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Spatial regulation of cyclic AMP-Epac1 signaling in cell adhesion by ERM proteins. Mol Cell Biol 2010; 30:5421-31. [PMID: 20855527 DOI: 10.1128/mcb.00463-10] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Epac1 is a guanine nucleotide exchange factor for the small G protein Rap and is involved in membrane-localized processes such as integrin-mediated cell adhesion and cell-cell junction formation. Cyclic AMP (cAMP) directly activates Epac1 by release of autoinhibition and in addition induces its translocation to the plasma membrane. Here, we show an additional mechanism of Epac1 recruitment, mediated by activated ezrin-radixin-moesin (ERM) proteins. Epac1 directly binds with its N-terminal 49 amino acids to ERM proteins in their open conformation. Receptor-induced activation of ERM proteins results in increased binding of Epac1 and consequently the clustered localization of Epac1 at the plasma membrane. Deletion of the N terminus of Epac1, as well as disruption of the Epac1-ERM interaction by an interfering radixin mutant or small interfering RNA (siRNA)-mediated depletion of the ERM proteins, impairs Epac1-mediated cell adhesion. We conclude that ERM proteins are involved in the spatial regulation of Epac1 and cooperate with cAMP- and Rap-mediated signaling to regulate adhesion to the extracellular matrix.
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Zemojtel T, Duchniewicz M, Zhang Z, Paluch T, Luz H, Penzkofer T, Scheele JS, Zwartkruis FJT. Retrotransposition and mutation events yield Rap1 GTPases with differential signalling capacity. BMC Evol Biol 2010; 10:55. [PMID: 20170508 PMCID: PMC2831893 DOI: 10.1186/1471-2148-10-55] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2010] [Accepted: 02/19/2010] [Indexed: 11/21/2022] Open
Abstract
Background Retrotransposition of mRNA transcripts gives occasionally rise to functional retrogenes. Through acquiring tempero-spatial expression patterns distinct from their parental genes and/or functional mutations in their coding sequences, such retrogenes may in principle reshape signalling networks. Results Here we present evidence for such a scenario, involving retrogenes of Rap1 belonging to the Ras family of small GTPases. We identified two murine and one human-specific retrogene of Rap1A and Rap1B, which encode proteins that differ by only a few amino acids from their parental Rap1 proteins. Markedly, human hRap1B-retro and mouse mRap1A-retro1 acquired mutations in the 12th and 59th amino acids, respectively, corresponding to residues mutated in constitutively active oncogenic Ras proteins. Statistical and structural analyses support a functional evolution scenario, where Rap1 isoforms of retrogenic origin are functionally distinct from their parental proteins. Indeed, all retrogene-encoded GTPases have an increased GTP/GDP binding ratio in vivo, indicating that their conformations resemble that of active GTP-bound Rap1. We furthermore demonstrate that these three Rap1 isoforms exhibit distinct affinities for the Ras-binding domain of RalGDS. Finally, when tested for their capacity to induce key cellular processes like integrin-mediated cell adhesion or cell spreading, marked differences are seen. Conclusions Together, these data lend strong support for an evolution scenario, where retrotransposition and subsequent mutation events generated species-specific Rap1 isoforms with differential signaling potential. Expression of the constitutively active human Rap1B-retro in cells like those derived from Ramos Burkitt's lymphoma and bone marrow from a patient with myelodysplastic syndrome (MDS) warrants further investigation into its role in disease development.
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Affiliation(s)
- Tomasz Zemojtel
- Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, Berlin, Germany.
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3
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Abstract
Epac1 is a guanine nucleotide exchange factor (GEF) for the small G protein Rap and is directly activated by cyclic AMP (cAMP). Upon cAMP binding, Epac1 undergoes a conformational change that allows the interaction of its GEF domain with Rap, resulting in Rap activation and subsequent downstream effects, including integrin-mediated cell adhesion and cell-cell junction formation. Here, we report that cAMP also induces the translocation of Epac1 toward the plasma membrane. Combining high-resolution confocal fluorescence microscopy with total internal reflection fluorescence and fluorescent resonance energy transfer assays, we observed that Epac1 translocation is a rapid and reversible process. This dynamic redistribution of Epac1 requires both the cAMP-induced conformational change as well as the DEP domain. In line with its translocation, Epac1 activation induces Rap activation predominantly at the plasma membrane. We further show that the translocation of Epac1 enhances its ability to induce Rap-mediated cell adhesion. Thus, the regulation of Epac1-Rap signaling by cAMP includes both the release of Epac1 from autoinhibition and its recruitment to the plasma membrane.
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D'Aiuto L, Robison CS, Gigante M, Nwanegbo E, Shaffer B, Sukhwani M, Castro CA, Chaillet JR. Human IL-12 p40 as a reporter gene for high-throughput screening of engineered mouse embryonic stem cells. BMC Biotechnol 2008; 8:52. [PMID: 18522747 PMCID: PMC2442052 DOI: 10.1186/1472-6750-8-52] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2008] [Accepted: 06/03/2008] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Establishing a suitable level of exogenous gene expression in mammalian cells in general, and embryonic stem (ES) cells in particular, is an important aspect of understanding pathways of cell differentiation, signal transduction and cell physiology. Despite its importance, this process remains challenging because of the poor correlation between the presence of introduced exogenous DNA and its transcription. Consequently, many transfected cells must be screened to identify those with an appropriate level of expression. To improve the screening process, we investigated the utility of the human interleukin 12 (IL-12) p40 cDNA as a reporter gene for studies of mammalian gene expression and for high-throughput screening of engineered mouse embryonic stem cells. RESULTS A series of expression plasmids were used to study the utility of IL-12 p40 as an accurate reporter of gene activity. These studies included a characterization of the IL-12 p40 expression system in terms of: (i) a time course of IL-12 p40 accumulation in the medium of transfected cells; (ii) the dose-response relationship between the input DNA and IL-12 p40 mRNA levels and IL-12 p40 protein secretion; (iii) the utility of IL-12 p40 as a reporter gene for analyzing the activity of cis-acting genetic elements; (iv) expression of the IL-12 p40 reporter protein driven by an IRES element in a bicistronic mRNA; (v) utility of IL-12 p40 as a reporter gene in a high-throughput screening strategy to identify successful transformed mouse embryonic stem cells; (vi) demonstration of pluripotency of IL-12 p40 expressing ES cells in vitro and in vivo; and (vii) germline transmission of the IL-12 p40 reporter gene. CONCLUSION IL-12 p40 showed several advantages as a reporter gene in terms of sensitivity and ease of the detection procedure. The IL-12 p40 assay was rapid and simple, in as much as the reporter protein secreted from the transfected cells was accurately measured by ELISA using a small aliquot of the culture medium. Remarkably, expression of Il-12 p40 does not affect the pluripotency of mouse ES cells. To our knowledge, human IL-12 p40 is the first secreted reporter protein suitable for high-throughput screening of mouse ES cells. In comparison to other secreted reporters, such as the widely used alkaline phosphatase (SEAP) reporter, the IL-12 p40 reporter system offers other real advantages.
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Affiliation(s)
- Leonardo D'Aiuto
- Department of Cell Biology and Physiology, Pittsburgh Development Center, Magee-Women's Research Institute, University of Pittsburgh School of Medicine, PA 15261, USA.
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5
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Abstract
Activation of caspases 3 and 9 is thought to commit a cell irreversibly to apoptosis. There are, however, several documented situations (e.g., during erythroblast differentiation) in which caspases are activated and caspase substrates are cleaved with no associated apoptotic response. Why the cleavage of caspase substrates leads to cell death in certain cases but not in others is unclear. One possibility is that some caspase substrates generate antiapoptotic signals when cleaved. Here we show that RasGAP is one such protein. Caspases cleave RasGAP into a C-terminal fragment (fragment C) and an N-terminal fragment (fragment N). Fragment C expressed alone induces apoptosis, but this effect could be totally blocked by fragment N. Fragment N could also block apoptosis induced by low levels of caspase 9. As caspase activity increases, fragment N is further cleaved into fragments N1 and N2. Apoptosis induced by high levels of caspase 9 or by cisplatin was strongly potentiated by fragment N1 or N2 but not by fragment N. The present study supports a model in which RasGAP functions as a sensor of caspase activity to determine whether or not a cell should survive. When caspases are mildly activated, the partial cleavage of RasGAP protects cells from apoptosis. When caspase activity reaches levels that allow completion of RasGAP cleavage, the resulting RasGAP fragments turn into potent proapoptotic molecules.
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Affiliation(s)
- J Y Yang
- Institut de Biologie Cellulaire et de Morphologie, Université de Lausanne, Lausanne, Switzerland
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Scita G, Tenca P, Frittoli E, Tocchetti A, Innocenti M, Giardina G, Di Fiore PP. Signaling from Ras to Rac and beyond: not just a matter of GEFs. EMBO J 2000; 19:2393-8. [PMID: 10835338 PMCID: PMC212757 DOI: 10.1093/emboj/19.11.2393] [Citation(s) in RCA: 173] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2000] [Revised: 04/06/2000] [Accepted: 04/06/2000] [Indexed: 11/12/2022] Open
Abstract
Members of a family of intracellular molecular switches, the small GTPases, sense modifications of the extracellular environment and transduce them into a variety of homeostatic signals. Among small GTPases, Ras and the Rho family of proteins hierarchically and/or coordinately regulate signaling pathways leading to phenotypes as important as proliferation, differentiation and apoptosis. Ras and Rho-GTPases are organized in a complex network of functional interactions, whose molecular mechanisms are being elucidated. Starting from the simple concept of linear cascades of events (GTPase-->activator--> GTPase), the work of several laboratories is uncovering an increasingly complex scenario in which upstream regulators of GTPases also function as downstream effectors and influence the precise biological outcome. Furthermore, small GTPases assemble into macromolecular machineries that include upstream activators, downstream effectors, regulators and perhaps even final biochemical targets. We are starting to understand how these macromolecular complexes work and how they are regulated and targeted to their proper subcellular localization. Ultimately, the acquisition of a cogent picture of the various levels of integration and regulation in small GTPase-mediated signaling should define the physiology of early signal transduction events and the pathological implication of its subversion.
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Affiliation(s)
- G Scita
- Department of Experimental Oncology, European Institute of Oncology, Via Ripamonti, 435, 20141 Milan, Italy.
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7
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Reedquist KA, Ross E, Koop EA, Wolthuis RM, Zwartkruis FJ, van Kooyk Y, Salmon M, Buckley CD, Bos JL. The small GTPase, Rap1, mediates CD31-induced integrin adhesion. J Cell Biol 2000; 148:1151-8. [PMID: 10725328 PMCID: PMC2174316 DOI: 10.1083/jcb.148.6.1151] [Citation(s) in RCA: 373] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/1999] [Accepted: 02/08/2000] [Indexed: 01/20/2023] Open
Abstract
Integrin-mediated leukocyte adhesion is a critical aspect of leukocyte function that is tightly regulated by diverse stimuli, including chemokines, antigen receptors, and adhesion receptors. How cellular signals from CD31 and other adhesion amplifiers are integrated with those from classical mitogenic stimuli to regulate leukocyte function remains poorly understood. Here, we show that the cytoplasmic tail of CD31, an important integrin adhesion amplifier, propagates signals that induce T cell adhesion via beta1 (VLA-4) and beta2 (LFA-1) integrins. We identify the small GTPase, Rap1, as a critical mediator of this effect. Importantly, CD31 selectively activated the small Ras-related GTPase, Rap1, but not Ras, R-Ras, or Rap2. An activated Rap1 mutant stimulated T lymphocyte adhesion to intercellular adhesion molecule (ICAM) and vascular cell adhesion molecule (VCAM), as did the Rap1 guanine nucleotide exchange factor C3G and a catalytically inactive mutant of RapGAP. Conversely, negative regulators of Rap1 signaling blocked CD31-dependent adhesion. These findings identify a novel important role for Rap1 in regulating ligand-induced cell adhesion and suggest that Rap1 may play a more general role in coordinating adhesion-dependent signals during leukocyte migration and extravasation. Our findings also suggest an alternative mechanism, distinct from interference with Ras-proximal signaling, by which Rap1 might mediate transformation reversion.
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Affiliation(s)
- Kris A. Reedquist
- Laboratory for Physiological Chemistry and Centre for Biomedical Genetics, Utrecht University Medical Center, Universiteitsweg 100, 3584 CG, Utrecht, The Netherlands
| | - Ewan Ross
- Division of Immunity and Infection, MRC Center for Immune Regulation, University of Birmingham, Birmingham B15 2TT, United Kingdom
| | - Elianne A. Koop
- Laboratory for Physiological Chemistry and Centre for Biomedical Genetics, Utrecht University Medical Center, Universiteitsweg 100, 3584 CG, Utrecht, The Netherlands
| | - Rob M.F. Wolthuis
- Laboratory for Physiological Chemistry and Centre for Biomedical Genetics, Utrecht University Medical Center, Universiteitsweg 100, 3584 CG, Utrecht, The Netherlands
| | - Fried J.T. Zwartkruis
- Laboratory for Physiological Chemistry and Centre for Biomedical Genetics, Utrecht University Medical Center, Universiteitsweg 100, 3584 CG, Utrecht, The Netherlands
| | - Yvette van Kooyk
- Department of Tumor Immunology, University Hospital Nijmegen, Nijmegen, The Netherlands
| | - Mike Salmon
- Division of Immunity and Infection, MRC Center for Immune Regulation, University of Birmingham, Birmingham B15 2TT, United Kingdom
| | - Christopher D. Buckley
- Division of Immunity and Infection, MRC Center for Immune Regulation, University of Birmingham, Birmingham B15 2TT, United Kingdom
| | - Johannes L. Bos
- Laboratory for Physiological Chemistry and Centre for Biomedical Genetics, Utrecht University Medical Center, Universiteitsweg 100, 3584 CG, Utrecht, The Netherlands
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Platelet-derived growth factor-dependent association of the GTPase-activating protein of Ras and Src. Biochem J 2000. [PMID: 10567236 DOI: 10.1042/bj3440519] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Here we report that the platelet-derived growth factor beta receptor (betaPDGFR) is not the only tyrosine kinase able to associate with the GTPase-activating protein of Ras (RasGAP). The interaction of non-betaPDGFR kinase(s) with RasGAP was dependent on stimulation with platelet-derived growth factor (PDGF) and seemed to require tyrosine phosphorylation of RasGAP. Because the tyrosine phosphorylation site of RasGAP is in a sequence context that is favoured by the Src homology 2 ('SH2') domain of Src family members, we tested the possibility that Src was the kinase that associated with RasGAP. Indeed, Src interacted with phosphorylated RasGAP fusion proteins; immunodepletion of Src markedly decreased the recovery of the RasGAP-associated kinase activity. Thus PDGF-dependent tyrosine phosphorylation of RasGAP results in the formation of a complex between RasGAP and Src. To begin to address the relevance of these observations, we focused on the consequences of the interaction of Src and RasGAP. We found that a receptor mutant that did not activate Src was unable to efficiently mediate the tyrosine phosphorylation of phospholipase Cgamma (PLCgamma). Taken together, these observations support the following hypothesis. When RasGAP is recruited to the betaPDGFR, it is phosphorylated and associates with Src. Once bound to RasGAP, Src is no longer able to promote the phosphorylation of PLCgamma. This hypothesis offers a mechanistic explanation for our previously published findings that the recruitment of RasGAP to the betaPDGFR attenuates the tyrosine phosphorylation of PLCgamma. Finally, these findings suggest a novel way in which RasGAP negatively regulates signal relay by the betaPDGFR.
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Abstract
Gene reporter systems play a key role in gene expression and regulation studies. This review describes the ideal reporter systems, including reporter expression vector design. It summarizes the many uses of genetic reporters and outlines the currently available and commonly used reporter systems. Each system is described in terms of the reporter gene, the protein it encodes, and the assays available for detecting presence of the reporter. In addition, each reporter system is analyzed in terms of its recommended uses, advantages, and limitations.
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Leblanc V, Delumeau I, Tocqué B. Ras-GTPase activating protein inhibition specifically induces apoptosis of tumour cells. Oncogene 1999; 18:4884-9. [PMID: 10490822 DOI: 10.1038/sj.onc.1202855] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Oncogenes and tumour suppressor genes control the balance between apoptotic death and anti-apoptotic survival signals determining whether a cell proliferates or dies. Through which effectors might oncoproteins generate sensitivity to apoptosis remains to be determined. Ras GTPase activating protein (Ras-GAP) is a key element in the Ras signalling pathway, being both a negative regulator and possibly an effector of Ras. Ras-GAP acts as a regulator of transcription, and possibly connects Ras to stress-activated protein kinases. A role for Ras-GAP in cell survival has been suspected from the study of knock-out mouse embryos. In search for selective killing of tumour cells, we asked whether Ras-GAP inhibition by other means would lead to apoptosis in established cell lines. We injected a monoclonal antibody directed against the SH3 domain of Ras-GAP (mAb200) that has been shown to block Ras-GAP downstream signalling into various human normal and tumour cell lines. We show that inhibition of Ras-GAP induces apoptosis specifically in tumour, but not in normal cells, therefore pointing at a specific role for Ras-GAP in tumour cell survival. MAb200-induced apoptosis is largely prevented by coinjection of activated RhoA or Cdc42 proteins, by injection of a constitutively activated mutant of phosphoinositide 3-OH kinase (PI3-K), but not by injection of v-Raf. These results show that targeting of Ras-GAP could represent a novel anticancer approach.
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Affiliation(s)
- V Leblanc
- ExonHit Therapeutics, 65 Bld Massena, 75013 Paris, France
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11
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Abdellatif M, Packer SE, Michael LH, Zhang D, Charng MJ, Schneider MD. A Ras-dependent pathway regulates RNA polymerase II phosphorylation in cardiac myocytes: implications for cardiac hypertrophy. Mol Cell Biol 1998; 18:6729-36. [PMID: 9774686 PMCID: PMC109256 DOI: 10.1128/mcb.18.11.6729] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/1998] [Accepted: 08/04/1998] [Indexed: 11/20/2022] Open
Abstract
Despite extensive evidence implicating Ras in cardiac muscle hypertrophy, the mechanisms involved are unclear. We previously reported that Ras, through an effector-like function of Ras GTPase-activating protein (GAP) in neonatal cardiac myocytes (M. Abdellatif et al., J. Biol. Chem. 269:15423-15426, 1994; M. Abdellatif and M. D. Schneider, J. Biol. Chem. 272:527-533, 1997), can up-regulate expression from a comprehensive set of promoters, including both cardiac cell-specific and constitutive ones. To investigate the mechanism(s) underlying these earlier findings, we have used recombinant adenoviruses harboring a dominant negative Ras (17N Ras) allele or the N-terminal domain of GAP (nGAP), responsible for the Ras-like effector function. Inhibition of endogenous Ras reduced basal levels of [3H]uridine and [3H]phenylalanine incorporation into total RNA, mRNA, and protein, with parallel changes in apparent cell size. In addition, 17N Ras markedly inhibited phosphorylation of the C-terminal domain (CTD) of RNA polymerase II (pol II), known to regulate transcript elongation, accompanied by down-regulation of its principal kinase, cyclin-dependent kinase 7 (Cdk7). In contrast, nGAP elicited the opposite effects on each of these parameters. Furthermore, cotransfection of constitutively active Ras (12R Ras) with wild-type pol II, rather than a truncated mutant lacking the CTD, demonstrated that Ras activation of transcription was dependent on the pol II CTD. Consistent with a potential role for this pathway in the development of cardiac myocyte hypertrophy, alpha1-adrenergic stimulation similarly enhanced pol II phosphorylation and Cdk7 expression, where both effects were inhibited by dominant negative Ras, while pressure overload hypertrophy led to an increase in both hyperphosphorylated and hypophosphorylated pol II in addition to Cdk7.
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Affiliation(s)
- M Abdellatif
- Molecular Cardiology Unit, Department of Medicine, Baylor College of Medicine, Houston, Texas 77030, USA.
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12
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Leblanc V, Tocque B, Delumeau I. Ras-GAP controls Rho-mediated cytoskeletal reorganization through its SH3 domain. Mol Cell Biol 1998; 18:5567-78. [PMID: 9710640 PMCID: PMC109141 DOI: 10.1128/mcb.18.9.5567] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Proteins of the Ras superfamily, Ras, Rac, Rho, and Cdc42, control the remodelling of the cortical actin cytoskeleton following growth factor stimulation. A major regulator of Ras, Ras-GAP, contains several structural motifs, including an SH3 domain and two SH2 domains, and there is evidence that they harbor a signalling function. We have previously described a monoclonal antibody to the SH3 domain of Ras-GAP which blocks Ras signalling in Xenopus oocytes. We now show that microinjection of this antibody into Swiss 3T3 cells prevents the formation of actin stress fibers stimulated by growth factors or activated Ras, but not membrane ruffling. This inhibition is bypassed by coinjection of activated Rho, suggesting that the Ras-GAP SH3 domain is necessary for endogenous Rho activation. In agreement, the antibody blocks lysophosphatidic acid-induced neurite retraction in differentiated PC12 cells. Furthermore, we demonstrate that microinjection of full-length Ras-GAP triggers stress fiber polymerization in fibroblasts in an SH3-dependent manner, strongly suggesting an effector function besides its role as a Ras downregulator. These results support the idea that Ras-GAP connects the Ras and Rho pathways and, therefore, regulates the actin cytoskeleton through a mechanism which probably does not involve p190 Rho-GAP.
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Affiliation(s)
- V Leblanc
- Rhône-Poulenc Rorer Central Research, Gene Medicine Department, Centre de Recherche de Vitry Alfortville, 94403 Vitry sur Seine, France.
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13
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Wolthuis RM, de Ruiter ND, Cool RH, Bos JL. Stimulation of gene induction and cell growth by the Ras effector Rlf. EMBO J 1997; 16:6748-61. [PMID: 9362489 PMCID: PMC1170279 DOI: 10.1093/emboj/16.22.6748] [Citation(s) in RCA: 145] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Rlf is a ubiquitously expressed distinct relative of RalGDS that interacts with active Ras in vitro. We now demonstrate that Rlf, when co-expressed with Ras mutants, associates in vivo with RasV12 and the effector-domain mutant RasV12G37, but not with RasV12E38 or RasV12C40. Rlf exhibits guanine nucleotide exchange activity towards the small GTPase Ral and, importantly, Rlf-induced Ral activation is stimulated by active Ras. In addition, RasV12 and RasV12G37 synergize with Rlf in the transcriptional activation of the c-fos promoter. Rlf, when targeted to the plasma membrane using the Ras farnesyl attachment site (Rlf-CAAX), is constitutively active, inducing both Ral activation and c-fos promoter activity. Rlf-CAAX-induced gene expression is insensitive to dominant negative Ras and the MEK inhibitor PD98059, and involves activation of the serum response element. Furthermore, expression of Rlf-CAAX is sufficient to induce proliferation of NIH 3T3 cells under low-serum conditions. These data demonstrate that Rlf is an effector of Ras which functions as an exchange factor for Ral. Rlf mediates a distinct Ras-induced signalling pathway to gene induction. Finally, a constitutively active form of Rlf can stimulate transcriptional activation and cell growth.
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Affiliation(s)
- R M Wolthuis
- Laboratory for Physiological Chemistry, Utrecht University, Universiteitsweg 100, 3584 CG Utrecht, The Netherlands
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14
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Hajnal A, Whitfield CW, Kim SK. Inhibition of Caenorhabditis elegans vulval induction by gap-1 and by let-23 receptor tyrosine kinase. Genes Dev 1997; 11:2715-28. [PMID: 9334333 PMCID: PMC316612 DOI: 10.1101/gad.11.20.2715] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
During induction of the Caenorhabditis elegans hermaphrodite vulva, a signal from the anchor cell activates the LET-23 epidermal growth factor receptor (EGFR)/LET-60 Ras/MPK-1 MAP kinase signaling pathway in the vulval precursor cells. We have characterized two mechanisms that limit the extent of vulval induction. First, we found that gap-1 may directly inhibit the LET-60 Ras signaling pathway. We identified the gap-1 gene in a genetic screen for inhibitors of vulval induction. gap-1 is predicted to encode a protein similar to GTPase-activating proteins that likely functions to inhibit the signaling activity of LET-60 Ras. A loss-of-function mutation in gap-1 suppresses the vulvaless phenotype of mutations in the let-60 ras signaling pathway, but a gap-1 single mutant does not exhibit excess vulval induction. Second, we found that let-23 EGFR prevents vulval induction in a cell-nonautonomous manner, in addition to its cell-autonomous role in activating the let-60 ras/mpk-1 signaling pathway. Using genetic mosaic analysis, we show that let-23 activity in the vulval precursor cell closest to the anchor cell (P6.p) prevents induction of vulval precursor cells further away from the anchor cell (P3.p, P4.p, and P8.p). This result suggests that LET-23 in proximal vulval precursor cells might bind and sequester the inductive signal LIN-3 EGF, thereby preventing diffusion of the inductive signal to distal vulval precursor cells.
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Affiliation(s)
- A Hajnal
- Department of Developmental Biology, Stanford University School of Medicine, Stanford, California 94305 USA
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15
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van der Geer P, Henkemeyer M, Jacks T, Pawson T. Aberrant Ras regulation and reduced p190 tyrosine phosphorylation in cells lacking p120-Gap. Mol Cell Biol 1997; 17:1840-7. [PMID: 9121432 PMCID: PMC232031 DOI: 10.1128/mcb.17.4.1840] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The Ras guanine nucleotide-binding protein functions as a molecular switch in signalling downstream of protein-tyrosine kinases. Ras is activated by exchange of GDP for GTP and is turned off by hydrolysis of bound GTP to GDP. Ras itself has a low intrinsic GTPase activity that can be stimulated by GTPase-activating proteins (GAPs), including p120-Gap and neurofibromin. These GAPs possess a common catalytic domain but contain distinct regulatory elements that may couple different external signals to control of the Ras pathway. p120-Gap, for example, has two N-terminal SH2 domains that directly recognize phosphotyrosine motifs on activated growth factor receptors and cytoplasmic phosphoproteins. To analyze the role of p120-Gap in Ras regulation in vivo, we have used fibroblasts derived from mouse embryos with a null mutation in the gene for p120-Gap (Gap). Platelet-derived growth factor stimulation of Gap-/- cells led to an abnormally large increase in the level of Ras-GTP and in the duration of mitogen-activated protein (MAP) kinase activation compared with wild-type cells, suggesting that p120-Gap is specifically activated following growth factor stimulation. Induction of DNA synthesis in response to platelet-derived growth factor and morphological transformation by the v-src and EJ-ras oncogenes were not significantly affected by the absence of p120-Gap. However, we found that normal tyrosine phosphorylation of p190-rhoGap, a cytoplasmic protein that associates with the p120-Gap SH2 domains, was dependent on the presence of p120-Gap. Our results suggest that p120-Gap has specific functions in downregulating the Ras/MAP kinase pathway following growth factor stimulation, and in modulating the phosphorylation of p190-rhoGap, but is not required for mitogenic signalling.
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Affiliation(s)
- P van der Geer
- Programme in Molecular Biology and Cancer, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada
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16
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Krautwald S, Büscher D, Kummer V, Buder S, Baccarini M. Involvement of the protein tyrosine phosphatase SHP-1 in Ras-mediated activation of the mitogen-activated protein kinase pathway. Mol Cell Biol 1996; 16:5955-63. [PMID: 8887625 PMCID: PMC231598 DOI: 10.1128/mcb.16.11.5955] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Ubiquitously expressed SH2-containing tyrosine phosphatases interact physically with tyrosine kinase receptors or their substrates and relay positive mitogenic signals via the activation of the Ras-mitogen-activated protein kinase (MAPK) pathway. Conversely, the structurally related phosphatase SHP-1 is predominantly expressed in hemopoietic cells and becomes tyrosine phosphorylated upon colony-stimulating factor 1 treatment of macrophages without associating with the colony-stimulating factor 1 receptor tyrosine kinase. Mice lacking functional SHP-1 (me/me and me(v)/me(v)) develop systemic autoimmune disease with accumulation of macrophages, suggesting that SHP-1 may be a negative regulator of hemopoietic cell growth. By using macrophages expressing dominant negative Ras and the me(v)/me(v) mouse mutant, we show that SHP-1 is activated in the course of mitogenic signal transduction in a Ras-dependent manner and that its activity is necessary for the Ras-dependent activation of the MAPK pathway but not of the Raf-1 kinase. Consistent with a role for SHP-1 as an intermediate between Ras and the MEK-MAPK pathway, Ras-independent activation of the latter kinases by bacterial lipopolysaccharide occurred normally in me(v)/me(v) cells. Our results sharply accentuate the diversity of signal transduction in mammalian cells, in which the same signaling intermediates can be rearranged to form different pathways.
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Affiliation(s)
- S Krautwald
- Department of Immunobiology, Fraunhofer Institute for Toxicology and Molecular Biology, Hannover, Germany
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17
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Pomerance M, Thang MN, Tocque B, Pierre M. The Ras-GTPase-activating protein SH3 domain is required for Cdc2 activation and mos induction by oncogenic Ras in Xenopus oocytes independently of mitogen-activated protein kinase activation. Mol Cell Biol 1996; 16:3179-86. [PMID: 8649428 PMCID: PMC231311 DOI: 10.1128/mcb.16.6.3179] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The Ras-GTPase-activating protein (RasGAP) is an important modulator of p21ras - dependent signal transduction in Xenopus oocytes and in mammalian cells. We investigated the role of the RasGAP SH3 domain in signal transduction with a monoclonal antibody against the SH3 domain of RasGaP. This antibody prevented the activation of the maturation-promoting factor complex (cyclin B-p34cdc2) by oncogenic Ras. The antibody appears to be specific because as little as 5 ng injected per oocyte reduced the level of Cdc2 activation by 50% whereas 100 ng of nonspecific immunoglobulin G did not affect Cdc2 activation. The antibody blocked the Cdc2 activation induced by oncogenic Ras but not that induced by progesterone, which acts independently of Ras. A peptide corresponding to positions 317 to 326 of a sequence in the SH3 domain of human RasGAP blocked Cdc2 activation, whereas a peptide corresponding to positions 273 to 305 of a sequence in the N-terminal moiety of the SH3 domain of RasGAP had no effect. The antibody did not block the mitogen-activated protein (MAP) kinase cascade (activation of MAPK/ERK kinase [MEK], MAP kinase, and S6 kinase p90rsk). Surprisingly, injection of the negative MAP kinase mutant protein ERK2 K52R (containing a K-to-R mutation at position 52) blocked the Cdc2 activation induced by oncogenic Ras as well as blocking the activation of MAP kinase. Thus, MAP kinase is also implicated in the regulation of Cdc2 activity. In this study, we further investigated the regulation of the synthesis of the c-mos oncogene product, which is necessary for the activation of Cdc2. We report that the synthesis of the c-mos oncogene product, which is necessary for the activation antibody to the SH3 domain of RasGAP and by injecting the negative MAP kinase mutant protein ERK2 K52R. These results suggest that oncogenic Ras activates two signaling mechanisms: the MAP kinase cascade and a signaling pathway implicating the SH3 domain of RasGAP. These mechanisms might control Mos protein expression implicated in Cdc2 activation.
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Affiliation(s)
- M Pomerance
- Unité de Recherche sur la Glande Thyroïde et la Régulation Hormonale, U96 Institut National de la Santé et de la Recherche Médicale, Le Kremlin-Bicêtre, France
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18
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Xu YY, Bhavani K, Wands JR, de la Monte SM. Ethanol inhibits insulin receptor substrate-1 tyrosine phosphorylation and insulin-stimulated neuronal thread protein gene expression. Biochem J 1995; 310 ( Pt 1):125-32. [PMID: 7646434 PMCID: PMC1135863 DOI: 10.1042/bj3100125] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Neuronal thread proteins (NTPs) are molecules that accumulate in the brains of patients with Alzheimer's disease, and may play a key role in both normal and neurodegenerative neuritic sprouting. In this investigation we determined whether NTP expression is up-regulated by insulin, an important neurotrophic factor that stimulates differentiation-associated neurite outgrowth, and studied the effects of ethanol, a known inhibitor of growth factor receptor tyrosine phosphorylation, on NTP expression and insulin-mediated signal transduction cascade in neuronal [primitive neuroectodermal tumour cell line 2; (PNET2)] cells. PNET2 cells were treated with 50 m-units/ml insulin in the presence or absence of 100 mM ethanol for 0.2-96 h, and cell proliferation and expression of NTP molecules were investigated by metabolic labelling, immunoprecipitation and immunohistochemical staining. Insulin stimulation resulted in an immediate increase in the levels of three (38, 18 and 15 kDa) of five NTP species (the others were of 26 and 21 kDa), followed by a decline in expression within 120 min; however, studies performed up to 96 h of culture demonstrated up-regulation by insulin of all five NTP species. Ethanol either abolished or severely muted the short- and long-term insulin-mediated upregulation of NTP expression, and substantially reduced insulin-mediated neuronal differentiation. The effects of ethanol on NTP gene expression were associated with impaired insulin-mediated tyrosine phosphorylation of both the insulin receptor beta subunit and the insulin receptor substrate-1 (IRS-1), resulting in decreased association of phosphatidylinositol 3-kinase with IRS-1. The findings suggest that ethanol may inhibit NTP expression associated with central nervous system neuronal differentiation by uncoupling the IRS-1-mediated insulin signal transduction pathway.
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Affiliation(s)
- Y Y Xu
- Department of Pathology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
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19
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Valius M, Secrist JP, Kazlauskas A. The GTPase-activating protein of Ras suppresses platelet-derived growth factor beta receptor signaling by silencing phospholipase C-gamma 1. Mol Cell Biol 1995; 15:3058-71. [PMID: 7760802 PMCID: PMC230537 DOI: 10.1128/mcb.15.6.3058] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The beta receptor for platelet-derived growth factor (beta PDGFR) is activated by binding of PDGF and undergoes phosphorylation at multiple tyrosine residues. The tyrosine-phosphorylated receptor associates with numerous SH2-domain-containing proteins which include phospholipase C-gamma 1 (PLC gamma), the GTPase-activating protein of Ras (GAP), the p85 subunit of phosphatidylinositol 3 kinase (PI3K), the phosphotyrosine phosphatase Syp, and several other proteins. Our previous studies indicated that PI3K and PLC gamma were required for relay of the mitogenic signal of beta PDGFR, whereas GAP and Syp did not appear to be required for this response. In this study, we further investigated the role of GAP and Syp in mitogenic signaling by beta PDGFR. Focusing on the PLC gamma-dependent branch of beta PDGFR signaling, we constructed a series of mutant beta PDGFRs that contained the binding sites for pairs of the receptor-associated proteins: PLC gamma and PI3K, PLC gamma and GAP, or PLC gamma and Syp. Characterization of these mutants showed that while all receptors were catalytically active and bound similar amounts of PLC gamma, they differed dramatically in their ability to initiate DNA synthesis. This signaling deficiency related to an inability to efficiently tyrosine phosphorylate and activate PLC gamma. Surprisingly, the crippled receptor was the one that recruited PLC gamma and GAP. Thus, GAP functions to suppress signal relay by the beta PDGFR, and it does so by silencing PLC gamma. These findings demonstrate that the biological response to PDGF depends not only on the ability of the beta PDGFR to recruit signal relay enzymes but also on the blend of these receptor-associated proteins.
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Affiliation(s)
- M Valius
- Department of Pediatrics, National Jewish Center for Immunology and Respiratory Medicine, Denver, Colorado 80206, USA
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20
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Muscarinic receptors transform NIH 3T3 cells through a Ras-dependent signalling pathway inhibited by the Ras-GTPase-activating protein SH3 domain. Mol Cell Biol 1994. [PMID: 7969134 DOI: 10.1128/mcb.14.12.7943] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Expression of certain subtypes of human muscarinic receptors in NIH 3T3 cells provides an agonist-dependent model of cellular transformation by formation of foci in response to carbachol. Although focus formation correlates with the ability of the muscarinic receptors to activate phospholipase C, the actual mitogenic signal transduction pathway is unknown. Through cotransfection experiments and measurement of the activation state of native and epitope-tagged Ras proteins, the contributions of Ras and Ras GTPase-activating protein (Ras-GAP) to muscarinic receptor-dependent transformation were defined. Transforming muscarinic receptors were able to activate Ras, and such activation was required for transformation because focus formation was inhibited by coexpression of either Ras with a dominant-negative mutation or constructs of Ras-GAP that include the catalytic domain. Coexpression of the N-terminal region of GAP or of its isolated SH3 (Src homology 3) domain, but not its SH2 domain, was also sufficient to suppress muscarinic receptor-dependent focus formation. Point mutations at conserved residues in the Ras-GAP SH3 domain reversed its action, leading to an increase in carbachol-dependent transformation. The inhibitory effect of expression of the Ras-GAP SH3 domain occurs proximal to Ras activation and is selective for the mitogenic pathway activated by carbachol, as cellular transformation by either v-Ras or trkA/nerve growth factor is unaffected.
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21
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Mattingly RR, Sorisky A, Brann MR, Macara IG. Muscarinic receptors transform NIH 3T3 cells through a Ras-dependent signalling pathway inhibited by the Ras-GTPase-activating protein SH3 domain. Mol Cell Biol 1994; 14:7943-52. [PMID: 7969134 PMCID: PMC359333 DOI: 10.1128/mcb.14.12.7943-7952.1994] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Expression of certain subtypes of human muscarinic receptors in NIH 3T3 cells provides an agonist-dependent model of cellular transformation by formation of foci in response to carbachol. Although focus formation correlates with the ability of the muscarinic receptors to activate phospholipase C, the actual mitogenic signal transduction pathway is unknown. Through cotransfection experiments and measurement of the activation state of native and epitope-tagged Ras proteins, the contributions of Ras and Ras GTPase-activating protein (Ras-GAP) to muscarinic receptor-dependent transformation were defined. Transforming muscarinic receptors were able to activate Ras, and such activation was required for transformation because focus formation was inhibited by coexpression of either Ras with a dominant-negative mutation or constructs of Ras-GAP that include the catalytic domain. Coexpression of the N-terminal region of GAP or of its isolated SH3 (Src homology 3) domain, but not its SH2 domain, was also sufficient to suppress muscarinic receptor-dependent focus formation. Point mutations at conserved residues in the Ras-GAP SH3 domain reversed its action, leading to an increase in carbachol-dependent transformation. The inhibitory effect of expression of the Ras-GAP SH3 domain occurs proximal to Ras activation and is selective for the mitogenic pathway activated by carbachol, as cellular transformation by either v-Ras or trkA/nerve growth factor is unaffected.
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Affiliation(s)
- R R Mattingly
- Department of Microbiology and Molecular Genetics, University of Vermont College of Medicine, Burlington 05405-0068
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22
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A novel mammalian Ras GTPase-activating protein which has phospholipid-binding and Btk homology regions. Mol Cell Biol 1994. [PMID: 7935405 DOI: 10.1128/mcb.14.10.6879] [Citation(s) in RCA: 81] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have previously purified a novel GTPase-activating protein (GAP) for Ras which is immunologically distinct from the known Ras GAPs, p120GAP and neurofibromin (M. Maekawa, S. Nakamura, and S. Hattori, J. Biol. Chem. 268:22948-22952, 1993). On the basis of the partial amino acid sequence, we have obtained a cDNA which encodes the novel Ras GAP. The predicted protein consists of 847 amino acids whose calculated molecular mass, 96,369 Da, is close to the apparent molecular mass of the novel Ras GAP, 100 kDa. The amino acid sequence shows a high degree of similarity to the entire sequence of the Drosophila melanogaster Gap1 gene. When the catalytic domain of the novel GAP was compared with that of Drosophila Gap1, p120GAP, and neurofibromin, the highest degree of similarity was again observed with Gap1. Thus, we designated this gene Gap1m, a mammalian counterpart of the Drosophila Gap1 gene. Expression of Gap1m was relatively high in brain, placenta, and kidney tissues, and it was expressed at low levels in other tissues. A recombinant protein consisting of glutathione-S-transferase and the GAP-related domain of Gap1m stimulated GTPase of normal Ras but not that of Ras having valine at the 12th residue. Expression of the same region in Saccharomyces cerevisiae suppressed the ira2- phenotype. In addition to the GAP catalytic domain, Gap1m has two domains with sequence closely related to those of the phospholipid-binding domain of synaptotagmin and a region with similarity to the unique domain of Btk tyrosine kinase. These results clearly show that Gap1m is a novel Ras GAP molecule of mammalian cells.
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23
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Maekawa M, Li S, Iwamatsu A, Morishita T, Yokota K, Imai Y, Kohsaka S, Nakamura S, Hattori S. A novel mammalian Ras GTPase-activating protein which has phospholipid-binding and Btk homology regions. Mol Cell Biol 1994; 14:6879-85. [PMID: 7935405 PMCID: PMC359218 DOI: 10.1128/mcb.14.10.6879-6885.1994] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
We have previously purified a novel GTPase-activating protein (GAP) for Ras which is immunologically distinct from the known Ras GAPs, p120GAP and neurofibromin (M. Maekawa, S. Nakamura, and S. Hattori, J. Biol. Chem. 268:22948-22952, 1993). On the basis of the partial amino acid sequence, we have obtained a cDNA which encodes the novel Ras GAP. The predicted protein consists of 847 amino acids whose calculated molecular mass, 96,369 Da, is close to the apparent molecular mass of the novel Ras GAP, 100 kDa. The amino acid sequence shows a high degree of similarity to the entire sequence of the Drosophila melanogaster Gap1 gene. When the catalytic domain of the novel GAP was compared with that of Drosophila Gap1, p120GAP, and neurofibromin, the highest degree of similarity was again observed with Gap1. Thus, we designated this gene Gap1m, a mammalian counterpart of the Drosophila Gap1 gene. Expression of Gap1m was relatively high in brain, placenta, and kidney tissues, and it was expressed at low levels in other tissues. A recombinant protein consisting of glutathione-S-transferase and the GAP-related domain of Gap1m stimulated GTPase of normal Ras but not that of Ras having valine at the 12th residue. Expression of the same region in Saccharomyces cerevisiae suppressed the ira2- phenotype. In addition to the GAP catalytic domain, Gap1m has two domains with sequence closely related to those of the phospholipid-binding domain of synaptotagmin and a region with similarity to the unique domain of Btk tyrosine kinase. These results clearly show that Gap1m is a novel Ras GAP molecule of mammalian cells.
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Affiliation(s)
- M Maekawa
- Division of Biochemistry and Cellular Biology, National Center of Neurology and Psychiatry, Tokyo, Japan
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24
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Skorski T, Kanakaraj P, Ku DH, Nieborowska-Skorska M, Canaani E, Zon G, Perussia B, Calabretta B. Negative regulation of p120GAP GTPase promoting activity by p210bcr/abl: implication for RAS-dependent Philadelphia chromosome positive cell growth. J Exp Med 1994; 179:1855-65. [PMID: 8195713 PMCID: PMC2191514 DOI: 10.1084/jem.179.6.1855] [Citation(s) in RCA: 82] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The p210bcr/abl tyrosine kinase appears to be responsible for initiating and maintaining the leukemic phenotype in chronic myelogenous leukemia (CML) patients. p21ras-p120GAP interactions play a central role in transducing mitogenic signals. Therefore, we investigated whether p21ras and p120GAP are regulated by p210bcr/abl, and whether this activation is functionally significant for CML cell proliferation. We report that transient expression of p210bcr/abl in fibroblast-like cells induces simultaneous activation of p21ras and inhibition of GTPase-promoting activity of p120GAP, and confirm these data showing that downregulation of p210bcr/abl expression in CML cells with bcr/abl antisense oligodeoxynucleotides induces both inhibition of p21ras activation and stimulation of GTPase-promoting activity of p120GAP. Tyrosine phosphorylation of two p120GAP-associated proteins, p190 and p62, which may affect p120GAP activity, also depends on p210bcr/abl tyrosine kinase expression. Direct dependence of these effects on the kinase activity is proven in experiments in which expression of c-MYB protein in fibroblast-like cells or downregulation of c-MYB expression resulting in analogous inhibition of CML cell proliferation does not result in the same changes. Use of specific antisense oligodeoxynucleotides to downregulate p21ras expression revealed a requirement for functional p21ras in the proliferation of Philadelphia chromosome-positive CML primary cells. Thus, the p210bcr/abl-dependent regulation of p120GAP activity is responsible, in part, for the maintenance of p21ras in the active GTP-bound form, a crucial requirement for CML cell proliferation.
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MESH Headings
- Base Sequence
- Cell Division/drug effects
- Cell Division/physiology
- Cell Line
- Chromosomes, Human, Pair 15
- Chromosomes, Human, Pair 17
- Chromosomes, Human, Pair 22
- Chromosomes, Human, Pair 9
- Fusion Proteins, bcr-abl/metabolism
- GTP Phosphohydrolases/metabolism
- GTPase-Activating Proteins
- Gene Expression Regulation, Neoplastic/drug effects
- Homeostasis
- Humans
- Leukemia, Myelogenous, Chronic, BCR-ABL Positive/genetics
- Molecular Sequence Data
- Oligonucleotides, Antisense/pharmacology
- Oncogenes/drug effects
- Philadelphia Chromosome
- Proteins/metabolism
- Proto-Oncogene Proteins p21(ras)/metabolism
- Proto-Oncogenes/drug effects
- Signal Transduction
- Translocation, Genetic
- Tumor Cells, Cultured
- ras GTPase-Activating Proteins
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Affiliation(s)
- T Skorski
- Department of Microbiology and Immunology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107
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25
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Abstract
Considerable progress has been made over the past year in elucidating the mechanisms by which extracellular signals are transduced via cell surface receptors to trigger changes in gene expression which determine the growth and differentiated state of a cell. In particular, Ras proteins have been implicated as key intermediates that mediate the signal from upstream tyrosine kinases to a downstream cascade of serine/threonine kinases, which then activate nuclear factors that control gene expression and protein synthesis. How Ras proteins function is regulated in this role as a molecular switch, and how the signal is transmitted between the various components of the pathway, are now being determined. Finally, the Rho family of Ras-related proteins, which regulate the actin cytoskeleton, have also been implicated as mediators of oncogenic Ras transformation. The brisk pace at which the key components of Ras-mediated signal transduction pathways are being identified hold great promise that new targets for therapeutic intervention in cancer may now be identified.
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Affiliation(s)
- R Khosravi-Far
- Department of Pharmacology, School of Medicine, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill 27599-7365
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26
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Skorski T, Kanakaraj P, Nieborowska-Skorska M, Ratajczak M, Szczylik C, Zon G, Arlinghaus RB, Gewirtz A, Perussia B, Calabretta B. p120 GAP requirement in normal and malignant human hematopoiesis. J Exp Med 1993; 178:1923-33. [PMID: 8245773 PMCID: PMC2191281 DOI: 10.1084/jem.178.6.1923] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
There is evidence to suggest that the p120 GAP (GAP), originally described as an inhibitor of p21ras, may also serve as a downstream effector of ras-regulated signal transduction. To determine whether GAP expression is required for the growth of human normal and leukemic hematopoietic cells, we used GAP antisense oligodeoxynucleotides to inhibit it and analyzed the effects of this inhibition on the colony-forming ability of nonadherent, T lymphocyte-depleted mononuclear cells and of highly purified progenitors (CD34+ MNC) obtained from the bone marrow and peripheral blood of healthy volunteers or chronic myeloid leukemia (CML, bcr-abl-positive) patients. The acute myelogenous leukemia cell line MO7, the Philadelphia BV173 cell line, and the acute promyelocytic leukemia NB4 and HL-60 cell lines were similarly examined. GAP antisense treatment inhibited colony formation from normal myelo-, erythro-, and megakaryopoietic progenitor cells as well as from CML progenitor cells. Proliferation of MO7 (growth factor-dependent) and BV173 (bcr-abl-dependent) cells, but not that of NB4 and HL-60 (growth factor-independent) cells, was also inhibited, even though a specific downregulation of GAP was observed in each cell line, as analyzed by either or both mRNA and protein expression. Stimulation of MO7 cells with hematopoietic growth factors increased the expression of GAP as well as the levels of active GTP-bound p21ras. Stimulation of GAP expression was inhibited upon GAP antisense treatment. These data indicate that p120 GAP is involved in human normal and leukemic hemopoiesis and strongly suggest that GAP is not only a p21ras inhibitor (signal terminator), but also a positive signal transducer.
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Affiliation(s)
- T Skorski
- Jefferson Cancer Institute, Thomas Jefferson University, Philadelphia, Pennsylvania 19107
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27
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Zhang W, Johnson JD, Rutter WJ. Association and phosphorylation-dependent dissociation of proteins in the insulin receptor complex. Proc Natl Acad Sci U S A 1993; 90:11317-21. [PMID: 7504303 PMCID: PMC47973 DOI: 10.1073/pnas.90.23.11317] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Receptor tyrosine kinases have been found to interact with a variety of specific signaling molecules. To detect molecules that interact with the insulin receptor, we have produced a modified insulin receptor with an additional epitope allowing rapid purification under mild conditions of the insulin receptor complex. By this method we have found multiple proteins (including the p85 subunit of phosphatidylinositol 3'-kinase and the ras GTPase-activating protein) that specifically associate with the activated (phosphorylated) insulin receptor (insulin receptor complex proteins) but are released from the complex after they are phosphorylated on tyrosine residues. We have also shown that tyrosine phosphorylation of p85 by the activated insulin receptor blocks binding to the activated receptor. These results suggest that association of proteins with the insulin receptor complex is controlled by phosphorylation of the receptor, while dissociation of insulin receptor complex proteins is controlled in turn by phosphorylation of the proteins in the insulin receptor complex. This process results in the dispersion of phosphorylated insulin receptor complex proteins into the cell.
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Affiliation(s)
- W Zhang
- Hormone Research Institute, University of California, San Francisco 94143-0534
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28
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Abstract
Morphological transformation of NIH 3T3 cells was observed following coexpression of a portion of the ras GTPase-activating protein (GAP) comprising the amino terminus (GAP-N) and a mutant of v-src (MDSRC) lacking the membrane-localizing sequence. Cells expressing either of these genes alone remained nontransformed. Coexpression of GAP-N with MDSRC did not alter the subcellular localization, kinase activity, or pattern of cellular substrates phosphorylated by the MDSRC product. In contrast to SHC, phospholipase C-gamma 1, and the p85 alpha phosphatidylinositol 3'-kinase subunit, the endogenous GAP product (p120GAP) was highly tyrosine-phosphorylated only in cells transformed by wild-type v-src. Furthermore, for transformation induced by wild-type v-src as well as by coexpression of MDSRC and GAP-N, a strict correlation was observed between cell transformation, elevated tyrosine phosphorylation of p62, p190, and a novel protein of 150 kDa, and complex formation between these proteins and p120GAP. As with cells transformed by wild-type v-src, the MDSRC plus GAP-N transformants remained dependent on endogenous Ras. The results suggest that tyrosine phosphorylation and complex formation involving p120GAP represent critical elements of cell transformation by v-src and that complementation of the cytosolic v-src mutant by GAP-N results, at least in part, from the formation of these complexes.
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29
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DeClue JE, Vass WC, Johnson MR, Stacey DW, Lowy DR. Functional role of GTPase-activating protein in cell transformation by pp60v-src. Mol Cell Biol 1993; 13:6799-809. [PMID: 7692232 PMCID: PMC364742 DOI: 10.1128/mcb.13.11.6799-6809.1993] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Morphological transformation of NIH 3T3 cells was observed following coexpression of a portion of the ras GTPase-activating protein (GAP) comprising the amino terminus (GAP-N) and a mutant of v-src (MDSRC) lacking the membrane-localizing sequence. Cells expressing either of these genes alone remained nontransformed. Coexpression of GAP-N with MDSRC did not alter the subcellular localization, kinase activity, or pattern of cellular substrates phosphorylated by the MDSRC product. In contrast to SHC, phospholipase C-gamma 1, and the p85 alpha phosphatidylinositol 3'-kinase subunit, the endogenous GAP product (p120GAP) was highly tyrosine-phosphorylated only in cells transformed by wild-type v-src. Furthermore, for transformation induced by wild-type v-src as well as by coexpression of MDSRC and GAP-N, a strict correlation was observed between cell transformation, elevated tyrosine phosphorylation of p62, p190, and a novel protein of 150 kDa, and complex formation between these proteins and p120GAP. As with cells transformed by wild-type v-src, the MDSRC plus GAP-N transformants remained dependent on endogenous Ras. The results suggest that tyrosine phosphorylation and complex formation involving p120GAP represent critical elements of cell transformation by v-src and that complementation of the cytosolic v-src mutant by GAP-N results, at least in part, from the formation of these complexes.
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Affiliation(s)
- J E DeClue
- Laboratory of Cellular Oncology, National Cancer Institute, Bethesda, Maryland 20892
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30
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Alpha 2-chimerin, an SH2-containing GTPase-activating protein for the ras-related protein p21rac derived by alternate splicing of the human n-chimerin gene, is selectively expressed in brain regions and testes. Mol Cell Biol 1993. [PMID: 8336731 DOI: 10.1128/mcb.13.8.4986] [Citation(s) in RCA: 59] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
n-Chimerin (alpha 1-chimerin) is a brain GTPase-activating protein (GAP) for the ras-related p21rac. We now report the occurrence of another form of chimerin, termed alpha 2-chimerin. This is the product of an alternately spliced transcript of the human n-chimerin gene encoding an N-terminal SH2 (src homology 2) domain in addition to the phorbol ester receptor and GAP domains. alpha 1- and alpha 2-chimerin mRNAs were expressed differently. In the rat brain, only alpha 1-chimerin mRNA was expressed in cerebellar Purkinje cells, although both alpha 1- and alpha 2-chimerin mRNAs occurred in neurons in the cerebral cortex, hippocampus, and thalamus. Only alpha 2-chimerin RNA was expressed in rat testes, in early pachytene spermatocytes. A 45-kDa SH2-containing chimerin corresponding to the alpha 2 form was purified from rat brain. As with Escherichia coli 45-kDa recombinant alpha 2-chimerin, purified brain alpha 2-chimerin exhibited racGAP activity which was stimulated by phosphatidylserine. The recombinant SH2 domain bound several 32P-labelled phosphoproteins of PC12 cells, whose phosphorylation increased in response to trophic factors, including nerve growth factor. To examine the relationships of alpha 1- and alpha 2-chimerin transcripts, human genomic DNA clones were characterized. In alpha 2-chimerin mRNA, a 3' splice acceptor site within exon 1 of alpha 1-chimerin mRNA was used, replacing its 5' untranslated region and N-terminal coding sequence. The single human n-chimerin gene was mapped to chromosome 2q31-q32.1, colocalizing with the CRE-BP1 transcription factor gene (2q32). It contained several splice junctions conserved with the sequence-related protein kinase C and bcr genes. alpha 2-Chimerin is only the second SH2-containing GAP and the first example of an SH2 domain generated by alternate splicing.
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Hall C, Sin WC, Teo M, Michael GJ, Smith P, Dong JM, Lim HH, Manser E, Spurr NK, Jones TA. Alpha 2-chimerin, an SH2-containing GTPase-activating protein for the ras-related protein p21rac derived by alternate splicing of the human n-chimerin gene, is selectively expressed in brain regions and testes. Mol Cell Biol 1993; 13:4986-98. [PMID: 8336731 PMCID: PMC360144 DOI: 10.1128/mcb.13.8.4986-4998.1993] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
n-Chimerin (alpha 1-chimerin) is a brain GTPase-activating protein (GAP) for the ras-related p21rac. We now report the occurrence of another form of chimerin, termed alpha 2-chimerin. This is the product of an alternately spliced transcript of the human n-chimerin gene encoding an N-terminal SH2 (src homology 2) domain in addition to the phorbol ester receptor and GAP domains. alpha 1- and alpha 2-chimerin mRNAs were expressed differently. In the rat brain, only alpha 1-chimerin mRNA was expressed in cerebellar Purkinje cells, although both alpha 1- and alpha 2-chimerin mRNAs occurred in neurons in the cerebral cortex, hippocampus, and thalamus. Only alpha 2-chimerin RNA was expressed in rat testes, in early pachytene spermatocytes. A 45-kDa SH2-containing chimerin corresponding to the alpha 2 form was purified from rat brain. As with Escherichia coli 45-kDa recombinant alpha 2-chimerin, purified brain alpha 2-chimerin exhibited racGAP activity which was stimulated by phosphatidylserine. The recombinant SH2 domain bound several 32P-labelled phosphoproteins of PC12 cells, whose phosphorylation increased in response to trophic factors, including nerve growth factor. To examine the relationships of alpha 1- and alpha 2-chimerin transcripts, human genomic DNA clones were characterized. In alpha 2-chimerin mRNA, a 3' splice acceptor site within exon 1 of alpha 1-chimerin mRNA was used, replacing its 5' untranslated region and N-terminal coding sequence. The single human n-chimerin gene was mapped to chromosome 2q31-q32.1, colocalizing with the CRE-BP1 transcription factor gene (2q32). It contained several splice junctions conserved with the sequence-related protein kinase C and bcr genes. alpha 2-Chimerin is only the second SH2-containing GAP and the first example of an SH2 domain generated by alternate splicing.
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Affiliation(s)
- C Hall
- Department of Neurochemistry, Institute of Neurology, London
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Tomáska L, Resnick RJ. Involvement of a phosphotyrosine protein phosphatase in the suppression of platelet-derived growth factor receptor autophosphorylation in ras-transformed cells. Biochem J 1993; 293 ( Pt 1):215-21. [PMID: 8328963 PMCID: PMC1134342 DOI: 10.1042/bj2930215] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The nature of the suppression of platelet-derived growth factor (PDGF) receptor autophosphorylation in ras-transformed NIH 3T3 fibroblasts was investigated. The PDGF receptor from ras-transformed cells that had been purified by wheatgerm-lectin affinity chromatography displayed normal PDGF-induced autophosphorylation, indicating that the receptor is not irreversibly modified. Various phosphotyrosine-protein-phosphatase inhibitors did not reverse the inhibition of PDGF-receptor kinase in crude membrane preparations from ras-transformed cells. However, treatment of intact ras-transformed cells both with 2 mM sodium orthovanadate and with 20 microM phenylarsine oxide restored PDGF-receptor tyrosine-kinase activity to a level similar to that observed in normal cells. Direct measurement of the phosphatase activities in crude cellular fractions revealed a 2.5-fold higher membrane-associated phosphotyrosine-protein-phosphatase activity in ras-transformed cells, whereas phosphoserine-protein-phosphatase activity remained unchanged between the cell lines. These data suggest that the suppression of the PDGF-receptor tyrosine-kinase activity in ras-transformed cells is mediated via an inhibitory component, distinct from the receptor, that may be positively regulated by the dephosphorylation of tyrosine residue(s).
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Affiliation(s)
- L Tomáska
- Section of Biochemistry, Molecular and Cell Biology, Cornell University, Ithaca, NY 14853
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Clark GJ, Quilliam LA, Hisaka MM, Der CJ. Differential antagonism of Ras biological activity by catalytic and Src homology domains of Ras GTPase activation protein. Proc Natl Acad Sci U S A 1993; 90:4887-91. [PMID: 8506332 PMCID: PMC46618 DOI: 10.1073/pnas.90.11.4887] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Ras p120 GTPase activation protein (GAP), a cytosolic protein, is a negative mediator and potential downstream effector of Ras function. Since membrane association is critical for Ras function, we introduced the Ras membrane-targeting signal (a 19-residue peptide ending in CAAX, where C = cysteine, A = aliphatic amino acid, and X = any amino acid) onto the GAP N-terminal Src homology 2 and 3 and the C-terminal catalytic domains (designated nGAP/CAAX and cGAP/CAAX, respectively) to determine the role of membrane association in GAP function. cGAP/CAAX and full-length GAP/CAAX, but not GAP or nGAP/CAAX, exhibited potent growth inhibitory activity. Whereas both oncogenic and normal Ras activity were inhibited by cGAP/CAAX, nGAP/CAAX, despite lacking the Ras binding domain, inhibited the activity of oncogenic Ras without affecting the action of normal Ras. Altogether, these results demonstrate that membrane association potentiates GAP catalytic activity, support an effector function for GAP, and suggest that normal and oncogenic Ras possess different downstream interactions.
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Affiliation(s)
- G J Clark
- University of North Carolina, Department of Pharmacology, School of Medicine, Chapel Hill
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Kozma L, Baltensperger K, Klarlund J, Porras A, Santos E, Czech MP. The ras signaling pathway mimics insulin action on glucose transporter translocation. Proc Natl Acad Sci U S A 1993; 90:4460-4. [PMID: 8389451 PMCID: PMC46531 DOI: 10.1073/pnas.90.10.4460] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Recent observations suggest that insulin increases cellular levels of activated, GTP-bound Ras protein. We tested whether the acute actions of insulin on hexose uptake and glucose-transporter redistribution to the cell surface are mimicked by activated Ras. 3T3-L1 fibroblasts expressing an activated mutant (Lys-61) N-Ras protein exhibited a 3-fold increase in 2-deoxyglucose uptake rates compared with non-transfected cells. Insulin stimulated hexose uptake by approximately 2-fold in parental fibroblasts but did not stimulate hexose uptake in the N-Ras61K-expressing fibroblasts. Overexpression of N-Ras61K also mimicked the large effect of insulin on 2-deoxyglucose transport in 3T3-L1 adipocytes, and again the effects of the two agents were not additive. Total glucose transporter protein (GLUT) 1 was similar between parental and N-Ras61K-expressing 3T3-L1 fibroblasts or adipocytes, whereas total GLUT-4 protein was actually lower in the N-Ras61K-expressing compared with parental adipocytes. However, expression of N-Ras61K in 3T3-L1 adipocytes markedly elevated both GLUT-1 and GLUT-4 in plasma membranes relative to intracellular membranes, and insulin had no further effect. These modulations of glucose transporters by N-Ras61K expression are not due to upstream regulation of insulin receptors because receptor tyrosine phosphorylation and association of phosphatidylinositol 3-kinase with tyrosine-phosphorylated proteins were unaffected. These results show that activated Ras mimics the actions of insulin on membrane trafficking of glucose transporters, consistent with the concept that Ras proteins function as intermediates in this insulin signaling pathway.
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Affiliation(s)
- L Kozma
- Program in Molecular Medicine, University of Massachusetts Medical Center, Worcester 01605
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In vivo binding properties of SH2 domains from GTPase-activating protein and phosphatidylinositol 3-kinase. Mol Cell Biol 1993. [PMID: 8382774 DOI: 10.1128/mcb.13.3.1737] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have used a transient expression system and mutant platelet-derived growth factor (PDGF) receptors to study the binding specificities of the Src homology 2 (SH2) regions of the Ras GTPase-activator protein (GAP) and the p85 alpha subunit of phosphatidylinositol 3-kinase (PI3 kinase). A number of fusion proteins, each tagged with an epitope allowing recognition by a monoclonal antibody, were expressed at levels comparable to those of endogenous GAP. Fusion proteins containing the central SH2-SH3-SH2 region of GAP or the C-terminal region of p85 alpha, which includes two SH2 domains, bound to PDGF receptors in response to PDGF stimulation. Both fusion proteins showed the same requirements for tyrosine phosphorylation sites in the PDGF receptor as the full-length proteins from which they were derived, i.e., binding of the GAP fusion protein was reduced by mutation of Tyr-771, and binding of the p85 fusion protein was reduced by mutation of Tyr-740, Tyr-751, or both residues. Fusion proteins containing single SH2 domains from either GAP or p85 alpha did not bind detectably to PDGF receptors in this system, suggesting that two SH2 domains in a single polypeptide cooperate to raise the affinity of binding. The sequence specificities of individual SH2 domains were deduced from the binding properties of fusion proteins containing one SH2 domain from GAP and another from p85. The results suggest that the C-terminal GAP SH2 domain specifies binding to Tyr-771, the C-terminal p85 alpha SH2 domain binds to either Tyr-740 or Tyr-751, and each protein's N-terminal SH2 domain binds to unidentified phosphorylation sites.(ABSTRACT TRUNCATED AT 250 WORDS)
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Cooper JA, Kashishian A. In vivo binding properties of SH2 domains from GTPase-activating protein and phosphatidylinositol 3-kinase. Mol Cell Biol 1993; 13:1737-45. [PMID: 8382774 PMCID: PMC359486 DOI: 10.1128/mcb.13.3.1737-1745.1993] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
We have used a transient expression system and mutant platelet-derived growth factor (PDGF) receptors to study the binding specificities of the Src homology 2 (SH2) regions of the Ras GTPase-activator protein (GAP) and the p85 alpha subunit of phosphatidylinositol 3-kinase (PI3 kinase). A number of fusion proteins, each tagged with an epitope allowing recognition by a monoclonal antibody, were expressed at levels comparable to those of endogenous GAP. Fusion proteins containing the central SH2-SH3-SH2 region of GAP or the C-terminal region of p85 alpha, which includes two SH2 domains, bound to PDGF receptors in response to PDGF stimulation. Both fusion proteins showed the same requirements for tyrosine phosphorylation sites in the PDGF receptor as the full-length proteins from which they were derived, i.e., binding of the GAP fusion protein was reduced by mutation of Tyr-771, and binding of the p85 fusion protein was reduced by mutation of Tyr-740, Tyr-751, or both residues. Fusion proteins containing single SH2 domains from either GAP or p85 alpha did not bind detectably to PDGF receptors in this system, suggesting that two SH2 domains in a single polypeptide cooperate to raise the affinity of binding. The sequence specificities of individual SH2 domains were deduced from the binding properties of fusion proteins containing one SH2 domain from GAP and another from p85. The results suggest that the C-terminal GAP SH2 domain specifies binding to Tyr-771, the C-terminal p85 alpha SH2 domain binds to either Tyr-740 or Tyr-751, and each protein's N-terminal SH2 domain binds to unidentified phosphorylation sites.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- J A Cooper
- Fred Hutchinson Cancer Research Center, Seattle, Washington 98104
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