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Wang X, Zheng S, Yang F, Zhang W, Zhao D, Xue X, Lin Q, He Y, Hu G, Hu Y. lncRNA HITT inhibits metastasis by attenuating Rab5-mediated endocytosis in lung adenocarcinoma. Mol Ther 2022; 30:1071-1088. [PMID: 35017116 PMCID: PMC8899701 DOI: 10.1016/j.ymthe.2022.01.014] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Revised: 10/15/2021] [Accepted: 01/06/2022] [Indexed: 10/19/2022] Open
Abstract
Endocytosis of cell surface receptors is essential for cell migration and cancer metastasis. Rab5, a small GTPase of the Rab family, is a key regulator of endosome dynamics and thus cell migration. However, how its activity is regulated still remains to be addressed. Here, we identified a Rab5 inhibitor, a long non-coding RNA, namely HITT (HIF-1α inhibitor at translation level). Our data show that HITT expression is inversely associated with advanced stages and poor prognosis of lung adenocarcinoma patients with area under receiver operating characteristics (ROC) curve (AUC) 0.6473. Further study reveals that both endogenous and exogenous HITT inhibits single-cell migration by repressing β1 integrin endocytosis in lung adenocarcinoma. Mechanistically, HITT is physically associated with Rab5 at switch I via 1248-1347 nt and suppresses β1 integrin endocytosis and subsequent cancer metastasis by interfering with guanine nucleotide exchange factors (GEFs) for Rab5 binding. Collectively, these findings suggest that HITT directly participates in the regulation of Rab5 activity, leading to a decreased integrin internalization and cancer metastasis, which provides important insights into a mechanistic understanding of endocytosis and cancer metastasis.
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Affiliation(s)
- Xingwen Wang
- School of Life Science and Technology, Harbin Institute of Technology, Harbin, Heilongjiang Province 150001, China
| | - Shanliang Zheng
- School of Life Science and Technology, Harbin Institute of Technology, Harbin, Heilongjiang Province 150001, China
| | - Fan Yang
- School of Life Science and Technology, Harbin Institute of Technology, Harbin, Heilongjiang Province 150001, China
| | - Wenxin Zhang
- School of Life Science and Technology, Harbin Institute of Technology, Harbin, Heilongjiang Province 150001, China
| | - Dong Zhao
- School of Life Science and Technology, Harbin Institute of Technology, Harbin, Heilongjiang Province 150001, China
| | - Xuting Xue
- School of Life Science and Technology, Harbin Institute of Technology, Harbin, Heilongjiang Province 150001, China
| | - Qingyu Lin
- School of Life Science and Technology, Harbin Institute of Technology, Harbin, Heilongjiang Province 150001, China
| | - Yunfei He
- Shanghai Institute of Nutrition and Health, University of Chinese Academy of Science, 320 Yuyang Road, Shanghai 200031, China
| | - Guohong Hu
- Shanghai Institute of Nutrition and Health, University of Chinese Academy of Science, 320 Yuyang Road, Shanghai 200031, China
| | - Ying Hu
- School of Life Science and Technology, Harbin Institute of Technology, Harbin, Heilongjiang Province 150001, China; Shenzhen Graduate School of Harbin Institute of Technology, Shenzhen 518055, China.
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2
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Magits W, Sablina AA. The regulation of the protein interaction network by monoubiquitination. Curr Opin Struct Biol 2022; 73:102333. [PMID: 35176591 DOI: 10.1016/j.sbi.2022.102333] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2021] [Revised: 11/24/2021] [Accepted: 01/06/2022] [Indexed: 11/03/2022]
Abstract
The conjugation of a single ubiquitin or monoubiquitination acts as a versatile signal that can have both degradative and non-degradative functions. The latter is of particular interest as emerging evidence indicates that ubiquitin-driven alterations of the protein interaction landscape play a key role in multiple signaling pathways. Whereas early studies were focused on how monoubiquitination alters the interactions of proteins containing ubiquitin-binding domains, more recent reports demonstrate that ubiquitin conjugation can also affect the binding mode by changing the surface of the ubiquitinated substrate. Furthermore, monoubiquitination modulates the interactions with other macromolecules, such as DNA or lipids, underscoring the diverse role of monoubiquitination in cellular processes. In this review, we discussed how monoubiquitination achieves its function by modulating the interaction landscape.
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Affiliation(s)
- Wout Magits
- VIB-KU Leuven Center for Cancer Biology, VIB, 3000 Leuven, Belgium; Department of Oncology, KU Leuven, Herestraat 49, 3000 Leuven, Belgium
| | - Anna A Sablina
- VIB-KU Leuven Center for Cancer Biology, VIB, 3000 Leuven, Belgium; Department of Oncology, KU Leuven, Herestraat 49, 3000 Leuven, Belgium.
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3
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Millarte V, Schlienger S, Kälin S, Spiess M. Rabaptin5 targets autophagy to damaged endosomes and Salmonella vacuoles via FIP200 and ATG16L1. EMBO Rep 2022; 23:e53429. [PMID: 34704340 PMCID: PMC8728625 DOI: 10.15252/embr.202153429] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Revised: 10/01/2021] [Accepted: 10/13/2021] [Indexed: 02/06/2023] Open
Abstract
Selective autophagy of damaged organelles is important to maintain cellular homeostasis. The mechanisms how autophagy selects specific targets is often poorly understood. Rabaptin5 was previously known as a major regulator of early endosome identity and maturation. Here, we identify two novel Rabaptin5 interactors: FIP200, a subunit of the ULK1 autophagy initiator complex, and ATG16L1, a central component of the E3-like enzyme in LC3 lipidation. Autophagy of early endosomes damaged by chloroquine or monensin treatment requires Rabaptin5 and particularly a short sequence motif that binds to the WD domain of ATG16L1. Rabaptin5 and its interaction with ATG16L1 further contributes to the autophagic elimination of Salmonella enterica early after infection, when it resides in phagosomes with early endosomal characteristics. Our results demonstrate a novel function of Rabaptin5 in quality control of early endosomes in the selective targeting of autophagy to damaged early endosomes and phagosomes.
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4
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Parkinson G, Roboti P, Zhang L, Taylor S, Woodman P. His domain protein tyrosine phosphatase and Rabaptin-5 couple endo-lysosomal sorting of EGFR with endosomal maturation. J Cell Sci 2021; 134:272512. [PMID: 34657963 PMCID: PMC8627557 DOI: 10.1242/jcs.259192] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2021] [Accepted: 09/13/2021] [Indexed: 01/20/2023] Open
Abstract
His domain protein tyrosine phosphatase (HD-PTP; also known as PTPN23) collaborates with endosomal sorting complexes required for transport (ESCRTs) to sort endosomal cargo into intralumenal vesicles, forming the multivesicular body (MVB). Completion of MVB sorting is accompanied by maturation of the endosome into a late endosome, an event that requires inactivation of the early endosomal GTPase Rab5 (herein referring to generically to all isoforms). Here, we show that HD-PTP links ESCRT function with endosomal maturation. HD-PTP depletion prevents MVB sorting, while also blocking cargo from exiting Rab5-rich endosomes. HD-PTP-depleted cells contain hyperphosphorylated Rabaptin-5 (also known as RABEP1), a cofactor for the Rab5 guanine nucleotide exchange factor Rabex-5 (also known as RABGEF1), although HD-PTP is unlikely to directly dephosphorylate Rabaptin-5. In addition, HD-PTP-depleted cells exhibit Rabaptin-5-dependent hyperactivation of Rab5. HD-PTP binds directly to Rabaptin-5, between its Rabex-5- and Rab5-binding domains. This binding reaction involves the ESCRT-0/ESCRT-III binding site in HD-PTP, which is competed for by an ESCRT-III peptide. Jointly, these findings indicate that HD-PTP may alternatively scaffold ESCRTs and modulate Rabex-5–Rabaptin-5 activity, thereby helping to coordinate the completion of MVB sorting with endosomal maturation. Summary: Sorting of endocytic cargo to the multivesicular body is accompanied by endosomal maturation. Here, we provide a potential mechanism by which these two processes are linked.
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Affiliation(s)
- Gabrielle Parkinson
- Faculty of Biology, Medicine and Health, Manchester Academic and Health Science Centre, The University of Manchester, Manchester M13 9PT, UK
| | - Peristera Roboti
- Faculty of Biology, Medicine and Health, Manchester Academic and Health Science Centre, The University of Manchester, Manchester M13 9PT, UK
| | - Ling Zhang
- Faculty of Biology, Medicine and Health, Manchester Academic and Health Science Centre, The University of Manchester, Manchester M13 9PT, UK
| | - Sandra Taylor
- Faculty of Biology, Medicine and Health, Manchester Academic and Health Science Centre, The University of Manchester, Manchester M13 9PT, UK
| | - Philip Woodman
- Faculty of Biology, Medicine and Health, Manchester Academic and Health Science Centre, The University of Manchester, Manchester M13 9PT, UK
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5
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Hargrove-Grimes P, Mondal AK, Gumerson J, Nellissery J, Aponte AM, Gieser L, Qian H, Fariss RN, Bonifacino JS, Li T, Swaroop A. Loss of endocytosis-associated RabGEF1 causes aberrant morphogenesis and altered autophagy in photoreceptors leading to retinal degeneration. PLoS Genet 2020; 16:e1009259. [PMID: 33362196 PMCID: PMC7790415 DOI: 10.1371/journal.pgen.1009259] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2020] [Revised: 01/07/2021] [Accepted: 11/09/2020] [Indexed: 12/17/2022] Open
Abstract
Rab-GTPases and associated effectors mediate cargo transport through the endomembrane system of eukaryotic cells, regulating key processes such as membrane turnover, signal transduction, protein recycling and degradation. Using developmental transcriptome data, we identified Rabgef1 (encoding the protein RabGEF1 or Rabex-5) as the only gene associated with Rab GTPases that exhibited strong concordance with retinal photoreceptor differentiation. Loss of Rabgef1 in mice (Rabgef1-/-) resulted in defects specifically of photoreceptor morphology and almost complete loss of both rod and cone function as early as eye opening; however, aberrant outer segment formation could only partly account for visual function deficits. RabGEF1 protein in retinal photoreceptors interacts with Rabaptin-5, and RabGEF1 absence leads to reduction of early endosomes consistent with studies in other mammalian cells and tissues. Electron microscopy analyses reveal abnormal accumulation of macromolecular aggregates in autophagosome-like vacuoles and enhanced immunostaining for LC3A/B and p62 in Rabgef1-/- photoreceptors, consistent with compromised autophagy. Transcriptome analysis of the developing Rabgef1-/- retina reveals altered expression of 2469 genes related to multiple pathways including phototransduction, mitochondria, oxidative stress and endocytosis, suggesting an early trajectory of photoreceptor cell death. Our results implicate an essential role of the RabGEF1-modulated endocytic and autophagic pathways in photoreceptor differentiation and homeostasis. We propose that RabGEF1 and associated components are potential candidates for syndromic traits that include a retinopathy phenotype. Endocytosis and autophagy are evolutionarily conserved processes that are essential for maintenance of cellular homeostasis. RabGEF1 is a major regulator of the Rab5-GTPase, which participates in key steps during endocytosis and autophagy. We demonstrate that loss of RabGEF1 in mice causes specific developmental defects during photoreceptor outer segment formation, leading to visual dysfunction as early as eye opening followed by retinal degeneration. Rabgef1-/- retina shows a clear reduction in early endosomes as well as accumulation of autophagic vacuoles in developing photoreceptors. Together with transcriptome analysis, our studies suggest a trajectory of cellular events including altered autophagy that precede photoreceptor cell death in the absence of RabGEF1 and establish a critical role of endocytosis and autophagy in retinal development and proteostasis.
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Affiliation(s)
- Passley Hargrove-Grimes
- Neurobiology, Neurodegeneration & Repair Laboratory, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States of America
- Institute of Biomedical Sciences, George Washington University, Washington, District of Columbia, United States of America
| | - Anupam K. Mondal
- Neurobiology, Neurodegeneration & Repair Laboratory, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Jessica Gumerson
- Neurobiology, Neurodegeneration & Repair Laboratory, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Jacob Nellissery
- Neurobiology, Neurodegeneration & Repair Laboratory, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Angel M. Aponte
- Proteomics Core, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Linn Gieser
- Neurobiology, Neurodegeneration & Repair Laboratory, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Haohua Qian
- Visual Function Core, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Robert N. Fariss
- Biological Imaging Core, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Juan S. Bonifacino
- Neurosciences and Cellular and Structural Biology Division, Eunice Kennedy Shriver National Institute for Child Health and Development, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Tiansen Li
- Neurobiology, Neurodegeneration & Repair Laboratory, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Anand Swaroop
- Neurobiology, Neurodegeneration & Repair Laboratory, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States of America
- * E-mail:
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6
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Wang TS, Coppens I, Saorin A, Brady NR, Hamacher-Brady A. Endolysosomal Targeting of Mitochondria Is Integral to BAX-Mediated Mitochondrial Permeabilization during Apoptosis Signaling. Dev Cell 2020; 53:627-645.e7. [PMID: 32504557 DOI: 10.1016/j.devcel.2020.05.014] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2018] [Revised: 01/03/2020] [Accepted: 05/13/2020] [Indexed: 12/29/2022]
Abstract
Mitochondrial outer membrane permeabilization (MOMP) is a core event in apoptosis signaling. However, the underlying mechanism of BAX and BAK pore formation remains incompletely understood. We demonstrate that mitochondria are globally and dynamically targeted by endolysosomes (ELs) during MOMP. In response to pro-apoptotic BH3-only protein signaling and pharmacological MOMP induction, ELs increasingly form transient contacts with mitochondria. Subsequently, ELs rapidly accumulate within the entire mitochondrial compartment. This switch-like accumulation period temporally coincides with mitochondrial BAX clustering and cytochrome c release. Remarkably, interactions of ELs with mitochondria control BAX recruitment and pore formation. Knockdown of Rab5A, Rab5C, or USP15 interferes with EL targeting of mitochondria and functionally uncouples BAX clustering from cytochrome c release, while knockdown of the Rab5 exchange factor Rabex-5 impairs both BAX clustering and cytochrome c release. Together, these data reveal that EL-mitochondrial inter-organelle communication is an integral regulatory component of functional MOMP execution during cellular apoptosis signaling.
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Affiliation(s)
- Tim Sen Wang
- W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD 21205, USA; Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Isabelle Coppens
- W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD 21205, USA
| | - Anna Saorin
- W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD 21205, USA
| | - Nathan Ryan Brady
- W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD 21205, USA.
| | - Anne Hamacher-Brady
- W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD 21205, USA; Department of Biochemistry and Molecular Biology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD 21205, USA.
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7
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Bezeljak U, Loya H, Kaczmarek B, Saunders TE, Loose M. Stochastic activation and bistability in a Rab GTPase regulatory network. Proc Natl Acad Sci U S A 2020; 117:6540-6549. [PMID: 32161136 PMCID: PMC7104049 DOI: 10.1073/pnas.1921027117] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The eukaryotic endomembrane system is controlled by small GTPases of the Rab family, which are activated at defined times and locations in a switch-like manner. While this switch is well understood for an individual protein, how regulatory networks produce intracellular activity patterns is currently not known. Here, we combine in vitro reconstitution experiments with computational modeling to study a minimal Rab5 activation network. We find that the molecular interactions in this system give rise to a positive feedback and bistable collective switching of Rab5. Furthermore, we find that switching near the critical point is intrinsically stochastic and provide evidence that controlling the inactive population of Rab5 on the membrane can shape the network response. Notably, we demonstrate that collective switching can spread on the membrane surface as a traveling wave of Rab5 activation. Together, our findings reveal how biochemical signaling networks control vesicle trafficking pathways and how their nonequilibrium properties define the spatiotemporal organization of the cell.
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Affiliation(s)
- Urban Bezeljak
- Institute of Science and Technology Austria, 3400 Klosterneuburg, Austria
| | - Hrushikesh Loya
- Department of Electrical Engineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra 400076, India
| | - Beata Kaczmarek
- Institute of Science and Technology Austria, 3400 Klosterneuburg, Austria
| | - Timothy E Saunders
- Mechanobiology Institute, National University of Singapore, Singapore 119077;
- Department of Biological Sciences, National University of Singapore, Singapore 119077
| | - Martin Loose
- Institute of Science and Technology Austria, 3400 Klosterneuburg, Austria;
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8
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Epithelial RABGEF1 deficiency promotes intestinal inflammation by dysregulating intrinsic MYD88-dependent innate signaling. Mucosal Immunol 2020; 13:96-109. [PMID: 31628426 DOI: 10.1038/s41385-019-0211-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2018] [Revised: 09/18/2019] [Accepted: 09/28/2019] [Indexed: 02/06/2023]
Abstract
Intestinal epithelial cells (IECs) contribute to the regulation of intestinal homeostasis and inflammation through their interactions with the environment and host immune responses. Yet our understanding of IEC-intrinsic regulatory pathways remains incomplete. Here, we identify the guanine nucleotide exchange factor RABGEF1 as a regulator of intestinal homeostasis and innate pathways dependent on IECs. Mice with IEC-specific Rabgef1 deletion (called Rabgef1IEC-KO mice) developed a delayed spontaneous colitis associated with the local upregulation of IEC chemokine expression. In mouse models of colitis based on Interleukin-10 deficiency or dextran sodium sulfate (DSS) exposure, we found that IEC-intrinsic RABGEF1 deficiency exacerbated development of intestinal pathology and dysregulated IEC innate pathways and chemokine expression. Mechanistically, we showed that RABGEF1 deficiency in mouse IECs in vitro was associated with an impairment of early endocytic events, an increased activation of the p38 mitogen-activated protein kinase (MAPK)-dependent pathway, and increased chemokine secretion. Moreover, we provided evidence that the development of spontaneous colitis was dependent on microbiota-derived signals and intrinsic MYD88-dependent pathways in vivo. Our study identifies mouse RABGEF1 as an important regulator of intestinal inflammation, MYD88-dependent IEC-intrinsic signaling, and chemokine production. This suggests that RABGEF1-dependent pathways represent interesting therapeutic targets for inflammatory conditions in the gut.
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9
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Nagano M, Toshima JY, Siekhaus DE, Toshima J. Rab5-mediated endosome formation is regulated at the trans-Golgi network. Commun Biol 2019; 2:419. [PMID: 31754649 PMCID: PMC6858330 DOI: 10.1038/s42003-019-0670-5] [Citation(s) in RCA: 40] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2019] [Accepted: 10/29/2019] [Indexed: 01/01/2023] Open
Abstract
Early endosomes, also called sorting endosomes, are known to mature into late endosomes via the Rab5-mediated endolysosomal trafficking pathway. Thus, early endosome existence is thought to be maintained by the continual fusion of transport vesicles from the plasma membrane and the trans-Golgi network (TGN). Here we show instead that endocytosis is dispensable and post-Golgi vesicle transport is crucial for the formation of endosomes and the subsequent endolysosomal traffic regulated by yeast Rab5 Vps21p. Fittingly, all three proteins required for endosomal nucleotide exchange on Vps21p are first recruited to the TGN before transport to the endosome, namely the GEF Vps9p and the epsin-related adaptors Ent3/5p. The TGN recruitment of these components is distinctly controlled, with Vps9p appearing to require the Arf1p GTPase, and the Rab11s, Ypt31p/32p. These results provide a different view of endosome formation and identify the TGN as a critical location for regulating progress through the endolysosomal trafficking pathway.
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Affiliation(s)
- Makoto Nagano
- Department of Biological Science and Technology, Tokyo University of Science, 6-3-1 Niijyuku, Katsushika-ku, Tokyo, 125-8585 Japan
| | - Junko Y. Toshima
- School of Health Science, Tokyo University of Technology, 5-23-22 Nishikamada, Ota-ku, Tokyo, 144-8535 Japan
| | | | - Jiro Toshima
- Department of Biological Science and Technology, Tokyo University of Science, 6-3-1 Niijyuku, Katsushika-ku, Tokyo, 125-8585 Japan
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10
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Lauer J, Segeletz S, Cezanne A, Guaitoli G, Raimondi F, Gentzel M, Alva V, Habeck M, Kalaidzidis Y, Ueffing M, Lupas AN, Gloeckner CJ, Zerial M. Auto-regulation of Rab5 GEF activity in Rabex5 by allosteric structural changes, catalytic core dynamics and ubiquitin binding. eLife 2019; 8:46302. [PMID: 31718772 PMCID: PMC6855807 DOI: 10.7554/elife.46302] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2019] [Accepted: 10/22/2019] [Indexed: 02/06/2023] Open
Abstract
Intracellular trafficking depends on the function of Rab GTPases, whose activation is regulated by guanine exchange factors (GEFs). The Rab5 GEF, Rabex5, was previously proposed to be auto-inhibited by its C-terminus. Here, we studied full-length Rabex5 and Rabaptin5 proteins as well as domain deletion Rabex5 mutants using hydrogen deuterium exchange mass spectrometry. We generated a structural model of Rabex5, using chemical cross-linking mass spectrometry and integrative modeling techniques. By correlating structural changes with nucleotide exchange activity for each construct, we uncovered new auto-regulatory roles for the ubiquitin binding domains and the Linker connecting those domains to the catalytic core of Rabex5. We further provide evidence that enhanced dynamics in the catalytic core are linked to catalysis. Our results suggest a more complex auto-regulation mechanism than previously thought and imply that ubiquitin binding serves not only to position Rabex5 but to also control its Rab5 GEF activity through allosteric structural alterations.
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Affiliation(s)
- Janelle Lauer
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Sandra Segeletz
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Alice Cezanne
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | | | - Francesco Raimondi
- Bioquant, Heidelberg University, Heidelberg, Germany.,Heidelberg University Biochemistry Centre (BZH), Heidelberg, Germany
| | - Marc Gentzel
- Molecular Analysis-Mass Spectrometry Center for Molecular and Cellular Bioengineering, Technical University Dresden, Dresden, Germany
| | - Vikram Alva
- Max Planck Institute for Developmental Biology, Tuebingen, Germany
| | - Michael Habeck
- Statistical Inverse Problems in Biophysics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.,Felix Bernstein Institute for Mathematical Statistics in the Biosciences, University of Göttingen, Göttingen, Germany
| | - Yannis Kalaidzidis
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Marius Ueffing
- Center for Ophthalmology, Institute for Ophthalmic Research, University of Tübingen, Tübingen, Germany
| | - Andrei N Lupas
- Max Planck Institute for Developmental Biology, Tuebingen, Germany
| | - Christian Johannes Gloeckner
- German Center for Neurodegenerative Diseases, Tübingen, Germany.,Center for Ophthalmology, Institute for Ophthalmic Research, University of Tübingen, Tübingen, Germany
| | - Marino Zerial
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
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11
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Remodeling Membrane Binding by Mono-Ubiquitylation. Biomolecules 2019; 9:biom9080325. [PMID: 31370222 PMCID: PMC6723200 DOI: 10.3390/biom9080325] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2019] [Revised: 07/22/2019] [Accepted: 07/29/2019] [Indexed: 01/17/2023] Open
Abstract
Ubiquitin (Ub) receptors respond to ubiquitylation signals. They bind ubiquitylated substrates and exert their activity in situ. Intriguingly, Ub receptors themselves undergo rapid ubiquitylation and deubiquitylation. Here we asked what is the function of ubiquitylation of Ub receptors? We focused on yeast epsin, a Ub receptor that decodes the ubiquitylation signal of plasma membrane proteins into an endocytosis response. Using mass spectrometry, we identified lysine-3 as the major ubiquitylation site in the epsin plasma membrane binding domain. By projecting this ubiquitylation site onto our crystal structure, we hypothesized that this modification would compete with phosphatidylinositol-4,5-bisphosphate (PIP2) binding and dissociate epsin from the membrane. Using an E. coli-based expression of an authentic ubiquitylation apparatus, we purified ubiquitylated epsin. We demonstrated in vitro that in contrast to apo epsin, the ubiquitylated epsin does not bind to either immobilized PIPs or PIP2-enriched liposomes. To test this hypothesis in vivo, we mimicked ubiquitylation by the fusion of Ub at the ubiquitylation site. Live cell imaging demonstrated that the mimicked ubiquitylated epsin dissociates from the membrane. Our findings suggest that ubiquitylation of the Ub receptors dissociates them from their products to allow binding to a new ubiquitylated substrates, consequently promoting cyclic activity of the Ub receptors.
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12
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Herman EK, Ali M, Field MC, Dacks JB. Regulation of early endosomes across eukaryotes: Evolution and functional homology of Vps9 proteins. Traffic 2018; 19:546-563. [PMID: 29603841 PMCID: PMC6032885 DOI: 10.1111/tra.12570] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2018] [Revised: 03/21/2018] [Accepted: 03/27/2018] [Indexed: 12/11/2022]
Abstract
Endocytosis is a crucial process in eukaryotic cells. The GTPases Rab 5, 21 and 22 that mediate endocytosis are ancient eukaryotic features and all available evidence suggests retained conserved function. In animals and fungi, these GTPases are regulated in part by proteins possessing Vps9 domains. However, the diversity, evolution and functions of Vps9 proteins beyond animals or fungi are poorly explored. Here we report a comprehensive analysis of the Vps9 family of GTPase regulators, combining molecular evolutionary data with functional characterization in the non-opisthokont model organism Trypanosoma brucei. At least 3 subfamilies, Alsin, Varp and Rabex5 + GAPVD1, are found across eukaryotes, suggesting that all are ancient features of regulation of endocytic Rab protein function. There are examples of lineage-specific Vps9 subfamily member expansions and novel domain combinations, suggesting diversity in precise regulatory mechanisms between individual lineages. Characterization of the Rabex5 + GAPVD1 and Alsin orthologues in T. brucei demonstrates that both proteins are involved in endocytosis, and that simultaneous knockdown prevents membrane recruitment of Rab5 and Rab21, indicating conservation of function. These data demonstrate that, for the Vps9-domain family at least, modulation of Rab function is mediated by evolutionarily conserved protein-protein interactions.
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Affiliation(s)
- Emily K. Herman
- Department of Cell Biology, Faculty of Medicine and DentistryUniversity of AlbertaEdmontonCanada
| | - Moazzam Ali
- School of Life SciencesUniversity of DundeeDundeeUK
| | | | - Joel B. Dacks
- Department of Cell Biology, Faculty of Medicine and DentistryUniversity of AlbertaEdmontonCanada
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13
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Cheng X, Zheng J, Li G, Göbel V, Zhang H. Degradation for better survival? Role of ubiquitination in epithelial morphogenesis. Biol Rev Camb Philos Soc 2018; 93:1438-1460. [PMID: 29493067 DOI: 10.1111/brv.12404] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2017] [Revised: 01/31/2018] [Accepted: 02/05/2018] [Indexed: 02/06/2023]
Abstract
As a prevalent post-translational modification, ubiquitination is essential for many developmental processes. Once covalently attached to the small and conserved polypeptide ubiquitin (Ub), a substrate protein can be directed to perform specific biological functions via its Ub-modified form. Three sequential catalytic reactions contribute to this process, among which E3 ligases serve to identify target substrates and promote the activated Ub to conjugate to substrate proteins. Ubiquitination has great plasticity, with diverse numbers, topologies and modifications of Ub chains conjugated at different substrate residues adding a layer of complexity that facilitates a huge range of cellular functions. Herein, we highlight key advances in the understanding of ubiquitination in epithelial morphogenesis, with an emphasis on the latest insights into its roles in cellular events involved in polarized epithelial tissue, including cell adhesion, asymmetric localization of polarity determinants and cytoskeletal organization. In addition, the physiological roles of ubiquitination are discussed for typical examples of epithelial morphogenesis, such as lung branching, vascular development and synaptic formation and plasticity. Our increased understanding of ubiquitination in epithelial morphogenesis may provide novel insights into the molecular mechanisms underlying epithelial regeneration and maintenance.
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Affiliation(s)
- Xiaoxiang Cheng
- Faculty of Health Sciences, University of Macau, Avenida da Universidade, Taipa, Macau 999078, China
| | - Jun Zheng
- Faculty of Health Sciences, University of Macau, Avenida da Universidade, Taipa, Macau 999078, China
| | - Gang Li
- Faculty of Health Sciences, University of Macau, Avenida da Universidade, Taipa, Macau 999078, China
| | - Verena Göbel
- Department of Pediatrics, Mucosal Immunology and Biology Research Center, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114,, U.S.A
| | - Hongjie Zhang
- Faculty of Health Sciences, University of Macau, Avenida da Universidade, Taipa, Macau 999078, China
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14
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Early Endosome Morphology in Health and Disease. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2018; 1074:335-343. [PMID: 29721961 DOI: 10.1007/978-3-319-75402-4_41] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Early endosomes are organelles that receive macromolecules and solutes from the extracellular environment. The major function of early endosomes is to sort these cargos into recycling and degradative compartments of the cell. Degradation of the cargo involves maturation of early endosomes into late endosomes, which, after acquisition of hydrolytic enzymes, form lysosomes. Endosome maturation involves recruitment of specific proteins and lipids to the early endosomal membrane, which drives changes in endosome morphology. Defects in early endosome maturation are generally accompanied by alterations in morphology, such as increase in volume and/or number. Enlarged early endosomes have been observed in Alzheimer's disease and Niemann Pick Disease type C, which also exhibit defects in endocytic sorting. This article discusses the mechanisms that regulate early endosome morphology and highlights the potential importance of endosome maturation in the retinal pigment epithelium.
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15
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Mattera R, Park SY, De Pace R, Guardia CM, Bonifacino JS. AP-4 mediates export of ATG9A from the trans-Golgi network to promote autophagosome formation. Proc Natl Acad Sci U S A 2017; 114:E10697-E10706. [PMID: 29180427 PMCID: PMC5740629 DOI: 10.1073/pnas.1717327114] [Citation(s) in RCA: 111] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
AP-4 is a member of the heterotetrameric adaptor protein (AP) complex family involved in protein sorting in the endomembrane system of eukaryotic cells. Interest in AP-4 has recently risen with the discovery that mutations in any of its four subunits cause a form of hereditary spastic paraplegia (HSP) with intellectual disability. The critical sorting events mediated by AP-4 and the pathogenesis of AP-4 deficiency, however, remain poorly understood. Here we report the identification of ATG9A, the only multispanning membrane component of the core autophagy machinery, as a specific AP-4 cargo. AP-4 promotes signal-mediated export of ATG9A from the trans-Golgi network to the peripheral cytoplasm, contributing to lipidation of the autophagy protein LC3B and maturation of preautophagosomal structures. These findings implicate AP-4 as a regulator of autophagy and altered autophagy as a possible defect in AP-4-deficient HSP.
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Affiliation(s)
- Rafael Mattera
- Cell Biology and Neurobiology Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892
| | - Sang Yoon Park
- Cell Biology and Neurobiology Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892
| | - Raffaella De Pace
- Cell Biology and Neurobiology Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892
| | - Carlos M Guardia
- Cell Biology and Neurobiology Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892
| | - Juan S Bonifacino
- Cell Biology and Neurobiology Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892
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16
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Millrine D, Kishimoto T. A Brighter Side to Thalidomide: Its Potential Use in Immunological Disorders. Trends Mol Med 2017; 23:348-361. [PMID: 28285807 DOI: 10.1016/j.molmed.2017.02.006] [Citation(s) in RCA: 49] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Revised: 02/10/2017] [Accepted: 02/17/2017] [Indexed: 12/13/2022]
Abstract
Thalidomide and its derivatives are immunomodulatory drugs (IMiDs) known for their sedative, teratogenic, anti-angiogenic, and anti-inflammatory properties. Commonly used in the treatment of cancers such as multiple myeloma and myelodysplastic syndrome (MDS), IMiDs have also been used in the treatment of an inflammatory skin pathology associated with Hansen's disease/leprosy. They have also shown promise in the treatment of autoimmune disorders including systemic lupus erythmatosus (SLE) and inflammatory bowel disease (IBD). Recent structural and experimental observations have revolutionized our understanding of these properties by revealing the fundamental molecular events underpinning IMiD activity. We review these findings, their relevance to IMiD therapy in immunological disorders, and discuss how further research might unlock the vast clinical potential of these compounds.
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Affiliation(s)
- David Millrine
- Cardiff Institute of Infection and Immunity, Cardiff University School of Medicine, Cardiff University, Cardiff, UK
| | - Tadamitsu Kishimoto
- Laboratory of Immune Regulation, World Premier Immunology Frontier Research Centre (IFReC), Osaka University, 565-0871, Japan.
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17
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Abstract
Rab GTPases act as organizers of protein networks defining identities and functions of organelles of the endocytic and secretory pathways. Various modes of coordination between different Rabs drive the timely maturation and conversion of membranes. Endosomal Rab5 has been known as the prime example for self-activation via a feedback loop recruiting Rabaptin5, which is complexed with the Rab5 exchange factor Rabex5, and couples to Rab4-GTP. Among other effectors, Rab5 also recruits the Mon1/SAND1-Ccz1 complex that both activates Rab7 and dissociates Rabex5 for Rab5-to-Rab7 conversion of early-to-late endosomes. A detailed deletion analysis now revealed 2 separate binding sites each for Rab4-GTP and Rab5-GTP and indicates a feedforward mechanism of Rab5 activation. Rabaptin5/Rabex5 is recruited to endosomal membranes positive for Rab4-GTP and ubiquitinated cargo (binding to the ubiquitin binding site of Rabex5). This mechanism also suggests additional criteria for Rab5 inactivation concomitant with increasing Rab7-GTP levels. The disappearance of ubiquitinated cargo upon ESCRT-mediated formation of intraluminal vesicles and inactivation of Rab4 may also contribute to loss of Rab5 activation. Rabaptin5/Rabex5 thus may integrate several cues of maturation to perform Rab conversion. Furthermore Rab5 binding to Rabaptin5 appears to prevent uncontrolled progression to late endosomes.
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Affiliation(s)
- Simone Kälin
- a Biozentrum, University of Basel , Basel, Switzerland
| | | | - Martin Spiess
- a Biozentrum, University of Basel , Basel, Switzerland
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18
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Rab5 and its effector FHF contribute to neuronal polarity through dynein-dependent retrieval of somatodendritic proteins from the axon. Proc Natl Acad Sci U S A 2016; 113:E5318-27. [PMID: 27559088 PMCID: PMC5018783 DOI: 10.1073/pnas.1601844113] [Citation(s) in RCA: 66] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
An open question in cell biology is how the general intracellular transport machinery is adapted to perform specialized functions in polarized cells such as neurons. Here we illustrate this adaptation by elucidating a role for the ubiquitous small GTPase Ras-related protein in brain 5 (Rab5) in neuronal polarity. We show that inactivation or depletion of Rab5 in rat hippocampal neurons abrogates the somatodendritic polarity of the transferrin receptor and several glutamate receptor types, resulting in their appearance in the axon. This loss of polarity is not caused primarily by increased transport from the soma to the axon but rather by decreased retrieval from the axon to the soma. Retrieval is also dependent on the Rab5 effector Fused Toes (FTS)-Hook-FTS and Hook-interacting protein (FHIP) (FHF) complex, which interacts with the minus-end-directed microtubule motor dynein and its activator dynactin to drive a population of axonal retrograde carriers containing somatodendritic proteins toward the soma. These findings emphasize the importance of both biosynthetic sorting and axonal retrieval for the polarized distribution of somatodendritic receptors at steady state.
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19
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Li J, Chai QY, Liu CH. The ubiquitin system: a critical regulator of innate immunity and pathogen-host interactions. Cell Mol Immunol 2016; 13:560-76. [PMID: 27524111 DOI: 10.1038/cmi.2016.40] [Citation(s) in RCA: 71] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2016] [Revised: 05/30/2016] [Accepted: 05/30/2016] [Indexed: 12/11/2022] Open
Abstract
The ubiquitin system comprises enzymes that are responsible for ubiquitination and deubiquitination, as well as ubiquitin receptors that are capable of recognizing and deciphering the ubiquitin code, which act in coordination to regulate almost all host cellular processes, including host-pathogen interactions. In response to pathogen infection, the host innate immune system launches an array of distinct antimicrobial activities encompassing inflammatory signaling, phagosomal maturation, autophagy and apoptosis, all of which are fine-tuned by the ubiquitin system to eradicate the invading pathogens and to reduce concomitant host damage. By contrast, pathogens have evolved a cohort of exquisite strategies to evade host innate immunity by usurping the ubiquitin system for their own benefits. Here, we present recent advances regarding the ubiquitin system-mediated modulation of host-pathogen interplay, with a specific focus on host innate immune defenses and bacterial pathogen immune evasion.
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Affiliation(s)
- Jie Li
- CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China
| | - Qi-Yao Chai
- CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China
| | - Cui Hua Liu
- CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China
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20
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Candiello E, Kratzke M, Wenzel D, Cassel D, Schu P. AP-1/σ1A and AP-1/σ1B adaptor-proteins differentially regulate neuronal early endosome maturation via the Rab5/Vps34-pathway. Sci Rep 2016; 6:29950. [PMID: 27411398 PMCID: PMC4944158 DOI: 10.1038/srep29950] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2016] [Accepted: 06/24/2016] [Indexed: 12/26/2022] Open
Abstract
The σ1 subunit of the AP-1 clathrin-coated-vesicle adaptor-protein
complex is expressed as three isoforms. Tissues express σ1A and one of
the σ1B and σ1C isoforms. Brain is the tissue with the
highest σ1A and σ1B expression. σ1B-deficiency
leads to severe mental retardation, accumulation of early endosomes in synapses and
fewer synaptic vesicles, whose recycling is slowed down. AP-1/σ1A and
AP-1/σ1B regulate maturation of these early endosomes into
multivesicular body late endosomes, thereby controlling synaptic vesicle protein
transport into a degradative pathway. σ1A binds ArfGAP1, and with higher
affinity brain-specific ArfGAP1, which bind Rabex-5.
AP-1/σ1A-ArfGAP1-Rabex-5 complex formation leads to more endosomal
Rabex-5 and enhanced, Rab5GTP-stimulated Vps34 PI3-kinase activity,
which is essential for multivesicular body endosome formation. Formation of
AP-1/σ1A-ArfGAP1-Rabex-5 complexes is prevented by σ1B
binding of Rabex-5 and the amount of endosomal Rabex-5 is reduced. AP-1 complexes
differentially regulate endosome maturation and coordinate protein recycling and
degradation, revealing a novel molecular mechanism by which they regulate protein
transport besides their established function in clathrin-coated-vesicle
formation.
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Affiliation(s)
- Ermes Candiello
- Georg-August University Göttingen, Department for Cellular Biochemistry, Humboldtallee 23, D-37073 Göttingen, Germany
| | - Manuel Kratzke
- Georg-August University Göttingen, Department for Cellular Biochemistry, Humboldtallee 23, D-37073 Göttingen, Germany
| | - Dirk Wenzel
- Electron microscopy, Max-Planck-Institut for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany
| | - Dan Cassel
- Israel Institute of Technology, Department Biology, Haifa 32000, Israel
| | - Peter Schu
- Georg-August University Göttingen, Department for Cellular Biochemistry, Humboldtallee 23, D-37073 Göttingen, Germany
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21
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Ishida M, E Oguchi M, Fukuda M. Multiple Types of Guanine Nucleotide Exchange Factors (GEFs) for Rab Small GTPases. Cell Struct Funct 2016; 41:61-79. [PMID: 27246931 DOI: 10.1247/csf.16008] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Rab small GTPases are highly conserved master regulators of membrane traffic in all eukaryotes. The same as the activation and inactivation of other small GTPases, the activation and inactivation of Rabs are tightly controlled by specific GEFs (guanine nucleotide exchange factors) and GAPs (GTPase-activating proteins), respectively. Although almost all Rab-GAPs reported thus far have a TBC (Tre-2/Bub2/Cdc16)/Rab-GAP domain in common, recent accumulating evidence has indicated the existence of a number of structurally unrelated types of Rab-GEFs, including DENN proteins, VPS9 proteins, Sec2 proteins, TRAPP complexes, heterodimer GEFs (Mon1-Ccz1, HPS1-HPS4 (BLOC-3 complex), Ric1-Rgp1 and Rab3GAP1/2), and other GEFs (e.g., REI-1 and RPGR). In this review article we provide an up-to-date overview of the structures and functions of all putative Rab-GEFs in mammals, with a special focus on their substrate Rabs, interacting proteins, associations with genetic diseases, and intracellular localizations.
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Affiliation(s)
- Morié Ishida
- Laboratory of Membrane Trafficking Mechanisms, Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University
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22
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Mahogunin regulates fusion between amphisomes/MVBs and lysosomes via ubiquitination of TSG101. Cell Death Dis 2015; 6:e1970. [PMID: 26539917 PMCID: PMC4670916 DOI: 10.1038/cddis.2015.257] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2015] [Revised: 07/31/2015] [Accepted: 07/31/2015] [Indexed: 12/23/2022]
Abstract
Aberrant metabolic forms of the prion protein (PrP), membrane-associated (Ctm)PrP and cytosolic (cyPrP) interact with the cytosolic ubiquitin E3 ligase, Mahogunin Ring Finger-1 (MGRN1) and affect lysosomes. MGRN1 also interacts with and ubiquitinates TSG101, an ESCRT-I protein, involved in endocytosis. We report that MGRN1 modulates macroautophagy. In cultured cells, functional depletion of MGRN1 or overexpression of (Ctm)PrP and cyPrP blocks autophagosome-lysosome fusion, alleviates the autophagic flux and its degradative competence. Concurrently, the degradation of cargo from the endo-lysosomal pathway is also affected. This is significant because catalytic inactivation of MGRN1 alleviates fusion of lysosomes with either autophagosomes (via amphisomes) or late endosomes (either direct or mediated through amphisomes), without drastically perturbing maturation of late endosomes, generation of amphisomes or lysosomal proteolytic activity. The compromised lysosomal fusion events are rescued by overexpression of TSG101 and/or its monoubiquitination in the presence of MGRN1. Thus, for the first time we elucidate that MGRN1 simultaneously modulates both autophagy and heterophagy via ubiquitin-mediated post-translational modification of TSG101.
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23
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Kälin S, Hirschmann DT, Buser DP, Spiess M. Rabaptin5 is recruited to endosomes by Rab4 and Rabex5 to regulate endosome maturation. J Cell Sci 2015; 128:4126-37. [PMID: 26430212 DOI: 10.1242/jcs.174664] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2015] [Accepted: 09/22/2015] [Indexed: 12/13/2022] Open
Abstract
Rab GTPases control membrane identity, fusion and transport by interaction with effector proteins. Effectors that influence the activation-inactivation cycle of their own or other Rab proteins contribute to the timely conversion of Rab membrane identities. Rab5 and its effector rabaptin5 (Rbpt5, also known as RABEP1) are generally considered the prime example for a positive-feedback loop in which Rab5-GTP recruits Rbpt5 in complex with Rabex5 (also known as RABGEF1), the GDP/GTP exchange factor of Rab5, to early endosomes, thus maintaining the Rab5 membrane identity. By deletion analysis, we found that the membrane recruitment of Rabaptin5 required binding to Rab4 and Rabex5, but not Rab5. Deletion of either one of the two Rab5-binding domains or silencing of Rab5 expression did not affect Rabaptin5 recruitment, but produced giant endosomes with early and late endosomal characteristics. The results contradict the model of feedback activation of Rab5 and instead indicate that Rbpt5 is recruited by both Rabex5 recognizing ubiquitylated cargo and by Rab4 to activate Rab5 in a feed-forward manner.
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Affiliation(s)
- Simone Kälin
- Biozentrum, University of Basel, Klingelbergstrasse 70, Basel CH-4056, Switzerland
| | - David T Hirschmann
- Biozentrum, University of Basel, Klingelbergstrasse 70, Basel CH-4056, Switzerland
| | - Dominik P Buser
- Biozentrum, University of Basel, Klingelbergstrasse 70, Basel CH-4056, Switzerland
| | - Martin Spiess
- Biozentrum, University of Basel, Klingelbergstrasse 70, Basel CH-4056, Switzerland
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24
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Levin-Kravets O, Shohat N, Prag G. Tetrameric Assembly of Monoubiquitin Accurately Mimics the Lys11 Polyubiquitin Chain Structure. Biochemistry 2015; 54:4704-10. [PMID: 26171660 DOI: 10.1021/acs.biochem.5b00498] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Specific lysine residues on the ubiquitin surface were selected during the course of evolution to form different polyubiquitin chain structures that signal diverse cellular processes. A vast number of ubiquitin receptors specifically recognize and decode the signals conferred by these polyubiquitin chains. The mechanisms of formation and the structure of Lys11-linked ubiquitin, which signals for cell-cycle and innate immune control, have been elucidated. Here, we present a new crystal structure of monomeric ubiquitin that accurately mimics one of the structures of Lys11-linked ubiquitin. Analysis of the ubiquitin:ubiquitin interface demonstrates structural fitness and specificity. The interaction is exclusively hydrophilic, leaving the Ile44 hydrophobic patch, a major recognition site for ubiquitin receptors, exposed. These noncovalent ubiquitin:ubiquitin interactions are nearly identical to those reported for Lys11-linked ubiquitin and seem to play a significant role in stabilizing the crystal structure without the isopeptide bond. In vitro cross-linking analysis with wild-type ubiquitin or its mutants partially mimics the interactions in the crystal. We suggest that these interactions may play a biological role in transmitting Lys11-linked ubiquitin chain-type cellular signals.
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Affiliation(s)
- Olga Levin-Kravets
- Department of Biochemistry and Molecular Biology and Institute for Structural Biology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Noa Shohat
- Department of Biochemistry and Molecular Biology and Institute for Structural Biology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Gali Prag
- Department of Biochemistry and Molecular Biology and Institute for Structural Biology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
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25
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Hierro A, Gershlick DC, Rojas AL, Bonifacino JS. Formation of Tubulovesicular Carriers from Endosomes and Their Fusion to the trans-Golgi Network. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2015; 318:159-202. [PMID: 26315886 DOI: 10.1016/bs.ircmb.2015.05.005] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Endosomes undergo extensive spatiotemporal rearrangements as proteins and lipids flux through them in a series of fusion and fission events. These controlled changes enable the concentration of cargo for eventual degradation while ensuring the proper recycling of other components. A growing body of studies has now defined multiple recycling pathways from endosomes to the trans-Golgi network (TGN) which differ in their molecular machineries. The recycling process requires specific sets of lipids, coats, adaptors, and accessory proteins that coordinate cargo selection with membrane deformation and its association with the cytoskeleton. Specific tethering factors and SNARE (SNAP (Soluble NSF Attachment Protein) Receptor) complexes are then required for the docking and fusion with the acceptor membrane. Herein, we summarize some of the current knowledge of the machineries that govern the retrograde transport from endosomes to the TGN.
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Affiliation(s)
- Aitor Hierro
- Structural Biology Unit, CIC bioGUNE, Derio, Spain; IKERBASQUE, Basque Foundation for Science, Bilbao, Spain
| | - David C Gershlick
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | | | - Juan S Bonifacino
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
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26
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Molecular dynamics at the endocytic portal and regulations of endocytic and recycling traffics. Eur J Cell Biol 2015; 94:235-48. [DOI: 10.1016/j.ejcb.2015.04.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2015] [Revised: 04/02/2015] [Accepted: 04/08/2015] [Indexed: 02/01/2023] Open
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27
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Shideler T, Nickerson DP, Merz AJ, Odorizzi G. Ubiquitin binding by the CUE domain promotes endosomal localization of the Rab5 GEF Vps9. Mol Biol Cell 2015; 26:1345-56. [PMID: 25673804 PMCID: PMC4454180 DOI: 10.1091/mbc.e14-06-1156] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Vps9 is a guanine nucleotide exchange factor that activates Rab5 GTPases in the yeast endolysosomal pathway. Ubiquitin binding by its CUE domain is dispensable for Vps9 function. The CUE domain is shown to target Vps9 to endosomes, supporting a model in which it senses ubiquitinated transmembrane proteins trafficking in the endolysosomal pathway. Vps9 and Muk1 are guanine nucleotide exchange factors (GEFs) in Saccharomyces cerevisiae that regulate membrane trafficking in the endolysosomal pathway by activating Rab5 GTPases. We show that Vps9 is the primary Rab5 GEF required for biogenesis of late endosomal multivesicular bodies (MVBs). However, only Vps9 (but not Muk1) is required for the formation of aberrant class E compartments that arise upon dysfunction of endosomal sorting complexes required for transport (ESCRTs). ESCRT dysfunction causes ubiquitinated transmembrane proteins to accumulate at endosomes, and we demonstrate that endosomal recruitment of Vps9 is promoted by its ubiquitin-binding CUE domain. Muk1 lacks ubiquitin-binding motifs, but its fusion to the Vps9 CUE domain allows Muk1 to rescue endosome morphology, cargo trafficking, and cellular stress-tolerance phenotypes that result from loss of Vps9 function. These results indicate that ubiquitin binding by the CUE domain promotes Vps9 function in endolysosomal membrane trafficking via promotion of localization.
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Affiliation(s)
- Tess Shideler
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309-0347
| | - Daniel P Nickerson
- Department of Biochemistry, University of Washington, Seattle, WA 98195-3750
| | - Alexey J Merz
- Department of Biochemistry, University of Washington, Seattle, WA 98195-3750
| | - Greg Odorizzi
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309-0347
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28
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Hamacher-Brady A, Choe SC, Krijnse-Locker J, Brady NR. Intramitochondrial recruitment of endolysosomes mediates Smac degradation and constitutes a novel intrinsic apoptosis antagonizing function of XIAP E3 ligase. Cell Death Differ 2014; 21:1862-76. [PMID: 25080938 DOI: 10.1038/cdd.2014.101] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2013] [Revised: 05/21/2014] [Accepted: 05/30/2014] [Indexed: 12/21/2022] Open
Abstract
Intrinsic apoptosis involves BH3-only protein activation of Bax/Bak-mediated mitochondrial outer membrane permeabilization (MOMP). Consequently, cytochrome c is released from the mitochondria to activate caspases, and Smac (second mitochondria-derived activator of caspases) to inhibit XIAP-mediated caspase suppression. Dysfunctional mitochondria can be targeted for lysosomal degradation via autophagy (mitophagy), or directly through mitochondria-derived vesicle transport. However, the extent of autophagy and lysosomal interactions with apoptotic mitochondria remains largely unknown. We describe here a novel pathway of endolysosomal processing of mitochondria, activated in response to canonical BH3-only proteins and mitochondrial depolarization. We report that expression of canonical BH3-only proteins, tBid, BimEL, Bik, Bad, and mitophagy receptor mutants of atypical BH3-only proteins, Bnip3 and Bnip3L/Nix, leads to prominent relocalization of endolysosomes into inner mitochondrial compartments, in a manner independent of mitophagy. As an upstream regulator, we identified the XIAP E3 ligase. In response to mitochondrial depolarization, XIAP actuates Bax-mediated MOMP, even in the absence of BH3-only protein signaling. Subsequently, in an E3 ligase-dependent manner, XIAP rapidly localizes inside all the mitochondria, and XIAP-mediated mitochondrial ubiquitylation catalyses interactions of Rab membrane targeting components Rabex-5 and Rep-1 (RFP-tagged Rab escort protein-1), and Rab5- and Rab7-positive endolysosomes, at and within mitochondrial membrane compartments. While XIAP-mediated MOMP permits delayed cytochrome c release, within the mitochondria XIAP selectively signals lysosome- and proteasome-associated degradation of its inhibitor Smac. These findings suggest a general mechanism to lower the mitochondrial apoptotic potential via intramitochondrial degradation of Smac.
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Affiliation(s)
- A Hamacher-Brady
- 1] Lysosomal Systems Biology, German Cancer Research Center (DKFZ), Heidelberg, Germany [2] Bioquant, University of Heidelberg, Heidelberg, Germany
| | - S C Choe
- 1] Bioquant, University of Heidelberg, Heidelberg, Germany [2] Systems Biology of Cell Death Mechanisms, German Cancer Research Center (DKFZ), Heidelberg, Germany [3] Department of Surgery, Heidelberg University Hospital, Heidelberg, Germany
| | - J Krijnse-Locker
- 1] Bioquant, University of Heidelberg, Heidelberg, Germany [2] Department of Virology, Hygiene Institute, University of Heidelberg Medical School, Heidelberg, Germany
| | - N R Brady
- 1] Bioquant, University of Heidelberg, Heidelberg, Germany [2] Systems Biology of Cell Death Mechanisms, German Cancer Research Center (DKFZ), Heidelberg, Germany [3] Department of Surgery, Heidelberg University Hospital, Heidelberg, Germany
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Zhang Z, Zhang T, Wang S, Gong Z, Tang C, Chen J, Ding J. Molecular mechanism for Rabex-5 GEF activation by Rabaptin-5. eLife 2014; 3. [PMID: 24957337 PMCID: PMC4102244 DOI: 10.7554/elife.02687] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2014] [Accepted: 06/20/2014] [Indexed: 01/30/2023] Open
Abstract
Rabex-5 and Rabaptin-5 function together to activate Rab5 and further promote early endosomal fusion in endocytosis. The Rabex-5 GEF activity is autoinhibited by the Rabex-5 CC domain (Rabex-5CC) and activated by the Rabaptin-5 C2-1 domain (Rabaptin-5C21) with yet unknown mechanism. We report here the crystal structures of Rabex-5 in complex with the dimeric Rabaptin-5C21 (Rabaptin-5C212) and in complex with Rabaptin-5C212 and Rab5, along with biophysical and biochemical analyses. We show that Rabex-5CC assumes an amphipathic α-helix which binds weakly to the substrate-binding site of the GEF domain, leading to weak autoinhibition of the GEF activity. Binding of Rabaptin-5C21 to Rabex-5 displaces Rabex-5CC to yield a largely exposed substrate-binding site, leading to release of the GEF activity. In the ternary complex the substrate-binding site of Rabex-5 is completely exposed to bind and activate Rab5. Our results reveal the molecular mechanism for the regulation of the Rabex-5 GEF activity. DOI:http://dx.doi.org/10.7554/eLife.02687.001 Cells need to allow various molecules to pass through the plasma membrane on their surface. Some molecules have to enter the cell, whereas others have to leave. Cells rely on a process called endocytosis to move large molecules into the cell. This involves part of the membrane engulfing the molecule to form a ‘bubble’ around it. This bubble, which is called an endosome, then moves the molecule to final destination inside the cell. A protein called Rab5 controls how a new endosome is produced. However, before this can happen, various other molecules—including two proteins called Rabex-5 and Rabaptin-5—must activate the Rab5 protein. Exactly how these three proteins interact with each other was unknown. Zhang et al. used X-ray crystallography to examine the structures of the complexes formed when Rabex-5 and Rabaptin-5 bind to each other, both when Rab5 is present, and also when it is absent. Biochemical and biophysical experiments confirmed that the Rabex-5/Rabaptin-5 complex is able to activate Rab5. Zhang et al. also found that Rabex-5, on its own, folds so that the site that normally binds to Rab5 instead binds to a different part of Rabex-5, thus preventing endocytosis. However, when Rabaptin-5 forms a complex with Rabex-5, the Rab5 binding site is freed up. The Rabex-5/Rabaptin-5 complex can switch between a V shape and a linear structure. Binding to Rab5 stabilizes the linear form of the complex, which then helps activate Rab5, and subsequently the activated Rab5 can interact with other downstream molecules, triggering endocytosis. DOI:http://dx.doi.org/10.7554/eLife.02687.002
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Affiliation(s)
- Zhe Zhang
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Tianlong Zhang
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Shanshan Wang
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Zhou Gong
- State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan, China
| | - Chun Tang
- State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan, China
| | - Jiangye Chen
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Jianping Ding
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
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30
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Pei G, Repnik U, Griffiths G, Gutierrez MG. Identification of an immune-regulated phagosomal Rab cascade in macrophages. J Cell Sci 2014; 127:2071-82. [PMID: 24569883 PMCID: PMC4004979 DOI: 10.1242/jcs.144923] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Interferon-γ (IFN-γ) has been shown to regulate phagosome trafficking and function in macrophages, but the molecular mechanisms involved are poorly understood. Here, we identify Rab20 as part of the machinery by which IFN-γ controls phagosome maturation. We found that IFN-γ stimulates the association of Rab20 with early phagosomes in macrophages. By using imaging of single phagosomes in live cells, we found that Rab20 induces an early delay in phagosome maturation and extends the time for which Rab5a and phosphatidylinositol 3-phosphate (PI3P) remain associated with phagosomes. Moreover, Rab20 depletion in macrophages abrogates the delay in phagosome maturation induced by IFN-γ. Finally, we demonstrate that Rab20 interacts with the Rab5a guanine nucleotide exchange factor Rabex-5 (also known as RABGEF1) and that Rab20 knockdown impairs the IFN-γ-dependent recruitment of Rabex-5 and Rab5a into phagosomes. Taken together, here, we uncover Rab20 as a key player in the Rab cascade by which IFN-γ induces a delay in phagosome maturation in macrophages.
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Affiliation(s)
- Gang Pei
- Research Group Phagosome Biology, Helmholtz Centre for Infection Research, Inhoffenstrasse 7, 38124 Braunschweig, Germany
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31
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Piper RC, Dikic I, Lukacs GL. Ubiquitin-dependent sorting in endocytosis. Cold Spring Harb Perspect Biol 2014; 6:6/1/a016808. [PMID: 24384571 DOI: 10.1101/cshperspect.a016808] [Citation(s) in RCA: 149] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
When ubiquitin (Ub) is attached to membrane proteins on the plasma membrane, it directs them through a series of sorting steps that culminate in their delivery to the lumen of the lysosome where they undergo complete proteolysis. Ubiquitin is recognized by a series of complexes that operate at a number of vesicle transport steps. Ubiquitin serves as a sorting signal for internalization at the plasma membrane and is the major signal for incorporation into intraluminal vesicles of multivesicular late endosomes. The sorting machineries that catalyze these steps can bind Ub via a variety of Ub-binding domains. At the same time, many of these complexes are themselves ubiquitinated, thus providing a plethora of potential mechanisms to regulate their activity. Here we provide an overview of how membrane proteins are selected for ubiquitination and deubiquitination within the endocytic pathway and how that ubiquitin signal is interpreted by endocytic sorting machineries.
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Affiliation(s)
- Robert C Piper
- Department of Molecular Physiology and Biophysics, University of Iowa, Iowa City, Iowa 52242
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Structural Characterization of a Noncovalent Complex between Ubiquitin and the Transactivation Domain of the Erythroid-Specific Factor EKLF. Structure 2013; 21:2014-24. [DOI: 10.1016/j.str.2013.08.027] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2013] [Revised: 08/14/2013] [Accepted: 08/30/2013] [Indexed: 11/20/2022]
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Thomas C, Strutt D. Rabaptin-5 and Rabex-5 are neoplastic tumour suppressor genes that interact to modulate Rab5 dynamics in Drosophila melanogaster. Dev Biol 2013; 385:107-21. [PMID: 24104056 PMCID: PMC3858806 DOI: 10.1016/j.ydbio.2013.09.029] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2013] [Revised: 09/25/2013] [Accepted: 09/29/2013] [Indexed: 01/08/2023]
Abstract
Endocytosis plays an important role in the regulation of tumour growth and metastasis. In Drosophila, a number of endocytic neoplastic tumour suppressor genes have been identified that when mutated cause epithelial disruption and over-proliferation. Here we characterise the Drosophila homologue of the Rab5 effector Rabaptin-5, and show that it is a novel neoplastic tumour suppressor. Its ability to bind Rab5 and modulate early endosomal dynamics is conserved in Drosophila, as is its interaction with the Rab5 GEF Rabex5, for which we also demonstrate neoplastic tumour suppressor characteristics. Surprisingly, we do not observe disruption of apico-basal polarity in Rabaptin-5 and Rabex-5 mutant tissues; instead the tumour phenotype is associated with upregulation of Jun N-terminal Kinase (JNK) and Janus Kinase (JAK)/Signal Transducer and Activator of Transcription (STAT) signalling. Drosophila Rabaptin-5 and Rabex-5 are endocytic neoplastic tumour suppressor genes. The Rab5 effector function of Rabaptin-5 is highly conserved in Drosophila. Rabaptin-5 interacts with Rabex-5 to modulate early endosomal dynamics in vivo. Tumour phenotypes are associated with upregulation of JNK and JAK/STAT signalling.
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Affiliation(s)
- Chloe Thomas
- MRC Centre for Developmental and Biomedical Genetics, Department of Biomedical Science, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
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Abstract
This review discusses how kinetic proofreading by Rab GTPases provides a speed-dating mechanism defining the identity of membrane domains in vesicle trafficking. Rab GTPases are highly conserved components of vesicle trafficking pathways that help to ensure the fusion of a vesicle with a specific target organelle membrane. Specific regulatory pathways promote kinetic proofreading of membrane surfaces by Rab GTPases, and permit accumulation of active Rabs only at the required sites. Emerging evidence indicates that Rab activation and inactivation are under complex feedback control, suggesting that ultrasensitivity and bistability, principles established for other cellular regulatory networks, may also apply to Rab regulation. Such systems can promote the rapid membrane accumulation and removal of Rabs to create time-limited membrane domains with a unique composition, and can explain how Rabs define the identity of vesicle and organelle membranes.
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Affiliation(s)
- Francis A Barr
- Department of Biochemistry, University of Oxford, Oxford OX1 3QU, England, UK.
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35
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Aikawa Y, Lee S. Role of Rabex-5 in the sorting of ubiquitinated cargo at an early stage in the endocytic pathway. Commun Integr Biol 2013; 6:e24463. [PMID: 23986801 PMCID: PMC3737748 DOI: 10.4161/cib.24463] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2013] [Accepted: 03/27/2013] [Indexed: 01/22/2023] Open
Abstract
The covalent modification of transmembrane receptors by ubiquitin (Ub) is a key biological mechanism controlling their internalization and endocytic sorting to recycling and degradative pathways to attenuate their signaling potential. In this Ub-dependent endocytic trafficking pathway, Ub-binding proteins (UBPs) play a critical role in the sorting of these ubiquitinated transmembrane proteins at the plasma membrane, early endosomes, and multivesicular bodies. We recently reported that Rabex-5, a UBP and guanine nucleotide exchange factor for Rab5, is translocated to the plasma membrane in an extracellular ligand-dependent manner to regulate the internalization of ligand-induced ubiquitinated transmembrane proteins upon stimulation with extracellular ligands. Here, we show that Rabex-5 predominantly localizes on Rab5- and syntaxin 13-positive endosomes, but not on Rab11-positive recycling endosomes before stimulation with extracellular ligands. We further discuss the significance of Rabex-5-mediated sorting of ubiquitinated transmembrane proteins as cargo at an early stage of the endocytic pathway.
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Affiliation(s)
- Yoshikatsu Aikawa
- Laboratory of Neural Membrane Biology; Graduate School of Brain Science; Doshisha University; Kyoto, Japan,* Correspondence to: Yoshikatsu Aikawa;
| | - Sangho Lee
- Department of Biological Sciences; Sungkyunkwan University; Suwon, Korea
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36
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Arf GTPase regulation through cascade mechanisms and positive feedback loops. FEBS Lett 2013; 587:2028-35. [DOI: 10.1016/j.febslet.2013.05.015] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2013] [Revised: 05/02/2013] [Accepted: 05/02/2013] [Indexed: 11/21/2022]
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Haglund K, Dikic I. The role of ubiquitylation in receptor endocytosis and endosomal sorting. J Cell Sci 2013; 125:265-75. [PMID: 22357968 DOI: 10.1242/jcs.091280] [Citation(s) in RCA: 224] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Ligand-induced activation of transmembrane receptors activates intracellular signaling cascades that control vital cellular processes, such as cell proliferation, differentiation, migration and survival. Receptor signaling is modulated by several mechanisms to ensure that the correct biological outcome is achieved. One such mechanism, which negatively regulates receptor signaling, involves the modification of receptors with ubiquitin. This post-translational modification can promote receptor endocytosis and targets receptors for lysosomal degradation, thereby ensuring termination of receptor signaling. In this Commentary, we review the roles of ubiquitylation in receptor endocytosis and degradative endosomal sorting by drawing on the epidermal growth factor receptor (EGFR) as a well-studied example. Furthermore, we elaborate on the molecular basis of ubiquitin recognition along the endocytic pathway through compartment-specific ubiquitin-binding proteins and highlight how endocytic sorting machineries control these processes. In addition, we discuss the importance of ubiquitin-dependent receptor endocytosis for the maintenance of cellular homeostasis and in the prevention of diseases such as cancer.
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Affiliation(s)
- Kaisa Haglund
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, Montebello, N-0310 Oslo, Norway.
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38
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Blümer J, Rey J, Dehmelt L, Mazel T, Wu YW, Bastiaens P, Goody RS, Itzen A. RabGEFs are a major determinant for specific Rab membrane targeting. ACTA ACUST UNITED AC 2013; 200:287-300. [PMID: 23382462 PMCID: PMC3563681 DOI: 10.1083/jcb.201209113] [Citation(s) in RCA: 145] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Analysis of three different Rab-RabGEF pairs reveals that RabGEFs contain the minimal targeting machinery for recruiting Rabs to specific membranes. Eukaryotic cells critically depend on the correct regulation of intracellular vesicular trafficking to transport biological material. The Rab subfamily of small guanosine triphosphatases controls these processes by acting as a molecular on/off switch. To fulfill their function, active Rab proteins need to localize to intracellular membranes via posttranslationally attached geranylgeranyl lipids. Each member of the manifold Rab family localizes specifically to a distinct membrane, but it is unclear how this specific membrane recruitment is achieved. Here, we demonstrate that Rab-activating guanosine diphosphate/guanosine triphosphate exchange factors (GEFs) display the minimal targeting machinery for recruiting Rabs from the cytosol to the correct membrane using the Rab-GEF pairs Rab5A–Rabex-5, Rab1A-DrrA, and Rab8-Rabin8 as model systems. Specific mistargeting of Rabex-5/DrrA/Rabin8 to mitochondria led to catalytic recruitment of Rab5A/Rab1A/Rab8A in a time-dependent manner that required the catalytic activity of the GEF. Therefore, RabGEFs are major determinants for specific Rab membrane targeting.
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Affiliation(s)
- Julia Blümer
- Department of Physical Biochemistry, Max-Planck-Institute of Molecular Physiology, 44227 Dortmund, Germany
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39
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Aikawa Y, Hirakawa H, Lee S. Spatiotemporal regulation of the ubiquitinated cargo-binding activity of Rabex-5 in the endocytic pathway. J Biol Chem 2012; 287:40586-97. [PMID: 23048039 DOI: 10.1074/jbc.m112.411793] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
BACKGROUND The regulatory mechanism underlying the interaction of the Rabex-5 MIU domain with ubiquitinated cargos remains unclear. RESULTS Rabex-5 guanine nucleotide exchange factor (GEF) mutants affected interactions of ubiquitinated cargos. CONCLUSION GDP/GTP exchange in the GEF domain controls the MIU domain interactions with the ubiquitinated cargos. SIGNIFICANCE Rabex-5 GEF activity acts as an intramolecular switch for spatiotemporal trafficking of the ubiquitinated cargos. Ubiquitin (Ub)-dependent endocytosis of membrane proteins requires precise molecular recognition of ubiquitinated cargo by Ub-binding proteins (UBPs). Many UBPs are often themselves monoubiquitinated, a mechanism referred to as coupled monoubiquitination, which prevents them from binding in trans to the ubiquitinated cargo. However, the spatiotemporal regulatory mechanism underlying the interaction of UBPs with the ubiquitinated cargo, via their Ub-binding domains (UBDs) remains unclear. Previously, we reported the interaction of Rabex-5, a UBP and guanine nucleotide exchange factor (GEF) for Rab5, with ubiquitinated neural cell adhesion molecule L1, via its motif interacting with Ub (MIU) domain. This interaction is critical for the internalization and sorting of the ubiquitinated L1 into endosomal/lysosomal compartments. The present study demonstrated that the interaction of Rabex-5 with Rab5 depends specifically on interaction of the MIU domain with the ubiquitinated L1 to drive its internalization. Notably, impaired GEF mutants and the Rabex-5(E213A) mutant increased the flexibility of the hinge region in the HB-VPS9 tandem domain, which significantly affected their interactions with the ubiquitinated L1. In addition, GEF mutants increased the catalytic efficiency, which resulted in a reduced interaction with the ubiquitinated L1. Furthermore, the coupled monoubiquitination status of Rabex-5 was found to be significantly associated with interaction of Rabex-5 and the ubiquitinated L1. Collectively, our study reveals a novel mechanism, wherein the GEF activity of Rabex-5 acts as an intramolecular switch orchestrating ubiquitinated cargo-binding activity and coupled monoubiquitination to permit the spatiotemporal dynamic exchange of the ubiquitinated cargos.
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Affiliation(s)
- Yoshikatsu Aikawa
- Laboratory of Neural Membrane Biology, Graduate School of Brain Science, Doshisha University, 1-3 Miyakodani, Kyotanabe, Kyoto 610-0394, Japan.
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40
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Clague M, Liu H, Urbé S. Governance of Endocytic Trafficking and Signaling by Reversible Ubiquitylation. Dev Cell 2012; 23:457-67. [DOI: 10.1016/j.devcel.2012.08.011] [Citation(s) in RCA: 126] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2012] [Revised: 06/27/2012] [Accepted: 08/21/2012] [Indexed: 12/17/2022]
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41
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Aikawa Y. Rabex-5 protein regulates the endocytic trafficking pathway of ubiquitinated neural cell adhesion molecule L1. J Biol Chem 2012; 287:32312-23. [PMID: 22846990 DOI: 10.1074/jbc.m112.374322] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ubiquitination of integral membrane proteins is a common posttranslational modification used to mediate endocytosis and endocytic sorting of cell surface proteins in eukaryotic cells. Ubiquitin (Ub)-binding proteins (UBPs) regulate the stability, function, and localization of ubiquitinated cell surface proteins in the endocytic pathway. Here, I report that the immunoglobulin superfamily cell adhesion molecule L1 undergoes ubiquitination and dephosphorylation on the plasma membrane upon L1 antibody-induced clustering, which mimics L1-L1 homophilic binding, and that these modifications are critical for obtaining the maximal rate of internalization and trafficking to the lysosome, but not to the proteasome. Notably, L1 antibody-induced clustering leads to the association of ubiquitinated L1 with Rabex-5, a UBP and guanine nucleotide exchange factor for Rab5, via interaction with the motif interacting with Ub (MIU) domain, but not the A20-type zinc finger domain. This interaction specifically depends on the presence of an Ub moiety on lysine residues in L1. Rabex-5 expression accelerates the internalization rates of L1(WT) and L1(Y1176A), a tyrosine-based motif mutant, but not L1(K11R), an ubiquitination-deficient mutant, leading to the accumulation of ubiquitinated L1 on endosomes. In contrast, RNA interference-mediated knockdown of Rabex-5 impairs the internalizations of L1(WT) and L1(Y1176A), but not L1(K11R) from the plasma membrane. Overall, these results provide a novel mechanistic insight into how Rabex-5 regulates internalization and postendocytic trafficking of ubiquitinated L1 destined for lysosomal degradation.
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Affiliation(s)
- Yoshikatsu Aikawa
- Laboratory of Neural Membrane Biology, Graduate School of Brain Science, Doshisha University, 1-3 Miyakodani, Kyotanabe, Kyoto 610-0394, Japan.
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42
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Shin D, Lee SY, Han S, Ren S, Kim S, Aikawa Y, Lee S. Differential polyubiquitin recognition by tandem ubiquitin binding domains of Rabex-5. Biochem Biophys Res Commun 2012; 423:757-62. [PMID: 22705550 DOI: 10.1016/j.bbrc.2012.06.032] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2012] [Accepted: 06/08/2012] [Indexed: 01/22/2023]
Abstract
Linkage-specific polyubiquitination regulates many cellular processes. The N-terminal fragment of Rabex-5 (Rabex-5(9-73)) contains tandem ubiquitin binding domains: A20_ZF and MIU. The A20_ZF-MIU of Rabex-5 is known to bind monoubiquitin but molecular details of polyubiquitin binding affinity and linkage selectivity by Rabex-5(9-73) remain elusive. Here we report that Rabex-5(9-73) binds linear, K63- and K48-linked tetraubiquitin (Ub(4)) chains with K(d) of 0.1-1 μM, determined by biolayer interferometry. Mutational analysis of qualitative and quantitative binding data reveals that MIU is more important than A20_ZF in linkage-specific polyubiquitin recognition. MIU prefers binding to linear and K63-linked Ub(4) with sub μM affinities. However, A20_ZF recognizes the three linkage-specific Ub(4) with similar affinities with K(d) of 3-4 μM, unlike ZnF4 of A20. Taken together, our data suggest differential physiological roles of the two ubiquitin binding domains in Rabex-5.
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Affiliation(s)
- Donghyuk Shin
- Department of Biological Sciences, Sungkyunkwan University, Suwon 440-746, Republic of Korea
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Greene W, Zhang W, He M, Witt C, Ye F, Gao SJ. The ubiquitin/proteasome system mediates entry and endosomal trafficking of Kaposi's sarcoma-associated herpesvirus in endothelial cells. PLoS Pathog 2012; 8:e1002703. [PMID: 22615563 PMCID: PMC3355089 DOI: 10.1371/journal.ppat.1002703] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2011] [Accepted: 03/30/2012] [Indexed: 01/12/2023] Open
Abstract
Ubiquitination, a post-translational modification, mediates diverse cellular functions including endocytic transport of molecules. Kaposi's sarcoma-associated herpesvirus (KSHV), an enveloped herpesvirus, enters endothelial cells primarily through clathrin-mediated endocytosis. Whether ubiquitination and proteasome activity regulates KSHV entry and endocytosis remains unknown. We showed that inhibition of proteasome activity reduced KSHV entry into endothelial cells and intracellular trafficking to nuclei, thus preventing KSHV infection of the cells. Three-dimensional (3-D) analyses revealed accumulation of KSHV particles in a cytoplasmic compartment identified as EEA1+ endosomal vesicles upon proteasome inhibition. KSHV particles are colocalized with ubiquitin-binding proteins epsin and eps15. Furthermore, ubiquitination mediates internalization of both KSHV and one of its receptors integrin β1. KSHV particles are colocalized with activated forms of the E3 ligase c-Cbl. Knock-down of c-Cbl or inhibition of its phosphorylation reduced viral entry and intracellular trafficking, resulting in decreased KSHV infectivity. These results demonstrate that ubiquitination mediates internalization of both KSHV and one of its cognate receptors integrin β1, and identify c-Cbl as a potential E3 ligase that facilitates this process. Ubiquitination, a post-translational modification, mediates important cellular functions including endocytic transport of molecules. Kaposi's sarcoma-associated herpesvirus (KSHV) is a gammaherpesvirus linked to the development of Kaposi's sarcoma, an endothelial malignancy commonly found in AIDS patients, and several other malignancies. KSHV enters endothelial cells primarily through clathrin-mediated endocytosis. In this study, we show that the proteasome activity is required for KSHV entry into endothelial cells and intracellular trafficking to nuclei. Inhibition of proteasome activity reduced KSHV infectivity and led to the accumulation of KSHV particles in EEA1+ early endosomal vesicles. Furthermore, we show that ubiquitination mediates the internalization of both KSHV and one of its receptors integrin β1. KSHV particles are colocalized with ubiquitin-binding proteins epsin and eps15, as well as activated forms of the E3 ligase c-Cbl. Knock-down of c-Cbl or inhibition of its phosphorylation blocked KSHV entry and trafficking, thus preventing KSHV infection of endothelial cells. Together, these results illustrate the essential role of ubiquitination during the internalization of KSHV and its cognate receptor integrin β1. The identification of an E3 ligase that mediates the ubiquitination of KSHV and its cognate receptor integrin β1 leading to viral entry provide a potential therapeutic target for this oncogenic virus.
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Affiliation(s)
- Whitney Greene
- Tumor Virology Program, Greehey Children's Cancer Research Institute, and Department of Pediatrics, University of Texas Health Science Center San Antonio, San Antonio, Texas, United States of America
| | - Wei Zhang
- Tumor Virology Program, Greehey Children's Cancer Research Institute, and Department of Pediatrics, University of Texas Health Science Center San Antonio, San Antonio, Texas, United States of America
- Department of Molecular Microbiology and Immunology, Keck School of Medicine, University of Southern California, Los Angeles, California, United States of America
| | - Meilan He
- Department of Molecular Microbiology and Immunology, Keck School of Medicine, University of Southern California, Los Angeles, California, United States of America
| | - Colleen Witt
- Department of Biology, College of Sciences, University of Texas at San Antonio, San Antonio, Texas, United States of America
| | - Fengchun Ye
- Tumor Virology Program, Greehey Children's Cancer Research Institute, and Department of Pediatrics, University of Texas Health Science Center San Antonio, San Antonio, Texas, United States of America
| | - Shou-Jiang Gao
- Tumor Virology Program, Greehey Children's Cancer Research Institute, and Department of Pediatrics, University of Texas Health Science Center San Antonio, San Antonio, Texas, United States of America
- Department of Molecular Microbiology and Immunology, Keck School of Medicine, University of Southern California, Los Angeles, California, United States of America
- * E-mail:
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Sigismund S, Confalonieri S, Ciliberto A, Polo S, Scita G, Di Fiore PP. Endocytosis and signaling: cell logistics shape the eukaryotic cell plan. Physiol Rev 2012; 92:273-366. [PMID: 22298658 DOI: 10.1152/physrev.00005.2011] [Citation(s) in RCA: 236] [Impact Index Per Article: 19.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Our understanding of endocytosis has evolved remarkably in little more than a decade. This is the result not only of advances in our knowledge of its molecular and biological workings, but also of a true paradigm shift in our understanding of what really constitutes endocytosis and of its role in homeostasis. Although endocytosis was initially discovered and studied as a relatively simple process to transport molecules across the plasma membrane, it was subsequently found to be inextricably linked with almost all aspects of cellular signaling. This led to the notion that endocytosis is actually the master organizer of cellular signaling, providing the cell with understandable messages that have been resolved in space and time. In essence, endocytosis provides the communications and supply routes (the logistics) of the cell. Although this may seem revolutionary, it is still likely to be only a small part of the entire story. A wealth of new evidence is uncovering the surprisingly pervasive nature of endocytosis in essentially all aspects of cellular regulation. In addition, many newly discovered functions of endocytic proteins are not immediately interpretable within the classical view of endocytosis. A possible framework, to rationalize all this new knowledge, requires us to "upgrade" our vision of endocytosis. By combining the analysis of biochemical, biological, and evolutionary evidence, we propose herein that endocytosis constitutes one of the major enabling conditions that in the history of life permitted the development of a higher level of organization, leading to the actuation of the eukaryotic cell plan.
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Affiliation(s)
- Sara Sigismund
- IFOM, Fondazione Istituto FIRC di Oncologia Molecolare, Milan, Italy
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Polo S. Signaling-mediated control of ubiquitin ligases in endocytosis. BMC Biol 2012; 10:25. [PMID: 22420864 PMCID: PMC3305638 DOI: 10.1186/1741-7007-10-25] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2011] [Accepted: 03/15/2012] [Indexed: 12/24/2022] Open
Abstract
Ubiquitin-dependent regulation of endocytosis plays an important part in the control of signal transduction, and a critical issue in the understanding of signal transduction therefore relates to regulation of ubiquitination in the endocytic pathway. We discuss here what is known of the mechanisms by which signaling controls the activity of the ubiquitin ligases that specifically recognize the targets of ubiquitination on the endocytic pathway, and suggest alternative mechanisms that deserve experimental investigation.
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Affiliation(s)
- Simona Polo
- IFOM, Fondazione Istituto FIRC di Oncologia Molecolare, Via Adamello 16, 20139, Milan, Italy.
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Synthetic biology approach to reconstituting the ubiquitylation cascade in bacteria. EMBO J 2011; 31:378-90. [PMID: 22081111 DOI: 10.1038/emboj.2011.397] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2011] [Accepted: 10/07/2011] [Indexed: 12/16/2022] Open
Abstract
Covalent modification of proteins with ubiquitin (Ub) is widely implicated in the control of protein function and fate. Over 100 deubiquitylating enzymes rapidly reverse this modification, posing challenges to the biochemical and biophysical characterization of ubiquitylated proteins. We circumvented this limitation with a synthetic biology approach of reconstructing the entire eukaryotic Ub cascade in bacteria. Co-expression of affinity-tagged substrates and Ub with E1, E2 and E3 enzymes allows efficient purification of ubiquitylated proteins in milligram quantity. Contrary to in-vitro assays that lead to spurious modification of several lysine residues of Rpn10 (regulatory proteasomal non-ATPase subunit), the reconstituted system faithfully recapitulates its monoubiquitylation on lysine 84 that is observed in vivo. Mass spectrometry revealed the ubiquitylation sites on the Mind bomb E3 ligase and the Ub receptors Rpn10 and Vps9. Förster resonance energy transfer (FRET) analyses of ubiquitylated Vps9 purified from bacteria revealed that although ubiquitylation occurs on the Vps9-GEF domain, it does not affect the guanine nucleotide exchanging factor (GEF) activity in vitro. Finally, we demonstrated that ubiquitylated Vps9 assumes a closed structure, which blocks additional Ub binding. Characterization of several ubiquitylated proteins demonstrated the integrity, specificity and fidelity of the system, and revealed new biological findings.
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Abstract
Being deeply connected to signalling, cell dynamics, growth, regulation, and defence, endocytic processes are linked to almost all aspects of cell life and disease. In this review, we focus on endosomes in the classical endocytic pathway, and on the programme of changes that lead to the formation and maturation of late endosomes/multivesicular bodies. The maturation programme entails a dramatic transformation of these dynamic organelles disconnecting them functionally and spatially from early endosomes and preparing them for their unidirectional role as a feeder pathway to lysosomes.
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Katsarou K, Tsitoura P, Georgopoulou U. MEK5/ERK5/mef2: a novel signaling pathway affected by hepatitis C virus non-enveloped capsid-like particles. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2011; 1813:1854-62. [PMID: 21767578 DOI: 10.1016/j.bbamcr.2011.06.015] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2011] [Revised: 06/24/2011] [Accepted: 06/27/2011] [Indexed: 11/17/2022]
Abstract
Hepatitis C virus (HCV) is an RNA positive strand virus, member of the Flaviviridae family. The viral particle is composed of a capsid containing the genome, surrounded by E1 and E2 proteins, however different forms of viral particles have been observed including non-enveloped particles. Previous reports have proposed that hepatitis C non-enveloped capsid-like particles (HCVne) enter cells of hepatic origin via clathrin-mediated endocytosis, during which different signaling events occur. In this report we show that HCVne particles are capable of inducing the recently discovered ERK5 pathway, in a dose dependent way. The ERK5 pathway can be activated by growth factors and other extracellular signals. This specific activation occurs through a well characterized upstream kinase, MEK5, and is capable of inducing gene regulation of mef2. In contrast, when HCV core structural and NS5A non-structural proteins were expressed endogenously no activation of this pathway was detected. These cell signaling events could be of critical importance and might give clues for the elucidation of cellular manifestations associated with HCV infection.
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de la Vega M, Burrows JF, Johnston JA. Ubiquitination: Added complexity in Ras and Rho family GTPase function. Small GTPases 2011; 2:192-201. [PMID: 22145091 DOI: 10.4161/sgtp.2.4.16707] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2011] [Revised: 07/08/2011] [Accepted: 07/08/2011] [Indexed: 12/17/2022] Open
Abstract
The regulation of the small GTPases leading to their membrane localization has long been attributed to processing of their C-terminal CAAX box. As deregulation of many of these GTPases have been implicated in cancer and other disorders, prenylation and methylation of this CAAX box has been studied in depth as a possibility for drug targeting, but unfortunately, to date no drug has proved clinically beneficial. However, these GTPases also undergo other modifications that may be important for their regulation. Ubiquitination has long been demonstrated to regulate the fate of numerous cellular proteins and recently it has become apparent that many GTPases, along with their GAPs, GeFs and GDis, undergo ubiquitination leading to a variety of fates such as re-localization or degradation. in this review we focus on the recent literature demonstrating that the regulation of small GTPases by ubiquitination, either directly or indirectly, plays a considerable role in controlling their function and that targeting these modifications could be important for disease treatment.
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Affiliation(s)
- Michelle de la Vega
- Centre for Infection and Immunity; School of Medicine, Dentistry and Biomedical Sciences; Queen's University; Belfast, UK
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Tarafder AK, Wasmeier C, Figueiredo AC, Booth AEG, Orihara A, Ramalho JS, Hume AN, Seabra MC. Rab27a targeting to melanosomes requires nucleotide exchange but not effector binding. Traffic 2011; 12:1056-66. [PMID: 21554507 PMCID: PMC3509405 DOI: 10.1111/j.1600-0854.2011.01216.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Rab GTPases are important determinants of organelle identity and regulators of vesicular transport pathways. Consequently, each Rab occupies a highly specific subcellular localization. However, the precise mechanisms governing Rab targeting remain unclear. Guanine nucleotide exchange factors (GEFs), putative membrane-resident targeting factors and effector binding have all been implicated as critical regulators of Rab targeting. Here, we address these issues using Rab27a targeting to melanosomes as a model system. Rab27a regulates motility of lysosome-related organelles and secretory granules. Its effectors have been characterized extensively, and we have identified Rab3GEP as the non-redundant Rab27a GEF in melanocytes (Figueiredo AC et al. Rab3GEP is the non-redundant guanine nucleotide exchange factor for Rab27a in melanocytes. J Biol Chem 2008;283:23209–23216). Using Rab27a mutants that show impaired binding to representatives of all four Rab27a effector subgroups, we present evidence that effector binding is not essential for targeting of Rab27a to melanosomes. In contrast, we observed that knockdown of Rab3GEP resulted in mis-targeting of Rab27a, suggesting that Rab3GEP activity is required for correct targeting of Rab27a. However, the identification of Rab27a mutants that undergo efficient GDP/GTP exchange in the presence of Rab3GEP in vitro but are mis-targeted in a cellular context indicates that nucleotide loading is not the sole determinant of subcellular targeting of Rab27a. Our data support a model in which exchange activity, but not effector binding, represents one essential factor that contributes to membrane targeting of Rab proteins.
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Affiliation(s)
- Abul K Tarafder
- Molecular Medicine, National Heart and Lung Institute (NHLI), Imperial College London, London SW7 2AZ, UK
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