E-cadherin, a transmembrane cell adhesion molecule, has been observed to have an altered pattern of immunoreactivity in several types of carcinomas. In lobular breast cancer, loss of immunoreactivity has been shown to be due either to out-of-frame deletions or to nonsense mutations of the E-cadherin gene. We analysed 29 cases of completely resected colon carcinoma with immunohistochemistry using the HEC-D1 antibody. Normal protein expression similar to that in the adjacent nonmalignant mucosa was seen in 6 cases, whereas 23 tumours had reduced or absent E-cadherin expression. In the 8 cases with no expression of E-cadherin revealed by immunohistochemistry, the entire E-cadherin cDNA sequence was analysed. In these cases, sequence analysis failed to reveal any cDNA mutations despite the negative immunohistochemistry. Possible explanations for this discrepancy include regulatory defects in the E-cadherin promoter, abnormalities at the translation or protein processing levels and mutations in other parts of the gene that were not investigated by the cDNA analysis (e.g. intronic sequences), which could play a role in causing abnormal processing of the E-cadherin protein.

A major function of the cell-to-cell adhesion molecule E-cadherin is the maintenance of cell adhesion and tissue integrity. E-cadherin deficiency in tumours leads to changes in cell morphology and motility, so that E-cadherin is considered to be a suppressor of invasion. In this study we investigated the functional consequences of three tumour-associated gene mutations that affect the extracellular portion of E-cadherin: in-frame deletions of exons 8 or 9 and a point mutation in exon 8, as they were found in human gastric carcinomas. Human MDA-MB-435S breast carcinoma cells and mouse L fibroblasts were stably transfected with the wild-type and mutant cDNAs, and the resulting changes in localization of E-cadherin, cell morphology, strength of calcium-dependent aggregation as well as cell motility and actin cytoskeleton organization were studied. We found that cells transfected with wild-type E-cadherin showed an epitheloid morphology, while all cell lines expressing mutant E-cadherin exhibited more irregular cell shapes. Cells expressing E-cadherin mutated in exon 8 showed the most scattered appearance, whereas cells with deletion of exon 9 had an intermediate state. Mutant E-cadherins were localized to the lateral regions of cell-to-cell contact sites. Additionally, both exon 8-mutated E-cadherins showed apical and perinuclear localization, and actin filaments were drastically reduced. MDA-MB-435S cells with initial calcium-dependent cell aggregation exhibited decreased aggregation and, remarkably, increased cell motility, when mutant E-cadherin was expressed. Therefore, we conclude that these E-cadherin mutations may not simply affect cell adhesion but may act in a trans-dominant-active manner, i.e. lead to increased cell motility. Our study suggests that E-cadherin mutations affecting exons 8 or 9 are the cause of multiple morphological and functional disorders and could induce the scattered morphology and the invasive behaviour of diffuse type-gastric carcinomas.