Protein kinase A-dependent derepression of the human prodynorphin gene via differential binding to an intragenic silencer element

Analgesia induced by dietary restriction is mediated by the kappa-opioid system

Progress in the control and treatment of pain may be facilitated by a better understanding of mechanisms underlying nociceptive processing. Here we show that mice subjected to an intermittent fasting diet (IFD) display markedly reduced responses in models of thermal and visceral pain compared with mice fed ad libitum (AL). Pharmacological analyses suggest that a change in the endogenous kappa-opioid system underlies IFD-induced analgesia. The levels of prodynorphin mRNA and kappa-opioid receptors in the spinal cord are higher in IFD than in AL mice. Furthermore, in spinal cord nuclear protein extracts, the activity of the transcriptional repressor DREAM (downstream regulatory element antagonist modulator), the main regulator of prodynorphin expression, is lower in IFD than in AL mice. Finally, c-Fos expression in dorsal spinal cord after noxious stimulation is significantly lower in IFD than in AL animals, indicating that dynorphin could block nociceptive information at the spinal cord. These results suggest that dietary restriction together with administration of kappa-opioid agonists could be useful as a new therapeutic approach for pain relief.

Analgesia induced by dietary restriction is mediated by the kappa-opioid system

Progress in the control and treatment of pain may be facilitated by a better understanding of mechanisms underlying nociceptive processing. Here we show that mice subjected to an intermittent fasting diet (IFD) display markedly reduced responses in models of thermal and visceral pain compared with mice fed ad libitum (AL). Pharmacological analyses suggest that a change in the endogenous kappa-opioid system underlies IFD-induced analgesia. The levels of prodynorphin mRNA and kappa-opioid receptors in the spinal cord are higher in IFD than in AL mice. Furthermore, in spinal cord nuclear protein extracts, the activity of the transcriptional repressor DREAM (downstream regulatory element antagonist modulator), the main regulator of prodynorphin expression, is lower in IFD than in AL mice. Finally, c-Fos expression in dorsal spinal cord after noxious stimulation is significantly lower in IFD than in AL animals, indicating that dynorphin could block nociceptive information at the spinal cord. These results suggest that dietary restriction together with administration of kappa-opioid agonists could be useful as a new therapeutic approach for pain relief.

Coupling gene chip analyses and rat genetic variances in identifying potential target genes that may contribute to neuropathic allodynia development

Genetic factors and nerve injury-induced changes of gene expression in sensory neurons are potential contributors to tactile allodynia, a neuropathic pain state manifested as hypersensitivity to innocuous mechanical stimulation. To uncover genes relevant to neuropathic allodynia, we analyzed gene expression profiles in dorsal root ganglia (DRG) of spinal nerve-ligated Harlan and Holtzman Sprague Dawley rats, strains with different susceptibilities to neuropathic allodynia. Using Affymetrix gene chips, we identified genes showing differential basal-level expression in these strains without injury-induced regulation. Of more than 8000 genes analyzed, less than 180 genes in each strain were regulated after injury, and 19-22% of that was regulated in a strain-specific manner. Importantly, we identified functionally related genes that were co-regulated post injury in one or both strains. In situ hybridization and real-time PCR analyses of a subset of identified genes confirmed the patterns of the microarray data, and the former also demonstrated that injury-induced changes occurred, not only in neurons, but also in non-neuronal cells. Together, our studies provide a global view of injury plasticity in DRG of these rat stains and support a plasticity-based mechanism mediating variations in allodynia susceptibility, thus providing a source for further characterization of neuropathic pain-relevant genes and potential pathways.

Neuropeptides: opportunities for drug discovery

The role of peptides as signalling molecules in the nervous system has been studied for more than 30 years. Neuropeptides and their G-protein-coupled receptors are widely distributed throughout the body and they commonly occur with, and are complementary to, classic neurotransmitters. The functions of neuropeptides range from neurotransmitter to growth factor. They are present in glial cells, are hormones in the endocrine system, and are messengers in the immune system. Much evidence indicates that neuropeptides are of particular importance when the nervous system is challenged (eg, by stress, injury, or drug abuse). These features and the large number of neuropeptides and neuropeptide receptors provide many opportunities for the discovery of new drug targets for the treatment of nervous-system disorders. In fact, receptor-subtype-selective antagonists and agonists have been developed, and recently a substance P receptor (neurokinin 1) antagonist has been shown to have clinical efficacy in the treatment of major depression and chemotherapy-induced emesis. Several other neuropeptide receptor ligands are in clinical trials for various indications.

Ca(2+)-dependent prodynorphin transcriptional derepression in neuroblastoma cells is exerted through DREAM protein activity in a kinase-independent manner

Prodynorphin transcription has been postulated as an important molecular mechanism involved in adaptation/repair processes. Expression of prodynorphin is modulated according to the levels of the second messengers cAMP and Ca(2+). In the neuroblastoma cell lines, the increase of prodynorphin mRNA levels is coupled to an elevation of intracellular cAMP levels. Promoter analyses have revealed that the DRE site, a silencer element present in the prodynorphin promoter, is involved in PKA-dependent prodynorphin derepression. In this way, DREAM, a calcium-dependent repressor, plays an outstanding role. In this study, Ca(2+) release from internal stores has been found to promote an increase of prodynorphin mRNA levels in NB69 cells. Surprisingly, Ca(2+)-dependent prodynorphin gene transcription was insensitive to the broad-spectrum kinase inhibitors and sensitive to agents that alter internal Ca(2+) accumulation. Moreover, we demonstrate that in NB69 cells, the Ca(2+) signaling pathway uses DREAM as an effector to evoke prodynorphin transcription derepression in a kinase-independent manner.

Dynorphin A (1–17) induces apoptosis in striatal neurons in vitro through α-amino-3-hydroxy-5-methylisoxazole-4-propionate/kainate receptor-mediated cytochrome C release and caspase-3 activation

Dynorphin A (1-17), an endogenous opioid neuropeptide, can have pathophysiological consequences at high concentrations through actions involving glutamate receptors. Despite evidence of excitotoxicity, the basic mechanisms underlying dynorphin-induced cell death have not been explored. To address this question, we examined the role of caspase-dependent apoptotic events in mediating dynorphin A (1-17) toxicity in embryonic mouse striatal neuron cultures. In addition, the role of opioid and/or glutamate receptors were assessed pharmacologically using dizocilpine maleate (MK(+)801), a non-equilibrium N-methyl-D-aspartate (NMDA) antagonist; 6-cyano-7-nitroquinoxaline-2,3-dione, a competitive alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA)/kainate antagonist; or (-)-naloxone, a general opioid antagonist. The results show that dynorphin A (1-17) (>or=10 nM) caused concentration-dependent increases in caspase-3 activity that were accompanied by mitochondrial release of cytochrome c and the subsequent death of cultured mouse striatal neurons. Moreover, dynorphin A-induced neurotoxicity and caspase-3 activation were significantly attenuated by the cell permeable caspase inhibitor, caspase-3 inhibitor-II (z-DEVD-FMK), further suggesting an apoptotic cascade involving caspase-3. AMPA/kainate receptor blockade significantly attenuated dynorphin A-induced cytochrome c release and/or caspase-3 activity, while NMDA or opioid receptor blockade typically failed to prevent the apoptotic response. Last, dynorphin-induced caspase-3 activation was mimicked by the ampakine CX546 [1-(1,4-benzodioxan-6-ylcarbonyl)piperidine], which suggests that the activation of AMPA receptor subunits may be sufficient to mediate toxicity in striatal neurons. These findings provide novel evidence that dynorphin-induced striatal neurotoxicity is mediated by a caspase-dependent apoptotic mechanism that largely involves AMPA/kainate receptors.

Seizure-mediated neuronal activation induces DREAM gene expression in the mouse brain

Various transcriptional activators are induced in neurons concomitantly with long-lasting neural activity, whereas only a few transcription factors are known to act as neural activity-inducible transcription repressors. In this study, mRNA of DREAM (DRE-antagonizing modulator), a Ca(2+)-modulated transcriptional repressor, was demonstrated to accumulate in the mouse brain after pentylenetetrazol (PTZ)-induced seizures. Accumulation in the mouse hippocampus reached maximal level in the late phase (at 7-8 h) after PTZ injection. Kainic acid induced the same response. Interestingly, the late induction of DREAM expression required new protein synthesis and was blocked by MK801 suggesting that Ca(2+)-influx via NMDA receptors is necessary for the PTZ-mediated DREAM expression. In situ hybridization revealed that PTZ-induced DREAM mRNA accumulation was observed particularly in the dentate gyrus, cerebral cortex, and piriform cortex. The results of the present study demonstrate that DREAM is a neural activity-stimulated late gene and suggest its involvement in adaptation to long-lasting neuronal activity.

Cloning and mRNA expression of the Ca2+-binding DREAM protein in the pituitary

It is well recognized that the level of intracellular calcium governs several cellular processes such as gene expression and secretion in the pituitary. Recently, a novel gene has been identified in neuroendocrine cells that encodes DREAM, a calcium-binding protein that acts as a transcriptional repressor by binding specific downstream regulatory elements (DRE) on DNA. To explore the possibility that DREAM may be expressed in the rat pituitary and may function in endocrine activity, we analyzed its mRNA expression by RT-PCR. Using oligonucleotide primers derived from the mouse DREAM cDNA, we amplified, cloned, and characterized a 852-bp RT-PCR product from rat pituitary tissue. Two splice variants of the rat DREAM gene differing by four nucleotides (tetramer ACAG) were identified. The ACAG(+) variant (ORF1) consisted of 768bp encoding a protein of 256 residues with an estimated molecular weight of 29.5kDa. Amino acid sequence analysis of ORF1 indicated 92.6% and 98.1% identity to the DREAM gene product from human and mouse, respectively. The second variant, ACAG(-) (ORF2), was 567-bp long and was predicted to encode a peptide of 189 residues with a molecular mass of about 20.8kDa. To determine which endocrine pituitary cells were expressing DREAM, we evaluated several different clonal populations containing cells that expressed specific pituitary hormones. We found that both DREAM splice variants were expressed in each pituitary cell types examined, which included the mammotropes (MMQ cells), somatotropes (GC cells), mammosomatotropes (GH(3) cells), gonadotropes (LbetaT2 cells), thyrotropes (TalphaT1 cells), and corticotropes (AtT-20 cells). Interestingly, the levels of the two variants differed between the cell types tested with the ACAG(+) variant comprising about two-thirds of the DREAM expression for the mammotropes, somatotropes, mammosomatotropes, and corticotropes as compared to less than one-half for the thyrotropes and the gonadotropes. Our initial attempts to identify pituitary-specific genes regulated by DREAM revealed that prolactin gene expression was not influenced by DREAM suggesting that an action of DREAM may involve other pituitary hormones or be mediated by other cell processes. When taken together, our findings of DREAM expression in the pituitary in a manner specific to pituitary endocrine cell type raises the possibility that this protein may play a role in determining specific pituitary cell function.

Ca2+-dependent block of CREB-CBP transcription by repressor DREAM

The calcium-binding protein DREAM binds specifically to DRE sites in the DNA and represses transcription of target genes. Derepression at DRE sites following PKA activation depends on a specific interaction between alphaCREM and DREAM. Two leucine-charged residue-rich domains (LCD) located in the kinase-inducible domain (KID) and in the leucine zipper of alphaCREM and two LCDs in DREAM participate in a two-site interaction that results in the loss of DREAM binding to DRE sites and derepression. Since the LCD motif located within the KID in CREM is also present in CREB, and maps in a region critical for the recruitment of CBP, we investigated whether DREAM may affect CRE-dependent transcription. Here we show that in the absence of Ca2+ DREAM binds to the LCD in the KID of CREB. As a result, DREAM impairs recruitment of CBP by phospho CREB and blocks CBP-mediated transactivation at CRE sites in a Ca2+-dependent manner. Thus, Ca2+-dependent interactions between DREAM and CREB represent a novel point of cross-talk between cAMP and Ca2+ signalling pathways in the nucleus.

The role of calcium-binding proteins in the control of transcription: structure to function

Transcriptional regulation is coupled with numerous intracellular signaling processes often mediated by second messengers. Now, growing evidence points to the importance of Ca(2+), one of the most versatile second messengers, in activating or inhibiting gene transcription through actions frequently mediated by members of the EF-hand superfamily of Ca(2+)-binding proteins. Calmodulin and calcineurin, representative members of this EF-hand superfamily, indirectly regulate transcription through phosphorylation/dephosphorylation of transcription factors in response to a Ca(2+) increase in the cell. Recently, a novel EF-hand Ca(2+)-binding protein called DREAM has been found to interact with regulatory sequences of DNA, thereby acting as a direct regulator of transcription. Finally, S100B, a dimeric EF-hand Ca(2+)-binding protein, interacts with the tumor suppressor p53 and controls its transcriptional activity. In light of the structural studies reported to date, this review provides an overview of the structural basis of EF-hand Ca(2+)-binding proteins linked with transcriptional regulation.

Inducible and brain region-specific CREB transgenic mice

To investigate the role of cAMP response element-binding protein (CREB) in the adaptive responses to psychotropic drugs, we have developed inducible, brain region-specific CREB transgenic mice using the tetracycline-regulated gene expression system. The tetracycline transactivator (tTA) was placed under the control of 1.8-kilobase neuron-specific enolase (NSE) promoter for this purpose. Different patterns of CREB overexpression were found in striatum, nucleus accumbens, and cingulate cortex in different lines of bitransgenic mice, and CREB expression was blocked by addition of doxycycline, an analog of tetracycline. Overexpression of CREB influenced the expression of other members of the CREB/ATF family of transcription factors, consistent with previous reports. In addition, psychostimulant induction of dynorphin, a neuropeptide regulated by drugs of abuse, was up-regulated in striatum. Finally, there was a significant reduction in cocaine-induced locomotor activity in the CREB bitransgenic mice. These results are consistent with a role for CREB in mediating adaptive changes that occur in response to drugs of abuse.

No DREAM, No pain. Closing the spinal gate

Pain transmission in the spinal cord is regulated by a balance of facilitatory and inhibitory influences operating on the neural circuits of the somatosensory system. The transcriptional repressor DREAM acts constitutively to suppress prodynorphin expression in spinal cord neurons. Knocking out DREAM results in sufficient dynorphin expression to produce a strong reduction in generalized pain behavior, highlighting the role that intracellular molecules play in modulating pain gating in the spinal cord.

Calcium signaling: a tale for all seasons

An experiment performed in London nearly 120 years ago, which by today's standards would be considered unacceptably sloppy, marked the beginning of the calcium (Ca(2+)) signaling saga. Sidney Ringer [Ringer, S. (1883) J. Physiol. 4, 29-43] was studying the contraction of isolated rat hearts. In earlier experiments, Ringer had suspended them in a saline medium for which he admitted to having used London tap water, which is hard: The hearts contracted beautifully. When he proceeded to replace the tap water with distilled water, he made a startling finding: The beating of the hearts became progressively weaker, and stopped altogether after about 20 min. To maintain contraction, he found it necessary to add Ca(2+) salts to the suspension medium. Thus, Ringer had serendipitously discovered that Ca(2+), hitherto exclusively considered as a structural element, was active in a tissue that has nothing to do with bone or teeth, and performed there a completely novel function: It carried the signal that initiated heart contraction. It was a landmark observation, which should have immediately aroused wide interest. Unexpectedly, however, for decades it attracted no particular attention. Occasionally, farsighted pioneers argued forcefully for a messenger role of Ca(2+), offering compelling experimental evidence. Among them, one could quote L. V. Heilbrunn [Heilbrunn, L. V. (1940) Physiol. Zool. 13, 88-94], who contracted frog muscle fibers by applying Ca(2+) salts to their cut ends, but not to their surfaces. Heilbrunn correctly concluded that Ca(2+) had diffused from the cut ends to the internal contractile elements to elicit their contraction. One could also quote K. Bailey [Bailey, K. (1942) Biochem. J. 36, 121-139], who showed that the ATPase activity of myosin was strongly activated by Ca(2+) (but not by Mg(2+)), and concluded that the liberation of Ca(2+) in the neighborhood of the myosin controlled muscle contraction. Clearly, enough evidence was there, but only a handful of people had the vision to see it and to foresee its far-reaching implications. Perhaps no better example of clairvoyance can be offered than the quip by O. Loewy in 1959: "Ja Kalzium, das ist alles!"

DREAM is a critical transcriptional repressor for pain modulation

Control and treatment of chronic pain remain major clinical challenges. Progress may be facilitated by a greater understanding of the mechanisms underlying pain processing. Here we show that the calcium-sensing protein DREAM is a transcriptional repressor involved in modulating pain. dream(-/-) mice displayed markedly reduced responses in models of acute thermal, mechanical, and visceral pain. dream(-/-) mice also exhibited reduced pain behaviors in models of chronic neuropathic and inflammatory pain. However, dream(-/-) mice showed no major defects in motor function or learning and memory. Mice lacking DREAM had elevated levels of prodynorphin mRNA and dynorphin A peptides in the spinal cord, and the reduction of pain behaviors in dream(-/-) mice was mediated through dynorphin-selective kappa (kappa)-opiate receptors. Thus, DREAM appears to be a critical transcriptional repressor in pain processing.

Calcium-regulated DNA binding and oligomerization of the neuronal calcium-sensing protein, calsenilin/DREAM/KChIP3

Calsenilin/DREAM/KChIP3, a member of the recoverin branch of the EF-hand superfamily, interacts with presenilins, serves as a calcium-regulated transcriptional repressor, and interacts with A-type potassium channels. Here we report physicochemical characterization of calcium binding, oligomerization, and DNA binding of human calsenilin/DREAM/KChIP3. Equilibrium Ca(2+) binding measurements indicate that the protein binds 3 Ca(2+) with a dissociation constant of 14 microM and a Hill coefficient of 0.7. Dynamic light scattering and size exclusion chromatography show that the Ca(2+)-bound protein exists as a dimer at protein concentrations lower than 150 microM and forms a tetramer at concentrations above 200 microM. The Ca(2+)-free protein is a tetramer in the concentration range 20-450 microM. Isothermal titration calorimetry and dynamic light scattering indicate that the Ca(2+)-free protein tetramer binds endothermically (DeltaH = +25 kcal/mol) to four molecules of DNA derived from the downstream regulatory element (DRE) of either the prodynorphin or c-fos genes. One DRE molecule binds tightly to the protein with a dissociation constant (K(d)) of 75 nM, and the other three bind more weakly (K(d) = 640 nM). No significant DNA binding was observed for the Ca(2+)-bound protein. The N-terminal protein fragment (residues 1-70) binds nonspecifically to DRE in a Ca(2+)-independent manner, whereas a C-terminal fragment containing the four EF-hands (residues 65-256) binds DRE (K(d) = 200 nM) in a Ca(2+)-regulated and sequence-specific fashion. The C-terminal fragment is a tetramer in the Ca(2+)-free state and dissociates into dimers at saturating Ca(2+) levels.

New roles for introns: sites of combinatorial regulation of Ca2+- and cyclic AMP-dependent gene transcription

Because some proteins can facilitate cell division or the expression of many genes simultaneously, it comes as no surprise that the expression of very important gene products is a tightly controlled process. Although gene expression is often thought of in terms of complexes of transcription factors binding to promoter elements, some studies indicate that intronic DNA sequences may also regulate gene expression. Finkbeiner examines recent work by Schlegel and colleagues demonstrating that sequences within the first intron of the c-fos gene help to regulate Fos expression under different conditions.

Mechanisms of Ca(2+)-dependent transcription

Ca(2+) has a central role in coupling synaptic activity and transcriptional responses. Recent studies have focused on Ca(2+)-dependent nuclear mechanisms that bring to the nucleosomal level cascades of events initiated in the submembranous space at the synapse. In addition, a new Ca(2+)-dependent interaction between a calcium sensor and DNA has been shown to regulate transcription directly.

Interleukin 3-dependent activation of DREAM is involved in transcriptional silencing of the apoptotic Hrk gene in hematopoietic progenitor cells

The apoptotic protein Hrk is expressed in hematopoietic progenitors after growth factor deprivation. Here we identify a silencer sequence in the 3' untranslated region of the hrk gene that binds to the transcriptional repressor DREAM in interleukin-3 (IL-3)-dependent hematopoietic progenitor cells, and abrogates the expression of reporter genes when located downstream of the open reading frame. In addition, the binding of DREAM to the hrk gene is reduced or eliminated when cells are cultured in the absence of IL-3 or treated with a calcium ionophore or a phosphatidylinositol 3-kinase-specific inhibitor, suggesting that both calcium mobilization and phosphorylation can regulate the transcriptional activity of DREAM. Furthermore, we have shown that DREAM is phosphorylated by a phosphatidylinositol 3-kinase-dependent, but Akt-independent pathway. In all cases, loss of the DREAM-DNA binding complex was correlated with increased levels of Hrk and apoptosis. These data suggest that IL-3 may trigger the activation of DREAM through different signaling pathways, which in turn binds to a silencer sequence in the hrk gene and blocks transcription, avoiding inappropriate cell death in hematopoietic progenitors.

Ca2+-dependent transcriptional repression and derepression: DREAM, a direct effector

Control of gene expression by Ca2+ is a well known phenomenon acting through three major pathways: (i) changes in the transactivating properties of transcription factors after induction of Ca2+-dependent kinases and phosphatases (ii) Ca2+-dependent interaction between calmodulin and S-100 proteins with basic helix-loop-helix (bHLH) transcription factors that prevents binding to DNA and (iii) direct interaction between Ca2+-free DREAM and DNA that represses transcription. Because the first mechanism has been extensively reviewed, (Gallin, W. J., Greenberg, M. E. (1995). Calcium regulation of gene expression in neurons: the mode of entry matters. Curr Opin Neurobiol 5: 367-374; Santella, L., Carafoli, E. (1997). Calcium signaling in the cell nucleus. FASEB J, 11: 1091-1109) this commentary will focus on the other two with special emphasis on DREAM, the first EF-hand protein known to specifically bind DNA and regulate transcription in a Ca2+-dependent manner (Carrion, A. M.; Link, W. A., Ledo, F., Mellstrom, B., Naranjo, J. R. (1999). DREAM is a Ca2+-regulated transcriptional repressor, Nature. 398: 80-84).

Galanin receptor 1 gene expression is regulated by cyclic AMP through a CREB-dependent mechanism

The galanin receptor-1 (GalR1) protein belongs to a family of G protein-coupled receptors for the neuropeptide galanin (GalR1, GalR2 and GalR3) distributed throughout the central and peripheral nervous system. Activation of galanin receptors by their ligands results in increased feeding, impaired learning, enhanced opiate analgesia and decreased opiate place preference. We have shown that opiate withdrawal, which is known to increase levels of cAMP in the locus coeruleus (LC), results in an increase in the number of galanin binding sites and the level of GalR1 mRNA in the LC. We have isolated a 3.6-kb fragment 5' of the inititiation codon of the mouse GalR1 gene and generated a series of deletion mutations of this fragment driving expression of luciferase for use in transient transfection assays in PC12 and Cath.a cell lines. Treatment with forskolin, but not dideoxyforskolin, up-regulates GalR1 transcription, likely through elevation of cAMP levels. The region between - 1050 and - 700 base pairs upstream of exon one is necessary both for basal activity of the GalR1 promoter and for forskolin-mediated increases in transcription. The forskolin effect can be blocked by simultaneous mutation of a CRE-like site and a CRE/DRE-like site, but not mutation of either site alone. Gel shift and super-shift experiments demonstrate that the transcription factor CREB can bind to both sites and is likely to be responsible for the cAMP-mediated increase in GalR1 promoter activity. This study provides a molecular mechanism for the increased GalR1 expression in the LC seen following opiate withdrawal.

The DREAM-DRE interaction: key nucleotides and dominant negative mutants

Transcriptional repressor DREAM, an EF-hand containing calcium-binding protein, blocks basal expression of target genes through specific interaction with DRE sites in the DNA. The sequence GTCA forms the central core of the DRE site, whereas flanking nucleotides contribute notably to the affinity for DREAM. Release of binding of DREAM from the DRE results in derepression, a process that is regulated by Ca(2+). Change of two amino acids within an EF-hand in DREAM blocks Ca(2+)-induced derepression and results in potent dominant negative mutants of endogenous DREAM.

DREAM-alphaCREM interaction via leucine-charged domains derepresses downstream regulatory element-dependent transcription

Protein kinase A-dependent derepression of the human prodynorphin gene is regulated by the differential occupancy of the Dyn downstream regulatory element (DRE) site. Here, we show that a direct protein-protein interaction between DREAM and the CREM repressor isoform, alphaCREM, prevents binding of DREAM to the DRE and suggests a mechanism for cyclic AMP-dependent derepression of the prodynorphin gene in human neuroblastoma cells. Phosphorylation in the kinase-inducible domain of alphaCREM is not required for the interaction, but phospho-alphaCREM shows higher affinity for DREAM. The interaction with alphaCREM is independent of the Ca(2+)-binding properties of DREAM and is governed by leucine-charged residue-rich domains located in both alphaCREM and DREAM. Thus, our results propose a new mechanism for DREAM-mediated derepression that can operate independently of changes in nuclear Ca(2+).

Transcription of genes encoding pregnancy-specific glycoproteins is regulated by negative promoter-selective elements

The human pregnancy-specific glycoprotein (PSG) genes comprise a family of 11 highly conserved members whose expression is maximal in placental cells and marginal in other cell types. We have investigated here the molecular basis of PSG regulation by analysing a large regulatory region of the PSG-5 gene in cells that do and do not express these genes. The promoter region (-254 to -43), which does not contain a TATA-box, large GC-rich sequences or a classical initiator, was active in all cell types analysed. Additional upstream sequences up to position -3204 repressed promoter activity. Two independent repressor regions were identified and found to operate effectively in HeLa, COS-7 and HTR8/SVneo placental cells. More significantly, these negatively acting modules failed to repress a heterologous TATA-containing thymidine kinase promoter. Detailed transcriptional and DNA-protein analyses of the proximal repressor region (-605 to -254) revealed the presence of both negative and positive cis-acting elements. Disruption of the repressive functions resulted in an enhanced transcription of the reporter constructs. In conclusion, these results demonstrate that PSG-5 gene transcription is highly repressed by promoter-selective negative regulatory regions and the relief of repression allows enhanced PSG-5 gene transcription irrespective of the cell type. Furthermore, our findings suggest that PSG genes are expressed mainly through a derepression mechanism.

DREAM is a Ca2+-regulated transcriptional repressor

Fluxes in amounts of intracellular calcium ions are important determinants of gene expression. So far, Ca2+-regulated kinases and phosphatases have been implicated in changing the phosphorylation status of key transcription factors and thereby modulating their function. In addition, direct effectors of Ca2+-induced gene expression have been suggested to exist in the nucleus, although no such effectors have been identified yet. Expression of the human prodynorphin gene, which is involved in memory acquisition and pain, is regulated through its downstream regulatory element (DRE) sequence, which acts as a location-dependent gene silencer. Here we isolate a new transcriptional repressor, DRE-antagonist modulator (DREAM), which specifically binds to the DRE. DREAM contains four Ca2+-binding domains of the EF-hand type. Upon stimulation by Ca2+, DREAM's ability to bind to the DRE and its repressor function are prevented. Mutation of the EF-hands abolishes the response of DREAM to Ca2+. In addition to the prodynorphin promoter, DREAM represses transcription from the early response gene c-fos. Thus, DREAM represents the first known Ca2+-binding protein to function as a DNA-binding transcriptional regulator.