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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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2
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Jönsson ÅLM, Hilberg O, Simonsen U, Christensen JH, Bendstrup E. New insights in the genetic variant spectrum of SLC34A2 in pulmonary alveolar microlithiasis; a systematic review. Orphanet J Rare Dis 2023; 18:130. [PMID: 37259144 DOI: 10.1186/s13023-023-02712-7] [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: 01/10/2023] [Accepted: 04/30/2023] [Indexed: 06/02/2023] Open
Abstract
Pulmonary alveolar microlithiasis (PAM) is a rare autosomal recessive lung disease caused by variants in the SLC34A2 gene encoding the sodium-dependent phosphate transport protein 2B, NaPi-2b. PAM is characterized by deposition of calcium phosphate crystals in the alveoli. Onset and clinical course vary considerably; some patients remain asymptomatic while others develop severe respiratory failure with a significant symptom burden and compromised survival. It is likely that PAM is under-reported due to lack of recognition, misdiagnosis, and mild clinical presentation. Most patients are genetically uncharacterized as the diagnostic confirmation of PAM has traditionally not included a genetic analysis. Genetic testing may in the future be the preferred tool for diagnostics instead of invasive methods. This systematic review aims to provide an overview of the growing knowledge of PAM genetics. Rare variants in SLC34A2 are found in almost all genetically tested patients. So far, 34 allelic variants have been identified in at least 68 patients. A majority of these are present in the homozygous state; however, a few are found in the compound heterozygous form. Most of the allelic variants involve only a single nucleotide. Half of the variants are either nonsense or frameshifts, resulting in premature termination of the protein or decay of the mRNA. There is currently no cure for PAM, and the only effective treatment is lung transplantation. Management is mainly symptomatic, but an improved understanding of the underlying pathophysiology will hopefully result in development of targeted treatment options. More standardized data on PAM patients, including a genetic diagnosis covering larger international populations, would support the design and implementation of clinical studies to the benefit of patients. Further genetic characterization and understanding of how the molecular changes influence disease phenotype will hopefully allow earlier diagnosis and treatment of the disease in the future.
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Affiliation(s)
- Åsa Lina M Jönsson
- Department of Clinical Genetics, Aarhus University Hospital, Aarhus, Denmark.
- Department of Biomedicine, Aarhus University, Aarhus, Denmark.
| | - Ole Hilberg
- Department of Regional Health Research, University of Southern Denmark, Odense, Denmark.
- Department of Medicine, Lillebaelt Hospital, Vejle, Denmark.
| | - Ulf Simonsen
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | | | - Elisabeth Bendstrup
- Centre for Rare Lung Diseases, Department of Respiratory Diseases and Allergy, Aarhus University Hospital, Aarhus, Denmark
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Expression of phosphate and calcium transporters and their regulators in parotid glands of mice. Pflugers Arch 2023; 475:203-216. [PMID: 36274099 PMCID: PMC9849193 DOI: 10.1007/s00424-022-02764-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2022] [Revised: 10/07/2022] [Accepted: 10/13/2022] [Indexed: 02/01/2023]
Abstract
The concentration of inorganic phosphate (Pi) in plasma is under hormonal control, with deviations from normal values promptly corrected to avoid hyper- or hypophosphatemia. Major regulators include parathyroid hormone (PTH), fibroblast growth factor 23 (FGF-23), and active vitamin D3 (calcitriol). This control is achieved by mechanisms largely dependent on regulating intestinal absorption and renal excretion, whose combined actions stabilise plasma Pi levels at around 1-2 mM. Instead, Pi concentrations up to 13 and 40 mM have been measured in saliva from humans and ruminants, respectively, suggesting that salivary glands have the capacity to concentrate Pi. Here we analysed the transcriptome of parotid glands, ileum, and kidneys of mice, to investigate their potential differences regarding the expression of genes responsible for epithelial transport of Pi as well as their known regulators. Given that Pi and Ca2+ homeostasis are tightly connected, the expression of genes involved in Ca2+ homeostasis was also included. In addition, we studied the effect of vitamin D3 treatment on the expression of Pi and Ca2+ regulating genes in the three major salivary glands. We found that parotid glands are equipped preferentially with Slc20 rather than with Slc34 Na+/Pi cotransporters, are suited to transport Ca2+ through the transcellular and paracellular route and are potential targets for PTH and vitamin D3 regulation.
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4
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Jönsson ÅLM, Hernando N, Knöpfel T, Mogensen S, Bendstrup E, Hilberg O, Christensen JH, Simonsen U, Wagner CA. Impaired phosphate transport in SLC34A2 variants in patients with pulmonary alveolar microlithiasis. Hum Genomics 2022; 16:13. [PMID: 35443721 PMCID: PMC9019944 DOI: 10.1186/s40246-022-00387-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Accepted: 03/23/2022] [Indexed: 11/26/2022] Open
Abstract
Background Variants in SLC34A2 encoding the sodium-dependent phosphate transport protein 2b (NaPi-IIb) cause the rare lung disease pulmonary alveolar microlithiasis (PAM). PAM is characterised by the deposition of calcium-phosphate concretions in the alveoli usually progressing over time. No effective treatment is available. So far, 30 allelic variants in patients have been reported but only a few have been functionally characterised. This study aimed to determine the impact of selected SLC34A2 variants on transporter expression and phosphate uptake in cellular studies. Methods Two nonsense variants (c.910A > T and c.1456C > T), one frameshift (c.1328delT), and one in-frame deletion (c.1402_1404delACC) previously reported in patients with PAM were selected for investigation. Wild-type and mutant c-Myc-tagged human NaPi-IIb constructs were expressed in Xenopus laevis oocytes. The transport function was investigated with a 32Pi uptake assay. NaPi-IIb protein expression and localisation were determined with immunoblotting and immunohistochemistry, respectively. Results Oocytes injected with the wild-type human NaPi-IIb construct had significant 32Pi transport compared to water-injected oocytes. In addition, the protein had a molecular weight as expected for the glycosylated form, and it was readily detectable in the oocyte membrane. Although the protein from the Thr468del construct was synthesised and expressed in the oocyte membrane, phosphate transport was similar to non-injected control oocytes. All other mutants were non-functional and not expressed in the membrane, consistent with the expected impact of the truncations caused by premature stop codons. Conclusions Of four analysed SLC34A2 variants, only the Thr468del showed similar protein expression as the wild-type cotransporter in the oocyte membrane. All mutant transporters were non-functional, supporting that dysfunction of NaPi-IIb underlies the pathology of PAM. Supplementary Information The online version contains supplementary material available at 10.1186/s40246-022-00387-y.
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Affiliation(s)
- Åsa Lina M Jönsson
- Department of Biomedicine, Aarhus University, Aarhus, Denmark. .,Department of Clinical Genetics, Aarhus University Hospital, Aarhus, Denmark.
| | - Nati Hernando
- Institute of Physiology, University of Zurich, Zurich, Switzerland.,Swiss National Center of Competence in Research NCCR Kidney.CH, Zurich, Switzerland
| | - Thomas Knöpfel
- Institute of Physiology, University of Zurich, Zurich, Switzerland.,Swiss National Center of Competence in Research NCCR Kidney.CH, Zurich, Switzerland
| | - Susie Mogensen
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | - Elisabeth Bendstrup
- Centre for Rare Lung Diseases, Department of Respiratory Diseases and Allergy, Aarhus University Hospital, Aarhus, Denmark
| | - Ole Hilberg
- Medical Department, Vejle Hospital, Vejle, Denmark
| | | | - Ulf Simonsen
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | - Carsten A Wagner
- Institute of Physiology, University of Zurich, Zurich, Switzerland.,Swiss National Center of Competence in Research NCCR Kidney.CH, Zurich, Switzerland
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Pastor-Arroyo EM, Rodriguez JMM, Pellegrini G, Bettoni C, Levi M, Hernando N, Wagner CA. Constitutive depletion of Slc34a2/NaPi-IIb in rats causes perinatal mortality. Sci Rep 2021; 11:7943. [PMID: 33846411 PMCID: PMC8042035 DOI: 10.1038/s41598-021-86874-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Accepted: 03/15/2021] [Indexed: 11/23/2022] Open
Abstract
Absorption of dietary phosphate (Pi) across intestinal epithelia is a regulated process mediated by transcellular and paracellular pathways. Although hyperphosphatemia is a risk factor for the development of cardiovascular disease, the amount of ingested Pi in a typical Western diet is above physiological needs. While blocking intestinal absorption has been suggested as a therapeutic approach to prevent hyperphosphatemia, a complete picture regarding the identity and regulation of the mechanism(s) responsible for intestinal absorption of Pi is missing. The Na+/Pi cotransporter NaPi-IIb is a secondary active transporter encoded by the Slc34a2 gene. This transporter has a wide tissue distribution and within the intestinal tract is located at the apical membrane of epithelial cells. Based on mouse models deficient in NaPi-IIb, this cotransporter is assumed to mediate the bulk of active intestinal absorption of Pi. However, whether or not this is also applicable to humans is unknown, since human patients with inactivating mutations in SLC34A2 have not been reported to suffer from Pi depletion. Thus, mice may not be the most appropriate experimental model for the translation of intestinal Pi handling to humans. Here, we describe the generation of a rat model with Crispr/Cas-driven constitutive depletion of Slc34a2. Slc34a2 heterozygous rats were indistinguishable from wild type animals under standard dietary conditions as well as upon 3 days feeding on low Pi. However, unlike in humans, homozygosity resulted in perinatal lethality.
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Affiliation(s)
- Eva Maria Pastor-Arroyo
- Institute of Physiology, University of Zürich, Winterthurerstrasse 190, 8057, Zurich, Switzerland
| | - Josep M Monné Rodriguez
- Laboratory for Animal Model Pathology (LAMP), Institute of Veterinary Pathology, Vetsuisse Faculty, University of Zurich, Winterthurerstrasse 268, 8057, Zurich, Switzerland
| | - Giovanni Pellegrini
- Laboratory for Animal Model Pathology (LAMP), Institute of Veterinary Pathology, Vetsuisse Faculty, University of Zurich, Winterthurerstrasse 268, 8057, Zurich, Switzerland
| | - Carla Bettoni
- Institute of Physiology, University of Zürich, Winterthurerstrasse 190, 8057, Zurich, Switzerland
| | - Moshe Levi
- Department of Biochemistry and Molecular and Cellular Biology, Georgetown University, Washington, DC, USA
| | - Nati Hernando
- Institute of Physiology, University of Zürich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
| | - Carsten A Wagner
- Institute of Physiology, University of Zürich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
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6
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Beck L. Expression and function of Slc34 sodium-phosphate co-transporters in skeleton and teeth. Pflugers Arch 2018; 471:175-184. [PMID: 30511265 DOI: 10.1007/s00424-018-2240-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Revised: 11/22/2018] [Accepted: 11/23/2018] [Indexed: 12/20/2022]
Abstract
Under normal physiological condition, the biomineralization process is limited to skeletal tissues and teeth and occurs throughout the individual's life. Biomineralization is an actively regulated process involving the progressive mineralization of the extracellular matrix secreted by osteoblasts in bone or odontoblasts and ameloblasts in tooth. Although the detailed molecular mechanisms underlying the formation of calcium-phosphate apatite crystals are still debated, it is suggested that calcium and phosphate may need to be transported across the membrane of the mineralizing cell, suggesting a pivotal role of phosphate transporters in bone and tooth mineralization. In this context, this short review describes the current knowledge on the role of Slc34 Na+-phosphate transporters in skeletal and tooth mineralization.
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Affiliation(s)
- Laurent Beck
- INSERM, UMR 1229, RMeS, Regenerative Medicine and Skeleton, Faculté de Chirurgie Dentaire, Université de Nantes, ONIRIS, 1 place Alexis Ricordeau, 44042, Nantes, France. .,Université de Nantes, UFR Odontologie, 44042, Nantes, France.
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Aniteli TM, de Siqueira FR, Dos Reis LM, Dominguez WV, de Oliveira EMC, Castelucci P, Moysés RMA, Jorgetti V. Effect of variations in dietary Pi intake on intestinal Pi transporters (NaPi-IIb, PiT-1, and PiT-2) and phosphate-regulating factors (PTH, FGF-23, and MEPE). Pflugers Arch 2018; 470:623-632. [PMID: 29372301 DOI: 10.1007/s00424-018-2111-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Revised: 01/10/2018] [Accepted: 01/11/2018] [Indexed: 11/29/2022]
Abstract
Hyperphosphatemia is a common condition in patients with chronic kidney disease (CKD) and can lead to bone disease, vascular calcification, and increased risks of cardiovascular disease and mortality. Inorganic phosphate (Pi) is absorbed in the intestine, an important step in the maintenance of homeostasis. In CKD, it is not clear to what extent Pi absorption is modulated by dietary Pi. Thus, we investigated 5/6 nephrectomized (Nx) Wistar rats to test whether acute variations in dietary Pi concentration over 2 days would alter hormones involved in Pi metabolism, expression of sodium-phosphate cotransporters, apoptosis, and the expression of matrix extracellular phosphoglycoprotein (MEPE) in different segments of the small intestine. The animals were divided into groups receiving different levels of dietary phosphate: low (Nx/LPi), normal (Nx/NPi), and high (Nx/HPi). Serum phosphate, fractional excretion of phosphate, intact serum fibroblast growth factor 23 (FGF-23), and parathyroid hormone (PTH) were significantly higher and ionized calcium was significantly lower in the Nx/HPi group than in the Nx/LPi group. The expression levels of NaPi-IIb and PiT-1/2 were increased in the total jejunum mucosa of the Nx/LPi group compared with the Nx/HPi group. Modification of Pi concentration in the diet affected the apoptosis of enterocytes, particularly with Pi overload. MEPE expression was higher in the Nx/HPi group than in the Nx/NPi. These data reveal the importance of early control of Pi in uremia to prevent an increase in serum PTH and FGF-23. Uremia may be a determining factor that explains the expressional modulation of the cotransporters in the small intestine segments.
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Affiliation(s)
| | | | | | | | | | - Patrícia Castelucci
- Department of Anatomy, Institute of Biomedical Sciences, Universidade de São Paulo, São Paulo, Brazil
| | - Rosa Maria Affonso Moysés
- Medical School, Division of Nephrology, Universidade de São Paulo, São Paulo, Brazil.,Universidade Nove de Julho - UNINOVE, São Paulo, Brazil
| | - Vanda Jorgetti
- Medical School, Division of Nephrology, Universidade de São Paulo, São Paulo, Brazil. .,Faculdade de Medicina, Serviço de Nefrologia, Universidade de São Paulo, Av. Dr. Arnaldo, 455, 3° andar, sala 3342, São Paulo, SP, 01246-903, Brazil.
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Chun S, Bamba T, Suyama T, Ishijima T, Fukusaki E, Abe K, Nakai Y. A High Phosphorus Diet Affects Lipid Metabolism in Rat Liver: A DNA Microarray Analysis. PLoS One 2016; 11:e0155386. [PMID: 27187182 PMCID: PMC4871335 DOI: 10.1371/journal.pone.0155386] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2015] [Accepted: 04/27/2016] [Indexed: 12/19/2022] Open
Abstract
A high phosphorus (HP) diet causes disorders of renal function, bone metabolism, and vascular function. We previously demonstrated that DNA microarray analysis is an appropriate method to comprehensively evaluate the effects of a HP diet on kidney dysfunction such as calcification, fibrillization, and inflammation. We reported that type IIb sodium-dependent phosphate transporter is significantly up-regulated in this context. In the present study, we performed DNA microarray analysis to investigate the effects of a HP diet on the liver, which plays a pivotal role in energy metabolism. DNA microarray analysis was performed with total RNA isolated from the livers of rats fed a control diet (containing 0.3% phosphorus) or a HP diet (containing 1.2% phosphorus). Gene Ontology analysis of differentially expressed genes (DEGs) revealed that the HP diet induced down-regulation of genes involved in hepatic amino acid catabolism and lipogenesis, while genes related to fatty acid β-oxidation process were up-regulated. Although genes related to fatty acid biosynthesis were down-regulated in HP diet-fed rats, genes important for the elongation and desaturation reactions of omega-3 and -6 fatty acids were up-regulated. Concentrations of hepatic arachidonic acid and eicosapentaenoic acid were increased in HP diet-fed rats. These essential fatty acids activate peroxisome proliferator-activated receptor alpha (PPARα), a transcription factor for fatty acid β-oxidation. Evaluation of the upstream regulators of DEGs using Ingenuity Pathway Analysis indicated that PPARα was activated in the livers of HP diet-fed rats. Furthermore, the serum concentration of fibroblast growth factor 21, a hormone secreted from the liver that promotes fatty acid utilization in adipose tissue as a PPARα target gene, was higher (p = 0.054) in HP diet-fed rats than in control diet-fed rats. These data suggest that a HP diet enhances energy expenditure through the utilization of free fatty acids released via lipolysis of white adipose tissue.
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Affiliation(s)
- Sunwoo Chun
- Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
| | - Takeshi Bamba
- Department of Biotechnology, Graduate School of Engineering, Osaka University, Suita, Osaka, Japan
| | - Tatsuya Suyama
- Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
| | - Tomoko Ishijima
- Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
| | - Eiichiro Fukusaki
- Department of Biotechnology, Graduate School of Engineering, Osaka University, Suita, Osaka, Japan
| | - Keiko Abe
- Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
- Project on Health and Anti-aging, Kanagawa Academy of Science and Technology Life Science & Environment Research Center, Kawasaki, Kanagawa, Japan
| | - Yuji Nakai
- Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
- * E-mail:
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Lin K, Rubinfeld B, Zhang C, Firestein R, Harstad E, Roth L, Tsai SP, Schutten M, Xu K, Hristopoulos M, Polakis P. Preclinical Development of an Anti-NaPi2b (SLC34A2) Antibody-Drug Conjugate as a Therapeutic for Non-Small Cell Lung and Ovarian Cancers. Clin Cancer Res 2015; 21:5139-50. [PMID: 26156394 DOI: 10.1158/1078-0432.ccr-14-3383] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2014] [Accepted: 06/15/2015] [Indexed: 11/16/2022]
Abstract
PURPOSE Antibody-drug conjugates (ADC) selectively deliver a cytotoxic drug to cells expressing an accessible antigenic target. Here, we have appended monomethyl auristatin E (MMAE) to an antibody recognizing the SLC34A2 gene product NaPi2b, the type II sodium-phosphate cotransporter, which is highly expressed on tumor surfaces of the lung, ovary, and thyroid as well as on normal lung pneumocytes. This study evaluated its efficacy and safety in preclinical studies. EXPERIMENTAL DESIGN The efficacy of anti-NaPi2b ADC was evaluated in mouse ovarian and non-small cell lung cancer (NSCLC) tumor xenograft models, and its toxicity was assessed in rats and cynomolgus monkeys. RESULTS We show here that an anti-NaPi2b ADC is effective in mouse ovarian and NSCLC tumor xenograft models and well-tolerated in rats and cynomolgus monkeys at levels in excess of therapeutic doses. Despite high levels of expression in normal lung of non-human primate, the cross-reactive ADC exhibited an acceptable safety profile with a dose-limiting toxicity unrelated to normal tissue target expression. The nonproliferative nature of normal pneumocytes, together with the antiproliferative mechanism of MMAE, likely mitigates the potential liability of this normal tissue expression. CONCLUSIONS Overall, our preclinical results suggest that the ADC targeting NaPi2b provides an effective new therapy for the treatment of NSCLC and ovarian cancer and is currently undergoing clinical developments.
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Affiliation(s)
- Kedan Lin
- Genentech Research and Early Development, South San Francisco, California
| | - Bonnee Rubinfeld
- Genentech Research and Early Development, South San Francisco, California
| | - Crystal Zhang
- Genentech Research and Early Development, South San Francisco, California
| | - Ron Firestein
- Genentech Research and Early Development, South San Francisco, California
| | - Eric Harstad
- Genentech Research and Early Development, South San Francisco, California
| | - Leslie Roth
- Genentech Research and Early Development, South San Francisco, California
| | - Siao Ping Tsai
- Genentech Research and Early Development, South San Francisco, California
| | - Melissa Schutten
- Genentech Research and Early Development, South San Francisco, California
| | - Keyang Xu
- Genentech Research and Early Development, South San Francisco, California
| | - Maria Hristopoulos
- Genentech Research and Early Development, South San Francisco, California
| | - Paul Polakis
- Genentech Research and Early Development, South San Francisco, California.
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10
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Hong SH, Park SJ, Lee S, Kim S, Cho MH. Biological effects of inorganic phosphate: potential signal of toxicity. J Toxicol Sci 2015; 40:55-69. [DOI: 10.2131/jts.40.55] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- Seong-Ho Hong
- Laboratory of Toxicology, BK21 PLUS Program for Creative Veterinary Science Research, Research Institute for Veterinary Science and College of Veterinary Medicine, Seoul National University, Korea
| | - Sung-Jin Park
- Laboratory of Toxicology, BK21 PLUS Program for Creative Veterinary Science Research, Research Institute for Veterinary Science and College of Veterinary Medicine, Seoul National University, Korea
| | - Somin Lee
- Graduate Group of Tumor Biology, Seoul National University, Korea
- Laboratory of Toxicology, BK21 PLUS Program for Creative Veterinary Science Research, Research Institute for Veterinary Science and College of Veterinary Medicine, Seoul National University, Korea
| | - Sanghwa Kim
- Graduate Group of Tumor Biology, Seoul National University, Korea
- Laboratory of Toxicology, BK21 PLUS Program for Creative Veterinary Science Research, Research Institute for Veterinary Science and College of Veterinary Medicine, Seoul National University, Korea
| | - Myung-Haing Cho
- Advanced Institute of Convergence Technology, Seoul National University, Korea
- Graduate Group of Tumor Biology, Seoul National University, Korea
- Graduate School of Convergence Science and Technology, Seoul National University, Korea
- Laboratory of Toxicology, BK21 PLUS Program for Creative Veterinary Science Research, Research Institute for Veterinary Science and College of Veterinary Medicine, Seoul National University, Korea
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11
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Lederer E, Miyamoto KI. Clinical consequences of mutations in sodium phosphate cotransporters. Clin J Am Soc Nephrol 2012; 7:1179-87. [PMID: 22516291 DOI: 10.2215/cjn.09090911] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Three families of sodium phosphate cotransporters have been described. Their specific roles in human health and disease have not been defined. Review of the literature reveals that the type II sodium phosphate cotransporters play a significant role in transepithelial transport in a number of tissues including kidney, intestine, salivary gland, mammary gland, and lung. The type I transporters seem to play a major role in renal urate handling and mutations in these proteins have been implicated in susceptibility to gout. The ubiquitously expressed type III transporters play a lesser role in phosphate homeostasis but contribute to cellular phosphate uptake, mineralization, and inflammation. The recognition of species differences in the expression, regulation, and function of these transport proteins suggests an urgent need to find ways to study them in humans.
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Affiliation(s)
- Eleanor Lederer
- University of Louisville School of Medicine, Louisville, KY 40202, USA.
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12
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Suyama T, Okada S, Ishijima T, Iida K, Abe K, Nakai Y. High phosphorus diet-induced changes in NaPi-IIb phosphate transporter expression in the rat kidney: DNA microarray analysis. PLoS One 2012; 7:e29483. [PMID: 22235299 PMCID: PMC3250443 DOI: 10.1371/journal.pone.0029483] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2011] [Accepted: 11/29/2011] [Indexed: 01/25/2023] Open
Abstract
The mechanism by which phosphorus levels are maintained in the body was investigated by analyzing changes in gene expression in the rat kidney following administration of a high phosphorus (HP) diet. Male Wistar rats were divided into two groups and fed a diet containing 0.3% (control) or 1.2% (HP) phosphorous for 24 days. Phosphorous retention was not significantly increased in HP rats, but fractional excretion of phosphorus was significantly increased in the HP group compared to controls, with an excessive amount of the ingested phosphorus being passed through the body. DNA microarray analysis of kidney tissue from both groups revealed changes in gene expression profile induced by a HP diet. Among the genes that were upregulated, Gene Ontology (GO) terms related to ossification, collagen fibril organization, and inflammation and immune response were significantly enriched. In particular, there was significant upregulation of type IIb sodium-dependent phosphate transporter (NaPi-IIb) in the HP rat kidney compared to control rats. This upregulation was confirmed by in situ hybridization. Distinct signals for NaPi-IIb in both the cortex and medulla of the kidney were apparent in the HP group, while the corresponding signals were much weaker in the control group. Immunohistochemical analysis showed that NaPi-IIb localized to the basolateral side of kidney epithelial cells surrounding the urinary duct in HP rats but not in control animals. These data suggest that NaPi-IIb is upregulated in the kidney in response to the active excretion of phosphate in HP diet-fed rats.
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Affiliation(s)
- Tatsuya Suyama
- Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
| | - Shinji Okada
- Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
| | - Tomoko Ishijima
- Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
| | - Kota Iida
- Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
| | - Keiko Abe
- Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
| | - Yuji Nakai
- Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
- * E-mail:
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13
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Gryshkova V, Lituiev D, Savinska L, Ovcharenko G, Gout I, Filonenko V, Kiyamova R. Generation of Monoclonal Antibodies Against Tumor-Associated Antigen MX35/sodium-Dependent Phosphate Transporter NaPi2b. Hybridoma (Larchmt) 2011; 30:37-42. [DOI: 10.1089/hyb.2010.0064] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Vitalina Gryshkova
- Department of Cell Signalling, Institute of Molecular Biology and Genetics, NAS of Ukraine, Kyiv, Ukraine
| | - Dmytro Lituiev
- Department of Cell Signalling, Institute of Molecular Biology and Genetics, NAS of Ukraine, Kyiv, Ukraine
| | - Liliya Savinska
- Department of Cell Signalling, Institute of Molecular Biology and Genetics, NAS of Ukraine, Kyiv, Ukraine
| | - Galina Ovcharenko
- Department of Cell Signalling, Institute of Molecular Biology and Genetics, NAS of Ukraine, Kyiv, Ukraine
| | - Ivan Gout
- Department of Cell Signalling, Institute of Molecular Biology and Genetics, NAS of Ukraine, Kyiv, Ukraine
- Department of Structural and Molecular Biology, University College London, London, United Kingdom
| | - Valeriy Filonenko
- Department of Cell Signalling, Institute of Molecular Biology and Genetics, NAS of Ukraine, Kyiv, Ukraine
| | - Ramziya Kiyamova
- Department of Cell Signalling, Institute of Molecular Biology and Genetics, NAS of Ukraine, Kyiv, Ukraine
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14
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Arsenate transport by sodium/phosphate cotransporter type IIb. Toxicol Appl Pharmacol 2010; 247:36-40. [DOI: 10.1016/j.taap.2010.05.012] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2010] [Revised: 05/17/2010] [Accepted: 05/19/2010] [Indexed: 12/26/2022]
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15
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Beck L, Leroy C, Beck-Cormier S, Forand A, Salaün C, Paris N, Bernier A, Ureña-Torres P, Prié D, Ollero M, Coulombel L, Friedlander G. The phosphate transporter PiT1 (Slc20a1) revealed as a new essential gene for mouse liver development. PLoS One 2010; 5:e9148. [PMID: 20161774 PMCID: PMC2818845 DOI: 10.1371/journal.pone.0009148] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2009] [Accepted: 01/12/2010] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND PiT1 (or SLC20a1) encodes a widely expressed plasma membrane protein functioning as a high-affinity Na(+)-phosphate (Pi) cotransporter. As such, PiT1 is often considered as a ubiquitous supplier of Pi for cellular needs regardless of the lack of experimental data. Although the importance of PiT1 in mineralizing processes have been demonstrated in vitro in osteoblasts, chondrocytes and vascular smooth muscle cells, in vivo evidence is missing. METHODOLOGY/PRINCIPAL FINDINGS To determine the in vivo function of PiT1, we generated an allelic series of PiT1 mutations in mice by combination of wild-type, hypomorphic and null PiT1 alleles expressing from 100% to 0% of PiT1. In this report we show that complete deletion of PiT1 results in embryonic lethality at E12.5. PiT1-deficient embryos display severely hypoplastic fetal livers and subsequent reduced hematopoiesis resulting in embryonic death from anemia. We show that the anemia is not due to placental, yolk sac or vascular defects and that hematopoietic progenitors have no cell-autonomous defects in proliferation and differentiation. In contrast, mutant fetal livers display decreased proliferation and massive apoptosis. Animals carrying two copies of hypomorphic PiT1 alleles (resulting in 15% PiT1 expression comparing to wild-type animals) survive at birth but are growth-retarded and anemic. The combination of both hypomorphic and null alleles in heterozygous compounds results in late embryonic lethality (E14.5-E16.5) with phenotypic features intermediate between null and hypomorphic mice. In the three mouse lines generated we could not evidence defects in early skeleton formation. CONCLUSION/SIGNIFICANCE This work is the first to illustrate a specific in vivo role for PiT1 by uncovering it as being a critical gene for normal developmental liver growth.
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MESH Headings
- Animals
- Apoptosis
- Cell Count
- Cell Proliferation
- Cells, Cultured
- Embryo, Mammalian/abnormalities
- Embryo, Mammalian/metabolism
- Erythrocytes/metabolism
- Female
- Gene Expression Regulation, Developmental
- Genes, Essential
- Genotype
- Hematopoietic Stem Cells/metabolism
- Liver/cytology
- Liver/embryology
- Liver/metabolism
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Inbred Strains
- Mice, Knockout
- Mutation
- Reverse Transcriptase Polymerase Chain Reaction
- Sodium-Phosphate Cotransporter Proteins, Type III/deficiency
- Sodium-Phosphate Cotransporter Proteins, Type III/genetics
- Time Factors
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Affiliation(s)
- Laurent Beck
- INSERM, U845, Centre de Recherche Croissance et Signalisation, Paris, France.
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16
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Villa-Bellosta R, Ravera S, Sorribas V, Stange G, Levi M, Murer H, Biber J, Forster IC. The Na+-Pi cotransporter PiT-2 (SLC20A2) is expressed in the apical membrane of rat renal proximal tubules and regulated by dietary Pi. Am J Physiol Renal Physiol 2009; 296:F691-9. [PMID: 19073637 PMCID: PMC2670642 DOI: 10.1152/ajprenal.90623.2008] [Citation(s) in RCA: 133] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2008] [Accepted: 12/08/2008] [Indexed: 12/26/2022] Open
Abstract
The principal mediators of renal phosphate (P(i)) reabsorption are the SLC34 family proteins NaPi-IIa and NaPi-IIc, localized to the proximal tubule (PT) apical membrane. Their abundance is regulated by circulatory factors and dietary P(i). Although their physiological importance has been confirmed in knockout animal studies, significant P(i) reabsorptive capacity remains, which suggests the involvement of other secondary-active P(i) transporters along the nephron. Here we show that a member of the SLC20 gene family (PiT-2) is localized to the brush-border membrane (BBM) of the PT epithelia and that its abundance, confirmed by Western blot and immunohistochemistry of rat kidney slices, is regulated by dietary P(i). In rats treated chronically on a high-P(i) (1.2%) diet, there was a marked decrease in the apparent abundance of PiT-2 protein in kidney slices compared with those from rats kept on a chronic low-P(i) (0.1%) diet. In Western blots of BBM from rats that were switched from a chronic low- to high-P(i) diet, NaPi-IIa showed rapid downregulation after 2 h; PiT-2 was also significantly downregulated at 24 h and NaPi-IIc after 48 h. For the converse dietary regime, NaPi-IIa showed adaptation within 8 h, whereas PiT-2 and NaPi-IIc showed a slower adaptive trend. Our findings suggest that PiT-2, until now considered as a ubiquitously expressed P(i) housekeeping transporter, is a novel mediator of P(i) reabsorption in the PT under conditions of acute P(i) deprivation, but with a different adaptive time course from NaPi-IIa and NaPi-IIc.
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Affiliation(s)
- Ricardo Villa-Bellosta
- Institute of Physiology, Univ. of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
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17
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Shibasaki Y, Etoh N, Hayasaka M, Takahashi MO, Kakitani M, Yamashita T, Tomizuka K, Hanaoka K. Targeted deletion of the tybe IIb Na(+)-dependent Pi-co-transporter, NaPi-IIb, results in early embryonic lethality. Biochem Biophys Res Commun 2009; 381:482-6. [PMID: 19233126 DOI: 10.1016/j.bbrc.2009.02.067] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2009] [Accepted: 02/17/2009] [Indexed: 11/25/2022]
Abstract
NaPi-IIb encodes a Na(+)-dependent Pi co-transporter, which is expressed in various adult tissues and mediates transport of extracellular Pi ions coupling with Na(+) ion. To define the role of NaPi-IIbin vivo, NaPi-IIb gene deficient mice were generated utilizing targeted mutagenesis, yielding viable, heterozygous NaPi-IIb mice. In contrast, homozygous NaPi-IIb mice died in utero soon after implantation, indicating that NaPi-IIb was essential for early embryonic development. In situ hybridization revealed NaPi-IIb mRNA expression in the parietal endoderm, followed by the visceral endoderm, at a time point prior to establishment of a functioning chorio-allantoic placenta. At the time point of functional placenta development, the main site of NaPi-IIb production resided in the labyrinthine zone, where embryonic and maternal circulations were in closest contact. Expression patterns of NaPi-IIb suggest that NaPi-IIb plays an important role in Pi absorption from maternal circulation.
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Affiliation(s)
- Yuri Shibasaki
- Department of Bioscience, Kitasato University School of Science, Sagamihara, Kanagawa, Japan
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18
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Kiyamova R, Gryshkova V, Ovcharenko G, Lituyev D, Malyuchik S, Usenko V, Khozhayenko Y, Gurtovyy V, Yin B, Ritter G, Old L, Filonenko V, Gout I. Development of monoclonal antibodies specific for the human sodium-dependent phosphate co-transporter NaPi2b. Hybridoma (Larchmt) 2008; 27:277-84. [PMID: 18724815 DOI: 10.1089/hyb.2008.0015] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Homeostasis of inorganic phosphate in the human body is maintained by regulated absorption, metabolism, and excretion. Sodium-dependent phosphate transporters (NaPi) mediate the transport of inorganic phosphate (P(i)) in cells in response to dietary phosphate consumption, hormones, and growth factors. NaPi2b is a member of the sodium-dependent phosphate transporter family, with a distinct pattern of expression and regulation. Signaling pathways activated by mitogens, glucocorticoids, and metabolic factors have been implicated in regulating P(i) transport via NaPi2b. Inactivation of NaPi2b function by mutations has been linked to human pathologies, such as pulmonary alveolar microlithiasis. In this study, we describe the generation and characterization of monoclonal antibodies against human NaPi2b. The monoclonal antibodies were shown to recognize specifically transiently overexpressed and endogenous NaPi2b in commonly used immunoassays, including Western blotting, immunoprecipitation, and immunohistochemistry. These properties make them particularly valuable reagents for elucidating NaPi2b function in health and disease.
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Affiliation(s)
- Ramziya Kiyamova
- Department of Cell Signaling, Institute of Molecular Biology and Genetics, NAS of Ukraine, Kyiv, Ukraine
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19
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Xu CX, Jin H, Lim HT, Kim JE, Shin JY, Lee ES, Chung YS, Lee YS, Beck G, Lee KH, Cho MH. High dietary inorganic phosphate enhances cap-dependent protein translation, cell-cycle progression, and angiogenesis in the livers of young mice. Am J Physiol Gastrointest Liver Physiol 2008; 295:G654-63. [PMID: 18703640 PMCID: PMC2575911 DOI: 10.1152/ajpgi.90213.2008] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Inorganic phosphate (P(i)) plays a key role in diverse physiological functions. Recent studies have indicated that P(i) affects Akt signaling through the sodium-dependent phosphate cotransporter. Akt signaling, in turn, plays an important role in liver development; however, the effects of high dietary P(i) on the liver have not been investigated. Here, we examined the effects of high dietary phosphate on the liver in developing mice. We found that high dietary P(i) increased liver mass through enhancing Akt-related cap-dependent protein translation, cell cycle progression, and angiogenesis. Thus careful regulation of P(i) consumption may be important in maintaining normal development of the liver.
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Affiliation(s)
- Cheng-Xiong Xu
- Laboratory of Toxicology, College of Veterinary Medicine, Nano Systems Institute-National Core Research Center, Department of Food and Nutrition, College of Human Ecology, Seoul National University, Seoul, Korea; Division of Endocrinology, Metabolism, and Lipids, Emory University School of Medicine, Atlanta, Georgia; Laboratory of Radiation Molecular Oncology, Korea Institute of Radiological & Medical Sciences, Seoul, Korea; Center for Developmental Pharmacology and Toxicology, Seattle Children's Hospital Research Institute, Seattle, Washington; and National Institute of Toxicological Research, Korea Food and Drug Administration, Seoul, Korea
| | - Hua Jin
- Laboratory of Toxicology, College of Veterinary Medicine, Nano Systems Institute-National Core Research Center, Department of Food and Nutrition, College of Human Ecology, Seoul National University, Seoul, Korea; Division of Endocrinology, Metabolism, and Lipids, Emory University School of Medicine, Atlanta, Georgia; Laboratory of Radiation Molecular Oncology, Korea Institute of Radiological & Medical Sciences, Seoul, Korea; Center for Developmental Pharmacology and Toxicology, Seattle Children's Hospital Research Institute, Seattle, Washington; and National Institute of Toxicological Research, Korea Food and Drug Administration, Seoul, Korea
| | - Hwang-Tae Lim
- Laboratory of Toxicology, College of Veterinary Medicine, Nano Systems Institute-National Core Research Center, Department of Food and Nutrition, College of Human Ecology, Seoul National University, Seoul, Korea; Division of Endocrinology, Metabolism, and Lipids, Emory University School of Medicine, Atlanta, Georgia; Laboratory of Radiation Molecular Oncology, Korea Institute of Radiological & Medical Sciences, Seoul, Korea; Center for Developmental Pharmacology and Toxicology, Seattle Children's Hospital Research Institute, Seattle, Washington; and National Institute of Toxicological Research, Korea Food and Drug Administration, Seoul, Korea
| | - Ji-Eun Kim
- Laboratory of Toxicology, College of Veterinary Medicine, Nano Systems Institute-National Core Research Center, Department of Food and Nutrition, College of Human Ecology, Seoul National University, Seoul, Korea; Division of Endocrinology, Metabolism, and Lipids, Emory University School of Medicine, Atlanta, Georgia; Laboratory of Radiation Molecular Oncology, Korea Institute of Radiological & Medical Sciences, Seoul, Korea; Center for Developmental Pharmacology and Toxicology, Seattle Children's Hospital Research Institute, Seattle, Washington; and National Institute of Toxicological Research, Korea Food and Drug Administration, Seoul, Korea
| | - Ji-Young Shin
- Laboratory of Toxicology, College of Veterinary Medicine, Nano Systems Institute-National Core Research Center, Department of Food and Nutrition, College of Human Ecology, Seoul National University, Seoul, Korea; Division of Endocrinology, Metabolism, and Lipids, Emory University School of Medicine, Atlanta, Georgia; Laboratory of Radiation Molecular Oncology, Korea Institute of Radiological & Medical Sciences, Seoul, Korea; Center for Developmental Pharmacology and Toxicology, Seattle Children's Hospital Research Institute, Seattle, Washington; and National Institute of Toxicological Research, Korea Food and Drug Administration, Seoul, Korea
| | - Eun-Sun Lee
- Laboratory of Toxicology, College of Veterinary Medicine, Nano Systems Institute-National Core Research Center, Department of Food and Nutrition, College of Human Ecology, Seoul National University, Seoul, Korea; Division of Endocrinology, Metabolism, and Lipids, Emory University School of Medicine, Atlanta, Georgia; Laboratory of Radiation Molecular Oncology, Korea Institute of Radiological & Medical Sciences, Seoul, Korea; Center for Developmental Pharmacology and Toxicology, Seattle Children's Hospital Research Institute, Seattle, Washington; and National Institute of Toxicological Research, Korea Food and Drug Administration, Seoul, Korea
| | - Youn-Sun Chung
- Laboratory of Toxicology, College of Veterinary Medicine, Nano Systems Institute-National Core Research Center, Department of Food and Nutrition, College of Human Ecology, Seoul National University, Seoul, Korea; Division of Endocrinology, Metabolism, and Lipids, Emory University School of Medicine, Atlanta, Georgia; Laboratory of Radiation Molecular Oncology, Korea Institute of Radiological & Medical Sciences, Seoul, Korea; Center for Developmental Pharmacology and Toxicology, Seattle Children's Hospital Research Institute, Seattle, Washington; and National Institute of Toxicological Research, Korea Food and Drug Administration, Seoul, Korea
| | - Yeon-Sook Lee
- Laboratory of Toxicology, College of Veterinary Medicine, Nano Systems Institute-National Core Research Center, Department of Food and Nutrition, College of Human Ecology, Seoul National University, Seoul, Korea; Division of Endocrinology, Metabolism, and Lipids, Emory University School of Medicine, Atlanta, Georgia; Laboratory of Radiation Molecular Oncology, Korea Institute of Radiological & Medical Sciences, Seoul, Korea; Center for Developmental Pharmacology and Toxicology, Seattle Children's Hospital Research Institute, Seattle, Washington; and National Institute of Toxicological Research, Korea Food and Drug Administration, Seoul, Korea
| | - George Beck
- Laboratory of Toxicology, College of Veterinary Medicine, Nano Systems Institute-National Core Research Center, Department of Food and Nutrition, College of Human Ecology, Seoul National University, Seoul, Korea; Division of Endocrinology, Metabolism, and Lipids, Emory University School of Medicine, Atlanta, Georgia; Laboratory of Radiation Molecular Oncology, Korea Institute of Radiological & Medical Sciences, Seoul, Korea; Center for Developmental Pharmacology and Toxicology, Seattle Children's Hospital Research Institute, Seattle, Washington; and National Institute of Toxicological Research, Korea Food and Drug Administration, Seoul, Korea
| | - Kee Ho Lee
- Laboratory of Toxicology, College of Veterinary Medicine, Nano Systems Institute-National Core Research Center, Department of Food and Nutrition, College of Human Ecology, Seoul National University, Seoul, Korea; Division of Endocrinology, Metabolism, and Lipids, Emory University School of Medicine, Atlanta, Georgia; Laboratory of Radiation Molecular Oncology, Korea Institute of Radiological & Medical Sciences, Seoul, Korea; Center for Developmental Pharmacology and Toxicology, Seattle Children's Hospital Research Institute, Seattle, Washington; and National Institute of Toxicological Research, Korea Food and Drug Administration, Seoul, Korea
| | - Myung-Haing Cho
- Laboratory of Toxicology, College of Veterinary Medicine, Nano Systems Institute-National Core Research Center, Department of Food and Nutrition, College of Human Ecology, Seoul National University, Seoul, Korea; Division of Endocrinology, Metabolism, and Lipids, Emory University School of Medicine, Atlanta, Georgia; Laboratory of Radiation Molecular Oncology, Korea Institute of Radiological & Medical Sciences, Seoul, Korea; Center for Developmental Pharmacology and Toxicology, Seattle Children's Hospital Research Institute, Seattle, Washington; and National Institute of Toxicological Research, Korea Food and Drug Administration, Seoul, Korea
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20
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Villa-Bellosta R, Sorribas V. Role of rat sodium/phosphate cotransporters in the cell membrane transport of arsenate. Toxicol Appl Pharmacol 2008; 232:125-34. [PMID: 18586044 DOI: 10.1016/j.taap.2008.05.026] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2008] [Revised: 05/29/2008] [Accepted: 05/29/2008] [Indexed: 01/20/2023]
Abstract
Inorganic arsenate (As(V)) is a common contaminant of underground water. Following oral exposure, it is assumed that As(V) is distributed and crosses cell membranes through inorganic phosphate (Pi) transporters. We have tested this hypothesis by studying the inhibition of rat Na/Pi cotransporters by As(V) in Xenopus laevis oocytes and in several rat tissues. The ubiquitously expressed type III Pi transporters (PiT-1 and PiT-2) showed a low affinity for As(V) (K(i) approximately 3.8 mM), similar to the Pi transport system in aortic vascular smooth muscle cells (K(i) 1.5 mM). The type II renal isoforms, NaPi-IIa and NaPi-IIc, were also poorly inhibited by As(V) (K(i) approximately 1 mM), similar to the Pi transport from kidney cortex brush-border membrane (BBM) vesicles. Conversely, the high-affinity intestinal transporter, NaPi-IIb, was very efficiently inhibited with a K(i) of 51 microM, similar to the Pi transport from intestinal BBM vesicles. Taking into account the 1.1 mM Pi in blood and renal ultrafiltrate, and the nanomolar range of As(V) exposures, we have determined that the contribution by Na/Pi cotransporters to As(V) membrane transport is negligible, given that 10-15 mM As(V) would be necessary in these fluids to be significantly transported. Intestinal transport is an exception, because Pi competition is weak, thereby considering that its concentration in lumen mainly depends on low Pi levels from ingested fresh water, and because As(V) very efficiently inhibits Pi intestinal transport. Our data agree with current toxicokinetic knowledge, and they explain the asymmetric excretion of trivalent and pentavalent arsenic species into bile and urine.
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21
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Virkki LV, Biber J, Murer H, Forster IC. Phosphate transporters: a tale of two solute carrier families. Am J Physiol Renal Physiol 2007; 293:F643-54. [PMID: 17581921 DOI: 10.1152/ajprenal.00228.2007] [Citation(s) in RCA: 175] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Phosphate is an essential component of life and must be actively transported into cells against its electrochemical gradient. In vertebrates, two unrelated families of Na+ -dependent P(i) transporters carry out this task. Remarkably, the two families transport different P(i) species: whereas type II Na+/P(i) cotransporters (SCL34) prefer divalent HPO(4)(2-), type III Na(+)/P(i) cotransporters (SLC20) transport monovalent H2PO(4)(-). The SCL34 family comprises both electrogenic and electroneutral members that are expressed in various epithelia and other polarized cells. Through regulated activity in apical membranes of the gut and kidney, they maintain body P(i) homeostasis, and in salivary and mammary glands, liver, and testes they play a role in modulating the P(i) content of luminal fluids. The two SLC20 family members PiT-1 and PiT-2 are electrogenic and ubiquitously expressed and may serve a housekeeping role for cell P(i) homeostasis; however, also more specific roles are emerging for these transporters in, for example, bone mineralization. In this review, we focus on recent advances in the characterization of the transport kinetics, structure-function relationships, and physiological implications of having two distinct Na+/P(i) cotransporter families.
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Affiliation(s)
- Leila V Virkki
- Institute of Physiology and Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland
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22
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Ravera S, Virkki LV, Murer H, Forster IC. Deciphering PiT transport kinetics and substrate specificity using electrophysiology and flux measurements. Am J Physiol Cell Physiol 2007; 293:C606-20. [PMID: 17494632 DOI: 10.1152/ajpcell.00064.2007] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Members of the SLC20 family or type III Na(+) -coupled P(i) cotransporters (PiT-1, PiT-2) are ubiquitously expressed in mammalian tissue and are thought to perform a housekeeping function for intracellular P(i) homeostasis. Previous studies have shown that PiT-1 and PiT-2 mediate electrogenic P(i) cotransport when expressed in Xenopus oocytes, but only limited kinetic characterizations were made. To address this shortcoming, we performed a detailed analysis of SLC20 transport function. Three SLC20 clones (Xenopus PiT-1, human PiT-1, and human PiT-2) were expressed in Xenopus oocytes. Each clone gave robust Na(+)-dependent (32)P(i) uptake, but only Xenopus PiT-1 showed sufficient activity for complete kinetic characterization by using two-electrode voltage clamp and radionuclide uptake. Transport activity was also documented with Li(+) substituted for Na(+). The dependence of the P(i)-induced current on P(i) concentration was Michaelian, and the dependence on Na(+) concentration indicated weak cooperativity. The dependence on external pH was unique: the apparent P(i) affinity constant showed a minimum in the pH range 6.2-6.8 of approximately 0.05 mM and increased to approximately 0.2 mM at pH 5.0 and pH 8.0. Xenopus PiT-1 stoichiometry was determined by dual (22)Na-(32)P(i) uptake and suggested a 2:1 Na(+):P(i) stoichiometry. A correlation of (32)P(i) uptake and net charge movement indicated one charge translocation per P(i). Changes in oocyte surface pH were consistent with transport of monovalent P(i). On the basis of the kinetics of substrate interdependence, we propose an ordered binding scheme of Na(+):H(2)PO(4)(-):Na(+). Significantly, in contrast to type II Na(+)-P(i) cotransporters, the transport inhibitor phosphonoformic acid did not inhibit PiT-1 or PiT-2 activity.
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Affiliation(s)
- Silvia Ravera
- Institute of Physiology, University of Zurich, Winterthurerstrasse 190, Zurich, Switzerland
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23
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Lundquist P, Murer H, Biber J. Type II Na+-Pi cotransporters in osteoblast mineral formation: regulation by inorganic phosphate. Cell Physiol Biochem 2007; 19:43-56. [PMID: 17310099 DOI: 10.1159/000099191] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/19/2006] [Indexed: 01/09/2023] Open
Abstract
During calcification of bone, large amounts of phosphate (P(i)) must be transported from the circulation to the osteoid. Likely candidates for osteoblast P(i) transport are the type II sodium-phosphate cotransporters NaPi-IIa and NaPi-IIb that facilitate transcellular P(i) flux in kidney and intestine, respectively. We have therefore determined the 'cotransporters' expression in osteoblast-like cells. We have also studied the 'cotransporters' regulation by P(i) and during mineralization in vitro. Phosphate uptake and cotransporter protein expression was investigated at early, late and mineralizing culture stages of mouse (MC3T3-E1) and rat (UMR-106) osteoblast-like cells. Both NaPi-IIa and NaPi-IIb were expressed by both osteoblast-like cell lines. NaPi-IIa was upregulated in both cell lines one week after confluency. After 7 days in 3mM P(i) NaPi-IIa was strongly upregulated in both cell lines. NaPi-IIb expression was unaffected by both culture stage and P(i) supplementation. The expression of both cotransporters was unaffected by P(i) deprivation. In vitro mineralization at 1.5mM P(i) was preceded by a three-fold increase in osteoblast sodium-dependent P(i) uptake and a corresponding upregulation of both NaPi-IIa and NaPi-IIb. Their expression thus seem regulated by phosphate in a manner consistent with their playing a role in transcellular P(i) flux during mineralization.
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Affiliation(s)
- Patrik Lundquist
- Institute for Physiology and Center for Integrative Human Physiology, University of Zürich, Switzerland.
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24
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Forster IC, Virkki L, Bossi E, Murer H, Biber J. Electrogenic kinetics of a mammalian intestinal type IIb Na(+)/P(i) cotransporter. J Membr Biol 2007; 212:177-90. [PMID: 17342377 DOI: 10.1007/s00232-006-0016-3] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2006] [Revised: 06/08/2006] [Indexed: 10/23/2022]
Abstract
The kinetics of a type IIb Na(+)-coupled inorganic phosphate (Pi) cotransporter (NaPi-IIb) cloned from mouse small intestine were studied using the two-electrode voltage clamp applied to Xenopus oocytes. In the steady state, mouse NaPi-IIb showed a curvilinear I-V relationship, with rate-limiting behavior only for depolarizing potentials. The Pi dose dependence was Michaelian, with an apparent affinity constant for Pi (Km(pi)) of 10 +/- 1 microM: at -60 mV. Unlike for rat NaPi-IIa, (Km(pi)) increased with membrane hyperpolarization, as reported for human NaPi-IIa, flounder NaPi-IIb and zebrafish NaPi-IIb2. The apparent affinity constant for Na(+) (Km(na)) was 23 +/- 1 mM: at -60 mV, and the Na(+) activation was cooperative with a Hill coefficient of approximately 2. Pre-steady-state currents were documented in the absence of Pi and showed a strong dependence on external Na(+). The hyperpolarizing shift of the charge distribution midpoint potential was 65 mV/log[Na]. Approximately half the moveable charge was attributable to the empty carrier. A comparison of the voltage dependence of steady-state Pi-induced current and pre-steady-state charge movement indicated that for -120 mV <or= V <or= 0 mV the voltage dependence of the empty carrier was the main determinant of the curvilinear steady-state cotransport characteristic. External protons partially inhibited NaPi-IIb steady-state activity, independent of the titration of mono- and divalent Pi, and immobilized pre-steady-state charge movements associated with the first Na(+) binding step.
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Affiliation(s)
- Ian C Forster
- Institute of Physiology and Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland.
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25
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Virkki LV, Murer H, Forster IC. Voltage clamp fluorometric measurements on a type II Na+-coupled Pi cotransporter: shedding light on substrate binding order. ACTA ACUST UNITED AC 2006; 127:539-55. [PMID: 16636203 PMCID: PMC2151518 DOI: 10.1085/jgp.200609496] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Voltage clamp fluorometry (VCF) combines conventional two-electrode voltage clamp with fluorescence measurements to detect protein conformational changes, as sensed by a fluorophore covalently attached to the protein. We have applied VCF to a type IIb Na+-coupled phosphate cotransporter (NaPi-IIb), in which a novel cysteine was introduced in the putative third extracellular loop and expressed in Xenopus oocytes. Labeling this cysteine (S448C) with methanethiosulfonate (MTS) reagents blocked cotransport function, however previous electrophysiological studies (Lambert G., I.C. Forster, G. Stange, J. Biber, and H. Murer. 1999. J. Gen. Physiol. 114:637–651) suggest that substrate interactions with the protein can still occur, thus permitting study of a limited subset of states. After labeling S448C with the fluorophore tetramethylrhodamine MTS, we detected voltage- and substrate-dependent changes in fluorescence (ΔF), which suggested that this site lies in an environment that is affected by conformational change in the protein. ΔF was substrate dependent (no ΔF was detectable in 0 mM Na+) and showed little correlation with presteady-state charge movements, indicating that the two signals provide insight into different underlying physical processes. Interpretation of ion substitution experiments indicated that the substrate binding order differs from our previous model (Forster, I., N. Hernando, J. Biber, and H. Murer. 1998. J. Gen. Physiol. 112:1–18). In the new model, two (rather than one) Na+ ions precede Pi binding, and only the second Na+ binding transition is voltage dependent. Moreover, we show that Li+, which does not drive cotransport, interacts with the first Na+ binding transition. The results were incorporated in a new model of the transport cycle of type II Na+/Pi cotransporters, the validity of which is supported by simulations that successfully predict the voltage and substrate dependency of the experimentally determined fluorescence changes.
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Affiliation(s)
- Leila V Virkki
- Institute for Physiology and the Center for Integrative Human Physiology, University of Zurich, Switzerland
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Shojaiefard M, Lang F. Stimulation of the intestinal phosphate transporter SLC34A2 by the protein kinase mTOR. Biochem Biophys Res Commun 2006; 345:1611-4. [PMID: 16730658 DOI: 10.1016/j.bbrc.2006.05.067] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2006] [Accepted: 05/12/2006] [Indexed: 01/27/2023]
Abstract
Adequate phosphate homeostasis is of critical importance for a wide variety of functions including bone mineralization and energy metabolism. Phosphate balance is a function of intestinal absorption and renal elimination, which are both under tight hormonal control. Intestinal phosphate absorption is accomplished by the Na(+), phosphate cotransporter NaPi IIb (SLC34A2). Signaling mechanisms mediating hormonal regulation of SLC34A2 are incompletely understood. The mammalian target of rapamycin (mTOR) is a kinase regulating a variety of nutrient transporters. The present experiments explored whether mTOR regulates the activity of SLC34A2. In Xenopus oocytes expressing SLC34A2 but not in water injected oocytes phosphate (1 mM) induced a current (Ip) which was significantly enhanced by coexpression of mTOR. Preincubation of the oocytes for 24 h with rapamycin (50 nM) did not significantly affect Ip in the absence of mTOR but virtually abolished the increase of Ip following coexpression of mTOR. The wild type serum and glucocorticoid inducible kinase SGK1 and the constitutively active (S422D)SGK1 similarly stimulated Ip, an effect again reversed by rapamycin. Coexpression of the inactive mutant of the serum and glucocorticoid inducible kinase (K119N)SGK1 significantly decreased Ip and abrogated the stimulating effect of mTOR on Ip. In conclusion, mTOR and SGK1 cooperate in the stimulation of the intestinal phosphate transporter SLC34A2.
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