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Kaykas A, Worringer K, Sugden B. LMP-1's transmembrane domains encode multiple functions required for LMP-1's efficient signaling. J Virol 2002; 76:11551-60. [PMID: 12388716 PMCID: PMC136760 DOI: 10.1128/jvi.76.22.11551-11560.2002] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The latent membrane protein-1 (LMP-1) of Epstein-Barr virus (EBV) contributes to the proliferation of infected B lymphocytes by signaling through its binding to cellular signaling molecules. It apparently mimics members of the tumor necrosis factor receptor family, in particular, CD40, by binding a similar set of cellular molecules as does CD40. LMP-1 differs dramatically in its structure from CD40. LMP-1 has six membrane-spanning domains as opposed to CD40's one. LMP-1 also differs from CD40 in its apparent independence of a ligand for its signaling. We have examined the role of LMP-1's membrane-spanning domains in its signaling. Their substitution with six membrane-spanning domains from the LMP-2A protein of EBV yields a derivative which neither coimmunoprecipitates with LMP-1 nor signals to increase the activity of NF-kappaB as does wild-type LMP-1. These observations indicate that LMP-1 has specific sequences in its membrane-spanning domains required for these activities. LMP-1's first and sixth membrane-spanning domains have multiple leucine residues potentially similar to leucine-heptad motifs that can mediate protein-protein interactions in membranes (Gurezka et al., J. Biol. Chem. 274:9265-9270, 1999). Substitution of seven leucines in LMP-1's sixth membrane-spanning domain has no effect on its function, whereas similar substitutions in its first membrane-spanning domain yielded a derivative which aggregates as does wild-type LMP-1 but has only 3% of wild-type's ability to signal through NF-kappaB. Importantly, this derivative complements a mutant of LMP-1 with wild-type membrane-spanning domains but no carboxy-terminal signaling domain. These findings together indicate that the membrane-spanning domains of LMP-1 contribute multiple functions to its signaling.
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Affiliation(s)
- Ajamete Kaykas
- McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Wisconsin 53706-1599, USA
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52
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Szymkiewicz I, Kowanetz K, Soubeyran P, Dinarina A, Lipkowitz S, Dikic I. CIN85 participates in Cbl-b-mediated down-regulation of receptor tyrosine kinases. J Biol Chem 2002; 277:39666-72. [PMID: 12177062 DOI: 10.1074/jbc.m205535200] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Cbl family of ubiquitin ligases in mammals contains three members, Cbl, Cbl-b, and Cbl-3, that are involved in down-regulation of receptor tyrosine kinases (RTKs) by mediating receptor ubiquitination and degradation. More recently, a novel pathway has been identified whereby Cbl promotes internalization of EGF receptor via a CIN85/endophilin pathway that is functionally separable from the ubiquitin ligase activity of Cbl (1). Here we show that Cbl-b, but not Cbl-3, utilize the same mechanism to down-regulate multiple RTKs. CIN85 was shown to bind to the minimal binding domain identified in the carboxyl terminus of Cbl-b. Ligand-induced phosphorylation of Cbl-b further increased their interactions and led to a rapid and sustained recruitment of CIN85 in the complex with EGF or PDGF receptors. Inhibition of binding between CIN85 and Cbl-b was sufficient to impair Cbl-b-mediated internalization of EGF receptors, while being dispensable for Cbl-b-directed polyubiquitination of EGF receptors. Moreover, CIN85 and Cbl/Cbl-b were constitutively associated with activated PDGF, EGF, or c-Kit receptors in several tumor cell lines. Our data reveal a common pathway utilized by Cbl and Cbl-b that may have an important and redundant function in negative regulation of ligand-activated as well as oncogenically activated RTKs in vivo.
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Affiliation(s)
- Iwona Szymkiewicz
- Ludwig Institute for Cancer Research, Box 595, Husargatan 3, Uppsala, S-75124, Sweden
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53
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Sekizawa R, Ikeno S, Nakamura H, Naganawa H, Matsui S, Iinuma H, Takeuchi T. Panepophenanthrin, from a mushroom strain, a novel inhibitor of the ubiquitin-activating enzyme. JOURNAL OF NATURAL PRODUCTS 2002; 65:1491-1493. [PMID: 12398550 DOI: 10.1021/np020098q] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Screening for inhibitors of the ubiquitin-proteasome pathway, considered to regulate important cellular events and linked to serious diseases as well, led to isolation of a new compound, panepophenanthrin, from the fermented broth of a mushroom strain, Panus rudis Fr. IFO 8994. This is the first inhibitor of the ubiquitin-activating enzyme, which is indispensable for the ubiquitin-proteasome pathway. The structure of panepophenanthrin was determined by NMR and X-ray crystallographic analyses as 1,3a,10-trihydroxy-10c-(3-hydroxy-3-methylbut-1-enyl)-5,5-dimethyl-1,2,3,3a,5,5a,8,9,10,10a,10b,10c-dodecahydro-4-oxa-2,3,8,9-diepoxyacephenanthrylen-7-one.
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Affiliation(s)
- Ryuichi Sekizawa
- Institute of Microbial Chemistry, 3-14-23 Kamiosaki, Shinagawa-ku, Tokyo 141-0021, Japan.
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54
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Katz M, Shtiegman K, Tal-Or P, Yakir L, Mosesson Y, Harari D, Machluf Y, Asao H, Jovin T, Sugamura K, Yarden Y. Ligand-independent degradation of epidermal growth factor receptor involves receptor ubiquitylation and Hgs, an adaptor whose ubiquitin-interacting motif targets ubiquitylation by Nedd4. Traffic 2002; 3:740-51. [PMID: 12230472 DOI: 10.1034/j.1600-0854.2002.31006.x] [Citation(s) in RCA: 118] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Ligand-dependent endocytosis of the epidermal growth factor receptor (EGFR) involves recruitment of a ubiquitin ligase, and sorting of ubiquitylated receptors to lysosomal degradation. By studying Hgs, a mammalian homolog of a yeast vacuolar-sorting adaptor, we provide information on the less understood, ligand-independent pathway of receptor endocytosis and degradation. Constitutive endocytosis involves receptor ubiquitylation and translocation to Hgs-containing endosomes. Whereas the lipid-binding motif of Hgs is necessary for receptor endocytosis, the ubiquitin-interacting motif negatively regulates receptor degradation. We demonstrate that the ubiquitin-interacting motif is endowed with two functions: it binds ubiquitylated proteins and it targets self-ubiquitylation by recruiting Nedd4, an ubiquitin ligase previously implicated in endocytosis. Based upon the dual function of the ubiquitin-interacting motif and its wide occurrence in endocytic adaptors, we propose a ubiquitin-interacting motif network that relays ubiquitylated membrane receptors to lysosomal degradation through successive budding events.
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Affiliation(s)
- Menachem Katz
- Department of Biological Regulation, The Weizmann Institute of Science, Rehovot 76100, Israel
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55
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Wong ESM, Fong CW, Lim J, Yusoff P, Low BC, Langdon WY, Guy GR. Sprouty2 attenuates epidermal growth factor receptor ubiquitylation and endocytosis, and consequently enhances Ras/ERK signalling. EMBO J 2002; 21:4796-808. [PMID: 12234920 PMCID: PMC126289 DOI: 10.1093/emboj/cdf493] [Citation(s) in RCA: 199] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Drosophila Sprouty (dSpry) was genetically identified as a novel antagonist of fibroblast growth factor receptor (FGFR), epidermal growth factor receptor (EGFR) and Sevenless signalling, ostensibly by eliciting its response on the Ras/MAPK pathway. Four mammalian sprouty genes have been cloned, which appear to play an inhibitory role mainly in FGF- mediated lung and limb morphogenesis. Evidence is presented herein that describes the functional implications of the direct association between human Sprouty2 (hSpry2) and c-Cbl, and its impact on the cellular localization and signalling capacity of EGFR. Contrary to the consensus view that Spry2 is a general inhibitor of receptor tyrosine kinase signalling, hSpry2 was shown to abrogate EGFR ubiquitylation and endocytosis, and sustain EGF-induced ERK signalling that culminates in differentiation of PC12 cells. Correlative evidence showed the failure of hSpry2DeltaN11 and mSpry4, both deficient in c-Cbl binding, to instigate these effects. hSpry2 interacts specifically with the c-Cbl RING finger domain and displaces UbcH7 from its binding site on the E3 ligase. We conclude that hSpry2 potentiates EGFR signalling by specifically intercepting c-Cbl-mediated effects on receptor down-regulation.
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Affiliation(s)
| | | | | | | | - Boon Chuan Low
- Signal Transduction Laboratory, Institute of Molecular and Cell Biology, National University of Singapore, 30 Medical Drive, Singapore 117609,
Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543 and Department of Pathology, M Block, Room 1.2, Queen Elizabeth II Medical Centre, University of Western Australia, WA, Australia Corresponding author e-mail:
| | - Wallace Y. Langdon
- Signal Transduction Laboratory, Institute of Molecular and Cell Biology, National University of Singapore, 30 Medical Drive, Singapore 117609,
Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543 and Department of Pathology, M Block, Room 1.2, Queen Elizabeth II Medical Centre, University of Western Australia, WA, Australia Corresponding author e-mail:
| | - Graeme R. Guy
- Signal Transduction Laboratory, Institute of Molecular and Cell Biology, National University of Singapore, 30 Medical Drive, Singapore 117609,
Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543 and Department of Pathology, M Block, Room 1.2, Queen Elizabeth II Medical Centre, University of Western Australia, WA, Australia Corresponding author e-mail:
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56
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Abstract
The structure of phospholipase Cgamma1 (PLC-gamma1) contains two SH2 domains and one SH3 domain. While the function of the SH2 domains in PLC-gamma1 are well described, to date no growth factor-dependent function for the SH3 domain has been presented. To assess SH3 domain function in the context of the full-length PLC-gamma1, this domain was deleted and the mutant was stably expressed in Plcg1 null mouse embryonic fibroblasts. Following EGF treatment of cells, the PLC-gamma1DeltaSH3 mutant displayed the same increased level of tyrosine phosphorylation and association with EGF receptor as wild-type PLC-gamma1. Also, the SH3 mutant demonstrated membrane translocation and mediated the mobilization of intracellular Ca(2+) in response to EGF. c-Cbl is shown to associate with tyrosine phosphorylated PLC-gamma1 in an EGF-dependent manner, but no association was detected with the PLC-gamma1DeltaSH3 mutant. Interestingly, PDGF, which also tyrosine phosphorylates PLC-gamma1, failed to induce c-Cbl association with PLC-gamma1 and also provoked no c-Cbl tyrosine phosphorylation. This suggests that c-Cbl tyrosine phosphorylation is necessary for its interaction with PLC-gamma1. Evidence of a direct association of c-Cbl with PLC-gamma1 was provided by pull-down and overlay experiments, using glutathione S-transferase fusion proteins that contain the SH3 domain of PLC-gamma1. The data, therefore, show an EGF-inducible direct association of PLC-gamma1 with c-Cbl in vivo that is mediated by the SH3 domain of PLC-gamma1.
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Affiliation(s)
- Denis Tvorogov
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
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57
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Seto ES, Bellen HJ, Lloyd TE. When cell biology meets development: endocytic regulation of signaling pathways. Genes Dev 2002; 16:1314-36. [PMID: 12050111 DOI: 10.1101/gad.989602] [Citation(s) in RCA: 172] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Elaine S Seto
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas 77030, USA
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58
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Portero-Otín M, Pamplona R, Bellmunt MJ, Ruiz MC, Prat J, Salvayre R, Nègre-Salvayre A. Advanced glycation end product precursors impair epidermal growth factor receptor signaling. Diabetes 2002; 51:1535-42. [PMID: 11978653 DOI: 10.2337/diabetes.51.5.1535] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Formation of advanced glycation end products (AGEs) is considered a potential link between hyperglycemia and chronic diabetic complications, including disturbances in cell signaling. It was hypothesized that AGEs alter cell signaling by interfering with growth factor receptors. Therefore, we studied the effects of two AGE precursors, glyoxal (GO) and methylglyoxal (MGO), on the epidermal growth factor receptor (EGFR) signaling pathway in cultured cells. Both compounds prevented tyrosine autophosphorylation induced by epidermal growth factor (EGF) in a time- and dose-dependent manner as well as phospholipase Cgamma1 recruitment and subsequent activation of extracellular signal-regulated kinases. AGE precursors inhibit EGF-induced EGFR autophosphorylation and tyrosine kinase activity in cell membranes and in EGFR immunoprecipitates. In addition, AGE precursors strongly inhibited cellular phosphotyrosine phosphatase activities and residual EGFR dephosphorylation. AGE precursors induced the formation of EGFR cross-links, as shown by the cross-reactivity of modified EGFR with an anti-N(epsilon)(carboxymethyl)lysine antibody, suggesting that altered EGFR signaling was related to carbonyl-amine reactions on EGFR. Aminoguanidine, an inhibitor of AGE formation, partially prevented the EGFR dysfunction induced by GO and MGO. These data introduce a novel mechanism for impaired cellular homeostasis in situations that lead to increased production of these reactive aldehydes, such as diabetes.
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Affiliation(s)
- Manuel Portero-Otín
- Metabolic Pathophysiology Research Group, Department of Basic Medical Sciences, University of Lleida, Lleida, Spain.
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59
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Salazar G, González A. Novel mechanism for regulation of epidermal growth factor receptor endocytosis revealed by protein kinase A inhibition. Mol Biol Cell 2002; 13:1677-93. [PMID: 12006662 PMCID: PMC111136 DOI: 10.1091/mbc.01-08-0403] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Current models put forward that the epidermal growth factor receptor (EGFR) is efficiently internalized via clathrin-coated pits only in response to ligand-induced activation of its intrinsic tyrosine kinase and is subsequently directed into a lysosomal-proteasomal degradation pathway by mechanisms that include receptor tyrosine phosphorylation and ubiquitylation. Herein, we report a novel mechanism of EGFR internalization that does not require ligand binding, receptor kinase activity, or ubiquitylation and does not direct the receptor into a degradative pathway. Inhibition of basal protein kinase A (PKA) activity by H89 and the cell-permeable substrate peptide Myr-PKI induced internalization of 40-60% unoccupied, inactive EGFR, and its accumulation into early endosomes without affecting endocytosis of transferrin and mu-opioid receptors. This effect was abrogated by interfering with clathrin function. Thus, the predominant distribution of inactive EGFR at the plasma membrane is not simply by default but involves a PKA-dependent restrictive condition resulting in receptor avoidance of endocytosis until it is stimulated by ligand. Furthermore, PKA inhibition may contribute to ligand-induced EGFR endocytosis because epidermal growth factor inhibited 26% of PKA basal activity. On the other hand, H89 did not alter ligand-induced internalization of EGFR but doubled its half-time of down-regulation by retarding its segregation into degradative compartments, seemingly due to a delay in the receptor tyrosine phosphorylation and ubiquitylation. Our results reveal that PKA basal activity controls EGFR function at two levels: 1) residence time of inactive EGFR at the cell surface by a process of "endocytic evasion," modulating the accessibility of receptors to stimuli; and 2) sorting events leading to the down-regulation pathway of ligand-activated EGFR, determining the length of its intracellular signaling. They add a new dimension to the fine-tuning of EGFR function in response to cellular demands and cross talk with other signaling receptors.
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Affiliation(s)
- Gloria Salazar
- Departamento de Inmunología Clínica y Reumatología, Facultad de Medicina. Centro de Regulación Celular y Patología, Pontificia Universidad Católica de Chile, Santiago, Chile
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60
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Junoy B, Maccario H, Mas JL, Enjalbert A, Drouva SV. Proteasome implication in phorbol ester- and GnRH-induced selective down-regulation of PKC (alpha, epsilon, zeta) in alpha T(3)-1 and L beta T(2) gonadotrope cell lines. Endocrinology 2002; 143:1386-403. [PMID: 11897696 DOI: 10.1210/endo.143.4.8752] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We investigated mechanisms underlying selective down-modulation of PKC isoforms (alpha, epsilon, zeta): 1) during 12-O-tetradecanoyl-phorbol-13 acetate (TPA) (10(-7) M) or GnRH (10(-7) M) desensitization conditions (2- to 6-h treatments) in two gonadotrope cell lines (alpha T(3)-1, L beta T(2)) and 2) in primary pituitary cell cultures from male rats during long-term phorbol ester administration. We demonstrated that, as in alpha T(3)-1 cells, in a more differentiated gonadotrope cell line L beta T(2) the GnRH-receptor coupling (PLC, PLA2, PLD) generated second messengers essential for PKCs activation; the characterized isoforms (alpha, beta II, delta, epsilon, zeta) were selectively and differentially down-regulated by TPA (alpha, beta II, delta, epsilon) or GnRH (delta, epsilon). In whole cell lysates, proteasome inhibitors (proteasome inhibitor I and II, Lactacystin, beta-Lactone, Calpain inhibitor I) prevented in both gonadotrope cell lines the TPA-induced depletion of PKC alpha, epsilon, and the GnRH-elicited PKC epsilon down-regulation; they counteracted in mixed pituitary cell cultures as well, the TPA-evoked PKC alpha, epsilon depletion. In contrast, the inhibitors of calpain(s) and lysosomal proteases (Calpeptin, E64d, Calpain inhibitor II, and PD150606), were ineffective. As shown in alpha T(3)-1 subcellular fractions, proteasome abrogation did not affect membrane translocation of TPA- and GnRH- target isoforms (alpha, epsilon) but, preventing their degradation, favored enzyme accumulation to the membrane compartment. Proteolysis processing of PKCs may be dependent upon their phosphorylated state and/or catalytic activity. Inhibition of PKC catalytic activity (GF109203X, Gö6976), selectively prevented the TPA-evoked PKC alpha depletion in both mixed pituitary cells and alpha T(3)-1 gonadotropes; in alpha T(3)-1 subcellular fractions, PKC alpha inactivation overcame the TPA-evoked isoenzyme degradation by inducing a pronounced membrane accumulation of the isoform without affecting its membrane relocalization. Thus, the proteasome system by adjusting PKC cellular levels, may represent a regulatory proteolytic pathway implicated in the adaptive mechanisms of the time dependent cell responses.
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Affiliation(s)
- Brice Junoy
- Centre National de la Recherche Scientifique UMR 6544, Université de la Méditerranée, Faculté de Médecine, 13916 Marseille, France
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61
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Sachse M, Urbé S, Oorschot V, Strous GJ, Klumperman J. Bilayered clathrin coats on endosomal vacuoles are involved in protein sorting toward lysosomes. Mol Biol Cell 2002; 13:1313-28. [PMID: 11950941 PMCID: PMC102271 DOI: 10.1091/mbc.01-10-0525] [Citation(s) in RCA: 270] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
In many cells endosomal vacuoles show clathrin coats of which the function is unknown. Herein, we show that this coat is predominantly present on early endosomes and has a characteristic bilayered appearance in the electron microscope. By immunoelectron microscopy we show that the coat contains clathrin heavy as well as light chain, but lacks the adaptor complexes AP1, AP2, and AP3, by which it differs from clathrin coats on endocytic vesicles and recycling endosomes. The coat is insensitive to short incubations with brefeldin A, but disappears in the presence of the phosphatidylinositol 3-kinase inhibitor wortmannin. No association of endosomal coated areas with tracks of tubulin or actin was found. By quantitative immunoelectron microscopy, we found that the lysosomal-targeted receptors for growth hormone (GHR) and epidermal growth factor are concentrated in the coated membrane areas, whereas the recycling transferrin receptor is not. In addition, we found that the proteasomal inhibitor MG 132 induces a redistribution of a truncated GHR (GHR-369) toward recycling vesicles, which coincided with a redistribution of endosomal vacuole-associated GHR-369 to the noncoated areas of the limiting membrane. Together, these data suggest a role for the bilayered clathrin coat on vacuolar endosomes in targeting of proteins to lysosomes.
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Affiliation(s)
- Martin Sachse
- Department of Cell Biology, University Medical Center Utrecht and Institute of Biomembranes, 3584 CX Utrecht, The Netherlands
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62
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Ringerike T, Blystad FD, Levy FO, Madshus IH, Stang E. Cholesterol is important in control of EGF receptor kinase activity but EGF receptors are not concentrated in caveolae. J Cell Sci 2002; 115:1331-40. [PMID: 11884532 DOI: 10.1242/jcs.115.6.1331] [Citation(s) in RCA: 165] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have investigated the localization and function of the epidermal growth factor receptor (EGFR) in normal cells, in cholesterol-depleted cells and in cholesterol enriched cells. Using immunoelectron microscopy we find that the EGFR is randomly distributed at the plasma membrane and not enriched in caveolae. Binding of EGF at 4°C does not change the localization of EGFR,and by immunoelectron microscopy we find that only small amounts of bound EGF localize to caveolae. However, upon patching of lipid rafts, we find that a significant amount of the EGFR is localized within rafts. Depletion of the plasma membrane cholesterol causes increased binding of EGF, increased dimerization of the EGFR, and hyperphosphorylation of the EGFR. Addition of cholesterol was found to reduce EGF binding and reduce EGF-induced EGFR activation. Our results suggest that the plasma membrane cholesterol content directly controls EGFR activation.
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Affiliation(s)
- Tove Ringerike
- Institute of Pathology, University of Oslo, Rikshospitalet University Hospital, N-0027 Oslo, Norway
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63
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Longva KE, Blystad FD, Stang E, Larsen AM, Johannessen LE, Madshus IH. Ubiquitination and proteasomal activity is required for transport of the EGF receptor to inner membranes of multivesicular bodies. J Cell Biol 2002; 156:843-54. [PMID: 11864992 PMCID: PMC2173306 DOI: 10.1083/jcb.200106056] [Citation(s) in RCA: 308] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
EGF, but not TGF alpha, efficiently induces degradation of the EGF receptor (EGFR). We show that EGFR was initially polyubiquitinated to the same extent upon incubation with EGF and TGF alpha, whereas the ubiquitination was more sustained by incubation with EGF than with TGF alpha. Consistently, the ubiquitin ligase c-Cbl was recruited to the plasma membrane upon activation of the EGFR with EGF and TGF alpha, but localized to endosomes only upon activation with EGF. EGF remains bound to the EGFR upon endocytosis, whereas TGF alpha dissociates from the EGFR. Therefore, the sustained polyubiquitination is explained by EGF securing the kinase activity of endocytosed EGFR. Overexpression of the dominant negative N-Cbl inhibited ubiquitination of the EGFR and degradation of EGF and EGFR. This demonstrates that EGF-induced ubiquitination of the EGFR as such is important for lysosomal sorting. Both lysosomal and proteasomal inhibitors blocked degradation of EGF and EGFR, and proteasomal inhibitors inhibited translocation of activated EGFR from the outer limiting membrane to inner membranes of multivesicular bodies (MVBs). Therefore, lysosomal sorting of kinase active EGFR is regulated by proteasomal activity. Immuno-EM showed the localization of intact EGFR on internal membranes of MVBs. This demonstrates that the EGFR as such is not the proteasomal target.
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Affiliation(s)
- Karianne E Longva
- Institute of Pathology, The University of Oslo, Rikshospitalet, N-0027 Oslo, Norway
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64
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Oksvold MP, Huitfeldt HS, Østvold AC, Skarpen E. UV induces tyrosine kinase-independent internalisation and endosome arrest of the EGF receptor. J Cell Sci 2002; 115:793-803. [PMID: 11865035 DOI: 10.1242/jcs.115.4.793] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have compared the activation and trafficking of epidermal growth factor receptor (EGFR) induced by UV light and EGF. Tyrosine phosphorylation of EGFR was not detected in UV-exposed cells by immunoblotting of whole cell lysates or EGFR immunoprecipitates with antibodies specific for each of the five activated autophosphorylation sites of EGFR. In addition, EGFR of UV-irradiated cells did not demonstrate increased 32P-incorporation. However, UV-exposed cells demonstrated a gel mobility shift of EGFR, which was not abolished by alkaline phosphatase treatment. UV-exposure did not induce dimerisation of EGFR. Furthermore, UV induced internalisation of EGFR without polyubiquitination or degradation. UV-exposed EGFR was transferred to early endosomes and arrested in transferrin-accessible endosomes close to the cell surface. Whereas inhibition of the EGFR tyrosine kinase effectively inhibited tyrosine phosphorylation and internalisation of EGF-activated EGFR, internalisation of UV-exposed EGFR was unaffected. UV induced neither relocalisation of Shc and Grb2 nor activation of Raf, but activation of MEK and MAPK was observed.
Our work indicates that UV induces internalisation of EGFR independent of its phosphorylation or receptor tyrosine kinase activation, and altered EGFR trafficking compared with ligand-activated receptor. In addition, MAPK activation by UV does not appear to be mediated by EGFR activation.
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Affiliation(s)
- Morten P Oksvold
- Laboratory for Toxicopathology, Institute of Pathology, The National Hospital, University of Oslo, N-0027 Oslo, Norway.
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65
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Waterman H, Katz M, Rubin C, Shtiegman K, Lavi S, Elson A, Jovin T, Yarden Y. A mutant EGF-receptor defective in ubiquitylation and endocytosis unveils a role for Grb2 in negative signaling. EMBO J 2002; 21:303-13. [PMID: 11823423 PMCID: PMC125825 DOI: 10.1093/emboj/21.3.303] [Citation(s) in RCA: 218] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Ligand-induced desensitization of the epidermal growth factor receptor (EGFR) is controlled by c-Cbl, a ubiquitin ligase that binds multiple signaling proteins, including the Grb2 adaptor. Consistent with a negative role for c-Cbl, here we report that defective Tyr1045 of EGFR, an inducible c-Cbl docking site, enhances the mitogenic response to EGF. Signaling potentiation is due to accelerated recycling of the mutant receptor and a concomitant defect in ligand-induced ubiquitylation and endocytosis of EGFR. Kinetic as well as morphological analyses of the internalization-defective mutant receptor imply that c-Cbl-mediated ubiquitylation sorts EGFR to endocytosis and to subsequent degradation in lysosomes. Unexpectedly, however, the mutant receptor displayed significant residual ligand-induced ubiquitylation, especially in the presence of an overexpressed c-Cbl. The underlying mechanism seems to involve recruitment of a Grb2 c-Cbl complex to Grb2-specific docking sites of EGFR, and concurrent acceleration of receptor ubiquitylation and desensitization. Thus, in addition to its well-characterized role in mediating positive signals, Grb2 can terminate signal transduction by accelerating c-Cbl-dependent sorting of active tyrosine kinases to destruction.
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Affiliation(s)
| | | | | | | | | | - Ari Elson
- Departments of Biological Regulation and
Molecular Genetics, The Weizmann Institute of Science, Rehovot 76100, Israel and Department of Molecular Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, D-37077 Gottingen, Germany Corresponding author e-mail:
| | - Thomas Jovin
- Departments of Biological Regulation and
Molecular Genetics, The Weizmann Institute of Science, Rehovot 76100, Israel and Department of Molecular Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, D-37077 Gottingen, Germany Corresponding author e-mail:
| | - Yosef Yarden
- Departments of Biological Regulation and
Molecular Genetics, The Weizmann Institute of Science, Rehovot 76100, Israel and Department of Molecular Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, D-37077 Gottingen, Germany Corresponding author e-mail:
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66
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Abstract
STAM/EAST/Hbp family of proteins consists of eight members well conserved from yeast to mammals. The basic domain architecture is comprised of an N-terminal Vps27, Hrs and STAM homology domain, a ubiquitin-interacting motif and a central Src homology-3 domain. Vertebrate members also carry an immunoreceptor tyrosine-based activation motif. STAM/EAST/Hbp proteins become tyrosine-phosphorylated by a variety of cytokines and growth factors. STAM 1 and STAM 2A are involved in cytokine-mediated signalling for DNA synthesis and c-myc induction. EAST and STAM 2A/Hbp play a role in receptor-mediated endo- and exocytosis and probably also in the regulation of actin cytoskeleton. Knockout experiments implicate a role for STAM 1 in neural cell survival. A picture is emerging of STAM/EAST/Hbp proteins acting as integrators of thus far mechanistically disparate cellular signalling events.
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Affiliation(s)
- O Lohi
- Department of Pediatrics, University of Tampere, Finland
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67
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Sachse M, van Kerkhof P, Strous GJ, Klumperman J. The ubiquitin-dependent endocytosis motif is required for efficient incorporation of growth hormone receptor in clathrin-coated pits, but not clathrin-coated lattices. J Cell Sci 2001; 114:3943-52. [PMID: 11719561 DOI: 10.1242/jcs.114.21.3943] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Endocytosis of the growth hormone receptor (GHR) requires an active ubiquitin-conjugation system. In addition, it depends on a 10 amino acid residues motif in the GHR-cytoplasmic tail, the ubiquitin dependent-endocytosis or UbE-motif. To gain insight into the role of ubiquitination in the early steps of endocytosis, we performed an ultrastructural analysis of GH-uptake in Chinese hamster cells expressing wild-type or mutant GHRs. In wild-type GHR cells, GH was found to be exclusively taken up via clathrin-coated pits. In early endosomes it was efficiently sorted from recycling transferrin and targeted to the degradative pathway. Mutation of all lysine residues of a truncated GHR (GHR-399K–) precludes ubiquitination of the receptor, but internalization of GHR-399K– still depends on an active ubiquitin system. We found that GHR-399K– incorporates GH into clathrin-coated vesicles with the same efficiency as wild-type GHR. By contrast, a mutation in the UbE-motif (GHR-F327A) largely abolished incorporation of GH into clathrin-coated vesicles. Notably, access of GH to clathrin-coated lattices was not affected in GHR-F327A cells. These data corroborate and extend previous data that the UbE-motif but not ubiquitination of the receptor itself recruits GHR into clathrin-coated vesicles. Moreover, they suggest that incorporation of GHR into clathrin-coated lattices is differentially regulated from incorporation into clathrin-coated pits.
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Affiliation(s)
- M Sachse
- Department of Cell Biology, AZU G02.525, Heidelberglaan 100, Utrecht University Medical Center and Institute of Biomembranes, 3584 CX Utrecht, The Netherlands
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68
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Abstract
The intimate relationship between receptor trafficking and signalling is beginning to reveal its secrets. Receptor endocytosis provides a mechanism for attenuation of signalling by transfer of receptors to degradative compartments. However, it can also determine signalling output by providing a different combination of downstream effectors at endocytic compartments compared with the plasma membrane. Rab5, Hrs and Cbl, are three examples of proteins that can influence both tyrosine kinase receptor trafficking and signalling pathways. By operating at this intersection, they are well placed to couple these aspects of cell function. Each element of the Rab5 GTPase cycle is influenced by signal transduction events, which will correspondingly influence recruitment of effector proteins and receptor distribution. Hrs and Cbl, which both undergo tyrosine phosphorylation in response to growth factor stimulation, are believed to influence receptor sorting in the early endosome and engage in multiple interactions, which may play a direct role in signalling cascades.
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Affiliation(s)
- M J Clague
- Physiological Laboratory, University of Liverpool, Crown St., Liverpool L69 3BX, UK.
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69
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de Melker AA, van der Horst G, Calafat J, Jansen H, Borst J. c-Cbl ubiquitinates the EGF receptor at the plasma membrane and remains receptor associated throughout the endocytic route. J Cell Sci 2001; 114:2167-78. [PMID: 11493652 DOI: 10.1242/jcs.114.11.2167] [Citation(s) in RCA: 139] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Cbl family members have an evolutionarily conserved role in attenuating receptor tyrosine kinase function. Their negative regulatory capacity depends on a Ring finger domain that interacts with ubiquitin conjugating enzymes. Cbl molecules constitute a novel type of E3 or ubiquitin ligase family that is recruited to phosphotyrosine motifs. Ubiquitination of the receptor system is coupled to its downregulation, but it is unclear at which point in the endocytic pathway Cbl molecules come into play. Using low temperature and a dynamin mutant, we find that c-Cbl associates with and ubiquitinates the activated epidermal growth factor (EGF) receptor at the plasma membrane in the absence of endocytosis. With the aid of confocal microscopy and immunogold electron microscopy, we could demonstrate that c-Cbl associates with the EGF receptor at the plasma membrane prior to receptor recruitment into clathrin-coated pits and remains associated throughout the clathrin-mediated endocytic pathway. c-Cbl and the EGF receptor also colocalize in internal vesicles of multivesicular endosomes. Our data are consistent with a role for c-Cbl in clathrin-mediated endocytosis of tyrosine kinase receptors, as well as their intracellular sorting.
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Affiliation(s)
- A A de Melker
- Division of Cellular Biochemistry, The Netherlands Cancer Institute, 1066 CX Amsterdam, The Netherlands
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70
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Kaykas A, Worringer K, Sugden B. CD40 and LMP-1 both signal from lipid rafts but LMP-1 assembles a distinct, more efficient signaling complex. EMBO J 2001; 20:2641-54. [PMID: 11387199 PMCID: PMC125480 DOI: 10.1093/emboj/20.11.2641] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
CD40, a member of the TNFR-1 receptor family, shares several features with LMP-1, an oncoprotein encoded by Epstein-Barr virus. CD40 and LMP-1 activate transcription by binding to TRAFs, JAK3 and/or TRADD. CD40's association with CD40L activates signaling. However, LMP-1 signals independently of a ligand but dependently on self-association. We demonstrate that activated CD40 and LMP-1 co-localize in lipid rafts and recruit TRAF3 there, findings consistent with signals of CD40 and LMP-1 being initiated from lipid rafts. To elucidate their signaling, we compared requirements for their aggregation and subcellular localization. Targeting CD40's monomeric C-terminal signaling domain to lipid rafts activates signaling, as does rendering it trimeric. Addition of both modifications supports signaling more efficiently. Parallel experiments with LMP-1 indicate that targeting the monomeric C-terminal signaling domain of LMP-1 to lipid rafts activates signaling, but trimerizing it does not. Fusing LMP-1's N-terminus and membrane-spanning domains to CD40's C-terminus supports signaling more efficiently than CD40 plus ligand or CD40's trimerized and/or localized derivatives. An activity of LMP-1's N-terminus and membrane-spanning domains other than trimerization must contribute to its efficient signaling.
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Affiliation(s)
| | | | - Bill Sugden
- McArdle Laboratory for Cancer Research, University of Wisconsin–Madison, Madison, WI 53706, USA
Corresponding author e-mail:
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71
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Keller SH, Lindstrom J, Ellisman M, Taylor P. Adjacent basic amino acid residues recognized by the COP I complex and ubiquitination govern endoplasmic reticulum to cell surface trafficking of the nicotinic acetylcholine receptor alpha-Subunit. J Biol Chem 2001; 276:18384-91. [PMID: 11279119 DOI: 10.1074/jbc.m100691200] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The nicotinic acetylcholine receptor in muscle is a ligand-gated ion channel with an ordered subunit arrangement of alpha-gamma-alpha-delta-beta. The subunits are sequestered in the endoplasmic reticulum (ER) and assembled into the pentameric arrangement prior to their exit to the cell surface. Mutating the Arg(313)-Lys(314) sequence in the large cytoplasmic loop of the alpha-subunit to K314Q promotes the trafficking of the mutant unassembled alpha-subunit from the ER to the Golgi in transfected HEK cells, identifying an important determinant that modulates the ER to Golgi trafficking of the subunit. The association of the K314Q alpha-subunit with gamma-COP, a component of COP I coats implicated in Golgi to ER anterograde transport, is diminished to a level comparable to that observed for wild-type alpha-subunits when co-expressed with the beta-, delta-, and gamma-subunits. This suggests that the Arg(313)-Lys(314) sequence is masked when the subunits assemble, thereby enabling ER to Golgi trafficking of the alpha-subunit. Although unassembled K314Q alpha-subunits accumulate in the Golgi, they are not detected at the cell surface, suggesting that a second post-Golgi level of capture exists. Expressing the K314Q alpha-subunit in the absence of the other subunits in ubiquitinating deficient cells (ts20) results in detecting this subunit at the cell surface, indicating that ubiquitination functions as a post-Golgi modulator of trafficking. Taken together, our findings support the hypothesis that subunit assembly sterically occludes the trafficking signals and ubiquitination at specific sites. Following the masking of these signals, the assembled ion channel expresses at the cell surface.
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Affiliation(s)
- S H Keller
- Department of Pharmacology, University of California, San Diego, La Jolla, Califronia 92093, USA
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72
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Johannessen LE, Haugen KE, østvold AC, Stang E, Madshus IH. Heterodimerization of the epidermal-growth-factor (EGF) receptor and ErbB2 and the affinity of EGF binding are regulated by different mechanisms. Biochem J 2001; 356:87-96. [PMID: 11336639 PMCID: PMC1221815 DOI: 10.1042/0264-6021:3560087] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
When clathrin-dependent endocytosis is inhibited in HeLa cells by overexpression of a K44A (Lys(44)-->Ala) mutant of the GTPase dynamin, high-affinity binding of epidermal growth factor (EGF) to the EGF receptor (EGFR) is disrupted [Ringerike, Stang, Johannessen, Sandnes, Levy and Madshus (1998) J. Biol. Chem. 273, 16639-16642]. We now report that the effect of [K44A]dynamin on EGF binding was counteracted by incubation with the non-specific kinase inhibitor staurosporine (SSP), implying that a protein kinase is responsible for disrupted high-affinity binding of EGF upon overexpression of [K44A]dynamin. The effect of [K44A]dynamin on EGF binding was not due to altered phosphorylation of the EGFR, suggesting that the activated kinase is responsible for phosphorylation of a substrate other than EGFR. The number of EGFR molecules was increased in cells overexpressing [K44A]dynamin, while the number of proto-oncoprotein ErbB2 molecules was unaltered. EGF-induced receptor dimerization was not influenced by overexpression of [K44A]dynamin. ErbB2-EGFR heterodimer formation was found to be ligand-independent, and the number of heterodimers was not altered by overexpression of [K44A]dynamin. Neither SSP nor the phorbol ester PMA, which disrupts high-affinity EGF-EGFR interaction, had any effect on the EGFR homo- or hetero-dimerization. Furthermore, the EGF-induced tyrosine phosphorylation of ErbB2 was not affected by overexpression of [K44A]dynamin, implying that EGFR-ErbB2 dimers were fully functional. Our results strongly suggest that high-affinity binding of EGF and EGFR-ErbB2 heterodimerization are regulated by different mechanisms.
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Affiliation(s)
- L E Johannessen
- Institute of Pathology, University of Oslo, The National Hospital, N-0027 Oslo, Norway
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73
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Abstract
Responses to extracellular stimuli are often transduced from cell-surface receptors to protein tyrosine kinases which, when activated, initiate the formation of protein complexes that transmit signals throughout the cell. A prominent component of these complexes is the product of the proto-oncogene c-Cbl, which specifically targets activated protein tyrosine kinases and regulates their signalling. How, then, does this multidomain protein shape the responses generated by these signalling complexes?
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Affiliation(s)
- C B Thien
- Department of Pathology, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia
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74
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Lafont F, Simons K. Raft-partitioning of the ubiquitin ligases Cbl and Nedd4 upon IgE-triggered cell signaling. Proc Natl Acad Sci U S A 2001; 98:3180-4. [PMID: 11248052 PMCID: PMC30627 DOI: 10.1073/pnas.051003498] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The high affinity receptor for IgE, FcepsilonRI on mast cells and basophils plays an essential role in immunological defense. Upon multivalent antigen binding, FcepsilonRI becomes phoshorylated by the protein-tyrosine kinase Lyn, as a result of receptor clustering in lipid rafts. FcepsilonRI has been shown to be ubiquitinated. Ubiquitination can lead to degradation by proteasomes, but it can also act as a sorting signal to internalize proteins destined to the endosomal/lysosomal pathway. We have analyzed whether FcepsilonRI ubiquitination takes place within rafts. We report biochemical and imaging evidence in rat basoleukemia cells for the presence of ubiquitinated FcepsilonRI in clustered rafts upon receptor activation. Moreover, we demonstrated that the ubiquitin ligases Cbl and Nedd4 colocalize with FcepsilonRI patches and showed that both ligases become associated with lipid rafts after activation of IgE signaling. Because Cbl is known to interact with the FcepsilonRI signaling complex, ubiquitination is likely to be an important parameter regulating IgE-triggered signaling occurring in rafts.
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Affiliation(s)
- F Lafont
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 110, D-01307 Dresden, Germany.
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75
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Waterman H, Yarden Y. Molecular mechanisms underlying endocytosis and sorting of ErbB receptor tyrosine kinases. FEBS Lett 2001; 490:142-52. [PMID: 11223029 DOI: 10.1016/s0014-5793(01)02117-2] [Citation(s) in RCA: 261] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The major process that regulates the amplitude and kinetics of signal transduction by tyrosine kinase receptors is endocytic removal of active ligand-receptor complexes from the cell surface, and their subsequent sorting to degradation or to recycling. Using the ErbB family of receptor tyrosine kinases we exemplify the diversity of the down regulation process, and concentrate on two sorting steps whose molecular details are emerging. These are the Eps15-mediated sorting to clathrin-coated regions of the plasma membrane and the c-Cbl-mediated targeting of receptors to lysosomal degradation. Like in yeast cells, sorting involves not only protein phosphorylation but also conjugation of ubiquitin molecules. The involvement of other molecules is reviewed and recent observations that challenge the negative regulatory role of endocytosis are described. Finally, we discuss the relevance of receptor down regulation to cancer therapy.
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Affiliation(s)
- H Waterman
- Department of Biological Regulation, the Weizmann Institute of Science, 76100, Rehovot, Israel
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76
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van Kerkhof P, Sachse M, Klumperman J, Strous GJ. Growth hormone receptor ubiquitination coincides with recruitment to clathrin-coated membrane domains. J Biol Chem 2001; 276:3778-84. [PMID: 11042179 DOI: 10.1074/jbc.m007326200] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Endocytosis of the growth hormone receptor (GHR) depends on a functional ubiquitin conjugation system. A 10-amino acid residue motif within the GHR cytosolic tail (the ubiquitin-dependent endocytosis motif) is involved in both GHR ubiquitination and endocytosis. As shown previously, ubiquitination of the receptor itself is not required. In this paper ubiquitination of the GHR was used as a tool to address the question of at which stage the ubiquitin conjugation system acts in the process of GHR endocytosis. If potassium depletion was used to interfere with early stages of coated pit formation, both GHR endocytosis and ubiquitination were inhibited. Treatment of cells with methyl-beta-cyclodextrin inhibited endocytosis at the stage of coated vesicle formation. Growth hormone addition to methyl-beta-cyclodextrin-treated cells resulted in an accumulation of ubiquitinated GHR at the cell surface. Using immunoelectron microscopy, the GHR was localized in flattened clathrin-coated membranes. In addition, when clathrin-mediated endocytosis was inhibited in HeLa cells expressing a temperature-sensitive dynamin mutant, ubiquitinated GHR accumulated at the cell surface. Together, these data show that the GHR is ubiquitinated at the plasma membrane, before endocytosis occurs, and indicate that the resident time of the GHR at the cell surface is regulated by the ubiquitin conjugation system together with the endocytic machinery.
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Affiliation(s)
- P van Kerkhof
- Department of Cell Biology, University Medical Center Utrecht and Institute of Biomembranes, 3584CX Utrecht, The Netherlands
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77
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De Wit R, Makkinje M, Boonstra J, Verkleij AJ, Post JA. Hydrogen peroxide reversibly inhibits epidermal growth factor (EGF) receptor internalization and coincident ubiquitination of the EGF receptor and Eps15. FASEB J 2001; 15:306-8. [PMID: 11156945 DOI: 10.1096/fj.00-0454fje] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Recently, we demonstrated that hydrogen peroxide (H2O2) inhibits the internalization of the epidermal growth factor (EGF) receptor and the EGF-induced mono-ubiquitination of EGF receptor pathway substrate clone #15 (Eps15) in fibroblasts. In addition, it was suggested that EGF receptor internalization might be inhibited by H2O2 by inhibition of ubiquitination of proteins involved in endocytosis. Here, we show that H2O2 also inhibits the poly-ubiquitination of the EGF receptor in fibroblasts. Furthermore, recovery of the cells resulted in re-establishment of ubiquitination of both the EGF receptor and Eps15 and coincided with restoration of internalization of those receptors that had bound EGF in the presence of H2O2. In addition, EGF receptor internalization was inhibited by the sulphydryl reagent N-ethylmaleimide (NEM), indicating that intact SH groups might be required for receptor-mediated endocytosis. Furthermore, H2O2 rapidly induced an increase in the cellular ratio of GSSG:GSH (oxidized glutathione:reduced glutathione) and removal of H2O2 resulted in a fast restoration of the ratio of GSSG:GSH. Therefore, these results suggest a relation between the inhibition of internalization ubiquitination and an increase in GSSG:GSH ratio, which strengthens the hypothesis that H2O2 inhibits EGF receptor internalization by an inhibition of ubiquitination of proteins involved in EGF receptor-mediated endocytosis.
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Affiliation(s)
- R De Wit
- Institute of Biomembranes, Department of Molecular Cell Biology, Utrecht University, Utrecht, The Netherlands.
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78
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Johannessen LE, Ringerike T, Molnes J, Madshus IH. Epidermal growth factor receptor efficiently activates mitogen-activated protein kinase in HeLa cells and Hep2 cells conditionally defective in clathrin-dependent endocytosis. Exp Cell Res 2000; 260:136-45. [PMID: 11010818 DOI: 10.1006/excr.2000.5004] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Epidermal growth factor (EGF)-induced signaling was investigated in cells conditionally defective in clathrin-dependent endocytosis by overexpression of K44A dynamin in HeLa cells and potassium depletion in Hep2 cells. Overexpression of mutant dynamin disrupts high-affinity EGF-EGF receptor (EGFR) interaction (T. Ringerike, E. Stang, L. E. Johannessen, D. Sandnes, F. O. Levy, and I. H. Madshus, 1998, J. Biol. Chem. 273, 16639-16642). However, the EGFR substrates Shc and c-Cbl were as efficiently tyrosine phosphorylated in endocytosis-deficient HeLa cells exhibiting only low-affinity EGFRs as in HeLa cells with intact endocytosis and with both high- and low-affinity EGFRs. Both Raf and mitogen-activated protein kinase (MAPK) were activated to the same extent and with the same kinetics. HeLa cells distributed equally in the cell cycle regardless of EGFR internalization. Upon potassium depletion of Hep2 cells, EGF-induced EGFR endocytosis was inhibited. However, the EGFR and MAPK were efficiently activated by EGF in both the absence and the presence of clathrin-dependent endocytosis. The EGFR was weakly tyrosine phosphorylated by potassium depletion even in the absence of EGF, and this activation resulted in detectable activation of MAPK. Our results demonstrate that internalization of EGFR by clathrin-dependent endocytosis is not required for activation of MAPK.
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