PROGRESSION OF CARCINOMA-CELLS IS ASSOCIATED WITH ALTERATIONS IN CHROMATIN STRUCTURE AND FACTOR-BINDING AT THE E-CADHERIN PROMOTER IN-VIVO

E-cadherin has been identified as a tumor (invasion) suppressor gene, which is mutated in 50% of diffuse-type human gastric carcinomas. In o ther carcinomas, the expression of E-cadherin is down-regulated in the poorly differentiated cells such as from breast, bladder, lung and co lon. We have here examined the in vivo properties of the genomic E-cad herin promoter in well and poorly differentiated carcinoma cell lines in order to gain insights into the mechanisms of E-cadherin downregula tion in tumors. In vivo footprinting analysis revealed that positive r egulatory elements of the E-cadherin promoter (a GC-rich region, the C CAAT-box and a palindromic element) are specifically bound by transcri ption factors in E-cadherin-expressing but not in non-expressing cells . The tested cell systems include more than a dozen carcinomas cell li nes as well as mammary epithelial cells where E-cadherin expression ca n be switched off by activation of a Fos-estrogen receptor fusion prot ein and rhabdomyosarcoma cells where E-cadherin expression was induced by transfection with E1A. Mapping of DNase I hypersensitive sites sho wed that the chromatin structure in the promoter region is loosened in expressing but condensed in nonexpressing cells. Furthermore, the end ogenous 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-cadherin-negative carcinoma cells are similar as in mesenchymal cells, i.e. fibroblasts or sarcoma cells. These data su ggest that silencing of the E-cadherin promoter during epithelial-mens enchymal transition and tumor progression is due to a loss of factor b inding in vivo and to chromatin rearrangement in the regulatory region .