GRIP1-associated SET-domain methyltransferase in glucocorticoid receptor target gene expression

Mechanisms of epigenomic and functional convergence between glucocorticoid- and IL4-driven macrophage programming

Macrophages adopt distinct phenotypes in response to environmental cues, with type-2 cytokine interleukin-4 promoting a tissue-repair homeostatic state (M2IL4). Glucocorticoids (GC), widely used anti-inflammatory therapeutics, reportedly impart a similar phenotype (M2GC), but how such disparate pathways may functionally converge is unknown. We show using integrative functional genomics that M2IL4 and M2GC transcriptomes share a striking overlap mirrored by a shift in chromatin landscape in both common and signal-specific gene subsets. This core homeostatic program is enacted by transcriptional effectors KLF4 and the glucocorticoid receptor, whose genome-wide occupancy and actions are integrated in a stimulus-specific manner by the nuclear receptor cofactor GRIP1. Indeed, many of the M2IL4:M2GC-shared transcriptomic changes were GRIP1-dependent. Consistently, GRIP1 loss attenuated phagocytic activity of both populations in vitro and macrophage tissue-repair properties in the murine colitis model in vivo. These findings provide a mechanistic framework for homeostatic macrophage programming by distinct signals, to better inform anti-inflammatory drug design.

Mechanisms of Epigenomic and Functional Convergence Between Glucocorticoid- and IL4-Driven Macrophage Programming

Macrophages adopt distinct phenotypes in response to environmental cues, with type-2 cytokine interleukin-4 promoting a tissue-repair homeostatic state (M2IL4). Glucocorticoids, widely used anti-inflammatory therapeutics, reportedly impart a similar phenotype (M2GC), but how such disparate pathways may functionally converge is unknown. We show using integrative functional genomics that M2IL4 and M2GC transcriptomes share a striking overlap mirrored by a shift in chromatin landscape in both common and signal-specific gene subsets. This core homeostatic program is enacted by transcriptional effectors KLF4 and the GC receptor, whose genome-wide occupancy and actions are integrated in a stimulus-specific manner by the nuclear receptor cofactor GRIP1. Indeed, many of the M2IL4:M2GC-shared transcriptomic changes were GRIP1-dependent. Consistently, GRIP1 loss attenuated phagocytic activity of both populations in vitro and macrophage tissue-repair properties in the murine colitis model in vivo. These findings provide a mechanistic framework for homeostatic macrophage programming by distinct signals, to better inform anti-inflammatory drug design.

The SUV4-20H Histone Methyltransferases in Health and Disease

The post-translational modification of histone tails is a dynamic process that provides chromatin with high plasticity. Histone modifications occur through the recruitment of nonhistone proteins to chromatin and have the potential to influence fundamental biological processes. Many recent studies have been directed at understanding the role of methylated lysine 20 of histone H4 (H4K20) in physiological and pathological processes. In this review, we will focus on the function and regulation of the histone methyltransferases SUV4-20H1 and SUV4-20H2, which catalyze the di- and tri-methylation of H4K20 at H4K20me2 and H4K20me3, respectively. We will highlight recent studies that have elucidated the functions of these enzymes in various biological processes, including DNA repair, cell cycle regulation, and DNA replication. We will also provide an overview of the pathological conditions associated with H4K20me2/3 misregulation as a result of mutations or the aberrant expression of SUV4-20H1 or SUV4-20H2. Finally, we will critically analyze the data supporting these functions and outline questions for future research.

The glucocorticoid receptor recruits the COMPASS complex to regulate inflammatory transcription at macrophage enhancers

Glucocorticoids (GCs) are effective anti-inflammatory drugs; yet, their mechanisms of action are poorly understood. GCs bind to the glucocorticoid receptor (GR), a ligand-gated transcription factor controlling gene expression in numerous cell types. Here, we characterize GR’s protein interactome and find the SETD1A (SET domain containing 1A)/COMPASS (complex of proteins associated with Set1) histone H3 lysine 4 (H3K4) methyltransferase complex highly enriched in activated mouse macrophages. We show that SETD1A/COMPASS is recruited by GR to specific cis-regulatory elements, coinciding with H3K4 methylation dynamics at subsets of sites, upon treatment with lipopolysaccharide (LPS) and GCs. By chromatin immunoprecipitation sequencing (ChIP-seq) and RNA-seq, we identify subsets of GR target loci that display SETD1A occupancy, H3K4 mono-, di-, or tri-methylation patterns, and transcriptional changes. However, our data on methylation status and COMPASS recruitment suggest that SETD1A has additional transcriptional functions. Setd1a loss-of-function studies reveal that SETD1A/COMPASS is required for GR-controlled transcription of subsets of macrophage target genes. We demonstrate that the SETD1A/COMPASS complex cooperates with GR to mediate anti-inflammatory effects.

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GR’s transcriptional complex in macrophages includes COMPASS proteins

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GR ligand changes SETD1A chromatin occupancy in activated macrophages

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Subsets of GR target sites show COMPASS binding and H3K4 methylation dynamics

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SETD1A is required for some of GR’s anti-inflammatory actions

MLL2 regulates glucocorticoid receptor-mediated transcription of ENACα in human retinal pigment epithelial cells

Glucocorticoids require the glucocorticoid receptor (GR), a type of ligand-dependent nuclear receptor to transmit their downstream effects. Upon glucocorticoid binding, GR associates with glucocorticoid response elements (GREs) and recruits other transcriptional coregulators to activate or repress target gene transcription. Many SET-domain family proteins have been demonstrated to contribute to GR-mediated transcriptional activity. However, whether histone H3K4-specific methyltransferase plays a cell-type-specific role in GR transcriptional regulation remains poorly understood. In this report, we examined MLL2 (KMT2D), a histone-lysine methyltransferase that catalyzes histone H3 lysine 4 methylation (H3K4me). Furthermore, we demonstrated that MLL2 specifically regulates the transcription of some GR target genes (e.g., ENACα and FLJ20371) in ARPE-19 cells, but has no effect in A549 cells. Mechanistically, co-immunoprecipitation assays revealed that MLL2 is associated with GR in a ligand-independent manner in APRE-19 cells. Moreover, chromatin immunoprecipitation analyses demonstrated that MLL2 could co-occupy glucocorticoid response elements (GREs) of GR target genes along with GR following Dex stimulation. Finally, the FAIRE-qPCR results illustrated that MLL2 is pivotal in establishing chromatin structure accessibility at the GREs of ARPE-19 specific genes in the presence of Dex. Taken together, our study determined that MLL2 regulates GR-mediated transcription in a cell-type-specific manner, and we provide a molecular mechanism to explain the specific role of MLL2 in regulating GR target gene expression in ARPE-19 cells.

H3K4 dimethylation at FosB promoter in the striatum of chronic stressed rats promotes morphine-induced conditioned place preference

Expression of FosB gene in striatum is essential in addiction establishment. Activated glucocorticoid receptors (GRs) induce FosB gene expression in response to stressor. Therefore, elevation of FosB expression in striatum serves as one mechanism by which stress increases risk for addiction. In this study, adult male Sprague-Dawley rats were used to investigate whether chronic stress result in histone modifications at FosB gene promoter in striatum and how these histone modifications affect FosB expression and the establishment of addiction behavior after administration of drugs of abuse. Animals were randomly assigned to three groups: Electric foot shock (EFS) group received 7-day EFS to induce chronic stress; electric foot shock plus mifepristone (EFS + Mif) group were injected with mifepristone, a nonspecific GRs antagonist, before EFS; control group did not receive any EFS. All groups then received 2-day conditioned place preference (CPP) training with morphine (5 mg/kg body weight) to test vulnerability to drug addiction. Before and after morphine administration, FosB mRNA in striatum was quantified by real-time RT-PCR. Levels of histone H3/H4 acetylation and histone H3K4 dimethylation at FosB promoter in striatum after morphine administration were measured by using chromatin immunoprecipitation (ChIP) plus real-time PCR. EFS group had stronger place preference to morphine and had significantly higher level of FosB mRNA in striatum than the other two groups. H3K4 dimethylation was 2.6-fold higher in EFS group than control group, while no statistical difference in H3/H4 acetylation. Mifepristone administration before EFS decreased histone H3K4 dimethylation and FosB mRNA in striatum, and also diminished morphine-induced conditioned place preference. Altogether, increased level of H3K4 dimethylation at FosB promoter in striatum is partially dependent on the activation of GR and responsible for the elevated level of morphine-induced FosB mRNA in chronic stressed animals.

Somatic Cancer Mutations in the SUV420H1 Protein Lysine Methyltransferase Modulate Its Catalytic Activity

SUV420H1 is a protein lysine methyltransferase that introduces di- and trimethylation of H4K20 and is frequently mutated in human cancers. We investigated the functional effects of eight somatic cancer mutations on SUV420H1 activity in vitro and in cells. One group of mutations (S255F, K258E, A269V) caused a reduction of the catalytic activity on peptide and nucleosome substrates. The mutated amino acids have putative roles in AdoMet binding and recognition of H4 residue D24. Group 2 mutations (E238V, D249N, E320K) caused a reduction of activity on peptide substrates, which was partially recovered when using nucleosomal substrates. The corresponding residues could have direct or indirect roles in peptide and AdoMet binding, but the effects of the mutations can be overcome by additional interactions between SUV420H1 and the nucleosome substrate. The third group of mutations (S283L, S304Y) showed enhanced activity with peptide substrates when compared with nucleosomal substrates, suggesting that these residues are involved in nucleosomal interaction or allosteric activation of SUV420H1 after nucleosome binding. Group 2 and 3 mutants highlight the role of nucleosomal contacts for SUV420H1 regulation in agreement with the high activity of this enzyme on nucleosomal substrates. Strikingly, seven of the somatic cancer mutations studied here led to a reduction of the catalytic activity of SUV420H1 in cells, suggesting that SUV420H1 activity might have a tumor suppressive function. This could be explained by the role of H4K20me2/3 in DNA repair, suggesting that loss or reduction of SUV420H1 activity could contribute to a mutator phenotype in cancer cells.

Increased stress and altered expression of histone modifying enzymes in brain are associated with aberrant behaviour in vitamin B12 deficient female mice

A sub-optimal nutritional environment from early life can be envisaged as a stressor that translates into mental health problems in adulthood. After considering (a) the widespread prevalence of vitamin B12 deficiency especially amongst women in developing countries and (b) the importance of vitamin B12 in normal brain function, in this study we have elucidated the behavioural correlates of chronic severe and moderate vitamin B12 deficiency in C57BL/6 mice. Female weanling mice were assigned to three dietary groups: (a) control AIN-76A diet with cellulose as dietary fibre (b) vitamin B12 restricted AIN-76A diet with pectin as dietary fibre (severe deficiency group) and (c) vitamin B12 restricted AIN-76A diet with cellulose as dietary fibre (moderate deficiency group). The mice received these diets throughout pregnancy, lactation and thereafter. Nest-building, maternal care, anxiety and depressive behaviours were evaluated. Oxidative stress, activities of antioxidant enzymes and expression of various histone modifying enzymes in brain were investigated to unravel the probable underlying mechanisms. Our data suggests that both severe and moderate vitamin B12 deficiency induced anxiety and impaired maternal care. However, only severe vitamin B12 deficiency induced depression. Oxidative stress and poor antioxidant defense underlie the deleterious effects of both severe and moderate vitamin B12 deficiency. Altered expression of histone modifying enzymes in the brain of severely deficient mice is suggestive of epigenetic reprogramming. This study suggests that chronic vitamin B12 deficiency leads to behavioural anomalies in female C57BL/6 mice and the severity of these outcomes can be correlated to the level of deficiency.

The first crystal structure of a DNA-free nuclear receptor DNA binding domain sheds light on DNA-driven allostery in the glucocorticoid receptor

The glucocorticoid receptor (GR) is a steroid hormone receptor of the nuclear receptor family that regulates gene expression in response to glucocorticoid hormone signaling. Interaction with specific GR DNA binding sequences causes conformational changes in the GR DNA binding domain (DBD) that result in recruitment of specific sets of co-regulators that determine transcriptional outcomes. We have solved the crystal structure of GR DBD in its DNA-free state, the first such crystal structure from any nuclear receptor. In contrast to previous NMR structures, this crystal structure reveals that free GR DBD adopts a conformation very similar to DNA-bound states. The lever arm region is the most variable element in the free GR DBD. Molecular dynamics of the free GR DBD as well as GR DBD bound to activating and repressive DNA elements confirm lever arm flexibility in all functional states. Cluster analysis of lever arm conformations during simulations shows that DNA binding and dimerization cause a reduction in the number of conformations sampled by the lever arm. These results reveal that DNA binding and dimerization drive conformational selection in the GR DBD lever arm region and show how DNA allosterically controls GR structure and dynamics.

Epigenetic Changes in Diabetes and Cardiovascular Risk

Cardiovascular complications remain the leading causes of morbidity and premature mortality in patients with diabetes mellitus. Studies in humans and preclinical models demonstrate lasting gene expression changes in the vasculopathies initiated by previous exposure to high glucose concentrations and the associated overproduction of reactive oxygen species. The molecular signatures of chromatin architectures that sensitize the genome to these and other cardiometabolic risk factors of the diabetic milieu are increasingly implicated in the biological memory underlying cardiovascular complications and now widely considered as promising therapeutic targets. Atherosclerosis is a complex heterocellular disease where the contributing cell types possess distinct epigenomes shaping diverse gene expression. Although the extent that pathological chromatin changes can be manipulated in human cardiovascular disease remains to be established, the clinical applicability of epigenetic interventions will be greatly advanced by a deeper understanding of the cell type-specific roles played by writers, erasers, and readers of chromatin modifications in the diabetic vasculature. This review details a current perspective of epigenetic mechanisms of macrovascular disease in diabetes mellitus and highlights recent key descriptions of chromatinized changes associated with persistent gene expression in endothelial, smooth muscle, and circulating immune cells relevant to atherosclerosis. Furthermore, we discuss the challenges associated with pharmacological targeting of epigenetic networks to correct abnormal or deregulated gene expression as a strategy to alleviate the clinical burden of diabetic cardiovascular disease.

Flightless-I homolog regulates glucocorticoid receptor-mediated transcription via direct interaction of the leucine-rich repeat domain

Flightless-I homolog (FLII) is a member of the gelsolin family of proteins, and has been identified as a coactivator of estrogen receptor-mediated transcription. Here, we investigate the role of FLII in the glucocorticoid receptor (GR) signaling pathway. Reporter gene assay and real-time quantitative PCR in A549 were performed to investigate the function of FLII in the expression of GR target genes. Co-immunoprecipitation assay and in vitro binding assay were used to identify binding domain of FLII. Chromatin immunoprecipitation assay were carried out with FLII-depleted A549 cells to determine the role of FLII at GR binding sites. We demonstrate that FLII potentiates GR-mediated reporter gene activity synergistically with CARM1 and p300 to enhance GR transcriptional activity in the presence of dexamethasone (Dex) in A549 cells. Depletion of endogenous FLII inhibited the expression of Dex-regulated GR target genes in A549 cells, indicating that FLII is required for GR-mediated transcription. Further, we observed that FLII binds to GR via its N-terminal leucine-rich repeat (LRR) region, suggesting that the enhancement of GR activation may occur through the interaction of GR and FLII. Moreover, chromatin immunoprecipitation analysis demonstrated that FLII is recruited to the GR binding sites. In addition, depletion of endogenous FLII decreased the recruitment of p300, and subsequently RNA polymerase II, to specific sites of GR target genes. Taken together, these studies reveal a functional involvement of FLII in activating transcription of GR target genes, suggesting a physiological role for FLII in the GR signaling pathway.

Gene Expression Control by Glucocorticoid Receptors during Innate Immune Responses

Glucocorticoids (GCs) are potent anti-inflammatory compounds that have been extensively used in clinical practice for several decades. GC's effects on inflammation are generally mediated through GC receptors (GRs). Signal transduction through these nuclear receptors leads to dramatic changes in gene expression programs in different cell types, typically due to GR binding to DNA or to transcription modulators. During the last decade, the view of GCs as exclusive anti-inflammatory molecules has been challenged. GR negative interference in pro-inflammatory gene expression was a landmark in terms of molecular mechanisms that suppress immune activity. In fact, GR can induce varied inhibitory molecules, including a negative regulator of Toll-like receptors pathway, or subject key transcription factors, such as NF-κB and AP-1, to a repressor mechanism. In contrast, the expression of some acute-phase proteins and other players of innate immunity generally requires GR signaling. Consequently, GRs must operate context-dependent inhibitory, permissive, or stimulatory effects on host defense signaling triggered by pathogens or tissue damage. This review aims to disclose how contradictory or comparable effects on inflammatory gene expression can depend on pharmacological approach (including selective GC receptor modulators; SEGRMs), cell culture, animal treatment, or transgenic strategies used as models. Although the current view of GR-signaling integrated many advances in the field, some answers to important questions remain elusive.

Androgen deprivation-induced NCoA2 promotes metastatic and castration-resistant prostate cancer

A major clinical hurdle for the management of advanced prostate cancer (PCa) in patients is the resistance of tumors to androgen deprivation therapy (ADT) and their subsequent development into castration-resistant prostate cancer (CRPC). While recent studies have identified potential pathways involved in CRPC development, the drivers of CRPC remain largely undefined. Here we determined that nuclear receptor coactivator 2 (NCoA2, also known as SRC-2), which is frequently amplified or overexpressed in patients with metastatic PCa, mediates development of CRPC. In a murine model, overexpression of NCoA2 in the prostate epithelium resulted in neoplasia and, in combination with Pten deletion, promoted the development of metastasis-prone cancer. Moreover, depletion of NCoA2 in PTEN-deficient mice prevented the development of CRPC. In human androgen-sensitive prostate cancer cells, androgen signaling suppressed NCoA2 expression, and NCoA2 overexpression in murine prostate tumors resulted in hyperactivation of PI3K/AKT and MAPK signaling, promoting tumor malignance. Analysis of PCa patient samples revealed a strong correlation among NCoA2-mediated signaling, disease progression, and PCa recurrence. Taken together, our findings indicate that androgen deprivation induces NCoA2, which in turn mediates activation of PI3K signaling and promotes PCa metastasis and CRPC development. Moreover, these results suggest that the inhibition of NCoA2 has potential for PCa therapy.

Resveratrol modulates the inflammatory response via an estrogen receptor-signal integration network

Resveratrol has beneficial effects on aging, inflammation and metabolism, which are thought to result from activation of the lysine deacetylase, sirtuin 1 (SIRT1), the cAMP pathway, or AMP-activated protein kinase. In this study, we report that resveratrol acts as a pathway-selective estrogen receptor-α (ERα) ligand to modulate the inflammatory response but not cell proliferation. A crystal structure of the ERα ligand-binding domain (LBD) as a complex with resveratrol revealed a unique perturbation of the coactivator-binding surface, consistent with an altered coregulator recruitment profile. Gene expression analyses revealed significant overlap of TNFα genes modulated by resveratrol and estradiol. Furthermore, the ability of resveratrol to suppress interleukin-6 transcription was shown to require ERα and several ERα coregulators, suggesting that ERα functions as a primary conduit for resveratrol activity.DOI: http://dx.doi.org/10.7554/eLife.02057.001.

Hic-5 is a transcription coregulator that acts before and/or after glucocorticoid receptor genome occupancy in a gene-selective manner

Ligand activation and DNA-binding dictate the outcome of glucocorticoid receptor (GR)-mediated transcriptional regulation by inducing diverse receptor conformations that interact differentially with coregulators. GR recruits many coregulators via the well-characterized AF2 interaction surface in the GR ligand-binding domain, but Lin11, Isl-1, Mec-3 (LIM) domain coregulator Hic-5 (TGFB1I1) binds to the relatively uncharacterized tau2 activation domain in the hinge region of GR. Requirement of hydrogen peroxide-inducible clone-5 (Hic-5) for glucocorticoid-regulated gene expression was defined by Hic-5 depletion and global gene-expression analysis. Hic-5 depletion selectively affected both activation and repression of GR target genes, and Hic-5 served as an on/off switch for glucocorticoid regulation of many genes. For some hormone-induced genes, Hic-5 facilitated recruitment of Mediator complex. In contrast, many genes were not regulated by glucocorticoid until Hic-5 was depleted. On these genes Hic-5 prevented GR occupancy and chromatin remodeling and thereby inhibited their hormone-dependent regulation. Transcription factor binding to genomic sites is highly variable among different cell types; Hic-5 represents an alternative mechanism for regulating transcription factor-binding site selection that could apply both within a given cell type and among different cell types. Thus, Hic-5 is a versatile coregulator that acts by multiple gene-specific mechanisms that influence genomic occupancy of GR as well transcription complex assembly.

Nuclear receptors in inflammation control: repression by GR and beyond

Inflammation is a protective response of organisms to pathogens, irritation or injury. Primary inflammatory sensors activate an array of signaling pathways that ultimately converge upon a few transcription factors such as AP1, NFκB and STATs that in turn stimulate expression of inflammatory genes to ultimately eradicate infection and repair the damage. A disturbed balance between activation and inhibition of inflammatory pathways can set the stage for chronic inflammation which is increasingly recognized as a key pathogenic component of autoimmune, metabolic, cardiovascular and neurodegenerative disorders. Nuclear receptors (NRs) are a large family of transcription factors many of which are known for their potent anti-inflammatory actions. Activated by small lipophilic ligands, NRs interact with a wide range of transcription factors, cofactors and chromatin-modifying enzymes, assembling numerous cell- and tissue-specific DNA-protein transcriptional regulatory complexes with diverse activities. Here we discuss established and emerging roles and mechanisms by which NRs and, in particular, the glucocorticoid receptor (GR) repress genes encoding cytokines, chemokines and other pro-inflammatory mediators.

A conserved protein motif is required for full modulatory activity of negative elongation factor subunits NELF-A and NELF-B in modifying glucocorticoid receptor-regulated gene induction properties

NELF-B is a BRCA1-interacting protein and subunit (with NELF-A, -C/D, and -E) of the human negative elongation factor (NELF) complex, which participates in RNA polymerase II pausing shortly after transcription initiation, especially for synchronized gene expression. We now report new activities of NELF-B and other NELF complex subunits, which are to attenuate glucocorticoid receptor (GR)-mediated gene induction, reduce the partial agonist activity of an antagonist, and increase the EC50 of an agonist during nonsynchronized expression of exogenous and endogenous reporters. Stable knockdown of endogenous NELF-B has the opposite effects on an exogenous gene. The GR ligand-binding domain suffices for these biological responses. ChIP assays reveal that NELF-B diminishes GR recruitment to promoter regions of two endogenous genes. Using a new competition assay, NELF-A and NELF-B are each shown to act independently as competitive decelerators at two steps after the site of GR action and before or at the site of reporter gene activity. A common motif in each NELF was identified that is required for full activity of both NELF-A and NELF-B. These studies allow us to position the actions of two new modulators of GR-regulated transactivation, NELF-A and NELF-B, relative to other factors in the overall gene induction sequence.

CCAR1 promotes chromatin loading of androgen receptor (AR) transcription complex by stabilizing the association between AR and GATA2

Androgen receptor (AR), a ligand-dependent transcription factor, plays a critical role in prostate cancer onset and progression, and its transcriptional function is mediated largely by distinct nuclear receptor co-regulators. Here, we show that cell cycle and apoptosis regulator 1 (CCAR1) functions as an AR co-activator. CCAR1 interacted with and enhanced the transcriptional activity of AR. Depletion of CCAR1 caused reduction in androgen-dependent expression of a subset of AR target genes. We further showed that CCAR1 is required for recruitment of AR, MED1 and RNA polymerase II to the enhancers of AR target genes and for androgen-induced long-range prostate specific antigen enhancer–promoter interaction. The molecular mechanism underlying CCAR1 function in AR-mediated transcription involves CCAR1-mediated enhanced recruitment of GATA2, a pioneer factor for AR, to AR-binding sites. CCAR1 stabilized the interaction between AR and GATA2 by interacting directly with both proteins, thereby facilitating AR and GATA2 occupancy on the enhancers. Furthermore, CCAR1 depletion inhibited the growth, migration, invasion of prostate cancer cells and reduced the tumorigenicity of prostate cancer cells in vivo. Our results firmly established CCAR1 as an AR co-activator that plays a key role in AR transcription complex assembly and has an important physiological role in androgen signaling and prostate tumorigenesis.

Role of transcriptional coregulator GRIP1 in the anti-inflammatory actions of glucocorticoids

Inhibition of cytokine gene expression by the hormone-activated glucocorticoid receptor (GR) is the key component of the anti-inflammatory actions of glucocorticoids, yet the underlying molecular mechanisms remain obscure. Here we report that glucocorticoid repression of cytokine genes in primary macrophages is mediated by GR-interacting protein (GRIP)1, a transcriptional coregulator of the p160 family, which is recruited to the p65-occupied genomic NFκB-binding sites in conjunction with liganded GR. We created a mouse strain enabling a conditional hematopoietic cell-restricted deletion of GRIP1 in adult animals. In this model, GRIP1 depletion in macrophages attenuated in a dose-dependent manner repression of NFκB target genes by GR irrespective of the upstream Toll-like receptor pathway responsible for their activation. Furthermore, genome-wide transcriptome analysis revealed a broad derepression of lipopolysaccharide (LPS)-induced glucocorticoid-sensitive targets in GRIP1-depleted macrophages without affecting their activation by LPS. Consistently, conditional GRIP1-deficient mice were sensitized, relative to the wild type, to a systemic inflammatory challenge developing characteristic signs of LPS-induced shock. Thus, by serving as a GR corepressor, GRIP1 facilitates the anti-inflammatory effects of glucocorticoids in vivo.

Nuclear epidermal growth factor receptor interacts with transcriptional intermediary factor 2 to activate cyclin D1 gene expression triggered by the oncoprotein latent membrane protein 1

The epidermal growth factor receptor (EGFR), a ubiquitously expressed receptor tyrosine kinase, is an important factor in carcinogenesis. Transcriptional intermediary factor 2 (TIF2), a member of the p160 nuclear receptor co-activator gene family, is linked to the proliferation of cancer cells. However, the direct interplay between the EGFR and the nuclear receptors remains unclear. Our previous study demonstrated that nuclear EGFR could directly bind to the cyclin D1 promoter under the regulation of the oncoprotein latent membrane protein 1 (LMP1), but it also indicated that other factors are involved in the activation of target genes. In this study, we found that LMP1 upregulated the expression of TIF2 and promoted the interaction of EGFR with TIF2 in nasopharyngeal carcinoma. Furthermore, we demonstrated that the intact complex was linked with cyclin D1 promoter activity in an LMP1-dependent manner. The physiological functions of the intact complex were associated with cell proliferation and cell cycle progression. These findings suggest that TIF2 is a novel binding partner for nuclear EGFR and is involved in regulating its target gene expression.

O-GlcNAc transferase is involved in glucocorticoid receptor-mediated transrepression

Recruitment of O-GlcNAc transferase (OGT) to promoters plays an important role in gene repression. Glucocorticoid signaling represses the transcriptional activities of NF-κB and AP-1 through direct binding, yet the molecular mechanisms remain to be elucidated. Here we report that OGT is an important component of GR-mediated transrepression. OGT associates with ligand-bound GR in a multi-protein repression complex. Overexpression of OGT potentiates the GR transrepression pathway, whereas depletion of endogenous OGT by RNA interference abolishes the repression. The recruitment of OGT by GR leads to increased O-GlcNAcylation and decreased phosphorylation of RNA polymerase II on target genes. Functionally, overexpression of OGT enhances glucocorticoid-induced apoptosis in resistant cell lines while knockdown of OGT prevents sensitive cell lines from apoptosis. These studies identify a molecular mechanism of GR transrepression, and highlight the function of O-GlcNAc in hormone signaling.

Maps and legends: the quest for dissociated ligands of the glucocorticoid receptor

Glucocorticoids are steroid hormones that have pleiotropic effects on development, metabolism, cognitive function and other aspects of physiology. Since the demonstration more than sixty years ago of their capacity to suppress inflammation, synthetic glucocorticoids have been extremely widely used in the treatment of inflammatory diseases. However, their clinical use is limited by numerous, unpredictable and potentially serious side effects. Glucocorticoids regulate gene expression both positively and negatively. Both of these effects are mediated by the glucocorticoid receptor, a ligand-dependent transcription factor. It has become widely accepted that anti-inflammatory effects of glucocorticoids are mostly due to inhibition of transcription, whereas the activation of transcription by the glucocorticoid receptor accounts for the majority of side effects. This dogma (which we refer to as the "transrepression hypothesis") predicts the possibility of uncoupling therapeutic, anti-inflammatory effects from side effects by identifying novel, selective ligands of the glucocorticoid receptor, which preferentially mediate inhibition rather than activation of transcription. It is argued that such "dissociated" glucocorticoid receptor ligands should retain anti-inflammatory potency but cause fewer side effects. Here we critically re-examine the history and foundations of the transrepression hypothesis. We argue that it is incompatible with the complexity of gene regulation by glucocorticoids and poorly supported by experimental evidence; that it no longer aids clear thinking about the actions of the glucocorticoid receptor; and that it will not prove a fruitful basis for continued refinement and improvement of anti-inflammatory drugs that target the glucocorticoid receptor.

Nuclear receptors and inflammation control: molecular mechanisms and pathophysiological relevance

Tissue inflammation is a tightly regulated process that normally serves to recruit the immune system to sites of infection and injury and to facilitate tissue repair processes. When an inflammatory state is excessive or prolonged, local and systemic damage to host tissues can result in loss of normal physiological functions. Here, we briefly review recent studies that advance our understanding of signaling pathways involved in initiation of inflammatory responses at the level of transcription and counterregulation of these pathways by selected members of the nuclear receptor superfamily. Studies of the intersection of nuclear receptors and inflammation have revealed mechanisms of positive and negative transcriptional control that may provide new targets for pharmacological intervention in chronic diseases, such as atherosclerosis.

The type I interferon signaling pathway is a target for glucocorticoid inhibition

Type I interferon (IFN) is essential for host defenses against viruses; however, dysregulated IFN signaling is causally linked to autoimmunity, particularly systemic lupus erythematosus. Autoimmune disease treatments rely on glucocorticoids (GCs), which act via the GC receptor (GR) to repress proinflammatory cytokine gene transcription. Conversely, cytokine signaling through cognate Jak/STAT pathways is reportedly unaffected or even stimulated by GR. Unexpectedly, we found that GR dramatically inhibited IFN-stimulated gene (ISG) expression in macrophages. The target of inhibition, the heterotrimeric STAT1-STAT2-IRF9 (ISGF3) transcription complex, utilized the GR cofactor GRIP1/TIF2 as a coactivator. Consequently, GRIP1 knockdown, genetic ablation, or depletion by GC-activated GR attenuated ISGF3 promoter occupancy, preinitiation complex assembly, and ISG expression. Furthermore, this regulatory loop was restricted to cell types such as macrophages expressing the GRIP1 protein at extremely low levels, and pharmacological disruption of the GR-GRIP1 interaction or transient introduction of GRIP1 restored RNA polymerase recruitment to target ISGs and the subsequent IFN response. Thus, type I IFN is a cytokine uniquely controlled by GR at the levels of not only production but also signaling through antagonism with the ISGF3 effector function, revealing a novel facet of the immunosuppressive properties of GCs.