Nitric oxide inhibits selectively the 17beta-estradiol-induced gene expression without affecting nongenomic events in HeLa cells

Genome-wide distribution of histone trimethylation reveals a global impact of bisphenol A on telomeric binding proteins and histone acetyltransferase factors: a pilot study with human and in vitro data

OBJECTIVE

To assess the genetic and epigenetic effects promoted by Bisphenol A (BPA) exposure in adolescent males from the Spanish INMA-Granada birth cohort, and in human cells.

METHODS

DNA methylation was analysed using MEDIP. Repeat number variation in genomic DNA was evaluated, along with the analysis of H3K4me3 by using chromatin immunoprecipitation followed by high-throughput sequencing (ChIP-seq). Analyses were performed with material extracted from whole blood of the adolescents, complemented by in vitro assessments of human (HeLa) cells exposed to 10 nM BPA, specifically, immunofluorescence evaluation of protein levels, gene expression analysis and ChIP‒qPCR analysis.

RESULTS

Adolescents in the high urinary BPA levels group presented a higher level of Satellite A (SATA) repetitive region copy numbers compared to those in the low BPA group and a tendency towards increase in telomere length. We also observed decreased DNA methylation at the promoters of the imprinted genes H19, KCNQ1, and IGF2; at LINE1 retroelements; and at the ARID2, EGFR and ESRRA and TERT genes. Genome-wide sequencing revealed increased H3K4me3 occupancy at the promoters of genes encoding histone acetyltransferases, telomeric DNA binding factors and DNA repair genes. Results were supported in HeLa cells exposed to 10 nM BPA in vitro. In accordance with the data obtained in blood samples, we observed higher H3K4me3 occupancy and lower DNA methylation at some specific targets in HeLa cells. In exposed cells, changes in the expression of genes encoding DNA repair factors (ATM, ARID2, TRP53) were observed, and increased expression of several genes encoding telomeric DNA binding factors (SMG7, TERT, TEN1, UPF1, ZBTB48) were also found. Furthermore, an increase in ESR1/ERa was observed in the nuclei of HeLa cells along with increased binding of ESR1 to KAT5, KMT2E and TERF2IP promoters and decreased ESR1 binding at the RARA promoter. The DNA damage marker p53/TP53 was also increased.

CONCLUSION

In this pilot study, genome-wide analysis of histone trimethylation in adolescent males exposed to BPA revealed a global impact on the expression of genes encoding telomeric binding proteins and histone acetyltransferase factors with similar results in HeLa cells. Nevertheless, larger studies should confirm our findings.

Nongenomic estrogen effects on nitric oxide synthase activity in rat adipocytes

Estrogens exert multiple genomic effects on adipose tissue through binding to nuclear estrogen receptors. However, there is evidence for additional nongenomic mechanisms whereby estrogens may exert their control on adipose tissue metabolism through rapid activation of various membrane-initiated kinase cascades. Here, we tested rapid effects of estrogens on nitric oxide production in white adipose tissue using 17-beta estradiol (E2) and its membrane impermeant albumin conjugated form (17-beta estradiol hemisuccinate BSA, E2-BSA). We found that both E2 and E2-BSA stimulate nitric oxide synthase (NOS) activity in adipocytes. These effects were abolished by 1) ICI 182-780, a selective estrogen receptor antagonist; 2) wortmannin, an inhibitor of phosphatidylinositol 3-kinase; and 3) N-[2-(p-bromocinnamylamino) ethyl]-5-isoquinolinesulfonamide (H-89) an inhibitor of protein kinase A. In contrast to NOS activation by E2, E2-BSA-induced NOS activity was abolished by UO126, an inhibitor of MAPK kinase/ERK (p42/p44 MAPKs). Immunoblotting studies have shown that both estrogens phosphorylate endothelial NOS (NOS III) on Ser(1179), an effect that is prevented by wortmannin and H89, suggesting that NOS III is the target for estrogen-induced NOS activity. Furthermore, only the E2-BSA-induced NOS III phosphorylation on Ser(1179) was totally abolished by UO126. These results indicate that the signaling cascades involved in adipocyte NOS stimulation by estrogens are different depending on whether estrogens are free or conjugated to albumin and therefore underline the importance of estrogen receptor locations in the nongenomic actions of estrogens in these cells.

Structure-function relationship of estrogen receptor alpha and beta: impact on human health

17Beta-estradiol (E2) controls many aspects of human physiology, including development, reproduction and homeostasis, through regulation of the transcriptional activity of its cognate receptors (ERs). The crystal structures of ERs with agonists and antagonists and the use of transgenic animals have revealed much about how hormone binding influences ER conformation(s) and how this conformation(s), in turn, influences the interaction of ERs with co-activators or co-repressors and hence determines ER binding to DNA and cellular outcomes. This information has helped to shed light on the connection between E2 and the development or progression of numerous diseases. Current therapeutic strategy in the treatment of E2-related pathologies relies on the modulation of ER trancriptional activity by anti-estrogens; however, data accumulated during the last five years reveal that ER activities are not only restricted to the nucleus. ERs are very mobile proteins continuously shuttling between protein targets located within various cellular compartments (e.g., membrane, nucleus). This allows E2 to generate different and synergic signal transduction pathways (i.e., non-genomic and genomic) which provide plasticity for cell response to E2. Understanding the structural basis and the molecular mechanisms by which ER transduce E2 signals in target cells will allow to create new pharmacologic therapies aimed at the treatment of a variety of human diseases affecting the cardiovascular system, the reproductive system, the skeletal system, the nervous system, the mammary gland, and many others.

Signaling regulation of genomic and nongenomic functions of estrogen receptors

Estrogen receptors (ERs) mediate the effects of 17beta-estradiol under physiologic and pathologic conditions. ERs trigger 17beta-estradiol-sensitive gene transcription by binding to specific estrogen response elements (i.e. genomic mechanism). The cellular effects of estrogen are also influenced by membrane- or cytoplasm-initiated responses (i.e. nongenomic mechanism). Both ER-evoked genomic and nongenomic effects originate from a unique signaling network. Furthermore, estrogen-initiated rapid pathways and ERalpha interactions with specific partners (e.g. AIB1, PELP1/MNAR; MTA1, MTA1s and p130Cas) influence both ER functions. Here, we summarize the recent findings related to multiple regulatory levels of the signaling networks responsible for ERs-mediated responses in breast cancer cells.

S-palmitoylation modulates estrogen receptor alpha localization and functions

17beta-Estradiol (E2) acts as a chemical messenger in target tissues inducing both slow nuclear and rapid extra-nuclear responses. E2 binds to its cognate nuclear receptors (ER) resulting in the activation of target gene transcription in the nucleus. In addition to these genomic effects, E2 modulates cell functions through rapid non-genomic actions. Stimulation of G-proteins, Ca(2+) influx, inositol phosphate generation as well as phospholipase C, ERK/MAPK, and PI3K/AKT activation all occur within seconds to minutes after E2 binding to a small population of ERalpha located at the plasma membrane. The great impact of these rapid signals on cell physiology renders central the knowledge of the structural bases and mechanisms that mediate extra-nuclear signaling by E2. Several laboratories, including our own, have recently elucidated the structural requirements for localization and function of plasma membrane ERalpha. This review summarizes the molecular mechanisms of E2-induced rapid non-genomic actions relevant for cell functions, highlighting the role of lipid modification (i.e., palmitoylation) in the ERalpha localization to and residence at the plasma membrane.

Estrogen signaling multiple pathways to impact gene transcription

Steroid hormones exert profound effects on cell growth, development, differentiation, and homeostasis. Their effects are mediated through specific intracellular steroid receptors that act via multiple mechanisms. Among others, the action mechanism starting upon 17beta-estradiol (E2) binds to its receptors (ER) is considered a paradigmatic example of how steroid hormones function. Ligand-activated ER dimerizes and translocates in the nucleus where it recognizes specific hormone response elements located in or near promoter DNA regions of target genes. Behind the classical genomic mechanism shared with other steroid hormones, E2 also modulates gene expression by a second indirect mechanism that involves the interaction of ER with other transcription factors which, in turn, bind their cognate DNA elements. In this case, ER modulates the activities of transcription factors such as the activator protein (AP)-1, nuclear factor-kappaB (NF-kappaB) and stimulating protein-1 (Sp-1), by stabilizing DNA-protein complexes and/or recruiting co-activators. In addition, E2 binding to ER may also exert rapid actions that start with the activation of a variety of signal transduction pathways (e.g. ERK/MAPK, p38/MAPK, PI3K/AKT, PLC/PKC). The debate about the contribution of different ER-mediated signaling pathways to coordinate the expression of specific sets of genes is still open. This review will focus on the recent knowledge about the mechanism by which ERs regulate the expression of target genes and the emerging field of integration of membrane and nuclear receptor signaling, giving examples of the ways by which the genomic and non-genomic actions of ERs on target genes converge.

Rapid nitric oxide-mediated S-nitrosylation of estrogen receptor: regulation of estrogen-dependent gene transcription

Nitric oxide (NO) and estrogen receptor (ER) are both important mediators of signal transduction in cardiovascular and reproductive tissues. In this study, we evaluated NO-mediated S-nitrosylation of ER and assessed the effect of this structural modification on transcription-related functions of ER. We have found selective inhibitory effects of NO on specific binding of ER to specific estrogen-responsive elements (ERE) that can be reversed in the presence of the reducing agent, DTT, thus suggesting that S-nitrosylation of thiolate-zinc centers may occur within the ER molecule. Furthermore, we examined inhibitory effects of NO on ER-dependent transcriptional activity by using an ERE-driven reporter gene system. By monitoring biophysical changes in the structure of NO-treated or untreated human recombinant ERalpha,we obtained evidence for the formation of S-nitrosothiols in the ER molecule. In addition, we have detected specific S-nitrosylation of cysteine residues within the ER molecule by immunodetection of S-nitrosocysteine moieties in ER. Collectively, these findings suggest an important physiological role for NO in modification of human ER structure by S-nitrosylation, an effect that leads, in turn, to impaired DNA-binding activity of ER and subsequent blockade of estrogen-dependent gene transcription. Thus, NO-induced S-nitrosylation of ER can occur at cysteine residues that coordinate Zn2+ within the two major DNA-binding Zn-finger domains of ER, resulting in selective inhibition of DNA-binding at specific ERE. This cross-communication between NO and ER may favor activation of rapid (nongenomic) signaling pathways and subsequent modulation of downstream genomic activity.

Nitrosative stress and transcription

Low NO concentrations synthesized by constitutively expressed NO synthases act on several signaling pathways activating transcription factors (TF), such as NF-kappaB or AP-1, and thereby influence gene expression. In contrast, during inflammatory reactions the inducible NO synthase produces NO for prolonged periods of time. The resulting nitrosative stress directly affects redox-sensitive TF like NF-kappaB, AP-1, Oct-1, c-Myb, or zinc finger-containing TF, but also additional mechanisms have been identified. Nitrosative stress in some cases induces expression of TF (AP-1, p53), indirectly modulates activity or stability of TF (HIF-1, p53) or their inhibitors (NF-kappaB), or modulates accessibility of promoters via increased DNA methylation or histone deacetylation. Depending on the promoter the result is induced, increased, decreased or even totally inhibited expression of various target genes. In unstimulated cells nitrosative stress increases NF-kappaB- or AP-1-dependent transcription, while in activated cells nitrosative stress rather abolishes NF-kappaB- or AP-1-dependent transcription. Sometimes the oxygen concentration also is of prime importance, since under normoxic conditions nitrosative stress activates HIF-1-dependent transcription, while under hypoxic conditions nitrosative stress leads to inhibition of HIF-1-dependent transcription. This review summarizes what is known about effects of physiological NO levels as well as of nitrosative stress on transcription.

S-palmitoylation modulates human estrogen receptor-α functions

17beta-Estradiol (E2)-induced rapid functions (from seconds to minutes) can be attributed to a fraction of nuclear estrogen receptor-alpha (ERalpha) localized at the plasma membrane. As a potential mechanism, we postulated that S-palmitoylation of the Cys447 residue may explain the ability of ERalpha to associate to plasma membrane making possible E2-dependent rapid functions [e.g., extracellular regulated kinase (ERK) activation]. Here, we report direct evidence that the mutation of the Cys447 residue to Ala impairs human ERalpha palmitoylation and E2-induced rapid ERK phosphorylation when transfected in ER-devoid HeLa cells. Moreover, the Cys447Ala mutation significantly decreases the E2-induced transactivation of an estrogen responsive element construct probe. Similar effects were obtained treating HeLa cells transfected with wild type ERalpha with the palmitoyl-acyltransferase inhibitor 2-bromo-hexadecanoic acid. Moreover, the deletion of the A-D domains (containing the DNA binding region) of ERalpha had no consequences on [(3)H]palmitate incorporation, whereas no palmitoylation occurred in the ERalpha mutant devoid of the E domain (i.e., ligand binding domain). These results point to the pivotal role of the Cys447 residue in ERalpha palmitoylation and in the modulation of E2-induced non-genomic functions.

Genomic effect of glucocorticoids on enzymes of intermediary metabolism in Oreochromis mossambicus

The present study examined the effect of long-term treatment with cortisol and corticosterone on enzymes of intermediary metabolism, namely malic enzyme (ME), glucose-6-phosphate dehydrogenase (G6PDH), isocitrate dehydrogenase (ICDH), glucose 6 phosphatase (G-6-Pase), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) in Oreochromis mossambicus. Cortisol and corticosterone regulate intermediary metabolism in the liver of O. mossambicus as evidenced by changes in the activity pattern of gluconeogenic and lipogenic enzymes and amino-transferases. The long-term in vivo ip administration of glucocorticoids (GCs) suggests hyperglycemic, gluconeogenic, and antilipogenic roles of the hormones in O. mossambicus. The genomic mode of action of GCs is well established in the present study since the long-term treatment is sensitive to the action of transcription and translation inhibitors.

Nitric oxide donors inhibit luciferase expression in a promoter-independent fashion

Nitric oxide (NO) is an important molecule with diverse bio-messenger functions including regulation of gene expression. Transcriptional studies using sensitive luciferase reporter systems have suggested that NO inhibits the promoter activity of a variety of genes. Here we report that NO donors (sodium nitroprusside, 2',2'-(hydroxynitrosohydrazono)bis-ethanimine, and (+/-)-(E)-4-ethyl-2-[(Z)-hydroxyimino]-5-nitro-3-hexen-1-yl-nicotinamide) decrease luciferase activity in a promoter-independent fashion in both viral and eukaryotic promoters, with a reduction to nearly 50% in the presence of 100 microm NO donor. Addition of an SV40 enhancer downstream of the luciferase coding region shifted NO donor inhibition to the right, with inhibition at approximately 300 microm. In contrast, when studied in a chloramphenicol acetyltransferase reporter, two promoters indicating inhibition by NO were unaffected. The decrease in luciferase activity was not caused by NO suppression of the luciferase enzyme. Real-time PCR data showed that luciferase mRNA half-life decreased by nearly half in the presence of NO donor (from 75 to 45 min). The SV40 enhancer prolonged luciferase mRNA half-life and somewhat blunted the NO effect. Our data suggest that exogenous NO inhibits luciferase activity in a dose-dependent manner through decreasing luciferase mRNA stability. Thus, the use of luciferase reporter systems to study transcriptional regulation by NO should be attempted with caution.

Sex steroids regulate intermediary metabolism in Oreochromis mossambicus

The effect of long-term administration of testosterone, progesterone, and a synthetic estrogen, diethylstilbestrol (DES), on intermediary metabolism was studied in a freshwater fish Oreochromis mossambicus. The present study reveals that testosterone, progesterone, and Des specifically control key enzymes involved in carbohydrate, protein and lipid metabolism in the liver of O. mossambicus implying a general influence of sex steroids on intermediary metabolism. The activities of malic enzyme (ME), glucose-6-phosphate dehydrogenase (G6PDH), isocitrate dehydrogenase (ICDH), glucose 6 phosphatase (G-6-Pase), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) are either stimulated or inhibited following the administration of sex steroids. The long-term in vivo i.p. injection of sex steroids intensely reveals that testosterone and progesterone are hyperglycemic, DES is hypoglycemic, testosterone and DES lipogenic, and progesterone antilipogenic (lipolytic) in the present study. It is also established that amino acid catabolism, mostly that of alanine, may be a major source of substrate for gluconeogenesis. A genomic mode of action is proposed for sex steroids for long term treatment, as their action is sensitive to transcription and translation inhibitors.