The Experts below are selected from a list of 69195 Experts worldwide ranked by ideXlab platform
Morag Park - One of the best experts on this subject based on the ideXlab platform.
-
Distinct Recruitment and Function of Gab1 and Gab2 in Met Receptor-mediated Epithelial Morphogenesis
Molecular biology of the cell, 2002Co-Authors: Lisa S Lock, Monica A. Naujokas, Christiane R. Maroun, Morag ParkAbstract:The Gab family of docking proteins (Gab1 and Gab2) are phosphorylated in response to various cytokines and growth factors. Gab1 acts to diversify the signal downstream from the Met receptor tyrosine kinase through the recruitment of multiple signaling proteins, and is essential for epithelial morphogenesis. To determine whether Gab1 and Gab2 are functionally redundant, we have examined the role of Gab2 in epithelial cells. Both Gab1 and Gab2 are expressed in epithelial cells and localize to cell-cell junctions. However, whereas overexpression of Gab1 promotes a morphogenic response, the overexpression of Gab2 fails to induce this response. We show that Gab2 recruitment to the Met receptor is dependent on the GRB2 adapter protein. In contrast, Gab1 recruitment to Met is both GRB2 dependent and GRB2 independent. The latter requires a novel amino acid sequence present in the Met-binding domain of Gab1 but not Gab2. Mutation of these residues in Gab1 impairs both association with the Met receptor and the ability of Gab1 to promote a morphogenic response, whereas their insertion into Gab2 increases Gab2 association with Met, but does not confer on Gab2 the ability to promote epithelial morphogenesis. We propose that the GRB2-independent recruitment of Gab proteins to Met is necessary but not sufficient to promote epithelial morphogenesis.
-
identification of an atypical GRB2 carboxyl terminal sh3 domain binding site in gab docking proteins reveals GRB2 dependent and independent recruitment of gab1 to receptor tyrosine kinases
Journal of Biological Chemistry, 2000Co-Authors: Lisa S Lock, Monica A. Naujokas, Isabelle Royal, Morag ParkAbstract:Abstract The Gab family of docking proteins is phosphorylated in response to various growth factors and cytokines and serves to recruit multiple signaling proteins. Gab1 acts downstream from the Met-hepatocyte growth factor receptor, and Gab1 overexpression promotes Met-dependent morphogenesis of epithelial cells. Recruitment of Gab1 to Met or epidermal growth factor (EGF) receptors requires a receptor-binding site for the GRB2 adapter protein and a proline-rich domain in Gab1, defined as the Met-binding domain. To determine the requirement for GRB2 in Gab1 recruitment, we have mapped two GRB2 carboxyl-terminal SH3 domain binding sites conserved in Gab1 and related protein Gab2. One corresponds to a canonical GRB2-binding motif, whereas the second, located within the Gab1 Met-binding domain, requires the proline and arginine residues of an atypical PXXXR motif. The PXXXR motif is required but not sufficient for GRB2 binding, whereas an extended motif, PX3RX2KPX7PLD, conserved in Gab proteins as well as the GRB2/Gads-docking protein, Slp-76, efficiently competes binding of GRB2 or Gads adapter proteins. The association of Gab1 with GRB2 is required for Gab1 recruitment to the EGF receptor but not the Met receptor. Hence different mechanisms of Gab1 recruitment may reflect the distinct biological functions for Gab1 downstream from the EGF and Met receptors.
-
Identification of an atypical GRB2 carboxyl-terminal SH3 domain binding site in Gab docking proteins reveals GRB2-dependent and -independent recruitment of Gab1 to receptor tyrosine kinases.
The Journal of biological chemistry, 2000Co-Authors: Lisa S Lock, Monica A. Naujokas, Isabelle Royal, Morag ParkAbstract:Abstract The Gab family of docking proteins is phosphorylated in response to various growth factors and cytokines and serves to recruit multiple signaling proteins. Gab1 acts downstream from the Met-hepatocyte growth factor receptor, and Gab1 overexpression promotes Met-dependent morphogenesis of epithelial cells. Recruitment of Gab1 to Met or epidermal growth factor (EGF) receptors requires a receptor-binding site for the GRB2 adapter protein and a proline-rich domain in Gab1, defined as the Met-binding domain. To determine the requirement for GRB2 in Gab1 recruitment, we have mapped two GRB2 carboxyl-terminal SH3 domain binding sites conserved in Gab1 and related protein Gab2. One corresponds to a canonical GRB2-binding motif, whereas the second, located within the Gab1 Met-binding domain, requires the proline and arginine residues of an atypical PXXXR motif. The PXXXR motif is required but not sufficient for GRB2 binding, whereas an extended motif, PX3RX2KPX7PLD, conserved in Gab proteins as well as the GRB2/Gads-docking protein, Slp-76, efficiently competes binding of GRB2 or Gads adapter proteins. The association of Gab1 with GRB2 is required for Gab1 recruitment to the EGF receptor but not the Met receptor. Hence different mechanisms of Gab1 recruitment may reflect the distinct biological functions for Gab1 downstream from the EGF and Met receptors.
Toshio Hirano - One of the best experts on this subject based on the ideXlab platform.
-
the role of gab family scaffolding adapter proteins in the signal transduction of cytokine and growth factor receptors
Cancer Science, 2003Co-Authors: Keigo Nishida, Toshio HiranoAbstract:The GRB2-associated binder (Gab) family adapter proteins are scaffolding adapter molecules that display sequence similarity with Drosophila DOS (daughter of sevenless), which is a substrate for the protein tyrosine phosphatase Corkscrew. Gab proteins contain a pleckstrin homology (PH) domain and binding sites for SH2 and SH3 domains. A number of studies in multiple systems have implicated Gab in signaling via many different types of receptors, such as growth factor, cytokine, and antigen receptors, and via oncoproteins. Recent studies of Gab1 and Gab2 knockout mice have clearly indicated an important role for Gabs in vivo. Gab1-deficient mice die as embryos with multiple defects in placental, heart, skin, and muscle development. Gab2-deficient mice are viable, but have a defect in the mast cell lineages and in allergic reactions. Given the apparently central role played by Gab signaling via many receptors, delineating the precise mechanism(s) of Gab-mediated signaling is critical to understanding how cytokines, growth factors, and oncoproteins mediate a variety of biological activities: cell growth, differentiation, survival and malignant transformation.
-
gads GRB2 mediated association with lat is critical for the inhibitory function of gab2 in t cells
Molecular and Cellular Biology, 2003Co-Authors: Sho Yamasaki, Toshio Hirano, Keigo Nishida, Machie Sakuma, Donna M. Berry, Jane C Mcglade, Takashi SaitoAbstract:A docking protein, Gab2, is recruited to the vicinity of the TCR complex and inhibits downstream signaling by interaction with negative regulators. However, the molecular mechanisms of this recruitment remain unclear. We have found that Gab2 associates with LAT upon TCR stimulation and that LAT is essential for Gab2 phosphorylation. By analysis of several Gab2 mutants, the c-Met binding domain (MBD) of Gab2 was found to be both necessary and sufficient for stimulation-induced LAT binding. Within the MBD domain, a novel GRB2 SH3 binding motif, PXXXR, is critical for constitutive association with Gads/GRB2. Through this association, Gab2 is recruited to the lipid raft after TCR ligation and exerts inhibitory function. The in vivo significance of this association is illustrated by the fact that T-cell responses are impaired in transgenic mice expressing wild-type Gab2 but not in mice expressing mutant Gab2 lacking the motif. Furthermore, T cells from Gab2-deficient mice showed enhanced proliferative responses upon TCR stimulation. These results indicate that Gads/GRB2-mediated LAT association is critical for the inhibitory function of Gab2, implying that Gab2 induced in stimulated T cells may exert an efficient negative feedback loop by recruiting inhibitory molecules to the lipid raft and competing with SLP-76 through Gads binding.
-
gab family adapter molecules in signal transduction of cytokine and growth factor receptors and t and b cell antigen receptors
Leukemia & Lymphoma, 2000Co-Authors: Masahiko Hibi, Toshio HiranoAbstract:Gab1 and Gab2 (GRB2 associated binder 1 and 2) are scaffolding adapter molecules that display sequence similarity with Drosophila DOS (daughter of sevenless), which is a potential substrate for the protein tyrosine phosphatase, Corkscrew. Both Gab1 and Gab2, like DOS, have a pleckstrin homology domain and potential binding sites for SH2 and SH3 domains. Gab1 and Gab2 are phosphorylated on tyrosine upon the stimulation of various cytokines, growth factors, and antigen receptors, and interact with signaling molecules, such as GRB2, SHP-2, and PI-3 kinase. Overexpression of Gab1 or Gab2 mimics or enhances growth factor or cytokine-mediated biological processes and activates ERK MAP kinase. These data imply that Gab 1 and Gab2 act downstream of a broad range of cytokine and growth factor receptors, as well as T and B antigen receptors, and link these receptors to ERK MAP kinase and biological actions.
-
gab family adapter molecules in signal transduction of cytokine and growth factor receptors and t and b cell antigen receptors
Leukemia & Lymphoma, 2000Co-Authors: Masahiko Hibi, Toshio HiranoAbstract:Gab1 and Gab2 (GRB2 associated binder 1 and 2) are scaffolding adapter molecules that display sequence similarity with Drosophila DOS (daughter of sevenless), which is a potential substrate for the protein tyrosine phosphatase, Corkscrew. Both Gab1 and Gab2, like DOS, have a pleckstrin homology domain and potential binding sites for SH2 and SH3 domains. Gab1 and Gab2 are phosphorylated on tyrosine upon the stimulation of various cytokines, growth factors, and antigen receptors, and interact with signaling molecules, such as GRB2, SHP-2, and PI-3 kinase. Overexpression of Gab1 or Gab2 mimics or enhances growth factor or cytokine-mediated biological processes and activates ERK MAP kinase. These data imply that Gab 1 and Gab2 act downstream of a broad range of cytokine and growth factor receptors, as well as T and B antigen receptors, and link these receptors to ERK MAP kinase and biological actions.
Tilman Brummer - One of the best experts on this subject based on the ideXlab platform.
-
abstract 5093 bcr abl leads to mast cell differentiation and promotes degranulation of cells derived from a chronic myeloid leukemia mouse model in a gab2 dependent manner
Cancer Research, 2018Co-Authors: Julia Ellermann, Julia Huber, Robert Zeiser, Konrad Aumann, Martin Köhler, Steffen Koschmieder, Tilman Brummer, Sebastian HalbachAbstract:Chronic myeloid leukemia (CML) is driven by the fusion kinase Bcr-Abl, caused by a chromosomal translocation between chromosome 9 and 22. This tyrosine kinase organizes its own signaling network with various proteins, especially the docking protein Gab2. By being recruited to Bcr-Abl via GRB2, Gab2 plays a critical role in this network. We recently applied a transgenic approach to investigate the role of Gab2 in Bcr-Abl driven disease. Using Gab2 knock-out mice, we analyzed the in vivo role of Gab2 in a chronic-phase CML mouse model in which a tetracycline regulated Bcr-Abl transgene is expressed in hematopoietic stem cells in their native microenvironment. We demonstrated that Gab2 deficiency impairs disease development in a steady-state in vivo setting. In the course of this work, we also identified an abnormal number of mast cells infiltrating the kidneys of Bcr-Abl expressing Gab2 proficient mice, a phenotype associated with an inflammatory urothelium and hydronephrosis. Interestingly, this phenotype was completely absent in Gab2 deficient mice. Therefore, we aimed to analyze the role of mast cells in the CML mouse model in more detail. First, we performed bone marrow transplantations, using Bcr-Abl positive donor mice and C57/BL6N mice as recipients. Also in these mice, we observed high mast cell counts in the bone marrow and developed hydronephrosis in some cases, which demonstrates that these alterations were induced by cell-autonomous properties of the Bcr-Abl positive donor cells. Next, we were interested whether these cells are Bcr-Abl transformed mast cell precursors or reactive mast cells resulting from secondary effects of the leukemic disease. Therefore, we isolated bone marrow cells from Bcr-Abl transgenic mice and analyzed them for Bcr-Abl activity and mast cell properties. Strikingly, Bcr-Abl positive progenitors differentiated into mast cells under cytokine free conditions. Next, we assessed mast cell functionality of these cells by degranulation assays measuring β-hexosaminidase activity and cytokine release. Importantly, Bcr-Abl positive cells were more sensitive towards antigen stimulation and displayed a stronger degranulation und higher levels of secreted cytokines compared to Bcr-Abl negative controls. This suggests that Bcr-Abl positive mast cells could be responsible for the inflammatory urothelium and the hydronephrosis which we observed in our CML mouse model. In line with our previous results, Gab2 deficient cells from Bcr-Abl transgenic mice showed no elevated degranulation. In summary, we could show that Bcr-Abl can drive the expansion of mast cells. In addition, Bcr-Abl leads to stronger degranulation in a Gab2 dependent manner. This data and our previous work on Gab2 invite for the further evaluation of Gab2 as a biomarker and as a valuable target in the treatment of CML and, possibly, systemic mastocytosis. Citation Format: Julia Ellermann, Franziska Maria Uhl, Martin Kohler, Julia Huber, Robert Zeiser, Steffen Koschmieder, Konrad Aumann, Tilman Brummer, Sebastian Halbach. Bcr-Abl leads to mast cell differentiation and promotes degranulation of cells derived from a chronic myeloid leukemia mouse model in a Gab2 dependent manner [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5093.
-
BRAF inhibition upregulates a variety of receptor tyrosine kinases and their downstream effector Gab2 in colorectal cancer cell lines
Oncogene, 2018Co-Authors: Ricarda Herr, Sebastian Halbach, Miriam Heizmann, Hauke Busch, Melanie Boerries, Tilman BrummerAbstract:BRAF mutations occur in ~10% of colorectal cancer (CRC) and are associated with poor prognosis. Inhibitors selective for the BRAF^V600E oncoprotein, the most common BRAF mutant, elicit only poor response rates in BRAF-mutant CRC as single agents. This unresponsiveness was mechanistically attributed to the loss of negative feedbacks on the epidermal growth factor receptor (EGFR) and initiated clinical trials that combine BRAF (and MEK) inhibitors, either singly or in combination, with the anti-EGFR antibodies cetuximab or panitumumab. First results of these combinatorial studies demonstrated improved efficacy, however, the response rates still were heterogeneous. Here, we show that BRAF inhibition leads to the upregulation of a variety of receptor tyrosine kinases (RTKs) in CRC cell lines, including not only the EGFR, but also human epidermal growth factor receptor (HER) 2 and HER3. Importantly, combination of the BRAF inhibitors (BRAFi) vemurafenib (PLX4032), dabrafenib, or encorafenib with inhibitors dually targeting the EGFR and HER2 (such as lapatinib, canertinib, and afatinib) significantly reduced the metabolic activity and proliferative potential of CRC cells. This re-sensitization was also observed after genetic depletion of HER2 or HER3. Interestingly, BRAF inhibitors did not only upregulate RTKs, but also increased the abundance of the GRB2-associated binders (Gab) 1 and Gab2, two important amplifiers of RTK signaling. An allele-specific shRNA-mediated knockdown of BRAF^V600E revealed that Gab2 upregulation was directly dependent on the loss of the oncoprotein and was not caused by an “off-target” effect of these kinase inhibitors. Furthermore, Gab2 and Gab2-mediated Shp2 signaling were shown to be functionally important in BRAFi resistance. These findings highlight potential new escape mechanisms to these targeted therapies and indicate that a broad suppression of RTK signaling might be beneficial and should be taken into account in future research addressing targeted therapy in BRAF -mutant CRC.
-
The docking protein and proto-oncogene product Gab2 is regulated via a novel negative feedback mechanism mediated by 14-3-3 binding
Cell Communication and Signaling, 2009Co-Authors: Tilman Brummer, Ruth J. Lyons, Daniel Schramek, Mark Larance, Mt Herrera Abreu, Paul Timpson, Ch Emmerich, Edg Fleuren, Gillian M Lehrbach, Michael GuilhausAbstract:In vertebrates, GRB2-associated binder (Gab)1–3 constitute a family of conserved docking proteins. Gab2 is tyrosine-phosphorylated upon activation of a variety of growth factor, hormone, antigen, cytokine and cell matrix receptors, leading to the recruitment of specific src homology (SH)2 domain-containing effectors, which include the p85 subunit of phosphatidylinositol (PI)3-kinase and the protein tyrosine phosphatase Shp2. These Gab2 effectors potentiate the activation of the PI3-K/AKT and Ras/ERK pathways, respectively. Studies using gene knock-out mice indicate that Gab2 is required for normal mast cell-mediated allergic responses and osteoclast differentiation, and in combination with Gab1, for cardiac function. In addition, Gab2 signals downstream of several oncogenic tyrosine kinases, and are overexpressed in breast cancer, and promotes erbB2-induced mammary tumourigenesis. Therefore, it is critical to define how Gab2 signalling is regulated in normal and pathological states. One critical event in Gab2 signalling is its interaction with the adaptor protein GRB2, which promotes its association with specific receptors and thereby sustains its tyrosine phosphorylation dependent recruitment of the aforementioned effectors. However, the molecular mechanisms that attenuate or limit Gab2 signals have remained unclear. In the presented study, we have addressed Gab2 regulation using an integrated approach that combines a proteomics-based definition of the Gab2 'phosphomap" with bioinformatics, biochemistry and cell biology. Here we report the discovery of 21 novel phosphorylation sites on human Gab2. Furthermore, we demonstrate that growth factor-induced and PI3K-dependent phosphorylation of Gab2 on two of these novel residues, S210 and T391, leads to recruitment of 14-3-3 proteins. These events mediate negative feedback regulation, since a Gab2 mutant that cannot be phosphorylated on these sites exhibits sustained receptor association and signalling, and promotes cell proliferation and transformation. Importantly, site-specific introduction of constitutive 14-3-3 binding sites into Gab2 renders it refractory to receptor activation, demonstrating that site-selective binding of 14-3-3 proteins is sufficient to terminate Gab2 signalling. Furthermore, this is associated with drastically reduced recruitment of GRB2 to the Gab2 signalosome suggesting a competition between 14-3-3 and GRB2 for Gab2 binding. These findings lead to a model where signal attenuation occurs, because 14-3-3 promotes dissociation of Gab2 from GRB2, and thereby uncouples Gab2 from the receptor complex. This represents a novel regulatory mechanism with implications for diverse tyrosine kinase signalling systems in various cell types.
-
phosphorylation dependent binding of 14 3 3 terminates signalling by the gab2 docking protein
The EMBO Journal, 2008Co-Authors: Tilman Brummer, Ruth J. Lyons, Mark Larance, Paul Timpson, Gillian M Lehrbach, Maria Teresa Herrera Abreu, Christoph H Emmerich, Emmy D G Fleuren, Daniel SchramekAbstract:GRB2-associated binder (Gab)2 functions downstream of a variety of receptor and cytoplasmic tyrosine kinases as a docking platform for specific signal transducers and performs important functions in both normal physiology and oncogenesis. Gab2 signalling is promoted by its association with specific receptors through the adaptor GRB2. However, the molecular mechanisms that attenuate Gab2 signals have remained unclear. We now demonstrate that growth factor-induced phosphorylation of Gab2 on two residues, S210 and T391, leads to recruitment of 14-3-3 proteins. Together, these events mediate negative-feedback regulation, as Gab2S210A/T391A exhibits sustained receptor association and signalling and promotes cell proliferation and transformation. Importantly, introduction of constitutive 14-3-3-binding sites into Gab2 renders it refractory to receptor activation, demonstrating that site-selective binding of 14-3-3 proteins is sufficient to terminate Gab2 signalling. Furthermore, this is associated with reduced binding of GRB2. This leads to a model where signal attenuation occurs because 14-3-3 promotes dissociation of Gab2 from GRB2, and thereby uncouples Gab2 from the receptor complex. This represents a novel regulatory mechanism with implications for diverse tyrosine kinase signalling systems.
-
Increased Proliferation and Altered Growth Factor Dependence of Human Mammary Epithelial Cells Overexpressing the Gab2 Docking Protein
The Journal of biological chemistry, 2005Co-Authors: Tilman Brummer, Daniel Schramek, Vanessa M. Hayes, Haley L. Bennett, C. Elizabeth Caldon, Elizabeth A. Musgrove, Roger J DalyAbstract:Abstract The docking protein Gab2 is a proto-oncogene product that is overexpressed in primary breast cancers. To determine the functional consequences of Gab2 overexpression, we utilized the immortalized human mammary epithelial cell line MCF-10A. In monolayer culture, expression of Gab2 at levels comparable with those detected in human breast cancer cells accelerated epidermal growth factor (EGF)-induced cell cycle progression and was associated with increased basal Stat5 tyrosine phosphorylation and enhanced and/or more sustained EGF-induced Erk and Akt activation. Three-dimensional Matrigel culture of MCF-10A cells resulted in the formation of polarized, growth-arrested acini with hollow lumina. Under these conditions, Gab2 increased cell proliferation during morphogenesis, leading to significantly larger acini, an effect dependent on Gab2 binding to GRB2 and Shp2 and enhanced by recruitment of the p85 subunit of phosphatidylinositol 3-kinase. Pharmacological inhibition of MEK revealed that, in addition to direct activation of phosphatidylinositol 3-kinase, increased Erk signaling also contributed to Gab2-mediated enhancement of acinar size. In addition, Gab2 overcame the proliferative suppression that normally occurs in late stage cultures and conferred independence of the morphogenetic program from exogenous EGF. Finally, higher levels of Gab2 expression led to the formation of large disorganized structures with defective luminal clearance. These findings support a role for Gab2 in mammary tumorigenesis.
Lisa S Lock - One of the best experts on this subject based on the ideXlab platform.
-
Distinct Recruitment and Function of Gab1 and Gab2 in Met Receptor-mediated Epithelial Morphogenesis
Molecular biology of the cell, 2002Co-Authors: Lisa S Lock, Monica A. Naujokas, Christiane R. Maroun, Morag ParkAbstract:The Gab family of docking proteins (Gab1 and Gab2) are phosphorylated in response to various cytokines and growth factors. Gab1 acts to diversify the signal downstream from the Met receptor tyrosine kinase through the recruitment of multiple signaling proteins, and is essential for epithelial morphogenesis. To determine whether Gab1 and Gab2 are functionally redundant, we have examined the role of Gab2 in epithelial cells. Both Gab1 and Gab2 are expressed in epithelial cells and localize to cell-cell junctions. However, whereas overexpression of Gab1 promotes a morphogenic response, the overexpression of Gab2 fails to induce this response. We show that Gab2 recruitment to the Met receptor is dependent on the GRB2 adapter protein. In contrast, Gab1 recruitment to Met is both GRB2 dependent and GRB2 independent. The latter requires a novel amino acid sequence present in the Met-binding domain of Gab1 but not Gab2. Mutation of these residues in Gab1 impairs both association with the Met receptor and the ability of Gab1 to promote a morphogenic response, whereas their insertion into Gab2 increases Gab2 association with Met, but does not confer on Gab2 the ability to promote epithelial morphogenesis. We propose that the GRB2-independent recruitment of Gab proteins to Met is necessary but not sufficient to promote epithelial morphogenesis.
-
identification of an atypical GRB2 carboxyl terminal sh3 domain binding site in gab docking proteins reveals GRB2 dependent and independent recruitment of gab1 to receptor tyrosine kinases
Journal of Biological Chemistry, 2000Co-Authors: Lisa S Lock, Monica A. Naujokas, Isabelle Royal, Morag ParkAbstract:Abstract The Gab family of docking proteins is phosphorylated in response to various growth factors and cytokines and serves to recruit multiple signaling proteins. Gab1 acts downstream from the Met-hepatocyte growth factor receptor, and Gab1 overexpression promotes Met-dependent morphogenesis of epithelial cells. Recruitment of Gab1 to Met or epidermal growth factor (EGF) receptors requires a receptor-binding site for the GRB2 adapter protein and a proline-rich domain in Gab1, defined as the Met-binding domain. To determine the requirement for GRB2 in Gab1 recruitment, we have mapped two GRB2 carboxyl-terminal SH3 domain binding sites conserved in Gab1 and related protein Gab2. One corresponds to a canonical GRB2-binding motif, whereas the second, located within the Gab1 Met-binding domain, requires the proline and arginine residues of an atypical PXXXR motif. The PXXXR motif is required but not sufficient for GRB2 binding, whereas an extended motif, PX3RX2KPX7PLD, conserved in Gab proteins as well as the GRB2/Gads-docking protein, Slp-76, efficiently competes binding of GRB2 or Gads adapter proteins. The association of Gab1 with GRB2 is required for Gab1 recruitment to the EGF receptor but not the Met receptor. Hence different mechanisms of Gab1 recruitment may reflect the distinct biological functions for Gab1 downstream from the EGF and Met receptors.
-
Identification of an atypical GRB2 carboxyl-terminal SH3 domain binding site in Gab docking proteins reveals GRB2-dependent and -independent recruitment of Gab1 to receptor tyrosine kinases.
The Journal of biological chemistry, 2000Co-Authors: Lisa S Lock, Monica A. Naujokas, Isabelle Royal, Morag ParkAbstract:Abstract The Gab family of docking proteins is phosphorylated in response to various growth factors and cytokines and serves to recruit multiple signaling proteins. Gab1 acts downstream from the Met-hepatocyte growth factor receptor, and Gab1 overexpression promotes Met-dependent morphogenesis of epithelial cells. Recruitment of Gab1 to Met or epidermal growth factor (EGF) receptors requires a receptor-binding site for the GRB2 adapter protein and a proline-rich domain in Gab1, defined as the Met-binding domain. To determine the requirement for GRB2 in Gab1 recruitment, we have mapped two GRB2 carboxyl-terminal SH3 domain binding sites conserved in Gab1 and related protein Gab2. One corresponds to a canonical GRB2-binding motif, whereas the second, located within the Gab1 Met-binding domain, requires the proline and arginine residues of an atypical PXXXR motif. The PXXXR motif is required but not sufficient for GRB2 binding, whereas an extended motif, PX3RX2KPX7PLD, conserved in Gab proteins as well as the GRB2/Gads-docking protein, Slp-76, efficiently competes binding of GRB2 or Gads adapter proteins. The association of Gab1 with GRB2 is required for Gab1 recruitment to the EGF receptor but not the Met receptor. Hence different mechanisms of Gab1 recruitment may reflect the distinct biological functions for Gab1 downstream from the EGF and Met receptors.
Isabelle Royal - One of the best experts on this subject based on the ideXlab platform.
-
Non-redundant roles of the Gab1 and Gab2 scaffolding adapters in VEGF-mediated signalling, migration, and survival of endothelial cells.
Cellular signalling, 2009Co-Authors: Christine Caron, Kathleen Spring, Mélanie Laramée, Catherine Chabot, Monikca Cloutier, Isabelle RoyalAbstract:Abstract Gab1 was previously described as a positive modulator of Akt, Src, ERK1/2, endothelial cell migration, and capillary formation in response to vascular endothelial growth factor (VEGF). However, its involvement in endothelial cell survival, as well as the potential contribution of the other family member Gab2 to signalling and biological responses remained unknown. Here, we show that Gab2 is tyrosine phosphorylated in a GRB2-dependent manner downstream of activated VEGF receptor-2 (VEGFR2), and that it associates with signalling proteins including PI3K and SHP2, but apparently not with the receptor. Similarly to Gab1, over-expression of Gab2 induces endothelial cell migration in response to VEGF, whereas its depletion using siRNAs results in its reduction. Importantly, depletion of both Gab1 and Gab2 leads to an even greater inhibition of VEGF-induced cell migration. However, contrary to what has been reported for Gab1, the silencing of Gab2 results in increased Src, Akt and ERK1/2 activation, slightly reduced p38 phosphorylation, and up-regulation of Gab1 protein levels. Accordingly, re-expression of Gab2 in Gab2−/− fibroblasts leads to opposite results, suggesting that the modulation of both Gab2 and Gab1 expression in these conditions might contribute to the impaired signalling observed. Consistent with their opposite roles on Akt, the depletion of Gab1, but not of Gab2, results in reduced FOXO1 phosphorylation and VEGF-mediated endothelial cell survival. Mutation of VEGFR2 Y801 and Y1214, which abrogates the phosphorylation of Gab1, also correlates with inhibition of Akt. Altogether, these results underscore the non-redundant and essential roles of Gab1 and Gab2 in endothelial cells, and suggest major contributions of these proteins during in vivo angiogenesis.
-
identification of an atypical GRB2 carboxyl terminal sh3 domain binding site in gab docking proteins reveals GRB2 dependent and independent recruitment of gab1 to receptor tyrosine kinases
Journal of Biological Chemistry, 2000Co-Authors: Lisa S Lock, Monica A. Naujokas, Isabelle Royal, Morag ParkAbstract:Abstract The Gab family of docking proteins is phosphorylated in response to various growth factors and cytokines and serves to recruit multiple signaling proteins. Gab1 acts downstream from the Met-hepatocyte growth factor receptor, and Gab1 overexpression promotes Met-dependent morphogenesis of epithelial cells. Recruitment of Gab1 to Met or epidermal growth factor (EGF) receptors requires a receptor-binding site for the GRB2 adapter protein and a proline-rich domain in Gab1, defined as the Met-binding domain. To determine the requirement for GRB2 in Gab1 recruitment, we have mapped two GRB2 carboxyl-terminal SH3 domain binding sites conserved in Gab1 and related protein Gab2. One corresponds to a canonical GRB2-binding motif, whereas the second, located within the Gab1 Met-binding domain, requires the proline and arginine residues of an atypical PXXXR motif. The PXXXR motif is required but not sufficient for GRB2 binding, whereas an extended motif, PX3RX2KPX7PLD, conserved in Gab proteins as well as the GRB2/Gads-docking protein, Slp-76, efficiently competes binding of GRB2 or Gads adapter proteins. The association of Gab1 with GRB2 is required for Gab1 recruitment to the EGF receptor but not the Met receptor. Hence different mechanisms of Gab1 recruitment may reflect the distinct biological functions for Gab1 downstream from the EGF and Met receptors.
-
Identification of an atypical GRB2 carboxyl-terminal SH3 domain binding site in Gab docking proteins reveals GRB2-dependent and -independent recruitment of Gab1 to receptor tyrosine kinases.
The Journal of biological chemistry, 2000Co-Authors: Lisa S Lock, Monica A. Naujokas, Isabelle Royal, Morag ParkAbstract:Abstract The Gab family of docking proteins is phosphorylated in response to various growth factors and cytokines and serves to recruit multiple signaling proteins. Gab1 acts downstream from the Met-hepatocyte growth factor receptor, and Gab1 overexpression promotes Met-dependent morphogenesis of epithelial cells. Recruitment of Gab1 to Met or epidermal growth factor (EGF) receptors requires a receptor-binding site for the GRB2 adapter protein and a proline-rich domain in Gab1, defined as the Met-binding domain. To determine the requirement for GRB2 in Gab1 recruitment, we have mapped two GRB2 carboxyl-terminal SH3 domain binding sites conserved in Gab1 and related protein Gab2. One corresponds to a canonical GRB2-binding motif, whereas the second, located within the Gab1 Met-binding domain, requires the proline and arginine residues of an atypical PXXXR motif. The PXXXR motif is required but not sufficient for GRB2 binding, whereas an extended motif, PX3RX2KPX7PLD, conserved in Gab proteins as well as the GRB2/Gads-docking protein, Slp-76, efficiently competes binding of GRB2 or Gads adapter proteins. The association of Gab1 with GRB2 is required for Gab1 recruitment to the EGF receptor but not the Met receptor. Hence different mechanisms of Gab1 recruitment may reflect the distinct biological functions for Gab1 downstream from the EGF and Met receptors.
