Analysis of co-factor function in a glucocorticoid-resistant small cell carcinoma cell line

A Novel Human Glucocorticoid Receptor Variant, G459V, is Hyperactive in Response to Steroids

ABSTRACT

A potential cause of the variable response to injury and sepsis is the variability of a patient's human glucocorticoid receptor (hGR) profile. To identify hGR variants, blood samples were collected on admission and biweekly thereafter from hospitalized patients who sustained at least a 20% total body surface area burn injury. A hyperactive G1376T single-nucleotide polymorphism (SNP) isoform was identified. This SNP led to a single amino acid change of glutamine to valine at site 459, "G459V," in the DNA-binding domain. The isoform's activity was tested in a reporter assay after treatment with steroids, the hGR antagonist RU486 (mifepristone) alone, or RU486 followed by steroids. When treated with hydrocortisone, the hGR G459V isoform had a hyperactive response; its activity was over 30 times greater than the reference hGRα. Unexpectedly, G459V had significantly increased activity when treated with the hGR antagonist RU486. With the combination of both RU486 and hydrocortisone, G459V activity was repressed, but greater than that of RU486 alone. Finally, when hGRα was cotransfected with G459V to simulate isoform interaction, the activity was closer to that of the hGRα profile than the G459V isoform. The unique activity of the G459V isoform shows that some variants of hGR have the potential to alter a person's response to stress and steroid treatment and may be a factor as to why mitigating the clinical response to sepsis and other stressors has been so elusive.

Significant random signatures reveals new biomarker for breast cancer

BACKGROUND

In 2012, Venet et al. proposed that at least in the case of breast cancer, most published signatures are not significantly more associated with outcome than randomly generated signatures. They suggested that nominal p-value is not a good estimator to show the significance of a signature. Therefore, one can reasonably postulate that some information might be present in such significant random signatures.

METHODS

In this research, first we show that, using an empirical p-value, these published signatures are more significant than their nominal p-values. In other words, the proposed empirical p-value can be considered as a complimentary criterion for nominal p-value to distinguish random signatures from significant ones. Secondly, we develop a novel computational method to extract information that are embedded within significant random signatures. In our method, a score is assigned to each gene based on the number of times it appears in significant random signatures. Then, these scores are diffused through a protein-protein interaction network and a permutation procedure is used to determine the genes with significant scores. The genes with significant scores are considered as the set of significant genes.

RESULTS

First, we applied our method on the breast cancer dataset NKI to achieve a set of significant genes in breast cancer considering significant random signatures. Secondly, prognostic performance of the computed set of significant genes is evaluated using DMFS and RFS datasets. We have observed that the top ranked genes from this set can successfully separate patients with poor prognosis from those with good prognosis. Finally, we investigated the expression pattern of TAT, the first gene reported in our set, in malignant breast cancer vs. adjacent normal tissue and mammospheres.

CONCLUSION

Applying the method, we found a set of significant genes in breast cancer, including TAT, a gene that has never been reported as an important gene in breast cancer. Our results show that the expression of TAT is repressed in tumors suggesting that this gene could act as a tumor suppressor in breast cancer and could be used as a new biomarker.

miR-137 inhibits the proliferation of human non-small cell lung cancer cells by targeting SRC3

Non-small cell lung cancer (NSCLC) is the most common type of lung cancer. The results of the present study demonstrate that high expression of microRNA (miR)-137 and low expression of steroid receptor coactivator-3 (SRC3) had a significant negative correlation in 40 NSCLC tissue samples. In addition, cell colony formation and proliferation was significantly reduced in miR-137-transfected A549 and NCI-H838 cells compared with scramble-transfected NSCLC cell lines. miR-137 was identified to induce G₁/S cell cycle arrest and dysregulate the mRNA expression of cell cycle-associated proteins (proliferating cell nuclear antigen, cyclin E, cyclin A1, cyclin A2 and p21) in NSCLC cells. Notably, miR-137 could significantly suppress SRC3 3' untranslated region (UTR) luciferase-reporter activity, an effect that was not detectable when the putative 3'-UTR target-site was mutated, further clarifying the molecular mechanisms underlying the role of miR-137 in NSCLC. In conclusion, the results of the present study suggest that miR-137 suppresses NSCLC cell proliferation by partially targeting SRC3.

The Non-Conventional Effects of Glucocorticoids in Cancer

Synthetic corticosteroids are widely used for the treatment of a variety of diseases, including pre-malignant and malignant conditions. In striking contrast, recent evidence suggests that corticosteroids can bear tumor-promoting effects in solid tumors of epithelial origin. We have recently shown that epithelial tissues, including the mucosa of the oral cavity and the skin, are able to modulate the local concentration of active corticosteroids and to produce steroids de novo. This has important clinical and physiopathological implications, because tissue-specific regulation of glucocorticoids plays a key role in the overall effect of these molecules. In the present review of the current English literature, performed using MEDLINE/PubMed/Ovid databases, we collected published evidence to demonstrate that corticosteroids induce effects that are more complex and controversial than previously acknowledged. Published studies clearly demonstrate that this class of molecules influences pathophysiological processes that are strictly related to malignancy, providing the rationale for further investigation. J. Cell. Physiol. 231: 2368-2373, 2016. © 2016 Wiley Periodicals, Inc.

The Interactome of the Glucocorticoid Receptor and Its Influence on the Actions of Glucocorticoids in Combatting Inflammatory and Infectious Diseases

Glucocorticoids (GCs) have been widely used for decades as a first-line treatment for inflammatory and autoimmune diseases. However, their use is often hampered by the onset of adverse effects or resistance. GCs mediate their effects via binding to glucocorticoid receptor (GR), a transcription factor belonging to the family of nuclear receptors. An important aspect of GR's actions, including its anti-inflammatory capacity, involves its interactions with various proteins, such as transcription factors, cofactors, and modifying enzymes, which codetermine receptor functionality. In this review, we provide a state-of-the-art overview of the protein-protein interactions (PPIs) of GR that positively or negatively affect its anti-inflammatory properties, along with mechanistic insights, if known. Emphasis is placed on the interactions that affect its anti-inflammatory effects in the presence of inflammatory and microbial diseases.

Transforming growth factor-β impairs glucocorticoid activity in the A549 lung adenocarcinoma cell line

BACKGROUND AND PURPOSE

The lung adenocarcinoma cell line, A549, undergoes epithelial-mesenchymal cell transition (EMT) in response to TGF-β. Glucocorticoids do not prevent the EMT response, but TGF-β induced resistance to the cytokine-regulatory action of glucocorticoids. We sought to characterize the impairment of glucocorticoid response in A549 cells.

EXPERIMENTAL APPROACH

A549 cells were exposed to TGF-β for up to 96 h before glucocorticoid treatment and challenge with IL-1α to assess glucocorticoid regulation of IL-6 and CXCL8 production. Nuclear localization of the glucocorticoid receptor α (GRα) was ascertained by immunofluorescence and Western blotting. Transactivation of the glucocorticoid response element (GRE) was measured with a transfected GRE-secreted human placental alkaline phosphatase reporter.

KEY RESULTS

TGF-β (40-400 pM) reduced the maximum inhibitory effect of dexamethasone on IL-1α-induced IL-6 and CXCL8 production. The impaired glucocorticoid response was detected with 4 h of TGF-β (40 pM) exposure (and 4 h IL-1α to induce CXCL8 expression) and therefore was not secondary to EMT, a process that requires longer incubation periods and higher concentrations of TGF-β. TGF-β also impaired dexamethasone regulation of granulocyte-macrophage colony-stimulating factor in thrombin-stimulated BEAS-2B epithelial cells. Impaired regulation of CXCL8 was associated with markedly reduced GRE transactivation and reduced induction of mRNA for IκBα, the glucocorticoid-inducible leucine zipper and the epithelial sodium channel (SCNN1A). The expression, cellular levels and nuclear localization of GRα were reduced by TGF-β.

CONCLUSIONS AND IMPLICATIONS

We have identified mechanisms underlying the impairment of responses to glucocorticoids by TGF-β in the A549 and BEAS-2B cell lines.

The tumour suppressor and chromatin-remodelling factor BRG1 antagonizes Myc activity and promotes cell differentiation in human cancer

BRG1, a member of the SWI/SNF complex, is mutated in cancer, but it is unclear how it promotes tumourigenesis. We report that re-expression of BRG1 in lung cancer cells up-regulates lung-specific transcripts, restoring the gene expression signature of normal lung. Using cell lines from several cancer types we found that those lacking BRG1 do not respond to retinoic acid (RA) or glucocorticoids (GC), while restoration of BRG1 restores sensitivity. Conversely, in SH-SY5Y cells, a paradigm of RA-dependent differentiation, abrogation of BRG1 prevented the response to RA. Further, our data suggest an antagonistic functional connection between BRG1 and MYC, whereby, refractoriness to RA and GC by BRG1 inactivation involves deregulation of MYC activity. Mechanistically, some of these effects are mediated by BRG1 binding to MYC and MYC-target promoters. The BRG1-MYC antagonism was also evident in primary tumours. Finally, BRG1 restoration significantly dampened invasion and progression and decreased MYC in lung cancer cells orthotopically implanted in nude mice. Thus, BRG1 inactivation enables cancer cells to sustain undifferentiated gene expression programs and prevent its response to environmental stimuli.

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

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

Cell cycle phase regulates glucocorticoid receptor function

The glucocorticoid receptor (GR) is a member of the nuclear hormone receptor superfamily of ligand-activated transcription factors. In contrast to many other nuclear receptors, GR is thought to be exclusively cytoplasmic in quiescent cells, and only translocate to the nucleus on ligand binding. We now demonstrate significant nuclear GR in the absence of ligand, which requires nuclear localisation signal 1 (NLS1). Live cell imaging reveals dramatic GR import into the nucleus through interphase and rapid exclusion of the GR from the nucleus at the onset of mitosis, which persists into early G(1). This suggests that the heterogeneity in GR distribution is reflective of cell cycle phase. The impact of cell cycle-driven GR trafficking on a panel of glucocorticoid actions was profiled. In G2/M-enriched cells there was marked prolongation of glucocorticoid-induced ERK activation. This was accompanied by DNA template-specific, ligand-independent GR transactivation. Using chimeric and domain-deleted receptors we demonstrate that this transactivation effect is mediated by the AF1 transactivation domain. AF-1 harbours multiple phosphorylation sites, which are consensus sequences for kinases including CDKs, whose activity changes during the cell cycle. In G2/M there was clear ligand independent induction of GR phosphorylation on residues 203 and 211, both of which are phosphorylated after ligand activation. Ligand-independent transactivation required induction of phospho-S211GR but not S203GR, thereby directly linking cell cycle driven GR modification with altered GR function. Cell cycle phase therefore regulates GR localisation and post-translational modification which selectively impacts GR activity. This suggests that cell cycle phase is an important determinant in the cellular response to Gc, and that mitotic index contributes to tissue Gc sensitivity.

Overexpression and gender-specific differences of SRC-3 (SRC-3/AIB1) immunoreactivity in human non-small cell lung cancer: an in vivo study

Steroid receptor coactivator-3 (SRC-3) has been reported to be overexpressed in the development and progression of many tumor types. SRC-3 has been detected in several lung cancer cell lines, but its expression and clinical significance in non-small cell lung cancer (NSCLC) remain unclear. In this study, 48 NSCLC tissues were collected and tissue microarrays were performed. The expression of SRC-3 was examined using nickel-intensified IHC. The results showed that of these 48 cases, 18 (37.5%) exhibited high levels of SRC-3 immunoreactivity, 23 (47.9%) exhibited moderate levels of SRC-3 immunoreactivity, and 7 (14.6%) were negative; thus, the total frequency of SRC-3 overexpression was 85.4% (41/48). This SRC-3 overexpression frequency was similar to the overexpression frequency observed for squamous cell carcinoma and adenocarcinoma (82.1% vs 90%) and for metastasis and non-metastasis patients (84.6% vs 85.7%). Data analysis demonstrated a significantly higher overexpression frequency in male patients compared with that in female patients (88.6% vs 76.9%). However, female patients tended to have higher expression levels of SRC-3, as measured by immunoreactivity, than male patients. These results demonstrate a high frequency of SRC-3 overexpression in NSCLC with a gender difference, suggesting that there is a specific role for SRC-3 in the pathogenesis of NSCLC.

Interferon-inducible factor 16 is a novel modulator of glucocorticoid action

Previously, we used cDNA expression profiling to identify genes associated with glucocorticoid (Gc) sensitivity. We now identify which of these directly influence Gc action. Interferon-inducible protein 16 (IFI16), bone morphogenetic protein receptor type II (BMPRII), and regulator of G-protein signaling 14 (RGS14) increased Gc transactivation, whereas sialyltransferase 4B (SIAT4B) had a negative effect. Amyloid β (A4) precursor-protein binding, family B, member 1 (APBB1/Fe65) and neural cell expressed developmentally down-regulated 9 (NEDD9) were without effect. Only IFI16 potentiated Gc repression of NF-κB. In addition, IFI16 affected basal expression, and Gc induction of endogenous target genes. IFI16 did not affect glucocorticoid receptor (GR) expression, ligand-dependent repression of GR expression, or the ligand-dependent induction of GR phosphorylation on Ser-211 or Ser-203. Coimmunoprecipitation revealed an interaction, suggesting that IFI16 modulation of GR function is mediated by protein crosstalk. Transfection analysis with GR mutants showed that the ligand-binding domain of GR binds IFI16 and is the target domain for IFI16 regulation. Analysis of human lung sections identified colocalization of GR and IFI16, suggesting a physiologically relevant interaction. We demonstrate that IFI16 is a novel modulator of GR function and show the importance of analyzing variation in Gc sensitivity in humans, using appropriate technology, to drive discovery.—Berry, A., Matthews, L. Jangani, M., Plumb, J., Farrow, S., Buchan, N., Wilson, P. A., Singh, D., Ray, D., W., Donn, R. P. Interferon-inducible factor 16 is a novel modulator of glucocorticoid action.

Hypoxia and glucocorticoid signaling converge to regulate macrophage migration inhibitory factor gene expression

OBJECTIVE

Macrophage migration inhibitory factor (MIF) is a proinflammatory mediator involved in the pathogenesis of rheumatoid arthritis. This study was undertaken to identify the MIF promoter elements responsible for regulating gene expression.

METHODS

Luciferase reporter gene assays were used to identify the MIF promoter sequence responsible for basal activity. Bioinformatic analysis was used to predict transcription factor binding sites, and electrophoretic mobility shift assay (EMSA) was used to demonstrate transcription factor binding. Chromatin immunoprecipitation (ChIP) was used to demonstrate transcription factor loading on the MIF promoter.

RESULTS

We identified the minimal promoter sequence required for basal MIF promoter activity that was also capable of conferring glucocorticoid-dependent inhibition in a T lymphocyte model cell line. Deletion studies and EMSA revealed 2 elements in the MIF promoter that were responsible for basal promoter activity. The 5' element binds CREB/activating transcription factor 1, and the 3' element is a functional hypoxia-responsive element binding hypoxia-inducible factor 1alpha. Further studies demonstrated that the cis elements are both required for glucocorticoid-dependent inhibition. ChIP demonstrated glucocorticoid-dependent recruitment of glucocorticoid receptor alpha to the MIF promoter in lymphocytes within 1 hour of treatment and a concomitant decrease in acetylated histone H3.

CONCLUSION

Our findings indicate that hypoxia and glucocorticoid signaling converge on a single element regulating MIF; this regulatory unit is a potential interacting node for microenvironment sensing of oxygen tension and glucocorticoid action in foci of inflammation.

ACTH: cellular peptide hormone synthesis and secretory pathways

Adrenocorticotrophic hormone (ACTH) is derived from the prohormone, pro-opiomelanocortin (POMC). This precursor undergoes proteolytic cleavage to yield a number of different peptides which vary depending on the tissue. In the anterior pituitary, POMC is processed to ACTH by the prohormone convertase, PC1 and packaged in secretory granules ready for stimulated secretion. In response to stress, corticotrophin releasing hormone (CRH), stimulates release of ACTH from the pituitary cell which in turn causes release of glucocorticoids from the adrenal gland. In tissues, such as the hypothalamus and skin, ACTH is further processed intracellularly to alpha melanocyte stimulating hormone (alphaMSH) which has distinct roles in these tissues. The prohormone, POMC, is itself released from cells and found in the human circulation at concentrations greater than ACTH. While much is known about the tightly regulated synthesis of POMC, there is still a lot to learn about the mechanisms for differentiating secretion of POMC, and the POMC-derived peptides. Understanding what happens to the POMC released from cells will provide new insights into its function.

Cross talk of signaling pathways in the regulation of the glucocorticoid receptor function

Several posttranslational modifications including phosphorylation have been detected on the glucocorticoid receptor (GR). However, the interdependence and combinatorial regulation of these modifications and their role in GR functions are poorly understood. We studied the effects of c-Jun N-terminal kinase (JNK)-dependent phosphorylation of GR on its sumoylation status and the impact that these modifications have on GR transcriptional activity. GR is targeted for phosphorylation at serine 246 (S246) by the JNK protein family in a rapid and transient manner. The levels of S246 phosphorylation of endogenous GR increased significantly in cells treated with UV radiation that activates JNK. S246 GR phosphorylation by JNK facilitated subsequent GR sumoylation at lysines 297 and 313. GR sumoylation increased with JNK activation and was inhibited in cells treated with JNK inhibitor. GR sumoylation in cells with activated JNK was mediated preferentially by small ubiquitin-like modifier (SUMO)2 rather than SUMO1. An increase in GR transcriptional activity was observed after inhibition of JNK or SUMO pathways and suppression of GR transcriptional activity after activation of both pathways in cells transfected with GR-responsive reporter genes. Endogenous GR transcriptional activity was inhibited on endogenous target genes IGF binding protein (IGFBP) and glucocorticoid-induced leucine zipper (GILZ) when JNK and SUMO pathways were induced individually or simultaneously. Activation of both of these signals inhibited GR-mediated regulation of human inhibitor of apoptosis gene (hIAP), whereas simultaneous activation had no effect. We conclude that phosphorylation aids GR sumoylation and that cross talk of JNK and SUMO pathways fine tune GR transcriptional activity in a target gene-specific manner, thereby modulating the hormonal response of cells exposed to stress.

Use of gene expression profiling to identify a novel glucocorticoid sensitivity determining gene, BMPRII

Wide variation in glucocorticoid (Gc) sensitivity exists between individuals which may influence susceptibility to, and treatment response of, inflammatory diseases. To determine a genetic fingerprint of Gc sensitivity 100 healthy human volunteers were polarized into the 10% most Gc-sensitive and 10% most Gc-resistant following a low dose dexamethasone (0.25 mg) suppression test. Gene expression profiling of primary lymphocytes identified the 98 most significantly Gc regulated genes. These genes were used to build a subnetwork of Gc signaling, with 54 genes mapping as nodes, and 6 non-Gc regulated genes inferred as signaling nodes. Twenty four of the 98 genes showed a difference in Gc response in vitro dependent on the Gc sensitivity of their donor individuals in vivo. A predictive model was built using both partial least squares discriminate analysis and support vector machines that predicted donor glucocorticoid sensitivity with 87% accuracy. Discriminating genes included bone morphogenetic protein receptor, type II (BMPRII). Transfection studies showed that BMPRII modulated Gc action. These studies reveal a broad base of gene expression that predicts Gc sensitivity and determine a Gc signaling network in human primary T lymphocytes. Furthermore, this combined gene profiling, and functional analysis approach has identified BMPRII as a modulator of Gc signaling.

Steroid receptor coactivator-1-deficient mice exhibit altered hypothalamic-pituitary-adrenal axis function

Steroidogenic factor-1 (SF-1), has emerged as a critical nuclear receptor regulating development and differentiation at several levels of the hypothalamic-pituitary-steroidogenic axis. Although many coregulatory factors have been shown to physically and functionally interact with SF-1, the relative importance of these interactions in SF-1 target tissues has not been thoroughly established. In this study we assessed roles of steroid receptor coactivator-1 (SRC-1) in hypothalamic-pituitary-adrenal (HPA) axis function using SRC-1-deficient (SRC-1-/-) mice in the absence or presence of SF-1 haploinsufficiency. Surprisingly, SRC-1 deficiency did not alter baseline HPA axis function or the acute rise in corticosterone after ACTH administration and failed to exacerbate adrenocortical dysfunction in SF-1+/- mice. However, after exposure to paradigms of acute and chronic stress, SRC-1-/- mice exhibited an elevation in serum corticosterone despite normal (nonsuppressed) ACTH, suggesting an increase in adrenal sensitivity as well as a concomitant defect in glucocorticoid-mediated feedback inhibition of the HPA axis. An examination of potential compensatory mechanism(s) revealed an increase in adrenal weight, selective elevation of melanocortin 2 receptor mRNA, and a coincident increase in SRC-2 and SRC-3 expression in SRC-1-/- adrenals. A reduction in blood glucose was observed in SRC-1-/- mice after chronic stress, consistent with a generalized state of glucocorticoid resistance. Dexamethasone suppression tests confirmed a weakened ability of glucocorticoids to 1) elevate serum glucose levels and induce hepatic phosphoenolpyruvate carboxykinase transcription and 2) suppress pituitary proopiomelanocortin transcript levels in SRC-1-/- animals. Collectively, these data are consistent with an indispensable role for SRC-1 in mediating actions of glucocorticoids in pituitary and liver.