Role of serine 249 of ezrin in the regulation of sodium-dependent phosphate transporter NaPi-IIa activity in renal proximal tubular cells

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  • Yamada Fumiyo
    Department of Clinical Nutrition, Institute of Health Biosciences, the University of Tokushima Graduate School
  • Horie Daisuke
    Department of Clinical Nutrition, Institute of Health Biosciences, the University of Tokushima Graduate School
  • Nakamura Asako
    Department of Clinical Nutrition, Institute of Health Biosciences, the University of Tokushima Graduate School
  • Tanimura Ayako
    Department of Clinical Nutrition, Institute of Health Biosciences, the University of Tokushima Graduate School
  • Yamamoto Hironori
    Department of Clinical Nutrition, Institute of Health Biosciences, the University of Tokushima Graduate School
  • Segawa Hiroko
    Department of Molecular Nutrition, Institute of Health Biosciences, the University of Tokushima Graduate School
  • Ito Mikiko
    University of Hyogo School of Human Science and Environment
  • Miyamoto Ken-ichi
    Department of Molecular Nutrition, Institute of Health Biosciences, the University of Tokushima Graduate School
  • Taketani Yutaka
    Department of Clinical Nutrition, Institute of Health Biosciences, the University of Tokushima Graduate School
  • Takeda Eiji
    Department of Clinical Nutrition, Institute of Health Biosciences, the University of Tokushima Graduate School

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Abstract

Type IIa sodium-dependent phosphate transporter (NaPi-IIa) is responsible for renal phosphate reabsorption and maintenance of systemic phosphate homeostasis in mammals. Macromolecular complex formation of NaPi-IIa with sodium-proton exchanger related factor-1 (NHERF-1) and ezrin is important for apical membrane localization in the proximal tubular cells. Here, we investigated the interactions of the ezrin phosphomimetic mutation of serine to aspartic acid at 249 with NHERF-1 and the inhibition of apical membrane localization of NaPi-IIa. In vitro phosphorylation analysis revealed that serine 249 of human ezrin serves as a phosphorylation site for protein kinase A. The N-terminal half of ezrin had a dominant negative effect on the phosphate transport activity and inhibited the apical localization of NaPi-IIa in renal proximal tubular cells. We found that the phosphomimetic S249D mutant interfered with the inhibitory effects of the dominant negative mutant on the transport and localization of NaPi-IIa. The S249D mutant also inhibited the interaction with NHERF-1. Therefore, serine 249 of ezrin can play important roles in the regulation of the complex formation and membrane localization of NaPi-IIa. J. Med. Invest. 60: 27-34, February, 2013

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