Jin J R, Wen P, Locker J
Department of Pathology, School of Medicine, University of Pittsburgh, PA 15261.
DNA Cell Biol. 1995 Mar;14(3):267-72. doi: 10.1089/dna.1995.14.267.
It has been proposed that the alpha-fetoprotein (AFP) enhancers also regulate the adjacent albumin gene, since the -10 kbp albumin enhancer is inactive in a number of cell lines that express albumin. In transfection experiments, the AFP enhancers strongly stimulate the albumin promoter in cells that silence the AFP promoter. These observations led us to develop a plasmid model of AFP-albumin gene switching, in which the albumin and AFP promoters would compete for the three AFP enhancers. However, when AFPCAT + ALBgal genes were combined with the AFP enhancers in one plasmid, both genes were driven at full activity. There was no change in the relative promoter expression over a wide range of transfected DNA concentrations, demonstrating that relative promoter activity was independent of DNA concentration and of promoter concentration, and that neither promoter was limiting the expression of the other. In contrast, a control plasmid containing two albumin promoters showed mutual inhibition, indicating the expected promoter competition. The albumin and AFP promoters noncompetitively shared the three enhancers on this plasmid, resulting in high levels of transcription from both promoters.
有人提出，甲胎蛋白（AFP）增强子也调控相邻的白蛋白基因，因为在许多表达白蛋白的细胞系中，-10kbp白蛋白增强子是无活性的。在转染实验中，AFP增强子在使AFP启动子沉默的细胞中强烈刺激白蛋白启动子。这些观察结果促使我们构建了一个AFP-白蛋白基因转换的质粒模型，其中白蛋白和AFP启动子将竞争三个AFP增强子。然而，当AFPCAT + ALBgal基因与AFP增强子在一个质粒中结合时，两个基因均以全活性驱动。在广泛的转染DNA浓度范围内，相对启动子表达没有变化，这表明相对启动子活性与DNA浓度和启动子浓度无关，并且两个启动子均未限制另一个的表达。相比之下，含有两个白蛋白启动子的对照质粒显示出相互抑制，表明存在预期的启动子竞争。白蛋白和AFP启动子在该质粒上非竞争性地共享三个增强子，导致两个启动子均有高水平的转录。
