Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.7.6 (RNA polymerase)
34,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mediator complex is essential for regulated transcription in vitro. In the yeast Saccharomyces cerevisiae, mediator comprises >15 subunits and interacts with the C-terminal domain of the largest subunit of RNA polymerase II, thus forming an RNA polymerase II holoenzyme. Here we describe the molecular cloning of the MED1 cDNA encoding the 70-kDa subunit of the mediator complex. Yeast cells lacking the MED1 gene are viable but show a complex phenotype including partial defects in both repression and induction of the GAL genes. Together with results on other mediator subunits, this implies that the mediator is involved in both transcriptional activation and repression. Similar to mutations in the SRB10 and SRB11 genes encoding cyclin C and the cyclin C-dependent kinase, a disruption of the MED1 gene can partially suppress loss of the Snf1 protein kinase. We further found that a lexA-Med1 fusion protein is a strong activator in srb11 cells, which suggests a functional link between Med1 and the Srb10/11 complex. Finally, we show that the Med2 protein is lost from the mediator on purification from Med1-deficient cells, indicating a physical interaction between Med1 and Med2.
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PMID:The Med1 subunit of the yeast mediator complex is involved in both transcriptional activation and repression. 989 41

Human TRAP/Mediator is a key coactivator for many transcription factors that act through direct interactions with distinct subunits, and MED1/TRAP220 is the main subunit target for various nuclear receptors. Remarkably, the current study shows that MED1/TRAP220 only exists in a TRAP/Mediator subpopulation (less then 20% of the total) that is greatly enriched in specific TRAP/Mediator subunits and is tightly associated with a near stoichiometeric level of RNA polymerase II. Importantly, this MED1/TRAP220-containing holoenzyme supports both basal- and activator-dependent transcription in an in vitro system lacking additional RNA polymerase II. Furthermore, chromatin immunoprecipitation experiments demonstrate an activator-selective recruitment of MED1/TRAP220-containing versus MED1/TRAP220-deficient TRAP/Mediator complexes to estrogen receptor (ER) and p53 target genes, respectively. Finally, RNAi studies show that MED1/TRAP220 is required for ER-mediated transcription and estrogen-dependent breast cancer cell growth. These observations have significant implications for our current understanding of the composition, heterogeneity, and functional specificity of TRAP/Mediator complexes.
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PMID:MED1/TRAP220 exists predominantly in a TRAP/ Mediator subpopulation enriched in RNA polymerase II and is required for ER-mediated transcription. 1598 67

The cellular retinoic acid binding protein I gene is induced by thyroid hormone (T3) through a T3 response element (TRE) approximately 1 kb upstream of the basal promoter. The upstream region is organized into a positioned nucleosomal array with the N1 nucleosome spanning the GC box region. T3 induces apparent interactions between chromatin segments containing the TRE and the GC box regions and the sliding of upstream nucleosomes toward N1 with concomitant N1 remodeling. Concurrently, the chromatin-remodeling factor BRM is replaced by BRG1 and histones are hyperacetylated. All these events are abolished in Med1/Trap220 null cells, indicating a key role for TRAP/Mediator in these processes. A MED1/TRAP220-containing Mediator complex constitutively occupies the GC box region but not the TRE, serving as a nexus for distal and proximal factors. This indicates new TRAP/Mediator functions in facilitating ultimate recruitment and function of RNA polymerase II and the general transcription machinery.
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PMID:Thyroid hormone-induced juxtaposition of regulatory elements/factors and chromatin remodeling of Crabp1 dependent on MED1/TRAP220. 1613 21

The Mediator subunits MED14 and MED1 have been implicated in transcriptional regulation by the glucocorticoid receptor (GR) by acting through its activation functions 1 and 2. To understand the contribution of these Mediator subunits to GR gene-specific regulation, we reduced the levels of MED14 and MED1 using small interfering RNAs in U2OS-hGR osteosarcoma cells and examined the mRNA induction by dexamethasone of four primary GR target genes, interferon regulatory factor 8 (IRF8), ladinin 1, IGF-binding protein 1 (IGFBP1), and glucocorticoid-inducible leucine zipper (GILZ). We found that the GR target genes differed in their requirements for MED1 and MED14. GR-dependent mRNA expression of ladinin 1 and IRF8 required both MED1 and MED14, whereas induction of IGFBP1 mRNA by the receptor was dependent upon MED14, but not MED1. In contrast, GILZ induction by GR was largely independent of MED1 and MED14, but required the p160 cofactor transcriptional intermediary factor 2. Interestingly, we observed higher GR occupancy at GILZ than at the IGFBP1 or IRF8 glucocorticoid response element (GREs). In contrast, recruitment of MED14 compared with GR at IGFBP1 and IRF8 was higher than that observed at GILZ. At GILZ, GR and RNA polymerase II were recruited to both the GRE and the promoter, whereas at IGFBP1, RNA polymerase II occupied the promoter, but not the GRE. Thus, MED14 and MED1 are used by GR in a gene-specific manner, and the requirement for the Mediator at GILZ may be bypassed by increased GR and RNA polymerase II occupancy at the GREs. Our findings suggest that modulation of the Mediator subunit activities would provide a mechanism for promoter selectivity by GR.
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PMID:MED14 and MED1 differentially regulate target-specific gene activation by the glucocorticoid receptor. 1623 57

The TRAP/Mediator coactivator complex serves as a functional interface between DNA-bound transactivators and the RNA polymerase II-associated basal transcription apparatus. TRAP220/MED1 is a variably associated subunit of the complex that plays a specialized role in selectively targeting TRAP/Mediator to specific genes. Ablation of the Trap220/Med1 gene in mice impairs embryonic cell growth, yet the underlying mechanism is unknown. In this report, we identified distinct cell growth regulatory genes whose expression is affected by the loss of TRAP220/MED1 by RNA interference. Among the down-regulated genes revealed by cDNA microarray analyses, we identified Aurora-A, a centrosome kinase that plays a critical role in regulating M phase events and is frequently amplified in several types of cancer. In general, we found that TRAP220/MED1 expression is required for high basal levels of Aurora-A gene expression and that ectopic overexpression of TRAP220/MED1 coactivates transcription from the Aurora-A gene promoter. Furthermore, chromatin immunoprecipitation assays show that TRAP220/MED1-containing TRAP/Mediator complexes directly bind to the Aurora-A promoter in vivo. Finally, we present evidence suggesting that TRAP/Mediator is recruited to the Aurora-A gene via direct interactions between TRAP220/MED1 and the Ets-related transcription factor GABP. Taken together, these findings suggest that TRAP220/MED1 plays a novel coregulatory role in facilitating the recruitment of TRAP/Mediator to specific target genes involved in growth and cell cycle progression.
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PMID:Regulation of Aurora-A kinase gene expression via GABP recruitment of TRAP220/MED1. 1657 58

Mediator is an evolutionarily conserved multisubunit protein complex that plays a key role in regulating transcription by RNA polymerase II. The complex functions by serving as a molecular bridge between DNA-bound transcriptional activators and the basal transcription apparatus. In humans, Mediator was first characterized as a thyroid hormone receptor (TR)-associated protein (TRAP) complex that facilitates ligand-dependent transcriptional activation by TR. More recently, Mediator has been established as an essential coactivator for a broad range of nuclear hormone receptors (NRs) as well as several other types of gene-specific transcriptional activators. A single subunit of the complex, MED1/TRAP220, is required for direct ligand-dependent interactions with NRs. Mediator coactivates NR-regulated gene expression by facilitating the recruitment and activation of the RNA polymerase II-associated basal transcription apparatus. Importantly, Mediator acts in concert with other NR coactivators involved in chromatin remodeling to initiate transcription of NR target genes in a multistep manner. In this review, we summarize the functional role of Mediator in NR signaling pathways with an emphasis on the underlying molecular mechanisms by which the complex interacts with NRs and subsequently facilitates their action. We also focus on recent advances in our understanding of TRAP/Mediator's pathophysiological role in mammalian disease and development.
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PMID:Role of the mediator complex in nuclear hormone receptor signaling. 1663 45

Mediator is a general coactivator complex connecting transcription activators and RNA polymerase II. Recent work has shown that the nuclear receptor-interacting MED1/TRAP220 subunit of Mediator is required for peroxisome proliferator-activated receptor gamma (PPARgamma)-stimulated adipogenesis of mouse embryonic fibroblasts (MEFs). However, the molecular mechanisms remain undefined. Here, we show an intracellular PPARgamma-Mediator interaction that requires the two LXXLL nuclear receptor recognition motifs on MED1/TRAP220 and, furthermore, we show that the intact LXXLL motifs are essential for optimal PPARgamma function in a reconstituted cell-free transcription system. Surprisingly, a conserved N-terminal region of MED1/TRAP220 that lacks the LXXLL motifs but gets incorporated into Mediator fully supports PPARgamma-stimulated adipogenesis. Moreover, in undifferentiated MEFs, MED1/TRAP220 is dispensable both for PPARgamma-mediated target gene activation and for recruitment of Mediator to a PPAR response element on the aP2 target gene promoter. However, PPARgamma shows significantly reduced transcriptional activity in cells deficient for a subunit (MED24/TRAP100) important for the integrity of the Mediator complex, indicating a general Mediator requirement for PPARgamma function. These results indicate that there is a conditional requirement for MED1/TRAP220 and that a direct interaction between PPARgamma and Mediator through MED1/TRAP220 is not essential either for PPARgamma-stimulated adipogenesis or for PPARgamma target gene expression in cultured fibroblasts. As Mediator is apparently essential for PPARgamma transcriptional activity, our data indicate the presence of alternative mechanisms for Mediator recruitment, possibly through intermediate cofactors or other cofactors that are functionally redundant with MED1/TRAP220.
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PMID:Alternative mechanisms by which mediator subunit MED1/TRAP220 regulates peroxisome proliferator-activated receptor gamma-stimulated adipogenesis and target gene expression. 1803 40

Mediator is a conserved multisubunit complex that acts as a functional interface between regulatory transcription factors and the general RNA polymerase II initiation apparatus. MED1 is a pivotal component of the complex that binds to nuclear receptors and a broad array of other gene-specific activators. Paradoxically, MED1 is found in only a fraction of the total cellular Mediator complexes, and the mechanisms regulating its binding to the core complex remain unclear. Here, we report that phosphorylation of MED1 by mitogen-activated protein kinase-extracellular signal-regulated kinase (MAPK-ERK) promotes its association with Mediator. We show that MED1 directly binds to the MED7 subunit and that ERK phosphorylation of MED1 enhances this interaction. Interestingly, we found that both thyroid and steroid hormones stimulate MED1 phosphorylation in vivo and that MED1 phosphorylation is required for its nuclear hormone receptor coactivator activity. Finally, we show that MED1 phosphorylation by ERK enhances thyroid hormone receptor-dependent transcription in vitro. Our findings suggest that ERK phosphorylation of MED1 is a regulatory mechanism that promotes MED1 association with Mediator and, as such, may facilitate a novel feed-forward action of nuclear hormones.
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PMID:MED1 phosphorylation promotes its association with mediator: implications for nuclear receptor signaling. 1839 Oct 15

The nuclear receptor vitamin D receptor (VDR) is known to associate with three vitamin D response element (VDREs)-containing regions within the CDKN1A (p21) gene region. Here we show in MDA-MB453 breast cancer cells that the natural VDR ligand 1alpha,25-dihydroxyvitamin D(3) causes cyclical transcription factor binding and chromatin looping of distal VDREs to the transcription start site (TSS) of the p21 gene, leading to cyclical accumulation of the p21 mRNA. At the chromatin level, association of the mediator protein MED1 precedes both the peaks of VDR binding to VDREs and phosphorylated RNA polymerase (p-Pol II) to the TSS. The loss of co-repressor NCoR1-histone deacetylase (HDAC) 3 complex and inhibitory chromatin looping from VDREs to the TSS are also initial events followed by increased acetylation of histone 3 at lysine 9 at the TSS prior to initiation of transcription. Simultaneous to VDR and p-Pol II peaks, chromatin loops between VDREs and the TSS are formed, and the lysine demethylase LSD1 and the histone acetyltransferase CBP are enriched in both regions. This is followed by a moderate peak in p21 transcript accumulation, repeated in cycles of 45-60 min. The transcript accumulation pattern is disturbed by siRNA inhibition of the mediator protein MED1, LSD1, NCoR1, or various HDACs, whereas CBP appears unnecessary for the response. Inhibition of MED1, HDAC4, or LSD1 by siRNA also attenuates ligand-induced chromatin looping. In conclusion, 1alpha,25-dihydroxyvitamin D(3) regulates p21 transcription by inducing cyclical chromatin looping that depends on both histone deacetylation and demethylation.
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PMID:Cyclical chromatin looping and transcription factor association on the regulatory regions of the p21 (CDKN1A) gene in response to 1alpha,25-dihydroxyvitamin D3. 1912 96

The Mediator subunit MED1/TRAP220/DRIP205/PBP interacts directly with many nuclear receptors and was long thought to be responsible for tethering Mediator to peroxisome proliferator-activated receptor (PPAR)-responsive promoters. However, it was demonstrated recently that PPARgamma can recruit Mediator by MED1-independent mechanisms. Here, we show that target gene activation by ectopically expressed PPARgamma and PPARalpha is independent of MED1. Consistent with this finding, recruitment of PPARgamma, MED6, MED8, TATA box-binding protein (TBP), and RNA polymerase II (RNAPII) to the enhancer and proximal promoter of the PPARgamma target gene Fabp4 is also independent of MED1. Using a small interfering RNA (siRNA)-based approach, we identify MED14 as a novel critical Mediator component for PPARgamma-dependent transactivation, and we demonstrate that MED14 interacts directly with the N terminus of PPARgamma in a ligand-independent manner. Interestingly, MED14 knockdown does not affect the recruitment of PPARgamma, MED6, and MED8 to the Fabp4 enhancer but does reduce their occupancy of the Fabp4 proximal promoter. In agreement with the necessity of MED14 for PPARgamma transcriptional activity, we show that knockdown of MED14 impairs adipogenesis of 3T3-L1 cells. Thus, MED14 constitutes a novel anchoring point between Mediator and the N-terminal domain of PPARgamma that is necessary for functional PPARgamma-mediated recruitment of Mediator and transactivation of PPARgamma subtype-specific target genes.
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PMID:MED14 tethers mediator to the N-terminal domain of peroxisome proliferator-activated receptor gamma and is required for full transcriptional activity and adipogenesis. 2019 23


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