Activation of nerve growth factor-induced B alpha by methylene-substituted diindolylmethanes in bladder cancer cells induces apoptosis and inhibits tumor growth

Nur77-IRF1 axis inhibits esophageal squamous cell carcinoma growth and improves anti-PD-1 treatment efficacy

The nuclear receptor Nur77 plays paradoxical roles in numerous cancers. However, whether Nur77 inhibits esophageal squamous cell carcinoma (ESCC) growth and affects immunological responses against ESCC has not been determined. The functional role of Nur77 in ESCC was investigated in this study using human ESCC cell lines, quantitative real-time polymerase chain reaction (PCR), cell proliferation and colony formation assays, flow cytometry analysis, western blotting and animal models. The target gene controlled by Nur77 was verified using dual-luciferase reporter assays, chromatin immunoprecipitation analysis and functional rescue experiments. To examine the clinical importance of Nur77, 72 human primary ESCC tissues were subjected to immunohistochemistry. Taken together, these findings showed that, both in vitro and in vivo, Nur77 dramatically reduced ESCC cell growth and triggered apoptosis. Nur77 directly interacts with the interferon regulatory factor 1 (IRF1) promoter to inhibit its activity in ESCC. Pharmacological induction of Nur77 using cytosporone B (CsnB) inhibited ESCC cell proliferation and promoted apoptosis both in vitro and in vivo. Furthermore, CsnB increased CD8+ T-cell infiltration and cytotoxicity to inhibit the formation of ESCC tumors in an immunocompetent mouse model. In ESCC tissues, Nur77 expression was downregulated, and IRF1 expression was increased; moreover, their expression levels were negatively related. IRF1 and Nur77 were strongly correlated with overall survival. These findings suggested that Nur77 targets and regulates the IRF1/PD-L1 axis to serve as a tumor suppressor in ESCC. Graphical abstract of the regulatory mechanism of Nur77 overexpression downregulates IRF1 in the inhibition of ESCC progression and enhance anti-PD-1 therapy efficacy.

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.

MicroRNA-766-3p-mediated downregulation of HNF4G inhibits proliferation in colorectal cancer cells through the PI3K/AKT pathway

Nuclear receptors (NRs) are a class of transcription factors that play a pivotal role in carcinogenesis, but their function in colorectal cancer (CRC) remains unclear. Here, we investigate the role NRs play in CRC pathogenesis. We found that hepatocyte nuclear factor 4 gamma (HNF4G; NR2A2), hepatocyte nuclear factor 4α (HNF4A; NR2A1), and retinoid-related orphan receptor γ (RORC; NR1F3) were significantly upregulated in CRC tissues analyzed by GEPIA bioinformatics tool. The expression of HNF4G was examined in CRC samples and cell lines by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and immunohistochemistry. Increased expression of HNF4G was strongly associated with high tumor-node-metastasis stage and poor prognosis. Moreover, overexpression of HNF4G significantly promoted the proliferation of CRC cells in vitro. Next, we found that HNF4G promoted CRC proliferation via the PI3K/AKT pathway through targeting of GNG12 and PTK2. In addition, HNF4G was verified as a direct target of microRNA-766-3p (miR-766-3p). miR-766-3p inhibited the proliferation of CRC cells by targeting HNF4G in vitro and in vivo. Collectively, our study indicates that miR-766-3p reduces the proliferation of CRC cells by targeting HNF4G expression and thus inhibits the PI3K/AKT pathway. Therefore, development of therapies which target the miR-766-3p/HNF4G axis may aid in the treatment of CRC.

Identification of novel anti-inflammatory Nur77 modulators by virtual screening

Orphan nuclear receptor Nur77 is a unique member of the NR4A nuclear receptor subfamily, which is critical for cellular processes especially the inflammatory responses. Many efforts have been made to discover novel scaffold small molecules targeting Nur77. Herein, we evaluated the previously reported binding sites in crystal structures of Nur77 with small molecules, and then discovered compound 13 as a hit of Nur77 via virtual screening targeting the best-scored binding site. Based on the results of fluorescence titration assay, structure-activity relationship (SAR) analysis was summarized for compound 13 and its analogs. Among these analogs, compound 13e displayed the most potent binding affinity (0.54 ± 0.02 μM). The binding mode of compound 13e was predicted via molecule docking. Moreover, 13e exhibited significant anti-inflammation activity in TNF-α induced HepG2 cell model. Taken together, these results provided a new insight into the understanding the functions of specific binding sites on Nur77 for small molecular compounds, and the development of new scaffold Nur77 modulators.

Isoharringtonine Induces Apoptosis of Non-Small Cell Lung Cancer Cells in Tumorspheroids via the Intrinsic Pathway

Lung cancer is the major cause of cancer-associated death worldwide, and development of new therapeutic drugs is needed to improve treatment outcomes. Three-dimensional (3D) tumorspheroids offer many advantages over conventional two-dimensional cell cultures due to the similarities to in vivo tumors. We found that isoharringtonine, a natural product purified from Cephalotaxus koreana Nakai, significantly inhibited the growth of tumorspheroids with NCI-H460 cells in a dose-dependent manner and induced apoptotic cell death in our 3D cell culture system. On the other hand, A549 tumorspheroids displayed low sensitivity to isoharringtonine-induced apoptosis. Nuclear receptor subfamily 4 group A member 1 (NR4A1) is an orphan nuclear receptor known to regulate proliferation and apoptosis of cancer cells. We observed that knockdown of NR4A1 dramatically increased isoharringtonine-induced cancer cell death in A549 tumorspheroids by activating the intrinsic apoptosis pathway. Furthermore, treatment with combined isoharringtonine and iNR4A1 significantly inhibited multivulva formation in a Caenorhabditis elegans model and tumor development in a xenograft mouse model. Taken together, our data suggest that isoharringtonine is a potential natural product for treatment of non-small cell lung cancers, and inhibition of NR4A1 sensitizes cancer cells to anti-cancer treatment.

Metal-free oxidative coupling of arylmethylamines with indoles: a simple, environmentally benign approach for the synthesis of 3,3'-bis(indolyl)methanes

The efficient metal-free oxidative coupling of arylmethylamines with indoles has been developed using molecular oxygen as a green oxidant. The present reaction provides a novel route towards the synthesis of 3,3'-bis(indolyl)methanes in excellent yields of up to 95% via C-C and C-N bond formation. This attractive and environmentally friendly one-pot protocol is a simple procedure that features inexpensive acetic acid as the catalyst and molecular oxygen as the sole oxidant, and it supports a wide substrate scope with the good tolerance of functional groups.

Orphan nuclear receptor TR3/Nur77 biologics inhibit tumor growth by targeting angiogenesis and tumor cells

Pathological angiogenesis is a hallmark of many diseases. Previously, we reported that orphan nuclear receptor TR3/Nur77 was a critical mediator of angiogenesis to regulate tumor growth, sepsis and skin wound healing. However, none of the TR3/Nur77 targeting molecule has been in clinical trial so far. Here, we designed and generated novel TR3 shRNAs and two minigenes that had therapeutic potential for cancer treatment. In addition to extend our previous findings that tumor growth was inhibited in Nur77 knockout mice, we found that metastasis of colorectal tumor was completely inhibited in Nur77-/- mice. Tumor masses were increased ~70% and decreased ~40% in our transgenic EC-Nur77-S mice and EC-Nur77-DN mice, in which the full-length cDNA and the dominant negative mutant of TR3/Nur77 were inducibly and specifically expressed in mouse endothelium, respectively. TR3 was highly expressed in the vasculature and tumor cells of human melanoma and colorectal cancer tissues, but not in normal tissues. The novel TR3 shRNAs and two minigenes almost completely inhibited the proliferation and migration of HUVECs and human melanoma A375sm cells. Angiogenesis induced by adenoviruses expressing VEGF and melanoma growth in mice were greatly and significantly inhibited by systemically administration of adenoviruses expressing TR3 shRNAs and two minigenes. Tumor angiogenesis and the expressions of genes associated with angiogenesis were greatly regulated in tumor tissues treated with TR3 shRNAs and minigenes. Taken together, these studies demonstrated that TR3/Nur77 was a specific therapeutic target for several human cancers by targeting both tumor cells and tumor microenvironment. These TR3/Nur77 biologics inhibit angiogenesis and tumor growth, and have translational potential.

Expression Signatures of Cisplatin- and Trametinib-Treated Early-Stage Medaka Melanomas

Small aquarium fish models provide useful systems not only for a better understanding of the molecular basis of many human diseases, but also for first-line screening to identify new drug candidates. For testing new chemical substances, current strategies mostly rely on easy to perform and efficient embryonic screens. Cancer, however, is a disease that develops mainly during juvenile and adult stage. Long-term treatment and the challenge to monitor changes in tumor phenotype make testing of large chemical libraries in juvenile and adult animals cost prohibitive. We hypothesized that changes in the gene expression profile should occur early during anti-tumor treatment, and the disease-associated transcriptional change should provide a reliable readout that can be utilized to evaluate drug-induced effects. For the current study, we used a previously established medaka melanoma model. As proof of principle, we showed that exposure of melanoma developing fish to the drugs cisplatin or trametinib, known cancer therapies, for a period of seven days is sufficient to detect treatment-induced changes in gene expression. By examining whole body transcriptome responses we provide a novel route toward gene panels that recapitulate anti-tumor outcomes thus allowing a screening of thousands of drugs using a whole-body vertebrate model. Our results suggest that using disease-associated transcriptional change to screen therapeutic molecules in small fish model is viable and may be applied to pre-clinical research and development stages in new drug discovery.

Forced expression of NR4A3 induced the differentiation of human neuroblastoma-derived NB1 cells

Nuclear receptor subfamily 4, group A, member 3 (NR4A3) is a member of the NR4A subgroup of orphan nuclear receptors, implicated in the regulation of diverse biological functions, including metabolism, angiogenesis, inflammation, cell proliferation, and apoptosis. Although many reports have suggested the involvement of NR4A3 in the development and/or progression of tumors, its role varies among tumor types. Previously, we reported that DNA hypomethylation at NR4A3 exon 3 is associated with lower survival rate of neuroblastoma (NB) patients. As hypomethylation of this region results in reduced expression of NR4A3, our observations suggested that NR4A3 functions as a tumor suppressor in NB. However, the exact mechanisms underlying its functions have not been clarified. In the present study, we analyzed public databases and showed that reduced NR4A3 expression was associated with shorter survival period of NB in two out of three datasets. An in vitro study revealed that forced expression of NR4A3 in human NB-derived cell line NB1 resulted in elongation of neurites along with overexpression of GAP43, one of the differentiation markers of NB. On the other hand, siRNA-mediated knockdown of NR4A3 suppressed the expression level of GAP43. Interestingly, the forced expression of NR4A3 induced only the GAP43 but not the other molecules involved in NB cell differentiation, such as MYCN, TRKA, and PHOX2B. These results indicated that NR4A3 directly activates the expression of GAP43 and induces differentiated phenotypes of NB cells, without affecting the upstream signals regulating GAP43 expression and NB differentiation.

DLL4 and Jagged1 are angiogenic targets of orphan nuclear receptor TR3/Nur77

Pathological angiogenesis is a hallmark of many diseases. Previously, we reported that orphan nuclear receptor TR3/Nur77 was a critical mediator of angiogenesis to regulate tumor growth and skin wound healing via regulating the expression of the junctional proteins and integrins. However, the molecular mechanism, by which TR3/Nur77 regulates angiogenesis is not completely understood. Here, we were the first to find that TR3/Nur77, via its various amino acid fragments, regulated the expression of DLL4 and Jagged 1 in cultured endothelial cells. DLL4 and Jagged1 mediated TR3/Nur77-induced angiogenic responses and signaling molecules, but not the expression of integrins. Instead, integrins regulated the expressions of DLL4 and Jagged1 induced by TR3/Nur77. Further, DLL4, Jagged1 and integrins α1, α2, β3 and β5 were regulated by TR3/Nur77 in animal sepsis models of lipopolysaccharide (LPS)-induced endotoxemia, and cecal ligation and puncture (CLP), in which, TR3/Nur77 expression was significantly and tranciently increased. Mouse survival rates were greatly increased in Nur77 knockout mice bearing both CLP and LPS models. The results elucidated a novel axis of VEGF/histamine ➔ TR3/Nur77 ➔ integrins ➔ DLL4/Jagged1 in angiogenesis, and demonstrated that TR3/Nur77 was an excellent target for sepsis. These studies supported our previous findings that TR3/Nur77 was an excellent therapeutic target, and further our understanding of the molecular mechanism, by which TR3/Nur77 regulated angiogenesis.

Key Functions and Therapeutic Prospects of Nur77 in Inflammation Related Lung Diseases

The transcription factor Nur77 belongs to the NR4A subfamily of nuclear hormone receptors. It features an atypical ligand-binding site that precludes canonical ligand binding, leading to the designation orphan nuclear receptor. However, recent studies show that small molecules can interact with the receptor and modulate its activity by inducing a conformational change in the Nur77 ligand-binding site. Nur77 expression and activation are rapidly induced by various physiological and pathologic stimuli. Once expressed, Nur77 initiates transcriptional activity and modulates expression of its target genes. Both in vitro and in vivo evidence shows that Nur77 dampens the immune response to proinflammatory stimuli, such as tumor necrosis factor-α, Toll-like receptor ligands, and oxidized lipids, primarily by suppressing NF-κB signaling. Although studies focusing on Nur77's role in lung pathophysiology are currently incomplete, available data support its involvement in the pathogenesis of lung diseases, including asthma, acute lung injury, and pulmonary fibrosis, and thus suggest a therapeutic potential for Nur77 activation in these diseases. This review addresses the mechanisms that control Nur77 as well as its known roles in inflammation-related lung diseases. Evidence regarding the therapeutic potential of Nur77-targeting molecules will also be presented. Although current knowledge is limited, additional research followed by clinical studies may firmly identify Nur77 as a pharmacologic target for inflammation-related lung diseases.

Orphan nuclear receptor TR3/Nur77 differentially regulates the expression of integrins in angiogenesis

Pathological angiogenesis is a hallmark of many diseases. Previously, we reported that orphan nuclear receptor TR3/Nur77 (human homolog, Nur77, mouse homolog) is a critical mediator of angiogenesis to regulate tumor growth and skin wound healing via down-regulating the expression of the junctional proteins and integrin β4. However, the molecular mechanism, by which TR3/Nur77 regulated angiogenesis, was still not completely understood. In this report by analyzing the integrin expression profile in endothelial cells, we found that the TR3/Nur77 expression highly increased the expression of integrins α1 and β5, decreased the expression of integrins α2 and β3, but had some or no effect on the expression of integrins αv, α3, α4, α5, α6, β1 and β7. In the angiogenic responses mediated by TR3/Nur77, integrin α1 regulated endothelial cell proliferation and adhesion, but not migration. Integrin β5 shRNA inhibited cell migration, but increased proliferation and adhesion. Integrin α2 regulated all of the endothelial cell proliferation, migration and adhesion. However, integrin β3 did not play any role in endothelial cell proliferation, migration and adhesion. TR3/Nur77 regulated the transcription of integrins α1, α2, β3 and β5, via various amino acid fragments within its transactivation domain and DNA binding domain. Furthermore, TR3/Nur77 regulated the integrin α1 promoter activity by directly interacting with a novel DNA element within the integrin α1 promoter. These studies furthered our understanding of the molecular mechanism by which TR3/Nur77 regulated angiogenesis, and supported our previous finding that TR3/Nur77 was an excellent therapeutic target for pathological angiogenesis. Therefore, targeting TR3/Nur77 inhibits several signaling pathways that are activated by various angiogenic factors.

Compensatory Expression of Nur77 and Nurr1 Regulates NF-κB-Dependent Inflammatory Signaling in Astrocytes

Inflammatory activation of glial cells promotes loss of dopaminergic neurons in Parkinson disease. The transcription factor nuclear factor κB (NF-κB) regulates the expression of multiple neuroinflammatory cytokines and chemokines in activated glial cells that are damaging to neurons. Thus, inhibition of NF-κB signaling in glial cells could be a promising therapeutic strategy for the prevention of neuroinflammatory injury. Nuclear orphan receptors in the NR4A family, including NR4A1 (Nur77) and NR4A2 (Nurr1), can inhibit the inflammatory effects of NF-κB, but no approved drugs target these receptors. Therefore, we postulated that a recently developed NR4A receptor ligand, 1,1bis (3'indolyl) 1(pmethoxyphenyl) methane (C-DIM5), would suppress NF-κB-dependent inflammatory gene expression in astrocytes after treatment with 1-methyl-4-phenyl 1, 2, 3, 6-tetrahydropyridine (MPTP) and the inflammatory cytokines interferon γ and tumor necrosis factor α C-DIM5 increased expression of Nur77 mRNA and suppressed expression of multiple neuroinflammatory genes. C-DIM5 also inhibited the expression of NFκB-regulated inflammatory and apoptotic genes in quantitative polymerase chain reaction array studies and effected p65 binding to unique genes in chromatin immunoprecipitation next-generation sequencing experiments but did not prevent p65 translocation to the nucleus, suggesting a nuclear-specific mechanism. C-DIM5 prevented nuclear export of Nur77 in astrocytes induced by MPTP treatment and simultaneously recruited Nurr1 to the nucleus, consistent with known transrepressive properties of this receptor. Combined RNAi knockdown of Nur77 and Nurr1 inhibited the anti-inflammatory activity of C-DIM5, demonstrating that C-DIM5 requires these receptors to inhibit NF-κB. Collectively, these data demonstrate that NR4A1/Nur77 and NR4A2/Nurr1 dynamically regulated inflammatory gene expression in glia by modulating the transcriptional activity of NF-κB.

Characteristics of Nur77 and its ligands as potential anticancer compounds (Review)

Nuclear receptor subfamily 4 group A member 1 (NR4A1; also termed Nur77/TR3/NGFIB), a member of the nuclear receptor superfamily, is expressed as an early response gene to regulate the expression of multiple target genes. Nur77 has the typical structure of a nuclear receptor, including an N‑terminal domain, a DNA binding domain, and a ligand‑binding domain. The expression and localization of Nur77 are closely associated with its roles in cell proliferation and apoptosis. Nur77 was first identified as an orphan receptor, the endogenous ligand of which has not yet been identified; however, an increasing number of compounds targeting Nur77 have been reported to have beneficial effects in the treatment of cancer and other diseases. This review provides a brief overview of the identification, structure, expression and localization, transcriptional role and non‑genomic function of Nur77, and summarizes the ligands that have been shown to interact with Nur77, including cytosporone B, cisplatin, TMPA, PDNPA, CCE9, THPN, Z‑ligustilide, celastrol and bisindole methane compounds, which may potentially be used to treat cancer in humans.

New Drug Candidate Targeting the 4A1 Orphan Nuclear Receptor for Medullary Thyroid Cancer Therapy

Medullary thyroid cancer (MTC) is a relatively rare thyroid cancer responsible for a substantial fraction of thyroid cancer mortality. More effective therapeutic drugs with low toxicity for MTC are urgently needed. Orphan nuclear receptor 4A1 (NR4A1) plays a pivotal role in regulating the proliferation and apoptosis of a variety of tumor cells. Based on the NR4A1 protein structure, 2-imino-6-methoxy-2H-chromene-3-carbothioamide (IMCA) was identified from the Specs compounds database using the protein structure-guided virtual screening approach. Computationally-based molecular modeling studies suggested that IMCA has a high affinity for the ligand binding pocket of NR4A1. MTT [3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide] and apoptosis assays demonstrated that IMCA resulted in significant thyroid cancer cell death. Immunofluorescence assays showed that IMCA induced NR4A1 translocation from the nucleus to the cytoplasm in thyroid cancer cell lines, which may be involved in the cell apoptotic process. In this study, the quantitative polymerase chain reaction results showed that the IMCA-induced upregulation of sestrin1 and sestrin2 was dose-dependent in thyroid cancer cell lines. Western blot showed that IMCA increased phosphorylation of adenosine 5′-monophosphate-activated protein kinase (AMPK) and decreased phosphorylation of ribosomal protein S6 kinase (p70S6K), which is the key enzyme in the mammalian target of rapamycin (mTOR) pathway. The experimental results suggest that IMCA is a drug candidate for MTC therapy and may work by increasing the nuclear export of NR4A1 to the cytoplasm and the tumor protein 53 (p53)-sestrins-AMPK-mTOR signaling pathway.

Nuclear receptor NR4A1 is a tumor suppressor down-regulated in triple-negative breast cancer

The nuclear receptor (NR) superfamily contains hormone-inducible transcription factors that regulate many physiological and pathological processes through regulating gene expression. NR4A1 is an NR family member that still does not have an identified endogenous ligand, and its role in cancer is also currently unclear and controversial. In this study, we aimed to define the expression profiles and specific role of NR4A1 in the highly malignant triple-negative breast cancer (TNBC), which still lacks available targeted therapies. Bioinformatic analysis revealed a decrease of NR4A1 mRNA expression in human TNBC samples. Semi-quantitative analysis of NR4A1 protein expression by immunohistochemistry also identified a progressive NR4A1 reduction during the development of mouse basal-like mammary tumors and a significant NR4A1 downregulation in human TNBC samples. Furthermore, the expression levels of NR4A1 in human TNBC were negatively associated with tumor stage, lymph node metastasis and disease recurrence. Moreover, ectopic expression of NR4A1 in MDA-MB-231, a TNBC cell line with little endogenous NR4A1, inhibited the proliferation, viability, migration and invasion of these cells, and these inhibitions were associated with an attenuated JNK1–AP-1–cyclin D1 pathway. NR4A1 expression also largely suppressed the growth and metastasis of these cell-derived tumors in mice. These results demonstrate that NR4A1 is downregulated in TNBC and restoration of NR4A1 expression inhibits TNBC growth and metastasis, suggesting that NR4A1 is a tumor suppressor in TNBC.

Nur77 deficiency in mice accelerates tumor invasion and metastasis by facilitating TNFα secretion and lowering CSF-1R expression

Nur77, an orphan member of the nuclear receptor superfamily, plays critical roles in inflammation and immunity. However, the role of Nur77 in tumor microenvironment remains elusive. Results showed that deletion of Nur77 strikingly enhanced tumor metastasis compared to WT mice. Additionally, compared to the conditioned media derived from Nur77+/+ peritoneal macrophages (CM1), the conditioned media derived from Nur77-/- peritoneal macrophages (CM2) significantly promoted the EMT of cancer cells, and greatly enhanced the migratory and invasive abilities of cancer cells. Moreover, studies using TNF-α blocking antibody demonstrated that pro-inflammatory cytokine TNF-α was indispensable in supporting CM2-induced EMT to drive cancer cells migration and invasion. Furthermore, we found that Nur77 promoted the expression of CSF-1R, a novel downstream target gene of Nur77, and subsequently enhanced the migration of inflammatory cells. Notably, infiltration of inflammatory cells in the tumors of Nur77-/- mice was markedly abrogated compared to Nur77+/+ mice. Collectively, these results revealed that host Nur77 expression was pivotal in antitumor immune response, and in inhibiting tumor metastasis.

Synthesis and biological evaluation of 1-(2-(adamantane-1-yl)-1H-indol-5-yl)-3-substituted urea/thiourea derivatives as anticancer agents

A series of novel 2,5-disubstituted indole derivatives were synthesized. Compounds 7n, 7s, and 7w induced Nur77-expression in a time- and dose- dependent manner in H460 cells. Furthermore, Nur77 served as a critical mediator for the anticancer action of 7s.

Nurr1 promotes intestinal regeneration after ischemia/reperfusion injury by inhibiting the expression of p21 (Waf1/Cip1)

Intestinal ischemia/reperfusion (I/R) injury is a potentially life-threatening condition that can cause injuries to remote organs at the end stage. The damage caused by intestinal I/R insult induces changes in the barrier functions of the intestine, and the intrinsic mechanism of regeneration is often insufficient to restore barrier functions, as indicated by the high mortality rate of patients experiencing intestinal I/R injury. However, little is known about the mechanisms of intestinal regeneration after I/R injury. Here, we reported that nuclear receptor-related protein 1 (Nurr1), a nuclear orphan receptor, was induced during intestinal regeneration after I/R. Our findings showed that Nurr1 expression was consistent with the expression of Ki-67 and phosphorylated histone H3 (pH 3) in the intestine after I/R injury. Nurr1 knockdown led to G1-phase arrest mediated by p21 (Waf1/Cip1) activation, but Nurr1 overexpression reduced the proportion of IEC-6 cells in G1 phase as a result of p21 inhibition in a p53-independent manner. Using chromatin immunoprecipitation assays, luciferase assays, and mutational analysis, we demonstrated that Nurr1 directly inhibited the transcription of p21. These results define a novel Nurr1/p21 pathway that is involved in intestinal regeneration after I/R injury. These findings provide novel molecular insights into the pathogenesis of intestinal regeneration after I/R and possibly support the development of new potential therapies for intestinal I/R injury.

KEY MESSAGE

Nurr1 was induced during intestinal regeneration after I/R injury. Nurr1 promoted proliferation of intestinal epithelial cells after H/R injury. Nurr1 inhibited p21 expression in a p53-independent manner. Nurr1 inhibited p21 gene transcription by binding to p21 promoter directly.

Requirement of novel amino acid fragments of orphan nuclear receptor TR3/Nur77 for its functions in angiogenesis

Pathological angiogenesis is a hallmark of many diseases. We demonstrated that TR3/Nur77 is an excellent target for pro-angiogenesis and anti-angiogenesis therapies. Here, we report that TR3 transcriptionally regulates endothelial cell migration, permeability and the formation of actin stress fibers that is independent of RhoA GTPase. 1) Amino acid residues 344-GRR-346 and de-phosphorylation of amino acid residue serine 351 in the DNA binding domain, and 2) phosphorylation of amino acid residues in the 41-61 amino acid fragment of the transactivation domain, of TR3 are required for its induction of the formation of actin stress fibers, cell proliferation, migration and permeability. The 41-61 amino acid fragment contains one of the three potential protein interaction motifs in the transactivation domain of TR3, predicted by computational modeling and analysis. These studies further our understanding of the molecular mechanism, by which TR3 regulates angiogenesis, identify novel therapeutic targeted sites of TR3, and set the foundation for the development of high-throughput screening assays to identify compounds targeting TR3/Nur77 for pro-angiogenesis and anti-angiogenesis therapies.

Identification of a Binding Site for Unsaturated Fatty Acids in the Orphan Nuclear Receptor Nurr1

Nurr1/NR4A2 is an orphan nuclear receptor, and currently there are no known natural ligands that bind Nurr1. A recent metabolomics study identified unsaturated fatty acids, including arachidonic acid and docosahexaenoic acid (DHA), that interact with the ligand-binding domain (LBD) of a related orphan receptor, Nur77/NR4A1. However, the binding location and whether these ligands bind other NR4A receptors were not defined. Here, we show that unsaturated fatty acids also interact with the Nurr1 LBD, and solution NMR spectroscopy reveals the binding epitope of DHA at its putative ligand-binding pocket. Biochemical assays reveal that DHA-bound Nurr1 interacts with high affinity with a peptide derived from PIASγ, a protein that interacts with Nurr1 in cellular extracts, and DHA also affects cellular Nurr1 transactivation. This work is the first structural report of a natural ligand binding to a canonical NR4A ligand-binding pocket and indicates a natural ligand can bind and affect Nurr1 function.

Regulation of Nuclear Receptor Nur77 by miR-124

The nuclear receptor Nur77 is commonly upregulated in adult cancers and has oncogenic functions. Nur77 is an immediate-early response gene that acts as a transcription factor to promote proliferation and protect cells from apoptosis. Conversely, Nur77 can translocate to the mitochondria and induce apoptosis upon treatment with various cytotoxic agents. Because Nur77 is upregulated in cancer and may have a role in cancer progression, it is of interest to understand the mechanism controlling its expression. MicroRNAs (miRNAs) are responsible for inhibiting translation of their target genes by binding to the 3'UTR and either degrading the mRNA or preventing it from being translated into protein, thereby making these non-coding endogenous RNAs vital regulators of every cellular process. Several miRNAs have been predicted to target Nur77; however, strong evidence showing the regulation of Nur77 by any miRNA is lacking. In this study, we used a luciferase reporter assay containing the 3'UTR of Nur77 to screen 296 miRNAs and found that miR-124, which is the most abundant miRNA in the brain and has a role in promoting neuronal differentiation, caused the greatest reduction in luciferase activity. Interestingly, we discovered an inverse relationship in Daoy medulloblastoma cells and undifferentiated granule neuron precursors in which Nur77 is upregulated and miR-124 is downregulated. Exogenous expression to further elevate Nur77 levels in Daoy cells increased proliferation and viability, but knocking down Nur77 via siRNA resulted in the opposite phenotype. Importantly, exogenous expression of miR-124 reduced Nur77 expression, cell viability, proliferation, and tumor spheroid size in 3D culture. In all, we have discovered miR-124 to be downregulated in instances of medulloblastoma in which Nur77 is upregulated, resulting in a proliferative state that abets cancer progression. This study provides evidence for increasing miR-124 expression as a potential therapy for cancers with elevated levels of Nur77.

Steroid Hormone Receptor Signals as Prognosticators for Urothelial Tumor

There is a substantial amount of preclinical or clinical evidence suggesting that steroid hormone receptor-mediated signals play a critical role in urothelial tumorigenesis and tumor progression. These receptors include androgen receptor, estrogen receptors, glucocorticoid receptor, progesterone receptor, vitamin D receptor, retinoid receptors, peroxisome proliferator-activated receptors, and others including orphan receptors. In particular, studies using urothelial cancer tissue specimens have demonstrated that elevated or reduced expression of these receptors as well as alterations of their upstream or downstream pathways correlates with patient outcomes. This review summarizes and discusses available data suggesting that steroid hormone receptors and related signals serve as biomarkers for urothelial carcinoma and are able to predict tumor recurrence or progression.

Differential function and regulation of orphan nuclear receptor TR3 isoforms in endothelial cells

TR3 has been reported to be an excellent target for angiogenesis therapies. We reported three TR3 transcript variant messenger RNAs (mRNAs) are expressed in human umbilical vein endothelial cell (HUVEC) and are differentially regulated by vascular endothelial growth factor (VEGF). TR3 transcript variant 1 (TR3-TV1) and variant 2 (TR3-TV2) encoding the same TR3 isoform 1 protein (TR3-iso1) that was named TR3 has been extensively studied. However, the function of TR3 isoform 2 protein (TR3-iso2) encoded by TR3 transcript variant 3 (TR3-TV3) is still not known. Here, we clone and express the novel TR3-iso2 protein and find that expression of TR3-iso2, in contrast to TR3-iso1, inhibits endothelial cell proliferation induced by VEGF-A, histamine, and phorbol-12-myristate-13-acetate (PMA). The differential function of TR3-iso2 correlates with the down-regulation of cyclin D1. However, TR3-iso2 plays similar roles in endothelial cell migration and monolayer permeability as TR3-iso1. We further demonstrate that several intracellular signaling pathways are involved in histamine-induced TR3 transcript variants, including histamine receptor H1-mediated phospholipase C (PLC)/calcium /calcineurin/protein kinase C (PKC)/protein kinase D (PKD) pathway and ERK pathway, as well as histamine receptor H3-mediated PKC-ERK pathway. Further, expressions of TR3-TV1, TR3-TV2, and TR3-TV3 by VEGF and histamine are regulated by different promoters, but not by their mRNA stability.

Nuclear receptor 4A1 as a drug target for breast cancer chemotherapy

The orphan nuclear receptor 4A1 (NR4A1) is overexpressed in mammary tumors and breast cancer cell lines. The functional activity of this receptor was investigated by RNA interference with oligonucleotides targeted to NR4A1 (siNR4A1) and by treatment with NR4A1 antagonists. Breast cancer cells were treated with NR4A1 antagonists or transfected with siNR4A. Effects on cell proliferation and apoptosis as well as specific genes associated with these responses were investigated in MCF-7, SKBR3, and MDA-MB-231 cells, and in athymic nude mice bearing MDA-MB-231 cells as xenografts. Transfection of MCF-7, MDA-MB-231, and SKBR3 breast cancer cells with siNR4A1 decreased cell proliferation and induced apoptosis in these cell lines. Transfection of breast cancer cells with siNR4A1 also decreased expression of Sp-regulated genes including survivin, bcl-2, and epidermal growth factor receptor, inhibited mTOR signaling in MCF-7 cells that express WT p53, and activated oxidative and endoplasmic reticulum stress through downregulation of thioredoxin domain-containing 5 and isocitrate dehydrogenase 1. 1,1-Bis(3'-indolyl)-1-(p-substituted phenyl)methanes (C-DIMs) are NR4A1 ligands that act as NR4A1 antagonists. Treatment with selected analogs also inhibited breast cancer cell and tumor growth and induced apoptosis. The effects of C-DIM/NR4A1 antagonists were comparable to those observed after NR4A1 knockdown. Results with siNR4A1 or C-DIMs/NR4A1 antagonists in breast cancer cells and tumors were similar to those previously reported in pancreatic, lung, and colon cancer cells. They demonstrate the potential clinical applications of NR4A1 antagonists in patients with tumors that overexpress this receptor.

Orphan nuclear receptors as drug targets for the treatment of prostate and breast cancers

Nuclear receptors (NRs), a family of 48 transcriptional factors, have been studied intensively for their roles in cancer development and progression. The presence of distinctive ligand binding sites capable of interacting with small molecules has made NRs attractive targets for developing cancer therapeutics. In particular, a number of drugs have been developed over the years to target human androgen- and estrogen receptors for the treatment of prostate cancer and breast cancer. In contrast, orphan nuclear receptors (ONRs), which in many cases lack known biological functions or ligands, are still largely under investigated. This review is a summary on ONRs that have been implicated in prostate and breast cancers, specifically retinoic acid-receptor-related orphan receptors (RORs), liver X receptors (LXRs), chicken ovalbumin upstream promoter transcription factors (COUP-TFs), estrogen related receptors (ERRs), nerve growth factor 1B-like receptors, and ‘‘dosage-sensitive sex reversal, adrenal hypoplasia critical region, on chromosome X, gene 1’’ (DAX1). Discovery and development of small molecules that can bind at various functional sites on these ONRs will help determine their biological functions. In addition, these molecules have the potential to act as prototypes for future drug development. Ultimately, the therapeutic value of targeting the ONRs may go well beyond prostate and breast cancers.

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.

miR-34a inhibits proliferation and invasion of bladder cancer cells by targeting orphan nuclear receptor HNF4G

miR-34a is a member of the miR-34 family and acts as a tumor suppressor in bladder cancer. This study explored the regulative role of miR-34a on an orphan nuclear receptor HNF4G, which has a well-confirmed role in bladder tumor growth and invasion. qRT-PCR analysis was applied to measure miR-34a expression in two tumorigenic bladder cancer cell lines 5637 and T24 and one normal human urothelial cell line SV-HUC-1. Luciferase assay was performed to verify the putative binding between miR-34a and HNF4G. The influence of miR-34a-HNF4G axis on cell viability, colony formation, and invasion was assessed with loss- and gain-of-function analysis. This study observed that the miR-34a expressions in 5637 and T24 cells were significantly lower than in SV-HUC-1, while the muscle invasive cell sublines 5637-M and T24-M had even lower miR-34a expression than in the nonmuscle invasive sublines. HNF4G has a 3'-UTR binding site with miR-34a and is a direct downstream target of miR-34a. miR-34a can directly downregulate the expression of HNF4G and thus inhibit tumor cell viability, colony formation, and invasion. Therefore, miR-34a-HNF4G axis is an important pathway modulating cell viability, proliferation, and invasion of bladder cancer cells.

Chiral Brønsted acid-catalyzed Friedel–Crafts alkylation of electron-rich arenes with in situ-generated ortho-quinone methides: highly enantioselective synthesis of diarylindolylmethanes and triarylmethanes

Hydrogen-bonded, in situ-generated ortho-quinone methides undergo highly enantioselective Friedel–Crafts reactions with indoles and naphthols under mild reaction conditions.

Insights into Orphan Nuclear Receptors as Prognostic Markers and Novel Therapeutic Targets for Breast Cancer

There is emerging evidence asserting the importance of orphan nuclear receptors (ONRs) in cancer initiation and progression. In breast cancer, there is a lot unknown about ONRs in terms of their expression profile and their transcriptional targets in the various stages of tumor progression. With the classification of breast tumors into distinct molecular subtypes, we assess ONR expression in the different breast cancer subtypes and with patient outcomes. Complementing this, we review evidence implicating ONR-dependent molecular pathways in breast cancer progression to identify candidate ONRs as potential prognostic markers and/or as therapeutic targets.

The interplay of NR4A receptors and the oncogene-tumor suppressor networks in cancer

Nuclear receptor (NR) subfamily 4 group A (NR4A) is a family of three highly homologous orphan nuclear receptors that have multiple physiological and pathological roles, including some in cancer. These NRs are reportedly dysregulated in multiple cancer types, with many studies demonstrating pro-oncogenic roles for NR4A1 (Nur77) and NR4A2 (Nurr1). Additionally, NR4A1 and NR4A3 (Nor-1) are described as tumor suppressors in leukemia. The dysregulation and functions of the NR4A members are due to many factors, including transcriptional regulation, protein-protein interactions, and post-translational modifications. These various levels of intracellular regulation result from the signaling cross-talk of the NR4A members with various signaling pathways, many of which are relevant to cancer and likely explain the family members' functions in oncogenesis and tumor suppression. In this review, we discuss the multiple functions of the NR4A receptors in cancer and summarize a growing body of scientific literature that describes the interconnectedness of the NR4A receptors with various oncogene and tumor suppressor pathways.

Diindolylmethane analogs bind NR4A1 and are NR4A1 antagonists in colon cancer cells

1,1-Bis(3'-indolyl)-1-(p-substituted phenyl)methane (C-DIM) compounds exhibit antineoplastic activity in multiple cancer cell lines and the p-hydroxyphenyl analog (DIM-C-pPhOH) inactivates nuclear receptor 4A1 (NR4A1) in lung and pancreatic cancer cell lines. Using a series of 14 different p-substituted phenyl C-DIMs, we show that several compounds including DIM-C-pPhOH directly interacted with the ligand binding domain of NR4A1. Computational-based molecular modeling studies showed high-affinity interactions of DIM-C-pPhOH and related compounds within the ligand binding pocket of NR4A1, and these same compounds decreased NR4A1-dependent transactivation in colon cancer cells transfected with a construct containing 3 tandem Nur77 binding response elements linked to a luciferase reporter gene. Moreover, we also show that knockdown of NR4A1 by RNA interference (small interfering NR4A1) or treatment with DIM-C-pPhOH and related compounds decreased colon cancer cell growth, induced apoptosis, decreased expression of survivin and other Sp-regulated genes, and inhibited mammalian target of rapamycin signaling. Thus, C-DIMs such as DIM-C-pPhOH directly bind NR4A1 and are NR4A1 antagonists in colon cancer cells, and their antineoplastic activity is due, in part, to their interactions with nuclear NR4A1.

Orphan nuclear receptor Nur77 promotes colorectal cancer invasion and metastasis by regulating MMP-9 and E-cadherin

Nur77, an orphan member of the nuclear receptor superfamily, has been implicated in tumorigenesis. However, its contributions to colorectal cancer (CRC) invasion and metastasis are largely under characterized. Here, we present the first evidence that the invasion and metastasis of CRC is regulated by Nur77. High expression of Nur77 was observed in clinical CRC tissues, and this elevated expression was significantly associated with advanced tumor, lymph nodes, distant metastasis stage (P = 0.003), lymph node metastasis (P = 0.001) and poor survival (P = 0.03). Overexpression of Nur77 in CRC cells enhanced cell invasion in vitro, whereas knockdown of Nur77 diminished cell invasion and metastasis both in vitro and in vivo. In studying the possible mechanism by which overexpression of Nur77 contributes to CRC invasion and metastasis, we observed that the nuclear protein Nur77 promoted the expression of matrix metalloproteinase (MMP)-9, a novel downstream target of Nur77, and subsequently decreased the expression of E-cadherin. Examination of clinical samples further showed that Nur77 expression is positively correlated with MMP-9, whereas negatively correlated with E-cadherin. Interestingly, Nur77-mediated CRC invasion via MMP-9 and E-cadherin could be mimicked by some metastasis-inducible factors including hypoxia and prostaglandin E2. Collectively, our study demonstrated that Nur77 could promote the invasion and metastasis of CRC cells through regulation of MMP-9/E-cadherin signaling. These observations provide a possible new strategy for potentially treating or preventing the metastasis of CRC through targeting of Nur77.

Nur77 inhibits androgen-induced bladder cancer growth

Currently, bladder cancer ranks as the second most common genitourinary malignancy which is exacting significant morbidity and mortality worldwide. Although there are abundant epidemiological and basic studies which strongly suggest the role of androgen hormone in bladder cancer, the underlying mechanism is not fully understood. In the current study, we sought to identify a new competitive inhibitor for androgen receptor in bladder cancer cells. Our results showed that Nur77 hyperexpression inhibits UM-UC-3 cell growth and cell cycle progression while Nur77 knockdown exerts the opposite effect. In our cell culture model, we also demonstrated that Nur77 competitively inhibits androgen-dependent transcription activity and more specifically, Nur77 competes with androgen receptor for binding to src-1, a well-known coactivator for steroids. More importantly, we also showed that a small molecule agonist for Nur77, Cytosporone B, significantly inhibits androgen-dependent bladder cancer cell growth in two different cell lines. These data provide a good proof-of-principle that Nur77 signaling machinery could be a new target for growth control of androgen-dependent bladder cancer cells.

Enantioselective synthesis of triarylmethanes by chiral imidodiphosphoric acids catalyzed Friedel-Crafts reactions

The first enantioselective synthesis of pyrrolyl-substituted triarylmethanes has been accomplished using a novel imidodiphosphoric acid catalyst, which is derived from two (R)-BINOL frameworks with different 3,3'-substituents. This strategy was also expanded to the synthesis of bis(indolyl)-substituted triarylmethanes with high enantioselectivities, which could only be obtained with moderate ee values in previous reports. These two efficient Friedel-Crafts alkylation processes feature low catalyst loading, broad functional group compatibilities, and the potential to provide practical pathways for the synthesis of enantioenriched bioactive triarylmethanes.

Dual roles of orphan nuclear receptor TR3/Nur77/NGFI-B in mediating cell survival and apoptosis

As a transcriptional factor, Nur77 has sparked interests across different research fields in recent years. A number of studies have demonstrated the functional complexity of Nur77 in mediating survival/apoptosis in a variety of cells, including tumor cells. Conflicting observations also exist in clinical reports, in that TR3 behaves like an oncogene in tumors of the GI tract, lung, and breast, that is negatively associated with tumor stage and patient prognosis; while functions as a tumor suppressor gene in malignancies of the hematological and lymphatic system, skin, and ovary whose malfunction results in carcinogenesis. This chapter summarizes the apparent opposing effects of Nur77 on cells and explicates the mechanisms that determine the functional preference of Nur77. We conclude that in addition to cell type and agent context, other factors such as cellular localization, signaling pathway, and posttranslational modification also determine the final effects of Nur77 on cells.

Minireview: role of orphan nuclear receptors in cancer and potential as drug targets

The nuclear orphan receptors for which endogenous ligands have not been identified include nuclear receptor (NR)0B1 (adrenal hypoplasia congenita critical region on chromosome X gene), NR0B2 (small heterodimer partner), NR1D1/2 (Rev-Erbα/β), NR2C1 (testicular receptor 2), NR2C2 (testicular receptor 4), NR2E1 (tailless), NR2E3 (photoreceptor-specific NR [PNR]), NR2F1 chicken ovalbumin upstream promoter transcription factor 1 (COUP-TFI), NR2F2 (COUP-TFII), NR2F6 (v-erbA-related protein), NR4A1 (Nur77), NR4A2 (Nurr1), NR4A3 (Nor1), and NR6A1 (GCNF). These receptors play essential roles in development, cellular homeostasis, and disease including cancer where over- or underexpression of some receptors has prognostic significance for patient survival. Results of receptor knockdown or overexpression in vivo and in cancer cell lines demonstrate that orphan receptors exhibit tumor-specific pro-oncogenic or tumor suppressor-like activity. For example, COUP-TFII expression is both a positive (ovarian) and negative (prostate and breast) prognostic factor for cancer patients; in contrast, the prognostic activity of adrenal hypoplasia congenita critical region on chromosome X gene for the same tumors is the inverse of COUP-TFII. Functional studies show that Nur77 is tumor suppressor like in acute leukemia, whereas silencing Nur77 in pancreatic, colon, lung, lymphoma, melanoma, cervical, ovarian, gastric, and some breast cancer cell lines induces one or more of several responses including growth inhibition and decreased survival, migration, and invasion. Although endogenous ligands for the orphan receptors have not been identified, there is increasing evidence that different structural classes of compounds activate, inactivate, and directly bind several orphan receptors. Thus, the screening and development of selective orphan receptor modulators will have important clinical applications as novel mechanism-based agents for treating cancer patients overexpressing one or more orphan receptors and also for combined drug therapies.

Orphan nuclear receptor HNF4G promotes bladder cancer growth and invasion through the regulation of the hyaluronan synthase 2 gene

Nuclear receptors (NRs) are a class of transcription factors that are closely involved in the progression of certain types of cancer. We aimed to study the relation between bladder cancer and NRs, with special focus on orphan NRs whose ligands and functions have not been identified. First, we examined the expression levels of 22 genes encoding orphan NRs in clinical bladder cancer and found that hepatocyte nuclear factor 4γ (HNF4G; NR2A2) and NR2F6 were the genes that were upregulated most frequently in cancer tissues compared with their paired normal tissues. Knockdown and overexpression of each of these orphan NRs suppressed and stimulated the growth of bladder cancer cells in vitro, respectively. HNF4G also promoted tumor growth in bladder cancer xenograft models in vivo. Furthermore, HNF4G was both necessary and sufficient for the invasion of bladder cancer cells in vitro. Moreover, using microarray analyses, we identified hyaluronan synthase 2 (HAS2) as one of the genes induced by HNF4G in bladder cancer cells. Transcription was activated by HNF4G in reporter assays using the promoter/enhancer region of the HAS2 gene. The endogenous expression of the HAS2 gene was suppressed by knockdown of HNF4G. In turn, knockdown of HAS2 inhibited the growth and invasion of bladder cancer cells. Taken together, our data suggest that some orphan NRs are involved in bladder cancer progression and that, among them, HNF4G promotes the growth and invasion of bladder cancer, at least in part, via the regulation of the HAS2 gene.

1,1-Bis (3'-indolyl)-1-(p-substitutedphenyl)methane compounds inhibit lung cancer cell and tumor growth in a metastasis model

1,1-Bis(3-indolyl)-1-(p-substitutedphenyl)methane (C-DIM) compounds exhibit remarkable antitumor activity with low toxicity in various cancer cells including lung tumors. Two C-DIM analogs, DIM-C-pPhOCH3 (C-DIM-5) and DIM-C-pPhOH (C-DIM-8) while acting differentially on the orphan nuclear receptor, TR3/Nur77 inhibited cell cycle progression from G0/G1 to S-phase and induced apoptosis in A549 cells. Combinations of docetaxel (doc) with C-DIM-5 or C-DIM-8 showed synergistic anticancer activity in vitro and these results were consistent with their enhanced antitumor activities invivo. Respirable aqueous formulations of C-DIM-5 (mass median aerodynamic diameter of 1.92±0.22μm and geometric standard deviation of 2.31±0.12) and C-DIM-8 (mass median aerodynamic diameter of 1.84±0.31μm and geometric standard deviation of 2.11±0.15) were successfully delivered by inhalation to athymic nude mice bearing A549 cells as metastatic tumors. This resulted in significant (p<0.05) lung tumor regression and an overall reduction in tumor burden. Analysis of lung tumors from mice treated with inhalational formulations of C-DIM-5 and C-DIM-8 showed decreased mRNA and protein expression of mediators of tumor initiation, metastasis, and angiogenesis including MMP2, MMP9, c-Myc, β-catenin, c-Met, c-Myc, and EGFR. Microvessel density assessment of lung tissue sections showed significant reduction (p<0.05) in angiogenesis and metastasis as evidenced by decreased distribution of immunohistochemical staining of VEGF, and CD31. Our studies demonstrate both C-DIM-5 and C-DIM-8 have similar anticancer profiles in treating metastatic lung cancer and possibly work as TR3 inactivators.

Molecular pathways: the role of NR4A orphan nuclear receptors in cancer

Nuclear receptors are of integral importance in carcinogenesis. Manipulation of classic ligand-activated nuclear receptors, such as estrogen receptor blockade in breast cancer, is an important established cancer therapy. Orphan nuclear receptors, such as nuclear family 4 subgroup A (NR4A) receptors, have no known natural ligand(s). These elusive receptors are increasingly recognized as molecular switches in cell survival and a molecular link between inflammation and cancer. NR4A receptors act as transcription factors, altering expression of downstream genes in apoptosis (Fas-ligand, TRAIL), proliferation, DNA repair, metabolism, cell migration, inflammation (interleukin-8), and angiogenesis (VEGF). NR4A receptors are modulated by multiple cell-signaling pathways, including protein kinase A/CREB, NF-κB, phosphoinositide 3-kinase/AKT, c-jun-NH(2)-kinase, Wnt, and mitogen-activated protein kinase pathways. NR4A receptor effects are context and tissue specific, influenced by their levels of expression, posttranslational modification, and interaction with other transcription factors (RXR, PPAR-Υ). The subcellular location of NR4A "nuclear receptors" is also important functionally; novel roles have been described in the cytoplasm where NR4A proteins act both indirectly and directly on the mitochondria to promote apoptosis via Bcl-2. NR4A receptors are implicated in a wide variety of malignancies, including breast, lung, colon, bladder, and prostate cancer; glioblastoma multiforme; sarcoma; and acute and/or chronic myeloid leukemia. NR4A receptors modulate response to conventional chemotherapy and represent an exciting frontier for chemotherapeutic intervention, as novel agents targeting NR4A receptors have now been developed. This review provides a concise clinical overview of current knowledge of NR4A signaling in cancer and the potential for therapeutic manipulation.

Nur77: a potential therapeutic target in cancer

INTRODUCTION

The orphan nuclear receptor Nur77 (also known as NR4A1, NGFIB, TR3, TIS1, NAK-1, or N10) is a unique transcription factor encoded by an immediate early gene. Nur77 signaling is deregulated in many cancers and constitutes an important molecule for drug targeting.

AREAS COVERED

Nur77 as a versatile transcription factor that displays distinct dual roles in cell proliferation and apoptosis. In addition, several recent insights into Nur77's non-genomic signaling through its physical interactions with various signaling proteins and its phosphorylation-dependent regulation will be highlighted. The possible mechanisms by which Nur77 supports carcinogenesis and specific examples in different human cancers will be summarized. Different approaches to target Nur77 using mimetics, natural products, and synthetic compounds are also described.

EXPERT OPINION

These latest findings shed light on the novel roles of Nur77 as an exploitable target for new cancer therapeutics. Further work which focuses on a more complete understanding of the Nur77 interactome as well as how the different networks of Nur77 functional interactions are orchestrated in a stimulus or context-specific way will aid the development of more selective, non-toxic approaches for targeting Nur77 in future.

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

NR4A2 (Nurr1) is an orphan nuclear receptor with no known endogenous ligands and is highly expressed in many cancer cell lines including Panc1 and Panc28 pancreatic cancer cells. Structure-dependent activation of NR4A2 by a series of 1,1-bis(3'-indolyl)-1-(aromatic)methane (C-DIM) analogs was determined in pancreatic cancer cells transfected with yeast GAL4-Nurr1 chimeras and a UASx5-luc reporter gene or constructs containing response elements that bind NR4A2. Among 23 different structural analogs, phenyl groups containing p-substituted trifluoromethyl, t-butyl, cyano, bromo, iodo and trifluoromethoxy groups were the most active compounds in transactivation assay. The p-bromophenyl analog (DIM-C-pPhBr) was used as a model for structure-activity studies among a series of ortho-, meta- and para-bromophenyl isomers and the corresponding indole 2- and N-methyl analogs. Results show that NR4A2 activation was maximal with the p-bromophenyl analog and methylation of the indole NH group abrogated activity. Moreover, using GAL4-Nurr1 (full length) or GAL-Nurr1-A/B and GAL4-Nurr1-(C-F) chimeras expressing N- and C-terminal domains of Nurr1, respectively, DIM-C-pPhBr activated all three constructs and these responses were differentially affected by kinase inhibitors. DIM-C-pPhBr also modulated expression of several Nurr1-regulated genes in pancreatic cancer cells including vasoactive intestinal peptide (VIP), and the immunohistochemical and western blot analyses indicated that DIM-C-pPhBr activates nuclear NR4A2.

Serine protease PRSS23 is upregulated by estrogen receptor α and associated with proliferation of breast cancer cells

Serine protease PRSS23 is a newly discovered protein that has been associated with tumor progression in various types of cancers. Interestingly, PRSS23 is coexpressed with estrogen receptor α (ERα), which is a prominent biomarker and therapeutic target for human breast cancer. Estrogen signaling through ERα is also known to affect cell proliferation, apoptosis, and survival, which promotes tumorigenesis by regulating the production of numerous downstream effector proteins.In the present study, we aimed to clarify the correlation between and functional implication of ERα and PRSS23 in breast cancer. Analysis of published breast cancer microarray datasets revealed that the gene expression correlation between ERα and PRSS23 is highly significant among all ERα-associated proteases in breast cancer. We then assessed PRSS23 expression in 56 primary breast cancer biopsies and 8 cancer cell lines. The results further confirmed the coexpression of PRSS23 and ERα and provided clinicopathological significance. In vitro assays in MCF-7 breast cancer cells demonstrated that PRSS23 expression is induced by 17β-estradiol-activated ERα through an interaction with an upstream promoter region of PRSS23 gene. In addition, PRSS23 knockdown may suppress estrogen-driven cell proliferation of MCF-7 cells.Our findings imply that PRSS23 might be a critical component of estrogen-mediated cell proliferation of ERα-positive breast cancer cells. In conclusion, the present study highlights the potential for PRSS23 to be a novel therapeutic target in breast cancer research.