Mechanism and consequences of E-cadherin induction by estrogen

Epithelial (E)-cadherin is a calcium-dependent cell adhesion molecule. As a crucial component of epithelial cell adherens junctions, E-cadherin is responsible for the establishment of cell polarity and the maintenance of tissue integrity. Appropriately regulated E-cadherin expression is essential for morphogenesis and its misregulation is an important factor in the progression of cancer.The regulation of E-cadherin expression by 17beta-estradiol was analyzed in human breast carcinoma MCF-7 cells. These cells are well-differentiated and display many epithelial characteristics. MCF-7 cell E-cadherin mRNA and protein levels were increased in response to 17beta-estradiol, but levels of the E-cadherin associated cytoplasmic proteins alpha-catenin, beta-catenin and plakoglobin were unchanged. Culture of MCF-7 cells in estrogen-deprived conditions, or in the presence of anti-estrogens led to an altered morphology, reminiscent of a decreased polarization. This was evidenced by changes in the subcellular localization of E-cadherin, beta-catenin and plakoglobin, as well as rearrangement of the actin-based cytoskeleton. Futhermore, the packing of the MCF-7 monolayer was less ordered under these conditions. The cells reverted to a well organized phenotype upon treatment with 17beta-estradiol. These data show that E-cadherin expression in a mammary epithelial-derived cell line is estrogen-responsive, and that changes in the estrogenic environment have consequences upon cell shape and monolayer packing. These findings suggest a novel role for estrogens in the regulation of mammary gland cadherins which has not previously been appreciated.The mechanism of E-cadherin gene regulation by 17beta-estradiol was studied using promoter-reporter assays and electrophoretic mobility shift assays. A 380 by fragment of the E-cadherin gene promoter was found to be sufficient to drive estrogen-responsive expression in MCF-7 cells. Mutagenesis studies revealed a non-consensus estrogen response element (ERE) within this fragment to be important for regulation by estrogen. Furthermore, the E-cadherin ERE specifically interacted with purified recombinant estrogen receptor (ER) alpha and beta in vitro, supporting the hypothesis that regulation of E-cadherin gene expression by estrogen occurs by direct interaction of the ER and the incomplete ERE in the gene promoter. The involvement of the ER in E-cadherin gene expression provides a functional explanation for the concomitant loss of both ER and E-cadherin expression manifested in aggressive breast cancers.The activity of the 380 by fragment of the E-cadherin promoter and its stimulation by 17beta-estradiol were compromised by overexpression of ErbB2 tyrosine kinase receptor in MCF-7 cells. The ErbB2 receptor is frequently overexpressed in advanced stage breast cancer, and signalling via this tyrosine kinase is implicated in the progression of the disease. The suppression of 17beta-estradiol's effect on E-cadherin promoter activity by ErbB2 may represent a functional intersection between the ErbB2 and estrogen-dependent signalling pathways.In summary, these studies demonstrate that alterations in estrogen levels can have profound consequences on E-cadherin expression and cell morphology. Furthermore, the expression of E-cadherin appears to be under the direct control of estrogens by virtue of the presence of a non-consensus ERE in the gene promoter