Wong M H, Rubinfeld B, Gordon J I
Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
J Cell Biol. 1998 May 4;141(3):765-77. doi: 10.1083/jcb.141.3.765.
beta-Catenin functions as a downstream component of the Wnt/Wingless signal transduction pathway and as an effector of cell-cell adhesion through its association with cadherins. To explore the in vivo effects of beta-catenin on proliferation, cell fate specification, adhesion, and migration in a mammalian epithelium, a human NH2-terminal truncation mutant (DeltaN89 beta-catenin) was expressed in the 129/Sv embryonic stem cell-derived component of the small intestine of adult C57Bl/6-ROSA26 left and right arrow 129/Sv chimeric mice. DeltaN89 beta-Catenin was chosen because mutants of this type are more stable than the wild-type protein, and phenocopy activation of the Wnt/Wingless signaling pathway in Xenopus and Drosophila. DeltaN89 beta-Catenin had several effects. Cell division was stimulated fourfold in undifferentiated cells located in the proliferative compartment of the intestine (crypts of Lieberkühn). The proliferative response was not associated with any discernible changes in cell fate specification but was accompanied by a three- to fourfold increase in crypt apoptosis. There was a marked augmentation of E-cadherin at the adherens junctions and basolateral surfaces of 129/Sv (DeltaN89 beta-catenin) intestinal epithelial cells and an accompanying slowing of cellular migration along crypt-villus units. 1-2% of 129/Sv (DeltaN89 beta-catenin) villi exhibited an abnormal branched architecture. Forced expression of DeltaN89 beta-catenin expression did not perturb the level or intracellular distribution of the tumor suppressor adenomatous polyposis coli (APC). The ability of DeltaN89 beta-catenin to interact with normal cellular pools of APC and/or augmented pools of E-cadherin may have helped prevent the 129/Sv gut epithelium from undergoing neoplastic transformation during the 10-mo period that animals were studied. Together, these in vivo studies emphasize the importance of beta-catenin in regulating normal adhesive and signaling functions within this epithelium.
β-连环蛋白作为Wnt/Wingless信号转导通路的下游成分，通过与钙黏着蛋白结合，作为细胞间黏附的效应分子发挥作用。为了探究β-连环蛋白在哺乳动物上皮组织中对增殖、细胞命运决定、黏附及迁移的体内效应，在成年C57Bl/6-ROSA26→129/Sv嵌合小鼠小肠的129/Sv胚胎干细胞衍生成分中表达了人氨基末端截短突变体（ΔN89β-连环蛋白）。选择ΔN89β-连环蛋白是因为这类突变体比野生型蛋白更稳定，并且模拟了非洲爪蟾和果蝇中Wnt/Wingless信号通路的激活。ΔN89β-连环蛋白产生了多种效应。位于肠道增殖区（利伯kühn隐窝）的未分化细胞的细胞分裂被刺激了四倍。增殖反应与细胞命运决定方面任何可辨别的变化无关，但伴随着隐窝凋亡增加三到四倍。129/Sv（ΔN89β-连环蛋白）肠上皮细胞的黏着连接和基底外侧表面的E-钙黏着蛋白显著增加，同时细胞沿隐窝-绒毛单元的迁移减缓。129/Sv（ΔN89β-连环蛋白）绒毛中有1%-2%表现出异常的分支结构。ΔN89β-连环蛋白的强制表达并未扰乱肿瘤抑制因子腺瘤性息肉病结肠蛋白（APC）的水平或细胞内分布。ΔN89β-连环蛋白与APC的正常细胞池和/或增加的E-钙黏着蛋白池相互作用的能力可能有助于防止在研究动物的10个月期间129/Sv肠上皮发生肿瘤转化。总之，这些体内研究强调了β-连环蛋白在调节该上皮组织内正常黏附及信号功能中的重要性。
