The related adhesion focal tyrosine kinase is tyrosine-phosphorylated after beta 1-integrin stimulation in B cells and binds to p130(cas)

Integrin ligation initiates intracellular signaling events, among which are the activation of protein tyrosine kinases. The related adhesion focal tyrosine kinase (RAFTK), also known as PYK2 and CAK beta, is a tyrosine kinase that is homologous to the focal adhesion kinase (FAK) p125(FAK). The structure of RAFTK is similar to p125(FAK) in that it lacks a transmembrane region, does not contain Src homology 2 or 3 domains, and has a proline rich region in its C terminus. Here we report that RAFTK is a target for beta 1-integrin-mediated tyrosine phosphorylation in both transformed and normal human B cells. Ligation of the B cell antigen receptor also induced tyrosine phosphorylation of RAFTK. Phosphorylation of RAFTK following integrin- or B cell antigen receptor-mediated stimulation was decreased by prior treatment of cells with cytochalasin B, indicating that this process was at least partially cytoskeleton-dependent. One of the tyrosine-phosphorylated substrates after integrin stimulation in fibroblasts is p130(cas), which can associate with p125(FAK). RAFTK also interacted constitutively with p130(cas) in B cells, since p130(cas) was detected in RAFTK immunoprecipitates. Although the function of RAFTK remains unknown, these data suggest that RAFTK may have a significant function in integrin-mediated signaling pathways in B cells.