Funakoshi Shinsuke, Ezaki Toshihiko, Kong Jianping, Guo Rong Jun, Lynch John P
Department of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
Mol Cancer Res. 2008 Sep;6(9):1478-90. doi: 10.1158/1541-7786.MCR-07-2161.
Desmosomes are intracellular junctions that provide strong cell-cell adhesion in epithelia and cardiac muscle. Their disruption causes several human diseases and contributes to the epithelial-to-mesenchymal transition observed in cancer. Desmocollin 2 (DSC2) is a cadherin superfamily member and a critical component of desmosomes found in intestinal epithelium. However, the mechanism regulating DSC2 gene expression in intestinal cells is not known. Cdx1 and Cdx2 are homeodomain transcription factors that regulate intestine-specific gene expression. Cdx expression in the past has been associated with the induction of desmosomes. We now show that the DSC2 gene is a transcriptional target for Cdx1 and Cdx2. Colon cancer cell lines retaining Cdx2 expression typically express DSC2. Restoration of Cdx expression in Colo 205 cells induced DSC2 mRNA and protein and the formation of desmosomes. The 5'-flanking region of the DSC2 promoter contains two consensus Cdx-binding sites. Electrophoretic mobility shift assays show that Cdx1 and Cdx2 bind these sites in vitro, and chromatin immunoprecipitation confirmed Cdx2 binding in vivo. DSC2 promoter truncations established that these regions are Cdx responsive. The truncations also identify a region of the promoter in which potent transcriptional repressors act. This repressor activity is relieved by Cdx binding. We conclude that the homeodomain transcription factors Cdx1 and Cdx2 regulate DSC2 gene expression in intestinal epithelia by reversing the actions of a transcriptional repressor. The regulation of desmosomal junctions by Cdx contributes to normal intestinal epithelial columnar morphology and likely antagonizes the epithelial-to-mesenchymal transition necessary for the metastasis of colon cancer cells in humans.
桥粒是细胞内的连接结构，在上皮组织和心肌中提供强大的细胞间黏附作用。它们的破坏会引发多种人类疾病，并促成癌症中观察到的上皮-间质转化。桥粒芯蛋白2（DSC2）是一种钙黏蛋白超家族成员，是肠道上皮中桥粒的关键组成部分。然而，肠道细胞中调节DSC2基因表达的机制尚不清楚。Cdx1和Cdx2是调控肠道特异性基因表达的同源域转录因子。过去，Cdx的表达与桥粒的诱导有关。我们现在表明，DSC2基因是Cdx1和Cdx2的转录靶点。保留Cdx2表达的结肠癌细胞系通常表达DSC2。在Colo 205细胞中恢复Cdx表达可诱导DSC2 mRNA和蛋白质的产生以及桥粒的形成。DSC2启动子的5'侧翼区域包含两个共有Cdx结合位点。电泳迁移率变动分析表明，Cdx1和Cdx2在体外结合这些位点，染色质免疫沉淀证实Cdx2在体内结合。DSC2启动子截短实验确定这些区域对Cdx有反应。截短实验还确定了启动子中的一个区域，强效转录抑制因子在该区域发挥作用。Cdx结合可解除这种抑制活性。我们得出结论，同源域转录因子Cdx1和Cdx2通过逆转转录抑制因子的作用来调节肠道上皮细胞中DSC2基因的表达。Cdx对桥粒连接的调节有助于正常肠道上皮柱状形态的维持，并可能拮抗人类结肠癌细胞转移所必需的上皮-间质转化。
