Hennig G, Behrens J, Truss M, Frisch S, Reichmann E, Birchmeier W
Max-Delbrück-Centrum für Molekulare Medizin, Berlin, Germany.
Oncogene. 1995 Aug 3;11(3):475-84.
E-cadherin has been identified as a tumor (invasion) suppressor gene, which is mutated in 50% of diffuse-type human gastric carcinomas. In other carcinomas, the expression of E-cadherin is down-regulated in the poorly differentiated cells such as from breast, bladder, lung and colon. We have here examined the in vivo properties of the genomic E-cadherin promoter in well and poorly differentiated carcinoma cell lines in order to gain insights into the mechanisms of E-cadherin down-regulation in tumors. In vivo footprinting analysis revealed that positive regulatory elements of the E-cadherin promoter (a GC-rich region, the CCAAT-box and a palindromic element) are specifically bound by transcription factors in E-cadherin-expressing but not in non-expressing cells. The tested cell systems include more than a dozen carcinomas cell lines as well as mammary epithelial cells where E-cadherin expression can be switched off by activation of a Fos-estrogen receptor fusion protein and rhabdomyosarcoma cells where E-cadherin expression was induced by transfection with E1A. Mapping of DNase I hypersensitive sites showed that the chromatin structure in the promoter region is loosened in expressing but condensed in non-expressing cells. Furthermore, the endogenous E-cadherin promoter is specifically methylated at CpG sites in the undifferentiated cells. We also show that the in vivo properties of the promoter in E-caherin-negative carcinoma cells are similar as in mesenchymal cells, i.e. fibroblasts or sarcoma cells. These data suggest that silencing of the E-cadherin promoter during epithelialmesenchymal transition and tumor progression is due to a loss of factor binding in vivo and to chromatin rearrangement in the regulatory region.
E-钙黏蛋白已被鉴定为一种肿瘤（侵袭）抑制基因，在50%的弥漫型人类胃癌中发生突变。在其他癌症中，E-钙黏蛋白在低分化细胞（如来自乳腺、膀胱、肺和结肠的细胞）中的表达下调。我们在此研究了基因组E-钙黏蛋白启动子在高分化和低分化癌细胞系中的体内特性，以深入了解肿瘤中E-钙黏蛋白下调的机制。体内足迹分析显示，E-钙黏蛋白启动子的正调控元件（富含GC的区域、CCAAT框和回文元件）在表达E-钙黏蛋白的细胞而非不表达的细胞中被转录因子特异性结合。所测试的细胞系统包括十多种癌细胞系以及乳腺上皮细胞（其中E-钙黏蛋白的表达可通过激活Fos-雌激素受体融合蛋白而关闭）和横纹肌肉瘤细胞（其中通过转染E1A诱导E-钙黏蛋白表达）。DNase I超敏位点的定位表明，启动子区域的染色质结构在表达细胞中松弛，但在不表达细胞中凝聚。此外，内源性E-钙黏蛋白启动子在未分化细胞的CpG位点特异性甲基化。我们还表明，E-钙黏蛋白阴性癌细胞中启动子的体内特性与间充质细胞（即成纤维细胞或肉瘤细胞）中的相似。这些数据表明，上皮-间充质转化和肿瘤进展过程中E-钙黏蛋白启动子的沉默是由于体内因子结合的丧失和调控区域染色质重排所致。
