Department of Physiology and Pharmacology, Children Health Research Institute and Lawson Health Research Institute, University of Western Ontario, London, Canada.
PLoS One. 2010 Nov 10;5(11):e13941. doi: 10.1371/journal.pone.0013941.
Regulation of gene expression requires transcription factor binding to specific DNA elements, and a large body of work has focused on the identification of such sequences. However, it is becoming increasingly clear that eukaryotic transcription factors can exhibit widespread, nonfunctional binding to genomic DNA sites. Conversely, some of these proteins, such as E2F, can also modulate gene expression by binding to non-consensus elements. E2F comprises a family of transcription factors that play key roles in a wide variety of cellular functions, including survival, differentiation, activation during tissue regeneration, metabolism, and proliferation. E2F factors bind to the Erb3-binding protein 1 (EBP1) promoter in live cells. We now show that E2F binding to the EBP1 promoter occurs through two tandem DNA elements that do not conform to typical consensus E2F motifs. Exogenously expressed E2F1 activates EBP1 reporters lacking one, but not both sites, suggesting a degree of redundancy under certain conditions. E2F1 increases the levels of endogenous EBP1 mRNA in breast carcinoma and other transformed cell lines. In contrast, in non-transformed primary epidermal keratinocytes, E2F, together with the retinoblastoma family of proteins, appears to be involved in decreasing EBP1 mRNA abundance in response to growth inhibition by transforming growth factor-β1. Thus, E2F is likely a central coordinator of multiple responses that culminate in regulation of EBP1 gene expression, and which may vary depending on cell type and context.
基因表达的调控需要转录因子结合到特定的 DNA 元件上，大量的工作都集中在这些序列的鉴定上。然而，越来越明显的是，真核转录因子可以广泛地、非功能地结合到基因组 DNA 位点上。相反，这些蛋白质中的一些，如 E2F，可以通过结合非共识元件来调节基因表达。E2F 由一组转录因子组成，它们在各种细胞功能中发挥关键作用，包括存活、分化、组织再生、代谢和增殖期间的激活。E2F 因子在活细胞中结合到 Erb3 结合蛋白 1（EBP1）启动子上。我们现在表明，E2F 结合到 EBP1 启动子上是通过两个串联的 DNA 元件实现的，这些元件不符合典型的 E2F 基序。外源性表达的 E2F1 激活缺乏一个但不是两个位点的 EBP1 报告基因，这表明在某些条件下存在一定程度的冗余性。E2F1 增加了乳腺癌和其他转化细胞系中内源性 EBP1 mRNA 的水平。相比之下，在非转化的原代表皮角质形成细胞中，E2F 与视网膜母细胞瘤家族蛋白一起，似乎参与了 TGF-β1 生长抑制后 EBP1 mRNA 丰度的降低。因此，E2F 很可能是多种反应的中心协调者，这些反应最终导致 EBP1 基因表达的调节，并且可能因细胞类型和环境而异。
