Differential signaling by the focal adhesion kinase and cell adhesion kinase beta.

pp125(FAK) and CAKbeta/Pyk2/CadTK/RAFTK are related protein-tyrosine kinases. It is therefore of interest whether CAKbeta shares some of the properties of pp125(FAK). Using recombinant glutathione S-transferase fusion proteins, we show that the C-terminal domains of both proteins bind paxillin in vitro. The C-terminal domain of CAKbeta was engineered to be autonomously expressed in chicken embryo cells and, like pp125(FAK) and p41/43(FRNK) (the C-terminal noncatalytic domain of pp125(FAK)), was found to localize to cellular focal adhesions. In contrast, full-length CAKbeta was generally found diffusely distributed throughout the cell, although a fraction of the cells exhibited focal adhesion localization. Vanadate treatment of pp125(FAK)- and CAKbeta-overexpressing CE cells induced a dramatic increase in the phosphotyrosine content of a common set of proteins including tensin, paxillin, and p130(Cas), but some of these substrates, particularly p130(Cas), appeared to be differentially phosphorylated by pp125(FAK) and CAKbeta. Levels of tyrosine phosphorylation were higher in CAKbeta-overexpressing cells, and additional phosphotyrosine-containing species were specifically immunoprecipitated. In addition, vanadate treatment of CE cells overexpressing CAKbeta, but not pp125(FAK) overexpressors, induced a profound morphological change, which could be a consequence of the observed differences in substrate phosphorylation.