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Aging Cell Oct 2022Autophagy is essential for protein quality control and regulation of the functional proteome. Failure of autophagy pathways with age contributes to loss of proteostasis...
Autophagy is essential for protein quality control and regulation of the functional proteome. Failure of autophagy pathways with age contributes to loss of proteostasis in aged organisms and accelerates the progression of age-related diseases. In this work, we show that activity of endosomal microautophagy (eMI), a selective type of autophagy occurring in late endosomes, declines with age and identify the sub-proteome affected by this loss of function. Proteomics of late endosomes from old mice revealed an aberrant glycation signature for Hsc70, the chaperone responsible for substrate targeting to eMI. Age-related Hsc70 glycation reduces its stability in late endosomes by favoring its organization into high molecular weight protein complexes and promoting its internalization/degradation inside late endosomes. Reduction of eMI with age associates with an increase in protein secretion, as late endosomes can release protein-loaded exosomes upon plasma membrane fusion. Our search for molecular mediators of the eMI/secretion switch identified the exocyst-RalA complex, known for its role in exocytosis, as a novel physiological eMI inhibitor that interacts with Hsc70 and acts directly at the late endosome membrane. This inhibitory function along with the higher exocyst-RalA complex levels detected in late endosomes from old mice could explain, at least in part, reduced eMI activity with age. Interaction of Hsc70 with components of the exocyst-RalA complex places this chaperone in the switch from eMI to secretion. Reduced intracellular degradation in favor of extracellular release of undegraded material with age may be relevant to the spreading of proteotoxicity associated with aging and progression of proteinopathies.
Topics: Aging; Animals; Autophagy; Endosomes; Lysosomes; Mice; Microautophagy; Protein Transport; Proteome
PubMed: 36116133
DOI: 10.1111/acel.13713 -
Autophagy Apr 2011Autophagy-related (Atg) pathways deliver cytosol and organelles to the vacuole in double-membrane vesicles called autophagosomes, which are formed at the phagophore...
Autophagy-related (Atg) pathways deliver cytosol and organelles to the vacuole in double-membrane vesicles called autophagosomes, which are formed at the phagophore assembly site (PAS), where most of the core Atg proteins assemble. Atg28 is a component of the core autophagic machinery partially required for all Atg pathways in Pichia pastoris. This coiled-coil protein interacts with Atg17 and is essential for micropexophagy. However, the role of Atg28 in micropexophagy was unknown. We used the yeast two-hybrid system to search for Atg28 interaction partners from P. pastoris and identified a new Atg protein, named Atg35. The atg35∆ mutant was not affected in macropexophagy, cytoplasm-to-vacuole targeting or general autophagy. However, both Atg28 and Atg35 were required for micropexophagy and for the formation of the micropexophagic apparatus (MIPA). This requirement correlated with a stronger expression of both proteins on methanol and glucose. Atg28 mediated the interaction of Atg35 with Atg17. Trafficking of overexpressed Atg17 from the peripheral ER to the nuclear envelope was required to organize a peri-nuclear structure (PNS), the site of Atg35 colocalization during micropexophagy. In summary, Atg35 is a new Atg protein that relocates to the PNS and specifically regulates MIPA formation during micropexophagy.
Topics: Autophagy; Carrier Proteins; Cytoplasm; Fungal Proteins; Gene Expression Regulation, Fungal; Gene Library; Glucose; Methanol; Models, Genetic; Mutation; Peroxisomes; Pichia; Protein Transport; Time Factors; Two-Hybrid System Techniques; Vacuoles
PubMed: 21169734
DOI: 10.4161/auto.7.4.14369 -
Cell Death and Differentiation Mar 2023Inflammation leads to systemic osteoporosis or local bone destruction, however, the underlying molecular mechanisms are still poorly understood. In this study, we report...
Inflammation leads to systemic osteoporosis or local bone destruction, however, the underlying molecular mechanisms are still poorly understood. In this study, we report that PRL2 is a negative regulator of osteoclastogenesis and bone absorption. Mice with PRL2 deficiency exhibit a decrease in bone volume and an increase in osteoclast numbers. PRL2 negatively regulates RANKL-induced reactive oxygen species production through the activation of RAC1, thus PRL2 deficient osteoclast precursors have both increased osteoclast differentiation ability and bone resorptive capacity. During inflammation, oxidized PRL2 is a selected substrate of HSC70 and conditions of oxidative stress trigger rapid degradation of PRL2 by HSC70 mediated endosomal microautophagy and chaperone-mediated autophagy. Ablation of PRL2 in mouse models of inflammatory bone disease leads to an increase in the number of osteoclasts and exacerbation of bone damage. Moreover, reduced PRL2 protein levels in peripheral myeloid cells are highly correlated with bone destruction in a mouse arthritis model and in human rheumatoid arthritis, while the autophagy inhibitor hydroxychloroquine blocked inflammation-induced PRL2 degradation and bone destruction in vivo. Therefore, our findings identify PRL2 as a new regulator in osteoimmunity, providing a link between inflammation and osteoporosis. As such, PRL2 is a potential therapeutic target for inflammatory bone disease and inhibition of HSC70 mediated autophagic degradation of PRL2 may offer new therapeutic tools for the treatment of inflammatory bone disease.
Topics: Animals; Humans; Mice; Autophagy; Bone Resorption; Cell Differentiation; Disease Models, Animal; Inflammation; Osteoclasts; Osteogenesis; Osteoporosis; RANK Ligand; HSC70 Heat-Shock Proteins
PubMed: 36182990
DOI: 10.1038/s41418-022-01068-y -
Renal Failure Nov 2017Autophagy, a highly conserved mechanism for cell survival, emerges as an important pathway in many biological processes and diseases conditions. Studies of cultured... (Review)
Review
Autophagy, a highly conserved mechanism for cell survival, emerges as an important pathway in many biological processes and diseases conditions. Studies of cultured renal cells, human kidney tissues and experimental animal models implicate that autophagy regulation is the critical aspects in chronic kidney diseases (CKD). Here, we summarize the current studies on the role of autophagy in CKD. Unveiling the precise regulation mechanism of autophagy in CKD is essential for developing potential prevention, diagnostic and therapeutic targets of these sticky clinical challenges.
Topics: Autophagy; Humans; Kidney; Renal Insufficiency, Chronic; Signal Transduction
PubMed: 28085532
DOI: 10.1080/0886022X.2016.1274662 -
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 -
Biochimica Et Biophysica Acta Feb 2015Autophagy, literally translated means self-eating, is a primary degradative pathway and plays an important role in the regulation of cellular homeostasis through... (Review)
Review
Autophagy, literally translated means self-eating, is a primary degradative pathway and plays an important role in the regulation of cellular homeostasis through elimination of aggregated proteins, damaged organelles, and intracellular pathogens. Autophagy has been classified into microautophagy, macroautophagy, and chaperone-mediated autophagy, depending on the choice of the pathway by which the cellular material is delivered to lysosomes. Dysregulation of autophagy may contribute to the development of cardiorenal metabolic syndrome (CRS), including insulin resistance, obesity, hypertension, maladaptive immune modulation, and associated cardiac and renal disease. Clarifying the pathways and mechanisms of autophagy under normal conditions is essential to understanding its dysregulation in the development of CRS. Here, we highlight a recent surge in autophagy research, such as the cellular quality control through the disposal and recycling of cellular components, and summarize our contemporary understanding of molecular mechanisms of autophagy in diverse organ or tissues involved in the pathogenesis of CRS. This article is part of a Special Issue entitled: Autophagy and protein quality control in cardiometabolic diseases.
Topics: Autophagy; Cardiovascular Diseases; Health; Humans; Kidney Diseases; Metabolic Diseases; Signal Transduction
PubMed: 24984281
DOI: 10.1016/j.bbadis.2014.06.025 -
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