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Heini Murer - One of the best experts on this subject based on the ideXlab platform.

  • functionally important residues in the predicted 3rd transmembrane domain of the type iia Sodium Phosphate Cotransporter napi iia
    The Journal of Membrane Biology, 2005
    Co-Authors: Leila V Virkki, Ian C. Forster, Jürg Biber, Andrea Bacconi, Heini Murer
    Abstract:

    The type IIa Na+/Pi, Cotransporter (NaPi-IIa) mediates electrogenic transport of three Na+ and one divalent Pi ion (and one net positive charge) across the cell membrane. Sequence comparison of electrogenic NaPi-IIa and IIb isoforms with the electroneutral NaPi-IIc isoform pointed to the third transmembrane domain (TMD-3) as a possibly significant determinant of substrate binding. To elucidate the role of TMD-3 in the topology and mechanism underlying NaPi-IIa function we subjected it to cysteine scanning mutagenesis. The constructs were expressed in Xenopus oocytes and Pi transport kinetics were assayed by electrophysiology and radiotracer uptake. Cys substitution resulted in only marginally altered kinetics of Pi transport in those mutants providing sufficient current for analysis. Only one site, at the extracellular end of TMD-3, appeared to be accessible to methanethiosulfonate reagents. However, additional mutations carried out at D224 (replaced by E, G or N) and N227 (replaced by D or Q) resulted in markedly altered voltage and substrate dependencies of the Pi-dependent currents. Replacing Asp-224 (highly conserved in electrogenic a and b isoforms) with Gly (the residue found in the electroneutral c isoform) resulted in a mutant that mediated electroneutral Na+-dependent Pi transport. Since electrogenic NaPi-II transports 3 Na+/transport cycle, whereas electroneutral NaPi-IIc only transports 2, we speculate that this loss of electrogenicity might result from the loss of one of the three Na+ binding sites in NaPi-IIa.

  • substrate interactions in the human type iia Sodium Phosphate Cotransporter napi iia
    American Journal of Physiology-renal Physiology, 2005
    Co-Authors: Leila V Virkki, Ian C. Forster, Jürg Biber, Heini Murer
    Abstract:

    We have characterized the kinetics of substrate transport in the renal type IIa human Sodium-Phosphate Cotransporter (NaPi-IIa). The transporter was expressed in Xenopus laevis oocytes, and steady-state and pre-steady-state currents and substrate uptakes were characterized by voltage-clamp and isotope flux. First, by measuring simultaneous uptake of a substrate (32Pi, 22Na) and charge in voltage-clamped oocytes, we established that the human NaPi-IIa isoform operates with a Na:Pi:charge stoichiometry of 3:1:1 and that the preferred transported Pi species is HPO42−. We then probed the complex interrelationship of substrates, pH, and voltage in the NaPi-IIa transport cycle by analyzing both steady-state and pre-steady-state currents. Steady-state current measurements show that the apparent HPO42− affinity is voltage dependent and that this voltage dependency is abrogated by lowering the pH or the Na+ concentration. In contrast, the voltage dependency of the apparent Na+ affinity increased when pH was lowere...

  • kidney specific inactivation of the megalin gene impairs trafficking of renal inorganic Sodium Phosphate Cotransporter napi iia
    Journal of The American Society of Nephrology, 2004
    Co-Authors: Sebastian Bachmann, Jürg Biber, Uwe Schlichting, Beate Geist, Kerim Mutig, Thomas Petsch, Desa Bacic, Carsten A Wagner, Brigitte Kaissling, Heini Murer
    Abstract:

    Renal reabsorption of inorganic Phosphate is mediated by the type IIa Sodium Phosphate Cotransporter (NaPi-IIa) of the proximal tubule. Changes in renal Phosphate handling are mainly attributable to altered NaPi-IIa brush border membrane (BBM) expression. Parathyroid hormone (PTH) induces inactivation of NaPi-IIa by endocytic membrane retrieval and degradation. The key elements triggering this process are not clear to date. Megalin serves as a receptor for the endocytosis of multiple ligands and is coexpressed with NaPi-IIa in the proximal tubule. Investigated was the role of megalin in the regulation of NaPi-IIa in steady state and during inactivation. Kidneys and tubular BBM fractions from mice with a renal-specific megalin gene defect and from controls were analyzed by light and electron microscopic histochemical techniques and Western blot test. Steady-state levels of NaPi-IIa in BBM were significantly enhanced, mRNA levels preserved, and phosphaturia reduced in the absence of megalin. Fluid-phase endocytosis was prevented and the apical endocytic apparatus markedly reduced. Systemic administration of PTH resulted in a defective retrieval and impaired degradation of NaPi-IIa. In vitro, the application of various stimuli of the PTH-induced signaling cascade had no effect either. Adequate steady-state expression of NaPi-IIa and the capacity of the proximal tubule cell to react on PTH-driven inactivation of NaPi-IIa by endocytosis and intracellular translocation require the presence of megalin.

  • functional characterization of two naturally occurring mutations in the human Sodium Phosphate Cotransporter type iia
    Journal of Bone and Mineral Research, 2003
    Co-Authors: Leila V Virkki, Ian C. Forster, Jürg Biber, Nati Hernando, Heini Murer
    Abstract:

    Mutations in the gene encoding the human Sodium-Phosphate Cotransporter (NPT2), causing reduced phos- phate affinity and dominant-negative behavior, were described. (1) We found no evidence of altered kinetics or dominant-negative effects. Thus, the mutations cannot account for the clinical phenotype. Introduction: Mutations in NPT2a, the gene encoding the Sodium-Phosphate Cotransporter NaPi-IIa, were for the first time linked to human disease by Prieand colleagues. Two patients are described with renal Phosphate wasting who were heterozygous for either the A48F or V147M mutation. Expressed in Xenopus oocytes, both mutants showed reduced Phosphate affinity. Furthermore, coexpression of mutants with wildtype (WT) NaPi-IIa resulted in reduced cotransport function, explaining the mutants' dominant-negative effect in the patients. Intrigued by the implications of these findings on transporter kinetics, we decided to examine the transport characteristics of the two mutants in more detail. Materials and Methods: We recreated the two mutants, expressed them in Xenopus oocytes, and analyzed their kinetic behavior by two-electrode voltage clamp. We also performed coexpression experiments where we injected mRNA for WT and mutants containing an additional S462C mutation, enabling complete inhibition of cotransport function with cysteine- modifying reagents. Finally, we expressed WT and mutant NaPi-IIa as C-terminal fusions to green fluorescent protein (GFP) in opossum kidney (OK) cells. Results and Conclusions: We found in our oocyte expression experiments that Pi-induced currents were reduced in both mutants, whereas Pi and Na affinities and other transport characteristics were not affected. The amount of cotransport activity remaining after cysteine modification, corresponding to WT activity, was not affected by coexpression of either mutant. Finally, GFP-tagged WT and mutants were expressed at the apical membrane in OK cells, showing that both mutants are correctly targeted in a mammalian cell. In conclusion, our data from oocyte and OK cell expression studies suggest that the heterozygous A48F and V147M mutations cannot explain the pathological phenotype observed by Prieand colleagues. J Bone Miner Res 2003;18:2135-2141

  • The Sodium Phosphate Cotransporter family SLC34
    Pflügers Archiv: European Journal of Physiology, 2003
    Co-Authors: Heini Murer, Ian C. Forster, Jürg Biber
    Abstract:

    This review summarizes the characteristics of the solute carrier family SLC34 that is represented by the type ll Na/Pi-Cotransporters NaPi-lla (SLC34A1), NaPi-llb (SLC34A2) and NaPi-llc (SLC34A3). Other Na/Pi-Cotransporters are described within the SLC17 and SLC20 families. Type ll Na/Pi-Cotransporters are expressed in several tissues and play a major role in the homeostasis of inorganic Phosphate. In kidney and small intestine, type ll Na/Pi-Cotransporters are located at the apical sites of epithelial cells and represent the rate limiting steps for transepithelial movement of Phosphate. Physiological and pathophysiological regulation of renal and small intestinal epithelial transport of Phosphate occurs through alterations in the abundance of type ll Na/Pi-Cotransporters.

Jürg Biber - One of the best experts on this subject based on the ideXlab platform.

  • functionally important residues in the predicted 3rd transmembrane domain of the type iia Sodium Phosphate Cotransporter napi iia
    The Journal of Membrane Biology, 2005
    Co-Authors: Leila V Virkki, Ian C. Forster, Jürg Biber, Andrea Bacconi, Heini Murer
    Abstract:

    The type IIa Na+/Pi, Cotransporter (NaPi-IIa) mediates electrogenic transport of three Na+ and one divalent Pi ion (and one net positive charge) across the cell membrane. Sequence comparison of electrogenic NaPi-IIa and IIb isoforms with the electroneutral NaPi-IIc isoform pointed to the third transmembrane domain (TMD-3) as a possibly significant determinant of substrate binding. To elucidate the role of TMD-3 in the topology and mechanism underlying NaPi-IIa function we subjected it to cysteine scanning mutagenesis. The constructs were expressed in Xenopus oocytes and Pi transport kinetics were assayed by electrophysiology and radiotracer uptake. Cys substitution resulted in only marginally altered kinetics of Pi transport in those mutants providing sufficient current for analysis. Only one site, at the extracellular end of TMD-3, appeared to be accessible to methanethiosulfonate reagents. However, additional mutations carried out at D224 (replaced by E, G or N) and N227 (replaced by D or Q) resulted in markedly altered voltage and substrate dependencies of the Pi-dependent currents. Replacing Asp-224 (highly conserved in electrogenic a and b isoforms) with Gly (the residue found in the electroneutral c isoform) resulted in a mutant that mediated electroneutral Na+-dependent Pi transport. Since electrogenic NaPi-II transports 3 Na+/transport cycle, whereas electroneutral NaPi-IIc only transports 2, we speculate that this loss of electrogenicity might result from the loss of one of the three Na+ binding sites in NaPi-IIa.

  • substrate interactions in the human type iia Sodium Phosphate Cotransporter napi iia
    American Journal of Physiology-renal Physiology, 2005
    Co-Authors: Leila V Virkki, Ian C. Forster, Jürg Biber, Heini Murer
    Abstract:

    We have characterized the kinetics of substrate transport in the renal type IIa human Sodium-Phosphate Cotransporter (NaPi-IIa). The transporter was expressed in Xenopus laevis oocytes, and steady-state and pre-steady-state currents and substrate uptakes were characterized by voltage-clamp and isotope flux. First, by measuring simultaneous uptake of a substrate (32Pi, 22Na) and charge in voltage-clamped oocytes, we established that the human NaPi-IIa isoform operates with a Na:Pi:charge stoichiometry of 3:1:1 and that the preferred transported Pi species is HPO42−. We then probed the complex interrelationship of substrates, pH, and voltage in the NaPi-IIa transport cycle by analyzing both steady-state and pre-steady-state currents. Steady-state current measurements show that the apparent HPO42− affinity is voltage dependent and that this voltage dependency is abrogated by lowering the pH or the Na+ concentration. In contrast, the voltage dependency of the apparent Na+ affinity increased when pH was lowere...

  • kidney specific inactivation of the megalin gene impairs trafficking of renal inorganic Sodium Phosphate Cotransporter napi iia
    Journal of The American Society of Nephrology, 2004
    Co-Authors: Sebastian Bachmann, Jürg Biber, Uwe Schlichting, Beate Geist, Kerim Mutig, Thomas Petsch, Desa Bacic, Carsten A Wagner, Brigitte Kaissling, Heini Murer
    Abstract:

    Renal reabsorption of inorganic Phosphate is mediated by the type IIa Sodium Phosphate Cotransporter (NaPi-IIa) of the proximal tubule. Changes in renal Phosphate handling are mainly attributable to altered NaPi-IIa brush border membrane (BBM) expression. Parathyroid hormone (PTH) induces inactivation of NaPi-IIa by endocytic membrane retrieval and degradation. The key elements triggering this process are not clear to date. Megalin serves as a receptor for the endocytosis of multiple ligands and is coexpressed with NaPi-IIa in the proximal tubule. Investigated was the role of megalin in the regulation of NaPi-IIa in steady state and during inactivation. Kidneys and tubular BBM fractions from mice with a renal-specific megalin gene defect and from controls were analyzed by light and electron microscopic histochemical techniques and Western blot test. Steady-state levels of NaPi-IIa in BBM were significantly enhanced, mRNA levels preserved, and phosphaturia reduced in the absence of megalin. Fluid-phase endocytosis was prevented and the apical endocytic apparatus markedly reduced. Systemic administration of PTH resulted in a defective retrieval and impaired degradation of NaPi-IIa. In vitro, the application of various stimuli of the PTH-induced signaling cascade had no effect either. Adequate steady-state expression of NaPi-IIa and the capacity of the proximal tubule cell to react on PTH-driven inactivation of NaPi-IIa by endocytosis and intracellular translocation require the presence of megalin.

  • functional characterization of two naturally occurring mutations in the human Sodium Phosphate Cotransporter type iia
    Journal of Bone and Mineral Research, 2003
    Co-Authors: Leila V Virkki, Ian C. Forster, Jürg Biber, Nati Hernando, Heini Murer
    Abstract:

    Mutations in the gene encoding the human Sodium-Phosphate Cotransporter (NPT2), causing reduced phos- phate affinity and dominant-negative behavior, were described. (1) We found no evidence of altered kinetics or dominant-negative effects. Thus, the mutations cannot account for the clinical phenotype. Introduction: Mutations in NPT2a, the gene encoding the Sodium-Phosphate Cotransporter NaPi-IIa, were for the first time linked to human disease by Prieand colleagues. Two patients are described with renal Phosphate wasting who were heterozygous for either the A48F or V147M mutation. Expressed in Xenopus oocytes, both mutants showed reduced Phosphate affinity. Furthermore, coexpression of mutants with wildtype (WT) NaPi-IIa resulted in reduced cotransport function, explaining the mutants' dominant-negative effect in the patients. Intrigued by the implications of these findings on transporter kinetics, we decided to examine the transport characteristics of the two mutants in more detail. Materials and Methods: We recreated the two mutants, expressed them in Xenopus oocytes, and analyzed their kinetic behavior by two-electrode voltage clamp. We also performed coexpression experiments where we injected mRNA for WT and mutants containing an additional S462C mutation, enabling complete inhibition of cotransport function with cysteine- modifying reagents. Finally, we expressed WT and mutant NaPi-IIa as C-terminal fusions to green fluorescent protein (GFP) in opossum kidney (OK) cells. Results and Conclusions: We found in our oocyte expression experiments that Pi-induced currents were reduced in both mutants, whereas Pi and Na affinities and other transport characteristics were not affected. The amount of cotransport activity remaining after cysteine modification, corresponding to WT activity, was not affected by coexpression of either mutant. Finally, GFP-tagged WT and mutants were expressed at the apical membrane in OK cells, showing that both mutants are correctly targeted in a mammalian cell. In conclusion, our data from oocyte and OK cell expression studies suggest that the heterozygous A48F and V147M mutations cannot explain the pathological phenotype observed by Prieand colleagues. J Bone Miner Res 2003;18:2135-2141

  • The Sodium Phosphate Cotransporter family SLC34
    Pflügers Archiv: European Journal of Physiology, 2003
    Co-Authors: Heini Murer, Ian C. Forster, Jürg Biber
    Abstract:

    This review summarizes the characteristics of the solute carrier family SLC34 that is represented by the type ll Na/Pi-Cotransporters NaPi-lla (SLC34A1), NaPi-llb (SLC34A2) and NaPi-llc (SLC34A3). Other Na/Pi-Cotransporters are described within the SLC17 and SLC20 families. Type ll Na/Pi-Cotransporters are expressed in several tissues and play a major role in the homeostasis of inorganic Phosphate. In kidney and small intestine, type ll Na/Pi-Cotransporters are located at the apical sites of epithelial cells and represent the rate limiting steps for transepithelial movement of Phosphate. Physiological and pathophysiological regulation of renal and small intestinal epithelial transport of Phosphate occurs through alterations in the abundance of type ll Na/Pi-Cotransporters.

Eleanor D Lederer - One of the best experts on this subject based on the ideXlab platform.

Ian C. Forster - One of the best experts on this subject based on the ideXlab platform.

  • the na1 binding site in the human Sodium Phosphate Cotransporter napi iia
    Biophysical Journal, 2015
    Co-Authors: Cristina Fenollarferrer, Ian C. Forster, Monica Patti, Thomas Knoepfel, Andreas Werner, Lucy R Forrest
    Abstract:

    The levels of inorganic Phosphate (Pi) in humans are tightly regulated to prevent pathologies such as bone loss and vascular calcification. Sodium-coupled Pi transporters of the SLC34 solute carrier family (NaPi-II) are responsible for intestinal Pi absorption and renal Pi reabsorption. These transporters move divalent Pi into the cell using the transmembrane Sodium electrochemical gradient. All three isoforms, NaPi-IIa, IIb, and IIc, are thought to bind three Sodium ions during the transport cycle, although NaPi-IIc co-transports only two of those ions, whereas the other isoforms (IIa, IIb) co-transport three Sodium ions and are consequently electrogenic. Although extensive functional studies have provided valuable insights into this family of transporters, unfortunately no three-dimensional structural data is available. Recently, we proposed a structural model of NaPi-IIa based on a crystal structure of a Sodium-coupled dicarboxylate transporter VcINDY. With this model, we successfully predicted the regions of the protein that mediate binding of the Phosphate anion and two of the Sodium ions (Na2 and Na3), but it was not possible to identify the position of the Sodium ion that binds first to the empty transporter (Na1). Here, we used molecular modeling techniques to refine the earlier model by adjusting the target-template sequence alignment for transmembrane helices 2, 5 and 6. We obtained two alternative structural models with different implications for a putative Na1 binding site, and with possible improvements to the coordination in the predicted Na3 binding site. These alternatives were assessed by biochemical and electrophysiological analysis of site-specific mutants of human NaPi-IIa. The experimental results strongly favor one of the two models, and identify residues with a key functional role in the transport process. The improved NaPi-IIa model provides a firmer foundation for a molecular-level understanding of Sodium-coupled Pi uptake by SLC34 transporters.

  • structural model of the human Sodium Phosphate Cotransporter napi ii
    Biophysical Journal, 2014
    Co-Authors: Maria Cristina Fenollarferrer, Ian C. Forster, Monica Patti, Thomas Knoepfel, Andreas Werner, Lucy R Forrest
    Abstract:

    Homeostasis of inorganic Phosphate (Pi) in vertebrates is maintained by control of intestinal absorption, storage and release in bones, and renal excretion. These processes depend on tightly regulated expression of Na+-coupled Pi transporters of the SLC34 solute carrier family (NaPi-II). Their crucial role in Pi homeostasis is underscored by pathologies resulting from naturally occurring SLC34 mutations and SLC34 knock-out animals. SLC34 isoforms have been extensively studied with respect to transport mechanism and structure-function relationships; however, the 3-dimensional structure is unknown. All SLC34 transporters share a duplicated motif comprising a glutamine followed by a stretch of threonine or serine residues, suggesting the presence of structural repeats as found in other transporter families. Nevertheless, standard bioinformatic approaches fail to clearly identify a suitable template for molecular modeling. Here, we used hydrophobicity profiles and hidden Markov Models to first define a structural repeat common to all SLC34 isoforms. Similar approaches identify a relationship with the core regions in a crystal structure of Vibrio cholerae Na+-dicarboxylate transporter VcINDY, from which we generated a homology model of human NaPi-IIa. The aforementioned SLC34 motifs in each repeat localize to the center of the model, and were predicted to form Na+ and Pi coordination sites. Functional relevance of key amino acids was confirmed by biochemical and electrophysiological analysis of expressed, mutated transporters. Moreover, the validity of the predicted architecture is corroborated by extensive published structure-function studies. The NaPi-IIa model provides a firm foundation for a molecular understanding of Na+-coupled Pi uptake by SLC34 transporters.

  • functionally important residues in the predicted 3rd transmembrane domain of the type iia Sodium Phosphate Cotransporter napi iia
    The Journal of Membrane Biology, 2005
    Co-Authors: Leila V Virkki, Ian C. Forster, Jürg Biber, Andrea Bacconi, Heini Murer
    Abstract:

    The type IIa Na+/Pi, Cotransporter (NaPi-IIa) mediates electrogenic transport of three Na+ and one divalent Pi ion (and one net positive charge) across the cell membrane. Sequence comparison of electrogenic NaPi-IIa and IIb isoforms with the electroneutral NaPi-IIc isoform pointed to the third transmembrane domain (TMD-3) as a possibly significant determinant of substrate binding. To elucidate the role of TMD-3 in the topology and mechanism underlying NaPi-IIa function we subjected it to cysteine scanning mutagenesis. The constructs were expressed in Xenopus oocytes and Pi transport kinetics were assayed by electrophysiology and radiotracer uptake. Cys substitution resulted in only marginally altered kinetics of Pi transport in those mutants providing sufficient current for analysis. Only one site, at the extracellular end of TMD-3, appeared to be accessible to methanethiosulfonate reagents. However, additional mutations carried out at D224 (replaced by E, G or N) and N227 (replaced by D or Q) resulted in markedly altered voltage and substrate dependencies of the Pi-dependent currents. Replacing Asp-224 (highly conserved in electrogenic a and b isoforms) with Gly (the residue found in the electroneutral c isoform) resulted in a mutant that mediated electroneutral Na+-dependent Pi transport. Since electrogenic NaPi-II transports 3 Na+/transport cycle, whereas electroneutral NaPi-IIc only transports 2, we speculate that this loss of electrogenicity might result from the loss of one of the three Na+ binding sites in NaPi-IIa.

  • substrate interactions in the human type iia Sodium Phosphate Cotransporter napi iia
    American Journal of Physiology-renal Physiology, 2005
    Co-Authors: Leila V Virkki, Ian C. Forster, Jürg Biber, Heini Murer
    Abstract:

    We have characterized the kinetics of substrate transport in the renal type IIa human Sodium-Phosphate Cotransporter (NaPi-IIa). The transporter was expressed in Xenopus laevis oocytes, and steady-state and pre-steady-state currents and substrate uptakes were characterized by voltage-clamp and isotope flux. First, by measuring simultaneous uptake of a substrate (32Pi, 22Na) and charge in voltage-clamped oocytes, we established that the human NaPi-IIa isoform operates with a Na:Pi:charge stoichiometry of 3:1:1 and that the preferred transported Pi species is HPO42−. We then probed the complex interrelationship of substrates, pH, and voltage in the NaPi-IIa transport cycle by analyzing both steady-state and pre-steady-state currents. Steady-state current measurements show that the apparent HPO42− affinity is voltage dependent and that this voltage dependency is abrogated by lowering the pH or the Na+ concentration. In contrast, the voltage dependency of the apparent Na+ affinity increased when pH was lowere...

  • functional characterization of two naturally occurring mutations in the human Sodium Phosphate Cotransporter type iia
    Journal of Bone and Mineral Research, 2003
    Co-Authors: Leila V Virkki, Ian C. Forster, Jürg Biber, Nati Hernando, Heini Murer
    Abstract:

    Mutations in the gene encoding the human Sodium-Phosphate Cotransporter (NPT2), causing reduced phos- phate affinity and dominant-negative behavior, were described. (1) We found no evidence of altered kinetics or dominant-negative effects. Thus, the mutations cannot account for the clinical phenotype. Introduction: Mutations in NPT2a, the gene encoding the Sodium-Phosphate Cotransporter NaPi-IIa, were for the first time linked to human disease by Prieand colleagues. Two patients are described with renal Phosphate wasting who were heterozygous for either the A48F or V147M mutation. Expressed in Xenopus oocytes, both mutants showed reduced Phosphate affinity. Furthermore, coexpression of mutants with wildtype (WT) NaPi-IIa resulted in reduced cotransport function, explaining the mutants' dominant-negative effect in the patients. Intrigued by the implications of these findings on transporter kinetics, we decided to examine the transport characteristics of the two mutants in more detail. Materials and Methods: We recreated the two mutants, expressed them in Xenopus oocytes, and analyzed their kinetic behavior by two-electrode voltage clamp. We also performed coexpression experiments where we injected mRNA for WT and mutants containing an additional S462C mutation, enabling complete inhibition of cotransport function with cysteine- modifying reagents. Finally, we expressed WT and mutant NaPi-IIa as C-terminal fusions to green fluorescent protein (GFP) in opossum kidney (OK) cells. Results and Conclusions: We found in our oocyte expression experiments that Pi-induced currents were reduced in both mutants, whereas Pi and Na affinities and other transport characteristics were not affected. The amount of cotransport activity remaining after cysteine modification, corresponding to WT activity, was not affected by coexpression of either mutant. Finally, GFP-tagged WT and mutants were expressed at the apical membrane in OK cells, showing that both mutants are correctly targeted in a mammalian cell. In conclusion, our data from oocyte and OK cell expression studies suggest that the heterozygous A48F and V147M mutations cannot explain the pathological phenotype observed by Prieand colleagues. J Bone Miner Res 2003;18:2135-2141

Fayez K Ghishan - One of the best experts on this subject based on the ideXlab platform.

  • age dependent regulation of rat intestinal type iib Sodium Phosphate Cotransporter by 1 25 oh 2 vitamin d3
    American Journal of Physiology-cell Physiology, 2002
    Co-Authors: Hua Xu, James F Collins, Fayez K Ghishan
    Abstract:

    The current studies were designed to characterize type IIb Sodium-inorganic Phosphate (Pi) Cotransporter (NaPi-IIb) expression and to assess the effect of 1,25-(OH)2 vitamin D3 on NaPi-IIb gene expression during rat ontogeny. Sodium-dependent Pi absorption by intestinal brush-border membrane vesicles (BBMVs) decreased with age, and NaPi-IIb gene expression also decreased proportionally with age. 1,25-(OH)2 vitamin D3 treatment increased intestinal BBMV Pi absorption by ∼2.5-fold in suckling rats and by ∼2.1-fold in adult rats. 1,25-(OH)2vitamin D3 treatment also increased NaPi-IIb mRNA abundance by ∼2-fold in 14-day-old rats but had no effect on mRNA expression in adults. Furthermore, in rat intestinal epithelial (RIE) cells, 1,25-(OH)2 vitamin D3 increased NaPi-IIb mRNA abundance, an effect that was abolished by actinomycin D. Additionally, human NaPi-IIb gene promoter activity in transiently transfected RIE cells showed ∼1.6-fold increase after 1,25-(OH)2 vitamin D3 treatment. In conclusion, we demonstr...

  • regulation of the human Sodium Phosphate Cotransporter napi iib gene promoter by epidermal growth factor
    American Journal of Physiology-cell Physiology, 2001
    Co-Authors: Hua Xu, James F Collins, Pawel R Kiela, Fayez K Ghishan
    Abstract:

    The intestinal Sodium-Phosphate Cotransporter (NaPi-IIb) plays a major role in intestinal Pi absorption. Epidermal growth factor (EGF) is involved in the regulation of Pihomeostasis. However, the r...

  • age dependent regulation of rat intestinal Sodium Phosphate Cotransporter napi iib by 1 25 oh 2 vitamin d3
    2001
    Co-Authors: Hua Xu, James F Collins, Fayez K Ghishan
    Abstract:

    The current studies were designed to characterize type IIb Sodium-Phosphate Cotransporter (NaPi-IIb) expression and to assess the effect of 1,25-(OH)2 vitamin D3 (vit-D3) on NaPi-IIb gene expression during rat ontogeny. Sodium-dependent Pi absorption by intestinal brush-border membrane vesicles (BBMV) decreases with age, and NaPi-IIb gene expression also decreases proportionally with age. Vit-D3 treatment increased intestinal BBMV Pi absorption by ~2.5 fold in suckling rats and by ~2.1 fold in adult rats. Vit-D3 treatment also increased NaPi-IIb mRNA abundance by ~2 fold in 14-day-old rats, but had no effect on mRNA expression in adults. Furthermore, in rat intestinal epithelial (RIE) cells, vit-D3 increased NaPi-IIb mRNA abundance, an effect that was abolished by actinomycin D. Additionally, human NaPi-IIb gene promoter activity in transiently transfected RIE cells showed ~1.6-fold increase after vit-D3 treatment. In conclusion, we demonstrate that the age-related decrease in intestinal Na/Pi absorption correlates with decreased NaPi-IIb mRNA expression. Our data also suggest that the vit-D3 effect on NaPi-IIb expression is at least partially mediated by gene transcription in suckling rats.

  • molecular cloning of murine Sodium Phosphate Cotransporter type iib na pi iib gene promoter and characterization of gene structure
    Biochimica et Biophysica Acta, 2000
    Co-Authors: Kayo Arima, James F Collins, Eric R Hines, Fayez K Ghishan
    Abstract:

    Abstract We report the cloning of the murine Na/Pi-IIb Cotransporter gene, which spans more than 18 kilobases and consists of 12 introns and 13 exons. Three promoter/reporter gene constructs, −159/+73, −429/+73 and −954/+73, showed significant luciferase activity (22–82-fold over background) when transfected into in rat intestinal epithelial (RIE-1) cells.