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Cells May 2020Lysosomes are the main proteolytic compartments of mammalian cells comprising of a battery of hydrolases. Lysosomes dispose and recycle extracellular or intracellular... (Review)
Review
Lysosomes are the main proteolytic compartments of mammalian cells comprising of a battery of hydrolases. Lysosomes dispose and recycle extracellular or intracellular macromolecules by fusing with endosomes or autophagosomes through specific waste clearance processes such as chaperone-mediated autophagy or microautophagy. The proteolytic end product is transported out of lysosomes via transporters or vesicular membrane trafficking. Recent studies have demonstrated lysosomes as a signaling node which sense, adapt and respond to changes in substrate metabolism to maintain cellular function. Lysosomal dysfunction not only influence pathways mediating membrane trafficking that culminate in the lysosome but also govern metabolic and signaling processes regulating protein sorting and targeting. In this review, we describe the current knowledge of lysosome in influencing sorting and nutrient signaling. We further present a mechanistic overview of intra-lysosomal processes, along with extra-lysosomal processes, governing lysosomal fusion and fission, exocytosis, positioning and membrane contact site formation. This review compiles existing knowledge in the field of lysosomal biology by describing various lysosomal events necessary to maintain cellular homeostasis facilitating development of therapies maintaining lysosomal function.
Topics: Animals; Disease; Humans; Ion Channels; Lysosomes; Models, Biological; Organelle Biogenesis; Proteolysis
PubMed: 32375321
DOI: 10.3390/cells9051131 -
Cells May 2020In all eukaryotic cells, intracellular organization and spatial separation of incompatible biochemical processes is established by individual cellular subcompartments in... (Review)
Review
In all eukaryotic cells, intracellular organization and spatial separation of incompatible biochemical processes is established by individual cellular subcompartments in form of membrane-bound organelles. Virtually all of these organelles are physically connected via membrane contact sites (MCS), allowing interorganellar communication and a functional integration of cellular processes. These MCS coordinate the exchange of diverse metabolites and serve as hubs for lipid synthesis and trafficking. While this of course indirectly impacts on a plethora of biological functions, including autophagy, accumulating evidence shows that MCS can also directly regulate autophagic processes. Here, we focus on the nexus between interorganellar contacts and autophagy in yeast and mammalian cells, highlighting similarities and differences. We discuss MCS connecting the ER to mitochondria or the plasma membrane, crucial for early steps of both selective and non-selective autophagy, the yeast-specific nuclear-vacuolar tethering system and its role in microautophagy, the emerging function of distinct autophagy-related proteins in organellar tethering as well as novel MCS transiently emanating from the growing phagophore and mature autophagosome.
Topics: Animals; Autophagosomes; Autophagy; Cell Membrane; Humans; Intracellular Membranes; Models, Biological
PubMed: 32397538
DOI: 10.3390/cells9051184 -
Science Advances Sep 2023Vitamin B is a vital micronutrient across cell types and tissues, and dysregulated B levels contribute to human disease. Despite its importance, how B vitamer levels are...
Vitamin B is a vital micronutrient across cell types and tissues, and dysregulated B levels contribute to human disease. Despite its importance, how B vitamer levels are regulated is not well understood. Here, we provide evidence that B dynamics are rapidly tuned by precise compartmentation of pyridoxal kinase (PDXK), the rate-limiting B enzyme. We show that canonical Wnt rapidly led to the accumulation of inactive B by shunting cytosolic PDXK into lysosomes. PDXK was modified with methyl-arginine Degron (MrDegron), a protein tag for lysosomes, which enabled delivery via microautophagy. Hyperactive lysosomes resulted in the continuous degradation of PDXK and B deficiency that promoted proliferation in Wnt-driven colorectal cancer (CRC) cells. Pharmacological or genetic disruption of the coordinated MrDegron proteolytic pathway was sufficient to reduce CRC survival in cells and organoid models. In sum, this work contributes to the repertoire of micronutrient-regulated processes that enable cancer cell growth and provides insight into the functional impact of B deficiencies for survival.
Topics: Humans; Vitamin B 6; Proteolysis; Peptide Hydrolases; Micronutrients; Vitamins
PubMed: 37682999
DOI: 10.1126/sciadv.adi2232 -
Oncology Reports Dec 2022Autophagy is a highly conserved process that maintains cellular homeostasis during evolution. Autophagy can occur in the form of macroautophagy, microautophagy or... (Review)
Review
Autophagy is a highly conserved process that maintains cellular homeostasis during evolution. Autophagy can occur in the form of macroautophagy, microautophagy or molecular chaperone autophagy, among which macroautophagy is the most common. Apoptosis exists in all kinds of cell organisms, and is a kind of programmed cell death which is regulated by pro‑apoptotic factors and anti‑apoptotic signals. The main biological feature of apoptosis is the activation of caspase. Apoptosis is induced by a variety of cell signals, such as endoplasmic reticulum stress, induction of toxic substances, stimulation of pathogenic microorganisms and DNA damage. Inextricable links are found between autophagy and apoptosis. Studies have found that numerous of the autophagy molecules and autophagy signaling pathways involved in the process of autophagy are related to apoptosis. In addition to regulating autophagy, the autophagy signaling pathway also regulates apoptosis. The interaction between the two can achieve a dynamic balance to certain extent, which maintains the basic physiological functions of cells and reduces the damage to the body under stress. Disease occurs when the balance between autophagy and apoptosis is disrupted. Tumors form due to the ability of cells to avoid apoptosis. Autophagy is closely related to apoptosis, there must be a close connection between the three. In the present review, the mechanism between autophagy and apoptosis and the impact of their interaction on tumorigenesis shall be discussed.
Topics: Apoptosis; Autophagy; Carcinogenesis; Caspases; Endoplasmic Reticulum Stress; Humans
PubMed: 36222296
DOI: 10.3892/or.2022.8423 -
Trends in Biochemical Sciences Apr 2020Autophagy is an evolutionarily conserved process whereby damaged and redundant components of the cell are degraded in structures called autophagolysosomes. Currently,... (Review)
Review
Autophagy is an evolutionarily conserved process whereby damaged and redundant components of the cell are degraded in structures called autophagolysosomes. Currently, three main types of autophagy are recognized: macroautophagy, microautophagy, and chaperone-mediated autophagy (CMA). However, we still know little about some specific types of autophagy that are linked to various intracellular compartments and their roles in the physiology of the whole organism and connections to various diseases. Here, we aim to shed light on the latest insights on and mechanisms of several selective forms of autophagy.
Topics: Animals; Autophagy; Humans; Lysosomes
PubMed: 32044127
DOI: 10.1016/j.tibs.2019.11.006 -
Autophagy Apr 2021Lysosomes play an essential role in quality control mechanisms by functioning as the primary digestive system in mammalian cells. However, the quality control mechanisms...
Lysosomes play an essential role in quality control mechanisms by functioning as the primary digestive system in mammalian cells. However, the quality control mechanisms governing healthy lysosomes are not fully understood. Using a method to study lysosome membrane turnover, we discovered that LC3-lipidation on the lysosome limiting membrane is involved in invagination and formation of intralumenal vesicles, an activity known as microautophagy. This activity occurs in response to metabolic stress, in the form of glucose starvation, or osmotic stress induced by treatment with lysosomotropic compounds. Cells rendered deficient in the ability to lipidate LC3 through knockout of show reduced ability to regulate lysosome size and degradative function in response to stress. These findings demonstrate that cells can adapt to changing metabolic conditions by turning over selective portions of the lysosomal membrane, using a mechanism that involves lysosome-targeted LC3 lipidation and the induction of selective microautophagy.
Topics: Animals; Autophagy; Glucose; Intracellular Membranes; Lysosomes; Nutrients
PubMed: 33499722
DOI: 10.1080/15548627.2021.1877935 -
Plant Signaling & Behavior Mar 2021Chloroplasts and mitochondria serve as intracellular energy production sites that are powered by the electron transport chain in their membranes. These organelles...
Chloroplasts and mitochondria serve as intracellular energy production sites that are powered by the electron transport chain in their membranes. These organelles constantly accumulate damage, as their energetic reactions generate reactive oxygen species. To prevent the accumulation of damaged organelles and perturbation of cellular homeostasis, eukaryotic cells must remove damaged mitochondria and chloroplasts. Autophagy is the main route by which organelles are degraded. A type of mitochondrion-targeted autophagy known as mitophagy removes damaged mitochondria in mammalian cells; dysfunctional mitochondria that lose their membrane potential are marked by protein ubiquitination, becoming targets of selective mitophagy. Studies of the quality control system for chloroplasts in plants revealed the involvement of both autophagy and ubiquitination in the degradation of damaged chloroplasts. We recently assessed the relationship between chloroplast-associated ubiquitination mediated by PLANT U-BOX4 (PUB4) and chloroplast-targeted autophagy (chlorophagy) in the turnover of oxidatively damaged chloroplasts. Multiple assays using an mutant revealed that PUB4-associated ubiquitination is dispensable for the induction of chlorophagy. Here, we describe the parallel functions of PUB4 and chlorophagy in chloroplast turnover and plant growth.
Topics: Arabidopsis; Arabidopsis Proteins; Autophagosomes; Chloroplasts; Microautophagy; Models, Biological; Mutation; Ubiquitin-Protein Ligases; Ubiquitination
PubMed: 33331806
DOI: 10.1080/15592324.2020.1861769 -
Autophagy May 2021Selective autophagy receptors have been implicated in the degradation of cellular constituents of various size and rigidity. However, the identity of protein cargo have...
Selective autophagy receptors have been implicated in the degradation of cellular constituents of various size and rigidity. However, the identity of protein cargo have largely remained elusive. In our recent study, we combined limited proteolysis-enhanced proximity biotinylation and organelle enrichment with quantitative proteomics to map the inventory of autophagosomes in a manner dependent on six different selective autophagy receptors, namely SQSTM1/p62, NBR1, CALCOCO2/NDP52, OPTN, TAX1BP1 and TOLLIP. Conducting this approach under basal and proteostasis-challenged conditions in mammalian cells led to the identification of various new autophagy substrates of which some were degraded through endosomal microautophagy rather than canonical autophagy dependent on the receptors TOLLIP and SQSTM1, respectively.
Topics: Animals; Autophagosomes; Autophagy; Carrier Proteins; HeLa Cells; Humans; Sequestosome-1 Protein
PubMed: 33779494
DOI: 10.1080/15548627.2021.1909410 -
The Journal of Cell Biology Oct 2022Liquid-liquid phase separation (LLPS) triages protein cargoes for autophagic degradation. In this issue, Ohshima et al. (2022. J. Cell...
Liquid-liquid phase separation (LLPS) triages protein cargoes for autophagic degradation. In this issue, Ohshima et al. (2022. J. Cell Biol.https://doi.org/10.1083/jcb.202203102) demonstrate that the autophagy receptor NCOA4 interacts with ferritin particles to form liquid-like condensates via LLPS. The NCOA4-ferritin condensates are delivered to lysosomes for degradation via either canonical macroautophagy or endosomal microautophagy to maintain intracellular iron homeostasis.
Topics: Autophagy; Ferritins; Iron; Lysosomes; Nuclear Receptor Coactivators
PubMed: 36112419
DOI: 10.1083/jcb.202209004 -
Frontiers in Molecular Neuroscience 2020Tauopathies are a class of neurodegenerative diseases, including Alzheimer's disease (AD), Frontotemporal Dementia (FTD), Progressive Supranuclear Palsy (PSP),... (Review)
Review
Tauopathies are a class of neurodegenerative diseases, including Alzheimer's disease (AD), Frontotemporal Dementia (FTD), Progressive Supranuclear Palsy (PSP), Corticobasal Degeneration (CBD), and many others where microtubule-associated protein tau (MAPT or tau) is hyperphosphorylated and aggregated to form insoluble paired helical filaments (PHFs) and ultimately neurofibrillary tangles (NFTs). Autophagic-endolysosomal networks (AELN) play important roles in tau clearance. Excessive soluble neurotoxic forms of tau and tau hyperphosphorylated at specific sites are cleared through the ubiquitin-proteasome system (UPS), Chaperon-mediated Autophagy (CMA), and endosomal microautophagy (e-MI). On the other hand, intra-neuronal insoluble tau aggregates are often degraded within lysosomes by macroautophagy. AELN defects have been observed in AD, FTD, CBD, and PSP, and lysosomal dysfunction was shown to promote the cleavage and neurotoxicity of tau. Moreover, several AD risk genes (e.g., , , ) have been associated with dysregulation of AELN in the late-onset sporadic AD. Conversely, tau dissociation from microtubules interferes with retrograde transport of autophagosomes to lysosomes, and that tau fragments can also lead to lysosomal dysfunction. Recent studies suggest that tau is not merely an intra-neuronal protein, but it can be released to brain parenchyma via extracellular vesicles, like exosomes and ectosomes, and thus spread between neurons. Extracellular tau can also be taken up by microglial cells and astrocytes, either being degraded through AELN or propagated via exosomes. This article reviews the complex roles of AELN in the degradation and transmission of tau, potential diagnostic/therapeutic targets and strategies based on AELN-mediated tau clearance and propagation, and the current state of drug development targeting AELN and tau against tauopathies.
PubMed: 33177989
DOI: 10.3389/fnmol.2020.586731