A cluster of phosphorylation sites on the cyclic AMP-regulated nuclear factor CREB predicted by its sequence

The role of CREB in depression and antidepressant treatment

Major depressive disorder is a severe clinical problem across the globe, with a lifetime risk of 10%-30% for women and 7%-15% for men. The World Health Organization ranks major depression at the top of the list in terms of disease burden, and this burden is expected to rise in the next decade as the prevalence of the disorder grows. Since the late 1950s, a wide range of antidepressant medications targeting the monoamine systems has been available to alleviate the symptoms of major depressive disorder. Although widely prescribed, such antidepressant medications are accompanied by a delay in effectiveness, as well as varied side effects. Therefore, further characterization of the biological mechanisms behind their function is crucial for the development of new and more effective treatments. One protein that could serve as a convergence point for multiple classes of antidepressant drugs is the transcription factor CREB (cyclic adenosine monophosphate response element binding protein). CREB is upregulated by chronic antidepressant treatment, and increasing CREB levels in rodent models results in antidepressant-like behaviors. Furthermore, postmortem studies indicate that CREB levels are increased in subjects taking antidepressants at the time of death. However, not all antidepressants increase CREB levels and/or activity, and reducing CREB levels in some brain regions also results in antidepressant-like behaviors. This review attempts to consolidate the information relevant to the structure and function of the CREB protein and describe how this relates to the mechanism of antidepressant drugs. Animal models in which CREB function is enhanced, by overexpression of the protein, or reduced, by expression of mutant forms of the protein or through gene deletion experiments, are summarized in terms of identifying a role for CREB in behavioral responses in depression tests that were originally designed to evaluate antidepressant efficacy. Human postmortem and genetic studies that implicate CREB in depression and antidepressant efficacy are also discussed.

Changes in accumbal and pallidal pCREB and deltaFosB in morphine-sensitized rats: correlations with receptor-evoked electrophysiological measures in the ventral pallidum

Activation of mu-opioid receptors in the ventral pallidum (VP) is important for the induction of behavioral sensitization to morphine in rats. The present study was designed to ascertain if neurons within the VP demonstrate sensitization at a time when morphine-induced behavioral sensitization occurred (ie 3 or 14 days after five once-daily injections of 10 mg/kg i.p. morphine) in rats. Western blotting was used to evaluate transcription factors altered by opiates, CREB and deltaFosB. CREB levels did not change in the VP, but there was a significant decrease in levels of its active, phosphorylated form (pCREB) at both 3- and 14-days withdrawal. DeltaFosB levels were elevated following a 3-day withdrawal, but returned to normal by 14 days. This profile also was obtained from nucleus accumbens tissue. In a separate group of similarly treated rats, in vivo electrophysiological recordings of VP neuronal responses to microiontophoretically applied ligands were carried out after 14-days withdrawal. The firing rate effects of local applications of morphine were diminished in rats withdrawn from i.p. morphine. Repeated i.p. morphine did not alter GABA-mediated suppression of firing, or the rate enhancing effects of the D1 dopamine receptor agonist SKF82958 or glutamate. However, VP neurons from rats withdrawn from repeated i.p. morphine showed a higher propensity to enter a state of depolarization inactivation to locally applied glutamate. Overall, these findings reveal that decreased pCREB in brain regions such as the VP accompanies persistent behavioral sensitization to morphine and that this biochemical alteration may influence the excitability of neurons in this brain region.

Glucagon-like peptide-1 inhibits LPS-induced IL-1beta production in cultured rat astrocytes

Glia play an important role in neurotoxicity in neurodegenerative diseases. In this study, we investigated the expression of glucagon-like peptide-1 (GLP-1) and its receptor, and the effects of GLP-1 on lipopolysaccharide (LPS)-induced IL-1beta mRNA expression and IL-1beta production in glia. GLP-1-like immunoreactivity was observed in amoeboid microglia, but not ramified microglia or astrocytes. GLP-1 binding and GLP-1 receptor mRNA expression were observed in both astrocytes and microglia. GLP-1-induced morphological changes in microglia from the ramified type to the amoeboid type, suggesting an increase in production and release of endogenous GLP-1. GLP-1 prevented the LPS-induced IL-1beta mRNA expression, which effect was, in turn, inhibited by pretreatment with SQ22536, an adenylate cyclase inhibitor. GLP-1 also increased cAMP concentration and cAMP response element-binding protein phosphorylation in astrocytes. These results suggest that GLP-1 may be a modulator of inflammation in the central nervous system.

Estrogen induces estrogen receptor alpha-dependent cAMP response element-binding protein phosphorylation via mitogen activated protein kinase pathway in basal forebrain cholinergic neurons in vivo

In addition to classical genomic mechanisms, estrogen also exerts nonclassical effects via a signal transduction system on neurons. To study whether estrogen has a nonclassical effect on basal forebrain cholinergic system, we measured the intensity of cAMP response element-binding protein (CREB) phosphorylation (pCREB) in cholinergic neurons after administration of 17beta-estradiol to ovariectomized (OVX) mice. A significant time-dependent increase in the number of pCREB-positive cholinergic cells was detected after estrogen administration in the medial septum-diagonal band (MS-DB) and the substantia innominata (SI). The increase was first observed 15 min after estrogen administration. The role of classical estrogen receptors (ERs) was evaluated using ER knock-out mice in vivo. The estrogen-induced CREB phosphorylation in cholinergic neurons was present in ERbeta knock-out mice but completely absent in ERalpha knock-out mice in MS-DB and SI. A series of in vitro studies demonstrated that estrogen acted directly on cholinergic neurons. Selective blockade of the mitogen activated protein kinase (MAPK) pathway in vivo completely prevented estrogen-induced CREB phosphorylation in cholinergic neurons in MS-DB and SI. In contrast, blockade of protein kinase A (PKA) was effective only in SI. Finally, studies in intact female mice revealed levels of CREB phosphorylation within cholinergic neurons that were similar to those of estrogen-treated OVX mice. These observations demonstrate an ERalpha-mediated nonclassical effect of estrogen on the cholinergic neurons and that these actions are present under physiological conditions. They also reveal the role of MAPK and PKA-MAPK pathway activation in nonclassical estrogen signaling in the basal forebrain cholinergic neurons in vivo.

Dual inhibition of protein phosphatase-1/2A and calpain rescues nerve growth factor-differentiated PC12 cells from oxygen-glucose deprivation-induced cell death

In the present study, we examined how the cell survival signaling via cyclic AMP-responsive element binding protein (CREB) and Akt, and the cell death signaling via cystein proteases, calpain and caspase-3, are involved in oxygen-glucose deprivation (OGD) followed by reoxygenation (OGD/reoxygenation)-induced cell death in nerve growth factor (NGF)-differentiated PC12 cells. OGD/reoxygenation-induced cell death was evaluated by LDH release into the culture medium. The level of LDH release was low (9.0% +/- 4.1%) immediately after 4 hr of OGD (0 hr of reoxygenation), was significantly increased to 28.6% +/- 6.6% at 3 hr of reoxygenation, and remained at similar levels at 6 and 20 hr of reoxygenation, suggesting that reoxygenation at least for 3 hr resulted in the loss of cell membrane integrity. After 4 hr of OGD followed by 3 hr of reoxygenation, dephosphorylation of phosphorylated CREB (pCREB), but not phosphorylated Akt (pAkt), was induced. Under these conditions, calpain- but not caspase-3-mediated alpha-spectrin breakdown product was increased, indicating that OGD/reoxygenation also induced an increase in calpain activity. The restoration of pCREB by protein phosphatase (PP)-1/2A inhibitors or the inhibition of excessive activation of calpain by calpain inhibitor did not reduce OGD/reoxygenation-induced LDH release. Cotreatment with PP-1/2A and calpain inhibitors reduced OGD/reoxygenation-induced LDH release. The present study suggests that a balance in the phosphorylation and proteolytic signaling is involved in the survival of NGF-differentiated PC12 cells.

Novel role of sphingosine kinase 1 as a mediator of neurotrophin-3 action in oligodendrocyte progenitors

We had found previously that neurotrophin-3 (NT-3) is a potent stimulator of cAMP-response element binding protein (CREB) phosphorylation in cultured oligodendrocyte progenitors. Here, we show that CREB phosphorylation in these cells is also highly stimulated by sphingosine-1-phosphate (S1P), a sphingolipid metabolite that is known to be a potent mediator of numerous biological processes. Moreover, CREB phosphorylation in response to NT-3 involves sphingosine kinase 1 (SphK1), the enzyme that synthesizes S1P. Immunocytochemistry and confocal microscopy indicated that NT-3 induces translocation of SphK1 from the cytoplasm to the plasma membrane of oligodendrocytes, a process accompanied by increased SphK1 activity in the membrane fraction where its substrate sphingosine resides. To examine the involvement of SphK1 in NT-3 function, SphK1 expression was down-regulated by treatment with SphK1 sequence-specific small interfering RNA. Remarkably, the capacity of NT-3 to protect oligodendrocyte progenitors from apoptotic cell death induced by growth factor deprivation was abolished by down-regulating the expression of SphK1, as assessed by terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay. Altogether, these results suggest that SphK1 plays a crucial role in the stimulation of oligodendrocyte progenitor survival by NT-3, and demonstrate a functional link between NT-3 and S1P signaling, adding to the complexity of mechanisms that modulate neurotrophin function and oligodendrocyte development.

Switching of NR5A proteins associated with the inhibin alpha-subunit gene promoter after activation of the gene in granulosa cells

The inhibin alpha-subunit gene is transcriptionally activated by FSH in ovarian granulosa cells during follicular growth. We have investigated the roles of the NR5A family nuclear receptors steroidogenic factor 1 (SF-1) and liver receptor homolog 1 (LRH-1) in transcriptional activation of the inhibin alpha-subunit gene. Transfection assays using an inhibin alpha-subunit promoter reporter in GRMO2 granulosa cells show that LRH-1 and SF-1 act similarly to increase promoter activity, and that the activity of both transcription factors is augmented by the coactivators cAMP response element-binding protein-binding protein and steroid receptor coactivator 1. However, chromatin immunoprecipitation experiments illustrate differential dynamic association of LRH-1 and SF-1 with the alpha-subunit inhibin promoter in both primary cells and the GRMO2 granulosa cell line such that hormonal stimulation of transcription results in an apparent replacement of SF-1 with LRH-1. Transcriptional stimulation of the inhibin alpha-subunit gene is dependent on MAPK kinase activity, as is the dynamic association/disassociation of SF-1 and LRH-1 with the promoter. Inhibition of the phosphatidylinositol 3-kinase signaling pathway influences promoter occupancy and transcriptional activation by SF-1 but not LRH-1, suggesting a possible mechanistic basis for the distinct functions of these NR5A proteins in inhibin alpha-subunit gene regulation.

Reciprocal interaction of serotonin and neuronal activity in regulation of cAMP-responsive element-dependent gene expression

Neuronal activity triggers multiple signal transduction pathways and potently regulates gene expression in the brain. In the central nervous system, in addition to the synaptic input, neurons are subject to neuromodulatory influences that can activate the same signaling elements. However, the principles that govern the interaction of neuromodulators and neuronal activity in the regulation of gene expression are unclear. Here, we examine how serotonergic neuromodulation interacts with neuronal activity in the regulation of gene expression in hippocampal neurons. We show that cAMP-response element binding protein (CREB) phosphorylation and gene expression were stimulated by serotonin (5-HT) in the absence of neuronal activity. In contrast, in the presence of neuronal activity, 5-HT inhibited gene expression down to the baseline, although neuronal activity alone was sufficient to maximally activate gene expression. The ability of 5-HT to stimulate CREB phosphorylation in the absence of neuronal activity or inhibit CREB phosphorylation during activity was due to a tight balance between protein kinases and phosphatases that could be physiologically tilted by different serotonergic receptors or exogenously influenced by phosphatase and kinase inhibitors. Taken together, these results suggest a reciprocal inhibitory interaction between neuronal activity and 5-HT in the regulation of cAMP response element-dependent gene expression in hippocampal neurons.

Involvement of cAMP-response element binding protein-1 in arachidonic acid-induced vascular smooth muscle cell motility

In addition to their role in many vital cellular functions, arachidonic acid (AA) and its eicosanoid metabolites are involved in the pathogenesis of several diseases, including atherosclerosis and cancer. To understand the potential mechanisms by which these lipid molecules could influence the disease processes, particularly cardiovascular diseases, we studied AA's effects on vascular smooth muscle cell (VSMC) motility and the role of cAMP-response element binding protein-1 (CREB-1) in this process. AA exerted differential effects on VSMC motility; at lower doses, it stimulated motility, whereas at higher doses, it was inhibitory. AA-induced VSMC motility requires its conversion via the lipoxygenase (LOX) and cyclooxygenase (COX) pathways. AA stimulated the phosphorylation of extracellular signal-regulated kinases (ERKs), Jun N-terminal kinases (JNKs), and p38 mitogen-activated protein kinase (p38MAPK) in a time-dependent manner, and blockade of these serine/threonine kinases significantly attenuated AA-induced VSMC motility. In addition, AA stimulated CREB-1 phosphorylation and activity in a manner that was also dependent on its metabolic conversion via the LOX and COX pathways and the activation of ERKs and p38MAPK but not JNKs. Furthermore, suppression of CREB-1 activation inhibited AA-induced VSMC motility. 15(S)-Hydroxyeicosatetraenoic acid and prostaglandin F2alpha, the 15-LOX and COX metabolites of AA, respectively, that are produced by VSMC at lower doses, were also found to stimulate motility in these cells. Together, these results suggest that AA induces VSMC motility by complex mechanisms involving its metabolism via the LOX and COX pathways as well as the ERK- and p38MAPK-dependent and JNK-independent activation of CREB-1.

IGF-II induces CREB phosphorylation and cell survival in human lung cancer cells

We have previously shown that lung tumors arising in MMTV-IGF-II transgenic mice displayed elevated levels of phosphorylated cAMP response element binding protein (CREB). To investigate the role that insulin-like growth factor II (IGF-II) and CREB play in human lung tumorigenesis, A549 and NCI-H358 cells were examined. In these cell lines, IGF-II administration enhances human tumor cell survival and CREB phosphorylation. Further, the effects of IGF-II on cell survival and CREB phosphorylation appeared to be mediated, at least in part, by activation of the Erk pathways, as inhibition of these signaling pathways reduced tumor cell survival and CREB phosphorylation. Specifically, Erk5 appeared as the predominant mediator of CREB phosporylation. To further verify the importance of CREB in human lung tumorigenesis, A549 and NCI-H358 cells were stably transfected with a vector containing a dominant negative CREB construct (KCREB). KCREB transfection significantly inhibited the soft agar growth of both human tumor cell lines. In contrast, overexpression of wild-type CREB in the normal human bronchial epithelial cell line, HBE135, enhanced soft agar growth. Therefore, our results indicate that CREB and its associated proteins play a significant role in lung adenocarcinoma and IGF-II induces CREB phosphorylation, at least in part, via the Erk5 signaling pathway.

Nonclassical action of retinoic acid on the activation of the cAMP response element-binding protein in normal human bronchial epithelial cells

Vitamin A (retinol) is essential for normal regulation of cell growth and differentiation. We have shown that the retinol metabolite retinoic acid (RA) induces mucous cell differentiation of normal human tracheobronchial epithelial (NHTBE) cells. However, early biological effects of RA in the differentiation of bronchial epithelia are largely unknown. Here, we showed that RA rapidly activated cAMP response element-binding protein (CREB). However, RA did not use the conventional retinoic acid receptor (RAR)/retinoid X receptor (RXR) to activate CREB. RA activated CREB in NHTBE and H1734 cells in which RARs/RXR were silenced with small interfering RNA (siRNA) targeting RAR/RXR expression or deactivated by antagonist. Inhibition of protein kinase C (PKC) or extracellular regulated kinase (ERK1/2) blocked the RA-mediated activation of CREB. In addition, depletion of p90 ribosomal S6 kinase (RSK) via siRSK1/2 completely abolished the activation, suggesting that PKC, ERK, and RSK are required for the activation. Altogether, this study provides the first evidence that RA rapidly activates CREB transcription factor via PKC, ERK, and RSK in a retinoid receptor-independent manner in normal bronchial epithelial cells. This noncanonical RA signaling pathway may play an important role in mediating early biological effects in the mucociliary differentiation of bronchial epithelia.

Excitation-transcription coupling in smooth muscle

Calcium (Ca2+) signals affect virtually every biological process, including both contraction and gene transcription in smooth muscle. Ca2+-regulated gene transcription is known to be important for both physiological and pathological responses in smooth muscle. The aim of this review is to discuss the current understanding of gene transcription regulated by excitation through Ca2+ signalling using a comparison of the two most characterized Ca2+-regulated transcription factors in smooth muscle, Ca2+-cyclic AMP response element binding protein (CREB) and nuclear factor of activated T-cells (NFAT). Recent studies have shown commonalities and differences in the regulation of CREB and NFAT through both voltage- and non-voltage-gated Ca2+ channels that lead to expression of smooth muscle cell specific differentiation markers as well as markers of proliferation. New insights into the regulation of specific genes through companion elements on the promoters of Ca2+-regulated genes have led to new models for transcriptional regulation by Ca2+ that are defined both by the source and duration of the Ca2+ signal and the composition of enhancer elements found within the regulatory regions of specific genes. Thus the combination of signalling pathways elicited by particular Ca2+ signals affect selective promoter elements that are key to the ultimate pattern of gene transcription.

Oxidant-mediated cAMP response element binding protein activation: calcium regulation and role in apoptosis of lung epithelial cells

Oxidant stress-mediated regulation of extracellular signal-regulated kinases (ERK1/2) is linked to pathologic outcomes in lung epithelium, yet a role for Ca2+ and Ca2+/cAMP-response element binding protein (CREB) in ERK1/2 signaling has not been defined. In this study, we tested the hypotheses that oxidants induce Ca2+-mediated phosphorylation of ERK and CREB, and that CREB is required for oxidant-induced proliferation and apoptosis. H2O2 initiated an influx of extracellular Ca2+ that was required for phosphorylation of both ERK and CREB in C10 lung epithelial cells. H2O2-mediated CREB phosphorylation was sensitive to MEK inhibition, suggesting that crosstalk between Ca2+, ERK, and CREB signaling pathways contributes to the oxidant-induced response. Reduction of CREB activity, using a dominant-negative CREB construct, inhibited c-fos steady-state mRNA levels, but unexpectedly enhanced bcl-2 steady-state mRNA levels after H2O2 exposure. Whereas inhibition of CREB activity had no detectable effect on H2O2 stimulation of cell cycle, loss of CREB activity significantly reduced the number of cells undergoing apoptosis. These data support a novel communication between Ca2+-ERK1/2 and CREB elicited by H2O2, and further provide evidence that CREB is an important regulator of apoptosis in oxidant-mediated responses of lung epithelial cells.

Differentiation of immature oligodendrocytes is regulated by phosphorylation of cyclic AMP-response element binding protein by a protein kinase C signaling cascade

Previous experiments showed that the expression and phosphorylation levels of cyclic AMP-response element binding protein (CREB) are important factors that regulate oligodendrocyte differentiation. The present study was designed to determine whether CREB phosphorylation advances oligodendrocyte differentiation or vice versa and to identify the protein kinase that primarily regulates CREB phosphorylation. We examined the expression and phosphorylation levels of CREB in developing oligodendrocytes at a specific differentiation stage by double-immunocytochemical staining with specific differentiation markers and antibody for phosphorylated CREB. We found that the CREB expression level increased along oligodendrocyte differentiation, and that its phosphorylated level was highest in immature oligodendrocytes. We also showed that CREB phosphorylation was regulated principally by protein kinase C (PKC) activity in immature oligodendrocytes. Our findings suggest that CREB phosphorylation is dependent on a PKC signaling cascade, and this phosphorylation activates CREB-mediated transcription and advances the differentiation of immature to mature oligodendrocytes.

Glial cell line-derived neurotrophic factor-induced signaling in Schwann cells

Glial cell line-derived neurotrophic factor (GDNF), a known survival factor for neurons, has recently been shown to stimulate the migration of Schwann cells (SCs) and to enhance myelination. GDNF exerts its biological effects by activating the Ret tyrosine kinase in the presence of glycosylphosphatidylinositol-linked receptor, GDNF family receptor (GFR) alpha1. In Ret-negative cells, the alternative transmembrane coreceptor is the 140-kDa isoform of neural cell adhesion molecule (NCAM) associated with a non-receptor tyrosine kinase Fyn. We confirmed that GDNF, GFRalpha1 and NCAM are expressed in neonatal rat SCs. We found that GDNF induces an increase in the partitioning of NCAM and heparan sulfate proteoglycan agrin into lipid rafts and that heparinase inhibits GDNF-signaling in SCs. In addition to activation of extracellular signal-regulated kinases, and phosphorylation of cAMP response element binding protein, we found that cAMP-dependent protein kinase A and protein kinase C are involved in GDNF-mediated signaling in SCs. Although GDNF did not promote the differentiation of purified SCs into the myelinating phenotype, it enhanced myelination in neuron-SC cocultures. We conclude that GDNF utilizes NCAM signaling pathways to regulate SC function prior to myelination and at early stages of myelin formation.

17beta-estradiol induces Ca2+ influx, dendritic and nuclear Ca2+ rise and subsequent cyclic AMP response element-binding protein activation in hippocampal neurons: a potential initiation mechanism for estrogen neurotrophism

Previous studies from our laboratory have shown that 17beta-estradiol (E2) promotes neurite outgrowth in hippocampal and cortical neurons. The neurotrophic effect of E2 seen in vitro has also been observed in vivo by other investigators who found that E2 enhances the density of dendritic spines involved in neuronal synaptic connection. To investigate the rapid upstream mechanisms initiating the E2 neurotrophic effect, we tested the hypothesis that E2 would directly activate Ca2+ influx in primary hippocampal neurons, which would result in activation of the transcription factor, cyclic AMP response element-binding protein (CREB), and regulate E2 enhancement of neurite outgrowth. Using fura-2 ratiometric and fluo-3 Ca2+ imaging, we demonstrated that E2 induced a significant rise in intracellular Ca2+ concentration ([Ca2+]i) through E2-induced Ca2+ influx. Interestingly, the rise in [Ca2+]i occurred not only in the cytoplasm, but also in the nucleus and dendrites of hippocampal neurons. Since CREB is activated by Ca2+-dependent kinases and is required for certain aspects of synaptic plasticity, we investigated whether E2 would lead to activation of CREB. Western immunoblotting and immunocytochemical analyses revealed that E2 induced rapid CREB activation consistent with rapid intracellular Ca2+ signaling, which was dependent on the influx of extracellular Ca2+. E2-induced increase in dendritic spine marker protein spinophilin was abolished following treatment with a small interfering RNA against CREB, indicating that E2-induced neurotrophic effect requires the upstream CREB activation. Results of these analyses indicate that E2-induced neurotrophic responses are mediated by a Ca2+ signaling cascade that is dependent upon extracellular Ca2+ and CREB activation. These data provide insights into the initiating mechanisms required to activate the estrogen neurotrophic response and provide a mechanistic framework for determining the neurotrophic efficacy of existing and emerging estrogen therapies for the brain.

Par-4 Links Dopamine Signaling and Depression

Prostate apoptosis response 4 (Par-4) is a leucine zipper containing protein that plays a role in apoptosis. Although Par-4 is expressed in neurons, its physiological role in the nervous system is unknown. Here we identify Par-4 as a regulatory component in dopamine signaling. Par-4 directly interacts with the dopamine D2 receptor (D2DR) via the calmodulin binding motif in the third cytoplasmic loop. Calmodulin can effectively compete with Par-4 binding in a Ca2+-dependent manner, providing a route for Ca2+-mediated downregulation of D2DR efficacy. To examine the importance of the Par-4/D2DR interaction in dopamine signaling in vivo, we used a mutant mouse lacking the D2DR interaction domain of Par-4, Par-4DeltaLZ. Primary neurons from Par-4DeltaLZ embryos exhibit an enhanced dopamine-cAMP-CREB signaling pathway, indicating an impairment in dopamine signaling in these cells. Remarkably, Par-4DeltaLZ mice display significantly increased depression-like behaviors. Collectively, these results provide evidence that Par-4 constitutes a molecular link between impaired dopamine signaling and depression.

A prostacyclin analog prevents radiocontrast nephropathy via phosphorylation of cyclic AMP response element binding protein

We reported previously that radiocontrast medium induces caspase-dependent apoptosis and that cAMP analogs inhibit cell injury in cultured renal tubular cells. In the present study, cellular mechanisms underlying the protective effects of cAMP were determined. Ioversol, a radiocontrast medium, caused cell injury accompanied by decreases in Bcl-2, increases in Bax, and caspase activation in LLC-PK1 cells. Both cell injury and cellular events induced by ioversol were inhibited by dibutyryl cAMP and the prostacyclin analog beraprost. Dibutyryl cAMP increased phosphorylation of Akt and CREB, both of which were reversed by H89, wortmannin and the Akt inhibitor SH-6. The protective effect of dibutyryl cAMP was also reversed by these kinase inhibitors. In dominant-negative CREB-transfected cells, dibutyryl cAMP no longer prevented cell injury or inhibited changes in mRNA expression of Bcl-2 and Bax. In mice with unilateral renal occlusion, ioversol increased urinary excretion of N-acetyl-beta-d-glucosaminidase with concomitant decreases in Bcl-2 mRNA, increases in Bax mRNA, activation of caspase-3, and induction of apoptosis in tubular and interstitial cells. Beraprost completely reversed these in vivo effects of ioversol. These findings suggest that elevation of endogenous cAMP effectively prevents radiocontrast nephropathy through activation of A kinase/PI 3-kinase/Akt followed by CREB phosphorylation and enhanced expression of Bcl-2.

Thromboxane A receptor-mediated cell proliferation, survival and gene expression in oligodendrocytes

Thromboxane A(2) receptors (TP) were previously localized to discrete regions in the rat brain on myelinated fiber tracts and oligodendrocytes (OLGs). The present studies extended these findings and investigated the effects of TP signaling on cell proliferation, survival, and gene expression in OLG progenitor cells (OPCs) and OLGs. It was found that the TP agonist, U46619 stimulated the proliferation of OPCs and promoted the survival of mature OLGs. Examination of the early gene expression events involved in OPC proliferation, revealed that c-fos expression was substantially increased by U46619 stimulation. Treatment of OPCs or OLGs with U46619 caused activation of the mitogen-activated protein kinases (MAPK) ERK 1/2. In OPCs this activation was blocked by inhibition of src. However, in OLGs this phosphorylation was not only blocked by inhibition of src but also by inhibition of protein kinase C (PKC). Furthermore, U46619 was found to increase CREB phosphorylation in both OPCs and OLGs. Similar to ERK 1/2 activation, there was a divergence in the mechanism of the TP-mediated CREB response for each cell type. Specifically, U46619 activation was attenuated by src and protein kinase A (PKA) inhibition in OPCs, whereas in OLGs this effect was blocked by inhibition of src, PKA as well as by inhibition of PKC. Collectively, these results provide the first demonstration that TP-activated nuclear signaling events are involved in the proliferation of OPCs, the survival of mature OLGs, and the stimulation of gene expression.

Repression of the inhibin alpha-subunit gene by the transcription factor CCAAT/enhancer-binding protein-beta

Inhibin is a dimeric peptide hormone produced in ovarian granulosa cells that suppresses FSH synthesis and secretion in the pituitary. Expression of inhibin alpha- and beta-subunit genes in the rodent ovary is positively regulated by FSH and negatively regulated after the preovulatory LH surge. We have investigated the role of the transcription factor CCAAT/enhancer-binding protein-beta (C/EBPbeta) in repressing the inhibin alpha-subunit gene. C/EBPbeta knockout mice fail to appropriately down-regulate inhibin alpha-subunit mRNA levels after treatment with human chorionic gonadotropin, indicating that C/EBPbeta may function to repress inhibin gene expression. The expression and regulation of C/EBPbeta were examined in rodent ovary, and these studies show that C/EBPbeta is expressed in ovary and granulosa cells and is induced in response to human chorionic gonadotropin. Transient cotransfections with an inhibin promoter-luciferase reporter in a mouse granulosa cell line, GRMO2 cells, show that C/EBPbeta is capable of repressing both basal and forskolin-stimulated inhibin gene promoter activities. An upstream binding site for C/EBPbeta in the inhibin alpha-subunit promoter was identified by electrophoretic mobility shift assays, which, when mutated, results in elevated inhibin promoter activity. However, C/EBPbeta also represses shorter promoter constructs lacking this site, and this component of repression is dependent on the more proximal promoter cAMP response element (CRE). Electrophoretic mobility shift assays show that C/EBPbeta effectively competes with CRE-binding protein for binding to this atypical CRE. Thus, there are two distinct mechanisms by which C/EBPbeta represses inhibin alpha-subunit gene expression in ovarian granulosa cells.

Functional role of a novel ternary complex comprising SRF and CREB in expression of Krox-20 in early embryos of Xenopus laevis

Krox-20, originally identified as a member of "immediate-early" genes, plays a crucial role in the formation of two specific segments in the hindbrain during early development of the vertebrate nervous system. Here we cloned a genomic sequence of Xenopus Krox-20 (XKrox-20) and studied functions of a promoter element in the flanking sequence and associated transcription factors, which function in early Xenopus embryos. Using the luciferase reporter assay system, we showed that the 5' flanking sequence was sufficient to induce luciferase activities when the reporter construct was injected into embryos at the eight-cell stage. Deletion and mutagenesis analyses of the 5' flanking sequence revealed a minimal promoter element that included two known subelements, a CArG-box and cAMP response element (CRE) within a stretch of 22 bp nucleotide sequence (-72 to -51 from the transcription initiation site), both of which were essential for the promoter activity. The gel mobility shift assay indicated that these two subelements bound to some components in whole cell extracts prepared from stage 20 Xenopus embryos. Antibody supershift and competition experiments revealed that these components in cell extracts were serum response factor (SRF) and a member of CRE binding protein (CREB) family proteins that bound the CArG-box and CRE, respectively. They appeared to assemble on the minimal promoter element to produce a novel ternary complex. When we injected mRNA of a dominant-negative version of Xenopus SRF (XSRFDeltaC) into animal pole blastomeres at the eight-cell stage, expression of XKrox-20 in the nervous system as well as the minimal promoter activity was strongly suppressed. Suppression by XSRFDeltaC was counteracted by coexpressed wild-type XSRF. These results indicate that XSRF functions as an endogenous activator of XKrox-20 by forming a ternary complex with CREB on the minimal promoter element.

Apotransferrin induces cAMP/CREB pathway and cell cycle exit in immature oligodendroglial cells

We have demonstrated previously that a single intracranial injection of apotransferrin (aTf) in neonatal rats increases myelination and accelerates differentiation of oligodendroglial cells (OLGc). In addition, we have shown through in vitro experiments that OLGc isolated from 4-day-old rats (OLGc-4) treated with aTf were more differentiated than were controls although aTf had no effect upon OLGc isolated from 10-day-old animals (OLGc-10). In the present work, we analyzed the role of second messengers in the effect of aTf upon the maturation of OLGc at different stages of development. We isolated OLGc-4 and OLGc-10 from rat brain using a Percoll density gradient and briefly treated the cells with a pulse of aTf or kept them in culture during 2 days in the presence or absence of aTf. In OLGc-4, after a short pulse of aTf, there was an increase in the levels of cyclic AMP (cAMP), in the phosphorylation of cAMP response element-binding protein (CREB) and in the DNA-binding capacity of cAMP-responsive transcription factors. Treatment of OLGc-4 with aTf diminished bromodeoxyuridine (BrdU) incorporation and changed levels of p27 and cyclin D1. This glycoprotein seemed to act on OLGc through the cAMP pathway only at early stages of development and on a certain sensitive cell population, accelerating their differentiation, probably as a consequence of premature withdrawal from the cell cycle.

N-methyl-D-aspartate induces phosphorylation of cAMP response element (CRE)-binding protein and increases DNA-binding activity of CRE in rat retina

The aim of this study was to investigate whether an excitotoxic concentration of N-methyl-D-aspartate (NMDA) increases the expression of the phosphorylated cAMP response element-binding protein (p-CREB) and the DNA-binding activity of the cAMP response element (CRE) in rat retina. Intravitreal injection of NMDA was performed in adult male Wistar rats. p-CREB protein levels in the retina were examined by Western blot analysis. DNA-binding activity of CRE in the retina was evaluated by an electrophoretic mobility gel shift assay (EMSA). We confirmed that NMDA induced the reduction of ganglion cells and the inner plexiform layer of the retina. Western blot analysis showed increases in the expression of p-CREB in the retina 12 and 24 h after intravitreal NMDA injection and dimer formation of CREB in the nuclear fraction at 24 h. Increases of DNA-binding activity were observed in the retina 24 h after NMDA injection by EMSA. Our results suggest that phosphorylation of CREB may involved in NMDA-induced excitotoxicity in rat retina. Phosphorylated CREB seems to be the active form and the one that is transcribed.

PGE2 inhibits chondrocyte differentiation through PKA and PKC signaling

Prostaglandins are ubiquitous metabolites of arachidonic acid, and cyclooxygenase inhibitors prevent their production and secretion. Animals with loss of cyclooxygenase-2 function have reduced reparative bone formation, but the role of prostaglandins during endochondral bone formation is not defined. The role of PGE2 as a regulator of chondrocyte differentiation in chick growth plate chondrocytes (GPCs) was examined. While PGE2, PGD2, PGF2alpha, and PGJ2 all inhibited colX expression, approximately 80% at 10(-6) M, PGE2 was the most potent activator of cAMP response element (CRE)-mediated transcription. PGE2 dose-dependently inhibited the expression of the differentiation-related genes, colX, VEGF, MMP-13, and alkaline phosphatase gene, and enzyme activity with significant effects at concentrations as low as 10(-10) M. PGE2 induced cyclic AMP response element binding protein (CREB) phosphorylation and increased c-Fos protein levels by 5 min, and activated transcription at CRE-Luc, AP-1-Luc, and c-Fos promoter constructs. The protein kinase A (PKA) inhibitor, H-89, completely blocked PGE2-mediated induction of CRE-Luc and c-Fos promoter-Luc promoters, and partially inhibited induction of AP-1-Luc, while the protein kinase C (PKC) inhibitor Go-6976 partially inhibited all three promoters, demonstrating substantial cross-talk between these signaling pathways. PGE2 inhibition of colX gene expression was dependent upon both PKA and PKC signaling. These observations demonstrate potent prostaglandin regulatory effects on chondrocyte maturation and show a role for both PKA and PKC signaling in PGE2 regulatory events.

Fad24, a mammalian homolog of Noc3p, is a positive regulator in adipocyte differentiation

Adipocyte differentiation is controlled by complex actions involving gene expression and signal transduction. From metaphase to anaphase, peroxisome proliferator-activated receptor γ, the CCAAT/enhancer-binding protein family and sterol regulatory element-binding protein-1 are known to function as master regulators. However, the mechanism underlying the earliest step, which triggers the initiation of differentiation, remains unknown. In previous reports, we have isolated a number of genes, whose expression increases in the early stage of differentiation in the mouse 3T3-L1 preadipocyte cell line. Here we report the cloning of the full-length cDNA and characterization of an unknown gene isolated previously and named fad24 (factor for adipocyte differentiation 24). Fad24 encodes a protein consisting of 807 amino acids. The deduced amino acid sequence was shown to have a basic leucine zipper motif and a NOC domain. Expression of fad24 was rapidly induced after stimulation with inducers. Furthermore, overexpression of fad24 in NIH-3T3 cells promoted adipogenesis in the presence of a ligand for peroxisome proliferator-activated receptor γ. FAD24 localizes in the nucleus, especially within nuclear speckles. As the nuclear speckle functions as a nascent transcription and pre-mRNA splicing machinery, there is a possibility that FAD24 functions as one of the components for transcription and/or pre-mRNA splicing and positively regulates adipocyte differentiation.

What turns CREB on?

The transactivation domain of the cAMP response element-binding protein (CREB) consists of two major domains. The glutamine-rich Q2 domain, which interacts with the general transcription factor TAFII130/135, is sufficient for the recruitment of a functional RNA polymerase II complex and allows basal transcriptional activity. The kinase-inducible domain, however, mediates signal-induced activation of CREB-mediated transcription. It is generally believed that recruitment of the coactivators CREB-binding protein (CBP) and p300 after signal-induced phosphorylation of this domain at serine-133 strongly enhances CREB-dependent transcription. Transcriptional activity of CREB can also be potentiated by phosphoserine-133-independent mechanisms, and not all stimuli that provoke phosphorylation of serine-133 stimulate CREB-dependent transcription. This review presents an overview of the diversity of stimuli that induce CREB phosphorylation at Ser-133, focuses on phosphoserine-133-dependent and -independent mechanisms that affect CREB-mediated transcription, and discusses different models that may explain the discrepancy between CREB Ser-133 phosphorylation and activation of CREB-mediated transcription.

Characterization of adrenomedullin in non-human primates

Adrenomedullin (AM) is a 52 amino acid peptide involved in the pathophysiology of several human diseases. Here we show the gene structure, organ distribution, and regulated expression of AM in monkey. The monkey AM (mAM) gene is located on the short arm of chromosome 9 and it codes for a 185 amino acid preprohormone, which contains two amidated peptides identical to the human AM and proadrenomedullin N-terminal 20 peptide. The promoter region of the mAM gene contains a variety of transcription factor binding motifs. mAM is widely expressed throughout many organs as shown by real-time PCR and immunohistochemical techniques, and we have found similar levels of circulating plasma AM in monkeys and humans. A significant upregulation of the mAM mRNA was observed in monkey cells exposed to low oxygen tension conditions, TGF-beta1, all-trans-retinoic acid, and dexamethasone. Our collective data show a high degree of homology between mAM and hAM, which renders the monkey an attractive animal model for future pharmacological and pre-clinical studies targeting AM.

Cell-type-specific binding of the transcription factor CREB to the cAMP-response element

The cAMP-response element-binding protein (CREB) transcription factor was initially identified as a mediator of cAMP-induced gene expression. CREB binds to a target sequence termed the cAMP-response element (CRE) found in many cellular and viral gene promoters. One of the best-characterized CREs resides in the promoter of the gene encoding the neuropeptide somatostatin, and this element has served as a model for studies of CREB function. Phosphorylation of CREB by protein kinase A allows recruitment of the coactivator CREB-binding protein (CBP). A central tenet of the CREB-CBP model is that CREB binds constitutively to the CRE and that regulation occurs through the phosphorylation-dependent recruitment of CBP. In this report, we use chromatin immunoprecipitation assays to show that CREB does not interact in vivo with the somatostatin CRE, or similar elements in several other genes, in PC12 cells, a standard model for studies of CREB function. Rather, CREB binding in vivo is regulated in a cell-specific manner, a finding that was confirmed by using in vivo genomic footprinting assays. The CREs in other genes were also found to interact differentially with CREB in PC12 cells, hepatoma cells, and cortical neurons. We conclude that the family of CREB target genes differs from one cell type to another and that the ability of CREB to bind to a particular CRE represents an important component of gene regulation.

A-kinase anchoring protein targeting of protein kinase A in the heart

There is increasing evidence that subcellular targeting of signaling molecules is an important means of regulating the protein kinase A (PKA) pathway. Subcellular organization of the signaling molecules in the PKA pathway insures that a signal initiated at the receptor level is transferred efficiently to a PKA substrate eliciting some cellular response. This subcellular targeting appears to regulate the function of a highly specialized cell such as the cardiac myocyte. This review focuses on A-kinase anchoring proteins (AKAPs) which are expressed in the heart. It has been determined that, of the approximately 13 different AKAPs expressed in cardiac tissue, several of these are expressed in cardiac myocytes. These AKAPs bind several PKA substrates and some appear to regulate PKA-dependent phosphorylation of these substrates. AKAP tethering of PKA may be essential for efficient regulation of cardiac muscle contraction. The ability of an AKAP to anchor PKA may be altered in the failing heart, thus compromising the ability of the myocyte to respond to stimuli which elicit the PKA pathway.

Isoforms of cyclic AMP response element binding proteins in Drosophila S2 cells

Activation or inhibition of the cyclic AMP (cAMP)-protein kinase A (PKA) pathway can ultimately regulate the transcription of a variety of genes. In vertebrates, the best characterized nuclear targets of PKA are the 'cAMP response element' (CRE) binding proteins (CREB). Differences in the transcriptional response to this pathway between cells and tissues can be based on the presence of distinct CREB isoforms. In this context, we have now investigated the presence of different dCREB transcripts in a stable, embryonic insect cell line, i.e., Drosophila Schneider 2 (S2) cells. In addition, we have studied the possible effect of cellular cAMP- and Ca2+ increases on the expression of a luciferase reporter in cells transfected with a CRE-containing reporter gene construct. In combination with recent data from the literature, our results indicate that the regulation of CRE-dependent gene expression shows some important differences between insects and vertebrates.

Decreased expression of brain cAMP response element-binding protein gene following pentylenetetrazol seizure

The present study investigated whether the expression of the cAMP response element-binding protein (CREB) in the rat brain is altered following an acute self-limited seizure induced by pentylenetetrazol (PTZ). Male rats were injected intraperitoneally with a single convulsive dose (45 mg/kg) of PTZ, and the matched controls were given saline. For immunohistochemistry, animals were perfused with 4% parafomaldehyde at 24 h following PTZ seizures, and CREB immunoreactivity was examined in rat brain. For real-time RT-PCR, animals were sacrificed at 2 and 24 h and 1 week following PTZ seizures. Tissues from different rat brain regions were micropunched and subjected to real-time RT-PCR using Taqman probe. The CREB immunoreactive profiles were significantly decreased in CA3 and dentate gyrus of hippocampal formation, sensory cerebral cortex and thalamus at 24 h after PTZ seizures. Consistent with changes in CREB immunoreactivity, levels of CREB mRNA were significantly decreased in the hippocampus, cerebral cortex, amygdala and thalamus at 24 h after PTZ seizures. No significant change was found for CREB mRNA expression in these regions at 2 h or 1 week following PTZ seizures. These results show that a brief seizure caused a decline in CREB expression up to 24 h later.

Interleukin-10 Induced Activating Transcription Factor 3 Transcriptional Suppression of Matrix Metalloproteinase-2 Gene Expression in Human Prostate CPTX-1532 Cells

Aberrant expression of the 72-kDa type IV collagenase [matrix metalloproteinase (MMP)-2] is implicated in the invasion and angiogenesis process of malignant tumors. We investigated the effects of interleukin (IL)-10 on MMP-2 expression in CPTX-1532 human prostate tumor cells. Our results demonstrate that IL-10 significantly inhibited MMP-2 transcription and protein expression induced by a phorbol ester, phorbol 12-myristate 13-acetate. The inhibitory effects of IL-10 on MMP-2 expression correlated with the suppression of MMP-2 promoter activity. To determine the mechanism of IL-10 action, we examined IL-10–dependent promoter activity with luciferase constructs from a 2-kbp promoter region of the human MMP-2 gene. We functionally characterized the promoter fragments by transient transfection experiments with CPTX-1532 cells. The experiments revealed that a cAMP responsive element binding protein (CREB) consensus domain was identified upstream of the 5′ transcriptional start site, which was highly responsive to IL-10–dependent down-regulation of promoter luciferase activity. Electrophoretic mobility shift assays combined with antibody “supershift assays” confirmed the data from the luciferase assays. Immunoblot assays of activating transcription factor (ATF) 3 immunoprecipitates with tyrosine specific antibodies revealed that IL-10 stimulated tyrosine phosphorylation of ATF3 to activate binding to the CREB domain and suppress MMP-2 expression. Studies with stable, IL-10 transfected CPTX-1532 subclones further showed that IL-10 failed to suppress MMP-2 expression in ATF3-deficient CPTX-1532 cells, where the ATF3 mRNA was destroyed with a DNAzyme oligonucleotide targeting the 5′ region of the mRNA. Finally, reconstitution of ATF3 successfully restored the inhibitory effects of IL-10 on MMP-2 gene expression. Taken together, these data demonstrate the critical role of tyrosine phosphorylated ATF3 and the CREB consensus domain in IL-10 suppression of MMP-2 gene expression in primary human prostate tumor cells.

Overexpression of inducible cyclic AMP early repressor inhibits transactivation of genes and cell proliferation in pancreatic beta cells

Transcriptional control mediated by the cyclic AMP-responsive element (CRE) represents an important mechanism of gene regulation. To test our hypothesis that increased inducible cyclic AMP early repressor (ICER) Igamma inhibits function of CRE-binding proteins and thus disrupts CRE-mediated transcription in pancreatic beta cells, we generated transgenic mice with beta-cell-directed expression of ICER Igamma, a powerful repressor that is greatly increased in diabetes. Three transgenic lines clearly show that increased ICER Igamma expression in beta cells results in early severe diabetes. From birth islets were severely disorganized with a significantly increased proportion of alpha cells throughout the islet. Diabetes results from the combined effects of impaired insulin expression and a decreased number of beta cells. The decrease in beta cells appears to result from impaired proliferation rather than from increased apoptosis after birth. Cyclin A gene expression is impaired by the strong inhibition of ICER; the suppression of cyclin A results in a substantially decreased proliferation of beta cells in the postnatal period. These results suggest that CRE and CRE-binding factors have an important role in pancreatic beta-cell physiology not only directly by regulation of gene trans-activation but also indirectly by regulation of beta-cell mass.

Orchestration of synaptic plasticity through AKAP signaling complexes

Significant progress has been made toward understanding the mechanisms by which organisms learn from experiences and how those experiences are translated into memories. Advances in molecular, electrophysiological and genetic technologies have permitted great strides in identifying biochemical and structural changes that occur at synapses during processes that are thought to underlie learning and memory. Cellular events that generate the second messenger cyclic AMP (cAMP) and activate protein kinase A (PKA) have been linked to synaptic plasticity and long-term memory. In this review we will focus on the role of PKA in synaptic plasticity and discuss how the compartmentalization of PKA through its association with A-Kinase Anchoring Proteins (AKAPs) affect PKA function in this process.

A novel retinoic acid-responsive element regulates retinoic acid-induced BLR1 expression

The mechanism of action of retinoic acid (RA) is of broad relevance to cell and developmental biology, nutrition, and cancer chemotherapy. RA is known to induce expression of the Burkitt's lymphoma receptor 1 (BLR1) gene which propels RA-induced cell cycle arrest and differentiation of HL-60 human myeloblastic leukemia cells, motivating the present analysis of transcriptional regulation of blr1 expression by RA. The RA-treated HL-60 cells used here expressed all RA receptor (RAR) and retinoid X receptor (RXR) subtypes (as detected by Northern analysis) except RXRgamma. Treatment with RAR- and RXR-selective ligands showed that RARalpha synergized with RXRalpha to transcriptionally activate blr1 expression. A 5'-flanking region capable of supporting RA-induced blr1 activation in HL-60 cells was found to contain a 205-bp sequence in the distal portion that was necessary for transcriptional activation by RA. Within this sequence DNase I footprinting revealed that RA induced binding of a nuclear protein complex to an element containing two GT boxes. Electromobility shift assays (EMSAs) and supershift assays showed that this element bound recombinant RARalpha and RXRalpha. Without RA there was neither complex binding nor transcriptional activation. Both GT boxes were needed for binding the complex, and mutation of either GT box caused the loss of transcriptional activation by RA. The ability of this cis-acting RAR-RXR binding element to activate transcription in response to RA also depended on downstream sequences where an octamer transcription factor 1 (Oct1) site and a nuclear factor of activated T cells (NFATc) site between this element and the transcriptional start, as well as a cyclic AMP response element binding factor (CREB) site between the transcriptional start and first exon of the blr1 gene, were necessary. Each of these sites bound its corresponding transcription factor. A transcription factor-transcription factor binding array analysis of nuclear lysate from RA-treated cells indicated several prominent RARalpha binding partners; among these, Oct1, NFATc3, and CREB2 were identified by competition EMSA and supershift and chromatin immunoprecipitation assays as components of the complex. RA upregulated expression of these three factors. In sum the results of the present study indicate that RA-induced expression of blr1 expression depends on a novel RA response element. This cis-acting element approximately 1 kb upstream of the transcriptional start consists of two GT boxes that bind RAR and RXR in a nuclear protein complex that also contains Oct1, NFATc3, and CREB2 bound to their cognate downstream consensus binding sites.

Store-operated Ca2+ entry activates the CREB transcription factor in vascular smooth muscle

Ca2+-regulated gene transcription is a critical component of arterial responses to injury, hypertension, and tumor-stimulated angiogenesis. The Ca2+/cAMP response element binding protein (CREB), a transcription factor that regulates expression of many genes, is activated by Ca2+-induced phosphorylation. Multiple Ca2+ entry pathways may contribute to CREB activation in vascular smooth muscle including voltage-dependent Ca2+ channels and store-operated Ca2+ entry (SOCE). To investigate a role for SOCE in CREB activation, we measured CREB phosphorylation using immunofluorescence, intracellular Ca2+ levels using a fluorescence resonance energy transfer (FRET)-based Cameleon indicator, and c-fos transcription using RT-PCR. In this study, we report that SOCE activates CREB in both cultured smooth muscle cells and intact arteries. Depletion of intracellular Ca2+ stores with thapsigargin increased nuclear phospho-CREB levels, intracellular Ca2+ concentration, and transcription of c-fos. These effects were abolished by inhibiting SOCE through lowering extracellular Ca2+ concentration or by application of 2-aminoethoxydiphenylborate and Ni2+. Inhibition of Ca2+ influx through voltage-dependent Ca2+ channels using nimodipine partially blocked intact artery responses, but was without effect in cultured smooth muscle cells. Our findings indicate that Ca2+ entry through store-operated Ca2+ channels leads to CREB activation, suggesting that SOCE contributes to the regulation of gene expression in vascular smooth muscle.

CREB Cooperates with BMP-stimulated Smad signaling to enhance transcription of the Smad6 promoter

Growth plate chondrocytes integrate a multitude of growth factor signals during maturation. PTHrP inhibits maturation through stimulation of PKA/CREB signaling while the bone morphogenetic proteins (BMPs) stimulate maturation through Smad mediated signaling. In this manuscript, we show that interactions between CREB and the BMP associated Smads are promoter specific, and demonstrate for the first time the requirement of CREB signaling for Smad mediated activation of a BMP responsive region of the Smad6 promoter. The 28 base pairs (bp) BMP responsive element of the Smad6 promoter contains an 11 bp Smad binding region and an adjacent 17 bp region in which we characterize a putative CRE site. PKA/CREB gain of function enhanced BMP stimulation of this reporter, while loss of CREB function diminished transcriptional activity. In contrast, ATF-2 and AP-1 transcription factors had minimal effects. Electrophoretic mobility shift assay (EMSA) confirmed CREB binding to the Smad6 promoter element. Mutations eliminating binding resulted in loss of transcriptional activity, while mutations that maintained CREB binding had continued reporter activation by CREB and BMP-2. The Smad6 gene was similarly regulated by CREB. Dominant negative CREB reduced BMP-2 stimulated Smad6 gene transcription by 50%, but markedly increased BMP-2 mediated stimulation of colX and Ihh expression. In contrast, PTHrP which activates CREB signaling, blocked the stimulatory effect of BMP-2 on colX and Ihh, but minimally inhibited the stimulatory effect of BMP on Smad6. These findings are the first to demonstrate a cooperative association between CREB and BMP regulated Smads in cells from vertebrates and demonstrate that promoter-specific rather than generalized interactions between PKA/CREB and BMP signaling regulate gene expression in chondrocytes.

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Cyclic AMP and tumor necrosis factor-alpha regulate CXCR4 gene expression in Schwann cells

Rat peripheral nerve Schwann cells have been shown to express the alpha-chemokine receptor CXCR4 as well as the corresponding ligand stromal cell-derived factor-1 (SDF-1). We have investigated gene regulatory mechanisms acting on the expression of CXCR4 in cultured rat Schwann cells and found that receptor expression at transcript- and protein levels is directly dependent on intracellular cyclic AMP. Such increased levels of CXCR4 expression were found to be efficiently reversed by the action of tumor necrosis factor-alpha (TNFalpha). We also provide evidence that the POU box transcription factor Oct-6/SCIP is involved in the control of CXCR4 transcription. Finally, we could demonstrate that CXCR4 activation by SDF-1alpha increases the number of dying Schwann cells, indicating that this receptor/ligand interaction is modulating cell survival. Our data, therefore, suggest that in the Schwann cell lineage signal transduction cascades controlled by the activation of TNF- and CXCR4 receptors are functionally coupled.

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Phosphorylation of conserved casein kinase sites regulates cAMP-response element-binding protein DNA binding in Drosophila

The Drosophila homolog of cAMP-response element-binding protein (CREB), dCREB2, exists with serine 231, equivalent to mammalian serine 133, in a predominantly phosphorylated state. Thus, unlike the mammalian protein, the primary regulation of dCREB2 may occur at a different step from serine 231 phosphorylation. Although bacterially expressed dCREB2 bound cAMP-response element sites, protein from Drosophila extracts was unable to do so unless treated with phosphatase. Phosphorylation of recombinant protein by casein kinase (CK) I or II, but not calcium-calmodulin kinase II or protein kinase A, inhibited DNA binding. Up to four conserved CK sites likely to be phosphorylated in vivo were responsible for this effect, and these sites were phosphorylated by a kinase present in Drosophila cell extracts that biochemically resembles CKII. We propose that the relative importance of different signaling pathways in regulating CREB activity may differ between Drosophila and mammals. In Drosophila, the dephosphorylation of CK sites appears to be the major regulatory step, while phosphorylation of serine 231 is necessary but secondary.

Neonatal alcohol exposure induces long-lasting impairment of visual cortical plasticity in ferrets

Fetal alcohol syndrome is a major cause of learning and sensory deficits. These disabilities may result from disruption of neocortex development and plasticity. Alcohol exposure during the third trimester equivalent of human gestation may have especially severe and long-lasting consequences on learning and sensory processing, because this is when the functional properties and connectivity of neocortical neurons start to develop. To address this issue, we used the monocular deprivation model of neural plasticity, which shares many common mechanisms with learning. Ferrets were exposed to ethanol (3.5 mg/kg, i.p.) on alternate days for 3 weeks starting on postnatal day (P) 10. Animals were then monocularly deprived at the peak of ocular dominance plasticity after a prolonged alcohol-free period (15-20 d). Quantitative single-unit electrophysiology revealed that alcohol exposure disrupted ocular dominance plasticity while preserving robust visual responses. Moreover, optical imaging of intrinsic signals revealed that the reduction in visual cortex area driven by the deprived eye was much less pronounced in ethanol-treated than in control animals. Alcohol exposure starting at a later age (P20) did not disrupt ocular dominance plasticity, indicating that timing of exposure is crucial for the effects on visual plasticity. In conclusion, alcohol exposure during a brief period of development impairs ocular dominance plasticity at a later age. This model provides a novel approach to investigate the consequences of fetal alcohol exposure and should contribute to elucidate how alcohol disrupts neural plasticity.

Transcriptional Control in Male Germ Cells: General Factor TFIIA Participates in CREM-Dependent Gene Activation

Regulation of gene expression in haploid male germ cells follows a number of specific rules that differ from somatic cells. In this physiological context, transcriptional control mediated by the activator CREM (cAMP-responsive element modulator) represents an established paradigm. In somatic cells activation by CREM requires its phosphorylation at a unique regulatory site (Ser117) and subsequent interaction with the ubiquitous coactivator CBP (cAMP response element binding protein-binding protein). In testis, CREM transcriptional activity is controlled through interaction with a tissue-specific partner, ACT (activator of CREM in testis), which confers a powerful, phosphorylation-independent activation capacity. In addition to specialized transcription factors and coactivators, a variety of general factors of the basal transcriptional machinery, and their distinct tissue-specific isoforms, are highly expressed in testis, supporting the general notion that testis-specific gene expression requires specialized mechanisms. Here, we describe that CREM interacts with transcription factor IIA (TFIIA), a general transcription factor that stimulates RNA polymerase II-directed transcription. This association was identified by a two-hybrid screen, using a testis-derived cDNA library, and confirmed by coimmunoprecipitation. The interaction is restricted to the activator isoforms of CREM and does not require Ser117. Importantly, CREM does not interact with TFIIAtau-ALF, a testis-specific TFIIA homolog. CREM and TFIIA are expressed in a spatially and temporally coordinated fashion during the differentiation program of germ cells. The two proteins also colocalize intracellularly in spermatocyte and spermatid cells. These findings contribute to the understanding of the highly specialized rules of transcriptional regulation in haploid germ cells.

Expression of steroidogenic acute regulatory protein (StAR) and LH receptor in MA-10 cells

LH stimulation is mediated by its own receptor at the first step of the cascade, after which intracellular cAMP increases to stimulate the transcription of steroidogenic acute regulatory protein (StAR) in mouse MA-10 Leydig tumor cells. StAR mediates the rate-limiting step of steroidogenesis, which is the transfer of cholesterol to the inner mitochondrial membrane. Northern blot analysis consistently revealed two major transcripts, of about 3.6 kb and 1.6 kb, that hybridized with rat StAR mRNA. In this culture, treatment with hCG led StAR mRNA levels to rapidly and strongly increase by 3 h. Parallel increases were observed in transcripts of both sizes. Compared to StAR mRNA expression, LH receptor mRNA levels gradually decreased and declined to 50% of control values between 6 and 12 h incubation. Compared to the control, StAR mRNA levels increased and LH receptor mRNA levels decreased in a dose-dependent manner in the presence of increasing concentrations of hCG (3-100 ng/ml) and of increasing concentrations of 8-Br-cAMP (0.2-2 mM) after 4 h incubation. Since the over production of steroid hormones might be toxic to the own cells, the LH signal transduction that stimulates steroidogenesis might concomitantly decrease the responsiveness of steroidogenesis to LH stimulation at the receptor level. This result should be further investigated to clarify the mechanism of LH receptor regulation and steroidogenesis.

Differential distribution of CREB in the mesolimbic dopamine reward pathway

The transcription factor cAMP response element binding protein (CREB) has been implicated in the long-term neuronal plasticity associated with addiction. While CREB is expressed in many cells throughout the brain, very little is known about the relative concentrations of CREB protein in various brain regions. Studies in which CREB levels have been altered, either constitutively throughout the brain via gene targeting or transiently in specific brain regions, demonstrate variable roles for this protein in mediating reinforcing properties of drugs of abuse. To investigate the complex nature of CREB function in addiction, we examined the distribution of CREB protein in the nucleus accumbens (NAc) and ventral tegmental area (VTA), two brain regions that are part of the well-defined mesolimbic dopamine pathway involved in reward processing. Our data demonstrate significantly more CRE binding activity and CREB protein in the NAc compared to levels present in the VTA of wild-type mice. Phospho-CREB levels are increased in the NAc of both wild-type and CREBalphaDelta mutant animals after cocaine. However, morphine-induced increases of phospho-CREB levels are seen in the VTA of wild-type mice but not CREBalphaDelta mutant mice. Consequently, the 90% reduction of CREB in CREBalphaDelta mutant mice differentially affects CREB phosphorylation and induction of downstream targets of CREB in the NAc and VTA.

Pharmacogenomic analysis of mechanisms mediating ethanol regulation of dopamine beta-hydroxylase

We previously showed that ethanol regulates dopamine beta-hydroxylase (DBH) mRNA and protein levels in human neuroblastoma cells (Thibault, C., Lai, C., Wilke, N., Duong, B., Olive, M. F., Rahman, S., Dong, H., Hodge, C. W., Lockhart, D. J., and Miles, M. F. (2000) Mol. Pharmacol. 58, 1593-1600). DBH catalyzes norepinephrine synthesis, and several studies have suggested a role for norepinephrine in ethanol-mediated behaviors. Here, we performed a detailed analysis of mechanism(s) underlying ethanol regulation of DBH expression in SH-SY5Y cells. Transient transfection analysis showed that ethanol (25-200 mM) caused concentration- and time-dependent increases in DBH gene transcription. Progressive deletions identified ethanol-responsive sequences in the -262 to -142 bp region of the DBH gene promoter. Mutagenesis of cAMP-response element (CRE) sequences in this region abolished ethanol responsiveness while maintaining responsiveness to phorbol esters. Coexpression of dominant-negative CRE-binding protein greatly reduced ethanol induction of DBH. Inhibitors of protein kinase A, casein kinase II, and MAPK reduced ethanol induction of DBH promoter activity. Pharmacogenomic studies with microarrays showed that protein kinase A, MEK, and casein kinase II inhibitors blocked induction of DBH and a large subset of ethanol-responsive genes. These genes had diverse functional groupings, including multiple members of the MAPK and phosphatidylinositol signaling cascades. Real-time PCR analysis validated select microarray results. Taken together, these results suggest that ethanol regulation of DBH requires a functional CRE and its binding protein and may require interaction of multiple kinase pathways. This mechanism may also mediate ethanol responsiveness of a complex subset of genes in neural cells. These studies may have implications for behavioral responses to ethanol or mechanisms underlying ethanol-related neurological disease.

Cyclic AMP response element-binding protein mediates reactive oxygen species-induced c-fos expression

Although the cyclic AMP response element-binding protein (CREB) plays an important role in the survival of neuronal cells and T lymphocytes, the role of CREB in vascular smooth muscle cells (VSMCs) is incompletely characterized. We examined the role of CREB in VSMCs stimulated with reactive oxygen species. Activation of CREB was examined by Western blot analysis with an antibody that specifically recognizes phosphorylation at serine 133 of CREB, which is a critical marker of activation. Hydrogen peroxide (H2O2) time-dependently induced phosphorylation of CREB, with a peak at 15 minutes. The H2O2-induced phosphorylation of CREB was partially blocked by inhibition of either extracellular signal-regulated protein kinase kinase by PD98059 or of p38 mitogen-activated protein kinase (MAPK) by SB203580. AG1478, an epidermal growth factor receptor (EGFR) inhibitor, suppressed the H2O2-induced phosphorylation of CREB and tyrosine phosphorylation of EGFR. Overexpression of the dominant-negative form of CREB by an adenovirus vector suppressed H2O2-induced c-fos expression. These findings suggest that H2O2 induces CREB phosphorylation through EGFR transactivation and mitogen-activated protein kinase pathways. CREB might be a novel redox-sensitive transcription factor involved in the regulation of VSMC gene expression.