Disease relevance of Grb2

• Mitogenic G protein-coupled receptors, such as those for lysophosphatidic acid (LPA) and thrombin, activate the Ras/MAP kinase pathway via pertussis toxin (PTX)-sensitive Gi, tyrosine kinase activity and recruitment of Grb2, which targets guanine nucleotide exchange activity to Ras [1].
• Therefore, we studied Raf-1 activity, its potential activators protein kinase C (PKC) and Ras, and expression and associations of adapter proteins Shc, Grb2, and Sos during experimental gastric ulcer healing [2].
• Different interactions of Grb2/Ash molecule with the NGF and EGF receptors in rat pheochromocytoma PC12 cells [3].
• In the present study, we investigated the adrenergic control of insulin-induced Shc phosphorylation and Shc-Grb2 association, and the modulating effect of streptozotocin-induced diabetes mellitus on Shc phosphorylation and Shc/Grb2 association [4].
• OBJECTIVE: To define the nature and mechanisms of neuromuscular effects of toxic principles in bark of Southern Prickly Ash tree (Zanthoxylum clava-herculis) that might contribute to its clinical toxicity in cattle [5].

High impact information on Grb2

• The Grb2 binding domain of mSos1 is not required for downstream signal transduction [6].
• These data argue against a role for Grb2 in the direct recruitment of Sos proteins to the plasma membrane and suggest that Grb2 may function to overcome negative regulation of Sos by its C terminus [6].
• We propose that Pyk2 acts with Src to link Gi- and Gq-coupled receptors with Grb2 and Sos to activate the MAP kinase signalling pathway in PC12 cells [7].
• The carboxy terminus, which is of different lengths in adult and developing neurons owing to the alternative use of two termination sites, is proline-rich, consistent with the reported interaction of synaptojanin with the SH3 domains of Grb2 (refs 1, 2) [8].
• LPA- or bradykinin-induced MAP kinase activation was also inhibited by overexpression of dominant interfering mutants of Grb2 and Sos [7].

Biological context of Grb2

• Thus, the kinetics of Grb2 association with IRS-1 and She corresponded closely to the time course of tyrosine phosphorylation of IRS-1 and Shc, respectively [9].
• In this study, we sought to determine the extent to which c-Src mediates vascular smooth muscle cell proliferation through the Shc/Grb2/ERK2 signaling pathway [10].
• Gi-mediated activation of the Ras/MAP kinase pathway involves a 100 kDa tyrosine-phosphorylated Grb2 SH3 binding protein, but not Src nor Shc [1].
• It also contains a putative binding site for Grb2 (YINID) [11].
• Yet overexpression or reduced expression of Grb2 in the mutant before and after complementation with crkII have little effect on its phenotype [12].

Anatomical context of Grb2

• In situ hybridization analysis revealed a more than 2-fold induction of Grb2 mRNA in the hippocampal dentate gyrus as well as superficial and deep layers of the cortex with both acute and chronic ECS [13].
• CONCLUSIONS: Long-term ethanol feeding suppressed EGF-induced receptor autophosphorylation in rat hepatocytes with differential inhibition of downstream signaling processes mediated by PLC gamma, Shc, and Grb2 [14].
• To test this hypothesis dominant-negative mutants of Grb2 with deletions of the SH3 domains were introduced into Tpr-Met transformed fibroblasts [15].
• Here we show that v-Crk complexes with both the tyrosine-phosphorylated EGF receptor and the Ras guanine nucleotide exchange factor SOS in PC12 cells and is involved in an pathway analogous to that of Grb2 [16].
• Antigen receptors on T- and B-cells activate Ras through a signaling pathway that results in the tyrosine phosphorylation of Shc and the formation of a complex of Shc with the Grb2 adaptor protein [17].

Associations of Grb2 with chemical compounds

• The SH2-containing protein Grb2 also possesses adjacent SH3 domains, which bind the Ras guanine nucleotide exchange factor Sos [18].
• The critical role of c-Src and the Shc/Grb2/ERK2 signaling pathway in angiotensin II-dependent VSMC proliferation [10].
• In the present study, we found Ang II rapidly induced the tyrosine phosphorylation of the epidermal growth factor (EGF) receptor and its association with Shc and Grb2 [19].
• Cholesterol-depleted caveolae had a reduced amount of several key protein components of the MAP kinase complex, including Ras, Grb2, Erk2, and Src [20].
• The roles of these substrates as signaling molecules for GH were further demonstrated by the finding that GH stimulated the association of IRS-1/2 with phosphatidylinositol 3-kinase, Grb2, and phosphotyrosine phosphatase and of Shc with Grb2 [21].

Physical interactions of Grb2

• Although phosphorylated EGFR can bind to both Shc and Grb2, the predominant linkage was observed between EGFR and Shc [22].
• We have shown that, heat shock activates Raf-1 kinase and causes an increase in phosphotyrosine content of the 52 kDa Shc protein accompanied by an increment in the amount of coimmunoprecipitated Grb2 [23].
• Downstream signal transduction events including Shc tyrosine phosphorylation, Shc/Grb2 complex formation and MAP kinase activation were similar in response to EGF and TGF alpha, thus indicating a dissociation between potency for receptor activation versus signal propagation [24].
• In addition, induced tyrosine phosphorylation of FGFR1 by hydrogen peroxide resulted in complex formation with Grb2 [25].
• We recently detected a 100 kDa protein (p100) that binds to the C-terminal SH3 domain of growth-factor-receptor-bound protein 2 (Grb2) and becomes tyrosine phosphorylated in a PTX-sensitive manner in LPA-treated Rat-1 cells [Kranenburg, Verlaan, Hordijk and Moolenaar (1997) EMBO J. 16, 3097-3105] [26].

Enzymatic interactions of Grb2

• We report here that Grb2 also interacts with tyrosine-phosphorylated IRS-1 in response to gastrin [27].
• Instead, we detect a 100 kDa tyrosine-phosphorylated protein (p100) that binds to the C-terminal SH3 domain of Grb2 in a strictly Gi- and agonist-dependent manner [1].
• Both TRH and EGF induced the association of tyrosine phosphorylated Shc proteins with a fusion protein containing SH2 and SH3 domains of Grb2, another important component in ras activation [28].

Regulatory relationships of Grb2

• In addition, PI 3-kinase was activated by insulin treatment in this cell line and Grb2, Ras-GAP, and MAP kinase were coprecipitated with Ras from both insulin-treated and NGF-treated cells [29].
• Surprisingly, the Grb2 mutants blocked activation of the JNK/SAPK but not MAP kinase activity induced by the Tpr-Met oncoprotein [15].
• Both NGF and EGF induced rapid tyrosine phosphorylation of Shc and its association with both the receptors and with Grb2/Ash [3].
• Gastrin induces tyrosine phosphorylation of Shc proteins and their association with the Grb2/Sos complex [30].

Other interactions of Grb2

• Importantly, 3-13-fold more Grb2 was associated with Shc than with IRS-1 [9].
• Our results demonstrate that gastric ulceration significantly increases Raf-1 kinase activity, Grb2 and Ras protein, and Shc-Grb2 and Grb2-Sos complex levels [2].
• We show that phosphorylation of tyrosine 490, but not 785, of Trk is essential for activation of both Ras and PI 3-kinase in vivo, correlating with tyrosine phosphorylation of Shc and binding of Shc to the adaptor Grb2 and the Ras exchange factor Sos [31].
• Moreover, insulin/IGF-I markedly increased the amount of Grb-2-associated SHC proteins by the same extent [32].
• However, IRS-2-associated Grb-2 phosphorylation was barely detected [32].

Analytical, diagnostic and therapeutic context of Grb2

• Microinjection of an anti-Grb2/Ash antibody, but not control IgG, inhibited the insulin-induced actin reorganization, whereas the TPA- and 8-bromo-cAMP-induced morphological changes were not inhibited by microinjection of the anti-Grb2/Ash antibody [33].
• SH3A competes with the SH3 domains of Grb2 in binding to mSos1, and the intersectin-mSos1 complex can be separated from Grb2 by sucrose gradient centrifugation [34].
• The embryonically expressed ShcA proteins were functionally active, since p52(ShcA) became phosphorylated on tyrosine and associated with Grb2 following intraventricular injection of epidermal growth factor in the embryonic brain [35].
• Shc is constitutively tyrosine phosphorylated in unstimulated cells and Fc epsilon R1 ligation induces no changes in its phosphorylation or binding to Grb2 [36].
• The stretch rapidly (within 2 min) induced association of tyrosine-phosphorylated EGFR with adaptor proteins (Shc/Grb2) as revealed by coprecipitation with glutathione-S-transferase-Grb2 fusion protein coupled with immunoblotting with anti-phosphotyrosine, anti-EGFR, and anti-Shc antibodies [37].

References