The Interactome of the Glucocorticoid Receptor and Its Influence on the Actions of Glucocorticoids in Combatting Inflammatory and Infectious Diseases. Microbiol Mol Biol Rev. 2016;80:495-522. [PMID: 27169854 DOI: 10.1128/mmbr.00064-15]

A General Introduction to Glucocorticoid Biology

Glucocorticoids (GCs) are steroid hormones widely used for the treatment of inflammation, autoimmune diseases, and cancer. To exert their broad physiological and therapeutic effects, GCs bind to the GC receptor (GR) which belongs to the nuclear receptor superfamily of transcription factors. Despite their success, GCs are hindered by the occurrence of side effects and glucocorticoid resistance (GCR). Increased knowledge on GC and GR biology together with a better understanding of the molecular mechanisms underlying the GC side effects and GCR are necessary for improved GC therapy development. We here provide a general overview on the current insights in GC biology with a focus on GC synthesis, regulation and physiology, role in inflammation inhibition, and on GR function and plasticity. Furthermore, novel and selective therapeutic strategies are proposed based on recently recognized distinct molecular mechanisms of the GR. We will explain the SEDIGRAM concept, which was launched based on our research results.

Transcriptomic Network Interactions in Human Skin Treated with Topical Glucocorticoid Clobetasol Propionate

Glucocorticoids are the most frequently used anti-inflammatory drugs in dermatology. However, the molecular signature of glucocorticoids and their receptor in human skin is largely unknown. Our validated bioinformatics analysis of human skin transcriptome induced by topical glucocorticoid clobetasol propionate (CBP) in healthy volunteers identified numerous unreported glucocorticoid-responsive genes, including over a thousand noncoding RNAs. We observed sexual and racial dimorphism in the CBP response including a shift toward IFN-α/IFN-γ and IL-6/Jak/Signal transducer and activator of transcription (STAT) 3 signaling in female skin; and a larger response to CBP in African-American skin. Weighted gene coexpression network analysis unveiled a dense skin network of 41 transcription factors including circadian Kruppel-like factor 9 (KLF9), and ∼260 of their target genes enriched for functional pathways representative of the entire CBP transcriptome. Using keratinocytes with Kruppel-like factor 9 knockdown, we revealed a feedforward loop in glucocorticoid receptor signaling, previously unreported. Interestingly, many of the CBP-regulated transcription factors were involved in the control of development, metabolism, circadian clock; and 80% of them were associated with skin aging showing similarities between glucocorticoid-treated and aged skin. Overall, these findings indicate that glucocorticoid receptor acts as an important regulator of gene expression in skin-both at the transcriptional and posttranscriptional level-via multiple mechanisms including regulation of noncoding RNAs and multiple core transcription factors.

β-Arrestin-1 inhibits glucocorticoid receptor turnover and alters glucocorticoid signaling

Glucocorticoids are among the most widely used drugs to treat many autoimmune and inflammatory diseases. Although much research has been focused on investigating glucocorticoid activity, it remains unclear how glucocorticoids regulate distinct processes in different cells. Glucocorticoids exert their effects through the glucocorticoid receptor (GR), which, upon glucocorticoid binding, interacts with regulatory proteins, affecting its activity and function. These protein-protein interactions are necessary for the resolution of glucocorticoid-dependent physiological and pharmacological processes. In this study, we discovered a novel protein interaction between the glucocorticoid receptor and β-arrestin-1, a scaffold protein with a well-established role in G protein-coupled receptor signaling. Using co-immunoprecipitation and in situ proximity ligation assays in A549 cells, we observed that β-arrestin-1 and unliganded GR interact in the cytoplasm and that, following glucocorticoid binding, the protein complex is found in the nucleus. We show that siRNA-mediated β-arrestin-1 knockdown alters GR protein turnover by up-regulating the E3 ubiquitin ligase Pellino-1, which catalyzes GR ubiquitination and thereby marks the receptor for proteasomal degradation. The enhanced GR turnover observed in β-arrestin-1-deficient cells limits the duration of the glucocorticoid response on GR target genes. These results demonstrate that β-arrestin-1 is a crucial player for the stability of the glucocorticoid receptor. The GR/β-arrestin-1 interaction uncovered here may help unravel mechanisms that contribute to the cell type-specific activities of glucocorticoids.

Nongenomic glucocorticoid effects and their mechanisms of action in vertebrates

Glucocorticoids (GC) act on multiple organ systems to regulate a variety of physiological processes in vertebrates. Due to their immunosuppressive and anti-inflammatory actions, glucocorticoids are an attractive target for pharmaceutical development. Accordingly, they are one of the most widely prescribed classes of therapeutics. Through the classical mechanism of steroid action, glucocorticoids are thought to mainly affect gene transcription, both in a stimulatory and suppressive fashion, regulating de novo protein synthesis that subsequently leads to the physiological response. However, over the past three decades multiple lines of evidence demonstrate that glucocorticoids may work through rapid, nonclassical mechanisms that do not require alterations in gene transcription or translation. This review assimilates evidence across the vertebrate taxa on the diversity of nongenomic actions of glucocorticoids and the membrane-associated cellular mechanisms that may underlie rapid glucocorticoid responses to include potential binding sites characterized to date.

Risks and benefits of corticosteroids in arthritic diseases in the clinic

Glucocorticoids (GCs) constitute a first line treatment for many autoimmune and inflammatory diseases. Due to their potent anti-inflammatory and immunosuppressive actions, GCs are added frequently to disease modifying antirheumatic drugs (DMARDs) in various arthritic diseases, such as rheumatoid arthritis. However, their prolonged administration or administration at high doses is associated with adverse effects that may be (quality of) life-threatening, including osteoporosis, metabolic, gastrointestinal and cardiovascular side effects. In this review, we summarize the clinical and pharmacological effects of GCs in different arthritic diseases, while documenting the current research efforts towards the identification of novel and more efficient GCs with reduced side effects.

Relapse-associated AURKB blunts the glucocorticoid sensitivity of B cell acute lymphoblastic leukemia

Glucocorticoids (GCs) are used in combination chemotherapies as front-line treatment for B cell acute lymphoblastic leukemia (B-ALL). Although effective, many patients relapse and become resistant to chemotherapy and GCs in particular. Why these patients relapse is not clear. We took a comprehensive, functional genomics approach to identify sources of GC resistance. A genome-wide shRNA screen identified the transcriptional coactivators EHMT2, EHMT1, and CBX3 as important contributors to GC-induced cell death. This complex selectively supports GC-induced expression of genes contributing to cell death. A metaanalysis of gene expression data from B-ALL patient specimens revealed that Aurora kinase B (AURKB), which restrains GC signaling by phosphorylating EHMT1-2, is overexpressed in relapsed B-ALL, suggesting it as a potential contributor to relapse. Inhibition of AURKB enhanced GC-induced expression of cell death genes, resulting in potentiation of GC cytotoxicity in cell lines and relapsed B-ALL patient samples. This function for AURKB is distinct from its canonical role in the cell cycle. These results show the utility of functional genomics in understanding mechanisms of resistance and rapidly identifying combination chemotherapeutics.

PI3K inhibitors protect against glucocorticoid-induced skin atrophy

Background

Skin atrophy is a major adverse effect of topical glucocorticoids. We recently reported that REDD1 (regulated in development and DNA damage 1) and FKBP51 (FK506 binding protein 5), negative regulators of mTOR/Akt signaling, are induced by glucocorticoids in mouse and human skin and are central drivers of steroid skin atrophy. Thus, we hypothesized that REDD1/FKBP51 inhibitors could protect skin against catabolic effects of glucocorticoids.

Methods

Using drug repurposing approach, we screened LINCS library (http://lincsproject.org/LINCS/) to identify repressors of REDD1/FKBP51 expression. Candidate compounds were tested for their ability to inhibit glucocorticoid-induced REDD1/FKBP51 expression in human primary/immortalized keratinocytes and in mouse skin. Reporter gene expression, microarray, and chromatin immunoprecipitation were employed to evaluate effect of these inhibitors on the glucocorticoid receptor (GR) signaling.

Findings

Bioinformatics analysis unexpectedly identified phosphoinositide-3-kinase (PI3K)/mTOR/Akt inhibitors as a pharmacological class of REDD1/FKBP51 repressors. Selected PI3K/mTOR/Akt inhibitors-Wortmannin (WM), LY294002, AZD8055, and two others indeed blocked REDD1/FKBP51expression in human keratinocytes. PI3K/mTOR/Akt inhibitors also modified global effect of glucocorticoids on trascriptome, shifting it towards therapeutically important transrepression; negatively impacted GR phosphorylation; nuclear translocation; and GR loading on REDD1/FKBP51 gene promoters. Further, topical application of LY294002 together with glucocorticoid fluocinolone acetonide (FA) protected mice against FA-induced proliferative block and skin atrophy but did not alter the anti-inflammatory activity of FA in ear edema test.

Interpretation

Our results built a strong foundation for development of safer GR-targeted therapies for inflammatory skin diseases using combination of glucocorticoids with PI3K/mTOR/Akt inhibitors.

Fund

Work is supported by NIH grants R01GM112945, R01AI125366, and HESI-THRIVE foundation.

Glucocorticoids promote the development of azoxymethane and dextran sulfate sodium-induced colorectal carcinoma in mice

BACKGROUND

Stress has been suggested as a promoter of tumor growth and development. Glucocorticoids (GCs) are the main stress hormones and widely prescribed as drugs. However, the effect of GCs on the development and progression of colorectal carcinoma (CRC) is unclear.

METHODS

We evaluated the effect of corticosterone (CORT) on azoxymethane and dextran sulfate sodium (AOM/DSS)-induced carcinogenesis in the colorectum of C57BL/6 strain mice. Plasma level of CORT was detected by radioimmunoassay. The expression of proliferation markers (Ki-67 and PCNA), nuclear factor (NF)-κB p65 and phosphoto-p65 (P-p65), as well as cyclooxygenase (COX)-2 were determined by immunohistochemistry. Inflammation in colorectum was evaluated by histopathology.

RESULTS

CORT feeding in drinking water of mice not only significantly elevated plasma CORT concentration, but also significantly increased the incidence and neoplasms burden (number and size of neoplasms) in colorectum. CORT also significant enhanced the expression of cell proliferation marker (Ki-67 and PCNA), NF-κB p65 and P-p65 as well as COX-2 in colorectal neoplasm of AOM/DSS-treated mice.

CONCLUSION

In this study, we have found for the first time that CORT at stress level potentially promotes the growth and development of AOM/DSS-induced colorectal adenoma and carcinoma in mice. Up-regulation of NF-κB and COX-2 may be involved in the promoting effect of CORT.

Stressful Newborn Memories: Pre-Conceptual, In Utero, and Postnatal Events

Early-life stressful experiences are critical for plasticity and development, shaping adult neuroendocrine response and future health. Stress response is mediated by the autonomous nervous system and the hypothalamic-pituitary-adrenal (HPA) axis while various environmental stimuli are encoded via epigenetic marks. The stress response system maintains homeostasis by regulating adaptation to the environmental changes. Pre-conceptual and in utero stressors form the fetal epigenetic profile together with the individual genetic profile, providing the background for individual stress response, vulnerability, or resilience. Postnatal and adult stressful experiences may act as the definitive switch. This review addresses the issue of how preconceptual in utero and postnatal events, together with individual differences, shape future stress responses. Putative markers of early-life adverse effects such as prematurity and low birth weight are emphasized, and the epigenetic, mitochondrial, and genomic architecture regulation of such events are discussed.

Human genome-wide measurement of drug-responsive regulatory activity

Environmental stimuli commonly act via changes in gene regulation. Human-genome-scale assays to measure such responses are indirect or require knowledge of the transcription factors (TFs) involved. Here, we present the use of human genome-wide high-throughput reporter assays to measure environmentally-responsive regulatory element activity. We focus on responses to glucocorticoids (GCs), an important class of pharmaceuticals and a paradigmatic genomic response model. We assay GC-responsive regulatory activity across >10⁸ unique DNA fragments, covering the human genome at >50×. Those assays directly detected thousands of GC-responsive regulatory elements genome-wide. We then validate those findings with measurements of transcription factor occupancy, histone modifications, chromatin accessibility, and gene expression. We also detect allele-specific environmental responses. Notably, the assays did not require knowledge of GC response mechanisms. Thus, this technology can be used to agnostically quantify genomic responses for which the underlying mechanism remains unknown.

Quantification of genomic responses to environmental stimuli by current genome-scale assays is limited to indirect measurements or requires knowledge of the transcription factors involved. Here, the authors use genome-wide high-throughput reporter assays to agnostically map enhancer activity in response to glucocorticoid treatment across the human genome.

Inhibition of microRNA-124-3p as a novel therapeutic strategy for the treatment of Gulf War Illness: Evaluation in a rat model

Gulf War Illness (GWI) is a chronic, multisymptom illness that continues to affect up to 30% of veterans deployed to the Persian Gulf during the 1990-1991 Gulf War. After nearly 30 years, useful treatments for GWI are lacking and underlying cellular and molecular mechanisms involved in its pathobiology remain poorly understood, although exposures to pyridostigmine bromide (PB) and pesticides are consistently identified to be among the strongest risk factors. Alleviation of the broad range of symptoms manifested in GWI, which involve the central nervous system, the neuroendocrine system, and the immune system likely requires therapies that are able to activate and inactivate a large set of orchestrated genes. Previous work in our laboratory using an established rat model of GWI identified persistent elevation of microRNA-124-3p (miR-124) levels in the hippocampus whose numerous gene targets are involved in cognition-associated pathways and neuroendocrine function. This study aimed to investigate the broad effects of miR-124 inhibition in the brain 9 months after completion of a 28-day exposure regimen of PB, DEET (N,N-diethyl-3-methylbenzamide), permethrin, and mild stress by profiling the hippocampal expression of genes known to play a critical role in synaptic plasticity, glucocorticoid signaling, and neurogenesis. We determined that intracerebroventricular infusion of a miR-124 antisense oligonucleotide (miR-124 inhibitor; 0.05-0.5 nmol/day/28 days), but not a negative control oligonucleotide, into the lateral ventricle of the brain caused increased protein expression of multiple validated miR-124 targets and increased expression of downstream target genes important for cognition and neuroendocrine signaling in the hippocampus. Off-target cardiotoxic effects were revealed in GWI rats receiving 0.1 nmol/day as indicated by the detection in plasma of 5 highly elevated protein cardiac injury markers and 6 upregulated cardiac-enriched miRNAs in plasma exosomes determined by next-generation sequencing. Results from this study suggest that in vivo inhibition of miR-124 function in the hippocampus is a promising, novel therapeutic approach to improve cognition and neuroendocrine dysfunction in GWI. Additional preclinical studies in animal models to assess feasibility and safety by developing a practical, noninvasive drug delivery system to the brain and exploring potential adverse toxicologic effects of miR-124 inhibition are warranted.

Fra2 Overexpression in Mice Leads to Non-allergic Asthma Development in an IL-13 Dependent Manner

Background: Asthma is a complex chronic inflammatory disease characterised by airway inflammation, remodelling and hyperresponsiveness (AHR). Members of the AP-1 transcription factor family play important roles in the activation of the immune system and the control of cellular responses; however, their role in the development of asthma has not been well studied. We aimed to investigate the role of the lesser known AP-1 family member, Fra2 in experimental asthma.

Methods: Phenotypic characterisation and gene expression profiling was performed on Fra2 (TG) overexpressing and wild-type mice. The efficacy of therapeutic interventions in regulating the Fra2 phenotype was determined.

Results: Transcriptional profiling of TG mice revealed a high abundance of regulated genes associated with airway remodelling, inflammation and mucus production. A concomitant increase in peribronchial collagen deposition, smooth muscle thickening and mucus production was observed. TG mice possessed increased inflammatory infiltration in the lung, predominantly consisting of eosinophils and T-cells and elevated expression of Th2 cytokines and eotaxin. Furthermore, TG mice possessed severe AHR in response to increasing doses of methacholine. Glucocorticoid treatment led to a partial improvement of the asthma phenotype, whereas blockade of IL-13 via neutralising antibodies ameliorated AHR and mucus production, but had no effect on collagen deposition.

Conclusion: We here describe a novel model for non-allergic asthma that does not require the application of exogenous allergens, which mimics several key features of the disease, such as airway inflammation, remodelling and hyperresponsiveness. Fra2 may represent a key molecule coordinating multiple aspects of asthma pathogenesis.

Chromatin reprogramming in breast cancer

Reprogramming of the chromatin landscape is a critical component to the transcriptional response in breast cancer. Effects of sex hormones such as estrogens and progesterone have been well described to have a critical impact on breast cancer proliferation. However, the complex network of the chromatin landscape, enhancer regions and mode of function of steroid receptors (SRs) and other transcription factors (TFs), is an intricate web of signaling and functional processes that is still largely misunderstood at the mechanistic level. In this review, we describe what is currently known about the dynamic interplay between TFs with chromatin and the reprogramming of enhancer elements. Emphasis has been placed on characterizing the different modes of action of TFs in regulating enhancer activity, specifically, how different SRs target enhancer regions to reprogram chromatin in breast cancer cells. In addition, we discuss current techniques employed to study enhancer function at a genome-wide level. Further, we have noted recent advances in live cell imaging technology. These single-cell approaches enable the coupling of population-based assays with real-time studies to address many unsolved questions about SRs and chromatin dynamics in breast cancer.

Roles of the Glucocorticoid and Mineralocorticoid Receptors in Skin Pathophysiology

The nuclear hormone receptor (NR) superfamily comprises approximately 50 evolutionarily conserved proteins that play major roles in gene regulation by prototypically acting as ligand-dependent transcription factors. Besides their central role in physiology, NRs have been largely used as therapeutic drug targets in many chronic inflammatory conditions and derivatives of their specific ligands, alone or in combination, are frequently prescribed for the treatment of skin diseases. In particular, glucocorticoids (GCs) are the most commonly used compounds for treating prevalent skin diseases such as psoriasis due to their anti-proliferative and anti-inflammatory actions. However, and despite their therapeutic efficacy, the long-term use of GCs is limited because of the cutaneous adverse effects including atrophy, delayed wound healing, and increased susceptibility to stress and infections. The GC receptor (GR/NR3C1) and the mineralocorticoid receptor (MR/NR3C2) are members of the NR subclass NR3C that are highly related, both structurally and functionally. While the GR is ubiquitously expressed and is almost exclusively activated by GCs; an MR has a more restricted tissue expression pattern and can bind GCs and the mineralocorticoid aldosterone with similar high affinity. As these receptors share 95% identity in their DNA binding domains; both can recognize the same hormone response elements; theoretically resulting in transcriptional regulation of the same target genes. However, a major mechanism for specific activation of GRs and/or MRs is at the pre-receptor level by modulating the local availability of active GCs. Furthermore, the selective interactions of each receptor with spatio-temporally regulated transcription factors and co-regulators are crucial for the final transcriptional outcome. While there are abundant genome wide studies identifying GR transcriptional targets in a variety of tissue and cell types; including keratinocytes; the data for MR is more limited thus far. Our group and others have studied the role of GRs and MRs in skin development and disease by generating and characterizing mouse and cellular models with gain- and loss-of-function for each receptor. Both NRs are required for skin barrier competence during mouse development and also play a role in adult skin homeostasis. Moreover, the combined loss of epidermal GRs and MRs caused a more severe skin phenotype relative to single knock-outs (KOs) in developing skin and in acute inflammation and psoriasis, indicating that these corticosteroid receptors play cooperative roles. Understanding GR- and MR-mediated signaling in skin should contribute to deciphering their tissue-specific relative roles and ultimately help to improve GC-based therapies.

Immunoregulatory Effects of Myeloid-Derived Suppressor Cell Exosomes in Mouse Model of Autoimmune Alopecia Areata

The treatment of autoimmune diseases still poses a major challenge, frequently relying on non-specific immunosuppressive drugs. Current efforts aim at reestablishing self tolerance using immune cells with suppressive activity like the regulatory T cells (Treg) or the myeloid-derived suppressor cells (MDSC). We have demonstrated therapeutic efficacy of MDSC in mouse Alopecia Areata (AA). In the same AA model, we now asked whether MDSC exosomes (MDSC-Exo) can replace MDSC. MDSC-Exo from bone marrow cells (BMC) cultures of healthy donors could substantially facilitate treatment. With knowledge on MDSC-Exo being limited, their suitability needs to be verified in advance. Protein marker profiles suggest comparability of BMC- to ex vivo collected inflammatory MDSC/MDSC-Exo in mice with a chronic contact dermatitis, which is a therapeutic option in AA. Proteome analyses substantiated a large overlap of function-relevant molecules in MDSC and MDSC-Exo. Furthermore, MDSC-Exo are taken up by T cells, macrophages, NK, and most avidly by Treg and MDSC-Exo uptake exceeds binding of MDSC themselves. In AA mice, MDSC-Exo preferentially target skin-draining lymph nodes and cells in the vicinity of remnant hair follicles. MDSC-Exo uptake is accompanied by a strong increase in Treg, reduced T helper proliferation, mitigated cytotoxic activity, and a slight increase in lymphocyte apoptosis. Repeated MDSC-Exo application in florid AA prevented progression and sufficed for partial hair regrowth. Deep sequencing of lymphocyte mRNA from these mice revealed a significant increase in immunoregulatory mRNA, including FoxP3 and arginase 1. Downregulated mRNA was preferentially engaged in prohibiting T cell hyperreactivity. Taken together, proteome analysis provided important insights into potential MDSC-Exo activities, these Exo preferentially homing into AA-affected organs. Most importantly, changes in leukocyte mRNA seen after treatment of AA mice with MDSC-Exo sustainably supports the strong impact on the adaptive and the non-adaptive immune system, with Treg expansion being a dominant feature. Thus, MDSC-Exo could potentially serve as therapeutic agents in treating AA and other autoimmune diseases.

Glucocorticoid hormones are both a major circadian signal and major stress signal: How this shared signal contributes to a dynamic relationship between the circadian and stress systems

Glucocorticoid hormones are a powerful mammalian systemic hormonal signal that exerts regulatory effects on almost every cell and system of the body. Glucocorticoids act in a circadian and stress-directed manner to aid in adaptation to an ever-changing environment. Circadian glucocorticoid secretion provides for a daily waxing and waning influence on target cell function. In addition, the daily circadian peak of glucocorticoid secretion serves as a timing signal that helps entrain intrinsic molecular clock phase in tissue cells distributed throughout the body. Stress-induced glucocorticoid secretion also modulates the state of these same cells in response to both physiological and psychological stressors. We review the strong functional interrelationships between glucocorticoids and the circadian system, and discuss how these interactions optimize the appropriate cellular and systems response to stress throughout the day. We also discuss clinical implications of this dual aspect of glucocorticoid signaling, especially for conditions of circadian and HPA axis dysregulation.

The regulation of the mitochondrial apoptotic pathway by glucocorticoid receptor in collaboration with Bcl-2 family proteins in developing T cells

Glucocorticoids (GC) are important in the regulation of selection and apoptosis of CD4⁺CD8⁺ double-positive (DP) thymocytes. The pronounced GC-sensitivity of DP thymocytes, observed earlier, might be due to the combination of classical (genomic) and alternative (non-genomic) glucocorticoid receptor (GR) signaling events modifying activation or apoptotic pathways. In particular, the previously demonstrated mitochondrial translocation of activated GR in DP thymocytes offered a fascinating explanation for their pronounced GC-induced apoptosis sensitivity. However, the fine molecular details how the mitochondrial translocation of GR might regulate apoptosis remained unclear. Therefore, in the present study, we intended to examine which apoptotic pathways could be involved in GC-induced thymocyte apoptosis. Furthermore we investigated the potential relationship between the GR and Bcl-2 proteins. Using an in vitro test system, thymocytes from 4-week-old BALB/c mice, were treated with the GC-analogue dexamethasone (DX). Bax accumulated in mitochondria upon DX treatment. Mitochondrial GR showed association with members of the Bcl-2 family: Bak, Bim, Bcl-x_L. Elevated Cytochrome C, and active caspase-3, -8, and -9 levels were detected in thymocytes after DX treatment. These results support the hypothesis that in early phases of GC-induced thymocyte apoptosis, the mitochondrial pathway plays a crucial role, confirmed by the release of Cytochrome C and the activation of caspase-9. The activation of caspase-8 was presumably due to cross-talk between apoptotic signaling pathways. We propose that the GC-induced mitochondrial accumulation of Bax and the interaction between the GR and Bim, Bcl-x_L and Bak could play a role in the regulation of thymocyte apoptosis.

Janus-Faced Myeloid-Derived Suppressor Cell Exosomes for the Good and the Bad in Cancer and Autoimmune Disease

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells originally described to hamper immune responses in chronic infections. Meanwhile, they are known to be a major obstacle in cancer immunotherapy. On the other hand, MDSC can interfere with allogeneic transplant rejection and may dampen autoreactive T cell activity. Whether MDSC-Exosomes (Exo) can cope with the dangerous and potentially therapeutic activities of MDSC is not yet fully explored. After introducing MDSC and Exo, it will be discussed, whether a blockade of MDSC-Exo could foster the efficacy of immunotherapy in cancer and mitigate tumor progression supporting activities of MDSC. It also will be outlined, whether application of native or tailored MDSC-Exo might prohibit autoimmune disease progression. These considerations are based on the steadily increasing knowledge on Exo composition, their capacity to distribute throughout the organism combined with selectivity of targeting, and the ease to tailor Exo and includes open questions that answers will facilitate optimizing protocols for a MDSC-Exo blockade in cancer as well as for strengthening their therapeutic efficacy in autoimmune disease.

Regulatory and Mechanistic Actions of Glucocorticoids on T and Inflammatory Cells

Glucocorticoids (GCs) play an important role in regulating the inflammatory and immune response and have been used since decades to treat various inflammatory and autoimmune disorders. Fine-tuning the glucocorticoid receptor (GR) activity is instrumental in the search for novel therapeutic strategies aimed to reduce pathological signaling and restoring homeostasis. Despite the primary anti-inflammatory actions of GCs, there are studies suggesting that under certain conditions GCs may also exert pro-inflammatory responses. For these reasons the understanding of the GR basic mechanisms of action on different immune cells in the periphery (e.g., macrophages, dendritic cells, neutrophils, and T cells) and in the brain (microglia) contexts, that we review in this chapter, is a continuous matter of interest and may reveal novel therapeutic targets for the treatment of immune and inflammatory response.

Adrenergic and glucocorticoid receptor antagonists reduce ozone-induced lung injury and inflammation

Recent studies showed that the circulating stress hormones, epinephrine and corticosterone/cortisol, are involved in mediating ozone-induced pulmonary effects through the activation of the sympathetic-adrenal-medullary (SAM) and hypothalamus-pituitary-adrenal (HPA) axes. Hence, we examined the role of adrenergic and glucocorticoid receptor inhibition in ozone-induced pulmonary injury and inflammation. Male 12-week old Wistar-Kyoto rats were pretreated daily for 7days with propranolol (PROP; a non-selective β adrenergic receptor [AR] antagonist, 10mg/kg, i.p.), mifepristone (MIFE; a glucocorticoid receptor [GR] antagonist, 30mg/kg, s.c.), both drugs (PROP+MIFE), or respective vehicles, and then exposed to air or ozone (0.8ppm), 4h/d for 1 or 2 consecutive days while continuing drug treatment. Ozone exposure alone led to increased peak expiratory flow rates and enhanced pause (Penh); with greater increases by day 2. Receptors blockade minimally affected ventilation in either air- or ozone-exposed rats. Ozone exposure alone was also associated with marked increases in pulmonary vascular leakage, macrophage activation, neutrophilic inflammation and lymphopenia. Notably, PROP, MIFE and PROP+MIFE pretreatments significantly reduced ozone-induced pulmonary vascular leakage; whereas PROP or PROP+MIFE reduced neutrophilic inflammation. PROP also reduced ozone-induced increases in bronchoalveolar lavage fluid (BALF) IL-6 and TNF-α proteins and/or lung Il6 and Tnfα mRNA. MIFE and PROP+MIFE pretreatments reduced ozone-induced increases in BALF N-acetyl glucosaminidase activity, and lymphopenia. We conclude that stress hormones released after ozone exposure modulate pulmonary injury and inflammatory effects through AR and GR in a receptor-specific manner. Individuals with pulmonary diseases receiving AR and GR-related therapy might experience changed sensitivity to air pollution.

Regulatory effects of dexamethasone on NK and T cell immunity

Glucocorticoids (GCs) act via the intracellular glucocorticoid receptor (GR), which can regulate the expression of target genes. With regard to the immune system, GCs may affect both innate and adaptive immunity. Our study analyzed the immunoregulatory effects of dexamethasone (Dex) treatment on splenic T, Treg, NK and NKT cells by treating C57Bl6 mice with various doses of Dex. We observed that treatment with Dex decreased the number of NK cells in the spleen and suppressed their activity. In particular, the expression of both Ly49G and NKG2D receptors was decreased by Dex. However, Dex did not affect the population of NKT cells. With regard to splenic T cells, our results show a dose-dependent reduction in CD3⁺, CD4⁺, CD8⁺, CD44⁺ and CD8⁺CD122⁺ T cells, but a stimulatory effect on CD4⁺CD25⁺ regulatory T cells by Dex treatment. In addition, treatment with Dex suppressed anti-tumor immune response in a mouse EG7 tumor model. We conclude that Dex may suppress both T- and NK-mediated immunity.

Glucocorticoid Receptor-mediated transactivation is hampered by Striatin-3, a novel interaction partner of the receptor

The transcriptional activity of the glucocorticoid receptor (GR) is co-determined by its ability to recruit a vast and varying number of cofactors. We here identify Striatin-3 (STRN3) as a novel interaction partner of GR that interferes with GR’s ligand-dependent transactivation capacity. Remarkably, STRN3 selectively affects only GR-dependent transactivation and leaves GR-dependent transrepression mechanisms unhampered. We found that STRN3 down-regulates GR transactivation by an additional recruitment of the catalytic subunit of protein phosphatase 2A (PPP2CA) to GR. We hypothesize the existence of a functional trimeric complex in the nucleus, able to dephosphorylate GR at serine 211, a known marker for GR transactivation in a target gene-dependent manner. The presence of STRN3 appears an absolute prerequisite for PPP2CA to engage in a complex with GR. Herein, the C-terminal domain of GR is essential, reflecting ligand-dependency, yet other receptor parts are also needed to create additional contacts with STRN3.

Modification of anti-tumor immunity by tolerogenic dendritic cells

Immunosuppressive functions of glucocorticoids (GC) can be mediated via various mechanisms, including the modulation of dendritic cells (DC). Our study investigates the effects of tolerogenic GC-treated DCs on NK and T cell anti-tumor responses in OT-1/Rag^-/- mice, expressing a transgenic TCR in CD8⁺ T cells. The effects caused by GC-treated DCs were compared to the responses to immunogenic, CpG-activated DCs. The effects of DCs on anti-tumor immune responses were analyzed using the EG7 tumor model, where the tumor cells express the peptide epitope recognized by OT-1 T cells. We observed that immunization with CpG and peptide-treated DCs protected against tumor growth by activation of NK cell response. Also, immunogenic DCs induced the expansion of cytotoxic CD8⁺OT-1 cells, expressing activation markers CD44 and CD69 and producing IFNγ. In contrast, the peptide and GC-treated DCs in OT-1 mice increased the numbers of immature Mac-1⁺CD27^- NK cells as well as Foxp3⁺ and IL-10 secreting CD8⁺OT-1 cells with suppressive properties. We conclude that the generation of tolerogenic DCs is one of many immunosuppressive mechanisms that can be induced by GC. Our study demonstrated that tolerogenic DCs modify anti-tumor immune response by suppressing NK cell activity and stimulating the formation of IL-10-secreting CD8⁺ Tregs.

Single-molecule analysis of steroid receptor and cofactor action in living cells

Population-based assays have been employed extensively to investigate the interactions of transcription factors (TFs) with chromatin and are often interpreted in terms of static and sequential binding. However, fluorescence microscopy techniques reveal a more dynamic binding behaviour of TFs in live cells. Here we analyse the strengths and limitations of in vivo single-molecule tracking and performed a comprehensive analysis on the intranuclear dwell times of four steroid receptors and a number of known cofactors. While the absolute residence times estimates can depend on imaging acquisition parameters due to sampling bias, our results indicate that only a small proportion of factors are specifically bound to chromatin at any given time. Interestingly, the glucocorticoid receptor and its cofactors affect each other’s dwell times in an asymmetric manner. Overall, our data indicate transient rather than stable TF-cofactors chromatin interactions at response elements at the single-molecule level.

Transcription factors (TFs) are thought to regulate gene expression by stably binding to target DNA elements. Here, the authors use single-molecule tracking to analyse the dynamic behaviour of steroid receptors TFs and show that most specific interactions with chromatin are transient and dynamic.

Active Ingredients of Epimedii Folium and Ligustri Lucidi Fructus Balanced GR/HSP90 to Improve the Sensitivity of Asthmatic Rats to Budesonide

This study aimed to investigate the possible molecular mechanisms of active ingredients of Epimedii Folium (EF) and Ligustri Lucidi Fructus (LLF) combined with Budesonide (Bun) in asthmatic rats. Rats were divided into 5 groups, including normal group, asthma model group, Bun group, group of active ingredients of EL and LLF (EL), and group of coadministration of Bun with EL (Bun&EL). The asthmatic model was prepared by ovalbumin sensitizing and challenging. Lymphocyte apoptosis, GR protein and binding, and the protein and mRNA of GRα, GRβ, and HSP90 were tested. The results showed that Bun&EL ① markedly increased lymphocyte apoptosis, GR and HSP90 protein, and GR binding in BALF and ② enhanced the expressions of GRα and HSP90 and the ratio of GRα to GRβ or to HSP90 both in protein and in mRNA levels in lung, ③ while decrease occurred in GRβ mRNA and the mRNA ratio of GRβ to HSP90 compared with asthma or Bun group. Moreover, there was a significant correlation between GRα and GRβ in protein level, or between GRα and HSP90 both in protein and in mRNA levels. EL may effectively enhance the sensitivity of asthmatic rats to Bun via balancing GR/HSP90. And these findings will be beneficial for the treatment of asthma in the future.

Management of excessive inflammatory response in perioperative period of abdominal surgery

Perioperative excessive inflammation of abdominal surgery is caused by many perioperative factors, with activation of inflammatory cells, abnormal expression of cytokines and inflammatory mediators, and imbalance of proinflammatory and anti-inflammatory network system being the major factors. Since perioperative excessive inflammatory response can lead to a series of pathophysiological processes and even multiple organ dysfunction, it is an important factor to hinder the rehabilitation of patients after abdominal surgery. Therefore, management of excessive inflammatory response can control stress response, inhibit the excessive inflammatory reaction and its adverse reactions, reduce postoperative morbidity and mortality, and protect the function of major organs, thereby speeding up the recovery of patients. However, the understanding of the pathophysiological process and the management of excessive inflammatory response during the perioperative period are currently still in the infancy stage. This article systematically reviews the measures of managing the excessive inflammatory response during the perioperative period of abdominal surgery.

Glucocorticoid and cytokine crosstalk: Feedback, feedforward, and co-regulatory interactions determine repression or resistance

Inflammatory signals induce feedback and feedforward systems that provide temporal control. Although glucocorticoids can repress inflammatory gene expression, glucocorticoid receptor recruitment increases expression of negative feedback and feedforward regulators, including the phosphatase, DUSP1, the ubiquitin-modifying enzyme, TNFAIP3, or the mRNA-destabilizing protein, ZFP36. Moreover, glucocorticoid receptor cooperativity with factors, including nuclear factor-κB (NF-κB), may enhance regulator expression to promote repression. Conversely, MAPKs, which are inhibited by glucocorticoids, provide feedforward control to limit expression of the transcription factor IRF1, and the chemokine, CXCL10. We propose that modulation of feedback and feedforward control can determine repression or resistance of inflammatory gene expression toglucocorticoid.

Glucocorticoids curtail stimuli-induced CREB phosphorylation in TRH neurons through interaction of the glucocorticoid receptor with the catalytic subunit of protein kinase A

PURPOSE

Corticosterone prevents cold-induced stimulation of thyrotropin-releasing hormone (Trh) expression in rats, and the stimulatory effect of dibutyryl cyclic-adenosine monophosphate (dB-cAMP) on Trh transcription in hypothalamic cultures. We searched for the mechanism of this interference.

METHODS

Immunohistochemical analyses of phosphorylated cAMP-response element binding protein (pCREB) were performed in the paraventricular nucleus (PVN) of Wistar rats, and in cell cultures of 17-day old rat hypothalami, or neuroblastoma SH-SY5Y cells. Cultures were incubated 1h with dB-cAMP, dexamethasone and both drugs combined; their nuclear extracts were used for chromatin immunoprecipitation; cytosolic or nuclear extracts for coimmunoprecipitation analyses of catalytic subunit of protein kinase A (PKAc) and of glucocorticoid receptor (GR); their subcellular distribution was analyzed by immunocytochemistry.

RESULTS

Cold exposure increased pCREB in TRH neurons of rats PVN, effect blunted by corticosterone previous injection. Dexamethasone interfered with forskolin increase in nuclear pCREB and its binding to Trh promoter; antibodies against histone deacetylase-3 precipitated chromatin from nuclear extracts of hypothalamic cells treated with tri-iodothyronine but not with dB-cAMP + dexamethasone, discarding chromatin compaction as responsible mechanism. Co-immunoprecipitation analyses of cytosolic or nuclear extracts showed protein:protein interactions between activated GR and PKAc. Immunocytochemical analyses of hypothalamic or SH-SY5Y cells revealed diminished nuclear translocation of PKAc and GR in cells incubated with forskolin + dexamethasone, compared to either forskolin or dexamethasone alone.

CONCLUSIONS

Glucocorticoids and cAMP exert mutual inhibition of Trh transcription through interaction of activated glucocorticoid receptor with protein kinase A catalytic subunit, reducing their nuclear translocation, limiting cAMP-response element binding protein phosphorylation and its binding to Trh promoter.