Department of Molecular and Cell Biology, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa.
Steroids. 2011 Sep-Oct;76(10-11):1176-84. doi: 10.1016/j.steroids.2011.05.007. Epub 2011 May 27.
The glucocorticoid receptor (GR) is a ligand-activated transcription factor for which a number of endogenous and synthetic ligands exist. A key question in steroid receptor biology is how different ligands elicit different maximal transcriptional responses via the same receptor and on the same promoter. This question was addressed quantitatively for the GR, using a panel of agonists, partial agonists and antagonists, on the endogenous GILZ gene in two different human cell lines. It was found that the extent of GR nuclear localization correlated with the efficacy for GILZ transactivation by the GR in U2OS cells. However, in A549 cells there was no significant correlation, with all ligands resulting in similar levels of GR nuclear localization, despite different levels of transcriptional activation of the GILZ gene. Chromatin immunoprecipitation analysis on the other hand, revealed ligand-specific differences in GILZ promoter occupancy in the A549 cells, which correlated with the transcriptional efficacy of the subset of ligands investigated. This suggests that ligand-specific differences in promoter occupancy by activated GR play a major role in discrimination between agonist, partial agonist and antagonist responses on the endogenous GILZ gene in A549 cells, while differences in nuclear localisation of liganded GR play a role in determining the transcriptional outcome in U2OS cells. These cell line-specific differences were not dependent on the amount of GR present, since transient overexpression of GR in U2OS did not alter the relative ligand-selective nuclear localisation. Our results show that there is a relationship between ligand-specific transactivation efficacy, extent of nuclear translocation and recruitment of GR to the promoter. However, the relative contribution of nuclear translocation and GR promoter recruitment to ligand-specific transactivation efficacy is cell-specific.
糖皮质激素受体 (GR) 是一种配体激活的转录因子，存在许多内源性和合成配体。甾体受体生物学中的一个关键问题是，不同的配体如何通过相同的受体和相同的启动子产生不同的最大转录反应。为了解决这个问题，我们使用了一组激动剂、部分激动剂和拮抗剂，对两种不同的人细胞系中的内源性 GILZ 基因进行了定量研究。结果发现，GR 的核定位程度与 GR 在 U2OS 细胞中转录激活 GILZ 的功效相关。然而，在 A549 细胞中，尽管 GR 对 GILZ 基因的转录激活水平不同，但 GR 的核定位没有显著相关性，所有配体均导致相似水平的 GR 核定位。另一方面，染色质免疫沉淀分析显示，在 A549 细胞中，配体特异性差异存在于 GILZ 启动子占据，这与所研究的配体子集的转录功效相关。这表明，在 A549 细胞中，激活的 GR 在启动子上的配体特异性差异在区分激动剂、部分激动剂和拮抗剂反应方面起着主要作用，而 liganded GR 的核定位差异在决定 U2OS 细胞中的转录结果方面起着作用。这些细胞系特异性差异不依赖于存在的 GR 量，因为在 U2OS 中瞬时过表达 GR 不会改变相对配体选择性核定位。我们的结果表明，配体特异性转录激活功效、核转位程度和 GR 向启动子的募集之间存在关系。然而，核转位和 GR 启动子募集对配体特异性转录激活功效的相对贡献是细胞特异性的。
