The Gab1 PH domain is required for localization of Gab1 at sites of cell-cell contact and epithelial morphogenesis downstream from the met receptor tyrosine kinase. Mol Cell Biol

Departments of Medicine, Molecular Oncology Group, Royal Victoria Hospital, McGill University, Montreal, Quebec, Canada H3A 1A1.
Molecular and Cellular Biology (Impact Factor: 4.78). 04/1999; 19(3):1784-99.
Source: PubMed

ABSTRACT Stimulation of the hepatocyte growth factor (HGF) receptor tyrosine kinase, Met, induces mitogenesis, motility, invasion, and branching tubulogenesis of epithelial and endothelial cell lines in culture. We have previously shown that Gab1 is the major phosphorylated protein following stimulation of the Met receptor in epithelial cells that undergo a morphogenic program in response to HGF. Gab1 is a member of the family of IRS-1-like multisubstrate docking proteins and, like IRS-1, contains an amino-terminal pleckstrin homology domain, in addition to multiple tyrosine residues that are potential binding sites for proteins that contain SH2 or PTB domains. Following stimulation of epithelial cells with HGF, Gab1 associates with phosphatidylinositol 3-kinase and the tyrosine phosphatase SHP2. Met receptor mutants that are impaired in their association with Gab1 fail to induce branching tubulogenesis. Overexpression of Gab1 rescues the Met-dependent tubulogenic response in these cell lines. The ability of Gab1 to promote tubulogenesis is dependent on its pleckstrin homology domain. Whereas the wild-type Gab1 protein is localized to areas of cell-cell contact, a Gab1 protein lacking the pleckstrin homology domain is localized predominantly in the cytoplasm. Localization of Gab1 to areas of cell-cell contact is inhibited by LY294002, demonstrating that phosphatidylinositol 3-kinase activity is required. These data show that Gab1 is an important mediator of branching tubulogenesis downstream from the Met receptor and identify phosphatidylinositol 3-kinase and the Gab1 pleckstrin homology domain as crucial for subcellular localization of Gab1 and biological responses.

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    • "Following binding of the active heterodimer HGF resulting from the conversion of its inactive precursor through proteolysis, the c-Met receptor undergoes dimerization and autophosphorylation on two tyrosine residues in its catalytic domain (Y1234 and Y1235) [32] [33]. Other tyrosine residues located outside the kinase domain (Y1349 and Y1356) are subsequently phosphorylated, forming a multifunctional docking site that recruits several Src-homology-2 domain (SH2 domain)-containing effectors, such as PI3K37 [34], the non-receptor tyrosine kinase Src [34], the growth factor receptor-bound protein 2 (Grb2) and SH2 domain-containing transforming protein (SHC) adaptors [34] [35] [36], SHP2 (also known as PTPN11; an upstream activator of Src and ras) [36], phospholipase Cγ1 (PLCγ1) [34], the transcription factor STAT3 [37] [38] and Grb2-associated-binding protein 1 (GAb1) [39] [40]. As a whole, this apparatus leads to the efficient activation of downstream signal transduction pathways that include the mitogen-activated protein kinase (MAPK) cascades (extracellular signal-regulated kinase 1 (ErK1) and ErK2, Jun aminoterminal kinases (JNKs) and p38), the phosphoinositide 3-kinase– Akt (PI3K–Akt) axis, signal transducer and activator of transcription proteins (STATs), and the nuclear factor-κb inhibitor-α (IκBα)– nuclear factor-κb (NF-κb) complex, responsible for driving proliferation, cell survival, morphogenesis, cell scattering, migration and invasiveness [39,41–43]. "
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    ABSTRACT: Despite significant improvements in systemic chemotherapy over the last two decades, the prognosis of patients with advanced gastric and gastroesophageal junction adenocarcinoma (GC) remains poor. Because of molecular heterogeneity, it is essential to classify tumors based on the underlying oncogenic pathways and to develop targeted therapies acting on individual tumors. High-quality research and advances in technology have contributed to the elucidation of molecular pathways underlying disease progression and have stimulated many clinical studies testing target therapies in an advanced disease setting. In particular, strong preclinical evidence for the aberrant activation of the HGF/c-Met signaling pathways in GC cancers exists. This review will cover the c-Met pathway, the mechanisms of c-Met activation and the different strategies of its inhibition. Next, we will focus on the current state of the art in the clinical evaluation of c-Met-targeted therapies and the description of ongoing randomized trials with the idea that in this disease, high quality translational research to identify and validate biomarkers is a priority task. Copyright © 2015. Published by Elsevier Ireland Ltd.
    Cancer Letters 06/2015; 365(1). DOI:10.1016/j.canlet.2015.05.028 · 5.62 Impact Factor
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    • "The physical association between p85 and Gab1 or Gab2 is critical in mediating the PI3K/Akt signaling pathway induced by a variety of stimuli [9,10,17-22]. Overexpression of Gab potentiates FGF-induced Akt activity, whereas overexpression of the p85 binding mutant of Gab1 results in decreased Akt activation [21]. The same mutant is also unable to provide anti-apoptotic signal in response to nerve growth factor stimulation [9]. "
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    ABSTRACT: Background Gab1 (Grb2-associated binder 1) is a key coordinator that belongs to the insulin receptor substrate-1 like family of adaptor molecules and is tyrosine phosphorylated in response to various growth factors, cytokines, and numerous other molecules. Tyrosine phosphorylated Gab1 is able to recruit a number of signaling effectors including PI3K, SHP2 and PLC-γ. In this study, we characterized the localization and regulation of tyrosine phosphorylation of Gab1 in the retina. Results Our immuno localization studies suggest that Gab1 is expressed in rod photoreceptor inner segments. We found that hydrogen peroxide activates the tyrosine phosphorylation of Gab1 ex vivo and hydrogen peroxide has been shown to inhibit the protein tyrosine phosphatase PTP1B activity. We found a stable association between the D181A substrate trap mutant of PTP1B and Gab1. Our studies suggest that PTP1B interacts with Gab1 through Tyrosine 83 and this residue may be the major PTP1B target residue on Gab1. We also found that Gab1 undergoes a light-dependent tyrosine phosphorylation and PTP1B regulates the phosphorylation state of Gab1. Consistent with these observations, we found an enhanced Gab1 tyrosine phosphorylation in PTP1B deficient mice and also in retinas treated ex vivo with a PTP1B specific allosteric inhibitor. Conclusions Our laboratory has previously reported that retinas deficient of PTP1B are resistant to light damage compared to wild type mice. Since Gab1 is negatively regulated by PTP1B, a part of the retinal neuroprotective effect we have observed previously in PTP1B deficient mice could be contributed by Gab1 as well. In summary, our data suggest that PTP1B regulates the phosphorylation state of retinal Gab1 in vivo.
    Cell Communication and Signaling 03/2013; 11(1):20. DOI:10.1186/1478-811X-11-20 · 3.38 Impact Factor
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    • "Gab1 contains six proline rich motifs, two of which (proline-rich motifs four and five) are implicated in the constitutive association with the adaptor protein growth factor receptor-bound protein 2 (Grb2) through its C-terminal SH3 domain (Lock et al., 2002). Once recruited to a Met–Gab1 complex, these proteins trigger activation of multiple signaling cascades, including PI3K–Akt (Maroun et al., 1999), Ras–MAPK (Maroun et al., 2000; Schaeper et al., 2000), Rac and Rap1 (Lamorte et al., 2000) and Nck/N-WASP (Abella et al., 2010) that promote cell survival, actin cytoskeleton remodeling, as well as increased migration and invasion (Benvenuti and Comoglio, 2007; Birchmeier et al., 2003; Lai et al., 2009; Peschard and Park, 2007). "
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    ABSTRACT: Invasive carcinoma cells form actin-rich matrix-degrading protrusions called invadopodia. These structures resemble podosomes produced by some normal cells and play a crucial role in extracellular matrix remodeling. In cancer, formation of invadopodia is strongly associated with invasive potential. Although deregulated signals from the receptor tyrosine kinase Met (also known as hepatocyte growth factor are linked to cancer metastasis and poor prognosis, its role in invadopodia formation is not known. Here we show that stimulation of breast cancer cells with the ligand for Met, hepatocyte growth factor, promotes invadopodia formation, and in aggressive gastric tumor cells where Met is amplified, invadopodia formation is dependent on Met activity. Using both GRB2-associated-binding protein 1 (Gab1)-null fibroblasts and specific knockdown of Gab1 in tumor cells we show that Met-mediated invadopodia formation and cell invasion requires the scaffold protein Gab1. By a structure-function approach, we demonstrate that two proline-rich motifs (P4/5) within Gab1 are essential for invadopodia formation. We identify the actin regulatory protein, cortactin, as a direct interaction partner for Gab1 and show that a Gab1-cortactin interaction is dependent on the SH3 domain of cortactin and the integrity of the P4/5 region of Gab1. Both cortactin and Gab1 localize to invadopodia rosettes in Met-transformed cells and the specific uncoupling of cortactin from Gab1 abrogates invadopodia biogenesis and cell invasion downstream from the Met receptor tyrosine kinase. Met localizes to invadopodia along with cortactin and promotes phosphorylation of cortactin. These findings provide insights into the molecular mechanisms of invadopodia formation and identify Gab1 as a scaffold protein involved in this process.
    Journal of Cell Science 02/2012; 125(Pt 12):2940-53. DOI:10.1242/jcs.100834 · 5.43 Impact Factor
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