Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.7.6 (RNA polymerase)
 34,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A novel human complex that can either repress activator-dependent transcription mediated by PC4, or, at limiting TFIIH, act synergistically with PC4 to enhance activator-dependent transcription has been purified. This complex contains homologs of a subset of yeast mediator/holoenzyme components (including SRB7, SRB10, SRB11, MED6, and RGR1), homologs of other yeast transcriptional regulatory factors (SOH1 and NUT2), and, significantly, some components (TRAP220, TRAP170/hRGR1, and TRAP100) of a human thyroid hormone receptor-associated coactivator complex. The complex shows direct activator interactions but, unlike yeast mediator, can act independently of the RNA polymerase II CTD. These findings demonstrate both positive and negative functional capabilities for the human complex, emphasize novel (CTD-independent) regulatory mechanisms, and link the complex to other human coactivator complexes.
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PMID:A novel human SRB/MED-containing cofactor complex, SMCC, involved in transcription regulation. 1002 83

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 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

The ETS domain transcription factor Elk-1 stimulates expression of immediate early genes (IEGs) in response to mitogens. These events require phosphorylation of Elk-1 by extracellular signal-regulated kinase (ERK) and phosphorylation-dependent interaction of Elk-1 with co-activators, including histone acetyltransferases and the Mediator complex. Elk-1 also recruits ERK to the promoters of its target genes, suggesting that ERK phosphorylates additional substrates in transcription complexes at mitogen-responsive promoters. Here we report that MED14, a core subunit of the Mediator, is a bona fide ERK substrate and identify serine 986 (S986) within a serine-proline rich region of MED14 as the major ERK phosphorylation site. Mitogens induced phosphorylation of MED14 on S986 at IEG promoters; RNAi knockdown of MED14 reduced CDK8 and RNA polymerase II (RNAPII) recruitment, RNAPII C-terminal domain phosphorylation and impaired activation of IEG transcription. A single alanine substitution at S986 reduced activation of an E26 (ETS)-responsive reporter by oncogenic Ras and mitogen-induced, Elk-1-dependent transcription, whereas activities of other transcriptional activators were unaffected. We also demonstrate that Elk-1 can associate with MED14 independently of MED23, which may facilitate phosphorylation of MED14 by ERK to impart a positive and selective impact on mitogen-responsive gene expression.
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PMID:ERK phosphorylation of MED14 in promoter complexes during mitogen-induced gene activation by Elk-1. 2404 75

The Mediator16 (MED16; formerly termed SENSITIVE TO FREEZING6 [SFR6]) subunit of the plant Mediator transcriptional coactivator complex regulates cold-responsive gene expression in Arabidopsis thaliana, acting downstream of the C-repeat binding factor (CBF) transcription factors to recruit the core Mediator complex to cold-regulated genes. Here, we use loss-of-function mutants to show that RNA polymerase II recruitment to CBF-responsive cold-regulated genes requires MED16, MED2, and MED14 subunits. Transcription of genes known to be regulated via CBFs binding to the C-repeat motif/drought-responsive element promoter motif requires all three Mediator subunits, as does cold acclimation-induced freezing tolerance. In addition, these three subunits are required for low temperature-induced expression of some other, but not all, cold-responsive genes, including genes that are not known targets of CBFs. Genes inducible by darkness also required MED16 but required a different combination of Mediator subunits for their expression than the genes induced by cold. Together, our data illustrate that plants control transcription of specific genes through the action of subsets of Mediator subunits; the specific combination defined by the nature of the stimulus but also by the identity of the gene induced.
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PMID:The Arabidopsis mediator complex subunits MED16, MED14, and MED2 regulate mediator and RNA polymerase II recruitment to CBF-responsive cold-regulated genes. 2441 70

HIV-1 exploits multiple host proteins during infection. siRNA-based screenings have identified new proteins implicated in different pathways of the viral cycle that participate in a broad range of cellular functions. The human Mediator complex (MED) is composed of 28 elements and represents a fundamental component of the transcription machinery, interacting with the RNA polymerase II enzyme and regulating its ability to express genes. Here, we provide an evaluation of the MED activity on HIV replication. Knockdown of 9 out of 28 human MED proteins significantly impaired viral replication without affecting cell viability, including MED6, MED7, MED11, MED14, MED21, MED26, MED27, MED28, and MED30. Impairment of viral replication by MED subunits was at a post-integration step. Inhibition of early HIV transcripts was observed by siRNA-mediated knockdown of MED6, MED7, MED11, MED14, and MED28, specifically affecting the transcription of the nascent viral mRNA transactivation-responsive element. In addition, MED14 and MED30 were shown to have special relevance during the formation of unspliced viral transcripts (p < 0.0005). Knockdown of the selected MED factors compromised HIV transcription induced by Tat, with the strongest inhibitory effect shown by siMED6 and siMED14 cells. Co-immunoprecipitation experiments suggested physical interaction between MED14 and HIV-1 Tat protein. A better understanding of the mechanisms and factors controlling HIV-1 transcription is key to addressing the development of new strategies required to inhibit HIV replication or reactivate HIV-1 from the latent reservoirs.
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PMID:Characterization of the influence of mediator complex in HIV-1 transcription. 2510 Jul 19

The evolutionarily conserved Mediator complex is a critical coactivator for RNA polymerase II (Pol II)-mediated transcription. Here we report the reconstitution of a functional 15-subunit human core Mediator complex and its characterization by functional assays and chemical cross-linking coupled to MS (CX-MS). Whereas the reconstituted head and middle modules can stably associate, basal and coactivator functions are acquired only after incorporation of MED14 into the bimodular complex. This results from a dramatically enhanced ability of MED14-containing complexes to associate with Pol II. Altogether, our analyses identify MED14 as both an architectural and a functional backbone of the Mediator complex. We further establish a conditional requirement for metazoan-specific MED26 that becomes evident in the presence of heterologous nuclear factors. This general approach paves the way for systematic dissection of the multiple layers of functionality associated with the Mediator complex.
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PMID:Reconstitution of active human core Mediator complex reveals a critical role of the MED14 subunit. 2538 69

Mediator is a highly conserved protein complex that functions as a transcriptional coactivator in RNA polymerase II (RNAPII)-mediated transcription. The Arabidopsis Mediator complex has recently been implicated in plant immune responses. Here, we compared salicylic acid (SA)-, methyl jasmonate (MeJA)-, and the ethylene (ET) precursor 1-aminocyclopropane-1-carboxylic acid (ACC)-induced defense and/or wound-responsive gene expression in 14 Arabidopsis Mediator subunit mutants. Our results show that MED14, MED15, and MED16 are required for SA-activated expression of the defense marker gene PATHOEGNESIS-RELATED GENE1, MED25 is required for MeJA-induced expression of the wound-responsive marker gene VEGATATIVE STORAGE PROTEIN1 (VSP1), MED8, MED14, MED15, MED16, MED18, MED20a, MED25, MED31, and MED33A/B (MED33a and MED33B) are required for MeJA-induced expression of the defense maker gene PLANT DEFENSIN1.2 (PDF1.2), and MED8, MED14, MED15, MED16, MED25, and MED33A/B are also required for ACC-triggered expression of PDF1.2. Furthermore, we investigated the involvement of MED14, MED15, and MED16 in plant defense signaling crosstalk and found that MED14, MED15, and MED16 are required for SA- and ET-mediated suppression of MeJA-induced VSP1 expression. This result suggests that MED14, MED15, and MED16 not only relay defense signaling from the SA and JA/ET defense pathways to the RNAPII transcription machinery, but also fine-tune defense signaling crosstalk. Finally, we show that MED33A/B contributes to the necrotrophic fungal pathogen Botrytis cinerea-induced expression of the defense genes PDF1.2, HEVEIN-LIKE, and BASIC CHITINASE and is required for full-scale basal resistance to B. cinerea, demonstrating a positive role for MED33 in plant immunity against necrotrophic fungal pathogens.
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PMID:The Mediator Complex Subunits MED14, MED15, and MED16 Are Involved in Defense Signaling Crosstalk in Arabidopsis. 2806 97

The senescence response to oncogenes is believed to be a barrier to oncogenic transformation in premalignant lesions, and describing the mechanisms by which tumor cells evade this response is important for early diagnosis and treatment. The male germ cell-associated protein SSX2 is ectopically expressed in many types of cancer and is functionally involved in regulating chromatin structure and supporting cell proliferation. Similar to many well-characterized oncogenes, SSX2 has the ability to induce senescence in cells. In this study, we performed a functional genetic screen to identify proteins implicated in SSX2-induced senescence and identified several subunits of the Mediator complex, which is central in regulating RNA polymerase-mediated transcription. Further experiments showed that reduced levels of MED1, MED4, and MED14 perturbed the development of senescence in SSX2-expressing cells. In contrast, knockdown of MED1 did not prevent development of B-Raf- and Epirubicin-induced senescence, suggesting that Mediator may be specifically linked to the cellular functions of SSX2 that may lead to development of senescence or be central in a SSX2-specific senescence response. Indeed, immunostaining of melanoma tumors, which often express SSX proteins, exhibited altered levels of MED1 compared to benign nevi. Similarly, RNA-seq analysis suggested that MED1, MED4, and MED14 were downregulated in some tumors, while upregulated in others. In conclusion, our study reveals the Mediator complex as essential for SSX2-induced senescence and suggests that changes in Mediator activity could be instrumental for tumorigenesis.
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PMID:A functional genetic screen identifies the Mediator complex as essential for SSX2-induced senescence. 3169 25