Ability of Egr1 to Activate Tyrosine Hydroxylase Transcription in PC12 Cells

Tyrosine hydroxylase gene promoter activity is upregulated in female catecholaminergic neuroblastoma cells following activation of a Gαq-coupled designer receptor

Tyrosine hydroxylase is the rate-limiting enzyme of catecholamine biosynthesis that catalyzes the conversion of L-tyrosine to L-3,4-dihydroxyphenylalanine. The tyrosine hydroxylase gene is regulated by extracellular signaling molecules such as epidermal growth factor, nerve growth factor and steroids. Here, we investigated whether the activity of the tyrosine hydroxylase gene promoter is upregulated by activation of G protein-coupled receptors, the largest group of plasma membrane receptors. We used catecholaminergic neuroblastoma cells as a cellular model and chromatin-integrated tyrosine hydroxylase promoter-luciferase reporter genes. The results show that stimulation of Rαq, a Gαq-coupled designer receptor, triggered transcription of a reporter gene driven by the tyrosine hydroxylase promoter. Transcription was attenuated by overexpression of regulator of G-protein signaling-2, which activates the GTPase activity of the G protein α-subunit, and by a truncated, dominant-negative mutant of phospholipase Cβ3. Extracellular signal-regulated protein kinase was identified as the signal transducer. At the transcriptional level, tyrosine hydroxylase promoter activity was found to be controlled by the transcription factor CREB. Expression experiments with the adenoviral regulator protein E1A, an inhibitor of CBP/p300 histone acetyltransferases, showed that transcription of the reporter gene controlled by the tyrosine hydroxylase is under epigenetic control. We identified the protein phosphatases MAP kinase phosphatase-1 and calcineurin as part of a shutdown device of the signaling cascade linking Rαq designer receptor activation to tyrosine hydroxylase gene transcription. We conclude that tyrosine hydroxylase promoter activity is controlled by Gαq-coupled receptors.

Sex differences in sympathetic gene expression and cardiac neurochemistry in Wistar Kyoto rats

The stellate ganglia are the predominant source of sympathetic innervation to the heart. Remodeling of sympathetic nerves projecting to the heart has been observed in several cardiovascular diseases, and sympathetic dysfunction contributes to cardiac pathology. Wistar Kyoto rats are a common model for the study of cardiovascular diseases, but we lack a profile of the baseline transcriptomic and neurochemical characteristics of their cardiac sympathetic neurons. Most studies of cardiovascular disease have used male animals only, but in the future both male and female animals will be used for these types of studies; therefore, we sought to characterize the transcriptome of male and female stellate ganglia and to correlate that with catecholamine and acetylcholine content in the heart. We have generated a dataset of baseline RNA expression in male and female Wistar Kyoto rat stellate ganglia using RNA-seq, and have measured neurotransmitter levels in heart and stellate ganglia using HPLC and mass spectrometry. We identified numerous gene expression differences between male and female stellates, including genes encoding important developmental factors, receptors and neuropeptides. Female hearts had significantly higher neurotransmitter content than male hearts; however, no significant differences were detected in expression of the genes encoding neurotransmitter synthetic enzymes. Similarly, no statistically significant differences were identified between the sexes in cardiac tyrosine hydroxylase levels.

Differential methylation of enhancer at IGF2 is associated with abnormal dopamine synthesis in major psychosis

Impaired neuronal processes, including dopamine imbalance, are central to the pathogenesis of major psychosis, but the molecular origins are unclear. Here we perform a multi-omics study of neurons isolated from the prefrontal cortex in schizophrenia and bipolar disorder (n = 55 cases and 27 controls). DNA methylation, transcriptomic, and genetic-epigenetic interactions in major psychosis converged on pathways of neurodevelopment, synaptic activity, and immune functions. We observe prominent hypomethylation of an enhancer within the insulin-like growth factor 2 (IGF2) gene in major psychosis neurons. Chromatin conformation analysis revealed that this enhancer targets the nearby tyrosine hydroxylase (TH) gene responsible for dopamine synthesis. In patients, we find hypomethylation of the IGF2 enhancer is associated with increased TH protein levels. In mice, Igf2 enhancer deletion disrupts the levels of TH protein and striatal dopamine, and induces transcriptional and proteomic abnormalities affecting neuronal structure and signaling. Our data suggests that epigenetic activation of the enhancer at IGF2 may enhance dopamine synthesis associated with major psychosis.

EPHB6 controls catecholamine biosynthesis by up-regulating tyrosine hydroxylase transcription in adrenal gland chromaffin cells

EPHB6 is a member of the erythropoietin-producing hepatocellular kinase (EPH) family and a receptor tyrosine kinase with a dead kinase domain. It is involved in blood pressure regulation and adrenal gland catecholamine (CAT) secretion, but several facets of EPHB6-mediated CAT regulation are unclear. In this study, using biochemical, quantitative RT-PCR, immunoblotting, and gene microarray assays, we found that EPHB6 up-regulates CAT biosynthesis in adrenal gland chromaffin cells (AGCCs). We observed that epinephrine content is reduced in the AGCCs from male Ephb6-KO mice, caused by decreased expression of tyrosine hydroxylase, the rate-limiting enzyme in CAT biosynthesis. We demonstrate that the signaling pathway from EPHB6 to tyrosine hydroxylase expression in AGCCs involves Rac family small GTPase 1 (RAC1), MAP kinase kinase 7 (MKK7), c-Jun N-terminal kinase (JNK), proto-oncogene c-Jun, activator protein 1 (AP1), and early growth response 1 (EGR1). On the other hand, signaling via extracellular signal-regulated kinase (ERK1/2), p38 mitogen-activated protein kinase, and ELK1, ETS transcription factor (ELK1) was not affected by EPHB6 deletion. We further report that EPHB6's effect on AGCCs was via reverse signaling through ephrin B1 and that EPHB6 acted in concert with the nongenomic effect of testosterone to control CAT biosynthesis. Our findings elucidate the mechanisms by which EPHB6 modulates CAT biosynthesis and identify potential therapeutic targets for diseases, such as hypertension, caused by dysfunctional CAT biosynthesis.

Phenylethanolamine N-methyltransferase gene expression in adrenergic neurons of spontaneously hypertensive rats

Epinephrine is synthesised by the catecholamine biosynthetic enzyme, phenylethanolamine N-methyltransferase (PNMT), primarily in chromaffin cells of the adrenal medulla and secondarily in brainstem adrenergic neurons of the medulla oblongata. Epinephrine is an important neurotransmitter/neurohormone involved in cardiovascular regulation; however, overproduction is detrimental with negative outcomes such as cellular damage, cardiovascular dysfunction, and hypertension. Genetic mapping studies have linked elevated expression of PNMT to hypertension. Adrenergic neurons are responsible for blood pressure regulation and are the only PNMT containing neurons in the brainstem. The purpose of the current study was to determine whether elevated blood pressure found in adult spontaneously hypertensive rats (SHR) is associated with altered regulation of the PNMT gene in catecholaminergic neurons. C1, C2, and C3 adrenergic regions of 16 week old Wistar Kyoto (WKY) and SHR rats were excised using micropunch microdissection for mRNA expression analyses. Results from the current study confirm high PNMT mRNA expression in all three brainstem adrenergic regions (C1: 2.96-fold; C2: 2.17-fold; C3 1.20-fold) of the SHR compared to normotensive WKY rats. Furthermore, the immediate early gene transcription factor (Egr-1) mRNA was elevated in the C1 (1.84-fold), C2 (8.57-fold) and C3 (2.41-fold) regions in the brainstem of the SHR. Low mRNA expression for transcription factors Sp1 and GR was observed, while no change was observed for AP-2. The findings presented propose that alterations in the PNMT gene regulation in the brainstem contribute to enhanced PNMT production and epinephrine synthesis in the SHR, a genetic model of hypertension.

Nucleotide sequence conservation of novel and established cis-regulatory sites within the tyrosine hydroxylase gene promoter

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in catecholamine biosynthesis and its gene proximal promoter ( < 1 kb upstream from the transcription start site) is essential for regulating transcription in both the developing and adult nervous systems. Several putative regulatory elements within the TH proximal promoter have been reported, but evolutionary conservation of these elements has not been thoroughly investigated. Since many vertebrate species are used to model development, function and disorders of human catecholaminergic neurons, identifying evolutionarily conserved transcription regulatory mechanisms is a high priority. In this study, we align TH proximal promoter nucleotide sequences from several vertebrate species to identify evolutionarily conserved motifs. This analysis identified three elements (a TATA box, cyclic AMP response element (CRE) and a 5'-GGTGG-3' site) that constitute the core of an ancient vertebrate TH promoter. Focusing on only eutherian mammals, two regions of high conservation within the proximal promoter were identified: a ∼250 bp region adjacent to the transcription start site and a ∼85 bp region located approximately 350 bp further upstream. Within both regions, conservation of previously reported cis-regulatory motifs and human single nucleotide variants was evaluated. Transcription reporter assays in a TH -expressing cell line demonstrated the functionality of highly conserved motifs in the proximal promoter regions and electromobility shift assays showed that brain-region specific complexes assemble on these motifs. These studies also identified a non-canonical CRE binding (CREB) protein recognition element in the proximal promoter. Together, these studies provide a detailed analysis of evolutionary conservation within the TH promoter and identify potential cis-regulatory motifs that underlie a core set of regulatory mechanisms in mammals.

A systems approach identifies co-signaling molecules of early growth response 1 transcription factor in immobilization stress

Background

Adaptation to stress is critical for survival. The adrenal medulla, the major source of epinephrine, plays an important role in the development of the hyperadenergic state and increased risk for stress associated disorders, such as hypertension and myocardial infarction. The transcription factor Egr1 plays a central role in acute and repeated stress, however the complexity of the response suggests that other transcription factor pathways might be playing equally important roles during acute and repeated stress. Therefore, we sought to discover such factors by applying a systems approach.

Results

Using microarrays and network analysis we show here for the first time that the transcription factor signal transducer and activator of transcription 3 (Stat3) gene is activated in acute stress whereas the prolactin releasing hormone (Prlh11) and chromogranin B (Chgb) genes are induced in repeated immobilization stress and that along with Egr1 may be critical mediators of the stress response.

Conclusions

Our results suggest possible involvement of Stat3 and Prlh1/Chgb up-regulation in the transition from short to repeated stress activation.

COUP-TFI controls activity-dependent tyrosine hydroxylase expression in adult dopaminergic olfactory bulb interneurons

COUP-TFI is an orphan nuclear receptor acting as a strong transcriptional regulator in different aspects of forebrain embryonic development. In this study, we investigated COUP-TFI expression and function in the mouse olfactory bulb (OB), a highly plastic telencephalic region in which continuous integration of newly generated inhibitory interneurons occurs throughout life. OB interneurons belong to different populations that originate from distinct progenitor lineages. Here, we show that COUP-TFI is highly expressed in tyrosine hydroxylase (TH)-positive dopaminergic interneurons in the adult OB glomerular layer (GL). We found that odour deprivation, which is known to downregulate TH expression in the OB, also downregulates COUP-TFI in dopaminergic cells, indicating a possible correlation between TH- and COUP-TFI-activity-dependent action. Moreover, we demonstrate that conditional inactivation of COUP-TFI in the EMX1 lineage results in a significant reduction of both TH and ZIF268 expression in the GL. Finally, lentiviral vector-mediated COUP-TFI deletion in adult-generated interneurons confirmed that COUP-TFI acts cell-autonomously in the control of TH and ZIF268 expression. These data indicate that COUP-TFI regulates TH expression in OB cells through an activity-dependent mechanism involving ZIF268 induction and strongly argue for a maintenance rather than establishment function of COUP-TFI in dopaminergic commitment. Our study reveals a previously unknown role for COUP-TFI in the adult brain as a key regulator in the control of sensory-dependent plasticity in olfactory dopaminergic neurons.

Epigenetic, transcriptional and posttranscriptional regulation of the tyrosine hydroxylase gene

The activity of tyrosine hydroxylase (TH, EC 1.14.16.2) gene and protein determines the catecholamine level, which, in turn, is crucial for the organism homeostasis. The TH gene expression is regulated by near all possible regulatory mechanisms on epigenetic, transcriptional and posttranscriptional levels. Ongoing molecular characteristic of the TH gene reveals some of the cis and trans elements necessary for its proper expression but most of them especially these responsible for tissue specific expression remain still obscure. This review will focus on some aspects of TH regulation including spatial chromatin organization of the TH locus and TH gene, regulatory elements mediating basal, induced and cell-specific activity, transcriptional elongation, alternative TH RNA processing, and the regulation of TH RNA stability in the cell.

PACAP: a master regulator of neuroendocrine stress circuits and the cellular stress response

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) is released from stress-transducing neurons. It exerts postsynaptic effects required to complete the hypothalamo-pituitary-adrenocortical (HPA) and hypothalamo-sympatho-adrenal (HSA) circuits activated by psychogenic and metabolic stressors. Upon activation of these circuits, PACAP-responsive (in cell culture models) and PACAP-dependent (in vivo) transcriptomic responses in the adrenal gland, hypothalamus, and pituitary have been identified. Gene products produced in response circuits during stress include additional neuropeptides, neurotransmitter biosynthetic enzymes, and neuroprotective factors. Major portions of HPA and HSA stress responses are abolished in PACAP-deficient mice. This deficit occurs at the level of both the hypothalamus (HPA axis) and the adrenal medulla (HSA axis). PACAP-dependent transcriptional stress responses are conveyed through noncanonical cyclic AMP- and calcium-initiated signaling pathways within the HSA circuit. PACAP transcriptional regulation of the HPA axis, in the hypothalamus, is likely to be mediated via canonical cyclic AMP signaling through protein kinase A.

Distinctive features of Egr transcription factor regulation and DNA binding activity in CA1 of the hippocampus in synaptic plasticity and consolidation and reconsolidation of fear memory

Activity-dependent regulation of Egr1/Zif268, a transcription factor (TF) of the Egr family, is essential for stabilization of dentate gyrus synaptic plasticity and consolidation and reconsolidation of several forms of memory. The gene can be rapidly induced in selective brain circuits after certain types of learning or after recall. Here, we focused on area CA1 and examined regulation of Egr1, Egr2, and Egr3 mRNA and protein, and their DNA binding activity to the Egr response element (ERE) at different times after LTP in vivo and after learning and recall of a fear memory. We found LTP in CA1 leads to rapid induction of the three Egrs, however only Egr1 protein was overexpressed without a co-ordinated change in binding activity, indicating a fundamental difference between CA1 and dentate gyrus LTP. Our investigations in fear memory reveal that both learning and retrieval lead to an increase in binding of constitutively expressed Egr1 and Egr3 to the ERE, but not Egr2. Memory recall was also associated with increased Egr1 protein translation. The nature and temporal dynamics of these changes and tests for interactions between TFs suggest that in addition to ERE-mediated transcription, Egr1 in CA1 may interact with the TF c-Fos to regulate genes via other DNA response elements.

Snail associates with EGR-1 and SP-1 to upregulate transcriptional activation of p15INK4b

Snail is a multifunctional transcriptional factor that has been described as a repressor in many different contexts. It is also proposed as an activator in a few cases relevant to tumor progression and cell-cycle arrest. This study investigated the detailed mechanisms by which Snail upregulates gene expression of the CDK inhibitor p15(INK4b) in HepG2 induced by the tumor promoter tetradecanoyl phorbol acetate (TPA). Using deletion mapping, the TPA-responsive element on the p15(INK4b) promoter was located between 77 and 228 bp upstream of the transcriptional initiation site, within which the putative binding regions of early growth response gene 1 (EGR-1) and stimulatory protein 1 (SP-1) were found. Gene expression of EGR-1, Snail and SP-1 can be induced by TPA within 0.5-6 h. In addition, basal levels of SP-1, but not of the other two transcriptional factors, were observed. Blockade of TPA-induced gene expression of Snail, EGR-1 or SP-1 suppressed activation of the p15-pro228 reporter plasmid harboring the TPA-responsive element. More detailed deletion mapping and site-directed mutagenesis further concluded that the overlapping EGR-1/SP-1-binding site was required for TPA-induced p15-pro228 activation. In an EMSA, a DNA-protein complex was elevated by TPA, which can be blocked by antibodies against EGR-1, SP-1 or Snail at 6 h. Immunoprecipitation/western blotting demonstrated that TPA could trigger the association of EGR-1 with Snail or SP-1. Furthermore, a double chromatin immunoprecipitation assay verified that EGR-1 could form a complex with Snail or SP-1 on the TPA-responsive element after treatment with TPA for 2-6 h. Finally, we demonstrated a novel Snail-target region which could be bound by Snail and was also required for TPA-induced p15-pro228 activation. In conclusion, Snail associates with EGR-1 and SP-1 to mediate TPA-induced transcriptional upregulation of p15(INK4b) in HepG2.

Expression of EGR-1 in a subset of olfactory bulb dopaminergic cells

In the adrenal medulla, binding of the immediate early gene (IEG) proteins, EGR-1 (ZIF-268/KROX-24/NGFI-A) and AP-1, to the tyrosine hydroxylase (Th) proximal promoter mediate inducible Th expression. The current study investigated the potential role of EGR-1 in inducible Th expression in the olfactory bulb (OB) since IEGs bound to the AP-1 site in the Th proximal promoter are also necessary for activity-dependent OB TH expression. Immunohistochemical analysis of a naris-occluded mouse model of odor deprivation revealed weak EGR-1 expression levels in the OB glomerular layer that were activity-dependent. Immunofluorescence analysis indicated that a majority of glomerular cells expressing EGR-1 also co-expressed TH, but only small subset of TH-expressing cells contained EGR-1. By contrast, granule cells, which lack TH, exhibited EGR-1 expression levels that were unchanged by naris closure. Together, these finding suggest that EGR-1 mediates activity-dependent TH expression in a subset of OB dopaminergic neurons, and that there is differential regulation of EGR-1 in periglomerular and granule cells.

Identifying the stress transcriptome in the adrenal medulla following acute and repeated immobilization

Stress triggers changes in gene expression mediating important adaptive and maladaptive responses. The full repertoire of genes whose expression in the adrenal medulla is altered by stress has not been previously determined. In this study, gene profiling (RAE 230 2.0 Affymetrix) was applied to elucidate global changes in gene expression in adrenal medulla of rats exposed to 2-h immobilization (IMO) stress once or repeatedly for 6 consecutive days. The number of transcripts significantly (P < 0.01) altered with single IMO (651 up, 487 down) was more than with repeated IMO (370 up, 195 down). The annotated transcripts were further analyzed and categorized. The largest numbers of changes were in mRNA levels in the transcription factor and cell signaling categories. Robust changes were also observed in transcripts related to growth factors, apoptosis, neurosecretion/neuropeptides, heat shock proteins, structural proteins, chemokines, cytokines, metabolism/lipid-metabolism, and proteases. Many (>80%) were uniquely induced by single IMO. About half of transcripts changed by repeated IMO were also responsive to single IMO. Pathway analysis was applied to identify direct interactions and common targets among gene products altered by single and repeated IMO. In this paper, we briefly describe the most pronounced changes observed, with emphasis on those that may provide new insight into the common and distinct mechanisms whereby the adrenal medulla responses to a first encounter with stress compared to repeated exposure to the same stressor.

Concomitant activation of adenylyl cyclase suppresses the opposite influences of CB(1) cannabinoid receptor agonists on tyrosine hydroxylase expression

The CB(1) cannabinoid receptor shows complex interactions with intracellular signalling partners, and responses to cannabinoid ligands are likely to be influenced by concomitant inputs modifying the overall tone of signalling cascades. This appears even more relevant as we previously evidenced opposite regulations of tyrosine hydroxylase (TH) expression by the two common cannabinoid agonists HU 210 and CP 55,940. Therefore, we studied the consequences of manipulating adenylyl cyclase activity with forskolin on the regulation of TH gene transcription in neuroblastoma cells (N1E-115). Reporter gene experiments performed with the luciferase sequence cloned under the control of modified fragments of the TH gene promoter revealed that the AP-1 consensus sequence is essential for cannabinoid-mediated regulation of TH expression. Consistently, inhibition of PKC totally blocked the responses mediated by both HU 210 and CP 55,940. In addition, forskolin which boosts adenylyl cyclase activity remarkably modified the responses to the cannabinoid agonists. Thus, in these conditions, both agonists efficiently reduced TH gene promoter activity, a response requiring functional PKA/CRE-dependent signallings. Finally, the modulations of the promoter were inhibited in pertussis toxin treated cells, suggesting that responses to both agonists are mediated through G(i/o)-dependent mechanisms. Emphasising on the importance of functional selectivity at GPCRs, these data demonstrate that the concomitant activation of adenylyl cyclase by forskolin strongly influences the biochemical responses triggered by distinct cannabinoid agonists. Together our results suggest that the physiological modulation of TH expression by cannabinoid agonists in dopaminergic neurons would be influenced by additional endogenous inputs.

Transcription of PRDM1, the master regulator for plasma cell differentiation, depends on an SP1/SP3/EGR-1 GC-box

The positive regulatory domain containing 1, encoded by the PRDM1 gene, is a transcriptional repressor considered as a master regulator that is required and sufficient for plasma cell differentiation. In the present study we have performed sequence analysis of the upstream region of the human PRDM1 gene to detect the minimal promoter region necessary for PRDM1 gene transcription. This region comprises the region upstream of the initiation site, as well as the first exon. Collectively, deletion and mutation analysis in conjunction with luciferase reporter assays, EMSA and supershift assays identified a phylogenetically conserved GC-box as an essential element for PRDM1 expression. This GC-box element matches to a binding site for multiple transcription factors such as SP1 and SP3 isoforms as well as early growth response 1. Chromatin immunoprecipitation assays confirmed the in vivo binding capability of these factors to the human PRDM1 promoter. These studies together characterize for the first time the basal activity of the human PRDM1 promoter, through which several factors, including SP1, SP3 and early growth response 1, modulate its expression through a conserved GC-box.

Early growth response-1 protein is induced by JC virus infection and binds and regulates the JC virus promoter

JC virus (JCV) is a human polyomavirus that can emerge from a latent state to cause the cytolytic destruction of oligodendrocytes in the brain resulting in the fatal demyelinating disease, progressive multifocal leukoencephalopathy (PML). Previous studies described a cis-acting transcriptional regulatory element in the JCV non-coding control region (NCCR) that is involved in the response of JCV to cytokines. This consists of a 23 base pair GGA/C rich sequence (GRS) near the replication origin (5112 to +4) that contains potential binding sites for Sp1 and Egr-1. Gel shift analysis showed that Egr-1, but not Sp1, bound to GRS. Evidence is presented that the GRS gel shift seen on cellular stimulation is due to Egr-1. Thus, TPA-induced GRS gel shift could be blocked by antibody to Egr-1. Further, the TPA-induced GRS DNA/protein complex was isolated and found to contain Egr-1 by Western blot. No other Egr-1 sites were found in the JCV NCCR. Functionally, Egr-1 was found to stimulate transcription of JCV late promoter but not early promoter reporter constructs. Mutation of the Egr-1 site abrogated Egr-1 binding and virus with the mutated Egr-1 site showed markedly reduced VP1 expression and DNA replication. Infection of primary astrocytes by wild-type JCV induced Egr-1 nuclear expression that was maximal at 5-10 days post-infection. Finally, upregulation of Egr-1 was detected in PML by immunohistochemistry. These data suggest that Egr-1 induction may be important in the life cycle of JCV and PML pathogenesis.

Specificity proteins Sp1 and Sp3 interact with the rat GTP cyclohydrolase I proximal promoter to regulate transcription

The role of the proximal promoter GC-box in regulating basal and cAMP-dependent GTP Cyclohydrolase I gene transcription was investigated using a variety of cell lines and techniques. These studies show that the GC-box is composed of a triad of cis-elements that in vitro bind specificity proteins Sp1 and Sp3. Sp1 and Sp3 were found associated with the native proximal promoter in PC12 cells but were not recruited to the promoter during cAMP-dependent transcription. Studies using Drosophila SL2 cells showed that Sp3 occupies two sites within the GC-box and enhances transcription when acting alone and synergistically when combined with nuclear factor-Y (NF-Y) and CCAAT/Enhancer-Binding Protein (C/EBP)beta, cognate binding proteins for the adjacent cAMP response element (CRE) and CCAAT-box cAMP response elements. In contrast, Sp1 bound only one site within the GC-box and did not enhance transcription unless combined with NF-Y and C/EBPbeta. Studies in SL2 cells also showed that Sp1 and Sp3 do not co-occupy the GC-box, and accordingly Sp1 competes for Sp3 binding to repress Sp3-dependent transcription. In PC12 cells, complete mutation of the GC-box reduced basal but not cAMP-dependent transcription, resulting in an overall increase in the cAMP response and demonstrating that formation of this enhanceosome does not require Sp1 or Sp3. Experiments in which the GC-box was replaced with a Gal4 element and the promoter challenged with Gal4 fusion proteins support this conclusion and a role for Sp3 in maintaining high levels of basal transcription in PC12 cells. Equivalent amounts of Sp1 and Sp3 were found associated with the native proximal promoter in PC12 and Rat2 cells, which differ 10-fold in basal transcription. Similar levels of methylation of CpG dinucleotides located within the GC-box were also observed in these two cells lines. These results suggest that Sp1 and Sp3 bound to the GC-box might help to preserve an open chromatin configuration at the proximal promoter in cells which constitutively express low levels of GTP Cyclohydrolase I.

Regulation of rat dopamine beta-hydroxylase gene transcription by early growth response gene 1 (Egr1)

Egr1, a transcription factor rapidly induced by various stimuli including stress, can elevate transcription of genes for the catecholamine biosynthetic enzymes TH and PNMT. To examine if Egr1 also regulates dopamine beta-hydroxylase (DBH) gene expression, PC12 cells were transfected with expression vector for full length or truncated inactive Egr1 and various DBH promoter-driven luciferase constructs. While Egr1 elevated TH promoter activity, DBH promoter activity was reduced. The reduction occurred as early as 4 h and reached maximal inhibition 16-40 h after transfection. Egr1 also reduced the expression of endogenous DBH mRNA and the induction of DBH promoter activity by cAMP. These effects were not observed with truncated Egr1 lacking the DNA binding domain. The first 247, but not 200, nucleotides of DBH promoter are sufficient for this suppression. Several putative Egr1 motifs were identified, and mutagenesis showed that the motif at -227/-224 is required. Binding of Egr1 to this region of the DBH promoter was verified by chromatin immunoprecipitation and electrophoretic mobility shift assays. This study demonstrates that DBH promoter contains at least one functional Egr1 motif; and indicates, for the first time, that Egr1 can play an inhibitory role in regulation of DBH gene transcription.

Neuronal PAS domain protein 1 regulates tyrosine hydroxylase level in dopaminergic neurons

Catecholamines (dopamine, norepinephrine, and epinephrine) are all synthesized from a common pathway in which tyrosine hydroxylase (TH) is the rate-limiting enzyme. Dopamine is the main neurotransmitter present in dopaminergic neurons of the ventral midbrain, where dysfunction of these neurons can lead to Parkinson's disease and schizophrenia. Neuronal PAS domain protein 1 (NPAS1) was identified as one of the genes up-regulated during dopaminergic MN9D cell differentiation. We found that there was a corresponding decrease in TH level during MN9D differentiation. Overexpression and siRNA experiments revealed that NPAS1, in concert with ARNT, negatively regulates the expression of TH and that this regulation is mediated by a direct binding of NPAS1 on the TH promoter. Expression studies also confirmed a decrease in TH level in the ventral midbrain during mouse development, concomitant with an increase in NPAS1 level. These results suggest that NPAS1 plays a novel and important role in regulating TH level of dopaminergic neurons in the ventral midbrain during development.

Short-term treatment of RAW264.7 macrophages with adiponectin increases tumor necrosis factor-alpha (TNF-alpha) expression via ERK1/2 activation and Egr-1 expression: role of TNF-alpha in adiponectin-stimulated interleukin-10 production

Adiponectin is an adipokine with potent anti-inflammatory properties. However, the mechanisms by which adiponectin suppresses macrophage function are not well understood. Treatment of RAW264.7 macrophages with adiponectin for 18 h decreased lipopolysaccharide (LPS)-stimulated tumor necrosis factor-alpha (TNF-alpha) production. Here we demonstrate that globular adiponectin (gAcrp) initially increased TNF-alpha expression in RAW264.7 macrophages; this TNF-alpha then contributed to increased expression of interleukin-10, which in turn was required for the development of tolerance to subsequent LPS exposure. gAcrp-mediated increases in TNF-alpha mRNA accumulation were associated with increased TNF-alpha promoter activity. gAcrp increased the DNA binding activity of both Egr-1 and NFkappaB; mutation of either the Egr-1 or NFkappaB binding sites in the TNF-alpha promoter decreased gAcrp-stimulated promoter activity. Further, co-transfection with either dominant negative Egr-1 or the IkappaB super-repressor prevented gAcrp-stimulated TNF-alpha promoter activity. gAcrp also increased Egr-1 promoter activity, mRNA accumulation, and DNA binding activity. Inhibition of ERK1/2 with U0126 potently suppressed gAcrp-stimulated Egr-1 promoter activity, as well as TNF-alpha promoter activity. In summary, these data demonstrate that adiponectin initially increases TNF-alpha production by macrophages via ERK1/2-->Egr-1 and NFkappaB-dependent mechanisms; these increases in TNF-alpha in turn lead to increased expression of interleukin-10 and an eventual dampening of LPS-mediated cytokine production in macrophages.

Molecular basis of neuroendocrine cell type-specific expression of the chromogranin B gene: Crucial role of the transcription factors CREB, AP-2, Egr-1 and Sp1

The molecular basis of neuroendocrine-specific expression of chromogranin B gene (Chgb) has remained elusive. Utilizing wild-type and mutant Chgb promoter/luciferase reporter constructs, this study established a crucial role for the cAMP response element (CRE) box at -102/-95 bp in endocrine [rat pheochromocytoma (chromaffin) cell line (PC12) and rat pituitary somatotrope cell line (GC)] and neuronal [rat dorsal root ganglion/mouse neuroblastoma hybrid cell line (F-11), cortical and hippocampal primary neurons] cells. Additionally, G/C-rich domains at -134/-127, -125/-117 and -115/-110 bp played especially important roles for endocrine-specific expression of the Chgb gene. Co-transfection of expression plasmids for CREB, activator protein-2 (transcription factor) (AP-2), early growth response protein (transcription factor) (Egr-1) or specificity protein 1 (transcription factor) (Sp1) with the Chgb promoter constructs trans-activated expression of the Chgb gene. Nuclear extracts from either PC12 or F-11 cells formed specific complexes with the Chgb (-110/-87 bp) (CRE) oligonucleotide, which were either supershifted or disrupted by anti-CREB antibodies. In addition PC12 nuclear extracts also formed a specific complex with a Chgb (-140/-104-bp) oligonucleotide containing three G/C-rich regions, which was dose-dependently disrupted by anti-AP-2, anti-Egr-1 or anti-Sp1 antibodies; indeed, any one of these three antibodies completely abolished the complex, suggesting that all three factors bind the region simultaneously, at least in vitro. Chromatin immunoprecipitation assays documented the binding of the transcription factors CREB, AP-2, Egr-1 and Sp1 to the chromosomal Chgb gene promoter in vivo in PC12 cells within the context of chromatin. We conclude that the neuroendocrine-specific expression of Chgb is mediated by the CRE and G/C boxes in cis and the transcription factors CREB, AP-2, Egr-1 and Sp1 in trans.

Chronic high-dose haloperidol has qualitatively similar effects to risperidone and clozapine on immediate-early gene and tyrosine hydroxylase expression in the rat locus coeruleus but not medial prefrontal cortex

Acute administration of clozapine has been reported to activate the locus coeruleus (LC) and beta-adrenoceptor-dependent Fos immunoreactivity in the medial prefrontal cortex (mPFC) in rodents. Haloperidol is reported to exhibit a similar acute effect on LC firing and beta-adrenoceptor dependent Fos immunoreactivity in the mPFC but only at high doses. We compared the effects of chronic 4-week treatment with risperidone (1mg/kg/day s.c.), clozapine (10mg/kg/day s.c.) or a high dose of haloperidol (4mg/kg/day s.c.) on immediate-early gene protein (c-Fos, Egr-1 and Egr-2) and tyrosine hydroxylase (TH) expression. In the mPFC, haloperidol decreased, whereas clozapine increased, c-Fos immunoreactivity. Only haloperidol increased Egr-1 immunoreactivity. There was no significant effect on Egr-2 immunoreactivity. In the LC, both Egr-1 and Egr-2 expression was down regulated by all three antipsychotics. Clozapine and risperidone increased TH immunoreactivity in both mPFC and LC. Haloperidol caused a smaller increase in TH expression in the LC, but did not alter expression in the mPFC. In conclusion, despite qualitatively similar effects in the LC, chronic treatment with haloperidol had different effects to clozapine and risperidone in the mPFC. This may relate to the reported advantage of clozapine and risperidone over haloperidol against prefrontal cortical-dependent cognitive and negative symptoms.

Up-regulation of tyrosine hydroxylase gene transcription by tetradecanoylphorbol acetate is mediated by the transcription factors Ets-like protein-1 (Elk-1) and Egr-1

Tyrosine hydroxylase is the rate-limiting enzyme in the biosynthesis of catecholamines. Expression of the tyrosine hydroxylase gene is regulated at the transcriptional level by extracellular signalling molecules, including epidermal growth factor (EGF), nerve growth factor (NGF) and glucocorticoids. We have analysed the stimulation of tyrosine hydroxylase gene transcription by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) in noradrenergic locus coeruleus-like CATH.a cells and observed a striking enhancement of the transcriptional activation potential of the ternary complex factor Ets-like protein-1 (Elk-1), a key transcriptional regulator of serum response element-driven gene transcription. Likewise, TPA strongly up-regulated the biosynthesis of the transcription factor Egr-1 via distal serum response elements within the Egr-1 5'-flanking region. Subsequently, enhancement of the transcriptional activation potential of Egr-1 was observed. Overexpression of Egr-1 was sufficient to activate transcription of a tyrosine hydroxylase promoter/reporter gene, corroborating the view that the tyrosine hydroxylase gene is a target gene of Egr-1. Expression of dominant-negative mutants of Elk-1 or Egr-1 impaired TPA-induced stimulation of a tyrosine hydroxylase promoter/reporter gene transcription. In contrast, dominant-negative mutants of the transcription factors activating transcription factor (ATF)-2, ATF4, cAMP response element-binding protein, c-Jun and CCAAT/enhancer binding protein (C/EBP) did not change TPA-induced tyrosine hydroxylase promoter activity, indicating that these proteins are not part of the TPA-mediated signalling cascade directed towards the tyrosine hydroxylase gene.

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.

Butyrate, a gut-derived environmental signal, regulates tyrosine hydroxylase gene expression via a novel promoter element

Butyrate is a diet-derived, gut fermentation product with an array of effects on cultured mammalian cells including inhibition of proliferation, induction of differentiation and regulation of gene expression. We showed that physiological concentrations of butyrate can regulate transcription of tyrosine hydroxylase (TH) and preproenkephalin (ppEnk) gene in PC12 cells. In promoter deletion studies, electrophoretic mobility shift assays and by site-directed mutagenesis, we identified a novel butyrate response element (BRE) in the 5' upstream region of the rat TH gene, homologous to the previously mapped motif in the ppEnk promoter. No such enhancers were found in DBH or PNMT promoters, and both catecholamine system-related gene promoters were unaffected by butyrate. The BRE motif interacts with nuclear proteins in a sequence-specific manner, shows binding potentiation in butyrate-differentiated PC12 cells and bound protein(s) are competed away with TH-CRE oligonucleotides or by the addition of CREB-specific antibodies, suggesting involvement of CREB or CREB-related transcription factors. Moreover, single point mutation in the distal BRE abolished binding of transcription factors and reduced the response to butyrate in transient transfection studies. The canonical CRE motif of the TH promoter was also found necessary for transcriptional activation of the TH gene by butyrate. Our data identified a novel functional element in the promoter of both the TH and ppEnk genes mediating transcriptional responses to butyrate. Dietary butyrate may have an extended role in the control of catecholamine and endogenous opioid production at the level of TH and ppEnk gene transcription neuronal plasticity, cardiovascular functions, stress adaptation and behavior.

Single and repeated immobilization stress differentially trigger induction and phosphorylation of several transcription factors and mitogen-activated protein kinases in the rat locus coeruleus

The locus coeruleus (LC) is a critical stress-responsive location that mediates many of the responses to stress. We used immunoblotting and immunohistochemistry to investigate changes in induction and phosphorylation of several transcription factors and kinases in the LC that may mediate the stress-triggered induction of tyrosine hydroxylase (TH) transcription. Rats were exposed to single or repeated immobilization stress (IMO) for brief (5 min), intermediate (30 min) or sustained (2 h) duration. Single IMO elicited rapid induction of c-Fos and phosphorylation of cyclic AMP response element-binding protein (CREB) without changing the expression of early growth response (Egr)1, Fos-related antigen (Fra)-2 or phosphorylated activating transcription factor-2. Repeated IMO triggered increased phosphorylation and levels of CREB along with transient induction of c-Fos and increased Fra-2 expression. Several mitogen-activated protein kinases were activated by repeated IMO, shown by increased phosphorylation of p38, c-Jun N-terminal kinase (JNK)1/2/3 and extracellular signal-regulated kinase (ERK1/2). ERK1 was the major isoform expressed, and ERK2 the predominant isoform phosphorylated. Repeated IMO elicited hyperphosphorylation of ERK1/2 selectively in TH immunoreactive neurons, with substantial nuclear localization. These distinct alterations in transcriptional pathways following repeated compared with single stress may be involved in mediating long-lasting neuronal remodeling and are implicated in the mechanisms by which acute beneficial responses to stress are converted into prolonged adaptive or maladaptive responses.

Short chain fatty acids regulate tyrosine hydroxylase gene expression through a cAMP-dependent signaling pathway

Multiple intracellular and extracellular regulatory factors affect transcription of the tyrosine hydroxylase (TH) gene encoding the rate-limiting enzyme in the biosynthesis of the neurotransmitters dopamine, norepinephrine and epinephrine. Short chain fatty acids like butyrate are known to alter TH gene expression, but the mechanism of action is unknown. In this report, transient transfection assays identified the proximal TH promoter to contain sufficient genetic information to confer butyrate responsiveness to a reporter gene. Deletion studies and gel shift analyses revealed that the promoter region spanning the cAMP response element is an absolute requirement for transcriptional activation by butyrate. The branched short chain fatty acid valproate is used for seizure control in humans. Significantly, it has a similar aliphatic structure to butyrate, and it was found to have similar effects on TH in PC12 cells. Site-directed mutagenesis indicated that the effects of both fatty acids were mediated through the canonical CRE. Butyrate treatment also resulted in CREB phosphorylation without changing CREB protein levels. The increased phosphorylation of CREB correlated with accumulation of TH mRNA. The adenylate cyclase inhibitor dideoxyadenosine blocked both CREB phosphorylation and accumulation of TH mRNA. The data are consistent with the conclusion that butyrate induces post-translational modifications of pre-existing CREB molecules in a cAMP/PKA-dependent manner to alter TH transcription. These results support the role of butyrate as a novel exogenous regulatory factor in TH gene expression. Our data delineate a molecular mechanism through which diet-derived environmental signals (e.g. butyrate) can modulate catecholaminergic systems by affecting TH gene transcription.

Increased susceptibility to transcriptional changes with novel stressor in adrenal medulla of rats exposed to prolonged cold stress

The response to stress is influenced by prior experience with the same or different stressor. For example, exposure of cold pre-stressed rats to heterotypic (novel) stressors, such as immobilization (IMO), triggers an exaggerated release of catecholamines and increase in gene expression for adrenomedullary tyrosine hydroxylase (TH), the rate limiting catecholamine biosynthetic enzyme. To study the mechanism, we examined induction or phosphorylation of several transcription factors, which are implicated in IMO-triggered regulation of TH transcription, in rats exposed to cold (4 degrees C) for up to 28 days and then subjected to IMO. Levels of c-fos increased transiently after 2-6 h and returned to basal levels after 1-28 days cold stress. Fra-2, was unaffected by short term cold, but was induced about 2-fold by 28 days continual cold. In contrast, there were no significant changes in CREB phosphorylation or Egr1 induction. Rats, with and without pre-exposure to 28 days cold, were subjected to single IMO for up to 2 h. Phosphorylation of CREB after 30 min IMO was greater in cold pre-exposed rats. Induction of Egr1 was three times higher in cold pre-exposed rats and remained significantly elevated even 3 h after cessation of IMO. Exposure to IMO triggered a 10-20-fold elevation in Fra-2 in both groups, which was even higher 3 h after the IMO. However, Fra-2 was more heavily phosphorylated following IMO stress in cold pre-exposed animals. The results reveal that sensitization to novel stress in cold pre-exposed animals is manifested by exaggerated response of several transcription factors.

Egr-1 modulation of synapsin I expression: permissive effect of forskolin via cAMP

A number of candidate Egr-1 neuronal target genes have been identified including the synapsin I gene. Previous studies have shown that over-expression of Egr-1 in cells transfected with an Egr-1 expression vector is sufficient to activate reporter genes linked to regions of the synapsin I promoter, but any effect on the expression of synapsin I within its genomic context has not been demonstrated. We tested our hypothesis that modulation of synapsin I expression by Egr-1 requires the presence of elevated cAMP which would normally be present during periods of neuronal plasticity. Both the adenyl cyclase activator, forskolin (frsk), and the cAMP analogue, Sp-Adenosine 3',5'-cyclic monophosphorothioate triethylammonium salt (Sp-cAMPS), enhanced the ability of Egr-1 to transactivate a CAT reporter plasmid containing multiple copies of the Egr-1 binding site (EBS). Furthermore, Egr-1 alone had minimal effects on synapsin I expression whereas forskolin treatment of PC12 cells profoundly affected the ability of Egr-1 to regulate synapsin I expression. These results suggest that Egr-1 transactivation during neuronal plasticity may rely on a permissive effect of cAMP.

Regulation of tyrosine hydroxylase gene transcription by Sry

Testes determining factor Sry is encoded by the Sry locus on the Y chromosome and may be involved in the regulation of blood pressure. Here we tested the hypothesis that Sry regulates transcription of tyrosine hydroxylase (TH), the rate-limiting enzyme in the biosynthesis of catecholamines. Sry was found to be expressed in catecholaminergic regions, in male but not female rats. Co-transfection of PC12 cells with expression vector for Sry and the reporter construct [p5'TH(-773/+27)/Luc], containing 773 of the proximal nucleotides of the TH promoter directing luciferase reporter activity, led to elevation of reporter activity. The reporter activity of a shorter construct [p5'TH(-272/+27)/Luc] lacking putative Sry sites also responded to Sry. However, mutation of the AP1 site in the TH promoter greatly reduced induction by Sry, indicating that the regulation is primarily at this motif. The remaining, significantly increased expression with the mutated TH promoter construct may reflect Sry function at other sites in addition to the AP1 motif. These results reveal that Sry can regulate TH transcription and suggest that this may be one of the mechanisms of Sry mediated regulation of catecholamine biosynthesis in catecholaminergic neurons in males.

Specific interaction of Egr1 and c/EBPbeta leads to the transcriptional activation of the human low density lipoprotein receptor gene

The sterol-independent regulatory element (SIRE) of the LDL receptor (LDLR) promoter mediates oncostatin M (OM)-induced transcription of the LDLR gene through a cholesterol-independent pathway. Our prior studies have detected specific associations of the zinc finger transcription factor Egr1 with the SIRE sequence in OM-stimulated HepG2 cells. Because the SIRE motif is composed of a c/EBP binding site and a cAMP response element, both of which are quite divergent from the classical GC-rich Egr1 recognition sequences, we hypothesized that Egr1 may regulate LDLR transcription through interacting with members of the c/EBP and CREB families. Here, we show that treating HepG2 cells with OM specifically leads to prominent increases of the levels of c/EBPbeta and Egr1 bound to the LDLR promoter in vivo. In vitro, the binding of Egr1 to the SIRE sequence is weak, but is strikingly enhanced in the presence of HepG2 nuclear extract. Mammalian two-hybrid assays demonstrate that the N-terminal transactivation domain of Egr1 specifically interacts with c/EBPbeta but not with c/EBPalpha or CREB. The OM treatment further enhances this interaction, resulting in a large increase in the Egr1 transactivating activity. The direct protein to protein contact between Egr1 and c/EBPbeta is also demonstrated by co-immunoprecipitation experiments. Furthermore, we show that a mutation of the phosphorylation motif of c/EBPbeta diminished the OM-stimulated interaction of Egr1 and c/EBPbeta. Taken together, we provide strong evidence that Egr1 regulates LDLR transcription via a novel mechanism of protein-protein interaction with c/EBPbeta.

Analysis of cellular, transgenic and human models of Huntington's disease reveals tyrosine hydroxylase alterations and substantia nigra neuropathology

Huntington's disease (HD) is a progressive, autosomal dominant neurodegenerative disorder that is pathologically characterized by a striatal-specific degeneration. Aberrant dopamine neurotransmission has been proposed as a mechanism underlying the movement disorder of HD. We report that the enzymatic activity of tyrosine hydroxylase (TH), the rate-limiting enzyme for dopamine biosynthesis, is decreased in a transgenic mouse model of HD. In addition, mutant huntingtin was found to disrupt transcription of TH and dopamine beta-hydroxylase (DbetaH) promoter reporter constructs. In situ hybridization revealed extensive loss of TH mRNA and decreased dopaminergic cell size in human HD substantia nigra. TH-immunoreactive protein was reduced in human grade 4 HD substantia nigra by 32% compared to age-matched controls. These findings implicate abnormalities in dopamine neurotransmission in HD and may provide new insights into targets for pharmacotherapy.

Contact call-driven zenk mRNA expression in the brain of the budgerigar (Melopsittacus undulatus)

Contact call-driven zenk (zif268, egr1, NGF1A, Krox 24) mRNA expression was mapped with in situ hybridization histochemistry in a vocal learning parrot, the budgerigar (M. undulatus). Relative to controls, call stimulation induced high zenk mRNA expression in all auditory areas including those closely associated with the vocal system within the anterior forebrain (Brauth et al. (2001) J. Comp. Neurol. 432, 481; (2002) Learn. Memory 9, 76). Thus there is a high correspondence between the distributions of neurons exhibiting contact call-driven zenk protein and mRNA expression in budgerigars. Field L2a, an area reported previously to express only perinucleolar zenk protein localization (Brauth et al. (2002) Learn. Memory 9, 76) also showed zenk mRNA expression.

c-Fos is essential for the response of the tyrosine hydroxylase gene to depolarization or phorbol ester

Tyrosine hydroxylase (TH) gene transcription rate increases in response to numerous pharmacological and physiological stimuli. The AP1 site within the TH gene proximal promoter is thought to play an important role in mediating many of these responses; however, it is unclear which AP1 factors are required. To investigate whether c-Fos is essential for the response of the TH gene to different stimuli, c-Fos-deficient PC12 cell lines were produced utilizing an antisense RNA strategy. In these cell lines, stimulus-induced increases in c-Fos protein levels were dramatically attenuated, while c-Jun and CREB levels remained unchanged. TH gene transcription rate increased from four- to eight-fold in control cells after treatment with either 50 mM KCl or TPA. These responses were dramatically decreased in the c-Fos-deficient cell lines. In contrast, c-Fos down-regulation had little effect on the response of the TH gene to forskolin. Stimulation of TH gene promoter activity, which was observed in control cell lines treated with either 50 mm KCl or TPA was also dramatically inhibited in the c-Fos-deficient cells. These results suggest that c-Fos induction is essential for maximal stimulation of the TH gene in response to either depolarization or PKC activation in PC12 cells.

Assessment by molecular dynamics simulations of the structural determinants of DNA-binding specificity for transcription factor Sp1

The DNA-binding domain (DBD) of the ubiquituous transcription factor Sp1 consists of three consecutive zinc fingers that recognize a number of nucleotide sequences different from, but related to and sometimes overlapping, those recognized by the structurally better characterized early growth response protein 1 (EGR1, also known as Zif268, Krox-24, and NGFI-A). The accepted consensus binding sequence for Sp1 is usually defined by the asymmetric hexanucleotide core GGGCGG but this sequence does not include, among others, the GAG (=CTC) repeat that constitutes a high-affinity site for Sp1 binding to the wt1 promoter. Since no 3D structure of the whole DBD of Sp1 is available, either alone or in complex with DNA, a homology-based model was built and its interaction with two DNA 14-mers was studied using nanosecond molecular dynamics simulations in the presence of explicit water molecules. These oligonucleotides represent Sp1 target sites that are present in the promoters of the mdr1 and wt1 genes. For comparative purposes and validation of the protocol, the complex between the DBD of EGR1 and its DNA target site within the proximal mdr1 promoter was simulated under the same conditions. Some water molecules were seen to play an important role in recognition and stabilization of the protein-DNA complexes. Our results, which are supported by the available experimental evidence, suggest that the accuracy in the prediction of putative Sp1-binding sites can be improved by interpreting a set of rules, which are a blend of both stringency and tolerance, for the juxtaposed triplet subsites to which each zinc finger binds. Our approach can be extrapolated to WT1 and other related natural or artificial zinc-finger-containing DNA-binding proteins and may aid in the assignment of particular DNA stretches as allowed or disallowed-binding sites.

Interactions between Egr1 and AP1 factors in regulation of tyrosine hydroxylase transcription

Several treatments which regulate tyrosine hydroxylase (TH) transcription, such as stress in vivo, or 12-O-tetradecanoylphorbol-13-acetate (TPA) in cell culture, induce both Egr1 and AP1 factors. Previously, we identified a functional Egr1 motif overlapping with Sp1 site in the rat TH promoter. Its response to Egr1 also required the presence of an AP1/Ebox motif. Here, we further examined the cross-talk between these sites. Insertion of 10- or 20-bp between the Sp1/Egr1 and AP1/Ebox elements, reduced the ability of Egr1 to upregulate luciferase reporter activity controlled by the proximal 272 nucleotides of the rat TH promoter in PC12 cells. Electrophoretic mobility shift assays with nuclear extracts from TPA treated cells were used to identify the composition of the factors which bound the AP1/Ebox motif and whether there is competition with factors which bind the Sp1/Egr1 motif. The complexes formed with labeled AP1/E box oligonucleotide were reduced or supershifted with antisera to Fos family, c-Fos, Fra-2, and Jun D. Excess Sp1/Egr1 oligonucleotide or anti Egr1 antisera did not compete. Fra-2 was a major component of the complex after 2-4 h TPA. Transfection of PC12 cells with Fra-2 induced reporter activity requiring the AP1, but not the Egr1 motif. However, when cotransfected with Fra-2, Egr1 expression plasmids elicited lower induction of luciferase activity than observed with Egr1 alone. Our results suggest that although it does not compete for binding to the promoter, Egr1 can modulate the regulation of TH transcription by AP1 factors.

Antioxidants induce different phenotypes by a distinct modulation of signal transduction

Antioxidants are known to exert a preventive activity against degenerative diseases. Here, we investigated the mechanism of action of three antioxidants: resveratrol, which causes differentiation of HL-60 cells, and hydroxytyrosol and pyrrolidine dithiocarbamate which, in the same model system, activate apoptosis. The expression profile of hydroxytyrosol-treated cells showed the up-regulation of several genes, including c-jun and egr1. Pyrrolidine dithiocarbamate activates both genes, while resveratrol increases uniquely egr1. A selective modulation of signalling pathway explained this finding. All antioxidants up-regulate Erk1/2, while only hydroxytyrosol and pyrrolidine dithiocarbamate activate c-Jun N-terminal kinase (JNK). Since JNK induces apoptosis by Bcl-2 phosphorylation, we investigated this event. Bcl-2 phosphorylation was increased by hydroxytyrosol and pyrrolidine dithiocarbamate and not by resveratrol. Our results indicate that the different phenotypical effects of antioxidants correlate with modulation of selective transduction pathways.

Heparin facilitates glial cell line-derived neurotrophic factor signal transduction

Glial cell-line neurotrophic factor (GDNF), a neurotrophic factor with heparin binding affinity, promotes the survival and differentiation of a variety of neuronal cells including dopaminergic neuron. The effect of heparin on GDNF signaling was investigated based on the expression of the tyrosine hydroxyrase (TH) gene in neurobalstoma cells. Up-regulation of TH gene mRNA by GDNF was enhanced by co-administration of heparin. This facilitation by heparin was particularly evident at suboptimal levels of GDNF, which was consistent with the luciferase assay using TH gene promoter. Pretreatment with heparitinase decreased TH promoter activity in the absence of heparin. Phosphorylation of extracellular regulated kinase was increased in the presence of heparin, although tyrosine phosphorylation of Ret receptor tyrosine kinase was not affected by heparin. Expression of early response genes such as c-fos or Egr1 increased and sustained in the presence of heparin more than that without heparin. These results indicate that interaction with glycosaminoglycans such as heparin affects GDNF signal transduction positively.

Molecular biology of the chromaffin cell

A large number of molecular biology studies have been performed on chromaffin cells, and many genes involved in catecholamine synthesis, storage, and release have been cloned and their function determined. Catecholamine synthesis takes place in different cellular compartments, and enzymes involved in this process are subject to a fine regulation, as demonstrated by recent studies on their gene promoters. Genes coding for such intravesicular proteins as chromogranin A, B, and secretogranin II (chromogranin C) are also regulated in response to a variety of stimuli. Chromogranin gene promoters and transcription factors involved in their regulation have been elucidated. This review serves as an introduction to the studies described in the chapters to follow.

Chronic ethanol increases lipopolysaccharide-stimulated Egr-1 expression in RAW 264.7 macrophages: contribution to enhanced tumor necrosis factor alpha production

Increased production of tumor necrosis factor alpha (TNFalpha) is associated with the development of alcoholic liver disease. Culture of RAW264.7 macrophages with 25 mm ethanol for 48 h increased lipopolysaccharide (LPS)-stimulated accumulation of tumor necrosis factor alpha (TNFalpha) peptide and mRNA by 2-fold. We investigated whether chronic ethanol-induced increases in the DNA binding and/or promoter activity of the key transcription factors regulating LPS-stimulated TNFalpha promoter activity contribute to increased TNFalpha expression. Binding of Egr-1 to the TNFalpha promoter was increased by 2.5-fold after ethanol exposure, whereas NFkappaB binding was decreased to 30% of control. AP-1 binding was not affected. Changes in binding activity were paralleled by an increased contribution of the Egr-1 binding site and a decreased contribution of the NFkappaB site to LPS-stimulated TNFalpha promoter activity. Overexpression of dominant negative Egr-1 prevented the ethanol-induced increase in LPS-stimulated TNFalpha mRNA accumulation. Chronic ethanol exposure enhanced LPS-stimulated Egr-1 promoter-driven CAT expression and transcription of Egr-1. Induction of Egr-1 is dependent on ERK1/2 activation in other systems. Therefore, we investigated whether the ERK1/2 pathway mediated the chronic ethanol-induced increases in Egr-1 and TNFalpha. Increased Egr-1 promoter activity and TNFalpha mRNA accumulation after chronic ethanol were both prevented by overexpression of dominant negative ERK1/2. LPS-stimulated ERK1/2 phosphorylation was increased 2-fold in cells cultured with ethanol compared with controls. These results demonstrate that enhanced LPS-dependent activation of Egr-1 contributes to increased TNFalpha production after chronic ethanol exposure.

Structure and expression of the scallop Omega-crystallin gene. Evidence for convergent evolution of promoter sequences

Omega-crystallin of the scallop lens is an inactive aldehyde dehydrogenase (1A9). Here we have cloned the scallop Omega-crystallin gene. Except for an extra novel first exon, its 14-exon structure agrees well with that of mammalian aldehyde dehydrogenases 1, 2, and 6. The -2120/+63, -714/+63, and -156/+63 Omega-crystallin promoter fragments drive the luciferase reporter gene in transfected alphaTN4-1 lens cells and L929 fibroblasts but not in Cos7 cells. Putative binding sequences for cAMP-responsive element-binding protein (CREB)/Jun, alphaACRYBP1, AP-1, and PAX-6 in the Omega-crystallin promoter are surprisingly similar to the cis-elements used for lens promoter activity of the mouse and chicken alphaA-crystallin genes, which encode proteins homologous to small heat shock proteins. Site-specific mutations in the overlapping CREB/Jun and Pax-6 sites abolished activity of the Omega-crystallin promoter in transfected cells. Gel shift experiments utilizing extracts from the alphaTN4-1, L929, and Cos7 cells and the scallop stomach and oligonucleotides derived from the putative binding sites of the Omega-crystallin promoter showed complex formation. Gel shift experiments showed binding of recombinant Pax-6 and CREB to their respective sites. Our data suggest convergent evolutionary adaptations that underlie the preferential expression of crystallin genes in the lens of vertebrates and invertebrates.

ERK induces p35, a neuron-specific activator of Cdk5, through induction of Egr1

The classical mitogen-activated protein kinase (MAPK; also known as extracellular-signal-regulated kinase), ERK cascade has been shown to have a crucial role in cell proliferation and differentiation. In PC12 cells, sustained activation of ERK induced by nerve-growth factor (NGF) is essential for neuronal differentiation. However, downstream targets of ERK that are essential for neuronal differentiation have not been defined. Here we show that NGF induces strong, sustained expression of p35, the neuron-specific activator of cyclin-dependent kinase 5 (Cdk5), through activation of the ERK pathway. The induced kinase activity of Cdk5 is required for NGF-induced neurite outgrowth. Our results indicate that sustained activation of ERK is necessary and sufficient for strong induction of p35. Furthermore, the transcription factor Egr1, is induced by NGF through the ERK pathway and mediates induction of p35 by ERK. Our results thus define an essential signalling pathway, downstream of ERK/MAPK, that leads to neuronal differentiation.

Stress-triggered activation of gene expression in catecholaminergic systems: dynamics of transcriptional events

Stress triggers important adaptive responses that enable an organism to cope with a changing environment. However, when prolonged or repeated, stress can be extremely harmful. The release of catecholamines is a key initial event in responses to stressors and is followed by an increase in the expression of genes that encode catecholamine-synthesizing enzymes. This process is mediated by transcriptional mechanisms in the adrenal medulla and the locus coeruleus. The persistence of transcriptional activation depends on the duration and repetition of the stress. Recent work has begun to identify the various transcription factors that are associated with brief or intermediate duration of a single or repeated stress. These studies suggest that dynamic interplay is involved in converting the transient increases in the rate of transcription into prolonged (potentially adaptive or maladaptive) changes in gene expression.