The binding site for Xenopus glucocorticoid receptor accessory factor and a single adjacent half-GRE form an independent glucocorticoid response unit.
The binding site for Xenopus glucocorticoid receptor accessory factor and a single adjacent half-GRE form an independent glucocorticoid response unit.
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DOI：
10.1021/bi000981s
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发表时间：
2000-10
期刊：
影响因子：
2.9
通讯作者：
B. Morin;C. Zhu;G. Woodcock;M. Li;R. Woodward;L. Nichols;L. Holland
中科院分区：
文献类型：
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作者：
B. Morin;C. Zhu;G. Woodcock;M. Li;R. Woodward;L. Nichols;L. Holland
在非洲爪蟾中，γ-纤维蛋白原亚基基因的转录被糖皮质激素激活。激素诱导受三个糖皮质激素反应元件（GRE）半位点和一个额外的DNA序列，它结合一种新的肝细胞核蛋白，爪蟾糖皮质激素受体辅助因子（XGRAF）。XGRAF结合位点（GAGTTAA）直接位于最远端半GRE的上游。XGRAF和糖皮质激素受体（GR）结合位点的接近导致了这两个位点形成糖皮质激素反应单位（GRU）的假设。通过将DNA转染到原代肝细胞中，我们发现这种GRU在没有其他半GRES的情况下赋予激素反应性。XGRAF结合位点增强了半GRE的功能，而其本身不响应糖皮质激素。GRU在相对于γ-纤维蛋白原基因启动子的其他位置保持功效，当以多个拷贝存在时进一步增加转录，并激活异源启动子。尽管XGRAF结合位点和半GRE的邻近性，但这两个位点可以在体外同时被占据。结合特征与功能相关，因为破坏同时XGRAF和GR结合的突变也损害转录。这种新的GRU代表了一种新的调节机制，可能适用于其他缺乏完整GRE的糖皮质激素反应基因。
In Xenopus laevis, transcription of the gamma-fibrinogen subunit gene is activated by glucocorticoids. Hormone induction is regulated by three glucocorticoid response element (GRE) half-sites and an additional DNA sequence which binds a novel hepatocyte nuclear protein, Xenopus glucocorticoid receptor accessory factor (XGRAF). The XGRAF binding site (GAGTTAA) is located directly upstream of the most distal half-GRE. The proximity of the binding sites for XGRAF and the glucocorticoid receptor (GR) led to the hypothesis that these two sites form a glucocorticoid response unit (GRU). By transfecting DNA into primary hepatocytes, we showed that this GRU confers hormone responsiveness in the absence of other half-GREs. The XGRAF binding site enhances function of the half-GRE without itself responding to glucocorticoids. The GRU retains efficacy in other locations relative to the gamma-fibrinogen gene promoter, further increases transcription when present in multiple copies, and activates a heterologous promoter. Despite the contiguity of the XGRAF binding site and half-GRE, the two sites can be occupied simultaneously in vitro. The binding characteristics correlate with function since mutations that disrupt concurrent XGRAF and GR binding also impair transcription. This novel GRU represents a new regulatory mechanism that may be applicable to other glucocorticoid responsive genes that lack a full GRE.