Mechanisms of Inactivation of E-Cadherin in Breast Cancer Cell

Loss of E-cadherin (CDH1) function is thought to contribute to pro gression in breast cancer and other solid tumors by increasing prolifera tion, invasion, and/or metastasis. In some cases, the restoration of CDH1 function may be an important therapeutic option. This possibility will depend on the mechanism by which CDH1 is inactivated. Here we present analyses of CDH1 expression, genetic mutation, and promoter methylation in CDH1 in 10 commonly used breast cancer cell lines. Five cell lines (BT-474, MCF-7, MDA-MB-361, MDA-MB-468, and T-47D) expressed CDH1 and were genetically normal. Five others (SK-BR-3, 600 MIT. MDA-MB-134 IV, CAMA1, and MDA-MB-435) did not express CDH1. Fluorescence in situ hybridization analyses of each of these cell lines showed evidence for the physical deletion of one alÃ-eleof CDH1, and three cell lines were found to carry homozygous deletions. SK-BR-3 was deleted from exon 12 through the promoter; exon 6 was deleted in MDA-MB-134 IV cells, and 600 MPE cells carried a 21-bp deletion in the splicing acceptor site for exon 9. CAMA1 seemed to have been inactivated through promoter methylation. No explanation was found for the inactivation of CDH1 in MDA-MB-435. used to modulate CDH1 expression in some cell lines. In addition, the treatment of breast tumor cells in a three-dimensional culture with a ß\ integrin antibody caused a reversion of the malignant phenotype and increased CDH1 expression (24). Thus, these and related com pounds are of interest as possible therapeutic agents capable of sup pressing tumor invasion and/or metastasis. However, the approach to the restoration of CDH1 expression will be governed by the mecha nism through which CDH1 expression was lost. This may occur through mutation (14-18), promoter methylation (25-27), and/or transcriptional down-regulation (28). Here we present analyses of CDH1 expression, genetic mutation, and promoter methylation in CDHI in 10 commonly used breast cancer cell lines. Five cell lines that expressed normal levels of CDHI were analyzed to identify the most common polymorphisms. The other five cell lines did not express CDHI. Information on the mechanisms by which CDHI is inactivated in these cell lines is presented to facilitate the interpreta tion of the responses of these cell lines to agents intended to restore CDHI function.