Orphan Nuclear Receptor NR4A1 Research Articles

Loss of glucose-stimulated β-cell Nr4a1 expression impairs insulin secretion and glucose homeostasis.

A central aspect of type 2 diabetes is decreased functional β-cell mass. The orphan nuclear receptor Nr4a1 is critical for fuel utilization, but little is known regarding its regulation and function in the β-cell. Nr4a1 expression is decreased in type 2 diabetes rodent β-cells and type 2 diabetes patient islets. We have shown that Nr4a1 deficient mice have reduced β-cell mass and that Nr4a1 knock-down impairs glucose-stimulated insulin secretion (GSIS) in INS-1 832/13 β-cells. Here, we demonstrate that glucose concentration directly regulates β-cell Nr4a1 expression. We show that 11 mM glucose increases Nr4a1 expression in INS-1 832/13 β-cells and primary mouse islets. We show that glucose functions through the cAMP/PKA/CREB pathway to regulate Nr4a1 mRNA and protein expression. Using Nr4a1-/- animals, we show that Nr4a1 is necessary for GSIS and systemic glucose handling. Using RNA-seq, we define Nr4a1-regulated pathways in response to glucose in the mouse islet, including Glut2 expression. Our data suggests that Nr4a1 plays a critical role in the β-cells response to the fed state.

Gender Specific Effects of Nr4a1 in Obese Mice

A central aspect of type 2 diabetes disease progression is impaired functional β-cell mass. The hyperglycemic and hyperlipidemic environment present in type 2 diabetes corresponds with impaired beta cell function. The orphan nuclear receptor Nr4a1 is critical for fuel utilization in various tissues, however little is known regarding its function in the β-cell. Nr4a1 expression is decreased in the β-cell of rodent models of type 2 diabetes, as well as in primary human islets from type 2 diabetics. Here we demonstrate sex specific effects of β-cell specific Nr4a1 deletion under high fat chow feeding. While female and male βNr4a1−/− mice were no different than wild type controls when fed a standard chow diet, a clear sex dependent difference is observed when fed a high fat diet. While high fat fed male βNr4a1−/− have improved fasting and non-fasting blood glucose levels and no change in glucose tolerance, high fat fed female βNr4a1−/− mice have impaired glucose tolerance as early as one month after beginning high fat feeding. We also found that βNr4a1−/− female mice have decreased β-cell mass and decreased expression in known targets of Nr4a1 regulation including Eno1 and SDHβ. Our data suggest that Nr4a1 is critical for maintenance of beta cell function, and that loss of Nr4a1 under conditions of obesity and overnutrition in females results in impaired beta cell compensation and function. NIH R15DK124835-01A1. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

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.

Nr4a1 enhances Wnt4 transcription to promote mesenchymal stem cell osteogenesis and alleviates inflammation-inhibited bone regeneration

Intense inflammatory response impairs bone marrow mesenchymal stem cell (BMSC)-mediated bone regeneration, with TGF-β1 being the most highly expressed cytokine. However, how to find effective and safe means to improve bone formation impaired by excessive TGF-β1 remains unclear. In this study, we found that the expression of orphan nuclear receptor Nr4a1, an endogenous repressor of TGF-β1, was suppressed directly by TGF-β1-induced Smad3 and indirectly by Hdac4, respectively. Importantly, Nr4a1 overexpression promoted BMSC osteogenesis and reversed TGF-β1-mediated osteogenic inhibition and pro-fibrotic effects. Transcriptomic and histologic analyses confirmed that upregulation of Nr4a1 increased the transcription of Wnt family member 4 (Wnt4) and activated Wnt pathway. Mechanistically, Nr4a1 bound to the promoter of Wnt4 and regulated its expression, thereby enhancing the osteogenic capacity of BMSCs. Moreover, treatment with Nr4a1 gene therapy or Nr4a1 agonist Csn-B could promote ectopic bone formation, defect repair, and fracture healing. Finally, we demonstrated the correlation of NR4A1 with osteogenesis and the activation of the WNT4/β-catenin pathway in human BMSCs and fracture samples. Taken together, these findings uncover the critical role of Nr4a1 in bone formation and alleviation of inflammation-induced bone regeneration disorders, and suggest that Nr4a1 has the potential to be a therapeutic target for accelerating bone healing.

NR4A1 PROMOTES OSTEOGENIC DIFFERENTIATION OF MESENCHYMAL STEM CELLS AND IMPROVES INFLAMMATION-INHIBITED BONE REGENERATION

Stem cell therapy is an effective means to address the repair of large segmental bone defects. However, the intense inflammatory response triggered by the implants severely impairs stem cell differentiation and tissue regeneration. High-dose transforming growth factor β1 (TGF-β1), the most locally expressed cytokine in implants, inhibits osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) and promotes tissue fibrosis, severely compromising the efficacy of stem cell therapy. Small molecule inhibitors of TGF-β1 can be used to ameliorate the osteogenic disorders caused by high concentrations of TGF-β1, but systemic inhibition of TGF-β1 function will cause strong adverse effects. How to find safe and reliable molecular targets to antagonize TGF-β1 remains to be elucidated. Orphan nuclear receptor Nr4a1, an endogenous inhibitory molecule of TGF-β1, suppresses tissue fibrosis, but its role in BMSC osteogenesis is unclear. We found that TGF-β1 inhibited Nr4a1 expression through HDAC4. Overexpression of Nr4a1 in BMSCs reversed osteogenic differentiation inhibited by high levels of TGF- β1. Mechanistically, RNA sequencing showed that Nr4a1 activated the ECM-receptor interaction and Hippo signaling pathway, which in turn promoted BMSC osteogenesis. In bone defect repair and fracture healing models, transplantation of Nr4a1-overexpressing BMSCs into C57BL/6J mice or treatment with the Nr4a1 agonist Csn-B significantly ameliorated inflammation-induced bone regeneration disorders. In summary, our findings confirm the endogenous inhibitory effect of Nr4a1 on TGF- β1 and uncover the effectiveness of Nr4a1 agonists as a therapeutic tool to improve bone regeneration, which provides a new solution strategy for the treatment of clinical bone defects and inflammatory skeletal diseases.

Orphan nuclear receptor nr4a1 regulates winter depression-like behavior in medaka

About 10% of the population suffers from depression in winter at high latitude. Although it has become a serious public health issue, its underlying mechanism remains unknown and new treatments and therapies are required. As an adaptive strategy, many animals also exhibit depression-like behavior in winter. Previously, it has been reported that celastrol, a traditional Chinese medicine, can rescue winter depression-like behavior in medaka, an excellent model of winter depression. Nuclear receptor subfamily 4 group A member 1 (nr4a1, also known as nur77) is a known target of celastrol, and the signaling pathway of nr4a1 was suggested to be inactive in medaka brain during winter, implying the association of nr4a1 and winter depression-like behavior. However, the direct evidence for its involvement in winter depression-like behavior remains unclear. The present study found that nr4a1 was suppressed in the medaka brain under winter conditions. Cytosporone B, nr4a1 chemical activator, reversed winter depression-like behavior under winter conditions. Additionally, nr4a1 mutant fish generated by CRISPR/Cas9 system showed decreased sociability under summer conditions. Therefore, our results demonstrate that the seasonal regulation of nr4a1 regulates winter depression-like behavior and offers potential therapeutic target.

Salt-induced maladaptive innate immune memory impedes stroke recovery

Abstract A high salt diet (HSD) is a top risk factor for human mortality. Beyond its heavily implicated role in hypertension, it is now linked to the development of inflammatory diseases before the onset of cardiovascular events. Even after salt reduction, HSD can induce prolonged tissue damage, yet the mechanisms by which HSD induces persistent negative effects on immune system are largely unexplored. While HSD is an established risk factor for stroke, its impact on long-term stroke recovery is unknown. Here, we model two major stroke types, intracerebral hemorrhage, and cerebral ischemia, to investigate how HSD induces unfavorable immune responses and subsequently impacts long-term tissue repair. We found HSD exclusively hampers alternative activation in monocytes-derived macrophages (MDMs) while sparing the major parenchymal macrophage—microglia—in the stroke brain. HSD induces innate immune memory in the hematopoietic stem and progenitor cells through downregulating mitochondrial oxidative phosphorylation and NR4a orphan nuclear receptors expression. This immunological memory was retained in the brain-infiltrating MDMs and restrained their reparative functions. Consequently lead to impaired tissue repair and neurobehavioral recovery during stroke recovery phase. Pharmacological treatment with NR4a1 activator and genetic overexpression of NR4a1 restored MDMs reparative phenotype suppressed by HSD and enabled stroke recovery. These findings establish a new mechanism linking HSD-induced maladaptive innate immune memory to a hindered macrophage alternative activation and delayed tissue recovery. Our data unveil innate immune memory and NR4a1 as potential therapeutic targets for treating HSD-associated diseases.

1446-P: Sex-Specific Effects of Nr4a1 in the Pancreatic Beta Cell

A central aspect of type 2 diabetes disease progression is impaired functional β-cell mass. The hyperglycemic and hyperlipidemic environment present in type 2 diabetes corresponds with impaired beta cell function. The orphan nuclear receptor Nr4a1 is critical for fuel utilization in various tissues, however little is known regarding its function in the β-cell. Nr4a1 expression is decreased in the β-cell of rodent models of type 2 diabetes, as well as in primary human islets from type 2 diabetics. Here we demonstrate sex specific effects of β-cell specific Nr4a1 deletion under high fat chow feeding. While female and male βNr4a1-/- mice were no different than wild type controls when fed a standard chow diet, a clear sex dependent difference is observed when fed a high fat diet. High fat fed male βNr4a1-/- have improved fasting and non-fasting blood glucose levels, high fat fed female βNr4a1-/- mice have impaired glucose tolerance as early as two months after beginning high fat feeding. Furthermore, female βNr4a1-/- mice have decreased β-cell mass and improved insulin tolerance. Given the sex specific differences in glucose tolerance, we demonstrated that female mice fed a high fat diet have increased circulating estrogen, and that treatment of INS-1 832/13 cells and primary mouse islets with estradiol resulted in increased expression of Nr4a1 and not the other two Nr4a family members. Our data suggest that Nr4a1 is critical for estrogen mediated maintenance of beta cell function and mass under obesogenic conditions, and that loss of Nr4a1 under conditions of obesity and overnutrition in females results in impaired beta cell compensation and function. Disclosure J.S.Tessem: None. J.Herring: None. Funding National Institutes of Health (1R15DK124835-01A1)

Glucose‐1‐phosphate regulates orphan nuclear receptor NR4A1 and apoptosis

Mitochondrial metabolic reprogramming is important for many different processes like apoptosis and inflammation. NR4A1 is necessary for many different pro‐apoptotic and inflammatory stimuli to induce mitochondrial metabolic reprogramming. However, despite the importance for small molecule ligands in the regulation of nuclear receptors, biological ligands regulating NR4A1 have not been identified. Here we report that glucose‐1‐phosphate (G1P), an intracellular metabolite from glycogen metabolism and glycolysis, is an NR4A1 ligand. In vitro, G1P specifically bound to NR4A1 ligand‐binding domain (NR4A1LBD) and alters its oligomerization state. In cells, a synthetic cell‐permeable G1P analog regulates transcriptional activity of NR4A1. This G1P analog suppressed mitochondrial respiration and induced apoptosis of H1299 lung adenocarcinoma cells in an NR4A1‐dependent manner. This result suggests that G1P might be an endogenous ligand regulating NR4A1 and NR4A1‐dependent mitochondrial metabolic reprogramming. It represents a rare case where a polar water‐soluble intracellular metabolite modulates a nuclear receptor function.

Orphan Nuclear Receptor NR4A2 Is Constitutively Expressed in Cartilage and Upregulated in Inflamed Synovium From hTNF-Alpha Transgenic Mice.

Orphan nuclear receptor 4A2 (NR4A2/Nurr1) is a constitutively active transcription factor with potential roles in the onset and progression of inflammatory arthropathies. NR4A2 is overexpressed in synovium and cartilage from individuals with rheumatoid arthritis (RA), psoriatic arthritis, and osteoarthritis. This study documents the expression and tissue localization of NR4A2 and upstream regulator nuclear factor kappa B (NF-κB) in the human tumor necrosis factor-alpha (hTNF-α) transgenic mouse model of RA. Since TNF-α is a potent inducer of NR4A2 in vitro, we hypothesized that NR4A2 would also be upregulated and active during disease progression in this model. Expression levels of NR4A2, related receptors NR4A1 (Nur77) and 3 (NOR1), and NF-κB1 transcripts were quantified by RT-qPCR in hTNF-α and wild-type joints at three stages of disease. The protein distribution of NR4A2 and NF-κB subunit RelA (p65) was analyzed by quantitative immunohistochemistry. Global gene expression of 88 RA-related genes was also screened and compared between groups. Consistent with previous reports on the hTNF-α model, transgenic mice exhibited significant weight loss and severely swollen paws by 19 weeks of age compared to age-matched wild-type controls. NR4A1-3 and NF-κB1 were constitutively expressed at disease onset and in healthy joints. NF-κB1 transcript levels increased 2-fold in hTNF-α paws with established disease (12 weeks), followed by a 2-fold increase in NR4A2 at the late disease stage (19 weeks). NR4A2 and RelA proteins were overexpressed in inflamed synovium prior to symptoms of arthritis, suggesting that gene expression changes documented in whole paws were largely driven by elevated expression in diseased synovium. Broader screening of RA-related genes by RT-qPCR identified several differentially expressed genes in hTNF-α joints including those encoding inflammatory cytokines and chemokines, matrix-degrading enzymes and inhibitors, cell surface receptors, intracellular signaling proteins and transcription factors. Consensus binding sites for NR4A receptors and NF-κB1 were enriched in the promoters of differentially expressed genes suggesting central roles for these transcription factors in this model. This study is the first comprehensive analysis of NR4A2 in an animal model of RA and validates the hTNF-α model for testing of small molecules and genetic strategies targeting this transcription factor.

Monocyte Gene and Molecular Expression Profiles Suggest Distinct Effector and Regulatory Functions in Beninese HIV Highly Exposed Seronegative Female Commercial Sex Workers.

We have previously reported that the female genital tract (FGT) of Beninese HIV highly-exposed seronegative (HESN) commercial sex workers (CSWs), presented elevated frequencies of a myeloid HLA-DR+CD14+CD11c+ population presenting “tolerogenic” monocyte derived dendritic cells (MoDC) features. In order to assess whether a differential profile of monocytes may be involved in the generation of these genital MoDCs, we have herein characterized the blood monocyte compartment of Beninese HESNs (HIV-uninfected ≥ 10 years CSWs) and relevant controls (HIV-uninfected 2.5–5 years CSWs herein termed “early HESNs”), HIV-infected CSWs, and low-risk HIV-uninfected women from the general population. Transcriptomic analyses by RNA-Seq of total sorted blood monocytes demonstrate that in comparison to the control groups, HESNs present increased expression levels of FCGR2C, FCAR, ITGAX, ITGAM, CR2, CD68, and CD163 genes, associated with effector functions. Moreover, we found increased expression levels of genes associated with protection/control against SHIV/HIV such as CCL3, CCL4, CCL5, BHLHE40, and TNFSF13, as well as with immune regulation such as IL-10, Ahr, CD83, and the orphan nuclear receptor (NR)4A1, NR4A2, and NR4A3. Through multicolor flow cytometry analyses, we noticed that the frequencies of intermediate and non-classical monocyte populations tended to be elevated in the blood of HESNs, and exhibited increased expression levels of effector CD16, CD11c, CD11b, as well as regulatory HLA-G, IL-10, and IFN-α markers when compared to HIV-uninfected women and/or HIV-infected CSWs. This profile is compatible with that previously reported in the FGT of HESNs, and likely confers an enormous advantage in their resistance to HIV infection.

NR4A1 Affects Endometrial Receptivity by Participating in Mesenchymal-Epithelial Transition of Endometrial Stromal Cells.

Decidualization is a substantive differentiation process experienced by endometrium to prepare for pregnancy. During this process, the endometrial stromal cells are transformed to endometrial epithelial cells. The receptivity of endometrium is necessary for the decidualization and successful implantation of endometrium, while the main hormones coordinating this process are estrogen and progesterone (P). In our study, the immunofluorescence, qPCR, and western blot experiments were conducted on different types of clinical endometrial tissue samples. The experimental results show that in the endometrium of normal subjects during the luteal phase, the protein level and serum P4 level of the orphan nuclear receptor NR4A1 messenger RNA were all significantly higher than those of patients with endometriosis or primary infertility, and the two levels presented positive correlation. Through decidualization induction of the human endometrial stromal cells (hESCs) cultured in vitro and additional P treatment, the results of chromatin immunoprecipitation and other experiments show that the P treatment could upregulate the expression of NR4A1 in hESCs, and this process was mediated under the direct effect of progesterone receptor (PR) and NR4A1. When the NR4A1 in hESCs was silenced, the promotion of hESC proliferation by P was inhibited. P and overexpressed NR4A1 increased the expression of epithelial cell marker in decidual hESCs, and qPCR showed that NR4A1's response to P was earlier than that of the epithelial cell marker. The results of spheroid adhesion assay show that the silent NR4A1 had reduced the adhesion of decidual hESCs induced in vitro to embryo. To sum it up, NR4A1 participated in the decidualization process by responding to the P regulation via and by promoting the hESCs' mesenchymal-epithelial transition, so as to further influence the receptivity of endometrium.

NR4A1 regulates expression of immediate early genes, suppressing replication stress in cancer

Deregulation of oncogenic signals in cancer triggers replication stress. Immediate early genes (IEGs) are rapidly and transiently expressed following stressful signals, contributing to an integrated response. Here, we find that the orphan nuclear receptor NR4A1 localizes across the gene body and 3' UTR of IEGs, where it inhibits transcriptional elongation by RNA Pol II, generating R-loops and accessible chromatin domains. Acute replication stress causes immediate dissociation of NR4A1 and a burst of transcriptionally poised IEG expression. Ectopic expression of NR4A1 enhances tumorigenesis by breast cancer cells, while its deletion leads to massive chromosomal instability and proliferative failure, driven by deregulated expression of its IEG target, FOS. Approximately half of breast and other primary cancers exhibit accessible chromatin domains at IEG gene bodies, consistent with this stress-regulatory pathway. Cancers that have retained this mechanism in adapting to oncogenic replication stress may be dependent on NR4A1 for their proliferation.

Abstract 2473: NR4A1 suppresses cancer replication stress through R-loop-dependent inhibition of immediate early gene transcriptional elongation

Abstract Deregulation of oncogenic proliferative signals triggers replication stress in cancer cells to which they must adapt. Immediate early genes (IEGs), identified by their rapid stress-induced transient bursts of expression, are critical to integrating downstream signaling pathways. In studying tumor initiation by patient-derived breast cancer cells, we observed acquisition of open chromatin domains at the genebody and 3'-UTR of IEGs, uniquely across the genome. Through in vivo and in vitro modeling, we show that the IEG and orphan nuclear receptor NR4A1 localizes across multiple IEG genebodies, where it binds to RNA Pol II, arresting transcriptional elongation and generating extensive R-loops and accessible chromatin. Acute stress promptly removes NR4A1 from IEG genebodies, triggering immediate release of their poised transcripts. In breast cancer cells, NR4A1 overexpression increases tumorigenesis; conversely, its deletion leads to uncompensated replication stress, chromosomal instability and mitotic catastrophe, driven by deregulation of its IEG target FOS. A large fraction of primary breast and other cancers exhibit open genebody chromatin at IEGs, consistent with preserved NR4A1 function. Thus, NR4A1 mediates a novel transcriptional elongation checkpoint, unique to stress-induced genes and required for their rapid bursts of expression. Cancers that have retained this mechanism in adapting to chronic replication stress may be dependent on NR4A1 for proliferation. Citation Format: Hongshan Guo, Gabriel Golczer, Shyamala Maheswaran, Michael S. Lawrence, Daniel A. Haber. NR4A1 suppresses cancer replication stress through R-loop-dependent inhibition of immediate early gene transcriptional elongation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2473.

Controlling for activity-dependent genes and behavioral states is critical for determining brain relationships within and across species.

The genetic profile of vertebrate pallia has long driven debate on homology across distantly related clades. Based on an expression profile of the orphan nuclear receptor NR4A2 in mouse and chicken brains, Puelles et al. (The Journal of Comparative Neurology, 2016, 524, 665–703) concluded that the avian lateral mesopallium is homologous to the mammalian claustrum, and the medial mesopallium homologous to the insula cortex. They argued that their findings contradict conclusions by Jarvis et al. (The Journal of Comparative Neurology, 2013, 521, 3614–3665) and Chen et al. (The Journal of Comparative Neurology, 2013, 521, 3666–3701) that the hyperpallium densocellare is instead a mesopallium cell population, and by Suzuki and Hirata (Frontiers in Neuroanatomy, 2014, 8, 783) that the avian mesopallium is homologous to mammalian cortical layers 2/3. Here, we find that NR4A2 is an activity‐dependent gene and cannot be used to determine brain organization or species relationships without considering behavioral state. Activity‐dependent NR4A2 expression has been previously demonstrated in the rodent brain, with the highest induction occurring within the claustrum, amygdala, deep and superficial cortical layers, and hippocampus. In the zebra finch, we find that NR4A2 is constitutively expressed in the arcopallium, but induced in parts of the mesopallium, and in sparse cells within the hyperpallium, depending on animal stimulus or behavioral state. Basal and induced NR4A2 expression patterns do not discount the previously named avian hyperpallium densocellare as dorsal mesopallium and conflict with proposed homology between the avian mesopallium and mammalian claustrum/insula at the exclusion of other brain regions. Broadly, these findings highlight the importance of controlling for behavioral state and neural activity to genetically define brain cell population relationships within and across species.

Complex regulation of orphan nuclear receptor Nur77 (Nr4a1) transcriptional activity by SUMO2 and PIASγ

Nur77 (NGFI-B) is a nuclear receptor that belongs to the Nr4a family of orphan nuclear receptors (Nr4a1). This transcription factor has been implicated in the regulation of multiple functions, such as cell cycle regulation, apoptosis, inflammation, glucose and lipid metabolism, and brain function. However, the mechanisms involved in its different regulatory properties remain unclear. In search for regulatory mechanisms of Nur77 function, we identified that Protein Inhibitor of Activated STAT gamma (PIASγ), an E3 SUMO-protein ligase, potently repressed Nur77 transcriptional activity in HEK-293T cells. This PIASγ activity was sensitive to Sentrin SUMO-specific protease 1 (SENP1). Substitution of two putative phylogenetically well-conserved small ubiquitin-like modifier (SUMO) acceptor sites, lysine 102 (K102) and 577 (K577) by arginine residues (R) modulated Nur77 transcriptional activity. In particular, Nur77-K102R and Nur77-K102R/K577R mutants strongly decreased the transcriptional activity of Nur77, whereas single K577R substitution increased transcriptional activity of Nur77. Repression of Nur77 transcriptional activity by SUMO2 and PIASγ was reduced by the K577R mutation, whereas the K102R mutant remained insensitive to SUMO2. Interestingly, the roles of these SUMO acceptor sites in Nur77 are distinct from previously observed activities on its close homolog Nurr1. Thus, the present study identified SUMO2 and PIASγ as important transcriptional co-regulators of Nur77.

A Bis-Indole-Derived NR4A1 Antagonist Induces PD-L1 Degradation and Enhances Antitumor Immunity.

PD-L1 is expressed in tumor cells and its interaction with PD-1 plays an important role in evading immune surveillance; this can be overcome using PD-L1 or PD-1 immunotherapy antibodies. This study reports a novel approach for targeting PD-L1. In human breast cancer cell lines and 4T1 mouse mammary tumor cells, PD-L1 expression was regulated by the nuclear receptor NR4A1/Sp1 complex bound to the proximal germinal center (GC)-rich region of the PD-L1 gene promoter. Treatment of breast cancer cells with bis-indole-derived NR4A1 antagonists including 1,1-bis(3'-indolyl)-1-(3-chloro-4-hydroxy-5-methoxyphenyl)methane (Cl-OCH3) decreased expression of PD-L1 mRNA, promoter-dependent luciferase activity, and protein. In in vivo studies using a syngeneic mouse model bearing orthotopically injected 4T1 cells, Cl-OCH3 decreased tumor growth and weight and inhibited lung metastasis. Cl-OCH3 also decreased expression of CD3+/CD4+/CD25+/FoxP3+ regulatory T cells and increased the Teff/Treg ratio. Therefore, the potent anticancer activities of NR4A1 antagonists are also accompanied by enhanced antitumor immunity in PD-L1-expressing triple-negative breast cancer and thus represent a novel class of drugs that mimic immunotherapy. SIGNIFICANCE: These findings show that the orphan nuclear receptor NR4A1 controls PD-L1 expression and identify a chemical probe capable of disrupting this regulatory axis.

Liposomal 9-Aminoacridine for Treatment of Ischemic Stroke: From Drug Discovery to Drug Delivery.

Neuroinflammation plays a pivotal part in the pathogenesis of stroke. Orphan nuclear receptor NR4A1 is involved in the inflammatory response of microglia and macrophages. In this study, we discovered an old drug, 9-aminoacridine (9-AA), as a novel NR4A1 activator from our in-house FDA-approved drug library, which exhibited anti-inflammatory activities through an NR4A1/IL-10/SOCS3 signaling pathway and modulated the microglia activation. To improve the druggability of 9-AA, different liposomal formulations were screened and investigated. 9-AA-loaded liposome (9-AA/L) was prepared to reduce the adverse effect of 9-AA. Furthermore, 9-AA-loaded PEG/cRGD dual-modified liposome (9-AA/L-PEG-cRGD) was obtained, which displayed prolonged circulation, improved biodistribution, and increased brain accumulation. In the transient middle cerebral artery occlusion (tMCAO) rat model, 9-AA/L-PEG-cRGD significantly reduced brain infarct area, ameliorated ischemic brain injury, and promoted long-term neurological function recovery. This "from drug discovery to drug delivery" methodology provides a potential therapeutic strategy using the liposomal 9-AA, the NR4A1 activator to suppress neuroinflammation for treatment of ischemic stroke.

Function of Nr4a Orphan Nuclear Receptors in Proliferation, Apoptosis and Fuel Utilization Across Tissues.

The Nr4a family of nuclear hormone receptors is composed of three members—Nr4a1/Nur77, Nr4a2/Nurr1 and Nr4a3/Nor1. While currently defined as ligandless, these transcription factors have been shown to regulate varied processes across a host of tissues. Of particular interest, the Nr4a family impinge, in a tissue dependent fashion, on cellular proliferation, apoptosis and fuel utilization. The regulation of these processes occurs through both nuclear and non-genomic pathways. The purpose of this review is to provide a balanced perspective of the tissue specific and Nr4a family member specific, effects on cellular proliferation, apoptosis and fuel utilization.

A novel lncRNA NR4A1AS up-regulates orphan nuclear receptor NR4A1 expression by blocking UPF1-mediated mRNA destabilization in colorectal cancer.

Long non-coding RNAs (lncRNAs) play important roles in tumorigenesis and cancer progression. The orphan nuclear receptor subfamily 4 group A member 1 (NR4A1) acts as an oncogene, and is involved in colorectal cancer (CRC) development. However, the mechanism through which lncRNA regulates NR4A1 expression remains unknown. We aimed to identify lncRNAs that regulate NR4A1 and assess their underlying mechanisms in CRC. We first identified an antisense lncRNA of NR4A1 that was up-regulated in CRC tissues and cells with rapid amplification of cDNA ends (RACE), and designated it as NR4A1AS. Spearman correlation analysis showed that NR4A1AS was positively correlated with NR4A1 mRNA levels in 37 CRC tissues. Mechanistically, NR4A1AS stabilized NR4A1 mRNA by forming RNA-RNA complexes via partial base-pairing and up-regulated NR4A1 expression in CRC cells. RNA immunoprecipitation (RIP) assays revealed that knockdown of NR4A1AS expression by siRNA enhanced up-frameshift 1 (UPF1) recruitment to NR4A1 mRNA, thereby decreasing NR4A1 mRNA stability. Moreover, depletion of NR4A1AS was found to mimic the effect of NR4A1 knockdown, specifically by suppressing cell proliferation, migration and invasion, and inducing apoptosis and cell cycle arrest. Accordingly, restoring NR4A1 expression ameliorated the effects of NR4A1AS knockdown on tumor growth and metastasis of CRC cells in vitro and in vivo Thus, we conclude that NR4A1AS up-regulates NR4A1 expression by forming RNA-RNA complexes and blocking UPF1-mediated mRNA destabilization, and it functions in tumor growth and metastasis of CRC cells at least partly through regulating NR4A1, suggesting that NR4A1AS might be as a potential target for RNA-based anti-CRC drug studies.