Porcu P, Graña X, Li S, Swantek J, De Luca A, Giordano A, Baserga R
Jefferson Cancer Institute, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
Oncogene. 1994 Aug;9(8):2125-34.
The promoter of the Insulin-like growth factor I (IGF-I) gene is activated by the Simian Virus 40 large T antigen (SVLT), and one of the elements responding to SVLT activation has been localized to a short 124 bp immediately upstream of the first initiation of transcription site. This short promoter contains an E2F binding site, that, in gel shifts, binds a protein complex, but only when the promoter activity is reduced or absent. A mutation in the E2F binding site deregulates the activity of the promoter, which becomes active even in those conditions in which the wild type promoter is inactive. By using antibodies in gel retardation analyses, we can show that the different protein complexes include, at least, the following proteins: E2F, cyclin A and p107. We conclude that the short IGF-I promoter is negatively regulated by an E2F binding site that complexes with several proteins. Our data suggest that disaggregation of these complexes by the action of SVLT (or other activators) increases expression from the promoter, thus establishing a link between the regulation of cell proliferation by growth factors and the E2F-associated proteins.
胰岛素样生长因子I（IGF-I）基因的启动子被猿猴病毒40大T抗原（SVLT）激活，且对SVLT激活作出反应的元件之一已定位到转录起始位点第一个起始点上游紧邻的一段124 bp的短片段。这个短启动子包含一个E2F结合位点，在凝胶迁移实验中，它能结合一个蛋白质复合物，但仅在启动子活性降低或缺失时才会如此。E2F结合位点的一个突变会使启动子活性失调，即使在野生型启动子无活性的条件下，该启动子也会变得活跃。通过在凝胶阻滞分析中使用抗体，我们可以证明不同的蛋白质复合物至少包括以下蛋白质：E2F、细胞周期蛋白A和p107。我们得出结论，短IGF-I启动子受到一个与多种蛋白质结合的E2F结合位点的负调控。我们的数据表明，SVLT（或其他激活剂）的作用使这些复合物解聚，从而增加了启动子的表达，由此在生长因子对细胞增殖的调控与E2F相关蛋白之间建立了联系。
