Cyclic-AMP-responsive transcriptional activation of CREB-327 involves interdependent phosphorylated subdomains

Multi-faceted regulation of CREB family transcription factors

cAMP response element-binding protein (CREB) is a ubiquitously expressed nuclear transcription factor, which can be constitutively activated regardless of external stimuli or be inducibly activated by external factors such as stressors, hormones, neurotransmitters, and growth factors. However, CREB controls diverse biological processes including cell growth, differentiation, proliferation, survival, apoptosis in a cell-type-specific manner. The diverse functions of CREB appear to be due to CREB-mediated differential gene expression that depends on cAMP response elements and multi-faceted regulation of CREB activity. Indeed, the transcriptional activity of CREB is controlled at several levels including alternative splicing, post-translational modification, dimerization, specific transcriptional co-activators, non-coding small RNAs, and epigenetic regulation. In this review, we present versatile regulatory modes of CREB family transcription factors and discuss their functional consequences.

CK2 negatively regulates the extinction of remote fear memory

Cognitive behavioral therapy, rooted in exposure therapy, is currently the primary approach employed in the treatment of anxiety-related conditions, including post-traumatic stress disorder (PTSD). In laboratory settings, fear extinction in animals is a commonly employed technique to investigate exposure therapy; however, the precise mechanisms underlying fear extinction remain elusive. Casein kinase 2 (CK2), which regulates neuroplasticity via phosphorylation of its substrates, has a significant influence in various neurological disorders, such as Alzheimer's disease and Parkinson's disease, as well as in the process of learning and memory. In this study, we adopted a classical Pavlovian fear conditioning model to investigate the involvement of CK2 in remote fear memory extinction and its underlying mechanisms. The results indicated that the activity of CK2 in the medial prefrontal cortex (mPFC) of mice was significantly upregulated after extinction training of remote cued fear memory. Notably, administration of the CK2 inhibitor CX-4945 prior to extinction training facilitated the extinction of remote fear memory. In addition, CX-4945 significantly upregulated the expression of p-ERK1/2 and p-CREB in the mPFC. Our results suggest that CK2 negatively regulates remote fear memory extinction, at least in part, by inhibiting the ERK-CREB pathway. These findings contribute to our understanding of the underlying mechanisms of remote cued fear extinction, thereby offering a theoretical foundation and identifying potential targets for the intervention and treatment of PTSD.

CK2 regulates 5-HT4 receptor signaling and modulates depressive-like behavior

The serotonergic neurotransmitter system has been widely implicated in the pathophysiology of mood-related disorders such as anxiety and major depressive disorder (MDD). The onset of therapeutic efficacy of traditional antidepressants is delayed by several weeks. The 5-HT₄ receptor has emerged as a new therapeutic target since agonists of this receptor induce rapid antidepressant-like responses in rodents. Here we show that the 5-HT₄ receptor is regulated by CK2, at transcriptional and post-transcriptional levels. We present evidence, in two different CK2α knockout mouse lines, that this regulation is region-specific, with the 5-HT₄ receptor upregulated in prefrontal cortex (PFC) but not striatum or hippocampus where CK2α is also ablated. 5-HT₄ receptor signaling is enhanced in vitro, as evidenced by enhanced cAMP production or receptor plasma membrane localization in the presence of CK2 inhibitor or shRNA targeting CK2α. In vivo, 5-HT₄ receptor signaling is also upregulated since ERK activation is elevated and sensitive to the inverse agonist, GR113808 in the PFC of CK2α KO mice. Behaviorally, KO mice as well as mice with AAV-mediated deletion of CK2α in the PFC show a robust 'anti-depressed-like' phenotype and display an enhanced response to antidepressant treatment when tested in paradigms for mood and anxiety. Importantly, it is sufficient to overexpress the 5-HT₄ receptor in the mPFC to generate mice with a similar 'anti-depressed-like' phenotype. Our findings identify the mPFC as the region that mediates the effect of enhanced 5-HT₄ receptor activity and CK2 as modulator of 5-HT4 receptor levels in this brain region that regulates mood-related phenotypes.

Mechanism of prostaglandin E2-induced transcriptional up-regulation of Oncostatin-M by CREB and Sp1

Oncostatin-M (OSM) is a pleotropic cytokine belonging to the interleukin-6 family. Differential expression of OSM in response to varying stimuli and exhibiting repertoire of functions in different cells renders it challenging to study the mechanism of its expression. Prostaglandin E₂ (PGE₂) transcriptionally increased osm levels. In silico studies of ∼1 kb upstream of osm promoter region yielded the presence of CRE (cyclic AMP response element)-like sites at the distal end (CRE_osm). Deletion and point mutation of CRE_osm clearly indicated that this region imparted an important role in PGE₂-mediated transcription. Nuclear protein(s) from PGE₂-treated U937 cells, bound to this region, was identified as CRE-binding protein (CREB). CREB was phosphorylated on treatment and was found to be directly associated with CRE_osm The presence of cofactors p300 and CREB-binding protein in the complex was confirmed. A marked decrease in CREB phosphorylation, binding and transcriptional inhibition on treatment with PKA (protein kinase A) inhibitor, H89 (N-[2-[[3-(4-bromophenyl)-2-propenyl]amino]ethyl]-5-soquinolinesulfonamide), revealed the role of phosphorylated CREB in osm transcription. Additionally, other nuclear protein(s) were specifically associated with the proximal GC region (GC_osm) post PGE₂ treatment, later confirmed to be specificity protein 1 (Sp1). Interestingly, Sp1 bound to the proximal osm promoter was found to be associated with phospho-CREB-p300 complex bound to the distal osm promoter. Knockdown of Sp1 abrogated the expression and functionality of OSM. Thus, the present study conclusively proves that these transcription factors, bound at the distal and proximal promoter elements are found to associate with each other in a DNA-dependent manner and both are responsible for the PGE₂-mediated transcriptional up-regulation of Oncostatin-M.

MiR-7-1 potentiated estrogen receptor agonists for functional neuroprotection in VSC4.1 motoneurons

Protection of motoneurons is an important goal in the treatment of spinal cord injury (SCI). We tested whether neuroprotective microRNAs (miRs) like miR-206, miR-17, miR-21, miR-7-1, and miR-106a could enhance efficacy of estrogen receptor (ER) agonists such as 1,3,5-tris (4-hydroxyphenyl)-4-propyl-1H-pyrazole (PPT, ERα agonist), Way200070 (WAY, ERβ agonist), and estrogen (EST, ERα and ERβ agonist) in preventing apoptosis in the calcium ionophore (CI)-insulted ventral spinal cord 4.1 (VSC4.1) motoneurons. We determined that 200 nM CI induced 70% cell death. Treatment with 50 nM PPT, 100 nM WAY, and 150 nM EST induced overexpression of ERα, ERβ, and both receptors, respectively, at mRNA and protein levels. Treatment with ER agonists significantly upregulated miR-206, miR-17, and miR-7-1 in the CI-insulted VSC4.1 motoneurons. Transfection with miR-206, miR-17, or miR-7-1 mimic potentiated WAY or EST to inhibit apoptosis in the CI-insulted VSC4.1 motoneurons. Overexpression of miR-7-1 maximally increased efficacy of WAY and EST for down regulation of pro-apoptotic Bax and upregulation of anti-apoptotic Bcl-2. A search using microRNA database (miRDB) indicated that miR-7-1 could inhibit the expression of L-type Ca(2+) channel protein alpha 1C (CPα1C). miR-7-1 overexpression and WAY or EST treatment down regulated CPα1C but upregulated p-Akt to trigger cell survival signaling. The same therapeutic strategy increased expression of the Ca(2+)/calmodulin-dependent protein kinase II beta (CaMKIIβ) and the phosphorylated cAMP response element binding protein (p-CREB) so as to promote Bcl-2 transcription. Whole cell membrane potential and mitochondrial membrane potential studies indicated that miR-7-1 highly potentiated EST to preserve functionality in the CI-insulted VSC4.1 motoneurons. In conclusion, our data indicated that miR-7-1 most significantly potentiated efficacy of EST for functional neuroprotection and this therapeutic strategy could be used in the future to attenuate apoptosis of motoneurons in SCI.

Functional interaction of protein kinase CK2 and activating transcription factor 4 (ATF4), a key player in the cellular stress response

Protein kinase CK2 is a pleiotropic enzyme, which is implicated in the regulation of numerous biological processes. It seems to regulate the various functions by binding to other proteins and by phosphorylation of many different substrates. Here, we identified the activating transcription factor 4 (ATF4), an essential component of the ER stress signaling, as a new binding partner and a new substrate of CK2 in vitro and in vivo. Bifluorescence complementation analysis (BiFC) revealed that CK2α and ATF4 associate in the nucleus. By using mutants of ATF4 we identified serine 215 as the main CK2 phosphorylation site. The ATF4 S215A mutant turned out to be more stable than the wild-type form. We further noticed that an inhibition of CK2 caused an increased transcription of the ATF4 gene. Analyses of the transcription factor activity revealed an impaired activity of the CK2 phosphorylation mutant of ATF4. Thus, we show that (i) ATF4 is a binding partner of CK2α (ii) ATF4 is a substrate of CK2, (iii) the phosphorylation of ATF4 by CK2 influences the stability of ATF4, (iv) the transcription of ATF4 is regulated by CK2 and (v) the transcription factor activity of ATF4 is regulated by the CK2 phosphorylation of ATF4. Thus, CK2 plays an essential role in the regulation of the ER-stress induced signaling pathway.

CREB in long-term potentiation in hippocampus: role of post-translational modifications-studies In silico

The multifunctionality of proteins is dictated by post-translational modifications (PTMs) which involve the attachment of small functional groups such as phosphate and acetate, as well as carbohydrate moieties. These functional groups make the protein perform various functions in different environments. PTMs play a crucial role in memory and learning. Phosphorylation of synaptic proteins and transcription factors regulate the generation and storage of memory. Among these is the cAMP-regulated element binding protein CREB that regulates CRE containing genes like c-fos. Both phosphorylation and acetylation control the function of CREB as a transcription factor. CREB is also susceptible to O-GlcNAc modification, which inhibits its activity. O-GlcNAc modification occurs on the same or neighboring Ser/Thr residues akin to phosphorylation. An interplay between these modifications was shown to operate in nuclear and cytoplasmic proteins. In this study computational methods were utilized to predict different modification sites in CREB. These in silico results suggest that phosphorylation, O-GlcNAc modification and acetylation modulate the transcriptional activity of CREB and thus dictate its contribution to synaptic plasticity.

Lipopolysaccharide stimulation of trophoblasts induces corticotropin-releasing hormone expression through MyD88

OBJECTIVE

We hypothesized that intrauterine infection may lead to placental corticotrophin-releasing hormone (CRH) expression via Toll-like receptor signaling.

STUDY DESIGN

To test this hypothesis JEG3 cells were stimulated with lipopolysaccharide (LPS), chlamydial heat shock protein 60, and interleukin (IL)-1. CRH expression was assessed by reverse transcription polymerase chain reaction (RT-PCR). The signaling mechanisms that were involved were examined in transient transfection experiments with beta-galactosidase, CRH-luciferase, cyclic adenosine monophosphate (AMP) response element-luciferase, dominant-negative (DN)-myeloid differentiation primary response gene (MyD88) and DN-toll-IL-1-receptor domain containing adapter inducing interferon (TRIF) vectors. Luciferase activity was determined by luciferase assay. Beta-galactosidase assay was performed to determine transfection efficiency.

RESULTS

LPS, chlamydial heat shock protein 60, and IL-1 stimulation led to CRH expression in the JEG3 cells. LPS-induced CRH expression was not due to the autocrine effect of LPS-induced IL-1 because the supernatant from LPS-conditioned JEG3 cells did not induce CRH expression in the naïve cells. DN-MyD88, but not DN-TRIF, blocked the LPS-induced CRH expression. The cAMP response element did not play a role in LPS-induced CRH expression.

CONCLUSION

Toll-like receptor signaling 4 may induce placental CRH expression through MyD88.

Protein kinase CK2 modulates synaptic plasticity by modification of synaptic NMDA receptors in the hippocampus

Synaptic plasticity is the foundation of learning and memory. The protein kinase CK2 phosphorylates many proteins related to synaptic plasticity, but whether it is directly involved in it has not been clarified. Here, we examined the role of CK2 in synaptic plasticity in hippocampal slices using the CK2 selective inhibitors 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) and 4,5,6,7-tetrabromobenzotriazole (TBB). These significantly inhibited N-methyl-D-aspartate (NMDA) receptor-dependent long-term potentiation (LTP). DRB also inhibited NMDA receptor-mediated synaptic transmission, while leaving NMDA receptor-independent LTP unaffected. NMDA receptors thus appear to be the primary targets of CK2. Although both long-term depression (LTD) and LTP are induced by the influx of Ca(2+) through NMDA receptors, surprisingly, LTD was not affected by CK2 inhibitors. We postulated that the LTP-selective modulation by CK2 is due to selective modulation of NMDA receptors, and tested two hypotheses concerning the modulation of NMDA receptors: (i) CK2 selectively modulates NR2A subunits possibly related to LTP, but not NR2B subunits possibly related to LTD; and (ii) CK2 selectively affects synaptic but not extrasynaptic NMDA receptors whose activation is sufficient to induce LTD. DRB decreased NMDA receptor-mediated synaptic transmission in the presence of selective NR2A subunit antagonist. The former hypothesis thus appears unlikely to be correct. However, DRB decreased synaptic NMDA receptor responses in cultured hippocampal neurons without affecting extrasynaptic NMDA receptor current. These findings support the latter hypothesis, that CK2 selectively affects LTP by selective modification of synaptic NMDA receptors in a receptor-location-specific manner.

Regulation of bone sialoprotein (BSP) gene transcription by lipopolysaccharide

Lipopolysaccharide (LPS) is a major mediator of inflammatory responses in periodontal disease that inhibits bone formation and stimulates bone resorption. To determine the molecular mechanisms involved in the suppression of bone formation, we have analyzed the effects of LPS on BSP gene expression. Bone sialoprotein (BSP) is a mineralized tissue-specific protein that appears to function in the initial mineralization of bone. Treatment of osteoblast-like ROS 17/2.8 cells with LPS (1 microg/ml) for 12 h caused a marked reduction in BSP mRNA levels. The addition of antioxidant N-acetylcysteine (NAC; 20 mM) 30 min prior to stimulation with LPS attenuated the inhibition of BSP mRNA levels. Transient transfection analyses, using chimeric constructs of the rat BSP gene promoter linked to a luciferase reporter gene, revealed that LPS (1 microg/ml) suppressed expression of luciferase construct, encompassing BSP promoter nucleotides -108 to +60, transfected into ROS17/2.8 cells. The effects of LPS were inhibited by protein kinase A (PKA) inhibitor, H89 and the tyrosine kinase inhibitor, herbimycin A (HA). Introduction of 2 bp mutations in the inverted CCAAT box (ATTGG; nts -50 and -46), a cAMP response element (CRE; nts -75 to -68), a FGF response element (FRE; nts -92 to -85), and a pituitary specific transcription factor binding element (Pit-1; nts -111 to -105) showed that the LPS effects were mediated by the CRE and FRE. Whereas the FRE and 3'-FRE DNA-protein complexes were decreased by LPS, CRE DNA-protein complex did not change after LPS treatment. These studies, therefore, show that LPS suppresses BSP gene transcription through PKA and tyrosine kinase-dependent pathways and that the LPS effects are mediated through CRE and FRE elements in the proximal BSP gene promoter.

Traditional Chinese medicine Bao Gan Ning increase phosphorylation of CREB in liver fibrosis in vivo and in vitro

Previous studies have demonstrated that traditional Chinese medicine Bao Gan Ning, which contains six different drugs: Trionyx sinensis Wiegmann shell, Prunus persica (L.) Batsch seed, Salvia miltiorrhiza Bge. root, Mallotus opelta (Lour.) Muell-Arg root, Astragalus membranaceus (Fisch.) Bge. var. mongho-licus (Bge.) Hsiao root and Scutellaria baicalensis Georgi root, was able to protect liver against fibrosis in CCL4 models. In an effort to elucidate molecular mechanisms by which Bao Gan Ning exerts its anti-fibrosis activity, effects of Bao Gan Ning on liver fibrosis and cAMP response element binding protein (CREB), an important transcription factor involved in liver fibrosis, were evaluated in animal and cell models in this work. Results showed that Bao Gan Ning (2.16 or 4.32 g/kg/day) significantly decreased alanine aminotransferase (ALT) and hyaluronidase levels and reversed liver fibrosis in rat liver fibrosis models. The proliferation of HSC-T6, a hepatic stellate cell line, was also significantly inhibited by incubation with serums that were prepared from rats fed with Bao Gan Ning. Most interestingly, results from Western blot, immunohistochemistry and electrophoretic mobility shift assay (EMSA) showed that Bao Gan Ning up-regulated CREB phosphorylation both in rat liver fibrosis models and in HSC-T6 cells, but did not affect protein level of CREB and the DNA binding activity of CREB. These results suggested that up-regulation of CREB phosphorylation may be involved in anti-fibrosis activity of Chinese medicine Bao Gan Ning.

Role of cyclic-AMP responsive element binding (CREB) proteins in cell proliferation in a rat model of hepatocellular carcinoma

The role of cyclic adenosine monophosphate (cAMP) is poorly understood in the regulation of normal and abnormal hepatic cell growth. In this study, we examined the regulation of intracellular cAMP levels and its effect on nuclear cAMP responsive elements (CREs) in a rat model of hepatocellular carcinoma (HCC). Tumorigenic liver cells were cultured from an in vivo model of HCC and the role of cAMP in cell mitogenesis determined. These data demonstrated agents that elevate intracellular cAMP ([cAMP]i) levels caused significant dose-dependent inhibition of serum-stimulated mitogenesis in HCC cells. Cells were next analyzed for transcription factor expression and activity following increased [cAMP]i. These data demonstrated time- and dose-dependent increases in CRE binding protein (pCREB) activity, a maximal response occurring after 10-20 min before returning to basal levels within 60 min. In contrast, increased [cAMP]i levels led to sustained inducible cAMP early repressor (ICER) II/IIgamma mRNA and protein induction. To understand these data in relation to the in vivo setting, HCC tumors were analyzed and compared to pair-matched normal liver (NL) samples. These studies demonstrated significantly elevated Gsalpha-protein expression in HCC versus NL in the absence of significant changes in basal cAMP levels. Analysis of total and active CREB demonstrated significantly increased total CREB/pCREB in HCC versus NL. Further analysis of CRE expression demonstrated significantly increased expression of ICER mRNA and protein in HCC versus sham operated (Sh). These data demonstrate cAMP, while capable of stimulating promitogenic CREB activation inhibits cell mitogenesis in HCC possibly via ICER induction.

Protein kinase inhibitor peptide (PKI): a family of endogenous neuropeptides that modulate neuronal cAMP-dependent protein kinase function

Signal transduction cascades involving cAMP-dependent protein kinase are highly conserved among a wide variety of organisms. Given the universal nature of this enzyme it is not surprising that cAMP-dependent protein kinase plays a critical role in numerous cellular processes. This is particularly evident in the nervous system where cAMP-dependent protein kinase is involved in neurotransmitter release, gene transcription, and synaptic plasticity. Protein kinase inhibitor peptide (PKI) is an endogenous thermostable peptide that modulates cAMP-dependent protein kinase function. PKI contains two distinct functional domains within its amino acid sequence that allow it to: (1) potently and specifically inhibit the activity of the free catalytic subunit of cAMP-dependent protein kinase and (2) export the free catalytic subunit of cAMP-dependent protein kinase from the nucleus. Three distinct PKI isoforms (PKIalpha, PKIbeta, PKIgamma) have been identified and each isoform is expressed in the brain. PKI modulates neuronal synaptic activity, while PKI also is involved in morphogenesis and symmetrical left-right axis formation. In addition, PKI also plays a role in regulating gene expression induced by cAMP-dependent protein kinase. Future studies should identify novel physiological functions for endogenous PKI both in the nervous system and throughout the body. Most interesting will be the determination whether functional differences exist between individual PKI isoforms which is an intriguing possibility since these isoforms exhibit: (1) cell-type specific tissue expression patterns, (2) different potencies for the inhibition of cAMP-dependent protein kinase activity, and (3) expression patterns that are hormonally, developmentally and cell-cycle regulated. Finally, synthetic peptide analogs of endogenous PKI will continue to be invaluable tools that are used to elucidate the role of cAMP-dependent protein kinase in a variety of cellular processes throughout the nervous system and the rest of the body.

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.

The robotic mouse: unravelling the function of AF4 in the cerebellum

The devastating nature and lack of effective treatments associated with neurodegenerative diseases have stimulated a world-wide search for the elucidation of their molecular basis to which mouse models have made a major contribution. In combination with transgenic and knockout technologies, large-scale mouse mutagenesis is a powerful approach for the identification of new genes and associated signalling pathways controlling neuronal cell death and survival. Here we review the characterization of the robotic mouse, a novel model of autosomal dominant cerebellar ataxia isolated from an ENU-mutagenesis programme, which develops adult-onset region-specific Purkinje cell loss and cataracts, and displays defects in early T-cell maturation and general growth retardation. The mutated protein, Af4, is a member of the AF4/LAF4/FMR2 (ALF) family of putative transcription factors previously implicated in childhood leukaemia and FRAXE mental retardation. The mutation, which lies in a highly conserved region among the ALF family members, significantly reduces the binding affinity of Af4 to the E3 ubiquitin-ligase Siah-1a, isolated with Siah-2 as interacting proteins in the brain. This leads to a markedly slower turnover of mutant Af4 by the ubiquitin-proteasome pathway and consequently to its abnormal accumulation in the robotic mouse. Importantly, the conservation of the Siah-binding domain of Af4 in all other family members reveals that Siah-mediated proteasomal degradation is a common regulatory mechanism that controls the levels, and thereby the function, of the ALF family. The robotic mouse represents a unique model in which to study the newly revealed role of Af4 in the maintenance of vital functions of Purkinje cells in the cerebellum and further the understanding of its implication in lymphopoeisis.

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.

Increased high-affinity phosphodiesterase PDE2 gene expression in germ tubes counteracts CAP1-dependent synthesis of cyclic AMP, limits hypha production and promotes virulence of Candida albicans

Frequent interconversion between yeasts, pseudohyphae and true hyphae is a hallmark of Candida albicans growth in mammalian tissues. The requirement for transient CAP1-dependent pulses of cAMP for generating true hyphae, Hwp1 and virulence raises questions about the role of yeast and pseudohyphal forms in the pathogenesis of candidiasis. In this study, hyperfilamentous mutants, limited in their capacity to produce buds, were generated by disrupting the high-affinity phosphodiesterase gene PDE2. Degradation of cAMP by the PDE2 gene product was confirmed by higher basal cAMP levels in the pde2/pde2 mutant and by accumulation of cAMP to levels permitting germ tube formation upon disrupting PDE2 in the cap1/cap1 mutant. Similar phenotypes of the C. albicans and Saccharomyces cerevisiae pde2/pde2 mutants were found, including sensitivity to nutritional starvation and exogenous cAMP and defective entry into stationary phase. Importantly, the hyperfilamentous mutants were as avirulent as hypofilamentous mutants in a systemic model of candidiasis. Growth in a multiplicity of forms appears to be a virulence attribute that is controlled by tight coupling of cAMP synthesis and degradation. Delayed increases in PDE2 mRNA in cAMP-deficient cap1/cap1 mutants during germ tube-inducing conditions suggested a mechanism of control involving cAMP-dependent induction of PDE2 mRNA.

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.

Prostaglandin E2 stimulates bone sialoprotein (BSP) expression through cAMP and fibroblast growth factor 2 response elements in the proximal promoter of the rat BSP gene

Bone sialoprotein (BSP), an early marker of osteoblast differentiation, has been implicated in the nucleation of hydroxyapatite during de novo bone formation. Prostaglandin E2 (PGE2) has anabolic effects on proliferation and differentiation of osteoblasts via diverse signal transduction systems. Because PGE2 increases the proportion of functional osteoblasts in fetal rat calvarial cell cultures, we investigated the regulation of BSP, as an osteoblastic marker, by PGE2. Treatment of rat osteosarcoma UMR 106 cells with 3 microm, 300 nm, and 30 nm PGE2 increased the steady state levels of BSP mRNA about 2.7-, 2.5-, and 2.4-fold after 12 h. From transient transfection assays, the constructs including the promoter sequence of nucleotides (nt) -116 to +60 (pLUC3) were found to enhance transcriptional activity 3.8- and 2.2-fold treated with 3 microm and 30 nm PGE2 for 12 h. 2-bp mutations were made in an inverted CCAAT box (between nt -50 and -46), a cAMP response element (CRE; between nt -75 and -68), a fibroblast growth factor 2 response element (FRE; nt -92 to -85), and a pituitary-specific transcription factor-1 motif (between nt -111 and -105) within pLUC3 and pLUC7 constructs. Transcriptional stimulation by PGE2 was almost completed abrogated in constructs that included 2-bp mutations in either the CRE and FRE. In gel shift analyses an increased binding of nuclear extract components to double-stranded oligonucleotide probes containing CRE and FRE was observed following treatment with PGE2. These studies show that PGE2 induces BSP transcription in UMR 106 cells through juxtaposed CRE and FRE elements in the proximal promoter of the BSP gene.

Emodin ameliorates glucose-induced matrix synthesis in human peritoneal mesothelial cells

Emodin ameliorates glucose-induced matrix synthesis in human peritoneal mesothelial cells. Prolonged exposure of human peritoneal mesothelial cells (HPMC) to high glucose concentrations in peritoneal dialysate is the principal factor leading to matrix accumulation and thickening of the peritoneal membrane, accompanied by progressive deterioration of transport functions. These changes are mediated in part through protein kinase C (PKC) activation and the induction of transforming growth factor-beta 1 (TGF-beta 1). Emodin (3-methyl-1,6,8 trihydroxyanthraquinone) has previously been demonstrated to reduce cell proliferation and fibronectin synthesis in cultured mesangial cells. How emodin modulates glucose-induced abnormalities in HPMC has not been elucidated and thus constitutes the theme of this study.

METHODS

We investigated the effects of emodin on the expression of PKC alpha, TGF-beta 1, fibronectin, and collagen type I in HPMC, and its effects on HPMC proliferation under physiologic (5 mmol) or high (30 mmol) glucose concentrations.

RESULTS

Exposure of HPMC cultured with 5 mmol or 30 mmol D-glucose to emodin (20 microg/mL) resulted in an initial lag of proliferation by 2.3 to 2.7 days, but did not affect cell viability or morphology at confluence. D-glucose (30 mmol) induced TGF-beta 1 secretion in a time-dependent manner (3.72 +/- 0.29 and 4.30 +/- 0.50 pg/microg cellular protein at 24 hours and 48 hours respectively, compared to 2.13 +/- 0.23 and 2.65 +/- 0.32 pg/microg cellular protein at 24 hours and 48 hours, respectively for 5 mmol glucose; P < 0.001 at both time points). Such induction was ameliorated by emodin (20 microg/mL) (TGF-beta 1 concentration 2.25 +/- 0.15 and 2.96 +/- 0.33 pg/microg cellular protein at 24 hours and 48 hours, respectively, in the presence of emodin and 30 mmol D-glucose; P < 0.001 compared to 30 mmol D-glucose alone at both time points). Induction of TGF-beta 1 synthesis by 30 mmol D-glucose was associated with induction of PKC alpha, phosphorylation of cAMP-responsive element binding protein (CREB) and activating transcription factor-1 (ATF-1), and increased fibronectin and type I collagen translation. Emodin abrogated all these effects of concentrated glucose. Immunohistochemical staining showed that 30 mmol D-glucose induced cytoplasmic, perinuclear, and extracellular fibronectin and type I collagen expression by HPMC. Emodin reduced 30 mmol D-glucose-induced cytoplasmic and extracellular matrix synthesis to near basal levels.

CONCLUSION

Our findings demonstrate that emodin ameliorates the undesirable effects of concentrated glucose on HPMC via suppression of PKC activation and CREB phosphorylation, and suggest that emodin may have a therapeutic potential in the prevention or treatment of glucose-induced structural and functional abnormalities in the peritoneal membrane.

A calcium/calmodulin kinase pathway connects brain-derived neurotrophic factor to the cyclic AMP-responsive transcription factor in the rat hippocampus

Brain-derived neurotrophic factor (BDNF) plays fundamental roles in synaptic plasticity in rat hippocampus. Recently, using rat hippocampal slices, we found that BDNF induces activation of calcium/calmodulin-dependent protein kinase 2 (CaMKII), a critical mediator of synaptic plasticity. CaMKII in turn activates the p38 subfamily of mitogen-activated protein kinases (MAPK) and its downstream effector, MAPK-activated protein kinase 2 (MAPKAPK-2). Herein, we determined whether some kinases of this pathway connect BDNF to the cyclic AMP response element -binding protein (CREB), a transcription factor also involved in plasticity and survival. Crude cytosolic and nuclear fractions were prepared from hippocampal slices of adult rat, and then kinase involvement in CREB phosphorylation was studied with a combination of pharmacologic inhibition and antibody depletion. In addition, the regional localization of this signaling pathway was immunohistochemically investigated. We show that: (i). the BDNF-stimulated CaMKII cascade phosphorylates the key positive regulatory site of CREB via its end MAPKAPK-2 component; (ii). this process appears to be highly localized in the outermost cell layer of the dentate gyrus. The present findings suggest that CaMKII is involved in neurotrophic-dependent activation of CREB in the dentate gyrus. Such a signaling process could be important for controlling synaptic plasticity in this major area for the afferent inputs to the hippocampal formation.

Interaction of early growth response protein 1 (Egr-1), specificity protein 1 (Sp1), and cyclic adenosine 3'5'-monophosphate response element binding protein (CREB) at a proximal response element is critical for gastrin-dependent activation of the chromogranin A promoter

Recently, binding of specific protein 1 (Sp1) and cAMP response element binding protein (CREB) to a GC-rich element at -92/-62 has been identified as a critical step in gastrin-dependent regulation of the chromogranin A (CgA) gene in gastric epithelial cells. Here we demonstrate that binding of early growth response protein 1 (Egr-1) to the distal part of the -92/-62 site is also required for gastrin-dependent CgA transactivation. Gastrin elevated cellular and nuclear Egr-1 levels in a time-dependent manner and also increased Egr-1 binding to the CgA -92/-73 region. Disruption of this site reduced gastrin responsiveness without influencing basal promoter activity, while loss of Sp1 and/or CREB binding sites diminished basal and gastrin-stimulated CgA promoter activity. Ectopic Egr-1 overexpression potently stimulated the CgA promoter, whereas coexpression of Egr-1 with Sp1 and/or CREB resulted in additive effects. Functional analysis of Sp1-, Egr-1-, or CREB-specific promoter mutations in transfection studies confirmed the tripartite organization of the CgA -92/-62 element. Signaling studies revealed that MAPK kinase 1 (MEK1)/ERK1/2 cascades are critical for gastrin-dependent Egr-1 protein accumulation as well as Egr-1 binding to the CgA promoter. Our studies for the first time identify Egr-1 as a nuclear target of gastrin and show that functional interplay of Egr-1, Sp1, and CREB is indispensable for gastrin-dependent CgA transactivation in gastric epithelial cells.

Mechanisms of basal and kinase-inducible transcription activation by CREB

The cAMP response element (CRE)-binding protein (CREB) stimulates basal transcription of CRE-containing genes and mediates induction of transcription upon phosphorylation by protein kinases. The basal activity of CREB maps to a carboxy-terminal constitutive activation domain (CAD), whereas phosphorylation and inducibility map to a central, kinase-inducible domain (KID). The CAD interacts with and recruits the promoter recognition factor TFIID through an interaction with a specific TATA-binding-protein-associated factor (TAF), dTAFII110/ hTAFII135. Interaction between the TAF and the CAD is mediated by a central cluster of hydrophobic amino acids, mutation of which disrupts TAF binding, polymerase recruitment, and transcription activation. Assessment of the contributions of the CAD and KID to recruitment of the polymerase complex versus enhancement of subsequent reaction steps (isomerization, promoter clearance, and reinitiation) showed that the CAD and P-KID act in a concerted mechanism to stimulate transcription. The CAD, but not the KID, mediated recruitment of a complex containing components of a transcription initiation complex, including pol II, IIB, and IID. However, the CAD was relatively ineffective in stimulating subsequent steps in the reaction mechanism. In contrast, phosphorylation of the KID in CREB effectively stimulated isomerization of the recruited polymerase complex and multiple-round transcription. A model for the activation of transcription by phosphorylated CREB is proposed, in which the polymerase is recruited by interaction of the CAD with TFIID and the recruited polymerase is activated further by phosphorylation of the KID in CREB.

Involvement of cAMP-response element binding protein in corticotropin-releasing factor (CRF)-induced down-regulation of CRF receptor 1 gene expression in rat anterior pituitary cells

Corticotropin-releasing factor (CRF) is a major secretagogue of adrenocorticotopic hormone from the anterior pituitary and a key activator of the hypothalamic-pituitary-adrenal axis. We previously reported that CRF down-regulates expression of the CRF type-1 receptor (CRF-R1) mRNA in cultured rat anterior pituitary cells. The present study was conducted to clarify the signal transduction systems involved in CRF-induced down-regulation of CRF-R1 gene expression in the anterior pituitary. Northern blot analysis revealed that, under serum-free conditions, 10 nM CRF decreased CRF-R1 mRNA levels in cultured rat anterior pituitary cells as we reported previously. Treatment with 5 mM 8-Br-cAMP reduced CRF-R1 mRNA levels within 2 h. The mRNA level fell to 37+/-3% of the basal level at 2 h and remained low for 16 h after treatment. This CRF-induced reduction of CRF-R1 mRNA expression was inhibited completely by pretreatment with protein kinase A (PKA) inhibitor (1 microM H-89). Further examination revealed that after pretreatment with 10 microM of antisense oligodeoxynucleotide for cyclic AMP-response element binding protein (CREB), the CRF-induced inhibition of CRF-R1 mRNA was partially decreased to 79+/-4% of the control level 2 h after administration of CRF. These findings indicate that CRF may down-regulate CRF-R1 mRNA expression via a cAMP-PKA-mediated mechanism in rat anterior pituitary cells, and that CREB may mediate at least a portion of this inhibitory effect.

Coupling cAMP signaling to transcription in the liver: pivotal role of CREB and CREM

Transcriptional factors binding to cAMP-responsive elements (CREs) in the promoters of various genes belong to the basic domain-leucine zipper superfamily and are composed of three genes in mammals, CREB, CREM, and ATF-1. A large number of CREB, CREM, and ATF-1 proteins are generated by posttranscriptional events, mostly alternative splicing, and regulate gene expression by acting as activators or repressors. Activation is classically brought about by signaling-dependent phosphorylation of a key acceptor site (Ser133 in CREB) by a number of possible kinases, including PKA, CamKIV, and Rsk-2. Phosphorylation is the prerequisite for the interaction of CBP (CREB-binding protein), a co-activator that has also histone acetyltransferase activity. Repression may involve dynamic dephosphorylation of the activators and thus decreased association with CBP. Another pathway of transcriptional repression on CRE sites implicates the inducible repressor ICER (inducible cAMP early repressor), a product of the CREM gene. Being an inducible repressor, ICER is involved in autoregulatory feedback loops of transcription that govern the down-regulation of early response genes, such as the proto-oncogene c-fos. The liver represents a remarkable physiological setting where cAMP-responsive signaling plays a major role. Indeed, a finely tuned program of gene expression is triggered by partial hepatectomy, so that through specific checkpoints a coordinated regeneration of the tissue is obtained. Temporal kinetics of transcriptional activation after hepatectomy reveals a pattern of early induction for several genes, some of them controlled by the CREB/CREM transcription factors. An important role of CREM in liver physiology was suggested by the robust induction of ICER after partial hepatectomy. The delay in tissue regeneration in CREM-deficient mice confirmed the important function of this factor in regulating hepatocyte proliferation. As gene induction is accompanied by critical changes in chromatin organization, the deciphering of the specific modification codes that histones display during liver regeneration and physiology will provide exciting new insights into the dynamics of chromatin architecture.

Sunghyangjungisan protects PC12 cells against neurotoxicity elicited by withdrawal of trophic support via CRE activation

Sunghyangjungisan (SHJS) is a commonly prescribed drug for cerebrovascular diseases in Oriental medicine. The water extract of SHJS was found to be protective against neurotoxicity elicited by deprivation of tropic factors. SHJS inhibited the activation of caspase 3-like protease and nucleosome-sized DNA fragmentation in serum-deprived PC12 Pheochromocytoma cells. Interestingly, pretreatment with an inhibitor of protein kinase A, KT5720 inhibited the neuroprotective effects of SHJS via inhibition of capase 3-like protease activation. When PC12 cells were treated with SHJS, Ser133 phosphorylation of cAMP-responsive elements binding protein (CREB), a transcription factor, was also increased in a time- and dose-dependent manner. In addition, CRE DNA binding activity of CREB was also increased in a time-dependent manner. SHJS-induced CRE binding activity was blocked by KT5720. Taken together, we suggest the possibility that SHJS may provide a neuroprotective effects on serum-deprived apoptosis of PC12 cells in a CREB- and CRE-dependent manner.

Glycosylated and phosphorylated proteins--expression in yeast and oocytes of Xenopus: prospects and challenges--relevance to expression of thermostable proteins

Phosphorylation and glycosylation are important posttranslational events in the biosynthesis of proteins. The different degrees of phosphorylation and glycosylation of proteins have been an intriguing phenomenon. Advances in genetic engineering have made it possible to control the degree of glycosylation and phosphorylation of proteins. Structural biology of phosphorylated and glycosylated proteins has been advancing at a much slower pace due to difficulties in using high-resolution NMR studies in solution phase. Major difficulties have arisen from the inherent mobilities of phosphorylated and glycosylated side chains. This paper reviews molecular and structural biology of phosphorylated and glycosylated proteins expressed in eukaryotic expression systems which are especially suited for large-scale production of these proteins. In our laboratory, we have observed that eukaryotic expression systems are particularly suited for the expression of thermostable light-activated proteins, e.g., bacteriorhodopsins and plastocyanins.

Interleukin-1beta enhances retinoic acid-mediated expression of bone-type alkaline phosphatase in rat IEC-6 cells

We previously showed that vitamin A upregulated the expression of bone-type alkaline phosphatase (ALP) in fetal rat small intestine and rat intestinal IEC-6 cells. In this study, we examined interactions between retinoic acid (RA) and several growth factors/cytokines on the isozyme expression in IEC-6 cells. Epidermal growth factor and interleukins (ILs)-2, -4, -5, and -6 completely blocked the RA-mediated increase in ALP activity. In contrast, IL-1beta markedly increased the activity, protein, and mRNA of the bone-type ALP only when RA was present. IL-1beta and/or RA did not change the type 1 IL-1 receptor transcript level, whereas IL-1beta enhanced the RA-induced expressions of retinoic acid receptor-beta (RAR-beta) and retinoid X receptor-beta (RXR-beta) mRNAs and RA-mediated RXR response element binding. The synergism of IL-1beta and RA on ALP activity was completely blocked by protein kinase C (PKC) inhibitors. Our results suggest that IL-1beta may modify the ALP isozyme expression in small intestinal epithelial cells by stimulating PKC-dependent, RAR-beta- and/or RXR-beta-mediated signaling pathways.

Dmrt1 expression is regulated by follicle-stimulating hormone and phorbol esters in postnatal Sertoli cells

Dmrt1 is a recently described gene that is expressed exclusively in the testis and is required for postnatal testis differentiation. Here we describe the expression of Dmrt1 in postnatal rat testis and Sertoli cells. RNase protection analysis was used to examine Dmrt1 messenger RNA (mRNA) levels in intact testis during postnatal development and in primary cultures of Sertoli cells under various culture conditions. We show that Dmrt1 mRNA levels rise significantly beginning approximately 10 days after birth and remain elevated until after the third postnatal week. Thereafter, mRNA levels drop coincident with the proliferation of germ cells in the testis. In freshly isolated Sertoli cells, Dmrt1 mRNA levels were robust but decreased significantly when the cells were placed in culture for 24 h. Treatment of Sertoli cells with either FSH or 8-bromo-cAMP resulted in a significant rise in Dmrt1 mRNA levels. This cAMP response was sensitive to treatment with the transcriptional inhibitor actinomycin D but not to the translational inhibitor cycloheximide. The cAMP-dependent rise in Dmrt1 mRNA also required activation of protein kinase A, as mRNA induction was sensitive to the inhibitor H89. Studies also show that Dmrt1 expression was inhibited by phorbol esters (PMA) but only modestly effected by serum.

Overexpression of a dominant negative CREB protein in HT-1080 cells selectively disrupts plasminogen activator inhibitor type 2 but not tissue-type plasminogen activator gene expression

The tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor type 2 (PAI-2) genes are differentially regulated by 12-phorbol 13-myristate acetate (PMA) in HT-1080 fibrosarcoma cells. PMA transcriptionally down-regulates the t-PA gene in HT-1080 cells, while the PAI-2 gene is simultaneously induced by this agonist. The t-PA and PAI-2 gene promoters harbour a cAMP-response element (CRE) which influences the expression of both genes. We have compared the binding activity of nuclear factors that recognise these CRE sites. We show that CREB (CRE binding protein) recognises each CRE and that the degree of constitutive Ser119-phosphorylated t-PA CRE-bound CREB was greater than for PAI-2 CRE bound CREB. Stable transfection of HT-1080 cells with a plasmid containing a CREB that could not be phosphorylated on Ser119 (pCI-CREB(ala119)) did not influence PMA-mediated suppression of t-PA mRNA, but markedly impaired PMA-mediated induction of PAI-2 mRNA. Our results demonstrate that the Ser119 residue of CREB plays a crucial role in PMA-mediated induction of PAI-2 gene expression, whereas PMA-mediated suppression of t-PA in HT-1080 cells requires a different process.

The decorin high glucose response element and mechanism of its activation in human mesangial cells

The decorin gene encodes a proteoglycan with putative structural and regulatory functions whose expression is markedly increased in human mesangial cells (HMC) exposed to high concentrations of glucose (15 to 30 mM). The gene has two promoters (P1 and P2) upstream of two alternative first exons. Transcripts driven by both promoters are present in HMC maintained in 4 mM D-glucose medium. After exposure to 30 mM D-glucose for 7 to 21 d, transcripts driven by P1 are markedly increased, whereas those driven by P2 decrease. Culture in 4 mM D-glucose medium containing transforming growth factor-beta1 (TGF-beta1) (1.25 ng/ml) has the same effect. However, addition of an excess of TGF-beta neutralizing antibody to the 30 mM D-glucose cultures only partly suppressed increased decorin transcription from P1. In transformed HMC transfected with a reporter (p-SAEP) driven by P1 or P2, P1 activity increased twofold on treatment with either 30 mM D-glucose or TGF-beta1 in 4 mM medium. P2 had little activity under any conditions. 5' deletion of P1 showed that basal transcriptional activity lies within the proximal 378 bp, while the major high glucose and TGF-beta response element is located in the -683 to -583-bp region. A putative cAMP response-like sequence (TGACGTTT) lies within this region. Electrophoretic mobility shift assays revealed the same pattern of multiple complexes between oligonucleotides containing this sequence and nuclear proteins extracted from HMC maintained in either 4 or 30 mM D-glucose conditions, but the latter were more prominent. cAMP response element binding protein (CREB) was identified as one transcription factor forming these complexes but other factors remain unidentified. Increased levels of phospho-(Ser 133) CREB were found in HMC exposed to 30 mM D-glucose. High glucose also activated and led to nuclear translocation of p42/44 mitogen-activated protein kinase and p38 mitogen-activated protein kinase, both of which can activate CREB by phosphorylation of serine 133.

Mechanisms of transcriptional activation of cAMP-responsive element-binding protein CREB

The CREB-CREM transcription factors are the main gene regulatory effectors of the cAMP signaling pathway. The investigations of this family of transcription factors had a profound impact on the understanding of signaling-induced gene transcription. Here we discuss some key aspects of the underlying biology, review transcriptional activation by CREB proteins through transcription cofactors and present novel insights into the context- and position-specific function of CREB on complex genes.

Stimulation of astrocyte-enriched culture with arachidonic acid increases proenkephalin mRNA: involvement of proto-oncoprotein and mitogen activated protein kinases

In astrocyte-enriched cultures, arachidonic acid (AA, 100 microM) significantly increased the proenkephalin (proENK) mRNA level (4. 9-fold at 8 h). In addition, AA also increased several AP-1 proteins, such as c-Fos, Fra-1, Fra-2, JunB, JunD, and c-Jun, or AP-1 and ENKCRE-2 DNA-binding activity. As well as AP-1 proteins and their DNA-binding activities, proENK mRNA level induced by AA was reduced by the pretreatment with 15 microM of cycloheximide (CHX; 1.6-fold). AA-dependent increase of proENK mRNA is not mediated by cyclooxygenase- or lipoxygenase-dependent metabolites, or free radicals, because the AA-induced increase of proENK mRNA levels was not affected by indomethacin (10 microM), nordihydroguaiaretic acid (10 microM), or N-acetylcysteine. However, as well as proto-oncoprotein levels, such as Fra-1, Fra-2, c-Jun, JunB, but not JunD, AA-induced increase of proENK mRNA was significantly reduced by the pretreatment with 10 microM of PD98059 (1.3-fold) or 10 microM of SB203580 (1.8-fold). These results strongly suggest that AA rather than one of its metabolites is involved in the increase of proENK mRNA. In addition, the activation of both the p38 and ERK pathways appears to be involved in the AA-induced increase of proENK mRNA via activating the expression of proto-oncoprotein, such as Fra-1, Fra-2, c-Jun, and JunB.

Corticotropin-releasing hormone gene expression in primary placental cells is modulated by cyclic adenosine 3',5'-monophosphate

CRH, the principal neuropeptide regulator of pituitary ACTH secretion, is also expressed in placenta. Placental CRH has been linked to the process of human parturition. However, the mechanisms regulating transcription of the CRH gene in placenta remain unclear. cAMP signaling pathways play important roles in regulating the expression of a diverse range of endocrine genes in the placenta. Therefore, we have explored the effect of cAMP on CRH promoter activity in primary cultures of human placental cells. Both forskolin and 8-bromo-cAMP, activators of protein kinase A, can increase CRH promoter activity 5-fold in transiently transfected human primary placental cells, in a manner that parallels the increase in endogenous CRH peptide. Maximal stimulation of CRH promoter activity occurs at 500 micromol/L 8-bromo-cAMP and 10 micromol/L forskolin. Electrophoretic mobility shift assay and mutation analysis combined with transient transfection demonstrate that in placental cells cAMP stimulates CRH gene expression through a cAMP regulatory element in the proximal CRH promoter region and involves a placental nuclear protein interacting specifically with the cAMP regulatory element.

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.

Regulation of inducible cAMP early repressor expression by gastrin and cholecystokinin in the pancreatic cell line AR42J

The CREM gene encodes both activators and repressors of cAMP-induced transcription. Inducible cAMP early repressor (ICER) isoforms are generated upon activation of an alternative, intronic promoter within the CREM gene. ICER is proposed to down-regulate both its own expression and the expression of other genes that contain cAMP-responsive elements such as a number of growth factors. Thus, ICER has been postulated to play a role in proliferation and differentiation. Here we show that ICER gene expression is induced by gastrin, cholecystokinin (CCK), and epidermal growth factor in AR42J cells. The time course of gastrin- and CCK-mediated ICER induction is rapid and transient, similar to forskolin- and phorbol 12-myristate 13-acetate-induced ICER expression. The specific CCK-B receptor antagonist L740,093 blocks the gastrin but not the CCK response, indicating that both the CCK-B and the CCK-A receptor can mediate ICER gene activation. Noteworthy, CREB is constitutively phosphorylated at Ser-133 in AR42J cells, and ICER induction proceeds in the absence of increased CREB Ser(P)-133. Gastrin-mediated ICER induction was not reduced in the presence of the protein kinase A inhibitor H-89, indicating a protein kinase A-independent mechanism. This is the first report on ICER inducibility via G(q)/G(11) protein-coupled receptors.

Casein kinase 2 as a potentially important enzyme in the nervous system

Protein kinase CK2 is a ubiquitous and pleiotropic seryl/threonyl protein kinase which is highly conserved in evolution indicating a vital cellular role for this kinase. The holoenzyme is generally composed of two catalytic (alpha and/or alpha') and two regulatory (beta) subunits, but the free alpha/alpha' subunits are catalytically active by themselves and can be present in cells under some circumstances. Special attention has been devoted to phosphorylation status and structure of these enzymic molecules, however, their regulation and roles remain intriguing. Until recently, CK2 was believed to represent a kinase especially required for cell cycle progression in non-neural cells. At present, with respect to recent findings, four essential features suggest potentially important roles for this enzyme in specific neural functions: (1) CK2 is much more abundant in brain than in any other tissue; (2) there appear to be a myriad of substrates for CK2 in both synaptic and nuclear compartments that have clear implications in development, neuritogenesis, synaptic transmission, synaptic plasticity, information storage and survival; (3) CK2 seems to be associated with mechanisms underlying long-term potentiation in hippocampus; and (4) neurotrophins stimulate activity of CK2 in hippocampus. In addition, some data are suggestive that CK2 might play a role in processes underlying progressive disorders due to Alzheimer's disease, ischemia, chronic alcohol exposure or immunodeficiency virus HIV. The present review focuses mainly on the latest data concerning the regulatory mechanisms and the possible neurophysiological functions of this enzyme.

Cyclic AMP-dependent activation of the proenkephalin gene requires phosphorylation of CREB at serine-133 and a Src-related kinase

The transcription factor CREB [cyclic AMP response element (CRE)-binding protein] is activated by several kinase pathways on phosphorylation of serine-133. Phosphorylation of CREB at serine-133 is required for the induction of target gene expression. The proenkephalin gene is a target of cyclic AMP-dependent agonists like forskolin, and its expression is driven by the enhancer element CRE-2. It has been shown that CREB binds CRE-2 in extracts from striatum and hypothalamus. However, these studies did not show a functional requirement for CREB serine-133 phosphorylation in CRE-2 function. We demonstrate that CREB binds CRE-2 in primary astrocyte cultures and that transcriptional activation of CRE-2 requires CREB phosphorylation at serine-133. In addition, it has recently been shown that, at least in some contexts, CREB phosphorylation is not sufficient to activate target gene expression and that another intracellular signal seems to be required. Therefore, we also sought to determine if another signaling event, in addition to CREB phosphorylation, might be involved in cyclic AMP-mediated induction of the proenkephalin gene. We have found that the inhibition of src-related nonreceptor tyrosine kinases blocks forskolin-induced proenkephalin gene expression without having any effect on serine-133-phosphorylated CREB levels and that constitutively activated src kinase can activate the proenkephalin promoter.

Mechanism of ubiquitous expression of mouse uncoupling protein 2 mRNA: control by cis-acting DNA element in 5'-flanking region

Uncoupling protein (UCP) 2 is a member of the uncoupling-protein family, and it appears to function as an uncoupler of oxidative phosphorylation. To identify cis-acting regulatory elements controlling this gene's expression, we cloned an approx. 6.2-kb region upstream from the translation-initiation site of the mouse UCP2 gene and analysed its transcription activity using chimaeric mouse UCP2 promoter-placental-alkaline-phosphatase (PLAP) reporter-gene constructs. Sequence analysis showed that the 5'-flanking region of the mouse UCP2 gene was not similar to those of mouse UCP1 or UCP3. For the mouse UCP2, the region near the transcription-initiation site lacked the typical TATA box, but was GC-rich, resulting in presence of several potential specificity protein 1 (Sp-1), activator protein (AP)-1 and AP-2 binding sites. The putative regulatory motifs for muscle-regulatory protein (MyoD), brown-fat regulatory element, CCAAT box, cAMP-response element and Y box were also found in the mouse UCP2 promoter region by computer-assisted analysis. From the results of Northern-blot analysis and transient expression assay, we found that the mouse UCP2 gene responded to the cAMP-dependent protein kinase alpha-catalytic subunit signal activation at the transcription level. Additionally, deletion analysis of the UCP2 promoter-PLAP constructs indicated that the minimal region exhibiting the promoter activity was located between nt -33 and +100, and that a strong enhancer was present within 601 bp of the 5'-promoter region. In particular, the region from nt -233 to -34 significantly induced PLAP activity in the cell lines derived from various tissues and in the primary culture cells of rat brown adipose tissue, suggesting that this region is most important for the ubiquitous expression of mouse UCP2 mRNA. Furthermore, it was shown that two silencer elements were involved in the mouse UCP2 gene; one was located between nt -2746 and -602, and the other was identified in intron 1. These regions deprived the enhancer of the ability to induce PLAP activity. This study shows a fundamental role for positive and negative cis-acting DNA elements in regulating the basal and cAMP-induced transcription activity of the mouse UCP2 gene.

The CREB constitutive activation domain interacts with TATA-binding protein-associated factor 110 (TAF110) through specific hydrophobic residues in one of the three subdomains required for both activation and TAF110 binding

The cAMP response element-binding protein (CREB) mediates both basal and PKA-inducible transcription through two separate and independently active domains, the constitutive activation domain (CAD) and the kinase-inducible domain, respectively. The CREB CAD interacts with the general transcription factor TFIID through one or more of the TATA-binding protein-associated factors (TAFs), one of which is TAF110. The CAD is composed of three subdomains, rich in either serine, hydrophobic amino acids, or glutamine. In the present study, analysis of deletion mutants of the CAD showed that all three CAD subdomains were required for effective interaction with TAF110 in a yeast two-hybrid assay. Therefore, a library of random point mutations within the CAD was analyzed in a reverse two-hybrid screen to identify amino acids that are essential for interaction with the TAF. Interaction defects resulted solely from mutations of hydrophobic amino acid residues within the hydrophobic cluster to charged amino acid residues. Together, the deletion and mutation analyses suggest that the entire CAD provides an environment for a specific hydrophobic interaction with TAF110 that is crucial for interaction. Our results provide further evidence for a model of basal activation by CREB involving interaction with TAF110 that promotes recruitment or stabilization of TFIID binding to the promoter, which facilitates pre-initiation complex assembly.

Cell-cycle-regulated phosphorylation of cAMP response element-binding protein: identification of novel phosphorylation sites

We report that the cAMP response element binding protein (CREB) undergoes cell-cycle-regulated phosphorylation. In human amnion FL cells, CREB was expressed as two forms with different molecular masses, 45 and 45.5 kDa. Although asynchronous cells contained predominantly the 45 kDa forms, this form shifted to 45.5 kDa when the cells were synchronized with the early S-phase. Furthermore the expression of the 45.5 kDa band was increased when cells were treated with okadaic acid, confirming that the 45.5 kDa band was a phosphorylated form of the 45 kDa band. Mutation analysis indicated that neither Ser133, the target of cAMP-dependent protein kinase and calcium calmodulin kinase, nor Ser129, the target of glycogen synthetase kinase 3, was responsible for the expression of the 45.5 kDa band, but that Ser108, Ser111 and Ser114, located in a region matching the consensus sequence for the casein kinase II target, were required. A mutant in which Ser111 and Ser114 were each replaced by a glutamic residue, mimicking a phosphorylated state, had a higher activation potential in cAMP response element-mediated transcription. These results strongly suggest that the casein kinase II target region is involved in cell cycle-regulated phosphorylation of the CREB protein and also in transcriptional enhancement.

Insulin-like growth factor I-mediated activation of the transcription factor cAMP response element-binding protein in PC12 cells. Involvement of p38 mitogen-activated protein kinase-mediated pathway

IGF-I is known to support growth and to prevent apoptosis in neuronal cells. Activation of the nuclear transcription factor cAMP response element-binding protein (CREB) has emerged as a central determinant in neuronal functions. In the present investigation, we examined the IGF-I-mediated phosphorylation and transcriptional activation of CREB in rat pheochromocytoma (PC12) cells, a cellular model for neuronal differentiation, and defined three distinct postreceptor signaling pathways important for this effect including the p38 mitogen-activated protein kinase (MAPK) pathway. CREB phosphorylation at serine 133 and its transcriptional activation as measured by a CREB-specific Gal4-CREB reporter and the neuroendocrine-specific gene chromogranin A was induced 2-3.3-fold by insulin-like growth factor (IGF)-I. This activation was significantly blocked (p < 0.001) by the dominant negative K-CREB or by mutation of the CRE site. IGF-I stimulated chromogranin A gene expression by Northern blot analysis 3.7-fold. Inhibition of MAPK kinase with PD98059, PI 3-kinase with wortmannin, and p38 MAPK with SB203580 blocked IGF-I-mediated phosphorylation and transcriptional activation of CREB by 30-50% (p < 0.001). Constitutively active and dominant negative regulators of the Ras and PI 3-kinase pathways confirmed the contribution of these pathways for CREB regulation by IGF-I. Cotransfection of PC12 cells with p38beta and constitutively active MAPK kinase 6 resulted in enhanced basal as well as IGF-I-stimulated chromogranin A promoter. IGF-I activated p38 MAPK, which was blocked by the inhibitor SB203580. This is the first description of a p38 MAPK-mediated nuclear signaling pathway for IGF-I leading to CREB-dependent neuronal specific gene expression.

Sp1 and CREB mediate gastrin-dependent regulation of chromogranin A promoter activity in gastric carcinoma cells

Chromogranin A (CgA) is a multifunctional acidic protein that in the stomach is expressed predominantly in enterochromaffin-like cells (ECL cells) where it is regulated by gastrin. In order to investigate the transcriptional response of the mouse CgA (mCgA) promoter to gastrin stimulation, we studied a 4.8-kilobase mCgA promoter-luciferase reporter gene construct in transiently transfected AGS-B cells. 5'-Deletion analysis and scanning mutagenesis of mCgA 5'-flanking DNA showed that a Sp1/Egr-1 site spanning -88 to -77 base pairs (bp) and a cyclic AMP-responsive element (CRE) at -71 to -64 bp are essential for gastrin-dependent mCgA transactivation. Gastrin stimulation increased cellular Sp1 protein levels and Sp1-binding to the mCgA -88 to -77 bp element, as well as binding of CREB to its consensus motif at -71 to -64 bp. Gastrin also stimulated CREB Ser-133 phosphorylation, and abundance of cellular CREB protein levels. Overexpression of either Sp1 or phosphorylated CREB transactivated the mCgA promoter dose dependently, while coexpression of both transcription factors resulted in an additive mCgA promoter response. mCgA -92 to -64 bp, comprising the Sp1/Egr-1 site and the CRE motif, conferred gastrin responsiveness to a heterologous thymidine kinase promoter system, and therefore functions as a "true" enhancer element. This report demonstrates that Sp1 and CREB mediate CCK-B/gastrin receptor-dependent gene regulation, and that the effect of gastrin on the CgA gene is brought about by cooperative action of both transcription factors.

Inhibition of the cyclic AMP signaling cascade and nuclear factor binding to CRE and kappaB elements by cannabinol, a minimally CNS-active cannabinoid

Immune suppression by cannabinoids has been widely demonstrated in a variety of experimental models. The identification of two major types of G-protein-coupled cannabinoid receptors expressed on leukocytes, CB1 and CB2, has provided a putative mechanism of action for immune modulation by cannabinoid compounds. Ligand binding to both receptors negatively regulates adenylate cyclase, thereby lowering intracellular cyclic AMP (cAMP) levels. In the present studies, we demonstrated that cannabinol (CBN), a ligand that exhibits higher binding affinity for CB2, modulates immune responses and cAMP-mediated signal transduction in mouse lymphoid cells. Direct addition of CBN to naive cultured splenocytes produced a concentration-dependent inhibition of lymphoproliferative responses to anti-CD3, lipopolysaccharide, and phorbol-12-myristate-13-acetate/ionomycin stimulation. Similarly, a concentration-related inhibition of the in vitro anti-sheep red blood cell IgM antibody forming cell response was also observed by CBN. Evaluation of cAMP signaling in the presence of CBN showed a rapid and concentration-related inhibition of adenylate cyclase activity in both splenocytes and thymocytes. This decrease in intracellular cAMP levels produced by CBN resulted in a reduction of protein kinase A activity, consequently leading to an inhibition of transcription factor binding to the cAMP response element and kappaB motifs in both cell preparations. Collectively, these results demonstrate that CBN, a cannabinoid with minimal CNS activity, inhibited both cAMP signal transduction and immune function, further supporting the involvement of CB2 receptors in immune modulation by cannabimimetic agents.

Co-stimulation of human peripheral blood mononuclear cells with IL-2 and anti-CD3 monoclonal antibodies induces phosphorylation of CREB

Phosphorylation of the cAMP-response element binding protein CREB within 1 h of CD2 but not CD3 cross-linking of human PBMC was recently demonstrated. The absence of P-CREB following CD3 cross-linking was unexpected, as other laboratories reported increased phosphorylation of CREB following CD3 cross-linking of the Jurkat lymphocyte cell line. Due to Jurkat T-cells being IL-2-independent, it was postulated that IL-2 might provide a necessary co-stimulus for phosphorylation of CREB in primary lymphocytes. Therefore, P-CREB was evaluated following co-stimulation of human PBMC through the IL-2 and CD2 or CD3 receptors. IL-2 did not further augment phosphorylation of CREB following CD2 cross-linking. However, while neither IL-2 nor CD3 cross-linking alone induced P-CREB, a 4.5-fold increase in phosphorylation of CREB within 1 h of IL-2/CD3 co-stimulation was observed. Phosphorylation was not associated with the induction of cAMP, and inhibition of PKA signaling had no effect on P-CREB. Consistent with signal transduction through p56lck or p59fyn, inhibition of PTK signaling reduced phosphorylation 50%. Interestingly, inhibiting PKC signaling with calphostin C further increased P-CREB levels 3-fold over that observed in IL-2/CD3 co-stimulated cells not pretreated with a PKC inhibitor. In contrast to previous studies performed in the absence of exogenous IL-2, no increase in binding of CREB to a 32P-labeled oligonucleotide probe was observed by electrophoretic mobility shift assay. These data suggest that the IL-2 and CD3 signaling pathways provide a necessary and co-operative stimulus promoting phosphorylation of CREB following receptor cross-linking.

The stimulation of rat astrocytes with phorbol-12-myristate-13-acetate increases the proenkephalin mRNA: involvement of proto-oncogenes

The effect of phorbol-12-myristate-13-acetate (PMA) on the regulation of proenkephalin (proENK) mRNA level, ENKCRE-2 or AP-1 DNA binding activity, and the mRNA and protein levels of proto-oncogenes (c-fos, fra-1, and c-jun) in primary cultured rat astrocytes were studied. The proENK mRNA level was elevated at 4 h after the treatment of PMA (2.5 microM) without altering the intracellular proENK protein level, and this increase was attenuated by pre-treatment with cycloheximide (CHX; 15 microM), a protein synthesis inhibitor. Both AP-1 and ENKCRE-2 DNA binding activities were markedly increased at 1-4 h by PMA treatment and these PMA-induced responses were inhibited by pre-treatment with CHX, showing that the increase of proENK mRNA level was well correlated with the AP-1 and ENKCRE-2 DNA binding activities. In contrast, although the phospho-CREBP level was also increased by PMA at 0.5-1 h, the pre-treatment with CHX further increased the PMA-induced phospho-CREBP level. In addition, PMA caused the induction of c-fos, c-jun and fra-1 mRNA level and, especially, PMA-induced increase of fra-1 mRNA level was further enhanced by CHX treatment at 4 h. Furthermore, western immunoblot assay showed that PMA caused induction of c-Fos, Fra-1, and c-Jun protein levels. PMA-induced increases of proto-oncoproteins levels were also inhibited by CHX treatment. The results suggest that newly synthesized AP-1 proteins, such as c-Fos, Fra-1, and c-Jun may play important roles in the regulation of PMA-induced proENK gene expression in cultured rat astrocytes. Phospho-CREB protein appears not to be involved in the regulation of PMA-induced proENK gene expression.

Insulin stimulates cAMP-response element binding protein activity in HepG2 and 3T3-L1 cell lines

Earlier studies from our laboratory demonstrated an insulin-mediated increase in cAMP-response element binding protein (CREB) phosphorylation. In this report, we show that insulin stimulates both CREB phosphorylation and transcriptional activation in HepG2 and 3T3-L1 cell lines, models of insulin-sensitive tissues. Insulin stimulated the phosphorylation of CREB at serine 133, the protein kinase A site, and mutation of serine 133 to alanine blocked the insulin effect. Many of the signaling pathways known to be activated by insulin have been implicated in CREB phosphorylation and activation. The ability of insulin to induce CREB phosphorylation and activity was efficiently blocked by PD98059, a potent inhibitor of mitogen-activated protein kinase kinase (MEK1), but not significantly by rapamycin or wortmannin. Likewise, expression of dominant negative forms of Ras or Raf-1 completely blocked insulin-stimulated CREB transcriptional activity. Finally, we demonstrate an essential role for CREB in insulin activation of fatty-acid synthase and fatty acid binding protein (FABP) indicating the potential physiologic relevance of insulin regulation of CREB. In summary, insulin regulates CREB transcriptional activity in insulin-sensitive tissues via the Raf --> MEK pathway and has an impact on physiologically relevant genes in these cells.

Determination of functional domains of the human transcription factor PAX8 responsible for its nuclear localization and transactivating potential

The conserved structure of the transcription factors of the Pax gene family may reflect functional conservation. We have demonstrated that the human Pax8 transcription factor is organized in several functional domains and contains two regions responsible for its nuclear localization, in addition to an activating region at the carboxy terminus of the protein and an inhibitory region encoded by the exon 9 present only in a splice variant PAX8a. Regions of PAX8 determining the nuclear localization of the PAX8A/lacZ fusions contain short amino acid sequences similar to several described nuclear localization sites (NLS). These NLS were identified in the paired domain and between the octapeptide and the residual homeodomain, respectively. The activating domain is encoded by the exons 10 and 11 and its function is modulated by the adjacent domains encoded by the exons 9 and 12. The domain encoded by exon 9 significantly inhibits the function of the activating domain. Pax8 is expressed in thyroid cells and its product binds promoters of the thyroglobulin and thyroperoxidase genes through its paired domain. Thyroid cell growth and differentiation depend on thyrotropin which, by stimulating cAMP synthesis, activates the cAMP-dependent protein kinase A (PKA). We have investigated a link between thyrotropin stimulation and gene activation by Pax8. Stimulation of cAMP synthesis augments Pax8-specific transcription in thyroid cells, indicating that PKA is involved in Pax8 activation. Cotransfection of GAL4/PAX8 fusions and the catalytic subunit of PKA in A126, a PKA-deficient derivative of the PC12 pheochromocytoma cell line, synergistically activates the GAL4-specific reporter, suggesting the activating domain of PAX8 is dependent upon the catalytic subunit of the PKA. We propose that this dependence is due to a hypothetical adaptor which forms a target for PKA and interacts with the activating domain of PAX8. We show that PAX8 isolated from the thyroid cell line FTRL5 is a phosphoprotein in which phosphorylation is not dependant on cAMP pathway activation. Our results suggest that Pax8 is part of the cAMP signaling pathway and mediates thyrotropin-dependent gene activation in thyroid cells. Investigation of the PAX8 expression in a panel of Wilms' tumors shows a striking correlation between the expression of PAX8 and another transcription factor, WT1, indicating that these two genes may interact in vivo.