Identification of the AFD neuron as the site of action of the CREB protein in Caenorhabditis elegans thermotaxis

Behaviour is a consequence of computation in neural circuits composed of massive synaptic connections among sensory neurons and interneurons. The cyclic AMP response element-binding protein (CREB) responsible for learning and memory is expressed in almost all neurons. Nevertheless, we find that the Caenorhabditis elegans CREB orthologue, CRH-1, is only required in the single bilateral thermosensory neuron AFD, for a memory-related behaviour. Restoration of CRH-1 in AFD of CREB-depleted crh-1 mutants rescues its thermotactic defect, whereas restorations in other neurons do not. In calcium-imaging analyses, the AFD neurons of CREB-depleted crh-1 mutants exhibit an abnormal response to temperature increase. We present a new platform for analysing the mechanism of behavioural memory at single-cellular resolution within the neural circuit.

Promoter characterization and role of CRE in the basal transcription of the rat SNAT2 gene

Small neutral amino acid transporter 2 (SNAT2) is the most abundant and ubiquitous transporter for zwitterionic short-chain amino acids. The activity of this amino acid transporter is stimulated in vivo or in vitro by glucagon or cAMP analogs. However, it is not known whether the increase in activity at the protein level is due to an increase in SNAT2 gene transcription. Thus, the aim of the present work was to study whether cAMP was able to stimulate SNAT2 gene expression and to localize and characterize the presence of cAMP response elements (CRE) in the promoter that controls the expression of the rat SNAT2 gene. We found that consumption of a high-protein diet that increased serum glucagon concentration or the administration of glucagon or incubation of hepatocytes with forskolin increased the SNAT2 mRNA level. We then isolated the 5' regulatory region of the SNAT2 gene and determined that the transcriptional start site was located 970 bp upstream of the translation start codon. We identified two potential CRE sites located at -354 and -48 bp. Our results, using deletion analysis of the 5' regulatory region of the SNAT2 gene, revealed that the CRE site located at -48 bp was fully responsible for SNAT2 regulation by cAMP. This evidence was strongly supported by mutation of the CRE site and EMSA and ChIP analysis. Alignment of rat, mouse, and human sequences revealed that this CRE site is highly conserved among species, indicating its essential role in the regulation of SNAT2 gene expression.

GSK-3β/CREB axis mediates IGF-1-induced ECM/adhesion molecule expression, cell cycle progression and monolayer permeability in retinal capillary endothelial cells: Implications for diabetic retinopathy

Various growth factors and cytokines are implicated in endothelial dysfunction and blood-retinal barrier (BRB) breakdown in early diabetic retinopathy (DR). However, cellular and molecular mechanisms that may underlie the pathology of DR are not fully understood yet. We therefore examined the effect of insulin-like growth factor (IGF)-1 on ECM/adhesion molecule expression, cell cycle regulation and monolayer permeability in an endothelial cell line (TR-iBRB2). We investigate whether the action of IGF-1 (1) involves glycogen synthase kinase 3beta (GSK-3β) and cAMP responsive transcription factor (CREB) and (2) alters ECM/adhesion molecule gene expression. Treatment of TR-iBRB2 cell with IGF-1 (100ng/ml for 0-24h) increases phosphorylation of (i) Akt Thr308, and its substrates including GSK-3β at Ser9, which inactivates its kinase function, and (ii) CREB at Ser133 (activation). These phosphorylations correlate positively with enhanced expression of CREB targets such as ECM protein fibronectin and cell cycle progression factor cyclin D1. However, stable transfection of a mutant GSK3β(S9A) or a dominant negative K-CREB in TR-iBRB2 prevents IGF-1-induced fibronectin and cyclin D1 expression. Furthermore, IGF-1 reduces the level of intercellular adherence molecule VE-cadherin and increases monolayer permeability in TR-iBRB2 cells when measured by FITC-dextran leakage. The effect of IGF-1 on VE-cadherin and membrane permeability is absent in TR-iBRB2 cells expressing the GSK-3β(S9A). Similarly, K-CREB reverses IGF-1 down-regulation of VE-cadherin and up-regulation of fibronectin. These results indicate that GSK-3β/CREB axis alters ECM/adhesion molecule expression and cell cycle progression in retinal endothelial cells, and may potentially contribute to endothelial dysfunction and BRB leakage in DR.

Genetically expressed HIV-1 viral proteins attenuate nicotine-induced behavioral sensitization and alter mesocorticolimbic ERK and CREB signaling in rats

The prevalence of tobacco smoking in HIV-1 positive individuals is 3-fold greater than that in the HIV-1 negative population; however, whether HIV-1 viral proteins and nicotine together produce molecular changes in mesolimbic structures that mediate psychomotor behavior has not been studied. This study determined whether HIV-1 viral proteins changed nicotine-induced behavioral sensitization in HIV-1 transgenic (HIV-1Tg) rats. Further, we examined cAMP response element binding protein (CREB) and extracellular regulated kinase (ERK1/2) signaling in the prefrontal cortex (PFC), nucleus accumbens (NAc) and ventral tegmental area (VTA). HIV-1Tg rats exhibited a transient decrease of activity during habituation, but showed attenuated nicotine (0.35mg/kg, s.c.)-induced behavioral sensitization compared to Fisher 344 (F344) rats. The basal levels of phosphorylated CREB and ERK2 were lower in the PFC of HIV-1Tg rats, but not in the NAc and VTA, relative to the controls. In the nicotine-treated groups, the levels of phosphorylated CREB and ERK2 in the PFC were increased in HIV-1Tg rats, but decreased in F344 animals. Moreover, repeated nicotine administration reduced phosphorylated ERK2 in the VTA of HIV-1Tg rats and in the NAc of F344 rats, but had no effect on phosphorylated CREB, indicating a region-specific change of intracellular signaling. These results demonstrate that HIV-1 viral proteins produce differences in basal and nicotine-induced alterations in CREB and ERK signaling that may contribute to the alteration in psychomotor sensitization. Thus, HIV-1 positive smokers are possibly more vulnerable to alterations in CREB and ERK signaling and this has implications for motivated behavior, including tobacco smoking, in HIV-1 positive individuals who self-administer nicotine.

Fine-tuned regulation of the PGC-1α gene transcription by different intracellular signaling pathways

It has previously been known that transcription of the PGC-1α gene can be either inhibited or stimulated by p38 MAP kinase (p38 MAPK). To determine whether p38 MAPK plays an inhibitory or stimulatory role in PGC-1α gene transcription, we further investigated the role of p38 MAPK in this study. Our results showed that the basal level of p38 MAPK phosphorylation was increased in gastrocnemius of mice under HFD and that p38 MAPK stimulated PGC-1α gene transcription in C(2)C(12) myotubes. Our results also provided new mechanisms in myotubes that the p38 MAPK-induced PGC-1α gene transcription was mediated by CREB. In exploring the role of the Akt-dependent insulin signaling on PGC-1α gene transcription, we found that the basal Akt-dependent signaling was increased in gastrocnemius of mice under HFD. The p38 MAPK-induced PGC-1α gene transcription was prevented by insulin. Insulin suppression of PGC-1α gene transcription was neutralized by overexpression of the constitutively nuclear form of FoxO1. Finally, we located three insulin response elements (IREs) in the PGC-1α promoter, and mutations of these IREs abolish or blunt activity of the PGC-1α promoter. Together, our results show that transcription of the PGC-1α gene is balanced by different intracellular signaling pathways.

Long-term memory of visually cued fear conditioning: roles of the neuronal nitric oxide synthase gene and cyclic AMP response element-binding protein

Nitric oxide (NO) produced by neuronal nitric oxide synthase (nNOS) has a role in late-phase long-term potentiation (LTP) and long-term memory (LTM) formation. Our recent studies implicated NO signaling in contextual and auditory cued fear conditioning. The present study investigated the role of NO signaling in visually cued fear conditioning. First, visually cued fear conditioning was investigated in wild-type (WT) and nNOS knockout (KO) mice. Second, the effects of pharmacological modulators of NO signaling on the acquisition of visually cued fear conditioning were investigated. Third, plasma levels of corticosterone were measured to determine a relationship between physiological and behavioral responses to fear conditioning. Fourth, levels of extracellular signal-related kinase (ERK1/2) and cyclic AMP response element binding protein (CREB) phosphorylation, downstream of NO signaling, were determined in the amygdala as potential correlates of fear learning. Mice underwent single or multiple (4) spaced trainings that consisted of a visual cue (blinking light) paired with footshock. WT mice acquired cued and contextual LTM following single and multiple trainings. nNOS KO mice acquired neither cued nor contextual LTM following a single training; however, multiple trainings improved contextual but not cued LTM. The selective nNOS inhibitor S-methyl-thiocitrulline (SMTC) impaired cued and contextual LTM in WT mice. The NO donor molsidomine recovered contextual LTM but had no effect on cued LTM in nNOS KO mice. Re-exposure to the visual cue 24 h posttraining elicited freezing response and a marked increase in plasma corticosterone levels in WT but not nNOS KO mice. The expression of CREB phosphorylation (Ser-133) was significantly higher in naive nNOS KO mice than in WT counterparts, and pharmacological modulators of NO had significant effects on levels of CREB phosphorylation and expression. These findings suggest that visual cue-dependent LTM is impaired in nNOS KO mice, and aberrant modulation of CREB in the absence of the nNOS gene may hinder cued and contextual LTM formation.

The roles of BDNF, pCREB and Wnt3a in the latent period preceding activation of progenitor cell mitosis in the adult dentate gyrus by fluoxetine

The formation of new neurons continues into adult life in the dentate gyrus of the rat hippocampus, as in many other species. Neurogenesis itself turns out to be highly labile, and is regulated by a number of factors. One of these is the serotoninergic system: treatment with drugs (such as the SSRI fluoxetine) markedly stimulates mitosis in the progenitor cells of the dentate gyrus. But this process has one remarkable feature: it takes at least 14 days of continuous treatment to be effective. This is despite the fact that the pharmacological action of fluoxetine occurs within an hour or so of first administration. This paper explores the role of BDNF in this process, using the effect of a Trk antagonist (K252a) on the labelling of progenitor cells with the mitosis marker Ki67 and the associated expression of pCREB and Wnt3a. These experiments show that (i) Fluoxetine increased Ki67 counts, as well as pCREB and Wnt3a expression in the dentate gyrus. The action of fluoxetine on the progenitor cells and on pCREB (but not Wnt3a) depends upon Trk receptor activation, since it was prevented by icv infusion of K252a. (ii) These receptors are required for both the first 7 days of fluoxetine action, during which no apparent change in progenitor mitosis occurs, as well as the second 7 days. Increased pCREB was always associated with progenitor cell mitosis, but Wnt3a expression may be necessary but not sufficient for increased progenitor cell proliferation. These results shed new light on the action of fluoxetine on neurogenesis in the adult dentate gyrus, and have both clinical and experimental interest.

DC-STAMP interacts with ER-resident transcription factor LUMAN which becomes activated during DC maturation

Dendritic cells (DCs) are the professional antigen-presenting cells (APC) which efficiently prime the immune response or induce tolerance. We recently identified Dendritic Cell Specific TrAnsMembrane Protein (DC-STAMP), a novel 470 amino acid protein preferentially expressed by dendritic cells. Previously we demonstrated that DC-STAMP re-localizes towards the Golgi upon DC maturation. To identify proteins that interact with DC-STAMP, a yeast-2-hybrid analysis was performed. Here, we report a physically interacting partner of DC-STAMP in the endoplasmic reticulum (ER), called LUMAN (also known as CREB3 or LZIP). LUMAN was previously described as an ER-resident transcription factor with unknown function. It is activated in a process called regulated intramembrane proteolysis (RIP), which involves translocation to the Golgi and subsequent proteolytic cleavage. The proteolytically activated form of the protein then translocates to the nucleus. Our data indicate that DC-STAMP plays an important role in the modulation of LUMAN activation. Moreover, we demonstrate that LUMAN is endogenously expressed by DC and becomes activated by RIP upon DC maturation induced by various different stimuli. These data define LUMAN/DC-STAMP as a novel regulatory circuit in DC.

cGMP-dependent protein kinase type I promotes CREB/CRE-mediated gene expression in neurons of the lateral amygdala

The process transforming newly learned information into stable long-term memory is called memory consolidation and, like the underlying long-term synaptic plasticity, critically depends on de novo RNA and protein synthesis. We have shown recently that the cGMP-dependent protein kinase Type I (cGKI) plays an important role for the consolidation of amygdala-dependent fear memory and long-term potentiation (LTP) in the lateral amygdala. Signalling downstream of cGKI at the level of transcriptional regulation remained unclear. A transcription factor of major importance for learning and memory is the cAMP-response element binding protein (CREB). The representation of fear memory in the lateral amygdala strikingly depends on the activity of CREB in individual neurons. Moreover, findings from in vitro experiments demonstrate CREB phosphorylation by cGK. In the hippocampus, CREB phosphorylation increases following activation of NO/cGMP signalling contributing to the late phase of LTP. To demonstrate a link from cGKI to activation of CREB and CREB-dependent transcription in neurons of the lateral amygdala as a possible mechanism for cGKI-mediated fear memory consolidation, we examined the effect of cGMP on activation of CREB/CRE using immunohistochemical staining specific for phospho-CREB and a reporter gene in control and cGKI-deficient mice, respectively. Supporting our hypothesis, marked CREB phosphorylation and CRE-mediated transcription was induced by cGMP in the lateral amygdala of control mice, but not in cGKI-deficient mice. It has been proposed that activation of cGKI is followed by its nuclear translocation that would allow direct phosphorylation of CREB. Therefore, we examined the cellular localisation of cGKI in neurons of the lateral amygdala in the presence of cGMP by double staining for cGKI and a nuclear marker in sections from areas showing prominent CREB phosphorylation, and did not observe prominent nuclear translocation of the enzyme. In summary, we provide evidence that cytosolic cGKI can support fear memory consolidation and LTP in neurons of the lateral amygdala via activation of CREB and CRE-dependent transcription.

The common aspects of pathophysiolgy of alcoholism and depression

Recent biological studies suggest the existence of the common pathophysiological aspects in alcoholism and depression. Postmortem studies have revealed the impairment of cAMP signaling in the patients with alcoholism. The similar alteration of cAMP signaling was also reported in postmortem brains of depressed patients. In this study, we supported the notion that neurogenesis would be essential in pathophysiology of both alcoholism and depression. Alcohol affected the function of neural stem cells (NSCs) and decreased neurogenesis at doses which did not affects cell survival, and treatment of antidepressant or moodstabilizer rescued the alcohol-induced suppression of neurogenesis. As the key mechanism of NSC differentiation change by ethanol and psychotropics, we focused on the transcriptional repressor, NRSF/REST activity change. Our in vitro studies demonstrated the NRSF/REST activation by ethanol and suppressive effect of antidepressants and lithium against its activation by ethanol. We further described the ERK reduction and ER stress in the cellular mechanism of NRSF/REST activation. All these findings suggested that cAMP-CREB cascade reduction and NRSF/REST activation may be common underlying mechanisms in the pathophysiology of alcoholism and depression.

Arachidonic acid induces acetyl-CoA carboxylase 1 expression via activation of CREB1

Acetyl-CoA carboxylase (ACC; EC 6.4.1.2) is the major enzyme of fatty acid synthesis and oxidation in response to dietary changes. In animals, there are two major isoforms of ACCs, ACC1 and ACC2, which are encoded by different genes and display distinct tissue and cellular distribution. We examined the effect of high concentration of arachidonic acid (AA) on the expression of ACC1 mRNA in HepG2 hepatoma cells cultured in the absence of insulin. After 12 h of treatment, AA was found to significantly up-regulate ACC1 mRNA level as well as that of cAMP regulatory element binding protein 1 (CREB1), implying the possible interactions between ACC1 and CREB1. In support of the hypothesis, several potential CREB1 binding sites were identified within the PII promoter of ACC1. Further experiments demonstrated that transient over-expression of CREB1 in HepG2 cells activates ACC1 PII promoter and induces the production of triacylglycerol in response to AA, indicating that the effect of AA on ACC1 is possibly regulated via CREB1.

[Effects of prenatal taurine on mRNA expression of PKA CREB signal pathway and glial cell line derived neurotrophic factor in fetal rat brains of intrauterine growth restriction]

OBJECTIVE

This study examined the effects of prenatal application of taurine on mRNA expression of protein kinase A cAMP response element binding protein (PKA-CREB) signal pathway and glial cell line derived neurotrophic factor (GDNF) in fetal rat brains of intrauterine growth restriction (IUGR).

METHODS

Pregnant rats were randomly divided into 4 groups: normal control, IUGR model, low dose (100 mg/kg x d) and high dose (300 mg/kg x d) taurine treatment IUGR (n = 5 each). IUGR was induced by food restriction throughout pregnancy. PKA, CREB and GDNF mRNA expression in brains of newborn rats was detected by reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

PKA, CREB and GDNF mRNA expression in the IUGR model group was significantly higher than that in the normal control group (p<0.05). Compared with the IUGR model group, mRNA expression of PKA and CREB in both the low dose and high dose taurine treatment groups increased significantly (p<0.05); GDNF mRNA expression in the high dose taurine treatment group also increased significantly (p<0.01).

CONCLUSIONS

Taurine can increase mRNA expression of PKA, CREB and GDNF in fetal rat brains of IUGR. This suggests that prenatal application of taurine may increase neurogenesis of the central nervous system and endogenous secretion of neurotrophic factors, thus providing neuroprotective effects.

Molecular and cellular approaches to memory allocation in neural circuits

Although memory allocation is a subject of active research in computer science, little is known about how the brain allocates information within neural circuits. There is an extensive literature on how specific types of memory engage different parts of the brain, and how neurons in these regions process and store information. Until recently, however, the mechanisms that determine how specific cells and synapses within a neural circuit (and not their neighbors) are recruited during learning have received little attention. Recent findings suggest that memory allocation is not random, but rather specific mechanisms regulate where information is stored within a neural circuit. New methods that allow tagging, imaging, activation, and inactivation of neurons in behaving animals promise to revolutionize studies of brain circuits, including memory allocation. Results from these studies are likely to have a considerable impact on computer science, as well as on the understanding of memory and its disorders.

CREB is a key regulator of striatal vulnerability in chemical and genetic models of Huntington's disease

Evidence of dysregulation of the CREB/CRE transcriptional pathway in animal models of Huntington's disease (HD) suggests that strategies designed to augment CRE-mediated transcription may be of therapeutic value. Here, we investigated the consequences of CREB activation and repression in chemical and transgenic mouse models of HD. In the 3-nitropropionic acid (3-NP) model, CREB phospho-activation in the striatum was potently repressed within the neurotoxic "core" region prior to cell death. Conversely, marked expression of phospho-CREB, as well the CREB-regulated cytoprotective gene Bcl-2, was detected in the "penumbral" region. To examine potential contributory roles for the CREB/CRE transcriptional pathway in striatal degeneration, we used both CREB loss- (A-CREB) and gain- (VP16-CREB) of-function transgenic mouse strains. 3-NP-induced striatal lesion size and motor dysfunction were significantly increased in A-CREB mice compared to controls. Conversely, striatal damage and motor deficits were diminished in VP16-CREB mice. Furthermore, transgenic A-CREB significantly accelerated motor impairment in the YAC128 mouse model of HD. Together, these results indicate that CREB functionality is lost during the early stages of striatal cell stress and that the repression of CREB-mediated transcription contributes to the pathogenic process.

Mechanisms of protein kinase C signaling in the modulation of 3',5'-cyclic adenosine monophosphate-mediated steroidogenesis in mouse gonadal cells

The protein kinase C (PKC) signaling pathway plays integral roles in the expression of the steroidogenic acute regulatory (StAR) protein that regulates steroid biosynthesis in steroidogenic cells. PKC can modulate the activity of cAMP/protein kinase A signaling involved in steroidogenesis; however, its mechanism remains obscure. In the present study, we demonstrate that activation of the PKC pathway, by phorbol 12-myristate 13-acetate (PMA), was capable of potentiating dibutyryl cAMP [(Bu)(2)cAMP]-stimulated StAR expression, StAR phosphorylation, and progesterone synthesis in both mouse Leydig (MA-10) and granulosa (KK-1) tumor cells. The steroidogenic potential of PMA and (Bu)(2)cAMP was linked with phosphorylation of ERK 1/2; however, inhibition of the latter demonstrated varying effects on steroidogenesis. Transcriptional activation of the StAR gene by PMA and (Bu)(2)cAMP was influenced by several factors, its up-regulation being dependent on phosphorylation of the cAMP response element binding protein (CREB). An oligonucleotide probe containing a CREB/activating transcription factor binding region in the StAR promoter was found to bind nuclear proteins in PMA and (Bu)(2)cAMP-treated MA-10 and KK-1 cells. Chromatin immunoprecipitation studies revealed that the induction of phosphorylated CREB was tightly correlated with in vivo protein-DNA interactions and recruitment of CREB binding protein to the StAR promoter. Ectopic expression of CREB binding protein enhanced CREB-mediated transcription of the StAR gene, an event that was markedly repressed by the adenovirus E1A oncoprotein. Further studies demonstrated that the activation of StAR expression and steroid synthesis by PMA and (Bu)(2)cAMP was associated with expression of the nuclear receptor Nur77, indicating its essential role in hormone-regulated steroidogenesis. Collectively, these findings provide insight into the mechanisms by which PKC modulates cAMP/protein kinase A responsiveness involved in regulating the steroidogenic response in mouse gonadal cells.

[Possible relation of BDNF and GDNF to neuropsychiatric disorders]

Structural abnormalities are demonstrated in various neuropsychiatric disorders, including Alzheimer's disease, Parkinson's disease, and even major depression. On the other hand, recent studies have demonstrated the structural and functional modifications in the adult brain that are associated with synaptic plasticity and neurogenesis. Accordingly, regulation of synaptic plasticity and neurogenesis may lead to the development of novel treatments for neuropsychiatric disorders. Brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) have important roles not only in neuronal survival and differentiation, but also in the formation and maintenance of neural circuits and synapse plasticity. Accumulating evidence suggests that these neurotrophic factors may be applied to the treatment of neuropsychiatric disorders. In addition, compounds that increase the expression of BDNF and/or GDNF in the brain should have potential therapeutic values. We have demonstrated that systemic administration of dipeptide Leu-Ile increases BDNF and GDNF production in the brain, and has a protective role in methamphetamine and morphine dependence. In this review, we discuss the potential role of BDNF, GDNF and their inducers in the treatment for neuropsychiatric disorders.

Molecular mechanisms of psychostimulant addiction

Drug addiction represents a pathological form of neuroplasticity along with the emergence of aberrant behaviors involving a cascade of neurochemical changes mainly in the brain's rewarding circuitry. The aberrant behavioral phenotypes can be assessed by an animal model of drug-induced behavioral sensitization, which is characterized by an initiation stage that is formed in the ventral tegmental area and a behavioral expression stage determined mainly in the nucleus accumbens. Numerous studies during past decades demonstrate that the mesocorticolimbic dopamine pathway plays an essential role in the development of behavioral sensitization. Moreover, a series of cellular signaling pathways and gene expression determine the severity of addictive behaviors. In addition to the well-characterized dopamine D1 receptor-mediated cAMP/protein kinase A up-regulation in the nucleus accumbens, recent reports indicate the cellular mediator dopamine- and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32) and transcription regulator DeltaFosB are associated with the accumbal PKA pathway to modulate the development of behavioral sensitization. The finding of cAMP-independent and dopamine D2 receptor-mediated Akt/GSK3 in activation in the nucleus accumbens of behaviorally sensitized animals implies that a signal cascade down-stream of both dopamine D1 and D2 receptors comprises the mainstay of the addiction network. This review outlines the cellular pathways that have been demonstrated to participate in psychostimulant addiction, focused particularly in the nucleus accumbens.

The beta-catenin axis integrates multiple signals downstream from RET/papillary thyroid carcinoma leading to cell proliferation

RET/papillary thyroid carcinoma (RET/PTC) oncoproteins result from the in-frame fusion of the RET receptor tyrosine kinase domain with protein dimerization motifs encoded by heterologous genes. Here, we show that RET/PTC stimulates the beta-catenin pathway. By stimulating PI3K/AKT and Ras/extracellular signal-regulated kinase (ERK), RET/PTC promotes glycogen synthase kinase 3beta (GSK3beta) phosphorylation, thereby reducing GSK3beta-mediated NH(2)-terminal beta-catenin (Ser33/Ser37/Thr41) phosphorylation. In addition, RET/PTC physically interacts with beta-catenin and increases its phosphotyrosine content. The increased free pool of S/T(nonphospho)/Y(phospho)beta-catenin is stabilized as a result of the reduced binding affinity for the Axin/GSK3beta complex and activates the transcription factor T-cell factor/lymphoid enhancer factor. Moreover, through the ERK pathway, RET/PTC stimulates cyclic AMP-responsive element binding protein (CREB) phosphorylation and promotes the formation of a beta-catenin-CREB-CREB-binding protein/p300 transcriptional complex. Transcriptional complexes containing beta-catenin are recruited to the cyclin D1 promoter and a cyclin D1 gene promoter reporter is active in RET/PTC-expressing cells. Silencing of beta-catenin by small interfering RNA inhibits proliferation of RET/PTC-transformed PC Cl3 thyrocytes, whereas a constitutively active form of beta-catenin stimulates autonomous proliferation of thyroid cells. Thus, multiple signaling events downstream from RET/PTC converge on beta-catenin to stimulate cell proliferation.

Expression of the transcriptional repressor ATF3 in gonadotrophs is regulated by Egr-1, CREB, and ATF2 after gonadotropin-releasing hormone receptor stimulation

Stimulation of GnRH receptors enhances expression of activating transcription factor (ATF) 3 in a pituitary gonadotroph cell line. The signaling pathway requires elevated cytosolic Ca2+ levels and activation of ERK and c-Jun N-terminal protein kinase. The signaling cascade was blocked by overexpression of either MAPK phosphatase (MKP)-1 or MAPK phosphatase-5 that dephosphorylate nuclear ERK and c-Jun N-terminal protein kinase. In addition, ATF3 biosynthesis was impaired after lentiviral-mediated expression of a constitutively active mutant of calcineurin A. Thus, MKP-1, MKP-5, and calcineurin may function as shut-off devices for GnRH receptor signaling. Expression of dominant-negative mutants of early growth response protein (Egr)-1, cAMP response element binding protein (CREB), and ATF2 blocked the biosynthesis of ATF3, indicating that these transcription factors connect the intracellular signaling cascade elicited by activation of GnRH receptors with transcription of the ATF3 gene. This view was corroborated by chromatin immunoprecipitation experiments revealing that Egr-1 and the phosphorylated forms of CREB and ATF2 bound to the 5'-upstream region of the ATF3 gene in buserelin-stimulated gonadotrophs. Together the data indicate that the ATF3 gene is a bona fide target gene of Egr-1, CREB, and ATF2 in gonadotrophs. Moreover, we show that in gonadotrophs ATF3 bound to its own promoter under physiological conditions. The analysis of a lentiviral-transmitted ATF3 promoter/luciferase reporter gene, embedded into the chromatin of the cells, revealed that ATF3 blocked the activity of its own promoter. We additionally identified the chromogranin B gene as bona fide target gene of ATF3 in gonadotrophs.

Drosophila melanogaster: an insect model for fundamental studies of sleep

In 2000, Drosophila melanogaster joined the ranks of vertebrates and invertebrates with a defined behavioral sleep state. The characterization of this sleep state revealed striking similarities to sleep in humans: sleep in flies has both circadian and homeostatic components, it is influenced by sex and age, and it is affected by pharmacological agents such as caffeine and antihistamines. As in mammals, arousal thresholds in flies increase with sleep deprivation. Furthermore, changes in brain electrical activity accompany the change from wake to sleep states. Not only do flies and vertebrates share these behavioral and physiological traits of sleep, but they are likely to share at least some genetic mechanisms underlying the regulation of sleep as well. This article reviews the methods currently used to identify and characterize the Drosophila sleep state. As these methods become more refined and our understanding of Drosophila sleep more detailed, the powerful techniques afforded by this organism are likely to unveil deep insights into the function(s) and regulatory mechanisms of sleep.

Characterization and function of CREB homologue from Crassostrea ariakensis stimulated by rickettsia-like organism

The cAMP response element-binding protein (CREB) is a transcription factor that plays important roles in cellular growth, proliferation and survival. Here, we report that a homologue of CREB transcription factor, Ca-CREB, was identified and functionally characterized in oyster, Crassostrea ariakensis. The full-length cDNA consists of 1397bp with an ORF encoding a 39.3kDa protein. Amino acid sequence analysis revealed that Ca-CREB shares conserved signature motifs with other CREB proteins. Ca-CREB was ubiquitously and constitutively expressed in oyster, and the expression level in hemocytes was higher than that in other tissues. The expression level of Ca-CREB was not modified after RLO stimulation, while tumor necrosis factor-alpha (TNF-alpha) expression was increased obviously, which was revealed by real-time reverse-transcriptase polymerase chain reaction (RT-PCR). Electrophoretic mobility shift assay (EMSA) and Western blotting showed that recombinant CREB proteins specifically bind the consensus CREB binding site, and DNA-binding activity and phosphorylation of Ca-CREB were induced by RLO. These results suggest that Ca-CREB is a CREB homologue and may be involved in immune responses against RLO.

Uncovering the mechanisms of estrogen effects on hippocampal function

Estrogens have direct effects on the brain areas controlling cognition. One of the most studied of these regions is the dorsal hippocampal formation, which governs the formation of spatial and episodic memories. In laboratory animals, most investigators report that estrogen enhances synaptic plasticity and improves performance on hippocampal-dependent cognitive behaviors. This review summarizes work conducted in our laboratory and others toward identifying estrogen's actions in the hippocampal formation, and the mechanisms for these actions. Physiologic and pharmacologic estrogen affects cognitive behavior in mammals, which may be applicable to human health and disease. The effects of estrogen in the hippocampal formation that lead to modulation of hippocampal function include effects on cell morphology, synapse formation, signaling, and excitability that have been studied in laboratory mice, rats, and primates. Finally, estrogen may signal through both nuclear and extranuclear hippocampal estrogen receptors to achieve its downstream effects.

Androgen cell signaling pathways involved in neuroprotective actions

As a normal consequence of aging in men, testosterone levels significantly decline in both serum and brain. Age-related testosterone depletion results in increased risk of dysfunction and disease in androgen-responsive tissues, including brain. Recent evidence indicates that one deleterious effect of age-related testosterone loss in men is increased risk for Alzheimer's disease (AD). We discuss recent findings from our laboratory and others that identify androgen actions implicated in protecting the brain against neurodegenerative diseases and begin to define androgen cell signaling pathways that underlie these protective effects. Specifically, we focus on the roles of androgens as (1) endogenous negative regulators of beta-amyloid accumulation, a key event in AD pathogenesis, and (2) neuroprotective factors that utilize rapid non-genomic signaling to inhibit neuronal apoptosis. Continued elucidation of cell signaling pathways that contribute to protective actions of androgens should facilitate the development of targeted therapeutic strategies to combat AD and other age-related neurodegenerative diseases.

Regulation of cholinergic phenotype in developing neurons

Specification of neurotransmitter phenotype is critical for neural circuit development and is influenced by intrinsic and extrinsic factors. Recent findings in rat hypothalamus in vitro suggest the role of neurotransmitter glutamate in the regulation of cholinergic phenotype. Here we extended our previous studies on the mechanisms of glutamate-dependent regulation of cholinergic phenotypic properties in hypothalamic neurons. Using immunocytochemistry, electrophysiology, and calcium imaging, we demonstrate that hypothalamic expression of choline acetyltransferase (the cholinergic marker) and responsiveness of neurons to acetylcholine (ACh) receptor agonists increase during chronic administration of an N-methyl-D-aspartate receptor (NMDAR) blocker, MK-801, in developing rats in vivo and genetic and pharmacological inactivation of NMDARs in mouse and rat developing neuronal cultures. In hypothalamic cultures, an inactivation of NMDA receptors also induces ACh-dependent synaptic activity, as do inactivations of PKA, ERK/MAPK, CREB, and NF-kappaB, which are known to be regulated by NMDA receptors. Interestingly, the increase in cholinergic properties in developing neurons that is induced by NMDAR blockade is prevented by the blockade of ACh receptors, suggesting that function of ACh receptor is required for the cholinergic up-regulation. Using dual recording of monosynaptic excitatory postsynaptic currents, we further demonstrate that chronic inactivation of ionotropic glutamate receptors induces the cholinergic phenotype in a subset of glutamatergic neurons. The phenotypic switch is partial as ACh and glutamate are coreleased. The results suggest that developing neurons may not only coexpress multiple transmitter phenotypes, but can also change the phenotypes following changes in signaling in neuronal circuits.

t-Darpp promotes cancer cell survival by up-regulation of Bcl2 through Akt-dependent mechanism

t-Darpp is a cancer-related truncated isoform of Darpp-32 (dopamine and cyclic-AMP-regulated phosphoprotein of M(r) 32,000). We detected overexpression of t-Darpp mRNA in two thirds of gastric cancers compared with normal samples (P = 0.004). Using 20 micromol/L ceramide treatment as a model for induction of apoptosis in AGS cancer cells, we found that expression of t-Darpp led to an increase in Bcl2 protein levels and blocked the activation of caspase-3 and caspase-9. The MitoCapture mitochondrial apoptosis and cytochrome c release assays indicated that t-Darpp expression enforces the mitochondrial transmembrane potential and protects against ceramide-induced apoptosis. Interestingly, the expression of t-Darpp in AGS cells led to >or=2-fold increase in Akt kinase activity with an increase in protein levels of p-Ser(473) Akt and p-Ser(9) GSK3 beta. These findings were further confirmed using tetracycline-inducible AGS cells stably expressing t-Darpp. We also showed transcriptional up-regulation of Bcl2 using the luciferase assay with Bcl2 reporter containing P1 full promoter, quantitative reverse transcription-PCR, and t-Darpp small interfering RNA. The Bcl2 promoter contains binding sites for cyclic AMP-responsive element binding protein CREB/ATF1 transcription factors and using the electrophoretic mobility shift assay with a CREB response element, we detected a stronger binding in t-Darpp-expressing cells. The t-Darpp expression led to an increase in expression and phosphorylation of CREB and ATF-1 transcription factors that were required for up-regulating Bcl2 levels. Indeed, knockdown of Akt, CREB, or ATF1 in t-Darpp-expressing cells reduced Bcl2 protein levels. In conclusion, the t-Darpp/Akt axis underscores a novel oncogenic potential of t-Darpp in gastric carcinogenesis and resistance to drug-induced apoptosis.

Physiological roles of the Ca2+/CaM-dependent protein kinase cascade in health and disease

Numerous hormones, growth factors and physiological processes cause a rise in cytosolic Ca2+, which is translated into meaningful cellular responses by interacting with a large number of Ca2(+)-binding proteins. The Ca2(+)-binding protein that is most pervasive in mediating these responses is calmodulin (CaM), which acts as a primary receptor for Ca2+ in all eukaryotic cells. In turn, Ca2+/CaM functions as an allosteric activator of a host of enzymatic proteins including a considerable number of protein kinases. The topic of this review is to discuss the physiological roles of a sub-set of these protein kinases which can function in cells as a Ca2+/CaM-dependent kinase signaling cascade. The cascade was originally believed to consist of a CaM kinase kinase that phosphorylates and activates one of two CaM kinases, CaMKI or CaMKIV. The unusual aspect of this cascade is that both the kinase kinase and the kinase require the binding of Ca2+/CaM for activation. More recently, one of the CaM kinase kinases has been found to activate another important enzyme, the AMP-dependent protein kinase so the concept of the CaM kinase cascade must be expanded. A CaM kinase cascade is important for many normal physiological processes that when misregulated can lead to a variety of disease states. These processes include: cell proliferation and apoptosis that may conspire in the genesis of cancer; neuronal growth and function related to brain development, synaptic plasticity as well as memory formation and maintenance; proper function of the immune system including the inflammatory response, activation of T lymphocytes and hematopoietic stem cell maintenance; and the central control of energy balance that, when altered, can lead to obesity and diabetes. Although the study of the CaM-dependent kinase cascades is still in its infancy continued analysis of the pathways regulated by these Ca2(+)-initiated signaling cascades holds considerable promise for the future of disease-related research.

Regulation of CREB-mediated gene expression by salt inducible kinase

Salt inducible kinase (SIK) was identified as a molecule induced in the adrenal glands of rats fed with a high-salt diet. A major downstream of SIK is regulation of camp-responsive element (CRE)-dependent gene expression. SIK represses the activity of CRE-binding protein (CREB) by phosphorylating a CREB-specific co-activator transducer of regulated CREB activity (TORC). When TORC is dephosphorylated it activates CREB in a CREB-phosphorylation independent manner. The importance of the dephosphorylation of TORC has been suggested by the fact that a kinase inhibitor staurosporine induces dephosphorylation of TORC and upregulates the gene expression of CYP11A, CYP11B1, CYP11B2 and StAR in adrenocortical cells. The identification of SIK caused a stir in the field of CREB studies and led to disclosure of cascades hidden behind the classical mechanism for CREB activity.

Interference of endocrine disrupting chemicals with aromatase CYP19 expression or activity, and consequences for reproduction of teleost fish

Many natural and synthetic compounds present in the environment exert a number of adverse effects on the exposed organisms, leading to endocrine disruption, for which they were termed endocrine disrupting chemicals (EDCs). A decrease in reproduction success is one of the most well-documented signs of endocrine disruption in fish. Estrogens are steroid hormones involved in the control of important reproduction-related processes, including sexual differentiation, maturation and a variety of others. Careful spatial and temporal balance of estrogens in the body is crucial for proper functioning. At the final step of estrogen biosynthesis, cytochrome P450 aromatase, encoded by the cyp19 gene, converts androgens into estrogens. Modulation of aromatase CYP19 expression and function can dramatically alter the rate of estrogen production, disturbing the local and systemic levels of estrogens. In the present review, the current progress in CYP19 characterization in teleost fish is summarized and the potential of several classes of EDCs to interfere with CYP19 expression and activity is discussed. Two cyp19 genes are present in most teleosts, cyp19a and cyp19b, primarily expressed in the ovary and brain, respectively. Both aromatase CYP19 isoforms are involved in the sexual differentiation and regulation of the reproductive cycle and male reproductive behavior in diverse teleost species. Alteration of aromatase CYP19 expression and/or activity, be it upregulation or downregulation, may lead to diverse disturbances of the above mentioned processes. Prediction of multiple transcriptional regulatory elements in the promoters of teleost cyp19 genes suggests the possibility for several EDC classes to affect cyp19 expression on the transcriptional level. These sites include cAMP responsive elements, a steroidogenic factor 1/adrenal 4 binding protein site, an estrogen-responsive element (ERE), half-EREs, dioxin-responsive elements, and elements related to diverse other nuclear receptors (peroxisome proliferator activated receptor, retinoid X receptor, retinoic acid receptor). Certain compounds including phytoestrogens, xenoestrogens, fungicides and organotins may modulate aromatase CYP19 activity on the post-transcriptional level. As is shown in this review, diverse EDCs may affect the expression and/or activity of aromatase cyp19 genes through a variety of mechanisms, many of which need further characterization in order to improve the prediction of risks posed by a contaminated environment to teleost fish population.

Hormesis: a promising strategy to sustain endogenous neuronal survival pathways against neurodegenerative disorders

The brain developed adaptive mechanisms in the face of changing environments and stresses imposed on the nervous system. The addition of glutamate as the major excitatory amino acid neurotransmitter to the brain's complement of amino acids and peptides dictated a coordinated transcriptional and translational program to meet the demands of excitatory neurotransmission. One such program is the ability of neurons to sustain and maintain their survival given the nature of glutamate-mediated receptor activation. The unique development of endogenous neuronal pathways activated by glutamate receptors transformed neurons and allowed them to survive under conditions of high energy demands. These same endogenous survival pathways also mediate plastic responses to meet another demand of the brain, adaptation. An endogenous protein that plays a central role in glutamate receptor-mediated survival pathways is brain-derived neurotrophic factor (BDNF). Intermittent but frequent synaptic ionotropic glutamate receptor activation ensures neuronal survival through a BDNF autocrine loop. In sharp contrast, overactivation of ionotropic glutamate receptors leads to neuronal cell death. Thus, innovative strategies that induce endogenous neuronal survival pathways through low-level activation of ionotropic glutamate receptors or those that bypass receptor activation but upregulate endogenous survival pathways may not only prevent neurodegenerative disorders that involve glutamate as a final common pathway that kills neurons, but may also provide treatment alternatives critical for neurons to survive stressful conditions such as stroke, status epilepticus and hypoglycemic-induced neuronal cell death.

Involvement of cAMP response element-binding protein in the regulation of cell proliferation and the prolactin promoter of lactotrophs in primary culture

Hypothalamic hormones, including dopamine, regulate critical functions of pituitary cells via the cAMP-protein kinase A (PKA) pathway. The PKA-downstream transcription factor cAMP response element (CRE)-binding protein (CREB) is an integrating molecule that is also activated by many other protein kinase pathways. We investigated the involvement of CREB in the regulation of cell proliferation and the PRL promoter of rat lactotrophs in primary cell culture. Recombinant adenoviruses were used for efficient gene delivery into pituitary cells. Bromocriptine, a dopaminergic agonist known to decrease intracellular cAMP concentrations, caused inhibition of PRL promoter activity and lactotroph proliferation, which was accompanied by decreases in CRE-mediated transcription and CREB phosphorylation in lactotrophs. Expression of a dominant-negative form of CREB (MCREB), which was effective in suppressing CRE-mediated transcription induced by the adenylate cyclase activator forskolin, inhibited basal and forskolin-induced PRL promoter activity and PRL mRNA expression. MCREB expression lowered basal proliferative levels and blocked forskolin-induced proliferation of lactotrophs. Insulin-like growth factor I (IGF-I), a potent mitogen in lactotrophs, did not affect intracellular cAMP concentrations but transiently increased lactotroph CREB phosphorylation. MCREB expression also inhibited IGF-I-induced lactotroph proliferation. These results suggest that CREB is involved in the regulation of cell proliferation and the PRL promoter in normal lactotrophs and that dopamine inhibition of these lactotroph functions is at least in part due to inhibition of the cAMP-PKA-CREB pathway.

Human nuclear pregnane X receptor cross-talk with CREB to repress cAMP activation of the glucose-6-phosphatase gene

The nuclear PXR (pregnane X receptor) was originally characterized as a key transcription factor that activated hepatic genes encoding drug-metabolizing enzymes. We have now demonstrated that PXR also represses glucagon-activated transcription of the G6Pase (glucose-6-phosphatase) gene by directly binding to CREB [CRE (cAMP-response element)-binding protein]. Adenoviral-mediated expression of human PXR (hPXR) and its activation by rifampicin strongly repressed cAMP-dependent induction of the endogenous G6Pase gene in Huh7 cells. Using the -259 bp G6Pase promoter construct in cell-based transcription assays, repression by hPXR of PKA (cAMP-dependent protein kinase)-mediated promoter activation was delineated to CRE sites. GST (glutathione transferase) pull-down and immunoprecipitation assays were employed to show that PXR binds directly to CREB, while gel-shift assays were used to demonstrate that this binding prevents CREB interaction with the CRE. These results are consistent with the hypothesis that PXR represses the transcription of the G6Pase gene by inhibiting the DNA-binding ability of CREB. In support of this hypothesis, treatment with the mouse PXR activator PCN (pregnenolone 16alpha-carbonitrile) repressed cAMP-dependent induction of the G6Pase gene in primary hepatocytes prepared from wild-type, but not from PXR-knockout, mice, and also in the liver of fasting wild-type, but not PXR-knockout, mice. Moreover, ChIP (chromatin immunoprecipitation) assays were performed to show a decreased CREB binding to the G6Pase promoter in fasting wild-type mice after PCN treatment. Thus drug activation of PXR can repress the transcriptional activity of CREB, down-regulating gluconeogenesis.

Binding of steroidogenic factor-1 to the regulatory region might not be critical for transcriptional regulation of the human CYP1B1 gene

Cytochrome P450 (CYP) 1B1, which catalyzes 17beta-estradiol 4-hydroxylation, is expressed in steroid-related tissues including ovary, testis, and adrenal gland. Generally, the expressions of steroidogenic CYPs are transcriptionally regulated by steroidogenic factor-1 (SF-1) and cAMP response element (CRE) binding protein (CREB). In the present study, we examined the possibility that the human CYP1B1 gene might be regulated by SF-1 and CREB. Gel shift analyses revealed that in vitro translated SF-1 can bind to the putative SF-1 binding sites, SF-1a (at -1722) and SF-1b (at -2474), on the CYP1B1 gene. In vitro translated CREB barely binds to the putative SF-1 binding sites. Luciferase analysis revealed that a reporter plasmid, pGL3 (-2623/+25), containing the SF-1a and SF-1b elements is transactivated by the concomitant co-expression of SF-1 and protein kinase A (PKA). However, the transcriptional activity is induced by PKA alone. Mutations in the SF-1a and SF-1b elements did not affect the luciferase activity. Thus, the binding of SF-1 to the putative SF-1 binding sites of the human CYP1B1 gene might not be essential for transcriptional regulation. Interestingly, deletion and mutation analyses indicated that the PKA signaling pathway is involved in the xenobiotic responsive element (XRE)-mediated transactivation of the human CYP1B1 gene.

Opposing functions of CREB and MKK1 synergistically regulate the geometry of dendritic spines in visual cortex

Most excitatory inputs onto pyramidal neurons are made on dendritic spines. The geometry of dendritic spines modulates synaptic function; yet we know little regarding the molecular signals that regulate spine geometry. Here we report that neurons coordinately regulate the geometry of spines to compensate for variability in spine number, by a process requiring the transcription factor CREB and the kinase MKK1. We find that CREB function is induced, whereas MKK1 is inhibited, by activity blockade. To obtain evidence that CREB and MKK1 regulate dendritic spine geometry in vivo, we coexpressed green fluorescent protein and dominant negative CREB or MKK1 in pyramidal neurons of the intact rat visual cortex. Spines on apical dendrites of layer 3 neurons were then characterized by confocal microscopy. We find that CREB and MKK1 regulate spine geometry in opposite ways. MKK1 is required to reduce spine head size when spine density is high, whereas CREB is required to enlarge spines when spine density is low. Our data suggest that CREB and MKK1 might function as complementary negative feedback mechanisms to maintain synaptic drive within bounds.

Transgenic mice expressing an inhibitory truncated form of p300 exhibit long-term memory deficits

The formation of many forms of long-term memory requires several molecular mechanisms including regulation of gene expression. The mechanisms directing transcription require not only activation of individual transcription factors but also recruitment of transcriptional coactivators. CBP and p300 are transcriptional coactivators that interact with a large number of transcription factors and regulate transcription through multiple mechanisms, including an intrinsic histone acetyltransferase (HAT) activity. HAT activity mediates acetylation of lysine residues on the amino-terminal tails of histone proteins, thereby increasing DNA accessibility for transcription factors to activate gene expression. CBP has been shown to play an important role in long-term memory formation. We have investigated whether p300 is also required for certain forms of memory. p300 shares a high degree of homology with CBP and has been shown to interact with transcription factors known to be critical for long-term memory formation. Here we demonstrate that conditional transgenic mice expressing an inhibitory truncated form of p300 (p300Delta1), which lacks the carboxy-terminal HAT and activation domains, have impaired long-term recognition memory and contextual fear memory. Thus, our study demonstrates that p300 is required for certain forms of memory and that the HAT and carboxy-terminal domains play a critical role.

The impact of CREB and its phosphorylation at Ser142 on inflammatory nociception

Peripheral noxious stimulation leads to phosphorylation and thereby activation of the transcription factor CREB in the spinal cord. CREB phosphorylation occurs mainly at serine 133, but the phosphorylation site at serine 142 may also be important. We investigated the impact of spinal CREB protein levels and phosphorylation at Ser142 on the nociceptive behaviour in rat and mouse models of inflammatory nociception. Downregulation of total CREB protein in the rat spinal cord by antisense-oligonucleotides resulted in antinociceptive effects. After peripheral noxious stimulation CREB was phosphorylated in the spinal cord at serine 133 and 142 indicating a potential role of both residues in nociceptive processing. However, Ser142 mutant mice developed equal behavioural correlates of hyperalgesia as wild-type mice in different inflammatory models. Thus, our data confirm that CREB is essential for spinal nociceptive processing. However, prevention of phosphorylation only at serine 142 is not sufficient to modulate the nociceptive response.

Dominant negative mutant forms of the cAMP response element binding protein induce apoptosis and decrease the anti-apoptotic action of growth factors in human islets

AIMS/HYPOTHESIS

Transplantation of islets is a viable option for the treatment of diabetes. A significant proportion of islets is lost during isolation, storage and after transplantation as a result of apoptosis. cAMP response element binding protein (CREB) is an important cell survival factor. The aim of the present study was to determine whether preservation of CREB function is needed for survival of human islets.

MATERIALS AND METHODS

To determine the effects of downregulation of CREB activity on beta cell apoptosis in a transplantation setting, adenoviral vectors were used to express two dominant negative mutant forms of CREB in human islets isolated from cadaveric donors. Markers of apoptosis were determined in these transduced islets under basal conditions and following treatment with growth factor.

RESULTS

Expression of CREB mutants in human islets resulted in significant (p < 0.001) activation of caspase-9, a key regulatory enzyme in the mitochondrial pathway of apoptosis, when compared with islets transduced with adenoviral beta galactosidase. Immunocytochemical analysis showed the activation of caspase-9 to be predominantly in beta cells. Other definitive markers of apoptosis such as parallel activation of caspase-3, accumulation of cleaved poly-(ADP-ribose) polymerase and nuclear condensation were also observed. Furthermore, the anti-apoptotic action of growth factors exendin-4 and betacellulin in human islets exposed to cytokines was partially lost when CREB function was impaired.

CONCLUSIONS/INTERPRETATION

Our findings suggest that impairment of CREB-mediated transcription could lead to loss of islets by apoptosis with potential implications in islet transplantation as well as in the mechanism of beta cell loss leading to diabetes.

Congenital bone fractures in spinal muscular atrophy: functional role for SMN protein in bone remodeling

Spinal muscular atrophy is the second most common fatal childhood disorder. Core clinical features include muscle weakness caused by degenerating lower motor neurons and a high incidence of bone fractures and hypercalcemia. Fractures further compromise quality of life by progression of joint contractures or additional loss of motor function. Recent observations suggest that bone disease in spinal muscular atrophy may not be attributed entirely to lower motor neuron degeneration. The presence of the spinal muscular atrophy disease-determining survival motor neuron gene (SMN), SMN expression, and differential splicing in bone-resorbing osteoclasts was recently discovered. Its ubiquitous expression and the differential expression of splice variants suggest that SMN has specific roles in bone cell function. SMN protein also interacts with osteoclast stimulatory factor. Mouse models of human spinal muscular atrophy disease suggest a potential role of SMN protein in skeletal development. Dual energy x-ray absorptiometry analysis demonstrated a substantial decrease in total bone area and poorly developed caudal vertebra in the mouse model. These mice also had pelvic bone fractures. Studies delineating SMN signaling mechanisms and gene transcription in a cell-specific manner will provide important molecular insights into the pathogenesis of bone disease in children with spinal muscular atrophy. Moreover, understanding bone remodeling in spinal muscular atrophy may lead to novel therapeutic approaches to enhance skeletal health and quality of life. This article reviews the skeletal complications associated with spinal muscular atrophy and describes a functional role for SMN protein in osteoclast development and bone resorption activity.

Activation of endoplasmic reticulum stress response by hepatitis viruses up-regulates protein phosphatase 2A

The up-regulation of protein phosphatase 2 A (PP2A) is an important factor leading to an inhibition of IFNalpha signaling caused by viral protein expression. Here, we describe the molecular mechanism involved in PP2Ac up-regulation by HCV and HBV. HCV and HBV protein expression in cells induces an ER stress response leading to calcium release from the ER. HCV protein expression induces CREB activation, probably through calcium/calmodulin-dependent protein kinase. CREB binds to a CRE element in the promoter of PP2Ac and induces its transcriptional up-regulation. Because PP2Ac is involved in many important cellular processes including cell-cycle regulation, apoptosis, cell morphology, development, signal transduction and translation, its up-regulation during ER stress has potentially important implications.

Regulation of human MC2-R gene expression by CREB, CREM, and ICER in the adrenocortical cell line Y1

The MC2-Receptor (melanocortin 2 receptor, MC2-R) is a Gs-protein coupled receptor that is upregulated by its own ligand ACTH and by forskolin. The mechanisms regulating MC2-R expression are still unclear. We therefore investigated the role of the stimulatory transcription factors CREB and CREM and the inhibitory factor ICER for regulation of human MC2-R expression. We cotransfected mouse adrenocortical Y1 cells with luciferase reporter gene vectors containing full length and deleted human MC2-R promoter constructs with expression plasmids for CREB, CREBS133A, CREMtau, CREMtauS117A, or ICER. Direct protein-DNA interaction was investigated by EMSA. Wild type CREB did not significantly affect promoter activity due to high endogenous CREB activity. However, CREBS133A decreased forskolin stimulated MC2-R promoter activity by 48+/-5% (mean+/-SEM) while unstimulated values remained unchanged. CREMtau moderately increased basal and forskolin stimulated luciferase activity in a dose-dependent manner (maximum effect 252+/-24% and 186+/-13% VS. control vector, respectively). While this effect required the full length promoter, cAMP stimulation was retained in shorter constructs. ICER reduced basal luciferase activity in Y1 cells by 17+/-28%, but completely abolished forskolin stimulation. Although 5'-deletion constructs mapped the minimum promoter region required for ICER effect to the shortest -64/+40 construct, direct protein DNA interaction in this promoter region could not be identified by EMSA. Moreover, mutation of the SF-1 binding sites, which retained ICER dependent inhibition, excluded SF-1 to be required for this effect. We conclude from these data that transcription factors of the CREB/CREM/ATF family have a moderate effect on human MC2-R promoter activity, but seem to play a minor role in transmitting stimulation of the cAMP pathway to increased MC2-R expression.

Calcineurin activity is required for depolarization-induced, CREB-dependent gene transcription in cortical neurons

Cyclic AMP response element binding protein (CREB) functions as an activity-dependent transcription factor in the nervous system. Increases in intracellular Ca(2+) due to neuronal activity lead to the phosphorylation and subsequent activation of CREB. Although phosphorylation of CREB at Ser-133 is necessary for the stimulation of transcriptional activity, it is not sufficient. Here we demonstrate that in mouse cortical neurons, inhibition of the Ca(2+)-dependent protein phosphatase calcineurin by FK506 or cyclosporine A blocks CREB-dependent gene expression induced by depolarization without inhibiting depolarization-induced Ca(2+) influx or CREB Ser-133 phosphorylation. Over-expression of a constitutively-active allele of the transducer of regulated CREB activity could not bypass the requirement for calcineurin activity. Stimulation of a CRE-luciferase reporter gene by depolarization was sensitive to FK506 throughout the entire time course of the transcriptional response, revealing that calcineurin activity is required to maintain CREB-dependent transcription. Stimulation of CRE-luciferase expression by forskolin and 8-Br-cAMP also required calcineurin activity. These results suggest that calcineurin functions as a critical determinant in shaping genome responses to CREB activation in cortical neurons.

PREGS induces LTP in the hippocampal dentate gyrus of adult rats via the tyrosine phosphorylation of NR2B coupled to ERK/CREB [corrected] signaling

An acute application of neurosteroid pregnenolone sulfate (PREGS) to hippocampal slices from adult rats induced a long-lasting potentiation (LLP PREGS) at the perforant path-granule cell synapse. As a partial mechanism of the LLP PREGS, we previously revealed that PREGS transiently increases the probability of presynaptic glutamate release via a sensitization of alpha7-nicotinic acetylcholine receptor (alpha7nAChR). We herein demonstrate that the LLP PREGS could be separated into two independent processes: the above-mentioned early presynaptic-origin short-term potentiation (STP PREGS) and a delayed postsynaptic N-methyl-d-aspartate receptor (NMDAr)-dependent long-term potentiation termed LTP(PREGS). This study focused on the analysis of the signaling mechanism underlying the LTP PREGS. PREGS increased the tyrosine phosphorylation of NR2B, a subunit of NMDAr, and the NMDAr-mediated Ca2+ influx in the granule cells. The enhanced Ca2+ influx was largely attenuated by the NR2B subunit inhibitor ifenprodil and the Src kinase family inhibitor PP2. PREGS also triggered a persistent phosphorylation of extracellular signal-regulated kinase 2 (ERK2) followed by an ERK-dependent phosphorylation of cAMP-response element-binding protein (CREB), which was crucial for the LTP PREGS induction and was sensitive to ifenprodil. These results suggest that PREGS induces an acute increase in the NR2B tyrosine phosphorylation which enhances the Ca2+ influx through NMDAr, followed by an activation of the ERK/CREB signaling cascade that leads to LTP PREGS.

Individual CREB-target genes dictate usage of distinct cAMP-responsive coactivation mechanisms

CREB is a key mediator of cAMP- and calcium-inducible transcription, where phosphorylation of serine 133 in its Kinase-Inducible Domain (KID) is often equated with transactivation. Phospho-Ser133 is required for CREB to bind the KIX domain of the coactivators CBP and p300 (CBP/p300) in vitro, although the importance of this archetype coactivator interaction for endogenous gene expression is unclear. Here, we show that the CREB interaction with KIX is necessary for only a part of cAMP-inducible transcription and CBP/p300 recruitment. Surprisingly, individual cAMP-inducible genes with CREB bound at their promoters differed in their reliance on KIX and none examined showed complete dependence. Alternatively, we found that arginine 314 (Arg314) in the CREB basic-leucine zipper (bZIP) domain contributed to CBP/p300 recruitment and KIX-independent CREB transactivation function. This implicates Transducer Of Regulated CREB (TORC), an unrelated cAMP-responsive coactivator that binds via Arg314, and which can bind CBP/p300, in these functions. Interestingly, KIX was also required for the full cAMP induction of a gene that did not require CREB. Thus, individual CREB-target gene context dictates the relative contribution of at least two different cAMP-responsive coactivation mechanisms.

CREB-regulated diurnal activity patterns are not indicative for depression-like symptoms in mice and men

Activation of the transcription factor CREB by Ser142 phosphorylation is implicated in synchronizing circadian rhythmicity, which is disturbed in many depressive patients. Hence, one could assume that emotional behaviour and neuroendocrinological markers would be altered in CREB(S142A) mice, in which serine 142 is replaced by alanine, preventing phosphorylation at this residue. Moreover, associations of CREB Ser142 and seasonal affective disorder (SAD) might be detectable by the analysis of single-nucleotide polymorphisms (SNPs) in the CREB gene close to the Ser142 residue in SAD patients. However, neither CREB(S142A) mice demonstrate features of depression, nor there is evidence for an association of SAD with the CREB genotypes. Nevertheless, in humans there is an association of a global seasonality score and circadian rhythmicity with the CREB genotypes in healthy control probands, but not SAD patients. This parallels the phenotype of CREB(S142A) mice, presenting alterations of circadian rhythm and light-induced entrainment. Thus it is reasonable to assume that CREB Ser142 represents a molecular switch in mice and men, which is responsible for the (dys)regulation of circadian rhythms.

TORC-SIK cascade regulates CREB activity through the basic leucine zipper domain

The transcription factor cAMP response element-binding protein (CREB) plays important roles in gene expression induced by cAMP signaling and is believed to be activated when its Ser133 is phosphorylated. However, the discovery of Ser133-independent activation by the activation of transducer of regulated CREB activity coactivators (TORC) and repression by salt inducible kinase cascades suggests that Ser133-independent regulation of CREB is also important. The activation and repression are mediated by the basic leucine zipper domain of CREB. In this review, we focus on the basic leucine zipper domain in the regulation of transcriptional activity of CREB and describe the functions of TORC and salt inducible kinase.

Transducer of regulated CREB and late phase long-term synaptic potentiation

In the central nervous system, long-term adaptive responses to changes in the environment, such as the processes involved in learning and memory, require the conversion of extracellular stimuli into intracellular signals. Many of these signals involve the induction of gene expression. The late, transcription- and translation-dependent phase of long-term synaptic potentiation (L-LTP) is an attractive cellular model for long-lasting memory formation. The transcription factor cAMP response element-binding protein (CREB) plays an essential role in the maintenance of L-LTP. However, how synaptic signals propagate to the nucleus to initiate CREB-target gene expression is unclear. Recent studies indicate that the CREB transducer of regulated CREB activity 1 coactivator undergoes neuronal activity-dependent translocation from the cytoplasm to the nucleus, a process required for CRE-dependent gene expression and the maintenance of L-LTP in the hippocampus.

CREB--a real culprit in oncogenesis

The cAMP response element-binding protein (CREB) is a stimulus-induced transcription factor that responds rapidly to phosphorylation and/or coactivator activation. Regulated activation of CREB has a significant impact on cellular growth, proliferation and survival. To overturn the cellular control of these processes, tumor cells have developed various mechanisms to achieve constitutive activation of CREB, including gene amplification, chromosome translocation, interaction with viral oncoproteins, and inactivation of tumor suppressor genes. These mechanisms converge on the phosphorylation of CREB and/or the activation of transducer of regulated CREB activity (TORC) coactivators to effect uncontrolled proliferation of cells. This minireview summarizes the different lines of existing evidence that support a direct role of CREB in oncogenesis.