In vitro transcription directed from the somatostatin promoter is dependent upon a purified 43-kDa DNA-binding protein

Regulatory Mechanisms of Somatostatin Expression

Somatostatin is a peptide hormone, which most commonly is produced by endocrine cells and the central nervous system. In mammals, somatostatin originates from pre-prosomatostatin and is processed to a shorter form, i.e., somatostatin-14, and a longer form, i.e., somatostatin-28. The two peptides repress growth hormone secretion and are involved in the regulation of glucagon and insulin synthesis in the pancreas. In recent years, the processing and secretion of somatostatin have been studied intensively. However, little attention has been paid to the regulatory mechanisms that control its expression. This review provides an up-to-date overview of these mechanisms. In particular, it focuses on the role of enhancers and silencers within the promoter region as well as on the binding of modulatory transcription factors to these elements. Moreover, it addresses extracellular factors, which trigger key signaling pathways, leading to an enhanced somatostatin expression in health and disease.

Regulation of gene promoters of hypothalamic peptides

In order to fulfill their roles in neuroendocrine regulation, specific hypothalamic neurons are devoted to produce and deliver biologically active peptides to the pituitary gland. The biosynthesis and release of peptides are strictly controlled by afferents to these hypothalamic neurons. Cell-specific expression and biosynthetic regulation largely relies on transcription from the gene promoter for which the 5(')-flanking regions of the peptidergic genes contain essential elements. Cell-specific transcription factors employ these regulatory elements to exert their control over the expression of the peptidergic gene. This article explores the properties of regulatory elements of the major hypothalamic peptides, somatostatin, growth hormone-releasing hormone, gonadotropin-releasing hormone, thyrotropin-releasing hormone, corticotropin-releasing hormone, vasopressin and oxytocin, and the transcription factors acting on them. These transcription factors are often endpoints of signal transduction pathways that can be activated by neurotransmitters or steroid hormones. Others are essential to provide cell-specific expression of the peptidergic gene during development and mature regulation.

Activation of the cytochrome c gene by electrical stimulation in neonatal rat cardiac myocytes. Role of NRF-1 and c-Jun

Activation of cytochrome c (cyt c) transcription in electrically stimulated neonatal rat cardiac myocytes is preceded by transient expression of the activating protein-1 family of transcription factors, c-Fos, c-Jun, and JunB, as well as nuclear respiratory factor-1 (NRF-1). Mutations in either the NRF-1 or in the two cyclic AMP response elements on the cyt c promoter significantly reduce cyt c promoter activation produced either by electrical stimulation (Xia, Y., Buja, L. M., Scarpulla, R. C., and McMillin, J. B. (1997) Proc. Natl. Acad. Sci. U. S. A. 94, 11399-11404) or by transfection of c-jun into nonpaced cardiac myocytes. Electrical stimulation of cardiac myocytes activates the c-Jun N-terminal kinase (McDonough, P. M., Hanford, D. S., Sprenkle, A. B., Mellon, N. R., and Glembotski, C. C. (1997) J. Biol. Chem. 272, 24046-24053) so that the fold-activation of the cyt c promoter is increased by pacing when either c-jun or c-fos/c-jun were cotransfected. Physical association of NRF-1 protein with the NRF-1 enhancer element and of c-Jun with the cyclic AMP response element binding sites on the cyt c promoter was demonstrated by gel shift competition assays and by antibody super shifts. This is the first demonstration that induction of NRF-1 and c-Jun by pacing of cardiac myocytes directly mediates cyt c gene expression and mitochondrial proliferation in response to hypertrophic stimuli in the heart.

Expression of rat thyrotropin-releasing hormone (TRH) gene in TRH-producing tissues of transgenic mice requires sequences located in exon 1

TRH, an amidated tripeptide secreted by certain hypothalamic neurons, is a principal regulator of TSH secretion and thyroid hormone release. TRH is also produced by other neurons in the central nervous system, where it appears to function as a neuromodulator or neurotransmitter, and by certain endocrine cells, where it may act as an autocrine or paracrine factor. The genomic organization of the rat TRH (rTRH) gene is well understood; however, the domains of the rTRH gene that regulate expression are less well characterized. We observed that the region between -47 and +6 of the rTRH gene (relative to the transcription start site at +1) was active in CA-77 cells, a medullary thyroid carcinoma cell line model of TRH production, but was not active in transgenic mice. Inclusion of most of exon 1 (84 out of 103 bp; -47 to +84) increased promoter activity in CA-77 cells and was active in transgenic mice, principally in tissues that normally express the TRH gene. Further lengthening of the 5' end to -243, -547, or -776 retained this expression in TRH-producing tissues in transgenic mice, while further increasing activity in CA-77 cells. These results suggest that cis element(s) located within exon 1 are necessary for the expression of the rTRH gene in vivo.

The hepatitis B virus X protein enhances the DNA binding potential and transcription efficacy of bZip transcription factors

The hepatitis B virus X protein interacts with the basic-region, leucine zipper protein (bZip) domain of cAMP response element-binding protein increasing its affinity for the cAMP response element site in vitro and its transcriptional efficacy in vivo (Williams, J. S., and Andrisani, O. M. (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 3819-3823). Here we examine pX interactions with bZip transcription factors ATF3, gadd153/Chop10, ICER IIgamma, and NF-IL6. We demonstrate direct interactions in vitro between pX and the bZip proteins tested. In contrast MyoD and Gal4(1-147) fail to interact with pX. We also demonstrate by the mammalian two-hybrid assay the direct interaction of pX with cAMP response element- binding protein, ICER IIgamma, ATF3, and NF-IL6 in hepatocytes. In addition, pX increases the DNA binding potential of bZip proteins for their cognate DNA-binding site in vitro. In transient transfections in hepatocytes (AML12 cell line), pX increases the transcriptional efficacy of the bZip transcription factors. NF-IL6-mediated transcriptional activation is enhanced 3-fold by pX. Most interestingly, pX augments the repression mediated by bZip repressors ATF3 and ICER IIgamma, by 6- and 7-fold, respectively, demonstrating for the first time the involvement of pX in gene repression. We conclude that pX is an enhancer of the DNA binding potential of bZip transcription factors, thereby increasing the transactivation or repression efficacy of bZip-responsive genes.

Structure/function relationship of the cAMP response element in tyrosine hydroxylase gene transcription

Expression of tyrosine hydroxylase (TH) is limited to catecholamine-producing neurons and neuroendocrine cells in a cell type-specific manner and is inducible by the cAMP-regulated signaling pathway. Previous results indicated that the cAMP response element (CRE) residing at -45 to -38 base pairs upstream of the transcription initiation site is essential for both basal and cAMP-inducible promoter activity of the 2.4-kilobase or shorter upstream sequence of the TH gene (Kim, K. S., Lee, M. K., Carroll, J. , and Joh, T. H. (1993) J. Biol. Chem. 268, 15689-15695; Lazaroff, M. , Patankar, S., Yoon, S. O., and Chikaraishi, D. M. (1995) J. Biol. Chem. 270, 21579-21589). Here, we further report that the CRE is critical for the promoter activity of the 5.6- or 9.0-kilobase upstream sequences of the rat TH gene, which had been shown to direct the cell-specific TH expression in vivo. To define the structure/function relationship of the CRE in transcriptional activation of the TH gene, we performed saturated mutational analyses of 12 nucleotides encompassing the CRE. Mutation of any nucleotide within the octamer motif results in a significant decrease of both basal and cAMP-inducible transcriptional activity of the TH reporter gene construct. Among the four nucleotides adjacent to the CRE (two 5' and two 3'), only the G residue at the immediate 3' position is important for full transcriptional activity. DNase I footprint analysis indicates a positive correlation between in vivo promoter activity and in vitro interaction between the CRE motif and its cognate protein factor(s). Reconstruction experiments using a TH promoter in which the native CRE was rendered inactive show that the CRE can transactivate transcription in either orientation through a window of approximately 200 base pairs upstream of the transcription initiation site, suggesting that CRE supports transcriptional activation of the TH gene in a distance-dependent manner. Finally, when the distance between the CRE and TATA box was changed by inserting an additional 5 or 10 bases, it was observed that both insertional mutations increased activity by approximately 3-fold. The cAMP inducibility was as intact as the wild type construct. Together, these results are consistent with a model in which transcriptional activation of the TH gene by the CRE requires that it be located within a certain proximity of the CAP site but does not depend on a stringent stereospecific alignment in relationship to the TATA element.

The hepatitis B virus X protein targets the basic region-leucine zipper domain of CREB

The X gene product encoded by the hepatitis B virus, termed pX, is a promiscuous transactivator of a variety of viral and cellular genes under the control of diverse cis-acting elements. Although pX does not appear to directly bind DNA, pX-responsive elements include the NF-kappa B, AP-1, and CRE (cAMP response element) sites. Direct protein-protein interactions occur between viral pX and the CRE-binding transcription factors CREB and ATF. Here we examine the mechanism of the protein-protein interactions occurring between CREB and pX by using recombinant proteins and in vitro DNA-binding assays. We demonstrate that pX interacts with the basic region-leucine zipper domain of CREB but not with the DNA-binding domain of the yeast transactivator protein Gal4. The interaction between CREB and pX increases the affinity of CREB for the CRE site by an order of magnitude, although pX does not alter the rate of CREB dimerization. Methylation interference footprinting reveals differences between the CREB DNA and CREB-pX DNA complexes. These experiments demonstrate that pX titers the way CREB interacts with the CRE DNA and suggest that the basic, DNA-binding region of CREB is the target of pX. Transfection assays in PC12 cells with the CREB-dependent somatostatin promoter demonstrate a nearly 15-fold transcriptional induction after forskolin stimulation in the presence of pX. These results support the significance of the CREB-pX protein-protein interactions in vivo.

Analysis of the rat lactate dehydrogenase A subunit gene promoter/regulatory region

The rat lactate dehydrogenase (LDH) A subunit gene promoter contains a putative AP-1 binding site at -295/-289 bp, two consensus Sp1 binding sites at -141/-136 bp and -103/-98 bp, and a single copy of a consensus cyclic AMP-responsive element (CRE) at -48 to -41 bp upstream of the transcription initiation site. Additionally, an as yet unidentified silencer element is located within the -1173/-830 bp 5'-flanking region. Transient transfection analyses of a -1173/+25 bp LDH A-chLoramphenicol acetyltransferase fusion gene has indicated a complete inability of the promoter fragment to direct basal or forskolin-induced transcription. Deletion of the -1173/-830 bp sequence restored basal and cyclic AMP (cAMP)-inducible activity. Point mutations in the Sp1 binding sites of a -830/+25 bp promoter fragment reduced basal but not the relative degree of cAMP-inducible activity. cAMP-regulated transcriptional activity was dependent upon an 8 bp CRE, -TGACGTCA-, located at the -48/-41 bp upstream region. Mutations in the CRE abolished cAMP-mediated induction and reduced basal activity by about 65%. The CRE binds a 47 kDa protein which has previously been identified as CRE binding protein (CREB)-327, an isoform of the activating transcription factor/CREB transcription factor gene family. Co-transfection of a vector that expresses the catalytic subunit of cAMP-dependent protein kinase stimulates LDH A subunit promoter activity suggesting that cAMP induces LDH A subunit gene expression through phosphorylative modification of CREB-327. This study emphasizes a fundamental role of several modules including Sp1 and CREB binding sites in regulating basal and cAMP-mediated transcriptional activity of the LDH A gene.

Bacterial expression and characterization of the CREB bZip module: circular dichroism and 2D 1H-NMR studies

In this paper we describe the expression and purification from bacteria of the recombinant basic leucine zipper (bZip) domain of the cAMP response element binding protein, CREB327. The bZip peptide, CREB259-327, purified to near homogeneity, maintains the sequence-specific CRE site recognition demonstrated by in vitro competition assays. Alkylation of the three cysteine residues of CREB259-327 was employed to prevent aggregation of the peptide due to cysteine oxidation. The Kd of the purified native and modified CREB259-327 for the CRE site was determined by gel retardation assays to be on the order of 10(-7) M. We employed CD spectroscopy to study the folding properties of the native and modified CREB259-327. The CD analyses of the native/modified CREB259-327 peptide demonstrated a 20% increase in the alpha-helical content upon binding to the cAMP response-element. Only a 5% increase in the alpha-helical content of CREB259-327 is observed upon binding to the AP-1 site. This observation contrasts with CREB from the GCN4 protein (Weiss, M.A., et al., 1990, Nature 347, 575-578). In addition, the two-dimensional (2D) 1H-NMR studies of the bZip CREB peptide further support the distinct features of the CREB protein, in comparison to GCN4. Analysis by CD and 2D NMR of the dimerization domain of CREB suggests that the distinct DNA binding characteristics of CREB reside in the basic portion of the bZip module.

Dissection of the functional architecture of a plant defense gene promoter using a homologous in vitro transcription initiation system

CHS15 is one of a family of bean genes encoding chalcone synthase, which catalyzes the first reaction in a branch pathway of phenylpropanoid biosynthesis for the production of flavonoid pigments and UV protectants and isoflavonoid-derived phytoalexins. The functional architecture of the CHS15 promoter was dissected by a novel homologous plant in vitro transcription initiation system in which whole-cell and nuclear extracts from suspension-cultured soybean cells direct accurate and efficient RNA polymerase II-mediated transcription from an immobilized promoter template. Authentic transcription from the CHS15 promoter template was also observed with whole-cell extracts from suspension-cultured cells of bean, tobacco, and the monocot rice, and the soybean whole-cell extract transcribed several other immobilized promoter templates. Hence, this procedure may be of general use in the study of plant gene regulation mechanisms in vitro. Assay of the effects of depletion of the soybean whole-cell extract by preincubation with small regions of the CHS15 promoter or defined cis elements showed that trans factors that bind to G-box (CACGTG, -74 to -69) and H-box (CCTACC, -61 to -56 and -121 to -126) cis elements, respectively, make major contributions to the transcription of the CHS15 promoter in vitro. Both cis element/trans factor interactions in combination are required for maximal activity. Delineation of these functional cis element/trans factor interactions in vitro provides the basis for study of the mechanisms underlying developmental expression of CHS15 in pigmented petal cells established by G-box and H-box combinatorial interactions, and for characterization of the terminal steps of the signal pathway for stress induction of the phytoalexin defense response.

Binding constant determination studies utilizing recombinant delta CREB protein

In this study, we report the binding constants (Kd) of the cAMP-responsive element binding protein (delta-CREB) for various cAMP-response element (CRE) motifs. We utilized purified recombinant delta CREB protein in binding reactions with natural CRE motifs found in the promoter of two neuropeptide hormone genes and with several variant CRE motifs. The Kd of delta CREB for the perfectly palindromic CRE, TGACG-TCA, found within the somatostatin promoter is estimated to be 5.0 x 10(-9) M. The Kd of delta CREB for the variant CRE motif TG_CGTCA found within the enkephalin promoter is calculated to be in the 3 x 10(-8) M. These studies provide an in vitro quantitative assessment of the binding affinity of delta CREB for various CRE motifs.

Cross-family dimerization of transcription factors Fos/Jun and ATF/CREB alters DNA binding specificity

The Fos/Jun and ATF/CREB families of transcription factors function in coupling extracellular signals to alterations in expression of specific target genes. Like many eukaryotic transcription factors, these proteins bind to DNA as dimers. Dimerization is mediated by a structure known as the "leucine-zipper" motif. Although Fos/Jun and ATF/CREB were previously thought to interact preferentially with different DNA regulatory elements (the AP-1/TRE and ATF/CRE sites, respectively), we find that members of these two families form selective cross-family heterodimers. The resulting heterodimers display distinguishable DNA binding specificities from each other and from their parental homodimers. These findings indicate that the Fos/Jun and ATF/CREB families of transcription factors are not as distinct as was previously thought. We suggest that they can be grouped into a superfamily of transcription factors.

The cellular transcription factor CREB corresponds to activating transcription factor 47 (ATF-47) and forms complexes with a group of polypeptides related to ATF-43

Promoter elements containing the sequence motif CGTCA are important for a variety of inducible responses at the transcriptional level. Multiple cellular factors specifically bind to these elements and are encoded by a multigene family. Among these factors, polypeptides termed activating transcription factor 43 (ATF-43) and ATF-47 have been purified from HeLa cells and a factor referred to as cyclic AMP response element-binding protein (CREB) has been isolated from PC12 cells and rat brain. We demonstrated that CREB and ATF-47 are identical and that CREB and ATF-43 form protein-protein complexes. We also found that the cis requirements for stable DNA binding by ATF-43 and CREB are different. Using antibodies to ATF-43 we have identified a group of polypeptides (ATF-43) in the size range from 40 to 43 kDa. ATF-43 polypeptides are related by their reactivity with anti-ATF-43, DNA-binding specificity, complex formation with CREB, heat stability, and phosphorylation by protein kinase A. Certain cell types vary in their ATF-43 complement, suggesting that CREB activity is modulated in a cell-type-specific manner through interaction with ATF-43. ATF-43 polypeptides do not appear simply to correspond to the gene products of the ATF multigene family, suggesting that the size of the ATF family at the protein level is even larger than predicted from cDNA-cloning studies.

Promoter elements and erythroid cell nuclear factors that regulate alpha-globin gene transcription in vitro

We have previously purified four factors (alpha-IRP, alpha-CP1, alpha-CP2, and NF-E1) that interact with the promoter of the alpha-globin gene. One of these (NF-E1) is a tissue-restricted factor that has recently been cloned. The binding sites of these factors identify DNA sequence elements that might mediate the tissue-specific and inducible transcription of the alpha-globin gene. This possibility was tested in a series of in vitro transcription experiments. An examination of 5' truncated templates and synthetic promoters constituted from individual factor-binding sites apposed to the alpha-TATAA box showed that the binding elements of three factors (alpha-CP1, alpha-IRP, and NF-E1) mediate four- to sixfold activation of transcription in vitro. In contrast, one element (alpha-CP2) stimulated transcription less than twofold. The 5- to 10-fold stimulation of these latter templates upon addition of a DNA sequence affinity-purified factor suggests that alpha-CP2 is functionally limiting in nuclear extracts. Additional experiments further tested the effect of supplementing extracts with factors purified from erythroid cell nuclear extracts or, in the case of NF-E1, enriched from a bacterial cDNA expression system. Each factor tested stimulated transcription in vitro in a binding-site-dependent manner. Our results provide a comprehensive functional view of the murine alpha-globin promoter and suggest possible mechanisms for activation of alpha-globin gene transcription during induced differentiation of murine erythroleukemia cells.

The cellular transcription factor CREB corresponds to activating transcription factor 47 (ATF-47) and forms complexes with a group of polypeptides related to ATF-43

Promoter elements containing the sequence motif CGTCA are important for a variety of inducible responses at the transcriptional level. Multiple cellular factors specifically bind to these elements and are encoded by a multigene family. Among these factors, polypeptides termed activating transcription factor 43 (ATF-43) and ATF-47 have been purified from HeLa cells and a factor referred to as cyclic AMP response element-binding protein (CREB) has been isolated from PC12 cells and rat brain. We demonstrated that CREB and ATF-47 are identical and that CREB and ATF-43 form protein-protein complexes. We also found that the cis requirements for stable DNA binding by ATF-43 and CREB are different. Using antibodies to ATF-43 we have identified a group of polypeptides (ATF-43) in the size range from 40 to 43 kDa. ATF-43 polypeptides are related by their reactivity with anti-ATF-43, DNA-binding specificity, complex formation with CREB, heat stability, and phosphorylation by protein kinase A. Certain cell types vary in their ATF-43 complement, suggesting that CREB activity is modulated in a cell-type-specific manner through interaction with ATF-43. ATF-43 polypeptides do not appear simply to correspond to the gene products of the ATF multigene family, suggesting that the size of the ATF family at the protein level is even larger than predicted from cDNA-cloning studies.

Promoter elements and erythroid cell nuclear factors that regulate alpha-globin gene transcription in vitro

We have previously purified four factors (alpha-IRP, alpha-CP1, alpha-CP2, and NF-E1) that interact with the promoter of the alpha-globin gene. One of these (NF-E1) is a tissue-restricted factor that has recently been cloned. The binding sites of these factors identify DNA sequence elements that might mediate the tissue-specific and inducible transcription of the alpha-globin gene. This possibility was tested in a series of in vitro transcription experiments. An examination of 5' truncated templates and synthetic promoters constituted from individual factor-binding sites apposed to the alpha-TATAA box showed that the binding elements of three factors (alpha-CP1, alpha-IRP, and NF-E1) mediate four- to sixfold activation of transcription in vitro. In contrast, one element (alpha-CP2) stimulated transcription less than twofold. The 5- to 10-fold stimulation of these latter templates upon addition of a DNA sequence affinity-purified factor suggests that alpha-CP2 is functionally limiting in nuclear extracts. Additional experiments further tested the effect of supplementing extracts with factors purified from erythroid cell nuclear extracts or, in the case of NF-E1, enriched from a bacterial cDNA expression system. Each factor tested stimulated transcription in vitro in a binding-site-dependent manner. Our results provide a comprehensive functional view of the murine alpha-globin promoter and suggest possible mechanisms for activation of alpha-globin gene transcription during induced differentiation of murine erythroleukemia cells.

Cyclic AMP-dependent protein kinase regulates transcription of the phosphoenolpyruvate carboxykinase gene but not binding of nuclear factors to the cyclic AMP regulatory element

We have examined the binding of factors in rat liver nuclear extracts to the phosphoenolpyruvate carboxykinase (PEPCK) gene cyclic AMP (cAMP) response element (CRE) and other CREs and have isolated a rat liver CRE-binding protein (CREBP) cDNA. In addition, we have examined the influence of altering the phosphorylation state of nuclear factors on both CRE binding and in vitro transcription. Specific binding to the PEPCK CRE was measured in a mobility shift assay. CRE sequences of the PEPCK, somatostatin, and glycoprotein hormone alpha subunit genes competed equally for binding of rat liver nuclear factors to the PEPCK CRE, whereas mutant PEPCK CRE sequences did not compete for binding. Oligonucleotides complementary to rat pheochromocytoma CREBP (Gonzalez et al., Nature [London] 337:749-752, 1989) were used to prime rat liver and brain cDNA in the polymerase chain reaction. The predominant CREBP molecule obtained was identical to the rat pheochromocytoma CREBP except for a 14-amino-acid deletion in the N-terminal half that was also present in a human placental cDNA (Hoeffler et al., Science 242:1430-1433, 1988). The regulation of transcription by cAMP was examined by coincubation of rat liver nuclear extract with the purified catalytic subunit of cAMP-dependent protein kinase (protein kinase A). Although binding to the CRE was unaffected, in vitro transcription directed by the PEPCK promoter was stimulated by catalytic subunit, and this effect was blocked by protein kinase inhibitor peptide. In contrast, when nuclear extract was coincubated with phosphatase, there was substantial inhibition of in vitro transcription directed by the PEPCK promoter, but there was no effect on binding to the CRE. The major effects of catalytic subunit were exerted through the CRE, but residual stimulation was evident in promoter fragments containing only the TATA element. These data suggest that factors are bound to the CRE at constitutively high levels and that their capacity for transcriptional activation is regulated by phosphorylation.

Cyclic AMP-dependent protein kinase regulates transcription of the phosphoenolpyruvate carboxykinase gene but not binding of nuclear factors to the cyclic AMP regulatory element

We have examined the binding of factors in rat liver nuclear extracts to the phosphoenolpyruvate carboxykinase (PEPCK) gene cyclic AMP (cAMP) response element (CRE) and other CREs and have isolated a rat liver CRE-binding protein (CREBP) cDNA. In addition, we have examined the influence of altering the phosphorylation state of nuclear factors on both CRE binding and in vitro transcription. Specific binding to the PEPCK CRE was measured in a mobility shift assay. CRE sequences of the PEPCK, somatostatin, and glycoprotein hormone alpha subunit genes competed equally for binding of rat liver nuclear factors to the PEPCK CRE, whereas mutant PEPCK CRE sequences did not compete for binding. Oligonucleotides complementary to rat pheochromocytoma CREBP (Gonzalez et al., Nature [London] 337:749-752, 1989) were used to prime rat liver and brain cDNA in the polymerase chain reaction. The predominant CREBP molecule obtained was identical to the rat pheochromocytoma CREBP except for a 14-amino-acid deletion in the N-terminal half that was also present in a human placental cDNA (Hoeffler et al., Science 242:1430-1433, 1988). The regulation of transcription by cAMP was examined by coincubation of rat liver nuclear extract with the purified catalytic subunit of cAMP-dependent protein kinase (protein kinase A). Although binding to the CRE was unaffected, in vitro transcription directed by the PEPCK promoter was stimulated by catalytic subunit, and this effect was blocked by protein kinase inhibitor peptide. In contrast, when nuclear extract was coincubated with phosphatase, there was substantial inhibition of in vitro transcription directed by the PEPCK promoter, but there was no effect on binding to the CRE. The major effects of catalytic subunit were exerted through the CRE, but residual stimulation was evident in promoter fragments containing only the TATA element. These data suggest that factors are bound to the CRE at constitutively high levels and that their capacity for transcriptional activation is regulated by phosphorylation.

Positive and negative regulatory elements of chicken vitellogenin II gene characterized by in vitro transcription competition assays in a homologous system

A homologous in vitro transcription system was developed in which the cloned chicken vitellogenin II gene is faithfully transcribed by extracts prepared from chicken liver nuclei. The use of template deleted of its upstream region resulted in poor transcriptional efficiency, as did the use of extracts prepared from rooster liver, in which the gene is silent. The influence of individual cis elements was determined by transcription competition analysis. Oligonucleotides covering greater than 500 base pairs of the promoter region were used as competitor DNA in the in vitro reactions. Competition with an oligonucleotide covering part of the expression-specific DNase I hypersensitivity site B2, which contains a demethylation site, mCpG, at nucleotide position + 10, increased transcription of the gene, suggesting the binding of a repressor to this region. The enhancement of transcription was even more pronounced when the same oligonucleotide was methylated at the corresponding + 10 cytosine. Competition with oligonucleotides covering the TATA box, or the estrogen response element half-palindromic motif (GGTCA) at nucleotide positions -198 to -194, resulted in a large decrease in vitellogenin gene transcription, indicating that strongly activating factors bind to these regions. Competing oligonucleotides covering other GGTCA-containing motifs situated further upstream at nucleotide positions -292 to -288, -367 to -351, and -626 to -614 were increasingly less effective in inhibiting transcription. The results indicate that factors other than the estrogen receptor are involved in transcriptional activation of the vitellogenin II gene.

Neuropeptide gene expression and neural activity: assessing a working hypothesis in nucleus caudalis and dorsal horn neurons expressing preproenkephalin and preprodynorphin

1. The working hypothesis that neuropeptide gene expression in a neuron is an indicator of that neuron's physiological activity is discussed. 2. Representative examples from the literature are presented to support the hypothesis. 3. Further, we discuss the regulation of expression of two opioid peptides, preproenkephalin and preprodynorphin, in laminae I and II of the spinal cord and in nucleus caudalis of the trigeminal nuclear complex, where they may play a role in pain modulation. 4. The expression of the opioid peptide genes can be induced by both painful and nonnoxious stimuli in neurons in time-dependent and sensory-specific fashions.