title: Cooperative activation of Src family kinases by SH3 and SH2 ligands.
abstract: Src family nonreceptor tyrosine kinases are kept in a repressed state by intramolecular interactions involving the SH3 and SH2 domains of the enzymes. Ligands for these domains can displace the intramolecular associations and activate the kinases. Here, we carried out in vitro activation experiments with purified, down-regulated hematopoietic cell kinase (Hck), a Src family kinase. We show that SH3 and SH2 ligands act cooperatively to activate Src family kinases: the presence of one ligand lowers the concentration of the second ligand necessary for activation. To confirm the findings in intact cells, we studied Cas, a Src substrate that possesses SH2 and SH3 ligands. In contrast to wild-type Cas, mutant forms of Cas lacking the SH3 or SH2 ligands were unable to stimulate Src autophosphorylation when expressed in Cas-deficient fibroblasts. Cells expressing the Cas mutants also showed decreased amounts of activated Src at focal adhesions. The results suggest that proteins containing ligands for both SH3 and SH2 domains can produce a synergistic activation of Src family kinases.
authors.affiliation: Department of Physiology and Biophysics, School of Medicine, Stony Brook University, Stony Brook, NY 11794-8661, USA.
authors.forename: Shalini S
authors.initials: SS
authors.lastname: Yadav
authors.forename: W Todd
authors.initials: WT
authors.lastname: Miller
mesh_terms: D000818:Animals; D019556:COS Cells; D002448:Cell Adhesion; D002522:Chlorocebus aethiops; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D007700:Kinetics; D008024:Ligands; D008856:Microscopy, Fluorescence; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D018909:src Homology Domains; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: D008024:Ligands; D019061:src-Family Kinases