Transcriptional regulation of the mouse presenilin-1 gene

Presenilin 2 overexpression is associated with apoptosis in Neuro2a cells

Presenilin 1 (PS1) and PS2 are evolutionarily conserved transmembrane proteins of the aspartyl protease family. Initially, they were reported to be associated with the early onset of familial, early-onset Alzheimer’s disease. PS1 has been implicated in several crucial brain functions including developmental processes, synaptic plasticity, and processing of various molecules, while PS2 has been poorly studied and is considered to be a compensatory partner of PS1. Certain controversial reports have suggested that PS2 has a role in apoptosis, though the underlying mechanism is not clear. To ascertain the role of PS2 in apoptosis, mouse neuroblastoma cells (Neuro2a) were transfected with a cDNA construct encoding full length mouse PS2 and analyzed for viability, expression of PS1, PS2, Bax and p53, Bax protein, and status of chromatin condensation. Our results showed reduced viability, condensed chromatin and higher expression of Bax at mRNA and protein levels, but no change in the expression of p53 and PS1 in PS2-overexpressing Neuro2a cells. Thus, it is evident that PS2, independent of PS1, is associated with apoptosis via a Bax-mediated pathway. These findings might help in the understanding of the involvement of PS2 in apoptosis and its associated brain disorders.

Mithramycin A Alleviates Cognitive Deficits and Reduces Neuropathology in a Transgenic Mouse Model of Alzheimer's Disease

Increasing evidence has shown that specificity protein 1 (Sp1) is abnormally increased in the brains of subjects with Alzheimer's disease (AD) and transgenic AD models. However, whether the Sp1 activation plays a critical role in the AD pathogenesis and selective inhibition of Sp1 activation may have a disease-modifying effect on the AD-like phenotypes remain elusive. In this study, we reported that Sp1 mRNA and protein expression were markedly increased in the brain of APPswe/PS1dE9 transgenic mice, whereas chronic administration of mithramycin A (MTM), a selective Sp1 inhibitor, potently inhibited Sp1 activation in the APPswe/PS1dE9 mice down to the levels of wild-type mice. Specifically, we found that MTM treatment resulted in a significant improvement of learning and memory deficits, a dramatic reduction in cerebral Aβ levels and plaque burden, a profound reduction in tau hyperphosphorylation, and a marked increase in synaptic marker in the APPswe/PS1dE9 mice. In addition, MTM treatment was powerfully effective in inhibiting amyloid precursor protein (APP) processing via suppressing APP, beta-site APP cleaving enzyme 1 (BACE1), and presenilin-1 (PS1) mRNA and protein expression to preclude Aβ production in the APPswe/PS1dE9 mice. Furthermore, MTM treatment strongly inhibited phosphorylated CDK5 and GSK3β signal pathways to reduce tau hyperphosphorylation in the APPswe/PS1dE9 mice. Collectively, our findings provide evidence that Sp1 activation may contribute to the AD pathogenesis and may serve as a novel therapeutic target in the treatment of AD. The present study highlights that selective Sp1 inhibitors may be considered as disease-modifying therapeutic agents for AD.

Role of Species-Specific Primary Structure Differences in Aβ42 Assembly and Neurotoxicity

A variety of species express the amyloid β-protein (Aβ (the term "Aβ" refers both to Aβ40 and Aβ42, whereas "Aβ40" and "Aβ42" refer to each isoform specifically). Those species expressing Aβ with primary structure identical to that expressed in humans have been found to develop amyloid deposits and Alzheimer's disease-like neuropathology. In contrast, the Aβ sequence in mice and rats contains three amino acid substitutions, Arg5Gly, His13Arg, and Tyr10Phe, which apparently prevent the development of AD-like neuropathology. Interestingly, the brush-tailed rat, Octodon degus, expresses Aβ containing only one of these substitutions, His13Arg, and does develop AD-like pathology. We investigate here the biophysical and biological properties of Aβ peptides from humans, mice (Mus musculus), and rats (Octodon degus). We find that each peptide displays statistical coil → β-sheet secondary structure transitions, transitory formation of hydrophobic surfaces, oligomerization, formation of annuli, protofibrils, and fibrils, and an inverse correlation between rate of aggregation and aggregate size (faster aggregation produced smaller aggregates). The rank order of assembly rate was mouse > rat > Aβ42. The rank order of neurotoxicity of assemblies formed by each peptide immediately after preparation was Aβ42 > mouse ≈ rat. These data do not support long-standing hypotheses that the primary factor controlling development of AD-like neuropathology in rodents is Aβ sequence. Instead, the data support a hypothesis that assembly quaternary structure and organismal responses to toxic peptide assemblies mediate neuropathogenetic effects. The implication of this hypothesis is that a valid understanding of disease causation within a given system (organism, tissue, etc.) requires the coevaluation of both biophysical and cell biological properties of that system.

Transcriptional regulation and its misregulation in Alzheimer's disease

Alzheimer’s disease (AD) is a devastating neurodegenerative disorder characterized by loss of memory and cognitive function. A key neuropathological event in AD is the accumulation of amyloid-β (Aβ) peptide. The production and clearance of Aβ in the brain are regulated by a large group of genes. The expression levels of these genes must be fine-tuned in the brain to keep Aβ at a balanced amount under physiological condition. Misregulation of AD genes has been found to either increase AD risk or accelerate the disease progression. In recent years, important progress has been made in uncovering the regulatory elements and transcriptional factors that guide the expression of these genes. In this review, we describe the mechanisms of transcriptional regulation for the known AD genes and the misregualtion that leads to AD susceptibility.

Current advanced bioluminescence technology in drug discovery

BACKGROUND

Bioluminescence technology is based on the luciferin-luciferase reaction and is generally well known as a reporter gene assay system that uses firefly luciferase. It has revolutionized the field of transcriptional analysis owing to its usability and quantitative capability. Several methods for transcription analysis have emerged in the past two decades. Recently, novel bioluminescence techniques that differ from typical approaches were developed for the detection of transcriptional regulation or direct protein-protein interactions.

OBJECTIVE

As each method has its own characteristics, this review summarizes the latest bioluminescence methods that are applicable to the field of drug discovery research.

METHODS

Considering the diversity of related techniques, this review covers several aspects that have been divided into the following classes: variation of reporter gene assays, secretion properties, protein-protein interaction assays in living cells and bioluminescence imaging of living cells.

RESULTS/CONCLUSIONS

The practical application of several luciferins and/or luciferases and the generation of novel applications by incorporating fluorescent molecules into bioluminescence techniques will become increasingly important because bioluminescence technology has a significant potential depending on how we use it.

Parkin differently regulates presenilin-1 and presenilin-2 functions by direct control of their promoter transcription

We previously established that besides its canonical function as E3-ubiquitin ligase, parkin also behaves as a transcriptional repressor of p53. Here we show that parkin differently modulates presenilin-1 and presenilin-2 expression and functions at transcriptional level. Thus, parkin enhances/reduces the protein expression, promoter activity and mRNA levels of presenilin-1 and presenilin-2, respectively, in cells and in vivo. This parkin-associated function is independent of its ubiquitin-ligase activity and remains unrelated to its capacity to repress p53. Accordingly, physical interaction of endogenous or overexpressed parkin with presenilins promoters is demonstrated by chromatin immunoprecipitation assays (ChIP). Furthermore, we identify a consensus sequence, the deletion of which abolishes parkin-dependent modulation of presenilins-1/2 and p53 promoter activities. Interestingly, electrophoretic mobility shift assays (EMSA) revealed a physical interaction between this consensus sequence and wild-type but not mutated parkin. Finally, we demonstrate that the RING1-IBR-RING2 domain of parkin harbors parkin's potential to modulate presenilins promoters. This transcriptional control impacts on presenilins-associated phenotypes, since parkin increases presenilin-1-associated γ-secretase activity and reduces presenilin-2-linked caspase-3 activation. Overall, our data delineate a promoter responsive element targeted by parkin that drives differential regulation of presenilin-1 and presenilin-2 transcription with functional consequences for γ-secretase activity and cell death.

Genetic studies in Alzheimer's disease

Alzheimer's disease (AD), the most common cause of dementia in aged populations, is believed to be caused by both environmental factors and genetic variations. Extensive linkage and association studies have established that a broad range of loci are associated with AD, including both causative and susceptibility (risk factor) genes. So far, at least three genes, APP, PS1, and PS2, have been identified as causative genes. Mutations in these genes have been found to cause mainly early-onset AD. On the other hand, APOE has been identified to be the most common high genetic risk factor for late-onset AD. Polymorphisms in the coding region, intron, and promoter region of certain genes constitute another kind of genetic variation associated with AD. A number of other genes or loci have been reported to have linkage with AD, but many show only a weak linkage or the results are not well reproduced. Currently, the measurable genetic associations account for about 50% of the population risk for AD. It is believed that more new loci will be found to associate with AD, either as causative genes or genetic risk factors, and that eventually the understanding of genetic factors in the pathogenesis of AD will be important for our efforts to cure this illness.

p53-dependent control of transactivation of the Pen2 promoter by presenilins

The senile plaques found in the brains of patients with Alzheimer's disease are mainly due to the accumulation of amyloid beta-peptides (A beta) that are liberated by gamma-secretase, a high molecular weight complex including presenilins, PEN-2, APH-1 and nicastrin. The depletion of each of these proteins disrupts the complex assembly into a functional protease. Here, we describe another level of regulation of this multimeric protease. The depletion of both presenilins drastically reduces Pen2 mRNA levels and its promoter transactivation. Furthermore, overexpression of presenilin-1 lowers Pen2 promoter transactivation, a phenotype abolished by a double mutation known to prevent presenilin-dependent gamma-secretase activity. PEN-2 expression is decreased by depletion of beta-amyloid precursor protein (APP) and increased by the APP intracellular domain (AICD). We show that AICD and APP complement for Pen2 mRNA levels in APP/APLP1-2 knockout fibroblasts. Interestingly, overexpression of presenilin-2 greatly increases Pen2 promoter transactivation. The opposite effect triggered by both presenilins was reminiscent of our previous study, which showed that these two proteins elicit antagonistic effects on p53. Therefore, we examined the contribution of p53 on Pen2 transcription. Pen2 promoter transactivation, and Pen2 mRNA and protein levels were drastically reduced in p53(-/-) fibroblasts. Furthermore, PEN-2 expression could be rescued by p53 complementation in p53- and APP-deficient cells. Interestingly, PEN-2 expression was also reduced in p53-deficient mouse brain. Overall, our study describes a p53-dependent regulation of PEN-2 expression by other members of the gamma-secretase complex, namely presenilins.

DNA methylation of Alzheimer disease and tauopathy-related genes in postmortem brain

DNA methylation occurs predominantly at cytosines that precede guanines in dinucleotide CpG sites; it is one of the most important mechanisms for epigenetic DNA regulation during normal development and for aberrant DNA in cancer. To determine the feasibility of DNA methylation studies in the postmortem human brain, we evaluated brain samples with variable postmortem artificially increased delays up to 48 hours. DNA methylation was analyzed in selected regions of MAPT, APP, and PSEN1 in the frontal cortex and hippocampus of controls (n=26) and those with Alzheimer disease at Stages I to II (n=17); Alzheimer disease at Stages III to IV (n=15); Alzheimer disease at Stages V to VI (n=12); argyrophilic grain disease (n=10); frontotemporal lobar degeneration linked to tau mutations (n=6); frontotemporal lobar degeneration with ubiquitin-immunoreactive inclusions (n=4); frontotemporal lobar degeneration with motor neuron disease (n=3); Pick disease (n=3); Parkinson disease (n=8); dementia with Lewy bodies, pure form (n=5); and dementia with Lewy bodies, common form (n=15). UCHL1 (ubiquitin carboxyl-terminal hydrolase 1 gene) was analyzed in the frontal cortex of controls and those with Parkinson disease and related synucleinopathies. DNA methylation sites were very reproducible in every case. No differences in the percentage of CpG methylation were found between control and disease samples or among the different pathological entities in any region analyzed. Because small changes in methylation of DNA promoters in vulnerable cells might have not been detected in total homogenates, however, these results should be interpreted with caution, particularly as they relate to chronic degenerative diseases in which small modifications may be sufficient to modulate disease progression.

Transcriptional regulation of the murine Presenilin-2 gene reveals similarities and differences to its human orthologue

Inherited Presenilin-2 mutations cause familial Alzheimer's disease, and its regulation may play a role in sporadic cases. The human Presenilin-2 (PSEN2) regulatory region includes two separate promoters modulated by Egr-1, a transcription factor involved in learning and memory. To enable in-vivo analysis of Presenilin-2 regulation, we characterized the murine Presenilin-2 (Psen2) promoter. We identified novel Psen2 Transcription start sites (TSSs) 10 kb upstream of previously reported sites, along with two new alternatively transcribed exons (1A, and 1BC) in the 5' untranslated region. Transcripts initiating in Exon 1A are ubiquitous, whereas exon 1BC-initiated transcripts are non-neuronal. Only the sequence surrounding exon 1A, which includes homologous sequences to the human PSEN2 promoter, harbored significant promoter activity. Sequences upstream of exon 1A and a downstream enhancer were specifically important in neuronal cells, but similar to the human promoter, the murine promoter was characteristic of a housekeeping gene, and its activity depended on Sp1 binding. Egr-1 did not bind the murine promoter. Egr-1 over-expression and down-regulation, as well as in-vivo examination of Egr-1 and Psen2 expression during fear conditioning in mice, showed that Egr-1 does not regulate the murine Psen2 promoter. Differential Psen2 regulation in human and mouse has implications for Alzheimer disease mouse models.

PS1 expression is downregulated by gonadal steroids in adult mouse brain

Mutations in presenilin (PS) 1 and PS2 genes are associated with early onset (< or =65 years) of Alzheimer's disease (AD). PS1 is involved in gamma-secretase mediated cleavage of beta-amyloid precursor protein (APP), but its regulation is poorly understood. Sex steroids influence APP cleavage pathways resulting in reduced burden of both intra- and extra-cellular nonamyloidogenic products. As gonadal hormones are implicated in AD and their levels change with age, we have analyzed the effect of 17beta-estradiol and testosterone on PS1 expression in the cerebral cortex of adult and old AKR mice of both sexes. Northern and Western-blot analysis revealed that PS1 mRNA and protein expression followed similar pattern of regulation. PS1 expression was downregulated by 17 beta-estradiol and testosterone in the cerebral cortex of females and adult male, but upregulated in old male mice. Such sex-dependent regulation of PS1 expression during aging by gonadal steroids might account for the PS-related brain functions.

Reelin signals survival through Src-family kinases that inactivate BAD activity

Reelin plays an important role in the migration of embryonic neurons, but its continuing presence suggests additional functions in the brain. We now report a novel function where reelin protects P19 embryonal cells from apoptosis during retinoic acid-induced neuronal differentiation. This increased survival is associated with reelin activation of the phosphatidyl-inositol-3-kinase (PI3 K)/Akt pathway. When PI3 K was inhibited with LY294002, reelin failed to protect against this retinoic acid-induced apoptosis. The protective effect of reelin includes activating the Src-family kinases/PI3 K/Akt pathway which then led to selective phosphorylation of Bcl-2/Bcl-XL associated death promoter (BAD) at serine-136, while the phosphorylation-incompetent mutation of BAD (S136A) suppressed this protection. These and additional studies define a novel pathway where reelin binds apoE receptors, significantly activates the PI3 K/Akt pathway causing phosphorylation of BAD which helps to protect cells from apoptosing, thus serving an important role in promoting the survival of maturing neurons in the brain.

Alpha-secretase activation--an approach to Alzheimer's disease therapy

The nonamyloidogenic pathway of processing the amyloid precursor protein (APP) involves the cleavage within the amyloid-beta peptide sequence, and thus precludes amyloid-beta formation. The identification of a member of the disintegrin and metalloproteinase family, ADAM10, as an alpha-secretase that prevents plaque formation and hippocampal deficits in vivo gave us the possibility to examine the alpha-secretase as a potential target for the therapy of Alzheimer's disease. Within the priority program Cellular Mechanisms of Alzheimer's Disease, we investigated several approaches to stimulate the alpha-secretase pathway. Two protein convertases were found to be responsible for the removal of the prodomain, and for the formation of the mature enzyme with alpha-secretase activity. The cloning and characterization of the human ADAM10 promoter provided the basis to examine ADAM10 gene expression. We found a common upregulation of ADAM10, APP, and APP-like protein 2 during differentiation of neuronal cells by retinoic acid, and increased alpha-secretase cleavage of the two substrates. Other approaches for enhancing alpha-secretase activity are the reduction of cellular cholesterol and the stimulation of G protein-coupled neuropeptide receptors. Our results suggest medications and dietary regiments which enhance the nonamyloidogenic pathway of APP processing to be a valuable approach to Alzheimer's disease therapy.

Transcriptional and translational regulation of BACE1 expression--implications for Alzheimer's disease

The proteolytical processing of the amyloid precursor protein (APP) gives rise to beta-amyloid peptides, which accumulate in brains of Alzheimer's disease (AD) patients. Different soluble or insoluble higher molecular weight forms of beta-amyloid peptides have been postulated to trigger a complex pathological cascade that may cause synaptic dysfunction, inflammatory processes, neuronal loss, cognitive impairment, and finally the onset of the disease. The generation of beta-amyloid peptides requires the proteolytical cleavage of APP by an aspartyl protease named beta-site APP-cleaving enzyme 1 (BACE1). The expression and enzymatic activity of BACE1 are increased in brains of AD patients. Here we discuss the importance of a number of recently identified transcription factors as well as post-transcriptional modifications and activation of intracellular signaling molecules for the regulation of BACE1 expression in brain. Importantly, some of these factors are known to be involved in the inflammatory and chronic stress responses of the brain, which are compromised during aging. Moreover, recent evidence indicates that beneficial effects of non-steriodal anti-inflammatory drugs on the progression of AD are mediated--at least in part--by effects on the peroxisome proliferator-activated receptor-gamma response element present in the BACE1 promoter. The identification of the cell type-specific expression and activation of NF-kappaB, Sp1 and YY1 transcription factors may provide a basis to specifically interfere with BACE1 expression and, thereby, to lower the concentrations of beta-amyloid peptides, which may prevent neuronal cell loss and cognitive decline in AD patients.

Expression of the fetal Alz-50 clone 1 protein induces apoptotic cell death

The fetal Alz-50 clone 1 (FAC1) protein exhibits altered expression patterns in neurodegenerative disease. Though it has been shown to bind DNA in a site-specific, phosphorylation-dependent manner, its cellular function remains unknown. Here, we demonstrate that overexpression of FAC1 in PT67 fibroblasts induces nuclear condensation and cleavage of caspase 3 to its active form indicating induction of apoptosis. The amino-terminal domain of FAC1 is necessary and sufficient to induce both nuclear condensation and activation of caspase 3. Disruption of FAC1 interaction with a known binding partner, kelch-like ECH-associated protein 1 (Keap1), enhances activation of caspase 3. Keap1 is known to block activation of the antioxidant response gene products by direct interaction with the transcriptional activator, Nrf2. Disruption of the Keap1:Nrf2 interaction enhances FAC1 induction of apoptosis. These findings suggest a role for FAC1 in apoptosis following release of Nrf2 from Keap1 in response to oxidative stress.

Characterization of the mouse myeloid-associated differentiation marker (MYADM) gene: promoter analysis and protein localization

Hematopoietic differentiation is a complex process involving many genes inducing functional changes and characteristics of different cell lineages. To understand this process, it is important to identify genes involved in lineage commitment and maturation of hematopoietic progenitor cells. Recently we isolated the novel gene MYADM which is strongly up-regulated as multipotent progenitor cells differentiate towards myeloid cells. Because it is not expressed in lymphocytes, understanding the transcriptional control of MYADM could further explain differences in gene expression between myeloid and lymphoid cells. To identify regulatory elements controlling its restricted expression, we have analyzed the 5'-flanking region of the MYADM gene. The proximal promoter was found to lack both TATA and CCAAT boxes, but contained several potential binding sites for both ubiquitous and myeloid-specific transcription factors. Maximal promoter activity was contained within 800 bp from the tentative transcription initiation site, which was reduced as portions of the 5'-end were deleted, and completely abolished when the transcription initiation site was deleted. This promoter sequence had higher activity in myeloid cells compared to B cells, and activity was enhanced during myeloid differentiation, suggesting that we have identified the MYADM core promoter. Computer predictions had suggested MYADM to encode a protein with multiple transmembrane domains. By immunofluorescence and confocal microscopy we demonstrate that the protein is localized to the nuclear envelope and to intracytoplasmic membranes, indicating that MYADM constitutes an integral membrane protein.

Genomic structure and functional characterization of the human ADAM10 promoter

The ADAM10 gene encodes a membrane-bound disintegrin-metalloproteinase, which, after overexpression in an Alzheimer disease (AD) mouse model, prevents amyloid pathology and improves long-term potentiation and memory. Because enhancing ADAM10 expression appears to be a reasonable approach for treatment of AD, we functionally analyzed the ADAM10 gene. Both human and mouse ADAM10 genes comprise approximately 160 kbp, are composed of 16 exons, and are evolutionarily highly conserved within 500 bp upstream of either translation initiation site. By using luciferase reporter assays, we demonstrate that nucleotides -2179 to -1 upstream of the human ADAM10 translation initiation site represent a functional TATA-less promoter. Within this region we identified and examined several single nucleotide polymorphisms, but did not detect significant differences in their appearance between AD and nondemented control subjects. By deletion analysis, site-directed mutagenesis, transcription factor overexpression and electrophoretic mobility shift assays, we identified nucleotides -508 to -300 as the core promoter and found Sp1, USF, and retinoic acid-responsive elements to modulate its activity. Finally, we identified vitamin A acid (RA) as an inducer of human ADAM10 promoter activity. This finding suggests that pharmacologic targeting of RA receptors may increase the expression of the alpha-secretase ADAM10 with beneficial effects on AD pathology.

Fetal Alz-50 clone 1 interacts with the human orthologue of the Kelch-like Ech-associated protein

The fetal Alz-50 reactive clone 1 (FAC1) protein exhibits altered expression and subcellular localization during neuronal development and neurodegenerative diseases such as Alzheimer's disease. Using the yeast two-hybrid screen, the human orthologue of Keap1 (hKeap1) was identified as a FAC1 interacting protein. Keap1 is an important regulator of the oxidative stress response pathway through its interaction with the Nrf family of transcription factors. An interaction between full-length FAC1 and hKeap1 proteins has been demonstrated, and the FAC1 binding domain of hKeap1 has been identified as the Kelch repeats. In addition, FAC1 colocalizes with endogenous Keap1 within the cytoplasm of PT67 cells. Exogenously introduced eGFP:hKeap1 fusion protein redistributed FAC1 to colocalize with eGFP:hKeap1 in perinuclear, spherical structures. The interaction between FAC1 and hKeap1 is reduced by competition with the Nrf2 protein. However, competition by Nrf2 for hKeap1 is reduced by diethylmaleate (DEM), a known disrupter of the Nrf2:Keap1 interaction. DEM does not affect the ability of FAC1 to bind hKeap1 in our assay. These results suggest that hKeap1 regulates FAC1 in addition to its known role in control of Nrf2. Furthermore, the observed competition between FAC1 and Nrf2 for binding hKeap1 indicates that the interplay between these three proteins has important implications for neuronal response to oxidative stress.

Cloning and expression of the rat BACE1 promoter

The pathogenic processing of the amyloid precursor protein (APP) into beta-amyloid peptides, which give rise to beta-amyloid plaques in the brains of Alzheimer's disease patients, requires the enzymatic activity of the beta-site APP-cleaving enzyme 1 (BACE1). We report the cloning and sequence of a 1.5-kb DNA fragment upstream of the coding sequence of the rat BACE1 gene and the construction of a BACE1 promoter/luciferase reporter construct. The basal activity of this promoter construct was highest in neuronal cell lines such as BE(2)-C and PC12 and in the pancreatic cell line AR42J, somewhat lower in rat primary neurons, and astrocytic and microglial cultures, very low in hepatocytes, and almost absent in fibroblasts and in the monocyte-macrophage cell line RAW264.7. The first 600 bp of this promoter are highly conserved among rat, mouse, and human, suggesting that this region contains regulatory elements that modulate BACE1 transcription. Indeed, this fragment contains several putative transcription factor binding sites such as MZF1, Sp1, four GATA-1 sites, and one YY1 site. Directed mutagenesis of GATA-1 elements led to altered luciferase expression, indicating that these sites are involved in the regulation of BACE1 transcription. Additionally, the analysis of promoter activities of deletion mutants suggests the presence of activators of BACE1 transcription between bases -514 to -753 and of suppressor elements between bases -754 and -1541. The BACE1 promoter sequence data and the constructs described here will be useful to identify factors that influence the expression of BACE1 in experimental paradigms in vitro.

c-Fos/activator protein-1 transactivates wee1 kinase at G(1)/S to inhibit premature mitosis in antigen-specific Th1 cells

M-phase promoting factor is a complex of cdc2 and cyclin B that is regulated positively by cdc25 phosphatase and negatively by wee1 kinase. We isolated the wee1 gene promoter and found that it contains one AP-1 binding motif and is directly activated by the immediate early gene product c-Fos at cellular G(1)/S phase. In antigen-specific Th1 cells stimulated by antigen, transactivation of the c-fos and wee1 kinase genes occurred sequentially at G(1)/S, and the substrate of wee1 kinase, cdc2-Tyr15, was subsequently phosphorylated at late G(1)/S. Under prolonged expression of the c-fos gene, however, the amount of wee1 kinase was increased and its target cdc2 molecule was constitutively phosphorylated on its tyrosine residue, where Th1 cells went into aberrant mitosis. Thus, an immediate early gene product, c-Fos/AP-1, directly transactivates the wee1 kinase gene at G(1)/S. The transient increase in c-fos and wee1 kinase genes is likely to be responsible for preventing premature mitosis while the cells remain in the G(1)/S phase of the cell cycle.

Activated cAMP-response element-binding protein regulates neuronal expression of presenilin-1

Upon binding to the cAMP-response element of a gene's promoter, the transcription factor known as cAMP-response element-binding protein (CREB) facilitates transcription of many different neuronal genes including those involved with synaptic function. Based on our previous reports of gene structure (GenBank accession number AF029701 ), we now demonstrate that activated CREB binds to the proximal promoter of the human presenilin-1 (PS-1) gene to activate PS-1 transcription in rat and in human neuronal cells. Specific stimulation of the N-methyl-d-aspartate subtype of neuronal glutamate receptors activates CREB and results in increased PS-1 expression. Similarly, treatment with brain-derived neurotrophic factor activates CREB and increases PS-1 expression in a dose-dependent fashion. By using adenovirus vectors expressing dominant negative forms of CREB, we were able to show that induction of PS-1 expression requires the activation of CREB. Conversely, constitutive expression of mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK) results in activation of CREB and increased PS-1 expression that can be blocked by the addition of selective MEK inhibitors. Our findings suggest a hypothesis where stimulation of N-methyl-d-aspartate receptors signals CREB activation to enhance PS-1 gene product expression that contributes to normal neuronal functions.

An upstream element containing an ETS binding site is crucial for transcription of the human presenilin-1 gene

Deletion mapping of the human presenilin-1 (PS1) promoter delineated the most active fragment from -118 to +178 in relation to the transcription start site mapped in this study, in both human neuroblastoma SK-N-SH and hepatoma HepG2 cells. 5' deletions revealed that a crucial element controlling over 90% of the promoter activity in these cell lines is located between -22 and -6. A mutation altering only two nucleotides of the ETS consensus sequence present at -12 (GGAA to TTAA) has a similar effect. Electrophoretic mobility shift assays showed that a set of specific complexes between nuclear factors and the PS1 promoter are eliminated by this point mutation, as well as by competition with an ETS consensus oligonucleotide. Competition experiments in DNase I footprinting correlated with electrophoretic mobility shift assays and showed that only one of several footprints over the PS1 promoter is eliminated by competition with an ETS consensus oligonucleotide. It extends from -14 to -6 and surrounds the ETS motif present at -12. Thus, a crucial ETS element is present at -12 and binds a protein(s) recognizing specifically the ETS consensus motif. At least one such complex is eliminated by preincubating the nuclear extract with an antibody with broad cross-reactivity with Ets-1 and Ets-2 proteins, thus confirming that an ETS transcription factor(s) recognizes the -12 motif. Several Sp1 binding motifs at positions -70, -55, and +20 surround this ETS element. Competition DNase I footprinting showed that Sp1-like nuclear factors recognize specifically these sites in both cell lines. Furthermore, a combination of 5' and 3' deletions indicated the presence of positive promoter elements between -96 and -35 as well as between +6 and +42. Thus, transfection and footprinting assays correlate to suggest that Sp1 transcription factor(s) bind at several sites upstream and downstream from the initiation site and activate the transcription of the PS1 promoter. Sequences downstream from the transcription initiation site also contain major control elements. 3' deletions from +178 to +107 decreased promoter activity by 80%. However, further deletion to +42 increased promoter activity by 3-4-fold. Collectively, these data indicate that sequences upstream and downstream from the transcription start site each control over 80% of the promoter activity. Hence, this suggests that protein-protein interactions between factors recognizing downstream and upstream sequences are involved.

Presenilins: structural aspects and posttranslational events

Most of early-onset forms of Alzheimer's disease (AD) are caused by inherited mutations located on chromosomes 14 and 1, the gene products of which have been recently identified and referred to as presenilins 1 (PS1) and 2 (PS2), respectively. The first phenotypic alterations triggered by mutated PS were reported to be an increased production of the amyloid peptide (Abeta) and, more precisely, its 42 amino-acids long counterpart Abeta42. This overproduction is thought to be responsible for the genesis of the senile plaques that invade the cortical and subcortical areas of these AD-affected brains. The discovery of PSs has triggered numerous studies aimed at better understanding their normal physiology and the dysfunctions brought by the mutations that could explain, at least in part, the neurodegenerative process taking place in this syndrome. In this review, I will focus on the structural aspects of PS and on the various posttranscriptional events they undergo. I will also briefly discuss that current hypotheses concerning their normal functions and the influence of FAD-linked mutations.