RAFTK/Pyk2 tyrosine kinase mediates the association of p190 RhoGAP with RasGAP and is involved in breast cancer cell invasion

Focal adhesions and actin cytoskeleton are involved in cell growth, shape a nd movement and in tumor invasion. Mitogen-induced changes in actin cytoske leton are accompanied by changes in the tyrosine phosphorylation of several focal adhesion proteins. in this study, we have investigated the role of R AFTK, a cytoplasmic tyrosine kinase related to focal adhesion kinase (FAK), in heregulin-mediated signal transduction in breast cancer cells. Stimulat ion of T47D cells with heregulin (HRG) induced the tyrosine phosphorylation of RAFTK and the formation of a multiprotein complex;, Analyses of the mem bers of the HRG-stimulated complex revealed that RAFTK is associated with p 190 RhoGAP (p190), RasGAP and ErbB-2, and plays an essential role in mediat ing the tyrosine phosphorylation of plop by Src, Mutation of the Src bindin g site within RAFTK (402) abolished the phosphorylation of p190. In additio n, upon HRG stimulation of T47D cells, association of ErbB-2 with RAFTK was observed and found to be indirect and mediated by Src. Expression of wild- type RAFTK (WT) significantly increased MDA-MB-435 and MCF-7 breast cancer cell invasion, while expression of the kinase-mutated RAFTK-R457 (KM) or th e Src binding site mutant RAFTM (402) did not affect this cell invasion. Fu rthermore, HRG leads to tbe activation of MAP kinase which is mediated by R AFTK. These findings indicate that RAFTK serves as a mediator and an integr ation paint between the GAP proteins and HRG-mediated signaling in breast c ancer cells, and implicate RAFTK involvement in the MAP kinase pathway and in breast cancer cell invasion.