Guo Rong-Jun, Huang Edward, Ezaki Toshihiko, Patel Neesha, Sinclair Kristen, Wu Jinling, Klein Peter, Suh Eun-Ran, Lynch John P
Division of Gastroenterology, the Department of Medicine, University of Pennsylvania, 415 Curie Boulevard, Philadelphia, PA 19104, USA.
J Biol Chem. 2004 Aug 27;279(35):36865-75. doi: 10.1074/jbc.M405213200. Epub 2004 Jun 23.
The cessation of proliferation and the induction of differentiation are highly coordinated processes that occur continuously in the intestinal crypts. The homeodomain transcription factors Cdx1 and Cdx2 regulate intestine-specific gene expression and enterocyte differentiation. Their roles in regulating proliferation are recognized but remain poorly understood. Previously, we demonstrated that Cdx1 expression diminished the proliferation of human colon cancer cells in part by reducing cyclin D1 gene expression. In order to elucidate further the molecular mechanisms underlying this phenomenon, we first hypothesized that Cdx1 or Cdx2 expression reduces colon cancer cell proliferation by inhibiting beta-catenin/T-cell factor (TCF) transcriptional activity. We report that Cdx1 or Cdx2 expression does inhibit beta-catenin/TCF transcriptional activity in colon cancer cells. This inhibitory effect is dose-dependent and is observed in different colon cancer cell lines, and the degree of inhibition correlates with the ability of Cdx1 to reduce cell proliferation. Cdx1 expression does not alter beta-catenin protein levels or intracellular distribution nor does it induce an inhibitory TCF isoform. We also find that Cdx1 expression is lost in Min mouse polyps with increased nuclear localization of beta-catenin, suggesting that Cdx1 does not support beta-catenin-mediated transformation. Finally, we show that colon cancer cells effectively reduce Cdx2-mediated inhibition of Wnt/beta-catenin/TCF transcriptional activity when compared with other model systems. This suggests that colon cancer and possibly crypt epithelial cells can modulate the effects of Cdx2 on beta-catenin signaling and proliferation. We conclude that Cdx1 and Cdx2 inhibit colon cancer cell proliferation by blocking beta-catenin/TCF transcriptional activity.
增殖的停止和分化的诱导是在小肠隐窝中持续发生的高度协调的过程。同源结构域转录因子Cdx1和Cdx2调节肠道特异性基因表达和肠上皮细胞分化。它们在调节增殖中的作用已得到认可，但仍了解甚少。此前，我们证明Cdx1表达部分通过降低细胞周期蛋白D1基因表达来减少人结肠癌细胞的增殖。为了进一步阐明这一现象背后的分子机制，我们首先假设Cdx1或Cdx2表达通过抑制β-连环蛋白/T细胞因子（TCF）转录活性来降低结肠癌细胞增殖。我们报告称，Cdx1或Cdx2表达确实会抑制结肠癌细胞中的β-连环蛋白/TCF转录活性。这种抑制作用是剂量依赖性的，在不同的结肠癌细胞系中均有观察到，且抑制程度与Cdx1减少细胞增殖的能力相关。Cdx1表达不会改变β-连环蛋白的蛋白质水平或细胞内分布，也不会诱导抑制性TCF异构体。我们还发现，在β-连环蛋白核定位增加的Min小鼠息肉中Cdx1表达缺失，这表明Cdx1不支持β-连环蛋白介导的转化。最后，我们表明，与其他模型系统相比，结肠癌细胞能有效降低Cdx2介导的对Wnt/β-连环蛋白/TCF转录活性的抑制。这表明结肠癌以及可能的隐窝上皮细胞可以调节Cdx2对β-连环蛋白信号传导和增殖的影响。我们得出结论，Cdx1和Cdx2通过阻断β-连环蛋白/TCF转录活性来抑制结肠癌细胞增殖。
