MAPK3 and breast cancer: This study showed an increase of phospho-Y397/FAK, phospho-Src, and phospho-paxillin levels and Rac1 activity, but the phospho-Y925/FAK was not altered, suggesting that the integrin α5β1–fibronectin complex promotes the adhesion and migration of breast cancer cells through the FA-mediated FAK (pY397)/Src/paxillin/Rac1 signaling pathway, rather than the FAK (pY925)-ERK1/2 cascade.