Involvement of the NGFI-A gene in the differentiation of neuroblastoma cells

The Lysine Demethylase KDM7A Regulates Immediate Early Genes in Neurons

Lysine demethylase KDM7A removes histone modifications H3K9me1/2 and H3K27me1/2. KDM7A plays critical roles in gene expression and contribute to biological processes including tumorigenesis, metabolism, and embryonic development. However, the functions of KDM7A in mammalian nervous system are still poorly explored. In this study, functional roles of KDM7A are comprehensively investigated in neuronal cells by applying CUT&Tag-seq, RNA-seq and mice models. Knockdown of Kdm7a in N2A cells result in the alteration of histone modifications near transcription start sites (TSSs) and the expression changes of a large number of genes. In particular, the expression of immediate early genes (IEGs), a series of genes maintaining the function of the nervous system and associating with neurological disorders, are significantly decreased upon Kdm7a knockdown. Furthermore, in vivo knockdown of Kdm7a in dentate gyrus (DG) neuron of mice hippocampus, via Adeno-associated virus (AAV)-based stereotaxic microinjection, led to a significant decrease of the expression of c-Fos, a marker of neuron activity. Behavior assays in mice further revealed that Kdm7a knockdown in hippocampus repress neuron activity, which leading to impairment of emotion and memory. Collectively, the study reveals that KDM7A affects neuron functions by regulating IEGs, which may provide new clues for understanding epigenetic mechanisms in neurological disorders.

Hyperglycemia: GDNF-EGR1 pathway target renal epithelial cell migration and apoptosis in diabetic renal embryopathy

Maternal hyperglycemia can inhibit morphogenesis of ureteric bud branching, Glial cell line-derived neurotrophilic factor (GDNF) is a key regulator of the initiation of ureteric branching. Early growth response gene-1 (EGR-1) is an immediate early gene. Preliminary study found EGR-1 persistently expressed with GDNF in hyperglycemic environment. To evaluate the potential relationship of hyperglycemia-GDNF-EGR-1 pathway, in vitro human renal proximal tubular epithelial (HRPTE) cells as target and in vivo streptozotocin-induced mice model were used. Our in vivo microarray, real time-PCR and confocal morphological observation confirmed apoptosis in hyperglycemia-induced fetal nephropathy via activation of the GDNF/MAPK/EGR-1 pathway at E12-E15. Detachment between ureteric branch and metanephrons, coupled with decreasing number and collapse of nephrons on Day 1 newborn mice indicate hyperglycemic environment suppress ureteric bud to invade metanephric rudiment. In vitro evidence proved that high glucose suppressed HRPTE cell migration and enhanced GDNF-EGR-1 pathway, inducing HRPTE cell apoptosis. Knockdown of EGR-1 by siRNA negated hyperglycemic suppressed GDNF-induced HRPTE cells. EGR-1 siRNA also reduced GDNF/EGR-1-induced cRaf/MEK/ERK phosphorylation by 80%. Our findings reveal a novel mechanism of GDNF/MAPK/EGR-1 activation playing a critical role in HRPTE cell migration, apoptosis and fetal hyperglycemic nephropathy.

Phospholipase C-η2 is required for retinoic acid-stimulated neurite growth

Phospholipase C-η2 is a recently identified phospholipase C (PLC) implicated in the regulation of neuronal differentiation/maturation. PLCη2 activity is triggered by intracellular calcium mobilization and likely serves to amplify Ca²⁺ signals by stimulating further Ca²⁺ release from Ins(1,4,5)P₃-sensitive stores. The role of PLCη2 in neuritogenesis was assessed during retinoic acid (RA)-induced Neuro2A cell differentiation. PLCη2 expression increased two-fold during a 4-day differentiation period. Stable expression of PLCη2-targetted shRNA led to a decrease in the number of differentiated cells and total length of neurites following RA-treatment. Furthermore, RA response element activation was perturbed by PLCη2 knockdown. Using a bacterial two-hybrid screen, we identified LIM domain kinase 1 (LIMK1) as a putative interaction partner of PLCη2. Immunostaining of PLCη2 revealed significant co-localization with LIMK1 in the nucleus and growing neurites in Neuro2A cells. RA-induced phosphorylation of LIMK1 and cAMP-responsive element-binding protein was reduced in PLCη2 knock-down cells. The phosphoinositide-binding properties of the PLCη2 PH domain, assessed using a FRET-based assay, revealed this domain to possess a high affinity toward PtdIns(3,4,5)P₃. Immunostaining of PLCη2 together with PtdIns(3,4,5)P₃ in the Neuro2A cells revealed a high degree of co-localization, indicating that PtdIns(3,4,5)P₃ levels in cellular compartments are likely to be important for the spatial control of PLCη2 signaling.

EGFR signaling upregulates expression of microsomal prostaglandin E synthase-1 in cancer cells leading to enhanced tumorigenicity

In this report we describe the contribution of prostaglandin E(2) (PGE(2)) derived from the inducible microsomal PGE-synthase type-1 (mPGES-1) to the epidermal growth factor receptor (EGFR) oncogenic drive in tumor epithelial cells and in tumor-bearing mice. EGFR stimulation upregulated expression of mPGES-1 in HT-29, A431 and A549 cancer cells. Egr-1, a transcription factor induced by EGF, mediated this response. The Egr-1 rise provoked the overexpression of mPGES-1 messenger and protein, and enhanced PGE(2) formation. These changes were suppressed either by silencing Egr-1, or by upstream blockade of EGFR or ERK1/2 signals. Further, in a clonogenic assay on tumor cells, EGF induced a florid tumorigenic phenotype, which regressed when mPGES-1 was silenced or knocked down. EGF-induced mPGES-1 overexpression in epithelial cell reduced E-cadherin expression, whereas enhancing that of vimentin, suggesting an incipient mesenchymal phenotype. Additionally, inhibiting the EGFR in mice bearing the A431 tumor, the mPGES-1 expression and the tumor growth, exhibited a parallel decline. In conclusion, these findings provide novel evidence that a tight cooperation between the EGF/EGFR and mPGES-1 leads to a significant tumorigenic gain in epithelial cells, and provide clues for controlling the vicious association.

Secreted amyloid precursor protein β and secreted amyloid precursor protein α induce axon outgrowth in vitro through Egr1 signaling pathway

Background

sAPPα released after α secretase cleavage of Amyloid Precursor Protein (APP) has several functions including the stimulation of neurite outgrowth although detailed morphometric analysis has not been done. Two domains involved in this function have been described and are present in sAPPβ released at the first step of amyloid peptide cleavage, raising the possibility that sAPPβ could also stimulate neurite outgrowth. We investigated the morphological effects of sAPPα and sAPPβ on primary neurons and identified a key signaling event required for the changes observed.

Methodology/Principal Findings

Final concentrations of 50 to 150 nM bacterial recombinant sAPPα or sAPPβ added to primary neuronal cultures after 1 day in vitro decreased cell adhesion 24 hours later and primary dendrite length 96 hours later. 150 nM sAPPα and sAPPβ induced a similar increase of axon outgrowth, although this increase was already significant at 100 nM sAPPα. These morphological changes induced by sAPPs were also observed when added to differentiated neurons at 5 days in vitro. Real time PCR and immunocytochemistry showed that sAPPα and sAPPβ stimulated Egr1 expression downstream of MAPK/ERK activation. Furthermore, in primary neurons from Egr1 −/− mice, sAPPs affected dendritic length but did not induce any increase of axon length.

Conclusion/Significance

sAPPα and sAPPβ decrease cell adhesion and increase axon elongation. These morphological changes are similar to what has been observed in response to heparan sulfate. The sAPPα/sAPPβ stimulated increase in axon growth requires Egr1 signaling. These data suggest that sAPPβ is not deleterious per se. Since sAPPβ and sAPPα are present in the embryonic brain, these two APP metabolites might play a role in axon outgrowth during development and in response to brain damage.

The transcription factors Egr1 and Egr2 have opposing influences on adipocyte differentiation

The zinc finger-containing transcription factors Egr1 (Krox24) and Egr2 (Krox20) have been implicated in the proliferation and differentiation of many cell types. Egr2 has earlier been shown to play a positive role in adipocyte differentiation, but the function of Egr1 in this context is unknown. We compared the roles of Egr1 and Egr2 in the differentiation of murine 3T3-L1 adipocytes. Egr1 protein was rapidly induced after addition of differentiation cocktail, whereas Egr2 protein initially remained low before increasing on days 1 and 2, concomitant with the disappearance of Egr1. In marked contrast to the effects of Egr2, differentiation was inhibited by ectopic expression of Egr1 and potentiated by knockdown of Egr1. The pro-adipogenic effects of Egr1 knockdown were particularly notable when isobutylmethylxanthine (IBMX) was omitted from the differentiation medium. However, knockdown of Egr1 did not affect CCAAT/enhancer binding protein (C/EBP)beta protein expression or phosphorylation of CREB Ser133. Further, Egr1 did not directly affect the activity of promoters for the master adipogenic transcription factors, C/EBPalpha or peroxisome proliferator-activated receptor-gamma2, as assessed in luciferase reporter assays. These data indicate that Egr1 and Egr2 exert opposing influences on adipocyte differentiation and that the careful regulation of both is required for maintaining appropriate levels of adipogenesis. Further, the pro-differentiation effects of IBMX involve suppression of the inhibitory influence of Egr1.

Acetylcholine-induced neuronal differentiation: muscarinic receptor activation regulates EGR-1 and REST expression in neuroblastoma cells

Neurotransmitters are considered part of the signaling system active in nervous system development and we have previously reported that acetylcholine (ACh) is capable of enhancing neuronal differentiation in cultures of sensory neurons and N18TG2 neuroblastoma cells. To study the mechanism of ACh action, in this study, we demonstrate the ability of choline acetyltransferase-transfected N18TG2 clones (e.g. 2/4 clone) to release ACh. Analysis of muscarinic receptors showed the presence of M1-M4 subtypes and the activation of both IP(3) and cAMP signal transduction pathways. Muscarinic receptor activation increases early growth response factor-1 (EGR-1) levels and treatments with agonists, antagonists, and signal transduction enzyme inhibitors suggest a role for M3 subtype in EGR-1 induction. The role of EGR-1 in the enhancement of differentiation was investigated transfecting in N18TG2 cells a construct for EGR-1. EGR-1 clones show increased neurite extension and a decrease in Repressor Element-1 silencing transcription factor (REST) expression: both these features have also been observed for the 2/4 clone. Transfection of this latter with EGR zinc-finger domain, a dominant negative inhibitor of EGR-1 action, increases REST expression, and decreases fiber outgrowth. The data reported suggest that progression of the clone 2/4 in the developmental program is dependent on ACh release and the ensuing activation of muscarinic receptors, which in turn modulate the level of EGR-1 and REST transcription factors.

A deleted prion protein that is neurotoxic in vivo is localized normally in cultured cells

The prion protein (PrP) possesses sequence-specific domains that endow the molecule with neuroprotective and neurotoxic activities, and that may contribute to the pathogenesis of prion diseases. To further define critical neurotoxic determinants within PrP, we previously generated Tg(DeltaCR) mice that express a form of PrP harboring a deletion of 21 amino acids within the central domain of the protein [Li et al., EMBO J. 26 (2007), 548]. These animals exhibit a neonatal lethal phenotype that is dose-dependently rescued by co-expression of wild-type PrP. In this study, we examined the localization and cell biological properties of the PrP(DeltaCR) protein in cultured cells to further understand the mechanism of PrP(DeltaCR) neurotoxicity. We found that the distribution of PrP(DeltaCR) was identical to that of wild-type PrP in multiple cell lines of both neuronal and non-neuronal origin, and that co-expression of the two proteins did not alter the localization of either one. Both proteins were found in lipid rafts, and both were localized to the apical surface in polarized epithelial cells. Taken together, our results suggest that PrP(DeltaCR) toxicity is not a result of mislocalization or aggregation of the protein, and more likely stems from altered binding interactions leading to the activation of deleterious signaling pathways.

Abnormal sympathetic nervous system development and physiological dysautonomia in Egr3-deficient mice

Sympathetic nervous system development depends upon many factors that mediate neuron migration, differentiation and survival. Target tissue-derived nerve growth factor (NGF) signaling-induced gene expression is required for survival, differentiation and target tissue innervation of post-migratory sympathetic neurons. However, the transcriptional regulatory mechanisms mediated by NGF signaling are very poorly defined. Here, we identify Egr3, a member of the early growth response (Egr) family of transcriptional regulators, as having an important role in sympathetic nervous system development. Egr3 is regulated by NGF signaling and it is expressed in sympathetic neurons during development when they depend upon NGF for survival and target tissue innervation. Egr3-deficient mice have severe sympathetic target tissue innervation abnormalities and profound physiological dysautonomia. Unlike NGF, which is essential for sympathetic neuron survival and for axon branching within target tissues, Egr3 is required for normal terminal axon extension and branching, but not for neuron survival. The results indicate that Egr3 is a novel NGF signaling effector that regulates sympathetic neuron gene expression required for normal target tissue innervation and function. Egr3-deficient mice have a phenotype that is remarkably similar to humans with sympathetic nervous system disease, raising the possibility that it may have a role in some forms of human dysautonomia, most of which have no known cause.

De novo identification of MIZ-1 (ZBTB17) encoding a MYC-interacting zinc-finger protein as a new favorable neuroblastoma gene

PURPOSE

Neuroblastoma is a childhood cancer that exhibits either a favorable or an unfavorable phenotype. Favorable neuroblastoma genes (EPHB6, EFNB2, EFNB3, NTRK1, and CD44) are genes whose high-level expression predicts favorable neuroblastoma disease outcome. Accordingly, the forced expression of these genes or their reactivation by gene silencing inhibitors in unfavorable neuroblastoma cells results in suppression of tumor growth and metastases. This study was undertaken to design an experimental strategy to identify additional favorable neuroblastoma genes.

EXPERIMENTAL DESIGN

Favorable neuroblastoma gene candidates were first identified by gene expression profiling analysis on IMR5 neuroblastoma cells treated with inhibitors of DNA methylation and histone deacetylase against the untreated control cells. Among the candidates, we focused on MIZ-1, which encodes a MYC-interacting zinc-finger protein, because it is known to enhance the expression of growth suppressive genes, such as CDKN1A.

RESULTS

High-level MIZ-1 expression was associated with favorable disease outcome of neuroblastoma (P = 0.0048). Forced MIZ-1 expression suppressed in vitro growth of neuroblastoma cell lines. High MIZ-1 expression was correlated with the small-size neuroblastoma xenografts treated with gene silencing inhibitors or a glucocorticoid. In addition, forced MIZ-1 expression enhanced the expression of CD44 and EFNB2 in neuroblastoma cell lines in vitro. Furthermore, MIZ-1 expression was positively correlated with the expression of favorable neuroblastoma genes (EFNB2, EFNB3, EPHB6, and NTRK1) in the human neuroblastoma xenograft therapeutic models.

CONCLUSION

MIZ-1 is a new favorable neuroblastoma gene, which may directly or indirectly regulate the expression of other favorable neuroblastoma genes.

Glial cell line-derived neurotrophic factor and neurturin inhibit neurite outgrowth and activate RhoA through GFR alpha 2b, an alternatively spliced isoform of GFR alpha 2

The glial cell line-derived neurotrophic factor (GDNF) and neurturin (NTN) belong to a structurally related family of neurotrophic factors. NTN exerts its effect through a multicomponent receptor system consisting of the GDNF family receptor alpha2 (GFR alpha2), RET, and/or NCAM (neural cell adhesion molecule). GFR alpha2 is alternatively spliced into at least three isoforms (GFR alpha2a, GFR alpha2b, and GFR alpha2c). It is currently unknown whether these isoforms share similar functional and biochemical properties. Using highly specific and sensitive quantitative real-time PCR, these isoforms were found to be expressed at comparable levels in various regions of the human brain. When stimulated with GDNF and NTN, both GFR alpha2a and GFR alpha2c, but not GFR alpha2b, promoted neurite outgrowth in transfected Neuro2A cells. These isoforms showed ligand selectivity in MAPK (mitogen-activated protein kinase) [ERK1/2 (extracellular signal-regulated kinase 1/2)] and Akt signaling. In addition, the GFR alpha2 isoforms regulated different early-response genes when stimulated with GDNF or NTN. In coexpression studies, GFR alpha2b was found to inhibit ligand-induced neurite outgrowth by GFR alpha2a and GFR alpha2c. Stimulation of GFR alpha2b also inhibited the neurite outgrowth induced by GFR alpha1a, another member of the GFR alpha. Furthermore, activation of GFR alpha2b inhibited neurite outgrowth induced by retinoic acid and activated RhoA. Together, these data suggest a novel paradigm for the regulation of growth factor signaling and neurite outgrowth via an inhibitory splice variant of the receptor. Thus, depending on the expressions of specific GFR alpha2 receptor spliced isoforms, GDNF and NTN may promote or inhibit neurite outgrowth through the multicomponent receptor complex.

Regulation of neuronal cdc20 (p55cdc) expression by the plasticity-related transcription factor zif268

Most forms of neuronal plasticity are associated with induction of the transcription factor zif268 (egr1). Down-regulation of cdc20 (p55(cdc))--a regulatory protein for the anaphase-promoting complex, which controls access of specific substrates to the proteasome--was observed after transfection of a neuronal cell line with zif268. Treatment of cultured hippocampal neurones with NMDA, which elevates endogenous zif268 levels, also decreased cdc20 levels. Conversely, the levels of cdc20 were found to be increased in the cerebral cortex of mice with targeted deletion of the zif268 gene, when compared with wild-type controls. Our findings indicate that expression of the cdc20 gene is down-regulated by zif268 in neuronal cells, and provide new evidence that altered expression of proteasome-regulatory genes following zif268 induction may be a key component of long-lasting CNS plasticity.

A calcium- and calmodulin-dependent kinase Ialpha/microtubule affinity regulating kinase 2 signaling cascade mediates calcium-dependent neurite outgrowth

Calcium is a critical regulator of neuronal differentiation and neurite outgrowth during development, as well as synaptic plasticity in adulthood. Calcium- and calmodulin-dependent kinase I (CaMKI) can regulate neurite outgrowth; however, the signal transduction cascades that lead to its physiological effects have not yet been elucidated. CaMKIalpha was therefore used as bait in a yeast two-hybrid assay and microtubule affinity regulating kinase 2 (MARK2)/Par-1b was identified as an interacting partner of CaMKI in three independent screens. The interaction between CaMKI and MARK2 was confirmed in vitro and in vivo by coimmunoprecipitation. CaMKI binds MARK2 within its kinase domain, but only if it is activated by calcium and calmodulin. Expression of CaMKI and MARK2 in Neuro-2A (N2a) cells and in primary hippocampal neurons promotes neurite outgrowth, an effect dependent on the catalytic activities of these enzymes. In addition, decreasing MARK2 activity blocks the ability of the calcium ionophore ionomycin to promote neurite outgrowth. Finally, CaMKI phosphorylates MARK2 on novel sites within its kinase domain. Mutation of these phosphorylation sites decreases both MARK2 kinase activity and its ability to promote neurite outgrowth. Interaction of MARK2 with CaMKI results in a novel, calcium-dependent pathway that plays an important role in neuronal differentiation.

Induction of Krox-24 by endogenous cannabinoid type 1 receptors in Neuro2A cells is mediated by the MEK-ERK MAPK pathway and is suppressed by the phosphatidylinositol 3-kinase pathway

Neuro2a cells endogenously express cannabinoid type 1 (CB1) receptors. CB1 stimulation with HU210 activated ERK and induced the transcription factor Krox-24. A functional MEK-ERK pathway is an important requirement for CB1-mediated Krox-24 induction as blockade of MEK signaling by UO126 reduces both basal and CB1-mediated activation of Krox-24. CB1 receptor stimulation did not activate either JNK or p38 MAPK pathways or the pro-proliferation phosphatidylinositol 3-kinase (PI3K)-Akt pathway. However, serum removal or blockade of PI3K signaling by LY294002 transiently stimulated basal Krox-24 expression and increased CB1-mediated induction of Krox-24. This was consistent with a transient increase in pMEK, pERK, and pCREB levels following PI3K blockade. These data demonstrate that CB1-mediated activation of the Krox-24 transcription factor is negatively regulated through the PI3K-Akt pathway and reveals several points of signaling cross-talk between these two important kinase pathways.

Genomic profiling of the neuronal target genes of the plasticity-related transcription factor -- Zif268

The later phases of neuronal plasticity are invariably dependent on gene transcription. Induction of the transcription factor Zif268 (Egr-1) in neurones is closely associated with many forms of functional plasticity, yet the neuronal target genes modulated by Zif268 have not been characterized. After transfection of a neuronal cell line with Zif268 we identified genes that show altered expression using high density microarrays. Although some of the genes identified have previously been associated with forms of neuronal plasticity, the majority have not been linked with neuronal plasticity or Zif268 action. Altered expression of a representative sample of the novel target genes was confirmed in Zif268-transfected PC12 neurones, and in in vitro and in vivo models of Zif268-associated neuronal plasticity. In particular, altered expression of the protease inhibitor Cystatin C and the chemokine Cxcl10 was observed in striatal tissue after haloperidol administration. Surprisingly, the group of identified genes is enriched for components of the proteasome and the major histocompatibility complex. Our findings suggest that altered expression of these genes following Zif268 induction may be a key component of long lasting plasticity in the CNS.

Signalling pathways leading to neuroblastoma differentiation after serum withdrawal: HDL blocks neuroblastoma differentiation by inhibition of EGFR

Neuroblastoma is the second most common pediatric malignancy, characterized by a high rate of unexplained spontaneous remissions. Much progress has been made in understanding neuroblastoma differentiation triggered by certain agents such as retinoic acid. However, little is known about the signalling pathways that lead to differentiation of neuroblastoma cells due to serum withdrawal. We found that in Neuro2a neuroblastoma cells, EGFR, ERK1/2 and Akt showed increased phosphorylation after serum withdrawal, and that the activation of EGFR was necessary for the activation of Akt and ERK1/2. Inhibition of EGFR, ERK1/2 and PI3K blocked neuroblastoma differentiation after serum withdrawal. Interestingly, addition of high-density lipoprotein (HDL) abrogated serum-withdrawal induced neuroblastoma differentiation, as well as the activation of EGFR. Our results demonstrate a novel role for serum-derived lipoproteins in the control of receptor tyrosine kinase activity.

Nxf and Fbxo33: novel seizure-responsive genes in mice

Much is understood about the response of the brain to seizure but little is known in relation to the underlying molecular mechanisms involved. We used microarray technology to investigate the complex genetic response of the brain to generalized seizure. For this investigation a seizure-specific mouse brain cDNA library was generated and spotted onto microarray slides with the aim of increasing the likelihood of identifying novel genes responsive to seizure. Microarray analysis was performed on mouse hippocampus 1 h after generalized seizure pharmacologically induced by pentylenetetrazol (PTZ). Using the custom microarray slides, six genes were identified as being up-regulated in this seizure model and results were validated by real-time PCR. Four of the seizure-responsive genes had previously-reported roles in apoptosis, proliferation or differentiation of neural cells. Two of the genes were novel and in situ hybridization analysis demonstrated heightened mRNA expression in the hippocampus 1 h following generalized convulsive seizure, in a pattern which is typical for other activity-dependant genes expressed in this structure. In addition to being up-regulated postseizure, the genes described in this paper appear to be expressed normally in the adult hippocampus and during development.

The transcription factor early growth response factor-1 (EGR-1) promotes apoptosis of neuroblastoma cells

Early growth response factor-1 (EGR-1) is an immediate early gene, which is rapidly activated in quiescent cells by mitogens or in postmitotic neurons after depolarization. EGR-1 has been involved in diverse biological functions such as cell growth, differentiation and apoptosis. Here we report that enforced expression of the EGR-1 gene induces apoptosis, as determined by flow cytometry and terminal deoxynucleotidyl transferase-mediated dUTP-fluorescein nick-end labelling (TUNEL) analysis, in murine Neuro2A cells. In accordance with this role of EGR-1 in cell death, antisense oligonucleotides increase cell viability in cells cultured in the absence of serum. This apoptotic activity of the EGR-1 appears to be mediated by p73, a member of the p53 family of proteins, since an increase in the amount of p73 is observed in clones stably expressing the EGR-1 protein. We also observed an increase in the transcriptional activity of the mdm2 promoter in cells overexpressing EGR-1, which is paralleled by a marked decrease in the levels of p53 protein, therefore excluding a role of this protein in mediating EGR-1-induced apoptosis. Our results suggest that EGR-1 is an important factor involved in neuronal apoptosis.

cDNA microarray analysis of gene expression in anxious PVG and SD rats after cat-freezing test

To identify genes involved in the development of anxiety or fear, we analyzed the gene expression profiles of the cortex of anxious hooded PVG and Sprague-Dawley (SD) rats after exposure to the cat-freezing test apparatus. These two rat strains showed a marked difference in the extent of anxious behavior on the cat-freezing test; the hooded PVG rats showed highly anxious behavior while a low anxiety state was observed in SD rats. A cDNA microarray consisting of 5,931 genes was employed to investigate the global mRNA expression profiles of anxiety-related genes. According to the assumption that an abundance ratio of > or =1.5 is indicative of a change in gene expression, we detected 16 upregulated and 38 downregulated genes in PVG hooded and SD rats. Some of these genes have not yet been associated with anxiety (e.g. FGF), while other genes were recently found to be expressed in an anxious state (e.g., rat nerve growth factor-induced gene, NGFI-A). Our study also focused on the expression of some neurotransmitter receptors that have already been proven to be relevant to anxiety or fear, e.g., gamma-aminobutyric acid (GABA), cholecystokinin (CCK) and 5-HT(3) receptors. To further confirm the microarray data, the mRNA expressions of three genes: rat activity-regulated cytoskeleton-associated gene (Arc), rat NGFI-A gene and rat 5-HT(3) receptor (5-HT(3)R) mRNA, were studied by reverse transcription-polymerase chain reaction (RT-PCR). The results of RT-PCR were basically consistent with those from cDNA microarray. Our study therefore demonstrated that the microarray technique is an efficient tool for analyzing global expression profiles of anxiety-related genes, which may also provide further insight into the molecular mechanisms underlying the states of anxiety and fear.

CCAAT/enhancer-binding protein beta plays a regulatory role in differentiation and apoptosis of neuroblastoma cells

The C/EBPbeta (CCAAT/enhancer-binding protein beta) is a transcription factor that belongs to basic region-leucine zipper class DNA-binding proteins. There is a significant body of evidence that suggests that this protein plays a central role in adipocytic and eosinophilic differentiation. However, there is no information available regarding the role of this transcription factor in the development of mammalian neuronal tissues. In this study, we have examined the effect of C/EBPbeta overexpression on the differentiation and survival of mouse Neuro2A cells. We found that C/EBPbeta induces neuronal differentiation and that this process is inhibited by transfection with the C/EBP homologous protein 10 (CHOP), strongly suggesting that the extension of neurites is indeed due to the C/EBPbeta transcriptional activity. As it has been suggested in adipocyte differentiation, here we show that C/EBPbeta induces the expression of the endogenous C/EBPalpha gene and that this protein by itself is also able to induce a differentiated phenotype in Neuro2A cells. Neuronal differentiation induced by C/EBPbeta requires activation of the phosphatidylinositol 3-kinase signaling pathway, whereas inhibition of the mitogen-activated protein kinase signaling does not have any effect. In addition, we show that C/EBPbeta is expressed in the brain of neonatal rats, suggesting that this protein could play an important role in neuronal maturation. Finally, cell death was also induced by C/EBPbeta through activation of the p53 protein and the cdk inhibitor p21.

Changes in Ca(2+) channel expression upon differentiation of SN56 cholinergic cells

The SN56 cell line, a fusion of septal neurons and neuroblastoma cells, has been used as a model for central cholinergic neurons. These cells show increased expression of cholinergic neurochemical features upon differentiation, but little is known about how differentiation affects their electrophysiological properties. We examined the changes in Ca(2+) channel expression that occur as these cells undergo morphological differentiation in response to serum withdrawal and exposure to dibutyryl-cAMP. Undifferentiated cells expressed a T-type current with biophysical and pharmacological properties similar, although not identical, to those reported for the current generated by the alpha(1H) (CaV3.2) Ca(2+) channel subunit. Differentiated cells expressed, in addition to this T-type current, high voltage activated currents which were inhibited 38% by the L-type channel antagonist nifedipine (5 microM), 37% by the N-type channel antagonist omega-conotoxin-GVIA (1 microM), and 15% by the P/Q-type channel antagonist omega-agatoxin-IVA (200 nM). Current resistant to these inhibitors accounted for 15% of the high voltage activated current in differentiated SN56 cells. Our data demonstrate that differentiation increases the expression of neuronal type voltage gated Ca(2+) channels in this cell line, and that the channels expressed are comparable to those reported for native basal forebrain cholinergic neurons. This cell line should thus provide a useful model system to study the relationship between calcium currents and cholinergic function and dysfunction.