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Title: A Novel Missense Mutation in AE1 Causing Autosomal Dominant Distal Renal Tubular Acidosis Retains Normal Transport Function but Is Mistargeted in Polarized Epithelial Cells
Authors: Nanyawan Rungroj
Mark A.J. Devonald
Alan W. Cuthbert
Frank Reimann
Varaporn Akkarapatumwong
Pa Thai Yenchitsomanus
William M. Bennett
Fiona E. Karet
University of Cambridge
Mahidol University
Northwest Renal Clinic
Addenbrooke's Hospital
Keywords: Biochemistry, Genetics and Molecular Biology
Issue Date: 2-Apr-2004
Citation: Journal of Biological Chemistry. Vol.279, No.14 (2004), 13833-13838
Abstract: Mutations in SLC4A1, encoding the chloride-bicarbonate exchanger AE1, cause distal renal tubular acidosis (dRTA), a disease of defective urinary acidification by the distal nephron. In this study we report a novel missense mutation, G609R, causing dominant dRTA in affected members of a large Caucasian pedigree who all exhibited metabolic acidosis with alkaline urine, prominent nephrocalcinosis, and progressive renal impairment. To investigate the potential disease mechanism, the consequent effects of this mutation were determined. We first assessed anion transport function of G609R by expression in Xenopus oocytes. Western blotting and immunofluorescence demonstrated that the mutant protein was expressed at the oocyte cell surface. Measuring chloride and bicarbonate fluxes revealed normal 4,4′ -diisothiocyanostilbene-2,2′-disulfonic acid-inhibitable anion exchange, suggesting that loss-of-function of kAE1 cannot explain the severe disease phenotype in this kindred. We next expressed epitope-tagged wild-type or mutant kAE1 in Madin-Darby canine kidney cells. In monolayers grown to polarity, mutant kAE1 was detected subapically and at the apical membrane, as well as at the basolateral membrane, in contrast to the normal basolateral appearance of wild-type kAE1. These findings suggest that the seventh transmembrane domain that contains Gly-609 plays an important role in targeting kAE1 to the correct cell surface compartment. They confirm that dominant dRTA is associated with non-polarized trafficking of the protein, with no significant effect on anion transport function in vitro, which remains an unusual mechanism of human disease.
ISSN: 00219258
Appears in Collections:Scopus 2001-2005

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