NF-I proteins from brain interact with the proenkephalin cAMP inducible enhancer

A genome-wide screen of CREB occupancy identifies the RhoA inhibitors Par6C and Rnd3 as regulators of BDNF-induced synaptogenesis

Neurotrophin-regulated gene expression is believed to play a key role in long-term changes in synaptic structure and the formation of dendritic spines. Brain-derived neurotrophic factor (BDNF) has been shown to induce increases in dendritic spine formation, and this process is thought to function in part by stimulating CREB-dependent transcriptional changes. To identify CREB-regulated genes linked to BDNF-induced synaptogenesis, we profiled transcriptional occupancy of CREB in hippocampal neurons. Interestingly, de novo motif analysis of hippocampal ChIP-Seq data identified a non-canonical CRE motif (TGGCG) that was enriched at CREB target regions and conferred CREB-responsiveness. Because cytoskeletal remodeling is an essential element of the formation of dendritic spines, within our screens we focused our attention on genes previously identified as inhibitors of RhoA GTPase. Bioinformatic analyses identified dozens of candidate CREB target genes known to regulate synaptic architecture and function. We showed that two of these, the RhoA inhibitors Par6C (Pard6A) and Rnd3 (RhoE), are BDNF-induced CREB-regulated genes. Interestingly, CREB occupied a cluster of non-canonical CRE motifs in the Rnd3 promoter region. Lastly, we show that BDNF-stimulated synaptogenesis requires the expression of Par6C and Rnd3, and that overexpression of either protein is sufficient to increase synaptogenesis. Thus, we propose that BDNF can regulate formation of functional synapses by increasing the expression of the RhoA inhibitors, Par6C and Rnd3. This study shows that genome-wide analyses of CREB target genes can facilitate the discovery of new regulators of synaptogenesis.

Breast cancer cells proliferation is regulated by tyrosine phosphatase SHP1 through c-jun N-terminal kinase and cooperative induction of RFX-1 and AP-4 transcription factors

In this study, we show that proliferation of breast cancer cells is suppressed by IGF-1-activated JNK MAPK pathway. The molecular mechanism by which c-jun-NH,-kinase (JNK) activation induces antiproliferative signals in IGF-1-stimulated breast cancer cells remains unknown. Tyrosine phosphatase SHP1 is known to negatively regulate signal transduction pathways activated by cell surface receptors including IGF-1. Moreover, SHP1 transcript and protein levels are increased in epithelial tumors. Therefore, we hypothesized that IGF-activated JNK induces expression of SHP1 in breast cancer cells. To further clarify the role of SHP1 in tumor growth, we correlated the proliferation rates of breast adenocarcinoma cells with SHP1 expression and JNK activation. We show that proliferation of serum- or IGF-1-stimulated breast adenocarcinoma cells is negatively regulated by SHP1 and show for the first time that IGF-1-activated JNK induces SHP1 expression in MCF-7 cells used as experimental model. In an attempt to understand the mechanism by which serum- or IGF-1-activated JNK induces SHP1 expression resulting in suppression of cell proliferation, we reveal for the first time that in serum- or IGF-1-stimulated breast cancer MCF-7 cells, JNK induces SHP1 expression through the binding of AP-4 and RFX-1 transcription factors to the epithelial tissue-specific SHP1 promoter. Overall, we show for the first time that IGF-1-stimulated proliferation of breast adenocarcinoma cells is negatively regulated by SHP1 through activation of JNK.

Protein Kinase D Induces Transcription through Direct Phosphorylation of the cAMP-response Element-binding Protein

Protein kinase D (PKD), a family of serine/threonine kinases, can be activated by a multitude of stimuli in a protein kinase C-dependent or -independent manner. PKD is involved in signal transduction pathways controlling cell proliferation, apoptosis, motility, and protein trafficking. Despite its versatile functions, few genuine in vivo substrates for PKD have been identified. In this study we demonstrate that the transcription factor cAMP-response element-binding protein (CREB) is a direct substrate for PKD. PKD1 and CREB interact in cells, and activated PKD1 provokes CREB phosphorylation at Ser-133 both in vitro and in vivo. A constitutive active mutant of PKD1 stimulates GAL4-CREB-mediated transcription in a Ser-133-dependent manner, activates CRE-responsive promoters, and increases the expression of CREB target genes. PKD1 also enhances transcription mediated by two other members of the CREB family, ATF-1 and CREM. Our results describe a novel mechanism for PKD-induced signaling through activation of the transcription factor CREB and suggest that stimulus-induced phosphorylation of CREB, reported to be mediated by protein kinase C, may involve downstream activated PKD.

A Role for Nuclear Factor I in the Intrinsic Control of Cerebellar Granule Neuron Gene Expression

Nervous system formation requires the elaboration of a complex series of differentiation events in both a spatially and maturation-regulated manner. A fundamental question is how neuronal subtype specification and developmental gene expression are controlled within maturing neurons. The alpha6 subunit of the gamma-aminobutyric acid type A (GABA(A)) receptor (GABRA6) is preferentially expressed in cerebellar granule neurons and is part of an intrinsic program directing their differentiation. We have employed a lentiviral approach to examine the transcriptional mechanisms controlling neuronal subtype-selective expression of this gene. These studies demonstrated that nuclear factor I (NFI) proteins are required for both transgenic GABRA6 promoter activity as well as endogenous expression of this gene in cerebellar granule neurons. Chromatin immunoprecipitation also showed that NFI proteins are bound to the GABRA6 promoter in these cells in vivo. Furthermore, analyses of gene knockout mice revealed that Nfia is specifically required for normal expression of the GABRA6 gene in cerebellar granule neurons. NFI expression and DNA binding activity are highly enriched in granule neurons, implicating this transcription factor family in the neuronal subtype-selective expression of the GABRA6 gene. These studies define a new role for NFI proteins as neuronal subtype-enriched transcriptional regulators that participate in an intrinsic transcriptional program directing the differentiation of cerebellar granule neurons.

Nuclear factor 1 is required for both hormone-dependent chromatin remodeling and transcriptional activation of the mouse mammary tumor virus promoter

The mouse mammary tumor virus (MMTV) promoter has been used as a model to study how the glucocorticoid receptor (GR) remodels chromatin to allow other transcription factors to bind and activate transcription. To dissect the precise role of nuclear factor 1 (NF1) in chromatin remodeling and transcriptional activation, we used linker-scanning mutants of transcription factor binding sites on the MMTV promoter. We compared the NF1 mutant MMTV promoter in the context of transiently transfected templates (transient transfection) and templates organized as chromatin (stable transfection) to understand the effect of chromatin on factor binding and transcription. We show that on a transiently transfected template, mutation in the NF1 binding site reduces both basal and hormone-dependent transcription. This suggests that NF1 is required for transcription in the absence of organized chromatin. We also found that binding of NF1 on a transiently transfected template is independent of mutation in hormone response elements or the octamer transcription factor (OTF) binding site. In contrast, the binding of OTF proteins to a transiently transfected template was found to be dependent on the binding of NF1, which may imply that NF1 has a stabilizing effect on OTF binding. On a chromatin template, mutation in the NF1 binding site does not affect the positioning of nucleosomes on the promoter. We also show that in the absence of NF1 binding, GR-mediated chromatin remodeling of nucleosome B is reduced and hormone-dependent activation of transcription is abolished. Further, we demonstrate that NF1 is required for both the association of BRG1 chromatin remodeling complex and the GR on the promoter in vivo. These results suggest the novel possibility that NF1 may participate in chromatin remodeling activities in addition to directly enhancing transcription and that in the absence of its binding site the GR is unable to effectively bind the promoter and recruit the remodeling complex.

The comparative analysis of proenkephalin mRNA expression induced by cholera toxin and pertussis toxin in primary cultured rat cortical astrocytes

In rat astrocytes, incubation with cholera toxin (CTX; 0.1 microg/ml) for 8 h increased proenkephalin (proENK) mRNA level (10-fold), which was further increased by dexamethasone (DEX; 1 microM) (2.2-fold as much as CTX alone). Although pertussis toxin (PTX; 0.1 microg/ml) did not affect the basal proENK mRNA level, DEX significantly increased proENK mRNA level in PTX-treated cells (6-fold). The inhibition of protein synthesis by cycloheximide (CHX; 15 microM) also increased proENK mRNA level in PTX-treated cells (5.2-fold), but not in CTX-stimulated cells. The treatment with CTX, but not PTX, increased c-Fos and Fra-2 protein levels as well as AP-1, CRE, or ENKCRE-2 DNA binding activity, but neither toxin affected Fra-1, c-Jun, JunB, and JunD protein levels. CHX significantly attenuated CTX-induced increase of c-Fos or Fra-2 protein level and AP-1, CRE, or ENKCRE-2 DNA binding activity, although CHX alone did not affect the basal AP-1, CRE, and ENKCRE-2 DNA binding activities. Phosphorylated CREB level was increased by both CTX and PTX, although the magnitude of phosphorylation of CREB by PTX was much less than that by CTX. In addition, CHX further or persistently increased PTX- or CTX-induced phosphorylated CREB levels in parallel with increases in proENK mRNA. However, DEX did not alter the basal or stimulated phosphorylated-CREB level. These results suggest that the elevation of phosphorylation of CREB rather than AP-1 level may be involved in CTX-induced and CHX-dependent-PTX-induced increase of proENK mRNA level. In addition, AP-1 expression or CREB phosphorylation appears not to be involved the potentiative action of DEX on proENK mRNA expression in CTX- and PTX-treated astrocytes.

Transcriptional regulation of the human prepronociceptin gene

We have cloned regions of the 5'-untranslated region of the human prepronociceptin (ppN/OFQ) gene into a luciferase reporter plasmid, pGL3 Basic Vector. By primer extension analysis, we determined that one start site of transcription lies within the known human cDNA sequence. There are two cyclic AMP response elements (CRE) with the consensus sequence CGTCA within 250 bp of the start of transcription. We designed various constructs around these sites, performed transient transfections, and measured luciferase activity in NS20Y cells. Transcriptional activity could be regulated by a variety of factors including cAMP levels, Ca(2+), and particularly by a 125-bp region adjacent to an intron located 23 bp upstream of the translation initiating ATG. These data should help in understanding the regulatory mechanisms of ppN/OFQ gene transcription.

Roles of the NFI/CTF gene family in transcription and development

The Nuclear Factor I (NFI) family of site-specific DNA-binding proteins (also known as CTF or CAAT box transcription factor) functions both in viral DNA replication and in the regulation of gene expression. The classes of genes whose expression is modulated by NFI include those that are ubiquitously expressed, as well as those that are hormonally, nutritionally, and developmentally regulated. The NFI family is composed of four members in vertebrates (NFI-A, NFI-B, NFI-C and NFI-X), and the four NFI genes are expressed in unique, but overlapping, patterns during mouse embryogenesis and in the adult. Transcripts of each NFI gene are differentially spliced, yielding as many as nine distinct proteins from a single gene. Products of the four NFI genes differ in their abilities to either activate or repress transcription, likely through fundamentally different mechanisms. Here, we will review the properties of the NFI genes and proteins and their known functions in gene expression and development.

The interaction between the forkhead thyroid transcription factor TTF-2 and the constitutive factor CTF/NF-1 is required for efficient hormonal regulation of the thyroperoxidase gene transcription

The forkhead thyroid-specific transcription factor TTF-2 is the main mediator of thyrotropin and insulin regulation of thyroperoxidase (TPO) gene expression. This function depends on multimerization and specific orientation of its DNA-binding site, suggesting that TTF-2 is part of a complex interaction network within the TPO promoter. This was confirmed by transfection experiments and by protein-DNA interaction studies, which demonstrated that CTF/NF1 proteins bind 10 base pairs upstream of the TTF-2-binding site to enhance its action in hormone-induced expression of the TPO gene. GST pull-down assays showed that TTF-2 physically interacts with CTF/NF1 proteins. In addition, we demonstrate that increasing the distance between both transcription factors binding sites by base pair insertion results in loss of promoter activity and in a drastic decrease on the ability of the promoter to respond to the hormones. CTF/NF1 is a family of transcription factors that contributes to constitutive and cell-type specific gene expression. Originally identified as factors implicated in the replication of adenovirus, this group of proteins (CTF/NF1-A, -B, -C, and -X) is now known to be involved in the regulation of several genes. In contrast to other reports regarding the involvement of these proteins in inducible gene expression, we show here that members of this family of transcription factors are regulated by hormones. With the use of specific CTF/NF1 DNA probes and antibodies we demonstrate that CTF/NF1-C is a thyrotropin-, cAMP-, and insulin-inducible protein. Thus CTF/NF1 proteins do not only mediate hormone-induced gene expression cooperating with TTF-2, but are themselves hormonally regulated. All these findings are clearly of important value in understanding the mechanisms governing the transcription regulation of RNA polymerase II promoters, which often contain binding sites for multiple transcription factors.

Pituitary adenylate cyclase-activating polypeptide stimulates proenkephalin gene transcription through AP1- and CREB-dependent mechanisms

The effects of the pituitary adenylase cyclate-activating peptides (PACAP) 27 and 38 on proenkephalin (PENK) gene transcription were examined in PC12 (rat pheochromocytoma) cells using transient transfection assays. Both ligands stimulated PENK gene transcription in a dose-dependent manner, with an apparent ED50 close to 5 x 10(-11) M. Inactivation of cAMP dependent-protein kinase (PKA) with a dominant inhibitory mutant strongly reduced PACAP-stimulated PENK transcription. Using reporter genes driven by either the minimal TPA-responsive element (TRE: TGACTCA) or cAMP-responsive element (CRE: TGACGTCA), we showed that the two PACAPs activate transcription through both regulatory sequences. These effects could result from direct post-translational activation of Jun and CREB, as shown using GAL4-Jun or GAL4-CREB fusion proteins. Expression of a dominant inhibitory mutant of CREB decreased by 60% the response to PACAP, suggesting that CREB is implicated in PENK transactivation. Similarly, expression of c-fos antisense RNA reduced by 80% the stimulatory effects of PACAP. Taken together, these results indicate that PACAP stimulates PENK transcription by members of both the AP1 and the CREB families. However, AP1 by itself is not sufficient to increase PENK transcription, as insulin-like growth factor 1 (IGF1), which stimulates AP1 activity but not cAMP production, is unable to stimulate PENK transcription. These results indicate a cooperative effect of AP1 and CREB on PENK transcription.

Second-site proviral enhancer alterations in lymphomas induced by enhancer mutants of SL3-3 murine leukemia virus: negative effect of nuclear factor 1 binding site

SL3-3 is a highly T-lymphomagenic murine retrovirus. Previously, mutation of binding sites in the U3 repeat region for the AML1 transcription factor family (also known as core binding factor [CBF], polyomavirus enhancer binding protein 2 [PEBP2], and SL3-3 enhancer factor 1 [SEF1]) were found to strongly reduce the pathogenicity of SL3-3 (B. Hallberg, J. Schmidt, A. Luz, F. S. Pedersen, and T. Grundström, J. Virol. 65:4177-4181, 1991). We have now examined the few cases in which tumors developed harboring proviruses that besides the AML1 (core) site mutations carried second-site alterations in their U3 repeat structures. In three distinct cases we observed the same type of alteration which involved deletions of regions known to contain binding sites for nuclear factor 1 (NF1) and the addition of extra enhancer repeat elements. In transient-expression experiments in T-lymphoid cells, these new U3 regions acted as stronger enhancers than the U3 regions of the original viruses. This suggests that the altered proviruses represent more-pathogenic variants selected for in the process of tumor formation. To analyze the proviral alterations, we generated a series of different enhancer-promoter reporter constructs. These constructs showed that the additional repeat elements are not critical for enhancer strength, whereas the NF1 sites down-regulate the level of transcription in T-lymphoid cells whether or not the AML1 (core) sites are functional. We therefore also tested SL3-3 viruses with mutated NF1 sites. These viruses have unimpaired pathogenic properties and thereby distinguish SL3-3 from Moloney murine leukemia virus.

Dexamethasone represses phorbol ester-, forskolin-, and calcium-stimulated expression of a preproenkephalin A promoter-chloramphenicol acetyltransferase gene via a receptor-mediated mechanism

CV-1 cells were stably transfected with a preproenkephalin A (PPE) promoter-chloramphenicol acetyltransferase (CAT) reporter plasmid containing -176 to +171 bp of the human PPE gene. Low levels of CAT were expressed constitutively. The reporter enzyme activity was induced by treatment of the cells for 6 h with drugs that increased intracellular cAMP (forskolin and 8-bromo-cAMP), intracellular calcium (A23187), or protein kinase C activity (tetradecanoyl phorbol-4-acetate, TPA) in the presence of the phosphodiesterase inhibitor isobutylmethylxanthine. Co-administration of dexamethasone reduced the magnitude of phorbol ester-stimulated CAT activity by about 50%, while there were smaller but not significant effects on forskolin- or A23187-stimulated expression of this reporter construct. In transient transfections which included the PPE-CAT reporter gene and a glucocorticoid receptor expression plasmid, dexamethasone significantly reduced stimulated expression of the reporter by TPA, forskolin, and A23187. The effect was observed with 10(-8)-10(-6) M dexamethasone and was blocked by the presence of the glucocorticoid antagonist RU486, suggesting that the effect of dexamethasone was mediated by the glucocorticoid receptor. The promoter region contained in this construct lacks a classical glucocorticoid response element or known negative elements; thus, dexamethasone may reduce stimulated expression of the PPE promoter via indirect effects.

Long-term expression of the 35,000 mol. wt fos-related antigen in rat brain after kainic acid treatment

Systemic injection of kainic acid, a rigid analogue of glutamate, induces both the short-term and the long-term expression of activator protein-1 transcription factors. The short-term responses of activator protein-1 factors such as c-fos and fos-related antigens have been well studied. However, the long-term expression of activator protein-1 factor(s) induced by kainic acid is poorly understood. The present study was designed to document the long-term expression (up to seven months) of the fos-related antigens and to map their distributions in the rat brain after systemic treatment with kainic acid. A single dose of kainic acid (8 mg/kg) was injected i.p. into Fischer 344 rats and their epileptic seizure behaviour was monitored. The rats with full limbic seizures were chosen for long-term study. By using immunocytochemistry with an antibody that cross-reacts with all known fos-related antigens, western blot analysis and a gel mobility-shift assay, we have now shown that a 35,000 mol. wt fos-related antigen was induced by kainic acid treatment and expressed at high levels for up to five months. This fos-related antigen still maintains the activator protein-1 DNA binding activity in the rat brain seven months after kainic acid treatment. The fos-related antigens and activator protein-1 binding activity were continuously expressed at high levels throughout the experimental period in the dentate granule cells where mossy fibre collateral sprouting occurred after kainic acid treatment. Our results suggested that long-term expression of fos-related antigen may reflect the pathophysiological changes after kainic acid administration.

Transcription factors in primary glial cultures: changes with neuronal interactions

Several astrocyte gene products, such as enkephalin and glial fibrillary acidic protein (GFAP), are expressed at higher levels under in vitro conditions relative to in vivo. We have observed that cultured glial cells express high basal levels of transcription factors, such as fos-related antigens (Fra), c-Jun, JunD, and cAMP responsive element binding protein (CREB). When neuronal cells are plated on top of the monolayers, the expression of Fra, c-Jun, JunD, and GFAP decreases in the astroglial cells. The DNA binding activity to the AP-1-like sites of the GFAP and proenkephalin genes was examined in these cultures. The protein complex from glial cultures which recognizes the GFAP AP-1 element contained Fra immunoreactivity while the DNA binding from mixed neuronal/glial cultures consists of CREB-immunoreactive proteins. In glial cultures, no binding occurred to the proenkephalin AP-1-like element but a CREB-immunoreactive complex recognized this sequence in the mixed cultures. Thus, with the addition of neurons, both transcription factors and target gene products decrease in astroglial cells. The proteins that compose gene modulatory complexes also change suggesting that regulation of astroglial gene expression is modulated by neurons.

Distinct positive and negative regulatory elements control neuronal and hepatic transcription of the human transferrin gene

Transferrin (Tf), the iron-transport protein, plays an essential role in the central nervous system development, plasticity, and aging. As a first step toward elucidating the role of each transcription factor involved in the regulation of Tf gene expression, we have recently shown that similar promoter elements direct cell-type specific transcription in oligodendrocytes, epithelial choroid plexus cells, and in the neuronal cell line B103. Here we have analyzed the regulatory elements that control the level of expression of the Tf gene in neuronal cells. Transient expression experiments in B103 cells revealed that the -164/+1 promoter region is stimulated by a position-dependent -1140/-1000 upstream region. DNase I footprinting, gel retardation assays, and antibody reactivity data allowed us to characterize the nuclear factors interacting with this region. The upstream region I-binding protein (URI-BP) belongs to the steroid/retinoid receptor family, while URII-BP is a member of the nuclear factor I (NF-I) family. Interestingly, no enhancer nor silencer activity is detected in B103 cells. This contrasts with our findings in hepatoma cells, where the activity of the -125/+1 promoter can be repressed by a -1000/-819 upstream negative-acting region and stimulated by the -3600/-3300 enhancer. We demonstrate that the negative-acting region presents the characteristics of a silencer that interacts with a nuclear protein present in liver and absent in B103 cells. Similarly, B103 cells lack a nuclear protein able to bind to an essential site of the enhancer. This shows that in B103 cells, the inactivity of the silencer and the enhancer regions results from the absence of at least one essential nuclear protein.

The affinity of nuclear factor 1 for its DNA site is drastically reduced by nucleosome organization irrespective of its rotational or translational position

A DNA-bending sequence has been used for in vitro reconstitution of nucleosomes in order to direct a nuclear factor 1 (NF-1) binding site into different nucleosome positions. By this strategy nucleosomes were obtained that had one of two rotational positions of the NF-1 binding site, one oriented toward the periphery and the other toward the histone octamer, translationally positioned 50 and 45 base pairs, respectively, from the nucleosome dyad. The affinity of partially purified NF-1 for these nucleosomal targets was compared with its affinity for free DNA by dimethylsulfate methylation protection and DNase I footprinting assays. The binding affinity of NF-1 to all nucleosomal targets was reduced 100-300-fold compared with its affinity for free DNA. The two rotational settings of the NF-1 site showed the same binding affinity for NF-1 as did other nucleosome constructs in which the NF-1 binding site was translationally positioned from 10 to 40 base pairs from the nucleosome dyad. We conclude that the nucleosomal inhibition of NF-1 binding is an inherent characteristic of NF-1 since another transcription factor, the glucocorticoid receptor, is able to bind to its DNA site in a nucleosome.

Proenkephalin gene regulation in the neuroendocrine hypothalamus: a model of gene regulation in the CNS

During the past decade, a great deal of progress has been made in studying the mechanisms by which transcription of neuropeptides is regulated by second messengers and neural activity. Such investigations, which have depended to a great extent on the use of transformed cell lines, are far from complete. Yet a major challenge for the coming decade is to understand the regulation of neuropeptide genes by physiologically and pharmacologically relevant stimuli in appropriate cell types in vivo. The proenkephalin gene, a member of the opioid gene family, has served as a model to study regulated transcription, not only in cell lines, but also in central (e.g., hypothalamic) and peripheral (e.g., adrenal) neuroendocrine tissues. Here we review regulation of proenkephalin gene expression in the hypothalamus. Several approaches, including in situ hybridization, use of transgenic mice, and the adaptation of electrophoretic mobility shift assays to complex tissues, have played critical roles in recent advances. A summary of possible future developments in this field of research is also presented.

Organization of the alpha-globin promoter and possible role of nuclear factor I in an alpha-globin-inducible and a noninducible cell line

Nuclear factor I (NFI) was suggested to be involved in the expression of the human alpha-globin gene. Two established cell lines, which express alpha-globin differentially, were therefore compared for differences in binding of NFI at the alpha-globin promoter in vivo. HeLa cells, in which alpha-globin is repressed, show a high density promoter occupation with several proteins associated with structurally distorted DNA. Cell line K562, which is inducible for alpha-globin, surprisingly was found to be heterogeneous consisting mainly of cells (approximately 95%) unable to express alpha-globin. However, the promoter of the nonexpressing K562 cells was clearly different from that of HeLa cells, being occupied only at basal transcriptional elements. Therefore, the alpha-globin gene in these K562 cells may not be truly repressed, but in an intermediate state between repression and active transcription. The NFI site of the alpha-globin promoter appeared occupied in HeLa but free of proteins in K562 cells. All cells of both cell lines produce NFI, but the composition and DNA binding affinity of NFI species differ significantly between the two cell lines. Therefore, distinct forms of NFI may repress alpha-globin transcription in HeLa cells. However, NFI is apparently not involved in establishing the latent transcriptional state of the majority of K562 cells.

Three immediate early gene response elements in the proximal preprotachykinin-A promoter in two functionally distinct domains

The preprotachykinin-A promoter contains two blocks of DNA sequence, with a high degree of homology to one another, both containing activator protein 1/cAMP response element-like elements which constitute cis-acting regulatory domains. These two domains are differentially regulated in HeLa cells and primary cultures of dorsal root ganglion neurons when they are placed in the context of a reporter gene driven by the c-fos minimum promoter. One of the domains, corresponding to a region of the preprotachykinin promoter spanning nucleotides -345 to -308, contains two activator protein 1 elements adjacent to an E-box binding protein consensus sequence. Both of the activator protein 1 elements can bind a complex containing c-fos/c-fos related antigen proteins and the adjacent E-box element is specifically recognized by proteins present in HeLa nuclear extract. This domain requires the synergistic action of both activator protein 1 elements to drive expression of the reporter gene in both HeLa and dorsal root ganglion cells. The second or proximal domain spans nucleotides -198 to -155 and contains a previously characterized activator protein 1/cAMP response element/ATF enhancer element which, in contrast to the activator protein 1 elements in the distal domain, functions in both HeLa and dorsal root ganglion cells as one copy. This domain is differentially regulated in HeLa and dorsal root ganglia. The previously characterized enhancer activity is repressed in the context of the extended cis-acting domain in HeLa cells but remains active in dorsal root ganglion, although no further enhancement of activity supported by the single enhancer is observed when in the context of the extended sequence. This proximal domain, in addition to binding the enhancer complex, can be bound by at least two other complexes, one of which binds to an E-box consensus sequence. As the elements corresponding to the E-box consensus in both domains cross-compete for binding of specific complex(es) it would appear that repression of the activity of the proximal domain is correlated with a specific protein complex binding adjacent to the characterized enhancer in the region spanning nucleotides -198 to -155. The preprotachykinin-A proximal promoter is therefore bound by multiple activator protein I complexes, which in the context of the cis-acting domains in which they are present can be differentially regulated. In the proximal domain their function may also be regulated in a tissue-specific manner by other proteins which bind to adjacent regulatory elements.

The transcriptional regulation of the preproenkephalin gene

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C/EBP-related sites in addition to a STAT site are necessary for ciliary neurotrophic factor-leukemia inhibitory factor-dependent transcriptional activation by the vasoactive intestinal peptide cytokine response element

The neuropoietic cytokines ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF) regulate VIP gene expression through a cytokine response element (CyRE) which interacts with members of the STAT transcription factor family. The CyRE STAT site is, however, insufficient to mediate full transcriptional activation by CNTF/LIF, suggesting that other sequences and nuclear proteins are also important. As C/EBP proteins participate in the transcriptional effects of the related cytokine, interleukin-6, we investigated the role of possible C/EBP-binding sites in the response of the VIP CyRE to CNTF/LIF. Using DNase I footprinting, transactivation studies, DNA mobility shift assays, and mutational analysis, three sites within the VIP CyRE were identified as C/EBP-related binding sites and shown to be important to CNTF/LIF-mediated transcriptional activation. The CyRE C/EBP-related sites interact with nuclear proteins from the human neuroblastoma cell line, NBFL, including a novel, protein synthesis-dependent, nuclear protein complex, induced by CNTF treatment. These nuclear proteins are not, however, recognized by antisera to known C/EBP proteins. Therefore, other nuclear proteins regulated by independent pathways act in concert with the JAK-STAT pathway to mediate CNTF/LIF regulation of VIP gene expression through the CyRE.

Protein-DNA interactions during phenotypic differentiation

We have been studying the molecular mechanism of neuronal differentiation through which the multipotent precursor becomes limited to the final transmitter phenotype. Here we focused on the role of the 5' proximal regulatory cassette (-190; +53 bp) of the rat enkephalin (rENK) gene in the developmental regulation of the enkephalin phenotype. Several well characterized cis-elements, including AP2, CREB, NF1, and NFkB, reside on this region of the rENK gene. These motifs were sufficient to confer activity-dependent expression of the gene during neurodifferentiation when it was tested using transient transfection assays of primary developing spinal cord neurons treated with tetrodotoxin (TTX). This region was then used as a DNA probe in mobility shift assays, with nuclear proteins derived from phenotypically and ontogenetically distinct brain regions. Only a few low abundance protein-DNA complexes were detected and only with nuclear proteins derived from developing but not from adult brain. The spatiotemporal pattern of these complexes did not show correlation with enkephalin expression which was assessed by RT-PCR. We employed synthetic probes corresponding to consensus as well as ENK-specific sequences of the individual motifs to identify the nature of the observed bands. Although both consensus NF1 and enkCRE1(NF1) formed complexes with nuclear proteins derived from the striatum and cortex at various ages, the appearance of the bands was not correlated with ENK expression. Surprisingly, no complexes were detected if other ENK-specific motifs were used as probes. We also tested nuclear extracts derived from forskolin-induced and control C6 glioma cells, again using the whole proximal regulatory cassette as well as individual motifs. These experiments showed the formation of elaborate protein-DNA bands. There was no direct correlation between the appearance of bands and forskolin-induced ENK expression. Unexpectedly, all ENK-specific motifs formed specific and highly abundant protein-DNA complexes when nuclear extracts from the human tumor cell line (HeLa), which does not express ENK, were used. Based on these observations, we concluded that: 1. Interactions between the proximal regulatory cassette and additional probably far distant regions of the rENK gene and their binding proteins may be necessary to confer developmentally regulated, cell-specific expression of the ENK gene; and 2. Inducibility of the gene by common cis-elements can be governed by this region; however, the cell-specificity of the induction remains elusive.

Fibroblast growth factor and cyclic AMP (cAMP) synergistically activate gene expression at a cAMP response element

Growth factors and cyclic AMP (cAMP) are known to activate distinct intracellular signaling pathways. Fibroblast growth factor (FGF) activates ras-dependent kinase cascades, resulting in the activation of MAP kinases, whereas cAMP activates protein kinase A. In this study, we report that growth factors and cAMP act synergistically to stimulate proenkephalin gene expression. Positive synergy between growth factor- and cAMP-activated signaling pathways on gene expression has not been previously reported, and we suggest that these synergistic interactions represent a useful model for analyzing interactions between these pathways. Transfection and mutational studies indicate that both FGF-dependent gene activation and cAMP-dependent gene activation require cAMP response element 2 (CRE-2), a previously characterized cAMP-dependent regulatory element. Furthermore, multiple copies of this element are sufficient to confer FGF regulation upon a minimal promoter, indicating that FGF and cAMP signaling converge upon transcription factors acting at CRE-2. Among many different ATF/AP-1 factors tested, two factors, ATF-3 and c-Jun, stimulate proenkephalin transcription in an FGF- or Ras-dependent fashion. Finally, we show that ATF-3 and c-Jun form heterodimeric complexes in SK-N-MC cells and that the levels of both proteins are increased in response to FGF but not cAMP. Together, these results indicate that growth factor- and cAMP-dependent signaling pathways converge at CRE-2 to synergistically stimulate gene expression and that ATF-3 and c-Jun regulate proenkephalin transcription in response to both growth factor- and cAMP-dependent intracellular signaling pathways.

Fibroblast growth factor and cyclic AMP (cAMP) synergistically activate gene expression at a cAMP response element

Growth factors and cyclic AMP (cAMP) are known to activate distinct intracellular signaling pathways. Fibroblast growth factor (FGF) activates ras-dependent kinase cascades, resulting in the activation of MAP kinases, whereas cAMP activates protein kinase A. In this study, we report that growth factors and cAMP act synergistically to stimulate proenkephalin gene expression. Positive synergy between growth factor- and cAMP-activated signaling pathways on gene expression has not been previously reported, and we suggest that these synergistic interactions represent a useful model for analyzing interactions between these pathways. Transfection and mutational studies indicate that both FGF-dependent gene activation and cAMP-dependent gene activation require cAMP response element 2 (CRE-2), a previously characterized cAMP-dependent regulatory element. Furthermore, multiple copies of this element are sufficient to confer FGF regulation upon a minimal promoter, indicating that FGF and cAMP signaling converge upon transcription factors acting at CRE-2. Among many different ATF/AP-1 factors tested, two factors, ATF-3 and c-Jun, stimulate proenkephalin transcription in an FGF- or Ras-dependent fashion. Finally, we show that ATF-3 and c-Jun form heterodimeric complexes in SK-N-MC cells and that the levels of both proteins are increased in response to FGF but not cAMP. Together, these results indicate that growth factor- and cAMP-dependent signaling pathways converge at CRE-2 to synergistically stimulate gene expression and that ATF-3 and c-Jun regulate proenkephalin transcription in response to both growth factor- and cAMP-dependent intracellular signaling pathways.

Cloning and functional analysis of spliced isoforms of human nuclear factor I-X: interference with transcriptional activation by NFI/CTF in a cell-type specific manner

Previous studies of the epithelial specificity of the human papillomavirus type 16 (HPV-16) enhancer pointed out an important role of nuclear factor I (NFI). In epithelial cells, NFI proteins are derived from the NFI-C gene and referred to as NFI/CTF. In contrast, fibroblasts, where the enhancer is inactive, express high levels of NFI from the NFI-X gene. To compare NFI-C and NFI-X derived transcription factors, we cloned and functionally investigated two differentially spliced forms of NFI-X from human fibroblasts. NFI-X1 has 95% homology with a transcript previously identified in hamster liver cells. NFI-X2, a spliced variant, misses 41 amino acids of the proline-rich activation domain. NFI-X expression, examined by Northern blots, shows strong cell-type specific variation in comparison with NFI/CTF. While the transcriptional activation domain of NFI-X2, functionally tested as GAL4-fusion protein in epithelial and fibroblast cells, activates transcription from promoter as well as enhancer position similar to NFI/CTF-1, the activation domain of NFI-X1 fails to activate transcription from enhancer position. In Drosophila cells, void of endogenous NFI proteins, full length NFI/CTF-1 and NFI-X2 activate a reporter construct containing only NFI sites as well as the NFI dependent HPV-16 enhancer. In contrast, NFI-X1 fails to activate the HPV-16 enhancer. Furthermore, overexpression of NFI-X1 in epithelial cells down-regulates the HPV-16 enhancer. Our findings suggest that the family of NFI transcription factors should not be viewed as constitutive activators, but rather, that NFI-C and NFI-X have divergent functions after binding in promoter or enhancer position. This property, combined with the differential expression of NFI-X, can achieve cell-type specificity of NFI dependent promoters and enhancers.

Analysis of the human MBP promoter in primary cultures of oligodendrocytes: positive and negative cis-acting elements in the proximal MBP promoter mediate oligodendrocyte-specific expression of MBP

Since the regulation of myelin basic protein expression depends primarily on the initiation of transcription, we analyzed the 5' flanking region of the human myelin basic protein gene in transient transfection studies in primary cultures of developing oligodendrocytes. We demonstrated that 149 base pairs 5' of the initiation of transcription was sufficient to direct oligodendrocyte-specific expression of myelin basic protein. The capsite of the fusion transcript was identical with that of the endogenous myelin basic protein transcript, and chloramphenicol acetyl transferase reporter gene expression was restricted to oligodendrocytes in these cultures. Within this 149 base pair region, one distal, negative cis-acting segment, containing a consensus nuclear factor I site, and one proximal, positive cis-acting segment were identified. The distal segment behaved more negatively in Cos-7 cells than in oligodendrocytes, reducing expression to background levels. Furthermore, these functionally important cis-acting segments bound oligodendrocyte nuclear proteins in a pattern differing from other cells, including Cos-7 cells. Interestingly, the distal segment increased heterologous SV40 promoter activity in oligodendrocytes but had no effect on the SV40 promoter in Cos-7 cells. We conclude that the functionally negative distal segment may mediate oligodendrocyte-specific expression of MBP by restricting its expression in other cells. These experiments strongly support using primary cultures of oligodendrocytes for analyzing the myelin-specific promoters.

Jun is phosphorylated by several protein kinases at the same sites that are modified in serum-stimulated fibroblasts

c-jun is a member of the family of immediate-early genes whose expression is induced by factors such as serum stimulation, phorbol ester, and differentiation signals. Here we show that increased Jun synthesis after serum stimulation is accompanied by a concomitant increase in phosphorylation. Several serine-threonine kinases were evaluated for their ability to phosphorylate Jun in vitro. p34cdc2, protein kinase C, casein kinase II, and pp44mapk phosphorylated Jun efficiently, whereas cyclic AMP-dependent protein kinase and glycogen synthase kinase III did not. The sites phosphorylated by p34cdc2 were similar to those phosphorylated in vivo after serum induction. The major sites of phosphorylation were mapped to serines 63, 73, and 246. Phosphorylation of full-length Jun with several kinases did not affect the DNA-binding activity of Jun homodimers or Fos-Jun heterodimers. Comparison of the DNA binding and in vitro transcription properties of wild-type and mutated proteins containing either alanine or aspartic acid residues in place of Ser-63, -73, and -246 revealed only minor differences among homodimeric complexes and no differences among Fos-Jun heterodimers. Thus, phosphorylation of Jun did not produce a significant change in dimerization, DNA-binding, or in vitro transcription activity. The regulatory role of phosphorylation in the modulation of Jun function is likely to be considerably more complex than previously suggested.

Jun is phosphorylated by several protein kinases at the same sites that are modified in serum-stimulated fibroblasts

c-jun is a member of the family of immediate-early genes whose expression is induced by factors such as serum stimulation, phorbol ester, and differentiation signals. Here we show that increased Jun synthesis after serum stimulation is accompanied by a concomitant increase in phosphorylation. Several serine-threonine kinases were evaluated for their ability to phosphorylate Jun in vitro. p34cdc2, protein kinase C, casein kinase II, and pp44mapk phosphorylated Jun efficiently, whereas cyclic AMP-dependent protein kinase and glycogen synthase kinase III did not. The sites phosphorylated by p34cdc2 were similar to those phosphorylated in vivo after serum induction. The major sites of phosphorylation were mapped to serines 63, 73, and 246. Phosphorylation of full-length Jun with several kinases did not affect the DNA-binding activity of Jun homodimers or Fos-Jun heterodimers. Comparison of the DNA binding and in vitro transcription properties of wild-type and mutated proteins containing either alanine or aspartic acid residues in place of Ser-63, -73, and -246 revealed only minor differences among homodimeric complexes and no differences among Fos-Jun heterodimers. Thus, phosphorylation of Jun did not produce a significant change in dimerization, DNA-binding, or in vitro transcription activity. The regulatory role of phosphorylation in the modulation of Jun function is likely to be considerably more complex than previously suggested.

Primary sequence of -1436 to +53 bp of the rat preproenkephalin gene putative Z-DNA and regulatory motifs

We report novel sequence data extending -1436 bases 5' of the rat proenkephalin gene start site known as E4. We noted an interesting stretch of 58 bases of alternating pyrimidines that lies immediately adjacent to 71 bases of an alternating purine-pyrimidine Z-DNA-like sequence that lies between -694 bp and -566 bp. Multiple sequence homologies to putative cis-acting regulatory factor binding sites were identified by a computer aided sequence search.

Preproenkephalin promoter "cassette" confers brain expression and synaptic regulation in transgenic mice

The preproenkephalin A gene is a neurotransmitter gene whose expression can be modulated "trans-synaptically" by changes in neuronal activity. DNA sequences lying within 200 base pairs of this gene's transcription start site resemble consensus binding sites for several transcription factor families. In nonneuronal cell cultures, this promoter region is sufficient to mediate gene responses to depolarization, phorbol esters, adenylate cyclase, and calcium fluxes. To assess the role that these cis-acting elements could play in preproenkephalin expression and regulation in vivo, the expression of a construct containing this 200-base-pair region fused to the chloramphenicol acetyltransferase gene was examined in transgenic mice. This promoter confers modest expression in brain, adrenal, and small intestine, with substantially higher levels in testis. These elements confer trans-synaptic regulation in two well-studied models of trans-synaptic preproenkephalin upregulation but not in a third system, underscoring the specificity of the regulatory sequence elements implicated in the synaptic regulation of neuronal genes.

Primary afferent stimulation acts through a 193 base pair promoter region to upregulate preproenkephalin expression in dorsal horn of transgenic mice

The expression of the principal opioid peptide gene, preproenkephalin A, is exquisitely regulated by primary afferent inputs to the spinal and medullary dorsal horns. This regulated expression in response to neural synaptic activity has been referred to as trans-synaptic regulation. To define which DNA regions could mediate this trans-synaptic regulation, transgenic 'HEC' mice whose genomes include 193 bp of the human preproenkephalin A promoter fused to a chloramphenicol acetyltransferase (CAT) reporter gene were studied. Mice received unilateral electrical stimulation of the trigeminal ganglion or adjuvant injection into the hindpaw, stimuli known to regulate dorsal horn proenkephalin expression in vivo. CAT activity conferred by this promoter displayed trans-synaptic upregulation with both stimuli. Although the level of the upregulation was 2- to 3-fold higher than the change in the wild type gene, several features of this induction paralleled aspects of the behavior of the wild-type gene: the rapidity of responses to trigeminal ganglion stimulation, the stimulation intensity dependence of responses to trigeminal ganglion stimulation and the time course of upregulation noted following adjuvant injection. Regulatory proteins binding to this restricted promoter region are thus likely to mediate aspects of dorsal horn enkephalin regulation by pain and other somatic stimuli.

Cell-type-specific expression of the rat thyroperoxidase promoter indicates common mechanisms for thyroid-specific gene expression

A 420-bp fragment from the 5' end of the rat thyroperoxidase (TPO) gene was fused to a luciferase reporter and shown to direct cell-type-specific expression when transfected into rat thyroid FRTL-5 cells. Analysis of this DNA fragment revealed four regions of the promoter which interact with DNA-binding proteins present in FRTL-5 cells. Mutation of the DNA sequence within any of these regions reduced TPO promoter activity. The trans-acting factors binding to these sequences were compared with thyroid transcription factor 1 (TTF-1) and TTF-2, previously identified as transcriptional activators of another thyroid-specific gene, the thyroglobulin (Tg) gene. Purified TTF-1 binds to three regions of TPO which are protected by FRTL-5 proteins. Two of the binding sites overlap with recognition sites for other DNA-binding proteins. One TTF-1 site can also bind a protein (UFB) present in the nuclei of both expressing and nonexpressing cells. TTF-1 binding to the proximal region overlaps with that for a novel protein present in FRTL-5 cells which can also recognize the promoter-proximal region of Tg. Using a combination of techniques, the factor binding to the fourth TPO promoter site was shown to be TTF-2. We conclude, therefore, that the FRTL-5-specific expression of two thyroid restricted genes, encoding TPO and Tg, relies on a combination of the same trans-acting factors present in thyroid cells.

Cell-type-specific expression of the rat thyroperoxidase promoter indicates common mechanisms for thyroid-specific gene expression

A 420-bp fragment from the 5' end of the rat thyroperoxidase (TPO) gene was fused to a luciferase reporter and shown to direct cell-type-specific expression when transfected into rat thyroid FRTL-5 cells. Analysis of this DNA fragment revealed four regions of the promoter which interact with DNA-binding proteins present in FRTL-5 cells. Mutation of the DNA sequence within any of these regions reduced TPO promoter activity. The trans-acting factors binding to these sequences were compared with thyroid transcription factor 1 (TTF-1) and TTF-2, previously identified as transcriptional activators of another thyroid-specific gene, the thyroglobulin (Tg) gene. Purified TTF-1 binds to three regions of TPO which are protected by FRTL-5 proteins. Two of the binding sites overlap with recognition sites for other DNA-binding proteins. One TTF-1 site can also bind a protein (UFB) present in the nuclei of both expressing and nonexpressing cells. TTF-1 binding to the proximal region overlaps with that for a novel protein present in FRTL-5 cells which can also recognize the promoter-proximal region of Tg. Using a combination of techniques, the factor binding to the fourth TPO promoter site was shown to be TTF-2. We conclude, therefore, that the FRTL-5-specific expression of two thyroid restricted genes, encoding TPO and Tg, relies on a combination of the same trans-acting factors present in thyroid cells.

Interaction of DNA-binding proteins with a milk protein gene promoter in vitro: identification of a mammary gland-specific factor

The minimal 5' regulatory region of the sheep beta-lactoglobulin gene (BLG), as defined in transgenic mice, was used to identify nuclear factors which may be involved in milk protein gene expression in the lactating mammary gland. This 406bp promoter region was dissected into short, overlapping, double-stranded oligonucleotides to facilitate identification of the bound proteins. A variety of sites, for both known and previously undescribed DNA-binding proteins, are occupied in vitro. Some of these factors were investigated in detail. Two forms of nuclear factor I (NFI), which have different recognition site affinities, are present in nuclear extracts from lactating mammary gland and bind to at least 5 sites in this BLG control element. In addition, a factor (milk protein binding factor, MPBF) which is specific to extracts from both mouse and sheep lactating mammary gland binds to 3 BLG promoter sites and may be a milk protein gene transcription factor.