Transcriptional regulation of the StAR gene

Differential Response of Transcription Factors to Activated Kinases in Steroidogenic and Non-Steroidogenic Cells

Hormone-induced Leydig cell steroidogenesis requires rapid changes in gene expression in response to various hormones, cytokines, and growth factors. These proteins act by binding to their receptors on the surface of Leydig cells leading to activation of multiple intracellular signaling cascades, downstream of which are several kinases, including protein kinase A (PKA), Ca2+/calmodulin-dependent protein kinase I (CAMKI), and extracellular signal-regulated protein kinase 1 and 2 (ERK1/2). These kinases participate in hormone-induced steroidogenesis by phosphorylating numerous proteins including transcription factors leading to increased steroidogenic gene expression. How these various kinases and transcription factors come together to appropriately induce steroidogenic gene expression in response to specific stimuli remains poorly understood. In the present work, we compared the effect of PKA, CAMKI and ERK1/2 on the transactivation potential of 15 transcription factors belonging to 5 distinct families on the activity of the Star gene promoter. We not only validated known cooperation between kinases and transcription factors, but we also identified novel cooperations that have not yet been before reported. Some transcription factors were found to respond to all three kinases, whereas others were only activated by one specific kinase. Differential responses were also observed within a family of transcription factors. The diverse response to kinases provides flexibility to ensure proper genomic response of steroidogenic cells to different stimuli.

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

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

Role of p38 MAPK Signalling in Testis Development and Male Fertility

The testis is an important male reproductive organ, which ensures reproductive function via the secretion of testosterone and the generation of spermatozoa. Testis development begins in the embryonic period, continues after birth, and generally reaches functional maturation at puberty. The stress-activated kinase, p38 mitogen-activated protein kinase (MAPK), regulates multiple cell processes including proliferation, differentiation, apoptosis, and cellular stress responses. p38 MAPK signalling plays a crucial role in testis development by regulating spermatogenesis, the fate determination of pre-Sertoli, and primordial germ cells during embryogenesis, the proliferation of testicular cells in the postnatal period, and the functions of mature Sertoli and Leydig cells. In addition, p38 MAPK signalling is involved in decreased male fertility when exposed to various harmful stimuli. This review will describe in detail the biological functions of p38 MAPK signalling in testis development and male reproduction, together with its pathological role in male infertility.

Chemerin Impairs In Vitro Testosterone Production, Sperm Motility, and Fertility in Chicken: Possible Involvement of Its Receptor CMKLR1

The chemokine chemerin is a novel adipokine involved in the regulation of energy metabolism but also female reproductive functions in mammals. Its effects on male fertility are less studied. Here, we investigated the involvement of chemerin in chicken male reproduction. Indeed, the improvement of the sperm of roosters is a challenge for the breeders since the sperm quantity and quality have largely decreased for several years. By using specific chicken antibodies, here we show that chemerin and its main receptor CMKLR1 (chemokine-like receptor 1) are expressed within the chicken testis with the lowest expression in adults as compared to the embryo or postnatal stages. Chemerin and CMKLR1 are present in all testicular cells, including Leydig, Sertoli, and germinal cells. Using in vitro testis explants, we observed that recombinant chicken chemerin through CMKLR1 inhibits hCG (human chorionic gonadotropin) stimulated testosterone production and this was associated to lower 3βHSD (3beta-hydroxysteroid dehydrogenase) and StAR (steroidogenic acute regulatory protein) expression and MAPK ERK2 (Mitogen-Activated Protein Kinase Extracellular signal-regulated kinase 2) phosphorylation. Furthermore, we demonstrate that chemerin in seminal plasma is lower than in blood plasma, but it is negatively correlated with the percentage of motility and the spermatozoa concentration in vivo in roosters. In vitro, we show that recombinant chicken chemerin reduces sperm mass and individual motility in roosters, and this effect is abolished when sperm is pre-incubated with an anti-CMKLR1 antibody. Moreover, we demonstrate that fresh chicken sperm treated with chemerin and used for artificial insemination (AI) in hen presented a lower efficiency in terms of eggs fertility for the four first days after AI. Taken together, seminal chemerin levels are negatively associated with the rooster fertility, and chemerin produced locally by the testis or male tract could negatively affect in vivo sperm quality and testosterone production through CMKLR1.

Dimethoate blocks pubertal differentiation of Leydig cells in rats

Dimethoate is an organophosphate pesticide. It is widely used in agriculture. However, whether it blocks pubertal development of Leydig cells remains unknown. In the current study, we exposed male Sprague Dawley rats with 7.5 and 15 mg kg^-1 dimethoate from postnatal day 35-56. We also exposed Leydig cells isolated from 35-day-old rats for 3 h. Dimethoate reduced serum testosterone levels at 7.5 and 15 mg kg-1 but increased serum luteinizing hormone and follicle stimulating hormone levels at 15 mg kg-1. Dimethoate did not influence Leydig cell number but reduced Leydig cell size and down-regulated Star, Cyp11a1, and Hsd3b1 in Leydig cells as well as their protein expression. Dimethoate inhibited basal androgen output in a dose-dependent manner with the inhibition starting at 0.05 μM. It significantly inhibited luteinizing hormone and 8Br-cAMP stimulated androgen outputs at 50 μM. It significantly inhibited 22R-hydroxycholesterol and progesterone-mediated androgen outputs at 50 μM. Further study demonstrated that dimethoate also down-regulated the expression of Star, Cyp11a1, and Hsd3b1 at 5 or 50 μM in vitro. Dimethoate did not directly inhibit rat testicular steroidogenic enzyme activities at 50 μM. In conclusion, dimethoate targets Star, Cyp11a1, and Hsd3b1 transcription, thus blocking Leydig cell differentiation during puberty.

Protective Effect of Resveratrol on Benzo(a)Pyrene Induced Dysfunctions of Steroidogenesis and Steroidogenic Acute Regulatory Gene Expression in Leydig Cells

Benzo(a)pyrene [B(a)P] is the toxic environmental Polycyclic Aromatic Hydrocarbon (PAH), that exerts male reproductive dysfunctions. In this study the molecular mechanism of B(a)P induced Leydig cell steroidogenic dysfunctions and its protective mechanism of action with a natural Aryl hydrocarbon receptor (AhR) antagonist and anti-oxidant, Resveratrol (Res) has been investigated. B(a)P exposure induced ROS mediated steroidogenic imbalance via activation of p38MAPK and repression of testosterone level as well as other steroidogenic enzymes like CYPIIA1, 3β-HSD, 17β-HSD expressions. B(a)P exposure decreased StAR protein expression along with increased DAX-1, a transcriptional repressor of StAR gene. Along with that B(a)P decreased the expression of SF-1 that acts as a transcriptional inducer of StAR gene expression. The study has established Resveratrol as a potential agent combating the deleterious effect of B(a)P on Leydig cell steroidogenesis. Resveratrol treatment resulted significant protection against B(a)P by scavenging ROS and modulating the transcriptional regulation of anti-oxidant enzymes. Furthermore, Resveratrol also prevented stress kinase like p38 MAPK activation and increased StAR protein expression through the reduction of DAX-1 expression. Moreover, the testosterone production was efficiently restored with Resveratrol treatment. ChIP assay also revealed that resveratrol improved SF-1expression which further increased the StAR gene expression. Resveratrol acted efficiently against B(a)P, through its anti-oxidative properties as well as inhibits p38MAPK and increased steroidogenesis and StAR expression through the modulation of SF-1 gene expression.

Curcumin downregulates 8-br-cAMP-induced steroidogenesis in mouse Leydig cells by suppressing the expression of Cyp11a1 and StAR independently of the PKA-CREB pathway

Although curcumin was widely applied as a functional food for different diseases, it was found to reduce serum testosterone level and fertility in male animals by unknown molecular mechanisms. Here in our study, we investigated the possible mechanisms of curcumin-suppressed testosterone production in Leydig cells. Our enzyme immunoassay results showed that curcumin cell-autonomously suppressed ovine luteinizing hormone-stimulated testosterone production in primary Leydig cells and 8-bromo-cyclic adenosine monophosphate (8-br-cAMP)-induced progesterone production in MA-10 cells. Furthermore, our real-time PCR, Western blot, and 22R-OHC/pregnenolone supplementing experiment data demonstrated that curcumin suppressed 8-br-cAMP-induced steroidogenesis in Leydig cells by inhibiting the expression of StAR and Cyp11a1. Interestingly, our Western blot data showed that although curcumin suppressed PKA activity, it did not alter the 8-br-cAMP-induced phosphorylation of CREB. On the contrary, the real-time PCR results showed that curcumin suppressed 8-br-cAMP-induced expression of Nr5a1 and Fos, which are crucial for cAMP-stimulated StAR and Cyp11a1 expression in Leydig cells. Collectively, our data demonstrated that curcumin may suppress cAMP-induced steroidogenesis in mouse Leydig cells by down-regulating Nr5a1/Fos-controlled StAR and Cyp11a1 expression independently of the PKA-CREB signaling pathway.

Characterization and expression of StAR2a and StAR2b in the olive flounder Paralichthys olivaceus

Steroidogenic acute regulatory protein 2 (StAR2) is a key protein in transporting cholesterol from the outer mitochondria membrane to the inner mitochondria membrane for sex steroid synthesis. In this study, two StAR2 gene isoforms, StAR2a and StAR2b, were isolated from the olive flounder Paralichthys olivaceus gonads. Semi-quantitative RT-PCR results indicated that their expression levels were higher in testis than those in ovary. StAR2a was mainly expressed in the thecal cells and ooplasm of ovary, and Leydig cells and spermatid of testis according to the results of in situ hybridization. The quantitative real-time PCR results showed that the expressions of StAR2a and StAR2b were high in undifferentiation gonads and differentiating testis, and then decreased in differentiated testis in the high temperature (28°C) and exogenous testosterone treatment groups. While, in the exogenous 17β-estradiol treatment group, both genes' expression levels were high in differentiating ovary, and then significantly decreased in differentiated ovary (P<0.05). StAR2a and StAR2b expression levels were significantly down-regulated in the cultured testis cells treated with the 75 and 150μM cAMP, but significantly up-regulated in the cultured testis cells treated with the 300μM cAMP (P<0.05). Moreover, their expression levels were significantly up-regulated by transfecting the cultured testis cells with pcDNA3.1-NR5a2 and pcDNA3.1-NR0b1 (P<0.05). Above study showed that expression of StAR2 was regulated by cAMP and the transcription factors, NR5a2 and NR0b1, indicating that StAR2 may have functions in flounder gonadal differentiation and maintenance.

Effects and mechanisms of waterborne copper exposure influencing ovary development and related hormones secretion in yellow catfish Pelteobagrus fulvidraco

The present study was conducted to determine the effects and mechanism of waterborne copper (Cu) exposure influencing ovary development and related hormones secretion in yellow catfish Pelteobagrus fulvidraco. To this end, two experiments were conducted. In Exp. 1, the partial cDNA sequences of three steroidogenesis-related genes (androgen receptor (ar), steroidogenic factor 1 (sf-1) and steroidogenic acute regulatory protein (star)) were firstly characterized from P. fulvidraco. The predicted amino acid sequences for the P. fulvidraco ar, sf-1 and star contained the main structural features characteristic in other species. In Exp. 2, P. fulvidraco were exposed to three waterborne Cu concentrations (control, 30μg/l and 60μg/l, respectively) for 56days. Sampling occurred on day 28 and day 56, respectively. On day 28, the levels of serum sex-steroid hormones (FSH and LH) and the mRNA levels of steroidogenesis-related genes (3β-hsd, cyp11a1, cyp17, cyp19a, sf-1 and star) were significantly increased in ovary of P. fulvidraco exposed to 30μg Cu/l. The immunohistochemical analysis showed the positive reaction of ER, VTG and aromatase in low dose exposure group. These indicated that in low dose and relative short-term exposure, Cu was beneficial. In contrast, 60μg Cu/l exposure significantly reduced the levels of serum FSH, LH, E2 and P, and the mRNA levels of ovarian 20β-hsd, cyp19a and erα in P. fulvidraco. On day 56, waterborne Cu concentration exposure reduced the levels of serum gonadotropins and sex hormones, and down-regulated the mRNA levels of steroidogenesis-related genes, indicating long-term Cu exposure had toxic effect on the secretion of sex-steroid hormone in P. fulvidraco. For the first time, our study cloned cDNA sequences of ar, sf-1 and star in P. fulvidraco, and demonstrated the effects and mechanism of waterborne Cu exposure influencing hormones secretion and synthesis in dose- and time-dependent manner in P. fulvidraco, which will help to understand the Cu-induced reproductive toxicity at both protein and transcriptional levels in fish.

Domestication Effects on Stress Induced Steroid Secretion and Adrenal Gene Expression in Chickens

Understanding the genetic basis of phenotypic diversity is a challenge in contemporary biology. Domestication provides a model for unravelling aspects of the genetic basis of stress sensitivity. The ancestral Red Junglefowl (RJF) exhibits greater fear-related behaviour and a more pronounced HPA-axis reactivity than its domesticated counterpart, the White Leghorn (WL). By comparing hormones (plasmatic) and adrenal global gene transcription profiles between WL and RJF in response to an acute stress event, we investigated the molecular basis for the altered physiological stress responsiveness in domesticated chickens. Basal levels of pregnenolone and dehydroepiandrosterone as well as corticosterone response were lower in WL. Microarray analysis of gene expression in adrenal glands showed a significant breed effect in a large number of transcripts with over-representation of genes in the channel activity pathway. The expression of the best-known steroidogenesis genes were similar across the breeds used. Transcription levels of acute stress response genes such as StAR, CH25 and POMC were upregulated in response to acute stress. Dampened HPA reactivity in domesticated chickens was associated with changes in the expression of several genes that presents potentially minor regulatory effects rather than by means of change in expression of critical steroidogenic genes in the adrenal.

Modulation of adrenocorticotrophin hormone (ACTH)-induced expression of stress-related genes by PUFA in inter-renal cells from European sea bass (Dicentrarchus labrax)

Dietary fatty acids have been shown to exert a clear effect on the stress response, modulating the release of cortisol. The role of fatty acids on the expression of steroidogenic genes has been described in mammals, but little is known in fish. The effect of different fatty acids on the release of cortisol and expression of stress-related genes of European sea bass (Dicentrarchus labrax) head kidney, induced by a pulse of adenocorticotrophin hormone (ACTH), was studied. Tissue was maintained in superfusion with 60 min of incubation with EPA, DHA, arachidonic acid (ARA), linoleic acid or α-linolenic acid (ALA) during 490 min. Cortisol was measured by RIA. The quantification of stress-related genes transcripts was conducted by One-Step TaqMan real-time RT-PCR. There was an effect of the type of fatty acid on the ACTH-induced release of cortisol, values from ALA treatment being elevated within all of the experimental period. The expression of some steroidogenic genes, such as the steroidogenic acute regulatory protein (StAR) and c-fos, were affected by fatty acids, ALA increasing the expression of StAR after 1 h of ACTH stimulation whereas DHA, ARA and ALA increased the expression of c-fos after 20 min. ARA increased expression of the 11β-hydroxylase gene. Expression of heat shock protein 70 (HSP70) was increased in all the experimental treatments except for ARA. Results corroborate previous studies of the effect of different fatty acids on the release of cortisol in marine fish and demonstrate that those effects are mediated by alteration of the expression of steroidogenic genes.

Follicular stage-dependent regulation of apoptosis and steroidogenesis by prohibitin in rat granulosa cells

BACKGROUND

Follicular growth and atresia are tightly regulated processes, which involve the participation of endocrine, autocrine and paracrine factors at the cellular level. Prohibitin (PHB) is a multifunctional intracellular protein playing an important role in the regulation of proliferation, apoptosis and differentiation. Here we examined the expression of PHB and its regulation by FSH in vitro and studied the role of PHB in the regulation of apoptosis and steroidogenesis in response to the apoptosis inducer staurosporine (STS) and to FSH, respectively.

METHODS

Undifferentiated and differentiated granulosa cells were collected from diethylstilbestrol (DES)- and equine chronic gonadotropin (eCG)-primed immature rats, respectively and then cultured with various treatments (FSH, adenovirus infection, STS) according to experimental design. The apoptosis rate, the production of estradiol and progesterone, and the expression of distinct proteins (PHB, caspase-3, phospho- and total Akt) were assessed.

RESULTS

PHB is anti-apoptotic and its action is dependent on the differentiated state of the granulosa cells. Data from gain- and loss-of-function experiments demonstrate that PHB inhibited STS-induced caspase-3 cleavage and apoptosis in undifferentiated granulosa cells, but was ineffective in differentiated cells. In contrast, PHB suppresses FSH-induced steroidogenesis and this response is evident irrespective of the differentiated state of granulosa cells.

CONCLUSION

These findings suggest that PHB regulates granulosa cell apoptosis and steroidogenesis in a follicular stage-dependent manner and that the dysregulation of PHB expression and action may be relevant to ovarian dysfunction.

FSH induces the development of circadian clockwork in rat granulosa cells via a gap junction protein Cx43-dependent pathway

The present study was designed to assess the relationship between gap junctions and the maturation of a clock system in rat granulosa cells stimulated by follicle-stimulating hormone (FSH). Immature and mature granulosa cells were prepared by puncturing the ovaries of diethylstilbestrol- and equine chorionic gonadotropin (eCG)-treated mouse Period2 (Per2)-dLuc reporter gene transgenic rats, respectively. Mature granulosa cells exposed to dexamethasone (DXM) synchronization displayed several Per2-dLuc oscillations and a rhythmic expression of clock genes. Intriguingly, we observed clear evidence that the FSH stimulation significantly increased the amplitude of Per2 oscillations in the granulosa cells, which was confirmed by the elevation of the Per2 and Rev-erbα (Nr1d1) mRNA levels. FSH also induced a major phase-advance shift of Per2 oscillations. The mature granulosa cells cultured for 2 days with FSH expressed higher mRNA levels of Per2, Rev-erbα, Bmal1 (Arnt1), Lhcgr, and connexin (Cx) 43 (Gja1) compared with the immature granulosa cells. Consistently, our immunofluorescence results revealed abundant Cx43 protein in antral follicles stimulated with eCG and weak or no fluorescence signal of Cx43 in primary and preantral follicles. Similar results were confirmed by Western blotting analysis. Two gap junction blockers, lindane and carbenoxolone (CBX), significantly decreased the amplitude of Per2 oscillations, which further adhered significant decreases in Per2 and Rev-erbα transcript levels. In addition, both lindane and CBX induced a clear phase-delay shift of Per2 oscillations. These findings suggest that FSH induces the development of the clock system by increasing the expression of Cx43.

Inhibitory roles of prohibitin and chemerin in FSH-induced rat granulosa cell steroidogenesis

Follicular differentiation is a tightly regulated process involving various endocrine, autocrine, and paracrine factors. The biosynthesis of progesterone and estradiol in response to FSH involves the regulation of multiple steroidogenic enzymes, such as p450 cholesterol side-chain cleavage enzyme and aromatase. Here we demonstrated that prohibitin (PHB), a multifunctional protein, inhibits FSH-induced progesterone and estradiol secretion in rat granulosa cells. The mRNA abundances of cyp11a (coding p450 cholesterol side-chain cleavage enzyme) and cyp19 (coding aromatase) were also suppressed by PHB in a time-dependent manner. It is known that a novel adipokine chemerin suppresses FSH-induced steroidogenesis in granulosa cells. Chemerin up-regulates the content of PHB, and PHB knockdown attenuates the suppressive role of chemerin on steroidogenesis. In addition, inhibition of phosphatidylinositol 3-kinase/Akt pathway enhances the suppressive action of PHB, whereas expression of constitutively active Akt attenuates this response. These findings suggest that PHB is a novel negative regulator of FSH-induced steroidogenesis, and its action with chemerin may contribute to the dysregulation of steroidogenesis in the pathogenesis of polycystic ovarian syndrome.

Exogenous arachidonate restores the dimethoate-induced inhibition of steroidogenesis in rat interstitial cells

The present work studies the potential restorative effect of polyunsaturated fatty acids (PUFA, 5 μM/24 h) on the dimethoate (DMT)-induced inhibition of testosterone biosynthesis in Leydig cells isolated from rat testes. Various fatty acids (FA) from the n-6 (18:2, 20:3, 20:4, 22:4 and 22:5) and n-3 (18.3, 20:5, 22:5, 22:6) series were assayed in Leydig cells, alone (as delipidated BSA complexes) and in combination with DMT (1 ppm). The n-6 FA stimulated lipid peroxidation (LPO) and inhibited the activities of steroidogenic enzymes (3β- and 17β-hydroxysteroid dehydrogenases). The n-3 FA exerted an anti-oxidant effect, decreasing the production of thiobarbituric-acid reactive substances (TBARS) and inhibiting phospholipase A(2) activity. The biosynthesis of testosterone in DMT-treated cultures was completely normalized by ARA (20:4n-6) and partially restored by the addition of 20:3n-6, increasing ARA content inside the mitochondria. The other FA assayed failed to restore androgenesis. COX-2 protein and prostaglandin F2α and E2 production were stimulated by 20:3n-6, ARA, 18:3n-3 and 20:5 n-3. COX-2 protein decreased upon addition of 22:5n-3 and 22:6n-3. StAR protein was increased by ARA and partially increased by 20:3n-6, likely due to its metabolic conversion into ARA. Both FA increased the mitochondrial cholesterol pool available for testosterone biosynthesis. The rate of androgenesis is likely the result of various regulatory factors acting concomitantly on the physiology of Leydig cells.

Effect of the metabolic environment at key stages of follicle development in cattle: focus on steroid biosynthesis

Cellular mechanisms that contribute to low estradiol concentrations produced by the preovulatory ovarian follicle in cattle with a compromised metabolic status are largely unknown. To gain insight into the main metabolic mechanisms affecting preovulatory follicle function, two different animal models were used. Experiment 1 compared Holstein-Friesian nonlactating heifers (n = 17) and lactating cows (n = 16) at three stages of preovulatory follicle development: 1) newly selected dominant follicle in the luteal phase (Selection), 2) follicular phase before the LH surge (Differentiation), and 3) preovulatory phase after the LH surge (Luteinization). Experiment 2 compared newly selected dominant follicles in the luteal phase in beef heifers fed a diet of 1.2 times maintenance (M, n = 8) or 0.4 M (n = 11). Lactating cows and 0.4 M beef heifers had higher concentrations of β-hydroxybutyrate, and lower concentrations of glucose, insulin, and IGF-I compared with dairy heifers and 1.2 M beef heifers, respectively. In lactating cows this altered metabolic environment was associated with reduced dominant follicle estradiol and progesterone synthesis during Differentiation and Luteinization, respectively, and in 0.4 M beef heifers with reduced dominant follicle estradiol synthesis. Using a combination of RNA sequencing, Ingenuity Pathway Analysis, and qRT-PCR validation, we identified several important molecular markers involved in steroid biosynthesis, such as the expression of steroidogenic acute regulatory protein (STAR) within developing dominant follicles, to be downregulated by the catabolic state. Based on this, we propose that the adverse metabolic environment caused by lactation or nutritional restriction decreases preovulatory follicle function mainly by affecting cholesterol transport into the mitochondria to initiate steroidogenesis.

Effects of cadmium chloride and nonylphenol on the expression of StAR-related lipid transfer domain containing protein (START1) gene in aquatic midge, Chironomus riparius

We identified and characterized a partial cDNA of StAR-related lipid transfer domain containing protein gene from Chironomus riparius (CrSTART1) having homology with human MLN64 and Drosophila melanogaster START1 (DmSTART1) and evaluated the effects of cadmium chloride (Cd) and nonylphenol (NP) on its expression. Pfam analysis identified the presence of two StAR-related lipid transfer (START) domains in CrSTART1 having several conserved amino acid residues, characteristic of the MLN64 and DmSTART1. The mRNA expression of CrSTART1 was observed in all developmental stages. The modulation in the mRNA expression of CrSTART1 was investigated after exposure to different concentrations Cd (0, 2, 10, and 20 mg/L) and NP (0, 10, 50, and 100 μg/L) for different time intervals in fourth instar larvae of C. riparius. Significant downregulation of CrSTART1 mRNA was observed after exposure to 2, 10 and 20 mg/L of Cd for 24, 48 and 72 h. Significant upregulation of CrSTART1 was observed after exposure to 10 and 50 μg/L of NP for 24, and 48 h period. At 100 μg/L of NP significant upregulation of CrSTART1 was observed after 12 h and downregulated after 24, 48 and 72 h.

Adiponectin (15-36) stimulates steroidogenic acute regulatory (StAR) protein expression and cortisol production in human adrenocortical cells: role of AMPK and MAPK kinase pathways

Adiponectin is an abundantly circulating adipokine, orchestrating its effects through two 7-transmembrane receptors (AdipoR1 and AdipoR2). Steroidogenesis is regulated by a variety of neuropeptides and adipokines. Earlier studies have reported adipokine mediated steroid production. A key rate-limiting step in steroidogenesis is cholesterol transportation across the mitochondrial membrane by steroidogenic acute regulatory protein (StAR). Several signalling pathways regulate StAR expression. The actions of adiponectin and its role in human adrenocortical steroid biosynthesis are not fully understood. The aim of this study was to investigate the effects of adiponectin on StAR protein expression, steroidogenic genes, and cortisol production and to dissect the signalling cascades involved in the activation of StAR expression. Using qRT-PCR, Western blot analysis and ELISA, we have demonstrated that stimulation of human adrenocortical H295R cells with adiponectin results in increased cortisol secretion. This effect is accompanied by increased expression of key steroidogenic pathway genes including StAR protein expression via ERK1/2 and AMPK-dependent pathways. This has implications for our understanding of adiponectin receptor activation and peripheral steroidogenesis. Finally, our study aims to emphasise the key role of adipokines in the integration of metabolic activity and energy balance partly via the regulation of adrenal steroid production. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.

Effects of the β2 -agonist clenbuterol on testicular steroidogenic acute regulatory protein mRNA expression in adult rats

This study was carried out to investigate the effects of clenbuterol (CLB) on the testicular (steroidogenic acute regulatory, StAR) protein mRNA expression in rats. Thirty adult male rats were administered CLB by gavage daily at the doses of 0.4, 2.0 and 18.5 mg/kg bw for 14 days in the subacute experiment, whereas 20 rats received a single treatment with CLB at the doses of 20 and 40 mg/kg bw in the acute experiment and 20 rats were treated with 0.9% NaCl solution as vehicle groups. Testicular tissues were collected and snap-frozen in liquid nitrogen and stored at -70 °C until use. The levels of StAR mRNA were detected by RT-PCR. The levels of StAR mRNA were markedly increased (P < 0.05) at both dosages of 20 and 40 mg/kg bw but the effects were not dose-dependent and the mRNA levels of StAR were returned to near normal level after 7 days of CLB withdrawal, compared with the control animals. In the subacute experiment, CLB induced a dose-dependent but no statistical significant reduction (P > 0.05) in the expression levels of StAR mRNA, and the mRNA levels were recovered to near normal level in the groups treated with CLB at dosages of 0.4 and 2.0 mg/kg bw/day following a 7-day withdrawal period, compared with the control animals. The mRNA levels of StAR showed a significant decrease in the groups treated with CLB at the dosage of 18.5 mg/kg bw/day (P < 0.05) after a 1- or 7-day withdrawal period with respect to the control animals. These results demonstrated transient stimulative effects of CLB on testicular StAR mRNA levels and inhibitory effects after treatment with CLB for 14 consecutive days.

Sildenafil treatment in vivo stimulates Leydig cell steroidogenesis via the cAMP/cGMP signaling pathway

Sildenafil citrate (Viagra), a cGMP-selective phosphodiesterase (PDE) inhibitor, is widely used to treat erectile dysfunction and pulmonary arterial hypertension. In contrast to its well established action on erectile dysfunction, little is known on the action of sildenafil on cGMP/cAMP signaling and testicular steroidogenesis. This study was designed to assess the effects of prolonged sildenafil treatment on NO synthase-dependent signaling and steroidogenic function of rat Leydig cells. Male adult rats were treated with Viagra (1.25 mg/kg body wt) daily for 30 days. In our studies, serum testosterone and ex vivo testosterone production significantly increased in sildenafil-treated animals. Human chorionic gonadotropin-stimulated testosterone production and cAMP accumulation were also significantly higher in Leydig cells obtained from sildenafil-treated rats. The expression of soluble guanylyl cyclase (GUCY1) subunits (Gucy1a1, Gucy1b1) significantly increased; cAMP-specific Pde4a, cGMP-specific Pde6c, and dual Pde1c and Nos2 were inhibited and expression of Nos3, protein kinase G1 (Pkg1), and Pde5 remained unchanged. Treatment of purified Leydig cells with NO donor caused a dose-dependent increase in both testosterone and cGMP production. Testosterone and cGMP production was significantly higher in Leydig cells obtained from sildenafil-treated animals. The stimulatory effect of NO donor was significantly enhanced by saturating concentrations of hCG in both Leydig cells obtained from control and sildenafil-treated animals. Occurrence of mature steroidogenic acute regulatory protein also increased in sildenafil treated animals in accord with increased cAMP and cGMP production. In summary, inhibition of PDE activity during prolonged sildenafil treatment increased serum testosterone level and Leydig cells' steroidogenic capacity by coordinated stimulatory action on cAMP and cGMP signaling pathway.

Involvement of lipids in dimethoate-induced inhibition of testosterone biosynthesis in rat interstitial cells

The mechanism involved in the inhibition of testosterone (Te) biosynthesis after a sub-chronic exposure to low doses of dimethoate (D) was studied in rat interstitial cells (IC). Expression of COX-2 in IC isolated from D-treated rats increased by 44% over C data, while transcription of StAR decreased by approx. 50% and the expression of this protein was diminished by approximately 40%. PGE(2) and PGF(2alpha) were increased by 61 and 78%, respectively. Te concentration decreased by 49% in IC homogenates. Concomitantly, plasma concentration of LH and FSH both increased. Araquidonate (ARA) and C(22) fatty acyl chains in phospholipids from IC mitochondrial fraction decreased by approx. 30% after D treatment. Protein carbonyls, lipoperoxides and nitrite content increased while alpha-tocopherol and the antioxidant capacity of the soluble cellular fraction decreased significantly. Stimulation with h-CG 10 nM overnight failed to overcome the inhibition caused by D on both Te biosynthesis and 3beta- and 17beta-hydroxysteroid dehydrogenases. Decreased Te biosynthesis may be attributed to (1) inhibition of StAR protein activity due to the stimulation of COX-2 and the overproduction of PGF(2alpha), (2) decreased stimulatory effect of ARA on StAR with a subsequent reduction in the availability of CHO for the androgenic pathway, and/or (3) indirect inhibition of steroidogenic enzymes by a lower transcriptional rate caused by elevated PGF(2alpha). Rofecoxib administration prevents the deleterious effect(s) exerted by D.

Involvement of the thromboxane A2 receptor in the regulation of steroidogenic acute regulatory gene expression in murine Leydig cells

Recent studies suggested an involvement of thromboxane A2 in cyclooxygenase-2-dependent inhibition of steroidogenic acute regulatory (StAR) gene expression. The present study further investigated the role of thromboxane A2 receptor in StAR gene expression and steroidogenesis in testicular Leydig cells. The thromboxane A2 receptor was detected in several Leydig cell lines. Blocking thromboxane A2 binding to the receptor using specific antagonist SQ29548 or BM567 resulted in dose-dependent increases in StAR protein and steroid production in MA-10 mouse Leydig cells. The results were confirmed with Leydig cells isolated from rats. StAR promoter activity and StAR mRNA level in the cells were also increased after the treatments, suggesting an involvement of the thromboxane A2 receptor in StAR gene transcription. Furthermore study indicated that blocking the thromboxane A2 receptor reduced dosage sensitive sex reversal-adrenal hypoplasia congenita critical region on the X chromosome, gene 1 protein, a transcriptional repressor of StAR gene expression. Specific binding of the antagonists to the receptors on cellular membrane was demonstrated by binding assays using (3)H-SQ29548 and binding competition between (3)H-SQ29548 and BM567. Whereas SQ29548 enhanced cAMP-induced StAR gene expression, in the absence of cAMP, it was unable to increase StAR protein and steroidogenesis. However, when the receptor was blocked by the antagonist, subthreshold levels of cAMP were able to induce maximal levels of StAR protein expression, suggesting that blocking the thromboxane A2 receptor increase sensitivity of MA-10 cells to cAMP stimulation. Taken together, the results from the present and previous studies suggest an autocrine loop, involving cyclooxygenase-2, thromboxane A synthase, and thromboxane A2 and its receptor, in cyclooxygenase-2-dependent inhibition of StAR gene expression.

Orexins stimulate steroidogenic acute regulatory protein expression through multiple signaling pathways in human adrenal H295R cells

Orexins mediate a variety of physiological processes, including feeding behavior, the circadian pathway, and cortisol secretion. Steroidogenesis is regulated by a variety of neuropeptides, and one of the key rate-limiting steps is cholesterol transport across the mitochondrial membrane by the steroidogenic acute regulatory protein (StAR). StAR expression can be regulated through several different signaling pathways. Despite the clear link between orexins and steroid production, the actions of the orexin family of hormones on steroid biosynthesis are not fully understood. We present data showing that 100 nm of both orexins A and B for 4 or 24 h significantly up-regulates StAR, in H295R pluripotent adrenocortical cells. We present the dose-dependent and time-dependent characteristics of StAR up-regulation at the protein level, showing significant increases after 4 h at a relatively low agonist concentration (1 nm). We have provided a key analysis of the precise G protein-coupled signaling pathways required for the up-regulation of StAR in response to orexins A and B. This has involved dominant-negative G protein analysis, and the direct inhibition of the protein kinase A, protein kinase C, ERK1/2, and p38 pathways. This shows a fundamental role for multiple G protein-coupled and MAPK-mediated signaling pathways leading to StAR expression. Antagonist analysis also showed that orexin effects on StAR were primarily, but not exclusively, acting through the orexin receptor type 1. This is the first study linking orexin action on StAR expression and comprehensively describes the signaling pathways involved in regulating the complexity of hormone biosynthesis.

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

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

Inhibition of thromboxane a synthase activity enhances steroidogenesis and steroidogenic acute regulatory gene expression in MA-10 mouse Leydig cells

The cyclooxygenase-2 (COX2)-dependent inhibition of Leydig cell steroidogenesis has been demonstrated. To understand the mechanism for this effect of COX2, the present study examined the role of an enzyme downstream of COX2, namely thromboxane A synthase (TBXAS), in steroidogenesis. Inhibition of TBXAS activity with the inhibitor furegrelate induced a concentration-dependent increase in cAMP-induced steroidogenic acute regulatory (StAR) protein in MA-10 mouse Leydig cells. The increase in StAR protein occurred concomitantly with a significant increase in steroid hormone production. Similar results were obtained in StAR promoter activity assays and RT-PCR analyses of StAR mRNA levels, suggesting that inhibition of TBXAS activity enhanced StAR gene transcription. These observations were corroborated when TBXAS expression was specifically inhibited by RNA interference. Although the RNA interference reduced mRNA levels of TBXAS, it increased StAR mRNA levels, StAR protein, and steroidogenesis. Additional studies indicated that inhibition of TBXAS activity reduced DAX-1 protein, a repressor in StAR gene transcription. In the absence of cAMP, inhibition of TBXAS activity did not induce a significant increase in steroid hormone and StAR protein. However, addition of a low level of cAMP analogs dramatically increased steroidogenesis. Lastly, inhibition of protein kinase A activity essentially abolished the steroidogenic effect of the TBXAS inhibitor. Thus, the results from the present study suggest that a minimal level of protein kinase A activity is required for the steroidogenic effect of the TBXAS inhibitor and that inhibition of TBXAS activity or its expression increase the steroidogenic sensitivity of MA-10 mouse Leydig cells to cAMP stimulation.

Fenvalerate inhibits progesterone production through cAMP-dependent signal pathway

Fenvalerate is a widely used synthetic pyrethroid insecticide and is known to impede the male reproductive function. However, the mechanisms remain to be elucidated. In this study, mouse Leydig tumor cells (MLTC-1) were used to investigate the effects of fenvalerate on progesterone production. Fenvalerate treatment inhibited progesterone secretion induced by human chorionic gonadotropin (hCG), cholera toxin (CT) or forskolin and decreased cAMP levels induced by hCG, but not by CT or forskolin, which suggested a repaired site on the upstream components of G protein or G protein per se by fenvalerate in the cAMP-mediated signal pathway. Furthermore, the addition of cAMP analog, 8-Br-cAMP, could not reverse fenvalerate-suppressed progesterone synthesis, indicating that fenvalerate interfered with the downstream molecules of cAMP. In addition, fenvalerate decreased steroidogenic acute regulatory protein (StAR) mRNA and protein levels, and also profoundly inhibited the activity of P450 side chain cleavage enzyme (P450scc) which was consistent with the decreased expression of P450scc mRNA and protein in MLTC-1 cells. These results suggested that fenvalerate might inhibit progesterone production by attenuating cAMP generation and inhibiting StAR expression and P450scc activity.

Human adipocytes induce an ERK1/2 MAP kinases-mediated upregulation of steroidogenic acute regulatory protein (StAR) and an angiotensin II — sensitization in human adrenocortical cells

OBJECTIVES

Hypertension is a major complication of overweight with frequently elevated aldosterone levels in obese patients. Our previous work suggests a direct stimulation of adrenal aldosterone secretion by adipocytes. Owing to aldosterone's important role in maintaining blood pressure homeostasis, its regulation in obesity is of major importance. One objective was to determine the signaling mechanisms involved in adipocyte-induced aldosterone secretion. In addition to a direct stimulation, a sensitization toward angiotensin II (AngII) might be involved. The second objective was to determine a possible adipokines-induced sensitization of human adrenocortical cells to AngII.

DESIGN

Human subcutaneous adipocytes and adrenocortical cells, and the adrenocortical cell line NCI-H295R were used. Adrenocortical cells were screened for signal transduction protein expression and phosphorylation. Subsequently, steroidogenic acute regulatory protein (StAR), cAMP response element-binding protein (CREB), cAMP and phosphorylated extracellular regulated kinase were analyzed by Western blot, enzyme-linked immunosorbent assay, quantitative PCR, reporter gene assay and confocal microscopy to investigate their role in adipocyte-mediated aldosterone secretion.

RESULTS

AngII-mediated aldosterone secretion was largely increased by preincubating H295R cells with adipocyte secretory products. StAR mRNA and StAR protein were upregulated in a time-dependent way. This steroidogenic effect was independent of the cAMP-protein kinase A (PKA) pathway as cellular cAMP was unaltered and inhibition of PKA by H89 failed to reduce aldosterone secretion. However, CREB reporter gene activity was moderately elevated. Upregulation of StAR was accompanied by ERK1/2 MAP kinase activation and nuclear translocation of the kinases. Inhibition of MAP kinase by UO126 abolished adipokine-stimulated aldosterone secretion from primary human adrenocortical and H295R cells, and inhibited StAR gene activity. Adipokines stimulated steroidogenesis also in primary human adrenocortical cells, supporting a role in human physiology and/or pathology.

CONCLUSIONS

Adipokines induce aldosterone secretion from human adrenocortical cells and sensitization of the cells to stimulation by AngII, possibly mediated via ERK1/2-dependent upregulation of StAR activity. This stimulation of aldosterone secretion could be one link between overweight and inappropriately elevated aldosterone levels.

The molecular control of corpus luteum formation, function, and regression

The corpus luteum (CL) is one of the few endocrine glands that forms from the remains of another organ and whose function and survival are limited in scope and time. The CL is the site of rapid remodeling, growth, differentiation, and death of cells originating from granulosa, theca, capillaries, and fibroblasts. The apparent raison d'etre of the CL is the production of progesterone, and all the structural and functional features of this gland are geared toward this end. Because of its unique importance for successful pregnancies, the mammals have evolved a complex series of checks and balances that maintains progesterone at appropriate levels throughout gestation. The formation, maintenance, regression, and steroidogenesis of the CL are among the most significant and closely regulated events in mammalian reproduction. During pregnancy, the fate of the CL depends on the interplay of ovarian, pituitary, and placental regulators. At the end of its life span, the CL undergoes a process of regression leading to its disappearance from the ovary and allowing the initiation of a new cycle. The generation of transgenic, knockout and knockin mice and the development of innovative technologies have revealed a novel role of several molecules in the reprogramming of granulosa cells into luteal cells and in the hormonal and molecular control of the function and demise of the CL. The current review highlights our knowledge on these key molecular events in rodents.

The imitation switch protein SNF2L regulates steroidogenic acute regulatory protein expression during terminal differentiation of ovarian granulosa cells

Luteinization is a complex process, stimulated by gonadotropins, that promotes ovulation and development of the corpus luteum through terminal differentiation of granulosa cells. The pronounced expression of the mammalian imitation switch (ISWI) genes, SNF2H and SNF2L, in adult ovaries prompted us to investigate the role of these chromatin remodeling proteins during follicular development and luteinization. SNF2H expression is highest during growth of preovulatory follicles and becomes less prevalent during luteinization. In contrast, both SNF2L transcript and SNF2L protein levels are rapidly increased in granulosa cells of the mouse ovary 8 h after human chorionic gonadotropin treatment, and continue to be expressed 36 h later within the functional corpus luteum. We demonstrate a physical interaction between SNF2L and the progesterone receptor A isoform, which regulates progesterone receptor-responsive genes required for ovulation. Moreover, chromatin immunoprecipitation demonstrated that, after gonadotropin stimulation, SNF2L is associated with the proximal promoter of the steroidogenic acute regulatory protein (StAR) gene, a classic marker of luteinization in granulosa cells. Interaction of SNF2L with the StAR promoter is required for StAR expression, because small interfering RNA knockdown of SNF2L prevents the activation of the StAR gene. Our results provide the first indication that ISWI chromatin remodeling proteins are responsive to the LH surge and that this response is required for the activation of the StAR gene and the overall development of a functional luteal cell.

Effect of ethanol on follicle stimulating hormone-induced steroidogenic acute regulatory protein (StAR) in cultured rat granulosa cells

Steroidogenic acute regulatory protein (StAR) plays a critical role in trophic hormone-stimulated steroid biosynthesis by facilitating the transfer of cholesterol across the mitochondrial membrane, where the cytochrome P450scc enzyme resides to initiate steroid hormone biosynthesis. Because follicle stimulating hormone (FSH) is a critically important regulator of estradiol (E2) synthesis in granulosa cells and because ethanol is known to suppress gonadotropin-stimulated ovarian steroidogenesis, we evaluated the effects of ethanol on FSH-stimulated StAR in ovarian granulosa cells. Granulosa cells from immature rats pretreated with pregnant mare serum gonadotropin were cultured for 24 h in serum-free medium, either alone (medium only) or with FSH (25 ng/ml) in the presence or absence of ethanol (50 mM). Real-time polymerase chain reaction (PCR) analysis showed increased (p < 0.01) expression of the StAR transcript in FSH-treated cells, when compared with cells that received medium only. The FSH stimulation of StAR transcript was blocked (p < 0.01) by the presence of ethanol. This effect coincided with a decrease in E2 secretion into the culture medium. We also examined whether ethanol could affect the production of cyclic AMP (cAMP), the main second messenger that mediates gonadotropin action within the ovary. FSH treatment of granulosa cells markedly increased (p < 0.001) cAMP levels, an effect that was not altered by ethanol. Importantly, FSH induced an increase (p < 0.01) in the release of prostaglandin E2 (PGE2), an effect that was blocked by ethanol. Real-time PCR analysis showed that ethanol had no effect on the expression of cyclooxygenase-1 (COX-1), but blocked (p < 0.01) FSH-stimulated expression of COX-2. These results demonstrate that ethanol is capable of inhibiting FSH-induced ovarian StAR and thus, contributing to suppressed E2 secretion, at least in part, through an inhibitory action on the COX-2-PGE2 pathway.

Analysis of gene expression in the bovine corpus luteum through generation and characterisation of 960 ESTs

To gain new insights into gene identity and gene expression in the bovine corpus luteum (CL) a directionally cloned CL cDNA library was constructed, screened with a total CL cDNA probe and clones representing abundant and rare mRNA transcripts isolated. The 5'-terminal DNA sequence of 960 cDNA clones, composed of 192 abundant and 768 rare mRNA transcripts was determined and clustered into 351 non-redundant expressed sequence tag (EST) groups. Bioinformatic analysis revealed that 309 (88%) of the ESTs showed significant homology to existing sequences in the protein and nucleotide public databases. Several previously unidentified bovine genes encoding proteins associated with key aspects of CL function including extracellular matrix remodelling, lipid metabolism/steroid biosynthesis and apoptosis, were identified. Forty-two (12%) of the ESTs showed homology with human or with other uncharacterised ESTs, some of these were abundantly expressed and may therefore play an important role in primary CL function. Tissue-specificity and temporal CL gene expression of selected clones previously unidentified in bovine CL tissue was also examined. The most interesting finds indicated that mRNA encoding squalene epoxidase was constitutively expressed in CL tissue throughout the oestrous cycle and 7-fold down-regulated (P < 0.05) in late luteal tissue, concomitant with the disappearance of systemic progesterone, suggesting that de novo cholesterol biosynthesis plays an important role in steroidogenesis. The mRNA encoding the growth factor, insulin-like growth factor-binding protein-related protein 1 (IGFBP-rP1), remained constant during the oestrous cycle and was 1.8-fold up-regulated (P < 0.05) in late luteal tissue implying a role in CL regression.

Liver receptor homolog-1 stimulates the progesterone biosynthetic pathway during follicle-stimulating hormone-induced granulosa cell differentiation

FSH-stimulated granulosa cell differentiation is associated with the induction of the LH receptor (LHr) as well as induction of the estrogen and progesterone biosynthetic pathways. Although activation of the cAMP-protein kinase A pathway is sufficient to stimulate progesterone production, additional pathways are required for the induction of the LHr and p450 aromatase. The orphan nuclear receptor, liver receptor homolog-1 (LRH-1), is expressed in granulosa cells and has been shown to synergize with the cAMP signaling system to regulate the gonadal type II aromatase promoter in transient transfection assays. To determine whether LRH-1 can interact with the cAMP pathway in the induction of aromatase and the LHr, we examined the effects of an adenoviral vector that directs the expression of human LRH-1 (Ad-LRH-1) on FSH-stimulated granulosa cell differentiation. Infection of undifferentiated granulosa cells with LRH-1 alone had no effect on estrogen production, progesterone production, or the expression of the LHr. However, combination of FSH stimulation and Ad-LRH-1 infection led to significantly greater progesterone production and increases in mRNA for p450 side-chain cleavage and 3beta-hydroxysteroid dehydrogenase than granulosa cells stimulated by FSH alone. However, infection with Ad-LRH-1 did not stimulate estradiol production or increases in mRNA for p450 aromatase or the LHr above that seen with FSH treatment alone. Moreover, infection with Ad-LRH-1 was able to overcome H-89 inhibition of FSH-stimulated progesterone but not estrogen production. Collectively, these observations support a direct role for LRH-1 in the induction of the progesterone but not the estrogen biosynthetic pathway during granulosa cell differentiation.

Involvement of multiple transcription factors in the regulation of steroidogenic acute regulatory protein gene expression

The rate-limiting, committed, and regulatable step in steroid hormone biosynthesis is the transport of cholesterol from the outer to the inner mitochondrial membrane, a process that is mediated by the steroidogenic acute regulatory (StAR) protein. In steroidogenic cells, the StAR protein is regulated by cAMP-dependent mechanisms. However, the StAR promoter lacks a consensus cAMP response-element (CRE), suggesting the involvement of alternate regulatory factor(s) in cAMP responsiveness. These regulatory elements are found to be located in a transcription factor-binding site-rich region (consisting of approximately 150 nucleotides upstream of the transcription start site) of the StAR promoter, and appears to be the most important region in regulating transcription of the StAR gene. The StAR promoter sequences in mouse, rat and human are highly homologous, and in the absence of a canonical CRE, multiple cis-elements have been shown to be instrumental in the regulation of StAR gene expression. Nevertheless, it has become apparent that functional cooperation, interaction, and alteration of different transcription factors are involved in the fine-tuning of the regulatory events associated with StAR gene transcription.

Cholesterol transport and steroidogenesis by the corpus luteum

The synthesis of progesterone by the corpus luteum is essential for the establishment and maintenance of early pregnancy. Regulation of luteal steroidogenesis can be broken down into three major events; luteinization (i.e., conversion of an ovulatory follicle), luteal regression, and pregnancy induced luteal maintenance/rescue. While the factors that control these events and dictate the final steroid end products are widely varied among different species, the composition of the corpus luteum (luteinized thecal and granulosa cells) and the enzymes and proteins involved in the steroidogenic pathway are relatively similar among all species. The key factors involved in luteal steroidogenesis and several new exciting observations regarding regulation of luteal steroidogenic function are discussed in this review.

Transactivation of steroidogenic acute regulatory protein in human endometriotic stromalcells is mediated by the prostaglandin EP2 receptor

Steroidogenic acute regulatory protein (StAR) regulates the first committed step in the biosynthesis of steroids, and thus aberrant expression of StAR in endometriotic implants plays a critical role in the etiology of endometriosis. However, the mechanism responsible for abnormal expression of StAR in ectopic endometriotic tissues remains unknown. In the present study, we demonstrate that prostaglandin (PG) E(2) stimulates StAR protein expression at the cellular and molecular levels. PGE(2) caused a rapid increase in StAR expression that involves activation of the EP2 receptor-coupled protein kinase A pathway. Activation of EP2 receptor-induced phosphorylation of ERK and cAMP response element binding protein (CREB). However, activation of ERK did not involve in CREB phosphorylation or concomitantly StAR expression. Phosphorylation of CREB induced by PGE(2) increased the recruitment of CREB binding protein and thus histone H3 acetylation. Chromatin immunoprecipitation experiments showed that acetylated histone H3 bound to the proximal region of the StAR promoter was increased after 30 min treatment with PGE(2), and this was mirrored by an increase in nascent StAR RNA transcription. Treatment with the histone deacetylase inhibitor, tricostatin A, enhanced PGE(2)-induced nascent StAR RNA transcription. We conclude that increased histone H3 acetylation involving the EP2 receptor, protein kinase A, CREB, and CREB binding protein is responsible for PGE(2)-induced StAR gene activation in endometriotic stromal cells. Our current report may provide new insights in understanding mechanism of abnormally local production of estrogen and the etiology of endometriosis.

Inhibition of cyclooxygenase-2 activity enhances steroidogenesis and steroidogenic acute regulatory gene expression in MA-10 mouse Leydig cells

To study the mechanism for the regulatory effect of arachidonic acid (AA) on steroidogenesis, the role of cyclooxygenase (COX) in steroid production and steroidogenic acute regulatory (StAR) gene expression was investigated. Although stimulation with 0.05 mM dibutyryl cAMP (Bt(2)cAMP) did not increase StAR protein or progesterone in MA-10 mouse Leydig cells, the addition of 1 microM of the COX inhibitor indomethacin increased StAR protein expression and progesterone production by 5.7-fold and 34.3-fold, respectively. In the presence of indomethacin, the level of Bt(2)cAMP required for maximal steroidogenesis was reduced from 1.0 mM to 0.25 mM. Similar results were obtained in studies on StAR promoter activity and in Northern blot analyses of StAR mRNA expression, suggesting that inhibition of COX activity enhanced StAR gene transcription. COX2 (an inducible isoform of COX) was constitutively detected in MA-10 cells. Although SC560, a selective COX1 inhibitor, did not affect steroidogenesis, the COX2 inhibitor NS398 significantly enhanced Bt(2)cAMP-stimulated StAR protein expression and steroid production. Overexpression of the COX2 gene in COS-1 cells significantly inhibited StAR promoter activity. The results of the present study suggest that inhibition of COX2 activity increases the sensitivity of steroidogenesis to cAMP stimulation in MA-10 Leydig cells.

Involvement of 5-lipoxygenase metabolites of arachidonic acid in cyclic AMP-stimulated steroidogenesis and steroidogenic acute regulatory protein gene expression

To understand the mechanism for the role of arachidonic acid (AA) in steroidogenic acute regulatory (StAR) gene transcription, sections of the -1/-966 StAR promoter were deleted to produce constructs of -1/-426, -1/-211, -1/-151, and -1/-110 and inserted into the PGL3 vector to drive luciferase expression. Results indicated that -1/-151 StAR promoter contains the elements that are most responsive to AA. Electrophoretic mobility shift assays using nuclear extracts from AA-treated MA-10 Leydig tumor cells showed that AA enhanced specific binding of the nuclear extract to a 30bp (-67/-96) sequence of the StAR promoter. Also, HPLC was used to identify AA metabolites involved in StAR gene transcription. It was found that 1mM N6,2-O-dibutyryladenosine 3:5-cyclic monophosphate (dbcAMP) significantly increased the 5-lipoxygenase metabolites, 5-hydroperoxyeicosatetraenoic acid (5-HPETE) and 5-hydroxyeicosatetraenoic acid (5-HETE). Moreover, in the presence of 0.2mM dbcAMP addition of 20 microM 5-HPETE or 5-HETE significantly enhanced StAR protein expression and progesterone production (P<0.05). Similar results were obtained for StAR gene transcription with StAR mRNA levels and StAR promoter activities being significantly increased (P<0.05) when 5-HPETE was added to MA-10 cell cultures. In summary, the present studies demonstrated that cyclic AMP (cAMP) stimulated the production of the AA metabolites, 5-HPETE and 5-HETE, and showed that these metabolites enhanced StAR gene expression and steroid hormone production. The results further suggested that the AA-responsive element resides in the -67/-96 region of the StAR promoter.

Regulation of the scavenger receptor BI and the LDL receptor by activators of aldosterone production, angiotensin II and PMA, in the human NCI-H295R adrenocortical cell line

In human adrenal cells, cholesterol for steroidogenesis is derived from both high-density lipoproteins (HDL) via the Scavenger Receptor Class B Type I (SR-BI) and low-density lipoproteins (LDL) via the LDL receptor pathway. We have previously shown that, in the human adrenocortical carcinoma cell line, NCI-H295R, SR-BI and LDL receptor expression and steroidogenesis are coordinately regulated by activators of protein kinase A (PKA) leading to glucocorticoid synthesis. In the present study, we studied whether SR-BI and LDL receptor expression are regulated by activators of the protein kinase C (PKC) signaling pathway, such as angiotensin II, which stimulate mineralocorticoid synthesis. First, it is shown that, in NCI-H295R cells, aldosterone synthesis is stimulated by a phorbol ester (phorbol-12-myristate-13 acetate, PMA), a potent PKC activator. Northern blot analysis indicated that both angiotensin II and PMA stimulated SR-BI expression in a time-dependent manner. LDL receptor expression is slightly stimulated by PMA. The induction of SR-BI gene expression occurs at the transcriptional level, via an activation of the human SR-BI promoter, as shown by transient transfection experiments. Finally, SR-BI protein level was increased in angiotensin II- and PMA-stimulated cells, resulting in higher lipoprotein binding and specific cholesteryl ester (CE) uptake from HDL, as well from LDL after angiotensin II and PMA stimulation.

Stimulatory effect of progesterone on the expression of steroidogenic acute regulatory protein in MA-10 Leydig cells

The steroidogenic acute regulatory protein (StAR), by virtue of its ability to facilitate the intramitochondrial transport of cholesterol, plays an important role in regulating steroid hormone biosynthesis in steroidogenic cells. In agreement with published data, both StAR expression and progesterone production in MA-10 mouse Leydig tumor cells could be stimulated with hCG and 8Br-cAMP. Addition of aminoglutethimide, an inhibitor of cholesterol side chain cleavage (P450(scc)) enzyme, not only resulted in a drastic inhibition of progesterone production but also in an attenuation of StAR expression in response to either hCG or 8-Br-cAMP. Therefore, we addressed the question of whether progesterone, the end product of the steroidogenic cascade in these cells, could be in a position to regulate the StAR gene expression. In MA-10 cells, we report here that progesterone in microgram amounts can induce StAR gene expression in a time- and dose-dependent manner. StAR expression in response to a maximally effective concentration of progesterone of 10 microg/ml was highest at 6 h and started decreasing thereafter. The effect of progesterone on StAR protein and StAR mRNA induction was mimicked by its synthetic analog, progestin R5020, but not by other steroids, including dexamethasone, estradiol, testosterone, and dihydrotestosterone. Dexamethasone, in contrast, was able to inhibit StAR expression in MA-10 cells. Surprisingly, RU486, a potent antagonist of progesterone and glucocorticoid action, had a stimulatory effect on StAR mRNA levels. Reverse transcription-polymerase chain reaction analysis demonstrated the absence of the classical form of progesterone receptor in MA-10 cells. Thus, for the first time, a direct stimulatory effect of a steroid on StAR gene expression has been demonstrated. Furthermore, these results provide a new insight, indicating that progesterone mediates the activation of StAR expression exerted presumably through a novel, nonclassical progesterone receptor in mouse Leydig cells.

Progesterone attenuates the inhibitory effects of cardiotonic digitalis on pregnenolone production in rat luteal cells

Previous studies have shown that digoxin decreases testosterone secretion in testicular interstitial cells. However, the effect of digoxin on progesterone secretion in luteal cells is unclear. Progesterone is known as an endogenous digoxin-like hormone (EDLH). This study investigates how digitalis affected progesterone production and whether progesterone antagonized the effects of digitalis. Digoxin or digitoxin, but not ouabain, decreased the basal and human chorionic gonadotropin (hCG)-stimulated progesterone secretion as well as the activity of cytochrome P450 side chain cleavage enzyme (P450scc) in luteal cells. 8-Br-cAMP and forskolin did not affect the reduction. Neither the amount of P450scc, the amount of steroidogenic acute regulatory (StAR) protein, nor the activity of 3beta-hydroxysteroid dehydrogenase (3beta-HSD) was affected by digoxin or digitoxin. Moreover, in testicular interstitial and luteal cells, progesterone partially attenuated the reduction of pregnenolone by digoxin or digitoxin and the progesterone antagonist, RU486, blocked this attenuation. These new findings indicated that (1) digoxin or digitoxin inhibited pregnenolone production by decreasing the activity of P450scc enzyme, but not Na(+)-K(+)-ATPase, resulting in a decrease on progesterone secretion in rat luteal cells, and (2) the inhibitory effect on pregnenolone production by digoxin or digitoxin was reversed partially by progesterone. In conclusion, digoxin or digitoxin decreased progesterone production via the inhibition of pregnenolone by decreasing P450scc activity. Progesterone, an EDLH, could antagonize the effects of digoxin or digitoxin in luteal cells.

Interaction between arachidonic acid and cAMP signaling pathways enhances steroidogenesis and StAR gene expression in MA-10 Leydig tumor cells

Previous studies have demonstrated that trophic hormone stimulation induced cyclic AMP (cAMP) formation and arachidonic acid (AA) release from phospholipids and that both these compounds were required for steroid biosynthesis and steroidogenic acute regulatory (StAR) gene expression in MA-10 mouse Leydig tumor cells. The present study further investigates the synergistic effects of the AA and cAMP interaction on steroidogenesis. To demonstrate cAMP-induced AA release, MA-10 cells were pre-loaded with 3H-AA and subsequently treated with dibutyryl cyclic AMP (dbcAMP). Stimulation with dbcAMP significantly induced AA release in MA-10 cells to a level 145.7% higher than that of controls. Lowering intracellular cAMP concentration by expressing a cAMP-phosphodiesterase significantly reduced human chorionic gonadotrophin (hCG)-induced AA release. The dbcAMP-induced AA release was inhibited significantly by the phospholipase A(2) (PLA(2)) inhibitor dexamethasone (Dex) and also by the protein kinase A (PKA) inhibitor H89, suggesting the involvement of PKA phosphorylation and/or PLA(2) activation in cAMP-induced AA release. The effect of the interaction between AA and cAMP on StAR gene expression and steroid production was also investigated. While 0.2 mM dbcAMP induced only very low levels of StAR protein, StAR mRNA, StAR promoter activity and steroid production, all of these parameters increased dramatically as AA concentration in the culture medium was increased from 0 to 200 microM. Importantly, AA was not able to induce a significant increase in steroidogenesis at any concentration when used in the absence of dbcAMP. However, when used in concert with submaximal concentrations of dbcAMP (0.05 mm to 0.5 mm), AA was capable of stimulating StAR gene expression and increasing steroid production significantly. The results from this study demonstrate that AA and cAMP act in a highly synergistic manner to increase the sensitivity of steroid production to trophic hormone stimulation and probably do so by increasing StAR gene expression.

Conditionally immortalized adrenocortical cell lines at undifferentiated states exhibit inducible expression of glucocorticoid-synthesizing genes

To facilitate studies on differentiation of adrenocortical cells and regulation of steroidogenic genes, we established cell lines from adrenals of adult transgenic mice harboring a temperature-sensitive large T-antigen gene of simian virus 40. Adrenal glands of the mice exhibited normal cortical zonation including a functionally undifferentiated cell-layer between the aldosterone-synthesizing zona glomerulosa cells and the corticosterone-synthesizing zona fasciculata cells. At a permissive temperature (33 degrees C), established cell lines AcA201, AcE60 and AcA101 expressed steroidogenic genes encoding steroidogenic factor-1, cholesterol side-chain cleavage P450scc, and steroidogenic acute regulatory protein, which are expressed throughout adrenal cortices and gonads. Genes encoding 3 beta-hydroxysteroid dehydrogenase and steroid 21-hydroxylase P450c21, which catalyze the intermediate steps for syntheses of both aldosterone and corticosterone, were inducible in the three cell lines in temperature- and/or dibutyryl cAMP-dependent manners. Notably, these cell lines displayed distinct expression patterns of the steroid 11 beta-hydroxylase P45011 beta gene responsible for the zone-specific synthesis of corticosterone. AcA201 cells expressed the P45011 beta gene at 33 degrees C, showing the property of the zona fasciculata cells, while AcE60 cells expressed it upon a shift to a nonpermissive temperature (39 degrees C). On the other hand, AcA101 expressed the P45011 beta gene at 39 degrees C synergistically with exposure to dibutyryl cAMP. None of these clones express the zona glomerulosa-specific aldosterone synthase P450aldo gene under the conditions we tested. These results show that AcE60 and AcA101 cells display a pattern of the steroidogenic gene expression similar to that of the undifferentiated cell-layer and are capable of differentiating into the zona fasciculata-like cells in vitro.

Transcriptional regulators of steroidogenesis, DAX-1 and SF-1, are expressed in human skin

DAX-1 and SF-1 are members of the orphan nuclear receptor superfamily that are critical regulatory components of the hypothalamic-pituitary-adrenal-gonadal axis. In adrenal and gonadal tissues they regulate the expression of the cytochrome P450 steroid hydroxylase genes, key mediators of steroidogenesis. The identification of a number of steroid hydroxylases in human skin prompted us to investigate the presence of DAX-1 and SF-1. Immuno histochemical analysis of human skin revealed a distinctive staining pattern for DAX-1 and SF-1 in skin and its appendages. Prominent staining for DAX-1 was confined to the epidermis, sebaceous glands, sweat glands, and outer root sheath of the hair follicle with weaker expression in the inner root sheath, matrix cells, and dermal papilla cells. Similarly, SF-1 was also detected in the epidermis but displayed a scattered nuclear pattern across all layers. SF-1 immunoreactivity was also detected in the exocrine glands and was stronger than DAX-1 in the inner root sheath, matrix cells, and dermal papilla cells. Co-localization of DAX-1 and SF-1 was demonstrated by immunocytochemistry in the HaCaT keratinocyte cell line, primary keratinocytes, preadipocytes, and dermal papilla cells. Reverse transcriptase-polymerase chain reaction analysis demonstrated the expression of DAX-1 and SF-1 mRNA in whole human skin and Western analysis also confirmed the presence of DAX-1 protein in skin-derived cells. Our investigations demonstrate that two important regulators of steroidogeneisis are present in human skin and its appendages. These transcription factors may have a role in cutaneous steroidogenesis and thus be involved in hair follicle cycling or pathologies associated with steroids. Further studies are needed to determine the functional roles of DAX-1 and SF-1 in human skin.

Steroidogenic acute regulatory protein: an update on its regulation and mechanism of action

Steroidogenic acute regulatory (StAR) protein controls the rate-limiting step in steroidogenesis: the transport of cholesterol from the outer to the inner mitochondrial membrane. Early studies indicated that rate of transcription of the StAR gene is a primary determinant of steroidogenesis. The transcription factors that govern basal and cAMP-dependent StAR expression are reviewed, as are new findings regarding chromatin modifications associated with activation of the StAR promoter. Molecular genetic studies of congenital lipoid adrenal hyperplasia, a rare disease caused by mutations in the StAR gene, and structure-function studies defined two major domains within the StAR protein, the N-terminal mitochondrial targeting sequence and the C-terminal StAR-related lipid transfer (START) domain, which promotes the translocation of cholesterol between the two mitochondrial membranes. Several models of StAR's mechanism of action have been proposed based on a combination of structure/function studies or on the crystal structure of a related START domain. The models-intermembrane shuttle hypothesis, and cholesterol desorption hypothesis-are discussed with respect to the known biochemical and biophysical events associated with steroidogenesis and the structure of StAR.