-
Molecular Cancer Jan 2024Eukaryotic cells engage in autophagy, an internal process of self-degradation through lysosomes. Autophagy can be classified as selective or non-selective depending on... (Review)
Review
Eukaryotic cells engage in autophagy, an internal process of self-degradation through lysosomes. Autophagy can be classified as selective or non-selective depending on the way it chooses to degrade substrates. During the process of selective autophagy, damaged and/or redundant organelles like mitochondria, peroxisomes, ribosomes, endoplasmic reticulum (ER), lysosomes, nuclei, proteasomes, and lipid droplets are selectively recycled. Specific cargo is delivered to autophagosomes by specific receptors, isolated and engulfed. Selective autophagy dysfunction is closely linked with cancers, neurodegenerative diseases, metabolic disorders, heart failure, etc. Through reviewing latest research, this review summarized molecular markers and important signaling pathways for selective autophagy, and its significant role in cancers. Moreover, we conducted a comprehensive analysis of small-molecule compounds targeting selective autophagy for their potential application in anti-tumor therapy, elucidating the underlying mechanisms involved. This review aims to supply important scientific references and development directions for the biological mechanisms and drug discovery of anti-tumor targeting selective autophagy in the future.
Topics: Humans; Autophagy; Neoplasms; Autophagosomes; Cell Nucleus; Drug Discovery
PubMed: 38262996
DOI: 10.1186/s12943-024-01934-y -
ELife Jun 2023Autophagy is an essential catabolic pathway which sequesters and engulfs cytosolic substrates via autophagosomes, unique double-membraned structures. ATG8 proteins are...
Autophagy is an essential catabolic pathway which sequesters and engulfs cytosolic substrates via autophagosomes, unique double-membraned structures. ATG8 proteins are ubiquitin-like proteins recruited to autophagosome membranes by lipidation at the C-terminus. ATG8s recruit substrates, such as p62, and play an important role in mediating autophagosome membrane expansion. However, the precise function of lipidated ATG8 in expansion remains obscure. Using a real-time in vitro lipidation assay, we revealed that the N-termini of lipidated human ATG8s (LC3B and GABARAP) are highly dynamic and interact with the membrane. Moreover, atomistic MD simulation and FRET assays indicate that N-termini of LC3B and GABARAP associate in on the membrane. By using non-tagged GABARAPs, we show that GABARAP N-terminus and its -membrane insertion are crucial to regulate the size of autophagosomes in cells irrespectively of p62 degradation. Our study provides fundamental molecular insights into autophagosome membrane expansion, revealing the critical and unique function of lipidated ATG8.
Topics: Humans; Autophagosomes; Microtubule-Associated Proteins; Autophagy-Related Protein 8 Family; Autophagy; Autophagy-Related Proteins
PubMed: 37288820
DOI: 10.7554/eLife.89185 -
The EMBO Journal Dec 2022Autophagy, a conserved eukaryotic intracellular catabolic pathway, maintains cell homeostasis by lysosomal degradation of cytosolic material engulfed in double membrane...
Autophagy, a conserved eukaryotic intracellular catabolic pathway, maintains cell homeostasis by lysosomal degradation of cytosolic material engulfed in double membrane vesicles termed autophagosomes, which form upon sealing of single-membrane cisternae called phagophores. While the role of phosphatidylinositol 3-phosphate (PI3P) and phosphatidylethanolamine (PE) in autophagosome biogenesis is well-studied, the roles of other phospholipids in autophagy remain rather obscure. Here we utilized budding yeast to study the contribution of phosphatidylcholine (PC) to autophagy. We reveal for the first time that genetic loss of PC biosynthesis via the CDP-DAG pathway leads to changes in lipid composition of autophagic membranes, specifically replacement of PC by phosphatidylserine (PS). This impairs closure of the autophagic membrane and autophagic flux. Consequently, we show that choline-dependent recovery of de novo PC biosynthesis via the CDP-choline pathway restores autophagosome formation and autophagic flux in PC-deficient cells. Our findings therefore implicate phospholipid metabolism in autophagosome biogenesis.
Topics: Autophagosomes; Phospholipids; Autophagy-Related Proteins; Autophagy; Choline; Cytidine Diphosphate
PubMed: 36300838
DOI: 10.15252/embj.2022110771 -
The Journal of Cell Biology Jul 2023During autophagy, rapid membrane assembly expands small phagophores into large double-membrane autophagosomes. Theoretical modeling predicts that the majority of...
During autophagy, rapid membrane assembly expands small phagophores into large double-membrane autophagosomes. Theoretical modeling predicts that the majority of autophagosomal phospholipids are derived from highly efficient non-vesicular phospholipid transfer (PLT) across phagophore-ER contacts (PERCS). Currently, the phagophore-ER tether Atg2 is the only PLT protein known to drive phagophore expansion in vivo. Here, our quantitative live-cell imaging analysis reveals a poor correlation between the duration and size of forming autophagosomes and the number of Atg2 molecules at PERCS of starving yeast cells. Strikingly, we find that Atg2-mediated PLT is non-rate limiting for autophagosome biogenesis because membrane tether and the PLT protein Vps13 localizes to the rim and promotes the expansion of phagophores in parallel with Atg2. In the absence of Vps13, the number of Atg2 molecules at PERCS determines the duration and size of forming autophagosomes with an apparent in vivo transfer rate of ∼200 phospholipids per Atg2 molecule and second. We propose that conserved PLT proteins cooperate in channeling phospholipids across organelle contact sites for non-rate-limiting membrane assembly during autophagosome biogenesis.
Topics: Autophagosomes; Phospholipids; Endoplasmic Reticulum; Autophagy; Saccharomyces cerevisiae; Autophagy-Related Proteins; Saccharomyces cerevisiae Proteins
PubMed: 37115156
DOI: 10.1083/jcb.202211039 -
Nature Communications May 2021Haematopoietic stem cells (HSCs) tightly regulate their quiescence, proliferation, and differentiation to generate blood cells during the entire lifetime. The mechanisms...
Haematopoietic stem cells (HSCs) tightly regulate their quiescence, proliferation, and differentiation to generate blood cells during the entire lifetime. The mechanisms by which these critical activities are balanced are still unclear. Here, we report that Macrophage-Erythroblast Attacher (MAEA, also known as EMP), a receptor thus far only identified in erythroblastic island, is a membrane-associated E3 ubiquitin ligase subunit essential for HSC maintenance and lymphoid potential. Maea is highly expressed in HSCs and its deletion in mice severely impairs HSC quiescence and leads to a lethal myeloproliferative syndrome. Mechanistically, we have found that the surface expression of several haematopoietic cytokine receptors (e.g. MPL, FLT3) is stabilised in the absence of Maea, thereby prolonging their intracellular signalling. This is associated with impaired autophagy flux in HSCs but not in mature haematopoietic cells. Administration of receptor kinase inhibitor or autophagy-inducing compounds rescues the functional defects of Maea-deficient HSCs. Our results suggest that MAEA provides E3 ubiquitin ligase activity, guarding HSC function by restricting cytokine receptor signalling via autophagy.
Topics: Animals; Autophagosomes; Autophagy; Cell Adhesion Molecules; Cytoskeletal Proteins; Gene Expression Profiling; Hematopoiesis; Hematopoietic Stem Cells; Mice; Mice, Inbred C57BL; Mice, Knockout; Microscopy, Electron, Transmission; Protein Stability; Receptors, Thrombopoietin; Signal Transduction; TOR Serine-Threonine Kinases; Ubiquitin-Protein Ligases; Ubiquitination; fms-Like Tyrosine Kinase 3
PubMed: 33947846
DOI: 10.1038/s41467-021-22749-1 -
FEBS Letters Apr 2021Mitophagy is one of the selective autophagy pathways that catabolizes dysfunctional or superfluous mitochondria. Under mitophagy-inducing conditions, mitochondria are... (Review)
Review
Mitophagy is one of the selective autophagy pathways that catabolizes dysfunctional or superfluous mitochondria. Under mitophagy-inducing conditions, mitochondria are labeled with specific molecular landmarks that recruit the autophagy machinery to the surface of mitochondria, enclosed into autophagosomes, and delivered to lysosomes (vacuoles in yeast) for degradation. As damaged mitochondria are the major sources of reactive oxygen species, mitophagy is critical for mitochondrial quality control and cellular health. Moreover, appropriate control of mitochondrial quantity via mitophagy is vital for the energy supply-demand balance in cells and whole organisms, cell differentiation, and developmental programs. Thus, it seems conceivable that defects in mitophagy could elicit pleiotropic pathologies such as excess inflammation, tissue injury, neurodegeneration, and aging. In this review, we will focus on the molecular basis and physiological relevance of mitophagy, and potential of mitophagy as a therapeutic target to overcome such disorders.
Topics: Aging; Animals; Autophagosomes; Autophagy; Humans; Inflammation; Mitochondria; Mitophagy; Neurodegenerative Diseases; Reactive Oxygen Species
PubMed: 33615465
DOI: 10.1002/1873-3468.14060 -
The Journal of Biological Chemistry May 2023Autophagy is a key process in eukaryotes to maintain cellular homeostasis by delivering cellular components to lysosomes/vacuoles for degradation and reuse of the...
Autophagy is a key process in eukaryotes to maintain cellular homeostasis by delivering cellular components to lysosomes/vacuoles for degradation and reuse of the resulting metabolites. Membrane rearrangements and trafficking events are mediated by the core machinery of autophagy-related (Atg) proteins, which carry out a variety of functions. How Atg9, a lipid scramblase and the only conserved transmembrane protein within this core Atg machinery, is trafficked during autophagy remained largely unclear. Here, we addressed this question in yeast Saccharomyces cerevisiae and found that retromer complex and dynamin Vps1 mutants alter Atg9 subcellular distribution and severely impair the autophagic flux by affecting two separate autophagy steps. We provide evidence that Vps1 interacts with Atg9 at Atg9 reservoirs. In the absence of Vps1, Atg9 fails to reach the sites of autophagosome formation, and this results in an autophagy defect. The function of Vps1 in autophagy requires its GTPase activity. Moreover, Vps1 point mutants associated with human diseases such as microcytic anemia and Charcot-Marie-Tooth are unable to sustain autophagy and affect Atg9 trafficking. Together, our data provide novel insights on the role of dynamins in Atg9 trafficking and suggest that a defect in this autophagy step could contribute to severe human pathologies.
Topics: Humans; Autophagosomes; Saccharomyces cerevisiae Proteins; Saccharomyces cerevisiae; Dynamins; Vacuoles; Autophagy; Autophagy-Related Proteins; Protein Transport; GTP-Binding Proteins; Vesicular Transport Proteins; Membrane Proteins
PubMed: 37060997
DOI: 10.1016/j.jbc.2023.104712 -
The EMBO Journal Apr 2022Synaptic function crucially relies on the constant supply and removal of neuronal membranes. The morphological complexity of neurons poses a significant challenge for... (Review)
Review
Synaptic function crucially relies on the constant supply and removal of neuronal membranes. The morphological complexity of neurons poses a significant challenge for neuronal protein transport since the machineries for protein synthesis and degradation are mainly localized in the cell soma. In response to this unique challenge, local micro-secretory systems have evolved that are adapted to the requirements of neuronal membrane protein proteostasis. However, our knowledge of how neuronal proteins are synthesized, trafficked to membranes, and eventually replaced and degraded remains scarce. Here, we review recent insights into membrane trafficking at synaptic sites and into the contribution of local organelles and micro-secretory pathways to synaptic function. We describe the role of endoplasmic reticulum specializations in neurons, Golgi-related organelles, and protein complexes like retromer in the synthesis and trafficking of synaptic transmembrane proteins. We discuss the contribution of autophagy and of proteasome-mediated and endo-lysosomal degradation to presynaptic proteostasis and synaptic function, as well as nondegradative roles of autophagosomes and lysosomes in signaling and synapse remodeling. We conclude that the complexity of neuronal cyto-architecture necessitates long-distance protein transport that combines degradation with signaling functions.
Topics: Autophagosomes; Autophagy; Endoplasmic Reticulum; Lysosomes; Proteostasis; Synapses
PubMed: 35285533
DOI: 10.15252/embj.2021110057 -
Autophagy Sep 2021As part of innate immune defenses, macroautophagy/autophagy targets viruses and viral components for lysosomal degradation and exposes pathogen-associated molecular...
As part of innate immune defenses, macroautophagy/autophagy targets viruses and viral components for lysosomal degradation and exposes pathogen-associated molecular patterns to facilitate recognition. However, viruses evolved sophisticated strategies to antagonize autophagy and even exploit it to promote their replication. In our recent study, we systematically analyzed the impact of individual SARS-CoV-2 proteins on autophagy. We showed that E, M, ORF3a, and ORF7a cause an accumulation of autophagosomes, whereas Nsp15 prevents the efficient formation of autophagosomes. Consequently, autophagic degradation of SQSTM1/p62 is decreased in the presence of E, ORF3a, ORF7a, and Nsp15. Notably, M does not alter SQSTM1 protein levels and colocalizes with accumulations of LC3B-positive membranes not resembling vesicles. Infection with SARS-CoV-2 prevents SQSTM1 degradation and increases lipidation of LC3B, indicating overall that the infection causes a reduction of autophagic flux. Our mechanistic analyses showed that the accessory proteins ORF3a and ORF7a both block autophagic degradation but use different strategies. While ORF3a prevents the fusion between autophagosomes and lysosomes, ORF7a reduces the acidity of lysosomes. In summary, we found that Nsp15, E, M, ORF3a, and ORF7a of SARS-CoV-2 manipulate cellular autophagy, and we determined the molecular mechanisms of ORF3a and ORF7a.
Topics: Autophagosomes; Autophagy; COVID-19; Humans; Lysosomes; SARS-CoV-2
PubMed: 34281462
DOI: 10.1080/15548627.2021.1953847 -
FEBS Letters Sep 2022Plant selective (macro)autophagy is a highly regulated process where eukaryotic cells spatiotemporally degrade some of their constituents that have become superfluous or... (Review)
Review
Plant selective (macro)autophagy is a highly regulated process where eukaryotic cells spatiotemporally degrade some of their constituents that have become superfluous or harmful. The identification and characterization of the factors determining this selectivity make it possible to integrate selective (macro)autophagy into plant cell physiology and homeostasis. The specific cargo receptors and/or scaffold proteins involved in this pathway are generally not structurally conserved, as are the biochemical mechanisms underlying recognition and integration of a given cargo into the autophagosome in different cell types. This review discusses the few specific cargo receptors described in plant cells to highlight key features of selective autophagy in the plant kingdom and its integration with plant physiology, aiming to identify evolutionary convergence and knowledge gaps to be filled by future research.
Topics: Autophagosomes; Autophagy; Homeostasis; Plant Cells
PubMed: 35638898
DOI: 10.1002/1873-3468.14412