201
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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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202
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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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203
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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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204
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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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205
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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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206
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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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207
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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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208
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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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209
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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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210
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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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211
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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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212
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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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213
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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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214
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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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215
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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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216
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Doronkin S, Reiter LT. Drosophila orthologues to human disease genes: an update on progress. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 2008; 82:1-32. [PMID: 18929137 DOI: 10.1016/s0079-6603(08)00001-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Affiliation(s)
- Sergey Doronkin
- Department of Neurology, Univeristy of Tennessee Health Science Center, Memphis, Tennessee 38163, USA
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217
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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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218
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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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219
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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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220
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Devergne O, Ghiglione C, Noselli S. The endocytic control of JAK/STAT signalling in Drosophila. J Cell Sci 2007; 120:3457-64. [PMID: 17855388 DOI: 10.1242/jcs.005926] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Domeless (Dome) is an IL-6-related cytokine receptor that activates a conserved JAK/STAT signalling pathway during Drosophila development. Despite good knowledge of the signal transduction pathway in several models, the role of receptor endocytosis in JAK/STAT activation remains poorly understood. Using both in vivo genetic analysis and cell culture assays, we show that ligand binding of Unpaired 1 (Upd1) induces clathrin-dependent endocytosis of receptor-ligand complexes and their subsequent trafficking through the endosomal compartment towards the lysosome. Surprisingly, blocking trafficking in distinct endosomal compartments using mutants affecting either Clathrin heavy chain, rab5, Hrs or deep orange led to an inhibition of the JAK/STAT pathway, whereas this pathway was unchanged when rab11 was affected. This suggests that internalization and trafficking are both required for JAK/STAT activity. The requirement for clathrin-dependent endocytosis to activate JAK/STAT signalling suggests a model in which the signalling `on' state relies not only on ligand binding to the receptor at the cell surface, but also on the recruitment of the complex into endocytic vesicles on their way to lysozomes. Selective activation of the pool of receptors marked for degradation thus provides a way to tightly control JAK/STAT activity.
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Affiliation(s)
- Olivier Devergne
- Institute of Developmental Biology and Cancer, CNRS-UMR 6543, University of Nice Sophia-Antipolis, Parc Valrose 06108 Nice cedex 2, France
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221
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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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222
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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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223
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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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224
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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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225
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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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226
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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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227
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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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228
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Hurlbut GD, Kankel MW, Lake RJ, Artavanis-Tsakonas S. Crossing paths with Notch in the hyper-network. Curr Opin Cell Biol 2007; 19:166-75. [PMID: 17317139 DOI: 10.1016/j.ceb.2007.02.012] [Citation(s) in RCA: 183] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2007] [Accepted: 02/09/2007] [Indexed: 12/31/2022]
Abstract
The development of complex and diverse metazoan morphologies is coordinated by a surprisingly small number of evolutionarily conserved signaling mechanisms. These signals can act in parallel but often appear to function as an integrated hyper-network. The nodes defining this complex molecular circuitry are poorly understood, but the biological significance of pathway cross-talk is profound. The importance of such large-scale signal integration is exemplified by Notch and its ability to cross-talk with all the major pathways to influence cell differentiation, proliferation, survival and migration. The Notch pathway is, thus, a useful paradigm to illustrate the complexity of pathway cross-talk: its pervasiveness, context dependency, and importance in development and disease.
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Affiliation(s)
- Gregory D Hurlbut
- Department of Cell Biology, Harvard Medical School, Massachusetts General Hospital Cancer Center, Charlestown, Massachusetts, USA
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229
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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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230
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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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231
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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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232
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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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233
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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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234
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Childress JL, Acar M, Tao C, Halder G. Lethal giant discs, a novel C2-domain protein, restricts notch activation during endocytosis. Curr Biol 2006; 16:2228-33. [PMID: 17088062 PMCID: PMC2683616 DOI: 10.1016/j.cub.2006.09.031] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2006] [Revised: 09/07/2006] [Accepted: 09/14/2006] [Indexed: 11/27/2022]
Abstract
The Notch signaling pathway plays a central role in animal growth and patterning, and its deregulation leads to many human diseases, including cancer. Mutations in the tumor suppressor lethal giant discs (lgd) induce strong Notch activation and hyperplastic overgrowth of Drosophila imaginal discs. However, the gene that encodes Lgd and its function in the Notch pathway have not yet been identified. Here, we report that Lgd is a novel, conserved C2-domain protein that regulates Notch receptor trafficking. Notch accumulates on early endosomes in lgd mutant cells and signals in a ligand-independent manner. This phenotype is similar to that seen when cells lose endosomal-pathway components such as Erupted and Vps25. Interestingly, Notch activation in lgd mutant cells requires the early endosomal component Hrs, indicating that Hrs is epistatic to Lgd. These data suggest that Lgd affects Notch trafficking between the actions of Hrs and the late endosomal component Vps25. Taken together, our data identify Lgd as a novel tumor-suppressor protein that regulates Notch signaling by targeting Notch for degradation or recycling.
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Affiliation(s)
- Jennifer L. Childress
- Department of Biochemistry and Molecular Biology, M.D. Anderson Cancer Center, University of Texas, Houston, Texas 77030 USA
- Program in Genes and Development, M.D. Anderson Cancer Center, University of Texas, Houston, Texas 77030 USA
| | - Melih Acar
- Program in Developmental Biology, Baylor College of Medicine, Houston, TX 77030 USA
| | - Chunyao Tao
- Department of Biochemistry and Molecular Biology, M.D. Anderson Cancer Center, University of Texas, Houston, Texas 77030 USA
| | - Georg Halder
- Department of Biochemistry and Molecular Biology, M.D. Anderson Cancer Center, University of Texas, Houston, Texas 77030 USA
- Program in Genes and Development, M.D. Anderson Cancer Center, University of Texas, Houston, Texas 77030 USA
- Program in Developmental Biology, Baylor College of Medicine, Houston, TX 77030 USA
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235
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Gallagher CM, Knoblich JA. The Conserved C2 Domain Protein Lethal (2) Giant Discs Regulates Protein Trafficking in Drosophila. Dev Cell 2006; 11:641-53. [PMID: 17084357 DOI: 10.1016/j.devcel.2006.09.014] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2006] [Revised: 07/11/2006] [Accepted: 09/15/2006] [Indexed: 10/23/2022]
Abstract
Drosophila sensory organ precursor (SOP) cells undergo several rounds of asymmetric cell division to generate the four different cell types that make up external sensory organs. Establishment of different fates among daughter cells of the SOP relies on differential regulation of the Notch pathway. Here, we identify the protein Lethal (2) giant discs (Lgd) as a critical regulator of Notch signaling in the SOP lineage. We show that lgd encodes a conserved C2 domain protein that binds to phospholipids present on early endosomes. When Lgd function is compromised, Notch and other transmembrane proteins accumulate in enlarged early endosomal compartments. These enlarged endosomes are positive for Rab5 and Hrs, a protein involved in trafficking into the degradative pathway. Our experiments suggest that Lgd is a critical regulator of endocytosis that is not present in yeast and acts in the degradative pathway after Hrs.
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Affiliation(s)
- Ciara M Gallagher
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Dr Bohr Gasse 3, 1030 Vienna, Austria
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236
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Jaekel R, Klein T. The Drosophila Notch Inhibitor and Tumor Suppressor Gene lethal (2) giant discs Encodes a Conserved Regulator of Endosomal Trafficking. Dev Cell 2006; 11:655-69. [PMID: 17084358 DOI: 10.1016/j.devcel.2006.09.019] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2006] [Revised: 07/12/2006] [Accepted: 09/21/2006] [Indexed: 11/19/2022]
Abstract
Notch signaling is involved in many developmental and pathological processes, and its activity must be precisely controlled in order to prevent aberrant development and disease. We have previously shown that the tumor suppressor gene lethal (2) giant discs (lgd) is required to prevent ectopic activation of Notch in developmental processes in Drosophila. Here we show that lgd is required in all imaginal disc cells to suppress the activity of the Notch pathway. lgd encodes a member of a poorly characterized protein family present in all animals, which includes a member that is involved in an inheritable form of mental retardation in humans. Our analysis reveals that Lgd is required for endosomal trafficking of Notch and other proteins. In the absence of Lgd, Notch is activated in a ligand-independent manner in probably all imaginal disc cells in an endosomal compartment downstream of the block in hrs mutants.
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Affiliation(s)
- Robert Jaekel
- Institute for Genetics, University of Cologne, Zülpicherstrasse 47, 50674 Cologne, Germany
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237
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Langelier C, von Schwedler UK, Fisher RD, De Domenico I, White PL, Hill CP, Kaplan J, Ward D, Sundquist WI. Human ESCRT-II complex and its role in human immunodeficiency virus type 1 release. J Virol 2006; 80:9465-80. [PMID: 16973552 PMCID: PMC1617254 DOI: 10.1128/jvi.01049-06] [Citation(s) in RCA: 138] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The budding of many enveloped RNA viruses, including human immunodeficiency virus type 1 (HIV-1), requires some of the same cellular machinery as vesicle formation at the multivesicular body (MVB). In Saccharomyces cerevisiae, the ESCRT-II complex performs a central role in MVB protein sorting and vesicle formation, as it is recruited by the upstream ESCRT-I complex and nucleates assembly of the downstream ESCRT-III complex. Here, we report that the three subunits of human ESCRT-II, EAP20, EAP30, and EAP45, have a number of properties in common with their yeast orthologs. Specifically, EAP45 bound ubiquitin via its N-terminal GRAM-like ubiquitin-binding in EAP45 (GLUE) domain, both EAP45 and EAP30 bound the C-terminal domain of TSG101/ESCRT-I, and EAP20 bound the N-terminal half of CHMP6/ESCRT-III. Consistent with its expected role in MVB vesicle formation, (i) human ESCRT-II localized to endosomal membranes in a VPS4-dependent fashion and (ii) depletion of EAP20/ESCRT-II and CHMP6/ESCRT-III inhibited lysosomal targeting and downregulation of the epidermal growth factor receptor, albeit to a lesser extent than depletion of TSG101/ESCRT-I. Nevertheless, HIV-1 release and infectivity were not reduced by efficient small interfering RNA depletion of EAP20/ESCRT-II or CHMP6/ESCRT-III. These observations indicate that there are probably multiple pathways for protein sorting/MVB vesicle formation in human cells and that HIV-1 does not utilize an ESCRT-II-dependent pathway to leave the cell.
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Affiliation(s)
- Charles Langelier
- Department of Biochemistry, 15 N. Medical Drive East, Room 4100, University of Utah School of Medicine, Salt Lake City, UT 84112-5650, USA
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238
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Lu X, Liu S, Kornberg TB. The C-terminal tail of the Hedgehog receptor Patched regulates both localization and turnover. Genes Dev 2006; 20:2539-51. [PMID: 16980583 PMCID: PMC1578677 DOI: 10.1101/gad.1461306] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Patched (Ptc) is a membrane protein whose function in Hedgehog (Hh) signal transduction has been conserved among metazoans and whose malfunction has been implicated in human cancers. Genetic analysis has shown that Ptc negatively regulates Hh signal transduction, but its activity and structure are not known. We investigated the functional and structural properties of Drosophila Ptc and its C-terminal domain (CTD), 183 residues that are predicted to reside in the cytoplasm. Our results show that Ptc, as well as truncated Ptc deleted of its CTD, forms a stable trimer. This observation is consistent with the proposal that Ptc is structurally similar to trimeric transporters. The CTD itself trimerizes and is required for both Ptc internalization and turnover. Two mutant forms of the CTD, one that disrupts trimerization and the other that mutates the target sequence of the Nedd4 ubiquitin ligase, stabilize Ptc but do not prevent internalization and sequestration of Hh. Ptc deleted of its CTD is stable and localizes to the plasma membrane. These data show that degradation of Ptc is regulated at a step subsequent to endocytosis, although endocytosis is a likely prerequisite. We also show that the CTD of mouse Ptc regulates turnover.
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Affiliation(s)
- Xingwu Lu
- Department of Biochemistry and Biophysics, University of California at San Francisco, 94143, USA
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239
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Cheng TH, Cohen SN. Human MDM2 isoforms translated differentially on constitutive versus p53-regulated transcripts have distinct functions in the p53/MDM2 and TSG101/MDM2 feedback control loops. Mol Cell Biol 2006; 27:111-9. [PMID: 17060450 PMCID: PMC1800643 DOI: 10.1128/mcb.00235-06] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Proteins encoded by the mdm2 gene, which has a pivotal role in the regulation of growth and differentiation, exist principally in human and murine cells as two isoforms that migrate in gels as 75-kDa and 90-kDa proteins. There is limited understanding of the respective biological roles of these isoforms, their molecular nature, and their mechanism of formation. We report here that human p75(MDM2) is an N-terminally truncated mixture of protein isoforms produced by the initiation of translation at two distinct internal AUG codons. The p75(MDM2) doublets and p90(MDM2), which is the full-length MDM2 protein, are expressed in approximately equal amounts from transcripts initiated at the constitutive P1 promoter of mdm2. Unlike murine transcripts initiated at the p53-activated P2 promoter, human cell transcripts initiated at the P2 promoter preferentially produce p90(MDM2). The ubiquitin enzyme variant protein TSG101, which interacts functionally with MDM2 in an autoregulatory loop that parallels the p53/MDM2 feedback control loop, interferes with degradation of both isoforms; however, only p90(MDM2) promotes proteolysis of TSG101 and p53. Our results reveal the mechanism of formation of the principal MDM2 isoforms, the differential effects of p53 on the production of these isoforms, and the differential abilities of human MDM2 isoforms as regulators of the MDM2/TSG101 and p53/MDM2 feedback control loops.
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Affiliation(s)
- Tzu-Hao Cheng
- Stanford University School of Medicine, Department of Genetics, 300 Pasteur Drive, Stanford, CA 94305-5120, USA
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240
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Voutev R, Killian DJ, Ahn JH, Hubbard EJA. Alterations in ribosome biogenesis cause specific defects in C. elegans hermaphrodite gonadogenesis. Dev Biol 2006; 298:45-58. [PMID: 16876152 DOI: 10.1016/j.ydbio.2006.06.011] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2006] [Revised: 05/21/2006] [Accepted: 06/02/2006] [Indexed: 12/16/2022]
Abstract
Ribosome biogenesis is a cell-essential process that influences cell growth, proliferation, and differentiation. How ribosome biogenesis impacts development, however, is poorly understood. Here, we establish a link between ribosome biogenesis and gonadogenesis in Caenorhabditis elegans that affects germline proliferation and patterning. Previously, we determined that pro-1(+)activity is required in the soma--specifically, the sheath/spermatheca sublineage--to promote normal proliferation and prevent germline tumor formation. Here, we report that PRO-1, like its yeast ortholog IPI3, influences rRNA processing. pro-1 tumors are suppressed by mutations in ncl-1 or lin-35/Rb, both of which elevate pre-rRNA levels. Thus, in this context, lin-35/Rb acts as a soma-autonomous germline tumor promoter. We further report the characterization of two additional genes identified for their germline tumor phenotype, pro-2 and pro-3, and find that they, too, encode orthologs of proteins involved in ribosome biogenesis in yeast (NOC2 and SDA1, respectively). Finally, we demonstrate that depletion of additional C. elegans orthologs of yeast ribosome biogenesis factors display phenotypes similar to depletion of progenes. We conclude that the C. elegans distal sheath is particularly sensitive to alterations in ribosome biogenesis and that ribosome biogenesis defects in one tissue can non-autonomously influence proliferation in an adjacent tissue.
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Affiliation(s)
- Roumen Voutev
- Department of Biology, New York University, New York, NY 10003-6688, USA
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241
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Arbouzova NI, Zeidler MP. JAK/STAT signalling in Drosophila: insights into conserved regulatory and cellular functions. Development 2006; 133:2605-16. [PMID: 16794031 DOI: 10.1242/dev.02411] [Citation(s) in RCA: 306] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
High levels of interspecies conservation characterise all signal transduction cascades and demonstrate the significance of these pathways over evolutionary time. Here, we review advances in the field of JAK/STAT signalling, focusing on recent developments in Drosophila. In particular, recent results from genetic and genome-wide RNAi screens, as well as studies into the developmental roles played by this pathway, highlight striking levels of physical and functional conservation in processes such as cellular proliferation, immune responses and stem cell maintenance. These insights underscore the value of model organisms for improving our understanding of this human disease-relevant pathway.
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Affiliation(s)
- Natalia I Arbouzova
- Department of Molecular Developmental Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
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242
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Rusten TE, Rodahl LM, Pattni K, Englund C, Samakovlis C, Dove S, Brech A, Stenmark H. Fab1 phosphatidylinositol 3-phosphate 5-kinase controls trafficking but not silencing of endocytosed receptors. Mol Biol Cell 2006; 17:3989-4001. [PMID: 16837550 PMCID: PMC1556381 DOI: 10.1091/mbc.e06-03-0239] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2006] [Revised: 06/13/2006] [Accepted: 07/03/2006] [Indexed: 11/11/2022] Open
Abstract
The trafficking of endocytosed receptors through phosphatidylinositol 3-phosphate [PtdIns(3)P]-containing endosomes is thought to attenuate their signaling. Here, we show that the PtdIns(3)P 5-kinase Fab1/PIKfyve controls trafficking but not silencing of endocytosed receptors. Drosophila fab1 mutants contain undetectable phosphatidylinositol 3,5-bisphosphate levels, show profound increases in cell and organ size, and die at the pupal stage. Mutant larvae contain highly enlarged multivesicular bodies and late endosomes that are inefficiently acidified. Clones of fab1 mutant cells accumulate Wingless and Notch, similarly to cells lacking Hrs, Vps25, and Tsg101, components of the endosomal sorting machinery for ubiquitinated membrane proteins. However, whereas hrs, vps25, and tsg101 mutant cell clones accumulate ubiquitinated cargo, this is not the case with fab1 mutants. Even though endocytic receptor trafficking is impaired in fab1 mutants, Notch, Wingless, and Dpp signaling is unaffected. We conclude that Fab1, despite its importance for endosomal functions, is not required for receptor silencing. This is consistent with the possibility that Fab1 functions at a late stage in endocytic receptor trafficking, at a point when signal termination has occurred.
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Affiliation(s)
- Tor Erik Rusten
- *Department of Biochemistry, The Norwegian Radium Hospital and the University of Oslo, Montebello, N-0310 Oslo, Norway
| | - Lina M.W. Rodahl
- *Department of Biochemistry, The Norwegian Radium Hospital and the University of Oslo, Montebello, N-0310 Oslo, Norway
| | - Krupa Pattni
- *Department of Biochemistry, The Norwegian Radium Hospital and the University of Oslo, Montebello, N-0310 Oslo, Norway
| | - Camilla Englund
- Department of Developmental Biology, Wenner-Gren Institute, Stockholm University, S-106 91 Stockholm, Sweden; and
| | - Christos Samakovlis
- Department of Developmental Biology, Wenner-Gren Institute, Stockholm University, S-106 91 Stockholm, Sweden; and
| | - Stephen Dove
- Department of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
| | - Andreas Brech
- *Department of Biochemistry, The Norwegian Radium Hospital and the University of Oslo, Montebello, N-0310 Oslo, Norway
| | - Harald Stenmark
- *Department of Biochemistry, The Norwegian Radium Hospital and the University of Oslo, Montebello, N-0310 Oslo, Norway
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243
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Abstract
A small number of signalling pathways are used iteratively to regulate cell fates, cell proliferation and cell death in development. Notch is the receptor in one such pathway, and is unusual in that most of its ligands are also transmembrane proteins; therefore signalling is restricted to neighbouring cells. Although the intracellular transduction of the Notch signal is remarkably simple, with no secondary messengers, this pathway functions in an enormous diversity of developmental processes and its dysfunction is implicated in many cancers.
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Affiliation(s)
- Sarah J Bray
- Department of Physiology, Development and Neuroscience, University of Cambridge, Downing Street, Cambridge CB2 3DY, UK.
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244
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Emery G, Knoblich JA. Endosome dynamics during development. Curr Opin Cell Biol 2006; 18:407-15. [PMID: 16806877 DOI: 10.1016/j.ceb.2006.06.009] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2006] [Accepted: 06/08/2006] [Indexed: 10/24/2022]
Abstract
Endocytosis has traditionally been studied in isolated cells. More recently, however, the analysis of protein trafficking in whole organisms has revealed that it plays exciting roles during development. Endocytic trafficking of cell adhesion molecules regulates epithelial polarity and cell migration. Developmental signaling pathways are regulated by the trafficking of receptors and their ligands through the endocytic pathway. Finally, impairment of the endocytic machinery can affect proliferation control and contribute to tumor development.
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Affiliation(s)
- Gregory Emery
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Dr Bohr Gasse 3, 1030 Vienna, Austria
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245
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Slagsvold T, Pattni K, Malerød L, Stenmark H. Endosomal and non-endosomal functions of ESCRT proteins. Trends Cell Biol 2006; 16:317-26. [PMID: 16716591 DOI: 10.1016/j.tcb.2006.04.004] [Citation(s) in RCA: 188] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2006] [Revised: 03/16/2006] [Accepted: 04/13/2006] [Indexed: 12/30/2022]
Abstract
The three endosomal sorting complexes required for transport (ESCRTs) are integral to the degradation of endocytosed membrane proteins and multivesicular body (MVB) biogenesis. Here, we review evidence that ESCRTs have evolved as a specialized machinery for the degradative sorting of ubiquitinated membrane proteins and we highlight recent studies that have shed light on the mechanisms by which these complexes mediate protein sorting, MVB biogenesis, tumour suppression and viral budding. We also discuss evidence that some ESCRT subunits have evolved additional functions that are unrelated to membrane trafficking.
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Affiliation(s)
- Thomas Slagsvold
- Department of Biochemistry, the Norwegian Radium Hospital and the University of Oslo, Montebello, N-0310 Oslo, Norway
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246
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Sweeney NT, Brenman JE, Jan YN, Gao FB. The Coiled-Coil Protein Shrub Controls Neuronal Morphogenesis in Drosophila. Curr Biol 2006; 16:1006-11. [PMID: 16713958 DOI: 10.1016/j.cub.2006.03.067] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2006] [Accepted: 03/23/2006] [Indexed: 11/18/2022]
Abstract
The diversity of neuronal cells, especially in the size and shape of their dendritic and axonal arborizations, is a striking feature of the mature nervous system. Dendritic branching is a complex process, and the underlying signaling mechanisms remain to be further defined at the mechanistic level. Here we report the identification of shrub mutations that increased dendritic branching. Single-cell clones of shrub mutant dendritic arborization (DA) sensory neurons in Drosophila larvae showed ectopic dendritic and axonal branching, indicating a cell-autonomous function for shrub in neuronal morphogenesis. shrub encodes an evolutionarily conserved coiled-coil protein homologous to the yeast protein Snf7, a key component in the ESCRT-III (endosomal sorting complex required for transport) complex that is involved in the formation of endosomal compartments known as multivesicular bodies (MVBs). We found that mouse orthologs could substitute for Shrub in mutant Drosophila embryos and that loss of Shrub function caused abnormal distribution of several early or late endosomal markers in DA sensory neurons. Our findings demonstrate that the novel coiled-coil protein Shrub functions in the endosomal pathway and plays an essential role in neuronal morphogenesis.
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Affiliation(s)
- Neal T Sweeney
- Gladstone Institute of Neurological Disease, University of California, San Francisco, San Francisco, California 94158, USA
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247
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Herz HM, Chen Z, Scherr H, Lackey M, Bolduc C, Bergmann A. vps25 mosaics display non-autonomous cell survival and overgrowth, and autonomous apoptosis. Development 2006; 133:1871-80. [PMID: 16611691 PMCID: PMC2519036 DOI: 10.1242/dev.02356] [Citation(s) in RCA: 138] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Appropriate cell-cell signaling is crucial for proper tissue homeostasis. Protein sorting of cell surface receptors at the early endosome is important for both the delivery of the signal and the inactivation of the receptor, and its alteration can cause malignancies including cancer. In a genetic screen for suppressors of the pro-apoptotic gene hid in Drosophila, we identified two alleles of vps25, a component of the ESCRT machinery required for protein sorting at the early endosome. Paradoxically, although vps25 mosaics were identified as suppressors of hid-induced apoptosis, vps25 mutant cells die. However, we provide evidence that a non-autonomous increase of Diap1 protein levels, an inhibitor of apoptosis, accounts for the suppression of hid. Furthermore, before they die, vps25 mutant clones trigger non-autonomous proliferation through a failure to downregulate Notch signaling, which activates the mitogenic JAK/STAT pathway. Hid and JNK contribute to apoptosis of vps25 mutant cells. Inhibition of cell death in vps25 clones causes dramatic overgrowth phenotypes. In addition, Hippo signaling is increased in vps25 clones, and hippo mutants block apoptosis in vps25 clones. In summary, the phenotypic analysis of vps25 mutants highlights the importance of receptor downregulation by endosomal protein sorting for appropriate tissue homeostasis, and may serve as a model for human cancer.
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Affiliation(s)
- Hans-Martin Herz
- University of Heidelberg/ZMBH, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany
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248
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Abstract
Signals through the Notch receptors are used throughout development to control cellular fate choices. Loss- and gain-of-function studies revealed both the pleiotropic action of the Notch signalling pathway in development and the potential of Notch signals as tools to influence the developmental path of undifferentiated cells. As we review here, Notch signalling affects the development of the nervous system at many different levels. Understanding the complex genetic circuitry that allows Notch signals to affect specific cell fates in a context-specific manner defines the next challenge, especially as such an understanding might have important implications for regenerative medicine.
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Affiliation(s)
- Angeliki Louvi
- Department of Neurosurgery, Yale University School of Medicine, P.O. Box 208082, New Haven, Connecticut 06520-8082, USA
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249
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Bowers K, Piper SC, Edeling MA, Gray SR, Owen DJ, Lehner PJ, Luzio JP. Degradation of endocytosed epidermal growth factor and virally ubiquitinated major histocompatibility complex class I is independent of mammalian ESCRTII. J Biol Chem 2006; 281:5094-105. [PMID: 16371348 DOI: 10.1074/jbc.m508632200] [Citation(s) in RCA: 139] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Models for protein sorting at multivesicular bodies in the endocytic pathway of mammalian cells have relied largely on data obtained from yeast. These data suggest the essential role of four ESCRT complexes in multivesicular body protein sorting. However, the putative mammalian ESCRTII complex (hVps25p, hVps22p, and hVps36p) has no proven functional role in endosomal transport. We have characterized the human ESCRTII complex and investigated its function in endosomal trafficking. The human ESCRTII proteins interact with one another, with hVps20p (a component of ESCRTIII), and with their yeast homologues. Our interaction data from yeast two-hybrid studies along with experiments with purified proteins suggest an essential role for the N-terminal domain of hVps22p in the formation of a heterotetrameric ESCRTII complex. Although human ESCRTII is found in the cytoplasm and in the nucleus, it can be recruited to endosomes upon overexpression of dominant-negative hVps4Bp. Interestingly, we find that small interference RNA depletion of mammalian ESCRTII does not affect degradation of epidermal growth factor, a known cargo of the multivesicular body protein sorting pathway. We also show that depletion of the deubiquitinating enzymes AMSH (associated molecule with the SH3 domain of STAM (signal transducing adaptor molecule)) and UBPY (ubiquitin isopeptidase Y) have opposite effects on epidermal growth factor degradation, with UBPY depletion causing dramatic swelling of endosomes. Down-regulation of another cargo, the major histocompatibility complex class I in cells expressing the Kaposi sarcoma-associated herpesvirus protein K3, is unaffected in ESCRTII-depleted cells. Our data suggest that mammalian ESCRTII may be redundant, cargo-specific, or not required for protein sorting at the multivesicular body.
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Affiliation(s)
- Katherine Bowers
- Cambridge Institute for Medical Research, Department of Clinical Biochemistry, University of Cambridge, Wellcome Trust/MRC Building, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2XY, United Kingdom.
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250
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Le Borgne R. Regulation of Notch signalling by endocytosis and endosomal sorting. Curr Opin Cell Biol 2006; 18:213-22. [PMID: 16488590 DOI: 10.1016/j.ceb.2006.02.011] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2005] [Accepted: 02/08/2006] [Indexed: 01/31/2023]
Abstract
Cell-cell signalling is an essential process in the formation of multicellular organisms. Notch is the receptor of an evolutionarily conserved signalling pathway regulating numerous developmental decisions. Indeed, its misregulation is linked to multiple developmental and physiological disorders. Notch and its ligands are distributed widely throughout development, yet Notch activity is highly controlled and restricted in time and space. Recent advances have highlighted that endocytosis followed by endosomal sorting of both the Notch receptor and its ligands is an essential mechanism by which Notch-mediated signalling is developmentally controlled.
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Affiliation(s)
- Roland Le Borgne
- CNRS UMR 6061, Faculté de Médecine, 2 avenue du Professeur Léon Bernard, CS 34317, 35043 Rennes Cedex, France.
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