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Cao S, Chung S, Kim S, Li Z, Manor D, Buck M. K-Ras G-domain binding with signaling lipid phosphatidylinositol (4,5)-phosphate (PIP2): membrane association, protein orientation, and function. J Biol Chem 2019; 294:7068-7084. [PMID: 30792310 DOI: 10.1074/jbc.ra118.004021] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2018] [Revised: 12/12/2018] [Indexed: 12/14/2022] Open
Abstract
Ras genes potently drive human cancers, with mutated proto-oncogene GTPase KRAS4B (K-Ras4B) being the most abundant isoform. Targeted inhibition of oncogenic gene products is considered the "holy grail" of present-day cancer therapy, and recent discoveries of small-molecule KRas4B inhibitors were made thanks to a deeper understanding of the structure and dynamics of this GTPase. Because interactions with biological membranes are key for Ras function, Ras-lipid interactions have become a major focus, especially because such interactions evidently involve both the Ras C terminus for lipid anchoring and its G-protein domain. Here, using NMR spectroscopy and molecular dynamics simulations complemented by biophysical- and cell-biology assays, we investigated the interaction between K-Ras4B with the signaling lipid phosphatidylinositol (4,5)-phosphate (PIP2). We discovered that the β2 and β3 strands as well as helices 4 and 5 of the GTPase G-domain bind to PIP2 and identified the specific residues in these structural elements employed in these interactions, likely occurring in two K-Ras4B orientation states relative to the membrane. Importantly, we found that some of these residues known to be oncogenic when mutated (D47K, D92N, K104M, and D126N) are critical for K-Ras-mediated transformation of fibroblast cells, but do not substantially affect basal and assisted nucleotide hydrolysis and exchange. Moreover, the K104M substitution abolished localization of K-Ras to the plasma membrane. The findings suggest that specific G-domain residues can critically regulate Ras function by mediating interactions with membrane-associated PIP2 lipids; these insights that may inform the future design of therapeutic reagents targeting Ras activity.
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Affiliation(s)
- Shufen Cao
- From the Departments of Physiology and Biophysics
| | | | | | - Zhenlu Li
- From the Departments of Physiology and Biophysics
| | - Danny Manor
- Nutrition, .,Pharmacology, and.,the Case Comprehensive Cancer Center and
| | - Matthias Buck
- From the Departments of Physiology and Biophysics, .,the Case Comprehensive Cancer Center and.,Neurosciences, Case Western Reserve University, School of Medicine, Cleveland, Ohio 44106 and.,Center for Proteomics and Bioinformatics, Case Western Reserve University, School of Medicine, Cleveland, Ohio 44106
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Stierwalt HD, Ehrlicher SE, Bergman BC, Robinson MM, Newsom SA. Insulin-stimulated Rac1-GTP binding is not impaired by palmitate treatment in L6 myotubes. Physiol Rep 2018; 6:e13956. [PMID: 30592185 PMCID: PMC6308110 DOI: 10.14814/phy2.13956] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2018] [Accepted: 11/28/2018] [Indexed: 01/01/2023] Open
Abstract
Ras-related C3 botulinum toxin substrate 1 (Rac1) is required for normal insulin-stimulated glucose transport in skeletal muscle and evidence indicates Rac1 may be negatively regulated by lipids. We investigated if insulin-stimulated activation of Rac1 (i.e., Rac1-GTP binding) is impaired by accumulation of diacylglycerols (DAG) and ceramides in cultured muscle cells. Treating L6 myotubes with 100 nmol/L insulin resulted in increased Rac1-GTP binding that was rapid (occurring within 2 min), relatively modest (+38 ± 19% vs. basal, P < 0.001), and short-lived, returning to near-basal levels within 15 min of continuous treatment. Incubating L6 myotubes overnight in 500 μmol/L palmitate increased the accumulation of DAG and ceramides (P < 0.05 vs. no fatty acid control). Despite significant accumulation of lipids, insulin-stimulated Rac1-GTP binding was not impaired during palmitate treatment (P = 0.39 vs. no fatty acid control). Nevertheless, phosphorylation of Rac1 effector protein p21-activated kinase (PAK) was attenuated in response to palmitate treatment (P = 0.02 vs. no fatty acid control). Palmitate treatment also increased inhibitory phosphorylation of insulin receptor substrate-1 and attenuated insulin-stimulated phosphorylation of Akt at both Thr308 and Ser473 (all P < 0.05 vs. no fatty acid control). Such signaling impairments resulted in near complete inhibition of insulin-stimulated translocation of glucose transporter protein 4 (GLUT4; P = 0.10 vs. basal during palmitate treatment). In summary, our finding suggests that Rac1 may not undergo negative regulation by DAG or ceramides. We instead provide evidence that attenuated PAK phosphorylation and impaired GLUT4 translocation during palmitate-induced insulin resistance can occur independent of defects in insulin-stimulated Rac1-GTP binding.
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Affiliation(s)
- Harrison D. Stierwalt
- School of Biological and Population Health SciencesCollege of Public Health and Human SciencesOregon State UniversityCorvallisOregon
| | - Sarah E. Ehrlicher
- School of Biological and Population Health SciencesCollege of Public Health and Human SciencesOregon State UniversityCorvallisOregon
| | - Bryan C. Bergman
- Division of Endocrinology, Metabolism and DiabetesSchool of MedicineUniversity of Colorado DenverDenverColorado
| | - Matthew M. Robinson
- School of Biological and Population Health SciencesCollege of Public Health and Human SciencesOregon State UniversityCorvallisOregon
| | - Sean A. Newsom
- School of Biological and Population Health SciencesCollege of Public Health and Human SciencesOregon State UniversityCorvallisOregon
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Czikora A, Pany S, You Y, Saini AS, Lewin NE, Mitchell GA, Abramovitz A, Kedei N, Blumberg PM, Das J. Structural determinants of phorbol ester binding activity of the C1a and C1b domains of protein kinase C theta. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2018; 1860:1046-1056. [PMID: 29317197 DOI: 10.1016/j.bbamem.2018.01.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2017] [Revised: 12/06/2017] [Accepted: 01/04/2018] [Indexed: 12/31/2022]
Abstract
The PKC isozymes represent the most prominent family of signaling proteins mediating response to the ubiquitous second messenger diacylglycerol. Among them, PKCθ is critically involved in T-cell activation. Whereas all the other conventional and novel PKC isoforms have twin C1 domains with potent binding activity for phorbol esters, in PKCθ only the C1b domain possesses potent binding activity, with little or no activity reported for the C1a domain. In order to better understand the structural basis accounting for the very weak ligand binding of the PKCθ C1a domain, we assessed the effect on ligand binding of twelve amino acid residues which differed between the C1a and C1b domains of PKCθ. Mutation of Pro9 of the C1a domain of PKCθ to the corresponding Lys9 found in C1b restored in vitro binding activity for [3H]phorbol 12,13-dibutyrate to 3.6 nM, whereas none of the other residues had substantial effect. Interestingly, the converse mutation in the C1b domain of Lys9 to Pro9 only diminished binding affinity to 11.7 nM, compared to 254 nM in the unmutated C1a. In confocal experiments, deletion of the C1b domain from full length PKCθ diminished, whereas deletion of the C1a domain enhanced 5-fold (at 100 nM PMA) the translocation to the plasma membrane. We conclude that the Pro168 residue in the C1a domain of full length PKCθ plays a critical role in the ligand and membrane binding, while exchanging the residue (Lys240) at the same position in C1b domain of full length PKCθ only modestly reduced the membrane interaction.
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Affiliation(s)
- Agnes Czikora
- Laboratory of Cancer Biology and Genetics, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, United States
| | - Satyabrata Pany
- Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Houston, TX 77204, United States
| | - Youngki You
- Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Houston, TX 77204, United States
| | - Amandeep S Saini
- Laboratory of Cancer Biology and Genetics, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, United States
| | - Nancy E Lewin
- Laboratory of Cancer Biology and Genetics, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, United States
| | - Gary A Mitchell
- Laboratory of Cancer Biology and Genetics, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, United States
| | - Adelle Abramovitz
- Laboratory of Cancer Biology and Genetics, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, United States
| | - Noemi Kedei
- Laboratory of Cancer Biology and Genetics, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, United States
| | - Peter M Blumberg
- Laboratory of Cancer Biology and Genetics, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, United States.
| | - Joydip Das
- Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Houston, TX 77204, United States.
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Czikora A, Kedei N, Kalish H, Blumberg PM. Importance of the REM (Ras exchange) domain for membrane interactions by RasGRP3. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2017; 1859:2350-2360. [PMID: 28912101 PMCID: PMC5659902 DOI: 10.1016/j.bbamem.2017.09.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2017] [Revised: 09/07/2017] [Accepted: 09/08/2017] [Indexed: 11/18/2022]
Abstract
RasGRP comprises a family of guanine nucleotide exchange factors, regulating the dissociation of GDP from Ras GTPases to enhance the formation of the active GTP-bound form. RasGRP1 possesses REM (Ras exchange), GEF (catalytic), EF-hand, C1, SuPT (suppressor of PT), and PT (plasma membrane-targeting) domains, among which the C1 domain drives membrane localization in response to diacylglycerol or phorbol ester and the PT domain recognizes phosphoinositides. The homologous family member RasGRP3 shows less plasma membrane localization. The objective of this study was to explore the role of the different domains of RasGRP3 in membrane translocation in response to phorbol esters. The full-length RasGRP3 shows limited translocation to the plasma membrane in response to PMA, even when the basic hydrophobic cluster in the PT domain, reported to be critical for RasGRP1 translocation to endogenous activators, is mutated to resemble that of RasGRP1. Moreover, exchange of the C-termini (SuPT-PT domain) of the two proteins had little effect on their plasma membrane translocation. On the other hand, while the C1 domain of RasGRP3 alone showed partial plasma membrane translocation, truncated RasGRP3 constructs, which contain the PT domain and are missing the REM, showed stronger translocation, indicating that the REM of RasGRP3 was a suppressor of its membrane interaction. The REM of RasGRP1 failed to show comparable suppression of RasGRP3 translocation. The marked differences between RasGRP3 and RasGRP1 in membrane interaction necessarily will contribute to their different behavior in cells and are relevant to the design of selective ligands as potential therapeutic agents.
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Affiliation(s)
- Agnes Czikora
- Laboratory of Cancer Biology and Genetics, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, United States
| | - Noemi Kedei
- Laboratory of Cancer Biology and Genetics, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, United States
| | - Heather Kalish
- Trans-NIH Shared Resource on Biomedical Engineering and Physical Science (BEPS), National Institute of Biomedical Imaging and Bioengineering (NIBIB) National Institutes of Health, United States
| | - Peter M Blumberg
- Laboratory of Cancer Biology and Genetics, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, United States.
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Czikora A, Lundberg DJ, Abramovitz A, Lewin NE, Kedei N, Peach ML, Zhou X, Merritt RC, Craft EA, Braun DC, Blumberg PM. Structural Basis for the Failure of the C1 Domain of Ras Guanine Nucleotide Releasing Protein 2 (RasGRP2) to Bind Phorbol Ester with High Affinity. J Biol Chem 2016; 291:11133-47. [PMID: 27022025 PMCID: PMC4900263 DOI: 10.1074/jbc.m116.725333] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2016] [Revised: 03/28/2016] [Indexed: 11/06/2022] Open
Abstract
The C1 domain represents the recognition module for diacylglycerol and phorbol esters in protein kinase C, Ras guanine nucleotide releasing protein (RasGRP), and related proteins. RasGRP2 is exceptional in that its C1 domain has very weak binding affinity (Kd = 2890 ± 240 nm for [(3)H]phorbol 12,13-dibutyrate. We have identified four amino acid residues responsible for this lack of sensitivity. Replacing Asn(7), Ser(8), Ala(19), and Ile(21) with the corresponding residues from RasGRP1/3 (Thr(7), Tyr(8), Gly(19), and Leu(21), respectively) conferred potent binding affinity (Kd = 1.47 ± 0.03 nm) in vitro and membrane translocation in response to phorbol 12-myristate 13-acetate in LNCaP cells. Mutant C1 domains incorporating one to three of the four residues showed intermediate behavior with S8Y making the greatest contribution. Binding activity for diacylglycerol was restored in parallel. The requirement for anionic phospholipid for [(3)H]phorbol 12,13-dibutyrate binding was determined; it decreased in going from the single S8Y mutant to the quadruple mutant. The full-length RasGRP2 protein with the mutated C1 domains also showed strong phorbol ester binding, albeit modestly weaker than that of the C1 domain alone (Kd = 8.2 ± 1.1 nm for the full-length protein containing all four mutations), and displayed translocation in response to phorbol ester. RasGRP2 is a guanyl exchange factor for Rap1. Consistent with the ability of phorbol ester to induce translocation of the full-length RasGRP2 with the mutated C1 domain, phorbol ester enhanced the ability of the mutated RasGRP2 to activate Rap1. Modeling confirmed that the four mutations helped the binding cleft maintain a stable conformation.
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Affiliation(s)
- Agnes Czikora
- From the Laboratory of Cancer Biology and Genetics, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892
| | - Daniel J Lundberg
- Department of Science, Technology, and Mathematics, Gallaudet University, Washington, D. C. 20002, and
| | - Adelle Abramovitz
- From the Laboratory of Cancer Biology and Genetics, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892
| | - Nancy E Lewin
- From the Laboratory of Cancer Biology and Genetics, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892
| | - Noemi Kedei
- From the Laboratory of Cancer Biology and Genetics, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892
| | - Megan L Peach
- Basic Science Program, Leidos Biomedical Research, Inc., Chemical Biology Laboratory, Frederick National Laboratory for Cancer Research, Frederick, Maryland 21702
| | - Xiaoling Zhou
- From the Laboratory of Cancer Biology and Genetics, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892
| | - Raymond C Merritt
- Department of Science, Technology, and Mathematics, Gallaudet University, Washington, D. C. 20002, and
| | - Elizabeth A Craft
- Department of Science, Technology, and Mathematics, Gallaudet University, Washington, D. C. 20002, and
| | - Derek C Braun
- Department of Science, Technology, and Mathematics, Gallaudet University, Washington, D. C. 20002, and
| | - Peter M Blumberg
- From the Laboratory of Cancer Biology and Genetics, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892,
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6
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Molecular regulation of synaptogenesis during associative learning and memory. Brain Res 2014; 1621:239-51. [PMID: 25485772 DOI: 10.1016/j.brainres.2014.11.054] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2014] [Revised: 11/24/2014] [Accepted: 11/25/2014] [Indexed: 01/06/2023]
Abstract
Synaptogenesis plays a central role in associative learning and memory. The biochemical pathways that underlie synaptogenesis are complex and incompletely understood. Nevertheless, research has so far identified three conceptually distinct routes to synaptogenesis: cell-cell contact mediated by adhesion proteins, cell-cell biochemical signaling from astrocytes and other cells, and neuronal signaling through classical ion channels and cell surface receptors. The cell adhesion pathways provide the physical substrate to the new synaptic connection, while cell-cell signaling may provide a global or regional signal, and the activity-dependent pathways provide the neuronal specificity that is required for the new synapses to produce functional neuronal networks capable of storing associative memories. These three aspects of synaptogenesis require activation of a variety of interacting biochemical pathways that converge on the actin cytoskeleton and strengthen the synapse in an information-dependent manner. This article is part of a Special Issue titled SI: Brain and Memory.
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Hallare AV, Ruiz PLS, Cariño JCED. Assessment of Jatropha curcas L. biodiesel seed cake toxicity using the zebrafish (Danio rerio) embryo toxicity (ZFET) test. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2014; 21:6044-6056. [PMID: 24464135 DOI: 10.1007/s11356-014-2539-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2013] [Accepted: 01/08/2014] [Indexed: 06/03/2023]
Abstract
Consequent to the growing demand for alternative sources of energy, the seeds from Jatropha curcas remain to be the favorite for biodiesel production. However, a significant volume of the residual organic mass (seed cake) is produced during the extraction process, which raises concerns on safe waste disposal. In the present study, we assessed the toxicity of J. curcas seed cake using the zebrafish (Danio rerio) embryotoxicity test. Within 1-h post-fertilization (hpf), the fertilized eggs were exposed to five mass concentrations of J. curcas seed cake and were followed through 24, 48, and 72 hpf. Toxicity was evaluated based on lethal endpoints induced on zebrafish embryos namely egg coagulation, non-formation of somites, and non-detachment of tail. The lowest concentration tested, 1 g/L, was not able to elicit toxicity on embryos whereas 100 % mortality (based also on lethal endpoints) was recorded at the highest concentration at 2.15 g/L. The computed LC50 for the J. curcas seed cake was 1.61 g/L. No further increase in mortality was observed in the succeeding time points (48 and 72 hpf) indicating that J. curcas seed cake exerted acute toxicity on zebrafish embryos. Sublethal endpoints (yolk sac and pericardial edema) were noted at 72 hpf in zebrafish embryos exposed to higher concentrations. The observed lethal endpoints induced on zebrafish embryos were discussed in relation to the active principles, notably, phorbol esters that have remained in the seed cake even after extraction.
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Affiliation(s)
- Arnold V Hallare
- Department of Biology, CAS, University of the Philippines, Manila, Padre Faura St., Manila, 1000, Philippines,
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Li W, Hu Y, Jiang T, Han Y, Han G, Chen J, Li X. Rab27A regulates exosome secretion from lung adenocarcinoma cells A549: involvement of EPI64. APMIS 2014; 122:1080-7. [PMID: 24673604 DOI: 10.1111/apm.12261] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2013] [Accepted: 01/18/2014] [Indexed: 12/11/2022]
Abstract
Exosomes are small membrane vesicles secreted into the extracellular compartment by exocytosis. The unique composition of exosomes can be transported to other cells which allow cells to exert biological functions at distant sites. However, in lung cancer, the regulation of exosome secretion was poorly understood. In this study, we employed human lung adenocarcinoma A549 cells to determine the exosome secretion and involved regulation mechanism. We found that Rab27A was expressed in A549 cells and the reduction of Rab27A by Rab27A-specific shRNA could significantly decrease the secretion of exosome by A549 cells. EPI64, a candidate GAP that is specific for Rab27, was also detected in A549 cells. By pull-down assay, we found that EPI64 participated in the exosome secretion of A549 cells by acting as a specific GAP for Rab27A, not Rab27B. Overexpression of EPI64 enhanced exosome secretion. Taken together, in A549 cells, EPI64 could regulate the exosome secretion by functioning as a GAP specific for Rab27A.
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Affiliation(s)
- Wenhai Li
- Department of Thoracic Surgery, Tangdu Hospital, The Fourth Military Medical University, Xi'an, 710038, China
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9
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Gutierrez-Uzquiza A, Colon-Gonzalez F, Leonard TA, Canagarajah BJ, Wang H, Mayer BJ, Hurley JH, Kazanietz MG. Coordinated activation of the Rac-GAP β2-chimaerin by an atypical proline-rich domain and diacylglycerol. Nat Commun 2013; 4:1849. [PMID: 23673634 PMCID: PMC3700536 DOI: 10.1038/ncomms2834] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2013] [Accepted: 04/04/2013] [Indexed: 02/08/2023] Open
Abstract
Chimaerins, a family of GTPase activating proteins (GAPs) for the small G-protein Rac, have been implicated in development, neuritogenesis, and cancer. These Rac-GAPs are regulated by the lipid second messenger diacylglycerol (DAG) generated by tyrosine-kinases such as the epidermal growth factor receptor (EGFR). Here we identify an atypical Pro-rich motif in chimaerins that binds to the adaptor protein Nck1. Unlike most Nck1 partners, chimaerins bind to the third SH3 domain of Nck1. This association is mediated by electrostatic interactions of basic residues within the Pro-rich motif with acidic clusters in the SH3 domain. EGF promotes the binding of β2-chimaerin to Nck1 in the cell periphery in a DAG-dependent manner. Moreover, β2-chimaerin translocation to the plasma membrane and its peripheral association with Rac1 requires Nck1. Our studies underscore a coordinated mechanism for β2-chimaerin activation that involves lipid interactions via the C1 domain and protein-protein interactions via the N-terminal Pro-rich region.
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Affiliation(s)
- Alvaro Gutierrez-Uzquiza
- Department of Pharmacology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6160, USA
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Shaping up the membrane: diacylglycerol coordinates spatial orientation of signaling. Trends Biochem Sci 2011; 36:593-603. [PMID: 21798744 DOI: 10.1016/j.tibs.2011.06.005] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2011] [Revised: 06/21/2011] [Accepted: 06/23/2011] [Indexed: 11/23/2022]
Abstract
Diacylglycerol signals by binding and activating C1 domain-containing proteins expressed principally in neuronal and immune tissues. This restricted expression profile suggests that diacylglycerol-regulated signals are particularly relevant in cell-cell communication processes in which active endocytosis and exocytosis take place. Not surprisingly, various experimental approaches have demonstrated a crucial role for diacylglycerol effectors and metabolizing enzymes in the control of immune responses, neuron communication and phagocytosis. Current research delineates a scenario in which coordinated decoding of diacylglycerol signals is translated into complex biological responses such as neuronal plasticity, T cell development or cytolytic killing. Diacylglycerol functions reach maximal diversity in these highly specialized systems in which signal intensity directly regulates distinct biological outcomes. This review brings together the most recent studies, emphasizing the contribution of compartmentalized DAG metabolism to orientated signaling events.
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Marland JRK, Pan D, Buttery PC. Rac GTPase-activating protein (Rac GAP) α1-Chimaerin undergoes proteasomal degradation and is stabilized by diacylglycerol signaling in neurons. J Biol Chem 2010; 286:199-207. [PMID: 21056981 DOI: 10.1074/jbc.m110.166728] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
α1-Chimaerin is a neuron-specific member of the Rho GTPase-activating protein family that selectively inactivates the small GTPase Rac. It is known to regulate the structure of dendrites and dendritic spines. We describe here that under basal conditions α1-chimaerin becomes polyubiquitinated and undergoes rapid proteasomal degradation. This degradation is partly dependent on the N-terminal region that is unique to this isoform. Mimicking diacylglycerol (DAG) signaling with a phorbol ester stabilizes endogenous α1-chimaerin against degradation and causes accumulation of the protein. The stabilization requires phorbol ester binding via the C1 domain of the protein and is independent of PKC activity. In addition, overexpression of a constitutively active Rac1 mutant is sufficient to cause an accumulation of α1-chimaerin through a phospholipase C-dependent mechanism, showing that endogenous DAG signaling can also stabilize the protein. These results suggest that signaling via DAG may regulate the abundance of α1-chimaerin under physiological conditions, providing a new model for understanding how its activity could be controlled.
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Affiliation(s)
- Jamie R K Marland
- Centre for Brain Repair, University of Cambridge, Cambridge CB2 0PY, United Kingdom
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12
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Griner EM, Caino MC, Sosa MS, Colón-González F, Chalmers MJ, Mischak H, Kazanietz MG. A novel cross-talk in diacylglycerol signaling: the Rac-GAP beta2-chimaerin is negatively regulated by protein kinase Cdelta-mediated phosphorylation. J Biol Chem 2010; 285:16931-41. [PMID: 20335173 DOI: 10.1074/jbc.m109.099036] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Although the family of chimaerin Rac-GAPs has recently gained significant attention for their involvement in development, cancer, and neuritogenesis, little is known about their molecular regulation. Chimaerins are activated by the lipid second messenger diacylglycerol via their C1 domain upon activation of tyrosine kinase receptors, thereby restricting the magnitude of Rac signaling in a receptor-regulated manner. Here we identified a novel regulatory mechanism for beta2-chimaerin via phosphorylation. Epidermal growth factor or the phorbol ester phorbol 12-myristate 13-acetate caused rapid phosphorylation of beta2-chimaerin on Ser(169) located in the SH2-C1 domain linker region via protein kinase Cdelta, which retained beta2-chimaerin in the cytosol and prevented its C1 domain-mediated translocation to membranes. Furthermore, despite the fact that Ser(169) phosphorylation did not alter intrinsic Rac-GAP activity in vitro, a non-phosphorylatable beta2-chimaerin mutant was highly sensitive to translocation, and displayed enhanced association with activated Rac, enhanced Rac-GAP activity, and anti-migratory properties when expressed in cells. Our results not only revealed a novel regulatory mechanism that facilitates Rac activation, but also identified a novel mechanism of cross-talk between diacylglycerol receptors that restricts beta2-chimaerin relocalization and activation.
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Affiliation(s)
- Erin M Griner
- Department of Pharmacology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6160, USA
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