Transcriptional regulation of CREB (cyclic AMP response element-binding protein) expression in CATH.a cells

Sex and the noradrenergic system

The central noradrenergic system comprises multiple brainstem nuclei whose cells synthesize and release the catecholamine transmitter norepinephrine (NE). The largest of these nuclei is the pontine locus coeruleus (LC), which innervates the vast majority of the forebrain. NE interacts with a number of pre- and postsynaptically expressed G protein-coupled receptors to affect a wide array of functions, including sensory signal processing, waking and arousal, stress responsiveness, mood, attention, and memory. Given the myriad functions ascribed to the locus coeruleus-noradrenergic (LC-NE) system, it is unsurprising that it is implicated in many disease states, including various mood, cognitive, neuropsychiatric, and neurodegenerative diseases. The LC-NE system is also notably sexually dimorphic with regard to its morphologic and anatomical features as well as how it responds to the peptide transmitter corticotropin releasing hormone (CRH), a major mediator of the central stress response. The sex-biased morphology and signaling that is observed in the LC could then be considered a potential contributor to the differential prevalence of various diseases between men and women. This chapter summarizes the primary differences between the male and female LC, based primarily on preclinical observations and how these disparities may relate to differential diagnoses of several diseases between men and women.

Sex-Specific Effects of Stress on Mood-Related Gene Expression

Women are twice as likely as men to be diagnosed with major depressive disorder (MDD). Recent studies report distinct molecular changes in depressed men and women across mesocorticolimbic brain regions. However, it is unclear which sex-related factors drive distinct MDD-associated pathology. The goal of this study was to use mouse experimental systems to investigate sex-specific mechanisms underlying the distinct molecular profiles of MDD in men and women. We used unpredictable chronic mild stress to induce an elevated anxiety-/depressive-like state and "four core genotypes" (FCG) mice to probe for sex-specific mechanisms. As predicted, based on previous implications in mood, stress impacted the expression of several dopamine-, GABA-, and glutamate-related genes. Some of these effects, specifically in the prefrontal cortex, were genetic sex-specific, with effects in XX mice but not in XY mice. Stress also impacted gene expression differently across the mesocorticolimbic circuit, with increased expression of mood-related genes in the prefrontal cortex and nucleus accumbens, but decreased expression in basolateral amygdala. Our results suggest that females are sensitive to the effects of chronic stress, partly due to their genetic sex, independent of gonadal hormones. Furthermore, these results point to the prefrontal cortex as the node in the mesocorticolimbic circuitry with the strongest female-specific effects.

Persistent Stress-Induced Neuroplastic Changes in the Locus Coeruleus/Norepinephrine System

Neural plasticity plays a critical role in mediating short- and long-term brain responses to environmental stimuli. A major effector of plasticity throughout many regions of the brain is stress. Activation of the locus coeruleus (LC) is a critical step in mediating the neuroendocrine and behavioral limbs of the stress response. During stressor exposure, activation of the hypothalamic-pituitary-adrenal axis promotes release of corticotropin-releasing factor in LC, where its signaling promotes a number of physiological and cellular changes. While the acute effects of stress on LC physiology have been described, its long-term effects are less clear. This review will describe how stress changes LC neuronal physiology, function, and morphology from a genetic, cellular, and neuronal circuitry/transmission perspective. Specifically, we describe morphological changes of LC neurons in response to stressful stimuli and signal transduction pathways underlying them. Also, we will review changes in excitatory glutamatergic synaptic transmission in LC neurons and possible stress-induced modifications of AMPA receptors. This review will also address stress-related behavioral adaptations and specific noradrenergic receptors responsible for them. Finally, we summarize the results of several human studies which suggest a link between stress, altered LC function, and pathogenesis of posttraumatic stress disorder.

NF-κB and CREB are required for angiotensin II type 1 receptor upregulation in neurons

Nuclear factor kappa B (NF-κB) and the Ets like gene-1 (Elk-1) are two transcription factors that have been previously established to contribute to the Angiotensin II mediated upregulation of Angiotensin II type 1 receptor (AT1R) in neurons. The cAMP response element binding protein (CREB) is another transcription factor that has also been implicated in AT1R gene transcription. The goal of the current study was to determine if NF-κB and CREB association was required for AT1R upregulation. We hypothesized that the transcription of the AT1R gene occurs via an orchestration of transcription factor interactions including NF-κB, CREB, and Elk-1. The synergistic role of CREB and NFκB in promoting AT1R gene expression was determined using siRNA-mediated silencing of CREB. Electrophorectic Mobility Shift Assay studies employing CREB and NF-κB demonstrated increased protein - DNA binding as a result of Ang II stimulation which was blunted by siRNA silencing of CREB. Upstream inhibition of p38 mitogen activated protein kinase (p38 MAPK) with SB203580 or inhibition of the calmodulin kinase (CAMK) pathway using KN-62 blunted changes in CREB and NF-κB expression. These findings suggest that Ang II may activate multiple signaling pathways involving p38 MAPK leading to the activation of NF-κB and CREB, which feed back to upregulate the AT1R gene. This study provides insight into the molecular mechanisms involving multiple transcription factor activation in a coordinated fashion which may be partially responsible for sympathoexcitation in clinical conditions associated with increased activation of the renin angiotensin system.

Alterations in phosphorylated CREB expression in different brain regions following short- and long-term morphine exposure: relationship to food intake

BACKGROUND

Activation of the cyclic adenosine monophosphate (cAMP)/phosphorylated CREB (P-CREB) system in different brain regions has been implicated in mediating opioid tolerance and dependence, while alteration of this system in the lateral hypothalamus (LH) has been suggested to have a role in food intake and body weight.

METHODS

Given that opioids regulate food intake, we measured P-CREB in different brain regions in mice exposed to morphine treatments designed to induce different degrees of tolerance and dependence.

RESULTS

We found that a single morphine injection or daily morphine injections for 8 days did not influence P-CREB levels, while the escalating dose of morphine regimen raised P-CREB levels only in the ventral tegmental area (VTA). Chronic morphine pellet implantation for 7 days raised P-CREB levels in the LH, VTA, and dorsomedial nucleus of the hypothalamus (DM) but not in the nucleus accumbens and amygdala. Increased P-CREB levels in LH, VTA, and DM following 7-day treatment with morphine pellets and increased P-CREB levels in the VTA following escalating doses of morphine were associated with decreased food intake and body weight.

CONCLUSION

The morphine regulation of P-CREB may explain some of the physiological sequelae of opioid exposure including altered food intake and body weight.

Effects of the A(-115)G variant on CREB1 promoter activity in two brain cell lines: Interactions with gonadal steroids

Major depressive disorder (MDD) is a leading contributor to disease burden worldwide. Previous genetic studies have revealed significant evidence of linkage of the CREB1 region to mood disorders among women from families with recurrent, early-onset MDD (RE-MDD), a severe and familial subtype of MDD. Systematic resequencing of the CREB1 gene in affected members of these families has identified rare sequence variants at positions -656 and -115 that appear to cosegregate with unipolar mood disorders in two large multigenerational families and three small nuclear families, respectively. Results from previous transfection experiments that employed constructs containing the wild-type or variant CREB1 promoters coupled to a reporter gene support the hypothesis that the A(-656) allele contributes to the development of MDD in women by selectively increasing the activity of the CREB1 promoter in brain cell lines exposed to 17 β-estradiol. Analogous transfection experiments described in the current study revealed that the G(-115) promoter variant reduced promoter activity in CATH.a neuronal cells regardless of the hormonal environment, consistent with the observation that increased risk for unipolar mood disorders conferred by this allele was not limited by sex. The effects of CREB1 promoter variants on promoter activity, their influence on the development of mood disorders and related clinical features, and the interaction of their phenotypic expression with sex seem likely to be complex and allele-specific rather than a general property of the CREB1 locus. © 2010 Wiley-Liss, Inc.

Effects of the G(-656)A variant on CREB1 promoter activity in a neuronal cell line: interactions with gonadal steroids and stress

Major depressive disorder (MDD) constitutes a major public health problem worldwide and affects women twice as frequently as men. Previous genetic studies have revealed significant evidence of linkage of the cAMP-responsive element-binding protein 1 (CREB1) gene region (2q33-35) to mood disorders among women from families with recurrent, early-onset MDD (RE-MDD), a severe and familial subtype of MDD. A rare G-to-A transition at position -656 in the CREB1 promoter co-segregates with mood disorders in women from these families, implicating CREB1 as a sex-related susceptibility gene for unipolar mood disorders. In the current study, the functional significance of the CREB1 promoter variant was determined using transfection experiments that employed plasmid constructs containing the wild-type or variant CREB1 promoters coupled to a reporter gene. The results support the hypothesis that the A(-656) allele contributes to the development of MDD in women through selective alteration of CREB1 promoter activity by female gonadal steroids in noradrenergic neuronal cells. Furthermore, exaggeration of these effects during a simulated stress condition may be relevant to reported gene-environment interactions that contribute to the emergence of MDD in clinical populations.

Effects of the G(-656)A variant on CREB1 promoter activity in a glial cell line: interactions with gonadal steroids and stress

Major depressive disorder (MDD) constitutes a major public health problem worldwide and affects women twice as frequently as men. Previous genetic studies have revealed significant evidence of linkage of the CREB1 region to mood disorders among women from families with recurrent, early-onset MDD (RE-MDD), a severe and familial subtype of MDD. A rare G to A transition at position -656 in the CREB1 promoter cosegregates with mood disorders in women from these families, implicating CREB1 as a sex-related susceptibility gene for unipolar mood disorders. In the current study, the functional significance of the CREB1 promoter variant was determined using transfection experiments that employed constructs containing the wild-type or variant CREB1 promoters coupled to a reporter gene. The results support the hypothesis that the A(-656) allele contributes to the development of MDD in women by selectively altering the activity of the CREB1 promoter in glial cells exposed to 17 beta-estradiol. Furthermore, the exaggeration of this effect during a simulated stress condition may be relevant to reported gene-environment interactions that contribute to the emergence of MDD in clinical populations. The results of in silico analysis revealed four putative binding sites for transcription factors that are affected by the G to A transition at position -656, of which CP2 best fit the experimental observations.

Opioid abuse and brain gene expression

Opiate addiction is a central nervous system disorder of unknown mechanism. Neuronal basis of positive reinforcement, which is essential to the action of opioids, relies on activation of dopaminergic neurons resulting in an increased dopamine release in the mesolimbic brain structures. Certain aspects of opioid dependence and withdrawal syndrome are also related to the activity of noradrenergic and serotonergic systems, as well as to both excitatory and inhibitory amino acid and peptidergic systems. The latter pathways have been recently proven to be involved both in the development of dependence and in counteracting the states related to relapse. An important role in neurochemical mechanisms of opioid reward, dependence and vulnerability to addiction has been ascribed to endogenous opioid peptides, particularly those acting via the mu- and kappa-opioid receptors. Opiate abuse leads to adaptive reactions in the nervous system which occur at the cellular and molecular levels. Recent research indicates that intracellular mechanisms of signal transmission-from the receptor, through G proteins, cyclic AMP, MAP kinases to transcription factors--also play an important role in opioid tolerance and dependence. The latter link in this chain of reactions may modify synthesis of target genes and in this manner, it may be responsible for opiate-induced long-lasting neural plasticity.

Transcriptional regulation of the CART promoter in CATH.a cells

Changes in Cocaine- and Amphetamine-Regulated Transcript (CART) mRNA levels have been observed in brain as a result of various physiologic stimuli including feeding, drugs of abuse, stress and glucocorticoids, and activators of the cyclic AMP (cAMP) and protein kinase A (PKA) pathway. Accordingly, we are interested in identifying factors involved in CART gene regulation. CATH.a cells, derived from the locus coeruleus (LC), express a 213-bp CART mRNA species that is translated and processed. The promoter activity of three CART-LUC constructs containing 3451, 641, and 102 bp of 5' upstream sequence, respectively, were tested in CATH.a cells. cAMP regulation was detected in the construct containing 641 bp of CART promoter sequence which contains a consensus CRE site. Mutation of the CRE site within -641CART-LUC significantly reduced basal and forskolin-induced promoter activity. Additionally, forskolin-induced transcription was inhibited by a dominant-negative mutant of CRE-binding protein (CREB) in CATH.a cells. Finally, tropin-releasing factor (CRF), an endogenously occurring activator of the cAMP/PKA pathway in CATH.a cells, was shown to increase transcriptional activity that was inhibited by a CRF receptor antagonist and a PKA inhibitor. This study provides evidence that the CRE site in the CART proximal promoter is involved in cAMP/PKA/CREB regulation in cells having a neuronal phenotype. Also, given the evidence for involvement of CREB in reward and reinforcement, these results are compatible with a role for CART in these processes as well.

Differential effects of opioid and adrenergic agonists on proliferation in a cultured cell line

A novel clonal cell line transfected with the delta-opioid receptor (delta-OR) encoding gene was used to study agonist-activated regulation of cell proliferation. In this cell line, endogenous beta2-adrenergic receptors (beta2-ARs) are coexpressed with the exogenous delta-ORs. Upon individual acute treatments with morphine and procaterol (a selective beta2-AR agonist), both the delta-OR and beta2-AR are coupled to differential modulation of cyclic AMP (cAMP) levels in accord with the classical second messenger response patterns to these agonists in the normal cellular settings of the receptors. But chronic morphine activation of the delta-OR inhibits cellular proliferation, while chronic procaterol activation of the beta2-AR stimulates it. Chronic treatment with the individual agonists is accompanied by differential activation of the mitogen-activated protein kinase (MAPK) isozymes, extracellular-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK). The findings suggest that chronic beta2-AR activation stimulates proliferation by interacting with the ERK signalling cascade independent of a cAMP-mediated pathway. In contrast to treatment with individual agonists, chronic dual agonist treatment suppresses procaterol-induced stimulation of ERK activity and stimulation of proliferation indicating that a cross-regulatory interaction occurs between the delta-OR and beta2-AR signalling systems in the cells under these conditions.

Acute delta-opioid receptor activation induces CREB phosphorylation in NG108-15 cells

A growing body of evidence supports an important role of the transcription factor cAMP responsive element binding protein (CREB) in mediating opioid-induced changes in the cAMP pathway. Regulation of CREB and subsequent changes in gene expression may underlie some long-term cellular adaptations associated with the administration of opioid drugs. The effect of morphine on the level of the transcription factor CREB, as well as CREB phosphorylation, was investigated in NG108-15 cells. Morphine and the delta-opioid receptor agonist [D-Pen(2,5)]enkephalin (DPDPE) produced a dose-dependent increase in CREB phosphorylation. The effect was reversed by naloxone and naltrindole, respectively. The calmodulin antagonist N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7), the protein kinase inhibitor staurosporine, as well as 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7), an inhibitor of protein kinase C and cAMP-dependent protein kinase, but not N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride (H-8), an inhibitor of cAMP- and cGMP-dependent protein kinase, blocked the opioid-induced CREB phosphorylation. The obtained results suggest that in the cells studied opioids affect, via the delta-opioid receptor, stimulatory intracellular mediator systems involving Ca(2+)/calmodulin and the protein kinase C pathway.

Identification and functional analysis of novel cAMP response element binding protein splice variants lacking the basic/leucine zipper domain

Two novel cAMP response element binding protein (CREB) splice variants were found by reverse transcription-polymerase chain reaction cloning by using mouse brain RNA as a template. One splice variant, named Delta-14, lacks 14 nucleotides at the beginning of exon 9 of the CREBDelta isoform. The other, named Delta-35, lacks 35 nucleotides at the beginning of exon 8 of CREBDelta. These nucleotide deletions cause frame shifts for codon usage, producing proteins which conserve the major phosphorylation site (Ser(133)) but lack the basic/leucine zipper domain, which is essential for binding to DNA and to other transcription factors. Both variants are widely expressed in peripheral tissues, but are enriched in brain, thymus, and testis. CREBDelta-14 and Delta-35 variant proteins were expressed by using an in vitro translation system and by transfecting into human embryonic kidney 293 cells. Both variants were detected by a CREB antibody that recognizes the CREBDelta amino terminus, but not by an antibody which recognizes the CREBDelta carboxy terminus, as would be predicted based on the frame shift. Activation of the cAMP pathway increased phospho-CREB immunoreactivity, indicating that these variants are substrates of cAMP-dependent protein kinase. In addition, immunocytochemical analysis demonstrated that CREBDelta-14 and Delta-35 are primarily cytosolic, whereas CREBalpha is predominantly in the nucleus. Finally, expression of CREBDelta-14 or Delta-35 decreased cAMP responsive element-chloramphenicol acetyltransferase reporter activity, demonstrating that both can function as repressors of endogenous CREB.

Critical role of cAMP response element binding protein expression in hypoxia-elicited induction of epithelial tumor necrosis factor-alpha

Tissue hypoxia is intimately associated with a number of chronic inflammatory conditions of the intestine. In this study, we investigated the impact of hypoxia on the expression of a panel of inflammatory mediators by intestinal epithelia. Initial experiments revealed that epithelial (T84 cell) exposure to ambient hypoxia evoked a time-dependent induction of the proinflammatory markers tumor necrosis factor-alpha (TNF-alpha), interleukin-8 (IL-8), and major histocompatibility complex (MHC) class II (37 +/- 6.1-, 7 +/- 0.8-, and 9 +/- 0.9-fold increase over normoxia, respectively, each p < 0.01). Since the gene regulatory elements for each of these molecules contains an NF-kappaB binding domain, we investigated the influence of hypoxia on NF-kappaB activation. Cellular hypoxia induced a time-dependent increase in nuclear p65, suggesting a dominant role for NF-kappaB in hypoxia-elicited induction of proinflammatory gene products. Further work, however, revealed that hypoxia does not influence epithelial intercellular adhesion molecule 1 (ICAM-1) or MHC class I, the promoters of which also contain NF-kappaB binding domains, suggesting differential responses to hypoxia. Importantly, the genes for TNF-alpha, IL-8, and MHC class II, but not ICAM-1 or MHC class I, contain cyclic AMP response element (CRE) consensus motifs. Thus, we examined the role of cAMP in the hypoxia-elicited phenotype. Hypoxia diminished CRE binding protein (CREB) expression. In parallel, T84 cell cAMP was diminished by hypoxia (83 +/- 13.2% decrease, p < 0.001), and pharmacologic inhibition of protein kinase A induced TNF-alpha and protein release (9 +/- 3.9-fold increase). Addback of cAMP resulted in reversal of hypoxia-elicited TNF-alpha release (86 +/- 3.2% inhibition with 3 mM 8-bromo-cAMP). Furthermore, overexpression of CREB but not mutated CREB by retroviral-mediated gene transfer reversed hypoxia-elicited induction of TNF-alpha defining a causal relationship between hypoxia-elicited CREB reduction and TNF-alpha induction. Such data indicate a prominent role for CREB in the hypoxia-elicited epithelial phenotype and implicate intracellular cAMP as an important second messenger in differential induction of proinflammatory mediators.

Cyclical alternative exon splicing of transcription factor cyclic adenosine monophosphate response element-binding protein (CREB) messenger ribonucleic acid during rat spermatogenesis

During spermatogenesis, the levels of cAMP in seminiferous tubules undergo stage-dependent cyclical fluctuations. We show that changes in cAMP levels are accompanied by alternative exon splicing of the RNA encoding the cAMP-responsive transcription factor CREB (cAMP response element-binding protein), expressed in both the Sertoli and germ cells. Exons Y and W are expressed exclusively in the testis, and they introduce stop codons into the normal protein coding frame of CREB. The splicing in of W was shown earlier to activate the internal translation of two alternative products of the CREB messenger RNA (mRNA) containing the DNA-binding domain (I-CREBs). The I-CREBs act as potent inhibitors of activator isoforms of CREB. The functions of the alternatively spliced exon Y are unknown. To investigate whether the splicing of exons W and Y is regulated during spermatogenesis, seminiferous tubules, isolated from adult rats, were dissected into segments representing different stages of the spermatogenic cycle and were analyzed by RT-PCR. The analyses of pooled-tubule segments revealed stage-dependent splicing of both exons W and Y in the CREB transcripts. Single tubules were dissected into smaller segments for greater staging accuracy and were analyzed by RT-PCR for CREB mRNAs containing either exons W or Y, as well as for FSH receptor mRNA. This analysis confirmed that a marked, cycle-dependent variation in CREB mRNA levels was occurring. Maximal splicing of exons W and Y occurs independently at different stages of the spermatogenic cycle, stages II-VI and IX, respectively. The distinct spermatogenic cycle-dependent regulation of the splicing of exons W and Y provides further evidence in support of a functional relevance for CREB-W and Y mRNA isoforms in spermatogenesis.

CREB (cAMP response element-binding protein) in the locus coeruleus: biochemical, physiological, and behavioral evidence for a role in opiate dependence

Chronic morphine administration increases levels of adenylyl cyclase and cAMP-dependent protein kinase (PKA) activity in the locus coeruleus (LC), which contributes to the severalfold activation of LC neurons that occurs during opiate withdrawal. A role for the transcription factor cAMP response element-binding protein (CREB) in mediating the opiate-induced upregulation of the cAMP pathway has been suggested, but direct evidence is lacking. In the present study, we first demonstrated that the morphine-induced increases in adenylyl cyclase and PKA activity in the LC are associated with selective increases in levels of immunoreactivity of types I and VIII adenylyl cyclase and of the catalytic and type II regulatory subunits of PKA. We next used antisense oligonucleotides directed against CREB to study the role of this transcription factor in mediating these effects. Infusion (5 d) of CREB antisense oligonucleotide directly into the LC significantly reduced levels of CREB immunoreactivity. This effect was sequence-specific and not associated with detectable toxicity. CREB antisense oligonucleotide infusions completely blocked the morphine-induced upregulation of type VIII adenylyl cyclase but not of PKA. The infusions also blocked the morphine-induced upregulation of tyrosine hydroxylase but not of Gialpha, two other proteins induced in the LC by chronic morphine treatment. Electrophysiological studies revealed that intra-LC antisense oligonucleotide infusions completely prevented the morphine-induced increase in spontaneous firing rates of LC neurons in brain slices. This blockade was completely reversed by addition of 8-bromo-cAMP (which activates PKA) but not by addition of forskolin (which activates adenylyl cyclase). Intra-LC infusions of CREB antisense oligonucleotide also reduced the development of physical dependence to opiates, based on attenuation of opiate withdrawal. Together, these findings provide the first direct evidence that CREB mediates the morphine-induced upregulation of specific components of the cAMP pathway in the LC that contribute to physical opiate dependence.