201
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Abstract
Cell–cell signaling mediated by the Notch receptor is iteratively involved in numerous developmental contexts, and its dysregulation has been associated with inherited genetic disorders and cancers. The core components of the signaling pathway have been identified for some time, but the study of the modulation of the pathway in different cellular contexts has revealed many layers of regulation. These include complex sugar modifications in the extracellular domain as well as transit of Notch through defined cellular compartments, including specific endosomes.
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Affiliation(s)
- An-Chi Tien
- Program in Developmental Biology, Baylor College of Medicine, Houston, TX 77030, USA
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202
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Igaki T, Pastor-Pareja JC, Aonuma H, Miura M, Xu T. Intrinsic tumor suppression and epithelial maintenance by endocytic activation of Eiger/TNF signaling in Drosophila. Dev Cell 2009; 16:458-65. [PMID: 19289090 PMCID: PMC2729686 DOI: 10.1016/j.devcel.2009.01.002] [Citation(s) in RCA: 230] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2007] [Revised: 10/31/2008] [Accepted: 01/14/2009] [Indexed: 01/15/2023]
Abstract
Oncogenic alterations in epithelial tissues often trigger apoptosis, suggesting an evolutionary mechanism by which organisms eliminate aberrant cells from epithelia. In Drosophila imaginal epithelia, clones of cells mutant for tumor suppressors, such as scrib or dlg, lose their polarity and are eliminated by cell death. Here, we show that Eiger, the Drosophila tumor necrosis factor (TNF), behaves like a tumor suppressor that eliminates oncogenic cells from epithelia through a local endocytic JNK-activation mechanism. In the absence of Eiger, these polarity-deficient clones are no longer eliminated; instead, they grow aggressively into tumors. We show that in scrib clones endocytosis is elevated, which translocates Eiger to endocytic vesicles and leads to activation of apoptotic JNK signaling. Furthermore, blocking endocytosis prevents both JNK activation and cell elimination. Our data indicate that TNF signaling and the endocytic machinery could be components of an evolutionarily conserved fail-safe mechanism by which animals protect against neoplastic development.
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Affiliation(s)
- Tatsushi Igaki
- Howard Hughes Medical Institute, Department of Genetics, Yale University School of Medicine, Boyer Center for Molecular Medicine, 295 Congress Avenue, New Haven, CT 06536, USA
| | - Jose Carlos Pastor-Pareja
- Howard Hughes Medical Institute, Department of Genetics, Yale University School of Medicine, Boyer Center for Molecular Medicine, 295 Congress Avenue, New Haven, CT 06536, USA
| | - Hiroka Aonuma
- Department of Genetics, Graduate School of Pharmaceutical Sciences, University of Tokyo, CREST, JST 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Masayuki Miura
- Department of Genetics, Graduate School of Pharmaceutical Sciences, University of Tokyo, CREST, JST 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Tian Xu
- Howard Hughes Medical Institute, Department of Genetics, Yale University School of Medicine, Boyer Center for Molecular Medicine, 295 Congress Avenue, New Haven, CT 06536, USA
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203
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Akbar MA, Ray S, Krämer H. The SM protein Car/Vps33A regulates SNARE-mediated trafficking to lysosomes and lysosome-related organelles. Mol Biol Cell 2009; 20:1705-14. [PMID: 19158398 PMCID: PMC2655250 DOI: 10.1091/mbc.e08-03-0282] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2008] [Revised: 11/25/2008] [Accepted: 01/09/2009] [Indexed: 01/18/2023] Open
Abstract
The SM proteins Vps33A and Vps33B are believed to act in membrane fusions in endosomal pathways, but their specific roles are controversial. In Drosophila, Vps33A is the product of the carnation (car) gene. We generated a null allele of car to test its requirement for trafficking to different organelles. Complete loss of car function is lethal during larval development. Eye-specific loss of Car causes late, light-independent degeneration of photoreceptor cells. Earlier in these cells, two distinct phenotypes were detected. In young adults, autophagosomes amassed indicating that their fusion with lysosomes requires Car. In eye discs, endocytosed receptors and ligands accumulate in Rab7-positive prelysosomal compartments. The requirement of Car for late endosome-to-lysosome fusion in imaginal discs is specific as early endosomes are unaffected. Furthermore, lysosomal delivery is not restored by expression of dVps33B. This specificity reflects the distinct pattern of binding to different Syntaxins in vitro: dVps33B predominantly binds the early endosomal Avl and Car to dSyntaxin16. Consistent with a role in Car-mediated fusion, dSyntaxin16 is not restricted to Golgi membranes but also present on lysosomes.
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Affiliation(s)
| | - Sanchali Ray
- Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9111
| | - Helmut Krämer
- Departments of *Neuroscience and
- Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9111
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204
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Grusche FA, Hidalgo C, Fletcher G, Sung HH, Sahai E, Thompson BJ. Sds22, a PP1 phosphatase regulatory subunit, regulates epithelial cell polarity and shape [Sds22 in epithelial morphology]. BMC DEVELOPMENTAL BIOLOGY 2009; 9:14. [PMID: 19228425 PMCID: PMC2652452 DOI: 10.1186/1471-213x-9-14] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/30/2008] [Accepted: 02/19/2009] [Indexed: 11/10/2022]
Abstract
Background How epithelial cells adopt their particular polarised forms is poorly understood. In a screen for genes regulating epithelial morphology in Drosophila, we identified sds22, a conserved gene previously characterised in yeast. Results In the columnar epithelia of imaginal discs or follicle cells, mutation of sds22 causes contraction of cells along their apical-basal axis, resulting in a more cuboidal morphology. In addition, the mutant cells can also display altered cell polarity, forming multiple layers in follicle cells and leaving the epithelium in imaginal discs. In yeast, sds22 encodes a PP1 phosphatase regulatory subunit. Consistent with this, we show that Drosophila Sds22 binds to all four Drosophila PP1s and shares an overlapping phenotype with PP1beta9c. We also show that two previously postulated PP1 targets, Spaghetti Squash and Moesin are hyper-phosphorylated in sds22 mutants. This function is shared by the human homologue of Sds22, PPP1R7. Conclusion Sds22 is a conserved PP1 phosphatase regulatory subunit that controls cell shape and polarity.
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205
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Abstract
The ESCRT (endosomal sorting complex required for transport) machinery consists of four protein complexes that mediate sorting of ubiquitinated membrane proteins into the intraluminal vesicles of multivesicular endosomes, thereby targeting them for degradation in lysosomes. In the present paper, we review how ESCRT-mediated receptor down-regulation affects signalling downstream of Notch and growth factor receptors, and how ESCRTs may control cell proliferation, survival and cytoskeletal functions and contribute to tumour suppression.
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206
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Abstract
The ESCRT (endosomal sorting complex required for transport) machinery plays a critical role in receptor down-regulation, retroviral budding, and other normal and pathological processes. The ESCRT components are conserved in all five major subgroups of eukaryotes. This review summarizes the growing number of links identified between ESCRT-mediated protein sorting in the MVB (multivesicular body) pathway and various human diseases.
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207
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Rodahl LM, Haglund K, Sem-Jacobsen C, Wendler F, Vincent JP, Lindmo K, Rusten TE, Stenmark H. Disruption of Vps4 and JNK function in Drosophila causes tumour growth. PLoS One 2009; 4:e4354. [PMID: 19194501 PMCID: PMC2632753 DOI: 10.1371/journal.pone.0004354] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2008] [Accepted: 12/25/2008] [Indexed: 11/30/2022] Open
Abstract
Several regulators of endocytic trafficking have recently been identified as tumour suppressors in Drosophila. These include components of the endosomal sorting complex required for transport (ESCRT) machinery. Disruption of subunits of ESCRT-I and -II leads to cell-autonomous endosomal accumulation of ubiquitinated receptors, loss of apicobasal polarity and epithelial integrity, and increased cell death. Here we report that disruption of the ATPase dVps4, the most downstream component of the ESCRT machinery, causes the same array of cellular phenotypes. We find that loss of epithelial integrity and increased apoptosis, but not loss of cell polarity, require the activation of JNK signalling. Abrogation of JNK signalling prevents apoptosis in dVps4 deficient cells. Indeed double deficiency in dVps4 and JNK signalling leads to the formation of neoplastic tumours. We conclude that dvps4 is a tumour suppressor in Drosophila and that JNK is central to the cell-autonomous phenotypes of ESCRT-deficient cells.
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Affiliation(s)
- Lina M. Rodahl
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo and Institute for Cancer Research, the Norwegian Radium Hospital, Rikshospitalet University Hospital, Montebello, Oslo, Norway
| | - Kaisa Haglund
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo and Institute for Cancer Research, the Norwegian Radium Hospital, Rikshospitalet University Hospital, Montebello, Oslo, Norway
| | - Catherine Sem-Jacobsen
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo and Institute for Cancer Research, the Norwegian Radium Hospital, Rikshospitalet University Hospital, Montebello, Oslo, Norway
| | - Franz Wendler
- MRC National Institute of Medical Research, Mill Hill, London, United Kingdom
| | - Jean-Paul Vincent
- MRC National Institute of Medical Research, Mill Hill, London, United Kingdom
| | - Karine Lindmo
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo and Institute for Cancer Research, the Norwegian Radium Hospital, Rikshospitalet University Hospital, Montebello, Oslo, Norway
| | - Tor Erik Rusten
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo and Institute for Cancer Research, the Norwegian Radium Hospital, Rikshospitalet University Hospital, Montebello, Oslo, Norway
| | - Harald Stenmark
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo and Institute for Cancer Research, the Norwegian Radium Hospital, Rikshospitalet University Hospital, Montebello, Oslo, Norway
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208
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Abstract
Mitogenic tyrosine kinase receptors such as the EGFR (epidermal growth factor receptor) are endocytosed once they are activated at the cell surface. After reaching the early endosome, they are ubiquitinated within their cytosolic domain and are consequently sorted away from recycling receptors. They are then incorporated into intraluminal vesicles within the MVB (multivesicular body) en route to the lysosome, where they are degraded. MVB formation requires the stabilization of the vacuolar domain of the early endosome, the segregation of degradative cargo within this domain (with subsequent incorporation of receptors such as EGFR into intraluminal vesicles) and the physical separation and movement of this domain away from the tubular regions of the early endosome. How these different aspects of MVB biogenesis are coupled is unknown, but ESCRTs (endosomal sorting complexes required for transport) have been identified as key molecular players in driving mitogenic receptor sequestration and formation of intraluminal vesicles. The present review summarizes recent findings within the field and from our laboratory regarding the detailed function of ESCRTs and associated proteins in driving the ubiquitin-dependent sorting of EGFR and in maintaining the domain organization of the early endosome.
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Affiliation(s)
- Philip Woodman
- Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, UK.
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209
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Genetic analysis of ESCRT function in Drosophila: a tumour model for human Tsg101. Biochem Soc Trans 2009; 37:204-7. [DOI: 10.1042/bst0370204] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Class E Vps (vacuolar protein sorting) proteins are components of the ESCRTs (endosomal sorting complexes required for transport) which are required for protein sorting at the early endosome. Most of these genes have been identified and genetically characterized in yeast. Recent genetic studies in Drosophila have revealed the phenotypic consequences of loss of vps function in multicellular organisms. In the present paper, we review these studies and discuss a mechanism which may explain how loss of the human Tsg101 (tumour susceptibility gene 101), a vps23 orthologue, causes tumours.
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210
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Nagaraj R, Banerjee U. Regulation of Notch and Wingless signalling by phyllopod, a transcriptional target of the EGFR pathway. EMBO J 2009; 28:337-46. [PMID: 19153610 DOI: 10.1038/emboj.2008.286] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2008] [Accepted: 12/09/2008] [Indexed: 11/09/2022] Open
Abstract
Spatial and temporal control of Notch and Wingless (Wg) pathways during development is regulated at multiple levels. Here, we present an analysis of Phyllopod as a coordinated regulator of these two critical signal transduction pathways. Phyl specifically helps traffic Notch and Wg pathway components within early endocytic vesicles, thereby controlling the amount of processed signal available for causing a transcriptional response within the nucleus. In Drosophila, the EGFR pathway transcriptionally activates phyl whose product then blocks Notch and Wg signalling pathways. This provides a mechanistic basis for an antagonistic relationship between receptor tyrosine kinase and Notch/Wg pathways during development. Furthermore, this study identifies a Phyl-regulated class of endosomal vesicles that specifically include components of Notch and Wg signalling.
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Affiliation(s)
- Raghavendra Nagaraj
- Department of Molecular, Cell and Developmental Biology, University of California, Los Angeles, CA 90095, USA
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211
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Herz HM, Woodfield SE, Chen Z, Bolduc C, Bergmann A. Common and distinct genetic properties of ESCRT-II components in Drosophila. PLoS One 2009; 4:e4165. [PMID: 19132102 PMCID: PMC2613530 DOI: 10.1371/journal.pone.0004165] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2008] [Accepted: 11/25/2008] [Indexed: 11/28/2022] Open
Abstract
Background Genetic studies in yeast have identified class E vps genes that form the ESCRT complexes required for protein sorting at the early endosome. In Drosophila, mutations of the ESCRT-II component vps25 cause endosomal defects leading to accumulation of Notch protein and increased Notch pathway activity. These endosomal and signaling defects are thought to account for several phenotypes. Depending on the developmental context, two different types of overgrowth can be detected. Tissue predominantly mutant for vps25 displays neoplastic tumor characteristics. In contrast, vps25 mutant clones in a wild-type background trigger hyperplastic overgrowth in a non-autonomous manner. In addition, vps25 mutant clones also promote apoptotic resistance in a non-autonomous manner. Principal Findings Here, we genetically characterize the remaining ESCRT-II components vps22 and vps36. Like vps25, mutants of vps22 and vps36 display endosomal defects, accumulate Notch protein and – when the tissue is predominantly mutant – show neoplastic tumor characteristics. However, despite these common phenotypes, they have distinct non-autonomous phenotypes. While vps22 mutations cause strong non-autonomous overgrowth, they do not affect apoptotic resistance. In contrast, vps36 mutations increase apoptotic resistance, but have little effect on non-autonomous proliferation. Further characterization reveals that although all ESCRT-II mutants accumulate Notch protein, only vps22 and vps25 mutations trigger Notch activity. Conclusions/Significance The ESCRT-II components vps22, vps25 and vps36 display common and distinct genetic properties. Our data redefine the role of Notch for hyperplastic and neoplastic overgrowth in these mutants. While Notch is required for hyperplastic growth, it appears to be dispensable for neoplastic transformation.
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Affiliation(s)
- Hans-Martin Herz
- Department of Biochemistry and Molecular Biology, The Genes & Development Graduate Program, The University of Texas M. D. Anderson Cancer Center, Houston, Texas, United States of America
| | - Sarah E. Woodfield
- Department of Biochemistry and Molecular Biology, The Genes & Development Graduate Program, The University of Texas M. D. Anderson Cancer Center, Houston, Texas, United States of America
- Baylor College of Medicine, Graduate Program in Developmental Biology, Houston, Texas, United States of America
| | - Zhihong Chen
- Department of Biochemistry and Molecular Biology, The Genes & Development Graduate Program, The University of Texas M. D. Anderson Cancer Center, Houston, Texas, United States of America
| | - Clare Bolduc
- Department of Biochemistry and Molecular Biology, The Genes & Development Graduate Program, The University of Texas M. D. Anderson Cancer Center, Houston, Texas, United States of America
| | - Andreas Bergmann
- Department of Biochemistry and Molecular Biology, The Genes & Development Graduate Program, The University of Texas M. D. Anderson Cancer Center, Houston, Texas, United States of America
- * E-mail:
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212
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213
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Winslow AR, Rubinsztein DC. Autophagy in neurodegeneration and development. BIOCHIMICA ET BIOPHYSICA ACTA 2008; 1782:723-9. [PMID: 18644437 PMCID: PMC2597715 DOI: 10.1016/j.bbadis.2008.06.010] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/01/2008] [Revised: 06/09/2008] [Accepted: 06/23/2008] [Indexed: 12/12/2022]
Abstract
Efficient protein turnover is essential for the maintenance of cellular health. Here we review how autophagy has fundamental functions in cellular homeostasis and possible uses as a therapeutic strategy for neurodegenerative diseases associated with intracytosolic aggregate formation, like Huntington's disease (HD). Drugs like rapamycin, that induce autophagy, increase the clearance of mutant huntingtin fragments and ameliorate the pathology in cell and animal models of HD and related conditions. In Drosophila, the beneficial effects of rapamycin in diseases related to HD are autophagy-dependent. We will also discuss the importance of autophagy in early stages of development and its possible contribution as a secondary disease mechanism in forms of fronto-temporal dementias, motor neuron disease, and lysosomal storage disorders.
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Affiliation(s)
| | - David C. Rubinsztein
- Department of Medical Genetics, Cambridge Institute for Medical Research, Wellcome Trust/MRC Building, Addenbrooke's Hospital, Hills Road, Cambridge CB2 0XY, UK
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214
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Rafel N, Milán M. Notch signalling coordinates tissue growth and wing fate specification in Drosophila. Development 2008; 135:3995-4001. [PMID: 18987026 DOI: 10.1242/dev.027789] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
During the development of a given organ, tissue growth and fate specification are simultaneously controlled by the activity of a discrete number of signalling molecules. Here, we report that these two processes are extraordinarily coordinated in the Drosophila wing primordium, which extensively proliferates during larval development to give rise to the dorsal thoracic body wall and the adult wing. The developmental decision between wing and body wall is defined by the opposing activities of two secreted signalling molecules, Wingless and the EGF receptor ligand Vein. Notch signalling is involved in the determination of a variety of cell fates, including growth and cell survival. We present evidence that growth of the wing primordium mediated by the activity of Notch is required for wing fate specification. Our data indicate that tissue size modulates the activity range of the signalling molecules Wingless and Vein. These results highlight a crucial role of Notch in linking proliferation and fate specification in the developing wing primordium.
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Affiliation(s)
- Neus Rafel
- ICREA and Institute for Research in Biomedicine (IRB Científic de Barcelona, Baldiri Reixac 10, 08028 Barcelona, Spain
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215
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Wilkin M, Tongngok P, Gensch N, Clemence S, Motoki M, Yamada K, Hori K, Taniguchi-Kanai M, Franklin E, Matsuno K, Baron M. Drosophila HOPS and AP-3 complex genes are required for a Deltex-regulated activation of notch in the endosomal trafficking pathway. Dev Cell 2008; 15:762-72. [PMID: 19000840 DOI: 10.1016/j.devcel.2008.09.002] [Citation(s) in RCA: 129] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2007] [Revised: 07/07/2008] [Accepted: 09/03/2008] [Indexed: 01/12/2023]
Abstract
DSL ligands promote proteolysis of the Notch receptor, to release active Notch intracellular domain (N(ICD)). Conversely, the E3 ubiquitin ligase Deltex can activate ligand-independent Notch proteolysis and signaling. Here we show that Deltex effects require endocytic trafficking by HOPS and AP-3 complexes. Our data suggest that Deltex shunts Notch into an endocytic pathway with two possible endpoints. If Notch transits into the lysosome lumen, it is degraded. However, if HOPS and AP-3 deliver Notch to the limiting membrane of the lysosome, degradation of the Notch extracellular domain allows subsequent Presenilin-mediated release of N(ICD). This model accounts for positive and negative regulatory effects of Deltex in vivo. Indeed, we uncover HOPS/AP-3 contributions to Notch signaling during Drosophila midline formation and neurogenesis. We discuss ways in which these endocytic pathways may modulate ligand-dependent and -independent events, as a mechanism that can potentiate Notch signaling or dampen noise in the signaling network.
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Affiliation(s)
- Marian Wilkin
- Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester, M13 9PT, UK
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216
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Abstract
Once engaged by soluble or matrix-anchored ligands, cell surface proteins are commonly sorted to lysosomal degradation through several endocytic pathways. Defective vesicular trafficking of growth factor receptors, as well as unbalanced recycling of integrin- and cadherin-based adhesion complexes, has emerged in the past 5 years as a multifaceted hallmark of malignant cells. In line with the cooperative nature of endocytic machineries, multiple oncogenic alterations underlie defective endocytosis, such as altered ubiquitylation (Cbl and Nedd4 ubiquitin ligases, for example), altered cytoskeletal interactions and alterations to Rab family members. Pharmaceutical interception of the propensity of tumour cells to derail their signalling and their adhesion receptors may constitute a novel target for cancer therapy.
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Affiliation(s)
- Yaron Mosesson
- Department of Biological Regulation, The Weizmann Institute of Science, Rehovot 76100, Israel
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217
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Stuffers S, Brech A, Stenmark H. ESCRT proteins in physiology and disease. Exp Cell Res 2008; 315:1619-26. [PMID: 19013455 DOI: 10.1016/j.yexcr.2008.10.013] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2008] [Revised: 10/15/2008] [Accepted: 10/15/2008] [Indexed: 10/21/2022]
Abstract
As a mechanism of signal attenuation, receptors for growth factors, peptide hormones and cytokines are internalized in response to ligand binding, followed by degradation in lysosomes. Receptor ubiquitination is a key signal for such downregulation, and four protein complexes known as endosomal sorting complex required for transport (ESCRT)-0, -I, -II and -III have been identified as the machinery required for degradative endosomal sorting of ubiquitinated membrane proteins in yeast and metazoans. Three of these complexes contain ubiquitin-binding domains whereas ESCRT-III instead recruits deubiquitinating enzymes. The concerted action of the ESCRTs not only serves to sort ubiquitinated cargo but is also thought to cause inward vesiculation of endosomal membranes, thereby mediating biogenesis of multivesicular endosomes (MVEs). Because ligand-mediated receptor downregulation plays an important role in signal attenuation, it is not surprising that dysfunction of ESCRT components is associated with disease. In this review we discuss the possible roles of ESCRTs in protection against cancer, neurodegenerative diseases and bacterial infections, and we highlight the fact that many RNA viruses exploit the ESCRT machinery for the final abscission step of their budding from cells. We also review the additional functions of ESCRT proteins in cytokinesis and discuss how these may be related to ESCRT-associated pathologies.
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Affiliation(s)
- Susanne Stuffers
- Centre for Cancer Biomedicine, Faculty Division, The Norwegian Radium Hospital, University of Oslo, Norway
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218
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Fan Y, Bergmann A. Apoptosis-induced compensatory proliferation. The Cell is dead. Long live the Cell! Trends Cell Biol 2008; 18:467-73. [PMID: 18774295 PMCID: PMC2705980 DOI: 10.1016/j.tcb.2008.08.001] [Citation(s) in RCA: 237] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2008] [Revised: 07/31/2008] [Accepted: 08/01/2008] [Indexed: 11/29/2022]
Abstract
In multi-cellular organisms, activation of apoptosis can trigger compensatory proliferation in surrounding cells to maintain tissue homeostasis. Genetic studies in Drosophila have indicated that distinct mechanisms of compensatory proliferation are employed in apoptotic tissues of different developmental states. In proliferating eye and wing tissues, the initiator caspase Dronc coordinates cell death and compensatory proliferation through the Jun N-terminal kinase and p53. The mitogens Decapentaplegic and Wingless are induced in this process. By contrast, in differentiating eye tissues, the effector caspases DrICE and Dcp-1 activate the Hedgehog signaling pathway to induce compensatory proliferation. In this review, we summarize these findings and discuss how activation of apoptosis is linked to the process of compensatory proliferation. The developmental and pathological relevance of compensatory proliferation is also discussed.
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Affiliation(s)
- Yun Fan
- Department of Biochemistry and Molecular Biology, University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, USA
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219
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Chastagner P, Israël A, Brou C. AIP4/Itch regulates Notch receptor degradation in the absence of ligand. PLoS One 2008; 3:e2735. [PMID: 18628966 PMCID: PMC2444042 DOI: 10.1371/journal.pone.0002735] [Citation(s) in RCA: 112] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2008] [Accepted: 06/25/2008] [Indexed: 01/17/2023] Open
Abstract
Background The regulation of Notch signaling heavily relies on ubiquitination events. Drosophila Su(dx), a member of the HECT family of ubiquitin-ligases, has been described as a negative regulator of Notch signaling, acting on the post-endocytic sorting of Notch. The mammalian ortholog of Su(dx), Itch/AIP4, has been shown to have multiple substrates, including Notch, but the precise events regulated by Itch/AIP4 in the Notch pathway have not been identified yet. Methodology/Principal Findings Using Itch-/- fibroblasts expressing the Notch1 receptor, we show that Itch is not necessary for Notch activation, but rather for controlling the degradation of Notch in the absence of ligand. Itch is indeed required after the early steps of Notch endocytosis to target it to the lysosomes where it is degraded. Furthermore Itch/AIP4 catalyzes Notch polyubiquitination through unusual K29-linked chains. We also demonstrate that although Notch is associated with Itch/AIP4 in cells, their interaction is not detectable in vitro and thus requires either a post-translational modification, or a bridging factor that remains to be identified. Conclusions/Significance Taken together our results identify a specific step of Notch regulation in the absence of any activation and underline differences between mammalian and Drosophila Notch pathways.
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Affiliation(s)
- Patricia Chastagner
- Unité de Signalisation Moléculaire et Activation Cellulaire, URA 2582, CNRS, Institut Pasteur, Paris, France
| | - Alain Israël
- Unité de Signalisation Moléculaire et Activation Cellulaire, URA 2582, CNRS, Institut Pasteur, Paris, France
| | - Christel Brou
- Unité de Signalisation Moléculaire et Activation Cellulaire, URA 2582, CNRS, Institut Pasteur, Paris, France
- * E-mail:
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220
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Tanaka N, Kyuuma M, Sugamura K. Endosomal sorting complex required for transport proteins in cancer pathogenesis, vesicular transport, and non-endosomal functions. Cancer Sci 2008; 99:1293-303. [PMID: 18429951 PMCID: PMC11158640 DOI: 10.1111/j.1349-7006.2008.00825.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2007] [Revised: 02/27/2008] [Accepted: 02/29/2008] [Indexed: 12/18/2022] Open
Abstract
Endosomal sorting complex required for transport (ESCRT) proteins form a multicomplex sorting machinery that controls multivesicular body (MVB) formation and the sorting of ubiquitinated membrane proteins to the endosomes. Being sorted to the MVB generally results in the lysosome-dependent degradation of cell-surface receptors, and defects in this machinery induce dysregulated receptor traffic and turnover. Recent lessons from gene targeting and silencing methodologies have implicated the ESCRT in normal development, cell differentiation, and growth, as well as in the budding of certain enveloped viruses. Furthermore, it is becoming apparent that the dysregulation of ESCRT proteins is involved in the development of various human diseases, including many types of cancers and neurodegenerative disorders. Here, we summarize the roles of ESCRT proteins in MVB sorting processes and the regulation of tumor cells, and we discuss some of their other functions that are unrelated to vesicular transport.
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Affiliation(s)
- Nobuyuki Tanaka
- Department of Microbiology, Tohoku University Graduate School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai 980-8575, Japan.
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221
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Im YJ, Hurley JH. Integrated structural model and membrane targeting mechanism of the human ESCRT-II complex. Dev Cell 2008; 14:902-13. [PMID: 18539118 PMCID: PMC2475506 DOI: 10.1016/j.devcel.2008.04.004] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2008] [Revised: 03/31/2008] [Accepted: 04/18/2008] [Indexed: 01/19/2023]
Abstract
ESCRT-II plays a pivotal role in receptor downregulation and multivesicular body biogenesis and is conserved from yeast to humans. The crystal structures of two human ESCRT-II complex structures have been determined at 2.6 and 2.9 A resolution, respectively. The complex has three lobes and contains one copy each of VPS22 and VPS36 and two copies of VPS25. The structure reveals a dynamic helical domain to which both the VPS22 and VPS36 subunits contribute that connects the GLUE domain to the rest of the ESCRT-II core. Hydrodynamic analysis shows that intact ESCRT-II has a compact, closed conformation. ESCRT-II binds to the ESCRT-I VPS28 C-terminal domain subunit through a helix immediately C-terminal to the VPS36-GLUE domain. ESCRT-II is targeted to endosomal membranes by the lipid-binding activities of both the Vps36 GLUE domain and the first helix of Vps22. These data provide a unifying structural and functional framework for the ESCRT-II complex.
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Affiliation(s)
- Young Jun Im
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, US Department of Health and Human Services, Bethesda, MD 20892, USA
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222
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Miura GI, Roignant JY, Wassef M, Treisman JE. Myopic acts in the endocytic pathway to enhance signaling by the Drosophila EGF receptor. Development 2008; 135:1913-22. [PMID: 18434417 PMCID: PMC2413058 DOI: 10.1242/dev.017202] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Endocytosis of activated receptors can control signaling levels by exposing the receptors to novel downstream molecules or by instigating their degradation. Epidermal growth factor receptor (EGFR) signaling has crucial roles in development and is misregulated in many cancers. We report here that Myopic, the Drosophila homolog of the Bro1-domain tyrosine phosphatase HD-PTP, promotes EGFR signaling in vivo and in cultured cells. myopic is not required in the presence of activated Ras or in the absence of the ubiquitin ligase Cbl, indicating that it acts on internalized EGFR, and its overexpression enhances the activity of an activated form of EGFR. Myopic is localized to intracellular vesicles adjacent to Rab5-containing early endosomes, and its absence results in the enlargement of endosomal compartments. Loss of Myopic prevents cleavage of the EGFR cytoplasmic domain, a process controlled by the endocytic regulators Cbl and Sprouty. We suggest that Myopic promotes EGFR signaling by mediating its progression through the endocytic pathway.
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Affiliation(s)
| | - Jean-Yves Roignant
- Kimmel Center for Biology and Medicine of the Skirball Institute, NYU School of Medicine, Department of Cell Biology, 540 First Avenue, New York, NY 10016
| | | | - Jessica E. Treisman
- Kimmel Center for Biology and Medicine of the Skirball Institute, NYU School of Medicine, Department of Cell Biology, 540 First Avenue, New York, NY 10016
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223
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Kanwar R, Fortini ME. The big brain aquaporin is required for endosome maturation and notch receptor trafficking. Cell 2008; 133:852-63. [PMID: 18510929 PMCID: PMC2488160 DOI: 10.1016/j.cell.2008.04.038] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2007] [Revised: 03/10/2008] [Accepted: 04/29/2008] [Indexed: 11/26/2022]
Abstract
Activity of the big brain (bib) gene influences Notch signaling during Drosophila nervous system development. We demonstrate that Bib, which belongs to the aquaporin family of channel proteins, is required for endosome maturation in Drosophila epithelial cells. In the absence of Bib, early endosomes arrest and form abnormal clusters, and cells exhibit reduced acidification of endocytic trafficking organelles. Bib acts downstream of Hrs in early endosome morphogenesis and regulates biogenesis of endocytic compartments prior to the formation of Rab7-containing late endosomes. Abnormal endosome morphology caused by loss of Bib is accompanied by overaccumulation of Notch, Delta, and other signaling molecules as well as reduced intracellular trafficking of Notch to nuclei. Analysis of several endosomal trafficking mutants reveals a correlation between endosomal acidification and levels of Notch signaling. Our findings reveal an unprecedented role for an aquaporin in endosome maturation, trafficking, and acidification.
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Affiliation(s)
- Ritu Kanwar
- Cancer and Developmental Biology Laboratory, National Cancer Institute, 1050 Boyles Street, Building 560, Room 22-12, Frederick, MD 21701 USA, Tel: 301-846-7599, Fax: 301-846-1666,
| | - Mark E. Fortini
- Cancer and Developmental Biology Laboratory, National Cancer Institute, 1050 Boyles Street, Building 560, Room 22-12, Frederick, MD 21701 USA, Tel: 301-846-7599, Fax: 301-846-1666,
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224
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From endocytosis to tumors through asymmetric cell division of stem cells. Curr Opin Cell Biol 2008; 20:462-9. [PMID: 18511252 DOI: 10.1016/j.ceb.2008.03.007] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2008] [Revised: 03/12/2008] [Accepted: 03/13/2008] [Indexed: 12/27/2022]
Abstract
Recent studies in vertebrate and invertebrate model organisms uncover the importance of endocytosis for biased signaling during asymmetric cell division. In stem cells, perturbing polarity and asymmetric division affect their selfrenewal causing exponential proliferation, thereby giving rise to cancer. An emerging pattern is that endocytosis controls asymmetric cell division, which underlies stem cell selfrenewal and defective selfrenewal is on the basis of tumorigenesis caused by cancer stem cells.
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225
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Hayward P, Kalmar T, Arias AM. Wnt/Notch signalling and information processing during development. Development 2008; 135:411-24. [PMID: 18192283 DOI: 10.1242/dev.000505] [Citation(s) in RCA: 230] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The Wnt and Notch signalling pathways represent two major channels of communication used by animal cells to control their identities and behaviour during development. A number of reports indicate that their activities are closely intertwined during embryonic development. Here, we review the evidence for this relationship and suggest that Wnt and Notch ('Wntch') signalling act as components of an integrated device that, rather than defining the fate of a cell, determines the probability that a cell will adopt that fate.
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Affiliation(s)
- Penelope Hayward
- Department of Genetics, University of Cambridge, Cambridge CB2 3EH, UK
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226
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Vaccari T, Lu H, Kanwar R, Fortini ME, Bilder D. Endosomal entry regulates Notch receptor activation in Drosophila melanogaster. J Cell Biol 2008; 180:755-62. [PMID: 18299346 PMCID: PMC2265571 DOI: 10.1083/jcb.200708127] [Citation(s) in RCA: 218] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2007] [Accepted: 01/25/2008] [Indexed: 11/26/2022] Open
Abstract
Signaling through the transmembrane receptor Notch is widely used throughout animal development and is a major regulator of cell proliferation and differentiation. During canonical Notch signaling, internalization and recycling of Notch ligands controls signaling activity, but the involvement of endocytosis in activation of Notch itself is not well understood. To address this question, we systematically assessed Notch localization, processing, and signaling in a comprehensive set of Drosophila melanogaster mutants that block access of cargo to different endocytic compartments. We find that gamma-secretase cleavage and signaling of endogenous Notch is reduced in mutants that impair entry into the early endosome but is enhanced in mutants that increase endosomal retention. In mutants that block endosomal entry, we also uncover an alternative, low-efficiency Notch trafficking route that can contribute to signaling. Our data show that endosomal access of the Notch receptor is critical to achieve physiological levels of signaling and further suggest that altered residence in distinct endocytic compartments could underlie pathologies involving aberrant Notch pathway activation.
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Affiliation(s)
- Thomas Vaccari
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA
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227
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Diverse cellular functions of the Hsp90 molecular chaperone uncovered using systems approaches. Cell 2008; 131:121-35. [PMID: 17923092 DOI: 10.1016/j.cell.2007.07.036] [Citation(s) in RCA: 380] [Impact Index Per Article: 22.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2006] [Revised: 05/18/2007] [Accepted: 07/20/2007] [Indexed: 01/31/2023]
Abstract
A comprehensive understanding of the cellular functions of the Hsp90 molecular chaperone has remained elusive. Although Hsp90 is essential, highly abundant under normal conditions, and further induced by environmental stress, only a limited number of Hsp90 "clients" have been identified. To define Hsp90 function, a panel of genome-wide chemical-genetic screens in Saccharomyces cerevisiae were combined with bioinformatic analyses. This approach identified several unanticipated functions of Hsp90 under normal conditions and in response to stress. Under normal growth conditions, Hsp90 plays a major role in various aspects of the secretory pathway and cellular transport; during environmental stress, Hsp90 is required for the cell cycle, meiosis, and cytokinesis. Importantly, biochemical and cell biological analyses validated several of these Hsp90-dependent functions, highlighting the potential of our integrated global approach to uncover chaperone functions in the cell.
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228
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Abstract
Nearly 1.7 billion people are infected with Mycobacterium tuberculosis. Its ability to survive intracellularly is thought to be central to its success as a pathogen, but how it does this is poorly understood. Using a Drosophila model of infection, we identify three host cell activities, Rab7, CG8743, and the ESCRT machinery, that modulate the mycobacterial phagosome. In the absence of these factors the cell no longer restricts growth of the non-pathogen Mycobacterium smegmatis. Hence, we identify factors that represent unique vulnerabilities of the host cell, because manipulation of any one of them alone is sufficient to allow a nonpathogenic mycobacterial species to proliferate. Furthermore, we demonstrate that, in mammalian cells, the ESCRT machinery plays a conserved role in restricting bacterial growth.
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229
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Hartmann C, Chami M, Zachariae U, de Groot BL, Engel A, Grütter MG. Vacuolar protein sorting: two different functional states of the AAA-ATPase Vps4p. J Mol Biol 2008; 377:352-63. [PMID: 18272179 DOI: 10.1016/j.jmb.2008.01.010] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2007] [Revised: 12/19/2007] [Accepted: 01/04/2008] [Indexed: 10/22/2022]
Abstract
The vacuolar protein sorting (Vps) pathway, in which Vps4 class I AAA-ATPases play a central role, regulates growth factor receptors, immune response, and developmental signaling, and participates in tumor suppression, apoptosis, and retrovirus budding. We present the first atomic structure of the nucleotide-free yeast His(6)DeltaNVps4p dimer and its AMPPNP (5'-adenylyl-beta,gamma-imidodiphosphate)-bound tetradecamer, derived from a cryo electron microscopy map. Vps4p dimers form two distinct heptameric rings and accommodate AAA cassettes in a head-to-head--not in a head-to-tail-fashion as in class II AAA-ATPases. Our model suggests a mechanism for disassembling ESCRT (endosomal sorting complex required for transport) complexes by movements of substrate-binding domains located at the periphery of the tetradecamer during ATP hydrolysis in one ring, followed by translocation through the central pore and ATP hydrolysis in the second ring.
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Affiliation(s)
- Claudia Hartmann
- Institute of Biochemistry, University of Zürich, Winterthurer Strasse 190, 8057 Zürich, Switzerland
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230
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Abstract
Endocytosis, with subsequent targeting to lysosomes for degradation, is traditionally seen as a way for cells to terminate signalling. However, in a few instances, endocytosis has been demonstrated to contribute positively to signalling. Here we review recent work on the role of endocytosis in Wnt signalling. Biochemical evidence suggests that the branch of Wnt signalling that controls planar cell polarity (PCP) does require endocytosis, although how endocytosis of Frizzled receptors is translated into PCP in vivo remains unknown. With respect to the main signalling branch (called the canonical or beta-catenin pathway), the literature is divided as to whether endocytosis is required. Results of in vivo experiments are inconclusive because of the toxic side-effects of blocking endocytosis. Some results with cultured cells suggest the need for endocytosis in canonical signalling; however, it remains unclear whether the ligand-receptor complex must enter the cell by clathrin-mediated or caveolae-mediated endocytosis in order to signal. Means of specifically altering Wnt trafficking as well as of tracking the internalization route in different cell types are needed.
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Affiliation(s)
- Maria Gagliardi
- National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK
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231
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Lee TV, Ding T, Chen Z, Rajendran V, Scherr H, Lackey M, Bolduc C, Bergmann A. The E1 ubiquitin-activating enzyme Uba1 in Drosophila controls apoptosis autonomously and tissue growth non-autonomously. Development 2008; 135:43-52. [PMID: 18045837 PMCID: PMC2277323 DOI: 10.1242/dev.011288] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Ubiquitination is an essential process regulating turnover of proteins for basic cellular processes such as the cell cycle and cell death (apoptosis). Ubiquitination is initiated by ubiquitin-activating enzymes (E1), which activate and transfer ubiquitin to ubiquitin-conjugating enzymes (E2). Conjugation of target proteins with ubiquitin is then mediated by ubiquitin ligases (E3). Ubiquitination has been well characterized using mammalian cell lines and yeast genetics. However, the consequences of partial or complete loss of ubiquitin conjugation in a multi-cellular organism are not well understood. Here, we report the characterization of Uba1, the only E1 in Drosophila. We found that weak and strong Uba1 alleles behave genetically differently with sometimes opposing phenotypes. Whereas weak Uba1 alleles protect cells from cell death, clones of strong Uba1 alleles are highly apoptotic. Strong Uba1 alleles cause cell cycle arrest which correlates with failure to reduce cyclin levels. Surprisingly, clones of strong Uba1 mutants stimulate neighboring wild-type tissue to undergo cell division in a non-autonomous manner giving rise to overgrowth phenotypes of the mosaic fly. We demonstrate that the non-autonomous overgrowth is caused by failure to downregulate Notch signaling in Uba1 mutant clones. In summary, the phenotypic analysis of Uba1 demonstrates that impaired ubiquitin conjugation has significant consequences for the organism, and may implicate Uba1 as a tumor suppressor gene.
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Affiliation(s)
- Tom V. Lee
- The University of Texas M. D. Anderson Cancer Center, Department of Biochemistry and Molecular Biology, 1515 Holcombe Boulevard, Unit 1000, Houston, TX 77030, USA
- The Genes and Development Graduate Program, The University of Texas Graduate School of Biomedical Sciences, 6767 Bertner Avenue, Houston, TX 77030, USA
| | - Tian Ding
- The University of Texas M. D. Anderson Cancer Center, Department of Biochemistry and Molecular Biology, 1515 Holcombe Boulevard, Unit 1000, Houston, TX 77030, USA
- The Genes and Development Graduate Program, The University of Texas Graduate School of Biomedical Sciences, 6767 Bertner Avenue, Houston, TX 77030, USA
| | - Zhihong Chen
- The University of Texas M. D. Anderson Cancer Center, Department of Biochemistry and Molecular Biology, 1515 Holcombe Boulevard, Unit 1000, Houston, TX 77030, USA
| | - Vani Rajendran
- The University of Texas M. D. Anderson Cancer Center, Department of Biochemistry and Molecular Biology, 1515 Holcombe Boulevard, Unit 1000, Houston, TX 77030, USA
| | - Heather Scherr
- The University of Texas M. D. Anderson Cancer Center, Department of Biochemistry and Molecular Biology, 1515 Holcombe Boulevard, Unit 1000, Houston, TX 77030, USA
| | - Melinda Lackey
- The University of Texas M. D. Anderson Cancer Center, Department of Biochemistry and Molecular Biology, 1515 Holcombe Boulevard, Unit 1000, Houston, TX 77030, USA
| | - Clare Bolduc
- The University of Texas M. D. Anderson Cancer Center, Department of Biochemistry and Molecular Biology, 1515 Holcombe Boulevard, Unit 1000, Houston, TX 77030, USA
| | - Andreas Bergmann
- The University of Texas M. D. Anderson Cancer Center, Department of Biochemistry and Molecular Biology, 1515 Holcombe Boulevard, Unit 1000, Houston, TX 77030, USA
- The Genes and Development Graduate Program, The University of Texas Graduate School of Biomedical Sciences, 6767 Bertner Avenue, Houston, TX 77030, USA
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232
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Rusten TE, Vaccari T, Lindmo K, Rodahl LMW, Nezis IP, Sem-Jacobsen C, Wendler F, Vincent JP, Brech A, Bilder D, Stenmark H. ESCRTs and Fab1 regulate distinct steps of autophagy. Curr Biol 2007; 17:1817-25. [PMID: 17935992 DOI: 10.1016/j.cub.2007.09.032] [Citation(s) in RCA: 265] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2007] [Revised: 09/16/2007] [Accepted: 09/17/2007] [Indexed: 11/16/2022]
Abstract
Eukaryotes use autophagy to turn over organelles, protein aggregates, and cytoplasmic constituents. The impairment of autophagy causes developmental defects, starvation sensitivity, the accumulation of protein aggregates, neuronal degradation, and cell death [1, 2]. Double-membraned autophagosomes sequester cytoplasm and fuse with endosomes or lysosomes in higher eukaryotes [3], but the importance of the endocytic pathway for autophagy and associated disease is not known. Here, we show that regulators of endosomal biogenesis and functions play a critical role in autophagy in Drosophila melanogaster. Genetic and ultrastructural analysis showed that subunits of endosomal sorting complex required for transport (ESCRT)-I, -II and -III, as well as their regulatory ATPase Vps4 and the endosomal PtdIns(3)P 5-kinase Fab1, all are required for autophagy. Although the loss of ESCRT or Vps4 function caused the accumulation of autophagosomes, probably because of inhibited fusion with the endolysosomal system, Fab1 activity was necessary for the maturation of autolysosomes. Importantly, reduced ESCRT functions aggravated polyglutamine-induced neurotoxicity in a model for Huntington's disease. Thus, this study links ESCRT function with autophagy and aggregate-induced neurodegeneration, thereby providing a plausible explanation for the fact that ESCRT mutations are involved in inherited neurodegenerative disease in humans [4].
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Affiliation(s)
- Tor Erik Rusten
- Centre for Cancer Biomedicine, University of Oslo, N-0310 Oslo, Norway
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233
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Nickerson DP, Russell MRG, Odorizzi G. A concentric circle model of multivesicular body cargo sorting. EMBO Rep 2007; 8:644-50. [PMID: 17603537 PMCID: PMC1905901 DOI: 10.1038/sj.embor.7401004] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2006] [Accepted: 05/07/2007] [Indexed: 11/08/2022] Open
Abstract
Targeting of ubiquitylated transmembrane proteins into luminal vesicles of endosomal multivesicular bodies (MVBs) depends on their recognition by endosomal sorting complexes required for transport (ESCRTs), which are also required for MVB vesicle formation. The model originally proposed for how ESCRTs function succinctly summarizes much of the protein-protein interaction and genetic data but oversimplifies the coordination of cargo recognition and cannot explain why ESCRTs are required for the budding of MVB vesicles. Recent structural and functional studies of ESCRT complexes suggest an alternative model that might direct the next series of breakthroughs in understanding protein sorting through the MVB pathway.
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Affiliation(s)
- Daniel P Nickerson
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado, 347 UCB, Boulder, Colorado 80309-0347, USA
| | - Matthew R G Russell
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado, 347 UCB, Boulder, Colorado 80309-0347, USA
| | - Greg Odorizzi
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado, 347 UCB, Boulder, Colorado 80309-0347, USA
- Tel: +1 303 735 0179; Fax: +1 303 492 7744;
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234
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A mosaic genetic screen for Drosophila neoplastic tumor suppressor genes based on defective pupation. Genetics 2007; 177:1667-77. [PMID: 17947427 DOI: 10.1534/genetics.107.078360] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
The Drosophila neoplastic tumor suppressor genes (TSGs) coordinately control cell polarity and proliferation in epithelial and neuronal tissues. While a small group of neoplastic TSG mutations have been isolated and their corresponding genes cloned, the regulatory pathways that normally prevent inappropriate growth remain unclear. Identification of additional neoplastic TSGs may provide insight into this question. We report here the design of an efficient screen for isolating neoplastic TSG mutations utilizing genetically mosaic larvae. This screen is based on a defective pupation phenotype seen when a single pair of imaginal discs is homozygous for a neoplastic TSG mutation, which suggests that continuously proliferating cells can interfere with metamorphosis. Execution of this screen on two chromosome arms led to the identification of mutations in at least seven new neoplastic TSGs. The isolation of additional loci that affect hyperplastic as well as neoplastic growth indicates the utility of this screening strategy for studying epithelial growth control.
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235
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Malerød L, Stuffers S, Brech A, Stenmark H. Vps22/EAP30 in ESCRT-II mediates endosomal sorting of growth factor and chemokine receptors destined for lysosomal degradation. Traffic 2007; 8:1617-29. [PMID: 17714434 DOI: 10.1111/j.1600-0854.2007.00630.x] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The ubiquitin-binding protein Hrs and endosomal sorting complex required for transport (ESCRT)-I and ESCRT-III are involved in sorting endocytosed and ubiquitinated receptors to lysosomes for degradation and efficient termination of signaling. In this study, we have investigated the role of the ESCRT-II subunit Vps22/EAP30 in degradative protein sorting of ubiquitinated receptors. Vps22 transiently expressed in HeLa cells was detected in endosomes containing endocytosed epidermal growth factor receptors (EGFRs) as well as Hrs and ESCRT-I and ESCRT-III. Depletion of Vps22 by small interfering RNA, which was accompanied by decreased levels of other ESCRT-II subunits, greatly reduced degradation of EGFR and its ligand EGF as well as the chemokine receptor CXCR4. EGFR accumulated on the limiting membranes of early endosomes and aberrantly small multivesicular bodies in Vps22-depleted cells. Phosphorylation and nuclear translocation of extracellular-signal-regulated kinase1/2 downstream of the EGF-activated receptor were sustained by depletion of Hrs or the ESCRT-I subunit Tsg101. In contrast, this was not the case when Vps22 was depleted. These results indicate an important role for Vps22 in ligand-induced EGFR and CXCR4 turnover and suggest that termination of EGF signaling occurs prior to ESCRT-II engagement.
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Affiliation(s)
- Lene Malerød
- Centre for Cancer Biomedicine, University of Oslo, Montebello, N-0310 Oslo, Norway
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236
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Lee J, Basak JM, Demehri S, Kopan R. Bi-compartmental communication contributes to the opposite proliferative behavior of Notch1-deficient hair follicle and epidermal keratinocytes. Development 2007; 134:2795-806. [PMID: 17611229 PMCID: PMC2583345 DOI: 10.1242/dev.02868] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Notch1-deficient epidermal keratinocytes become progressively hyperplastic and eventually produce tumors. By contrast, Notch1-deficient hair matrix keratinocytes have lower mitotic rates, resulting in smaller follicles with fewer cells. In addition, the ratio of melanocytes to keratinocytes is greatly reduced in hair follicles. Investigation into the underlying mechanism for these phenotypes revealed significant changes in the Kit, Tgfbeta and insulin-like growth factor (IGF) signaling pathways, which have not been previously shown to be downstream of Notch signaling. The level of Kitl (Scf) mRNA produced by Notch1-deficient follicular keratinocytes was reduced when compared with wild type, resulting in a decline in melanocyte population. Tgfbeta ligands were elevated in Notch1-deficient keratinocytes, which correlated with elevated expression of several targets, including the diffusible IGF antagonist Igfbp3 in the dermal papilla. Diffusible stromal targets remained elevated in the absence of epithelial Tgfbeta receptors, consistent with paracrine Tgfbeta signaling. Overexpression of Igf1 in the keratinocyte reversed the phenotype, as expected if Notch1 loss altered the IGF/insulin-like growth factor binding protein (IGFBP) balance. Conversely, epidermal keratinocytes contained less stromal Igfbp4 and might thus be primed to experience an increase in IGF signaling as animals age. These results suggest that Notch1 participates in a bi-compartmental signaling network that controls homeostasis, follicular proliferation rates and melanocyte population within the skin.
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Affiliation(s)
- Jonghyeob Lee
- Department of Molecular Biology and Pharmacology, and Division of Dermatology, Department of Medicine, Washington University School of Medicine, Box 8103, 660 South Euclid Avenue, Saint Louis, Missouri 63110, USA
| | - Jacob M. Basak
- Department of Molecular Biology and Pharmacology, and Division of Dermatology, Department of Medicine, Washington University School of Medicine, Box 8103, 660 South Euclid Avenue, Saint Louis, Missouri 63110, USA
| | - Shadmehr Demehri
- Department of Molecular Biology and Pharmacology, and Division of Dermatology, Department of Medicine, Washington University School of Medicine, Box 8103, 660 South Euclid Avenue, Saint Louis, Missouri 63110, USA
| | - Raphael Kopan
- Department of Molecular Biology and Pharmacology, and Division of Dermatology, Department of Medicine, Washington University School of Medicine, Box 8103, 660 South Euclid Avenue, Saint Louis, Missouri 63110, USA
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237
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Leibfried A, Bellaïche Y. Functions of endosomal trafficking in Drosophila epithelial cells. Curr Opin Cell Biol 2007; 19:446-52. [PMID: 17651956 DOI: 10.1016/j.ceb.2007.06.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2007] [Revised: 05/13/2007] [Accepted: 06/08/2007] [Indexed: 12/20/2022]
Abstract
The mechanisms underlying endosomal trafficking have been mostly dissected in yeast and mammalian tissue culture cells. Here, we review recent advances in the understanding of the role of endosomal trafficking in Drosophila epithelial cells. We focus on endosomal pathways that control cell polarization, cell growth, cell fate and epithelial cell rearrangement. We expect that mechanistic studies in mammalian cells and functional studies in invertebrates will continue to synergize to provide a comprehensive view of the role of endosomal trafficking in epithelial tissue organization and functions.
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Affiliation(s)
- Andrea Leibfried
- Institut CURIE, UMR144, Cell Polarity in Drosophila, 26 rue d'Ulm, 75248 Paris, Cedex 05, France
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238
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Abstract
The Notch pathway is a highly conserved and ubiquitous signaling system that functions in determining a diverse array of cell fates and regulates many cellular processes during embryonic development and throughout adulthood. Links to cancer, stroke and Alzheimer's disease underscore the need to define the molecular basis of Notch activation. Notch signaling is induced through direct cell-cell interactions that promote receptor activation following engagement with a membrane-bound Delta, Serrate, Lag-2 (DSL) ligand on adjacent cells. Cells take on distinct fates because Notch signaling is consistently activated in only one of the two interacting cells, highlighting the importance of establishing and maintaining signaling polarity. Studies in flies and worms have identified positive and negative transcriptional feedback mechanisms that amplify small differences in Notch and DSL ligand expression to bias which cells send or receive signals. However, endocytosis by signal-sending and signal-receiving cells also appears critical for directing and regulating Notch activation. In particular, endocytosis and membrane trafficking of DSL ligands, Notch and modulators can determine the competence of cells to send or receive signals that ensure reproducibility in generating cell types regulated by Notch signaling.
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Affiliation(s)
- James T Nichols
- Department of Biological Chemistry, David Geffen School of Medicine, UCLA, 650 Charles Young Drive South, Los Angeles, CA 90095, USA
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239
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Mathieu J, Sung HH, Pugieux C, Soetaert J, Rorth P. A sensitized PiggyBac-based screen for regulators of border cell migration in Drosophila. Genetics 2007; 176:1579-90. [PMID: 17483425 PMCID: PMC1931525 DOI: 10.1534/genetics.107.071282] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Migration of border cells during Drosophila melanogaster oogenesis is a good model system for investigating the genetic requirements for cell migration in vivo. We present a sensitized loss-of-function screen used to identify new genes required in border cells for their migration. Chromosomes bearing FRTs on all four major autosomal arms were mutagenized by insertions of the transposable element PiggyBac, allowing multiple parallel clonal screens and easy identification of the mutated gene. For border cells, we analyzed homozygous mutant clones positively marked with lacZ and sensitized by expression of dominant-negative PVR, the guidance receptor. We identified new alleles of genes already known to be required for border cell migration, including aop/yan, DIAP1, and taiman as well as a conserved Slbo-regulated enhancer downstream of shg/DE-cadherin. Mutations in genes not previously described to be required in border cells were also uncovered: hrp48, vir, rme-8, kismet, and puckered. puckered was unique in that the migration defects were observed only when PVR signaling was reduced. We present evidence that an excess of JNK signaling is deleterious for migration in the absence of PVR activity at least in part through Fos transcriptional activity and possibly through antagonistic effects on DIAP1.
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240
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Abstract
The past two years have seen an explosion in the structural understanding of the endosomal sorting complex required for transport (ESCRT) machinery that facilitates the trafficking of ubiquitylated proteins from endosomes to lysosomes via multivesicular bodies (MVBs). A common organization of all ESCRTs is a rigid core attached to flexibly connected modules that recognize other components of the MVB pathway. Several previously unsuspected key links between multiple ESCRT subunits, phospholipids and ubiquitin have now been elucidated, which, together with the detailed morphological analyses of ESCRT-depletion phenotypes, provide new insights into the mechanism of MVB biogenesis.
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Affiliation(s)
- Roger L Williams
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK.
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241
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Marco E, Wedlich-Soldner R, Li R, Altschuler SJ, Wu LF. Endocytosis optimizes the dynamic localization of membrane proteins that regulate cortical polarity. Cell 2007; 129:411-22. [PMID: 17448998 PMCID: PMC2000346 DOI: 10.1016/j.cell.2007.02.043] [Citation(s) in RCA: 172] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2006] [Revised: 12/15/2006] [Accepted: 02/09/2007] [Indexed: 10/23/2022]
Abstract
Diverse cell types require the ability to maintain dynamically polarized membrane-protein distributions through balancing transport and diffusion. However, design principles underlying dynamically maintained cortical polarity are not well understood. Here we constructed a mathematical model for characterizing the morphology of dynamically polarized protein distributions. We developed analytical approaches for measuring all model parameters from single-cell experiments. We applied our methods to a well-characterized system for studying polarized membrane proteins: budding yeast cells expressing activated Cdc42. We found that a balance of diffusion, directed transport, and endocytosis was sufficient for accurately describing polarization morphologies. Surprisingly, the model predicts that polarized regions are defined with a precision that is nearly optimal for measured endocytosis rates and that polarity can be dynamically stabilized through positive feedback with directed transport. Our approach provides a step toward understanding how biological systems shape spatially precise, unambiguous cortical polarity domains using dynamic processes.
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Affiliation(s)
- Eugenio Marco
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Roland Wedlich-Soldner
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
- Max-Planck-Institute of Biochemistry, 82152 Martinsried, Germany
| | - Rong Li
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
- The Stowers Institute for Medical Research, Kansas City, MO 64112, USA
| | - Steven J. Altschuler
- Department of Pharmacology and Green Center Division for Systems Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Lani F. Wu
- Department of Pharmacology and Green Center Division for Systems Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
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242
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Sasamura T, Ishikawa HO, Sasaki N, Higashi S, Kanai M, Nakao S, Ayukawa T, Aigaki T, Noda K, Miyoshi E, Taniguchi N, Matsuno K. The O-fucosyltransferase O-fut1 is an extracellular component that is essential for the constitutive endocytic trafficking of Notch in Drosophila. Development 2007; 134:1347-1356. [PMID: 17329366 DOI: 10.1242/dev.02811] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Notch is a transmembrane receptor that mediates the cell-cell interactions necessary for many cell-fate decisions. Endocytic trafficking of Notch plays important roles in the activation and downregulation of this receptor. A Drosophila O-FucT-1 homolog, encoded by O-fut1, catalyzes the O-fucosylation of Notch, a modification essential for Notch signaling and ligand binding. It was recently proposed that O-fut1 acts as a chaperon for Notch in the endoplasmic reticulum and is required for Notch to exit the endoplasmic reticulum. Here, we report that O-fut1 has additional functions in the endocytic transportation of Notch. O-fut1 was indispensable for the constitutive transportation of Notch from the plasma membrane to the early endosome, which we show was independent of the O-fucosyltransferase activity of O-fut1. We also found that O-fut1 promoted the turnover of Notch, which consequently downregulated Notch signaling. O-fut1 formed a stable complex with the extracellular domain of Notch. In addition, O-fut1 protein added to conditioned medium and endocytosed was sufficient to rescue normal Notch transportation to the early endosome in O-fut1 knockdown cells. Thus, an extracellular interaction between Notch and O-fut1 is essential for the normal endocytic transportation of Notch. We propose that O-fut1 is the first example, except for ligands, of a molecule that is required extracellularly for receptor transportation by endocytosis.
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Affiliation(s)
- Takeshi Sasamura
- Precursory Research for Embryonic Science and Technology (PRESTO Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama, Japan
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243
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Hufnagel L, Teleman AA, Rouault H, Cohen SM, Shraiman BI. On the mechanism of wing size determination in fly development. Proc Natl Acad Sci U S A 2007; 104:3835-40. [PMID: 17360439 PMCID: PMC1820670 DOI: 10.1073/pnas.0607134104] [Citation(s) in RCA: 267] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
A fundamental and unresolved problem in animal development is the question of how a growing tissue knows when it has achieved its correct final size. A widely held view suggests that this process is controlled by morphogen gradients, which adapt to tissue size and become flatter as tissue grows, leading eventually to growth arrest. Here, we present evidence that the decapentaplegic (Dpp) morphogen distribution in the developing Drosophila wing imaginal disk does not adapt to disk size. We measure the distribution of a functional Dpp-GFP transgene and the Dpp signal transduced by phospho-Mad and show that the characteristic length scale of the Dpp profile remains approximately constant during growth. This finding suggests an alternative scenario of size determination, where disk size is determined relative to the fixed morphogen distribution by a certain threshold level of morphogen required for growth. We propose that when disk boundary reaches the threshold the arrest of cell proliferation throughout the disk is induced by mechanical stress in the tissue. Mechanical stress is expected to arise from the nonuniformity of morphogen distribution that drives growth. This stress, through a negative feedback on growth, can compensate for the nonuniformity of morphogen, achieving uniform growth with the rate that vanishes when disk boundary reaches the threshold. The mechanism is demonstrated through computer simulations of a tissue growth model that identifies the key assumptions and testable predictions. This analysis provides an alternative hypothesis for the size determination process. Novel experimental approaches will be needed to test this model.
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Affiliation(s)
- Lars Hufnagel
- *Kavli Institute for Theoretical Physics, Kohn Hall, University of California, Santa Barbara, CA 93106
| | - Aurelio A. Teleman
- European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany; and
| | - Hervé Rouault
- Laboratoire de Physique Statistique, Ecole Normale Superieure, 24 Rue Lhomond, Paris Cedex 5, France
| | - Stephen M. Cohen
- European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany; and
| | - Boris I. Shraiman
- *Kavli Institute for Theoretical Physics, Kohn Hall, University of California, Santa Barbara, CA 93106
- To whom correspondence should be addressed. E-mail:
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244
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de Souza N, Vallier LG, Fares H, Greenwald I. SEL-2, theC. elegansneurobeachin/LRBA homolog, is a negative regulator oflin-12/Notchactivity and affects endosomal traffic in polarized epithelial cells. Development 2007; 134:691-702. [PMID: 17215302 DOI: 10.1242/dev.02767] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The vulval precursor cells (VPCs) of Caenorhabditis elegans are polarized epithelial cells that adopt a precise pattern of fates through regulated activity of basolateral LET-23/EGF receptor and apical LIN-12/Notch. During VPC patterning, there is reciprocal modulation of endocytosis and trafficking of both LET-23 and LIN-12. We identified sel-2 as a negative regulator of lin-12/Notch activity in the VPCs, and found that SEL-2 is the homolog of two closely related human proteins, neurobeachin(also known as BCL8B) and LPS-responsive, beige-like anchor protein (LRBA). SEL-2, neurobeachin and LRBA belong to a distinct subfamily of BEACH-WD40 domain-containing proteins. Loss of sel-2 activity leads to basolateral mislocalization and increased accumulation of LIN-12 in VPCs in which LET-23 is not active, and to impaired downregulation of basolateral LET-23 in VPCs in which LIN-12 is active. Downregulation of apical LIN-12 in the VPC in which LET-23 is active is not affected. In addition, in sel-2 mutants, the polarized cells of the intestinal epithelium display an aberrant accumulation of the lipophilic dye FM4-64 when the dye is presented to the basolateral surface. Our observations indicate that SEL-2/neurobeachin/LRBA is involved in endosomal traffic and may be involved in efficient delivery of cell surface proteins to the lysosome. Our results also suggest that sel-2 activity may contribute to the appropriate steady-state level of LIN-12 or to trafficking events that affect receptor activation.
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Affiliation(s)
- Natalie de Souza
- Department of Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute, 701 W. 168th Street, Hammer Health Sciences, New York, NY 10032, USA
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245
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Irion U, St Johnston D. bicoid RNA localization requires specific binding of an endosomal sorting complex. Nature 2007; 445:554-8. [PMID: 17268469 PMCID: PMC1997307 DOI: 10.1038/nature05503] [Citation(s) in RCA: 146] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2006] [Accepted: 12/01/2006] [Indexed: 11/09/2022]
Abstract
bicoid messenger RNA localizes to the anterior of the Drosophila egg, where it is translated to form a morphogen gradient of Bicoid protein that patterns the head and thorax of the embryo. Although bicoid was the first localized cytoplasmic determinant to be identified, little is known about how the mRNA is coupled to the microtubule-dependent transport pathway that targets it to the anterior, and it has been proposed that the mRNA is recognized by a complex of many redundant proteins, each of which binds to the localization element in the 3' untranslated region (UTR) with little or no specificity. Indeed, the only known RNA-binding protein that co-localizes with bicoid mRNA is Staufen, which binds non-specifically to double-stranded RNA in vitro. Here we show that mutants in all subunits of the ESCRT-II complex (VPS22, VPS25 and VPS36) abolish the final Staufen-dependent step in bicoid mRNA localization. ESCRT-II is a highly conserved component of the pathway that sorts ubiquitinated endosomal proteins into internal vesicles, and functions as a tumour-suppressor by removing activated receptors from the cytoplasm. However, the role of ESCRT-II in bicoid localization seems to be independent of endosomal sorting, because mutations in ESCRT-I and III components do not affect the targeting of bicoid mRNA. Instead, VPS36 functions by binding directly and specifically to stem-loop V of the bicoid 3' UTR through its amino-terminal GLUE domain, making it the first example of a sequence-specific RNA-binding protein that recognizes the bicoid localization signal. Furthermore, VPS36 localizes to the anterior of the oocyte in a bicoid-mRNA-dependent manner, and is required for the subsequent recruitment of Staufen to the bicoid complex. This function of ESCRT-II as an RNA-binding complex is conserved in vertebrates and may clarify some of its roles that are independent of endosomal sorting.
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Affiliation(s)
| | - Daniel St Johnston
- Wellcome Trust/Cancer Research UK Gurdon Institute and Department of Genetics University of Cambridge Tennis Court Road Cambridge CB2 1QN United Kingdom
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246
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Wang X, Shaw WR, Tsang HTH, Reid E, O'Kane CJ. Drosophila spichthyin inhibits BMP signaling and regulates synaptic growth and axonal microtubules. Nat Neurosci 2007; 10:177-85. [PMID: 17220882 PMCID: PMC2464677 DOI: 10.1038/nn1841] [Citation(s) in RCA: 150] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2006] [Accepted: 12/27/2006] [Indexed: 11/09/2022]
Abstract
To understand the functions of NIPA1, mutated in the neurodegenerative disease hereditary spastic paraplegia, and of ichthyin, mutated in autosomal recessive congenital ichthyosis, we have studied their Drosophila melanogaster ortholog, spichthyin (Spict). Spict is found on early endosomes. Loss of Spict leads to upregulation of bone morphogenetic protein (BMP) signaling and expansion of the neuromuscular junction. BMP signaling is also necessary for a normal microtubule cytoskeleton and axonal transport; analysis of loss- and gain-of-function phenotypes indicate that Spict may antagonize this function of BMP signaling. Spict interacts with BMP receptors and promotes their internalization from the plasma membrane, implying that it inhibits BMP signaling by regulating BMP receptor traffic. This is the first demonstration of a role for a hereditary spastic paraplegia protein or ichthyin family member in a specific signaling pathway, and implies disease mechanisms for hereditary spastic paraplegia that involve dependence of the microtubule cytoskeleton on BMP signaling.
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Affiliation(s)
- Xinnan Wang
- Department of Genetics, University of Cambridge, Downing Street, Cambridge, CB2 3EH, UK
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247
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Luque CM, Milán M. Growth control in the proliferative region of the Drosophila eye–head primordium: The elbow–noc gene complex. Dev Biol 2007; 301:327-39. [PMID: 17014842 DOI: 10.1016/j.ydbio.2006.07.050] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2006] [Revised: 07/27/2006] [Accepted: 07/28/2006] [Indexed: 11/25/2022]
Abstract
Notch signaling is involved in cell differentiation and patterning, as well as in the regulation of growth and cell survival. Notch activation at the dorsal-ventral boundary of the Drosophila eye-head primordium leads to the expression of the secreted protein Unpaired, a ligand of the JAK-STAT pathway that induces cell proliferation in the undifferentiated tissue. The zinc finger proteins encoded by elbow and no ocelli are expressed in the highly proliferative region of the eye-head primordium. Loss of elbow and no ocelli activities induces overgrowths of the head capsule, without inducing Upd expression de novo. These overgrowths depend on Notch activity suggesting that elbow and noc repress a Upd independent role of Notch in driving cell proliferation. When the size of the overgrown tissue is increased, ectopic antenna and eye structures can be found. Thus, tight regulation of the size of the eye-head primordium by elbow and no ocelli is crucial for proper fate specification and generation of the adult structures.
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Affiliation(s)
- Carlos M Luque
- ICREA and Institute for Research in Biomedicine (IRB), Parc Científic de Barcelona, Josep Samitier, 1-5, 08028 Barcelona, Spain
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248
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Abstract
Genetic defects of the endosomal 'ESCRT' machinery in Drosophila have been found to cause loss of epithelial cell polarity, accompanied by overproliferation of mutant and adjacent wild-type cells. These results can be attributed to defective endocytosis of transmembrane proteins that control cell polarity and proliferation, including Crumbs and Notch.
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Affiliation(s)
- Bernd Giebel
- Institute for Transplantation Diagnostics and Cell Therapeutics, Heinrich-Heine-University Düsseldorf, Moorenstr. 5, Geb. 14.80, 40225 Düsseldorf, Germany
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249
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Abstract
Inactivating mutations in the Drosophila tumor-suppressor genes result in tissue overgrowth. This can occur because the mutant tissue either grows faster than wild-type tissue and/or continues to grow beyond a time when wild-type tissue stops growing. There are three general classes of tumor-suppressor genes that regulate the growth of imaginal disc epithelia. Mutations in the hyperplastic tumor-suppressor genes result in increased cell proliferation but do not disrupt normal tissue architecture. These genes include pten, Tsc1, Tsc2, and components of the hippo/salvador/warts pathway. Mutations in a second class of genes, the neoplastic tumor-suppressor genes, disrupt proteins that function either as scaffolds at cell-cell junctions (scribble, discs large, lgl) or as components of the endocytic pathway (avalanche, rab5, ESCRT components). For the third group, the nonautonomous tumor-suppressor genes, mutant cells stimulate the proliferation of adjacent wild-type cells. Understanding the interactions between these three classes of genes will improve our understanding of how cell and tissue growth are coordinated during organismal development and perturbed in disease states such as cancer.
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Affiliation(s)
- Iswar K Hariharan
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California 94720, USA.
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250
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Curtiss M, Jones C, Babst M. Efficient cargo sorting by ESCRT-I and the subsequent release of ESCRT-I from multivesicular bodies requires the subunit Mvb12. Mol Biol Cell 2006; 18:636-45. [PMID: 17135292 PMCID: PMC1783790 DOI: 10.1091/mbc.e06-07-0588] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The endosomal sorting complex required for transport (ESCRT)-I protein complex functions in recognition and sorting of ubiquitinated transmembrane proteins into multivesicular body (MVB) vesicles. It has been shown that ESCRT-I contains the vacuolar protein sorting (Vps) proteins Vps23, Vps28, and Vps37. We identified an additional subunit of yeast ESCRT-I called Mvb12, which seems to associate with ESCRT-I by binding to Vps37. Transient recruitment of ESCRT-I to MVBs results in the rapid degradation of Mvb12. In contrast to mutations in other ESCRT-I subunits, which result in strong defects in MVB cargo sorting, deletion of MVB12 resulted in only a partial sorting phenotype. This trafficking defect was fully suppressed by overexpression of the ESCRT-II complex. Mutations in MVB12 did not affect recruitment of ESCRT-I to MVBs, but they did result in delivery of ESCRT-I to the vacuolar lumen via the MVB pathway. Together, these observations suggest that Mvb12 may function in regulating the interactions of ESCRT-I with cargo and other proteins of the ESCRT machinery to efficiently coordinate cargo sorting and release of ESCRT-I from the MVB.
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Affiliation(s)
- Matt Curtiss
- Department of Biology, University of Utah, Salt Lake City, UT 84112-9202
| | - Charles Jones
- Department of Biology, University of Utah, Salt Lake City, UT 84112-9202
| | - Markus Babst
- Department of Biology, University of Utah, Salt Lake City, UT 84112-9202
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