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المؤلفون: Jing Zhu, Hui Xu, Yanhong Xue, Rakhilya Murtazina, Liangyi Chen, Wenjing Li, Rui Li, Yongheng Liang, Haiqian Xu, Liuju Li, Zhiping Xie, Juan Cai, Ao Zhang, Mengzhu Zhao, Xiaoshuai Huang, Qunli Li, Zulin Wu, Yi Ting Zhou, Xiaoxia Cong, Nava Segev, Valeriya Gyurkovska, Dan Sun, Fan Zhou, Lei Zhao
المصدر: Autophagy
The Journal of Cell Biologyمصطلحات موضوعية: Autophagosome, Saccharomyces cerevisiae Proteins, Endosome, Endocytic cycle, Autophagy-Related Proteins, Endosomes, Saccharomyces cerevisiae, macromolecular substances, Biology, Article, ESCRT, 03 medical and health sciences, 0302 clinical medicine, Lysosome, Autophagy, medicine, Research Articles, rab5 GTP-Binding Proteins, 030304 developmental biology, 0303 health sciences, Endosomal Sorting Complexes Required for Transport, Autophagosomes, Intracellular Membranes, Cell Biology, Transport protein, Cell biology, ESCRT complex, Protein Transport, medicine.anatomical_structure, Vacuoles, Commentary, Lysosomes, 030217 neurology & neurosurgery
الوصف: Zhou et al. identify the mechanism of autophagosome (AP) closure. They show that Rab5 GTPase regulates an interaction between the ESCRT subunit Snf7 and Atg17 to bring ESCRT to APs where it catalyzes AP closure. These findings highlight the convergence of the endocytic and autophagic pathways at this step.
In the conserved autophagy pathway, autophagosomes (APs) engulf cellular components and deliver them to the lysosome for degradation. Before fusing with the lysosome, APs have to close via an unknown mechanism. We have previously shown that the endocytic Rab5-GTPase regulates AP closure. Therefore, we asked whether ESCRT, which catalyzes scission of vesicles into late endosomes, mediates the topologically similar process of AP sealing. Here, we show that depletion of representative subunits from all ESCRT complexes causes late autophagy defects and accumulation of APs. Focusing on two subunits, we show that Snf7 and the Vps4 ATPase localize to APs and their depletion results in accumulation of open APs. Moreover, Snf7 and Vps4 proteins complement their corresponding mutant defects in vivo and in vitro. Finally, a Rab5-controlled Atg17–Snf7 interaction is important for Snf7 localization to APs. Thus, we unravel a mechanism in which a Rab5-dependent Atg17–Snf7 interaction leads to recruitment of ESCRT to open APs where ESCRT catalyzes AP closure.الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::e4f388fa8467bed00c6cf9a8d6685d27Test
https://doi.org/10.1083/jcb.201811173Test -
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المؤلفون: Yong Chen, Fan Zhou, Zulin Wu, Zhanna Lipatova, Weiming You, Zhiping Xie, Shenshen Zou, Xiaolong Zhu, Wenjing Li, Jie Cheng, Dan Sun, Nava Segev, Yongheng Liang, Yi Ting Zhou, Xiaoxia Cong, Yutao Liu, Qunli Li, Valeriya Gyurkovska, Rui Li
المصدر: PLoS Genetics, Vol 13, Iss 9, p e1007020 (2017)
PLoS Geneticsمصطلحات موضوعية: 0301 basic medicine, Autophagosome, Cancer Research, Hydrolases, Endocytic cycle, Autophagy-Related Proteins, GTPase, QH426-470, Biochemistry, Phosphatidylinositol 3-Kinases, Fluorescence Microscopy, Genetics (clinical), Microscopy, Cell Death, Kinase, Light Microscopy, Eukaryota, Proteases, Endocytosis, Cell biology, Enzymes, Protein Transport, medicine.anatomical_structure, Cell Processes, Cellular Structures and Organelles, Research Article, Saccharomyces cerevisiae Proteins, Endosome, Autophagic Cell Death, Endosomes, Saccharomyces cerevisiae, Biology, Research and Analysis Methods, 03 medical and health sciences, Lysosome, medicine, Autophagy, Genetics, Vesicles, Molecular Biology, Ecology, Evolution, Behavior and Systematics, rab5 GTP-Binding Proteins, Autophagosomes, Organisms, Fungi, Biology and Life Sciences, Proteins, Cell Biology, Yeast, Guanosine Triphosphatase, 030104 developmental biology, rab GTP-Binding Proteins, Vacuoles, Enzymology, Rab, Lysosomes
الوصف: In the conserved autophagy pathway, the double-membrane autophagosome (AP) engulfs cellular components to be delivered for degradation in the lysosome. While only sealed AP can productively fuse with the lysosome, the molecular mechanism of AP closure is currently unknown. Rab GTPases, which regulate all intracellular trafficking pathways in eukaryotes, also regulate autophagy. Rabs function in GTPase modules together with their activators and downstream effectors. In yeast, an autophagy-specific Ypt1 GTPase module, together with a set of autophagy-related proteins (Atgs) and a phosphatidylinositol-3-phosphate (PI3P) kinase, regulates AP formation. Fusion of APs and endosomes with the vacuole (the yeast lysosome) requires the Ypt7 GTPase module. We have previously shown that the Rab5-related Vps21, within its endocytic GTPase module, regulates autophagy. However, it was not clear which autophagy step it regulates. Here, we show that this module, which includes the Vps9 activator, the Rab5-related Vps21, the CORVET tethering complex, and the Pep12 SNARE, functions after AP expansion and before AP closure. Whereas APs are not formed in mutant cells depleted for Atgs, sealed APs accumulate in cells depleted for the Ypt7 GTPase module members. Importantly, depletion of individual members of the Vps21 module results in a novel phenotype: accumulation of unsealed APs. In addition, we show that Vps21-regulated AP closure precedes another AP maturation step, the previously reported PI3P phosphatase-dependent Atg dissociation. Our results delineate three successive steps in the autophagy pathway regulated by Rabs, Ypt1, Vps21 and Ypt7, and provide the first insight into the upstream regulation of AP closure.
Author summary In autophagy, a cellular recycling pathway, the double-membrane autophagosome (AP) engulfs excess or damaged cargo and delivers it for degradation in the lysosome for the reuse of its building blocks. While plenty of information is currently available regarding AP formation, expansion and fusion, not much is known about the regulation of AP closure, which is required for fusion of APs with the lysosome. Here, we use yeast genetics to characterize a novel mutant phenotype, accumulation of unsealed APs, and identify a role for the Rab5-related Vps21 GTPase in this process. Rab GTPases function in modules that include upstream activators and downstream effectors. We have previously shown that the same Vps21 module that regulates endocytosis also plays a role in autophagy. Using single and double mutant analyses, we find that this module is important for AP closure. Moreover, we delineate three Rab GTPase-regulated steps in the autophagy pathway: AP formation, closure, and fusion, which are regulated by Ypt1, Vps21 and Ypt7, respectively. This study provides the first insight into the mechanism of the elusive process of AP closure.الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::d0bef356536ed628bba11d5dba899c51Test
https://doaj.org/article/c18c3b7a623e42bba1a6abfa803f5825Test -
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المؤلفون: Nava Segev, Zhanna Lipatova
المصدر: PLoS Genetics
PLoS Genetics, Vol 11, Iss 7, p e1005390 (2015)مصطلحات موضوعية: Cancer Research, Protein Folding, Saccharomyces cerevisiae Proteins, lcsh:QH426-470, Autophagy-Related Proteins, Vacuole, Saccharomyces cerevisiae, Endoplasmic-reticulum-associated protein degradation, Biology, Endoplasmic Reticulum, Lysosome, Genetics, medicine, Autophagy, Animals, Molecular Biology, Integral membrane protein, Genetics (clinical), Ecology, Evolution, Behavior and Systematics, Membrane Proteins, Endoplasmic Reticulum-Associated Degradation, Endoplasmic Reticulum Stress, Cell biology, lcsh:Genetics, medicine.anatomical_structure, Membrane protein, rab GTP-Binding Proteins, Proteolysis, Unfolded protein response, Rab, Lysosomes, Research Article
الوصف: The endoplasmic-reticulum quality-control (ERQC) system shuttles misfolded proteins for degradation by the proteasome through the well-defined ER-associated degradation (ERAD) pathway. In contrast, very little is known about the role of autophagy in ERQC. Macro-autophagy, a collection of pathways that deliver proteins through autophagosomes (APs) for degradation in the lysosome (vacuole in yeast), is mediated by autophagy-specific proteins, Atgs, and regulated by Ypt/Rab GTPases. Until recently, the term ER-phagy was used to describe degradation of ER membrane and proteins in the lysosome under stress: either ER stress induced by drugs or whole-cell stress induced by starvation. These two types of stresses induce micro-ER-phagy, which does not use autophagic organelles and machinery, and non-selective autophagy. Here, we characterize the macro-ER-phagy pathway and uncover its role in ERQC. This pathway delivers 20–50% of certain ER-resident membrane proteins to the vacuole and is further induced to >90% by overexpression of a single integral-membrane protein. Even though such overexpression in cells defective in macro-ER-phagy induces the unfolded-protein response (UPR), UPR is not needed for macro-ER-phagy. We show that macro-ER-phagy is dependent on Atgs and Ypt GTPases and its cargo passes through APs. Moreover, for the first time the role of Atg9, the only integral-membrane core Atg, is uncoupled from that of other core Atgs. Finally, three sequential steps of this pathway are delineated: Atg9-dependent exit from the ER en route to autophagy, Ypt1- and core Atgs-mediated pre-autophagsomal-structure organization, and Ypt51-mediated delivery of APs to the vacuole.
Author Summary ER-quality control (ERQC) ensures delivery of “native” proteins through the secretory pathway. Currently, ER-associated degradation (ERAD), which delivers misfolded proteins for degradation by the proteasome, is considered a major ERQC pathway, with autophagy as its backup. Until now, the role of autophagy, which shuttles cellular components for degradation in the lysosome through autophagosomes (APs), in ERQC was ill defined. Recently, the process of ER degradation induced by ER stress was defined as micro-ER-phagy, which does not require autophagic machinery and does not pass through APs. Here, we characterize the macro-ER-phagy pathway, which delivers excess membrane proteins for degradation in the lysosome, as a novel ERQC pathway. This pathway functions in the absence of cellular or ER stress and can be further induced by overexpression of a single integral-membrane protein. Unlike the micro-ER-phagy pathway, the marco-ER-phagy pathway requires core autophagy-specific proteins, Atgs, and Ypt/Rab GTPases. In addition, for the first time, the function of the only membrane core Atg, Atg9, was uncoupled from that of the other core Atgs. Whereas Atg9 plays a role in the assembly of ER-to-autophagy membranes (ERAM), other core Atgs and Ypt1 assemble the Atg-protein complex on ERAM to form the pre-autophagosomal structure.الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::357c6b08b28cea638db23e5d0d1ef5c8Test
http://europepmc.org/articles/PMC4504476Test -
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المؤلفون: Nissim Hay, Nava Segev
المصدر: Molecular Cell. 46:4-6
مصطلحات موضوعية: chemistry.chemical_classification, Saccharomyces cerevisiae Proteins, Leucyl-tRNA synthetase, Cell, Saccharomyces cerevisiae, Cell Biology, Biology, Article, Amino acid, medicine.anatomical_structure, chemistry, Biochemistry, Leucine, medicine, Leucine-tRNA Ligase, Molecular Biology, Signal Transduction, Transcription Factors
الوصف: The target of rapamycin complex 1 (TORC1) is an essential regulator of eukaryotic cell growth that responds to growth factors, energy levels, and amino acids. The mechanisms through which the preeminent amino acid leucine signals to the TORC1-regulatory Rag GTPases, which activate TORC1 within the yeast EGO complex (EGOC) or the structurally related mammalian Rag-Ragulator complex, remain elusive. We find that the leucyl-tRNA synthetase (LeuRS) Cdc60 interacts with the Rag GTPase Gtr1 of the EGOC in a leucine-dependent manner. This interaction is necessary and sufficient to mediate leucine signaling to TORC1 and is disrupted by the engagement of Cdc60 in editing mischarged tRNA(Leu). Thus, the EGOC-TORC1 signaling module samples, via the LeuRS-intrinsic editing domain, the fidelity of tRNA(Leu) aminoacylation as a proxy for leucine availability.
الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::b4cba3a70147ddf7cde9fb269242bd1bTest
https://doi.org/10.1016/j.molcel.2012.03.028Test -
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المؤلفون: Zhanna Lipatova, Jonathan W. Mulholland, Nava Segev, Ankur H. Shah, Jane J. Kim
المصدر: Molecular Biology of the Cell
مصطلحات موضوعية: Saccharomyces cerevisiae Proteins, Golgi Apparatus, GTPase, Saccharomyces cerevisiae, Biology, Endoplasmic Reticulum, 03 medical and health sciences, symbols.namesake, 0302 clinical medicine, Lysosome, Gene Expression Regulation, Fungal, medicine, Autophagy, Molecular Biology, 030304 developmental biology, 0303 health sciences, Endoplasmic reticulum, Membrane Proteins, Cell Biology, Articles, Golgi apparatus, Cell biology, Transport protein, Protein Transport, medicine.anatomical_structure, rab GTP-Binding Proteins, Membrane Trafficking, Mutation, Proteolysis, symbols, Unfolded protein response, Rab, Lysosomes, 030217 neurology & neurosurgery
الوصف: Ypt1 GTPase, in the context of an autophagy-specific module, regulates ER-phagy. Because Ypt1 is a known regulator of ER-to-Golgi transport, this means that a single Ypt/Rab can regulate two alternative transport steps from one compartment, the ER, to two different destinations, the Golgi and the autophagy pathway.
Accumulation of misfolded proteins on intracellular membranes has been implicated in neurodegenerative diseases. One cellular pathway that clears such aggregates is endoplasmic reticulum autophagy (ER-phagy), a selective autophagy pathway that delivers excess ER to the lysosome for degradation. Not much is known about the regulation of ER-phagy. The conserved Ypt/Rab GTPases regulate all membrane trafficking events in eukaryotic cells. We recently showed that a Ypt module, consisting of Ypt1 and autophagy-specific upstream activator and downstream effector, regulates the onset of selective autophagy in yeast. Here we show that this module acts at the ER. Autophagy-specific mutations in its components cause accumulation of excess membrane proteins on aberrant ER structures and induction of ER stress. This accumulation is due to a block in transport of these membranes to the lysosome, where they are normally cleared. These findings establish a role for an autophagy-specific Ypt1 module in the regulation of ER-phagy. Moreover, because Ypt1 is a known key regulator of ER-to-Golgi transport, these findings establish a second role for Ypt1 at the ER. We therefore propose that individual Ypt/Rabs, in the context of distinct modules, can coordinate alternative trafficking steps from one cellular compartment to different destinations.الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::1484d74c6534006210bb0a7ffbde1d9fTest
https://pubmed.ncbi.nlm.nih.gov/23924895Test