title: Dominant and recessive distal renal tubular acidosis mutations of kidney anion exchanger 1 induce distinct trafficking defects in MDCK cells.
abstract: Distal renal tubular acidosis (dRTA), a kidney disease resulting in defective urinary acidification, can be caused by dominant or recessive mutations in the kidney Cl-/HCO3- anion exchanger (kAE1), a glycoprotein expressed in the basolateral membrane of alpha-intercalated cells. We compared the effect of two dominant (R589H and S613F) and two recessive (S773P and G701D) dRTA point mutations on kAE1 trafficking in Madin-Darby canine kidney (MDCK) epithelial cells. In contrast to wild-type (WT) kAE1 that was localized to the basolateral membrane, the dominant mutants (kAE1 R589H and S613F) were retained in the endoplasmic reticulum (ER) in MDCK cells, with a few cells showing in addition some apical localization. The recessive mutant kAE1 S773P, while misfolded and largely retained in the ER in non-polarized MDCK cells, was targeted to the basolateral membrane after polarization. The other recessive mutants, kAE1 G701D and designed G701E, G701R but not G701A or G701L mutants, were localized to the Golgi in both non-polarized and polarized cells. The results suggest that introduction of a polar mutation into a transmembrane segment resulted in Golgi retention of the recessive G701D mutant. When coexpressed, the dominant mutants retained kAE1 WT intracellularly, while the recessive mutants did not. Coexpression of recessive G701D and S773P mutants in polarized cells showed that these proteins could interact, yet no G701D mutant was detected at the basolateral membrane. Therefore, compound heterozygous patients expressing both recessive mutants (G701D/S773P) likely developed dRTA due to the lack of a functional kAE1 at the basolateral surface of alpha-intercalated cells.
authors.affiliation: Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Cordat
authors.forename: Saranya
authors.initials: S
authors.lastname: Kittanakom
authors.forename: Pa-Thai
authors.initials: PT
authors.lastname: Yenchitsomanus
authors.forename: Jing
authors.initials: J
authors.lastname: Li
authors.forename: Kai
authors.initials: K
authors.lastname: Du
authors.forename: Gergely L
authors.initials: GL
authors.lastname: Lukacs
authors.forename: Reinhart A F
authors.initials: RA
authors.lastname: Reithmeier
mesh_terms: D000141:Acidosis, Renal Tubular / Q000235:genetics* / Q000378:metabolism*; D000818:Animals; D001457:Anion Exchange Protein 1, Erythrocyte / Q000235:genetics* / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D016764:Cell Polarity; D004285:Dogs; D004721:Endoplasmic Reticulum / Q000378:metabolism; D015870:Gene Expression; D005799:Genes, Dominant; D005808:Genes, Recessive; D006801:Humans; D017136:Ion Transport; D007686:Kidney Tubules, Distal / Q000378:metabolism; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D014162:Transfection
chemical_list: D001457:Anion Exchange Protein 1, Erythrocyte; D011994:Recombinant Proteins; C454201:SLC4A1 protein, human