(636b) Activation of the Protein Tyrosine Phosphatase SHP2 Promotes Complete Epithelial-Mesenchymal Transition

Epithelial-mesenchymal transition (EMT) is a cellular developmental program that can be hijacked in cancer to drive metastasis and therapeutic resistance. Transforming growth factor beta (TGFβ) is one of the most potent and common drivers of EMT, but it is well known that the ability of TGFβ to promote mesenchymal cellular characteristics can be augmented by growth factors such as epidermal growth factor (EGF), which are unable to drive EMT by themselves. We hypothesized that this augmentation could arise from the ability of growth factors such as EGF to promote strong activity of the extracellular regulated kinase (ERK) pathway, given that we have previously demonstrated a crucial role for ERK in EMT initiation and maintenance. Here, we validate that hypothesis by demonstrating that activation of SH2 domain-containing phosphatase 2 (SHP2), a protein tyrosine phosphatase required for complete activation of ERK downstream of many receptors, is required for the augmented EMT that occurs in lung and pancreatic cancer cells when EGF is combined with TGFβ. In both cancer cell types, SHP2 knockdown inhibited EMT in response to TGFβ and EGF, as determined by monitoring changes in epithelial and mesenchymal marker expression and cell migration rates. We further demonstrated that EGF’s ability to promote ERK activity and EMT induction depends on the ability of SHP2 to complex with the scaffolding adaptor GRB2-associated binder 1 (GAB1) when GAB1 becomes tyrosine phosphorylated in response to EGF receptor activation, an event that stabilizes an open and active conformation of SHP2. In support of this conclusion, we found that TGFβ has no capacity to drive the formation of GAB1-SHP2 complexes on its own and that knockdown of endogenous SHP2 followed by reconstitution with an SHP2 mutant with reduced capacity to form GAB1 complexes diminished the ability of EGF to augment EMT. The results of this work add to growing motivation to develop ways to specifically antagonize SHP2 activity in cancer and identify a previously unknown mechanistic basis for the EMT augmentation effect provided by growth factors such as EGF when combined with TGFβ.