cAMP regulates P450scc gene expression by a cycloheximide-insensitive mechanism in cultured mouse Leydig MA-10 cells

Omega-6 highly unsaturated fatty acids in Leydig cells facilitate male sex hormone production

Highly unsaturated fatty acids (HUFAs) are fatty acids with more than three double bonds in the molecule. Mammalian testes contain very high levels of omega-6 HUFAs compared with other tissues. However, the metabolic and biological significance of these HUFAs in the mammalian testis is poorly understood. Here we show that Leydig cells vigorously synthesize omega-6 HUFAs to facilitate male sex hormone production. In the testis, FADS2 (Fatty acid desaturase 2), the rate-limiting enzyme for HUFA biosynthesis, is highly expressed in Leydig cells. In this study, pharmacological and genetic inhibition of FADS2 drastically reduces the production of omega-6 HUFAs and male steroid hormones in Leydig cells; this reduction is significantly rescued by supplementation with omega-6 HUFAs. Mechanistically, hormone-sensitive lipase (HSL; also called LIPE), a lipase that supplies free cholesterol for steroid hormone production, preferentially hydrolyzes HUFA-containing cholesteryl esters as substrates. Taken together, our results demonstrate that Leydig cells highly express FADS2 to facilitate male steroid hormone production by accumulating omega-6 HUFA-containing cholesteryl esters, which serve as preferred substrates for HSL. These findings unveil a previously unrecognized importance of omega-6 HUFAs in the mammalian male reproductive system.

Leydig cells highly express FADS2 to facilitate male steroid hormone production by accumulating omega-6 HUFA-containing cholesteryl esters, which serve as preferred substrates for hormone-sensitive lipase

Gigantol Improves Cholesterol Metabolism and Progesterone Biosynthesis in MA-10 Leydig Cells

In aging males, androgen production by testicular Leydig cells decreases at a rate of approximately 1% per year. Phenolic compounds may enhance testosterone biosynthesis and delay the onset of male hypogonadism. Gigantol is a bibenzyl compound isolated from several types of orchids of the genus Dendrobium. This compound has various biological activities, including antioxidant activity. However, its capacity to regulate gene expression and steroid production in testicular Leydig cells has never been evaluated. We investigated the effect of gigantol on MA-10 Leydig cells’ gene expression using an RNA-Seq approach. To further investigate the structure-function relationship of the hydroxy-methoxyphenyl moiety of gigantol, experiments were also performed with ferulic acid and isoferulic acid. According to transcriptomic analysis, all genes coding for cholesterol biosynthesis-related enzymes are increased in response to gigantol treatment, resulting in increased lipid droplets accumulation. Moreover, treatments with 10 μM gigantol increased StAR protein levels and progesterone production from MA-10 Leydig cells. However, neither ferulic acid nor isoferulic acid influenced StAR protein synthesis and progesterone production in MA-10 Leydig cells. Thus, our findings indicate that gigantol improves cholesterol and steroid biosynthesis within testicular Leydig cells.

Drp1 Phosphorylation Is Indispensable for Steroidogenesis in Leydig Cells

The initial steps of steroidogenesis occur in the mitochondria. Dynamic changes in the mitochondria are associated with their fission and fusion. Therefore, understanding the cellular and molecular relationships between steroidogenesis and mitochondrial dynamics is important. The hypothesis of the current study is that mitochondrial fission and fusion are closely associated with steroid hormone synthesis in testicular Leydig cells. Steroid hormone production, induced by dibutyryl cAMP (dbcAMP) in Leydig cells, was accompanied by increased mitochondrial mass. Mitochondrial elongation increased during the dbcAMP-induced steroid production, whereas mitochondrial fragmentation was reduced. Among the mitochondrial-shaping proteins, the level of dynamin-associated protein 1 (Drp1) was altered in response to dbcAMP stimulation. The increase in Drp1 Ser 637 phosphorylation correlated with steroid hormone production in the MA-10 Leydig cells as well as in the primary adult rat Leydig cells. Drp1 was differentially expressed in the Leydig cells during testicular development. Finally, gonadotropin administration altered the status of Drp1 phosphorylation in the Leydig cells of immature rat testes. Overall, mitochondrial dynamics is directly linked to steroidogenesis, and Drp1 plays an important regulatory role during steroidogenesis. This study shows that Drp1 level is regulated by cAMP and that its phosphorylation via protein kinase A (PKA) activation plays a decisive role in mitochondrial shaping by offering an optimal environment for steroid hormone biosynthesis in Leydig cells. Therefore, it is suggested that PKA-mediated Drp1 Ser 637 phosphorylation is indispensable for steroidogenesis in the Leydig cells, and this phosphorylation results in mitochondrial elongation via the relative attenuation of mitochondrial fission during steroidogenesis.

Organophosphate Flame Retardants Act as Endocrine-Disrupting Chemicals in MA-10 Mouse Tumor Leydig Cells

The organophosphate flame retardants (OPFRs) have emerged as alternatives to banned brominated flame retardants but little is known about their possible activity as endocrine disruptors. Our goal was to compare the effects of 7 commonly used OPFRsin vitroon MA-10 mouse Leydig tumor cells to those of a major brominated flame retardant, 2,2',4,4'-tetrabromodiphenyl ether (BDE-47). The effects of OPFRs and BDE-47 on mitochondrial activity, cell counts, oxidative stress, steroid secretion and gene expression were investigated. BDE-47 and all 7 OPFRs tested significantly reduced MA-10 cell mitochondrial activity (concentrations ≥50 μM) and cell number (concentrations ≥10 μM). All of the OPFRs significantly increased (10 μM, 1.7-4.4-fold) superoxide production whereas BDE-47 had no significant effect. Basal progesterone production was significantly increased (10 μM, 1.5 to 3-fold) by 2-ethylhexyl diphenyl phosphate, isodecyl diphenyl phosphate, isopropylated triphenyl phosphate, tert-butylphenyl diphenyl phosphate, and tricresyl phosphate, while BDE-47, triphenyl phosphate and tri-o-cresyl phosphate had no effect. Interestingly, isopropylated triphenyl phosphate enhanced dbcAMP-stimulated steroid production (∼2-fold), while tri-o-cresyl phosphate decreased (∼2/3) LH-stimulated steroid production. Several OPFRs affected the expression of genes involved in the biosynthesis of progesterone. In conclusion, all the OPFRs tested affected mitochondrial activity, cell survival, and superoxide production. Basal or stimulated steroid secretion was affected by all of the OPFRs except triphenyl phosphate; BDE-47 had no effect. Hence, the OPFRs currently used as alternatives affect Leydig cells to a greater extent than the brominated flame retardants that they have replaced.

Murine Inhibin α-Subunit Haploinsufficiency Causes Transient Abnormalities in Prepubertal Testis Development Followed by Adult Testicular Decline

Activin production and signaling must be strictly regulated for normal testis development and function. Inhibins are potent activin inhibitors; mice lacking the inhibin-α gene (Inha-/- mice) cannot make inhibin and consequently have highly elevated activin and FSH serum concentrations and excessive activin signaling, resulting in somatic gonadal tumors and infertility. Dose-dependent effects of activin in testicular biology have been widely reported; hence, we hypothesized that male mice lacking one copy of the Inha gene would produce less inhibin and have an abnormal reproductive phenotype. To test this, we compared hormone concentrations, testis development, and sperm production in Inha+/+ and Inha+/- mice. Serum and testicular inhibin-α concentrations in adult Inha+/- mice were approximately 33% lower than wild type, whereas activin A, activin B, FSH, LH, and T were normal. Sixteen-day-old Inha+/- mice had a mixed phenotype, with tubules containing extensive germ cell depletion juxtaposed to tubules with advanced Sertoli and germ cell development. This abnormal phenotype resolved by day 28. By 8 weeks, Inha+/- testes were 11% larger than wild type and supported 44% greater daily sperm production. By 26 weeks of age, Inha+/- testes had distinct abnormalities. Although still fertile, Inha+/- mice had a 27% reduction in spermatogenic efficiency, a greater proportion of S-phase Sertoli cells and lower Leydig cell CYP11A1 expression. This study is the first to identify an intratesticular role for inhibin/inhibin-α subunit, demonstrating that a threshold level of this protein is required for normal testis development and to sustain adult somatic testicular cell function.

Retinoic acid receptor beta and angiopoietin-like protein 1 are involved in the regulation of human androgen biosynthesis

Androgens are essential for sexual development and reproduction. However, androgen regulation in health and disease is poorly understood. We showed that human adrenocortical H295R cells grown under starvation conditions acquire a hyperandrogenic steroid profile with changes in steroid metabolizing enzymes HSD3B2 and CYP17A1 essential for androgen production. Here we studied the regulatory mechanisms underlying androgen production in starved H295R cells. Microarray expression profiling of normal versus starved H295R cells revealed fourteen differentially expressed genes; HSD3B2, HSD3B1, CYP21A2, RARB, ASS1, CFI, ASCL1 and ENC1 play a role in steroid and energy metabolism and ANGPTL1, PLK2, DUSP6, DUSP10 and FREM2 are involved in signal transduction. We discovered two new gene networks around RARB and ANGPTL1, and show how they regulate androgen biosynthesis. Transcription factor RARB stimulated the promoters of genes involved in androgen production (StAR, CYP17A1 and HSD3B2) and enhanced androstenedione production. For HSD3B2 regulation RARB worked in cooperation with Nur77. Secretory protein ANGPTL1 modulated CYP17A1 and DUSP6 expression by inducing ERK1/2 phosphorylation. By contrast, our studies revealed no evidence for hormones or cell cycle involvement in regulating androgen biosynthesis. In summary, these studies establish a firm role for RARB and ANGPTL1 in the regulation of androgen production in H295R cells.

A yeast-based chemical screen identifies a PDE inhibitor that elevates steroidogenesis in mouse Leydig cells via PDE8 and PDE4 inhibition

A cell-based high-throughput screen (HTS) was developed to detect phosphodiesterase 8 (PDE8) and PDE4/8 combination inhibitors. By replacing the Schizosaccharomyces pombe PDE gene with the murine PDE8A1 gene in strains lacking adenylyl cyclase, we generated strains whose protein kinase A (PKA)-stimulated growth in 5-fluoro orotic acid (5FOA) medium reflects PDE8 activity. From our previously-identified PDE4 and PDE7 inhibitors, we identified a PDE4/8 inhibitor that allowed us to optimize screening conditions. Of 222,711 compounds screened, ∼0.2% displayed composite Z scores of >20. Additional yeast-based assays using the most effective 367 compounds identified 30 candidates for further characterization. Among these, compound BC8-15 displayed the lowest IC₅₀ value for both PDE4 and PDE8 inhibition in in vitro enzyme assays. This compound also displays significant activity against PDE10A and PDE11A. BC8-15 elevates steroidogenesis in mouse Leydig cells as a single pharmacological agent. Assays using BC8-15 and two structural derivatives support a model in which PDE8 is a primary regulator of testosterone production by Leydig cells, with an additional role for PDE4 in this process. BC8-15, BC8-15A, and BC8-15C, which are commercially available compounds, display distinct patterns of activity against PDE4, PDE8, PDE10A, and PDE11A, representing a chemical toolkit that could be used to examine the biological roles of these enzymes in cell culture systems.

NGF induces adult stem Leydig cells to proliferate and differentiate during Leydig cell regeneration

Nerve growth factor (NGF) has been reported to be involved in male reproductive physiology. However, few reports have described the activity of NGF during Leydig cell development. The objective of the present study was to examine the role of NGF during stem-Leydig-cell (SLC) regeneration. We investigated the effects of NGF on Leydig-cell (LC) regeneration by measuring mRNA levels in the adult rat testis after ethane dimethanesulfonate (EDS) treatment. Furthermore, we used the established organ culture model of rat seminiferous tubules to examine the regulation of NGF during SLC proliferation and differentiation using EdU staining, real-time PCR and western blotting. Progenitor Leydig cells (PLCs) and immature Leydig cells (ILCs) were also used to investigate the effects of NGF on LCs at different developmental stages. NGF mRNA levels changed significantly during Leydig-cell regeneration in vivo. In vitro, NGF significantly promoted the proliferation of stem Leydig cells and also induced steroidogenic enzyme gene expression and 3β-HSD protein expression. The data from PLCs and ILCs showed that NGF could increase Cyclin D1 and Hsd 17b3 mRNA levels in PLCs and Cyclin D1 mRNA levels in ILCs. These results indicate that NGF may play an important role during LC regeneration by regulating the proliferation and differentiation of LCs at different developmental stages, from SLCs to PLCs and from PLCs to ILCs. The discovery of this effect of NGF on Leydig cells will provide useful information for developing new potential therapies for PADAM (Partial Androgen Deficiency in the Aging Male).

Molecular Mechanism of Isocupressic Acid Supresses MA-10 Cell Steroidogenesis

Consumption of ponderosa pine needles causes late-term abortions in cattle and is a serious poisonous plant problem in foothill and mountain rangelands. Isocupressic acid (IA) is the component of pine needles responsible for the abortifacient effect, its abortifacient effect may be due to inhibition of steroidogenesis. To investigate the more detail molecular mechanism, we used MA-10 cell, which is wild used to investigate molecular mechanism of steroidogenesis, to characterize the molecular mechanisms underlying the actions of IA in more detail. In this report, we focus on the function of IA on important steroidogenic genes, including steroidogenic acute regulatory protein (StAR), cytochrome P450 cholesterol side-chain cleavage (P450scc), and 3β-hydroxysteroid dehydrogenase (3β-HSD). We found that IA does not affect enzyme activities of these genes but inhibits transcription of P450scc and translation of StAR and P450scc through attenuating cAMP-PKA signaling. Thus, steroid productions of cells were suppressed.

The adiponectin paralog C1q/TNF-related protein 3 (CTRP3) stimulates testosterone production through the cAMP/PKA signaling pathway

CTRP3, a paralog of adiponectin, is a member of the C1q and tumor necrosis factor (TNF)-related protein (CTRP) superfamily. It is expressed at high levels in adipose tissue and has recently emerged as a novel adipokine. In the present study, we provide the first evidence for a physiological role of the new adipokine, CTRP3, in the reproductive system. CTRP3 was specifically expressed in interstitial Leydig cells, where testosterone is produced, in the adult mouse testis. CTRP3 increased testosterone production by TM3 mouse Leydig cells in a dose-dependent manner. The increased testosterone production was linked to upregulation of steroidogenic proteins expression, such as steroidogenic acute regulatory (StAR) protein and cholesterol side-chain cleavage cytochrome P450 (P450scc). Moreover, increases in intracellular cyclic AMP (cAMP) concentrations and the phosphorylation of cAMP-response element binding protein (CREB) in CTRP3-stimulated TM3 Leydig cells were observed. Inhibition of this signaling pathway by a specific protein kinase A (PKA) inhibitor, H89, blocked testosterone production in CTRP3-stimulated Leydig cells, suggesting that the stimulatory effect of CTRP3 on testosterone production is associated with activation of the cAMP/PKA signaling pathway. Thus, our results demonstrate a physiological role for CTRP3 in testicular steroidogenesis and provide novel insights in the intracellular mechanisms activated by this protein.

Regulation of cytochrome P450 1B1 expression by luteinizing hormone in mouse MA-10 and rat R2C Leydig cells: role of protein kinase A

In the present study, we investigated the signaling pathway involved in luteinizing hormone (LH)-mediated regulation of testicular CYP1B1 in mouse MA-10 and rat R2C Leydig cells. CYP1B1 mRNA and protein levels were measured in MA-10 and R2C cells treated with LH and protein kinase activators or inhibitors. Treatment with LH or 8-bromo-cAMP, a protein kinase A (PRKA) activator, increased CYP1B1 expression and PRKA activity in a concentration-dependent manner in both cell lines, albeit to different extents. Treatment with 8-(4-chlorophenylthio)adenosine-3',5'-cyclic monophosphorothioate, Rp-isomer, a PRKA inhibitor, decreased basal CYP1B1 expression and attenuated LH-elicited increases in CYP1B1 mRNA and protein levels and PRKA activity. In contrast, treatment with a protein kinase G activator or an inhibitor of protein kinase C had no effect on basal or LH-induced CYP1B1 expression in MA-10 or R2C cells. Collectively, the results identify PRKA as the major signaling pathway involved in the LH-mediated regulation of testicular CYP1B1 expression in Leydig tumor cells.

The molecular biology, biochemistry, and physiology of human steroidogenesis and its disorders

Steroidogenesis entails processes by which cholesterol is converted to biologically active steroid hormones. Whereas most endocrine texts discuss adrenal, ovarian, testicular, placental, and other steroidogenic processes in a gland-specific fashion, steroidogenesis is better understood as a single process that is repeated in each gland with cell-type-specific variations on a single theme. Thus, understanding steroidogenesis is rooted in an understanding of the biochemistry of the various steroidogenic enzymes and cofactors and the genes that encode them. The first and rate-limiting step in steroidogenesis is the conversion of cholesterol to pregnenolone by a single enzyme, P450scc (CYP11A1), but this enzymatically complex step is subject to multiple regulatory mechanisms, yielding finely tuned quantitative regulation. Qualitative regulation determining the type of steroid to be produced is mediated by many enzymes and cofactors. Steroidogenic enzymes fall into two groups: cytochrome P450 enzymes and hydroxysteroid dehydrogenases. A cytochrome P450 may be either type 1 (in mitochondria) or type 2 (in endoplasmic reticulum), and a hydroxysteroid dehydrogenase may belong to either the aldo-keto reductase or short-chain dehydrogenase/reductase families. The activities of these enzymes are modulated by posttranslational modifications and by cofactors, especially electron-donating redox partners. The elucidation of the precise roles of these various enzymes and cofactors has been greatly facilitated by identifying the genetic bases of rare disorders of steroidogenesis. Some enzymes not principally involved in steroidogenesis may also catalyze extraglandular steroidogenesis, modulating the phenotype expected to result from some mutations. Understanding steroidogenesis is of fundamental importance to understanding disorders of sexual differentiation, reproduction, fertility, hypertension, obesity, and physiological homeostasis.

Adrenal glands and testes as steroidogenic tissue are affected by retinoylation reaction

This study was undertaken to better understand the physiological role of the retinoylation process in steroidogenic tissues. In adrenal gland mitochondria, the retinoylation extent was found equal to that of testes mitochondria but without ATP in the incubation buffer. We pointed out that the endogenous mitochondrial ATP in adrenal glands is much higher than in testes, about 1.3 x 10(-2) M and 5.2 x 10(-8) M, respectively. In addition, less CoASH is required for the maximal acylation activity of the retinoyl moiety to protein(s) compared to testes. The fatty acid analysis revealed a different composition of mitochondrial membranes of these two tissues. Among the different values of fatty acids, it is important to note that adrenal glands contain a much higher amount of C18:0 and a much lower amount of C22:5 omega6 and C22:6 omega3 than testes in the mitochondrial membranes. In addition, there were also differences in arachidonic acid (ARA, C20:4 omega6) content between adrenal glands and testes mitochondria. These different values in the fatty acids composition should explain the different extent of the retinoylation process between the two organs.

Transcriptional regulation of steroidogenic genes: STARD1, CYP11A1 and HSD3B

Expression of the genes that mediate the first steps in steroidogenesis, the steroidogenic acute regulatory protein (STARD1), the cholesterol side-chain cleavage enzyme, cytochrome P450scc (CYP11A1) and 3beta-hydroxysteroid dehydrogenase/Delta5-Delta4 isomerase (HSD3B), is tightly controlled by a battery of transcription factors in the adrenal cortex, the gonads and the placenta. These genes generally respond to the same hormones that stimulate steroid production through common pathways such as cAMP signaling and common actions on their promoters by proteins such as NR5A and GATA family members. However, there are distinct temporal, tissue and species-specific differences in expression between the genes that are defined by combinatorial regulation and unique promoter elements. This review will provide an overview of the hormonal and transcriptional regulation of the STARD1, CYP11A1 and specific steroidogenic HSD3B genes in the adrenal, testis, ovary and placenta and discuss the current knowledge regarding the key transcriptional factors involved.

Effects of ACTH and expression of the melanocortin-2 receptor in the neonatal mouse testis

ACTH has been shown to stimulate androgen production by the fetal/neonatal mouse testis through the melanocortin type 2 receptor (MC2R). This study was designed to localize the expression of MC2R in the neonatal mouse testis and characterize the effects of ACTH on testicular androgen production. Using immunohistochemistry, MC2R was localized to the fetal-type Leydig cell population of the neonatal testis. ACTH caused a time-dependent increase in cyclic AMP (cAMP) and testosterone production by isolated cells with an increase in cAMP apparent in < 3 min. There was no additive effect of maximally stimulating doses of ACTH and human chorionic gonadotropin (hCG). Androgen production in response to ACTH and hCG was reduced by UO126 and dexamethasone, which are the inhibitors of ERK1/2 and phospholipase A2 respectively. Expression of mRNA encoding StAR was increased fourfold by both ACTH and hCG, although expression of mRNA encoding for steroidogenic enzymes was not markedly affected. The potency of N-terminal fragments of ACTH to stimulate androgen production was similar to that seen previously in the adrenal. Data indicate that both LH and ACTH, acting through their respective receptors, stimulate steroidogenesis by fetal-type Leydig cells via arachidonic acid, protein kinase A, and ERK1/2 activation of StAR.

StAR Search—What We Know about How the Steroidogenic Acute Regulatory Protein Mediates Mitochondrial Cholesterol Import

Cholesterol is the starting point for biosynthesis of steroids, oxysterols and bile acids, and is also an essential component of cellular membranes. The mechanisms directing the intracellular trafficking of this insoluble molecule have received attention through the discovery of the steroidogenic acute regulatory protein (StAR) and related proteins containing StAR-related lipid transfer domains. Much of our understanding of the physiology of StAR derives from studies of congenital lipoid adrenal hyperplasia, which is caused by StAR mutations. Multiple lines of evidence show that StAR moves cholesterol from the outer to inner mitochondrial membrane, but acts exclusively on the outer membrane. The precise mechanism by which StAR's action on the outer mitochondrial membrane stimulates the flow of cholesterol to the inner membrane remains unclear. When StAR interacts with protonated phospholipid head groups on the outer mitochondrial membrane, it undergoes a conformational change (molten globule transition) that opens and closes StAR's cholesterol-binding pocket; this conformational change is required for cholesterol binding, which is required for StAR activity. The action of StAR probably requires interaction with the peripheral benzodiazepine receptor.

Reconstituted expression of menin in Men1-deficient mouse Leydig tumour cells induces cell cycle arrest and apoptosis

Multiple endocrine neoplasia type 1 (MEN1) is a hereditary syndrome caused by the inactivation of the responsible gene, MEN1. To date, the lack of MEN1-deficient cell lines derived directly from MEN1 tumours has hampered the detailed study of the MEN1 gene. We have established several stable Men1-deficient Leydig cell tumour (LCT) lines derived from a Leydig cell tumour developed in a male heterozygous Men1 mutant mouse. Our data show that these cell lines maintain the basic characteristics of Leydig cells in terms of both androgen synthesis and gene expression. Interestingly, reconstituted menin expression in one of Men1-deficient LCT cell lines resulted in cell growth inhibition, suggesting that the function of cell growth suppression of the menin pathway, apart from menin itself, is essentially preserved in these cells. Furthermore, we show that menin re-expression in these Men1-deficient cells leads to a block in the transition from G0/G1 to S phase of the cell cycle and an increase in apoptosis, accompanied by a marked increase of p18INK4C and p27Kip1 expression. The current study therefore highlights the importance of menin expression in cell cycle and cell survival control in endocrine cells, and may provide insights into the mechanisms of tumour suppression by menin in related endocrine tumours.

The regulatory mechanism of Tremella mesenterica on steroidogenesis in MA-10 mouse Leydig tumor cells

Tremella mesenterica (TM), a yellow jelly mushroom, has been traditionally used as tonic food to improve body condition in Chinese society for a long time. We have previously demonstrated that TM reduced in vitro hCG-treated steroidogenesis in MA-10 mouse Leydig tumor cells without any toxicity effect. In the present study, the mechanism how TM suppressed hCG-treated steroidogenesis in MA-10 cells was investigated. MA-10 cells were treated with vehicle, human chorionic gonadotropin (hCG, 50 ng/ml), or different reagents with or without TM to clarify the effects. TM significantly suppressed progesterone production with the presences of forskolin (10 and 100 microM) or dbcAMP (0.5 and 1mM), respectively, in MA-10 cells (p<0.05), which indicated that TM suppressed steroidogenesis after PKA activation along the signal pathway. Beyond our expectation, TM induced the expression of steroidogenic acute regulatory (StAR) protein with or without hCG treatments. However, TM profoundly decreased P450 side chain cleavage (P450scc) and 3beta-hydroxysteroid dehydrogenase (3beta-HSD) enzyme activities without any influences on the expression of both enzymes. These inhibitions on steroidogenic enzyme activities might counteract the stimulation of StAR protein expression. In conclusion, results suggest that TM suppressed hCG-treated steroidogenesis in MA-10 cells by inhibiting PKA signal pathway and steroidogenic enzyme activities.

Effects of Tremella mesenterica on steroidogenesis in MA-10 mouse Leydig tumor cells

Tremella mesenterica (TM), a yellow jelly mushroom, has been traditionally used as food and crude medicine to improve several kinds of symptoms in Chinese society for a long time. Recent studies have illustrated that the fractions of fruiting bodies of TM exhibit a significant hypoglycemic activity in diabetic mouse models, which usually suffer from sexual dysfunction. In a previous study, we showed that TM reduced plasma testosterone production in normal rats without any positive effect in diabetic rats. It evolved a question of TM directly regulating Leydig cell steroidogenesis. In this study, MA-10 mouse Leydig tumor cells were treated with vehicle, different dosages of TM with or without human chorionic gonadotropin (hCG 50 ng/ml) to clarify the effects. Results showed that TM at different dosages (0.01-10 mg/ml) did not have any effect on MA-10 cell steroidogenesis (p > 0.05). In the presence of hCG, there was an inhibitory trend that TA suppressed MA-10 cell progesterone production at 3 hr treatment with a statistically significant difference by the 10 mg/ml TM (p < 0.05). In time course effect, TM alone did not have any effect on MA-10 cell steroidogenesis from at 1, 2, 3, 6 and 12 hr (p > 0.05). However, TM did reduce hCG-treated MA-10 cell progesterone production at 1, 2 and 3 hr (p < 0.05), respectively. To determine whether TM would have adverse effects on MA-10 cell steroidogenesis in the presence of hCG, MTT assay and recovery studies were conducted. MTT assay indicated that TM had no effect on surviving cells. In addition, with the removal of TM, and then the addition of hCG (2 and 4 hr), progesterone levels were restored within 4 hr. Taken together, present studies suggested that TM suppressed hCG-treated steroidogenesis in MA-10 cells without any toxicity effect.

DNA sequence-dependent regulation of SF-1-mediated transcription

Rat P450c17 gene transcription is regulated by several nuclear factors, including steroidogenic factor-1 (SF-1), nerve growth factor-inducible protein B (NGF-IB, Nurr77), COUP-TF, SET, and Ku autoimmune antigen. A region of this gene, -447/-419, that mediates both basal and cAMP-stimulated transcription, contains two binding sites for orphan nuclear receptors. While SF-1 activates transcription through a single binding site, we show that both binding sites at -447/-419 are required for transcriptional activation by SF-1 and cAMP. Both SF-1 and a novel factor, Steroidogenic Factor-Inducer of Transcription-2 (StF-IT-2) bind to this region, suggesting that a DNA-dependent interaction between StF-IT-2 and SF-1 may be required for full transcriptional activity. Each of the two orphan nuclear receptor sites -429/-424 and at -444/-439 are sufficient for SF-1 binding but are insufficient for SF-1-mediated transcription. Increasing the distance between or changing the orientation of these two sites does not affect basal or SF-1-stimulated activity. Circular permutation analysis, which measures the degree of DNA bending caused by protein binding, indicates that SF-1 binding to -447/-419 induces a different degree of DNA bending than it does at another SF-1-responsive site. However, similar domains of the SF-1 protein are required for its actions at these two regions. Southwestern blots suggest that StF-IT-2 is a approximately 33 kDa protein, and gel shift assays suggest it is expressed primarily in the gonad and brain early in rodent development. These data suggest that the mechanism by which SF-1 stimulates transcription is DNA sequence dependent, and may require additional proteins, such as StF-IT-2, for activation at specific regions of DNA.

Deletion of the mouse P450c17 gene causes early embryonic lethality

Dehydroepiandrosterone (DHEA), a 19-carbon precursor of sex steroids, is abundantly produced in the human but not the mouse adrenal. However, mice produce DHEA and DHEA-sulfate (DHEAS) in the fetal brain. DHEA stimulates axonal growth from specific populations of mouse neocortical neurons in vitro, while DHEAS stimulates dendritic growth from those cells. The synthesis of DHEA and sex steroids, but not mouse glucocorticoids and mineralocorticoids, requires P450c17, which catalyzes both 17 alpha-hydroxylase and 17,20-lyase activities. We hypothesized that P450c17-knockout mice would have disordered sex steroid synthesis and disordered brain DHEA production and thus provide phenotypic clues about the functions of DHEA in mouse brain development. We deleted the mouse P450c17 gene in 127/SvJ mice and obtained several lines of mice from two lines of targeted embryonic stem cells. Heterozygotes were phenotypically and reproductively normal, but in all mouse lines, P450c17(-/-) zygotes died by embryonic day 7, prior to gastrulation. The cause of this early lethality is unknown, as there is no known function of fetal steroids at embryonic day 7. Immunocytochemistry identified P450c17 in embryonic endoderm in E7 wild-type and heterozygous embryos, but its function in these cells is unknown. Enzyme assays of wild-type embryos showed a rapid rise in 17-hydroxylase activity between E6 and E7 and the presence of C(17,20)-lyase activity at E7. Treatment of pregnant females with subcutaneous pellets releasing DHEA or 17-OH pregnenolone at a constant rate failed to rescue P450c17(-/-) fetuses. Treatment of normal pregnant females with pellets releasing pregnenolone or progesterone did not cause fetal demise. These data suggest that steroid products of P450c17 have heretofore-unknown essential functions in early embryonic mouse development.

Endocrine disruption by cadmium, a common environmental toxicant with paradoxical effects on reproduction

Cadmium (Cd(2+)) is a common environmental pollutant and a major constituent of tobacco smoke. Exposure to this heavy metal, which has no known beneficial physiological role, has been linked to a wide range of detrimental effects on mammalian reproduction. Intriguingly, depending on the identity of the steroidogenic tissue involved and the dosage used, it has been reported to either enhance or inhibit the biosynthesis of progesterone, a hormone that is inexorably linked to both normal ovarian cyclicity and the maintenance of pregnancy. Thus, Cd(2+) has been shown to exert significant effects on ovarian and reproductive tract morphology, with extremely low dosages reported to stimulate ovarian luteal progesterone biosynthesis and high dosages inhibiting it. In addition, Cd(2+) exposure during human pregnancy has been linked to decreased birth weights and premature birth, with the enhanced levels of placental Cd(2+) resulting from maternal exposure to industrial wastes or tobacco smoke being associated with decreased progesterone biosynthesis by the placental trophoblast. The stimulatory effects of Cd(2+) on ovarian progesterone synthesis, as revealed by the results of studies using stable porcine granulosa cells, appear centered on the enhanced conversion of cholesterol to pregnenolone by the cytochrome P450 side chain cleavage (P450scc). However, in the placenta, the Cd(2+)-induced decline in progesterone synthesis is commensurate with a decrease in P450scc. Additionally, placental low-density lipoprotein receptor (LDL-R) mRNA declines in response to Cd(2+) exposure, suggesting an inhibition in the pathway that provides cholesterol precursor from the maternal peripheral circulation. Potential mechanisms by which Cd(2+) may affect steroidogenesis include interference with the DNA binding zinc (Zn(2+))-finger motif through the substitution of Cd(2+) for Zn(2+) or by taking on the role of an endocrine disrupting chemical (EDC) that could mimic or inhibit the actions of endogenous estrogens. Divergent, tissue-specific (ovary vs. placenta) effects of Cd(2+) also cannot be ruled out. Therefore, in consideration of the data currently available and in light of the potentially serious consequences of environmental Cd(2+) exposure to human reproduction, we propose that priority should be given to studies dedicated to further elucidating the mechanisms involved.

Mouse Leydig tumor cells produce C-19 steroids, including testosterone

The mouse Leydig tumor cells (MLTC-1) were derived from a transplantable Leydig cell tumor carried in C57BL/6 mice. The original cell line (M5480) produced testosterone and little progesterone. However, it was later shown that there were two subtypes of the cell line, one producing mainly progesterone and termed M5480P and the other which produced androgens and termed M5480A. MLTC-1 cells are reportedly derived from the former. We studied the production of testosterone by MLTC-1 cells using a specific and sensitive testosterone RIA, tandem mass spectrometry (TMS) and examined the expression of mRNA of some key enzymes involved in steroidogenesis. Although the molar yields were 1:20:60 for testosterone, androstenedione and progesterone, respectively, in response to human chorionic gonadotropin (hCG), testosterone measured by our RIA accounted for 94% of the testosterone immunoreactivity. Both MLTC-1 and Balb/c Leydig cells expressed Steroidogenic Acute Response (StAR) protein mRNA in response to hCG. Cytochrome P450 17alpha-hydroxylase/17,20-lyase mRNA was expressed constitutively in MLTC-1 and Balb/c Leydig cells. Whereas the latter expressed 17beta-hydroxydehydrogenase/17-ketoreductase isoform Type 3mRNA in response to hCG, MLTC-1 cells expressed isoform Type 7 constitutively. The absence of isoform Type 3 in MLTC-1 cells thus may account for the low conversion of androstenedione to testosterone in this cell line. However, with a very specific and sensitive RIA even the low production of testosterone becomes meaningful. In conclusion MLTC-1 cells produce testosterone.

Placental endocrine disruption induced by cadmium: effects on P450 cholesterol side-chain cleavage and 3beta-hydroxysteroid dehydrogenase enzymes in cultured human trophoblasts

We previously suggested that cadmium (Cd), an environmental toxicant and constituent of tobacco smoke, inhibits progesterone secretion in cultured human placental trophoblasts by inhibiting low-density lipoprotein receptor mRNA expression. In the current study, we investigated whether Cd also disrupts progesterone synthesis via P450 cholesterol side-chain cleavage (P450(scc)) and 3beta-hydroxysteroid dehydrogenase (3beta-HSD), enzymes that play important roles in placental steroidogenesis. Human cytotrophoblasts were purified by density gradient centrifugation and incubated in Dulbecco modified Eagle medium + 10% fetal bovine serum with 0, 5, 10, or 20 microM CdCl(2) for 96 h. Cells progressed to syncytiotrophoblastic maturity regardless of treatment. No differences (P > 0.05) in cell protein and lactate dehydrogenase activity were observed between untreated trophoblasts and those treated with CdCl(2). However, P450(scc) and 3beta-HSD mRNA transcript levels declined in a dose-dependent manner (P <0.05) in trophoblasts cocultured with 5, 10, or 20 microM CdCl(2). P450(scc) activity was similarly inhibited (P < 0.05) by CdCl(2) treatment, although 3beta-HSD activity was not significantly affected. Coculture with 8-bromo-cAMP enhanced progesterone secretion in untreated cultures but did not reverse the decline in progesterone secretion induced by CdCl(2) treatment. CdCl(2) failed to influence cAMP content in cultured cells. Collectively, results suggest that P450(scc) enzyme is another site at which Cd interferes with placental progesterone production. However, it is unlikely that an inhibition of cAMP is involved with the inhibition of progesterone biosynthesis by Cd in human trophoblasts.

Developmental gonadal expression of the transcription factor SET and its target gene, P450c17 (17alpha-hydroxylase/c17,20 lyase)

Cytochrome P450c17 catalyzes the 17alpha-hydroxylase/17,20 lyase activity needed for sex steroid synthesis. We recently characterized the nuclear phosphoprotein SET as a novel transcriptional regulator that binds to the -447/-399 region of the rat P450c17 gene, along with the transcription factors COUP-TF II, NGF-IB, and SF-1. Gel shift studies localized SET binding to nucleotides -410/-402. We have shown that SET activates transcription of the rat P450c17 gene in neuronal precursor cells and now show that it also activates transcription from the -418/-399 region of the rat P450c17 gene in mouse Leydig MA-10 cells. Studying the ontogenic expression of SET and P450c17 in the rodent gonad, we found that SET expression preceded P450c17 expression in the embryonic genital ridge, suggesting that SET may be important for initiating P450c17 expression in this region. Expression of SET also preceded P450c17 expression in the testis and ovary, and its expression was much greater during embryogenesis than in the adult gonad. In the adult rat testis, P450c17 was expressed only in Leydig cells, while SET was expressed in Leydig cells and in spermatocytes. In the adult rat ovary, P450c17 was expressed only in theca cells, while SET was expressed in theca cells and also in oocytes. Because SET is expressed early in development in the genital ridge and in the testis and ovary, and because SET has many functions in addition to its activity as a transcription factor, we determined whether SET acts a transcription factor in oocytes. The SET protein was detected by Western blots in Xenopus oocytes from stages II through VI and in mature oocytes. Using extracts of Xenopus oocytes in gel shift assays, we detected a protein that bound to the -418/-399 region of the rat P450c17 gene, to which SET binds. Nuclear injection of either a -418/-399TK32LUC wildtype reporter construct or a construct containing a mutant SET site into Xenopus oocytes from stages III through VI resulted in activation of luciferase activity with the wildtype but not the mutant construct in all stages. These data suggest that Xenopus SET is able to bind to specific DNA sequences to activate transcription at all stages of Xenopus oogenesis. These data indicate that SET is an evolutionarily conserved transcription factor that participates in the early ontogenesis of the gonadal system, regulates P450c17 gene transcription in Leydig cells, and may also activate other genes expressed in immature oocytes, thus playing a role in oocyte development.

Assessment of mechanisms of thyroid hormone action in mouse Leydig cells: regulation of the steroidogenic acute regulatory protein, steroidogenesis, and luteinizing hormone receptor function

Recently, we demonstrated that triiodothyronine (T(3)) stimulated steroid hormone biosynthesis and steroidogenic acute regulatory (StAR) protein expression in mLTC-1 mouse Leydig tumor cells through the mediation of steroidogenic factor 1 (SF-1). We now report a dual response mechanism of T(3) on steroidogenesis and StAR expression, and on LH receptor (LHR) expression and binding in mLTC-1 cells. T(3) acutely (8 h), induced a 260% increase in StAR messenger RNA (mRNA) expression over the basal level which was coincident with an increase in progesterone (P) production. In contrast, chronic stimulation with T(3) (beyond 8 h), resulted in an attenuation of StAR expression and P production. This attenuation was most likely caused by a decrease in cholesterol delivery to the inner mitochondrial membrane as demonstrated by incubations with the hydrophilic steroid precursors, 22R hydroxycholesterol and pregnenolone, which restored P synthesis. In similar studies, chronic treatment with T(3) increased the levels of cytochrome P450scc mRNA by 83%, whereas those of cytochrome P450 17alpha-hydroxylase and 3ss-hydroxysteroid dehydrogenase decreased. The diminished response in steroidogenesis following chronic T(3) exposure was not a result of alterations in StAR mRNA stability, but rather was due to inhibition of transcription of the StAR gene. Similar acute stimulatory and chronic inhibitory responses to T(3) were found when LHR mRNA expression and LHR ligand binding were examined. Transfections with an LHR or StAR promoter/luciferase reporter construct demonstrated that a 173-bp fragment of the LHR promoter containing an SF-1 binding motif was involved in T(3) response, as was the SF-1 recognition site at -135 bp in the StAR promoter. Furthermore, the importance of SF-1 in T(3) function was also verified employing mutation in the bases of SF-1 sequences using electrophoretic mobility shift assays. The potential physiological relevance of these findings was demonstrated when similar responses were obtained in mice rendered hypo and hyperthyroid. Collectively, these observations further characterize the thyroid-gonadal connection and provide insights into the mechanisms for a dual regulatory role of thyroid hormone in Leydig cell functions.

Novel role for the nuclear phosphoprotein SET in transcriptional activation of P450c17 and initiation of neurosteroidogenesis

Neurosteroids are important endogenous regulators of gamma-aminobutryic acid (GABA(A)) and N-methyl-D-aspartate (NMDA) receptors and also influence neuronal morphology and function. Neurosteroids are produced in the brain using many of the same enzymes found in the adrenal and gonad. The crucial enzyme for the synthesis of DHEA (dehydroepiandrosterone) in the brain is cytochrome P450c17. The transcriptional strategy for the expression of P450c17 is clearly different in the brain from that in the adrenal or gonad. We previously characterized a novel transcriptional regulator from Leydig MA-10 cells, termed StF-IT-1, that binds at bases -447/-399 of the rat P450c17 promoter, along with the known transcription factors COUP-TF (chicken ovalbumin upstream promoter transcription factor), NGF-IB (nerve growth factor inducible protein B), and SF-1 (steroidogenic factor-1). We have now purified and sequenced this protein from immature porcine testes, identifying it as the nuclear phosphoprotein SET; a role for SET in transcription was not established previously. Binding of bacterially expressed human and rat SET to the DNA site at -418/-399 of the rat P450c17 gene transactivates P450c17 in neuronal and in testicular Leydig cells. We also found SET expressed in human NT2 neuronal precursor cells, implicating a role in neurosteroidogenesis. Immunocytochemistry and in situ hybridization in the mouse fetus show that the ontogeny and distribution of SET in the developing nervous system are consistent with SET being crucial for initiating P450c17 transcription. SET's developmental pattern of expression suggests it may participate in the early ontogenesis of the nervous, as well as the skeletal and hematopoietic, systems. These studies delineate an important new factor in the transcriptional regulation of P450c17 and consequently, in the production of DHEA and sex steroids.

Ku autoimmune antigen is involved in placental regulation of rat P450c17 gene transcription

The steroidogenic enzyme P450c17 (17alpha hydroxylase/C17,20 lyase) regulates a key branchpoint in steroidogenesis, as its activity directs the steroid biosynthetic pathways toward glucocorticoid or sex hormone synthesis. Expression of the P450c17 gene is transcriptionally regulated in steroidogenic tissues by cAMP. We showed that DNA between -84 and -55 in the rat P450c17 gene was bound uniquely by steroidogenic factor-1 (SF-1), which regulated both basal and cAMP-stimulated transcription in mouse adrenocortical and Leydig cells. SF-1 gene ablation experiments in mice indicate that SF-1 is not mandatory for placental steroidogenesis. We studied P450c17 gene regulation in the placenta using human placental JEG-3 trophoblast cells. Transfection of reporter luciferase gene constructs containing serial deletions of the 5' flanking region of the rat P450c17 gene showed that DNA between -98 and +13 mediated basal and cAMP-regulated transcription in placental JEG-3 cells, as it did in adrenal and Leydig cells. DNase footprints further identified a region between -88 and the TATA box that was bound by protein. Transfection of luciferase reporter constructs containing -84 to -55 of the rat P450c17 DNA ligated to the minimal promoter of the thymidine kinase gene showed that this DNA increased both basal and cAMP-simulated luciferase activity. Gel mobility shift assays identified two DNA-protein complexes with JEG-3 cell nuclear extracts that were different from complexes formed with MA-10 cell extracts and did not involve SF-1. Mutational analysis of the -84/-55 DNA showed that JEG-3 nuclear proteins bound to a site containing, but not identical to, the SF-1 sequence. One complex involved Ku autoimmune antigen, which bound to DNA sequence specifically. Overexpression of Ku antigen in MA-10 cells stimulated rat P450c17 gene transcription, thus demonstrating a biologic effect of Ku. Ku also bound to a similar region of the human P450c17 gene, and the DNA region to which Ku bound was transcriptionally active in JEG-3 cells. Ku was also found in extracts from rat placenta and bound to the -84/-55 rat P450c17 DNA. These data demonstrate a role of Ku in regulating P450c17 gene expression. These data further indicate that although human P450c17 is not normally expressed in the placenta, factors that could activate this gene are indeed present.

Maternal adrenalectomy eliminates a surge of plasma dehydroepiandrosterone in the mother and attenuates the prenatal testosterone surge in the male fetus

Previous work has established a number of sex-related deficits in immune function, behavior, and endocrine responses to stress in the offspring of dams exposed to ethanol. To examine the potential role of maternal glucocorticoids as a mediator of these sexually dimorphic effects in the fetus, we examined the influence of prenatal alcohol exposure in the presence or absence of maternal glucocorticoids on fetal plasma corticosterone (CORT) production. An additional question to be addressed by these studies was whether maternal adrenalectomy could eliminate the known inhibition by ethanol of the prenatal surge of plasma testosterone in male fetuses. Pregnant dams were adrenalectomized (ADX) or sham-adrenalectomized on gestational day (G) 7 and placed on a liquid diet containing 35% ethanol-derived calories or pair-fed an isocaloric control diet throughout the experiment. On G18, G19, and G21, plasma levels of CORT, testosterone, and dehydroepiandrosterone (DHEA) were measured in male and female fetuses and their mothers. Ethanol administration consistently increased maternal plasma CORT levels but did not significantly alter CORT levels in the fetus. Maternal ADX resulted in compensatory increases in fetal CORT levels that were lower in fetuses of ADX dams on alcohol, suggesting a direct effect of ethanol on fetal pituitary-adrenal activity. There were no significant sex differences in fetal plasma CORT levels in response to any of these manipulations. A novel surge of maternal plasma DHEA was found on G19 that was absent in plasma from ADX dams. In spite of the absence of a surge on G19, plasma DHEA levels of ADX dams rose from very low levels at G18 to levels on G21 that were significantly higher than in Sham dams. A normal testosterone surge was observed in male fetuses on G18 and G19 from sham-adrenalectomized dams administered the pair-fed diet. However, this surge was greatly attenuated in males administered ethanol and also in male fetuses from ADX dams. These results reveal a direct inhibitory influence of ethanol on fetal CORT secretion as well as on the prenatal testosterone surge in males. Furthermore, these studies demonstrate the presence of a surge of DHEA in the pregnant rat. Overall, these data suggest that there is a critical adrenal factor in the rat that regulates the maternal surge of DHEA on G19 and the prenatal testosterone surge of male fetuses on G18-19.

Regulation of cholesterol side-chain cleavage cytochrome P450 in mouse testis Leydig cell line I-10

We have characterized regulation of steroidogenesis in a mouse testis Leydig cell line, I-10. Progesterone secretion was increased in a time- and dose-dependent fashion by 8-Br-cAMP treatment. The amount of cholesterol side-chain cleavage enzyme (P450scc), the first and rate-limiting enzyme for the synthesis of steroids, as detected by immunoblotting, was also increased. The calcium ionophore A23187 decreased the amount of P450scc, but it did not interfere with cAMP stimulation of the accumulation of P450scc. This regulation of P450scc expression by cAMP and A23187 is at the post-transcriptional level because the amount of P450scc mRNA was not affected by either treatment. This result was further confirmed by direct measurement of transcription in the presence or absence of forskolin treatment. I-10, however, supported cAMP-dependent transcriptional activation of the exogenous gene, as shown by the increased expression of a reporter gene under the control of the -600 to -2,500 fragment of the P450scc gene. The ability for transcriptional activation of the exogenous but not endogenous P450scc gene makes I-10 a unique steroidogenic cell line.

Transcriptional regulation of rat cytochrome P450c17 expression in mouse Leydig MA-10 and adrenal Y-1 cells: identification of a single protein that mediates both basal and cAMP-induced activities

Cytochrome P450c17, 17 alpha-hydroxylase/17,20 lyase, is a key enzyme in the steroidogenic pathway leading to the production of corticosteroids and androgens from the adrenal gland and sex steroids from the gonads. Both enzymatic activities of the protein are encoded by a single gene, CYP17, which is expressed in both the human adrenal and gonad but not in the placenta, and in the rodent gonad and placenta but not the rodent adrenal. We isolated and sequenced a full-length rat genomic clone (7,553 bases) containing the entire coding region of the rat P450c17 gene, and all intronic sequences and 1,560 bp of 5'-flanking DNA (EMBL Acc#X69816). To determine which sequences in the rat P450c17 promoter may be responsible for basal and cAMP-stimulated gene transcription, deletion constructs containing between -1,560 and -53 base pairs of 5'-flanking DNA from the rat P450c17 gene were ligated to plasmids expressing the reporter gene luciferase and transfected into two mouse cell lines, adrenal Y-1 cells, and testicular Leydig MA-10 cells. Highest basal and cAMP-stimulated luciferase activity were found in constructions containing 156 bp of 5'-flanking DNA. This construction contains a sequence very similar to the consensus cis element reported to be responsible for cAMP enhancement of the rat somatostatin gene and also overlaps a sequence similar to the consensus element for the orphan steroid receptor SF-1. Gel mobility-shift analysis, using a 30-bp oligonucleotide containing this region incubated with cellular extracts from cultured mouse adrenal Y-1 and mouse Leydig MA-10 cells, revealed all the extracts to contain two proteins that bind to this sequence. Neither DNA-protein complex was further retarded by co-incubation with an anti-CREB antibody, suggesting that cAMP regulation of this gene occurs via a non-CREB protein. Mutation of this oligonucleotide resulted in loss of binding of only one of these proteins, but resulted in loss of both basal and cAMP stimulation of rat P450c17 promoter-regulated gene transcription. Southwestern analysis suggests that one of these proteins is larger than SF-1. This study suggests that a protein that binds to an SF-1 like sequence regulates both basal and cAMP-stimulated rat P450c17 gene expression in rodent cells.

Differential regulation of the CYP11A1 (P450scc) and ferredoxin genes in adrenal and placental cells

The regulation of the genes encoding cholesterol side-chain cleavage enzyme (P450scc) and ferredoxin, two components in the first step of steroid synthetic pathways, was studied by RNA analyses of endogenous and transfected genes. cAMP rather than calcium was the major secondary messenger that stimulated expression of both P450scc and ferredoxin genes in human placental JEG-3 cells. The effect of cAMP on P450scc expression was abolished by cycloheximide in JEG-3 cells, but it was superinduced in mouse adrenal Y1 cells. For ferredoxin expression, both reagents have synergistic effect in Y1 and JEG-3 cells. To test the mechanism of regulation, DNA segments containing regulatory elements of the P450scc and ferredoxin genes were connected to reporter genes and analyzed in cotransfection experiments. The results showed that the proximal cAMP-responsive sequences of both P450scc and ferredoxin genes were stimulated by cAMP early in both Y1 and JEG-3 cells, requiring no new protein synthesis. This indicates a common mechanism for the regulated expression of both genes. P450scc possessed an additional upstream cAMP-responsive sequence that also responded to cAMP induction in a different manner from the proximal element. The presence of additional upstream regulatory elements makes it possible for the P450scc gene to be further regulated.

Tenascin-X: a novel extracellular matrix protein encoded by the human XB gene overlapping P450c21B

A human gene termed XB overlaps the P450c21B gene encoding steroid 21-hydroxylase and encodes a protein that closely resembles extracellular matrix proteins. Sequencing of phage and cosmid clones and of cDNA fragments shows that the XB gene spans 65 kb of DNA, consisting of 39 exons that encode a 12-kb mRNA. The predicted protein of over 400 kD consists of five distinct domains: a signal peptide, a hydrophobic domain containing three heptad repeats, a series of 18.5 EGF-like repeats, 29 fibronectin type III repeats, and a carboxy-terminal fibrinogen-like domain. Because the structure of the protein encoded by the XB gene closely resembles tenascin, we term this protein tenascin-X (TN-X), and propose a simplified nomenclature system for the family of tenascins. RNase protection experiments show that the TN-X transcript is expressed ubiquitously in human fetal tissues, with the greatest expression in the fetal testis and in fetal skeletal, cardiac, and smooth muscle. Two adrenal-specific transcripts, P450c21B (steroid 21-hydroxylase) and Y (an untranslated transcript) overlap the XB gene on the complementary strand of DNA, yielding a unique array of overlapping transcripts: a "polygene." In situ hybridization histochemistry experiments show that the TN-X transcript and the P450c21 and Y transcripts encoded on the complementary DNA strand are all expressed in the same cells of the human adrenal cortex. Genetic data suggest that TN-X may be essential for life.

cAMP post-transcriptionally diminishes the abundance of adrenodoxin reductase mRNA

Adrenodoxin reductase (AR; ferridoxin: NADP+ oxidoreductase, EC 1.18.1.2) is a flavoprotein that mediates electron transport from NADPH to all known mitochondrial forms of cytochrome P450. AR mRNA was found in all human adult and fetal tissues examined; however, it was vastly more abundant in tissues that synthesize steroid hormones. The ratio of the 18- form of mRNA lacking 18 alternately spliced bases to the 18+ form was approximately 100:1 and remained constant irrespective of the tissue or hormonal manipulation, indicating that the alternate splicing is a passive nonregulated event. AR protein was unchanged by forskolin treatment of human JEG-3 cytotrophoblast cells for 24 h, but the mRNA diminished. Phorbol 12-myristate 13-acetate and cycloheximide had no effect, even though these agents had the expected effects on P450scc and adrenodoxin mRNAs. cAMP decreased the abundance of AR mRNA expressed from both transfected plasmids and the endogenous gene, indicating the effect was post-transcriptional. AR gene transcription in JEG-3 cells and promoter-chloramphenicol acetyltransferase constructs transfected into JEG-3 cells were unresponsive to forskolin. Powerful basal transcription elements were identified between -46 and -214 bases from the principal transcriptional initiation site, a region containing six elements closely resembling the binding site for transcription factor SP1.

Basic fibroblast growth factor expression is regulated by corticotropin in the human fetal adrenal: a model for adrenal growth regulation

Human fetal adrenal growth after midgestation is very rapid and appears to be dependent upon pituitary adrenocorticotropin (ACTH) in vivo. We hypothesized that the regulation of fetal adrenal growth by ACTH is mediated by ACTH-stimulated local growth factor production. As we have found basic fibroblast growth factor (bFGF) to be a potent mitogen for human fetal adrenal cells in culture, we conducted studies to determine whether bFGF is synthesized by the human fetal adrenal gland and whether bFGF gene expression in primary cultures of human fetal adrenal cells is regulated by ACTH. Bioassayable bFGF-like activity was detected in extracts of whole human fetal adrenal glands and primary cultures of human fetal adrenal cells. Northern blot analysis of total RNA from whole human fetal adrenal glands revealed a characteristic 7-kilobase bFGF mRNA, indicating that the fetal adrenal bFGF bioactivity was most likely due to local synthesis. Slot blot and ribonuclease protection analysis showed that bFGF mRNA was present in very low amounts in total RNA from primary cultures of unstimulated human fetal adrenal cells but was increased 2- to 3-fold in cells exposed to 10 nM ACTH-(1-24) or 1 mM 8-bromoadenosine 3',5'-cyclic monophosphate for 24 hr. bFGF mRNA was localized to adrenocortical cells and not fibroblasts by in situ hybridization. bFGF mRNA was barely detectable in unstimulated cells, whereas it was markedly increased in cells exposed to either ACTH or 8-bromoadenosine 3',5'-cyclic monophosphate. These data support our hypothesis that the regulation of human fetal adrenal growth by ACTH at midgestation may be mediated by the stimulation of local growth factor production, and we suggest that bFGF may play a major role in this process.

Zone-specific regulation of two messenger RNAs for P450c11 in the adrenals of pregnant and nonpregnant rats

Adrenal mitochondria possess two steroidogenic cytochrome P450s. P450c11 converts deoxycorticosterone to corticosterone and aldosterone, and P450scc converts cholesterol to pregnenolone. These P450s receive electrons from NADPH via adrenodoxin reductase and adrenodoxin. A single bovine P450c11 protein has 11-hydroxylase, 18-hydroxylase, and 18-oxidase activities, but this series of enzymatic steps may be mediated by more than one enzyme in rats. Enzymatic assays of purified rat mitochondrial proteins have suggested that one enzyme found in all zones of the adrenal cortex has both 11- and 18-hydroxylase activities, whereas another enzyme, found exclusively in the zona glomerulosa, catalyzes 18-hydroxylation and 18-oxidation of corticosterone. We studied the number and zonal distribution of P450c11 mRNA species in the rat adrenal and how these mRNAs are regulated in the adrenals of normal and pregnant rats. Rats synthesize two similar, but distinct, P450c11 mRNAs. One, P450c11A, is found in both the zona glomerulosa and fasciculata/reticularis, whereas the second, P450c11B, is found only in the zona glomerulosa. The abundance of neither P450c11A mRNA nor P450c11B mRNA is affected by a high-salt diet. However, when rats receive a low-salt diet, P450c11A mRNA decreases and P450c11B mRNA increases. Dexamethasone decreases the amount of P450c11A mRNA without affecting P450c11B mRNA. The combination of a high-salt diet and dexamethasone decreases the amount of both mRNAs further to almost undetectable amounts. Rats given a low-salt diet and dexamethasone have a dramatic increase in the abundance of P450c11B mRNA. Thus both forms of P450c11 mRNA are regulated independently in the rat adrenal cortex. In situ hybridization studies show that only the P450c11 found in the zona glomerulosa is regulated by salt treatment in vivo, whereas glucocorticoid treatment in vivo regulates P450c11 in all zones. In the adrenals of pregnant rats, P450c11B is regulated in a similar fashion to its regulation in the nonpregnant rat adrenal, despite major differences in sodium retention and intravascular volume in pregnant and nonpregnant rats. In the pregnant rat, a low-salt diet increases the abundance of P450c11B to a greater degree than in the nonpregnant rat. By contrast, dexamethasone does not diminish the abundance of P450c11A mRNA in the pregnant rat but reduces it to an almost undetectable amount in the nonpregnant rat. Thus, the regulation of glucocorticoid and mineralocorticoid production in the pregnant and nonpregnant rat occurs by different mechanisms.

Expression and regulation of adrenodoxin and P450scc mRNA in rodent tissues

The rate-limiting step in steroidogenesis is the conversion of cholesterol to pregnenolone. This reaction occurs in steroidogenic tissue in the inner mitochondrial membrane, and is mediated by the cholesterol side-chain cleavage enzyme. This enzyme system transfers electrons from NADPH to cholesterol through its three protein components: adrenodoxin reductase, adrenodoxin, and the terminal oxidase, P450scc. We have previously shown that P450scc mRNA is regulated by tropic hormones and cAMP by a cycloheximide-independent mechanism in mouse Leydig tumor MA-10 cells. We now show that the mRNA for adrenodoxin, another component of the cholesterol side-chain cleavage enzyme system, is regulated by tropic hormones and cAMP in MA-10 cells. We cloned rat adrenodoxin cDNA to analyze adrenodoxin mRNA in various rat tissues and in MA-10 cells by RNase protection assays. Adrenodoxin mRNA is found in virtually all rat tissues examined, although it is most abundant in adrenals, ovaries, and testes. MA-10 cells synthesize two species of adrenodoxin mRNA, one of 1.2 kb and the other of 0.8 kb. Both of these adrenodoxin mRNAs are increased approximately six-fold by 1 mM 8-Br-cAMP, five-fold by 10 microM forskolin, and three-fold by both 25 ng/ml hCG and by 100 ng/ml LH. Maximal adrenodoxin mRNA accumulation occurs by 4 h of hormonal stimulation. The cAMP-mediated increase in adrenodoxin mRNA accumulation is independent of protein synthesis, since treatment with cycloheximide or puromycin in the absence or presence of cAMP does not inhibit, and even increases, adrenodoxin mRNA accumulation.

The P450 superfamily: update on new sequences, gene mapping, and recommended nomenclature

We provide here a list of 154 P450 genes and seven putative pseudogenes that have been characterized as of October 20, 1990. These genes have been described in a total of 23 eukaryotes (including nine mammalian and one plant species) and six prokaryotes. Of 27 gene families so far described, 10 exist in all mammals. These 10 families comprise 18 subfamilies, of which 16 and 14 have been mapped in the human and mouse genomes, respectively; to date, each subfamily appears to represent a cluster of tightly linked genes. We propose here a modest revision of the initially proposed (Nebert et al., DNA 6, 1-11, 1987) and updated (Nebert et al., DNA 8, 1-13, 1989) nomenclature system based on evolution of the superfamily. For the gene we recommend that the italicized root symbol CYP for human (Cyp for mouse), representing cytochrome P450, be followed by an Arabic number denoting the family, a letter designating the subfamily (when two or more exist), and an Arabic numeral representing the individual gene within the subfamily. A hyphen should precede the final number in mouse genes. We suggest that the human nomenclature system be used for other species. This system is consistent with our earlier proposed nomenclature for P450 of all eukaryotes and prokaryotes, except that we are discouraging the future use of cumbersome Roman numerals.

Human P450scc gene transcription is induced by cyclic AMP and repressed by 12-O-tetradecanoylphorbol-13-acetate and A23187 through independent cis elements

Long-term regulation of mammalian steroid hormone synthesis occurs principally by transcriptional regulation of the gene for the rate-limiting cholesterol side-chain cleavage enzyme P450scc. Adrenal steroidogenesis is regulated primarily by two hormones: adrenocorticotropin, which works via cyclic AMP (cAMP) and protein kinase A, and angiotensin II, which works via Ca2+ and protein kinase C. Forskolin and 8-bromo-cAMP stimulated, while prolonged treatment with a phorbol ester (12-O-tetradecanoylphorbol-13-acetate [TPA]) and a calcium ionophore (A23187) additively suppressed accumulation of endogenous P450scc mRNA in transformed murine adrenal Y1 cells. In Y1 cells transfected with 2,327 base pairs of the human P450scc promoter fused to the bacterial gene for chloramphenicol acetyltransferase (CAT), forskolin increased CAT activity 900% while combined TPA plus A23187 reduced CAT activity to 15% of the control level. Forskolin induced the P450scc promoter as rapidly as a promoter containing two cAMP-responsive elements fused to a simian virus 40 promoter, a system known to respond directly to cAMP. Basal expression was increased by sequences between -89 and -152 and was increased further by sequences between -605 and -2327. This upstream region also conferred inducibility by cAMP. TPA plus A23187 transiently increased CAT activity before repressing it, reflecting the complex actions of angiotensin II in vivo. Repression by prolonged treatment with TPA plus A23187 was mediated by multiple elements between -89 and -343. Induction of CAT activity by forskolin was not diminished by treatment with TPA plus A23187, nor were the regions of the promoter responsible for regulation by the two pathways coisolated. Thus, the human gene for P450scc is repressed by TPA plus A23187 by mechanisms and sequences independent of those that mediate induction by cAMP.

Human P450scc gene transcription is induced by cyclic AMP and repressed by 12-O-tetradecanoylphorbol-13-acetate and A23187 through independent cis elements

Long-term regulation of mammalian steroid hormone synthesis occurs principally by transcriptional regulation of the gene for the rate-limiting cholesterol side-chain cleavage enzyme P450scc. Adrenal steroidogenesis is regulated primarily by two hormones: adrenocorticotropin, which works via cyclic AMP (cAMP) and protein kinase A, and angiotensin II, which works via Ca2+ and protein kinase C. Forskolin and 8-bromo-cAMP stimulated, while prolonged treatment with a phorbol ester (12-O-tetradecanoylphorbol-13-acetate [TPA]) and a calcium ionophore (A23187) additively suppressed accumulation of endogenous P450scc mRNA in transformed murine adrenal Y1 cells. In Y1 cells transfected with 2,327 base pairs of the human P450scc promoter fused to the bacterial gene for chloramphenicol acetyltransferase (CAT), forskolin increased CAT activity 900% while combined TPA plus A23187 reduced CAT activity to 15% of the control level. Forskolin induced the P450scc promoter as rapidly as a promoter containing two cAMP-responsive elements fused to a simian virus 40 promoter, a system known to respond directly to cAMP. Basal expression was increased by sequences between -89 and -152 and was increased further by sequences between -605 and -2327. This upstream region also conferred inducibility by cAMP. TPA plus A23187 transiently increased CAT activity before repressing it, reflecting the complex actions of angiotensin II in vivo. Repression by prolonged treatment with TPA plus A23187 was mediated by multiple elements between -89 and -343. Induction of CAT activity by forskolin was not diminished by treatment with TPA plus A23187, nor were the regions of the promoter responsible for regulation by the two pathways coisolated. Thus, the human gene for P450scc is repressed by TPA plus A23187 by mechanisms and sequences independent of those that mediate induction by cAMP.

Human placental protein 14 gene: sequence and characterization of a short duplication

Differential hybridization of cDNAs corresponding to mRNAs expressed in the human endometrium during the secretory phase or during the first trimester of pregnancy, but not during the proliferative phase, allowed us to isolate and characterize cDNAs encoding human placental protein 14 (PP14). The cDNA was used to isolate the PP14 gene from a human genomic library. The entire gene encompasses 5.05 kb divided into seven exons by six introns. The human PP14 gene shows identical organization with the ovine beta-lactoglobulin gene, as expected from protein homology. Sequencing of 3 kb of the 5'-flanking region of the gene allowed us to characterize a 400-bp duplication of the PP14 gene lying at position -2,660. This duplication was homologous to 100 bp of exon 4 and 300 bp of intron 4, including 180 bp corresponding exactly to the right arm of an Alu element lying on the complementary strand. This homology suggests that this duplication may have arisen through a retroposition event.

Extraadrenal steroid 21-hydroxylation is not mediated by P450c21

The 21-hydroxylation of progesterone to deoxycorticosterone (DOC) and of 17-hydroxyprogesterone to 11-deoxycortisol in the human adrenal cortex is mediated by a single enzyme termed P450c21. Extraadrenal tissues can clear circulating progesterone and progesterone sulfate by 21-hydroxylation to DOC and DOC-sulfate. It has previously been established that such extraadrenal 21-hydroxylase activity is widely distributed in adult and fetal tissues, but it has not been known if extra-adrenal 21-hydroxylation is mediated by the same P450c21 enzyme found in the adrenal. We examined human RNA from fetal adrenal, liver, kidney, lung, brain, heart, skin, spleen, testis, and placenta by solution hybridization to human P450c21 probes transcribed from cloned human P450c21 cDNA, followed by nuclease protection and acrylamide gel electrophoresis. No P450c21 mRNA was detectable in any extraadrenal tissue. The sensitivity of the assay would have detected P450c21 mRNA at 0.01% of its abundance in the human fetal adrenal. Similar experiments in rats showed no P450c21 mRNA in brain, heart, kidney, liver, lung, testis, ovary, or uterus. These results clearly demonstrate that one or more enzymes other than the classical adrenal 21-hydroxylase are responsible for human and rat extraadrenal 21-hydroxylation.