Dual mechanisms of regulation of transcription of luteinizing hormone receptor gene by nuclear orphan receptors and histone deacetylase complexes

Testosterone-Induced H3K27 Deacetylation Participates in Granulosa Cell Proliferation Suppression and Pathogenesis of Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is the leading cause of infertility in reproductive-age women. Hyperandrogenism, polycystic ovaries, and chronic anovulation are its typical clinical features. However, the correlation between hyperandrogenism and ovarian follicle growth aberrations remains poorly understood. To advance our understanding of the molecular alterations in ovarian granulosa cells (GCs) with excessive androgen, epigenetic changes and affected gene expression in human granulosa-lutein cells and immortalized human GCs were evaluated. A PCOS mouse model induced by dihydrotestosterone was also established. This study found that excessive testosterone significantly decreased the acetylation of lysine 27 on histone H3 (H3K27Ac). H3K27Ac chromatin immunoprecipitation-sequencing data showed down-regulated expression of cell cycle-related genes CCND1, CCND3, and PCNA, which was confirmed by real-time quantitative PCR and Western blot analysis. Testosterone application impeding cell proliferation was also shown by Ki-67 immunofluorescence and flow-cytometric analysis. Moreover, testosterone influenced casein kinase 2 alpha (CK2α) nuclear translocation, which increased the phosphorylation level of histone deacetylase 2 (HDAC2). Inhibition of CK2α nuclear translocation or silenced HDAC2 expression efficiently retarded H3K27 acetylation. PCOS mouse model experiments also demonstrated decreased H3K27Ac and enhanced HDAC2 phosphorylation in GCs. Cell proliferation-related genes were also down-regulated in PCOS mouse GCs. In conclusion, hyperandrogenism in human and mouse GCs caused H3K27Ac aberrations, which are associated with CK2α nuclear translocation and HDAC2 phosphorylation, participating in abnormal follicle development in patients with PCOS.

Ovulatory signal-triggered chromatin remodeling in ovarian granulosa cells by HDAC2 phosphorylation activation-mediated histone deacetylation

BACKGROUND

Epigenetic reprogramming is involved in luteinizing hormone (LH)-induced ovulation; however, the underlying mechanisms are largely unknown.

RESULTS

We here observed a rapid histone deacetylation process between two waves of active transcription mediated by the follicle-stimulating hormone (FSH) and the LH congener human chorionic gonadotropin (hCG), respectively. Analysis of the genome-wide H3K27Ac distribution in hCG-treated granulosa cells revealed that a rapid wave of genome-wide histone deacetylation remodels the chromatin, followed by the establishment of specific histone acetylation for ovulation. HDAC2 phosphorylation activation coincides with histone deacetylation in mouse preovulatory follicles. When HDAC2 was silenced or inhibited, histone acetylation was retained, leading to reduced gene transcription, retarded cumulus expansion, and ovulation defect. HDAC2 phosphorylation was associated with CK2α nuclear translocation, and inhibition of CK2α attenuated HDAC2 phosphorylation, retarded H3K27 deacetylation, and inactivated the ERK1/2 signaling cascade.

CONCLUSIONS

This study demonstrates that the ovulatory signal erases histone acetylation through activation of CK2α-mediated HDAC2 phosphorylation in granulosa cells, which is an essential prerequisite for subsequent successful ovulation.

miR-195-3p alleviates homocysteine-mediated atherosclerosis by targeting IL-31 through its epigenetics modifications

Atherosclerosis is a serious age-related disease, which has a tremendous impact on health care globally. Macrophage inflammation is crucial for the initiation and progression of atherosclerosis, and microRNAs (miRNAs) recently have emerged as potent modulators of inflammation, while the underlying mechanisms of its involvement in homocysteine (Hcy)-mediated macrophage inflammation of atherosclerosis remain largely unknown. Here, we demonstrated that elevated Hcy inhibits the expression of miR-195-3p, which in turn enhances IL-31 expression and thereby causes the secretion of macrophages pro-inflammatory factors IL-1β, IL-6 and TNF-α and accelerate atherosclerosis. Furthermore, we identified that Hcy can induce DNA hypermethylation and H3K9 deacetylation of miR-195-3p promoter due to the increased the binding of DNMT3a and HDAC11 at its promoter. More importantly, Sp1 interacts with DNMT3a suppressed the binding of HDAC11 at miR-195-3p promoter and promoted its transcription. In summary, our results revealed a novel mechanism that transcriptional and epigenetic regulation of miR-195-3p inhibits macrophage inflammation through targeting IL-31, which provides a candidate diagnostic marker and novel therapeutic target in cardiovascular diseases induced by Hcy.

Thyroid Hormone Receptor Beta as Tumor Suppressor: Untapped Potential in Treatment and Diagnostics in Solid Tumors

There is compelling evidence that the nuclear receptor TRβ, a member of the thyroid hormone receptor (TR) family, is a tumor suppressor in thyroid, breast, and other solid tumors. Cell-based and animal studies reveal that the liganded TRβ induces apoptosis, reduces an aggressive phenotype, decreases stem cell populations, and slows tumor growth through modulation of a complex interplay of transcriptional networks. TRβ-driven tumor suppressive transcriptomic signatures include repression of known drivers of proliferation such as PI3K/Akt pathway, activation of novel signaling such as JAK1/STAT1, and metabolic reprogramming in both thyroid and breast cancers. The presence of TRβ is also correlated with a positive prognosis and response to therapeutics in BRCA+ and triple-negative breast cancers, respectively. Ligand activation of TRβ enhances sensitivity to chemotherapeutics. TRβ co-regulators and bromodomain-containing chromatin remodeling proteins are emergent therapeutic targets. This review considers TRβ as a potential biomolecular diagnostic and therapeutic target.

Mechanism underlying the stimulation by IGF-1 of LHCGR expression in porcine granulosa cells

IGF-1 plays important roles in mammalian fertility by promoting cell growth and increasing steroid hormone secretion. Although IGF-1 significantly upregulated luteinizing hormone/choriogonadotropin receptor (LHCGR) gene expression in granulosa cells in a previous study, the mechanism was unclear. The present experiment was designed to primarily explore the regulation of LHCGR expression by IGF-1. First, based on a porcine LHCGR double-luciferase reporter experiment, c-Fos significantly inhibited the activity of the LHCGR promoter. Second, porcine granulosa cells were cultured in vitro with IGF-1, and we observed that the expression of LHCGR was significantly increased and the expression of c-Fos mRNA significantly reduced. After c-Fos overexpression in granulosa cells, IGF-1 attenuated the inhibitory effect of c-Fos on LHCGR. Furthermore, the level of LHCGR mRNA stimulated by IGF-1 in the presence of SB203580 was markedly lower than that of IGF-1 alone action. In conclusion, IGF-1 enhanced the expression of LHCGR by regulating c-Fos in granulosa cells, which may be mediated by the p38MAPK-signaling pathway.

Retinoblastoma binding protein 4 represses HIV-1 long terminal repeat-mediated transcription by recruiting NR2F1 and histone deacetylase

Human immunodeficiency virus (HIV) transcription is closely associated with chromatin remodeling. Retinoblastoma binding protein 4 (RBBP4) is a histone chaperone implicated in chromatin remodeling. However, the role of RBBP4 in HIV-1 infection and the underlying mechanism remain elusive. In the present study, we showed that RBBP4 plays a negative regulatory role during HIV-1 infection. RBBP4 expression was significantly increased in HIV-1-infected T cells. RBBP4 binds to the HIV-1 long terminal repeat (LTR)， represses HIV-1 LTR-mediated transcription through recruiting nuclear receptor subfamily 2 group F member 1(NR2F1) and histone deacetylase 1 and 2 (HDAC1/2) to HIV-1 LTR, and further controls local histone 3 (H3) deacetylation and chromatin compaction. Furthermore, the occupancy of RBBP4, HDAC1/2, and NR2F1 on LTR in HIV-latent J-lat cells was significantly higher than that in HIV-1-activated cells. In conclusion, our results establish RBBP4 as a new potent antiretroviral factor, which may provide theoretical basis for the treatment of HIV in the future.

Histone Acetylation and the Regulation of Major Histocompatibility Class II Gene Expression

Major histocompatibility complex (MHC) class II molecules are essential for processing and presenting exogenous pathogen antigens to activate CD4⁺ T cells. Given their central role in adaptive immune responses, MHC class II genes are tightly regulated in a tissue- and activation-specific manner. The regulation of MHC class II gene expression involves various transcription factors that interact with conserved proximal cis-acting regulatory promoter elements, as well as MHC class II transactivator that interacts with a variety of chromatin remodeling machineries. Recent studies also identified distal regulatory elements within MHC class II gene locus that provide enormous insight into the long-range coordination of MHC class II gene expression. Novel therapeutic modalities that can modify MHC class II genes at the epigenetic level are emerging and are currently in preclinical and clinical trials. This review will focus on the role of chromatin remodeling, particularly remodeling that involves histone acetylation, in the constitutive and inducible regulation of MHC class II gene expression.

TNF-α Suppressed FSH-Induced LH Receptor Expression Through Transcriptional Regulation in Rat Granulosa Cells

Several inflammatory cytokines regulate ovarian function. TNF-α is produced in granulosa cells under physiological conditions and has a reciprocal action on follicle development. In contrast, in pelvic inflammatory diseases, TNF-α is excessively produced in the pelvic cavity and has an adverse effect on reproductive functions. The objective of this study was to elucidate the mechanism of action of TNF-α on the expression of LH receptor (LHR) in immature rat granulosa cells. TNF-α suppressed FSH-induced LHR mRNA and protein expression and was not associated with cAMP accumulation. By using a luciferase assay, the construct containing base pairs -1389 to -1 of the rat Lhcgr promoter revealed that TNF-α decreased FSH-induced promoter activity. In response to TNF-α, nuclear factor (NF)-κB p65 was translocated to the nucleus, and the suppressive effect of TNF-α on LHR mRNA expression was abrogated by an NF-κB inhibitor. In a chromatin immunoprecipitation assay, TNF-α induced the association of NF-κB p65 with the rat Lhcgr transcriptional promoter region. NF-κB p65 and histone deacetylase (HDAC) interact to mediate expression of several genes at a transcriptional level. HDAC activity is thought to induce tight connections within local chromatin structures and repress gene transcription. Furthermore, the TNF-α-induced suppression of LHR mRNA expression was blocked by an HDAC inhibitor. Taken together, these results suggest that the interaction of NF-κB p65 with HDAC in the promoter region of rat Lhcgr might be responsible for TNF-α action on the regulation of LHR.

Vitamin D represses dentin matrix protein 1 in cementoblasts and osteocytes

Calcium and phosphorus homeostasis is achieved by interplay among hormones, including 1,25(OH)2D3 (1,25D), parathyroid hormone, and fibroblast growth factor 23 (FGF23), and their interactions with other proteins. For example, mutations in dentin matrix protein 1 (DMP-1) result in increased FGF23 and hypophosphatemic rickets. 1,25D is reported to modulate FGF23; thus, we hypothesized that 1,25D may be involved in modulating DMP-1 in an intermediary step. Murine cementoblasts (OCCM-30) and osteocyte-like cells (MLO-Y4 and MLO-A5), known to express DMP-1, were used to analyze effects of 1,25D on DMP-1 expression in vitro. DMP-1 mRNA levels decreased by 50% (p < .05) in the presence of 1,25D in all cell types, while use of a vitamin D receptor (VDR) agonist (EB1089) and antagonist (23S,25S)-DLAM-2P confirmed that VDR pathway activation was required for this response. Further analysis showed that histone deacetylase recruitment was necessary, but neither protein kinase A nor C pathways were required. In conclusion, our results support the hypothesis that 1,25D regulates DMP-1 expression through a VDR-dependent mechanism, possibly contributing to local changes in bone/tooth mineral homeostasis.

Orally applied doxazosin disturbed testosterone homeostasis and changed the transcriptional profile of steroidogenic machinery, cAMP/cGMP signalling and adrenergic receptors in Leydig cells of adult rats

Doxazosin (Doxa) is an α1-selective adrenergic receptor (ADR) antagonist widely used, alone or in combination, to treat high blood pressure, benign prostatic hyperplasia symptoms, and recently has been suggested as a potential drug for prostate cancer prevention/treatment. This study was designed to evaluate the effect of in vivo Doxa po-application, in clinically relevant dose, on: (i) steroidogenic machinery homeostasis; (ii) cAMP/cGMP signalling; (iii) transcription profile of ADR in Leydig cells of adult rats. The results showed that po-application of Doxa for once (1×Doxa), or for two (2×Doxa) or 10 (10×Doxa) consecutive days significantly disturbed steroidogenic machinery homeostasis in Leydig cells. Doxa po-application significantly decreased circulating luteinizing hormone and androgens levels. The level of androgens in testicular interstitial fluid and that extracted from testes obtained from 1×Doxa/2×Doxa rats decreased, although it remained unchanged in 10×Doxa rats. Similarly, the ex vivo basal androgen production followed in testes isolated from 1×Doxa/2×Doxa rats decreased, while remained unchanged in 10×Doxa rats. Differently, ex vivo testosterone production and steroidogenic capacity of Leydig cells isolated from 1×Doxa/2×Doxa rats was stimulated, while 10×Doxa had opposite effect. In the same cells, cAMP content/release showed similar stimulatory effect, but back to control level in Leydig cells of 10×Doxa. 1×Doxa/2×Doxa decreased transcripts for cAMP specific phosphodiesterases Pde7b/Pde8b, whereas 10×Doxa increased Pde4d. All types of treatment reduced the expression of genes encoding protein kinase A (PRKA) regulatory subunit (Prkar2b), whereas only 10×Doxa stimulated catalytic subunit (Prkaca). Doxa application more affected cGMP signalling: stimulated transcription of constitutive nitric oxide synthases (Nos1, Nos3) in time-dependent manner, whereas reduced inducible Nos2. 10×Doxa increased guanylyl cyclase 1 transcript and PRKG1 protein in Leydig cells. Orally applied Doxa significantly disturbed the transcriptional 'signature' of steroidogenic machinery, cAMP/cGMP signalling and ADRs and β-ADRs kinases in Leydig cells, thus giving new molecular insights into the role of cAMP/cGMP/adrenalin signalling in Leydig cells homeostasis.

Neuron-restrictive silencer factor functions to suppress Sp1-mediated transactivation of human secretin receptor gene

In the present study, a functional neuron restrictive silencer element (NRSE) was initially identified in the 5' flanking region (-83 to -67, relative to ATG) of human secretin receptor (hSCTR) gene by promoter assays coupled with scanning mutation analyses. The interaction of neuron restrictive silencer factor (NRSF) with this motif was later indicated via gel mobility shift and ChIP assays. The silencing activity of NRSF was confirmed by over-expression and also by shRNA knock-down of endogenous NRSF. These studies showed an inverse relationship between the expression levels of NRSF and hSCTR in the cells. As hSCTR gene was previously shown to be controlled by two GC-boxes which are regulated by the ratio of Sp1 to Sp3, in the present study, the functional interactions of NRSF and Sp proteins to regulate hSCTR gene was investigated. By co-immunoprecipitation assays, we found that NRSF could be co-precipitated with Sp1 as well as Sp3 in PANC-1 cells. Interestingly, co-expressions of these factors showed that NRSF could suppress Sp1-mediated, but not Sp3-mediated, transactivation of hSCTR. Taken together, we propose here that the down-regulatory effects of NRSF on hSCTR gene expression are mediated via its suppression on Sp1-mediated transactivation.

Okadaic acid inhibits the trichostatin A-mediated increase of human CYP46A1 neuronal expression in a ERK1/2-Sp3-dependent pathway

The CYP46A1 gene codes for the cholesterol 24-hydroxylase, a cytochrome P450 specifically expressed in neurons and responsible for the majority of cholesterol turnover in the central nervous system. Previously, we have demonstrated the critical participation of Sp transcription factors in the CYP46A1 response to histone deacetylase (HDAC) inhibitors, and in this study we investigated the involvement of intracellular signaling pathways in the trichostatin A (TSA) effect. Our results show that pretreatment of neuroblastoma cells with chemical inhibitors of mitogen-activated kinase kinase (MEK)1 significantly potentiates the TSA-dependent induction of cholesterol 24-hydroxylase, whereas inhibition of protein phosphatases by okadaic acid (OA) or overexpression of MEK1 partially impairs the TSA effect without affecting histone hyperacetylation at the promoter. Immunoblotting revealed that TSA treatment decreases ERK1/2 phosphorylation concomitantly with a decrease in Sp3 binding activity, which are both reversed by pretreatment with OA. Chromatin immunoprecipitation analysis demonstrated that TSA induces the release of p-ERK1/2 from the CYP46A1 proximal promoter, whereas pretreatment with OA restores the co-occupancy of Sp3-ERK1/2 in the same promoter fragments. We demonstrate for the first time the participation of MEK-ERK1/2 signaling pathway in HDAC inhibitor-dependent induction of cytochrome P450 gene expression, underlying the importance of this regulatory signaling mechanism in the control of brain cholesterol elimination.

Association of luteinizing hormone receptor gene expression with cell cycle progression in granulosa cells

During hormonally induced ovarian follicle growth, granulosa cell proliferation increases and returns to baseline prior to the administration of an ovulatory stimulus. Several key genes appear to follow a similar pattern, including the luteinizing hormone receptor (LHCGR), suggesting an association between cell cycle progression and gene expression. The expression of LHCGR mRNA in granulosa cells isolated from immature rats and treated in culture with FSH increased in a time-dependent manner, whereas administration of the cell cycle inhibitor mimosine completely suppressed expression. Although forskolin was able to induce luteinization in cells treated with mimosine, human chorionic gonadotropin had no effect, indicating the functional loss of LHCGR. The effects of mimosine on cell cycle progression and LHCGR mRNA expression were reversible within 24 h of mimosine removal. Cell cycle inhibition did not alter the stability of LHCGR mRNA, indicating that the primary effect was at the transcriptional level. To determine whether the relationship between LHCGR expression and cell cycle were relevant in vivo, immature rats were given a bolus of PMSG, followed by a second injection of either saline or PMSG 24 h later to augment levels of proliferation. The expression of LHCGR mRNA was elevated in the ovaries of animals receiving a supplement of PMSG. Mimosine also blocked cell cycle progression and LHCGR mRNA expression in macaque granulosa cells isolated following controlled ovarian stimulation cycles and in two different mouse Leydig tumor lines. These data collectively indicate that LHCGR mRNA is expressed as a function of the passage of cells across the G1-S phase boundary.

In vitro nuclear interactome of the HIV-1 Tat protein

BACKGROUND

One facet of the complexity underlying the biology of HIV-1 resides not only in its limited number of viral proteins, but in the extensive repertoire of cellular proteins they interact with and their higher-order assembly. HIV-1 encodes the regulatory protein Tat (86-101aa), which is essential for HIV-1 replication and primarily orchestrates HIV-1 provirus transcriptional regulation. Previous studies have demonstrated that Tat function is highly dependent on specific interactions with a range of cellular proteins. However they can only partially account for the intricate molecular mechanisms underlying the dynamics of proviral gene expression. To obtain a comprehensive nuclear interaction map of Tat in T-cells, we have designed a proteomic strategy based on affinity chromatography coupled with mass spectrometry.

RESULTS

Our approach resulted in the identification of a total of 183 candidates as Tat nuclear partners, 90% of which have not been previously characterised. Subsequently we applied in silico analysis, to validate and characterise our dataset which revealed that the Tat nuclear interactome exhibits unique signature(s). First, motif composition analysis highlighted that our dataset is enriched for domains mediating protein, RNA and DNA interactions, and helicase and ATPase activities. Secondly, functional classification and network reconstruction clearly depicted Tat as a polyvalent protein adaptor and positioned Tat at the nexus of a densely interconnected interaction network involved in a range of biological processes which included gene expression regulation, RNA biogenesis, chromatin structure, chromosome organisation, DNA replication and nuclear architecture.

CONCLUSION

We have completed the in vitro Tat nuclear interactome and have highlighted its modular network properties and particularly those involved in the coordination of gene expression by Tat. Ultimately, the highly specialised set of molecular interactions identified will provide a framework to further advance our understanding of the mechanisms of HIV-1 proviral gene silencing and activation.

Assessment of female and male fertility in Sprague-Dawley rats administered vorinostat, a histone deacetylase inhibitor

BACKGROUND

Histone deacetylase (HDAC) inhibitors have been shown to mediate the regulation of gene expression, induce cell growth, cell differentiation, and apoptosis of tumor cells. These compounds are now marketed or are in clinical development. One such HDAC inhibitor, vorinostat (suberoylanilide hydroxamic acid [SAHA], Zolinza), was assessed for its potential effects on fertility in Sprague-Dawley rats.

METHODS

Female rats were administered oral dose levels of 0 (vehicle only), 15, 50, or 150 mg/kg/day of vorinostat for 14 days before cohabitation, during cohabitation, and through Gestation Day (GD) 7. In a separate study, male rats were administered oral dose levels of 0 (vehicle only), 20, 50, or 150 mg/kg/day for 10 weeks before cohabitation, during cohabitation, and until the day before scheduled sacrifice (approximately 14 weeks total). In both studies, % peri-implantation loss and % postimplantation loss were evaluated on GD 15-17. Testicular weight and histomorphology, cauda epididymal sperm count, and sperm motility were evaluated in the male rat study at termination.

RESULTS

There were treatment-related decreases in body weight gain at 150 mg/kg/day in both studies. There were no effects on mating or fertility indices in either study. In the female study there were increased numbers of corpora lutea in all drug-treated groups (only 1 or 2 affected dams in low and mid-dose groups), and a marked increase in percent postimplantation loss only in the high-dose group. No treatment-related effects were observed on litter or sperm parameters of the male study.

CONCLUSIONS

Vorinostat had no effects on mating or fertility in rats up to 150 mg/kg/day. There were no indications of reproductive toxicity in drug-treated male rats. Increases in corpora lutea or resorptions were observed in treated female rats.

Competitive inhibition of histone deacetylase activity by trichostatin A and butyrate

Histone deacetylases (HDACs) play a pivotal role in gene expression through their involvement in chromatin remodeling. The abnormal targeting or retention of HDACs to DNA regulatory regions is observed in many cancers, and hence HDAC inhibitors are being tested as promising anti-tumor agents. The results of previous kinetic studies, characterizing trichostatin A (TSA), as well as butyrate, as HDAC noncompetitive inhibitors, conflict with crystallographic and homology modeling data suggesting that TSA should act as a competitive inhibitor. Our results demonstrate that each of the HDAC inhibitors TSA and butyrate inhibits HDAC activity in a competitive fashion. Co-immunoprecipitation studies show that the inhibition of HDAC1 and HDAC2 activity by TSA does not disturb the extensive level of their association in the human breast cancer cell line MCF-7. Moreover, the inhibition of HDAC activity by TSA does not interfere with the interaction of HDAC1 and HDAC2 with Sin3A, a core component of the Sin3 complex. Thus, repressor complexes such as Sin3, appear to be stable in the presence of TSA. The association of HDAC2 with transcription factor Sp1 is also not affected by TSA.

Dihydrotestosterone influenced numbers of healthy follicles and follicular amounts of LH receptor mRNA during the follicular phase of the estrous cycle in gilts

The present experiments were conducted to determine androgenic effects on numbers, health, and amounts of gonadotropin receptor mRNA in late developing follicles of gilts. Gilts (n=5 per group) received daily injections of one of the following treatments on days 13–16 or days 13–18 of the estrous cycle: corn oil, 5α-dihydrotestosterone (DHT, 10 mg), flutamide (1.5 g, an androgen receptor inhibitor), DHT (10 mg) plus flutamide (1.5 g), testosterone (10 mg), and testosterone (10 mg) plus flutamide (1.5 g). Ovarian follicles ≥5 mm in diameter were evaluated on day 17 or 19, 24 h after receiving the last treatment dose. Follicles were classified as healthy (H), moderately atretic (MA), or very atretic (VA). Treatment with DHT increased (P<0.05) the numbers of H follicles relative to control gilts on days 17 and 19. DHT administration from days 13 to 16 diminished (P<0.05) the amounts of LH receptor (LHR) mRNA in H follicles from day 17 (relative amounts: 1.45±0.33 and 2.72±0.33 for DHT- and vehicle-treated gilts respectively). The effects of DHT on numbers of H follicles and LHR mRNA were not observed in gilts receiving DHT plus flutamide. Androgens did not influence numbers of MA, VA, and total follicles, or follicular estradiol-17β concentrations and amounts of FSHR mRNA. Treating gilts with DHT during follicular recruitment and selection did not induce changes in the numbers of total follicles ≥5 mm, but rather increased the numbers of healthy follicles in this follicular population in association with decreased amounts of LHR mRNA.

The histone deacetylase inhibitor trichostatin A mediates upregulation of 5-lipoxygenase promoter activity by recruitment of Sp1 to distinct GC-boxes

The histone deacetylase inhibitor trichostatin A (TsA) potently induces 5-lipoxygenase (5-LO) promoter activity in reporter gene assays as well as 5-LO mRNA expression. We identified two proximal Sp1/Sp3 binding sites in the 5-LO gene promoter mediating the TsA effect in both 5-LO-negative HeLa cells and in 5-LO expressing Mono Mac 6 (MM6) cells, the tandem GC-boxes, by contrast, were not important for the TsA effect. TsA neither altered the protein expression levels of Sp1/Sp3 nor of the histone deacetylases HDAC1/2, nor did it apparently change the protein complex formation by these factors. Also, treatment of cells with TsA did not change the binding affinity of Sp1/Sp3 in cell extracts, as tested by DAPA analysis using probes containing the proximal GC boxes. However, in the living cell TsA induced Sp1, Sp3 and RNA polymerase II recruitment to the 5-LO promoter without changing the acetylation status of histone protein H4. Cotransfection studies suggest that both Sp1 and Sp3 can mediate the TsA effect. This is the first report demonstrating that Sp3 is involved in the regulation of 5-LO promoter activity. In summary, we show that TsA increases 5-LO promoter activity by the enhanced recruitment of Sp1 and Sp3 to the 5-LO promoter.

Novel biological and possible applicable roles of LH/hCG receptor

Luteinizing hormone/human chorionic gonadotropin (LH/hCG) receptors are widely expressed in gonadal cells, however, the presence of these receptors has also been demonstrated in several other non-gonadal female and male tissues. The expression level of non-gonadal LH/hCG receptors is much lower than in gonads, although their expression is regulated by similar mechanisms and they also exert biological effects using similar signaling pathways. Hormonally regulated LH/hCG receptor expression in the oviduct suggests that LH could be involved in the regulation of its contraction, gametes/embryos transport and synchronization of the fertilization. One of the major roles of the myometrial LH/hCG receptors may also be the stimulation of growth and maintenance of the uterine relaxation during pregnancy. In pigs, LH seems to be one of the pleiotropic factors which influence the endometrial prostaglandin F(2alpha) synthesis and initiation of the luteolysis. The LH/hCG receptor expression in several cancer cells provides new possibilities for developing new strategies for targeted cancer therapy based on lytic LH/hCG conjugates.

Molecular mechanisms of ovulation: co-ordination through the cumulus complex

Successful ovulation requires that developmentally competent oocytes are released with appropriate timing from the ovarian follicle. Somatic cells of the follicle sense the ovulatory stimulus and guide resumption of meiosis and release of the oocyte, as well as structural remodelling and luteinization of the follicle. Complex intercellular communication co-ordinates critical stages of oocyte maturation and links this process with release from the follicle. To achieve these outcomes, ovulation is controlled through multiple inputs, including endocrine hormones, immune and metabolic signals, as well as intrafollicular paracrine factors from the theca, mural and cumulus granulosa cells and the oocyte itself. This review focuses on the recent advances in understanding of molecular mechanisms that commence after the gonadotrophin surge and culminate with release of the oocyte. These mechanisms include intracellular signalling, gene regulation and remodelling of tissue structure in each of the distinct ovarian compartments. Most critical ovulatory mediators exert effects through the cumulus cell complex that surrounds and connects with the oocyte. The convergence of ovulatory signals through the cumulus complex co-ordinates the key mechanistic processes that mediate and control oocyte maturation and ovulation.

FSH signaling pathways in immature granulosa cells that regulate target gene expression: branching out from protein kinase A

Follicle-stimulating hormone (FSH) is necessary and sufficient to induce maturation of ovarian follicles to a mature, preovulatory phenotype in the intact animal, resulting in the generation of mature eggs and production of estrogen. FSH accomplishes these actions by inducing a complex pattern of gene expression in target granulosa cells that is regulated by input from many different signaling cascades, including those for the extracellular regulated kinases (ERKs), p38 mitogen-activated protein kinases (MAPKs), and phosphatidylinositol-3 kinase (PI3K). The upstream kinase that appears to be responsible for initiating all of the signaling that regulates gene expression in these epithelial cells is protein kinase A (PKA). PKA not only signals to directly phosphorylate transcription factors like cAMP response element binding protein and to promote chromatin remodeling by phosphorylating histone H3, this versatile kinase also enhances the activity of the p38 MAPK, ERK, and PI3K pathways. Additionally, accumulating evidence suggests that activation of a single signaling cascade downstream of PKA is not sufficient to activate target gene expression. Rather, cross-talk between and among signaling cascades is required. We will review the signaling cascades activated by FSH in granulosa cells and how these cascades contribute to the regulation of select target gene expression.

Regulation of histone deacetylase 4 expression by the SP family of transcription factors

Histone deacetylases mediate critical cellular functions but relatively little is known about mechanisms controlling their expression, including expression of HDAC4, a class II HDAC implicated in the modulation of cellular differentiation and viability. Endogenous HDAC4 mRNA, protein levels and promoter activity were all readily repressed by mithramycin, suggesting regulation by GC-rich DNA sequences. We validated consensus binding sites for Sp1/Sp3 transcription factors in the HDAC4 promoter through truncation studies and targeted mutagenesis. Specific and functional binding by Sp1/Sp3 at these sites was confirmed with chromatin immunoprecipitation (ChIP) and electromobility shift assays (EMSA). Cotransfection of either Sp1 or Sp3 with a reporter driven by the HDAC4 promoter led to high activities in SL2 insect cells (which lack endogenous Sp1/Sp3). In human cells, restored expression of Sp1 and Sp3 up-regulated HDAC4 protein levels, whereas levels were decreased by RNA-interference-mediated knockdown of either protein. Finally, variable levels of Sp1 were in concordance with that of HDAC4 in a number of human tissues and cancer cell lines. These studies together characterize for the first time the activity of the HDAC4 promoter, through which Sp1 and Sp3 modulates expression of HDAC4 and which may contribute to tissue or cell-line-specific expression of HDAC4.

Epigenetic control of ovarian function: the emerging role of histone modifications

The dynamic nature of the ovarian follicle makes it an ideal model to study the coordinated activation and inactivation of genes related to cell growth and differentiation. Much progress has been made in identifying transcription factors that promote the transcription of ovarian genes mediating gonadotropin action and steroidogenesis, but how these factors promote transcription in the context of chromatin is not well understood. Over the past 5 years, epigenetic regulation of ovarian genes through histone modifications has been the focus of an increasing number of studies. Several coactivators and corepressors associated with transcription factors are in fact histone acetyltransferases and histone deacetylases mediating the hyperacetylation and hypoacetylation of histones, respectively. Hyperacetylation of lysine residues in the core histone tails promotes chromatin alterations that favor transcription, whereas hypoacetylation of histones promotes gene silencing or repression. Not only does the acetylation status of the core histones determine whether chromatin remodeling occurs, but histone phosphorylation and methylation may serve equally important roles. For example, the combination of histone H3 phosphorylation and acetylation concertedly favors transcription. In addition, specific lysine methylations (e.g., K9 of histone H3) repress gene expression whereas other methylations promote gene expression. It is most likely the combination of histone modification events that regulate the initiation of transcription. Understanding how ovarian hormones control specific histone modifications will help us understand how follicular cells can switch from active gene pools governing cell proliferation to those gene groups controlling terminal differentiation. Progress in elucidating the ovarian specific regulation of histone modifying enzymes as well as identification of their target gene pools at different stages of the follicular cycle is expected in the next few years.

Coordinated changes in DNA methylation and histone modifications regulate silencing/derepression of luteinizing hormone receptor gene transcription

We have previously demonstrated that transcription of the luteinizing hormone receptor (LHR) gene is subject to repression by histone deacetylation at its promoter region, where a histone deacetylase (HDAC)/mSin3A complex is anchored at a proximal Sp1 site. The present studies have shown that epigenetic silencing and activation of the LHR gene is achieved through coordinated regulation at both the histone and DNA levels. The HDAC inhibitor trichostatin A (TSA) evoked robust but significantly lower activation of the LHR gene in JAR than in MCF-7 cells. This effect was localized to the 176-bp promoter region, which is highly methylated in JAR and lightly methylated in MCF-7 cells. Consequently, TSA and the DNA demethylating reagent 5-azacytidine (5-AzaC) caused marked synergistic activation of the LHR gene in JAR but not in MCF-7 cells. Multiple site-specific lysine acetylation of H3/H4 is associated with such LHR gene activation. Methylation or acetylation of H3 at K9 is present at the silenced and derepressed LHR promoter, respectively. While DNA methylation levels did not affect the histone code of the LHR gene promoter, demethylation of the promoter CpG sites was necessary for maximal stimulation of this gene. Mechanistically, the combined actions of TSA and 5-AzaC, but not either 5-AzaC or TSA alone, resulted in complete demethylation of the LHR gene promoter in JAR cells. Release of the repressive HDAC/mSin3A complex from the LHR gene promoter in both cell types required both TSA-induced changes of histone modifications and, concurrently, a demethylated promoter. Also, Dnmt1 was largely dissociated from the LHR gene promoter in the presence of TSA or TSA plus 5-AzaC, and binding of MBD2 in JAR cells was diminished upon conversion of the promoter to a demethylated state. Such changes induced a more permissive chromatin where recruitment of polymerase II and TFIIB to the promoter was significantly increased. The activated state of the LHR gene induced by TSA and 5-AzaC in JAR and MCF-7 cells was observed basally in LHR-expressing PLC cells, in which the promoter is unmethylated and associated with hyperacetylated histones. Consequently, PLC cells are unresponsive to drug treatment. These findings have elucidated a regulatory mechanism whereby concurrent dissociation of repressors and association of activators and basal transcriptional components, resulting from coordinated histone hyperacetylation and DNA demethylation, lead to derepression of the LHR gene expression.

Association of the mSin3A-histone deacetylase 1/2 corepressor complex with the mouse steroidogenic acute regulatory protein gene

Several factors have been identified in the transcriptional repression of the steroidogenic acute regulatory protein (StAR) gene promoter; yet, no associating corepressor complexes have been characterized for the mouse promoter in MA-10 mouse Leydig tumor cells. We now report that Sp3, CAGA element binding proteins, and a corepressor complex consisting of mSin3A, histone deacetylase (HDAC)1, and HDAC2 associates with a transcriptional repressor region within the mouse StAR promoter. 5'-Promoter deletion analysis localized the negative regulatory region between -180 and -150 bp upstream of the transcription start site, and mutations in both the CAGA and Sp binding elements were required to relieve the repression of basal StAR promoter activity. Protein-DNA binding analysis revealed Sp3 and specific CAGA element-binding protein(s) associated with the repressor region. Coimmunoprecipitation analysis identified the presence of the mSin3A, HDAC1, and HDAC2 corepressor complex in MA-10 cells. Furthermore, chromatin immunoprecipitation assays revealed Sp3, mSin3A, and HDAC1/2 association with the proximal region of the StAR promoter in situ. In addition, HDAC inhibition resulted in a dose-dependent activation of a mouse StAR reporter construct, whereas mutations within the repressor region diminished this effect by 44%. In sum, these data support a novel regulatory mechanism for transcriptional repression of the mouse StAR promoter by DNA binding of Sp3 and CAGA element-binding proteins, and association of the Sin3 corepressor complex exhibiting HDAC activity.

Functional interaction between −629C/A, −971G/A and −1337C/T polymorphisms in the CETP gene is a major determinant of promoter activity and plasma CETP concentration in the REGRESS Study

Cholesteryl ester transfer protein (CETP) plays a key role in the determination of high-density lipoprotein (HDL) levels via its action on intravascular HDL metabolism. The TaqIB polymorphism of the CETP gene is associated with plasma CETP and high-density lipoprotein cholesterol (HDL-C) levels and with premature coronary artery disease. Such associations appear to result from linkage disequilibrium between TaqIB and other functional polymorphisms. To date, only one functional promoter variant, which may explain the effects of TaqIB, has been identified at position -629 in the CETP gene. Here we describe a C/T polymorphism located at position -1337 in the human CETP gene (C allele frequency: 0.684), which is significantly associated with plasma HDL-C and CETP levels (P=0.0001 and P<0.0001, respectively). Transient transfection of a reporter gene construct containing the CETP promoter from -1707/+28 in liver cells (HepG2) revealed that the -1337T allele was expressed to a significantly lower degree (-34%, P<0.0001) than the -1337C allele. In addition, we clearly demonstrated that the -971G/A polymorphism is functional and that its functionality is intimately linked to the presence of the -1337 site. In vitro evaluation of potential interaction between -1337C/T and other functional variants of the CETP gene (-971G/A and -629C/A) demonstrated that these three functional CETP promoter polymorphisms can interact together to determine the overall activity of the CETP gene and thus contribute significantly to variation in plasma CETP mass concentration.

Characterization of promoter 3 of the human thromboxane A receptor gene. A functional AP-1 and octamer motif are required for basal promoter activity

The TPalpha and TPbeta isoforms of the human thromboxane A(2) receptor (TP) arise by differential splicing but are under the transcriptional control of two distinct promoters, termed Prm1 and Prm3, respectively (Coyle et al. 2002 Eur J Biochem269, 4058-4073). The aim of the current study was to determine the key factors regulating TPbeta expression by functionally characterizing Prm3, identifying the core promoter and the cis-acting elements regulating basal Prm3 activity. Hence, the ability of Prm3 and a series of Prm3 deleted/mutated subfragments to direct reporter gene expression in human erythroleukemia 92.1.7 and human embryonic kidney 293 cells was investigated. It was established that nucleotides -118 to +1 are critical for core Prm3 activity in both cell types. Furthermore, three distinct regulatory regions comprising of an upstream repressor sequence, located between -404 to -320, and two positive regulatory regions required for efficient basal gene expression, located between -154 to -106 and -50 to +1, were identified within the core Prm3. Deletion and site-directed mutagenesis of consensus Oct-1/2 and AP-1 elements within the latter -154 to -106 and -50 to +1 regions, respectively, substantially reduced Prm3 activity while mutation of both elements abolished Prm3 activity. Electromobility shift and supershift assays confirmed the specificity of nuclear factor binding to the latter Oct-1/2 and AP-1 elements. Moreover, herein it was established that the core AP-1 element mediates phorbol myristic acid-induction of Prm3 activity hence providing a mechanistic explanation of phorbol ester up-regulation of TPbeta mRNA expression.

Gene regulation by Sp1 and Sp3

The Sp family of transcription factors is united by a particular combination of three conserved Cys2His2 zinc fingers that form the sequence-specific DNA-binding domain. Within the Sp family of transcription factors, Sp1 and Sp3 are ubiquitously expressed in mammalian cells. They can bind and act through GC boxes to regulate gene expression of multiple target genes. Although Sp1 and Sp3 have similar structures and high homology in their DNA binding domains, in vitro and in vivo studies reveal that these transcription factors have strikingly different functions. Sp1 and Sp3 are able to enhance or repress promoter activity. Regulation of the transcriptional activity of Sp1 and Sp3 occurs largely at the post-translational level. In this review, we focus on the roles of Sp1 and Sp3 in the regulation of gene expression.Key words: Sp1, Sp3, gene regulation, sub-cellular localization.

Follicle-stimulating hormone activation of hypoxia-inducible factor-1 by the phosphatidylinositol 3-kinase/AKT/Ras homolog enriched in brain (Rheb)/mammalian target of rapamycin (mTOR) pathway is necessary for induction of select protein markers of follicular differentiation

We sought to elucidate the role of AKT in follicle-stimulating hormone (FSH)-mediated granulosa cell (GC) differentiation. Our results define a signaling pathway in GCs whereby the inactivating phosphorylation of tuberin downstream of phosphatidylinositol (PI) 3-kinase/AKT activity leads to Rheb (Ras homolog enriched in brain) and subsequent mTOR (mammalian target of rapamycin) activation. mTOR then stimulates translation by phosphorylating p70 S6 kinase and, consequently, the 40 S ribosomal protein S6. Activation of this pathway is required for FSH-mediated induction of several follicular differentiation markers, including luteinizing-hormone receptor (LHR), inhibin-alpha, microtubule-associated protein 2D, and the PKA type IIbeta regulatory subunit. FSH also promotes activation of the transcription factor hypoxia-inducible factor-1 (HIF-1). FSH-stimulated HIF-1 activity is inhibited by the PI 3-kinase inhibitor LY294002, the Rheb inhibitor FTI-277 (farnesyltransferase inhibitor-277), and the mTOR inhibitor rapamycin. Finally, we find that the FSH-mediated up-regulation of reporter activities for LHR, inhibin-alpha, and vascular endothelial growth factor is dependent upon HIF-1 activity, because a dominant negative form of HIF-1alpha interferes with the up-regulation of these genes. These results show that FSH enhances HIF-1 activity downstream of the PI 3-kinase/AKT/Rheb/mTOR pathway in GCs and that HIF-1 activity is necessary for FSH to induce multiple follicular differentiation markers.

Gene Silencing by Nuclear Orphan Receptors

Nuclear orphan receptors represent a large and diverse subgroup in the nuclear receptor superfamily. Although putative ligands for these orphan members remain to be identified, some of these receptors possess intrinsic activating, inhibitory, or dual regulatory functions in development, differentiation, homeostasis, and reproduction. In particular, gene-silencing events elicited by chicken ovalbumin upstream promoter-transcription factors (COUP-TFs); dosage-sensitive sex reversal-adrenal hypoplasia congenita critical region on the X chromosome, gene 1 (DAX-1); germ cell nuclear factor (GCNF); short heterodimer partner (SHP); and testicular receptors 2 and 4 (TR2 and TR4) are among the best characterized. These orphan receptors are critical in controlling basal activities or hormonal responsiveness of numerous target genes. They employ multiple and distinct mechanisms to mediate target gene repression. Complex cross-talk exists between these orphan receptors at their cognate DNA binding elements and an array of steroid?nonsteroid hormone receptors, other transcriptional activators, coactivators and corepressors, histone modification enzyme complexes, and components of basal transcriptional components. Therefore, perturbation induced by these orphan receptors at multiple levels, including DNA binding activities, receptor homo- or heterodimerization, recruitment of cofactor proteins, communication with general transcriptional machinery, and changes at histone acetylation status and chromatin structures, may contribute to silencing of target gene expression in a specific promoter or cell-type context. Moreover, the findings derived from gene-targeting studies have demonstrated the significance of these orphan receptors' function in physiologic settings. Thus, COUP-TFs, DAX-1, GCNF, SHP, and TR2 and 4 are known to be required for multiple physiologic and biologic functions, including neurogenesis and development of the heart and vascular system steroidogenesis and sex determination, gametogenesis and embryonic development, and cholesterol?lipid homeostasis.

Transcriptional regulation by the estrogen receptor of antioxidative stress enzymes and its functional implications

We previously reported that antiestrogen-liganded estrogen receptor beta (ERbeta) transcriptionally activates the major detoxifying enzyme quinone reductase (QR) (NAD(P)H:quinone oxidoreductase). Our studies also indicate that upregulation of QR, either by overexpression or induction by tamoxifen, can protect breast cells against oxidative DNA damage caused by estrogen metabolites. We now report on the upregulation of glutathione S-transferases Pi (GST-Pi) and gamma-glutamylcysteine synthetase heavy subunit (GCSh) expression by antiestrogens. Studies indicate the regulation of GST-Pi and GCSh transcriptional activity by ER. While ER regulation is mediated by an electrophile response element (EpRE), we identified mechanistic differences in the involvement of other transcription factors. Regardless of these differences, ER beta-mediated regulation of GST-Pi and GCSh point towards an important role for ER beta in cellular protection against oxidative stress. A protective role is supported by our observation of inhibition of estrogen-induced DNA damage upon upregulation of GST-Pi and GCSh expression.