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1
Li, Yuan, Baohui Chen, Wei Zou, Xin Wang, Yanwei Wu, Dongfeng Zhao, Yanan Sun i in. "The lysosomal membrane protein SCAV-3 maintains lysosome integrity and adult longevity". Journal of Cell Biology 215, nr 2 (17.10.2016): 167–85. http://dx.doi.org/10.1083/jcb.201602090.
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Lysosomes degrade macromolecules and recycle metabolites as well as being involved in diverse processes that regulate cellular homeostasis. The lysosome is limited by a single phospholipid bilayer that forms a barrier to separate the potent luminal hydrolases from other cellular constituents, thus protecting the latter from unwanted degradation. The mechanisms that maintain lysosomal membrane integrity remain unknown. Here, we identified SCAV-3, the Caenorhabditis elegans homologue of human LIMP-2, as a key regulator of lysosome integrity, motility, and dynamics. Loss of scav-3 caused rupture of lysosome membranes and significantly shortened lifespan. Both of these phenotypes were suppressed by reinforced expression of LMP-1 or LMP-2, the C. elegans LAMPs, indicating that longevity requires maintenance of lysosome integrity. Remarkably, reduction in insulin/insulin-like growth factor 1 (IGF-1) signaling suppressed lysosomal damage and extended the lifespan in scav-3(lf) animals in a DAF-16–dependent manner. Our data reveal that SCAV-3 is essential for preserving lysosomal membrane stability and that modulation of lysosome integrity by the insulin/IGF-1 signaling pathway affects longevity.
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Stark, Michal, Tomás F. D. Silva, Guy Levin, Miguel Machuqueiro i Yehuda G. Assaraf. "The Lysosomotropic Activity of Hydrophobic Weak Base Drugs is Mediated via Their Intercalation into the Lysosomal Membrane". Cells 9, nr 5 (27.04.2020): 1082. http://dx.doi.org/10.3390/cells9051082.
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Lipophilic weak base therapeutic agents, termed lysosomotropic drugs (LDs), undergo marked sequestration and concentration within lysosomes, hence altering lysosomal functions. This lysosomal drug entrapment has been described as luminal drug compartmentalization. Consistent with our recent finding that LDs inflict a pH-dependent membrane fluidization, we herein demonstrate that LDs undergo intercalation and concentration within lysosomal membranes. The latter was revealed experimentally and computationally by (a) confocal microscopy of fluorescent compounds and drugs within lysosomal membranes, and (b) molecular dynamics modeling of the pH-dependent membrane insertion and accumulation of an assortment of LDs, including anticancer drugs. Based on the multiple functions of the lysosome as a central nutrient sensory hub and a degradation center, we discuss the molecular mechanisms underlying the alteration of morphology and impairment of lysosomal functions as consequences of LDs’ intercalation into lysosomes. Our findings bear important implications for drug design, drug induced lysosomal damage, diseases and pertaining therapeutics.
3
Mangalanathan, Malathi, Tamiloli Devendhiran, Saraswathi Uthamaramasamy, Keerthika Kumarasamy, K. Mohanraj, Kannagi Devendhiran, Saroj Adhikari i Mei –. Ching Lin. "Isolation and characterization of mitochondria and lysosome from isoproterenol induced cardiotoxic rats". South Asian Journal of Engineering and Technology 8, nr 1 (8.02.2019): 12–18. http://dx.doi.org/10.26524/sajet190804.
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Mitochondrial and lysosomal membranes are prominent membranes of cardiac cells and are the factors that determine membrane function in myocardial ischemia. In this study, isolation of mitochondria and lysosome from heart tissue under the control, isoproterenol (ISO) (8.5mg/100g) induced cardiotoxic rats and oral pretreatment with Z. armatum fruit (200, 400mg/kg body weight) treated rats. Further characterization of marker enzymes was done. A decreased in the activity of all the mitochondrial and lysosomal marker enzymes in ISO administered cardiotoxic rats when compared to control rats which indicate ISO decreased the stability of the membrane. Pretreatment with hydroethanolic extract of Z. armatum fruit to ISO induced rats significantly reverted these biochemical alterations near to normal. The possible mechanism for the protection of heart mitochondria and lysosome against oxidative damage induced by ISO might be due to quenching of free radicals and enhancing the action of marker enzymes.
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Boonen, Marielle, Isabelle Hamer, Muriel Boussac, Anne-Françoise Delsaute, Bruno Flamion, Jérôme Garin i Michel Jadot. "Intracellular localization of p40, a protein identified in a preparation of lysosomal membranes". Biochemical Journal 395, nr 1 (15.03.2006): 39–47. http://dx.doi.org/10.1042/bj20051647.
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Unlike lysosomal soluble proteins, few lysosomal membrane proteins have been identified. Rat liver lysosomes were purified by centrifugation on a Nycodenz density gradient. The most hydrophobic proteins were extracted from the lysosome membrane preparation and were identified by MS. We focused our attention on a protein of approx. 40 kDa, p40, which contains seven to ten putative transmembrane domains and four lysosomal consensus sorting motifs in its sequence. Knowing that preparations of lysosomes obtained by centrifugation always contain contaminant membranes, we combined biochemical and morphological methods to analyse the subcellular localization of p40. The results of subcellular fractionation of mouse liver homogenates validate the lysosomal residence of p40. In particular, a density shift of lysosomes induced by Triton WR-1339 similarly affected the distributions of p40 and β-galactosidase, a lysosomal marker protein. We confirmed by fluorescence microscopy on eukaryotic cells transfected with p40 or p40–GFP (green fluorescent protein) constructs that p40 is localized in lysosomes. A first molecular characterization of p40 in transfected Cos-7 cells revealed that it is an unglycosylated protein tightly associated with membranes. Taken together, our results strongly support the hypothesis that p40 is an authentic lysosomal membrane protein.
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Tang, Tuoxian, Boshuo Jian i Zhenjiang Liu. "Transmembrane Protein 175, a Lysosomal Ion Channel Related to Parkinson’s Disease". Biomolecules 13, nr 5 (9.05.2023): 802. http://dx.doi.org/10.3390/biom13050802.
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Lysosomes are membrane-bound organelles with an acidic lumen and are traditionally characterized as a recycling center in cells. Lysosomal ion channels are integral membrane proteins that form pores in lysosomal membranes and allow the influx and efflux of essential ions. Transmembrane protein 175 (TMEM175) is a unique lysosomal potassium channel that shares little sequence similarity with other potassium channels. It is found in bacteria, archaea, and animals. The prokaryotic TMEM175 consists of one six-transmembrane domain that adopts a tetrameric architecture, while the mammalian TMEM175 is comprised of two six-transmembrane domains that function as a dimer in lysosomal membranes. Previous studies have demonstrated that the lysosomal K+ conductance mediated by TMEM175 is critical for setting membrane potential, maintaining pH stability, and regulating lysosome–autophagosome fusion. AKT and B-cell lymphoma 2 regulate TMEM175’s channel activity through direct binding. Two recent studies reported that the human TMEM175 is also a proton-selective channel under normal lysosomal pH (4.5–5.5) as the K+ permeation dramatically decreased at low pH while the H+ current through TMEM175 greatly increased. Genome-wide association studies and functional studies in mouse models have established that TMEM175 is implicated in the pathogenesis of Parkinson’s disease, which sparks more research interests in this lysosomal channel.
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Feng, Xinghua, Zhuangzhuang Zhao, Qian Li i Zhiyong Tan. "Lysosomal Potassium Channels: Potential Roles in Lysosomal Function and Neurodegenerative Diseases". CNS & Neurological Disorders - Drug Targets 17, nr 4 (6.07.2018): 261–66. http://dx.doi.org/10.2174/1871527317666180202110717.
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Background & Objective: The lysosome is a membrane-enclosed organelle widely found in every eukaryotic cell. It has been deemed as the stomach of the cells. Recent studies revealed that it also functions as an intracellular calcium store and is a platform for nutrient-dependent signal transduction. Similar with the plasma membrane, the lysosome membrane is furnished with various proteins, including pumps, ion channels and transporters. So far, two types of lysosomal potassium channels have been identified: large-conductance and Ca2+-activated potassium channel (BK) and TMEM175. TMEM175 has been linked to several neurodegeneration diseases, such as the Alzheimer and Parkinson disease. Recent studies showed that TMEM175 is a lysosomal potassium channel with novel architecture and plays important roles in setting the lysosomal membrane potential and maintaining pH stability. TMEM175 deficiency leads to compromised lysosomal function, which might be responsible for the pathogenesis of related diseases. BK is a well-known potassium channel for its function on the plasma membrane. Studies from two independent groups revealed that functional BK channels are also expressed on the lysosomal plasma membrane. Dysfunction of BK causes impaired lysosomal calcium signaling and abnormal lipid accumulation, a featured phenotype of most lysosomal storage diseases (LSDs). Boosting BK activity could rescue the lipid accumulation in several LSD cell models. Overall, the lysosomal potassium channels are essential for the lysosome physiological function, including lysosomal calcium signaling and autophagy. The dysfunction of lysosomal potassium channels is related to some neurodegeneration disorders. Conclusion: Therefore, lysosomal potassium channels are suggested as potential targets for the intervention of lysosomal disorders.
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Israels, S. J., E. M. McMillan, C. Robertson, S. Singhroy i A. McNicol. "The Lysosomal Granule Membrane Protein, Lamp-2, Is also Present in Platelet Dense Granule Membranes". Thrombosis and Haemostasis 75, nr 04 (1996): 623–29. http://dx.doi.org/10.1055/s-0038-1650333.
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SummaryLysosomal Associated Membrane Protein-2 (LAMP-2) is an inherent component of lysosomal granule membranes in diverse cell types, including platelets. We examined platelets for evidence of LAMP-2 in dense granule membranes as CD63 has previously been shown to be present in both lysosomal and dense granule membranes. Immunological techniques were used to examine the localization of LAMP-2 in control platelets and those from an individual with Hermansky-Pudlak syndrome (HPS), a condition characterised by platelet dense granule deficiency. Immunoblotting studies demonstrated that LAMP-2 was enriched in a dense granule preparation. Flow cytometry of thrombin-stimulated control platelets was consistent with biphasic surface expression of LAMP-2. The early expression was accompanied by dense granule, but minimal lysosomal granule, release. The late expression was accompanied by additional lysosomal granule release only. Thrombin stimulation of HPS platelets showed only late, lysosome-associated LAMP-2 expression. Immunoelectron microscopy indicated the presence of LAMP-2 in the membranes of serotonin-containing granules as identified by an anti-serotonin polyclonal antibody. These data indicate that LAMP-2 is present in the membranes of platelet dense granules in addition to lysosomal granules, and has a similar distribution to CD63.
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Chen, J. W., T. L. Murphy, M. C. Willingham, I. Pastan i J. T. August. "Identification of two lysosomal membrane glycoproteins." Journal of Cell Biology 101, nr 1 (1.07.1985): 85–95. http://dx.doi.org/10.1083/jcb.101.1.85.
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Two murine lysosome-associated membrane proteins, LAMP-1 of 105,000-115,000 D and LAMP-2 of 100,000-110,000 D, have been identified by monoclonal antibodies that bind specifically to lysosomal membranes. Both glycoproteins were distinguished as integral membrane components solubilized by detergent solutions but not by various chaotropic agents. The lysosome localization was demonstrated by indirect immunofluorescent staining, co-localization of the antigen to sites of acridine orange uptake, and immunoelectron microscopy. Antibody binding was predominantly located at the limiting lysosomal membrane, distinctly separated from colloidal gold-labeled alpha-2-macroglobulin accumulated in the lumen during prolonged incubation. LAMP-1 and LAMP-2 also appeared to be present in low concentrations on Golgi trans-elements but were not detected in receptosomes marked by the presence of newly endocytosed alpha-2-macroglobulin, or in other cellular structures. LAMP-1 and LAMP-2 were distinguished as different molecules by two-dimensional gel analysis, 125I-tryptic peptide mapping, and sequential immunoprecipitations of 125I-labeled cell extracts. Both glycoproteins were synthesized as a precursor protein of approximately 90,000 D, and showed a marked heterogeneity of apparent molecular weight expression in different cell lines. LAMP-2 was closely related or identical to the macrophage antigen, MAC-3, as indicated by antibody adsorption and tryptic peptide mapping. It is postulated that these glycoproteins, as major protein constituents of the lysosomal membrane, have important roles in lysosomal structure and function.
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Wang, Wuyang, Xiaoli Zhang, Qiong Gao, Maria Lawas, Lu Yu, Xiping Cheng, Mingxue Gu i in. "A voltage-dependent K+ channel in the lysosome is required for refilling lysosomal Ca2+ stores". Journal of Cell Biology 216, nr 6 (3.05.2017): 1715–30. http://dx.doi.org/10.1083/jcb.201612123.
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The resting membrane potential (Δψ) of the cell is negative on the cytosolic side and determined primarily by the plasma membrane’s selective permeability to K+. We show that lysosomal Δψ is set by lysosomal membrane permeabilities to Na+ and H+, but not K+, and is positive on the cytosolic side. An increase in juxta-lysosomal Ca2+ rapidly reversed lysosomal Δψ by activating a large voltage-dependent and K+-selective conductance (LysoKVCa). LysoKVCa is encoded molecularly by SLO1 proteins known for forming plasma membrane BK channels. Opening of single LysoKVCa channels is sufficient to cause the rapid, striking changes in lysosomal Δψ. Lysosomal Ca2+ stores may be refilled from endoplasmic reticulum (ER) Ca2+ via ER–lysosome membrane contact sites. We propose that LysoKVCa serves as the perilysosomal Ca2+ effector to prime lysosomes for the refilling process. Consistently, genetic ablation or pharmacological inhibition of LysoKVCa, or abolition of its Ca2+ sensitivity, blocks refilling and maintenance of lysosomal Ca2+ stores, resulting in lysosomal cholesterol accumulation and a lysosome storage phenotype.
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Wilson, J. M., J. A. Whitney i M. R. Neutra. "Biogenesis of the apical endosome-lysosome complex during differentiation of absorptive epithelial cells in rat ileum". Journal of Cell Science 100, nr 1 (1.09.1991): 133–43. http://dx.doi.org/10.1242/jcs.100.1.133.
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Absorptive cells of the neonatal rat ileum have an elaborate apical endocytic complex consisting of tubular and vesicular endosomes, multivesicular bodies (MVB), and a giant lysosomal vacuole. This system develops rapidly over the last 3 days (20–22) of gestation. We followed the assembly of this complex by ultrastructural analysis and immunocytochemistry using antigenic markers for microvilli, endosomal tubules and lysosomal membranes. At 19 days gestation, low levels of lactase appeared on microvilli but specialized apical endosomal tubules and lysosomes were absent. At 20 days, expression of microvillar lactase increased and the endosomal marker entubin appeared, in parallel with the appearance of specialized apical endosomal tubules. The compartments of the apical endosome-lysosome system were assembled sequentially after differentiation of the apical plasma membrane domains; first endosomal tubules and vesicles, followed by MVB, and ending with the assembly of the giant lysosome shortly after birth. During early stages of the assembly process, membrane components of the tubular endosomes and lysosomes appeared in the apical plasma membrane before being restricted to their respective intracellular compartments.
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Saftig, Paul, Bernd Schröder i Judith Blanz. "Lysosomal membrane proteins: life between acid and neutral conditions". Biochemical Society Transactions 38, nr 6 (24.11.2010): 1420–23. http://dx.doi.org/10.1042/bst0381420.
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Whereas we have a profound understanding about the function and biogenesis of the protein constituents in the lumen of the lysosomal compartment, much less is known about the functions of proteins of the lysosomal membrane. Proteomic analyses of the lysosomal membrane suggest that, apart from the well-known lysosomal membrane proteins, additional and less abundant membrane proteins are present. The identification of disease-causing genes and the in-depth analysis of knockout mice leading to mutated or absent membrane proteins of the lysosomal membrane have demonstrated the essential role of these proteins in lysosomal acidification, transport of metabolites resulting from hydrolytic degradation and interaction and fusion with other cellular membrane systems. In addition, trafficking pathways of lysosomal membrane proteins are closely linked to the biogenesis of this compartment. This is exemplified by the recent finding that LIMP-2 (lysosomal integral membrane protein type-2) is responsible for the mannose 6-phosphate receptor-independent delivery of newly synthesized β-glucocerebrosidase to the lysosome. Similar to LIMP-2, which could also be linked to vesicular transport processes in certain polarized cell types, the major constituents of the lysosomal membrane, the glycoproteins LAMP (lysosome-associated membrane protein)-1 and LAMP-2 are essential for regulation of lysosomal motility and participating in control of membrane fusion events between autophagosomes or phagosomes with late endosomes/lysosomes. Our recent investigations into the role of these proteins have not only increased our understanding of the endolysosomal system, but also supported their major role in cell physiology and the development of different diseases.
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Tan, Sin-Lih, Muruj Barri, Peace Atakpa-Adaji, Colin W. Taylor, Ewan St. John Smith i Ruth D. Murrell-Lagnado. "P2X4 Receptors Mediate Ca2+ Release from Lysosomes in Response to Stimulation of P2X7 and H1 Histamine Receptors". International Journal of Molecular Sciences 22, nr 19 (28.09.2021): 10492. http://dx.doi.org/10.3390/ijms221910492.
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The P2X4 purinergic receptor is targeted to endolysosomes, where it mediates an inward current dependent on luminal ATP and pH. Activation of P2X4 receptors was previously shown to trigger lysosome fusion, but the regulation of P2X4 receptors and their role in lysosomal Ca2+ signaling are poorly understood. We show that lysosomal P2X4 receptors are activated downstream of plasma membrane P2X7 and H1 histamine receptor stimulation. When P2X4 receptors are expressed, the increase in near-lysosome cytosolic [Ca2+] is exaggerated, as detected with a low-affinity targeted Ca2+ sensor. P2X4-dependent changes in lysosome properties were triggered downstream of P2X7 receptor activation, including an enlargement of lysosomes indicative of homotypic fusion and a redistribution of lysosomes towards the periphery of the cell. Lysosomal P2X4 receptors, therefore, have a role in regulating lysosomal Ca2+ release and the regulation of lysosomal membrane trafficking.
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Mammadova, Jamila, Rojin Fatirkhorani, Shuzhen Liu, Ken Chen i Zhigao Wang. "Abstract 2529: Necrosome translocates to lysosome to induce lysosome membrane permeabilization and subsequent necroptotic cell death". Cancer Research 83, nr 7_Supplement (4.04.2023): 2529. http://dx.doi.org/10.1158/1538-7445.am2023-2529.
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Abstract Introduction: Necroptosis is a cellular process known to be downregulated by cancer cells, and its molecular steps have been described in the literature. Mixed-lineage kinase domain like (MLKL) protein is the most terminal effector of necroptosis. Necroptosis has previously been shown to be activated by the formation of necrosome complex consisting of receptor interacting serine/threonine kinase 1 (RIPK1)-RIPK3-MLKL. MLKL is activated by RIPK3 via phosphorylation, forming phospho-MLKL (P-MLKL), leading to MLKL polymerization and cell necroptosis via lysosome membrane permeabilization (LMP) and plasma membrane rupture. We propose that the necrosome locates onto the lysosome, leading to MLKL-activation induced LMP before cell membrane rupture. Objectives: Our objective is to show that necrosome formation occurs on lysosomal membrane, which then leads to the formation of P-MLKL, and, subsequently, necroptosis via LMP and plasma membrane rupture. Methods: HT-29 cells with hemagglutinin (HA) tagged lysosomal transmembrane protein were induced to undergo necroptosis with the treatment of TNF (T), Smac-mimetic (S) and Z-VAD-FMK (Z) (abbreviated as T/S/Z). Lysosomes were extracted first by cell rupture via homogenization and then immunoprecipitation using anti-HA magnetic beads. Results: Our results suggest that LMP precedes plasma membrane permeability and that MLKL activation takes place on lysosomal membrane. Western blotting demonstrated that lysosomal cathepsin proteases, including CTSA, CTSB, CTSC, CTSD and CTSK, were released into cytosol during necroptosis, confirming lysosomal damage. Furthermore, P-RIPK1, P-RIPK3, P-MLKL and MLKL tetramer were found to be specifically associated with purified lysosomes upon necroptosis induction. Conclusions: MLKL activation on lysosomal membrane and LMP constitute an important step of necroptosis. [J.M. and R.F. contributed equally to this work.] Citation Format: Jamila Mammadova, Rojin Fatirkhorani, Shuzhen Liu, Ken Chen, Zhigao Wang. Necrosome translocates to lysosome to induce lysosome membrane permeabilization and subsequent necroptotic cell death [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2529.
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Ebner, Michael, Philipp Alexander Koch i Volker Haucke. "Phosphoinositides in the control of lysosome function and homeostasis". Biochemical Society Transactions 47, nr 4 (5.08.2019): 1173–85. http://dx.doi.org/10.1042/bst20190158.
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Abstract Lysosomes are the main degradative compartments of mammalian cells and serve as platforms for cellular nutrient signaling and sterol transport. The diverse functions of lysosomes and their adaptation to extracellular and intracellular cues are tightly linked to the spatiotemporally controlled synthesis, turnover and interconversion of lysosomal phosphoinositides, minor phospholipids that define membrane identity and couple membrane dynamics to cell signaling. How precisely lysosomal phosphoinositides act and which effector proteins within the lysosome membrane or at the lysosomal surface recognize them is only now beginning to emerge. Importantly, mutations in phosphoinositide metabolizing enzyme cause lysosomal dysfunction and are associated with numerous diseases ranging from neurodegeneration to cancer. Here, we discuss the phosphoinositides and phosphoinositide metabolizing enzymes implicated in lysosome function and homeostasis and outline perspectives for future research.
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Ziglari, Tahereh, Zifan Wang i Andrij Holian. "Contribution of Particle-Induced Lysosomal Membrane Hyperpolarization to Lysosomal Membrane Permeabilization". International Journal of Molecular Sciences 22, nr 5 (25.02.2021): 2277. http://dx.doi.org/10.3390/ijms22052277.
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Lysosomal membrane permeabilization (LMP) has been proposed to precede nanoparticle-induced macrophage injury and NLRP3 inflammasome activation; however, the underlying mechanism(s) of LMP is unknown. We propose that nanoparticle-induced lysosomal hyperpolarization triggers LMP. In this study, a rapid non-invasive method was used to measure changes in lysosomal membrane potential of murine alveolar macrophages (AM) in response to a series of nanoparticles (ZnO, TiO2, and CeO2). Crystalline SiO2 (micron-sized) was used as a positive control. Changes in cytosolic potassium were measured using Asante potassium green 2. The results demonstrated that ZnO or SiO2 hyperpolarized the lysosomal membrane and decreased cytosolic potassium, suggesting increased lysosome permeability to potassium. Time-course experiments revealed that lysosomal hyperpolarization was an early event leading to LMP, NLRP3 activation, and cell death. In contrast, TiO2- or valinomycin-treated AM did not cause LMP unless high doses led to lysosomal hyperpolarization. Neither lysosomal hyperpolarization nor LMP was observed in CeO2-treated AM. These results suggested that a threshold of lysosomal membrane potential must be exceeded to cause LMP. Furthermore, inhibition of lysosomal hyperpolarization with Bafilomycin A1 blocked LMP and NLRP3 activation, suggesting a causal relation between lysosomal hyperpolarization and LMP.
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Trivedi, Purvi C., Jordan J. Bartlett i Thomas Pulinilkunnil. "Lysosomal Biology and Function: Modern View of Cellular Debris Bin". Cells 9, nr 5 (4.05.2020): 1131. http://dx.doi.org/10.3390/cells9051131.
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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.
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Rodríguez, Ana, Paul Webster, Javier Ortego i Norma W. Andrews. "Lysosomes Behave as Ca2+-regulated Exocytic Vesicles in Fibroblasts and Epithelial Cells". Journal of Cell Biology 137, nr 1 (7.04.1997): 93–104. http://dx.doi.org/10.1083/jcb.137.1.93.
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Lysosomes are considered to be a terminal degradative compartment of the endocytic pathway, into which transport is mostly unidirectional. However, specialized secretory vesicles regulated by Ca2+, such as neutrophil azurophil granules, mast cell–specific granules, and cytotoxic lymphocyte lytic granules, share characteristics with lysosomes that may reflect a common biogenesis. In addition, the involvement of Ca2+ transients in the invasion mechanism of the parasite Trypanosoma cruzi, which occurs by fusion of lysosomes with the plasma membrane, suggested that lysosome exocytosis might be a generalized process present in most cell types. Here we demonstrate that elevation in the intracellular free Ca2+ concentration of normal rat kidney (NRK) fibroblasts induces fusion of lysosomes with the plasma membrane. This was verified by measuring the release of the lysosomal enzyme β-hexosaminidase, the appearance on the plasma membrane of the lysosomal glycoprotein lgp120, the release of fluid-phase tracers previously loaded into lysosomes, and the release of the lysosomally processed form of cathepsin D. Exposure to the Ca2+ ionophore ionomycin or addition of Ca2+containing buffers to streptolysin O–permeabilized cells induced exocytosis of ∼10% of the total lysosomes of NRK cells. The process was also detected in other cell types such as epithelial cells and myoblasts. Lysosomal exocytosis was found to require micromolar levels of Ca2+ and to be temperature and ATP dependent, similar to Ca2+-regulated secretory mechanisms in specialized cells. These findings highlight a novel role for lysosomes in cellular membrane traffic and suggest that fusion of lysosomes with the plasma membrane may be an ubiquitous form of Ca2+-regulated exocytosis.
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Stahl-Meyer, Kamilla, Mesut Bilgin, Lya K. K. Holland, Jonathan Stahl-Meyer, Thomas Kirkegaard, Nikolaj Havnsøe Torp Petersen, Kenji Maeda i Marja Jäättelä. "Galactosyl- and glucosylsphingosine induce lysosomal membrane permeabilization and cell death in cancer cells". PLOS ONE 17, nr 11 (21.11.2022): e0277058. http://dx.doi.org/10.1371/journal.pone.0277058.
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Isomeric lysosphingolipids, galactosylsphingosine (GalSph) and glucosylsphingosine (GlcSph), are present in only minute levels in healthy cells. Due to defects in their lysosomal hydrolysis, they accumulate at high levels and cause cytotoxicity in patients with Krabbe and Gaucher diseases, respectively. Here, we show that GalSph and GlcSph induce lysosomal membrane permeabilization, a hallmark of lysosome-dependent cell death, in human breast cancer cells (MCF7) and primary fibroblasts. Supporting lysosomal leakage as a causative event in lysosphingolipid-induced cytotoxicity, treatment of MCF7 cells with lysosome-stabilizing cholesterol prevented GalSph- and GlcSph-induced cell death almost completely. In line with this, fibroblasts from a patient with Niemann-Pick type C disease, which is caused by defective lysosomal cholesterol efflux, were significantly less sensitive to lysosphingolipid-induced lysosomal leakage and cell death. Prompted by the data showing that MCF7 cells with acquired resistance to lysosome-destabilizing cationic amphiphilic drugs (CADs) were partially resistant to the cell death induced by GalSph and GlcSph, we compared these cell death pathways with each other. Like CADs, GalSph and GlcSph activated the cyclic AMP (cAMP) signalling pathway, and cAMP-inducing forskolin sensitized cells to cell death induced by low concentrations of lysosphingolipids. Contrary to CADs, lysosphingolipid-induced cell death was independent of lysosomal Ca2+ efflux through P2X purinerigic receptor 4. These data reveal GalSph and GlcSph as lysosome-destabilizing lipids, whose putative use in cancer therapy should be further investigated. Furthermore, the data supports the development of lysosome stabilizing drugs for the treatment of Krabbe and Gaucher diseases and possibly other sphingolipidoses.
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Monastyrska, Iryna, Congcong He, Jiefei Geng, Adam D. Hoppe, Zhijian Li i Daniel J. Klionsky. "Arp2 Links Autophagic Machinery with the Actin Cytoskeleton". Molecular Biology of the Cell 19, nr 5 (maj 2008): 1962–75. http://dx.doi.org/10.1091/mbc.e07-09-0892.
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Macroautophagy involves lysosomal/vacuolar elimination of long-lived proteins and entire organelles from the cytosol. The process begins with formation of a double-membrane vesicle that sequesters bulk cytoplasm, or a specific cargo destined for lysosomal/vacuolar delivery. The completed vesicle fuses with the lysosome/vacuole limiting membrane, releasing its content into the organelle lumen for subsequent degradation and recycling of the resulting macromolecules. A majority of the autophagy-related (Atg) proteins are required at the step of vesicle formation. The integral membrane protein Atg9 cycles between certain intracellular compartments and the vesicle nucleation site, presumably to supply membranes necessary for macroautophagic vesicle formation. In this study we have tracked the movement of Atg9 over time in living cells by using real-time fluorescence microscopy. Our results reveal that an actin-related protein, Arp2, briefly colocalizes with Atg9 and directly regulates the dynamics of Atg9 movement. We propose that proteins of the Arp2/3 complex regulate Atg9 transport for specific types of autophagy.
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Schieweck, Oliver, Markus Damme, Bernd Schröder, Andrej Hasilik, Bernhard Schmidt i Torben Lübke. "NCU-G1 is a highly glycosylated integral membrane protein of the lysosome". Biochemical Journal 422, nr 1 (29.07.2009): 83–90. http://dx.doi.org/10.1042/bj20090567.
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Until recently, a modest number of approx. 40 lysosomal membrane proteins had been identified and even fewer were characterized in their function. In a proteomic study, using lysosomal membranes from human placenta we identified several candidate lysosomal membrane proteins and proved the lysosomal localization of two of them. In the present study, we demonstrate the lysosomal localization of the mouse orthologue of the human C1orf85 protein, which has been termed kidney-predominant protein NCU-G1 (GenBank® accession number: AB027141). NCU-G1 encodes a 404 amino acid protein with a calculated molecular mass of 39 kDa. The bioinformatics analysis of its amino acid sequence suggests it is a type I transmembrane protein containing a single tyrosine-based consensus lysosomal sorting motif at position 400 within the 12-residue C-terminal tail. Its lysosomal localization was confirmed using immunofluorescence with a C-terminally His-tagged NCU-G1 and the lysosomal marker LAMP-1 (lysosome-associated membrane protein-1) as a reference, and by subcellular fractionation of mouse liver after a tyloxapol-induced density shift of the lysosomal fraction using an anti-NCU-G1 antiserum. In transiently transfected HT1080 and HeLa cells, the His-tagged NCU-G1 was detected in two molecular forms with apparent protein sizes of 70 and 80 kDa, and in mouse liver the endogenous wild-type NCU-G1 was detected as a 75 kDa protein. The remarkable difference between the apparent and the calculated molecular masses of NCU-G1 was shown, by digesting the protein with N-glycosidase F, to be due to an extensive glycosylation. The lysosomal localization was impaired by mutational replacement of an alanine residue for the tyrosine residue within the putative sorting motif.
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Pellerin-Massicotte, Jocelyne, Bruno Vincent i Émilien Pelletier. "Évaluation écotoxicologique de la baie des Anglais à Baie-Comeau (Québec)". Water Quality Research Journal 28, nr 4 (1.11.1993): 665–86. http://dx.doi.org/10.2166/wqrj.1993.035.
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Résumé La baie des Anglais à Baie-Comeau (Québec) est un site industriel reconnu comme étant contaminé aux hydrocarbures et aux biphényls polychlorés (BPC). Une expérience de transfert à moyen terme de deux bivalves marins, Mya arenaria et Mytilus edulis L., a été réalisée entre un site de référence en aval de la baie des Anglais (Franquelin) et des sites contaminés près de Baie-Comeau suivant un gradient de contamination déterminé selon des données physico-chimiques antérieures. Les analyses chimiques de contaminants ont montré qu’il n’y a pas eu d’enrichissement en hydrocarbures, au mercure et en BPC pour toute la durée du protocole mais, parmi les sondes bioanalytiques choisies pour évaluer l’état de santé de cet écosystème, celles qui se sont avérées les plus sensibles chez Mya arenaria furent le glycogène et les lipides dans les gonades, et pour les deux bivalves, la fragilité de la membrane lysosomale de la glande digestive qui est un excellent indicateur de stress toxique. Les présents résultats sont compatibles avec un modèle qui consisterait à établir une évaluation ecotoxicologique d’un écosystème que l’on soupçonne perturbé par la pollution par (i) l’analyse de la bioaccumulation des substances toxiques que l’on croit présentes dans l’écosystème (hydrocarbures, BPC et métaux lourds) et (ii) l’évaluation des effets physiologiques et biochimiques des polluants à l’aide de sondes bioanalytiques appropriées.
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Chen, Dong, Paula P. Lemons, Todd Schraw i Sidney W. Whiteheart. "Molecular mechanisms of platelet exocytosis: role of SNAP-23 and syntaxin 2 and 4 in lysosome release". Blood 96, nr 5 (1.09.2000): 1782–88. http://dx.doi.org/10.1182/blood.v96.5.1782.
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Abstract On stimulation by strong agonists, platelets release the contents of 3 storage compartments in 2 apparent waves of exocytosis. The first wave is the release of α- and dense core granule contents and the second is the release of lysosomal contents. Using a streptolysin O-permeabilized platelet exocytosis assay, we show that hexosaminidase release is stimulated by either Ca++ or by GTP-γ-S. This release step retains the same temporal separation from serotonin release as seen in intact platelets. This assay system was also used to dissect the molecular mechanisms of lysosome exocytosis. Lysosome release requires adenosine triphosphate and the general membrane fusion protein, N-ethylmaleimide sensitive factor. Uniquely, 2 syntaxin t-SNAREs, syntaxin 2 and 4, which localize to granules and open canalicular membranes, together with the general target membrane SNAP receptor (t-SNARE) protein SNAP-23 appear to make up the heterodimeric t-SNAREs required for lysosome exocytosis. These studies further show that regardless of stimuli (Ca++or GTP-γ-S) serotonin and hexosaminidase release requires the same membrane fusion machinery.
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Chen, Dong, Paula P. Lemons, Todd Schraw i Sidney W. Whiteheart. "Molecular mechanisms of platelet exocytosis: role of SNAP-23 and syntaxin 2 and 4 in lysosome release". Blood 96, nr 5 (1.09.2000): 1782–88. http://dx.doi.org/10.1182/blood.v96.5.1782.h8001782_1782_1788.
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On stimulation by strong agonists, platelets release the contents of 3 storage compartments in 2 apparent waves of exocytosis. The first wave is the release of α- and dense core granule contents and the second is the release of lysosomal contents. Using a streptolysin O-permeabilized platelet exocytosis assay, we show that hexosaminidase release is stimulated by either Ca++ or by GTP-γ-S. This release step retains the same temporal separation from serotonin release as seen in intact platelets. This assay system was also used to dissect the molecular mechanisms of lysosome exocytosis. Lysosome release requires adenosine triphosphate and the general membrane fusion protein, N-ethylmaleimide sensitive factor. Uniquely, 2 syntaxin t-SNAREs, syntaxin 2 and 4, which localize to granules and open canalicular membranes, together with the general target membrane SNAP receptor (t-SNARE) protein SNAP-23 appear to make up the heterodimeric t-SNAREs required for lysosome exocytosis. These studies further show that regardless of stimuli (Ca++or GTP-γ-S) serotonin and hexosaminidase release requires the same membrane fusion machinery.
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Fomina, M. A., i A. M. Kudlaeva. "In vitro effects of L-arginine on lysosomal cysteine proteases activity in isolated experiment and in the state of oxidative stress". Kazan medical journal 96, nr 5 (15.10.2015): 876–82. http://dx.doi.org/10.17750/kmj2015-876.
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Aim. Assessment of direct influence of arginine on lysosomal cysteine proteases activity in vitro, in isolation as well as the stimulation of oxidative stress.
Methods. The study was conducted on the 72 female conventional mature Wistar rats 280-320 g divided into 6 series of 12 rats each. Lysosome slurries were isolated from the liver of intact animals with a subsequent in vitro incubation in a sucrose solution, in the presence of L-arginine, as well as in the presence of L-arginine accompanied by the stimulation of oxidative stress. Samples of control groups were exposed in vitro with the addition of isolate and oxidant, respectively. Each batch was reproduced three times, incubation was performed at 37 °C in a water bath for 1, 2 and 4 hours. The activity of cathepsins B, L and H was studied using spectrofluorimetric method in two fractions - intra- and extralysosomal. Acid phosphatase activity was used as the main marker of membrane labialization.
Results. One hour Incubation with 5 mM arginine in vitro led to inhibition of the cathepsin H activity and lysosomal membrane damage, however, further increase in incubation time led to its stabilization. In vitro exposure to 5 mM H2O2 caused an increase in activity of cathepsines B and L and the drop in the cathepsin H activity without obvious changes in the distribution of enzymes between extra and intralysosomal fractions. In a state of oxidative stress 2-hour in vitro incubation with 5 mM arginine reduced the permeability of lysosomal membranes for cathepsines B, H and L; while 4-hour incubation led to the destabilization of lysosomal membranes.
Conclusion. The direct effect of arginine at a concentration of 5 mM within the 1,2 and 4-hour time intervals leads to a distinct change as a lysosomal cysteine protease activity and stability of lysosomal membranes.
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Martínez-Menárguez, J. A., H. J. Geuze i J. Ballesta. "Evidence for a nonlysosomal origin of the acrosome." Journal of Histochemistry & Cytochemistry 44, nr 4 (kwiecień 1996): 313–20. http://dx.doi.org/10.1177/44.4.8601690.
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We studied the biogenesis of the acrosome in sperm cells in immunogold-labeled ultrathin cryosections of rat testis, using a variety of antibodies against endosomal/lysosomal marker protein and acrosin, the major secretory protein of sperm cells. As expected, acrosomes and proacrosomal vesicles in the trans-Golgi region contained abundant acrosin. Rat lysosomal membrane glycoprotein (lgp) 120 and mouse lysosome-associated membrane protein-1 were not detectable in the acrosomal membrane. Similarly, the late endosomal markers cation-dependent and -independent mannose 6-phosphate receptors were absent from the acrosome and proacrosomal vesicles. Therefore, acrosomes do not exhibit these endosomal/lysosomal features. Apart from (pro) acrosomal vesicles, both spermatocytes and spermatids contained classical lysosomes (positive for rat lgp 120, mouse lysosome-associated membrane protein-1, and cathepsin D) that were negative for acrosin. Quantitative analysis of the immunogold labeling showed that spermatocytes express more mannose 6-phosphate receptors and lgp 120 than spermatids, whereas the opposite situation existed for acrosin. These data indicate differential synthetic activity of lysosomal and acrosomal constituents in different states of sperm differentiation. Together, our observations argue against a lysosomal /endosomal origin of the acrosome.
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Bandyopadhyay, Urmi, Susmita Kaushik, Lyuba Varticovski i Ana Maria Cuervo. "The Chaperone-Mediated Autophagy Receptor Organizes in Dynamic Protein Complexes at the Lysosomal Membrane". Molecular and Cellular Biology 28, nr 18 (21.07.2008): 5747–63. http://dx.doi.org/10.1128/mcb.02070-07.
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ABSTRACT Chaperone-mediated autophagy (CMA) is a selective type of autophagy by which specific cytosolic proteins are sent to lysosomes for degradation. Substrate proteins bind to the lysosomal membrane through the lysosome-associated membrane protein type 2A (LAMP-2A), one of the three splice variants of the lamp2 gene, and this binding is limiting for their degradation via CMA. However, the mechanisms of substrate binding and uptake remain unknown. We report here that LAMP-2A organizes at the lysosomal membrane into protein complexes of different sizes. The assembly and disassembly of these complexes are a very dynamic process directly related to CMA activity. Substrate proteins only bind to monomeric LAMP-2A, while the efficient translocation of substrates requires the formation of a particular high-molecular-weight LAMP-2A complex. The two major chaperones related to CMA, hsc70 and hsp90, play critical roles in the functional dynamics of the LAMP-2A complexes at the lysosomal membrane. Thus, we have identified a novel function for hsc70 in the disassembly of LAMP-2A from these complexes, whereas the presence of lysosome-associated hsp90 is essential to preserve the stability of LAMP-2A at the lysosomal membrane.
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Zhong, Xi Zoë, Yuanjie Zou, Xue Sun, Gaofeng Dong, Qi Cao, Aditya Pandey, Jan K. Rainey, Xiaojuan Zhu i Xian-Ping Dong. "Inhibition of Transient Receptor Potential Channel Mucolipin-1 (TRPML1) by Lysosomal Adenosine Involved in Severe Combined Immunodeficiency Diseases". Journal of Biological Chemistry 292, nr 8 (13.01.2017): 3445–55. http://dx.doi.org/10.1074/jbc.m116.743963.
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Impaired adenosine homeostasis has been associated with numerous human diseases. Lysosomes are referred to as the cellular recycling centers that generate adenosine by breaking down nucleic acids or ATP. Recent studies have suggested that lysosomal adenosine overload causes lysosome defects that phenocopy patients with mutations in transient receptor potential channel mucolipin-1 (TRPML1), a lysosomal Ca2+ channel, suggesting that lysosomal adenosine overload may impair TRPML1 and then lead to subsequent lysosomal dysfunction. In this study, we demonstrate that lysosomal adenosine is elevated by deleting adenosine deaminase (ADA), an enzyme responsible for adenosine degradation. We also show that lysosomal adenosine accumulation inhibits TRPML1, which is rescued by overexpressing ENT3, the adenosine transporter situated in the lysosome membrane. Moreover, ADA deficiency results in lysosome enlargement, alkalinization, and dysfunction. These are rescued by activating TRPML1. Importantly, ADA-deficient B-lymphocytes are more vulnerable to oxidative stress, and this was rescued by TRPML1 activation. Our data suggest that lysosomal adenosine accumulation impairs lysosome function by inhibiting TRPML1 and subsequently leads to cell death in B-lymphocytes. Activating TRPML1 could be a new therapeutic strategy for those diseases.
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Dahlgren, C., S. R. Carlsson, A. Karlsson, H. Lundqvist i C. Sjölin. "The lysosomal membrane glycoproteins Lamp-1 and Lamp-2 are present in mobilizable organelles, but are absent from the azurophil granules of human neutrophils". Biochemical Journal 311, nr 2 (15.10.1995): 667–74. http://dx.doi.org/10.1042/bj3110667.
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The subcellular localization of two members of a highly glycosylated protein group present in lysosomal membranes in most cells, the lysosome-associated membrane proteins 1 and 2 (Lamp-1 and Lamp-2), was examined in human neutrophil granulocytes. Antibodies that were raised against purified Lamp-1 adn Lamp-2 gave a distinct granular staining of the cytoplasm upon immunostaining of neutrophils. Subcellular fractionation was used to separate the azurophil and specific granules from a light-membrane fraction containing plasma membranes and secretory vesicles, and Western blotting was used to determine the presence of the Lamps in these fractions. The results show that Lamp-1 and Lamp-2 are present in the specific-granule-enriched fraction and in the light-membrane fraction, but not in the azurophil granules. Separation of secretory vesicles from plasma membranes disclosed that the light-membrane Lamps were present primarily in the secretory-vesicle-enriched fraction. During phagocytosis both Lamp-1 and Lamp-2 became markedly concentrated around the ingested particle and they both appear on the cell surface when the secretory organelles are mobilized.
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Santo, Manuela, i Ivan Conte. "Emerging Lysosomal Functions for Photoreceptor Cell Homeostasis and Survival". Cells 11, nr 1 (26.12.2021): 60. http://dx.doi.org/10.3390/cells11010060.
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Lysosomes are membrane-bound cell organelles that respond to nutrient changes and are implicated in cell homeostasis and clearance mechanisms, allowing effective adaptation to specific cellular needs. The relevance of the lysosome has been elucidated in a number of different contexts. Of these, the retina represents an interesting scenario to appreciate the various functions of this organelle in both physiological and pathological conditions. Growing evidence suggests a role for lysosome-related mechanisms in retinal degeneration. Abnormal lysosomal activation or inhibition has dramatic consequences on photoreceptor cell homeostasis and impacts extensive cellular function, which in turn affects vision. Based on these findings, a series of therapeutic methods targeting lysosomal processes could offer treatment for blindness conditions. Here, we review the recent findings on membrane trafficking, subcellular organization, mechanisms by which lysosome/autophagy pathway impairment affects photoreceptor cell homeostasis and the recent advances on developing efficient lysosomal-based therapies for retinal disorders.
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Ju, Xiangwu, Yiwu Yan, Qiang Liu, Ning Li, Miaomiao Sheng, Lifang Zhang, Xiao Li i in. "Neuraminidase of Influenza A Virus Binds Lysosome-Associated Membrane Proteins Directly and Induces Lysosome Rupture". Journal of Virology 89, nr 20 (5.08.2015): 10347–58. http://dx.doi.org/10.1128/jvi.01411-15.
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ABSTRACTAs a recycling center, lysosomes are filled with numerous acid hydrolase enzymes that break down waste materials and invading pathogens. Recently, lysosomal cell death has been defined as “lysosomal membrane permeabilization and the consequent leakage of lysosome contents into cytosol.” Here, we show that the neuraminidase (NA) of H5N1 influenza A virus markedly deglycosylates and degrades lysosome-associated membrane proteins (LAMPs; the most abundant membrane proteins of lysosome), which induces lysosomal rupture, and finally leads to cell death of alveolar epithelial carcinoma A549 cells and human tracheal epithelial cells. The NA inhibitors peramivir and zanamivir could effectively block the deglycosylation of LAMPs, inhibit the virus cell entry, and prevent cell death induced by the H5N1 influenza virus. The NA of seasonal H1N1 virus, however, does not share these characteristics. Our findings not only reveal a novel role of NA in the early stage of the H5N1 influenza virus life cycle but also elucidate the molecular mechanism of lysosomal rupture crucial for influenza virus induced cell death.IMPORTANCEThe integrity of lysosomes is vital for maintaining cell homeostasis, cellular defense and clearance of invading pathogens. This study shows that the H5N1 influenza virus could induce lysosomal rupture through deglycosylating lysosome-associated membrane proteins (LAMPs) mediated by the neuraminidase activity of NA protein. NA inhibitors such as peramivir and zanamivir could inhibit the deglycosylation of LAMPs and protect lysosomes, which also further interferes with the H5N1 influenza virus infection at early stage of life cycle. This work is significant because it presents new concepts for NA's function, as well as for influenza inhibitors' mechanism of action, and could partially explain the high mortality and high viral load after H5N1 virus infection in human beings and why NA inhibitors have more potent therapeutic effects for lethal avian influenza virus infections at early stage.
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Newell-Litwa, Karen, Gloria Salazar, Yoland Smith i Victor Faundez. "Roles of BLOC-1 and Adaptor Protein-3 Complexes in Cargo Sorting to Synaptic Vesicles". Molecular Biology of the Cell 20, nr 5 (marzec 2009): 1441–53. http://dx.doi.org/10.1091/mbc.e08-05-0456.
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Neuronal lysosomes and their biogenesis mechanisms are primarily thought to clear metabolites and proteins whose abnormal accumulation leads to neurodegenerative disease pathology. However, it remains unknown whether lysosomal sorting mechanisms regulate the levels of membrane proteins within synaptic vesicles. Using high-resolution deconvolution microscopy, we identified early endosomal compartments where both selected synaptic vesicle and lysosomal membrane proteins coexist with the adaptor protein complex 3 (AP-3) in neuronal cells. From these early endosomes, both synaptic vesicle membrane proteins and characteristic AP-3 lysosomal cargoes can be similarly sorted to brain synaptic vesicles and PC12 synaptic-like microvesicles. Mouse knockouts for two Hermansky–Pudlak complexes involved in lysosomal biogenesis from early endosomes, the ubiquitous isoform of AP-3 (Ap3b1−/−) and muted, defective in the biogenesis of lysosome-related organelles complex 1 (BLOC-1), increased the content of characteristic synaptic vesicle proteins and known AP-3 lysosomal proteins in isolated synaptic vesicle fractions. These phenotypes contrast with those of the mouse knockout for the neuronal AP-3 isoform involved in synaptic vesicle biogenesis (Ap3b2−/−), in which the content of select proteins was reduced in synaptic vesicles. Our results demonstrate that lysosomal and lysosome-related organelle biogenesis mechanisms regulate steady-state synaptic vesicle protein composition from shared early endosomes.
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Deng, Y. P., G. Griffiths i B. Storrie. "Comparative behavior of lysosomes and the pre-lysosome compartment (PLC) in in vivo cell fusion experiments". Journal of Cell Science 99, nr 3 (1.07.1991): 571–82. http://dx.doi.org/10.1242/jcs.99.3.571.
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Interspecies cell fusion was used to compare protein intermixing within the mannose 6-phosphate receptor (MPR)-enriched pre-lysosome compartment (PLC) and within the MPR-negative lysosomal compartment. Both compartments were positive for lysosomal glycoprotein (lgp) membrane markers but were morphologically distinct. In most experiments, rat-mouse cell syncytia were formed by u.v.-inactivated Sindbis virus-mediated fusion. By immunogold electron microscopy of syncytia, extensive intermixing of species-specific lysosomal membrane proteins was observed in both lysosomes and PLC. At 3 h post cell fusion, multiple-label immunogold studies showed that 82% of the lysosome-like structures positive for the rat lysosomal membrane protein LIMP-I were also positive for the mouse lysosomal membrane protein mLAMP-1. By immunofluorescence, LIMP-I and mLAMP-1 co-localized with a t1/2 of 30 min after cell fusion; although the lgp-positive organelle populations had evidently interchanged their proteins, the lysosomal structures remained small, punctate bodies distributed throughout the syncytoplasm as observed in single cells. In contrast, the initially separate units of the PLC congregated with a t1/2 of 1 h to form large, pre-lysosome complexes associated with individual nuclear clusters. At the electron-microscope level, gold markers endocytized by the rat and mouse parent cells in a 1 h uptake followed by a 16–20 h chase co-localized in these extended PLC complexes, as did the membrane markers mLAMP-1 and LIMP-I. The density of labeling for rat MPR in the extended PLCs was markedly decreased, consistent with membrane fusions and dilution of the antigen upon congregation of the PLC compartments from the donor cells. The extended PLC complex behaved as a late endocytic compartment, as shown by co-localization of the MPR and rhodamine-dextran following a 10 min dextran uptake and a 50 min chase. These differences in behavior between lysosomes and the PLC in rat-mouse cell syncytia suggest that the pathway(s) of protein intermixing with respect to the two organelles may be different.
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Jeschke, Andreas, i Albert Haas. "Sequential actions of phosphatidylinositol phosphates regulate phagosome-lysosome fusion". Molecular Biology of the Cell 29, nr 4 (15.02.2018): 452–65. http://dx.doi.org/10.1091/mbc.e17-07-0464.
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Phagosomes mature into phagolysosomes by sequential fusion with early endosomes, late endosomes, and lysosomes. Phagosome-with-lysosome fusion (PLF) results in the delivery of lysosomal hydrolases into phagosomes and in digestion of the cargo. The machinery that drives PLF has been little investigated. Using a cell-free system, we recently identified the phosphoinositide lipids (PIPs) phosphatidylinositol 3-phosphate (PI(3)P) and phosphatidylinositol 4-phosphate (PI(4)P) as regulators of PLF. We now report the identification and the PIP requirements of four distinct subreactions of PLF. Our data show that (i) PI(3)P and PI(4)P are dispensable for the disassembly and activation of (phago)lysosomal soluble N-ethylmaleimide-sensitive factor attachment protein receptors, that (ii) PI(3)P is required only after the tethering step, and that (iii) PI(4)P is required during and after tethering. Moreover, our data indicate that PI(4)P is needed to anchor Arl8 (Arf-like GTPase 8) and its effector homotypic fusion/vacuole protein sorting complex (HOPS) to (phago)lysosome membranes, whereas PI(3)P is required for membrane association of HOPS only. Our study provides a first link between PIPs and established regulators of membrane fusion in late endocytic trafficking.
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Guo, Yanxia, Shikang Wang, Qun Liu, Yan Dong i Yongqing Liu. "St-N, a novel alkaline derivative of stevioside, reverses docetaxel resistance by targeting lysosomes in vitro and in vivo". PLOS ONE 19, nr 12 (27.12.2024): e0316268. https://doi.org/10.1371/journal.pone.0316268.
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Drug resistance of cancers remains a major obstacle due to limited therapeutics. Lysosome targeting is an effective method for overcoming drug resistance in cancer cells. St-N (ent-13-hydroxy-15-kaurene-19-acid N-methylpiperazine ethyl ester) is a novel alkaline stevioside derivative with an amine group. In this study, we found that docetaxel (Doc)-resistant prostate cancer (PCa) cells were sensitive to St-N. Mechanistically, the alkaline characteristic of St-N led to targeting lysosomes, as evidenced by lysosomal swelling and rupture through transmission electron microscopy and Lyso-tracker Red staining. St-N destabilized lysosomal membrane by impairing lysosomal membrane proteins and acid sphingomyelinase. As a result, St-N caused cathepsins to release from the lysosomes into the cytosol, eventually triggering apoptotic and necrotic cell death. Meanwhile, the cytoprotective role of lysosomal activation under docetaxel treatment was interrupted by St-N, leading to significant synergistic cytotoxicity of docetaxel and St-N. In docetaxel-resistant PCa homograft mice, St-N significantly inhibited the growth of RM-1/Doc homografts and enhanced the anticancer effects of docetaxel, but did not show significant toxicity. Taken together, these findings demonstrated that St-N reversed docetaxel resistance in vitro and in vivo by destabilizing lysosomal membranes to promote cell death, thus providing a strong rationale for applying St-N in docetaxel-resistant PCa.
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Kavčič, Nežka, Katarina Pegan i Boris Turk. "Lysosomes in programmed cell death pathways: from initiators to amplifiers". Biological Chemistry 398, nr 3 (1.03.2017): 289–301. http://dx.doi.org/10.1515/hsz-2016-0252.
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Abstract Lysosome is the central organelle for intracellular degradation of biological macromolecules and organelles. The material destined for degradation enters the lysosomes primarily via endocytosis, autophagy and phagocytosis, and is degraded through the concerted action of more than 50 lysosomal hydrolases. However, lysosomes are also linked with numerous other processes, including cell death, inflammasome activation and immune response, as well as with lysosomal secretion and cholesterol recycling. Among them programmed cell death pathways including apoptosis have received major attention. In most of these pathways, cell death was accompanied by lysosomal membrane permeabilization and release of lysosomal constituents with an involvement of lysosomal hydrolases, including the cathepsins. However, it is less clear, whether lysosomal membrane permeabilization is really critical for the initiation of cell death programme(s). Therefore, the role of lysosomal membrane permeabilization in various programmed cell death pathways is reviewed, as well as the mechanisms leading to it.
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Zhang, Ming, Li Chen, Shicong Wang i Tuanlao Wang. "Rab7: roles in membrane trafficking and disease". Bioscience Reports 29, nr 3 (27.04.2009): 193–209. http://dx.doi.org/10.1042/bsr20090032.
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The endocytosis pathway controls multiple cellular and physiological events. The lysosome is the destination of newly synthesized lysosomal hydrolytic enzymes. Internalized molecules or particles are delivered to the lysosome for degradation through sequential transport along the endocytic pathway. The endocytic pathway is also emerging as a signalling platform, in addition to the well-known role of the plasma membrane for signalling. Rab7 is a late endosome-/lysosome-associated small GTPase, perhaps the only lysosomal Rab protein identified to date. Rab7 plays critical roles in the endocytic processes. Through interaction with its partners (including upstream regulators and downstream effectors), Rab7 participates in multiple regulation mechanisms in endosomal sorting, biogenesis of lysosome [or LRO (lysosome-related organelle)] and phagocytosis. These processes are closely related to substrates degradation, antigen presentation, cell signalling, cell survival and microbial pathogen infection. Consistently, mutations or dysfunctions of Rab7 result in traffic disorders, which cause various diseases, such as neuropathy, cancer and lipid metabolism disease. Rab7 also plays important roles in microbial pathogen infection and survival, as well as in participating in the life cycle of viruses. Here, we give a brief review on the central role of Rab7 in endosomal traffic and summarize the studies focusing on the participation of Rab7 in disease pathogenesis. The underlying mechanism governed by Rab7 and its partners will also be discussed.
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Press, Barry, Yan Feng, Bernard Hoflack i Angela Wandinger-Ness. "Mutant Rab7 Causes the Accumulation of Cathepsin D and Cation-independent Mannose 6–Phosphate Receptor in an Early Endocytic Compartment". Journal of Cell Biology 140, nr 5 (9.03.1998): 1075–89. http://dx.doi.org/10.1083/jcb.140.5.1075.
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Stable BHK cell lines inducibly expressing wild-type or dominant negative mutant forms of the rab7 GTPase were isolated and used to analyze the role of a rab7-regulated pathway in lysosome biogenesis. Expression of mutant rab7N125I protein induced a dramatic redistribution of cation-independent mannose 6–phosphate receptor (CI-MPR) from its normal perinuclear localization to large peripheral endosomes. Under these circumstances ∼50% of the total receptor and several lysosomal hydrolases cofractionated with light membranes containing early endosome and Golgi markers. Late endosomes and lysosomes were contained exclusively in well-separated, denser gradient fractions. Newly synthesized CI-MPR and cathepsin D were shown to traverse through an early endocytic compartment, and functional rab7 was crucial for delivery to later compartments. This observation was evidenced by the fact that 2 h after synthesis, both markers were more prevalent in fractions containing light membranes. In addition, both were sensitive to HRP-DAB– mediated cross-linking of early endosomal proteins, and the late endosomal processing of cathepsin D was impaired. Using similar criteria, the lysosomal membrane glycoprotein 120 was not found accumulated in an early endocytic compartment. The data are indicative of a post-Golgi divergence in the routes followed by different lysosome-directed molecules.
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Beauvarlet, Jennifer, Rabindra Nath Das, Karla Alvarez-Valadez, Isabelle Martins, Alexandra Muller, Elodie Darbo, Elodie Richard i in. "Triarylpyridine Compounds and Chloroquine Act in Concert to Trigger Lysosomal Membrane Permeabilization and Cell Death in Cancer Cells". Cancers 12, nr 6 (18.06.2020): 1621. http://dx.doi.org/10.3390/cancers12061621.
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Lysosomes play a key role in regulating cell death in response to cancer therapies, yet little is known on the possible role of lysosomes in the therapeutic efficacy of G-quadruplex DNA ligands (G4L) in cancer cells. Here, we investigate the relationship between the modulation of lysosomal membrane damage and the degree to which cancer cells respond to the cytotoxic effects of G-quadruplex ligands belonging to the triarylpyridine family. Our results reveal that the lead compound of this family, 20A promotes the enlargement of the lysosome compartment as well as the induction of lysosome-relevant mRNAs. Interestingly, the combination of 20A and chloroquine (an inhibitor of lysosomal functions) led to a significant induction of lysosomal membrane permeabilization coupled to massive cell death. Similar effects were observed when chloroquine was added to three new triarylpyridine derivatives. Our findings thus uncover the lysosomal effects of triarylpyridines compounds and delineate a rationale for combining these compounds with chloroquine to increase their anticancer effects.
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Mattie, Sevan, Erin K. McNally, Mahmoud A. Karim, Hojatollah Vali i Christopher L. Brett. "How and why intralumenal membrane fragments form during vacuolar lysosome fusion". Molecular Biology of the Cell 28, nr 2 (15.01.2017): 309–21. http://dx.doi.org/10.1091/mbc.e15-11-0759.
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Lysosomal membrane fusion mediates the last step of the autophagy and endocytosis pathways and supports organelle remodeling and biogenesis. Because fusogenic proteins and lipids concentrate in a ring at the vertex between apposing organelle membranes, the encircled area of membrane can be severed and internalized within the lumen as a fragment upon lipid bilayer fusion. How or why this intralumenal fragment forms during fusion, however, is not entirely clear. To better understand this process, we studied fragment formation during homotypic vacuolar lysosome membrane fusion in Saccharomyces cerevisiae. Using cell-free fusion assays and light microscopy, we find that GTPase activation and trans-SNARE complex zippering have opposing effects on fragment formation and verify that this affects the morphology of the fusion product and regulates transporter protein degradation. We show that fragment formwation is limited by stalk expansion, a key intermediate of the lipid bilayer fusion reaction. Using electron microscopy, we present images of hemifusion diaphragms that form as stalks expand and propose a model describing how the fusion machinery regulates fragment formation during lysosome fusion to control morphology and protein lifetimes.
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Feng, Tuancheng, Rory R. Sheng, Santiago Solé-Domènech, Mohammed Ullah, Xiaolai Zhou, Christina S. Mendoza, Laura Camila Martinez Enriquez i in. "A role of the frontotemporal lobar degeneration risk factor TMEM106B in myelination". Brain 143, nr 7 (23.06.2020): 2255–71. http://dx.doi.org/10.1093/brain/awaa154.
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Abstract TMEM106B encodes a lysosomal membrane protein and was initially identified as a risk factor for frontotemporal lobar degeneration. Recently, a dominant D252N mutation in TMEM106B was shown to cause hypomyelinating leukodystrophy. However, how TMEM106B regulates myelination is still unclear. Here we show that TMEM106B is expressed and localized to the lysosome compartment in oligodendrocytes. TMEM106B deficiency in mice results in myelination defects with a significant reduction of protein levels of proteolipid protein (PLP) and myelin oligodendrocyte glycoprotein (MOG), the membrane proteins found in the myelin sheath. The levels of many lysosome proteins are significantly decreased in the TMEM106B-deficient Oli-neu oligodendroglial precursor cell line. TMEM106B physically interacts with the lysosomal protease cathepsin D and is required to maintain proper cathepsin D levels in oligodendrocytes. Furthermore, we found that TMEM106B deficiency results in lysosome clustering in the perinuclear region and a decrease in lysosome exocytosis and cell surface PLP levels. Moreover, we found that the D252N mutation abolished lysosome enlargement and lysosome acidification induced by wild-type TMEM106B overexpression. Instead, it stimulates lysosome clustering near the nucleus as seen in TMEM106B-deficient cells. Our results support that TMEM106B regulates myelination through modulation of lysosome function in oligodendrocytes.
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Zimmerli, S., M. Majeed, M. Gustavsson, O. Stendahl, D. A. Sanan i J. D. Ernst. "Phagosome-lysosome fusion is a calcium-independent event in macrophages." Journal of Cell Biology 132, nr 1 (1.01.1996): 49–61. http://dx.doi.org/10.1083/jcb.132.1.49.
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Phagosome-lysosome membrane fusion is a highly regulated event that is essential for intracellular killing of microorganisms. Functionally, it represents a form of polarized regulated secretion, which is classically dependent on increases in intracellular ionized calcium ([Ca2+]i). Indeed, increases in [Ca2+]i are essential for phagosome-granule (lysosome) fusion in neutrophils and for lysosomal fusion events that mediate host cell invasion by Trypanosoma cruzi trypomastigotes. Since several intracellular pathogens survive in macrophage phagosomes that do not fuse with lysosomes, we examined the regulation of phagosome-lysosome fusion in macrophages. Macrophages (M phi) were treated with 12.5 microM bis-(2-amino-S-methylphenoxy) ethane-N,N,N',N',-tetraacetic acid tetraacetoxymethyl ester (MAPT/AM), a cell-permeant calcium chelator which reduced resting cytoplasmic [Ca2+]; from 80 nM to < or = 20 nM and completely blocked increases in [Ca2+]i in response to multiple stimuli, even in the presence of extracellular calcium. Subsequently, M phi phagocytosed serum-opsonized zymosan, staphylococci, or Mycobacterium bovis. Microbes were enumerated by 4',6-diamidino-2-phenylindole, dihydrochloride (DAPI) staining, and phagosome-lysosome fusion was scored using both lysosome-associated membrane protein (LAMP-1) as a membrane marker and rhodamine dextran as a content marker for lysosomes. Confirmation of phagosome-lysosome fusion by electron microscopy validated the fluorescence microscopy findings. We found that phagosome-lysosome fusion in M phi occurs noramlly at very low [Ca2+]i (< or = 20 nM). Kinetic analysis showed that in M phi none of the steps leading from particle binding to eventual phagosome-lysosome fusion are regulated by [Ca2+]i in a rate-limiting way. Furthermore, confocal microscopy revealed no difference in the intensity of LAMP-1 immunofluorescence in phagolysosome membranes in calcium-buffered vs. control macrophages. We conclude that neither membrane recognition nor fusion events in the phagosomal pathway in macrophages are dependent on or regulated by calcium.
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Rupar, C. Anthony, Susan Albo i Jeffery D. Whitehall. "Rat liver lysosome membranes are enriched in α-tocopherol". Biochemistry and Cell Biology 70, nr 6 (1.06.1992): 486–88. http://dx.doi.org/10.1139/o92-075.
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The subcellular distribution of α-tocopherol has been studied in rat liver. Lysosomal membranes were found to be considerably enriched in α-tocopherol with 6300 pmol/mg membrane protein, whereas mitochondrial membranes and microsomes contained 530 and 200 pmol/mg membrane protein, respectively. The 37-fold higher specific content of α-tocopherol in lysosomal membranes relative to homogenate indicates that lysosomes could be a target of cellular pathology in vitamin E deficiency states.Key words: α-tocopherol, lysosomes, mitochondria, membrane.
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Li, Yuyin, Yuejun Sun, Lifang Jing, Jianjun Wang, Yali Yan, Yajuan Feng, Yueying Zhang, Zhenxing Liu, Long Ma i Aipo Diao. "Lysosome Inhibitors Enhance the Chemotherapeutic Activity of Doxorubicin in HepG2 Cells". Chemotherapy 62, nr 2 (21.10.2016): 85–93. http://dx.doi.org/10.1159/000448802.
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The lysosome inhibitors bafilomycin A1 and chloroquine have both lysosomotropic properties and autophagy inhibition ability, and are promising clinical agents to be used in combination with anticancer drugs. In order to investigate this combination effect, HepG2 cells were treated with bafilomycin A1, chloroquine, or/and doxorubicin, and their proliferative ability, induction of apoptosis, and the changes of lysosomal membrane permeabilization and mitochondrial membrane potential were studied. The results demonstrate that treatment with bafilomycin A1 or chloroquine alone at a relatively low concentration promotes the inhibitory effect of doxorubicin on cell growth and apoptosis. Further studies reveal that bafilomycin A1 and chloroquine promote lysosomal membrane permeabilization and the reduction of mitochondrial membrane potential induced by doxorubicin. Our findings suggest that bafilomycin A1 and chloroquine potentiate the anticancer effect of doxorubicin in hepatic cancer cells and that supplementation of conventional chemotherapy with lysosome inhibitors may provide a more efficient anticancer therapy.
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Mušálková, D., J. Lukáš, F. Majer, O. Hřebíček, E. Svobodová, L. Kuchař, J. Honzíková, H. Hůlková, J. Ledvinová i Martin Hřebíček. "Rapid Isolation of Lysosomal Membranes from Cultured Cells". Folia Biologica 59, nr 1 (2013): 41–46. http://dx.doi.org/10.14712/fb2013059010041.
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We present a simple method for enrichment of lysosomal membranes from HEK293 and HeLa cell lines taking advantage of selective disruption of lysosomes by methionine methyl ester. Organelle concentrate from postnuclear supernatant was treated with 20 mmol/l methionine methyl ester for 45 min to lyse the lysosomes. Subsequently, lysosomal membranes were resolved on a step sucrose gradient. An enriched lysosomal membrane fraction was collected from the 20%/35% sucrose interface. The washed lysosomal membrane fraction was enriched 30 times relative to the homogenate and gave the yield of more than 8 %. These results are comparable to lysosomal membranes isolated by magnetic chromatography from cultured cells (Diettrich et al., 1998). The procedure effectively eliminated mitochondrial contamination and minimized contamination from other cell compartments. The enriched fractions retained the ability to acidify membrane vesicles through the activity of lysosomal vacuolar ATPase. The method avoids non-physiological overloading of cells with superparamagnetic particles and appears to be quite robust among the tested cell lines. We expect it may be of more general use, adaptable to other cell lines and tissues.
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Tsuboi, M., K. Harasawa, T. Izawa, T. Komabayashi, H. Fujinami i K. Suda. "Intralysosomal pH and release of lysosomal enzymes in the rat liver after exhaustive exercise". Journal of Applied Physiology 74, nr 4 (1.04.1993): 1628–34. http://dx.doi.org/10.1152/jappl.1993.74.4.1628.
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The mechanism underlying exhaustive exercise-induced release of lysosomal enzymes was studied in the rat liver. Exhaustive exercise resulted in the release of beta-glucuronidase and cathepsin D, but not beta-glucosidase and acid phosphatase, into the blood and cytosol, suggesting that the release of lysosomal enzymes is not due to disruption of lysosomal membranes. The intralysosomal pH of the liver, which was approximately 5.5 at the resting level, rose significantly after exhaustive exercise to pH 6.3. In vitro, beta-glucuronidase and cathepsin D were released at an intralysosomal pH exceeding 6.2. In contrast, beta-glucosidase and acid phosphatase were not released. The elevation of intralysosomal pH reduced the aggregation of beta-glucuronidase and cathepsin D. The rate of ammonia accumulation increased markedly in the lysosome-enriched subcellular fraction after exercise. There was a positive relationship between the rate of ammonia accumulation and the elevation of intralysosomal pH in vitro. Lysosomes isolated after exhaustive exercise showed significantly increased osmotic fragility. Our findings suggest that, during exhaustive exercise, the accumulation of ammonia in lysosomes leads to the elevation of intralysosomal pH, resulting in the reduced aggregation of certain lysosomal enzymes. Thus, less aggregated lysosomal enzymes may be released into the cytosol through the lysosomal membrane, the permeability of which has been increased.
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Noda, T., i M. G. Farquhar. "A non-autophagic pathway for diversion of ER secretory proteins to lysosomes." Journal of Cell Biology 119, nr 1 (1.10.1992): 85–97. http://dx.doi.org/10.1083/jcb.119.1.85.
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Intracisternal granules (ICG) develop in the rough ER of hyperstimulated thyrotrophs or thyroid hormone-secreting cells of the anterior pituitary gland. To determine the fate of these granules, we carried out morphological and immunocytochemical studies on pituitaries of thyroxine-treated, thyroidectomized rats. Under these conditions the ER of thyrotrophs is dramatically dilated and contains abundant ICG; the latter contain beta subunits of thyrotrophic hormone (TSH-beta). Based on purely morphologic criteria, intermediates were identified that appeared to represent stages in the transformation of a part rough/part smooth ER cisterna into a lysosome. Using immunocytochemical and cytochemical markers, two major types of intermediates were distinguished: type 1 lacked ribosomes but were labeled with antibodies against both ER markers (PDI, KDEL, ER membrane proteins) and a lysosomal membrane marker, lgp120. They also were reactive for the lysosomal enzyme, acid phosphatase, by enzyme cytochemistry. Type 2 intermediates were weakly reactive for ER markers and contained both lgp120 and lysosomal enzymes (cathepsin D, acid phosphatase). Taken together these results suggest that in hyperstimulated thyrotrophs part rough/part smooth ER elements containing ICG lose their ribosomes, their membrane is modified, and they sequentially acquire a lysosome-type membrane and lysosomal enzymes. The findings are compatible with the conclusion that a pathway exists by which under certain conditions, secretory proteins present in the ER as well as ER membrane and content proteins can be degraded by direct conversion of ER cisternae into lysosomes.
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Raiborg, Camilla, i Harald Stenmark. "Plasma membrane repairs by small GTPase Rab3a". Journal of Cell Biology 213, nr 6 (20.06.2016): 613–15. http://dx.doi.org/10.1083/jcb.201606006.
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Lysosomes fuse with the plasma membrane to help repair membrane lesions, but how they are positioned close to these lesions is not fully understood. Now, Encarnação et al. (2016. J. Cell Biol. http://dx.doi.org/10.1083/jcb.201511093) demonstrate that the lysosomal GTPase Rab3a and its effectors orchestrate lysosome positioning and plasma membrane repair.
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Cieutat, A. M., P. Lobel, J. T. August, L. Kjeldsen, H. Sengeløv, N. Borregaard i D. F. Bainton. "Azurophilic Granules of Human Neutrophilic Leukocytes Are Deficient in Lysosome-Associated Membrane Proteins but Retain the Mannose 6-Phosphate Recognition Marker". Blood 91, nr 3 (1.02.1998): 1044–58. http://dx.doi.org/10.1182/blood.v91.3.1044.
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Abstract During granulocyte differentiation in the bone marrow (BM), neutrophilic leukocyte precursors synthesize large amounts of lysosomal enzymes. These enzymes are sequestered into azurophilic storage granules until used days later for digestion of phagocytized microorganisms after leukocyte emigration to inflamed tissues. This azurophil granule population has previously been defined as a primary lysosome, ie, a membrane-bound organelle containing acid hydrolases that have not entered into a digestive event. In this study, azurophil granules were purified and shown to contain large amounts of mannose 6-phosphate-containing glycoproteins (Man 6-P GP) but little lysosome-associated membrane proteins (LAMP). In addition, the fine structural localization of Man 6-P GP and LAMP was investigated at various stages of maturation in human BM and blood. Man 6-P GP were present within the azurophilic granules at all stages of maturation and in typical multivesicular bodies (MVB) as well as in multilaminar compartments (MLC), identified by their content of concentric arrays of internal membranes. LAMP was absent in all identified granule populations, but was consistently found in the membranes of vesicles, MVB, and MLC. The latter compartment has not been previously described in this cell type. In conclusion, the azurophilic granules, which contain an abundance of lysosomal enzymes and Man 6-P GP, lack the LAMP glycoproteins. By current criteria, they therefore cannot be classified as lysosomes, but rather may have the functional characteristics of a regulated secretory granule. Rather, the true lysosomes of the resting neutrophil are probably the MVB and MLC. Finally, the typical “dense bodies” or mature lysosomes described in other cells are not present in resting neutrophils.
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Cieutat, A. M., P. Lobel, J. T. August, L. Kjeldsen, H. Sengeløv, N. Borregaard i D. F. Bainton. "Azurophilic Granules of Human Neutrophilic Leukocytes Are Deficient in Lysosome-Associated Membrane Proteins but Retain the Mannose 6-Phosphate Recognition Marker". Blood 91, nr 3 (1.02.1998): 1044–58. http://dx.doi.org/10.1182/blood.v91.3.1044.1044_1044_1058.
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During granulocyte differentiation in the bone marrow (BM), neutrophilic leukocyte precursors synthesize large amounts of lysosomal enzymes. These enzymes are sequestered into azurophilic storage granules until used days later for digestion of phagocytized microorganisms after leukocyte emigration to inflamed tissues. This azurophil granule population has previously been defined as a primary lysosome, ie, a membrane-bound organelle containing acid hydrolases that have not entered into a digestive event. In this study, azurophil granules were purified and shown to contain large amounts of mannose 6-phosphate-containing glycoproteins (Man 6-P GP) but little lysosome-associated membrane proteins (LAMP). In addition, the fine structural localization of Man 6-P GP and LAMP was investigated at various stages of maturation in human BM and blood. Man 6-P GP were present within the azurophilic granules at all stages of maturation and in typical multivesicular bodies (MVB) as well as in multilaminar compartments (MLC), identified by their content of concentric arrays of internal membranes. LAMP was absent in all identified granule populations, but was consistently found in the membranes of vesicles, MVB, and MLC. The latter compartment has not been previously described in this cell type. In conclusion, the azurophilic granules, which contain an abundance of lysosomal enzymes and Man 6-P GP, lack the LAMP glycoproteins. By current criteria, they therefore cannot be classified as lysosomes, but rather may have the functional characteristics of a regulated secretory granule. Rather, the true lysosomes of the resting neutrophil are probably the MVB and MLC. Finally, the typical “dense bodies” or mature lysosomes described in other cells are not present in resting neutrophils.
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Saftig, Paul, i Judith Klumperman. "Lysosome biogenesis and lysosomal membrane proteins: trafficking meets function". Nature Reviews Molecular Cell Biology 10, nr 9 (12.08.2009): 623–35. http://dx.doi.org/10.1038/nrm2745.
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