Involvement of JunD in transcriptional activation of the orphan receptor gene nur77 by nerve growth factor and membrane depolarization in PC12 cells

Transcriptional and epigenetic substrates of methamphetamine addiction and withdrawal: evidence from a long-access self-administration model in the rat

Methamphetamine use disorder is a chronic neuropsychiatric disorder characterized by recurrent binge episodes, intervals of abstinence, and relapses to drug use. Humans addicted to methamphetamine experience various degrees of cognitive deficits and other neurological abnormalities that complicate their activities of daily living and their participation in treatment programs. Importantly, models of methamphetamine addiction in rodents have shown that animals will readily learn to give themselves methamphetamine. Rats also accelerate their intake over time. Microarray studies have also shown that methamphetamine taking is associated with major transcriptional changes in the striatum measured within a short or longer time after cessation of drug taking. After a 2-h withdrawal time, there was increased expression of genes that participate in transcription regulation. These included cyclic AMP response element binding (CREB), ETS domain-containing protein (ELK1), and members of the FOS family of transcription factors. Other genes of interest include brain-derived neurotrophic factor (BDNF), tyrosine kinase receptor, type 2 (TrkB), and synaptophysin. Methamphetamine-induced transcription was found to be regulated via phosphorylated CREB-dependent events. After a 30-day withdrawal from methamphetamine self-administration, however, there was mostly decreased expression of transcription factors including junD. There was also downregulation of genes whose protein products are constituents of chromatin-remodeling complexes. Altogether, these genome-wide results show that methamphetamine abuse might be associated with altered regulation of a diversity of gene networks that impact cellular and synaptic functions. These transcriptional changes might serve as triggers for the neuropsychiatric presentations of humans who abuse this drug. Better understanding of the way that gene products interact to cause methamphetamine addiction will help to develop better pharmacological treatment of methamphetamine addicts.

Angiopoietin-1 and vascular endothelial growth factor regulation of leukocyte adhesion to endothelial cells: role of nuclear receptor-77

OBJECTIVE

Vascular endothelial growth factor (VEGF) promotes leukocyte adhesion to endothelial cells (ECs). Angiopoietin-1 (Ang-1) inhibits this response. Nuclear receptor-77 (Nur77) is a proangiogenic nuclear receptor. In the present study, we assessed the influence of Ang-1 and VEGF on Nur77 expression in ECs, and evaluated its role in Ang-1/VEGF-mediated leukocyte adhesion.

METHODS AND RESULTS

Expression of Nur77 was evaluated with real-time polymerase chain reaction and immunoblotting. Adhesion of leukocytes to ECs was monitored with inverted microscopy. Nur77 expression or activity was inhibited using adenoviruses expressing dominant-negative form of Nur77, retroviruses expressing Nur77 in the antisense direction, and small interfering RNA oligos. Both Ang-1 and VEGF induce Nur77 expression, by >5- and 30-fold, respectively. When combined, Ang-1 potentiates VEGF-induced Nur77 expression. Ang-1 induces Nur77 through the phosphoinositide 3-kinase and extracellular signal-regulated protein kinase 1/2 pathways. VEGF induces Nur77 expression through the protein kinase D/histone deacetylase 7/myocyte enhancer factor 2 and extracellular signal-regulated protein kinase 1/2 pathways. VEGF induces nuclear factor-kappaB transcription factor, vascular cell adhesion molecule-1, and E-selectin expressions, and promotes leukocyte adhesion to ECs. Ang-1 inhibits these responses. This inhibitory effect of Ang-1 disappears when Nur77 expression is disrupted, restoring the inductive effects of VEGF on adhesion molecule expression, and increased leukocyte adhesion to ECs.

CONCLUSIONS

Nur77 promotes anti-inflammatory effects of Ang-1, and functions as a negative feedback inhibitor of VEGF-induced EC activation.

Regulation of IGF-1 but not TGF-β1 by NGF in the smooth muscle of the inflamed urinary bladder

Intraperitoneal injection of cyclophosphamide (CYP) causes hemorrhagic cystitis with excess growth of muscular layer leading to bladder hypertrophy; this could be attributable to changes in the expression profiles of growth factors in the inflamed urinary bladder. The growth factors characterized in the current study include nerve growth factor (NGF), insulin-like growth factor (IGF)-1, and transforming growth factor (TGF)-β1. We found that following CYP injection for 8 h and 48 h, the mRNA levels of all three factors were increased in the inflamed bladder when compared to control. The level of NGF mRNA was mainly increased in the urothelium layer while the levels of IGF-1 mRNA and TGF-β1 mRNA were increased in the smooth muscle layer. The level of NGF high affinity receptor TrkA mRNA was also increased in both the urothelium and the smooth muscle layers during bladder inflammation. When we blocked NGF action with NGF neutralizing antibody in vivo, we found that the up-regulation of IGF-1 in the inflamed bladder was reversed while the up-regulation of TGF-β1 was not affected by NGF neutralization. The effect of NGF on regulating IGF-1 expression was further confirmed in bladder smooth muscle culture showing that exogenous NGF increased the mRNA level of IGF-1 after 30 min to 1 h stimulation. These results suggested that bladder inflammation induced region-specific changes in the expression profiles of NGF, IGF-1 and TGF-β1. The up-regulation of NGF in the urothelium may have a role in affecting bladder smooth muscle cell physiology by regulating IGF-1 expression.

Regulation of Nur77 expression by β-catenin and its mitogenic effect in colon cancer cells

The orphan nuclear receptor Nur77 is an immediate-early response gene whose expression is rapidly induced by various extracellular stimuli. The aims of this study were to study the role of Nur77 expression in the growth and survival of colon cancer cells and the mechanism by which Nur77 expression was regulated. We showed that levels of Nur77 were elevated in a majority of human colon tumors (9/12) compared to their nontumorous tissues and that Nur77 expression could be strongly induced by different colonic carcinogens including deoxycholic acid (DCA). DCA-induced Nur77 expression resulted in up-regulation of antiapoptotic BRE and angiogenic VEGF, and it enhanced the growth, colony formation, and migration of colon cancer cells. In studying the mechanism by which Nur77 was regulated in colon cancer cells, we found that β-catenin was involved in induction of Nur77 expression through its activation of the transcriptional activity of AP-1 (c-Fos/c-Jun) that bound to and transactivated the Nur77 promoter. Together, our results demonstrate that Nur77 acts to promote the growth and survival of colon cancer cells and serves as an important mediator of the Wnt/β-catenin and AP-1 signaling pathways.

Endogenous nerve growth factor regulates collagen expression and bladder hypertrophy through Akt and MAPK pathways during cystitis

Type I collagen forms the main constituent of the extracellular matrix in visceral organs. We reported here that cyclophosphamide (CYP)-induced cystitis significantly increased the production of type I collagen in the inflamed bladder leading to increases in the bladder weight and the thickness of the bladder wall. The endogenous nerve growth factor (NGF) in the urinary bladder regulated type I collagen expression because the neutralizing NGF antibody attenuated cystitis-induced type I collagen up-regulation in the inflamed bladder. Neutralizing NGF antibody also subsequently reversed cystitis-induced increases in bladder weight. Further studies on the intermediate signaling pathways mediating NGF-induced type I collagen expression in the inflamed bladder during cystitis revealed that Akt, JNK, and ERK1/2 activities were increased in the inflamed bladder, whereas p38 MAPK remained unchanged. Suppression of endogenous NGF level with neutralizing NGF antibody significantly blocked the increased activity of Akt, JNK, and ERK1/2 in the inflamed bladder during cystitis. These results indicate that endogenous NGF plays an important role in the activation of Akt and MAPK in the urinary bladder and in bladder hypertrophy during cystitis.

Nur77 upregulates HIF-alpha by inhibiting pVHL-mediated degradation

In this study, we investigated the role of Nur77, an orphan nuclear receptor, in HIF-alpha transcriptional activity. We found that Nur77 associates and stabilizes HIF-1alpha via indirect interaction. Nur77 was found to interact with pVHL in vivo via the alpha-domain of pVHL. By binding to pVHL, Nur77 competed with elongin C for pVHL binding. Moreover, Nur77-binding to pVHL inhibited the pVHL-mediated ubiquitination of HIF-1alpha and ultimately increased the stability and transcriptional activity of HIF-1alpha. The ligand-binding domain of Nur77 was found to interact with pVHL and the expression of this ligand-binding domain was sufficient to stabilize and transactivate HIF-1alpha. Under the conditions that cobalt chloride was treated or pVHL was knocked down, Nur77 could not stabilize HIF-alpha. Moreover, Nur77 could not further stabilize HIF-2alpha in A498/VHL stable cells, which is consistent with our finding that Nur77 indirectly stabilizes HIF-alpha by binding to pVHL. Thus, our results suggest that an orphan nuclear receptor Nur77 binds to pVHL, thereby stabilizes and increases HIF-alpha transcriptional activity under the non-hypoxic conditions.

Nerve Growth factor regulation of cyclin D1 in PC12 cells through a p21RAS extracellular signal-regulated kinase pathway requires cooperative interactions between Sp1 and nuclear factor-kappaB

The PC12 pheochromocytoma cell line responds to nerve growth factor (NGF) by exiting from the cell cycle and differentiating to induce extending neurites. Cyclin D1 is an important regulator of G1/S phase cell cycle progression, and it is known to play a role in myocyte differentiation in cultured cells. Herein, NGF induced cyclin D1 promoter, mRNA, and protein expression via the p21(RAS) pathway. Antisense- or small interfering RNA to cyclin D1 abolished NGF-mediated neurite outgrowth, demonstrating the essential role of cyclin D1 in NGF-mediated differentiation. Expression vectors encoding mutants of the Ras/mitogen-activated protein kinase pathway, and chemical inhibitors, demonstrated NGF induction of cyclin D1 involved cooperative interactions of extracellular signal-regulated kinase, p38, and phosphatidylinositol 3-kinase pathways downstream of p21(RAS). NGF induced the cyclin D1 promoter via Sp1, nuclear factor-kappaB, and cAMP-response element/activated transcription factor sites. NGF induction via Sp1 involved the formation of a Sp1/p50/p107 complex. Cyclin D1 induction by NGF governs differentiation and neurite outgrowth in PC12 cells.

MSKs are required for the transcription of the nuclear orphan receptors Nur77, Nurr1 and Nor1 downstream of MAPK signalling

MSK (mitogen- and stress-activated protein kinase) 1 and MSK2 are kinases activated downstream of either the ERK (extracellular-signal-regulated kinase) 1/2 or p38 MAPK (mitogen-activated protein kinase) pathways in vivo and are required for the phosphorylation of CREB (cAMP response element-binding protein) and histone H3. Here we show that the MSKs are involved in regulating the transcription of the immediate early gene Nur77. Stimulation of mouse embryonic fibroblasts with PMA, EGF (epidermal growth factor), TNF (tumour necrosis factor) or anisomycin resulted in induction of the Nur77 mRNA. The induction of Nur77 by TNF and anisomycin was abolished in MSK1/2 double-knockout cells, whereas induction was significantly reduced in response to PMA or EGF. The MSK responsive elements were mapped to two AP (activator protein)-1-like elements in the Nur77 promoter. The induction of Nur77 was also blocked by A-CREB, suggesting that MSKs control Nur77 transcription by phosphorylating CREB bound to the two AP-1-like elements. Consistent with the decrease in Nur77 mRNA levels in the MSK1/2-knockout cells, it was also found that MSKs were required for the induction of Nur77 protein by PMA and TNF. MSKs were also found to be required for the transcription of two genes related to Nur77, Nurr1 and Nor1, which were also transcribed in a CREB- or ATF1 (activating transcription factor-1)-dependent manner. Downstream of anisomycin signalling, a second ERK-dependent pathway, independent of MSK and CREB, was also required for the transcription of Nurr1 and Nor1.

Upregulation of orphan nuclear receptor Nur77 following PGF(2alpha), Bimatoprost, and Butaprost treatments. Essential role of a protein kinase C pathway involved in EP(2) receptor activated Nur77 gene transcription

1. Using gene chip technology, we first identified that PGF(2alpha) (FP agonist) and Butaprost (EP(2) agonist) induced about a five-fold upregulation of Nur77 mRNA expression in hFP-HEK 293/EBNA and hEP(2)-HEK293/EBNA cells. Northern Blot analysis revealed that PGF(2alpha)- and Butaprost-induced upregulation of Nur77 expression are dose- and time-dependent. 2. Both PGF(2alpha) and Butaprost upregulated Nur77 gene expression through the protein kinase C (PKC) pathway. These data are the first showing a link between EP(2) receptor stimulation and protein kinase C activation. Calcineurin was found to be involved downstream of the PKC pathway in PGF(2alpha)-induced Nur77 expression, but not in Butaprost-induced Nur77 expression. 3. We also used Nur77 as a marker gene to compare the effects of PGF(2alpha), Butaprost, and Bimatoprost (a prostamide) on Nur77 expression in human primary trabecular meshwork and ciliary smooth muscle (SM) cells, which are target cells for antiglaucoma drugs. The results showed that PGF(2alpha) and Butaprost, but not Bimatoprost, induced upregulation of Nur77 expression in human TM cells. PGF(2alpha), but not Bimatoprost, dramatically induced upregulation of Nur77 mRNA expression in human ciliary SM cells, whereas Butaprost slightly upregulated Nur77 mRNA expression in SM cells. 4. Nur77 promoter deletion analysis indicated that PGF(2alpha), but not Bimatoprost, activated Nur77 promoter-luciferase reporter in hFP-HEK 293/EBNA cells. Butaprost was less efficacious in inducing Nur77 promoter-luciferase reporter activity in hEP(2)-HEK293/EBNA cells relative to PGF(2alpha) in the comparable assay. The data for Nur77 promoter functional analysis were matched to the Northern blot analysis. 5. It appears that PGF(2alpha) and Butaprost activate Nur77 transcription mechanisms through the activation of FP and EP(2) receptor-coupled signaling pathways, whereas Bimatoprost stimulates neither FP nor EP(2) receptors.

Nur77 activated by hypoxia-inducible factor-1alpha overproduces proopiomelanocortin in von Hippel-Lindau-mutated renal cell carcinoma

Mutation in the von Hippel-Lindau (VHL) protein associated with renal cell carcinoma causes hypoxia-inducible factor (HIF) to stabilize and consequently to induce various HIF-targeting proteins. In this study, we found that proopiomelanocortin (POMC), an adrenocorticotropic hormone precursor, is up-regulated constitutively in VHL-mutated renal cell carcinoma. A critical transcription factor responsible for POMC overproduction was identified as Nur77, a member of the orphan steroid receptor superfamily. Little is known about how VHL mutation leads to activation of Nur77. We report that Nur77 is directly regulated by HIF. We show that HIF-1alpha, but not HIF-2alpha, binds to a putative HIF responsive element in the Nur77 promoter, activating the expression of Nur77. Mutation or deletion of the HIF binding site in the Nur77 promoter abrogates activation of a luciferase reporter gene under the control of Nur77 promoter by HIF-1alpha. The treatment of Nur77 antisense oligonucleotide reduces POMC transcription under hypoxic conditions. We confirmed that Nur77 and POMC are up-regulated in VHL-mutated renal cell carcinoma. In this study, we provide the first molecular evidence that Nur77 activated by HIF under hypoxic conditions regulates production of the peptide hormone precursor POMC.

Induction of apoptosis by TPA and VP-16 is through translocation of TR3

AIM: To investigate the role of TR3 in induction of apoptosis in gastric cancer cells.

METHODS: Human gastric cancer cell line, MGC80-3, was used. Expression of TR3 mRNA and its protein was detected by Northern blot and Western blot. Localization of TR3 protein was showed by immunofluorescence analysis under laser-scanning confocal microscope. Apoptotic morphology was observed by DAPI fluorescence staining, and apoptotic index was counted among 1000 cells randomly. Stable transfection assay was carried out by Lipofectamine.

RESULTS: Treatment of MGC80-3 cells with TPA and VP-16 resulted in apoptosis, accompanied by the repression of Bcl-2 protein in a time-dependent manner. At the same time, TPA and VP-16 also up-regulated expression level of TR3 mRNA in MGC80-3 cells that expressed TR3 mRNA. When antisense-TR3 expression vector was transfected into the cells, expression of TR3 protein was repressed. In this case, TPA and VP-16 did not induce apoptosis. In addition, TPA and VP-16-induced apoptosis involved in translocation of TR3. In MGC80-3 cells, TR3 localized concentrative in nucleus, after treatment of cells with TPA and VP-16, TR3 translocated from nucleus to cytosol obviously. However, when this nuclear translocation was blocked by LMB, apoptosis was not occurred in MGC80-3 cells even in the presence of TPA and VP-16.

CONCLUSION: Induction of apoptosis by TPA and VP-16 is through induction of TR3 expression and translocation of TR3 from nucleus to cytosol, which may be a novel signal pathway for TR3, and represent the new biological function of TR3 to exert its effect on apoptosis in gastric cancer cells.

Mediation of NGF signaling by post-translational inhibition of HES-1, a basic helix-loop-helix repressor of neuronal differentiation

The induction of neurite outgrowth by NGF is a transcription-dependent process in PC12 cells, but the transcription factors that mediate this process are not known. Here we show that the bHLH transcriptional repressor HES-1 is a mediator of this process. Inactivation of endogenous HES-1 by forced expression of a dominant-negative protein induces neurite outgrowth in the absence of NGF and increases response to NGF. In contrast, expression of additional wild-type HES-1 protein represses and delays response to NGF. Endogenous HES-1 DNA-binding activity is post-translationally inhibited during NGF signaling in vivo, and phosphorylation of PKC consensus sites in the HES-1 DNA-binding domain inhibits DNA binding by purified HES-1 in vitro. Mutation of these sites generates a constitutively active protein that strongly and persistently blocks response to NGF. These results suggest that post-translational inhibition of HES-1 is both essential for and partially mediates the induction of neurite outgrowth by NGF signaling.

Regulation of the neural-specific gene VGF in PC12 cells. Identification of transcription factors interacting with NGF-responsive elements

Nerve growth factor (NGF) is an important regulator of differentiation and survival in both the peripheral and central nervous systems. We have begun to analyze the mechanism by which NGF induces the expression of a neural specific gene, VGF, in PC12 cells. Using DNase I footprinting and transient transfection analysis, we identified two VGF promoter regions, V1 and V2, that are required for basal promoter expression as well as gene induction by NGF, epidermal growth factor (EGF), and cAMP. The V1 element is essential for VGF promoter function, but it is not sufficient to confer NGF responsiveness to a heterologous promoter. In contrast, the V2 element can independently stimulate the expression of a linked herpes simplex virus (HSV) thymidine kinase promoter in response to NGF. We showed that the V2 region also contains a sequence that acts as a promoter-specific negative regulator of basal VGF gene expression. As determined by gel mobility shift and Southwestern analysis, the V1 sequence is recognized by a novel PC12 nuclear protein of about 110-kDa molecular mass. Using oligonucleotide competition and antibody supershift assays, we demonstrated that the cAMP-response element (CRE) motif within the V2 element interacted specifically with proteins related to cAMP-response element binding (CREB), JunB, and JunD transcription factors. The JunB-related binding activities were transiently induced by NGF, suggesting that part of the mechanism utilized by NGF to activate VGF transcription includes increased synthesis of a V2 binding protein. Taken together, our analysis suggests that the VGF promoter is regulated by a complex mechanism, and its activation requires combinatorial action of several transcription factors interacting with multiple promoter elements.