Cell-biologic and functional analyses of five new Aquaporin-2 missense mutations that cause recessive nephrogenic diabetes insipidus.
Mutations in the Aquaporin-2 gene, which encodes a renal water channel, have been shown to cause autosomal nephrogenic diabetes insipidus (NDI), a disease in which the kidney is unable to concentrate urine in response to vasopressin. Most AQP2 missense mutants in recessive NDI are retained in the endoplasmic reticulum (ER), but AQP2-T125M and AQP2-G175R were reported to be nonfunctional channels unimpaired in their routing to the plasma membrane. In five families, seven novel AQP2 gene mutations were identified and their cell-biologic basis for causing recessive NDI was analyzed. The patients in four families were homozygous for mutations, encoding AQP2-L28P, AQP2-A47V, AQP2-V71M, or AQP2-P185A. Expression in oocytes revealed that all these mutants, and also AQP2-T125M and AQP2-G175R, conferred a reduced water permeability compared with wt-AQP2, which was due to ER retardation. The patient in the fifth family had a G>A nucleotide substitution in the splice donor site of one allele that results in an out-of-frame protein. The other allele has a nucleotide deletion (c652delC) and a missense mutation (V194I). The routing and function of AQP2-V194I in oocytes was not different from wt-AQP2; it was therefore concluded that c652delC, which leads to an out-of-frame protein, is the NDI-causing mutation of the second allele. This study indicates that misfolding and ER retention is the main, and possibly only, cell-biologic basis for recessive NDI caused by missense AQP2 proteins. In addition, the reduced single channel water permeability of AQP2-A47V (40%) and AQP2-T125M (25%) might become of therapeutic value when chemical chaperones can be found that restore their routing to the plasma membrane.
Department of Cell Physiology, UMC St. Radboud, Nijmegen, The Netherlands.
Nannette
N
Marr
Daniel G
DG
Bichet
Susan
S
Hoefs
Paul J M
PJ
Savelkoul
Irene B M
IB
Konings
Fabrizio
F
De Mattia
Michael P J
MP
Graat
Marie-Françoise
MF
Arthus
Michele
M
Lonergan
T Mary
TM
Fujiwara
Nine V A M
NV
Knoers
Daniel
D
Landau
William J
WJ
Balfe
Alexander
A
Oksche
Walter
W
Rosenthal
Dominik
D
Müller
Carel H
CH
Van Os
Peter M T
PM
Deen
D000595:Amino Acid Sequence; D000818:Animals; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D018500:Diabetes Insipidus, Nephrogenic / Q000235:genetics* / Q000378:metabolism; D005192:Family Health; D005260:Female; D005808:Genes, Recessive; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D009865:Oocytes / Q000378:metabolism; D010375:Pedigree; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000235:genetics; D014867:Water / Q000378:metabolism; D014981:Xenopus
C496023:AQP2 protein, human; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins; D014867:Water