Cloning and characterization of cell adhesion kinase β, a novel protein-tyrosine kinase of the focal adhesion kinase subfamily

Abstract

A second protein-tyrosine kinase (PTK) of the focal adhesion kinase (FAK) subfamily, cell adhesion kinase β (CAKβ), was identified by cDNA cloning. The rat CAKβ is a 115.7-kDa PTK that contains N- and C-terminal domains of 418 and 330 amino acid residues besides the central kinase domain. The rat CAKβ has a homology with mouse FAK over their entire lengths except for the extreme N-terminal 88 residues and shares 45% overall sequence identity (60% identical in the catalytic domain), which indicates that CAKβ is a protein structurally related to but different from FAK. The CAKβ gene is less evenly expressed in a variety of rat organs than the FAK gene. Anti-CAKβ antibody immunoprecipitated a 113-kDa protein from rat brain, 3Y1 fibroblasts, and COS-7 cells transfected with CAKβ cDNA. The tyrosinephosphorylated state of CAKβ was not reduced on trypsinization, nor enhanced in response to plating 3Y1 cells onto fibronectin. CAKβ localized to sites of cell-to-cell contact in COS-7 transfected with CAK cDNA, in which FAK was found at the bottom of the cells. Thus, CAKβ is a PTK possibly participating in the signal transduction regulated by cell-to-cell contacts.