EGF augments TGFβ-induced epithelial-mesenchymal transition by promoting SHP2 binding to GAB1

Abstract

In many epithelial cells, epidermal growth factor (EGF) augments the epithelial-mesenchymal transition (EMT) that occurs when cells are treated with transforming growth factor beta (TGFβ). Here, we demonstrate that this augmentation requires activation of SH2 domain-containing phosphatase-2 (SHP2), a proto-oncogene. In lung and pancreatic cancer cell lines, reductions in E-cadherin expression, increases in vimentin expression, and increases in cell scatter rates were larger when cells were treated with TGFβ and EGF versus TGFβ or EGF alone. SHP2 knockdown promoted epithelial characteristics basally and antagonized EMT in response to TGFβ alone or in combination with EGF. Whereas EGF promoted SHP2 binding to tyrosine phosphorylated GAB1, which promotes SHP2 activity, TGFβ did not induce SHP2 association with phosphotyrosine-containing proteins. Knockdown of endogenous SHP2 and reconstitution with an SHP2 mutant with impaired phosphotyrosine binding ability eliminated the EGF-mediated EMT augmentation that was otherwise restored with wild-type SHP2 reconstitution. These results demonstrate roles for basal and ligand-induced SHP2 activity in EMT and further motivate efforts to identify specific ways to inhibit SHP2, given the role of EMT in tumor dissemination and chemoresistance.