The 4T1 breast carcinoma model possesses hybrid epithelial/mesenchymal traits linked to a highly metastatic phenotype

Epithelial-mesenchymal transitions (EMTs) have emerged as a mechanism for carcinomas to gain metastatic capabilities. As classically defined, EMTs entail downregulation of E-cadherin, viewed as a master enforcer of an epithelial phenotype, and upregulation of mesenchymal markers such as N-cadherin and vimentin. Contrary to this, E-cadherin appears to be retained in many invasive carcinomas and promote collective cell invasion. Therefore, major questions remain concerning the role of E-cadherin in metastasis. To investigate how E-cadherin regulates metastasis, we selected murine 4T1 breast carcinoma cells, a widely utilized model of stage IV metastatic breast cancer that retains E-cadherin expression. Using RNA interference and constitutive expression, we demonstrate that the expression level of E-cadherin does not determine 4T1 metastatic capacity in mice. Despite high levels of expression, E-cadherin is unable to confer an epithelial phenotype with stable organized cell-cell junctions. Moreover, orthotopic 4T1 tumors in mice display co-expression of E-cadherin and vimentin and contain subregions of EMT-like loss of E-cadherin. In addition, we find that 4T1 cells co-express epithelial and mesenchymal isoforms of p120-catenin. These findings support 4T1 cells as a model for carcinomas that possess hybrid traits of epithelial and mesenchymal states that promote invasion and metastasis. As such, the 4T1 model provides a platform for investigating strategies to reinstate E-cadherins ability to promote stable cell-cell junctions in E-cadherin-positive cancers, and for identifying which aspects of an epithelial phenotype may serve to facilitate the macroscopic growth of metastatic colonies.