Mechanisms of glucocorticoid signalling.
ABSTRACT It has become increasingly clear that glucocorticoid signalling not only comprises the binding of the glucocorticoid receptor (GR) to its response element (GRE), but also involves indirect regulation glucocorticoid-responsive genes by regulating or interacting with other transcription factors. In addition, they can directly regulate gene expression by binding to negative glucocorticoid response elements (nGREs), to simple GREs, to GREs, or to GREs and GRE half sites (GRE1/2s) that are part of a regulatory unit. A response unit allows a higher level of glucocorticoid induction than simple GREs and, in addition, allows the integration of tissue-specific information with the glucocorticoid response. Presumably, the complexity of such a glucocorticoid response unit (GRU) depends on the number of pathways that integrate at this unit. Because GRUs are often located at distant sites relative to the transcription-start site, the GRU has to find a way to communicate with the basal-transcription machinery. We propose that the activating signal of a distal enhancer can be relayed onto the transcription-initiation complex by coupling elements located proximal to the promoter.
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ABSTRACT: Dissociating anti-inflammatory efficacy from the metabolic side effects of glucocorticoids is an attractive therapeutic goal. 5α-Tetrahydro-corticosterone (5αTHB), produced from corticosterone by 5α-reductases, activates glucocorticoid receptors. This study compares the effects of 5αTHB on inflammation and metabolism in vitro and in vivo. Suppression of cytokine release by 5αTHB and corticosterone were studied following LPS activation of mouse bone marrow derived macrophages. In vivo the efficacy of these steroids to dysregulate metabolic homeostasis and modulate immune suppression and the responses to thioglycollate-induced peritonitis in C57BL/6 mice were studied following acute injection (1.5-15 mg) and chronic infusion (50 µg·day(-1) , 14 days). In macrophages, 5αTHB increased secretion of IL-10 similarly to corticosterone (180%, 340%; data are % vehicle, treated with 5αTHB and corticosterone, respectively) and suppressed LPS-induced secretion of TNF-α (21.9%, 74.2%) and IL-6 (16.4%, 69.4%). In mice with thioglycollate-induced peritonitis, both 5αTHB and corticosterone reduced the numbers of neutrophils (58.6%, 49.9%) and inflammatory monocytes (69.5%, 96.4%), and also suppressed MCP-1 (48.7%, 80.9%) and IL-6 (53.5%, 86.7%) in peritoneal exudate. In mice chronically infused with 5αTHB and corticosterone LPS-induced production of TNF-α from whole blood was suppressed to the same degree (63.2%, 37.2%). However, in contrast to corticosterone, 5αTHB did not induce body weight loss, increase blood pressure or induce hyperinsulinaemia. 5αTHB has anti-inflammatory effects in vitro and in vivo. At doses with equivalent anti-inflammatory efficacy to corticosterone, 5αTHB did not induce metabolic toxicity and thus may be a prototype for a safer anti-inflammatory drug.British Journal of Pharmacology 05/2011; 164(6):1661-71. DOI:10.1111/j.1476-5381.2011.01465.x · 4.99 Impact Factor
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ABSTRACT: Glucocorticoid actions on the immune system are diverse and cell type dependent, and little is known about cell type-specific interactions and cross-talk between hormones and cytokines. In this study we have analyzed the gene expression patterns of the rainbow trout macrophage cell line RTS-11 by quantitative PCR, after exposure to combinations of cortisol plus a pro-inflammatory cytokine (e.g. recombinant trout IL-1β, IFN-γ), type I IFN or a PAMP (LPS or poly I:C). Several key genes of the inflammatory process were targetted to assess whether any modulation of their expression occurred due to the addition of cortisol to this cell line. Incubation of macrophages for 3 or 6 h with a physiological concentration of cortisol caused a decrease in expression of IL-6 and IL-8, but no significant changes were observed for the other genes examined. Co-stimulation of cortisol with the inflammatory agents resulted in a general suppression of genes related to the inflammatory response. Cortisol inhibited the up-regulation of IL-8 by all the stimulants after 3 h of co-incubation. Suppression of the up-regulation of IL-6 by rIL-1β, rIFN-γ and poly I:C, of γIP by rIFN-γ or poly I:C, and of Cox-2 by rIL-1β was seen after 6 h. In contrast, cortisol in combination with the pro-inflammatory agents has a synergistic effect on IL-10 expression, an anti-inflammatory molecule, suggesting that the activation of certain macrophage functions that lead to the resolution of inflammation occurs in fish macrophages in response to cortisol treatment.Fish & Shellfish Immunology 10/2010; 30(1):215-23. DOI:10.1016/j.fsi.2010.10.010 · 3.03 Impact Factor
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ABSTRACT: The glucocorticoid receptor (GR) is a ligand-dependent transcription factor mediating the genomic effects of glucocorticoids. Two activation functions (AFs) are present in the GR. While the N-terminal AF1 is ligand independent, the C-terminal AF2 overlaps with the ligand-binding domain and is ligand dependent. In this study, we have mapped AF1 in duplicated rainbow trout GRs, called rtGR1 and rtGR2, showing a limited homology (24.5%) in the N-terminal domain. Ablation of this domain from rtGR1 or rtGR2 resulted in a marked decrease (>97%) in maximal hormone-dependent transactivation, but did not affect dexamethasone-binding activity or expression levels. This suggested that, similar to the situation in the human GR (hGR), AF1 is the main AF in the trout GRs. Sequence alignments with hGR suggested a localisation of AF1 to residues 70-230 of rtGR1 and 1-119 of rtGR2. These assignments were generally confirmed in the transactivation experiments with rtGR1- and rtGR2-derived mutants showing partial deletions of their N-terminal domains. In dexamethsone-treated cells (10⁻⁷ M, 2 h), the subcellular distribution of rtGR1 and rtGR2 mutants lacking the entire N-terminal domain, as well that of an rtGR1 mutant lacking the most N-terminal 234 amino acids, was similar to that of the corresponding wild-type GRs, suggesting that the disruption of transactivation activity was not caused by impairment of nuclear access of the mutants. Bioinformatic analyses predicted the presence of potential helical segments in the core of AF1 of rtGR1 and rtGR2, and further revealed that AF1 in rtGR1, rtGR2, and hGR shares a motif composed of hydrophobic and acidic amino acids.Journal of Molecular Endocrinology 10/2010; 45(6):391-404. DOI:10.1677/JME-09-0152 · 3.62 Impact Factor