Structure-dependent activation of NR4A2 (Nurr1) by 1,1-bis(3'-indolyl)-1-(aromatic)methane analogs in pancreatic cancer cells

A novel NR4A2-HuR axis promotes pancreatic cancer growth and tumorigenesis that is inhibited by NR4A2 antagonists

Pancreatic ductal adenocarcinoma (PDAC) patients' express higher levels of the orphan Nuclear Receptor 4A2 (NR4A2, NURR1) compared to normal pancreas and NR4A2 is a prognostic factor for patient survival. Knockdown of NR4A2 by RNA interference (RNAi) inhibited cell proliferation, invasion, and migration. RNA sequencing performed in NR4A2(+/+) and NR4A2(-/-) MiaPaCa2 cells demonstrated that NR4A2 played a significant role in cellular metabolism. Human antigen R (HuR) and isocitrate dehydrogenase 1 (IDH1) were identified as NR4A2 target genes. HuR is a pro-oncogenic RNA binding protein and silencing of HuR by RNAi significantly downregulated expression of NR4A2. Expression of HuR and IDH1 were significantly downregulated after treatment with NR4A2 inverse agonist, 1,1-bis(3'-indolyl)-1-(p-chlorophenyl)methane resulting in significant inhibition of tumor growth in an athymic nude mouse xenograft model. This study demonstrates that NR4A2 and HuR regulate genes and signaling pathways that enhance tumorigenesis and targeting NR4A2 and HuR expression with an NR4A2 inverse agonist represents a novel regimen for treating PDAC.

New opportunities to overcome T cell dysfunction: the role of transcription factors and how to target them

Immune checkpoint blockade (ICB) therapies, which block inhibitory receptors on T cells, can be efficacious in reinvigorating dysfunctional T cell responses. However, most cancers do not respond to these therapies and even in those that respond, tumors can acquire resistance. New strategies are needed to rescue and recruit T cell responses across patient populations and disease states. In this review, we define mechanisms of T cell dysfunction, focusing on key transcription factor (TF) networks. We discuss the complex and sometimes contradictory roles of core TFs in both T cell function and dysfunction. Finally, we review strategies to target TFs using small molecule modulators, which represent a challenging but highly promising opportunity to tune the T cell response toward sustained immunity.

Natural products and synthetic analogs as selective orphan nuclear receptor 4A (NR4A) modulators

Although endogenous ligands for the orphan nuclear receptor 4A1 (NR4A1, Nur77), NR4A2 (Nurr1), and NR4A3 (Nor-1) have not been identified, several natural products and synthetic analogs bind NR4A members. These studies are becoming increasingly important since members of the NR4A subfamily of 3 receptors are potential drug targets for treating cancer and non-cancer endpoints and particularly those conditions associated with inflammatory diseases. Ligands that bind NR4A1, NR4A2, and NR4A3 including Cytosporone B, celastrol, bis-indole derived (CDIM) compounds, tryptophan/indolic, metabolites, prostaglandins, resveratrol, piperlongumine, fatty acids, flavonoids, alkaloids, peptides, and drug families including statins and antimalarial drugs. The structural diversity of NR4A ligands and their overlapping and unique effects on NR4A1, NR4A2, and NR4A3 suggest that NR4A ligands are selective NR4A modulators (SNR4AMs) that exhibit tissue-, structure-, and response-specific activities. The SNR4AM activities of NR4A ligands are exemplified among the Cytosporone B analogs where n-pentyl-2-[3,5-dihydroxy-2-(nonanoyl)]phenyl acetate (PDNPA) binds NR4A1, NR4A2 and NR4A3 but activates only NR4A1 and exhibits significant functional differences with other Cytosporone B analogs. The number of potential clinical applications of agents targeting NR4A is increasing and this should spur future development of SNR4AMs as therapeutics that act through NR4A1, NR4A2 and NR4A3.

International Union of Basic and Clinical Pharmacology CXIII: Nuclear Receptor Superfamily-Update 2023

The NR superfamily comprises 48 transcription factors in humans that control a plethora of gene network programs involved in a wide range of physiologic processes. This review will summarize and discuss recent progress in NR biology and drug development derived from integrating various approaches, including biophysical techniques, structural studies, and translational investigation. We also highlight how defective NR signaling results in various diseases and disorders and how NRs can be targeted for therapeutic intervention via modulation via binding to synthetic lipophilic ligands. Furthermore, we also review recent studies that improved our understanding of NR structure and signaling. SIGNIFICANCE STATEMENT: Nuclear receptors (NRs) are ligand-regulated transcription factors that are critical regulators of myriad physiological processes. NRs serve as receptors for an array of drugs, and in this review, we provide an update on recent research into the roles of these drug targets.

Medicinal Chemistry and Chemical Biology of Nurr1 Modulators: An Emerging Strategy in Neurodegeneration

Nuclear receptor related 1 (Nurr1) is a transcription factor with neuroprotective and antineuroinflammatory properties. Observations from genetic studies and human patients support potential of Nurr1 as a therapeutic target in neurodegeneration, but due to a lack of high-quality chemical tools for pharmacological control of Nurr1, its target validation is pending. Nevertheless, considerable progress has recently been made in elucidating structural and functional characteristics of Nurr1, and several ligand scaffolds have been discovered. Here, we analyze Nurr1's structure and mechanisms compared to other nuclear receptors, summarize the known small molecule Nurr1 ligands, and discuss the available evidence for the therapeutic potential of Nurr1 in neurodegeneration.

Transcriptional Regulation of the Synaptic Vesicle Protein Synaptogyrin-3 (SYNGR3) Gene: The Effects of NURR1 on Its Expression

Synaptogyrin-3 (SYNGR3) is a synaptic vesicular membrane protein. Amongst four homologues (SYNGR1 to 4), SYNGR1 and 3 are especially abundant in the brain. SYNGR3 interacts with the dopamine transporter (DAT) to facilitate dopamine (DA) uptake and synaptic DA turnover in dopaminergic transmission. Perturbed SYNGR3 expression is observed in Parkinson’s disease (PD). The regulatory elements which affect SYNGR3 expression are unknown. Nuclear-receptor-related-1 protein (NURR1) can regulate dopaminergic neuronal differentiation and maintenance via binding to NGFI-B response elements (NBRE). We explored whether NURR1 can regulate SYNGR3 expression using an in silico analysis of the 5′-flanking region of the human SYNGR3 gene, reporter gene activity and an electrophoretic mobility shift assay (EMSA) of potential cis-acting sites. In silico analysis of two genomic DNA segments (1870 bp 5′-flanking region and 1870 + 159 bp of first exon) revealed one X Core Promoter Element 1 (XCPE1), two SP1, and three potential non-canonical NBRE response elements (ncNBRE) but no CAAT or TATA box. The longer segment exhibited gene promoter activity in luciferase reporter assays. Site-directed mutagenesis of XCPE1 decreased promoter activity in human neuroblastoma SH-SY5Y (↓43.2%) and human embryonic kidney HEK293 cells (↓39.7%). EMSA demonstrated NURR1 binding to these three ncNBRE. Site-directed mutagenesis of these ncNBRE reduced promoter activity by 11–17% in SH-SY5Y (neuronal) but not in HEK293 (non-neuronal) cells. C-DIM12 (Nurr1 activator) increased SYNGR3 protein expression in SH-SY5Y cells and its promoter activity using a real-time luciferase assay. As perturbed vesicular function is a feature of major neurodegenerative diseases, inducing SYNGR3 expression by NURR1 activators may be a potential therapeutic target to attenuate synaptic dysfunction in PD.

Nuclear receptor 4A1 (NR4A1) antagonists target paraspeckle component 1 (PSPC1) in cancer cells

Paraspeckles compound 1 (PSPC1) is a multifunctional protein that plays an important role in cancer cells, where PSPC1 is a master regulator of pro-oncogenic responses that includes activation of TGFβ (TGFβ1), TGFβ-dependent EMT, and metastasis. The pro-oncogenic activities of PSPC1 closely resembled those observed for the orphan nuclear receptor 4A1 (NR4A1, Nur77) and knockdown of NR4A1 decreased expression of PSPC1 in MDA-MB-231 breast, H1299 lung, and SNU449 liver cancer cells. Similar results were observed in these same cell lines after treatment with bisindole-derived (CDIMs) NR4A1 antagonists. Moreover, PSPC1-dependent regulation of TGFβ, genes associated with cancer stem cells and epithelial to mesenchymal transition (EMT) were also downregulated after NR4A1 silencing or treatment of breast, lung, and liver cancer cells with CDIM/NR4A1 antagonists. Results of chromatin immunoprecipitation (ChIP) assays suggest that NR4A1 regulates PSPC1 through interaction with an NBRE sequence in the PSPC1 gene promoter. These results coupled with in vivo studies showing that NR4A1 antagonists inhibit breast tumor growth and downregulate PSPC1 in tumors indicate that the pro-oncogenic nuclear PSPC1 factor can be targeted by CDIM/NR4A1 antagonists.

Orphan nuclear receptor 4A1 (NR4A1) and novel ligands

The nuclear receptor (NR) superfamily of transcription factors encodes expression of 48 human genes that are important for maintaining cellular homeostasis and in pathophysiology, and this has been observed for all sub-families including orphan receptors for which endogenous ligands have not yet been identified. The orphan NR4A1 (Nur77 and TR3) and other members of this sub-family (NR4A2 and NR4A3) are immediate early genes induced by diverse stressors, and these receptors play an important role in the immune function and are up-regulated in some inflammatory diseases including solid tumors. Although endogenous ligands for NR4A have not been identified, several different classes of compounds have been characterized as NR4A1 ligands that bind the receptor. These compounds include cytosporone B and structurally related analogs, bis-indole derived (CDIM) compounds, the triterpenoid celastrol and a number of other chemicals including polyunsaturated fatty acids. NR4A1 ligands bind different regions/surfaces of NR4A1 and exhibit selective NR4A1 modulator (SNR4AM) activities that are dependent on ligand structure and cell/tissue context. NR4A1 ligands exhibit pharmacologic activities in studies on cancer, endometriosis metabolic and inflammatory diseases and are promising agents with clinical potential for treating multiple diseases.

Nr4a2 Transcription Factor in Hippocampal Synaptic Plasticity, Memory and Cognitive Dysfunction: A Perspective Review

Long-lasting changes of synaptic efficacy are largely mediated by activity-induced gene transcription and are essential for neuronal plasticity and memory. In this scenario, transcription factors have emerged as pivotal players underlying synaptic plasticity and the modification of neural networks required for memory formation and consolidation. Hippocampal synaptic dysfunction is widely accepted to underlie the cognitive decline observed in some neurodegenerative disorders including Alzheimer’s disease. Therefore, understanding the molecular pathways regulating gene expression profiles may help to identify new synaptic therapeutic targets. The nuclear receptor 4A subfamily (Nr4a) of transcription factors has been involved in a variety of physiological processes within the hippocampus, ranging from inflammation to neuroprotection. Recent studies have also pointed out a role for the activity-dependent nuclear receptor subfamily 4, group A, member 2 (Nr4a2/Nurr1) in hippocampal synaptic plasticity and cognitive functions, although the underlying molecular mechanisms are still poorly understood. In this review, we highlight the specific effects of Nr4a2 in hippocampal synaptic plasticity and memory formation and we discuss whether the dysregulation of this transcription factor could contribute to hippocampal synaptic dysfunction, altogether suggesting the possibility that Nr4a2 may emerge as a novel synaptic therapeutic target in brain pathologies associated to cognitive dysfunctions.

Nuclear Receptor 4A2 (NR4A2/NURR1) Regulates Autophagy and Chemoresistance in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive cancer with poor prognosis and chemotherapy with gemcitabine has limited effects and is associated with development of drug resistance. Treatment of Panc1 and MiaPaca2 pancreatic cancer cells with gemcitabine induced expression of the orphan nuclear receptor 4A2 (NURR1) and analysis of the cancer genome atlas indicated the NURR1 is overexpressed in pancreatic tumors and is a negative prognostic factor for patient survival. Results of NURR1 knockdown or treatment with the NURR1 antagonist 1,1-bis(3΄-indolyl)-1-(p-chlorophenyl)methane (C-DIM 12) demonstrated that NURR1 was pro-oncogenic in pancreatic cancer cells and regulated cancer cell and tumor growth and survival. NURR1 is induced by gemcitabine and serves as a key drug-resistance factor and is also required for gemcitabine-induced cytoprotective autophagy. NURR1 regulated genes were determined by RNA sequencing of mRNAs expressed in MiaPaCa2 cells expressing NURR1 and in CRISPR/Cas9 gene edited cells for NURR1 knockdown and KEGG enrichment analysis of the differentially expressed genes showed that autophagy was the major pathway regulated by NURR1. Moreover, NURR1 regulated expression of two major autophagic genes ATG7 and ATG12 which are also overexpressed in pancreatic tumors and like NURR1 are negative prognostic factors for patient survival. Thus, gemcitabine-induced cytoprotective autophagy is due to the NURR1 - ATG7/ATG12 axis and this can be targeted and disrupted by NURR1 antagonist C-DIM12 demonstrating the potential clinical applications for combination therapies with gemcitabine and NURR1 antagonists.

Targeting Nuclear Receptors in Neurodegeneration and Neuroinflammation

Nuclear receptors, also known as ligand-activated transcription factors, regulate gene expression upon ligand signals and present as attractive therapeutic targets especially in chronic diseases. Despite the therapeutic relevance of some nuclear receptors in various pathologies, their potential in neurodegeneration and neuroinflammation is insufficiently established. This perspective gathers preclinical and clinical data for a potential role of individual nuclear receptors as future targets in Alzheimer's disease, Parkinson's disease, and multiple sclerosis, and concomitantly evaluates the level of medicinal chemistry targeting these proteins. Considerable evidence suggests the high promise of ligand-activated transcription factors to counteract neurodegenerative diseases with a particularly high potential of several orphan nuclear receptors. However, potent tools are lacking for orphan receptors, and limited central nervous system exposure or insufficient selectivity also compromises the suitability of well-studied nuclear receptor ligands for functional studies. Medicinal chemistry efforts are needed to develop dedicated high-quality tool compounds for the therapeutic validation of nuclear receptors in neurodegenerative pathologies.

Assessment of NR4A Ligands That Directly Bind and Modulate the Orphan Nuclear Receptor Nurr1

Nurr1/NR4A2 is an orphan nuclear receptor transcription factor implicated as a drug target for neurological disorders including Alzheimer's and Parkinson's diseases. Previous studies identified small-molecule NR4A nuclear receptor modulators, but it remains unclear if these ligands affect transcription via direct binding to Nurr1. We assessed 12 ligands reported to affect NR4A activity for Nurr1-dependent and Nurr1-independent transcriptional effects and the ability to bind the Nurr1 ligand-binding domain (LBD). Protein NMR structural footprinting data show that amodiaquine, chloroquine, and cytosporone B bind the Nurr1 LBD; ligands that do not bind include C-DIM12, celastrol, camptothecin, IP7e, isoalantolactone, ethyl 2-[2,3,4-trimethoxy-6-(1-octanoyl)phenyl]acetate (TMPA), and three high-throughput screening hit derivatives. Importantly, ligands that modulate Nurr1 transcription also show Nurr1-independent effects on transcription in a cell type-specific manner, indicating that care should be taken when interpreting the functional response of these ligands in transcriptional assays. These findings should help focus medicinal chemistry efforts that desire to optimize Nurr1-binding ligands.

The Paradoxical Roles of Orphan Nuclear Receptor 4A (NR4A) in Cancer

The three-orphan nuclear receptor 4A genes are induced by diverse stressors and stimuli, and there is increasing evidence that NR4A1 (Nur77), NR4A2 (Nurr1), and NR4A3 (Nor1) play an important role in maintaining cellular homeostasis and in pathophysiology. In blood-derived tumors (leukemias and lymphomas), NR4A expression is low and NR4A1^-/-/NR4A3^-/- double knockout mice rapidly develop acute myelocytic leukemia, suggesting that these receptors exhibit tumor suppressor activity. Treatment of leukemia and most lymphoma cells with drugs that induce expression of NR4A1and NR4A3 enhances apoptosis, and this represents a potential clinical application for treating this disease. In contrast, most solid tumor-derived cell lines express high levels of NR4A1 and NR4A2, and both receptors exhibit pro-oncogenic activities in solid tumors, whereas NR4A3 exhibits tumor-specific activities. Initial studies with retinoids and apoptosis-inducing agents demonstrated that their cytotoxic activity is NR4A1 dependent and involved drug-induced nuclear export of NR4A1 and formation of a mitochondrial proapoptotic NR4A1-bcl-2 complex. Drug-induced nuclear export of NR4A1 has been reported for many agents/biologics and involves interactions with multiple mitochondrial and extramitochondrial factors to induce apoptosis. Synthetic ligands for NR4A1, NR4A2, and NR4A3 have been identified, and among these compounds, bis-indole derived (CDIM) NR4A1 ligands primarily act on nuclear NR4A1 to inhibit NR4A1-regulated pro-oncogenic pathways/genes and similar results have been observed for CDIMs that bind NR4A2. Based on results of laboratory animal studies development of NR4A inducers (blood-derived cancers) and NR4A1/NR4A2 antagonists (solid tumors) may be promising for cancer therapy and also for enhancing immune surveillance.

Recent Advances in Drug Repurposing for Parkinson's Disease

As a long-term degenerative disorder of the central nervous system that mostly affects older people, Parkinson's disease is a growing health threat to our ever-aging population. Despite remarkable advances in our understanding of this disease, all therapeutics currently available only act to improve symptoms but cannot stop the disease progression. Therefore, it is essential that more effective drug discovery methods and approaches are developed, validated, and used for the discovery of disease-modifying treatments for Parkinson's disease. Drug repurposing, also known as drug repositioning, or the process of finding new uses for existing or abandoned pharmaceuticals, has been recognized as a cost-effective and timeefficient way to develop new drugs, being equally promising as de novo drug discovery in the field of neurodegeneration and, more specifically for Parkinson's disease. The availability of several established libraries of clinical drugs and fast evolvement in disease biology, genomics and bioinformatics has stimulated the momentums of both in silico and activity-based drug repurposing. With the successful clinical introduction of several repurposed drugs for Parkinson's disease, drug repurposing has now become a robust alternative approach to the discovery and development of novel drugs for this disease. In this review, recent advances in drug repurposing for Parkinson's disease will be discussed.

Nuclear receptor 4A2 (NR4A2) is a druggable target for glioblastomas

INTRODUCTION

The orphan nuclear receptor 4A2 (NR4A2) has been extensively characterized in subcellular regions of the brain and is necessary for the function of dopaminergic neurons. The NR4A2 ligand, 1,1-bis (3¹-indoly1)-1-(p-chlorophenyl)methane (DIM-C-pPhCl) inhibits markers of neuroinflammation and degeneration in mouse models and in this study we investigated expression and function of NR4A2 in glioblastoma (GBM).

METHODS

Established and patient-derived cell lines were used as models and the expression and functions of NR4A2 were determined by western blots and NR4A2 gene silencing by antisense oligonucleotides respectively. Effects of NR4A2 knockdown and DIM-C-pPhCl on cell growth, induction of apoptosis (Annexin V Staining) and migration/invasion (Boyden chamber and spheroid invasion assay) and transactivation of NR4A2-regulated reporter genes were determined. Tumor growth was investigated in athymic nude mice bearing U87-MG cells as xenografts.

RESULTS

NR4A2 knockdown and DIM-C-pPhCl inhibited GBM cell and tumor growth, induced apoptosis and inhibited migration and invasion of GBM cells. DIM-C-pPhCl and related analogs also inhibited NR4A2-regulated transactivation (luciferase activity) confirming that DIM-C-pPhCl acts as an NR4A2 antagonist and blocks NR4A2-dependent pro-oncogenic responses in GBM.

CONCLUSION

We demonstrate for the first time that NR4A2 is pro-oncogenic in GBM and thus a potential druggable target for patients with tumors expressing this receptor. Moreover, our bis-indole-derived NR4A2 antagonists represent a novel class of anti-cancer agents with potential future clinical applications for treating GBM.

Pharmacological activation of Nr4a rescues age-associated memory decline

Age-associated cognitive impairments affect an individual's quality of life and are a growing problem in society. Therefore, therapeutic strategies to treat age-related cognitive decline are needed to enhance the quality of life among the elderly. Activation of the Nr4a family of transcription factors has been closely linked to memory formation and dysregulation of these transcription factors is thought to be associated with age-related cognitive decline. Previously, we have shown that Nr4a transcription can be activated by synthetic bisindole-derived compounds (C-DIM). C-DIM compounds enhance synaptic plasticity and long-term contextual fear memory in young healthy mice. In this study, we show that activation of Nr4a2 by 1,1-bis(3'-Indolyl)-1-(p-chlorophenyl) methane (C-DIM12), enhances long-term spatial memory in young mice and rescues memory deficits in aged mice. These findings suggest that C-DIM activators of Nr4a transcription may be suitable to prevent memory deficits associated with aging.

Structure-dependent activation of gene expression by bis-indole and quinoline-derived activators of nuclear receptor 4A2

Bis-indole derivatives including 1,1-bis(3'-indolyl)-1-(4-chlorophenyl)methane (DIM-C-pPhCl) and substituted quinolines such as chloroquine (CQ) and amodiaquine (AQ) are nuclear receptor 4A2 (NR4A2, Nurr1) ligands, and they exhibit anti-inflammatory activities in mouse and rat models of Parkinson's disease, respectively. However, computational modeling demonstrates that the quinoline derivatives interact with the ligand-binding domain, whereas the bis-indoles preferentially interact with a C-terminal cofactor binding site of NR4A2. In this study, the effects of DIM-C-pPhCl and related analogs were compared with CQ/AQ as inducers of NR4A2-responsive genes including vasoactive intestinal peptide, osteopontin, proopiomelanocortin, and neuropilin 1 in Panc1 and Panc28 pancreatic cancer cells. The results demonstrate that, among the bis-indole analogs, their relative potencies as inducers were structure-gene- and cell context dependent. In contrast, CQ and AQ were significantly less potent than the bis-indole derivatives and, for some of the NR4A2-regulated genes, CQ and AQ were inactive as inducers. These results demonstrate that although bis-indole and quinoline derivatives have been characterized as activators of NR4A2-dependent gene expression, these two classes of compounds exhibit different activities, indicating that they are selective NR4A2 modulators.

Zn(OTf)2-catalyzed access to symmetrical and unsymmetrical bisindoles from α-keto amides

Zn(OTf)2-catalyzed synthesis of 3,3'-bisindolyl acetamides from α-keto amides is developed. Both aromatic α-keto amides substituted with electron-donating as well as -withdrawing groups and aliphatic α-keto amides are well tolerated to provide symmetrical bisindoles in moderate to excellent yields. The chemoselective bisindolylation of the keto group of α-keto amides in the presence of a simple keto functionality is successfully achieved in good yields. The transformation is further extended to the synthesis of challenging unsymmetrical bisindoles by treating indolyl α-hydroxy amides with substituted indoles. The unsymmetrical bisindoles are isolated in good to excellent yields.

Structural insights into ligand-binding pocket formation in Nurr1 by molecular dynamics simulations

The nuclear receptor Nurr1 (NR4A2) has been identified as a potential target for the treatment of Parkinson's disease. In contrast to most other nuclear receptors, the X-ray crystal structure of the Nurr1 ligand-binding domain (LBD) lacks any ligand-binding pocket (LBP). However, NMR spectroscopy measurements have revealed that the known Nurr1 agonist docosahexaenoic acid (DHA) binds to a region within the LBD that corresponds to the classical NR ligand-binding pocket (LBP). In order to investigate the structural dynamics of the Nurr1 LBD and to study potential LBP formation, the conformational space of the receptor was sampled using a molecular dynamics (MD) simulation. Docking of DHA into 50,000 LBD structures extracted from the simulation revealed the existence of a transient LBP that is capable to fully harbor the compound. The location of the identified pocket overlaps with the ligand-binding site suggested by NMR experiments. Structural analysis of the protein-ligand complex showed that only modest structural rearrangements within the Nurr1 LBD are required for LBP formation. These findings may support structure-based drug discovery campaigns for the development of receptor-specific agonists.

Molecular Insights into NR4A2(Nurr1): an Emerging Target for Neuroprotective Therapy Against Neuroinflammation and Neuronal Cell Death

NR4A2 is a nuclear receptor and a transcription factor, with distinctive physiological features. In the cell nuclei of the central nervous system, it is widely expressed and identified as a crucial regulator of dopaminergic (DA) neuronal differentiation, survival, and maintenance. Importantly, it has regulated different genes crucial for dopaminergic signals, and its expression has been diminished in both aged and PD post-mortem brains and reduced in PD patients. In microglia and astrocytes, the expression of NR4A2 has been found where it can be capable of inhibiting the expression of proinflammatory mediators; hence, it protected inflammation-mediated DA neuronal death. In addition, NR4A2 plays neuroprotective role via regulating different signals. However, NR4A2 has been mainly focused on Parkinson's research, but, in recent times, it has been studied in Alzheimer's disease (AD), multiple sclerosis (MS), and stroke. Altered expression of NR4A2 is connected to AD progression, and activation of its may improve cognitive function. It is downregulated in peripheral blood mononuclear cells of MS patients; nonetheless, its role in MS has not been fully clear. miR-145-5p known as a putative regulator of NR4A2 and in a middle cerebral artery occlusion/reperfusion model, anti-miR-145-5p administration promoted neurological outcomes in rat. To date, various activators and modulators of NR4A2 have been discovered and investigated as probable therapeutic drugs in neuroinflammatory and neuronal cell death models. The NR4A2 gene and cell-based therapy are described as promising drug candidates for neurodegenerative diseases. Moreover, microRNA might have a crucial role in neurodegeneration via affecting NR4A2 expression. Herein, we present the role of NR4A2 in neuroinflammation and neuronal cell death focusing on neurodegenerative conditions and display NR4A2 as a promising therapeutic target for the therapy of neuroprotection.

Hetero-bimetallic cooperative catalysis for the synthesis of heteroarenes

Review covering the synthesis of 5- and 6-membered as well as condensed heteroarenes, focussing on the combinations in cooperative catalytic systems in strategies used to achieve selectivity and also highlights the mode of action for the cooperative catalysis leading to the synthesis of commercially and biologically relevant heteroarenes.

Chiral Phosphoric Acid Catalyzed Asymmetric Synthesis of Hetero-triarylmethanes from Racemic Indolyl Alcohols

The direct enantioselective 1,4- and 1,8-arylations of 7-methide-7H-indoles and 6-methide-6H-indoles, respectively, generated in situ from diarylmethanols, with electron-rich arenes as nucleophiles, has been achieved in the presence of chiral phosphoric acids (CPAs). These two remote activation protocols provide an efficient approach for the construction of diverse hetero-triarylmethanes in high yields (up to 97 %) and with excellent enantioselectivities (up to 96 %). Mechanistically inspired experiments tentatively indicate that the catalytic enantioselective 1,4-addition as well as the formal S_N 1 substitution could proceed efficiently in the similar catalytic systems. Furthermore, the modification of the catalytic system and diarylmethanol structure successfully deviates the reactivity toward a remote, highly enantioselective 1,8-arylation reaction. This flexible activation mode and novel reactivity of diarylmethanols expand the synthetic potential of chiral phosphoric acids.

A novel diindolylmethane analog, 1,1-bis(3'-indolyl)-1-(p-chlorophenyl) methane, inhibits the tumor necrosis factor-induced inflammatory response in primary murine synovial fibroblasts through a Nurr1-dependent mechanism

The progression of rheumatoid arthritis involves the thickening of the synovial lining due to the proliferation of fibroblast-like synoviocytes (FLS) and infiltration by inflammatory cells. Tumor necrosis factor alpha (TNFα) is a pro-inflammatory cytokine involved in progression of the disease. Under rheumatoid conditions, FLS express the tumor necrosis factor (TNF)-recognition complex (TNFR1, TNFR2, VCAM-1 and ICAM-1), which induces local macrophage activation and leads to downstream nuclear factor κB (NF-κB) signaling. The NF-κB-regulated inflammatory gene, cyclooxygenase (COX), increases synthesis of prostaglandins that contribute to the propagation of inflammatory damage within the joint. Because the nuclear orphan receptor, NR4A2 (Nurr1), can negatively regulate NF-κB-dependent inflammatory gene expression in macrophages, we postulated that activation of this receptor by the Nurr1 ligand 1,1-bis(3'-indolyl)-1-(p-chlorophenyl) methane (C-DIM12) would modulate inflammatory gene expression in synovial fibroblasts by inhibiting NF-κB. Treatment with C-DIM12 suppressed TNFα-induced expression of adhesion molecules and NF-κB regulated genes in primary synovial fibroblasts including vascular adhesion molecule 1 (VCAM-1), PGE2 and COX-2. Immunofluorescence studies indicated that C-DIM12 did not prevent translocation of p65 and stabilized nuclear localization of Nurr1 in synovial fibroblasts. Knockdown of Nurr1 expression by RNA interference prevented the inhibitory effects of C-DIM12 on inflammatory gene expression, indicating that the anti-inflammatory effects of this compound are Nurr1-dependent. Collectively, these data suggest that this receptor may be a viable therapeutic target in RA.

The Nurr1 Ligand,1,1-bis(3'-Indolyl)-1-(p-Chlorophenyl)Methane, Modulates Glial Reactivity and Is Neuroprotective in MPTP-Induced Parkinsonism

The orphan nuclear receptor Nurr1 (also called nuclear receptor-4A2) regulates inflammatory gene expression in glial cells, as well as genes associated with homeostatic and trophic function in dopaminergic neurons. Despite these known functions of Nurr1, an endogenous ligand has not been discovered. We postulated that the activation of Nurr1 would suppress the activation of glia and thereby protect against loss of dopamine (DA) neurons after subacute lesioning with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Our previous studies have shown that a synthetic Nurr1 ligand, 1,1-bis(3'-indolyl)-1-(p-chlorophenyl)methane (C-DIM12), suppresses inflammatory gene expression in primary astrocytes and induces a dopaminergic phenotype in neurons. Pharmacokinetic analysis of C-DIM12 in mice by liquid chromatography-mass spectrometry demonstrated that approximately three times more compound concentrated in the brain than in plasma. Mice treated with four doses of MPTP + probenecid over 14 days were monitored for neurobehavioral function, loss of dopaminergic neurons, and glial activation. C-DIM12 protected against the loss of DA neurons in the substantia nigra pars compacta and DA terminals in the striatum, maintained a ramified phenotype in microglia, and suppressed activation of astrocytes. In vitro reporter assays demonstrated that C-DIM12 was an effective activator of Nurr1 transcription in neuronal cell lines. Computational modeling of C-DIM12 binding to the three-dimensional structure of human Nurr1 identified a high-affinity binding interaction with Nurr1 at the coactivator domain. Taken together, these data suggest that C-DIM12 is an activator of Nurr1 that suppresses glial activation and neuronal loss in vivo after treatment with MPTP, and that this receptor could be an efficacious target for disease modification in individuals with Parkinson's disease and related disorders.

Synthesis of Bis(indolyl)methanes Using Hyper-Cross-Linked Polyaromatic Spheres Decorated with Bromomethyl Groups as Efficient and Recyclable Catalysts

Highly uniform and hyper-cross-linked polyphenanthrene and polypyrene microspheres were synthesized by Friedel-Crafts bromomethylation of phenanthrene (Phn) and pyrene (Py) in the presence of zinc bromide as a catalyst, followed by self-polymerization of bromomethylated Phn and Py. The resultant 3-D carbon microspheres consisting of micro-, meso-, and macropores bear peripheral unreacted bromomethyl groups, which are directly utilized as catalysts to efficiently promote the electrophilic substitution reaction of indoles with aldehydes to yield a variety of bis(indolyl)methanes. The important features of this catalysis are easy catalyst synthesis, high product yields, environmental benignity, short reaction time, broad substrate scope, use of nontoxic solvents, and recyclability.

Nuclear receptor 4A1 (NR4A1) as a drug target for treating rhabdomyosarcoma (RMS)

The orphan nuclear receptor NR4A1 is expressed in tumors from rhabdomyosarcoma (RMS) patients and Rh30 and RD RMS cell lines, and we used RNA interference (RNAi) to investigate the role of this receptor in RMS cells. Knockdown of NR4A1 in Rh30 cells decreased cell proliferation, induced Annexin V staining and induced polyADPribose polymerase (PARP) cleavage and these results were similar to those observed in other solid tumors. Previous studies show that NR4A1 regulates expression of growth promoting/pro-survival genes with GC-rich promoters, activates mTOR through suppression of p53, and maintains low oxidative stress by regulating expression of isocitrate dehydrogenase 1 (IDH1) and thioredoxin domain containing 5 (TXNDC5). Results of RNAi studies demonstrated that NR4A1 also regulates these pathways and associated genes in RMS cells and thereby exhibits pro-oncogenic activity. 1,1-Bis(3-indolyl)-1-(p-substituted phenyl)methane (C-DIM) analogs containing p-hydroxyl (DIM-C-pPhOH) and p-carboxymethyl (DIM-C-pPhCO₂Me) substituents are NR4A1 ligands that decreased NR4A1-dependent transactivation in RMS cells and inhibited RMS cell and tumor growth and induced apoptosis. Moreover, the effects of NR4A1 knockdown and the C-DIM/NR4A1 antagonists were comparable as inhibitors of NR4A1-dependent genes/pathways. Both NR4A1 knockdown and treatment with DIM-C-pPhOH and DIM-C-pPhCO₂Me also induced ROS which activated stress genes and induced sestrin 2 which activated AMPK and inhibited mTOR in the mutant p53 RMS cells. Since NR4A1 regulates several growth-promoting/pro-survival pathways in RMS, the C-DIM/NR4A1 antagonists represent a novel mechanism-based approach for treating this disease alone or in combination and thereby reducing the adverse effects of current cytotoxic therapies.

A one-pot synthesis of 2,2'-disubstituted diindolylmethanes (DIMs) via a sequential Sonogashira coupling and cycloisomerization/C3-functionalization of 2-iodoanilines

A Pd(ii)-Ag(i) catalyzed highly efficient synthesis of diindolylmethane has been developed. This transformation consists of a one-pot sequential Sonogashira coupling (and desilylation) followed by cycloisomerization/C3-functionalization of 2-iodoanilines. Six new bonds (four C-C and two C-N) are formed in a one-pot fashion. A variety of diindolylmethanes were obtained in excellent yields (up to 94%) under mild reaction conditions and this strategy is amenable to gram scale synthesis also. The products were transformed into various synthetically useful compounds.

Modulatory Role of Nurr1 Activation and Thrombin Inhibition in the Neuroprotective Effects of Dabigatran Etexilate in Rotenone-Induced Parkinson's Disease in Rats

Recently, it has been shown that both decreased nuclear receptor-related 1 (Nurr1) expression and thrombin accumulation are involved in the degeneration of dopaminergic neurons in Parkinson's disease (PD). The new anticoagulant dabigatran etexilate (DE) is a direct thrombin inhibitor that owns benzimidazole group, which has been proposed to activate Nurr1. In the present study, we examined the neuroprotective effects of DE in rotenone model of PD. Rotenone was injected subcutaneously at a dose of 1.5 mg/kg every other day for 21 days. An oral regimen of DE (15 mg/kg) was started after the 5th rotenone injection following the manifestations of PD. Treatment of PD rats with DE mitigated rotenone-induced neuronal degeneration and restored striatal dopamine level with motor recovery. As well, DE enhanced Nurr1 expression in substantia nigra along with increasing transcriptional activation of Nurr1-controlled genes namely tyrosine hydroxylase, vascular monoamine transporter, glial cell line-derived neurotrophic factor, and its receptor gene c-Ret, which are critical for development and maintenance of dopaminergic neurons. DE also suppressed thrombin accumulation in substantia nigra. Both effects probably contributed to repressing neurotoxic proinflammatory cytokines, which was manifested by decreased level of nuclear factor kappa beta and tumor necrosis factor alpha. In conclusion, the present results suggest that DE could possess significant neuroprotective and regenerative effects in a rotenone-induced PD animal model as consequence of Nurr1 activation and thrombin inhibition.

Pharmacological Activators of the NR4A Nuclear Receptors Enhance LTP in a CREB/CBP-Dependent Manner

Nr4a nuclear receptors contribute to long-term memory formation and are required for long-term memory enhancement by a class of broad-acting drugs known as histone deacetylase (HDAC) inhibitors. Understanding the molecular mechanisms that regulate these genes and identifying ways to increase their activity may provide novel therapeutic approaches for ameliorating cognitive dysfunction. In the present study, we find that Nr4a gene expression after learning requires the cAMP-response element binding (CREB) interaction domain of the histone acetyltransferase CREB-binding protein (CBP). These gene expression deficits emerge at a time after learning marked by promoter histone acetylation in wild-type mice. Further, mutation of the CREB-CBP interaction domain reduces Nr4a promoter acetylation after learning. As memory enhancement by HDAC inhibitors requires CREB-CBP interaction and Nr4a gene function, these data support the notion that the balance of histone acetylation at the Nr4a promoters is critical for memory formation. NR4A ligands have recently been described, but the effect of these drugs on synaptic plasticity or memory has not been investigated. We find that the 'C-DIM' NR4A ligands, para-phenyl substituted di-indolylmethane compounds, enhance long-term contextual fear memory and increase the duration of long-term potentiation (LTP), a form of hippocampal synaptic plasticity. LTP enhancement by these drugs is eliminated in mice expressing a dominant negative form of NR4A and attenuated in mice with mutation of the CREB-CBP interaction domain. These data define the molecular connection between histone acetylation and Nr4a gene expression after learning. In addition, they suggest that NR4A-activating C-DIM compounds may serve as a potent and selective means to enhance memory and synaptic plasticity.

Orphan nuclear receptor Nurr1 as a potential novel marker for progression in human pancreatic ductal adenocarcinoma

Nuclear receptor related-1 protein (Nurr1) is a novel orphan member of the nuclear receptor superfamily (the NR4A family) involved in tumorigenesis. The aim of the present study was to investigate the expression and possible function of Nurr1 in pancreatic ductal adenocarcinoma (PDAC). The expression pattern of Nurr1 protein was determined using immunohistochemical staining in 138 patients with PDAC. Elevated Nurr1 expression was more commonly observed in PDAC tissues and cell lines compared with healthy controls. Elevated expression was significantly associated with histological differentiation (P=0.041), lymph node metastasis (P=0.021), TNM classification of malignant tumors stage (P=0.031) and poor survival (P=0.001). Further experiments demonstrated that suppression of endogenous Nurr1 expression attenuated cell proliferation, migration and invasion, and induced apoptosis of PDAC cells. In conclusion, these results suggest that Nurr1 has an important role in the progression of PDAC and may be used as a novel marker for therapeutic targets.

Penfluridol Represses Integrin Expression in Breast Cancer through Induction of Reactive Oxygen Species and Downregulation of Sp Transcription Factors

It was recently demonstrated the penfluridol inhibited breast tumor growth and metastasis and this was associated with downregulation of α6- and β4-integrins. In this study, we observed the penfluridol induced reactive oxygen species (ROS) and this was the primary mechanism of action. Penfluridol-mediated growth inhibition, induction of apoptosis, and inhibition of breast cancer cell migration was attenuated after cotreatment with glutathione. Penfluridol also downregulated Sp transcription factors Sp1, Sp3, and Sp4 through epigenetic downregulation of cMyc and cMyc-regulated miRNAs (miR27a and miR20a/miR17) and induction of the miR-regulated Sp transcriptional repressors ZBTB10 and ZBTB4. α6- and β4-integrins as well as α5- and β1-integrins are Sp-regulated genes that are also coregulated by the orphan nuclear receptor NR4A1 and these integrins can be targeted by agents such as penfluridol that suppress Sp1, Sp3, and Sp4 and also by NR4A1 antagonists. Mol Cancer Ther; 16(1); 205-16. ©2016 AACR.

Nuclear receptor function in skin health and disease: therapeutic opportunities in the orphan and adopted receptor classes

The skin forms a vital barrier between an organism's external environment, providing protection from pathogens and numerous physical and chemical threats. Moreover, the intact barrier is essential to prevent water and electrolyte loss without which terrestrial life could not be maintained. Accordingly, acute disruption of the skin through physical or chemical trauma needs to be repaired timely and efficiently as sustained skin pathologies ranging from mild irritations and inflammation through to malignancy impact considerably on morbidity and mortality. The Nuclear Hormone Receptor Family of transcriptional regulators has proven to be highly valuable targets for addressing a range of pathologies, including metabolic syndrome and cancer. Indeed members of the classic endocrine sub-group, such as the glucocorticoid, retinoid, and Vitamin D receptors, represent mainstay treatment strategies for numerous inflammatory skin disorders, though side effects from prolonged use are common. Emerging evidence has now highlighted important functional roles for nuclear receptors belonging to the adopted and orphan subgroups in skin physiology and patho-physiology. This review will focus on these subgroups and explore the current evidence that suggests these nuclear receptor hold great promise as future stand-alone or complementary drug targets in treating common skin diseases and maintaining skin homeostasis.

Nurr1-Based Therapies for Parkinson's Disease

Previous studies have documented that orphan nuclear receptor Nurr1 (also known as NR4A2) plays important roles in the midbrain dopamine (DA) neuron development, differentiation, and survival. Furthermore, it has been reported that the defects in Nurr1 are associated with Parkinson's disease (PD). Thus, Nurr1 might be a potential therapeutic target for PD. Emerging evidence from in vitro and in vivo studies has recently demonstrated that Nurr1-activating compounds and Nurr1 gene therapy are able not only to enhance DA neurotransmission but also to protect DA neurons from cell injury induced by environmental toxin or microglia-mediated neuroinflammation. Moreover, modulators that interact with Nurr1 or regulate its function, such as retinoid X receptor, cyclic AMP-responsive element-binding protein, glial cell line-derived neurotrophic factor, and Wnt/β-catenin pathway, have the potential to enhance the effects of Nurr1-based therapies in PD. This review highlights the recent progress in preclinical studies of Nurr1-based therapies and discusses the outlook of this emerging therapy as a promising new generation of PD medication.

Nuclear receptor 4A (NR4A) family - orphans no more

The orphan nuclear receptors NR4A1, NR4A2 and NR4A3 are immediate early genes induced by multiple stressors, and the NR4A receptors play an important role in maintaining cellular homeostasis and disease. There is increasing evidence for the role of these receptors in metabolic, cardiovascular and neurological functions and also in inflammation and inflammatory diseases and in immune functions and cancer. Despite the similarities of NR4A1, NR4A2 and NR4A3 and their interactions with common cis-genomic elements, they exhibit unique activities and cell-/tissue-specific functions. Although endogenous ligands for NR4A receptors have not been identified, there is increasing evidence that structurally-diverse synthetic molecules can directly interact with the ligand binding domain of NR4A1 and act as agonists or antagonists, and ligands for NR4A2 and NR4A3 have also been identified. Since NR4A receptors are key factors in multiple diseases, there are opportunities for the future development of NR4A ligands for clinical applications in treating multiple health problems including metabolic, neurologic and cardiovascular diseases, other inflammatory conditions, and cancer.

A novel synthetic activator of Nurr1 induces dopaminergic gene expression and protects against 6-hydroxydopamine neurotoxicity in vitro

Degeneration of dopaminergic neurons in Parkinson's disease (PD) is associated with decreased expression of the orphan nuclear receptor Nurr1 (NR4A2), which is critical for both homeostasis and development of dopamine (DA) neurons. The synthetic, phytochemical-based compound, 1,1-bis (3'-indolyl)-1-(p-chlorophenyl) methane (C-DIM12) activates Nurr1 in cancer cells and prevents loss of dopaminergic neurons in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD in mice. In the present study, we examined the capacity of C-DIM12 to induce expression of Nurr1-regulated genes in two dopaminergic neuronal cell lines (N2A, N27) and to protect against 6-hydroxydopamine (6-OHDA) neurotoxicity. C-DIM12 induced expression of Nurr1-regulated genes that was abolished by Nurr1 knockdown. C-DIM12 increased expression of transfected human Nurr1, induced Nurr1 protein expression in primary dopaminergic neurons and enhanced neuronal survival from exposure to 6-OHDA. These data indicate that C-DIM12 stimulates neuroprotective expression Nurr1-regulated genes in DA neurons.

Selective ligand activity at Nur/retinoid X receptor complexes revealed by dimer-specific bioluminescence resonance energy transfer-based sensors

Retinoid X receptors (RXRs) play a role as master regulators because of their capacity to form heterodimers with other nuclear receptors (NRs). Accordingly, retinoid signaling is involved in multiple biologic processes, including development, cell differentiation, metabolism, and cell death. However, the role and function of RXRs in different heterodimer complexes remain unidentified, mainly because most RXR drugs (called rexinoids) are not selective of specific heterodimer complexes. The lack of selectivity strongly limits the use of rexinoids for specific therapeutic approaches. To better characterize rexinoids at specific NR complexes, we have developed and optimized luciferase (Luc) protein complementation(PCA)-based bioluminescence resonance energy transfer (BRET) assays that can directly measure recruitment of a coactivator (CoA) motif fused to yellow fluorescent protein (YFP) by specific NR dimers. To validate the assays, we compared rexinoid modulation of CoA recruitment by the RXR homodimer and by the heterodimers Nur77/RXR and Nurr1/RXR. Results revealed that some rexinoids display selective CoA recruitment activities with homo- or heterodimer complexes. In particular, SR11237 (BMS649) has stronger potency for recruitment of CoA motif and transcriptional activity with the heterodimer Nur77/RXR than other complexes. This technology should be useful in identifying new compounds with specificity for individual dimeric species formed by NRs.

Nuclear Receptor Nr4a2 Promotes Alternative Polarization of Macrophages and Confers Protection in Sepsis

The orphan nuclear receptor Nr4a2 is known to modulate both inflammatory and metabolic processes, but the mechanism by which it regulates innate inflammatory homeostasis has not been adequately addressed. This study shows that exposure to ligands for Toll-like receptors (TLRs) robustly induces Nr4a2 and that this induction is tightly regulated by the PI3K-Akt signaling axis. Interestingly, exogenous expression of Nr4a2 in macrophages leads to their alternative phenotype with induction of genes that are prototypical M2 markers. Moreover, Nr4a2 transcriptionally activates arginase 1 expression by directly binding to its promoter. Adoptive transfer experiments revealed that increased survival of animals in endotoxin-induced sepsis is Nr4a2-dependent. Thus our data identify a previously unknown role for Nr4a2 in the regulation of macrophage polarization.

The Nurr1 Activator 1,1-Bis(3'-Indolyl)-1-(p-Chlorophenyl)Methane Blocks Inflammatory Gene Expression in BV-2 Microglial Cells by Inhibiting Nuclear Factor κB

NR4A family orphan nuclear receptors are an important class of transcription factors for development and homeostasis of dopaminergic neurons that also inhibit expression of inflammatory genes in glial cells. The identification of NR4A2 (Nurr1) as a suppressor of nuclear factor κB (NF-κB)-related neuroinflammatory genes in microglia and astrocytes suggests that this receptor could be a target for pharmacologic intervention in neurologic disease, but compounds that promote this activity are lacking. Selected diindolylmethane compounds (C-DIMs) have been shown to activate or inactivate nuclear receptors, including Nurr1, in cancer cells and also suppress astrocyte inflammatory signaling in vitro. Based upon these data, we postulated that C-DIM12 [1,1-bis(3'-indolyl)-1-(p-chlorophenyl) methane] would suppress inflammatory signaling in microglia by a Nurr1-dependent mechanism. C-DIM12 inhibited lipopolysaccharide (LPS)-induced expression of NF-κB-regulated genes in BV-2 microglia including nitric oxide synthase (NOS2), interleukin-6 (IL-6), and chemokine (C-C motif) ligand 2 (CCL2), and the effects were attenuated by Nurr1-RNA interference. Additionally, C-DIM12 decreased NF-κB activation in NF-κB-GFP (green fluorescent protein) reporter cells and enhanced nuclear translocation of Nurr1 primary microglia. Chromatin immunoprecipitation assays indicated that C-DIM12 decreased lipopolysaccharide-induced p65 binding to the NOS2 promoter and concurrently enhanced binding of Nurr1 to the p65-binding site. Consistent with these findings, C-DIM12 also stabilized binding of the Corepressor for Repressor Element 1 Silencing Transcription Factor (CoREST) and the Nuclear Receptor Corepressor 2 (NCOR2). Collectively, these data identify C-DIM12 as a modulator of Nurr1 activity that results in inhibition of NF-κB-dependent gene expression in glial cells by stabilizing nuclear corepressor proteins, which reduces binding of p65 to inflammatory gene promoters.

Orphan nuclear receptor NR4A2 induces transcription of the immunomodulatory peptide hormone prolactin

Background

Nuclear receptor 4A2 (NR4A2) is an orphan nuclear receptor and constitutively active transcription factor expressed at elevated levels in inflamed joint tissues from patients with arthritis. Inflammatory mediators rapidly and potently induce NR4A2 expression in resident joint cells and infiltrating immune cells. This receptor promotes synovial hyperplasia by increasing proliferation of synoviocytes and inducing transcription of matrix degrading enzymes and pro-inflammatory mediators. In order to further elucidate the molecular mechanisms of NR4A2, we conducted a gene expression screen to identify novel transcriptional targets of NR4A2 that may contribute to arthritis progression.

Methods

NR4A2 was over-expressed in human synoviocytes by lentiviral transduction and gene expression changes were measured using qPCR arrays specific for inflammation, proliferation, adhesion, and migration pathways. Subsequent analysis focused on the most potently induced gene prolactin (PRL). Messenger RNA levels of PRL and PRL receptor (PRL-R) were measured by RT-qPCR and protein levels were measured by ELISA. PRL promoter studies were conducted in synoviocytes transiently transfected with NR4A2 and PRL reporter constructs. Molecular responses to PRL in synoviocytes were addressed using qPCR arrays specific for JAK/STAT signaling pathways.

Results

PRL was the most potently induced gene on the qPCR arrays, exhibiting a 68-fold increase in response to ectopic NR4A2. This gene encodes an immunomodulatory peptide hormone with roles in autoimmune diseases and inflammation. Induction of PRL mRNA and secreted protein by NR4A2 was confirmed in subsequent experiments, with increases of 300-fold and 18-fold respectively. Depletion of endogenous NR4A receptors with shRNA reduced basal and PGE₂-induced PRL levels by 95%. At the transcriptional level, NR4A2 requires a functional DNA binding domain to transactivate the distal PRL promoter. Deletional analysis indicates that NR4A2 targets a region of the distal PRL promoter spanning −270 to -32 bp. In synoviocytes, recombinant PRL regulates several genes involved in inflammation, proliferation, and cell survival, suggesting that NR4A2 induced PRL may also impact these pathways and contribute to arthritis progression.

Conclusions

These results provide the first evidence for transcriptional regulation of the immunomodulatory peptide hormone PRL by NR4A2 in synoviocytes, and highlight a novel molecular pathway in inflammatory arthritis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12950-015-0059-2) contains supplementary material, which is available to authorized users.

Enantioselective construction of a 2,2′-bisindolylmethane scaffold via catalytic asymmetric reactions of 2-indolylmethanols with 3-alkylindoles

A chiral phosphoric acid-catalyzed asymmetric reaction of 2-indolylmethanols with 3-alkylindoles has been established to construct 2,2′-bisindolylmethane scaffold in good enantioselectivities.