Brüggemeier U, Rogge L, Winnacker E L, Beato M
Institut für Molekularbiologie und Tumorforschung, Philipps Universität, Marburg, FRG.
EMBO J. 1990 Jul;9(7):2233-9. doi: 10.1002/j.1460-2075.1990.tb07393.x.
Several steroid hormones induce transcription of the mouse mammary tumor virus (MMTV) promoter, through an interaction of their respective receptors with the hormone responsive elements (HREs) in the long terminal repeat (LTR) region. The molecular mechanism underlying transcriptional activation is not known, but binding of nuclear factor I (NFI) to a site adjacent to the HRE appears to be required for efficient transcription of the MMTV promoter. In JEG-3 choriocarcinoma cells the MMTV promoter is transcribed inefficiently, even after transfection of the receptor cDNA and treatment with glucocorticoids or progestins. These cells contain low levels of NFI as cotransfection of NFI cDNA enhances MMTV transcription and this effect is inhibited by mutation of the NFI binding site. In DNA binding experiments with purified NFI from pig liver, the glucocorticoid and progesterone receptors do not co-operate but rather compete with NFI for binding to their respective sites on the LTR. Similar results are obtained with a functional recombinant NFI synthesized in vitro. Competition for DNA binding is probably due to steric hindrance as the DNase I footprints of the hormone receptors and NFI do overlap. These results suggest that, though NFI acts as a transcription factor on the MMTV promoter, transcriptional activation does not take place through a direct facilitation of DNA binding of NFI by steroid hormone receptors.
几种甾体激素可诱导小鼠乳腺肿瘤病毒（MMTV）启动子的转录，这是通过它们各自的受体与长末端重复序列（LTR）区域中的激素反应元件（HREs）相互作用实现的。转录激活的分子机制尚不清楚，但核因子I（NFI）与HRE相邻位点的结合似乎是MMTV启动子高效转录所必需的。在JEG-3绒毛膜癌细胞中，即使转染了受体cDNA并用糖皮质激素或孕激素处理后，MMTV启动子的转录效率仍然很低。这些细胞中NFI水平较低，因为共转染NFI cDNA可增强MMTV转录，而这种效应会被NFI结合位点的突变所抑制。在用从猪肝中纯化的NFI进行的DNA结合实验中，糖皮质激素和孕激素受体并不协同作用，而是与NFI竞争结合LTR上各自的位点。用体外合成的功能性重组NFI也得到了类似的结果。DNA结合竞争可能是由于空间位阻，因为激素受体和NFI的DNase I足迹确实有重叠。这些结果表明，尽管NFI在MMTV启动子上作为转录因子起作用，但转录激活并不是通过甾体激素受体直接促进NFI与DNA的结合来实现的。
