A Genome-Wide Screen for β-Catenin Binding Sites Identifies a Downstream Enhancer Element That Controls c-Myc Gene Expression
A Genome-Wide Screen for β-Catenin Binding Sites Identifies a Downstream Enhancer Element That Controls c-Myc Gene Expression
复制标题
DOI：
10.1128/mcb.00744-08
复制
发表时间：
2008-12-15
影响因子：
5.3
通讯作者：
Goodman, Richard H.
中科院分区：
文献类型：
--
作者：
Yochum, Gregory S.;Cleland, Ryan;Goodman, Richard H.
Wnt信号通路组分的突变通过去调节β-连环蛋白转录辅激活因子启动结直肠癌发生。β-连环蛋白激活一个靶点，特别是c-Myc原癌基因，是结肠癌发病所必需的。已知β-连环蛋白通过转录起始位点上游的序列调节c-Myc表达。在这里，我们报告说，一个更强大的β-连环蛋白结合区域定位在下游1.4 kb的c-Myc转录终止位点。该位点是使用全基因组方法发现的，该方法用于鉴定转录因子结合位点，称为染色质占有率的系列分析。染色质免疫沉淀扫描分析表明，5'增强子和3'结合元件是跨c-Myc基因座的仅有的β-连环蛋白和TCF 4结合区域。当置于猿病毒40驱动的启动子-荧光素酶构建体的下游时，当引入HCT 116细胞时，3'元件激活荧光素酶转录。c-Myc转录在静止的HCT 116细胞中是可忽略的，但当细胞在添加有丝分裂原后重新进入细胞周期时被诱导。使用这些细胞，我们发现β-连环蛋白和TCF 4在3'增强子处的占据先于在5'增强子处的占据。c-Jun、β-连环蛋白和TCF 4特异性与下游增强子的关联是c-Myc转录的有丝分裂原刺激的基础。我们的研究结果表明，下游增强子元件提供了c-Myc表达的主要调节。
Mutations in components of the Wnt signaling pathway initiate colorectal carcinogenesis by deregulating the beta-catenin transcriptional coactivator. beta-Catenin activation of one target in particular, the c-Myc protooncogene, is required for colon cancer pathogenesis. beta-Catenin is known to regulate c-Myc expression via sequences upstream of the transcription start site. Here, we report that a more robust beta-catenin binding region localizes 1.4 kb downstream from the c-Myc transcriptional stop site. This site was discovered using a genome-wide method for identifying transcription factor binding sites termed serial analysis of chromatin occupancy. Chromatin immunoprecipitation-scanning assays demonstrate that the 5' enhancer and the 3' binding element are the only beta-catenin and TCF4 binding regions across the c-Myc locus. When placed downstream of a simian virus 40-driven promoter-luciferase construct, the 3' element activated luciferase transcription when introduced into HCT116 cells. c-Myc transcription is negligible in quiescent HCT116 cells but is induced when cells reenter the cell cycle after the addition of mitogens. Using these cells, we found that beta-catenin and TCF4 occupancy at the 3' enhancer precede occupancy at the 5' enhancer. Association of c-Jun, beta-catenin, and TCF4 specifically with the downstream enhancer underlies mitogen stimulation of c-Myc transcription. Our findings indicate that a downstream enhancer element provides the principal regulation of c-Myc expression.