Glucocorticoid receptor (GR) β has intrinsic, GRα-independent transcriptional activity (original) (raw)
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Autoregulation of glucocorticoid receptor gene expression
Steroids, 1991
Glucocorticoid receptors are members of a highly conservedfamily of steroid receptor proteins, which are ligand-dependent transcription j;lctors. Previous studies huve shown that the presence offunctional glucocorticoid receptors is N prerequisitefor manifestation of cellular responses to hormone. Glucocorticoid receptors undergo down-regulation following treutment with glucocorticoids. To define the molecular mechanisms that are involved in this process n'e have analyzed the down-regulation of glucocorticoid receptors both in HeLa cells, which contain endogenous receptors, and in cells containing receptors that have been introduced by DNA transfection. Our results show that cells that contain glucocorticoid receptors-either endogenous or trrmsfected-undergo down-regulation of steroid-binding capabilities, us well NS reductions in receptor protein rend mRNA levels, in a remarkably similar fashion. DNA sequences in the coding region of the humrrn glucocorticoid receptor cDNA appear to be sufJicient to uccount jtir down-regulution of receptor. This novel jinding suggests that unique mechanisms are involved in controlling glucocorticoid receptor homeostcrsis.
Determinants of Cell- and Gene-Specific Transcriptional Regulation by the Glucocorticoid Receptor
PLoS Genetics, 2007
The glucocorticoid receptor (GR) associates with glucocorticoid response elements (GREs) and regulates selective gene transcription in a cell-specific manner. Native GREs are typically thought to be composite elements that recruit GR as well as other regulatory factors into functional complexes. We assessed whether GR occupancy is commonly a limiting determinant of GRE function as well as the extent to which core GR binding sequences and GRE architecture are conserved at functional loci. We surveyed 100-kb regions surrounding each of 548 known or potentially glucocorticoidresponsive genes in A549 human lung cells for GR-occupied GREs. We found that GR was bound in A549 cells predominately near genes responsive to glucocorticoids in those cells and not at genes regulated by GR in other cells. The GREs were positionally conserved at each responsive gene but across the set of responsive genes were distributed equally upstream and downstream of the transcription start sites, with 63% of them .10 kb from those sites. Strikingly, although the core GR binding sequences across the set of GREs varied extensively around a consensus, the precise sequence at an individual GRE was conserved across four mammalian species. Similarly, sequences flanking the core GR binding sites also varied among GREs but were conserved at individual GREs. We conclude that GR occupancy is a primary determinant of glucocorticoid responsiveness in A549 cells and that core GR binding sequences as well as GRE architecture likely harbor gene-specific regulatory information.
Molecular Cell, 2005
and rheumatoid arthritis often have altered glucocorticoid sensitivity (Leung et al., 1998). Moreover, how one Molecular Endocrinology Group Laboratory of Signal Transduction hormone acts via one receptor to induce apoptosis in lymphocytes while inhibiting the same process in hepa-Department of Health and Human Services National Institute of Environmental Health Sciences tocytes remains a mystery. Clearly, the molecular basis for these cell-type specific effects of glucocorticoids is National Institutes of Health Research Triangle Park, North Carolina 27709 not well understood. Although differential cofactor recruitment has been proposed to contribute to variations in glucocorticoid sensitivities among different cells, strong evidence supports that a cell's sensitivity Summary is directly determined by the level and molecular nature of the GR therein (Lu and Cidlowski, 2004). Glucocorticoids regulate diverse physiological func-We report here the discovery of translational regulations ranging from mitosis to apoptosis, although tory mechanisms that generate eight N-terminal GR only one glucocorticoid receptor (GR) gene has been isoforms from a single GR mRNA species. Furthermore, discovered. We report here that one single GR mRNA we show that these GR isoforms all have unique tissue species unexpectedly produces at least eight functional distribution patterns and transcriptional regulatory pro-GR N-terminal isoforms via translational mechanisms. files. These data provide a basis for a mechanism in These GR isoforms display diverse cytoplasm-togenerating specificity in GR, and possibly other nuclear nucleus trafficking patterns and distinct transcripreceptor, signaling. tional activities. In human osteosarcoma cells, the transcriptional responses to glucocorticoids closely reflect the identity and abundance of the GR iso-Results forms. In addition, each GR isoform regulates both a common and a unique set of genes in the same cell. Detection of Multiple GR Isoforms Interestingly, the levels of these GR isoforms differ When the human (h)GRα was expressed in COS-1 cells, significantly among tissues. Based on these observawhich lack endogenous GR, multiple proteins of 94, 91, tions, we propose that cell-type specific GR isoforms 82-84, and 53-56 kDa were detected by using a GRgenerate specificity in glucocorticoid control of transelective anti-peptide antibody 57 (Cidlowski et al., scription in different tissues. 1990) in the absence and presence of the cognate hormone (Figure 1A). Therefore, ligand binding and its con-Introduction sequences on receptor turnover are not contributing factors to the expression of multiple GR proteins. The Glucocorticoids are essential for embryo maturation, 94 and 91 kDa bands correspond to the previously dedevelopment, metabolism, and survival (Barnes, 1998; scribed hGRα-A and hGRα-B isoforms, the latter of Tronche et al., 2004). Drugs that mimic the actions of which lacks the N-terminal 27 amino acids (aa) (Yudt these hormones are widely used to treat diseases such and Cidlowski, 2001). The 82-84 and 53-56 kDa proas cancer, inflammation, and autoimmune disorders. teins were previously thought to reflect degradation Glucocorticoids bind and activate the GR, which mediproducts of GR (Hollenberg et al., 1985; Yudt and Cidates the physiological and therapeutic actions of the lowski, 2001). However, when the wild-type (wt) hGRα ligand by directly or indirectly regulating transcription cDNA was expressed in vitro by using the TNT T7-couof target genes. Like other members of the nuclear repled rabbit reticulocyte lysate system (Promega, Madiceptor family, GR is a modular protein comprised of a son, WI), all protein bands observed in vivo were demajor transactivation activity (τ1) domain, a DNA bindtected as well, suggesting that the 82-84 and 53-56 ing domain, and a ligand binding domain that also has kDa proteins are unlikely to be degradation products a minor transactivation domain (τ2). Depending on the (Figure 1B). Similar results were also obtained with cell type and promoter context, GR can either up-or cDNAs for the rat GR and mouse GR (data not shown). downregulate gene expression via coordinated recruit-To elucidate the identities of these GR immunoreactive ing of cofactors and interaction with transcriptional maproteins, three specific anti-GR antibodies were used: chinery. 59, 57 (Cidlowski et al., 1990), and the C terminus-spe-Sensitivity to glucocorticoids varies considerably cific AshGR (Oakley et al., 1999), whose epitopes correamong individuals and, even within the same individual, spond to distinct peptide segments aa 245-259, 346responsiveness to glucocorticoids differs among tis-367, and 755-771 on the hGRα, respectively (Figure sues (Bronnegard et al., 1996). Within a cell, glucocorti-1C). Both antibodies 57 and AShGR detected all procoid responsiveness shifts dynamically during the cell teins, whereas anti-GR 59 detected all, but not the 53cycle (King and Cidlowski, 1998). In addition, patients 56 kDa proteins, suggesting that like hGRα-B, the 82with certain inflammatory conditions such as asthma 84, and 53-56 kDa proteins are likely N-terminal shortened forms of hGR. In addition, we performed experiments to exclude
Characterization of the Human Glucocorticoid Receptor Promoter
Biochemistry, 1995
To elucidate the functional elements that are involved in the regulation of the human glucocorticoid receptor (hGR) gene, transient expression, DNase I footprinting, and gel mobility shift analyses were conducted. We found that the hGR promoter region between-700 and +38 bp contained 1 1 footprinted sites. Deletion of the-374 to-183 bp region, which is highly conserved between human and mouse (93%), induced a 5-24-fold reduction in promoter activity in HeLa, NIH3T3, CV1, and HepG2 cells. Three footprints, FP5, FP6, and FP7, were shown to map to this region. In particular, the FP7 site was found to be within the-374 to-347 bp region. Deletion of this region triggered a significant decline in promoter activity in HeLa and NIH3T3 cells but not in HepG2 cells. AP2 was found to bind FP7. In HepG2 cells AP2 elicited transactivation of the hGR promoter activity. Transfection data revealed that the upstream GC box-rich fragment between-700 and-375 bp induced a 4-7-fold activation of the heterologous tk promoter in an orientation-independent manner. Our studies demonstrate that several transcription factors are involved in regulating GR expression and that AP2 could function as an important positive regulator of GR promoter activity.
Mechanism of gene expression by the glucocorticoid receptor: Role of protein-protein interactions
BioEssays, 1997
The glucocorticoid receptor belongs to an important class of transcription factors that alter the expression of target genes in response to a specific hormone signal. The glucocorticoid receptor can function at least at three levels: (1) recruitment of the general transcription machinery; (2) modulation of transcription factor action, independent of DNA binding, through direct proteinprotein interactions; and (3) modulation of chromatin structure to allow the assembly of other gene regulatory proteins and/or the general transcription machinery on the DNA. This review will focus on the multifaceted nature of protein-protein interactions involving the glucocorticoid receptor and basal transcription factors, coactivators and other transcription factors, occurring at Accepted these different levels of regulation.
The human glucocorticoid receptor: One gene, multiple proteins and diverse responses
Steroids, 2005
Glucocorticoids are a vital class of endogenous steroid hormones that regulate essential biological processes including growth, development, metabolism, behavior and apoptosis. Most, if not all, of these actions are thought to be mediated through the glucocorticoid receptor. The exact mechanisms of how one hormone, via one receptor, modulates such diverse biological functions are largely unknown. However, recent studies from our lab and others have suggested that a contribution for the diversity results from multiple isoforms of the glucocorticoid receptor that result from alternative RNA splicing and translation initiation of the glucocorticoid receptor mRNA. Additionally, each isoform is subject to several post-translational modifications, including phosphorylation, ubiquitination and sumoylation, which have been shown to modulate the receptor protein stability and/or function. Together these data provide potentially diverse mechanisms to establish cell type specific regulation of gene expression by a single transcription factor. Here, we summarize the recent advances and processes that generate these receptor isoforms and these post-translational modifications. We speculate that the composition and proportion of individual isoforms expressed in particular cellular contexts account for the diverse effects of glucocorticoid hormones.
The biology of the glucocorticoid receptor: New signaling mechanisms in health and disease
Journal of Allergy and Clinical Immunology, 2013
Glucocorticoids are primary stress hormones necessary for life that regulate numerous physiological processes in an effort to maintain homeostasis. Synthetic derivatives of these hormones have been mainstays in the clinic for treating inflammatory diseases, autoimmune disorders, and hematological cancers. The physiological and pharmacological actions of glucocorticoids are mediated by the glucocorticoid receptor (GR), a member of the nuclear receptor superfamily of ligand-dependent transcription factors. Ligand-occupied GR induces or represses the transcription of thousands of genes by direct binding to DNA response elements and/or by physically associating with other transcription factors. The traditional view that glucocorticoids act through a single GR protein has changed dramatically with the discovery of a large cohort of receptor isoforms with unique expression, gene-regulatory, and functional profiles. These GR subtypes are derived from a single gene by alternative splicing and alternative translation initiation mechanisms. Post-translational modification of these GR isoforms further expands the diversity of glucocorticoid responses. Here, we discuss the origin and molecular properties of the GR isoforms and their contribution to the specificity and sensitivity of glucocorticoid signaling in healthy and diseased tissues.
Expression of glucocorticoid receptor α- and β-isoforms in human cells and tissues
American Journal of Physiology-Cell Physiology, 2002
Alternative splicing of the human glucocorticoid receptor (GR) primary transcript generates two protein isoforms: GR-α and GR-β. We investigated the expression of both GR isoforms in healthy human cells and tissues. GR-α mRNA abundance (×106cDNA copies/μg total RNA) was as follows: brain (3.83 ± 0.80) > skeletal muscle > macrophages > lung > kidney > liver > heart > eosinophils > peripheral blood mononuclear cells (PBMCs) > nasal mucosa > neutrophils > colon (0.33 ± 0.04). GR-β mRNA was much less expressed than GR-α mRNA. Its abundance (×103cDNA copies/μg total RNA) was as follows: eosinophils (1.55 ± 0.58) > PBMCs > liver ≥ skeletal muscle > kidney > macrophages > lung > neutrophils > brain ≥ nasal mucosa > heart (0.15 ± 0.08). GR-β mRNA was not found in colon. While GR-α protein was detected in all cells and tissues, GR-β was not detected in any specimen. Our results suggest that, in physiological conditions, the default spl...
The human glucocorticoid receptor: Molecular basis of biologic function
Steroids, 2010
The characterization of the subfamily of steroid hormone receptors has enhanced our understanding of how a set of hormonally derived lipophilic ligands controls cellular and molecular functions to influence development and help achieve homeostasis. The glucocorticoid receptor (GR), the first member of this subfamily, is a ubiquitously expressed intracellular protein, which functions as a ligand-dependent transcription factor that regulates the