The related adhesion focal tyrosine kinase forms a complex with paxillin in hematopoietic cells

Related adhesion focal tyrosine kinase (RAFTK), also known as proline-rich tyrosine kinase 2 and cellular adhesion kinase beta, has been recently cloned and characterized as a member of the focal adhesion kinase (FAK) subfamily. RAFTK has an overall 48% amino acid homology to p125(FAK) and contains a kinase domain but lacks a transmembrane region, myristylation sites, and Src homology region 2 and 3 domains. By Northern blot analysis, RAFTK is expressed in myeloid, lymphoid, and megakaryocytic hematopoietic cells. Like p125(FAK), we found that RAFTK interacts with the focal adhesion protein paxillin. In the lymphoid cell line BaF3 and the myeloid cell line 32Dcl3, RAFTK coprecipitates with paxillin. Using in vitro binding assays, RAFTK and paxillin were shown to bind directly, through a segment of paxillin that required amino acids 100-227 and a domain in the C terminus of RAFTK. In vitro, RAFTK could phosphorylate paxillin on tyrosine residues. These results suggest that RAFTK, as well as p125(FAK), may be important in phosphotyrosine-signaling events within the focal adhesion.