Potent inhibition of breast cancer by bis-indole-derived nuclear receptor 4A1 (NR4A1) antagonists

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.

Thioredoxin Domain Containing 5 (TXNDC5): Friend or Foe?

This review focuses on the thioredoxin domain containing 5 (TXNDC5), also known as endoplasmic reticulum protein 46 (ERp46), a member of the protein disulfide isomerase (PDI) family with a dual role in multiple diseases. TXNDC5 is highly expressed in endothelial cells, fibroblasts, pancreatic β-cells, liver cells, and hypoxic tissues, such as cancer endothelial cells and atherosclerotic plaques. TXNDC5 plays a crucial role in regulating cell proliferation, apoptosis, migration, and antioxidative stress. Its potential significance in cancer warrants further investigation, given the altered and highly adaptable metabolism of tumor cells. It has been reported that both high and low levels of TXNDC5 expression are associated with multiple diseases, such as arthritis, cancer, diabetes, brain diseases, and infections, as well as worse prognoses. TXNDC5 has been attributed to both oncogenic and tumor-suppressive features. It has been concluded that in cancer, TXNDC5 acts as a foe and responds to metabolic and cellular stress signals to promote the survival of tumor cells against apoptosis. Conversely, in normal cells, TXNDC5 acts as a friend to safeguard cells against oxidative and endoplasmic reticulum stress. Therefore, TXNDC5 could serve as a viable biomarker or even a potential pharmacological target.

Bis-Indole Derivatives as Dual Nuclear Receptor 4A1 (NR4A1) and NR4A2 Ligands

Bis-indole derived compounds such as 1,1-bis(3'-indolyl)-1-(3,5-disubstitutedphenyl) methane (DIM-3,5) and the corresponding 4-hydroxyl analogs (DIM8-3,5) are NR4A1 ligands that act as inverse NR4A1 agonists and are potent inhibitors of tumor growth. The high potency of several DIM-3,5 analogs (IC50 < 1 mg/kg/day), coupled with the >60% similarity of the ligand-binding domains (LBDs) of NR4A1 and NR4A2 and the pro-oncogenic activities of both receptors lead us to hypothesize that these compounds may act as dual NR4A1 and NR4A2 ligands. Using a fluorescence binding assay, it was shown that 22 synthetic DIM8-3,5 and DIM-3,5 analogs bound the LBD of NR4A1 and NR4A2 with most KD values in the low µM range. Moreover, the DIM-3,5 and DIM8-3,5 analogs also decreased NR4A1- and NR4A2-dependent transactivation in U87G glioblastoma cells transfected with GAL4-NR4A1 or GAL4-NR4A2 chimeras and a UAS-luciferase reporter gene construct. The DIM-3,5 and DIM8-3,5 analogs were cytotoxic to U87 glioblastoma and RKO colon cancer cells and the DIM-3,5 compounds were more cytotoxic than the DIM8-3,5 compounds. These studies show that both DIM-3,5 and DIM8-3,5 compounds previously identified as NR4A1 ligands bind both NR4A1 and NR4A2 and are dual NR4A1/2 ligands.

3,3'-Diindolylmethane and indole-3-carbinol: potential therapeutic molecules for cancer chemoprevention and treatment via regulating cellular signaling pathways

Dietary compounds in cancer prevention have gained significant consideration as a viable method. Indole-3-carbinol (I3C) and 3,3'-diindolylmethane (DIM) are heterocyclic and bioactive chemicals found in cruciferous vegetables like broccoli, cauliflower, cabbage, and brussels sprouts. They are synthesized after glycolysis from the glucosinolate structure. Clinical and preclinical trials have evaluated the pharmacokinetic/pharmacodynamic, effectiveness, antioxidant, cancer-preventing (cervical dysplasia, prostate cancer, breast cancer), and anti-tumor activities of I3C and DIM involved with polyphenolic derivatives created in the digestion showing promising results. However, the exact mechanism by which they exert anti-cancer and apoptosis-inducing properties has yet to be entirely understood. Via this study, we update the existing knowledge of the state of anti-cancer investigation concerning I3C and DIM chemicals. We have also summarized; (i) the recent advancements in the use of I3C/DIM as therapeutic molecules since they represent potentially appealing anti-cancer agents, (ii) the available literature on the I3C and DIM characterization, and the challenges related to pharmacologic properties such as low solubility, and poor bioavailability, (iii) the synthesis and semi-synthetic derivatives, (iv) the mechanism of anti-tumor action in vitro/in vivo, (v) the action in cellular signaling pathways related to the regulation of apoptosis and anoikis as well as the cell cycle progression and cell proliferation such as peroxisome proliferator-activated receptor and PPARγ agonists; SR13668, Akt inhibitor, cyclins regulation, ER-dependent-independent pathways, and their current medical applications, to recognize research opportunities to potentially use these compounds instead chemotherapeutic synthetic drugs.

The nuclear receptor subfamily 4 group A1 in human disease

Nuclear receptor 4A1 (NR4A1), a member of the NR4A subfamily, acts as a gene regulator in a wide range of signaling pathways and responses to human diseases. Here, we provide a brief overview of the current functions of NR4A1 in human diseases and the factors involved in its function. A deeper understanding of these mechanisms can potentially improve drug development and disease therapy.

Therapeutic potential of NR4A1 in cancer: Focus on metabolism

Metabolic reprogramming is a vital hallmark of cancer, and it provides the necessary energy and biological materials to support the continuous proliferation and survival of tumor cells. NR4A1 is belonging to nuclear subfamily 4 (NR4A) receptors. NR4A1 plays diverse roles in many tumors, including melanoma, colorectal cancer, breast cancer, and hepatocellular cancer, to regulate cell growth, apoptosis, metastasis. Recent reports shown that NR4A1 exhibits unique metabolic regulating effects in cancers. This receptor was first found to mediate glycolysis via key enzymes glucose transporters (GLUTs), hexokinase 2 (HK2), fructose phosphate kinase (PFK), and pyruvate kinase (PK). Then its functions extended to fatty acid synthesis by modulating CD36, fatty acid-binding proteins (FABPs), sterol regulatory element-binding protein 1 (SREBP1), glutamine by Myc, mammalian target of rapamycin (mTOR), and hypoxia-inducible factors alpha (HIF-1α), respectively. In addition, NR4A1 is involving in amino acid metabolism and tumor immunity by metabolic processes. More and more NR4A1 ligands are found to participate in tumor metabolic reprogramming, suggesting that regulating NR4A1 by novel ligands is a promising approach to alter metabolism signaling pathways in cancer therapy. Basic on this, this review highlighted the diverse metabolic roles of NR4A1 in cancers, which provides vital references for the clinical application.

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.

Gut bacterial metabolites modulate endoplasmic reticulum stress

Background

The endoplasmic reticulum (ER) is a membranous organelle that maintains proteostasis and cellular homeostasis, controlling the fine balance between health and disease. Dysregulation of the ER stress response has been implicated in intestinal inflammation associated with inflammatory bowel disease (IBD), a chronic condition characterized by changes to the mucosa and alteration of the gut microbiota. While the microbiota and microbially derived metabolites have also been implicated in ER stress, examples of this connection remain limited to a few observations from pathogenic bacteria. Furthermore, the mechanisms underlying the effects of bacterial metabolites on ER stress signaling have not been well established.

Results

Utilizing an XBP1s-GFP knock-in reporter colorectal epithelial cell line, we screened 399 microbiome-related metabolites for ER stress pathway modulation. We find both ER stress response inducers (acylated dipeptide aldehydes and bisindole methane derivatives) and suppressors (soraphen A) and characterize their activities on ER stress gene transcription and translation. We further demonstrate that these molecules modulate the ER stress pathway through protease inhibition or lipid metabolism interference.

Conclusions

Our study identified novel links between classes of gut microbe-derived metabolites and the ER stress response, suggesting the potential for these metabolites to contribute to gut ER homeostasis and providing insight into the molecular mechanisms by which gut microbes impact intestinal epithelial cell homeostasis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13059-021-02496-8.

Indole Alkaloids, Synthetic Dimers and Hybrids with Potential In Vivo Anticancer Activity

Indole, a heterocyclic organic compound, is one of the most promising heterocycles found in natural and synthetic sources since its derivatives possess fascinating structural diversity and various therapeutic properties. Indole alkaloids, synthetic dimers and hybrids could act on diverse targets in cancer cells, and consequently, possess potential antiproliferative effects on various cancers both in vitro and in vivo. Vinblastine, midostaurin, and anlotinib as the representative of indole alkaloids, synthetic dimers and hybrids respectively, have already been clinically applied to treat many types of cancers, demonstrating indole alkaloids, synthetic dimers and hybrids are useful scaffolds for the development of novel anticancer agents. Covering articles published between 2010 and 2020, this review emphasizes the recent development of indole alkaloids, synthetic dimers and hybrids with potential in vivo therapeutic application for cancers.

3,3-Diindolylmethane (DIM): a nutritional intervention and its impact on breast density in healthy BRCA carriers. A prospective clinical trial

Women who carry the BRCA mutation are at high lifetime risk of breast cancer, but there is no consensus regarding an effective and safe chemoprevention strategy. A large body of evidence suggests that 3,3-diindolylmethane (DIM), a dimer of indole-3-carbinol found in cruciferous vegetables, can potentially prevent carcinogenesis and tumor development. The primary aim of this prospective single-arm study was to investigate the effect of DIM supplementation on breast density, a recognized predictive factor of breast cancer risk. Participants were 23 healthy female BRCA carriers (median age 47 years; 78% postmenopausal) who were treated with oral DIM 100 mg × 1/day for 1 year. The amount of fibroglandular tissue (FGT) and background parenchymal enhancement (BPE) on magnetic resonance imaging (MRI) performed before and after the intervention was scored by two independent expert radiologists using the Breast Imaging and Reporting Data System. The results showed a decrease in the average score for FGT amount from 2.8 ± 0.8 at the onset to 2.65 ± 0.84 after 1 year (P = 0.031), with no significant change in BPE (P = 0.429). A group of DIM-untreated age- and menopausal-status-matched women from the BRCA clinic did not show a significant change in FGT amount (P = 0.33) or BPE (P = 0.814) in a parallel year. Mean estradiol level decreased from 159 to 102 pmol/l (P = 0.01), and mean testosterone level decreased from 0.42 to 0.31 pmol/l (P = 0.007). Side effects were grade 1. In conclusion, 1 year’s supplementation with DIM 100 mg × 1/day in BRCA carriers was associated with a significant decline in FGT amount on MRI. Larger randomized studies are warranted to corroborate these findings.

NR4A1 Ligands as Potent Inhibitors of Breast Cancer Cell and Tumor Growth

Nuclear receptor 4A1 (NR4A1, Nur77, TR3) is more highly expressed in breast and solid tumors compared to non-tumor tissues and is a pro-oncogenic factor in solid tumor-derived cancers. NR4A1 regulates cancer cell growth, survival, migration, and invasion, and bis-indole-derived compounds (CDIMs) that bind NR4A1 act as antagonists and inhibit tumor growth. Preliminary structure-binding studies identified 1,1-bis(3'-indolyl)-1-(3,5-disubstitutedphenyl)methane analogs as NR4A1 ligands with low K_D values; we further investigated the anticancer activity of the four most active analogs (K_D's ≤ 3.1 µM) in breast cancer cells and in athymic mouse xenograft models. The treatment of MDA-MB-231 and SKBR3 breast cancer cells with the 3-bromo-5-methoxy, 3-chloro-5-trifluoromethoxy, 3-chloro-5-trifluoromethyl, and 3-bromo-5-trifluoromethoxy phenyl-substituted analogs decreased cell growth and the expression of epidermal of growth factor receptor (EGFR), hepatocyte growth factor receptor (cMET), and PD-L1 as well as inhibited mTOR phosphorylation. In addition, all four compounds inhibited tumor growth in athymic nude mice bearing MDA-MB-231 cells (orthotopic) at a dose of 1 mg/kg/d, which was not accompanied by changes in body weight. These 3,5-disubstituted analogs were the most potent CDIM/NR4A1 ligands reported and are being further developed for clinical applications.

The Histone Methyltransferase Gene G9A Is Regulated by Nuclear Receptor 4A1 in Alveolar Rhabdomyosarcoma Cells

The histone methyltransferase G9A (EHMT2) gene catalyzes methylation of histone 3 lysine 9 (H3K9), and this gene silencing activity contributes to the tumor promoter-like activity of G9A in several tumor types including alveolar rhabdomyosarcoma (ARMS). Previous studies show the orphan nuclear receptor 4A1 (NR4A1, Nur77) is overexpressed in rhabdomyosarcoma and exhibits pro-oncogenic activity. In this study, we show that knockdown of NR4A1 in ARMS cells decreased expression of G9A mRNA and protein. Moreover, treatment of ARMS cells with several bis-indole-derived NR4A1 ligands (antagonists) including 1,1-bis(3'-indolyl)-1-(4-hydroxyphenyl)methane (CDIM8), 3,5-dimethyl (3,5-(CH₃)₂), and 3-bromo-5-methoxy (3-Br-5-OCH₃) analogs also decreased G9A expression. Furthermore, NR4A1 antagonists also decreased G9A expression in breast, lung, liver, and endometrial cancer cells confirming that G9A is an NR4A1-regulated gene in ARMS and other cancer cell lines. Mechanistic studies showed that the NR4A1/Sp1 complex interacted with the GC-rich 511 region of the G9A promoter to regulate G9A gene expression. Moreover, knockdown of NR4A1 or treatment with NR4A1 receptor antagonists decreased overall H3K9me2, H3K9me2 associated with the PTEN promoter, and PTEN-regulated phospho-Akt. In vivo studies showed that the NR4A1 antagonist (3-Br-5-OCH₃) inhibited tumor growth in athymic nude mice bearing Rh30 ARMS cells and confirmed that G9A was an NR4A1-regulated gene that can be targeted by NR4A1 receptor antagonists.

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.

3,3'-Diindolylmethane and its derivatives: nature-inspired strategies tackling drug resistant tumors by regulation of signal transduction, transcription factors and microRNAs

Indoles of cruciferous vegetables are promising anti-tumor agents. Studies with indole-3-carbinol and its dimeric product, 3,3'-diindolylmethane (DIM), suggest that these compounds have the ability to deregulate multiple cellular signaling pathways that are essential for tumor growth and spread. These natural compounds are also effective modulators of transcription factors and non-coding RNAs. These effects explain their ability to inhibit tumor spread and to overcome drug resistance. In this work, pertinent literature on the effects of DIM and its synthetic derivatives on resistant tumors and resistance mechanisms in tumors is highlighted.

NR4A1 Deletion in Marginal Zone B Cells Exacerbates Atherosclerosis in Mice-Brief Report

Supplemental Digital Content is available in the text.

NR4A orphan receptors have been well studied in vascular and myeloid cells where they play important roles in the regulation of inflammation in atherosclerosis. NR4A1 (nerve growth factor IB) is among the most highly induced transcription factors in B cells following BCR (B-cell receptor) stimulation. Given that B cells substantially contribute to the development of atherosclerosis, we examined whether NR4A1 regulates B-cell function during atherogenesis.

Reactivation of NR4A1 Restrains Chondrocyte Inflammation and Ameliorates Osteoarthritis in Rats

Osteoarthritis (OA) is the most prevalent joint disease and uncontrolled inflammation is now recognized to play vital roles in OA development. Targeting the endogenous counterpart of inflammation may develop new therapeutic approaches in resolving inflammation persistence and treating inflammatory disease including OA. The orphan nuclear receptor 4A1 (NR4A1) is a key negative regulator of inflammatory responses but its role in osteoarthritis remains unclear. In the present study, we found that the NR4A1 expression was elevated in human osteoarthritis cartilage and in vitro OA model, which could be blocked by NF-κB signal inhibitor JSH23. The overexpression of NR4A1 inhibited, whereas knockdown of NR4A1 enhanced IL-1β induced COX-2, iNOS, MMP3, MMP9 and MMP13 expression, and luciferase reporter activity of NF-κB response element. Though NR4A1 was upregulated in inflammatory stimulation and creates a negative feedback loop, persistent inflammatory stimulation inhibited NR4A1 expression and activation. The expression of NR4A1 declined rapidly after an initial peak in conditions of chronic IL-1β stimulation, which could be partially restored by HDACs inhibitor SAHA. The phosphorylation of NR4A1 was increased in human osteoarthritis cartilage, and p38 inhibitor SB203580, JNK inhibitor SP600125 and ERK inhibitor FR180204 could significantly inhibited IL-1β induced NR4A1 phosphorylation. Reactivation of NR4A1 by its agonist cytosporone B could inhibit IL-1β induced chondrocyte inflammation and expression of COX-2, iNOS, MMP3, MMP9, and MMP13. In rat OA model, intra-articular injection of cytosporone B protected cartilage damage and ameliorated osteoarthritis. Thus, our study demonstrated that the NR4A1 is a key endogenous inhibitor of chondrocyte inflammation, which was relatively inactivated under chronic inflammatory stimulation through HDACs mediated transcriptional suppression and MAKP dependent phosphorylation in osteoarthritis. NR4A1 agonist cytosporone B could reactivate and restore the inhibitory regulatory ability of NR4A1, prevent excessive inflammation, and ameliorates osteoarthritis.

Transcriptional analysis of deoxynivalenol-induced apoptosis of sow ovarian granulosa cell

Litter size is one of the most important economic traits in pig production. Recent studies identified that deoxynivalenol (DON), a widespread toxin in fodder, was associated with animal prolificacy. However, the underlying mechanisms have not yet been completely elucidated. Here, we used porcine ovary granulosa cells (pGCs) as a vector to establish DON concentration-time models and performed cell morphology and transcriptome analysis to identify and analyse the effects of DON on reproductive performance in swine. The results showed that DON can induce morphological changes and apoptosis of pGCs, while inhibiting cell proliferation. Moreover, these effects of DON on pGCs were dose-dependent. After treatment of pGCs with different concentrations of DON, the percentage of cells in S phase and G2/M phase increased. RNA-seq analyses revealed 5,937 differentially expressed genes, of which 1995 were down-regulated and 3,942 were up-regulated after DON treatment. KEGG enrichment analysis indicated important metabolic pathways such as IL-17 signalling pathway, eukaryotic ribosome synthesis pathway, RNA transport pathway and RNA degradation. Based on our results, we speculate that the effects of DON are related to the DNA damage process. Our study provides novel insights and a foundation to further understand the effect of DON on swine prolificacy.

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.

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.

Inhibition of NR4A1 Promotes ROS Accumulation and IL24-Dependent Growth Arrest in Rhabdomyosarcoma

Nuclear receptor 4A1 (NR4A1, Nur77) is overexpressed in rhabdomyosarcoma (RMS), and inactivation of NR4A1 (siNR4A1) or treatment with the NR4A1 antagonist 1,1-bis(3'-indoly)-1-(p-hydroxy-phenyl)methane (DIM-C-pPhOH) has antiproliferative and proapoptotic effects on RMS cells. However, the mechanism by which NR4A1 inhibition exerts these effects is poorly defined. Here, we report that NR4A1 silencing or inhibition resulted in accumulation of reactive oxygen species (ROS) and ROS-dependent induction of the tumor suppressor-like cytokine IL24 in RMS cells. Mechanistically, NR4A1 was found to regulate the expression of the proreductant genes thioredoxin domain-containing 5 (TXNDC5) and isocitrate dehydrogenase 1 (IDH1), which are downregulated in RMS cells following NR4A1 knockdown or inhibition. Silencing TXNDC5 and IDH1 also induced ROS accumulation and IL24 expression in RMS cells, suggesting that NR4A1 antagonists mediate their antiproliferative and apoptotic effects through modulation of proreductant gene expression. Finally, cotreatment with the antioxidant glutathione or IL24-blocking antibody reversed the effects of NR4A1 inhibition, demonstrating the importance of both ROS and IL24 in mediating the cellular responses. IMPLICATIONS: Overall, these data elucidate the mechanism by which NR4A1 inhibition functions to inhibit the proliferation, survival, and migration of RMS cells.