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

Expression and functional analysis of Fushi Tarazu transcription factor 1 (FTZ-F1) in the regulation of steroid hormones during the gonad development of Fujian Oyster, Crassostrea angulata

Crassostrea angulata, a major shellfish cultivated in Southern China, has experienced a notable surge in commercial value in recent years. Understanding the molecular mechanisms governing their reproductive processes holds significant implications for advancing aquaculture practices. In this study, we cloned the orphan nuclear receptor gene, Fushi Tarazu transcription factor 1 (FTZ-F1), of C. angulata and investigated its functional role in the gonadal development. The full-length cDNA of FTZ-F1 spans 2357 bp and encodes a protein sequence of 530 amino acids. Notably, the amino acid sequence of FTZ-F1 in C. angulata shares remarkable similarity with its homologues in other species, particularly in the DNA-binding region (>90%) and ligand-binding region (>44%). In C. angulata, the highest expression level of FTZ-F1 was observed in the ovary, exhibiting more than a 200-fold increase during the maturation stage compared to the initiation stage (P < 0.001). Specifically, FTZ-F1 was mainly expressed in the follicular cells surrounding the oocytes of C. angulata. Upon inhibiting FTZ-F1 gene expression in C. angulata through RNA interference (RNAi), a substantial reduction in the expression of genes involved in the synthesis of sex steroids in the gonads, including 3β-HSD, Cyp17, and follistatin, was observed. In addition, estradiol (E2) and testosterone (T) levels also showed a decrease upon FTZ-F1 silencing, resulting in a delayed gonadal development. These results indicate that FTZ-F1 acts as a steroidogenic factor, participating in the synthesis and regulation of steroid hormones and thus playing an important role in the reproductive and endocrine systems within oysters.

Nitric oxide synthase and its function in animal reproduction: an update

Nitric oxide (NO), a free radical labile gas, is involved in the regulation of various biological functions and physiological processes during animal reproduction. Recently, increasing evidence suggests that the biological role and chemical fate of NO is dependent on dynamic regulation of its biosynthetic enzyme, three distinct nitric oxide synthase (NOS) according to their structure, location and function. The impact of NOS isoforms on reproductive functions need to be timely elucidated. Here, we focus on and the basic background and latest studies on the development, structure, importance inhibitor, location pattern, complex functions. Moreover, we summarize the exactly mechanisms which involved some cell signal pathways in the regulation of NOS with cellular and molecular level in the animal reproduction. Therefore, this growing research area provides the new insight into the important role of NOS male and female reproduction system. It also provides the treatment evidence on targeting NOS of reproductive regulation and diseases.

The Genetic Backdrop of Hypogonadotropic Hypogonadism

The pituitary is an organ of dual provenance: the anterior lobe is epithelial in origin, whereas the posterior lobe derives from the neural ectoderm. The pituitary gland is a pivotal element of the axis regulating reproductive function in mammals. It collects signals from the hypothalamus, and by secreting gonadotropins (FSH and LH) it stimulates the ovary into cyclic activity resulting in a menstrual cycle and in ovulation. Pituitary organogenesis is comprised of three main stages controlled by different signaling molecules: first, the initiation of pituitary organogenesis and subsequent formation of Rathke’s pouch; second, the migration of Rathke’s pouch cells and their proliferation; and third, lineage determination and cellular differentiation. Any disruption of this sequence, e.g., gene mutation, can lead to numerous developmental disorders. Gene mutations contributing to disordered pituitary development can themselves be classified: mutations affecting transcriptional determinants of pituitary development, mutations related to gonadotropin deficiency, mutations concerning the beta subunit of FSH and LH, and mutations in the DAX-1 gene as a cause of adrenal hypoplasia and disturbed responsiveness of the pituitary to GnRH. All these mutations lead to disruption in the hypothalamic–pituitary–ovarian axis and contribute to the development of primary amenorrhea.

A novel stop-loss DAX1 variant affecting its protein-interaction with SF1 precedes the adrenal hypoplasia congenital with rare spontaneous precocious puberty and elevated hypothalamic-pituitary-gonadal/adrenal axis responses

The case study unveils the likely mechanism of a novel stop-loss DAX1 variant preceding the prolonged precocious puberty in the adrenal hypoplasia congenital (AHC) boy. A boy aged five years and nine months initially examined for the primary adrenal insufficiency symptoms. Next-generation sequencing confirmed the X-linked inheritance of a novel stop-loss DAX1 variant: c.1411T>C/p.Ter471Gln associated with AHC in the patient. The patient was subjected to a brief clinical follow-up from 11 to 15.1 years of age. The effect of the mutant-DAX1 variant (p.Ter471Gln) on DAX1-steroidogenic factor 1 (SF1) (protein-protein) interaction was studied by protein-protein docking using the ClusPro-online tool. At 5.9 yrs of age, the patient exhibited precocious puberty with the secondary sexual characteristics of Tanner 2 stage (of 9-14 yrs of age). The patient showed primary adrenal insufficiency with diminished cortisol concentrations at blood serum (25 ng/ml) and urine (3.55 μg/24 h) levels. Upon steroidal exposure, the patient showed normalized serum cortisol levels of 45-61 ng/ml. However, the precocious puberty got prolonged with the increased penis length of 8.5 cm and the bone age of 18 yrs old during the follow-up. The patient showed increased basal serum adrenocorticotropic hormone (110->2000 pg/ml) and follicle-stimulating hormone (18.4-22.3 mIU/ml) concentrations. Following an elevated hypothalamic-pituitary-gonadal axis activity witnessed upon gonarellin stimulation. Protein-protein docking confirmed a weaker interaction between the mutant-DAX1 (p.Ter471Gln) protein and the wild-SF1 protein. Overall, we hypothesize the weakened mutant-DAX1-SF1 (protein-protein) interaction could govern the prolonged precocious puberty augmented with the elevated hypothalamic-pituitary-gonadal/adrenal axis responses via SF1-induced neuronal nitric oxide synthetase activation in the patient.

Gene Expression Changes Underlying Idiopathic Central Hypogonadism in Cryptorchidism with Defective Mini-Puberty

The whole genome RNA profiling of testicular biopsies by DNA strand-specific RNA sequencing was examined to determine a potential causative role of isolated congenital cryptorchidism in azoospermia and/or infertility in the context of our previously published GeneChip data. Cryptorchid patients, aged 7 months to 5 years and otherwise healthy, were enrolled in this prospective study. During surgery, testicular tissue biopsies were obtained for histological examination and RNA sequencing. Fifteen patients were selected based on the histological results and were divided into 2 groups. Seven were classified as belonging to the high infertility risk (HIR) and 8 to the low infertility risk (LIR) group. Cryptorchid boys in the HIR group lacked transformation of gonocytes into Ad spermatogonia due to impaired mini-puberty. This group of patients will be infertile despite successful surgery. The new important finding was a decreased PROK2, CHD7, FGFR1, and SPRY4 gene expression in the HIR group. Furthermore, identification of multiple differences in gene expression between HIR and LIR groups underscores the importance of an intact hypothalamic-pituitary-gonadal axis for fertility development. Our RNA profiling data strongly support the theory that in the HIR group of cryptorchid boys insufficient PROK2/CHD7/FGFR1/SPRY4 gene expression induces deficient LH secretion, resulting in impaired mini-puberty and infertility. We therefore recommend hormonal treatment for this cohort of cryptorchid boys with defective mini-puberty following a seemingly successful orchidopexy.

Role of Orphan Nuclear Receptor DAX-1/NR0B1 in Development, Physiology, and Disease

DAX-1/NR0B1 is an unusual orphan receptor that has a pivotal role in the development and function of steroidogenic tissues and of the reproductive axis. Recent studies have also indicated that this transcription factor has an important function in stem cell biology and in several types of cancer. Here I critically review the most important findings on the role of DAX-1 in development, physiology, and disease of endocrine tissues since the cloning of its gene twenty years ago.

Molecular mechanisms of gonadotropin-releasing hormone signaling: integrating cyclic nucleotides into the network

Gonadotropin-releasing hormone (GnRH) is the primary regulator of mammalian reproductive function in both males and females. It acts via G-protein coupled receptors on gonadotropes to stimulate synthesis and secretion of the gonadotropin hormones luteinizing hormone and follicle-stimulating hormone. These receptors couple primarily via G-proteins of the Gq/ll family, driving activation of phospholipases C and mediating GnRH effects on gonadotropin synthesis and secretion. There is also good evidence that GnRH causes activation of other heterotrimeric G-proteins (Gs and Gi) with consequent effects on cyclic AMP production, as well as for effects on the soluble and particulate guanylyl cyclases that generate cGMP. Here we provide an overview of these pathways. We emphasize mechanisms underpinning pulsatile hormone signaling and the possible interplay of GnRH and autocrine or paracrine regulatory mechanisms in control of cyclic nucleotide signaling.

Particulate matter, DNA methylation in nitric oxide synthase, and childhood respiratory disease

BACKGROUND

Air pollutants have been associated with childhood asthma and wheeze. Epigenetic regulation of nitric oxide synthase--the gene responsible for nitric oxide production--may be affected by air pollutants and contribute to the pathogenesis of asthma and wheeze.

OBJECTIVE

Our goal was to investigate the association between air pollutants, DNA methylation, and respiratory outcomes in children.

METHODS

Given residential address and buccal sample collection date, we estimated 7-day, 1-month, 6-month, and 1-year cumulative average PM₂.₅ and PM₁₀ (particulate matter ≤ 2.5 and ≤ 10 µm aerodynamic diameter, respectively) exposures for 940 participants in the Children's Health Study. Methylation of 12 CpG sites in three NOS (nitric oxide synthase) genes was measured using a bisulfite-polymerase chain reaction Pyrosequencing assay. Beta regression models were used to estimate associations between air pollutants, percent DNA methylation, and respiratory outcomes.

RESULTS

A 5-µg/m³ increase in PM₂.₅ was associated with a 0.20% [95% confidence interval (CI): -0.32, -0.07] to 1.0% (95% CI: -1.61, -0.56) lower DNA methylation at NOS2A position 1, 0.06% (95% CI: -0.18, 0.06) to 0.58% (95% CI: -1.13, -0.02) lower methylation at position 2, and 0.34% (95% CI: -0.57, -0.11) to 0.89% (95% CI: -1.57, -0.21) lower methylation at position 3, depending on the length of exposure and CpG locus. One-year PM2.5 exposure was associated with 0.33% (95% CI: 0.01, 0.65) higher in average DNA methylation of 4 loci in the NOS2A CpG island. A 5-µg/m³ increase in 7-day and 1-year PM₂.₅ was associated with 0.6% (95% CI: 0.13, 0.99) and 2.8% (95% CI: 1.77, 3.75) higher NOS3 DNA methylation. No associations were observed for NOS1. PM₁₀ showed similar but weaker associations with DNA methylation in these genes.

CONCLUSIONS

PM₂.₅ exposure was associated with percent DNA methylation of several CpG loci in NOS genes, suggesting an epigenetic mechanism through which these pollutants may alter production of nitric oxide.

The roles of testicular nuclear receptor 4 (TR4) in male fertility-priapism and sexual behavior defects in TR4 knockout mice

BACKGROUND

Successful reproductive efforts require the establishment of a situation favorable for reproduction that requires integration of both behavior and internal physiological events. TR4 nuclear receptor is known to be involved in male fertility via controlling spermatogenesis, yet its roles in regulating other biological events related to reproduction have not been completely revealed.

METHODS

Male TR4 knockout (TR4 -/-) and wild type mice were used for the sexual behavior and penile dysfunction studies. Mice were sacrificed for histological examination and corresponding genes profiles were analyzed by quantitative RT-PCR. Reporter gene assays were performed.

RESULTS

We describe an unexpected finding of priapism in TR4 -/- mice. As a transcriptional factor, we demonstrated that TR4 transcriptionally modulates a key enzyme regulating penis erection and neuronal nitric oxide synthese NOS (nNOS). Thereby, elimination of TR4 results in nNOS reduction in both mRNA and protein levels, consequently may lead to erectile dysfunction. In addition, male TR4 -/- mice display defects in sexual and social behavior, with increased fear or anxiety, as well as reduced mounting, intromission, and ejaculation. Reduction of ER alpha, ER beta, and oxytocin in the hypothalamus may contribute to defects in sexual behavior and stress response.

CONCLUSIONS

Together, these results provide in vivo evidence of important TR4 roles in penile physiology, as well as in male sexual behavior. In conjunction with previous finding, TR4 represents a key factor that controls male fertility via regulating behavior and internal physiological events.

Current Screens Based on the AlphaScreen Technology for Deciphering Cell Signalling Pathways

Global deciphering of signal transduction pathways represents a new challenge of the post-genomic era. However, for the majority of these signaling pathways the role(s), the function(s) and the interaction(s) of the signaling intermediates remain to be characterized in an integrated fashion. The global molecular study of cell signaling pathways and networks consequently requires sensitive, robust technologies which may allow in addition multi-parallel and highthroughput applications. The Alphascreen™ technology, relying on a bead-based homogenous approach, constitutes a valuable tool to detect and quantify a wide range of signaling events such as enzymatic activities or biomolecular interactions. In this article, we exhaustively review the literature and report the broad spectrum of Alphascreen™-based applications in the study of signal transduction pathways.

Research progress on neurobiology of neuronal nitric oxide synthase

Neuronal nitric oxide synthase (nNOS) is mainly expressed in neurons, to some extent in astrocytes and neuronal stem cells. The alternative splicing of nNOS mRNA generates 5 isoforms of nNOS, including nNOS-α, nNOS-β, nNOS-µ, nNOS-γ and nNOS-2. Monomer of nNOS is inactive, and dimer is the active form. Dimerization requires tetrahydrobiopterin (BH4), heme and L-arginine binding. Regulation of nNOS expression relies largely on cAMP response element-binding protein (CREB) activity, and nNOS activity is regulated by heat shock protein 90 (HSP90)/HSP70, calmodulin (CaM), phosphorylation and dephosphorylation at Ser847 and Ser1412, and the protein inhibitor of nNOS (PIN). There are primarily 9 nNOS-interacting proteins, including post-synaptic density protein 95 (PSD95), clathrin assembly lymphoid leukemia (CALM), calcium/calmodulin-dependent protein kinase II alpha (CAMKIIA), Disks large homolog 4 (DLG4), DLG2, 6-phosphofructokinase, muscle type (PFK-M), carboxy-terminal PDZ ligand of nNOS (CAPON) protein, syntrophin and dynein light chain (LC). Among them, PSD95, CAPON and PFK-M are important nNOS adapter proteins in neurons. The interaction of PSD95 with nNOS controls synapse formation and is implicated in N-methyl-D-aspartic acid-induced neuronal death. nNOS-derived NO is implicated in synapse loss-mediated early cognitive/motor deficits in several neuropathological states, and negatively regulates neurogenesis under physiological and pathological conditions.

DNA methylation in the arginase-nitric oxide synthase pathway is associated with exhaled nitric oxide in children with asthma

RATIONALE

Genetic variation in arginase (ARG) and nitric oxide synthase (NOS) has been associated with exhaled nitric oxide (FeNO) levels in children. Little is known about whether epigenetic variation in these genes modulates FeNO.

OBJECTIVES

To evaluate whether DNA methylation in ARG and NOS genes is associated with FeNO.

METHODS

A subset of 940 participants in the Children's Health Study were selected for this study. Children were eligible if they had FeNO measurements and buccal cells collected on the same day. CpG loci located in the promoter regions of NOS1, NOS2A, NOS3, ARG1, and ARG2 genes were analyzed. Multiple loci in each gene were evaluated individually and averaged together. DNA methylation was measured using a bisulfite-polymerase chain reaction pyrosequencing assay. Linear regression models were used to investigate the association between DNA methylation and FeNO and whether associations differed by asthma status.

MEASUREMENTS AND MAIN RESULTS

DNA methylation in ARG2 was significantly associated with FeNO. A 1% increase in average DNA methylation of ARG2 was associated with a 2.3% decrease in FeNO (95% confidence interval, -4 to -0.6). This association was significantly larger in children with asthma (%diff = -8.7%) than in children with no asthma (%diff = -1.6%; p(int) = 0.01). Differences in FeNO by asthma status were also observed for ARG1 (%diff(asthma) = -4.4%; %diff(non-asthma) = 0.3%; p(int) = 0.02). DNA methylation in NOS genes was not associated with FeNO.

CONCLUSIONS

DNA methylation in ARG1 and ARG2 is associated with FeNO in children with asthma and suggests a possible role for epigenetic regulation of nitric oxide production.

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.

Identification of alternate transcripts of neuronal nitric oxide synthase in the mouse retina

Nitric oxide (NO) is a major signaling molecule in the retina and CNS, with physiological roles in every cell type in the retina. Previous work shows that neuronal nitric oxide synthase (nNOS) is an important source of NO in the vertebrate retina. There are distinct, active alternative transcripts of nNOS observed in many tissues, including testes and brain, that may differ in both localization and enzyme kinetics. The present study characterized nNOS and the NO production from nNOS in the mouse retina in terms of its alternate transcripts, namely, nNOS alpha, nNOS beta, and nNOS gamma. We examined both basal and light-stimulated NO production as imaged using the NO-sensitive dye 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate-FM (DAF-FM), and we compared the NO production with the immunocytochemical localization of nNOS using antisera that recognize nNOS alpha/beta or nNOS alpha/beta/gamma. Western blots suggested the presence of NOS alpha/gamma protein in retina, but not nNOS beta, and we confirmed this at the message level by using a combination of RT-PCR and quantitative real-time PCR. Our findings indicated that the primary source of NO in the mammalian retina is nNOS alpha and that nNOS gamma may contribute to NO production as well.

Retinoic acid-induced nNOS expression depends on a novel PI3K/Akt/DAX1 pathway in human TGW-nu-I neuroblastoma cells

Neuronal nitric oxide synthase (nNOS)-derived nitric oxide (NO) acts as a neurotransmitter and intracellular signaling molecule in the central and peripheral nervous system. NO regulates multiple processes like neuronal development, plasticity, and differentiation and is a mediator of neurotoxicity. The nNOS gene is highly complex with 12 alternative first exons, exon 1a-1l, transcribed from distinct promoters, leading to nNOS variants with different 5'-untranslated regions. Transcriptional control of the nNOS gene is not understood in detail. To investigate regulation of nNOS gene expression by retinoic acid (RA), we used the human neuroblastoma cell line TGW-nu-I as a model system. We show that RA induces nNOS transcription in a protein synthesis-dependent fashion. We identify the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway and the atypical orphan nuclear receptor DAX1 (NR0B1) as critical mediators involved in RA-induced nNOS gene transcription. RA treatment increases DAX1 expression via PI3K/Akt signaling. Upregulation of DAX1 expression in turn induces nNOS transcription in response to RA. These results identify nNOS as a target gene of a novel RA/PI3K/Akt/DAX1-dependent pathway in human neuroblastoma cells and stress the functional importance of the transcriptional regulator DAX1 for nNOS gene expression in response to RA treatment.

Estrous cycle influences the expression of neuronal nitric oxide synthase in the hypothalamus and limbic system of female mice

BACKGROUND

Nitric oxide plays an important role in the regulation of male and female sexual behavior in rodents, and the expression of the nitric oxide synthase (NOS) is influenced by testosterone in the male rat, and by estrogens in the female. We have here quantitatively investigated the distribution of nNOS immunoreactive (ir) neurons in the limbic hypothalamic region of intact female mice sacrificed during different phases of estrous cycle.

RESULTS

Changes were observed in the medial preoptic area (MPA) (significantly higher number in estrus) and in the arcuate nucleus (Arc) (significantly higher number in proestrus). In the ventrolateral part of the ventromedial nucleus (VMHvl) and in the bed nucleus of the stria terminalis (BST) no significant changes have been observed. In addition, by comparing males and females, we observed a stable sex dimorphism (males have a higher number of nNOS-ir cells in comparison to almost all the different phases of the estrous cycle) in the VMHvl and in the BST (when considering only the less intensely stained elements). In the MPA and in the Arc sex differences were detected only comparing some phases of the cycle.

CONCLUSION

These data demonstrate that, in mice, the expression of nNOS in some hypothalamic regions involved in the control of reproduction and characterized by a large number of estrogen receptors is under the control of gonadal hormones and may vary according to the rapid variations of hormonal levels that take place during the estrous cycle.

Estrous cycle influences the expression of neuronal nitric oxide synthase in the hypothalamus and limbic system of female mice

BACKGROUND

Nitric oxide plays an important role in the regulation of male and female sexual behavior in rodents, and the expression of the nitric oxide synthase (NOS) is influenced by testosterone in the male rat, and by estrogens in the female. We have here quantitatively investigated the distribution of nNOS immunoreactive (ir) neurons in the limbic hypothalamic region of intact female mice sacrificed during different phases of estrous cycle.

RESULTS

Changes were observed in the medial preoptic area (MPA) (significantly higher number in estrus) and in the arcuate nucleus (Arc) (significantly higher number in proestrus). In the ventrolateral part of the ventromedial nucleus (VMHvl) and in the bed nucleus of the stria terminalis (BST) no significant changes have been observed. In addition, by comparing males and females, we observed a stable sex dimorphism (males have a higher number of nNOS-ir cells in comparison to almost all the different phases of the estrous cycle) in the VMHvl and in the BST (when considering only the less intensely stained elements). In the MPA and in the Arc sex differences were detected only comparing some phases of the cycle.

CONCLUSION

These data demonstrate that, in mice, the expression of nNOS in some hypothalamic regions involved in the control of reproduction and characterized by a large number of estrogen receptors is under the control of gonadal hormones and may vary according to the rapid variations of hormonal levels that take place during the estrous cycle.

Pituitary homeobox 2 regulates adrenal4 binding protein/steroidogenic factor-1 gene transcription in the pituitary gonadotrope through interaction with the intronic enhancer

Ad4BP/SF-1 [adrenal4 binding protein/steroidogenic factor-1 (NR5A1)] is a factor important for animal reproduction and endocrine regulation, and its expression is tightly regulated in the gonad, adrenal gland, ventromedial hypothalamic nucleus, and pituitary gonadotrope. Despite its functional significance in the pituitary, the mechanisms underlying pituitary-specific expression of the gene remain to be uncovered. In this study, we demonstrate by transgenic mouse assays that the pituitary gonadotrope-specific enhancer is localized within the sixth intron of the gene. Functionally, the enhancer recapitulates endogenous Ad4BP/SF-1 expression in the fetal Rathke's pouch to the adult pituitary gonadotrope. Structurally, the enhancer consists of several elements conserved among animal species. Mutational analyses confirmed the significance of these elements for the enhancer function. One of these elements was able to interact both in vitro and in vivo with Pitx2 (pituitary homeobox 2), demonstrating that pituitary homeobox 2 regulates Ad4BP/SF-1 gene transcription in the pituitary gonadotrope via interaction with the gonadotrope-specific enhancer.

Nuclear factor kappa-B mediates selective induction of neuronal nitric oxide synthase in astrocytes during low-level inflammatory stimulation with MPTP

Recent advances in understanding the progression of Parkinson's disease (PD) implicate perturbations in astrocyte function and induction of constitutively expressed neuronal nitric oxide synthase (NOS1) in both human PD and in the MPTP model of the disease. Transcriptional regulation of NOS1 is complex but recent data suggest that nuclear factor kappa-B (NF-kappaB) is an important transcription factor involved in inducible expression of the gene. The data presented here demonstrate that mild activation of primary astrocytes with low or 'sub-optimal' concentrations of MPTP (1 microM) and the inflammatory cytokine tumor necrosis factor alpha (10 pg/ml) and interferon gamma (1 ng/ml) results in selective induction of Nos1 mRNA and protein, increased production of nitric oxide (NO), and a significant elevation in global protein nitration. This mild inflammatory stimulus also resulted in activation and recruitment of p65 to a putative NF-kappaB response element located in the Nos1 promoter region flanking exon 1. A role for NF-kappaB in MPTP-dependent induction of NOS1 was confirmed through overexpression of a mutant IkappaBalpha super repressor of NF-kappaB that prevented induction of NOS1. The data presented here thus demonstrate a role for NF-kappaB in selective induction of NOS1 during early inflammatory activation of astrocytes stimulated by low-dose MPTP and inflammatory cytokines.

Transcriptional regulation of human Oct4 by steroidogenic factor-1

Oct4 encodes a transcription factor that is involved in the maintenance of self-renewal in stem cells. Recently, the molecular mechanisms that regulate Oct4 expression have come under investigation. In this study, we demonstrate that the orphan nuclear receptor steroidogenic factor-1 (SF-1) behaves as a transcriptional activator of human Oct4 (hOct4) through direct interaction with a SF-1 binding element in the hOct4 proximal promoter. We found that Oct4 and SF-1 were co-expressed in undifferentiated human embryonal carcinoma NCCIT cells and downregulated during retinoic acid-mediated differentiation. We examined the functional role played by SF-1 in regulation of hOct4 transcription using a luciferase reporter assay and Western blot analysis. Overexpression of SF-1 increased up to about threefold hOct4 promoter activity and endogenous hOct4 protein expression. Sequence analysis of the hOct4 promoter revealed that the transcriptional activity was closely linked to Conserved Regions 1 (CR1) and 2 (CR2), which contain three putative SF-1-binding sites (1st, 2nd, and 3rd SF-1). Binding assays and mutagenesis of binding sites indicated that the 1st and 2nd SF-1 elements (in CR1 and CR2, respectively) might be important cis-regulatory elements in hOct4 promoter activity. However, differences in response to SF-1 overexpression between wild-type and mutant hOct4 promoters revealed that the 1st SF-1 element is the key binding site for SF-1-mediated transcriptional activation. Thus, our data indicate that SF-1 plays a crucial role in the regulation of hOct4 transcription through direct binding to the 1st SF-1 in CR1 of the hOct4 proximal promoter.

The untranslated region of exon 2 of the human neuronal nitric oxide synthase (NOS1) gene exerts regulatory activity

Expressional dysregulation of the human neuronal nitric oxide synthase (NOS1) gene represents an important mechanism in the pathogenesis of certain neuronal disease states. The structure and regulation of the human NOS1 gene is highly complex based on cell type- and stimulus-dependent usage of multiple exon 1 variants. Here we demonstrate that the untranslated region of exon 2 exerts promoter and enhancer functions as well, facilitated in large part by cooperative interaction of two conserved adjacent CREB/AP-1 binding sites. In human neuronal A673 cells, NOS1 expression is stimulated by several compounds which act through these sites, but also stimulate the combined promoter region of exons 1f and 1g. While stimulation of NOS1 expression by dibutyryl-cAMP is mediated by protein kinase A (blocked by H-89), the antiepileptic drug valproic acid is likely to activate phosphatidylinositol-3 kinase (inhibited by LY 294002).

Nitric oxide synthesis in the kidney: isoforms, biosynthesis, and functions in health

Nitric oxide (NO) is a gaseous free radical that serves cell signaling, cellular energetics, host defense, and inflammatory functions in virtually all cells. In the kidney and vasculature, NO plays fundamental roles in the control of systemic and intrarenal hemodynamics, the tubuloglomerular feedback response, pressure natriuresis, release of sympathetic neurotransmitters and renin, and tubular solute and water transport. NO is synthesized from L-arginine by NO synthases (NOS). Because of its high chemical reactivity and high diffusibility, NO production by each of the 3 major NOS isoforms is regulated tightly at multiple levels from gene transcription to spatial proximity near intended targets to covalent modification and allosteric regulation of the enzyme itself. Many of these regulatory mechanisms have yet to be tested in renal cells. The NOS isoforms are distributed differentially and regulated in the kidney, and there remains some controversy over the specific expression of functional protein for the NOS isoforms in specific renal cell populations. Mice with targeted deletion of each of the NOS isoforms have been generated, and these each have unique phenotypes. Studies of the renal and vascular phenotypes of these mice have yielded important insights into certain vascular diseases, ischemic acute renal failure, the tubuloglomerular feedback response, and some mechanisms of tubular fluid and electrolyte transport, but thus far have been underexploited. This review explores the collective knowledge regarding the structure, regulation, and function of the NOS isoforms gleaned from various tissues, and highlights the progress and gaps in understanding in applying this information to renal and vascular physiology.

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

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

The rat pituitary promoter of the neuronal nitric oxide synthase gene contains an Sp1-, LIM homeodomain-dependent enhancer and a distinct bipartite gonadotropin-releasing hormone-responsive region

The neuronal nitric oxide synthase (NOS I) is expressed and hormonally regulated in rat anterior pituitary gonadotropes. In the present study, we investigated the mechanisms that underlie the constitutive and GnRH up-regulated activity of the pituitary exon 1p promoter of the NOS I gene in these cells. Through the use of 5'-deletions and transient transfections in L beta T2, a gonadotrope-derived cell line, we delineated a NOS I cell-specific (NCS) enhancer region (-73/-59) that is required for constitutive activity. Independently of the NCS enhancer, GnRH responsiveness is supported by a bipartite regulatory domain referred to as the GnRH response element I and II located between -33/-10 and -4/+4, the latter consisting of a cAMP-like response element. By combining transient transfections, gel shift, and supershift assays, we demonstrate that Sp1 and LIM-homeodomain-related protein bind the NCS enhancer, whereas cAMP response element binding protein and cAMP regulatory element modulator-like factors bind the GnRH response element II motif. We further show that factors involved in GnRH regulation are also implicated in constitutive activity, suggesting intimate links between constitutive and regulated promoter activity. We speculate that specific expression of the NOS I gene in gonadotropes together with its regulation by GnRH is suggestive of a critical participation of NOS I in gonadotrope function.

DAX-1, an unusual orphan receptor at the crossroads of steroidogenic function and sexual differentiation

The unusual orphan member of the nuclear hormone receptor superfamily DAX-1 (NR0B1) owes its name to its double role in human pathology. On one side, duplications in Xp21, containing the DAX-1 gene, cause phenotypic sex reversal in XY individuals. On the other side, DAX-1 gene mutations are responsible for adrenal hypoplasia congenita, invariably associated with hypogonadotropic hypogonadism. DAX-1 functions as a global negative regulator of steroid hormone production by repressing the expression of multiple genes involved in the steroidogenic pathway. Here we review the mechanism of DAX-1 function in adrenal and gonadal differentiation, with special emphasis on recent results showing the critical role of DAX-1 protein misfolding in the pathogenesis of adrenal hypoplasia congenita.