title: An SH3 domain-containing GTPase-activating protein for Rho and Cdc42 associates with focal adhesion kinase.
abstract: The integrin family of cell surface receptors mediates cell adhesion to components of the extracellular matrix (ECM). Integrin engagement with the ECM initiates signaling cascades that regulate the organization of the actin-cytoskeleton and changes in gene expression. The Rho subfamily of Ras-related low-molecular-weight GTP-binding proteins and several protein tyrosine kinases have been implicated in mediating various aspects of integrin-dependent alterations in cell homeostasis. Focal adhesion kinase (FAK or pp125FAK) is one of the tyrosine kinases predicted to be a critical component of integrin signaling. To elucidate the mechanisms by which FAK participates in integrin-mediated signaling, we have used expression cloning to identify cDNAs that encode potential FAK-binding proteins. We report here the identification of a cDNA that encodes a new member of the GTPase-activating protein (GAP) family of GTPase regulators. This GAP, termed Graf (for GTPase regulator associated with FAK), binds to the C-terminal domain of FAK in an SH3 domain-dependent manner and preferentially stimulates the GTPase activity of the GTP-binding proteins RhoA and Cdc42. Subcellular localization studies using Graf-transfected chicken embryo cells indicates that Graf colocalizes with actin stress fibers, cortical actin structures, and focal adhesions. Graf mRNA is expressed in a variety of avian tissues and is particularly abundant in embryonic brain and liver. Graf represents the first example of a regulator of the Rho family of small GTP-binding proteins that exhibits binding to a protein tyrosine kinase. We suggest that Graf may function to mediate cross talk between the tyrosine kinases such as FAK and the Rho family GTPase that control steps in integrin-initiated signaling events.
authors.affiliation: Department of Microbiology, Health Sciences Center, University of Virginia, Charlottesville 22908, USA.
authors.forename: J D
authors.initials: JD
authors.lastname: Hildebrand
authors.forename: J M
authors.initials: JM
authors.lastname: Taylor
authors.forename: J T
authors.initials: JT
authors.lastname: Parsons
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D002642:Chick Embryo; D003001:Cloning, Molecular; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D019204:GTP-Binding Proteins / Q000378:metabolism*; D020690:GTPase-Activating Proteins; D008969:Molecular Sequence Data; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011506:Proteins / Q000235:genetics* / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions / Q000378:metabolism; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae; D020703:ras GTPase-Activating Proteins; D020742:rhoA GTP-Binding Protein; D018909:src Homology Domains
chemical_list: D015815:Cell Adhesion Molecules; D018797:Cell Cycle Proteins; D020690:GTPase-Activating Proteins; D011506:Proteins; D012333:RNA, Messenger; D020703:ras GTPase-Activating Proteins; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D019204:GTP-Binding Proteins; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae; D020742:rhoA GTP-Binding Protein