Two Modes of Transcriptional Activation at Native Promoters by NF-κB p65

Article (PDF Available)inPLoS Biology 7(3):e73 · April 2009with30 Reads
DOI: 10.1371/journal.pbio.1000073 · Source: PubMed
Abstract
The NF-kappaB family of transcription factors is crucial for the expression of multiple genes involved in cell survival, proliferation, differentiation, and inflammation. The molecular basis by which NF-kappaB activates endogenous promoters is largely unknown, but it seems likely that it should include the means to tailor transcriptional output to match the wide functional range of its target genes. To dissect NF-kappaB-driven transcription at native promoters, we disrupted the interaction between NF-kappaB p65 and the Mediator complex. We found that expression of many endogenous NF-kappaB target genes depends on direct contact between p65 and Mediator, and that this occurs through the Trap-80 subunit and the TA1 and TA2 regions of p65. Unexpectedly, however, a subset of p65-dependent genes are transcribed normally even when the interaction of p65 with Mediator is abolished. Moreover, a mutant form of p65 lacking all transcription activation domains previously identified in vitro can still activate such promoters in vivo. We found that without p65, native NF-kappaB target promoters cannot be bound by secondary transcription factors. Artificial recruitment of a secondary transcription factor was able to restore transcription of an otherwise NF-kappaB-dependent target gene in the absence of p65, showing that the control of promoter occupancy constitutes a second, independent mode of transcriptional activation by p65. This mode enables a subset of promoters to utilize a wide choice of transcription factors, with the potential to regulate their expression accordingly, whilst remaining dependent for their activation on NF-kappaB.

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    • "RelA Is Necessary for Recruitment of P-TEFb, Mediator, Brd4, and the SEC to T-bet Target Genes The ability of T-bet to recruit P-TEFb also requires cell restimulation (Figures 2A, 2B, 5A, and S5A), suggesting that additional factors were also necessary. In other cell types, RelA can recruit P-TEFb to genes directly (Barboric et al., 2001), through Brd4 (Brown et al., 2014; Huang et al., 2009; Sharma et al., 2007), or through Mediator (van Essen et al., 2009; Wienerroither et al., 2015). In Th1 cells, RelA binds to, and is necessary for, activation of Ifng (Balasubramani et al., 2010; Sica et al., 1997). "
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    • "A number of well-studied inflammatory genes require chromatin remodeling to remove nucleosomes prior to Pol II recruitment and transcription initiation (Ramirez-Carrozzi et al., 2006; Weinmann et al., 2001). Formation of preinitiation complexes is facilitated by the signal-dependent recruitment of coactivators (Figure 2A, green arrow) such as the large, multisubunit Mediator complex (van Essen et al., 2009) or the histone acetyltransferase p300/CBP (Zhong et al., 1998). However, many genes, including critical inflammatory genes like tumor necrosis factor alpha (TNFa ), exhibit accessible promoter regions, histone acetylation, and Pol II occupancy in unstimulated macrophages (Figure 2B; Bhatt et al., 2012; Escoubet-Lozach et al., 2011; Ramirez-Carrozzi et al., 2009 ). "
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