The NR4A orphan nuclear receptor NOR1 is induced by platelet-derived growth factor and mediates vascular smooth muscle cell proliferation

miR-17 and -20a Target the Neuron-Derived Orphan Receptor-1 (NOR-1) in Vascular Endothelial Cells

Neuron-derived orphan receptor-1 (NOR-1) plays a major role in vascular biology by controlling fibroproliferative and inflammatory responses. Because microRNAs (miRNAs) have recently emerged as key players in the regulation of gene expression in the vasculature, here we have investigated the regulation of NOR-1 by miRNAs in endothelial cells. Computational algorithms suggest that NOR-1 could be targeted by members of the miR-17 family. Accordingly, ectopic over-expression of miR-17 or miR-20a in endothelial cells using synthetic premiRNAs attenuated the up-regulation of NOR-1 expression induced by VEGF (as evidenced by real time PCR, Western blot and immunocitochemistry). Conversely, the antagonism of these miRNAs by specific antagomirs prevented the down-regulation of NOR-1 promoted by miR-17 or miR-20a in VEGF-stimulated cells. Disruption of the miRNA-NOR-1 mRNA interaction using a custom designed target protector evidenced the selectivity of these responses. Further, luciferase reporter assays and seed-sequence mutagenesis confirmed that miR-17 and -20a bind to NOR-1 3’-UTR. Finally, miR-17 and -20a ameliorated the up-regulation of VCAM-1 mediated by NOR-1 in VEGF-stimulated cells. Therefore, miR-17 and -20a target NOR-1 thereby regulating NOR-1-dependent gene expression.

The TFG-TEC oncoprotein induces transcriptional activation of the human β-enolase gene via chromatin modification of the promoter region

Recurrent chromosome translocations are the hallmark of many human cancers. A proportion of human extraskeletal myxoid chondrosarcomas (EMCs) are associated with the characteristic chromosomal translocation t(3;9)(q11-12;q22), which results in the formation of a chimeric protein in which the N-terminal domain of the TRK-fused gene (TFG) is fused to the translocated in extraskeletal chondrosarcoma (TEC; also called CHN, CSMF, MINOR, NOR1, and NR4A3) gene. The oncogenic effect of this translocation may be due to the higher transactivation ability of the TFG-TEC chimeric protein; however, downstream target genes of TFG-TEC have not yet been identified. The results presented here, demonstrate that TFG-TEC activates the human β-enolase promoter. EMSAs, ChIP assays, and luciferase reporter assays revealed that TFG-TEC upregulates β-enolase transcription by binding to two NGFI-B response element motifs located upstream of the putative transcription start site. In addition, northern blot, quantitative real-time PCR, and Western blot analyses showed that overexpression of TFG-TEC up-regulated β-enolase mRNA and protein expression in cultured cell lines. Finally, ChIP analyses revealed that TFG-TEC controls the activity of the endogenous β-enolase promoter by promoting histone H3 acetylation. Overall, the results presented here indicate that TFG-TEC triggers a regulatory gene hierarchy implicated in cancer cell metabolism. This finding may aid the development of new therapeutic strategies for the treatment of human EMCs. © 2015 Wiley Periodicals, Inc.

Predicting Response to Histone Deacetylase Inhibitors Using High-Throughput Genomics

BACKGROUND

Many disparate biomarkers have been proposed as predictors of response to histone deacetylase inhibitors (HDI); however, all have failed when applied clinically. Rather than this being entirely an issue of reproducibility, response to the HDI vorinostat may be determined by the additive effect of multiple molecular factors, many of which have previously been demonstrated.

METHODS

We conducted a large-scale gene expression analysis using the Cancer Genome Project for discovery and generated another large independent cancer cell line dataset across different cancers for validation. We compared different approaches in terms of how accurately vorinostat response can be predicted on an independent out-of-batch set of samples and applied the polygenic marker prediction principles in a clinical trial.

RESULTS

Using machine learning, the small effects that aggregate, resulting in sensitivity or resistance, can be recovered from gene expression data in a large panel of cancer cell lines.This approach can predict vorinostat response accurately, whereas single gene or pathway markers cannot. Our analyses recapitulated and contextualized many previous findings and suggest an important role for processes such as chromatin remodeling, autophagy, and apoptosis. As a proof of concept, we also discovered a novel causative role for CHD4, a helicase involved in the histone deacetylase complex that is associated with poor clinical outcome. As a clinical validation, we demonstrated that a common dose-limiting toxicity of vorinostat, thrombocytopenia, can be predicted (r = 0.55, P = .004) several days before it is detected clinically.

CONCLUSION

Our work suggests a paradigm shift from single-gene/pathway evaluation to simultaneously evaluating multiple independent high-throughput gene expression datasets, which can be easily extended to other investigational compounds where similar issues are hampering clinical adoption.

Neuron-derived orphan receptor 1 promoted human pulmonary artery smooth muscle cells proliferation

AIMS

As a transcription factor of the nuclear receptor superfamily, neuron-derived orphan receptor 1 (NOR1) is induced rapidly in response to various extracellular stimuli. But, it is still unclear its role in pulmonary artery smooth muscle cells proliferation.

MATERIALS AND METHODS

Human PASMCs were cultured in vitro and stimulated by serum. The special antisense oligodeoxynucleotides (AS-ODNs) were used to knockdown human NOR1 gene expression. Real-time PCR and Western-blot were used to evaluate the gene expression and protein levels.

RESULTS

Fetal bovine serum (FBS) induced human PASMCs proliferation in a dose dependent manner. Furthermore, FBS promoted NOR1 gene expression in a dose dependent manner and a time dependent manner. 10% FBS induced a maximal NOR1 mRNA levels at 2 h. FBS also induced a significant higher NOR1 protein levels as compared with control. The NOR1 over-expressed plasmid significantly promoted DNA synthesis and cells proliferation. Moreover, the special AS-ODNs against human NOR1 not only prevented NOR1 expression but also inhibited DNA synthesis and cells proliferation significantly. The NOR1 over-expression plasmid could up-regulate cyclin D1 expression markedly, but the AS-ODNs inhibited cyclin D1 expression significantly.

CONCLUSION

So, we concluded that NOR1 could promote human PASMCs proliferation. Cyclin D1 might be involved in this process.

NR4A receptors up-regulate the antiproteinase alpha-2 macroglobulin (A2M) and modulate MMP-2 and MMP-9 in vascular smooth muscle cells

Matrix metalloproteinases (MMPs) are associated with tissue remodelling and repair. In non-vascular tissues, NR4A receptors have been involved in the regulation of MMPs by transcriptional repression mechanisms. Here, we analyse alternative mechanisms involving NR4A receptors in the modulation of MMP activity in vascular smooth muscle cells (VSMC). Lentiviral overexpression of NR4A receptors (NOR-1, Nurr1 and Nur77) in human VSMC strongly decreased MMP-2 and MMP-9 activities (analysed by zymography and DQ-gelatin assays) and protein levels. NR4A receptors also down-regulated MMP-2 mRNA levels. Real-time PCR analysis evidenced that alpha-2-macroglobulin (A2M), but not other MMP inhibitors (TIMP-1 and TIMP-2) were up-regulated in NR4A-transduced cells. Interestingly, A2M was expressed in human vascular tissues including the smooth muscle media layer. While NR4A receptors increased A2M expression and secretion in VSMC, NR4A knockdown significantly reduced basal A2M expression in these cells. The direct transcriptional regulation of the human A2M promoter by NR4A receptors was characterised in luciferase reporter assays, electrophoretic mobility shift assays and by chromatin immunoprecipitation, identifying a NGFI-B response element (NBRE-71/-64) essential for the NR4A-mediated induction. The blockade of A2M partially prevented the reduction of MMPs activity observed in NR4A-transduced cells. Although mouse A2M promoter was unresponsive to NR4A receptors, vascular MMP expression was attenuated in transgenic mice over-expressing human NOR-1 in VSMC challenged with lipopolysaccharide. Our results show that the pan-proteinase inhibitor A2M is expressed in the vasculature and that NR4A receptors modulate VSMC MMP activity by several mechanisms including the up-regulation of A2M.

The C. elegans NR4A nuclear receptor gene nhr-6 promotes cell cycle progression in the spermatheca lineage

BACKGROUND

NR4A nuclear receptors are a conserved, functionally diverse group of nuclear receptors that regulate multiple cellular processes including proliferation and differentiation. The gene nhr-6 encodes the sole Caenorhabditis elegans NR4A nuclear receptor homolog with an essential role in reproduction by regulating morphogenesis of the spermatheca, a somatic gonad organ involved in ovulation and fertilization.

RESULTS

Here, we identify the spermatheca cell lineage defects that occur in nhr-6 mutants. Utilizing cell marker analysis, we find that nhr-6 is required for cell cycle progression and that the cell proliferation phenotype is not due to premature cell cycle exit. We also show that loss of the negative cell cycle regulators fzr-1 and lin-35 suppresses the cell proliferation defects. We further demonstrate that NHR-6 activity intersects with Eph receptor signaling during spermatheca cell proliferation.

CONCLUSIONS

NHR-6 has an essential function in promoting cell cycle progression during G1 phase in a specific spermatheca cell lineage. Genetic suppression of the proliferation phenotype does not affect the differentiation phenotypes observed in nhr-6 mutants, indicating a dualistic role for nhr-6 in regulating cell proliferation and cell differentiation during spermatheca organogenesis.

NOR-1 modulates the inflammatory response of vascular smooth muscle cells by preventing NFκB activation

Recent work has highlighted the role of NR4A receptors in atherosclerosis and inflammation. In vascular smooth muscle cell (VSMC) proliferation, however, NOR-1 (neuron-derived orphan receptor-1) exerts antagonistic effects to Nur77 and Nurr1. The aim of this study was to analyse the effect of NOR-1 in VSMC inflammatory response. We assessed the consequence of a gain-of-function of this receptor on the response of VSMC to inflammatory stimuli. In human VSMC, lentiviral over-expression of NOR-1 reduced lipopolysaccharide (LPS)-induced up-regulation of cytokines (IL-1β, IL-6 and IL-8) and chemokines (MCP-1 and CCL20). Similar effects were obtained in cells stimulated with TNFα or oxLDL. Conversely, siRNA-mediated NOR-1 inhibition significantly increased the expression of pro-inflammatory mediators. Interestingly, in the aortas from transgenic mice that over-express human NOR-1 in VSMC (TgNOR-1), the up-regulation of cytokine/chemokine by LPS was lower compared to wild-type littermates. Similar results were obtained in VSMC from transgenic animals. NOR-1 reduced the transcriptional activity of NFκB sensitive promoters (in transient transfections), and the binding of NFκB to its responsive element (in electrophoretic mobility shift assays). Furthermore, NOR-1 prevented the activation of NFκB pathway by decreasing IκBα phosphorylation/degradation and inhibiting the phosphorylation and subsequent translocation of p65 to the nucleus (assessed by Western blot and immunocytochemistry). These effects were associated with an attenuated phosphorylation of ERK1/2, p38 MAPK and Jun N-terminal kinase, pathways involved in the activation of NFκB. In mouse challenged with LPS, the activation of the NFκB signalling was also attenuated in the aorta from TgNOR-1. Our data support a role for NOR-1 as a negative modulator of the acute response elicited by pro-inflammatory stimuli in the vasculature.

Epigenetic regulation of the NR4A orphan nuclear receptor NOR1 by histone acetylation

The nuclear receptor NOR1 is an immediate-early response gene implicated in the transcriptional control of proliferation. Since the expression level of NOR1 is rapidly induced through cAMP response element binding (CREB) protein-dependent promoter activation, we investigated the contribution of histone acetylation to this transient induction. We demonstrate that NOR1 transcription is induced by histone deacetylase (HDAC) inhibition and by depletion of HDAC1 and HDAC3. HDAC inhibition activated the NOR1 promoter, increased histone acetylation and augmented the recruitment of phosphorylated CREB to the promoter. Furthermore, HDAC inhibition increased Ser133 phosphorylation of CREB and augmented NOR1 protein stability. These data outline previously unrecognized mechanisms of NOR1 regulation and illustrate a key role for histone acetylation in the rapid induction of NOR1.

Exendin-4, a GLP-1 receptor agonist, attenuates prostate cancer growth

Recently, pleiotropic benefits of incretin therapy beyond glycemic control have been reported. Although cancer is one of the main causes of death in diabetic patients, few reports describe the anticancer effects of incretin. Here, we examined the effect of the incretin drug exendin (Ex)-4, a GLP-1 receptor (GLP-1R) agonist, on prostate cancer. In human prostate cancer tissue obtained from patients after they had undergone radical prostatectomy, GLP-1R expression colocalized with P504S, a marker of prostate cancer. In in vitro experiments, Ex-4 significantly decreased the proliferation of the prostate cancer cell lines LNCap, PC3, and DU145, but not that of ALVA-41. This antiproliferative effect depended on GLP-1R expression. In accordance with the abundant expression of GLP-1R in LNCap cells, a GLP-1R antagonist or GLP-1R knockdown with small interfering RNA abolished the inhibitory effect of Ex-4 on cell proliferation. Although Ex-4 had no effect on either androgen receptor activation or apoptosis, it decreased extracellular signal-regulated kinase (ERK)-mitogen-activated protein kinase (MAPK) phosphorylation in LNCap cells. Importantly, Ex-4 attenuated in vivo prostate cancer growth induced by transplantation of LNCap cells into athymic mice and significantly reduced the tumor expression of P504S, Ki67, and phosphorylated ERK-MAPK. These data suggest that Ex-4 attenuates prostate cancer growth through the inhibition of ERK-MAPK activation.

Nur77 suppresses pulmonary artery smooth muscle cell proliferation through inhibition of the STAT3/Pim-1/NFAT pathway

The orphan nuclear receptor 4A (NR4A) family plays critical roles in the regulation of cell proliferation, differentiation, and survival in the cardiovascular system. However, the molecular mechanisms underlying the regulation of NR4A receptor expression and its role in pulmonary artery smooth muscle cell (PASMC) function remain unclear. Here, we investigated whether the NR4A family regulates PASMC proliferation, and if so, which mechanisms are involved. By using quantitative real-time RT-PCR, we showed that the orphan nuclear receptor Nur77 was the most abundant member of NR4A family expressed in rat PASMCs, as compared with the two other members, NOR-1 and Nurr1. In rat PASMCs, expression of Nur77 was robustly induced in response to several pathologic stimuli of pulmonary arterial hypertension (PAH), such as hypoxia, 5-hydroxytryptamine (5-HT), platelet-derived growth factor, and endothelin-1. Importantly, Nur77 was also significantly increased in lungs of rats with monocrotaline-induced PAH. Furthermore, we demonstrated that 5-HT markedly up-regulated Nur77 expression through the mitogen-activated protein kinases/extracellular signal-regulated kinase 1/2 pathway. Overexpression of Nur77 inhibited 5-HT-induced PASMC proliferation, as well as the expression of cyclin D1 and proliferating cell nuclear antigen. Mechanistically, we demonstrated that Nur77 specifically interacts with signal transducer and activator of transcription 3, thus inhibiting its phosphorylation and expression of its target genes, such as Pim-1, nuclear factor of activated T cells c2, and survivin in PASMCs. These results indicate that Nur77 is a novel negative-feedback regulator of PASMC proliferation through inhibition of the signal transducer and activator of transcription 3/Pim-1/nuclear factor of activated T cells axis. Modulation of Nur77 activity may potentially represent a novel therapeutic strategy for the treatment of PAH.

Nkx6.1 regulates islet β-cell proliferation via Nr4a1 and Nr4a3 nuclear receptors

Loss of functional β-cell mass is a hallmark of type 1 and type 2 diabetes, and methods for restoring these cells are needed. We have previously reported that overexpression of the homeodomain transcription factor NK6 homeobox 1 (Nkx6.1) in rat pancreatic islets induces β-cell proliferation and enhances glucose-stimulated insulin secretion, but the pathway by which Nkx6.1 activates β-cell expansion has not been defined. Here, we demonstrate that Nkx6.1 induces expression of the nuclear receptor subfamily 4, group A, members 1 and 3 (Nr4a1 and Nr4a3) orphan nuclear receptors, and that these factors are both necessary and sufficient for Nkx6.1-mediated β-cell proliferation. Consistent with this finding, global knockout of Nr4a1 results in a decrease in β-cell area in neonatal and young mice. Overexpression of Nkx6.1 and the Nr4a receptors results in increased expression of key cell cycle inducers E2F transcription factor 1 and cyclin E1. Furthermore, Nkx6.1 and Nr4a receptors induce components of the anaphase-promoting complex, including ubiquitin-conjugating enzyme E2C, resulting in degradation of the cell cycle inhibitor p21. These studies identify a unique bipartite pathway for activation of β-cell proliferation, suggesting several unique targets for expansion of functional β-cell mass.

Nuclear receptor 4a3 (nr4a3) regulates murine mast cell responses and granule content

Nuclear receptor 4a3 (Nr4a3) is a transcription factor implicated in various settings such as vascular biology and inflammation. We have recently shown that mast cells dramatically upregulate Nuclear receptor 4a3 upon activation, and here we investigated the functional impact of Nuclear receptor 4a3 on mast cell responses. We show that Nuclear receptor 4a3 is involved in the regulation of cytokine/chemokine secretion in mast cells following activation via the high affinity IgE receptor. Moreover, Nuclear receptor 4a3 negatively affects the transcript and protein levels of mast cell tryptase as well as the mast cell's responsiveness to allergen. Together, these findings identify Nuclear receptor 4a3 as a novel regulator of mast cell function.

Orphan nuclear receptor nurr1 as a potential novel marker for progression in human prostate cancer

A number of studies have indicated that Nurr1, which belongs to a novel class of orphan nuclear receptors (the NR4A family), is important for carcinogenesis. Here we investigated expression of Nurr1 protein in benign and malignant human prostate tissues and association with clinicopathologic features using immunohistochemical techniques. Moreover, we also investigated the ability of Nurr1 to influence proliferation, migration, invasion and apoptosis of human prostate cancer cells using small interfering RNA silencing. Immunohistochemical analysis revealed that the expression of Nurr1 protein was higher in prostate cancer tissues than in benign prostate tissue (P < 0.001), levels being positively correlated with tumor T classification (P = 0.003), N classification (P = 0.017), M classification (P = 0.011) and the Gleason score (P = 0.020) of prostate cancer patients. In vitro, silencing of endogenous Nurr1 attenuated cell proliferation, migration and invasion, and induced apoptosis of prostate cancer cells. These results suggest that Nurr1 may be used as an indicator for prostate cancer progression and be useful for novel potential therapeutic strategies.

Chromosomal translocations highlighted in Primitive Neuroectodermal Tumors (PNET) and Ewing sarcoma

Almost 200 molecular markers in oncology, very important in the diagnosis, prognostic and treatment were identified. The cell and tissue markers and also the circulating (sanguine) ones are genetic markers of the hereditary and non-hereditary tumors. Also extremely important are the regulatory ways of cell growth and differentiation, of the cell "senescence" and cell death (apoptosis). The term of "tumor marker" concerns a variety of molecules or processes that are different in the normal cell compared with the malign cell. The tumor markers may include modifications to the genetic level (mutations, deletions or genes amplifications) to the transcription level (super expression or sub-expression), to the translation level (high or low quantities of proteins, abnormal glycosylation of proteins) and/or to the functional level (the level of cell differentiation or presence of neo-vascularisation). Cancer is a genetic disease. There is a deregulation at the genes level that controls the cell division and withdrawal from the cell cycle or there is a genetic susceptibility. In other words, cancer is an end point for several phases in which the oncogenes and stimulatory signals and inhibitors produced and controlled by the products of these oncogenes are involved.

Control of energy balance by hypothalamic gene circuitry involving two nuclear receptors, neuron-derived orphan receptor 1 and glucocorticoid receptor

Nuclear receptors (NRs) regulate diverse physiological processes, including the central nervous system control of energy balance. However, the molecular mechanisms for the central actions of NRs in energy balance remain relatively poorly defined. Here we report a hypothalamic gene network involving two NRs, neuron-derived orphan receptor 1 (NOR1) and glucocorticoid receptor (GR), which directs the regulated expression of orexigenic neuropeptides agouti-related peptide (AgRP) and neuropeptide Y (NPY) in response to peripheral signals. Our results suggest that the anorexigenic signal leptin induces NOR1 expression likely via the transcription factor cyclic AMP response element-binding protein (CREB), while the orexigenic signal glucocorticoid mobilizes GR to inhibit NOR1 expression by antagonizing the action of CREB. Also, NOR1 suppresses glucocorticoid-dependent expression of AgRP and NPY. Consistently, relative to wild-type mice, NOR1-null mice showed significantly higher levels of AgRP and NPY and were less responsive to leptin in decreasing the expression of AgRP and NPY. These results identify mutual antagonism between NOR1 and GR to be a key rheostat for peripheral metabolic signals to centrally control energy balance.

Nuclear Receptors in atherosclerosis: a superfamily with many 'Goodfellas'

Nuclear Receptors form a superfamily of 48 transcription factors that exhibit a plethora of functions in steroid hormone signaling, regulation of metabolism, circadian rhythm and cellular differentiation. In this review, we describe our current knowledge on the role of Nuclear Receptors in atherosclerosis, which is a multifactorial disease of the vessel wall. Various cell types are involved in this chronic inflammatory pathology in which multiple cellular processes and numerous genes are dysregulated. Systemic risk factors for atherosclerosis are among others adverse blood lipid profiles, enhanced circulating cytokine levels, as well as increased blood pressure. Since many Nuclear Receptors modulate lipid profiles or regulate blood pressure they indirectly affect atherosclerosis. In the present review, we focus on the functional involvement of Nuclear Receptors within the atherosclerotic vessel wall, more specifically on their modulation of cellular functions in endothelial cells, smooth muscle cells and macrophages. Collectively, this overview shows that most of the Nuclear Receptors are athero-protective in atherosclerotic lesions.

MicroRNA-638 is highly expressed in human vascular smooth muscle cells and inhibits PDGF-BB-induced cell proliferation and migration through targeting orphan nuclear receptor NOR1

AIMS

Aberrant vascular smooth muscle cell (VSMC) proliferation and migration contribute significantly to the development of vascular pathologies, such as atherosclerosis and restenosis. MicroRNAs have recently emerged as critical modulators in cellular processes and the purpose of this study is to identify novel miRNA regulators implicated in human aortic VSMC proliferation and migration.

METHODS AND RESULTS

To identify miRNAs that are differentially expressed in human VSMCs, we performed miRNA microarray analysis in human aortic smooth muscle cells (SMCs) at different time points after platelet-derived growth factor (PDGF) stimulation. Here, we identified microRNA-638 (miR-638) as a transcript that was one of the most significantly down-regulated in human VSMCs after PDGF stimulation. Furthermore, we confirmed, by Quantitative RT-PCR, that miR-638 is highly expressed in human VSMCs, and its expression is markedly down-regulated in a dose- and time-dependent manner upon PDGF treatment. Consistent with a critical role in SMC proliferation, we found that miR-638 expression was significantly up-regulated in human VSMCs cultured in differentiation medium, a condition that inhibits SMC proliferation. Furthermore, we identified the orphan nuclear receptor NOR1 as a downstream target gene product of miR-638 and down-regulation of NOR1 is critical for miR-638-mediated inhibitory effects on PDGF-induced cyclin D1 expression, cell proliferation, and migration in human aortic SMCs.

CONCLUSION

These results indicate that miR-638 is a key molecule in regulating human VSMC proliferation and migration by targeting the NOR1/cyclin D pathway and suggest that specific modulation of miR-638 in human VSMCs may represent an attractive approach for the treatment of proliferative vascular diseases.

Over-expression of neuron-derived orphan receptor-1 (NOR-1) exacerbates neointimal hyperplasia after vascular injury

We have previously shown that NOR-1 (NR4A3) modulates the proliferation and survival of vascular cells in culture. However, in genetically modified animal models, somewhat conflicting results have been reported concerning the involvement of NOR-1 in neointimal formation after vascular injury. The aim of this study was to generate a transgenic mouse model over-expressing NOR-1 in smooth muscle cells (SMCs) and assess the consequence of a gain of function of this receptor on intimal hyperplasia after vascular injury. The transgene construct (SM22-NOR1) was prepared by ligating the full-length human NOR-1 cDNA (hNOR-1) and a mouse SM22α minimal promoter able to drive NOR-1 expression to SMC. Two founders were generated and two stable transgenic mouse lines (TgNOR-1) were established by backcrossing the transgene-carrying founders with C57BL/6J mice. Real-time PCR and immunohistochemistry confirmed that hNOR-1 was mainly targeted to vascular beds such as aorta and carotid arteries, and was similar in both transgenic lines. Vascular SMC from transgenic animals exhibit increased NOR-1 transcriptional activity (assessed by electrophoretic mobility shift assay and luciferase assays), increased mitogenic activity (determined by [(3)H]-thymidine incorporation; 1.58-fold induction, P < 0.001) and increased expression of embryonic smooth muscle myosin heavy chain (SMemb) than wild-type cells from control littermates. Using the carotid artery ligation model, we show that neointima formation was increased in transgenic versus wild-type mice (2.36-fold induction, P < 0.01). Our in vivo data support a role for NOR-1 in VSMC proliferation and vascular remodelling. This NOR-1 transgenic mouse could be a useful model to study fibroproliferative vascular diseases.

Peroxisome proliferator-activated receptor γ coactivator 1β (PGC-1β) protein attenuates vascular lesion formation by inhibition of chromatin loading of minichromosome maintenance complex in smooth muscle cells

Proliferation of vascular smooth muscle cells (VSMCs) in response to vascular injury plays a critical role in vascular lesion formation. Emerging data suggest that peroxisome proliferator-activated receptor γ coactivator 1 (PGC-1) is a key regulator of energy metabolism and other biological processes. However, the physiological role of PGC-1β in VSMCs remains unknown. A decrease in PGC-1β expression was observed in balloon-injured rat carotid arteries. PGC-1β overexpression substantially inhibited neointima formation in vivo and markedly inhibited VSMC proliferation and induced cell cycle arrest at the G(1)/S transition phase in vitro. Accordingly, overexpression of PGC-1β decreased the expression of minichromosome maintenance 4 (MCM4), which leads to a decreased loading of the MCM complex onto chromatin at the replication origins and decreased cyclin D1 levels, whereas PGC-1β loss of function by adenovirus containing PGC-1β shRNA resulted in the opposite effect. The transcription factor AP-1 was involved in the down-regulation of MCM4 expression. Furthermore, PGC-1β is up-regulated by metformin, and metformin-associated anti-proliferative activity in VSMCs is at least partially dependent on PGC-1β. Our data show that PGC-1β is a critical component in regulating DNA replication, VSMC proliferation, and vascular lesion formation, suggesting that PGC-1β may emerge as a novel therapeutic target for control of proliferative vascular diseases.

Orphan nuclear receptor NR4A2 induces synoviocyte proliferation, invasion, and matrix metalloproteinase 13 transcription

OBJECTIVE

To address the role of the nuclear receptor 4A (NR4A) family of orphan nuclear receptors in synoviocyte transformation, hyperplasia, and regulation of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) in models of inflammatory arthritis.

METHODS

NR4A messenger RNA levels in synovial tissue and primary synoviocytes were measured by quantitative reverse transcription-polymerase chain reaction (RT-PCR). NR4A2 was stably overexpressed in normal synoviocytes, and cell proliferation, survival, anchorage-independent growth, migration, and invasion were monitored in vitro. MMP and TIMP expression levels were analyzed by quantitative RT-PCR, and MMP-13 promoter activity was measured using reporter assays. Stable depletion of endogenous NR4A levels was achieved by lentiviral transduction of NR4A short hairpin RNA (shRNA), and the effects on proliferation, migration, and MMP-13 expression were analyzed.

RESULTS

NR4A2 was expressed at elevated levels in normal, OA, and RA synovial tissue and in primary RA synoviocytes. Tumor necrosis factor α (TNFα) rapidly and selectively induced expression of NR4A2 in synoviocytes. Ectopic expression of NR4A2 in normal synoviocytes significantly increased proliferation and survival, promoted anchorage-independent growth, and induced migration and invasion. MMP-13 gene expression was synergistically induced by NR4A2 and TNFα, while expression of TIMP-2 was antagonized. NR4A2 directly transactivated the proximal MMP-13 promoter, and a point mutation in the DNA binding domain of NR4A2 abolished transcriptional activation. Depletion of endogenous NR4A receptors with shRNA reduced synoviocyte proliferation, migration, and MMP-13 expression.

CONCLUSION

The orphan nuclear receptor NR4A2 is a downstream mediator of TNFα signaling in synovial tissue. NR4A2 transcriptional activity contributes to the hyperplastic and invasive phenotype of synoviocytes that leads to cartilage destruction, suggesting that this receptor may show promise as a therapeutic target in inflammatory arthritis.

Dual function of Pin1 in NR4A nuclear receptor activation: enhanced activity of NR4As and increased Nur77 protein stability

Nur77, Nurr1 and NOR-1 form the NR4A subfamily of the nuclear receptor superfamily and have been shown to regulate various biological processes among which are cell survival and differentiation, apoptosis, inflammation and metabolism. These nuclear receptors have been proposed to act in a ligand-independent manner and we aim to gain insight in the regulation of NR4A activity. A yeast two-hybrid screen identified the peptidyl-prolyl isomerase Pin1 as a novel binding partner of NR4As, which was confirmed by co-immunoprecipitation. Pin1 enhances the transcriptional activity of all three NR4A nuclear receptors and increases protein stability of Nur77 through inhibition of its ubiquitination. Enhanced transcriptional activity of NR4As requires the WW-domain of Pin1 that interacts with the N-terminal transactivation domain and the DNA-binding domain of Nur77. Most remarkably, this enhanced activity is independent of Pin1 isomerase activity. A systematic mutation analysis of all 17 Ser/Thr-Pro-motifs in Nur77 revealed that Pin1 enhances protein stability of Nur77 in an isomerase-dependent manner by acting on phosphorylated Nur77 involving protein kinase CK2-mediated phosphorylation of the Ser(152)-Pro(153) motif in Nur77. Given the role of Nur77 in vascular disease and metabolism, this novel regulation mechanism provides perspectives to manipulate Nur77 activity to attenuate these processes.

NR4All in the vessel wall

A number of nuclear receptors are involved in maintenance of normal vessel wall physiology as well as in pathophysiological processes such as atherosclerosis, restenosis and remodelling. Recent studies revealed a previously unrecognized function of the NR4A subfamily of nuclear receptors as key regulatory proteins in vascular disease. The NR4A subfamily comprises the members Nur77, Nurr1 and NOR-1 and in the current review a comprehensive overview is given of the data supporting functional involvement of these nuclear receptors in three major cell types in vascular (patho)physiology; endothelial cells, smooth muscle cells and monocytes-macrophages.

The TFG-TEC fusion gene created by the t(3;9) translocation in human extraskeletal myxoid chondrosarcomas encodes a more potent transcriptional activator than TEC

The t(3;9)(q11-q12;q22) translocation associated with human extraskeletal myxoid chondrosarcomas results in a chimeric molecule in which the N-terminal domain (NTD) of the TFG (TRK-fused gene) is fused to the TEC (Translocated in Extraskeletal Chondrosarcoma) gene. Little is known about the biological function of TFG-TEC. Because the NTDs of TFG-TEC and TEC are structurally different, and the TFG itself is a cytoplasmic protein, the functional consequences of this fusion in extraskeletal myxoid chondrosarcomas were examined. The results showed that the chimeric gene encoded a nuclear protein that bound DNA with the same sequence specificity as the parental TEC protein. Comparison of the transactivation properties of TFG-TEC and TEC indicated that the former has higher transactivation activity for a known target reporter containing TEC-binding sites. Additional reporter assays for TFG (NTD) showed that the TGF (NTD) of TFG-TEC induced a 12-fold increase in the activation of luciferase from a reporter plasmid containing GAL4 binding sites when fused to the DNA-binding domain of GAL4, indicating that the TFG (NTD) of the TFG-TEC protein has intrinsic transcriptional activation properties. Finally, deletion analysis of the functional domains of TFG (NTD) indicated that the PB1 (Phox and Bem1p) and SPYGQ-rich region of TFG (NTD) were capable of activating transcription and that full integrity of TFG (NTD) was necessary for full transactivation. These results suggest that the oncogenic effect of the t(3;9) translocation may be due to the TFG-TEC chimeric protein and that fusion of the TFG (NTD) to the TEC protein produces a gain-of-function chimeric product.

FHL2 protein is a novel co-repressor of nuclear receptor Nur77

The three members of the NR4A orphan nuclear receptor subfamily Nur77, Nurr1, and NOR-1, regulate a variety of biological functions including vascular disease and metabolism. In this study, we identified Four and a half LIM domains protein-2 (FHL2) as a novel interacting protein of NR4A nuclear receptors by yeast two-hybrid screen and co-immunoprecipitation studies. Each of the four LIM domains of FHL2 can bind Nur77, and both the amino-terminal domain and the DNA binding domain of Nur77 are involved in the interaction between FHL2 and Nur77. FHL2 represses Nur77 transcriptional activity in a dose-dependent manner, and short hairpin RNA-mediated knockdown of FHL2 results in increased Nur77 transcriptional activity. ChIP experiments on the enolase3 promoter revealed that FHL2 inhibits the association of Nur77 with DNA. FHL2 is highly expressed in human endothelial and smooth muscle cells, but not in monocytes or macrophages. To substantiate functional involvement of FHL2 in smooth muscle cell physiology, we demonstrated that FHL2 overexpression increases the growth of these cells, whereas FHL2 knockdown results in reduced DNA synthesis. Collectively, these studies suggest that association of FHL2 with Nur77 plays a pivotal role in vascular disease.

Transcriptional regulation of S phase kinase-associated protein 2 by NR4A orphan nuclear receptor NOR1 in vascular smooth muscle cells

Members of the NR4A subgroup of the nuclear hormone receptor superfamily have emerged as key transcriptional regulators of proliferation and inflammation. NOR1 constitutes a ligand-independent transcription factor of this subgroup and induces cell proliferation; however, the transcriptional mechanisms underlying this mitogenic role remain to be defined. Here, we demonstrate that the F-box protein SKP2 (S phase kinase-associated protein 2), the substrate-specific receptor of the ubiquitin ligase responsible for the degradation of p27(KIP1) through the proteasome pathway, constitutes a direct transcriptional target for NOR1. Mitogen-induced Skp2 expression is silenced in vascular smooth muscle cells (VSMC) isolated from Nor1-deficient mice or transfected with Nor1 siRNA. Conversely, adenovirus-mediated overexpression of NOR1 induces Skp2 expression in VSMC and decreases protein abundance of its target p27. Transient transfection experiments establish that NOR1 transactivates the Skp2 promoter through a nerve growth factor-induced clone B response element (NBRE). Electrophoretic mobility shift and chromatin immunoprecipitation assays further revealed that NOR1 is recruited to this NBRE site in the Skp2 promoter in response to mitogenic stimulation. In vivo Skp2 expression is increased during the proliferative response underlying neointima formation, and this transcriptional induction depends on the expression of NOR1. Finally, we demonstrate that overexpression of Skp2 rescues the proliferative arrest of Nor1-deficient VSMC. Collectively, these results characterize Skp2 as a novel NOR1-regulated target gene and detail a previously unrecognized transcriptional cascade regulating mitogen-induced VSMC proliferation.

Nuclear receptors Nur77 and Nurr1 modulate mesenchymal stromal cell migration

Detailed understanding of mesenchymal stromal cells (MSC) migration is imperative for future cellular therapies. To identify genes involved in the process of MSC migration, we generated gene expression profiles of migrating and nonmigrating fetal bone marrow MSC (FBMSC). Only 12 genes showed differential expression in migrating versus nonmigrating FBMSC. The nuclear receptors Nur77 and Nurr1 showed the highest expression in migratory MSC. Nur77 and Nurr1 are members of NR4A nuclear orphan receptor family, and we found that their expression is rapidly increased upon exposure of FBMSC to the migratory stimuli stromal-derived factor-1α (SDF-1α) and platelet-derived growth factor-BB. Lentiviral expression of Nur77 or Nurr1 resulted in enhanced migration of FBMSC toward SDF-1α compared with mock-transduced FBMSC. Analysis of the cell cycle, known to be involved in MSC migration, revealed that expression of Nur77 and Nurr1 decreases the proportion of cells in S-phase compared with control cells. Further, gain-of-function experiments showed increased hepatocyte growth factor expression and interleukin (IL)-6 and IL-8 production in MSC. Despite the altered cytokine profile, FBMSC expressing Nur77 or Nurr1 maintained the capacity to inhibit T-cell proliferation in a mixed lymphocyte reaction. Our results demonstrate that Nur77 and Nurr1 promote FBMSC migration. Modulation of Nur77 and Nurr1 activity may therefore offer perspectives to enhance the migratory potential of FBMSC which may specifically regulate the local immune response.

PDGF-induced proliferation of smooth muscular cells is related to the regulation of CREB phosphorylation and Nur77 expression

This study examined the relationship between PDGF-induced proliferation of vascular smooth muscle cells (VSMCs) and Nur77 expression and the effect of atorvastatin on VSMC proliferation and Nur77 in PDGF-treated VSMCs. Rat VSMCs were isolated and cultured. After incubation with atorvastatin or Nur77 siRNA, the cells were stimulated with PDGF and detected for BrdU incorporation to measure the proliferation of the VSMCs. Quantitative PCR and Western blotting were used to determine the Nur77 protein and the CREB phosphorylation level, to observe their relations with PDGF-induced VSMC proliferation. Our results showed that PDGF increased the BrdU incorporation in VSMCs, suggesting that it induced the proliferation of the cells. The VSMC proliferation was associated with increased Nur77 expression and elevated CREB phosphorylation. Atorvastatin inhibited the PDGF-induced VSMC proliferation, suppressed Nur77 expression. After silencing of Nur77 gene, the PDGF-induced VSMC proliferation was decreased. It was concluded that PDGF-induced VSMC proliferation was related to the Nur77 expression and CREB phosphorylation. Atorvastatin reduced the Nur77 expression and, at the same time, inhibited the VSMC proliferation.

PYK2 signaling is required for PDGF-dependent vascular smooth muscle cell proliferation

Aberrant vascular smooth muscle cell (VSMC) growth is associated with many vascular diseases including atherosclerosis, hypertension, and restenosis. Platelet-derived growth factor-BB (PDGF) induces VSMC proliferation through control of cell cycle progression and protein and DNA synthesis. Multiple signaling cascades control VSMC growth, including members of the mitogen-activated protein kinase (MAPK) family as well as phosphatidylinositol 3-kinase (PI3K) and its downstream effector AKT/protein kinase B (PKB). Little is known about how these signals are integrated by mitogens and whether there are common receptor-proximal signaling control points that synchronize the execution of physiological growth functions. The nonreceptor proline-rich tyrosine kinase 2 (PYK2) is activated by a variety of growth factors and G protein receptor agonists in VSMC and lies upstream of both PI3K and MAPK cascades. The present study investigated the role of PYK2 in PDGF signaling in cultured rat aortic VSMC. PYK2 downregulation attenuated PDGF-dependent protein and DNA synthesis, which correlated with inhibition of AKT and extracellular signal-regulated kinases 1 and 2 (ERK1/2) but not p38 MAPK activation. Inhibition of PDGF-dependent protein kinase B (AKT) and ERK1/2 signaling by inhibitors of upstream kinases PI3K and MEK, respectively, as well as downregulation of PYK2 resulted in modulation of the G(1)/S phase of the cell cycle through inhibition of retinoblastoma protein (Rb) phosphorylation and cyclin D(1) expression, as well as p27(Kip) upregulation. Cell division kinase 2 (cdc2) phosphorylation at G(2)/M was also contingent on PDGF-dependent PI3K-AKT and ERK1/2 signaling. These data suggest that PYK2 is an important upstream mediator in PDGF-dependent signaling cascades that regulate VSMC proliferation.

The effects of β-adrenergic stimulation and exercise on NR4A3 protein expression in rat skeletal muscle

β-Adrenergic stimulation and exercise up-regulate the mRNA expression of nuclear receptor NR4A3, which is involved in the regulation of glucose and fatty acid utilization genes in skeletal muscle. The objective of our study was to examine the effects of β-adrenergic stimulation and exercise on the expression of NR4A3 protein in rat skeletal muscle. A single subcutaneous injection of clenbuterol, which is a β2-adrenergic receptor (β2-AR) agonist, increased NR4A3 mRNA and protein expression in the fast-twitch glycolytic triceps muscle. On the other hand, an acute 3-h session of either treadmill running or swimming did not increase the NR4A3 protein level in the exercised muscle, although both treadmill running and swimming increased NR4A3 mRNA. Finally, loss of postural contractile activity because of hindlimb immobilization reduced NR4A3 mRNA and protein in the slow-twitch oxidative soleus muscle. These results suggest that: β-adrenergic stimulation up-regulates not only NR4A3 mRNA but also NR4A3 protein in fast-twitch glycolytic muscle; exercise may increase NR4A3 mRNA but not NR4A3 protein in skeletal muscle; and local postural contractile activity plays a crucial role in maintaining NR4A3 protein expression level in postural muscle.

Microarray analysis of ox-LDL (oxidized low-density lipoprotein)-regulated genes in human coronary artery smooth muscle cells

Recent studies suggest that circulating LDL (low-density lipoproteins) play a central role in the pathogenesis of atherosclerosis, and the oxidized form (ox-LDL) is highly atherogenic. Deposits of ox-LDL have been found in atherosclerotic plaques, and ox-LDL has been shown to promote monocyte recruitment, foam cell formation and the transition of quiescent and contractile vascular SMCs (smooth muscle cells) to the migratory and proliferative phenotype. SMC phenotype transition and hyperplasia are the pivotal events in the pathogenesis of atherosclerosis. To comprehend the complex molecular mechanisms involved in ox-LDL-mediated SMC phenotype transition, we have compared the differential gene expression profiles of cultured quiescent human coronary artery SMCs with cells induced with ox-LDL for 3 and 21 h using Affymetrix HG-133UA cDNA microarray chips. Assignment of the regulated genes into functional groups indicated that several genes involved in metabolism, membrane transport, cell-cell interactions, signal transduction, transcription, translation, cell migration, proliferation and apoptosis were differentially expressed. Our data suggests that the interaction of ox-LDL with its cognate receptors on SMCs modulates the induction of several growth factors and cytokines, which activate a variety of intracellular signalling mechanisms (including PI3K, MAPK, Jak/STAT, sphingosine, Rho kinase pathways) that contribute to SMC transition from the quiescent and contractile phenotype to the proliferative and migratory phenotype. Our study has also identified several genes (including CDC27, cyclin A1, cyclin G2, glypican 1, MINOR, p15 and apolipoprotein) not previously implicated in ox-LDL-induced SMC phenotype transition and substantially extends the list of potential candidate genes involved in atherogenesis.

An integrated approach to uncover drivers of cancer

Systematic characterization of cancer genomes has revealed a staggering number of diverse aberrations that differ among individuals, such that the functional importance and physiological impact of most tumor genetic alterations remain poorly defined. We developed a computational framework that integrates chromosomal copy number and gene expression data for detecting aberrations that promote cancer progression. We demonstrate the utility of this framework using a melanoma data set. Our analysis correctly identified known drivers of melanoma and predicted multiple tumor dependencies. Two dependencies, TBC1D16 and RAB27A, confirmed empirically, suggest that abnormal regulation of protein trafficking contributes to proliferation in melanoma. Together, these results demonstrate the ability of integrative Bayesian approaches to identify candidate drivers with biological, and possibly therapeutic, importance in cancer.

A₂B receptors mediate the induction of early genes and inhibition of arterial smooth muscle cell proliferation via Epac

AIMS

Extracellular adenosine and adenine nucleotides play important roles in the regulation of the blood vessel tonus and platelet aggregation. Less is known about the effects of these extracellular signalling molecules on gene expression in vascular smooth muscle cells involved in long-term vascular effects. In the present study, we therefore searched for adenosine-induced changes in the expression of early genes in cultured human coronary artery smooth muscle cells (HCASMCs).

METHODS AND RESULTS

Whole-genome DNA array hybridization revealed that adenosine induced a set of early genes including the nuclear receptor subfamily 4, group A, member 1 (NR4A1/Nur77/TR3). The pattern of the effects of adenosine on gene expression resembles the change in expression induced by the direct activator of adenylate cyclase forskolin. Real-time reverse-transcriptase PCR confirmed that adenosine and its analogue N-ethyl-carboxamidoadenosine elicited a strong induction of NR4A1. These effects were markedly attenuated by A(2B) receptor antagonists including 8-[4-(4-benzylpiperazide-1-sulfonyl)phenyl]-1-propylxanthine (PSB-601) and were mimicked by a cyclic AMP (cAMP) analogue [8-(4-chlorophenylthio)-2'-O-methyl-cAMP, 8CPT] acting on the exchange protein activated by cAMP (Epac). Long-term experiments over 5 days showed that 2-chloroadenosine decreased cell proliferation in the presence of platelet-derived growth factor. This effect of 2-chloroadenosine was also attenuated by PSB-601 and mimicked by 8CPT. Treatment with small interfering RNA directed against NR4A1 attenuated the inhibitory effect of 8CPT on proliferation.

CONCLUSIONS

In summary, our results demonstrate the operation of adenosine A₂(B) receptors mediating an early induction of NR4A1 and a decrease in cell proliferation via the cAMP/Epac pathway in HCASMCs.

Telomerase activation in atherosclerosis and induction of telomerase reverse transcriptase expression by inflammatory stimuli in macrophages

OBJECTIVE

Telomerase serves as a critical regulator of tissue renewal. Although telomerase activity is inducible in response to various environmental cues, it remains unknown whether telomerase is activated during the inflammatory remodeling underlying atherosclerosis formation. To address this question, we investigated in the present study the regulation of telomerase in macrophages and during atherosclerosis development in low-density lipoprotein receptor-deficient mice.

METHODS AND RESULTS

We demonstrate that inflammatory stimuli activate telomerase in macrophages by inducing the expression of the catalytic subunit telomerase reverse transcriptase (TERT). Reporter and chromatin immunoprecipitation assays identified a previously unrecognized nuclear factor-κB (NF-κB) response element in the TERT promoter, to which NF-κB is recruited during inflammation. Inhibition of NF-κB signaling completely abolished the induction of TERT expression, characterizing TERT as a bona fide NF-κB target gene. Furthermore, functional experiments revealed that TERT deficiency results in a senescent cell phenotype. Finally, we demonstrate high levels of TERT expression in macrophages of human atherosclerotic lesions and establish that telomerase is activated during atherosclerosis development in low-density lipoprotein receptor-deficient mice.

CONCLUSIONS

These results characterize TERT as a previously unrecognized NF-κB target gene in macrophages and demonstrate that telomerase is activated during atherosclerosis. This induction of TERT expression prevents macrophage senescence and may have important implications for the development of atherosclerosis.

NR4A orphan nuclear receptors: transcriptional regulators of gene expression in metabolism and vascular biology

Members of the nuclear hormone receptor superfamily, including the peroxisome proliferator-activated receptor and the liver X receptor subfamilies, orchestrate transcriptional networks involved in the control of metabolism and the development of vascular disease. In addition to these well-characterized ligand-activated transcription factors, the nuclear receptor (NR) superfamily comprises many orphan receptors, whose ligands and physiological functions remain unknown. Among this group of orphan receptors is the NR4A subfamily, including Nur77 (NR4A1), Nurr1 (NR4A2), and NOR1 (NR4A3). These orphan NRs constitute an evolutionary ancient and highly conserved group of transcription factors. In contrast to other members of the superfamily, NR4A receptors function as ligand-independent transcription factors and immediate- or early-response genes, which are rapidly induced by a pleiotropy of environmental cues. Early functional studies have pointed to a critical role of NR4A receptors in regulating differentiation, proliferation, and apoptosis. More recent research has characterized NR4A receptors as key transcriptional regulators of glucose and lipid homeostasis, adipogenesis, inflammation, and vascular remodeling. In this review, we will summarize recent advances in understanding the molecular biology and physiological functions of NR4A receptors and discuss their role in the transcriptional control of metabolism and vascular remodeling.

Deficiency of the NR4A orphan nuclear receptor NOR1 decreases monocyte adhesion and atherosclerosis

RATIONALE

The orphan nuclear receptor NOR1 is a member of the evolutionary highly conserved and ligand-independent NR4A subfamily of the nuclear hormone receptor superfamily. Members of this subfamily have been characterized as early response genes regulating essential biological processes including inflammation and proliferation; however, the role of NOR1 in atherosclerosis remains unknown.

OBJECTIVE

The goal of the present study was to determine the causal contribution of NOR1 to atherosclerosis development and to identify the mechanism by which this nuclear receptor participates in the disease process.

METHODS AND RESULTS

In the present study, we demonstrate expression of NOR1 in endothelial cells of human atherosclerotic lesions. In response to inflammatory stimuli, NOR1 expression is rapidly induced in endothelial cells through a nuclear factor kappaB-dependent transactivation of the NOR1 promoter. Overexpression of NOR1 in human endothelial cells increased the expression of vascular cell adhesion molecule (VCAM)-1 and intercellular adhesion molecule-1, whereas NOR1 deficiency altered adhesion molecule expression in response to inflammatory stimuli. Transient transfection experiments and chromatin immunoprecipitation assays revealed that NOR1 induces VCAM-1 promoter activity by binding to a canonical response element for NR4A receptors in the VCAM-1 promoter. Further functional studies confirmed that NOR1 mediates monocyte adhesion by inducing VCAM-1 and intercellular adhesion molecule-1 expression in endothelial cells. Finally, we demonstrate that NOR1 deficiency reduces hypercholesterolemia-induced atherosclerosis formation in apoE(-/-) mice by decreasing the macrophage content of the lesion.

CONCLUSIONS

In concert, these studies identify a novel pathway underlying monocyte adhesion and establish that NOR1 serves a previously unrecognized atherogenic role in mice by positively regulating monocyte recruitment to the vascular wall.

Inhibition of monocyte adhesion to endothelial cells and attenuation of atherosclerotic lesion by a glucagon-like peptide-1 receptor agonist, exendin-4

OBJECTIVE

Exogenous administration of glucagon-like peptide-1 (GLP-1) or GLP-1 receptor agonists such as an exendin-4 has direct beneficial effects on the cardiovascular system. However, their effects on atherosclerogenesis have not been elucidated. The aim of this study was to investigate the effects of GLP-1 on accumulation of monocytes/macrophages on the vascular wall, one of the earliest steps in atherosclerogenesis.

RESEARCH DESIGN AND METHODS

After continuous infusion of low (300 pmol . kg(-1) . day(-1)) or high (24 nmol . kg(-1) . day(-1)) dose of exendin-4 in C57BL/6 or apolipoprotein E-deficient mice (apoE(-/-)), we evaluated monocyte adhesion to the endothelia of thoracic aorta and arteriosclerotic lesions around the aortic valve. The effects of exendin-4 were investigated in mouse macrophages and human monocytes.

RESULTS

Treatment with exendin-4 significantly inhibited monocytic adhesion in the aortas of C57BL/6 mice without affecting metabolic parameters. In apoE(-/-) mice, the same treatment reduced monocyte adhesion to the endothelium and suppressed atherosclerogenesis. In vitro treatment of mouse macrophages with exendin-4 suppressed lipopolysaccharide-induced mRNA expression of tumor necrosis factor-alpha and monocyte chemoattractant protein-1, and suppressed nuclear translocation of p65, a component of nuclear factor-kappaB. This effect was reversed by either MDL-12330A, a cAMP inhibitor or PKI(14-22), a protein kinase A-specific inhibitor. In human monocytes, exendin-4 reduced the expression of CD11b.

CONCLUSIONS

Our data suggested that GLP-1 receptor agonists reduced monocyte/macrophage accumulation in the arterial wall by inhibiting the inflammatory response in macrophages, and that this effect may contribute to the attenuation of atherosclerotic lesion by exendin-4.

The hypoxia-inducible factor 1/NOR-1 axis regulates the survival response of endothelial cells to hypoxia

Hypoxia induces apoptosis but also triggers adaptive mechanisms to ensure cell survival. Here we show that the prosurvival effects of hypoxia-inducible factor 1 (HIF-1) in endothelial cells are mediated by neuron-derived orphan receptor 1 (NOR-1). The overexpression of NOR-1 decreased the rate of endothelial cells undergoing apoptosis in cultures exposed to hypoxia, while the inhibition of NOR-1 increased cell apoptosis. Hypoxia upregulated NOR-1 mRNA levels in a time- and dose-dependent manner. Blocking antibodies against VEGF or SU5614 (a VEGF receptor 2 inhibitor) did not prevent hypoxia-induced NOR-1 expression, suggesting that NOR-1 is not induced by the autocrine secretion of VEGF in response to hypoxia. The reduction of HIF-1 alpha protein levels by small interfering RNAs, or by inhibitors of the phosphatidylinositol-3 kinase (PI3K)/Akt pathway or mTOR, significantly counteracted hypoxia-induced NOR-1 upregulation. Intracellular Ca(2+) was involved in hypoxia-induced PI3K/Akt activation and in the downstream NOR-1 upregulation. A hypoxia response element mediated the transcriptional activation of NOR-1 induced by hypoxia as we show by transient transfection and chromatin immunoprecipitation assays. Finally, the attenuation of NOR-1 expression reduced both basal and hypoxia-induced cIAP2 (cellular inhibitor of apoptosis protein 2) mRNA levels, while NOR-1 overexpression upregulated cIAP2. Therefore, NOR-1 is a downstream effector of HIF-1 signaling involved in the survival response of endothelial cells to hypoxia.

Activation of thromboxane A(2) receptors induces orphan nuclear receptor Nurr1 expression and stimulates cell proliferation in human lung cancer cells

Previous studies implicate that activation of thromboxane A(2) receptor (TP) induced cell proliferation and transformation in several cell lines. We report here that the activation of TP by its agonist, [1S-[1alpha, 2alpha (Z), 3beta (1E, 3S*), 4alpha]]-7-[3-[3-hydroxy-4-(4-iodophenoxy)-1-butenyl]-7-oxabicyclo [2.2.1] hept-2-yl]-5-heptenoic acid (I-BOP), induced Nurr1 expression and stimulated proliferation of human lung cancer cells. Nurr1, an orphan nuclear receptor in the nuclear receptor subfamily 4A subfamily, has been implicated in cell proliferation, differentiation and apoptosis. I-BOP markedly induced Nurr1 messenger RNA and protein levels as compared with other subfamily members, Nur77 and Nor-1. The signaling pathways of I-BOP-induced Nurr1 expression were examined by using various inhibitors of signaling molecules. The induction of Nurr1 expression by I-BOP appeared to be mediated through protein kinase A (PKA)/cAMP response element binding (CREB), protein kinase C and mitogen-activated protein kinase/extracellular signal-regulated kinase pathways and not related to epidermal growth factor receptor and prostaglandin E(2) pathways. Transcriptional activation of Nurr1 gene by I-BOP was further investigated at the promoter level in H157 cells. 5'-Deletion analysis, site-directed mutagenesis and luciferase reporter assay demonstrated that Nurr1 expression was induced by I-BOP in a PKA/CREB-dependent manner. Further studies have revealed that Nurr1 may mediate cyclin D1 expression and I-BOP-induced cell proliferation in H157 cells since small interfering RNA of Nurr1 blocked I-BOP-induced cyclin D1 expression and cell proliferation and also decreased cell growth rate. These results provide strong evidence that Nurr1 plays a significant role in cell proliferation and may mediate TP agonist-induced proliferation in lung cancer cells.

Serotonin 5-HT2C receptor-independent expression of hypothalamic NOR1, a novel modulator of food intake and energy balance, in mice

NOR1, Nur77 and Nurr1 are orphan nuclear receptors and members of the NR4A subfamily. Here, we report that the expression of hypothalamic NOR1 was remarkably decreased in mildly obese beta-endorphin-deficient mice and obese db/db mice with the leptin receptor mutation, compared with age-matched wild-type mice, whereas there were no genotypic differences in the expression of hypothalamic Nur77 or Nurr1 in these animals. The injection of NOR1 siRNA oligonucleotide into the third cerebral ventricle significantly suppressed food intake and body weight in mice. On the other hand, the decreases in hypothalamic NOR1 expression were not found in non-obese 5-HT2C receptor-deficient mice. Moreover, systemic administration of m-chlorophenylpiperazine (mCPP), a 5-HT2C/1B receptor agonist, had no effect on hypothalamic NOR1 expression, while suppressing food intake in beta-endorphin-deficient mice. These findings suggest that 5-HT2C receptor-independent proopiomelanocortin-derived peptides regulate the expression of hypothalamic NOR1, which is a novel modulator of feeding behavior and energy balance.

The orphan nuclear receptor Nur77 suppresses endothelial cell activation through induction of IkappaBalpha expression

Endothelial inflammation plays a critical role in the development and progression of cardiovascular disease, albeit the mechanisms need to be fully elucidated. Nur77 is highly expressed in vascular endothelial cells (ECs) and plays a role in the regulation of cell proliferation and angiogenesis; its role in vascular inflammation, however, remains unknown. Treatment of human umbilical vein ECs (HUVECs) with tumor necrosis factor (TNF)-alpha substantially increased the transcription and protein expression of Nur77 in a dose and time-dependent manner, as determined by Northern blot and Western blot analysis. Adenovirus mediated overexpression of Nur77 markedly increased the intracellular levels of IkappaBalpha by approximately 4-fold, whereas overexpression of dominant negative Nur77 (DN-Nur77), which lacks its transactivation domain, had no effect on IkappaBalpha expression, suggesting that Nur77 is an important transcriptional factor in controlling IkappaBalpha expression in ECs. Furthermore, overexpression of Nur77 significantly increased IkappaBalpha promoter activity via directly binding to a Nur77 response element in the IkappaBalpha promoter. Importantly, overexpression of Nur77, but not DN-Nur77, protected ECs against the TNF-alpha- and interleukin-1beta-induced endothelial activation, as characterized by attenuation in the nuclear factor kappaB activation, expression of adhesion molecules ICAM-1 and VCAM-1, and monocytic adherence to ECs. These results indicate that Nur77 negatively regulates the TNF-alpha- and interleukin-1beta-induced vascular EC activation by transcriptionally upregulation of IkappaBalpha expression.

Deficiency of the NR4A neuron-derived orphan receptor-1 attenuates neointima formation after vascular injury

BACKGROUND

The neuron-derived orphan receptor-1 (NOR1) belongs to the evolutionary highly conserved and most ancient NR4A subfamily of the nuclear hormone receptor superfamily. Members of this subfamily function as early-response genes regulating key cellular processes, including proliferation, differentiation, and survival. Although NOR1 has previously been demonstrated to be required for smooth muscle cell proliferation in vitro, the role of this nuclear receptor for the proliferative response underlying neointima formation and target genes trans-activated by NOR1 remain to be defined.

METHODS AND RESULTS

Using a model of guidewire-induced arterial injury, we demonstrate decreased neointima formation in NOR1(-/-) mice compared with wild-type mice. In vitro, NOR1-deficient smooth muscle cells exhibit decreased proliferation as a result of a G(1)-->S phase arrest of the cell cycle and increased apoptosis in response to serum deprivation. NOR1 deficiency alters phosphorylation of the retinoblastoma protein by preventing mitogen-induced cyclin D1 and D2 expression. Conversely, overexpression of NOR1 induces cyclin D1 expression and the transcriptional activity of the cyclin D1 promoter in transient reporter assays. Gel shift and chromatin immunoprecipitation assays identified a putative response element for NR4A receptors in the cyclin D1 promoter, to which NOR1 is recruited in response to mitogenic stimulation. Finally, we provide evidence that these observations are applicable in vivo by demonstrating decreased cyclin D1 expression during neointima formation in NOR1-deficient mice.

CONCLUSIONS

These experiments characterize cyclin D1 as an NOR1-regulated target gene in smooth muscle cells and demonstrate that NOR1 deficiency decreases neointima formation in response to vascular injury.

NR4A Orphan Nuclear Receptors in Cardiovascular Biology

The NR4A orphan nuclear receptor subfamily is comprised of the highly homologous receptors Nur77 (NR4A1), Nurr1 (NR4A2), and NOR1 (NR4A3). These evolutionarily conserved and ancient receptors function as ligand-independent transcription factors that regulate the expression of overlapping target genes. As early response genes, the basal expression level of these receptors is low but rapidly induced as a result of changes in environmental cues. The transcriptional activity of these receptors is primarily regulated by gene induction and posttranslational modifications of the receptor including phosphorylation. NR4A receptors were initially identified in the brain and early functional studies suggested a role for these receptors in signal- and cell-specific stimulation of both apoptosis and proliferation. More recent studies have revealed much broader functions of these orphan receptors including the regulation of genes involved in cancer, metabolism, energy balance, atherosclerosis, and vascular remodeling. In this review, we will discuss our current understanding of the molecular biology of NR4A receptors and summarize recent studies suggesting an important role of these orphan receptors in vascular biology.

Differential transactivation by orphan nuclear receptor NOR1 and its fusion gene product EWS/NOR1: possible involvement of poly(ADP-ribose) polymerase I, PARP-1

In extraskeletal myxoid chondrosarcoma, a chromosomal translocation creates a gene fusion between EWS and an orphan nuclear receptor, NOR1. The resulting fusion protein EWS/NOR1 has been believed to lead to malignant transformation by functioning as a transactivator for NOR1-target genes. By comparing the gene expression profiles of NOR1- and EWS/NOR1-overexpressing cells, we found that they largely shared up-regulated genes, but no significant correlation was observed with respect to the transactivation levels of each gene. In addition, the proteins associated with NOR1 and EWS/NOR1 were mostly the same in these cells. The results suggest that these proteins differentially transactivate overlapping target genes through a similar transcriptional machinery. To clarify the mechanisms underlying the transcriptional divergence between NOR1 and EWS/NOR1, we searched for alternatively associated proteins, and identified poly(ADP-ribose) polymerase I (PARP-1) as an NOR1-specific binding protein. Consistent with its binding properties, PARP-1 acted as a transcriptional repressor of NOR1, but not EWS/NOR1, in a luciferase reporter assay employing PARP-1(-/-) fibroblasts. Interestingly, suppressive activity of PARP-1 was observed in a DNA response element-specific manner, and in a subtype-specific manner toward the NR4A family (Nur77, Nurr1, and NOR1), suggesting that PARP-1 plays a role in the diversity of transcriptional regulation mediated by the NR4A family in normal cells. Altogether, our findings suggest that NOR1 and EWS/NOR1 regulate overlapping target genes differently by utilizing associated proteins, including PARP-1; and that EWS/NOR1 may acquire oncogenic activities by avoiding (or gaining) transcription factor-specific modulation by the associated proteins.

Whole-genome microarray analysis identifies up-regulation of Nr4a nuclear receptors in muscle and liver from diet-restricted rats

One of the most conserved methods to significantly increase lifespan in animals is through dietary restriction (DR). The mechanisms by which DR increases survival are controversial but are thought to include improvements in mitochondrial function concomitant with reductions in reactive oxygen species production and alterations in the insulin signalling pathway, resulting in global metabolic adaptation. In order to identify novel genes that may be important for lifespan extension of Brown Norway rats, we compared gene expression profiles from skeletal muscle of 28-month-old animals fed ad libitum or DR diets using whole-genome arrays. Following DR, 426 transcripts were significantly down-regulated whilst only 52 were up-regulated. Included in the up-regulated transcripts were three functionally related previously unidentified DR-regulated genes: Nr4a1, Nr4a2, and Nr4a3. Up-regulation of all three Nr4a receptors was also observed in liver - but not brain - of DR-fed animals. Furthermore, RT-PCR revealed up-regulation of several NR4A transcriptional targets (Ucp-3, Ampk-gamma3, Pgc-1alpha and Pgc-1beta) in skeletal muscle of DR animals. Due to the proposed roles of the NR4A nuclear receptors in sensing and responding to changes in the nutritional environment and in regulating glucose and lipid metabolism and insulin sensitivity, we hypothesise that these proteins may contribute to DR-induced metabolic adaptation.