Activation of human monoamine oxidase B gene expression by a protein kinase C MAPK signal transduction pathway involves c-Jun and Egr-1

Song-induced gene expression: a window on song auditory processing and perception

We review here evidence that a large portion of the caudomedial telencephalon of songbirds, distinct from the song control circuit, is involved in the perceptual processing of birdsong. When songbirds hear song, a number of caudomedial pallial areas are activated, as revealed by expression of the activity-dependent gene zenk. These areas, which include field L subfields L1 and L3, as well as the adjacent caudomedial nidopallium (NCM) and caudomedial mesopallium (CMM), are part of the central auditory pathway and constitute a lobule in the caudomedial aspect of the telencephalon. Several lines of evidence indicate that the neural circuits integrating this lobule are capable of performing the auditory processing of song based on fine acoustic features. Thus, this lobule is well positioned to mediate song perceptual processing and discrimination, which are required for vocal communication and vocal learning. Importantly, the zenk gene encodes a transcription factor linked to synaptic plasticity, and it regulates the expression of target genes associated with specific neuronal cell functions. The induction of zenk likely represents a key regulatory event in a gene cascade triggered by song and leading to neuronal plasticity. Thus, zenk may be linked to molecular and cellular mechanisms underlying experience-dependent modification of song-responsive circuits. In summary, songbirds possess an elaborate system for song perceptual processing and discrimination that potentially also subserves song-induced neuronal plasticity and song memory formation. The continued use of a multidisciplinary approach that integrates molecular, anatomical, physiological and behavioral methodologies has the potential to provide further significant insights into the underlying neurobiology of the perceptual aspects of vocal communication and learning.

A spontaneous point mutation produces monoamine oxidase A/B knock-out mice with greatly elevated monoamines and anxiety-like behavior

A spontaneous monoamine oxidase A (MAO A) mutation (A863T) in exon 8 introduced a premature stop codon, which produced MAO A/B double knock-out (KO) mice in a MAO B KO mouse colony. This mutation caused a nonsense-mediated mRNA decay and resulted in the absence of MAO A transcript, protein, and catalytic activity and abrogates a DraI restriction site. The MAO A/B KO mice showed reduced body weight compared with wild type mice. Brain levels of serotonin, norepinephrine, dopamine, and phenylethylamine increased, and serotonin metabolite 5-hydroxyindoleacetic acid levels decreased, to a much greater degree than in either MAO A or B single KO mice. Observed chase/escape and anxiety-like behavior in the MAO A/B KO mice, different from MAO A or B single KO mice, suggest that varying monoamine levels result in both a unique biochemical and behavioral phenotype. These mice will be useful models for studying the molecular basis of disorders associated with abnormal monoamine neurotransmitters.

Phorbol ester-dependent activation of peroxiredoxin I gene expression via a protein kinase C, Ras, p38 mitogen-activated protein kinase signaling pathway

The antioxidant protein peroxiredoxin (Prx) I is a thioredoxin peroxidase that is involved in the regulation of proliferation and differentiation of mammalian cells. Here, it is shown that Prx I gene expression was induced transcriptionally by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) in cultured rat liver tissue macrophages and RAW264.7 monocytic cells. TPA-dependent induction of Prx I gene expression was mediated by two proximal activator protein-1 sites of the rat Prx I promoter region that were nuclear targets of c-Jun as determined by transfection studies with luciferase reporter gene constructs and electrophoretic mobility shift assays. The transcription factor Nrf2, however, was not involved in the regulation of Prx I promoter activity. Prx I gene induction by TPA was decreased by protein kinase C inhibitors and overexpressed dominant negative forms of Ras and MEKK1, but not Raf-1. The p38 MAPK inhibitor SB202190 and overexpression of dominant negative mutants of MAPK kinase 4 (MKK4), MKK6, and p38 inhibited the TPA-dependent induction of Prx I gene transcription. In contrast, inhibitors of the JNK, SP600125, and the NF-kappaB signaling pathway, caffeic acid phenethyl ester, respectively, as well as overexpressed dominant negative MKK7 and IkappaB, had no effect on the up-regulation of Prx I reporter gene activity by TPA. Cotransfection of wild-type p38alpha and p38beta, but not that of p38gamma and p38delta, increased Prx I promoter activity. The data indicate that a protein kinase C, Ras, MEKK1, p38 MAPK signaling pathway plays a major role for the transcriptional up-regulation of Prx I gene expression.

Use of an array technology for profiling and comparing transcription factors activated by TNFalpha and PMA in HeLa cells

Multiple signal transduction pathways are generally triggered simultaneously by a single extracellular stimulus. As a result, multiple transcription factors (TFs) can be activated downstream to mediate the inducible expression of target genes. Profiling the activation of all TFs will aid in the dissection of the numerous pathways of signal transduction. Tumor necrosis factor alpha (TNFalpha) and phorbol 12-myristate 13-acetate (PMA) mediate many biological functions, including cell proliferation and apoptosis, by stimulating signaling pathways. Two TFs, nuclear factor kappaB (NFkappaB) and activating factor 1 (AP1), have been identified as targets of both TNFalpha and PMA activation. Here, we describe the use of a protein/DNA array system to identify additional TFs activated by TNFalpha and PMA in HeLa cells. From a total of 150 targeted TFs, six-CREB, E2F, CETP/CRE, c-Rel, MSP1, and Pax6-were identified whose activities, like NFkappaB and AP1, were regulated by both TNFalpha- and PMA-induced pathways. Interestingly, the TF E47 was shown to be specifically activated by TNFalpha but was not affected by treatment with PMA. In addition, GATA, NF-E1, and ISRE were shown to be specifically activated by PMA but not TNFalpha. These findings suggest that TNFalpha and PMA both stimulate unique signaling pathways while mediating transcriptional activation through common pathways.

Decreased methylation and transcription repressor Sp3 up-regulated human monoamine oxidase (MAO) B expression during Caco-2 differentiation

Monoamine oxidase (MAO) A and B catalyze the oxidative deamination of neuroactive and dietary monoamines such as serotonin, tyramine, and phenylethylamine. Here we show that MAO B, but not MAO A, gene expression was induced during Caco-2 cell differentiation; thus this cell line was used as a model system to study the gene regulation unique for MAO B. Luciferase and gel shift assays showed that transcription factors Sp1 and Sp3 binding to -246 and -99 bp were responsible for the observed gene activation. Overexpression of Sp3 inhibited the induction of MAO B gene by Sp1, and the expression of Sp3 was decreased during Caco-2 cell differentiation. Computer analysis revealed a putative CpG island containing 22 potential CpG methylation sites between -261 and -58 bp. In vitro methylation of MAO B promoter with 5-aza-2'-deoxycytidine, a DNA methyltransferase inhibitor, up-regulated MAO B gene expression in both HeLa and Caco-2 cells. Sodium bisulfite sequencing showed a gradually reduced methylation of the CpG sites during Caco-2 cell differentiation. These results suggested that MAO B gene expression is selectively induced by a decreased Sp3/Sp1 ratio and reduced DNA methylation. This new information may provide insights on the tissue-specific expression of these two isoenzymes.

Serotonin transporter and MAO-B levels in monoamine nuclei of the human brainstem are normal in major depression

Neurochemical imbalance between noradrenergic and serotonergic systems has been postulated to underlie the pathophysiology of psychiatric illnesses involving mood disorders. The present study was designed to examined the possibility that serotonergic innervation of the locus coeruleus (LC) is abnormal in major depression, by measuring two proteins expressed by serotonergic neurons, but not by noradrenergic neurons, in the region of the LC. The specific binding of [(3)H]paroxetine to serotonin transporter (SERT) and of [(3)H]lazabemide to monoamine oxidase (MAO-B) were measured autoradiographically in tissue sections cut transversely at multiple levels along the rostro-caudal extent of the LC, as well as in the caudal portion of the dorsal raphe nucleus, from psychiatrically normal subjects and age-matched subjects with major depression. Under the conditions of the assays, [(3)H]paroxetine binding in the LC was specific for the SERT, based on the rank order of affinity of compounds for inhibiting [(3)H]paroxetine binding in the LC, i.e. citalopram > imipramine > desipramine > mazindol. The binding of [(3)H]paroxetine to SERT and [(3)H]lazabemide to MAO-B were higher in the raphe nuclei than in the LC. Comparison of control subjects to major depressive subjects revealed no differences in the amount of [(3)H]paroxetine binding to SERT and [(3)H]lazabemide to MAO-B in the LC, as well as in the raphe nuclei. These findings imply that serotonergic innervation of the LC is intact in major depression.

ERK and p38 inhibit the expression of 4E-BP1 repressor of translation through induction of Egr-1

4E-BP1 plays a major role in translation by inhibiting cap-dependent translation initiation. Several reports have investigated the regulation of 4E-BP1 phosphorylation, which varies along with cell differentiation and upon various stimulations, but very little is known about the regulation of its expression. In a first part, we show that the expression of 4E-BP1 protein and transcript decreases in hematopoietic cell lines cultivated in the presence of phorbol 12-myristate 13-acetate (PMA). This decrease depends on the activation of the ERK/mitogen-activated protein kinases. 4E-BP1 expression also decreases when the p38/mitogen-activated protein kinase pathway is activated by granulocyte/macrophage colony-stimulating factor but to a lesser extent than with PMA. In a second part, we examine how 4e-bp1 promoter activity is regulated. PMA and granulocyte/macrophage colony-stimulating factor induce Egr-1 expression through ERK and p38 activation, respectively. Using a dominant negative mutant of Egr, ZnEgr, we show that this transcription factor is responsible for the inhibition of 4e-bp1 promoter activity. In a third part we show that histidine decarboxylase, whose activity and expression are inversely correlated with 4E-BP1 expression, is a potential target for the translational machinery. These data (i) are the first evidence of a new role of ERK and p38 on the translational machinery and (ii) demonstrate that 4E-BP1 is a new target for Egr-1.