Steroidogenic acute regulatory (StAR) protein: what's new?

NR5A1 and NR5A2 regulate follicle development in chicken (Gallus gallus) by altering proliferation, apoptosis, and steroid hormone synthesis of granulosa cells

Chicken ovarian follicle development is regulated by complex and dynamic gene expression. Nuclear receptor 5A1 and 5A2 (NR5A1 and NR5A2, respectively) are key genes that regulate steroid hormone production and gonadal development in mammals; however, studies on follicular development in the chicken ovary are scarce. In this study, we investigated the functions of NR5A1 and NR5A2 on follicle development in chickens. The results showed that the expression of NR5A1 and NR5A2 was significantly higher in small yellow follicles and F5. Furthermore, the expression of NR5A1 and NR5A2 was significantly higher in follicular tissues of peak-laying hens (30 wk) than in follicular tissues of late-laying hens (60 wk), with high expression abundance in granulosa cells (GC). The overexpression of NR5A1 and NR5A2 significantly promoted proliferation and inhibited apoptosis of cultured GC; upregulated STAR, CYP11A1, and CYP19A1 expression and estradiol (E2) and progesterone (P4) synthesis in GC from preovulatory follicles (po-GC); and increased STAR, CYP11A1, and CYP19A1 promoter activities. In addition, follicle-stimulating hormone treatment significantly upregulated NR5A1 and NR5A2 expression in po-GC and significantly promoted FSHR, CYP11A1, and HSD3B1 expression in GC from pre-hierarchical follicles and po-GC. The core promoter region of NR5A1 was identified at the -1,095- to -483-bp and -2,054- to -1,536-bp regions from the translation start site (+1), and the core promoter region of NR5A2 was at -998 to -489 bp. Two single nucleotide polymorphisms (SNP) were identified in the core promoter region of the NR5A1 gene, which differed between high- and low-yielding chicken groups. Our study suggested that NR5A1 and NR5A2 promoted chicken follicle development by promoting GC proliferation and E2 and P4 hormone synthesis and inhibiting apoptosis. Moreover, we identified the promoter core region or functional site that regulates NR5A1 and NR5A2 expression.

Pentachloronitrobenzene alters progesterone production and primordial follicle recruitment in cultured granulosa cells and rat ovary†

Pentachloronitrobenzene (PCNB) is an organochlorine fungicide widely used for crop production and has become an environmental concern. Little is known about the effect of PCNB on ovarian steroidogenesis and follicular development. We found that PCNB stimulated Star expression and progesterone production in cultured rat granulosa cells in a dose-dependent manner. PCNB activated mitogen-activated protein kinase (MAPK3/1) extracellulat regulated kinase (ERK1/2), thus inhibition of either protein kinase A (PKA) or MAPK3/1 signaling pathway significantly attenuated progesterone biosynthesis caused by PCNB, suggesting that PCNB induced progesterone production by activating the cyclic adenosine monophosphate (cAMP/PKA) and MAPK3/1 signaling pathways. Further investigation demonstrated that PCNB induced Star expression and altered MAPK3/1 signaling in ovary tissues of immature SD rats treated with PCNB at the dose of 100, 200, or 300 mg/kg by daily gavage for 7 days, while serum progesterone level was dose-dependently decreased. We demonstrated that PCNB exposure accelerated the recruitment of primordial follicles into the growing follicle pool in ovary tissues, accompanied by increased levels of anti-Mullerian hormone (AMH) in both ovary tissues and serum. Taken together, our data demonstrate for the first time that PCNB stimulated Star expression, altered MAPK3/1 signaling and progesterone production in vivo and in vitro, and accelerated follicular development with a concomitant increase in AMH in ovary tissues and serum. Our findings provide novel insight into the toxicity of PCNB to animal ovary function.

CYP11A1 Upregulation Leads to Trophoblast Oxidative Stress and Fetal Neurodevelopmental Toxicity That can be Rescued by Vitamin D

During normal pregnancy, the placental trophoblast secretes a variety of steroid hormones and participates in the regulation of maternal physiological functions and fetal development. The CYP11A1 gene encodes the cholesterol side-chain cleavage enzyme P450scc, which catalyzes the production of pregnenolone from cholesterol, which is the first step in the synthesis of all steroid hormones. Under the influence of genetic susceptibility and certain environmental factors, such as drugs and toxins, the expression of CYP11A1 can be upregulated, thereby affecting steroid metabolism and physiological functions in trophoblast cells, as well as fetal development. Here, we demonstrate that upregulation of CYP11A1 in the BeWo cell line triggers excessive mitochondrial oxidative stress, leads to mitochondrial damage and interleukin-6 release, and contributes to the inhibition of proliferation and DNA damage in neuronal stem cells (NSCs). Furthermore, oxidative stress and inflammation can be ameliorated by vitamin D₃ in a dose-dependent manner, thereby facilitating the rescue of NSC impairment. Our findings reveal the underlying mechanism in which upregulation of CYP11A1 is detrimental to the physiological function of trophoblasts and demonstrate the beneficial effects of vitamin D supplementation in preventing placental and neurodevelopmental damage associated with CYP11A1 upregulation during pregnancy.

Changes in Sex Steroids and Ovarian Steroidogenic Enzyme mRNA Levels in Artificially Maturing Japanese Eel (Anguilla japonica) and Naturally Maturing New Zealand Longfin Eel (Anguilla dieffenbachii) during Vitellogenesis

Repeated hormone injections are routinely used to induce advanced stages of oogenesis in freshwater eels, but this approach may result in aberrant germ cell development. To investigate the underlying causes, levels of sex steroids (testosterone, T; estradiol-17β, E2) and ovarian steroidogenic enzyme mRNAs were compared between artificially maturing Japanese eels and wild-caught, spontaneously maturing New Zealand longfin eels. The latter were employed as reference, as wild Japanese eels in advanced stages of oogenesis are near-impossible to catch. Serum T levels in artificially maturing Japanese eel changed with stage in a pattern that was comparable to that in longfin eels. Likewise, ovarian mRNA levels of most steroidogenic enzyme genes were not qualitatively dissimilar between both eel species when taking developmental stage into account. However, aromatase (cyp19a) mRNA levels, together with serum E2 levels, rapidly increased in artificially maturing Japanese eels in mid-late stages of oogenesis (gonadosomatic index, GSI = 13.8%), whereas no such increase was evident in longfin eels (GSI ~ 6.9%). In addition, sex steroid and target gene mRNA levels fluctuated drastically with each hormone injection. We contend that expression of most target genes, possibly even that of cyp19a, during induced oogenesis could be “normal”, with the drastic fluctuations due most likely to hormone delivery through repeated injections. The effects of these fluctuations on gamete quality remain unknown and resolving this issue may prove fruitful in the future to further artificial propagation of anguillid eels.

Autophagy in male reproduction

Autophagy is a fundamental process that exists in all eukaryotic organisms, with a primary function of catabolizing undesirable components to provide energy and essential materials. Increasing evidence illustrates that autophagy is invovled in a broad range of cellular events within the male reproductive system. In the process of spermatogenesis, autophagy is crucial for the formation of specific structures that guarantee successful spermatogenesis, as well as for the degradation of certain constituents. The underlying connections between autophagy and androgen binding protein, lipid metabolism and testosterone biosynthesis would increase our understanding of male testicular endocrinology. Moreover, cumulative studies reveal that autophagy is a double-edged sword when the organism suffers from endocrine disrupting chemicals. This review contains a collection of the current literature concerning the above aspects of autophagy, which may provide insights for future study and exploration. Abbreviations: 3-MA: 3-methyladenine; ABP: androgen-binding protein; AKT: protein kinase B; AMPK: adenosine monophosphate-activated protein kinase; ART: assisted reproductive technologies; Atg: autophagy-related gene; CE: cholesteryl ester; CL: corpus luteum; CQ: chloroquine; CYP11A1: cholesterol side chain cleavage enzyme; CytC: cytochrome C; DEHP: di-2-ethylhexyl phthalate; DFCP1: double FYVE-containing protein 1; EDCs: endocrine-disrupting chemicals; ERK1/2: extracellular signal-regulated kinase 1/2; ES: ectoplasmic specialization; FC: free cholesterol; FIP2000: focal adhesion kinase family interacting protein of 200kDa; FSH: follicle stimulating hormone; HDL: high-density lipoprotein; IVF: in vitro fertilization; LC3: microtubule-associated protein light chain 3; LD: lipid droplet; LH: luteinising hormone; MC-LR: microcystin-LR; MEFs: mouse embryonic fibroblast cells; MT: microtubule; mtDNA: mitochondrial DNA; mTOR: mammalian target of rapamycin; NHERF2: Na⁺/H⁺ exchanger regulatory factor 2; NMR: naked mole-rat; PCD: programmed cell death; PDLIM1: PDZ and LIM domain 1; PGCs: primordial germ cells; PGF_2α: prostaglandin F_2α; PI3K: phosphatidylinositol-3-kinase; PI3P: phosphatidylinositol-3-phosphate; ROS: reactive oxygen species; SCG10: superior cervical ganglia protein 10; SR-BI: scavenger receptor class B, type I; StAR protein: steroidogenic acute regulatory protein; TC: total cholesterol; TEM: transmission electron microscopy; TUNEL: terminal deoxynucleotidyl transferase mediated dUTP nick end labeling; ULK1: mammalian uncoordinated-51-like kinase 1; WIPI: WD-repeat domain phosphoinositide-interacting.

Sexual Dimorphism in Circadian Physiology Is Altered in LXRα Deficient Mice

The mammalian circadian timing system coordinates key molecular, cellular and physiological processes along the 24-h cycle. Accumulating evidence suggests that many clock-controlled processes display a sexual dimorphism. In mammals this is well exemplified by the difference between the male and female circadian patterns of glucocorticoid hormone secretion and clock gene expression. Here we show that the non-circadian nuclear receptor and metabolic sensor Liver X Receptor alpha (LXRα) which is known to regulate glucocorticoid production in mice modulates the sex specific circadian pattern of plasma corticosterone. Lxrα^-/- males display a blunted corticosterone profile while females show higher amplitude as compared to wild type animals. Wild type males are significantly slower than females to resynchronize their locomotor activity rhythm after an 8 h phase advance but this difference is abrogated in Lxrα^-/- males which display a female-like phenotype. We also show that circadian expression patterns of liver 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) and Phosphoenolpyruvate carboxykinase (Pepck) differ between sexes and are differentially altered in Lxrα^-/- animals. These changes are associated with a damped profile of plasma glucose oscillation in males but not in females. Sex specific alteration of the insulin and leptin circadian profiles were observed in Lxα^-/- females and could be explained by the change in corticosterone profile. Together this data indicates that LXRα is a determinant of sexually dimorphic circadian patterns of key physiological parameters. The discovery of this unanticipated role for LXRα in circadian physiology underscores the importance of addressing sex differences in chronobiology studies and future LXRα targeted therapies.

Microarray analysis of Foxl2 mediated gene regulation in the mouse ovary derived KK1 granulosa cell line: Over-expression of Foxl2 leads to activation of the gonadotropin releasing hormone receptor gene promoter

BACKGROUND

The Foxl2 transcription factor is required for ovarian function during follicular development. The mechanism of Foxl2 regulation of this process has not been elucidated. Our approach to begin to understand Foxl2 function is through the identification of Foxl2 regulated genes in the ovary.

METHODS

Transiently transfected KK1 mouse granulosa cells were used to identify genes that are potentially regulated by Foxl2. KK1 cells were transfected in three groups (mock, activated, and repressed) and twenty-four hours later RNA was isolated and submitted for Affymetrix microarray analysis. Genesifter software was used to carry out analysis of microarray data. One identified target, the gonadotropin releasing hormone receptor (GnRHR) gene, was chosen for further study and validation of Foxl2 responsiveness. Transient transfection analyses were carried out to study the effect of Foxl2 over-expression on GnRHR gene promoter-luciferase fusion activity. Data generated was analyzed with GraphPad Prism software.

RESULTS

Microarray analysis identified 996 genes of known function that are potentially regulated by Foxl2 in mouse KK1 granulosa cells. The steroidogenic acute regulatory protein (StAR) gene that has been identified as Foxl2 responsive by others was identified in this study also, thereby supporting the effectiveness of our strategy. The GnRHR gene was chosen for further study because it is known to be expressed in the ovary and the results of previous work has indicated that Foxl2 may regulate GnRHR gene expression. Cellular levels of Foxl2 were increased via transient co-transfection of KK1 cells using a Foxl2 expression vector and a GnRHR promoter-luciferase fusion reporter vector. The results of these analyses indicate that over-expression of Foxl2 resulted in a significant increase in GnRHR promoter activity. Therefore, these transfection data validate the microarray data which suggest that Foxl2 regulates GnRHR and demonstrate that Foxl2 acts as an activator of the GnRHR gene.

CONCLUSIONS

Potential Foxl2 regulated ovarian genes have been identified through microarray analysis and comparison of these data to other microarray studies. The Foxl2 responsiveness of the GnRHR gene has been validated and provided evidence of Foxl2 transcriptional activation of the GnRHR gene promoter in the mouse ovary derived KK1 granulosa cell line.

GnRH-mediated DAN production regulates the transcription of the GnRH receptor in gonadotrope cells

The primary function of gonadotropin-releasing hormone (GnRH) is the regulation of pituitary gonadotropin hormone gene transcription, biosynthesis and release. These effects are mediated through intracellular mobilization of Ca2+ and activation of PKC isoforms and MAP kinases. We show here that DAN (differential screening-selected gene aberrative in neuroblastoma) which is a secreted bone morphogenic protein (BMP) antagonist belonging to the TGFbeta protein superfamily, is controlled by GnRH in murine gonadotrope cells. Acute GnRH stimulation induced a rapid, 27-fold, elevation of DAN mRNA, accompanied by an approximate 3-fold increase in the amount of mature DAN glycoprotein in the cell cytoplasm and in DAN secretion into the culture medium. Incubation of L beta T2 cells in DAN-containing medium altered the levels of a number of cellular proteins. Two of these were identified as the steroidogenic acute regulatory protein (StAR) and the actin-related protein 2/3 complex subunits 2 (p34-ARC) which are primarily involved in steroidogenesis and cytoskeleton remodelling, respectively. DAN caused an approximate 2-fold specific elevation in the cytoplasmic levels of both these proteins in L beta T2 cells. We further tested the effects of DAN on classical GnRH effects viz. gonadotropin and GnRH receptor gene expression. Co-transfection of L beta T2 cells with DAN and gonadotropin subunit promoter luciferase reporter genes had no effect on GnRH stimulation of alpha GSU and LH beta or on the additive GnRH and activin induction of FSH beta subunit transcription. However, co-transfection of DAN markedly inhibited the synergistic activation of GnRH and activin on GnRH receptor gene expression thus implicating DAN as a novel autocrine/paracrine factor that modulates GnRH function in pituitary gonadotropes.

Modeling the structure of the StART domains of MLN64 and StAR proteins in complex with cholesterol

Steroidogenic acute regulatory protein-related lipid transfer (StART) domains are ubiquitously involved in intracellular lipid transport and metabolism and other cell-signaling events. In this work, we use a flexible docking algorithm, comparative modeling, and molecular dynamics (MD) simulations to generate plausible three-dimensional atomic models of the StART domains of human metastatic lymph node 64 (MLN64) and steroidogenic acute regulatory protein (StAR) proteins in complex with cholesterol. Our results show that cholesterol can adopt a similar conformation in the binding cavity in both cases and that the main contribution to the protein-ligand interaction energy derives from hydrophobic contacts. However, hydrogen-bonding and water-mediated interactions appear to be important in the fine-tuning of the binding affinity and the position of the ligand. To gain insights into the mechanism of binding, we carried out steered MD simulations in which cholesterol was gradually extracted from within the StAR model. These simulations indicate that a transient opening of loop Omega1 may be sufficient for uptake and release, and they also reveal a pathway of intermediate states involving residues known to be crucial for StAR activity. Based on these observations, we suggest specific mutagenesis targets for binding studies of cholesterol and its derivatives that could improve our understanding of the structural determinants for ligand binding by sterol carrier proteins.

Energized, polarized, and actively respiring mitochondria are required for acute Leydig cell steroidogenesis

The first and rate-limiting step in the biosynthesis of steroid hormones is the transfer of cholesterol into mitochondria, which is facilitated by the steroidogenic acute regulatory (StAR) protein. Recent study of Leydig cell function has focused on the mechanisms regulating steroidogenesis; however, few investigations have examined the importance of mitochondria in this process. The purpose of this investigation was to determine which aspects of mitochondrial function are necessary for acute cAMP-stimulated Leydig cell steroidogenesis. MA-10 cells were treated with 8-bromoadenosine 3',5'-cyclic monophosphate (cAMP) and different site-specific agents that disrupt mitochondrial function, and the effects on acute cAMP-stimulated progesterone synthesis, StAR mRNA and protein, mitochondrial membrane potential (Deltapsim), and ATP synthesis were determined. cAMP treatment of MA-10 cells resulted in significant increases in both cellular respiration and Deltapsim. Dissipating Deltapsim with carbonyl cyanide m-chlorophenyl hydrazone resulted in a profound reduction in progesterone synthesis, even in the presence of newly synthesized StAR protein. Preventing electron transport in mitochondria with antimycin A significantly reduced cellular ATP, potently inhibited steroidogenesis, and reduced StAR protein levels. Inhibiting mitochondrial ATP synthesis with oligomycin reduced cellular ATP, inhibited progesterone synthesis and StAR protein, but had no effect on Deltapsim. Disruption of intramitochondrial pH with nigericin significantly reduced progesterone production and StAR protein but had minimal effects on Deltapsim. 22(R)-hydroxycholesterol-stimulated progesterone synthesis was not inhibited by any of the mitochondrial reagents, indicating that neither P450 side-chain cleavage nor 3beta-hydroxysteroid dehydrogenase activity was inhibited. These results indicate that Deltapsim, mitochondrial ATP synthesis, and mitochondrial pH are all required for acute steroid biosynthesis. These results suggest that mitochondria must be energized, polarized, and actively respiring to support Leydig cell steroidogenesis, and alterations in the state of mitochondria may be involved in regulating steroid biosynthesis.

Mitochondrial function in Leydig cell steroidogenesis

The first and rate-limiting step in the biosynthesis of steroid hormones is the transfer of cholesterol into mitochondria, which is facilitated by the steroidogenic acute regulatory (StAR) protein. Recent studies of Leydig cell function have focused on the molecular events controlling steroidogenesis; however, few studies have examined the importance of the mitochondria. The purpose of this investigation was to determine which aspects of mitochondrial function are necessary for Leydig cell steroidogenesis. MA-10 tumor Leydig cells were treated with 8-bromo-cAMP (cAMP) and site-specific mitochondrial disrupters, pro-oxidants, and their effects on progesterone synthesis, StAR expression, mitochondrial membrane potential (delta psi(m)) and ATP synthesis were determined. Dissipating delta psi(m) with CCCP inhibited progesterone synthesis, even in the presence of newly synthesized StAR protein. The electron transport inhibitor antimycin A significantly reduced cellular ATP, inhibited steroidogenesis, and reduced StAR protein expression. The F0/F1 ATPase inhibitor oligomycin reduced cellular ATP and inhibited progesterone synthesis and StAR protein expression, but had no effect on delta psi(m). Disruption of pH with nigericin significantly reduced progesterone production and StAR protein, but had minimal effects on delta psi(m). Sodium arsenite at low concentrations inhibited StAR protein but not mRNA expression and inhibited progesterone without disrupting delta psi(m). The mitochondrial Ca2+ inhibitor Ru360 also inhibited StAR protein expression. These results demonstrate that delta psi(m), ATP synthesis, delta pH and [Ca2+]mt are all required for steroid biosynthesis, and that mitochondria are sensitive to oxidative stress. These results suggest that mitochondria must be energized, polarized, and actively respiring to support Leydig cell steroidogenesis and alterations in the state of mitochondria may be involved in regulating steroid biosynthesis.

Gene expression profiling of androgen receptor antagonists in the rat fetal testis reveals few common gene targets

The androgen receptor (AR) is expressed in the fetal testis; however, the role of AR in fetal testicular development is poorly understood. Disrupted AR activity and subsequent gene expression alterations may disturb developmental programming of the fetal testis and result in testicular abnormalities later in life. The present study was performed to examine global gene expression patterns in rat fetal testis following in utero exposure to various AR antagonists. Pregnant Sprague-Dawley rats were treated with flutamide (50 mg/kg/day), linuron (50 mg/kg/day), vinclozolin (200 mg/kg/day), p,p'-DDE (100 mg/kg/day) or corn oil vehicle by gavage daily from gestation day (GD) 12-19. Testes were isolated on GD 19, and AR immunostaining, histology, and global changes in gene expression were determined. There were no alterations in the pattern or expression level of AR and no apparent histological changes in the fetal testes in any treatment group. Microarray analysis using Dunnett's test with multiple testing correction revealed no significant gene expression alterations following exposure to flutamide, linuron, vinclozolin, and p,p'-DDE. A less stringent analysis yielded some chemical specific effects on gene expression, and these effects were further evaluated by real-time RT-PCR. Vinclozolin treatment reduced the expression of several genes involved in cholesterol biosynthesis, though the testosterone levels were unchanged in the fetal testes in any treatment group. In flutamide, linuron, and p,p'-DDE treatment groups, the expression of hemoglobin Y, beta-like embryonic chain (Hbb-y) was reduced. Myomesin 2 (Myom2) expression was increased following linuron treatment. Given the lack of a common set of genes and the absence of overt histopathology, we conclude that the fetal testis is not a major target for AR activity at this stage of development although some cell-type specific gene expression changes cannot be ruled out.

Bacterial lipopolysaccharide-induced oxidative stress in the impairment of steroidogenesis and spermatogenesis in rats

Microbial infections, localized as well as systemic, are known to cause transitive or permanent male infertility. However, the mechanisms of infection-induced infertility are largely unknown. Earlier reports showed that steroidogenesis and spermatogenesis are affected during bacterial lipopolysaccharide (LPS)-induced acute inflammation. The present study used an LPS rat model to investigate the role of oxidative stress in spermatogenesis. Intraperitoneal administration of bacterial LPS (5mg/kg body weight) to adult male albino rats elevated testicular malondialdehyde (MDA) and 4-hydroxy-2-nonenal (HNE), and decreased the activities of testicular antioxidant enzymes such as catalase, superoxide dismutase, glutathione peroxidase, and glutathione reductase. The GSH/GSSG ratio also decreased significantly. Time series analysis revealed transitory oxidative stress and expression of inflammatory mediators such as interleukin-1beta (IL-1beta), inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2) from 3h to 12h after LPS. Testicular expression of steroidogenic acute regulatory (StAR) protein decreased to 24h, in correlation with damage to spermatogenesis. These data are consistent with oxidative stress as a major causal factor in altered steroidogenesis, spermatogenesis, and perhaps male infertility during endotoxin-induced acute inflammation.

New facets of androgen replacement therapy during childhood and adolescence

The goals of androgen therapy for adolescents are to promote linear growth and secondary sexual characteristics, at the same time as permitting the normal accrual of muscle mass and bone mineral content. Secondary goals are mainly in the psychosocial sphere, in which pubertally delayed boys feel that they look too young, are not considered a 'peer' in their age group and have difficulty competing in athletic endeavours. These goals are irrespective of the causes of delayed pubertal development: constitutional delay of growth and puberty (CDGP), a transient but very common form of pubertal delay and, much less commonly, primary or secondary permanent hypogonadism. Not all boys with CDGP require testosterone therapy, but those that come to a referral practice are likely candidates, as the watchful waiting period has finished. Although a range of androgen preparations is available for adults (injectable, oral, implantable and cutaneous patches and gels), most are drug delivery devices that are appropriate for full adult androgen replacement. These doses are too large for the induction of puberty. Therefore, at present, the injectable form is the only one that is easily adaptable for the increasing amounts of androgen necessary for the various stages of pubertal development. All preparations deliver testosterone that is readily converted to dihydrotestosterone by 5-alpha reductase. The author's practice is to begin with injecting 50-75 mg of one of the long-acting esters (enanthate or cypionate) per month, and gradually escalate to 100-150 mg/month, before changing to twice monthly dosage. As most adolescents have delayed puberty, the therapy is needed for 6-18 months before the hypothalamic-pituitary-gonadal axis functions at the late adolescent/adult level in those with CDGP. Those with permanent hypogonadism will require lifelong therapy. Once adequate virilisation is induced, and virtually full adult height is reached, any of the therapies noted above can be used in those permanently hypogonadal, whether primarily or secondarily.

Volume-sensitive Cl- current in bovine adrenocortical cells: comparison with the ACTH-induced Cl- current

In a previous study performed on zona fasciculata (ZF) cells isolated from calf adrenal glands, we identified an ACTH-induced Cl- current involved in cell membrane depolarization. In the present work, we describe a volume-sensitive Cl- current and compare it with the ACTH-activated Cl- current. Experiments were performed using the whole-cell patch-clamp recording method, video microscopy and cortisol-secretion measurements. In current-clamp experiments, hypotonic solutions induced a membrane depolarization to -22 mV. This depolarization, correlated with an increase in the membrane conductance, was sensitive to different Cl- channel inhibitors. In voltage-clamp experiments, hypotonic solution induced a membrane current that slowly decayed and reversed at -21 mV. This ionic current displayed no time dependence and showed a slight outward rectification. It was blocked to variable extent by different conventional Cl- channel inhibitors. Under hypotonic conditions, membrane depolarizations were preceded by an increase in cell volume that was not detected under ACTH stimulation. It was concluded that hypotonic solution induced cell swelling, which activated a Cl- current involved in membrane depolarization. Although cell volume change was not observed in the presence of ACTH, biophysical properties and pharmacological profile of the volume-sensitive Cl- current present obvious similarities with the ACTH-activated Cl- current. As compared to ACTH, hypotonic solutions failed to trigger cortisol production that was weakly stimulated in the presence of high-K+ solution. This shows that in ZF cells, membrane depolarization is not a sufficient condition to fully activate secretory activities.

Bacterial endotoxin lipopolysaccharide and reactive oxygen species inhibit Leydig cell steroidogenesis via perturbation of mitochondria

Chronic inflammatory disease and acute infection are well known to inhibit gonadal steroidogenesis. Previous studies have demonstrated that immune activation in response to lipopolysaccharide (LPS) results in reductions in serum testosterone, and this is a direct effect on the Leydig cell. We hypothesize that during the early onset of LPS endotoxemia in vivo, testicular macrophages produce reactive oxygen species (ROS) leading to perturbation of Leydig cell mitochondria and an inhibition in steroidogenesis. To investigate the mechanism of LPS inhibition of Leydig cell steroidogenesis, alterations in mitochondria and markers of oxi-dative stress were assessed in vivo and in Leydig cell pri- mary culture. After a single injection of mice with LPS, serum testosterone was significantly decreased within 2 h. LPS injection of mice resulted in significant reductions in steroidogenic acute regulatory protein (StAR) and 3beta-hydroxysteroid dehydogenase-Delta4-Delta5 isomerase (3beta-HSD) proteins. LPS significantly increased lipid peroxidation of Leydig cell membranes, indicating that LPS results in oxidative damage in vivo. Mitochondria in Leydig cells isolated from LPS-injected mice were disrupted and showed a marked reduction in the mitochondrial membrane potential (DeltaPsim). Similar to the effects of LPS, treatment of Leydig cells with hydrogen peroxide acutely inhibited steroidogenesis, reduced StAR and 3beta-HSD protein levels, and disrupted DeltaPsim. These results suggest that LPS acutely inhibits Leydig cell function by ROS-mediated disruption of Leydig cell mitochondria. Taken together, these results demonstrate the necessity of having respiring mitochondria with an intact DeltaPsim to facilitate StAR function and Leydig cell steroidogenesis. The acute effects of LPS demonstrate how sensitive Leydig cell mitochondrial steroidogenesis is to inflammation-induced oxidative stress.

Differential actions of metyrapone on the fetal pituitary-adrenal axis in the sheep fetus in late gestation

It is not clear if an increase in intra-adrenal cortisol is required to mediate the actions of adrenocorticotropic hormone (ACTH) on adrenal growth and steroidogenesis during the prepartum stimulation of the fetal pituitary-adrenal axis. We infused metyrapone, a competitive inhibitor of cortisol biosynthesis, into fetal sheep between 125 and 140 days of gestation (term = 147 +/- 3 days) and measured fetal plasma cortisol, 11-desoxycortisol, and ACTH; pituitary pro-opiomelanocortin mRNA and adrenal expression of ACTH receptor (melanocortin type 2 receptor), steroidogenic acute regulatory protein (StAR), 11beta-hydroxysteroid dehydrogenase type 2 (11betaHSD2), cytochrome P450 cholesterol side-chain cleavage (CYP11A1), cytochrome P450 17-hydroxylase (CYP17), 3beta-hydroxysteroid dehydrogenase, and cytochrome P450 21-hydroxylase mRNA; and StAR protein in the fetal adrenal gland. Plasma ACTH and 11-desoxycortisol concentrations were higher (P < 0.05), whereas plasma cortisol concentrations were not significantly different in metyrapone- compared with vehicle-infused fetuses. The ratio of plasma cortisol to ACTH concentrations was higher (P < 0.0001) between 136 and 140 days than between 120 and 135 days of gestation in both metyrapone- and vehicle-infused fetuses. The combined adrenal weight and adrenocortical thickness were greater (P < 0.001), and cell density was lower (P < 0.01), in the zona fasciculata of adrenals from the metyrapone-infused group. Adrenal StAR mRNA expression was lower (P < 0.05), whereas the levels of mature StAR protein (30 kDa) were higher (P < 0.05), in the metyrapone-infused fetuses. In addition, adrenal mRNA expression of 11betaHSD2, CYP11A1, and CYP17 were higher (P < 0.05) in the metyrapone-infused fetuses. Thus, metyrapone administration may represent a unique model that allows the investigation of dissociation of the relative actions of ACTH and cortisol on fetal adrenal steroidogenesis and growth during late gestation.

Molecular cloning, chromosomal localization of human peripheral-type benzodiazepine receptor and PKA regulatory subunit type 1A (PRKAR1A)-associated protein PAP7, and studies in PRKAR1A mutant cells and tissues

A mouse protein that interacts with the peripheral-type benzodiazepine receptor (PBR) and cAMP-dependent protein kinase A (PKA) regulatory subunit RIalpha (PRKAR1A), named PBR and PKA-associated protein 7 (PAP7), was identified and shown to be involved in hormone-induced steroid biosynthesis. We report the identification of the human PAP7 gene, its expression pattern, genomic structure, and chromosomal mapping to 1q32-1q41. Human PAP7 is a 60-kDa protein highly homologous to the rodent protein. PAP7 is widely present in human tissues and highly expressed in seminal vesicles, pituitary, thyroid, pancreas, renal cortex, enteric epithelium, muscles, myocardium and in steroidogenic tissues, including the gonads and adrenal cortex. These tissues are also targets of Carney complex (CNC), a multiple neoplasia syndrome caused by germline inactivating PRKAR1A mutations (PRKAR1A-mut) and associated with primary pigmented nodular adrenocortical disease (PPNAD) and increased steroid synthesis. PAP7 and PRKAR1A expression were studied in PPNAD and in lymphoblasts from patients bearing PRKAR1A-mut. Like PRKAR1A, PAP7 was decreased in CNC lymphocytes and PPNAD nodules, but not in the surrounding cortex. These studies showed that, like in the mouse, human PAP7 is highly expressed in steroidogenic tissues, where it follows the pattern of PRKAR1A expression, suggesting that it participates in PRKAR1A-mediated tumorigenesis and hypercortisolism.

Inhibitory effects of bromocriptine on corticosterone secretion in male rats

Bromocriptine, a dopamine D2 receptor agonist, is widely used for treating prolactinoma, Parkinson's disease and galactorrhea. However, the influence of bromocriptine on the endocrine system, especially adrenal function, is not clear. The present study was aimed to investigate the effects of bromocriptine on corticosterone production in rats. Male rats were treated or not treated by bromocriptine (5 mg/kg, s.c.) twice per day for 2 days before decapitation. The adrenal zona fasciculata-reticularis cells were prepared and incubated with adrenocorticotropic hormone (ACTH), forskolin (an adenylyl cyclase activator), 8-bromo-adenosine 3':5' cyclic monophosphate (8-Br-cAMP, a membrane-permeable analogue of cAMP), and steroidogenic precursors including 25-OH-cholesterol and pregnenolone. The concentrations of prolactin, corticosterone and pregnenolone in the plasma and/or medium were measured by radioimmunoassay (RIA). The protein expression of cytochrome P450 side-chain cleavage (P450scc) enzyme and steroidogenic acute regulatory protein (StAR) was analyzed by Western blotting. Administration of bromocriptine in vivo resulted in a decrease in the levels of plasma prolactin and corticosterone. Basal--and ACTH--as well as forskolin-stimulated corticosterone secretion by zona fasciculata-reticularis cells was also lower in bromocriptine-treated rats than in control animals. The decreased production of corticosterone in zona fasciculata-reticularis cells could be reversed by administration of 8-Br-cAMP. The corticosterone and pregnenolone release induced by 25-OH-cholesterol in zona fasciculata-reticularis cells was reduced by administration of bromocriptine. The protein expression of both StAR protein and P450scc in zona fasciculata-reticularis cells was inhibited in the bromocriptine-treated group. Administration of bromocriptine in vitro reduced the release of corticosterone stimulated by ACTH and forskolin in rat zona fasciculata-reticularis cells. These results suggested that bromocriptine caused adrenal dysfunction through inhibition of ACTH action and of the activity of adenylyl cyclase, and impaired the early steps of corticosterone biosynthesis.

Molecular cloning, genomic organization, chromosomal mapping and subcellular localization of mouse PAP7: a PBR and PKA-RIalpha associated protein

A mouse protein that interacts with the peripheral-type benzodiazepine receptor (PBR) and the cAMP-dependent protein kinase A (PKA) regulatory subunit RIalpha (PKA-RIalpha), named PBR and PKA associated protein 7 (PAP7) was identified and shown to be involved in hormone-induced steroid biosynthesis in testicular Leydig cells. In the present study, mouse PAP7 cDNA was extended by 5'-rapid amplification of cDNA ends; and a 3432 bp sequence, encoding a 525-amino-acid protein with a calculated molecular weight of 60 kDa, was re-assembled. Mouse and human PAP7 share an 85% amino acid identity and contain a conserved acyl-CoA-binding protein/diazepam binding inhibitor (ACBP/DBI) motif. ACBP/DBI has been identified as the endogenous PBR ligand able to stimulate mitochondrial steroid formation in all steroidogenic cells. The full-length mouse PAP7 gene was cloned and assembled by screening a BAC clone, polymerase chain reaction and searching the mouse genome database. The gene is approximately 29 kb in length and includes eight exons and seven introns. Although it is shorter than the human PAP7 gene, all exons are conserved between the mouse and human. The mouse PAP7 gene was mapped to chromosome 1H3-5 by fluorescence in situ hybridization in agreement with in silico search of the mouse genome database that mapped the PAP7 cDNA sequence to the 1H4 area. Immunofluorescence confocal microscopy demonstrated that PAP7 is mainly localized in the trans-Golgi apparatus and mitochondria in mouse tumor Leydig cells, in agreement with its proposed function in targeting the PKA isoenzyme to organelles rich in PBR, i.e. mitochondria, where phosphorylation of specific protein substrates mediates the hormone-induced steroid formation.

Changes of steroidogenic acute regulatory protein mRNA expression in postnatal rat development

The present study investigated the expression pattern of steroidogenic acute regulatory protein (StAR) mRNA in several brain regions and peripheral endocrine organs using Northern blot, RT-PCR and in situ hybridization. StAR mRNA in the adrenal gland was detected at birth and decreased for 2 weeks postnatally. In gonads, it was also detected at birth though at a lower level than adrenal, and was maintained until week 3. Thereafter StAR mRNA expression in both endocrine organs was increased. Though the amount of StAR mRNA in the brain was much less than that of peripheral endocrine organs, it was expressed from birth and, in general, appeared to gradually increase during postnatal development. A gradual increase was found in the hypothalamus, while a sigmoidal expression was shown in the olfactory bulb. The increased expression of StAR mRNA in the postnatal period suggests that it might have a role in the regulation of neurosteroidogenesis needed in neuronal cell growth and differentiation in postnatal rat brain development.

Relationship Between Steroidogenic Acute Regulatory Protein Expression and Progesterone Production in Hen Granulosa Cells During Follicle Development1

The present studies were conducted to address cellular mechanisms responsible for regulating steroidogenic acute regulatory protein (StAR) expression and progesterone synthesis at maturational stages corresponding to both the time of hen follicle selection, as well as before and after the LH surge in preovulatory follicle granulosa cells. A recently published report has established that mitogen-activated protein (MAP) kinase signaling induced by transforming growth factor alpha (TGFalpha) treatment blocks FSH-induced differentiation and StAR expression in cultured hen granulosa cells, whereas inhibitors of MAP kinase signaling enhance FSH-induced differentiation. The present in vitro studies demonstrate that in addition to MAP kinase signaling, activation of protein kinase C (PKC) blocks both FSH-induced StAR expression and the initiation of progesterone production in prehierarchal follicle granulosa cells, whereas the pharmacologic inhibitor of PKC, GF109203X, potentiates FSH-induced StAR expression and, as a consequence, the initiation of progesterone synthesis. Moreover, we demonstrate in granulosa cells collected from preovulatory follicles that although an acute increase in progesterone production in response to LH treatment requires rapid transcription and translation of StAR, the magnitude of progesterone production is rate-limited by one or more factors other than StAR (e.g., the P450 cholesterol side-chain enzyme). Finally, the rapid turnover of StAR protein, such as occurs following the withdrawal of LH, provides an additional mechanism for the tight regulation of progesterone production that occurs during the hen ovulatory cycle, and explains the rapid loss of steroidogenesis in the postovulatory follicle. In summary, data reported herein support the proposal that paracrine/autocrine factors (including but not necessarily limited to TGFalpha) prevent premature expression of StAR in prehierarchal follicle granulosa cells by more than one receptor-mediated signaling pathway. Furthermore, subsequent to follicle selection into the preovulatory hierarchy, StAR transcription and translation is necessary but not sufficient for the full potentiation of the preovulatory surge of serum progesterone.

Cardiotonic steroids: potential endogenous sodium pump ligands with diverse function

The highly conserved cardiotonic steroid (CS) binding site present on the ubiquitous membrane sodium pump, sodium, potassium-ATPase, appears to have been conserved by no force other than its capacity to bind CS: a family that includes plant-derived cardiac glycosides and putative endogenous vertebrate counterparts. Binding of ligand is inhibited by increased extracellular potassium. This implies functional coordination because inhibition of the sodium pump would be counterproductive when extracellular potassium is elevated. The interesting biology of the CS binding site continues to stimulate investigations into the identity of endogenous ligands, their role as pump regulators at the cellular level, and as mediators of body fluid balance and blood pressure regulation. In addition to inhibition of sodium and potassium transport, there is considerable recent evidence suggesting that the sodium pump may act as a cell signaling receptor activated by CS binding and responding by coordination of intracellular signaling pathways that can be dependent on and also independent of the reduction in transmembrane ion flux resulting directly from pump inhibition. This signaling may influence cell survival, growth, and differentiation. Recent insight into the biology of pump regulation by CS is reviewed.

Differences in steroidogenic acute regulatory protein expression from the luteinizing-granulosa cells of patients undergoing in vitro fertilization with embryo transfer: implications for cycle outcomes

OBJECTIVE

Previous research has suggested a correlation between the subtle rise in progesterone induced by the administration of human chorionic gonadotropin (hCG) and cycle outcome in patients undergoing in vitro fertilization with embryo transfer (IVF-ET). The data suggest that patients who have <2-fold increase in progesterone levels will not conceive as a result of that IVF-ET attempt (poor responders). Further, if the luteinizing-granulosa cells of poor responders are placed in culture, their steroid hormone production will be significantly less than that of the luteinizing-granulosa cells of patients with a normal response to hCG (>3-fold; normal responders). Recent studies have demonstrated that steroidogenic acute regulatory protein (StAR) regulates the rate-limiting step in steroid hormone biosynthesis. The objective of the present study was to determine whether StAR expression differed in normal responders and poor responders undergoing IVF-ET.

STUDY DESIGN

The luteinizing-granulosa cells of 6 patients were isolated after follicular aspiration and assayed for StAR expression. Three sets of cells were from patients exhibiting a normal response to hCG administration and 3 sets were from patients exhibiting a poor response.

RESULTS

Data suggest a 17% drop in StAR protein in patients with a poor response to hCG administration when compared with those with a normal response.

CONCLUSIONS

Although StAR protein was expressed in all 6 cellular extracts, expression appeared greatest in cells recovered from normal responders. Further, although two thirds of the patients with a normal response reported term pregnancies, no pregnancies were reported in the poor responders. Low levels of progesterone and absence of pregnancy may be due to a defect in the mechanism that converts granulosa and theca-lutein cells to luteal cells after the luteinizing hormone surge (or hCG administration). Data from the current study would suggest that the StAR protein may be involved.

Role of the peripheral-type benzodiazepine receptor in adrenal and brain steroidogenesis

The peripheral-type benzodiazepine receptor (PBR) has been demonstrated to be critical for steroidogenesis in all steroid-producing tissues. Here, we review the identification and characterization of the PBR, the evidence pointing to its function as a cholesterol pore involved in transporting cholesterol from the cytoplasm of steroid-producing cells into the inner mitochondrial membrane where it is metabolized, and the known mechanisms regulating its function. We present data on the functions of the PBR in the adrenal gland, a classical steroidogenic tissue, and in the brain, which has only recently been proven to be steroidogenic. Finally, we discuss other potential roles for the PBR in pathological conditions, including cancer, neurodegeneration, and neurotoxicity, and a broader role for the PBR in mediating intracellular cholesterol transport/compartmentalization, which may or may not be linked to steroid biosynthesis.

Identification, localization, and function in steroidogenesis of PAP7: a peripheral-type benzodiazepine receptor- and PKA (RIalpha)-associated protein

Peptide hormones and cAMP acutely stimulate steroid biosynthesis by accelerating the transport of cholesterol into the mitochondria. The peripheral-type benzodiazepine receptor (PBR) has been shown to be an indispensable element of the cholesterol transport machinery. Using the yeast two-hybrid system and PBR as bait, we identified a protein that interacts with PBR, the PBR-associated protein PAP7. Using the regulatory subunit RIalpha of PKA as bait, we also isolated PAP7. Glutathione-S-transferase -PAP7 interacted with both the mitochondrial PBR and cytosolic PKA-RIalpha in MA-10 Leydig cells. PAP7 is a novel 52-kDa protein present in mouse, rat, and human tissues, and it has a major 3-kb mRNA transcript in all tissues examined. Immunohistochemical and in situ hybridization studies indicated that PAP7 is highly expressed in the gonads, adrenal, hippocampus, and distinct brain neuronal and glial populations. Overexpression of the full length PAP7 increased the hCG-induced steroid production. However, overexpression of a partial PAP7, which includes the PBR- and PKA-RIalpha-binding domains, inhibited the hormone-stimulated cholesterol transport and steroid synthesis. Treatment of MA-10 cells with oligonucleotides antisense to PAP7 also inhibited the hCG-stimulated steroid formation, suggesting that PAP7 is a functional element of the hormone-induced signal transduction cascade leading to steroidogenesis. PAP7 may function by targeting the PKA isoenzyme to organelles rich in PBR, i.e. mitochondria, where phosphorylation of specific protein substrates may induce the reorganization of PBR topography and function.

Regulation of steroidogenic acute regulatory protein and luteinizing hormone receptor messenger ribonucleic acid in hen granulosa cells

The regulation of steroidogenic acute regulatory protein (StAR) in vitro by gonadotropins was investigated in granulosa cells from prehierarchal and preovulatory hen follicles. Basal levels of StAR messenger RNA (mRNA) in undifferentiated granulosa cells from prehierarchal (6- to 8-mm) follicles were consistently low, but detectable, and were significantly increased by treatment with 8-bromo-cAMP and FSH (but not LH) within 3-6 h of culture. After 20 h of culture, 8-bromo-cAMP, FSH, and LH each increased StAR mRNA levels above those in control cultured cells, and the delayed response to LH treatment was associated with increased levels of LH receptor (LH-R) mRNA. On the other hand, inhibition of mitogen-activated protein (MAP) kinase signaling, using the MAP kinase kinase inhibitors U0126 and PD98059, in the presence of FSH further increased StAR mRNA and protein levels, LH-R mRNA levels, and progesterone synthesis compared with those in cells cultured with FSH alone. The highest basal expression of StAR mRNA during follicle development was found in granulosa from the largest (F1) preovulatory follicle, with comparatively lower levels in granulosa from less mature (F2 plus F3) preovulatory follicles. Treatment with LH rapidly increased StAR mRNA and protein (but not LH-R mRNA) expression in cultures of F1 granulosa and in combined F2 plus F3 granulosa within 3 h, although the magnitude of stimulation was greater in F2 plus F3 granulosa. Compared with results from granulosa cells from prehierarchal follicles cultured for 20 h, inhibition of MAP kinase signaling in the presence of LH for 1 h failed to further enhance levels of StAR or LH-R expression or progesterone production in F2 plus F3 follicle granulosa compared with the effect of LH treatment alone. These results demonstrate that StAR expression in the hen ovary is up-regulated by gonadotropins at least in part via cAMP signaling. The ability of MAP kinase kinase inhibitors to potentiate gonadotropin-induced StAR and LH-R expression plus progesterone synthesis in prehierarchal follicle granulosa cells in vitro suggests that inhibition of paracrine or autocrine factor-mediated MAP kinase signaling in vivo may be a prerequisite for the full potentiation of granulosa cell steroidogenesis that occurs after recruitment into the preovulatory hierarchy. Finally, these results fail to support a role for MAP kinase signaling in acutely modulating LH-mediated StAR expression or progesterone production in hierarchal follicles, such as occurs during the preovulatory surge of progesterone.

Identification of mesoderm development (mesd) candidate genes by comparative mapping and genome sequence analysis

The proximal albino deletions identify several functional regions on mouse Chromosome 7 critical for differentiation of mesoderm (mesd), development of the hypothalamus neuroendocrine lineage (nelg), and function of the liver (hsdr1). Using comparative mapping and genomic sequence analysis, we have identified four novel genes and Il16 in the mesd deletion interval. Two of the novel genes, mesdc1 and mesdc2, are located within the mesd critical region defined by BAC transgenic rescue. We have investigated the fetal role of genes located outside the mesd critical region using BAC transgenic complementation of the mesd early embryonic lethality. Using human radiation hybrid mapping and BAC contig construction, we have identified a conserved region of human chromosome 15 homologous to the mesd, nelg, and hsdr1 functional regions. Three human diseases cosegregate with microsatellite markers used in construction of the human BAC/YAC physical map, including autosomal dominant nocturnal frontal lobe epilepsy (ENFL2; also known as ADNFLE), a syndrome of mental retardation, spasticity, and tapetoretinal degeneration (MRST); and a pyogenic arthritis, pyoderma gangrenosum, and acne syndrome (PAPA).

Steroidogenic acute regulatory protein (StAR) and the intramitochondrial translocation of cholesterol

The steroidogenic acute regulatory (StAR) protein regulates the rate limiting step in steroidogenesis, the transport of cholesterol from the outer to the inner mitochondrial membrane. Insight into the structure and function of StAR was attained through molecular genetic studies of congenital lipoid adrenal hyperplasia, a rare disease caused by mutations in the StAR gene. Subsequent functional analysis defined two major domains within the StAR protein, the N-terminal mitochondrial targeting sequence and the C-terminus, which promotes the translocation of cholesterol between the two mitochondrial membranes. Two models of StAR's mechanism of action, (1) stimulation of cholesterol desorption from the outer mitochondrial membrane and (2) an intermembrane shuttle hypothesis, are discussed with respect to the known biochemical and biophysical events associated with the process of steroidogenesis and the structure of StAR. StAR gene expression is regulated primarily at the transcriptional level, and the roles of transcription factors that govern basal and cAMP-dependent StAR expression including SF-1, C/EBP beta, Sp1 and GATA-4 are reviewed.

Diametric effects of bacterial endotoxin lipopolysaccharide on adrenal and Leydig cell steroidogenic acute regulatory protein

Immune activation results in the activation of adrenal steroidogenesis and inhibition of gonadal steroidogenesis. Previous studies indicated that these effects were caused primarily by activation and suppression of the secretion of ACTH and LH, respectively. However, other evidence indicated a direct effect of the immune system on the gonads. In this study, serum testosterone, quantitated by RIA after lipopolysaccharide injection, showed a significant decrease within 2 h. Parallel measurement of serum LH showed no change. There were no differences in LH receptor or cAMP produced in Leydig cells between vehicle- and lipopolysaccharide-injected mice. The 30-kDa form of the steroidogenic acute regulatory (StAR) protein was quantitated, by Western blot, in Leydig cells and was found to decrease in a time-dependent manner. No change in StAR protein messenger RNA (mRNA) was detected by Northern analysis during this time, nor were any changes found in the levels of mRNA for the steroidogenic enzymes P450scc, 3beta-hydroxysteroid dehydrogenase delta4-delta5-isomerase, or P450c17. In the adrenal, StAR protein was increased, as was StAR protein mRNA. No changes were observed in the levels of mRNA for P450scc, 3beta-hydroxysteroid dehydrogenase delta4-delta5-isomerase, or P450c21. Thus, although the mechanisms of regulation differ, changes in the levels of StAR protein are a sensitive indicator of the steroidogenic capacity of these two tissues.

Conservation of steroidogenic acute regulatory (StAR) protein structure and expression in vertebrates

Complementary DNAs for the open reading frames of the chicken, Xenopus and zebrafish StAR homologs were cloned along with a partial cDNA of the zebrafish homolog to MLN64, a StAR-related protein. A comparison of the amino acid sequences of piscine, amphibian, avian and mammalian StARs, indicates strong conservation of the protein across divergent vertebrate groups. On Northern blots probed with species specific StAR cDNAs, expression of StAR transcripts was observed in the ovary and adrenal of chicken, and the ovary, testis, kidney and head of zebrafish. The expression of StAR mRNA in various compartments of the hen ovary was consistent with the results of past studies on steroidogenesis; expression was first observed in follicles selected into the preovulatory hierarchy and was greatest in the largest preovulatory follicle. The expression of StAR mRNA was also consistent with aromatase expression in zebrafish ovaries. The conserved deduced protein sequence and expression pattern of StAR transcripts in chicken and zebrafish tissues, strongly suggest that StAR is also involved in the regulation of steroidogenesis in nonmammalian vertebrates.

Mammalian bufadienolide is synthesized from cholesterol in the adrenal cortex by a pathway that Is independent of cholesterol side-chain cleavage

An increasing body of evidence suggests that an endogenous mammalian bufadienolide (BD) may be involved in the regulation of Na(+),K(+)-ATPase activity and the pathogenesis of arterial hypertension. We developed a purification scheme for marinobufagenin (MBG), an amphibian cardiotonic BD, and applied it to purify and characterize material in human plasma, culture medium conditioned by Y-1 adrenocortical cells, and rat adrenal tissue. MBG immunoreactivity purified from plasma and measured by ELISA showed important similarities (chromatography and antibody cross-reactivity) to material secreted into cell culture medium by Y-1 cells. This observation indicates that circulating mammalian BD may have an adrenocortical origin. Release of mammalian BD from adrenocortical cells grown in the absence of exogenous cholesterol was reduced by treatment of cultures with mevastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor. Supplementation of the serum and cholesterol-free cell culture medium with the LDL fraction of human plasma increased the production of MBG material in the presence of mevastatin, supporting its origin from cholesterol. We used Y-1 cell lines transfected with genes shown to inhibit steroidogenesis through cholesterol side-chain cleavage (Y-1/DAX and Y-1/RIAB) to investigate the dependence of MBG biosynthesis on side-chain cleavage. Our results indicate that the mammalian BD is synthesized in the adrenal cortex from cholesterol and shares important similarities with the amphibian BD MBG, that its biosynthesis is independent of transfer of cholesterol to the side-chain cleavage enzyme complex mediated by steroidogenic acute regulatory protein, and that neither cAMP nor protein kinase A appears to be a critical component of the pathway controlling its biosynthesis.

Expression of RUSH transcription factors in developing and adult rabbit gonads

The RUSH transcription factors 1alpha and 1beta bind to the Rabbit Uteroglobin promoter and are members of the SWI/SNF complex that facilitates transcription by remodeling chromatin (Helicase). To characterize gonadal expression of RUSH, a cRNA probe that recognizes both isoforms was used for in situ hybridization studies. We found RUSH mRNA to be abundant in Sertoli cells from embryonic, neonatal, prepubertal, and pubertal rabbit testes. In adults, RUSH mRNA was detected in tubules with preleptotene spermatocytes and mature spermatids lining the lumen. However, RUSH was undetectable in tubules that contained leptotene spermatocytes and that lacked mature spermatids. In females, RUSH was expressed in presumptive granulosa cells of embryonic and neonatal ovaries before follicle organization. Abundant RUSH mRNA was detected in granulosa and theca cells surrounding preantral follicles of prepubertal and adult ovaries. Expression of RUSH remained high in granulosa cells of antral follicles in mature ovaries but was negligible in late-stage atretic follicles and in corpora lutea. Western blot analysis confirmed the RUSH-1alpha isoform predominated in both testicular and ovarian tissues. The expression pattern of RUSH indicates transcriptional activity in Sertoli cells and during multiple stages of differentiating granulosa cells, especially those of primordial follicles, which heretofore were considered to be dormant.