p.R254Q mutation in the aquaporin-2 water channel causing dominant nephrogenic diabetes insipidus is due to a lack of arginine vasopressin-induced phosphorylation.
Vasopressin regulates human water homeostasis by re-distributing homotetrameric aquaporin-2 (AQP2) water channels from intracellular vesicles to the apical membrane of renal principal cells, a process in which phosphorylation of AQP2 at S256 by cAMP-dependent protein kinase A (PKA) is thought to be essential. Dominant nephrogenic diabetes insipidus (NDI), a disease in which the kidney is unable to concentrate urine in response to vasopressin, is caused by AQP2 gene mutations. Here, we investigated a reported patient case of dominant NDI caused by a novel p.R254Q mutation. Expressed in oocytes, AQP2-p.R254Q appeared to be a functional water channel, but was impaired in its transport to the cell surface to the same degree as AQP2-p.S256A, which mimics non-phosphorylated AQP2. In polarized MDCK cells, AQP2-p.R254Q was retained and was distributed similarly to that of unstimulated wt-AQP2 or AQP2-p.S256A. Upon co-expression, AQP2-p.R254Q interacted with, and retained wt-AQP2 in intracellular vesicles. In contrast to wild-type AQP2, forskolin did not increase AQP2-p.R254Q phosphorylation at S256 or its translocation to the apical membrane. Mimicking constitutive phosphorylation in AQP2-p.R254Q with the p.S256D mutation, however, rescued its apical membrane expression. These date indicate that a lack of S256 phosphorylation is the sole cause of dominant NDI here, and thereby, p.R254Q is a loss of function instead of a gain of function mutation in dominant NDI.
Savelkoul
Paul J M
PJ
Dept of Physiology, Radboud University Nijmegen Medical Center, Nijmegen, The Netherlands.
De Mattia
Fabrizio
F
Li
Yuedan
Y
Kamsteeg
Erik-Jan
EJ
Konings
Irene B M
IB
van der Sluijs
Peter
P
Deen
Peter M T
PM
D000818:Animals; D051399:Aquaporin 2 / Q000235:genetics* / Q000378:metabolism; D001127:Arginine Vasopressin / Q000378:metabolism*; D001483:Base Sequence; D001704:Biopolymers; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D017931:DNA Primers; D018500:Diabetes Insipidus, Nephrogenic / Q000235:genetics*; D004285:Dogs; D005799:Genes, Dominant; D006801:Humans; D009154:Mutation; D010766:Phosphorylation
D051399:Aquaporin 2; D001704:Biopolymers; D017931:DNA Primers; D001127:Arginine Vasopressin