Glucocorticoid receptor alpha, beta and gamma expression vs in vitro glucocorticod resistance in childhood leukemia

Genetic Profiling of Pediatric Patients with B-Cell Precursor Acute Lymphoblastic Leukemia

B-cell precursor acute lymphoblastic leukemia (BCP-ALL) is a heterogeneous leukemia subgroup. It has multiple sub-types that are likely to be classified by prognostic factors. Following a systematic literature review, this study analyzed the genes correlated with BCP-ALL prognosis ( IKZF1, PAX5, EBF1, CREBBP, CRLF2, JAK2, ERG, CXCR4, ZAP70, VLA4, NF1, NR3C1, RB1, TSLP, ZNRF1, and FOXO3A) , specifically their nucleotide variations and expression profiles in pediatric BCP-ALL samples. The study included 45 pediatric BCP-ALL patients with no cytogenetic anomaly and a control group of 10 children. The selected genes' hot-spot regions were sequenced using next-generation sequencing, while Polymorphism Phenotyping v2 and Supplemental Nutrition Assistance Program were used to identify pathogenic mutations. The expression analysis was performed using quantitative real-time polymerase chain reaction. The mutation analysis detected 328 variants (28 insertions, 47 indels, 74 nucleotide variants, 75 duplications, and 104 deletions). The most and least frequently mutated genes were IKZF1 and CREBBP , respectively. There were statistically significant differences between patients and controls for mutation distribution in eight genes ( ERG, CRLF2, CREBBP, TSLP, JAK2, ZAP70, FOXO3A, and NR3C1 ). The expression analysis revealed that JAK and ERG were significantly overexpressed in patients compared with controls (respectively, p  = 0.004 and p  = 0.003). This study combined genes and pathways previously analyzed in pediatric BCP-ALL into one dataset for a comprehensive analysis from the same samples to unravel candidate prognostic biomarkers. Novel mutations were identified in all of the studied genes.

Emerging Epigenetic and Posttranslational Mechanisms Controlling Resistance to Glucocorticoids in Acute Lymphoblastic Leukemia

Glucocorticoids are extensively used for the treatment of acute lymphoblastic leukemia as they pressure cancer cells to undergo apoptosis. Nevertheless, glucocorticoid partners, modifications, and mechanisms of action are hitherto poorly characterized. This hampers our understanding of therapy resistance, frequently occurring in leukemia despite the current therapeutic combinations using glucocorticoids in acute lymphoblastic leukemia. In this review, we initially cover the traditional view of glucocorticoid resistance and ways of targeting this resistance. We discuss recent progress in our understanding of chromatin and posttranslational properties of the glucocorticoid receptor that might be proven beneficial in our efforts to understand and target therapy resistance. We discuss emerging roles of pathways and proteins such as the lymphocyte-specific kinase that antagonizes glucocorticoid receptor activation and nuclear translocation. In addition, we provide an overview of ongoing therapeutic approaches that sensitize cells to glucocorticoids including small molecule inhibitors and proteolysis-targeting chimeras.

Dexamethasone-Induced Fatty Acid Oxidation and Autophagy/Mitophagy Are Essential for T-ALL Glucocorticoid Resistance

ALL is a highly aggressive subtype of leukemia that affects children and adults. Glucocorticoids (GCs) are a critical component of the chemotherapeutic strategy against T-ALL. Cases of resistance to GC therapy and recurrent disease require novel strategies to overcome them. The present study analyzed the effects of Dex, one of the main GCs used in ALL treatment, on two T-ALL cell lines: resistant Jurkat and unselected CCRF-CEM, representing a mixture of sensitive and resistant clones. In addition to nuclear targeting, we observed a massive accumulation of Dex in mitochondria. Dex-treated leukemic cells suffered metabolic reprogramming from glycolysis and glutaminolysis towards lipolysis and increased FAO, along with increased membrane polarization and ROS production. Dex provoked mitochondrial fragmentation and induced autophagy/mitophagy. Mitophagy preceded cell death in susceptible populations of CCRF-CEM cells while serving as a pro-survival mechanism in resistant Jurkat. Accordingly, preventing FAO or autophagy greatly increased the Dex cytotoxicity and overcame GC resistance. Dex acted synergistically with mitochondria-targeted drugs, curcumin, and cannabidiol. Collectively, our data suggest that GCs treatment should not be neglected even in apparently GC-resistant clinical cases. Co-administration of drugs targeting mitochondria, FAO, or autophagy can help to overcome GC resistance.

Glucocorticoid receptor gene mutations confer glucocorticoid resistance in B-cell precursor acute lymphoblastic leukemia

Glucocorticoid (GC) is a key drug in the treatment of B-cell precursor acute lymphoblastic leukemia (BCP-ALL), and the initial GC response is an important prognostic factor. GC receptors play an essential role in GC sensitivity, and somatic mutations of the GC receptor gene, NR3C1, are reportedly identified in some BCP-ALL cases, particularly at relapse. Moreover, associations of somatic mutations of the CREB-binding protein (CREBBP) and Wolf-Hirschhorn syndrome candidate 1 (WHSC1) genes with the GC-resistance of ALL have been suggested. However, the significance of these mutations in the GC sensitivity of BCP-ALL remains to be clarified in the intrinsic genes. In the present study, we sequenced NR3C1, WHSC1, and CREBBP genes in 99 BCP-ALL and 22 T-ALL cell lines (32 and 67 cell lines were known to be established at diagnosis and at relapse, respectively), and detected their mutations in 19 (2 cell lines at diagnosis and 15 cell lines at relapse), 26 (6 and 15), and 38 (11 and 15) cell lines, respectively. Of note, 14 BCP-ALL cell lines with the NR3C1 mutations were significantly more resistant to GC than those without mutations. In contrast, WHSC1 and CREBBP mutations were not associated with GC resistance. However, among the NR3C1 unmutated BCP-ALL cell lines, WHSC1 mutations tended to be associated with GC resistance and lower NR3C1 gene expression. Finally, we successfully established GC-resistant sublines of the GC-sensitive BCP-ALL cell line (697) by disrupting ligand binding and DNA binding domains of the NR3C1 gene using the CRISPR/Cas9 system. These observations demonstrated that somatic mutations of the NR3C1 gene, and possibly the WHSC1 gene, confer GC resistance in BCP-ALL.

Prednisone stimulates white adipocyte browning via β3-AR/p38 MAPK/ERK signaling pathway

AIMS

Prednisone is a corticosteroid-derived drug which is widely used for its role in immunosuppression and treatment of lung disorders. The current study reports, for the first time, the critical role of prednisone in the induction of white fat browning, thereby promoting thermogenic effect in cultured white adipocytes.

MAIN METHODS

The fat-browning activity of prednisone was evaluated in 3T3-L1 cells by quantitative real-time PCR, immunoblot analysis, immunofluorescence, and molecular docking techniques.

KEY FINDINGS

Exposure to prednisone stimulated browning in 3T3-L1 white adipocytes by increasing the expressions of core fat browning marker proteins (UCP1, PGC-1α and PRDM16) as well as beige-specific genes (Cd137, Cidea, Cited1, and Tbx1) via ATF2 and CREB activation mediated by p38 MAPK and ERK signaling, respectively. Prednisone exposure also resulted in the robust activation of lipolytic and fatty acid oxidation marker proteins, thereby increasing mitochondrial biogenesis. In addition, prednisone treatment resulted in reduced expression levels of adipogenic transcription factors while elevating SIRT1, as well as attenuation of lipogenesis and lipid droplets formation. Furthermore, molecular docking and mechanistic studies demonstrated the recruitment of beige fat by prednisone via the β3-AR/p38 MAPK/ERK signaling pathway.

SIGNIFICANCE

Taken together, these results indicate the unique role of prednisone as a fat-browning stimulant, and demonstrate its therapeutic potential in the treatment of obesity by enhancing thermogenesis.

GRβ Regulates Glucocorticoid Resistance in Sudden Sensorineural Hearing Loss

BACKGROUND

In recent years, the incidence of sudden deafness has gradually increased, with a very limited understanding of its etiology and pathogenesis. Glucocorticoids are the first choice of the treatment, but some hormone-resistant patients are not sensitive to glucocorticoid therapy. The pathogenesis is not yet known. In this study, we aim to construct the HEI-OC1 cell line stably overexpressing Glucocorticoid Receptor Beta (GRβ), and identify its exact role in the cases of glucocorticoidresistant sudden deafness.

METHODS

We used the endotoxin lipopolysaccharide-stimulated cochlear hair cells (HEI-OC1) to investigate the relationship of inflammation factor IL-2, TNF alpha, and SRp30c with the high expression GRβ. We built a stable GRβ high expression HEI-OC1 cell line and clarified its effects on the therapeutic effect of dexamethasone. MTT assay, colony formation assay, CCK-8 assay, Western blot, and RT-qPCR were utilized for characterizations.

RESULTS

Dexamethasone reduced the LPS-induced inflammatory response from HEI-OC1 cells (p<0.05), detected by MTT assay. Dexamethasone could protect HEI-OC1 cells, but its protective effect was weakened due to the transfection of SRp30c over-expression plasmid (p<0.05). The transfection of SRp30c over-expression plasmid in HEI-OC1 cells could elevate the expressions of GRβ (p<0.05).

CONCLUSION

We clarified the mechanisms of high expression of GRβ in glucocorticoid-resistant sudden sensorineural hearing loss, and proved that the inhibition of SRp30c may act as a new treatment way of glucocorticoid-resistant sudden sensorineural hearing loss.

Generalized and tissue specific glucocorticoid resistance

Glucocorticoids (GCs) are steroid hormones that influence several physiologic functions and are among the most frequently prescribed drugs worldwide. Resistance to GCs has been observed in the context of the familial generalized GC resistance (Chrousos' syndrome) or tissue specific GC resistance in chronic inflammatory states. In this review, we have summarized the major factors that influence individual glucocorticoid sensitivity/resistance. The fine-tuning of GC action is determined in a tissue-specific fashion that includes the combination of different GC receptor promoters, translation initiation sites, splice isoforms, interacting proteins, post-translational modifications, and alternative mechanisms of signal transduction.

Overcoming Glucocorticoid Resistance in Acute Lymphoblastic Leukemia: Repurposed Drugs Can Improve the Protocol

Glucocorticoids (GCs) are a central component of multi-drug treatment protocols against T and B acute lymphoblastic leukemia (ALL), which are used intensively during the remission induction to rapidly eliminate the leukemic blasts. The primary response to GCs predicts the overall response to treatment and clinical outcome. In this review, we have critically analyzed the available data on the effects of GCs on sensitive and resistant leukemic cells, in order to reveal the mechanisms of GC resistance and how these mechanisms may determine a poor outcome in ALL. Apart of the GC resistance, associated with a decreased expression of receptors to GCs, there are several additional mechanisms, triggered by alterations of different signaling pathways, which cause the metabolic reprogramming, with an enhanced level of glycolysis and oxidative phosphorylation, apoptosis resistance, and multidrug resistance. Due to all this, the GC-resistant ALL show a poor sensitivity to conventional chemotherapeutic protocols. We propose pharmacological strategies that can trigger alternative intracellular pathways to revert or overcome GC resistance. Specifically, we focused our search on drugs, which are already approved for treatment of other diseases and demonstrated anti-ALL effects in experimental pre-clinical models. Among them are some “truly” re-purposed drugs, which have different targets in ALL as compared to other diseases: cannabidiol, which targets mitochondria and causes the mitochondrial permeability transition-driven necrosis, tamoxifen, which induces autophagy and cell death, and reverts GC resistance through the mechanisms independent of nuclear estrogen receptors (“off-target effects”), antibiotic tigecycline, which inhibits mitochondrial respiration, causing energy crisis and cell death, and some anthelmintic drugs. Additionally, we have listed compounds that show a classical mechanism of action in ALL but are not used still in treatment protocols: the BH3 mimetic venetoclax, which inhibits the anti-apoptotic protein Bcl-2, the hypomethylating agent 5-azacytidine, which restores the expression of the pro-apoptotic BIM, and compounds targeting the PI3K-Akt-mTOR axis. Accordingly, these drugs may be considered for the inclusion into chemotherapeutic protocols for GC-resistant ALL treatments.

Latest perspectives on glucocorticoid-induced apoptosis and resistance in lymphoid malignancies

Glucocorticoids are essential drugs in the treatment protocols of lymphoid malignancies. These steroidal hormones trigger apoptosis of the malignant cells by binding to the glucocorticoid receptor (GR), which is a member of the nuclear receptor superfamily. Long term glucocorticoid treatment is limited by two major problems: the development of glucocorticoid-related side effects, which hampers patient quality of life, and the emergence of glucocorticoid resistance, which is a gradual process that is inevitable in many patients. This emphasizes the need to reevaluate and optimize the widespread use of glucocorticoids in lymphoid malignancies. To achieve this goal, a deep understanding of the mechanisms governing glucocorticoid responsiveness is required, yet, a recent comprehensive overview is currently lacking. In this review, we examine how glucocorticoids mediate apoptosis by detailing GR's genomic and non-genomic action mechanisms in lymphoid malignancies. We continue with a discussion of the glucocorticoid-related problems and how these are intertwined with one another. We further zoom in on glucocorticoid resistance by critically analyzing the plethora of proposed mechanisms and highlighting therapeutic opportunities that emerge from these studies. In conclusion, early detection of glucocorticoid resistance in patients remains an important challenge as this would result in a timelier treatment reorientation and reduced glucocorticoid-instigated side effects.

Loss of glucocorticoid receptor expression mediates in vivo dexamethasone resistance in T-cell acute lymphoblastic leukemia

Despite decades of clinical use, mechanisms of glucocorticoid resistance are poorly understood. We treated primary murine T lineage acute lymphoblastic leukemias (T-ALLs) with the glucocorticoid dexamethasone (DEX) alone and in combination with the pan-PI3 kinase inhibitor GDC-0941 and observed a robust response to DEX that was modestly enhanced by GDC-0941. Continuous in vivo treatment invariably resulted in outgrowth of drug-resistant clones, ~30% of which showed markedly reduced glucocorticoid receptor (GR) protein expression. A similar proportion of relapsed human T-ALLs also exhibited low GR protein levels. De novo or preexisting mutations in the gene encoding GR (Nr3c1) occurred in relapsed clones derived from multiple independent parental leukemias. CRISPR/Cas9 gene editing confirmed that loss of GR expression confers DEX resistance. Exposing drug-sensitive T-ALLs to DEX in vivo altered transcript levels of multiple genes, and this response was attenuated in relapsed T-ALLs. These data implicate reduced GR protein expression as a frequent cause of glucocorticoid resistance in T-ALL.

The shift in the balance between osteoblastogenesis and adipogenesis of mesenchymal stem cells mediated by glucocorticoid receptor

Mesenchymal stem cells (MSCs) are multipotent cells capable of differentiating into several tissues, such as bone, cartilage, and fat. Glucocorticoids affect a variety of biological processes such as proliferation, differentiation, and apoptosis of various cell types, including osteoblasts, adipocytes, or chondrocytes. Glucocorticoids exert their function by binding to the glucocorticoid receptor (GR). Physiological concentrations of glucocorticoids stimulate osteoblast proliferation and promote osteogenic differentiation of MSCs. However, pharmacological concentrations of glucocorticoids can not only induce apoptosis of osteoblasts and osteocytes but can also reduce proliferation and inhibit the differentiation of osteoprogenitor cells. Several signaling pathways, including the Wnt, TGFβ/BMP superfamily and Notch signaling pathways, transcription factors, post-transcriptional regulators, and other regulators, regulate osteoblastogenesis and adipogenesis of MSCs mediated by GR. These signaling pathways target key transcription factors, such as Runx2 and TAZ for osteogenesis and PPARγ and C/EBPs for adipogenesis. Glucocorticoid-induced osteonecrosis and osteoporosis are caused by various factors including dysfunction of bone marrow MSCs. Transplantation of MSCs is valuable in regenerative medicine for the treatment of osteonecrosis of the femoral head, osteoporosis, osteogenesis imperfecta, and other skeletal disorders. However, the mechanism of inducing MSCs to differentiate toward the osteogenic lineage is the key to an efficient treatment. Thus, a better understanding of the molecular mechanisms behind the imbalance between GR-mediated osteoblastogenesis and adipogenesis of MSCs would not only help us to identify the pathogenic causes of glucocorticoid-induced osteonecrosis and osteoporosis but also promote future clinical applications for stem cell-based tissue engineering and regenerative medicine. Here, we primarily review the signaling mechanisms involved in adipogenesis and osteogenesis mediated by GR and discuss the factors that control the adipo-osteogenic balance.

Mechanisms of glucocorticoid resistance in hypereosinophilic syndromes

BACKGROUND

Glucocorticoids (GC) are considered first-line therapy for most patients with hypereosinophilic syndrome (HES). Although response rates are generally high, many patients require moderate to high doses for control of eosinophilia and symptoms, and up to 15% of patients do not respond at all. Despite this, little is known about the mechanisms of GC resistance in patients with HES.

OBJECTIVE

To explore the aetiology of GC resistance in HES.

METHODS

Clinical data and samples from 26 patients with HES enrolled on a prospective study of GC responsiveness and 23 patients with HES enrolled on a natural history study of eosinophilia for whom response to GC was known were analysed retrospectively. Expression of GC receptor isoforms was assessed by quantitative RT-PCR in purified eosinophils. Serum cytokine levels were quantified by suspension array assay in multiplex.

RESULTS

Despite an impaired eosinophil response to GC after 7 days of treatment, the expected rise in absolute neutrophil count was seen in 7/7 GC-resistant patients, suggesting that GC resistance in HES is not a global phenomenon. Eosinophil mRNA expression of glucocorticoid receptor (GR) isoforms (α, β, and P) was similar between GC-sensitive (n = 20) and GC-resistant (n = 9) patients with HES. Whereas geometric mean serum levels were also comparable between GC-r (n = 11) and GC-s (n = 19) for all cytokines tested, serum IL-5 levels were >100 pg/mL only in GC-r patients.

CONCLUSIONS AND CLINICAL RELEVANCE

These data suggest that the mechanism of GC resistance in HES is not due to a global phenomenon affecting all lineages, but may be due, at least in some patients, to impairment of eosinophil apoptosis by increased levels of IL-5.

Glucocorticoids Shape Macrophage Phenotype for Tissue Repair

Inflammation is a complex process which is highly conserved among species. Inflammation occurs in response to injury, infection, and cancer, as an allostatic mechanism to return the tissue and to return the organism back to health and homeostasis. Excessive, or chronic inflammation is associated with numerous diseases, and thus strategies to combat run-away inflammation is required. Anti-inflammatory drugs were therefore developed to switch inflammation off. However, the inflammatory response may be beneficial for the organism, in particular in the case of sterile tissue injury. The inflammatory response can be divided into several parts. The first step is the mounting of the inflammatory reaction itself, characterized by the presence of pro-inflammatory cytokines, and the infiltration of immune cells into the injured area. The second step is the resolution phase, where immune cells move toward an anti-inflammatory phenotype and decrease the secretion of pro-inflammatory cytokines. The last stage of inflammation is the regeneration process, where the tissue is rebuilt. Innate immune cells are major actors in the inflammatory response, of which, macrophages play an important role. Macrophages are highly sensitive to a large number of environmental stimuli, and can adapt their phenotype and function on demand. This change in phenotype in response to the environment allow macrophages to be involved in all steps of inflammation, from the first mounting of the pro-inflammatory response to the post-damage tissue repair.

Splicing variant profiles and single nucleotide polymorphisms of the glucocorticoid receptor gene in relation to glucocorticoid sensitivity of B-cell precursor acute lymphoblastic leukaemia

Glucocorticoid (GC) shows antileukaemic activity via binding to the GC receptor (GR). The human GR gene has 4 splicing variants besides the functional isoform GRα, but their significance in GC sensitivity of acute lymphoblastic leukaemia (ALL) has been inconsistent. Additionally, several studies evaluated the relevance of GR gene single nucleotide polymorphisms (SNPs) in the GC sensitivity of ALL, but the current cumulative evidence appears inconclusive. Addressing limitations in previous studies, we used a large series of B-cell precursor ALL (BCP-ALL) cell lines established from Japanese patients to comprehensively examine all 5 splicing variants of the GR gene and candidate SNPs, and their association with GC-sensitivity. We performed real-time reverse transcription polymerase chain reaction (RT-PCR) analyses with 10 sets of primers that differentially quantify the 5 isoforms in different combinations, and the strongest correlations with GC sensitivity were observed for the real-time RT-PCR of exons 7 and 8 (prednisolone sensitivity; r = -0.534, R²  = 0.29, P = 1.4 × 10^-6 ) and exons 8 and 9a (r = -0.583, R²  = 0.34, P = 7.6 × 10^-8 ), both specific for GRα and GRγ isoforms. In contrast, the real-time RT-PCR of junction of exons 3g and 4 and exon 4, specific for GRγ isoform alone, did not show significant correlation with GC sensitivity (prednisolone sensitivity; r = -0.403, R²  = 0.16, P = 4.6 × 10^-4 ). These observations are consistent with the notion that GRα plays a central role in the GC-mediated proapoptotic activity in BCP-ALL. In addition, a promoter region SNP genotype (rs72555796) showed a significant association with GC sensitivity (prednisolone sensitivity; P = .010) and tended to show an association with GR gene expression (RT-PCR of exons 7 and 8; P = .170). These findings indicate that isoform profiles and SNP genotypes of the GR gene may be useful indicators of GC sensitivity in BCP-ALL.

Glucocorticoid receptor expression on circulating leukocytes differs between healthy male and female adults

Introduction

The glucocorticoid receptor (GR) is a key receptor involved in inflammatory responses and is influenced by sex steroids. This study measured GR expression on circulating leukocyte subtypes in males and females.

Methods

A total of 23 healthy adults (12 female) participated in this study. GR expression was measured in leukocyte subtypes using flow cytometry. Peripheral blood mononuclear cell (PBMC) gene expression of GR (NR3C1), GR β, TGF-β1 and 2, and glucocorticoid-induced leucine zipper (GILZ) were determined by real-time polymerase chain reaction.

Results

Leukocyte GR was lower in females, particularly in granulocytes, natural killer cells, and peripheral blood mononuclear cells (p≤0.01). GR protein expression was different across leukocyte subtypes, with higher expression in eosinophils compared with granulocytes, T lymphocytes, and natural killer cells (p<0.05). There was higher gene expression of GR β in males (p=0.03).

Conclusions

This is the first study to identify sexual dimorphism in GR expression in healthy adults using flow cytometry. These results may begin to explain the sexual dimorphism seen in many diseases and sex differences in glucocorticoid responsiveness.

Genetic variation in the glucocorticoid pathway involved in interindividual differences in the glucocorticoid treatment

Glucocorticoids (GCs) are widely used for treating asthma, rheumatoid arthritis, nephrotic syndrome, acute lymphoblastic leukemia and other autoimmune diseases. However, in a subgroup of patients, failure to respond to GCs is known as GC resistance or GC insensitivity. This represents an important barrier to effective treatment and a clinical problem requiring an urgent solution. Genetic variation in the GC pathway is a significant factor in interindividual differences in GC treatment. This article reviews the pharmacogenetics of GCs in diverse diseases based on the GC pathway.

Endothelial Response to Glucocorticoids in Inflammatory Diseases

The endothelium plays a crucial role in inflammation. A balanced control of inflammation requires the action of glucocorticoids (GCs), steroidal hormones with potent cell-specific anti-inflammatory properties. Besides the classic anti-inflammatory effects of GCs on leukocytes, recent studies confirm that endothelial cells also represent an important target for GCs. GCs regulate different aspects of endothelial physiology including expression of adhesion molecules, production of pro-inflammatory cytokines and chemokines, and maintenance of endothelial barrier integrity. However, the regulation of endothelial GC sensitivity remains incompletely understood. In this review, we specifically examine the endothelial response to GCs in various inflammatory diseases ranging from multiple sclerosis, stroke, sepsis, and vasculitis to atherosclerosis. Shedding more light on the cross talk between GCs and endothelium will help to improve existing therapeutic strategies and develop new therapies better tailored to the needs of patients.

IL-7 Receptor Mutations and Steroid Resistance in Pediatric T cell Acute Lymphoblastic Leukemia: A Genome Sequencing Study

BACKGROUND

Pediatric acute lymphoblastic leukemia (ALL) is the most common childhood cancer and the leading cause of cancer-related mortality in children. T cell ALL (T-ALL) represents about 15% of pediatric ALL cases and is considered a high-risk disease. T-ALL is often associated with resistance to treatment, including steroids, which are currently the cornerstone for treating ALL; moreover, initial steroid response strongly predicts survival and cure. However, the cellular mechanisms underlying steroid resistance in T-ALL patients are poorly understood. In this study, we combined various genomic datasets in order to identify candidate genetic mechanisms underlying steroid resistance in children undergoing T-ALL treatment.

METHODS AND FINDINGS

We performed whole genome sequencing on paired pre-treatment (diagnostic) and post-treatment (remission) samples from 13 patients, and targeted exome sequencing of pre-treatment samples from 69 additional T-ALL patients. We then integrated mutation data with copy number data for 151 mutated genes, and this integrated dataset was tested for associations of mutations with clinical outcomes and in vitro drug response. Our analysis revealed that mutations in JAK1 and KRAS, two genes encoding components of the interleukin 7 receptor (IL7R) signaling pathway, were associated with steroid resistance and poor outcome. We then sequenced JAK1, KRAS, and other genes in this pathway, including IL7R, JAK3, NF1, NRAS, and AKT, in these 69 T-ALL patients and a further 77 T-ALL patients. We identified mutations in 32% (47/146) of patients, the majority of whom had a specific T-ALL subtype (early thymic progenitor ALL or TLX). Based on the outcomes of these patients and their prednisolone responsiveness measured in vitro, we then confirmed that these mutations were associated with both steroid resistance and poor outcome. To explore how these mutations in IL7R signaling pathway genes cause steroid resistance and subsequent poor outcome, we expressed wild-type and mutant IL7R signaling molecules in two steroid-sensitive T-ALL cell lines (SUPT1 and P12 Ichikawa cells) using inducible lentiviral expression constructs. We found that expressing mutant IL7R, JAK1, or NRAS, or wild-type NRAS or AKT, specifically induced steroid resistance without affecting sensitivity to vincristine or L-asparaginase. In contrast, wild-type IL7R, JAK1, and JAK3, as well as mutant JAK3 and mutant AKT, had no effect. We then performed a functional study to examine the mechanisms underlying steroid resistance and found that, rather than changing the steroid receptor's ability to activate downstream targets, steroid resistance was associated with strong activation of MEK-ERK and AKT, downstream components of the IL7R signaling pathway, thereby inducing a robust antiapoptotic response by upregulating MCL1 and BCLXL expression. Both the MEK-ERK and AKT pathways also inactivate BIM, an essential molecule for steroid-induced cell death, and inhibit GSK3B, an important regulator of proapoptotic BIM. Importantly, treating our cell lines with IL7R signaling inhibitors restored steroid sensitivity. To address clinical relevance, we treated primary T-ALL cells obtained from 11 patients with steroids either alone or in combination with IL7R signaling inhibitors; we found that including a MEK, AKT, mTOR, or dual PI3K/mTOR inhibitor strongly increased steroid-induced cell death. Therefore, combining these inhibitors with steroid treatment may enhance steroid sensitivity in patients with ALL. The main limitation of our study was the modest cohort size, owing to the very low incidence of T-ALL.

CONCLUSIONS

Using an unbiased sequencing approach, we found that specific mutations in IL7R signaling molecules underlie steroid resistance in T-ALL. Future prospective clinical studies should test the ability of inhibitors of MEK, AKT, mTOR, or PI3K/mTOR to restore or enhance steroid sensitivity and improve clinical outcome.

Glucocorticoid receptor isoforms direct distinct mitochondrial programs to regulate ATP production

The glucocorticoid receptor (GR), a nuclear receptor and major drug target, has a highly conserved minor splice variant, GRγ, which differs by a single arginine within the DNA binding domain. GRγ, which comprises 10% of all GR transcripts, is constitutively expressed and tightly conserved through mammalian evolution, suggesting an important non-redundant role. However, to date no specific role for GRγ has been reported. We discovered significant differences in subcellular localisation, and nuclear-cytoplasmic shuttling in response to ligand. In addition the GRγ transcriptome and protein interactome was distinct, and with a gene ontology signal for mitochondrial regulation which was confirmed using Seahorse technology. We propose that evolutionary conservation of the single additional arginine in GRγ is driven by a distinct, non-redundant functional profile, including regulation of mitochondrial function.

Glucocorticoid-induced changes in glucocorticoid receptor mRNA and protein expression in the human placenta as a potential factor for altering fetal growth and development

Glucocorticoids (GCs) control essential metabolic processes in virtually every cell in the body and play a vital role in the development of fetal tissues and organ systems. The biological actions of GCs are mediated via glucocorticoid receptors (GRs), the cytoplasmic transcription factors that regulate the transcription of genes involved in placental and fetal growth and development. Several experimental studies have demonstrated that fetal exposure to high maternal GC levels early in gestation is associated with adverse fetal outcomes, including low birthweight, intrauterine growth restriction and anatomical and structural abnormalities that may increase the risk of cardiovascular, metabolic and neuroendocrine disorders in adulthood. The response of the fetus to GCs is dependent on gender, with female fetuses becoming hypersensitive to changes in GC levels whereas male fetuses develop GC resistance in the environment of high maternal GCs. In this paper we review GR function and the physiological and pathological effects of GCs on fetal development. We propose that GC-induced changes in the placental structure and function, including alterations in the expression of GR mRNA and protein levels, may play role in inhibiting in utero fetal growth.

Identification of Eight Different Isoforms of the Glucocorticoid Receptor in Guinea Pig Placenta: Relationship to Preterm Delivery, Sex and Betamethasone Exposure

The placental glucocorticoid receptor (GR) is central to glucocorticoid signalling and for mediating steroid effects on pathways associated with fetal growth and lung maturation but the GR has not been examined in the guinea pig placenta even though this animal is regularly used as a model of preterm birth and excess glucocorticoid exposure. Guinea pig dams received subcutaneous injections of either vehicle or betamethasone at 24 and 12 hours prior to preterm or term caesarean-section delivery. At delivery pup and organ weights were recorded. Placentae were dissected, weighed and analysed using Western blot to examine GR isoform expression in nuclear and cytoplasmic extracts. A comparative examination of the guinea pig GR gene identified it is capable of producing seven of the eight translational GR isoforms which include GRα-A, C1, C2, C3, D1, D2, and D3. GRα-B is not produced in the Guinea Pig. Total GR antibody identified 10 specific bands from term (n = 29) and preterm pregnancies (n = 27). Known isoforms included GRγ, GRα A, GRβ, GRP, GRA and GRα D1-3. There were sex and gestational age differences in placental GR isoform expression. Placental GRα A was detected in the cytoplasm of all groups but was significantly increased in the cytoplasm and nucleus of preterm males and females exposed to betamethasone and untreated term males (KW-ANOVA, P = 0.0001, P = 0.001). Cytoplasmic expression of GRβ was increased in female preterm placentae and preterm and term male placentae exposed to betamethasone (P = 0.01). Nuclear expression of GRβ was increased in all placentae exposed to betamethasone (P = 0.0001). GRα D2 and GRα D3 were increased in male preterm placentae when exposed to betamethasone (P = 0.01, P = 0.02). The current data suggests the sex-specific placental response to maternal betamethasone may be dependent on the expression of a combination of GR isoforms.

The prognostic value of glucocorticoid receptors for adult acute lymphoblastic leukemia

BACKGROUND

Therapeutic protocols used in adult acute lymphoblastic leukemia (ALL) are widely variable, and glucocorticoids (GCs) are essential components in ALL treatment. Therefore, this study aimed to evaluate the distribution of prominent glucocorticoid receptor (GR) gene polymorphic variants among adult ALL patients. We also investigated the association between GR messenger ribonucleic acid (mRNA) isoform expressions and the response to chemotherapy.

METHODS

Fifty-two newly diagnosed Philadelphia-negative adult ALL patients and 30 healthy control subjects were enrolled in this study. Genotyping was carried out using a polymerase chain reaction (PCR)-restriction fragment length polymorphism analysis. GR mRNA isoform expressions were assayed by quantitative real-time PCR.

RESULTS

ALL patients in this study had a median age of 34 years (range, 18-75). GRα expression was associated with complete remission (P=0.03), while GRγ mRNA expression was significantly higher in GC resistant patients (P=0.032) and in non-responders (P=0.019). However, there were no significant associations with GC resistance. The BclI polymorphic variant of the GR gene was the most frequent in adult ALL patients and was not associated with the GC response. Both higher GRα expression and lower GRγ expression were associated with achievement of complete remission, while higher GRγ expression was associated with GC-resistance.

CONCLUSION

Our data suggest that the level of GR isoform expression may be useful in predicting GC response, achievement of complete remission, and better event-free survival in ALL patients. However, further evaluation with a larger cohort of patients is warranted.

Genetic alterations in glucocorticoid signaling pathway components are associated with adverse prognosis in children with relapsed ETV6/RUNX1-positive acute lymphoblastic leukemia

The ETV6/RUNX1 gene fusion defines the largest genetic subgroup of childhood ALL with overall rapid treatment response. However, up to 15% of cases relapse. Because an impaired glucocorticoid pathway is implicated in disease recurrence we studied the impact of genetic alterations by SNP array analysis in 31 relapsed cases. In 58% of samples, we found deletions in various glucocorticoid signaling pathway-associated genes, but only NR3C1 and ETV6 deletions prevailed in minimal residual disease poor responding and subsequently relapsing cases (p<0.05). To prove the necessity of a functional glucocorticoid receptor, we reconstituted wild-type NR3C1 expression in mutant, glucocorticoid-resistant REH cells and studied the glucocorticoid response in vitro and in a xenograft mouse model. While these results prove that glucocorticoid receptor defects are crucial for glucocorticoid resistance in an experimental setting, they do not address the essential clinical situation where glucocorticoid resistance at relapse is rather part of a global drug resistance.

Glucocorticoid receptor function in health and disease

Glucocorticoid hormones are essential for life in vertebrates. They act through the glucocorticoid receptor (GR), which is expressed in virtually all cells of the human body. Yet the actions of glucocorticoids (GCs) are specific to particular cell types. Broadly GCs regulate carbohydrate metabolism, inflammation, stress and cell fate. Synthetic GCs are widely used in medicine and are by far the most frequent cause of Cushing's syndrome in routine practice. The advent of novel drugs targeting the GR offers new opportunities to treat patients with immune, or malignant disease, and may also offer new opportunities to manage patients with adrenal insufficiency also. This review covers the latest understanding of how GCs work, how their actions are affected by disease, and where the new drugs may take us.

Expression of eight glucocorticoid receptor isoforms in the human preterm placenta vary with fetal sex and birthweight

INTRODUCTION

Administration of betamethasone to women at risk of preterm delivery is known to be associated with reduced fetal growth via alterations in placental function and possibly direct effects on the fetus. The placental glucocorticoid receptor (GR) is central to this response and recent evidence suggests there are numerous isoforms for GR in term placentae. In this study we have questioned whether GR isoform expression varies in preterm placentae in relation to betamethasone exposure, fetal sex and birthweight.

METHODS

Preterm (24-36 completed weeks of gestation, n = 55) and term placentae (>37 completed weeks of gestation, n = 56) were collected at delivery. Placental GR expression was examined using Western Blot and analysed in relation to gestational age at delivery, fetal sex, birthweight and betamethasone exposure. Data was analysed using non-parametric tests.

RESULTS

Eight known isoforms of the GR were detected in the preterm placenta and include GRα (94 kDa), GRβ (91 kDa), GRα C (81 kDa) GR P (74 kDa) GR A (65 kDa), GRα D1-3 (50-55 kDa). Expression varied between preterm and term placentae with a greater expression of GRα C in preterm placentae relative to term placentae. The only sex differences in preterm placentae was that GRα D2 expression was higher in males than females. There were no alterations in preterm placental GR expression in association with betamethasone exposure.

DISCUSSION

GRα C is the isoform involved in glucocorticoid induced apoptosis and suggests that its predominance in preterm placentae may contribute to the pathophysiology of preterm birth.

Mechanisms of Glucocorticoid-Regulated Gene Transcription

One fascinating aspect of glucocorticoid signaling is their broad range of physiological and pharmacological effects. These effects are at least in part a consequence of transcriptional regulation by the glucocorticoid receptor (GR). Activation of GR by glucocorticoids results in tissue-specific changes in gene expression levels with some genes being activated whereas others are repressed. This raises two questions: First, how does GR regulate different subsets of target genes in different tissues? And second, how can GR both activate and repress the expression of genes?To answer these questions, this chapter will describe the function of the various "components" and how they cooperate to mediate the transcriptional responses to glucocorticoids. The first "component" is GR itself. The second "component" is the chromatin and its role in specifying where in the genome GR binds. Binding to the genome however is just the first step in regulating the expression of genes and transcriptional regulation by GR depends on the recruitment of coregulator proteins that either directly or indirectly influence the recruitment and or activity of RNA polymerase II. Ultimately, the integration of inputs including GR isoform, DNA sequence, chromatin and cooperation with coregulators determines which genes are regulated and the direction of their regulation.

Mechanisms of glucocorticoid action and insensitivity in airways disease

Glucocorticoids are the mainstay for the treatment of chronic inflammatory diseases including asthma and chronic obstructive pulmonary disease (COPD). However, it has been recognized that glucocorticoids do not work well in certain patient populations suggesting reduced sensitivity. The ultimate biologic responses to glucocorticoids are determined by not only the concentration of glucocorticoids but also the differences between individuals in glucocorticoid sensitivity, which is influenced by multiple factors. Studies are emerging to understand these mechanisms in detail, which would help in increasing glucocorticoid sensitivity in patients with chronic airways disease. This review aims to highlight both classical and emerging concepts of the anti-inflammatory mechanisms of glucocorticoids and also review some novel strategies to overcome steroid insensitivity in airways disease.

High-throughput screening of human leukemia xenografts to identify dexamethasone sensitizers

Acute lymphoblastic leukemia (ALL) is the most common pediatric malignancy. Glucocorticoids (e.g., dexamethasone) form a critical component of chemotherapy regimens for pediatric ALL, and the initial response to glucocorticoid therapy is a major prognostic factor, where resistance is predictive of poor outcome. We have previously established a clinically relevant ALL xenograft model, consisting of primary pediatric ALL biopsies engrafted into immune-deficient mice, in which in vitro and in vivo dexamethasone sensitivity significantly correlated with patient outcome. In this study, we used high-throughput screening (HTS) to identify novel compounds that reverse dexamethasone resistance in a xenograft (ALL-19) derived from a chemoresistant pediatric ALL patient that is representative of the most common pediatric ALL subtype (B-cell precursor [BCP-ALL]). The compound 2-(4-chlorophenoxy)-2-methyl-N-(2-(piperidin-1-yl)phenyl)propanamide showed little cytotoxic activity alone (IC50 = 31 µM), but when combined with dexamethasone, it caused a marked decrease in cell viability. Fixed-ratio combination assays were performed against a broad panel of dexamethasone-resistant and -sensitive xenografts representative of BCP-ALL, T-cell ALL, and Mixed Lineage Leukemia-rearranged ALL, and synergy was observed in six of seven xenografts. We describe here the development of a novel 384-well cell-based high-throughput screening assay for identifying potential dexamethasone sensitizers using a clinically relevant ALL xenograft model.

Glucocorticoid sensitivity in health and disease

Glucocorticoids regulate many physiological processes and have an essential role in the systemic response to stress. For example, gene transcription is modulated by the glucocorticoid-glucocorticoid receptor complex via several mechanisms. The ultimate biologic responses to glucocorticoids are determined by not only the concentration of glucocorticoids but also the differences between individuals in glucocorticoid sensitivity, which is influenced by multiple factors. Differences in sensitivity to glucocorticoids in healthy individuals are partly genetically determined by functional polymorphisms of the gene that encodes the glucocorticoid receptor. Hereditary syndromes have also been identified that are associated with increased and decreased sensitivity to glucocorticoids. As a result of their anti-inflammatory properties, glucocorticoids are widely used in the treatment of allergic, inflammatory and haematological disorders. The variety in clinical responses to treatment with glucocorticoids reflects the considerable variation in glucocorticoid sensitivity between individuals. In immune-mediated disorders, proinflammatory cytokines can induce localized resistance to glucocorticoids via several mechanisms. Individual differences in how tissues respond to glucocorticoids might also be involved in the predisposition for and pathogenesis of the metabolic syndrome and mood disorders. In this Review, we summarize the mechanisms that influence glucocorticoid sensitivity in health and disease and discuss possible strategies to modulate glucocorticoid responsiveness.

A naturally occurring insertion of a single amino acid rewires transcriptional regulation by glucocorticoid receptor isoforms

In addition to guiding proteins to defined genomic loci, DNA can act as an allosteric ligand that influences protein structure and activity. Here we compared genome-wide binding, transcriptional regulation, and, using NMR, the conformation of two glucocorticoid receptor (GR) isoforms that differ by a single amino acid insertion in the lever arm, a domain that adopts DNA sequence-specific conformations. We show that these isoforms differentially regulate gene expression levels through two mechanisms: differential DNA binding and altered communication between GR domains. Our studies suggest a versatile role for DNA in both modulating GR activity and also in directing the use of GR isoforms. We propose that the lever arm is a "fulcrum" for bidirectional allosteric signaling, conferring conformational changes in the DNA reading head that influence DNA sequence selectivity, as well as conferring changes in the dimerization domain that connect functionally with remote regulatory surfaces, thereby influencing which genes are regulated and the magnitude of their regulation.

Low expression of glucocorticoid receptor alpha isoform in adult immune thrombocytopenia correlates with glucocorticoid resistance

The expression of glucocorticoid receptor (GR) isoforms has been linked to glucocorticoid (GC) resistance in various diseases treated with GC. However, existing data are conflicting in these diseases, and little information is available regarding immune thrombocytopenia (ITP). To further investigate the role of GR isoforms in GC resistance in adult ITP patients, we measured the mRNA expression of GR isoforms (GRα, GRβ, GRγ, GRp) in peripheral blood mononuclear cells (PBMC) from 54 newly diagnosed ITP patients, including GC-sensitive (GCS) and GC-resistant (GCR) patients and 35 healthy volunteers. The GRα and GRβ proteins in PBMC, nuclear factor-κB (NF-κB), and activator protein-1 (AP-1) in the nucleus were detected by Western blotting. Compared to normal subjects, both GRα and GRβ mRNAs were significantly increased in ITP patients (p < 0.05), while there was no significant difference in the mRNA expression of GRγ and GRp. Compared to GCR patients, the expressions of GRα mRNA and GRα protein were significantly higher in GCS patients (p < 0.05). Moreover, no significant difference in the mRNA expression of the GRβ, GRγ, and GRp isoforms was observed between GCS and GCR patients and the GRβ protein could not be detected. Compared to GCS group, the expression of p65/NF-κB was significantly higher in the GCR group (p < 0.05). Overall, we did not find differences in c-Jun/AP-1 protein expression between GCS and GCR patients. In summary, GC resistance in adult ITP patients is associated with a reduced expression of GRα, which may be related with increased NF-κB. GRβ was very low and may not be involved in GC resistance in adult ITP, warranting further exploration.

MicroRNAs and Glucocorticoid-Induced Apoptosis in Lymphoid Malignancies

The initial response of lymphoid malignancies to glucocorticoids (GCs) is a critical parameter predicting successful treatment. Although being known as a strong inducer of apoptosis in lymphoid cells for almost a century, the signaling pathways regulating the susceptibility of the cells to GCs are only partly revealed. There is still a need to develop clinical tests that can predict the outcome of GC therapy. In this paper, I discuss important parameters modulating the pro-apoptotic effects of GCs, with a specific emphasis on the microRNA world comprised of small players with big impacts. The journey through the multifaceted complexity of GC-induced apoptosis brings forth explanations for the differential treatment response and raises potential strategies for overcoming drug resistance.

Current concepts in glucocorticoid resistance

Glucocorticoids (GCs) are the most potent anti-inflammatory agents known. A major factor limiting their clinical use is the wide variation in responsiveness to therapy. The high doses of GC required for less responsive patients means a high risk of developing very serious side effects. Variation in sensitivity between individuals can be due to a number of factors. Congenital, generalized GC resistance is very rare, and is due to mutations in the glucocorticoid receptor (GR) gene, the receptor that mediates the cellular effects of GC. A more common problem is acquired GC resistance. This localized, disease-associated GC resistance is a serious therapeutic concern and limits therapeutic response in patients with chronic inflammatory disease. It is now believed that localized resistance can be attributed to changes in the cellular microenvironment, as a consequence of chronic inflammation. Multiple factors have been identified, including alterations in both GR-dependent and -independent signaling downstream of cytokine action, oxidative stress, hypoxia and serum derived factors. The underlying mechanisms are now being elucidated, and are discussed here. Attempts to augment tissue GC sensitivity are predicted to permit safe and effective use of low-dose GC therapy in inflammatory disease.

Glucocorticoid resistance in paediatric acute lymphoblastic leukaemia

Glucocorticoids (GCs), such as prednisolone and dexamethasone, are key components in multi-agent chemotherapy protocols used for the treatment of acute lymphoblastic leukaemia (ALL). Approximately 10% of children with ALL will respond poorly to GCs, and GC resistance is associated with a significantly inferior outcome. This review summarises the current knowledge of GC resistance in ALL, including the roles of the GC receptor and its co-chaperone molecules, the pro-apoptotic and pro-survival B-cell lymphoma 2 family members and alternative non-apoptotic mechanisms of cell death. It concludes with a discussion on therapeutic attempts to overcome GC resistance.

Glucocorticoid receptor-mediated apoptosis: mechanisms of resistance in cancer cells

Glucocorticoids (Gcs) are commonly used to treat patients suffering from a wide range of cancers. Their main therapeutic role is based on Gc receptor (GR)-mediated mechanisms that trigger cell death but this varies depending on the cancer type. This review aims to provide an overview of the mechanisms of Gc-induced cell death and more importantly the changes in GR that lead to resistance to Gc treatment in cancer. The three main cancer types, which are susceptible to Gc resistance and therefore loss of Gc-induced apoptotic effects, are acute lymphoblastic leukaemia, osteosarcoma and small-cell lung carcinoma. A common theme is the loss of GR function and/or a downregulation of GR expression which leads to failure of the cell death-inducing effects of Gcs. Loss of GR function is attributed to mutations in the GR gene, and in some cases a dominant-negative effect on any functional GR still present. The downregulation of GR expression can be due to decreased GR promoter activation, increased GR promoter methylation or increased expression of alternative splice isoforms of GR that have decreased transcriptional activity. Understanding the mechanisms behind Gc-triggered apoptosis and the resistance to it in these cancer types will help in further refining treatment regimens for patients and will decrease the chance of relapse caused by Gc-resistant cancer phenotypes.

Glucocorticoid receptor alpha isoform-selective regulation of antiapoptotic genes in osteosarcoma cells: a new mechanism for glucocorticoid resistance

Glucocorticoids regulate a variety of physiological processes and are commonly used to treat disorders of inflammation, autoimmune diseases, and cancer. Glucocorticoid action is predominantly mediated through the classic glucocorticoid receptor (GR)α isoform. Recent data suggest that the mature GRα mRNA is translated into multiple N-terminal isoforms that have distinct biochemical properties and gene regulatory profiles. Interestingly, osteosarcoma cells stably expressing the GRα-D translational isoform are unique in that they are resistant to glucocorticoid-induced apoptosis. In this study, we investigate whether GRα isoform-specific differences in the regulation of antiapoptotic genes contribute to this resistant phenotype. We now show that GRα-D, unlike the other receptor isoforms, does not inhibit the activity of a nuclear factor κB (NF-κB)-responsive reporter gene and does not efficiently repress either the transcription or protein production of the antiapoptotic genes Bcl-xL, cellular inhibitor of apoptosis protein 1, and survivin. The inability of GRα-D to down-regulate the expression of these genes appears to be associated with a diminished interaction between GRα-D and NF-κB that is observed in cells, but not in vitro, and likely reflects the sequestration of GRα-D in the nucleus. Deletion of the GRα N-terminal amino acids 98-335 also results in a nuclear resident GR, which fails to interact with NF-κB in cells and promote apoptosis in response to glucocorticoids. These data suggest that the N-terminal translational isoforms of GRα selectively regulate antiapoptotic genes and that the GRα-D isoform may contribute to the resistance of certain cancer cells to glucocorticoid-induced apoptosis.

Protein kinase networks regulating glucocorticoid-induced apoptosis of hematopoietic cancer cells: fundamental aspects and practical considerations

Glucocorticoids (GCs) are integral components in the treatment protocols of acute lymphoblastic leukemia, multiple myeloma, and non-Hodgkin lymphoma owing to their ability to induce apoptosis of these malignant cells. Resistance to GC therapy is associated with poor prognosis. Although they have been used in clinics for decades, the signal transduction pathways involved in GC-induced apoptosis have only partly been resolved. Accumulating evidence shows that this cell death process is mediated by a communication between nuclear GR affecting gene transcription of pro-apoptotic genes such as Bim, mitochondrial GR affecting the physiology of the mitochondria, and the protein kinase glycogen synthase kinase-3 (GSK3), which interacts with Bim following exposure to GCs. Prevention of Bim up-regulation, mitochondrial GR translocation, and/or GSK3 activation are common causes leading to GC therapy failure. Various protein kinases positively regulating the pro-survival Src-PI3K-Akt-mTOR and Raf-Ras-MEK-ERK signal cascades have been shown to be activated in malignant leukemic cells and antagonize GC-induced apoptosis by inhibiting GSK3 activation and Bim expression. Targeting these protein kinases has proven effective in sensitizing GR-positive malignant lymphoid cells to GC-induced apoptosis. Thus, intervening with the pro-survival kinase network in GC-resistant cells should be a good means of improving GC therapy of hematopoietic malignancies.

Epigenetic silencing of BIM in glucocorticoid poor-responsive pediatric acute lymphoblastic leukemia, and its reversal by histone deacetylase inhibition

Glucocorticoids play a critical role in the therapy of lymphoid malignancies, including pediatric acute lymphoblastic leukemia (ALL), although the mechanisms underlying cellular resistance remain unclear. We report glucocorticoid resistance attributable to epigenetic silencing of the BIM gene in pediatric ALL biopsies and xenografts established in immune-deficient mice from direct patient explants as well as a therapeutic approach to reverse resistance in vivo. Glucocorticoid resistance in ALL xenografts was consistently associated with failure to up-regulate BIM expression after dexamethasone exposure despite confirmation of a functional glucocorticoid receptor. Although a comprehensive assessment of BIM CpG island methylation revealed no consistent changes, glucocorticoid resistance in xenografts and patient biopsies significantly correlated with decreased histone H3 acetylation. Moreover, the histone deacetylase inhibitor vorinostat relieved BIM repression and exerted synergistic antileukemic efficacy with dexamethasone in vitro and in vivo. These findings provide a novel therapeutic strategy to reverse glucocorticoid resistance and improve outcome for high-risk pediatric ALL.

Glucocorticoid-induced apoptosis of healthy and malignant lymphocytes

Glucocorticoids exert a wide range of physiological effects, including the induction of apoptosis in lymphocytes. The progression of glucocorticoid-induced apoptosis is a multi-component process requiring contributions from both genomic and cytoplasmic signaling events. There is significant evidence indicating that the transactivation activity of the glucocorticoid receptor is required for the initiation of glucocorticoid-induced apoptosis. However, the rapid cytoplasmic effects of glucocorticoids may also contribute to the glucocorticoid-induced apoptosis-signaling pathway. Endogenous glucocorticoids shape the T-cell repertoire through both the induction of apoptosis by neglect during thymocyte maturation and the antagonism of T-cell receptor (TCR)-induced apoptosis during positive selection. Owing to their ability to induce apoptosis in lymphocytes, synthetic glucocorticoids are widely used in the treatment of haematological malignancies. Glucocorticoid chemotherapy is limited, however, by the emergence of glucocorticoid resistance. The development of novel therapies designed to overcome glucocorticoid resistance will dramatically improve the efficacy of glucocorticoid therapy in the treatment of haematological malignancies.

Characterization of conserved tandem donor sites and intronic motifs required for alternative splicing in corticosteroid receptor genes

Alternative splicing events from tandem donor sites result in mRNA variants coding for additional amino acids in the DNA binding domain of both the glucocorticoid (GR) and mineralocorticoid (MR) receptors. We now show that expression of both splice variants is extensively conserved in mammalian species, providing strong evidence for their functional significance. An exception to the conservation of the MR tandem splice site (an A at position +5 of the MR+12 donor site in the mouse) was predicted to decrease U1 small nuclear RNA binding. In accord with this prediction, we were unable to detect the MR+12 variant in this species. The one exception to the conservation of the GR tandem splice site, an A at position +3 of the platypus GRgamma donor site that was predicted to enhance binding of U1 snRNA, was unexpectedly associated with decreased expression of the variant from the endogenous gene as well as a minigene. An intronic pyrimidine motif present in both GR and MR genes was found to be critical for usage of the downstream donor site, and overexpression of TIA1/TIAL1 RNA binding proteins, which are known to bind such motifs, led to a marked increase in the proportion of GRgamma and MR+12. These results provide striking evidence for conservation of a complex splicing mechanism that involves processes other than stochastic spliceosome binding and identify a mechanism that would allow regulation of variant expression.

Glucocorticoid Receptor in Health and Disease

Glucocorticoid hormones are essential for life, have a vital place in the treatment of inflammatory and autoimmune diseases and are increasingly implicated in the pathogenesis of a number of common disorders. Their action is mediated by an intracellular receptor protein, the glucocorticoid receptor (GR), functioning as a ligand-inducible transcription factor. Multiple synthetic glucocorticoids are used as potent antiinflammatory and immunosuppressive agents, but their therapeutic usefulness is limited by a wide range and severity of side-effects. One of the most important pharmaceutical goals has been to design steroidal and non-steroidal GR ligands with profound therapeutic efficacy and reduced unwanted effects. The therapeutic benefit of glucocorticoid agonists is frequently compromised by resistance to glucocorticoids, which may depend on: access of the hormones to target cells, steroid metabolism, expression level and isoform composition of the GR protein, mutations and polymorphisms in the GR gene and association of the receptor with chaperone proteins. The major breakthrough into the critical role of glucocorticoid signaling in the maintenance of homeostasis and pathogenesis of diseases, as well as into the molecular mechanisms underlying the therapeutic usefulness of antiinflammatory drugs acting through the GR is expected to result from the current progress in large-scale gene expression profiling technologies and computational biology.

Flow cytometry analysis of glucocorticoid receptor expression and binding in steroid-sensitive and steroid-resistant patients with systemic lupus erythematosus

Introduction

Glucocorticoid (GC) therapy is the main treatment for systemic lupus erythematosus (SLE). However, some patients are resistant to these agents. Abnormalities of glucocorticoid receptor (GR) seem to be related to steroid resistance. This study evaluated GRs in T lymphocytes and monocytes of SLE patients by flow cytometry (FCM) using a monoclonal antibody (mAb) and FITC-Dex probes.

Methods

Thirty-five patients with SLE before treatment and 27 age- and sex-matched normal controls were studied. Disease activity scores were determined before and after treatment and used to divide the patients into steroid-resistant (SR) and steroid-sensitive (SS) groups. GRs in T lymphocytes (CD3⁺) and monocytes (CD14⁺) were examined by FCM with GR-mAb and FITC-Dex probes before treatment. Peripheral blood mononuclear cells (PBMCs) were isolated for in vitro GCs sensitivity assays. The validity of FCM analysis of intracellular staining for GR with GR-mAb and FITC-Dex probes was evaluated through comparison with western blot and radioligand binding assay (RLBA) in U937 and K562 cells in vitro. One-way ANOVA, student's t test, linear regression and spearman correlation were performed.

Results

A significant decrease in GR binding and the expression in K562 and U937 cells with 10^-6 M dexamethasone (Dex) was found compared with those without Dex. In addition, a positive correlation was found between FCM and RLBA as well as FCM and Western blot. The expression and binding of both CD3/GR and CD14/GR in SR patients with SLE, detected by FCM, were all lower than those in SS patients with SLE, whereas there was no significant difference in SS patients and controls. In vitro corticosteroid sensitivity assay indicated that PHA-stimulated tumour necrosis factor-α (TNF-α), IL-12 and interferon-γ (IFN-γ) secretion was significantly inhibited by 10^-6 M Dexamethasone in all controls and SS patients, compared with that in SR group, which confirms patient classification as SR and SS by disease activity index (SLEDAI) score.

Conclusions

Abnormalities of expression and binding of the GR may be involved in tissue resistance to steroids in SLE patients. Determination of GR expression and binding by FCM may be useful in predicting the response to steroid treatment of SLE patients.

Trial registration

Clinical trial registration number NCT00600652.

Molecular mechanisms regulating glucocorticoid sensitivity and resistance

Glucocorticoid receptor agonists are mainstays in the treatment of various malignancies of hematological origin. Glucocorticoids are included in therapeutic regimens for their ability to stimulate intracellular signal transduction cascades that culminate in alterations in the rate of transcription of genes involved in cell cycle progression and programmed cell death. Unfortunately, subpopulations of patients undergoing systemic glucocorticoid therapy for these diseases are or become insensitive to glucocorticoid-induced cell death, a phenomenon recognized as glucocorticoid resistance. Multiple factors contributing to glucocorticoid resistance have been identified. Here we summarize several of these mechanisms and describe the processes involved in generating a host of glucocorticoid receptor isoforms from one gene. The potential role of glucocorticoid receptor isoforms in determining cellular responsiveness to glucocorticoids is emphasized.

Mechanisms regulating the susceptibility of hematopoietic malignancies to glucocorticoid-induced apoptosis

Glucocorticoids (GCs) are commonly used in the treatment of hematopoietic malignancies owing to their ability to induce apoptosis of these cancerous cells. Whereas some types of lymphoma and leukemia respond well to this drug, others are resistant. Also, GC-resistance gradually develops upon repeated treatments ultimately leading to refractory relapsed disease. Understanding the mechanisms regulating GC-induced apoptosis is therefore uttermost important for designing novel treatment strategies that overcome GC-resistance. This review discusses updated data describing the complex regulation of the cell's susceptibility to apoptosis triggered by GCs. We address both the genomic and nongenomic effects involved in promoting the apoptotic signals as well as the resistance mechanisms opposing these signals. Eventually we address potential strategies of clinical relevance that sensitize GC-resistant lymphoma and leukemia cells to this drug. The major target is the nongenomic signal transduction machinery where the interplay between protein kinases determines the cell fate. Shifting the balance of the kinome towards a state where Glycogen synthase kinase 3alpha (GSK3alpha) is kept active, favors an apoptotic response. Accumulating data show that it is possible to therapeutically modulate GC-resistance in patients, thereby improving the response to GC therapy.

The SWI/SNF chromatin-remodeling complex and glucocorticoid resistance in acute lymphoblastic leukemia

BACKGROUND

Glucocorticoids are used in the curative treatment of acute lymphoblastic leukemia (ALL). Resistance to glucocorticoids is an important adverse prognostic factor in newly diagnosed ALL patients but its mechanism is unknown. Because SWI/SNF complex-mediated chromatin remodeling is required for glucocorticoid transcriptional activity in vitro, we investigated whether expression of subunits of the SWI/SNF complex was related to glucocorticoid resistance in ALL.

METHODS

Gene expression and in vitro sensitivity to prednisolone and dexamethasone were assessed in a training set of primary ALL cells from 177 children with newly diagnosed ALL and a validation set of cells from an independent cohort of 95 ALL patients. The global test method was used to select pathways whose genes were associated with drug sensitivity. Genes involved in chromatin remodeling were identified by use of the Gene Ontology database. Short hairpin RNA (shRNA) was used to knock down mRNA expression of SMARCA4 in glucocorticoid-sensitive Jurkat human ALL cells. Spearman rank correlation, multiple linear regression, and logistic regression were used to investigate associations between gene expression and glucocorticoid sensitivity. All statistical tests were two-sided.

RESULTS

Statistically significant associations between decreased expression in ALL cells of genes for core subunits of the SWI/SNF complex-SMARCA4, ARID1A, and SMARCB1-and resistance to prednisolone and dexamethasone were identified in the training cohort. In the validation cohort, expression of SMARCA4 (P < .001 and r = -0.43), ARID1A (P = .016 and r = -0.29), and SMARCB1 (P = .019 and r = -0.29) in ALL cells was statistically significantly associated with dexamethasone sensitivity, and SMARCA4 expression (P = .018 and r = -0.28) was statistically significantly associated with prednisolone sensitivity. Prednisolone resistance was higher in SMARCA4 shRNA-transfected Jurkat cells (drug concentration lethal to 50% of the leukemia cells [LC(50)] = 277 microM) than in control shRNA-transfected cells (LC(50) = 174 microM, difference = 103 microM, 95% confidence interval of the difference = 100 to 106 microM; P < .001, t test).

CONCLUSION

Decreased expression of as many as three subunits of the SWI/SNF complex appears to be associated with glucocorticoid resistance in primary ALL cells.