A steroidogenic factor-1-binding site and cyclic adenosine 3',5'-monophosphate response element-like elements are required for the activity of the rat aromatase promoter in rat Leydig tumor cell lines

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

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

Heat stress upregulates aromatases expression through nuclear DAX-1 deficiency in R2C Leydig tumor cells

An appropriate balance between testicular testosterone and estradiol is required for spermatogenesis. Excess estradiol is often identified in the semen and serum of infertile men; however, the mechanisms behind this observation remain unclear. This study indicates the relationship between heat stress and aromatase synthesis in Leydig cells. We used R2C rat Leydig tumor cells, which can synthesize both testosterone and estradiol. Aromatase transcription was regulated by the PⅡ promoter with or without heat stress. Heat stress at 40 °C increased aromatase expression and decreased testosterone to estradiol ratio and nuclear DAX-1 (dosage-sensitive sex reversal, adrenal hypoplasia critical region, on chromosome X, gene 1), which is a suppressor of steroidogenic factor 1 (SF-1). Leptomycin B and KPT-185, a nuclear export inhibitor, prevented nuclear DAX-1 deficiency induced by heat stress and inhibited aromatase transcription. These results indicate that heat stress interferes with DAX-1-SF-1 interaction and induces SF-1-dependent aromatase transcription.

Lactational polychlorinated biphenyls exposure induces epigenetic alterations in the Leydig cells of progeny rats

The present study was designed to establish the epigenetic mechanisms by which lactational exposure to PCBs affects the Leydig cell function in progeny rats. The lactating dams were oral gavaged with different doses of PCBs [1, 2 and 5 mg/kg or corn oil ] and Leydig cells were isolated from the testes of progeny rats at postnatal day (PND) 60. We assessed the expression of transcription factors regulating steroidogenic machinery and the promoter methylation of LHR and AR in the Leydig cells. Our results confirmed hypermethylation of SF-1, Sp1/3, LHR and AR genes. There was a significant reduction in the gene expression of SF-1 and Sp1. The mRNA expression of Sp3 was decreased. Interestingly, there was an increased gene expression levels of DNA methyltransferases (Dnmts) (Dnmt1, Dnmt3a/b and Dnmt3l) and unaltered histone deacetylase-1 (Hdac-1). Furthermore, increased percentage of 5-methylcytosine was observed in PCBs exposed Leydig cells. Taken together, our findings suggest that promoter hypermethylation of SF-1, Sp1/3, LHR and AR could have led to transcriptional repression of these genes in Leydig cells. In conclusion, our study demonstrates that lactational exposure to PCBs caused epigenetic changes in the Leydig cells which could have impaired the Leydig cell function in progeny (PND60) rats.

Modulation of the transcriptomic profile of the R2C tumor Leydig cell line by the adipose tissue derived hormone leptin

Leptin is an important adipose derived hormone being secreted by adipocytes and involved in appetite regulation. Disruption of normal plasma levels of leptin has been associated with the pathogenesis of obesity. It is now well established that obesity is associated to an increased risk of cancer development, including testicular cancers. Recently, we have shown that high levels of leptin have inhibitory effects on cAMP-dependent steroidogenic genes expression in MA-10 Leydig cells. Hence, we examined if leptin could alter the transcriptome of the constitutively steroidogenic rat tumor Leydig cell line R2C. These cells were treated with high levels of leptin (1000 ng/ml) for 4 h, followed by mRNA extraction and RNA-Seq analysis. Interestingly, leptin had no effect on steroidogenic gene expression or pathways promoting tumorigenesis of this cell line. Genes being upregulated or downregulated by leptin were enriched in biological processes that were non-relevant to Leydig cell function. Surprisingly, lepr isoforms were weakly expressed in R2C cells and may explain in part the low levels of leptin's response for tumor Leydig cells. Hence, the current findings suggest that acute treatments of tumor Leydig cells with high levels of leptin have negligible effects on transcriptomics and rather supports that leptin would have a central effect on the hypothalamus to influence testicular function.

Glucocorticoid Receptor as a Potential Target to Decrease Aromatase Expression and Inhibit Leydig Tumor Growth

Leydig cell tumors are the most frequent interstitial neoplasms of the testis with increased incidence in recent years. They are hormonally active and are considered one of the steroid-secreting tumors. Although usually benign, the malignant phenotype responds poorly to conventional chemotherapy or radiation, highlighting the need to identify new therapeutic targets for treatment. Here, we identified a novel glucocorticoid-mediated mechanism that controls cell growth in Leydig cell tumors. We found that a synthetic glucocorticoid receptor agonist, dexamethasone, reduces cell proliferation in rat Leydig tumor cells by decreasing the expression and the enzymatic activity of the estrogen-producing enzyme aromatase. This inhibitory effect relies on the ability of activated glucocorticoid receptor to regulate the aromatase gene transcriptional activity through the recruitment of nuclear receptor corepressor protein and silencing mediator of retinoid and thyroid hormone receptors to a newly identified putative glucocorticoid responsive element within the aromatase promoter II. Our in vivo studies reveal a reduction of tumor growth, after dexamethasone treatment, in animal xenografts. Tumors from dexamethasone-treated mice exhibit a decrease in the expression of the proliferation marker Ki-67 and the aromatase enzyme. Our data demonstrate that activated glucocorticoid receptor, decreasing aromatase expression, induces Leydig tumor regression both in vitro and in vivo, suggesting that glucocorticoid receptor might be a potential target for the therapy of Leydig cell tumors.

Expression Patterns of CREBs in Oocyte Growth and Maturation of Fish

In fish, oocyte meiotic maturation is regulated by 17α, 20β-dihydroxy-progesterone through cAMP. To study the role of cAMP response element binding protein (CREB) in meiotic maturation, we cloned and characterized the expression pattern of CREBs from two fish models, the Nile tilapia and catfish. In the Nile tilapia three different CREBs were identified where in CREB1 was found in many tissues including gonads with abundant expression in testis. CREB2, few amino acids shorter than CREB1, was expressed in several tissues with abundant expression in ovary. In addition, a 3’UTR variant form, CREB3 was exclusively found in ovary. During natural 14-day ovarian cycle of the Nile tilapia, CREB1 expression was stable throughout vitellogenesis with a sharp decrease on the day of spawning. In contrast, CREB2 remain unchanged throughout the ovarian cycle, however elevated in 11-day full-grown immature ovarian follicle and after hCG-induction. Interestingly, CREB3 expression was induced three folds on the day of spawning as well as during hCG-induced oocyte maturation. Based on the synergistic expression pattern, CREB1 is likely to control oocyte growth, whereas CREB 2 and 3 contribute to oocyte maturation in tilapia and the latter seems to be critical. In catfish, a single form of CREB showed a maximum expression during spawning phase and hCG-induced maturation both in vivo and in vitro augmented CREB expression. These results suggest that spatial and temporal expression of CREBs seems to be important for final oocyte maturation and may also regulate oocyte growth in fish.

Gonadotropins in European sea bass: Endocrine roles and biotechnological applications

Follicle stimulating hormone (Fsh) and luteinizing hormone (Lh) are central endocrine regulators of the gonadal function in vertebrates. They act through specific receptors located in certain cell types found in the gonads. In fish, the differential roles of these hormones are being progressively elucidated due to the development of suitable tools for their study. In European sea bass (Dicentrarchus labrax), isolation of the genes coding for the gonadotropin subunits and receptors allowed in first instance to conduct expression studies. Later, to overcome the limitation of using native hormones, recombinant dimeric gonadotropins, which show different functional characteristics depending on the cell system and DNA construct, were generated. In addition, single gonadotropin beta-subunits have been produced and used as antigens for antibody production. This approach has allowed the development of detection methods for native gonadotropins, with European sea bass being one of the few species where both gonadotropins can be detected in their native form. By administering recombinant gonadotropins to gonad tissues in vitro, we were able to study their effects on steroidogenesis and intracellular pathways. Their administration in vivo has also been tested for use in basic studies and as a biotechnological approach for hormone therapy and assisted reproduction strategies. In addition to the production of recombinant hormones, gene-based therapies using somatic gene transfer have been offered as an alternative. This approach has been tested in sea bass for gonadotropin delivery in vivo. The hormones produced by the genes injected were functional and have allowed studies on the action of gonadotropins in spermatogenesis.

Early methyl donor deficiency alters cAMP signaling pathway and neurosteroidogenesis in the cerebellum of female rat pups

Early deficiency of the methyl donors folate and vitamin B12 produces hyperhomocysteinemia and cognitive and motor disorders in 21-day-old rat pups from dams fed a diet deficient in methyl donors during gestation and lactation. These disorders are associated with impaired neurogenesis and altered synaptic plasticity in cerebellum. We aimed to investigate whether these disorders could be related to impaired expression of neurosteroidogenesis-associated proteins, key regulator receptors, and some steroid content in the cerebellum. The methyl donor deficiency produced a decreased concentration of folate and vitamin B12, along with accumulation of homocysteine in Purkinje cells in both sexes, whereas the S-adenosylmethionine/S-adenosylhomocysteine ratio was reduced only in females. The transcription level and protein expression of StAR, aromatase, ERα, ERβ, and LH receptors were decreased only in females, with a marked effect in Purkinje cells, as shown by immunohistochemistry. Consistently, reduced levels of estradiol and pregnenolone were measured in cerebellar extracts of females only. The decreased expression levels of the transcriptional factors CREB, phospho-CREB, and SF-1, the lesser increase of cAMP concentration, and the lower level of phospho-PKC in the cerebellum of deficient females suggest that the activation of neurosteroidogenesis via cAMP-mediated signaling pathways associated with LHR activation would be altered. In conclusion, a gestational methyl donor deficiency impairs neurosteroidogenesis in cerebellum in a sex-dependent manner.

Aromatase induction in tamoxifen-resistant breast cancer: Role of phosphoinositide 3-kinase-dependent CREB activation

Estrogens are important for the development and growth of estrogen receptor (ER)-positive breast cancer, for which anti-estrogen therapy is one of the most effective treatments. However, its efficacy can be limited by either de novo or acquired resistance. Aromatase is a key enzyme for the biosynthesis of estrogens, and inhibition of this enzyme leads to profound hypoestrogenism. Here, we found that the basal expression and activity of aromatase were significantly increased in tamoxifen (TAM)-resistant human breast cancer (TAMR-MCF-7) cells compared to control MCF-7 cells. We further revealed that aromatase immunoreactivity in tumor tissues was increased in recurrence group after TAM therapy compared to non-recurrence group after TAM therapy. Phosphorylation of Akt, extracellular signal-regulated kinase (ERK), and p38 kinase were all increased in TAMR-MCF-7 cells. Inhibition of phosphoinositide 3-kinase (PI3K) suppressed the transactivation of the aromatase gene and its enzyme activity. Furthermore, we have also shown that PI3K/Akt-dependent cAMP-response element binding protein (CREB) activation was required for the enhanced expression of aromatase in TAMR-MCF-7 cells. Our findings suggest that aromatase expression is up-regulated in TAM-resistant breast cancer via PI3K/Akt-dependent CREB activation.

Functional Importance of 1α,25(OH)2-Vitamin D3 and the Identification of Its Nongenomic and Genomic Signaling Pathways in the Testis

The 1α,25(OH)2-vitamin D3 (1,25-D3) is known by its classic effects on Ca2+ metabolism and regulation of cellular proliferation and differentiation. The hormone 1,25-D3 acts in the testis through nongenomic and genomic events being implicated in the success of spermatogenesis in rats and in human being. The aim of this review was to highlight the effect and intracellular pathways of 1,25-D3 to modulate the spermatogenesis. The pivotal role of 1,25-D3 in male reproduction is reinforced by the presence of VDR and 1α-hydroxylase in reproductive tract. Also, the marked expression of VDR and the VD metabolizing enzymes in human testis, ejaculatory tract, and mature spermatozoa implicates the 1,25-D3 in spermatogenesis and maturation of human spermatozoa. Among genomic events, 1,25-D3 influences the expression of calcium binding protein and stimulates aromatase gene expression through a nongenomic activation of the membrane-bound VDR receptor involving the PKA pathway in the testis. Also, 1,25-D3 stimulates amino acid transport and exocytosis in testis by nongenomic events coupled to ionic currents triggered at plasma membrane. All together, the demonstration that 1,25-D3 regulates both Sertoli cell and sperm function may be useful for the study and development of new therapeutic strategies for the male reproductive disorders.

Steroidogenic factor 1 promotes aggressive growth of castration-resistant prostate cancer cells by stimulating steroid synthesis and cell proliferation

The dependence of prostate cancer on androgens provides a targeted means of treating advanced disease. Unfortunately, androgen deprivation therapies eventually become ineffective, leading to deadly castration-resistant prostate cancer (CRPC). One of many factors implicated in the transition to CRPC is the onset of de novo steroidogenesis. Although reactivation of steroid receptors likely plays a pivotal role in aggressive CRPC, little is understood regarding the mechanisms whereby prostate cancer cells initiate and maintain steroidogenesis. We hypothesize that steroidogenic factor 1 (SF1, NR5A1, AD4BP), a key regulator of steroidogenesis in normal endocrine tissues, is expressed in CRPC where it stimulates aberrant steroidogenesis and fuels aggressive growth. Notably, SF1 is not expressed in normal prostate tissue. Our results indicated that SF1 was absent in benign cells but present in aggressive prostate cancer cell lines. Introduction of ectopic SF1 expression in benign human prostate epithelial cells (BPH-1) stimulated increased steroidogenic enzyme expression, steroid synthesis, and cell proliferation. In contrast, data from an aggressive human prostate cancer cell line (BCaPT10) demonstrated that SF1 was required for steroid-mediated cell growth because BCaPT10 cell growth was diminished by abiraterone treatment and short hairpin RNA-mediated knockdown of SF1 (shSF1). SF1-depleted cells also exhibited defective centrosome homeostasis. Finally, whereas xenograft experiments in castrated hosts with BCaPT10 control transplants grew large, invasive tumors, BCaPT10-shSF1 knockdown transplants failed to grow. Therefore, we conclude that SF1 stimulates steroid accumulation and controls centrosome homeostasis to mediate aggressive prostate cancer cell growth within a castrate environment. These findings present a new molecular mechanism and therapeutic target for deadly CRPC.

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

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

Elevated levels of the steroidogenic factor 1 are associated with over-expression of CYP19 in an oestrogen-producing testicular Leydig cell tumour

BACKGROUND AND OBJECTIVES

Testicular Leydig cell tumours (LCTs) are rare, steroid-secreting tumours. Elevated levels of aromatase (CYP19 or CYP19A1) mRNA have been previously described in LCTs; however, little is known about the mechanism(s) causing CYP19 over-expression. We report an LCT in a 29-year-old male with elevated plasma oestradiol caused by enhanced CYP19 transcription.

DESIGN AND METHODS

First, we measured the intra-tumour expression of CYP19 and determined the use of CYP19 promoters by qPCR. Secondly, we explored CYP19 and promoter II (PII) for gene amplifications and activating mutations in PII by sequencing. Thirdly, we analysed intra-tumour expression of steroidogenic factor 1 (SF-1 (NR5A1)), liver receptor homologue-1 (LRH-1 (NR5A2)) and cyclooxygenase-2 (COX2 (PTGS2)). Finally, we analysed SF-1 for promoter mutations and gene amplifications.

RESULTS

Similar to what has been recorded in normal Leydig cells, we first found the bulk of tumour CYP19 transcripts to be PII derived, excluding promoter shift as a cause of enhanced transcription. Secondly, we excluded CYP19 and PII gene amplifications, and activating mutations in PII, as causes of elevated CYP19 mRNA. We found SF-1 mRNA to be up-regulated in the tumour, while LRH-1 and COX2 were down-regulated. The finding of elevated SF-1 levels in the tumour was confirmed by immunohistochemistry. The elevated level of SF-1 was not due to promoter mutations or amplifications of the SF-1 gene.

CONCLUSIONS

Our results strongly suggest that the elevated levels of SF-1 have induced PII-regulated CYP19 transcription in this tumour. These findings are of relevance to the understanding of CYP19 up-regulation in general, which may occur in several tissues, including breast cancer.

Teasing out the role of aromatase in the healthy and diseased testis

Scientific discoveries over the past decade have shifted the stereotypical view of androgens as male hormones and estrogens as female hormones. It is now recognized that a delicate balance of both androgens and estrogens, a process controlled by aromatase, is fundamental for normal testicular development and fertility. While the site-specific actions of these two classes of steroids within the testis are becoming better documented, the role and regulation of estrogen biosynthesis by aromatase within the testis remains unclear. The majority of data comes from a wide range of animal species, particularly genetically modified mouse models; aromatase knockout (ArKO) and overexpressing (AROM(+)), with limited information on humans, however the existence of congenital aromatase mutations has provided some insight into its effects on individual parameters of the testis. This review dissects out the localization and activity of aromatase in the healthy and diseased testis, addresses the cellular insult to the testis that occurs in its absence and over abundance and proposes potential molecular mechanisms of aromatase regulation in the testis.

Intrauterine growth restriction alters hippocampal expression and chromatin structure of Cyp19a1 variants

We evaluated the impact of uteroplacental insufficiency (UPI), and subsequent intrauterine growth restriction (IUGR), on serum testosterone and hippocampal expression of Cyp19a1 variants and aromatase in rats. Additionally, we determined UPI induced histone modification of the promoter regions of Cyp19a1 variants using chromatin immunoprecipitation. Cyp19a1 is the gene encoding the protein aromatase, that catalyzes the biosynthesis of estrogens from androgens and is necessary for masculinization of the brain. IUGR was induced via bilateral uterine artery. UPI increased serum testosterone in day of life 0 (D(0)) and day of life 21 (D(21)) IUGR males to 224% and 299% of control values, respectively. While there was no significant impact of UPI on testosterone in D(0) females, testosterone in D(21) IUGR females was 187% of controls. Cyp19a1 variant 1.f and variant II are expressed in the rat hippocampus at D(0) and D(21). UPI significantly reduced expression of Cyp19a1 variant 1.f in D(0) males, with no impact in females. Similarly at D(0), UPI reduced expression of aromatase, the protein encoded by Cyp19a1, in males. Dimethylation of H3K4 was increased in the promoter region of variant 1.f (P1.f) and trimethylation of H3K4 was decreased in the promoter region of variant II (PII). At D(21), dimethylation of H3K4 is significantly reduced in PII of IUGR males. We conclude that UPI increases serum testosterone and reduces Cyp19a1 variant 1.f expression in the hippocampus of D(0) IUGR males. Additionally, UPI alters the chromatin structure of CYP19a1 at both D(0) and D(21).

Oestrogens and spermatogenesis

The role of oestrogens in male reproductive tract physiology has for a long time been a subject of debate. The testis produces significant amounts of oestrogenic hormones, via aromatase, and oestrogen receptors (ERs)alpha (ESR1) and ERbeta (ESR2) are selectively expressed in cells of the testis as well as the epididymal epithelium, depending upon species. This review summarizes the current knowledge concerning the presence and activity of aromatase and ERs in testis and sperm and the potential roles that oestrogens may have in mammalian spermatogenesis. Data show that physiology of the male gonad is in part under the control of a balance of androgens and oestrogens, with aromatase serving as a modulator.

The role of cyclooxygenase-2-dependent signaling via cyclic AMP response element activation on aromatase up-regulation by o,p'-DDT in human breast cancer cells

o,p'-Dichlorodiphenyltrichloroethane (o,p'-DDT) is a DDT isomer and xenoestrogen that can induce inflammation and cancer. However, the effect of o,p'-DDT on aromatase is unclear. Thus, we investigated the effects of o,p'-DDT on aromatase expression in human breast cancer cells. We also examined whether cyclooxygenase-2 (COX-2) is involved in o,p'-DDT-mediated aromatase expression. Treatment with o,p'-DDT-induced aromatase protein expression in MCF-7 and MDA-MB-231 human breast cancer cells; enhancing aromatase gene expression, and enzyme and promoter activity. Treatment with ICI 182.780, a estrogen receptor antagonist, did not affect the inductive effects of o,p'-DDT on aromatase expression. In addition, o,p'-DDT increased COX-2 protein levels markedly, increased COX-2 mRNA expression and promoter activity, enhanced the production of prostaglandin E(2) (PGE(2)), induced cyclic AMP response element (CRE) activation, and cAMP levels and binding of CREB. o,p'-DDT also increased the phosphorylation of PKA, Akt, ERK, and JNK in their signaling pathways in MCF-7 and MDA-MB-231 cells. Finally, o,p'-DDT induction of aromatase was inhibited by various inhibitors [COX-2 (by NS-398), PKA (H-89), PI3-K/Akt (LY 294002), EP2 (AH6809), and EP4 receptor (AH23848)]. Together, these results suggest that o,p'-DDT increases aromatase, and that o,p'-DDT-induced aromatase is correlated with COX-2 up-regulation, mediated via the CRE activation and PKA and PI3-kinase/Akt signaling pathways in breast cancer cells.

Androgen receptor of the frog Rana rugosa: molecular cloning and its characterization

The androgen receptor(AR) gene is located on the Z and W sex chromosomes in the frog Rana rugosa, designated Z- and W-AR, respectively. Among various tissues of an adult frog, AR expression levels were highest in the testis and brain. In the testis, AR was expressed in germ cells. AR expression occured in developing embryos from stage 21 and was very high in the gonad of a male tadpole before the onset of sex determination. When Z- and W-AR were expressed in Xenopus A6 cells, they activated androgen-dependent transcription of a luciferase reporter gene. By contrast, estrogen receptor (ER) alpha and beta showed no sexually dimorphic expression during sex determination, but their expressions became much higher in the gonad of a female tadpole after sex determination. In addition, AR transcripts in the ZZ-tadpoles were twice as abundant as in the ZW genotype. In contrast, W-AR expression was extremely low although when W-AR was expressed in A6 cells, it activated transcription in the luciferase assay. In this regard it is worth noting that the promoter regions of Z- and W-AR are not identical. The results suggest that Z-AR plays an important role in the testis formation in a R. rugosa tadpole, whereas ERbeta is involved in ovary differentiation. Very low expression of W-AR may be due to its promoter region having mutations in key transcription factor binding sites, although these remain to be identified. Thus, it is proposed that AR could be a candidate for a male-determining gene in R. rugosa.

Doublesex- and Mab-3-related transcription factor-1 repression of aromatase transcription, a possible mechanism favoring the male pathway in tilapia

Doublesex- and Mab-3-related transcription factor-1 (Dmrt1) is an important transcription factor implicated in early testicular differentiation in vertebrates, but its target genes are largely unknown. In the Nile tilapia, estrogen is the natural inducer of ovarian differentiation. Our recent studies have shown that Forkhead-l2 up-regulated transcription of the Cyp19a1a gene (aromatase) in the gonads in a female-specific manner. However, the upstream factor(s) down-regulating Cyp19a1a expression during testicular differentiation remains unclear. In the present study, we used in vitro (promoter analysis) and in vivo (transgenesis and in situ hybridization) approaches to examine whether Dmrt1 inhibits Cyp19a1a's transcriptional activity. The in vitro analysis using luciferase assays revealed that Dmrt1 repressed basal as well as Ad4BP/SF-1-activated Cyp19a1a transcription in HEK 293 cells. Luciferase assays with various deletions of Dmrt1 also showed that the Doublesex and Mab-3 domain is essential for the repression. In vitro-translated Dmrt1 and the nuclear extract from tilapia testis could directly bind to the palindrome sequence ACATATGT in the Cyp19a1a promoter, as determined by EMSAs. Transgenic overexpression of Dmrt1 in XX fish resulted in decreased aromatase gene expression, reduced serum estradiol-17beta levels, retardation of the ovarian cavity's development, varying degrees of follicular degeneration, and even a partial to complete sex reversal. Our results indicate that aromatase is one of the targets of Dmrt1. Dmrt1 suppresses the female pathway by repressing aromatase gene transcription and estrogen production in the gonads of tilapia and possibly other vertebrates.

Farnesoid X receptor, through the binding with steroidogenic factor 1-responsive element, inhibits aromatase expression in tumor Leydig cells

The farnesoid X receptor (FXR) is a member of the nuclear receptor superfamily that regulates bile acid homeostasis. It is expressed in the liver and the gastrointestinal tract, but also in several non-enterohepatic tissues including testis. Recently, FXR was identified as a negative modulator of the androgen-estrogen-converting aromatase enzyme in human breast cancer cells. In the present study we detected the expression of FXR in Leydig normal and tumor cell lines and in rat testes tissue. We found, in rat Leydig tumor cells, R2C, that FXR activation by the primary bile acid chenodeoxycholic acid (CDCA) or a synthetic agonist GW4064, through a SHP-independent mechanism, down-regulates aromatase expression in terms of mRNA, protein levels, and its enzymatic activity. Transient transfection experiments, using vector containing rat aromatase promoter PII, evidenced that CDCA reduces basal aromatase promoter activity. Mutagenesis studies, electrophoretic mobility shift, and chromatin immunoprecipitation analysis reveal that FXR is able to compete with steroidogenic factor 1 in binding to a common sequence present in the aromatase promoter region interfering negatively with its activity. Finally, the FXR-mediated anti-proliferative effects exerted by CDCA on tumor Leydig cells are at least in part due to an inhibition of estrogen-dependent cell growth. In conclusion our findings identify for the first time the activators of FXR as negative modulators of the aromatase enzyme in Leydig tumor cell lines.

Inhibition of cyclooxygenase-2 down-regulates aromatase activity and decreases proliferation of Leydig tumor cells

Our recent studies have revealed that estrogens stimulate an autocrine mechanism determining Leydig tumor cell proliferation. Estrogen overproduction is due to an elevated steroidogenic factor-1 (SF-1) expression and cAMP-response element-binding protein (CREB) phosphorylation, both inducing aromatase overexpression. Although we have shown that increased SF-1 expression depends mainly on higher local insulin-like growth factor I production, the mechanisms and factors determining increased CREB activation in Leydig tumor cells are not completely understood. In this study, we investigated the role of cyclooxygenase-2 (COX-2) in CREB dependent-aromatase expression in Leydig tumor cells. We found that COX-2 is expressed in rat and human Leydigiomas as well as in the rat Leydig tumor cell line R2C, but not in normal testis. Our data indicate that in R2C cells the COX-2-derived prostaglandin E2 (PGE2) binds the PGE2 receptor EP4 and activates protein kinase A (PKA) and ultimately CREB. Inhibitors for COX-2 (NS398), EP4 (AH23848), and PKA (H89) decreased aromatase expression and activity as a consequence of a decreased phosphorylated CREB recruitment to the PII promoter of the aromatase gene. The COX-2/PGE2/PKA pathway also seems to be involved in aromatase post-translational activation, an observation that requires further studies. The reduction in aromatase activity was responsible for a drop in estrogen production and subsequent reduction in cyclin E expression resulting in a decrease in tumor Leydig cell proliferation. Furthermore, COX-2 silencing caused a significant decrease in CREB phosphorylation, aromatase expression, and R2C cell proliferation. These novel findings clarify the mechanisms involved in the growth of Leydig cell tumors and should be taken into account in determining new therapeutic approaches.

Insulin-like growth factor-I, regulating aromatase expression through steroidogenic factor 1, supports estrogen-dependent tumor Leydig cell proliferation

The aim of this study was to investigate the role of estrogens in Leydig cell tumor proliferation. We used R2C rat Leydig tumor cells and testicular samples from Fischer rats with a developed Leydig tumor. Both experimental models express high levels of aromatase and estrogen receptor alpha (ERalpha). Treatment with exogenous 17beta-estradiol (E(2)) induced proliferation of R2C cells and up-regulation of cell cycle regulators cyclin D1 and cyclin E, the expression of which was blocked by addition of antiestrogens. These observations led us to hypothesize an E(2)/ERalpha-dependent mechanism for Leydig cell tumor proliferation. In determining the molecular mechanism responsible for aromatase overexpression, we found that total and phosphorylated levels of transcription factors cyclic AMP-responsive element binding protein and steroidogenic factor 1 (SF-1) were higher in tumor samples. Moreover, we found that tumor Leydig cells produce high levels of insulin-like growth factor I (IGF-I), which increased aromatase mRNA, protein, and activity as a consequence of increased total and phosphorylated SF-1 levels. Specific inhibitors of IGF-I receptor, protein kinase C, and phosphatidylinositol 3-kinase determined a reduction in SF-1 expression and in IGF-I-dependent SF-1 recruitment to the aromatase PII promoter. The same inhibitors also inhibited aromatase expression and activity and, consequently, R2C cell proliferation. We can conclude that one of the molecular mechanisms determining Leydig cell tumorigenesis is an excessive estrogen production that stimulates a short autocrine loop determining cell proliferation. In addition, cell-produced IGF-I amplifies estrogen signaling through an SF-1-dependent up-regulation of aromatase expression. The identification of this molecular mechanism will be helpful in defining new therapeutic approaches for Leydig cell tumors.

Prostaglandin E2 increases cyp19 expression in rat granulosa cells: implication of GATA-4

The expression of Cyp19, the key gene of estrogen biosynthesis, in granulosa cells (GC) is essential for follicular growth and coordination of the ovulatory process. The goal of this study was to examine the effect of PGE2 and PGF2alpha on Cyp19 expression in undifferentiated and luteinized GC (UGC and LGC). In UGC, PGE2 increased Cyp19 mRNA and Cyp19 protein levels whereas PGF2alpha had no effect. In LGC, PGF2alpha decreased Cyp19 expression whereas PGE2 had no effect. Gene-reporter experiments demonstrated that PGE2 increases Cyp19 transcription in UGC. A protein kinase A inhibitor blocked PGE2-induced increase in Cyp19 promoter activity. PGE2 increased GATA-4 binding to the Cyp19 promoter. Mutation of the GATA binding site resulted in the loss of PGE2 stimulation. This study demonstrates that PGE2 stimulates Cyp19 expression in rat GC and suggests that GATA-4 may mediate (at least in part) the stimulatory effect of PGE2.

Foxl2 up-regulates aromatase gene transcription in a female-specific manner by binding to the promoter as well as interacting with ad4 binding protein/steroidogenic factor 1

Increasing evidence suggests the crucial role of estrogen in ovarian differentiation of nonmammalian vertebrates including fish. The present study has investigated the plausible role of Foxl2 in ovarian differentiation through transcriptional regulation of aromatase gene, using monosex fry of tilapia. Foxl2 expression is sexually dimorphic, like Cyp19a1, colocalizing with Cyp19a1 and Ad4BP/SF-1 in the stromal cells and interstitial cells in gonads of normal XX and sex-reversed XY fish, before the occurrence of morphological sex differentiation. Under in vitro conditions, Foxl2 binds to the sequence ACAAATA in the promoter region of the Cyp19a1 gene directly through its forkhead domain and activates the transcription of Cyp19a1 with its C terminus. Foxl2 can also interact through the forkhead domain with the ligand-binding domain of Ad4BP/SF-1 to form a heterodimer and enhance the Ad4BP/SF-1 mediated Cyp19a1 transcription. Disruption of endogenous Foxl2 in XX tilapia by overexpression of its dominant negative mutant (M3) induces varying degrees of testicular development with occasional sex reversal from ovary to testis. Such fish display reduced expression of Cyp19a1 as well as a drop in the serum levels of 17beta-estradiol and 11-ketotestosterone. Although the XY fish with wild-type tilapia Foxl2 (tFoxl2) overexpression never exhibited a complete sex reversal, there were significant structural changes, such as tissue degeneration, somatic cell proliferation, and induction of aromatase, with increased serum levels of 17beta-estradiol and 11-ketotestosterone. Altogether, these results suggest that Foxl2 plays a decisive role in the ovarian differentiation of the Nile tilapia by regulating aromatase expression and possibly the entire steroidogenic pathway.

The expression of aromatase in gonadotropes is regulated by estradiol and gonadotropin-releasing hormone in a manner that differs from the regulation of luteinizing hormone

The role of estrogens is dual: they suppress basal expression of gonadotropins and enhance GnRH responsiveness at the time of the LH surge. Estrogens are synthesized by cytochrome P450 aromatase (P450arom), encoded by the cyp19 gene. We focused on the cyp19 gene in rat and showed that it is expressed in gonadotropes through promoters PII and PI.f, using RT-PCR and dual fluorescence labeling with anti-P450arom and -LH antibodies. Real-time PCR quantification revealed that aromatase mRNA levels varied during the estrous cycle and were significantly increased after ovariectomy. This effect is prevented by estradiol (E2) as well as GnRH antagonist administration, suggesting that GnRH may mediate the steroid effect. Interestingly, the long-acting GnRH agonist that induces LH desensitization does not modify aromatase expression in ovariectomized rats. Administration of E2 in ovariectomized rats receiving either GnRH agonist or GnRH antagonist clearly demonstrated that E2 also reduces cyp19 expression at the pituitary level. The selective estrogen receptor-alpha ligand propyl pyrazole triol and the selective estrogen receptor-beta ligand diarylpropionitrile both mimic the E2 effects. By contrast, propyl pyrazole triol reduces LH beta expression whereas diarylpropionitrile does not. In addition, using transient transfection assays in an L beta T2 gonadotrope cell line, we provided evidence that GnRH agonist stimulated, in a dose-dependant manner, cyp19 promoters PII and PI.f and that E2 decreased the GnRH stimulation. In conclusion, our data demonstrate that GnRH is an important signal in the regulation of cyp19 in gonadotrope cells. Both common and specific intracellular factors were responsible for dissociated variations of LH beta and cyp19 expression.

Aromatase in testis: expression and role in male reproduction

The mammalian testis serves two main functions: production of spermatozoa and synthesis of steroids, among them estrogens are the end products obtained from the irreversible transformation of androgens by aromatase (P450arom). In the rat the pattern of P450arom expression differs among the testicular somatic cell types according to age; in addition, we have shown that gonocytes, spermatogonia, spermatocytes (preleptotene, pachytene), spermatids and spermatozoa, represent an important source of estrogens; the expression of aromatase is three-fold higher in pachytene spermatocyte (PS) compared to gonocytes. In man both Leydig cells and immature germ cells (PS and round spermatids, RS) as well as ejaculated spermatozoa expressed a biologically active aromatase revealed as a single band of 49 kDa on western blots. Up today P450arom has been demonstrated in male germ cells of all mammals so far studied (mice, bank vole, bear and monkey). The aromatase gene is highly conserved and is unique in humans; its expression is regulated in a cell-specific manner via the alternative use of various promoters located in the first exon. Nevertheless, data concerning the regulation of P450arom especially in germ cells are scarce. We have demonstrated that TGFbeta inhibits the expression of Cyp19 in PS and RS via the SMAD pathway although TNFalpha exerts a stimulatory role in PS, which is amplified in presence of dexamethasone. It is noteworthy that dexamethasone alone exerts a positive effect on Cyp19 expression in PS and a negative one in RS. Cyclic AMP is also a positive regulator of P450arom gene expression in germ cells. In addition, we have shown that androgens and estrogens modulate Cyp19 gene expression, whatever the testicular cell type studied, which favored the presence of androgens and estrogens responsive elements on the Cyp19 gene promoter(s). Moreover, in presence of seminiferous tubules conditioned media, the amount of aromatase transcripts is increased in Leydig cells, therefore, suggesting that other locally produced modulators are involved in the regulation of the aromatase gene expression and among them the liver receptor homolog-1 (LRH-1) from germ cells origin is concerned. Using RACE-PCR we have confirmed that promoter II directs the expression of aromatase gene, whatever the testicular cell type studied in the rat but the involvement of another promoter, such as PI.4 is suggested. Finally, the aromatase gene is constitutively expressed both in somatic and germ cells of the testis and the identification of the promoter(s) concerned as well as their detailed regions which direct(s) the expression of Cyp19 gene is obviously very important but largely unknown especially according to the ontogeny of the male gonad.

CREB binds to multiple loci on human chromosome 22

The cyclic AMP-responsive element-binding protein (CREB) is an important transcription factor that can be activated by hormonal stimulation and regulates neuronal function and development. An unbiased, global analysis of where CREB binds has not been performed. We have mapped for the first time the binding distribution of CREB along an entire human chromosome. Chromatin immunoprecipitation of CREB-associated DNA and subsequent hybridization of the associated DNA to a genomic DNA microarray containing all of the nonrepetitive DNA of human chromosome 22 revealed 215 binding sites corresponding to 192 different loci and 100 annotated potential gene targets. We found binding near or within many genes involved in signal transduction and neuronal function. We also found that only a small fraction of CREB binding sites lay near well-defined 5' ends of genes; the majority of sites were found elsewhere, including introns and unannotated regions. Several of the latter lay near novel unannotated transcriptionally active regions. Few CREB targets were found near full-length cyclic AMP response element sites; the majority contained shorter versions or close matches to this sequence. Several of the CREB targets were altered in their expression by treatment with forskolin; interestingly, both induced and repressed genes were found. Our results provide novel molecular insights into how CREB mediates its functions in humans.

Differential expression of steroidogenic factor-1/adrenal 4 binding protein and liver receptor homolog-1 (LRH-1)/fetoprotein transcription factor in the rat testis: LRH-1 as a potential regulator of testicular aromatase expression

Aromatase converts testicular androgens to estrogens, which are essential for male fertility. Aromatase expression in testis occurs via transcription from promoter II, and requires the presence of a nuclear receptor half-site that binds the orphan receptor steroidogenic factor-1 [SF-1 (nuclear receptor 5A1)] to mediate basal and (in part) cAMP-induced transcription. We hypothesized that liver receptor homolog-1 (LRH-1) (nuclear receptor 5A2), a receptor closely related to SF-1, could also play a role in regulating aromatase expression in the testis. We demonstrate expression of LRH-1 in adult rat and immature mouse Leydig cells (LHR-1 > SF-1) as well as in pachytene spermatocytes and round spermatids but not in Sertoli cells, which in contrast, express high levels of SF-1. In transient transfection assays using TM3 Leydig cells and TM4 Sertoli cells, a rat promoter II luciferase reporter construct was stimulated by cotransfection of LRH-1 expression vector. Mutation analysis showed that induction by LRH-1 in TM3 and TM4 cells requires an AGGTCA motif at position -90, to which LRH-1 bound in gel shift analysis. We therefore provide evidence that LRH-1 plays an important role in the regulation of aromatase expression in Leydig cells. The colocalization of LRH-1 and aromatase to multiple testis cell types suggests that LRH-1 may have important effects on estrogen production, testis development, spermatogenesis, and testicular carcinogenesis.

A benzimidazole fungicide, benomyl, and its metabolite, carbendazim, induce aromatase activity in a human ovarian granulose-like tumor cell line (KGN)

Endocrine disruptor chemicals are known to cause a range of abnormalities in sexual differentiation and reproduction. One mechanism underlying such effects may be via alteration of aromatase activity, which is responsible for estrogen production. A good screening system for identifying endocrine disruptors has long been desired. We have recently established a human ovarian granulosa-like tumor cell line, KGN, which possesses a relatively high level of aromatase expression and is considered a useful mammalian model for investigating the in vitro effects of various chemicals on aromatase activity. In this study we screened 55 different candidate chemicals for endocrine disruptors by assaying aromatase activity. Only benomyl, known as both a benzimidazole fungicide and a microtubule-interfering agent, was found to induce aromatase activity in association with increased levels of aromatase mRNA in KGN cells. The effect of benomyl was presumed to be mediated by its metabolite carbendazim, because it produced an effect equivalent to that of benomyl. The mechanism underlying the benomyl-induced increase in aromatase activity appears independent of the cAMP-protein kinase A pathway. Treatment with taxol, another class of microtubule-interfering agents, also caused induction of aromatase in KGN cells. Both benomyl and taxol changed KGN cell morphology, including the development of cell roundness and a disorganized network of microtubules. These results indicate that benomyl is a potential endocrine disruptor that provides a novel estrogenicity and operates through a microtubule-interfering mechanism.

A shift in steroidogenesis occurring in ovarian follicles prior to oocyte maturation

Gonadotropins (GTHs; FSH and LH) require two major steroidal mediators, estradiol-17 beta (E(2)) and 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17 alpha,20 beta-DP) to act as critical hormones to execute oocyte growth and maturation, respectively. A two-cell type model has been proposed, where the theca cells provide the precursor steroids, and the granulosa cells produce the two steroidal mediators under the direct influence of FSH and LH. A distinct shift in steroidogenesis, i.e. from E(2) to 17 alpha,20 beta-DP as well as the steroidogenic enzyme genes from ovarian cytochrome P450 aromatase (oP450arom) to 20 beta-hydroxysteroid dehydrogenase (20 beta-HSD), occurs in the granulosa layers of ovarian follicles prior to oocyte maturation. The triggering of the steroidogenic shift by GTHs in granulosa cells occurs through the subjugation of Ad4BP/SF-1 expression in respect of oP450arom, followed by an over-expression of 20 beta-HSD probably through the CREB.

The role of the orphan nuclear receptor, liver receptor homologue-1, in the regulation of human corpus luteum 3beta-hydroxysteroid dehydrogenase type II

After ovulation, ovarian 3beta-hydroxysteroid dehydrogenase type II (HSD3B2) expression increases to enhance the shift of steroidogenesis toward progesterone biosynthesis. Steroidogenic factor-1 (SF-1) is a transcription factor for several genes encoding steroidogenic enzymes. However, the level of SF-1 expression decreases in the human corpus luteum (CL) after ovulation. Liver receptor homolog-1 (LRH-1) is another member of the orphan nuclear receptor family. We hypothesize that LRH-1, rather than SF-1, plays an essential role in the regulation of corpus luteum steroidogenesis. Semiquantitative RT-PCR and real-time PCR were performed to quantify the level of LRH-1 expression and correlate with HSD3B2 level. Cell transfection, mutation analysis, and EMSA were performed to examine the role of LRH-1 in the regulation of HSD3B2. LRH-1 expression was higher in CL, compared with mature ovarian follicles. Cotransfection of granulosa cells with HSD3B2 and LRH-1 resulted in a 10-fold increase of transcription. DAX-1 inhibited LRH-1-stimulated HSD3B2, which was maintained in the presence of dibutyryl cAMP. Mutation of the either of the two putative LRH-1 binding sites, which were confirmed by EMSA, in the HSD3B2 promoter decreased LRH-1 stimulation. Our findings suggest that LRH-1 is highly expressed in CL, and it plays an essential role in the regulation of HSD3B2.

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

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

Protein kinase B is obligatory for follicle-stimulating hormone-induced granulosa cell differentiation

Although FSH receptors are linked to the cAMP second messenger system, additional intracellular signaling pathways appear to be required for the induction of aromatase and the LH receptor during granulosa cell differentiation. We employed adenovirus vectors to modulate specific intracellular signaling systems in undifferentiated granulosa cells to identify the signaling pathway(s) that may be involved in the FSH-mediated induction of aromatase and the LH receptor. Expression of either the constitutively activated human LH receptor D578H or the constitutively active human G(s)alpha Q227L resulted in increased cAMP production without increasing aromatase activity or mRNA levels for the LH receptor. To explore the contributions of other pathways, we expressed the constitutively activated forms MAPK kinase (MEK) and protein kinase B (PKB). Neither MEK nor PKB alone increased estrogen or progesterone production by undifferentiated granulosa cells. Stimulation of granulosa cells by FSH in the presence of the constitutively active PKB, but not MEK, led to an amplification of FSH-induced aromatase and LH receptor mRNA levels, whereas a dominant negative PKB vector completely abolished the actions of FSH. The expression of the constitutively active PKB in combination with the constitutively active LH receptor D578H, the constitutively active G(s)alpha Q227L, or 8-bromo-cAMP led to an induction of aromatase as well as LH receptor mRNA comparable to that seen in cells stimulated with FSH alone. These results demonstrate that PKB is an essential component of the FSH-mediated granulosa cell differentiation and that both PKB and G(s)alpha signaling pathways are required.

Regulation of aromatase gene expression in purified germ cells of adult male rats: effects of transforming growth factor beta, tumor necrosis factor alpha, and cyclic adenosine 3',5'-monosphosphate

Estrogens are key regulators of sexual differentiation and development in vertebrates. The P450 aromatase (P450arom) is the steroidogenic enzyme responsible for the synthesis of estrogens from androgens. In the adult rat testis, aromatase transcripts and activity have been observed in somatic cells and germ cells, including pachytene spermatocytes (PS) and round spermatids (RS), but little is known concerning regulation of the aromatase gene expression, especially in germ cells. The quality of germ cell preparations was assessed by the absence of androgen-binding protein and stem cell factor transcripts, two specific markers for Sertoli cells. By employing a competitive quantitative reverse transcriptase-polymerase chain reaction technique, we confirmed that germ cells contained P450arom transcripts and demonstrated that the aromatase gene was up-regulated by cAMP. Conversely, transforming growth factor (TGF) beta1 inhibited Cyp19 gene expression in a dose- and a time-dependent manner in both PS and RS. The addition of tumor necrosis factor (TNF) alpha to purified germ cells induced an increase of the amount of P450arom mRNA in PS, although an inhibitory effect was observed in RS. When PS were treated with dexamethasone (Dex), a similar enhancement of the aromatase transcript level was observed, whereas an inhibitory effect was recorded for RS. Furthermore, in either TGFbeta1- or TNFalpha-treated germ cells, the addition of Dex stimulated the aromatase gene transcription. Experiments using 5' rapid amplification of cDNA ends suggested that promoter PII is mainly concerned in the regulation of the aromatase gene expression in germ cells of adult male rats; however, the presence of other promoters could not be excluded.

Cell selective cAMP induction of rat CYP1B1 in adrenal and testis cells. Identification of a novel cAMP-responsive far upstream enhancer and a second Ah receptor-dependent mechanism

CYP1B1 is unique among P450 cytochromes in exhibiting inductive responses mediated by both the Ah receptor (AhR) and cAMP. cAMP induction was mediated either by a 189bp far upstream enhancer region (FUER, -5110 to -5298) or by a 230bp AhR-responsive enhancer region (AhER) (-797 to -1026). CYP1B1 luciferase reporters respond selectively to cAMP and TCDD in adrenal Y-1 cells (only cAMP), testis MA10 cells (cAMP>TCDD), and C3H10T1/2 mouse embryo fibroblasts (only TCDD). In Y-1 cells, which lack AhR, cAMP induction is totally dependent on the FUER, including absolute requirements for upstream and downstream halves of this region, and for CREB activity at a CRE sequence located at the 3(')-end. cAMP stimulation of the FUER was remarkably high (27-fold) and equally effective when linked to an HSV-TK promoter, indicating direct cAMP activation of the FUER. Binding of CREB to the essential CRE was demonstrated along with dominant negative effects of functionally impaired mutants. cAMP induction in MA10 cells was partially mediated by the FUER mechanism but was regulated additionally by AhER through AhR activity. MA10 cells also exhibit cAMP-dependent AhR down-regulation and AhR/Arnt complex formation. Mutations in AhER including XRE5 were similarly inhibitory to cAMP stimulation in MA10 cells and to TCDD stimulation in C3H10T1/2 cells. Transfection of AhR into the AhR-deficient Y-1 cells did not introduce this second mechanism, which indicated a need for additional components that are present in MA10 cells.

Leydig cell-specific expression of DAX1 improves fertility of the Dax1-deficient mouse

Dax1 is an orphan nuclear receptor expressed in both Leydig and Sertoli cells of the testis. Mutation of DAX1 in humans causes adrenal failure and hypogonadotropic hypogonadism. Targeted mutagenesis of Dax1 in mice reveals a primary gonadal defect characterized by overexpression of aromatase and cellular obstruction of the seminiferous tubules and efferent ductules, leading to germ cell death and infertility. Transgenic expression of DAX1 under the control of the müllerian-inhibiting substance promoter, which is selectively expressed in Sertoli cells, improves fertility but does not fully correct the histological abnormalities in the testes of Dax1 knockout (Dax1KO) mice. We therefore hypothesized that Dax1 may also play a crucial role in other somatic cells of the testis, namely the Leydig cells. A 2.1-kilobase fragment of the murine LH receptor 5'-promoter (LHR-DAX1) was used to generate transgenic mice that selectively express DAX1 in Leydig cells. Expression of the LHR-DAX1 transgene caused no observable phenotype in wild-type mice but improved fertility when expressed in Dax1KO males (rescue [RS]). Although testicular size was not increased in LHR-DAX1 RS animals, aromatase expression was restored to normal levels, and sperm production was increased. Testicular pathology was only slightly improved in RS mice compared to Dax1KO animals. Taken together with the result of previous studies of DAX1 expression in Sertoli cells, we conclude that the testis phenotype of Dax1KO mice reflects the combined effects of Dax1 deficiency in both Sertoli and Leydig cells.

Synergistic expression of Ad4BP/SF-1 and cytochrome P-450 aromatase (ovarian type) in the ovary of Nile tilapia, Oreochromis niloticus, during vitellogenesis suggests transcriptional interaction

Involvement of Ad4BP/SF-1 in the ovarian cytochrome P-450 aromatase (oP450arom) gene expression was investigated using ovarian follicles of the Nile tilapia, possessing an average 14-day spawning cycle. The promoter region (5' flanking region) of oP450arom gene cloned from tilapia contains two Ad4 binding sites. Subsequently, a cDNA encoding Ad4BP/SF-1 was cloned from the ovarian follicles. It is expressed in gonadal tissues, brain, and kidney. Oligonucleotide probes containing putative orphan nuclear receptor binding motifs (derived from promoter region of the aromatase gene) formed complexes with in vitro-translated Ad4BP/SF-1 and nuclear extracts of tilapia ovarian (midvitellogenic) follicles, indicating that Ad4BP/SF-1 is one of the transcriptional regulators for aromatase gene expression. Northern blot analysis revealed that the expression of both oP450arom and Ad4BP/SF-1 increased in parallel with ovarian growth from Day 0 to Day 5 after spawning and declined sharply from Day 8 to Day 11. On the day of spawning (Day 14), the expression of both correlates became undetectable. In vitro incubation of post vitellogenic full-grown immature follicles (corresponding to Day 11 after spawning) with hCG purged both oP450arom and Ad4BP/SF-1 messenger RNA transcripts at 18 h. Conversely, in vitro incubation of late vitellogenic follicles (corresponding to Day 8 after spawning) with hCG retained Ad4BP/SF-1 messenger RNA transcripts more or less steadily and up-regulated oP450arom. Ad4BP/SF-1 probably acts as a transcriptional modulator to implement the paradoxical actions of gonadotropins on oP450arom gene.

Triiodothyronine decreases the activity of the proximal promoter (PII) of the aromatase gene in the mouse Sertoli cell line, TM4

Estrogens and thyroid hormones play a significant role in regulating functions and development of the testis. The synthesis of estrogens from androgens is catalyzed by the enzyme complex termed aromatase, which in the testis displays an age-related cellular compartmentalization, primarily in Sertoli cells in immature animals, whereas in adults it is expressed in Leydig and germ cells. T3 induces a precocious terminal differentiation of prepubertal Sertoli cells together with a dramatic decrease of their aromatase activity. In the present work, we have examined the mechanism by which T3 exerts this inhibitory action on aromatase expression. As an experimental model, we used the mouse Sertoli cell line TM4, which conserves a large spectrum of functional features present in immature Sertoli cells. For instance, after revealing the presence of aromatase by immunocytochemistry and measuring its enzymatic activity, we confirmed in this cell line the functional events previously characterized in primary cultures of immature rat Sertoli cells: 1) a strong stimulation of aromatase activity by dibutyryl-cAMP [(Bu)2cAMP] (simulating FSH action); and 2) the inhibition of aromatase activity by incubation with T3 under basal condition and after (Bu)2cAMP stimulation. After identifying promoter II as the regulatory region located immediately upstream of the transcriptional initiation site in the TM4 cell line by rapid amplification of cDNA ends analysis, we conducted experiments to examine the molecular mechanism by which thyroid hormones modulate aromatase gene expression in this cell line. TM4 cells were transfected with plasmids containing different segments of the rat promoter II sequence ligated to a luciferase reporter gene. Analysis of the activities of these promoter fusions demonstrated that T3 inhibits basal and (Bu)2cAMP-stimulated activity of the aromatase promoter. This effect was not revealed in T3-treated cells transfected with construct in which the steroidogenic factor-1 (SF-1) response element was mutated. These results indicate that the inhibitory effect of T3 requires the integrity of the SF-1 response element and are further supported in the EMSA. The EMSA experiments demonstrated that thyroid hormone/thyroid receptor alpha1 complex (TH/TRalpha1) is able to compete with SF-1 in binding to oligonucleotides containing an SF-1 motif, an element essential for the activity of the PII aromatase promoter. The findings suggest that the binding of the thyroid hormone/thyroid receptor alpha1 complex to the SF-1 motif is the molecular mechanism by which T3 exerts an inhibitory effect on aromatase gene expression in the TM4 cell line.

Regulation of niemann-pick c1 gene expression by the 3'5'-cyclic adenosine monophosphate pathway in steroidogenic cells

The Niemann Pick-C1 (NPC-1) protein is essential for intracellular transport of cholesterol derived from low-density lipoprotein import in mammalian cells. The role of the protein kinase A (PKA) pathway in regulation of expression of the NPC-1 gene was investigated. NPC-1 promoter activity was induced by treatment with dibutryl cAMP (dbcAMP), alone or in combination with the cAMP response element (CRE) binding protein (CREB) overexpressed in adrenal Y-1 cells. When the catalytic subunit of PKA was overexpressed in Y-1 cells, there were similar increases in NPC-1 promoter activity in the presence of CREB. Responses were attenuated by blockade of the PKA pathway, and in the Kin-8 cell line deficient in PKA. Promoter deletion analysis revealed that this response was present in promoter fragments of 186 bp and larger but not present in the 121-bp fragment. Two promoter regions, one at -430 and one at -120 upstream of the translation initiation site, contained CRE consensus sequences. These bound recombinant CREB in EMSA, confirming their authenticity as CREB response elements. Promoters bearing mutations of both CRE displayed no response to dbcAMP. The orphan nuclear receptor, steroidogenic factor-1 (SF-1), was implicated in NPC-1 transactivation by the presence of SF-1 target sequence that formed a complex with recombinant SF-1 in EMSA. Furthermore, transfection of a plasmid that overexpressed SF-1 into ovarian granulosa cells increased promoter activity in response to dbcAMP, an effect abrogated by mutation of the SF-1 target sequence. Chromatin immunoprecipitation assays demonstrated that the CRE region of the endogenous and transfected NPC-1 promoter associated with both acetylated and phosphorylated histone H-3 and that this association was increased by dbcAMP treatment. Treatment with dbcAMP also increased the association of the CRE region of the promoter with CREB binding protein, which has histone acetyltransferase activity. Together, these results demonstrate a mechanism of regulation of NPC-1 expression by the cAMP-PKA pathway that includes PKA phosphorylation of CREB, recruitment of the coactivator CREB binding protein and the phosphorylation and acetylation of histone H-3 to transactivate the NPC-1 promoter.

An alternative promoter of the human neuronal nitric oxide synthase gene is expressed specifically in Leydig cells

Neuronal nitric oxide synthase (nNOS) plays a modulatory role in the biology of a variety of neuroendocrine tissues and is especially relevant to gonadal function. We have previously reported the cloning and characterization of a variant of the nNOS protein, termed testis nNOS (TnNOS), the mRNA for which was restricted in expression to male gonadal tissues. To examine the cell-specificity of the testis-specific NOS regulatory regions we defined patterns of beta-galactosidase expression of an insertional transgene in which the reporter gene lacZ was under the transcriptional control of the human TnNOS promoter. beta-galactosidase activity was detected exclusively in the interstitial cells of the testis in transgenic mice. These cells also evidenced positive staining for nNOS protein and were identified as androgen-producing Leydig cells by staining with the Leydig cell marker, P(450)scc. Expression of the promoter was absent in cells of the seminiferous tubules, specifically germline cells of different stages and Sertoli cells. In contrast to the male gonad, beta-galactosidase activity was not detected in ovaries of adult female mice. Activity was also not evident in organs known to express full-length nNOS, such as skeletal muscle, kidney, or cerebellum. The same pattern of beta-galactosidase staining was observed in independent transgenic founders and was distinct from that observed for an endothelial NOS promoter/reporter transgene. In the testis of male adult eNOS promoter-reporter transgenic mice, beta-galactosidase activity was expressed only in endothelial cells of large- and medium-sized arterial blood vessels. Transcriptional activity of the human TnNOS promoter could not be detected in a variety of cell types, including Leydig cells, using episomal promoter-reporter constructs suggesting that a nuclear environment and higher order genomic complexity are required for appropriate promoter function. The restricted expression pattern of an nNOS variant in Leydig cells of the male gonad suggests an important role in the regulation of testosterone release and represents an intriguing model with which to dissect the molecular basis of Leydig cell-specific gene expression.

Aromatase messenger RNA is derived from the proximal promoter of the aromatase gene in Leydig, Sertoli, and germ cells of the rat testis

It has long been recognized that individual cell types within the testes possess the capacity to synthesize estrogen. A number of studies on different species have demonstrated that the levels of aromatase expression and the patterns of regulation are distinct between the different cell types of the testes. Whereas a variety of promoters have been shown to contribute to the patterns of aromatase expression in different cell lineages, studies using ovarian RNA, testis RNA, and Leydig cell tumor lines have demonstrated that the same promoter (promoter II) was used in each. Recent experiments using potent aromatase inhibitors or analysis of animals in which the genes encoding the estrogen receptor-alpha (ER-alpha) or the aromatase, P450, are defective, have confirmed the importance of local estrogen formation in normal testicular function. In order to permit experiments to identify the elements controlling aromatase expression in the individual cell compartments of the testes, we prepared RNA from purified preparations of Leydig, Sertoli, and germ cells. Using specific oligonucleotide primers, the sites of initiation of the aromatase mRNA were determined using rapid amplification of cDNA ends (RACE) and nucleotide sequence analysis of the resulting cDNA fragments. Our results indicate that aromatase mRNA is derived from the proximal promoter (PII) of the aromatase gene in each of the major cell types of the rat testes.

Hormonal and seminal evaluation of Leydig cell tumour patients before and after orchiectomy

Seven patients (aged 25-38 years) were admitted because of mono- or bilateral gynaecomastia. Plasma levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin, testosterone, 17-beta-estradiol, delta4-androstenedione, dehydropiandrosterone sulphate (DHEA-S) and 17-OH-progesterone were determined and semen analysis was carried out. FSH and LH levels were also measured after acute LH-RH administration (100 microg intravenously), and testosterone and 17-beta-estradiol were also evaluated after acute human chorionic gonadotrophin (hCG) administration (5000 IU intramuscularly). Testicular echography demonstrated the presence of a solid hypoechoic tumour. Therefore all patients were submitted to hemicastration by orchidofuniculotomy and a benign Leydig cell tumour was diagnosed in the removed testes. Hormonal and semen evaluations were repeated 3, 6, 9 and 12 months after surgery. The data before and after surgery were compared with a control group of 10 age-matched males. Before surgery, patients showed low FSH basal plasma levels; high levels of 17-beta-estradiol and low testosterone levels similar to those after hCG administration. A dyspermia was observed. Unilateral orchidectomy eliminated the autonomous secretion of oestrogen(s) so an increase of LH, FSH and testosterone levels, together with an improvement of spermatogenesis, were obtained.