Feng Ying, Sakamoto Naoya, Wu Rong, Liu Jie-Yu, Wiese Alexandra, Green Maranne E, Green Megan, Akyol Aytekin, Roy Badal C, Zhai Yali, Cho Kathleen R, Fearon Eric R
Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan, United States of America.
Department of Pathology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America.
PLoS Genet. 2015 Nov 3;11(11):e1005638. doi: 10.1371/journal.pgen.1005638. eCollection 2015 Nov.
Adenomatous polyposis coli (APC) inactivating mutations are present in most human colorectal cancers and some other cancers. The APC protein regulates the β-catenin protein pool that functions as a co-activator of T cell factor (TCF)-regulated transcription in Wnt pathway signaling. We studied effects of reduced dosage of the Ctnnb1 gene encoding β-catenin in Apc-mutation-induced colon and ovarian mouse tumorigenesis and cell culture models. Concurrent somatic inactivation of one Ctnnb1 allele, dramatically inhibited Apc mutation-induced colon polyposis and greatly extended Apc-mutant mouse survival. Ctnnb1 hemizygous dose markedly inhibited increases in β-catenin levels in the cytoplasm and nucleus following Apc inactivation in colon epithelium, with attenuated expression of key β-catenin/TCF-regulated target genes, including those encoding the EphB2/B3 receptors, the stem cell marker Lgr5, and Myc, leading to maintenance of crypt compartmentalization and restriction of stem and proliferating cells to the crypt base. A critical threshold for β-catenin levels in TCF-regulated transcription was uncovered for Apc mutation-induced effects in colon epithelium, along with evidence of a feed-forward role for β-catenin in Ctnnb1 gene expression and CTNNB1 transcription. The active β-catenin protein pool was highly sensitive to CTNNB1 transcript levels in colon cancer cells. In mouse ovarian endometrioid adenocarcinomas (OEAs) arising from Apc- and Pten-inactivation, while Ctnnb1 hemizygous dose affected β-catenin levels and some β-catenin/TCF target genes, Myc induction was retained and OEAs arose in a fashion akin to that seen with intact Ctnnb1 gene dose. Our findings indicate Ctnnb1 gene dose exerts tissue-specific differences in Apc mutation-instigated tumorigenesis. Differential expression of selected β-catenin/TCF-regulated genes, such as Myc, likely underlies context-dependent effects of Ctnnb1 gene dosage in tumorigenesis.
大多数人类结直肠癌及其他一些癌症中存在腺瘤性息肉病 coli（APC）失活突变。APC 蛋白调节 β-连环蛋白的蛋白库，该蛋白库在 Wnt 信号通路中作为 T 细胞因子（TCF）调节转录的共激活因子发挥作用。我们在 Apc 突变诱导的结肠和卵巢小鼠肿瘤发生及细胞培养模型中研究了编码 β-连环蛋白的 Ctnnb1 基因剂量降低的影响。一个 Ctnnb1 等位基因的同时体细胞失活显著抑制了 Apc 突变诱导的结肠息肉形成，并大大延长了 Apc 突变小鼠的生存期。Ctnnb1 半合子剂量显著抑制了结肠上皮细胞中 Apc 失活后细胞质和细胞核中 β-连环蛋白水平的升高，关键的 β-连环蛋白/TCF 调节靶基因的表达减弱，包括编码 EphB2/B3 受体、干细胞标志物 Lgr5 和 Myc 的基因，从而维持隐窝分隔，并将干细胞和增殖细胞限制在隐窝底部。发现了 TCF 调节转录中 β-连环蛋白水平的一个关键阈值，该阈值与 Apc 突变在结肠上皮细胞中的诱导效应有关，同时有证据表明 β-连环蛋白在 Ctnnb1 基因表达和 CTNNB1 转录中具有前馈作用。活性 β-连环蛋白蛋白库对结肠癌细胞中的 CTNNB1 转录水平高度敏感。在由 Apc 和 Pten 失活引起的小鼠卵巢子宫内膜样腺癌（OEA）中，虽然 Ctnnb1 半合子剂量影响了 β-连环蛋白水平和一些 β-连环蛋白/TCF 靶基因，但 Myc 的诱导得以保留，并且 OEA 的发生方式与完整 Ctnnb1 基因剂量时相似。我们的研究结果表明，Ctnnb1 基因剂量在 Apc 突变引发的肿瘤发生中发挥组织特异性差异。所选的 β-连环蛋白/TCF 调节基因（如 Myc）的差异表达可能是 Ctnnb1 基因剂量在肿瘤发生中依赖背景的效应的基础。
