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Hernando N. Is XPR1 mediating phosphate efflux? Pflugers Arch 2024; 476:717-719. [PMID: 38512477 DOI: 10.1007/s00424-024-02946-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2024] [Revised: 03/11/2024] [Accepted: 03/12/2024] [Indexed: 03/23/2024]
Affiliation(s)
- Nati Hernando
- Institute of Physiology, University of Zürich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
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2
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Wagner CA. Pharmacology of Mammalian Na +-Dependent Transporters of Inorganic Phosphate. Handb Exp Pharmacol 2024; 283:285-317. [PMID: 36592227 DOI: 10.1007/164_2022_633] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Inorganic phosphate (Pi) is an essential component of many biologically important molecules such as DNA, RNA, ATP, phospholipids, or apatite. It is required for intracellular phosphorylation signaling events and acts as pH buffer in intra- and extracellular compartments. Intestinal absorption, uptake into cells, and renal reabsorption depend on a set of different phosphate transporters from the SLC20 (PiT transporters) and SLC34 (NaPi transporters) gene families. The physiological relevance of these transporters is evident from rare monogenic disorders in humans affecting SLC20A2 (Fahr's disease, basal ganglia calcification), SLC34A1 (idiopathic infantile hypercalcemia), SLC34A2 (pulmonary alveolar microlithiasis), and SLC34A3 (hereditary hypophosphatemic rickets with hypercalciuria). SLC34 transporters are inhibited by millimolar concentrations of phosphonoformic acid or arsenate while SLC20 are relatively resistant to these compounds. More recently, a series of more specific and potent drugs have been developed to target SLC34A2 to reduce intestinal Pi absorption and to inhibit SLC34A1 and/or SLC34A3 to increase renal Pi excretion in patients with renal disease and incipient hyperphosphatemia. Also, SLC20 inhibitors have been developed with the same intention. Some of these substances are currently undergoing preclinical and clinical testing. Tenapanor, a non-absorbable Na+/H+-exchanger isoform 3 inhibitor, reduces intestinal Pi absorption likely by indirectly acting on the paracellular pathway for Pi and has been tested in several phase III trials for reducing Pi overload in patients with renal insufficiency and dialysis.
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Affiliation(s)
- Carsten A Wagner
- Institute of Physiology, University of Zurich, Zurich, Switzerland.
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Jennings ML. Role of transporters in regulating mammalian intracellular inorganic phosphate. Front Pharmacol 2023; 14:1163442. [PMID: 37063296 PMCID: PMC10097972 DOI: 10.3389/fphar.2023.1163442] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Accepted: 03/17/2023] [Indexed: 03/31/2023] Open
Abstract
This review summarizes the current understanding of the role of plasma membrane transporters in regulating intracellular inorganic phosphate ([Pi]In) in mammals. Pi influx is mediated by SLC34 and SLC20 Na+-Pi cotransporters. In non-epithelial cells other than erythrocytes, Pi influx via SLC20 transporters PiT1 and/or PiT2 is balanced by efflux through XPR1 (xenotropic and polytropic retrovirus receptor 1). Two new pathways for mammalian Pi transport regulation have been described recently: 1) in the presence of adequate Pi, cells continuously internalize and degrade PiT1. Pi starvation causes recycling of PiT1 from early endosomes to the plasma membrane and thereby increases the capacity for Pi influx; and 2) binding of inositol pyrophosphate InsP8 to the SPX domain of XPR1 increases Pi efflux. InsP8 is degraded by a phosphatase that is strongly inhibited by Pi. Therefore, an increase in [Pi]In decreases InsP8 degradation, increases InsP8 binding to SPX, and increases Pi efflux, completing a feedback loop for [Pi]In homeostasis. Published data on [Pi]In by magnetic resonance spectroscopy indicate that the steady state [Pi]In of skeletal muscle, heart, and brain is normally in the range of 1–5 mM, but it is not yet known whether PiT1 recycling or XPR1 activation by InsP8 contributes to Pi homeostasis in these organs. Data on [Pi]In in cultured cells are variable and suggest that some cells can regulate [Pi] better than others, following a change in [Pi]Ex. More measurements of [Pi]In, influx, and efflux are needed to determine how closely, and how rapidly, mammalian [Pi]In is regulated during either hyper- or hypophosphatemia.
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Abstract
Phosphate is an essential nutrient for life and is a critical component of bone formation, a major signaling molecule, and structural component of cell walls. Phosphate is also a component of high-energy compounds (i.e., AMP, ADP, and ATP) and essential for nucleic acid helical structure (i.e., RNA and DNA). Phosphate plays a central role in the process of mineralization, normal serum levels being associated with appropriate bone mineralization, while high and low serum levels are associated with soft tissue calcification. The serum concentration of phosphate and the total body content of phosphate are highly regulated, a process that is accomplished by the coordinated effort of two families of sodium-dependent transporter proteins. The three isoforms of the SLC34 family (SLC34A1-A3) show very restricted tissue expression and regulate intestinal absorption and renal excretion of phosphate. SLC34A2 also regulates the phosphate concentration in multiple lumen fluids including milk, saliva, pancreatic fluid, and surfactant. Both isoforms of the SLC20 family exhibit ubiquitous expression (with some variation as to which one or both are expressed), are regulated by ambient phosphate, and likely serve the phosphate needs of the individual cell. These proteins exhibit similarities to phosphate transporters in nonmammalian organisms. The proteins are nonredundant as mutations in each yield unique clinical presentations. Further research is essential to understand the function, regulation, and coordination of the various phosphate transporters, both the ones described in this review and the phosphate transporters involved in intracellular transport.
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Affiliation(s)
- Nati Hernando
- University of Zurich-Irchel, Institute of Physiology, Zurich, Switzerland; Department of Medicine, University of Louisville School of Medicine, Louisville, Kentucky; and Robley Rex VA Medical Center, Louisville, Kentucky
| | - Kenneth Gagnon
- University of Zurich-Irchel, Institute of Physiology, Zurich, Switzerland; Department of Medicine, University of Louisville School of Medicine, Louisville, Kentucky; and Robley Rex VA Medical Center, Louisville, Kentucky
| | - Eleanor Lederer
- University of Zurich-Irchel, Institute of Physiology, Zurich, Switzerland; Department of Medicine, University of Louisville School of Medicine, Louisville, Kentucky; and Robley Rex VA Medical Center, Louisville, Kentucky
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5
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Abstract
We have studied inorganic phosphate (Pi) handling in rat aortic vascular smooth muscle cells (VSMC) using 32P-radiotracer assays. Our results have revealed a complex set of mechanisms consisting of 1) well-known PiT1/PiT2-mediated sodium-dependent Pi transport; 2) Slc20-unrelated sodium-dependent Pi transport that is sensitive to the stilbene derivatives 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) and 4-acetamido-4-isothiocyanostilbene-2,2-disulfonate (SITS); 3) a sodium-independent Pi uptake system that is competitively inhibited by sulfate, bicarbonate, and arsenate and is weakly inhibited by DIDS, SITS, and phosphonoformate; and 4) an exit pathway from the cell that is partially chloride dependent and unrelated to the known anion-exchangers expressed in VSMC. The inhibitions of sodium-independent Pi transport by sulfate and of sodium-dependent transport by SITS were studied in greater detail. The maximal inhibition by sulfate was similar to that of Pi itself, with a very high inhibition constant (212 mM). SITS only partially inhibited sodium-dependent Pi transport, but the Ki was very low (14 µM). Nevertheless, SITS and DIDS did not inhibit Pi transport in Xenopus laevis oocytes expressing PiT1 or PiT2. Both the sodium-dependent and sodium-independent transport systems were highly dependent on VSMC confluence and on the differentiation state, but they were not modified by incubating VSMC for 7 days with 2 mM Pi under nonprecipitating conditions. This work not only shows that the Pi handling by cells is highly complex but also that the transport systems are shared with other ions such as bicarbonate or sulfate.NEW & NOTEWORTHY In addition to the inorganic phosphate (Pi) transporters PiT1 and PiT2, rat vascular smooth muscle cells show a sodium-dependent Pi transport system that is inhibited by DIDS and SITS. A sodium-independent Pi uptake system of high affinity is also expressed, which is inhibited by sulfate, bicarbonate, and arsenate. The exit of excess Pi is through an exchange with extracellular chloride. Whereas the metabolic effects of the inhibitors, if any, cannot be discarded, kinetic analysis during initial velocity suggests competitive inhibition.
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Affiliation(s)
- Luis Hortells
- Veterinary Faculty, Department of Toxicology, University of Zaragoza, Zaragoza, Spain
| | - Natalia Guillén
- Veterinary Faculty, Department of Toxicology, University of Zaragoza, Zaragoza, Spain
| | - Cecilia Sosa
- Veterinary Faculty, Department of Toxicology, University of Zaragoza, Zaragoza, Spain
| | - Víctor Sorribas
- Veterinary Faculty, Department of Toxicology, University of Zaragoza, Zaragoza, Spain
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6
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Abstract
Our understanding of the regulation of phosphate balance has benefited tremendously from the molecular identification and characterization of genetic defects leading to a number of rare inherited or acquired disorders affecting phosphate homeostasis. The identification of the key phosphate-regulating hormone, fibroblast growth factor 23 (FGF23), as well as other molecules that control its production, such as the glycosyltransferase GALNT3, the endopeptidase PHEX, and the matrix protein DMP1, and molecules that function as downstream effectors of FGF23 such as the longevity factor Klotho and the phosphate transporters NPT2a and NPT2c, has permitted us to understand the complex interplay that exists between the kidneys, bone, parathyroid, and gut. Such insights from genetic disorders have allowed not only the design of potent targeted treatment of FGF23-dependent hypophosphatemic conditions, but also provide clinically relevant observations related to the dysregulation of mineral ion homeostasis in health and disease.
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Affiliation(s)
- Marta Christov
- Division of Nephrology, Department of Medicine, New York Medical College, Valhalla, NY, USA
| | - Harald Jüppner
- Endocrine Unit and Pediatric Nephrology Unit, Massachusetts General Hospital, Boston, MA, USA; Harvard Medical School, Boston, MA, USA.
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Meireles AM, Shiau CE, Guenther CA, Sidik H, Kingsley DM, Talbot WS. The phosphate exporter xpr1b is required for differentiation of tissue-resident macrophages. Cell Rep. 2014;8:1659-1667. [PMID: 25220463 DOI: 10.1016/j.celrep.2014.08.018] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2014] [Revised: 07/23/2014] [Accepted: 08/08/2014] [Indexed: 12/23/2022] Open
Abstract
Phosphate concentration is tightly regulated at the cellular and organismal levels. The first metazoan phosphate exporter, XPR1, was recently identified, but its in vivo function remains unknown. In a genetic screen, we identified a mutation in a zebrafish ortholog of human XPR1, xpr1b. xpr1b mutants lack microglia, the specialized macrophages that reside in the brain, and also displayed an osteopetrotic phenotype characteristic of defects in osteoclast function. Transgenic expression studies indicated that xpr1b acts autonomously in developing macrophages. xpr1b mutants display no gross developmental defects that may arise from phosphate imbalance. We constructed a targeted mutation of xpr1a, a duplicate of xpr1b in the zebrafish genome, to determine whether Xpr1a and Xpr1b have redundant functions. Single mutants for xpr1a were viable, and double mutants for xpr1b;xpr1a were similar to xpr1b single mutants. Our genetic analysis reveals a specific role for the phosphate exporter Xpr1 in the differentiation of tissue macrophages.
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8
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Wege S, Poirier Y. Expression of the mammalian Xenotropic Polytropic Virus Receptor 1 (XPR1) in tobacco leaves leads to phosphate export. FEBS Lett 2014; 588:482-9. [PMID: 24374333 DOI: 10.1016/j.febslet.2013.12.013] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2013] [Revised: 12/06/2013] [Accepted: 12/06/2013] [Indexed: 10/25/2022]
Abstract
Phosphate homeostasis in multicellular eukaryotes depends on both phosphate influx and efflux. The mammalian Xenotropic Polytropic Virus Receptor 1 (XPR1) shares homology to the Arabidopsis PHO1, a phosphate exporter expressed in roots. However, phosphate export activity of XPR1 has not yet been demonstrated in a heterologous system. Here, wedemonstrate that transient expression in tobacco leaves of XPR1-GFP leads to specific phosphate export. Like PHO1-GFP, XPR1-GFP is localized predominantly to the endomembrane system in tobacco cells. These results show that tobacco leaves are a good heterologous system to study the transport activity of members of the PHO1/XPR1 family.
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Affiliation(s)
- Stefanie Wege
- Department of Plant Molecular Biology, University of Lausanne, 1015 Lausanne, Switzerland
| | - Yves Poirier
- Department of Plant Molecular Biology, University of Lausanne, 1015 Lausanne, Switzerland.
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9
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Giovannini D, Touhami J, Charnet P, Sitbon M, Battini JL. Inorganic Phosphate Export by the Retrovirus Receptor XPR1 in Metazoans. Cell Rep 2013; 3:1866-73. [DOI: 10.1016/j.celrep.2013.05.035] [Citation(s) in RCA: 114] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2012] [Revised: 04/05/2013] [Accepted: 05/22/2013] [Indexed: 12/11/2022] Open
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Abstract
Transport of inorganic phosphate (P(i)) is mediated by proteins belonging to two solute carrier families (SLC20 and SLC34). Members of both families transport P(i) using the electrochemical gradient for Na(+). The role of the SLC34 members as essential players in mammalian P(i) homeostasis is well established, whereas that of SLC20 proteins is less well defined. The SLC34 family comprises the following three isoforms that preferentially cotransport divalent P(i) and are expressed in epithelial tissue: the renal NaPi-IIa and NaPi-IIc are responsible for reabsorbing P(i) in the proximal tubule, whereas NaPi-IIb is more ubiquitously expressed, including the small intestine, where it mediates dietary P(i) absorption. The SLC20 family comprises two members (PiT-1, PiT-2) that preferentially cotransport monovalent P(i) and are expressed in epithelial as well as nonepithelial tissue. The transport kinetics of members of both families have been characterized in detail using heterologous expression in Xenopus oocytes. For the electrogenic NaPi-IIa/b, and PiT-1,-2, conventional electrophysiological techniques together with radiotracer methods have been applied, as well as time-resolved fluorometric measurements that allow new insights into local conformational changes of the protein during the cotransport cycle. For the electroneutral NaPi-IIc, conventional tracer uptake and fluorometry have been used to elucidate its transport properties. The 3-D structures of these proteins remain unresolved and structure-function studies have so far concentrated on defining the topology and identifying sites of functional importance.
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Affiliation(s)
- Ian C Forster
- Institute of Physiology and Zurich Center for Integrative Human Physiology, University of Zurich, Winterthurerstrasse, Zurich, Switzerland.
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Crans DC, Trujillo AM, Pharazyn PS, Cohen MD. How environment affects drug activity: Localization, compartmentalization and reactions of a vanadium insulin-enhancing compound, dipicolinatooxovanadium(V). Coord Chem Rev 2011; 255:2178-92. [DOI: 10.1016/j.ccr.2011.01.032] [Citation(s) in RCA: 91] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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Cohen MD, Sisco M, Prophete C, Yoshida K, Chen LC, Zelikoff JT, Smee J, Holder AA, Stonehuerner J, Crans DC, Ghio AJ. Effects of metal compounds with distinct physicochemical properties on iron homeostasis and antibacterial activity in the lungs: chromium and vanadium. Inhal Toxicol 2010; 22:169-78. [PMID: 19757987 PMCID: PMC4018818 DOI: 10.3109/08958370903161232] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
In situ reactions of metal ions or their compounds are important mechanisms by which particles alter lung immune responses. The authors hypothesized that major determinants of the immunomodulatory effect of any metal include its redox behavior/properties, oxidation state, and/or solubility, and that the toxicities arising from differences in physicochemical parameters are manifest, in part, via differential shifts in lung iron (Fe) homeostasis. To test the hypotheses, immunomodulatory potentials for both pentavalent vanadium (VV; as soluble metavanadate or insoluble vanadium pentoxide) and hexavalent chromium (CrVI; as soluble sodium chromate or insoluble calcium chromate) were quantified in rats after inhalation (5h/day for 5 days) of each at 100 microg metal/m3. Differences in effects on local bacterial resistance between the two VV, and between each CrVI, agents suggested that solubility might be a determinant of in situ immunotoxicity. For the soluble forms, VV had a greater impact on resistance than CrVI, indicating that redox behavior/properties was likely also a determinant. The soluble VV agent was the strongest immunomodulant. Regarding Fe homeostasis, both VV agents had dramatic effects on airway Fe levels. Both also impacted local immune/airway epithelial cell Fe levels in that there were significant increases in production of select cytokines/chemokines whose genes are subject to regulation by HIF-1 (whose intracellular longevity is related to cell Fe status). Our findings contribute to a better understanding of the role that metal compound properties play in respiratory disease pathogenesis and provide a rationale for differing pulmonary immunotoxicities of commonly encountered ambient metal pollutants.
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Affiliation(s)
- Mitchell D Cohen
- Department of Environmental Medicine, New York University School of Medicine, Tuxedo, New York, USA
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Cohen MD, Sisco M, Prophete C, Chen LC, Zelikoff JT, Ghio AJ, Stonehuerner JD, Smee JJ, Holder AA, Crans DC. Pulmonary Immunotoxic Potentials of Metals Are Governed by Select Physicochemical Properties: Vanadium Agents. J Immunotoxicol 2008; 4:49-60. [DOI: 10.1080/15476910601119350] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
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Abstract
In opossum kidney (OK) cells as well as in kidney proximal tubules, Pi depletion increases apical (A) and basolateral (B) Na+-dependent Pi cell influxes. In OK cells' monolayers in contrast to proximal tubules, there is no increase in transepithelial Pi transport. This limitation may be due to altered cell-matrix interactions. A and B cell 32Pi uptakes and transepithelial 32Pi and [14C]mannitol fluxes were measured in OK cells grown on uncoated or on Matrigel-coated filter inserts. Cells were exposed overnight to solution of either low (0.25 mM) or high (2.5 mM) Pi. When grown on Matrigel, immunofluorescence of apical NaPi4 (an isoform of the sodium-phosphate cotransporter) transporters increased and A and B 32Pi uptakes into Pi depleted cells were five and threefold higher than in Pi replete cells ( P < 0.001). Pi deprivation resulted in larger increase in A to B (4.6×, P < 0.001) than in B to A (3.5×, P < 0.001) Pi flux and net Pi transport from A to B increased 10-fold ( P < 0.001). With Pi depletion increases in B to A (3.4×) and A to B (3.3×) paracellular [14C]mannitol fluxes were similar, and its net flux was opposite to that of Pi. In cells grown on uncoated filters, transepithelial and paracellular unidirectional and net Pi fluxes decreased or did not change with Pi depletion, despite twofold increases in apical and basolateral Pi cell influxes. In summary, Matrigel-OK cell interactions, particularly in Pi-depleted cells, led to enhanced expression of apical NaPi4 transporters resulting in higher Pi transport rates across cell boundaries; apical Pi readily entered the transcellular transport pool and paracellular fluxes were smaller fractions of transepithelial Pi fluxes. These Matrigel-induced changes led to an increase in net transepithelial apical to basolateral Pi transport.
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Ito M, Haito S, Furumoto M, Uehata Y, Sakurai A, Segawa H, Tatsumi S, Kuwahata M, Miyamoto KI. Unique uptake and efflux systems of inorganic phosphate in osteoclast-like cells. Am J Physiol Cell Physiol 2007; 292:C526-34. [PMID: 16971494 DOI: 10.1152/ajpcell.00357.2006] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
During bone resorption, a large amount of inorganic phosphate (Pi) is generated within the osteoclast hemivacuole. The mechanisms involved in the disposal of this Pi are not clear. In the present study, we investigated the efflux of Pi from osteoclast-like cells. Pi efflux was activated by acidic conditions in osteoclast-like cells derived by the treatment of RAW264.7 cells with receptor activator of nuclear factor-κB ligand. Acid-induced Pi influx was not observed in renal proximal tubule-like opossum kidney cells, osteoblast-like MC3T3-E1 cells, or untreated RAW264.7 cells. Furthermore, Pi efflux was stimulated by extracellular Pi and several Pi analogs [phosphonoformic acid (PFA), phosphonoacetic acid, arsenate, and pyrophosphate]. Pi efflux was time dependent, with 50% released into the medium after 10 min. The efflux of Pi was increased by various inhibitors that block Pi uptake, and extracellular Pi did not affect the transport of [14C]PFA into the osteoclast-like cells. Preloading of cells with Pi did not stimulate Pi efflux by PFA, indicating that the effect of Pi was not due to transstimulation of Pi transport. Pi uptake was also enhanced under acidic conditions. Agents that prevent increases in cytosolic free Ca2+ concentration, including acetoxymethyl ester of 1,2-bis(2-aminophenoxy)ethane- N,N,N′,N′-tetraacetic acid, 2-aminoethoxydiphenyl borate, and bongkrekic acid, significantly inhibited Pi uptake in the osteoclast-like cells, suggesting that Pi uptake is regulated by Ca2+ signaling in the endoplasmic reticulum and mitochondria of osteoclast-like cells. These results suggest that osteoclast-like cells have a unique Pi uptake/efflux system and can prevent Pi accumulation within osteoclast hemivacuoles.
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Affiliation(s)
- Mikiko Ito
- Department of Molecular Nutrition, Institute of Health Biosciences, University of Tokushima Graduate School, Kuramoto-Cho 3-18-15, Tokushima City 770-8503, Japan
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16
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Abstract
Members of the SLC34 gene family of solute carriers encode for three Na+-dependent phosphate (P i) cotransporter proteins, two of which (NaPi-IIa/SLC34A1 and NaPi-IIc/SLC34A3) control renal reabsorption of P i in the proximal tubule of mammals, whereas NaPi-IIb/SCLC34A2 mediates P i transport in organs other than the kidney. The P i transport mechanism has been extensively studied in heterologous expression systems and structure-function studies have begun to reveal the intricacies of the transport cycle at the molecular level using techniques such as cysteine scanning mutagenesis, and voltage clamp fluorometry. Moreover, sequence differences between the three types of cotransporters have been exploited to obtain information about the molecular determinants of hormonal sensitivity and electrogenicity. Renal handling of P i is regulated by hormonal and non-hormonal factors. Changes in urinary excretion of P i are almost invariably mirrored by changes in the apical expression of NaPi-IIa and NaPi-IIc in proximal tubules. Therefore, understanding the mechanisms that control the apical expression of NaPi-IIa and NaPi-IIc as well as their functional properties is critical to understanding how an organism achieves P i homeostasis.
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MESH Headings
- Animals
- Homeostasis
- Humans
- Kidney Tubules, Proximal/metabolism
- Mice
- Parathyroid Hormone/physiology
- Phosphates/metabolism
- Sodium-Phosphate Cotransporter Proteins, Type IIa/chemistry
- Sodium-Phosphate Cotransporter Proteins, Type IIa/genetics
- Sodium-Phosphate Cotransporter Proteins, Type IIa/metabolism
- Sodium-Phosphate Cotransporter Proteins, Type IIb/chemistry
- Sodium-Phosphate Cotransporter Proteins, Type IIb/genetics
- Sodium-Phosphate Cotransporter Proteins, Type IIb/metabolism
- Sodium-Phosphate Cotransporter Proteins, Type IIc/chemistry
- Sodium-Phosphate Cotransporter Proteins, Type IIc/genetics
- Sodium-Phosphate Cotransporter Proteins, Type IIc/metabolism
- Structure-Activity Relationship
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Affiliation(s)
- I C Forster
- Institute of Physiology and ZIHP, Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland.
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