Conserved regulatory elements in the promoter region of the N-CAM gene

Psychological stress and aging: role of glucocorticoids (GCs)

Psychological stress has extreme adverse consequences on health. However, the molecular mechanisms that mediate and accelerate the process of aging due to stress hormone are not well defined. This review has focused on diverse molecular paths that come out in response to chronic psychological stress via releasing of excessive glucocorticoids (GCs), involved in the aging process. GCs suppress transcription of nuclear cell adhesion molecules which impair synaptic plasticity, memory formation, and cognitive ability. Again, GCs promote muscle atrophy by means of motivating ubiquitin proteasome system and can repress muscle protein synthesis by inhibition of PI3-kinase/Akt pathway. GCs also inhibit interleukin-2 synthesis through suppressing T cell receptor signal that leads to loss of T cell activation, proliferation, and B-cell activation. Moreover, GCs increase the expression of collagenase-3, RANK ligand, and colony stimulating factor-1 that induce bone resorption. In general, stress-induced GCs can play causal role for aging and age-related disorders.

Transcriptional regulation of PSA-NCAM expression by NMDA receptor activation in RA-differentiated C6 glioma cultures

N-Methyl-d-aspartate (NMDA) receptors exhibit a dichotomy of signaling with both toxic and plastic responses. Recent reports have shown that exposure to subtoxic concentration of NMDA results in a neuroprotective state that was measured when these neurons were subsequently challenged with toxic doses of glutamate or kainate. Control of polysialylated neural cell adhesion molecule (PSA-NCAM) expression by NMDA receptor activation has been described in several systems, suggesting a functional link between these two proteins. The perception of glial role in CNS function has changed dramatically over the past few years from simple trophic functions to that of cells with important roles in development and maintenance of CNS in cooperation with neurons. We report here the transcriptional regulation of PSA-NCAM expression by subtoxic dose of NMDA in retinoic acid differentiated C6 glioma cell cultures. C6 glioma cell cultures differentiated with retinoic acid (10microM) were exposed to NMDA (100microM) or to antagonist MK-801 (200nM) prior to treatment with NMDA and cells were harvested after 24h of treatment to study the expression of total NCAM, PSA-NCAM, nuclear factor kappaB (NF-kappaB) and activator protein-1 (AP-1) by Western blotting and dual immunocytofluorescence and expression of PST mRNA by fluorescent in situ hybridization (FISH). Significant increase in the levels of PSA-NCAM, NF-kappaB, AP-1 and PST mRNA was observed in NMDA treated cultures. Treatment of cultures with MK-801, a non-competitive NMDA receptor antagonist, prior to NMDA exposure prevented the NMDA-mediated changes indicating the involvement of NMDA receptor activation. The results elucidate the possible cellular and molecular mechanisms of regulation of PSA-NCAM expression in astroglial cultures by extracellular signals.

Exposure to stressors during juvenility disrupts development-related alterations in the PSA-NCAM to NCAM expression ratio: potential relevance for mood and anxiety disorders

Childhood trauma is associated with higher rates of both mood and anxiety disorders in adulthood. The exposure of rats to stressors during juvenility has comparable effects, and was suggested as a model of induced predisposition for these disorders. The neural cell adhesion molecule (NCAM) and its polysialylated form PSA-NCAM are critically involved in neural development, activity-dependent synaptic plasticity, and learning processes. We examined the effects of exposure to stressors during juvenility on coping with stressors in adulthood and on NCAM and PSA-NCAM expression within the rat limbic system both soon after the exposure and in adulthood. Exposure to stressors during juvenility reduced novel-setting exploration and impaired two-way shuttle avoidance learning in adulthood. Among naive rats, a development-related decrease of about 50% was evident in the PSA-NCAM to NCAM expression ratio in the basolateral amygdala, in the CA1 and dentate gyrus regions of the hippocampus, and in the entorhinal cortex. In juvenile-stressed rats, we found no such decrease, but rather an increase in the polysialylation of NCAM ( approximately 50%), evident soon after the exposure to juvenile stress and also in adulthood. Our results suggest that exposure to stressors during juvenility alters the maturation of the limbic system, and potentially underlies the predisposition to exhibit stress-related symptoms in adulthood.

Transcriptional regulation of polysialylated neural cell adhesion molecule expression by NMDA receptor activation in retinoic acid-differentiated SH-SY5Y neuroblastoma cultures

NMDA receptors exhibit a dichotomy of signaling with excessive stimulation leading to neuronal damage that occurs during neurodegenerative disorders, whereas the normal burst of activity results in plastic responses with the expression of molecular substrates of long-term plasticity, growth and survival. Control of polysialylated neural cell adhesion molecule (PSA-NCAM) expression by NMDA receptor activation has been described in several systems, suggesting a functional link between these two proteins. The coordinated induction of several different transcription factors initiated by NMDA receptor stimulation may be a key mechanism in the orchestration of specific target gene expression that underlies various aspects of CNS function, including plastic responses. We report here the transcriptional regulation of PSA-NCAM expression by subtoxic dose of NMDA in retinoic acid-differentiated SH-SY5Y cell cultures. SH-SY5Y cell cultures differentiated with retinoic acid (10 microM) were exposed to NMDA (100 microM) or to antagonist MK-801 (200 nM) prior to treatment with NMDA and cells were harvested after 24 h of treatment to study the expression of PSA-NCAM, nuclear factor kappaB (NF-kappaB) and activator protein-1 (AP-1) by Western blotting and dual immunocytofluorescence and expression of polysialyltransferase (PST) mRNA by fluorescent in situ hybridization (FISH). We observed the induction of transcription factors NF-kappaB and AP-1 along with PSA-NCAM expression in response to NMDA receptor activation. Also, PSA-NCAM regulation in response to NMDA receptor activity was shown to be transcriptionally controlled, as seen by temporal and spatial changes observed in the expression of PST mRNA in NMDA-treated SH-SY5Y cell cultures. This raises the interesting possibility that NF-kappaB and AP-1 expression is involved in propagating the signals of NMDA receptor activity that leads to downstream strengthening of long-term plasticity changes in differentiated SH-SY5Y neuroblastoma cell cultures. Thus understanding the regulation of PSA-NCAM expression by NMDA receptor-mediated activity may represent a fundamental prerequisite for the development of therapies in order to maintain neuronal plasticity throughout life and functional recovery after brain damage.

Stress, cognitive impairment and cell adhesion molecules

Stress has profound effects on brain structure and function, but the underlying mechanisms are still poorly understood. Recent studies imply that neuronal cell adhesion molecules of the immunoglobulin superfamily--NCAM and L1--are important mediators of the effects of stress on the brain. Chronic stress regimes that lead to hippocampal atrophy and spatial-learning impairment in rodents simultaneously induce a pattern of changes in cell adhesion molecule expression that fits with a role for these molecules in stress-induced neuronal damage and neuroprotective mechanisms. These findings highlight cell adhesion molecules as potential therapeutic targets to treat stress-related cognitive disturbances.

Characterization of the genomic structure of the mouse limbic system-associated membrane protein (Lsamp) gene

The Lsamp gene encodes the limbic system-associated membrane protein (LAMP) an immunoglobulin (Ig) superfamily member with three Ig domains and a glycosylphosphatidylinositol anchor. LAMP is expressed by neurons composing the limbic system, is highly conserved between rodents and human, and has structural and functional properties that substantiate its role in the formation of limbic circuits. We report here the genomic organization of the Lsamp gene. The Lsamp gene is composed of 11 exons distributed over 2.2 megabases (Mb). Two exons 1 are separated by approximately 1.6 Mb and contribute to the unusual large size of the gene. Alternative spliced Lsamp mRNAs are generated from distinct promoter regions associated with the two exons 1 that encode distinct signal peptides and thus generate identical native mature polypetides. Additional diversity is created by the use of two small exons to include an insertion of 23 amino acids within the polypeptide C-terminal region of the mature protein. The genomic features of the Lsamp gene described here indicate an intricate mechanism of gene expression regulation that may be relevant in the context of human neuropsychiatric and neurological disorders, where LAMP expression may be altered.

Neuronal differentiation and protection from nitric oxide-induced apoptosis require c-Jun-dependent expression of NCAM140

c-Jun, a crucial component of the dimeric transcription factor activating protein 1 (AP-1), can regulate apoptosis induced by oxidative stress and has been implicated in neuronal differentiation, but the mechanisms are largely unknown. We found that specific inhibition of transcription or stable transfection with cDNA encoding dominant-negative c-Jun sensitized SH-SY5Y neuroblastoma cells (TAM-67 cells) to apoptosis induced by the nitric oxide (NO) donor sodium nitroprusside or SIN-1. TAM-67 cells also became refractory to nerve growth factor (NGF)-induced neuronal differentiation. Dominant-negative c-Jun abolished expression of a 140-kDa neural cell adhesion molecule (NCAM140) and dramatically enhanced the expression of NCAM180 in TAM-67 cells. Inhibition of c-Jun in TAM-67 cells also resulted in a corresponding decrease in the amount of NCAM140 mRNA and an increase in the amount of NCAM180 mRNA. Reexpression of NCAM140 in TAM-67 cells restored NGF-induced neuronal differentiation and resistance to NO-induced apoptosis. Our results show that c-Jun/AP-1, through up-regulation of NCAM140, plays an important role in both NGF-induced neuronal differentiation and resistance to apoptosis induced by NO in neuroblastoma cells. As NCAM140 and NCAM180 are translated from differentially spliced mRNAs transcribed from the same gene, alternative splicing of NCAM pre-mRNA (and consequently the synthesis of the smaller NCAM140 species) appears to be regulated by c-Jun/AP-1.

DSCAM, a highly conserved gene in mammals, expressed in differentiating mouse brain

Down Syndrome Cell Adhesion molecule (DSCAM) is a member of the immunoglobulin superfamily, and represents a novel class of neuronal cell adhesion molecules. In order to understand the cellular functions of DSCAM, we isolated full-length mouse and human cDNA clones, and analysed its expression during mouse development and differentiation. Sequence analysis of the human DSCAM cDNA predicted at least 33 exons that are distributed over 840 kb. When compared to human DSCAM, the mouse homologue showed 90 and 98% identity at the nucleotide and amino acid levels, respectively. In mouse, DSCAM is located on 16C, the syntenic region for human chromosome band 21q22 and also the region duplicated in mouse DS models. DSCAM gene is predicted to encode an approximately 220-kDa protein, and its expression shows dynamic changes that correlate with neuronal differentiation during mouse development. Our results suggest that DSCAM may play critical roles in the formation and maintenance of specific neuronal networks in brain.

The genomic structure of the chicken ICSBP gene and its transcriptional regulation by chicken interferon

The chicken interferon consensus sequence binding protein (ChICSBP) gene spans over 9 kb of DNA and consists, as its murine homolog, of nine exons. The first untranslated exon was identified by 5'-RACE technology. The second exon contains the translation initiation codon. Canonical consensus splice sites are found on every exon/intron junction. The introns are generally smaller than their mammalian counterparts. The ChICSBP and ChIRF-1 genes have been mapped by fluorescence in situ hybridization to different microchromosomes. The transcription start site has been mapped by primer extension. Inspection of the DNA sequence of a genomic clone containing the first exon and the region 1700-bp upstream revealed several potential cisregulatory elements of transcription. The ChICSBP mRNA is induced by recombinant ChIFN type I and ChIFN-gamma. A palindromic IFN regulatory element (pIRE) with high sequence homology to gamma activation site (GAS) sequences was functionally required in transient transfection assays for the induction of transcription by ChIFN-gamma.

Organization of the neurofascin gene and analysis of developmentally regulated alternative splicing

Neurofascin is an axonal member of the L1 subgroup of the immunoglobulin superfamily implicated in neurite extension in the course of embryonic development. Here we have isolated and characterized the gene encoding chicken neurofascin. Comparison of genomic sequences with cDNA sequences provides the structure and localization of intron/exon boundaries and indicates that neurofascin isoforms are generated by alternative splicing of its pre-mRNA. The neurofascin gene is composed of 33 exons distributed over 72 kilobases. Each of the six immunoglobulin- and five fibronectin-type III-like domains is encoded by two exons. While introns between domains are of phase 1, others are of phase 0, 1, or 2. Alternative splicing of neurofascin is developmentally regulated as shown by polymerase chain reaction analysis. Furthermore, plasmid libraries from long range polymerase chain reaction-amplified cDNA of neurofascin were used to examine and quantify the distribution of alternatively spliced exons in individual neurofascin molecules. We found 50 different neurofascin isoforms at different developmental stages and revealed the existence of one major "early" in comparison with multiple "late" neurofascin isoforms.

The gene of the neural cell recognition molecule F11: conserved exon-intron arrangement in genes of neural members of the immunoglobulin superfamily

The chicken neural glycoprotein F11 is a cell recognition molecule implicated in neurohistogenesis, in particular in the context of neurite outgrowth and fasciculation. F11 is a glycosyl-phosphatidylinositol-linked member of the immunoglobulin superfamily that is also termed contactin or F3 in humans and rodents, respectively. In this study, we report the complete structure of the F11 gene. It is composed of 23 exons distributed over more than 100 kb of genomic DNA and each of the ten domains of the F11 protein is encoded by two exons. The sizes of the introns vary by two orders of magnitude ranging from 150 bp to more than 15 kb. All interdomain introns are in phase one, i.e. are inserted after the first nucleotide of a codon, being consistent with assembly of a F11 progenitor gene via exon shuffling. The intradomain introns are localized at variable sites within the domains and have different intron phases. This study reveals a remarkable similarity of the F11 gene with the gene of axonin-1, a related neural immunoglobulin superfamily member which is also implicated in neurite outgrowth and fasciculation. The intron positions with respect to the protein domain organization are found to be identical, strongly suggesting that both genes are derived from a common ancestor that already had this exon-intron structure.

Isolation and characterization of the promoter region of the chicken N-cadherin gene

N-cadherin (CDH2) is a member of the cadherin family of Ca2(+)-dependent cell-cell adhesion molecules. To investigate mechanisms controlling CDH2 transcription, we isolated and analyzed a genomic DNA sequence containing 2.8 kb of 5' flanking region and the first two exons of chicken CDH2. Sequence analysis of the promoter region of CDH2 revealed no CCATT or TATA boxes, but showed a high overall GC content, high CpG dinucleotide content, and several consensus Sp1 and Ap2 binding sequences. When fused to the cat reporter gene in transient transfection experiments, the sequence from positions -3231 to -118 (relative to the translation start site) directed high-level expression in CDH2-expressing chicken primary retinal cells and mouse N2A cells, but was much less active in chicken embryonic fibroblast cells and mouse 3T3 cells which do not express CDH2. Similarly, this promoter fragment directed variable, but neuronal-specific, expression of reporter genes in adult transgenic mice, but failed to produce the correct pattern of expression in other tissues, implying that additional sequences further upstream and/or within introns of CDH2 may play important roles in the transcriptional control.

Structural and functional similarities between the promoters for mouse tenascin and chicken cytotactin

Cytotactin/tenascin is an extracellular matrix glycoprotein expressed in a restricted anteroposterior pattern during vertebrate development and is reexpressed in the adult during wound healing, tumorigenesis, and nerve regeneration. Previously, we have characterized the chicken cytotactin promoter and have shown its regulation by homeobox gene products in vitro. We have now isolated the promoter for the mouse tenascin gene in order to determine whether common or different DNA regulatory elements control the expression of this gene in these two species. Like the chicken cytotactin gene, the mouse tenascin gene has a single RNA start site that lies 27 bp downstream of a TATA box. A 4028-bp region of DNA upstream of the mouse tenascin gene was sequenced and examined for regulatory motifs in common with the upstream sequence from the chicken cytotactin promoter. Two hundred thirty base pairs of the proximal promoter regions from both genes had an extended sequence similarity and contained common regulatory motifs such as two tracts of homopolymeric dA.dT sequence, an octamer motif, an ATTA (TAAT) motif which is a common core sequence for binding of homeodomain transcription factors, and a TATA-box/cap-site region. Reporter gene constructs with various 5' deletions of the mouse tenascin upstream sequence were tested in transient transfections of mouse NIH 3T3 and chicken embryo fibroblasts. The conserved proximal promoter region of tenascin was responsible for most of the positive regulatory activity. In addition, an upstream region (-2478 to -247) repressed proximal promoter activity in mouse fibroblasts and also in chicken embryo fibroblasts. These data indicate that both the structure and function of the cytotactin/tenascin proximal promoters have remained conserved over 250 million years.

The biology of perlecan: the multifaceted heparan sulphate proteoglycan of basement membranes and pericellular matrices

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