DIFFERENTIAL SIGNALING BY THE FOCAL ADHESION KINASE AND CELL-ADHESIONKINASE-BETA

pp125(FAK) and CAK beta/Pyk2/CadTK/RAFTK are related protein-tyrosine kinases. It is therefore of interest whether CAK beta shares some of t he properties of pp125(FAK). Using recombinant glutathione S-transfera se fusion proteins, we show that the C-terminal domains of both protei ns bind paxillin in vitro. The C-terminal domain of CAK beta was engin eered to be autonomously expressed in chicken embryo cells and, like p p125(FAK) and p41/43(FRNK) (the C-terminal noncatalytic domain of pp12 5(FAK)) was found to localize to cellular focal adhesions. In contrast , full-length CAK beta was generally found diffusely distributed throu ghout the cell, although a fraction of the cells exhibited focal adhes ion localization. Vanadate treatment of pp125(FAK) and CAK beta-overex pressing CE cells induced a dramatic increase in the phosphotyrosine c ontent of a common set of proteins including tensin, paxillin, and p13 0(Cas), but some of these substrates, particularly p130(Cas), appeared to be differentially phosphorylated by pp125(FAK) and CAK beta. Level s of tyrosine phosphorylation were higher in CAK beta-overexpressing c ells, and additional phosphotyrosine-containing species were specifica lly immunoprecipitated, In addition, vanadate treatment of CE cells ov erexpressing CAK beta, but not pp125(FAK) overexpressors, induced a pr ofound morphological change, which could be a consequence of the obser ved differences in substrate phosphorylation.