Cytochrome c release and apoptosis induced by mitochondrial targeting of nuclear orphan receptor TR3

Role of Nurr1 in Carcinogenesis and Tumor Immunology: A State of the Art Review

Simple Summary

Nuclear receptor related-1 protein (Nurr1) emerges as a therapeutic target in multiple malignancies and immunotherapies. Previous studies have highlighted its association with clinicopathological parameters, tumorigenesis and therapeutic resistance in cancers. In addition, recent studies unraveled its contribution to the suppression of antitumor immunity, suggesting that inhibition of Nurr1 is a potential method to repress cancer aggressiveness and disrupt tumor immune tolerance. In line with this evidence, the present review provides the roles of Nurr1 in tumor progression and the associated underlying molecular mechanisms. Moreover, the significance of Nurr1 in promoting immune tolerance and potential strategies for Nurr1 inhibition are highlighted.

Abstract

Nuclear receptor related-1 protein (Nurr1), coded by an early response gene, is involved in multiple cellular and physiological functions, including proliferation, survival, and self-renewal. Dysregulation of Nurr1 has been frequently observed in many cancers and is attributed to multiple transcriptional and post-transcriptional mechanisms. Besides, Nurr1 exhibits extensive crosstalk with many oncogenic and tumor suppressor molecules, which contribute to its potential pro-malignant behaviors. Furthermore, Nurr1 is a key player in attenuating antitumor immune responses. It not only potentiates immunosuppressive functions of regulatory T cells but also dampens the activity of cytotoxic T cells. The selective accessibility of chromatin by Nurr1 in T cells is closely associated with cell exhaustion and poor efficacy of cancer immunotherapy. In this review, we summarize the reported findings of Nurr1 in different malignancies, the mechanisms that regulate Nurr1 expression, and the downstream signaling pathways that Nurr1 employs to promote a wide range of malignant phenotypes. We also give an overview of the association between Nurr1 and antitumor immunity and discuss the inhibition of Nurr1 as a potential immunotherapeutic strategy.

HPV-induced Nurr1 promotes cancer aggressiveness, self-renewal, and radioresistance via ERK and AKT signaling in cervical cancer

Human papillomavirus (HPV) is the etiological agent of cervical cancer; however, the mechanisms underlying HPV-mediated carcinogenesis remain poorly understood. Here, we showed that nuclear receptor related-1 protein (Nurr1) was upregulated in primary cervical cancer tissue-derived spheroid cells and HPV-positive cell lines, and Nurr1 upregulation was correlated with cancer grade. Nurr1 promoted cell proliferation, migration, invasion, and anchorage-independent cell growth. In addition to its effect on cancer aggressiveness, Nurr1 enhanced the self-renewal ability of cells in vitro and in vivo, underscoring the importance of Nurr1 in maintaining the stemness of cancer stem-like cells (CSLCs). Mechanistically, Nurr1 independently activated the MEK/ERK and PI3K/Akt/mTOR signaling cascades. The MEK inhibitor trametinib (GSK) and PI3K/mTOR dual inhibitor dactolisib (BEZ) were shown to abrogate Nurr1-augmented tumorigenesis by upregulating p21 and p27 expression and by suppressing MMP9 and KLF4 expression. We provided further evidence that BEZ, but not GSK, could abolish Nurr1-enhanced radioresistance, suggesting its potential value for radiosensitizing CSLCs in the clinical setting. This study highlights the unprecedented roles of Nurr1 and elucidates mechanisms by which Nurr1 promotes tumor progression and radioresistance, providing a novel therapeutic strategy for cervical cancer treatment.

Cantharidin Induces Apoptosis and Promotes Differentiation of AML Cells Through Nuclear Receptor Nur77-Mediated Signaling Pathway

Background

Acute myeloid leukemia (AML) is a hematopoietic malignancy characterized by uncontrolled proliferation and accumulation of myeloblasts in the bone marrow (BM), blood, and other organs. The nuclear receptors Nur77 is a common feature in leukemic blasts and has emerged as a key therapeutic target for AML. Cantharidin (CTD), a main medicinal component of Mylabris (blister beetle), exerts an anticancer effect in multiple types of cancer cells.

Purpose

This study aims to characterize the anti-AML activity of CTD in vitro and in vivo and explore the potential role of Nur77 signaling pathway.

Study Design/Methods

The inhibition of CTD on cell viability was performed in different AML cells, and then the inhibition of CTD on proliferation and colony formation was detected in HL-60 cells. Induction of apoptosis and promotion of differentiation by CTD were further determined. Then, the potential role of Nur77 signaling pathway was assessed. Finally, anti-AML activity was evaluated in NOD/SCID mice.

Results

In our study, CTD exhibited potent inhibition on cell viability and colony formation ability of AML cells. Moreover, CTD significantly induced the apoptosis, which was partially reversed by Z-VAD-FMK. Meanwhile, CTD promoted the cleavage of caspases 8, 3 and PARP in HL-60 cells. Furthermore, CTD obviously suppressed the proliferation and induced the cell cycle arrest of HL-60 cells at G2/M phase. Meanwhile, CTD effectively promoted the differentiation of HL-60 cells. Notably, CTD transiently induced the expression of Nur77 protein. Interestingly, CTD promoted Nur77 translocation from the nucleus to the mitochondria and enhanced the interaction between Nur77 and Bcl-2, resulting in the exposure of the BH3 domain of Bcl-2, which is critical for the conversion of Bcl-2 from an antiapoptotic to a proapoptotic protein. Importantly, silencing of Nur77 attenuated CTD-induced apoptosis, reversed CTD-mediated cell cycle arrest and differentiation of HL-60 cells. Additionally, CTD also exhibited an antileukemic effect in NOD/SCID mice with the injection of HL-60 cells into the tail vein.

Conclusions

Our studies suggest that Nur77-mediated signaling pathway may play a critical role in the induction of apoptosis and promotion of differentiation by CTD on AML cells.

JuBei Oral Liquid Induces Mitochondria-Mediated Apoptosis in NSCLC Cells

Background

Although gefitinib brings about tremendous advances in the treatment of non-small cell lung cancer (NSCLC) harboring epidermal growth factor receptor (EGFR) mutations, most of patients become incurable due to drug resistance. JuBei oral liquid (JB) has been widely used to treat pneumonia in clinic. Components of JB were reported to induce apoptosis in NSCLC, which indicated that JB could be a potential antitumor agent for NSCLC patients. In this study, we investigated the effect of JB on gefitinib-sensitive PC-9 and gefitinib-resistant PC-9/GR, H1975 cells as well as its underlying molecular mechanisms.

Methods

PC-9, PC-9/GR and H1975 cells were treated with JB, LY294002, SCH772984, gefitinib alone or in combination. Then, cell viability, colony formation, cell death, expression of mitochondria-dependent pathway proteins, expression of EGFR, PI3K/AKT, MAPK signal pathway proteins, Bcl-2 mitochondrial translocation, ROS generation and cell apoptosis were examined by MTT, colony forming, live/dead cell staining, Western blot, immunofluorescence and flow cytometry assay.

Results

Our results showed that JB significantly induced cell growth inhibition and apoptotic cell death in PC-9, PC-9/GR and H1975 cells. JB activated mitochondria-mediated apoptotic pathway through inhibiting Bcl-2 mitochondrial translocation while inducing Bax translocated into mitochondria along with accumulated ROS production, thereby increasing the release of cytochrome c, subsequently cleaving procaspase9 into cleaved-caspase9 and then cleaving procaspase3 into cleaved-caspase3. Furthermore, the employment of protein kinase inhibitors LY294002 and SCH772984 revealed that the induction of mitochondria-mediated apoptosis by JB was reliant on inactivation of PI3K/AKT and MAPK signal pathways. Moreover, JB could synergize with gefitinib to induce apoptosis in PC-9, PC-9/GR and H1975 cells.

Conclusion

These data indicated that JB could be a potential therapeutic agent for NSCLC patients harboring EGFR mutations as well as those under gefitinib resistance.

Carotenoid metabolism in mitochondrial function

Mitochondria are highly dynamic organelles that are found in most eukaryotic organisms. It is broadly accepted that mitochondria originally evolved from prokaryotic bacteria, e.g. proteobacteria. The mitochondrion has its independent genome that encodes 37 genes, including 13 genes for oxidative phosphorylation. Accumulative evidence demonstrates that mitochondria are not only the powerhouse of the cells by supplying adenosine triphosphate, but also exert roles as signalling organelles in the cell fate and function. Numerous factors can affect mitochondria structurally and functionally. Carotenoids are a large group of fat-soluble pigments commonly found in our diets. Recently, much attention has been paid in carotenoids as dietary bioactives in mitochondrial structure and function in human health and disease, though the mechanistic research is limited. Here, we update the recent progress in mitochondrial functioning as signalling organelles in human health and disease, summarize the potential roles of carotenoids in regulation of mitochondrial redox homeostasis, biogenesis, and mitophagy, and discuss the possible approaches for future research in carotenoid regulation of mitochondrial function.

12-Deacetyl-12-epi-Scalaradial, a Scalarane Sesterterpenoid from a Marine Sponge Hippospongia sp., Induces HeLa Cells Apoptosis via MAPK/ERK Pathway and Modulates Nuclear Receptor Nur77

12-Deacetyl-12-epi-scalaradial, a scalarane sesterterpenoid from a marine sponge Hippospongia sp, has been reported to possess cytotoxic activity on HepG2, MCF-7, and HCT-116 cells. However, there is no research to indicate that 12-deacetyl-12-epi-scalaradial exhibited anticancer effect on cervical cancer HeLa cells. The aim of this study was to investigate the anticancer activity of 12-deacetyl-12-epi-scalaradial against HeLa cells and to explore the mechanism. The results from a methylthiazolyldiphenyl-tetrazolium (MTT) assay suggested that 12-deacetyl-12-epi-scalaradial suppressed the proliferation of HeLa cells and flow cytometry analysis showed 12-deacetyl-12-epi-scalaradial could induce the apoptosis of HeLa cells in dose- and time-dependent manner. Western blotting analysis demonstrated that 12-deacetyl-12-epi-scalaradial triggered apoptosis via mediating the extrinsic pathway and was found to suppress MAPK/ERK pathway which was associate with cancer cell death. Nur77, a critical number of orphan nuclear receptors, plays diverse roles in tumor development as a transcription factor and has been considered as a promising anticancer drug target. The dual-luciferase reporter assays suggested that 12-deacetyl-12-epi-scalaradial could selectively enhance the trans-activation activity of Nur77. Furthermore, Western blotting analysis and fluorescence quenching showed that 12-deacetyl-12-epi-scalaradial could induce the phosphorylation of Nur77 and interact with the ligand-binding domain (LBD) of Nur77. Our research confirmed 12-deacetyl-12-epi-scalaradial as a potential agent for cervical cancer therapy and provided a view that 12-deacetyl-12-epi-scalaradial may be a modulator of Nur77.

Absence of Cytosolic 2-Cys Prx Subtypes I and II Exacerbates TNF-α-Induced Apoptosis via Different Routes

There are abundant peroxiredoxin (Prx) enzymes, but an increase of cellular H₂O₂ level always happens in apoptotic cells. Here, we show that cellular H₂O₂ switches different apoptosis pathways depending on which type of Prx enzyme is absent. TNF-α-induced H₂O₂ burst preferentially activates the DNA damage-dependent apoptosis pathway in the absence of PrxI. By contrast, the same H₂O₂ burst stimulates the RIPK1-dependent apoptosis pathway in the absence of PrxII by inducing the destruction of cIAP1 in caveolar membrane. Specifically, H₂O₂ induces the oxidation of Cys308 residue in the cIAP1-BIR3 domain, which induces the dimerization-dependent E3 ligase activation. Thus, the reduction in cIAP level by the absence of PrxII triggers cell-autonomous apoptosis in cancer cells and tumors. Such differential functions of PrxI and PrxII are mediated by interaction with H2AX and cIAP1, respectively. Collectively, this study reveals the distinct switch roles of 2-Cys Prx isoforms in apoptosis signaling.

Cigarette smoke downregulates Nur77 to exacerbate inflammation in chronic obstructive pulmonary disease (COPD)

Cigarette smoke (CS) contains multiple gaseous and particulate materials that can cause lung inflammation, and smoking is the major cause of chronic obstructive pulmonary disease (COPD). We sought to determine the mechanisms of how CS triggers lung inflammation. Nur77, a nuclear hormone receptor belonging to the immediate-early response gene family, controls inflammatory responses, mainly by suppressing the NF-κB signaling pathway. Because it is unknown if Nur77's anti-inflammatory role modulates COPD, we assessed if and how Nur77 expression and activity are altered in CS-induced airway inflammation. In lung tissues and bronchial epithelial cells from COPD patients, we found Nur77 was downregulated. In a murine model of CS-induced airway inflammation, CS promoted lung inflammation and also reduced Nur77 activity in wild type (WT) mice, whereas lungs of Nur77-deficient mice showed exaggerated CS-induced inflammatory responses. Our findings in in vitro studies of human airway epithelial cells complemented those in vivo data in mice, together showing that CS induced threonine-phosphorylation of Nur77, which is known to interfere with its anti-inflammatory functions. In summary, our findings point to Nur77 as an important regulator of CS-induced inflammatory responses and support the potential benefits of Nur77 activation for COPD treatment.

Gastric Cancer Stem Cells: Current Insights into the Immune Microenvironment and Therapeutic Targets

Gastric cancer (GC) is a leading cause of cancer-related death worldwide. Cancer stem cells (CSCs) are known to be involved in chemotherapy resistance and the development of metastases. Although CSCs harbor self-renewal and tumorigenic abilities, the immune microenvironment surrounding CSCs provides various factors and supports the maintenance of CSC properties. The current review summarizes the accumulating findings regarding the relationship between the immune microenvironment and gastric CSCs (GCSCs), which will support the possibility of developing novel therapeutic strategies for targeting GCSCs.

Role of the Orphan Nuclear Receptor NR4A Family in T-Cell Biology

The nuclear orphan receptors NR4A1, NR4A2, and NR4A3 are immediate early genes that are induced by various signals. They act as transcription factors and their activity is not regulated by ligand binding and are thus regulated via their expression levels. Their expression is transiently induced in T cells by triggering of the T cell receptor following antigen recognition during both thymic differentiation and peripheral T cell responses. In this review, we will discuss how NR4A family members impact different aspects of the life of a T cell from thymic differentiation to peripheral response against infections and cancer.

Unorthodox Transcriptional Mechanisms of Lipid-Sensing Nuclear Receptors in Macrophages: Are We Opening a New Chapter?

Work over the past 30 years has shown that lipid-activated nuclear receptors form a bridge between metabolism and immunity integrating metabolic and inflammatory signaling in innate immune cells. Ligand-induced direct transcriptional activation and protein-protein interaction-based transrepression were identified as the most common mechanisms of liganded-nuclear receptor-mediated transcriptional regulation. However, the integration of different next-generation sequencing-based methodologies including chromatin immunoprecipitation followed by sequencing and global run-on sequencing allowed to investigate the DNA binding and ligand responsiveness of nuclear receptors at the whole-genome level. Surprisingly, these studies have raised the notion that a major portion of lipid-sensing nuclear receptor cistromes are not necessarily responsive to ligand activation. Although the biological role of the ligand insensitive portion of nuclear receptor cistromes is largely unknown, recent findings indicate that they may play roles in the organization of chromatin structure, in the regulation of transcriptional memory, and the epigenomic modification of responsiveness to other microenvironmental signals in macrophages. In this review, we will provide an overview and discuss recent advances of our understanding of lipid-activated nuclear receptor-mediated non-classical or unorthodox actions in macrophages.

Coadministration of kla peptide with HPRP-A1 to enhance anticancer activity

The apoptosis-inducing peptide kla (KLAKLAK)2 possesses the ability to disrupt mitochondrial membranes and induce cancer cell apoptosis, but this peptide has a poor eukaryotic cell-penetrating potential. Thus, it requires the assistance of other peptides for effective translocation at micromolar concentrations. In this study, breast and lung cancer cells were treated by kla peptide co-administrated with membrane-active anticancer peptide HPRP-A1. HPRP-A1 assisted kla to enter cancer cells and localized on mitochondrial membranes to result in cytochrome C releasing and mitochondrial depolarization which ultimately induced apoptosis.The apoptosis rate was up to 65%and 45% on MCF-7 and A549 cell lines, respectively, induced by HPRP-A1 coadministration with kla group. The breast cancer model was constructed in mice, and the anticancer peptides were injected to observe the changes in cancer volume, andimmunohistochemical analysis was performed on the tissues and organs after the drug was administered. Both the weight and volume of tumor tissue were remarkable lower in HPRP-A1 with kla group compared with thosepeptidealonggroups. The results showed that the combined drug group effectively inhibited the growth of cancer and did not cause toxic damage to normal tissues, as well as exhibited significantly improvement on peptide anticancer activity in vitro and in vivo.

Fenretinide-induced Apoptosis of Acute Myeloid Leukemia Cells via NR4A1 Translocation into Mitochondria and Bcl-2 Transformation

OBJECTIVE: Fenretinide is reported to induce NR4A1-associated apoptosis in several types of cancer cells. However, it remains unclear about its specific role and the underlying mechanism in acute myeloid leukemia (AML). Therefore, this study aimed to explore the role and mechanism of fenretinide-induced apoptosis in AML.

METHOD: Firstly, the NR4A1 mRNA level in the newly diagnosed AML patients was measured, then AML cells were treated with fenretinide at various time points and doses, and cell viability was investigated by using the cell-counting kit-8 (CCK-8) assay. Additionally, apoptosis and cell cycles were analyzed by using flow cytometry. Moreover, siNR4A1 was utilized to knockdown NR4A1 expression, and leptomycin B (LMB) was adopted to inhibit the nuclear export; afterwards, the apoptosis rate and expression of apoptotic proteins in AML cells were detected. In addition, the expression levels of NR4A1 in the nuclei and mitochondria of fenretinide-treated AML cells were also measured. Meanwhile, the interaction between NR4A1 and Bcl-2, as well as the Bcl-2 transformation, was also examined. The anti-leukemic effect of fenretinide on NOD/SCID mice was also determined through subcutaneous injection of HL-60 cells.

RESULTS: NR4A1 expression in AML patients was markedly down-regulated compared with that in normal donors. Fenretinide induced the expression of NR4A1 and mitochondria-mediated apoptotic pathway-associated proteins in a time- and concentration-dependent manner. Importantly, both siNR4A1 alone or the combination of fenretinide with LMB could attenuate the fenretinide-induced apoptosis and expression of apoptotic proteins. Under the action of fenretinide, the NR4A1 protein expression was down-regulated in nuclear extracts whereas up-regulated in mitochondrial extracts. At the same time, fenretinide promoted NR4A1 translocation from nuclei into mitochondria, and enhanced the interaction between NR4A1 and Bcl-2, thereby exposing the BH3 domain of Bcl-2 to exert the anti-apoptotic effect. Moreover, fenretinide also exhibited an anti-leukemic effect and induced NR4A1 expression in the AML mouse model.

CONCLUSIONS: Fenretinide exerts an obvious effect on AML cells both in vitro and in vivo. Besides, the NR4A1-mediated signaling pathway is highly involved in the fenretinide-induced apoptosis of AML cells.

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

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

Macroporous organosilicon nanocomposites co-deliver Bcl2-converting peptide and chemotherapeutic agent for synergistic treatment against multidrug resistant cancer

Therapeutic biomacromolecules are confronted with in vivo challenges of low bio-stability and poor tumor tissue-penetration. Herein, we report for the first time, our development and characterization of a hybrid nanocomposite for delivering a Bcl-2-converting peptide (NuBCP9, N9 hereafter) and testing its efficacy alone or together with doxorubicin (DOX). The hybrid nanocomposite is composed of the internal large pore sized-mesoporous silica nanoparticles (MSNs) and the external highly-branched polyamidoamine (PAMAM) dendrimers, into which N9 peptide and DOX were encapsulated for the different sub-cellular delivery to treat drug-resistant cancer. The nanocomposite possessed the particle and pore sizes of ~37 nm and ~8 nm, which displayed the superior tumor penetration capacity over naked MSNs both in cultured-3D tumor sphere and in live animal models. Moreover, the dual drug nanocomposite exhibited a great synergistic anticancer effect on Bcl-2-positive cancer cells in vitro and animals with the negligible toxic side effects. The tumor inhibition rate of the nanocomposite (89%) was five times as much as the two drugs combination. This design provides a new effective, safe and versatile strategy to fabricate large pore-sized MSNs with the organic-inorganic hybrid framework to concurrently transport therapeutic peptides and chemotherapeutics to the specific sub-cellular locations for the synergistic cancer therapy and drug resistance reversal, which has significant impact on the development of improved cancer therapeutics.

Targeted photoredox catalysis in cancer cells

Hypoxic tumours are a major problem for cancer photodynamic therapy. Here, we show that photoredox catalysis can provide an oxygen-independent mechanism of action to combat this problem. We have designed a highly oxidative Ir(III) photocatalyst, [Ir(ttpy)(pq)Cl]PF₆ ([1]PF₆, where 'ttpy' represents 4'-(p-tolyl)-2,2':6',2''-terpyridine and 'pq' represents 3-phenylisoquinoline), which is phototoxic towards both normoxic and hypoxic cancer cells. Complex 1 photocatalytically oxidizes 1,4-dihydronicotinamide adenine dinucleotide (NADH)-an important coenzyme in living cells-generating NAD^• radicals with a high turnover frequency in biological media. Moreover, complex 1 and NADH synergistically photoreduce cytochrome c under hypoxia. Density functional theory calculations reveal π stacking in adducts of complex 1 and NADH, facilitating photoinduced single-electron transfer. In cancer cells, complex 1 localizes in mitochondria and disrupts electron transport via NADH photocatalysis. On light irradiation, complex 1 induces NADH depletion, intracellular redox imbalance and immunogenic apoptotic cancer cell death. This photocatalytic redox imbalance strategy offers a new approach for efficient cancer phototherapy.

The orphan nuclear receptor NUR77 promotes trophoblast invasion at early pregnancy through paracrine placental growth factor

NR4A1 (NUR77) is an orphan nuclear receptor that has been implicated in both cell survival and apoptosis. However, the role of NUR77 in trophoblast function during early placenta development has not been fully elucidated. In this study, we showed that NUR77 expression was significantly lower in the villi of the recurrent miscarriage (RM) group compared to that in the healthy controls (HCs) group. We used immunohistochemistry and found that NUR77 was highly expressed in human placental villi during early pregnancy, especially in syncytiotrophoblast (STB), and was expressed at a much lower level in STB from the RM group than in those from HC group. Western blotting data further confirmed that NUR77 was highly expressed in primary human term placental STB and the FSK-induced BeWo cell line. Moreover, antibody array screening and ELISA revealed that NUR77 promoted significant placental growth factor (PGF) expression during trophoblast fusion. Ectopic overexpression and knockdown experiments demonstrated that PGF was a novel downstream target of NUR77, and serum PGF expression correlated positively with trophoblast NUR77 mRNA levels in HCs and RM patients. Importantly, bioinformatics analysis identified two NUR77 binding sites in the PGF promoter region, and chromatin immunoprecipitation (ChIP) coupled with Western blotting analysis further verified that NUR77 bound directly to the PGF promoter region and promoted PGF expression. Furthermore, in a BeWo/HTR-8 co-culture system, FSK-induced BeWo-secreted PGF promoted HTR-8 cell migration and invasion, and an anti-PGF antibody reversed this effect. Collectively, these results indicated that NUR77 may play a key role in regulating trophoblast invasion at early pregnancy. KEY MESSAGES: NUR77 expression was significantly decreased in the syncytiotrophoblast of the recurrent miscarriage group compared to that in the healthy control group. NUR77 promoted PGF expression during trophoblast fusion. ChIP and western blotting experiments verified that NUR77 bound directly to the PGF promoter region and activated PGF expression in trophoblast. Trophoblast-derived PGF promoted HTR-8 cell migration and invasion in a cell co-culture system.

Nuclear receptor 4A1 (NR4A1) antagonists induce ROS-dependent inhibition of mTOR signaling in endometrial cancer

OBJECTIVES

NR4A1 is overexpressed in many solid tumors, and the objectives of this study were to investigate the expression and functional role of this receptor in endometrial cancer cells and demonstrate that NR4A1 antagonist inhibit mTOR.

METHODS

Ishikawa and Hec-1B endometrial cells were used as models to investigate the parallel effects of NR4A1 knockdown by RNA interference (siNR4A1) and treatment with bis-indole-derived NR4A1 ligands (antagonists) on cell growth and survival by determining cell numbers and effects on Annexin V staining. Western blot analysis of whole cell lysates was used to determine effects of these treatments on expression of growth promoting, survival and apoptotic genes and mTOR signaling. Effects of NR4A1 antagonists on tumor growth were determined in athymic nude mice bearing Hec-1B cells as xenografts.

RESULTS

siNR4A1 or treatment with bis-indole-derived NR4A1 antagonists inhibited growth of endometrial cancer cells in vitro and endometrial tumors in vivo and this was accompanied by decreased expression of growth promoting and survival genes and mTOR inhibition.

CONCLUSIONS

NR4A1 exhibited pro-oncogenic activity in endometrial cells due, in part, to regulation of cell growth, survival and mTOR signaling, and all of these pathways and their associated gene products were inhibited after treatment with bis-indole-derived NR4A1 antagonists. Moreover, these compounds also blocked endometrial tumor growth in vivo demonstrating that NR4A1 is a potential novel drug target for treatment of endometrial cancer.

Photostimulation and thermotaxis of sperm: Overview and practical implications in porcine reproduction

The journey of mammalian sperm through the female genital tract requires the existence of a myriad of mechanisms that allow cells to reach the oviduct in a timely manner from the place of semen deposition. Several biochemical mechanisms such as signaling through molecules like bicarbonate, neurotransmitters or even glycosaminoglycanes are known and have been studied by several relevant groups worldwide. However, biophysical mechanisms for sperm transport are much less studied and understood. Thermotaxis, for example, is a powerful, physical signaling system that is known to direct sperm inside the female genital tract, although the intimate mechanisms by which this effect is launched are yet to be elucidated. This review is focuses on the analysis of thermotaxis and its possible relationship with another phenomenon that has been observed in sperm from a variety of species, namely photostimulation. An overall review on sperm thermotaxis and putative mechanism/s that can be involved in this phenomenon is developed, followed by a description of the most recent findings on the mechanisms underlying sperm photostimulation, highlighting its possible relationship with thermotactic mechanisms. Finally, an overview regarding some practical implications of the phototactic/thermotactic phenomenon has been included in order to evaluate the possible use of techniques based on these phenomena as tools for improving pig reproduction.

Oncogenic potential of truncated RXRα during colitis-associated colorectal tumorigenesis by promoting IL-6-STAT3 signaling

Retinoid X receptor-alpha (RXRα) is a potent regulator of inflammatory responses; however, its therapeutic potential for inflammatory cancer remains to be explored. We previously discovered that RXRα is abnormally cleaved in tumor cells and tissues, producing a truncated RXRα (tRXRα). Here, we show that transgenic expression of tRXRα in mice accelerates the development of colitis-associated colon cancer (CAC). The tumorigenic effect of tRXRα is primarily dependent on its expression in myeloid cells, which results in interleukin-6 (IL-6) induction and STAT3 activation. Mechanistic studies reveal an extensive interaction between tRXRα and TRAF6 in the cytoplasm of macrophages, leading to TRAF6 ubiquitination and subsequent activation of the NF-κB inflammatory pathway. K-80003, a tRXRα modulator derived from nonsteroidal anti-inflammatory drug (NSAID) sulindac, suppresses the growth of tRXRα-mediated colorectal tumor by inhibiting the NF-κB-IL-6-STAT3 signaling cascade. These results provide new insight into tRXRα action and identify a promising tRXRα ligand for treating CAC.

BI1071, a Novel Nur77 Modulator, Induces Apoptosis of Cancer Cells by Activating the Nur77-Bcl-2 Apoptotic Pathway

Nur77 (also called TR3 or NGFI-B), an orphan member of the nuclear receptor superfamily, induces apoptosis by translocating to mitochondria where it interacts with Bcl-2 to convert Bcl-2 from an antiapoptotic to a pro-apoptotic molecule. Nur77 posttranslational modification such as phosphorylation has been shown to induce Nur77 translocation from the nucleus to mitochondria. However, small molecules that can bind directly to Nur77 to trigger its mitochondrial localization and Bcl-2 interaction remain to be explored. Here, we report our identification and characterization of DIM-C-pPhCF₃ ⁺MeSO₃ ^- (BI1071), an oxidized product derived from indole-3-carbinol metabolite, as a modulator of the Nur77-Bcl-2 apoptotic pathway. BI1071 binds Nur77 with high affinity, promotes Nur77 mitochondrial targeting and interaction with Bcl-2, and effectively induces apoptosis of cancer cells in a Nur77- and Bcl-2-dependent manner. Studies with animal model showed that BI1071 potently inhibited the growth of tumor cells in animals through its induction of apoptosis. Our results identify BI1071 as a novel Nur77-binding modulator of the Nur77-Bcl-2 apoptotic pathway, which may serve as a promising lead for treating cancers with overexpression of Bcl-2.

ISG12a and its interaction partner NR4A1 are involved in TRAIL-induced apoptosis in hepatoma cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) can induce apoptosis in cancer cells while sparing normal cells, thereby leading to the development of TRAIL receptor agonists for cancer treatment. However, these agonist-based therapeutics exhibit little clinical benefits due to the lack of biomarkers to predict whether patients are responsive to the treatment, as well as determine the resistance of cancer cells to TRAIL-based agonists. Our previous study has demonstrated that ISG12a enhances TRAIL-induced apoptosis and might serve as a biomarker to predict the TRAIL response. The downstream mechanism by which ISG12a augments TRAIL-induced apoptosis remains to be elucidated. In this study, we found that ISG12a was localized in the mitochondria and nucleus and augmented TRAIL-induced apoptosis through intrinsic apoptotic pathway. In addition, ISG12a interacted with NR4A1 and promoted its nuclear-to-cytoplasm translocation. Upon translocate to cytoplasm, NR4A1 targeted mitochondria and induced Bcl2 conformational change, thereby exposing its BH3 domain. Moreover, TRAIL treatment can induce NR4A1 expression through the activation of NF-κB in TRAIL-resistant Huh7 hepatoma cells. Knockdown of NR4A1 could overcome TRAIL resistance. However, in TRAIL-sensitive LH86 liver cancer cells, TRAIL activated the Jun N-terminal kinases signalling pathway. Overall, these results showed that both ISG12a and its interaction partner NR4A1 are involved in TRAIL-mediated apoptosis in hepatoma cells.

Design and synthesis of biotinylated cardiac glycosides for probing Nur77 protein inducting pathway

The orphan nuclear receptor Nur77 (also known as TR3 or nerve growth factor-induced clone B NGFI-B) functions as a nuclear transcription factor in the regulation of target gene expression and plays a critical role in the regulation of differentiation, proliferation, apoptosis, and survival of many different cell types. Recent studies demonstrate that Nur77 also involves many important physiological and pathological processes including cancer, inflammation and immunity, cardiovascular diseases, and bone diseases. Our previous studies showed that cardiac glycosides could induce the expression of Nur77 protein and its translocation from the nucleus to the cytoplasm and subsequent targeting to mitochondria, leading to apoptosis of cancer cells. In order to probe the Nur77 protein inducting pathway, we designed and synthesized a series of novel biotinylated cardiac glycosides from β-Antiarin and α-Antiarin, two typical cardiac glycosides from the plant of Antiaris toxicaria. The induction of Nur77 protein expression of these biotinylated cardiac glycosides and their inhibitory effects on NIH-H460 cancer cell proliferation were evaluated. Results displayed that some biotinylated cardiac glycosides could significantly induce the expression of Nur77 protein comparable with their parent compounds β-Antiarin and α-Antiarin. Also, their streptavidin binding activities were evaluated. Among them, biotinylated cardiac glycosides P4b and P5a exhibited significant effect on the induction of Nur77 expression along with high binding capacity with streptavidin, suggesting that they can be used as probes for probing Nur77 protein inducting pathway.

Mitochondrial targeting of TR3 is involved in TPA induced apoptosis in breast cancer cells

TPA is considered to be a tumor promoting molecule that induces the expression of COX-2 protein. However, it is contradictory to find that TPA can induce tumor cell apoptosis and exert antitumor activity. Therefore, the role of TPA in tumorigenesis and development has not yet been elucidated. Here we show that TPA can promote the apoptosis of breast cancer cells and increase the ratio of Bax/Bcl-2. It is suggested that TPA may induce apoptosis of breast cancer cells through mitochondrial apoptosis pathway. Further studies showed that TPA could cause mitochondrial dysfunction and trigger mitochondrial apoptotic pathway. In mechanism, the mitochondrial targeting of TR3 is involved in TPA induced apoptosis in breast cancer cells. In conclusion, our findings suggest that TPA can play a role in inhibiting cancer by inducing apoptosis and TR3 is expected to be a new target for cancer treatment.

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.

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.

Cytoplasmic location of NR4A1 in aggressive lymphomas is associated with a favourable cancer specific survival

The nuclear orphan receptor NR4A1 functions as tumour suppressor in aggressive lymphomas by pro-apoptotic genomic and non-genomic effects. Here, we immunohistochemically studied the clinico-pathological relevance of NR4A1 protein expression patterns in a cohort of 60 diffuse large B cell lymphoma (DLBCL) patients and non-neoplastic lymph nodes. We observed a significant association between high cytoplasmic NR4A1 and favourable cancer-specific survival and the germinal centre B cell-like subtype, respectively. Moreover, the percentage of lymphoma cells exhibiting cytoplasmic NR4A1 significantly correlated to those showing cleaved caspase 3. Complementary, functional profiling using gene set enrichment of Reactome pathways based on publicly available microarray data was applied to determine pathways potentially implicated in cytoplasmic localization of NR4A1 and validated by means of semi quantitative real-time PCR. The pathway analysis revealed changes in the ERK1/2 pathway, and this was corroborated by the finding that high cytoplasmic NR4A1 was associated with higher expression of ERK1/2 targets in our cohort. These data indicate that high cytoplasmic NR4A1 is associated with a favourable lymphoma-specific survival and highlights the importance of NR4A1 expression patterns as potential prognostic marker for risk assessment in aggressive lymphomas.

Nur77 is a promoting factor in traumatic brain injury-induced nerve cell apoptosis

Traumatic brain injury (TBI) poses a serious threat to human health. TBI has a high mortality rate, resulting in a great burden on the affected individual's family as well as society as a whole. The incidence of craniocerebral fractures continues to rise as both the economy and transportation options grow, making it imperative that the mortality and disability rate of craniocerebral trauma be reduced. Nur77 is a transcription factor of the nuclear receptor superfamily. Following stimulation of extracellular apoptosis, Nur77 is involved in a variety of diseases as a powerful pro-apoptotic molecule. Here, we determined the effect and mechanism of Nur77 in TBI-induced nerve cell apoptosis in vitro and in vivo. We found that Nur77 and Bcl-2 protein expression increased as nerve cell apoptosis increased in TBI tissues. Furthermore, inhibition of Nur77 improved nerve cell injury by regulation of Bcl-2 and downstream pathways in vitro and in vivo.

The mitochondrial DNA copy number, cytochrome c oxidase activity and reactive oxygen species level in metaphase II oocytes obtained from in vitro culture of cryopreserved ovarian tissue in comparison with in vivo-obtained oocyte

AIM

To evaluate the mitochondrial DNA (mtDNA) copy number, reactive oxygen species (ROS) level and intensity of mitochondrial enzyme activity in metaphase II oocytes derived from vitrified cultured immature mouse ovarian tissue in comparison with nonvitrified group and in vivo-obtained oocytes.

METHODS

Vitrified and nonvitrified ovaries from neonate female mice were cultured for 7 days. Then, preantral follicles were isolated and cultured in a three-dimensional culture system. Follicular development and oocyte maturation were evaluated and compared in both groups. Some of the collected metaphase II oocytes derived from in vitro and in vivo conditions were inseminated with capacitated spermatozoa, and then, the fertilization and embryo developmental rates were assessed. In the other series of oocytes, mtDNA copy number, distribution and enzyme activity and ROS level were analyzed.

RESULTS

The embryo development, mtDNA copy number and mitochondrial enzyme activity in collected metaphase II oocytes from two in vitro-cultured groups were significantly lower, and the ROS level was higher than those of the in vivo group (P < 0.05), but there was no significant difference between vitrified and nonvitrified groups.

CONCLUSION

This study showed that a two-step in vitro culture of mouse ovarian tissue decreased the mtDNA copy number and cytochrome c oxidase activity of metaphase II oocytes through an increase in their ROS level in comparison with in vivo-obtained oocytes. Thus, the in vitro culture methods should be improved.

Induction of apoptosis and suppression of tumor growth by Nur77-derived Bcl-2 converting peptide in chemoresistant lung cancer cells

Resistance to chemotherapy is a major cause of treatment failure and poor overall survival in patients with lung cancer. Identification of molecular targets present in resistant cancer cells is essential for addressing therapeutic resistance and prolonging lung cancer patient survival. Members of the B-cell lymphoma 2 (Bcl-2) family of proteins are associated with chemotherapeutic resistance. In this study, we found that pro-survival protein Bcl-2 is upregulated in paclitaxel resistant cells, potentially contributing to chemotherapy resistance. To exploit the increase in Bcl-2 expression for targeting therapy resistance, we investigated the effects of a peptide derived from the nuclear receptor Nur77 that converts Bcl-2 from an anti-apoptotic protein to a pro-apoptotic protein. The Nur77 derived peptide preferentially induced apoptosis in paclitaxel-resistant cancer cells with high expression of Bcl-2. This peptide also induced apoptosis of multidrug resistant H69AR lung cancer cells that express Bcl-2 and inhibited their growth in 3D spheroids. The Nur77 peptide strongly suppressed the growth of paclitaxel-resistant lung cancer cells in a zebrafish xenograft tumor model. Taken together, our data supports a new strategy for treating lung cancers that acquire resistance to chemotherapy through overexpression of Bcl-2.

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.

Moving nuclear receptor Nur77 to damaged mitochondria for clearance by mitophagy

Selective clearance of damaged mitochondria can reverse pathological status in chronic inflammatory diseases. We recently identified a critical role of nuclear receptor Nur77 and celastrol in priming inflamed mitochondria for autophagy through its mitochondrial targeting and interaction with tumor necrosis factor receptor-associated factor 2 (TRAF2) and the autophagic adaptor p62/SQSTM1.

B cell lymphoma 2 (Bcl-2) residues essential for Bcl-2's apoptosis-inducing interaction with Nur77/Nor-1 orphan steroid receptors

Apoptosis is mediated through the extrinsic or intrinsic pathway. Key regulators of the intrinsic apoptotic pathway are the family of B cell lymphoma 2 (Bcl-2) proteins. The activity of the prototypical Bcl-2 protein is usually considered antiapoptotic. However, under some conditions, Bcl-2 associates with the orphan nuclear hormone receptors Nur77 and Nor-1, converting Bcl-2 into a proapoptotic molecule. Expression of Nur77 and Nor-1 is induced by a variety of signals, including those leading to apoptosis. Translocation of Nur77/Nor-1 to mitochondria results in their association with Bcl-2, exposing the Bcl-2 homology (BH) 3 domain and causing apoptosis. However, the molecular details of this interaction are incompletely understood. Here, through extensive Bcl-2 mutagenesis and functional assays, we identified residues within Bcl-2 that are essential for its interaction with Nur77/Nor-1. Although an initial report has suggested that an unstructured loop region between the Bcl-2 BH4 and BH3 domains is required for Bcl-2's interaction with Nur77/Nor-1, we found that it is dispensable for this interaction. Instead, we found important interacting residues at the BH4 domain and crucial interacting residues between the BH1 and BH2 domains. Bcl-2 alanine mutants at this region could no longer interact with Nur77/Nor-1 and could not initiate Nur77/Bcl-2-mediated cell death. However, they still retained their anti-apoptotic capability in two different death assays. These results establish crucial residues in Bcl-2 required for Nur77/Nor-1-mediated apoptosis and point to potential new strategies for manipulating Bcl-2 function.

Nr4a1 plays a crucial modulatory role in Th1/Th17 cell responses and CNS autoimmunity

Nuclear receptor4 group A1 (Nr4a1), an orphan nuclear receptor, is down-regulated in peripheral blood mononuclear cells (MNCs) of individuals with multiple sclerosis (MS), and Nr4a1 deficiency results in severe experimental autoimmune encephalomyelitis (EAE), an animal model of MS, caused by increased macrophage infiltration into the central nervous system (CNS). However, the role of Nr4a1 in macrophage phenotype and T cell responses remains poorly understood. In the present study we show that macrophages/microglia of Nr4a1^-/- mice, which exhibited earlier onset and more severe clinical EAE, were polarized to an enhanced type 1 (M1) phenotype and produced higher levels of IL-12 and TNF-α than wild type mice. Significantly increased numbers of CD4⁺ T cells and frequency of CD4⁺IFN-γ⁺ and CD4⁺IL-17⁺ T cells were observed in the CNS and spleen of Nr4a1^-/- mice, with decreased percentages of apoptosis in CD4⁺ T cells. The percentages of CD4⁺Foxp3⁺ Treg cells in the CNS of Nr4a1^-/- mice were also reduced. Furthermore, purified CD4⁺ T cells from naïve Nr4a1^-/- mice exhibited enhanced Th1 and Th17 differentiation capacity, and MOG-reactive Th17 cells from Nr4a1^-/- mice adoptively transferred more severe EAE in recipient mice. Our results, for the first time, demonstrate that Nr4a1 not only induces Type 2 macrophages/microglia phenotype, but is also a critical inhibitory molecule for Th1/Th17 cell differentiation. This finding indicates that Nr4a1-related molecule(s) may have therapeutic potential in MS and likely other autoimmune disorders.

Characterization of the Giardia intestinalis secretome during interaction with human intestinal epithelial cells: The impact on host cells

BACKGROUND

Giardia intestinalis is a non-invasive protozoan parasite that causes giardiasis in humans, the most common form of parasite-induced diarrhea. Disease mechanisms are not completely defined and very few virulence factors are known.

METHODOLOGY

To identify putative virulence factors and elucidate mechanistic pathways leading to disease, we have used proteomics to identify the major excretory-secretory products (ESPs) when Giardia trophozoites of WB and GS isolates (assemblages A and B, respectively) interact with intestinal epithelial cells (IECs) in vitro.

FINDINGS

The main parts of the IEC and parasite secretomes are constitutively released proteins, the majority of which are associated with metabolism but several proteins are released in response to their interaction (87 and 41 WB and GS proteins, respectively, 76 and 45 human proteins in response to the respective isolates). In parasitized IECs, the secretome profile indicated effects on the cell actin cytoskeleton and the induction of immune responses whereas that of Giardia showed anti-oxidation, proteolysis (protease-associated) and induction of encystation responses. The Giardia secretome also contained immunodominant and glycosylated proteins as well as new candidate virulence factors and assemblage-specific differences were identified. A minor part of Giardia ESPs had signal peptides (29% for both isolates) and extracellular vesicles were detected in the ESPs fractions, suggesting alternative secretory pathways. Microscopic analyses showed ESPs binding to IECs and partial internalization. Parasite ESPs reduced ERK1/2 and P38 phosphorylation and NF-κB nuclear translocation. Giardia ESPs altered gene expression in IECs, with a transcriptional profile indicating recruitment of immune cells via chemokines, disturbances in glucose homeostasis, cholesterol and lipid metabolism, cell cycle and induction of apoptosis.

CONCLUSIONS

This is the first study identifying Giardia ESPs and evaluating their effects on IECs. It highlights the importance of host and parasite ESPs during interactions and reveals the intricate cellular responses that can explain disease mechanisms and attenuated inflammatory responses during giardiasis.

Inactivation of the orphan nuclear receptor NR4A1 contributes to apoptosis induction by fangchinoline in pancreatic cancer cells

Previous studies have demonstrated that the orphan nuclear receptor NR4A1 is overexpressed in human pancreatic cancer and antagonizing this receptor promotes apoptosis and inhibits pancreatic cancer cells and tumor growth. In the present study, we identified fangchinoline, a bisbenzyltetrahydroisoquinoline alkaloid from Stephania tetrandra, as a new inactivator of nuclear NR4A1 and demonstrated that fangchinoline inhibits cell proliferation and induces apoptosis, in part, via the NR4A1-dependent pro-apoptotic pathways in human pancreatic cancer cells. It decreased expression of the antiapoptotic protein survivin by inhibiting Sp1-mediated transcription and induced oxidative stress-mediated endoplasmic reticulum (ER) stress in pancreatic cancer cells. These results suggest that inhibition of NR4A1-mediated transcriptional activity was involved in the anticancer effects of fangchinoline, and fangchinoline represents a novel class of mechanism-based anticancer agents targeting NR4A1 that is overexpressed in pancreatic cancer.

Celastrol-Induced Nur77 Interaction with TRAF2 Alleviates Inflammation by Promoting Mitochondrial Ubiquitination and Autophagy

Mitochondria play an integral role in cell death, autophagy, immunity, and inflammation. We previously showed that Nur77, an orphan nuclear receptor, induces apoptosis by targeting mitochondria. Here, we report that celastrol, a potent anti-inflammatory pentacyclic triterpene, binds Nur77 to inhibit inflammation and induce autophagy in a Nur77-dependent manner. Celastrol promotes Nur77 translocation from the nucleus to mitochondria, where it interacts with tumor necrosis factor receptor-associated factor 2 (TRAF2), a scaffold protein and E3 ubiquitin ligase important for inflammatory signaling. The interaction is mediated by an LxxLL motif in TRAF2 and results not only in the inhibition of TRAF2 ubiquitination but also in Lys63-linked Nur77 ubiquitination. Under inflammatory conditions, ubiquitinated Nur77 resides at mitochondria, rendering them sensitive to autophagy, an event involving Nur77 interaction with p62/SQSTM1. Together, our results identify Nur77 as a critical intracellular target for celastrol and unravel a mechanism of Nur77-dependent clearance of inflamed mitochondria to alleviate inflammation.

Ginsenoside 20(S)-Rh2 Induces Apoptosis and Differentiation of Acute Myeloid Leukemia Cells: Role of Orphan Nuclear Receptor Nur77

Ginsenoside 20(S)-Rh2 has been shown to induce apoptosis and differentiation of acute myeloid leukemia (AML) cells. However, the underlying molecular mechanisms are not fully understood. In our study, 20(S)-Rh2 induced the expression of orphan nuclear receptor Nur77 and death receptor proteins Fas, FasL, DR5, and TRAIL, as well as the cleavage of caspase 8 and caspase 3 in HL-60 cells. Importantly, shNur77 attenuated 20(S)-Rh2-induced apoptosis and Fas and DR5 expression. Meanwhile, 20(S)-Rh2 promoted Nur77 translocation from the nucleus to mitochondria and enhanced the interaction between Nur77 and Bcl-2, resulting in the exposure of the BH3 domain of Bcl-2 and activation of Bax. Furthermore, 20(S)-Rh2 promoted the differentiation of HL-60 cells as evidenced by Wright-Giemsa staining, NBT reduction assay, and detection of the myeloid differentiation marker CD11b by flow cytometry. Notably, shNur77 reversed 20(S)-Rh2-mediated HL-60 differentiation. Additionally, 20(S)-Rh2 also exhibited an antileukemic effect and induced Nur77 expression in NOD/SCID mice with the injection of HL-60 cells into the tail vein. Together, our studies suggest that the Nur77-mediated signaling pathway is highly involved in 20(S)-Rh2-induced apoptosis and differentiation of AML cells.

Synthesis and biological evaluation of novel aliphatic acid-conjugated antimicrobial peptides as potential agents with anti-tumor, multidrug resistance-reversing activity and enhanced stability

Compared with traditional anti-tumor drugs, antimicrobial peptides as novel anti-tumor agents have prominent advantages of higher specificity and circumvention of multi-drug resistance. BP100 is a multifunctional membrane-active peptide with high antimicrobial activity. Taking BP100 as a lead peptide, we designed and synthesized a series of aliphatic chain-conjugated peptides through solid-phase synthesis. Biological evaluation revealed that these peptides exhibited better anti-cancer activity than BP100. Further investigations revealed that these peptides could disrupt the cell membrane and trigger the cytochrome C release into cytoplasm, which ultimately resulted in apoptosis. Meanwhile, these peptides also exhibited effective anti-tumor activity against multidrug resistant cells and had multidrug resistance-reversing effect. Additionally, conjugation of aliphatic acid to those peptides could enhance their stability in plasma. In conclusion, aliphatic acid-modified peptides might be promising anti-tumor agents for cancer therapy.

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.

Modulation of the Nur77-Bcl-2 apoptotic pathway by p38α MAPK

Orphan nuclear receptor Nur77 promotes apoptosis by targeting mitochondria through interaction with Bcl-2, an event that converts Bcl-2 from a survival to killer. However, how the Nur77-Bcl-2 apoptotic pathway is regulated remains largely unknown. In this study, we examined the regulation of the Nur77-Bcl-2 pathway by CCE9, a xanthone compound. Our results demonstrated that the apoptotic effect of CCE9 depended on its induction of Nur77 expression, cytoplasmic localization, and mitochondrial targeting. The activation of the Nur77-Bcl-2 pathway by CCE9 was associated with its activation of p38α MAPK. Inhibition of p38α MAPK activation by knocking down or knocking out p38α MAPK impaired the effect of CCE9 on inducing apoptosis and the expression and cytoplasmic localization of Nur77. In addition, CCE9 activation of p38α MAPK resulted in Bcl-2 phosphorylation and Bcl-2 interaction with Nur77, whereas inhibition of p38α MAPK activation or expression suppressed the interaction. Moreover, mutating Ser87 and Thr56 in the loop of Bcl-2, which are known to be phosphorylated by p38α MAPK, impaired the ability Bcl-2 to interact with Nur77. Together, our results reveal a profound role of p38α MAPK in regulating the Nur77-Bcl-2 apoptotic pathway through its modulation of Nur77 expression, Bcl-2 phosphorylation, and their interaction.

SUMO-triggered ubiquitination of NR4A1 controls macrophage cell death

Nuclear receptor NR4A1 has been implicated as a key regulator in a wide range of pathophysiological responses. As an immediate early response gene, NR4A1 can be rapidly and potently induced by a variety of stimuli. Its induction is followed by its rapid degradation, but the mechanism by which NR4A1 is degraded remains poorly understood. Here we show that nuclear receptor NR4A1 is sumoylated by SUMO2/3. Upon poly-SUMO modification, NR4A1 can be targeted by the SUMO-dependent E3 ubiquitin ligase RNF4 for polyubiquitination and subsequent degradation. The SUMO E3 ligase PIAS3 promotes SUMOylation and polyubiquitination of NR4A1, while the SUMO protease SENP1 acts to de-conjugate SUMO. We demonstrate that this pathway is important for rapid degradation of NR4A1 after induced by stress. Moreover, we identify two SUMO modification sites in NR4A1 that are critical for maintaining low levels of NR4A1 expression. Mutation of these two NR4A1 SUMO modification sites enhances the stability of NR4A1. Importantly, we show that SUMOylation is critical in controlling NR4A1 function in inflammatory cytokine signaling and controlling macrophage cell death. SUMOylation and subsequent ubiquitination on NR4A1 mitigates its inhibition of innate immune signaling, such as TNF-α- and IL-1β-induced NF-κB activation. This mechanism of sequential SUMOylation and ubiquitination, which together control the degradation of NR4A1, could be exploited for the therapeutic treatment of diseases with NR4A1 involvement.

Selective cytotoxicity of the antibacterial peptide ABP-dHC-Cecropin A and its analog towards leukemia cells

Some cationic antibacterial peptides, with typical amphiphilic α-helical conformations in a membrane-mimicking environment, exhibit anticancer properties as a result of a similar mechanism of action towards both bacteria and cancer cells. We previously reported the cDNA sequence of the antimicrobial peptide ABP-dHC-Cecropin A precursor cloned from drury (Hyphantria cunea) (dHC). In the present study, we synthesized and structurally characterized ABP-dHC-Cecropin A and its analog, ABP-dHC-Cecropin A-K(24). Circular dichroism spectroscopy showed that ABP-dHC-Cecropin A and its analog adopt a well-defined α-helical structure in a 50% trifluorethanol solution. The cytotoxicity and cell selectivity of these peptides were further examined in three leukemia cell lines and two non-cancerous cell lines. The MTT assay indicated both of these peptides have a concentration-dependent cytotoxic effect in leukemia cells, although the observed cytotoxicity was greater with ABP-dHC-Cecropin A-K(24) treatment, whereas they were not cytotoxic towards the non-cancerous cell lines. Moreover, ABP-dHC-Cecropin A and its analog had a lower hemolytic effect in human red blood cells. Together, these results suggest the peptides are selectively cytotoxic towards leukemia cells. Confocal laser scanning microscopy determined that the peptides were concentrated at the surface of the leukemia cells, and changes in the cell membrane were determined with a permeability assay, which suggested that the anticancer activity of ABP-dHC-Cecropin A and its analog is a result of its presence at the leukemia cell membrane. ABP-dHC-Cecropin A and its analog may represent a novel anticancer agent for leukemia therapy, considering its cancer cell selectivity and relatively low cytotoxicity in normal cells.

PAX3-FOXO1A Expression in Rhabdomyosarcoma Is Driven by the Targetable Nuclear Receptor NR4A1

Alveolar rhabdomyosarcoma (ARMS) is a devastating pediatric disease driven by expression of the oncogenic fusion gene PAX3-FOXO1A. In this study, we report overexpression of the nuclear receptor NR4A1 in rhabdomyosarcomas that is sufficient to drive high expression of PAX3-FOXO1A there. RNAi-mediated silencing of NR4A1 decreased expression of PAX3-FOXO1A and its downstream effector genes. Similarly, cell treatment with the NR4A1 small-molecule antagonists 1,1-bis(3-indolyl)-1-(p-hydroxy or p-carbomethoxyphenyl)methane (C-DIM) decreased PAX3-FOXO1A. Mechanistic investigations revealed a requirement for the NR4A1/Sp4 complex to bind GC-rich promoter regions to elevate transcription of the PAX3-FOXO1A gene. In parallel, NR4A1 also regulated expression of β1-integrin, which with PAX3-FOXO1A, contributed to tumor cell migration that was blocked by C-DIM/NR4A1 antagonists. Taken together, our results provide a preclinical rationale for the use of NR4A1 small-molecule antagonists to treat ARMS and other rhabdomyosarcomas driven by PAX3-FOXO1A. Cancer Res; 77(3); 732-41. ©2016 AACR.

Calcium-induced apoptosis of developing cerebellar granule neurons depends causally on NGFI-B

Immediate early gene nerve growth factor-induced clone B (NGFI-B), a nuclear receptor important for differentiation and apoptosis, is expressed in mice and rat cerebellum from an early stage of postnatal development. Following apoptotic stimuli NGFI-B translocates to mitochondria to initiate cell death processes. Controlled cell death is critical for correct cerebellar development. Immunohistochemical analysis of NGFI-B in sections of mice cerebella showed NGFI-B to be expressed in granule neurons in vivo at a time (P8-11) when apoptosis is known to occur. The importance of NGFI-B for apoptosis of cultured rat cerebellar granule neurons was investigated by inducing apoptosis with calcium ionophore A23187 (CaI, 0.1μM). Imaging studies of gfp-tagged NGFI-B confirmed that mitochondrial translocation of NGFI-B occurred following treatment with CaI and was reduced by addition of 9-cis-retinoic acid (1μM), a retinoid X receptor (RXR) agonist that prevents dimerization of RXR and NGFI-B that is known to occur before translocation. Consequently, 9-cis-retinoic acid partly reduced cell death. To address the causality of NGFI-B in apoptosis further, knock-down by siRNA was performed and it removed 85% of the NGFI-B protein. This resulted in a complete inhibition of apoptosis after CaI exposure. Together these findings suggest that NGFI-B plays a role in controlling correct cerebellar development.