Activator protein 2alpha associates with adenomatous polyposis coli/beta-catenin and Inhibits beta-catenin/T-cell factor transcriptional activity in colorectal cancer cells.
Activator protein 2alpha associates with adenomatous polyposis coli/beta-catenin and Inhibits beta-catenin/T-cell factor transcriptional activity in colorectal cancer cells.
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发表时间：
2004
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通讯作者：
Qingjie Li;R. Dashwood
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作者：
Qingjie Li;R. Dashwood
在大多数人类结直肠癌中，腺瘤性息肉病结肠基因(APC)或CTNNB1基因的突变结构性地激活了β-连环蛋白/T细胞因子(TCF)/淋巴增强因子(LEF)信号通路。在这里，我们证明了转录因子激活蛋白(AP)-2α抑制了人胚胎肾脏293细胞和两个人结直肠癌细胞系中的β-连环蛋白/TCF反应报告，尽管在细胞核中β-连环蛋白和TCF-4蛋白水平没有变化。免疫共沉淀研究表明，AP-2α与APC和β-连环蛋白形成复合体，并破坏核内β-连环蛋白/TCF-4的相互作用。因此，AP-2αAPCβ-连环蛋白复合体的形成似乎通过将核β-连环蛋白池转移到一种非活性形式来抑制β-连环蛋白的反式激活，减少了与TCF/LEF转录因子的结合。谷胱甘肽S-转移酶下拉分析表明，AP-2α与APC结合，而不是与β-连环素结合，AP-2α结合部位位于APC的N端，既有七肽重复结构域，也有重复序列，而AP-2α中的AP-2α结合部位位于C-末端DNA结合域的碱性区域。这些发现为肿瘤抑制蛋白APC和转录因子AP-2pha之间的特定相互作用提供了第一个证据，并表明Wnt信号通路与与AP-2pha相关的其他各种发育和分化途径之间存在联系。
In most human colorectal cancers, mutations in the adenomatous polyposis coli gene (APC) or CTNNB1 constitutively activate the beta-catenin/T-cell factor (TCF)/lymphoid enhancer factor (LEF) signaling pathway. Here, we show that the transcription factor activator protein (AP)-2alpha inhibited a beta-catenin/TCF-responsive reporter in human embryonic kidney 293 cells and in two human colorectal cancer lines, despite the fact that beta-catenin and TCF-4 protein levels were unchanged in the nucleus. Co-immunoprecipitation studies revealed that AP-2alpha formed a complex with APC and beta-catenin and that AP-2alpha disrupted beta-catenin/TCF-4 interactions in the nucleus. Thus, AP-2alpha.APC.beta-catenin complex formation appears to suppress beta-catenin transactivation by shifting the pool of nuclear beta-catenin toward an inactive form, having reduced binding to TCF/LEF transcription factors. Glutathione S-transferase pull-down assays showed that AP-2alpha physically associated with APC rather than with beta-catenin, and the AP-2alpha binding site was identified in the N terminus of APC, involving both the heptad and armadillo repeat domains, whereas the APC binding site in AP-2alpha was in the basic region of the C-terminal DNA binding domain. These findings provide the first evidence for a specific interaction between the tumor suppressor protein APC and the transcription factor AP-2alpha, and they suggest a link between the Wnt signaling pathway and various other pathways of development and differentiation associated with AP-2alpha.