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Mol. Cell. Biol., Jun 1996, 3169-3178, Vol 16, No. 6
JD Hildebrand, JM Taylor and JT Parsons
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.
Copyright © 1996, American Society for Microbiology
An SH3 domain-containing GTPase-activating protein for Rho and Cdc42 associates with focal adhesion kinase
Department of Microbiology, Health Sciences Center, University of Virginia, Charlottesville 22908, USA.
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