Naishiro Y, Yamada T, Takaoka A S, Hayashi R, Hasegawa F, Imai K, Hirohashi S
Pathology Division, National Cancer Center Research Institute, Tokyo, Japan.
Cancer Res. 2001 Mar 15;61(6):2751-8.
Beta-catenin acts as a transcriptional coactivator by forming a complex with T-cell factor/lymphoid enhancer factor (TCF/LEF) DNA-binding proteins. Aberrant transactivation of a certain set of target genes by beta-catenin and TCF4 complexes has been implicated in familial and sporadic colorectal tumorigenesis. A colorectal cancer cell line, DLD-1, becomes irregularly multilayered, when maintained confluent for 2-3 weeks, and forms numerous dome-like polypoid foci piled-up over the surface of cell sheets. By the use of a strict tetracycline-regulation system, we found that the continuous suppression of beta-catenin/TCF4-mediated gene transactivation by dominant-negative TCF4B (deltaN30) reduced these piled-up foci and restored a simple monolayer of polarized columnar cells resembling normal intestinal epithelium. The restoration of epithelial cell polarity was evident in two ways: (a) the formation of microvilli over the apical surface; and (b) the distribution of a tight junction protein, ZO-1, to the lateral plasma membrane. Retroviral expression of stabilized beta-catenin (deltaN89) induced the formation of similar piled-up foci in untransformed IEC6 intestinal epithelial cells. Sulindac, a nonsteroidal antiinflammatory drug effective against colorectal tumorigenesis in familial adenomatous polyposis syndrome, suppressed the formation of foci. The loss of epithelial cell polarity may be a critical cellular event driving beta-catenin/TCF4-mediated intestinal tumorigenesis.
β-连环蛋白通过与T细胞因子/淋巴样增强因子（TCF/LEF）DNA结合蛋白形成复合物，充当转录共激活因子。β-连环蛋白和TCF4复合物对某些靶基因的异常反式激活与家族性和散发性结直肠癌的发生有关。一种结肠癌细胞系DLD-1，当汇合培养2-3周时会变得不规则多层，并在细胞片表面形成许多穹顶状息肉样病灶。通过使用严格的四环素调控系统，我们发现用显性负性TCF4B（deltaN30）持续抑制β-连环蛋白/TCF4介导的基因反式激活可减少这些堆积的病灶，并恢复类似于正常肠上皮的简单单层极化柱状细胞。上皮细胞极性的恢复通过两种方式明显表现出来：（a）在顶端表面形成微绒毛；（b）紧密连接蛋白ZO-1分布到侧质膜。稳定化的β-连环蛋白（deltaN89）的逆转录病毒表达在未转化的IEC6肠上皮细胞中诱导形成类似的堆积病灶。舒林酸是一种对家族性腺瘤性息肉病综合征中的结直肠癌发生有效的非甾体抗炎药，可抑制病灶的形成。上皮细胞极性的丧失可能是驱动β-连环蛋白/TCF4介导的肠肿瘤发生的关键细胞事件。
