Andreu Pauline, Colnot Sabine, Godard Cécile, Gad Sophie, Chafey Philippe, Niwa-Kawakita Michiko, Laurent-Puig Pierre, Kahn Axel, Robine Sylvie, Perret Christine, Romagnolo Béatrice
Institut Cochin, INSERM U567, CNRS UMR8104, Université Paris V, 24 rue du Fb St-Jacques, 75014 Paris, France.
Development. 2005 Mar;132(6):1443-51. doi: 10.1242/dev.01700. Epub 2005 Feb 16.
Loss of Apc appears to be one of the major events initiating colorectal cancer. However, the first events responsible for this initiation process are not well defined and the ways in which different epithelial cell types respond to Apc loss are unknown. We used a conditional gene-ablation approach in transgenic mice expressing tamoxifen-dependent Cre recombinase all along the crypt-villus axis to analyze the immediate effects of Apc loss in the small intestinal epithelium, both in the stem-cell compartment and in postmitotic epithelial cells. Within 4 days, Apc loss induced a dramatic enlargement of the crypt compartment associated with intense cell proliferation, apoptosis and impairment of cell migration. This result confirms the gatekeeper role of Apc in the intestinal epithelium in vivo. Although Apc deletion activated beta-catenin signaling in the villi, we observed neither proliferation nor morphological change in this compartment. This highlights the dramatic difference in the responses of immature and differentiated epithelial cells to aberrant beta-catenin signaling. These distinct biological responses were confirmed by molecular analyses, revealing that Myc and cyclin D1, two canonical beta-catenin target genes, were induced in distinct compartments. We also showed that Apc is a crucial determinant of cell fate in the murine intestinal epithelium. Apc loss perturbs differentiation along the enterocyte, goblet and enteroendocrine lineages, and promotes commitment to the Paneth cell lineage through beta-catenin/Tcf4-mediated transcriptional control of specific markers of Paneth cells, the cryptdin/defensin genes.
Apc缺失似乎是引发结直肠癌的主要事件之一。然而，引发这一过程的首个事件尚未明确界定，不同上皮细胞类型对Apc缺失的反应方式也不清楚。我们在沿隐窝 - 绒毛轴全程表达他莫昔芬依赖性Cre重组酶的转基因小鼠中采用条件性基因敲除方法，来分析Apc缺失在小肠上皮干细胞区室和有丝分裂后上皮细胞中的即时效应。在4天内，Apc缺失导致隐窝区室显著扩大，伴有强烈的细胞增殖、凋亡及细胞迁移受损。这一结果证实了Apc在体内肠道上皮中的守门人作用。尽管Apc缺失激活了绒毛中的β-连环蛋白信号通路，但我们在该区室未观察到增殖或形态变化。这突出了未成熟和分化上皮细胞对异常β-连环蛋白信号通路反应的巨大差异。这些不同的生物学反应通过分子分析得到证实，揭示出Myc和细胞周期蛋白D1这两个典型的β-连环蛋白靶基因在不同区室中被诱导。我们还表明，Apc是小鼠肠道上皮细胞命运的关键决定因素。Apc缺失扰乱了沿肠细胞、杯状细胞和肠内分泌细胞谱系的分化，并通过β-连环蛋白/Tcf4介导的对潘氏细胞特异性标志物（隐窝蛋白/防御素基因）的转录调控，促进细胞向潘氏细胞谱系分化。
