Differentiation of mesenchymal stem cells into gonad and adrenal steroidogenic cells

Hormone replacement therapy is necessary for patients with adrenal and gonadal failure. Steroid hormone treatment is also employed in aging people for sex hormone deficiency. These patients undergo such therapies, which have associated risks, for their entire life. Stem cells represent an innovative tool for tissue regeneration and the possibility of solving these problems. Among various stem cell types, mesenchymal stem cells have the potential to differentiate into steroidogenic cells both in vivo and in vitro. In particular, they can effectively be differentiated into steroidogenic cells by expressing nuclear receptor 5A subfamily proteins (steroidogenic factor-1 and liver receptor homolog-1) with the aid of cAMP. This approach will provide a source of cells for future regenerative medicine for the treatment of diseases caused by steroidogenesis deficiencies. It can also represent a useful tool for studying the molecular mechanisms of steroidogenesis and its related diseases.

Activation of focal adhesion kinase via M1 muscarinic acetylcholine receptor is required in restitution of intestinal barrier function after epithelial injury

Impairment of epithelial barrier is observed in various intestinal disorders including inflammatory bowel diseases (IBD). Numerous factors may cause temporary damage of the intestinal epithelium. A complex network of highly divergent factors regulates healing of the epithelium to prevent inflammatory response. However, the exact repair mechanisms involved in maintaining homeostatic intestinal barrier integrity remain to be clarified. In this study, we demonstrate that activation of M1 muscarinic acetylcholine receptor (mAChR) augments the restitution of epithelial barrier function in T84 cell monolayers after ethanol-induced epithelial injury, via ERK-dependent phosphorylation of focal adhesion kinase (FAK). We have shown that ethanol injury decreased the transepithelial electrical resistance (TER) along with the reduction of ERK and FAK phosphorylation. Carbachol (CCh) increased ERK and FAK phosphorylation with enhanced TER recovery, which was completely blocked by either MT-7 (M1 antagonist) or atropine. The CCh-induced enhancement of TER recovery was also blocked by either U0126 (ERK pathway inhibitor) or PF-228 (FAK inhibitor). Treatment of T84 cell monolayers with interferon-γ (IFN-γ) impaired the barrier function with the reduction of FAK phosphorylation. The CCh-induced ERK and FAK phosphorylation were also attenuated by the IFN-γ treatment. Immunological and binding experiments exhibited a significant reduction of M1 mAChR after IFN-γ treatment. The reduction of M1 mAChR in inflammatory area was also observed in surgical specimens from IBD patients, using immunohistochemical analysis. These findings provide important clues regarding mechanisms by which M1 mAChR participates in the maintenance of intestinal barrier function under not only physiological but also pathological conditions.

Transcriptional regulation of human ferredoxin reductase through an intronic enhancer in steroidogenic cells

Ferredoxin reductase (FDXR, also known as adrenodoxin reductase) is a mitochondrial flavoprotein that transfers electrons from NADPH to mitochondrial cytochrome P450 enzymes, mediating the function of an iron-sulfur cluster protein, ferredoxin. FDXR functions in various metabolic processes including steroidogenesis. It is well known that multiple steroidogenic enzymes are regulated by a transcription factor steroidogenic factor-1 (SF-1, also known as Ad4BP). Previously, we have shown that SF-1 transduction causes human mesenchymal stem cell differentiation into steroidogenic cells. Genome-wide analysis of differentiated cells, using a combination of DNA microarray and promoter tiling array analyses, showed that FDXR is a novel SF-1 target gene. In this study, the transcriptional regulatory mechanism of FDXR was examined in steroidogenic cells. A chromatin immunoprecipitation assay revealed that a novel SF-1 binding region was located within intron 2 of the human FDXR gene. Luciferase reporter assays showed that FDXR transcription was activated through the novel SF-1 binding site within intron 2. Endogenous SF-1 knockdown in human adrenocortical H295R and KGN cells decreased FDXR expression. In H295R cells, strong binding of two histone markers of active enhancers, histones H3K27ac and H3K4me2, were detected near the SF-1 binding site within intron 2. Furthermore, the binding of these histone markers was decreased concurrent with SF-1 knockdown in H295R cells. These results indicated that abundant FDXR expression in these steroidogenic cells was maintained through SF-1 binding to the intronic enhancer of the FDXR gene.

Increased IL-17 production correlates with immunosuppression involving myeloid-derived suppressor cells and nutritional impairment in patients with various gastrointestinal cancers

Although a causal relationship between inflammation and innate immunity of cancer is more widely accepted today, many of the precise cell mechanisms mediating this relationship have not been elucidated. Th17 cells, which produce the proinflammatory cytokine interleukin 17 (IL-17), have been recognized as one of the key factors in the regulation of inflammatory bowel disease and rheumatoid arthritis. This study demonstrated that, in patients with various types of gastrointestinal cancer, IL-17 production was correlated with myeloid-derived suppressor cell (MDSC) levels and with markers for nutritional impairment, immune suppression and chronic inflammation. IL-17 was significantly higher in patients with various types of gastrointestinal cancer compared to normal volunteers. In addition, IL-17 levels were significantly correlated with neutrophil counts and the neutrophil/lymphocyte ratio (NLR) and significantly inversely correlated with cell-mediated immune response indicators [lymphocyte phytohemagglutinin (PHA)-blastogenesis and IL-12 induction] and patient nutritional status (prealbumin levels). Circulating MDSC levels were significantly correlated with IL-17 production. These results suggest that, in human gastrointestinal cancers, chronic inflammation involving IL-17 may be an important mechanism contributing to disease progression through enhancement of immune suppression or cachexia. Controlling the activation of Th17 cells may prove to be a valuable strategy for the treatment of gastrointestinal cancer patients.

Circulating myeloid-derived suppressor cells (MDSC) and correlation to poor prognosis, Th2-polarization, inflammation, and nutritional damages in patients with gastric cancer

3063

Background: Recent studies have shown that myeloid-derived suppressor cells (MDSC), which have been identified in most patients, are potent suppressors of T cell activation. MDSC have been reported to be correlated with tumorigenesis and the progression of tumors. We have previously reported significant correlations of MDSC with nutritional damage and inflammation in many types of cancer. In this study the quantitative detection of MDSC in peripheral blood was analyzed in the prognosis in patients with gastric cancer. Methods: We tested PBMCs from 29 preoperative patients with gastric cancer and 18 healthy volunteers using flow cytometric analysis (CD14-CD11b+CD33+). Markers for nutritional status (serum levels of total protein), inflammation (NLR: neurphil/lymphocyte ratio, serum levels of vascular endothelial growth factor: VEGF) and Th2-polarization (PBMC’s production of IL-6 and IL-10) were measured in this study. The prognosis of the patients was assessed by Kaplan-Meier tests for correlation with levels of MDSC. Results: MDSC levels in 29 preoperative patients with gastric cancer were significantly higher than in normal volunteers. These levels were not associated with pathological characteristics. However they were significantly correlated with the production of IL-6 and IL-10, VEGF levels and NLR. A significant inverse correlation with levels of total protein was obtained. MDSCs were increased in stage IV patients compared with healthy volunteer and 2-year survival rate of the patients with higher levels of MDSC (> 1.104%PBMC) was significantly poorer (median OS, 498 vs 473 days; p = 0.048), while there was no significant difference in patients with stages I, II, and III. Conclusions: These data suggest that increased MDSC is an effective biomarker for immunosuppression due to Th2-polarization, nutritional impairment, systemic inflammation and poor prognosis in advanced patients with gastric cancer.

Human glutathione S-transferase A (GSTA) family genes are regulated by steroidogenic factor 1 (SF-1) and are involved in steroidogenesis

Steroidogenic factor 1 (SF-1) is a master regulator for steroidogenesis. In this study, we identified novel SF-1 target genes using a genome-wide promoter tiling array and a DNA microarray. SF-1 was found to regulate human glutathione S-transferase A (GSTA) family genes (hGSTA1-hGSTA4), a superfamily of detoxification enzymes clustered on chromosome 6p12. All hGSTA genes were up-regulated by transduction of SF-1 into human mesenchymal stem cells, while knockdown of endogenous SF-1 in H295R cells down-regulated all hGSTA genes. Chromatin immunoprecipitation assays, however, revealed that SF-1 bound directly to the promoters of hGSTA3 and weakly of hGSTA4. Chromosome conformation capture assays revealed that the coordinated expression of the genes was based on changes in higher-order chromatin structure triggered by SF-1, which enables the formation of long-range interactions, at least between hGSTA1 and hGSTA3 gene promoters. In steroidogenesis, dehydrogenation of the 3-hydroxy group and subsequent Δ(5)-Δ(4) isomerization are thought to be enzymatic properties of 3β-hydroxysteroid dehydrogenase (3β-HSD). Here, we demonstrated that, in steroidogenic cells, the hGSTA1 and hGSTA3 gene products catalyze Δ(5)-Δ(4) isomerization in a coordinated fashion with 3β-HSD II to produce progesterone or Δ(4)-androstenedione from their Δ(5)-precursors. Thus, hGSTA1 and hGSTA3 gene products are new members of steroidogenesis working as Δ(5)-Δ(4) isomerases.

Transcriptional regulation of human ferredoxin 1 in ovarian granulosa cells

Ferredoxin 1 (FDX1; adrenodoxin) is an iron-sulfur protein that is involved in various metabolic processes, including steroid hormone synthesis in mammalian tissues. We investigated the transcriptional regulation of FDX1 in ovarian granulosa cells. Previously, we reported that the NR5A family, including steroidogenic factor-1 (SF-1) and liver receptor homolog-1 could induce differentiation of human mesenchymal stem cells (hMSCs) into steroidogenic cells. A ChIP assay showed that SF-1 could bind to the FDX1 promoter in differentiated hMSCs. Luciferase reporter assays showed that transcription of FDX1 was synergistically activated by the NR5A family and 8Br-cAMP treatment through two SF-1 binding sites and a CRE-like sequence in a human ovarian granulosa cell line, KGN. Knockdown of FDX1 attenuated progesterone production in KGN cells. These results indicate transcription of FDX1 is regulated by the NR5A family and cAMP signaling, and participates in steroid hormone production in ovarian granulosa cells.

Androgen/androgen receptor pathway regulates expression of the genes for cyclooxygenase-2 and amphiregulin in periovulatory granulosa cells

It is well known that the androgen/androgen receptor (AR) pathway is involved in both male and female fertility in mammals. AR knockout female mice are reported to exhibit various abnormalities in follicle development, and a subfertile phenotype. In exogenous gonadotropin-induced superovulation, serum androgen levels were robustly elevated in female mice at the periovulatory stage after human chorionic gonadotropin (hCG) treatment. At this stage, ovarian AR proteins were strongly expressed in cumulus cells. Because these results suggested that the androgen/AR pathway is involved in ovulation, we investigated the expression of ovulation-related genes in the mouse ovary treated with the nonaromatizable androgen, 5α-dihydrotestosterone (DHT). DHT treatment induced the expression of the genes for cyclooxyganase-2 (Cox-2 or prostaglandin endoperoxidase synthase 2) and the epidermal growth factor-like factor, amphiregulin (Areg), in the ovary, whereas their hCG-induced expression was suppressed by the AR antagonist flutamide. These genes were also induced by DHT in AR-expressing primary granulosa and granulosa tumor-derived cells. Reporter assays, electrophoretic shift mobility assays and chromatin immunoprecipitation assays demonstrated that androgen response sequence(s) existing upstream of each gene were responsible for androgen responsiveness and were occupied by the AR in periovulatory granulosa cells. Our results suggest that the androgen/AR pathway is involved in the ovulatory process via expression of the Cox-2 and Areg genes in periovulatory granulosa cells.

A novel isoform of liver receptor homolog-1 is regulated by steroidogenic factor-1 and the specificity protein family in ovarian granulosa cells

Liver receptor homolog-1 (LRH-1) is a member of the nuclear receptor 5A (NR5A) subfamily. It is expressed in granulosa cells of the ovary and is involved in steroidogenesis and ovulation. To reveal the transcriptional regulatory mechanism of LRH-1, we determined its transcription start site in the ovary using KGN cells, a human granulosa cell tumor cell line. 5'-rapid amplification of cDNA ends PCR revealed that human ovarian LRH-1 was transcribed from a novel transcription start site, termed exon 2o, located 41 bp upstream of the reported exon 2. The novel LRH-1 isoform was expressed in the human ovary but not the liver. Promoter analysis and an EMSA indicated that a steroidogenic factor-1 (SF-1) binding site and a GC box upstream of exon 2o were required for promoter activity, and that SF-1 and specificity protein (Sp)-1/3 bind to the respective regions in ovarian granulosa cells. In KGN cells, transfection of SF-1 increased ovarian LRH-1 promoter activity and SF-1-dependent reporter activity was further enhanced when peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) was cotransfected. In Drosophila SL2 cells, Sp1 was more effective than Sp3 in enhancing promoter activity, and co-transfection of the NR5A-family synergistically increased activity. Infection with adenoviruses expressing SF-1 or PGC-1α induced LRH-1 expression in KGN cells. These results indicate that the expression of human LRH-1 is regulated in a tissue-specific manner, and that the novel promoter region is controlled by the Sp-family, NR5A-family and PGC-1α in ovarian granulosa cells in a coordinated fashion.

Serum levels of vascular endothelial growth factor are increased and correlate with malnutrition, immunosuppression involving MDSCs and systemic inflammation in patients with cancer of the digestive system

Vascular endothelial growth factor (VEGF) reportedly has an important role in the progression of malignant neoplasms and has been reported to induce myeloid-derived suppressor cells (MDSCs) that appear in cancer and inflammation. In the present study, serum concentrations of VEGF were measured in patients with digestive system cancer and the correlations with nutritional damage, immune suppression and systemic inflammation were analyzed. A significant increase in VEGF serum levels was observed in patients with esophageal, gastric and colorectal cancers compared with healthy volunteers. Levels of VEGF were inversely correlated with the serum concentrations of albumin, prealbumin and retinol-binding protein. The serum concentrations of VEGF were inversely correlated with the production of interleukin (IL)-12 and correlated with MDSC counts. VEGF levels were also correlated with neutrophil and neutrophil/lymphocyte counts and inversely correlated with lymphocyte count. Serum VEGF levels were divided at a cutoff of 500 pg/ml, with levels of prealbumin and retinol-binding protein significantly decreased in patients with higher VEGF levels. The stimulation index and IL-12 production were significantly decreased in the group with higher VEGF levels and MDSC counts tended to be higher in this group. These results demonstrated that increased production of VEGF was correlated with systemic inflammation, nutritional impairment and the inhibition of cell-mediated immunity involving MDSCs.

Correlation of production of IL-17 with immune suppression relating myeloid-derived suppressor cells (MDSC) and nutritional damages in patients with digestive system cancer

437

Background: Although a causal relationship between inflammation and innate immunity of cancer is more widely accepted today, many of the precise cellular mechanisms mediating this relationship remain unclear. Th17 cells, which produce the proinflammatory cytokine IL-17, have been recognized as one of the key factors in regulation of inflammatory bowel disease and rheumatoid arthritis. Methods: This study demonstrated that, in patients with digestive system cancers including 7 patients with esophageal, 14 with gastric, 20 with colorectal, 5 with hepatocellular, 7 with cholangiocellular, and 7 with pancreatic carcinomas, IL-17 production was correlated with MDSC level and with markers for nutritional impairment, immune suppression and chronic inflammation. Results: IL-17 production was significantly higher in patients with all types of digestive cancer than in normal volunteers. In addition, IL-17 production levels were significantly correlated with neutrophil counts and the neutrophil/lymphocyte ratio, and significantly inversely correlated with cell mediated immune response indicators (lymphocyte PHA-blastogenesis and IL-12 production) and patients’ nutritional status (prealbumin levels). Circulating MDSC levels were significantly correlated with IL-17 production. Conclusions: These results suggest that, in human gastrointestinal cancers, chronic inflammation involving IL-17 may be an important mechanism for disease progression through enhancement of immune suppression or cachexia. Controlling activation of Th17 cells may prove to be a valuable strategy for treatment of patients with gastrointestinal cancer.

Nuclear receptor 5A (NR5A) family regulates 5-aminolevulinic acid synthase 1 (ALAS1) gene expression in steroidogenic cells

5-Aminolevulinic acid synthase 1 (ALAS1) is a rate-limiting enzyme for heme biosynthesis in mammals. Heme is essential for the catalytic activities of P450 enzymes including steroid metabolic enzymes. Nuclear receptor 5A (NR5A) family proteins, steroidogenic factor-1 (SF-1), and liver receptor homolog-1 (LRH-1) play pivotal roles in regulation of steroidogenic enzymes. Recently, we showed that expression of SF-1/LRH-1 induces differentiation of mesenchymal stem cells into steroidogenic cells. In this study, genome-wide analysis revealed that ALAS1 was a novel SF-1-target gene in differentiated mesenchymal stem cells. Chromatin immunoprecipitation and reporter assays revealed that SF-1/LRH-1 up-regulated ALAS1 gene transcription in steroidogenic cells via binding to a 3.5-kb upstream region of ALAS1. The ALAS1 gene was up-regulated by overexpression of SF-1/LRH-1 in steroidogenic cells and down-regulated by knockdown of SF-1 in these cells. Peroxisome proliferator-activated receptor-γ coactivator-1α, a coactivator of nuclear receptors, also strongly coactivated expression of NR5A-target genes. Reporter analysis revealed that peroxisome proliferator-activated receptor-γ coactivator-1α strongly augmented ALAS1 gene transcription caused by SF-1 binding to the 3.5-kb upstream region. Finally knockdown of ALAS1 resulted in reduced progesterone production by steroidogenic cells. These results indicate that ALAS1 is a novel NR5A-target gene and participates in steroid hormone production.

Proximal promoter of the cytochrome P450 oxidoreductase gene: identification of microdeletions involving the untranslated exon 1 and critical function of the SP1 binding sites

CONTEXT

POR (cytochrome P450 oxidoreductase) is a ubiquitously expressed gene encoding an electron donor to all microsomal P450 enzymes and several non-P450 enzymes. POR mutations cause an autosomal recessive disorder characterized by skeletal dysplasia, adrenal dysfunction, and disorders of sex development. Although recent studies have indicated the presence of a CpG-rich region characteristic of housekeeping genes around the untranslated exon 1 (exon 1U) and a tropic effect of thyroid hormone on POR expression via thyroid hormone receptor-β, detailed regulatory mechanisms for the POR expression remain to be clarified.

OBJECTIVE

Our objective was to report a pivotal element of the proximal promoter of POR.

RESULTS

We first studied three patients (cases 1-3) with POR deficiency due to compound heterozygosity with an p.R457H mutation and transcription failure of an apparently normal allele, by oligoarray comparative genomic hybridization and serial direct sequencing of the deletion fusion points. Consequently, a 2,487-bp microdeletion involving exon 1U was identified in case 1 and an identical 49,604-bp deletion involving exon 1U and exon 1 was found in cases 2 and 3. We next analyzed the 2,487-bp region commonly deleted in cases 1-3 by in silico analysis, DNA binding analysis, luciferase assays, and methylation analysis. The results showed a critical function of the evolutionally conserved SP1 binding sites just upstream of exon 1U, especially the binding site at the position -26/-17, in the transcription of POR.

CONCLUSIONS

The results suggest that the SP1 binding sites constitute an essential element of the POR proximal promoter.

Stem cell differentiation into steroidogenic cell lineages by NR5A family

Transformants of mesenchymal stem cells (MSCs) stably expressing steroidogenic factor-1 (SF-1) undergo differentiation into steroidogenic cell-lineages by stimulation with cyclic-adenosine mono-phosphate (cAMP). Another member of NR5A nuclear orphan receptors, Liver-specific receptor homologue-1 (LRH-1), was also able to differentiate MSCs. On the other hand, we found that embryonic stem (ES) cells were hardly induced to differentiate into steroidogenic cell-lineage by the similar treatment. In this study, we developed a novel method to differentiate ES cells into steroidogenic cells. We introduced SF-1 into mouse ES cells at ROSA26 locus under regulation of Tetracycline-off (Tet-off) in order to express SF-1 in the cells at desired period. When SF-1 was induced to express after the ES cells had been differentiated into mesenchymal cell-lineage, steroid hormones were produced from the SF-1 expressing cells. This provides a safer method for supplying sufficient amount of differentiated cells toward future regenerative medicine.

Differentiation of mesenchymal stem cells and embryonic stem cells into steroidogenic cells using steroidogenic factor-1 and liver receptor homolog-1

Previously, we have demonstrated that mesenchymal stem cells could be differentiated into steroidogenic cells through steroidogenic factor-1 and 8bromo-cAMP treatment. Use of liver receptor homolog-1, another of the nuclear receptor 5A family nuclear receptors, with 8bromo-cAMP also resulted in the differentiation of human mesenchymal stem cells into steroid hormone-producing cells. The same approaches could not be applied to other undifferentiated cells such as embryonic stem cells or embryonal carcinoma cells, because the over-expression of the nuclear receptor 5A family is cytotoxic to these cells. We established embryonic stem cells carrying tetracycline-regulated steroidogenic factor-1 gene at the ROSA26 locus. The embryonic stem cells were first differentiated into a mesenchymal cell lineage by culturing on collagen IV-coated dishes and treating with pulse exposures of retinoic acid before expression of steroidogenic factor-1. Although the untreated embryonic stem cells could not be converted into steroidogenic cells by expression of steroidogenic factor-1 in the absence of leukemia inhibitory factor due to inability of the cells to survive, the differentiated cells could be successfully converted into steroidogenic cells when expression of steroidogenic factor-1 was induced. They exhibited characteristics of adrenocortical-like cells and produced a large amount of corticosterone. These results indicated that pluripotent stem cells could be differentiated into steroidogenic cells by the nuclear receptor 5A family of protein via the mesenchymal cell lineage. This approach may provide a source of cells for future gene therapy for diseases caused by steroidogenesis deficiencies.

High temperature causes masculinization of genetically female medaka by elevation of cortisol

In poikilothermic vertebrates, sex determination is sometimes influenced by environmental factors such as temperature. However, little is known about the molecular mechanisms underlying environmental sex determination. The medaka (Oryzias latipes) is a teleost fish with an XX/XY sex determination system. Recently, it was reported that XX medaka can be sex-reversed into phenotypic males by high water temperature (HT; 32-34 degrees C) treatment during the sex differentiation period. Here we report that cortisol caused female-to-male sex reversal and that metyrapone (an inhibitor of cortisol synthesis) inhibited HT-induced masculinization of XX medaka. HT treatment caused elevation of whole-body levels of cortisol, while metyrapone suppressed the elevation by HT treatment during sexual differentiation. Moreover, cortisol and 33 degrees C treatments inhibited female-type proliferation of germ cells as well as expression of follicle-stimulating hormone receptor (fshr) mRNA in XX medaka during sexual differentiation. These results strongly suggest that HT induces masculinization of XX medaka by elevation of cortisol level, which, in turn, causes suppression of germ cell proliferation and of fshr mRNA expression.

Cortisol is involved in temperature-dependent sex determination in the Japanese flounder

In vertebrates, sex is normally determined by genotype. However, in poikilothermal vertebrates, including reptiles, amphibians, and fishes, sex determination is greatly influenced by environmental factors, such as temperature. Little is known about the molecular mechanisms underlying environmental sex determination in these species. The Japanese flounder (Paralichthys olivaceus) is a teleost fish with an XX/XY sex determination system. However, XX flounder can be induced to develop into predominantly either phenotypic females or males, by rearing at 18 or 27 C, respectively, during the sex differentiation period. Therefore, the flounder provides an excellent model to study the molecular mechanisms underlying temperature-dependent sex determination. We previously showed that an aromatase inhibitor, an antiestrogen, and 27 C treatments cause masculinization of XX flounder, as well as suppression of mRNA expression of ovary-type aromatase (cyp19a1), a steroidogenic enzyme responsible for the conversion of androgens to estrogens in the gonads. Furthermore, estrogen administration completely inhibits masculinization by these treatments, suggesting suppression of cyp19a1 mRNA expression, and the resultant estrogen biosynthesis may trigger masculinization of the XX flounder induced by high water temperature. Here, we demonstrated that cortisol causes female-to-male sex reversal by directly suppressing cyp19a1 mRNA expression via interference with cAMP-mediated activation and that metyrapone (an inhibitor of cortisol synthesis) inhibits 27 C-induced masculinization of XX flounder. Moreover, cortisol concentrations in 27 C-reared juveniles were significantly higher than in 18 C-reared fishes during sexual differentiation. These results strongly suggest that masculinization by high water temperature is ascribable to elevation of cortisol concentration during gonadal sex differentiation in the flounder.

Identification of a novel distal control region upstream of the human steroidogenic acute regulatory protein (StAR) gene that participates in SF-1-dependent chromatin architecture

StAR (steroidogenic acute regulatory protein) mediates the transport of cholesterol from the outer to the inner mitochondrial membrane, the process of which is the rate-limiting step for steroidogenesis. Transcriptional regulation of the proximal promoter of the human StAR gene has been well characterized, whereas analysis of its distal control region has not. Recently, we found that SF-1 (steroidogenic factor 1) induced the differentiation of mesenchymal stem cells (MSCs) into steroidogenic cells with the concomitant strong induction of StAR expression. Here, we show, using differentiated MSCs, that StAR expression is regulated by a novel distal control region. Using electrophoretic mobility shift (EMSA) and chromatin immunoprecipitation (ChIP) assays, we identified novel SF-1 binding sites between 3,000 and 3,400 bp upstream of StAR. A luciferase reporter assay revealed that the region worked as a strong regulator to exert maximal transcription of StAR. ChIP analysis of histone H3 revealed that upon SF-1 expression, nucleosome eviction took place at the SF-1 binding sites, not only in the promoter but also in the distal SF-1 binding sites. Chromosome conformation capture analysis revealed that the region upstream of StAR formed a chromatin loop both in the differentiated MSCs and in KGN cells, a human granulosa cell tumor cell line, where SF-1 is endogenously expressed. Finally, SF-1 knockdown resulted in disrupted formation of this chromatin loop in KGN cells. These results indicate that the novel distal control region participate in StAR activation through SF-1 dependent alterations of chromatin structure, including histone eviction and chromatin loop formation.

PPAR-gamma coactivator-1alpha regulates progesterone production in ovarian granulosa cells with SF-1 and LRH-1

Previously, we demonstrated that bone marrow-derived mesenchymal stem cells (MSCs) differentiate into steroidogenic cells such as Leydig and adrenocortical cells by the introduction of steroidogenic factor-1 (SF-1) and treatment with cAMP. In this study, we employed the same approach to differentiate umbilical cord blood (UCB)-derived MSCs. Despite UCB-MSCs differentiating into steroidogenic cells, they exhibited characteristics of granulosa-luteal-like cells. We found that peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) was expressed and further induced by cAMP stimulation in UCB-MSCs. Consistent with these results, tissue-specific expression of Pgc-1alpha was observed in rat ovarian granulosa cells. PGC-1alpha binds to the NR5A family [SF-1 and liver receptor homolog-1 (LRH-1)] of proteins and markedly enhances their transcriptional activities. Reporter assays revealed that PGC-1alpha activated the promoter activities of SF-1 and LRH-1 target genes. Infection of KGN cells (a human cell line derived from granulosa cells) with adenoviruses expressing PGC-1alpha resulted in the induction of steroidogenesis-related genes and stimulation of progesterone production. PGC-1alpha also induced SF-1 and LRH-1, with the latter induced to a greater extent. Knockdown of Pgc-1alpha in cultured rat granulosa cells resulted in attenuation of gene expression as well as progesterone production. Transactivation of the NR5A family by PGC-1alpha was repressed by Dax-1. PGC-1alpha binds to the activation function 2 domain of NR5A proteins via its consensus LXXLL motif. These results indicate that PGC-1alpha is involved in progesterone production in ovarian granulosa cells by potentiating transcriptional activities of the NR5A family proteins.

Liver receptor homolog-1 regulates the transcription of steroidogenic enzymes and induces the differentiation of mesenchymal stem cells into steroidogenic cells

Steroidogenic factor-1 (SF-1, also known as Ad4BP) has been demonstrated to be a primary transcriptional regulator of steroidogenic-related genes. However, mRNA for liver receptor homolog-1 (LRH-1), which together with SF-1, belongs to the NR5A nuclear receptor family, is expressed at much higher levels than SF-1 mRNA in the human gonad. In our previous studies, we demonstrated that SF-1 induced the differentiation of bone marrow-derived mesenchymal stem cells (MSCs) into steroidogenic cells such as Leydig or adrenocortical cells. The introduction of LRH-1 into human MSCs (hMSCs) with the aid of cAMP also induced the expression of steroidogenic enzymes, including CYP17, and their differentiation into steroid hormone-producing cells. Promoter analysis, EMSA, and chromatin immunoprecipitation assay using LRH-1-transduced hMSCs indicated that three LRH-1 binding sites were responsible for CYP17 transactivation. Immunohistochemical studies showed that LRH-1 protein was expressed in human Leydig cells. The CYP17 promoter region was highly methylated in hMSCs, whereas it was demethylated by the introduction of LRH-1 and cAMP treatment. These results indicate that LRH-1 could represent another key regulator of the steroidogenic lineage in MSCs and play a vital role in steroid hormone production in human Leydig cells.

Regulation of P450 oxidoreductase by gonadotropins in rat ovary and its effect on estrogen production

BACKGROUND

P450 oxidoreductase (POR) catalyzes electron transfer to microsomal P450 enzymes. Its deficiency causes Antley-Bixler syndrome (ABS), and about half the patients with ABS have ambiguous genitalia and/or impaired steroidogenesis. POR mRNA expression is up-regulated when mesenchymal stem cells (MSCs) differentiate into steroidogenic cells, suggesting that the regulation of POR gene expression is important for steroidogenesis. In this context we examined the regulation of POR expression in ovarian granulosa cells by gonadotropins, and its possible role in steroidogenesis.

METHODS

Changes in gene expression in MSCs during differentiation into steroidogenic cells were examined by DNA microarray analysis. Changes in mRNA and protein expression of POR in the rat ovary or in granulosa cells induced by gonadotropin treatment were examined by reverse transcription-polymerase chain reaction and western blotting. Effects of transient expression of wild-type or mutant (R457H or V492E) POR proteins on the production of estrone in COS-7 cells were examined in vitro. Effects of POR knockdown were also examined in estrogen producing cell-line, KGN cells.

RESULTS

POR mRNA was induced in MSCs following transduction with the SF-1 retrovirus, and was further increased by cAMP treatment. Expression of POR mRNA, as well as Cyp19 mRNA, in the rat ovary were induced by equine chorionic gonadotropin and human chorionic gonadotropin. POR mRNA and protein were also induced by follicle stimulating hormone in primary cultured rat granulosa cells, and the induction pattern was similar to that for aromatase. Transient expression of POR in COS-7 cells, which expressed a constant amount of aromatase protein, greatly increased the rate of conversion of androstenedione to estrone, in a dose-dependent manner. The expression of mutant POR proteins (R457H or V492E), such as those found in ABS patients, had much less effect on aromatase activity than expression of wild-type POR proteins. Knockdown of endogenous POR protein in KGN human granulosa cells led to reduced estrone production, indicating that endogenous POR affected aromatase activity.

CONCLUSION

We demonstrated that the expression of POR, together with that of aromatase, was regulated by gonadotropins, and that its induction could up-regulate aromatase activity in the ovary, resulting in a coordinated increase in estrogen production.