and androgen in the local cellular environment may play important roles in AR transactivation regulation in several clinical situations including refractory PC.

Functional potentiation of leptin-signal transducer and activator of transcription 3 signaling by the androgen receptor

Hypogonadism is associated with increased fat mass and dysregulation of metabolic homeostasis in men. Our previous study revealed that androgen receptor (AR)-null male mice (ARL-/Y) develop late-onset obesity and are leptin-resistant. The present study evaluated how hypothalamic AR contributes to central leptin-signal transducer and activator of transcription 3 (STAT3) signaling. We evaluated leptin action in wild-type and ARL-/Y mice, the anatomic co-relationship between AR and leptin signaling in the hypothalamus, and the effects of AR on leptin-mediated STAT3 transactivation and nuclear translocation. AR deletion in male mice results in a weaker leptin-induced suppression of food intake and body weight drop even before the onset of overt obesity. In wild-type male but not female mice, AR was highly expressed in various hypothalamic nuclei that also expressed the long-form leptin receptor (OBRB) and co-resided with OBRB directly in the arcuate neurons. In vitro, AR significantly enhanced STAT3-mediated transcription of leptin target genes including POMC and SOCS3. This effect relied on the AR N-terminal activation function-1 (AF-1) domain and was specific to AR in that none of the other sex steroid hormone receptors tested showed similar effects. AR enhanced the low concentrations of leptin-induced STAT3 nuclear translocation in vitro, and ARL-/Y mice receiving leptin had impaired STAT3 nuclear localization in the arcuate neurons. These findings indicate that AR in the hypothalamus functions as a regulator of central leptin-OBRB-STAT3 signaling and has a physiological role in energy homeostasis and metabolic regulation in male mice.

Developmental links between the fetal and adult zones of the adrenal cortex revealed by lineage tracing

The nuclear receptor Ad4BP/SF-1 is essential for development of the adrenal cortex and the gonads, which derive from a common adrenogonadal primordium. The adrenal cortex subsequently forms morphologically distinct compartments: the inner (fetal) and outer (definitive or adult) zones. Despite considerable effort, the mechanisms that mediate the differential development of the adrenal and gonadal primordia and the fetal and adult adrenal cortices remain incompletely understood. We previously identified a fetal adrenal-specific enhancer (FAdE) in the Ad4BP/SF-1 locus that directs transgene expression to the fetal adrenal cortex and demonstrated that this enhancer is autoregulated by Ad4BP/SF-1. We now combine the FAdE with the Cre/loxP system to trace cell lineages in which the FAdE was active at some stage in development. These lineage-tracing studies establish definitively that the adult cortex derives from precursor cells in the fetal cortex in which the FAdE was activated before the organization into two distinct zones. The potential of these fetal adrenocortical cells to enter the pathway that eventuates in cells of the adult cortex disappeared by embryonic day 14.5. Thus, these studies demonstrate a direct link between the fetal and adult cortices involving a transition that must occur before a specific stage of development.

Growth factor regulation of estrogen receptor coregulator PELP1 functions via Protein Kinase A pathway

PELP1 (proline-rich, glutamic acid-rich, and leucine-rich protein-1) is a potential proto-oncogene that functions as a coregulator of estrogen receptor (ER), and its expression is deregulated during breast cancer progression. Emerging evidence suggests growth factor signaling crosstalk with ER as one possible mechanism by which breast tumors acquire resistance to therapy. In this study, we examined mechanisms by which growth factors modulate PELP1 functions, leading to activation of ER. Using in vivo labeling assays, we have found that growth factors promote phosphorylation of PELP1. Utilizing a panel of substrate-specific phosphorylated antibodies, we discovered that growth factor stimulation promotes phosphorylation of PELP1 that is recognized by a protein kinase A (PKA) substrate-specific antibody. Accordingly, growth factor-mediated PELP1 phosphorylation was effectively blocked by PKA-specific inhibitor H89. Utilizing purified PKA enzyme and in vitro kinase assays, we obtained evidence of direct PELP1 phosphorylation by PKA. Using deletion and mutational analysis, we identified PELP1 domains that are phosphorylated by PKA. Interestingly, site-directed mutagenesis of the putative PKA site in PELP1 compromised growth factor-induced activation and subnuclear localization of PELP1 and also affected PELP1-mediated transactivation function. Utilizing MCF-7 cells expressing a PELP1 mutant that cannot be phosphorylated by PKA, we provide mechanistic insights by which growth factor signaling regulates ER transactivation in a PELP1-dependent manner. Collectively, these findings suggest that growth factor signals promote phosphorylation of ER coactivator PELP1 via PKA pathway, and such modification may have functional implications in breast tumors with deregulated growth factor signaling.

Adipose tissue-derived and bone marrow-derived mesenchymal cells develop into different lineage of steroidogenic cells by forced expression of steroidogenic factor 1

Steroidogenic factor 1 (SF-1)/adrenal 4 binding protein is an essential nuclear receptor for steroidogenesis, as well as for adrenal and gonadal gland development. We have previously clarified that adenovirus-mediated forced expression of SF-1 can transform long-term cultured mouse bone marrow mesenchymal cells (BMCs) into ACTH-responsive steroidogenic cells. In the present study, we extended this work to adipose tissue-derived mesenchymal cells (AMCs) and compared its steroidogenic capacity with those of BMCs prepared from the identical mouse. Several cell surface markers, including potential mesenchymal cell markers, were identical in both cell types, and, as expected, forced expression of SF-1 caused AMCs to be transformed into ACTH-responsive steroidogenic cells. However, more elaborate studies revealed that the steroidogenic property of AMCs was rather different from that of BMCs, especially in steroidogenic lineage. In response to increased SF-1 expression and/or treatment with retinoic acid, AMCs were much more prone to produce adrenal steroid, corticosterone rather than gonadal steroid, testosterone, whereas the contrary was evident in BMCs. Such marked differences in steroidogenic profiles between AMCs and BMCs were also evident by the changes of steroidogenic enzymes. These novel results suggest a promising utility of AMCs for autologous cell regeneration therapy for patients with steroid insufficiency and also a necessity for appropriate tissue selection in preparing mesenchymal stem cells according to the aim. The different steroidogenic potency of AMCs or BMCs might provide a good model for the clarification of the mechanism of tissue- or cell-specific adrenal and gonadal steroidogenic cell differentiation.

Methylation of a conserved intronic CpG island of mouse SF-1 is associated with cell-specific expression of SF-1 in a culture system but not with tissue-specific expression

The mechanism for the steroidogenic tissue or cell-specific expression of SF-1 has not been well clarified. We examined whether the methylation status of a large CpG island in the first intron of mouse SF-1 gene is associated with the expression level of SF-1 in cultured cells and in tissues. The island consists of three small islands (ICI-1, ICI-2, and ICI-3). In cultured adrenocortical Y-1 cells and in Leydig tumor cells, I-10, that both express high levels of SF-1, the upstream region of ICI-2, ICI-2-1, was clearly hypomethylated compared to cultured mouse bone marrow cells that do not express SF-1. However, this methylation status was not clearly associated with the tissue-specific expression of SF-1, in either adult or during development. These results suggest that methylation of ICI-2-1of SF-1 may partly determine the level of SF-1 expression at the cellular level, but may not be essential at the tissue level.

Luteinizing hormone beta promoter stimulation by adenylyl cyclase and cooperation with gonadotropin-releasing hormone 1 in transgenic mice and LBetaT2 Cells

Rat luteinizing hormone beta (Lhb) gene transcription is stimulated by hypothalamic gonadotropin-releasing hormone 1 (GnRH1), and this response may be modulated by other signaling pathways such as cAMP. Here we characterize the ability of cAMP, alone or with GnRH1, to stimulate Lhb gene transcription in mouse pituitary and clonal gonadotroph cells. Both cAMP and pituitary adenylyl cyclase-activating peptide increase GnRH1 stimulation of luciferase activity in pituitaries of mice expressing the rat Lhb-luciferase transgene, suggesting cAMP and GnRH1 pathways interact in vivo. cAMP stimulation of the Lhb-luciferase transgene was similar between females in metestrus and proestrus, but GnRH1 stimulation was greater at proestrus. Additive effects with combined treatments were observed at metestrus and proestrus. Elevated intracellular cAMP stimulated Lhb promoter activity in LbetaT2 clonal gonadotroph cells, alone and with GnRH1. In LbetaT2 cells, cAMP stimulation of the Lhb promoter was eliminated by inhibition of protein kinase A (PKA); GnRH1 stimulation was partially suppressed by either PKA or protein kinase C inhibitors. Only the proximal GnRH1-responsive region of the promoter was required for cAMP stimulation, and mutation of the 3' NR5A1 site diminished the response. Regulation of primary mRNA transcripts from the endogenous Lhb gene by cAMP and GnRH1 correlated with results from the Lhb-luciferase transgene or transfected promoter. Occupancy of the endogenous promoter by EGR1 was increased by GnRH1 with or without forskolin, but forskolin alone had little effect. Thus, cAMP stimulation of Lhb promoter activity, and enhancement of GnRH1 stimulation, occurs in multiple physiological states independent of steroid status, via a PKA-dependent mechanism.

Orchestration of chromatin-based processes: mind the TRRAP

Chromatin modifications at core histones including acetylation, methylation, phosphorylation and ubiquitination play an important role in diverse biological processes. Acetylation of specific lysine residues within the N terminus tails of core histones is arguably the most studied histone modification; however, its precise roles in different cellular processes and how it is disrupted in human diseases remain poorly understood. In the last decade, a number of histone acetyltransferases (HATs) enzymes responsible for histone acetylation, has been identified and functional studies have begun to unravel their biological functions. The activity of many HATs is dependent on HAT complexes, the multiprotein assemblies that contain one HAT catalytic subunit, adapter proteins, several other molecules of unknown function and a large protein called TRansformation/tRanscription domain-Associated Protein (TRRAP). As a common component of many HAT complexes, TRRAP appears to be responsible for the recruitment of these complexes to chromatin during transcription, replication and DNA repair. Recent studies have shed new light on the role of TRRAP in HAT complexes as well as mechanisms by which it mediates diverse cellular processes. Thus, TRRAP appears to be responsible for a concerted and context-dependent recruitment of HATs and coordination of distinct chromatin-based processes, suggesting that its deregulation may contribute to diseases. In this review, we summarize recent developments in our understanding of the function of TRRAP and TRRAP-containing HAT complexes in normal cellular processes and speculate on the mechanism underlying abnormal events that may lead to human diseases such as cancer.

Atrazine-induced aromatase expression is SF-1 dependent: implications for endocrine disruption in wildlife and reproductive cancers in humans

BACKGROUND

Atrazine is a potent endocrine disruptor that increases aromatase expression in some human cancer cell lines. The mechanism involves the inhibition of phosphodiesterase and subsequent elevation of cAMP.

METHODS

We compared steroidogenic factor 1 (SF-1) expression in atrazine responsive and non-responsive cell lines and transfected SF-1 into nonresponsive cell lines to assess SF-1's role in atrazine-induced aromatase. We used a luciferase reporter driven by the SF-1-dependent aromatase promoter (ArPII) to examine activation of this promoter by atrazine and the related simazine. We mutated the SF-1 binding site to confirm the role of SF-1. We also examined effects of 55 other chemicals. Finally, we examined the ability of atrazine and simazine to bind to SF-1 and enhance SF-1 binding to ArPII.

RESULTS

Atrazine-responsive adrenal carcinoma cells (H295R) expressed 54 times more SF-1 than nonresponsive ovarian granulosa KGN cells. Exogenous SF-1 conveyed atrazine-responsiveness to otherwise nonresponsive KGN and NIH/3T3 cells. Atrazine induced binding of SF-1 to chromatin and mutation of the SF-1 binding site in ArPII eliminated SF-1 binding and atrazine-responsiveness in H295R cells. Out of 55 chemicals examined, only atrazine, simazine, and benzopyrene induced luciferase via ArPII. Atrazine bound directly to SF-1, showing that atrazine is a ligand for this "orphan" receptor.

CONCLUSION

The current findings are consistent with atrazine's endocrine-disrupting effects in fish, amphibians, and reptiles; the induction of mammary and prostate cancer in laboratory rodents; and correlations between atrazine and similar reproductive cancers in humans. This study highlights the importance of atrazine as a risk factor in endocrine disruption in wildlife and reproductive cancers in laboratory rodents and humans.

Heterozygous missense mutations in steroidogenic factor 1 (SF1/Ad4BP, NR5A1) are associated with 46,XY disorders of sex development with normal adrenal function

CONTEXT

Steroidogenic factor 1 (SF1/AdBP4/FTZF1, NR5A1) is a nuclear receptor transcription factor that plays a key role in regulating adrenal and gonadal development, steroidogenesis, and reproduction. Targeted deletion of Nr5a1 (Sf1) in the mouse results in adrenal and gonadal agenesis, XY sex-reversal, and persistent Müllerian structures in males. Consistent with the murine phenotype, human mutations in SF1 were described initially in two 46,XY individuals with female external genitalia, Müllerian structures (uterus), and primary adrenal failure.

OBJECTIVE

Given recent case reports of haploinsufficiency of SF1 affecting testicular function in humans, we aimed to identify SF1 mutations in a cohort of individuals with a phenotypic spectrum of 46,XY gonadal dysgenesis/impaired androgenization (now termed 46,XY disorders of sex development) with normal adrenal function.

METHODS AND PATIENTS

The study included mutational analysis of NR5A1 in 30 individuals with 46,XY disorders of sex development, followed by functional studies of SF1 activity.

RESULTS

Heterozygous missense mutations in NR5A1 were found in four individuals (four of 30, 13%) with this phenotype. These mutations (V15M, M78I, G91S, L437Q) were shown to impair transcriptional activation through abnormal DNA binding (V15M, M78I, G91S), altered subnuclear localization (V15M, M78I), or disruption of the putative ligand-binding pocket (L437Q). Two mutations appeared to be de novo or germline changes. The other two mutations appeared to be inherited in a sex-limited dominant manner because the mother is heterozygous for the change.

CONCLUSIONS

These studies demonstrate that SF1 mutations are more frequent than previously suspected causes of impaired fetal and postnatal testicular function in 46,XY individuals.

Herbicide atrazine activates SF-1 by direct affinity and concomitant co-activators recruitments to induce aromatase expression via promoter II

The popular herbicide atrazine is an endocrine disruptor that demasculinizes and feminizes several species of animals, and co-relates with breast and reproductive disorders in mammalians. We recently reported that atrazine induces human aromatase gene expression via promoter II (ArPII) in a steroidogenic factor 1 (SF-1)-dependent manner. Here, we show that knockdown of SF-1 abolishes ArPII induction by atrazine in H295R cells, which harbor high SF-1 expression and are originally atrazine-responsive. Conversely, exogenous SF-1 enables atrazine to induce ArPII in the otherwise non-responsive KGN cells. Atrazine's effect is independent from protein kinase A and LRH-1, a close relative of SF-1. However, it binds directly to the SF-1, and concomitantly, enhances interactions of SF-1 with co-activator TIF2, and renders more SF-1 binding to ArPII chromatin. Intriguingly, LBD mutations do not alter SF-1's ability to mediate atrazine stimulation, suggesting that atrazine interacts with SF-1 via a region(s) other than the ligand binding pocket. These data suggest that atrazine binds to and activates SF-1 to induce ArPII.

Insulin-like growth factor 1/insulin signaling activates androgen signaling through direct interactions of Foxo1 with androgen receptor

The androgen-androgen receptor (AR) system plays vital roles in a wide array of biological processes, including prostate cancer development and progression. Several growth factors, such as insulin-like growth factor 1 (IGF1), can induce AR activation, whereas insulin resistance and hyperinsulinemia are correlated with an elevated incidence of prostate cancer. Here we report that Foxo1, a downstream molecule that becomes phosphorylated and inactivated by phosphatidylinositol 3-kinase/Akt kinase in response to IGF1 or insulin, suppresses ligand-mediated AR transactivation. Foxo1 reduces androgen-induced AR target gene expressions and suppresses the in vitro growth of prostate cancer cells. These inhibitory effects of Foxo1 are attenuated by IGF1 but are enhanced when it is rendered Akt-nonphosphorylatable. Foxo1 interacts directly with the C terminus of AR in a ligand-dependent manner and disrupts ligand-induced AR subnuclear compartmentalization. Foxo1 is recruited by liganded AR to the chromatin of AR target gene promoters, where it interferes with AR-DNA interactions. IGF1 or insulin abolish the Foxo1 occupancy of these promoters. Of interest, a positive feedback circuit working locally in an autocrine/intracrine manner may exist, because liganded AR up-regulates IGF1 receptor expression in prostate cancer cells, presumably resulting in higher IGF1 signaling tension and further enhancing the functions of the receptor itself. Thus, Foxo1 is a novel corepressor for AR, and IGF1/insulin signaling may confer stimulatory effects on AR by attenuating Foxo1 inhibition. These results highlight the potential involvement of metabolic syndrome and hyperinsulinemia in prostate diseases and further suggest that intervention of IGF1/insulin-phosphatidylinositol 3-kinase-Akt signaling may be of clinical value for prostate diseases.

Coregulator exchange and sphingosine-sensitive cooperativity of steroidogenic factor-1, general control nonderepressed 5, p54, and p160 coactivators regulate cyclic adenosine 3',5'-monophosphate-dependent cytochrome P450c17 transcription rate

Transcription of the cytochrome P450 17 (CYP17) gene is regulated by cAMP-dependent binding of steroidogenic factor-1 (SF-1) to its promoter in the adrenal cortex. Using temporal chromatin immunoprecipitation and mammalian two-hybrid experiments, we establish the reciprocal presence of coactivators [general control nonderepressed (GCN5), cAMP response element-binding protein-binding protein, p300, p300/cAMP response element-binding protein-binding protein CBP associated factor, p160s, polypyrimidine tract associated splicing factor, and p54(nrb)], corepressors (class I histone deacetylases, receptor interacting protein, nuclear receptor corepressor, and Sin3A), and SWI/SNF (human homolog of yeast mating type switching/sucrose nonfermenting) and imitation SWI chromatin remodeling ATPases on the CYP17 promoter during transcription cycles in the H295R adrenocortical cell line. A ternary GCN5/SRC-1/SF-1 complex forms on the CYP17 promoter with cAMP-dependence within 30 min of cAMP stimulation, and corresponds with SWI/SNF chromatin remodeling. This complex is sensitive to the SF-1 antagonist sphingosine and results in decreased transcription of CYP17. GCN5 acetyltransferase activity and carboxy terminus binding proteins alternatively mediate disassembly of the complex. This work establishes the temporal order of cAMP-induced events on the promoter of a key steroidogenic gene during SF-1-mediated transcription.

Androgen receptor regulates nuclear trafficking and nuclear domain residency of corepressor HDAC7 in a ligand-dependent fashion

In addition to chromosomal proteins, histone deacetylases (HDACs) target transcription factors in transcriptional repression. Here, we show that the class II HDAC family member HDAC7 is an efficient corepressor of the androgen receptor (AR). HDAC7 resided in the cytoplasm in the absence of AR or a cognate ligand, but hormone-occupancy of AR induced nuclear transfer of HDAC7. Nuclear colocalization pattern of AR and HDAC7 was dependent on the nature of the ligand. In the presence of testosterone, a portion of HDAC7 localized to pearl-like nuclear domains, whereas AR occupied with antagonistic ligands cyproterone acetate- or casodex (bicalutamide) recruited HDAC7 from these domains to colocalize with the receptor in speckles and nucleoplasm in a more complete fashion. Ectopic expression of PML-3 relieved the repressive effect of HDAC7 on AR function by sequestering HDAC7 to PML-3 domains. AR acetylation at Lys630/632/633 was not the target of HDAC7 repression, since repression of AR function was independent of these acetylation sites. Moreover, the deacetylase activity of HDAC7 was in part dispensable in the repression of AR function. In sum, our results identify HDAC7 as a novel AR corepressor whose subcellular and subnuclear compartmentalization can be regulated in an androgen-selective manner.

Nuclear compartmentalization of N-CoR and its interactions with steroid receptors

The repression mechanisms by the nuclear receptor corepressor (N-CoR) of steroid hormone receptor (SHR)-mediated transactivation were examined. Yellow fluorescent protein (YFP)-N-CoR was distributed as intranuclear discrete dots, while coexpression of androgen receptor (AR), glucocorticoid receptor alpha, and estrogen receptor alpha ligand-dependently triggered redistribution of YFP-N-CoR. In fluorescence recovery after photobleaching analysis, mobility of the N-CoR was reduced by 5alpha-dihydrotestosterone (DHT)-bound AR. The middle region of N-CoR mostly contributed to the interaction with agonist-bound SHRs and the suppression of their transactivation function. N-CoR impaired the DHT-induced N-C interaction of AR, and the impaired interaction was dose-dependently recovered by coexpression of SRC-1 and CBP. N-CoR also impaired the intranuclear complete (distinct) focus formation of SHRs. Coexpression of SRC-1 or CBP released YFP-N-CoR or endogenous N-CoR from incomplete foci and simultaneously recovered complete foci of AR-green fluorescent protein. These results indicate that the relative ratio of coactivators and corepressors determines the conformational equilibrium between transcriptionally active and inactive SHRs in the presence of agonists. The intranuclear foci formed by agonist-bound SHRs were completely destroyed by actinomycin D and alpha-amanitin, indicating that the focus formation does not precede the transcriptional activation. The focus formation may reflect the accumulation of SHR/coactivator complexes released from the transcriptionally active sites and thus be a mirror of transcriptionally active complex formation.

The Gly146Ala variation in human SF-1 gene: its association with insulin resistance and type 2 diabetes in Chinese

AIMS

While steroidogenic factor 1 (SF-1) is traditionally an essential nuclear receptor for steroidogenic tissues, current emerging studies revealed that the receptor is also closely implicated in metabolism. Mutations of SF-1 gene cause metabolic disorders like obesity in both human and mice. The aim of the present study is to examine whether the Gly146Ala variation in the gene for SF-1, that is known to impair SF-1 function and related to adrenal disorders, affects susceptibility to type 2 diabetes.

METHODS

Hundred and fifty-one type 2 diabetic subjects and 141 non-diabetic control subjects of Han Chinese were recruited and the SF-1 genotype were analyzed by PCR-RFLP method.

RESULTS

The Gly146Ala variation occurs frequently in the Han Chinese. Allele Ala frequency in the control subjects (27.3%) was significantly lower than that in type 2 diabetic subjects (37.1%, chi2=6.37, p=0.01). The Gly/Ala and Ala/Ala genotypes frequencies were also higher in diabetic subjects. In both the diabetic and control populations, subjects carrying allele Ala, as compared to those not, had higher fasting insulin levels and higher HOMA values.

CONCLUSIONS

The SF-1 Gly146Ala variation may constitute a susceptible factor for development of type 2 diabetes and impairment of insulin actions.

Differentiation and regeneration of adrenal tissues: An initial step toward regeneration therapy for steroid insufficiency

In animal experiments, adrenal cortical tissue has been successfully regenerated through xenotransplantation of cloned adrenocortical cells, suggesting that the intraadrenal stem cells required for such tissue formation may be present in the adrenal cortex. Stable expression of Ad4BP/SF-1, a key factor for adrenal and gonadal development and steroidogenesis, has been shown to direct embryonic stem cells toward the steroidogenic lineage. However, this steroidogenic capacity was very limited since progesterone was only produced in the presence of an exogenous substrate. Bone marrow mesenchymal cells are thought to contain pluripotent progenitor cells, which differentiate into multiple lineages. We have demonstrated that adenovirus-mediated forced expression of SF-1 in long-term cultured bone marrow cells can produce steroidogenic cells with the capacity for de novo synthesis of various steroid hormones in response to ACTH. This discovery may represent the first step in autologous cell transplantation therapy for patients with steroid hormone deficiency.

DAX-1 expression is regulated during mammary epithelial cell differentiation

In recent studies, we have found that DAX-1 (dosage-sensitive sex reversal/adrenal hypoplasia congenita critical region on the X chromosome) is expressed in the mouse mammary epithelial cell line HC11. In this study, we focused on the regulation of DAX-1 expression and subcellular localization throughout mouse mammary epithelial cell differentiation and its hormonal regulation in the mouse mammary gland. Proliferating HC11 cells grown in epidermal growth factor (EGF)-containing medium, expressed very low levels of DAX-1 as detected by Western blotting and quantitative real-time PCR, whereas, upon EGF withdrawal and induction of differentiation, DAX-1 expression increased. Inhibition of MAPK pathway with PD 098059 resulted in increased DAX-1 levels even in the presence of EGF. Using confocal microscopy, we showed that DAX-1 cytoplasmic levels increased as cells differentiated. DAX-1 staining was nuclear in luminal cells of mouse mammary glands from 3-month-old virgin mice. A nucleo-cytoplasmic pattern was observed in pseudopregnant mice and a cytoplasmic pattern was found in mammary glands from 6-d lactating mice. The influence of DAX-1 on transcriptional activity of endogenously expressed estrogen receptors alpha (ERalpha) and beta (ERbeta) in HC11 mammary epithelial cells was evaluated with an estrogen response element-luciferase reporter assay and by quantitative real-time PCR of the ER-regulated gene receptor-interacting protein 140 kDa. Cotransfection of HC11 cells with human DAX-1 inhibited estrogen response element-reporter and receptor-interacting protein 140 kDa expression induced by 17beta-estradiol, the ERalpha-selective agonist 4,4',4'-(4-propyl-(1H)-pyrazole-1,3,5-triyl)trisphenol, or the ERbeta-selective agonist 2,3-bis(4-hydroxyphenyl)-propionitrile. In summary, DAX-1 expression increased upon differentiation induced by EGF withdrawal, and DAX-1 decreased response to estrogens in HC11 cells. Further studies are needed to determine whether DAX-1 is also important in regulation of differentiation of HC11 cells.

A familial missense mutation in the hinge region of DAX1 associated with late-onset AHC in a prepubertal female

Mutations in the DAX1 (Dosage-sensitive sex reversal-Adrenal hypoplasia congenita (AHC) critical region on the X chromosome gene 1; NR0B1) cause X-linked AHC, a disease characterized by primary adrenal failure in infancy and hypogonadotropic hypogonadism. All known missense mutations impair DAX1 repression of steroidogenic factor 1 (SF1) transactivation and have been localized to the putative ligand binding domain. Here, an asymptomatic father and his late-onset AHC daughter were both shown to share a novel DAX1 mutation (C200W), the first missense mutation identified in the hinge region of DAX1. Using immunohistochemistry we demonstrate that the sub-cellular localization of the C200W mutant DAX1 protein is shifted from the nucleus to the cytoplasm. The disturbed localization of the C200W mutant in transfected cells correlates with impaired transcriptional repression activity. The import defect is relatively mild, retaining 80% of wild-type activity, which may explain the unusually mild phenotype. Import of DAX1 into the nucleus involves a direct interaction with SF1. In vitro assays demonstrate that the C200W mutant retains the ability to functionally interact with SF1, which suggests that SF1-independent interactions of DAX1 could be responsible for the import defect.

Dosage-sensitive sex reversal adrenal hypoplasia congenita critical region on the X chromosome, gene 1 (DAX1) (NR0B1) and small heterodimer partner (SHP) (NR0B2) form homodimers individually, as well as DAX1-SHP heterodimers

Dosage-sensitive sex reversal adrenal hypoplasia congenita critical region on the X chromosome, gene 1 (DAX1) (NR0B1), and small heterodimer partner (SHP) (NR0B2) are atypical nuclear receptor superfamily members that function primarily as corepressors through heterodimeric interactions with other nuclear receptors. Mutations in DAX1 cause adrenal hypoplasia congenita, and mutations in SHP lead to mild obesity and insulin resistance, but the mechanisms are unclear. We investigated the existence and subcellular localization of DAX1 and SHP homodimers and the dynamics of homodimerization. We demonstrated DAX1 homodimerization in the nucleus and cytoplasm, and dissociation of DAX1 homodimers upon heterodimerization with steroidogenic factor 1 (SF1) or ligand-activated estrogen receptor-alpha (ERalpha). DAX1 homodimerization involved an interaction between its amino and carboxy termini involving its LXXLL motifs and activation function (AF)-2 domain. We observed SHP homodimerization in the nucleus of mammalian cells and showed dissociation of SHP homodimers upon heterodimerization with ligand-activated ERalpha. We observed DAX1-SHP heterodimerization in the nucleus of mammalian cells and demonstrated the involvement of the LXXLL motifs and AF-2 domain of DAX1 in this interaction. We further demonstrate heterodimerization of DAX1 with its alternatively spliced isoform, DAX1A. This is the first evidence of homodimerization of individual members of the unusual NR0B nuclear receptor family and heterodimerization between its members. Our results suggest that DAX1 forms antiparallel homodimers through the LXXLL motifs and AF-2 domain. These homodimers may function as holding reservoirs in the absence of heterodimeric partners. The formation of DAX1 and SHP homodimers and DAX1-SHP and DAX1-DAX1A heterodimers suggests the possibility of novel functions independent of their coregulator roles, suggesting additional complexity in the molecular mechanisms of DAX1 and SHP action.

Mechanisms for pulsatile regulation of the gonadotropin subunit genes by GNRH1

The frequency of gonadotropin-releasing hormone (GNRH1, or GnRH) pulses secreted from the hypothalamus determine the ratios of the gonadotropin subunit genes luteinizing hormone beta (Lhb), follicle-stimulating hormone beta (Fshb) and the common alpha-glycoprotein subunit gene (Cga) transcribed in the anterior pituitaries of mammals. Fshb is preferentially transcribed at slower GNRH1 pulse frequencies, whereas Lhb and Cga are preferentially transcribed at more rapid pulse frequencies. Producing the gonadotropins in the correct proportions is critical for normal fertility. Currently, there is no definitive explanation for how GNRH1 pulses differentially activate gonadotropin subunit gene transcription. Several pathways may contribute to this regulation. For example, GNRH1-regulated GNRH1-receptor concentrations may lead to variable signaling pathway activation. Several signaling pathways are activated by GnRH, including mitogen-activated protein kinase, protein kinase C, calcium influx, and calcium-calmodulin kinase, and these may be preferentially regulated under certain conditions. In addition, some signaling proteins feed back to downregulate their own levels. Other arms of gonadotroph signaling appear to be regulated by synthesis, modification, and degradation of either transcription factors or regulatory proteins. Finally, the dynamic binding of proteins to the chromatin, and how that might be regulated by chromatin-modifying proteins, is addressed. Oscillations in expression, modification, and chromatin binding of the proteins involved in gonadotropin gene expression are likely a link between GNRH1 pulsatility and differential gonadotropin transcription.

Switching of NR5A proteins associated with the inhibin alpha-subunit gene promoter after activation of the gene in granulosa cells

The inhibin alpha-subunit gene is transcriptionally activated by FSH in ovarian granulosa cells during follicular growth. We have investigated the roles of the NR5A family nuclear receptors steroidogenic factor 1 (SF-1) and liver receptor homolog 1 (LRH-1) in transcriptional activation of the inhibin alpha-subunit gene. Transfection assays using an inhibin alpha-subunit promoter reporter in GRMO2 granulosa cells show that LRH-1 and SF-1 act similarly to increase promoter activity, and that the activity of both transcription factors is augmented by the coactivators cAMP response element-binding protein-binding protein and steroid receptor coactivator 1. However, chromatin immunoprecipitation experiments illustrate differential dynamic association of LRH-1 and SF-1 with the alpha-subunit inhibin promoter in both primary cells and the GRMO2 granulosa cell line such that hormonal stimulation of transcription results in an apparent replacement of SF-1 with LRH-1. Transcriptional stimulation of the inhibin alpha-subunit gene is dependent on MAPK kinase activity, as is the dynamic association/disassociation of SF-1 and LRH-1 with the promoter. Inhibition of the phosphatidylinositol 3-kinase signaling pathway influences promoter occupancy and transcriptional activation by SF-1 but not LRH-1, suggesting a possible mechanistic basis for the distinct functions of these NR5A proteins in inhibin alpha-subunit gene regulation.

SF-1 (nuclear receptor 5A1) activity is activated by cyclic AMP via p300-mediated recruitment to active foci, acetylation, and increased DNA binding

Steroidogenic factor 1 (SF-1) is a nuclear receptor essential for steroidogenic gene expression, but how its activity is regulated is unclear. Here we demonstrate that p300 plays an important role in regulating SF-1 function. SF-1 was acetylated in vitro and in vivo by p300 at the KQQKK motif in the Ftz-F1 (Fushi-tarazu factor 1) box adjacent to its DNA-binding domain. Mutation of the KQQKK motif reduced the DNA-binding activity and p300-dependent activation of SF-1. When stimulated with cyclic AMP (cAMP), adrenocortical Y1 cells expressed more p300, leading to additional SF-1 association with p300 and increased SF-1 acetylation and DNA binding. It also increased SF-1 colocalization with p300 in nuclear foci. Collectively, these results indicate that SF-1 transcriptional activity is regulated by p300 in response to the cAMP signaling pathway by way of increased acetylation, DNA binding, and recruitment to nuclear foci.

Androgen receptor null male mice develop late-onset obesity caused by decreased energy expenditure and lipolytic activity but show normal insulin sensitivity with high adiponectin secretion

Androgen receptor (AR) null male mice (AR(L-/Y)) revealed late-onset obesity, which was confirmed by computed tomography-based body composition analysis. AR(L-/Y) mice were euphagic compared with the wild-type male (AR(X/Y)) controls, but they were also less dynamic and consumed less oxygen. Transcript profiling indicated that AR(L-/Y) mice had lower transcripts for the thermogenetic uncoupling protein 1, which was subsequently found to be ligand-dependently activated by AR. We also found enhanced secretion of adiponectin, which is insulin sensitizing, from adipose tissue and a relatively lower expression of peroxisome proliferator-activated receptor-gamma in white adipose tissue in comparison to AR(X/Y) mice. Both factors might explain why the overall insulin sensitivity of AR(L-/Y) mice remained intact, despite their apparent obesity. The results revealed that AR plays important roles in male metabolism by affecting the energy balance, and it is negative to both adiposity and insulin sensitivity.

Molecular mechanisms of DAX1 action

DAX1 (dosage sensitive sex reversal (DSS), adrenal hypoplasia congenita (AHC) critical region on the X chromosome, gene 1) encoded by the gene NR0B1, is an unusual orphan nuclear receptor that when mutated causes AHC with associated hypogonadotropic hypogonadism (HH), and when duplicated causes DSS. DAX1 expression has been shown in all regions of the hypothalamic-pituitary-adrenal-gonadal (HPAG) axis during development and in adult tissues, suggesting a critical role for DAX1 in the normal development and function of this axis. Steroidogenic factor 1 (SF1, NR5A1) knockout mice show similar developmental defects as AHC and HH patients, but paradoxically, DAX1 is a negative coregulator of SF1 transactivation. The function of DAX1 as an antagonist of SF1 in gonadal development is consistent with the fact that in humans, duplication of the region of the X chromosome containing DAX1 causes a similar phenotype as mutations in SF1. However, how disruption of DAX1 leads to adrenal, hypothalamic, and pituitary developmental defects similar to SF1 disruption remains to be clarified. The exact mechanism of DAX1 action in each of these tissues during adulthood and critical stages of development are not fully understood. Recent evidence suggests a broader functional role for DAX1 as a negative coregulator of estrogen receptor (ER, NR3A1-2), liver receptor homologue-1 (LRH-1, NR5A2), androgen receptor (AR, NR3C4), and progesterone receptor (PR, NR3C3), each by distinct repression mechanisms. DAX1 may have pleiotropic roles in addition to its function as a negative regulator of steroidogenesis during the development and adult function of the HPAG axis.

Nuclear structure-associated TIF2 recruits glucocorticoid receptor and its target DNA

Assembly of multi-protein complexes on promoter and enhancer elements is a prerequisite for onset of gene transcription. At the beginning of this process, transcription factors are thought to act as nucleating centers for complex formation through the binding of their target DNA sequences, and thereafter recruit coactivators. Here, we investigated this process of assembly by determining the distribution of the glucocorticoid receptor (GR) and its coactivator, TIF2. Both endogenously and ectopically expressed TIF2 were shown to form foci in the nucleus, and GR could be recruited to the TIF2 foci upon GR agonist but not antagonist treatment. Moreover, we show that the coactivators, p300 and PCAF, are also recruited to the TIF2 foci. The TIF2 foci could recruit GR carrying a microinjected GR responsive element. We propose that TIF2 provides a nuclear compartment that allows the assembly of multi-protein complexes required for GR-mediated gene activation.