Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.17 (lysozyme)
 21,489 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Silencer elements, by analogy to enhancer elements, function independently of their position and orientation. We show that the chicken lysozyme silencer S-2.4 kb has many other characteristics in common with enhancer elements. The silencer is comprised of modules that independently repress gene activity--repression being increased synergistically when different or identical modules are combined. Repression is effective both on a complete and on a minimal promoter consisting of a TATA box only. One silencer module is bound in vitro by a 75-93 kd protein, termed NeP1; the other can be bound either by the product of the oncogene v-erbA or by the thyroid hormone receptor. This erbA binding site is unusual in that the palindromic sequence is inverted.
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PMID:Modular structure of a chicken lysozyme silencer: involvement of an unusual thyroid hormone receptor binding site. 215 85

v-erbA, a viral oncogenic homolog of thyroid hormone receptor (TR), blocks the effect of T3 in TR-mediated transcription. The mechanism(s) for this dominant negative effect by v-erbA on TRs is unknown but may involve competition between v-erbA and TR-containing complexes for binding to thyroid hormone response elements (TREs) and/or protein-protein interactions between v-erbA and TR. To investigate these potential mechanisms, we used the electrophoretic mobility shift assay to compare in vitro translated v-erbA and TR alpha binding to two TREs-chick lysozyme TRE (F2) and direct repeat TRE (DR4). v-erbA bound as a homodimer to these TREs, whereas TR alpha bound as a homodimer and monomer. T3 decreased TR alpha homodimer binding to the TREs as we reported previously; however, surprisingly, high concentrations of T3 (10(-6) M) also decreased v-erbA homodimer binding to the TREs. Additionally, v-erbA formed heterodimers with nuclear proteins such as retinoid X receptor and T3 receptor auxiliary protein as well as with TR alpha. These dimers remained bound to DNA in the presence of T3. Finally, v-erbA could not mediate ligand-dependent transcriptional activation even at 10(-6) M T3 but could block ligand-dependent TR-mediated transactivation in co-transfection experiments. v-erbA also exhibited differential dominant negative activity on F2 and DR4 suggesting that half-site sequence and/or orientation may influence v-erbA-dominant negative activity. In sum, there are multiple v-erbA complexes that bind to TREs in the presence of T3, which all may contribute to v-erbA's dominant negative effect on TR-mediated transcription by competing with TR-containing complexes for binding to TREs.
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PMID:Roles of v-erbA homodimers and heterodimers in mediating dominant negative activity by v-erbA. 790 4

Three "P-box" amino acids within the DNA recognition alpha-helix of members of the steroid hormone and thyroid hormone families of nuclear receptors are known to determine the identity of two of the six base pairs within the half-sites of cognate DNA elements. We introduced P-box substitutions derived from different members of the thyroid hormone/estrogen receptor (T3R/ER) family into the beta-isoform of human thyroid hormone receptor (hT3R beta) and tested the DNA binding and transactivation activities of these mutants using thyroid hormone response elements (TREs) with half-sites composed of different sequences and arranged in different orientations. Different P-box sequences derived from the T3R/ER family resulted in distinct DNA binding specificities determined by the fourth base pair of the half-site. Thyroid hormone receptor mutants containing EGA, EAA, EGS substitutions for the wild type EGG P-box bound with wild type affinity to consensus AGGTCA half-sites, regardless of orientation. TREs composed of AGGACA half-sites bound hT3R beta s with an EGG or EAA P-box sequence, but not those with EGA or EGS P-box sequence. A reversal of this specificity was observed on a direct repeat TRE with AGGGCA half-sites. Additionally, an ESG P-box substitution in hT3R beta prevented the receptor from binding to a direct repeat as a homodimer, but this mutant could bind as a heterodimer with retinoid X receptor or to the everted repeat TRE from the chicken lysozyme promoter.
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PMID:The effects of P-box substitutions in thyroid hormone receptor on DNA binding specificity. 798 45

One of the chicken lysozyme gene silencers binds two transcription factors, v-ERBA or the thyroid hormone receptor and NeP1 (negative protein 1), a new silencer binding protein. NeP1 is neutral on a monomeric binding site, but mediates weak repression on a multimerized site and strong synergistic repression in conjunction with v-ERBA on the wild-type silencer. Depending on the presence or absence of ligand, synergistic induction or repression is seen with the thyroid hormone receptor. This synergism is not based on cooperative DNA-binding as measured in vitro. The NeP1 DNA-binding activity is dependent on zinc ions, the binding site is characterized by a footprint of approximately 50 bp. NeP1 has a molecular weight of 140 to 160 kDa and has been enriched by affinity columns.
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PMID:NeP1. A ubiquitous transcription factor synergizes with v-ERBA in transcriptional silencing. 810 52

Using both a protein phosphatase inhibitor, okadaic acid (OA), and a protein kinase inhibitor, H7, to modify phosphorylation events in the cell, we investigated the effects of these agents on transcriptional activation via exogenous rat thyroid hormone receptor (TR) isoforms in transiently transfected cells and endogenous TRs. CV-1 cells were transiently cotransfected with expression plasmids encoding either the rat TR alpha 1 or TR beta 1, and luciferase reporter plasmids containing either the synthetic DR4 or the chick lysozyme F2 thyroid hormone response elements (TREs). For both receptor isoforms, there was an enhancement of transcriptional activity after incubation with 5 nM T3 for 24 h compared to hypothyroid levels. There was little change in transcriptional activation in the presence of 25 nM OA alone; however, for both TR isoforms and both TREs studied, OA augmented the stimulatory effects of T3. For the F2 TRE, transcriptional activation via TR alpha 1 increased from 19- to 35-fold, and that via TR beta 1 increased from 6- to 10-fold in the presence of T3 and OA compared to that with T3 alone. Similar results were found for the DR4 TRE. OA enhanced transcriptional activation by T3 in a dose-dependent manner. Increasing concentrations of OA (0, 5, 25, and 50 nM) further increased relative luciferase activity from 11-fold in the absence of OA to 45-fold in the presence of 50 nM OA. The protein kinase inhibitor, H7, caused no change in the transcriptional activity of the reporter plasmids via TR alpha 1 in the absence of T3, but completely blocked transcriptional activation by T3 for both the DR4 and the F2 TREs. H7 also blocked stimulation of endogenous GH and inhibition of endogenous TR beta 2 mRNAs by T3 in GH3 cells. These results indicate that phosphorylation events in the cell play an important role in transcriptional activation via both TR isoforms.
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PMID:Evidence that phosphorylation events participate in thyroid hormone action. 829 53

The chicken lysozyme silencer F2 (F2) thyroid hormone response element (TRE) contains an unusual everted palindromic arrangement, has a high affinity for thyroid hormone receptor (TR) homodimers, and is especially sensitive to dominant negative inhibition by, the T3 resistance (RTH) mutant TR beta P453H. We used various TREs and TR mutations to determine the mechanisms for this sensitivity. Changing the F2 orientation from an everted palindrome to a direct repeat with a 4-bp gap (DR+4) (F2-DR) decreased the sensitivity to inhibition at high T3 concentrations, while a loss of this sensitivity occurred with a palindromic arrangement of these same half-sites. F2 contains the dinucleotide TG 5' to each consensus half-site conforming to the optimal TR-binding octamer, YRRGGTCA. A T to A change in position 1 of both F2 half-sites markedly reduced T3-induction, yet only slightly reduced TR homodimer or TR-retinoid X receptor (RXR) heterodimer binding. The TR beta ninth heptad mutation, L428R, prevents TR heterodimerization with RXR and eliminates the inhibitory effect of the P453H mutant TR on the F2-DR, but not the F2 element. Structural features of a TRE that favor strong TR binding of both TR homodimers and TR-RXR heterodimers containing the mutant TR, such as the everted palindromic conformation or the optimal TR-binding consensus octamer, enhance the sensitivity of a TRE to inhibition by the mutant TR. Thus, both half-site orientation and sequence contribute to the sensitivity of a given TRE to dominant negative inhibition by a mutant TR.
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PMID:Structural features of thyroid hormone response elements that increase susceptibility to inhibition by an RTH mutant thyroid hormone receptor. 877 Sep 4

The transcriptional repressor negative protein 1 (NeP1) binds specifically to the F1 element of the chicken lysozyme gene silencer and mediates synergistic repression by v-ERBA, thyroid hormone receptor, or retinoic acid receptor. Another protein, CCCTC-binding factor (CTCF), specifically binds to 50-bp-long sequences that contain repetitive CCCTC elements in the vicinity of vertebrate c-myc genes. Previously cloned chicken, mouse, and human CTCF cDNAs encode a highly conserved 11-Zn-finger protein. Here, NeP1 was purified and DNA bases critical for NeP1-F1 interaction were determined. NeP1 is found to bind a 50-bp stretch of nucleotides without any obvious sequence similarity to known CTCF binding sequences. Despite this remarkable difference, these two proteins are identical. They have the same molecular weight, and NeP1 contains peptide sequences which are identical to sequences in CTCF. Moreover, NeP1 and CTCF specifically recognize each other's binding DNA sequence and induce identical conformational alterations in the F1 DNA. Therefore, we propose to replace the name NeP1 with CTCF. To analyze the puzzling sequence divergence in CTCF binding sites, we studied the DNA binding of 12 CTCF deletions with serially truncated Zn fingers. While fingers 4 to 11 are indispensable for CTCF binding to the human c-myc P2 promoter site A, a completely different combination of fingers, namely, 1 to 8 or 5 to 11, was sufficient to bind the lysozyme silencer site F1. Thus, CTCF is a true multivalent factor with multiple repressive functions and multiple sequence specificities.
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PMID:Negative protein 1, which is required for function of the chicken lysozyme gene silencer in conjunction with hormone receptors, is identical to the multivalent zinc finger repressor CTCF. 903 55

Although different expression patterns of thyroid hormone receptor (TR) alpha1 and beta1 have been reported, no essential distinction has been established in their functions. Unlike the TR beta gene, a mutation in the TR alpha1 gene has never been found in patients with resistance to thyroid hormone (RTH). Previously we found a mutant TR beta with an 11-carboxyl (C)-terminal amino acid truncation (betaF451X) in a girl with severe RTH. BetaF451X is a natural mutant with disruption of the transactivation domain, tau4, and it had very strong dominant negative activities. Based on the fact that the 46 amino acid sequence in the extreme C-terminal region is identical in TR alpha1 and TR beta, except for a C-terminal three amino acid extension of TR alpha1, we constructed a mutant TR alpha1 (alphaF397X) with the identical C-terminal truncation to betaF451X, to study functional differences between TR alpha1 and beta1. Both betaF451X and alphaF397X had negligible T3 binding and transcriptional activities even with 1 microM T3. The dominant negative activities of the mutant TRs were remarkable and T3 response element (TRE)-dependent. Co-expression of betaF451X decreased the CAT activity of either wild-type TR alpha1 or beta1 at 100 nM T3 by approximately 90% on the TRE-pal2 and 70% on DR4. AlphaF397X inhibited the transcriptional activities of both wild-type TR alpha1 and beta1 by approximately 50% on TRE-pal2 and by 60% on DR4. The dominant negative potency of betaF451X was significantly stronger than that of alphaF397X on the TRE-pal2, -DR4 and chicken lysozyme silencer F2, but similar on TRE-myosin heavy chain alpha and malic enzyme. No partiality for the TR subtypes was found in the dominant negative effects of betaF451X and alphaF397X. Co-expression with RXR enhanced the dominant negative effects of alphaF397X, but not of betaF451X. The results indicate that there are different dominant negative properties between alphaF397X and betaF451X, which are TRE-dependent, despite their identical C-terminal truncation. Deletion in the tau4 domain might affect the receptor structures of TR alpha1 and beta1 differently.
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PMID:Difference in dominant negative activities between mutant thyroid hormone receptors alpha1 and beta1 with an identical truncation in the extreme carboxyl-terminal tau4 domain. 968 18

Thyroid hormone (triiodothyronine [T3]) actions are mediated through binding of thyroid hormone receptors (TRs) to specific DNA sequences (thyroid hormone response elements [TREs]) as monomers, homodimers, and heterodimers with thyroid hormone receptor auxiliary proteins (TRAPs). We quantitatively characterized dimerization of wild-type (WT) and mutant TRbetas by coimmunoprecipitation, and binding to DNA by electrophoretic gel mobility shift assays (EMSA). Binding affinities of TR retinoid X receptor-alpha (RXRalpha) heterodimers to DNA were determined by competing with excess nonradiolabeled TREs in EMSA. TRs in vitro synthesized in reticulocyte lysates (RL), and human RXRalpha expressed in a Sf9 cell-baculovirus system (BAC), were coincubated with 32P-labeled rat malic enzyme (ME), palindromic (PAL), or chicken lysozyme F2 (F2) TREs. The mutant TRbetas tested were R316H and G345R, which have nondetectable T3 binding and have previously been reported to show weak and potent dominant negative effect, respectively. Scatchard analysis showed no significant differences in Kas between WT and mutant TR-RXRalpha heterodimers binding to DNA. We measured affinity of heterodimerization between TRs and RXRalpha in solution in the absence of DNA, and by coimmunoprecipitation using anti-TRbeta1WT specific antibodies. 35S-labeled RL-RXRalpha was incubated with BAC-WT or TRbeta or R316H in the absence or presence of increasing amounts of nonlabeled BAC-RXRalpha. Displacement curves were obtained by counting radioactivity of precipitated 35S-RXRalpha, that was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and autoradiography. Kds of WT and TRbeta R316H heterodimerizing with RXRalpha were approximately the same. Binding affinity of TR homodimers for F2-TRE was studied because this TRE binds homodimers strongly. Scatchard analysis clearly showed that DNA binding affinity of BAC-WT homodimers did not differ with or without 100 nM T3, but maximal binding capacity (MBC) was reduced three-fold to fourfold in the presence of 100 nM T3. In contrast, BACTRbeta-R316H homodimers showed a fivefold reduction in DNA binding affinity for F2, both in the presence and absence of T3, and approximately the same MBC as WT in the absence of T3. Mutant RL-G345R homodimers showed approximately the same Ka as RL-WT homodimers for binding to F2 and the same MBC in the presence and absence of T3. These results indicate that (1) T3 reduced TRbeta homodimerization in solution but does not effect DNA binding of formed homodimers; (2) T3 does not influence DNA binding affinity of TR/RxR heterodimers; and (3) TRbeta mutant R316H homodimers have reduced DNA binding affinity but homodimerization and heterodimerization in solution does not differ from WT TRbeta.
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PMID:Quantitative analysis of DNA binding affinity and dimerization properties of wild-type and mutant thyroid hormone receptor beta1. 1069 8

Alterations in histone acetylation status appear to play a central role in the regulation of neoplasia, tumor suppression, cell cycle control, hormone responsiveness and senescence. These alterations of chromatin control gene transcription. The histone acetylation status is regulated by the equilibrium of histone acetyl-transferase activity (HAT) and the histone deacetylase activity (HDAC). Commonly, DNA-transfection assays are used to measure the effect of histone acetylation and deacetylation on gene transcription. Here we have analyzed the response of various viral long terminal repeats and vertebrate promoters to the specific histone deacetylase inhibitor trichostatin A (TSA). We show that the activity of many, but not all, promoters is increased upon TSA treatment. Interestingly, the lysozyme promoter exhibited TSA resistance, while the activity of metallothionine, the human growth hormone, and the thymidine kinase promoters was increased. Furthermore, we found that all tested viral promoters are induced by TSA. Analysis of the transcriptional behaviour of the thyroid hormone receptor (TR), the cellular homologue of the v-erbA oncogene, revealed that TSA reduced the gene silencing function but had no influence on the hormone-induced gene activation function of the receptor. These results on gene specific effects, together with the HDAC structural data (1), may be a basis for the development of HDAC inhibitors as antitumor agents.
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PMID:Promoter specific sensitivity to inhibition of histone deacetylases: implications for hormonal gene control, cellular differentiation and cancer. 1081 Mar 90


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