Human Mediator Subunit MED26 Functions as a Docking Site for Transcription Elongation Factors

Stowers Institute for Medical Research, Kansas City, MO 64110, USA.
Cell (Impact Factor: 32.24). 07/2011; 146(1):92-104. DOI: 10.1016/j.cell.2011.06.005
Source: PubMed

ABSTRACT Promoter-proximal pausing by initiated RNA polymerase II (Pol II) and regulated release of paused polymerase into productive elongation has emerged as a major mechanism of transcription activation. Reactivation of paused Pol II correlates with recruitment of super-elongation complexes (SECs) containing ELL/EAF family members, P-TEFb, and other proteins, but the mechanism of their recruitment is an unanswered question. Here, we present evidence for a role of human Mediator subunit MED26 in this process. We identify in the conserved N-terminal domain of MED26 overlapping docking sites for SEC and a second ELL/EAF-containing complex, as well as general initiation factor TFIID. In addition, we present evidence consistent with the model that MED26 can function as a molecular switch that interacts first with TFIID in the Pol II initiation complex and then exchanges TFIID for complexes containing ELL/EAF and P-TEFb to facilitate transition of Pol II into the elongation stage of transcription.

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Available from: Michael Washburn, Sep 25, 2015
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    • "Recent studies have suggested that the Mediator complex can facilitate transcriptional elongation (Donner et al, 2010; Takahashi et al, 2011; Galbraith et al, 2013; Wang et al, 2013b), and H2Bub plays a positive role in transcription elongation through an association with the PAF complex (Fig 3C) (Zhu et al, 2005; Tanny et al, 2007; Weake & Workman, 2008). Surprisingly, our study found that corporation of Mediator and PAF complexes can enhance RNF20/40- mediated H2B ubiquitination in vitro (Figs 3B and EV3), revealing interplays between Mediator, PAF complex, and RNF20/40 in regulating the ubiquitination level of H2B lysine 120 in transcription (Fig 8). "
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    ABSTRACT: The Mediator complex orchestrates multiple transcription factors with the Pol II apparatus for precise transcriptional control. However, its interplay with the surrounding chromatin remains poorly understood. Here, we analyze differential histone modifications between WT and MED23(-/-) (KO) cells and identify H2B mono-ubiquitination at lysine 120 (H2Bub) as a MED23-dependent histone modification. Using tandem affinity purification and mass spectrometry, we find that MED23 associates with the RNF20/40 complex, the enzyme for H2Bub, and show that this association is critical for the recruitment of RNF20/40 to chromatin. In a cell-free system, Mediator directly and substantially increases H2Bub on recombinant chromatin through its cooperation with RNF20/40 and the PAF complex. Integrative genome-wide analyses show that MED23 depletion specifically reduces H2Bub on a subset of MED23-controlled genes. Importantly, MED23-coupled H2Bub levels are oppositely regulated during myogenesis and lung carcinogenesis. In sum, these results establish a mechanistic link between the Mediator complex and a critical chromatin modification in coordinating transcription with cell growth and differentiation. © 2015 The Authors.
    The EMBO Journal 09/2015; DOI:10.15252/embj.201591279 · 10.43 Impact Factor
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    • "A key transcription cofactor is the highly conserved Mediator complex, which has multiple subunits and is involved in various biological processes by transmitting information between gene-specific transcription factors and RNA polymerase II (RNAPII)8,9,10. In addition to its classic recruitment role in RNAPII preinitiation complex assembly, Mediator is a critical complex at multiple post-recruitment steps, such as the transition of RNAPII from pause to elongation as well as transcription termination11,12,13,14,15,16,17,18,19. The Mediator complex also participates in the regulation of chromatin architecture20, epigenetic silencing21, and mRNA processing22. "
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    ABSTRACT: Mediator complex is a molecular hub integrating signaling, transcription factors, and RNA polymerase II (RNAPII) machinery. Mediator MED23 is involved in adipogenesis and smooth muscle cell differentiation, suggesting its role in energy homeostasis. Here, through the generation and analysis of a liver-specific Med23-knockout mouse, we found that liver Med23 deletion improved glucose and lipid metabolism, as well as insulin responsiveness, and prevented diet-induced obesity. Remarkably, acute hepatic Med23 knockdown in db/db mice significantly improved the lipid profile and glucose tolerance. Mechanistically, MED23 participates in gluconeogenesis and cholesterol synthesis through modulating the transcriptional activity of FOXO1, a key metabolic transcription factor. Indeed, hepatic Med23 deletion impaired the Mediator and RNAPII recruitment and attenuated the expression of FOXO1 target genes. Moreover, this functional interaction between FOXO1 and MED23 is evolutionarily conserved, as the in vivo activities of dFOXO in larval fat body and in adult wing can be partially blocked by Med23 knockdown in Drosophila. Collectively, our data revealed Mediator MED23 as a novel regulator for energy homeostasis, suggesting potential therapeutic strategies against metabolic diseases.Cell Research advance online publication 16 September 2014; doi:10.1038/cr.2014.120.
    Cell Research 09/2014; 24(10). DOI:10.1038/cr.2014.120 · 12.41 Impact Factor
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    • "Though first linked to initiation, a role for Mediator in recruiting Pol II transcription elongation factors and phosphorylation of the Pol II CTD regulating Pol II pausing and elongation has emerged [41]. The Mediator complex most strongly associated with Pol II includes MED26, which has been shown to increase activation of transcription in vitro to a greater degree than other forms of the Mediator complex and play a key role in SEC recruitment and MYC transcription [41]. Gdown1 is a Pol II binding protein shown to be necessary for a Mediator-dependent response to activation of transcription [42]. "
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    ABSTRACT: High level MYC expression is associated with almost all human cancers. JQ1, a chemical compound that inhibits MYC expression is therapeutically effective in preclinical animal models in midline carcinoma, and Burkitt's lymphoma (BL). Here we show that JQ1 does not inhibit MYC expression to a similar extent in all tumor cells. The BL cells showed a ∼90% decrease in MYC transcription upon treatment with JQ1, however, no corresponding reduction was seen in several non-BL cells. Molecularly, these differences appear due to requirements of Brd4, the most active version of the Positive Transcription Elongation Factor B (P-TEFb) within the Super Elongation Complex (SEC), and transcription factors such as Gdown1, and MED26 and also other unknown cell specific factors. Our study demonstrates that the regulation of high levels of MYC expression in different cancer cells is driven by unique regulatory mechanisms and that such exclusive regulatory signatures in each cancer cells could be employed for targeted therapeutics.
    PLoS ONE 01/2014; 9(1):e87003. DOI:10.1371/journal.pone.0087003 · 3.23 Impact Factor
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