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Abstract
Autophagy is a highly conserved process and is essential for the maintenance of cellular homeostasis. Autophagy occurs at a basal level in all cells, but it can be up-regulated during stress, starvation, or infection. Misregulation of autophagy has been linked to various disorders, including cancer, neurodegeneration, and immune diseases. Here, we discuss the essential proteins acting in the formation of an autophagosome, with a focus on the ULK and VPS34 kinase complexes, phosphatidylinositol 3-phosphate effector proteins, and the transmembrane autophagy-related protein ATG9. The function and regulation of these and other autophagy-related proteins acting during formation will be addressed, in particular during amino acid starvation.
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Affiliation(s)
- Thomas J Mercer
- From the Molecular Cell Biology of Autophagy Laboratory, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, United Kingdom
| | - Andrea Gubas
- From the Molecular Cell Biology of Autophagy Laboratory, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, United Kingdom
| | - Sharon A Tooze
- From the Molecular Cell Biology of Autophagy Laboratory, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, United Kingdom
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52
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Qiao Y, Liang X, Yan Y, Lu Y, Zhang D, Yao W, Wu W, Yan Z. Identification of Exosomal miRNAs in Rats With Pulmonary Neutrophilic Inflammation Induced by Zinc Oxide Nanoparticles. Front Physiol 2018; 9:217. [PMID: 29593572 PMCID: PMC5859358 DOI: 10.3389/fphys.2018.00217] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2017] [Accepted: 02/26/2018] [Indexed: 12/22/2022] Open
Abstract
It has been previously shown that inhaled zinc oxide nanoparticles (ZnO-NPs) can modulate inflammation. MicroRNAs (miRNAs) enclosed in exosomes have been identified as an important signature for inflammatory responses. However, the role of exosomal miRNAs during pathogenic inflammation has not been investigated. Healthy rats were exposed to ZnO-NPs (41.7 nm; 2, 4, and 8 mg/kg) or saline (control) via oropharyngeal aspiration. ZnO-NPs induced significant increases in the serum levels of interleukin 8 (IL-8), interleukin-1 beta (IL-1β), and tumor necrosis factor α (TNF-α), and elevated the number of cells and the percentage of neutrophils in the blood. Moreover, exposure to ZnO-NPs increased the levels of lactate dehydrogenase (LDH) activity and total protein in bronchoalveolar lavage fluid (BALF). Differential profiling of miRNAs in isolated serum exosomes revealed that 16 miRNAs were up-regulated and 7 down-regulated in ZnO-NP-treated rats compared with the controls. Functional and pathway analysis indicated that miRNAs may participate in inflammation directly and indirectly through protein and vesicle-mediated transport or regulation of IL-1, oxidative stress, apoptosis, and autophagy. These results suggest that miRNAs in serum exosomes are involved in pulmonary neutrophilic inflammation induced by ZnO-NPs.
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Affiliation(s)
- Yamei Qiao
- Department of Occupational and Environmental Health Sciences, College of Public Health, Zhengzhou University, Zhengzhou, China
| | - Xiao Liang
- Department of Occupational and Environmental Health Sciences, College of Public Health, Zhengzhou University, Zhengzhou, China
| | - Yingjie Yan
- Department of Occupational and Environmental Health Sciences, College of Public Health, Zhengzhou University, Zhengzhou, China
| | - Yake Lu
- Department of Occupational and Environmental Health Sciences, College of Public Health, Zhengzhou University, Zhengzhou, China
| | - Di Zhang
- Department of Occupational and Environmental Health Sciences, College of Public Health, Zhengzhou University, Zhengzhou, China
| | - Wu Yao
- Department of Occupational and Environmental Health Sciences, College of Public Health, Zhengzhou University, Zhengzhou, China
| | - Weidong Wu
- Department of Occupational and Environmental Health Sciences, School of Public Health, Xinxiang Medical University, Xinxiang, China
| | - Zhen Yan
- Department of Occupational and Environmental Health Sciences, School of Public Health, Hainan Medical University, Haikou, China
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53
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Stjepanovic G, Baskaran S, Lin MG, Hurley JH. Vps34 Kinase Domain Dynamics Regulate the Autophagic PI 3-Kinase Complex. Mol Cell 2017; 67:528-534.e3. [PMID: 28757208 DOI: 10.1016/j.molcel.2017.07.003] [Citation(s) in RCA: 69] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2017] [Revised: 05/16/2017] [Accepted: 06/30/2017] [Indexed: 12/29/2022]
Abstract
The class III phosphatidylinositol 3-kinase complex I (PI3KC3-C1) is required for the initiation of essentially all macroautophagic processes. PI3KC3-C1 consists of the lipid kinase catalytic subunit VPS34, the VPS15 scaffold, and the regulatory BECN1 and ATG14 subunits. The VPS34 catalytic domain and BECN1:ATG14 subcomplex do not touch, and it is unclear how allosteric signals are transmitted to VPS34. We used EM and crosslinking mass spectrometry to dissect five conformational substates of the complex, including one in which the VPS34 catalytic domain is dislodged from the complex but remains tethered by an intrinsically disordered linker. A "leashed" construct prevented dislodging without interfering with the other conformations, blocked enzyme activity in vitro, and blocked autophagy induction in yeast cells. This pinpoints the dislodging and tethering of the VPS34 catalytic domain, and its regulation by VPS15, as a master allosteric switch in autophagy induction.
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Affiliation(s)
- Goran Stjepanovic
- Department of Molecular and Cell Biology and California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA 94720, USA; Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Sulochanadevi Baskaran
- Department of Molecular and Cell Biology and California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Mary G Lin
- Department of Molecular and Cell Biology and California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA 94720, USA
| | - James H Hurley
- Department of Molecular and Cell Biology and California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA 94720, USA; Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
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54
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Reidick C, Boutouja F, Platta HW. The class III phosphatidylinositol 3-kinase Vps34 in Saccharomyces cerevisiae. Biol Chem 2017; 398:677-685. [PMID: 27935849 DOI: 10.1515/hsz-2016-0288] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2016] [Accepted: 11/14/2016] [Indexed: 12/23/2022]
Abstract
The class III phosphatidylinositol 3-kinase Vps34 (vacuolar protein sorting 34) catalyzes for the formation of the signaling lipid phosphatidylinositol-3-phopsphate, which is a central factor in the regulation of autophagy, endocytic trafficking and vesicular transport. In this article, we discuss the functional role of the lipid kinase Vps34 in Saccharomyces cerevisiae.
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Affiliation(s)
- Christina Reidick
- Biochemie Intrazellulärer Transportprozesse, Ruhr-Universität Bochum, D-44801 Bochum
| | - Fahd Boutouja
- Biochemie Intrazellulärer Transportprozesse, Ruhr-Universität Bochum, D-44801 Bochum
| | - Harald W Platta
- Biochemie Intrazellulärer Transportprozesse, Ruhr-Universität Bochum, D-44801 Bochum
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55
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Abstract
Autophagy is the process of cellular self-eating by a double-membrane organelle, the autophagosome. A range of signaling processes converge on two protein complexes to initiate autophagy: the ULK1 (unc51-like autophagy activating kinase 1) protein kinase complex and the PI3KC3-C1 (class III phosphatidylinositol 3-kinase complex I) lipid kinase complex. Some 90% of the mass of these large protein complexes consists of noncatalytic domains and subunits, and the ULK1 complex has essential noncatalytic activities. Structural studies of these complexes have shed increasing light on the regulation of their catalytic and noncatalytic activities in autophagy initiation. The autophagosome is thought to nucleate from vesicles containing the integral membrane protein Atg9 (autophagy-related 9), COPII (coat protein complex II) vesicles, and possibly other sources. In the wake of reconstitution and super-resolution imaging studies, we are beginning to understand how the ULK1 and PI3KC3-C1 complexes might coordinate the nucleation and fusion of Atg9 and COPII vesicles at the start of autophagosome biogenesis.
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Affiliation(s)
- James H Hurley
- Department of Molecular and Cell Biology and California Institute of Quantitative Biosciences, University of California, Berkeley, California, and Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California, 94720;
| | - Lindsey N Young
- Department of Molecular and Cell Biology and California Institute of Quantitative Biosciences, University of California, Berkeley, California, and Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California, 94720;
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Keller CW, Lünemann JD. Autophagy and Autophagy-Related Proteins in CNS Autoimmunity. Front Immunol 2017; 8:165. [PMID: 28289410 PMCID: PMC5326760 DOI: 10.3389/fimmu.2017.00165] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2016] [Accepted: 02/02/2017] [Indexed: 12/13/2022] Open
Abstract
Autophagy comprises a heterogeneous group of cellular pathways that enables eukaryotic cells to deliver cytoplasmic constituents for lysosomal degradation, to recycle nutrients, and to survive during starvation. In addition to these primordial functions, autophagy has emerged as a key mechanism in orchestrating innate and adaptive immune responses and to shape CD4+ T cell immunity through delivery of peptides to major histocompatibility complex (MHC) class II-containing compartments (MIICs). Individual autophagy proteins additionally modulate expression of MHC class I molecules for CD8+ T cell activation. The emergence and expansion of autoreactive CD4+ and CD8+ T cells are considered to play a key role in the pathogenesis of multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis. Expression of the essential autophagy-related protein 5 (Atg5), which supports T lymphocyte survival and proliferation, is increased in T cells isolated from blood or brain tissues from patients with relapsing-remitting MS. Whether Atgs contribute to the activation of autoreactive T cells through autophagy-mediated antigen presentation is incompletely understood. Here, we discuss the complex functions of autophagy proteins and pathways in regulating T cell immunity and its potential role in the development and progression of MS.
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Affiliation(s)
- Christian W Keller
- Institute of Experimental Immunology, Laboratory of Neuroinflammation, University of Zürich , Zürich , Switzerland
| | - Jan D Lünemann
- Institute of Experimental Immunology, Laboratory of Neuroinflammation, University of Zürich, Zürich, Switzerland; Department of Neurology, University Hospital Zürich, Zürich, Switzerland
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Nguyen N, Shteyn V, Melia TJ. Sensing Membrane Curvature in Macroautophagy. J Mol Biol 2017; 429:457-472. [PMID: 28088480 PMCID: PMC5276735 DOI: 10.1016/j.jmb.2017.01.006] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2016] [Revised: 01/07/2017] [Accepted: 01/08/2017] [Indexed: 10/20/2022]
Abstract
In response to intracellular stress events ranging from starvation to pathogen invasion, the cell activates one or more forms of macroautophagy. The key event in these related pathways is the de novo formation of a new organelle called the autophagosome, which either surrounds and sequesters random portions of the cytoplasm or selectively targets individual intracellular challenges. Thus, the autophagosome is a flexible membrane platform with dimensions that ultimately depend upon the target cargo. The intermediate membrane, termed the phagophore or isolation membrane, is a cup-like structure with a clear concave face and a highly curved rim. The phagophore is largely devoid of integral membrane proteins; thus, its shape and size are governed by peripherally associated membrane proteins and possibly by the lipid composition of the membrane itself. Growth along the phagophore rim marks the progress of both organelle expansion and ultimately organelle closure around a particular cargo. These two properties, a reliance on peripheral membrane proteins and a structurally distinct membrane architecture, suggest that the ability to target or manipulate membrane curvature might be an essential activity of proteins functioning in this pathway. In this review, we discuss the extent to which membranes are naturally curved at each of the cellular sites believed to engage in autophagosome formation, review basic mechanisms used to sense this curvature, and then summarize the existing literature concerning which autophagy proteins are capable of curvature recognition.
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Affiliation(s)
- Nathan Nguyen
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA.
| | - Vladimir Shteyn
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA.
| | - Thomas J Melia
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA.
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Ma X, Zhang S, He L, Rong Y, Brier LW, Sun Q, Liu R, Fan W, Chen S, Yue Z, Kim J, Guan KL, Li D, Zhong Q. MTORC1-mediated NRBF2 phosphorylation functions as a switch for the class III PtdIns3K and autophagy. Autophagy 2017; 13:592-607. [PMID: 28059666 DOI: 10.1080/15548627.2016.1269988] [Citation(s) in RCA: 68] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
NRBF2/Atg38 has been identified as the fifth subunit of the macroautophagic/autophagic class III phosphatidylinositol 3-kinase (PtdIns3K) complex, along with ATG14/Barkor, BECN1/Vps30, PIK3R4/p150/Vps15 and PIK3C3/Vps34. However, its functional mechanism and regulation are not fully understood. Here, we report that NRBF2 is a fine tuning regulator of PtdIns3K controlled by phosphorylation. Human NRBF2 is phosphorylated by MTORC1 at S113 and S120. Upon nutrient starvation or MTORC1 inhibition, NRBF2 phosphorylation is diminished. Phosphorylated NRBF2 preferentially interacts with PIK3C3/PIK3R4. Suppression of NRBF2 phosphorylation by MTORC1 inhibition alters its binding preference from PIK3C3/PIK3R4 to ATG14/BECN1, leading to increased autophagic PtdIns3K complex assembly, as well as enhancement of ULK1 protein complex association. Consequently, NRBF2 in its unphosphorylated form promotes PtdIns3K lipid kinase activity and autophagy flux, whereas its phosphorylated form blocks them. This study reveals NRBF2 as a critical molecular switch of PtdIns3K and autophagy activation, and its on/off state is precisely controlled by MTORC1 through phosphorylation.
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Affiliation(s)
- Xi Ma
- a State Key Lab of Animal Nutrition, Ministry of Agriculture Feed Industry Center , China Agricultural University , Beijing , China.,b Center for Autophagy Research, Department of Internal Medicine , University of Texas Southwestern Medical Center , Dallas , TX , USA.,c Department of Biochemistry , University of Texas Southwestern Medical Center , Dallas , TX , USA
| | - Shen Zhang
- a State Key Lab of Animal Nutrition, Ministry of Agriculture Feed Industry Center , China Agricultural University , Beijing , China.,b Center for Autophagy Research, Department of Internal Medicine , University of Texas Southwestern Medical Center , Dallas , TX , USA.,c Department of Biochemistry , University of Texas Southwestern Medical Center , Dallas , TX , USA
| | - Long He
- a State Key Lab of Animal Nutrition, Ministry of Agriculture Feed Industry Center , China Agricultural University , Beijing , China.,b Center for Autophagy Research, Department of Internal Medicine , University of Texas Southwestern Medical Center , Dallas , TX , USA.,c Department of Biochemistry , University of Texas Southwestern Medical Center , Dallas , TX , USA
| | - Yueguang Rong
- b Center for Autophagy Research, Department of Internal Medicine , University of Texas Southwestern Medical Center , Dallas , TX , USA.,c Department of Biochemistry , University of Texas Southwestern Medical Center , Dallas , TX , USA
| | - Livia Wilz Brier
- d Division of Biochemistry, Biophysics and Structural Biology, Department of Molecular and Cell Biology , University of California , Berkeley , CA , USA
| | - Qiming Sun
- d Division of Biochemistry, Biophysics and Structural Biology, Department of Molecular and Cell Biology , University of California , Berkeley , CA , USA
| | - Rong Liu
- b Center for Autophagy Research, Department of Internal Medicine , University of Texas Southwestern Medical Center , Dallas , TX , USA.,c Department of Biochemistry , University of Texas Southwestern Medical Center , Dallas , TX , USA
| | - Weiliang Fan
- d Division of Biochemistry, Biophysics and Structural Biology, Department of Molecular and Cell Biology , University of California , Berkeley , CA , USA
| | - She Chen
- e National Institute of Biological Sciences , Beijing , China
| | - Zhenyu Yue
- f Department of Neurology and Neuroscience , Friedman Brain Institute, Icahn School of Medicine at Mount Sinai , New York , NY , USA
| | - Joungmok Kim
- g Department of Pharmacology and Moores Cancer Center , University of California , San Diego, La Jolla , CA , USA
| | - Kun-Liang Guan
- g Department of Pharmacology and Moores Cancer Center , University of California , San Diego, La Jolla , CA , USA
| | - Defa Li
- a State Key Lab of Animal Nutrition, Ministry of Agriculture Feed Industry Center , China Agricultural University , Beijing , China
| | - Qing Zhong
- b Center for Autophagy Research, Department of Internal Medicine , University of Texas Southwestern Medical Center , Dallas , TX , USA.,c Department of Biochemistry , University of Texas Southwestern Medical Center , Dallas , TX , USA
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59
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Hurley JH, Nogales E. Next-generation electron microscopy in autophagy research. Curr Opin Struct Biol 2016; 41:211-216. [PMID: 27614295 DOI: 10.1016/j.sbi.2016.08.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2016] [Revised: 08/25/2016] [Accepted: 08/25/2016] [Indexed: 12/24/2022]
Abstract
Autophagy is the process whereby cytosol, organelles, and inclusions are taken up in a double-membrane vesicle known as the autophagosome, and transported to the lysosome for destruction and recycling. Electron microscopy (EM) led to the discovery of autophagy in the 1950s and has been a central part of its characterization ever since. New capabilities in single particle EM studies of the autophagy machinery are beginning to provide exciting insights into the mechanisms of autophagosome initiation, growth, and substrate targeting. These include EM structures at various resolutions of part of the Atg1 protein kinase complex and all of the class III phosphatidylinositol 3-phosphate complex I that initiate autophagy; the mTORC1 complex that regulates autophagy initiation; the Ape1 particle, a major substrate for selective autophagy in yeast; and p62, a mammalian selective autophagy adaptor. Equally exciting are the prospects for increased resolution and insight into autophagosome formation in cells from advances in cryo-EM tomography and focused ion beam-scanning electron microscopy (FIB-SEM). This review considers recent accomplishments, prospects for progress, and remaining obstacles that still need to be overcome.
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Affiliation(s)
- James H Hurley
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA; California Institute for Quantitative Biosciences, University of California, Berkeley, CA 94720, USA; Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
| | - Eva Nogales
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA; California Institute for Quantitative Biosciences, University of California, Berkeley, CA 94720, USA; Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA; Howard Hughes Medical Institute, University of California, Berkeley, CA 94720, USA.
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