Eggert H, Schulz M, Fackelmayer F O, Renkawitz R, Eggert M
Institut für Genetik der Justus-Liebig-Universität, Heinrich-Buff-Ring 58-62, D-35392 Giessen, Germany.
J Steroid Biochem Mol Biol. 2001 Jul;78(1):59-65. doi: 10.1016/s0960-0760(01)00074-7.
The glucocorticoid receptor (GR) is a ligand dependent transcription factor, which regulates the transcription of multiple hormone-dependent genes. The transcriptional regulation by GR takes place by interaction of GR with the basal transcription machinery and by recruiting glucocorticoid receptor interacting proteins (GRIPs). Previously we identified hnRNP U/SAF-A as a factor interfering with GR-dependent transcription by repressing glucocorticoid induced activation. To gain insight into the mechanisms that govern this interference, we have now investigated the transcription of GR-dependent reporter genes in Ltk(-) cells transiently transfected with a variety of hnRNP U constructs. We demonstrate that a hnRNP U construct lacking the GR-binding domain acts as a dominant negative factor that now enhances GR-driven transcription. In addition, hnRNP U repression of glucocorticoid induced transcription was found to be dependent on the amount of cotransfected GR, where a high amount of GR leads to ligand-inducible repression of GR-dependent reporter gene activity by hnRNP U, whereas low amounts of GR showed nearly no effect. The relative concentrations of GR, hnRNP U and DNA-binding sites for GR are important for the effect of hnRNP U on transcription, suggesting a model where hnRNP-U acts as a storage site for intranuclear GR.
糖皮质激素受体（GR）是一种依赖配体的转录因子，它调控多个激素依赖性基因的转录。GR的转录调控通过GR与基础转录机制的相互作用以及募集糖皮质激素受体相互作用蛋白（GRIPs）来实现。此前我们鉴定出hnRNP U/SAF-A是一种通过抑制糖皮质激素诱导的激活来干扰GR依赖性转录的因子。为了深入了解控制这种干扰的机制，我们现在研究了用多种hnRNP U构建体瞬时转染的Ltk(-)细胞中GR依赖性报告基因的转录。我们证明，缺乏GR结合结构域的hnRNP U构建体作为一种显性负性因子，现在增强了GR驱动的转录。此外，发现hnRNP U对糖皮质激素诱导转录的抑制取决于共转染的GR的量，其中大量的GR导致hnRNP U对GR依赖性报告基因活性的配体诱导性抑制，而少量的GR几乎没有影响。GR、hnRNP U和GR的DNA结合位点的相对浓度对hnRNP U对转录的影响很重要，这提示了一种模型，即hnRNP-U作为核内GR的储存位点。
