151
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Koppen T, Weckmann A, Müller S, Staubach S, Bloch W, Dohmen RJ, Schwientek T. Proteomics analyses of microvesicles released by Drosophila Kc167 and S2 cells. Proteomics 2011; 11:4397-410. [PMID: 21901833 DOI: 10.1002/pmic.201000774] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2010] [Revised: 08/19/2011] [Accepted: 08/24/2011] [Indexed: 01/30/2023]
Abstract
Distinct types of vesicles are formed in eukaryotic cells that conduct a variable set of functions depending on their origin. One subtype designated circulating microvesicles (MVs) provides a novel form of intercellular communication and recent work suggested the release and uptake of morphogens in vesicles by Drosophila cells. In this study, we have examined cells of the hemocyte-like cell lines Kc167 and S2 and identified secreted vesicles in the culture supernatant. The vesicles were isolated and found to have characteristics comparable to exosomes and plasma membrane MVs released by mammalian cells. In wingless-transfected cells, the full-length protein was detected in the vesicle isolates. Proteomics analyses of the vesicles identified 269 proteins that include various orthologs of marker proteins and proteins with putative functions in vesicle formation and release. Analogous to their mammalian counterparts, the subcellular origin of the vesicular constituents of both cell lines is dominated by membrane-associated and cytosolic proteins with functions that are consistent with their localization in MVs. The analyses revealed a significant overlap of the Kc167 and S2 vesicle proteomes and confirmed a close correlation with non-mammalian and mammalian exosomes.
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Affiliation(s)
- Tim Koppen
- Center for Biochemistry, Medical Faculty, University of Cologne, Köln, Germany
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152
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Hermle T, Petzoldt AG, Simons M. The role of proton transporters in epithelial Wnt signaling pathways. Pediatr Nephrol 2011; 26:1523-7. [PMID: 21380625 DOI: 10.1007/s00467-011-1823-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/05/2010] [Revised: 01/07/2011] [Accepted: 02/07/2011] [Indexed: 02/06/2023]
Abstract
The planar cell polarity (PCP) pathway polarizes epithelia in the plane of a tissue. It regulates form and function of tissues and manifests itself by the polarized formation of cellular appendages such as epidermal hairs and cilia. Defects in the pathway are often associated with organ malformation and disease. In the kidney, the molecular events leading to cyst formation in polycystic kidney disease involve the PCP pathway. PCP is, however, best understood in Drosophila where genetic screens have identified a group of PCP core proteins including the Wnt receptor Frizzled (Fz), Dishevelled (Dsh), and Flamingo (Fmi). These proteins can localize to opposite parts of the plasma membrane in response to a poorly understood symmetry breaking event. Recent evidence suggests that proton transporters may play a role in regulating the asymmetric localization of PCP core proteins. Several papers have reported that the (pro)renin receptor, which is an associated subunit of the proton pumping V-ATPase, is required for PCP, but also for canonical Wnt signaling. Here, we discuss the implications of these findings for diverse developmental settings.
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Affiliation(s)
- Tobias Hermle
- Center for Systems Biology (ZBSA), University of Freiburg, Habsburgerstrasse 49, 79104, Freiburg, Germany
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153
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Song R, Yosypiv IV. (Pro)renin Receptor in Kidney Development and Disease. Int J Nephrol 2011; 2011:247048. [PMID: 21755055 PMCID: PMC3132641 DOI: 10.4061/2011/247048] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2011] [Revised: 03/20/2011] [Accepted: 04/20/2011] [Indexed: 12/24/2022] Open
Abstract
The renin-angiotensin system (RAS), a key regulator of the blood pressure and fluid/electrolyte homeostasis, also plays a critical role in kidney development. All the components of the RAS are expressed in the developing metanephros. Moreover, mutations in the genes encoding components of the RAS in mice or humans are associated with a broad spectrum of congenital anomalies of the kidney and urinary tract (CAKUT). These forms of CAKUT include renal papillary hypoplasia, hydronephrosis, duplicated collecting system, renal tubular dysgenesis, renal vascular abnormalities, and aberrant glomerulogenesis. Emerging evidence indicates that (pro)renin receptor (PRR), a novel component of the RAS, is essential for proper kidney development and that aberrant PRR signaling is causally linked to cardiovascular and renal disease. This paper describes the role of the RAS in kidney development and highlights emerging insights into the cellular and molecular mechanisms by which the PRR may regulate this critical morphogenetic process.
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Affiliation(s)
- Renfang Song
- Section of Pediatric Nephrology, Department of Pediatrics, Hypertension and Renal Center of Excellence, Tulane University Health Sciences Center, 1430 Tulane Avenue, New Orleans, LA 70112, USA
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154
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Sun Y, Yan Y, Denef N, Schüpbach T. Regulation of somatic myosin activity by protein phosphatase 1β controls Drosophila oocyte polarization. Development 2011; 138:1991-2001. [PMID: 21490061 DOI: 10.1242/dev.062190] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The Drosophila body axes are established in the oocyte during oogenesis. Oocyte polarization is initiated by Gurken, which signals from the germline through the epidermal growth factor receptor (Egfr) to the posterior follicle cells (PFCs). In response the PFCs generate an unidentified polarizing signal that regulates oocyte polarity. We have identified a loss-of-function mutation of flapwing, which encodes the catalytic subunit of protein phosphatase 1β (PP1β) that disrupts oocyte polarization. We show that PP1β, by regulating myosin activity, controls the generation of the polarizing signal. Excessive myosin activity in the PFCs causes oocyte mispolarization and defective Notch signaling and endocytosis in the PFCs. The integrated activation of JAK/STAT and Egfr signaling results in the sensitivity of PFCs to defective Notch. Interestingly, our results also demonstrate a role of PP1β in generating the polarizing signal independently of Notch, indicating a direct involvement of somatic myosin activity in axis formation.
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Affiliation(s)
- Yi Sun
- Howard Hughes Medical Institute, Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
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155
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Rishikesan S, Thaker YR, Grüber G. NMR solution structure of subunit E (fragment E1–69) of the Saccharomyces cerevisiae V1VO ATPase. J Bioenerg Biomembr 2011; 43:187-93. [DOI: 10.1007/s10863-011-9342-y] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2010] [Accepted: 01/31/2011] [Indexed: 11/29/2022]
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156
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Cho B, Fischer JA. Ral GTPase promotes asymmetric Notch activation in the Drosophila eye in response to Frizzled/PCP signaling by repressing ligand-independent receptor activation. Development 2011; 138:1349-59. [PMID: 21350007 DOI: 10.1242/dev.056002] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Ral is a small Ras-like GTPase that regulates membrane trafficking and signaling. Here, we show that in response to planar cell polarity (PCP) signals, Ral modulates asymmetric Notch signaling in the Drosophila eye. Specification of the initially equivalent R3/R4 photoreceptor precursor cells in each developing ommatidium occurs in response to a gradient of Frizzled (Fz) signaling. The cell with the most Fz signal (R3) activates the Notch receptor in the adjacent cell (R4) via the ligand Delta, resulting in R3/R4 cell determination and their asymmetric positions within the ommatidium. Two mechanisms have been proposed for ensuring that the cell with the most Fz activation sends the Delta signal: Fz-dependent transcriptional upregulation in R3 of genes that promote Delta signaling, and direct blockage of Notch receptor activation in R3 by localization of an activated Fz/Disheveled protein complex to the side of the plasma membrane adjacent to R4. Here, we discover a distinct mechanism for biasing the direction of Notch signaling that depends on Ral. Using genetic experiments in vivo, we show that, in direct response to Fz signaling, Ral transcription is upregulated in R3, and Ral represses ligand-independent activation of Notch in R3. Thus, prevention of ligand-independent Notch activation is not simply a constitutive process, but is a target for regulation by Ral during cell fate specification and pattern formation.
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Affiliation(s)
- Bomsoo Cho
- Section of Molecular Cell and Developmental Biology, Institute for Cell and Molecular Biology, The University of Texas at Austin, 1 University Station A4800, Austin, TX 78712, USA
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157
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Lange C, Prenninger S, Knuckles P, Taylor V, Levin M, Calegari F. The H(+) vacuolar ATPase maintains neural stem cells in the developing mouse cortex. Stem Cells Dev 2011; 20:843-50. [PMID: 21126173 DOI: 10.1089/scd.2010.0484] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The vacuolar H(+) ATPase (v-ATPase) is crucial for endosome acidification, endocytosis, and trafficking in essentially all eukaryotic cells. Recent studies have shown that inhibition of the v-ATPase also leads to downregulation of important signaling pathways, including Notch and Wnt, which are key regulators of cell differentiation and tissue homeostasis across the animal kingdom. However, the requirement of endosome acidification and endocytosis in the transduction of Notch signaling is still highly debated. Moreover, no study has yet investigated the role of the v-ATPase during mammalian development. Here we show that expression of a dominant-negative subunit of the v-ATPase in neural precursors of the developing mouse cortex depleted neural stem cells by promoting their differentiation and the generation of neurons. Moreover, inhibition of the v-ATPase reduced endogenous Notch signaling and prevented the proliferative effect of a transmembrane, γ-secretase-dependent, active Notch without blocking the effects of its cytoplasmic intracellular domain (NICD). Our data are consistent with recent reports in Drosophila in which the v-ATPase has been suggested to be important for the transduction of Notch signaling. By extending these reports to mammalian embryos, our data may contribute to a better understanding of the role of the v-ATPase, endosome acidification, and endocytosis in signal transduction during neural stem cell differentiation and brain development.
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Affiliation(s)
- Christian Lange
- DFG-Research Center and Cluster of Excellence for Regenerative Therapies, Technische Universität Dresden, Dresden, Germany
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158
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Williamson WR, Yang T, Terman JR, Hiesinger PR. Guidance receptor degradation is required for neuronal connectivity in the Drosophila nervous system. PLoS Biol 2010; 8:e1000553. [PMID: 21151882 PMCID: PMC2998435 DOI: 10.1371/journal.pbio.1000553] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2010] [Accepted: 10/21/2010] [Indexed: 12/23/2022] Open
Abstract
Axon pathfinding and synapse formation rely on precise spatiotemporal localization of guidance receptors. However, little is known about the neuron-specific intracellular trafficking mechanisms that underlie the sorting and activity of these receptors. Here we show that loss of the neuron-specific v-ATPase subunit a1 leads to progressive endosomal guidance receptor accumulations after neuronal differentiation. In the embryo and in adult photoreceptors, these accumulations occur after axon pathfinding and synapse formation is complete. In contrast, receptor missorting occurs sufficiently early in neurons of the adult central nervous system to cause connectivity defects. An increase of guidance receptors, but not of membrane proteins without signaling function, causes specific gain-of-function phenotypes. A point mutant that promotes sorting but prevents degradation reveals spatiotemporally specific guidance receptor turnover and accelerates developmental defects in photoreceptors and embryonic motor neurons. Our findings indicate that a neuron-specific endolysosomal degradation mechanism is part of the cell biological machinery that regulates guidance receptor turnover and signaling.
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Affiliation(s)
- W. Ryan Williamson
- Department of Physiology and Green Center for Systems Biology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America
| | - Taehong Yang
- Departments of Neuroscience and Pharmacology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America
| | - Jonathan R. Terman
- Departments of Neuroscience and Pharmacology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America
| | - P. Robin Hiesinger
- Department of Physiology and Green Center for Systems Biology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America
- * E-mail:
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159
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Schumacher K, Krebs M. The V-ATPase: small cargo, large effects. CURRENT OPINION IN PLANT BIOLOGY 2010; 13:724-30. [PMID: 20801076 DOI: 10.1016/j.pbi.2010.07.003] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/07/2010] [Revised: 07/20/2010] [Accepted: 07/30/2010] [Indexed: 05/18/2023]
Abstract
About 30 years ago seminal reports of anion-sensitive proton-pumping activity associated with microsomal membranes initiated research on the plant vacuolar-type H(+)-ATPase (V-ATPase, VHA). Since, it has been firmly established that these complex molecular machines are essential for what can be defined as cellular logistics. In a eukaryotic cell, the flow of goods between compartments is achieved either by protein-mediated membrane transport or via vesicular trafficking. Over the past years, it has become increasingly clear that V-ATPases do not only energize secondary active transport but are also important regulators of membrane trafficking.
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Affiliation(s)
- Karin Schumacher
- Heidelberg Institute for Plant Sciences (HIP), Universität Heidelberg, Im Neuenheimer Feld 230, 69120 Heidelberg, Germany.
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160
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Moretti J, Chastagner P, Gastaldello S, Heuss SF, Dirac AM, Bernards R, Masucci MG, Israël A, Brou C. The translation initiation factor 3f (eIF3f) exhibits a deubiquitinase activity regulating Notch activation. PLoS Biol 2010; 8:e1000545. [PMID: 21124883 PMCID: PMC2990700 DOI: 10.1371/journal.pbio.1000545] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2010] [Accepted: 10/07/2010] [Indexed: 01/03/2023] Open
Abstract
The translation initiation factor complex eIF3f has an intrinsic deubiquitinase activity and regulates the Notch signaling pathway. Activation of the mammalian Notch receptor after ligand binding relies on a succession of events including metalloprotease-cleavage, endocytosis, monoubiquitination, and eventually processing by the gamma-secretase, giving rise to a soluble, transcriptionally active molecule. The Notch1 receptor was proposed to be monoubiquitinated before its gamma-secretase cleavage; the targeted lysine has been localized to its submembrane domain. Investigating how this step might be regulated by a deubiquitinase (DUB) activity will provide new insight for understanding Notch receptor activation and downstream signaling. An immunofluorescence-based screening of an shRNA library allowed us to identify eIF3f, previously known as one of the subunits of the translation initiation factor eIF3, as a DUB targeting the activated Notch receptor. We show that eIF3f has an intrinsic DUB activity. Knocking down eIF3f leads to an accumulation of monoubiquitinated forms of activated Notch, an effect counteracted by murine WT eIF3f but not by a catalytically inactive mutant. We also show that eIF3f is recruited to activated Notch on endocytic vesicles by the putative E3 ubiquitin ligase Deltex1, which serves as a bridging factor. Finally, catalytically inactive forms of eIF3f as well as shRNAs targeting eIF3f repress Notch activation in a coculture assay, showing that eIF3f is a new positive regulator of the Notch pathway. Our results support two new and provocative conclusions: (1) The activated form of Notch needs to be deubiquitinated before being processed by the gamma-secretase activity and entering the nucleus, where it fulfills its transcriptional function. (2) The enzyme accounting for this deubiquitinase activity is eIF3f, known so far as a translation initiation factor. These data improve our knowledge of Notch signaling but also open new avenues of research on the Zomes family and the translation initiation factors. The highly conserved signaling pathway involving the transmembrane receptor Notch is essential for development, and misregulation of this pathway is linked to many diseases. We previously proposed that the Notch1 receptor is monoubiquitinated during its activation. With the aim of identifying a deubiquinating enzyme that could regulate Notch activation, we demonstrated that eIF3f, known previously as part of the multiprotein translation initiation factor eIF3 complex, harbors an enzymatic activity that acts on Notch. The activated form of Notch is able to interact with eIF3f only in the presence of the E3 ubiquitin ligase Deltex, and Notch needs to be deubiquitinated before it can be cleared and its intracellular domain can enter the nucleus and fulfill its transcriptional function. Our results further decipher the molecular mechanisms of Notch signaling activation, showing that ubiquitination and deubiquitination events are required. Additionally, we show that beyond acting as a translation initiation factor, eIF3f fulfills other functions and has an intrinsic enzymatic activity.
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Affiliation(s)
- Julien Moretti
- Institut Pasteur, Unité de Signalisation Moléculaire et Activation Cellulaire and CNRS URA 2582, rue du Dr. Roux, Paris, France
| | - Patricia Chastagner
- Institut Pasteur, Unité de Signalisation Moléculaire et Activation Cellulaire and CNRS URA 2582, rue du Dr. Roux, Paris, France
| | - Stefano Gastaldello
- Department of Cell and Molecular Biology, Karolinska Institutet, Stockholm, Sweden
| | - Sara F. Heuss
- Institut Pasteur, Unité de Signalisation Moléculaire et Activation Cellulaire and CNRS URA 2582, rue du Dr. Roux, Paris, France
| | - Annette M. Dirac
- Division of Molecular Carcinogenesis and Center for Biomedical Genetics, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - René Bernards
- Division of Molecular Carcinogenesis and Center for Biomedical Genetics, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Maria G. Masucci
- Department of Cell and Molecular Biology, Karolinska Institutet, Stockholm, Sweden
| | - Alain Israël
- Institut Pasteur, Unité de Signalisation Moléculaire et Activation Cellulaire and CNRS URA 2582, rue du Dr. Roux, Paris, France
| | - Christel Brou
- Institut Pasteur, Unité de Signalisation Moléculaire et Activation Cellulaire and CNRS URA 2582, rue du Dr. Roux, Paris, France
- * E-mail:
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161
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Le Bras S, Loyer N, Le Borgne R. The multiple facets of ubiquitination in the regulation of notch signaling pathway. Traffic 2010; 12:149-61. [PMID: 21029288 DOI: 10.1111/j.1600-0854.2010.01126.x] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The Notch signaling pathway regulates numerous aspects of metazoan development and tissue renewal. Deregulation or loss of Notch signaling is associated with a wide range of human disorders from developmental syndromes to cancer. Notch receptors and their ligands are widely expressed throughout development, yet Notch activation is robustly controlled in a spatio-temporal manner. Within the past decades, genetic screens and biochemical approaches led to the identification of more than 10 E3 ubiquitin ligases and deubiquitinating enzymes implicated in the regulation of the Notch pathway. In this review, we highlight the recent studies in Notch signaling that reveal how ubiquitination of components of the Notch pathway, ranging from degradation to regulation of membrane trafficking, impacts on the developmental control of the signaling activities of both Notch receptors and their ligands.
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Affiliation(s)
- Stéphanie Le Bras
- CNRS UMR 6061-Institut de Génétique et Développement de Rennes, 2 av du Pr. Bernard, 35000 Rennes, Université de Rennes 1, France
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162
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Abstract
We describe a molecularly defined duplication kit for the X chromosome of Drosophila melanogaster. A set of 408 overlapping P[acman] BAC clones was used to create small duplications (average length 88 kb) covering the 22-Mb sequenced portion of the chromosome. The BAC clones were inserted into an attP docking site on chromosome 3L using ΦC31 integrase, allowing direct comparison of different transgenes. The insertions complement 92% of the essential and viable mutations and deletions tested, demonstrating that almost all Drosophila genes are compact and that the current annotations of the genome are reasonably accurate. Moreover, almost all genes are tolerated at twice the normal dosage. Finally, we more precisely mapped two regions at which duplications cause diplo-lethality in males. This collection comprises the first molecularly defined duplication set to cover a whole chromosome in a multicellular organism. The work presented removes a long-standing barrier to genetic analysis of the Drosophila X chromosome, will greatly facilitate functional assays of X-linked genes in vivo, and provides a model for functional analyses of entire chromosomes in other species.
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163
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Sethi N, Yan Y, Quek D, Schupbach T, Kang Y. Rabconnectin-3 is a functional regulator of mammalian Notch signaling. J Biol Chem 2010; 285:34757-64. [PMID: 20810660 DOI: 10.1074/jbc.m110.158634] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The Notch signaling pathway is important for cell fate decisions in embryonic development and adult life. Defining the functional importance of the Notch pathway in these contexts requires the elucidation of essential signal transduction components that have not been fully characterized. Here, we show that Rabconnectin-3B is required for the Notch pathway in mammalian cells. siRNA-mediated silencing of Rabconnectin-3B in mammalian cells attenuated Notch signaling and disrupted the activation and nuclear accumulation of the Notch target Hes1. Rabconnectin-3B knockdown also disrupted V-ATPase activity in mammalian cells, consistent with previous observations in Drosophila. Pharmacological inhibition of the V-ATPase complex significantly reduced Notch signaling in mammalian cells. Finally, Rabconnectin-3B knockdown phenocopied functional disruption of Notch signaling during osteoclast differentiation. Collectively, these findings define an important role for Rabconnectin-3 and V-ATPase activity in the Notch signaling pathway in mammalian cells.
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Affiliation(s)
- Nilay Sethi
- Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA
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164
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165
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Williamson WR, Wang D, Haberman AS, Hiesinger PR. A dual function of V0-ATPase a1 provides an endolysosomal degradation mechanism in Drosophila melanogaster photoreceptors. ACTA ACUST UNITED AC 2010; 189:885-99. [PMID: 20513768 PMCID: PMC2878941 DOI: 10.1083/jcb.201003062] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A vesicular ATPase regulates both vesicle fusion and subsequent acidification of a subset of neuronal lysosomes and autophagosomes. The vesicular adenosine triphosphatase (v-ATPase) is a proton pump that acidifies intracellular compartments. In addition, mutations in components of the membrane-bound v-ATPase V0 sector cause acidification-independent defects in yeast, worm, fly, zebrafish, and mouse. In this study, we present a dual function for the neuron-specific V0 subunit a1 orthologue v100 in Drosophila melanogaster. A v100 mutant that selectively disrupts proton translocation rescues a previously characterized synaptic vesicle fusion defect and vesicle fusion with early endosomes. Correspondingly, V100 selectively interacts with syntaxins on the respective target membranes, and neither synaptic vesicles nor early endosomes require v100 for their acidification. In contrast, V100 is required for acidification once endosomes mature into degradative compartments. As a consequence of the complete loss of this neuronal degradation mechanism, photoreceptors undergo slow neurodegeneration, whereas selective rescue of the acidification-independent function accelerates cell death by increasing accumulations in degradation-incompetent compartments. We propose that V100 exerts a temporally integrated dual function that increases neuronal degradative capacity.
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Affiliation(s)
- W Ryan Williamson
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
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166
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A combined ex vivo and in vivo RNAi screen for notch regulators in Drosophila reveals an extensive notch interaction network. Dev Cell 2010; 18:862-76. [PMID: 20493818 DOI: 10.1016/j.devcel.2010.03.013] [Citation(s) in RCA: 115] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2009] [Revised: 02/10/2010] [Accepted: 03/12/2010] [Indexed: 01/26/2023]
Abstract
Notch signaling plays a fundamental role in cellular differentiation and has been linked to human diseases, including cancer. We report the use of comprehensive RNAi analyses to dissect Notch regulation and its connections to cellular pathways. A cell-based RNAi screen identified 900 candidate Notch regulators on a genome-wide scale. The subsequent use of a library of transgenic Drosophila expressing RNAi constructs enabled large-scale in vivo validation and confirmed 333 of 501 tested genes as Notch regulators. Mapping the phenotypic attributes of our data on an interaction network identified another 68 relevant genes and revealed several modules of unexpected Notch regulatory activity. In particular, we note an intriguing relationship to pyruvate metabolism, which may be relevant to cancer. Our study reveals a hitherto unappreciated diversity of tissue-specific modulators impinging on Notch and opens new avenues for studying Notch regulation and function in development and disease.
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167
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Dechant R, Binda M, Lee SS, Pelet S, Winderickx J, Peter M. Cytosolic pH is a second messenger for glucose and regulates the PKA pathway through V-ATPase. EMBO J 2010; 29:2515-26. [PMID: 20581803 DOI: 10.1038/emboj.2010.138] [Citation(s) in RCA: 207] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2010] [Accepted: 05/28/2010] [Indexed: 01/04/2023] Open
Abstract
Glucose is the preferred carbon source for most cell types and a major determinant of cell growth. In yeast and certain mammalian cells, glucose activates the cAMP-dependent protein kinase A (PKA), but the mechanisms of PKA activation remain unknown. Here, we identify cytosolic pH as a second messenger for glucose that mediates activation of the PKA pathway in yeast. We find that cytosolic pH is rapidly and reversibly regulated by glucose metabolism and identify the vacuolar ATPase (V-ATPase), a proton pump required for the acidification of vacuoles, as a sensor of cytosolic pH. V-ATPase assembly is regulated by cytosolic pH and is required for full activation of the PKA pathway in response to glucose, suggesting that it mediates, at least in part, the pH signal to PKA. Finally, V-ATPase is also regulated by glucose in the Min6 beta-cell line and contributes to PKA activation and insulin secretion. Thus, these data suggest a novel and potentially conserved glucose-sensing pathway and identify a mechanism how cytosolic pH can act as a signal to promote cell growth.
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168
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Wnt/Frizzled signaling requires dPRR, the Drosophila homolog of the prorenin receptor. Curr Biol 2010; 20:1263-8. [PMID: 20579883 DOI: 10.1016/j.cub.2010.05.028] [Citation(s) in RCA: 94] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2009] [Revised: 05/05/2010] [Accepted: 05/06/2010] [Indexed: 12/18/2022]
Abstract
Wnt/Wg signaling pathways are of key importance during development and disease. Canonical and noncanonical Wnt/Frizzled (Fz) pathways share a limited number of signaling components that are part of the membrane proximal signaling complex. In Drosophila, Fz and Dishevelled (Dsh) are the only two components known to be involved in both Wnt/beta-catenin and planar cell polarity (PCP) signaling. PCP signaling is required for the planar polarization of epithelial cells, which occurs, for instance, during hair orientation and gastrulation in vertebrates. Both pathways have been studied intensively in the past years. However, it still remains unresolved whether additional components are required at the receptor complex. Here we identify the Drosophila homolog of the mammalian prorenin receptor (dPRR) as a conserved modulator of canonical Wnt/beta-cat and Fz/PCP signaling. We show that dPRR depletion affects Wg target genes in cultured cells and in vivo. PRR is required for epithelial planar polarity in Drosophila and for convergent extension movements in Xenopus gastrulae. Furthermore, dPRR binds to Fz and Fz2 receptors. In summary, our data suggest that dPRR has an evolutionarily conserved role at the receptor level for activation of canonical and noncanonical Wnt/Fz signaling pathways.
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169
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Hermle T, Saltukoglu D, Grünewald J, Walz G, Simons M. Regulation of Frizzled-dependent planar polarity signaling by a V-ATPase subunit. Curr Biol 2010; 20:1269-76. [PMID: 20579879 DOI: 10.1016/j.cub.2010.05.057] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2009] [Revised: 05/13/2010] [Accepted: 05/20/2010] [Indexed: 12/17/2022]
Abstract
Frizzled (Fz) is a seven-pass transmembrane receptor that acts in both Wingless (Wg) and planar cell polarity (PCP) pathways. A prerequisite for PCP signaling is the asymmetric subcellular distribution of Fz. However, the regulation of Fz asymmetry is currently not well understood. Here we describe that the transmembrane protein CG8444 (here termed VhaPRR) is needed for PCP signaling in Drosophila. VhaPRR is an accessory subunit of the vacuolar (V)-ATPase proton pump, but it also functions as a receptor for (pro)renin (PRR) in mammals. We show that VhaPRR function is tightly linked with Fz but not other PCP core proteins. Fz fails to localize asymmetrically in the absence of VhaPRR, and this is accompanied by prehair mispolarization of pupal wing cells. In addition, VhaPRR forms a protein complex with Fz receptors and interacts genetically with Fz in the Drosophila eye. VhaPRR also acts as a modulator of canonical Wnt signaling in larval and adult wing tissue. Its loss leads to an expansion of the Wg morphogen gradient and a reduction of Wg target gene expression. The requirement for additional V-ATPase subunits suggests that proton fluxes contribute to normal Fz receptor function and signaling.
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Affiliation(s)
- Tobias Hermle
- Center for Systems Biology (ZBSA), University of Freiburg, Habsburgerstrasse 49, 79104 Freiburg, Germany
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170
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Vaccari T, Duchi S, Cortese K, Tacchetti C, Bilder D. The vacuolar ATPase is required for physiological as well as pathological activation of the Notch receptor. Development 2010; 137:1825-32. [PMID: 20460366 PMCID: PMC2867318 DOI: 10.1242/dev.045484] [Citation(s) in RCA: 123] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/25/2010] [Indexed: 01/23/2023]
Abstract
Evidence indicates that endosomal entry promotes signaling by the Notch receptor, but the mechanisms involved are not clear. In a search for factors that regulate Notch activation in endosomes, we isolated mutants in Drosophila genes that encode subunits of the vacuolar ATPase (V-ATPase) proton pump. Cells lacking V-ATPase function display impaired acidification of the endosomal compartment and a correlated failure to degrade endocytic cargoes. V-ATPase mutant cells internalize Notch and accumulate it in the lysosome, but surprisingly also show a substantial loss of both physiological and ectopic Notch activation in endosomes. V-ATPase activity is required in signal-receiving cells for Notch signaling downstream of ligand activation but upstream of gamma-secretase-dependent S3 cleavage. These data indicate that V-ATPase, probably via acidification of early endosomes, promotes not only the degradation of Notch in the lysosome but also the activation of Notch signaling in endosomes. The results also suggest that the ionic properties of the endosomal lumen might regulate Notch cleavage, providing a rationale for physiological as well as pathological endocytic control of Notch activity.
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Affiliation(s)
- Thomas Vaccari
- Molecular and Cell Biology, University of California, LSA #3200, Berkeley, CA 94720, USA
- IFOM, Istituto FIRC di Oncologia Molecolare, via Adamello 16, 20139, Milano, Italy
| | - Serena Duchi
- IFOM, Istituto FIRC di Oncologia Molecolare, via Adamello 16, 20139, Milano, Italy
| | - Katia Cortese
- Centro di Ricerca MicroSCoBio/IFOM Fondazione Istituto FIRC di Oncologia Molecolare, Dipartimento di Medicina Sperimentale, Università di Genova, Via de Toni 14, 16132, Genoa, Italy
| | - Carlo Tacchetti
- Centro di Ricerca MicroSCoBio/IFOM Fondazione Istituto FIRC di Oncologia Molecolare, Dipartimento di Medicina Sperimentale, Università di Genova, Via de Toni 14, 16132, Genoa, Italy
| | - David Bilder
- Molecular and Cell Biology, University of California, LSA #3200, Berkeley, CA 94720, USA
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171
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Windler SL, Bilder D. Endocytic internalization routes required for delta/notch signaling. Curr Biol 2010; 20:538-43. [PMID: 20226669 DOI: 10.1016/j.cub.2010.01.049] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2009] [Revised: 01/25/2010] [Accepted: 01/25/2010] [Indexed: 12/15/2022]
Abstract
The internalization of transmembrane receptors from the cell surface plays a central role in signal regulation. Receptor internalization can occur through different routes; however, because of the difficulty in selectively blocking these routes in vivo, their roles in signaling are poorly understood. Here we use null mutations in Drosophila dynamin, clathrin, and AP-2 adaptor subunits to analyze internalization requirements for the Delta ligand and its receptor, Notch. Bulk Notch is internalized via AP-2-dependent endocytosis, but signaling by Notch requires AP-2-independent clathrin-dependent endocytosis, highlighting a distinction between Notch endocytic routes required for degradation versus signaling activation. Signaling by Delta requires dynamin, but whether this generates a pulling force of Delta on Notch or allows for Delta entry into a recycling pathway to gain signaling competence is widely debated. Surprisingly, we show that signaling by Delta in germline cells can occur by clathrin-independent endocytosis, when endosomal entry is blocked, and when activity of Rab11 or its effectors is reduced, suggesting that Delta need not pass through a recognized recycling pathway to achieve signaling competence. The absolute requirement for dynamin-dependent endocytosis but not endosomal entry or Rab11 activity supports "pulling force" rather than "recycling" models for Delta activation.
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Affiliation(s)
- Sarah L Windler
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720-3200, USA
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172
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Richardson ECN, Pichaud F. Crumbs is required to achieve proper organ size control during Drosophila head development. Development 2010; 137:641-50. [PMID: 20110329 DOI: 10.1242/dev.041913] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Crumbs (Crb) is a conserved apical polarity determinant required for zonula adherens specification and remodelling during Drosophila development. Interestingly, crb function in maintaining apicobasal polarity appears largely dispensable in primary epithelia such as the imaginal discs. Here, we show that crb function is not required for maintaining epithelial integrity during the morphogenesis of the Drosophila head and eye. However, although crb mutant heads are properly developed, they are also significantly larger than their wild-type counterparts. We demonstrate that in the eye, this is caused by an increase in cell proliferation that can be attributed to an increase in ligand-dependent Notch (N) signalling. Moreover, we show that in crb mutant cells, ectopic N activity correlates with an increase in N and Delta endocytosis. These data indicate a role for Crb in modulating endocytosis at the apical epithelial plasma membrane, which we demonstrate is independent of Crb function in apicobasal polarity. Overall, our work reveals a novel function for Crb in limiting ligand-dependent transactivation of the N receptor at the epithelial cell membrane.
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Affiliation(s)
- Emily C N Richardson
- MRC Laboratory for Molecular Cell Biology and Cell Biology Unit, University College London, London, UK
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173
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Levitte S, Salesky R, King B, Coe Smith S, Depper M, Cole M, Hermann GJ. A Caenorhabditis elegans model of orotic aciduria reveals enlarged lysosome-related organelles in embryos lacking umps-1 function. FEBS J 2010; 277:1420-39. [DOI: 10.1111/j.1742-4658.2010.07573.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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174
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Abstract
Peptide hormones and growth factors initiate signalling by binding to and activating their cell surface receptors. The activated receptors interact with and modulate the activity of cell surface enzymes and adaptor proteins which entrain a series of reactions leading to metabolic and proliferative signals. Rapid internalization of ligand-receptor complexes into the endosomal system both prolongs and augments events initiated at the cell surface. In addition endocytosis brings activated receptors into contact with a wider range of substrates giving rise to unique signalling events critical for modulating proliferation and apoptosis. Within the endosomal system, receptor function is regulated by lowering vacuolar pH, augmenting ligand proteolysis and promoting receptor kinase dephosphorylation. Ubiquitination-deubiquitination plays a key role in regulating receptor traffic through the endosomal system resulting in either recycling to the cell surface or degradation in multivesicular-lysosomal elements. From a clinical perspective there are several studies showing that manipulating endosomal processes may constitute a new therapeutic strategy.
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175
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Abstract
Notch signaling occurs through direct interaction between Notch, the receptor, and its ligands, presented on the surface of neighboring cells. Endocytosis has been shown to be essential for Notch signal activation in both signal-sending and signal-receiving cells, and numerous genes involved in vesicle trafficking have recently been shown to act as key regulators of the pathway. Defects in vesicle trafficking can lead to gain- or loss-of-function defects in a context-dependent manner. Here, we discuss how endocytosis and vesicle trafficking regulate Notch signaling in both signal-sending and signal-receiving cells. We will introduce the key players in different trafficking steps, and further illustrate how they impact the signal outcome. Some of these players act as general factors and modulate Notch signaling in all contexts, whereas others modulate signaling in a context-specific fashion. We also discuss Notch signaling during mechanosensory organ development in the fly to exemplify how endocytosis and vesicle trafficking are effectively used to determine correct cell fates. In summary, endocytosis plays an essential role in Notch signaling, whereas intracellular vesicle trafficking often plays a context-dependent or regulatory role, leading to divergent outcomes in different developmental contexts.
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