EGFR regulates RhoA-GTP dependent cell motility in E-cadherin mutant cells

Gastric cancer associated E-cadherin germline missense mutations lead to significant functional consequences, in both the structural and signalling properties of the protein. In this study, we have characterized the effect of four E-cadherin germline missense mutations (T340A, A634V, P799R and V832M) in the interaction with the epidermal growth factor receptor (EGFR). We challenged the hypothesis that E-cadherin mutations perturb its ability to bind to EGFR, leading to constitutional activation of the EGFR, triggering activation of downstream effectors. We verified that missense mutations localized in the extracellular domain of the protein T340A and A634V) exhibited reduced stability of the EGFR/E-cadherin heterodimers in contrast to germline mutations localized at the cytoplasmatic domain of the protein (P799R and V832M). We observed that cells expressing E-cadherin extracellular mutants displayed increased levels of phosphorylated EGFR upon ligand stimulation, when compared with cells expressing wild-type E-cadherin or intracellular mutants. We showed that upon treatment of E-cadherin extracellular mutant cells with the EGFR inhibitor, the increase of RhoA activation is abrogated and accompanied by decreased migratory behaviour, supporting the idea that Rho-like proteins are EGFR downstream effectors. Our results bring new insights into the understanding of the distinct in vitro behaviours observed for E-cadherin missense mutations localized in different domains of the protein. Furthermore, we demonstrate that E-cadherin-dependent EGFR activation contributes to enhanced cell motility, in a mechanism involving RhoA activation.