Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Studies with live cells demonstrate that agonist and antagonist rapidly (within minutes) modulate the subnuclear dynamics of estrogen receptor alpha (ER) and steroid receptor coactivator 1 (SRC-1). A functional cyan fluorescent protein (CFP)-tagged lac repressor-ER chimera (CFP-LacER) was used in live cells to discretely immobilize ER on stably integrated lac operator arrays to study recruitment of yellow fluorescent protein (YFP)-steroid receptor coactivators (YFP-SRC-1 and YFP-CREB binding protein [CBP]). In the absence of ligand, YFP-SRC-1 is found dispersed throughout the nucleoplasm, with a surprisingly high accumulation on the CFP-LacER arrays. Agonist addition results in the rapid (within minutes) recruitment of nucleoplasmic YFP-SRC-1, while antagonist additions diminish YFP-SRC-1-CFP-LacER associations. Less ligand-independent colocalization is observed with CFP-LacER and YFP-CBP, but agonist-induced recruitment occurs within minutes. The agonist-induced recruitment of coactivators requires helix 12 and critical residues in the ER-SRC-1 interaction surface, but not the F, AF-1, or DNA binding domains. Fluorescence recovery after photobleaching indicates that YFP-SRC-1, YFP-CBP, and CFP-LacER complexes undergo rapid (within seconds) molecular exchange even in the presence of an agonist. Taken together, these data suggest a dynamic view of receptor-coregulator interactions that is now amenable to real-time study in living cells.
Mol Cell Biol 2001 Jul
PMID:Ligand-mediated assembly and real-time cellular dynamics of estrogen receptor alpha-coactivator complexes in living cells. 1139 Jun 68

Estrogen-regulated gene expression is dependent on interaction of the estrogen receptor (ER) with the estrogen response element (ERE). We assessed the ability of the ER to activate transcription of reporter plasmids containing either the consensus vitellogenin A2 ERE or the imperfect pS2, vitellogenin B1, or oxytocin (OT) ERE. The A2 ERE was the most potent activator of transcription. The OT ERE was significantly more effective in activating transcription than either the pS2 or B1 ERE. In deoxyribonuclease I (DNase I) footprinting experiments, MCF-7 proteins protected A2 and OT EREs more effectively than the pS2 and B1 EREs. Limited protease digestion of the A2, pS2, B1, or OT ERE-bound receptor with V8 protease or proteinase K produced distinct cleavage products demonstrating that individual ERE sequences induce specific changes in ER conformation. Receptor interaction domains of glucocorticoid receptor interacting protein 1 and steroid receptor coactivator 1 bound effectively to the A2, pS2, B1, and OT ERE-bound receptor and significantly stabilized the receptor-DNA interaction. Similar levels of the full-length p160 protein amplified in breast cancer 1 were recruited from HeLa nuclear extracts by the A2, pS2, B1, and OT ERE-bound receptors. In contrast, significantly less transcriptional intermediary factor 2 was recruited by the B1 ERE-bound receptor than by the A2 ERE-bound receptor. These studies suggest that allosteric modulation of ER conformation by individual ERE sequences influences the recruitment of specific coactivator proteins and leads to differential expression of genes containing divergent ERE sequences.
Mol Endocrinol 2001 Jul
PMID:Allosteric modulation of estrogen receptor conformation by different estrogen response elements. 1143 12

Thyroid hormone receptors (T3Rs) are hormone-regulated transcription factors that play important roles in vertebrate homeostasis, differentiation, and development. T3Rs are synthesized as multiple isoforms that display tissue-specific expression patterns and distinct transcriptional properties. Most T3R isoforms associate with co-activator proteins and mediate transcriptional activation only in the presence of thyroid hormone. The pituitary-specific T3Rbeta-2 isoform departs from this general rule and is able to interact with p160 co-activators, and to mediate transcriptional activation in both the absence and presence of hormone. We report here that this hormone-independent activation is mediated by contacts between the unique N terminus of T3Rbeta-2 and an internal interaction domain in the SRC-1 (steroid receptor co-activator-1) and GRIP-1 (glucocorticoid receptor interacting protein 1) co-activators. These hormone-independent contacts between T3Rbeta-2 and the p160 co-activators are distinct in sequence and function from the LXXLL motifs that mediate hormone-dependent transcriptional activation and resemble instead a mode of co-activator recruitment previously observed only for the steroid hormone receptors and only in the presence of steroid hormone. Our results suggest that the transcriptional properties of the different T3R isoforms represent a combinatorial mixture of repression, antirepression, and hormone-independent and hormone-dependent activation functions that operate in conjunction to determine the ultimate transcriptional outcome.
Mol Endocrinol 2001 Jul
PMID:Isoform-specific transcriptional regulation by thyroid hormone receptors: hormone-independent activation operates through a steroid receptor mode of co-activator interaction. 1143 16

Oncogenesis associated with human T-cell leukemia virus (HTLV) infection is directly linked to the virally encoded transcription factor Tax. To activate HTLV-1 transcription Tax interacts with the cellular protein CREB and the pleiotropic coactivators CBP and p300. While extensively studied, the molecular mechanisms of Tax transcription function and coactivator utilization are not fully understood. Previous studies have focused on Tax binding to the KIX domain of CBP, as this was believed to be the key step in recruiting the coactivator to the HTLV-1 promoter. In this study, we identify a carboxy-terminal region of CBP (and p300) that strongly interacts with Tax and mediates Tax transcription function. Through deletion mutagenesis, we identify amino acids 2003 to 2212 of CBP, which we call carboxy-terminal region 2 (CR2), as the minimal region for Tax interaction. Interestingly, this domain corresponds to the steroid receptor coactivator 1 (SRC-1)-interacting domain of CBP. We show that a double point mutant targeted to one of the putative alpha-helical motifs in this domain significantly compromises the interaction with Tax. We also characterize the region of Tax responsible for interaction with CR2 and show that the previously identified transactivation domain of Tax (amino acids 312 to 319) participates in CR2 binding. This region of Tax corresponds to a consensus amphipathic helix, and single point mutations targeted to amino acids on the face of this helix abolish interaction with CR2 and dramatically reduce Tax transcription function. Finally, we demonstrate that Tax and SRC-1 bind to CR2 in a mutually exclusive fashion. Together, these studies identify a novel Tax-interacting site on CBP/p300 and extend our understanding of the molecular mechanism of Tax transactivation.
Mol Cell Biol 2001 Aug
PMID:The oncoprotein Tax binds the SRC-1-interacting domain of CBP/p300 to mediate transcriptional activation. 1146 34

The DNA-binding domain of nuclear hormone receptors functions as an interaction interface for other transcription factors. Using the DNA-binding domain of TRbeta1 as bait in the yeast two-hybrid system, we cloned the Tat binding protein-1 that was originally isolated as a protein binding to the human immunodeficiency virus type 1 Tat transactivator. Tat binding protein-1 has subsequently been identified as a member of the ATPase family and a component of the 26S proteasome. Tat binding protein-1 interacted with the DNA-binding domain but not with the ligand binding domain of TR in vivo and in vitro. TR bound to the amino-terminal portion of Tat binding protein-1 that contains a leucine zipper-like structure. In mammalian cells, Tat binding protein-1 potentiated the ligand-dependent transactivation by TRbeta1 and TRalpha1 via thyroid hormone response elements. Both the intact DNA-binding domain and activation function-2 of the TR were required for the transcriptional enhancement in the presence of Tat binding protein-1. Tat binding protein-1 did not augment the transactivation function of the RAR, RXR, PPARgamma, or ER. The intrinsic activation domain in Tat binding protein-1 resided within the carboxyl-terminal conserved ATPase domain, and a mutation of a putative ATP binding motif but not a helicase motif in the carboxyl-terminal conserved ATPase domain abolished the activation function. Tat binding protein-1 synergistically activated the TR-mediated transcription with the steroid receptor coactivator 1, p120, and cAMP response element-binding protein, although Tat binding protein-1 did not directly interact with these coactivators in vitro. In contrast, the N-terminal portion of Tat binding protein-1 directly interacted in vitro and in vivo with the TR-interacting protein 1 possessing an ATPase activity that interacts with the activation function-2 of liganded TR. Collectively, Tat binding protein-1 might function as a novel DNA-binding domain-binding transcriptional coactivator specific for the TR probably in cooperation with other activation function-2-interacting cofactors such as TR-interacting protein 1.
Mol Endocrinol 2001 Aug
PMID:Human immunodeficiency virus type 1 Tat binding protein-1 is a transcriptional coactivator specific for TR. 1146 57

Aldosterone effects are mediated by the MR, which possesses the same affinity for mineralocorticoids and glucocorticoids. In addition to the existence of mechanisms regulating intracellular hormone availability, we searched for human MR splice variants involved in tissue-specific corticosteroid function. We have identified a new human MR isoform, hMRDelta5,6, resulting from an alternative splicing event skipping exons 5 and 6 of the human MR gene. hMRDelta5,6 mRNAs are expressed in several human tissues at different levels compared with wild-type human MR, as shown by real time PCR. Introduction of a premature stop codon results in a 75-kDa protein lacking the entire hinge region and ligand binding domain. Interestingly, hMRDelta5,6 is still capable of binding to DNA and acts as a ligand-independent transactivator, with maximal transcriptional induction corresponding to approximately 30-40% of aldosterone-activated wild-type human MR. Coexpression of hMRDelta5,6 with human MR or human GR increases their transactivation potential at high doses of hormone. Finally, hMRDelta5,6 is able to recruit the coactivators, steroid receptor coactivator 1, receptor interacting protein 140, and transcription intermediary factor 1alpha, which enhance its transcriptional activity. Ligand-independent transactivation and enhancement of both wild-type MR and GR activities by hMRDelta5,6 suggests that this new variant might play a role in modulating corticosteroid effects in target tissues.
Mol Endocrinol 2001 Sep
PMID:A new human MR splice variant is a ligand-independent transactivator modulating corticosteroid action. 1151 8

Cell proliferation requires precise control to prevent mutations from replication of (unrepaired) damaged DNA in cells exposed spontaneously to mutagens. Here we show that the modified human DNA repair enzyme O(6)-methylguanine-DNA methyltransferase (R-MGMT), formed from the suicidal repair of the mutagenic O(6)-alkylguanine (6RG) lesions by MGMT in the cells exposed to alkylating carcinogens, functions in such control by preventing the estrogen receptor (ER) from transcription activation that mediates cell proliferation. This function is in contrast to the phosphotriester repair domain of bacterial ADA protein, which acts merely as a transcription activator for its own synthesis upon repair of phosphotriester lesions. First, MGMT, which is constitutively present at active transcription sites, coprecipitates with the transcription integrator CREB-binding protein CBP/p300 but not R-MGMT. Second, R-MGMT, which adopts an altered conformation, utilizes its exposed VLWKLLKVV peptide domain (codons 98 to 106) to bind ER. This binding blocks ER from association with the LXXLL motif of its coactivator, steroid receptor coactivator-1, and thus represses ER effectively from carrying out transcription that regulates cell growth. Thus, through a change in conformation upon repair of the 6RG lesion, MGMT switches from a DNA repair factor to a transcription regulator (R-MGMT), enabling the cell to sense as well as respond to mutagens. These results have implications in chemotherapy and provide insights into the mechanisms for linking transcription suppression with transcription-coupled DNA repair.
Mol Cell Biol 2001 Oct
PMID:The modified human DNA repair enzyme O(6)-methylguanine-DNA methyltransferase is a negative regulator of estrogen receptor-mediated transcription upon alkylation DNA damage. 1156 93

Steroid/thyroid actions in the brain are exerted through their receptors which belong to the nuclear receptor superfamily. Transcriptional transactivation mediated by these receptors depends on recruited co-activators, among which steroid receptor co-activators (SRCs) seem to be restricted to the nuclear receptor family. By using Northern and Western blot analysis we have estimated the mRNA and protein levels, respectively, of SRC-1 in the brain and pituitary of male and female rats, under physiological conditions and following restraint stress. Under basal conditions, SRC-1 is expressed at higher levels in the hippocampus and the pituitary of male, compared to female rats. Acute stress results in decreased, compared to the control, SRC-1 levels in the hypothalamus of both sexes, in the pituitary and frontal cortex of male rats, and in increased SRC-1 levels in the hippocampus of female rats. The observed changes at the mRNA level are supported by analogous changes at the protein level. The apparent regulation of SRC-1 gene expression in the nervous system by the endocrine status of the animal, adds another level of complexity in the mechanism controlling steroid hormone actions. Furthermore, the variability in SRC-1 expression within the brain provides a means to explain the cell-specificity of steroid hormone actions in this tissue.
J Steroid Biochem Mol Biol 2001 Nov
PMID:Effects of gender and stress on the regulation of steroid receptor coactivator-1 expression in the rat brain and pituitary. 1173 50

Gene activation mediated by nuclear receptors is regulated in a tissue-specific manner and requires interactions between nuclear receptors and their cofactors. Here, we identified and characterized a tissue-specific coactivator, GT198, that interacts with the DNA-binding domains of nuclear receptors. GT198 was originally described as a genomic transcript that mapped to the human breast cancer susceptibility locus 17q12-q21 with unknown function. We show that GT198 exhibits a tissue-specific expression pattern in which its mRNA is elevated in testis, spleen, thymus, pituitary cells, and several cancer cell lines. GT198 is a 217-amino-acid nuclear protein that contains a leucine zipper required for its dimerization. In vitro binding and yeast two-hybrid assays indicated that GT198 interacted with nuclear receptors through their DNA-binding domains. GT198 potently stimulated transcription mediated by estrogen receptor alpha and beta, thyroid hormone receptor beta1, androgen receptor, glucocorticoid receptor, and progesterone receptor. However, the action of GT198 was distinguishable from that of the ligand-binding domain-interacting nuclear receptor coactivators, such as TRBP, CBP, and SRC-1, with respect to basal activation and hormone sensitivity. Furthermore, protein kinase A, protein kinase C, and mitogen-activated protein kinase can phosphorylate GT198 in vitro, and cotransfection of these kinases regulated the transcriptional activity of GT198. These data suggest that GT198 is a tissue-specific, kinase-regulated nuclear receptor coactivator that interacts with the DNA-binding domains of nuclear receptors.
Mol Cell Biol 2002 Jan
PMID:Identification and characterization of a tissue-specific coactivator, GT198, that interacts with the DNA-binding domains of nuclear receptors. 1173 47

Steroid receptor RNA activator (SRA) is a novel coactivator for steroid receptors that acts as an RNA molecule, whereas steroid receptor coactivator (SRC) family members, such as steroid receptor coactivator-1 (SRC-1) and transcriptional intermediary factor 2 (TIF2) exert their biological effects as proteins. Individual overexpression of each of these coactivators, which can form multimeric complexes in vivo, results in stimulated ERalpha transcriptional activity in transient transfection assays. However there is no information on the consequences of reducing SRC-1, TIF2, or SRA expression, singly or in combination, on ERalpha transcriptional activity. We therefore developed antisense oligodeoxynucleotides (asODNs) to SRA, SRC-1, and TIF2 mRNAs, which rapidly and specifically reduced the expression of each of these coactivators. ERalpha-dependent gene expression was reduced in a dose-dependent fashion by up to 80% in cells transfected with these oligonucleotides. Furthermore, treatment of cells with combinations of SRA, SRC-1, and TIF2 asODNs reduced ERalpha transcriptional activity to an extent greater than individual asODN treatment alone, suggesting that these coactivators cooperate, in at least an additive fashion, to activate ERalpha-dependent target gene expression. Finally, treatment of MCF-7 cells with asODN against SRC-1 and TIF2 revealed a requirement of these coactivators, but not SRA, for hormone-dependent DNA synthesis and induction of estrogen-dependent pS2 gene expression, indicating that SRA and SRC family coactivators can fulfill specific functional roles. Taken together, we have developed a rapid method to reduce endogenous coactivator expression that enables an assessment of the in vivo role of specific coactivators on ERalpha biological action and avoids potential artifacts arising from overexpression of coactivators in transient transfection assays.
Mol Endocrinol 2002 Feb
PMID:Reduction of coactivator expression by antisense oligodeoxynucleotides inhibits ERalpha transcriptional activity and MCF-7 proliferation. 1181 99


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