Involvement of TR3/Nur77 translocation to the endoplasmic reticulum in ER stress-induced apoptosis

Design, synthesis, and biological evaluation of N1-(2-(adamantan-1-yl)-1H-indol-5-yl)-N2-(substituent)-1,2-dicarboxamides as anticancer agents targeting Nur77-mediated endoplasmic reticulum stress

Targeting endoplasmic reticulum (ER) stress-induced apoptosis has attracted considerable research interest in anti-cancer drug development. Nur77 is a potential therapeutic target in many cancers and several Nur77 modulators have recently been identified as effective anticancer agents by activating ER stress. As an ongoing work, this study reports a new series of novel N1-(2-(adamantan-1-yl)-1H-indol-5-yl)-N2-(substituent)-1,2-dicarboxamides as potent Nur77 modulators that cause ER stress-induced apoptosis. Among this new series, most compounds show improved cytotoxicity against liver cancer (HepG2 and Huh7) and breast cancer (MCF-7 and MDA-MB-231) cell lines. The representative analog 15h dramatically induces Nur77 expression and cell apoptosis, showing excellent growth inhibition of HepG2 and MCF-7 cells (IC50 < 5.0 μM). Mechanistically, 15h binds (KD = 0.477 μM) and activates Nur77-mediated ER stress through the PERK-ATF4 and IRE1 signaling pathways, thereby inducing cell apoptosis. In vivo, 15h treatment strongly suppresses HepG2 xenograft tumor growth (tumor shrink by 54.06 %). In summary, we synthesize a series of novel indole derivatives, among which 15h has significantly improved pharmacological activity against various cancer cells. We further identify 15h as a novel ligand of Nur77, which may serve a therapeutic lead for developing new cancer therapy.

Discovery of a novel exceptionally potent and orally active Nur77 ligand NB1 with a distinct binding mode for cancer therapy

The orphan nuclear receptor Nur77 is emerging as an attractive target for cancer therapy, and activating Nur77's non-genotypic anticancer function has demonstrated strong therapeutic potential. However, few Nur77 site B ligands have been identified as excellent anticancer compounds. There are no co-crystal structures of effective anticancer agents at Nur77 site B, which greatly limits the development of novel Nur77 site B ligands. Moreover, the lack of pharmaceutical ligands restricts Nur77's therapeutic proof of concept. Herein, we developed a first-in-class Nur77 site B ligand (NB1) that significantly inhibited cancer cells by mediating the Nur77/Bcl-2-related apoptotic effect at mitochondria. The X-ray crystallography suggests that NB1 is bound to the Nur77 site B with a distinct binding mode. Importantly, NB1 showed favorable pharmacokinetic profiles and safety, as evidenced by its good oral bioavailability in rats and lack of mortality, bodyweight loss, and pathological damage at the 512.0 mg/kg dose in mice. Furthermore, oral administration of NB1 demonstrated remarkable in vivo anticancer efficacy in an MDA-MB-231 xenograft model. Together, our work discovers NB1 as a new generation Nur77 ligand that activates the Nur77/Bcl-2 apoptotic pathway with a safe and effective cancer therapeutic potency.

Endoplasmic reticulum stress as a target for retinoids in cancer treatment

Retinoids, natural and synthetic derivatives of vitamin A, have various regulatory activities including controlling cellular proliferation, differentiation, and death. Furthermore, they have been used to treat specific cancers with satisfying results. Nevertheless, retinoids have yet to be converted into effective systemic therapies for the majority of tumor types. Regulation of unfolded protein response signaling, and persistent activation of endoplasmic reticulum stress (ER-stress) are promising treatment methods for cancer. The present article reviews the current understanding of how vitamin A and its derivatives may aid to cause ER-stress-activated apoptosis, as well as therapeutic options for exploiting ER-stress for achieving beneficial goal. The therapeutic use of some retinoids discussed in this article was related to decreased disease recurrence and improved therapeutic outcomes via ER-stress activation and promotion, indicating that retinoids may play an important role in cancer treatment and prevention. More research is needed to expand the use of vitamin A derivatives in cancer therapy, either alone or in combination with unfolded protein response inducers.

Nur77 increases mitophagy and decreases aggregation of α-synuclein by modulating the p-c-Abl/p-PHB2 Y121 in α-synuclein PFF SH-SY5Y cells and mice

Parkinson's disease (PD) is characterized by the progressive death of dopamine (DA) neurons and the pathological accumulation of α-synuclein (α-syn) fibrils. In our previous study, simulated PHB2 phosphorylation was utilized to clarify the regulatory role of c-Abl in PHB2-mediated mitophagy in PD models. In this investigation, we employed an independently patented PHB2Y121 phosphorylated antibody in the PD model to further verify that the c-Abl inhibitor STI571 can impede PHB2Y121 phosphorylation, decrease the formation of α-Syn polymers, and improve autophagic levels. The specific involvement of Nur77 in PD pathology has remained elusive. We also investigate the contribution of Nur77, a nuclear transcription factor, to α-syn and mitophagy in PD. Our findings demonstrate that under α-syn, Nur77 translocates from the cytoplasm to the mitochondria, improving PHB-mediated mitophagy by regulating c-Abl phosphorylation. Moreover, Nur77 overexpression alleviates the expression level of pS129-α-syn and the loss of DA neurons in α-syn PFF mice, potentially associated with the p-c-Abl/p-PHB2 Y121 axis. This study provides initial in vivo and in vitro evidence that Nur77 protects PD DA neurons by modulating the p-c-Abl/p-PHB2 Y121 axis, and STI571 holds promise as a treatment for PD.

PHLDA1 is a P53 target gene involved in P53-mediated cell apoptosis

Pleckstrin homeolike domain, family A, member 1 (PHLDA1) is a multifunctional protein that plays diverse roles in A variety of biological processes, including cell death, and hence its altered expression has been found in different types of cancer. Although studies have shown a regulatory relationship between p53 and PHLDA1, the molecular mechanism is still unclear. Especially, the role of PHLDA1 in the process of apoptosis is still controversial. In this study, we found that the expression of PHLDA1 in human cervical cancer cell lines was correlated with the up-expression of p53 after treatment with apoptosis-inducing factors. Subsequently, the binding site and the binding effect of p53 on the promoter region of PHLDA1 were verified by our bioinformatics data analysis and luciferase reporter assay. Indeed, we used CRISPR-Cas9 to knockout the p53 gene in HeLa cells and further confirmed that p53 can bind to the promoter region of PHLDA1 gene, and then directly regulate the expression of PHLDA1 by recruiting P300 and CBP to change the acetylation and methylation levels in the promoter region. Finally, a series of gain-of-function experiments further confirmed that p53 re-expression in HeLap53-/- cell can up-regulate the reduction of PHLDA1 caused by p53 knockout, and affect cell apoptosis and proliferation. Our study is the first to explore the regulatory mechanism of p53 on PHLDA1 by using the p53 gene knockout cell model, which further proves that PHLDA1 is a target-gene in p53-mediated apoptosis, and reveals the important role of PHLDA1 in cell fate determination.

Discovery of 5-(Pyrimidin-2-ylamino)-1H-indole-2-carboxamide Derivatives as Nur77 Modulators with Selective and Potent Activity Against Triple-Negative Breast Cancer

The orphan nuclear receptor Nur77 has been validated as a potential drug target for treating breast cancer. Therefore, focusing on the SAR study of the lead 8b (KDSPR(Nur77) = 354 nM), we found the active compound ja which exhibited improved Nur77-binding capability (KDSPR(Nur77) = 91 nM) and excellent antiproliferative activities against breast cancer cell lines. Interestingly, ja acted as a potent and selective Nur77 antagonist, displaying good potency against triple-negative breast cancer (TNBC) cell lines but did not inhibit human normal breast cancer cell line MCF-10A (SI > 20). Exceptionally, ja Nur77-dependently caused mitochondria dysfunction and induced the caspase-dependent apoptosis by mediating the TP53 phosphorylation pathway. Moreover, ja significantly suppressed MDA-MB-231 xenograft tumor growth but had no apparent side effects in mice and zebrafish. Overall, ja demonstrated to be the first Nur77 modulator mediating the TP53 phosphorylation pathway that has the potential as a novel anticancer agent for TNBC.

Orphan Nuclear Receptor Nur77 Mediates the Lethal Endoplasmic Reticulum Stress and Therapeutic Efficacy of Cryptomeridiol in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) commonly possesses chronical elevation of IRE1α-ASK1 signaling. Orphan nuclear receptor Nur77, a promising therapeutic target in various cancer types, is frequently silenced in HCC. In this study, we show that cryptomeridiol (Bkh126), a naturally occurring sesquiterpenoid derivative isolated from traditional Chinese medicine Magnolia officinalis, has therapeutic efficacy in HCC by aggravating the pre-activated UPR and activating the silenced Nur77. Mechanistically, Nur77 is induced to sense IRE1α-ASK1-JNK signaling and translocate to the mitochondria, which leads to the loss of mitochondrial membrane potential (Δψm). The Bkh126-induced aggravation of ER stress and mitochondrial dysfunction result in increased cytotoxic product of reactive oxygen species (ROS). The in vivo anti-HCC activity of Bkh126 is superior to that of sorafenib, currently used to treat advanced HCC. Our study shows that Bkh126 induces Nur77 to connect ER stress to mitochondria-mediated cell killing. The identification of Nur77 as a molecular target of Bhk126 provides a basis for improving the leads for the further development of anti-HCC drugs.

Progress and Promise of Nur77-based Therapeutics for Central Nervous System Disorders

Nur77 belongs to the NR4A subgroup of the nuclear receptor superfamily. Unlike other nuclear receptors, a natural ligand for Nur77 has not been identified yet. However, a few small molecules can interact with this receptor and induce a conformational change to mediate its activity. The expression and activation of Nur77 can be rapidly increased using various physiological and pathological stimuli. In vivo and in vitro studies have demonstrated its regulatory role in tissues and cells of multiple systems by means of participation in cell differentiation, apoptosis, metabolism, mitochondrial homeostasis, and other processes. Although research on Nur77 in the pathophysiology of the central nervous system (CNS) is currently limited, the present data support the fact that Nur77 is involved in many neurological disorders such as stroke, multiple sclerosis, Parkinson’s disease. This indicates that activation of Nur77 has considerable potential in treating these diseases. This review summarizes the regulatory mechanisms of Nur77 in CNS diseases and presents available evidence for its potential as targeted therapy, especially for cerebrovascular and inflammation-related CNS diseases.

Design, synthesis, and biological evaluation of 5-((8-methoxy-2-methylquinolin-4-yl)amino)-1H-indole-2-carbohydrazide derivatives as novel Nur77 modulators

Nur77 is a potential target for the treatment of cancer such as HCC. Herein, we detailed the discovery of a novel series of 5-((8-methoxy-2-methylquinolin-4-yl)amino)-1H-indole-2-carbohydrazide derivatives as potential Nur77 modulators. The studies of antiproliferative activity and Nur77-binding affinity of target compounds resulted in the discovery of a lead candidate (10g), which was a good Nur77 binder (K_D = 3.58 ± 0.16 μM) with a broad-spectrum antiproliferative activity against all tested hepatoma cells (IC₅₀ < 2.0 μM) and was low toxic to normal LO2 cells. 10g could up-regulate Nur77 expression and mediate sub-cellular localization of Nur77 to induce apoptosis in hepatocellular carcinoma cell lines, which relied on 10g inducing Nur77-dependent autophagy and endoplasmic reticulum stress as the upstream of apoptosis. Moreover, the in vivo assays verified that 10g significantly inhibited xenograft tumor growth. These results indicate that 10g has the potential to be developed as a novel Nur77-targeting anti-hepatoma drug.

Nur77 promotes cigarette smoke‑induced autophagic cell death by increasing the dissociation of Bcl2 from Beclin-1

Chronic obstructive pulmonary disease (COPD) is characterized by partially reversible airflow limitation and persistent alveolar destruction, and autophagy is involved in the pathogenesis of cigarette smoke (CS)‑induced COPD. Nuclear receptor 77 (Nur77) participates in a number of biological processes, including apoptosis, autophagy and in disease pathogenesis; however, the role of Nur77 in COPD remains unknown. Thus, in this study, we aimed to elucidate the role of Nur77 in COPD. We report that CS promotes Nur77 expression and nuclear export in vivo and in vitro, which increases cigarette smoke extract (CSE)‑induced autophagy. In addition, we found that lung tissues, human bronchial epithelial (HBE) cells and A549 cells exposed to CS or CSE expressed lower levels of LC3 and Beclin‑1 and contained fewer autophagosomes following Nur77 knockdown with siRNA‑Nur77. Moreover, a co‑immunoprecipitation assay demonstrated that CSE promoted autophagy, partly by accelerating the interaction between Nur77 and Bcl2, in turn leading to the increased dissociation of Bcl2 from Beclin‑1; by contrast, leptomycin B (LMB) suppressed the dissociation of Bcl2 from Beclin‑1. Taken together, the findings of this study demonstrate that Nur77 is involved in the CSE‑induced autophagic death of lung cells, and that this process is partially dependent on the increased interaction between Nur77 and Bcl2, and on the dissociation of Bcl2 from Beclin‑1. This study illustrates the role of Nur77 in bronchial and alveolar destruction following exposure to CS.

The involvement of NR4A1 and NR4A2 in the regulation of the luteal function in rats

The nuclear receptor 4A (NR4A) members play important roles in cellular proliferation, differentiation and apoptosis. The current study first evaluate the expression of ovarian NR4A1 during different luteal stages in rats. Immature rats aged 28 days were treated with sequential Pregnant mare serum gonadotropin (PMSG) (D -2) / human chorionic gonadotropin (hCG) (D 0) to induce pseudopregnancy. Serum progesterone (P₄) and ovarian expression of NR4A1 were detected by RIA and WB, respectively, at follicle stage (D 0), early (D 2), middle (D 7) and late (D 14 and D 20) luteal stages. To confirm the role of NR4A1 during the luteal regression, rats were treated with prostaglandin F_2α analog (PGF) for 0-8 h on D 7 to detect the expressions of NR4A1 and NR4A2. RIA result showed that serum P₄ reached highest level on D 7 and then declined. WB results showed that there were two types of NR4A1 (NR4A1-L and NR4A1-S) expressed in the ovary. The ovarian NR4A1-L decreased at the late luteal stage (D 20). However, the NR4A1-S increased at the late luteal stage (D 14). After PGF treatment on D 7, the expression of NR4A1-S increased which peaked at 0.5-1 h and then declined; while NR4A1-L expression did not change within 8 h. Real-time PCR results showed that the ovarian NR4A1 mRNA increased within 0.5 h, maintained high at 1 h and then declined. The NR4A2 mRNA expression exhibited a similar pattern to that of NR4A1 mRNA, though its abundance was not as high as NR4A1. IHC results revealed that NR4A1-L was expressed mainly in the cytoplasm of luteal steroidogenic cells, faintly expressed in the follicle theca cells, oocytes and the pericytes; while NR4A2 was primarily localized in the cytoplasm of luteal steroidogenic cells. In conclusion, all these results demonstrate that NR4A2 as well as NR4A1 might be involved in the luteal development and luteolysis in rats.

Proteolipid Protein 2 Overexpression Indicates Aggressive Tumor Behavior and Adverse Prognosis in Human Gliomas

Proteolipid protein 2 (PLP2), a membrane protein of the endoplasmic reticulum, is related to tumor proliferation and metastasis in some human cancers, but not in gliomas. First, we performed western-blot analysis, real-time quantitative PCR and immunohistochemical stains to detect PLP2 expression in 4 glioma cell lines and human glioma tissues. In addition, we used small interfering RNA (SiPLP2) and short hairpin RNA (shPLP2) to knockdown PLP2 expression in GBM8401 and LN229 glioma cell lines. After then, the alteration of PLP2 suppressed glioma cells behavior were examined by cell proliferation, wound healing, cell invasion, and colonies formation assays. Finally, the possible mechanism of PLP2 was analyzed by detecting the expression of the proteins related to cell-cycle checkpoints, cell-proliferative signaling factors, and cell-matrix interaction. Compared with normal brain cell lysates and mRNA, all glioma cell lines displayed PLP2 protein and mRNA overexpression. Besides, higher PLP2 IHC staining significantly correlated with more advanced tumor grades and poorer prognosis in human gliomas. Both siPLP2 transfected gliomas showed a clear inhibition of glioma cell proliferation, migration, and invasion as well as down-regulating p-p38, p-ERK, MMP-2, and MMP-9 expression. In conclusion, we successfully demonstrated that PLP2 overexpression played an oncogenic role in glioma development and aggressive tumor behavior.

Oxidized analogs of Di(1H-indol-3-yl)methyl-4-substituted benzenes are NR4A1-dependent UPR inducers with potent and safe anti-cancer activity

Di(1H-indol-3-yl)(4-trifluoromethylphenyl)methane (DIM-Ph-4-CF3) is an analog of orphan nuclear receptor 4A1 (NR4A1) ligand cytosporone B. We have synthesized several oxidation products of DIM-Ph-4-CF3, focusing on analogs with electron-withdrawing or donating groups at their phenyl ring 4-positions, and examined their anti-cancer activity and mechanism-of-action. Mesylates (DIM-Ph-4-X+ OMs-s) having CF3, CO2Me and Cl groups were more effective inhibitors of cancer cell viability than their precursors. 19F NMR spectroscopy and differential scanning calorimetry strongly indicated interactions of DIM-Ph-4-CF3+ OMs- with the NR4A1 ligand binding domain, and compound-induced apoptosis of prostate cancer cells was dependent on NR4A1. DIM-Ph-4-CF3+ OMs- showed robust inhibition of LNCaP prostate cancer xenografts with no apparent toxicity. In vitro and in vivo, DIM-Ph-4-CF3+ OMs- activated proapoptotic unfolded protein response (UPR) signaling in prostate cancer cells. Independently of DIM-Ph-4-CF3+ OMs-, the bulk of NR4A1 localized to the cytoplasm in various cancer cell lines, suggesting a cytoplasmic mechanism-of-action of DIM-Ph-4-CF3+ OMs- in UPR induction and cell death. In summary, the data suggest that oxidized analogs of DIM-Ph-4-CF3 possess potent and safe anti-cancer activity which is mediated through UPR signaling downstream of NR4A1 binding.

Identification of two novel isoforms of mouse NUR77 lacking N-terminal domains

Nur77 is a member of nuclear receptor superfamily that acts as a transcription factor and regulates expression of multiple genes. Subcellular localization of Nur77 protein plays an important role in the survival and cell death. In this study, we have predicted and confirmed alternatively spliced two new transcripts of Nur77 gene in mouse. The newly identified transcripts have their alternatively spliced first exon located upstream of published 5'-UTR of the gene. Transcription factor binding sites in the possible promoter regions of these transcripts were also analyzed. Expression of novel transcript variants was found to be significantly lower than the already published transcript. New transcript variants encode for NUR77 protein isoforms which are significantly smaller in size due to lack of transactivation domain and a part of DNA binding domain. Western blot analysis using NUR77 specific antibody confirmed the existence of these smaller variants in mouse. Localization of these new isoforms was predicted to be majorly outside the nucleus. In silico analysis of the conceptually translated proteins was performed using different bioinformatics tools. The results obtained in this study offer further insight into novel area of research on extensively studied Nur77. © 2017 IUBMB Life, 69(2):106-114, 2017.

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.

Nur77 exacerbates PC12 cellular injury in vitro by aggravating mitochondrial impairment and endoplasmic reticulum stress

The nuclear orphan receptor, Nur77 plays important roles in neuroimflammation, apoptosis, and dopaminergic neurodegeneration. We conducted a further mechanistic investigation into the association of Nur77 with cell death. Cytosporone B (Csn-B), an agonist for Nur77, and Nur77 knockdown were adopted in the 6-hydroxydopamine (OHDA)-lesioned PC12 cells to investigate the mechanisms underlying Nur77-mediated injury. The 6-OHDA incubation caused Nur77 translocation from the nucleus to cytosol and Endoplasm reticulum (ER) and induced co-localization of Tom20/Nur77 and Protein Disulfide Isomerase (PDI)/Nur77. Nur77 activation further decreased cell viability, aggravated intracellular LDH release, intracellular Ca²⁺, ROS levels, apoptosis, ER tress and, mitochondrial transmembrane potential (ΔΨm) decline. In addition, Nur77 activation significantly enhanced the efficiency of autophagy as indicated by an up-regulation of Beclin-1/LC-3 and downregulation of p62, and aggravated mitochondrial dysfunctions and ER stress as shown by increased HSP60/Cytochrome C (Cyt C) and CHOP-ATF3 levels respectively. These changes could be partially reversed by Nur77 knockdown. Moreover, Nur77 activation upregulated PINK1 and downregulated Parkin levels. We conclude that Nur77 exacerbates PC12 cell death at least partially by aggravating the mitochondrial impairment and ER stress and enhancing autophagy. We propose that Nur77 is likely a critical target in the PD therapy.

The orphan nuclear receptor NR4A1 specifies a distinct subpopulation of quiescent myeloid-biased long-term HSCs

Hematopoiesis is maintained throughout life by self-renewing hematopoietic stem cells (HSCs) that differentiate to produce both myeloid and lymphoid cells. The NR4A family of orphan nuclear receptors, which regulates cell fate in many tissues, appears to play a key role in HSC proliferation and differentiation. Using a NR4A1(GFP) BAC transgenic reporter mouse we have investigated NR4A1 expression and its regulation in early hematopoiesis. We show that NR4A1 is most highly expressed in a subset of Lin(-) Sca-1(+) c-Kit(+) CD48(-) CD150(+) long-term (LT) HSCs, and its expression is tightly associated with HSC quiescence. We also show that NR4A1 expression in HSCs is induced by PGE2, a known enhancer of stem cell engraftment potential. Finally, we find that both NR4A1(GFP+) and NR4A1(GFP-) HSCs successfully engraft primary and secondary irradiated hosts; however, NR4A1(GFP+) HSCs are distinctly myeloid-biased. These results show that NR4A1 expression identifies a highly quiescent and distinct population of myeloid-biased LT-HSCs.

The Orphan Nuclear Receptor NR4A1 Protects Pancreatic β-Cells from Endoplasmic Reticulum (ER) Stress-mediated Apoptosis

The role of NR4A1 in apoptosis is controversial. Pancreatic β-cells often face endoplasmic reticulum (ER) stress under adverse conditions such as high free fatty acid (FFA) concentrations and sustained hyperglycemia. Severe ER stress results in β-cell apoptosis. The aim of this study was to analyze the role of NR4A1 in ER stress-mediated β-cell apoptosis and to characterize the related mechanisms. We confirmed that upon treatment with the ER stress inducers thapsigargin (TG) or palmitic acid (PA), the mRNA and protein levels of NR4A1 rapidly increased in both MIN6 cells and mouse islets. NR4A1 overexpression in MIN6 cells conferred resistance to cell loss induced by TG or PA, as assessed by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, and TUNEL assays indicated that NR4A1 overexpression also protected against ER stress-induced apoptosis. This conclusion was further confirmed by experiments exploiting siRNA to knockdown NR4A1 expression in MIN6 cells or exploiting NR4A1 knock-out mice. NR4A1 overexpression in MIN6 cells reduced C/EBP homologous protein (CHOP) expression and Caspase3 activation induced by TG or PA. NR4A1 overexpression in MIN6 cells or mouse islets resulted in Survivin up-regulation. A critical regulatory element was identified in Survivin promoter (-1872 bp to -1866 bp) with a putative NR4A1 binding site; ChIP assays demonstrated that NR4A1 physically associates with the Survivin promoter. In conclusion, NR4A1 protects pancreatic β-cells against ER stress-mediated apoptosis by up-regulating Survivin expression and down-regulating CHOP expression, which we termed as "positive and negative regulation."

Non-genomic effects of the NR4A1/Nur77/TR3/NGFIB orphan nuclear receptor

The orphan nuclear receptor NR4A1/Nur77/TR3/NGFIB acts primarily as a transcription factor to regulate the expression of multiple genes. However, increasing research attention has recently been given to non-genomic activities of NR4A1. The first description of a non-genomic action of NR4A1 referred to the conversion of anti-apoptotic Bcl-2 into a pro-apoptotic protein by direct interaction with NR4A1. In response to certain apoptotic stimuli, NR4A1 translocates from the nucleus to the mitochondrial outer membrane (MOM) where it associates with Bcl-2 and thereby causes apoptosis. Afterwards, it appeared that NR4A1 could also bind and convert other anti-apoptotic Bcl-2 family members. The latest studies indicate a significant role of NR4A1 in the process of autophagy. For example, a new NR4A1-mediated pathway specific for melanoma cells has been described where NR4A1 interacts with the adenine nucleotide translocase 1 (ANT1) on the mitochondrial inner membrane (MIM) leading to induction of the autophagy pathway. Moreover, NR4A1 interaction with cytoplasmic p53 may also contribute to the induction of autophagy. In addition to mitochondria, NR4A1 could be translocated to the outer membrane of the endoplasmic reticulum (ER) and associate with Bcl-2 or translocon-associated protein subunit γ (TRAPγ) causing ER stress-induced apoptosis. NR4A1 also contributes to the proteasomal degradation of β-catenin in colon cancer cells in vitro and in vivo, as well as to the stabilization of hypoxia-inducible factor-1α (HIF-1α) under non-hypoxic conditions. This review summarizes research findings on non-genomic effects of NR4A1 in normal and cancer cells.

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.

Nuclear receptor subfamily 4, group A, member 1 inhibits extrinsic apoptosis and reduces caspase-8 activity in H2O2-induced human HUC-F2 fibroblasts

Objective: Apoptosis is characterized by distinct morphological and biochemical changes that occur upon activation of a family of serine proteases known as caspases. Reactive oxygen species (ROS) induce apoptosis in many cell systems. Nuclear receptor subfamily 4, group A, member 1 (NR4A1) has been shown to induce apoptosis in a number of cell lineages, but can also paradoxically act as a death inhibitory factor. In the current study, we focused on the potential role of NR4A1 in hydrogen peroxide (H2O2)-induced apoptosis of normal human umbilical cord fibroblast (HUC-F2) cells.

Methods: Growth of HUC-F2 cells treated with H2O2 was measured by MTT assay. Analysis of gene expression was performed with a STEP ONE PLUS Real Time PCR system. Inactivation of NR4A1 was treated with siRNA. Apoptosis was measured by Beckman Coulter flow cytometer after inhibition of NR4A1 with siRNA and H2O2 treatment. Caspase -3, -8 and -9 was measured by caspase assay kit.

Results: H2O2 treatment led to enhanced NR4A1 expression. Moreover inhibition of NR4A1 with specific siRNA in HUC-F2 cells triggered an increase in apoptosis and caspase-8 and -3 activities following the addition of H2O2.

Discussion: Our results collectively suggest that NR4A1 is a regulator that inhibits extrinsic apoptosis in HUC-F2 cells during oxidative stress through reduction of caspase-8 and -3 activities.

Nuclear receptors and pathogenesis of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a devastating disease with a median overall survival time of 5 mo and the five years survival less than 5%, a rate essentially unchanged over the course of the years. A well defined progression model of accumulation of genetic alterations ranging from single point mutations to gross chromosomal abnormalities has been introduced to describe the origin of this disease. However, due to the its subtle nature and concurring events PDAC cure remains elusive. Nuclear receptors (NR) are members of a large superfamily of evolutionarily conserved ligand-regulated DNA-binding transcription factors functionally involved in important cellular functions ranging from regulation of metabolism, to growth and development. Given the nature of their ligands, NR are very tempting drug targets and their pharmacological modulation has been widely exploited for the treatment of metabolic and inflammatory diseases. There are now clear evidences that both classical ligand-activated and orphan NR are involved in the pathogenesis of PDAC from its very early stages; nonetheless many aspects of their role are not fully understood. The purpose of this review is to highlight the striking connections that link peroxisome proliferator activated receptors, retinoic acid receptors, retinoid X receptor, androgen receptor, estrogen receptors and the orphan NR Nur, chicken ovalbumin upstream promoter transcription factor II and the liver receptor homologue-1 receptor to PDAC development, connections that could lead to the identification of novel therapies for this disease.

AMP-activated protein kinase is required for cell survival and growth in HeLa-S3 cells in vivo

Activation of the AMP-dependent protein kinase (AMPK) is linked to cancer cell survival in a variety of cancer cell lines, particularly under conditions of stress. As a potent activator of AMPK, metformin has become a hot topic of discussion for its effect on cancer cell. Here, we report that AMPK activated by metformin promotes HeLa-S3 cell survival and growth in vivo. Our results show that metformin inhibited cell proliferation in MCF-7 cells, but not in LKB1-deficient HeLa-S3 cells. Re-expression of LKB-1 in HeLa-S3 cells restored the growth inhibitory effect of metformin, indicating a requirement for LKB-1 in metformin-induced growth inhibition. Moreover, AMPK activation exerted a protective effect in HeLa-S3 cells by relieving ER stress, modulating ER Ca(2+) storage, and finally contributing to cellular adaptation and resistance to apoptosis. Our findings identify a link between AMPK activation and cell survival in HeLa-S3 cells, which demonstrates a beneficial effect of AMPK activated by metformin in cancer cell, and suggests a discrete re-evaluation on the role of metformin/AMPK activation on tumor cell growth, proliferation, and on clinical application in cancer therapy.

Chymase mediates injury and mitochondrial damage in cardiomyocytes during acute ischemia/reperfusion in the dog

Cardiac ischemia and reperfusion (I/R) injury occurs because the acute increase in oxidative/inflammatory stress during reperfusion culminates in the death of cardiomyocytes. Currently, there is no drug utilized clinically that attenuates I/R injury in patients. Previous studies have demonstrated degranulation of mast cell contents into the interstitium after I/R. Using a dog model of I/R, we tested the role of chymase, a mast cell protease, in cardiomyocyte injury using a specific oral chymase inhibitor (CI). 15 adult mongrel dogs had left anterior descending artery occlusion for 60 min and reperfusion for 100 minutes. 9 dogs received vehicle and 6 were pretreated with a specific CI. In vivo cardiac microdialysis demonstrated a 3-fold increase in interstitial fluid chymase activity in I/R region that was significantly decreased by CI. CI pretreatment significantly attenuated loss of laminin, focal adhesion complex disruption, and release of troponin I into the circulation. Microarray analysis identified an I/R induced 17-fold increase in nuclear receptor subfamily 4A1 (NR4A1) and significantly decreased by CI. NR4A1 normally resides in the nucleus but can induce cell death on migration to the cytoplasm. I/R caused significant increase in NR4A1 protein expression and cytoplasmic translocation, and mitochondrial degradation, which were decreased by CI. Immunohistochemistry also revealed a high concentration of chymase within cardiomyocytes after I/R. In vitro, chymase added to culture HL-1 cardiomyocytes entered the cytoplasm and nucleus in a dynamin-dependent fashion, and promoted cytoplasmic translocation of NR4A1 protein. shRNA knockdown of NR4A1 on pre-treatment of HL-1 cells with CI significantly decreased chymase-induced cell death and mitochondrial damage. These results suggest that the beneficial effects of an orally active CI during I/R are mediated in the cardiac interstitium as well as within the cardiomyocyte due to a heretofore-unrecognized chymase entry into cardiomyocytes.

Elevation of NR4A3 expression and its possible role in modulating insulin expression in the pancreatic beta cell

Background

NR4A3/NOR-1 is a member of the NR4A orphan nuclear receptor subfamily, which contains early response genes that sense and respond to a variety of stimuli in the cellular environment. The role of NR4A3 in insulin expression in pancreatic beta cells remains unknown.

Methods

Dynamic changes in NR4A3 were examined in a pancreatic beta-cell line, MIN6, treated with thapsigargin (TG), palmitate (PA), tunicamycin (TM), and dithiothreitol (DTT), chemicals that produce cell stress and even apoptosis. We exploited virus infection techniques to induce expression of NR4A3 or three deletion mutants, and determined expression of insulin and insulin regulatory genes in MIN6 cells.

Results

TG and PA, two endoplasmic reticulum (ER) stress inducers, were able to induce unfolded protein response (UPR) activation and elevation of NR4A3 expression in MIN6 cells, whereas TM and DTT, two other ER stress inducers, were able to induce UPR activation but not NR4A3 elevation. MIN6 cells over-expressing NR4A3 protein after adenoviral infection exhibited reduced transcription of the insulin genes Ins1 and Ins2, and reduced insulin protein secretion, which were negatively correlated with NR4A3 expression levels. Functional analysis of different deletion mutants of NR4A3 showed that deleting the activation domain AF1 or the DNA-binding domain abolished the down-regulation of insulin transcription by NR4A3 in MIN6 cells, indicating that this down-regulative role was closely related to the NR4A3 trans-activation activity. Over-expression of NR4A3 in MIN6 cells resulted in reduced mRNA transcription of the insulin positive-regulation genes, Pdx1 and NeuroD1.

Conclusion

Some ER stress inducers, such as TG or PA, are able to elevate NR4A3 expression in MIN6 cells, while others, such as TM or DTT, are not. Over-expression of NR4A3 in MIN6 cells results in down-regulation of insulin gene transcription and insulin secretion. NR4A3 reduces insulin gene expression by modulating the expression of Pdx1 and NeuroD1.

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.

Overexpression of WRAP53 is associated with development and progression of esophageal squamous cell carcinoma

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) is a highly aggressive cancer whose underlying molecular mechanisms are poorly understood. The natural antisense transcript (NAT) WRAP53 regulates p53 expression and WRAP53 protein is a component of telomerase. NATs play key roles in carcinogenesis, and although WRAP53 is known to increase cancer cell survival, its role in ESCC clinicopathology is unknown. The aim of this study was to investigate WRAP53 expression in ESCC and to correlate it with clinicopathological characteristics.

METHODS

WRAP53 mRNA and protein expression was measured by quantitative PCR (qRT-PCR) and western blotting, respectively, in 4 ESSC cells lines and in 45 paired ESCC and non-neoplastic esophageal mucosa tissues. To correlate WRAP53 protein expression with clinicopathological characteristics, immunohistochemistry (IHC) was performed on 134 ESCC and 85 non-neoplastic esophageal mucosa tissues.

RESULTS

Expression of WRAP53 was detected in all ESCC cell lines and was upregulated in the ESCC tissues compared with the corresponding non-neoplastic tissues (P<0.01). More cells expressed WRAP53 protein in the ESCC tissues than in the non-neoplastic tissues (P<0.01). Overexpression of WRAP53 was significantly correlated with tumor infiltration depth (P = 0.000), clinical stage (P = 0.001), and lymph node metastasis (P = 0.025). Wrap53 expression was not correlated with age, gender, or tumor differentiation.

CONCLUSION

This report indicates increased expression of WRAP53 in ESCC and that WRAP53 overexpression is correlated with tumor progression. WRAP53 may play a significant role in ESCC; accordingly, WRAP53 could be a useful biomarker for ESCC.

Identification of Target Genes Involved in the Antiproliferative Effect of Enzyme-Modified Ginseng Extract in HepG2 Hepatocarcinoma Cell

Ginsenosides are ginseng saponins, which are the major biologically active components of Panax ginseng, often metabolized by intestinal bacteria into more effective forms. In this study, we found that the antiproliferative activity of ginseng increased after enzymatic processing of ginseng saponin (50% inhibitory concentration [IC₅₀], >30 μg/mL), which may be the result of the accumulation of minor saponins, such as Rh1, Rg3, compound K, and PPT constituents in ginseng saponin. Using the Agilent PrimeView Human Gene Expression Array, we found that the expression of several genes involved in apoptosis (caspase-4, Annexin A2, HSPA9, AIFM1, UQCRC2, and caspase-7) were increased in HepG2 human hepatocarcinoma cells after their treatment with enzyme-modified ginseng extract (EMGE). Furthermore, several genes implicated in cell cycle progression (CDCA3, CDCA8, CABLES2, CDC25B, CNNM3, and CCNK) showed decreased expression in HepG2 cells treated with EMGE. Finally, from flow cytometric analysis, we found that EMGE-treated HepG2 cells showed increased apoptotic sub-G1 population (24%), compared with that observed in DMSO-treated control cells (1.6%). Taken together, our results suggest that EMGE induces anticancer activity through the induction of apoptosis-related genes and cell cycle arrest via decreased expression of cell cycle regulatory genes.

The orphan nuclear receptor TR3/Nur77 regulates ER stress and induces apoptosis via interaction with TRAPγ

The orphan nuclear receptor TR3 (also known as Nur77) belongs to the steroid/thyroid/retinoid nuclear receptor superfamily and plays important roles in regulating cell proliferation, differentiation and apoptosis. No physiological ligand for TR3 has been found thus far; the determination of its binding partners is therefore important to clarify the biological functions of TR3. Here, we identified translocon-associated protein subunit γ (TRAPγ) as a novel TR3 binding partner using a tandem affinity purification method. This interaction between TR3 and TRAPγ was further confirmed, and the interacting regions were mapped. The ligand-binding domain of TR3 was required for TRAPγ binding, and the C terminus of TRAPγ was responsible for its interaction with TR3. When stimulated with 12-O-tetradecanoylphorbol 13-acetate (TPA) or CD437, this TR3-TRAPγ interaction not only induced Ca(2+) depletion in the endoplasmic reticulum (ER) but also promoted the expression of the proapoptotic transcriptional regulator CHOP. Notably, both TR3 and TRAPγ were required for ER stress-induced apoptosis in HepG2 cells. Overall, this study demonstrated a novel, TR3-initiated signaling pathway in which TR3 regulates ER stress and induces apoptosis of hepatoma cells through its interaction with TRAPγ.

The nuclear receptor NR4A1 induces a form of cell death dependent on autophagy in mammalian cells

The control of cell death is a biological process essential for proper development, and for preventing devastating pathologies like cancer and neurodegeneration. On the other hand, autophagy regulation is essential for protein and organelle degradation, and its dysfunction is associated with overlapping pathologies like cancer and neurodegeneration, but also for microbial infection and aging. In the present report we show that two evolutionarily unrelated receptors--Neurokinin 1 Receptor (NK(1)R,) a G-protein coupled receptor, and Insulin-like Growth Factor 1 Receptor (IGF1R), a tyrosine kinase receptor--both induce non-apoptotic cell death with autophagic features and requiring the activity of the autophagic core machinery proteins PI3K-III, Beclin-1 and Atg7. Remarkably, this form of cell death occurs in apoptosis-competent cells. The signal transduction pathways engaged by these receptors both converged on the activation of the nuclear receptor NR4A1, which has previously been shown to play a critical role in some paradigms of apoptosis and in NK(1)R-induced cell death. The activity of NR4A1 was necessary for IGF1R-induced cell death, as well as for a canonical model of cell death by autophagy induced by the presence of a pan-caspase inhibitor, suggesting that NR4A1 is a general modulator of this kind of cell death. During cell death by autophagy, NR4A1 was transcriptionally competent, even though a fraction of it was present in the cytoplasm. Interestingly, NR4A1 interacts with the tumor suppressor p53 but not with Beclin-1 complex. Therefore the mechanism to promote cell death by autophagy might involve regulation of gene expression, as well as protein interactions. Understanding the molecular basis of autophagy and cell death mediation by NR4A1, should provide novel insights and targets for therapeutic intervention.

KHDC1A, a novel translational repressor, induces endoplasmic reticulum-dependent apoptosis

RNA binding proteins are characterized as a new family of apoptosis inducers; however, the mechanism by which they induce apoptosis is poorly understood. KHDC1 family members were recently identified as K-homology (KH)-domain containing RNA binding proteins that are unique to eutherian mammals and highly expressed in oocytes. In this study, we report that the expression of KHDC1A induces caspase-3 dependent apoptosis and inhibits mRNA translation, and the translational repression is independent of apoptosis. We demonstrate that both the N-terminus and C-terminus of KHDC1A are required for its pro-apoptotic and translational repression activities. Furthermore, in the C-terminus of KHDC1A, a putative trans-membrane motif (TMM) is critical for these activities. In addition, the ectopically expressed KHDC1A is localized to the endoplasmic reticulum (ER) and changes the morphology of the ER. The inhibition of ER-specific caspase-12 successfully rescues KHDC1A-induced apoptosis, but not Fas-induced apoptosis. Taken together, we conclude that KHDC1A functions as a global translational repressor and induces apoptosis through an ER-dependent signaling pathway.

Synthetic retinoid CD437 induces apoptosis and acts synergistically with TRAIL receptor-2 agonist in malignant melanoma

The novel synthetic retinoid, CD437, shows potent anti-tumor activity in a range of different cancer cell lines and now serves as a prototype for development of new retinoid related molecules (RRMs). The purpose of this study was to examine the effect and cellular targets of CD437 in the human metastatic melanoma cell lines FEMX-1 and WM239. We showed that treatment with CD437 led to cell cycle arrest and induced apoptosis through both the extrinsic- and intrinsic pathways (caspase 8, -9 and PARP cleavage) in both cell lines. Interestingly, apoptosis was induced independently of DNA-fragmentation in FEMX-1 cells, and appeared partially caspase-independent in the WM239 cells. Additionally, up-regulation of CHOP mRNA and cathepsin D protein expression, following retinoid treatment, suggests involvement of the endoplasmatic reticulum (ER) and lysosomes, respectively. Combination of suboptimal concentrations of CD437 and lexatumumab, a TRAIL death receptor-2 agonist, resulted in synergistic reduction of viable cells, along with increased PARP cleavage. These results indicate that CD437 has a strong anti-neoplastic effect alone and in combination with lexatumumab in melanoma cell lines.

Cholesterol enhances neuron susceptibility to apoptotic stimuli via cAMP/PKA/CREB-dependent up-regulation of Kv2.1

Cholesterol is a major component of membrane lipid rafts. It is more abundant in the brain than in other tissues and plays a critical role in maintaining brain function. We report here that a significant enhancement in apoptosis in rat cerebellar granule neurons (CGNs) was observed upon incubation with 5mM K(+) /serum free (LK-S) medium. Cholesterol enrichment further potentiated CGN apoptosis incubated under LK-S medium. On the contrary, cholesterol depletion using methyl-beta-cyclodextrin protected the CGNs from apoptosis induced by LK-S treatment. Cholesterol enrichment, however, did not induce apoptosis in CGNs that have been incubated with 25mM K(+) /serum medium. Mechanistically, increased I(K) currents and DNA fragmentation were found in CGNs incubated in LK-S, which was further potentiated in the presence of cholesterol. Cholesterol-treated CGNs also exhibited increased cAMP levels and up-regulation of Kv2.1 expression. Increased levels of activated form of PKA and phospho-CREB further supported activation of the cAMP/PKA pathway upon treatment of CGNs with cholesterol-containing LK-S medium. Conversely, inhibition of PKA or small G protein Gs abolished the increase in I(K) current and the potentiation of Kv2.1 expression, leading to reduced susceptibility of CGNs to LK-S and cholesterol-induced apoptosis. Our results demonstrate that the elevation of membrane cholesterol enhances CGN susceptibility to apoptotic stimuli via cAMP/PKA/CREB-dependent up-regulation of Kv2.1. Our data provide new evidence for the role of cholesterol in eliciting neuronal cell death.

DNA methylation profiling identifies epigenetic dysregulation in pancreatic islets from type 2 diabetic patients

In addition to genetic predisposition, environmental and lifestyle factors contribute to the pathogenesis of type 2 diabetes (T2D). Epigenetic changes may provide the link for translating environmental exposures into pathological mechanisms. In this study, we performed the first comprehensive DNA methylation profiling in pancreatic islets from T2D and non-diabetic donors. We uncovered 276 CpG loci affiliated to promoters of 254 genes displaying significant differential DNA methylation in diabetic islets. These methylation changes were not present in blood cells from T2D individuals nor were they experimentally induced in non-diabetic islets by exposure to high glucose. For a subgroup of the differentially methylated genes, concordant transcriptional changes were present. Functional annotation of the aberrantly methylated genes and RNAi experiments highlighted pathways implicated in β-cell survival and function; some are implicated in cellular dysfunction while others facilitate adaptation to stressors. Together, our findings offer new insights into the intricate mechanisms of T2D pathogenesis, underscore the important involvement of epigenetic dysregulation in diabetic islets and may advance our understanding of T2D aetiology.

Norcantharidin induces melanoma cell apoptosis through activation of TR3 dependent pathway

Norcantharidin (NCTD) has been reported to induce tumor cell apoptosis. However, the underlying mechanism behinds its antitumor effect remains elusive. We have previously shown that TR3 expression is significantly decreased in metastatic melanomas and involved in melanoma cell apoptosis. In this study, we showed that NCTD inhibited melanoma cell proliferation and induced apoptosis in a dose related manner. NCTD induced translocation of TR3 from nucleus to mitochondria where it co-localized with Bcl-2 in melanoma cells. NCTD also increased cytochome c release from mitochondria to the cytoplasm. These changes were accompanied by increased expression of Bax and cleaved caspase-3 along with decreased expression of Bcl2 and NF-κB2. The effects of NCTD were inhibited by knockdown of TR3 expression using TR3 specific shRNA in melanoma cells. Furthermore, NCTD significantly decreased tumor volume and improved survival of Tyr::CreER; BRAF(Ca/+); Pten(lox/lox) transgenic mice. Our data indicates that NCTD inhibits melanoma growth by inducing tumor cell apoptosis via activation of a TR3 dependent pathway. These results suggest that NCTD is a potential therapeutic agent for melanoma.

Inhibition of β-catenin signaling by nongenomic action of orphan nuclear receptor Nur77

Dysregulation of β-catenin turnover due to mutations of its regulatory proteins including adenomatous polyposis coli (APC) and p53 is implicated in the pathogenesis of cancer. Thus, intensive effort is being made to search for alternative approaches to reduce abnormally activated β-catenin in cancer cells. Nur77, an orphan member of the nuclear receptor superfamily, has a role in the growth and apoptosis of cancer cells. Here, we reported that Nur77 could inhibit transcriptional activity of β-catenin by inducing β-catenin degradation via proteasomal degradation pathway that is glycogen synthase kinase 3β and Siah-1 independent. Nur77 induction of β-catenin degradation required both the N-terminal region of Nur77, which was involved in Nur77 ubiquitination, and the C-terminal region, which was responsible for β-catenin binding. Nur77/ΔDBD, a Nur77 mutant lacking its DNA-binding domain, resided in the cytoplasm, interacted with β-catenin, and induced β-catenin degradation, demonstrating that Nur77-mediated β-catenin degradation was independent of its DNA binding and transactivation, and might occur in the cytoplasm. In addition, we reported our identification of two digitalis-like compounds (DLCs), H-9 and ATE-i2-b4, which potently induced Nur77 expression and β-catenin degradation in SW620 colon cancer cells expressing mutant APC protein in vitro and in animals. DLC-induced Nur77 protein was mainly found in the cytoplasm, and inhibition of Nur77 nuclear export by the CRM1-dependent nuclear export inhibitor leptomycin B or Jun N-terminal kinase inhibitor prevented the effect of DLC on inducing β-catenin degradation. Together, our results demonstrate that β-catenin can be degraded by cytoplasmic Nur77 through their interaction and identify H-9 and ATE-i2-b4 as potent activators of the Nur77-mediated pathway for β-catenin degradation.

Botanical Drugs and Stem Cells

The potential to generate virtually any differentiated cell type from stem cells offers the possibility of creating new sources of cells for regenerative medicine. To realize this potential, it will be essential to control stem cell differentiation. Chinese herbal medicine is a major aspect of traditional Chinese medicine and is a rich source of unique chemicals. As such, individual herbs or extracts may play a role in the proliferation and differentiation of stem cells. In this review, we discuss some of the Chinese herbal medicines that are used to treat human diseases such as neuronal degenerative diseases, cardiovascular diseases, and osteoporosis. We also describe the relationship between Chinese herbal medicines and stem cell regulation.

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

BACKGROUND

In previous study, n-butylidenephthalide (BP), a natural compound from Angelica sinensis, has anti-glioblastoma multiform (GBM) cell effects. In this study, we modified BP structure to increase anti-GBM cell effects. The anti-GBM cell effects of one derivative of BP, (Z)-N-(2-(dimethylamino)ethyl)-2-(3-((3-oxoisobenzofuran-1(3H)-ylidene)methyl)phenoxy)acetamide (PCH4) were tested in vitro and in vivo.

METHODS

MTT assay and PI/Annexin V assay were performed to evaluate the anti-GBM effects of PCH4. The Nur77 expression and translocation were assayed by RT-PCR and Western blot. The Nur77 siRNA was used to downregulate the Nur77 expression. The JNK inhibitor (SP600125) was used to block the JNK pathway.

RESULTS

The anti-GBM effect of PCH4 is four times more than BP. The IC(50) of PCH4 on DBTRG-05MG cells was 50 µg/ml. Nur77 expression and translocation from the nucleus to the cytoplasm were important in PCH4-induced apoptosis. Furthermore, the downregulation of PCH4-induced Nur77 expression by Nur77 siRNA reduced PCH4-induced apoptosis. In addition, PCH4-induced apoptosis was associated with the JNK pathway. The JNK inhibitor, SP600125, inhibited Nur77 mRNA expression and reduced PCH4-induced apoptosis.

CONCLUSIONS

In conclusion, PCH4, a derivative of BP, induced Nur77-mediated apoptosis via the JNK pathway and this mechanism, which is different from that of BP, may explain the increase in the anti-tumor effects on GBM.

Dual involvement of caspase-4 in inflammatory and ER stress-induced apoptotic responses in human retinal pigment epithelial cells

PURPOSE

To investigate the functional involvement of caspase-4 in human retinal pigment epithelial (hRPE) cells.

METHODS

Expression and activation of caspase-4 in hRPE cells were measured after stimulation with proinflammatory agents IL-1beta (2 ng/mL), TNF-alpha (20 ng/mL), lipopolysaccharide (1000 ng/mL), interferon-gamma (500 U/mL), or monocyte coculture in the absence or presence of immunomodulating agent cyclosporine (3 or 30 ng/mL), dexamethasone (10 microM), or IL-10 (100 U/mL) and endoplasmic reticulum (ER) stress inducer thapsigargin (25 nM) or tunicamycin (3 or 10 microM). The onset of ER stress was determined by expression of GRP78. The involvement of caspase-4 in inflammation and apoptosis was further examined by treating the cells with caspase-4 inhibitor Z-LEVD-fmk, caspase-1 and -4 inhibitor Z-YVAD-fmk, and pan-caspase inhibitor Z-VAD-fmk.

RESULTS

Caspase-4 mRNA expression and protein activation were induced by all the proinflammatory agents and ER stress inducers tested in this study. Caspase-4 activation was blocked or reduced by dexamethasone and IL-10. Elevated ER stress by proinflammatory agents and ER stress inducers was shown by increased expression of the ER stress marker GRP78. The induced caspase-4 and caspase-3 activities by tunicamycin and the stimulated IL-8 protein expression by IL-1beta were markedly reduced by caspase-4 inhibitor Z-LEVD-fmk. Although caspase-4 inhibitor Z-LEVD-fmk and caspase-1 and -4 inhibitor Z-YVAD-fmk reduced tunicamycin-induced hRPE apoptotic cell death by 59% and 86%, respectively, pan-caspase inhibitor Z-VAD-fmk completely abolished the induced apoptosis.

CONCLUSIONS

Caspase-4 is dually involved in hRPE proinflammatory and proapoptotic responses. Various proinflammatory stimuli and ER stress induce hRPE caspase-4 mRNA synthesis and protein activation. ER stress-induced hRPE cell death is caspase and, in part, caspase-4 dependent.

NGFI-B targets mitochondria and induces cardiomyocyte apoptosis in restraint-stressed rats by mediating energy metabolism disorder

NGFI-B/Nur77/TR3, originally identified as an immediate-early gene rapidly induced by serum and growth factors, is a member of the steroid hormone nuclear receptor superfamily with no identified endogenous ligand. NGFI-B induces apoptosis in a number of cell lineages exposed to proapoptotic stimuli by directly targeting the mitochondria, inducing cytochrome c release. The present study was designed to determine the role of NGFI-B in cardiomyocytes of restraint-stressed rats. The NGFI-B content was increased in mitochondria and reduced in plasma as apoptosis increased. Analysis showed that NGFI-B induces cardiomyocyte apoptosis in restraint-stressed rats by mediating mitochondrial energy metabolism disorder. Several novel mitochondrial proteins, which correlate with NGFI-B, were reported in cardiomyocyte apoptosis of restraint-stressed rats. Five proteins associated with NGFI-B participate directly in mitochondrial energy metabolism. Studies of mitochondrial respiratory efficiency and ATP synthase activity strongly support the findings. These results provide significant information for comprehensively understanding the cellular mechanism of cardiovascular diseases.