Functional analysis of FAK tyrosine kinase in intracellular signaling pathways

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The FAK protein-tyrosine kinase plays important roles in cell adhesion in vertebrates. Using PCR-based cloning strategy, we cloned a Drosophila gene that was homologous to the vertebrate FAK family of protein-tyrosine kinases. We designated this gene Dfak56, and characterized its gene product. The overall protein structure and deduced amino acid sequence of Dfak56 showed significant similarity to FAK and PYK2. Dfak56 had in, vitro autophosphorylation activity on tyrosine residues. Expression of the Dfak56 mRNA and the protein was observed in the central nervous system and muscle-epidermis attachment site in the embryo, where Drosophila position-specific integrins are localized. The results suggest that like FAK in vertebrates, Dfak56 functions downstream of integrins. Dfak56 was tyrosine-phosphorylated upon integrin-dependent attachment of the cell to the extracellular matrix. We conclude that the Dfak56 tyrosine kinase is involved in integrin-mediated cell adhesion signaling and thus, is a functional homolog of vertebrate FAK.