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Journal of Cell Science Feb 2022The proteasome is central to proteolysis by the ubiquitin-proteasome system under normal growth conditions but is itself degraded through macroautophagy under nutrient...
The proteasome is central to proteolysis by the ubiquitin-proteasome system under normal growth conditions but is itself degraded through macroautophagy under nutrient stress. A recently described AMP-activated protein kinase (AMPK)-regulated endosomal sorting complex required for transport (ESCRT)-dependent microautophagy pathway also regulates proteasome trafficking and degradation in low-glucose conditions in yeast. Aberrant proteasomes are more prone to microautophagy, suggesting the ESCRT system fine-tunes proteasome quality control under low-glucose stress. Here, we uncover additional features of the selective microautophagy of proteasomes in budding yeast. Genetic or pharmacological induction of aberrant proteasomes is associated with increased mono- or oligo-ubiquitylation of proteasome components, which appears to be recognized by ESCRT-0. AMPK controls this pathway in part by regulating the trafficking of ESCRT-0 to the vacuole surface, which also leads to degradation of the Vps27 subunit of ESCRT-0. The Rsp5 ubiquitin ligase contributes to proteasome subunit ubiquitylation, and multiple ubiquitin-binding elements in Vps27 are involved in their recognition. We propose that ESCRT-0 at the vacuole surface recognizes ubiquitylated proteasomes and initiates their microautophagic elimination during glucose depletion. This article has an associated First Person interview with the first author of the paper.
Topics: Endosomal Sorting Complexes Required for Transport; Humans; Microautophagy; Proteasome Endopeptidase Complex; Saccharomyces cerevisiae Proteins; Ubiquitination
PubMed: 35099016
DOI: 10.1242/jcs.259393 -
Autophagy Reports 2022Lipid droplets (LDs) are organelles that function as sites for lipid storage. LDs have also been implicated in the cellular response to proteotoxic or lipotoxic stress...
Lipid droplets (LDs) are organelles that function as sites for lipid storage. LDs have also been implicated in the cellular response to proteotoxic or lipotoxic stress as sites for sequestering dysfunctional or excess proteins or lipids, and targeting those cargos for degradation by LD microautophagy (microlipophagy, μLP). Here, we describe two mechanisms for μLP in yeast, which are triggered by different stressors. μLP occurs at raft-like liquid ordered microdomains in the vacuolar membrane in yeast exposed to severe nutrient limitations. In contrast, in yeast exposed to ER stress or less severe nutrient limitations, LD uptake at the vacuole is liquid ordered (L) microdomain-independent and dependent upon vacuolar membrane remodeling mediated by endosomal sorting complexes required for transport (ESCRT).
PubMed: 37840550
DOI: 10.1080/27694127.2022.2067643 -
Frontiers in Cellular and Infection... 2021Lysosome incorporate and degrade proteins in a process known as autophagy. There are three types of autophagy; macroautophagy, microautophagy, and chaperone-mediated... (Review)
Review
Lysosome incorporate and degrade proteins in a process known as autophagy. There are three types of autophagy; macroautophagy, microautophagy, and chaperone-mediated autophagy (CMA). Although autophagy is considered a nonselective degradation process, CMA is known as a selective degradation pathway. All proteins internalized in the lysosome CMA contain a pentapeptide KFERQ-motif, also known as a CMA-targeting motif, which is necessary for selectivity. CMA directly delivers a substrate protein into the lysosome lumen using the cytosolic chaperone HSC70 and the lysosomal receptor LAMP-2A for degradation. Hepatitis C virus (HCV) NS5A protein interacts with hepatocyte-nuclear factor 1α (HNF-1α) together with HSC70 and promotes the lysosomal degradation of HNF-1α CMA, resulting in HCV-induced pathogenesis. HCV NS5A promotes recruitment of HSC70 to the substrate protein HNF-1α. HCV NS5A plays a crucial role in HCV-induced CMA. Further investigations of HCV NS5A-interacting proteins containing CMA-targeting motifs may help to elucidate HCV-induced pathogenesis.
Topics: Autophagy; Chaperone-Mediated Autophagy; Hepacivirus; Hepatitis C; Humans; Lysosomal-Associated Membrane Protein 2; Lysosomes; Molecular Chaperones
PubMed: 34926330
DOI: 10.3389/fcimb.2021.796664 -
Cellular and Molecular Life Sciences :... Dec 2021Secretion and quality control of large extracellular matrix proteins remain poorly understood and debated, particularly transport intermediates delivering folded...
Secretion and quality control of large extracellular matrix proteins remain poorly understood and debated, particularly transport intermediates delivering folded proteins from the ER to Golgi and misfolded ones to lysosomes. Discrepancies between different studies are related to utilization of exogenous cargo, off-target effects of experimental conditions and cell manipulation, and identification of transport intermediates without tracing their origin and destination. To address these issues, here we imaged secretory and degradative trafficking of type I procollagen in live MC3T3 osteoblasts by replacing a region encoding N-propeptide in endogenous Col1a2 gDNA with GFP cDNA. We selected clones that produced the resulting fluorescent procollagen yet had normal expression of key osteoblast and ER/cell stress genes, normal procollagen folding, and normal deposition and mineralization of extracellular matrix. Live-cell imaging of these clones revealed ARF1-dependent transport intermediates, which had no COPII coat and delivered procollagen from ER exit sites (ERESs) to Golgi without stopping at ER-Golgi intermediate compartment (ERGIC). It also confirmed ERES microautophagy, i.e., lysosomes engulfing ERESs containing misfolded procollagen. Beyond validating these trafficking models for endogenous procollagen, we uncovered a probable cause of noncanonical cell stress response to procollagen misfolding. Recognized and retained only at ERESs, misfolded procollagen does not directly activate the canonical UPR, yet it disrupts the ER lumen by blocking normal secretory export from the ER.
Topics: Animals; Autophagy; COP-Coated Vesicles; Cells, Cultured; Collagen Type I; Endoplasmic Reticulum; Golgi Apparatus; Lysosomes; Mice; Osteoblasts; Procollagen; Protein Transport
PubMed: 34779895
DOI: 10.1007/s00018-021-04017-z -
Cellular and Molecular Life Sciences :... Dec 2021Lysosomes are single membrane-bound organelles containing acid hydrolases responsible for the degradation of cellular cargo and maintenance of cellular homeostasis.... (Review)
Review
Lysosomes are single membrane-bound organelles containing acid hydrolases responsible for the degradation of cellular cargo and maintenance of cellular homeostasis. Lysosomes could originate from pre-existing endolysosomes or autolysosomes, acting as a critical juncture between autophagy and endocytosis. Stress that triggers lysosomal membrane permeabilization can be altered by ESCRT complexes; however, irreparable damage to the membrane results in the induction of a selective lysosomal degradation pathway, specifically lysophagy. Lysosomes play an indispensable role in different types of autophagy, including microautophagy, macroautophagy, and chaperone-mediated autophagy, and various cell death pathways such as lysosomal cell death, apoptotic cell death, and autophagic cell death. In this review, we discuss lysosomal reformation, maintenance, and degradation pathways following the involvement of the lysosome in autophagy and cell death, which are related to several pathophysiological conditions observed in humans.
Topics: Aging; Animals; Apoptosis; Autophagy; Cell Membrane; Endocytosis; Humans; Intracellular Membranes; Lysosomes
PubMed: 34716768
DOI: 10.1007/s00018-021-03988-3 -
Molecular Biology of the Cell Dec 2021Microlipophagy (µLP), degradation of lipid droplets (LDs) by microautophagy, occurs by autophagosome-independent direct uptake of LDs at lysosomes/vacuoles in response...
Microlipophagy (µLP), degradation of lipid droplets (LDs) by microautophagy, occurs by autophagosome-independent direct uptake of LDs at lysosomes/vacuoles in response to nutrient limitations and ER stressors in . In nutrient-limited yeast, liquid-ordered (L) microdomains, sterol-rich raftlike regions in vacuolar membranes, are sites of membrane invagination during LD uptake. The endosome sorting complex required for transport (ESCRT) is required for sterol transport during L formation under these conditions. However, ESCRT has been implicated in mediating membrane invagination during µLP induced by ER stressors or the diauxic shift from glycolysis- to respiration-driven growth. Here we report that ER stress induced by lipid imbalance and other stressors induces L microdomain formation. This process is ESCRT independent and dependent on Niemann-Pick type C sterol transfer proteins. Inhibition of ESCRT or L microdomain formation partially inhibits lipid imbalance-induced µLP, while inhibition of both blocks this µLP. Finally, although the ER stressors dithiothreitol or tunicamycin induce L microdomains, µLP in response to these stressors is ESCRT dependent and L microdomain independent. Our findings reveal that L microdomain formation is a yeast stress response, and stress-induced L microdomain formation occurs by stressor-specific mechanisms. Moreover, ESCRT and L microdomains play functionally distinct roles in LD uptake during stress-induced µLP.
Topics: Carrier Proteins; Endoplasmic Reticulum Stress; Endosomal Sorting Complexes Required for Transport; Lipid Droplets; Membrane Microdomains; Microautophagy; Oxidation-Reduction; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins; Vacuoles; Vesicular Transport Proteins
PubMed: 34668753
DOI: 10.1091/mbc.E21-04-0179 -
Autophagy Feb 2022Nucleophagy, the selective subtype of autophagy that predominantly targets only a selected and (nonessential) portion of the nucleus, and rarely the nucleus in its...
Nucleophagy, the selective subtype of autophagy that predominantly targets only a selected and (nonessential) portion of the nucleus, and rarely the nucleus in its entirety, for degradation, reinforces the paradigm that nucleophagy recycling is a meticulous and highly delicate process guarded by fail-safe mechanisms. Our goal in this commentary is to encourage autophagy researchers and other scientists to explore nucleophagy blind spots and gain advanced insights into the diverse roles of this process and its selective modality as they pertain to intranuclear quality control and cellular homeostasis. Identifying and deciphering nucleophagic signaling, regulation, molecular mechanism(s) and its mediators, cargo composition and nuclear membrane dynamics under numerous physiological and/or pathological settings will provide important advances in our understanding of this critical type of organelle-selective autophagy.: INM, inner nuclear membrane; LN, late nucleophagy; mRNA, messenger RNA; NE, nuclear envelope; NL, nuclear lamina; NPC(s), nuclear pore complex(es); NVJ(s), nucleus-vacuole junction(s); ONM, outer nuclear membrane; PMN, piecemeal microautophagy of the nucleus; PND, programmed nuclear death; PNuD, programmed nuclear destruction; rDNArRNA, ribosomal DNA/RNA.
Topics: Autophagy; Cell Nucleus; DNA, Ribosomal; Microautophagy; Nuclear Envelope; Saccharomyces cerevisiae
PubMed: 34643473
DOI: 10.1080/15548627.2021.1971380 -
Molecular Cell Nov 2021The interferon (IFN) pathway is critical for cytotoxic T cell activation, which is central to tumor immunosurveillance and successful immunotherapy. We demonstrate here...
The interferon (IFN) pathway is critical for cytotoxic T cell activation, which is central to tumor immunosurveillance and successful immunotherapy. We demonstrate here that PKCλ/ι inactivation results in the hyper-stimulation of the IFN cascade and the enhanced recruitment of CD8 T cells that impaired the growth of intestinal tumors. PKCλ/ι directly phosphorylates and represses the activity of ULK2, promoting its degradation through an endosomal microautophagy-driven ubiquitin-dependent mechanism. Loss of PKCλ/ι results in increased levels of enzymatically active ULK2, which, by direct phosphorylation, activates TBK1 to foster the activation of the STING-mediated IFN response. PKCλ/ι inactivation also triggers autophagy, which prevents STING degradation by chaperone-mediated autophagy. Thus, PKCλ/ι is a hub regulating the IFN pathway and three autophagic mechanisms that serve to maintain its homeostatic control. Importantly, single-cell multiplex imaging and bioinformatics analysis demonstrated that low PKCλ/ι levels correlate with enhanced IFN signaling and good prognosis in colorectal cancer patients.
Topics: Adult; Aged; Aged, 80 and over; Animals; Autophagy; CD8-Positive T-Lymphocytes; Carcinogenesis; Cell Transformation, Neoplastic; Colorectal Neoplasms; Cycloheximide; Female; HEK293 Cells; Humans; Immunophenotyping; Interferon Regulatory Factor-3; Interferons; Isoenzymes; Male; Membrane Proteins; Mice; Middle Aged; Neoplasm Transplantation; Phosphorylation; Prognosis; Protein Kinase C; Protein Serine-Threonine Kinases; Signal Transduction; Transcription Factors; Up-Regulation
PubMed: 34560002
DOI: 10.1016/j.molcel.2021.08.039 -
Frontiers in Plant Science 2021Autophagy is a catabolic and recycling pathway that maintains cellular homeostasis under normal growth and stress conditions. Two major types of autophagy,...
Autophagy is a catabolic and recycling pathway that maintains cellular homeostasis under normal growth and stress conditions. Two major types of autophagy, microautophagy and macroautophagy, have been described in plants. During macroautophagy, cellular content is engulfed by a double-membrane vesicle called autophagosome. This vesicle fuses its outer membrane with the tonoplast and releases the content into the vacuole for degradation. During certain developmental processes, autophagy is enhanced by induction of several autophagy-related genes ( genes). Autophagy in crop development has been studied in relation to leaf senescence, seed and reproductive development, and vascular formation. However, its role in fruit ripening has only been partially addressed. Strawberry is an important berry crop, representative of non-climacteric fruit. We have analyzed the occurrence of autophagy in developing and ripening fruits of the cultivated strawberry. Our data show that most genes are conserved in the genome of the cultivated strawberry and they are differentially expressed along the ripening of the fruit receptacle. ATG8-lipidation analysis proves the presence of two autophagic waves during ripening. In addition, we have confirmed the presence of autophagy at the cellular level by the identification of autophagy-related structures at different stages of the strawberry ripening. Finally, we show that blocking autophagy either biochemically or genetically dramatically affects strawberry growth and ripening. Our data support that autophagy is an active and essential process with different implications during strawberry fruit ripening.
PubMed: 34512686
DOI: 10.3389/fpls.2021.688481 -
Autophagy Jan 2022Clearance of misfolded proteins from the secretory pathway often occurs soon after their biosynthesis by endoplasmic reticulum (ER)-associated protein degradation...
Clearance of misfolded proteins from the secretory pathway often occurs soon after their biosynthesis by endoplasmic reticulum (ER)-associated protein degradation (ERAD). However, certain types of misfolded proteins are not ERAD substrates and exit the ER. They are then scrutinized by ill-defined post-ER quality control (post-ERQC) mechanisms and are frequently routed to the vacuole/lysosome for degradation. Glycosylphosphatidylinositol-anchored proteins (GPI-APs) constitute a class of proteins of the secretory pathway that mostly depends on post-ERQC. How misfolded GPI-APs are detected, transported to the vacuole/lysosome and taken up by this organelle was poorly defined. Originating from the intriguing observation that several misfolded GPI-APs accumulate in the yeast vacuolar membrane in the absence of the major vacuolar protease Pep4, we designed an unbiased genome-wide screen in yeast and followed the trafficking of the misfolded fluorescent GPI-AP Gas1* from the ER to the vacuolar lumen. Our results reveal that post-ERQC of GPI-APs is linked with a novel type of microautophagy.
Topics: Aspartic Acid Endopeptidases; Autophagy; Endoplasmic Reticulum; GPI-Linked Proteins; Glycosylphosphatidylinositols; Microautophagy; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins
PubMed: 34491884
DOI: 10.1080/15548627.2021.1971929