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The Novel Phosphatase Domain Mutations Q171R and Y65S Switch PTEN from Tumor Suppressor to Oncogene. Cells 2021; 10:cells10123423. [PMID: 34943931 PMCID: PMC8700245 DOI: 10.3390/cells10123423] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2021] [Revised: 11/28/2021] [Accepted: 12/02/2021] [Indexed: 11/17/2022] Open
Abstract
Phosphatase and tensin homolog deleted on chromosome 10, or PTEN, is a well-characterized tumor suppressor with both lipid and protein phosphatase activities. PTEN is often downregulated by epigenetic mechanisms such as hypermethylation, which leads to constitutive activation of the PI3K-Akt pathway. Large datasets from next-generation sequencing, however, revealed that mutations in PTEN may not only hamper protein function but may also affect interactions with downstream effectors, leading to variable oncogenic readouts. Here, two novel PTEN mutations, Q171R and Y65S, identified in Filipino colorectal cancer patients, were phenotypically characterized in NIH3T3 and HCT116 cells, alongside the C124S canonical mutant and wild-type controls. The novel mutants increased cellular proliferation, resistance to apoptosis and migratory capacity. They induced gross morphological changes including cytoplasmic shrinkage, increased cellular protrusions and extensive cytoskeletal reorganization. The mutants also induced a modest increase in Akt phosphorylation. Further mechanistic studies will help determine the differential oncogenic potencies of these mutants, and resolve whether the structural constraints imposed by the mutations may have altered associations with downstream effectors.
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Angeles AKJ, Yu RTD, Cutiongco-De La Paz EM, Garcia RL. Phenotypic characterization of the novel, non-hotspot oncogenic KRAS mutants E31D and E63K. Oncol Lett 2019; 18:420-432. [PMID: 31289513 PMCID: PMC6540134 DOI: 10.3892/ol.2019.10325] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2018] [Accepted: 04/02/2019] [Indexed: 12/13/2022] Open
Abstract
KRAS proto-oncogene, GTPase (KRAS) functions as a molecular switch at the apex of multiple signaling pathways controlling cell proliferation, differentiation, migration, and survival. Canonical KRAS mutants, such as those in codons 12 and 13, produce constitutively active oncoproteins that short-circuit epidermal growth factor receptor (EGFR)-initiated signaling, resulting in dysregulated downstream effectors associated with cellular transformation. Therefore, anti-EGFR therapy provides little to no clinical benefit to patients with activating KRAS mutations. Current genotyping procedures based on canonical mutation detection only account for ~40% of non-responders, highlighting the need to identify additional predictive biomarkers. In the present study, two novel non-hotspot KRAS mutations were functionally characterized in vitro: KRAS E31D was identified from a genetic screen of colorectal cancer specimens at the UP-National Institutes of Health. KRAS E63K is curated in the Catalogue of Somatic Mutations in Cancer database. Similar to the canonical mutants KRAS G12D and KRAS G13D, NIH3T3 cells overexpressing KRAS E31D and KRAS E63K showed altered morphology and were characteristically smaller, rounder, and highly refractile compared with their non-transformed counterparts. Filamentous actin staining also indicated cytoplasmic shrinkage, membrane ruffling, and formation of pseudopod protrusions. Further, they displayed higher proliferative rates and higher migratory rates in scratch wound assays compared with negative controls. These empirical findings suggest the activating impact of the novel KRAS mutations, which may contribute to resistance to anti-EGFR therapy. Complementary studies to elucidate the molecular mechanisms underlying the transforming effect of the rare mutants are required. In parallel, their oncogenic capacity in vivo should also be investigated.
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Affiliation(s)
- Arlou Kristina J Angeles
- Disease Molecular Biology and Epigenetics Laboratory, National Institute of Molecular Biology and Biotechnology, National Science Complex, University of the Philippines Diliman, Quezon City 1101, Philippines
| | - Ryan Timothy D Yu
- Disease Molecular Biology and Epigenetics Laboratory, National Institute of Molecular Biology and Biotechnology, National Science Complex, University of the Philippines Diliman, Quezon City 1101, Philippines
| | - Eva Maria Cutiongco-De La Paz
- Institute of Human Genetics, National Institutes of Health, University of the Philippines Manila, Manila 1000, Philippines.,Philippine Genome Center, University of the Philippines System, Quezon City 1101, Philippines
| | - Reynaldo L Garcia
- Disease Molecular Biology and Epigenetics Laboratory, National Institute of Molecular Biology and Biotechnology, National Science Complex, University of the Philippines Diliman, Quezon City 1101, Philippines.,Philippine Genome Center, University of the Philippines System, Quezon City 1101, Philippines
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Liu S, Iaria J, Simpson RJ, Zhu HJ. Ras enhances TGF-β signaling by decreasing cellular protein levels of its type II receptor negative regulator SPSB1. Cell Commun Signal 2018. [PMID: 29534718 PMCID: PMC5850916 DOI: 10.1186/s12964-018-0223-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Background Transformation by oncogene Ras overcomes TGF-β mediated growth inhibition in epithelial cells. However, it cooperates with each other to mediate epithelial to mesenchymal transition (EMT). The mechanism of how these two pathways interact with each other is controversial. Methods Molecular techniques were used to engineer expression plasmids for Ras, SPRY, TGF-β receptors, type I and II and ubiquitin. Immunoprecipitation and western blots were employed to determine protein-protein interactions, preotein levels, protein phosphorylation while immunofluorecesent staining for molecular co-localization. TGF-β signalling activities is also determined by its luciferase reporter assay. Trans-well assays were used to measure cell migration and invasion. Results Ras interacts with the SPSB1’s SPRY domain to enhance TGF-β signaling. Ras interacts and colocalizes with the TGF-β type II receptor’s (TβRII) negative regulator SPSB1 on the cell membrane, consequently promoting SPSB1 protein degradation via enhanced mono- and di-ubiquitination. Reduced SPSB1 levels result in the stablization of TβRII, in turn the increase of receptor levels significantly enhance Smad2/3 phosphorylation and signaling. Importantly, forced expression of SPSB1 in Ras transformed cells suppresses TGF-β signaling and its mediated migration and invasion. Conclusion Ras positively cooperates with TGF-β signaling by reducing the cellular protein levels of TβRII negative regualtor SPSB1. Electronic supplementary material The online version of this article (10.1186/s12964-018-0223-4) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Sheng Liu
- Department of Surgery (RMH), The University of Melbourne, The Royal Melbourne Hospital, Parkville, VIC, 3010, Australia
| | - Josephine Iaria
- Department of Surgery (RMH), The University of Melbourne, The Royal Melbourne Hospital, Parkville, VIC, 3010, Australia
| | - Richard J Simpson
- Department of Biochemistry, La Trobe Institute for Molecular Science, La Trobe University, Bundoora, VIC, Australia
| | - Hong-Jian Zhu
- Department of Surgery (RMH), The University of Melbourne, The Royal Melbourne Hospital, Parkville, VIC, 3010, Australia.
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Knyphausen P, Lang F, Baldus L, Extra A, Lammers M. Insights into K-Ras 4B regulation by post-translational lysine acetylation. Biol Chem 2016; 397:1071-85. [DOI: 10.1515/hsz-2016-0118] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2016] [Accepted: 05/03/2016] [Indexed: 11/15/2022]
Abstract
Abstract
Ras is a molecular switch cycling between an active, GTP-bound and an inactive, GDP-bound state. Mutations in Ras, mostly affecting the off-switch, are found in many human tumours. Recently, it has been shown that K-Ras 4B is targeted by lysine acetylation at K104. Based on results obtained for an acetylation mimetic Ras mutant (K104Q), it was hypothesised that K104-acetylation might interfere with its oncogenicity by impairing SOS-catalysed guanine-nucleotide exchange. We prepared site-specifically K104-acetylated K-Ras 4B and the corresponding oncogenic mutant protein G12V using the genetic-code expansion concept. We found that SOS-catalysed nucleotide exchange, also of allosterically activated SOS, was neither affected by acetylation of K104 in wildtype K-Ras 4B nor in the G12V mutant, suggesting that glutamine is a poor mimetic for acetylation at this site. In vitro, the lysine-acetyltransferases CBP and p300 were able to acetylate both, wildtype and G12V K-Ras 4B. In addition to K104 we identified further acetylation sites in K-Ras 4B, including K147, within the important G5/SAK-motif. However, the intrinsic and the SOS-catalysed nucleotide exchange was not affected by K147-acetylation of K-Ras 4B. Finally, we show that Sirt2 and HDAC6 do neither deacetylate K-Ras 4B if acetylated at K104 nor if acetylated at K147 in vitro.
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Liu XJ, Li YQ, Chen QY, Xiao SJ, Zeng SE. Up-regulating of RASD1 and Apoptosis of DU-145 Human Prostate Cancer Cells Induced by Formononetin in Vitro. Asian Pac J Cancer Prev 2014; 15:2835-9. [DOI: 10.7314/apjcp.2014.15.6.2835] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Gremer L, Merbitz-Zahradnik T, Dvorsky R, Cirstea IC, Kratz CP, Zenker M, Wittinghofer A, Ahmadian MR. Germline KRAS mutations cause aberrant biochemical and physical properties leading to developmental disorders. Hum Mutat 2011; 32:33-43. [PMID: 20949621 PMCID: PMC3117284 DOI: 10.1002/humu.21377] [Citation(s) in RCA: 112] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2010] [Accepted: 09/05/2010] [Indexed: 02/06/2023]
Abstract
The KRAS gene is the most common locus for somatic gain-of-function mutations in human cancer. Germline KRAS mutations were shown recently to be associated with developmental disorders, including Noonan syndrome (NS), cardio-facio-cutaneous syndrome (CFCS), and Costello syndrome (CS). The molecular basis of this broad phenotypic variability has in part remained elusive so far. Here, we comprehensively analyzed the biochemical and structural features of ten germline KRAS mutations using physical and cellular biochemistry. According to their distinct biochemical and structural alterations, the mutants can be grouped into five distinct classes, four of which markedly differ from RAS oncoproteins. Investigated functional alterations comprise the enhancement of intrinsic and guanine nucleotide exchange factor (GEF) catalyzed nucleotide exchange, which is alternatively accompanied by an impaired GTPase-activating protein (GAP) stimulated GTP hydrolysis, an overall loss of functional properties, and a deficiency in effector interaction. In conclusion, our data underscore the important role of RAS in the pathogenesis of the group of related disorders including NS, CFCS, and CS, and provide clues to the high phenotypic variability of patients with germline KRAS mutations.
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Affiliation(s)
- Lothar Gremer
- Institute of Biochemistry and Molecular Biology II, Medical Faculty, Heinrich-Heine University, Düsseldorf, Germany
- Max-Planck Institute of Molecular Physiology, Department of Structural Biology, Dortmund, Germany
| | - Torsten Merbitz-Zahradnik
- Institute of Biochemistry and Molecular Biology II, Medical Faculty, Heinrich-Heine University, Düsseldorf, Germany
- Max-Planck Institute of Molecular Physiology, Department of Structural Biology, Dortmund, Germany
| | - Radovan Dvorsky
- Institute of Biochemistry and Molecular Biology II, Medical Faculty, Heinrich-Heine University, Düsseldorf, Germany
- Max-Planck Institute of Molecular Physiology, Department of Structural Biology, Dortmund, Germany
| | - Ion C. Cirstea
- Institute of Biochemistry and Molecular Biology II, Medical Faculty, Heinrich-Heine University, Düsseldorf, Germany
| | | | - Martin Zenker
- Institute of Human Genetics, University Hospital Magdeburg, Magdeburg, Germany
| | - Alfred Wittinghofer
- Max-Planck Institute of Molecular Physiology, Department of Structural Biology, Dortmund, Germany
| | - Mohammad Reza Ahmadian
- Institute of Biochemistry and Molecular Biology II, Medical Faculty, Heinrich-Heine University, Düsseldorf, Germany
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Vaidyanathan G, Cismowski MJ, Wang G, Vincent TS, Brown KD, Lanier SM. The Ras-related protein AGS1/RASD1 suppresses cell growth. Oncogene 2004; 23:5858-63. [PMID: 15184869 DOI: 10.1038/sj.onc.1207774] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
AGS1/RASD1 is a Ras-related protein identified as a dexamethasone-inducible cDNA and as a signal regulator in various functional and protein-interaction screens. As an initial approach to define the role of AGS1/RASD1 as a Ras-family member, we determined its influence on cell growth/survival. In clonogenic assays with NIH-3T3 murine fibroblast cells, the MCF-7 human breast cancer cell line and the human lung adenocarcinoma cell line A549, AGS1/RASD1 markedly diminished the number of G418-resistant colonies, whereas the Ras subgroup member K-Ras was without effect. A549 cell infection with adenovirus engineered to express AGS1/RASD1 (Ad.AGS1) inhibited log phase growth in vitro and increased the percentage of cells undergoing apoptosis. The anti-growth action was also observed in vivo as the expression of AGS1/RASD1 inhibited the subcutaneous tumor growth of A549 cells in athymic nude mice. These data indicate that AGS1/RASD1, a member of the Ras superfamily of small G-proteins that often promotes cell growth and tumor expansion, plays an active role in preventing aberrant cell growth.
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Affiliation(s)
- Govindan Vaidyanathan
- Department of Pharmacology and Experimental Therapeutics, Louisiana State University Health Sciences Center, New Orleans, LA 70112, USA
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Reuveni H, Geiger T, Geiger B, Levitzki A. Reversal of the Ras-induced transformed phenotype by HR12, a novel ras farnesylation inhibitor, is mediated by the Mek/Erk pathway. J Cell Biol 2000; 151:1179-92. [PMID: 11121434 PMCID: PMC2190591 DOI: 10.1083/jcb.151.6.1179] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We have used the selective farnesylation inhibitor HR12 [cysteine-N(methyl)valine-N(cyclohexyl) glycine-methionine-O-methyl-ester] to study the role of oncogenic Ras in cytoskeletal reorganization in Ha-ras(V12)-transformed Rat1 cells (Rat1/ras). Application of HR12 resulted in complete restoration of the cytoskeleton and associated cell adhesions disrupted by oncogenic Ras. This included an increase in the number and size of focal adhesions, accompanied by massive stress fiber formation and enhanced tyrosine phosphorylation. Furthermore, HR12 induced assembly of adherens junctions and dramatically elevated the level of the junctional components, cadherin and beta-catenin. HR12 was unable to restore the nontransformed phenotype in cells expressing farnesylation-independent, myristylated Ras. Examination of the main Ras-regulated signaling pathways revealed that HR12 induced a dose- and time-dependent decline in Erk1&2 activation (t(1/2) approximately 6 h), which correlated with the accumulation of nonfarnesylated oncogenic-Ras. Inhibition of the Mek/Erk pathway in Rat1/ras cells, using the Mek inhibitor, PD98059, resulted in complete cytoskeletal recovery, indistinguishable from that induced by HR12. Moreover, a constitutively active Mek mimicked the effect of ras transformation in Rat1 cells, and prevented HR12-induced cytoskeletal effects in Rat1/ras cells. No such effects were observed after treatment of Rat1/ras cells with the phosphatidylinositol 3-kinase inhibitor LY294002. These findings establish the Mek/Erk pathway as the dominant pathway involved in conferring the cytoskeletal and junctional manifestations of the Ras-induced transformed phenotype.
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Affiliation(s)
- Hadas Reuveni
- Department of Biological Chemistry, The Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - Tamar Geiger
- Department of Biological Chemistry, The Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - Benjamin Geiger
- Department of Molecular Cell Biology, The Weizmann Institute of Science, Rehovot 76100, Israel
| | - Alexander Levitzki
- Department of Biological Chemistry, The Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
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Affiliation(s)
- R L Juliano
- Department of Pharmacology, University of North Carolina School of Medicine, Chapel Hill 27599
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10
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Su LN, Little JB. Transformation and radiosensitivity of human diploid skin fibroblasts transfected with activated ras oncogene and SV40 T-antigen. Int J Radiat Biol 1992; 62:201-10. [PMID: 1355514 DOI: 10.1080/09553009214552021] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Three normal human diploid cell strains were transfected with an activated Ha-ras oncogene (EJ ras) or SV40 T-antigen. Multiple clones were examined for morphological alterations, growth requirements, ability to grow under anchorage independent conditions, immortality and tumorigenicity in nude mice. Clones expressing SV40 T-antigen alone or in combination with ras protein p21 were significantly radioresistant as compared with their parent cells or clones transfected with the neo gene only. This radioresistant phenotype persisted in post-crisis, immortalized cell lines. Cells transfected with EJ ras alone showed no morphological alterations nor significant changes in radiosensitivity. Cell clones expressing ras and/or SV40 T-antigen showed a reduced requirement for serum supplements, an increase in aneuploidy and chromosomal aberrations, and enhanced growth in soft agar as an early cellular response to SV40 T-antigen expression. The sequential order of transfection with SV40 T-antigen and ras influenced radio-sensitivity but not the induction of morphological changes. These data suggest that expression of the SV40 T-antigen but not activated Ha-ras plays an important role in the radiosensitivity of human diploid cells. The radioresistant phenotype in SV40 T transfected cells was not related to the enhanced level of genetic instability seen in pre-crisis and newly immortalized cells, nor to the process of immortalization itself.
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Affiliation(s)
- L N Su
- Laboratory of Radiobiology, Harvard School of Public Health, Boston, MS 02115
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Mendonca MS, Boukamp P, Stanbridge EJ, Redpath JL. The radiosensitivity of human keratinocytes: influence of activated c-H-ras oncogene expression and tumorigenicity. Int J Radiat Biol 1991; 59:1195-206. [PMID: 1675238 DOI: 10.1080/09553009114551071] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
We have investigated the gamma-ray sensitivity of several activated c-H-ras (EJ) containing clones that have been established after transfection of the spontaneously immortalized non-tumorigenic human keratinocyte cell line HaCaT. The clones were grouped according to their tumorigenic potential after subcutaneous injection into nude mice, and fell into three classes: Class I clones A-4 and I-6 are non-tumorigenic and express very low levels of c-H-ras mRNA and no mutated ras protein (p21); Class II clones I-5 and I-7 grow to large (benign) epidermal cysts, express intermediate to high c-H-ras mRNA and variable levels of mutated ras p21 protein with clone I-5 expressing little and clone I-7 expressing high levels of p21; Class III clones II-3 and II-4 grow to solid squamous cell carcinomas, express high c-H-ras mRNA and high level of mutated p21 ras protein similar to clone I-7. Comparison of the single-hit multitarget or linear-quadratic survival curve parameters, and survival at 2 Gy (S2) indicate that there appears to be no general correlation with either activated c-H-ras expression level or tumorigenic potential, and increased radioresistance.
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Affiliation(s)
- M S Mendonca
- Department of Radiological Sciences, University of California, Irvine 92717
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Biochemical characterization of baculovirus-expressed rap1A/Krev-1 and its regulation by GTPase-activating proteins. Mol Cell Biol 1990. [PMID: 2160589 DOI: 10.1128/mcb.10.6.2901] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Normal human rap1A and 35A rap1A (which encodes a protein with a Thr-35----Ala mutation) were cloned into a baculovirus transfer vector and expressed in Sf9 insect cells. The resulting proteins were purified, and their nucleotide binding, GTPase activities, and responsiveness to GTPase-activating proteins (GAPs) were characterized and compared with those of Rap1 purified from human neutrophils. Recombinant wild-type Rap1A bound GTP gamma S, GTP, and GDP with affinities similar to those observed for neutrophil Rap1 protein. The rate of exchange of GTP by Rap1 without Mg2+ was much slower than that by Ras. The basal GTPase activities by both recombinant proteins were lower than that observed with the neutrophil Rap1, but the GTPase activity of the neutrophil and wild-type recombinant Rap1 proteins could be stimulated to similar levels by Rap-GAP activity in neutrophil cytosol. In contrast to wild-type Rap1A, the GTPase activity of 35A Rap was unresponsive to Rap-GAP stimulation. Neither recombinant Rap1A nor neutrophil Rap1 protein GTPase activity could be stimulated by recombinant Ras-GAP at a concentration 25-fold higher than that required to hydrolyze 50% of H-Ras-bound GTP under similar conditions. These results suggest that the putative effector domains (amino acids 32 to 40) shared between Rap1 and Ras are functionally similar and interact with their respective GAPs. However, although Rap1 and Ras are identical in this region, secondary structure or additional regions must confer the ability to respond to GAPs.
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Quilliam LA, Der CJ, Clark R, O'Rourke EC, Zhang K, McCormick F, Bokoch GM. Biochemical characterization of baculovirus-expressed rap1A/Krev-1 and its regulation by GTPase-activating proteins. Mol Cell Biol 1990; 10:2901-8. [PMID: 2160589 PMCID: PMC360652 DOI: 10.1128/mcb.10.6.2901-2908.1990] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Normal human rap1A and 35A rap1A (which encodes a protein with a Thr-35----Ala mutation) were cloned into a baculovirus transfer vector and expressed in Sf9 insect cells. The resulting proteins were purified, and their nucleotide binding, GTPase activities, and responsiveness to GTPase-activating proteins (GAPs) were characterized and compared with those of Rap1 purified from human neutrophils. Recombinant wild-type Rap1A bound GTP gamma S, GTP, and GDP with affinities similar to those observed for neutrophil Rap1 protein. The rate of exchange of GTP by Rap1 without Mg2+ was much slower than that by Ras. The basal GTPase activities by both recombinant proteins were lower than that observed with the neutrophil Rap1, but the GTPase activity of the neutrophil and wild-type recombinant Rap1 proteins could be stimulated to similar levels by Rap-GAP activity in neutrophil cytosol. In contrast to wild-type Rap1A, the GTPase activity of 35A Rap was unresponsive to Rap-GAP stimulation. Neither recombinant Rap1A nor neutrophil Rap1 protein GTPase activity could be stimulated by recombinant Ras-GAP at a concentration 25-fold higher than that required to hydrolyze 50% of H-Ras-bound GTP under similar conditions. These results suggest that the putative effector domains (amino acids 32 to 40) shared between Rap1 and Ras are functionally similar and interact with their respective GAPs. However, although Rap1 and Ras are identical in this region, secondary structure or additional regions must confer the ability to respond to GAPs.
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Affiliation(s)
- L A Quilliam
- Department of Immunology, Scripps Clinic & Research Foundation, La Jolla, California 92037
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