The glucocorticoid receptor inhibits NFkappaB by interfering with serine-2 phosphorylation of the RNA polymerase II carboxy-terminal domain

Aspergillus fumigatus germ tube growth and not conidia ingestion induces expression of inflammatory mediator genes in the human lung epithelial cell line A549

Inhalation of conidia is the main cause of invasive pulmonary aspergillosis (IPA) and the respiratory epithelium is the first line of defence. To explore the triggering factor for the inflammatory response to Aspergillus fumigatus, the species mainly responsible for IPA, this study analysed the differential expression of three inflammatory genes in A549 cells after challenge with live and killed conidia. The influence of steroids, one of the main risk factors for developing IPA, was also investigated. Quantification of mRNAs of the inflammatory mediator genes encoding interleukin (IL)-8, tumour necrosis factor (TNF)-alpha and granulocyte-monocyte colony-stimulating factor (GM-CSF) was carried out using real-time PCR. Ingestion rates were studied for the conidia of A. fumigatus and Penicillium chrysogenum using a fluorescence brightener. Similar results were obtained for both species, with ingestion rates ranging from 35 to 40 %. Exposure of A549 cells to live A. fumigatus conidia only induced a four- to fivefold increase in the mRNA levels of the three genes, starting 8 h after the initial contact. Both inactivation of live A. fumigatus conidia and treatment by dexamethasone (10(-7) M) prevented the overexpression of TNF-alpha, IL-8 and GM-CSF. Fungal growth, rather than conidia ingestion, appears to be the main stimulus for the production of inflammatory mediators by epithelial cells, and this production is inhibited by steroid therapy. These results underline the role that the epithelium plays in the innate response against IPA.

Inhibition of DNA methyltransferase activates tumor necrosis factor alpha-induced monocytic differentiation in acute myeloid leukemia cells

Transcriptional silencing via promoter methylation of genes important for cell growth and differentiation plays a key role in myeloid leukemogenesis. We find that clinically achievable levels of 5-aza-2'-deoxycytidine (5-AZA-dC), a potent inhibitor of DNA methylation, can modify chromatin and restore the ability of tumor necrosis factor alpha (TNFalpha) to induce monocytic differentiation of the acute myeloid leukemia cells NB4 and U937. Although 5-AZA-dC cannot fully induce differentiation, we show that 5-AZA-dC acts directly on TNFalpha-responsive promoters to facilitate TNFalpha-induced transcriptional pathways leading to differentiation. 5-AZA-dC regulates the expression of Dif-2, a TNFalpha target gene, by deacetylating chromatin domains in a methylation-dependent manner. Chromatin immunoprecipitation analyses of the Dif-2 promoter show histone hyperacetylation and a recruitment of the nuclear factor-kappaB transcription factor in response to 5-AZA-dC. Furthermore, 5-AZA-dC plus TNFalpha enhances the level of phosphorylated RNA Pol II at the Dif-2 promoter via synergistic recruitment of TFIIH. We conclude that nonspecific changes in chromatin can allow a specific transcriptional inducer to overcome blocks in leukemic cell differentiation. Our results support the concept of low doses of 5-AZA-dC acting in combination with other agents to target epigenetic changes that drive malignant growth in leukemic cells. [Cancer Res 2009;69(1):55-64].

Endothelin-stimulated human B-type natriuretic peptide gene expression is mediated by Yin Yang 1 in association with histone deacetylase 2

Increased B-type natriuretic peptide (BNP) gene expression is regarded as one of the hallmarks of cardiac myocyte hypertrophy. Here we demonstrate that both basal- and endothelin-1-dependent stimulation of human (h) BNP gene transcription requires the presence of an intact Yin Yang 1 (YY1) binding site positioned at -62 bp relative to the transcription start site. Mutation of this site reduced both basal and stimulated hBNP promoter activity. This site was shown to bind YY1 both in vitro and within the context of the intact cell. The latter interaction increased after endothelin-1 treatment. Exposure to endothelin-1 also resulted in increased nuclear localization of YY1 and a reduction in acetylation of the YY1 protein. Overexpression of wild-type YY1 increased both basal and endothelin-stimulated hBNP promoter activity, whereas a carboxy-terminal deletion mutant of YY1 was devoid of activity. Treatment with the histone deacetylase inhibitor trichostatin A resulted in decreased hBNP reporter activity. YY1 was shown to associate with histone deacetylase 2, and histone deacetylase 2 was shown to associate directly with the hBNP promoter in the intact cell. Collectively these findings demonstrate that YY1 plays an important role in regulating the transcriptional activity of the hBNP gene promoter. These data suggest a model in which YY1 activates hBNP transcription through interaction with histone deacetylase 2.

Suberoylanilide hydroxamic acid reactivates HIV from latently infected cells

Human immunodeficiency virus (HIV) persists in a latent form in infected individuals treated effectively with highly active antiretroviral therapy (HAART). In part, these latent proviruses account for the rebound in viral replication observed after treatment interruption. A major therapeutic challenge is to purge this reservoir. In this study, we demonstrate that suberoylanilide hydroxamic acid (SAHA) reactivates HIV from latency in chronically infected cell lines and primary cells. Indeed, P-TEFb, a critical transcription cofactor for HIV, is released and then recruited to the viral promoter upon stimulation with SAHA. The phosphatidylinositol 3-kinase/Akt pathway is involved in the initiation of these events. Using flow cytometry-based single cell analysis of protein phosphorylation, we demonstrate that SAHA activates this pathway in several subpopulations of T cells, including memory T cells that are the major viral reservoir in peripheral blood. Importantly, SAHA activates HIV replication in peripheral blood mononuclear cells from individuals treated effectively with HAART. Thus SAHA, which is a Food and Drug Administration-approved drug, might be considered to accelerate the decay of the latent reservoir in HAART-treated infected humans.

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.

Glucocorticoids inhibit GATA-3 phosphorylation and activity in T cells

Glucocorticoid (GC) immunosuppression and anti-inflammatory action involve the regulation of several transcription factors (TFs). GCs inhibit the acute production of T-helper (Th) 1 and Th2 cytokines but ultimately favor a shift toward Th2 phenotype. GCs inhibit the transcriptional activity of T-bet Th1 TF by a transrepression mechanism. Here we analyze GC regulation of GATA-3, the master driver of Th2 differentiation. We found that GCs inhibit GATA-3 transcriptional activity. We demonstrate that this mechanism does not involve physical interaction between the glucocorticoid receptor (GR) and GATA-3 or reduction of GATA-3 binding to DNA, as described previously for T-bet. Instead, GCs inhibit GATA-3 activity by inhibition of p38 mitogen-activated protein kinase induced GATA-3 phosphorylation. GCs also inhibit GATA-3 mRNA and protein expression. Finally, GATA-3 inhibition affects the interleukin-5 gene, a central Th2 cytokine. The IC(50) of dexamethasone is 10 nM with a maximum effect at 100 nM. All inhibitory actions were blocked by the GR antagonist RU38486 (1 uM), proving the specificity of GR action. In view of the crucial role of GATA-3 in T-cell differentiation and inflammation, we propose that the mechanism of GATA-3 inhibition compared with that in T-bet may have relevant implications in understanding and modulating the anti-inflammatory and Th-regulatory properties of GCs.

Thiazolidinediones are partial agonists for the glucocorticoid receptor

Although thiazolidinediones were designed as specific peroxisome proliferator-activated receptor (PPAR)-gamma-ligands, there is evidence for some off-target effects mediated by a non-PPARgamma mechanism. Previously we have shown that rosiglitazone has antiinflammatory actions not explicable by activation of PPARgamma,but possibly by the glucocorticoid receptor (GR). Rosiglitazone induces nuclear translocation both of GR-green fluorescent protein, and endogenous GR in HeLa and U20S cells but with slower kinetics than dexamethasone. Rosiglitazone also induces GR phosphorylation (Ser211), a GR ligand-binding-specific effect. Rosiglitazone drives luciferase expression from a simple glucocorticoid-response element containing reporter gene in a GR-dependent manner (EC50 4 microm), with a similar amplitude response to the partial GR agonist RU486. Rosiglitazone also inhibits dexamethasone-driven reporter gene activity (IC50 2.9 microm) in a similar fashion to RU486, suggesting partial agonist activity. Importantly we demonstrate a similar effect in PPARgamma-null cells, suggesting both GR dependence and PPARgamma independence. Rosiglitazone also activates a GAL4-GR chimera, driving a upstream activating sequence promoter, demonstrating DNA template sequence independence and furthermore enhanced steroid receptor coactivator-1-GR interaction, measured by a mammalian two-hybrid assay. Both ciglitazone and pioglitazone, structurally related to rosiglitazone, show similar effects on the GR. The antiproliferative effect of rosiglitazone is increased in U20S cells that overexpress GR, suggesting a biologically important GR-dependent component of rosiglitazone action. Rosiglitazone is a partial GR agonist, affecting GR activation and trafficking to influence engagement of target genes and affect cell function. This novel mode of action may explain some off-target effects observed in vivo. Additionally, antagonism of glucocorticoid action may contribute to the antidiabetic actions of rosiglitazone.

Kindling and Oxidative Stress as Contributors to Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Myalgic Encephalomyelitis/chronic fatigue syndrome (ME/CFS) is one of the more complex illnesses involving multiple systems within the body. Onset of ME/CFS frequently occurs quickly, and many patients report a prior exposure to a viral infection. This debilitating illness can affect the immune, neuroendocrine, autonomic, and neurologic systems. Abnormal biological findings among some patients have included aberrant ion transport and ion channel activity, cortisol deficiency, sympathetic nervous system hyperactivity, EEG spike waves, left ventricular dysfunction in the heart, low natural killer cell cytotoxicity, and a shift from Th1 to Th2 cytokines. We propose that the kindling and oxidative stress theories provide a heuristic template for better understanding the at times conflicting findings regarding the etiology and pathophysiology of this illness.

Glucocorticoids and mitogen- and stress-activated protein kinase 1 inhibitors: possible partners in the combat against inflammation

In the combat against inflammation, glucocorticoids (GCs) are a widespread therapeutic. These ligands of the glucocorticoid receptor (GR) inhibit the transactivation of various transcription factors, including nuclear factor-kappaB (NF-kappaB), and alter the composition of the pro-inflammatory enhanceosome, culminating in the repression of pro-inflammatory gene expression. However, pharmacological usage of GCs in long-term treatment is burdened with a detrimental side-effect profile. Recently, we discovered that GCs can lower NF-kappaB transactivation and pro-inflammatory gene expression by abolishing the recruitment of mitogen- and stress-activated protein kinase 1 (MSK1) (EC 2.7.11.1) to pro-inflammatory gene promoters and displacing a significant fraction of MSK1 to the cytoplasm. In our current investigation in L929sA fibroblasts, upon combining GCs and MSK1 inhibitors, we discovered a dose-dependent additive repression of pro-inflammatory gene expression, most likely due to diverse and multilayered repression mechanisms employed by GCs and MSK1 inhibitors. Therefore, the combined application of GCs and MSK1 inhibitors enabled a similar level of repression of pro-inflammatory gene expression, using actually a lower concentration of GCs and MSK1 inhibitors combined than would be necessary when using these inhibitors separately. Although H89 can inhibit both MSK1 and PKA, TNF does not activate PKA (EC 2.7.11.11) and as such PKA inhibition does not mediate H89-instigated repression of TNF-stimulated gene expression. Furthermore, the additional repressive effects of liganded GR and inhibition of MSK1, are not mediated via GR transactivation mechanisms. In conclusion, these results could entail a new therapeutic strategy using lower drug concentrations, potentially leading to a more beneficial side-effect profile.

Adenovirus E1A regulates lung epithelial ICAM-1 expression by interacting with transcriptional regulators at its promoter

We focused on the regulation of inflammatory mediator expression by adenovirus E1A in lung epithelial cells and the role of this viral protein in the pathogenesis of chronic obstructive pulmonary disease (COPD). We previously reported that E1A, a well-known regulator of host genes, increased ICAM-1 expression in human bronchial epithelial (HBE) and A549 cells in response to LPS stimulation. In this report, we clarified the mechanism of this regulation. We found NF-kappaB translocation to the nucleus after LPS stimulation in both E1A-positive and -negative HBE cells. ICAM-1 promoter reporter constructs revealed that a mutation in the proximal NF-kappaB binding site completely inhibited increased transcription, whereas the mutation in a distal site did not. We analyzed the participation of E1A in transcriptional complex formation at this promoter using chromatin immunoprecipitation. In E1A-positive HBE and A549 cells, LPS stimulation increased ICAM-1 promoter immunoprecipitation by NF-kappaB p65 and p300 but not activator protein-1 antibodies with a concomitant increase by the E1A antibody. No increase was found in E1A-negative cells except in HBE cells with p65 antibody. The association of E1A with the increased promoter immunoprecipitation with p300 was also observed after TNF-alpha stimulation of A549 cells. These results suggest that adenovirus E1A regulates the ICAM-1 promoter through its proximal NF-kappaB binding site, most likely by interacting with the transcriptional complex that forms at this site. E1A regulation of the LPS response may play a role in acute exacerbations as a consequence of bacterial infections in COPD.

Minireview: latest perspectives on antiinflammatory actions of glucocorticoids

Taking into consideration that glucocorticoid (GC) hormones have been used clinically for over half a century and that more than 20 yr have passed since the cloning of the GC receptor (GR), it is hard to imagine that novel aspects in the molecular mechanism by which GCs mediate their antiinflammatory actions are still being unveiled today. Partly, this is because almost on a daily basis, novel insights arise from parallel fields, e.g. nuclear receptor cofactor and chromatin regulation and their concomitant impact on gene transcription events, eventually leading to a revisitation or refinement of old hypotheses. On the other hand, it does remain striking and puzzling why GCs use different mechanisms in so many different cell types and on many different target genes to elicit an antiinflammatory effect. Meanwhile, the obvious question for the clinic remains: is the separation of GR functionalities through differential ligand design the strategy of choice to avoid most GC-mediated side effects? This minireview aims to highlight some of the latest findings on aspects of the antiinflammatory working mechanisms of GCs.

UPF201 archaeal specific family members reveal structural similarity to RNA-binding proteins but low likelihood for RNA-binding function

We have determined X-ray crystal structures of four members of an archaeal specific family of proteins of unknown function (UPF0201; Pfam classification: DUF54) to advance our understanding of the genetic repertoire of archaea. Despite low pairwise amino acid sequence identities (10-40%) and the absence of conserved sequence motifs, the three-dimensional structures of these proteins are remarkably similar to one another. Their common polypeptide chain fold, encompassing a five-stranded antiparallel beta-sheet and five alpha-helices, proved to be quite unexpectedly similar to that of the RRM-type RNA-binding domain of the ribosomal L5 protein, which is responsible for binding the 5S- rRNA. Structure-based sequence alignments enabled construction of a phylogenetic tree relating UPF0201 family members to L5 ribosomal proteins and other structurally similar RNA binding proteins, thereby expanding our understanding of the evolutionary purview of the RRM superfamily. Analyses of the surfaces of these newly determined UPF0201 structures suggest that they probably do not function as RNA binding proteins, and that this domain specific family of proteins has acquired a novel function in archaebacteria, which awaits experimental elucidation.

Inhibition of extracellular signal-regulated kinase (ERK) signaling participates in repression of nuclear factor (NF)-kappaB activity by glucocorticoids

Glucocorticoid (GC) effects are mediated via the GC-receptor (GR), which either stimulates or represses gene expression. Repression of target genes often involves negative cross-talk between the GR and other transcription factors e.g. NF-kappaB, important for gene activation. Using HEK293 cells we here describe that repression of NF-kappaB requires functions of the GR that are dependent on the signaling pathways employed to activate NF-kappaB. While a GR mutant was able to repress NF-kappaB activity following activation by TNFalpha, it did not so following activation by the phorbol ester TPA. In these cells, TPA stimulation but not TNFalpha, activated extracellular signal-regulated kinase (ERK). We demonstrated that the ability of the dexamethasone activated GR mutant to repress TPA-induced NF-kappaB activity was restored in conjunction with ERK1/2 inhibition. Previous reports have shown GC-mediated inhibition of ERK1/2 phosphorylation to involve GC induction of MAPK phosphatase-1 (MKP-1). Here, we demonstrated that the GRR488Q mutant was incapable of inducing gene expression of endogenous MKP-1 following dexamethasone treatment, in contrast to the GRwt. However, TPA treatment alone resulted in much stronger MKP-1 expression in both GRwt and GRR488Q containing cells than that of dexamethasone suggesting that the inability of GRR488Q to inhibit TPA-induced NF-kappaB activity did not involve a lack of MKP-1 expression. In line with this, RNAi targeted towards MKP-1 did not abolish or inhibit the ability of the GRwt to repress NF-kappaB activity. Importantly, we observed no difference in activated ERK1/2 (phospho-ERK1/2) expression over time between GRwt and GRR488Q containing cells following co-treatment with TPA and dexamethasone. Based on these results we suggest that GRwt does not directly regulate ERK1/2 but rather alters ERK1/2-mediated effects allowing it to repress NF-kappaB activity, a capacity lacked by the GRR488Q mutant.

Modulation of transcription parameters in glucocorticoid receptor-mediated repression

Glucocorticoid receptors (GRs) affect both gene induction and gene repression. The disparities of receptor binding to DNA and increased vs. decreased gene expression have suggested significant mechanistic differences between GR-mediated induction and repression. Numerous transcription factors are known to modulate three parameters of gene induction: the total activity (Vmax) and position of the dose-response curve with glucocorticoids (EC50) and the percent partial agonist activity with antiglucocorticoids. We have examined the effects on GR-mediated repression of five modulators (coactivators TIF2 [GRIP1, SRC-2] and SRC-1, corepressor SMRT, and comodulators STAMP and Ubc9), a glucocorticoid steroid (deacylcortivazol [DAC]) of very different structure, and an inhibitor of histone deacetylation (trichostatin A [TSA]). These factors interact with different domains of GR and thus are sensitive topological probes of GR action. These agents altered the Vmax, EC50, and percent partial agonist activity of endogenous and exogenous repressed genes similarly to that previously observed for GR-regulated gene induction. Collectively, these results suggest that GR-mediated induction and repression share many of the same molecular interactions and that the causes for different levels of gene transcription arise from more distal downstream steps.

Farnesoid X receptor antagonizes nuclear factor kappaB in hepatic inflammatory response

The farnesoid X receptor (FXR) is a nuclear receptor that plays key roles in hepatoprotection by maintaining the homeostasis of liver metabolism. FXR null mice display strong hepatic inflammation and develop spontaneous liver tumors. In this report, we demonstrate that FXR is a negative modulator of nuclear factor kappaB (NF-kappaB)-mediated hepatic inflammation. Activation of FXR by its agonist ligands inhibited the expression of inflammatory mediators in response to NF-kappaB activation in both HepG2 cells and primary hepatocytes cultured in vitro. In vivo, compared with wild-type controls, FXR(-/-) mice displayed elevated messenger RNA (mRNA) levels of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), interferon-inducible protein 10, and interferon-gamma in response to lipopolysaccharide (LPS). Examination of FXR(-/-) livers showed massive necroses and inflammation after treatment with LPS at a dose that does not induce significant liver damage or inflammation in wild-type mice. Moreover, transfection of a constitutively active FXR expression construct repressed the iNOS, COX-2, interferon-inducible protein 10 and interferon-gamma mRNA levels induced by LPS administration. FXR activation had no negative effects on NF-kappaB-activated antiapoptotic genes, suggesting that FXR selectively inhibits the NF-kappaB-mediated hepatic inflammatory response but maintains or even enhances the cell survival response. On the other hand, NF-kappaB activation suppressed FXR-mediated gene expression both in vitro and in vivo, indicating a negative crosstalk between the FXR and NF-kappaB signaling pathways. Our findings reveal that FXR is a negative mediator of hepatic inflammation, which may contribute to the critical roles of FXR in hepatoprotection and suppression of hepatocarcinogenesis.

MNAR functionally interacts with both NH2- and COOH-terminal GR domains to modulate transactivation

Glucocorticoids are potent anti-inflammatory agents, acting through the glucocorticoid receptor (GR) to regulate target gene transcription. However, GR may also exert acute effects, including activation of signaling kinases such as c-Src and protein kinase B, possibly via the scaffold protein, modulator of nongenomic action of the estrogen receptor (MNAR). MNAR inhibited GR transactivation in A549 cells, but in HEK293 cells there was a ligand concentration-dependent biphasic effect. Transactivation driven by low ligand concentrations was inhibited by MNAR expression, whereas higher ligand concentrations were potentiating. Further analysis revealed that MNAR inhibited transactivation by the ligand-independent activation function (AF)1 but potentiated the COOH-terminal AF2 domain. The effect of MNAR was independent of c-Src activity, demonstrated by inhibitors and c-Src knockdown studies. In support of the role of MNAR in modulating GR transactivation, coimmunoprecipitation studies showed interaction between MNAR and GR in the nucleus but not the cytoplasm. Furthermore, MNAR and c-Src were also found to physically interact in the nucleus. Immunofluorescence studies showed MNAR to be predominantly a nuclear protein, with significant colocalization with GR. Deletion studies revealed that MNAR 884-1130 was coimmunoprecipitated with GR, and furthermore this fragment inhibited GR transactivation function when overexpressed. In addition, MNAR 1-400, which contains multiple LxxLL motifs, also inhibited GR transactivation. Taken together, MNAR interacts with GR in the nucleus but not cytoplasm and regulates GR transactivation in a complex manner depending on cell type. MNAR is capable of regulating both AF1 and AF2 functions of the GR independently. MNAR expression is likely to mediate important cell variation in glucocorticoid responsiveness, in a c-Src-independent mechanism.

A novel mitogen-activated protein kinase phosphatase-1 and glucocorticoid receptor (GR) interacting protein-1-dependent combinatorial mechanism of gene transrepression by GR

Glucocorticoids have major antiinflammatory effects. Because COX-2 is the rate-limiting enzyme for proinflammatory prostaglandins, this study investigated the combinatorial inhibitory role of glucocorticoid receptor (GR) in COX-2 gene induction in macrophages and sought to identify the molecular mechanisms for that inhibition. Glucocorticoid-activated GR repressed COX-2 gene induction by lipopolysaccharide (LPS). Activated GR inhibited LPS-induced activator protein 1 activity, which in turn decreased activating transcription factor 2/c-Jun phosphorylation. The inhibition of MAPK-dependent activating transcription factor 2/c-Jun phosphorylation by GR in COX-2 repression was a result of MAPK phosphatase-1 (MKP-1) induction. Although GR did not inhibit LPS-induced p65 phosphorylation or nuclear factor-kappaB DNA binding activity, deletion of the nuclear factor-kappaB binding site in the COX-2 gene suppressed the ability of glucocorticoid to attenuate COX-2 induction. Chromatin immunoprecipitation and transfection assays revealed that a p65 DNA complex involving GR-bound GR-interacting protein 1 (GRIP1) also contributed to COX-2 repression. Additional knockdown and transfection assays identified other inflammatory genes coordinately regulated by MKP-1 and GRIP1. In summary, activated GR was found to antagonize the LPS-dependent induction of the COX-2 gene via a novel combinatorial mechanism involving MKP-1-mediated activator protein 1 inhibition and GR/GRIP1 recruitment to the p65 DNA complex; moreover, this work facilitated the identification of other GR-responding MKP-1/GRIP1-regulated genes.

Expression of the vitamin d receptor is increased in the hypertrophic heart

The liganded vitamin D receptor (VDR) is thought to play an important role in controlling cardiac function. Specifically, this system has been implicated as playing an antihypertrophic role in the heart. Despite this, studies of VDR in the heart have been limited in number and scope. In the present study, we used a combination of real-time polymerase chain reaction, Western blot analysis, immunofluorescence, and transient transfection analysis to document the presence of functional VDR in both the myocytes and fibroblasts of the heart, as well as in the intact ventricular myocardium. We also demonstrated the presence of 1-alpha-hydroxylase and 24-hydroxylase in the heart, 2 enzymes involved in the synthesis and metabolism of 1,25 dihydroxyvitamin D. VDR is shown to interact directly with the human B-type natriuretic peptide gene promoter, a surrogate marker of the transcriptional response to hypertrophy. Of note, induction of myocyte hypertrophy either in vitro or in vivo leads to an increase in VDR mRNA and protein levels. Collectively, these findings suggest that the key components required for a functional 1,25 dihydroxyvitamin D-dependent signaling system are present in the heart and that this putatively antihypertrophic system is amplified in the setting of cardiac hypertrophy.

Novel insights into mechanisms of glucocorticoid action and the development of new glucocorticoid receptor ligands

Glucocorticoids (GCs) are potent anti-inflammatory and immunosuppressant agents. Unfortunately, they also produce serious side effects that limit their usage. This discrepancy is the driving force for the intensive search for novel GC receptor ligands with a better benefit-risk ratio as compared to conventional GCs. A better understanding of the molecular mode of GC action might result in the identification of novel drug targets. Genomic GC effects are mediated by transrepression or transactivation, the latter being largely responsible for GC side effects. We here discuss novel GC receptor ligands, such as selective glucocorticoid receptor agonists (SEGRAs), which might optimize genomic GC effects as they preferentially induce transrepression with little or no transactivating activity. In addition to genomic GC effects, GCs also produce rapid genomic-independent activities, termed nongenomic, and we here review the possible implications of a recently reported mechanism underlying nongenomic GC-induced immunosuppression in T cells. It was shown that the synthetic GC dexamethasone targets membrane-bound GC receptors leading to impaired T cell receptor signaling. As a consequence, membrane-linked GC receptors might be a potential candidate target for GC therapy. The ultimate goal is to convert these molecular insights into new GC receptor modulators with an improved therapeutic index.

Genomic and nongenomic effects of glucocorticoids

The strong anti-inflammatory and immunosuppressive effects of glucocorticoids are mediated primarily by the cytosolic glucocorticoid receptors. These receptors are members of the steroid hormone receptor family, a superfamily of ligand-inducible transcription factors, and exert genomic effects that can result in increased expression of regulatory-including anti-inflammatory-proteins (transactivation), or decreased production of proinflammatory proteins (transrepression). Transactivation is thought to be responsible for numerous adverse effects of glucocorticoids; transrepression is thought to be responsible for many of the clinically desirable anti-inflammatory and immunosuppressive effects of glucocorticoids. Optimized glucocorticoids, such as selective glucocorticoid receptor agonists, are being developed to try to minimize the adverse effects many patients experience. Glucocorticoids also exert their effects via rapid, nongenomic mechanisms that can be classified as involving nonspecific interactions of glucocorticoids with cellular membranes, nongenomic effects that are mediated by cytosolic glucocorticoid receptors, or specific interactions with membrane-bound glucocorticoid receptors. Increased understanding of these mechanisms of glucocorticoid action could enable the development of novel drugs with which to treat patients with inflammatory and autoimmune disease.

Identification and functional analysis of SKA2 interaction with the glucocorticoid receptor

Glucocorticoid (GC) receptors (GRs) have profound anti-survival effects on human small cell lung cancer (SCLC). To explore the basis of these effects, protein partners for GRs were sought using a yeast two-hybrid screen. We discovered a novel gene, FAM33A, subsequently identified as a SKA1 partner and involved in mitosis, and so renamed Ska2. We produced an anti-peptide antibody that specifically recognized full-length human SKA2 to measure expression in human cell lines and tissues. There was a wide variation in expression across multiple cell lines, but none was detected in the liver cell line HepG2. A xenograft model of human SCLC had intense staining and archival tissue revealed SKA2 in several human lung and breast tumours. SKA2 was found in the cytoplasm, where it co-localized with GR, but nuclear expression of SKA2 was seen in breast tumours. SKA2 overexpression increased GC transactivation in HepG2 cells while SKA2 knockdown in A549 human lung epithelial cells decreased transactivation and prevented dexamethasone inhibition of proliferation. GC treatment decreased SKA2 protein levels in A549 cells, as did Staurosporine, phorbol ester and trichostatin A; all agents that inhibit cell proliferation. Overexpression of SKA2 potentiated the proliferative response to IGF-I exposure, and knockdown with shRNA caused cells to arrest in mitosis. SKA2 has recently been identified in HeLa S3 cells as part of a complex, which is critical for spindle checkpoint silencing and exit from mitosis. Our new data show involvement in cell proliferation and GC signalling, with implications for understanding how GCs impact on cell fate.

Salmeterol with fluticasone enhances the suppression of IL-8 release and increases the translocation of glucocorticoid receptor by human neutrophils stimulated with cigarette smoke

The combination of inhaled corticosteroids and long-acting beta2-adrenoceptor agonists is increasingly used in chronic obstructive pulmonary disease (COPD). Recently, we have demonstrated that combination of salmeterol and fluticasone propionate (FP) additionally suppress the production of IL-8 by human monocyte. In this study, the molecular mechanism behind the effectiveness of this combination therapy is investigated in human neutrophils. Human neutrophils were preincubated with salmeterol or FP or the combination. The amount of interleukin-8 (IL-8), elastase and matrix metalloproteinases (MMP)-2 and -9 releases, and reactive oxygen species (ROS) generation and expression of MAP kinase phosphatase (MKP-1) and glucocorticoid receptor (GR) were determined. Cigarette smoke medium (CSM) induces an increased expression of CXC receptors and the production of ROS that may explain the strong production of IL-8 by neutrophils. The expression of CXC receptors, the production of ROS, and the release of elastase and MMP-2 and -9 were not influenced by salmeterol, FP, or the combination. Interestingly, the combination therapy had an additive suppressive effect on the CSM-induced production of IL-8. The latter could be explained by an increased mRNA expression of MKP-1, the GR and an increased translocation of the GR to the nucleus. This leads eventually to suppression of both the NF-kappaB and MAPK pathways and, hence, to less IL-8 production by the neutrophil. These data are in support for the use of a combination therapy in COPD patients.

Prostate tumor progression is mediated by a paracrine TGF-beta/Wnt3a signaling axis

Transforming growth factor (TGF)-beta is an important paracrine factor in tumorigenesis. Ligand binding of the type I and II TGF-beta receptors initiate downstream signaling. The role of stromal TGF-beta signaling in prostate cancer progression is unknown. In mice, the conditional stromal knockout of the TGF-beta type II receptor expression (Tgfbr2(fspKO)) resulted in the development of prostatic intraepithelial neoplasia and progression to adenocarcinoma within 7 months. Clinically, we observed a loss of TGF-beta receptor type II expression in 69% of human prostate cancer-associated stroma, compared to 15% of stroma associated with benign tissues (n=140, P-value <0.0001). To investigate the mechanism of paracrine TGF-beta signaling in prostate cancer progression, we compared the effect of the prostatic stromal cells from Tgfbr2(fspKO) and floxed TGF-beta type II receptor Tgfbr2(floxE2/floxE2) mice on LNCaP human prostate cancer cells in vitro and tissue recombination xenografts. Induction of LNCaP cell proliferation and tumorigenesis was observed by Tgfbr2(fspKO) prostate stroma as a result of elevated Wnt3a expression. Neutralizing antibodies to Wnt3a reversed LNCaP tumorigenesis. The TGF-beta inhibition of Wnt3a expression was in part through the suppression of Stat3 activity on the Wnt3a promoter. In conclusion, the frequent loss of stromal TGF-beta type II receptor expression in human prostate cancer can relieve the paracrine suppression of Wnt3a expression.

The aryl hydrocarbon receptor complex and the control of gene expression

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that controls the expression of a diverse set of genes. The toxicity of the potent AhR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin is almost exclusively mediated through this receptor. However, the key alterations in gene expression that mediate toxicity are poorly understood. It has been established through characterization of AhR-null mice that the AhR has a required physiological function, yet how endogenous mediators regulate this orphan receptor remains to be established. A picture as to how the AhR/ARNT heterodimer actually mediates gene transcription is starting to emerge. The AhR/ARNT complex can alter transcription both by binding to its cognate response element and through tethering to other transcription factors. In addition, many of the coregulatory proteins necessary for AhR-mediated transcription have been identified. Cross talk between the estrogen receptor and the AhR at the promoter of target genes appears to be an important mode of regulation. Inflammatory signaling pathways and the AhR also appear to be another important site of cross talk at the level of transcription. A major focus of this review is to highlight experimental efforts to characterize nonclassical mechanisms of AhR-mediated modulation of gene transcription.

Silencing mediator for retinoid and thyroid hormone receptor and nuclear receptor corepressor attenuate transcriptional activation by the beta-catenin-TCF4 complex

beta-Catenin is a multifunctional mediator of cellular signaling and an oncogene. Nuclear beta-catenin, when complexed with members of the T-cell factor (TCF)/leukocyte enhancer factor family of DNA-binding proteins, mediates transcriptional activation important for embryonic development and adult cell homeostasis. Deregulation of intracellular levels of beta-catenin is an early event in the development of a variety of cancers. We observed that the proteins silencing mediator for retinoid and thyroid hormone receptor (SMRT) and the nuclear receptor corepressor (NCoR) are negative regulators of transcription induced by the beta-catenin-TCF4 complex. Overexpression of SMRT and NCoR attenuated the transcription of beta-catenin-TCF4-specific reporter gene and of CCND1, an endogenous beta-catenin target gene. Knockdown of endogenous SMRT or NCoR by short interfering RNA augmented the beta-catenin-TCF4-mediated reporter gene expression. Glutathione S-transferase pulldown experiments showed there was a direct physical association of SMRT and NCoR with both beta-catenin and TCF4. DNA-protein interaction studies revealed that the interactions between either SMRT or NCoR and beta-catenin or TCF4 occurred at the promoter regions of CCND1 and other target genes. These findings demonstrate an important role for corepressors SMRT and NCoR in the regulation of beta-catenin-TCF4-mediated gene transcription.

Altered subcellular distribution of MSK1 induced by glucocorticoids contributes to NF-kappaB inhibition

Glucocorticoids are widely used anti-inflammatory and immunomodulatory agents, of which the action mechanism is mainly based on interference of hormone-activated glucocorticoid receptor (GR) with the activity of transcription factors, such as nuclear factor-kappaB (NF-kappaB). In addition to the well described interaction-based mutual repression mechanism between the GR and NF-kappaB, additional mechanisms are at play, which help to explain the efficacy of glucocorticoid-mediated gene repression. In this respect, we found that glucocorticoids counteract the recruitment of activated Mitogen- and Stress-activated protein Kinase-1 (MSK1) at inflammatory gene promoters resulting in the inhibition of NF-kappaB p65 transactivation and of concurrent histone H3 phosphorylation. Additionally, we observed that activated GR can trigger redistribution of nuclear MSK1 to the cytoplasm through a CRM1-dependent export mechanism, as a result of an interaction between liganded GR and activated MSK1. These findings unveil a novel aspect within the GR-mediated NF-kappaB-targeting anti-inflammatory mechanism.

Restriction to Fos family members of Trip6-dependent coactivation and glucocorticoid receptor-dependent trans-repression of activator protein-1

The term activator protein (AP)-1 describes homodimeric and heterodimeric transcription factors composed of members of the Jun, Fos, and cAMP response element-binding protein (CREB)/activating transcription factor (ATF) families of proteins. Distinct AP-1 dimers, for instance the prototypical c-Jun:c-Fos and c-Jun:ATF2 dimers, are differentially regulated by signaling pathways and bind related yet distinct response elements in the regulatory regions of AP-1 target genes. Little is known about the dimer-specific regulation of AP-1 activity at the promoter of its target genes. We have previously shown that nTrip6, the nuclear isoform of the LIM domain protein Trip6, acts as an AP-1 coactivator. Moreover, nTrip6 is an essential component of glucocorticoid receptor (GR)-mediated trans-repression of AP-1, in that it mediates the tethering of GR to the promoter-bound AP-1. We have now discovered a striking specificity of nTrip6 actions determined by the binding preference of its LIM domains. We show that nTrip6 interacts only with Fos family members. Consequently, nTrip6 is a selective coactivator for AP-1 dimers containing Fos. nTrip6 also assembles activated GR to c-Jun:c-Fos-driven promoters. Neither nTrip6 nor GR are recruited to a promoter occupied by c-Jun:ATF2. Thus, only Fos-containing dimers are trans-repressed by GR. Thus, the dimer composition of AP-1 determines the mechanism of both the positive and negative regulation of AP-1 transcriptional activity. Interestingly, on a second level of action, GR represses the increase in transcriptional activity of c-Jun:ATF2 induced by c-Jun N-terminal kinase (JNK)-dependent phosphorylation. This repression depends on GR-mediated induction of MAPK phosphatase 1 (MKP-1) expression, which results in c-Jun N-terminal kinase inactivation.

High-mobility group protein A1 binds herpes simplex virus gene regulatory sequences and affects their expression

The high-mobility group protein A1 (HMGA1), which regulates mammalian gene expression by altering chromatin architecture, was found to bind at multiple sites within the promoter regions of all of the herpes simplex virus type 1 (HSV-1) immediate early genes, as well as a representative early (tk) gene and one late (gC) gene, both in vitro and in vivo. Infected cell polypeptide (ICP) 4, the major HSV-1 regulatory protein, binds these promoters both in vitro and in vivo, and HMGA1 enhances its in vitro binding. In transient expression experiments, HMGA1 modified the effects of both ICP4 and ICP0, another virus transactivator, on virus gene expression in a promoter-specific manner, but it had no effect on the transactivation of immediate-early promoters by VP16. These data indicate that host-cell architectural chromatin proteins could influence the interactions of host-cell and viral transcription factors with the virus DNA regulatory elements and affect HSV-1 gene expression.

Msx2 exerts bone anabolism via canonical Wnt signaling

Msx2 is a homeodomain transcription factor first identified in craniofacial bone and human femoral osteoblasts. We hypothesized that Msx2 might activate skeletal Wnt signaling. Therefore, we analyzed the effects of CMV-Msx2 transgene (Msx2Tg) expression on skeletal physiology and composition. Skeletal Msx2 expression was increased 2-3-fold by Msx2Tg, with expanded protein accumulation in marrow, secondary ossification centers, and periosteum. Microcomputed tomography established increased bone volume in Msx2Tg mice, with increased numbers of plate-like trabeculae. Histomorphometry revealed increased bone formation in Msx2Tg mice versus non-Tg siblings, arising from increased osteoblast numbers. While decreasing adipogenesis, Msx2Tg increased osteogenic differentiation via mechanisms inhibited by Dkk1, an antagonist of Wnt receptors LRP5 and LRP6. Bone from Msx2Tg mice elaborated higher levels of Wnt7 canonical agonists, with diminished Dkk1, changes that augment canonical signaling. Analysis of non-Tg and Msx2Tg siblings possessing the TOPGAL reporter confirmed this; Msx2Tg up-regulated skeletal beta-galactosidase expression (p </= 0.01), along with Wnt7a and Wnt7b, and reduced circulating Dkk1. To better understand molecular mechanisms, we studied C3H10T1/2 osteoprogenitor cells. As in bone, Msx2 increased Wnt7 genes and down-regulated Dkk1, while inducing the osteoblast gene alkaline phosphatase. Msx2-directed RNA interference increased Dkk1 expression and promoter activity, while reducing Wnt7a, Wnt7b, and alkaline phosphatase. Moreover, Msx2 inhibited Dkk1 promoter activity and reduced RNA polymerase association with Dkk1 chromatin. RNA interference-mediated knockdown of Wnt7a, Wnt7b, and LRP6 significantly reduced Msx2-induced alkaline phosphatase. Msx2 exerts bone anabolism in part by reducing Dkk1 expression and enhancing Wnt signaling, thus promoting osteogenic differentiation of skeletal progenitors.

RelA Ser276 phosphorylation is required for activation of a subset of NF-kappaB-dependent genes by recruiting cyclin-dependent kinase 9/cyclin T1 complexes

NF-kappaB plays a central role in cytokine-inducible inflammatory gene expression. Previously we empirically determined the identity of 92 members of the genetic network under direct NF-kappaB/RelA control that show marked heterogeneity in magnitude of transcriptional induction and kinetics of peak activation. To investigate this network further, we have applied a recently developed two-step chromatin immunoprecipitation assay that accurately reflects association and disassociation of RelA binding to its chromatin targets. Although inducible RelA binding occurs with similar kinetics on all NF-kappaB-dependent genes, serine 276 (Ser(276))-phosphorylated RelA binding is seen primarily on a subset of genes that are rapidly induced by tumor necrosis factor (TNF), including Gro-beta, interleukin-8 (IL-8), and IkappaBalpha. Previous work has shown that TNF-inducible RelA Ser(276) phosphorylation is controlled by a reactive oxygen species (ROS)-protein kinase A signaling pathway. To further understand the role of phospho-Ser(276) RelA in target gene expression, we inhibited its formation by ROS scavengers and antioxidants, treatments that disrupt phospho-Ser(276) formation but not the translocation and DNA binding of nonphosphorylated RelA. Here we find that phospho-Ser(276) RelA is required only for activation of IL-8 and Gro-beta, with IkappaBalpha being unaffected. These data were confirmed in experiments using RelA(-/-) murine embryonic fibroblasts reconstituted with a RelA Ser(276)Ala mutation. In addition, we observe that phospho-Ser(276) RelA binds the positive transcription elongation factor b (P-TEFb), a complex containing the cyclin-dependent kinase 9 (CDK-9) and cyclin T1 subunits. Inhibition of P-TEFb activity by short interfering RNA (siRNA)-mediated knockdown shows that the phospho-Ser(276) RelA-P-TEFb complex is required for IL-8 and Gro-beta gene activation but not for IkappaBalpha gene activation. These studies indicate that TNF induces target gene expression by heterogeneous mechanisms. One is mediated by phospho-Ser(276) RelA formation and chromatin targeting of P-TEFb controlling polymerase II (Pol II) recruitment and carboxy-terminal domain phosphorylation on the IL-8 and Gro-beta genes. The second involves a phospho-Ser(276) RelA-independent activation of genes preloaded with Pol II, exemplified by the IkappaBalpha gene. Together, these data suggest that the binding kinetics, selection of genomic targets, and mechanisms of promoter induction by RelA are controlled by a phosphorylation code influencing its interactions with coactivators and transcriptional elongation factors.

NFkappaB selectivity of estrogen receptor ligands revealed by comparative crystallographic analyses

Our understanding of how steroid hormones regulate physiological functions has been significantly advanced by structural biology approaches. However, progress has been hampered by misfolding of the ligand binding domains in heterologous expression systems and by conformational flexibility that interferes with crystallization. Here, we show that protein folding problems that are common to steroid hormone receptors are circumvented by mutations that stabilize well-characterized conformations of the receptor. We use this approach to present the structure of an apo steroid receptor that reveals a ligand-accessible channel allowing soaking of preformed crystals. Furthermore, crystallization of different pharmacological classes of compounds allowed us to define the structural basis of NFkappaB-selective signaling through the estrogen receptor, thus revealing a unique conformation of the receptor that allows selective suppression of inflammatory gene expression. The ability to crystallize many receptor-ligand complexes with distinct pharmacophores allows one to define structural features of signaling specificity that would not be apparent in a single structure.

Glycyrrhizin inhibits interleukin-8 production and nuclear factor-kappaB activity in lung epithelial cells, but not through glucocorticoid receptors

This study was designed to examine the glucocorticoid-like inhibitory effect of glycyrrhizin (GL) on interleukin (IL)-8 production in A549 lung epithelial cells. GL, as well as dexamethasone (DEX) inhibited both tumor necrosis factor (TNF)-α –and IL-1β –induced IL-8 production, mRNA expression, and promoter activity in A549 cells. Both GL and DEX inhibited transactivation of nuclear factor (NF)-κ B, without inhibiting translocation of the NF-κ B p65 subunit to the nucleus. However, the effect of GL was insensitive to RU486, a GR antagonist, and to GR knockdown by siRNA. Furthermore, only GL inhibited DNA binding of p65 to the IL-8 promoter region. These findings indicated that GL had a glucocorticoid-like inhibitory effect on IL-8 production via a mechanism that differs from that of glucocorticoids.

Caveolin mediates rapid glucocorticoid effects and couples glucocorticoid action to the antiproliferative program

Many glucocorticoid (Gc) actions are of rapid onset and therefore require acute regulation of intracellular signaling cascades. Integration of diverse extracellular signals requires cross-talk between intracellular pathways, suggesting the existence of nodes for signal interaction, such as the specialized membrane microdomains caveolae. We have identified rapid Gc-dependent phosphorylation of caveolin, and protein kinase B (PKB)/Akt, in the lung epithelial cell line A549 and found this was dependent on src kinases. There was also activation of PKB downstream molecules glycogen synthase kinase-3beta, and mammalian target of rapamycin. Subcellular fractionation colocalized glucocorticoid receptor (GR) and c-src to caveolin-containing membrane fractions. Coimmunoprecipitation studies also identified interactions between GR and caveolin and suggested that the activation function 1 domain within the GR may serve to support an interaction between GR and caveolin. Disruption of lipid raft formation, impairment of caveolin function using dominant-negative caveolin, down-regulation of caveolin-1 using short hairpin RNA or complete ablation of caveolin-1 prevented Gc-induced activation of PKB. Loss of caveolin-1 also prevents Gc activation of glycogen synthase kinase-3beta and mammalian target of rapamycin. In contrast, caveolin interference/down-regulation had no effect on Gc transactivation. Functional analysis of caveolin-1 knockdown and knockout cells identified profound loss of Gc-mediated growth inhibition compared with controls, with a requirement for caveolin in order for Gc to regulate cell cycle progression. Therefore, disruption of caveolae leads to dissociation of Gc action, with impaired induction of PKB activation, and cell growth inhibition, but with negligible effects on Gc transactivation. These observations have implications for understanding the diverse physiological actions of Gc.

Glucocorticoid suppression of CX3CL1 (fractalkine) by reduced gene promoter recruitment of NF-kappaB

Glucocorticoids are an important anti-inflammatory treatment of many inflammatory diseases including asthma. However, the mechanisms by which they mediate their suppressive effects are not fully understood. Respiratory epithelial cells are a source of CX(3)CL1 (fractalkine), which mediates cell adhesion and acts as a chemoattractant for monocytes, T cells, and mast cells. We show, in lung A549 epithelial cells, that the tumor necrosis factor-alpha (TNF-alpha) and IFNgamma synergistically induced protein release and mRNA expression of CX(3)CL1 is inhibited by dexamethasone, without interfering with cytokine-induced nuclear translocation of NF-kappaB, and by an inhibitor of IkappaB kinase 2, AS602868. DNA binding assays confirmed the ability of NF-kappaB to bind to the proximal CX(3)CL1 promoter. Chromatin immunoprecipitation assays showed a 5-fold increase in the recruitment of NF-kappaB to the CX(3)CL1 gene promoter in response to IFNgamma/TNF-alpha; this too was reversed by dexamethasone. In contrast, dexamethasone did not displace NF-kappaB from the granulocyte-macrophage colony-stimulating factor gene promoter. We conclude that CX(3)CL1 expression is regulated through the NF-kappaB pathway and that dexamethasone inhibits CX(3)CL1 expression through a glucocorticoid receptor-dependent (RU486 sensitive) mechanism. This study also provides support for the action of glucocorticoids mediating their suppressive effects on expression by interfering with the binding of transcriptional activators at native gene promoters.

Impact of steroids on hepatitis C virus replication in vivo and in vitro

Chronic hepatitis C virus (HCV) infection is the leading indication for liver transplantation. Transplantation outcome is often compromised by a rapid re-infection of the graft. Several factors have been implicated in the increased severity of recurrence, including steroid-based immunosuppression. Evidence suggests that steroid boluses used to treat acute rejection are associated with an increase in HCV viral load and the severity of recurrence. Two possible mechanisms for a steroid-mediated effect on HCV viral loads can be postulated, the first being a direct effect of steroids on the virus by enhancing its replication. The second, an indirect effect due to the suppression of the HCV immune response, allows unrestricted HCV replication. To investigate the direct effect of steroids on HCV replication, dexamethasone (Dex) and prednisolone (Pred) were tested in an in vitro replicon model. HCV replication was assessed on the basis of luciferase reporter expression (luminescence) and HCV RNA (RT-PCR). At clinically relevant concentrations (1-10 nM), treatment with both Dex and Pred did not enhance, but resulted in a slight reduction of relative luciferase activity (HCV replication), which was independent of increased cellular protein content and reduced cell proliferation. This minor reduction of HCV replication was confirmed by RT-PCR showing more than 41% reduction in HCV RNA levels. In conclusion, despite clinical evidence that the use of steroids aggravates recurrence of HCV, our in vitro study suggests that there is no direct stimulatory effect of steroids on the replication of HCV. As such, the increased viral loads after high-dose steroid treatment are more likely due to a downregulation of the immune response. In such patients, a dampened immune response allows viruses like HCV to replicate free of immune-mediated killing of their host cells. When a change occurs, such as a tapering or an alteration of immunosuppressant drugs, the immune system reinitiates and vigorously attempts to control the virus, resulting in acceleration of liver damage. Therefore, either steroid avoidance or maintaining low levels, coupled with a slow tapering of corticosteroids, may be beneficial to HCV-infected transplantation recipients.

Retinoic acid modulates chromatin to potentiate tumor necrosis factor alpha signaling on the DIF2 promoter

Transcriptional activation by nuclear hormone receptors is well characterized, but their cooperation with other signaling pathways to activate transcription remains poorly understood. Tumor necrosis factor alpha (TNFα) and all-trans retinoic acid (RA) induce monocytic differentiation of acute promyelocytic leukemia (APL) cells in a synergistic manner. We used the promoter of DIF2, a gene involved in monocytic differentiation, to model the mechanism underlying the cooperative induction of target genes by RA and TNFα. We show a functional RA response element in the DIF2 promoter, which is constitutively bound by PML/RARα in APL cells. RA stimulates release of corepressors and recruitment of chromatin modifying proteins and additional transcription factors to the promoter, but these changes cause only a modest induction of DIF2 mRNA. Co-stimulation with RA plus TNFα facilitates binding of NF-κB to the promoter, which is crucial for full induction of transcription. Furthermore, RA plus TNFα greatly enhanced the level of RNA Pol II phosphorylation on the DIF2 promoter, via synergistic recruitment of TFIIH. We propose that RA mediates remodeling of chromatin to facilitate binding of transcription factors, which cooperate to enhance Pol II phosphorylation, providing a mechanism whereby nuclear receptors interact with other signaling pathways on the level of transcription.

HMBA releases P-TEFb from HEXIM1 and 7SK snRNA via PI3K/Akt and activates HIV transcription

Hexamethylene bisacetamide (HMBA) is a potent inducer of cell differentiation and HIV production in chronically infected cells. However, its mechanism of action remains poorly defined. In this study, we demonstrate that HMBA activates transiently the PI3K/Akt pathway, which leads to the phosphorylation of HEXIM1 and the subsequent release of active positive transcription elongation factor b (P-TEFb) from its transcriptionally inactive complex with HEXIM1 and 7SK small nuclear RNA (snRNA). As a result, P-TEFb is recruited to the HIV promoter to stimulate transcription elongation and viral production. Despite the continuous presence of HMBA, the released P-TEFb reassembles rapidly with 7SK snRNA and HEXIM1. In contrast, a mutant HEXIM1 protein that cannot be phosphorylated and released from P-TEFb and 7SK snRNA via the PI3K/Akt pathway antagonizes this HMBA-mediated induction of viral production. Thus, our studies reveal how HIV transcription is induced by HMBA and suggest how modifications in the equilibrium between active and inactive P-TEFb could contribute to cell differentiation.

The reservoir of HIV in infected people remains an insurmountable problem in the era of highly active antiretroviral therapy. Thus, the virus persists despite the best possible treatment. HIV hides in many cells and tissues, where its genome is not expressed. Thus, neither drugs nor the immune system can eradicate it from the body. One hope is to activate the production of HIV in these reservoirs in the presence of optimal treatment. Strategies aimed at activating hematopoetic cells and thus viral replication have been tried and failed. In this report, we targeted a specific host transcriptional complex that is essential for the transcription of HIV genome. Its activation should not lead to generalized stimulation of the immune system. Indeed, paradoxically, hexamethylene bisacetamide (HMBA) and related compounds lead to cellular differentiation and apoptosis. By studying properties of these differentiation agents, we discovered that they activate transiently transcription of HIV, be it in stable cell lines or in primary infected cells. Thus, compounds related to HMBA, some of which have now been approved for clinical use, could be tried to diminish or eliminate the reservoir of HIV in optimally treated infected individuals.

Crosstalk between the glucocorticoid receptor and other transcription factors: molecular aspects

Glucocorticoids (GCs) regulate cell fate by altering gene expression via the glucocorticoid receptor (GR). Ligand-bound GR can activate the transcription of genes carrying the specific GR binding sequence, the glucocorticoid response element (GRE). In addition, GR can modulate, positively or negatively, directly or indirectly, the activity of other transcription factors (TFs), a process referred to as "crosstalk". In the indirect crosstalk, GR interferes with transduction pathways upstream of other TFs. In the direct crosstalk, GR and other TFs modulate each other's activity when bound to the promoters of their target genes. The multiplicity of molecular actions exerted by TFs, particularly the GR, is not only fascinating in terms of molecular structure, it also implies that the TFs participate in a wide range of regulatory processes, broader than anticipated. This review focuses on the molecular mechanisms involved in the crosstalk, on both current ideas and unresolved questions, and discusses the possible significance of the crosstalk for the physiologic and therapeutic actions of GCs.

Glucocorticoid receptor action in beneficial and side effects of steroid therapy: lessons from conditional knockout mice

Glucocorticoids (GCs) are potent immune suppressive drugs with unfortunately severe side effects. Different molecular modes of actions of the GC receptor (GR) have been identified. Transcriptional transactivation by binding of a dimerized GR protein complex to the promoter of GC regulated genes or interference with activity of pro-inflammatory transcription factors by GR monomers are considered as the two major mechanisms. It has been hypothesized that selective GR agonists (SEGRAs) addressing dimer-independent function would reveal potent steroid therapeutic activity with reduced side effects. Recent studies of a mouse knock-in strain with a dimerization-deficient GR demonstrate that some inflammatory processes can be suppressed by GCs, while others cannot. Also side effects of GCs occur in these mice. Thus, depending on the process that is treated, SEGRA could be therapeutically more or less effective and not all side effects of steroid therapy may be reduced.

Selective glucocorticoid receptor agonists (SEGRAs): novel ligands with an improved therapeutic index

Glucocorticoids are among the most successful therapies in the treatment of chronic inflammatory and autoimmune diseases. Their efficacy seems to be caused by the interference of the ligand-activated glucocorticoid receptor with many pro-inflammatory pathways via different mechanisms. The ubiquitous expression of the glucocorticoid receptor is a prerequisite for efficacy. Their main drawback, however, is due to their potential to induce adverse effects, in particular upon high dosage and prolonged usage. For the purpose reducing systemic side effects, topical glucocorticoids that act locally have been developed. Nevertheless, undesirable cutaneous effects such as skin atrophy persist from the use of topical glucocorticoids. Therefore a high medical need exists for drugs as effective as glucocorticoids but with a reduced side effect profile. Glucocorticoids function by binding to and activating the glucocorticoid receptor which positively or negatively regulates the expression of specific genes. Several experiments suggest that negative regulation of gene expression by the glucocorticoid receptor accounts for its anti-inflammatory action. This occurs through direct or indirect binding of the receptor to pro-inflammatory transcription factors that are already bound to their regulatory sites. The positive action of the receptor occurs through homodimer binding of the ligand receptor complex to discrete nucleotide sequences and this contributes to some of the adverse effects of the hormone. Glucocorticoid receptor ligands that promote the negative regulatory action of the receptor with reduced positive regulatory function should therefore show an improved therapeutic index. A complete separation of the positive from the negative regulatory activities of the receptor has so far not been possible because of the interdependent nature of the two regulatory processes. Nevertheless, recent understanding of the molecular mechanisms of the GR has triggered several drug discovery programs and these have led to the identification of dissociated GR-ligands. Such selective GR agonists (SEGRAs) are likely to enter clinical testing soon.

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.

Anti-inflammatory functions of glucocorticoid-induced genes

There is a broad consensus that glucocorticoids (GCs) exert anti-inflammatory effects largely by inhibiting the function of nuclear factor kappaB (NFkappaB) and consequently the transcription of pro-inflammatory genes. In contrast, side effects are thought to be largely dependent on GC-induced gene expression. Biochemical and genetic evidence suggests that the positive and negative effects of GCs on transcription can be uncoupled from one another. Hence, novel GC-related drugs that mediate inhibition of NFkappaB but do not activate gene expression are predicted to retain therapeutic effects but cause fewer or less severe side effects. Here, we critically re-examine the evidence in favor of the consensus, binary model of GC action and discuss conflicting evidence, which suggests that anti-inflammatory actions of GCs depend on the induction of anti-inflammatory mediators. We propose an alternative model, in which GCs exert anti-inflammatory effects at both transcriptional and post-transcriptional levels, both by activating and inhibiting expression of target genes. The implications of such a model in the search for safer anti-inflammatory drugs are discussed.

Suppression of lipopolysaccharide- and tumour necrosis factor-alpha-induced interleukin (IL)-8 expression by glucocorticoids involves changes in IL-8 promoter acetylation

There is accumulating evidence that the transrepressional effect of glucocorticoids in down-regulating proinflammatory gene expression might be regulated by an action on histone acetylation. To investigate this, we studied the effect of two glucocorticoids (dexamethasone and triamcinolone acetonide) on reducing lipopolysaccharide (LPS)- and tumour necrosis factor (TNF)-alpha-induced interleukin (IL)-8 release in a monocytic cell line and two lymphocytic cell lines (HUT-78 and Jurkat). The effect of the histone deacetylase inhibitor trichostatin A (TSA) on LPS- and TNF-alpha-induced IL-8 release and its repression by glucocorticoids was also examined. LPS and TNF-alpha induced IL-8 release in all three cell lines and this induction was inhibited by both dexamethasone and triamcinolone. Pretreatment of cells with TSA enhanced basal and LPS- and TNFalpha-stimulated IL-8 release in all three cell lines. TSA also attenuated the inhibitory effect of glucocorticoids on stimulated IL-8 release. Chromatin immunoprecipitation assays confirmed that LPS and TNF-alpha enhanced histone acetylation at the IL-8 promoter and that this was inhibited by triamcinolone in all three cell types. Changes in histone acetylation at the IL-8 are important in its regulation by proinflammatory and anti-inflammatory agents, and modulation of this activity may have therapeutic potential in inflammatory conditions.

Glucocorticoid action and the development of selective glucocorticoid receptor ligands

Glucocorticoids are important endocrine regulators of a wide range of physiological systems ranging from respiratory development, immune function to responses to stress. Glucocorticoids in cells activate the cytoplasmic glucocorticoid receptor (GR) that dimerizes, translocates to the nucleus and functions as a ligand-dependent transcriptional regulator. Synthetic glucocorticoids such as dexamethasone and prednisolone have for decades been the cornerstone for the clinical treatment of inflammatory diseases, such as rheumatoid arthritis and asthma, and in some lymphoid cancers, yet its prolonged use has undesirable side effects such as obesity, diabetes, immune suppression and osteoporosis. Detailed knowledge on the mechanism of GR action has led to the development of novel selective glucocorticoid receptor modulators (SGRMs) that show promise of being efficacious for specific treatments of disease but with fewer side effects. SGRMs promote specific recruitment of transcriptional co-regulators that elicit specific gene responses and show promise of greater efficacy and specificity in treatment of inflammatory diseases and type-2 diabetes.

Direct interaction between estrogen receptor alpha and NF-kappaB in the nucleus of living cells

Inhibition of NF-kappaB transcriptional activity by steroid receptors is the basis for the antiinflammatory actions of steroid hormones and the molecular mechanism underlying this cross-talk is thought to involve direct protein-protein interactions. In this study, we show that estrogen receptor (ER)alpha and NF-kappaB interact in vivo by using fluorescence resonance energy transfer (FRET) and co-immunoprecipitation. U2-OS cells were used to study direct interactions between fluorescent fusion proteins of ERalpha and the NF-kappaB subunits p50 and p65. Interactions were observed only in the nucleus and maximal FRET signal was detected when ERalpha is co-expressed with both NF-kappaB subunits and cells were stimulated with estrogen. This is in agreement with the induction of nuclear co-localization of the proteins under this condition. Moreover, in a U2-OS clone stably expressing ERalpha, interaction with NF-kappaB was confirmed. A p65 deletion mutant lacking the Rel homology domain was strongly impaired in its interaction with ERalpha showing the importance of this domain. Taken together, these findings provide a strong basis for the direct protein-protein interaction model for cross-talk between ERalpha and NF-kappaB.

Separating transrepression and transactivation: a distressing divorce for the glucocorticoid receptor?

Glucocorticoids (corticosteroids) are highly effective in combating inflammation in the context of a variety of diseases. However, clinical utility can be compromised by the development of side effects, many of which are attributed to the ability of the glucocorticoid receptor (GR) to induce the transcription of, or transactivate, certain genes. By contrast, the anti-inflammatory effects of glucocorticoids are due largely to their ability to reduce the expression of pro-inflammatory genes. This effect has been predominantly attributed to the repression of key inflammatory transcription factors, including AP-1 and NF-kappaB, and is termed transrepression. The ability to functionally separate these transcriptional functions of GR has prompted a search for dissociated GR ligands that can differentially induce transrepression but not transactivation. In this review, we present evidence that post-transcriptional mechanisms of action are highly important to the anti-inflammatory actions of glucocorticoids. Furthermore, we present the case that mechanistically distinct forms of glucocorticoid-inducible gene expression are critical to the development of anti-inflammatory effects by repressing inflammatory signaling pathways and inflammatory gene expression at multiple levels. Considerable care is therefore required to avoid loss of anti-inflammatory effectiveness in the development of novel transactivation-defective ligands of GR.

Oxidative stress and steroid resistance in asthma and COPD: pharmacological manipulation of HDAC-2 as a therapeutic strategy

Insensitivity to corticosteroid treatment in inflammatory conditions, such as asthma and chronic obstructive pulmonary disease, present considerable management problems and cost burdens to health services. Oxidative stress is a major component of chronic inflammation and can have a significant suppressive effect on corticosteroid efficacy. Recent advances in the understanding of both the mechanisms of corticosteroid action and corticosteroid insensitivity have provided hope for a therapeutic strategy of restoring corticosteroid sensitivity. Histone deacetylase 2 (HDAC-2) plays a pivotal role in corticosteroid action and is reduced in many cases of steroid insensitivity. Moreover, it has shown that oxidative stress can be responsible for this reduction in HDAC-2 activity. Two structurally different compounds; methyl-xanthine theophylline and polyphenol curcumin restore HDAC activity, thereby restoring corticosteroid function. Low, subbronchodilator doses of theophylline can also act as corticosteroid-sparing drugs in asthmatics. Although these compounds appear to restore corticosteroid function and may initially provide therapeutic potential, they lack specificity and the mechanism of their action is unknown. Once their mechanisms of action are established, it is likely that derivatives of these compounds may be used as a therapeutic strategy to restore corticosteroid insensitivity in the future.