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

eThe integrin-activated Src-focal adhesion kinase (FAK) kinase complex phosphorylates PTP␣ at Tyr789, initiating PTP␣-mediated signaling that promotes cell migration. Recruitment of the BCAR3-Cas complex by PTP␣-phospho-Tyr789 at focal adhesions is one mechanism of PTP␣ signaling. The adaptor protein Grb2 is also recruited by PTP␣-phospho-Tyr789, although the role of the PTP␣-Grb2 complex in integrin signaling is unknown. We show that silencing Grb2 expression in fibroblasts abolishes PTP␣-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 PTP␣-Tyr789 phosphorylation involves Grb2-mediated coupling of Src-FAK and PTP␣. This requires two phosphosites, FAK-Tyr925 and PTP␣-Tyr789, for Grb2-Src homology 2 (SH2) binding. We propose that a Grb2 dimer links FAK and PTP␣, and this positions active Src-FAK in proximity with other, perhaps integrin-clustered, molecules of PTP␣ to enable maximal PTP␣-Tyr789 phosphorylation. These findings identify Grb2 as a new FAK activator and reveal its essential role in coordinating PTP␣ tyrosine phosphorylation to enable downstream integrin signaling and migration.

Receptor Protein Tyrosine Phosphatase α–Mediated Enhancement of Rheumatoid Synovial Fibroblast Signaling and Promotion of Arthritis in Mice

“…RPTPa, which is encoded by the PTPRA gene, is ubiquitously expressed (15,16). It is a critical positive regulator of signaling through dephosphorylation of the SFK C-terminal inhibitory tyrosine residue (Y 527 in Src) (13,14,(16)(17)(18). Dephosphorylation of Src-Y 527 enhances Src activation, leading to tyrosine phosphorylation of FAK-Y 397 and other substrates.…”

Proteomic Analysis Reveals Grb2 as a Key Regulator of Periodic Mechanical Stress Transduction in Chondrocytes

“…Moreover, Cheng etal. detected that integrin-induced FAK-Tyr397 autophosphorylation was suppressed in Grb2 down-regulated fibroblasts, while Levy-Apter reported that Grb2 promoted Src activation via PTPe and phosphorylate FAK-Tyr576/577 [38, 39]. These findings identified Grb2 as a new FAK and Src activator, which could partly point the FAK and ERK1/2 phosphorylation and the subsequent acceleration of chondrocytes proliferation and matrix synthesis in the presence of cyclic mechanical stress.…”

Regulation of RPTPα–c‐Src signalling pathway by miR‐218

“…In this model, pTyr789 specifically enables RPTPa to dephosphorylate pTyr530 via pTyr789 binding to the Src SH2 domain that displaces intramolecular pTyr530-SH2 binding. Recently, Pallen et al proposed another indirect model in which Grb2 stabilizes paxillin, and promotes the autophosphorylation of focal adhesion kinase at Tyr397, enabling the phosphorylation of RPTPa at Tyr789 by the Src-FAK kinase complex [11]. pTyr789 RPTPa binds BCAR3 (breast cancer anti-estrogen resistance-3) to Cas to enhance downstream signalling in focal adhesions [12].…”