Transcriptional cross-talk, the second mode of steroid hormone receptor action

The activated glucocorticoid receptor inhibits the transcription factor T-bet by direct protein-protein interaction

Glucocorticoids (GCs) immunosuppression acts via regulation of several transcription factors (TF), including activating protein (AP)-1, NF-kappaB, and NFAT. GCs inhibit Th1 cytokines and promote a shift toward Th2 differentiation. Th1 phenotype depends on TF T-bet. In this study, we examined GC regulation of T-bet. We found that GCs inhibit T-bet transcriptional activity. We show that glucocorticoid receptor (GR) physically interacts with T-bet both in transfected cell lines and in primary splenocyte cultures with endogenous GR and T-bet. This interaction also blocks GR-dependent transcription. We show both in vitro and in vivo at endogenous binding sites that the mechanism underlying T-bet inhibition further involves reduction of T-bet binding to DNA. Using specific mutations of GR, we demonstrate that the first zinc finger region of GR is required for T-bet inhibition. GCs additionally inhibit T-bet both at mRNA and protein expression levels, revealing another layer of GR action on T-bet. Finally, we examined the functional consequences of GR/T-bet interaction on IFN-gamma, showing that GCs inhibit transcriptional activity of T-bet on its promoter. In view of the crucial role of T-bet in T cell differentiation and inflammation, we propose that GR inhibitory interaction with T-bet may be an important mechanism underlying the immunosuppressive properties of GCs.

MUC1 gene overexpressed in breast cancer: structure and transcriptional activity of the MUC1 promoter and role of estrogen receptor alpha (ERalpha) in regulation of the MUC1 gene expression

BACKGROUND

The MUC1 gene encodes a mucin glycoprotein(s) which is basally expressed in most epithelial cells. In breast adenocarcinoma and a variety of epithelial tumors its transcription is dramatically upregulated. Of particular relevance to breast cancer, steroid hormones also stimulate the expression of the MUC1 gene. The MUC1 gene directs expression of several protein isoforms, which participate in many crucial cell processes. Although the MUC1 gene plays a critical role in cell physiology and pathology, little is known about its promoter organization and transcriptional regulation. The goal of this study was to provide insight into the structure and transcriptional activity of the MUC1 promoter.

RESULTS

Using TRANSFAC and TSSG soft-ware programs the transcription factor binding sites of the MUC1 promoter were analyzed and a map of transcription cis-elements was constructed. The effect of different MUC1 promoter regions on MUC1 gene expression was monitored. Different regions of the MUC1 promoter were analyzed for their ability to control expression of specific MUC1 isoforms. Differences in the expression of human MUC1 gene transfected into mouse cells (heterologous artificial system) compared to human cells (homologous natural system) were observed. The role of estrogen on MUC1 isoform expression in human breast cancer cells, MCF-7 and T47D, was also analyzed. It was shown for the first time that synthesis of MUC1/SEC is dependent on estrogen whereas expression of MUC1/TM did not demonstrate such dependence. Moreover, the estrogen receptor alpha, ERalpha, could bind in vitro estrogen responsive cis-elements, EREs, that are present in the MUC1 promoter. The potential roles of different regions of the MUC1 promoter and ER in regulation of MUC1 gene expression are discussed.

CONCLUSION

Analysis of the structure and transcriptional activity of the MUC1 promoter performed in this study helps to better understand the mechanisms controlling transcription of the MUC1 gene. The role of different regions of the MUC1 promoter in expression of the MUC1 isoforms and possible function of ERalpha in this process has been established. The data obtained in this study may help in development of molecular modalities for controlled regulation of the MUC1 gene thus contributing to progress in breast cancer gene therapy.

High throughput assays for analyzing transcription factors

Transcription factors are a group of proteins that modulate the expression of genes involved in many biological processes, such as cell growth and differentiation. Alterations in transcription factor function are associated with many human diseases, and therefore these proteins are attractive potential drug targets. A key issue in the development of such therapeutics is the generation of effective tools that can be used for high throughput discovery of the critical transcription factors involved in human diseases, and the measurement of their activities in a variety of disease or compound-treated samples. Here, a number of innovative arrays and 96-well format assays for profiling and measuring the activities of transcription factors will be discussed.

Altered glucocorticoid receptor signaling cascade in lymphocytes of bipolar disorder patients

Bipolar disorder (BD) is characterized by hypothalamic pituitary adrenal (HPA) axis hyperactivity, glucocorticoid insensitivity and alterations in serotonin and inflammatory mediators. The glucocorticoid receptor (GR), activator protein-1 (AP-1), nuclear factor-kappa B (NF-kappaB) and c-jun N-terminal kinase (JNK) regulate the above mentioned processes; we therefore assessed their role in BD. Fifteen bipolar depressed patients under multiple anti-depressant therapy, 15 bipolar euthymics under lithium monotherapy and 25 matched controls were studied. Whole cell and nuclear extracts from lymphocytes were immunoblotted for GR, c-fos, JNK and NF-kappaB and nuclear aliquots were submitted to electrophoretic mobility shift assay for GR, AP-1 and NF-kappaB. Associations with the anti-depressant therapy and the state of the disease were also sought. Results, expressed as percentage of pooled protein standard sample intergraded optical density (IOD) (mean +/- SD), revealed: (a) depressed patients had significantly higher GR levels than controls in whole cell (82.63 +/- 6.18 versus 76.27 +/- 4.21%, P < 0.01) and nuclear extracts (86.66 +/- 3.81 versus 81.72 +/- 2.71%, P < 0.001) but lower GR-DNA binding (68.75 +/- 7.91 versus 81.84 +/- 4.25%, P < 0.05). Euthymics had normalized whole cell GR content (73.64 +/- 5.95%) and GR-DNA binding activity (76.82 +/- 7.29%) but higher nuclear GR content (86.89+/-3.96%, P<0.01) than controls; (b) nuclear c-fos content and AP-1-DNA-binding were significantly lower in depressed patients than controls (80.49 +/- 2.03 versus 84.82 +/- 3.48%, P < 0.05 and 78.46 +/- 4.17 versus 84.80 +/- 5.79%, P < 0.05, respectively). Euthymics however, showed similar nuclear c-fos and AP-1-DNA-binding to controls (85.48 +/- 2.71 and 87.78 +/- 3.54%, respectively) but lower whole cell c-fos than in controls (81.18 +/- 3.87 versus 87.01 +/- 4.22%, P < 0.001); (c) depressed patients had significantly lower whole cell and nuclear JNK than controls (67.01 +/- 4.29 versus 72.00 +/- 3.68%, P < 0.05 and 80.10 +/- 2.53 versus 86.96 +/- 2.49%, P < 0.001) whereas euthymics showed lower nuclear JNK (83.27 +/- 1.93%, P < 0.01); (d) whole cell NF-kB was higher in the depressed patients than in controls (67.30 +/- 5.00 versus 63.63 +/- 3.3%, P < 0.05). Concluding, intracellular signaling of GR, AP-1 and JNK are altered in BD and may underly disease aetiopathogenesis and/or reflect the effect of the anti-depressants.

Do corticosteroids damage the brain?

Corticosteroids are an essential component of the body's homeostatic system. In common with other such systems, this implies that corticosteroid levels in blood and, more importantly, in the tissues remain within an optimal range. It also implies that this range may vary according to circumstance. Lack of corticosteroids, such as untreated Addison's disease, can be fatal in humans. In this review, we are principally concerned with excess or disturbed patterns of circulating corticosteroids in the longer or shorter term, and the effects they have on the brain.

Differential effects of selected natural compounds with anti-inflammatory activity on the glucocorticoid receptor and NF-κB in HeLa cells

Natural compounds have been used in the treatment of various diseases for centuries. Herein, we investigated the effects of structurally diverse alkaloids with anti-inflammatory activity (berberine, sanguinarine, chelerythrine, and colchicine) on two important anti-inflammatory and pro-inflammatory players, i.e. glucocorticoid receptor (GR) and nuclear factor kappa B (NF-kappaB), respectively. Sanguinarine and chelerythrine elicited nuclear translocation of the p65 subunit of NF-kappaB. The nuclear import of p65 was strongly augmented by these akaloids in non-stimulated cells as well as in cells challenged with tumor necrosis factor alpha (TNFalpha). Colchicine and berberine had no effect on p65 nuclear translocation regardless of the presence or absence of TNFalpha. Colchicine caused rapid degradation of the GR protein, whereas berberine had no effect on GR content or cellular localization. Sanguinarine and chelerythrine induced accumulation of GR in the nucleus with concomitant diminution of cytosolic GR. Analyses on the transcriptional activity of GR and NF-kappaB monitored by reporter assays using HeLa cells transiently transfected with glucocorticoid response element (pGRE-LUC) and/or NF-kappaB elements fused to luciferase gene (pNF-kappaB-luc) showed that none of the compounds tested had the capability to trigger GR and/or NF-kappaB transcriptional activities, respectively. The ligand binding assay showed that colchicine and berberine are not GR ligands whereas sanguinarine and chelerythrine significantly decreased binding of (3)H-labelled dexamethasone to GR. In conclusion, structurally diverse natural antiflogistics displayed differential effects on GR and NF-kappaB in HeLa cells.

Prednisolone inhibits hyperosmolarity-induced expression of MCP-1 via NF-κB in peritoneal mesothelial cells

The mechanism of peritoneal fibrosis in patients on continuous ambulatory peritoneal dialysis (CAPD) is poorly elucidated. We investigated the cellular mechanism of high-glucose-induced expression of monocyte chemoattractant protein-1 (MCP-1), which is important in recruiting monocytes into the peritoneum and progression of peritoneal fibrosis, and examined the inhibitory mechanism of glucocorticoids. Rat peritoneal mesothelial cells were cultured in high-glucose-containing medium and then analyzed for phosphorylation levels of p42/44 and p38 mitogen-activated protein (MAP) kinases (MAPK), MAPK or extracellular signal-regulated kinase kinase (MEK)1/2, c-Jun N-terminal kinase (JNK)1/2, and protein kinase C (PKC) by Western blotting. Expression of MCP-1 was examined by reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. DNA-binding activity of nuclear factor (NF)-kappaB was measured by electrophoretic mobility shift assay. High glucose increased MCP-1 mRNA and MCP-1 protein expression. Although glucose increased phosphorylation of MEK1/2, p42/44 MAPK, p38 MAPK, JNK1/2, and PKC, and DNA-binding activity of NF-kappaB, its effect on MCP-1 expression was suppressed only by PKC and NF-kappaB inhibitors. Mannitol caused a similar increase in PKC and NF-kappaB activation and MCP-1 synthesis. Prednisolone increased I-kappaB-alpha expression and inhibited glucose/mannitol-induced NF-kappaB DNA binding and MCP-1 expression without affecting PKC phosphorylation. The inhibitory effects of prednisolone on MCP-1 expression were reversed by mifepristone, a glucocorticoid receptor antagonist. Our results indicate that glucose induces MCP-1 mainly through hyperosmolarity by activating PKC and its downstream NF-kappaB, and that such effect was inhibited by prednisolone, suggesting the efficacy of prednisolone in preventing peritoneal fibrosis in patients on CAPD.

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.

Estrogen signaling multiple pathways to impact gene transcription

Steroid hormones exert profound effects on cell growth, development, differentiation, and homeostasis. Their effects are mediated through specific intracellular steroid receptors that act via multiple mechanisms. Among others, the action mechanism starting upon 17beta-estradiol (E2) binds to its receptors (ER) is considered a paradigmatic example of how steroid hormones function. Ligand-activated ER dimerizes and translocates in the nucleus where it recognizes specific hormone response elements located in or near promoter DNA regions of target genes. Behind the classical genomic mechanism shared with other steroid hormones, E2 also modulates gene expression by a second indirect mechanism that involves the interaction of ER with other transcription factors which, in turn, bind their cognate DNA elements. In this case, ER modulates the activities of transcription factors such as the activator protein (AP)-1, nuclear factor-kappaB (NF-kappaB) and stimulating protein-1 (Sp-1), by stabilizing DNA-protein complexes and/or recruiting co-activators. In addition, E2 binding to ER may also exert rapid actions that start with the activation of a variety of signal transduction pathways (e.g. ERK/MAPK, p38/MAPK, PI3K/AKT, PLC/PKC). The debate about the contribution of different ER-mediated signaling pathways to coordinate the expression of specific sets of genes is still open. This review will focus on the recent knowledge about the mechanism by which ERs regulate the expression of target genes and the emerging field of integration of membrane and nuclear receptor signaling, giving examples of the ways by which the genomic and non-genomic actions of ERs on target genes converge.

Glucocorticoid receptor beta in acute and chronic inflammatory conditions: clinical implications

Glucocorticoids (GC) are hormones with a wide variety of actions, including profound anti-inflammatory/immunosuppressive effects. Their actions are mediated by an intracellular receptor called the glucocorticoid receptor (GCR). The classical GCR that mediates the hormone response is called GCR alpha. Recently however, many GCR isotypes have been described. A defective GC action has been proposed as an etio-pathogenic mechanism for the development of inflammatory/autoimmune diseases. Inadequate GC actions may have multiple causes such as: defective hypothalamic-pituitary-adrenal axis function, GC export from cells, hormone metabolization into inactive compounds and modifications of the GC receptor, among others. In 1995, a dominant negative effect of a GC receptor isotype termed beta was described; starting a still unsolved controversy about the role of GCR beta as an inducer of GC resistance in certain pathological conditions. The present article will review the data about a possible role for GCR beta in the development of GC resistance in inflammatory diseases. This review will especially focus on the role of the GCR beta in rheumatoid arthritis and in septic shock as examples of a chronic inflammatory disease and an acute systemic inflammatory condition. Original data supporting possible hyperexpression of GCR beta in both conditions will be shown.

Steroid hormone receptor signaling in tumorigenesis

Excessive activation of the hormone signaling pathways is implicated in several disorders of the target tissues, with cancer being one of the most serious fallouts. Steroid hormone receptors are key proteins through which steroid hormones convey their signals to the cells. Deregulated activity of the hormone receptors due to their altered activation; stability or sub-cellular localization is heavily implicated in the onset and progress of cancers. The role played by estrogen and its receptors in breast cancer remains the most thoroughly investigated steroid-dependent cancer system till date. Choosing it as an example, we have summarized the molecular mechanisms underlying the action of the estrogen receptors (ERs) in manifesting the effects of the estrogens in the cells. A special emphasis is placed on the molecular mechanism of their functionality, role of the coactivator proteins, and the reasons for the deregulated signaling. The therapeutic approaches resulting from the mechanistic study of the ER action and their efficacies are also discussed.

20-Hydroxyecdysone indirectly regulates Hemolin gene expression in Hyalophora cecropia

Development and innate immune defence are two vital processes that have been demonstrated to use the same or similar molecules and signalling pathways in insects. Hemolin is a moth haemolymph protein belonging to the immunoglobulin superfamily. It is strongly induced upon bacterial infection. However, recent studies indicate a developmental regulation of hemolin. We show that the steroid hormone 20-hydroxyecdysone (20E) can activate the expression of Hyalophora cecropia Hemolin (HcHemolin) in the fat body of diapausing pupae. Using the protein synthesis inhibitor cycloheximide we demonstrate that Hemolin up-regulation by 20E requires ongoing protein synthesis. Moreover, 20E enhances transcription of the Hemolin gene in response to bacteria. Comparing the upstream regions of Manduca sexta Hemolin (MsHemolin) and HcHemolin, we identified four putative regulatory sites. Two are putative hormone response elements (HREs), one with an imperfect inverted repeat (HRE-IR) and one with a monomeric site (HRE-M). An additional monomeric hormone receptor site (MRE) is present only in HcHemolin. The third conserved motif is similar to the interferon (IFN) regulatory factor binding element (IRF-E) and IFN-stimulated response element (ISRE). The fourth conserved element is a kappaB motif situated between the Cap-site and the TATA-box. Finally, by electrophoresis mobility shift assay we demonstrate that the HRE-IR forms specific complexes with nuclear extract proteins of normal pupae that increase after 20E stimulation.

Effects of glucocorticoids on the growth and chemosensitivity of carcinoma cells are heterogeneous and require high concentration of functional glucocorticoid receptors

AIM: To determine how glucocorticoids (GCs) may affect the growth and chemosensitivity of common carcinoma cells.

METHODS: The effect of dexamethasone (DEX) on growth and chemosensitivity was assessed in 14 carcinoma cell lines. The function of GC receptors (GR) was assessed by MMTV reporter assay. Overexpression of GR was done by in vitro transfection and expression of a GR-expressing vector. Immunohistochemical stain of tissues and cells were done by PA1-511A, an anti-GR monoclonal antibody.

RESULTS: DEX inhibited cell growth of four (MCF-7, MCF-7/MXR1, MCF-7/TPT300, and HeLa), increased cisplatin cytotoxicity of one (SiHa), and decreased cisplatin cytotoxicity of two (H460 and Hep3B) cell lines. The GR content of the seven cell lines affected by DEX was significantly higher than those of the seven cell lines unaffected by DEX (5.2±2.5×104 sites/cell vs 1.3±1.4×104 sites/cell, P = 0.005). Only two DEX-unresponsive cell lines (NPC-TW01 and NPC-TW04) contained high GR amounts in the range (1.9-8.1×104 sites/cell) of the seven DEX-responsive cell lines. The GR function of NPC-TW01 and NPC-TW04, however, was found to be impaired. The importance of high cellular amount of GR in mediating DEX susceptibility of the cells was further exemplified by GR dose-dependent drug resistance to cisplatin of AGS, a cell line with low GR content and was unaffected by DEX before transfection of GR-expressing vector. Immunohistochemical studies of human cancer tissues showed that 5 of the 45 (11.1%) breast cancer and 43 of the 85 (50.6%) non-small cell lung cancer had high GR contents at the ranges of the GC-responsive carcinoma cell lines.

CONCLUSION: The growth and chemosensitivity of human carcinomas with high GR contents may be affected by GC. However, in light of the heterogeneous and even contradictive effects of GC on these cells, routine examination of GR contents of human carcinoma tissues may not be clinically useful until other markers that help predict the ultimate effect of GC on individual patients are identified.

Dissociated glucocorticoids equipotently inhibit cytokine- and cAMP-induced matrix degrading proteases in rat mesangial cells

Dissociated glucocorticoids are synthetic ligands of the glucocorticoid receptor (GR) and which discriminate between transrepression and transactivation. These compounds were predicted to have large therapeutic benefits when compared to conventional glucocorticoids because of reduced side effects. In this study, we compared the transrepressive properties of different dissociated glucocorticoids on the interleukin-1beta (IL-1beta)-activated metalloproteinase-9 (MMP-9) and tissue plasminogen activator (tPA) expression in rat mesangial cells (MC). Both proteinases regulate the turnover of extracellular matrix (ECM). We demonstrate that the GR agonist RU 24858, equipotent to dexamethasone (DEX), exhibited strong suppressive effects on the IL-1beta-induced MMP-9 and tPA mRNA levels concomitant with an inhibition of corresponding enzyme activities. In contrast, RU 24782 and RU 40066 exhibited weaker inhibitory activities on both proteinases. Mechanistically, the changes in MMP-9 expression level by different RUs were accompanied by an inhibition of cytokine-induced promoter activity indicating that the inhibition occurs on a transcriptional level. In parallel to the reduction in mRNA levels, we observed an attenuation of cytokine-induced DNA binding of nuclear factor kappa B (NF-kappaB) and reduced contents of the p65 subunit of NF-kappaB within cell nuclei. Along with these transrepressive activities RU 24858, RU 24782 and RU 40066 displayed similar transactivation potentials as indicated by induction of the glucocorticoid-inducible mouse mammary tumor virus (MMTV) reporter gene and by induced expression level of plasminogen activator inhibitor 1 (PAI-1). Interestingly, the different RUs affected the expression of cAMP-induced tPA and inducible NO synthase with the same potency as the IL-1beta-induced protease expression thus indicating that these compounds equipotently modulate cytokine- and cAMP-driven gene expression.

Novel heterocyclic glucocorticoids: in vitro profile and in vivo efficacy

A series of novel ligands for the glucocorticoid receptor containing two heterocycles were synthesized. These compounds were investigated for a dissociative profile using transrepression and transactivation assays. Several compounds were tested in vivo and showed the ability to reduce inflammation in a mouse.

Environmental xenobiotics and nuclear receptors--interactions, effects and in vitro assessment

A group of intracellular nuclear receptors is a protein superfamily including arylhydrocarbon AhR, estrogen ER, androgen AR, thyroid TR and retinoid receptors RAR/RXR as well as molecules with unknown function known as orphan receptors. These proteins play an important role in a wide range of physiological as well as toxicological processes acting as transcription factors (ligand-dependent signalling macromolecules modulating expression of various genes in a positive or negative manner). A large number of environmental pollutants and other xenobiotics negatively affect signaling pathways, in which nuclear receptors are involved, and these modulations were related to important in vivo toxic effects such as immunosuppression, carcinogenesis, reproduction or developmental toxicity, and embryotoxicity. Presented review summarizes current knowledge on major nuclear receptors (AhR, ER, AR, RAR/RXR, TR) and their relationship to known in vivo toxic effects. Special attention is focused on priority organic environmental contaminants and experimental approaches for determination and studies of specific toxicity mechanisms.

Glucocorticoids inhibit activation-induced cell death (AICD) via direct DNA-dependent repression of the CD95 ligand gene by a glucocorticoid receptor dimer

Glucocorticoids (GCs) play an important role in the regulation of peripheral T-cell survival. Their molecular mechanism of action and the question of whether they have the ability to inhibit apoptosis in vivo, however, are not fully elucidated. Signal transduction through the glucocorticoid receptor (GR) is complex and involves different pathways. Therefore, we used mice with T-cell-specific inactivation of the GR as well as mice with a function-selective mutation in the GR to determine the signaling mechanism. Evidence is presented for a functional role of direct binding of the GR to 2 negative glucocorticoid regulatory elements (nGREs) in the CD95 (APO-1/Fas) ligand (L) promoter. Binding of GRs to these nGREs reduces activation-induced CD95L expression in T cells. These in vitro results are fully supported by data obtained in vivo. Administration of GCs to mice leads to inhibition of activation-induced cell death (AICD). Thus, GC-mediated inhibition of CD95L expression of activated T cells might contribute to the anti-inflammatory function of steroid drugs. (Blood. 2005;106:617-625)

Glucocorticoids suppress transcriptional up-regulation of bradykinin receptors in a murine in vitro model of chronic airway inflammation

BACKGROUND

Glucocorticoids are effective drugs for controlling symptoms and airway inflammation in respiratory diseases such as asthma and chronic obstructive pulmonary disease. However, the mechanisms behind their effects are not fully understood. We have recently demonstrated that prolonged exposure to the pro-inflammatory mediator tumour necrosis factor-alpha (TNF-alpha) markedly enhanced contractile responses to des-Arg9-bradykinin (selective bradykinin B1 receptor agonist) and bradykinin (selective bradykinin B2 receptor agonist) in murine airways. This increase was paralleled with elevated mRNA levels for bradykinin B1 and B2 receptors, a process involving intracellular mitogen-activated protein kinase pathways.

OBJECTIVE

To investigate the effects of glucocorticoids on the TNF-alpha up-regulated bradykinin B1 and B2 receptor response.

METHODS

Tracheal segments from BALB/c J mice were cultured with and without TNF-alpha, in the absence and presence of the transcriptional inhibitor actinomycin D or the glucocorticoid, dexamethasone. The contractile response induced by des-Arg9-bradykinin and bradykinin was subsequently assessed in a myograph system and mRNA for bradykinin B1 and B2 receptors was quantified using real-time polymerase chain reaction.

RESULTS

Actinomycin D abolished and dexamethasone concentration-dependently suppressed the TNF-alpha-induced enhancement of the des-Arg9-bradykinin and bradykinin responses. This was paralleled by a reduction of the mRNA expression for the bradykinin B1 and B2 receptors.

CONCLUSION

The presented data suggests the involvement of transcriptional mechanisms in the up-regulation of bradykinin B1 and B2 receptors during asthmatic airway inflammation, as well as in their down-regulation following glucocorticoid treatment.

Enhancement of steroid receptor-mediated transcription for the development of highly responsive bioassays

We have previously generated several transformed human mammary cell lines for the detection of steroid receptor-mediated activities and used these cell lines to detect and characterize steroid hormone (ant)agonistic compounds. In this report, we describe the specific optimization procedures used to enhance receptor-mediated transcription through the human glucocorticoid, progesterone and androgen receptors, respectively. Sodium arsenite-induced chemical stress leads to a substantial and specific increase in the glucocorticoid receptor-mediated transcription, resulting in maximal stimulations of more than 2000-fold by the agonist dexamethasone. Similarly, a combined treatment with forskolin (an activator of adenylate cyclase) and trichostatin A (an inhibitor of histone deacetylases) leads to a synergistic enhancement of progesterone or androgen stimulation, resulting in a maximal induction of more than 200-fold or about 100-fold, respectively. The enhanced responses to specific steroids are mediated by the corresponding nuclear receptor. We show that by using these enhanced transcriptional stimulation protocols, it is possible to detect lower amounts of steroid hormones without substantially affecting the relative biological activities of various agonists. Finally, the application of these enhanced reporter cell assays to real biological samples from meat-producing animals is evaluated, and some validation parameters are presented.

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.

Alcohol, vitamin A, and cancer

Chronic and excessive alcohol intake is associated with an increased risk of a variety of cancers (e.g., oral cavity, larynx, esophagus, liver, lung, colorectal, and breast). Retinoids (vitamin A and its derivatives) are known to exert profound effects on cellular growth, cellular differentiation, and apoptosis, thereby controlling carcinogenesis. Lower hepatic vitamin A levels have been well documented in alcoholics. Substantial research has been done, investigating the mechanisms by which excessive alcohol interferes with retinoid metabolism. More specifically, (1) alcohol acts as a competitive inhibitor of vitamin A oxidation to retinoic acid involving alcohol dehydrogenases and acetaldehyde dehydrogenases; (2) alcohol-induced cytochrome P450 enzymes (CYP), particularly CYP2E1, enhance catabolism of vitamin A and retinoic acid; and (3) alcohol alters retinoid homeostasis by increasing vitamin A mobilization from liver to extrahepatic tissues. As a consequence, long-term and excessive alcohol intake results in impaired status of retinoic acid, the most active derivative of vitamin A and a ligand for both retinoic acid receptors and retinoid X receptors. Moreover, this alcohol-impaired retinoic acid homeostasis interferes with (1) retinoic acid signaling (e.g., down-regulates retinoid target gene expression) and (2) retinoic acid "cross-talk" with the mitogen-activated protein kinase [(MAPK), including Jun N-terminal kinase, extracellular signal-regulated kinase, and p38 kinase] signaling pathway. In addition, restoration of retinoic acid homeostasis by retinoic acid supplementation restored the normal status of both retinoid and MAPK signaling, thereby maintaining normal cell proliferation and apoptosis in alcohol-fed animals. These observations would have implications for the prevention of alcohol-promoted liver (and peripheral tissue) carcinogenesis. However, a better understanding of the alcohol-retinoid interaction and the molecular mechanisms involved is needed before retinoids can be pursued in the prevention of alcohol-related carcinogenesis in human beings, particularly regarding the detrimental effects of polar metabolites of vitamin A.

Effects of interleukin-1beta and dexamethasone on the expression of matrix metalloprotease mRNA by trabecular cells exposed to elevated hydrostatic pressure

PURPOSE

We investigated the effects of interleukin-1beta (Il-1beta) and dexamethasone (Dex) on the expression of matrix metalloprotease-1, -2, -3 and -14 (membrane type-1 MMP-MT1-MMP) as well as tissue inhibitors of matrix metalloproteases (TIMP-1 and -2) mRNA by trabecular cells exposed not only to normal, but also to elevated levels of hydrostatic pressure.

METHODS

Confluent primary cultures of porcine trabecular cells were incubated in a serum-free medium (SFM) as controls, or in SFM containing either 10 ng/ml Il-1beta or 10 nm Dex and exposed to pressures of 15 mmHg or 50 mmHg (corresponding to normal and high intraocular pressure, respectively) in specially designed pressure chambers. After 72 hours, total RNA was extracted from the harvested cells, reverse transcribed and amplified using primers specific to MMP-1, -2, -3 and -14, and TIMP-1 and -2.

RESULTS

The most significant changes were detected in the levels of MMP-3 mRNA in control cells (2.4-fold increase), of TIMP-1 and -2 mRNA in cells treated with Il-1beta (2.6-fold increase) and of MMP-3 mRNA in cells treated with Dex (3.5-fold increase) exposed to 50 mmHg pressure.

CONCLUSION

Because MMP-3 (stromelysin) mRNA showed the highest upregulation, our findings suggest that trabecular cells preferentially degrade and turn over the proteoglycan components of the extracellular matrix in response to short-term exposure to increased hydrostatic pressure with and without Dex as a homeostatic mechanism.

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.

Mechanisms of estrogen receptor signaling: convergence of genomic and nongenomic actions on target genes

Estrogen receptors (ERs) act by regulating transcriptional processes. The classical mechanism of ER action involves estrogen binding to receptors in the nucleus, after which the receptors dimerize and bind to specific response elements known as estrogen response elements (EREs) located in the promoters of target genes. However, ERs can also regulate gene expression without directly binding to DNA. This occurs through protein-protein interactions with other DNA-binding transcription factors in the nucleus. In addition, membrane-associated ERs mediate nongenomic actions of estrogens, which can lead both to altered functions of proteins in the cytoplasm and to regulation of gene expression. The latter two mechanisms of ER action enable a broader range of genes to be regulated than the range that can be regulated by the classical mechanism of ER action alone. This review surveys our knowledge about the molecular mechanism by which ERs regulate the expression of genes that do not contain EREs, and it gives examples of the ways in which the genomic and nongenomic actions of ERs on target genes converge. Genomic and nongenomic actions of ERs that do not depend on EREs influence the physiology of many target tissues, and thus, increasing our understanding of the molecular mechanisms behind these actions is highly relevant for the development of novel drugs that target specific receptor actions.

Disruption of microtubules leads to glucocorticoid receptor degradation in HeLa cell line

The role of microtubules (MTs) in steroid hormone-dependent human glucocorticoid receptor (hGR) activation/translocation is controversial. It was demonstrated recently that colchicine (COL) down-regulates hGR-driven genes in primary human hepatocytes by a mechanism involving inhibition of hGR translocation to the nucleus. To investigate whether inhibition of hGR translocation is the sole reason for its inactivation, we used human cervical carcinoma cells (HeLa) as a model. Herein we present evidence that perturbation of microtubules in HeLa cells leads to rapid time- and dose-dependent degradation of hGR protein. Degradation is proteasome mediated as revealed by its reversibility by proteasome inhibitor MG132. Moreover, degradation was observed for neither wt-hGR nor hGR mutants S226A and K419A in transiently transfected COS-1 cells. On the other hand, c-jun N-terminal kinase (JNK) seems not to be involved in the process because JNK inhibitor 1,9-Pyrazoloanthrone (SP600125) does not reverse hGR degradation. Similarly, another hGR functional antagonist, nuclear factor kappa beta (NFkappaB), did not play any role in the degradation process.

A nuclear isoform of the focal adhesion LIM-domain protein Trip6 integrates activating and repressing signals at AP-1- and NF-kappaB-regulated promoters

Glucocorticoid receptor (GR)-mediated transrepression of the transcription factors AP-1 and NF-kappaB, responsible for most of the anti-inflammatory effects of glucocorticoids, is initiated by the tethering of GR to the promoters of target genes. We report that this tethering is mediated by a nuclear isoform of the focal adhesion LIM domain protein Trip6. Trip6 functions as a coactivator for both AP-1 and NF-kappaB. As shown by chromatin immunoprecipitation, Trip6 is recruited to the promoters of target genes together with AP-1 or NF-kappaB. In the presence of glucocorticoids, GR joins the Trip6 complex. Reducing the level of Trip6 by RNA interference or abolishing its interaction with GR by dominant-negative mutation eliminates transrepression. We propose that GR tethering to the target promoter through Trip6 forms the basis of transrepression, and that Trip6 exerts its nuclear functions by acting as a molecular platform, enabling target promoters to integrate activating or repressing signals.

Gene analysis of the glucocorticoid receptor alpha in Alzheimer's disease

BACKGROUND

In Alzheimer's disease (AD), the hypothalamic-pituitary-adrenal (HPA) axis is hyperactive and the sensitivity to dexamethasone is decreased, suggesting a possible involvement of glucocorticoid receptor alpha (GRalpha) defects in the aetiopathology of the disease.

METHODS

We, therefore, searched for the presence of mutations in the human GRalpha (hGRalpha) gene, focusing on the hormone-binding domain due to its importance in mediating glucocorticoids' effects. RNA isolated from peripheral blood mononuclear cells (PBMCs) of 15 patients with Alzheimer's disease and 20 healthy individuals was subjected to reverse transcription-polymerase chain reaction amplification (RT-PCR) analysis followed by denaturing gradient gel electrophoresis (DGGE).

RESULTS

No mutations could be detected in the region of the hGRalpha gene examined.

CONCLUSIONS

We conclude that the hormone-binding domain of GRalpha is not altered in Alzheimer's disease and molecular defects in other gene regions of the GRalpha or in its isoform GRbeta warrant further investigation in Alzheimer's disease.

Differentiation of in vitro transcriptional repression and activation profiles of selective glucocorticoid modulators

The SAR at C-5 of the 10-methoxy-2,2,4-trimethylbenzopyrano[3,4-f]quinoline core leading to identification of (-) anti 1-methylcyclohexen-3-yl as the optimum substituent that imparts minimal GR mediated in vitro transcriptional activation while maintaining full transcriptional repression is described. The in vitro profile of these candidates in human cell assays relevant to the therapeutic window of glucocorticoid modulators is outlined.

Interleukin 1beta inhibits CAR-induced expression of hepatic genes involved in drug and bilirubin clearance

During the inflammatory response, intrahepatic cholestasis and decreased drug metabolism are frequently observed. At the hepatic level, the orphan nuclear constitutive androstane receptor (CAR) (NR1I3) controls phase I (cytochrome P450 [CYP] 2B and CYP3A), phase II (UGT1A1), and transporter (SLC21A6, MRP2) genes involved in drug metabolism and bilirubin clearance in response to xenobiotics such as phenobarbital or endobiotics such as bilirubin. We investigated the negative regulation of CAR, a glucocorticoid-responsive gene, via proinflammatory cytokine interleukin 1beta (IL-1beta) and lipopolysaccharides (LPSs) in human hepatocytes. We show that IL-1beta decreases CAR expression and decreases phenobarbital- or bilirubin-mediated induction of CYP2B6, CYP2C9, CYP3A4, UGT1A1, GSTA1, GSTA2, and SLC21A6 messenger RNA. This occurs via nuclear factor kappaB (NF-kappaB) p65 activation, which interferes with the enhancer function of the distal glucocorticoid response element that we have identified recently in the CAR promoter. We demonstrate that: (1) LPSs, IL-1beta, or overexpression of p65RelA inhibit glucocorticoid receptor (GR)-mediated CAR transactivation; (2) these suppressive effects can be blocked both by pyrrolidine dithiocarbamate, an inhibitor of NF-kappaB activation, or by overexpression of SRIkBalpha, a NF-kappaB repressor; and (3) the GR agonist dexamethasone induces histone H4 acetylation at the proximal CAR promoter region, whereas LPSs and IL-1beta inhibit this acetylation as assessed via chromatin immunoprecipitation assay. In conclusion, GR/NF-kappaB interaction affects CAR gene transcription through chromatin remodeling and provide a mechanistic explanation for the long-standing observation that inflammation and sepsis inhibit drug metabolism while inducing intrahepatic cholestasis or hyperbilirubinemia.

The thyroid hormone receptor is a suppressor of ras-mediated transcription, proliferation, and transformation

The thyroid hormone triiodothyronine (T3) has a profound effect on growth, differentiation, and metabolism in higher organisms. Here we demonstrate that T3 inhibits ras-induced proliferation in neuroblastoma cells and blocks induction of cyclin D1 expression by the oncogene. The hormone, at physiological concentrations, strongly antagonizes the transcriptional response mediated by the Ras/mitogen-activated protein kinase/ribosomal-S6 subunit kinase (Rsk) signaling pathway in cells expressing thyroid hormone receptors (TRs). T3 blocks the response to the oncogenic forms of the three ras isoforms (H-, K-, and N-ras) and both TRalpha and TRbeta can mediate this action. The main target for induction of cyclin D1 transcription by oncogenic ras in neuroblastoma cells is a cyclic AMP response element (CRE) located in proximal promoter sequences, and T3 represses the transcriptional activity of b-Zip transcription factors such as CREB (CRE-binding protein) or ATF-2 (activation transcription factor 2) that are direct targets of Rsk2 and bind to this sequence. The hormone also blocks fibroblast transformation by oncogenic ras when TR is expressed. Furthermore, TRs act as suppressors of tumor formation by the oncogene in vivo in nude mice. The TRbeta isoform has stronger antitransforming properties than the alpha isoform and can inhibit tumorigenesis even in hypothyroid mice. These results show the existence of a previously unrecognized transcriptional cross talk between the TRs and the ras oncogene which influences relevant processes such as cell proliferation, transformation, or tumorigenesis.

Estrogen receptor-dependent activation of AP-1 via non-genomic signalling

Background

Ligand-bound estrogen receptor α (ERα) and estrogen receptor β (ERβ) modulate AP-1-dependent transcription via protein-protein interactions on DNA, in a manner that depends on the type of cells and the subtype of ER. We present here evidence for an additional mechanism by which ERs modulate the transcriptional activity of AP-1.

Results

We show that ERs located in the cytoplasm efficiently activate transcription at AP-1 sites in response to 17β-estradiol, while ERs present in the nucleus repress transcription under the same conditions. 17β-estradiol-induced activation of the coll-73-luc reporter correlated with cytoplasmic localization of various ERα and ERβ mutant receptors, and was inhibited in the presence of the full estrogen antagonist ICI 182,780 and the MAP-kinase inhibitor UO126. We also show that the selective estrogen receptor modulator (SERM) tamoxifen is as potent as 17β-estradiol in inducing activation of AP-1 when ERα is present in the cytoplasm.

Conclusions

These results suggest that non-genomic signalling is involved in the mechanism by which ERα and ERβ influence AP-1-dependent transcription. We have previously shown that Stat3 and Stat5 are targeted by non-genomic actions of ERs, and the results presented here allow us to conclude that ERs bound to 17β-estradiol mediate the transcriptional activation of promoters regulated by AP-1 and by Stat proteins via different combinations of signal transduction pathways. Our observations thereby provide new insights into the mechanisms by which ERs act at alternate response elements, and suggest a mechanism by which tamoxifen exerts its action as a tissue-selective agonist.

The role of corepressors in transcriptional regulation by nuclear hormone receptors

Nuclear receptors (also known as nuclear hormone receptors) are hormone-regulated transcription factors that control many important physiological and developmental processes in animals and humans. Defects in receptor function result in disease. The diverse biological roles of these receptors reflect their surprisingly versatile transcriptional properties, with many receptors possessing the ability to both repress and activate target gene expression. These bipolar transcriptional properties are mediated through the interactions of the receptors with two distinct classes of auxiliary proteins: corepressors and coactivators. This review focuses on how corepressors work together with nuclear receptors to repress gene transcription in the normal organism and on the aberrations in this process that lead to neoplasia and endocrine disorders. The actions of coactivators and the contributions of the same corepressors to the functions of nonreceptor transcription factors are also touched on.

Requirements for transcriptional regulation by the orphan nuclear receptor ERRgamma

Estrogen-related receptor gamma (ERRgamma) is an orphan nuclear receptor lacking identified natural ligands. We have addressed the requirements for ERRgamma-mediated gene regulation. ERRgamma transactivates constitutively reporter genes driven by ERR response elements (ERREs) or estrogen response elements (EREs). The activation depends on an intact DNA-binding domain (DBD) and activation function-2 (AF2). ERRgamma-mediated transactivation is further enhanced by peroxisome proliferator-activated receptor coactivator-1. Interestingly, ligand-binding domain (LBD) mutations predicted to either enlarge or diminish the putative ligand-binding pocket have no effect on the transcriptional activity implying that ERRgamma activity does not depend on any ligands. Antiestrogens 4OH-tamoxifen (4OHT) and 4-hydroxytoremifene (4OHtor) inhibit the ability of ERR to transactivate ERRE and ERE reporters. In contrast, ERRgamma activates transcription at AP-1 sites in the presence of 4OHT and 4OHtor. Thus, the transcriptional activity of ERRgamma seems not to require ligand binding but is modulated by binding of certain small synthetic ligands.

An in vitro bioassay to determine individual sensitivity to glucocorticoids: induction of FKBP51 mRNA in peripheral blood mononuclear cells

Individual variation in sensitivity to glucocorticoids (GCs) poses a dilemma to the clinician. Currently available assays to determine individual sensitivity to GCs either seem imprecise, or they are based on mitogen-activated lymphocytes, although mitogens themselves may affect cellular GC sensitivity. To avoid these disadvantages, we developed an assay based on the GC-induced accumulation of the 51kDa FK506 binding protein (FKBP51) mRNA in unstimulated peripheral blood mononuclear cells (PBMC), measured using real time PCR. Of several family members tested, only FKBP51 transcript levels showed to be GC-inducible. Furthermore, our bioassay was not affected by progesterone, estradiol, and testosterone. Immunological stimulation of PBMC using tetanus toxoid did not affect bioassay results, and isolated T- and B-lymphocytes showed a similar response to GC stimulation. The intra- and inter-assay variations were 10.6 and 15.9%, respectively. Our bioassay confirms previous reports that a wide variation in GC sensitivity exists in the normal population, yet is able to clearly discriminate a patient with familial GC hyposensitivity from controls. Our bioassay may be suitable to assess altered individual GC sensitivity, and the small amount of PBMC needed for a determination makes this assay easily applicable in a pediatric setting.

Steroid receptor action

The ovarian hormones oestradiol and progesterone exert their actions on target cells predominantly through the binding and activation of the oestrogen receptor (ER) and progesterone receptor (PR), respectively. These receptors are members of the steroid/thyroid hormone superfamily of ligand-dependent transcription factors and bind to the control regions (promoters) of specific genes, where they recruit co-activators or co-repressors and the transcriptional machinery necessary to elicit gene expression. The ability of a nuclear receptor to modulate gene transcription is further dependent on its interaction with other transcription factors, which in turn can be regulated by either distinct or multiple cytoplasmic signalling pathways. This chapter summarises the extraordinary diversity of factors involved in determining the cellular response to a hormonal signal and emphasises the role of ER and PR in regulating ovarian and uterine functions.

Stress and amphetamine induce Fos expression in medial prefrontal cortex neurons containing glucocorticoid receptors

Exposure to stress or amphetamine potently activates the immediate early gene, c-fos, within medial prefrontal cortex neurons, but the phenotype of these neurons is not known. Fluorescence immunohistochemistry was used to determine that a large subpopulation of medial prefrontal cortex cells expressing Fos protein after restraint and amphetamine also co-express nuclear glucocorticoid receptors (GRs). These findings suggest exposure to amphetamine activates the same medial prefrontal cortex regions responsible for integration of responses to stress, and suggest the potential for AP1-glucocorticoid cross-talk in these cell populations.

Dexamethasone regulation of cFos mRNA in osteoprogenitors

The glucocorticoid, dexamethasone (Dex), has a beneficial effect on osteogenesis by increasing the activation and differentiation of osteoblastic cells. We investigated the effect of Dex on osteoblasts and detected changes in pattern of expression of cFos mRNA. cFos is an early response gene that is expressed as unspliced and spliced mRNAs. We analyzed the regulation of cFos mRNA in correlation with the cell proliferation status and following the induction by Dex. Treatment of osteoblastic cells with Dex for 30 min resulted in elevated levels of spliced form of cFos mRNA, which was maintained with extended treatment of cultured cells for 24 h. In addition, we demonstrated interaction between glucocorticoid receptor (GR) and cFos mRNA. This study provides evidence for the action of Dex on osteoblasts through dynamic cell responses involving with cFos.

Retinoids and TRAIL: two cooperating actors to fight against cancer

Multiple studies performed in in vitro and in vivo settings have confirmed the cancer therapeutic and cancer preventive capacity of retinoids and rexinoids. These compounds mediate their actions through the retinoid and rexinoid receptors, respectively, which exist in multiple isoforms and form a plethora of distinct heterodimers. Despite their apparent anticancer potential, with one exception the molecular basis of this activity has remained largely elusive. The exception concerns acute promyelocytic leukemia (APL), the prototype of retinoic acid-dependent differentiation therapy, for which both the molecular nature of the disease and the mechanism of action of retinoids are well understood. However, retinoids and rexinoids are active beyond the borderlines of the well-defined chromosomal translocation that gives rise to curable APL. In this context, particularly interesting is that retinoic acid induces a member of the tumor necrosis factor family, tumor necrosis factor-related apoptosis inducing ligand (TRAIL) or Apo2L. This ligand is exceptional in that it is capable of inducing apoptosis in cancer cells but not in normal cells. It is possible that this connection to the TRAIL signaling pathway contributes to the anti-tumor activity of retinoids and rexinoids. This review focuses on what is presently known about the regulation of cell life and death by the retinoid/rexinoid and TRAIL signaling pathways.

Glucocorticoid receptor expression in inflammatory bowel disease: evidence for a mucosal down-regulation in steroid-unresponsive ulcerative colitis

BACKGROUND

Glucocorticoids (GC) play a major role in the attenuation of inflammation. Glucocorticoid receptor (GR) expression is an important determinant of steroid sensitivity.

AIMS

To investigate whether GR mRNA expression is altered in inflammatory bowel disease, and whether GR mRNA expression correlates with disease activity and may predict response to GC therapy.

METHODS

Mucosal biopsies were taken from 33 patients with ulcerative colitis, 21 with Crohn's disease and 11 controls. Peripheral blood mononuclear cells were isolated from 24 ulcerative colitis and 18 Crohn's disease patients and 11 controls. GR mRNA was measured by quantitative reverse transcriptase polymerase chain reaction (RT-PCR), and correlated to endoscopic findings, clinical activity and outcome of GC therapy. In a subset of subjects GR localisation was shown by immunohistochemistry.

RESULTS

In patients with inflammatory bowel disease GR expression was not different from controls. However, GR was decreased in biopsies from ulcerative colitis patients with impaired GC response. The inhibitory subtype GRbeta was expressed 100-1000 times lower than GRalpha. GR immunoreactivity was identified in immune and epithelial cells except for colonic crypts.

CONCLUSION

In inflammatory bowel disease systemic and mucosal GR mRNA expression is not altered. However, in ulcerative colitis patients, low mucosal GR expression may predict the outcome of GC therapy. The low expression of GRbeta challenges its role in steroid refractoriness in inflammatory bowel disease.

Kruppel-like factors regulate the Lama1 gene encoding the laminin alpha1 chain

Laminin-1 (alpha1beta1gamma1), a basement membrane (BM) constituent, has been associated with differentiation processes and also with malignant progression. In the intestinal tissue, the alpha1 chain is expressed and secreted in the subepithelial BM during the developmental period; in the adult rodent tissue, it is restricted to the BM of the dividing cells. To understand how laminin alpha1 chain expression is regulated, we cloned and characterized a 2-kb promoter region of the Lama1 mouse gene. Analysis of the promoter was conducted in the Caco2-TC7 intestinal epithelial cells by transient transfection of serially deleted and site-directed mutated promoter constructs, by electrophoretic mobility shift assays, and expression of selected transcription factors. We determined that a proximal region, which includes an Sp1-binding GC box and a Krüppel-like element, was important for the promoter activity. This region is conserved between the human and mouse genes. Interestingly, two Krüppel-like factors KLF4 and KLF5 exhibit opposing effects on the Lama1 promoter activity that are decreased and increased, respectively, in the intestinal epithelial cells. These data corroborate the complementary expression of KLF4 and KLF5 along the intestinal crypt-villus axis and the parallel expression of KLF5 and laminin alpha1 chain in the crypt region. Finally, we showed that glucocorticoids stimulate the promoter activity. This study is the first characterization of the Lama1 promoter; we identified regulatory elements that may account for the expression pattern of the endogenous protein in the mouse intestine.

Glucocorticoid receptor-JNK interaction mediates inhibition of the JNK pathway by glucocorticoids

Inhibition of the c-Jun N-terminal kinase (JNK) pathway by glucocorticoids (GCs) results in AP-1 repression. GC antagonism of AP-1 relies mainly on the transrepression function of the GC receptor (GR) and mediates essential physiological and pharmacological actions. Here we show that GCs induce the disassembly of JNK from mitogen-activated protein kinase kinase 7 (MKK7) by promoting its association with GR. Moreover, we have characterized a hormone-regulated JNK docking site in the GR ligand-binding domain that mediates GR-JNK interaction. The binding of GR to JNK is required for inhibition of JNK activation and induction of inactive JNK nuclear transfer by GCs. The dissociation of these two hormone actions shows that JNK nuclear transfer is dispensable for the downregulation of JNK activation by GCs. Nonetheless, nuclear accumulation of inactive JNK may still be relevant for enhancing the repression of AP-1 activity by GCs. In this regard, chromatin immunoprecipitation assays show that GC-induced GR-JNK association correlates with an increase in the loading of inactive JNK on the AP-1-bound response elements of the c-jun gene.

Steroid hormone regulation of the human kallikrein 10 (KLK10) gene in cancer cell lines and functional characterization of the KLK10 gene promoter

BACKGROUND

The human kallikrein 10 (KLK10) gene is a new member of the human tissue kallikrein gene family. It encodes for a secreted serine protease (hK10) with predicted trypsin-like enzymatic activity. KLK10 is highly expressed in the sex organs and its expression level changes in malignancy.

METHODS

To determine the role of steroid hormones in KLK10 gene expression, we investigated its modulation by 17beta-estradiol, 5alpha-dihydrotestosterone, norgestrel, dexamethasone and aldosterone, at both the transcription and translation level, in a panel of cancer cell lines. After steroid hormone stimulation, the change of KLK10 mRNA was monitored with reverse transcriptase polymerase chain reaction and hK10 protein levels in the culture supernatant were quantified with an hK10-specific immunoassay. The presence of hormone response elements in the KLK10 gene promoter was examined with the chloramphenicol acetyltransferase reporter gene system.

RESULTS

The KLK10 expression was mainly up-regulated by estrogens, androgens and progestins, and to a lesser extent by dexamethasone and aldosterone in the breast cancer cell lines BT-474, MCF-7 and T-47D, both at the mRNA and protein levels. The effect of stimulation of these steroids on KLK10 expression varied among the cell lines. Estrogens, androgens and progestins were most potent in the BT-474, T-47D and MCF-7 cells, respectively. The up-regulation effect of estrogens, androgens, and progestins on KLK10 expression can be blocked by their antagonists ICI-182, 780, RU-56,187, and mifepristone, respectively. Time course studies showed that hK10 protein started to increase 1 day after steroid hormone stimulation and this increase persisted for 7 days. These data suggest that steroid hormones up-regulate KLK10 gene expression through direct interaction between hormone-receptor complexes and their cognate hormone response elements. To search for hormone response elements, we functionally characterized the KLK10 promoter by placing it upstream of the chloramphenicol acetyltransferase reporter gene. We found that KLK10 promoter activity did not rely on the presence of functional estrogen and androgen receptors. Also, the presence of functional estrogen and androgen receptors did not increase its constitutive activity. We suggest that the hormone response elements that mediate the transcriptional regulation of KLK10 are unlikely to locate in the KLK10 promoter.

CONCLUSIONS

Estrogens, androgens and progestins modulate KLK10 expression through their own receptors but this regulation is not mediated by steroid hormone response elements in the promoter of the KLK10 gene.

Molecular determinants of the balance between co-repressor and co-activator recruitment to the retinoic acid receptor

The repressive and activating states of nuclear hormone receptors are achieved through the recruitment of cofactor proteins. The binding of co-repressors and co-activators is believed to be mutually exclusive and principally regulated by ligand binding. To understand the molecular determinants of the switch induced by ligand in the retinoic acid receptor and in particular the intrinsic role of the ligand binding domain (LBD) in cofactor binding and release, we carried out extensive mutational analysis of surface residues of the LBD. As seen previously we found that co-repressor and co-activator molecules bind to overlapping docking sites on the surface of the retinoic acid receptor alpha LBD. Perturbation of this surface impaired both co-activator and co-repressor association resulting in a transcriptionally inert receptor. Unexpectedly mutation of two residues, Trp-225 and Ala-392, which lie outside the docking site, had opposite effects on co-activator and co-repressor binding. W225A was a constitutive repressor that failed to bind co-activator and exhibited an increased, and ligand-insensitive, interaction with co-repressor. A392R, on the other hand, had reduced affinity for co-repressors and increased affinity for co-activators and behaved as a constitutive, but still ligand-inducible, activator. Analysis of known structures showed that these mutations lie in the proximity of helix 12 (H12), and their effects are likely to be the result of perturbations in the behavior of H12. These data suggest that residues in the close vicinity of H12 regulate cofactor affinity and determine the basal activity of receptors.

Identification of glucocorticoid receptor domains involved in transrepression of transforming growth factor-beta action

The transforming growth factor-beta (TGF-beta) and glucocorticoid signaling pathways interact both positively and negatively in regulating a variety of physiological and pathologic processes. We previously reported that liganded glucocorticoid receptor (GR) repressed TGF-beta induction of human plasminogen activator inhibitor-1 gene transcription by directly targeting the transcriptional activation function of Smad3. To identify the domain(s) in the glucocorticoid receptor involved in this repression, we have examined the ability of various GR truncation, deletion, and substitution mutants to repress TGF-beta transactivation in Hep3B human hepatoma cells that lack functional endogenous GR. Partial deletions in the ligand-binding domain (LBD), including the tau2 and tauc regions, greatly reduced or eliminated GR repression, whereas deletion of the N-terminal AF1 (tau1) domain and substitution mutations in the DNA-binding domain had little or no effect. Liganded androgen receptor repressed TGF-beta transactivation, whereas mineralocorticoid receptor did not, and studies with rat GR-mineralocorticoid receptor chimeras confirmed that the GR C-terminal domains were required for repression. RU486, a strong antagonist of transactivation by GR, partially reversed repression by wild type GR. Co-immunoprecipitation experiments in Hep3B cells indicated that physical interaction between GR and Smad3 is necessary but not sufficient for repression. Physical interaction required activation of Smad3 by TGF-beta but not dexamethasone binding to GR. Glutathione S-transferase pull-down assays demonstrated that several regions of the LBD could mediate GR-Smad3 physical interaction. We conclude that the LBD of GR, but not the DNA-binding domain or the N-terminal activation domain, is required for GR-mediated transrepression of TGF-beta transactivation.

Modeling of corticosteroid pharmacogenomics in rat liver using gene microarrays

Corticosteroid (CS) pharmacogenomics was studied using gene microarrays in rat liver. Methylprednisolone (MPL) was administered intravenously at 50 mg/kg. Rats were sacrificed and liver excised at 17 time points over 72 h. RNAs from individual livers were used to query Affymetrix GeneChips that contain sequences for 8000 genes. Cluster analysis revealed six temporal patterns consisting of 197 CS-responsive probes representing 143 genes. Based on our fifth-generation model of CS pharmacokinetics/pharmacodynamics (PK/PD), mechanistic models were developed to describe the time pattern for each CS-responsive gene. Two clusters showed increased expression with different effect duration. PK/PD models assuming CS stimulation of mRNA synthesis were applied. Another two clusters showed an initial decline followed by delayed increase, suggesting two mechanisms might be involved jointly. The initial suppression was captured by CS inhibition of mRNA synthesis or stimulation of degradation. CS may also stimulate the production of a biosignal (transcription factors or other hormones), which can cause secondary induction of the target mRNA. One cluster showed a very abrupt increase in message followed by rapid decrease. These genes were lymphocytic in origin and were modeled combining the fast gene induction effect of CS in lymphoid cells and its direct lymphocyte trafficking effect. Another cluster showed reduction persisting for 18 h, which was described by CS inhibition of mRNA synthesis. Our results reveal the marked diversity of genes regulated by CS via a limited array of mechanisms. These PK/PD models provide quantitation of CS pharmacogenomics and new hypotheses regarding understanding of diverse mechanisms of CS receptor-gene mediated action.

Estrogen-induced genes, WISP-2 and pS2, respond divergently to protein kinase pathway

Recently, we identified WISP-2 (Wnt-1 inducible signaling pathway protein 2) as a novel estrogen-inducible gene in the MCF-7 human breast cancer cell line. In this study, we examined whether WISP-2 expression is modulated by PK activators. Treatment with protein kinase A (PKA) activators [cholera toxin plus 3-isobutyl-1-methylxanthine (CT/IBMX)] induced WISP-2 expression. CT/IBMX induced expression of the other estrogen-responsive gene, pS2, more dramatically than maximum stimulation by 17beta-estradiol (E2). Treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA), which directly stimulates protein kinase C (PKC) activity, completely prevented WISP-2 mRNA induction by E2, whereas it increased pS2 mRNA expression more dramatically than maximum stimulation by E2. Results of treatments with the protein synthesis inhibitor cycloheximide and the pure antiestrogen ICI182,780 suggest that these PK pathways modulate WISP-2 gene expression via different molecular mechanisms than those for pS2. Because TPA inhibits cell proliferation, we investigated whether WISP-2 induction was dependent on cell growth. Cells were treated with insulin-like growth factor-1 (IGF-1) or interleukin-1alpha (IL-1alpha) to stimulate or inhibit cell growth, respectively. These treatments had no effect on WISP-2 mRNA expression either alone or in combination with E2, suggesting that WISP-2 induction is independent of cell growth.