Fujimoto K, Sheng H, Shao J, Beauchamp R D
Department of Surgery, Vanderbilt University Medical Center and Vanderbilt-Ingram Cancer Center, Nashville, Tennessee 37232, USA.
Exp Cell Res. 2001 Jun 10;266(2):239-49. doi: 10.1006/excr.2000.5229.
Invasion is a defining event in carcinoma progression. In general, invasive carcinoma is characterized by an epithelial-fibroblastoid conversion associated with loss of cell-cell adhesion receptors such as E-cadherin and beta-catenin. We report here that TGF-beta1 promotes the invasiveness by modulating the alterations of cellular plasticity including a loss of cell-cell contact in Ras-transformed epithelial cells. In order to examine the role of TGF-beta1 in the Ras-induced responses, intestinal epithelial cells expressing a conditionally activated Ha-Ras(Val12) (RIE-iRas cells) were used in this study. Induced expression of activated Ha-Ras(Val12) caused morphologic transformation of the RIE-iRas cells with an increase in vimentin expression and a decrease of E-cadherin levels. There was also redistribution of beta-catenin from the cytoplasm to the nucleus after the induction of Ras. TGF-beta1 treatment enhanced both the decrease in E-cadherin levels and the redistribution of beta-catenin. Interestingly, the activation of Ras markedly decreased the level of TGF-beta receptor type II (TbetaRII) in RIE-iRas cells. However, the expression of plasminogen activator inhibitor-1, which is known to be transcriptionally induced by TGF-beta1, was strongly induced by TGF-beta1 despite the marked downregulation of TbetaRII. The induction of Ha-Ras(Val12) markedly increased the invasiveness in RIE-iRas cells, as evaluated by a collagen type I-coated Boyden-chamber assay, and the Ras-mediated invasiveness was significantly enhanced by TGF-beta1 treatment. Expression of a dominant-negative form of TbetaRII in the RIE-iRas cells abrogated both growth-inhibitory and invasion responses to TGF-beta1. Collectively, these results suggest that TGF-beta1 and oncogenic Ras collaborate in promoting cellular invasiveness in intestinal epithelial cells. The enhancement of invasiveness was correlated with decreased E-cadherin levels and subcellular distribution of beta-catenin. The enhancement of oncogenic Ras-mediated cell transformation by TGF-beta1 occurs via TbetaRII.
侵袭是癌进展过程中的一个决定性事件。一般来说，浸润性癌的特征是上皮-成纤维细胞样转化，伴有细胞间黏附受体如E-钙黏蛋白和β-连环蛋白的丢失。我们在此报告，转化生长因子β1（TGF-β1）通过调节细胞可塑性的改变来促进侵袭，这些改变包括Ras转化的上皮细胞中细胞间接触的丧失。为了研究TGF-β1在Ras诱导反应中的作用，本研究使用了表达条件性激活的Ha-Ras（Val12）的肠上皮细胞（RIE-iRas细胞）。激活的Ha-Ras（Val12）的诱导表达导致RIE-iRas细胞发生形态学转化，波形蛋白表达增加，E-钙黏蛋白水平降低。Ras诱导后，β-连环蛋白也从细胞质重新分布到细胞核。TGF-β1处理增强了E-钙黏蛋白水平的降低和β-连环蛋白的重新分布。有趣的是，Ras的激活显著降低了RIE-iRas细胞中II型TGF-β受体（TβRII）的水平。然而，尽管TβRII明显下调，但已知由TGF-β1转录诱导的纤溶酶原激活物抑制剂-1的表达仍被TGF-β1强烈诱导。通过I型胶原包被的博伊登小室试验评估，Ha-Ras（Val12）的诱导显著增加了RIE-iRas细胞的侵袭性，并且TGF-β1处理显著增强了Ras介导的侵袭性。在RIE-iRas细胞中表达TβRII的显性负性形式消除了对TGF-β1的生长抑制和侵袭反应。总的来说，这些结果表明TGF-β1和致癌性Ras协同促进肠上皮细胞的细胞侵袭性。侵袭性的增强与E-钙黏蛋白水平的降低和β-连环蛋白的亚细胞分布有关。TGF-β1通过TβRII增强致癌性Ras介导的细胞转化。
