Development of a Potent Nurr1 Agonist Tool for In Vivo Applications.

Nuclear receptor related 1 (Nurr1) is a neuroprotective transcription factor and an emerging target in neurodegenerative diseases. Despite strong evidence for a role in Parkinson's and Alzheimer's disease, pharmacological control and validation of Nurr1 are hindered by a lack of suitable ligands. We have discovered considerable Nurr1 activation by the clinically studied dihydroorotate dehydrogenase (DHODH) inhibitor vidofludimus calcium and systematically optimized this scaffold to a Nurr1 agonist with nanomolar potency, strong activation efficacy, and pronounced preference over the highly related receptors Nur77 and NOR1. The optimized compound induced Nurr1-regulated gene expression in astrocytes and exhibited favorable pharmacokinetics in rats, thus emerging as a superior chemical tool to study Nurr1 activation in vitro and in vivo.

Aspirin inhibits prostaglandins to prevents colon tumor formation via down-regulating Wnt production.

According to numerous epidemiological studies, aspirin is a non-steroidal anti-inflammatory drug (NSAID) that reduces the occurrence and mortality of colorectal cancer (CRC). However, the underlying mechanisms are not well identified. In an effort to fill these gaps, we administered aspirin on mice one day before induction in an azoxymethane (AOM)/dextran sulfate sodium (DSS) induced CRC model. In this study, we assessed the effects of aspirin on tumorigenesis and tumor cell proliferation. Multi-layer analyses were carried out to identify changes in cytokines, metabolites, level of gene expressions, and proteins associated with tumorigenesis and aspirin treatment. The results showed that aspirin-treated mice developed fewer colon tumors in response to AOM/DSS, and aspirin can actively block cyclooxygenase (COX) metabolism and reduce levels of pro-inflammatory cytokines. In addition, the transcriptomic and proteomic analyses both indicated that aspirin has an inhibitory effect on the Wnt pathway. The in vitro results further indicated that aspirin inhibits WNT6 production, possibly by suppressing its transcription factor NR4A2, which in turn is regulated by prostaglandin E2, thereby ultimately inhibiting the Wnt pathway. These findings improve our understanding of the mechanisms behind aspirin's chemoprevention effect on CRC.

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.

Nurr1 (NR4A2) regulates Alzheimer's disease-related pathogenesis and cognitive function in the 5XFAD mouse model.

The orphan nuclear receptor Nurr1 (also known as NR4A2) is critical for the development and maintenance of midbrain dopaminergic neurons, and is associated with Parkinson's disease. However, an association between Nurr1 and Alzheimer's disease (AD)-related pathology has not previously been reported. Here, we provide evidence that Nurr1 is expressed in a neuron-specific manner in AD-related brain regions; specifically, it is selectively expressed in glutamatergic neurons in the subiculum and the cortex of both normal and AD brains. Based on Nurr1's expression patterns, we investigated potential functional roles of Nurr1 in AD pathology. Nurr1 expression was examined in the hippocampus and cortex of AD mouse model and postmortem human AD subjects. In addition, we performed both gain-of-function and loss-of-function studies of Nurr1 and its pharmacological activation in 5XFAD mice. We found that knockdown of Nurr1 significantly aggravated AD pathology while its overexpression alleviated it, including effects on Aß accumulation, neuroinflammation, and neurodegeneration. Importantly, 5XFAD mice treated with amodiaquine, a highly selective synthetic Nurr1 agonist, showed robust reduction in typical AD features including deposition of Aß plaques, neuronal loss, microgliosis, and impairment of adult hippocampal neurogenesis, leading to significant improvement of cognitive impairment. These in vivo and in vitro findings suggest that Nurr1 critically regulates AD-related pathophysiology and identify Nurr1 as a novel AD therapeutic target.

Developmental Vitamin D (DVD) Deficiency Reduces Nurr1 and TH Expression in Post-mitotic Dopamine Neurons in Rat Mesencephalon.

Developmental vitamin D (DVD) deficiency has been proposed as an important risk factor for schizophrenia. Our previous study using Sprague Dawley rats found that DVD deficiency disrupted the ontogeny of mesencephalic dopamine neurons by decreasing the mRNA level of a crucial differentiation factor of dopamine cells, the nuclear receptor related 1 protein (Nurr1). However, it remains unknown whether this reflects a reduction in dopamine cell number or in Nurr1 expression. It is also unclear if any particular subset of developing dopamine neurons in the mesencephalon is selectively affected. In this study, we employed state-of-the-art spinning disk confocal microscopy optimized for the imaging of tissue sections and 3D segmentation to assess post-mitotic dopamine cells on a single-cell basis in the rat mesencephalon at embryonic day 15. Our results showed that DVD deficiency did not alter the number, morphology, or positioning of post-mitotic dopamine cells. However, the ratio of Nurr1+TH+ cells in the substantia nigra pars compacta (SNc) compared with the ventral tegmental area (VTA) was increased in DVD-deficient embryos. In addition, the expression of Nurr1 in immature dopamine cells and mature dopamine neurons in the VTA was decreased in DVD-deficient group. Tyrosine hydroxylase was selectively reduced in SNc of DVD-deficient mesencephalon. We conclude that DVD deficiency induced early alterations in mesencephalic dopamine development may in part explain the abnormal dopamine-related behaviors found in this model. Our findings may have broader implications for how certain environmental risk factors for schizophrenia may shape the ontogeny of dopaminergic systems and by inference increase the risk of schizophrenia.

Ligand Dependent Switch from RXR Homo- to RXR-NURR1 Heterodimerization.

Retinoid X receptors (RXRs) play key roles in many physiological processes in both the periphery and central nervous system. In addition, RXRs form heterodimers with other nuclear receptors to exert their physiological effects. The nuclear receptor related 1 protein (NURR1) is particularly interesting because of its role in promoting differentiation and survival of dopamine neurons. However, only a small number of RXR-heterodimer selective modulators are available, with limited chemical diversity. This work describes the synthesis, biochemical evaluation, and structural elucidation of a novel series of RXR ligands with strongly biased interactions with RXRα-NURR1 heterodimers. Targeted modifications to the small molecule biaryl scaffold caused local RXRα side-chain disturbances and displacement of secondary structural elements upon ligand binding. This resulted in the repositioning of protein helices in the heterodimer interface of RXRα, alterations in homo- versus heterodimer formation, and modulation of activation function 2 (AF2). The data provide a rationale for the design of RXR ligands consisting of a highly conserved hydrophilic region, strongly contributing to the ligand affinity, and a variable hydrophobic region, which efficiently probes the effects of structural changes at the level of the ligand on co-regulator recruitment or the RXRα-NURR1 dimerization interface.

Nemo-like kinase as a negative regulator of nuclear receptor Nurr1 gene transcription in prostate cancer.

BACKGROUND: Nurr1, a member of the orphan receptor family, plays an important role in several types of cancer. Our previous work demonstrated that increased expression of Nurr1 plays a significant role in the initiation and progression of prostate cancer (PCa), though the mechanisms for regulation of Nurr1 expression remain unknown. In this study, we investigated the hypothesis that Nemo-like kinase (NLK) is a key regulator of Nurr1 expression in PCa. METHODS: Immunohistochemistry and Western blot analysis were used to evaluate levels of NLK and Nurr1 in prostatic tissues and cell lines. The effects of overexpression or knockdown of Nurr1 were evaluated in PCa cells through use of PCR, Western blots and promoter reporter assays. The role of Nurr1 promoter cis element was studied by creation of two mutant Nurr1 promoter luciferase constructs, one with a mutated NF-κB binding site and one with a mutated CREB binding site. In addition, three specific inhibitors were used to investigate the roles of these proteins in transcriptional activation of Nurr1, including BAY 11-7082 (NF-κB inhibitor), KG-501 (CREB inhibitor) and ICG-001 (CREB binding protein, CBP, inhibitor). The function of CBP in NLK-mediated regulation of Nurr1 expression was investigated using immunofluorescence, co-immunoprecipitation (Co-IP) and chromatin immunoprecipitation assays (ChIPs). RESULTS: NLK expression was inversely correlated with Nurr1 expression in prostate cancer tissues and cell lines. Overexpression of NLK suppressed Nurr1 promoter activity, leading to downregulation of Nurr1 expression. In contrast, knockdown of NLK demonstrated opposite results, leading to upregulation of Nurr1. When compared with the wild-type Nurr1 promoter, mutation of NF-κB- and CREB-binding sites of the Nurr1 promoter region significantly reduced the upregulation of Nurr1 induced by knockdown of NLK in LNCaP cells; treatment with inhibitors of CREB, CBP and NF-κB led to similar results. We also found that NLK directly interacts with CBP, that knockdown of NLK significantly increases the recruitment of CBP to both NF-κB- and CREB-binding sites, and that regulation of NLK on Nurr1 expression is abrogated by knockdown of CBP. CONCLUSIONS: Our results suggest that NLK inhibits transcriptional activation of Nurr1 gene by impeding CBP's role as a co-activator of NF-κB and CREB in prostate cancer.

MicroRNA-132 promotes estradiol synthesis in ovarian granulosa cells via translational repression of Nurr1.

BACKGROUND: Estrogen synthesis is an important function of the mammalian ovary. Estrogen plays important roles in many biological processes, including follicular development, oocyte maturation and endometrial proliferation, and dysfunctions in estrogen synthesis contribute to the development of polycystic ovary syndrome and premature ovarian failure. Classical signaling cascades triggered by follicle-stimulating hormone induce estrogen synthesis via the upregulation of Cyp19a1 in granulosa cells (GCs). This study aimed to determine the effect of microRNA-132 (miR-132) on estradiol synthesis in GCs. METHODS: Primary mouse GCs were collected from ovaries of 21-day-old immature ICR mice through follicle puncture. GCs were cultured and treated with the stable cyclic adenosine monophosphate analog 8-Br-cAMP or transfected with miR-132 mimics, Nurr1-specific small interfering RNA oligonucleotides and Flag-Nurr1 plasmids. Concentrations of estradiol and progesterone in culture medium were determined by an automated chemiluminescence-based assay. Quantitative real time PCR and western blot were performed to identify the effect of miR-132 on Cyp19a1, Cyp11a1 and an orphan nuclear receptor-Nurr1 expression in GCs. Direct suppression of Nurr1 via its 3'-untranslated region by miR-132 were further verified using luciferase reporter assays. RESULTS: The expression level of miR-132 in cultured mouse GCs was significantly elevated during 48 h of treatment with 8-Br-cAMP. The synthesis of estradiol increased after the overexpression of miR-132 in mouse GCs. The real-time PCR results demonstrated that miR-132 induced the expression of Cyp19a1 significantly. Nurr1, an orphan nuclear receptor that suppresses Cyp19a1 expression, was found to be a direct target of miR-132. Nurr1 was suppressed by miR-132, as indicated by a luciferase assay and Western blotting. The knockdown of Nurr1 primarily elevated the synthesis of estradiol and partially attenuated the miR-132-induced estradiol elevation, and the ectopic expression of Flag-Nurr1 abrogated the stimulatory effect of miR-132 on estradiol synthesis in mouse GCs. CONCLUSIONS: Our findings suggest that miR-132 is involved in the cAMP signaling pathway and promotes estradiol synthesis via the translational repression of Nurr1 in ovarian GCs.

Apoptosis Signal-regulating Kinase 1 (ASK1)-p38 Pathway-dependent Cytoplasmic Translocation of the Orphan Nuclear Receptor NR4A2 Is Required for Oxidative Stress-induced Necrosis.

p38 mitogen-activated protein kinases (MAPKs) play important roles in various cellular stress responses, including cell death, which is roughly categorized into apoptosis and necrosis. Although p38 signaling has been extensively studied, the molecular mechanisms of p38-mediated cell death are unclear. ASK1 is a stress-responsive MAP3K that acts as an upstream kinase of p38 and is activated by various stresses, such as oxidative stress. Here, we show that NR4A2, a member of the NR4A nuclear receptor family, acts as a necrosis promoter downstream of ASK1-p38 pathway during oxidative stress. Although NR4A2 is well known as a nucleus-localized transcription factor, we found that it is translocated into the cytosol after phosphorylation by p38. Because the phosphorylation site mutants of NR4A2 cannot rescue the cell death-promoting activity, ASK1-p38 pathway-dependent phosphorylation and subsequent cytoplasmic translocation of NR4A2 may be required for oxidative stress-induced cell death. In addition, NR4A2-mediated cell death does not depend on caspases and receptor-interacting protein 1 (RIP1)-RIP3 complex, suggesting that NR4A2 promotes an RIP kinase-independent necrotic type of cell death. Our findings may enable a more precise understanding of molecular mechanisms that regulate oxidative stress-induced and p38-mediated necrosis.

Orphan nuclear receptor nurr1 as a potential novel marker for progression in human prostate cancer.

A number of studies have indicated that Nurr1, which belongs to a novel class of orphan nuclear receptors (the NR4A family), is important for carcinogenesis. Here we investigated expression of Nurr1 protein in benign and malignant human prostate tissues and association with clinicopathologic features using immunohistochemical techniques. Moreover, we also investigated the ability of Nurr1 to influence proliferation, migration, invasion and apoptosis of human prostate cancer cells using small interfering RNA silencing. Immunohistochemical analysis revealed that the expression of Nurr1 protein was higher in prostate cancer tissues than in benign prostate tissue (P < 0.001), levels being positively correlated with tumor T classification (P = 0.003), N classification (P = 0.017), M classification (P = 0.011) and the Gleason score (P = 0.020) of prostate cancer patients. In vitro, silencing of endogenous Nurr1 attenuated cell proliferation, migration and invasion, and induced apoptosis of prostate cancer cells. These results suggest that Nurr1 may be used as an indicator for prostate cancer progression and be useful for novel potential therapeutic strategies.

Conditional expression of Parkinson's disease-related mutant α-synuclein in the midbrain dopaminergic neurons causes progressive neurodegeneration and degradation of transcription factor nuclear receptor related 1.

α-Synuclein (α-syn) plays a prominent role in the degeneration of midbrain dopaminergic (mDA) neurons in Parkinson's disease (PD). However, only a few studies on α-syn have been performed in the mDA neurons in vivo, which may be attributed to a lack of α-syn transgenic mice that develop PD-like severe degeneration of mDA neurons. To gain mechanistic insights into the α-syn-induced mDA neurodegeneration, we generated a new line of tetracycline-regulated inducible transgenic mice that overexpressed the PD-related α-syn A53T missense mutation in the mDA neurons. Here we show that the mutant mice developed profound motor disabilities and robust mDA neurodegeneration, resembling some key motor and pathological phenotypes of PD. We also systematically examined the subcellular abnormalities that appeared in the mDA neurons of mutant mice and observed a profound decrease of dopamine release, the fragmentation of Golgi apparatus, and the impairments of autophagy/lysosome degradation pathways in these neurons. To further understand the specific molecular events leading to the α-syn-dependent degeneration of mDA neurons, we found that overexpression of α-syn promoted a proteasome-dependent degradation of nuclear receptor-related 1 protein (Nurr1), whereas inhibition of Nurr1 degradation ameliorated the α-syn-induced loss of mDA neurons. Given that Nurr1 plays an essential role in maintaining the normal function and survival of mDA neurons, our studies suggest that the α-syn-mediated suppression of Nurr1 protein expression may contribute to the preferential vulnerability of mDA neurons in the pathogenesis of PD.

Overexpression of the orphan receptor Nur77 and its translocation induced by PCH4 may inhibit malignant glioma cell growth and induce cell apoptosis.

BACKGROUND: In previous study, n-butylidenephthalide (BP), a natural compound from Angelica sinensis, has anti-glioblastoma multiform (GBM) cell effects. In this study, we modified BP structure to increase anti-GBM cell effects. The anti-GBM cell effects of one derivative of BP, (Z)-N-(2-(dimethylamino)ethyl)-2-(3-((3-oxoisobenzofuran-1(3H)-ylidene)methyl)phenoxy)acetamide (PCH4) were tested in vitro and in vivo. METHODS: MTT assay and PI/Annexin V assay were performed to evaluate the anti-GBM effects of PCH4. The Nur77 expression and translocation were assayed by RT-PCR and Western blot. The Nur77 siRNA was used to downregulate the Nur77 expression. The JNK inhibitor (SP600125) was used to block the JNK pathway. RESULTS: The anti-GBM effect of PCH4 is four times more than BP. The IC(50) of PCH4 on DBTRG-05MG cells was 50 µg/ml. Nur77 expression and translocation from the nucleus to the cytoplasm were important in PCH4-induced apoptosis. Furthermore, the downregulation of PCH4-induced Nur77 expression by Nur77 siRNA reduced PCH4-induced apoptosis. In addition, PCH4-induced apoptosis was associated with the JNK pathway. The JNK inhibitor, SP600125, inhibited Nur77 mRNA expression and reduced PCH4-induced apoptosis. CONCLUSIONS: In conclusion, PCH4, a derivative of BP, induced Nur77-mediated apoptosis via the JNK pathway and this mechanism, which is different from that of BP, may explain the increase in the anti-tumor effects on GBM.

Retinoid X receptor α acts as a negative regulator in Nurr1-induced dopaminergic differentiation in rat neural precursor cells.

To investigate the role of retinoid X receptor (RXRα)­Nurr1 heterodimers in tyrosine hydroxylase (TH) expression, we observed retrovirus-induced RXRα­Nurr1 heterodimer interactions with, and transactivation of, the TH promoter region in cultured rat embryonic neural precursor cells. Interestingly, forced expression of RXRα with Nurr1 remarkably reduced Nurr1 activity in TH+ dopaminergic neuron generation and significantly down-regulated TH promoter activity. These regulatory activities were altered in both Nurr1dim- and RXRαdim- that disrupted dimeric binding, verifying that the Nurr1­RXRα heterodimer represses TH promoter activity. Therefore, a plausible explanation for the inhibitory role of RXRα in Nurr1-induced TH expression is that RXRα differentially affects an inhibitory element of the TH promoter.