Coactivator assembly at the promoter: Efficient recruitment of SRC2 is coupled to cooperative DNA binding by the progesterone receptor
Coactivator assembly at the promoter: Efficient recruitment of SRC2 is coupled to cooperative DNA binding by the progesterone receptor
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DOI：
10.1021/bi700850v
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发表时间：
2007-10-02
期刊：
影响因子：
2.9
通讯作者：
Bain, David L.
中科院分区：
文献类型：
--
作者：
Heneghan, Aaron F.;Connaghan-Jones, Keith D.;Bain, David L.
真核生物基因调控中的一个尚未解决的问题主要集中在dna结合转录因子招募共激活因子到启动子的机制上。最近的研究表明，启动子DNA作为一种变构配体，不仅可以结合和定位转录因子，还可以触发蛋白质内部的结构变化，以引发辅激活因子的招募。不幸的是，对这一现象的定量和分子理解仍然不清楚。我们之前已经解决了孕激素受体a -异构体（PR-A）组装在多个启动子上的微态相互作用能量；在这里，我们将这项工作扩展到PR-A在介导辅激活子SRC2的启动子依赖性招募中的作用。PR-A启动子相互作用的定量足迹和统计热力学模型在存在和不存在共激活剂的情况下表明，受体与单个响应元件的结合最大程度地耦合到SRC2结合的2倍增强。相比之下，PR-A在多个响应元件上的组装与SRC2亲和力的额外6至10倍增加有关。这种效应的产生是由于SRC2摄取和邻接结合的PR-A二聚体之间增强的合作相互作用之间的耦合反应。换句话说，增加的辅激活因子水平稳定了高阶受体-启动子复合物。因此，这些结果可能不仅提供了一种机制，可以解释含有单个结合位点的启动子转录活性较弱，而含有多个结合位点的启动子转录活性较强，而且还表明，体内共激活子水平的波动可能是PR-A（和其他核受体）在启动子上组装的生理调节剂。
A largely unsolved problem in eukaryotic gene regulation focuses on the mechanisms by which DNA-bound transcription factors recruit coactivators to a promoter. Recent work has suggested that promoter DNA acts as an allosteric ligand, serving not only to bind and localize transcription factors but also to trigger structural changes within the proteins in order to elicit coactivator recruitment. Unfortunately, a quantitative and molecular understanding of this phenomenon remains unclear. We have previously resolved the microstate interaction energetics of progesterone receptor A-isoform (PR-A) assembly at multiple promoters; here we extend this work to the role of PR-A in mediating promoter-dependent recruitment of the coactivator, SRC2. Quantitative footprinting and statistical thermodynamic modeling of PR-A:promoter interactions in the presence and absence of coactivator demonstrate that receptor binding to a single response element is maximally coupled to a 2-fold enhancement in SRC2 binding. By contrast, PR-A assembly at multiple response elements is linked to an additional 6- to 10-fold increase in SRC2 affinity. This effect arises due to a coupled reaction between SRC2 uptake and enhanced cooperative interactions between adjacently bound PR-A dimers. Put another way, increased coactivator levels stabilize a higher-order receptor-promoter complex. These results may thus not only offer a mechanism for explaining the weak transcriptional activity seen for promoters containing a single binding site and the synergistically strong activity seen for multisite promoters but also suggest that in vivo fluctuations of coactivator levels might serve as a physiological regulator of assembly for PR-A (and for other nuclear receptors) at the promoter.