Regulation Of Receptor Gene Expression Research Articles

Control of oocyte release by progesterone receptor-regulated gene expression

The progesterone receptor (PGR) is a nuclear receptor transcription factor that is essential for female fertility, in part due to its control of oocyte release from the ovary, or ovulation. In all mammals studied to date, ovarian expression of PGR is restricted primarily to granulosa cells of follicles destined to ovulate. Granulosa cell expression of PGR is induced by the pituitary Luteinizing Hormone (LH) surge via mechanisms that are not entirely understood, but which involve activation of Protein Kinase A and modification of Sp1/Sp3 transcription factors on the PGR promoter. Null mutations for PGR or treatment with PGR antagonists block ovulation in all species analyzed, including humans. The cellular mechanisms by which PGR regulates ovulation are currently under investigation, with several downstream pathways having been identified as PGR-regulated and potentially involved in follicular rupture. Interestingly, none of these PGR-regulated genes has been demonstrated to be a direct transcriptional target of PGR. Rather, in ovarian granulosa cells, PGR may act as an inducible coregulator for constitutively bound Sp1/Sp3 transcription factors, which are key regulators for a discrete cohort of ovulatory genes.

Nongenomic actions of thyroxine modulate intermediate filament phosphorylation in cerebral cortex of rats

The developmental effects of thyroid hormones (TH) in mammalian brain are mainly mediated by nuclear receptors regulating gene expression. However, there are increasing evidences of nongenomic mechanisms of these hormones associated with kinase- and calcium-activated signaling pathways. In this context, the aim of the present work was to investigate the signaling pathways involved in the mechanism of action of TH on cytoskeletal phosphorylation in cerebral cortex of 15-day-old male rats. Results showed that l-thyroxine (L-T 4) increased the intermediate filament (IF) phosphorylation independently of protein synthesis, without altering the total immunocontent of these proteins. Otherwise, neither 3,5,3′-triiodo- l-thyronine (L-T 3) nor neurotransmitters (GABA, ATP, l-glutamate or epinephrine) acted on the IF-associated phosphorylation level. We also demonstrated that the mechanisms underlying the L-T 4 effect on the cytoskeleton involve membrane initiated actions through G i protein–coupled receptor. This evidence was reinforced by the inhibition of cyclic adenosine 5′-monophosphate (cAMP) levels. Moreover, we showed the participation of phospholipase C, protein kinase C, mitogen-activated protein kinase, calcium/calmodulin-dependent protein kinase II, intra- and extracellular Ca 2+ mediating the effects of L-T 4 on the cytoskeleton. Stimulation of 45Ca 2+ uptake by L-T 4 was also demonstrated. These findings demonstrate that L-T 4 has important physiological roles modulating the cytoskeleton of neural cells during development.

Progesterone Induction of the 11β-Hydroxysteroid Dehydrogenase Type 2 Promoter in Breast Cancer Cells Involves Coordinated Recruitment of STAT5A and Progesterone Receptor to a Distal Enhancer and Polymerase Tracking

Steroid hormone receptors regulate gene expression, interacting with target DNA sequences but also activating cytoplasmic signaling pathways. Using the human 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) gene as a model, we have investigated the contributions of both effects on a human progesterone-responsive promoter in breast cancer cells. Chromatin immunoprecipitation has identified two different mechanisms of hormone-induced progesterone receptor (PR) recruitment to the 11beta-HSD2 promoter: (i) direct PR binding to DNA at the proximal promoter, abrogated when PR contains a mutated DNA binding domain (DBD), and (ii) STAT5A (signal transducer and activator of transcription 5A)-mediated recruitment of PR to an upstream distal region, impaired by AG490, a JAK/STAT pathway inhibitor. The JAK/STAT inhibitor, as well as expression of dominant-negative STAT5A, impairs hormone induction of 11beta-HSD2. On the other hand, the DBD-mutated PR fully supports 11beta-HSD2 expression. These results, along with data from a deletion analysis, indicate that the distal region is crucial for hormone regulation of 11beta-HSD2. We show active RNA polymerase II tracking from the distal region upon PR and STAT5A binding, concomitant with synthesis of noncoding, hormone-dependent RNAs, suggesting that this region works as a hormone-dependent transcriptional enhancer. In conclusion, coordination of PR transcriptional effects and cytoplasmic signaling activation, in particular the JAK/STAT pathway, are critical in regulating progestin-induced endogenous 11beta-HSD2 gene expression in breast cancer cells. This is not unique to this promoter, as AG490 also alters the expression of other progesterone-regulated genes.

Compartmentalization of androgen receptor protein–protein interactions in living cells

Steroid receptors regulate gene expression in a ligand-dependent manner by binding specific DNA sequences. Ligand binding also changes the conformation of the ligand binding domain (LBD), allowing interaction with coregulators via LxxLL motifs. Androgen receptors (ARs) preferentially interact with coregulators containing LxxLL-related FxxLF motifs. The AR is regulated at an extra level by interaction of an FQNLF motif in the N-terminal domain with the C-terminal LBD (N/C interaction). Although it is generally recognized that AR coregulator and N/C interactions are essential for transcription regulation, their spatiotemporal organization is largely unknown. We performed simultaneous fluorescence resonance energy transfer and fluorescence redistribution after photobleaching measurements in living cells expressing ARs double tagged with yellow and cyan fluorescent proteins. We provide evidence that AR N/C interactions occur predominantly when ARs are mobile, possibly to prevent unfavorable or untimely cofactor interactions. N/C interactions are largely lost when AR transiently binds to DNA, predominantly in foci partly overlapping transcription sites. AR coregulator interactions occur preferentially when ARs are bound to DNA.

Regulation of mitogen‐activated protein kinases by glutamate receptors

Glutamate receptors regulate gene expression in neurons by activating intracellular signaling cascades that phosphorylate transcription factors within the nucleus. The mitogen-activated protein kinase (MAPK) cascade is one of the best characterized cascades in this regulatory process. The Ca(2+)-permeable ionotropic glutamate receptor, mainly the NMDA receptor subtype, activates MAPKs through a biochemical route involving the Ca(2+)-sensitive Ras-guanine nucleotide releasing factor, Ca(2+)/calmodulin-dependent protein kinase II, and phosphoinositide 3-kinase. The metabotropic glutamate receptor (mGluR), however, activates MAPKs primarily through a Ca(2+)-insensitve pathway involving the transactivation of receptor tyrosine kinases. The adaptor protein Homer also plays a role in this process. As an information superhighway between surface glutamate receptors and transcription factors in the nucleus, active MAPKs phosphorylate specific transcription factors (Elk-1 and CREB), and thereby regulate distinct programs of gene expression. The regulated gene expression contributes to the development of multiple forms of synaptic plasticity related to long-lasting changes in memory function and addictive properties of drugs of abuse. This review, by focusing on new data from recent years, discusses the signaling mechanisms by which different types of glutamate receptors activate MAPKs, features of each MAPK cascade in regulating gene expression, and the importance of glutamate/MAPK-dependent synaptic plasticity in memory and addiction.

How Much is Enough? Modulation of Dose-Response Curve for Steroid Receptor-Regulated Gene Expression by Changing Concentrations of Transcription Factor

The position of the dose-response curve for steroid-regulated gene expression determines how much variation in response will accompany the normal physiological changes in circulating steroid. Over the last several years, it has become clear that the concentration of steroid hormone required for half-maximal induction or repression by a given receptor-steroid complex, which is normally called the EC50, is not constant for all responsive genes. Thus, the position of the dose-response curve can change so that a single concentration of steroid produces very different percentages of maximal activity. This, in turn, allows for the differential expression of genes by a common steroid hormone concentration during development, differentiation, and homeostasis. Here we review the variety of factors that influence the EC50 and position of the dose-response curve for steroid hormone receptors, discuss what is known about the mechanisms, and highlight promising areas for future research.

The Pregnane X Receptor Regulates Gene Expression in a Ligand- and Promoter- Selective Fashion

Recent studies have revealed that pregnane X receptor (PXR) can function as a master regulator to control the expression of phase I and phase II drug-metabolizing enzymes, as well as members of the drug transporter family, including multiple drug resistance (MDR) 1, which has a major role in multidrug resistance. Previously, we have demonstrated that steroid/xenobiotics metabolism by tumor tissue through the PXR-cytochrome P-450 3A (CYP3A) pathway might play an important role in endometrial cancer. In this study, we examined which endocrine-disrupting chemicals (EDCs) and anticancer agents might be ligands for PXR and whether these chemicals enhanced PXR-mediated transcription through two different PXR-responsive elements (PXREs), CYP3A4 and MDR1, in endometrial cancer cell lines. Some steroids/EDCs strongly activated PXR-mediated transcription through the CYP3A4-responsive element compared with the MDR1-responsive element, whereas these steroids/EDCs also enhanced the CYP3A4 expression compared with the MDR1 expression. In contrast, the anticancer agents, cisplatin and paclitaxel, strongly activated PXR-mediated transcription through the MDR1-responsive element compared with the CYP3A4-responsive element, whereas these drugs also enhanced the MDR1 expression compared with the CYP3A4 expression. We also analyzed how these ligands regulated PXR-mediated transcription through two different PXREs. In the presence of PXR ligands, there was no difference in the DNA binding affinity of the PXR/retinoid X receptor heterodimer to each PXRE, but there were different interactions of the coactivator to each PXR/PXRE complex. These data suggested that PXR ligands enhanced PXR-mediated transcription in a ligand- and promoter-dependent fashion, which in turn differentially regulated the expression of individual PXR targets, especially CYP3A4 and MDR1.

Modulation of aryl hydrocarbon receptor-regulated gene expression by arsenite, cadmium, and chromium.

Aryl hydrocarbon receptor (AhR) ligands and heavy metals are environmental co-contaminants and their molecular interaction may disrupt the coordinated regulation of AhR-dependent phase I and II drug metabolizing enzymes. To determine the effect of heavy metals on the AhR-regulated genes: cytochrome P4501A1 (Cyp1a1), NAD(P)H: quinone oxidoreductase (QOR) and glutathione S-transferase Ya (GST Ya), murine hepatoma Hepa 1c1c7 cells were treated with increasing concentrations of As3+ (1-10 microM), Cd2+ (1-25 microM) and Cr6+ (1-25 microM) with or without the AhR ligands: 2,3,7,8-tetrachlorodibenzo-p-dioxin (0.1 nM), 3-methylcholanthrene (0.25 microM), beta-naphthoflavone (10 uM), or benzo[a]pyrene (1 microM). Our results show that AhR ligands alone and As3+ or Cd2+ alone increased the catalytic activities and mRNA levels of all AhR-regulated genes. When metals were co-administered with an AhR ligand, all three metals inhibited the induction of Cyp1a1 activity by the AhR ligands but potentiated its mRNA and protein expression. In addition, all metals enhanced QOR and GST Ya at the activity and mRNA levels but modulated their induction by AhR ligands in a concentration, metal, and AhR ligand-dependent manner. Generally, Cr6+ inhibited while As3+ and Cd2+ potentiated the induction of QOR and GST Ya activities and mRNA levels. The three metals enhanced the expression of heme oxygenase-1, which coincided with the changes in the phase I and phase II enzyme activities. These results show that the ability of metals to alter the capacity of AhR ligands to induce the bioactivating phase I and the detoxifying phase II enzymes will influence the carcinogenicity and mutagenicity of the AhR ligands.

Stress and immunological phagocytosis: possible nongenomic action of corticosterone

Some immunological responses triggered by stress can be mediated by corticosterone activity through cytosolic receptors regulating gene expression. There are, however some reports on the possibility of a nongenomic effect of this hormone to explain phenomena observed in a few minutes. We have found that macrophages from mice subjected to 10 min of cold stress (at −15 °C) showed a lower phagocytic capacity mediated by Fcγ-receptors than cells from control animals. Treating mice with glucocorticoid antagonist RU 486 did not block the decrease in phagocytic capacity. This inhibitory effect on phagocytosis was also observed by experiments in vitro with corticosterone in the concentration found in serum after stress, and could not be prevented by RU 486, actinomicyn D or cycloheximide. These results indicate that corticosterone could affect phagocytosis by macrophages through a nongenomic mechanism, and may have physiological implications.

Schizophrenia, vitamin D, and brain development

Schizophrenia research is invigorated at present by the recent discovery of several plausible candidate susceptibility genes identified from genetic linkage and gene expression studies of brains from persons with schizophrenia. It is a current challenge to reconcile this gathering evidence for specific candidate susceptibility genes with the "neurodevelopmental hypothesis," which posits that schizophrenia arises from gene-environment interactions that disrupt brain development. We make the case here that schizophrenia may result not from numerous genes of small effect, but a few genes of transcriptional regulation acting during brain development. In particular we propose that low vitamin D during brain development interacts with susceptibility genes to alter the trajectory of brain development, probably by epigenetic regulation that alters gene expression throughout adult life. Vitamin D is an attractive "environmental" candidate because it appears to explain several key epidemiological features of schizophrenia. Vitamin D is an attractive "genetic" candidate because its nuclear hormone receptor regulates gene expression and nervous system development. The polygenic quality of schizophrenia, with linkage to many genes of small effect, maybe brought together via this "vitamin D hypothesis." We also discuss the possibility of a broader set of environmental and genetic factors interacting via the nuclear hormone receptors to affect the development of the brain leading to schizophrenia.

The basic helix-loop-helix-PAS protein ARNT functions as a potent coactivator of estrogen receptor-dependent transcription.

The biological effects of estrogens are mediated by the estrogen receptors ERalpha and ERbeta. These receptors regulate gene expression through binding to DNA enhancer elements and subsequently recruiting factors such as coactivators that modulate their transcriptional activity. Here we show that ARNT (aryl hydrocarbon receptor nuclear translocator), the obligatory heterodimerization partner for the aryl hydrocarbon receptor and hypoxia inducible factor 1alpha, functions as a potent coactivator of ERalpha- and ERbeta- dependent transcription. The coactivating effect of ARNT depends on physical interaction with the ERs and involves the C-terminal domain of ARNT and not the structurally conserved basic helix-loop-helix and PAS (Per-ARNT-Sim) motifs. Moreover, we show that ARNT/ER interaction requires the E2-activated ligand binding domain of ERalpha or ERbeta. These observations, together with the previous role of ARNT as an obligatory partner protein for conditionally regulated basic helix-loop-helix-PAS proteins like the aryl hydrocarbon receptor or hypoxia inducible factor 1alpha, expand the cellular functions of ARNT to include regulation of ERalpha and ERbeta transcriptional activity. ARNT was furthermore recruited to a natural ER target gene promoter in a estrogen-dependent manner, supporting a physiological role for ARNT as an ER coactivator.

Integrins regulate neuronal neurotrophin gene expression through effects on voltage-sensitive calcium channels

Integrin adhesion receptors regulate gene expression during growth and differentiation in various cell types. Recent work, implicating integrins in functional synaptic plasticity, suggest they may have similar activities in adult brain. The present study tested if integrins binding the arginine–glycine–aspartate (RGD) matrix sequence regulate neurotrophin and neurotrophin receptor gene expression in cultured hippocampal slices. The soluble RGD-containing peptide glycine–arginine–glycine–aspartate–serine–proline (GRGDSP) increased neurotrophin mRNA levels in transcript- and subfield-specific fashions. Integrin ligand effects were greatest for brain-derived neurotrophic factor transcripts I and II and barely detectable for transcript III. In accordance with increased nerve growth factor mRNA levels, GRGDSP increased c- fos expression as well. In contrast, growth-associated protein-43, amyloid precursor protein and fibroblast growth factor-1 mRNAs were not elevated. Ligand effects on brain-derived neurotrophic factor transcript II and c- fos mRNA did not depend on the integrity of the actin cytoskeleton, neuronal activity, or various signaling pathways but were blocked by L-type voltage-sensitive calcium-channel blockers. These results indicate that in mature hippocampal neurons integrin engagement regulates expression of a subset of growth-related genes at least in part through effects on calcium influx. Accordingly, these synaptic adhesion receptors may play the same role in maintaining an adult, differentiated state in brain as they do in other tissues and changes in integrin activation and/or engagement may contribute to dynamic changes in neurotrophin expression and to neuronal calcium signaling.

Iron acquisition and its control in Pseudomonas aeruginosa: many roads lead to Rome.

Iron plays an important role in the pathogenesis and rhizosphere competence of the fluorescent group of pseudomonads and it is, thus, fitting that the characteristic fluorescence of these organisms is attributable to an iron-chelating molecule, pyoverdine. Pseudomonas aeruginosa is likely the best-studied member of this group, and while it synthesizes two siderophores, pyochelin and pyoverdine, it is also able to use a number of heterologous siderophores of fungal and bacterial origin and its genome is rich with homologues of iron-siderophore receptor genes, reflecting the enormous flexibility of the organism vis-a-vis iron carriers that it can use in nature. The ability to utilize a variety of heterologous siderophores is shared by other fluorescent pseudomonads and likely reflects both the importance of this vital nutrient for growth and survival and the need to compete with other microorganisms in the aquatic and terrestrial environments that they inhabit. Expression of the various receptors is, however, regulated, with receptor production responding positively to available siderophores only, and selection from multiple available siderophores based on their successful chelation of iron and subsequent transport. Thus, the superior siderophore in a given environment will upregulate the cognate receptor at the expense of other receptors. Such siderophore-dependent regulation of receptor gene expression is common in bacteria, particularly the fluorescent pseudomonads, and typically requires a signal transduction cascade that involves the receptor itself, whose binding to the siderophore initiates the cascade, as well as a regulatory protein pair that includes an environmentally-responsive so-called extracytoplasmic function (ECF) sigma factor, which activates receptor gene expression, and an anti-sigma factor that controls sigma factor activity. Despite the plethora of ferric siderophore receptors in P. aeruginosa, its genome sequence reveals a striking lack of obvious periplasmic and cytoplasmic membrane transport components capable of accommodating these molecules. Unlike e.g. Escherichia coli, then, where ferric siderophore permeases providing transport to the cytoplasm are clearly in evidence, iron-siderophore complexes in P. aeruginosa may be dissociated in the periplasm, with a common iron carrier then responsible for iron uptake into the cell interior.

Expression and role of retinoic acid receptor alpha in lens regeneration.

The role of retinoids in eye development has been well studied. Retinoids and their receptors regulate gene expression and morphogenesis of the eye. In this study, a highly specific antagonist of retinoic acid receptor (RAR)-alpha was used in an attempt to study its function in lens regeneration. It was found that this antagonist inhibited lens regeneration and lens fiber differentiation. It was also shown that RAR-alpha is expressed in the lens during the process of regeneration. These results indicate that different RAR might have unique as well as redundant effects and patterns of expression in the regenerating lens.

The tomato ethylene receptor gene family: Form and function.

Phytohormones are essential for integrating many aspects of plant development and responses to the environment. Regulation of hormonally controlled events occurs at multiple levels: synthesis, catabolism and perception (Trewavas 1983, Bradford and Trewavas 1994). At the level of perception, sensitivity to hormones can be regulated both spatially and temporally during the life cycle. An example of spatial regulation is the differential response to a hormone that occurs during organ abscission. Temporally, sensitivity of an organ to a hormone may change during maturation, as occurs during fruit ripening. In this review, we will focus on the initial event in recognition of one hormone, ethylene. The ethylene receptor was the first plant hormone receptor to be unambiguously identified. Over the last few years, great progress has been made in elucidating the genes involved in ethylene action. Nonetheless, the mechanisms of signal transduction remain to be established. Here, we will address the status of the tomato receptor gene family and the evidence that regulation of receptor gene expression can influence the response of the plant to the hormone.

The Metabotropic GABAB Receptor Directly Interacts with the Activating Transcription Factor 4

G protein-coupled receptors regulate gene expression by cellular signaling cascades that target transcription factors and their recognition by specific DNA sequences. In the central nervous system, heteromeric metabotropic gamma-aminobutyric acid type B (GABA(B)) receptors through adenylyl cyclase regulate cAMP levels, which may control transcription factor binding to the cAMP response element. Using yeast-two hybrid screens of rat brain libraries, we now demonstrate that GABA(B) receptors are engaged in a direct and specific interaction with the activating transcription factor 4 (ATF-4), a member of the cAMP response element-binding protein /ATF family. As confirmed by pull-down assays, ATF-4 associates via its conserved basic leucine zipper domain with the C termini of both GABA(B) receptor (GABA(B)R) 1 and GABA(B)R2 at a site which serves to assemble these receptor subunits in heterodimeric complexes. Confocal fluorescence microscopy shows that GABA(B)R and ATF-4 are strongly coclustered in the soma and at the dendritic membrane surface of both cultured hippocampal neurons as well as retinal amacrine cells in vivo. In oocyte coexpression assays short term signaling of GABA(B)Rs via G proteins was only marginally affected by the presence of the transcription factor, but ATF-4 was moderately stimulated in response to receptor activation in in vivo reporter assays. Thus, inhibitory metabotropic GABA(B)Rs may regulate activity-dependent gene expression via a direct interaction with ATF-4.

Nuclear receptor coactivators in neuroendocrine function.

Steroid hormones influence a variety of neuroendocrine events, including brain development, sexual differentiation and reproduction. Hormones elicit many of these effects by binding to neuronal steroid receptors, which are members of a nuclear receptor superfamily of transcriptional activators. However, the mechanisms by which activated steroid receptors regulate gene expression in brain are not well understood. Recently, a new class of proteins, known as nuclear receptor coactivators, have been found to dramatically enhance steroid receptor mediated transactivation of genes in vitro. Here, the proposed molecular mechanisms of how these coactivators enhance the transcriptional activity of steroid receptors are summarized. While much is known about the mechanisms of these coactivators in vitro, it is unclear how these cofactors function in hormone action in vivo or in the brain. This paper discusses some of the initial and enticing investigations into the role of these important coregulatory proteins in neuroendocrine events. Finally, some of the critical issues and future directions in nuclear receptor coactivator function in neuroendocrinology are highlighted.

Molecular mechanisms and regulation of opioid receptor signaling.

Cloning of multiple opioid receptors has presented opportunities to investigate the mechanisms of multiple opioid receptor signaling and the regulation of these signals. The subsequent identification of receptor gene structures has also provided opportunities to study the regulation of receptor gene expression and to manipulate the concentration of the gene products in vivo. Thus, in the current review, we examine recent advances in the delineation basis for the multiple opioid receptor signaling, and their regulation at multiple levels. We discuss the use of receptor knockout animals to investigate the function and the pharmacology of these multiple opioid receptors. The reasons and basis for the multiple opioid receptor are addressed.

Opposing effects of corepressor and coactivators in determining the dose-response curve of agonists, and residual agonist activity of antagonists, for glucocorticoid receptor-regulated gene expression.

A distinguishing, but unexplained, characteristic of steroid hormone action is the dose-response curve for the regulation of gene expression. We have previously reported that the dose-response curve for glucocorticoid induction of a transfected reporter gene in CV-1 and HeLa cells is repositioned in the presence of increasing concentrations of glucocorticoid receptors (GRs). This behavior is now shown to be independent of the reporter, promoter, or enhancer, consistent with our proposal that a transacting factor(s) was being titrated by added receptors. Candidate factors have been identified by the observation that changes in glucocorticoid induction parameters in CV-1 cells could be reproduced by varying the cellular levels of coactivators [transcriptional intermediary factor 2 (TIF2), steroid receptor coactivator 1 (SRC-1), and amplified in breast cancer 1 (AIB1)], comodulator [CREB-binding protein (CBP)], or corepressor [silencing mediator for retinoid and thyroid-hormone receptors (SMRT)] without concomitant increases in GR. Significantly, the effects of TIF2 and SMRT were mutually antagonistic. Similarly, additional SMRT could reverse the action of increased levels of GRs in HeLa cells, thus indicating that the effects of cofactors on transcription may be general for GR in a variety of cells. These data further indicate that GRs are yet an additional target of the corepressor SMRT. At the same time, these cofactors were found to be capable of regulating the level of residual agonist activity displayed by antiglucocorticoids. Finally, these observations suggest that a novel role for cofactors is to participate in processes that determine the dose-response curve, and partial agonist activity, of GR-steroid complexes. This new activity of cofactors is disconnected from their ability to increase or decrease GR transactivation. An equilibrium model is proposed in which the ratio of coactivator-corepressor bound to either receptor-agonist or -antagonist complexes regulates the final transcriptional properties.

Opposing Effects of Corepressor and Coactivators in Determining the Dose-Response Curve of Agonists, and Residual Agonist Activity of Antagonists, for Glucocorticoid Receptor-Regulated Gene Expression

Opposing Effects of Corepressor and Coactivators in Determining the Dose-Response Curve of Agonists, and Residual Agonist Activity of Antagonists, for Glucocorticoid Receptor-Regulated Gene Expression