PTPN11 and breast cancer: To determine if tyrosine phosphorylation of Shp2 regulates IL-6-induced EMT in breast cancer cells, a phospho-mimicking mutant form of Shp2 (Shp22YE) and a phospho-deficient mutant form of Shp2 (Shp22YF), were introduced into the Shp2 knockdown cells.