Binding of a nuclear protein to the cyclic-AMP response element of the somatostatin gene

Increased PKA signaling disrupts recognition memory and spatial memory: role in Huntington's disease

Huntington's disease (HD) patients and mouse models show learning and memory impairment even before the onset of motor symptoms. However, the molecular events involved in this cognitive decline are still poorly understood. Here, using three different paradigms, the novel object recognition test, the T-maze spontaneous alternation task and the Morris water maze, we detected severe cognitive deficits in the R6/1 mouse model of HD before the onset of motor symptoms. When we examined the putative molecular pathways involved in these alterations, we observed hippocampal cAMP-dependent protein kinase (PKA) hyper-activation in naïve R6/1 mice compared with wild-type (WT) mice, whereas extracellular signal-regulated kinase 1/2 and calcineurin activities were not modified. Increased PKA activity resulted in hyper-phosphorylation of its substrates N-methyl-D-aspartate receptor subunit 1, Ras-guanine nucleotide releasing factor-1 and striatal-enriched protein tyrosine phosphatase, but not cAMP-responsive element binding protein or the microtubule-associated protein tau. In correlation with the over-activation of the PKA pathway, we found a down-regulation of the protein levels of some phosphodiesterase (PDE) 4 family members. Similar molecular changes were found in the hippocampus of R6/2 mice and HD patients. Furthermore, chronic treatment of WT mice with the PDE4 inhibitor rolipram up-regulated PKA activity, and induced learning and memory deficits similar to those seen in R6 mice, but had no effect on R6/1 mice cognitive impairment. Importantly, hippocampal PKA inhibition by infusion of Rp-cAMPS restored long-term memory in R6/2 mice. Thus, our results suggest that occlusion of PKA-dependent processes is one of the molecular mechanisms underlying cognitive decline in R6 animals.

Transcriptional control of adrenal steroidogenesis: novel connection between Janus kinase (JAK) 2 protein and protein kinase A (PKA) through stabilization of cAMP response element-binding protein (CREB) transcription factor

In the adrenal gland, adrenocorticotropin (ACTH) acting through the cAMP protein kinase (PKA) transduction pathway is the main regulator of genes involved in glucocorticoid synthesis. The prolactin (PRL) receptor is expressed in the adrenal cortex of most mammals, but experimental proof that PRL ensures direct control on glucocorticoid synthesis in rodents remains elusive. To unravel the physiological importance of PRL in adrenocortical functions, we measured steroidogenic capacity of Prlr-deficient mice (Prlr(-/-)) and explored the influence of JAK/STAT signaling, the major PRL transduction pathway, on the steroidogenic activity of adrenocortical cell cultures. We demonstrate that lack of Prlr does not affect basal (nor stress-induced) corticosterone levels in mice. PRL triggers JAK2/STAT5-dependent transcription in adrenal cells, but this does not influence corticosterone release. In contrast, pharmacological or siRNA-mediated inhibition of JAK2 reveals its essential role in both basal and ACTH/cAMP-induced steroidogenesis. We demonstrate that nuclear JAK2 regulates the amount of active transcription factor CREB (cAMP response element-binding protein) through tyrosine phosphorylation and prevention of proteasomal degradation, which in turn leads to transcriptional activation of the rate-limiting steroidogenic Star gene. Hence, we describe a novel link between PKA and JAK2 by which nuclear JAK2 signaling controls adrenal steroidogenesis by increasing the stability of CREB.

Mechanisms of specificity in neuronal activity-regulated gene transcription

The brain is a highly adaptable organ that is capable of converting sensory information into changes in neuronal function. This plasticity allows behavior to be accommodated to the environment, providing an important evolutionary advantage. Neurons convert environmental stimuli into long-lasting changes in their physiology in part through the synaptic activity-regulated transcription of new gene products. Since the neurotransmitter-dependent regulation of Fos transcription was first discovered nearly 25 years ago, a wealth of studies have enriched our understanding of the molecular pathways that mediate activity-regulated changes in gene transcription. These findings show that a broad range of signaling pathways and transcriptional regulators can be engaged by neuronal activity to sculpt complex programs of stimulus-regulated gene transcription. However, the shear scope of the transcriptional pathways engaged by neuronal activity raises the question of how specificity in the nature of the transcriptional response is achieved in order to encode physiologically relevant responses to divergent stimuli. Here we summarize the general paradigms by which neuronal activity regulates transcription while focusing on the molecular mechanisms that confer differential stimulus-, cell-type-, and developmental-specificity upon activity-regulated programs of neuronal gene transcription. In addition, we preview some of the new technologies that will advance our future understanding of the mechanisms and consequences of activity-regulated gene transcription in the brain.

Direct observation of dimerization between different CREB1 isoforms in a living cell

Cyclic AMP-responsive element binding protein 1 (CREB1) plays multiple functions as a transcription factor in gene regulation. CREB1 proteins are also known to be expressed in several spliced isoforms that act as transcriptional activators or repressors. The activator isoforms, possessing the functional domains for kinase induction and for interaction with other transcriptional regulators, act as transcriptional activators. On the other hand, some isoforms, lacking those functional domains, are reported to be repressors that make heterodimers with activator isoforms. The complex and ingenious function for CREB1 arises in part from the variation in their spliced isoforms, which allows them to interact with each other. To date, however, the dimerization between the activator and repressor isoforms has not yet been proved directly in living cells. In this study, we applied fluorescence cross-correlation spectroscopy (FCCS) to demonstrate direct observation of dimerization between CREB1 activator and repressor. The FCCS is a well established spectroscopic method to determine the interaction between the different fluorescent molecules in the aqueous condition. Using differently labeled CREB1 isoforms, we successfully observed the interaction of CREB1 activator and repressor via dimerization in the nuclei of cultured cells. As a result, we confirmed the formation of heterodimer between CREB1 activator and repressor isoforms in living cells.

CREB influences timing and entrainment of the SCN circadian clock

The transcriptional feedback circuit, which is at the core of the suprachiasmatic nucleus (SCN) circadian (i.e., 24 h) clock, is tightly coupled to both external entrainment cues, such as light, as well as rhythmic cues that arise on a system-wide level within the SCN. One potential signaling pathway by which these cues are conveyed to the molecular clock is the CREB/CRE transcriptional cascade. In this study, we employed a tetracycline-inducible CREB repressor mouse strain, in which approximately 60% of the SCN neurons express the transgene, to test CREB functionality in the clock and its effects on overt rhythmicity. We show that attenuated CREB signaling in the SCN led to a significant reduction in light-evoked clock entrainment. An examination of circadian timing revealed that CREB repressor mice exhibited normal free-running rhythms in the absence of external lighting cues. However, under conditions of constant light, which typically leads to a lengthening of the circadian period, CREB repressor mice exhibited a dramatic arrhythmic phenotype, which could be reversed with doxycycline. At a cellular level, the repression of CREB led to a significant reduction in both the expression of the circadian clock proteins PERIOD1 and PERIOD2 and the clock output hormones AVP and VIP. Together, these data support the idea that the CRE transcriptional pathway orchestrates transcriptional events that are essential for both the maintenance of SCN timing and light entrainment of the circadian clock.

Calcium signaling in cognition and aging-dependent cognitive decline

Calcium-dependent signals are key triggers of the molecular mechanisms underlying learning and memory and dysregulation of calcium homeostasis in the aging brain has been proposed to underlie aging-dependent cognitive decline. Mechanisms triggered by calcium in neurons include activity-dependent activation of transcription responsible for the synthesis of molecules underlying the long-term changes of neuronal function. Effectors of calcium signaling with a primordial role in transcription regulation are calcium signal-regulated transcription factors. In this review, we summarize the current knowledge of the contribution of key calcium signal-regulated transcription factors, namely CREB, NFAT, and DREAM, to memory formation. We further describe evidence for dysregulation of the activity of these factors during aging.

Regulation of γ-globin gene expression involves signaling through the p38 MAPK/CREB1 pathway

In response to sodium butyrate and trichostatin A treatment in erythroid cells, p38 mitogen activated protein kinase (MAPK) mediates fetal hemoglobin (HbF) induction by activating cAMP response element binding protein 1 (CREB1). To expand on this observation, we completed studies to determine the role of p38 MAPK in steady-state γ-globin regulation. We propose that p38 signaling regulates Gγ-globin transcription during erythroid maturation through its downstream effector CREB1 which binds the Gγ-globin cAMP response element (G-CRE). We demonstrated that a loss of p38 or CREB1 function by siRNA knockdown resulted in target gene silencing. Moreover, gain of p38 or CREB1 function augments γ-globin transcription. These regulatory effects were conserved under physiological conditions tested in primary erythroid cells. When the G-CRE was mutated in a stable chromatin environment Gγ-globin promoter activity was nearly abolished. Furthermore, introduction of mutations in the G-CRE abolished Gγ-globin activation via p38 MAPK/CREB1 signaling. Chromatin immunoprecipitation assays (ChIP) demonstrated that CREB1 and its binding partner CREB binding protein (CBP) co-localize at the G-CRE region. These data support the role of p38 MAPK/CREB1 signaling in Gγ-globin gene transcription under steady-state conditions.

Differential gene expression profiling in the mouse brain during motor skill learning: focus on the striatum structure

Much research has implicated the striatum in motor learning, but the underlying mechanism is still under extensive investigation. In this study, genome-wide analysis of gene expression was conducted in mice that have learned a complex motor task. It is well recognized that successful learning requires repetitive training and is learned slowly over several training sessions. We therefore used mice that have fully learned the accelerating rotarod task that discriminates the faster and slower phases of motor learning. As important modulators of movement behavior, the striatum was the target of this analysis along with the cerebellum and anterior cortex. To identify potential genes implicated in long memorization process, we compared the lists of genes modulated in the striatum to those modulated in the cerebellum and cortex. As a second approach, we also determined which gene ontology categories were enriched in modulated striatal genes and identified genes with the highest numbers of annotation throughout categories. Although only some of these changes were further confirmed by RT-PCR, these two complementary analyses allowed the identification of highly relevant genes like calcium/calmodulin-dependent protein kinase 2, protein kinase C zeta and N-methyl-D-aspartate receptors. Notably, these genes are all associated with synaptic plasticity, suggesting that stabilized neuronal connections in the striatum are the foundation of durable motor memory. Our study provides the first report of a whole genome analysis of gene expression in mice that have memorized a new complex motor task, and expands our knowledge on striatal gene expression changes associated with motor skill learning.

Hepatocyte metabolic signalling pathways and regulation of hepatitis B virus expression

Hepatitis B virus (HBV) is a small DNA virus responsible for significant morbidity and mortality worldwide. The liver, which is the main target organ for HBV infection, provides the virus with the machinery necessary for persistent infection and propagation, a process that might ultimately lead to severe liver pathologies such as chronic hepatitis, cirrhosis and liver cancer. HBV gene expression is regulated mainly at the transcriptional level by recruitment of a whole set of cellular transcription factors (TFs) and co-activators to support transcription. Over the years, many of these TFs were identified and interestingly enough most are associated with the body's nutritional state. These include the hepatocyte nuclear factors, forkhead Box O1, Farnesoid X receptor, cyclic-AMP response element-binding (CREB), CCAAT/enhancer-binding protein (C/EBP) and glucocorticoid receptor TFs and the transcription coactivator PPARγ coactivator-1α. Consequently, HBV gene expression is linked to hepatic metabolic processes such as glucose and fat production and utilization as well as bile acids' production and secretion. Furthermore, recent evidence indicates that HBV actively interferes with some of these hepatic metabolic processes by manipulating key TFs, such as CREB and C/EBP, to meet its requirements. The discovery of the mechanisms by which HBV is controlled by the hepatic metabolic milieu may broaden our understanding of the unique regulation of HBV expression and may also explain the mechanisms by which HBV induces liver pathologies. The emerging principle of the intimate link between HBV and liver metabolism can be further exploited for host-targeted therapeutic strategies.

Protein kinase A type I activates a CRE-element more efficiently than protein kinase A type II regardless of C subunit isoform

Background

Protein kinase A type I (PKAI) and PKAII are expressed in most of the eukaryotic cells examined. PKA is a major receptor for cAMP and specificity is achieved partly through tissue-dependent expression and subcellular localization of subunits with different biochemical properties. In addition posttranslational modifications help fine tune PKA activity, distribution and interaction in the cell. In spite of this the functional significance of two forms of PKA in one cell has not been fully determined. Here we have tested the ability of PKAI and PKAII formed by expression of the regulatory (R) subunits RIα or RIIα in conjunction with Cα1 or Cβ2 to activate a co-transfected luciferace reporter gene, controlled by the cyclic AMP responsive element-binding protein (CREB) in vivo.

Results

We show that PKAI when expressed at equal levels as PKAII was significantly (p < 0.01) more efficient in inducing Cre-luciferace activity at saturating concentrations of cAMP. This result was obtained regardless of catalytic subunit identity.

Conclusion

We suggest that differential effects of PKAI and PKAII in inducing Cre-luciferace activity depend on R and not C subunit identity.

The porcine circovirus type 1 capsid gene promoter improves antigen expression and immunogenicity in a HIV-1 plasmid vaccine

Background

One of the promising avenues for development of vaccines against Human immunodeficiency virus type 1 (HIV-1) and other human pathogens is the use of plasmid-based DNA vaccines. However, relatively large doses of plasmid must be injected for a relatively weak response. We investigated whether genome elements from Porcine circovirus type 1 (PCV-1), an apathogenic small ssDNA-containing virus, had useful expression-enhancing properties that could allow dose-sparing in a plasmid vaccine.

Results

The linearised PCV-1 genome inserted 5' of the CMV promoter in the well-characterised HIV-1 plasmid vaccine pTHgrttnC increased expression of the polyantigen up to 2-fold, and elicited 3-fold higher CTL responses in mice at 10-fold lower doses than unmodified pTHgrttnC. The PCV-1 capsid gene promoter (Pcap) alone was equally effective. Enhancing activity was traced to a putative composite host transcription factor binding site and a "Conserved Late Element" transcription-enhancing sequence previously unidentified in circoviruses.

Conclusions

We identified a novel PCV-1 genome-derived enhancer sequence that significantly increased antigen expression from plasmids in in vitro assays, and improved immunogenicity in mice of the HIV-1 subtype C vaccine plasmid, pTHgrttnC. This should allow significant dose sparing of, or increased responses to, this and other plasmid-based vaccines. We also report investigations of the potential of other circovirus-derived sequences to be similarly used.

Endothelial cell behaviour within a microfluidic mimic of the flow channels of a modular tissue engineered construct

To study the effect of disturbed flow patterns on endothelial cells, the channels found within a modular tissue engineering construct were reproduced in a microfluidic chip and lined with endothelial cells whose resulting phenotype under flow was assessed using confocal microscopy. Modular tissue engineered constructs formed by the random packing of sub-millimetre, cylindrically shaped, endothelial cell-covered modules into a larger container creates interconnected channels that permit the flow of fluids such as blood. Due to the random packing, the flow path is tortuous and has the potential to create disturbed flow, resulting in an activated endothelium. At an average shear stress of 2.8 dyn cm⁻², endothelial cells within channels of varying geometries showed higher amounts of activation, as evidenced by an increase in ICAM-1 and VCAM-1 levels with respect to static controls. VE-cadherin expression also increased, however, it appeared discontinuous around the perimeter of the cells. An increase in flow (15.6 dyn cm⁻²) was sufficient to reduce ICAM-1 and VCAM-1 expression to a level below that of static controls for many disturbed flow-prone channels that contained branches, curves, expansions and contractions. VE-cadherin expression was also reduced and became discontinuous in all channels, possibly due to paracrine signaling. Other than showing a mild correlation to VE-cadherin, which may be linked through a cAMP-initiated pathway, KLF2 was found to be largely independent of shear stress for this system. To gauge the adhesiveness of the endothelium to leukocytes, THP-1 cells were introduced into flow-conditioned channels and their attachment measured. Relative to static controls, THP-1 adhesion was reduced in straight and bifurcating channels. However, even in the presence of flow, areas where multiple channels converged were found to be the most prone to THP-1 attachment. The microfluidic system enabled a full analysis of the effect of the tortuous flow expected in a modular construct on endothelial cell phenotype.

Epigenetic mechanisms of mental retardation

Mental retardation is a common form of cognitive impairment affecting approximately 3% of the population in industrialized countries. The mental retardation syndrome incorporates a highly diverse group of mental disorders characterized by the combination of cognitive impairment and defective adaptive behavior. The genetic basis of the disease is strongly supported by identification of the genetic lesions associated with impaired cognition, learning, and social adaptation in many mental retardation syndromes. Several of the impaired genes encode epigenetic regulators of gene expression. These regulators exert their function through genome-wide posttranslational modification of histones or by mediating and/or recognizing DNA methylation. In this chapter, we review the most recent advances in the field of epigenetic mechanisms of mental retardation. In particular, we focus on animal models of the human diseases and the mechanism of transcriptional deregulation associated with changes in the cell epigenome.

The CrebA/Creb3-like transcription factors are major and direct regulators of secretory capacity

CrebA up-regulates expression of both the general protein machinery required in all cells for secretion and genes encoding cell type–specific secreted components.

Secretion occurs in all cells, with relatively low levels in most cells and extremely high levels in specialized secretory cells, such as those of the pancreas, salivary, and mammary glands. How secretory capacity is selectively up-regulated in specialized secretory cells is unknown. Here, we find that the CrebA/Creb3-like family of bZip transcription factors functions to up-regulate expression of both the general protein machinery required in all cells for secretion and of cell type–specific secreted proteins. Drosophila CrebA directly binds the enhancers of secretory pathway genes and is both necessary and sufficient to activate expression of every secretory pathway component gene examined thus far. Microarray profiling reveals that CrebA also up-regulates expression of genes encoding cell type–specific secreted components. Finally, we found that the human CrebA orthologues, Creb3L1 and Creb3L2, have the ability to up-regulate the secretory pathway in nonsecretory cell types.

CREB: a multifaceted regulator of neuronal plasticity and protection

Since its initial characterization over 20 years ago, there has been intense and unwavering interest in understanding the role of the transcription factor cAMP-responsive element binding protein (CREB) in nervous system physiology. Through an array of experimental approaches and model systems, researchers have begun to unravel the complex and multifaceted role of this transcription factor in such diverse processes as neurodevelopment, synaptic plasticity, and neuroprotection. Here we discuss current insights into the molecular mechanisms by which CREB couples synaptic activity to long-term changes in neuronal plasticity, which is thought to underlie learning and memory. We also discuss work showing that CREB is a critical component of the neuroprotective transcriptional network, and data indicating that CREB dysregulation contributes to an array of neuropathological conditions.

Loss of Serum Response Factor Activity Is the Basis of Reduced C-FOS Expression in Aging Human Fibroblasts

Les fibroblastes diploïdes humains subissent un nombre limité de dédoublements de population in vitro et sont largement utilisés comme modèle de vieillissement cellulaire. Malgré l'évidence grandissante que le vieillissement cellulaire est dû à une modification de l'expression du gène, l'activité des facteurs de transcription des cellules âgées est encore mal connue. Ici, nous rapportons que la réduction dramatique de l'expression du facteur de transcription fos durant le vieillissement cellulaire semble due à l'incapacité d'un autre facteur de transcription, le facteur réponse de sérum (FRS), de se lier à son site de reconnaissance appelé élément de réponse du sérum (ERS). Ce site est situé en amont de plusieurs gènes comprenant le gène humain c-fos. À l'opposé, les activités des protéines liées à la boîte TATA de la polymérase ARN ainsi qu'à l'élément réponse AMPc sont conservées chez les fibroblastes humains vieillissants. Nous présentons l'évidence que l'hyperphosphorilation du FRS induit une baisse du pouvoir de liaison observée au cours des dernières divisions cellulaires comme ceci a été précédemment suggéré pour la protéine fos.

Downregulation of uPAR and cathepsin B induces apoptosis via regulation of Bcl-2 and Bax and inhibition of the PI3K/Akt pathway in gliomas

BACKGROUND

Glioma is the most commonly diagnosed primary brain tumor and is characterized by invasive and infiltrative behavior. uPAR and cathepsin B are known to be overexpressed in high-grade gliomas and are strongly correlated with invasive cancer phenotypes.

METHODOLOGY/PRINCIPAL FINDINGS

In the present study, we observed that simultaneous downregulation of uPAR and cathepsin B induces upregulation of some pro-apoptotic genes and suppression of anti-apoptotic genes in human glioma cells. uPAR and cathepsin B (pCU)-downregulated cells exhibited decreases in the Bcl-2/Bax ratio and initiated the collapse of mitochondrial membrane potential. We also observed that the broad caspase inhibitor, Z-Asp-2, 6-dichlorobenzoylmethylketone rescued pCU-induced apoptosis in U251 cells but not in 5310 cells. Immunoblot analysis of caspase-9 immunoprecipitates for Apaf-1 showed that uPAR and cathepsin B knockdown activated apoptosome complex formation in U251 cells. Downregulation of uPAR and cathepsin B also retarded nuclear translocation and interfered with DNA binding activity of CREB in both U251 and 5310 cells. Further western blotting analysis demonstrated that downregulation of uPAR and cathepsin B significantly decreased expression of the signaling molecules p-PDGFR-β, p-PI3K and p-Akt. An increase in the number of TUNEL-positive cells, increased Bax expression, and decreased Bcl-2 expression in nude mice brain tumor sections and brain tissue lysates confirm our in vitro results.

CONCLUSIONS/SIGNIFICANCE

In conclusion, RNAi-mediated downregulation of uPAR and cathepsin B initiates caspase-dependent mitochondrial apoptosis in U251 cells and caspase-independent mitochondrial apoptosis in 5310 cells. Thus, targeting uPAR and cathepsin B-mediated signaling using siRNA may serve as a novel therapeutic strategy for the treatment of gliomas.

Molecular changes in brain aging and Alzheimer's disease are mirrored in experimentally silenced cortical neuron networks

Activity-dependent modulation of neuronal gene expression promotes neuronal survival and plasticity, and neuronal network activity is perturbed in aging and Alzheimer's disease (AD). Here we show that cerebral cortical neurons respond to chronic suppression of excitability by downregulating the expression of genes and their encoded proteins involved in inhibitory transmission (GABAergic and somatostatin) and Ca(2+) signaling; alterations in pathways involved in lipid metabolism and energy management are also features of silenced neuronal networks. A molecular fingerprint strikingly similar to that of diminished network activity occurs in the human brain during aging and in AD, and opposite changes occur in response to activation of N-methyl-D-aspartate (NMDA) and brain-derived neurotrophic factor (BDNF) receptors in cultured cortical neurons and in mice in response to an enriched environment or electroconvulsive shock. Our findings suggest that reduced inhibitory neurotransmission during aging and in AD may be the result of compensatory responses that, paradoxically, render the neurons vulnerable to Ca(2+)-mediated degeneration.

Targeting CREB for cancer therapy: friend or foe

The cyclic-AMP response element-binding protein (CREB) is a nuclear transcription factor activated by phosphorylation at Ser133 by multiple serine/threonine (Ser/Thr) kinases. Upon phosphorylation, CREB binds the transcriptional co-activator, CBP (CREB-binding protein), to initiate CREB-dependent gene transcription. CREB is a critical regulator of cell differentiation, proliferation and survival in the nervous system. Recent studies have shown that CREB is involved tumor initiation, progression and metastasis, supporting its role as a proto-oncogene. Overexpression and over-activation of CREB were observed in cancer tissues from patients with prostate cancer, breast cancer, non-small-cell lung cancer and acute leukemia while down-regulation of CREB in several distinct cancer cell lines resulted in inhibition of cell proliferation and induction of apoptosis, suggesting that CREB may be a promising target for cancer therapy. Although CREB, as a transcription factor, is a challenging target for small molecules, various small molecules have been discovered to inhibit CREB phosphorylation, CREB-DNA, or CREB-CBP interaction. These results suggest that CREB is a suitable transcription factor for drug targeting and therefore targeting CREB could represent a novel strategy for cancer therapy.

Nuclear transcription factors in mammalian mitochondria

Nuclear transcription factors have been detected in mammalian mitochondria and may directly regulate mitochondrial gene expression. Emerging genomics techniques may overcome outstanding challenges in this field.

The nuclear transcription factor CREB: involvement in addiction, deletion models and looking forward

Addiction involves complex physiological processes, and is characterised not only by broad phenotypic and behavioural traits, but also by ongoing molecular and cellular adaptations. In recent years, increasingly effective and novel techniques have been developed to unravel the molecular implications of addiction. Increasing evidence has supported a contribution of the nuclear transcription factor CREB in the development of addiction, both in contribution to phenotype and expression in brain regions critical to various aspects of drug-seeking behaviour and drug reward. Abstracting from this, models have exploited these data by removing the CREB gene from the developing or developed mouse, to crucially determine its impact upon addiction-related processes. More recent models, however, hold greater promise in unveiling the contribution of CREB to disorders such as addiction.

Learning-Dependent Gene Expression of CREB1 Isoforms in the Molluscan Brain

Cyclic AMP-responsive element binding protein1 (CREB1) has multiple functions in gene regulation. Various studies have reported that CREB1-dependent gene induction is necessary for memory formation and long-lasting behavioral changes in both vertebrates and invertebrates. In the present study, we characterized Lymnaea CREB1 (LymCREB1) mRNA isoforms of spliced variants in the central nervous system (CNS) of the pond snail Lymnaea stagnalis. Among these spliced variants, the three isoforms that code a whole LymCREB1 protein are considered to be the activators for gene regulation. The other four isoforms, which code truncated LymCREB1 proteins with no kinase inducible domain, are the repressors. For a better understanding of the possible roles of different LymCREB1 isoforms, the expression level of these isoform mRNAs was investigated by a real-time quantitative RT-PCR method. Further, we examined the changes in gene expression for all the isoforms in the CNS after conditioned taste aversion (CTA) learning or backward conditioning as a control. The results showed that CTA learning increased LymCREB1 gene expression, but it did not change the activator/repressor ratio. Our findings showed that the repressor isoforms, as well as the activator ones, are expressed in large amounts in the CNS, and the gene expression of CREB1 isoforms appeared to be specific for the given stimulus. This was the first quantitative analysis of the expression patterns of CREB1 isoforms at the mRNA level and their association with learning behavior.

Activity-dependent somatostatin gene expression is regulated by cAMP-dependent protein kinase and Ca2+-calmodulin kinase pathways

Ca(2+) influx through L-type voltage-gated Ca(2+) channels (L-VSCC) is required for K(+)-induced somatostatin (SS) mRNA. Increase in intracellular Ca(2+) concentration leads to the activation of cyclic AMP-responsive element binding protein (CREB), a key regulator of SS gene transcription. Several different protein kinases possess the capability of driving CREB upon membrane depolarization. We investigated which of the signalling pathways involved in CREB activation mediates SS gene induction in response to membrane depolarization in cerebrocortical cells exposed to 56 mM K(+). Activity dependent phosphorylation of CREB in Ser(133) was immunodetected. Activation of CREB was biphasic showing two peaks at 5 and 60 min. The selective inhibitors of extracellular signal related protein kinase/mitogen-activated protein kinase (ERK/MAPK) PD098059, cyclic-AMPdependent protein kinase (cAMP/PKA) H89 and RpcAMPS, and Ca(2+)/calmodulin-dependent protein kinases (CaMKs) pathways KN62 and KN93 were used to determine the signalling pathways involved in CREB activation. Here we show that the early activation of CREB was dependent on cAMP/PKA along with CaMKs pathways whereas the ERK/MAPK and CaMKs were implicated in the second peak. We observed that H89, RpcAMPS, KN62 and KN93 blocked K(+)-induced SS mRNA whereas PD098059 did not. These findings indicate that K(+)-induced SSmRNA is mediated by the activation of cAMP/PKA and CaMKs pathways, thus suggesting that the early activation of CREB is involved in the induction of SS by neuronal activity. We also demonstrated, using transient transfections of cerebrocortical cells, that K(+) induces the transcriptional regulation of the SS gene through the cAMP-responsive element (CRE) sequence located in the SS promoter.

Selective transcription in response to an inflammatory stimulus

An inflammatory response is initiated by the temporally controlled activation of genes encoding a broad range of regulatory and effector proteins. A central goal is to devise strategies for the selective modulation of proinflammatory gene transcription, to allow the suppression of genes responsible for inflammation-associated pathologies while maintaining a robust host response to microbial infection. Toward this goal, recent studies have revealed an unexpected level of diversity in the mechanisms by which chromatin structure and individual transcription factors contribute to the selective regulation of inflammatory genes.

Inhibition of heat shock protein 90 attenuates adenylate cyclase sensitization after chronic morphine treatment

Cellular adaptations to chronic opioid treatment result in enhanced responsiveness of adenylate cyclase and an increase in forskolin- or agonist-stimulated cAMP production. It is, however, not known whether chaperone molecules such as heat shock proteins contribute to this adenylate cyclase sensitization. Here, we report that treatment of cells with geldanamycin, an inhibitor of heat shock protein 90 (Hsp90), led to effective attenuation of morphine-induced adenylate cyclase sensitization. In SK-N-SH human neuroblastoma cells, morphine significantly increased RNA transcript and protein levels of type I adenylate cyclase, leading to sensitization. Whole-genome tiling array analysis revealed that cAMP response element-binding protein, an important mediator for cellular adaptation to morphine, associated with the proximal promoter of Hsp90AB1 not only in SK-N-SH cells but also in rat PC12 and human embryonic kidney cells. Hsp90AB1 transcript and protein levels increased significantly during morphine treatment, and co-application of geldanamycin (0.1-10 nM) effectively suppressed the increase in forskolin-activated adenylate cyclase activation by 56%. Type I adenylate cyclase, but not Hsp90AB1, underwent significant degradation during geldanamycin treatment. These results indicate that Hsp90 is a new pharmacological target for the suppression of adenylate cyclase sensitization induced by chronic morphine treatment.

Context-specific modulation of cocaine-induced locomotor sensitization and ERK and CREB phosphorylation in the rat nucleus accumbens

Learned associations are hypothesized to develop between drug effects and contextual stimuli during repeated drug administration to produce context-specific sensitization that is expressed only in the drug-associated environment and not in a non-drug-paired environment. The neuroadaptations that mediate such context-specific behavior are largely unknown. We investigated context-specific modulation of cAMP-response element-binding protein (CREB) phosphorylation and that of four upstream kinases in the nucleus accumbens that phosphorylate CREB, including extracellular signal-regulated kinase (ERK), cAMP-dependent protein kinase, calcium/calmodulin-dependent kinase (CaMK) II and CaMKIV. Rats received seven once-daily injections of cocaine or saline in one of two distinct environments outside their home cages. Seven days later, test injections of cocaine or saline were administered in either the paired or the non-paired environment. CREB and ERK phosphorylation were assessed with immunohistochemistry, and phosphorylation of the remaining kinases, as well as of CREB and ERK, was assessed by western blotting. Repeated cocaine administration produced context-specific sensitized locomotor responses accompanied by context-specific enhancement of the number of cocaine-induced phosphoCREB-immunoreactive and phosphoERK-immunoreactive nuclei in a minority of neurons. In contrast, CREB and CaMKIV phosphorylation in nucleus accumbens homogenates were decreased by cocaine test injections. We have recently shown that a small number of cocaine-activated accumbens neurons mediate the learned association between cocaine effects and the drug administration environment to produce context-specific sensitization. Context-specific phosphorylation of ERK and CREB in the present study suggests that this signal transduction pathway is selectively activated in the same set of cocaine-activated accumbens neurons that mediate this learned association.

Cell cycle regulatory effects of retinoic Acid and forskolin are mediated by the cyclin C gene

As a partner of cyclin-dependent kinase (CDK) 3, Cyclin C controls cellular proliferation and, together with CDK8, represses gene transcription. In this study, we showed that the highly expressed Cyclin C gene is a direct target of the nuclear hormone all-trans retinoic acid (RA) in HEK293 human embryonal kidney cells. The RA receptor (RAR) gamma associates with a Cyclin C promoter region containing two RAR binding sites. The Cyclin C gene also directly responds to the cAMP activator Forskolin via the transcription factor CREB1 (cAMP response element-binding protein 1), for which we identified four binding sites within the first 2250 bp of its promoter. RARgamma and CREB1 show functional convergence via the corepressor NCoR1, which controls in particular the Forskolin response of Cyclin C. The histone deacetylases 1, 5, 6, 7 and 11 are involved in the basal expression of Cyclin C, but in HEK293 and MCF-7 human breast carcinoma cells the antiproliferative effects of the histone deacetylase inhibitor SAHA (suberoylanilide hydroxamic acid) are not mediated by Cyclin C. However, cell cycle progressing effects of all-trans RA and Forskolin are dependent on Cyclin C expression levels. This suggests that the primary regulation of Cyclin C by all-trans RA and Forskolin mediates some of the cell cycle control actions of these compounds.

Sequence and expression analysis of the gene encoding inducible cAMP early repressor in tilapia

Suppression subtractive hybridization library was generated by comparison of cDNA populations isolated from peripheral leukocytes of pre- and post-immunized tilapia. One cDNA sequence encoding complete inducible cAMP early repressor was obtained from the library. The sequence was characterized by the presence of the basic structure of ICER IIgamma. Expression of ICER was in the tissues of four types of tilapia was decreased after infection with Streptococcus. After immunization, expression of ICER was initially decreased and then increased after 7 days. In addition, the order for the overall expression of ICER gene after infection and the increases of ICER expression later after immunization in these four types of tilapia was positively correlated to the disease resistance and productivity of these four species of tilapia. Our results provided molecular mechanisms for the different disease resistance capability in different species of tilapia. In addition, our results also provided reference molecular marker for breeding disease resistant tilapia, cAMP responsive element modulator.

ATF3 transcription factor and its emerging roles in immunity and cancer

Activating transcription factor 3 (ATF3) is a member of the ATF/cyclic AMP response element-binding (ATF/CREB) family of transcription factors. It is an adaptive-response gene that participates in cellular processes to adapt to extra- and/or intracellular changes, where it transduces signals from various receptors to activate or repress gene expression. Advances made in understanding the immunobiology of Toll-like receptors have recently generated new momentum for the study of ATF3 in immunity. Moreover, the role of ATF3 in the regulation of the cell cycle and apoptosis has important implications for understanding susceptibility to and progression of several cancers.

Functional versatility of transcription factors in the nervous system: the SRF paradigm

Individual transcription factors in the brain frequently display broad functional versatility, thereby controlling multiple cellular outputs. In accordance, neuron-restricted mutagenesis of the murine Srf gene, encoding the transcription factor serum response factor (SRF), revealed numerous SRF functions in the nervous system. First, SRF controls immediate early gene (IEG) activation associated with perception of synaptic activity, learning and memory. Second, processes linked to actin cytoskeletal dynamics are mediated by SRF, such as developmental neuronal migration, outgrowth and pathfinding of neurites, as well as synaptic targeting. Therefore, SRF seems to be instrumental in converting synaptic activity into plasticity-associated structural changes in neuronal connectivities. This highlights the decisive role of SRF in integrating cytoskeletal actin dynamics and nuclear gene expression. Finally, we relate SRF to the multi-functional transcription factor CREB and point out overlapping, distinct and concerted functions of these two transcriptional regulators in the brain.

Regulation of the hyaluronan synthase 2 gene by convergence in cyclic AMP response element-binding protein and retinoid acid receptor signaling

The human hyaluronan synthase 2 (HAS2) gene encodes for an enzyme making hyaluronan, altered concentrations of which are associated with many pathological situations including wounding, several inflammatory conditions, and malignant tumors. In this study we showed that HAS2 is a primary target of the cAMP activator forskolin and the nuclear hormone all-trans-retinoic acid (RA). The first 2250 bp of the promoter contain three response elements (REs) for the transcription factor CREB1 as well as two REs for the nuclear receptor RAR. Chromatin immunoprecipitation and re-chromatin immunoprecipitation assays using selected fragments of the promoter containing the putative REs showed that forskolin and all-trans-RA modulate the formation of complexes between CREB1 and RAR with various co-regulators at the predicted sites. Interestingly, CREB1 complexes are regulated by all-trans-RA as are RAR complexes by forskolin. Reporter gene assays using nested promoter fragments supported these findings. Forskolin and all-trans-RA co-stimulation reduced the binding of CREB1, RAR, and the co-repressor nuclear receptor co-repressor 1 (NCoR1), but enhanced the association of co-activators MED1 and CREB-binding protein (CBP). RNA interference experiments suggested that MED1 and NCoR1 are central for the all-trans-RA induction of the HAS2 gene and CBP dominates its forskolin response. In general, our findings suggest a convergence of CREB1 and RAR signaling, and demonstrate the individual character of each RE in terms of co-regulator use.

Epigenetic regulation of adipocyte differentiation by a Rho guanine nucleotide exchange factor, WGEF

Epigenetic regulation, including DNA methylation, plays an important role in several differentiation processes and possibly in adipocyte differentiation. To search for genes that show methylation change during adipogenesis, genome-wide DNA methylation analysis in insulin-induced adipogenesis of 3T3-L1 preadipocyte cells was performed using a method called microarray-based integrated analysis of methylation by isoschizomers (MIAMI). The MIAMI revealed that Hpa II sites of exon 1 in a Rho guanine nucleotide exchange factor 19 (ARHGEF19; WGEF) gene were demethylated during adipocyte differentiation of 3T3-L1 cells. Deletion of the region containing cytosine-guanine (CpG) sites that showed methylation change suppressed transcriptional activity in the reporter assay, indicating that this region regulates WGEF transcription. WGEF expression in 3T3-L1 cells was reduced during adipocyte differentiation, and high-fat diet-induced obese mice also showed lower expression of WGEF gene than control mice in white adipose tissue. Additionally, forced expression of WGEF in 3T3-L1 cells down-regulated the expression of adipogenic marker genes and inhibited the adipogenic program. This study clarified that adipogenesis was regulated by WGEF expression through DNA methylation change.

Combinatorial transcription factor regulation of the cyclic AMP-response element on the Pgc-1alpha promoter in white 3T3-L1 and brown HIB-1B preadipocytes

Cold stress in rodents increases the expression of UCP1 and PGC-1alpha in brown and white adipose tissue. We have previously reported that C/EBPbeta specifically binds to the CRE on the proximal Pgc-1alpha promoter and increases forskolin-sensitive Pgc-1alpha and Ucp1 expression in white 3T3-L1 preadipocytes. Here we show that in mice exposed to a cold environment for 24 h, Pgc-1alpha, Ucp1, and C/ebpbeta but not C/ebpalpha or C/ebpdelta expression were increased in BAT. Conversely, expression of the C/EBP dominant negative Chop10 was increased in WAT but not BAT during cold exposure. Reacclimatization of cold-exposed mice to a warm environment for 24 h completely reversed these changes in gene expression. In HIB-1B, brown preadipocytes, forskolin increased expression of Pgc-1alpha, Ucp1, and C/ebpbeta early in differentiation and inhibited Chop10 expression. Employing chromatin immunoprecipitation, we demonstrate that C/EBPbeta, CREB, ATF-2, and CHOP10 are bound to the Pgc-1alpha proximal CRE, but CHOP10 does not bind in HIB-1B cell lysates. Forskolin stimulation and C/EBPbeta overexpression in 3T3-L1 cells increased C/EBPbeta and CREB but displaced ATF-2 and CHOP10 binding to the Pgc-1alpha proximal CRE. Overexpression of ATF-2 and CHOP10 in 3T3-L1 cells decreased Pgc-1alpha transcription. Knockdown of Chop10 in 3T3-L1 cells using siRNA increased Pgc-1alpha transcription, whereas siRNA against C/ebpbeta in HIB-1B cells decreased Pgc-1alpha and Ucp1 expression. We conclude that the increased cAMP stimulation of Pgc-1alpha expression is regulated by the combinatorial effect of transcription factors acting at the CRE on the proximal Pgc-1alpha promoter.

Inducible cAMP early repressor (ICER) and brain functions

The inducible cAMP early repressor (ICER) is an endogenous repressor of cAMP-responsive element (CRE)-mediated gene transcription and belongs to the CRE-binding protein (CREB)/CRE modulator (CREM)/activating transcription factor 1 (ATF-1) gene family. ICER plays an important role in regulating the neuroendocrine system and the circadian rhythm. Other aspects of ICER function have recently attracted heightened attention. Being a natural inducible CREB antagonist, and more broadly, an inducible repressor of CRE-mediated gene transcription, ICER regulates long-lasting plastic changes that occur in the brain in response to incoming stimulation. This review will bring together data on ICER and its functions in the brain, with a special emphasis on recent findings highlighting the involvement of ICER in the regulation of long-term plasticity underlying learning and memory.

Inhibition of CREB function in mouse epidermis reduces papilloma formation

We used a double transgenic tetracycline system to conditionally express A-CREB, a dominant negative protein that prevents the DNA binding and function of cAMP-responsive element binding protein (CREB) family members, in mouse basal epidermis using the keratin 5 promoter. There was no phenotype in the adult. However, following a 7,12-dimethylbenz(a)anthracene (DMBA)/phorbol-12-myristate-13-acetate two-stage skin carcinogenesis experiment, A-CREB-expressing epidermis develop 5-fold fewer papillomas than wild-type controls. However, A-CREB expression one month after DMBA treatment does not prevent papilloma formation, suggesting that CREB functions at an early stage of papilloma formation. Oncogenic H-Ras genes with A-->T mutations in codon 61 were found in wild-type skin but not in A-CREB-expressing skin 2 days after DMBA treatment, suggesting that A-CREB either prevents DMBA mutagenesis or kills oncogenic H-Ras cells. In primary keratinocyte cultures, A-CREB expression induced apoptosis of v-Ras(Ha)-infected cells and suppressed the expression of cell cycle proteins cyclin B1 and cyclin D1. These results suggest that inhibiting CREB function is a valuable cancer prevention strategy.

The cAMP-responsive element binding protein (CREB) regulates the expression of acid ceramidase (ASAH1) in H295R human adrenocortical cells

Acid ceramidase (encoded by ASAH1) is a lipid hydrolase that catalyzes the conversion of ceramide (cer) into sphingosine (SPH) and a free fatty acid. Adrenocortical steroidogenesis is regulated by the trophic peptide hormone adrenocorticotropin (ACTH), which induces the expression of steroidogenic genes in the human adrenal cortex primarily via a cAMP/protein kinase A (PKA)-dependent pathway. ACTH also stimulates sphingolipid metabolism in H295R adrenocortical cells leading to changes in steroidogenic gene expression. Based on our previous data identifying SPH as an antagonist for the nuclear receptor steroidogenic factor 1 (SF-1) and the role of ACTH-stimulated changes in sphingolipid metabolism on steroidogenic gene transcription, the aim of the current study was to determine the role of ACTH signaling in regulating the expression of the ASAH1 gene in H295R cells. We show that activation of the ACTH signaling pathway induces ASAH1 gene expression by stimulating the binding of the cAMP-responsive element binding protein (CREB) to multiple regions of the ASAH1 promoter. CREB binding promotes the recruitment of the coactivators CREB binding protein (CBP) and p300 to the CREB-responsive regions of the promoter. Consistent with transcriptional activation, we show that cAMP signaling increases the trimethylation of Lys 4 on histone H3 (H3K4) along the ASAH1 promoter. Finally, RNA interference (RNAi) experiments demonstrate that CREB is indispensable for cAMP-induced ASAH1 transcription. These data identify the ACTH/cAMP signaling pathway and CREB as transcriptional regulators of the ASAH1 gene in the human adrenal cortex.

Transcribe to survive: transcriptional control of antioxidant defense programs for neuroprotection in Parkinson's disease

Parkinson's disease (PD) is a progressive, primarily motor disorder that is characterized by loss of dopaminergic (DA) neurons within the substantia nigra (SN). Cell death in PD has been associated with impaired mitochondrial function and increased oxidative stress. Strategies to reduce the oxidative load in DA cells may be beneficial in slowing the progression of PD. The transcription factor nuclear factor-erythroid 2 (NF-E2) related factor 2 (NRF2) is emerging as a master regulator of antioxidant defense systems, which makes it an attractive target for manipulations that aim to increase cellular resistance to oxidative stress. Peroxisome proliferator-activated receptor gamma (PPARgamma) coactivator-1 alpha (PGC1alpha) is a regulator of mitochondrial biogenesis genes that simultaneously upregulates many genes known to protect against oxidative stress. Pgc-1alpha knockout mice show enhanced susceptibility to SN neuronal loss following MPTP exposure, whilst overexpression of Pgc-1alpha appears to protect against oxidative stress in vitro. This makes PGC-1alpha a highly attractive target for neuroprotective therapies in PD. This review will explore the mechanisms behind the induction of NRF2 and PGC-1alpha in response to oxidative stress and identify common pathways that may provide targets for upregulating antioxidant defense programs.

Transcription factors in long-term memory and synaptic plasticity

Transcription is a molecular requisite for long-term synaptic plasticity and long-term memory formation. Thus, in the last several years, one main interest of molecular neuroscience has been the identification of families of transcription factors that are involved in both of these processes. Transcription is a highly regulated process that involves the combined interaction and function of chromatin and many other proteins, some of which are essential for the basal process of transcription, while others control the selective activation or repression of specific genes. These regulated interactions ultimately allow a sophisticated response to multiple environmental conditions, as well as control of spatial and temporal differences in gene expression. Evidence based on correlative changes in expression, genetic mutations, and targeted molecular inhibition of gene expression have shed light on the function of transcription in both synaptic plasticity and memory formation. This review provides a brief overview of experimental work showing that several families of transcription factors, including CREB, C/EBP, Egr, AP-1, and Rel, have essential functions in both processes. The results of this work suggest that patterns of transcription regulation represent the molecular signatures of long-term synaptic changes and memory formation.

The serum response factor and a putative novel transcription factor regulate expression of the immediate-early gene Arc/Arg3.1 in neurons

The immediate-early effector gene Arc/Arg3.1 is robustly upregulated by synaptic activity associated with learning and memory. Here we show in primary cortical neuron culture that diverse stimuli induce Arc expression through new transcription. Searching for regulatory regions important for Arc transcription, we found nine DNaseI-sensitive nucleosome-depleted sites at this genomic locus. A reporter gene encompassing these sites responded to synaptic activity in an NMDA receptor-dependent manner, consistent with endogenous Arc mRNA. Responsiveness mapped to two enhancer regions approximately 6.5 kb and approximately 1.4 kb upstream of Arc. We dissected these regions further and found that the proximal enhancer contains a functional and conserved "Zeste-like" response element that binds a putative novel nuclear protein in neurons. Therefore, activity regulates Arc transcription partly by a novel signaling pathway. We also found that the distal enhancer has a functional and highly conserved serum response element. This element binds serum response factor, which is recruited by synaptic activity to regulate Arc. Thus, Arc is the first target of serum response factor that functions at synapses to mediate plasticity.

TOX3 regulates calcium-dependent transcription in neurons

We report the cloning and characterization of TOX3, a high mobility group box protein involved in mediating calcium-dependent transcription. TOX3 was identified as a calcium-dependent transactivator using the Transactivator Trap screen. We find that TOX3 interacts with both cAMP response element (CRE)-binding protein (CREB) and CREB-binding protein (CBP), and knockdown of the endogenous TOX3 by RNAi leads to significant reduction of calcium-induced c-fos expression and complete inhibition of calcium activation of the c-fos promoter. The effects of TOX3 on calcium-dependent transcription require the CRE elements. These observations identify TOX3 as an important regulator of calcium-dependent transcription and suggest that TOX3 exerts its effect on CRE-mediated transcription via its association with the CREB-CBP complex.

Ionizing radiation induces prostate cancer neuroendocrine differentiation through interplay of CREB and ATF2: implications for disease progression

Radiation therapy is a first-line treatment for prostate cancer patients with localized tumors. Although some patients respond well to the treatment, approximately 10% of low-risk and up to 60% of high-risk prostate cancer patients experience recurrent tumors. However, the molecular mechanisms underlying tumor recurrence remain largely unknown. Here we show that fractionated ionizing radiation (IR) induces differentiation of LNCaP prostate cancer cells into neuroendocrine (NE)-like cells, which are known to be implicated in prostate cancer progression, androgen-independent growth, and poor prognosis. Further analyses revealed that two cyclic AMP-responsive element binding transcription factors, cyclic AMP-response element binding protein (CREB) and activating transcription factor 2 (ATF2), function as a transcriptional activator and a repressor, respectively, of NE-like differentiation and that IR induces NE-like differentiation by increasing the nuclear content of phospho-CREB and cytoplasmic accumulation of ATF2. Consistent with this notion, stable expression of a nonphosphorylatable CREB or a constitutively nuclear-localized ATF2 in LNCaP cells inhibits IR-induced NE-like differentiation. IR-induced NE-like morphologies are reversible, and three IR-resistant clones isolated from dedifferentiated cells have acquired the ability to proliferate and lost the NE-like cell properties. In addition, these three IR-resistant clones exhibit differential responses to IR- and androgen depletion-induced NE-like differentiation. However, they are all resistant to cell death induced by IR and the chemotherapeutic agent docetaxel and to androgen depletion-induced growth inhibition. These results suggest that radiation therapy-induced NE-like differentiation may represent a novel pathway by which prostate cancer cells survive the treatment and contribute to tumor recurrence.