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PubMed2004

The N termini of Friend of GATA (FOG) proteins define a novel transcriptional repression motif and a superfamily of transcriptional repressors.

Members of the Friend of GATA (FOG) family of transcriptional co-factors are required for the development of both the cardiovascular and hematopoietic systems. FOG proteins physically interact with members of the GATA family of transcriptional activators and modulate their activity. We have previously shown that FOG-2 can bind to the N-terminal zinc finger of GATA4 and, via this interaction, repress GATA4-mediated transcriptional activation of various cardiac promoters. In this report we further characterize the domain of FOG-2 necessary for repression of GATA4 transcriptional activity. We show that FOG-2-mediated repression is not blocked by the histone deacetylase inhibitor tricostatin A, suggesting that FOG-2 repression of GATA4 occurs via a histone deacetylase independent mechanism. N-terminal deletion mutants of FOG-2 revealed that the first 12 amino acids of FOG-2 are necessary for FOG-2-mediated repression. Fusion of these 12 amino acids to the DNA binding domain of GAL4 demonstrated that this region is sufficient to mediate transcriptional repression even when recruited to a heterologous promoter. Single amino acid substitutions within this N-terminal domain of FOG-2 defined the critical amino acid sequence as RRKQxxPxxI. Interestingly, a search of the NCBI protein data base identified several other partially characterized zinc finger transcriptional repressors from various vertebrate species that contained this motif at their N terminus. Taken together, these observations define a novel transcriptional repression motif and a superfamily of zinc finger transcriptional repressors.

Amino Acid Motifs↗
PubMed2000

Cofactor competition between the ligand-bound oestrogen receptor and an intron 1 enhancer leads to oestrogen repression of ERBB2 expression in breast cancer.

Overexpression of the ERBB2 proto-oncogene in breast tumours, which occurs in 25-30% of patients, correlates with poor prognosis. In oestrogen receptor (ER) positive breast epithelial cells oestrogens reduce ERBB2 mRNA and protein levels, an effect that is reversed in the presence of anti-oestrogens such as tamoxifen and ICI 182780. Our previous studies have shown that the major effect of oestrogen on ERBB2 expression is at the level of transcription and that this is mediated through a region within the ERBB2 first intron which can act as an oestrogen-suppressible enhancer in ER positive breast cells. In vitro footprinting of the smallest DNA fragment that retained full activity revealed four transcription factor binding sites. We report here that two of these sites are recognized by AP-2 proteins and the other two are bound by a variety of bZIP factors, including CREB and ATFI, with a major complex containing ATFa/ JunD. However, by using ER mutants it is clear that repression occurs essentially off the DNA. Indeed, the essential domain of the ER responsible for repression of the ERBB2 enhancer is a region termed AF2 which is required for the ligand-dependent association of non-DNA binding cofactors. We further demonstrate that one of these ER cofactors, SRC-1, can relieve oestrogen repression of the ERBB2 enhancer and conclude that these data fit with a model whereby the ER and the ERBB2 enhancer compete for this limiting, non-DNA binding cofactor. Thus, in oestrogenic conditions SRC-1 preferentially binds to the ER which effectively sequesters it thereby reducing enhancer activity, but in antioestrogenic media the cofactor is released from the ER and is therefore available to activate the ERBB2 enhancer.

Binding Sites↗
PubMed2001

Recombinant human DNA (cytosine-5) methyltransferase. III. Allosteric control, reaction order, and influence of plasmid topology and triplet repeat length on methylation of the fragile X CGG.CCG sequence.

Steady-state kinetic analyses revealed that the methylation reaction of the human DNA (cytosine-5) methyltransferase 1 (DNMT1) is repressed by the N-terminal domain comprising the first 501 amino acids, and that repression is relieved when methylated DNA binds to this region. DNMT1 lacking the first 501 amino acids retains its preference for hemimethylated DNA. The methylation reaction proceeds by a sequential mechanism, and either substrate (S-adenosyl-l-methionine and unmethylated DNA) may be the first to bind to the active site. However, initial binding of S-adenosyl-l-methionine is preferred. The binding affinities of DNA for both the regulatory and the catalytic sites increase in the presence of methylated CpG dinucleotides and vary considerably (more than one hundred times) according to DNA sequence. DNA topology strongly influences the reaction rates, which increased with increasing negative superhelical tension. These kinetic data are consistent with the role of DNMT1 in maintaining the methylation patterns throughout development and suggest that the enzyme may be involved in the etiology of fragile X, a syndrome characterized by de novo methylation of a greatly expanded CGG.CCG triplet repeat sequence.

Allosteric Regulation↗
PubMed2006

Role of the C-terminal binding protein PXDLS motif binding cleft in protein interactions and transcriptional repression.

C-terminal binding proteins (CtBPs) are multifunctional proteins that can mediate gene repression. CtBPs contain a cleft that binds Pro-X-Asp-Leu-Ser (PXDLS) motifs. PXDLS motifs occur in numerous transcription factors and in effectors of gene repression, such as certain histone deacetylases. CtBPs have been depicted as bridging proteins that self-associate and link PXDLS-containing transcription factors to PXDLS-containing chromatin-modifying enzymes. CtBPs also recruit effectors that do not contain recognizable PXDLS motifs. We have investigated the importance of the PXDLS binding cleft to CtBP's interactions with various partner proteins and to its ability to repress transcription. We used CtBP cleft mutant and cleft-filled fusion derivatives to distinguish between partner proteins that bind in the cleft and elsewhere on the CtBP surface. Functional assays demonstrate that CtBP mutants that carry defective clefts retain repression activity when fused to heterologous DNA-binding domains. This result suggests that the cleft is not essential for recruiting effectors. In contrast, when tested in the absence of a fused DNA-binding domain, disruption of the cleft abrogates repression activity. These results demonstrate that the PXDLS binding cleft is functionally important but suggest that it is primarily required for localization of the CtBP complex to promoter-bound transcription factors.

Alcohol Oxidoreductases↗
PubMedDate not supplied

Induction of transcription through the p300 CRD1 motif by p21WAF1/CIP1 is core promoter specific and cyclin dependent kinase independent.

The tumor suppressors p300 and CREB-binding protein (CBP) are both multifunctional transcriptional coactivators. We have previously found that the cyclin dependent kinase (CDK) inhibitor p21(WAF1/CIP1) can stimulate transactivation by p300 and CBP through inhibiting transcriptional repression by a discrete domain within these proteins termed CRD1. Given the large number of p300/CBP associated functions, it is unlikely that p21 regulates the expression of every gene under their control, however. Here we have investigated the factors that help determine this specificity. We have discovered that while CRD1 can repress the activity of p300 at multiple promoters, induction of transcription by p21 though this motif is highly variable. Analysis of this effect revealed that p21 inducibility is determined by sequences flanking the TATA box. Significantly, p21 regulation of CRD1 domain function is independent of Cyclin /CDK inhibition suggesting a novel function of this protein. p21 does not interact directly with the CRD1 motif, however. These results give further insight into how regulators of cell growth and tumorigenesis, such as p21, can specifically target and induce the expression of select groups of genes.

Amino Acid Motifs↗
PubMed2005

Novel human BTB/POZ domain-containing zinc finger protein ZNF295 is directly associated with ZFP161.

Human ZNF295 protein harbors a BTB/POZ domain and multiple krüppel (C(2)H(2)) type zinc finger domains, and thus belongs to a family of POK (POZ and krüppel) transcription factor. We have identified many transcript variants generated by the alternative splicing in 5' non-coding exons, an intra-exonic splicing in a coding region, and the use of three polyadenylation signals in the 3' UTR. The intra-exonic splicing removes 603-bp coding sequence, and thus ZNF295 gene produces two protein isoforms: ZNF295L with 1066 amino acid residues and ZNF295S with 865 amino acid residues, containing 9 and 5 zinc finger domains, respectively. ZNF295 is ubiquitously expressed in human fetal and adult tissues. Analysis of transcription activity of ZNF295 using various promoter-reporters demonstrated that ZNF295 acts as a transcription repressor, and contains two separate regions for repression activity: the BTB/POZ domain and the central region between BTB/POZ and ZF domains. Both ZNF295L and ZNF295S could interact not only with themselves and each other, but also with another POK protein ZFP161 known to function as a transcription repressor and an activator. We postulated that ZNF295 may be involved in the bi-directional control of gene expression in concert with ZFP161.

Amino Acid Sequence↗
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↗
PubMed2003

A Domain in the C-terminal region of latency-associated nuclear antigen 1 of Kaposi's sarcoma-associated Herpesvirus affects transcriptional activation and binding to nuclear heterochromatin.

The latency-associated nuclear antigen 1 (LANA-1) of Kaposi's sarcoma-associated herpesvirus (KSHV) is required for the maintenance and replication of viral episomal DNA. The binding sites for nuclear heterochromatin and transcriptional repressor complexes are located in an amino-terminal region of LANA-1, whereas those for viral episomal DNA, p53, pRB, and members of the BRD/fsh family of nuclear proteins are located in its carboxy-terminal domain. LANA-1 activates or represses several cellular and viral promoters. In this report we show that a domain of 15 amino acids (amino acids 1129 to 1143), located close to the carboxy-terminal end of LANA-1, is required for the interaction of LANA-1 with nuclear heterochromatin or nuclear matrix, and for the ability of LANA-1 to activate the Epstein-Barr virus Cp promoter. LANA-1 proteins that are tightly associated with nuclear heterochromatin or matrix differ in molecular weight from LANA-1 proteins that can be dissociated from the nuclear matrix by high-salt buffers, suggesting that posttranslational modifications may determine the association of LANA-1 with nuclear heterochromatin or matrix.

Amino Acid Sequence↗
PubMed2003

FEV acts as a transcriptional repressor through its DNA-binding ETS domain and alanine-rich domain.

Although most Ets transcription factors have been characterized as transcriptional activators, some of them display repressor activity. Here we characterize an Ets-family member, the very specifically expressed human Fifth Ewing Variant (FEV), as a transcriptional repressor. We show that among a broad range of human cell lines, only Dami megakaryocytic cells express FEV. This nuclear protein binds to Ets-binding sites, such as that of the human ICAM-1 promoter. We used this promoter to demonstrate that FEV can repress both basal transcription and, even more strongly, ectopically Ets-activated transcription. We identified two domains responsible for FEV-mediated repression: the ETS domain, responsible for passive repression, and the carboxy-terminal alanine-rich domain, involved in active repression. In the Ets-independent LEXA system also, FEV acts as a transcriptional repressor via its alanine-rich carboxy-terminal domain. The mechanism by which FEV actively represses transcription is currently unknown, since FEV-triggered repression is not reversed by the histone deacetylase inhibitor trichostatin A. We also showed that long-term overexpression of FEV proteins containing the alanine-rich domain prevents cell clones from growing, whereas clones expressing a truncated FEV protein lacking this domain develop like control cells. This confirms the importance of this domain in FEV-triggered repression.

Alanine↗
PubMed1997

Mammalian homologues of the Polycomb-group gene Enhancer of zeste mediate gene silencing in Drosophila heterochromatin and at S. cerevisiae telomeres.

Gene silencing is required to stably maintain distinct patterns of gene expression during eukaryotic development and has been correlated with the induction of chromatin domains that restrict gene activity. We describe the isolation of human (EZH2) and mouse (Ezh1) homologues of the Drosophila Polycomb-group (Pc-G) gene Enhancer of zeste [E(z)], a crucial regulator of homeotic gene expression implicated in the assembly of repressive protein complexes in chromatin. Mammalian homologues of E(z) are encoded by two distinct loci in mouse and man, and the two murine Ezh genes display complementary expression profiles during mouse development. The E(z) gene family reveals a striking functional conservation in mediating gene repression in eukaryotic chromatin: extra gene copies of human EZH2 or Drosophila E(z) in transgenic flies enhance position effect variegation of the heterochromatin-associated white gene, and expression of either human EZH2 or murine Ezh1 restores gene repression in Saccharomyces cerevisiae mutants that are impaired in telomeric silencing. Together, these data provide a functional link between Pc-G-dependent gene repression and inactive chromatin domains, and indicate that silencing mechanism(s) may be broadly conserved in eukaryotes.

Amino Acid Sequence↗
PubMed2001

A specific lysine in c-Jun is required for transcriptional repression by E1A and is acetylated by p300.

The adenovirus E1A protein regulates transcription of cellular genes via its interaction with the transcriptional coactivators p300/CBP. The collagenase promoter activated by the c-Jun protein is repressed by E1A. Here we show that E1A repression is specific for c-Jun, as E1A does not repress the collagenase promoter activated by the homologous transcription factor EB1. Using chimeras of c-Jun and EB1, we demonstrate that a 12 amino acid region in the basic region of the c-Jun DNA-binding domain is essential for repression by E1A. Since repression requires the binding of p300 to E1A, we studied the involvement of p300 acetyltransferase activity in the repression mechanism. We demonstrate that c-Jun is acetylated in vivo, and mutational analysis identified Lys271 in the c-Jun basic region to be essential for repression of the collagenase promoter by E1A. In addition, Lys271 is acetylated both in vitro and in vivo. These results suggest that the specific repression of the collagenase promoter by E1A involves acetylation of c-Jun.

Acetylation↗
PubMed1988

The function and structure of the metal coordination sites within the glucocorticoid receptor DNA binding domain.

The glucocorticoid receptor enhances or represses transcription by binding to specific DNA sequences termed glucocorticoid response elements, or GREs. Studies of cloned glucocorticoid receptors reveal that the protein is organized as functional domains, in an arrangement that appears to be common among members of the steroid receptor family. A segment near the centre of the gene specifies DNA binding activity in vitro and contains two sequence motifs similar to 'zinc fingers' found in Xenopus transcription factor IIIA (TFIIIA). Such sequence motifs have been identified in nucleic acid binding proteins from a wide range of organisms. Steroid receptor protein fingers are proposed to bind zinc through two pairs of conserved cysteine residues. We report here that a protein of relative molecular mass 19,000 (Mr = 19 K) encompassing the DNA-binding domain of the glucocorticoid receptor that has been overexpressed in Escherichia coli and purified to homogeneity reversibly ligates two Zn(II) or Cd(II) ions. We show that metal ions are required for specific DNA binding and proper folding. Using EXAFS (extended X-ray absorption fine structure) and visible light spectroscopies, we find that each Zn atom is coordinated in a tetrahedral arrangement by four cysteines.

Amino Acid Sequence↗
PubMed2006

Protein-DNA interactions in the promoter region of the gene encoding diapause hormone and pheromone biosynthesis activating neuropeptide of the cotton bollworm, Helicoverpa armigera.

Diapause hormone (DH) and pheromone biosynthesis activating neuropeptide (PBAN) are two crucial neuropeptides which regulate insect development and sex pheromone biosynthesis respectively. These peptides are encoded by a single gene, termed DH-PBAN gene. In this study, we characterized the promoter of the DH-PBAN gene in Helicoverpa armigera (Har). Transient transfection assays using a series of stepwise deletion fragments linked to the luciferase reporter gene indicate that the promoter contains multiple regulator domains that can activate and repress reporter gene expression. The fragment spanning -467 to -371 bp of the DH-PBAN promoter is an activator domain of transcription, whereas the region from -965 to -534 bp represses the promoter activity in the insect cell line BmN. Electrophoretic mobility shift assays demonstrate that at least two nuclear protein factors from the nuclear protein extracts of H. armigera suboesophageal ganglion, Har-DHMBP-1 and-2 (DH-modulator-binding protein) can specifically bind to the activating region. Furthermore, we characterized in detail that the nuclear protein factor Har-DHMBP-3 can specifically bind to a classical E-box, CAGCTG localized at positions -360 to -355 bp, a potential site for interaction with basic helix-loop-helix transcription factors. Mutation of this E-box results in a significant reduction of the promoter activity, suggesting it can modulate the previously identified activator domain. Taken together, multipartite cis-elements and transcription factors in the DH-PBAN promoter are involved in regulation of the gene expression.

Animals↗
PubMed1996

The Gfi-1 proto-oncoprotein contains a novel transcriptional repressor domain, SNAG, and inhibits G1 arrest induced by interleukin-2 withdrawal.

The Gfi-1 proto-oncogene is activated by provirus insertion in T-cell lymphoma lines selected for interleukin-2 (IL-2) independence in culture and in primary retrovirus-induced thymomas and encodes a nuclear, sequence-specific DNA-binding protein. Here we show that Gfi-1 is a position- and orientation-independent active transcriptional repressor, whose activity depends on a 20-amino-acid N-terminal repressor domain, coincident with a nuclear localization motif. The sequence of the Gfi-1 repressor domain is related to the sequence of the repressor domain of Gfi-1B, a Gfi-1-related protein, and to sequences at the N termini of the insulinoma-associated protein, IA-1, the homeobox protein Gsh-1, and the vertebrate but not the Drosophila members of the Snail-Slug protein family (Snail/Gfi-1, SNAG domain). Although not functionally characterized, these SNAG-related sequences are also likely to mediate transcriptional repression. Therefore, the Gfi-1 SNAG domain may be the prototype of a novel family of evolutionarily conserved repressor domains that operate in multiple cell lineages. Gfi-1 overexpression in IL-2-dependent T-cell lines allows the cells to escape from the G1 arrest induced by IL-2 withdrawal. Since a single point mutation in the SNAG domain (P2A) inhibits both the Gfi-1-mediated transcriptional repression and the G1 arrest induced by IL-2 starvation, we conclude that the latter depends on the repressor activity of the SNAG domain. Induction of Gfi-1 may therefore contribute to T-cell activation and tumor progression by repressing the expression of genes that inhibit cellular proliferation.

3T3 Cells↗
PubMed1997

The proliferation potential protein-related (P2P-R) gene with domains encoding heterogeneous nuclear ribonucleoprotein association and Rb1 binding shows repressed expression during terminal differentiation.

Terminal differentiation is associated with repression in the expression of the proliferation potential proteins (P2P) subset of heterogeneous nuclear ribonucleoprotein (hnRNP) proteins. We report here the cloning and characterization of a 5173-bp P2P-related (P2P-R) cDNA that contains a 4214-bp open reading frame. Probes to this cDNA detect a single 8-kb mRNA in multiple murine tissues and in proliferating 3T3T cells, but not in terminally differentiated 3T3T adipocytes. Evidence that this cDNA can encode peptides with domains for hnRNP association was established by showing that such peptides are recognized by two monoclonal antibodies known to detect core hnRNP proteins, and by showing that the C130 monoclonal antibody, produced against a cDNA-derived fusion protein, also selectively detects native P2P hnRNP proteins. In addition, P2P-R cDNA-derived fusion proteins bind single-stranded nucleic acids, and a P2P-R cDNA-derived antisense oligonucleotide selectively represses P2P expression. Because terminal differentiation is associated with modulation in Rb1 function, we assayed if products of this cDNA might interact with Rb1. Evidence that the P2P-R cDNA encodes a protein domain that binds Rb1 was established using a glutathione S-transferase fusion protein to selectively precipitate Rb1 from cellular extracts. Data also show that this binding is reduced by competition with the adenovirus E1a protein, indicating that binding occurs through the "pocket" domain of Rb1. These results establish that the P2P-R cDNA encodes protein domains involved in both hnRNP association and Rb1 binding and complement recent reports that localize Rb1 to sites of RNA processing in the nucleus.

Adipocytes↗
PubMed1999

Estradiol repression of tumor necrosis factor-alpha transcription requires estrogen receptor activation function-2 and is enhanced by coactivators.

The tumor necrosis factor-alpha (TNF-alpha) promoter was used to explore the molecular mechanisms of estradiol (E(2))-dependent repression of gene transcription. E(2) inhibited basal activity and abolished TNF-alpha activation of the TNF-alpha promoter. The E(2)-inhibitory element was mapped to the -125 to -82 region of the TNF-alpha promoter, known as the TNF-responsive element (TNF-RE). An AP-1-like site in the TNF-RE is essential for repression activity. Estrogen receptor (ER) beta is more potent than ERalpha at repressing the -1044 TNF-alpha promoter and the TNF-RE upstream of the herpes simplex virus thymidine kinase promoter, but weaker at activating transcription through an estrogen response element. The activation function-2 (AF-2) surface in the ligand-binding domain is required for repression, because anti-estrogens and AF-2 mutations impair repression. The requirement of the AF-2 surface for repression is probably due to its capacity to recruit p160 coactivators or related coregulators, because overexpressing the coactivator glucocorticoid receptor interacting protein-1 enhances repression, whereas a glucocorticoid receptor interacting protein-1 mutant unable to interact with the AF-2 surface is ineffective. Furthermore, receptor interacting protein 140 prevents repression by ERbeta, probably by interacting with the AF-2 surface and blocking the binding of endogenous coactivators. These studies demonstrate that E(2)-mediated repression requires the AF-2 surface and the participation of coactivators or other coregulatory proteins.

Adaptor Proteins, Signal Transducing↗
PubMed1990

Requirement for the C-terminal domain of the v-erbA oncogene protein for biological function and transcriptional repression.

In contrast to the normal thyroid hormone receptor, the v-erbA product fails to bind hormone due to mutations in the C-terminal ligand binding domain and thus appears to represent a hormone-independent, oncogenic transcription factor. Therefore, we asked whether or not the C-terminal domain of v-erbA is required for its biological activity and putative transcriptional control functions by analysing mutants with altered C-termini. A v-erbA protein truncated in the C-terminal domain lacked detectable biological activity in transformed erythroblasts and its transcriptional repression function with respect to the band 3 gene was abolished. The protein displayed a nuclear location and could still bind to DNA, indicating that the N-terminal region retained DNA-binding activity but was insufficient to produce characteristic v-erbA changes in erythroblasts. Another biologically defective v-erbA variant with a small frameshift towards the extreme C-terminus also failed to repress band 3, indicating a requirement for a specific C-terminal structure in repression. However, this mutant retained partial biological activity, stimulating erythroblasts to grow at a higher rate than cells containing a completely inactive, deleted v-erbA gene. The results demonstrate that the mutated hormone-binding domain, in addition to the DNA-binding region, is critical for v-erbA biological and transcriptional control functions.

Amino Acid Sequence↗
PubMed2006

Polycomb recruitment to DNA in vivo by the YY1 REPO domain.

Polycomb group (PcG) proteins are responsible for maintaining transcriptional repression of developmentally important genes. However, the mechanism of PcG recruitment to specific DNA sequences is poorly understood. Transcription factor YY1 is one of the few PcG proteins with sequence-specific DNA binding activity. We previously showed that YY1 can recruit other PcG proteins to DNA, leading to histone posttranslational modifications and stable transcriptional repression. Using Drosophila transgenic approaches, we identified YY1 sequences 201-226 as necessary and sufficient for PcG transcriptional repression in vivo. When fused to a heterologous DNA-binding domain, this short 26-aa motif was sufficient for transcriptional repression, recruitment of PcG proteins to DNA, and methylation of histone H3 lysine 27. Deletion of this short YY1 motif did not affect transient transcriptional repression but ablated PcG repression, PcG protein recruitment to DNA, and methylation of H3 lysine 27. We propose that this motif be named the REPO domain for its function in recruitment of Polycomb. The REPO domain is well conserved in YY1 orthologs and in related proteins.

Animals↗