Saegusa Makoto, Hashimura Miki, Kuwata Takeshi, Hamano Mieko, Wani Yoji, Okayasu Isao
Department of Pathology, Kitasato University School of Medicine, 1-15-1 Kitasato, Sagamihara, Kanagawa 228-8555, Japan.
Carcinogenesis. 2007 Sep;28(9):1885-92. doi: 10.1093/carcin/bgm105. Epub 2007 Apr 29.
Nuclear beta-catenin is required for changes in morphology from glandular to morular phenotypes of endometrial carcinoma (Em Ca) cells, with activation of p14(ARF)/p53/p21(Waf1) and alteration of p16(INK4A)/pRb pathways. Having demonstrated previously that the homeodomain transcription factor Cdx2 increases markedly during intestinal epithelial cell differentiation, we have examined its effects in beta-catenin signaling during transdifferentiation of Em Ca cells. In clinical cases, Cdx2 immunoreactivity, along with increased mRNA signals, was found to overlap with nuclear accumulation of beta-catenin and p21(Waf1) in morules, demonstrating an inverse correlation with cell proliferation. In cell lines, over-expression of active form beta-catenin resulted in a significant increase in endogenous Cdx2 expression at both mRNA and protein levels. Furthermore, the Cdx2 promoter was activated by T-cell factor 4 (TCF4) -independent activated beta-catenin, as well as Cdx2 itself, through the region from -39 to +9 bp relative to transcription start site. Cells over-expressing exogenous Cdx2 showed high levels of p21(Waf1) expression due to stabilization of the mRNA status, resulting in significant decrease in the proliferation rate, in contrast to the lack of apparent changes in morphology. Moreover, transfected Cdx2 could inhibit beta-catenin/TCF4-mediated transcriptional activation of target genes, including p14(ARF) and cyclin D1, probably through indirect mechanisms. These data suggest that over-expression of Cdx2 mediated by nuclear beta-catenin and Cdx2 itself can cause an inhibition of Em Ca cell proliferation through up-regulation of p21(Waf1) expression, modulating beta-catenin/TCF4-mediated transcription. We therefore conclude that an association between Cdx2 and beta-catenin signaling may participate in induction of transdifferentiation of Em Ca cells.
核β-连环蛋白是子宫内膜癌细胞（Em Ca）从腺型向桑葚型表型转变所必需的，其过程伴随着p14（ARF）/p53/p21（Waf1）的激活以及p16（INK4A）/pRb通路的改变。先前已证明，同源结构域转录因子Cdx2在肠上皮细胞分化过程中显著增加，我们研究了其在Em Ca细胞转分化过程中对β-连环蛋白信号通路的影响。在临床病例中，发现Cdx2免疫反应性以及mRNA信号增加，与桑葚体中β-连环蛋白和p21（Waf1）的核积累重叠，表明其与细胞增殖呈负相关。在细胞系中，活性形式β-连环蛋白的过表达导致内源性Cdx2在mRNA和蛋白质水平上显著增加。此外，Cdx2启动子通过相对于转录起始位点-39至+9 bp的区域，被不依赖T细胞因子4（TCF4）的激活型β-连环蛋白以及Cdx2自身激活。过表达外源性Cdx2的细胞由于mRNA状态的稳定而显示出高水平的p21（Waf1）表达，导致增殖率显著降低，而形态上没有明显变化。此外，转染的Cdx2可能通过间接机制抑制β-连环蛋白/TCF4介导的靶基因转录激活，包括p14（ARF）和细胞周期蛋白D1。这些数据表明，由核β-连环蛋白和Cdx2自身介导的Cdx2过表达可通过上调p21（Waf1）表达来抑制Em Ca细胞增殖，调节β-连环蛋白/TCF4介导的转录。因此，我们得出结论，Cdx2与β-连环蛋白信号通路之间的关联可能参与Em Ca细胞转分化的诱导。
