151
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Webster BM, Colombi P, Jäger J, Lusk CP. Surveillance of nuclear pore complex assembly by ESCRT-III/Vps4. Cell 2015; 159:388-401. [PMID: 25303532 DOI: 10.1016/j.cell.2014.09.012] [Citation(s) in RCA: 166] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2014] [Revised: 07/07/2014] [Accepted: 09/04/2014] [Indexed: 12/19/2022]
Abstract
The maintenance of nuclear compartmentalization by the nuclear envelope and nuclear pore complexes (NPCs) is essential for cell function; loss of compartmentalization is associated with cancers, laminopathies, and aging. We uncovered a pathway that surveils NPC assembly intermediates to promote the formation of functional NPCs. Surveillance is mediated by Heh2, a member of the LEM (Lap2-emerin-MAN1) family of integral inner nuclear membrane proteins, which binds to an early NPC assembly intermediate, but not to mature NPCs. Heh2 recruits the endosomal sorting complex required for transport (ESCRT)-III subunit Snf7 and the AAA-ATPase Vps4 to destabilize and clear defective NPC assembly intermediates. When surveillance or clearance is compromised, malformed NPCs accumulate in a storage of improperly assembled nuclear pore complexes compartment, or SINC. The SINC is retained in old mothers to prevent loss of daughter lifespan, highlighting a continuum of mechanisms to ensure nuclear compartmentalization.
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Affiliation(s)
- Brant M Webster
- Department of Cell Biology, Yale School of Medicine, New Haven, CT 06520, USA
| | - Paolo Colombi
- Department of Cell Biology, Yale School of Medicine, New Haven, CT 06520, USA
| | - Jens Jäger
- Department of Cell Biology, Yale School of Medicine, New Haven, CT 06520, USA
| | - C Patrick Lusk
- Department of Cell Biology, Yale School of Medicine, New Haven, CT 06520, USA.
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152
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Kralt A, Carretta M, Mari M, Reggiori F, Steen A, Poolman B, Veenhoff LM. Intrinsically Disordered Linker and Plasma Membrane-Binding Motif Sort Ist2 and Ssy1 to Junctions. Traffic 2014; 16:135-47. [DOI: 10.1111/tra.12243] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2014] [Revised: 11/17/2014] [Accepted: 11/18/2014] [Indexed: 12/25/2022]
Affiliation(s)
- Annemarie Kralt
- European Institute for the Biology of Ageing (ERIBA); University of Groningen, University Medical Center Groningen, Netherlands Proteomics Centre; Antonius Deusinglaan 1 9713 AV Groningen The Netherlands
| | - Marco Carretta
- European Institute for the Biology of Ageing (ERIBA); University of Groningen, University Medical Center Groningen, Netherlands Proteomics Centre; Antonius Deusinglaan 1 9713 AV Groningen The Netherlands
- Current address: Department of Hematology, University of Groningen, Hanzeplein 1, 9713 GZ Groningen, The Netherlands
| | - Muriel Mari
- Department of Cell Biology; Center for Molecular Medicine, University Medical Center Utrecht; Heidelberglaan 100 3584 CX Utrecht The Netherlands
| | - Fulvio Reggiori
- Department of Cell Biology; Center for Molecular Medicine, University Medical Center Utrecht; Heidelberglaan 100 3584 CX Utrecht The Netherlands
| | - Anton Steen
- European Institute for the Biology of Ageing (ERIBA); University of Groningen, University Medical Center Groningen, Netherlands Proteomics Centre; Antonius Deusinglaan 1 9713 AV Groningen The Netherlands
| | - Bert Poolman
- Department of Biochemistry; University of Groningen; Nijenborgh 4 9747 AG Groningen The Netherlands
| | - Liesbeth M. Veenhoff
- European Institute for the Biology of Ageing (ERIBA); University of Groningen, University Medical Center Groningen, Netherlands Proteomics Centre; Antonius Deusinglaan 1 9713 AV Groningen The Netherlands
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153
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Mijaljica D, Prescott M, Devenish RJ. The intricacy of nuclear membrane dynamics during nucleophagy. Nucleus 2014. [DOI: 10.4161/nucl.11738] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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154
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Elbaz-Alon Y, Rosenfeld-Gur E, Shinder V, Futerman AH, Geiger T, Schuldiner M. A dynamic interface between vacuoles and mitochondria in yeast. Dev Cell 2014; 30:95-102. [PMID: 25026036 DOI: 10.1016/j.devcel.2014.06.007] [Citation(s) in RCA: 276] [Impact Index Per Article: 27.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2013] [Revised: 04/14/2014] [Accepted: 06/09/2014] [Indexed: 12/18/2022]
Abstract
Cellular life depends on continuous transport of lipids and small molecules between mitochondria and the endomembrane system. Recently, endoplasmic reticulum-mitochondrial encounter structure (ERMES) was identified as an important yet nonessential contact for such transport. Using a high-content screen in yeast, we found a contact site, marked by Vam6/Vps39, between vacuoles (the yeast lysosomal compartment) and mitochondria, named vCLAMP (vacuole and mitochondria patch). vCLAMP is enriched with ion and amino-acid transporters and has a role in lipid relay between the endomembrane system and mitochondria. Critically, we show that mitochondria are dependent on having one of two contact sites, ERMES or vCLAMP. The absence of one causes expansion of the other, and elimination of both is lethal. Identification of vCLAMP adds to our ability to understand the complexity of interorganellar crosstalk.
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Affiliation(s)
- Yael Elbaz-Alon
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Eden Rosenfeld-Gur
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Vera Shinder
- Electron Microscopy Unit, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Anthony H Futerman
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Tamar Geiger
- Department of Human Molecular Genetics and Biochemistry, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 6997801, Israel
| | - Maya Schuldiner
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel.
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155
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Prinz WA. Bridging the gap: membrane contact sites in signaling, metabolism, and organelle dynamics. ACTA ACUST UNITED AC 2014; 205:759-69. [PMID: 24958771 PMCID: PMC4068136 DOI: 10.1083/jcb.201401126] [Citation(s) in RCA: 297] [Impact Index Per Article: 29.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Regions of close apposition between two organelles, often referred to as membrane contact sites (MCSs), mostly form between the endoplasmic reticulum and a second organelle, although contacts between mitochondria and other organelles have also begun to be characterized. Although these contact sites have been noted since cells first began to be visualized with electron microscopy, the functions of most of these domains long remained unclear. The last few years have witnessed a dramatic increase in our understanding of MCSs, revealing the critical roles they play in intracellular signaling, metabolism, the trafficking of metabolites, and organelle inheritance, division, and transport.
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Affiliation(s)
- William A Prinz
- Laboratory of Cell and Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892
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156
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Hönscher C, Mari M, Auffarth K, Bohnert M, Griffith J, Geerts W, van der Laan M, Cabrera M, Reggiori F, Ungermann C. Cellular Metabolism Regulates Contact Sites between Vacuoles and Mitochondria. Dev Cell 2014; 30:86-94. [DOI: 10.1016/j.devcel.2014.06.006] [Citation(s) in RCA: 247] [Impact Index Per Article: 24.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2013] [Revised: 04/04/2014] [Accepted: 06/09/2014] [Indexed: 11/25/2022]
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157
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Xue Y, Vashisht AA, Tan Y, Su T, Wohlschlegel JA. PRB1 is required for clipping of the histone H3 N terminal tail in Saccharomyces cerevisiae. PLoS One 2014; 9:e90496. [PMID: 24587380 PMCID: PMC3938757 DOI: 10.1371/journal.pone.0090496] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2013] [Accepted: 02/03/2014] [Indexed: 11/18/2022] Open
Abstract
Cathepsin L, a lysosomal protein in mouse embryonic stem cells has been shown to clip the histone H3 N- terminus, an activity associated with gene activity during mouse cell development. Glutamate dehydrogenase (GDH) was also identified as histone H3 specific protease in chicken liver, which has been connected to gene expression during aging. In baker's yeast, Saccharomyces cerevisiae, clipping the histone H3 N-terminus has been associated with gene activation in stationary phase but the protease responsible for the yeast histone H3 endopeptidase activity had not been identified. In searching for a yeast histone H3 endopeptidase, we found that yeast vacuolar protein Prb1 is present in the cellular fraction enriched for the H3 N-terminus endopeptidase activity and this endopeptidase activity is lost in the PRB1 deletion mutant (prb1Δ). In addition, like Cathepsin L and GDH, purified Prb1 from yeast cleaves H3 between Lys23 and Ala24 in the N-terminus in vitro as shown by Edman degradation. In conclusion, our data argue that PRB1 is required for clipping of the histone H3 N-terminal tail in Saccharomyces cerevisiae.
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Affiliation(s)
- Yong Xue
- Department of Biological Chemistry, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, United States of America
- * E-mail:
| | - Ajay A. Vashisht
- Department of Biological Chemistry, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, United States of America
| | - Yuliang Tan
- Department of Biological Chemistry, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, United States of America
| | - Trent Su
- Department of Biological Chemistry, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, United States of America
| | - James A. Wohlschlegel
- Department of Biological Chemistry, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, United States of America
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158
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Hönscher C, Ungermann C. A close-up view of membrane contact sites between the endoplasmic reticulum and the endolysosomal system: from yeast to man. Crit Rev Biochem Mol Biol 2014; 49:262-8. [PMID: 24382115 DOI: 10.3109/10409238.2013.875512] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Maintenance of organelle identity is crucial for the functionality of eukaryotic cells. Hence, transfer reactions between different compartments must be highly efficient and tightly regulated at the same time. Membrane contact sites (MCSs) represent an important route for inter-organelle transport and communication independent of vesicular trafficking. Due to extensive research, the mechanistic understanding of these sites increases constantly. However, how the formation and the versatile functions of MCSs are regulated is mainly unclear. Within this review, we focus on one well-known MCS, the nucleus-vacuole junction in yeast and discuss its analogy to endoplasmic reticulum-late endosome contacts in metazoan. Formation of the junction in yeast requires Vac8, a protein that is involved in various cellular processes at the yeast vacuole and a target of multiple posttranslational modifications. We discuss the possibility that dual functionality of proteins involved in contact formation is a common principle to coordinate inter-organelle transfer with organellar biogenesis.
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Affiliation(s)
- Carina Hönscher
- Department of Biology/Chemistry, Biochemistry Section, University of Osnabrück , Osnabrück , Germany
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159
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Abstract
Autophagy refers to a group of processes that involve degradation of cytoplasmic components including cytosol, macromolecular complexes, and organelles, within the vacuole or the lysosome of higher eukaryotes. The various types of autophagy have attracted increasing attention for at least two reasons. First, autophagy provides a compelling example of dynamic rearrangements of subcellular membranes involving issues of protein trafficking and organelle identity, and thus it is fascinating for researchers interested in questions pertinent to basic cell biology. Second, autophagy plays a central role in normal development and cell homeostasis, and, as a result, autophagic dysfunctions are associated with a range of illnesses including cancer, diabetes, myopathies, some types of neurodegeneration, and liver and heart diseases. That said, this review focuses on autophagy in yeast. Many aspects of autophagy are conserved from yeast to human; in particular, this applies to the gene products mediating these pathways as well as some of the signaling cascades regulating it, so that the information we relate is relevant to higher eukaryotes. Indeed, as with many cellular pathways, the initial molecular insights were made possible due to genetic studies in Saccharomyces cerevisiae and other fungi.
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160
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Tsai IT, Lin JL, Chiang YH, Chuang YC, Liang SS, Chuang CN, Huang TN, Wang TF. Interorganelle interactions and inheritance patterns of nuclei and vacuoles in budding yeast meiosis. Autophagy 2013; 10:285-95. [PMID: 24345927 PMCID: PMC5396080 DOI: 10.4161/auto.27192] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Many of the mechanisms by which organelles are inherited by spores during meiosis are not well understood. Dramatic chromosome motion and bouquet formation are evolutionarily conserved characteristics of meiotic chromosomes. The budding yeast bouquet genes (NDJ1, MPS3, CSM4) mediate these movements via telomere attachment to the nuclear envelope (NE). Here, we report that during meiosis the NE is in direct contact with vacuoles via nucleus-vacuole junctions (NVJs). We show that in meiosis NVJs are assembled through the interaction of the outer NE-protein Nvj1 and the vacuolar membrane protein Vac8. Notably, NVJs function as diffusion barriers that exclude the nuclear pore complexes, the bouquet protein Mps3 and NE-tethered telomeres from the outer nuclear membrane and nuclear ER, resulting in distorted NEs during early meiosis. An increase in NVJ area resulting from Nvj1-GFP overexpression produced a moderate bouquet mutant-like phenotype in wild-type cells. NVJs, as the vacuolar contact sites of the nucleus, were found to undergo scission alongside the NE during meiotic nuclear division. The zygotic NE and NVJs were partly segregated into 4 spores. Lastly, new NVJs were also revealed to be synthesized de novo to rejoin the zygotic NE with the newly synthesized vacuoles in the mature spores. In conclusion, our results revealed that budding yeast nuclei and vacuoles exhibit dynamic interorganelle interactions and different inheritance patterns in meiosis, and also suggested that nvj1Δ mutant cells may be useful to resolve the technical challenges pertaining to the isolation of intact nuclei for the biochemical study of meiotic nuclear proteins.
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Affiliation(s)
- I-Ting Tsai
- Department of Life Sciences and Institute of Genome Sciences; National Yang-Ming University; Taipei, Taiwan; Institute of Molecular Biology; Academia Sinica; Taipei, Taiwan
| | - Jyun-Liang Lin
- Institute of Molecular Biology; Academia Sinica; Taipei, Taiwan
| | - Yi-Hsuan Chiang
- Department of Life Sciences and Institute of Genome Sciences; National Yang-Ming University; Taipei, Taiwan; Institute of Molecular Biology; Academia Sinica; Taipei, Taiwan
| | - Yu-Chien Chuang
- Institute of Molecular Biology; Academia Sinica; Taipei, Taiwan; Taiwan International Graduate Program in Molecular and Cellular Biology; Academia Sinica; Taipei, Taiwan
| | - Shu-Shan Liang
- Institute of Molecular Biology; Academia Sinica; Taipei, Taiwan; Institute of Biochemical Sciences; National Taiwan University; Taipei, Taiwan
| | - Chi-Ning Chuang
- Institute of Molecular Biology; Academia Sinica; Taipei, Taiwan
| | - Tzyy-Nan Huang
- Institute of Molecular Biology; Academia Sinica; Taipei, Taiwan
| | - Ting-Fang Wang
- Department of Life Sciences and Institute of Genome Sciences; National Yang-Ming University; Taipei, Taiwan; Institute of Molecular Biology; Academia Sinica; Taipei, Taiwan; Taiwan International Graduate Program in Molecular and Cellular Biology; Academia Sinica; Taipei, Taiwan; Institute of Biochemical Sciences; National Taiwan University; Taipei, Taiwan
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161
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Helle SC, Kanfer G, Kolar K, Lang A, Michel AH, Kornmann B. Organization and function of membrane contact sites. BIOCHIMICA ET BIOPHYSICA ACTA (BBA) - MOLECULAR CELL RESEARCH 2013. [DOI: 10.1016.j.bbamcr.2013.01.02810.1016/j.bbamcr.2013.01.028] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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162
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John Peter AT, Lachmann J, Rana M, Bunge M, Cabrera M, Ungermann C. The BLOC-1 complex promotes endosomal maturation by recruiting the Rab5 GTPase-activating protein Msb3. ACTA ACUST UNITED AC 2013; 201:97-111. [PMID: 23547030 PMCID: PMC3613695 DOI: 10.1083/jcb.201210038] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Yeast BLOC-1 acts as both a Rab5–Vps21 effector and an adapter for the Rab-GAP Msb3 to promote endosomal maturation. Membrane microcompartments of the early endosomes serve as a sorting and signaling platform, where receptors are either recycled back to the plasma membrane or forwarded to the lysosome for destruction. In metazoan cells, three complexes, termed BLOC-1 to -3, mediate protein sorting from the early endosome to lysosomes and lysosome-related organelles. We now demonstrate that BLOC-1 is an endosomal Rab-GAP (GTPase-activating protein) adapter complex in yeast. The yeast BLOC-1 consisted of six subunits, which localized interdependently to the endosomes in a Rab5/Vps21-dependent manner. In the absence of BLOC-1 subunits, the balance between recycling and degradation of selected cargoes was impaired. Additionally, our data show that BLOC-1 is both a Vps21 effector and an adapter for its GAP Msb3. BLOC-1 and Msb3 interacted in vivo, and both mutants resulted in a redistribution of active Vps21 to the vacuole surface. We thus conclude that BLOC-1 controls the lifetime of active Rab5/Vps21 and thus endosomal maturation along the endocytic pathway.
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Affiliation(s)
- Arun T John Peter
- Department of Biology/Chemistry, Biochemistry Section, University of Osnabrück, 49076 Osnabrück, Germany
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163
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English AR, Voeltz GK. Endoplasmic reticulum structure and interconnections with other organelles. Cold Spring Harb Perspect Biol 2013; 5:a013227. [PMID: 23545422 DOI: 10.1101/cshperspect.a013227] [Citation(s) in RCA: 226] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The endoplasmic reticulum (ER) is a large, continuous membrane-bound organelle comprised of functionally and structurally distinct domains including the nuclear envelope, peripheral tubular ER, peripheral cisternae, and numerous membrane contact sites at the plasma membrane, mitochondria, Golgi, endosomes, and peroxisomes. These domains are required for multiple cellular processes, including synthesis of proteins and lipids, calcium level regulation, and exchange of macromolecules with various organelles at ER-membrane contact sites. The ER maintains its unique overall structure regardless of dynamics or transfer at ER-organelle contacts. In this review, we describe the numerous factors that contribute to the structure of the ER.
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Affiliation(s)
- Amber R English
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO 80309, USA
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164
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Helle SCJ, Kanfer G, Kolar K, Lang A, Michel AH, Kornmann B. Organization and function of membrane contact sites. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2013; 1833:2526-41. [PMID: 23380708 DOI: 10.1016/j.bbamcr.2013.01.028] [Citation(s) in RCA: 329] [Impact Index Per Article: 29.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2012] [Revised: 01/18/2013] [Accepted: 01/21/2013] [Indexed: 11/16/2022]
Abstract
Membrane-bound organelles are a wonderful evolutionary acquisition of the eukaryotic cell, allowing the segregation of sometimes incompatible biochemical reactions into specific compartments with tailored microenvironments. On the flip side, these isolating membranes that crowd the interior of the cell, constitute a hindrance to the diffusion of metabolites and information to all corners of the cell. To ensure coordination of cellular activities, cells use a network of contact sites between the membranes of different organelles. These membrane contact sites (MCSs) are domains where two membranes come to close proximity, typically less than 30nm. Such contacts create microdomains that favor exchange between two organelles. MCSs are established and maintained in durable or transient states by tethering structures, which keep the two membranes in proximity, but fusion between the membranes does not take place. Since the endoplasmic reticulum (ER) is the most extensive cellular membrane network, it is thus not surprising to find the ER involved in most MCSs within the cell. The ER contacts diverse compartments such as mitochondria, lysosomes, lipid droplets, the Golgi apparatus, endosomes and the plasma membrane. In this review, we will focus on the common organizing principles underlying the many MCSs found between the ER and virtually all compartments of the cell, and on how the ER establishes a network of MCSs for the trafficking of vital metabolites and information. This article is part of a Special Issue entitled: Functional and structural diversity of endoplasmic reticulum.
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Affiliation(s)
- Sebastian C J Helle
- Institute of Biochemistry, ETH Zürich, HPM G16 Schafmattstrasse, Zürich, Switzerland
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165
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Abstract
There is increasing evidence that certain Vacuolar protein sorting (Vps) proteins, factors that mediate vesicular protein trafficking, have additional roles in regulating transcription factors at the endosome. We found that yeast mutants lacking the phosphatidylinositol 3-phosphate [PI(3)P] kinase Vps34 or its associated protein kinase Vps15 display multiple phenotypes indicating impaired transcription elongation. These phenotypes include reduced mRNA production from long or G+C-rich coding sequences (CDS) without affecting the associated GAL1 promoter activity, and a reduced rate of RNA polymerase II (Pol II) progression through lacZ CDS in vivo. Consistent with reported genetic interactions with mutations affecting the histone acetyltransferase complex NuA4, vps15Δ and vps34Δ mutations reduce NuA4 occupancy in certain transcribed CDS. vps15Δ and vps34Δ mutants also exhibit impaired localization of the induced GAL1 gene to the nuclear periphery. We found unexpectedly that, similar to known transcription elongation factors, these and several other Vps factors can be cross-linked to the CDS of genes induced by Gcn4 or Gal4 in a manner dependent on transcriptional induction and stimulated by Cdk7/Kin28-dependent phosphorylation of the Pol II C-terminal domain (CTD). We also observed colocalization of a fraction of Vps15-GFP and Vps34-GFP with nuclear pores at nucleus-vacuole (NV) junctions in live cells. These findings suggest that Vps factors enhance the efficiency of transcription elongation in a manner involving their physical proximity to nuclear pores and transcribed chromatin.
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166
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Ramsdale M. Programmed cell death in the cellular differentiation of microbial eukaryotes. Curr Opin Microbiol 2012; 15:646-52. [DOI: 10.1016/j.mib.2012.09.005] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2012] [Revised: 09/21/2012] [Accepted: 09/25/2012] [Indexed: 01/22/2023]
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167
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Cabrera A, Herrmann S, Warszta D, Santos JM, John Peter AT, Kono M, Debrouver S, Jacobs T, Spielmann T, Ungermann C, Soldati-Favre D, Gilberger TW. Dissection of minimal sequence requirements for rhoptry membrane targeting in the malaria parasite. Traffic 2012; 13:1335-50. [PMID: 22759070 DOI: 10.1111/j.1600-0854.2012.01394.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2012] [Revised: 06/28/2012] [Accepted: 07/03/2012] [Indexed: 12/20/2022]
Abstract
Rhoptries are specialized secretory organelles characteristic of single cell organisms belonging to the clade Apicomplexa. These organelles play a key role in the invasion process of host cells by accumulating and subsequently secreting an unknown number of proteins mediating host cell entry. Despite their essential role, little is known about their biogenesis, components and targeting determinants. Here, we report on a conserved apicomplexan protein termed Armadillo Repeats-Only (ARO) protein that we localized to the cytosolic face of Plasmodium falciparum and Toxoplasma gondii rhoptries. We show that the first 20 N-terminal amino acids are sufficient for rhoptry membrane targeting. This protein relies on both - myristoylation and palmitoylation motifs - for membrane attachment. Although these lipid modifications are essential, they are not sufficient to direct ARO to the rhoptry membranes. Mutational analysis revealed additional residues within the first 20 amino acids of ARO that play an important role for rhoptry membrane attachment: the positively charged residues R9 and K14. Interestingly, the exchange of R9 with a negative charge entirely abolishes membrane attachment, whereas the exchange of K14 (and to a lesser extent K16) alters only its membrane specificity. Additionally, 17 proteins predicted to be myristoylated and palmitoylated in the first 20 N-terminal amino acids were identified in the genome of the malaria parasite. While most of the corresponding GFP fusion proteins were trafficked to the parasite plasma membrane, two were sorted to the apical organelles. Interestingly, these proteins have a similar motif identified for ARO.
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Affiliation(s)
- Ana Cabrera
- M.G. DeGroote Institute for Infectious Disease Research, Department of Pathology and Molecular Medicine, McMaster University, Hamilton, ON, Canada
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168
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Zieger M, Mayer A. Yeast vacuoles fragment in an asymmetrical two-phase process with distinct protein requirements. Mol Biol Cell 2012; 23:3438-49. [PMID: 22787281 PMCID: PMC3431934 DOI: 10.1091/mbc.e12-05-0347] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Yeast vacuoles fragment and fuse in response to environmental conditions, such as changes in osmotic conditions or nutrient availability. Here we analyze osmotically induced vacuole fragmentation by time-lapse microscopy. Small fragmentation products originate directly from the large central vacuole. This happens by asymmetrical scission rather than by consecutive equal divisions. Fragmentation occurs in two distinct phases. Initially, vacuoles shrink and generate deep invaginations that leave behind tubular structures in their vicinity. Already this invagination requires the dynamin-like GTPase Vps1p and the vacuolar proton gradient. Invaginations are stabilized by phosphatidylinositol 3-phosphate (PI(3)P) produced by the phosphoinositide 3-kinase complex II. Subsequently, vesicles pinch off from the tips of the tubular structures in a polarized manner, directly generating fragmentation products of the final size. This phase depends on the production of phosphatidylinositol-3,5-bisphosphate and the Fab1 complex. It is accelerated by the PI(3)P- and phosphatidylinositol 3,5-bisphosphate-binding protein Atg18p. Thus vacuoles fragment in two steps with distinct protein and lipid requirements.
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Affiliation(s)
- Martin Zieger
- Département de Biochimie, Université de Lausanne, 1066 Epalinges, Switzerland
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169
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Mijaljica D, Prescott M, Devenish RJ. A late form of nucleophagy in Saccharomyces cerevisiae. PLoS One 2012; 7:e40013. [PMID: 22768199 PMCID: PMC3386919 DOI: 10.1371/journal.pone.0040013] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2011] [Accepted: 06/04/2012] [Indexed: 12/19/2022] Open
Abstract
Autophagy encompasses several processes by which cytosol and organelles can be delivered to the vacuole/lysosome for breakdown and recycling. We sought to investigate autophagy of the nucleus (nucleophagy) in the yeast Saccharomyces cerevisiae by employing genetically encoded fluorescent reporters. The use of such a nuclear reporter, n-Rosella, proved the basis of robust assays based on either following its accumulation (by confocal microscopy), or degradation (by immunoblotting), within the vacuole. We observed the delivery of n-Rosella to the vacuole only after prolonged periods of nitrogen starvation. Dual labeling of cells with Nvj1p-EYFP, a nuclear membrane reporter of piecemeal micronucleophagy of the nucleus (PMN), and the nucleoplasm-targeted NAB35-DsRed.T3 allowed us to detect PMN soon after the commencement of nitrogen starvation whilst delivery to the vacuole of the nucleoplasm reporter was observed only after prolonged periods of nitrogen starvation. This later delivery of nuclear components to the vacuole has been designated LN (late nucleophagy). Only a very few cells showed simultaneous accumulation of both reporters (Nvj1p-EYFP and NAB35-DsRed.T3) in the vacuole. We determined, therefore, that delivery of the two respective nuclear reporters to the vacuole is temporally and spatially separated. Furthermore, our data suggest that LN is mechanistically distinct from PMN because it can occur in nvj1Δ and vac8Δ cells, and does not require ATG11. Nevertheless, a subset of the components of the core macroautophagic machinery is required for LN as it is efficiently inhibited in null mutants of several autophagy-related genes (ATG) specifying such components. Moreover, the inhibition of LN in some mutants is accompanied by alterations in nuclear morphology.
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Affiliation(s)
- Dalibor Mijaljica
- Department of Biochemistry and Molecular Biology, School of Biomedical Sciences, Faculty of Medicine, Nursing and Health Sciences, Monash University, Victoria, Australia
| | - Mark Prescott
- Department of Biochemistry and Molecular Biology, School of Biomedical Sciences, Faculty of Medicine, Nursing and Health Sciences, Monash University, Victoria, Australia
| | - Rodney J. Devenish
- Department of Biochemistry and Molecular Biology, School of Biomedical Sciences, Faculty of Medicine, Nursing and Health Sciences, Monash University, Victoria, Australia
- * E-mail:
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170
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Abstract
Due to its genetic tractability and increasing wealth of accessible data, the yeast Saccharomyces cerevisiae is a model system of choice for the study of the genetics, biochemistry, and cell biology of eukaryotic lipid metabolism. Glycerolipids (e.g., phospholipids and triacylglycerol) and their precursors are synthesized and metabolized by enzymes associated with the cytosol and membranous organelles, including endoplasmic reticulum, mitochondria, and lipid droplets. Genetic and biochemical analyses have revealed that glycerolipids play important roles in cell signaling, membrane trafficking, and anchoring of membrane proteins in addition to membrane structure. The expression of glycerolipid enzymes is controlled by a variety of conditions including growth stage and nutrient availability. Much of this regulation occurs at the transcriptional level and involves the Ino2–Ino4 activation complex and the Opi1 repressor, which interacts with Ino2 to attenuate transcriptional activation of UASINO-containing glycerolipid biosynthetic genes. Cellular levels of phosphatidic acid, precursor to all membrane phospholipids and the storage lipid triacylglycerol, regulates transcription of UASINO-containing genes by tethering Opi1 to the nuclear/endoplasmic reticulum membrane and controlling its translocation into the nucleus, a mechanism largely controlled by inositol availability. The transcriptional activator Zap1 controls the expression of some phospholipid synthesis genes in response to zinc availability. Regulatory mechanisms also include control of catalytic activity of glycerolipid enzymes by water-soluble precursors, products and lipids, and covalent modification of phosphorylation, while in vivo function of some enzymes is governed by their subcellular location. Genome-wide genetic analysis indicates coordinate regulation between glycerolipid metabolism and a broad spectrum of metabolic pathways.
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171
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Abstract
Autophagy is a bulk degradation system, widely conserved in eukaryotes. Upon starvation, autophagosomes enclose a portion of the cytoplasm and ultimately fuse with the vacuole. The contents of autophagosomes are degraded in the vacuole, and recycled to maintain the intracellular amino-acid pool required for protein synthesis and survival under starvation conditions. Previously, autophagy was thought to be an essentially nonselective pathway, but recent evidence suggests that autophagosomes carry selected cargoes. These studies have identified two categories of selective autophagy - one highly selective and dependent on autophagy-related 11 (Atg11); another, less selective, that is, independent of Atg11. The former, selective category comprises the Cvt pathway, mitophagy, pexophagy and piecemeal microautophagy of the nucleus; acetaldehyde dehydrogenase 6 degradation and ribophagy belong to the latter, less selective category. In this review, I focus on the mechanisms and the physiological roles of these selective types of autophagy.
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172
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Triggering of Ca2+ signals by NAADP-gated two-pore channels: a role for membrane contact sites? Biochem Soc Trans 2012; 40:153-7. [PMID: 22260682 DOI: 10.1042/bst20110693] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
NAADP (nicotinic acid-adenine dinucleotide phosphate) is a potent Ca2+-mobilizing messenger implicated in many Ca2+-dependent cellular processes. It is highly unusual in that it appears to trigger Ca2+ release from acidic organelles such as lysosomes. These signals are often amplified by archetypal Ca2+ channels located in the endoplasmic reticulum. Recent studies have converged on the TPCs (two-pore channels) which localize to the endolysosomal system as the likely primary targets through which NAADP mediates its effects. 'Chatter' between TPCs and endoplasmic reticulum Ca2+ channels is disrupted when TPCs are directed away from the endolysosomal system. This suggests that intracellular Ca2+ release channels may be closely apposed, possibly at specific membrane contact sites between acidic organelles and the endoplasmic reticulum.
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173
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Stradalova V, Blazikova M, Grossmann G, Opekarová M, Tanner W, Malinsky J. Distribution of cortical endoplasmic reticulum determines positioning of endocytic events in yeast plasma membrane. PLoS One 2012; 7:e35132. [PMID: 22496901 PMCID: PMC3322162 DOI: 10.1371/journal.pone.0035132] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2011] [Accepted: 03/10/2012] [Indexed: 11/18/2022] Open
Abstract
In many eukaryotes, a significant part of the plasma membrane is closely associated with the dynamic meshwork of cortical endoplasmic reticulum (cortical ER). We mapped temporal variations in the local coverage of the yeast plasma membrane with cortical ER pattern and identified micron-sized plasma membrane domains clearly different in cortical ER persistence. We show that clathrin-mediated endocytosis is initiated outside the cortical ER-covered plasma membrane zones. These cortical ER-covered zones are highly dynamic but do not overlap with the immobile and also endocytosis-inactive membrane compartment of Can1 (MCC) and the subjacent eisosomes. The eisosomal component Pil1 is shown to regulate the distribution of cortical ER and thus the accessibility of the plasma membrane for endocytosis.
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Affiliation(s)
- Vendula Stradalova
- Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic
| | - Michaela Blazikova
- Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic
- Faculty of Mathematics and Physics, Charles University in Prague, Prague, Czech Republic
| | - Guido Grossmann
- Department for Plant Biology, Carnegie Institution for Science, Stanford, California, United States of America
| | - Miroslava Opekarová
- Institute of Microbiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic
| | - Widmar Tanner
- Institute of Cell Biology and Plant Physiology, University of Regensburg, Regensburg, Germany
| | - Jan Malinsky
- Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic
- * E-mail:
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174
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Rapid cytoplasmic turnover of yeast ribosomes in response to rapamycin inhibition of TOR. Mol Cell Biol 2012; 32:2135-44. [PMID: 22451491 DOI: 10.1128/mcb.06763-11] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The target of rapamycin (TOR) pathway is the central regulator of cell growth in eukaryotes. Inhibition of TOR by rapamycin elicits changes in translation attributed mainly to altered translation initiation and repression of the synthesis of new ribosomes. Using quantitative analysis of rRNA, we found that the number of existing ribosomes present in a Saccharomyces cerevisiae culture during growth in rich medium rapidly decreases by 40 to 60% when the cells are treated with rapamycin. This process is not appreciably affected by a suppression of autophagy, previously implicated in degradation of ribosomes in eukaryotes upon starvation. Yeast cells deficient in the exosome function or lacking its cytoplasmic Ski cofactors show an abnormal pattern of rRNA degradation, particularly in the large ribosomal subunit, and accumulate rRNA fragments after rapamycin treatment and during diauxic shift. The exosome and Ski proteins are thus important for processing of rRNA decay intermediates, although they are probably not responsible for initiating rRNA decay. The role of cytoplasmic nucleases in rapamycin-induced rRNA degradation suggests mechanistic parallels of this process to nutrient-controlled ribosome turnover in prokaryotes. We propose that ribosome content is regulated dynamically in eukaryotes by TOR through both ribosome synthesis and the cytoplasmic turnover of mature ribosomes.
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175
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Infection-associated nuclear degeneration in the rice blast fungus Magnaporthe oryzae requires non-selective macro-autophagy. PLoS One 2012; 7:e33270. [PMID: 22448240 PMCID: PMC3308974 DOI: 10.1371/journal.pone.0033270] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2012] [Accepted: 02/13/2012] [Indexed: 11/23/2022] Open
Abstract
Background The rice blast fungus Magnaporthe oryzae elaborates a specialized infection structure called an appressorium to breach the rice leaf surface and gain access to plant tissue. Appressorium development is controlled by cell cycle progression, and a single round of nuclear division occurs prior to appressorium formation. Mitosis is always followed by programmed cell death of the spore from which the appressorium develops. Nuclear degeneration in the spore is known to be essential for plant infection, but the precise mechanism by which it occurs is not known. Methodology/Principal Findings In yeast, nuclear breakdown requires a specific form of autophagy, known as piecemeal microautophagy of the nucleus (PMN), and we therefore investigated whether this process occurs in the rice blast fungus. Here, we report that M. oryzae possesses two conserved components of a putative PMN pathway, MoVac8 and MoTsc13, but that both are dispensable for nuclear breakdown during plant infection. MoVAC8 encodes a vacuolar membrane protein and MoTSC13 a peri-nuclear and peripheral ER protein. Conclusions/Significance We show that MoVAC8 is necessary for caffeine resistance, but dispensable for pathogenicity of M. oryzae, while MoTSC13 is involved in cell wall stress responses and is an important virulence determinant. By functional analysis of ΔMoatg1 and ΔMoatg4 mutants, we demonstrate that infection-associated nuclear degeneration in M. oryzae instead occurs by non-selective macroautophagy, which is necessary for rice blast disease.
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176
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Toulmay A, Prinz WA. A conserved membrane-binding domain targets proteins to organelle contact sites. J Cell Sci 2012; 125:49-58. [PMID: 22250200 DOI: 10.1242/jcs.085118] [Citation(s) in RCA: 188] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Membrane contact sites (MCSs), where the membranes of two organelles are closely apposed, are regions where small molecules such as lipids or calcium are exchanged between organelles. We have identified a conserved membrane-binding domain found exclusively in proteins at MCSs in Saccharomyces cerevisiae. The synaptotagmin-like-mitochondrial-lipid binding protein (SMP) domain is conserved across species. We show that all seven proteins that contain this domain in yeast localize to one of three MCSs. Human proteins with SMP domains also localize to MCSs when expressed in yeast. The SMP domain binds membranes and is necessary for protein targeting to MCSs. Proteins containing this domain could be involved in lipid metabolism. This is the first protein domain found exclusively in proteins at MCSs.
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Affiliation(s)
- Alexandre Toulmay
- Laboratory of Cell and Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA
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177
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Pereira L, Girardi JP, Bakovic M. Forms, crosstalks, and the role of phospholipid biosynthesis in autophagy. Int J Cell Biol 2012; 2012:931956. [PMID: 22291708 PMCID: PMC3265067 DOI: 10.1155/2012/931956] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2011] [Revised: 10/04/2011] [Accepted: 10/13/2011] [Indexed: 12/30/2022] Open
Abstract
Autophagy is a highly conserved cellular process occurring during periods of stress to ensure a cell's survival by recycling cytosolic constituents and making products that can be used in energy generation and other essential processes. Three major forms of autophagy exist according to the specific mechanism through which cytoplasmic material is transported to a lysosome. Chaperone-mediated autophagy is a highly selective form of autophagy that delivers specific proteins for lysosomal degradation. Microautophagy is a less selective form of autophagy that occurs through lysosomal membrane invaginations, forming tubes and directly engulfing cytoplasm. Finally, macroautophagy involves formation of new membrane bilayers (autophagosomes) that engulf cytosolic material and deliver it to lysosomes. This review provides new insights on the crosstalks between different forms of autophagy and the significance of bilayer-forming phospholipid synthesis in autophagosomal membrane formation.
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Affiliation(s)
- Leanne Pereira
- Department of Human Health and Nutritional Sciences, University of Guelph, 50 Stone Road East, Guelph, ON, Canada N1G 2W1
| | - John Paul Girardi
- Department of Human Health and Nutritional Sciences, University of Guelph, 50 Stone Road East, Guelph, ON, Canada N1G 2W1
| | - Marica Bakovic
- Department of Human Health and Nutritional Sciences, University of Guelph, 50 Stone Road East, Guelph, ON, Canada N1G 2W1
- Department of Human Health and Nutritional Sciences, University of Guelph, Animal Science and Nutrition Building, Room 346, Guelph, ON, Canada N1G 2W1
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178
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Lipid transfer and signaling at organelle contact sites: the tip of the iceberg. Curr Opin Cell Biol 2011; 23:458-63. [PMID: 21555211 DOI: 10.1016/j.ceb.2011.04.006] [Citation(s) in RCA: 139] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2011] [Revised: 03/11/2011] [Accepted: 04/18/2011] [Indexed: 01/31/2023]
Abstract
Membrane contact sites (MCSs) are formed by the close apposition of membranes of two organelles. They are zones where signals and small molecules, such as lipids and calcium, are exchanged between intracellular compartments. The past few years have seen considerable progress in our understanding of how MCSs form and facilitate the exchange of lipids and signals. Here we summarize what has been learned about MCSs between the endoplamic reticulum (ER) and the plasma membrane, the ER and mitochondria, and the ER and endosomes or lysosomes. These findings suggest that we are just beginning to understand how MCSs form and function.
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179
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Abstract
Eukaryotic organelles can interact with each other through stable junctions where the two membranes are kept in close apposition. The junction that connects the endoplasmic reticulum to the plasma membrane (ER-PM junction) is unique in providing a direct communication link between the ER and the PM. In a recently discovered signaling process, STIM (stromal-interacting molecule) proteins sense a drop in ER Ca(2+) levels and directly activate Orai PM Ca(2+) channels across the junction space. In an inverse process, a voltage-gated PM Ca(2+) channel can directly open ER ryanodine-receptor Ca(2+) channels in striated-muscle cells. Although ER-PM junctions were first described 50 years ago, their broad importance in Ca(2+) signaling, as well as in the regulation of cholesterol and phosphatidylinositol lipid transfer, has only recently been realized. Here, we discuss research from different fields to provide a broad perspective on the structures and unique roles of ER-PM junctions in controlling signaling and metabolic processes.
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Affiliation(s)
- Silvia Carrasco
- Department of Chemical and Systems Biology, School of Medicine, Stanford University, Stanford, California 94305, USA.
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180
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Elbaz Y, Schuldiner M. Staying in touch: the molecular era of organelle contact sites. Trends Biochem Sci 2011; 36:616-23. [PMID: 21958688 DOI: 10.1016/j.tibs.2011.08.004] [Citation(s) in RCA: 178] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2011] [Revised: 08/09/2011] [Accepted: 08/15/2011] [Indexed: 01/10/2023]
Abstract
Membrane contact sites (MCS) are close appositions between two organelles that facilitate both signaling and the passage of ions and lipids from one cellular compartment to another. Despite the fact that MCS have been observed for over 50 years now, we still know very little about the molecular machinery required to create them or their structure, function and regulation. In this review, we focus on the three best-characterized contact sites to date: the nucleus-vacuole junction and mitochondria-ER and plasma membrane-ER contact sites. In addition, we discuss principles arising from recent research and highlight several unanswered questions in the field.
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Affiliation(s)
- Yael Elbaz
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel
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181
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Hayes MJ, Bryon K, Satkurunathan J, Levine TP. Yeast homologues of three BLOC-1 subunits highlight KxDL proteins as conserved interactors of BLOC-1. Traffic 2011; 12:260-8. [PMID: 21159114 DOI: 10.1111/j.1600-0854.2010.01151.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Biogenesis of lysosome-related organelle complex-1 (BLOC-1) is one of the four multi-subunit complexes implicated in sorting cargo to lysosome-related organelles, as loss of function of any of these complexes causes Hermansky-Pudlak syndrome. Eight subunits of BLOC-1 interact with each other and with many other proteins. Identifying new interactors of BLOC-1 will increase understanding of its mechanism of action, and studies in model organisms are useful for finding such interactors. PSI-BLAST searches identify homologues in diverse model organisms, but there are significant gaps for BLOC-1, with none of its eight subunits found in Saccharomyces cerevisiae. Here we use more sensitive searches to identify distant homologues for three BLOC-1 subunits in S. cerevisiae: Blos1, snapin and cappuccino (cno). Published data on protein interactions show that in yeast these are likely to form a complex with three other proteins. One of these is the yeast homologue of the previously uncharacterized KxDL protein, which also interacts with Blos1 and cno in higher eukaryotes, suggesting that KxDL proteins are key interactors with BLOC-1.
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Affiliation(s)
- Matthew J Hayes
- Department of Cell Biology, UCL Institute of Ophthalmology, Bath Street, London EC1V9EL, UK
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182
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Derré I, Swiss R, Agaisse H. The lipid transfer protein CERT interacts with the Chlamydia inclusion protein IncD and participates to ER-Chlamydia inclusion membrane contact sites. PLoS Pathog 2011; 7:e1002092. [PMID: 21731489 PMCID: PMC3121800 DOI: 10.1371/journal.ppat.1002092] [Citation(s) in RCA: 209] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2010] [Accepted: 04/04/2011] [Indexed: 12/21/2022] Open
Abstract
Bacterial pathogens that reside in membrane bound compartment manipulate the host cell machinery to establish and maintain their intracellular niche. The hijacking of inter-organelle vesicular trafficking through the targeting of small GTPases or SNARE proteins has been well established. Here, we show that intracellular pathogens also establish direct membrane contact sites with organelles and exploit non-vesicular transport machinery. We identified the ER-to-Golgi ceramide transfer protein CERT as a host cell factor specifically recruited to the inclusion, a membrane-bound compartment harboring the obligate intracellular pathogen Chlamydia trachomatis. We further showed that CERT recruitment to the inclusion correlated with the recruitment of VAPA/B-positive tubules in close proximity of the inclusion membrane, suggesting that ER-Inclusion membrane contact sites are formed upon C. trachomatis infection. Moreover, we identified the C. trachomatis effector protein IncD as a specific binding partner for CERT. Finally we showed that depletion of either CERT or the VAP proteins impaired bacterial development. We propose that the presence of IncD, CERT, VAPA/B, and potentially additional host and/or bacterial factors, at points of contact between the ER and the inclusion membrane provides a specialized metabolic and/or signaling microenvironment favorable to bacterial development.
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Affiliation(s)
- Isabelle Derré
- Section of Microbial Pathogenesis, Yale University School of Medicine, New Haven, Connecticut, United States of America.
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183
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Lin TH, Murphy RF, Bar-Joseph Z. Discriminative motif finding for predicting protein subcellular localization. IEEE/ACM TRANSACTIONS ON COMPUTATIONAL BIOLOGY AND BIOINFORMATICS 2011; 8:441-51. [PMID: 21233524 PMCID: PMC3050600 DOI: 10.1109/tcbb.2009.82] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Many methods have been described to predict the subcellular location of proteins from sequence information. However, most of these methods either rely on global sequence properties or use a set of known protein targeting motifs to predict protein localization. Here, we develop and test a novel method that identifies potential targeting motifs using a discriminative approach based on hidden Markov models (discriminative HMMs). These models search for motifs that are present in a compartment but absent in other, nearby, compartments by utilizing an hierarchical structure that mimics the protein sorting mechanism. We show that both discriminative motif finding and the hierarchical structure improve localization prediction on a benchmark data set of yeast proteins. The motifs identified can be mapped to known targeting motifs and they are more conserved than the average protein sequence. Using our motif-based predictions, we can identify potential annotation errors in public databases for the location of some of the proteins. A software implementation and the data set described in this paper are available from http://murphylab.web.cmu.edu/software/2009_TCBB_motif/.
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Affiliation(s)
- Tien-ho Lin
- Carnegie Mellon University, Pittsburgh, Pittsburgh, PA 15213, USA.
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184
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Abstract
Mitochondria are essential for oxidative energy production in aerobic eukaryotic cells, where they are also required for multiple biosynthetic pathways to take place. Mitochondria also monitor and evaluate complex information from the environment and intracellular milieu, including the presence or absence of growth factors, oxygen, reactive oxygen species, and DNA damage. It follows that disturbances of the integrity of mitochondrial function lead to the disruption of cell function, expressed as disease, aging, or cell death. It has been assumed that the degradation of damaged mitochondria by an autophagy-related pathway specific to mitochondria (mitophagy), recently found to be strictly regulated, is a fundamental process essential for cell homeostasis. Until now, the main role of mitophagy has been tentatively defined as a 'house-cleaning' pathway that allows to eliminate altered mitochondria, but mitophagy may also play a role in the adaptation of the number and quality of mitochondria to new environmental conditions. In yeast, recent data defined two categories of mitophagy actors: ones constitutively required for mitophagy and those with mitophagy-regulatory functions. Situations were also uncovered in normal physiology in which cells utilize mitophagy to eliminate damaged, dysfunctional, and superfluous mitochondria to adjust to changing physiological demands.
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185
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Dawaliby R, Mayer A. Microautophagy of the nucleus coincides with a vacuolar diffusion barrier at nuclear-vacuolar junctions. Mol Biol Cell 2010; 21:4173-83. [PMID: 20943953 PMCID: PMC2993746 DOI: 10.1091/mbc.e09-09-0782] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Nuclei bind yeast vacuoles via nucleus-vacuole (NV) junctions. Under nutrient restriction, NV junctions invaginate and release vesicles filled with nuclear material into vacuoles, resulting in piecemeal microautophagy of the nucleus (PMN). We show that the electrochemical gradient across the vacuolar membrane promotes invagination of NV junctions. Existing invaginations persist independently of the gradient, but final release of PMN vesicles requires again V-ATPase activity. We find that NV junctions form a diffusion barrier on the vacuolar membrane that excludes V-ATPase but is enriched in the VTC complex and accessible to other membrane-integral proteins. V-ATPase exclusion depends on the NV junction proteins Nvj1p,Vac8p, and the electrochemical gradient. It also depends on factors of lipid metabolism, such as the oxysterol binding protein Osh1p and the enoyl-CoA reductase Tsc13p, which are enriched in NV junctions, and on Lag1p and Fen1p. Our observations suggest that NV junctions form in two separable steps: Nvj1p and Vac8p suffice to establish contact between the two membranes. The electrochemical potential and lipid-modifying enzymes are needed to establish the vacuolar diffusion barrier, invaginate NV junctions, and form PMN vesicles.
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Affiliation(s)
- Rosie Dawaliby
- Département de Biochimie, Université de Lausanne, Chemin des Boveresses 155, 1066 Epalinges, Switzerland
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186
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Abstract
Oxysterol-binding protein (OSBP)-related proteins (ORPs) are lipid-binding proteins that are conserved from yeast to humans. They are implicated in many cellular processes including signaling, vesicular trafficking, lipid metabolism, and nonvesicular sterol transport. All ORPs contain an OSBP-related domain (ORD) that has a hydrophobic pocket that binds a single sterol. ORDs also contain additional membrane-binding surfaces, some of which bind phosphoinositides and may regulate sterol binding. Studies in yeast suggest that ORPs function as sterol transporters, perhaps in regions where organelle membranes are closely apposed. Yeast ORPs also participate in vesicular trafficking, although their role is unclear. In mammalian cells, some ORPs function as sterol sensors that regulate the assembly of protein complexes in response to changes in cholesterol levels. This review will summarize recent advances in our understanding of how ORPs bind lipids and membranes and how they function in diverse cellular processes.
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Affiliation(s)
- Sumana Raychaudhuri
- Laboratory of Cell Biochemistry and Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
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187
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188
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Mijaljica D, Prescott M, Devenish RJ. The intricacy of nuclear membrane dynamics during nucleophagy. Nucleus 2010; 1:213-23. [PMID: 21327066 PMCID: PMC3027025 DOI: 10.4161/nucl.1.3.11738] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2009] [Revised: 02/11/2010] [Accepted: 02/16/2010] [Indexed: 12/17/2022] Open
Abstract
The cell nucleus is an organelle bounded by a double-membrane which undergoes drastic reorganization during major cellular events such as cell division and apoptosis. Maintenance of proper nuclear structure, function and dynamics is central to organelle vitality. Over recent years growing evidence has shown that parts of the nucleus can be specifically degraded by an autophagic process termed nucleophagy. The process is best described in the yeast, Saccharomyces cerevisiae, where piecemeal microautophagy of the nucleus or nucleophagy (micronucleophagy) requires direct interaction of the nuclear membrane with that of the vacuole (the yeast lytic compartment). Here, we review the process of nucleophagy in the context of nuclear membrane dynamics, and examine the evidence for autophagic degradation of the nucleus in mammalian cells. Finally, we discuss the importance of nucleophagy as a 'housecleaning' mechanism for the nucleus under both normal and disease conditions.
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Affiliation(s)
- Dalibor Mijaljica
- Department of Biochemistry and Molecular Biology, Monash University, Victoria, Australia
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189
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Lafontaine DLJ. A 'garbage can' for ribosomes: how eukaryotes degrade their ribosomes. Trends Biochem Sci 2010; 35:267-77. [PMID: 20097077 DOI: 10.1016/j.tibs.2009.12.006] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2009] [Revised: 12/16/2009] [Accepted: 12/18/2009] [Indexed: 12/19/2022]
Abstract
Ribosome synthesis is a major metabolic activity that involves hundreds of individual reactions, each of which is error-prone. Ribosomal insults occur in cis (alteration in rRNA sequences) and in trans (failure to bind to, or loss of, an assembly factor or ribosomal protein). In addition, specific growth conditions, such as starvation, require that excess ribosomes are turned over efficiently. Recent work indicates that cells evolved multiple strategies to recognize specifically, and target for clearance, ribosomes that are structurally and/or functionally deficient, as well as in excess. This surveillance is active at every step of the ribosome synthesis pathway and on mature ribosomes, involves nearly entirely different mechanisms for the small and large subunits, and requires specialized subcellular organelles.
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Affiliation(s)
- Denis L J Lafontaine
- Fonds de la Recherche Scientifique (FRS-F.N.R.S.), Institut de Biologie et de Médecine Moléculaire (IBMM), Université Libre de Bruxelles (ULB), Charleroi-Gosselies, Belgium.
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190
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Fischer MA, Temmerman K, Ercan E, Nickel W, Seedorf M. Binding of Plasma Membrane Lipids Recruits the Yeast Integral Membrane Protein Ist2 to the Cortical ER. Traffic 2009; 10:1084-97. [PMID: 19453974 DOI: 10.1111/j.1600-0854.2009.00926.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- Marcel André Fischer
- Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Alliance, Heidelberg, Germany
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191
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Isola M, Isola R, Lantini MS, Riva A. The three-dimensional morphology of Candida albicans as seen by high-resolution scanning electron microscopy. J Microbiol 2009; 47:260-4. [PMID: 19557342 DOI: 10.1007/s12275-008-0212-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2008] [Accepted: 02/24/2009] [Indexed: 10/20/2022]
Abstract
The fine structure of Candida albicans has been repeatedly described by transmission electron microscopy, whereas studies by high-resolution scanning electron microscopy (HRSEM) are rare and devoted solely to the study of its external morphology. This report describes the results of an HRSEM study on C. albicans carried out by an osmium maceration protocol modified to better retain the structural characteristics of this yeast. Thus, we visualized various intracellular structures including invaginations of cell membrane (plasmalemmasomes), nuclear envelope, mitochondria, the vacuolar system, and two additional structures that might represent a form of endoplasmic reticulum and the Golgi apparatus. The present investigation, which for the first time shows the organelles of C. albicans at the 3D level, may lead to a better understanding of its cell physiology.
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Affiliation(s)
- Michela Isola
- Department of Cytomorphology, Cittadella Universitaria di Monserrato, University of Cagliari, Monserrato 09042, Italy
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192
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Hou H, John Peter AT, Meiringer C, Subramanian K, Ungermann C. Analysis of DHHC acyltransferases implies overlapping substrate specificity and a two-step reaction mechanism. Traffic 2009; 10:1061-73. [PMID: 19453970 DOI: 10.1111/j.1600-0854.2009.00925.x] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Asp-His-His-Cys (DHHC) cysteine-rich domain (CRD) acyltransferases are polytopic transmembrane proteins that are found along the endomembrane system of eukaryotic cells and mediate palmitoylation of peripheral and integral membrane proteins. Here, we address the in vivo substrate specificity of five of the seven DHHC acyltransferases for peripheral membrane proteins by an overexpression approach. For all analysed DHHC proteins we detect strongly overlapping substrate specificity. In addition, we now show acyltransferase activity for Pfa5. More importantly, the DHHC protein Pfa3 is able to trap several substrates at the vacuole. For Pfa3 and its substrate Vac8, we can distinguish two consecutive steps in the acylation reaction: an initial binding that occurs independently of its central cysteine in the DHHC box, but requires myristoylation of its substrate Vac8, and a DHHC-motif dependent acylation. Our data also suggest that proteins can be palmitoylated on several organelles. Thus, the intracellular distribution of DHHC proteins provides an acyltransferase network, which may promote dynamic membrane association of substrate proteins.
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Affiliation(s)
- Haitong Hou
- University of Osnabrück, Department of Biology, Biochemistry section, Osnabrück, Germany
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193
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Nadolski MJ, Linder ME. Molecular recognition of the palmitoylation substrate Vac8 by its palmitoyltransferase Pfa3. J Biol Chem 2009; 284:17720-30. [PMID: 19416974 DOI: 10.1074/jbc.m109.005447] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Palmitoylation of the yeast vacuolar protein Vac8 is important for its role in membrane-mediated events such as vacuole fusion. It has been established both in vivo and in vitro that Vac8 is palmitoylated by the Asp-His-His-Cys (DHHC) protein Pfa3. However, the determinants of Vac8 critical for recognition by Pfa3 have yet to be elucidated. This is of particular importance because of the lack of a consensus sequence for palmitoylation. Here we show that Pfa3 was capable of palmitoylating each of the three N-terminal cysteines of Vac8 and that this reaction was most efficient when Vac8 is N-myristoylated. Additionally, when we analyzed the Src homology 4 (SH4) domain of Vac8 independent of the rest of the protein, palmitoylation by Pfa3 still occurred. However, the specificity of palmitoylation seen for the full-length protein was lost, and the SH4 domain was palmitoylated by all five of the yeast DHHC proteins tested. These data suggested that a region of the protein C-terminal to the SH4 domain was important for conferring specificity of palmitoylation. This was confirmed by use of a chimeric protein in which the SH4 domain of Vac8 was swapped for that of Meh1, another palmitoylated and N-myristoylated protein in yeast. In this case we saw specificity mimic that of wild type Vac8. Competition experiments revealed that the 11th armadillo repeat of Vac8 is an important element for recognition by Pfa3. This demonstrates that regions distant from the palmitoylated cysteines are important for recognition by DHHC proteins.
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Affiliation(s)
- Marissa J Nadolski
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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194
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Deffieu M, Bhatia-Kissová I, Salin B, Galinier A, Manon S, Camougrand N. Glutathione participates in the regulation of mitophagy in yeast. J Biol Chem 2009; 284:14828-37. [PMID: 19366696 DOI: 10.1074/jbc.m109.005181] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The antioxidant N-acetyl-l-cysteine prevented the autophagy-dependent delivery of mitochondria to the vacuoles, as examined by fluorescence microscopy of mitochondria-targeted green fluorescent protein, transmission electron microscopy, and Western blot analysis of mitochondrial proteins. The effect of N-acetyl-l-cysteine was specific to mitochondrial autophagy (mitophagy). Indeed, autophagy-dependent activation of alkaline phosphatase and the presence of hallmarks of non-selective microautophagy were not altered by N-acetyl-l-cysteine. The effect of N-acetyl-l-cysteine was not related to its scavenging properties, but rather to its fueling effect of the glutathione pool. As a matter of fact, the decrease of the glutathione pool induced by chemical or genetical manipulation did stimulate mitophagy but not general autophagy. Conversely, the addition of a cell-permeable form of glutathione inhibited mitophagy. Inhibition of glutathione synthesis had no effect in the strain Deltauth1, which is deficient in selective mitochondrial degradation. These data show that mitophagy can be regulated independently of general autophagy, and that its implementation may depend on the cellular redox status.
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Affiliation(s)
- Maika Deffieu
- CNRS, Institut de Biochimie et de Génétique Cellulaires (UMR 5095), Université de Bordeaux 2, 1 rue Camille Saint-Saëns, 33077 Bordeaux Cedex, France
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195
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Lebiedzinska M, Szabadkai G, Jones AWE, Duszynski J, Wieckowski MR. Interactions between the endoplasmic reticulum, mitochondria, plasma membrane and other subcellular organelles. Int J Biochem Cell Biol 2009; 41:1805-16. [PMID: 19703651 DOI: 10.1016/j.biocel.2009.02.017] [Citation(s) in RCA: 132] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2008] [Revised: 02/22/2009] [Accepted: 02/23/2009] [Indexed: 02/02/2023]
Abstract
Several recent works show structurally and functionally dynamic contacts between mitochondria, the plasma membrane, the endoplasmic reticulum, and other subcellular organelles. Many cellular processes require proper cooperation between the plasma membrane, the nucleus and subcellular vesicular/tubular networks such as mitochondria and the endoplasmic reticulum. It has been suggested that such contacts are crucial for the synthesis and intracellular transport of phospholipids as well as for intracellular Ca(2+) homeostasis, controlling fundamental processes like motility and contraction, secretion, cell growth, proliferation and apoptosis. Close contacts between smooth sub-domains of the endoplasmic reticulum and mitochondria have been shown to be required also for maintaining mitochondrial structure. The overall distance between the associating organelle membranes as quantified by electron microscopy is small enough to allow contact formation by proteins present on their surfaces, allowing and regulating their interactions. In this review we give a historical overview of studies on organelle interactions, and summarize the present knowledge and hypotheses concerning their regulation and (patho)physiological consequences.
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196
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Riechers SP, Stahl U, Lang C. Defects in intracellular trafficking and endocytic/vacuolar acidification determine the efficiency of endocytotic DNA uptake in yeast. J Cell Biochem 2009; 106:327-36. [PMID: 19115284 DOI: 10.1002/jcb.22009] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The yeast Saccharomyces cerevisiae is a standard model system to study endocytosis. Here we describe the examination of a representative subset of deletion mutants to identify and locate steps in endocytic transport, endosomal/lysosomal acidification and in intracellular transport of hydrolases in non-viral transfection processes. When transport in late endocytosis is inhibited, transfection efficiency is significantly enhanced. Similarly, transfection efficiency is enhanced when the pH-value of the endosomal/vacuolar system is modified. Transfection efficiency is furthermore elevated when the N+/K+ transport in the endosomal system is disturbed. Finally, we observe enhanced transfection efficiency in mutants disturbed in the CVT/autophagy pathway and in hydrolase transport to the vacuole. In summary, non-viral transfection efficiency can be significantly increased by either (i) inhibiting the transport of endocytosed material before it enters the vacuole, or (ii) inducing a non-natural pH-value of the endosomal/vacuolar system, or (iii) slowing down degradative processes by inhibiting vacuolar hydrolases or the transport between Golgi and late endosome/vacuole.
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Affiliation(s)
- Sean-Patrick Riechers
- Department of Microbiology and Genetics, Institute for Biotechnology, Technische Universität Berlin, Gustav-Meyer-Allee 25, D-13355 Berlin, Germany
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197
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Kraft C, Reggiori F, Peter M. Selective types of autophagy in yeast. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2009; 1793:1404-12. [PMID: 19264099 DOI: 10.1016/j.bbamcr.2009.02.006] [Citation(s) in RCA: 111] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/27/2009] [Revised: 02/17/2009] [Accepted: 02/18/2009] [Indexed: 12/19/2022]
Abstract
Autophagy is the process through which cytosol and organelles are sequestered into a double-membrane vesicle called an autophagosome and delivered to the vacuole/lysosome for breakdown and recycling. One of its primary roles in unicellular organisms is to regulate intracellular homeostasis and to adjust organelle numbers in response to stress such as changes in nutrient availability. In higher eukaryotes, autophagy plays also an important role in stress-response, development, cell differentiation, immunity and tumor suppression. Importantly, a misregulation in this catabolic pathway is associated with diseases such as cancer, neurodegeneration and myopathies. For a long time, starvation-induced autophagy has been considered a non-selective pathway, however, numerous recent observations revealed that autophagy can also selectively eliminate specific proteins, protein complexes and organelles. Most of these studies used yeast Saccharomyces cerevisiae as a model organism. In this compendium, we will review what is known about the mechanisms and roles of selective types of autophagy in yeast and highlight possible connections of these pathways with human diseases. In addition, we will discuss some selective types of autophagy, which have so far only been described in higher eukaryotes.
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Affiliation(s)
- Claudine Kraft
- Institute of Biochemistry, HPM, ETH Hönggerberg, 8093 Zürich, Switzerland.
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198
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Down-regulation of epidermal growth factor receptor signalling within multivesicular bodies. Biochem Soc Trans 2009; 37:173-7. [PMID: 19143625 DOI: 10.1042/bst0370173] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Activated EGFR (epidermal growth factor receptor) undergoes ESCRT (endosomal sorting complex required for transport)-mediated sorting on to the intraluminal vesicles of MVBs (multivesicular bodies) before degradation in the lysosome. Sorting of endocytosed EGFR on to the intraluminal vesicles of MVBs removes the catalytic domain of the EGFR from the cytoplasm, resulting in termination of receptor signalling. The formation of intraluminal vesicles that contain EGFR is promoted by EGF stimulation in a mechanism that depends on the EGFR substrate, annexin 1. Signalling from endocytosed EGFR is also subject to down-regulation through receptor dephosphorylation by PTPs (protein tyrosine phosphatases), such as PTP1B, an enzyme thought to reside on the ER (endoplasmic reticulum). In the present paper, we review how the phosphorylation state of components of the MVB sorting machinery, as well as the EGFR, may play a critical role in regulating EGFR sorting and signalling.
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199
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Mitofusin 2 tethers endoplasmic reticulum to mitochondria. Nature 2009; 456:605-10. [PMID: 19052620 DOI: 10.1038/nature07534] [Citation(s) in RCA: 1851] [Impact Index Per Article: 123.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2008] [Accepted: 10/08/2008] [Indexed: 12/11/2022]
Abstract
Juxtaposition between endoplasmic reticulum (ER) and mitochondria is a common structural feature, providing the physical basis for intercommunication during Ca(2+) signalling; yet, the molecular mechanisms controlling this interaction are unknown. Here we show that mitofusin 2, a mitochondrial dynamin-related protein mutated in the inherited motor neuropathy Charcot-Marie-Tooth type IIa, is enriched at the ER-mitochondria interface. Ablation or silencing of mitofusin 2 in mouse embryonic fibroblasts and HeLa cells disrupts ER morphology and loosens ER-mitochondria interactions, thereby reducing the efficiency of mitochondrial Ca(2+) uptake in response to stimuli that generate inositol-1,4,5-trisphosphate. An in vitro assay as well as genetic and biochemical evidences support a model in which mitofusin 2 on the ER bridges the two organelles by engaging in homotypic and heterotypic complexes with mitofusin 1 or 2 on the surface of mitochondria. Thus, mitofusin 2 tethers ER to mitochondria, a juxtaposition required for efficient mitochondrial Ca(2+) uptake.
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200
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Krick R, Muehe Y, Prick T, Bremer S, Schlotterhose P, Eskelinen EL, Millen J, Goldfarb DS, Thumm M. Piecemeal microautophagy of the nucleus requires the core macroautophagy genes. Mol Biol Cell 2008; 19:4492-505. [PMID: 18701704 DOI: 10.1091/mbc.e08-04-0363] [Citation(s) in RCA: 157] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Autophagy is a diverse family of processes that transport cytoplasm and organelles into the lysosome/vacuole lumen for degradation. During macroautophagy cargo is packaged in autophagosomes that fuse with the lysosome/vacuole. During microautophagy cargo is directly engulfed by the lysosome/vacuole membrane. Piecemeal microautophagy of the nucleus (PMN) occurs in Saccharomyces cerevisiae at nucleus-vacuole (NV) junctions and results in the pinching-off and release into the vacuole of nonessential portions of the nucleus. Previous studies concluded macroautophagy ATG genes are not absolutely required for PMN. Here we report using two biochemical assays that PMN is efficiently inhibited in atg mutant cells: PMN blebs are produced, but vesicles are rarely released into the vacuole lumen. Electron microscopy of arrested PMN structures in atg7, atg8, and atg9 mutant cells suggests that NV-junction-associated micronuclei may normally be released from the nucleus before their complete enclosure by the vacuole membrane. In this regard PMN is similar to the microautophagy of peroxisomes (micropexophagy), where the side of the peroxisome opposite the engulfing vacuole is capped by a structure called the "micropexophagy-specific membrane apparatus" (MIPA). The MIPA contains Atg proteins and facilitates terminal enclosure and fusion steps. PMN does not require the complete vacuole homotypic fusion genes. We conclude that a spectrum of ATG genes is required for the terminal vacuole enclosure and fusion stages of PMN.
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Affiliation(s)
- R Krick
- Center of Biochemistry and Molecular Cell Biology, Georg-August University, D-37073 Göttingen, Germany
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