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Murchison AK, Abu-Remaileh M. Sharing is caring: TMEM165 a Golgi calcium importer used by the lysosome. Trends Biochem Sci 2024:S0968-0004(24)00131-2. [PMID: 38816278 DOI: 10.1016/j.tibs.2024.05.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2024] [Accepted: 05/20/2024] [Indexed: 06/01/2024]
Abstract
Calcium is a crucial second messenger in the cell that is stored in organelles including lysosomes. Proteins that facilitate calcium entry to the lysosome were unknown. A recent report by Zajac et al. identified TMEM165 as a proton-activated calcium importer on the lysosome, thus discovering a key player in subcellular calcium homeostasis.
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Affiliation(s)
- Austin K Murchison
- Department of Chemical Engineering, Stanford University, Stanford, CA 94305, USA; Department of Genetics, Stanford University, Stanford, CA 94305, USA; The Institute for Chemistry, Engineering, and Medicine for Human Health (Sarafan ChEM-H), Stanford University, Stanford, CA 94305, USA; Department of Biology, Stanford University, Stanford, CA 94305, USA
| | - Monther Abu-Remaileh
- Department of Chemical Engineering, Stanford University, Stanford, CA 94305, USA; Department of Genetics, Stanford University, Stanford, CA 94305, USA; The Institute for Chemistry, Engineering, and Medicine for Human Health (Sarafan ChEM-H), Stanford University, Stanford, CA 94305, USA.
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2
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Zajac M, Mukherjee S, Anees P, Oettinger D, Henn K, Srikumar J, Zou J, Saminathan A, Krishnan Y. A mechanism of lysosomal calcium entry. SCIENCE ADVANCES 2024; 10:eadk2317. [PMID: 38354239 PMCID: PMC10866540 DOI: 10.1126/sciadv.adk2317] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Accepted: 01/16/2024] [Indexed: 02/16/2024]
Abstract
Lysosomal calcium (Ca2+) release is critical to cell signaling and is mediated by well-known lysosomal Ca2+ channels. Yet, how lysosomes refill their Ca2+ remains hitherto undescribed. Here, from an RNA interference screen in Caenorhabditis elegans, we identify an evolutionarily conserved gene, lci-1, that facilitates lysosomal Ca2+ entry in C. elegans and mammalian cells. We found that its human homolog TMEM165, previously designated as a Ca2+/H+ exchanger, imports Ca2+ pH dependently into lysosomes. Using two-ion mapping and electrophysiology, we show that TMEM165, hereafter referred to as human LCI, acts as a proton-activated, lysosomal Ca2+ importer. Defects in lysosomal Ca2+ channels cause several neurodegenerative diseases, and knowledge of lysosomal Ca2+ importers may provide previously unidentified avenues to explore the physiology of Ca2+ channels.
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Affiliation(s)
- Matthew Zajac
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
- Neuroscience Institute, The University of Chicago, Chicago, IL 60637, USA
| | - Sourajit Mukherjee
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
- Neuroscience Institute, The University of Chicago, Chicago, IL 60637, USA
| | - Palapuravan Anees
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
- Neuroscience Institute, The University of Chicago, Chicago, IL 60637, USA
| | - Daphne Oettinger
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
- Neuroscience Institute, The University of Chicago, Chicago, IL 60637, USA
| | - Katharine Henn
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
- Neuroscience Institute, The University of Chicago, Chicago, IL 60637, USA
| | - Jainaha Srikumar
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
- Neuroscience Institute, The University of Chicago, Chicago, IL 60637, USA
| | - Junyi Zou
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
- Neuroscience Institute, The University of Chicago, Chicago, IL 60637, USA
| | - Anand Saminathan
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
- Neuroscience Institute, The University of Chicago, Chicago, IL 60637, USA
| | - Yamuna Krishnan
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
- Neuroscience Institute, The University of Chicago, Chicago, IL 60637, USA
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, IL 60637, USA
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3
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Zajac M, Modi S, Krishnan Y. The evolution of organellar calcium mapping technologies. Cell Calcium 2022; 108:102658. [PMID: 36274564 PMCID: PMC10224794 DOI: 10.1016/j.ceca.2022.102658] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2022] [Revised: 10/05/2022] [Accepted: 10/08/2022] [Indexed: 01/25/2023]
Abstract
Intracellular Ca2+ fluxes are dynamically controlled by the co-involvement of multiple organellar pools of stored Ca2+. Endolysosomes are emerging as physiologically critical, yet underexplored, sources and sinks of intracellular Ca2+. Delineating the role of organelles in Ca2+ signaling has relied on chemical fluorescent probes and electrophysiological strategies. However, the acidic endolysosomal environment presents unique issues, which preclude the use of traditional chemical reporter strategies to map lumenal Ca2+. Here, we broadly address the current state of knowledge about organellar Ca2+ pools. We then outline the application of traditional probes, and their sensing paradigms. We then discuss how a new generation of probes overcomes the limitations of traditional Ca2+probes, emphasizing their ability to offer critical insights into endolysosomal Ca2+, and its feedback with other organellar pools.
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Affiliation(s)
- Matthew Zajac
- Department of Chemistry, The University of Chicago, Chicago, Illinois, 60637, USA; Neuroscience Institute, The University of Chicago, Chicago, IL, 60637, USA
| | - Souvik Modi
- Esya Labs, Translation and Innovation Hub, Imperial College White City Campus, 84 Wood Lane, London, W12 0BZ, UK
| | - Yamuna Krishnan
- Department of Chemistry, The University of Chicago, Chicago, Illinois, 60637, USA; Neuroscience Institute, The University of Chicago, Chicago, IL, 60637, USA; Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois, 60637, USA.
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4
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Atakpa P, Thillaiappan NB, Mataragka S, Prole DL, Taylor CW. IP 3 Receptors Preferentially Associate with ER-Lysosome Contact Sites and Selectively Deliver Ca 2+ to Lysosomes. Cell Rep 2019; 25:3180-3193.e7. [PMID: 30540949 PMCID: PMC6302550 DOI: 10.1016/j.celrep.2018.11.064] [Citation(s) in RCA: 117] [Impact Index Per Article: 23.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2018] [Revised: 07/30/2018] [Accepted: 11/15/2018] [Indexed: 12/22/2022] Open
Abstract
Inositol 1,4,5-trisphosphate (IP3) receptors (IP3Rs) allow extracellular stimuli to redistribute Ca2+ from the ER to cytosol or other organelles. We show, using small interfering RNA (siRNA) and vacuolar H+-ATPase (V-ATPase) inhibitors, that lysosomes sequester Ca2+ released by all IP3R subtypes, but not Ca2+ entering cells through store-operated Ca2+ entry (SOCE). A low-affinity Ca2+ sensor targeted to lysosomal membranes reports large, local increases in cytosolic [Ca2+] during IP3-evoked Ca2+ release, but not during SOCE. Most lysosomes associate with endoplasmic reticulum (ER) and dwell at regions populated by IP3R clusters, but IP3Rs do not assemble ER-lysosome contacts. Increasing lysosomal pH does not immediately prevent Ca2+ uptake, but it causes lysosomes to slowly redistribute and enlarge, reduces their association with IP3Rs, and disrupts Ca2+ exchange with ER. In a "piston-like" fashion, ER concentrates cytosolic Ca2+ and delivers it, through large-conductance IP3Rs, to a low-affinity lysosomal uptake system. The involvement of IP3Rs allows extracellular stimuli to regulate Ca2+ exchange between the ER and lysosomes.
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Affiliation(s)
- Peace Atakpa
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, UK
| | | | - Stefania Mataragka
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, UK
| | - David L Prole
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, UK
| | - Colin W Taylor
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, UK.
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5
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Molecular mechanisms of endolysosomal Ca2+ signalling in health and disease. Biochem J 2011; 439:349-74. [PMID: 21992097 DOI: 10.1042/bj20110949] [Citation(s) in RCA: 295] [Impact Index Per Article: 22.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Endosomes, lysosomes and lysosome-related organelles are emerging as important Ca2+ storage cellular compartments with a central role in intracellular Ca2+ signalling. Endocytosis at the plasma membrane forms endosomal vesicles which mature to late endosomes and culminate in lysosomal biogenesis. During this process, acquisition of different ion channels and transporters progressively changes the endolysosomal luminal ionic environment (e.g. pH and Ca2+) to regulate enzyme activities, membrane fusion/fission and organellar ion fluxes, and defects in these can result in disease. In the present review we focus on the physiology of the inter-related transport mechanisms of Ca2+ and H+ across endolysosomal membranes. In particular, we discuss the role of the Ca2+-mobilizing messenger NAADP (nicotinic acid adenine dinucleotide phosphate) as a major regulator of Ca2+ release from endolysosomes, and the recent discovery of an endolysosomal channel family, the TPCs (two-pore channels), as its principal intracellular targets. Recent molecular studies of endolysosomal Ca2+ physiology and its regulation by NAADP-gated TPCs are providing exciting new insights into the mechanisms of Ca2+-signal initiation that control a wide range of cellular processes and play a role in disease. These developments underscore a new central role for the endolysosomal system in cellular Ca2+ regulation and signalling.
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Gekle M, Serrano OK, Drumm K, Mildenberger S, Freudinger R, Gassner B, Jansen HW, Christensen EI. NHE3 serves as a molecular tool for cAMP-mediated regulation of receptor-mediated endocytosis. Am J Physiol Renal Physiol 2002; 283:F549-58. [PMID: 12167607 DOI: 10.1152/ajprenal.00206.2001] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Receptor-mediated, clathrin-dependent endocytosis (RME) is important for macromolecular transport and regulation of cell-surface protein expression. Pharmacological studies have shown that the plasma membrane transport protein Na(+)/H(+) exchanger 3 (NHE3), which shuttles between the plasma membrane and the early endosomal compartment by means of clathrin-mediated endocytosis, contributes to endosomal pH homeostasis and endocytic fusion events. Furthermore, it is known that NHE3 is phosphorylated and inhibited by cAMP-dependent kinase (protein kinase A). Here, we show, in a cellular knockout/retransfection approach, that NHE3 supports RME and confers cAMP sensitivity to RME, using megalin/cubilin-mediated albumin uptake in opossum kidney cells. RME, but not fluid-phase endocytosis, was dependent on NHE3 activity and expression. Furthermore, NHE3 deficiency or inhibition reduced the relative surface expression of megalin without altering total expression. In wild-type cells, cAMP inhibits NHE3 activity, leads to endosomal alkalinization, and reduces RME. In NHE3-deficient cells, endosomal pH is not sensitive to NHE3 inhibition, and cAMP does not affect endosomal pH or RME. NHE3 transfection into deficient cells restores RME and the effects of cAMP. Thus our data show that NHE3 is important for cAMP sensitivity of clathrin-dependent RME.
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Affiliation(s)
- Michael Gekle
- Physiologisches Institut, University of Würzburg, 97070 Würzburg, Germany.
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7
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Stober CB, Lammas DA, Li CM, Kumararatne DS, Lightman SL, McArdle CA. ATP-mediated killing of Mycobacterium bovis bacille Calmette-Guérin within human macrophages is calcium dependent and associated with the acidification of mycobacteria-containing phagosomes. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2001; 166:6276-86. [PMID: 11342651 DOI: 10.4049/jimmunol.166.10.6276] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We previously demonstrated that extracellular ATP stimulated macrophage death and mycobacterial killing within Mycobacterium bovis Bacille Calmette-Guérin (BCG)-infected human macrophages. ATP increases the cytosolic Ca(2+) concentration in macrophages by mobilizing intracellular Ca(2+) via G protein-coupled P2Y receptors, or promoting the influx of extracellular Ca(2+) via P2X purinoceptors. The relative contribution of these receptors and Ca(2+) sources to ATP-stimulated macrophage death and mycobacterial killing was investigated. We demonstrate that 1) ATP mobilizes Ca(2+) in UTP-desensitized macrophages (in Ca(2+)-free medium) and 2) UTP but not ATP fails to deplete the intracellular Ca(2+) store, suggesting that the pharmacological properties of ATP and UTP differ, and that a Ca(2+)-mobilizing P2Y purinoceptor in addition to the P2Y(2) subtype is expressed on human macrophages. ATP and the Ca(2+) ionophore, ionomycin, promoted macrophage death and BCG killing, but ionomycin-mediated macrophage death was inhibited whereas BCG killing was largely retained in Ca(2+)-free medium. Pretreatment of cells with thapsigargin (which depletes inositol (1,4,5)-trisphosphate-mobilizable intracellular stores) or 1,2-bis-(2-aminophenoxy)ethane-N, N, N',N'-tetraacetic acid acetoxymethyl ester (an intracellular Ca(2+) chelator) failed to inhibit ATP-stimulated macrophage death but blocked mycobacterial killing. Using the acidotropic molecular probe, 3-(2,4-dinitroanilino)-3'-amino-N-methyl dipropylamine, it was revealed that ATP stimulation promoted the acidification of BCG-containing phagosomes within human macrophages, and this effect was similarly dependent upon Ca(2+) mobilization from intracellular stores. We conclude that the cytotoxic and bactericidal effects of ATP can be uncoupled and that BCG killing is not the inevitable consequence of death of the host macrophage.
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Affiliation(s)
- C B Stober
- Medical Research Council Center for Immune Regulation, Division of Immunity and Infection, University of Birmingham, Birmingham, United Kingdom
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8
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Pryor PR, Mullock BM, Bright NA, Gray SR, Luzio JP. The role of intraorganellar Ca(2+) in late endosome-lysosome heterotypic fusion and in the reformation of lysosomes from hybrid organelles. J Cell Biol 2000; 149:1053-62. [PMID: 10831609 PMCID: PMC2174832 DOI: 10.1083/jcb.149.5.1053] [Citation(s) in RCA: 278] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
We have investigated the requirement for Ca(2+) in the fusion and content mixing of rat hepatocyte late endosomes and lysosomes in a cell-free system. Fusion to form hybrid organelles was inhibited by 1,2-bis(2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid (BAPTA), but not by EGTA, and this inhibition was reversed by adding additional Ca(2+). Fusion was also inhibited by methyl ester of EGTA (EGTA-AM), a membrane permeable, hydrolyzable ester of EGTA, and pretreatment of organelles with EGTA-AM showed that the chelation of lumenal Ca(2+) reduced the amount of fusion. The requirement for Ca(2+) for fusion was a later event than the requirement for a rab protein since the system became resistant to inhibition by GDP dissociation inhibitor at earlier times than it became resistant to BAPTA. We have developed a cell-free assay to study the reformation of lysosomes from late endosome-lysosome hybrid organelles that were isolated from the rat liver. The recovery of electron dense lysosomes was shown to require ATP and was inhibited by bafilomycin and EGTA-AM. The data support a model in which endocytosed Ca(2+) plays a role in the fusion of late endosomes and lysosomes, the reformation of lysosomes, and the dynamic equilibrium of organelles in the late endocytic pathway.
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Affiliation(s)
- Paul R. Pryor
- Department of Clinical Biochemistry, Cambridge Institute for Medical Research, University of Cambridge, Addenbrooke's Hospital, Cambridge, CB2 2XY, United Kingdom
- Wellcome Trust Centre for the Study of Molecular Mechanisms in Disease, Cambridge Institute for Medical Research, University of Cambridge, Addenbrooke's Hospital, Cambridge, CB2 2XY, United Kingdom
| | - Barbara M. Mullock
- Department of Clinical Biochemistry, Cambridge Institute for Medical Research, University of Cambridge, Addenbrooke's Hospital, Cambridge, CB2 2XY, United Kingdom
- Wellcome Trust Centre for the Study of Molecular Mechanisms in Disease, Cambridge Institute for Medical Research, University of Cambridge, Addenbrooke's Hospital, Cambridge, CB2 2XY, United Kingdom
| | - Nicholas A. Bright
- Department of Clinical Biochemistry, Cambridge Institute for Medical Research, University of Cambridge, Addenbrooke's Hospital, Cambridge, CB2 2XY, United Kingdom
- Wellcome Trust Centre for the Study of Molecular Mechanisms in Disease, Cambridge Institute for Medical Research, University of Cambridge, Addenbrooke's Hospital, Cambridge, CB2 2XY, United Kingdom
| | - Sally R. Gray
- Department of Clinical Biochemistry, Cambridge Institute for Medical Research, University of Cambridge, Addenbrooke's Hospital, Cambridge, CB2 2XY, United Kingdom
- Wellcome Trust Centre for the Study of Molecular Mechanisms in Disease, Cambridge Institute for Medical Research, University of Cambridge, Addenbrooke's Hospital, Cambridge, CB2 2XY, United Kingdom
| | - J. Paul Luzio
- Department of Clinical Biochemistry, Cambridge Institute for Medical Research, University of Cambridge, Addenbrooke's Hospital, Cambridge, CB2 2XY, United Kingdom
- Wellcome Trust Centre for the Study of Molecular Mechanisms in Disease, Cambridge Institute for Medical Research, University of Cambridge, Addenbrooke's Hospital, Cambridge, CB2 2XY, United Kingdom
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9
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Gerasimenko JV, Tepikin AV, Petersen OH, Gerasimenko OV. Calcium uptake via endocytosis with rapid release from acidifying endosomes. Curr Biol 1998; 8:1335-8. [PMID: 9843688 DOI: 10.1016/s0960-9822(07)00565-9] [Citation(s) in RCA: 204] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A number of specific cellular Ca2+ uptake pathways have been described in many different cell types [1] [2] [3]. The possibility that substantial quantities of Ca2+ could be imported via endocytosis has essentially been ignored, although it has been recognized that endosomes can store Ca2+ [4] [5]. Exocrine cells can release significant amounts of Ca2+ via exocytosis [6], so we have investigated the fate of Ca2+ taken up via endocytosis into endosomes. Ca2+-sensitive and H+-sensitive fluorescent probes were placed in the extracellular solution and subsequently taken up into fibroblasts by endocytosis. Confocal microscopy was used to assess the distribution of fluorescence intensity. Ca2+ taken up by endocytosis was lost from the endosomes within a few minutes, over the same period as endosomal acidification took place. The acidification was inhibited by reducing the extracellular Ca2+ concentration, and Ca2+ loss from the endosomes was blocked by bafilomycin (100 nM), a specific inhibitor of the vacuolar proton ATPase. Quantitative evaluation indicated that endocytosis causes substantial import of Ca2+ because of rapid loss from early endosomes.
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Affiliation(s)
- J V Gerasimenko
- MRC Secretory Control Research Group The Physiological Laboratory University of Liverpool Crown Street Liverpool L69 3BX UK
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10
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Abstract
Lysosomes, endosomes, and a variety of other intracellular organelles are acidified by a family of unique proton pumps, termed the vacuolar H(+)-ATPases, that are evolutionarily related to bacterial membrane proton pumps and the F1-F0 H(+)-ATPases that catalyze ATP synthesis in mitochondria and chloroplasts. The electrogenic vacuolar H(+)-ATPase is responsible for generating electrical and chemical gradients across organelle membranes with the magnitude of these gradients ultimately determined by both proton pump regulatory mechanisms and, more importantly, associated ion and organic solute transporters located in vesicle membranes. Analogous to Na+, K(+)-ATPase on the cell membrane, the vacuolar proton pump not only acidifies the vesicle interior but provides a potential energy source for driving a variety of coupled transporters, many of them unique to specific organelles. Although the basic mechanism for organelle acidification is now well understood, it is already apparent that there are many differences in both the function of the proton pump and the associated transporters in different organelles and different cell types. These differences and their physiologic and pathophysiologic implications are exciting areas for future investigation.
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Affiliation(s)
- R W Van Dyke
- Department of Internal Medicine, University of Michigan Medical School, Ann Arbor 48109, USA
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11
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Abraham MI, Burckhardt G, Kempson SA. Sodium-dependent phosphate transport in a rat kidney endosomal fraction. Kidney Int 1992; 42:1070-8. [PMID: 1453594 DOI: 10.1038/ki.1992.389] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
An endosome-enriched fraction was prepared from rat kidney cortex by a standard procedure employing centrifugation on a Percoll gradient. This fraction showed time-dependent accumulation of inorganic phosphate (Pi) which was stimulated two- to threefold during the initial phase by an inwardly directed Na+ gradient. Na+ gradient-dependent Pi accumulation decreased with increasing medium osmolality and Pi binding accounted for only 16% of the total accumulation at two minutes. Like the Pi transporter in the brush border membrane (BBM), the Na+ gradient-dependent Pi uptake (but not the Na(+)-independent component) by the endosomal fraction was stimulated by intravesicular Pi and by an outwardly directed proton gradient, and was inhibited by extravesicular arsenate. Unlike the Pi transporter in BBM, the endosomal Pi transporter was not changed by acidic pH under non-gradient conditions. Activation of the endosomal proton pump by extravesicular ATP, leading to acidification of the vesicle interior, was accompanied by stimulation of endosomal Na+ gradient-dependent Pi transport. Inhibition of the proton pump by deletion of chloride or addition of N-ethylmaleimide abolished the stimulation of Pi uptake by ATP. The data indicate that the Na(+)-dependent Pi transporter in renal endosomal fractions is an intrinsic endosomal component. It remains to be determined if the endosomal Pi transporter plays a role in regulation of renal Pi transport.
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Affiliation(s)
- M I Abraham
- Department of Physiology and Biophysics, Indiana University School of Medicine, Indianapolis
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12
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Hilden SA, Madias NE. Effect of sulfhydryl compounds on ATP-stimulated H+ transport and Cl- uptake in rabbit renal cortical endosomes. J Membr Biol 1991; 124:139-49. [PMID: 1662284 DOI: 10.1007/bf01870458] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The vacuolar H+ ATPase is inhibited by N-ethylmaleimide (NEM), a sulfhydryl compound, suggesting the involvement of a sulfhydryl group in this transport process. We have examined the effects of several sulfhydryl-containing compounds on the vacuolar H+. ATPase of rabbit renal cortical endosomes. A number of such compounds were effective inhibitors of endosomal H+ transport at 10(-5)-10(-6) M, including NEM, mersalyl, aldrithiol, 5,5' dithiobis (2-nitrobenzoic acid), p-chloromercuribenzoic acid (PCMB) and p-chloromercuriphenyl sulfonic acid (PCMBS). NEM, mersalyl, aldrithiol and PCMBS had no effect on pH-gradient dissipation, whereas PCMB decreased the pH gradient faster than control. In the absence of ATP, PCMB (10(-4) M) stimulated endosomal 36Cl- uptake, particularly in the presence of an inside-alkaline pH gradient (pHin = 7.6/pHout = 5.5). This result was not an effect of PCMB on the Cl(-)-conductive pathway. The less permeable PCMBS did not stimulate 36Cl- uptake. The effects of PCMB were concentration dependent and were prevented by dithioerithritol. ATP-dependent 36Cl- uptake was decreased by addition of PCMB. Finally, PCMB had no effect on 45Ca2+ uptake. These results support the presence of two functionally important sulfhydryl groups in this endosomal preparation. One such group is involved with ATP-driven H+ transport and must be located on the cytoplasmic surface of the endosomal membrane. The second sulfhydryl group must reside on the internal surface of the endosomal membrane and relates to a PCMB-activated Cl-/OH- exchanger that is functional both in the presence and absence of ATP. This endosomal transporter is similar to the PCMB-activated Cl-/OH- exchanger recently described in rabbit renal brush-border membranes.
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Affiliation(s)
- S A Hilden
- Department of Medicine, Tufts University School of Medicine, Boston, Massachusetts
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13
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Núñez MT, Gaete V, Escobar A. Endocytic vesicles contain a calmodulin-activated Ca2+ pump that mediates the inhibition of acidification by calcium. BIOCHIMICA ET BIOPHYSICA ACTA 1990; 1028:21-4. [PMID: 2169879 DOI: 10.1016/0005-2736(90)90260-u] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Endocytic vesicles isolated from rabbit reticulocytes contained an intrinsic Ca2(+)-pump activity that was dependent on ATP, activated by calmodulin and inhibited by vanadate. 45Ca2+ uptake and acidification studies indicated that acidification of the endocytic vesicles inversely correlated with the Ca2(+)-pump activity. Acidification was inhibited by externally added Ca2+ and calmodulin and activated by vanadate and EGTA. It is suggested that intravesicular Ca2+ can act as a modulator of endocytic vesicle acidification.
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Affiliation(s)
- M T Núñez
- Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago
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