Overexpression of GRB2 Enhances Epithelial to Mesenchymal Transition of A549 Cells by Upregulating SNAIL Expression

GRB2 is an adaptor protein which interacts with phosphorylated TGF-β receptor and is critical for mammary tumour growth. We found that TGF-β1-induced EMT increased GRB2 expression in A549 cells (non-small cell lung cancer). Overexpression of GRB2 (A549^GRB2) enhanced cell invasion while knocking down GRB2 (A549^GRB2KD) reduced cell migration and invasion, probably due to increased vinculin and reduced Paxillin patches in A549^GRB2KD cell. TGF-β1-induced EMT was more pronounced in A549^GRB2 cells and attenuated in A549^GRB2KD cells. This could be due to the reduced expression of E-cadherin in A549^GRB2 and increased expression of E-cadherin in A549^GRB2KD cells, even before TGF-β1 stimulation. Expression of SNAIL was elevated in A549^GRB2 cells and was further enhanced by TGF-β1 stimulation, suggesting that GRB2 down-regulates E-cadherin by enhancing the expression of SNAIL. The N-SH3 domain of GRB2 was critical for suppressing E-cadherin expression, while the C-SH3 domain of GRB2 mediating interaction with proteins such as N-WASP was critical for promoting invasion, and the SH2 domain was critical for suppressing E-cadherin expression and invasion. Thus, our data suggests that GRB2 enhances EMT by suppressing E-cadherin expression and promoting invasion probably through N-WASP to promote metastasis.