Gene expression profiles of proliferating vs. G1/G0 arrested human leukemia cells suggest a mechanism for glucocorticoid-induced apoptosis

Interdisciplinary Approach to Biological and Health Implications in Selected Professional Competences

Everyday life’s hygiene and professional realities, especially in economically developed countries, indicate the need to modify the standards of pro-health programs as well as modern hygiene and work ergonomics programs. These observations are based on the problem of premature death caused by civilization diseases. The biological mechanisms associated with financial risk susceptibility are well described, but there is little data explaining the biological basis of neuroaccounting. Therefore, the aim of the study was to present relationships between personality traits, cognitive competences and biological factors shaping behavioral conditions in a multidisciplinary aspect. This critical review paper is an attempt to compile biological and psychological factors influencing the development of professional competences, especially decent in the area of accounting and finance. We analyzed existing literature from wide range of scientific disciplines (including economics, psychology, behavioral genetics) to create background to pursuit multidisciplinary research models in the field of neuroaccounting. This would help in pointing the best genetically based behavioral profile of future successful financial and accounting specialists.

Establishment of reporter cells that respond to glucocorticoids by a transposon-mediated promoter-trapping system

Previously, we had established a highly sensitive trap vector system for the efficient isolation of reporter cells for a certain condition of interest. In this study, we used this system to screen reporter cells that express the luciferase and enhanced green fluorescent protein genes in response to dexamethasone, a glucocorticoid receptor agonist to facilitate glucocorticoid signaling research. In total, 10 clones were isolated. The insertion sites of the trap vector were analyzed using 5' rapid amplification of cDNA ends (5' RACE), whereupon LPIN1, PKP2, and FKBP5 were identified as genes that were upregulated by the dexamethasone treatment. Specifically, PKP2 has not previously been focused as a gene that responds to glucocorticoids. The PKP2 mRNA was analyzed and induction of the endogenous gene was confirmed by real-time polymerase chain reaction. Given that PKP2 does not appear to have a consensus glucocorticoid response element (GRE) sequence, this reporter clone could supplement the current GRE-based reporter systems that are prevalently used. Because different clones showed different responses to glucocorticoids, these clones should provide more information than analysis with a single reporter clone. This paper demonstrates that the previously developed trap vector technology can contribute to the rapid construction of drug evaluation systems.

Dual Mechanisms of Metabolism and Gene Expression of the CCRF-CEM Leukemia Cells under Glucocorticoid Treatment

BACKGROUND

Glucocorticoids play an essential part in anti-leukemic therapies, but resistance is a crucial event for the prognosis of the disease. Glucocorticoids influence the metabolic properties of leukemic cells. The inherent plasticity of clinically evolving cancer cells justifies the characterization of drug-induced early oncogenic pathways, which represent a likely source of detrimental secondary effects.

AIM

The present work aims to investigate the effect of glucocorticoids in metabolic pathways in the CCRF-CEM leukemic cells. Metabolic factors and gene expression profiles were examined in order to unravel the possible mechanisms of the CCRF-CEM leukemic cell growth dynamics.

METHODS

CCRF-CEM cells were used as a model. Cells were treated with prednisolone with concentrations 0-700 μM. Cell culture supernatants were used for glucose, lactic acid, LDH, Na⁺, K⁺ and Ca⁺⁺ measurements. Cytotoxicity was determined with flow cytometry. Microarray analysis was performed using two different chips of 1.2 k and 4.8 k genes. Gene Ontology enrichment analysis was applied to find metabolism- and GC-related genes.

RESULTS

Higher prednisolone concentrations inhibited glucose uptake, without exhibiting any cytotoxic effects. Glucose consumption did not correlate with the total cell population, or the viable population, indicating that growth is not directly proportional to glucose consumption. Neither of the subpopulations, i.e., viable, necrotic, or apoptotic cells, contributed to this.

CONCLUSIONS

Different types of leukemic cells seem to exhibit different patterns of glucose metabolism. Both resistant and sensitive CCRF-CEM cells followed the aerobic pathway of glycolysis. There is probably a rapid change in membrane permeability, causing a general shutdown towards everything that is outside the cell. This could in part also explain the observed resistance. Glucocorticoids do not enter the cell passively anymore and therefore no effects are observed. Based on our observations, ion concentrations are measurable factors both in vitro and in vivo, which makes them possible markers of glucocorticoid cytotoxic action.

Gene Expression and Resistance to Glucocorticoid-Induced Apoptosis in Acute Lymphoblastic Leukemia: A Brief Review and Update

BACKGROUND

Resistance to glucocorticoid (GC)-induced apoptosis in Acute Lymphoblastic Leukemia (ALL), is considered one of the major prognostic factors for the disease. Prednisolone is a corticosteroid and one of the most important agents in the treatment of acute lymphoblastic leukemia. The mechanics of GC resistance are largely unknown and intense ongoing research focuses on this topic.

AIM

The aim of the present study is to review some aspects of GC resistance in ALL, and in particular of Prednisolone, with emphasis on previous and present knowledge on gene expression and signaling pathways playing a role in the phenomenon.

METHODS

An electronic literature search was conducted by the authors from 1994 to June 2019. Original articles and systematic reviews selected, and the titles and abstracts of papers screened to determine whether they met the eligibility criteria, and full texts of the selected articles were retrieved.

RESULTS

Identification of gene targets responsible for glucocorticoid resistance may allow discovery of drugs, which in combination with glucocorticoids may increase the effectiveness of anti-leukemia therapies. The inherent plasticity of clinically evolving cancer justifies approaches to characterize and prevent undesirable activation of early oncogenic pathways.

CONCLUSION

Study of the pattern of intracellular signal pathway activation by anticancer drugs can lead to development of efficient treatment strategies by reducing detrimental secondary effects.

Influence of BCL2L11 polymorphism on osteonecrosis during treatment of childhood acute lymphoblastic leukemia

Osteonecrosis (ON) is corticosteroid-related complication, reported in children with acute lymphoblastic leukemia (ALL). We have previously found that polymorphisms in BCL2L11 gene coding for pro-apoptotic Bim protein influence reduction of overall survival (OS) in a corticosteroid (CS) dose-dependent manner in childhood ALL patients. The same set of SNPs was here investigated for an association with CS-related ON assessed retrospectively in 304 children with ALL from Quebec (QcALL cohort) who received Dana-Farber Cancer Institute (DFCI) ALL treatment protocols. Two-year cumulative incidence of symptomatic ON was 10.6%. Two BCL2L11 polymorphisms, the 891T>G (rs2241843) in all QcALL patients and 29201C>T (rs724710) in high-risk group were significantly associated with ON, P = 0.009 and P = 0.003, respectively. The association remained significant in multivariate model (HR_891TT = 2.4, 95% CI 1.2-4.8, P = 0.01 and HR_29201CC = 5.7, 95% CI 1.6-20.9, P = 0.008). Both polymorphisms influenced viability of dexamethasone treated lymphoblastoid cell lines (P ≤ 0.03). The 891T>G influenced Bim gamma isoform levels (0.03) and its association with ON was also confirmed in replication DFCI cohort (N = 168, P = 0.03). QcALL children had a high incidence of ON during therapy, which was highly associated with BCL2L11 polymorphisms.

MicroRNA-185-5p restores glucocorticoid sensitivity by suppressing the mammalian target of rapamycin complex (mTORC) signaling pathway to enhance glucocorticoid receptor autoregulation

Overexpression of microRNA-185-5p (miR-185-5p) in glucocorticoid (GC)-sensitive acute lymphoblastic leukemia (ALL) was identified using a microarray and reverse transcription polymerase chain reaction and was further confirmed in ALL cell lines. A reporter assay confirmed that the Rictor-one component of mammalian target of rapamycin complex 2 (mTORC2) is a target of miR-185-5p. Decreased mTORC activity was also confirmed in GC-sensitive patients. Overexpression of miR-185-5p significantly enhanced GC sensitivity in CEM-C1 cells (GC resistance) by increasing the rate of cell apoptosis and cycle arrest, and decreasing cell survival, accompanied by a decrease in mTORC activity and an increase in GC-induced glucocorticoid receptor (GR) expression. Rapamycin, an mTORC1 inhibitor, showed similar effects to miR-185-5p. These results demonstrated that miR-185-5p enhances GC sensitivity via suppression of mTORC activity by enhancing GR autoupregulation and that miR-185-5p is a potential target for the diagnosis and reversion of GC resistance.

Integrated analysis of gene network in childhood leukemia from microarray and pathway databases

Glucocorticoids (GCs) have been used as therapeutic agents for children with acute lymphoblastic leukaemia (ALL) for over 50 years. However, much remains to be understood about the molecular mechanism of GCs actions in ALL subtypes. In this study, we delineate differential responses of ALL subtypes, B- and T-ALL, to GCs treatment at systems level by identifying the differences among biological processes, molecular pathways, and interaction networks that emerge from the action of GCs through the use of a selected number of available bioinformatics methods and tools. We provide biological insight into GC-regulated genes, their related functions, and their networks specific to the ALL subtypes. We show that differentially expressed GC-regulated genes participate in distinct underlying biological processes affected by GCs in B-ALL and T-ALL with little to no overlap. These findings provide the opportunity towards identifying new therapeutic targets.

"Bam," a novel glucocorticoid-induced BH3-only transcript from the BCL2L11/Bim locus, does not appear to be translated

Glucocorticoids (GCs) are steroid hormones that induce cell death and cell cycle arrest in lymphoid tissues. By virtue of this property, GCs are widely exploited in the therapy of acute lymphoblastic leukemia (ALL) in children. We reported a novel BH3-only transcript, "Bam," from the BCL2L11 locus, which was first described in patients with multiple myeloma. The Bam gene consists of two exons, and became of particular interest to us when we found that it was regulated in the majority of children with ALL and many in vitro systems in which GCs induce cell death. Being a BH3-only transcript, Bam retains a BH3 domain identical to that of Bim, although Bam has a unique C-terminus that is totally different from that of its relative Bim. The present work analyzes whether Bam is translated or not. Since we could not detect Bam in the endogenous situation, we evaluated its 5' untranslated region (UTR). This revealed that there are three out-of-frame initiation codons preceding the Bam open reading frame (ORF). Experiments with constructs without out-of-frame initiation codons and constructs harboring such codons in their 5' UTR revealed that Bam translation is handicapped by their presence. Moreover, there was no Kozak translational initiation sequence surrounding any of the AUGs. Taken together, results of the present study strongly suggest that this transcript is translated at a very low rate, if at all.

Combined multivariate and pathway analyses show that allergen-induced gene expression changes in CD4+ T cells are reversed by glucocorticoids

BACKGROUND

Glucocorticoids (GCs) play a key role in the treatment of allergy. However, the genome-wide effects of GCs on gene expression in allergen-challenged CD4(+) T cells have not been described. The aim of this study was to perform a genome-wide analysis to investigate whether allergen-induced gene expression changes in CD4(+) T cells could be reversed by GCs.

METHODOLOGY/PRINCIPAL FINDINGS

Gene expression microarray analysis was performed to profile gene expression in diluent- (D), allergen- (A), and allergen + hydrocortisone- (T) challenged CD4(+) T cells from patients with seasonal allergic rhinitis. Principal component analysis (PCA) showed good separation of the three groups. To identify the correlation between changes in gene expression in allergen-challenged CD4(+) T cells before and after GC treatment, we performed orthogonal partial least squares discriminant analysis (OPLS-DA) followed by Pearson correlation analysis. This revealed that allergen-induced genes were widely reversed by GC treatment (r = -0.77, P<0.0001). We extracted 547 genes reversed by GC treatment from OPLS-DA models based on their high contribution to the discrimination and found that those genes belonged to several different inflammatory pathways including TNFR2 Signalling, Interferon Signalling, Glucocorticoid Receptor Signalling and T Helper Cell Differentiation. The results were supported by gene expression microarray analyses of two independent materials.

CONCLUSIONS/SIGNIFICANCE

Allergen-induced gene expression changes in CD4(+) T cells were reversed by treatment with glucocorticoids. The top allergen-induced genes that reversed by GC treatment belonged to several inflammatory pathways and genes of known or potential relevance for allergy.

Evaluation of the NOD/SCID xenograft model for glucocorticoid-regulated gene expression in childhood B-cell precursor acute lymphoblastic leukemia

Background

Glucocorticoids such as prednisolone and dexamethasone are critical drugs used in multi-agent chemotherapy protocols used to treat acute lymphoblastic leukemia (ALL), and response to glucocorticoids is highly predictive of outcome. The NOD/SCID xenograft mouse model of ALL is a clinically relevant model in which the mice develop a systemic leukemia which retains the fundamental biological characteristics of the original disease. Here we report a study evaluating the NOD/SCID xenograft mouse model to investigate glucocorticoid-induced gene expression. Cells from a glucocorticoid-sensitive xenograft derived from a child with B-cell precursor ALL were inoculated into NOD/SCID mice. When highly engrafted the mice were randomized into groups of 4 to receive dexamethasone 15 mg/kg by intraperitoneal injection or vehicle control. Leukemia cells were harvested from mice spleens at 0, 8, 24 or 48 hours thereafter, and gene expression analyzed on Illumina WG-6_V3 chips, comparing all groups to time 0 hours.

Results

The 8 hour dexamethasone-treated timepoint had the highest number of significantly differentially expressed genes, with fewer observed at the 24 and 48 hour timepoints, and with minimal changes seen across the time-matched controls. When compared to publicly available datasets of glucocorticoid-induced gene expression from an in vitro cell line study and from an in vivo study of patients with ALL, at the level of pathways, expression changes in the 8 hour xenograft samples showed a similar response to patients treated with glucocorticoids. Replicate analysis revealed that at the 8 hour timepoint, a dataset with high signal and differential expression, using data from 3 replicates instead of 4 resulted in excellent recovery scores of > 0.9. However at other timepoints with less signal very poor recovery scores were obtained with 3 replicates.

Conclusions

The NOD/SCID xenograft mouse model provides a reproducible experimental system in which to investigate clinically-relevant mechanisms of drug-induced gene regulation in ALL; the 8 hour timepoint provides the highest number of significantly differentially expressed genes; time-matched controls are redundant and excellent recovery scores can be obtained with 3 replicates.

Glucocorticoid elevation of dexamethasone-induced gene 2 (Dig2/RTP801/REDD1) protein mediates autophagy in lymphocytes

Glucocorticoid hormones, including dexamethasone, induce apoptosis in lymphocytes and consequently are used clinically as chemotherapeutic agents in many hematologic malignancies. Dexamethasone also induces autophagy in lymphocytes, although the mechanism is not fully elucidated. Through gene expression analysis, we found that dexamethasone induces the expression of a gene encoding a stress response protein variously referred to as Dig2, RTP801, or REDD1. This protein is reported to inhibit mammalian target of rapamycin (mTOR) signaling. Because autophagy is one outcome of mTOR inhibition, we investigated the hypothesis that Dig2/RTP801/REDD1 elevation contributes to autophagy induction in dexamethasone-treated lymphocytes. In support of this hypothesis, RNAi-mediated suppression of Dig2/RTP801/REDD1 reduces mTOR inhibition and autophagy in glucocorticoid-treated lymphocytes. We observed similar results in Dig2/Rtp801/Redd1 knock-out murine thymocytes treated with dexamethasone. Dig2/RTP801/REDD1 knockdown also leads to increased levels of dexamethasone-induced cell death, suggesting that Dig2/RTP801/REDD1-mediated autophagy promotes cell survival. Collectively, these findings demonstrate for the first time that elevation of Dig2/RTP801/REDD1 contributes to the induction of autophagy.

Establishing a sensitive and specific assay for determination of glucocorticoid bioactivity

Glucocorticoids are hormones that play a major role in energy homeostasis and stress response of the body. As drugs they are most frequently used for immunosuppressive and anti-inflammatory purposes. Glucocorticoids are exploited successfully in the treatment of a wide variety of diseases; however, some patients develop side-effects, while others fail to respond to this form of therapy. Alterations in pharmacodynamic and pharmacokinetic actions might contribute to individual differences in glucocorticoid sensitivity. Antibody-based methods such as RIA (Radioimmunoassay) and ELISA (Enzyme-linked immunosorbent assay) are routinely used to determine glucocorticoid serum levels. However, as these techniques measure the total amount of a specific glucocorticoid and do not discriminate between protein-bound and freely available (i.e. biologically active) glucocorticoids, the results do not necessarily reflect the active levels of glucocorticoid, i.e. the "glucocorticoid milieu" in a patient. Being able to determine glucocorticoid bioactivity in serum or other body fluids could help identifying glucocorticoid-sensitive or -resistant patients and help finding explanations for different responses in individual patients. For this reason, we established a glucocorticoid bioactivity assay that is based on the measurement of glucocorticoid-dependent reporter gene activity. Making use of a human T-cell leukemia line, equipped with the glucocorticoid receptor and the fluorescence protein Venus as the assay's reporter (Jurkat(GR)-MMTV-VNP), glucocorticoid bioactivity can be determined from small amounts of serum or other biologic fluids. The developed glucocorticoid bioassay is both sensitive and reproducible, without any relevant cross-reactivity with steroid hormones other than glucocorticoids and can be practically applied in daily laboratory routine.

Influence of wild-type MLL on glucocorticoid sensitivity and response to DNA-damage in pediatric acute lymphoblastic leukemia

Background

Rearrangement of the mixed-lineage leukemia gene (MLL) is found in 80% of infant acute lymphoblastic leukemia (ALL) and is associated with poor prognosis and resistance to glucocorticoids (GCs). We have recently observed that GC resistance in T-ALL cell lines is associated with a proliferative metabolism and reduced expression of MLL. In this study we have further explored the relationship between MLL status and GC sensitivity.

Results

Negative correlation of MLL expression with GC resistance in 15 T-ALL cell lines was confirmed by quantitative RT-PCR. The absence of MLL-rearrangements suggested that this relationship represented expression of wild-type MLL. Analysis of MLL expression patterns revealed a negative relationship with cellular metabolism, proliferation and anti-apoptotic transcriptional networks. In silico analysis of published data demonstrated that reduced levels of MLL mRNA are associated with relapse and prednisolone resistance in T-ALL patients and adverse clinical outcome in children with MLL-rearranged ALL. RNAi knockdown of MLL expression in T-ALL cell lines significantly increased resistance to dexamethasone and gamma irradiation indicating an important role for wild-type MLL in the control of cellular apoptosis.

Conclusions

The data suggests that reduced expression of wild-type MLL can contribute to GC resistance in ALL patients both with and without MLL-translocations.

Use of recombinant cell-permeable small peptides to modulate glucocorticoid sensitivity of acute lymphoblastic leukemia cells

Glucocorticoid (GC) hormones induce apoptosis in T-cell and pre-B-cell acute lymphoblastic leukemia (ALL) cells. Steroid-mediated apoptosis requires a threshold level of the glucocorticoid receptor (GR) protein, and increasing the intracellular GR levels in ALL cells would augment their hormone sensitivity. A protein transduction domain (PTD) approach was used to accomplish this. We produced an HIV Tat PTD domain fusion protein (Tat-GR(554-777)) that potentially competes for the degradation of GR protein by the ubiquitin-proteasome system and should thus increase its intracellular levels by "stabilizing" the GR. We also designed a fusion peptide for the c-Myb DNA binding domain, Tat-c-Myb DBD, since the biological function of this peptide as a dominant negative inhibitor of the c-Myb protein was already known. Purified, bacterially expressed Tat-c-Myb DBD and Tat-GR(554-777) exhibited highly efficient transduction into cultured ALL cell lines including 697 (pre-B-ALL) and CEM-C7 (T-ALL) cells. As expected, the transduced Tat-c-Myb DBD peptide inhibited steroid-mediated stimulation of a GR promoter-luciferase reporter gene. Significantly, transduced Tat-GR(554-777) effectively increased intracellular GR levels in the GC-resistant T-ALL cell line, CEM-C1, and in the pre-B-ALL 697 cell line. Furthermore, transduction of Tat-GR(554-777) rendered GC-resistant CEM-C1 cells sensitive to steroid killing and further sensitized 697 cells to steroid. The use of Tat-fusion peptide transduction may eventually lead to innovative therapeutic modalities to improve the clinical response of patients suffering from T-cell and pre-B-cell acute lymphoblastic leukemia by increasing steroid responsiveness and perhaps converting steroid-resistant leukemia to a hormone-responsive phenotype.

Paired hormone response elements predict caveolin-1 as a glucocorticoid target gene

Glucocorticoids act in part via glucocortocoid receptor binding to hormone response elements (HREs), but their direct target genes in vivo are still largely unknown. We developed the criterion that genomic occurrence of paired HREs at an inter-HRE distance less than 200 bp predicts hormone responsiveness, based on synergy of multiple HREs, and HRE information from known target genes. This criterion predicts a substantial number of novel responsive genes, when applied to genomic regions 10 kb upstream of genes. Multiple-tissue in situ hybridization showed that mRNA expression of 6 out of 10 selected genes was induced in a tissue-specific manner in mice treated with a single dose of corticosterone, with the spleen being the most responsive organ. Caveolin-1 was strongly responsive in several organs, and the HRE pair in its upstream region showed increased occupancy by glucocorticoid receptor in response to corticosterone. Our approach allowed for discovery of novel tissue specific glucocorticoid target genes, which may exemplify responses underlying the permissive actions of glucocorticoids.

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.

Crosstalk in inflammation: the interplay of glucocorticoid receptor-based mechanisms and kinases and phosphatases

Glucocorticoids (GCs) are steroidal ligands for the GC receptor (GR), which can function as a ligand-activated transcription factor. These steroidal ligands and derivatives thereof are the first line of treatment in a vast array of inflammatory diseases. However, due to the general surge of side effects associated with long-term use of GCs and the potential problem of GC resistance in some patients, the scientific world continues to search for a better understanding of the GC-mediated antiinflammatory mechanisms. The reversible phosphomodification of various mediators in the inflammatory process plays a key role in modulating and fine-tuning the sensitivity, longevity, and intensity of the inflammatory response. As such, the antiinflammatory GCs can modulate the activity and/or expression of various kinases and phosphatases, thus affecting the signaling efficacy toward the propagation of proinflammatory gene expression and proinflammatory gene mRNA stability. Conversely, phosphorylation of GR can affect GR ligand- and DNA-binding affinity, mobility, and cofactor recruitment, culminating in altered transactivation and transrepression capabilities of GR, and consequently leading to a modified antiinflammatory potential. Recently, new roles for kinases and phosphatases have been described in GR-based antiinflammatory mechanisms. Moreover, kinase inhibitors have become increasingly important as antiinflammatory tools, not only for research but also for therapeutic purposes. In light of these developments, we aim to illuminate the integrated interplay between GR signaling and its correlating kinases and phosphatases in the context of the clinically important combat of inflammation, giving attention to implications on GC-mediated side effects and therapy resistance.

Activation of CD44 facilitates DNA repair in T-cell lymphoma but has differential effects on apoptosis induced by chemotherapeutic agents and ionizing radiation

Expression of CD44s (standard form) in malignant lymphoma is a poor indicator of survival. To investigate whether activation of CD44s can protect from cell death, this study compared the extent of apoptosis induced by chemotherapeutic agents and ionizing radiation (IR) on T-lymphoma cell lines in the presence or absence of adherent hyaluronan and monoclonal antibodies (MoAbs). Growth in the presence of adherent ligands enhanced apoptosis induced by dexamethasone (Dex), but protected cells from epirubicin-induced apoptosis. In IR-induced apoptosis, mouse lymphoma cells had resistance against apoptosis when treated with hyaluronan (HA), although acute cell death reached the same plateau regardless of treatment with adherent MoAbs in human lymphoma cell line. However, the post-irradiated repopulation of lymphoma cells was strikingly accelerated in those treated with CD44 adherent ligands. This repopulation process correlated with the remarkable upregulation of proliferating cell nuclear antigen (PCNA), which is a protein involved in DNA repair. Unscheduled DNA synthesis (UDS), a measure of DNA repair, was consistently enhanced in CD44s-stimulated cells after exposure to radiation. The results suggest that the poor prognostic indication of CD44 expression is more a consequence of enhanced DNA repair following genotoxic damage than of direct resistance to apoptosis.

Prednisolone exerts late mitogenic and biphasic effects on resistant acute lymphoblastic leukemia cells: Relation to early gene expression

Resistance or sensitivity to glucocorticoids is considered to be of crucial importance for disease prognosis in childhood acute lymphoblastic leukemia. Prednisolone exerted a delayed biphasic effect on the resistant CCRF-CEM leukemic cell line, necrotic at low doses and apoptotic at higher doses. At low doses, prednisolone exerted a pre-dominant mitogenic effect despite its induction on total cell death, while at higher doses, prednisolone's mitogenic and cell death effects were counterbalanced. Early gene microarray analysis revealed notable differences in 40 genes. The mitogenic/biphasic effects of prednisolone are of clinical importance in the case of resistant leukemic cells. This approach might lead to the identification of gene candidates for future molecular drug targets in combination therapy with glucocorticoids, along with early markers for glucocorticoid resistance.

Glucocorticoid resistance in T-lineage acute lymphoblastic leukaemia is associated with a proliferative metabolism

Glucocorticoids (GCs) are among the most important drugs for acute lymphoblastic leukaemia (ALL), yet despite their clinical importance, the exact mechanisms involved in GC cytotoxicity and the development of resistance remain uncertain. We examined the baseline profile of a panel of T-ALL cell lines to determine factors that contribute to GC resistance without prior drug selection. Transcriptional profiling indicated GC resistance in T-ALL is associated with a proliferative phenotype involving upregulation of glycolysis, oxidative phosphorylation, cholesterol biosynthesis and glutamate metabolism, increased growth rates and activation of PI3K/AKT/mTOR and MYC signalling pathways. Importantly, the presence of these transcriptional signatures in primary ALL specimens significantly predicted patient outcome. We conclude that in lymphocytes the activation of bioenergetic pathways required for proliferation may suppress the apoptotic potential and offset the metabolic crisis initiated by GC signalling. It is likely that the link between GC resistance and proliferation in T-ALL has not been fully appreciated to date because such effects would be masked in the context of current multiagent therapies. The data also provide the first evidence that altered expression of wild-type MLL may contribute to GC-resistant phenotypes. Our findings warrant the continued development of selective metabolic inhibitors for the treatment of ALL.

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.

Converting cell lines representing hematological malignancies from glucocorticoid-resistant to glucocorticoid-sensitive: signaling pathway interactions

Mitogen-activated protein kinases (MAPKs), protein kinase A (PKA) and mTOR pathways modulate the apoptotic effects of glucocorticoids (GCs) in human lymphoblastic leukemia CEM cells. We now show that manipulation of these pathways converts several cell lines, representing other lymphoid malignancies, from GC-resistant to GC-sensitive. Basal levels of phosphorylated JNK and ERK were elevated in the GC-resistant cells. Treatments that directly or indirectly reduced phosphorylated JNK and ERK resulted in Dex sensitivity in five resistant lymphoid cell lines. Sensitivity to GC-driven apoptosis correlated with GC-dependent increases in phosphorylated and total glucocorticoid receptor, and in increased levels of the pro-apoptotic protein Bim.

Apoptosis inhibition by Bcl-2 gives way to autophagy in glucocorticoid-treated lymphocytes

Glucocorticosteroid hormones, including prednisone and dexamethasone (Dex), have been used to treat lymphoid malignancies for many years because they readily induce apoptosis in immature lymphocytes lacking Bcl-2. However, elevated expression of the anti-apoptotic protein Bcl-2 inhibits apoptosis and contributes to glucocorticoid resistance. Using the Bcl-2-negative WEHI7.2 lymphoma line as an experimental model, we found that Dex not only induces apoptosis but also induces autophagy. The caspase inhibitor Z-VAD-fmk inhibited apoptosis but not autophagy in Dex-treated cells. Bcl-2 overexpression inhibited Dex-induced apoptosis even more potently than Z-VAD-fmk and, contrary to previous reports, Bcl-2 neither interacted with Beclin-1 nor inhibited autophagy. Rather, Bcl-2 overexpression facilitated detection of Dex-induced autophagy by both steady state methods and flux measurements, ostensibly due to apoptosis inhibition. Autophagy contributed to prolonged survival of Bcl-2-positive lymphoma cells following Dex treatment, as survival was reduced when autophagy was inhibited by 3-methyladenine. These findings emphasize the important interplay between apoptosis and autophagy and suggest a novel mechanism by which Bcl-2, which is frequently elevated in lymphoid malignancies, contributes to glucocorticoid resistance and survival of lymphoma cells.

Dexamethasone-induced inositol 1,4,5-trisphosphate receptor elevation in murine lymphoma cells is not required for dexamethasone-mediated calcium elevation and apoptosis

Glucocorticosteroid hormones, including dexamethasone, have diverse effects on immature lymphocyte function that ultimately lead to cell death. Previous studies established that glucocorticoid-induced alterations in intracellular calcium homeostasis promote apoptosis, but the mechanism by which glucocorticoids disrupt calcium homeostasis is unknown. Through gene expression array analysis, we found that dexamethasone induces a striking elevation of inositol 1,4,5-trisphosphate receptor (IP(3)R) levels in two murine lymphoma cell lines, WEHI7.2 and S49.A2. IP(3)R elevation was confirmed at both mRNA and protein levels. However, there was not a strong correlation between IP(3)R elevation and altered calcium homeostasis in terms of either kinetics or dose response. Moreover, IP(3)R knockdown, by either antisense or small interfering RNA, did not prevent either calcium disruption or apoptosis. Finally, DT40 lymphoma cells lacking all three IP(3)R isoforms were just as sensitive to dexamethasone-induced apoptosis as wild-type DT40 cells expressing all three IP(3)R isoforms. Thus, although alterations in intracellular calcium homeostasis contribute to glucocorticoid-induced apoptosis, these calcium alterations are not directly attributable to IP(3)R elevation.

Glucocorticoids and the innate immune system: crosstalk with the toll-like receptor signaling network

Toll-like receptors (TLRs) are responsible for the recognition of a variety of microbial pathogens and the initial induction of immune and inflammatory responses. These responses are normally restricted by the adrenally produced glucocorticoid hormones which provide a feedback mechanism to curb unabated inflammation. Glucocorticoids act through a ligand-dependent transcription factor-the glucocorticoid receptor (GR), which engages in a complex network of protein:protein and protein:DNA interactions ultimately activating or repressing target gene transcription. Not surprisingly, multiple mechanisms account for the glucocorticoid interference with TLR signaling including enhanced expression of the natural inhibitors of TLR pathways, direct repression of TLR-activated transcriptional regulators and cross-utilization of cofactors essential for both GR and TLR signaling. Here we discuss recent and unexpected examples of crosstalk between the two transcriptional networks and the emerging role of GR in the regulation of innate immunity.

Regulation of differential pro- and anti-apoptotic signaling by glucocorticoids

More than a quarter of a century ago, the phenomenon of glucocorticoid-induced apoptosis in the majority of hematological cells was first recognized. More recently, glucocorticoid-induced antiapoptotic signaling associated with apoptosis resistance has been identified in cells of epithelial origin, most of malignant solid tumors and some other tissues. Despite these huge amount of data demonstrating differential pro- and anti-apoptotic effects of glucocorticoids, the underlying mechanisms of cell type specific glucocorticoid signaling are just beginning to be described. This review summarizes our present understanding of cell type-specific pro- and anti-apoptotic signaling induced by glucocorticoids. In the first section we give a summary and update of known glucocorticoid-induced pathways mediating apoptosis in hematological cells. We shortly introduce mechanisms of glucocorticoid resistance of hematological cells. We highlight and discuss the emerging molecular evidence of a general induction of survival signaling in epithelial cells and carcinoma cells by glucocorticoids. We provide a model for glucocorticoid-induced resistance in cells growing in a tissue formation. Thus, attachment to the extracellular matrix and cell-cell contacts typical for e.g. epithelial and tumor cells may be crucially involved in switching the balance of several interacting pathways to survival upon treatment with glucocorticoids.

Gene expression shift towards normal B cells, decreased proliferative capacity and distinct surface receptors characterize leukemic blasts persisting during induction therapy in childhood acute lymphoblastic leukemia

In childhood acute lymphoblastic leukemia (ALL), persistence of leukemic blasts during therapy is of crucial prognostic significance. In the present study, we address molecular and cell biologic features of blasts persisting after 1 week of induction glucocorticoid therapy. Genome-wide gene expression analysis of leukemic samples from precursor B-cell ALL patients (n=18) identified a set of genes differentially expressed in blasts at diagnosis day 0 (d0) and persisting on day 8 (d8). Expression changes indicate a shift towards mature B cells, inhibition of cell cycling and increased expression of adhesion (CD11b/ITGAM) and cytokine (CD119/IFNGR1) receptors. A direct comparison with normal B cells, which are largely therapy resistant, confirmed the differentiation shift at the mRNA (n=10) and protein (n=109) levels. Flow cytometric analysis in independent cohorts of patients confirmed both a decreased proliferative activity (n=13) and the upregulation of CD11b and CD119 (n=29) in d8 blasts. The differentiation shift and low proliferative activity in d8 blasts may account for the persistence of blasts during therapy and affect their sensitivity to further therapeutic treatment. CD11b and CD119 are potential specific markers for d8 blast persistence and detection of minimal residual disease, which warrant further investigation.

Genomewide identification of prednisolone-responsive genes in acute lymphoblastic leukemia cells

Glucocorticoids are keystone drugs in the treatment of childhood acute lymphoblastic leukemia (ALL). To get more insight in signal transduction pathways involved in glucocorticoid-induced apoptosis, Affymetrix U133A GeneChips were used to identify transcriptionally regulated genes on 3 and 8 hours of prednisolone exposure in leukemic cells of 13 children as compared with nonexposed cells. Following 3 hours of exposure no significant changes in gene expression could be identified. Following 8 hours of exposure, 51 genes were differentially expressed (P < .001 and false discovery rate < 10%) with 39 genes being up-regulated (median, 2.4-fold) and 12 genes were down-regulated (median, 1.7-fold). Twenty-one of those genes have not been identified before to be transcriptionally regulated by prednisolone. Two of the 3 most highly up-regulated genes were tumor suppressor genes, that is, thioredoxin-interacting protein (TXNIP; 3.7-fold) and zinc finger and BTB domain containing 16 (ZBTB16; 8.8-fold). About 50% of the differentially expressed genes were functionally categorized in 3 major routes, namely MAPK pathways (9 genes), NF-kappaB signaling (11 genes), and carbohydrate metabolism (5 genes). Biologic characterization of these genes and pathways might elucidate the action of glucocorticoids in ALL cells, possibly suggesting causes of glucocorticoid resistance and new potential targets for therapy.

Tissue specific glucocorticoid receptor expression, a role for alternative first exon usage?

The CpG island upstream of the GR is highly structured and conserved at least in all the animal species that have been investigated. Sequence alignment of these CpG islands shows inter-species homology ranging from 64 to 99%. This 3.1kb CpG rich region upstream of the GR exon 2 encodes 5' untranslated mRNA regions. These CpG rich regions are organised into multiple first exons and, as we and others have postulated, each with its own promoter region. Alternative mRNA transcript variants are obtained by the splicing of these alternative first exons to a common acceptor site in the second exon of the GR. Exon 2 contains an in-frame stop codon immediately upstream of the ATG start codon to ensure that this 5' heterogeneity remains untranslated, and that the sequence and structure of the GR is unaffected. Tissue specific differential usage of exon 1s has been observed in a range of human tissues, and to a lesser extent in the rat and mouse. The GR expression level is tightly controlled within each tissue or cell type at baseline and upon stimulation. We suggest that no single promoter region may be capable of containing all the necessary promoter elements and yet preserve the necessary proximity to the transcription initiation site to produce such a plethora of responses. Thus we further suggest that alternative first exons each under the control of specific transcription factors control both the tissue specific GR expression and are involved in the tissue specific GR transcriptional response to stimulation. Spreading the necessary promoter elements over multiple promoter regions, each with an associated alternative transcription initiation site would appear to vastly increase the capacity for transcriptional control of GR.

Glucocorticoid-induced glucocorticoid-receptor expression and promoter usage is not linked to glucocorticoid resistance in childhood ALL

Glucocorticoid (GC) resistance is an adverse prognostic factor in childhood acute lymphoblastic leukemia (ALL), but little is known about causes of GC resistance. Up-regulation of the glucocorticoid receptor (GR) has been suggested as an essential step to the induction of apoptosis in leukemic cells. In this study we investigated whether baseline mRNA expression levels of the 5 different GR promoter transcripts (1A1, 1A2, 1A3, 1B, and 1C) or differences in the degree of regulation of the GR or GR promoter transcripts upon GC exposure are related to GC resistance. Therefore, mRNA levels of the 5 GR promoter transcripts and of the GR were measured by quantitative real-time reverse transcriptase–polymerase chain reaction (RT-PCR; Taqman) technology in primary ALL cells prior to and after 3, 8, and 24 hours of prednisolone exposure. GR expression is induced upon GC exposure in primary ALL patient samples, which is opposite to what is found in tissues in which GCs do not induce apoptosis. GC resistance in childhood ALL cannot be attributed to an inability of resistant cells to up-regulate the expression of the GR upon GC exposure, nor to differences in GR promoter usage (at baseline and upon GC exposure).

Understanding stress through the genome

Stress-induced glucocorticoid hormones support coping with and adaptation to different stressors. They act to modulate gene expression in a tissue and stressor-specific manner through activation of corticosteroid receptors, which act as transcription factors. Here, a number of recent insights in gene regulation under the influence of glucocorticoids are discussed. Emphasis is put on distinct classes of target genes that may be defined, based on categorization of (combinations of) transcription factor binding sites in responsive genes. These categories depend on insights into different mechanisms of transcriptional regulation, such as transactivation vs transrepression, and high affinity vs low affinity hormone receptor response elements. It is argued that such classes, based on mechanistic understanding of transcription regulation, in combination with the availability of complete genomic sequences and expression data from different organs, may enhance our understanding of the way in which organisms deal with different forms of stress.

Glucocorticoid receptor isoforms generate transcription specificity

Glucocorticoids are necessary for life and are essential in all aspects of health and disease as they regulate processes from mitosis to apoptosis, from metabolism to growth and development. However, responses to glucocorticoids vary among individuals, cells and tissues. Recent evidence indicates that multiple glucocorticoid receptor (GR) isoforms are generated from one single GR gene by alternative splicing and alternative translation initiation. These isoforms all have unique tissue distribution patterns and transcriptional regulatory profiles. Furthermore, each is subject to various post-translational modifications that affect receptor function. Thus, increasing evidence suggests that unique GR isoform compositions within cells could determine the cell-specific response to glucocorticoids. Here, we discuss a new molecular model potentially underlying tissue-specific glucocorticoid resistance and selectivity.

Glucocorticoids engage different signal transduction pathways to induce apoptosis in thymocytes and mature T cells

Glucocorticoids (GC) induce apoptosis in a variety of cells, but their exact mode of action is controversial. Although initiation relies on the GC receptor (GR) and de novo gene expression, the effector phase differs among cell types. Proteasomal degradation as well as caspase-3, - 8, and -9 activity are essential for GC-induced apoptosis in murine thymocytes, but the same enzymes are dispensable in splenic T cells. Live imaging by confocal microscopy revealed that lysosomal cathepsin B, an unrecognized component of this pathway to date, becomes rapidly activated in thymocytes after GC exposure. This is followed by leakage of cathepsin B into the cytosol, nuclear condensation, and processing of caspase-8 and -3. According to our model, activation of caspase-3 by caspase-9 in thymocytes occurs both directly as well as indirectly via a lysosomal amplification loop. Interestingly, acute T lymphoblastic leukemia cells depend on caspase activity to undergo GC-induced cell death similar to thymocytes. Collectively, the apoptotic program induced by GCs comprises cell type-specific as well as common features.

Glucocorticoids in T cell apoptosis and function

Glucocorticoids (GCs) are a class of steroid hormones which regulate a variety of essential biological functions. The profound anti-inflammatory and immunosuppressive activity of synthetic GCs, combined with their power to induce lymphocyte apoptosis place them among the most commonly prescribed drugs worldwide. Endogenous GCs also exert a wide range of immunomodulatory activities, including the control of T cell homeostasis. Most, if not all of these effects are mediated through the glucocorticoid receptor, a member of the nuclear receptor superfamily. However, the signaling pathways and their cell type specificity remain poorly defined. In this review, we summarize our present knowledge on GC action, the mechanisms employed to induce apoptosis and the currently discussed models of how they may participate in thymocyte development. Although our knowledge in this field has substantially increased during recent years, we are still far from a comprehensive picture of the role that GCs play in T lymphocytes.

Identification of glucocorticoid-response genes in children with acute lymphoblastic leukemia

The ability of glucocorticoids (GCs) to kill lymphoid cells led to their inclusion in essentially all chemotherapy protocols for lymphoid malignancies, particularly childhood acute lymphoblastic leukemia (ALL). GCs mediate apoptosis via their cognate receptor and subsequent alterations in gene expression. Previous investigations, including expression profiling studies with subgenome microarrays in model systems, have led to a number of attractive, but conflicting, hypotheses that have never been tested in a clinical setting. Here, we present a comparative whole-genome expression profiling approach using lymphoblasts (purified at 3 time points) from 13 GC-sensitive children undergoing therapy for ALL. For comparisons, expression profiles were generated from an adult patient with ALL, peripheral blood lymphocytes from GC-exposed healthy donors, GC-sensitive and -resistant ALL cell lines, and mouse thymocytes treated with GCs in vivo and in vitro. This generated an essentially complete list of GC-regulated candidate genes in clinical settings and experimental systems, allowing immediate analysis of any gene for its potential significance to GC-induced apoptosis. Our analysis argued against most of the model-based hypotheses and instead identified a small number of novel candidate genes, including PFKFB2, a key regulator of glucose metabolism; ZBTB16, a putative transcription factor; and SNF1LK, a protein kinase implicated in cell-cycle regulation.

BH3-only proteins Puma and Bim are rate-limiting for gamma-radiation- and glucocorticoid-induced apoptosis of lymphoid cells in vivo

Numerous p53 target genes have been implicated in DNA damage-induced apoptosis signaling, but proapoptotic Bcl-2 (B-cell leukemia 2) family members of the BH3 (Bcl-2 homolog region [BH] 3)-only subgroup appear to play the critical initiating role. In various types of cultured cells, 3 BH3-only proteins, namely Puma (p53 up-regulated modulator of apoptosis), Noxa, and Bim (Bcl-2 interacting mediator of cell death), have been shown to initiate p53-dependent as well as p53-independent apoptosis in response to DNA damage and treatment with anticancer drugs or glucocorticoids. In particular, the absence of Puma or Bim renders thymocytes and mature lymphocytes refractory to varying degrees to death induced in vitro by growth factor withdrawal, DNA damage, or glucocorticoids. To assess the in vivo relevance of these findings, we subjected mice lacking Puma, Noxa, or Bim to whole-body gamma-radiation or the glucocorticoid dexamethasone and compared lymphocyte survival with that in wild-type and BCL2-transgenic mice. Absence of Puma or Bcl-2 overexpression efficiently protected diverse types of lymphocytes from the effects of gamma-radiation in vivo, and loss of Bim provided lower but significant protection in most lymphocytes, whereas Noxa deficiency had no impact. Furthermore, both Puma and Bim were found to contribute significantly to glucocorticoid-induced killing. Our results thus establish that Puma and Bim are key initiators of gamma-radiation- and glucocorticoid-induced apoptosis in lymphoid cells in vivo.

Pathophysiological effects of glucocorticoids on nasal polyps: an update

PURPOSE OF REVIEW

The exact mechanisms by which glucocorticoids exert their beneficial effects on nasal polyps are not clearly defined. Nasal polyps, asthma and allergic rhinitis share common features such as mucosal infiltration with eosinophils and mast cells as well as local IgE production. The present review is an update on the pathophysiological mechanisms of glucocorticoids on nasal polyps described during the last 2 years.

RECENT FINDINGS

The reduction of leukocyte numbers in nasal polyps following glucocorticoid treatment depends on several mechanisms, for example altered balance between the two isoforms of the human glucocorticoid receptors, GRalpha and GRbeta. Another explanation may be inhibition of CD4+ T by CD8+ T cells. Increased expression of the antiinflammatory cytokine transforming growth factor beta may contribute to this. A DNA microarray study which examined the expression of some 22 000 genes showed increased expression of several antiinflammatory genes in nasal polyps after treatment with glucocorticoids. The antiinflammatory gene that increased most was uteroglobin (also known as Clara cell protein 16) which is abundantly expressed in airway secretions and thought to have an important role in regulating inflammation.

SUMMARY

Glucocorticoids affect both pro and antiinflammatory pathways in nasal polyps. Upregulation of antiinflammatory genes such as transforming growth factor beta and uteroglobin may play an important role. Elucidation of these mechanisms may help us to understand not only the effects of glucocorticoids on nasal polyps, but also on related disorders such as allergic rhinitis and asthma.

Molecular mechanisms of glucocorticoids in the control of inflammation and lymphocyte apoptosis

The immune system must be tightly controlled not only to guarantee efficient protection from invading pathogens and oncogenic cells but also to avoid exaggerated immune responses and autoimmunity. This is achieved through interactions amongst leukocytes themselves, by signals from stromal cells and also by various hormones, including glucocorticoids. The glucocorticoids are a class of steroid hormones that exert a wide range of anti-inflammatory and immunosuppressive activities after binding to the glucocorticoid receptor. The power of these hormones was acknowledged many decades ago, and today synthetic derivatives are widely used in the treatment of inflammatory disorders, autoimmunity and cancer. In this review, we summarize our present knowledge of the molecular mechanisms of glucocorticoid action, their influence on specific leukocytes and the induction of thymocyte apoptosis, with an emphasis on how molecular genetics has contributed to our growing, although still incomplete, understanding of these processes.

Glucocorticoid receptor heterozygosity combined with lack of receptor auto-induction causes glucocorticoid resistance in Jurkat acute lymphoblastic leukemia cells

Glucocorticoids (GC) induce apoptosis in malignant lymphoblasts, but the mechanism of this process as well as that of the clinically important GC resistance is unknown. We investigated GC resistance in Jurkat T-ALL cells in which ectopic GC receptor (GR) restores GC sensitivity, suggesting deficient GR expression. Jurkat cells expressed one wild-type and one mutated (R477H) GR allele. GR(R477H) ligand-binding-dependent nuclear import, as revealed by live-cell microscopy of YFP-tagged GR, was unaffected. Transactivation and transrepression were markedly impaired; however, GR(R477H) did not act in a dominant-negative manner, that is, did not prevent cell death, when introduced into a GC-sensitive cell line by retroviral gene transfer. Contrary to another GR heterozygous, but GC-sensitive, T-ALL model (CCRF-CEM), Jurkats expressed lower basal GR levels and did not auto-induce their GR, as revealed by 'real-time' RT-PCR and immunoblotting. Absent GR auto-induction could not be restored by transgenic GR and, hence, was not caused by reduced basal GR levels. Thus, inactivation of one GR gene results in haploinsufficiency if associated with lack of GR auto-induction.

Glucocorticoid-induced apoptosis and glucocorticoid resistance: molecular mechanisms and clinical relevance

The ability of glucocorticoids (GC) to efficiently kill lymphoid cells has led to their inclusion in essentially all chemotherapy protocols for lymphoid malignancies. This review summarizes recent findings related to the molecular basis of GC-induced apoptosis and GC resistance, and discusses their potential clinical implications. Accumulating evidence suggests that GC may induce cell death via different pathways resulting in apoptotic or necrotic morphologies, depending on the availability/responsiveness of the apoptotic machinery. The former might result from regulation of typical apoptosis genes such as members of the Bcl-2 family, the latter from detrimental GC effects on essential cellular functions possibly perpetuated by GC receptor (GR) autoinduction. Although other possibilities exist, GC resistance might frequently result from defective GR expression, perhaps the most efficient means to target multiple antileukemic GC effects. Numerous novel drug combinations are currently being tested to prevent resistance and improve GC efficacy in the therapy of lymphoid malignancies.

Early lymphoid progenitors in mouse and man are highly sensitive to glucocorticoids

Glucocorticoids are extensively used in anti-inflammatory therapy and may contribute to the normal regulation of lymphopoiesis. This study utilized new information about the early stages of lymphopoiesis in mouse and man to determine precisely which cell types are hormone sensitive. Cycling B lineage precursors were depleted in dexamethasone-treated mice, while mature, non-dividing CD45R(Hi) CD19(Hi) lymphocytes, myeloid progenitors and stem cells with the potential for lymphocyte generation on transplantation were spared. Lineage marker-negative (Lin(-)) IL-7R(+) Flk-2(+) pro-lymphocytes also declined, but not as rapidly as the terminal deoxynucleotidyl transferase-positive cells within an early Lin(-) c-kit(Hi) Sca-1(Hi) fraction of bone marrow. Hormone-sensitive cells with additional properties of early lymphoid progenitors (ELP) were identified within the same Lin(-) c-kit(Hi) Sca-1(Hi) subset using human mu transgenic mice and recombination-activating gene 1 (RAG1)/green fluorescent protein knock-in animals. Furthermore, cells with a recent history of RAG1 expression were more glucocorticoid sensitive than mature lymphocytes in marrow and spleen. Lymphocyte progenitors in mice bearing a human bcl-2 transgene were protected from dexamethasone treatment. However, isolated progenitors from either wild-type or bcl-2 transgenic mice were directly sensitive to the hormone in stromal cell-free cultures, suggesting that additional factors must determine vulnerability to glucocorticoids. B lineage lymphocyte precursors were found to be abnormally elevated in the bone marrow of adrenalectomized or RU486-treated mice. This suggests that glucocorticoids may normally contribute to steady-state regulation of lymphopoiesis. Finally, parallel studies revealed that the earliest events in human lymphopoiesis are susceptible to injury during glucocorticoid therapy.

Glucocorticoid-induced apoptosis and glucocorticoid resistance in acute lymphoblastic leukemia

Glucocorticoids (GC) induce cell cycle arrest and apoptosis in lymphoid cells, and therefore constitute a central component in the treatment of lymphoid malignancies, particularly childhood acute lymphoblastic leukemia (ALL). In spite of its clinical significance and considerable efforts in many laboratories, however, the molecular basis of GC-induced apoptosis and the clinically important resistance phenomenon remains poorly defined. The anti-leukemic GC effects are critically dependent upon sufficient expression of the GC receptor (GR) throughout the response. In ALL cell lines, this is associated with, and may depend upon, GR autoinduction. In corresponding in vitro models, GC resistance frequently results from mutations in the GR gene and/or deficient regulation of its expression. The downstream components of the pathway, i.e., the GC-regulated genes responsible for cell death induction, have been studied by microarray-based comparative expression profiling, resulting in identification of a considerable number of GC-regulated candidate genes. Their possible function in the death response is, however, still undefined. One model predicts direct regulation of the apoptotic machinery, e.g., components of the "Bcl-2 rheostat", while a complementary hypothesis suggests deleterious GC effects on essential cellular functions, such as metabolism, production of and/or response to oxygen radicals, general transcription/translation, pH and volume control, etc. These regulatory effects may entail cell death, particularly if maintained for sufficient time through GR autoinduction. The latter form of cell death may occur even in the absence of functional apoptotic machinery (e.g., when caspases are blocked), but in this case appears to entail a more necrotic morphology. Taken together, GC may induce different types of cell death through distinct molecular pathways, depending on the cellular context. GC resistance might frequently result from defective GR expression, perhaps the most efficient means to target multiple antileukemic pathways.

Identification of novel direct transcriptional targets of glucocorticoid receptor

Transcription of the genes Granzyme A (GZMA), FK506 binding protein 51 (FKBP5), and Down syndrome critical region gene 1 (DSCR1) is upregulated in leukemic cells upon treatment with glucocorticoids (GCs). Several lines of evidence suggest that these genes are implicated in GC-induced apoptosis upstream of the Bcl-2 family of proteins. These genes were upregulated by GC even in the presence of an inhibitor of protein synthesis, cycloheximide, indicating that they are direct target genes of glucocorticoid receptors. DSCR1 is reported to have four isoforms, each of which has a distinct first exon, E1-E4. Among these isoforms, the one with E1 was selectively upregulated by GC. GZMA and FKBP5 have a cluster of putative glucocorticoid response elements (GREs) in introns 1 and 2, respectively, that was identified to be responsible for the response to GC. They were composed of one complete (A/T)G(A/T)(A/T)C(A/T) sequence surrounded by two incomplete (A/T)G(A/T)(A/T)C(A/T) sequences separated by one to four nucleotides. DSCR1, however, did not have a functional GRE upstream or downstream of exon 1. These studies may lead to improved therapeutic uses of GCs in leukemia and lymphoma based upon the expression of these GC target genes.

Overexpression of catalase or Bcl-2 alters glucose and energy metabolism concomitant with dexamethasone resistance

Glucocorticoids induce apoptosis in lymphocytes by causing the release of cytochrome c into the cytosol; however, the events in the signaling phase between translocation of the steroid-receptor complex to the nucleus and the release of cytochrome c have not been elucidated. Previously, we found that, in response to steroid treatment, WEHI7.2 mouse thymic lymphoma cells overexpressing catalase (CAT38) show delayed apoptosis (delayed cytochrome c release) compared to the parental cells, while Bcl-2 overexpressing cells (Hb12) are protected from steroid-induced apoptosis. In lymphocytes, glucocorticoid treatment decreases glucose uptake. Both glucose deprivation and the attendant ATP drop are known inducers of apoptosis. Therefore, we used (31)P and (1)H NMR spectroscopy to compare metabolic profiles of WEHI7.2, CAT38 and Hb12 cells in the presence and absence of dexamethasone to determine: (1) whether glucocorticoid effects on glucose metabolism contribute to the mechanism of steroid-induced apoptosis; and (2) whether catalase or Bcl-2 overexpression altered metabolism thereby providing a mechanism of steroid resistance. Loss of mitochondrial hexokinase activity was correlated to the induction of apoptosis in WEHI7.2 and CAT38 cells. CAT38 and Hb12 cells have an altered basal metabolism which includes increases in hexokinase activity, lactate production when subcultured into new medium, use of mitochondria for ATP production and potentially increased glutaminolysis. These data suggest that: (1) glucocorticoid effects on glucose metabolism may contribute to the mechanism of steroid-induced lymphocyte apoptosis; and (2) the altered metabolism seen in catalase and Bcl-2 overexpressing cells may contribute to both the steroid resistance and increased tumorigenicity of these variants.

Identification of genes leading to glucocorticoid-induced leukemic cell death

Glucocorticoidal steroids (GC) are capable of causing apoptotic death of many varieties of lymphoid cells; consequently, GC are used in therapy for many lymphoid malignancies. Gene transcription in the GC-treated cells is required for subsequent apoptosis, but only a few of the actual genes involved have been identified. We employed gene microarray analysis to find the network of genes involved in GC-evoked cell death, using three clones derived from the CEM lymphoid leukemia cell line. Clone C1-15 was resistant to GC-evoked apoptosis, although not necessarily to GC-induced gene transcription; the other two underwent apoptosis in the presence of GC. Clone C7-14 was subcloned from the apoptosis-sensitive parental C7 clone to establish karyotypic uniformity. The second sensitive clone, C1-6, was a spontaneous revertant from parental resistant clone C1. A period of > or = 24 h in the constant presence of receptor-occupying concentrations of synthetic GC dexamethasone (Dex) was necessary for apoptosis to begin. To identify the steps leading to this dramatic event, we identified the changes in gene expression in the 20-h period preceding the onset of overt apoptosis. Cells in the log phase of growth were treated with 10(-6) M Dex, and 2-20 h later, mRNA was prepared and analyzed using the Affymetrix HG_U95Av2 chip, containing probes for about 12,600 genes. Of these, approximately 6,000 were expressed above background. Comparisons of the basal and expressed genes in the three clones led to several conclusions: The Dex-sensitive clones shared the regulation of a limited set of genes. The apoptosis-resistant clone C1-15 showed Dex effects on a largely different set of genes. Promoter analysis of the regulated genes suggested that primary gene targets for GC often lack a classic GC response element.

Cyclin D3 and c-MYC control glucocorticoid-induced cell cycle arrest but not apoptosis in lymphoblastic leukemia cells

Glucocorticoids (GC) induce cell cycle arrest and apoptosis in lymphoblastic leukemia cells. To investigate cell cycle effects of GC in the absence of obscuring apoptotic events, we used human CCRF-CEM leukemia cells protected from cell death by transgenic bcl-2. GC treatment arrested these cells in the G1 phase of the cell cycle due to repression of cyclin D3 and c-myc. Cyclin E and Cdk2 protein levels remained high, but the kinase complex was inactive due to increased levels of bound p27(Kip1). Conditional expression of cyclin D3 and/or c-myc was sufficient to prevent GC-induced G1 arrest and p27(Kip1) accumulation but, importantly, did not interfere with the induction of apoptosis. The combined data suggest that repression of both, c-myc and cyclin D3, is necessary to arrest human leukemia cells in the G1 phase of the cell division cycle, but that neither one is required for GC-induced apoptosis.