ArticleLiterature Review

The GRB2/Sem-5 adaptor protein

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Abstract

GRB2/Sem-5 is a 25-kDa adaptor protein which contains a central Src homology type 2 (SH2) domain flanked by two Src homology type 3 (SH3) domains. GRB2/Sem-5 was first identified due to the essential role of the sem-5 gene product in the vulval induction pathway in Caenorhabditis elegans. The SH2 domain of GRB2/Sem-5 binds to a number of tyrosine phosphorylated proteins, most notably the epidermal growth factor receptor, the insulin receptor substrate IRS-1 and another putative adaptor protein, Shc. The SH3 domains bind to Sos, a guanine nucleotide exchange factor for Ras proteins. GRB2/Sem-5 brings together Sos and tyrosine phosphoproteins into a complex and thereby may regulate the nucleotide exchange rate of Ras and hence its activation state.

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... Once phosphorylated on Tyr925, FAK serves as a docking site for p85 regulatory subunit of PI3K (35)(36)(37)(38) through recruitment of growth factor receptor-bound protein 2 (Grb2) (36), which is known to be involved in Raf/MEK/ERK signalling (35,36). We then focussed on the activation of PI3k/Akt and MAPK/ERK in response to exogenous addition of PN at various time points. ...
... Once phosphorylated on Tyr925, FAK serves as a docking site for p85 regulatory subunit of PI3K (35)(36)(37)(38) through recruitment of growth factor receptor-bound protein 2 (Grb2) (36), which is known to be involved in Raf/MEK/ERK signalling (35,36). We then focussed on the activation of PI3k/Akt and MAPK/ERK in response to exogenous addition of PN at various time points. ...
... Once phosphorylated on Tyr925, FAK serves as a docking site for p85 regulatory subunit of PI3K (35)(36)(37)(38) through recruitment of growth factor receptor-bound protein 2 (Grb2) (36), which is known to be involved in Raf/MEK/ERK signalling (35,36). We then focussed on the activation of PI3k/Akt and MAPK/ERK in response to exogenous addition of PN at various time points. ...
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Periostin (PN), a novel fasciclin-related, matricellular protein, has been implicated in cardiac development and postnatal remodeling, but the mechanism remains unknown. We examined the role of PN in mediating intracellular kinase activation for atrioventricular valve morphogenesis using well defined explant cultures, gene transfection systems and Western blotting. The results show that valve progenitor (cushion) cells secrete PN into the extracellular matrix (ECM), where it can bind to integrins and activate integrin/FAK signaling pathways and downstream kinases, PI3K/Akt and Erk. Functional assays with prevalvular progenitor cells showed that activating these signaling pathways promoted adhesion, migration and anti-apoptosis. Through activation of PI3K/Erk, PN directly enhanced collagen expression. Comparing PN null to WT mice also revealed that expression of hyaluronan (HA), and activation of hyaluronan-synthase-2 (Has2) is also enhanced upon PN/integrin/focal-adhesion-kinase (FAK)-mediated activation of PI3K, and/or Erk; an effect confirmed by the reduction of HA synthase 2 in PN null mice. We also identified in valve progenitor cells a potential autocrine signaling feedback loop between PN and HA through PI3K, and/or Erk. Finally, in a 3D assay to simulate normal valve maturation in vitro, PN promoted collagen compaction in a kinase dependent fashion. In summary, this study provides the first, direct evidence that PN can act to stimulate a valvulogenic signaling pathway.
... Once phosphorylated on Tyr925, FAK is predicted to recruit growth factor receptor-bound protein 2 (Grb2), an adaptor protein known to be involved in Ras/MAPK signaling [29]. In the canonical Ras/MAPK signaling pathway, Grb2 binds phosphotyrosine motifs via the Src homology 2 (SH2) domain, while two flanking Src homology 3 (SH3) domains bind Son of Sevenless (SOS), the guanine nucleotide exchange factor (GEF) for small GTPase Ras which acts upstream of the Raf/MEK/ERK cascade [30]. ...
... The FGF and Ephrin pathways both control, in opposite ways, the activation of the Ras protein at the top of the ERK signaling pathway. Binding of FGF to its receptor leads to the activation by recruitment to the membrane of the SOS Ras-GEF [Downward, 1994]. Binding of EphrinA to its Eph receptor activates p120RasGAP [Haupaix et al., 2013] (Figure S30C). ...
... The q value and P value for the MutSigCV calculation are shown for each gene as dark and light gray bars, respectively (right panel). The histogram at the left and percentages are as in Fig. 2. Patients are sorted as in Fig. 1b (SH2) domain and transduces growth signals through the RAS-MAPK pathway [7]. We detected six missense and one nonsense mutation of GRB2 in six patients (Fig. 5a, Supplementary Fig. 9). ...
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Primary central nervous system lymphoma (PCNSL) is a rare malignancy confined to the central nervous system (CNS), and majority of PCNSL is pathologically classified as diffuse large B-cell lymphoma (DLBCL). We have now performed whole-exome sequencing for 41 tumor tissues of DLBCL-type PCNSL and paired normal specimens and also RNA-sequencing for 30 tumors, revealing a very high frequency of nonsynonymous somatic mutations in PIM1 (100 %), BTG2 (92.7 %), and MYD88 (85.4 %). Many genes in the NF-κB pathway are concurrently mutated within the same tumors. Further, focal deletion or somatic mutations in the HLA genes are associated with poor prognosis. Copy number amplification and overexpression of genes at chromosome 7q35 were both found to predict short progression-free survival as well. Oncogenic mutations in GRB2 were also detected, the effects of which in cultured cells were attenuated by inhibitors of the downstream kinases MAP2K1 and MAP2K2. Individuals with tumors positive for MYD88 mutations also harbored the same mutations at a low frequency in peripheral blood mononuclear cells, suggesting that MYD88 mutation-positive precancerous cells originate outside of the CNS and develop into lymphoma after additional genetic hits that confer adaptation to the CNS environment.
... A good example of pathway structure retention despite component divergence is the receptor tyrosine kinase-ras signal transduction pathway. The pathway is so well conserved that its components are interchangeable between mice, nematodes, and fruit flies (Downward 1994;Gilbert et al. 1996). All of these examples show discontinuous events in development that can be co-opted to create novel morphological structures. ...
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The introduction of novel phenotypic structures is one of the most significant aspects of organismal evolution. Yet the concept of evolutionary novelty is used with drastically different connotations in various fields of research, and debate exists about whether novelties represent features that are distinct from standard forms of phenotypic variation. This article contrasts four separate uses for novelty in genetics, population genetics, morphology, and behavioral science, before establishing how novelties are used in evolutionary developmental biology (EvoDevo). In particular, it is detailed how an EvoDevo-specific research approach to novelty produces insight distinct from other fields, gives the concept explanatory power with predictive capacities, and brings new consequences to evolutionary theory. This includes the outlining of research strategies that draw attention to productive areas of inquiry, such as threshold dynamics in development. It is argued that an EvoDevo-based approach to novelty is inherently mechanistic, treats the phenotype as an agent with generative potential, and prompts a distinction between continuous and discontinuous variation in evolutionary theory.
... It has been shown that the N-terminal SH3 (nSH3) domain of Grb2 binds a proline-rich region present in the guanine nucleotide releasing factor, son of sevenless (Sos). The Grb2/Sos complex is an important component of a highly conserved pathway that transmits signals from the receptor to the nucleus and controls cell multiplication and differentiation 9 . Several structural studies for Grb2 nSH3 complexed with the Sos-derived peptide, which has a sequence of VPPPVPPRRR (denoted as VPP peptide), have been reported [10][11][12] . ...
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Growth factor receptor-bound protein 2 (Grb2) is a small adapter protein composed of a single SH2 domain flanked by two SH3 domains. The N-terminal SH3 (nSH3) domain of Grb2 binds a proline-rich region present in the guanine nucleotide releasing factor, son of sevenless (Sos). Using NMR relaxation dispersion and chemical shift analysis methods, we investigated the conformational change of the Sos-derived proline-rich peptide during the transition between the free and Grb2 nSH3-bound states. The chemical shift analysis revealed that the peptide does not present a fully random conformation but has a relatively rigid structure. The relaxation dispersion analysis detected conformational exchange of several residues of the peptide upon binding to Grb2 nSH3.
... of-function and gain-of-function mutations in fibroblasts modulate Grb2 protein levels. Grb2 is a broadly expressed adaptor protein of 217 amino acids (25 kDa) that provides a critical link between cell surface RTK and downstream proliferation pathways (Downward 1994). While the gain of function of Grb2 promotes cell proliferation and transformation, decreased Grb2 function impairs developmental processes and Grb2 null mice are lethal at early embryonic stage (Cheng et al. 1998; Tari and Lopez-Berestein 2001; Giubellino et al. 2008). ...
... Activation of these pathways enhances HCV entry [23,39] and increases the proliferation of hepatocytes, which may contribute to hepatocellular carcinogenesis [40]. Three R6 proteins are associated with receptor signaling: PIK3R1, a PI3K subunit and a crucial participant in PI3K-AKT signaling [41], and GRB2 [42] and SHC1 [43], two key adaptor proteins of EGFR signaling, which when silenced substantially impair HCV entry [39]. ...
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Author Summary Viruses recruit host proteins, called entry factors, to help gain entry to host cells. Identification of entry factors can provide targets for developing antiviral drugs. By exploring the concept that short linear peptide motifs involved in human protein-protein interactions may be mimicked by viruses to hijack certain host cellular processes and thereby assist viral infection/survival, we developed a bioinformatics strategy to computationally identify entry factors of hepatitis C virus (HCV) infection, which is a worldwide health problem. Analysis of cellular functions and biochemical pathways indicated that the human proteins we identified usually play a role in cell entry and/or carcinogenesis, and results of the analysis are generally supported by experimental studies on HCV infection, including the ~80% (15 of 19) prediction rate of known HCV hepatocyte entry factors. Because molecular mimicry is a general concept, our bioinformatics strategy is a timely approach to identify new targets for antiviral research, not only for HCV but also for other viruses.
... A nice example for such diverse regulatory functions is the adaptor Grb2, which is involved in different signaling cascades and the activation of various effectors. Grb2 is the predominant constitutive binding partner of the Ras activator Sos and bridges the Epidermal growth factor (EGF) receptor directly to Sos (Downward 1994). However, Grb2 can bind other adaptor molecules, e.g. ...
... Ras becomes active when bound to GTP while they are inactive when bound to GDP. As a result, activation of Ras triggers the stimulation of Raf, ERK, and MAPK cascade [9,10]. The Grb2 through its nSH3-SH2-cSH3 architecture has strict controls over binding and follows the constitutive equilibrium in which Grb2 exists in monomeric and dimeric forms. ...
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Background: Growth factor receptor-bound protein 2 (Grb2) is a 25 kDa adaptor protein, which was originally discovered to accomplish basic cellular events such as cell growth, cell proliferation, and metabolism. However, recent studies evidenced that Grb2 was largely involved in multiple tumor malignancies. The mature Grb2 is a 217 amino acid sequence, which consists of one Src homology 2 (SH2) domain flanked by two Src homology 3 (SH3) domains. Using these binding motives, the ubiquitously expressed Grb2 acts as an intermediate between cell-surface activated receptors and downstream targets. Objectives: Consequently, the Grb2 becomes the key element of this oncogenesis and launched a number of defected signaling cascades. Therefore, vast concern of the Grb2 in multiple cancer patterns makes it an attractive therapeutic target. In this review, we have compiled the maximum tumor conformations caused by the involvement of the Grb2, the central role of Grb2 in numerous oncogenic pathways and particular approaches that can be useful to downregulate the Grb2 overexpression. We will discuss in details the activity of different types of novel peptides, their high affinity for the Grb2 protein and blockade of Grb2 mediated signaling pathways by targeting the SH2/SH3 binding sites. Methods & results: There is a three-fold aspect to this review: Grb2 protein introduction, Grb2 protein involvement in cancer, and the role of peptides as Grb2 antagonists. First, Grb2 and compiled maximum tumor conformations induced by Grb2 involvement were introduced. Secondly, several oncogenic pathways of Grb2 involvement and particular approaches potentially useful to downregulate Grb2 overexpression were outlined. The activity of different types of novel peptides for the Grb2 protein was also detailed. Last but not least, the blockade of Grb2-mediated signaling pathways by targeting SH2/SH3 binding sites were summarized. Conclusion: We have epitomized the utmost cancer malignancies caused by abnormal signaling of the Grb2 adaptor molecule. Indeed, Grb2's enormous involvement in the progression and development of different cancers broaden our tactics to build anticancer drug candidates. Depending on the high affinity and increased specificity we have described the major potent peptides which may efficiently target and block the SH2 or SH3 arms of the Grb2. It may be of benefit for developing novel anticancer peptides. However, further work is needed to pinpoint more binding motives of Grb2 to generate efficacious anticancer agents for diverse human cancers in the near future.
... Regulation of Molecular Interactions of Dbl by Tyr 510 Phosphorylation-To understand the molecular consequences of tyrosine phosphorylation in Dbl, we examined its ability to associate with established effectors. Grb2 is an adapter molecule that contains an Src homology 2 domain that binds phosphorylated tyrosine residues and an Src homology 3 domain that binds proline-rich sequences (37). Due to this dual-recognition capacity, Grb2 often functions as a "bridging" adapter, allowing it to recruit multiple proteins to their cellular site of activation, as seen in the activation of Ras, where Grb2 recruits Son of Sevenless to the tyrosine-phosphorylated EGF receptor (38,39). ...
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Rho GTPases are molecular “switches” that cycle between “on” (GTP-bound) and “off” (GDP-bound) states and regulate numerous cellular activities such as gene expression, protein synthesis, cytoskeletal rearrangements, and metabolic responses. Dysregulation of GTPases is a key feature of many diseases, especially cancers. Guanine nucleotide exchange factors (GEFs) of the Dbl family are activated by mitogenic cell surface receptors and activate the Rho family GTPases Cdc42, Rac1, and RhoA. The molecular mechanisms that regulate GEFs from the Dbl family are poorly understood. Our studies reveal that Dbl is phosphorylated on tyrosine residues upon stimulation by growth factors and that this event is critical for the regulated activation of the GEF. These findings uncover a novel layer of complexity in the physiological regulation of this protein.
... The sequence of sem5 revealed the protein consisted of two SH3 domains and one SH2 domain. Genetic experiments demonstrated that SEM5 serves as an adapter protein linking tyrosine kinase receptors and Ras(179). Therefore, this discovery immediately suggested a function for the independently cloned human homologue GRB2. ...
Article
The questions outlined in this thesis dissertation were proposed in order to provide insight regarding the mechanism by which the Drosophila Son of sevenless (dSOS) protein activates Ras. Ras proteins are GTP-binding proteins which bind guanine nucleotides very tightly and cycle between the inactive GDP-bound state and the active GTP-bound state. To address the mechanism by which the dSOS proteins activates Ras, a structure-function analysis of the dSOS protein was performed using truncation and deletion mutants of dSOS. In vivo Ras activation experiments using transiently transfected cells revealed that the NH2-terminal domain of dSOS is required in order for the catalytic domain of dSOS to exhibit exchange activity in cultured mammalian cells. The COOH-terminal GRB2 (Growth Factor Receptor Binding Protein) binding domain on the otherhand was insufficient to confer Ras exchange activity to the dSOS catalytic domain. Further analysis of the NH2-terminal domain of the dSOS protein demonstrated that the function of promoting catalytic domain activity could be localized by mutational analysis to the pleckstrin (PH) and DBL (Diffuse B-cell Lymphoma) homology sequences. Fractionation studies of cells transiently transfected with various dSOS mutant proteins demonstrated that the NH2-terminus of dSOS is also necessary for membrane association. These findings suggested that the model proposing that the recruitment of SOS via the adaptor protein GRB2 to the membrane is the main mechanism by which SOS activates Ras is unlikely to be the only mechanism by which SOS can activate Ras. From our data, a model can be proposed which postulates that SOS can activate Ras as a consequence of at least two steps. One step involves the SOS/GRB2 interaction and the second step involves the NH2-terminal domain of SOS associating with unidentified cellular elements.
... Meq also upregulated Grb2, an adaptor protein, which acts as a critical downstream intermediary in several oncogenic signaling pathways. Grb2 has also been shown to link the ErbB receptor to the activation of Ras and its downstream kinases, ERK1/2 (75,76). Overexpression of Grb2 has been noted in several malignancies, including breast cancer and bladder cancer (77)(78)(79). ...
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Marek's disease (MD) is an economically significant disease in chickens caused by the highly oncogenic Marek's disease virus (MDV). A major unanswered question is the mechanism of MDV-induced tumor formation. Meq, a bZIP transcription factor discovered in the 1990s, is critically involved in viral oncogenicity but only a few of its host target genes have been described impeding our understanding of MDV-induced tumorigenesis. Using ChIP-seq and microarray analysis, a high confidence list of Meq-binding sites in the chicken genome and a global transcriptome of Meq-responsive genes was generated. Meq binding sites were found to be enriched in the promoter regions of up-regulated genes, but not in those of down-regulated genes. ChIP-seq was also performed for c-Jun, a known heterodimeric partner of Meq. Close location of binding sites of Meq and c-Jun was noted, suggesting cooperativity between these two factors in modulating transcription. Pathway analysis indicated that Meq transcriptionally regulates many genes that are part of several signaling pathways include the ERK/MAPK, Jak-STAT, and ErbB pathways that are critical for oncogenesis and/or include signaling mediators involved in apoptosis. Meq activates oncogenic signaling cascades by transcriptionally activating major kinases in the ERK/MAPK pathway and simultaneously repressing phosphatases, as verified using inhibitors of MEK and ERK1/2 in a cell proliferation assay. This study provides significant insights into the mechanistic basis of Meq-dependent cell transformation.
... SOS is a GEF (guanine nucleotide exchange factor) for small GTPase Ras that activates the Raf/MEK/ERK cascade involving, in its turn, kinases successively phosphorylat ing and activating each other. Activated kinases, in their turn, phosphorylate and activate a wide spectrum of effector proteins, including other kinases, phosphatases, and transcription factors (Fos, Jun, etc.) (Fig. 1a) [8,27]. Incubation of breast cancer T 47D and T 47Dco cells expressing PRLR long and short isoforms with prolactin antagonists inhibited MAPK signaling and, consequently, suppressed cell proliferation [28]. ...
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The review describes functional and structural features of different isoforms of prolactin receptor, mechanisms of signaling pathway activation, and molecular messengers involved in the transmission and termination of signal from the prolactin receptor isoforms. Changes in the ratio between prolactin receptor isoforms, key mediators of prolactin signal transduction and termination in various organs and tissues, are analyzed. Special attention is given to the role of molecular mediators and the ratio between the isoforms in normal physiological functions and pathologies. Approaches for therapeutic correction of prolactin signaling impairments are discussed.
... It is able to recognise the phospho-tyrosine and the amino acids surrounding it in a specific way [51,53]. The Grb2 protein name, standing for growth factor receptor-bound protein 2, reflects the protocol by which this protein was identified, which was by screening a bacterial cDNA expression library with the tyrosine phosphorylated carboxy terminal region of the EGFR [76,77]. Some adaptor proteines present only this SH2 domain in their sequence, but most of the signalling proteins in general also present other domains responsible for driving on the signal cascade [78]. ...
... For example, the Ras-MAP kinase cascade, which has been widely implicated in the initiation of cell growth responses, is also activated during ligation of the TCR. Although the mechanism by which the TCR couples to Ras remains uncertain, the recruitment of a complex containing the adapter protein, Grb2, and the Rasspecific guanine nucleotide exchange factor, mSOS, to the plasma membrane may be an important step (15,16). Another adapter protein, Shc, binds with low affinity to phospho-ITAMs, and it has been proposed that tyrosine-phosphorylated Shc supplies a membrane docking site for the Grb2-mSOS complex during TCR stimulation (17). ...
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Stimulation of the T cell antigen receptor (TCR) triggers a complex series of signaling events that culminate in T cell activation and proliferation. The complex structure of the TCR has hindered efforts to link specific signaling events induced by TCR cross-linkage to downstream activation responses, such as interleukin-2 (IL-2) gene transcription. Previous studies have shown that the polyomavirus-derived oncoprotein, middle T antigen (mT), transforms rodent fibroblasts by interacting with and activating several cytoplasmic signaling proteins (Src kinases, phospholipase C (PLC)-γ1, Shc, and phosphoinositide 3-kinase (PI3-K) implicated in cell growth control. In this study, we demonstrate that expression of mT activates Jurkat T cells, as measured by increases in IL-2 promoter- and NFAT (nuclear factor of activated T cells)-dependent reporter gene transcription. The transcriptional response provoked by mT was blocked by the immunosuppressive drug FK506, a potent inhibitor of TCR-mediated IL-2 gene expression. Mutations that disrupted the binding of mT to Src kinases or PLC-γ1 abrogated the ability of mT to deliver the signals needed for IL-2 promoter activation. In contrast, a mT mutant that failed to bind PI3-K induced a markedly elevated transcriptional response in Jurkat cells, whereas mutation of the Shc binding site in mT had little effect on the transactivating potential of this viral oncoprotein. Additional studies demonstrated that the association of mT with PLC-γ1 was necessary and sufficient to activate both Ca2+- and Ras-dependent signaling cascades in Jurkat cells. These results indicate that PLC-γ1 activation plays pivotal and pleiotropic roles in the stimulation of IL-2 gene expression, whereas activation of PI3-K negatively modulates this response in Jurkat T cells.
... A 23-kDa growth factor receptor-bound protein termed Grb2 (Lowenstein et al, 1992) or Ash (Matuoka et al, 1992) has been reported to play a role as an adapter molecule linking the upstream receptor tyrosine kinases to Ras (Downward, 1994;Gale et al, 1993), similar to its homologueue from Caenorhabditis elegans, Sem-5 or from Drosophila melanogaster, Drk (Olivier et al, 1993;Simon et al, 1993). ...
Thesis
rasgenes encode guanine nucleotide binding proteins that act as molecular switches for signal transduction pathways controlling cell growth and differentiation. In the GTP- bound form the Ras protein is active and interacts with effector proteins to propagate a signal from the outside of the cell to the nucleus or cytoskeleton. Ras has a low intrinsic GTPase activity which is accelerated by the GTPase-activating proteins (GAPs), p120-GAP and neurofibromin. Two aspects of the interaction between Ras and the catalytic domain of neurofibromin (NF1334) have been studied. (1) The GTPase-activating activity of both p120-GAP and neurofibromin are inhibited by mitogenic lipids such as phosphatidic acid and arachidonic acid. Previous data on the differential inhibition of the two GAPs led to the hypothesis that both were effectors in a Ras-controlled mitogenic pathway. The mechanism of inhibition of NF1334 by arachidonic acid was studied by measuring the catalytic activity under multiple turnover conditions, using p-((6-phenyl)-1,3,5-hexatrienyl)benzoic acid as a fluorescent probe for ligands binding to GAPs and using a scintillation proximity assay to measure direct binding of Ras to NF1334. The inhibition by arachidonic acid included a major component that is competitive with Ras.GTP and an additional non-competitive type effect consistent with protein denaturing activity. This suggested that insomuch as the mitogenic effects of lipids are mediated via inhibition of GAPs, GAPs are not Ras effector proteins. (2) Basic residues within the catalytic domains of p120-GAP and neurofibromin have been suggested to play an important role in GAP-stimulated catalysis and Ras binding. Two invariant arginine residues within NF1334, R1276 and R1391, were mutated to alanine and their effects on maximal catalysis (kcat) affinity (Kd) for Ras measured under single turnover conditions. Both R1276 and R1391 are required for efficient catalysis by NF1334 as removal of either results in a 1000-fold loss of activity. R1276 is not thought to be directly involved in Ras binding as the affinity of R1276A for H-Ras or [Leu61]H-Ras is only moderately reduced (ca. 3-fold). The reduction in affinity of R1391A for H-Ras is more marked (ca. 10-20 fold) but most notable for [Leu61]H-Ras (ca. 100-fold) suggesting a role for this residue in Ras binding. The high affinity of [Leu61]H-Ras for NF1334 over H-Ras is completely lost with the R1391 NF1334, suggesting that the high affinity is related to an interaction with R1391 of NF1334
... Our present data show for the first time that ATXN2 indeed interacts with the SH3 motif containing protein Grb2 in the endocytosis machinery and that ATXN2 loss-of-function and gain-of-function mutations in fibroblasts modulate Grb2 protein levels. Grb2 is a broadly expressed adaptor protein of 217 amino acids (25 kDa) that provides a critical link between cell surface RTK and downstream proliferation pathways (Downward 1994). While the gain of function of Grb2 promotes cell proliferation and transformation, decreased Grb2 function impairs developmental processes and Grb2 null mice are lethal at early embryonic stage (Cheng et al. 1998;Tari and Lopez-Berestein 2001;Giubellino et al. 2008). ...
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Ataxin-2 (ATXN2) is implicated mainly in mRNA processing. Some ATXN2 associates with receptor tyrosine kinases (RTK), inhibiting their endocytic internalization through interaction of proline-rich domains (PRD) in ATXN2 with SH3 motifs in Src. Gain of function of ATXN2 leads to neuronal atrophy in the diseases spinocerebellar ataxia type 2 (SCA2) and amyotrophic lateral sclerosis (ALS). Conversely, ATXN2 knockout (KO) mice show hypertrophy and insulin resistance. To elucidate the influence of ATXN2 on trophic regulation, we surveyed interactions of ATXN2 with SH3 motifs from numerous proteins and observed a novel interaction with Grb2. Direct binding in glutathione S-transferase (GST) pull-down assays and coimmunoprecipitation of the endogenous proteins indicated a physiologically relevant association. In SCA2 patient fibroblasts, Grb2 more than Src protein levels were diminished, with an upregulation of both transcripts suggesting enhanced protein turnover. In KO mouse embryonal fibroblasts (MEF), the protein levels of Grb2 and Src were decreased. ATXN2 absence by itself was insufficient to significantly change Grb2-dependent signaling for endogenous Ras levels, Ras-GTP levels, and kinetics as well as MEK1 phosphorylation, suggesting that other factors compensate for proliferation control. In KO tissue with postmitotic neurons, a significant decrease of Src protein levels is prominent rather than Grb2. ATXN2 mutations modulate the levels of several components of the RTK endocytosis complex and may thus contribute to alter cell proliferation as well as translation and growth.
... Here, we found the significant correlations of KPNA2 with many BCR signaling pathway genes including GRB2 and NRAS, which were shown to be dysregulated both at mRNA and protein levels. As a ubiquitously expressed adapter protein, GRB2 is crucial for normal development (Cheng et al., 1998) and implicated in cell proliferation (Downward, 1994). With its Src homology 2 (SH2) domain, GRB2 can also interact with several proteins in oncogenic signaling pathways including epidermal growth factor receptor, hepatocyte growth factor receptor, platelet-derived growth factor receptor, Bcr/Abl, and focal adhesion kinase (Lowenstein et al., 1992;Schlaepfer et al., 1994;Verbeek et al., 1997;Liu and McGlade, 1998; Fredericks and Ren, 2013). ...
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Karyopherin α2 (KPNA2) was reported to be overexpressed and have unfavorable prognostic effects in many malignancies including hepatocellular carcinoma (HCC). Although its contributions to inflammatory response were reported in many studies, its specific associations with immune infiltrations and immune pathways during cancer progression were unclear. Here, we aimed to identify new markers for HCC diagnosis and prognosis through KPNA2-associated immune analyses. RNA-seq expression data of HCC datasets were downloaded from The Cancer Genome Atlas and International Cancer Genome Consortium. The gene expressions were counts per million normalized. The infiltrations of 24 kinds of immune cells in the samples were evaluated with ImmuCellAI (Immune Cell Abundance Identifier). The Spearman correlations of the immune infiltrations with KPNA2 expression were investigated, and the specific positive correlation of B-cell infiltration with KPNA2 expression in HCC tumors was identified. Fifteen genes in KEGG (Kyoto Encyclopedia of Genes and Genomes) B-cell receptor signaling pathway presented significant correlations with KPNA2 expression in HCC. Among them, GRB2 and NRAS were indicated to be independent unfavorable prognostic factors for HCC overall survival. Clinical Proteomic Tumor Analysis Consortium HCC dataset was investigated to validate the results at protein level. The upregulation and unfavorable prognostic effects of KPNA2 and GRB2 were confirmed, whereas, unlike its mRNA form, NRAS protein was presented to be downregulated and have favorable prognostic effects. Through receiver operating characteristic curve analysis, the diagnostic potential of the three proteins was shown. The RNA-binding proteins (RBPs) of KPNA2, NRAS, and GRB2, downloaded via The Encyclopedia of RNA Interactomes, were investigated for their clinical significance in HCC at protein level. An eight-RBP signature with independent prognostic value and dysregulations in HCC was identified. All the RBPs were significantly correlated with MKI67 expression and at least one of KPNA2, GRB2, and NRAS at protein level in HCC, indicating their roles in HCC progression and the regulation of the three proteins. We concluded that KPNA2, GRB2, NRAS, and their RBPs might have coordinating roles in HCC immunoregulation and progression. They might be new markers for HCC diagnosis and prognosis predication and new targets for HCC immunotherapy.
... The interaction between Grb2 and SH3BGRL3 was suggested to occur through the SH3BGRL3 proline-rich motif [12]. However, SH3BGRL3 does not have a canonical SH3-binding domain [6], which is required for binding to the SH3 domain on Grb2 [28], leaving open the question of how these two proteins interact. Based on these considerations, literature data, and our own findings, it could be envisaged that Myo1c may transfer the signal triggered by ErbB2 to the actin cytoskeleton by means of a protein complex that includes Grb2 and SH3BGRL3 as two of multiple 'adaptor proteins'. ...
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Background The human SH3 domain Binding Glutamic acid Rich Like 3 (SH3BGRL3) gene is highly conserved in phylogeny and widely expressed in human tissues. However, its function is largely undetermined. The protein was found to be overexpressed in several tumors, and recent work suggested a possible relationship with EGFR family members. We aimed at further highlighting on these issues and investigated SH3BGRL3 molecular interactions and its role in cellular migration ability. Results We first engineered the ErbB2-overexpressing SKBR3 cells to express exogenous SH3BGRL3, as well as wild type Myo1c or different deletion mutants. Confocal microscopy analysis indicated that SH3BGRL3 co-localized with Myo1c and ErbB2 at plasma membranes. However, co-immunoprecipitation assays and mass spectrometry demonstrated that SH3BGRL3 did not directly bind ErbB2, but specifically recognized Myo1c, on its IQ-bearing neck region. Importantly, the interaction with Myo1c was Ca²⁺-dependent. A role for SH3BGRL3 in cell migration was also assessed, as RNA interference of SH3BGRL3 in MDA-MB-231 cells, used as a classical migration model, remarkably impaired the migration ability of these cells. On the other side, its over-expression increased cell motility. Conclusion The results of this study provide insights for the formulation of novel hypotheses on the putative role of SH3BGRL3 protein in the regulation of myosin-cytoskeleton dialog and in cell migration. It could be envisaged the SH3BGRL3-Myo1c interaction as a regulation mechanism for cytoskeleton dynamics. It is well known that, at low Ca²⁺ concentrations, the IQ domains of Myo1c are bound by calmodulin. Here we found that binding of Myo1c to SH3BGRL3 requires instead the presence of Ca²⁺. Thus, it could be hypothesized that Myo1c conformation may be modulated by Ca²⁺-driven mechanisms that involve alternative binding by calmodulin or SH3BGRL3, for the regulation of cytoskeletal activity.
... RTKs transduce signals by autophosphorylation and subsequent binding to cytosolic phospho-tyrosine binding adaptor proteins, which then recruit other factors (Lemmon and Schlessinger, 2010). LET-23 acts primarily through the adaptor SEM-5 (related to vertebrate Grb2) , which recruits SOS-1 (Downward, 1994), but also in part through SOC-1 (related to mammalian Gab1), which recruits PTP-2/Shp2 (Hopper, 2006) ( Figure 1B). EGL-15 acts through both SEM-5 and SOC-1-PTP-2 ) ( Figure 1C). ...
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Receptor Tyrosine Kinase (RTK)-Ras-Extracellular signal-regulated kinase (ERK) signaling pathways control many aspects of C. elegans development and behavior. Studies in C. elegans helped elucidate the basic framework of the RTK-Ras-ERK pathway and continue to provide insights into its complex regulation, its biological roles, how it elicits cell-type appropriate responses, and how it interacts with other signaling pathways to do so. C. elegans studies have also revealed biological contexts in which alternative RTK- or Ras-dependent pathways are used instead of the canonical pathway.
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The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase whose physiological signaling activity regulates the morphogenesis and homeostasis of several tissues from worms to man. In contrast, aberrant signaling caused by overexpression or mutational activation of the EGFR plays a causal role in the pathogenesis of a number of human tumors. The fidelity of EGFR signals, which must be robust enough to convey instructive cues to the cell while also preventing the threat posed by excess receptor activity, is guaranteed by a complex regulatory circuitry. A pervasive role in EGFR regulation is played by endocytosis. Owing to its capacity to instruct degradation of activated EGFRs and reduce receptor expression at the cell surface, endocytosis has been regarded historically as the main cellular mechanism deputed to the attenuation of EGFR signaling. More recently, a great deal of attention has been focused on understanding endocytosis also as an element of spatial regulation of EGFR activity. Herein, we discuss molecular mechanisms controlling EGFR endocytosis, as they relate to the regulation of EGFR signal output and the implementation of EGFR-driven biological programs. We will then focus on reviewing the variegated mechanisms through which the EGFR escapes from downregulation in cancer cells. The emerging picture assigns to faulty endocytosis, in concert with constitutive catalytic activation, a prominent role in the ominous oncogenic conversion of EGFR. © 2013 Springer Science+Business Media New York. All rights are reserved.
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Posterior capsular opacification (PCO) can cause postoperative visual loss after cataract surgery. Residual human lens epithelial cell (HLEC) proliferation, migration, epithelial-mesenchymal transition (EMT) and synthesis of extracellular matrix (ECM) are the entitative reasons for PCO. Low expression of Ral-binding protein 1-associated Eps domain-containing 2 (REPS2) and high levels of basic fibroblast growth factor (b-FGF) were observed in the lens and postoperative aqueous humor of cataract patients. REPS2 was identified as a negative regulator in growth factor signaling; however, its function in HLECs is unknown. This was first investigated in the present study by evaluating REPS2 expression in anterior lens capsules from cataract patients, a mouse cataract model, and HLE-b3 cells. The biological function of REPS2 in HLE-B3 cells was assessed by REPS2 silencing and Cell Counting Kit 8, wound healing, Transwell migration, F-actin staining, G-protein pulldown and western blot assays. In the present study, REPS2 was significantly downregulated in human and mouse cataract capsules and H2O2-treated HLE-B3 cells. REPS2 knockdown increased fibronectin, type I collagen, and α-smooth muscle actin expression levels and stimulated HLECs proliferation and migration; these effects were enhanced by FGF treatment and accompanied with focal adhesion kinase (FAK) phosphorylation, cell division cycle 42 (Cdc42) activation, focal adhesion protein upregulation, and F-actin cytoskeleton reorganization. However, treatment with the FAK inhibitor PF573228 abolished these effects. Thus, REPS2 downregulation in cataract HLECs induces their proliferation and facilitates FGF-induced ECM synthesis, EMT, cell adhesion and migration by activating FAK/Cdc42 signaling, which may underlie PCO pathogenesis.
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Ras gene mutations have been found with variable prevalence in different tumor types. While during the past decade a lot o f information has been accumulated on the frequency of ras oncogene activation in tumors, the last two years brought considerable progress in elucidating molecular mechanisms o f signal transduction for which cellular ras proteins are key elements. They transmit signals from upstream tyrosine kinases to downstream serinelthreonine kinases ultimately leading to changes of gene expression, cytoskeletal architecture, cell-to-cell interactions and metabolism. These signalling pathways are o f interest for the physiological regulation o f proliferation and differentiation in normal, as well as in cancer tissue. Mutational activation o f cellular ras genes to transforming oncogenes is thought to promote cell growth even in the absence o f extracellular stimuli, and may thereby contribute to the initiation andlor progression o f tumors.
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Cytokines are soluble messengers that play a pivotal role in regulating immune responses. They operate within a network where their effects are pleiotropic and their function is often redundant. Cytokines typically affect adjacent cells or even the cell of origin and act as paracrine, juxtacrine, autocrine or intracrine mediators. As with any biological system this regulation is in a delicate balance. An organism responds to disturbances in its physiological homeostasis by mounting an acute phase response, which is characterised by dramatic changes in the concentration of some plasma proteins termed acute phase proteins. IL-6 has been identified in vitro and in vivo as the major hepatocyte stimulating factor. Other pro-inflammatory cytokines, such as IL-1, IL-12 and TNFα, are produced to orchestrate a cellular response to trauma or invasion of the body by pathogenic organisms. The cytokines mediate a wide range of symptoms associated with trauma and infection such as fever, anorexia, tissue wasting, and immunomodulation. Inappropriate or over-production of these same cytokines is associated with mortality and pathology in a wide range of diseases, such as malaria, sepsis, rheumatoid arthritis, inflammatory bowel disease, cancer and AIDS. As well as pro-inflammatory cytokines, there are anti-inflammatory cytokines, including IL-1ra, IL-4, IL-10, IL-11, IL-13 and TGFβ, whose function is to ameliorate the potentially harmful effects of pro-inflammatory mediators, thus restricting the magnitude and duration of the inflammatory response.
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Receptors on macrophages for the Fc region of IgG (FcγR) mediate a number of responses important for host immunity. Signaling events necessary for these responses are likely initiated by the activation of Src-family and Syk-family tyrosine kinases after FcγR cross-linking. Macrophages derived from Syk-deficient (Syk−) mice were defective in phagocytosis of particles bound by FcγRs, as well as in many FcγR-induced signaling events, including tyrosine phosphorylation of a number of cellular substrates and activation of MAP kinases. In contrast, Syk− macrophages exhibited normal responses to another potent macrophage stimulus, lipopolysaccharide. Phagocytosis of latex beads and Escherichia coli bacteria was also not affected. Syk− macrophages exhibited formation of polymerized actin structures opposing particles bound to the cells by FcγRs (actin cups), but failed to proceed to internalization. Interestingly, inhibitors of phosphatidylinositol 3-kinase also blocked FcγR-mediated phagocytosis at this stage. Thus, PI 3-kinase may participate in a Syk-dependent signaling pathway critical for FcγR-mediated phagocytosis. Macrophages derived from mice deficient for the three members of the Src-family of kinases expressed in these cells, Hck, Fgr, and Lyn, exhibited poor Syk activation upon FcγR engagement, accompanied by a delay in FcγR-mediated phagocytosis. These observations demonstrate that Syk is critical for FcγR-mediated phagocytosis, as well as for signal transduction in macrophages. Additionally, our findings provide evidence to support a model of sequential tyrosine kinase activation by FcγR's analogous to models of signaling by the B and T cell antigen receptors.
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A small peptide mimic of the Grb2-SH2 domain, which was previously prepared through the template-assisted click approach and exhibited selective A431 tumor growth inhibition both in vitro and in vivo, was further elaborated on to enhance the interaction with target phosphorylated proteins. A conformationally fixed analog was efficiently synthesized by solid-supported ring-closing metathesis and Cu(i)/His-mediated self-activating Huisgen [3+2] cycloadditon as the key steps, and exhibited a 10-fold enhanced affinity to a phosphorylated peptide, a truncated peptide analog of the Grb2-SH2-interacting phosphoproteins. A stronger interaction with the target phosphorylated proteins gave this cyclic analog cytotoxic activity in A431 cells.
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Insulin receptor signaling acutely stimulates GTP loading of p21, apparently by mobilizing complexes of Grb2 and the guanine nucleotide exchangers Son-of-sevenless (Sos) 1 and 2 to associate with tyrosine-phosphorylated proteins in the plasma membrane. Here we show that in P-labeled 3T3-L1 adipocytes the elevated cellular concentrations of [P]GTP-bound p21 in response to insulin return to near basal levels after 20-30 min of hormone stimulation, while insulin receptors remain activated. Lysates of such desensitized cells were quantitatively immunoprecipitated with an antiserum recognizing both Sos1 and Sos2 proteins or a specific anti-Sos2 antiserum. Immunoblot analysis of these precipitates revealed that insulin causes a marked hyperphosphorylation of Sos1 and a 50% decrease in Grb2 associated with Sos proteins under these conditions. Similarly, anti-Grb2 immunoprecipitates of such lysates revealed the presence of decreased Sos1 protein due to insulin action. The disassembly of Grb2 from Sos proteins slightly precedes the time course of p21 deactivation in response to insulin. These data are consistent with the hypothesis that the dissociation of Grb2 from Sos proteins caused by insulin in 3T3-L1 cells mediates p21deactivation and desensitization.
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AIM: To investigate the effects of Qigesan, Shashenmaidongtang, Tongyoutang and Buqiyunpitang on the proliferation of human esophageal carcinoma EC9706 cells stimulated with human epidermal growth factor (hEGF), and to explore potential mechanisms involved. METHODS: After cultured EC9706 cells were stimulated with hEGF and then treated with Qigesan, Shashenmaidongtang, Tongyoutang and Buqiyunpitang, respectively, cell morphological changes were observed under an inverted microscope, cell proliferation was determined by MTT assay, cell cycle progression was measured by flow cytometry, and protein expression and tyrosine phosphorylation in PLC-γ1 and PI3K-mediated signaling pathways were determined by Western blot. RESULTS: The half-maximum inhibitory concentrations (IC50) of Qigesan, Shashenmaidongtang and Tongyoutang were 849, 1 004 and 1 615 mg/L, respectively. These drugs at a concentration of IC50 inhibited hEGF-stimulated cell proliferation and prevented cell cycle progression into S phase. Buqiyunpitang could only weakly inhibit the proliferation of EC9706 cells. Qigesan, Shashenmaidongtang and Tongyoutang inhibited the protein expression and tyrosine phosphorylation of EGFR and PLC-γ1 as well as the protein expression of PKCα, MARCKS, PI3K, AKT-1 and NF-κB p50. Tongyoutang had the strongest inhibitory effects on the PLC-γ1 signaling pathway, followed by Qigesan and Shashenmaidongtang. In contrast, the order of the inhibitory potency for the PI3K signaling pathway was Tongyoutang, Shashenmaidongtang and Qigesan. CONCLUSION: Qigesan, Shashenmaidongtang and Tongyoutang can, to varying degrees, inhibit hEGF-stimulated cell proliferation by suppressing PLC-γ1 and PI3K-mediated signaling pathways.
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E3b1, a binding partner of Eps8, plays a critical role in receptor tyrosine kinase (RTK)-mediated Rac activation by facilitating the interaction of Eps8 with Sos-1 and the consequent activation of the Rac-specific guanine nucleotide exchange factor activity of Sos-1. Here we present evidence that E3b1 levels are regulated by the Ca2+-activated protease calpain, and also by Pak, a downstream target of Rac signaling. Serum starvation of Rat2 or COS7 cells resulted in rapid loss of E3b1 that was reversed by calpain inhibitors. Loss was also prevented by expressing the constitutively active Pak1 mutant, Pak1H83,86L. Activation of endogenous Pak by platelet-derived growth factor or the constitutively active Rac1 mutant, Rac1G12V, also inhibited degradation. In contrast, inhibition of endogenous Pak activity by expressing the Pak auto-inhibitory domain caused degradation of over-expressed E3b1 even in the presence of serum. Taken together, these findings indicate that E3b1 is down-regulated by calpain activation and stabilized by Pak activation. They also suggest that RTK-mediated Rac activation can be modulated by changes in the level of E3b1 in response to signals that affect the activity of calpain or Pak.
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Published experimental evidence for relations between SLiMs and R6 proteins and between R6 proteins and module functions in Fig 3. (PDF)
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Marine invertebrate ascidians display embryonic reproducibility: Their early embryonic cell lineages are considered invariant and are conserved between distantly related species, despite rapid genomic divergence. Here, we address the drivers of this reproducibility. We used light-sheet imaging and automated cell segmentation and tracking procedures to systematically quantify the behavior of individual cells every 2 minutes during Phallusia mammillata embryogenesis. Interindividual reproducibility was observed down to the area of individual cell contacts. We found tight links between the reproducibility of embryonic geometries and asymmetric cell divisions, controlled by differential sister cell inductions. We combined modeling and experimental manipulations to show that the area of contact between signaling and responding cells is a key determinant of cell communication. Our work establishes the geometric control of embryonic inductions as an alternative to classical morphogen gradients and suggests that the range of cell signaling sets the scale at which embryonic reproducibility is observed.
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Effective analgesic treatment for neuropathic pain remains an unmet need, so previous evidence that epidermal growth factor receptor inhibitors (EGFRIs) provide unexpected rapid pain relief in a clinical setting points to a novel therapeutic opportunity. The present study utilises rodent models to address the cellular and molecular basis for the findings, focusing on primary sensory neurons because clinical pain relief is provided not only by small molecule EGFRIs, but also by the anti-EGFR antibodies cetuximab and panitumumab, which are unlikely to access the central nervous system in therapeutic concentrations. We report robust, rapid and dose-dependent analgesic effects of EGFRIs in two neuropathic pain models, matched by evidence with highly selective antibodies that expression of the EGFR (ErbB1 protein) is limited to small nociceptive afferent neurons. As other ErbB family members can heterodimerise with ErbB1, we investigated their distribution, showing consistent co-expression of ErbB2 but not ErbB3 or ErbB4, with ErbB1 in cell bodies of nociceptors, as well as providing evidence for direct molecular interaction of ErbB1 with ErbB2 in situ. Co-administration of selective ErbB1 and ErbB2 inhibitors produced clear evidence of greater-than-additive, synergistic analgesia; highlighting the prospect of a unique new combination therapy in which enhanced efficacy could be accompanied by minimisation of side-effects. Peripheral (intraplantar) administration of EGF elicited hypersensitivity only following nerve injury and this was reversed by local co-administration of selective inhibitors of either ErbB1 or ErbB2. Investigating how ErbB1 is activated in neuropathic pain, we found evidence for a role of Src tyrosine kinase, which can be activated by signals from inflammatory mediators, chemokines and cytokines during neuroinflammation. Considering downstream consequences of ErbB1 activation in neuropathic pain, we found direct recruitment to ErbB1 of an adapter for PI 3-kinase and Akt signalling together with clear Akt activation and robust analgesia from selective Akt inhibitors. The known Akt target and regulator of vesicular trafficking, AS160 was strongly phosphorylated at a perinuclear location during neuropathic pain in an ErbB1-, ErbB2- and Akt-dependent manner, corresponding to clustering and translocation of an AS160-partner, the vesicular chaperone, LRP1. Exploring whether neuronal ion channels that could contribute to hyperexcitability might be transported by this vesicular trafficking pathway we were able to identify Nav1.9, (Nav1.8) and Cav1.2 moving towards the plasma membrane or into proximal axonal locations – a process prevented by ErbB1 or Akt inhibitors. Overall these findings newly reveal both upstream and downstream signals to explain how ErbB1 can act as a signalling hub in neuropathic pain models and identify the trafficking of key ion channels to neuronal subcellular locations likely to contribute to hyperexcitability. The new concept of combined treatment with ErbB1 plus ErbB2 blockers is mechanistically validated as a promising strategy for the relief of neuropathic pain.
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Protein enhancer of sevenless 2B, E(sev)2B, is a key adapter protein in the Ras/MAPK signaling pathway which has been reported to be involved in innate immunity. In this study, the gene that encodes AsE(sev)2B was isolated from A. sinica. It was found to contain a 636 bp open reading frame encoding 211 amino acids with a calculated molecular mass of 24.357 kDa and a predicted isoelectric point of 5.39. The predicted protein contains a N-terminal Src homology 3 domain (SH3), a central Src homology 2 domain (SH2), and a C-terminal Src homology 3 domain (SH3). Homology analysis revealed that AsE(sev)2B shares 49%–95% identity with E(sev)2B homologs from other species. In this study, the expression pattern and location of AsE(sev)2B during different stages of embryonic development and bacterial challenge were investigated by means of real-time qPCR, Western blotting and immunohistochemistry. Results showed that the highest expression level of AsE(sev)2B was at 0 h. After challenged by Gram-positive bacteria and Gram-negative bacteria, AsE(sev)2B was remarkably upregulated at 10 ⁶ cellsL ⁻¹ bacterial concentrations. These results suggested that AsE(sev)2B plays a vital role during early embryonic development and in immune responses against bacterial challenge.
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Los efectos de los factores de crecimiento y de ciertas hormonas se deben a la activación de receptores con actividad intrínseca de cinasa de tirosina (o RTK’s, por receptor tyrosine kinases), cuya estimulación inicia cascadas de señalización intracelular que regulan eventos transcripcionales esenciales para la proliferación y la diferenciación celulares. Entre los efectos debidos a la estimulación de los RTK’s, destaca la activación de la familia de cinasas de proteína activadas por mitógeno o MAPK’s (mitogen-activated protein kinases). Existen evidencias que indican que la estimulación de algunos receptores acoplados a proteínas G (o GPCR’s, por G protein-coupled receptors) resulta en la activación de RTK’s en ausencia de un ligando para estos últimos. Este proceso ha sido denominado transactivación, y depende de señales intracelulares inducidas por la estimulación de GPCR’s en las que participan tanto las subunidades a como los complejos bg de las proteínas G, así como fenómenos de fosforilación mediados por diferentes cinasas. En este artículo se revisan las características estructurales de ambos tipos de receptores (GPCR’s y RTK’s), los mecanismos responsables de su activación y los procesos involucrados en el fenómeno de transactivación de RTK’s por activación de GPCR’s.
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This chapter will outline novel treatment strategies predicated on the modulation of growth factor or cytokine-mediated signal transduction pathways. Several excellent recent monographs have addressed this tissue from the point of view of inhibitors of individual pathway constituents (1,2).The current focus will be on defining the pathways potentially relevant to the common neoplasms, followed by a consideration of approaches to modulating processes common to the action of various pathways, with mention of individual agents as they exemplify these strategies. In addition, opportunities for interdigitation of “growth-factor directed” and “traditional” therapeutic agents will be considered.
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The mitogen-activated protein kinases (MAPKs) mediate intracellular signals activated by a wide variety of extracellular stimuli. The activation of the RAS-RAF-MEK-MAPK cascade culminates in the regulation of gene transcription promoting cancer cell proliferation, survival, migration and angiogenesis. MEK (mitogen-activated protein kinase kinase-MAPKK) 1/2 is a transducer of the growth factor receptor-RAS-RAF-MAPK signalling cascade and plays a relevant role in development and progression of human cancers, such as colorectal cancer (CRC), non small cell lung cancer (NSCLC). Direct inhibition of MEK is a promising strategy and several inhibitors are currently under evaluation in clinical trials showing initial clinical activity in different tumours. MEK activation, by different genetic mechanisms, has been described for both intrinsic and acquired resistance to drugs targeting the EGFR (Epidermal Growth Factor Receptor)-RAS-RAF pathway in CRC, NSCLC. Combination therapies with chemotherapy and/or with molecular targeted agents are warranted and biomarkers studies are needed to identify those tumours dependent on MEK signalling.
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Adaptor proteins are key regulators of intracellular signaling. Many aspects of their functions have been elucidated and the structures of many members of this family of proteins have been resolved. The adaptor protein Grb2 is a critical component of the cell signaling machinery that is deregulated in several pathological processes, including cancer. A plurality of interactions make Grb2 an important cellular hub linking activated cell surface receptors to downstream targets by binding to specific phosphotyrosine-containing and proline-rich sequence motifs. Its critical roles in epithelial morphogenesis and in processes such as proliferation, actin-based cell motility, invasion, and angiogenesis make it a logical therapeutic target for several pathological processes, including human cancer. In this chapter Grb2 will be used as a paradigm to illustrate how adaptor proteins are involved in cancer and how it is possible to selectively target adaptor proteins for cancer therapy.
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The recent identification and characterization of the c-mpl proto-oncogene set off an explosive wave of research that has advanced our understanding of megakaryocyte and platelet biology immensely. The mechanisms by which this member of the hemopoietic cytokine receptor family promotes the survival, proliferation, and differentiation of megakaryocytic progenitors resulting in platelet production will require many years, if not decades, to unravel completely. However, important insights into this process have already been achieved, and will be reviewed in this chapter.
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Sre homology 2 (SH2) domains are protein modules that mediate intracellular protein-protein interactions in signal transduction pathways. The specific association of an SH2 domain with a phosphotyrosine-containing sequence of another protein induces a cascade of molecular interactions that effect a wide range of cellular processes. Alterations in these signaling pathways have been associated with the development and progression of a broad range of pathologies. Because of the regulatory role of SH2 domains in these signal transduction pathways, specific SH2 domains can be ideal targets for intervention with therapeutic agents in many different disease indications (e.g. cancer, osteoporosis, disorders of the immune and cardiovascular systems). Among the SH2 domains pursued as drug discovery targets in the last few years are those of Grb2, Src, Lck and ZAP-70. This review focuses on contributions in the design and synthesis of antagonists of these particular SH2 domains. Specific examples have been selected to illustrate how structure-based design approaches have been used to progress in this area of research.
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A necessary downstream element of Abelson murine leukemia virus (Ab-MLV)-mediated transformation is Ras, which can be activated by the phosphotyrosine-dependent association of Shc with the Grb2-mSos complex. Here we show that Shc is tyrosine phosphorylated and associates with Grb2 in v-Abl-transformed cells, whereas Shc in NIH3T3 cells is phosphorylated solely on serine and is not Grb2 associated. In addition, Shc co-precipitates with P120 v-Abl and P70 v-Abl, which lacks the carboxyl terminus. Surprisingly, a kinase defective mutant of P120 also binds Shc, demonstrating that Shc/v-Abl association is a phosphotyrosine-independent interaction. Glutathione S-transferase fusion proteins were used to map the interacting domains and showed that Shc from both NIH3T3 and v-Abl-transformed cells binds to the Abl SH2 domain and that P120 v-Abl binds to a region in the amino terminus of Shc. Consistent with these data, a v-Abl mutant encoding only the Gag and SH2 regions was able to bind Shc in vivo. The unique non-phosphotyrosine-mediated binding of Shc may allow direct tyrosine phosphorylation of Shc by v-Abl and subsequent activation of the Ras pathway through assembly of a signaling complex with Grb2-mSos.
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Previous work suggested that desensitization of p21(ras) in response to growth factors such as epidermal growth factor (EGF) results from receptor down-regulation, Here we show that p21(ras) is desensitized by insulin in 3T3-L1 adipocytes in the continued presence of activated insulin receptors, while loss of epidermal growth factor and platelet-derived growth factor (PDGF) receptors in response to their ligands correlates with p21(ras) desensitization. Furthermore, elevated amounts of Grb2/Shc complexes persisted throughout p21(ras) desensitization by insulin. However, immunoblotting of anti Son-of-sevenless (Sos) 1 and 2 immunoprecipitates with anti-Grb2 antisera revealed that p21(ras) desensitization in response to insulin and PDGF, but not EGF, is associated with a marked decrease in cellular complexes containing Sos and Grb2 proteins, Nonetheless, the desensitization of p21(ras) in response to these stimuli was homologous, in that each peptide could reactivate [P-32]GTP loading of p21(ras) after desensitization by any of the others, Taken together, these data indicate that insulin, EGF, and PDGF all cause disassembly of Sos proteins from signaling complexes during p21(ras) desensitization, but at least two mechanisms are involved, Insulin elicits dissociation of Sos from Grb2 SH3 domains, whereas EGF signaling is reversed by receptor down-regulation and She dephosphorylation, releasing Grb2 SH2 domains, PDGF action triggers both mechanisms of Grb2 disassembly, which probably operate in concert with GAP to attenuate p21(ras) signaling.
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Nerve impulses regulate expression of genes that control receptors, channels, enzymes, and structural proteins. This activity-dependent feedback allows adaptation to changing requirements and environmental conditions. The signal transduction mechanisms carrying information from the cell membrane to the nucleus are becoming well characterized, but a more dynamic view of intracellular signaling is emerging to explain cellular responses to specific patterns of neural impulses. This review analyzes this interface between electrophysiology and molecular cell biology to examine the signals, substrates, and processes that enable the nervous system to regulate its structure and function as a consequence of its own operation.
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Loss of muscle mass can lead to diseases such as sarcopenia, diabetes, and obesity, which can worsen the quality of life and increase the incidence of disease. Therefore, understanding the mechanism underlying skeletal muscle differentiation is vital to prevent muscle diseases. We previously found that microRNA-320 (miR-320) is highly expressed in the lean muscle-type pigs, but its regulatory role in myogenesis remains unclear. The bioinformatics prediction indicated that miR-320 could bind to the 3 'untranslated region of growth factor receptor-bound protein-2 (Grb2). We hypothesized that miR-320 targets Grb2 to regulate myoblasts differentiation. To verify this, we transfected miR-320 mimic and inhibitor into C2C12 myoblasts to assess the role of miR-320 during myoblasts differentiation. We used real-time qPCR, luciferase reporter assays, and western blotting to confirm that miR-320 directly targets Grb2 to promote myoblasts differentiation. Moreover, by using a dexamethasone-induced atrophic model of myotubes, we discovered that miR-320 promotes the repair of damaged myotubes. Our findings expand understanding of miRNAs and genes related to regulating skeletal muscle differentiation, and provide insight into underlying therapeutic strategies for muscle diseases.
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Cbl, a 120-kDa proto-oncogene product, whose gene was first identified as part of a transforming gene of a murine retrovirus and whose expression is predominant in haematopoietic cells, consists of an amino-terminal transforming region, a zinc Ring finger, multiple proline-rich stretches, and several potential phosphotyrosine-containing motifs. Cbl is rapidly tyrosine-phosphorylated in response to stimulation of a variety of cell-surface receptors and becomes associated with a number of intracellular signalling molecules such as protein tyrosine kinases, phosphatidylinositol 3-kinase, Crk, and 14-3-3 proteins through different protein-interacting modules, leading to the formation of multimolecular signalling complexes. Cbl and its transforming mutants have been shown to display both negative and positive regulatory activities in protein tyrosine kinase– and Ras-mediated signalling pathways. Nevertheless, the exact biological function of this adaptor protein remains largely unknown. The present review summarizes recent progress in our understanding of the structure, regulation and biological function of Cbl and defines open questions for future research.
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Publisher Summary To a large degree cellular signal transduction pathways are choreographed by modular Src homology 2 (SH2) and Src homology 3 (SH3) domains that mediate well-specific protein: protein interactions. SH2 domains are modules of ∼100 amino acids that specifically bind phosphotyrosine-containing proteins and peptides. SH3 domains are modules of ∼60 amino acids that bind to the proline-rich sequences. This chapter includes a list of selected therapeutic targets, possessing SH2 or SH3 domains. The design of specific antagonists to these domains holds the promise of targeted treatment of a broad range of pathologies. The role of SH2 and SH3 domains in signal transduction has been extensively studied. In growth factor, cytokine and antigen signaling, occupancy of a receptor by agonist results in receptor dimerization and the phosphorylation of regulatory tyrosines on the cytoplasmic surface. Phosphorylation is catalyzed by kinases that are a part of the receptor (receptor tyrosine kinases) or recruited to the receptor from the cytoplasm (non-receptor tyrosine kinases). The resulting phosphotyrosines permit binding of specific SH2-containing proteins and initiate a cascade of the sequential protein interactions. SH3 domains are independently folded protein modules of 55-70 amino acids that selectively bind proline-rich protein sequences. Although generally of lower affinity than SH2-mediated interactions, SH3 interactions are essential for multiple signaling cascades.
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Several findings suggest that signals from tyrosine kinases are transduced, at least in part, through ras proteins. These findings include (i) blockage of the transforming activity of constitutively active tyrosine kinases by inhibiting ras function and (ii) genetic screens in Caenorhabditis elegans and in Drosophila that identified ras genes as downstream effectors of tyrosine kinases. The recently isolated Drosophila gene Son of sevenless (Sos) is postulated to act as a positive regulatory link between tyrosine kinase and ras proteins by catalyzing exchange of GDP for GTP on ras protein. Such exchange proteins have been reported in extracts of mammalian cells but have not been previously characterized at a molecular level. As Sos appears to function in this role in Drosophila, we sought to isolate a vertebrate counterpart(s). We have characterized two widely expressed murine genes with a high degree of homology to Sos. Hybridization with human DNA and RNA indicates a high degree of conservation of these genes in other vertebrates.
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We report the isolation and molecular characterization of the mouse grb2 gene. The product of this gene, the Grb2 protein, is highly related to the Caenorhabditis elegans sem-5 gene product and the human GRB2 protein and displays the same SH3-SH2-SH3 structural motifs. In situ hybridization studies revealed that the mouse grb2 gene is widely expressed throughout embryonic development (E9.5 to P0). However, grb2 transcripts are not uniformly distributed, and in certain tissues (e.g., thymus) they appear to be regulated during development. Recent genetic and biochemical evidence has implicated the Grb2 protein in the signaling pathways that link cell surface tyrosine kinase receptors with Ras. We have investigated the association of the Grb2 protein with epidermal growth factor (EGF) and nerve growth factor (NGF) receptors in PC12 pheochromocytoma cells. EGF treatment of PC12 cells results in the rapid association of Grb2 with the activated EGF receptors, an interaction mediated by the Grb2 SH2 domain. However, Grb2 does not bind to NGF-activated Trk receptors. Mitogenic signaling of NGF in NIH 3T3 cells ectopically expressing Trk receptors also takes place without detectable association between Grb2 and Trk. These results suggest that whereas EGF and NGF can activate the Ras signaling pathway in PC12 cells, only the EGF receptor is likely to do so through a direct interaction with Grb2. Finally, binding studies with glutathione S-transferase fusion proteins indicate that Grb2 binds two distinct subsets of proteins which are individually recognized by its SH2 and SH3 domains. These observations add further support to the concept that Grb2 is a modular adaptor protein.
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The Src homology (SH) region 2 binds to phosphorylated tyrosine residues and SH3 domains may interact with cytoskeletal molecules and GTPase-activating proteins for Rho/Rac proteins (the small GTP-binding proteins related to Ras). The recently cloned Ash/Grb-2 protein, a 25-28 kDa molecule composed entirely of SH2 and SH3 domains, is a mammalian homolog of the Caenorhabditis elegans Sem-5 protein, which communicates between a receptor protein tyrosine kinase and a Ras protein. In the present study the function of Ash/Grb-2 was investigated by microinjecting cells with an anti-Ash antibody. The antibody abolished both S phase entry and the reorganization of actin assembly to ruffle formation upon stimulation with epidermal growth factor (EGF) and platelet-derived growth factor (PDGF). On the other hand, anti-Ash antibody had no effect on S phase entry or actin stress fiber formation induced by either serum or lysophosphatidic acid. Since the induction of DNA synthesis, ruffle induction and stress fiber formation involve a function of Ras, Rac activation and Rho activation respectively, the findings strongly suggest that Ash plays a critical role in the signaling of both pathways downstream from growth factor receptors to Ras and Rac. Consistent with this, Ash co-precipitated with EGF receptor from EGF-stimulated cells. Other proteins of approximately 21, 29, 135 and 160 kDa were also detected in the anti-Ash antibody immunoprecipitates, suggesting a role of Ash as a linker molecule in signal transduction downstream of growth factor receptors.
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Insulin-induced activation of extracellular signal-regulated kinases [ERKs, also known as mitogen-activated protein (MAP) kinases] is mediated by Ras. Insulin activates Ras primarily by increasing the rate of guanine nucleotide-releasing activity. Here, we show that insulin-induced activation of ERKs was enhanced by stable overexpression of growth factor receptor-bound protein 2 (GRB2) but not by overexpression of GRB2 proteins with point mutations in the Src homology 2 and 3 domains. Moreover, a dominant negative form of Ras (with Ser17 substituted with Asn) blocked insulin-induced activation of ERKs in cells that overexpressed GRB2. GRB2 overexpression led to increased formation of a complex between the guanine nucleotide-releasing factor Sos (the product of the mammalian homolog of son of sevenless gene) and GRB2. In response to insulin stimulation, this complex bound to tyrosine-phosphorylated IRS-1 (insulin receptor substrate-1) and Shc. In contrast to the activated epidermal growth factor receptor that binds the GRB2-Sos complex directly, activation of the insulin receptor results in the interaction of GRB2-Sos with IRS-1 and Shc, thus linking the insulin receptor to Ras signaling pathways.
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Insulin activates the ras proto-oncogene product p21ras (Ras) by stimulating conversion of the inactive GDP-bound form of Ras to the active GTP-bound form. The protein ASH (for abundant Src homology) (Matuoka, K., Shibata, M., Yamakawa, A., and Takenawa, T. (1992) Proc. Natl. Acad. Sci. U. S. A. 89, 9015-9019) is composed of one Src homology (SH)2 and two SH3 domains and highly homologous to the Caenorhabditis elegans protein sem-5 that couples a tyrosine kinase to a Ras protein. We have studied an interaction of ASH with insulin-stimulated tyrosine-phosphorylated proteins in Chinese hamster ovary cells overexpressing human insulin receptors (CHO-HIR cells). In an anti-ASH (alpha ASH) immunoprecipitates, we detected a 170-kDa phosphoprotein that was recognized by an anti-phosphotyrosine antibody and an anti-insulin receptor substrate 1 antibody (alpha IRS-1) from the insulin-stimulated [32P]orthophosphate-labeled CHO-HIR cells. We failed to detect the tyrosine phosphorylation of the protein ASH. These data suggested that insulin stimulates IRS-1.ASH complex formation in intact cells. Incubation of an ASH fusion protein with the lysates of insulin-stimulated CHO-HIR cells revealed that the fusion protein of ASH was able to bind the tyrosine-phosphorylated 170-kDa protein that was recognized by alpha IRS-1. We also demonstrated that fusion protein of ASH was able to bind the fusion protein of tyrosine-phosphorylated IRS-1 fragments, suggesting that ASH is able to bind tyrosine-phosphorylated IRS-1 directly. These data suggest that IRS-1.ASH complex formation may play a role in coupling the insulin receptor kinase to a Ras signaling pathway. Furthermore, we observed an insulin-stimulated phosphatidylinositol (PI) 3-kinase activity in alpha ASH immunoprecipitates, suggesting the formation of an ASH.IRS-1.PI 3-kinase complex. This complex formation was detected as early as 10 s after insulin stimulation in intact CHO-HIR cells. This is the first report that supports the notion that IRS-1 binds several signal transducing molecules containing SH2 domains, thus serves as an SH2 docking protein that transduces insulin's signal multidirectionally.
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A number of growth factors, including insulin and epidermal growth factor (EGF), induce accumulation of the GTP-bound form of p21ras. This accumulation could be caused either by an increase in guanine nucleotide exchange on p21ras or by a decrease in the GTPase activity of p21ras. To investigate whether insulin and EGF affect nucleotide exchange on p21ras, we measured binding of [alpha-32P]GTP to p21ras in cells permeabilized with streptolysin O. For this purpose, we used a cell line which expressed elevated levels of p21 H-ras and which was highly responsive to insulin and EGF. Stimulation with insulin or EGF resulted in an increase in the rate of nucleotide binding to p21ras. To determine whether this increased binding rate is due to the activation of a guanine nucleotide exchange factor, we made use of the inhibitory properties of a dominant negative mutant of p21ras, p21ras (Asn-17). Activation of p21ras by insulin and EGF in intact cells was abolished in cells infected with a recombinant vaccinia virus expressing p21ras (Asn-17). In addition, the enhanced nucleotide binding to p21ras in response to insulin and EGF in permeabilized cells was blocked upon expression of p21ras (Asn-17). From these data, we conclude that the activation of a guanine nucleotide exchange factor is involved in insulin- and EGF-induced activation of p21ras.
Article
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Treatment of intact Rat-1 fibroblasts with epidermal growth factor (EGF) leads to rapid activation of cellular ras-encoded proteins. By using the bacterial toxin streptolysin O to permeabilize these cells, it was shown that the low basal rate at which guanine nucleotides bind to, and dissociate from, ras-encoded protein in quiescent fibroblasts was greatly accelerated by EGF treatment. Nucleotide binding to other proteins was not affected. Stimulation of nucleotide exchange on ras-encoded protein required tyrosine kinase but not phospholipase activity. EGF had no effect on total GTPase-activating protein activity. Regulation of ras-encoded protein in Rat-1 fibroblasts is therefore mediated by stimulation, either directly or indirectly, of ras-encoded protein-specific guanine nucleotide exchange factors by the EGF receptor tyrosine kinase.
Article
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Many tyrosine kinases, including the receptors for hormones such as epidermal growth factor (EGF), nerve growth factor and insulin, transmit intracellular signals through Ras proteins. Ligand binding to such receptors stimulates Ras guanine-nucleotide-exchange activity and increases the level of GTP-bound Ras, suggesting that these tyrosine kinases may activate a guanine-nucleotide releasing protein (GNRP). In Caenorhabditis elegans and Drosophila, genetic studies have shown that Ras activation by tyrosine kinases requires the protein Sem-5/drk, which contains a single Src-homology (SH) 2 domain and two flanking SH3 domains. Sem-5 is homologous to the mammalian protein Grb2, which binds the autophosphorylated EGF receptor and other phosphotyrosine-containing proteins such as Shc through its SH2 domain. Here we show that in rodent fibroblasts, the SH3 domains of Grb2 are bound to the proline-rich carboxy-terminal tail of mSos1, a protein homologous to Drosophila Sos. Sos is required for Ras signalling and contains a central domain related to known Ras-GNRPs. EGF stimulation induces binding of the Grb2-mSos1 complex to the autophosphorylated EGF receptor, and mSos1 phosphorylation. Grb2 therefore appears to link tyrosine kinases to a Ras-GNRP in mammalian cells.
Article
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GRB2, a small protein comprising one SH2 domain and two SH3 domains, represents the human homologue of the Caenorhabditis elegans protein, sem-5. Both GRB2 and sem-5 have been implicated in a highly conserved mechanism that regulates p21ras signalling by receptor tyrosine kinases. In this report we show that in response to insulin, GRB2 forms a stable complex with two tyrosine-phosphorylated proteins. One protein is the major insulin receptor substrate IRS-1 and the second is the SH2 domain-containing oncogenic protein, Shc. The interactions between GRB2 and these two proteins require ligand activation of the insulin receptor and are mediated by the binding of the SH2 domain of GRB2 to phosphotyrosines on both IRS-1 and Shc. Although GRB2 associates with IRS-1 and Shc, it is not tyrosine-phosphorylated after insulin stimulation, implying that GRB2 is not a substrate for the insulin receptor. Furthermore, we have identified a short sequence motif (YV/IN) present in IRS-1, EGFR and Shc, which specifically binds the SH2 domain of GRB2 with high affinity. Interestingly, both GRB2 and phosphatidylinositol-3 (PI-3) kinase can simultaneously bind distinct tyrosine phosphorylated regions on the same IRS-1 molecule, suggesting a mechanism whereby IRS-1 could provide the core for a large signalling complex. We propose a model whereby insulin stimulation leads to formation of multiple protein--protein interactions between GRB2 and the two targets IRS-1 and Shc. These interactions may play a crucial role in activation of p21ras and the control of downstream effector molecules.
Article
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A human complementary DNA was isolated that encodes a widely expressed protein, hSos1, that is closely related to Sos, the product of the Drosophila son of sevenless gene. The hSos1 protein contains a region of significant sequence similarity to CDC25, a guanine nucleotide exchange factor for Ras from yeast. A fragment of hSos1 encoding the CDC25-related domain complemented loss of CDC25 function in yeast. This hSos1 domain specifically stimulated guanine nucleotide exchange on mammalian Ras proteins in vitro. Mammalian cells overexpressing full-length hSos1 had increased guanine nucleotide exchange activity. Thus hSos1 is a guanine nucleotide exchange factor for Ras. The hSos1 interacted with growth factor receptor-bound protein 2 (GRB2) in vivo and in vitro. This interaction was mediated by the carboxyl-terminal domain of hSos1 and the Src homology 3 (SH3) domains of GRB2. These results suggest that the coupling of receptor tyrosine kinases to Ras signaling is mediated by a molecular complex consisting of GRB2 and hSos1.
Article
BCR-ABL is a chimeric oncoprotein that exhibits deregulated tyrosine kinase activity and is implicated in the pathogenesis of Philadelphia chromosome (Ph1)-positive human leukemias. Sequences within the first exon of BCR are required to activate the transforming potential of BCR-ABL. The SH2/SH3 domain-containing GRB-2 protein links tyrosine kinases to Ras signaling. We demonstrate that BCR-ABL exists in a complex with GRB-2 in vivo. Binding of GRB-2 to BCR-ABL is mediated by the direct interaction of the GRB-2 SH2 domain with a phosphorylated tyrosine, Y177, within the BCR first exon. The BCR-ABL-GRB-2 interaction is required for activation of the Ras signaling pathway. Mutation of Y177 to phenylalanine (Y177F) abolishes GRB-2 binding and abrogates BCR-ABL-induced Ras activation. The BCR-ABL (Y177F) mutant is unable to transform primary bone marrow cultures and is impaired in its ability to transform Rat1 fibroblasts. These findings implicate activation of Ras function as an important component in BCR-ABL-mediated transformation and demonstrate that GRB-2 not only functions in normal development and mitogenesis but also plays a role in oncogenesis.
Article
Cell-fate specification of R7 photoreceptors in the developing Drosophila eye depends on an inductive signal from neighbouring R8 cells. Mutations in three genes, sevenless (sev), bride-of-sevenless (boss) and seven-in-absentia (sina) cause the R7 precursor to become a non-neural cone cell. The sev gene encodes a receptor protein tyrosine kinase (Sev) localized on the R7 surface, activated by a boss-encoded ligand presented by R8. The sina gene encodes a nuclear factor required in R7. Reduction in the dosage of the Ras1 gene impairs Sev-mediated signalling, suggesting that activation of Ras1 may be an important consequence of Sev activation. We report here that Ras1 activation may account for all of the signalling action of Sev; an activated Ras1Va112 protein rescues the normal R7 precursor from transformation into a cone cell in sev and boss null mutants and induces the formation of supernumerary R7 cells. Similar activation of the Drosophila Ras2 protein does not produce these effects, demonstrating Ras protein specificity.
Article
A cDNA clone encoding a novel, widely expressed protein (called growth factor receptor-bound protein 2 or GRB2) containing one src homology 2 (SH2) domain and two SH3 domains was isolated. Immunoblotting experiments indicate that GRB2 associates with tyrosine-phosphorylated epidermal growth factor receptors (EGFRs) and platelet-derived growth factor receptors (PDGFRs) via its SH2 domain. Interestingly, GRB2 exhibits striking structural and functional homology to the C. elegans protein sem-5. It has been shown that sem-5 and two other genes called let-23 (EGFR like) and let-60 (ras like) lie along the same signal transduction pathway controlling C. elegans vulval induction. To examine whether GRB2 is also a component of ras signaling in mammalian cells, microinjection studies were performed. While injection of GRB2 or H-ras proteins alone into quiescent rat fibroblasts did not have mitogenic effect, microinjection of GRB2 together with H-ras protein stimulated DNA synthesis. These results suggest that GRB2/sem-5 plays a crucial role in a highly conserved mechanism for growth factor control of ras signaling.
Article
The induction of the hermaphrodite vulva and the migration of the sex myoblasts in the nematode Caenorhabditis elegans are both controlled by intercellular signalling. The gonadal anchor cell induces formation of the vulva from nearby hypodermal cells, and a set of somatic gonadal cells attract the migrating sex myoblasts to their final positions. Many genes required for vulval induction have been identified, including the let-23 receptor tyrosine kinase gene and the let-60 ras gene. We report here the identification and characterization of a new gene, sem-5 (sem, sex muscle abnormal), that acts both in vulval induction and in sex myoblast migration. On the basis of its DNA sequence, sem-5 encodes a novel 228-amino-acid protein which consists almost entirely of one SH2 (SH, src homology region) and two SH3 domains. SH2 and SH3 domains are present in many signalling proteins regulated by receptor and non-receptor tyrosine kinases. Mutations that impair sem-5 activity alter residues that are highly conserved among different SH2 and SH3 domains. Our results indicate that the sem-5 gene encodes a novel protein that functions in at least two distinct cell-signalling processes.
Article
The protein ASH (for abundant Src homology), composed of one Src homology region (SH) 2 and two SH3 domains, was cloned by screening human and rat cDNA libraries with an oligonucleotide probe directed to a consensus sequence of the SH2 domains. The rat-derived ASH peptide was comprised of 217 amino acids with a molecular mass of 25-28 kDa and was found to be ubiquitous in rat tissues. A human cDNA clone was also found to code for part of the same protein, suggesting that ASH is common to human and rat. The amino acid sequence of ASH was strikingly similar to Sem-5, the product of a nematode cell-signaling gene, and ASH is most probably a mammalian homologue of Sem-5. ASH bound in vitro to phosphotyrosine-containing proteins, including activated epidermal growth factor receptor, the ASH SH2 domain being responsible for the binding. Induced expression of an antisense ASH cDNA led to a reduction in cell growth. Considering these observations and the structural homology to Sem-5, ASH is likely to function as a ubiquitous signal transducer, possibly resembling Sem-5, which communicates between a receptor protein tyrosine kinase and a Ras protein.
Article
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Article
The mammalian shc gene encodes two overlapping, widely expressed proteins of 46 and 52K, with a carboxy-terminal SH2 domain that binds activated growth factor receptors, and a more amino-terminal glycine/proline-rich region. These shc gene products (Shc) are transforming when overexpressed in fibroblasts. Shc proteins become phosphorylated on tyrosine in cells stimulated with a variety of growth factors, and in cells transformed by v-src (ref. 2), suggesting that they are tyrosine kinase targets that control a mitogenic signalling pathway. Here we report that tyrosine-phosphorylated Shc proteins form a specific complex with a non-phosphorylated 23K polypeptide encoded by the grb2/sem-5 gene. The grb2/sem-5 gene product itself contains an SH2 domain, which mediates binding to Shc, and is implicated in activation of the Ras guanine nucleotide-binding protein by tyrosine kinases in both Caenorhabditis elegans and mammalian cells. Consistent with a role in signalling through Ras, shc overexpression induced Ras-dependent neurite outgrowth in PC12 cells. These results suggest that Shc tyrosine phosphorylation can couple tyrosine kinases to Grb2/Sem-5, through formation of a Shc-Grb2/Sem-5 complex, and thereby regulate the mammalian Ras signalling pathway.
Article
The proteins encoded by the ras proto-oncogenes play critical roles in normal cellular growth, differentiation and development in addition to their potential for malignant transformation. Several proteins that are involved in the control of the activity of p21ras have now been characterised. p120GAP stimulates the GTPase activity of p21ras and hence acts as a negative regulator of ras proteins. It may be controlled by tyrosine phosphorylation or association with tyrosine phosphorylated proteins. The neurofibromatosis type 1 (NF 1) gene also encodes a potential GTPase activating protein which is likely to be subject to a different control mechanism. Guanosine nucleotide exchange factors for p21ras have now been identified: these may be positive regulators of ras protein function. It appears that p21ras is subject to rapid regulation by several distinct mechanisms which are likely to vary in different cell types; the ras proteins are thereby able to act as very sensitive cellular monitors of the extracellular environment.
Article
The biological activity of Ras proteins is thought to be controlled by the guanine nucleotide exchange factor and the guanosine triphosphatase activating protein (GAP). Treatment of rat pheochromocytoma PC-12 cells with nerve growth factor (NGF) increased the amount of active Ras guanosine triphosphate complex and stimulated the activities of both the guanine nucleotide exchange factor and GAP. In PC-12 cells that overexpressed the tyrosine kinase encoded by the trk proto-oncogene (a component of the high-affinity NGF receptor), the NGF-induced activation of the regulatory proteins was potentiated. These results suggest that the NGF receptor system enhances the activities of both the guanine nucleotide exchange factor and GAP and that the activation of Ras might be controlled by the balance in activity between these two regulatory proteins.
Article
A new SH2-containing sequence, SHC, was isolated by screening cDNA libraries with SH2 representative DNA probes. The SHC cDNA is predicted to encode overlapping proteins of 46.8 and 51.7 kd that contain a single C-terminal SH2 domain, and an adjacent glycine/proline-rich motif with regions of homology with the alpha 1 chain of collagen, but no identifiable catalytic domain. Anti-SHC antibodies recognized three proteins of 46, 52, and 66 kd in a wide range of mammalian cell lines. These SHC proteins complexed with and were phosphorylated by activated epidermal growth factor receptor. The physical association of SHC proteins with activated receptors was recreated in vitro by using a bacterially expressed SHC SH2 domain. NIH 3T3 mouse fibroblasts that constitutively overexpressed SHC acquired a transformed phenotype in culture and formed tumors in nude mice. These results suggest that the SHC gene products couple activated growth factor receptors to a signaling pathway that regulates the proliferation of mammalian cells.
Article
We have isolated a dominant mutation in a gene called Son of sevenless (Sos) that is an allele-specific suppressor of the sevenless phenotype. This suppressor function is autonomously required in R7 and is sensitive to the dosage of the Sos and bride of sevenless genes. Loss-of-function alleles of Sos are recessive lethals, but in the eye Sos has a role in R cell development. Mutations in Sos also interact with the Ellipse allele of the Drosophila EGF receptor. We propose a model suggesting that the Sos product is downstream of sevenless and the EGF receptor, and that the dominant suppression results from the overexpression or increased activity of the gene product.
Article
We have conducted a genetic screen for mutations that decrease the effectiveness of signaling by a protein tyrosine kinase, the product of the Drosophila melanogaster sevenless gene. These mutations define seven genes whose wild-type products may be required for signaling by sevenless. Four of the seven genes also appear to be essential for signaling by a second protein tyrosine kinase, the product of the Ellipse gene. The putative products of two of these seven genes have been identified. One encodes a ras protein. The other locus encodes a protein that is homologous to the S. cerevisiae CDC25 protein, an activator of guanine nucleotide exchange by ras proteins. These results suggest that the stimulation of ras protein activity is a key element in the signaling by sevenless and Ellipse and that this stimulation may be achieved by activating the exchange of GTP for bound GDP by the ras protein.
Article
The let-23 gene is required for induction of the Caenorhabditis elegans vulva. It is shown that let-23 encodes a putative tyrosine kinase of the epidermal growth factor receptor subfamily. Thus, let-23 might encode the receptor for the inductive signal required for vulval development. Because let-23 acts upstream of let-60 ras in the vulval determination pathway, the identification of the let-23 product provides support for a link in vivo between tyrosine kinase growth factor receptors and ras proteins in a pathway of cell-type determination.
Article
The let-60 gene, an essential ras gene of the nematode Caenorhabditis elegans, acts as a switch in the inductive signalling pathway that initiates vulva formation. Recessive let-60 mutations that cause a vulvaless phenotype prevent let-60 function in response to the inductive signal. These mutations are clustered and define regions necessary either for the activation or for the action of the let-60 ras protein. Dominant let-60 mutations that cause a multivulva phenotype alter codon 13 and activate let-60 in vivo, rendering it independent of the inductive signal. The let-60 gene acts within an extensively defined genetic pathway, and other genes within this pathway seem likely to encode molecules that regulate let-60 function as well as molecules that are targets of let-60 action.
Article
External signals that control the activity of proteins encoded by the ras proto-oncogenes have not previously been characterized. It is now shown that stimulation of the antigen receptor of T lymphocytes causes a rapid activation of p21ras. The mechanism seems to involve a decrease in the activity of GAP, the GTPase-activating protein, on stimulation of protein kinase C. In lymphocytes, p21ras may therefore be an important mediator of the action of protein kinase C.
Article
Genetic analysis previously suggested that the let-60 gene controls the switch between vulval and hypodermal cell fates during C. elegans vulval induction. We have cloned the let-60 gene, and shown that it encodes a gene product identical in 84% of its first 164 amino acids to ras gene products from other vertebrate and invertebrate species. This conservation suggests that the let-60 product contains all the biochemical functions of ras proteins. Extrachromosomal arrays of let-60 ras DNA cause cell-type misspecification (extra vulval fates) phenotypically opposite to that caused by let-60 ras loss-of-function mutations (no vulval fates), and suppress the vulvaless phenotype of mutations in two other genes necessary for vulval induction. Thus, the level and pattern of let-60 ras expression may be under strict regulation; increase in let-60 ras activity bypasses or reduces the need for upstream genes in the vulval induction pathway.
Article
Numerous oncogenes have been isolated from acutely transforming retroviruses. To date, the products of these viral oncogenes have been protein kinases, nuclear proteins, growth factors, or GTP-binding proteins. We have cloned the previously uncharacterized avian sarcoma virus CT10 and sequenced its genome. This virus encodes a protein, p47gag-crk, that has blocks of sequence similarity to the amino-terminal, non-catalytic region of the non-receptor class of tyrosine kinases. In addition, the structure of p47gag-crk has striking similarity to a 180-amino acid region of bovine brain phospholipase C. Biochemical data suggest that p47gag-crk activates one or several endogenous tyrosine kinases.
Article
In this study we describe the cellular distribution of the SH2 and SH3 domains of phospholipase C-gamma (PLC-gamma) and of the adaptor protein GRB2 following their microinjection into living rat embryo fibroblasts. Using immunofluorescence microscopy, we show that a truncated protein composed of the SH2 and SH3 domains of PLC-gamma was localized to the actin cytoskeleton. A similar localization pattern was observed when only the SH3 domain of PLC-gamma was microinjected. In contrast, a truncated protein composed of only the SH2 domains of PLC-gamma exhibited diffuse cytoplasmic distribution. Microinjected GRB2 protein was localized primarily to membrane ruffles, as was GRB2 protein containing SH2 loss-of-function point mutations. Hence, the localization of GRB2 to membrane ruffles does not require interaction with tyrosine-phosphorylated moieties. However, GRB2 proteins with SH3 loss-of-function point mutations exhibited diffuse cytoplasmic distribution. These results indicate that SH3 domains are responsible for the targeting of signaling molecules to specific subcellular locations.
Article
Activation of receptor tyrosine kinases such as those for epidermal growth factor (EGF), platelet-derived growth factor, or nerve growth factor converts the inactive, GDP-bound form of Ras to the active, GTP-bound form, and a dominant negative mutant of Ras interferes with signalling from such receptors. The mechanisms by which receptor tyrosine kinases and Ras are coupled, however, are not well understood. Many cytoplasmic proteins regulated by such receptors contain Src-homology (SH) 2 and 3 domains, and the SH2- and SH3-containing protein Grb2, like its homologue from Caenorhabditis elegans, Sem-5, appears to play an important role in the control of Ras by receptor tyrosine kinases. Here we show that overexpression of Grb2 potentiates the EGF-induced activation of Ras and mitogen-activated protein kinase by enhancing the rate of guanine nucleotide exchange on Ras. Cellular Grb2 appears to form a complex with a guanine-nucleotide-exchange factor for Ras, which binds to the ligand-activated EGF receptor, allowing the tyrosine kinase to modulate Ras activity.
Article
Signal transmission by insulin involves tyrosine phosphorylation of a major insulin receptor substrate (IRS-1) and exchange of Ras-bound guanosine diphosphate for guanosine triphosphate. Proteins containing Src homology 2 and 3 (SH2 and SH3) domains, such as the p85 regulatory subunit of phosphatidylinositol-3 kinase and growth factor receptor-bound protein 2 (GRB2), bind tyrosine phosphate sites on IRS-1 through their SH2 regions. Such complexes in COS cells were found to contain the heterologously expressed putative guanine nucleotide exchange factor encoded by the Drosophila son of sevenless gene (dSos). Thus, GRB2, p85, or other proteins with SH2-SH3 adapter sequences may link Sos proteins to IRS-1 signaling complexes as part of the mechanism by which insulin activates Ras.
Article
Src homology 3 (SH3) domains have been implicated in mediating protein-protein interactions in receptor signaling processes; however, the precise role of this domain remains unclear. In this report, affinity purification techniques were used to identify the GTPase dynamin as an SH3 domain-binding protein. Selective binding to a subset of 15 different recombinant SH3 domains occurs through proline-rich sequence motifs similar to those that mediate the interaction of the SH3 domains of Grb2 and Abl proteins to the guanine nucleotide exchange protein, Sos, and to the 3BP1 protein, respectively. Dynamin GTPase activity is stimulated by several of the bound SH3 domains, suggesting that the function of the SH3 module is not restricted to protein-protein interactions but may also include the interactive regulation of GTP-binding proteins.
Article
BCR-ABL is a chimeric oncoprotein that exhibits deregulated tyrosine kinase activity and is implicated in the pathogenesis of Philadelphia chromosome (Ph1)-positive human leukemias. Sequences within the first exon of BCR are required to activate the transforming potential of BCR-ABL. The SH2/SH3 domain-containing GRB-2 protein links tyrosine kinases to Ras signaling. We demonstrate that BCR-ABL exists in a complex with GRB-2 in vivo. Binding of GRB-2 to BCR-ABL is mediated by the direct interaction of the GRB-2 SH2 domain with a phosphorylated tyrosine, Y177, within the BCR first exon. The BCR-ABL-GRB-2 interaction is required for activation of the Ras signaling pathway. Mutation of Y177 to phenylalanine (Y177F) abolishes GRB-2 binding and abrogates BCR-ABL-induced Ras activation. The BCR-ABL (Y177F) mutant is unable to transform primary bone marrow cultures and is impaired in its ability to transform Rat1 fibroblasts. These findings implicate activation of Ras function as an important component in BCR-ABL-mediated transformation and demonstrate that GRB-2 not only functions in normal development and mitogenesis but also plays a role in oncogenesis.
Article
The Src homology 3 (SH3) region is a small protein domain present in a very large group of proteins, including cytoskeletal elements and signaling proteins. It is believed that SH3 domains serve as modules that mediate protein-protein associations and, along with Src homology 2 (SH2) domains, regulate cytoplasmic signaling. The SH3 binding sites of two SH3 binding proteins were localized to a nine- or ten-amino acid stretch very rich in proline residues. Similar SH3 binding motifs exist in the formins, proteins that function in pattern formation in embryonic limbs of the mouse, and one subtype of the muscarinic acetylcholine receptor. Identification of the SH3 binding site provides a basis for understanding the interaction between the SH3 domains and their targets.
Article
A Drosophila gene (drk) encodes a widely expressed protein with a single SH2 domain and two flanking SH3 domains, which is homologous to the Sem-5 protein of C. elegans and mammalian GRB2. Genetic analysis suggests that drk function is essential for signaling by the sevenless receptor tyrosine kinase. Drk biological activity correlates with binding of its SH2 domain to activated receptor tyrosine kinases and concomitant localization of drk to the plasma membrane. In vitro, drk also binds directly to the C-terminal tail of Sos, a Ras guanine nucleotide-releasing protein (GNRP), which, like Ras1 and drk, is required for sevenless signaling. These results suggest that drk binds autophosphorylated receptor tyrosine kinases with its SH2 domain and the Sos GNRP through its SH3 domains, thereby coupling receptor tyrosine kinases to Ras activation. The conservation of these signaling proteins during evolution indicates that this is a general mechanism for linking tyrosine kinases to Ras.
Article
Activation of the sevenless protein-tyrosine kinase is required for the proper specification of R7 photoreceptors in the Drosophila eye. The activation of a Ras protein, p21Ras1, is a crucial early event in the signaling pathway, and constitutive activation of p21Ras1 is sufficient to induce all of the effects of sevenless action. Here we report that another gene, E(sev)2B, required for proper signaling by sevenless encodes a protein of the structure SH3-SH2-SH3. We further provide evidence that the E(sev)2B protein is required for activation of p21Ras1 but not for any subsequent events, and that this protein can bind in vitro to sevenless and to Son of sevenless (Sos), a putative guanine nucleotide exchange factor for p21Ras1. These results suggest that the E(sev)2B protein may act to stimulate the ability of Sos to catalyze p21Ras1 activation by linking sevenless and Sos in a signaling complex. We have renamed the E(sev)2B locus downstream of receptor kinases (drk).
Article
Many of the actions of receptor tyrosine kinases are mediated by the protein Ras, including the activation of various downstream serine/threonine kinases and the stimulation of growth and differentiation. The human protein Grb2 binds to ligand-activated growth factor receptors and downstream effector proteins through its Src-homology (SH) domains SH2 and SH3, respectively, and like its homologue from Caenorhabditis elegans, Sem-5, apparently forms part of a highly conserved pathway by which these receptors can control Ras activity. Here we show that the SH3 domains of Grb2 bind to the carboxy-terminal part of hSos1, the human homologue of the Drosophila guanine-nucleotide-releasing factor for Ras, which is essential for control of Ras activity by epidermal growth factor receptor and sevenless. Moreover, a synthetic 10-amino-acid peptide containing the sequence PPVPPR specifically blocks the interaction. These results indicate that the Grb2/hSos1 complex couples activated EGF receptor to Ras signalling.
Article
The proteins Grb2-Sem-5, Shc and Sos have been implicated in the signalling pathway from tyrosine kinase receptors to Ras. Grb2-Sem-5 binds directly to murine Sos1, a Ras exchange factor, through two SH3 domains. Sos is also associated with ligand-activated tyrosine kinase receptors which bind Grb2-Sem-5, and with the Grb2-Sem-5 binding protein, Shc. Ectopic expression of Drosophila Sos stimulates morphological transformation of rodent fibroblasts. These data define a pathway by which tyrosine kinases act through Ras to control cell growth and differentiation.
Article
Antisera against murine Son of sevenless (Sos) recognize a protein of M(r) 155,000 in rat-1 fibroblasts with specific guanine nucleotide exchange activity toward p21c-Ha-ras. Epidermal growth factor (EGF) receptor coimmunoprecipitates with Sos from EGF-stimulated, but not quiescent, cells. The SH2 and SH3 domain-containing "adapter" protein Grb2 is also found in Sos immunoprecipitates in an EGF-inducible manner. In vitro reconstitution shows that Grb2 is required for the binding of activated EGF receptor to Sos. A phosphopeptide corresponding to tyrosine 1068 of the EGF receptor blocks both the assembly of the complex and EGF stimulation of nucleotide exchange on p21ras in a permeabilized cell system. These results suggest that EGF-induced activation of nucleotide exchange on p21ras proceeds through the recruitment of cytosolic Sos to a complex with EGF receptor and Grb2 at the plasma membrane.
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