Tumour-associated E-cadherin mutations alter cellular morphology, decreasecellular adhesion and increase cellular motility

A major function of the cell-to-cell adhesion molecule E-cadherin is the ma intenance of cell adhesion and tissue integrity. E-cadherin deficiency in r umours leads to changes in cell morphology and motility, so that E-cadherin is considered to be a suppressor of invasion. In this study we investigate d the functional consequences of three tumour-associated gene mutations tha t affect the extracellular portion of E-cadherin: in-frame deletions of exo ns 8 or 9 and a point mutation in exon 8, as they were found in human gastr ic carcinomas. Human MDA-MB-435S breast carcinoma cells and mouse L fibrobl asts were stably transfected with the wild-type and mutant cDNAs, and the r esulting changes in localization of E-cadherin, cell morphology, strength o f calcium-dependent aggregation as well as cell motility and actin cytoskel eton organization were studied. We found that cells transfected with wild-t y pe E-cadherin showed an epitheloid morphology, while all cell lines expre ssing mutant E-cadherin exhibited more irregular cell shapes. Cells express ing E-cadherin mutated in exon 8 showed the most scattered appearance, wher eas cells with deletion of exon 9 had an intermediate state, Mutant E-cadhe rins were localized to the lateral regions of cell-to-cell contact sites. A dditionally, both exon 8-mutated E-cadherins showed apical and perinuclear localization, and actin filaments were drastically reduced. MDA-MB-435S cel ls with initial calcium-dependent cell aggregation exhibited decreased aggr egation and, remarkably, increased cell motility, when mutant E-cadherin wa s 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 m utations affecting exons 8 or 9 are the cause of multiple morphological and functional disorders and could induce the scattered morphology and the inv asive behaviour of diffuse type-gastric carcinomas.