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This Article Full Text Full Text (PDF) All Versions of this Article: 294/4/F840    most recent 00180.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Khundmiri, S. J. Articles by Lederer, E. D. PubMed PubMed Citation Articles by Khundmiri, S. J. Articles by Lederer, E. D.

Novel regulatory function for NHERF-1 in Npt2a transcription

¹Department of Medicine, University of Louisville, Louisville, Kentucky; ²Department of Veterans Affairs and ³Department of Medicine, University of Maryland, Baltimore, Maryland; ⁴Department of Biology, University of Memphis, Memphis, Tennessee; ⁵Department of Molecular, Cellular, and Craniofacial Biology, University of Louisville Birth Defects Center, School of Dentistry, and ⁶Department of Biochemistry and Molecular Biology, University of Louisville, Louisville, Kentucky; and ⁷Department of Veterans Affairs, Louisville, Kentucky

Submitted 16 April 2007 ; accepted in final form 12 January 2008

Several lines of evidence show that sodium/hydrogen exchanger regulatory factor 1 (NHERF-1) regulates the expression and activity of the type IIa sodium-dependent phosphate transporter (Npt2a) in renal proximal tubules. We have previously demonstrated that expression of a COOH-terminal ezrin binding domain-deficient NHERF-1 in opossum kidney (OK) cells decreased expression of Npt2a in apical membranes but did not affect responses to parathyroid hormone. We hypothesized that NHERF-1 regulates apical membrane expression of Npt2a in renal proximal tubule cells. To address this hypothesis, we compared regulation of Npt2a expression and function in NHERF-deficient OK cells (OK-H) and wild-type cells (OK-WT). In OK-H cells, phosphate uptake and expression of Npt2a protein in apical membranes were significantly lower than in OK-WT cells. Transient transfection of green fluorescent protein-tagged Npt2a cDNA into OK-H cells resulted in aberrant localization of an Npt2a fragment to the cytosol but not to the apical membrane. OK-H cells also exhibited a marked decrease in Npt2a mRNA expression. As demonstrated by luciferase assay, Npt2a promoter activity was significantly decreased in OK-H cells compared with that shown in OK-WT cells. Transfection of OK-H cells with human NHERF-1 restored Npt2a expression at both the protein and mRNA levels and regulation by parathyroid hormone. Expression of NHERF-1 constructs with mutations in the PDZ domains or the ezrin binding domain in OK-H cells suggested that the PDZ2 domain is critical for apical translocation of Npt2a and for expression at the mRNA level. Our data demonstrate for the first time that NHERF-1 regulates Npt2a transcription and membrane insertion.

parathyroid hormone; sodium/hydrogen exchanger regulatory factor; type IIa sodium-dependent phosphate cotransporter; low phosphate; opossum kidney cell