Equilibrium interactions of corepressors and coactivators with agonist and antagonist complexes of glucocorticoid receptors
Equilibrium interactions of corepressors and coactivators with agonist and antagonist complexes of glucocorticoid receptors
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DOI：
10.1210/me.2003-0421
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发表时间：
2004-06-01
影响因子：
--
通讯作者：
Simons, SS
中科院分区：
文献类型：
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作者：
Wang, Q;Blackford, JA;Simons, SS
辅阻遏物和辅激活物可以调节完整细胞中糖皮质激素受体（GR）与激动剂和拮抗剂类固醇复合的剂量-反应曲线和部分激动剂活性。我们最近报道，GR-拮抗剂复合物结合到共激活因子TIF 2（转录中介因子2），这是一致的共激活因子的全细胞效应介导的直接相互作用与GR复合物。我们现在要问的是，辅阻遏物的全细胞调节活性是否也需要与GR激动剂和拮抗剂复合物结合，以及辅阻遏物和辅激活剂与GR复合物的结合是否涉及竞争性平衡反应。在两种不同细胞系的哺乳动物双杂交试验以及无细胞下拉和全细胞免疫沉淀试验中，辅阻遏物NCoR（核受体辅阻遏物）和SMRT（类维生素A和甲状腺激素受体的沉默介体）与GR的激动剂和拮抗剂复合物相关。GR的N-和C-末端区域都需要辅阻遏物结合，这需要介导辅阻遏物与其他核/类固醇受体结合的CoRNR盒基序。重要的是，全细胞GR与辅阻遏物的相互作用被过量的辅激活物竞争性抑制，反之亦然。然而，竞争GR与辅阻遏物和辅激活物结合的辅激活物TIF 2的区域是不相同的，这意味着GR与辅激活物和辅阻遏物的结合存在分子差异。最后，当辅因子与外源性甲状腺受体β +/-甲状腺激素的选择性辅因子结合改变辅激活因子与辅抑制因子的全细胞比例时，GR剂量-反应曲线和部分激动剂活性被适当修改。这种修饰不依赖于组蛋白乙酰化。我们的结论是相互拮抗平衡相互作用的corepressors和coactivators调制的剂量-反应曲线和部分激动剂活性的GR复合物的方式，是响应于这两类辅因子的细胞内比例。这种调节为发育、分化、稳态和内分泌治疗过程中的基因表达差异控制提供了一种有吸引力的机制。
Corepressors and coactivators can modulate the dose-response curve and partial agonist activity of glucocorticoid receptors (GRs) complexed with agonist and antagonist steroids, respectively, in intact cells. We recently reported that GR-antagonist complexes bind to the coactivator TIF2, (transcriptional intermediary factor 2), which is consistent with the whole-cell effects of coactivators being mediated by direct interactions with GR complexes. We now ask whether the whole-cell modulatory activity of corepressors also entails binding to both GR-agonist and -antagonist complexes and whether the association of corepressors and coactivators with GR complexes involves competitive equilibrium reactions. In mammalian two-hybrid assays with two different cell lines and in cell-free pull-down and whole-cell immunoprecipitation assays, the corepressors NCoR (nuclear receptor corepressor) and SMRT (silencing mediator of retinoid and thyroid hormone receptor) associate with agonist and antagonist complexes of GRs. Both N- and C-terminal regions of GR are needed for corepressor binding, which requires the CoRNR box motifs that mediate corepressor binding to other nuclear/steroid receptors. Importantly, whole-cell GR interactions with corepressors are competitively inhibited by excess coactivator and vice versa. However, the regions of the coactivator TIF2 that compete for GR binding to corepressor and coactivator are not the same, implying a molecular difference in GR association with coactivators and corepressors. Finally, when the whole-cell ratio of coactivators to corepressors is altered by selective cofactor binding to exogenous thyroid receptor beta+/-thyroid hormone, the GR dose-response-curve and partial agonist activity are appropriately modified. Such modifications are independent of histone acetylation. We conclude that mutually antagonistic equilibrium interactions of corepressors and coactivators modulate the dose-response curve and partial agonist activity of GR complexes in a manner that is responsive to the intracellular ratio of these two classes of cofactors. This modulation provides an attractive mechanism for differential control of gene expression during development, differentiation, homeostasis, and endocrine therapies.