Shen W J, Kim H S, Tsai S Y
Department of Cell Biology, Baylor College of Medicine, Houston, Texas 77030, USA.
J Biol Chem. 1995 Sep 1;270(35):20525-9. doi: 10.1074/jbc.270.35.20525.
Multiple cis-acting elements have been defined to be important for the transcriptional regulation of the human insulin receptor (hIR) gene expression. We report here that one of these elements also mediated the stimulation of hIR promoter activity by the retinoblastoma gene product (Rb). The cis-element responsible for Rb stimulation was localized to the GA and GC boxes situated between -643 to -607 of the hIR gene. We have previously demonstrated that these GA and GC boxes bind Sp1 with high affinity and are responsible for E1a activation of hIR promoter activity. Mutation of these sequences completely abolished Rb-dependent enhancement of hIR promoter activity. In addition, we localized three regions in the N-terminal domain of Rb to be involved in stimulation of hIR promoter activity. Our results represent one of the first studies to demonstrate a functional importance assigned to the multiple phosphorylation sites in the N terminus of Rb. Finally, the mechanism by which Rb activates the hIR promoter are presented.
多种顺式作用元件已被确定对人类胰岛素受体（hIR）基因表达的转录调控很重要。我们在此报告，这些元件之一也介导了视网膜母细胞瘤基因产物（Rb）对hIR启动子活性的刺激。负责Rb刺激的顺式元件定位于hIR基因-643至-607之间的GA和GC框。我们之前已经证明，这些GA和GC框以高亲和力结合Sp1，并负责E1a对hIR启动子活性的激活。这些序列的突变完全消除了Rb依赖的hIR启动子活性增强。此外，我们确定Rb的N端结构域中的三个区域参与了对hIR启动子活性的刺激。我们的结果是最早证明Rb N端多个磷酸化位点具有功能重要性的研究之一。最后，本文介绍了Rb激活hIR启动子的机制。
