title: Grb2 promotes integrin-induced focal adhesion kinase (FAK) autophosphorylation and directs the phosphorylation of protein tyrosine phosphatase α by the Src-FAK kinase complex.
abstract: The integrin-activated Src-focal adhesion kinase (FAK) kinase complex phosphorylates PTPα at Tyr789, initiating PTPα-mediated signaling that promotes cell migration. Recruitment of the BCAR3-Cas complex by PTPα-phospho-Tyr789 at focal adhesions is one mechanism of PTPα signaling. The adaptor protein Grb2 is also recruited by PTPα-phospho-Tyr789, although the role of the PTPα-Grb2 complex in integrin signaling is unknown. We show that silencing Grb2 expression in fibroblasts abolishes PTPα-Tyr789 phosphorylation and that this is due to two unexpected actions of Grb2. First, Grb2 promotes integrin-induced autophosphorylation of FAK-Tyr397. This is impaired in Grb2-depleted cells and prohibits FAK activation and formation of the Src-FAK complex. Grb2-depleted cells contain less paxillin, and paxillin overexpression rescues FAK-Tyr397 phosphorylation, suggesting that the FAK-activating action of Grb2 involves paxillin. A second distinct role for Grb2 in PTPα-Tyr789 phosphorylation involves Grb2-mediated coupling of Src-FAK and PTPα. This requires two phosphosites, FAK-Tyr925 and PTPα-Tyr789, for Grb2-Src homology 2 (SH2) binding. We propose that a Grb2 dimer links FAK and PTPα, and this positions active Src-FAK in proximity with other, perhaps integrin-clustered, molecules of PTPα to enable maximal PTPα-Tyr789 phosphorylation. These findings identify Grb2 as a new FAK activator and reveal its essential role in coordinating PTPα tyrosine phosphorylation to enable downstream integrin signaling and migration.
authors.affiliation: Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Suzanne Y S
authors.initials: SY
authors.lastname: Cheng
authors.forename: Guobin
authors.initials: G
authors.lastname: Sun
authors.forename: David D
authors.initials: DD
authors.lastname: Schlaepfer
authors.forename: Catherine J
authors.initials: CJ
authors.lastname: Pallen
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004622:Embryo, Mammalian / Q000166:cytology; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism*; D051417:Focal Adhesion Kinase 1 / Q000235:genetics / Q000378:metabolism*; D051380:GRB2 Adaptor Protein / Q000235:genetics / Q000378:metabolism*; D015151:Immunoblotting; D016023:Integrins / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D051419:Paxillin / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D034622:RNA Interference; D054630:Receptor-Like Protein Tyrosine Phosphatases, Class 4 / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014443:Tyrosine / Q000235:genetics / Q000378:metabolism; D018909:src Homology Domains
chemical_list: D051380:GRB2 Adaptor Protein; C495949:Grb2 protein, mouse; D016023:Integrins; D051419:Paxillin; D014443:Tyrosine; D051417:Focal Adhesion Kinase 1; C496051:Ptk2 protein, mouse; C516843:Ptpra protein, mouse; D054630:Receptor-Like Protein Tyrosine Phosphatases, Class 4