Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “REPRESSION”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 181 records · Page 10Linked to original sources
PubMed1995

Binding sites for transcription factor NTF-1/Elf-1 contribute to the ventral repression of decapentaplegic.

The Dorsal morphogen is a transcription factor that activates some genes and represses others to establish multiple domains of gene expression along the dorsal/ventral axis of the early Drosophila embryo. Repression by Dorsal appears to require accessory proteins that bind to corepression elements in Dorsal-dependent regulatory modules called ventral repression regions (VRRs). We have identified a corepression element in decapentaplegic (dpp), a zygotically active gene that is repressed by the Dorsal morphogen. This dpp repression element (DRE) is located within a previously identified VRR and close to essential Dorsal-binding sites. We have purified a factor from Drosophila embryo extracts that binds to the DRE but not to mutant forms of the DRE that fail to support efficient repression. This protein also binds to an apparently essential region in a VRR associated with the zerknüllt (zen) gene. One of the DREs in the dpp VRR overlaps the binding site for a potential activator protein suggesting that one mechanism of ventral repression may be the mutually exclusive binding of repressor and activator proteins. We have found the DRE-binding protein to be identical to NTF-1 (equivalent to Elf-1, the product of the grainyhead gene), a factor originally identified as an activator of the Ultrabithorax and Dopa decarboxylase promoters. NTF-1 mRNA is synthesized during oogenesis and deposited in the developing oocyte where it is available to contribute to ventral repression during early embryogenesis. Previous studies have shown that overexpression of NTF-1 in the postblastoderm embryo results in a phenotype that is consistent with a role for this factor in the repression of dpp later in embryogenesis.

Animals↗
PubMed2001

Active repression of RAR signaling is required for head formation.

The retinoic acid receptors (RARs) recruit coactivator and corepressor proteins to activate or repress the transcription of target genes depending on the presence of retinoic acid (RA). Despite a detailed molecular understanding of how corepressor complexes function, there is no in vivo evidence to support a necessary function for RAR-mediated repression. Signaling through RARs is required for patterning along the anteroposterior (A-P) axis, particularly in the hindbrain and posterior, although the absence of RA is required for correct anterior patterning. Because RARs and corepressors are present in regions in which RA is absent, we hypothesized that repression mediated through unliganded RARs might be important for anterior patterning. To test this hypothesis, specific reagents were used that either reduce or augment RAR-mediated repression. Derepression of RAR signaling by expressing a dominant-negative corepressor resulted in embryos that exhibited phenotypes similar to those treated by RA. Anterior structures such as forebrain and cement gland were greatly reduced, as was the expression of molecular markers. Enhancement of target gene repression using an RAR inverse agonist resulted in up-regulation of anterior neural markers and expansion of anterior structures. Morpholino antisense oligonucleotide-mediated RARalpha loss-of-function phenocopied the effects of RA treatment and dominant-negative corepressor expression. Microinjection of wild-type or dominant-negative RARalpha rescued the morpholino phenotype, confirming that RAR is functioning anteriorly as a transcriptional repressor. Lastly, increasing RAR-mediated repression potentiated head-inducing activity of the growth factor inhibitor cerberus, whereas releasing RAR-mediated repression blocked cerberus from inducing ectopic heads. We conclude that RAR-mediated repression of target genes is critical for head formation. This requirement establishes an important biological role for active repression of target genes by nuclear hormone receptors and illustrates a novel function for RARs during vertebrate development.

Animals↗
PubMed2001

Isolation and phenotypic characterization of Pseudomonas aeruginosa pseudorevertants containing suppressors of the catabolite repression control-defective crc-10 allele.

The amiE gene encodes an aliphatic amidase capable of converting fluoroacetamide to the toxic compound fluoroacetate and is one of many genes whose expression is subject to catabolite repression control in Pseudomonas aeruginosa. The protein product of the crc gene, Crc, is required for repression of amiE and most other genes subject to catabolite repression control in this bacterium. When grown in a carbon source such as succinate, wild-type P. aeruginosa is insensitive to fluoroacetamide (due to repression of amiE expression). In contrast, mutants harboring the crc-10 null allele cannot grow in the presence of fluoroacetamide (due to lack of repression of amiE). Selection for succinate-dependent, fluoroacetamide-resistant derivatives of the crc-10 mutant yielded three independent pseudorevertants containing suppressors that restored a degree of catabolite repression control. Synthesis of Crc protein was not reestablished in these pseudorevertants. All three suppressors of crc-10 were extragenic, and all three also suppressed a Delta crc::tetA allele. In each of the three pseudorevertants, catabolite repression control of amidase expression was restored. Catabolite repression control of mannitol dehydrogenase production was also restored in two of the three isolates. None of the suppressors restored repression of glucose-6-phosphate dehydrogenase or pyocyanin production.

Amidohydrolases↗
PubMed1971

Catabolite repression of tryptophanase in Escherichia coli.

Catabolite repression of tryptophanase was studied in detail under various conditions in several strains of Escherichia coli and was compared with catabolite repression of beta-glactosidase. Induction of tryptophanase and beta-galactosidase in cultures grown with various carbon sources including succinate, glycerol, pyruvate, glucose, gluconate, and arabinose is affected differently by the various carbon sources. The extent of induction does not seem to be related to the growth rate of the culture permitted by the carbon source during the course of the experiment. In cultures grown with glycerol as carbon source, preinduced for beta-galactosidase or tryptophanase and made permeable by ethylenediaminetetraacetic acid (EDTA) treatment, catabolite repression of tryptophanase was not affected markedly by the addition of cAMP (3',5'-cyclic adenosine monophosphate). Catabolite repression by glucose was only partially relieved by the addition of cAMP. In contrast, under the same conditions, cAMP completely relieved catabolite repression of beta-galactosidase by either pyruvate or glucose. Under conditions of limited oxygen, induction of tryptophanase is sensitive to catabolite repression; under the same conditions, beta-galactosidase induction is not sensitive to catabolite repression. Induction of tryptophanase in cells grown with succinate as carbon source is sensitive to catabolite repression by glycerol and pyruvate as well as by glucose. Studies with a glycerol kinaseless mutant indicate that glycerol must be metabolized before it can cause catabolite repression. The EDTA treatment used to make the cells permeable to cAMP was found to affect subsequent growth and induction of either beta-galactosidase or tryptophanase much more adversely in E. coli strain BB than in E. coli strain K-12. Inducation of tryptophanase was reduced by the EDTA treatment significantly more than induction of beta-galactosidase in both strains. Addition of 2.5 x 10(-3)m cAMP appeared partially to reverse the inhibitory effect of the EDTA treatment on enzyme induction but did not restore normal growth.

Arabinose↗
PubMed1992

Catabolite repression of the xyl operon in Bacillus megaterium.

We characterized catabolite repression of the genes encoding xylose utilization in Bacillus megaterium. A transcriptional fusion of xylA encoding xylose isomerase to the spoVG-lacZ indicator gene on a plasmid with a temperature-sensitive origin of replication was constructed and efficiently used for single-copy replacement cloning in the B. megaterium chromosome starting from a single transformant. In the resulting strain, beta-galactosidase expression is 150-fold inducible by xylose and 14-fold repressed by glucose, showing that both regulatory effects occur at the level of transcription. Insertion of a kanamycin resistance gene into xylR encoding the xylose-dependent repressor leads to the loss of xylose-dependent regulation and to a small drop in the efficiency of glucose repression to eightfold. Deletion of 184 bp from the 5' part of the xylA reading frame reduces glucose repression to only twofold. A potential glucose-responsive element in this region is discussed on the basis of sequence similarities to other glucose-repressed genes in Bacillus subtilis. The sequence including the glucose-responsive element is also necessary for repression exerted by the carbon sources fructose and mannitol. Their efficiencies of repression correlate to the growth rate of B. megaterium, as is typical for catabolite repression. Glycerol, ribose, and arabinose exert only a basal twofold repression of the xyl operon, which is independent of the presence of the cis-active glucose-responsive element within the xylA reading frame.

Aldose-Ketose Isomerases↗
PubMed1996

Catabolite repression resistance of gnt operon expression in Bacillus subtilis conferred by mutation of His-15, the site of phosphoenolpyruvate-dependent phosphorylation of the phosphocarrier protein HPr.

Carbon catabolite repression of the gnt operon of Bacillus subtilis is mediated by the catabolite control protein CcpA and by HPr, a phosphocarrier protein of the phosphotransferase system. ATP-dependent phosphorylation of HPr at Ser-46 is required for carbon catabolite repression as ptsH1 mutants in which Ser-46 of HPr is replaced with an unphosphorylatable alanyl residue are resistant to carbon catabolite repression. We here demonstrate that mutation of His-15 of HPr, the site of phosphoenolpyruvate-dependent phosphorylation, also prevents carbon catabolite repression of the gnt operon. A strain which expressed two mutant HPrs (one in which Ser-46 is replaced by Ala [S46A HPr] and one in which His-15 is replaced by Ala [H15A HPr]) on the chromosome was barely sensitive to carbon catabolite repression, although the H15A mutant HPr can be phosphorylated at Ser-46 by the ATP-dependent HPr kinase in vitro and in vivo. The S46D mutant HPr which structurally resembles seryl-phosphorylated HPr has a repressive effect on gnt expression even in the absence of a repressing sugar. By contrast, the doubly mutated H15E,S46D HPr, which resembles the doubly phosphorylated HPr because of the negative charges introduced by the mutations at both phosphorylation sites, had no such effect. In vitro assays substantiated these findings and demonstrated that in contrast to the wild-type seryl-phosphorylated HPr and the S46D mutant HPr, seryl-phosphorylated H15A mutant HPr and H15E,S46D doubly mutated HPr did not interact with CcpA. These results suggest that His-15 of HPr is important for carbon catabolite repression and that either mutation or phosphorylation at His-15 can prevent carbon catabolite repression.

Bacillus subtilis↗
PubMed2002

Glycerol-3-phosphate-induced catabolite repression in Escherichia coli.

The formation of glycerol-3-phosphate (G3P) in cells growing on TB causes catabolite repression, as shown by the reduction in malT expression. For this repression to occur, the general proteins of the phosphoenolpyruvate-dependent phosphotransferase system (PTS), in particular EIIA(Glc), as well as the adenylate cyclase and the cyclic AMP-catabolite activator protein system, have to be present. We followed the level of EIIA(Glc) phosphorylation after the addition of glycerol or G3P. In contrast to glucose, which causes a dramatic shift to the dephosphorylated form, glycerol or G3P only slightly increased the amount of dephosphorylated EIIA(Glc). Isopropyl-beta-D-thiogalactopyranoside-induced overexpression of EIIA(Glc) did not prevent repression by G3P, excluding the possibility that G3P-mediated catabolite repression is due to the formation of unphosphorylated EIIA(Glc). A mutant carrying a C-terminally truncated adenylate cyclase was no longer subject to G3P-mediated repression. We conclude that the stimulation of adenylate cyclase by phosphorylated EIIA(Glc) is controlled by G3P and other phosphorylated sugars such as D-glucose-6-phosphate and is the basis for catabolite repression by non-PTS compounds. Further metabolism of these compounds is not necessary for repression. Two-dimensional polyacrylamide gel electrophoresis was used to obtain an overview of proteins that are subject to catabolite repression by glycerol. Some of the prominently repressed proteins were identified by peptide mass fingerprinting. Among these were periplasmic binding proteins (glutamine and oligopeptide binding protein, for example), enzymes of the tricarboxylic acid cycle, aldehyde dehydrogenase, Dps (a stress-induced DNA binding protein), and D-tagatose-1,6-bisphosphate aldolase.

Adenylyl Cyclases↗
PubMed1990

The repressing and enhancing functions of the herpes simplex virus regulatory protein ICP27 map to C-terminal regions and are required to modulate viral gene expression very early in infection.

The phenotypic properties of ICP27 temperature-sensitive and deletion mutants and the results of transient expression assays have demonstrated that ICP27 has a modulatory effect on viral gene expression induced by ICPs 0 and 4. In order to identify the regions of the ICP27 molecule that are responsible for its enhancing and repressing activities, 10 nonsense and 3 in-frame deletion mutations were introduced into the coding sequence of the cloned ICP27 gene. These mutant genes were tested in transient expression assays for their ability to complement an ICP27 null mutant and to enhance and repress expression from a spectrum of herpes simplex virus type 1 promoters in reporter CAT genes when expression was induced by ICP0 or ICP4. The results of assays with cloned mutant genes demonstrate that the ICP27 polypeptide contains two regions, located between amino acid residues 327 and 407 and residues 465 and 511, that contribute to its repressing activity. The amino acid region located between the two repressing regions (residues 407 to 465) is able to interfere with ICP27 repressing activity. None of the mutant genes exhibited efficient enhancing activity for any of the herpes simplex type 1 promoters tested, demonstrating that amino acids comprising the carboxy-terminal half of the ICP27 molecule, including the terminal phenylalanine residue, are required for wild-type enhancement as well as for efficient complementation of an ICP27 null mutant. Phenotypic characterization of an in-frame deletion mutant, vd3, and a previously isolated null mutant, 5dl 1.2 (A. M. McCarthy, L. and P. A. Schaffer, J. Virol. 63:18-27, 1989), demonstrated that ICP27 is required to induce the expression of all classes of viral genes very early in infection and confirmed the requirement for ICP27 later in infection (i) to repress early gene expression, (ii) to induce wild-type levels of delayed-early or gamma 1 gene expression, and (iii) to induce true late or gamma 2 gene expression. The vd3 mutant, which specifies an ICP27 peptide lacking the repressing region between residues 327 and 407, is able to (i) repress early gene expression, consistent with the repressing ability of the d3 mutation in transient expression assays, (ii) induce the synthesis of significant but reduced levels of delayed-early (gamma 1) proteins and no gamma 2 proteins (thus vd3 exhibits a late protein phenotype intermediate between that of the wild-type virus and 5dl 1.2), and (iii) confer altered electrophoretic mobility on ICP4, demonstrating a role for ICP27 in the posttranslational modification of this essential regulatory protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1994

Human papillomavirus type 11 E2 proteins repress the homologous E6 promoter by interfering with the binding of host transcription factors to adjacent elements.

The E6 promoter of human papillomaviruses (HPVs) trophic for epithelia for the lower genital tract and the upper respiratory tract is regulated in vitro by homologous and heterologous papillomaviral E2 proteins that bind to a consensus responsive sequence (E2-RS) ACCN6GGT. When HPV type 11 (HPV-11) expression is examined in epithelial cell lines, the HPV-11 E2-C protein, which lacks the amino-terminal transactivating domain of the full-length E2 protein, invariably represses the homologous viral E6 promoter. In contrast, when the novel constitutive enhancer (CE) CE II is deleted, not only is the basal promoter activity much reduced, it is further repressed by the intact HPV-11 E2 protein (M. T. Chin, T. R. Broker, and L. T. Chow, J. Virol. 63:2967-2976, 1989). Here, we demonstrated that, when expressed from a stronger surrogate promoter, the HPV-11 E2 protein represses the E6 promoter effectively, regardless of CE II. By performing systematic mutational analyses of the four highly conserved copies of the HPV-11 E2-RS and of the adjacent enhancer-promoter elements, we show that the furthest upstream, promoter-distal E2-RS copy 1 plays no apparent role in E6 promoter regulation. Repression by the homologous HPV-11 E2 proteins is mediated through each of the three promoter-proximal copies of the E2-RS, but the presence of CE II abrogates the full-length E2 protein repression exerted at E2-RS copy 2. Repression is alleviated when the two (for E2) or three (for E2-C) promoter-proximal copies of E2-RS are mutated. We specifically demonstrate that repression exerted at E2-RS 3 is due to preclusion of binding of the host transcription factor Sp1 or Sp1-like proteins to a nonconsensus sequence AGGAGG located 1 bp upstream of the tandem E2 protein binding sites 3 and 4. A 3-bp insertion between the adjacent Sp1 and E2-RS 3 sites permits both Sp1 and E2 proteins to bind, with a concomitant relief of E2-RS 3-mediated repression. Similar mutational analyses show that proteins that bind to the GT-1 motif near the upstream E2-RS 2 help abrogate repression by the E2 protein in the presence of CE II. The implications of these results with respect to the viral infectious cycle and during viral oncogenesis are discussed.

Base Sequence↗
PubMed1997

Repression of host RNA polymerase II transcription by herpes simplex virus type 1.

Lytic infection of mammalian cells with herpes simplex virus type 1 (HSV-1) results in rapid repression of host gene expression and selective activation of the viral genome. This transformation in gene expression is thought to involve repression of host transcription and diversion of the host RNA polymerase (RNAP II) transcription machinery to the viral genome. However, the extent of virus-induced host transcription repression and the mechanisms responsible for these major shifts in transcription specificities have not been examined. To determine how HSV-1 accomplishes repression of host RNAP II transcription, we assayed transcription patterns on several cellular genes in cells infected with mutant and wild-type HSV-1. Our results suggest that HSV-1 represses RNAP II transcription on most cellular genes. However, each cellular gene we examined responds differently to the transcription repressive effects of virus infection, both quantitatively and with respect to the involvement of viral gene products. Virus-induced shutoff of host RNAP II transcription requires expression of multiple immediate-early genes. In contrast, expression of delayed-early and late genes and viral DNA replication appear to contribute little to repression of host cell RNAP II transcription. Modification of RNAP II to the intermediately phosphorylated (II(I)) form appears unlinked to virus-induced repression of host cell transcription. However, full repression of host transcription is correlated with depletion of the hyperphosphorylated (IIO) form of RNAP II.

Cell Line↗
PubMed1993

Three downstream sites repress transcription of a Ty2 retrotransposon in Saccharomyces cerevisiae.

Transcription of Ty1 and Ty2 retrotransposons of the yeast Saccharomyces cerevisiae is modulated by multiple downstream regulatory sites. Both transposon families include a positively acting site within the transcribed region which resembles a higher eukaryotic enhancer. We have demonstrated the existence of a repression site distal to the enhancer of the Ty2-917 element. Here we describe experiments investigating the internal structure of this site. We show that this 200-bp region includes three distinct repression sites which we term DRSI (downstream repression site I), DRSII, and DRSIII. Individually each site causes almost twofold repression, and together the sites repress eightfold. Unexpectedly, when the entire region encompassing the DRS sites is moved outside the transcription unit, it acts as a qualitatively positively acting element. In this context the DRS sites still repress transcription, since eliminating them increases transcription further. That the region can activate transcription implies that it includes activation sites in addition to the three repression sites. The change from qualitatively negatively acting to positively acting must reflect a change in the relative effects of the multiple positive and negative sites; when moved outside the transcription unit, the activators predominate. Importantly, DRSII and DRSIII repress transcription autonomously when inserted upstream of a heterologous promoter activated by the transcriptional activator GCN4, showing that they are indeed transcriptional repression sites.

Base Sequence↗
PubMed1996

Mad proteins contain a dominant transcription repression domain.

Transcription repression by the basic region-helix-loop-helix-zipper (bHLHZip) protein Mad1 requires DNA binding as a ternary complex with Max and mSin3A or mSin3B, the mammalian orthologs of the Saccharomyces cerevisiae transcriptional corepressor SIN3. The interaction between Mad1 and mSin3 is mediated by three potential amphipathic alpha-helices: one in the N terminus of Mad (mSin interaction domain, or SID) and two within the second paired amphipathic helix domain (PAH2) of mSin3A. Mutations that alter the structure of the SID inhibit in vitro interaction between Mad and mSin3 and inactivate Mad's transcriptional repression activity. Here we show that a 35-residue region containing the SID represents a dominant repression domain whose activity can be transferred to a heterologous DNA binding region. A fusion protein comprising the Mad1 SID linked to a Ga14 DNA binding domain mediates repression of minimal as well as complex promoters dependent on Ga14 DNA binding sites. In addition, the SID represses the transcriptional activity of linked VP16 and c-Myc transactivation domains. When fused to a full-length c-Myc protein, the Mad1 SID specifically represses both c-Myc's transcriptional and transforming activities. Fusions between the GAL DNA binding domain and full-length mSin3 were also capable of repression. We show that the association between Mad1 and mSin3 is not only dependent on the helical SID but is also dependent on both putative helices of the mSin3 PAH2 region, suggesting that stable interaction requires all three helices. Our results indicate that the SID is necessary and sufficient for transcriptional repression mediated by the Mad protein family and that SID repression is dominant over several distinct transcriptional activators.

Amino Acid Sequence↗
PubMed1997

Amino termini of histones H3 and H4 are required for a1-alpha2 repression in yeast.

The Saccharomyces cerevisiae alpha2 repressor controls two classes of cell-type-specific genes in yeast through association with different partners. alpha2-Mcm1 complexes repress a cell-specific gene expression in haploid alpha cells and diploid a/alpha cells, while a1-alpha2 complexes repress haploid-specific genes in diploid cells. In both cases, repression is mediated through Ssn6-Tu1 corepressor complexes that are recruited via direct interactions with alpha2. We have previously shown that nucleosomes are positioned adjacent to the alpha2-Mcm1 operator under conditions of repression and that Tupl interacts directly with histones H3 and H4. Here, we examine the role of chromatin in a1-alpha2 repression to determine if chromatin is a general feature of repression by Ssn6-Tup1. We find that mutations in the amino terminus of histone H4 cause a 4- to 11-fold derepression of a reporter gene under a1-alpha2 control, while truncation of the H3 amino terminus has a more modest (3-fold or less) effect. Strikingly, combination of the H3 truncation with an H4 mutation causes a 40-fold decrease in repression, clearly indicating a central role for these histones in a1-alpha2-mediated repression. However, in contrast to the ordered positioning of nucleosomes adjacent to the alpha2-Mcm1 operator, nucleosomes are not positioned adjacent to the a1-alpha2 operator in diploid cells. Our data indicate that chromatin is important to Ssn6-Tup1-mediated repression but that the degrees of chromatin organization directed by these proteins differ at different promoters.

Chromatin↗
PubMed1998

Nab1, a corepressor of NGFI-A (Egr-1), contains an active transcriptional repression domain.

Nab proteins constitute an evolutionarily conserved family of corepressors that specifically interact with and repress transcription mediated by three members of the NGFI-A (Egr-1, Krox24, zif/268) family of immediate-early gene transcription factors, which includes NGFI-C, Krox20, and Egr3. We explored the mechanism of Nab1 repression and identified structural domains required for Nab1 function. Nab1 does not act by blocking DNA binding or nuclear localization of NGFI-A. In fact, Nab1 repression is not unique to NGFI-A because multiple types of non-NGFI-A activation domains were repressed, as was a heterologous transcription factor carrying the NGFI-A R1 domain, which is required for Nab1 interaction. Additionally, Nab1 tethered directly to DNA repressed constitutively active promoters. Tethered repression was not dependent on the identity of the basal promoter elements, the presence of a distal enhancer, or the distance separating the binding sites from the promoter. These results suggest that Nab1 repression is not specific to particular activators and that Nab1 is an active repressor that works by a direct mechanism. We identified a bipartite-like nuclear localization sequence and localized the repression function to the Nab conserved domain 2 (NCD2), a region found in the carboxy-terminal half of all Nab proteins. Three small regions of homology between Nab1 and previously characterized corepressors, Dr1 and E1b 55-kDa protein, were identified within NCD2. Replacement mutagenesis of residues conserved between these proteins interfered with Nab1 repression, although Nab1 does not function by the same mechanism as Dr1. The human NAB1 genomic locus was mapped to chromosome 2q32.3-33.

Amino Acid Sequence↗
PubMed2000

E2F-Rb complexes assemble and inhibit cdc25A transcription in cervical carcinoma cells following repression of human papillomavirus oncogene expression.

Expression of the bovine papillomavirus E2 protein in cervical carcinoma cells represses expression of integrated human papillomavirus (HPV) E6/E7 oncogenes, followed by repression of the cdc25A gene and other cellular genes required for cell cycle progression, resulting in dramatic growth arrest. To explore the mechanism of repression of cell cycle genes in cervical carcinoma cells following E6/E7 repression, we analyzed regulation of the cdc25A promoter, which contains two consensus E2F binding sites and a consensus E2 binding site. The wild-type E2 protein inhibited expression of a luciferase gene linked to the cdc25A promoter in HT-3 cervical carcinoma cells. Mutation of the distal E2F binding site in the cdc25A promoter abolished E2-induced repression, whereas mutation of the proximal E2F site or the E2 site had no effect. None of these mutations affected the activity of the promoter in the absence of E2 expression. Expression of the E2 protein also led to posttranscriptional increase in the level of E2F4, p105(Rb), and p130 and induced the formation of nuclear E2F4-p130 and E2F4-p105(Rb) complexes. This resulted in marked rearrangement of the protein complexes that formed at the distal E2F site in the cdc25A promoter, including the replacement of free E2F complexes with E2F4-p105(Rb) complexes. These experiments indicated that repression of E2F-responsive promoters following HPV E6/E7 repression was mediated by activation of the Rb tumor suppressor pathway and the assembly of repressing E2F4-Rb DNA binding complexes. Importantly, these experiments revealed that HPV-induced alterations in E2F transcription complexes that occur during cervical carcinogenesis are reversed by repression of HPV E6/E7 expression.

Binding Sites↗
PubMed2004

CtBP contributes quantitatively to Knirps repression activity in an NAD binding-dependent manner.

Transcriptional repressors often employ multiple activities, but the molecular mechanisms and physiological relevance of this functional diversity remain obscure. The Drosophila melanogaster Knirps repressor uses CtBP corepressor-dependent and -independent pathways. To separately analyze the components of Knirps repression activity, we elucidated the specific repression properties of CtBP and of Knirps subdomains. Like Knirps, CtBP represses adjacent transcriptional activators; but unlike Knirps, CtBP is unable to repress basal promoter elements. We determined that the ability of CtBP to recapitulate only a subset of Knirps activities is due to a quantitative, rather than qualitative, deficiency in repression activity. The CtBP-dependent portion of Knirps synergizes with the CtBP-independent repression activity to potently repress promoter elements from enhancer- or promoter-proximal positions. This result indicates that multiple repression activities are combined to exceed critical thresholds on target genes. CtBP mutant proteins unable to bind NAD fail to interact with DNA-bound factors. We show that DNA-binding Gal4-CtBP fusion proteins also require NAD binding for activity, indicating that NAD plays a role in repression at a step subsequent to CtBP recruitment to the promoter.

Alcohol Oxidoreductases↗
PubMed2002

Different signaling pathways control acute induction versus long-term repression of LHbeta transcription by GnRH.

GnRH regulates pituitary gonadotropin gene expression through GnRH receptor activation of the protein kinase C (PKC) and calcium signaling cascades. The pulsatile pattern of GnRH release is crucial for induction of LHbeta-subunit (LHbeta) gene expression; however, continuous prolonged GnRH exposure leads to repression of LHbeta gene transcription. Although in part, long-term repression may be due to receptor down-regulation, the molecular mechanisms of this differential regulation of LHbeta transcription are unknown. Using transfection into the LH-secreting immortalized mouse gonadotrope cell line (LbetaT4), we have demonstrated that LHbeta gene transcription is increased by acute activation (6 h) of GnRH receptor or PKC but not calcium influx; in contrast long-term activation (24 h) of GnRH receptor, PKC, or calcium influx each repress LHbeta transcription. Whereas blockade of PKC prevented the acute action of GnRH and unmasked an acute repression of LHbeta transcription by calcium, it did not prevent long-term repression by GnRH or calcium. Removal of calcium resulted in potentiation of acute GnRH and PKC induction of LHbeta gene expression but prevented long-term repression by GnRH and reduced long-term repression by either calcium or 12-O-tetradecanoyl-phorbol-13-acetate (TPA). We conclude that GnRH uses PKC for acute induction, and calcium signaling is responsible for long-term repression of LHbeta gene expression by GnRH. Furthermore, analysis of the responsiveness of truncated and mutated LHbeta promoter regions demonstrated that not only do acute induction and long-term repression use different signaling systems, but they also use different target sequences for regulating the LHbeta gene.

Animals↗
PubMed1995

Studies on the repression of basal transcription (silencing) by artificial and natural human thyroid hormone receptor-beta mutants.

Thyroid hormone receptors (TRs) are ligand-dependent transcription factors that regulate target gene transcription. Interestingly, in the absence of ligand, TRs also can repress basal transcription of positively regulated target genes, suggesting that unliganded TR may have a distinct role in gene regulation. In this paper, DNA binding, truncation, and natural human TR beta mutants were used in cotransfection and electrophoretic mobility shift assays to study various aspects of TR-mediated basal repression. Presently, little is known about the role(s) of natural human TR beta mutants on basal repression. These results show that: 1) TR binding to DNA likely is required for basal repression; 2) the amino-terminal region of TR is not required for basal repression; 3) TR homodimer binding is not absolutely required for basal repression, as TR mutants that selectively form TR-retinoid X receptor heterodimers can mediate basal repression; and 4) TR mutants with poor T3-binding affinity likely have constitutive basal repression, even in the presence of ligand. These findings provide new insight on the mechanism of basal repression by unliganded TRs.

Base Sequence↗