Kolligs F T, Hu G, Dang C V, Fearon E R
Division of Molecular Medicine & Genetics and the Cancer Center, Departments of Internal Medicine, University of Michigan School of Medicine, Ann Arbor, Michigan 48109, USA.
Mol Cell Biol. 1999 Aug;19(8):5696-706. doi: 10.1128/MCB.19.8.5696.
Current models predict that beta-catenin (beta-cat) functions in Wnt signaling via activation of Tcf/Lef target genes and that its abundance is regulated by the adenomatous polyposis coli (APC) and glycogen synthase kinase 3beta (GSK3beta) proteins. In colon and other cancers, mutations in APC or presumptive GSK3beta phosphorylation sites of beta-cat are associated with constitutive activation of Tcf/Lef transcription. In spite of assumptions about its oncogenic potential, prior efforts to demonstrate that mutated beta-cat will induce neoplastic transformation have yielded equivocal results. We report here that mutated, but not wild-type, beta-cat proteins induced neoplastic transformation of RK3E, an adenovirus E1A-immortalized epithelial cell line. Analysis of the properties of mutant beta-cat proteins and studies with a dominant negative Tcf-4 mutant indicated that the ability of beta-cat to bind and activate Tcf/Lef factors is crucial for transformation. c-myc has recently been implicated as a critical Tcf-regulated target gene. However, c-myc was not consistently activated in beta-cat-transformed RK3E cells, and a dominant negative c-Myc mutant protein failed to inhibit beta-cat transformation. Our findings underscore the role of beta-cat mutations and Tcf/Lef activation in cancer and illustrate a useful system for defining critical factors in beta-cat transformation.
当前模型预测，β-连环蛋白（β-cat）通过激活Tcf/Lef靶基因在Wnt信号通路中发挥作用，其丰度受腺瘤性息肉病大肠杆菌（APC）和糖原合酶激酶3β（GSK3β）蛋白调节。在结肠癌和其他癌症中，APC突变或β-cat假定的GSK3β磷酸化位点与Tcf/Lef转录的组成性激活有关。尽管对其致癌潜力有种种假设，但此前证明突变的β-cat会诱导肿瘤转化的努力结果并不明确。我们在此报告，突变而非野生型的β-cat蛋白可诱导RK3E（一种腺病毒E1A永生化上皮细胞系）发生肿瘤转化。对突变β-cat蛋白特性的分析以及对显性负性Tcf-4突变体的研究表明，β-cat结合并激活Tcf/Lef因子的能力对转化至关重要。c-myc最近被认为是一个关键的Tcf调控靶基因。然而，在β-cat转化的RK3E细胞中，c-myc并未持续激活，且显性负性c-Myc突变体蛋白未能抑制β-cat转化。我们的研究结果强调了β-cat突变和Tcf/Lef激活在癌症中的作用，并阐明了一个用于确定β-cat转化关键因素的有用系统。
